Heat exchanger insulation coating and preparation process thereof

Abstract

This invention relates to the field of coating technology and discloses a heat exchanger insulating coating and its preparation process. The preparation process is as follows: epoxy resin and modified cashew nut shell powder are added to xylene and stirred at 600-800 r / min for 10-15 min. While stirring, a dispersant, defoamer, modified graphene, and titanium dioxide are added sequentially and dispersed at high speed for 20-30 min. Then, the stirring speed is reduced to 300-500 r / min, hollow glass microspheres are added, and the mixture is stirred at low speed for 8-10 min. Finally, a curing agent is added, and stirring is continued for 5-8 min. The mixture is then filtered and allowed to stand to obtain the heat exchanger insulating coating. The heat exchanger insulating coating prepared by this invention has good heat insulation, water resistance, and salt spray resistance properties.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a heat-insulating coating for heat exchangers and its preparation process. Background Technology

[0002] During operation, heat exchangers often face challenges such as high temperature, high pressure, corrosive media, and complex environmental conditions. Their surface temperature is often significantly higher than the surrounding environment, leading to severe heat loss. This not only wastes a lot of energy but can also cause production interruptions due to equipment failure, increasing maintenance costs and creating safety hazards. To improve the thermal efficiency of heat exchangers, extend their service life, and enhance their operational reliability, thermal insulation and protective coatings are usually applied to their surfaces. However, currently common thermal insulation coatings for heat exchangers suffer from an imbalance between thermal insulation and temperature resistance, as well as poor mechanical properties and adaptability to operating conditions, making it difficult to meet the stringent requirements of industrial scenarios. Therefore, avoiding this phenomenon is key to solving the problem.

[0003] For example, patent application CN114181571A discloses a heat-insulating coating and its preparation method. In this heat-insulating coating, acrylic resin, aluminum silicate fiber and alumina gel microspheres have a synergistic effect, which can inhibit the effect of solid and gaseous heat conduction in the heat-insulating coating and improve the heat insulation performance and mechanical properties of the obtained heat-insulating coating. However, the water resistance and salt spray resistance need to be improved. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a heat exchanger insulation coating and its preparation process. The heat exchanger insulation coating prepared by the present invention has good heat insulation, water resistance and salt spray resistance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a heat-insulating coating for heat exchangers, comprising the following weight components: 35-40 parts by weight of epoxy resin, 10-15 parts by weight of modified cashew nut shell, 0.5-1 parts by weight of modified graphene, 12-15 parts by weight of hollow glass microspheres, 6-8 parts by weight of titanium dioxide, 8-12 parts by weight of curing agent, 1-1.5 parts by weight of dispersant, 0.2-0.4 parts by weight of defoamer, and 15-20 parts by weight of xylene;

[0006] The modified cashew phenol is obtained by reacting cashew phenol with epichlorohydrin to obtain epoxy cashew phenol, and then reacting it with hydrogen-terminated silicone oil.

[0007] The modified graphene is obtained by reacting graphene oxide with 2-bromoisobutyryl bromide, followed by reaction with diperfluorobutyl ethyl itaconic acid.

[0008] Furthermore, the preparation method of the modified cashew phenol is as follows:

[0009] Step 1: Add cashew nut shellac, epichlorohydrin, and tetrabutylammonium bromide to the reactor, heat to 90-100℃, stir for 3-4 hours, then cool to 40-50℃, add 10% sodium hydroxide aqueous solution to the system, adjust the pH to 7-8, add ethyl acetate, stir for 0.5-1 hours, separate the organic layer, wash the organic layer with saturated brine, dry with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to obtain epoxy cashew nut shellac;

[0010] In the above steps, the phenolic hydroxyl group of cashew phenol undergoes a ring-opening etherification reaction with the epoxy group of epichlorohydrin, and then the epoxy group is introduced into the cashew phenol molecule through intramolecular ring closure to generate epoxy cashew phenol with epoxy group.

[0011] Step 2: Under nitrogen protection, add epoxy cashew phenol and hydrogen-terminated silicone oil to toluene solvent, heat to 90-100℃, add isopropanol solution of chloroplatinic acid dropwise, then heat to 105-115℃ and react for 5-7 hours. After the reaction is complete, cool to room temperature, then add an equal volume of deionized water and wash 3-4 times. After each wash, allow the mixture to stand and separate the layers. Separate the organic layer, dry the obtained organic layer with anhydrous sodium sulfate for 12-14 hours, filter, concentrate the precipitate, wash and dry to obtain modified cashew phenol.

[0012] In the above steps, the unsaturated double bonds in the epoxy cashew phenol molecule and the active silane-hydrogen bonds in the terminal hydrogen-containing silicone oil undergo a hydrosilylation reaction under the action of chloroplatinic acid catalyst, grafting the silicon-containing segments onto the cashew phenol molecule through stable C-Si bonds, to obtain modified cashew phenol containing organosilicon segments.

[0013] Furthermore, in step one, the ratio of cashew phenol, epichlorohydrin, tetrabutylammonium bromide, and ethyl acetate is 6-7g:18-21g:0.15-0.2g:8-9g.

[0014] Furthermore, in step two, the ratio of the amount of toluene, epoxy cashew phenol, hydrogen-terminated silicone oil, and isopropanol solution of chloroplatinic acid is 60-80mL:5-6g:35-38g:0.1-0.12mL.

[0015] Furthermore, the method for preparing the modified graphene is as follows:

[0016] S1: Add concentrated sulfuric acid and concentrated phosphoric acid to the reactor and mix to prepare a solution. In an ice-water bath at 0-5℃, disperse graphite powder and potassium permanganate in the mixed solution. Then stir and react at 50-60℃ for 12-14 hours. Pour the mixture onto ice containing 30% hydrogen peroxide by mass, filter, and wash 2-3 times with deionized water, 30% concentrated hydrochloric acid by mass, and ethanol, respectively. Centrifuge and filter to obtain graphene oxide.

[0017] S2: Add graphene oxide and triethylamine to N,N-dimethylformamide solvent, ultrasonically disperse for 15-20 min, add 2-bromoisobutyryl bromide dropwise under 0-5℃ ice-water bath conditions, stir at room temperature for 24-26 h after the addition is complete, wash and centrifuge to obtain brominated graphene oxide.

[0018] In the above steps, the hydroxyl groups on the surface of graphene oxide undergo an esterification reaction with the acyl bromide group of 2-bromoisobutyryl bromide, introducing bromoisobutyryl groups onto the surface of graphene oxide to obtain brominated graphene oxide. Triethylamine acts as an acid-binding agent to neutralize the hydrogen bromide generated in the reaction and promote the forward reaction.

[0019] S3: Under nitrogen protection, itaconic acid, p-toluenesulfonic acid, and perfluorobutylethanol are added to the reactor, stirred and mixed, and reacted at 130-140℃ for 5-7 hours. After the reaction is completed, the mixture is cooled to room temperature, washed and dried to obtain diperfluorobutyl ethyl itaconic acid.

[0020] In the above steps, the two carboxyl groups of itaconic acid and the hydroxyl group of perfluorobutyl ethanol undergo an esterification reaction under the catalysis of p-toluenesulfonic acid, removing two water molecules to obtain diperfluorobutyl ethyl itaconic acid with double bonds.

[0021] S4: Add brominated graphene oxide, difluorobutyl ethyl itaconic acid, and pentamethyldiethylenetriamine to N,N-dimethylformamide solvent, and ultrasonically disperse for 15-20 min. Place the reaction system in a complete nitrogen environment using a freeze-evacuate-thaw method. Then add cuprous bromide and stir at 60-70℃ for 24-26 h. After the reaction is complete, wash and centrifuge, and vacuum dry at 40-50℃ for 3-4 h to obtain modified graphene.

[0022] In the above steps, bromoisobutyryl groups on the surface of brominated graphene oxide are used as initiators, di-perfluorobutyl ethyl itaconic acid is used as a monomer, and cuprous bromide / pentamethyldiethylenetriamine is used as a catalytic system. Fluorine-containing segments are grafted onto the surface of graphene oxide through atom transfer radical polymerization to obtain modified graphene.

[0023] Furthermore, the ratio of concentrated sulfuric acid, concentrated phosphoric acid, graphite powder, potassium permanganate, and hydrogen peroxide with a mass fraction of 30% in S1 is 360-400mL:40-50mL:3-3.3g:18-19.5g:3-3.3mL.

[0024] Furthermore, the ratio of N,N-dimethylformamide, graphene oxide, triethylamine, and 2-bromoisobutyryl bromide in S2 is 50-60 mL: 1-1.2 g: 6-7 mL: 10-12 mL.

[0025] Furthermore, the ratio of itaconic acid, p-toluenesulfonic acid, and perfluorobutyl ethanol in S3 is 1-1.1g:0.01-0.02g:4.3-4.4g.

[0026] Furthermore, the ratio of N,N-dimethylformamide, brominated graphene oxide, difluorobutyl ethyl itaconic acid, pentamethyldiethylenetriamine, and cuprous bromide in S4 is 12-15 mL: 0.1-0.12 g: 4.5-4.6 g: 62-64 μL: 85-87 mg.

[0027] Further, the preparation process of the heat exchanger insulation coating is as follows: epoxy resin and modified cashew phenol are added to xylene, and stirred at 600-800 r / min for 10-15 min while maintaining stirring. Dispersant, defoamer, modified graphene, and titanium dioxide are added sequentially, and dispersed at high speed for 20-30 min. Then, the speed is reduced to 300-500 r / min, hollow glass microspheres are added, and stirred at low speed for 8-10 min. Finally, curing agent is added, and stirring is continued for 5-8 min. The mixture is then filtered, allowed to stand, and the heat exchanger insulation coating is obtained.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] This invention modifies cashew nut shells with silicon, allowing the modified cashew nut shells to synergistically form a film with epoxy resin. The introduced organosilicon segments act as a flexible framework to alleviate internal stress in the coating. Combined with modified graphene, this forms a uniform mechanical reinforcement network within the coating, enhancing the mechanical properties and adhesion of the coating. The fluorine-containing segments grafted onto the modified graphene surface possess low surface energy and hydrophobic properties, forming a dense hydrophobic barrier on the coating surface to prevent the adsorption and penetration of corrosive media such as moisture and salt spray. Simultaneously, the dense coating structure formed by the cross-linking of the modified cashew nut shell's organosilicon segments with epoxy resin further blocks the transmission channels of corrosive media, thereby improving the coating's water resistance and salt spray resistance. Hollow glass microspheres are used as the core thermal insulation filler. Their hollow structure can encapsulate still air, and combined with the uniform dispersion and barrier effect of modified graphene, a highly efficient dual thermal insulation system is constructed, endowing the coating with excellent thermal insulation performance and heat resistance stability. Attached Figure Description

[0030] Figure 1 This is the infrared spectrum of the modified cashew phenol in Example 1;

[0031] Figure 2 This is an electron microscope image of the modified cashew phenol in Example 1;

[0032] Figure 3 This is the infrared spectrum of the modified graphene in Example 1;

[0033] Figure 4This is an electron microscope image of the modified graphene in Example 1. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. 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.

[0035] The reagents used in the following specific embodiments are of analytical grade. Additionally:

[0036] Epoxy resin: Grade E51, industrial grade;

[0037] Dispersant: Model BYK-163;

[0038] Defoamer: Model BYK-035;

[0039] Graphite powder: fixed carbon content 98%;

[0040] Titanium dioxide: grade DHA-100;

[0041] Hollow glass microspheres: grade HS46, industrial grade;

[0042] Phenolic amine curing agent: brand name T-31, industrial grade;

[0043] Hydrogen-containing silicone oil: hydrogen content 0.18%;

[0044] Isopropanol solution of chloroplatinic acid: chloroplatinic acid content is 2 mg / mL.

[0045] Example 1

[0046] (1) Add 6g of cashew nut powder, 18g of epichlorohydrin and 0.15g of tetrabutylammonium bromide to the reactor, heat to 90°C, stir for 3h, then cool to 40°C, add 10% sodium hydroxide aqueous solution to the system, adjust the pH to 7, add 8g of ethyl acetate, stir for 0.5h, separate the organic layer, wash the organic layer with saturated brine, dry with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to obtain epoxy cashew nut powder;

[0047] (2) Under nitrogen protection, 5g of epoxy cashew phenol and 35g of end-hydrogen silicone oil were added to 60mL of toluene solvent. The temperature was raised to 90℃, and 0.1mL of isopropanol solution of chloroplatinic acid was added dropwise. The temperature was then raised to 105℃ and the reaction was carried out for 5h. After the reaction was completed, the mixture was cooled to room temperature. Then an equal volume of deionized water was added and the mixture was washed 3 times. After each wash, the mixture was allowed to stand and separate into layers. The organic layer was separated and dried with anhydrous sodium sulfate for 12h. The mixture was then filtered, concentrated and precipitated, washed and dried to obtain modified cashew phenol.

[0048] (3) Add 360 mL of concentrated sulfuric acid and 40 mL of concentrated phosphoric acid to the reactor and mix to prepare a solution. In an ice-water bath at 0°C, disperse 3 g of graphite powder and 18 g of potassium permanganate in the mixed solution. Then stir the reaction at 50°C for 12 h. Pour the mixture onto ice containing 3 mL of 30% hydrogen peroxide, filter, and wash twice with deionized water, 30% hydrochloric acid and ethanol, centrifuge, and filter to obtain graphene oxide.

[0049] (4) Add 1g of graphene oxide and 6mL of triethylamine to 50mL of N,N-dimethylformamide solvent, sonicate for 15min, add 10mL of 2-bromoisobutyryl bromide dropwise under 0℃ ice-water bath conditions, stir at room temperature for 24h after the addition is complete, wash and centrifuge to obtain brominated graphene oxide.

[0050] (5) Under nitrogen protection, 1g of itaconic acid, 0.01g of p-toluenesulfonic acid and 4.3g of perfluorobutylethanol were added to the reactor, stirred and mixed, and reacted at 130°C for 5h. After the reaction was completed, the mixture was cooled to room temperature, washed and dried to obtain di-perfluorobutyl ethyl itaconic acid.

[0051] (6) Add 0.1 g of brominated graphene oxide, 4.5 g of difluorobutyl ethyl itaconic acid, and 62 μL of pentamethyldiethylenetriamine to 12 mL of N,N-dimethylformamide solvent. Disperse the mixture by sonication for 15 min. Place the reaction system in a complete nitrogen environment by freezing-evacuation-thawing. Then add 85 mg of cuprous bromide and stir at 60 °C for 24 h. After the reaction is completed, wash and centrifuge the mixture and vacuum dry it at 40 °C for 3 h to obtain modified graphene.

[0052] (7) Add 35 parts by weight of epoxy resin and 10 parts by weight of modified cashew phenol to 15 parts by weight of xylene, stir at 600 r / min for 10 min, and continue stirring. Then add 1 part by weight of dispersant, 0.2 parts by weight of defoamer, 0.5 parts by weight of modified graphene and 6 parts by weight of titanium dioxide in sequence, disperse at high speed for 20 min, then reduce the speed to 300 r / min, add 12 parts by weight of hollow glass microspheres, stir at low speed for 8 min, and finally add 8 parts by weight of curing agent, continue stirring for 5 min, filter, and let stand to obtain heat insulation coating for heat exchangers.

[0053] from Figure 1 It can be seen that at 3400 cm -1 The characteristic peak of the phenolic hydroxyl group of cashew phenol was significantly weakened at 910 cm⁻¹. -1 Characteristic peak of epoxy ring at 2160 cm⁻¹ -1 The Si-H characteristic peaks completely disappeared at 2924 cm⁻¹; -1 2854 cm -1 A saturated CH stretching vibration peak appears at 1600 cm⁻¹. -1 1585 cm -1 1510 cm -1 The benzene ring skeletal vibration peak is retained at 1260 cm⁻¹. -1 The characteristic peaks of Si-CH3 appear at 1020-1090 cm⁻¹. -1 Extremely strong characteristic peaks of the Si-O-Si main chain appear at 800-820 cm⁻¹. -1 The presence of Si-C / Si-CH3 superimposed characteristic peaks confirms the formation of stable C-Si covalent bonds. These results indicate that cardamom nutshellol was successfully grafted with organosilicon segments after epoxylation and hydrosilylation reactions, resulting in the successful preparation of the target modified cardamom nutshellol.

[0054] from Figure 2 As can be seen, the modified cashew nut shell phenol exhibits a continuous and dense organic phase structure. Its fracture cross-section displays typical ductile fracture characteristics, with an uneven surface and abundant nanoscale wrinkles and clusters, completely altering the smooth and flat morphology of the original cashew nut shell phenol. This transformation from smooth to rough morphology reflects the construction of a highly cross-linked network between molecular chains and the effective modification of the matrix by organosilicon segments. Furthermore, the absence of obvious microcracks or pore defects caused by phase separation in the matrix indicates that the reaction process was controlled and the product structure was uniform. These morphological characteristics, at the microscopic level, confirm the successful preparation of the target modified cashew nut shell phenol.

[0055] from Figure 3 It can be seen that at 3400 cm -1The characteristic peak of hydroxyl groups in graphene oxide is significantly weakened; the characteristic peak of the monomer C=C double bond (1640 cm⁻¹) is also significantly weakened. -1 ) and C-Br characteristic peak (560 cm) -1 650 cm -1 Completely disappeared; at 2926 cm -1 2855 cm -1 An alkyl chain CH stretching vibration peak appears at 1732 cm⁻¹. -1 A strong ester carbonyl characteristic peak appears at 1630 cm⁻¹. -1 The C=C vibration peak of the graphene framework is retained at 1230 cm⁻¹. -1 1190 cm -1 1145 cm -1 A series of extremely strong CF characteristic absorption peaks appear at 1100 cm⁻¹. -1 A broad peak appears at 830 cm⁻¹, representing the superposition of COC stretching vibration and CF secondary absorption. -1 805 cm -1 650 cm -1 625 cm -1 The characteristic peaks of the perfluoroalkyl fingerprint region appeared. These results indicate that after bromination modification of graphene oxide to introduce ATRP initiation sites, itaconic acid di-perfluorobutyl ethyl ester fluoropolymer segments were successfully grafted onto the graphene oxide via atom transfer radical polymerization, resulting in the successful preparation of the target modified graphene.

[0056] from Figure 4 As can be seen, the modified graphene retains the typical continuous wrinkled sheet matrix structure of graphene, with a large number of spherical polymer microphase regions ranging in size from tens to hundreds of nanometers uniformly dispersed in the matrix. Some large-sized microspheres show cracks on their surfaces due to stress release. The microphase regions are tightly bonded to the matrix interface, with no obvious large agglomerates. These morphological characteristics indicate that polymer segments have been successfully grafted onto the graphene surface, and typical microphase separation has occurred, indicating that the target modified graphene has been successfully prepared.

[0057] Example 2

[0058] (1) Add 7g of cashew nut powder, 21g of epichlorohydrin and 0.2g of tetrabutylammonium bromide to the reactor, heat to 100℃, stir for 4h, then cool to 50℃, add 10% sodium hydroxide aqueous solution to the system, adjust the pH to 8, add 9g of ethyl acetate, stir for 1h, separate the organic layer, wash the organic layer with saturated brine, dry with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to obtain epoxy cashew nut powder;

[0059] (2) Under nitrogen protection, 6g of epoxy cashew phenol and 38g of end-hydrogen silicone oil were added to 80mL of toluene solvent. The temperature was raised to 100℃, and 0.12mL of isopropanol solution of chloroplatinic acid was added dropwise. The temperature was then raised to 115℃ and the reaction was carried out for 7h. After the reaction was completed, the mixture was cooled to room temperature. Then an equal volume of deionized water was added and the mixture was washed 4 times. After each wash, the mixture was allowed to stand and separate into layers. The organic layer was separated and dried with anhydrous sodium sulfate for 14h. The mixture was then filtered, concentrated and precipitated, washed and dried to obtain modified cashew phenol.

[0060] (3) Add 400 mL of concentrated sulfuric acid and 50 mL of concentrated phosphoric acid to the reactor and mix to prepare a solution. In an ice-water bath at 5 °C, disperse 3.3 g of graphite powder and 19.5 g of potassium permanganate in the mixed solution. Then stir and react at 60 °C for 14 h. Pour the mixture onto ice containing 3.3 mL of 30% hydrogen peroxide, filter, and wash three times with deionized water, 30% hydrochloric acid and ethanol respectively. Centrifuge and filter to obtain graphene oxide.

[0061] (4) Add 1.2 g of graphene oxide and 7 mL of triethylamine to 60 mL of N,N-dimethylformamide solvent, sonicate for 20 min, add 12 mL of 2-bromoisobutyryl bromide dropwise under 5 °C ice-water bath conditions, stir at room temperature for 26 h after the addition is complete, wash and centrifuge to obtain brominated graphene oxide.

[0062] (5) Under nitrogen protection, 1.1 g of itaconic acid, 0.02 g of p-toluenesulfonic acid and 4.4 g of perfluorobutyl ethanol were added to the reactor, stirred and mixed, and reacted at 140 °C for 7 h. After the reaction was completed, the mixture was cooled to room temperature, washed and dried to obtain di-perfluorobutyl ethyl itaconic acid.

[0063] (6) Add 0.12 g of brominated graphene oxide, 4.6 g of difluorobutyl ethyl itaconic acid and 64 μL of pentamethyldiethylenetriamine to 15 mL of N,N-dimethylformamide solvent, sonicate for 20 min, place the reaction system in a complete nitrogen environment by freezing-evacuation-thawing, then add 87 mg of cuprous bromide, stir at 70 °C for 26 h, after the reaction is completed, wash and centrifuge, and vacuum dry at 50 °C for 4 h to obtain modified graphene;

[0064] (7) Add 40 parts by weight of epoxy resin and 15 parts by weight of modified cashew phenol to 20 parts by weight of xylene, stir at 800 r / min for 15 min, and continue stirring. Then add 1.5 parts by weight of dispersant, 0.4 parts by weight of defoamer, 1 part by weight of modified graphene and 8 parts by weight of titanium dioxide in sequence, disperse at high speed for 30 min, then reduce the speed to 500 r / min, add 15 parts by weight of hollow glass microspheres, stir at low speed for 10 min, and finally add 12 parts by weight of curing agent. Continue stirring for 8 min, filter, and let stand to obtain the heat insulation coating for heat exchangers.

[0065] Example 3

[0066] (1) Add 6.5g of cashew nut powder, 20.5g of epichlorohydrin and 0.18g of tetrabutylammonium bromide to the reactor, heat to 95°C, stir for 3.5h, then cool to 45°C, add 10% sodium hydroxide aqueous solution to the system, adjust the pH to 7, add 8.5g of ethyl acetate, stir for 1h, separate the organic layer, wash the organic layer with saturated brine, dry with anhydrous sodium sulfate, and remove the solvent by rotary evaporation to obtain epoxy cashew nut powder;

[0067] (2) Under nitrogen protection, 5.5 g of epoxy cashew phenol and 36 g of end-hydrogen silicone oil were added to 70 mL of toluene solvent. The temperature was raised to 95 °C, and 0.11 mL of isopropanol solution of chloroplatinic acid was added dropwise. The temperature was then raised to 110 °C and the reaction was carried out for 6 h. After the reaction was completed, the mixture was cooled to room temperature and then an equal volume of deionized water was added. The mixture was washed 3 times. After each wash, the mixture was allowed to stand and separate into layers. The organic layer was separated and dried with anhydrous sodium sulfate for 13 h. The organic layer was then filtered, concentrated, precipitated, washed and dried to obtain modified cashew phenol.

[0068] (3) Add 380 mL of concentrated sulfuric acid and 45 mL of concentrated phosphoric acid to the reactor and mix to prepare a solution. In an ice-water bath at 2 °C, disperse 3.15 g of graphite powder and 19 g of potassium permanganate in the mixed solution. Then stir the reaction at 55 °C for 13 h. Pour the mixture onto ice containing 3.15 mL of 30% hydrogen peroxide, filter, wash twice with deionized water, 30% hydrochloric acid and ethanol, centrifuge, filter, and obtain graphene oxide.

[0069] (4) Add 1.1 g of graphene oxide and 6.5 mL of triethylamine to 55 mL of N,N-dimethylformamide solvent, sonicate for 18 min, add 11 mL of 2-bromoisobutyryl bromide dropwise under 2℃ ice-water bath conditions, stir at room temperature for 25 h after the addition is complete, wash and centrifuge to obtain brominated graphene oxide.

[0070] (5) Under nitrogen protection, 1.05 g of itaconic acid, 0.01 g of p-toluenesulfonic acid and 4.35 g of perfluorobutyl ethanol were added to the reactor, stirred and mixed, and reacted at 135 °C for 6 h. After the reaction was completed, the mixture was cooled to room temperature, washed and dried to obtain di-perfluorobutyl ethyl itaconic acid.

[0071] (6) Add 0.11 g of brominated graphene oxide, 4.55 g of difluorobutyl ethyl itaconic acid and 63 μL of pentamethyldiethylenetriamine to 13 mL of N,N-dimethylformamide solvent, sonicate for 18 min, place the reaction system in a complete nitrogen environment by freezing-evacuation-thawing, then add 86 mg of cuprous bromide, stir at 65 °C for 25 h, after the reaction is completed, wash and centrifuge, and vacuum dry at 45 °C for 3 h to obtain modified graphene;

[0072] (7) Add 38 parts by weight of epoxy resin and 12 parts by weight of modified cashew phenol to 18 parts by weight of xylene, stir at 700 r / min for 12 min, and continue stirring. Then add 1.2 parts by weight of dispersant, 0.3 parts by weight of defoamer, 0.8 parts by weight of modified graphene and 7 parts by weight of titanium dioxide in sequence, disperse at high speed for 25 min, then reduce the speed to 400 r / min, add 13 parts by weight of hollow glass microspheres, stir at low speed for 9 min, and finally add 10 parts by weight of curing agent, continue stirring for 6 min, filter, and let stand to obtain heat insulation coating for heat exchangers.

[0073] Comparative Example 1

[0074] The main difference between this comparative example and Example 3 is that epoxy cashew phenol is used instead of modified cashew phenol.

[0075] Comparative Example 2

[0076] The main difference between this comparative example and Example 3 is that graphene oxide is used instead of modified graphene.

[0077] Comparative Example 3

[0078] The main difference between this comparative example and Example 3 is that the timing of adding the hollow glass microspheres and the stirring method are changed.

[0079] The specific steps are as follows: In step (7), 38 parts by weight of epoxy resin and 12 parts by weight of modified cashew phenol are added to 18 parts by weight of xylene. Stir at 700 r / min for 12 min. Keep stirring and add 1.2 parts by weight of dispersant, 0.3 parts by weight of defoamer, 0.8 parts by weight of modified graphene, 7 parts by weight of titanium dioxide and 13 parts by weight of hollow glass microspheres in sequence. Disperse at high speed for 25 min. Then add 10 parts by weight of curing agent and continue stirring for 6 min. Filter and let stand to obtain the heat insulation coating for heat exchangers.

[0080] Comparative Example 4

[0081] The main difference between this comparative example and Example 3 is that the amount of dispersant used is 0.6 parts by weight.

[0082] Performance testing

[0083] The heat exchangers prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to performance testing using heat-insulating coatings.

[0084] (1) Mechanical properties and adhesion tests

[0085] The flexibility of the coating was tested according to GB / T1731-2020 "Determination of Flexibility of Paint Film and Putty Film"; the impact resistance of the coating was tested according to GB / T1732-2020 "Determination of Impact Resistance of Paint Film"; and the adhesion of the coating in dry and wet conditions was tested according to GB / T5210-2006 "Adhesion Test of Paint and Varnish by Pull-Off Method". The test results are shown in Table 1.

[0086] Table 1: Mechanical Properties and Adhesion Tests

[0087]

[0088] As can be seen from Table 1, the heat exchanger insulation coatings prepared in Examples 1-3 have good mechanical properties and adhesion.

[0089] (2) Thermal insulation performance test

[0090] The thermal conductivity of the coating was tested according to GB / T10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method"; the retention rate of thermal insulation performance of the coating after high-temperature aging was tested according to GB / T1735-2009 "Determination of Heat Resistance of Paints and Varnishes". The test results are shown in Table 2.

[0091] Table 2: Thermal Insulation Performance Test

[0092]

[0093] As can be seen from Table 2, the heat exchanger insulation coatings prepared in Examples 1-3 have good heat insulation performance.

[0094] (3) Water resistance and salt spray resistance tests

[0095] The water resistance of the coating was tested according to GB / T1733-1993 "Determination of Water Resistance of Coating Film"; the salt spray resistance of the coating was tested according to GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". The test results are shown in Table 3.

[0096] Table 3: Water resistance and salt spray resistance tests

[0097]

[0098] As can be seen from Table 3, the heat exchanger insulation coatings prepared in Examples 1-3 have good water resistance and salt spray resistance.

[0099] The comparison shows that Comparative Example 1, which uses epoxy cashew phenol instead of modified cashew phenol, lacks organosilicon segments and cannot alleviate the internal stress of the coating. This leads to increased brittleness after film formation, increased flexibility to 2 mm, decreased impact resistance to 45 kg·cm, and decreased dry adhesion to 6.2 MPa. Furthermore, the lack of low surface energy characteristics of organosilicon segments weakens the hydrophobic effect of the coating, allowing water molecules to easily penetrate and worsening the bonding between the microbeads and resin. This results in a thermal conductivity increase to 0.075 W / (m·K), a decrease in water resistance to 816 h, and a decrease in salt spray resistance to 1206 h. Comparative Example 2, which uses graphene oxide instead of modified graphene, has a surface rich in oxygen-containing functional groups, making it prone to aggregation and poor dispersibility. This accelerates heat transfer, causing the thermal conductivity to increase to 0.068 W / (m·K). Lacking the low surface energy and hydrophobic properties of fluorine-containing segments, it cannot prevent the adsorption of water and salt ions, thus reducing water resistance to 895 h and salt spray resistance to [missing information]. The haze resistance decreased to 1458h; Comparative Example 3 changed the timing of adding hollow glass microspheres and the stirring method. High-speed dispersion caused a large number of microspheres to break, destroying the hollow structure and losing the core heat insulation function, resulting in the thermal conductivity increasing to 0.098W / (m·K). Moreover, the broken microsphere fragments and pores would destroy the continuous film structure of the coating, becoming stress concentration points and channels for corrosive media penetration, making it easier for corrosive media to penetrate into the interior of the coating. Therefore, the neutral salt spray resistance time dropped sharply to 956h; Comparative Example 4 used 0.6 parts by weight of dispersant. The powder could not be effectively dispersed and formed agglomerates. The poor density of the agglomerates would destroy the continuous structure of the coating, accelerate heat transfer, and increase the thermal conductivity to 0.085W / (m·K). At the same time, the agglomerate interface became a defect point, becoming a preferred penetration path in water and corrosive media, resulting in the water resistance decreasing to 654h and the salt spray resistance decreasing to 1129h.

[0100] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0101] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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 of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0102] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments.

Claims

1. A heat insulating coating material for a heat exchanger, characterized by comprising: It comprises the following components by weight: 35-40 parts by weight of epoxy resin, 10-15 parts by weight of modified cashew nut shell, 0.5-1 parts by weight of modified graphene, 12-15 parts by weight of hollow glass microspheres, 6-8 parts by weight of titanium dioxide, 8-12 parts by weight of curing agent, 1-1.5 parts by weight of dispersant, 0.2-0.4 parts by weight of defoamer, and 15-20 parts by weight of xylene; The modified cashew phenol is obtained by reacting cashew phenol with epichlorohydrin to obtain epoxy cashew phenol, and then reacting it with hydrogen-terminated silicone oil. The modified graphene is obtained by reacting graphene oxide with 2-bromoisobutyryl bromide, followed by reaction with diperfluorobutyl ethyl itaconic acid.

2. The heat exchanger insulation paint according to claim 1, characterized by The method for preparing the modified cashew phenol is as follows: Step 1: Cashew nut phenol reacts with epichlorohydrin in the presence of tetrabutylammonium bromide to obtain epoxy cashew nut phenol; Step 2: Dissolve epoxy cashew phenol and hydrogen-terminated silicone oil in toluene solvent, and react them under the catalysis of isopropanol solution of chloroplatinic acid to obtain modified cashew phenol.

3. The heat exchanger insulation paint according to claim 2, characterized by In step one, the ratio of cashew phenol, epichlorohydrin, and tetrabutylammonium bromide is 6-7g:18-21g:0.15-0.2g.

4. The heat exchanger insulation paint according to claim 2, characterized by In step two, the ratio of the amount of epoxy cashew phenol, hydrogen-terminated silicone oil, toluene, and isopropanol solution of chloroplatinic acid is 5-6g:35-38g:60-80mL:0.1-0.12mL.

5. The heat exchanger insulation paint according to claim 1, characterized by, The method for preparing the modified graphene is as follows: S1: Graphite powder and potassium permanganate are reacted in a mixed acid of concentrated sulfuric acid and concentrated phosphoric acid to obtain graphene oxide; S2: Graphene oxide and 2-bromoisobutyryl bromide are dissolved in N,N-dimethylformamide and reacted in the presence of triethylamine to obtain brominated graphene oxide. S3: Itaconic acid and perfluorobutyl ethanol are reacted under the catalysis of p-toluenesulfonic acid to obtain diperfluorobutyl ethyl itaconic acid; S4: Brominated graphene oxide and di-perfluorobutyl ethyl itaconic acid are dissolved in N,N-dimethylformamide solvent and reacted under the catalysis of pentamethyldiethylenetriamine and cuprous bromide to obtain modified graphene.

6. The heat-insulating coating for heat exchangers according to claim 5, characterized in that, The ratio of graphite powder, potassium permanganate, concentrated sulfuric acid, and concentrated phosphoric acid in S1 is 3-3.3g:18-19.5g:360-400mL:40-50mL.

7. The heat exchanger insulation paint according to claim 5, wherein The ratio of graphene oxide, 2-bromoisobutyryl bromide, N,N-dimethylformamide, and triethylamine in S2 is 1-1.2g:10-12mL:50-60mL:6-7mL.

8. The heat exchanger insulation paint according to claim 5, wherein The ratio of itaconic acid, perfluorobutyl ethanol, and p-toluenesulfonic acid in S3 is 1-1.1g:4.3-4.4g:0.01-0.02g.

9. The heat exchanger insulation paint according to claim 5, wherein The ratio of the amounts of brominated graphene oxide, difluorobutyl ethyl itaconic acid, N,N-dimethylformamide, pentamethyldiethylenetriamine, and cuprous bromide in S4 is 0.1-0.12g:4.5-4.6g:12-15mL:62-64μL:85-87mg.

10. A process for the preparation of a heat exchanger insulation coating as claimed in any one of claims 1 to 9, characterized in that, The preparation process of the heat exchanger insulation coating is as follows: epoxy resin and modified cashew nut powder are added to xylene and stirred at 600-800 r / min for 10-15 min. While stirring, dispersant, defoamer, modified graphene, and titanium dioxide are added in sequence and dispersed at high speed for 20-30 min. Then, the speed is reduced to 300-500 r / min, hollow glass microspheres are added, and the mixture is stirred at low speed for 8-10 min. Finally, curing agent is added, and stirring is continued for 5-8 min. The mixture is then filtered and allowed to stand to obtain the heat exchanger insulation coating.

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