Synchronous foaming method for heterogeneous materials

Abstract

The invention provides a synchronous foaming method for heterogeneous materials. The synchronous foaming method comprises the following steps that S10, a solid blank made of a first elastomer material and a granular material made of a second elastomer material are provided; s20, a foaming mold is filled with the solid blank and the granular materials; the foaming mold is provided with a first area and a second area, the mold cavity depth of the first area is a first depth, the mold cavity depth of the second area is a second depth, and the ratio of the second depth to the first depth is 0.65-0.75; the solid blank is placed in the first area, and the second area is filled with the granular materials; s30, the foaming mold is closed, and vacuumizing is started when the gap between the upper mold body and the lower mold body of the mold ranges from 5 mm to 10 mm, so that the vacuum degree in a foaming mold cavity reaches-0.08 MPa to-0.10 MPa within 5 s; and S40, the vacuum state is kept, the foaming mold is heated, and the solid blank and the granular materials are synchronously foamed, cured and combined in the same mold cavity. The synchronous foaming method can improve the problem of low interface bonding strength of two materials.

Description

Technical Field

[0001] This invention relates to the field of simultaneous foaming technology, and more specifically to a method for simultaneous foaming of heterogeneous materials. Background Technology

[0002] In the manufacturing of footwear materials, packaging, and cushioning pads, it is often necessary to produce heterogeneous foamed products with two colors or two densities to give different physical properties (such as a combination of high resilience and shock absorption) in local areas of the product. Currently, the main methods for bonding heterogeneous materials include secondary cold bonding and simultaneous foaming processes. The secondary cold bonding process typically involves foaming the two materials separately, then bonding them by surface polishing, applying chemical treatment agents, and using adhesives. This process is cumbersome, and the use of chemical agents can pollute the environment. Furthermore, the bonding strength at the interface is greatly affected by the quality of the adhesive and the consistency of the process, making the product prone to delamination during use. The simultaneous foaming process involves placing both materials together in the same mold for a single heating and foaming process. In existing simultaneous foaming technologies, because the heated areas and heating rates of the two materials are basically the same, they often reach the cross-linking reaction point simultaneously during the heating process. During the cross-linking reaction, the polymer chains inside the material are rapidly locked by their respective network structures, which prevents the polymer chains at the interface from fully penetrating and diffusing with each other, resulting in low interfacial bonding strength and making it difficult to meet the requirements for high-strength applications. Summary of the Invention

[0003] The purpose of this invention is to overcome the aforementioned defects or problems in the prior art and to provide a method for simultaneous foaming of heterogeneous materials, which can improve the problem of low interfacial bonding strength between two materials.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: Technical Solution 1: A method for simultaneous foaming of heterogeneous materials, comprising the following steps: S10: providing a solid preform made of a first elastomer material and granular material made of a second elastomer material; both the first elastomer material and the second elastomer material are blends of ethylene-vinyl acetate copolymer and styrene-ethylene-butene-styrene block copolymer, and both contain azodicarbonamide foaming agent and dicumyl peroxide crosslinking agent; wherein, the linear shrinkage rate of the first elastomer material is 1.2% to 1.4%, and the linear shrinkage rate of the second elastomer material is 1.8% to 2.0%; S20: filling the solid preform and the granular material into a foaming mold; the foaming mold has a first region and a second region, the first region... The cavity depth of the first region is a first depth, the cavity depth of the second region is a second depth, and the ratio of the second depth to the first depth is 0.65 to 0.75; the solid preform is placed in the first region, and the granular material is filled in the second region; S30: the foaming mold is closed, and when the gap between the upper and lower molds is 5mm to 10mm, vacuuming is started so that the vacuum degree in the foaming cavity reaches -0.08MPa to -0.10MPa within 5s; S40: while maintaining the vacuum state, the foaming mold is heated at a temperature of 172℃ to 178℃ for a time of 520s to 580s, so that the solid preform and the granular material foam and solidify together synchronously in the same cavity.

[0005] Technical Solution 2 based on Technical Solution 1: The difference between the mass percentage content of vinyl acetate in the first elastomer material and the mass percentage content of vinyl acetate in the second elastomer material is within ±3%.

[0006] Technical Solution 3, based on Technical Solution 1: The diameter of the granular material is 3mm to 5mm.

[0007] Technical Solution 4 based on Technical Solution 1: Based on 100 parts by mass of the first elastomer material, the amount of azodicarbonamide foaming agent added is 3.0 to 5.0 parts by mass, and the amount of dicumyl peroxide crosslinking agent added is 0.8 to 1.2 parts by mass.

[0008] Technical Solution 5 based on Technical Solution 1: The prefabrication process of the solid preform in S10 is as follows: the first elastomer material is heated to 100°C to 110°C and injected into a cold preform mold at a temperature of 21°C to 25°C with a pressure of 120 bar to 130 bar.

[0009] Technical Solution Six based on Technical Solution One: The design foaming ratio of the first elastomer material is 1.80 to 1.85, and the design foaming ratio of the second elastomer material is 1.86 to 1.92.

[0010] Technical solution seven based on technical solution one: In S20, when filling the granular material, the starting point of the feeding is located in the second region at the position with the largest distance from the boundary of the first region, and the feeding is continuously carried out in the direction of decreasing distance.

[0011] Technical solution eight based on technical solution one: After S40, it also includes step S50: open the foaming mold and take out the molded blank, and let the molded blank stand for 48 hours.

[0012] Technical solution nine based on technical solution eight: after S50, there is also step S60: placing the molded blank into the molding mold, heating the molding mold to 155°C to 165°C and holding it for 520s to 580s for secondary shaping.

[0013] Technical solution ten based on technical solution nine: In S60, after heating is completed, cooling water is introduced into the molding die to reduce the temperature of the molding die to below 30°C and maintain it for 470s to 530s.

[0014] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for simultaneous foaming of heterogeneous materials, which improves the bonding strength and warpage issues of two different elastomer materials during simultaneous foaming. Specifically, this method improves the morphological structure of the two materials. Conventional methods typically involve simultaneously pouring in two granular materials. Due to their similar heating surfaces, the two materials begin cross-linking almost simultaneously. Once cross-linked, the molecular chains are locked, preventing interpenetration at the contact surface and resulting in weak bonding. This method uses a solid preform in conjunction with the granular materials. The granular materials have a large heating surface area and melt first upon heating. Because of their larger volume and the time required for heat conduction, the solid preform reaches its cross-linking reaction temperature later than the melting of the granules. During this period—when the granules have melted but the solid preform surface has not yet cross-linked—the molecular chains of the granules can diffuse and penetrate the surface of the solid preform. Subsequently, the two materials complete cross-linking simultaneously. Therefore, this solution controls the heating sequence of the two materials by adjusting their physical state differences, allowing them to connect at the interface through molecular chain penetration. This eliminates the need for additional adhesive media or forced alignment of reaction times by changing the formula, thus greatly improving the connection strength between the two materials.

[0015] However, granular materials create numerous physical gaps during accumulation, trapping air within these gaps. During simultaneous foaming, the pressure within the mold cavity rises rapidly. Because the granules cannot completely expel the air from these gaps before melting, the residual air undergoes intense adiabatic compression under extremely high pressure, generating instantaneous high temperatures. This high temperature causes yellowing and scorching at the material contact surface, and the resulting scorched layer hinders further diffusion of the molecular chains. To address this, this solution includes a specific vacuuming step. This vacuuming is not performed after mold closing but begins during the mold closing process, utilizing the gaps between the granules as venting channels to pre-expel air from deep within the mold cavity. This solves the scorching problem caused by residual air, ensuring the finished product interface maintains high strength without any aesthetic defects.

[0016] Furthermore, due to the different performance requirements of the first and second elastomer materials, their linear shrinkage rates differ. Since the bonding strength between the two materials in this design is relatively high, the material with the larger shrinkage rate pulls on the material with the smaller shrinkage rate during cooling, preventing the release of internal stress and causing severe warping or bending deformation of the finished product. To address this, this design makes the second region corresponding to the material with the larger linear shrinkage rate shallower and the first region corresponding to the material with the smaller linear shrinkage rate deeper. The depth ratio of the two regions is directly related to the linear shrinkage rates of the two materials. This ensures that although the two materials have different shrinkage rates, the difference in thickness balances the absolute shrinkage displacement at the interface during cooling. This difference in geometric dimensions offsets the difference in physical properties, solving the stress deformation problem caused by strong bonding and ensuring the flatness of the product.

[0017] In technical solution two, the difference in the mass percentage content of vinyl acetate (VA) in the first elastomer material and the second elastomer material is controlled within ±3%, which improves the compatibility of the two materials at the contact interface. This allows the molecular chain segments of the second material to penetrate and entangle more effectively across the interface into the interior of the first material during the diffusion window period generated by heating, thereby improving the interfacial bonding strength. In technical solution three, the diameter range of the granular material is limited to ensure that the physical gaps generated when the particles are stacked are appropriate. This allows for the formation of smooth exhaust channels in conjunction with the vacuuming process, preventing increased exhaust resistance due to excessively fine particles. It also avoids problems such as uneven heating and mismatched melting speed caused by excessively large particles. In technical solution four, the specific addition ratio of foaming agent and crosslinking agent is limited, thereby stabilizing the expansion force of the first material and the density of the crosslinked network structure during the foaming process. This ensures that the solid preform can generate sufficient extrusion force when heated and expanded, pressing the contact interface between it and the granular melt, which is beneficial to the diffusion of molecular chains.

[0018] In technical solution five, the parameters of the solid preform prefabrication process are defined. By using a lower preform mold temperature and a specific injection pressure, the first elastomer material can maintain a dense morphology without premature foaming or cross-linking reactions. During subsequent synchronous foaming and heating, a significant heating delay can be generated, thereby extending the penetration and diffusion time of the molecular chains. In technical solution six, by limiting the design foaming ratio of the first material and the second material, and making the foaming ratio of the second material higher than that of the first material, during the foaming process in S40, the second region will generate a greater internal expansion pressure than the first region. This pressure will act on the contact interface of the two materials, thereby providing an additional driving force for the molten granular molecular chains to penetrate into the surface of the solid preform, further improving the interfacial bonding strength. In technical solution seven, by limiting the filling sequence and direction of granular materials, the position of the solid preform is stabilized by the hydrodynamic pressure generated by the material during the filling process, preventing preform displacement that may occur under mold closing and foaming impact. At the same time, it can be combined with a vacuuming step to expel air from the interface from far to near, further reducing the risk of air trapping at the interface. In technical solution eight, a 48-hour static treatment is added after the synchronous foaming is completed. This allows the residual stress inside the foamed preform to be fully released and the gas pressure inside the cells to reach a uniform balance with the external atmospheric pressure, which can improve the dimensional stability of the finished product. In technical solution nine, the foamed preform is placed into a molding die for secondary heating and shaping, causing the material to expand slightly and fill the molding cavity, thereby eliminating surface textures or dimensional deviations that may occur during primary foaming, and further improving the surface quality and dimensional accuracy of the product. In technical solution ten, cooling water is introduced after the molding heating is completed for pressing and cooling, so that the material can be quickly hardened and shaped under the mold pressure, which suppresses the thermal expansion force of the residual gas inside the material and prevents the size rebound or shape distortion caused by the softening of the material at the moment of mold opening. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] In the claims and description of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0021] This invention relates to a method for simultaneous foaming of heterogeneous materials, which includes the following steps: S10: Provide a solid preform made of a first elastomer material and granular pellets made of a second elastomer material; both the first and second elastomer materials are blends of ethylene-vinyl acetate copolymer and styrene-ethylene-butene-styrene block copolymer, and both contain azodicarbonamide blowing agent and dicumyl peroxide crosslinking agent; wherein the linear shrinkage rate of the first elastomer material is 1.2% to 1.4%, and the linear shrinkage rate of the second elastomer material is 1.8% to 2.0%; S20: The solid preform and the granular material are filled into a foaming mold; the foaming mold has a first region and a second region, the cavity depth of the first region is a first depth, the cavity depth of the second region is a second depth, and the ratio of the second depth to the first depth is 0.65 to 0.75; the solid preform is placed in the first region, and the granular material is filled into the second region; S30: Close the foaming mold, and start vacuuming when the gap between the upper and lower molds is 5mm to 10mm, so that the vacuum degree in the foaming cavity reaches -0.08MPa to -0.10MPa within 5s; S40: Maintain a vacuum state and heat the foaming mold at a temperature of 172°C to 178°C for 520s to 580s, so that the solid preform and the granular material foam and solidify together synchronously in the same mold cavity. S50: Open the foaming mold and take out the molded preform. Let the molded preform stand for 48 hours. S60: Place the preform into a molding die, heat the molding die to 155°C to 165°C and hold for 520s to 580s for secondary shaping.

[0022] The following is a detailed explanation of each of the above steps.

[0023] In step S10, the preparation and processing of the first elastomer material and the second elastomer material are carried out first.

[0024] The first elastomer material is used to prepare a solid preform with damping properties. In the batching stage, the matrix resin component, composed of ethylene-vinyl acetate copolymer and styrene-ethylene-butene-styrene block copolymer, is weighed. To impart damping properties to the first elastomer material, the proportion of styrene-ethylene-butene-styrene block copolymer is increased in the matrix resin, setting its mass percentage to 45% to 55% of the total matrix resin mass. The selected ethylene-vinyl acetate copolymer contains 18% to 21% vinyl acetate by mass. Based on 100 parts by mass of the total matrix resin mass, 3.0 to 5.0 parts by mass of azodicarbonamide foaming agent, 0.8 to 1.2 parts by mass of dicumyl peroxide crosslinking agent, 2 parts by mass of zinc oxide, and 1 part by mass of stearic acid are weighed. All the above materials are added to an internal mixer for mixing. The rotor speed of the internal mixer is set to 35 revolutions per minute, and the heating temperature of the mixing chamber is set to 100 degrees Celsius. The material is continuously stirred and sheared in an internal mixer for 10 minutes to ensure complete dispersion of the additives in the molten matrix resin. After mixing, the material is discharged and fed into a twin-screw extruder for granulation. The heating zones of each section of the extruder are sequentially set to 85°C, 90°C, 95°C, and 95°C. The extruded strip is cooled to room temperature in a cooling water bath and then cut into intermediate masterbatches by a pelletizer.

[0025] Subsequently, the intermediate masterbatch is processed into a solid preform using a disc injection molding machine. The intermediate masterbatch is added to the hopper of the injection molding machine, and the heating temperature of the injection gun barrel is controlled at 100°C to 110°C. A cold preform mold is prepared, the internal cavity shape of which corresponds to the first area of ​​the subsequent foaming mold. The cold preform mold is connected to cooling circulating water to maintain the mold temperature at 21°C to 25°C. The injection molding machine injects the molten material into the cavity of the cold preform mold at a pressure of 120 bar to 130 bar. The material rapidly cools and solidifies within the mold at a constant low temperature, forming a dense solid preform that does not undergo a foaming reaction. The density of this solid preform is controlled at 0.9 g / cm³ to 1.1 g / cm³. The designed foaming ratio of the obtained solid preform under subsequent processing conditions is 1.80 to 1.85, and the linear shrinkage rate is 1.2% to 1.4%.

[0026] The second elastomer material is used to prepare high-resilience granules. During the batching stage, an ethylene-vinyl acetate copolymer with the same vinyl acetate content as the first elastomer material is selected, ensuring the difference in vinyl acetate content between the two is within ±3%. To achieve high resilience, the proportion of the ethylene-vinyl acetate copolymer in the matrix resin of the second elastomer material is increased, setting its mass percentage to 70% to 80% of the total matrix resin mass, while correspondingly reducing the mass percentage of the styrene-ethylene-butene-styrene block copolymer. Based on 100 parts by mass of the total matrix resin mass, 5.5 to 7.5 parts by mass of azodicarbonamide foaming agent and 1.0 to 1.5 parts by mass of dicumyl peroxide crosslinking agent are added. The material is fed into a mixer and mixed for 8 minutes at 100 degrees Celsius and 35 revolutions per minute. The mixed material is discharged and fed into a single-screw granulator unit, with the extruder temperature set at 90 to 100 degrees Celsius. The material is cut into cylindrical granules with a diameter of 3 mm to 5 mm using a die-cutting system. The resulting granules have a designed foaming ratio of 1.86 to 1.92 and a linear shrinkage rate of 1.8% to 2.0% under subsequent processing conditions. The prepared solid preforms and granules are stored separately in dry containers for later use.

[0027] In step S20, a foaming mold with differentiated cavity depths is used. The cavity of the foaming mold is divided into a first region and a second region. The cavity depth of the first region is set to a first depth, and the cavity depth of the second region is set to a second depth. The ratio of the second depth to the first depth is maintained within the range of 0.65 to 0.75 through mold machining. Before the loading operation begins, the solid preform prepared in step S10 is taken out of the storage container, and the surface temperature of the solid preform is confirmed to be within the range of 21 degrees Celsius to 25 degrees Celsius using an infrared thermometer. The solid preform at this temperature is then precisely placed into the first region of the foaming mold by hand or robotic arm.

[0028] The second elastomeric material granules are then filled. Granules with a diameter of 3mm to 5mm are poured into the hopper of the feeding device. During the filling process, the geometric point with the greatest distance from the boundary between the second region and the first region is first determined, and the discharge port of the feeding device is aligned with this point as the starting point for feeding. The feeding device is then activated, allowing the granules to enter the second region from the starting point. The feeding device moves along a preset path, continuously filling the granules in the direction of decreasing distance, i.e., gradually spreading them from a position away from the first region towards its boundary. During the filling process, the granules gradually accumulate and fill the entire cavity space of the second region until they contact the sidewalls of the placed solid preform and completely fill the second region.

[0029] After material filling is completed, the hydraulic system of the foaming machine controls the foaming mold to perform a mold closing action, proceeding to step S30. During the mold closing process, a high-precision displacement sensor mounted on the machine frame is used to detect the movement position of the upper mold relative to the lower mold in real time. When the value fed back by the displacement sensor shows that the vertical gap between the upper and lower molds has decreased to the range of 5mm to 10mm, the control system automatically opens the vacuum control valve connected to the vacuum pump station. The vacuum pump station begins to expel air from the inside of the foaming cavity through the air extraction pipeline laid around the mold. At this time, the pressure change in the cavity is monitored in real time by a pressure transmitter installed on the air extraction circuit. The pumping power of the vacuum pump is adjusted so that the air pressure in the foaming cavity completes the process of decreasing within 5 seconds until the vacuum value displayed by the pressure transmitter reaches the range of -0.08 MPa to -0.10 MPa. As the vacuum degree reaches the target value, the hydraulic system drives the upper mold to continue to descend until it is completely fitted and locked with the lower mold, maintaining the mold closing pressure to enter the subsequent stage.

[0030] While maintaining the vacuum level of the foaming mold cavity at -0.08 MPa to -0.10 MPa, proceed to step S40. The mold heating program is initiated through the central control system of the foaming machine, using electric heating tubes or a circulating hot oil system embedded inside the foaming mold to heat the cavity space. The control system monitors the mold temperature through temperature sensors and uses PID control to maintain the working temperature of the upper and lower molds of the foaming mold within the range of 172°C to 178°C. When the temperature returned by the temperature sensor reaches the set range, the machine timer starts and begins a heating timer for 520 to 580 seconds.

[0031] During this heating process, the granular material transforms from a granular state to a molten fluid state through heat conduction through the mold wall. The molten second elastomer material flows within the mold cavity and coats the surface of the solid preform. As heat penetrates into the material, the azodicarbonamide foaming agent in both the first and second elastomer materials decomposes to generate gas, while the dicumyl peroxide crosslinking agent initiates a crosslinking reaction. The first elastomer material expands in volume within the first region at a design ratio of 1.80 to 1.85, and the second elastomer material expands in volume within the second region at a design ratio of 1.86 to 1.92. Both materials expand within their respective regions and fill the entire foaming mold cavity. During a heating cycle lasting 520 to 580 seconds, the two materials undergo a crosslinking reaction at the interface. Once the timer reaches the set time, the machine stops heating and maintains a closed and locked state, ready to execute the command to open the mold.

[0032] After the heating timer in step S40 ends, the hydraulic system of the foaming machine performs a pressure relief action, and the hydraulic cylinder drives the upper mold to move upward, thereby opening the foaming mold. During the mold opening process, the preform is driven by the internal gas pressure to expand in volume and detach from the foaming cavity. The operator uses a hand tool or a robotic arm to remove the preform from the mold. The removed preform is then transferred to a constant temperature storage area and placed flat on a support surface. The ambient temperature of the storage area is maintained between 20 and 30 degrees Celsius, and the ambient humidity is maintained between 40% and 60%. The time recording device is activated, and the preform is left to stand under the above environmental conditions for 48 hours. During the entire standing period, the preform is kept horizontally and is not stacked on top of each other or subjected to external mechanical loads until the predetermined standing time is reached.

[0033] After a 48-hour settling period, proceed to step S60. The settling preform is removed from the storage area and placed into the cavity of the molding die. This molding die is installed between the heating plates of the hydraulic molding press, and its cavity dimensions are preset according to the final product's dimensions. The molding press is closed, and clamping pressure is applied. The heating medium is adjusted using the molding press's temperature control system to raise and maintain the molding die's temperature within the range of 155°C to 165°C. Once the mold's temperature sensor indicates that the temperature has reached the preset range, a timing device is activated to perform a secondary heating operation for 520 to 580 seconds.

[0034] After the heating timer completes, maintain the clamping pressure of the molding die and disconnect the heat source from the heating system. Activate the cooling circulation system of the molding press, circulating cooling water into the cooling pipes inside the molding die. Monitor the temperature changes inside the mold cavity in real time using a temperature monitoring instrument until the temperature of the molding die drops below 30 degrees Celsius. At this low temperature, continue circulating cooling water and maintain the clamping pressure, performing a pressing and cooling operation for 470 to 530 seconds. Once the cooling timer ends, the hydraulic system drives the molding press to open the molding die, from which the final molded product of the heterogeneous material is removed.

[0035] This invention relates to a method for simultaneous foaming of heterogeneous materials, which improves the bonding strength and warpage issues of two different elastomer materials during simultaneous foaming. Specifically, this method improves the morphological structure of the two materials. Conventional methods typically involve simultaneously pouring in two granular materials. Due to their similar heating surfaces, the two materials begin cross-linking almost simultaneously. Once the materials reach the cross-linking state, the molecular chains are locked, preventing interpenetration at the contact surface and resulting in weak bonding. This method uses a solid preform in conjunction with the granular materials. The granular materials have a large heating surface area and melt first upon heating. Because of their larger volume and the time required for heat conduction, the solid preform reaches its cross-linking reaction temperature later than the melting of the granules. During the period between the melting of the granules and the uncross-linked state of the solid preform, the molecular chains of the granules can diffuse and penetrate the surface of the solid preform. Subsequently, the two materials complete cross-linking simultaneously. Therefore, this solution controls the heating sequence of the two materials by adjusting their physical state differences, allowing them to connect at the interface through molecular chain penetration. This eliminates the need for additional adhesive media or forced alignment of reaction times by changing the formula, thus greatly improving the connection strength between the two materials.

[0036] However, granular materials create numerous physical gaps during accumulation, trapping air within these gaps. During simultaneous foaming, the pressure within the mold cavity rises rapidly. Because the granules cannot completely expel the air from these gaps before melting, the residual air undergoes intense adiabatic compression under extremely high pressure, generating instantaneous high temperatures. This high temperature causes yellowing and scorching at the material contact surface, and the resulting scorched layer hinders further diffusion of the molecular chains. To address this, this solution includes a specific vacuuming step. This vacuuming is not performed after mold closing but begins during the mold closing process, utilizing the gaps between the granules as venting channels to pre-expel air from deep within the mold cavity. This solves the scorching problem caused by residual air, ensuring the finished product interface maintains high strength without any aesthetic defects.

[0037] Furthermore, due to the different performance requirements of the first and second elastomer materials, their linear shrinkage rates differ. Since the bonding strength between the two materials in this design is relatively high, the material with the larger shrinkage rate pulls on the material with the smaller shrinkage rate during cooling, preventing the release of internal stress and causing severe warping or bending deformation of the finished product. To address this, this design makes the second region corresponding to the material with the larger linear shrinkage rate shallower and the first region corresponding to the material with the smaller linear shrinkage rate deeper. The depth ratio of the two regions is directly related to the linear shrinkage rates of the two materials. This ensures that although the two materials have different shrinkage rates, the difference in thickness balances the absolute shrinkage displacement at the interface during cooling. This difference in geometric dimensions offsets the difference in physical properties, solving the stress deformation problem caused by strong bonding and ensuring the flatness of the product.

[0038] To further illustrate the technical effects of the present invention, the following embodiments and comparative examples are provided.

[0039] To ensure the feasibility of this invention and the accuracy of the test results, the raw material specifications used in the examples and comparative examples are as follows (unless otherwise specified, all components are expressed in parts by mass): The first elastomer material uses SEETEC 1518 resin, manufactured by LG Chem of South Korea, which has a vinyl acetate content of 18% by mass and a melt index of 2.5 g / 10 min. The second elastomer material uses SEETEC 1521 resin, also manufactured by LG Chem of South Korea, which has a vinyl acetate content of 21% by mass and a melt index of 2.0 g / 10 min.

[0040] The styrene-ethylene-butene-styrene block copolymer used was Taipol 6151 resin manufactured by TSRC Corporation, Taiwan. The azodicarbonamide blowing agent used was AC-3000 manufactured by Yung-Chia Fu-Tai. The dicumyl peroxide crosslinking agent used was Perkadox BC-FF manufactured by AkzoNobel. Zinc oxide and stearic acid were commercially available industrial-grade products. Unless otherwise specified, all component proportions are by weight.

[0041] Example 1 In step S10, the first elastomer material is first prepared. 50 parts by mass of an ethylene-vinyl acetate copolymer with a vinyl acetate content of 18% and 50 parts by mass of a styrene-ethylene-butene-styrene block copolymer are weighed. Based on this 100 parts by mass of the matrix resin, 4.0 parts by mass of azodicarbonamide foaming agent, 1.0 part by mass of dicumyl peroxide crosslinking agent, 2 parts by mass of zinc oxide, and 1 part by mass of stearic acid are added. The materials are fed into a mixer, the speed is set to 35 revolutions per minute, the mixing temperature is 100 degrees Celsius, and the mixing is continued for 10 minutes. After mixing, the material is discharged and fed into a twin-screw extruder for granulation to obtain the first elastomer intermediate material.

[0042] A disc injection molding machine is used to process the first elastomer intermediate material into a solid preform. The intermediate material is added to the injection molding machine hopper, and the injection gun barrel temperature is set to 105 degrees Celsius. The cold preform mold is connected to cooling water, and the mold temperature is maintained at 23 degrees Celsius. The injection molding machine injects the molten material into the cold preform mold cavity at a pressure of 125 bar. After cooling and solidification, a solid preform with a density of 1.0 g / cm³ is removed. The linear shrinkage rate of this solid preform is 1.3%, and the designed foaming ratio is 1.82.

[0043] The second elastomer material was then prepared. 75 parts by mass of an ethylene-vinyl acetate copolymer with a vinyl acetate content of 21% and 25 parts by mass of a styrene-ethylene-butene-styrene block copolymer were weighed, ensuring the difference in vinyl acetate content between the two elastomer materials was 3%. 6.5 parts by mass of azodicarbonamide foaming agent and 1.3 parts by mass of dicumyl peroxide crosslinking agent were added. The mixture was prepared under the same intensive mixing conditions as the first elastomer material and then processed into cylindrical granules with a diameter of 4 mm using a granulator. This material had a linear shrinkage rate of 1.9% and a designed foaming ratio of 1.88.

[0044] In step S20, a foaming mold is prepared. The first region of the mold has a depth of 10 mm, and the second region has a depth of 7 mm, with a depth ratio of 0.7. A solid preform with a surface temperature of 23 degrees Celsius is placed in the first region of the foaming mold. Granular material is poured into the feeder. Starting from the point in the second region farthest from the boundary of the first region, the granular material is filled at a uniform speed in the direction of decreasing distance until the second region is completely covered.

[0045] In step S30, the hydraulic system drives the foaming mold to close. When the displacement sensor shows that the gap between the upper and lower molds is 8 mm, the vacuum pump is turned on. The vacuum level of the mold cavity reaches -0.09 MPa within 5 seconds. Subsequently, the mold is completely locked.

[0046] In step S40, the temperature of the foaming mold is heated and maintained at 175 degrees Celsius via a central control system. A timer executes a heating duration of 550 seconds. During this process, the solid preform and granular material complete foaming within the same mold cavity.

[0047] In step S50, the hydraulic cylinder drives the upper mold to open. The preform is removed and placed flat on the support surface of the constant temperature storage area, and left to stand for 48 hours at a temperature of 25 degrees Celsius and a humidity of 50%.

[0048] In step S60, the preform after being left to stand is placed into a molding die. The molding die is heated to 160 degrees Celsius and held for 550 seconds. After heating, circulating cooling water is introduced to lower the die temperature to 28 degrees Celsius, and the pressing and cooling process is continued for 500 seconds. The final product is then removed.

[0049] Example 2 In step S10, 5.0 parts by weight of azodicarbonamide foaming agent and 1.2 parts by weight of dicumyl peroxide crosslinking agent are added to the first elastomer material. The linear shrinkage rate of the first elastomer material is 1.4%. The linear shrinkage rate of the second elastomer material is 2.0%. During the preforming of the solid preform, the injection gun barrel temperature is 110 degrees Celsius, the cold preform mold temperature is 25 degrees Celsius, and the injection pressure is 130 bar. The diameter of the granular material is 5 mm.

[0050] In step S20, the ratio of the second depth to the first depth of the foaming mold is set to 0.75. The surface temperature of the solid preform is 25 degrees Celsius upon mold entry. In step S30, vacuuming is initiated when the gap between the upper and lower molds is 10 mm, and the vacuum level reaches -0.10 MPa within 5 seconds. In step S40, the foaming mold is heated to 178 degrees Celsius for 580 seconds. In step S60, the molding die is heated to 165 degrees Celsius for 580 seconds. Cooling water is introduced to lower the temperature to 29 degrees Celsius for 530 seconds.

[0051] The formulation ratios and preparation steps of the remaining materials are the same as in Example 1.

[0052] Example 3 In step S10, 3.0 parts by mass of azodicarbonamide foaming agent and 0.8 parts by mass of dicumyl peroxide crosslinking agent are added to the first elastomer material. The linear shrinkage rate of the first elastomer material is 1.2%. The linear shrinkage rate of the second elastomer material is 1.8%. During the preforming of the solid preform, the injection gun barrel temperature is 100 degrees Celsius, the cold preform mold temperature is 21 degrees Celsius, and the injection pressure is 120 bar. The diameter of the granular material is 3 mm.

[0053] In step S20, the ratio of the second depth to the first depth of the foaming mold is set to 0.65. The surface temperature of the solid preform is 21 degrees Celsius upon mold entry. In step S30, vacuuming is initiated when the gap between the upper and lower molds is 5 mm, and the vacuum level reaches -0.08 MPa within 5 seconds. In step S40, the foaming mold is heated to 172 degrees Celsius for 520 seconds. In step S60, the molding die is heated to 155 degrees Celsius for 520 seconds. Cooling water is introduced to lower the temperature to 25 degrees Celsius for 470 seconds.

[0054] The formulation ratios and preparation steps of the remaining materials are the same as in Example 1.

[0055] Comparative Example 1 This comparative example alters the physical composition of the initial materials. Except for the following, the formulation and process parameters are the same as in Example 1: In step S20, instead of placing a solid preform in the first region, it is filled with an equal mass of first elastomeric material particles, each with a diameter of 4 mm. This means that simultaneous foaming is achieved within the foaming mold through the mixing of two granular materials.

[0056] Comparative Example 2 This comparative example changed the vacuuming operation point. Except for the following, the rest of the formula and process parameters are the same as in Example 1: In step S30, after the foaming mold is completely closed and locked and the mold closing pressure is stable, the vacuum pump is turned on to perform vacuuming.

[0057] Comparative Example 3 This comparative example did not undergo geometric thickness compensation. Except for the following contents, the remaining formulations and process parameters are the same as in Example 1: In step S20, the first depth and the second depth of the foaming mold are both set to 10mm, that is, the depth ratio is 1.0.

[0058] Comparative Example 4 This comparative example reduces the initial temperature difference between the materials. Except for the following, the formulation and process parameters are the same as in Example 1: In step S20, before placing the solid preform into the first region, the solid preform is first placed in an oven and preheated to 85 degrees Celsius.

[0059] The foamed materials prepared in the above embodiments and comparative examples were subjected to performance tests. The test items and the standards used are as follows: The interfacial peel strength was tested according to the Chinese national standard GB / T 3903.3-2011, and a sample with a width of 20 mm was cut at the interface of the heterogeneous materials.

[0060] The method for measuring the warpage of the finished product is as follows: Place the finished product horizontally on a standard marble platform and use a feeler gauge to measure the maximum vertical gap between the edge of the finished product and the platform surface.

[0061] The interface appearance is determined by visually inspecting the cut surfaces.

[0062] The test results are as follows:

[0063] According to the test results, Examples 1 to 3 all exhibited excellent peel strength, showing bulk failure of the elastomer material, indicating that the strength of the bonding interface exceeded the strength of the material itself. Comparative Example 1 used a combination of all-granular materials; due to synchronous heating, the crosslinking points arrived almost simultaneously, resulting in a lack of diffusion windows for the molecular chains and a significant decrease in strength. Comparative Example 4 reduced the temperature difference through preheating, weakening the mechanism of utilizing physical delay in manufacturing time difference, leading to a decrease in bonding strength. The results of Comparative Example 2 demonstrate the criticality of the vacuuming node. After mold closing and locking, air was evacuated, but because the material particles were compressed, the interstitial air could not be completely expelled. Under the high temperature and pressure of foaming, the air was adiabatically compressed, resulting in a scorched layer at the bonding interface. This scorched layer caused the interface to yellow and formed a physically weak layer, making the peel strength lower than that of the Examples. The warpage of Comparative Example 3 was much greater than that of the Examples. This indicates that even with a strong interface bond, if the materials with high and low shrinkage rates have the same thickness, the shrinkage stress cannot be balanced, leading to severe warpage deformation in the finished product. Examples 1 to 3, through thickness inverse compensation, maintained a low warpage after cooling.

[0064] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A method for simultaneous foaming of heterogeneous materials, characterized in that, Includes the following steps: S10: Provide a solid preform made of a first elastomer material and granular pellets made of a second elastomer material; both the first and second elastomer materials are blends of ethylene-vinyl acetate copolymer and styrene-ethylene-butene-styrene block copolymer, and both contain azodicarbonamide blowing agent and dicumyl peroxide crosslinking agent; wherein the linear shrinkage rate of the first elastomer material is 1.2% to 1.4%, and the linear shrinkage rate of the second elastomer material is 1.8% to 2.0%; S20: The solid preform and the granular material are filled into a foaming mold; the foaming mold has a first region and a second region, the cavity depth of the first region is a first depth, the cavity depth of the second region is a second depth, and the ratio of the second depth to the first depth is 0.65 to 0.75; the solid preform is placed in the first region, and the granular material is filled into the second region; S30: Close the foaming mold, and start vacuuming when the gap between the upper and lower molds is 5mm to 10mm, so that the vacuum degree in the foaming cavity reaches -0.08MPa to -0.10MPa within 5s; S40: Maintain a vacuum state and heat the foaming mold at a temperature of 172°C to 178°C for a time of 520s to 580s, so that the solid preform and the granular material foam and solidify together synchronously in the same cavity.

2. The method for simultaneous foaming of heterogeneous materials as described in claim 1, characterized in that, The difference between the mass percentage content of vinyl acetate in the first elastomer material and the mass percentage content of vinyl acetate in the second elastomer material is within ±3%.

3. The method for simultaneous foaming of heterogeneous materials as described in claim 1, characterized in that, The diameter of the granular material is 3 mm to 5 mm.

4. The method for simultaneous foaming of heterogeneous materials as described in claim 1, characterized in that, Based on 100 parts by mass of the first elastomer material, the amount of azodicarbonamide foaming agent added is 3.0 to 5.0 parts by mass, and the amount of dicumyl peroxide crosslinking agent added is 0.8 to 1.2 parts by mass.

5. The method for simultaneous foaming of heterogeneous materials as described in claim 1, characterized in that, The prefabrication process of the solid preform in S10 is as follows: the first elastomer material is heated to 100°C to 110°C and injected into a cold preform mold at a temperature of 21°C to 25°C with a pressure of 120 bar to 130 bar.

6. The method for simultaneous foaming of heterogeneous materials as described in claim 1, characterized in that, The design foaming ratio of the first elastomer material is 1.80 to 1.85, and the design foaming ratio of the second elastomer material is 1.86 to 1.

92.

7. The method for simultaneous foaming of heterogeneous materials as described in claim 1, characterized in that, In step S20, when filling the granular material, the starting point of the feeding is located in the second region at the position with the largest distance from the boundary of the first region, and the feeding is carried out continuously in the direction of decreasing distance.

8. The method for simultaneous foaming of heterogeneous materials as described in claim 1, characterized in that, The step S40 is followed by step S50: opening the foaming mold and taking out the preform, and then letting the preform stand for 48 hours.

9. The method for simultaneous foaming of heterogeneous materials as described in claim 8, characterized in that, The step S50 is followed by step S60: placing the preform into a molding die, heating the molding die to 155°C to 165°C and holding it for 520s to 580s for secondary shaping.

10. The method for simultaneous foaming of heterogeneous materials as described in claim 9, characterized in that, In step S60, after heating is completed, cooling water is introduced into the molding die to reduce the temperature of the molding die to below 30°C and maintain it for 470s to 530s.

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