Method for preparing wave-absorbing coating by using modified carbon black as wave-absorbing agent

Abstract

The invention relates to the technical field of coating preparation, and particularly discloses a method for preparing a wave-absorbing coating by using modified carbon black as a wave-absorbing agent, which comprises the following steps: modifying N550 carbon black, uniformly mixing with porous ceramic microspheres, and sintering at 1680 DEG C under the protection of argon to prepare the wave-absorbing agent; then adding the water-borne epoxy resin, the water-borne polyurethane emulsion, the mica powder, the flatting agent and the dispersing agent into the solvent, and then adding the curing agent to prepare the wave-absorbing coating. The prepared coating is low in price, high in wave absorbing performance and environmentally friendly, and further has certain wear-resistant and anti-corrosion effects.

Description

Technical Field

[0001] The invention relates to the technical field of coating preparation, and in particular to a method for preparing microwave absorbing coating by using modified carbon black as microwave absorbing agent. Background Art

[0002] With the development of science and technology, electronic products are being used more and more widely in various fields. With the sharp increase in the use of electronic products and the development of wireless communication technology, more and more people are more directly exposed to electromagnetic waves, which seriously endangers people's health. In order to reduce the harm caused by electromagnetic waves, people have begun to conduct research and application from various aspects. Absorbing paint is one of the applications. For example, using absorbing paint on household appliances with strong electromagnetic fields such as microwave ovens and induction cookers can reduce their interference with other electronic equipment and improve their safety of use. Spraying absorbing paint in offices and living rooms can absorb the electromagnetic waves and electronic fog radiated by household appliances and office equipment in offices and living rooms and convert them into harmless substances, while absorbing or isolating most of the external electromagnetic waves.

[0003] The application field of radar-absorbing coatings is relatively wide, but the actual application of radar-absorbing materials has not met expectations because the current radar-absorbing coatings have defects such as high price and poor radar-absorbing ability, which limits the application and promotion of radar-absorbing coatings. Therefore, the above problems need to be solved urgently. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing microwave absorbing coatings by using modified carbon black as microwave absorbing agent, so as to overcome the defects of the prior art and prepare microwave absorbing coatings with low price and strong microwave absorbing performance.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing an absorbing coating by using modified carbon black as an absorbing agent, comprising adding 20 to 40 parts by weight of an aqueous epoxy resin and 2 to 4 parts of an aqueous polyurethane emulsion to 18 to 30 parts of a solvent, stirring and mixing at 300 rpm, and then sequentially adding 14 to 20 parts of an absorbing agent, 8 to 18 parts of mica powder, 1 to 1.5 parts of a leveling agent and 0.5 to 1 part of a dispersant, and after all are added, increasing the speed to 600 rpm, stirring for 10 minutes, and then increasing the speed to 1000 rpm, stirring for 10 minutes, and finally adding 8 to 16 parts of a curing agent, stirring for 20 minutes, and fully mixing; The absorber is prepared by mixing modified carbon black and porous ceramic microspheres in a weight ratio of 4:6 and sintering at 1680°C under argon protection; Preparation of modified carbon black: 100 parts by weight of carbon black and 8 parts by weight of epoxy silane are mixed, heated at 130° C., mixed with 400 parts by weight of ethanol, ball milled, then ultrasonically dispersed, and spray dried to obtain modified carbon black powder; Preparation of porous ceramic microspheres: aluminum oxide, magnesium oxide, calcium oxide, acetylene black powder, polyvinyl alcohol, a special ceramic dispersant and ammonium bicarbonate are added in proportion to deionized water while stirring; the ammonium bicarbonate is heated until it is fully volatilized, and then spray-dried to form microspheres; the microspheres are dried and sintered to obtain porous ceramic microspheres; wherein the weight proportions of aluminum oxide, magnesium oxide, calcium oxide, acetylene black powder, deionized water, polyvinyl alcohol, a special ceramic dispersant and ammonium bicarbonate are 80:10:8:2:150:5:1:15 respectively.

[0006] Preferably, the weight parts of the waterborne epoxy resin are 30 parts, the weight parts of the waterborne polyurethane emulsion are 3 parts, the weight parts of the solvent are 24 parts, the weight parts of the absorber are 17 parts, the weight parts of the mica powder are 13 parts, the weight parts of the leveling agent are 1.25 parts, the weight parts of the dispersant are 0.75 parts, and the weight parts of the curing agent are 12 parts.

[0007] Preferably, the solvent is xylene; the leveling agent is leveling agent BD-3033; the dispersant is dispersant SDJ8009; and the curing agent is aliphatic diisocyanate.

[0008] Preferably, the carbon black is N550 carbon black; the modified carbon black is prepared by adding 8 parts by weight of epoxy silane to 100 parts by weight of N550 carbon black, stirring thoroughly, then heating at 130°C for 1.5 hours, then mixing with 400 parts by weight of ethanol, putting into a ball mill for 5 hours, then treating with an ultrasonic disperser, and then spray drying the dispersed carbon black suspension to obtain a dry modified carbon black powder; wherein the inlet air temperature during spray drying is 200°C, the spray pressure is 2MPa, and the air flow velocity is 20m / s; the ultrasonic disperser has a working power of 1KW, a frequency of 20KHz, and the ultrasonic treatment is for 10 minutes.

[0009] Preferably, the porous ceramic microspheres are prepared by adding 80 parts by weight of aluminum oxide, 10 parts by weight of magnesium oxide, 8 parts by weight of calcium oxide and 2 parts by weight of acetylene black powder to 150 parts by weight of deionized water, then adding 5 parts by weight of polyvinyl alcohol and 1 part by weight of a special ceramic dispersant, and mixing them thoroughly with a magnetic stirrer to obtain a slurry; then adding 15 parts by weight of ammonium bicarbonate to the slurry, and continuing to stir until it is evenly dispersed; heating the slurry to 60 to 70° C., the decomposition temperature of ammonium bicarbonate, and after the ammonium bicarbonate is fully volatilized, atomizing the slurry into microspheres by spray drying; drying the microspheres obtained by spray drying at 40 to 50° C. to remove residual moisture; then sintering the dried microspheres at 1200 to 1500° C. to obtain porous ceramic microspheres; wherein the spray drying conditions are set as a dry air temperature of 200° C., a spray head speed of 10,000 rpm, and a pressure of -120 Pa in the spray tower.

[0010] Furthermore, when preparing the porous ceramic microspheres, the foamed slurry is atomized by spray drying to form microspheres with a particle size of 60 to 200 μm, a pore size of 10 to 800 nm, and a sphericity greater than 95%.

[0011] Furthermore, the decomposition temperature of ammonium bicarbonate is 70°C; the microspheres are dried at 45°C and then sintered at 1350°C.

[0012] Due to the adoption of the above technical solution, the beneficial effects of the present invention are: The present invention can optimize the dielectric properties of the coating through a reasonable ratio of water-based epoxy resin and water-based polyurethane emulsion, and is more environmentally friendly than using other organic substances; by modifying carbon black, the wave absorbing performance of carbon black is improved, and the defects of small absorption peak and narrow absorption bandwidth of carbon black are overcome; at the same time, combined with the wave absorbing performance of porous ceramic microspheres, excessive modified carbon black is mixed and sintered with porous ceramic microspheres, the modified carbon black can be effectively infiltrated into the porous ceramic microspheres and attached to the surface of the porous ceramic microspheres, the electrical conductivity, thermal conductivity and dispersibility of the modified carbon black are fully improved, and finally the wave absorbing performance of the coating is effectively improved; at the same time, because the prices of carbon black and ceramic raw materials are low and the preparation process is simple, the product price can be reduced.

[0013] In short, the coating of the present invention is cheap, has strong wave-absorbing performance, is environmentally friendly, and also has certain wear-resistant and anti-corrosion effects. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further described below in conjunction with embodiments: Among them, the performance parameters and sources of some raw materials are as follows: The water-based epoxy resin is the water-based epoxy resin CYDW-100 produced by Guangzhou Yingrun Chemical Co., Ltd., the water-based polyurethane emulsion is the water-based polyurethane resin emulsion 1624 produced by Shenzhen Yoshida Chemical Co., Ltd., and the leveling agent is the leveling agent BD-3033 produced by Hangzhou Baoerde Silicone Co., Ltd.; the dispersant is the dispersant SDJ8009 produced by Guangdong Sandingjia New Material Technology Co., Ltd., the aliphatic diisocyanate is the aliphatic diisocyanate monomer produced by Shanghai Kain Chemical Co., Ltd., the special dispersant for ceramics is the special dispersant for ceramics produced by Shandong Zhengji Chemical Co., Ltd., the carbon black is the carbon black N550 produced by Qingzhou Bio Carbon Black Co., Ltd., and the acetylene black is the acetylene black produced by Hebei Moyu Chemical Co., Ltd.

[0015] Example 1 Preparation of Radiation Absorbent Preparation of modified carbon black: add 8 grams of epoxy silane to 100 grams of N550 carbon black, stir well, heat at 130°C for 1.5 hours, mix with 400 grams of ethanol, put into a ball mill for 5 hours, and then treat with an ultrasonic disperser (power 1KW, frequency 20KHz, 10 minutes), and then spray dry the dispersed carbon black suspension (inlet air temperature 200°C, spray pressure 2MPa, air flow velocity 20m / s) to obtain dry modified carbon black powder; Preparation of porous ceramic microspheres: 150 g of deionized water, 5 g of polyvinyl alcohol and 1 g of a special ceramic dispersant were added to 80 g of aluminum oxide, 10 g of magnesium oxide, 8 g of calcium oxide and 2 g of acetylene black powder, and the mixture was fully mixed using a magnetic stirrer to obtain a slurry; 15 g of ammonium bicarbonate was added to the slurry, and stirring was continued until the slurry was uniformly dispersed; the slurry was heated to 70°C, the decomposition temperature of ammonium bicarbonate, and after the ammonium bicarbonate was fully volatilized, the foamed slurry was atomized into microspheres using a spray dryer (dry air temperature 200°C, spray head speed 10000 rpm, pressure in the spray tower of -120 Pa), and the obtained microspheres had a particle size of 60 to 200 μm and a pore size of 10 to 800 nm; the spray-dried microspheres were dried in an oven at 45°C to remove residual moisture; the dried microspheres were then sintered at 1350°C in a sintering furnace to obtain porous ceramic microspheres.

[0016] 400 g of modified carbon black and 600 g of porous ceramic microspheres were mixed and then sintered at 1680° C. in an argon-protected sintering furnace to prepare a wave absorbing agent.

[0017] Example 2 Preparation of Radar Absorbing Coating 18 kg of xylene was added to the reactor, and stirring was started at 300 rpm. Then, 20 kg of water-based epoxy resin CYDW-100, 4 kg of water-based polyurethane resin emulsion 1624, 14 kg of the absorber prepared in Example 1, 18 kg of mica powder, 1 kg of leveling agent BD-3033 and 0.5 kg of dispersant SDJ8009 were added in sequence. After all were added, the speed was increased to 600 rpm and stirred for 10 minutes, and then increased to 1000 rpm and stirred for 10 minutes. Finally, 16 kg of aliphatic diisocyanate monomer was added. After the addition was completed, the stirring speed was increased to 1000 rpm and stirred for 20 minutes. The absorbing coating was obtained by fully mixing.

[0018] Example 3 Preparation of Radar Absorbing Coating II 24 kg of xylene was added to the reactor, and stirring was started at 300 rpm. Then, 30 kg of water-based epoxy resin CYDW-100, 3 kg of water-based polyurethane resin emulsion 1624, 17 kg of the absorber prepared in Example 1, 13 kg of mica powder, 1.25 kg of leveling agent BD-3033 and 0.75 kg of dispersant SDJ8009 were added in sequence. After all were added, the speed was increased to 600 rpm and stirred for 10 minutes, and then increased to 1000 rpm and stirred for 10 minutes. Finally, 12 kg of aliphatic diisocyanate monomer was added. After the addition was completed, the stirring speed was increased to 1000 rpm and stirred for 20 minutes. The absorbing coating was obtained by fully mixing.

[0019] Example 4 Preparation of Radar Absorbing Coating III 30 kg of xylene was added to the reactor, and stirring was started at 300 rpm. Then, 40 kg of water-based epoxy resin CYDW-100, 2 kg of water-based polyurethane resin emulsion 1624, 20 kg of the absorber prepared in Example 1, 8 kg of mica powder, 1.5 kg of leveling agent BD-3033 and 1 kg of dispersant SDJ8009 were added in sequence. After all were added, the speed was increased to 600 rpm, stirred for 10 minutes, and then increased to 1000 rpm and stirred for 10 minutes. Finally, 8 kg of aliphatic diisocyanate monomer was added, stirred for 20 minutes, and mixed thoroughly to obtain the absorbing coating.

[0020] Comparative Example 1 In Example 3, the aqueous polyurethane resin emulsion 1624 is not added, and the other steps are the same as those in Example 3.

[0021] Comparative Example 2 In Example 3, the absorber is made by sintering unmodified carbon black and porous ceramic microspheres, and the rest is the same as in Example 3.

[0022] Comparative Example 3 In Example 3, the modified carbon black and porous ceramic microspheres are mixed without sintering to prepare the absorber, and the rest is the same as Example 3.

[0023] The absorbing coatings obtained in Examples 2-4 and Comparative Examples 1-3 were sprayed onto an aluminum plate to prepare a coating with a thickness of 2 mm, and cured at 25° C. for 24 hours to obtain an absorbing coating. The absorbing coating was then subjected to a performance test. The test results are shown in Table 1. The test standards are: Appearance: Observe the absorbing coating visually under scattered sunlight to check its flatness and whether there is sagging, blooming, pinholes, cracking and peeling; Adhesion: According to the provisions of 9.4.3 of GB / T5210-2006; Hardness: According to the provisions of GB / T6739-2006 coating hardness pencil test method.

[0024] Corrosion resistance: According to the provisions of GB / T9274-1988, the acid, alkali and salt water resistance of the coating were tested. The corrosive media were 3wt.% H2SO4 solution, 3wt.% NaOH solution and 2wt.% NaCl solution respectively. The details are as follows: Place the sample horizontally with the coating side facing up, add several drops of the corrosive medium, and keep at least 20mm between the centers of adjacent liquids; place the sample at 23℃ for 24h to allow it to fully contact the air but not be disturbed by other factors; then wash the coating surface thoroughly with clean water and immediately check the coating changes; Wave absorbing performance: 8-18GHz reflectivity is tested using the bow method.

[0025] Table 1 Test results of coatings prepared in Examples 2-4 and Comparative Examples 1-3

[0026] It can be seen from the test results of the products of Examples 2-4 that the combination of different components in Example 3 is the best and its wave absorbing performance is the strongest.

[0027] In Comparative Example 1, there is no water-based polyurethane resin emulsion, the hardness of the absorbing coating is enhanced, and the wear resistance and scratch resistance are improved, but the absorbing performance is reduced; in Comparative Example 2, the carbon black is not modified, and the absorbing performance of the coating is significantly reduced; in Comparative Example 3, the modified carbon black is not sintered with the porous ceramic microspheres, and the absorbing performance of the coating is also significantly reduced.

[0028] Through the above experiments, it can be concluded that the absorber prepared by sintering modified carbon black and porous ceramic microspheres has a strong absorbing ability. At the same time, with the precise ratio of water-based epoxy resin and water-based polyurethane resin emulsion, a cheap, absorbing and environmentally friendly coating product can be produced.

Claims

1. A method for preparing a microwave absorbing coating using modified carbon black as a microwave absorbing agent, characterized in that: 20-40 parts of waterborne epoxy resin and 2-4 parts of waterborne polyurethane emulsion are added to 18-30 parts of solvent by weight, and 14-20 parts of absorber, 8-18 parts of mica powder, 1-1.5 parts of leveling agent and 0.5-1 part of dispersant are added in sequence while stirring at 300 rpm. After all are added, the speed is increased to 600 rpm, stirred for 10 minutes, and then increased to 1000 rpm and stirred for 10 minutes. Finally, 8-16 parts of curing agent are added, stirred for 20 minutes, and fully mixed; The absorber is prepared by mixing modified carbon black and porous ceramic microspheres in a weight ratio of 4:6 and sintering at 1680°C under argon protection; Preparation of modified carbon black: 100 parts by weight of carbon black and 8 parts by weight of epoxy silane are mixed, heated at 130° C., mixed with 400 parts by weight of ethanol, ball milled, then ultrasonically dispersed, and spray dried to obtain modified carbon black powder; Preparation of porous ceramic microspheres: aluminum oxide, magnesium oxide, calcium oxide, acetylene black powder, polyvinyl alcohol, a ceramic special dispersant and ammonium bicarbonate are added in proportion to deionized water while stirring; the ammonium bicarbonate is heated until it is fully volatilized, and then spray-dried to form microspheres; the microspheres are dried and sintered to obtain porous ceramic microspheres.

2. The method for preparing microwave absorbing coating using modified carbon black as microwave absorbing agent according to claim 1, characterized in that: The weight parts of the waterborne epoxy resin are 30 parts, the weight parts of the waterborne polyurethane emulsion are 3 parts, the weight parts of the solvent are 24 parts, the weight parts of the absorber are 17 parts, the weight parts of the mica powder are 13 parts, the weight parts of the leveling agent are 1.25 parts, the weight parts of the dispersant are 0.75 parts, and the weight parts of the curing agent are 12 parts.

3. The method for preparing microwave absorbing coating using modified carbon black as microwave absorbing agent according to claim 1, characterized in that: The solvent is xylene; the leveling agent is leveling agent BD-3033; the dispersant is dispersant SDJ8009; and the curing agent is aliphatic diisocyanate.

4. The method for preparing microwave absorbing coating using modified carbon black as microwave absorbing agent according to claim 1, characterized in that: The modified carbon black is prepared by adding 8 parts by weight of epoxy silane to 100 parts by weight of N550 carbon black, stirring the mixture thoroughly, heating the mixture at 130° C. for 1.5 hours, mixing the mixture with 400 parts by weight of ethanol, and milling the mixture in a ball mill for 5 hours. The mixture is then treated with an ultrasonic disperser, and then the dispersed carbon black suspension is spray-dried to obtain a dried modified carbon black powder. During the spray drying, the air inlet temperature is 200° C., the spray pressure is 2 MPa, and the air flow velocity is 20 m / s. The ultrasonic disperser has a working power of 1 KW, a frequency of 20 KHz, and the ultrasonic treatment lasts for 10 minutes.

5. The method for preparing microwave absorbing coating by using modified carbon black as microwave absorbing agent according to claim 1, characterized in that: The porous ceramic microspheres are prepared by adding 80 parts by weight of aluminum oxide, 10 parts by weight of magnesium oxide, 8 parts by weight of calcium oxide and 2 parts by weight of acetylene black powder to 150 parts by weight of deionized water, fully mixing, then adding 5 parts by weight of polyvinyl alcohol and 1 part by weight of a special ceramic dispersant, and fully mixing with a magnetic stirrer to obtain a slurry; then adding 15 parts by weight of ammonium bicarbonate to the slurry, and continuing to stir until it is uniformly dispersed; heating the slurry to 60-70° C., which is the decomposition temperature of ammonium bicarbonate, and after the ammonium bicarbonate is fully volatilized, atomizing the slurry into microspheres by spray drying; drying the microspheres obtained by spray drying at 40-50° C., and then sintering them at 1200-1500° C. to obtain porous ceramic microspheres; wherein the spray drying conditions are set as a drying air temperature of 200° C., a spray head rotation speed of 10000 rpm, and a pressure in a spray tower of -120 Pa.

6. The method for preparing microwave absorbing coating using modified carbon black as microwave absorbing agent according to claim 5, characterized in that: The ammonium bicarbonate decomposition temperature is 70°C, the microspheres are dried at 45°C, and then sintered at 1350°C.

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