Resistive film, wave-absorbing material prepared by warm forming and preparation method thereof

Abstract

The present application relates to a kind of resistance film, warm forming preparation wave-absorbing material and preparation method in it, the resistance film is sequentially arranged substrate layer, conductive coating and isolation coating from bottom to top;Wherein substrate layer, conductive coating and isolation coating all contain resin material, and the thickness of isolation coating is 50 μm~200 μm, the thickness of substrate layer is 20 μm~150 μm.The resistance film when warm forming preparation wave-absorbing material, isolation coating can prevent adhesive liquid from swelling and penetrating into the conductive coating of resistance film, leading to the change of square resistance, so that the resistance film can be matched with structural adhesive film for 85 ℃~150 ℃ warm forming preparation wave-absorbing material, ensure the high quality stability and high production efficiency of batch production wave-absorbing material, significantly broaden the application range of resistance film.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic functional materials technology, specifically relating to a resistive film, a microwave absorbing material prepared by mid-temperature molding, and a preparation method thereof. Background Technology

[0002] With the rapid development of detection and identification technologies in the military field, modern warfare has entered a new form of warfare based on rapid reconnaissance and precision strikes. Military targets are increasingly threatened by reconnaissance and strikes, and the development of stealth technology and radar-absorbing materials faces greater challenges. Traditional radar-absorbing materials such as carbon-based and iron-based materials are no longer able to meet the application requirements of broadband radar absorption and strong radar absorption (anti-electromagnetic interference) in a limited thickness. There is an urgent need to develop new radar-absorbing materials.

[0003] The emergence of metamaterials has offered solutions to the aforementioned problems to some extent. Resistive frequency-selective surfaces, or resistive films, are important metamaterials. They typically consist of absorbing arrays composed of periodic absorbing units. These units are designed with subwavelength microstructures to effectively adjust their equivalent permittivity and equivalent permeability, thereby matching their wave impedance with free-space impedance and achieving perfect absorption. Compared to traditional absorbing materials, resistive film absorbing materials have advantages such as strong absorption and high designability, enabling flexible control of electromagnetic waves and possessing significant application value in the field of electromagnetic wave absorption.

[0004] Resistive film absorbing materials are typically formed by alternating layers of resistive film and dielectric material, bonded together with adhesive, and then cured under pressure. The dielectric material is often made of foam, honeycomb, or similar materials. However, during the pressure-heat curing process, the adhesive in existing resistive film preparations swells and penetrates into the polymer network of the conductive coating of the resistive film, "diluting" the conductive coating. This causes a significant change in the sheet resistance of the resistive film, leading to a significant alteration or even failure of the absorbing material's absorption performance. To ensure that the sheet resistance of the resistive film does not change during the molding process, the molding temperature must be controlled to a maximum of 60℃, ideally between 20℃ and 45℃. Therefore, applying adhesive to the resistive film and dielectric material surfaces can only be done by liquid coating. The adhesive needs to be prepared in small batches and used immediately, resulting in low uniformity and production efficiency. This leads to poor quality stability of the absorbing material, limiting the application range of resistive films. Summary of the Invention

[0005] This invention provides a resistive film, a medium-temperature molding microwave absorbing material prepared therefrom, and a preparation method thereof. When the resistive film material is heated and pressurized, the isolation coating can prevent the adhesive liquid from penetrating into the resistive film coating through swelling, thus preventing changes in sheet resistance. This allows the resistive film to be used for medium-temperature molding at 85℃ to 150℃ to prepare microwave absorbing materials.

[0006] The technical solution of the present invention is a resistive film, wherein a substrate layer, a conductive coating layer and an isolation coating layer are sequentially disposed from bottom to top; wherein the substrate layer, the conductive coating layer and the isolation coating layer all contain resin material, and the thickness of the isolation coating layer is 50μm to 200μm.

[0007] Furthermore, the resin material is one of polyimide resin, polybutylene terephthalate resin, bismaleimide resin, polyetheretherketone resin, polyarylene sulfide resin, and epoxy resin.

[0008] Furthermore, the resin materials in the substrate layer, conductive coating, and insulating coating are the same.

[0009] Furthermore, the thickness of the substrate layer is 20μm to 150μm.

[0010] The present invention also relates to a method for preparing the resistive film, comprising the following steps:

[0011] Step 1: Use screen printing equipment to print the conductive coating paste onto the substrate layer. After the conductive paste cures, a resistive film intermediate is formed.

[0012] Step 2: Use screen printing equipment to print the slurry of the isolation coating onto the surface of the conductive coating of the resistive film. After the isolation slurry cures, the resistive film is obtained.

[0013] The present invention also relates to a microwave absorbing material prepared by medium-temperature molding of the resistive film, wherein the microwave absorbing material prepared by medium-temperature molding includes a dielectric layer and a resistive film alternately stacked from bottom to top; the dielectric layer and the resistive film are alternately stacked at least once; and the layers are bonded and fixed together by structural adhesive film.

[0014] Furthermore, the medium layer is one of PMI foam or aramid paper honeycomb core.

[0015] Furthermore, the structural adhesive film is a pre-fabricated, medium-temperature curing epoxy structural adhesive film with a curing temperature of 85℃ to 150℃. The epoxy structural adhesive film is a commercially available, mature, and inexpensive medium-temperature curing adhesive film product with a curing temperature above 85℃. The curing agent in the epoxy resin structural adhesive film is a latent curing agent. When the curing temperature of the adhesive film is below 85℃, the product shelf life is significantly reduced, the price is high, and the economic benefits are low, thus preventing large-scale industrial production. On the other hand, room-temperature curing epoxy resin has insufficient curing degree due to its low curing temperature, resulting in inferior adhesion performance compared to medium-temperature curing epoxy resin. Therefore, it is necessary to provide a resistive film that can be used for medium-temperature curing molding. This resistive film can be used in conjunction with the epoxy structural adhesive film for medium-temperature molding at 85℃ to 150℃ to prepare microwave absorbing materials, ensuring high-quality stability and high production efficiency in the mass production of microwave absorbing materials, and significantly broadening the application range of the resistive film.

[0016] This invention also relates to a method for preparing the microwave absorbing material by the aforementioned medium-temperature molding, the specific steps of which are as follows:

[0017] S1. A dielectric layer, a structural adhesive film, and a resistive film are sequentially laid on the mold from bottom to top to form a blank;

[0018] S2. The blank is subjected to medium-temperature molding, with the temperature controlled at 85℃~150℃, to obtain the microwave absorbing material prepared by medium-temperature molding.

[0019] Furthermore, the curing time at medium temperature is 2–8 hours.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention adds a resin isolation coating to the surface of a conventional resistive film. During the heating and pressurization process of preparing the absorbing material, this resin isolation coating prevents the adhesive from seeping into the resistive film coating through swelling, thus preventing changes in sheet resistance. This allows the resistive film to be molded at medium temperatures (85℃~150℃) to prepare the absorbing material. Epoxy resin film can be used as the adhesive between the resistive film and the dielectric material. Since the thickness of epoxy film can be customized, it is easy to control the precision within ±0.05mm. By directly laying the pre-made adhesive film between the resistive film and the dielectric material layers, the uniformity, quality stability, and production efficiency of the interlayer adhesive layer in the absorbing material prepared by medium-temperature pressurization are significantly improved compared to existing technologies, thereby significantly broadening the application range of the resistive film. This invention also relates to a method for preparing the aforementioned resistive film for medium-temperature molding of absorbing materials, which has the advantages of simple process, convenient operation, and suitability for large-scale production. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the resistive film prepared in Embodiment 1 of the present invention; in the figure, 1 is the isolation coating, 2 is the conductive coating, and 3 is the substrate layer.

[0023] Figure 2 The reflectivity curves of absorbing material A in Example 1 and absorbing materials A2 and A3 in Comparative Examples 1 are shown.

[0024] Figure 3 The reflectivity curves are for absorbing material B in Example 2 and absorbing materials B2 and B3 in Comparative Examples 2. Detailed Implementation

[0025] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0026] Example 1

[0027] I. Preparation of resistive films for medium-temperature molding of microwave absorbing materials:

[0028] A resistive film was formed by screen printing a conductive paste based on polybutylene terephthalate (PET) resin onto a 50 μm thick PET film substrate. Then, a PET isolation resin paste was screen printed onto the conductive coating surface of the resistive film to form a 50 μm thick resin isolation coating, thus obtaining a resistive film for medium-temperature molding of microwave absorbing materials. Using this method, by adjusting only the conductive filler content, resistive films of type BD-Fh01-220 (220 Ω sheet resistance) and type BD-Fh01-410 (410 Ω sheet resistance) for medium-temperature molding of microwave absorbing materials were produced by Wuhan Magnetoelectric Co., Ltd. (hereinafter referred to as Wuhan Magnetoelectric).

[0029] II. Preparation of microwave absorbing materials using BD-Fh01-220 and BD-Fh01-410 type resistive films:

[0030] A microwave absorbing material A was prepared by sequentially laying a 2mm thick PMI foam, a 0.2mm thick epoxy film (J-351B type) from the Heilongjiang Petrochemical Research Institute, a BD-Fh01-220 type resistive film, a 2mm thick PMI foam, a BD-Fh01-410 type resistive film, and pressing them at 85℃ for 8 hours.

[0031] Example 2

[0032] I. Preparation of resistive films for medium-temperature molding of microwave absorbing materials:

[0033] A resistive film was formed by screen printing a conductive paste based on imide resin onto a 150 μm thick imide resin film substrate. Then, an imide isolating resin paste was screen printed onto the conductive coating surface of the resistive film to form a 200 μm thick resin isolating coating, thus producing a resistive film for medium-temperature molding of microwave absorbing materials. Using this method, by adjusting only the conductive filler content, resistive films of type BD-Fh03-65 (65 Ω sheet resistance) and type BD-Fh03-93 (93 Ω sheet resistance) for medium-temperature molding of microwave absorbing materials were produced.

[0034] II. Preparation of microwave absorbing materials using BD-Fh03-65 and BD-Fh03-93 type resistive films:

[0035] A 2mm thick aramid honeycomb core, a 0.3mm thick epoxy film (HY-BQ-JM-0300 type) from Hubei Hangyu New Material Co., Ltd., a BD-Fh03-65 type resistive film, a HY-BQ-JM-0300 type epoxy film, a 2.1mm thick aramid honeycomb core, a HY-BQ-JM-0300 type epoxy film, and a BD-Fh03-93 type resistive film were sequentially laid on a flat mold from bottom to top. The mold was then pressed at 150℃ for 2 hours to obtain microwave absorbing material B.

[0036] Comparative Example 1

[0037] I. Preparation of resistive film:

[0038] A resistive film was formed by screen printing a conductive paste based on polybutylene terephthalate resin onto a 50μm thick polybutylene terephthalate film substrate. Using this method, resistive films with a sheet resistance of 220Ω (type BD-Fi01-220) and 410Ω (type BD-Fi01-410) were prepared by adjusting only the conductive filler content.

[0039] Note: The only difference between the BD-Fi01-220 type resistive film and the BD-Fh01-220 type resistive film is that the BD-Fi01-220 type resistive film does not have an isolation coating printed on it; the only difference between the BD-Fi01-410 type and the BD-Fh01-410 type resistive film is that the BD-Fi01-410 type resistive film does not have an isolation coating printed on it.

[0040] II. Preparation of microwave absorbing materials using BD-Fi01-220 and BD-Fi01-410 type resistive films:

[0041] PMI foam with a thickness of 2mm, BD-Fi01-220 type resistive film, PMI foam with a thickness of 2mm and BD-Fi01-410 type resistive film are laid sequentially from bottom to top on a flat mold. Epoxy adhesive with a thickness of 0.2mm that cures at room temperature is applied between the layers. The mold is then pressed at 40℃ for 8 hours to obtain microwave absorbing material A2.

[0042] A microwave absorbing material A3 was prepared by sequentially laying a 2mm thick PMI foam, a 0.2mm thick epoxy film (J-351B type) from the Heilongjiang Petrochemical Research Institute, a BD-Fi01-220 type resistive film, another 2mm thick PMI foam, a J-351B type epoxy film, and a BD-Fi01-410 type resistive film on a flat mold from bottom to top, and molding at 85℃ for 8 hours.

[0043] Comparative Example 2

[0044] I. Preparation of resistive film:

[0045] A resistive film was formed by printing a conductive paste based on imide resin onto an imide resin film substrate with a thickness of 150 μm using screen printing equipment. Using this method, resistive films with a sheet resistance of 65Ω (type BD-Fi03-65) and 93Ω (type BD-Fi03-93) were prepared by adjusting only the content of conductive filler.

[0046] Note: The only difference between the BD-Fi03-65 type resistive film and the BD-Fh03-65 type resistive film is that the BD-Fi03-65 type resistive film does not have an isolation coating printed on it; the only difference between the BD-Fi03-93 type and the BD-Fh03-93 type resistive film is that the BD-Fi03-93 type resistive film does not have an isolation coating printed on it.

[0047] II. Preparation of microwave absorbing materials using BD-Fi03-65 and BD-Fi03-93 type resistive films:

[0048] A 2mm thick aramid honeycomb core, a BD-Fi03-65 type resistive film, a 2.1mm thick aramid honeycomb core, and a BD-Fi03-93 type resistive film are sequentially laid on a flat mold from bottom to top. An epoxy adhesive (0.2mm thick) that cures at room temperature is scraped between the layers. The mold is then pressed at 40℃ for 8 hours to obtain microwave absorbing material B2.

[0049] A 2mm thick aramid honeycomb core, a 0.3mm thick epoxy film (HY-BQ-JM-0300 type) from Hubei Hangyu New Material Co., Ltd., a BD-Fi03-65 type resistive film, a HY-BQ-JM-0300 type epoxy film, a 2.1mm thick aramid honeycomb core, a HY-BQ-JM-0300 type epoxy film, and a BD-Fi03-93 type resistive film were sequentially laid on a flat mold from bottom to top. The mold was then pressed at 150℃ for 2 hours to obtain microwave absorbing material B3.

[0050] The reflectivity curves of the absorbing materials obtained in the above embodiments and comparative examples are shown in the figure. Figure 2 and Figure 3 In the comparative examples, the reflectance of absorbing materials A3 and B3, prepared using resistive films, foams, and adhesive films without resin isolation coatings, was around -2dB. Compared with absorbing materials A and B in the examples, the absorption performance of absorbing materials A3 and B3 was significantly worse, almost losing their absorption performance. Although the reflectance curves of absorbing materials A2 and B2, prepared using resistive films and foams without resin isolation coatings and with room-temperature curing adhesive applied between the layers, showed a high degree of overlap with the reflectance curves of absorbing materials A and B in the examples, and their absorption performance was comparable, the uniformity of the adhesive applied between the layers heavily relied on manual experience, resulting in low stability and repeatability of absorption performance and low production efficiency.

[0051] In addition, the tensile strength of the above-mentioned microwave absorbing material was tested according to GB / T1452-2005 "Test Method for Tensile Strength of Sandwich Structures", and the results are shown in the table below.

[0052] Table 1 Tensile Strength of Microwave Absorbing Materials

[0053] 1 Wave-absorbing material A 0.86 2 Wave-absorbing material A2 0.58 3 A3 absorbing material 0.89 4 Wave-absorbing material B 0.91 5 Wave-absorbing material B2 0.63 6 Wave-absorbing material B3 0.96

[0054] As shown in the table above, the interlayer bonding strength (tensile strength) of the medium-temperature cured epoxy structural adhesive film used for bonding is significantly higher than that of the room-temperature cured epoxy resin used for bonding the interlayer of the microwave absorbing materials A, A3, B, and B3.

[0055] The resistive film prepared by the above embodiments for medium-temperature molding of microwave absorbing materials can be bonded and molded using a pre-made high-thickness and high-precision epoxy structural film to prepare microwave absorbing materials. The prepared microwave absorbing materials have stable performance, good repeatability, and high interlayer bonding strength.

[0056] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A microwave absorbing material prepared by medium-temperature molding, characterized in that: The microwave absorbing material includes dielectric layers and resistive films that are alternately stacked from bottom to top. The dielectric layers and resistive films are alternated at least once, and the layers are bonded and fixed together by structural adhesive film. The resistive film consists of a substrate layer, a conductive coating, and an isolation coating arranged sequentially from bottom to top. All three layers contain resin material, and the resin material used in all three layers is the same. The thickness of the isolation coating is 50μm to 200μm. The structural adhesive film is a pre-made, medium-temperature curing epoxy structural adhesive film with a curing temperature of 85℃ to 150℃ and a curing time of 2 to 8 hours. By adding a resin material isolation coating, the resin isolation coating can prevent the adhesive liquid from penetrating into the resistive film coating through swelling during the preparation of the microwave absorbing material under heat and pressure, thus preventing changes in sheet resistance and enabling the resistive film to be formed at medium temperature of 85℃~150℃.

2. The microwave absorbing material prepared by medium-temperature molding according to claim 1, characterized in that: The resin material is one of the following: polyimide resin, polybutylene terephthalate resin, bismaleimide resin, polyetheretherketone resin, polyarylene sulfide resin, and epoxy resin.

3. The microwave absorbing material prepared by medium-temperature molding according to claim 1, characterized in that: The thickness of the substrate layer is 20μm~150μm.

4. The microwave absorbing material prepared by intermediate-temperature molding according to any one of claims 1 to 3, characterized in that: The medium layer is one of PMI foam or aramid paper honeycomb core.

5. The method for preparing the resistive film in the microwave absorbing material prepared by intermediate-temperature molding according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1: Use screen printing equipment to print the conductive coating paste onto the substrate layer. After the conductive paste cures, a resistive film intermediate is formed. Step 2: Use screen printing equipment to print the slurry of the isolation coating onto the surface of the conductive coating of the resistive film. After the isolation slurry cures, the resistive film is obtained.

6. A method for preparing the microwave absorbing material prepared by intermediate-temperature molding according to any one of claims 1 to 3, characterized in that, The specific steps are as follows: S1. A dielectric layer, a structural adhesive film, and a resistive film are sequentially laid on the mold from bottom to top to form a blank; S2. The blank is subjected to medium-temperature molding, with the temperature controlled at 85℃~150℃ and the medium-temperature curing time at 2~8h, thus obtaining the microwave absorbing material prepared by medium-temperature molding.

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