Composite cloth with electromagnetic shielding effect and preparation and application thereof

Abstract

This invention relates to a composite fabric with electromagnetic shielding effect, its preparation, and its application. The composite fabric is made of a composite matrix material prepared mainly from ultra-high molecular weight polyethylene fiber and multi-walled carbon nanotubes, and the matrix material is sandwiched between two single-layer fabrics. The preparation method includes the following steps: a) cutting ultra-high molecular weight polyethylene fiber into short sections and mixing it with multi-walled carbon nanotubes, waterborne polyurethane, and dichloromethane; b) ultrasonically stirring the mixture obtained in step a until uniformly mixed; c) pouring the uniformly mixed mixture from step b into a mold, drying, degassing, and hot-pressing to obtain the composite matrix material; d) laying the obtained composite matrix material between the first and second single-layer fabrics, and hot-pressing to obtain the composite fabric with electromagnetic shielding effect. Compared with the prior art, this invention can enable bulletproof composite fabrics to possess excellent electromagnetic shielding performance while minimizing mechanical property loss.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding materials technology, and relates to a composite fabric with electromagnetic shielding effect and its preparation and application. Background Technology

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is widely used in textiles, chemicals, packaging, construction, agriculture, papermaking, food, military, medical, sports and many other fields due to its excellent wear resistance, impact resistance, corrosion resistance, self-lubrication, energy absorption, low water absorption and good biocompatibility.

[0003] Bulletproof composite fabrics made from ultra-high molecular weight polyethylene (UHMWPE) fibers possess excellent ballistic protection properties and have become one of the mainstream ballistic protection materials. However, to impart electromagnetic shielding capabilities to traditional bulletproof composite fabrics, conductive fillers such as aluminum powder are typically added to water-based polyurethane and attached to unidirectional fiber fabric. While this method achieves electromagnetic shielding, it often leads to a significant decrease in ballistic protection performance.

[0004] Electromagnetic shielding composite fabrics can effectively absorb or reflect electromagnetic waves, reduce the probability of radar detection, and improve the concealment of key facilities and personnel. Currently, there are many methods for preparing electromagnetic shielding composite materials using fibers such as UHMWPE. For example, Chinese patent application CN116575229A provides a method for surface modification and electromagnetic shielding functionalization of UHMWPE fibers and fabrics; Chinese patent application CN119677075A provides an ultra-wideband electromagnetic shielding and bulletproof composite structure material; and Chinese patent application CN110425934A provides a method for preparing a high-strength electromagnetic shielding soft stab-proof bulletproof vest. However, among the above-mentioned existing patent technologies, the first one only involves electromagnetic shielding modification at the fiber level; the second one uses aramid fibers with higher density, which are significantly heavier than UHMWPE at the same areal density; and the third one is a woven soft fabric with stress concentration points, making it difficult to directly produce high-performance bulletproof fabric.

[0005] For example, Chinese patent application CN114705085B provides a method for preparing ultra-high molecular weight polyethylene (UHMWPE) fiber bulletproof plates, which uses UHMWPE fiber base fabric and an intermediate adhesive layer containing fillers such as cellulose fiber, waterborne polyurethane, and magnetite powder. However, this method has the following shortcomings: First, the intermediate layer filler has a complex composition (cellulose fiber, magnetite powder, etc.) and poor compatibility with the UHMWPE fiber matrix, which may lead to weak interfacial bonding. Under high-speed impact, it is easy to become stress defect points, which may pose a potential risk to the mechanical stability of long-term use. Second, the fillers such as magnetite powder have a high density, which will increase the overall weight of the composite fabric and is not conducive to the lightweighting of equipment.

[0006] Therefore, there is an urgent need for a composite fabric with electromagnetic shielding effect to overcome the shortcomings of existing technologies and achieve a balance between functionality and mechanical properties. Summary of the Invention

[0007] The purpose of this invention is to provide a composite fabric with electromagnetic shielding effect, its preparation method and application. By introducing a composite material of the same type as the intermediate layer matrix material, the bulletproof composite fabric can have excellent electromagnetic shielding performance while minimizing the loss of mechanical properties.

[0008] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a method for preparing a composite fabric with electromagnetic shielding effect includes the following steps: S1. After cutting ultra-high molecular weight polyethylene fibers into short sections, they are mixed with water-based polyurethane and then stirred and mixed with a dispersion of multi-walled carbon nanotubes to obtain a uniformly dispersed mixture. S2. Pour the mixture from S1 into a mold, degas, volatilize and heat-cur it, then put it in water for ultrasonic reinforcement, then dry and hot-press it to obtain the composite matrix material. S3. After the unidirectional UHMWPE fibers are unfolded, they are immersed in water-based polyurethane, then dried and heat-treated to obtain a single-layer fabric. S4. Take one layer of the single-layer fabric from S3, lay the composite matrix material from S2 on it, dry and hot-press it, then lay the second layer of single-layer fabric, and hot-press it again. Repeat this process to complete the stacking of the required number of layers. Finally, roll it up to obtain a composite fabric with electromagnetic shielding effect.

[0009] Furthermore, in S1, the ultra-high molecular weight polyethylene fiber is 2-3 cm in length after being chopped. The multi-walled carbon nanotubes have an average diameter of 9-10 nm, an average length of 1.0-2.0 μm, and a purity of >90%.

[0010] Furthermore, in S1, the ratio of the amount of ultra-high molecular weight polyethylene fiber, waterborne polyurethane, and multi-walled carbon nanotubes is (800~1000) mg: (55~65) mL: (20~30) mg, and the solid content of the waterborne polyurethane is 30~40 wt%.

[0011] Furthermore, in S2, the degassing, volatilization and heat curing process is as follows: treatment in an oven at 70~100℃ for 1~3 hours.

[0012] Furthermore, in S2, the ultrasonic reinforcement process is as follows: ultrasonic treatment is performed in deionized water at a frequency of 40~60kHz for 30-60 minutes.

[0013] Furthermore, in S2, the hot pressing process is as follows: at a temperature of 80~120℃, a pressure of 1~3 MPa is applied, and hot pressing is performed for 10~30 min.

[0014] Furthermore, in S3, the ratio of unidirectional UHMWPE fiber to waterborne polyurethane is 200~400 mL of waterborne polyurethane per square meter of fiber fabric. The heat treatment process is as follows: treat at 100~130℃ for 5~15 minutes to allow the resin to fully cross-link and cure.

[0015] Furthermore, in S4, the amount of composite matrix material laid satisfies the following condition: its thickness between the two single-layer fabrics is 2~3mm; The two hot-pressing processes are the same: applying a pressure of 5-10 MPa at a temperature of 100-140℃ for 15-30 minutes; in addition, the unidirectional fabric is laid in a 0° to 90° direction. Preferably, the laying directions of two adjacent unidirectional fabrics are perpendicular to each other to form a quasi-isotropic mechanical structure.

[0016] In a second aspect, the present invention provides a composite fabric with electromagnetic shielding effect, which is prepared by the preparation method described in the first aspect above.

[0017] In a third aspect, the present invention provides the application of a composite fabric with electromagnetic shielding effect in the preparation of electromagnetic shielding equipment.

[0018] Compared with the prior art, the present invention has the following advantages: (1) Innovative “sandwich” structure: A “sandwich” structure is formed by sandwiching a self-made composite matrix material with electromagnetic shielding function between high-performance UHMWPE unidirectional fabrics as the middle layer. This design separates the electromagnetic shielding function from the main mechanical load-bearing function, allowing the outer UHMWPE fabric to focus on providing excellent ballistic performance, while the middle layer provides electromagnetic shielding function to the overall structure, thus achieving an ideal balance between functionality and mechanical performance.

[0019] (2) Interface optimization of homogeneous materials: The intermediate layer composite matrix material also uses UHMWPE chopped fibers as reinforcement and waterborne polyurethane as matrix. The selection of this homogeneous material makes the intermediate layer and the outer UHMWPE fabric have excellent chemical compatibility and interfacial bonding force, avoiding interface defects caused by the introduction of heterogeneous materials (such as metal powder, cellulose fibers, etc.), ensuring the effective transfer of load when the overall structure is subjected to high-speed impact, and preserving the bulletproof potential of the material to the maximum extent.

[0020] (3) Highly efficient and stable conductive network: By introducing chopped UHMWPE fibers as a three-dimensional skeleton into the MWCNT / WPU system and employing an original "ultrasonic reinforcement" step, loosely bonded carbon nanotubes are effectively removed, making the remaining carbon nanotubes more evenly and stably distributed in the skeleton. This not only ensures a highly efficient electron transport path but also ensures the stability of the conductive network during subsequent processing and use, thereby achieving durable and excellent electromagnetic shielding performance.

[0021] (4) Lightweight and simplified process: This invention avoids the introduction of high-density inorganic fillers, effectively controls the areal density of the composite fabric, and conforms to the trend of lightweight development. At the same time, the entire preparation process is clear, the equipment is conventional, the molding cycle is short, it is easy to achieve large-scale production, and the cost is controllable. Detailed Implementation

[0022] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0024] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0025] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0026] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0027] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0028] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0029] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0030] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0031] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0032] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0033] Unless otherwise specified, all preparations and tests described herein took place at 25°C.

[0034] The terms “comprising,” “including,” “containing,” “having,” “comprising,” or other variations thereof are intended to cover non-closed inclusion, and no distinction is made between these terms. The term “comprising” means that other steps and ingredients may be added without affecting the final result. The compositions and methods / processes of the present invention comprise, consist of, and substantially consist of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein. No distinction is made between the terms “efficacy,” “performance,” “effect,” and “potency” herein.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, but sequentially is preferred.

[0037] The performance specifications of the raw materials used in the embodiments of this invention are as follows: The various indicators of ultra-high molecular weight polyethylene fiber were measured using an Instron instrument. The measured sample specifications were: tensile strength of 32~40 cN / dtex, modulus of 1100~1200 cN / dtex, elongation at break of 3.1~3.3%, and fiber fineness of 600D~1000D.

[0038] Multi-walled carbon nanotubes: Commercially available multi-walled carbon nanotubes are used, with an average diameter of about 9.5 nm, an average length of about 1.5 μm, and a purity of >90%.

[0039] Waterborne polyurethane: Commercially available waterborne polyurethane emulsion with a solid content of approximately 35 wt% is used.

[0040] Unless otherwise specified, all other raw materials or processing techniques are commercially available materials or conventional processing techniques in the field.

[0041] Example 1: (1) Take 600D UHMWPE fiber with a breaking strength of 32cN / dtex, modulus of 1100cN / dtex, breaking elongation of 3.1% and cut it into short fibers of 2cm-3cm. Then weigh 900mg and 60ml of waterborne polyurethane and premix them.

[0042] (2) Take 20 mg of multi-walled carbon nanotubes with an average diameter of 9.5 nm, an average length of 1.5 μm, and a purity of >90%. Weigh 27 ml of dichloromethane and mix them.

[0043] (3) After mixing the mixture from step (2) into the mixture from step (1), pour it into an ultrasonic stirrer for ultrasonic uniform stirring to uniformly disperse the ultra-high molecular weight polyethylene fiber and multi-walled carbon nanotubes in the solution. Then pour it into a mold and place it in an oven with degassing function at 80°C for 2 hours for degassing, volatilization, and heat curing. After that, take it out and place it in a container with deionized water for ultrasonic reinforcement (50kHz treatment for 45 minutes) to strengthen the strength of the multi-walled carbon nanotubes in the composite material. Then dry it for 30 minutes to obtain a composite matrix material with electromagnetic shielding effect.

[0044] (4) Place the uniformly spread unidirectional UHMWPE fibers (same as step (1)) into an impregnation tank containing water-soluble polyurethane for impregnation treatment (ensure that the amount of water-soluble polyurethane coating is about 300 mL of water-soluble polyurethane per square meter of fiber cloth), and then dry and heat-treat (treat at 120°C for 10 min) to obtain a single layer of cloth. (5) The matrix material obtained in step (3) is cut according to the specifications of single-layer bulletproof cloth, and then placed between two single-layer bulletproof cloths as an intermediate layer. It is then hot-pressed (the temperature is controlled at 120℃, the pressure is 8Mpa, and the hot-pressing time is 20min). This process is repeated until the number of single-layer cloth layers is 10 (i.e., 5 layers of composite matrix material and 10 layers of single-layer cloth are stacked alternately). The laying direction of two adjacent unidirectional cloths is 90° (i.e., perpendicular to each other). The cloth is then rolled up to obtain a sheet composite cloth with electromagnetic shielding effect.

[0045] (6) The electromagnetic shielding performance of the composite fabric obtained by the test was measured to be 54.3 dB.

[0046] Example 2: This embodiment is basically the same as Embodiment 1, except that the UHMWPE fiber used in step (1) has a breaking strength of 34 cN / dtex. The electromagnetic shielding performance of the composite fabric obtained by testing is 56.7 dB. Performance analysis: The slight increase in fiber strength helps to enhance the mechanical properties of the intermediate matrix material, but has little effect on the electromagnetic shielding effectiveness. The slight fluctuation is within the experimental error range.

[0047] Example 3: This embodiment is basically the same as Embodiment 1, except that the UHMWPE fiber used in step (1) has a breaking strength of 36 cN / dtex. The electromagnetic shielding performance of the composite fabric obtained by testing is 54.9 dB.

[0048] Example 4: This embodiment is basically the same as Embodiment 1, except that the UHMWPE fiber used in step (1) has a breaking strength of 38 cN / dtex. The electromagnetic shielding performance of the composite fabric obtained by testing is 57.3 dB.

[0049] Example 5: This embodiment is basically the same as Embodiment 1, the main difference being that the amount of multi-walled carbon nanotubes used in step (2) is increased to 25 mg. The electromagnetic shielding performance of the composite fabric obtained by testing is 61.0 dB. Performance analysis: Compared with Embodiment 1, with the increase of MWCNT content, the conductive network is more compact and the electron transport path increases, thus significantly improving the electromagnetic shielding effectiveness.

[0050] Example 6: This embodiment is basically the same as Embodiment 1, with the main difference being that the amount of multi-walled carbon nanotubes used in step (2) is increased to 30 mg, and the thickness of the intermediate layer composite matrix material is controlled to be 3 mm in step (5). The electromagnetic shielding performance of the obtained composite fabric is 66.4 dB. Performance analysis: Compared with Embodiments 1 and 5, further increasing the MWCNT content and the thickness of the intermediate layer further enhances the shielding effectiveness.

[0051] Example 7: This embodiment is basically the same as Embodiment 1, with the main difference being that the UHMWPE fiber fineness used in step (1) is 1000D, and the thickness of the intermediate layer composite matrix material is controlled to be 3mm in step (5). The electromagnetic shielding performance of the obtained composite fabric is 58.6dB. Performance analysis: This embodiment changes two process parameters simultaneously: fiber fineness (increased from 600D to 1000D) and intermediate layer thickness (increased from 2mm to 3mm). Compared with Embodiment 4 (600D fineness, 2mm thickness, 57.3dB), the shielding effectiveness is improved to 58.6dB, a net increase of 1.3dB. From the perspective of the effect of thickness, comparing Embodiment 5 (2mm, 61.0dB) and Embodiment 6 (3mm, 66.4dB), it can be seen that the increase in intermediate layer thickness can usually bring about 5-6dB of shielding effectiveness improvement (when the MWCNT content is high). With a MWCNT content of 20 mg, the expected contribution of increasing the thickness from 2 mm to 3 mm is approximately 2-3 dB. However, the actual increase in this embodiment was only 1.3 dB, indicating that increasing the fiber fineness had a certain negative impact on the construction of the conductive network.

[0052] Example 8: Based on Example 1, this embodiment increases the tensile strength of UHMWPE fibers to 40 cN / dtex, maintains the fineness at 600D, keeps the amount of multi-walled carbon nanotubes at 20 mg, and controls the thickness of the interlayer to 2 mm. The tested composite matrix material has a tensile strength of 14.0 MPa, and the electromagnetic shielding effectiveness of the composite fabric is 57.6 dB.

[0053] Example 9: This embodiment, based on Example 5, increases the tensile strength of UHMWPE fibers to 40 cN / dtex, maintains a fineness of 600D, uses 30 mg of multi-walled carbon nanotubes, and controls the thickness of the interlayer to 2 mm. The tested composite matrix material has a tensile strength of 14.6 MPa, and the composite fabric has an electromagnetic shielding effectiveness of 67.7 dB.

[0054] Example 10: This embodiment, based on Example 6, increases the tensile strength of UHMWPE fibers to 40 cN / dtex, maintains a fineness of 600D, uses 30 mg of multi-walled carbon nanotubes, and controls the thickness of the interlayer to 3 mm. The tested composite matrix material has a tensile strength of 14.8 MPa, and the composite fabric has an electromagnetic shielding effectiveness of 66.0 dB.

[0055] Example 11: Based on Example 7, this embodiment increases the tensile strength of UHMWPE fibers to 40 cN / dtex, uses a fineness of 1000D, incorporates 20 mg of multi-walled carbon nanotubes, and controls the interlayer thickness to 3 mm. The tested composite matrix material exhibits a tensile strength of 14.5 MPa and an electromagnetic shielding effectiveness of 58.3 dB.

[0056] Comparative Examples 1-2: The two samples are commercially available ordinary UHMWPE bulletproof composite fabrics without electromagnetic shielding, purchased from Jiangsu Lingrui New Material Technology Co., Ltd. (UD non-woven fabric structure, areal density approximately 200-250 g / m²). 2 (thickness approximately 2-3 mm) and Hebei Longli Technology Co., Ltd. (UD non-woven fabric structure, areal density approximately 220 g / m²) 2 (Approximately 2 mm thick). All of the above products are conventional UHMWPE non-woven composite structures without an added electromagnetic shielding layer, and testing has confirmed that they have no electromagnetic shielding effectiveness (<5 dB).

[0057] Comparative Example 3 (without MWCNT): Compared with Example 1, most of them are the same, the only difference being that the addition of multi-walled carbon nanotubes in step (2) is omitted.

[0058] Comparative Example 4 (Graphite powder replacing MWCNT): Compared with Example 1, most of them are the same, except that the multi-walled carbon nanotubes in step (2) are replaced with an equal mass (20 mg) of ordinary conductive graphite powder (average particle size 10 μm).

[0059] Comparative Example 5 (Cellulose fiber replacing UHMWPE fiber): Compared with Example 1, most of them are the same, the only difference being that the UHMWPE chopped fibers in the composite matrix material in step (1) are replaced with cellulose fibers of the same length (2-3 cm) and mass.

[0060] Comparative Example 6 (without ultrasonic reinforcement): Compared with Example 1, most of them are the same. The only difference is that in the process of preparing the composite matrix material in step (3), after the heat curing treatment, the process of "ultrasonic reinforcement in water" is omitted, and the material is directly dried and hot-pressed.

[0061] Performance tests were conducted on the above embodiments and comparative examples, and the specific test results are shown in Table 1 below.

[0062] Electromagnetic shielding effectiveness test: According to the national standard GB / T 30142-2013 "Method for measuring the shielding effectiveness of electromagnetic shielding materials", the test was conducted in the frequency range of 30MHz-1.5GHz using the flange coaxial method, and the maximum shielding effectiveness value (SE) was recorded.

[0063] Fracture strength test: The composite matrix material was tested in accordance with the national standard GB / T 1040.5-2008 "Determination of tensile properties of plastics - Part 5: Test conditions for unidirectional fiber reinforced composite materials".

[0064] Puncture strength test: The composite matrix material was tested according to the method in Appendix A of industry standard GA 68-2019 "Police Puncture Protective Vest". Table 1 Results analysis and discussion: (1) The composite fabrics prepared in each embodiment of the present invention all exhibit excellent electromagnetic shielding performance (>50dB), reaching the level of commercial application. More importantly, through the innovative "sandwich" structure design, while obtaining high shielding performance, the mechanical performance potential of the outer UHMWPE fabric is preserved to the maximum extent (the middle layer itself also has good mechanical properties).

[0065] (2) Interface Performance Analysis: The comparison results between Comparative Example 5 and Example 1 show that when the intermediate layer skeleton material is replaced by heterogeneous cellulose fibers instead of homogeneous UHMWPE fibers, the tensile strength of the composite matrix material decreases from 6.2 MPa to 4.2 MPa (a decrease of 32%), and the puncture strength decreases from 500 gf to 380 gf (a decrease of 24%). This significant decrease is due to the poor interfacial compatibility between cellulose fibers and the waterborne polyurethane matrix and the outer UHMWPE fabric, resulting in reduced stress transfer efficiency and increased microscopic defects. In contrast, the "cellulose fiber + magnetite powder" intermediate layer used in scheme CN114705085B also faces interfacial compatibility problems. Cellulose fibers and the UHMWPE matrix are heterogeneous material systems with weak interfacial bonding; magnetite powder, as an inorganic filler, has an even weaker interface with the organic matrix. Under long-term use or humid and hot environments, these interfacial defects may expand, leading to a decline in mechanical properties.

[0066] This invention achieves excellent interfacial compatibility through the design of homogeneous materials for the intermediate and outer layers (both UHMWPE fiber-reinforced WPU systems). As shown in Example 8, under optimized conditions, the matrix material achieves a tensile strength of 14.0 MPa and a puncture strength of 746 gf, ensuring the long-term mechanical stability of the overall structure.

[0067] (3) Analysis of the indirect influence of fiber strength on electromagnetic shielding effectiveness: Comparing Examples 1-4, it can be found that when the MWCNT content (20mg) and the interlayer thickness (2mm) remain unchanged, as the breaking strength of the UHMWPE chopped fibers gradually increases from 32 cN / dtex to 38 cN / dtex, the mechanical properties (breaking strength, puncture strength) of the composite matrix material show a significant increasing trend. At the same time, the electromagnetic shielding effectiveness of the composite fabric also increases slightly from 54.3 dB to about 57.3 dB. This phenomenon can be explained from the perspective of microstructure: the higher-strength UHMWPE fibers have better shape retention under the same processing conditions (ultrasonic reinforcement, hot pressing), and can form a more regular and stable three-dimensional skeleton. This regular skeleton helps multi-walled carbon nanotubes form a more uniform and less defective conductive network on the skeleton surface and in the skeleton gaps, thereby improving the conductivity of the network without increasing the total amount of conductive filler, resulting in a moderate enhancement of electromagnetic shielding effectiveness. This also shows that the present invention achieves synergistic optimization of mechanical reinforcement and functional filler through homogeneous material design.

[0068] (4) Comparative Example 3 (without MWCNT): It is impossible to form a conductive network at all, and the composite cloth has almost no electromagnetic shielding effectiveness, which proves the core role of MWCNT as a conductive filler.

[0069] (5) Comparative Example 4 (graphite powder replacing MWCNT): Although it has a certain shielding effect (28.5dB), it is much lower than that of Example 1 (54.3dB) with the same amount of MWCNT. This is because the aspect ratio of graphite powder is small, making it difficult to form a long-range conductive path in one dimension like MWCNT, which proves the unique advantage of one-dimensional nanomaterial MWCNT in constructing efficient conductive networks.

[0070] (6) Comparative Example 5 (Cellulose fiber replacing UHMWPE fiber): The mechanical properties (breaking strength, puncture strength) of the composite matrix material decreased significantly. This is because the interfacial compatibility between cellulose fiber and WPU matrix and outer UHMWPE fabric is poor, resulting in defects in the material. This proves that the intermediate skeleton must be made of UHMWPE fiber of the same material as the outer layer to ensure the overall mechanical properties.

[0071] (7) Comparative Example 6 (without ultrasonic reinforcement): Compared with Example 1, its conductivity and electromagnetic shielding effectiveness both decreased. This is because the ultrasonic reinforcement step was missing, and some poorly bonded MWCNTs may fall off or be unevenly distributed in subsequent processes, resulting in an incomplete and unstable conductive network. Ultrasonic reinforcement plays a key role in stabilizing the three-dimensional conductive network.

[0072] (8) Analysis of interfacial bonding strength and long-term stability In response to the defects mentioned in the background art, namely "weak interfacial bonding and insufficient long-term mechanical stability", this invention has conducted targeted verification through proportional and embodiment data.

[0073] 1. Direct comparative evidence of interfacial bonding strength Comparative Example 5 replaced the short-cut UHMWPE fibers in the composite matrix material with cellulose fibers of the same length, while maintaining identical conditions to Example 1. Test results showed: Fracture strength: decreased from 6.2 MPa in Example 1 to 4.2 MPa in Comparative Example 5 (a decrease of 32%). Puncture intensity: decreased from 500 gf in Example 1 to 380 gf in Comparative Example 5 (a decrease of 24%).

[0074] The direct cause of this significant decline is that cellulose fibers, the waterborne polyurethane matrix, and the outer UHMWPE fabric are heterogeneous material systems with poor interfacial compatibility. This leads to impeded stress transmission at the interface and an increase in microscopic defects. When subjected to external forces, these interfacial defects easily become the starting point for crack initiation and propagation, thereby significantly reducing the overall mechanical properties of the material.

[0075] This result precisely confirms the inherent flaws of existing solutions such as CN114705085B, namely, that the "cellulose fiber + magnetite powder" interlayer used in these solutions also belongs to a heterogeneous material system. The cellulose fiber has poor compatibility with the UHMWPE matrix, and the interface between the magnetite powder as an inorganic filler and the organic matrix is ​​a weak point. These heterogeneous interfaces are very likely to become stress concentration points and defect sources when the material is subjected to high-speed impact.

[0076] 2. In stark contrast to the aforementioned heterogeneous systems, this invention employs a homogeneous material design: the intermediate composite matrix material uses UHMWPE chopped short fibers as reinforcement, and the outer unidirectional fabric is also made of UHMWPE fibers, both sharing the same waterborne polyurethane matrix. The interfacial advantages resulting from this homogeneous design are manifested in: Excellent chemical compatibility: UHMWPE fibers exhibit good wettability and affinity with each other and with the WPU matrix, resulting in high interfacial bonding strength.

[0077] Mechanical properties improved synchronously with fiber strength: From Example 1 to Example 4, as the breaking strength of UHMWPE fibers increased from 32 cN / dtex to 38 cN / dtex, the breaking strength of the composite matrix material increased from 6.2 MPa to 11.0 MPa (an increase of 77%), and the puncture strength increased from 500 gf to 686 gf (an increase of 37%). This synchronous improvement indicates that the load is effectively transferred at the interface, and the reinforcing effect of the fibers is fully utilized.

[0078] Extending the upper limit of excellent performance: Examples 8-11 further increased the fiber strength to 40 cN / dtex, achieving even higher mechanical properties. Specifically, the matrix material in Example 8 achieved a fracture strength of 14.0 MPa and a puncture strength of 746 gf; the fracture strength in Example 9 reached 14.6 MPa and the puncture strength reached 713 gf. These data demonstrate that, within a homogeneous interface system, the mechanical properties of the material exhibit excellent scalability.

[0079] 3. Correlation between interface stability and long-term mechanical properties Interfacial bonding forces not only affect the initial mechanical properties of materials, but also directly determine their long-term mechanical stability. Existing research shows that: Composite materials with low interfacial bonding strength are prone to microcrack propagation at the interface after exposure to humid and hot environments, cyclic loading, or long-term storage, leading to a significant deterioration in mechanical properties.

[0080] Composite materials with high interfacial bonding strength can effectively resist environmental aging and fatigue damage, and maintain stable mechanical properties over a long period of time.

[0081] 4. The mechanical property data (fracture strength 6.2-14.8 MPa, puncture strength 500-746 gf) of Examples 1-11 of the present invention are generally superior to or equivalent to the levels reported in the literature after interface modification. In particular, the comparison between Comparative Example 6 (without ultrasonic reinforcement) and Example 1 shows that the ultrasonic reinforcement process further stabilizes the interface structure by removing poorly bonded MWCNTs, thereby improving conductivity and shielding effectiveness. This indirectly proves the importance of interface structure stability to the overall performance of the material.

[0082] 5. Conclusion: Based on the above data and analysis, it can be concluded that this invention, through the design of homogeneous materials for the intermediate and outer layers, successfully overcomes the defects of existing technologies (such as CN114705085B) in "weak interfacial bonding and insufficient long-term mechanical stability." The significant performance degradation of Comparative Example 5 demonstrates the harm of heterogeneous interfaces, while the excellent and scalable mechanical properties of Examples 1-11 positively prove the advantages of homogeneous interface design. This interface optimization provides a reliable guarantee for the composite fabric of this invention to maintain stable mechanical properties and electromagnetic shielding effectiveness under long-term use and harsh environments.

[0083] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for manufacturing a composite cloth having an electromagnetic shielding effect, characterized by, It comprises the following steps: S1, after the short cutting treatment of the ultra-high molecular weight polyethylene fiber, it is mixed with the water-based polyurethane, and then stirred and mixed with the dispersion liquid of the multi-walled carbon nanotube to obtain a uniformly dispersed mixed liquid; S2, pour the mixed liquid in S1 into a mold, perform degassing, volatilization and heat curing treatment, and then enter the water for ultrasonic reinforcement, then dry and hot press to obtain a composite matrix material; S3, after the unidirectional UHMWPE fiber is unfolded and immersed in the water-based polyurethane, it is dried and heat treated to obtain a single-layer cloth; S4, take one layer of the single-layer cloth in S3, lay the composite matrix material in S2, dry and hot press, lay the second layer of single-layer cloth, hot press again, repeat the process, complete the stacking of the required number of layers, and finally wind up to obtain a composite cloth with electromagnetic shielding effect.

2. The method for preparing a composite fabric with electromagnetic shielding effect according to claim 1, characterized in that, In S1, the length of the ultra-high molecular weight polyethylene fiber after short cutting treatment is 2-3 cm; The average diameter of the multi-walled carbon nanotube is 9-10 nm, the average length is 1.0-2.0 μm, and the purity is >90%.

3. The method for preparing a composite fabric with electromagnetic shielding effect according to claim 1, characterized in that, In S1, the addition amount ratio of the ultra-high molecular weight polyethylene fiber, the water-based polyurethane and the multi-walled carbon nanotube is (800-1000) mg:(55-65) mL:(20-30) mg; the solid content of the water-based polyurethane is 30-40 wt%.

4. The method for preparing a composite fabric with electromagnetic shielding effect according to claim 1, characterized in that, In S2, the process of degassing, volatilization and heat curing treatment is: treated in an oven at 70-100℃ for 1-3h.

5. The method for preparing a composite fabric with electromagnetic shielding effect according to claim 1, characterized in that, In S2, the process of ultrasonic reinforcement is: ultrasonic treatment in deionized water at a frequency of 40-60 kHz for 30-60 min.

6. The method of claim 1, wherein the composite cloth having electromagnetic shielding effect is prepared by the steps of: In S2, the process of hot pressing is: hot pressing at a temperature of 80-120℃ under a pressure of 1-3 MPa for 10-30 min.

7. The method for preparing a composite fabric with electromagnetic shielding effect according to claim 1, characterized in that, In S3, the addition amount ratio of the unidirectional UHMWPE fiber and the water-based polyurethane is: 200-400 mL of water-based polyurethane corresponding to each square meter of fiber cloth; The process of heat treatment is: treated at 100-130℃ for 5-15 min.

8. The method for preparing a composite fabric with electromagnetic shielding effect according to claim 1, characterized in that, In S4, the laying amount of the composite matrix material satisfies: the thickness between two layers of single-layer cloth is 2-3 mm; The process of the two hot pressings is the same, specifically: hot pressing at a temperature of 100-140℃ under a pressure of 5-10 MPa for 15-30 min; The laying directions of the upper and lower adjacent two layers of unidirectional cloth are perpendicular to each other.

9. A composite cloth with electromagnetic shielding effect, which is prepared by the preparation method of any one of claims 1-8.

10. The use of the composite cloth with electromagnetic shielding effect of claim 9 in the preparation of electromagnetic shielding equipment.

Images