A method for preparing a rectangular closed cell structure microcellular foam

Abstract

This invention discloses a method for preparing a rectangular closed-cell micro-foamed material, belonging to the technical field of functional micro-foamed materials. The method involves drying a matrix resin to obtain dried matrix resin particles; hot-pressing and annealing the dried matrix resin particles at high temperature to obtain a matrix resin sheet; coating the upper and lower surfaces of the matrix resin sheet with solvent and placing it in a first mold, which is then locked; placing the locked first mold in a vacuum oven for drying; after drying, placing the first mold in an autoclave for high-pressure permeation saturation treatment; after the high-pressure permeation saturation treatment, releasing the pressure in the autoclave and removing the matrix resin sheet from the first mold for ice-water bath shaping to obtain a rectangular closed-cell micro-foamed material. This method helps improve the effective electromagnetic loss efficiency, the overall electromagnetic parameter stability of the material, the energy absorption efficiency, and the load stability.

Description

Technical Field

[0001] This invention belongs to the field of functional microfoamed materials technology, specifically relating to a method for preparing a rectangular closed-cell microfoamed material. Background Technology

[0002] With the rapid development of modern electronic information technology, high-end equipment manufacturing, aerospace, rail transportation and precision protection, the demand for integrated microwave electromagnetic protection and structural buffer protection continues to increase. Multifunctional foamed materials with electromagnetic loss, energy buffering and lightweight load-bearing characteristics have become the key direction of industry research and industrialization.

[0003] Currently, most foamed materials used in microwave absorbing applications are open-cell or disordered microporous foamed structures, which have significant technical limitations. Open-cell foamed materials have strong pore connectivity, easily forming electromagnetic wave transmission channels, resulting in low effective electromagnetic loss efficiency. Meanwhile, disordered microporous structures have uneven pore sizes and varying wall thicknesses, leading to poor structural consistency and insufficient overall electromagnetic parameter stability. In the field of buffer and energy-absorbing materials, conventional foamed materials are mostly irregular porous structures, which, while possessing some buffering and shock-absorbing capabilities, suffer from low energy absorption efficiency and poor load stability. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, this invention provides a rectangular closed-cell microfoamed material.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a rectangular closed-cell microfoamed material, comprising the following steps: Step 1: Dry the matrix resin to obtain dried matrix resin particles; Step 2: The dried matrix resin particles are hot-pressed and annealed at high temperature to obtain matrix resin sheets. Step 3: After coating the upper and lower surfaces of the base resin sheet with solvent, place it in the first mold and lock the first mold; Step 4: Place the locked first mold in a vacuum oven for drying. Step 5: After drying, place the first mold in an autoclave for high-pressure permeation saturation treatment; Step Six: After the high-pressure permeation saturation treatment is completed, the pressure inside the autoclave is released, and the matrix resin sheet after high-pressure permeation saturation treatment is taken out from the first mold and shaped in an ice-water bath to obtain a rectangular closed-cell micro-foamed material.

[0006] Furthermore, the matrix resin is at least one of thermoplastic polyamide elastomer and thermoplastic polyurethane elastomer.

[0007] Further, step one includes: vacuum drying the matrix resin at a temperature of 80-90°C for 4-6 hours to obtain dried matrix resin particles.

[0008] Further, step two includes: placing the dried matrix resin particles into a second mold wrapped with Teflon high-temperature cloth, hot-pressing at a temperature of 120-160°C for 1-10 minutes, and then placing the second mold in ice water for annealing treatment to obtain a matrix resin sheet.

[0009] Furthermore, step three includes: dissolving the surface layer of the matrix resin sheet with solvent coated on the upper and lower surfaces of the matrix resin sheet to produce stringing behavior.

[0010] Further, step four includes: placing the locked first mold in a vacuum oven and drying it at a temperature of 40–90°C for 4–12 hours.

[0011] Further, step five includes: after drying, placing the first mold containing the dried matrix resin sheet in an autoclave, and introducing carbon dioxide or nitrogen into the autoclave to maintain the pressure in the autoclave between 1 and 10 MPa, and controlling the temperature in the autoclave at 80 to 150°C for 5 minutes to 6 hours, so as to achieve high-pressure permeation saturation of the dried matrix resin sheet.

[0012] Furthermore, the solvent includes: dimethylformamide, tetrahydrofuran, and ethanol.

[0013] Furthermore, step two also includes controlling the thickness of the matrix resin sheet between 10 and 1000 μm.

[0014] Furthermore, the first mold includes: a groove, a raised cover plate that matches the groove, and a spring for engaging the groove and the raised cover plate.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) By coating the surface of the matrix resin sheet with solvent, locking it in the first mold and then performing vacuum drying, high-pressure permeation saturation and ice-water bath shaping in sequence, the gas diffusion direction and cell growth space during the foaming process are controlled in a coordinated manner, and a micro-foamed material with a regular rectangular closed cell structure is successfully prepared. This material can effectively suppress electromagnetic wave transmission channels and improve the effective electromagnetic loss efficiency. In addition, the regular rectangular closed cell structure and uniform pore walls give the material better energy absorption efficiency and load stability, which helps to improve the stability of electromagnetic parameters and structural buffer performance. (2) This application uses two drying processes to perform vacuum drying on the matrix resin particles before hot pressing, which can completely remove the moisture adsorbed inside the resin and prevent it from vaporizing or causing polymer hydrolysis and chain breakage during subsequent high-temperature hot pressing and high-pressure infiltration. This avoids uncontrollable defects such as bubbles and pores inside the sheet, ensures the density and uniformity of the matrix resin, and provides a pure and defect-free matrix for uniform gas infiltration and synchronous nucleation of cells. After coating the sheet surface with solvent and locking the mold, vacuum drying is performed. On the one hand, the surface solvent is completely removed, preventing it from interfering with the regular growth of cells due to volatilization or occupying gas infiltration sites during the high-pressure infiltration high-temperature and high-pressure stage. On the other hand, the slightly soluble surface resin is solidified and forms a strong bond with the mold interface, creating a constraint layer that restricts expansion in the thickness direction. This forces the gas to grow into rectangular pores when the pressure is released, forming a dense surface skin. Through two drying processes, the material is purified from the inside to the constraint construction of the foaming interface, ensuring the efficient molding and stable performance of the rectangular closed-cell structure from the inside out.

[0016] (3) The first mold adopts an elastic constraint structure with grooves, raised cover plates and spring locking, which can provide continuous and uniform mechanical restraint force during the foaming expansion process. It can effectively restrain the excessive expansion of the sheet in the thickness direction and guide the formation of rectangular bubbles. It can also provide appropriate space for bubble growth through the micro-movement of the spring, ensuring that the product has stable dimensions, flat surface and consistent structure. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing a rectangular closed-cell microfoamed material according to an embodiment of the present invention; Figure 2 This is an electron microscope image of the internal rectangular pore structure of a rectangular closed-cell microfoam material according to an embodiment of the present invention; Figure 3 This is an electron microscope image of the internal rectangular pore structure of a rectangular closed-cell microfoam material according to another embodiment of the present invention; Figure 4 This is an electron microscope image of the internal rectangular pore structure of a rectangular closed-cell microfoam material according to another embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: like Figure 1 As shown, this embodiment provides a method for preparing a rectangular closed-cell microfoamed material, including the following steps: S1: Dry the matrix resin to obtain dried matrix resin particles; The matrix resin is at least one of thermoplastic polyamide elastomer and thermoplastic polyurethane elastomer; Specifically, the matrix resin is vacuum dried at a temperature of 80–90°C for 4–6 hours to obtain dried matrix resin particles.

[0020] In this embodiment, thermoplastic polyamide elastomer and / or thermoplastic polyurethane elastomer are selected as the matrix resin, which can endow the final rectangular closed-cell microfoam material with excellent elastic recovery, flexibility and wear resistance, ensuring the structural reliability and performance stability of the material under electromagnetic protection and repeated buffering energy absorption conditions.

[0021] In addition, vacuum drying can effectively remove moisture and volatile impurities from the resin particles, avoiding internal defects such as bubbles and hydrolysis during subsequent high-temperature hot pressing and high-pressure infiltration, ensuring the density and purity of the matrix resin sheet, and laying the foundation for forming a uniform rectangular closed-cell structure.

[0022] S2: Dry matrix resin particles are hot-pressed at high temperature, and then annealed after hot pressing to produce matrix resin sheets. Specifically, the dried matrix resin particles are placed in a second mold wrapped with Teflon high-temperature cloth and hot-pressed at 120-160°C for 1-10 minutes. Then, the hot-pressed second mold is placed in ice water for annealing to obtain a matrix resin sheet. It should be noted that the thickness of the matrix resin sheet can be controlled between 10 and 1000 μm by setting the thickness of the second mold, according to actual needs.

[0023] In this embodiment, a second mold wrapped with Teflon high-temperature cloth is hot-pressed at 120-160°C for 1-10 minutes and then annealed in ice water. This not only facilitates demolding but also allows the resin particles to fully melt and form a film before rapid cooling and shaping, resulting in a matrix resin sheet with uniform thickness, low internal stress, and a smooth surface. This ensures the uniformity of subsequent gas permeation and the controllability of cell formation.

[0024] S3: After coating the upper and lower surfaces of the matrix resin sheet with solvent, place it in the first mold and lock the first mold; The first mold includes a groove, a raised cover plate that matches the groove, and a spring for fastening the groove and the raised cover plate together. In this embodiment, the first mold adopts an elastic constraint structure with grooves, raised cover plates and spring locking, which can provide continuous and uniform mechanical restraint force during the foaming expansion process. It can effectively restrain the excessive expansion of the sheet in the thickness direction and guide the formation of rectangular bubbles. It can also provide appropriate space for bubble growth through the micro-movement of the spring, ensuring that the product has accurate dimensions, a flat surface and a consistent structure.

[0025] Specifically, it includes the following steps: S3-1: A solvent is coated on the upper and lower surfaces of the matrix resin sheet to dissolve the surface layer of the matrix resin sheet until it exhibits stringing behavior; wherein, the solvent includes: dimethylformamide, tetrahydrofuran and ethanol. S3-2: Place the dissolved matrix resin sheet into the groove, cover the groove with the raised cover plate, and lock the groove and the raised cover plate together with a spring.

[0026] In this embodiment, the upper and lower surfaces of the base resin sheet are coated with solvent until they exhibit stringing behavior. This achieves uniform and slight dissolution of the surface resin. After the mold is locked, a tight adhesive layer is formed between the sheet and the mold interface. This helps to limit the excessive growth of cells in the thickness direction during foaming, guides the formation of a regular rectangular pore structure, and simultaneously forms a dense surface skin, enhancing the structural integrity of the material.

[0027] S4: Place the locked first mold in a vacuum oven for drying; Specifically, the first mold containing the locked matrix resin sheet with surface dissolution is placed in a vacuum oven and dried at a temperature of 40–90°C for 4–12 hours.

[0028] In this embodiment, the first mold is locked by a spring, which helps the foaming material expand during the foaming process. The elasticity of the spring provides a certain expansion space for compression.

[0029] In this embodiment, vacuum drying at 40–90°C for 4–12 hours can gently and thoroughly remove residual solvent after coating, preventing it from evaporating during high-pressure penetration and causing pore defects or affecting the uniformity of gas penetration. Furthermore, the low-temperature condition avoids thermal deformation of the substrate sheet, ensuring the original flatness of the sheet.

[0030] S5: After drying, the first mold is placed in an autoclave for high-pressure permeation saturation treatment; Specifically, a first mold containing a dried matrix resin sheet is placed in an autoclave, and carbon dioxide or nitrogen is introduced into the autoclave to maintain the pressure between 1 and 10 MPa. The temperature in the autoclave is controlled at 80 to 150°C for 5 minutes to 6 hours to achieve high-pressure permeation saturation of carbon dioxide or nitrogen into the dried matrix resin sheet, thereby obtaining a micro-foamed matrix resin sheet.

[0031] In this embodiment, the high-pressure permeation saturation treatment is carried out with carbon dioxide or nitrogen at 1-10 MPa and 80-150°C. A safe and environmentally friendly physical foaming agent is used. By precisely controlling the pressure, temperature and time, the solubility and saturation of the gas in the matrix can be flexibly adjusted, which is conducive to obtaining a rectangular pore structure with uniform cell size, high closed-cell rate and aspect ratio much greater than 1, ensuring the consistency and designability of material properties.

[0032] S6: After the high-pressure permeation saturation treatment is completed, the pressure inside the autoclave is released, and the micro-foamed matrix resin sheet is taken out from the first mold and shaped in an ice-water bath to obtain a rectangular closed-cell micro-foamed material.

[0033] It should be noted that Examples 2, 3 and 4 are specific methods for preparing rectangular closed-cell micro-foamed materials based on Example 1.

[0034] Example 2: This embodiment provides a method for preparing a rectangular closed-cell microfoamed material, including the following steps: A1: Place (for example, 5g) thermoplastic polyurethane elastomer particles in a vacuum oven at 80°C and dry for 6 hours to obtain dried thermoplastic polyurethane elastomer particles. A2: Place thermoplastic polyurethane elastomer granules in a second mold wrapped with Teflon high-temperature cloth, hot press at 150°C for 5 minutes, then place the second mold in an ice water bath for annealing treatment, remove the Teflon high-temperature cloth to obtain thermoplastic polyurethane elastomer sheet, and wipe the surface of the thermoplastic polyurethane elastomer sheet clean.

[0035] A3: Coat the upper and lower surfaces of the thermoplastic polyurethane elastomer sheet with tetrahydrofuran until the surface layer of thermoplastic polyurethane elastomer sheet melts and becomes stringy. Then place it in the groove of the first mold, cover it with a raised cover plate that matches the groove, and tighten it with screws on the four corner springs of the first mold to lock the groove and the raised cover plate. A4: Place the locked first mold in a vacuum oven at 60°C and dry for 12 hours; A5: The first mold containing the dried thermoplastic polyurethane elastomer sheet is placed in an autoclave, and carbon dioxide is introduced into the autoclave to make the pressure in the autoclave 2MPa. The temperature in the autoclave is set to 100 degrees Celsius. Under the conditions of 2MPa pressure and 100 degrees Celsius in the autoclave, the autoclave is kept for 5 hours to perform carbon dioxide high-pressure permeation saturation treatment to obtain micro-foamed sheets.

[0036] A6: After the holding time is completed, the pressure in the autoclave is released to atmospheric pressure, and the micro-foamed sheet is removed from the first mold. The micro-foamed sheet is then placed in an ice-water bath to cool and solidify, thus obtaining a rectangular closed-cell micro-foamed material (the internal micropore morphology of the rectangular closed-cell micro-foamed material is as follows). Figure 2 (as shown) In this embodiment, the aspect ratio of the internal micropores of the rectangular closed-cell microfoam material is much greater than 1.

[0037] Example 3: This embodiment provides another method for preparing a rectangular closed-cell microfoamed material, including the following steps: Q1: Place (for example, 5g) thermoplastic polyamide elastomer particles in a vacuum oven at 60°C and dry for 6 hours to obtain dried thermoplastic polyamide elastomer particles. Q2: Place the thermoplastic polyamide elastomer granules in a second mold wrapped with Teflon high-temperature cloth, and hot press at 170°C for 5 minutes. Then, place the second mold in an ice water bath for annealing treatment, remove the Teflon high-temperature cloth to obtain a thermoplastic polyamide elastomer sheet, and wipe the surface of the thermoplastic polyamide elastomer sheet clean.

[0038] Q3: Coat the upper and lower surfaces of the thermoplastic polyamide elastomer sheet with ethanol until the surface layer of the thermoplastic polyamide elastomer sheet is dissolved to the point of being stringy. Then place it in the groove of the first mold, cover it with a raised cover plate that matches the groove, and tighten it with the screws on the four corner springs of the first mold to lock the groove and the raised cover plate. Q4: Place the locked first mold in a vacuum oven at 40°C and dry for 12 hours; Q5: Place the first mold containing the dried thermoplastic polyamide elastomer sheet into an autoclave and introduce carbon dioxide into the autoclave to increase the pressure in the autoclave to 2.5 MPa. Set the temperature in the autoclave to 130 degrees Celsius and maintain it for 4 hours to perform high-pressure permeation saturation treatment on the thermoplastic polyamide elastomer sheet.

[0039] Q6: After the high-pressure permeation saturation treatment, the pressure in the autoclave is released to atmospheric pressure. The micro-foamed sheet is removed from the first mold and placed in an ice-water bath to cool, solidify, and shape, thus obtaining a rectangular closed-cell micro-foamed material (the internal micropore morphology of the rectangular closed-cell micro-foamed material is shown in the figure). Figure 3 (as shown) In this embodiment, the aspect ratio of the internal micropores of the rectangular closed-cell microfoam material is much greater than 1.

[0040] Example 4: This embodiment provides another method for preparing a rectangular closed-cell microfoamed material, including the following steps: K1: Place (for example, 5g) thermoplastic polyurethane elastomer particles in a vacuum oven at 80°C and dry for 6 hours to obtain dried thermoplastic polyurethane elastomer particles. K2: Place the dried thermoplastic polyurethane elastomer granules into a second mold wrapped with Teflon high-temperature cloth, hot press at 150°C for 5 minutes, then anneal the second mold in an ice water bath, remove the Teflon high-temperature cloth to obtain a thermoplastic polyurethane elastomer sheet, and wipe the surface dry.

[0041] K3: Tetrahydrofuran is coated on the upper and lower surfaces of the thermoplastic polyurethane elastomer sheet until the thermoplastic polyurethane elastomer on the surface of the sheet dissolves. Then it is placed in the groove of the first mold and covered with a raised cover plate that matches the groove. The groove and the raised cover plate are locked by tightening the screws on the four corner springs of the first mold. K4: Place the locked first mold in a vacuum oven at 60°C and dry for 12 hours; K5: Place the first mold containing the dried thermoplastic polyurethane elastomer sheet into an autoclave and introduce carbon dioxide into the autoclave to increase the pressure in the autoclave to 2.5 MPa. Set the temperature in the autoclave to 100 degrees Celsius and maintain it for 5 hours to perform high-pressure carbon dioxide permeation saturation treatment on the thermoplastic polyurethane elastomer sheet to obtain micro-foamed thermoplastic polyurethane elastomer sheet.

[0042] K5: After the high-pressure permeation saturation treatment is completed, the pressure in the autoclave is released to atmospheric pressure. The micro-foamed thermoplastic polyurethane elastomer sheet is removed from the first mold and placed in an ice-water bath to cool, solidify, and shape the sheet, thus obtaining a rectangular closed-cell micro-foamed material (the internal micropore morphology of the rectangular closed-cell micro-foamed material is as follows). Figure 4 (as shown) In this embodiment, the aspect ratio of the internal micropores of the rectangular closed-cell microfoam material is much greater than 1.

Claims

1. A method for preparing a rectangular closed-cell microfoamed material, characterized in that, Includes the following steps: Step 1: Dry the matrix resin to obtain dried matrix resin particles; Step 2: The dried matrix resin particles are hot-pressed and annealed at high temperature to obtain matrix resin sheets. Step 3: After coating the upper and lower surfaces of the base resin sheet with solvent, place it in the first mold and lock the first mold; Step 4: Place the locked first mold in a vacuum oven for drying. Step 5: After drying, place the first mold in an autoclave for high-pressure permeation saturation treatment; Step Six: After the high-pressure permeation saturation treatment is completed, the pressure inside the autoclave is released, and the matrix resin sheet after high-pressure permeation saturation treatment is taken out from the first mold and shaped in an ice-water bath to obtain a rectangular closed-cell micro-foamed material.

2. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, The matrix resin is at least one of thermoplastic polyamide elastomer and thermoplastic polyurethane elastomer.

3. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, Step one includes: vacuum drying the matrix resin at a temperature of 80-90°C for 4-6 hours to obtain dried matrix resin particles.

4. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, Step two includes: placing the dried matrix resin particles into a second mold wrapped with Teflon high-temperature cloth, hot-pressing them at a temperature of 120-160°C for 1-10 minutes, and then annealing the second mold in ice water to obtain a matrix resin sheet.

5. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, Step three includes: dissolving the surface layer of the matrix resin sheet with solvent coated on the upper and lower surfaces of the matrix resin sheet to produce stringing behavior.

6. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, Step four includes: placing the locked first mold in a vacuum oven and drying it at a temperature of 40-90°C for 4-12 hours.

7. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, Step five includes: after drying, placing the first mold containing the dried matrix resin sheet in an autoclave, and introducing carbon dioxide or nitrogen into the autoclave to maintain the pressure in the autoclave between 1 and 10 MPa, and controlling the temperature in the autoclave at 80 to 150°C for 5 minutes to 6 hours, so as to achieve high-pressure permeation saturation of the dried matrix resin sheet.

8. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, The solvents include: dimethylformamide, tetrahydrofuran, and ethanol.

9. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, Step two also includes controlling the thickness of the matrix resin sheet between 10 and 1000 μm.

10. The method for preparing the rectangular closed-cell microfoamed material according to claim 1, characterized in that, The first mold includes: a groove, a raised cover plate that matches the groove, and a spring for engaging the groove and the raised cover plate.

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