Low shrinkage electromagnetic shielding coating and preparation method thereof, modified absorbent, modified epoxy resin and preparation method and application thereof

Abstract

The application discloses a kind of low shrinkage electromagnetic protection coating and preparation method thereof, modified absorbent, modified epoxy resin and preparation method and application thereof, and the composition of electromagnetic protection coating is generally mass fraction composition and includes modified absorbent, modified epoxy resin, auxiliary agent, solvent, toughening agent, curing agent, curing agent accelerator and absorbent;Preparation method includes: stirring, premixing, dispersion grinding, screen filtering and high-speed mixing.The absorbent and epoxy resin are modified in the application, and then the modified absorbent, modified epoxy resin, toughening agent, solvent and other auxiliary agents are mixed and treated, and the coating is sprayed after curing, and the long-term shrinkage of the coating is less than 2%, and all performance indicators meet the requirements.The preparation method provided by the application is simple and feasible, and the process is mature and stable, with low production cost and large-scale production.

Description

Technical Field

[0001] This invention relates to a coating and its preparation method, and more particularly to a low-shrinkage electromagnetic shielding coating and its preparation method, a modified absorbent, a modified epoxy resin, their preparation methods and applications. Background Technology

[0002] Paint is a mixture of organic and inorganic substances in liquid or powder form. It is generally a composite system composed of base material (film-forming substance) or pigments, fillers, solvents, and additives. When applied to the surface of an object, it dries and cures to form a thin film that evenly covers and adheres well to the surface of the object, serving various purposes such as protection, decoration, marking, or special functions.

[0003] Electromagnetic shielding absorbing coatings are a type of special functional coating. They possess the common characteristics of general coatings, such as film-forming properties, leveling properties, and high adhesion. At the same time, special applications endow them with other special functional characteristics, such as high absorption rate, thin thickness, and wide bandwidth.

[0004] Existing general-purpose room temperature curing solvent-based coatings have low dimensional requirements, small coating thickness (generally below 150μm), fast solvent evaporation, fast curing speed, and rapid dimensional stabilization. However, the thickness of electromagnetic shielding and absorbing coatings has a significant impact on performance. In contrast, coatings with large thicknesses (generally greater than 400μm) have slow solvent evaporation, slow curing speed, and difficulty in controlling the coating thickness after complete curing.

[0005] Existing electromagnetic shielding absorbing coatings have long curing cycles and slow solvent evaporation, resulting in severe coating shrinkage and significant changes in the material's electromagnetic shielding and absorbing performance. Figure 1 Table 1 shows the changes in the absorption performance and physical parameters of the existing 1mm electromagnetic shielding. It can be seen that the coating performance changes significantly, mainly due to the shrinkage of the coating size caused by post-curing and solvent evaporation.

[0006] Figure 1 The figure shows the changes in the absorption performance of the existing 1mm electromagnetic shielding absorbing coating after curing at room temperature (23℃, 50% RH) for 7 days and 180 days. Table 1 shows the changes in the relevant physical parameters of the existing 1mm electromagnetic shielding absorbing coating after curing at room temperature (23℃, 50% RH) for 7 days and 180 days.

[0007] The performance characterization of existing electromagnetic shielding absorbing coatings has certain limitations. Electromagnetic shielding absorbing coatings use two-component room-temperature curing resins, resulting in a long curing cycle. To accelerate curing, heated airflow is often used to speed up solvent evaporation and cross-linking reactions, replacing the room-temperature curing process. However, this method cannot completely replace room-temperature curing, leading to differences between the final coating state and the actual coating state.

[0008] The above problems have not yet been effectively resolved and can no longer meet people's needs, so they urgently need to be improved. Summary of the Invention

[0009] The purpose of this invention is to provide a low-shrinkage electromagnetic protective coating and its preparation method, a modified absorbent, a modified epoxy resin and their preparation methods and applications, thereby overcoming the shortcomings of the existing technology.

[0010] This invention provides the following solution:

[0011] A low-shrinkage electromagnetic shielding coating comprises the following raw material components in parts by weight:

[0012] Modified absorbent: Modified epoxy resin: Additives: Solvent: = 100: 10~40: 0.5~2.5: 5~25;

[0013] Modified epoxy resin: toughening agent = 100: 1~10;

[0014] Modified epoxy resin: curing agent = 100: 5~45;

[0015] Curing agent: Curing accelerator = 100: 1~5.

[0016] Furthermore, it also includes a diluent, wherein the mass of the diluent and the solvent accounts for 15 wt% to 28 wt% of the total mass of the electromagnetic protective coating.

[0017] Furthermore, the trade names of each raw material component include:

[0018] Toughening agents, including: Desmocap 14CNB, Desmocap 11A, and Desmocap 12A;

[0019] Additives, including: leveling agents, antisettling agents, defoamers, wetting and dispersing agents, and coupling agents;

[0020] Curing agents include: T31, ethylenediamine, G328, G240, IPDA, 1,3-BAC, and D230;

[0021] Curing accelerators include: benzyl dimethylamine, diethylaminopropylamine, tetramethylethylenediamine, triphenylphosphine, N,N-dimethylaniline, 2-thiol benzothiazole, 2,4,6-tris(dimethylaminomethyl)phenol, and 2-ethyl-4-methylimidazole;

[0022] The diluent is a volatile substance, including: ethyl acetate, acetone, and methyl ethyl ketone;

[0023] The solvent is a reactive solvent, including: propylene oxide butyl ether, monoepoxypropylene glycidyl ether, phenyl glycidyl ether, diepoxyethylene glycol diglycidyl ether, and resorcinol diglycidyl ether.

[0024] A method for preparing a low-shrinkage electromagnetic shielding coating, comprising:

[0025] Step 1, Stirring: Add modified epoxy resin, toughening agent, additives, and solvent to the stirring equipment;

[0026] Step 2, Premixing: Add the modified absorbent and increase the speed of the stirring equipment;

[0027] Step 3, Dispersion and Grinding: The material generated in Step 2 is dispersed and ground using a grinding mill;

[0028] Step 4, sieve filtration: Filter the material after dispersing and grinding in step 3 through a sieve to remove impurities from the material;

[0029] Step 5, high-speed mixing: Add curing agent, curing accelerator and diluent according to a certain mass ratio, stir and mix for a certain time to generate coating.

[0030] Furthermore, it also includes:

[0031] Step 6, Paint Curing: Let the paint from Step 5 sit for a certain period of time to cure.

[0032] In step one, the stirring device is used to stir for 30 minutes at a speed of 400 rpm to 600 rpm;

[0033] In step two, the speed of the stirring device is increased to 900 rpm-1200 rpm;

[0034] In step three, the grinding machine is a basket mill or a three-roll mill;

[0035] In step five, the mixing process is carried out for a certain period of time to generate a coating, specifically by mixing and stirring in a mixing device with a rotation speed of 400 rpm to 600 rpm for at least 30 minutes.

[0036] A method for preparing a modified absorbent for low-shrinkage electromagnetic shielding coatings, comprising:

[0037] Raw material preparation: Prepare the raw material solution according to the following mass ratios: absorbent: treatment agent: solvent: deionized water = 100: 1~2: 2~5: 0.2~1, and stir the prepared solution.

[0038] The absorbent includes at least metal absorbents and ferrite absorbents, the treatment agent includes at least a silicon coupling agent, and the solvent includes at least anhydrous ethanol, n-butanol, acetone, and deionized water.

[0039] Mixing process; mixing and stirring under a protective atmosphere;

[0040] Drying process: The mixed materials are dried to form powder;

[0041] Dispersion treatment involves dispersing the powder formed during the drying process.

[0042] Furthermore, in the mixing process, a 10L high-speed mixer with an inert gas atmosphere is used. The initial speed of the mixer is 20 rpm. The solution is added and mixed at 20 rpm, and the speed is adjusted to 1000 rpm to continue mixing.

[0043] Furthermore, the metal absorbent comprises:

[0044] Spherical carbonyl iron powder, flake carbonyl iron powder, iron-silicon-aluminum, iron-silicon-chromium, amorphous iron fiber, carbonyl nickel powder, iron-nickel alloy powder, cobalt powder;

[0045] The ferrites include: barium ferrite, strontium ferrite, and cobalt-containing ferrite;

[0046] The silicon coupling agents include: KH540, KH550, KH560, KH570, KH590, phosphate ester coupling agents, aluminate coupling agents, aluminum zirconate coupling agents, and zirconate coupling agents.

[0047] A method for preparing a modified epoxy resin for low-shrinkage electromagnetic shielding coatings, comprising:

[0048] First component: Dissolve epoxy resin in an organic solvent until the viscosity of the solution reaches 100 mPas to 300 mPas to generate the first component;

[0049] Second component: Dissolve low molecular weight polyamide in an organic solvent until the viscosity of the solution reaches 100 mPas to 300 mPas to generate the second component;

[0050] The first component is placed in a container and stirred and heated. Then the second component is added dropwise to the container so that the molar ratio of low molecular weight polyamide to epoxy resin in the container is 0.40 to 0.48. The addition is completed within 1 to 1.5 hours. Then the mixture is stirred. After stirring, heating is stopped and the mixture is cooled to room temperature for later use.

[0051] Furthermore, the epoxy resins in the first component include: E03, E06, E12, E20, E44, and E51;

[0052] Organic solvents include: cyclohexanone, xylene, n-butanol, butanone, ethyl acetate, acetone, or mixtures of two or more of the above;

[0053] The second component consists of low molecular weight polyamides including: 650#, 651#, and 300#.

[0054] Furthermore, the container is a four-necked flask. The first component is placed into the four-necked flask and stirred and heated. The stirring speed is 500 rpm to 1000 rpm, and the temperature is gradually increased to 80°C to 120°C and kept at that temperature for at least 10 minutes.

[0055] Add the second component dropwise, adjusting the ratio of low molecular weight polyamide to epoxy resin to a certain value. Complete the dropwise addition within a certain time, then continue stirring for 1 hour. After that, stop heating and cool to room temperature for later use.

[0056] A low-shrinkage electromagnetic shielding coating, wherein the low-shrinkage electromagnetic shielding coating is prepared by the preparation method of the low-shrinkage electromagnetic shielding coating described above.

[0057] Application of a modified absorbent and a modified epoxy resin in the preparation method of low-shrinkage electromagnetic protective coatings.

[0058] Compared with the prior art, the present invention has the following advantages:

[0059] This invention first modifies the absorbent to improve its dispersibility. Simultaneously, it modifies a general-purpose epoxy resin with polyamide to obtain a modified epoxy resin. Then, the modified absorbent, modified epoxy resin, toughening agent, solvent, and other additives are mixed and dispersed at high speed using a three-roll mill or basket mill for further homogenization. The filtered product is component one. During application, component two (curing agent), component three (curing accelerator), and diluent are added in proportion and mixed. After curing, an electromagnetic shielding absorbing coating is prepared. This coating exhibits a long-term shrinkage rate of less than 2%, and all performance indicators meet the requirements. The preparation method provided by this invention is simple and feasible, the process is mature and stable, the production cost is low, and it can be mass-produced. Attached Figure Description

[0060] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0061] Figure 1 The graph shown is a coordinate graph showing the change in the absorption performance of a 1mm electromagnetic shielding absorbing coating cured at room temperature (23℃, 50% RH) for 7 days and 180 days.

[0062] Figure 2 This is a graph showing the influence of the performance of the eight-layer electromagnetic shielding absorption system.

[0063] Figure 3 This is a coordinate graph showing the effect of the thickness of the electromagnetic shielding absorbing coating on reflectivity.

[0064] Figure 4 This is a coordinate graph showing the effect of powder content in electromagnetic shielding absorbing coatings on reflectivity.

[0065] Figure 5 This is a flowchart of a method for preparing low-shrinkage electromagnetic protective coatings.

[0066] Figure 6 This is a flowchart of a method for preparing low-shrinkage electromagnetic protective coatings. Detailed Implementation

[0067] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068]

[0069] Table 1

[0070] like Figure 1 As shown in Figure 1 and in conjunction with Table 1, Table 1 illustrates the changes in relevant physical parameters of a current 1mm electromagnetic shielding absorbing coating after 7 days and 180 days of curing at room temperature (23℃, 50% RH). Table 1 shows the changes in the absorption performance of a current 1mm electromagnetic shielding absorbing coating after 7 days and 180 days of curing at room temperature (23℃, 50% RH). It can be seen that the performance characterization of current electromagnetic shielding absorbing coatings has certain limitations.

[0071] like Figure 2 As shown, Figure 2 The relationship between the state of the coating and the performance of the electromagnetic shielding and absorbing coating is presented in the form of a knowledge graph. As can be seen from the graph, the coating thickness decreases due to the curing state of the coating and solvent evaporation after construction, which affects the electromagnetic shielding and absorbing performance of the coating. On the other hand, the coating curing state and solvent evaporation increase the weight percentage of the absorbent in the coating, thereby changing the electromagnetic parameters of the coating and indirectly affecting the electromagnetic shielding and absorbing performance of the coating.

[0072] like Figure 3 As shown, Figure 3The effect of electromagnetic shielding absorbing coating thickness on reflectivity (approximately 1 mm, 89 wt%) is demonstrated. With a fixed weight percentage of absorbent in the coating, changing its thickness shows the trend of electromagnetic shielding absorbing performance. It can be seen that as the coating thickness changes, the position of the material's resonance peak changes, and the material properties change at specific frequencies.

[0073] like Figure 4 As shown, Figure 4 The effect of powder content in electromagnetic shielding absorbing coating on reflectivity was demonstrated. With a coating thickness of 1 mm, as the weight percentage of absorber decreased, the coating resonance peak shifted to higher frequencies, and the electromagnetic shielding absorbing performance at specific frequencies changed.

[0074] Combination Figures 1 to 4 As shown, the influence of the shrinkage rate of the electromagnetic shielding absorbing coating on its absorbing performance can be seen. This invention reveals the problems existing in the prior art, such as the long curing cycle of electromagnetic shielding absorbing coatings and the lack of attention to the coating after long-term curing. In order to address the influence of the shrinkage rate of the electromagnetic shielding absorbing coating on its absorbing performance, a method of rapid curing of a two-component epoxy system is adopted, and a low-boiling-point, highly volatile solvent is selected. Through a large number of formulation experiments, the material composition, preparation method and application of an electromagnetic shielding absorbing coating with a shrinkage rate of less than 2% are finally obtained.

[0075] Example 1:

[0076] I. Preparation of modified absorbent:

[0077] Step 1: Solution preparation: Add 75g of KH560, 125g of acetone, and 25g of deionized water to a beaker in sequence, and stir with an electric mixer for about 5 minutes.

[0078] Step 2: Mixing: Using a 10L high-speed mixer under inert gas protection, add 5000g of spherical carbonyl iron powder absorbent (Shaanxi Xinghua Chemical Co., Ltd., brand P1, phosphating powder) to the equipment. Adjust the mixer speed to 20 RPM, slowly add the solution prepared in Step 1, and mix for about 1 minute. Adjust the speed to 1000 RPM and mix for about 5 minutes.

[0079] Step 3: Drying: Place the material from step 3 into a vacuum drying oven and dry at 80°C for 2 hours until the solvent is completely evaporated.

[0080] Step 4: Dispersion: A high-speed pulverizer under nitrogen atmosphere is used to disperse the dry powder at high speed to break up any agglomerations in the powder.

[0081] II. Preparation of Modified Epoxy Resin

[0082] (1) Dissolving:

[0083] A.E20 epoxy resin is dissolved in a mixed solvent of xylene and n-butanol in a ratio of 7:3. The epoxy resin content is 60 wt%, labeled as component A. Grade: E20, Nan Ya Electronic Materials (Kunshan) Co., Ltd., epoxy equivalent 471 g / eq.

[0084] B.650# low molecular weight polyamide is dissolved in a mixed solvent of xylene and n-butanol in a ratio of 7:3. The dissolution ratio of 650# is 80 wt%. 650# is manufactured by Zhenjiang Danbao Resin Co., Ltd. 650# indicates that the epoxy resin has a viscosity grade of 650. Viscosity refers to the degree to which a fluid resists flow. Here, 650# indicates that the epoxy resin is relatively viscous.

[0085] (2) Preparation of modified epoxy resin:

[0086] Place component A into a four-necked flask, start stirring at 750 rpm, gradually increase the temperature to 100°C, maintain the temperature for about 10 minutes, then slowly add component B dropwise at a ratio of 0.45 for 650 to E20, and complete the addition in 1 hour. Continue stirring for another hour, then stop heating and cool to room temperature for later use.

[0087] III. Grades of various reagents:

[0088] Toughening agent: Desmocap 14CNB, Covestro Resins (Shanghai) Co., Ltd.

[0089] Curing agent: G240, Mitsubishi Gas Chemical Trading (Shanghai) Co., Ltd.

[0090] Curing accelerator: 2,4,6-tris(dimethylaminomethyl)phenol

[0091] Diluent: Ethyl acetate.

[0092] Leveling agent: BYK378, BYK Chemicals (Shanghai) Co., Ltd.

[0093] Antisettling agent: AEROSIL R972G, Evonik Specialty Chemicals (Shanghai) Co., Ltd.

[0094] Defoamer: BYK-A525, BYK Chemicals (Shanghai) Co., Ltd.

[0095] Wetting and dispersing agent: BYK104S, BYK Chemicals Shanghai Co., Ltd.

[0096] Coupling agent: KH550

[0097] IV. Specific Implementation Process:

[0098] 1. Raw material ratio:

[0099] Modified absorbent: Modified epoxy resin: Additives: Solvent: = 100:17:2:10;

[0100] Modified epoxy resin: toughening agent = 100:8;

[0101] Modified epoxy resin: curing agent = 100:12;

[0102] Curing agent : Curing accelerator = 100 : 1.5

[0103] Diluent: Adjusted according to the final coating viscosity; the total amount of solvent and diluent should account for 15wt% to 28wt% of the entire coating system.

[0104] 2. Step 1: Prepare the coating using a high-speed mixing device. Add modified epoxy resin, toughening agent, additives, and solvent to the mixing tank and stir at 500 rpm for 30 minutes.

[0105] 3. Step 2: Premixing: Slowly add the modified absorbent, and after wetting the material, increase the rotation speed to 900 rpm to 1200 rpm.

[0106] 4. Step 3: Dispersion and grinding: Use a basket mill or a three-roll mill to further disperse the material from step 2, reduce the agglomeration of the absorbent in the system, and obtain a uniformly dispersed coating component.

[0107] 5. Step 4: Filter the coating from Step 3 through a 60-mesh sieve to remove impurities.

[0108] 6. Step 5: High-speed mixing: Add the curing agent, curing accelerator and diluent to the materials in Step 5 according to the above ratio, and stir and mix at 300 rpm for 30 minutes.

[0109] 7. Step Six: Curing: Let the paint from Step Five sit for 10 minutes.

[0110] 8. Step Seven: Spraying: Prepare two standard 180mm×180mm×5mm aluminum plates (for electromagnetic shielding absorption performance testing and mechanical performance testing), one 120mm×50mm×0.28mm tinplate plate (for impact testing), and one 120mm×25mm×0.28mm tinplate plate (for flexibility testing). Clean the surfaces with 120-grit sandpaper. Spray the electromagnetic shielding absorption coating prepared in Step Six onto the material surfaces. The coating thickness should be 0.95mm~1.05mm.

[0111] V. Testing

[0112] Test the performance indicators of the coating: reflectivity of a 1.0mm coating at 8GHz to 18GHz.

[0113] ≤-8dB, adhesion 11MPa, flexibility: 10mm, impact strength: greater than 50cm·cm, shrinkage ε=0.9%

[0114] Comparative Example 1:

[0115] I. Raw materials: Spherical carbonyl iron powder (Shaanxi Xinghua Chemical Co., Ltd., grade P1, phosphating powder), epoxy resin E20 (NPES901), Nanya Electronic Materials (Kunshan) Co., Ltd., epoxy equivalent 471g / eq, curing agent: 650#, Zhenjiang Danbao Resin Co., Ltd. Solvent: Cyclohexanone.

[0116] II. Coating Preparation:

[0117] S1: Dissolve the epoxy resin in cyclohexanone, with a solvent ratio of 40 wt%.

[0118] S2: Carbonyl iron powder: epoxy resin solution = 100:25. The two are dispersed and mixed in a high-speed disperser for 60 minutes, and then filtered to obtain component A.

[0119] S3: Mix component A and 650 curing agent at a ratio of 125:4 until homogeneous. After curing for 15 minutes, prepare a standard electromagnetic shielding absorption performance test board, a flexibility test board, and an impact test board.

[0120] S4: The coating is cured for 7 days and 180 days, and the coating thickness, shrinkage rate, flexibility, impact strength and other indicators are tested respectively.

[0121] S5: Test the performance indicators of the coating: 1.0mm coating reflectivity ≤ -8dB at 8GHz~18GHz, adhesion 6MPa, flexibility: greater than 15mm, impact strength: less than 50cm, shrinkage ε=10%.

[0122] Other embodiments can be obtained based on Embodiment 1 and Comparative Example 1, such as Embodiments 2-5 in the table below. The contents of Embodiments 2-5 are largely the same as those of Embodiment 1. The contents with different amounts of certain materials are listed in tabular form below:

[0123]

[0124] As can be seen from Examples 1 to 5, the electromagnetic shielding absorbing coating prepared by the present invention has a shrinkage rate of less than 2% due to the synthesis of modified epoxy resin, the application of curing agent and accelerator, and the application of low volatile solvent, which meets the requirements of existing industrial production.

[0125] Example 6:

[0126] Based on the above embodiments, a material composition of a low-shrinkage electromagnetic shielding coating can be obtained, wherein the low-shrinkage electromagnetic shielding coating comprises the following raw material components in parts by mass:

[0127] Modified absorbent: Modified epoxy resin: Additives: Solvent: = 100: 10~40: 0.5~2.5: 5~25;

[0128] Modified epoxy resin: toughening agent = 100: 1~10;

[0129] Modified epoxy resin: curing agent = 100: 5~45;

[0130] Curing agent: Curing accelerator = 100: 1~5.

[0131] Specifically, it also includes a diluent, the mass percentage of which is adjusted according to the viscosity of the final coating, and the mass of the diluent and the solvent accounts for 15wt% to 28wt% of the total mass of the electromagnetic protective coating.

[0132] Specifically, in this embodiment, the trade names of each raw material component include:

[0133] Toughening agents, including: Desmocap 14CNB, Desmocap 11A, and Desmocap 12A;

[0134] Additives, including: leveling agents, antisettling agents, defoamers, wetting and dispersing agents, and coupling agents;

[0135] Curing agents include: T31, ethylenediamine, G328, G240, IPDA, 1,3-BAC, and D230;

[0136] Curing accelerators include: benzyl dimethylamine, diethylaminopropylamine, tetramethylethylenediamine, triphenylphosphine, N,N-dimethylaniline, 2-thiol benzothiazole, 2,4,6-tris(dimethylaminomethyl)phenol, and 2-ethyl-4-methylimidazole;

[0137] The diluent is a volatile substance, including: ethyl acetate, acetone, and methyl ethyl ketone;

[0138] The solvent is a reactive solvent, including: propylene oxide butyl ether, monoepoxypropylene glycidyl ether, phenyl glycidyl ether, diepoxyethylene glycol diglycidyl ether, and resorcinol diglycidyl ether.

[0139] Example 7:

[0140] This embodiment discloses a low-shrinkage electromagnetic protective coating and its preparation method based on embodiments 1-5 and the prior art, belonging to the fields of functional coatings and electromagnetic protection.

[0141] like Figure 5 As shown, the steps of this embodiment are summarized as follows: First, the absorbent is modified to improve its dispersibility. Simultaneously, a general-purpose epoxy resin is modified with polyamide to obtain a modified epoxy resin. Then, the modified absorbent, modified epoxy resin, toughening agent, solvent, and other additives are mixed and dispersed at high speed using a three-roll mill or basket mill for further uniform dispersion. The filtered product is component one. During construction, component two (curing agent), component three (curing accelerator), and diluent are added in proportion and mixed. After curing, an electromagnetic shielding absorbing coating is prepared. This coating exhibits a long-term shrinkage rate of less than 2%, and all performance indicators meet the requirements. The preparation method provided by this invention is simple and feasible, with a mature and stable process, low production cost, and is suitable for large-scale production.

[0142] I. Modified absorbent:

[0143] The purpose of modifying the absorbent is: (1) to improve the dispersion characteristics and wettability of the absorbent in the coating, improve the compatibility between the absorbent and the resin, and improve the adhesion between the coating and the substrate.

[0144] (2) Modified absorbents can increase the volume concentration (PVC) of pigments without affecting the performance and appearance of the coating.

[0145] (3) For magnetic absorbers, modification can reduce the dielectric constant of the powder and improve the impedance matching characteristics of the coating.

[0146] Specific implementation steps for modified absorbents:

[0147] (1) Prepare the raw materials:

[0148] Metal absorbents mainly include: spherical carbonyl iron powder, flake carbonyl iron powder, iron-silicon-aluminum, iron-silicon-chromium, amorphous iron fiber, carbonyl nickel powder, iron-nickel alloy powder, cobalt powder, etc.

[0149] Ferrite absorbents include: barium ferrite, strontium ferrite, cobalt-containing ferrite, etc.

[0150] Treatment agents: Silicon coupling agents, including KH540, KH550, KH560, KH570, KH590, etc., phosphate coupling agents, aluminate coupling agents, aluminum zirconate coupling agents, zirconate coupling agents, etc.

[0151] Solvents: anhydrous ethanol, n-butanol, acetone, etc.

[0152] Deionized water.

[0153] (2) Step 1: Solution preparation: ratio of absorbent: treatment agent: solvent: deionized water = 100: 1~2: 2~5: 0.2~1. Add the treatment agent, solvent and deionized water to the beaker in sequence and stir with an electric mixer for about 5 minutes, or at least 5 minutes.

[0154] (3) Step 2: Mixing: Use a 10L high-speed mixer with an inert gas atmosphere. Add the absorbent to the equipment, adjust the mixer speed to 20 rpm, slowly add the solution prepared in Step 1, and mix for about 1 minute. Adjust the speed to 1000 rpm and mix for about 5 minutes.

[0155] (4) Step 3: Drying: Place the material from step 2 into a vacuum drying oven and dry at 70℃~90℃ for 2 hours until the solvent is completely evaporated.

[0156] During the drying process, the treatment agent hydrolyzes and reacts chemically with the surface groups of the powder. The hydrolyzed molecules cross-link with each other, achieving the coating of the powder by the coupling agent. On the other hand, the coating of the coupling agent can cause agglomeration between the powder particles, thereby increasing the particle size and deteriorating the electromagnetic parameters of the powder, which is not conducive to the subsequent production of coatings. Therefore, it is necessary to disperse the absorbent after step 3 to remove the agglomeration between the powder particles.

[0157] (5) Step 4, Dispersion: High-speed dispersion of the powder from step 3 is carried out using a high-speed pulverizer under nitrogen atmosphere protection to break up the agglomeration in the powder.

[0158] II. Preparation of modified epoxy resin:

[0159] Epoxy resin is a general term for compounds that contain two or more epoxy groups in one molecule and can form a three-dimensional cross-linked network cured material in the presence of appropriate chemical reagents.

[0160] Commonly used epoxy resin grades include E03, E06, E12, E20, E44, and E51, while commonly used low molecular weight polyamide grades include 650#, 651#, and 300#.

[0161] (1) Dissolving:

[0162] A. E03, E06, E12, and E20 are solids at room temperature, while E44 and E51 are liquids at room temperature. For subsequent reactions, the epoxy resin is dissolved in an organic solvent in a specific ratio. The final solution viscosity is between 100 mPas and 300 mPas. Specific organic solvents include cyclohexanone, xylene, n-butanol, butanone, ethyl acetate, acetone, or a mixture of two or more of these, hereinafter referred to as component A.

[0163] B. Low molecular weight polyamide is the same as above. Hereinafter referred to as component B.

[0164] (2) Preparation of modified epoxy resin:

[0165] Epoxy resin was modified in a four-necked flask, which consisted of a stirrer, temperature control unit, DC condenser, liquid dropper, and oil bath heating unit. Component A was loaded into the four-necked flask, and stirring was started at a speed of 500 rpm to 1000 rpm. The temperature was gradually increased to 80℃ to 120℃ and maintained for about 10 minutes. Then, component B was slowly added dropwise. The molar ratio of low molecular weight polyamide to epoxy resin was 0.40 to 0.48. The addition was completed in 1 hour to 1.5 hours. Stirring was then continued for 1 hour. After that, heating was stopped, and the mixture was cooled to room temperature for later use.

[0166] III. List of reagent brands in this embodiment:

[0167] Toughening agents: Desmocap 14CNB, Desmocap 11A, Desmocap 12A.

[0168] Additives: leveling agents, antisettling agents, defoamers, wetting and dispersing agents, coupling agents, etc.

[0169] Curing agents: T31, ethylenediamine, G328, G240, IPDA, 1,3-BAC, D230, etc.

[0170] Curing accelerators: benzyl dimethylamine, diethylaminopropylamine, tetramethylethylenediamine, triphenylphosphine, N,N-dimethylaniline, 2-thiol benzothiazole, 2,4,6-tris(dimethylaminomethyl)phenol, 2-ethyl-4-methylimidazole, etc.

[0171] Diluents: Volatile diluents: ethyl acetate, acetone, methyl ethyl ketone, etc. Reactive solvents: propylene oxide butyl ether, monoepoxypropylene glycidyl ether, phenyl glycidyl ether, diepoxyethylene glycol diglycidyl ether, resorcinol diglycidyl ether.

[0172] IV. Specific preparation process:

[0173] 1. Raw material ratio:

[0174] Modified absorbent: Modified epoxy resin: Additives: Solvent: = 100: 10~40: 0.5~2.5: 5~25;

[0175] Modified epoxy resin: toughening agent = 100: 1~10;

[0176] Modified epoxy resin: curing agent = 100: 5~45;

[0177] Curing agent: Curing accelerator = 100: 1~5

[0178] Diluent: Adjusted according to the final coating viscosity; the total amount of solvent and diluent should account for 15wt% to 28wt% of the entire coating system.

[0179] 2. Step 1: Prepare the coating using a high-speed mixing device. Add modified epoxy resin, toughening agent, additives, and solvent to the mixing tank and stir at 400 rpm to 600 rpm for 30 minutes.

[0180] 3. Step 2: Premixing: Slowly add the modified absorbent. After the material is wetted, increase the rotation speed to 900 rpm to 1200 rpm.

[0181] 4. Step 3: Dispersion and grinding: Use a basket mill or a three-roll mill to further disperse the material from step 2, reduce the agglomeration of the absorbent in the system, and obtain a uniformly dispersed coating component.

[0182] 5. Step 4: Filter the coating from Step 3 through a 60-mesh sieve to remove impurities.

[0183] 6. Step 5: High-speed mixing: Add the curing agent, curing accelerator and diluent to the materials in Step 5 according to the above ratio, and stir and mix at 400rpm~600rpm for 30 minutes.

[0184] 7. Step Six: Curing: Let the paint from Step Five sit for 10 to 15 minutes.

[0185] 8. Step Seven: Spraying: Prepare two standard aluminum plates of 180mm×180mm×5mm (for electromagnetic protection and absorption performance testing and mechanical performance testing), one tinplate of 120mm×50mm×0.28mm (for impact testing) and one tinplate of 120mm×25mm×0.28mm (for flexibility testing), clean them with 120-grit sandpaper, and spray the electromagnetic protection and absorption coating prepared in Step Six onto the material surface.

[0186] Relevant testing items, including standards and testing methods:

[0187] 1. Reflectivity: Complies with GJB 2038A-2011 "Test Method for Reflectivity of Radar Electromagnetic Protection Absorbing Materials"

[0188] 2. Adhesion: Complies with GB / T5210-2006

[0189] 3. Flexibility: Complies with GB / T 1731-2020

[0190] 4. Impact resistance: Complies with GB / T 1732-2020

[0191] 5. Thickness Test: A digital micrometer with an arc shape is used to test the thickness of the sheet material by direct contact with the surface of the object. Aluminum substrate test: A square aluminum plate is divided into nine 3×3 sections, and the thickness h0 at the center of each section is measured. The average value of the final data is the aluminum plate thickness. Similarly, the thickness h1 of the aluminum material after spraying is tested. The coating thickness is h1-h0. The thickness h7 is measured 7 days after coating application, and the thickness h180 is measured 180 days after coating application. The shrinkage rate ε = (h180-h7)×100% / h7.

[0192] 6. Coating density calculation: Weigh the original aluminum plate and the coated aluminum plate using an electronic balance. The difference between the two is the coating weight. Calculate the coating density based on the coating thickness and the thickness of the standard plate.

[0193] 7. Coating curing conditions: Temperature: 23℃, Humidity: 50%RH.

[0194] Example 8:

[0195] like Figure 6 As shown, this embodiment discloses a method for preparing a low-shrinkage electromagnetic shielding coating, comprising:

[0196] Step 1, Stirring: Add modified epoxy resin, toughening agent, additives, and solvent to the stirring equipment;

[0197] Step 2, Premixing: Add the modified absorbent and increase the speed of the stirring equipment;

[0198] Step 3, Dispersion and Grinding: The material generated in Step 2 is dispersed and ground using a grinding mill;

[0199] Step 4, sieve filtration: Filter the material after dispersing and grinding in step 3 through a sieve to remove impurities from the material;

[0200] Step 5, high-speed mixing: Add curing agent, curing accelerator and diluent according to a certain mass ratio, stir and mix for a certain time to generate coating.

[0201] Preferred options also include:

[0202] Step 6, coating maturation: Place the coating from Step 5 for a certain period of time, preferably 10 to 15 minutes, to allow the coating to mature and obtain an electromagnetic shielding absorbing coating.

[0203] Step 7, Spraying: Prepare two standard aluminum plates of 180mm×180mm×5mm (for electromagnetic protection absorption performance testing and mechanical performance testing), one tinplate of 120mm×50mm×0.28mm (for impact testing) and one tinplate of 120mm×25mm×0.28mm (for flexibility testing), clean them with 120-grit sandpaper, and spray the electromagnetic protection absorption coating prepared in step 6 onto the material surface.

[0204] Preferred:

[0205] In step one, the stirring device is used to stir for 30 minutes at a speed of 400 rpm to 600 rpm;

[0206] In step two, the speed of the stirring device is increased to 900 rpm-1200 rpm;

[0207] In step three, the grinding machine is a basket mill or a three-roll mill;

[0208] In step five, the addition of curing agent, curing accelerator, and diluent according to a certain mass proportion specifically involves adding curing agent, curing accelerator, and diluent according to the mass proportions of the raw material components described in Example 6.

[0209] In step five, the mixing process is carried out for a certain period of time to generate a coating, specifically by mixing and stirring in a mixing device with a rotation speed of 400 rpm to 600 rpm for at least 30 minutes.

[0210] The relevant test items, including standards and test methods, are the same as in Example 7 and will not be repeated here.

[0211] Example 9:

[0212] This embodiment discloses a method for preparing a modified absorbent for low-shrinkage electromagnetic shielding coatings. The preparation method includes the following steps:

[0213] Raw material preparation: Prepare the raw material solution according to the following mass ratios: absorbent: treatment agent: solvent: deionized water = 100: 1~2: 2~5: 0.2~1, and stir the prepared solution.

[0214] The absorbent includes at least metal absorbents and ferrite absorbents, the treatment agent includes at least a silicon coupling agent, and the solvent includes at least anhydrous ethanol, n-butanol, acetone, and deionized water.

[0215] Mixing process; mixing and stirring are carried out under a protective atmosphere. For example, the mixing and stirring equipment is used for mixing and stirring under a 10L inert gas protection environment. The initial speed of the mixing and stirring equipment is 20 rpm. The solution is slowly added at 20 rpm and mixed for about 1 minute. The speed is then adjusted to 1000 rpm and mixed for about 5 minutes.

[0216] Drying process: The mixed materials are dried to form powder. For example, a vacuum drying oven is used, with the temperature controlled between 70℃ and 90℃, and the drying time is 2 hours.

[0217] Dispersion treatment involves dispersing the powder formed during the drying process to break up any agglomerations in the powder.

[0218] Specifically, in the mixing process of this embodiment, a 10L high-speed mixer with an inert gas protection is used. The initial speed of the mixer is 20 rpm. The solution is slowly added and mixed at 20 rpm for about 1 minute, or at least 1 minute. The speed is then adjusted to 1000 rpm and mixing continues for about 5 minutes, or at least 5 minutes.

[0219] Specifically, the metal absorbent includes:

[0220] Spherical carbonyl iron powder, flake carbonyl iron powder, iron-silicon-aluminum, iron-silicon-chromium, amorphous iron fiber, carbonyl nickel powder, iron-nickel alloy powder, cobalt powder;

[0221] The ferrites include: barium ferrite, strontium ferrite, and cobalt-containing ferrite;

[0222] The silicon coupling agents include: KH540, KH550, KH560, KH570, KH590, phosphate ester coupling agents, aluminate coupling agents, aluminum zirconate coupling agents, and zirconate coupling agents.

[0223] Example 10:

[0224] This embodiment discloses a method for preparing modified epoxy resin for low-shrinkage electromagnetic shielding coatings, including:

[0225] First component: Dissolve epoxy resin in an organic solvent in a certain proportion until the viscosity of the solution reaches 100 mPas to 300 mPas to generate the first component. The first component in this embodiment corresponds to component A in Example 1.

[0226] Second component: Dissolve low molecular weight polyamide in an organic solvent until the viscosity of the solution reaches 100 mPas to 300 mPas to generate the second component; the second component in this embodiment corresponds to component B in Example 1.

[0227] The first component is placed in a container and stirred and heated. Then the second component is added dropwise to the container so that the molar ratio of low molecular weight polyamide to epoxy resin in the container is 0.40 to 0.48. The addition is completed within 1 to 1.5 hours. Then the mixture is stirred. After stirring, heating is stopped and the mixture is cooled to room temperature for later use.

[0228] Specifically, the epoxy resins in the first component (component A) include: E03, E06, E12, E20, E44, and E51;

[0229] Organic solvents include: cyclohexanone, xylene, n-butanol, butanone, ethyl acetate, acetone, or mixtures of two or more of the above;

[0230] The second component (component B) consists of low molecular weight polyamides including: 650#, 651#, and 300#.

[0231] Specifically, the container is a four-necked flask, which consists of a stirring unit, a temperature control unit, a direct current condenser, a liquid dropper, and an oil bath heating unit. Different ports on the flask perform different functions. The first component (component A) is loaded into the four-necked flask and stirred and heated at a stirring speed of 500 rpm to 1000 rpm, gradually increasing the temperature to 80°C to 120°C and holding it at that temperature for at least 10 minutes. Then, the second component (component B) is gradually and slowly added dropwise at a ratio of 650 to E20 of 0.45, completing the addition over one hour. Stirring continues for another hour, then heating is stopped, and the flask is cooled to room temperature for later use.

[0232] For the purpose of simplicity, the method steps disclosed in the above embodiments are described as a series of actions. However, those skilled in the art should understand that the embodiments of the present invention are not limited to the described order of actions, because according to the embodiments of the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily essential to the embodiments of the present invention.

[0233] Example 11:

[0234] This embodiment discloses a low-shrinkage electromagnetic shielding coating, which is prepared by the preparation method of low-shrinkage electromagnetic shielding coating disclosed in any one or more embodiments of Examples 1 to 10.

[0235] Meanwhile, this embodiment also discloses the application of a modified absorbent and a modified epoxy resin in the preparation method of a low-shrinkage electromagnetic protective coating.

[0236] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0237] It should be noted that certain terms are used in this specification and claims to refer to specific elements. Those skilled in the art will understand that different manufacturers or producers may use different terms to refer to the same element. This specification and claims do not distinguish elements based on differences in terminology, but rather on differences in function.

[0238] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0239] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, any one of the embodiments claimed in the claims can be used in any combination of embodiments of the invention. As another example, Embodiment 1 can be combined with any embodiment other than Embodiment 1 to form more embodiments, such as Embodiment 1 combined with Embodiment 2, Embodiment 1 combined with Embodiment 3, and so on up to Embodiment 1 combined with Embodiment 11. Such combinations are not limited to two embodiments; combinations of three, four, or even more embodiments can form more new embodiments, but these will not be elaborated upon due to space limitations. That is, all features disclosed in this specification, or steps in all disclosed methods or processes, except for mutually exclusive features and / or steps, can be combined in any way. Any feature disclosed in this specification, unless specifically stated otherwise, can be replaced by other equivalent or similar alternative features. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0240] In this application, the term "exemplary" is used to mean "used as an example, illustration, or description." Any embodiment described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use this application. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that this application can be made without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0241] 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; and these 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 low-shrinkage electromagnetic shielding coating, characterized in that, The raw material components include the following parts by weight: Modified absorbent: modified epoxy resin: additives: second solvent = 100: 10~40: 0.5~2.5: 5~25; Modified epoxy resin: toughening agent = 100: 1~10; Modified epoxy resin: curing agent = 100: 5~45; Curing agent: Curing accelerator = 100: 1~5 Methods for preparing modified epoxy resins include: First component: Dissolve epoxy resin in a first organic solvent until the viscosity of the solution reaches 100 mPa·s to 300 mPa·s to generate the first component; Second component: Dissolve low molecular weight polyamide in the first organic solvent until the viscosity of the solution reaches 100 mPa·s to 300 mPa·s to generate the second component; The first component is placed in a container and stirred and heated. Then the second component is added dropwise to the container so that the molar ratio of low molecular weight polyamide to epoxy resin in the container is 0.40 to 0.

48. The addition is completed in 1 to 1.5 hours. Then the mixture is stirred. After stirring, the heating is stopped and the mixture is cooled to room temperature for later use. It also includes a diluent, wherein the mass of the diluent and the second solvent accounts for 15 wt% to 28 wt% of the total mass of the electromagnetic protective coating; The diluent is a volatile substance, including: ethyl acetate, acetone, and methyl ethyl ketone; The second solvent is a reactive solvent, including: propylene oxide butyl ether, monoepoxypropylene glycidyl ether, phenyl glycidyl ether, diepoxyethylene glycol diglycidyl ether, and resorcinol diglycidyl ether.

2. The low-shrinkage electromagnetic protective coating according to claim 1, characterized in that, The epoxy resins in the first component include: E03, E06, E12, E20, E44, and E51; The first organic solvent includes: cyclohexanone, xylene, n-butanol, butanone, ethyl acetate, acetone, or a mixture of two or more of the above; The low molecular weight polyamides in the second component include: 650#, 651#, and 300#.

3. The low-shrinkage electromagnetic protective coating according to claim 1, characterized in that, The container is a four-necked flask. The first component is placed into the four-necked flask and stirred and heated. The stirring speed is 500 rpm to 1000 rpm, and the temperature is gradually increased to 80°C to 120°C and kept at that temperature for at least 10 minutes.

4. The low-shrinkage electromagnetic protective coating according to claim 1, characterized in that, The trade names of each raw material component include: Toughening agents, including: Desmocap 14CNB, Desmocap 11A, and Desmocap 12A; Additives, including: leveling agents, antisettling agents, defoamers, wetting and dispersing agents, and coupling agents; Curing agents include: T31, ethylenediamine, G328, G240, IPDA, 1,3-BAC, and D230; Curing accelerators include: benzyl dimethylamine, diethylaminopropylamine, tetramethylethylenediamine, triphenylphosphine, N,N-dimethylaniline, 2-thiol benzothiazole, 2,4,6-tris(dimethylaminomethyl)phenol, and 2-ethyl-4-methylimidazole.

5. The low-shrinkage electromagnetic protective coating according to claim 1, characterized in that, Methods for preparing modified absorbents include: Raw material preparation: Prepare the raw material solution according to the following mass ratios: absorbent: treatment agent: solvent: deionized water = 100: 1~2: 2~5: 0.2~1. Stir the prepared solution. The absorbent includes at least metal absorbents and ferrite absorbents, the treatment agent includes at least a silicon coupling agent, and the solvent includes at least anhydrous ethanol, n-butanol, acetone, and deionized water. Mixing process; mixing and stirring under a protective atmosphere; Drying process: The mixed materials are dried to form powder; Dispersion treatment involves dispersing the powder formed during the drying process.

6. The low-shrinkage electromagnetic protective coating according to claim 5, characterized in that, In the mixing process, a 10L high-speed mixer with an inert gas atmosphere was used. The initial speed of the mixer was 20 rpm. The solution was added and mixed at 20 rpm. The speed was then adjusted to 1000 rpm and mixing continued.

7. The low-shrinkage electromagnetic protective coating according to claim 5, characterized in that, The metal absorbent comprises: Spherical carbonyl iron powder, flake carbonyl iron powder, iron-silicon-aluminum, iron-silicon-chromium, amorphous iron fiber, carbonyl nickel powder, iron-nickel alloy powder, cobalt powder; The ferrites include: barium ferrite, strontium ferrite, and cobalt-containing ferrite; The silicon coupling agents include: KH540, KH550, KH560, KH570, and KH590.

8. The method for preparing the low-shrinkage electromagnetic protective coating according to any one of claims 1-7, characterized in that, include: Step 1, Stirring: Add modified epoxy resin, toughening agent, additives, and solvent to the stirring equipment; Step 2, Premixing: Add the modified absorbent and increase the speed of the stirring equipment; Step 3, Dispersion and Grinding: The material generated in Step 2 is dispersed and ground using a grinding mill; Step 4, sieve filtration: Filter the material after dispersing and grinding in step 3 through a sieve to remove impurities from the material; Step 5, high-speed mixing: Add curing agent, curing accelerator and diluent according to a certain mass ratio, stir and mix for a certain time to generate coating.

9. The method for preparing the low-shrinkage electromagnetic protective coating according to claim 8, characterized in that, Also includes: Step 6, Paint Curing: Let the paint from Step 5 sit for a certain period of time to cure. In step one, the stirring device is used to stir for 30 minutes at a speed of 400 rpm to 600 rpm; In step two, the speed of the stirring device is increased to 900 rpm-1200 rpm; In step three, the grinding machine is a basket mill or a three-roll mill; In step five, the mixing process is carried out for a certain period of time to generate a coating, specifically by mixing and stirring in a mixing device with a rotation speed of 400 rpm to 600 rpm for at least 30 minutes.

10. A low-shrinkage electromagnetic shielding coating, characterized in that, The low-shrinkage electromagnetic protective coating is prepared using the preparation method of the low-shrinkage electromagnetic protective coating as described in claim 8 or 9.

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