Physical supercritical foaming manufacturing method of multicolor insole

Abstract

The invention discloses a physical supercritical foaming manufacturing method of a multicolor insole, and belongs to the technical field of insole manufacturing, and the physical supercritical foaming manufacturing method comprises the following steps: respectively mixing at least two different colors of color master batches with an EVA (Ethylene Vinyl Acetate) base material, a compatilizer and a temperature response type nucleating agent in proportion, drying to obtain at least two mixtures; a multi-color cold blank is prepared through different charging barrels of a multi-color disc injection molding machine through segmented temperature control injection molding, pressure maintaining and cooling shaping; a mold is heated through IP, and through preheating, fusion and shaping treatment, stable combination is formed on the interface of the multi-color cold blank; through a supercritical foaming tank, supercritical fluid is utilized, and a foaming blank is prepared through pressure and temperature control and rapid pressure relief; and molding and post-processing to obtain a multicolor insole finished product. The technical problems that a multi-color forming mode is tedious, the interface fusion degree is poor, the product performance is unstable, and the application scene is limited are effectively solved.

Description

Technical Field

[0001] This invention mainly relates to the field of insole manufacturing technology, specifically a physical supercritical foaming method for manufacturing multi-colored insoles. Background Technology

[0002] As consumers increasingly demand greater functionality and aesthetic diversity insoles, supercritical fluid foaming technology has become the mainstream technology for high-end insole manufacturing due to its advantages such as eliminating the need for chemical foaming agents, being environmentally friendly and pollution-free, and producing insoles with excellent elasticity and uniform density after foaming. This technology involves injecting supercritical fluids (such as ammonia, nitrogen, and carbon dioxide) into a polymer substrate, followed by rapid depressurization to allow the fluid to precipitate and form uniform pores, thereby obtaining lightweight and highly elastic insole products.

[0003] However, existing technologies for manufacturing insoles using physical supercritical foaming have significant limitations: due to limitations in molding processes and material compatibility, traditional methods can only achieve one-piece molding of single-color insoles. To meet the demand for multi-color appearances, the industry generally adopts two auxiliary solutions, but both have insurmountable drawbacks: First, a post-processing painting technique is used to color the single-color supercritical foamed insoles. In this method, the adhesion between the paint film and the insole substrate is poor, and wear and fading are likely to occur during long-term use. Moreover, the painting process introduces volatile harmful substances, which violates the environmental protection intention of physical supercritical foaming technology. Second, a staged small-scale foaming process is used, that is, different colored single-color insole blanks are first made separately, and then multi-color combinations are achieved by bonding with adhesives or hot pressing with molds. This solution is not only cumbersome and inefficient, but also suffers from weak interface bonding and easy delamination. Furthermore, the hot pressing process may damage the cell structure of the foamed blanks, leading to a decrease in the core performance of the insole, such as elasticity and shock absorption.

[0004] To resolve the contradiction between multi-color molding and interface fusion, some improvements have been attempted in existing technologies. For example, Chinese invention patent application CN119699719A discloses a two-color, dual-density shoe sole and its molding process. This process uses supercritical TPU beads as raw materials, forming a dual-chamber structure with a meltable partition plate within the mold. Different colored supercritical TPU beads are injected into each chamber, and the partition plate melts during the heating and foaming process, achieving a one-piece molding of the two-color shoe sole. This solves the problems of obvious dividing lines and poor fusion in traditional layered shoe soles. While this technology has made progress in interface fusion during multi-color physical supercritical foaming, it still has the following limitations and cannot meet the specific manufacturing requirements of insoles:

[0005] Limited applicability: This technology is designed for shoe soles. There are significant differences between shoe soles and insoles in terms of thickness, foot fit, and local cushioning performance. Its mold structure and foaming parameters cannot be directly adapted to the thinning and fine molding requirements of insoles.

[0006] Insufficient substrate compatibility: It uses TPU beads as the foaming substrate, while EVA material is the mainstream substrate in the insole field due to its superior softness, comfort and cost advantages. However, this technology does not involve the multi-color supercritical foaming compatibility design of EVA substrate.

[0007] Poor multi-color scalability: It can only achieve two-color molding and relies on the structural design of the mold partition plate. For three-color or more multi-color molding, the mold complexity will increase significantly and the production flexibility will be insufficient.

[0008] Insufficient interface reinforcement: Physical fusion is achieved only by melting the separator, without introducing active chemical or process reinforcement methods. The interface peel strength depends on the compatibility of the substrate itself. Under long-term pressure and bending use scenarios, there is still a risk of peeling.

[0009] In summary, existing physical supercritical foaming technology and related improvements still cannot efficiently and stably achieve the integrated fabrication of multi-colored insoles, resulting in problems such as cumbersome multi-color molding methods, poor interface fusion, unstable product performance, and limited application scenarios. Therefore, developing a physical supercritical foaming method that adapts to the characteristics of insoles, enables integrated multi-color molding, eliminates color migration at the interface, and achieves high fusion strength has become an urgent technical problem to be solved in this field. Summary of the Invention

[0010] The present invention addresses the problem of overly simplistic solutions in existing technologies by providing a significantly different approach. It offers a physical supercritical foaming method for manufacturing multi-colored insoles, thereby resolving the technical issues mentioned in the background section, such as cumbersome multi-color (two or more) color molding processes, poor interface integration, unstable product performance, and limited applicability.

[0011] In existing technologies, nucleating agents (such as nano-calcium carbonate) used in supercritical foaming are all added directly. The industry generally believes that uneven dispersion of nucleating agents is caused by insufficient mixing intensity of the equipment, and the solutions focus on optimizing stirring parameters or adding dispersants, without recognizing the possibility of temperature-responsive design. The PEG-400-coated nano-calcium carbonate in this invention requires precise matching of the coating layer's melting point (60°C) and foaming temperature (100-110°C). It is necessary to ensure the stability of the coating layer during low-temperature storage and to ensure that the coating layer melts precisely during foaming to release the nucleating agent. This design requires cross-processing of material synthesis and foaming processes. Existing technologies cannot easily conceive of solving the dispersion problem through core-shell structure design, and there is no industry precedent for the quantitative matching of coating layer thickness, foaming temperature, and nucleation rate.

[0012] Existing multi-color molding technologies employ a physical isolation approach, but the core challenge lies in the following: to prevent color migration, the heating temperature needs to be lowered (to avoid pigment migration), but low temperatures lead to insufficient interfacial physical fusion strength; conversely, to improve bonding strength, the temperature needs to be increased, which in turn triggers color migration. This invention resolves this contradiction through the amidation reaction of different compatibilizers (MAH-EVA / NH2-EVA), low-temperature heating at 105±3℃, and ultrasonic assistance. It allows the compatibilizers to undergo a chemical reaction at a specific temperature to form covalent bonds, while controlling the temperature to not exceed the pigment migration threshold. Simultaneously, ultrasound promotes molecular diffusion. This multi-parameter synergy of chemical bonding, precise temperature control, and physical assistance requires mastery of materials chemistry, process thermodynamics, and ultrasonic application technologies, which existing technologies struggle to achieve simultaneously.

[0013] EVA is the mainstream base material in the field of shoe insoles, but existing technologies suggest that there is an inherent conflict between the VA content, MFR parameters, and multi-color formulations of EVA: adding more than 3% masterbatch will reduce the melt flowability of EVA and affect the uniformity of cells in supercritical foaming; the introduction of compatibilizers may destroy the cross-linking structure of EVA, leading to a decrease in resilience. This invention achieves a balance between multi-color molding, uniform cells, and high resilience by limiting EVA parameters (MFR 2-5 g / 10 min, VA 18%-28%), precisely proportioning masterbatch at 3-5%, and optimizing compatibilizer at 3%. This precise formulation synergy requires extensive orthogonal experimental verification. Existing technologies mostly rely on empirical formulations and lack quantitative research on the interaction between EVA and additives, making it difficult to overcome the bottleneck of formulation compatibility.

[0014] The industry generally believes that multi-color molding of supercritical foam can only be achieved through equipment structure improvement or physical isolation. Few people realize that strengthening the interface bonding through material chemical reaction is the core prejudice. The core prejudice is that it is difficult to control the specificity of chemical reaction (avoiding pigment migration or material degradation) under the high temperature and high pressure environment of supercritical foam. Therefore, the chemical bonding path is abandoned by default, which makes it impossible to think of the amidation reaction design of different compatibilizers.

[0015] In existing technologies, the core function of nucleating agents is limited to refining cell structure. The industry generally believes that nucleating agents only need to be dispersible, failing to recognize the importance of their process adaptability. Traditional improvement approaches focus on optimizing nucleating agent particle size and increasing dispersant dosage, never considering the controllable timing of nucleating agent release. The temperature-responsive coating design of this invention requires transforming the nucleating agent from passive dispersion to active response to process temperature. This functional expansion exceeds the current understanding of nucleating agents, making it difficult to conceive of.

[0016] There's a prevailing misconception in the industry that EVA is unsuitable for multi-color supercritical foaming: fluctuations in EVA's VA content are believed to cause differences in foaming ratios across different color regions, leading to product deformation; furthermore, EVA's low melt strength makes multi-color interfaces prone to delamination due to uneven foaming pressure. Therefore, existing multi-color supercritical foaming technologies prioritize materials with high melt strength, such as TPU, over EVA. This invention overcomes this prejudice by precisely controlling EVA parameters and using compatibilizers for interfacial reinforcement. However, this reverse adaptation requires overturning traditional understandings of EVA material properties, making it extremely challenging.

[0017] Existing improvements to supercritical foaming technologies are mostly single-point optimizations: either improving foaming equipment (such as increasing pressure control precision) or adjusting material formulations, lacking a cross-process collaborative approach. The industry generally believes that ultrasound is only used for dispersion or welding, never realizing its dual function in different processes of supercritical foaming. This collaborative process innovation transcends the single-point improvement framework of existing technologies. This invention applies ultrasound assistance simultaneously to heating and fusion (28kHz, promoting interfacial molecular diffusion) and foaming depressurization (10kHz, increasing cell density), with precise matching of ultrasound parameters to temperature and pressure.

[0018] In summary, faced with the contradictions of multi-color molding, uniform cell structure, and interfacial bonding, the industry has traditionally resorted to sacrificing a single performance aspect or optimizing a single point (such as abandoning EVA in favor of TPU, or abandoning chemical bonding in favor of physical isolation). This long-term focus on single-point improvements has created path dependence, making it difficult for the industry to conceive of collaborative innovation across materials, processes, and equipment. This invention requires simultaneously solving three major challenges: temperature matching, formulation compatibility, and process synergy. Furthermore, it overturns the conventional wisdom of prioritizing physical properties, limiting functionality, and restricting material limitations, making it difficult to conceive of under current technological levels.

[0019] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0020] A physical supercritical foaming method for manufacturing multi-colored insoles includes the following steps:

[0021] S1. Raw material pretreatment: At least two different colored masterbatches are mixed with EVA substrate, compatibilizer, and temperature-responsive nucleating agent in proportion. The compatibilizer added to adjacent two different colored masterbatches is different. After drying, at least two mixtures are obtained. The compatibilizer includes maleic anhydride modified EVA and amine modified EVA.

[0022] S2. Preparation of multi-color cold preforms: The mixture is added to different barrels of a multi-color disc injection molding machine, and multi-color cold preforms are prepared by segmented temperature-controlled injection molding, pressure holding, and cooling and shaping.

[0023] S3, Heating and Fusion: The multi-color cold blanks are placed in the IP heating mold and preheated, fused and shaped to form a stable bond at the interface of the multi-color cold blanks;

[0024] S4. Physical supercritical foaming: The heated and fused preform is placed in a supercritical foaming tank, and supercritical fluid is introduced. The foamed preform is obtained by controlling the pressure and temperature and rapidly depressurizing.

[0025] S5. Shaping and post-processing: The foamed preform is shaped by a mold, cooled and demolded, and the rough edges are trimmed to obtain multi-colored insoles.

[0026] Preferably, in step S1, the melt flow rate of the EVA substrate is 2-5 g / 10 min, and the VA content is 18%-28%.

[0027] Specifically, the mass ratio of the masterbatch, EVA substrate, compatibilizer, and temperature-responsive nucleating agent is 3-5:100:3:1.

[0028] Specifically, in step S1, the temperature-responsive nucleating agent is PEG-400 coated nano-calcium carbonate with a particle size ≤5μm.

[0029] Furthermore, the preparation of the PEG-400-coated nano-calcium carbonate includes: ultrasonically dispersing nano-calcium carbonate in anhydrous ethanol and adding sorbitan oleate to obtain a calcium carbonate dispersion; adding a PEG-400 ethanol solution dropwise to the calcium carbonate dispersion; and then filtering, drying, crushing, air jet milling, and sieving to obtain PEG-400-coated nano-calcium carbonate.

[0030] Specifically, in step S2, the segmented temperature-controlled injection molding includes: front section temperature control of 175±3℃, middle section temperature control of 180±3℃, and rear section temperature control of 185±3℃; the injection pressure is 80~100MPa;

[0031] Preferably, the pressure holding time is 15 to 20 seconds;

[0032] Preferably, the cooling water temperature is 20–25°C.

[0033] Specifically, in step S3, the specific parameters for the heating and fusion are: during the preheating stage, the mold is heated to 90±5℃ and kept at that temperature for 4 to 6 minutes;

[0034] Specifically, during the fusion stage, the mold temperature is raised to 105±3℃ and held for 10 to 14 minutes;

[0035] Specifically, during the shaping stage, the mold temperature drops to 80±2℃.

[0036] Preferably, in step S3, the IP heating mold is integrated with an ultrasonic vibration device. During the fusion stage, the ultrasonic vibration device is turned on, with an ultrasonic frequency of 28kHz, an amplitude of 10μm, and a power of 800W.

[0037] Preferably, in step S4, the supercritical fluid is nitrogen.

[0038] Specifically, the preset pressure of the supercritical foaming tank is 20-25 MPa, the temperature is 100-110℃, and the residence time of the preform in the tank is 60-80 minutes.

[0039] Preferably, the rapid depressurization time is ≤8 seconds.

[0040] Preferably, in step S4, a low-frequency ultrasonic device is integrated inside the foaming tank. The ultrasonic device is activated during the rapid depressurization phase, with an ultrasonic frequency of 10kHz and an amplitude of 5μm.

[0041] Specifically, in step S5, the conditions for mold shaping include: mold temperature of 60-70°C, mold closing pressure of 50-60 MPa, and holding pressure time of 15-25 seconds;

[0042] Specifically, during cooling and demolding, the cooling water temperature is 20±3℃, and the cooling time is 20 to 30 seconds.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] (1) This invention achieves precise injection of mixed materials of different colors by controlling the temperature of the independent barrel and switching the rotation of the mold in a multi-color disc injection molding machine, and directly produces multi-color cold blanks. The multi-color cold blanks are formed in one step. No additional splicing or painting process is required afterward. The cold blanks can be integrated into one piece after heating and fusion, supercritical foaming and post-molding treatment, which reduces the time spent on process connection. It completely abandons the cumbersome mode of single-color foaming followed by painting and multiple small foaming followed by hot pressing in the existing technology, avoids secondary defects such as paint fading and lamination delamination, improves production efficiency, and greatly reduces production complexity and cost.

[0045] (2) The compatibilizers used in this invention include MAH-EVA and NH2-EVA, and different compatibilizers are suitable for adjacent color mixtures. In the heating and fusion step, the MAH groups and NH2 groups of the compatibilizer undergo an amidation reaction at 105±3℃ (below the heat migration threshold of the pigment), forming chemical covalent bonds, which upgrades the multicolor interface from physical adhesion to chemical bonding. Furthermore, ultrasonic vibration can promote the diffusion of interfacial molecules, making the thickness of the two-phase molecular diffusion layer ≥5μm, further improving the bonding strength. This solves the contradiction of existing technologies that require low temperature for color migration prevention (leading to weak bonding) and high temperature for strong bonding (leading to color migration), achieving the dual effect of no color migration and high peel strength.

[0046] (3) This invention uses a temperature-responsive nucleating agent, which is stable and does not agglomerate at room temperature. After entering a supercritical foaming tank at 135-145℃, the coating layer melts and releases the core, which is uniformly dispersed and rapidly nucleates, resulting in a cell diameter ≤0.3mm. Furthermore, the parameters of the EVA substrate are precisely matched with the ratio of color masterbatch, compatibilizer, and nucleating agent, taking into account both melt flowability and crosslinking stability, ensuring a balance between elasticity and density after foaming. Low-frequency ultrasound can also be activated during the foaming depressurization stage to promote uniform nitrogen precipitation, thereby increasing the cell density and preventing large cells from accounting for more than 5%. This overcomes the defects of uneven nucleating agent dispersion and inconsistent cell size in the prior art, and significantly improves the consistency of core performance indicators.

[0047] (4) This invention selects EVA with a medium melt flow rate and VA content, which ensures the injection flowability of the multi-color mixture and avoids the foaming ratio fluctuation caused by excessive VA content; and the amount of color masterbatch added is controlled at 3-5%, which satisfies the color depth requirements without damaging the melt strength of EVA; the amount of compatibilizer just meets the requirements of interfacial chemical reaction and does not affect the cross-linking structure of EVA, ensuring the core characteristics of soft and comfortable insoles. It breaks the industry's inherent perception that EVA is not suitable for multi-color supercritical foaming. Compared with the TPU substrate used in the existing technology, EVA material is not only cheaper, but also more suitable for the insole usage scenarios in terms of softness and foot shape fit, while avoiding the defects of TPU substrate that are too hard and not comfortable enough.

[0048] (5) This invention prepares mixtures of different colors separately. Only by adjusting the type of masterbatch and the compatibilizer (MAH-EVA and NH2-EVA are used alternately) can two-color, three-color and more multi-color molding be achieved without changing the core process parameters and mold structure. It overcomes the limitations of the existing technology, which can only achieve two-color molding and requires complex mold modification for multi-color molding. The production flexibility is significantly improved, and it can quickly respond to the market demand for different color combinations, thereby solving the problem of poor multi-color scalability.

[0049] The present invention will be explained in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0050] Figure 1 This is a process flow diagram of the present invention;

[0051] Figure 2 This is a bar chart showing the color deviation between the embodiment of the invention and the comparative example product;

[0052] Figure 3 This is a bar chart showing the interfacial peel strength of the embodiments and comparative examples of the present invention.

[0053] Figure 4 The graph shows the cell diameter and density of the products in the embodiments and comparative examples of this invention.

[0054] Figure 5 This is a bar chart showing the compression rebound rate of the embodiments and comparative products of the present invention;

[0055] Figure 6 This is a bar graph showing the Martindale abrasion resistance of the embodiments and comparative products of the present invention;

[0056] Figure 7 This is a product illustration of the present invention. Detailed Implementation

[0057] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the present invention. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. Rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly associated with those skilled in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0059] Example 1: Please refer to the appendix for details. Figure 1 A physical supercritical foaming method for manufacturing multi-colored insoles includes the following steps:

[0060] 1. Raw material preparation

[0061] (1) Substrate: Select EVA particles suitable for physical supercritical foaming, with a melt flow rate (MFR) of 4g / 10min and a VA content of 22% to ensure the balance of elasticity and density after foaming.

[0062] (2) Color masterbatch: Select at least two different colors (such as white and yellow) of color masterbatch. The color masterbatch must have good compatibility with the EVA substrate. The color concentration should be adjusted in advance according to the target color depth. The color masterbatch addition ratio is 4% of EVA.

[0063] (3) Additives: compatibilizer, temperature-responsive nucleating agent (to refine the pores, with a target pore diameter ≤ 0.3 mm).

[0064] Compatibilizers include maleic anhydride-modified EVA (MAH-EVA) and amino-modified EVA (NH2-EVA). The grafting rate of MAH-EVA is 0.8–1.5%; amino-modified EVA (NH2-EVA) is a product of chemically modifying ethylene-vinyl acetate copolymer (EVA) by introducing amino groups, for example, by combining amino groups with the EVA molecular chain through a Schiff base reaction to achieve chemical grafting, with an amino content of 0.3–0.8 mmol / g.

[0065] The temperature-responsive nucleating agent uses coated nano-calcium carbonate, specifically polyethylene glycol-400 (melting point 60℃) coated on the outer layer of nano-calcium carbonate. The selected particles have a particle size of 10–50 nm and a specific surface area of ​​15–20 m². 2 / g of nano-calcium carbonate; the thickness of the polyethylene glycol-400 coating layer is 10-30nm. The nucleating agent is stable at room temperature; after entering the supercritical foaming tank (100-110℃), the nucleating agent is rapidly released and dispersed, which increases the cell nucleation rate and avoids the uneven cell structure caused by nucleating agent agglomeration at low temperatures. Through the temperature-responsive release mechanism of this nucleating agent, the pain point of uneven premature dispersion of nucleating agents in existing processes can be solved.

[0066] The preparation method of coated nano-calcium carbonate is as follows:

[0067] S1. Pretreatment of nano-calcium carbonate: Nano-calcium carbonate is ultrasonically dispersed in anhydrous ethanol at a ratio of 80g:500mL; sorbitan oleate (Span-80) is added at a ratio of 0.5g:80g to nano-calcium carbonate. The mixture is stirred at a temperature below 30°C to obtain a uniform and transparent calcium carbonate dispersion.

[0068] S2, PEG-400 coating reaction: First, mix PEG-400 with anhydrous ethanol and stir until PEG-400 is completely melted to form a transparent PEG-400 ethanol solution, wherein the ratio of PEG-400 to anhydrous ethanol is 10g:50mL; then, add the PEG-400 ethanol solution dropwise to the calcium carbonate dispersion, controlling the dropping rate at 1-1.5mL / min, while maintaining a stirring speed of 400rpm and a reaction temperature of 65-70℃. This temperature is slightly higher than the melting point of PEG to ensure that PEG is in a molten state and uniformly adsorbed on the surface of calcium carbonate; after the addition is complete, maintain the temperature and stirring speed for 1-1.5 hours to allow PEG molecules to fully form a tight adsorption layer on the surface of calcium carbonate;

[0069] S3. Filtration and Drying: Pour the mixture after the coating reaction into a Buchner funnel and filter using a vacuum pump at a vacuum degree ≤ -0.08 MPa. Collect the filter cake and wash it 2-3 times with a small amount of anhydrous ethanol to remove unadsorbed free PEG. Then transfer the filter cake to a vacuum drying oven, set the temperature to 50-55℃ (below the melting point of PEG 60℃ to avoid melting and agglomeration of the coating layer, which would damage the core-shell structure), and the vacuum degree ≤ -0.09 MPa. Dry for 4-6 hours. The dried filter cake will be in block form. Then gently crush the dried filter cake with a mortar and pestle to a particle size ≤ 5 μm to avoid damaging the coating layer by grinding too hard.

[0070] S4. Post-processing: The pre-crushed sample is fed into an air jet mill, the milling pressure is adjusted to 0.6-0.8 MPa, and the sample is passed through a 5000-mesh sieve to obtain coated nano-calcium carbonate with uniform particle size.

[0071] (4) Raw material pretreatment: The color masterbatch of different colors is mixed with EVA substrate, compatibilizer and temperature-responsive nucleating agent in a mass ratio of 4:100:3:1. The compatibilizer is one of maleic anhydride modified EVA (MAH-EVA) or amino modified EVA (NH2-EVA), and the compatibilizer added to the two adjacent different color masterbatches is different. Then, it is dried at 85°C for 5 hours to remove moisture, so as to avoid the generation of bubble defects during foaming and to make the additives evenly dispersed, so as to obtain at least two kinds of mixtures.

[0072] 2. Equipment debugging:

[0073] (1) Check the barrel temperature and injection pressure system of the two-color disc injection molding machine to ensure that each barrel has independent temperature control and injection accuracy error ≤0.5%.

[0074] (2) Preheat the IP heating mold and the nitrogen supercritical foaming tank. The temperature control range of the IP mold is set to 90-110℃, and the preset pressure of the foaming tank is 20-25MPa and the temperature is 100-110℃.

[0075] (3) Ultrasonic system: A 28kHz ultrasonic vibration device is integrated in the IP heating mold, with an amplitude adjustment range of 0 to 15μm and a power of 500 to 1000W, to ensure that the vibration energy is uniformly applied to the interface of the two-color preform.

[0076] (4) Infrared temperature measurement system: Install an online infrared thermal imager to monitor the temperature distribution of the embryo in real time. The temperature resolution is ≤0.1℃ and it is used for closed-loop control of the heating process.

[0077] 3. Multicolor cold preform preparation process

[0078] (1) The dried mixtures are added to different cylinders of the multicolor disc machine. The cylinder temperature is controlled in sections: 175℃ in the front section, 180℃ in the middle section, and 185℃ in the back section.

[0079] (2) Start the injection molding program. Through the rotation of the disc mold, multiple colors are accurately injected into the mold. The injection time is controlled at 8-10 seconds / mold, and the injection pressure is controlled at 90MPa.

[0080] (3) After the injection is completed, hold the pressure for 18 seconds, turn on the mold cooling water circuit (water temperature 25℃), and cool for 30 seconds to solidify the cold blank.

[0081] (4) After mold opening, remove the multi-color cold blanks and check the clarity of color boundaries and the integrity of the blanks. The first piece of each day needs to be dimensionally inspected, with a length error of ≤0.2mm. The production capacity is 100 pairs / mold / day.

[0082] 4. Heating and fusion process

[0083] (1) Embryo body placed into mold

[0084] Place the multi-color cold blank into the cavity of the IP heating mold, ensuring that the blank and the mold cavity fit completely to avoid wrinkles during heating; set an ultrasonic vibration module in the mold cavity corresponding to the two-color interface area.

[0085] (2) Multi-stage process:

[0086] ① Preheating stage: After closing the mold, start the heating program and heat the entire mold to 90℃. Keep it warm for 5 minutes to soften the surface of the blank.

[0087] ②Ultrasonic fusion stage: Turn on the ultrasonic waves at a frequency of 28kHz, an amplitude of 10μm, and a power of 800W. At the same time, raise the mold temperature to 105℃ (5℃ lower than the traditional process to avoid heat migration of the pigment) and keep it at that temperature for about 12 minutes.

[0088] In the IP heating mold, the MAH group and the NH2 group undergo an amidation reaction to form a chemically covalently bonded interface, which improves the interfacial peel strength and avoids pigment migration caused by high temperature.

[0089] ③ Shaping stage: Turn off the ultrasonic waves, lower the mold temperature to 80℃, and keep it warm for 3 minutes to shape the fusion interface.

[0090] Infrared closed-loop control: The temperature of the preform is monitored in real time by a thermal imager. When the interface temperature deviation is greater than 2°C, the mold heating power is automatically adjusted to ensure improved molecular fusion uniformity. This avoids pigment migration caused by localized high temperatures and ensures that the chemical reaction proceeds fully.

[0091] (4) Validation of fusion effect

[0092] After heating, open the mold and observe the fusion state of the preform: there should be no obvious layering in the color transition area, and no color migration should occur (if color migration occurs, the heating temperature or time needs to be adjusted). Alternatively, use an optical microscope (500x magnification) to observe the interface microstructure, requiring the thickness of the two-phase molecular diffusion layer to be ≥5μm, and no obvious migration of pigment particles across regions.

[0093] 5. Physical supercritical foaming process

[0094] (1) Embryo transfer and in-tank treatment

[0095] ① Let the heated and fused embryo stand for 6 minutes to make the temperature uniform, and then put it into a nitrogen supercritical foaming tank. The tank is pre-filled with nitrogen to a pressure of 23MPa and a temperature of 105℃ (to maintain the supercritical state).

[0096] ② Foaming time control: The preform is kept in the tank for 70 minutes to allow nitrogen to fully dissolve in the EVA material.

[0097] (2) Ultrasonic-assisted foaming

[0098] ① Quickly open the pressure relief valve of the foaming tank to reduce the pressure inside the tank to normal pressure within 8 seconds, and nitrogen gas will be released from the EVA to form uniform bubbles.

[0099] ② A low-frequency ultrasonic device with a frequency of 10kHz and an amplitude of 5μm is integrated into the foaming tank; the ultrasonic wave is turned on during the depressurization foaming stage to promote uniform nucleation of the foam cells and increase the foam cell density.

[0100] ③ Remove the preform after foaming: After the pressure inside the tank stabilizes, remove the preform; the production capacity of this process is 120 pairs / hour / tank.

[0101] (3) Quality inspection after foaming

[0102] Density testing: The water displacement method is used, with a target density of 0.18–0.22 g / cm³ (which can be tested using the water displacement method), and a density deviation of ≤0.01 g / cm³ for the same batch.

[0103] Pore ​​detection: Cut open the sample and observe it with a scanning electron microscope (SEM). The pores should be uniform and free of large pores (pores with a diameter > 0.4 mm account for < 5%).

[0104] 6. Mold shaping

[0105] (1) Shaping treatment

[0106] ① Place the foamed preform into a molding mold (such as a shoe insole mold with embossed texture), set the mold temperature to 65℃, the mold closing pressure to 55MPa, and the holding time to 20 seconds.

[0107] ② Cooling and demolding: Turn on the cooling water channel of the mold (water temperature 20℃), cool for 25 seconds, open the mold and take out the molded insole.

[0108] (2) Quality Inspection

[0109] After each mold is removed, the shape, texture clarity, and dimensional accuracy of the insole must be checked (length and width error ≤ 0.3mm).

[0110] 7. Post-processing and final inspection procedures

[0111] (1) Trimming rough edges

[0112] Pneumatic trimmers are used to remove rough edges from the insoles, ensuring smooth, burr-free edges; alternatively, laser trimming equipment is used for precise removal of rough edges, achieving an edge roughness Ra ≤ 1.6μm. Insole products such as... Figure 7 As shown.

[0113] (2) Quality inspection

[0114] ① Foam cell inspection: Cut open the insole to observe the foam cell structure. The foam cells should be uniform and free of large foam cells (foam cell diameter ≤ 0.5 mm).

[0115] ② Color detection: A spectrophotometer is used for detection, and the color deviation is compared with the standard color card. The color deviation △E ≤ 2.0.

[0116] ③ Yellowing resistance test: After 168 hours of irradiation in a UV aging chamber, the yellowing level is ≤3.

[0117] ④ Performance testing: Randomly select samples for compression rebound test (rebound rate ≥60%) and abrasion resistance test (Martindale abrasion resistance ≥50,000 cycles).

[0118] (3) Packaging and warehousing

[0119] The qualified insoles are packed according to specifications, labeled with batch and quantity, and placed in the finished product warehouse for shipment.

[0120] Example 2: The difference between this example and Example 1 is that:

[0121] The EVA particles have a melt flow rate (MFR) of 2 g / 10 min and a VA content of 18%.

[0122] During raw material pretreatment, masterbatches of different colors are mixed with EVA substrate, compatibilizer, and temperature-responsive nucleating agent in a mass ratio of 3:100:3:1.

[0123] Multi-color disc mill barrel temperature is controlled in segments: front section 172℃, middle section 177℃, rear section 182℃;

[0124] Start the injection molding process, and control the injection pressure at 80MPa;

[0125] After the material is injected, the pressure is held for 15 seconds, and the cooling water temperature is 20℃.

[0126] In the heating and fusion process, during the preheating stage, the mold is heated to 85°C and held for 6 minutes; during the ultrasonic fusion stage, the mold temperature is raised to 102°C and held for about 14 minutes; during the shaping stage, the mold temperature is lowered to 78°C.

[0127] In the physical supercritical foaming process, the heated and fused preform is left to stand for 5 minutes to ensure uniform temperature, and then placed in a nitrogen supercritical foaming tank. The tank is pre-filled with nitrogen to a pressure of 20 MPa and a temperature of 110°C; the preform is kept in the tank for 60 minutes.

[0128] During the mold forming process, the mold temperature is set to 60℃, the mold closing pressure is 50MPa, and the holding time is 25 seconds. The cooling and demolding water temperature is 17℃, the cooling time is 20 seconds, and the molded insole is then removed.

[0129] The rest is the same as in Example 1.

[0130] Example 3: The difference between this example and Example 1 is that:

[0131] The EVA particles have a melt flow rate (MFR) of 5 g / 10 min and a VA content of 28%.

[0132] During raw material pretreatment, masterbatches of different colors are mixed with EVA substrate, compatibilizer, and temperature-responsive nucleating agent in a mass ratio of 5:100:3:1.

[0133] Multi-color disc mill barrel temperature is controlled in segments: front section 178℃, middle section 183℃, rear section 188℃;

[0134] Start the injection molding process, and control the injection pressure at 100MPa;

[0135] After injection, maintain pressure for 20 seconds, and keep the cooling water temperature at 25°C.

[0136] In the heating and fusion process, during the preheating stage, the mold is heated to 95°C and held for 4 minutes; during the ultrasonic fusion stage, the mold temperature is raised to 108°C and held for about 10 minutes; during the shaping stage, the mold temperature is lowered to 82°C.

[0137] In the physical supercritical foaming process, the heated and fused preform is left to stand for 8 minutes to ensure uniform temperature, and then placed in a nitrogen supercritical foaming tank. The tank is pre-filled with nitrogen to a pressure of 25 MPa and a temperature of 100°C; the preform is kept in the tank for 80 minutes.

[0138] During the mold forming process, the mold temperature is set to 70℃, the mold closing pressure is 60MPa, and the holding time is 15 seconds. The cooling and demolding water temperature is 23℃, the cooling time is 30 seconds, and the molded insole is then removed.

[0139] The rest is the same as in Example 1.

[0140] Comparative Example 1: The difference from Example 1 is that:

[0141] A single-color material is used for physical supercritical foaming, followed by subsequent painting to create multi-color effects.

[0142] The rest is the same as in Example 1.

[0143] Comparative Example 2: The difference from Example 1 is that:

[0144] First, single-color insole blanks of different colors are made separately, and then multi-color combinations are achieved by bonding with adhesives or hot pressing with molds.

[0145] The rest is the same as in Example 1.

[0146] Comparative Example 3: The difference from Example 1 is that:

[0147] A single compatibilizer is used, consisting only of MAH-EVA.

[0148] The rest is the same as in Example 1.

[0149] Comparative Example 4: The difference from Example 1 is that:

[0150] Ultrasonic assistance is not used in the heating and fusion process.

[0151] The rest is the same as in Example 1.

[0152] Comparative Example 5: The difference from Example 1 is that:

[0153] Ultrasonic assistance is not used in the foaming process.

[0154] The rest is the same as in Example 1.

[0155] Comparative Example 6: The difference from Example 1 is that:

[0156] Nano-calcium carbonate (without PEG-400 coating) was used as a nucleating agent.

[0157] The rest is the same as in Example 1.

[0158] Comparative Example 7: The difference from Example 1 is that:

[0159] The mass ratio of color masterbatch, EVA substrate, compatibilizer, and nucleating agent is 8:100:5:2.

[0160] The rest is the same as in Example 1.

[0161] Comparative Example 8: The difference from Example 1 is that:

[0162] The mass ratio of color masterbatch, EVA substrate, compatibilizer, and nucleating agent is 2:100:2:0.5.

[0163] The rest is the same as in Example 1.

[0164] Comparative Example 9: The difference from Example 1 is that:

[0165] The multi-color disc injection molding machine does not have segmented temperature control; the temperature is controlled at 180℃ throughout the entire process.

[0166] The rest is the same as in Example 1.

[0167] Comparative Example 10: The difference from Example 1 is that:

[0168] The fusion stage of the heating and fusion process involves heating at a high temperature above 110℃.

[0169] The rest is the same as in Example 1.

[0170] The insole products prepared in Examples 1-3 and Comparative Examples 1-10 are compared and tested below:

[0171] (1) Color deviation (ΔE)

[0172] Referring to the CIE Lab standard, a spectrophotometer is used to compare the sample with the standard color chart and calculate the color difference value. The smaller the ΔE, the more stable the color.

[0173] (2) Color migration at multi-color interfaces

[0174] Referring to the industry visual rating (0-5 levels), the interface is observed with an optical microscope (500x). Level 0 shows no color transfer, while level 5 shows severe color transfer.

[0175] (3) Interfacial peel strength (N / cm)

[0176] A T-shaped peel test was performed using a universal tensile testing machine at a speed of 50 mm / min, and the average value of three tests was taken.

[0177] (4) Cell diameter (mm) and cell density (cells / cm³)

[0178] According to the industry standard for foam material cell testing, the cross-section of the sample was observed using a scanning electron microscope (SEM), the diameter of 100 cells was counted, and the average value was taken; the number of cells per unit volume was counted using a scanning electron microscope (SEM).

[0179] (5) Compression rebound rate (%)

[0180] Referring to the method in GB / T 20671.2-2025, compress to 50% and then release, then calculate the rebound recovery ratio.

[0181] (6) Martindale wear resistance (10,000 cycles)

[0182] The abrasion resistance of antibacterial insoles was tested using a Martindale abrasion tester at a pressure of 12 kPa and with standard wool cloth as the abrasive. The test was conducted to determine the number of times the sample would break.

[0183] (7) Yellowing resistance grade

[0184] Referring to the ASTM D1148-2013 method, the yellowing was compared after 168 hours of UV aging chamber irradiation. Level 1 was the most severe, while Level 5 showed no yellowing.

[0185] Please see Table 1 for the test data. Figure 2-6 .

[0186] Table 1 Summary of experimental data for examples and comparative examples

[0187] project Color deviation (ΔE) Color bleeding level Interfacial peel strength (N / cm) Bubble diameter (mm) <![CDATA[Cell density (×10 6 cells / cm³)]]> Compression rebound rate (%) Martindale abrasion resistance (10,000 cycles) Yellowing resistance rating Example 1 1.2 Level 0 32.6 0.22 8.6 65.3 6.2 Level 4 Example 2 1.5 Level 0 30.8 0.25 7.9 63.8 5.8 Level 4 Example 3 1.3 Level 0 31.5 0.23 8.3 64.5 6.0 Level 4 Comparative Example 1 3.8 Level 2 / 0.35 5.2 62.1 2.3 Level 3 Comparative Example 2 2.5 Level 1 15.3 0.32 5.8 58.7 3.5 Level 3 Comparative Example 3 1.4 Level 0 18.7 0.24 8.1 63.2 5.5 Level 4 Comparative Example 4 1.6 Level 0 22.5 0.23 7.5 61.5 5.3 Level 4 Comparative Example 5 1.3 Level 0 31.2 0.28 6.3 60.8 5.1 Level 4 Comparative Example 6 1.5 Level 0 30.5 0.41 4.1 57.3 4.8 Level 3 Comparative Example 7 2.8 Level 1 25.4 0.30 6.8 59.2 4.2 Level 3 Comparative Example 8 3.2 Level 2 16.8 0.27 7.2 62.5 5.6 Level 4 Comparative Example 9 2.1 Level 1 28.3 0.26 7.0 61.3 5.4 Level 3 Comparative Example 10 4.5 Level 4 29.7 0.24 8.0 63.7 5.7 Level 3

[0188] Note: Comparative Example 1 is a single-color foaming process followed by painting, and does not include data on interfacial peel strength.

[0189] From Table 1 and Figure 2-6 It can be known that:

[0190] (1) Multicolor stability: No color migration was observed in the examples, and the color deviation was better than that of the comparative examples.

[0191] Comparative Example 1 (Post-painting): ΔE=3.8, color migration level 2. Slight color fading occurred due to poor adhesion between the paint film and the substrate. Comparative Example 7 (Excessive masterbatch): Color deviation ΔE=2.8, color migration level 1. Excessive masterbatch is difficult to fully integrate with the EVA substrate, resulting in uneven color dispersion and slight color migration at the edges. At the same time, excessive masterbatch occupies the space of the EVA melt, affecting the diffusion of interfacial molecules and indirectly leading to increased color deviation. Comparative Example 8 (Insufficient masterbatch): ΔE=3.2, color migration level 2. Insufficient color depth and slight diffusion at the edges. Comparative Example 9 (Multi-color disc injection molding machine with constant temperature throughout): Color deviation ΔE=2.1, color migration level 1. This resulted in insufficient melting of the melt in the front section of the barrel and low melt viscosity in the rear section. During injection, different colored melts mixed and diffused, resulting in slight color migration. Comparative Example 10 (High-temperature fusion): ΔE=4.5, color migration level 4. High temperature caused severe migration of the colorant. The color deviation ΔE of Examples 1 to 3 is ≤1.5, and the color migration level is 0, indicating that the combination of different compatibilizers, low temperature fusion, and ultrasonic assistance in this invention effectively avoids pigment migration and has extremely strong color stability.

[0192] (2) Interface performance: The peel strength of the example is better than that of the comparative example.

[0193] The interfacial peel strength of Examples 1 to 3 was ≥30.8 N / cm, significantly higher than that of Comparative Example 2 (lamination process, 15.3 N / cm) and Comparative Example 3 (single compatibilizer, 18.7 N / cm), demonstrating that the present invention upgrades the interface from physical adhesion to chemical bonding through the MAH-EVA / NH2-EVA chemical reaction and ultrasonic molecular diffusion. Furthermore, the peel strength of Comparative Example 4 (no ultrasonic fusion) was 22.5 N / cm, approximately 25% lower than the examples, indicating that ultrasonic vibration can significantly promote interfacial molecular diffusion and enhance bonding strength. The peel strength of Comparative Example 7 (excessive masterbatch) was 25.4 N / cm, approximately 22% lower than Example 1. Excessive compatibilizer aggregated at the interface, hindering the amidation reaction between MAH and NH2 groups, leading to a reduction in chemical bonding sites. The interfacial bonding strength degenerated from chemical dominance to a mixed chemical and physical bond, resulting in a decrease in strength.

[0194] (3) Cell structure: The cells in the example are more uniform and have higher density.

[0195] In Examples 1 to 3, the cell diameter was ≤0.25mm and the cell density was ≥7.9×10⁻⁶. 6 Cells / cm³, due to the precise nucleation achieved by the PEG-400-coated nucleating agent, and the ultrasonic assistance during the foaming stage promoting uniform nitrogen release. Comparative Example 6 (without nucleating agent coating) had a cell diameter of 0.41 mm and a density of 4.1 × 10⁻⁶. 6 Cells / cm³, nucleating agent aggregation leads to large and uneven pores; Comparative Example 5 (without ultrasonic foaming) has a pore density of 6.3 × 10⁻⁶. 6 The density per centimeter was approximately 20% lower than in the previous example, demonstrating that ultrasound assistance significantly improved the cell density.

[0196] (4) Performance in use: The example shows leading resilience and abrasion resistance, and stable resistance to yellowing.

[0197] The example showed a compression rebound rate of ≥63.8%, a Martindale abrasion resistance of ≥58,000 cycles, and a yellowing resistance level of 4. This was due to the precise matching of EVA substrate parameters and formulation, resulting in a uniform cell structure and strong interfacial bonding. Comparative Example 6 (without nucleating agent coating) showed a rebound rate of 57.3% and abrasion resistance of 48,000 cycles, with uneven cell structure leading to performance degradation. Comparative Example 1 (post-painting) only showed abrasion resistance of 23,000 cycles, with the paint film easily worn away and peeling off.

[0198] In summary, this invention, through a synergistic technical solution involving chemical reactions with different compatibilizers, temperature-responsive nucleating agents, two-stage ultrasonic assistance, and precise temperature control, comprehensively outperforms the comparative example in terms of multicolor stability, interfacial strength, cell uniformity, performance, and production efficiency. Furthermore, the parameters in Example 1 represent the optimal combination, with the most balanced performance indicators, making them suitable as preferred parameters for industrial production.

[0199] The present invention has been described by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvement made by adopting the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, shall be within the protection scope of the present invention.

Claims

1. A method for manufacturing multi-colored insoles using physical supercritical foaming, characterized in that: Includes the following steps: S1. Raw material pretreatment: At least two different colored masterbatches are mixed with EVA substrate, compatibilizer, and temperature-responsive nucleating agent in proportion. The compatibilizer added to adjacent two different colored masterbatches is different. After drying, at least two mixtures are obtained. The compatibilizer includes maleic anhydride modified EVA and amine modified EVA. S2. Preparation of multi-color cold preforms: The mixture is added to different barrels of a multi-color disc injection molding machine, and multi-color cold preforms are prepared by segmented temperature-controlled injection molding, pressure holding, and cooling and shaping. S3, Heating and Fusion: The multi-color cold blanks are placed in the IP heating mold and preheated, fused and shaped to form a stable bond at the interface of the multi-color cold blanks; S4. Physical supercritical foaming: The heated and fused preform is placed in a supercritical foaming tank, and supercritical fluid is introduced. The foamed preform is obtained by controlling the pressure and temperature and rapidly depressurizing. S5. Shaping and post-processing: The foamed preform is shaped by a mold, cooled and demolded, and the rough edges are trimmed to obtain multi-colored insoles.

2. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S1, the melt flow rate of the EVA substrate is 2-5 g / 10 min, and the VA content is 18%-28%. And / or, the mass ratio of the masterbatch, EVA substrate, compatibilizer and temperature-responsive nucleating agent is 3-5:100:3:

1.

3. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S1, the temperature-responsive nucleating agent is PEG-400 coated nano-calcium carbonate with a particle size ≤5μm.

4. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 3, characterized in that: The preparation of the PEG-400-coated nano-calcium carbonate includes: ultrasonically dispersing nano-calcium carbonate in anhydrous ethanol and adding sorbitan oleate to obtain a calcium carbonate dispersion; adding PEG-400 ethanol solution dropwise to the calcium carbonate dispersion; and then filtering, drying, crushing, air jet milling, and sieving to obtain PEG-400-coated nano-calcium carbonate.

5. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S2, the segmented temperature-controlled injection molding includes: front section temperature control of 175±3℃, middle section temperature control of 180±3℃, and rear section temperature control of 185±3℃; the injection pressure is 80~100MPa; And / or, the pressure holding time is 15 to 20 seconds; And / or, the cooling water temperature is 20–25°C.

6. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S3, the specific parameters for the heating and fusion are as follows: during the preheating stage, the mold is heated to 90±5℃ and kept at that temperature for 4 to 6 minutes; And / or, during the fusion stage, the mold temperature is raised to 105±3℃ and held for 10 to 14 minutes; And / or, during the shaping stage, the mold temperature is reduced to 80±2℃.

7. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S3, the IP heating mold is integrated with an ultrasonic vibration device. During the fusion stage, the ultrasonic vibration device is turned on with an ultrasonic frequency of 28kHz, an amplitude of 10μm, and a power of 800W.

8. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S4, the supercritical fluid is nitrogen. And / or, the preset pressure of the supercritical foaming tank is 20-25 MPa, the temperature is 100-110℃, and the residence time of the preform in the tank is 60-80 minutes; And / or, rapid pressure relief time ≤ 8 seconds.

9. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S4, a low-frequency ultrasonic device is integrated inside the foaming tank. The ultrasonic device is activated during the rapid depressurization phase, with an ultrasonic frequency of 10kHz and an amplitude of 5μm.

10. The method for manufacturing multi-colored insoles using physical supercritical foaming according to claim 1, characterized in that: In step S5, the conditions for mold shaping include: mold temperature of 60-70°C, mold closing pressure of 50-60 MPa, and holding pressure time of 15-25 seconds; And / or, during cooling and demolding, the cooling water temperature is 20±3℃, and the cooling time is 20 to 30 seconds.

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