Microporous high-void polyether sulfone foam for electromagnetic shielding and its compression molding foaming preparation method

Abstract

The present application relates to a kind of microporous high magnification polyether sulfone foam material for electromagnetic shielding and its moulding foaming preparation method, belong to polymer material technical field, solve the problem that the high foaming magnification of existing polyether sulfone foam material, excellent mechanical properties and electromagnetic shielding performance cannot be obtained simultaneously.The foam material of the present application comprises the following mass percentage components: PES matrix resin 50.0%-90.0%;Functional second component 4.0%-30.0%;Conductive filler 5.0%-15.0%;Initiator 0.5%-3.0%;Cell stabilizer 0.3%-1.0%;Composite foaming agent 0.2%-1.0%;The sum of the mass percentage of all components is 100%;Functional second component includes one or more of methyl p-toluenesulfonyl acetate, 4-vinyl phenyl ether, 4,4'-diphenyl methane diisocyanate, bis (4-vinyl phenyl) sulfone, phenyl glycidyl ether, N-phenyl-2-naphthylamine.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a microporous high-expansion PES foam material for electromagnetic shielding and its molding foaming preparation method. Background Technology

[0002] In recent years, polyethersulfone (PES), a high-performance specialty engineering plastic, has been widely used in aerospace, automotive manufacturing, electronics, and medical devices due to its excellent heat resistance, chemical corrosion resistance, mechanical strength, and dimensional stability. However, despite its superior performance in the solid state, PES's application in foam materials has been significantly limited. With continuous technological advancements and sustained market demand growth, high-ratio microporous PES foam materials (average cell size 1-10 μm) are expected to play a crucial role in several high-end fields. For example, in aerospace, high-ratio microporous PES foam materials can be used to manufacture lightweight structural components, such as aircraft interior panels and satellite shells; in automotive manufacturing, they can be used to produce sound and heat insulation materials, such as car headliners and door trim; and in electronics, they can be applied to the manufacture of high-performance insulating materials, such as circuit board substrates and cable insulation layers.

[0003] The limited application of PES foam materials stems primarily from the technical challenges posed by its high melt viscosity and rigid molecular chains. During the foaming process, PES's high viscosity makes it difficult for bubbles to nucleate and grow uniformly, resulting in a generally low expansion ratio, typically only 2-3 times, far from meeting the demands of high-expansion foam materials. Current modifications to PES mainly involve blending with inorganic fillers or other high-temperature resistant materials. Blending PES with other high-temperature resistant materials, such as melt mixing with PEN, yields micro / nano foams at lower foaming temperatures in a PES-rich, PEN-poor composite system, but the expansion ratio is generally very low. Due to the low expansion ratio, PES foam materials have a high density, resulting in poor thermal insulation, sound insulation, and vibration damping performance, making it difficult to meet the stringent performance requirements of high-end applications such as aerospace and automotive manufacturing. These technical bottlenecks severely restrict the market promotion of PES foam materials. Currently, its application is mainly limited to low-end fields with less demanding performance requirements, failing to fully realize its potential as a specialty engineering plastic and limiting its application prospects in a wider range of fields. However, a high foaming ratio will reduce the mechanical properties of the foam material.

[0004] Furthermore, to improve the electromagnetic shielding performance of polyethersulfone (PES) foam materials, researchers have adopted various modification strategies, such as adding conductive fillers and optimizing the cell structure. Among these, adding conductive fillers such as carbon nanotubes and graphene can enhance the conductivity and electromagnetic shielding performance of the material to some extent. However, due to the poor dispersion and stability of these conductive fillers in the material, the enhancement of conductivity and electromagnetic shielding performance is limited. For example, introducing a porous structure through phase inversion, embedding graphene nanosheets into the pore walls of porous PES, requires only a small amount of graphene nanosheets to construct an effective conductive network within the pore walls, thus giving the graphene nanosheet / porous PES film excellent conductivity. Simultaneously, the porous structure also endows the film with good thermal insulation properties. However, the poor dispersion and stability of these conductive fillers in the material remain a key problem that urgently needs to be solved.

[0005] In summary, there is an urgent need for a PES microporous foam material that simultaneously possesses high foaming ratio, excellent mechanical properties, and electromagnetic shielding performance. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a polyethersulfone microporous foam material with excellent comprehensive performance and its preparation method, so as to solve the problem that existing polyethersulfone foam materials cannot simultaneously achieve high foaming ratio, excellent mechanical properties and electromagnetic shielding performance.

[0007] The objective of this invention is mainly achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides a microporous high-ratio PES foam material for electromagnetic shielding, comprising the following components in weight percentage:

[0009]

[0010] The sum of the mass percentages of all components is 100%;

[0011] The second functional component includes one or more of the following: methyl p-toluenesulfonyl acetate, 4-vinylphenyl ether, 4,4'-diphenylmethane diisocyanate, bis(4-vinylphenyl) sulfone, phenyl glycidyl ether, and N-phenyl-2-naphthylamine.

[0012] Optionally, the conductive filler includes one or more of carbon nanotubes (CNTs), carbon black, and graphene oxide.

[0013] Optionally, the conductive filler is a modified conductive filler.

[0014] Optionally, the initiator includes one or more of iodonium salts, thionium salts, and ferrocene salts.

[0015] Optionally, the cell stabilizer includes one or a mixture of several of the following: polyether type, siloxane, fatty acid ester, polyarylether sulfone-polyethylene glycol copolymer, and polytetrafluoroethylene-grafted acrylic acid copolymer.

[0016] Optionally, the foam material has a high foaming ratio of more than 25 times, a closed-cell rate of >90%, uniform cell size with an average cell size of <90μm, a compressive strength of ≥1.5MPa, an electrical conductivity of >60S / cm, and an electromagnetic shielding effectiveness of >50dB.

[0017] Secondly, the present invention also provides a method for preparing a microporous high-expansion PES foam material for electromagnetic shielding, comprising the following steps:

[0018] Step 1: Modify the conductive filler to obtain the modified conductive filler;

[0019] Step 2: Melt blending: Mix the PES matrix resin, functional second component, modified conductive filler, initiator, and cell stabilizer, then melt blend and extrude to obtain a molded foamed blend;

[0020] Step 3: Compression foaming: Place the blend in a mold, introduce the composite foaming agent, and after saturation for a period of time, release the pressure to foam, and obtain the foamed sample;

[0021] Step 4: Curing: Irradiate the foamed sample with an electron beam.

[0022] Optionally, in step 2, the melt blending temperature is 150-300℃.

[0023] Optionally, in step 3, the saturation time is 0.5-5 hours.

[0024] Optionally, in step 3, the mold heating temperature is 100-300℃.

[0025] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0026] (1) This invention significantly reduces the high melt viscosity of PES, improves its processing performance, and increases the foaming ratio by introducing a specific functional second component into the PES matrix resin. Simultaneously, it forms good compatibility with the PES matrix resin, providing a favorable foundation for high-ratio foaming and further improving the foaming ratio. Furthermore, the aforementioned specific functional second component can also play a role in radiation crosslinking during the subsequent electron beam post-curing process, significantly improving the mechanical properties of the PES foam.

[0027] (2) By adding the modified conductive filler, on the one hand, the dispersion and stability of the conductive filler in the material are improved, thereby significantly improving the conductivity and electromagnetic shielding performance of the material; on the other hand, the conductive filler can also play the role of heterogeneous nucleation of bubbles, increase the nucleation sites, which is conducive to the formation of microporous structure, thereby improving mechanical properties.

[0028] (3) By adding a cell stabilizer, the present invention supports the cells during the foaming process, promotes the formation of a uniform microporous structure, and improves the closed-cell rate. By limiting the foaming agent to an air-based composite foaming agent, the closed-cell rate and compressive strength of the foam material can be improved, thereby further improving the mechanical properties of the foam material.

[0029] (4) Generally speaking, a high expansion ratio of foam materials will reduce the mechanical properties of the foam materials. In the preparation method of the present invention, an electron beam curing process is used after molding foaming, and a specific functional second component is selected in the raw materials to play a role in radiation crosslinking in the curing process. At a high expansion ratio, the mechanical properties of the foam materials will not be significantly reduced, thereby effectively maintaining the compressive strength of the foam materials.

[0030] (5) The present invention uses a specific modification process to modify the conductive filler, which further ensures the good dispersibility and stability of the conductive filler in the material.

[0031] (6) The specific functional second component, the specific conductive filler modification process, and the specific curing process in this invention work synergistically to achieve precise control of the cell structure of the foam material and to improve multiple functions, resulting in a foam material with excellent comprehensive performance. Specifically, the foam material of this invention has a high foaming ratio of more than 10 times (e.g., 11-19 times), a closed-cell rate of >90% (e.g., 93%-96%), uniform cell size, and an average cell size of <10μm (e.g., 8-9.6μm), a compressive strength of ≥1.5MPa (e.g., 1.65-1.79MPa), an electrical conductivity of >50S / cm (e.g., 51.5-62.8S / cm), and an electromagnetic shielding effectiveness of >40dB (e.g., 40.6-54.3dB). The special engineering plastic PES microporous high-expansion foam material of the present invention has a high foaming ratio (>10 times), uniform microporous structure and excellent mechanical properties, while maintaining the inherent chemical corrosion resistance and mechanical strength of PES matrix resin, which can meet the stringent requirements of high-end fields such as aerospace, automobile manufacturing, and electronics for high-performance foam materials.

[0032] (7) The preparation method of this invention is simple to operate and easy to industrialize. By combining a twin-screw extruder with compression molding, efficient melt blending of the PES matrix resin and modified components is achieved. Simultaneously, air and supercritical carbon dioxide or supercritical nitrogen are used as composite foaming agents, which not only avoids the problem of residual chemical foaming agents but also meets the development needs of a green and low-carbon economy. The PES microporous high-ratio foam material prepared by this method has broad application prospects and can be widely used in aerospace, automobile manufacturing, and other fields, meeting the current urgent need for high-performance and environmentally friendly materials.

[0033] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages will become apparent from the description or may be learned by practicing the invention. Detailed Implementation

[0034] In a first aspect, the present invention provides a microporous high-ratio PES foam material for electromagnetic shielding, comprising the following components in weight percentage:

[0035]

[0036] The sum of the mass percentages of all components is 100%.

[0037] The second functional component in this invention has three main functions: first, it increases the plasticity of PES, improves its processing performance, and increases the foaming ratio; second, it plays a role in radiation crosslinking in the subsequent electron beam post-curing process, significantly improving the mechanical properties of PES foam; and third, it forms good compatibility with the PES matrix resin, providing a basic condition for high-ratio foaming and further improving the foaming ratio.

[0038] Specifically, the functional second component of the present invention includes one or more of the following: methyl p-toluenesulfonyl acetate, 4-vinylphenyl ether, 4,4'-diphenylmethane diisocyanate, bis(4-vinylphenyl) sulfone, phenyl glycidyl ether, and N-phenyl-2-naphthylamine.

[0039] The functional second component of this invention has the characteristics of boiling point above 350℃ and high temperature (290-310℃) stability. Its mass percentage content in the microporous high-ratio PES foam material is 4.0%-30.0%, for example, 4.0%, 6.0%, 10.0%, 12.0%, 15.0%, 20.0%, 24.0%, 26.0%, 28.0%, and 30.0%.

[0040] Existing plasticizers, such as dioctyl phthalate (DOP / DEHP), dibutyl phthalate (DBP), dioctyl adipate (DOA), dioctyl sebacate (DOS), tricresyl phosphate (TCP), and triphenyl phosphate (TPP), can only play a plasticizing role and cannot play a role in radiation crosslinking in the subsequent electron beam post-curing process, which is not conducive to improving the mechanical properties of PES.

[0041] This invention, by selecting a specific functional second component, can significantly reduce the high melt viscosity of PES, improve its processing performance, and increase the foaming ratio; it also achieves good compatibility with the PES matrix resin, providing a favorable foundation for high-ratio foaming and further improving the foaming ratio. Furthermore, this specific functional second component can also play a role in radiation crosslinking during the subsequent electron beam post-curing process, significantly improving the mechanical properties of the PES foam.

[0042] The PES matrix resin in this invention is polyethersulfone with a density of 1.37 g / cm³. 3 The melt flow index is 5-60 g / 10 min (380℃, 2.16 kg).

[0043] Specifically, the conductive filler in this invention is one or more of carbon nanotubes (CNTs), carbon black, and graphene oxide. Furthermore, the conductive filler is a modified conductive filler.

[0044] The modified conductive fillers in this invention can, on the one hand, construct a complete conductive network within the matrix material, improving conductivity and electromagnetic shielding performance; on the other hand, these conductive fillers can also act as heterogeneous nucleation sites for pores, increasing nucleation sites and facilitating the formation of microporous structures, thereby improving mechanical properties.

[0045] The initiator in this invention is one or more of iodonium salts, thionium salts, and ferrocene salts.

[0046] Examples of iodonium salts include: 4,4'-dimethyl iodohexafluorophosphate, diphenyl iodonium hexafluoroantimonate, and hydroxyphenyl iodonium salt.

[0047] Examples of thionium salts include: triphenylthionium trifluoromethanesulfonate, triphenylthionium perfluorobutylsulfonate, and triphenylthionium hexafluorophosphate.

[0048] Examples of ferroaluminates include: cyclopentadienyl iron biphenyl salt, cyclopentadienyl iron toluene salt, and cyclopentadienyl iron naphthalene salt.

[0049] The cell stabilizer in this invention is one or a mixture of several of the following: polyether type, siloxane type, fatty acid ester, polyarylether sulfone-polyethylene glycol copolymer, and polytetrafluoroethylene-grafted acrylic acid copolymer. The function of the cell stabilizer is to support the cells during the foaming process, promote the formation of a uniform microporous structure, and increase the closed-cell rate.

[0050] Siloxane-based cell stabilizers include polydimethylsiloxane-ethylene oxide block copolymers, polyether-epoxy co-modified silicone oils, and polyether-polysiloxane copolymers.

[0051] Fatty acid ester cell stabilizers include polyoxyethylene sorbitan stearate, polyoxypropylene styrene phenyl ether stearate, sodium dodecylbenzene sulfonate polyoxyethylene ether laurate, etc.

[0052] The composite foaming agent of this invention includes air and a second foaming component, the second foaming component including one or more of supercritical nitrogen, supercritical carbon dioxide, and fluorinated olefins. Using the composite foaming agent of this invention can improve the closed-cell ratio and compressive strength of foam materials, thereby improving the mechanical properties of the foam materials.

[0053] The volume ratio of air to the second foaming component in the composite foaming agent is (1-10):1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0054] Secondly, the present invention also provides a method for preparing a microporous high-expansion PES foam material for electromagnetic shielding, comprising the following steps:

[0055] Step 1: Modify the conductive filler to obtain the modified conductive filler;

[0056] Step 2: Melt blending: Mix the PES matrix resin, functional second component, modified conductive filler, initiator, and cell stabilizer, then place them in an extruder for melt blending and extrusion to obtain a molded foamed blend;

[0057] Step 3: Compression foaming: Place the blend in a mold, introduce the composite foaming agent, and after saturation for a period of time, quickly release the pressure to foam, and obtain the foamed sample;

[0058] Step 4: Curing: The foamed sample is rapidly irradiated with an electron beam.

[0059] Step 1, modifying the conductive filler, includes the following steps:

[0060] Step a: Prepare a mixed acid solution by mixing concentrated sulfuric acid and concentrated nitric acid in a certain proportion;

[0061] Step b: Add a certain mass of conductive filler to the mixed acid solution, and perform acidification treatment under water bath heating conditions to obtain acidified conductive filler;

[0062] Step c: Post-process the acidified conductive filler to obtain the modified conductive filler.

[0063] In step a, the volume ratio of concentrated sulfuric acid to concentrated nitric acid is (0.1-10):1, for example, 0.1:1, 0.5:1, 1:1, 3:1, 5:1, 7:1, 9:1, 10:1.

[0064] In step b, the mass-to-volume ratio of the conductive filler to the mixed acid solution is 1:(10-200), for example, 1:10, 1:20, 1:30, 1:50, 1:80, 1:100, 1:120, 1:150, 1:170, 1:180, or 1:200. Here, mass is measured in grams and volume in milliliters.

[0065] The water bath temperature is 60℃-100℃, for example, 60℃, 70℃, 80℃, 90℃, 95℃, 100℃. The water bath time is 1-5 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours.

[0066] In step c, the post-processing includes: washing, drying, and grinding.

[0067] Washing includes: washing with deionized water until neutral.

[0068] Drying includes vacuum drying at 60-100℃ for 10-30 hours.

[0069] The modified filler obtained after grinding has a particle size of 50-300 mesh, for example, 50 mesh, 70 mesh, 90 mesh, 100 mesh, 150 mesh, 200 mesh, 250 mesh, and 300 mesh.

[0070] In this invention, the conductive filler is treated with the above-mentioned specific modification process, so that the modified conductive filler can, on the one hand, build a complete conductive network inside the matrix material, improving conductivity and electromagnetic shielding performance; on the other hand, these conductive fillers can also play a role in heterogeneous nucleation of cells, increasing cell density.

[0071] In step 2, before melt blending, the raw materials are pretreated, including: vacuum drying the PES matrix resin, functional second component, modified conductive filler, cell stabilizer and initiator at 80-100℃ for 4-6 hours and mixing them evenly.

[0072] In step 2, the extruder is a twin-screw extruder, and nitrogen is introduced as a protective gas during the extrusion process. The melt blending temperature (temperature of each section of the extruder) is 150-300℃, for example, 150℃, 170℃, 200℃, 230℃, 250℃, 280℃, and 300℃.

[0073] The screw speed is 50-400 r / min, for example, 50 r / min, 100 r / min, 150 r / min, 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min.

[0074] The blending time is 3-20 minutes, for example, 3 minutes, 6 minutes, 8 minutes, 10 minutes, 13 minutes, 15 minutes, 17 minutes, and 20 minutes.

[0075] In step 3, the mold heating temperature of the molding machine is 100-300℃, for example, 100℃, 120℃, 150℃, 180℃, 200℃, 230℃, 250℃, 270℃, 300℃.

[0076] The foaming time (saturation time) is 0.5-5h, for example, 0.5h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h.

[0077] In step 4, the electron beam irradiation dose is 10–200 kGy, for example, 10 kGy, 30 kGy, 50 kGy, 80 kGy, 100 kGy, 120 kGy, 140 kGy, 160 kGy, 180 kGy, and 200 kGy. The irradiation time is 0.1–3 h, for example, 0.1 h, 0.3 h, 0.5 h, 1 h, 1.2 h, 1.4 h, 1.8 h, 2 h, 2.3 h, 2.5 h, and 3 h.

[0078] In the preparation method of the present invention, the foam material has excellent comprehensive performance through the synergistic effect of a specific conductive filler modification process and an electron beam process. Specifically, it has a high foaming ratio of more than 25 times, a closed-cell rate of >85%, uniform cell size of <100μm, a compressive strength of ≥1.5MPa, and an electromagnetic shielding effectiveness of >50dB.

[0079] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the preferred embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention.

[0080] In this invention, unless otherwise specified, all methods are conventional methods, and all experimental instruments and reagents are commercially available products that can be purchased through commercial channels.

[0081] Examples 1-5 of this invention provide a PES microporous foam material with excellent comprehensive performance and its preparation method. The raw material composition of the foam materials in Examples 1-5 is shown in Table 1. The PES substrate was purchased from Fuhai (Dongying) New Material Technology Co., Ltd., model T600.

[0082] Example 1

[0083] Step 1: Prepare a mixed acid solution by mixing concentrated sulfuric acid and concentrated nitric acid in a ratio of 3:1 (volume ratio). Add 10 g of conductive filler (carbon nanotubes) to 1000 mL of the mixed acid solution. Acidify the solution under water bath heating conditions (water bath temperature 90℃, water bath time 3 hours) to obtain the acidified conductive filler. Wash the filler with deionized water until neutral, vacuum dry (90℃, 24 hours), and grind it to obtain the modified conductive filler (particle size 150 mesh).

[0084] Step 2: The PES matrix resin, functional second component (bis(4-vinylphenyl)sulfone), modified conductive filler, initiator (4,4'-xylyl iodide hexafluorophosphate), and cell stabilizer (polyarylene ether sulfone-polyethylene glycol copolymer) are vacuum dried at 80°C for 6 hours and mixed evenly; the mixture is then melt-blended at 240°C for 10 minutes in a twin-screw extruder with nitrogen protective gas and a screw speed of 50 r / min, and extruded and molded to form a foamed blend.

[0085] Step 3: Compression foaming: Place the blend in a mold (heating temperature is 160℃), introduce a composite foaming agent (air and supercritical carbon dioxide volume ratio is 2:1), saturate for 2 hours, and then quickly depressurize to foam;

[0086] Step 4: Curing: The foamed sample is rapidly irradiated with an electron beam (70 kGy, 1 h).

[0087] Example 2

[0088] Step 1: Prepare a mixed acid solution by mixing concentrated sulfuric acid and concentrated nitric acid in a ratio of 0.1:1 (volume ratio). Add 100 g of conductive filler (carbon black) to 1000 mL of the mixed acid solution. Acidify the solution under water bath heating conditions (water bath temperature 60℃, water bath time 5 hours) to obtain the acidified conductive filler. Wash the filler with deionized water until neutral, vacuum dry (90℃, 24 hours), and grind it to obtain the modified conductive filler (particle size 50 mesh).

[0089] Step 2: The PES matrix resin, functional second component (methyl p-toluenesulfonyl acetate), modified conductive filler, initiator (triphenylthionium trifluoromethanesulfonate), and cell stabilizer (polytetrafluoroethylene-grafted acrylic acid copolymer) are vacuum dried at 80°C for 6 hours and mixed evenly; the mixture is then melt-blended at 150°C for 20 minutes in a twin-screw extruder with nitrogen protective gas and a screw speed of 400 r / min, and extruded and molded to form a foamed blend.

[0090] Step 3: Compression foaming: Place the blend in a mold (heating temperature is 100℃), introduce a composite foaming agent (the volume ratio of air and supercritical nitrogen is 1:1), saturate for 0.5 hours, and then quickly depressurize to foam;

[0091] Step 4: Curing: The foamed sample is rapidly irradiated with an electron beam (200 kGy, 0.1 h).

[0092] Example 3

[0093] Step 1: Prepare a mixed acid solution by mixing concentrated sulfuric acid and concentrated nitric acid in a ratio of 10:1 (volume ratio). Add 5 grams of conductive filler (graphene oxide) to 1000 mL of the mixed acid solution. Acidify the solution under water bath heating conditions (water bath temperature 70℃, water bath time 4 hours) to obtain the acidified conductive filler. Wash the filler with deionized water until neutral, vacuum dry (90℃, 24 hours), and grind it to obtain the modified conductive filler (particle size 300 mesh).

[0094] Step 2: The PES matrix resin, functional second component (phenyl glycidyl ether and N-phenyl-2-naphthylamine, with a mass ratio of 1:1), modified conductive filler, initiator (cyclopentadienyl ferrobiphenyl salt), and cell stabilizer (polydimethylsiloxane ethylene oxide block copolymer) are vacuum dried at 80°C for 6 hours and mixed evenly; the mixture is then melt-blended at 300°C for 3 minutes in a twin-screw extruder with nitrogen protective gas and a screw speed of 200 r / min, and extruded and molded to form a foamed blend.

[0095] Step 3: Compression foaming: Place the blend in a mold (heating temperature is 300℃), introduce a composite foaming agent (the volume ratio of air to the sum of supercritical nitrogen and supercritical carbon dioxide is 3:1), and after saturation for 5 hours, quickly depressurize and foam.

[0096] Step 4: Curing: The foamed sample is rapidly irradiated with an electron beam (120 kGy, 0.5 h).

[0097] Example 4

[0098] Step 1: Prepare a mixed acid solution by mixing concentrated sulfuric acid and concentrated nitric acid in a 1:1 volume ratio. Add 20 g of conductive filler (carbon nanotubes) to 1000 mL of the mixed acid solution. Acidify the solution under water bath heating conditions (70°C, 4 hours) to obtain the acidified conductive filler. Wash the filler with deionized water until neutral, vacuum dry (90°C, 24 hours), and grind it to obtain the modified conductive filler (170 mesh).

[0099] Step 2: The PES matrix resin, functional second component (4,4'-diphenylmethane diisocyanate), modified conductive filler, initiator (diphenyliodonium hexafluoroantimonate), and cell stabilizer (polyoxyethylene sorbitan stearate) are vacuum dried at 80°C for 6 hours and mixed evenly; the mixture is then melt-blended at 200°C for 15 minutes in a twin-screw extruder with nitrogen protective gas, and the screw speed is 50 r / min (150 r / min). The resulting foamed blend is then extruded and molded.

[0100] Step 3: Compression foaming: Place the blend in a mold (heating temperature is 220℃), introduce a composite foaming agent (air and supercritical nitrogen volume ratio is 4:1), saturate for 3 hours, and then quickly depressurize to foam;

[0101] Step 4: Curing: The foamed sample is rapidly irradiated with an electron beam (50 kGy, 1 h).

[0102] Example 5

[0103] Step 1: Prepare a mixed acid solution by mixing concentrated sulfuric acid and concentrated nitric acid in a ratio of 3:1 (volume ratio). Add 50 g of conductive filler (graphene oxide) to 1000 mL of the mixed acid solution. Acidify the solution under water bath heating conditions (water bath temperature 80℃, water bath time 4 hours) to obtain the acidified conductive filler. Wash the filler with deionized water until neutral, vacuum dry (90℃, 24 hours), and grind it to obtain the modified conductive filler (particle size 100 mesh).

[0104] Step 2: The PES matrix resin, functional second component (bis(4-vinylphenyl)sulfone), modified conductive filler, initiator (4,4'-xylyl iodide hexafluorophosphate), and cell stabilizer (sodium dodecylbenzene sulfonate polyoxyethylene ether laurate) are vacuum dried at 80°C for 6 hours and mixed evenly; the mixture is then melt-blended at 260°C for 18 minutes in a twin-screw extruder with nitrogen protective gas and a screw speed of 50 r / min, and extruded and molded to form a foamed blend.

[0105] Step 3: Compression foaming: Place the blend in a mold (heating temperature is 160℃), introduce a composite foaming agent (volume ratio of air and supercritical carbon dioxide is 2:1), saturate for 2 hours, and then quickly depressurize to foam;

[0106] Step 4: Curing: The foamed sample is rapidly irradiated with an electron beam (70 kGy, 1 h).

[0107] The main performance test results of the foam material in the examples are shown in Table 2.

[0108] Table 1 Chemical composition, wt%

[0109]

[0110] The inventors conducted extensive experimental research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0111] Comparative Example 1

[0112] This comparative example is basically the same as Example 1, except that no functional second component is added and the mass percentage of PES is 82.5%.

[0113] Comparative Example 2

[0114] This comparative example is basically the same as Example 1, except that the conductive filler was not modified.

[0115] Comparative Example 3

[0116] This comparative example is basically the same as Example 1, except that electron beam curing is not performed.

[0117] Comparative Example 4

[0118] This comparative example is basically the same as Example 1, except that the second functional component uses an existing plasticizer—dibutyl phthalate.

[0119] Comparative Example 5

[0120] This comparative example is basically the same as Example 1, except that the composite foaming agent is a mixture of supercritical nitrogen and supercritical carbon dioxide.

[0121] Comparative Example 6

[0122] This comparative example is basically the same as Example 1, except that the mass percentage of the second functional component is 33%.

[0123] Comparative Example 7

[0124] This comparative example is basically the same as Example 1, except that the mass percentage of the second functional component is 2%.

[0125] Table 2. Test results of the foamed products obtained in the examples and comparative examples.

[0126]

[0127]

[0128] As shown in Table 2, the foam material of this invention has an expansion ratio of 11-19 times, a closed-cell rate of 93%-96%, an average cell size of 8-9.6 μm, a compressive strength of 1.65-1.79 MPa, an electrical conductivity of 51.5-62.8 S / cm, and an electromagnetic shielding effectiveness of 40.6-54.3 dB. This foam material not only possesses a high expansion ratio and excellent mechanical properties, but also good electrical conductivity and electromagnetic shielding performance, making it a foam material with excellent comprehensive performance.

[0129] As can be seen from the data of Example 1 and Comparative Example 1 in Table 2, the foaming ratio of the foam material obtained without adding the functional second component is only 5 times, while the foaming ratio with the addition of the functional second component is as high as 19 times. This indicates that the addition of the functional second component has the effect of plasticizer, reducing the viscosity of the PES matrix and thus increasing the foaming ratio.

[0130] As can be seen from the data in Table 2 of Example 1 and Comparative Example 2, the electrical conductivity of the foam material obtained without modification of the filler is only 34.2 S / cm (far lower than 62.8 S / cm in Example 1), and the electromagnetic shielding effectiveness is only 33.5 dB (far lower than 54.3 dB in Example 1). This proves that the modification of the filler improves its dispersibility in the material, thereby significantly improving the conductivity and electromagnetic shielding performance of the material.

[0131] As can be seen from the data in Table 2 for Example 1 and Comparative Example 3, the compressive strength of the foam material obtained without electron beam curing is only 0.53 MPa, which is significantly lower than the compressive strength of the foam material obtained with electron beam curing (1.72 MPa).

[0132] As can be seen from the data of Example 1 and Comparative Example 4 in Table 2, the existing plasticizer can only play a plasticizing role and increase the foaming ratio, but cannot play a role in radiation crosslinking in the subsequent electron beam post-curing process. Therefore, the compressive strength of the obtained foam material is only 1.22 MPa, which cannot significantly improve the mechanical properties of PES foam material.

[0133] As can be seen from the data in Table 2 for Example 1 and Comparative Example 5, the closed-cell rate of the foam material obtained by using a mixture of supercritical nitrogen and supercritical carbon dioxide as the composite foaming agent is only 85%, which is much lower than the 95% obtained by using air and supercritical carbon dioxide as the composite foaming agent. The compressive strength is only 0.86 MPa, which is much lower than the 1.72 MPa obtained by using air and supercritical carbon dioxide as the composite foaming agent. This proves that using the air-based composite foaming agent of the present invention can improve the closed-cell rate and compressive strength of the obtained foam material, thus significantly improving the mechanical properties of the foam material.

[0134] As can be seen from the data in Example 1 and Comparative Example 6 in Table 2, the mass percentage of the added functional second component is too high. It can increase the foaming ratio of the foam material, but it will cause the open cell ratio to decrease and the cell size to increase, exceeding 10 micrometers (no longer within the range of microporous foam).

[0135] As can be seen from the data in Table 2 of Example 1 and Comparative Example 7, the mass percentage of the added functional second component is too low, and the improvement on the foaming ratio and mechanical properties of the foam material is not significant, thus proving the importance of controlling the amount of the functional second component added in this invention.

[0136] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A microporous high-ratio polyethersulfone foam material for electromagnetic shielding, characterized in that, It contains the following components by mass percentage: PES matrix resin 50.0%-90.0%; Functional component 2: 4.0%-30.0%; Modified conductive filler 5.0%-15.0%; Initiator 0.5%-3.0%; Cell stabilizer 0.3%-1.0%; Composite foaming agent 0.2%-1.0%; The sum of the mass percentages of all components is 100%. The second functional component comprises a mixture of phenyl glycidyl ether and N-phenyl-2-naphthylamine, or bis(4-vinylphenyl) sulfone; The foam material has a high foaming ratio of more than 10 times, a closed-cell rate of >90%, uniform cell size, and an average cell size of <10μm, a compressive strength of ≥1.5MPa, an electrical conductivity of >50S / cm, and an electromagnetic shielding effectiveness of >40dB. The modified conductive filler was obtained by modification using the following method: Step a: Prepare a mixed acid solution by mixing concentrated sulfuric acid and concentrated nitric acid in a certain proportion; Step b: Add a certain mass of conductive filler to the mixed acid solution, and perform acidification treatment under water bath heating conditions to obtain acidified conductive filler; Step c: Post-process the acidified conductive filler to obtain the modified conductive filler; Conductive fillers include one or more of carbon nanotubes (CNTs), carbon black, and graphene oxide.

2. The foam material according to claim 1, characterized in that, Initiators include one or more of iodonium salts, thionium salts, and ferrocene salts.

3. The foam material according to claim 1 or 2, characterized in that, Cell stabilizers include one or a mixture of several of the following: polyether type, siloxane type, fatty acid ester type, polyarylether sulfone-polyethylene glycol copolymer, and polytetrafluoroethylene-grafted acrylic acid copolymer.

4. A method for preparing microporous high-ratio PES foam material for electromagnetic shielding, characterized in that, The method for preparing the foam material according to any one of claims 1-3 comprises the following steps: Step 1: Modify the conductive filler to obtain the modified conductive filler; Step 2: Melt blending: Mix the PES matrix resin, functional second component, modified conductive filler, initiator, and cell stabilizer, then melt blend and extrude to obtain a molded foamed blend; Step 3: Compression foaming: Place the blend in a mold, introduce the composite foaming agent, and after saturation for a period of time, release the pressure to foam, and obtain the foamed sample; Step 4: Curing: Irradiate the foamed sample with an electron beam.

5. The preparation method according to claim 4, characterized in that, In step 2, the melt blending temperature is 240-300℃.

6. The preparation method according to claim 4, characterized in that, In step 3, the saturation time is 0.5-5 hours.

7. The preparation method according to any one of claims 4-6, characterized in that, In step 3, the mold heating temperature is 160-300℃.

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