Wave-absorbing filler based on lamellar graphite and application of wave-absorbing filler in solvent-based coating

Abstract

The invention discloses a wave-absorbing filler based on lamellar graphite and application of the wave-absorbing filler in a solvent-based coating, and belongs to the technical field of coatings. The in-situ growth catalyst and ethyl alcohol are mixed, then phenolic resin and lamellar graphite are added, the mixture is cured and calcined into wave-absorbing filler, carbon nanowires with morphological characteristics are formed on the surface of the lamellar graphite, and the wave-absorbing filler is applied to preparation of solvent-based paint. The metal powder is used as a catalyst and a magnetic loss main substance to promote the growth of the carbon nanowires, and the surface conductivity of the lamellar graphite is adjusted by changing the incomplete graphitization of the phenolic resin, so that the behavior of the material on electromagnetic waves is changed from reflection to absorption, and the electromagnetic waves are converted into heat energy to be released.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings, and in particular relates to a wave-absorbing filler based on flake graphite and application thereof in solvent-based coatings. Background Art

[0002] In recent years, with the rapid development of electronic devices and wireless communication technologies, electromagnetic wave pollution has become increasingly serious, posing a potential threat to human health, equipment stability, and information security. To address this issue, research on electromagnetic wave absorbing materials has gradually become a hot topic in the engineering field. Absorbing materials absorb electromagnetic waves by converting their energy into heat. Currently, a wide variety of absorbing materials exist, including metals, conductive polymers, and carbon-based materials. However, traditional metal-based absorbing materials suffer from high density, poor corrosion resistance, and difficult processing, which limits their widespread adoption in practical applications.

[0003] Lamellar graphite, a carbon-based material with a unique structure and excellent electrical conductivity, has attracted considerable attention in the field of microwave absorbing materials in recent years. Due to its layered structure, lamellar graphite can effectively increase the path of electromagnetic waves within the material, thereby enhancing absorption. Lamellar graphite also offers advantages such as low density, high-temperature resistance, and strong chemical stability, giving it broad application potential in the design of lightweight and efficient microwave absorbing materials. However, the excessive electrical conductivity of lamellar graphite causes its electromagnetic wave behavior to shift to a shielding mode, reflecting electromagnetic waves rather than converting them into heat energy. This has no positive impact on the problem of electromagnetic pollution.

[0004] Adding flake graphite absorbing fillers to solvent-based coatings can impart excellent wave-absorbing properties, meeting the electromagnetic wave attenuation requirements of various applications. This new coating can not only be used as a surface coating for electronic devices, but also play an important role in aerospace, military equipment and other fields, providing a new solution for electromagnetic wave pollution control. Summary of the Invention

[0005] In view of the problem that the above-mentioned high conductivity of graphite leads to electromagnetic wave shielding, and electromagnetic wave reflection cannot solve the problem of electromagnetic wave pollution, the present invention provides an absorbing filler based on flake graphite and its application in solvent-based coatings. It uses in-situ growth of carbon nanowires to adjust the graphitization structure of the graphite surface and further change the interlayer spacing of the flake graphite to achieve the technical purpose of promoting electromagnetic wave absorption and increasing the coordinated positive development of electromagnetic wave consumption, achieving the system requirements of transforming and enhancing the absorbing performance, and finally becoming the main raw material of solvent-based coatings to play a practical and realistic role.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for preparing a wave-absorbing filler based on flake graphite comprises the following steps:

[0008] Step 1: Under normal pressure, at a temperature of 25-50° C. and a rotation speed of 300-500 r / min, 1-2 parts of the in-situ growth catalyst and 100-120 parts of ethanol are uniformly stirred and mixed in a magnetic water bath to form a solution.

[0009] Step 2: 80-95 parts of phenolic resin and 80-100 parts of flake graphite are added to the solution prepared in step 1 to form a resin mixed solution, and then cured in stages of 80-100°C / 1-1.5h and 160-180°C / 2-4h to form an integrated material.

[0010] Step 3: Use a tube furnace to heat the material to 1000-1100°C at a heating rate of 2-4°C / min, and carbonize the integrated material at high temperature for 3-4 hours to obtain a lamellar graphite material with in-situ grown carbon nanowires as an absorbing filler.

[0011] Furthermore, in step 1, the in-situ growth catalyst is one or more of Y2O3 nanopowder, Ni nanopowder, and Co nanopowder, which are prepared by ball milling.

[0012] Furthermore, the phenolic resin in step 2 has a phenolic content of less than 10% and is soluble in ethanol.

[0013] A wave-absorbing filler based on flaky graphite is prepared by the above-mentioned preparation method. The wave-absorbing filler has the morphological characteristics of carbon nanowires, and the carbon nanowires are on the surface of the flaky graphite.

[0014] A method for preparing a solvent-based coating using a wave-absorbing filler based on flake graphite comprises the following steps:

[0015] Step 1: Mix 30-50 parts of the graphite filler with 100-120 parts of phenolic resin, and perform coarse dispersion by mechanical dispersion at a rotation speed of 500-800 r / min.

[0016] Step 2: The mixed solution after coarse dispersion in step 1 is further ultrasonically dispersed using a cell crusher for 30-50 minutes to form a finely dispersed solution.

[0017] Step 3: Extruding the solution prepared in step 2 for 30-50 minutes by impact pressure at room temperature to form a dispersed solution of flake graphite with in-situ grown carbon nanowires, thereby preparing a flake graphite-based solvent-based coating with excellent dispersion.

[0018] Furthermore, the phenolic resin in step 1 is a single-component solvent-based resin, and its curing system is 80-100° C. / 1-1.5 h and 160-180° C. / 2-4 h.

[0019] Furthermore, the impact pressure in step three is in the range of 800-900 MPa.

[0020] Beneficial effects of the present invention:

[0021] 1. Using metal powder as a catalyst and the main substance of magnetic loss will promote the growth of carbon nanowires with metal as the top after the phenolic resin is pyrolyzed. By changing the incomplete graphitization of the phenolic resin and adjusting the conductivity of the lamellar graphite surface, the material's behavior towards electromagnetic waves changes from reflection to absorption, converting electromagnetic waves into heat energy and releasing them.

[0022] 2. The intrinsic conductive behavior between the carbon nanowires and the graphene sheets in the top growth mechanism forms interactive contact, which increases the conductive network structure and forms multiple heterogeneous interfaces to increase the reflection loss performance of electromagnetic waves, thereby enhancing the electromagnetic wave absorption performance.

[0023] 3. The carbon nanowires grown in situ on the top change the van der Waals force between the graphite sheets, causing the interlayer spacing of the graphite sheets to shift or expand, extending the reflection and propagation path of electromagnetic waves between the graphite sheets, and further enhancing the electromagnetic wave loss capacity.

[0024] Fourth, the present invention uses a multi-level dispersion method to visualize the free state of flake graphite in phenolic resin, forming a spatial arrangement of multi-oriented flake graphite, emphasizing the full distribution state of the coating's absorbing effect, and thereby enhancing the coating's electromagnetic wave absorption capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the electromagnetic wave reflection loss diagram of Example 1.

[0026] Figure 2 This is the electromagnetic wave reflection loss diagram of comparative example 1.

[0027] Figure 3 SEM morphology of in situ grown carbon nanowires. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the embodiments described are only a part of the embodiments of the present invention, rather than all of the embodiments. These embodiments should be understood to be merely illustrative of the present invention and not intended to limit the scope of protection of the present invention. After reading the contents described in the present invention, all other embodiments obtained after various modifications or alterations made to the present invention based on the technical solutions and embodiments of the present invention also fall within the scope of protection of the claims of the present invention.

[0029] Example 1:

[0030] A method for preparing a wave-absorbing filler based on flake graphite and a solvent-based coating thereof comprises the following steps:

[0031] Step 1: Under normal pressure, at 25° C. and 300 r / min, 1 part of Co nanopowder and 100 parts of ethanol were uniformly stirred and mixed to form a solution using a magnetic water bath stirrer, wherein the Co nanopowder was prepared by ball milling.

[0032] Step 2: 90 parts of barium phenolic resin and 80 parts of flake graphite are added to the solution prepared in step 1 to form a resin mixed solution, which is then cured at 80°C / 1h and 160°C / 2h to form an integrated material.

[0033] Step 3: Use a tube furnace to heat the material to 1000℃ at a heating rate of 4℃ / min, and then carbonize the integrated material at high temperature for 3 hours to form a lamellar graphite material with in-situ grown carbon nanowires, which is used as an absorbing filler. The morphology of the prepared absorbing filler is characterized, and the SEM morphology of the in-situ generated carbon nanowires is shown in Figure 2. Figure 3 As can be seen from the figure, the carbon nanowires grown by metal in situ catalysts have a structural characteristic of a large aspect ratio. The wire structures with various orientations can easily form a conductive network structure and support the interlayer graphite sheets, and can easily form a stable in situ grown graphite sheet structure with wave absorbing effect.

[0034] Step 4: Mix 30 parts of lamellar graphite with in-situ grown carbon nanowires with 100 parts of phenolic resin and coarsely disperse them using a mechanical disperser at a speed of 500 r / min; wherein the phenolic resin is a single-component solvent-based barium phenolic resin, and its curing system is 80°C / 1.5h and 170°C / 2h.

[0035] Step 5: Further use a cell crusher to ultrasonically disperse the coarsely dispersed mixed solution in step 4 for 30 minutes to form a finely dispersed solution.

[0036] Step 6: At room temperature, the solution prepared in step 5 is extruded for 30 minutes at an impact pressure of 800 MPa to form a monodisperse solution of flake graphite with in-situ grown carbon nanowires, thereby preparing a flake graphite-based solvent-based radar absorbing coating with excellent dispersion.

[0037] Example 2:

[0038] A method for preparing a wave-absorbing filler based on flake graphite and a solvent-based coating thereof comprises the following steps:

[0039] Step 1: 1.5 parts of Ni nanopowder and 110 parts of ethanol were uniformly stirred and mixed with a magnetic water bath stirrer at 40° C. and 500 r / min under normal pressure to form a solution, wherein the Ni nanopowder was prepared by ball milling.

[0040] Step 2: 95 parts of boron-modified phenolic resin and 90 parts of flake graphite are added to the above solution to form a resin mixed solution, and then cured in stages at 100°C / 1.5h and 170°C / 3h to form an integrated material.

[0041] Step 3: Use a tube furnace to heat the material to 1100°C at a heating rate of 2°C / min, and carbonize the integrated material at high temperature for 4 hours to form a lamellar graphite material with in-situ grown carbon nanowires, which serves as an absorbing filler.

[0042] Step 4: Mix 50 parts of lamellar graphite with in-situ grown carbon nanowires with 110 parts of phenolic resin and coarsely disperse them using a mechanical disperser at a speed of 800 r / min; wherein the phenolic resin is a single-component solvent-based boron-modified phenolic resin, and its curing system is 100°C / 1h and 180°C / 3h.

[0043] Step 5: The mixed solution was further ultrasonically dispersed for 50 minutes using a cell crusher to form a finely dispersed solution.

[0044] Step 6: At room temperature, the solution prepared in step 5 is extruded for 50 minutes at an impact pressure of 900 MPa to form a monodisperse flake graphite with in-situ grown carbon nanowires, thereby preparing a flake graphite-based solvent-based radar absorbing coating with excellent dispersion.

[0045] Example 3:

[0046] A method for preparing a wave-absorbing filler based on flake graphite and a solvent-based coating thereof comprises the following steps:

[0047] Step 1: Under normal pressure, 50° C. and 450 rpm, 2 parts of Y2O3 nanopowder and 120 parts of ethanol were uniformly stirred and mixed into a solution using a magnetic water bath stirrer, wherein the Y2O3 nanopowder was prepared by ball milling.

[0048] Step 2: 80 parts of phenol-formaldehyde-free resin and 100 parts of flake graphite are added to the solution prepared in step 1 to form a resin mixed solution, which is then cured at 90°C / 1.2h and 180°C / 4h to form an integrated material.

[0049] Step 3: Use a tubular furnace to heat the material to 1080°C at a heating rate of 3°C / min, and carbonize the integrated material at high temperature for 3.5 hours to form a lamellar graphite material with in-situ grown carbon nanowires.

[0050] Step 4: Mix 40 parts of lamellar graphite with in-situ grown carbon nanowires with 120 parts of phenolic resin, and coarsely disperse them using a mechanical disperser at a speed of 600 r / min. The phenolic resin is a single-component solvent-based ammonia-free phenolic resin, and its curing system is 90°C / 1.2h and 160°C / 4h.

[0051] Step 5: The mixed solution was further ultrasonically dispersed for 40 minutes using a cell crusher to form a finely dispersed solution.

[0052] Step 6: The solution prepared in step 5 is extruded at room temperature for 40 minutes at an impact pressure of 950 MPa to form a monodisperse flake graphite with in-situ grown carbon nanowires, thereby preparing a flake graphite-based solvent-based radar absorbing coating with excellent dispersion.

[0053] Comparative Example 1: (without catalyst)

[0054] This comparative example is basically the same as Example 1, except that step 1 is not performed in this comparative example, that is, no in-situ growth catalyst is added during the preparation of the absorbing filler.

[0055] Comparative Example 2: (Difference in dispersion method)

[0056] This comparative example is basically the same as Example 1, except that step 5 and step 6 are not performed, that is, only mechanical dispersion is performed when preparing the coating, and ultrasonic dispersion and extrusion treatment are not performed.

[0057] Comparative Example 3: (Low Temperature)

[0058] This comparative example is basically the same as Example 1, except that the carbonization treatment temperature in step 3 is 500°C.

[0059] test:

[0060] 1) The electromagnetic wave absorption performance of the coatings prepared in Example 1 and Comparative Example 1 was tested in a test frequency band of 2 to 18 GHz. When the reflection loss was less than -10 dB, it indicated that the material had the effect of reflecting and consuming electromagnetic waves.

[0061] Figure 1 is the electromagnetic wave reflection loss diagram of Example 1, Figure 2 This is a graph of electromagnetic wave reflection loss for Comparative Example 1. It is clearly evident that Example 1 achieves a maximum reflection loss of -20 dB and a channel width of 15 GHz, due to the heterogeneous structure created by the in-situ growth of carbon nanowires on top of the graphite sheet surface, as well as the inherent conduction losses from the conductivity itself. This is a significant difference compared to the low reflection loss of Comparative Example 1. The coating utilizes pure carbon-based materials as the aggregate to achieve its absorbing properties, resulting in its inherent lightweight properties.

[0062] 2) Viscosity testing of the coatings prepared in Examples 1-3 and Comparative Example 2: 50 ml of the coating was tested using a DV-T2 viscosity and temperature control instrument at a speed of 60.0 rpm. The test results are shown in Table 1:

[0063] Table 1 Comparison of coating viscosity between Example 1 and Comparative Example 2

[0064]

[0065] Table 1 shows that the viscosity of the absorbing coatings prepared using the multi-stage dispersion method in Examples 1, 2, and 3 is approximately 40 Cp, which is greater than the 20.8 Cp viscosity of the absorbing coating prepared using the conventional mechanical dispersion method in Comparative Example 2. This is because the multi-stage dispersion method increases the contact area between the flake graphite filler and the phenolic resin, achieving full coverage of the filler within the resin system. In contrast, the dispersion effect in Comparative Example 2 is poor, resulting in filler sedimentation within the resin system, causing the system viscosity to approach that of the resin itself, resulting in the coating being unable to fully absorb electromagnetic waves.

[0066] 3) The electrical conductivity of the coatings prepared in Examples 1-3 and Comparative Example 3 was tested using an RTS-8 four-probe resistance meter. The test results are shown in Table 2:

[0067] Table 2 Comparison of conductivity between Example 2 and Comparative Example 3

[0068]

[0069] Table 2 shows that the conductivity of the coatings in Examples 1, 2, and 3 is approximately 0.4 S / cm, while the conductivity of Comparative Example 3 is approximately 0.1 S / cm, one-quarter the conductivity of the examples. This is due to the high degree of graphitization and low resistance of the graphite and carbon nanowires after high-temperature calcination, which facilitates the formation of a conductive network structure. The low-conductivity coating reduces conductive losses, the primary electromagnetic wave consumption mechanism of carbon-based absorbing coatings. This, in turn, demonstrates a decrease in electromagnetic wave conductive losses and a decrease in absorbing performance.

Claims

1. A method for preparing a wave-absorbing filler based on flake graphite, characterized in that: include: The in-situ growth catalyst ethanol is uniformly stirred and mixed, and then phenolic resin and flake graphite are added to form a resin mixed solution, which is solidified into an integrated material and then carbonized at high temperature to obtain a flake graphite material with in-situ grown carbon nanowires.

2. The method for preparing a wave-absorbing filler based on flake graphite according to claim 1, characterized in that: The specific steps include: Step 1: uniformly stirring and mixing 1-2 parts of in-situ growth catalyst with 100-120 parts of ethanol at 25-50°C and 300-500 r / min under normal pressure to form a solution; Step 2: 80-95 parts of phenolic resin and 80-100 parts of flake graphite are added to the solution prepared in step 1 to form a resin mixed solution, and then cured at 80-100°C / 1-1.5h and 160-180°C / 2-4h to form an integrated material; Step 3: Use a tube furnace to heat the material to 1000-1100°C at a heating rate of 2-4°C / min, and carbonize the integrated material at high temperature for 3-4 hours to obtain a lamellar graphite material with in-situ grown carbon nanowires as an absorbing filler.

3. The method for preparing a wave-absorbing filler based on flake graphite according to claim 1 or 2, characterized in that: In the step 1, the in-situ growth catalyst is one or more of Y2O3 nanopowder, Ni nanopowder, and Co nanopowder.

4. The method for preparing a wave-absorbing filler based on flake graphite according to claim 3, characterized in that: The in-situ growth catalyst is prepared by ball milling.

5. The method for preparing a wave-absorbing filler based on flake graphite according to claim 2, characterized in that: The phenolic resin in step 2 has a phenolic content of less than 10% and is soluble in ethanol.

6. A wave-absorbing filler based on flake graphite, prepared by the preparation method according to any one of claims 1 to 5, having the morphological characteristics of carbon nanowires, wherein the carbon nanowires are on the surface of the flake graphite.

7. Use of the flaky graphite-based absorbing filler according to claim 6 in the preparation of solvent-based coatings.

8. The use of a wave-absorbing filler based on flake graphite in the preparation of a solvent-based coating according to claim 7, characterized in that: The preparation method of the solvent-based coating comprises the following steps: Step 1: Mix 30-50 parts of the graphite filler with 100-120 parts of phenolic resin, and coarsely disperse them by mechanical dispersion at a speed of 500-800 r / min; Step 2: ultrasonically disperse the coarsely dispersed mixed solution in step 1 for 30-50 minutes to form a finely dispersed solution; Step 3: Extruding the solution prepared in step 2 for 30-50 minutes by impact pressure at room temperature to form a flake graphite-based solvent-based coating.

9. The use of a wave-absorbing filler based on flake graphite in the preparation of a solvent-based coating according to claim 8, characterized in that: The phenolic resin in step 1 is a single-component solvent-based resin, and its curing system is 80-100° C. / 1-1.5 h and 160-180° C. / 2-4 h.

10. The use of a wave-absorbing filler based on flake graphite in the preparation of a solvent-based coating according to claim 8, characterized in that: The impact pressure in step three is in the range of 800-900 MPa.

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