A method for preparing a directional enhanced wave-absorbing coating based on ink direct writing

Abstract

This invention discloses a method for preparing a directional enhanced microwave absorbing coating based on ink direct writing, comprising the following steps: 1) preparing a surface-treated sheet-like absorber; 2) uniformly mixing the prepared sheet-like absorber with epoxy resin monomer to obtain a mixture slurry; 3) coating with an epoxy resin hardener, and then uniformly printing the prepared mixture slurry onto the surface of the part along a set path using an ink direct writing device; 4) before curing, the rollers behind the printhead automatically apply a fixed pressure above the slurry, pressing the cylindrical slurry into a flat shape, with the internal sheet-like additives oriented parallel to the plane of the part; 5) after printing, cleaning the uncured mixture slurry to obtain the directional enhanced microwave absorbing coating. The directional enhanced microwave absorbing coating prepared by this invention has stronger microwave absorption performance than conventional spray-applied microwave absorbing coatings, and the imaginary part of the complex permeability is higher in the directional enhanced microwave absorbing coating than in the non-directional microwave absorbing coating throughout the entire measurement frequency range.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically to a method for preparing a directional enhanced microwave absorbing coating based on ink direct writing. Background Technology

[0002] Microwave absorbing materials are important functional materials that dissipate energy through electromagnetic losses, converting it into heat or other forms of energy. Coated microwave absorbing materials, as a type of microwave absorbing material, are characterized by simple construction, convenient use, easy maintenance, and good absorption performance, making them an important research direction in the field of radar absorption. Magnetic loss-type microwave absorbing materials are the earliest and most widely used type of microwave absorbing material, possessing high permeability, high resistivity, and good impedance matching performance. They mainly dissipate electromagnetic waves through magnetic polarization mechanisms such as hysteresis loss, peripheral resonance, and aftereffect loss, such as ferrites and carbonyl iron. Research has found that the sheet-like structure of the magnetic absorber and the directional distribution of the sheet-like absorber in the coating often have a significant impact on the absorption performance: with the increase of the inherent anisotropy of ferromagnetic materials, microwave absorbing materials prepared with sheet-like absorbers may have better high-frequency application characteristics.

[0003] However, existing methods are complex, often requiring external equipment, and are not applicable to all materials. Furthermore, these methods can only achieve layered distribution of sheet-like absorbents, failing to meet the requirement of oriented distribution along specific paths, and are somewhat inadequate for preparing metamaterials with special path distributions. Therefore, designing a method for preparing coatings with controllable path-oriented alignment applicable to various sheet-like absorbents is particularly important. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a directional enhanced microwave absorbing coating based on direct ink writing, applicable to a variety of sheet-like absorbers with controllable path orientation.

[0005] This invention is achieved through the following technical solution: a method for preparing a directional enhanced microwave absorbing coating based on direct ink writing, comprising the following steps:

[0006] (1) The surface of the sheet absorbent is treated with an acidic solution and then chemically coated by phosphating to obtain a surface-treated sheet absorbent.

[0007] (2) The prepared flake absorbent is uniformly mixed with epoxy resin monomer to obtain a mixture paste that can be used for direct ink writing printing;

[0008] (3) Apply epoxy resin hardener evenly to the surface of the part, and use ink direct writing equipment to print the prepared mixture slurry evenly on the surface of the part according to the set path.

[0009] (4) Before it has solidified, the roller behind the print head automatically applies a fixed pressure above the slurry. The lower surface of the roller is lower than the height of the print head, which presses the cylindrical slurry into a flat shape. The orientation of the internal sheet-like additives will also be parallel to the plane of the part due to the shear force.

[0010] (5) After printing, the uncured mixture slurry is cured and cleaned to obtain the directional reinforced microwave absorbing coating.

[0011] Inspired by additive manufacturing processes and incorporating the characteristics of roll forming, this technical solution proposes a method based on direct ink writing. The coating is printed onto the part surface along a predetermined path. Subsequently, a roll forming device is installed behind the printhead to apply pressure to the uncured slurry, thereby improving interlayer adhesion and adjusting the orientation of the reinforcing phase. Taking a sheet-like graphene-oriented reinforced microwave absorbing coating as an example, we can chemically encapsulate it through surface passivation and phosphating treatments, significantly reducing the dielectric constant and improving impedance matching. Next, resin, such as epoxy resin monomer, is uniformly mixed with graphene to form a fluid component A slurry, which is placed in the direct ink writing printing equipment. The epoxy resin hardener, acting as component B, is then laid on the surface of the part where the coating needs to be formed. Next, rollers behind the printhead roll this uncured slurry. Finally, a microwave heating device is used to heat the coating layer to cure it. It is worth noting that in conventional water-based ink direct-write slurries, the evaporation of the aqueous solvent generates strong internal stress, causing the coating, which already has low mechanical strength, to warp and peel off from the part surface. However, the slurry curing principle designed based on the thermosetting principle of epoxy resin can effectively reduce warping. Furthermore, in conventional ink direct-write printing processes, the cylindrical printhead, while allowing shearing forces to align the sheet-like additives within the slurry parallel to the printing direction during extrusion, cannot guarantee that the planar structure of these additives is parallel to the part surface. The roller pressing device behind the printhead can orient the sheet-like additives within the material, resulting in a much higher conductivity in the oriented direction than in the vertical direction, thus improving microwave absorption performance. Simultaneously, when the coating is heated by a microwave heating device, the uniformly distributed graphene within the slurry acts as a heat source in the microwave environment, stabilizing the heating rate at all locations within the slurry, reducing internal stress, and preventing warping.

[0012] To better implement the method of the present invention, the acidic solution in step (1) is a mixed solution of hydrochloric acid and sulfuric acid.

[0013] To better implement the method of the present invention, the sheet-like absorbent in step (1) is at least one of sheet-like carbonyl iron powder or sheet-like graphene.

[0014] To better implement the method of the present invention, further, in step (2), the content of the flake absorbent in the prepared mixture slurry is 50wt%-75wt%, and the content of the epoxy resin monomer is 25wt%-50wt%.

[0015] To better implement the method of the present invention, the epoxy resin monomer in step (2) is further selected from at least one of bisphenol A epoxy resin, bisphenol F glycidyl ether, and tetraepoxyphenyl diaminodiphenylmethane.

[0016] To better implement the method of the present invention, further, the process of uniformly mixing the flake absorbent and epoxy resin monomer in step (2) to obtain a mixture slurry suitable for direct ink writing printing is as follows: dissolve the flake absorbent and epoxy resin monomer in acetone, and then mechanically stir and ultrasonically disperse them to obtain a mixture slurry suitable for direct ink writing printing, wherein the acetone content is about 50% of the mass of the epoxy resin monomer.

[0017] To better implement the method of the present invention, in step (4), the roller material is 38CrMoAl, and the roller surface is coated with an anti-stick coating.

[0018] To better implement the method of the present invention, in step (5), a microwave heating device is used to heat the uncured mixture coating to cure it.

[0019] To better implement the method of the present invention, the step microwave heating device further controls the heating temperature to 150℃-200℃.

[0020] To better implement the method of the present invention, in step (5), ethanol is used to clean the uncured mixture slurry.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] (1) The directional enhanced absorbing coating prepared by the method provided in this invention has stronger absorbing performance than conventional sprayed absorbing coatings. The imaginary part of the complex permeability of the directional enhanced absorbing coating is higher than that of the non-directional absorbing coating throughout the entire measurement frequency range. At 2 GHz, the imaginary part of the complex permeability of the non-directional absorbing coating is about 0.8-0.9, while that of the directional enhanced absorbing coating can reach 1.1-1.2. Furthermore, the bandwidth of the directional enhanced absorbing coating can be up to twice that of the non-directional absorbing coating.

[0023] (2) The surface treatment of the flake additives by acid etching process can enhance the surface roughness of the additives, which can not only promote a stronger mechanical engagement between the additives and the resin, but also improve the phosphating effect and the dispersibility of the additives, further reduce the dielectric constant, and improve the impedance matching.

[0024] (3) This invention combines ink direct writing process. According to the shearing force applied to the slurry by the print head during extrusion, the internal sheet absorber can produce an oriented arrangement structure, which can significantly improve the electrical anisotropy of the material and significantly improve the magnetic permeability and wave absorption performance of the coating.

[0025] (4) The present invention enhances the performance of the printing nozzle moving direction, and can achieve directional enhancement of the printed component by changing the path distribution;

[0026] (5) The present invention uses epoxy resin as a solvent to prepare a microwave absorbing coating, which can effectively reduce the warping phenomenon caused by the drying of water-based slurry and enhance the adhesion between the coating and the surface of the part according to the principle of heating cross-linking and curing.

[0027] (6) The present invention provides a roller pressing device behind the print head, which can effectively adjust the arrangement of the sheet-like additives inside the material, further improve the electrical anisotropy, and make the conductivity of the directional arrangement direction much higher than that of the vertical direction, thereby improving the wave absorption performance.

[0028] (7) The present invention uses the uniformly distributed flake absorbent inside the slurry as the heating source in the microwave heating process, so that the heating rate of each part of the slurry is stable, reducing internal stress and avoiding warping. Attached Figure Description

[0029] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 This is a schematic diagram showing the roller behind the nozzle pressing the printing paste during the printing process of the present invention;

[0031] Figure 2 This is a schematic diagram of the longitudinal section of the slurry parallel to the printing direction during the rolling process of the present invention. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0033] Example 1:

[0034] This embodiment provides a method for preparing a directional enhanced microwave absorbing coating based on direct ink writing, characterized by the following steps:

[0035] (1) The surface of the sheet absorbent is treated with an acidic solution and then chemically coated by phosphating to obtain a surface-treated sheet absorbent.

[0036] (2) The prepared flake absorbent is uniformly mixed with epoxy resin monomer to obtain a mixture paste that can be used for direct ink writing printing;

[0037] (3) Apply epoxy resin hardener evenly to the surface of the part, and use ink direct writing equipment to print the prepared mixture slurry evenly on the surface of the part according to the set path.

[0038] (4) Before the ink has cured, the rollers behind the printhead automatically apply a fixed pressure above the ink. The lower surface of the rollers is lower than the height of the printhead, pressing the cylindrical ink into a flat shape. Figure 1 As shown, the orientation of the internal sheet-like additives will also be parallel to the part plane due to shear force. Figure 2 As shown;

[0039] (5) After printing, the uncured mixture slurry is cured and cleaned to obtain the directional reinforced microwave absorbing coating.

[0040] The acidic solution in step (1) is a mixture of hydrochloric acid and sulfuric acid.

[0041] The sheet-like absorbent in step (1) is at least one of sheet-like carbonyl iron powder or sheet-like graphene.

[0042] In step (2), the content of the flake absorbent in the prepared mixture slurry is 50wt%-75wt%, and the content of the epoxy resin monomer is 25wt%-50wt%.

[0043] The epoxy resin monomer in step (2) is at least one of bisphenol A epoxy resin, bisphenol F glycidyl ether, and tetraepoxyphenyl diaminodiphenylmethane.

[0044] The process of uniformly mixing the flake absorbent and epoxy resin monomer in step (2) to obtain a mixture slurry suitable for direct ink writing printing is as follows: the flake absorbent and epoxy resin monomer are dissolved in acetone, and after mechanical stirring and ultrasonic dispersion, a mixture slurry suitable for direct ink writing printing is obtained. The amount of acetone used needs to be controlled, and it should not be too much, which would make the solution too dilute and thus affect printing. The acetone content is about 50% of the mass of epoxy resin monomer.

[0045] In step (3), the epoxy resin hardener is diethyltoluenediamine.

[0046] In step (3), the path planning can be adjusted according to actual needs and can be combined with metamaterial principles to obtain the most suitable printing path.

[0047] In step (3), the ink direct writing process parameters can be adjusted according to actual needs and raw materials.

[0048] In step (4), the height of the lower surface of the roller is slightly lower than the height of the lower surface of the print head, and the height difference is less than the layer height.

[0049] In step (4), the roller material is 38CrMoAl, and the roller surface is coated with an anti-stick coating.

[0050] In step (5), a microwave heating device is used to heat the uncured mixture coating to cure it.

[0051] The microwave heating device controls the heating temperature to be between 150℃ and 200℃.

[0052] In step (5), ethanol is used to clean the uncured mixture slurry.

[0053] Example 2:

[0054] This embodiment takes a sheet-like graphene-oriented reinforced microwave absorbing coating as an example, and its specific preparation process is as follows:

[0055] 1) Surface treatment of sheet graphene by dilute acid, the steps are as follows: (1) Prepare a mixed solution of hydrochloric acid and sulfuric acid, and mix 0.3 mol / L hydrochloric acid and 0.3 mol / L sulfuric acid at a volume ratio of 1:1; (2) Weigh a certain amount of graphene and put it into the mixed solution of hydrochloric acid and sulfuric acid, and heat it in a water bath at 60°C for 5 hours; (3) After deposition and layering, take out the sheet graphene, wash it with distilled water and dry it.

[0056] 2) Graphene sheets were blended with bisphenol A epoxy resin at a mass fraction of 75 wt%. To ensure uniform mixing, 50% acetone was added to the mixture as a solvent, and the mixture was stirred for 10 minutes using a spiral stirrer at 300 rpm. Subsequently, the slurry was ultrasonically dispersed in a constant temperature water bath at 65°C for 5 minutes. The mixed solution was then removed and allowed to stand for 6 hours to allow the acetone to evaporate.

[0057] 3) The target structure to be prepared is modeled using modeling software, and the path is planned and sliced ​​according to the performance enhancement requirements using slicing software. The data is then imported into the printing equipment.

[0058] 4) Apply diethyltoluenediamine evenly to the surface of the part that needs the coating; set the lower surface of the roller behind the printhead to be 0.1mm lower than the lower surface of the printhead.

[0059] 5) Using the graphene / epoxy resin slurry obtained in step 2), start printing according to the printing parameters and path set in step 3. The settings are: (1) layer thickness 0.2mm; (2) line width 0.6mm; (3) extrusion rate 0.85.

[0060] 6) A microwave heating device was used to control the heating temperature at 150℃ and hold it at that temperature for 2 hours. The resulting directional enhanced microwave absorbing coating was then prepared.

[0061] This technical solution is based on the effect of acid etching on sheet-like additives, which enhances the surface roughness of the additives. This not only promotes stronger mechanical interlocking between the additives and the resin, but also improves the phosphating effect and additive dispersibility, further reducing the dielectric constant and improving impedance matching.

[0062] This technical solution is based on ink direct writing process. The shearing force applied by the print head to the slurry during extrusion can cause the internal sheet-like absorber to form an oriented structure, which can significantly improve the electrical anisotropy of the material and significantly improve the magnetic permeability and wave absorption performance of the coating.

[0063] This technical solution is based on additive manufacturing technology. As a type of 3D printing technology, ink direct writing technology allows the print head to move along a specified path during operation, thereby playing a role in directional reinforcement.

[0064] This technical solution introduces epoxy resin as a solvent to prepare a microwave absorbing coating. Based on its thermosetting principle, it can effectively reduce the warping phenomenon caused by the drying of water-based slurry, enhance the adhesion between the coating and the surface of the part, and prevent the coating from peeling off from the surface of the part.

[0065] This technical solution is based on the principle of roller pressing. A roller pressing device is set behind the print head, which can effectively adjust the arrangement of the sheet-like additives inside the material, further improving the electrical anisotropy. The conductivity in the directional arrangement direction is much higher than that in the vertical direction, thereby improving the wave absorption performance.

[0066] This technical solution uses the uniformly distributed flake absorbent inside the slurry as the heating source during the microwave heating process, which stabilizes the heating rate at various locations of the slurry, reduces internal stress, and avoids warping.

[0067] The other parts of this embodiment are the same as those in the above embodiments, and will not be described again.

[0068] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a directional enhanced microwave absorbing coating based on direct ink writing, characterized in that, Includes the following steps: (1) The surface of the sheet absorbent is treated with an acidic solution and chemically coated by phosphating to obtain a surface-treated sheet absorbent; the sheet absorbent is at least one of sheet carbonyl iron powder or sheet graphene. (2) The prepared flake absorbent is uniformly mixed with epoxy resin monomer to obtain a mixture slurry suitable for direct ink writing printing; in the prepared mixture slurry, the content of flake absorbent is 50wt%-75wt% of the total content of flake absorbent and epoxy resin monomer, and the content of epoxy resin monomer is 25wt%-50wt% of the total content of flake absorbent and epoxy resin monomer; the epoxy resin monomer is at least one of bisphenol A type epoxy resin, bisphenol F glycidyl ether, and tetraepoxyphenyl diaminodiphenylmethane; (3) Apply epoxy resin hardener evenly to the surface of the part, and print the prepared mixture slurry evenly on the surface of the part according to the set path using an ink direct writing device. (4) Before it has solidified, the roller behind the print head automatically applies a fixed pressure above the slurry. The lower surface of the roller is lower than the height of the print head, which presses the cylindrical slurry into a flat shape. The orientation of the internal sheet-like additives will also be parallel to the plane of the part due to the shear force. (5) After printing, the uncured mixture slurry is cured and cleaned to obtain a directional reinforced microwave absorbing coating. The uncured mixture slurry is cured by heating it with a microwave heating device. The microwave heating device controls the heating temperature to be 150℃-200℃.

2. The method for preparing a directional enhanced microwave absorbing coating based on direct ink writing according to claim 1, characterized in that, The acidic solution in step (1) is a mixture of hydrochloric acid and sulfuric acid.

3. A method for preparing a directional enhanced microwave absorbing coating based on direct ink writing according to claim 1 or 2, characterized in that, The process of uniformly mixing the flake absorbent and epoxy resin monomer in step (2) to obtain a mixture slurry suitable for direct ink writing printing is as follows: the flake absorbent and epoxy resin monomer are dissolved in acetone, and after mechanical stirring and ultrasonic dispersion, a mixture slurry suitable for direct ink writing printing is obtained, wherein the acetone content is 50% of the mass of the epoxy resin monomer.

4. A method for preparing a directional enhanced microwave absorbing coating based on direct ink writing according to claim 1 or 2, characterized in that, In step (4), the roller material is 38CrMoAl, and the roller surface is coated with an anti-stick coating.

5. A method for preparing a directional enhanced microwave absorbing coating based on direct ink writing according to claim 1 or 2, characterized in that, In step (5), ethanol is used to clean the uncured mixture slurry.

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