Nonwoven wave-absorbing fabric having a layer structure and integrated molding method

Abstract

The present application relates to a kind of non-woven wave-absorbing fabric with layer structure, which is formed by wet-laid technology with the mixed suspension pulp of wave-absorbing fiber and ordinary fiber into an integrated structure including three layers of surface layer, intermediate layer and bottom layer;The surface layer is an impedance matching layer, the intermediate layer is an absorption layer, and the bottom layer is a reflective layer;Wherein, the center length of wave-absorbing fiber contained in the surface layer is L1, the center length of wave-absorbing fiber contained in the intermediate layer is L2, and the center length of wave-absorbing fiber contained in the bottom layer is L3;Wherein L1<L2<L3.The present application forms a structure with gradient distribution of wave-absorbing fiber in the thickness direction of layer by regulating the length and content of wave-absorbing fiber, so that the wave-absorbing frequency is wide;The non-woven fabric structure is integrally formed by wet-laid technology, which realizes light, soft, wave-absorbing frequency spectrum easy to control, wide frequency, high strength and other advantages.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, specifically to a nonwoven microwave absorbing fabric with a layered structure and an integrated molding method. Background Technology

[0002] Currently, many microwave absorbing materials use non-woven fabric as a base, coating it with a microwave absorbing material, and then layering them to form a microwave absorbing composite material. For example, patents CN215040904U, CN210590815U, CN209274083U, CN208277551U, and CN206999754U disclose microwave absorbing non-woven fabrics, all of which are composed of multiple layers of non-woven fabric and microwave absorbing layers. They achieve the effect of weakening radiation through multiple reflections and dissipation of electromagnetic waves within the fabric. However, these materials suffer from problems such as being relatively stiff, having poor breathability, and being difficult to manufacture into wearable equipment. Patent CN109234918B discloses a method for preparing Schiff base composite / PP / PLA nonwoven fabric. By forming microwave-absorbing material both inside the fibers and on the surface of the nonwoven fabric, it has advantages such as low areal density, good flexibility, easy processing, and low price. However, carbon nanotubes are black and easily conductive, leading to limitations in application and safety issues. Application CN201810127388.X discloses an ultrafine fiber composite microwave-absorbing material and its preparation method. By repeatedly impregnating and coating the surface of ultrafine fiber nonwoven fabric with the microwave-absorbing material, it achieves excellent broadband microwave absorption effects; however, the material is relatively hard and not breathable. Application CN201510595810.0 discloses a method for preparing microwave-absorbing nonwoven fabric by scraping and coating the nonwoven fabric with the microwave-absorbing material, resulting in a microwave-absorbing composite material that is relatively hard and not breathable.

[0003] In summary, existing microwave absorbing materials formed by scraping or coating methods suffer from problems such as stiffness, poor breathability, and low softness and comfort due to the use of large amounts of adhesive resins, resulting in poor wearability and applicability. Furthermore, the microwave absorbing materials studied above are relatively uniform in their molding process, resulting in a narrow electromagnetic wave absorption bandwidth, which limits their wide-bandwidth and multi-field applications. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a nonwoven microwave absorbing fabric with a layered structure and its integrated molding method. By adjusting the length and content of the microwave absorbing fibers, a structure with a gradient distribution of microwave absorbing fibers in the layer thickness direction is formed, thereby achieving broadband microwave absorption. The integrated molding nonwoven fabric structure is prepared by wet web forming technology, which realizes that the microwave absorbing fabric is lightweight, soft, and has an easily adjustable microwave absorption spectrum, with the advantages of broadband and high strength.

[0006] (II) Technical Solution

[0007] In a first aspect, the present invention also provides a nonwoven microwave absorbing fabric with a layered structure, which is formed into a whole by a wet web forming technology from a mixed suspension of microwave absorbing fibers and ordinary fibers and includes a three-layer structure of a surface layer, a middle layer and a bottom layer.

[0008] The surface layer is an impedance matching layer, the middle layer is an absorption layer, and the bottom layer is a reflection layer; wherein, the center length of the absorbing fibers in the surface layer is L1, the center length of the absorbing fibers in the middle layer is L2, and the center length of the absorbing fibers in the bottom layer is L3; wherein L1 <L2<L3。

[0009] According to a preferred embodiment of the present invention, the length of the microwave absorbing fibers in the surface layer is normally distributed with a center length L1 in the range of 0.5-4 mm, and the content of the microwave absorbing material in the surface layer is 0.4-6 g / m². 2 The surface layer has a thickness of 1-5 mm; the length of the absorbing fibers in the intermediate layer is normally distributed with a center length L2 in the range of 5-15 mm, and the content of the absorbing material in the intermediate layer is 2-10 g / m. 2 The thickness of the intermediate layer is 1-8 mm; the length of the absorbing fibers in the bottom layer is normally distributed with a center length L3 in the range of 18-38 mm, and the content of the absorbing material in the bottom layer is 3-10 g / m. 2 The thickness of the bottom layer is 0.5-2.5mm.

[0010] According to a preferred embodiment of the present invention, the surface layer, the intermediate layer and the bottom layer are formed separately and then combined into one piece by hot roll forming.

[0011] According to a preferred embodiment of the present invention, the ordinary fiber includes modified branched fiber and / or bonding fiber.

[0012] Secondly, the present invention discloses an integrated molding method for a nonwoven wave-absorbing fabric with a layered structure, comprising:

[0013] The first microwave-absorbing fiber is mixed and dispersed with ordinary fiber in a solvent to form a first suspension.

[0014] The second microwave-absorbing fiber is mixed and dispersed with ordinary fiber in a solvent to form a second suspension.

[0015] The third microwave-absorbing fiber is mixed and dispersed with ordinary fiber in a solvent to form a third suspension.

[0016] The center length of the first absorbing fiber is L1, the center length of the second absorbing fiber is L2, and the center length of the third absorbing fiber is L3, where L1 <L2<L3;

[0017] The third suspension slurry is introduced into the inclined wire mesh forming area and filtered under negative pressure to obtain the first layer of mesh fabric; the second suspension slurry is introduced into the inclined wire mesh forming area and filtered under negative pressure to form the second layer of mesh fabric on the first layer of mesh fabric; the first suspension slurry is then introduced into the inclined wire mesh forming area and filtered under negative pressure to form the third layer of mesh fabric on the second layer of mesh fabric; the three layers of mesh fabric finally obtained in the inclined wire mesh forming area are dried and hot-rolled to form an integrally formed non-woven wave-absorbing fabric;

[0018] Alternatively, the third, second, and first suspensions can be sequentially and continuously introduced into the inclined mesh forming area in a undisturbed manner, filtered under negative pressure, and three layers of mesh fabric can be directly obtained. After drying and hot rolling, an integrally formed non-woven wave-absorbing fabric can be obtained.

[0019] Preferably, the inclined mesh forming area is relatively deep, and the suspended slurry falls slowly and sequentially along the material pipe or the side wall of the feeding area without causing large turbulence, so that the absorbing fibers of different lengths are clearly layered.

[0020] Preferably, the drying process involves the fabric entering a heating tunnel via a conveyor belt, where it is heated evenly by two rows of hot air vents. The hot roll forming process involves using hot roll forming after drying to strengthen the bond between the three layers and improve the smoothness of the non-woven absorbent fabric.

[0021] According to a preferred embodiment of the present invention, the first absorbing fiber, the second absorbing fiber, and the third absorbing fiber are one or more of glass-coated amorphous magnetic fibers, stainless steel fibers, carbon fibers, modified carbon fibers, modified silicon carbide fibers, polycrystalline iron fibers, iron-nickel fibers, and iron-cobalt-nickel fibers, preferably glass-coated amorphous magnetic fibers.

[0022] According to a preferred embodiment of the present invention, the length of the first absorbing fiber is normally distributed with L1 as the center in the range of 0.5-4 mm; the length of the second absorbing fiber is normally distributed with L2 as the center in the range of 5-15 mm; and the length of the third absorbing fiber is normally distributed with L3 as the center in the range of 18-38 mm.

[0023] According to a preferred embodiment of the present invention, the ordinary fiber includes modified branched fiber and / or bonding fiber; the preparation method of the suspension slurry is as follows: placing the corresponding microwave absorbing fiber, ordinary fiber, solvent and dispersant in a mixer, stirring, dispersing evenly, to form a suspension slurry.

[0024] According to a preferred embodiment of the present invention, the solvent is water; the dispersant is a surfactant. Preferably, the surfactant is an anionic surfactant or a nonionic surfactant; the anionic surfactant may be sodium dodecylbenzenesulfonate; the nonionic surfactant is PEO dispersant. PEO is both a novel water-soluble resin and a nonionic surfactant.

[0025] According to a preferred embodiment of the present invention, the modified branched fiber is a fiber obtained by modifying and branching one or more of viscose fiber, polyester fiber, nylon fiber, cellulose fiber, polypropylene fiber and polyethylene fiber; the modified branching process includes: mechanical treatment, chemical or radiation-induced grafting to increase the interweaving strength between fibers, and the length of the modified branched fiber is 5-20 mm.

[0026] According to a preferred embodiment of the present invention, the bonding fiber is one or a combination of several of the following: water-soluble vinylon fiber, polyacrylic acid fiber, ethylene-vinyl acetate copolymer fiber, PE / PP bicomponent fiber, and PE / PET bicomponent fiber, and the length of the bonding fiber is 5-20 mm.

[0027] According to a preferred embodiment of the present invention, the first, second, and third microwave absorbing fibers are microwave absorbing fibers with a polymer coating film on their surface; the polymer coating film is polypropylene, polyester, or nylon, and the film thickness is 1-5 μm.

[0028] The thickness of each layer of mesh is controlled by the content of ordinary fibers.

[0029] The polymer coating film is formed by coating a polymer melt during the forming and drawing process of the microwave absorbing fiber, which can improve the dispersion and suspension of the microwave absorbing fiber; and avoid the problem of uneven distribution of the microwave absorbing fiber in each layer of mesh and non-woven microwave absorbing fabric products caused by aggregation and settling in the suspension slurry.

[0030] Thirdly, the present invention also provides a nonwoven wave-absorbing fabric with a layered structure, which is prepared by the integrated molding method of any of the above embodiments.

[0031] (III) Beneficial Effects

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The nonwoven microwave absorbing fabric of this invention has a three-layer structure consisting of a surface layer, a middle layer, and a bottom layer. All layers are formed using a wet web-forming technique with a mixed suspension of microwave absorbing fibers and ordinary fibers (modified branched fibers and bonding fibers). The thickness of each layer can be adjusted by controlling the content of microwave absorbing fibers and ordinary fibers. After the three layers are integrally formed, the nonwoven microwave absorbing fabric exhibits a structural characteristic of a gradient distribution of the center length of the microwave absorbing fibers in the thickness direction. This achieves impedance matching capability of the surface layer, resonance loss effect of the middle layer, and interference effect of the overall sample in the thickness direction. The nonwoven microwave absorbing fabric of this invention has advantages such as being lightweight, soft, breathable, and having broadband microwave absorption capabilities, making it suitable as a material for wearable anti-radiation equipment. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of an integrated molded nonwoven wave-absorbing fabric structure with a layered structure, which is a preferred embodiment of the present invention.

[0035] Figure 2 The results show the microwave absorption performance test results of the nonwoven microwave absorbing fabric in Example 1.

[0036] Figure 3 The results show the microwave absorption performance test results of the nonwoven microwave absorbing fabric in Example 2.

[0037] Figure 4 The results show the microwave absorption performance test results of the nonwoven microwave absorbing fabric in Example 3.

[0038] Figure 5 The results show the microwave absorption performance test results of the nonwoven microwave absorbing fabric in Example 4.

[0039] Figure 6 The results show the microwave absorption performance test results of the nonwoven microwave absorbing fabric in Example 5. Detailed Implementation

[0040] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Wet-laid fabrication is a technology that uses water as a medium and papermaking technology as a basis to lay fibers into a web to prepare nonwoven fabrics. It has advantages such as a wide range of raw material sources, broad product applications, and large market potential. However, there is currently no existing technology for using wet-laid fabrication to prepare microwave absorbing protective materials. This invention utilizes wet-laid fabrication technology to integrally mold and prepare nonwoven microwave absorbing fabrics with a layered structure. The microwave absorbing fibers and ordinary fibers form a disordered nonwoven fabric structure through interfiber bonding. This structure has advantages such as being lightweight, soft, breathable, and having broadband microwave absorption capabilities, making it suitable as a material for wearable radiation protection equipment.

[0042] like Figure 1The diagram shows a preferred embodiment of the integrated nonwoven microwave-absorbing fabric with a layered structure, comprising a surface layer P, a middle layer A, and a bottom layer F. The surface layer P, middle layer A, and bottom layer F are formed from a mixed suspension of microwave-absorbing fibers and ordinary fibers using a wet web-forming technique, and the surface layer, middle layer, and bottom layer are integrated. The modified branched fiber is obtained by modifying and branching one or more of viscose fibers, polyester fibers, nylon fibers, cellulose fibers, polypropylene fibers, and polyethylene fibers. The modification and branching process includes mechanical treatment, chemical or radiation-induced grafting to increase the interweaving strength between fibers, and the length of the modified branched fiber is 5-20 mm. The ordinary fiber includes modified branched fibers and / or bonding fibers. The bonding fiber is one or a combination of water-soluble vinylon fibers, polyacrylic acid fibers, ethylene-vinyl acetate copolymer fibers, PE / PP bicomponent fibers, and PE / PET bicomponent fibers, and the length of the bonding fiber is 5-20 mm. The microwave-absorbing fiber is a fiber with a polymer coating on its surface; the polymer coating is made of polypropylene, polyester, or nylon, and the film thickness is 1-5 μm. Specifically, it can include two methods:

[0043] Method 1:

[0044] (1) The surface absorbing fiber, ordinary fiber, dispersant and water are stirred and mixed to form a surface suspension slurry; the middle layer absorbing fiber, ordinary fiber, dispersant and water are stirred and mixed to form a middle layer suspension slurry; the bottom layer absorbing fiber, ordinary fiber, dispersant and water are stirred and mixed to form a bottom layer suspension slurry.

[0045] (2) The bottom layer of suspension slurry is introduced into the inclined wire mesh forming area and filtered under negative pressure to obtain the first layer of mesh fabric; the middle layer of suspension slurry is introduced into the inclined wire mesh forming area and filtered under negative pressure to form the second layer of mesh fabric on the first layer of mesh fabric; finally, the bottom layer of suspension slurry is introduced into the inclined wire mesh forming area and filtered under negative pressure to form the third layer of mesh fabric on the second layer of mesh fabric; the three layers of mesh fabric finally obtained in the inclined wire mesh forming area are dried and hot rolled to form an integral non-woven wave-absorbing fabric.

[0046] Method 2:

[0047] (1) The surface absorbing fiber, ordinary fiber, dispersant and water are stirred and mixed to form a surface suspension slurry; the middle layer absorbing fiber, ordinary fiber, dispersant and water are stirred and mixed to form a middle layer suspension slurry; the bottom layer absorbing fiber, ordinary fiber, dispersant and water are stirred and mixed to form a bottom layer suspension slurry.

[0048] (2) The bottom layer suspension, the middle layer suspension, and the bottom layer suspension are sequentially and continuously introduced into the inclined web forming zone in a undisturbed manner. After negative pressure filtration, a three-layer mesh is directly obtained. The mesh is then dried and hot-rolled to form an integrally formed non-woven microwave absorbing fabric. Preferably, the inclined web forming zone is relatively deep, and the suspension falls slowly and sequentially along the feed pipe or sidewall of the inclined web forming zone without causing large turbulence, resulting in clear layering of microwave absorbing fibers of different lengths.

[0049] Preferably, the drying process involves the fabric entering a heating tunnel via a conveyor belt, where it is uniformly heated by two rows of hot air vents. The hot roll forming process involves strengthening the bond between the three layers, as well as improving the stability, mechanical strength, tear resistance, and smoothness of the nonwoven absorbent fabric after drying.

[0050] The outermost layer P is the impedance matching layer, the middle layer A is the absorption layer, and the bottom layer F is the reflection layer; wherein, the center length of the absorbing fibers contained in the outermost layer P is L1, the center length of the absorbing fibers contained in the middle layer A is L2, and the center length of the absorbing fibers contained in the bottom layer F is L3; where L1 <L2<L3。

[0051] It should be noted that experiments have shown that the center lengths of the absorbing fibers in the surface layer P, the middle layer A, and the bottom layer F cannot decrease in descending order or be randomly distributed; otherwise, they cannot sequentially perform impedance matching, absorption, and reflection of the radiated waves, resulting in a weakening of their absorption performance.

[0052] The length of the microwave absorbing fibers in the surface layer P is normally distributed with a center length L1 within the range of 0.5-4 mm, and the content of the microwave absorbing material in the surface layer P is 0.4-6 g / m. 2 The thickness of the surface layer P is 1-5mm; the length of the absorbing fibers in the intermediate layer A is normally distributed with a center length L2 in the range of 5-15mm, and the content of the absorbing material in the intermediate layer A is 2-10g / m. 2 The surface layer thickness is 1-8mm; the length of the absorbing fibers in the bottom layer F is normally distributed with a center length L3 in the range of 18-38mm, and the content of the absorbing material in the bottom layer F is 3-10g / m. 2 The thickness of the bottom layer F is 0.5-2.5mm.

[0053] The thickness of each layer of the nonwoven fabric—the surface layer P, the middle layer A, and the bottom layer F—is controlled by the content of ordinary fibers. The main function of each layer is to create a structure with an increasing gradient distribution of absorbing fiber lengths along the layer thickness direction by controlling the length and content of the absorbing fibers. This achieves impedance matching of the nonwoven fabric surface, resonance loss in the middle layer, and interference effect of the entire sample in the thickness direction. The center lengths L1, L2, and L3 of each absorbing fiber layer follow the pattern L1... <L2<L3。

[0054] The following description, in conjunction with preferred embodiments of the present invention, provides further details.

[0055] Example 1

[0056] The method for preparing the nonwoven microwave absorbing fabric in this embodiment is as follows:

[0057] (1) Preparation of suspension: Carbon fibers with a diameter of 5μm and a length of 1mm, modified branched PP fibers with a diameter of 5d×5mm, water-soluble vinylon with a diameter of 6d×5mm and sodium dodecylbenzenesulfonate at 50℃ are placed in mixing tank I and stirred and dispersed evenly to form suspension I; carbon fibers with a diameter of 5μm and a length of 6mm, modified branched PP fibers with a diameter of 5d×8mm, water-soluble vinylon with a diameter of 6d×8mm and sodium dodecylbenzenesulfonate at 80℃ are placed in mixing tank II and stirred and dispersed evenly to form suspension II; carbon fibers with a diameter of 5μm and a length of 15mm, modified branched PP fibers with a diameter of 5d×12mm, water-soluble vinylon with a diameter of 6d×8mm and sodium dodecylbenzenesulfonate at 80℃ are placed in mixing tank III and stirred and dispersed evenly to form suspension III.

[0058] (2) Wet mesh formation: Suspension slurry III, suspension slurry II and suspension slurry I are sequentially introduced into the inclined mesh forming area, and the negative pressure filtration is used to lay the mesh.

[0059] (3) Reinforcement: The composite material obtained in (2) is fed into the heating tunnel via a conveyor belt and heated evenly by the upper and lower rows of hot air vents;

[0060] (4) Post-processing: After drying, it is formed by hot roller pressing.

[0061] The resulting nonwoven wave-absorbing fabric has a weight of 159 g / m². 2 Thickness 3.5mm. For example... Figure 2 The absorption performance test results shown indicate that, within the 2-18GHz range, peak values ​​occur at 4.5GHz and 14.5GHz, respectively, with absorption losses of -12dB and -14.6dB. The effective absorption bandwidth with a reflectivity less than -5dB is 14.5GHz, and the effective absorption bandwidth with a reflectivity less than -10dB is 4.8GHz.

[0062] Example 2

[0063] The method for preparing the nonwoven microwave absorbing fabric in this embodiment is as follows:

[0064] (1) Preparation of suspension: Stainless steel fibers with a diameter of 12μm and a length of 2mm (coated with a 2μm layer of PP polymer), 5d×5mm modified branched PP fibers, 6d×5mm 80℃ water-soluble vinylon and sodium dodecylbenzenesulfonate were placed in mixing tank I and stirred and dispersed evenly to form suspension I; Stainless steel fibers with a diameter of 12μm and a length of 8mm (coated with a 1μm layer of PP polymer), 5d×8mm modified branched PP fibers, 6d×8mm 80℃ water-soluble vinylon and sodium dodecylbenzenesulfonate were placed in mixing tank II and stirred and dispersed evenly to form suspension II; Stainless steel fibers with a diameter of 12μm and a length of 18mm (coated with a 1μm layer of PP polymer), 5d×12mm modified branched PP fibers, 6d×8mm 80℃ water-soluble vinylon and sodium dodecylbenzenesulfonate were placed in mixing tank III and stirred and dispersed evenly to form suspension III.

[0065] (2) Wet mesh formation: Suspension slurry III, suspension slurry II and suspension slurry I are sequentially introduced into the inclined mesh forming area, and the negative pressure filtration is used to lay the mesh.

[0066] (3) Reinforcement: The composite material obtained in (2) is fed into the heating tunnel via a conveyor belt and heated evenly by the upper and lower rows of hot air vents;

[0067] (4) Post-processing: After drying, it is formed by hot roller pressing.

[0068] The resulting nonwoven wave-absorbing fabric has a weight of 197 g / m². 2 Thickness 3.4mm. For example... Figure 3 The absorption performance test results shown indicate that, within the 2-18GHz range, peak values ​​occur at 5.5GHz and 14.9GHz, respectively, with absorption losses of -15.4dB and -10dB, respectively. The effective absorption bandwidth with a reflectivity less than -5dB is 13.9GHz, and the effective absorption bandwidth with a reflectivity less than -10dB is 2.1GHz.

[0069] Example 3

[0070] The method for preparing the nonwoven microwave absorbing fabric in this embodiment is as follows:

[0071] (1) Preparation of suspension: Glass-coated amorphous magnetic fibers with a diameter of 14μm and a length of 3mm (coated with a 3μm layer of PE polymer), 5d×5mm modified branched PET fibers, 6d×5mm water-soluble vinylon at 80℃ and PEO dispersant were placed in mixing tank I and stirred and dispersed evenly to form suspension I; Glass-coated amorphous magnetic fibers with a diameter of 14μm and a length of 10mm (coated with a 3μm layer of PE polymer), 5d×8mm modified branched PET fibers, 6d×8mm water-soluble vinylon at 80℃ and PEO dispersant were placed in mixing tank II and stirred and dispersed evenly to form suspension II; Glass-coated amorphous magnetic fibers with a diameter of 14μm and a length of 20mm (coated with a 3μm layer of PE polymer), 5d×12mm modified branched PET fibers, 6d×8mm water-soluble vinylon at 80℃ and PEO dispersant were placed in mixing tank III and stirred and dispersed evenly to form suspension III.

[0072] (2) Wet mesh formation: Suspension slurry III, suspension slurry II and suspension slurry I are sequentially introduced into the inclined mesh forming area, and the negative pressure filtration is used to lay the mesh.

[0073] (3) Reinforcement: The composite material obtained in (2) is fed into the heating tunnel via a conveyor belt and heated evenly by the upper and lower rows of hot air vents;

[0074] (4) Post-processing: After drying, it is formed by hot roller pressing.

[0075] The resulting nonwoven wave-absorbing fabric has a weight of 187 g / m². 2 Thickness 3.3mm. For example... Figure 4 The absorption performance test results shown indicate that, within the 2-18GHz range, peak values ​​occur at 3.4GHz, 8.5GHz, and 17.9GHz, respectively, with absorption losses of -10.4dB, -12.3dB, and -21dB, respectively. The effective absorption bandwidth with a reflectivity less than -5dB is 14.6GHz, and the effective absorption bandwidth with a reflectivity less than -10dB is 11GHz.

[0076] Example 4

[0077] The method for preparing the nonwoven microwave absorbing fabric in this embodiment is as follows:

[0078] (1) Preparation of suspension: Nickel-plated carbon fiber with a diameter of 9μm and a length of 4mm (coated with a layer of 1μm PET polymer), 5d×5mm modified branched PET fiber, 6d×5mm 80℃ water-soluble vinylon and PEO dispersant were placed in mixing tank I and stirred and dispersed evenly to form suspension I; Nickel-plated carbon fiber with a diameter of 9μm and a length of 12mm (coated with a layer of 1μm PET polymer), 5d×8mm modified branched PET fiber, 6d×8mm 80℃ water-soluble vinylon and PEO dispersant were placed in mixing tank II and stirred and dispersed evenly to form suspension II; Nickel-plated carbon fiber with a diameter of 9μm and a length of 22mm (coated with a layer of 1μm PET polymer), 5d×12mm modified branched PET fiber, 6d×8mm 80℃ water-soluble vinylon and PEO dispersant were placed in mixing tank III and stirred and dispersed evenly to form suspension III.

[0079] (2) Wet mesh formation: Suspension slurry III, suspension slurry II and suspension slurry I are sequentially introduced into the inclined mesh formation area, and the negative pressure filtration is used to lay the mesh.

[0080] (3) Reinforcement: The composite material obtained in (2) is fed into the heating tunnel via a conveyor belt and heated evenly by the upper and lower rows of hot air vents;

[0081] (4) Post-processing: After drying, it is formed by hot roller pressing.

[0082] The resulting nonwoven wave-absorbing fabric has a weight of 179 g / m². 2 Thickness 2.8mm. For example... Figure 5 The absorption performance test results shown indicate that, within the 2-18GHz range, peak values ​​occur at 4.7GHz and 14.9GHz, respectively, with absorption losses of -10dB and -9.5dB, and an effective absorption bandwidth of 14.2GHz with a reflectivity of less than -5dB.

[0083] Example 5

[0084] The method for preparing the nonwoven microwave absorbing fabric in this embodiment is as follows:

[0085] (1) Preparation of suspension: Modified silicon carbide fiber (coated with a 5μm layer of PET polymer), 5d×5mm modified branched PET fiber, 6d×5mm 80℃ water-soluble vinylon and PEO dispersant were placed in mixing tank I and stirred and dispersed evenly to form suspension I; Modified silicon carbide fiber (coated with a 5μm layer of PET polymer), 5d×8mm modified branched PET fiber, 6d×8mm 80℃ water-soluble vinylon and PEO dispersant were placed in mixing tank II and stirred and dispersed evenly to form suspension II; Modified silicon carbide fiber (coated with a 5μm layer of PE polymer), 5d×12mm modified branched PET fiber, 6d×8mm 80℃ water-soluble vinylon and PEO dispersant were placed in mixing tank III and stirred and dispersed evenly to form suspension III.

[0086] (2) Wet mesh formation: Suspension slurry III, suspension slurry II and suspension slurry I are sequentially introduced into the inclined mesh forming area, and the negative pressure filtration is used to lay the mesh.

[0087] (3) Reinforcement: The composite material obtained in (2) is fed into the heating tunnel via a conveyor belt and heated evenly by the upper and lower rows of hot air vents;

[0088] (4) Post-processing: After drying, it is formed by hot roller pressing.

[0089] The resulting nonwoven wave-absorbing fabric has a weight of 192 g / m². 2 Thickness 2.7mm. For example... Figure 6 The absorption performance test results shown indicate that, within the 2-18GHz range, peak values ​​occur at 5GHz and 13.8GHz, respectively, with absorption losses of -9.4dB and -13.5dB. Furthermore, the effective absorption bandwidth with a reflectivity less than -5dB is 14GHz, and the effective absorption bandwidth with a reflectivity less than -10dB is 4.5GHz.

[0090] Compared with the prior art, the nonwoven wave-absorbing fabric of the present invention has the following effects:

[0091] (1) The amount of absorbing fiber used is small, which solves the problem of the heavy weight of existing absorbing composite materials. It is lightweight (159g / m²). 2 -197g / m 2 With its advantages of being soft, breathable, and having broadband wave absorption, it can be used as a material for wearing anti-radiation equipment.

[0092] (2) The surface of the microwave absorbing fiber is treated with polymers, which improves the smoothness and cleanliness of the surface, improves its dispersibility and suspension in the solution, facilitates interweaving with other fibers and hot pressing composite molding, strengthens the uniformity and retention of the microwave absorbing fiber in the non-woven microwave absorbing fabric, and prevents its loss.

[0093] (3) The branching modification of ordinary fibers improves the interweaving strength between fibers;

[0094] (4) The wet web forming integrated molding technology realizes the synergistic integration of different microwave absorbing materials and different microwave absorbing mechanisms, solves the problems of high density, hardness and impermeability of existing multi-layer composite materials, simplifies the production process and is suitable for mass production.

[0095] (5) The microwave absorbing fiber / nonwoven fabric of the present invention combines load-bearing capacity and electromagnetic wave absorption function, realizing the integration of material functions. The matrix fiber has the advantages of low density and high strength, and has structural designability, while the microwave absorbing fiber has excellent microwave absorption performance, and the adjustable aspect ratio is also highly compatible with the molding of the matrix fiber fabric. At the same time, the integrated microwave absorbing fabric can adjust the overall electromagnetic parameters of the sample by simply adjusting the length, mass and other parameters of the microwave absorbing fiber, thereby adjusting the impedance matching and achieving ideal microwave absorption performance.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A nonwoven wave-absorbing fabric with a layered structure, characterized in that, It is formed into a single unit by wet web forming technology using a mixture of microwave absorbing fibers and ordinary fibers in a suspension. It consists of three layers: a surface layer, a middle layer, and a bottom layer. The surface layer is an impedance matching layer, the middle layer is an absorption layer, and the bottom layer is a reflection layer; wherein, the center length of the absorbing fibers in the surface layer is L1, the center length of the absorbing fibers in the middle layer is L2, and the center length of the absorbing fibers in the bottom layer is L3; wherein L1 <L2<L3; The length of the absorbing fibers in the surface layer is normally distributed with a center length L1 in the range of 0.5-4 mm; the length of the absorbing fibers in the middle layer is normally distributed with a center length L2 in the range of 5-15 mm; and the length of the absorbing fibers in the bottom layer is normally distributed with a center length L3 in the range of 18-38 mm.

2. The nonwoven wave-absorbing fabric according to claim 1, characterized in that, The content of microwave absorbing fibers in the surface layer is 0.4-6 g / m². 2 The surface layer thickness is 1-5mm; the content of microwave absorbing fibers in the intermediate layer is 2-10g / m². 2 The thickness of the intermediate layer is 1-8mm; the content of microwave absorbing fiber in the bottom layer is 3-10g / m². 2 The thickness of the bottom layer is 0.5-2.5mm.

3. The nonwoven wave-absorbing fabric according to claim 1, characterized in that, The surface layer, intermediate layer and bottom layer are formed by wet web forming technology, and then combined into one piece by hot roll forming.

4. An integrated molding method for a nonwoven wave-absorbing fabric with a layered structure, characterized in that, It includes: The first microwave-absorbing fiber is mixed and dispersed with ordinary fiber in a solvent to form a first suspension. The second microwave-absorbing fiber is mixed and dispersed with ordinary fiber in a solvent to form a second suspension. The third microwave-absorbing fiber is mixed and dispersed with ordinary fiber in a solvent to form a third suspension. The center length of the first absorbing fiber is L1, the center length of the second absorbing fiber is L2, and the center length of the third absorbing fiber is L3, where L1 <L2<L3; The length of the first absorbing fiber is normally distributed with L1 as the center, ranging from 0.5 to 4 mm; the length of the second absorbing fiber is normally distributed with L2 as the center, ranging from 5 to 15 mm; the length of the third absorbing fiber is normally distributed with L3 as the center, ranging from 18 to 38 mm. The third suspension is introduced into the inclined wire mesh forming area and filtered under negative pressure to obtain the first layer of mesh fabric. The second suspension is introduced into the inclined wire mesh forming area and filtered under negative pressure to form the second layer of mesh fabric. The first suspension is then introduced into the inclined wire mesh forming area and filtered under negative pressure to form the third layer of mesh fabric. The three layers of mesh fabric obtained in the inclined wire mesh forming area are dried and hot-rolled to obtain an integrally formed non-woven absorbing fabric. or The third, second, and first suspensions are sequentially and continuously introduced into the inclined mesh forming area in a undisturbed manner. After negative pressure filtration, a three-layer mesh is directly obtained. The mesh is then dried and hot-rolled to form an integral non-woven wave-absorbing fabric.

5. The integrated molding method according to claim 4, characterized in that, The first, second, and third absorbing fibers are one or more of the following: glass-coated amorphous magnetic fibers, stainless steel fibers, carbon fibers, modified carbon fibers, modified silicon carbide fibers, polycrystalline iron fibers, iron-nickel fibers, and iron-cobalt-nickel fibers.

6. The integrated molding method according to claim 4, characterized in that, The ordinary fibers include modified branched fibers and / or bonding fibers; the preparation methods of the suspension slurry are as follows: placing the corresponding microwave absorbing fibers, ordinary fibers, solvent and dispersant in a mixer, stirring, dispersing evenly to form a suspension slurry; the solvent is water; the dispersant is a surfactant.

7. The integrated molding method according to claim 6, characterized in that, The modified branched fiber is a fiber obtained by modifying and branching one or more of viscose fiber, polyester fiber, nylon fiber, cellulose fiber, polypropylene fiber and polyethylene fiber. The modified branching process includes: mechanical treatment, chemical or radiation-induced grafting to increase the interweaving strength between fibers, and the length of the modified branched fibers is 5-20 mm. The bonding fiber is one or a combination of several of the following: water-soluble vinylon fiber, polyacrylic acid fiber, ethylene-vinyl acetate copolymer fiber, PE / PP bicomponent fiber, and PE / PET bicomponent fiber, and the length of the bonding fiber is 5-20 mm.

8. The integrated molding method according to claim 4, characterized in that, The first, second, and third microwave absorbing fibers are microwave absorbing fibers with a polymer coating film on their surface; the polymer coating film is made of polypropylene, polyester, or nylon, and the film thickness is 1-5 μm.

9. A nonwoven wave-absorbing fabric with a layered structure, characterized in that, It is prepared by the integrated molding method described in any one of claims 4-8.

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