A graphene water-based coating

Abstract

This invention provides a water-based graphene coating comprising highly dispersed graphene, which is obtained by anodic-cathode exfoliation. By preparing a nickel foam cage, multiple electrode exfoliations can be effectively achieved, avoiding large-area exfoliation or electrode dissociation of the electrode material, thereby obtaining few-layer graphene.

Description

Technical Field

[0001] This invention relates to an aqueous epoxy resin coating, and more specifically, to an epoxy resin coating containing highly dispersed graphene. Background Technology

[0002] Epoxy resin refers to resin compounds whose molecules contain at least two reactive epoxy groups. It is a thermosetting resin, and since its introduction in 1930 and industrial production in the United States in 1947, it has been used for over 50 years. Epoxy resin (EP) is one of the most widely used matrix resins in polymer-based composites. It is a product obtained by the polycondensation reaction of epichlorohydrin with bisphenol A or polyols, polyphenols, polyacids, polyamines, etc., and is widely used in adhesives, electronic instruments, light industry, construction, machinery, aerospace, coatings, bonding, electronic and electrical insulation materials, and advanced composite matrix materials.

[0003] Epoxy resin has many outstanding properties, such as strong adhesion to various materials, especially metals, excellent chemical resistance, high mechanical strength, good electrical insulation, and corrosion resistance. In addition, epoxy resin can be cured over a fairly wide temperature range, and the volume shrinkage during curing is very small. Due to these important characteristics, it has very important applications in many fields, and is widely used in adhesives, coatings, composite materials, etc., such as (1) good processability: Epoxy resin, especially low molecular weight resin, becomes a flowing liquid at room temperature or with slight heating due to its small molecular weight. This makes it easy to mix with various reagents, facilitates full reaction with curing agents, is conducive to the uniform addition of various fillers, is easy to make into various styles, and is simple to operate. (2) high adhesiveness: Epoxy resin has unique adhesive ability. It can bond various metal and non-metal materials and is known as "universal glue". This is due to the presence of hydroxyl, ether groups and extremely active epoxy functional groups in the molecular structure of epoxy resin. Hydroxyl and ether groups are highly polar, and the attraction between opposite poles causes epoxy resin molecules to generate electromagnetic attraction with adjacent interfaces. Epoxy groups can react with free bonds on the surface of the medium, especially the metal surface, to form chemical bonds, thus epoxy resin has particularly strong adhesion. (3) Fast chemical reaction rate: Epoxy resin generally has a relatively fast chemical reaction rate, especially when amines are used as curing agents, it hardens even faster. Depending on different needs, it can be cured and hardened within minutes to hours, and has sufficient strength. (4) Low shrinkage: The shrinkage rate of general plastics and rubber products is relatively large, while epoxy resin reacts with the curing agent through a direct addition reaction, without the production of other by-products or gases, so its spontaneous shrinkage rate is very small. Its coefficient of thermal expansion is also very small, generally 6×10. -5 / ℃ means that for every 10 meters of epoxy plastic, the temperature increases by 1℃ and the elongation is 0.6 mm, so its deformation is relatively small. (5) High mechanical strength: Because epoxy resin contains epoxy groups, ether groups and hydroxyl groups, the intermolecular attraction is enhanced. After curing, the epoxy resin changes from a linear structure to a three-dimensional structure. At the same time, its structure is compact, so its mechanical strength is high. (6) Excellent chemical resistance: Because the cured epoxy resin contains stable benzene rings and ether bonds, and the hydroxyl groups of epoxy resin do not react chemically with alkali, and the phenolic hydroxyl groups in the cured epoxy resin have been etherified, and the existing hydroxyl groups have fatty alcohol properties, so the cured epoxy resin has excellent chemical corrosion resistance.

[0004] Graphene is a two-dimensional sheet-like nanomaterial formed by a single layer of carbon atoms with sp2 hybridization. The theoretical thickness of a single layer of graphene is about 0.35 nm, and the σ-σ bond length between two adjacent carbon atoms is about 0.187 nm. In principle, graphene refers to graphite with a single atom thickness, but in actual research, any graphite with less than ten atomic layers stacked in the thickness direction can be called graphene.

[0005] Graphene composite coatings are organic coatings using graphene as a filler, representing an application of graphene / polymer composite materials. Researchers both domestically and internationally have conducted extensive work in this field, and currently, commonly used graphene-reinforced coatings include epoxy resin coatings, polyurethane coatings, and polyacrylic resin coatings. Among these, research on graphene-reinforced epoxy resin composite coatings is the most mature.

[0006] Epoxy resins possess advantages such as strong adhesion, good thermal stability, low cost, and convenient curing, making them the most commonly chosen film-forming material in organic coatings. Developing composite coatings by combining graphene with waterborne epoxy resins leverages graphene's large specific surface area and excellent chemical stability to mitigate the erosion of the substrate material by corrosive media and extend its service life. Summary of the Invention

[0007] This invention provides a graphene-based water-based coating, characterized in that the water-based coating is composed of the following components in parts by weight:

[0008] 20-60 parts water-based epoxy resin;

[0009] 30-60 parts curing agent;

[0010] 20-40 parts of highly dispersed graphene;

[0011] 1-2 parts wetting and dispersing agent;

[0012] 1-5 parts film-forming aid;

[0013] 0.5-1 defoamer;

[0014] Deionized water.

[0015] The mass percentages of the components in the highly dispersed graphene solution are as follows: graphene 5-50 wt.%, alkylphenol polyoxyethylene ether 1-2 wt.%, glycerol 20-30 wt.%, and the balance deionized water.

[0016] The curing agent is selected from at least one of diaminodiphenylmethane, diaminodiphenyl ether, or dicyandiamide.

[0017] The wetting and dispersing agent is BYK-P104 dispersant.

[0018] The film-forming aid is propylene glycol methyl ether.

[0019] The defoamer is selected from BYK-054 defoamer.

[0020] A method for preparing a graphene-based waterborne coating includes the following steps:

[0021] (I) Add the highly dispersed graphene solution to deionized water and ultrasonically disperse for 10-15 min, then add waterborne epoxy resin and wetting and dispersing agent, stir for 30 min, and ultrasonically disperse for 30 min.

[0022] (II) Add curing agent, defoamer and film-forming aid, stir for 10 minutes until the system is uniform to obtain graphene / waterborne epoxy resin composite coating;

[0023] The highly dispersed graphene is prepared by the following steps:

[0024] (1) Preparation of three-dimensional bulk graphene cathode material:

[0025] (a) Preparation of graphene aqueous solution by the Hummer method;

[0026] (b) Centrifugation to obtain graphene sol;

[0027] (c) Preparation of bulk graphene by hydrothermal method: The temperature is increased to 150℃ at a heating rate of 10-15℃ / min and held for 2 hours, then increased to 300-320℃ at a heating rate of 10-15℃ / min and held for 30-40 hours, then cooled to room temperature, filtered, frozen in a refrigerator for 10-12 hours, and then freeze-dried to remove excess water to obtain bulk graphene. The bulk graphene is cylindrical in shape with a diameter of 2-3 cm and a height of 5-8 cm. The macropores of the bulk graphene are in the range of 30-80 μm and the mesopores are in the range of 10-15 nm.

[0028] (2) Preparation of graphene cathode nickel foam cage: Nickel foam is cut and bent to obtain nickel foam cylindrical cage. The upper end of the nickel foam cylindrical cage is not closed and is connected to the negative power supply wire. The lower end is closed. The pore size of the nickel foam is 0.5-3mm and the porosity is ≥95%. The size of the nickel foam cylindrical cage is larger than the size of the block graphene. The block graphene is put into the nickel foam cylindrical cage through the unclosed part of the upper end.

[0029] (3) First anode stripping: The bulk graphene obtained in step (c) is placed in a nickel foam cylindrical cage, and then the upper end is sealed. The nickel foam cylindrical cage sinks to the bottom of the electrolyte. The nickel foam cylindrical cage is connected to the power supply wire as the anode and the platinum electrode as the cathode. The electrolyte is 95-98 wt.% H2SO4, DC power supply, voltage is 5-7V, time is 3-5min. Take it out and clean the nickel foam cylindrical cage with deionized water.

[0030] (4) Secondary cathode stripping: Then connect the foamed nickel cylindrical cage to the cathode, Pt sheet as anode, and use tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF as electrolyte, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.3-0.7mol / L, the concentration of hexadecyltrimethylammonium chloride is 1-2g / L, and the cathode stripping is performed at a constant voltage of 5-10V for 1-2h.

[0031] (5) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and washing with ethanol, and then disperse the graphene a second time using alkylphenol polyoxyethylene ether, glycerol and deionized water. The second dispersion is carried out by a high-shear homogenizer at 10000-15000 rpm for 2-4 hours at a temperature of 10-20℃. The resulting highly dispersed graphene solution is obtained. The mass fractions of each component in the highly dispersed graphene solution are as follows:

[0032] Graphene 5-50 wt.%, alkylphenol polyoxyethylene ether 1-2 wt.%, glycerol 20-30 wt.%, and balance deionized water.

[0033] The present invention needs to clarify the problems existing in the prior art: (1) The prior art usually uses chemical oxidation-reduction method or anodic exfoliation method to prepare graphene materials. For example, the chemical oxidation-reduction method for preparing graphene mainly utilizes the mixed reaction of graphite and strong oxidant. In graphene oxide (GO), a large number of oxygen-containing functional groups such as hydroxyl, epoxy and carboxyl groups are covalently bonded to the bottom and edge of graphene. The electrochemical method is to apply voltage in the electrolyte to promote the intercalation of ions into the graphite interlayer, causing it to expand and fall off to obtain graphene sheets. Both methods have a significant problem: by using harsh conditions or electrical conditions, the edge points and grain boundaries of graphite are attacked. Oxidation reaction occurs at the edge points and grain boundaries, causing depolarization and expansion of the graphite interlayer. Then, insertion is performed. That is, the material obtained is graphene oxide, not graphene material; (2) The problem of electrochemical exfoliation, regardless of Whether it is anodic or cathodic stripping, the electrolytic material is usually graphite, such as natural flake graphite, microcrystalline graphite, artificial graphite, highly oriented pyrolytic graphite, graphite rods or graphite paper. The electrochemical stripping process is not stripping layer by layer. This leads to the graphite in pieces entering the electrolyte before it is completely stripped, and thus cannot be further stripped, resulting in extremely low stripping efficiency. (3) Graphite material is not simply graphite material. In order to maintain the shape of the electrode during the electrolysis process, binders and thickeners need to be added to the graphite, which leads to a decrease in the conductivity of the graphite and low stripping efficiency.

[0034] Based on the above problems, this invention uses bulk graphene oxide as raw material. The material is subjected to oxidation-reduction and hydrothermal treatment to obtain bulk graphene monoliths. These bulk graphene monoliths have high mechanical strength, good stability, and a large specific surface area. The mechanical strength endows them with electrode potential, and the specific surface area allows for a large peeling area, facilitating multi-directional peeling and making it easier to obtain graphene materials with a low number of layers. Then, the graphene is placed in a nickel foam cage, which acts as both the anode and cathode. The nickel foam has a porous structure, so if the bulk graphene undergoes large-area sheet peeling or block dissociation, the peeled portion can be effectively confined within the nickel foam cage and continue to peel as an electrode. Only when peeled to a very small size and a small number of layers can it escape the nickel foam cage and become a suspension. The electrolysis process includes a primary anode peeling assistance and a secondary cathode peeling to obtain highly dispersed graphene materials. The radial size of the graphene is less than 3 μm, the number of layers is less than 10, the yield is high, there is no obvious oxidation, and there are few defects. When applied to the field of epoxy resin coatings, the resulting coatings have extremely high physicochemical properties such as corrosion resistance.

[0035] Specifically, this invention first refers to CN108404949B from Xi'an Petroleum University, and by modifying some parameters, obtains bulk graphene with high mechanical strength, good stability, and large specific surface area. The preparation process includes (a) preparing graphene aqueous solution by the Hummer method: adding 25 ml of concentrated sulfuric acid to a flask, cooling to 0-2°C, adding 0.5 g of natural flake graphite, 0.5 g of NaNO3, and 3 g of... KMnO4 particles were stirred evenly; then the flask was placed in a constant temperature water bath at 35℃±2℃. When the temperature of the reaction solution rose to 35±2℃, stirring was continued; then 46ml of deionized water was added to the solution, and the mixture was stirred at 98±2℃ for 15min. After the high-temperature reaction, 140ml of deionized water and 3ml of H2O2 (30wt.%) were added and reacted for 40min; finally, the graphene oxide solution was washed with 1-3wt% HCl solution, and then washed several times with deionized water until neutral to obtain graphene oxide ink solution; (b) Centrifugation to obtain graphene sol: Centrifugation was performed at 2000rpm for 1-2min, the supernatant was taken, and then centrifuged at 9000rpm for 3- (c) Prepare bulk graphene by hydrothermal method: heat to 150℃ at a heating rate of 10-15℃ / min, hold for 2 hours, then heat to 300-320℃ at a heating rate of 10-15℃ / min, hold for 30-40 hours, cool to room temperature, then filter, freeze in a refrigerator for 10-12 hours, and then freeze dry to remove excess water to obtain bulk graphene. The bulk graphene is cylindrical with a diameter of 2-3 cm and a height of 5-8 cm. The macropores of the bulk graphene are in the range of 30-80 μm, and the mesopores are in the range of 10-15 nm.

[0036] The aforementioned block graphene is then placed in a self-made nickel foam cage and submerged to the bottom of the electrolyte. The upper part of the nickel foam cage can be opened to facilitate the insertion of graphene. Electrode stripping will only occur when the graphene comes into contact with the nickel foam; otherwise, electrochemical stripping will not be possible.

[0037] Then, an anodic stripping is performed: the bulk graphene is placed in a nickel foam cylindrical cage, and the upper end is sealed. The nickel foam cylindrical cage sinks to the bottom of the electrolyte. The nickel foam cylindrical cage is connected to a power supply wire as the anode, and a platinum electrode is used as the cathode. The electrolyte is 95-98 wt.% H2SO4, the power supply is DC, the voltage is 5-7V, and the time is 3-5 minutes. After removal, the nickel foam cylindrical cage is rinsed with deionized water. During the first anodic stripping process, the three-dimensional bulk graphene undergoes pretreatment. The bulk graphene will expand significantly, with the overall volume expanding by 1.5-2 times, indicating that the interlayer spacing of the graphene has significantly expanded. During the first anodic stripping process, it should be noted that since strong concentrated sulfuric acid is used, the nickel foam needs to be passivated to avoid unnecessary ion introduction and material loss. In addition, the anodic stripping process should not be too long to avoid excessive oxidation of the graphene bulk.

[0038] Then, a secondary cathode stripping process is performed. The cathode treatment uses an organic solution system with cations as the electrolyte, and a positive potential is applied to the cathode to initiate the stripping process. This process is non-oxidative and does not cause graphene oxidation, thus ensuring the integrity of the graphene structure. Tetrabutylammonium ions gradually insert into the edges and interior of the multilayer graphene. Subsequently, the bulk graphene can be clearly observed to expand further. Graphene with fewer layers can effectively overflow its cage and float into the electrolysis. The cathode stripping electrolyte of this invention also includes a cationic surfactant, hexadecyltrimethylammonium chloride. With the insertion of tetrabutylammonium ions, the interlayer spacing of the graphene is further stretched. The long-chain cations in the cationic surfactant further enter and expand the multilayer graphene structure until thinner graphene sheets gradually detach from the surface of the bulk graphene.

[0039] The thinner graphene in the electrolyte is then collected and dispersed a second time for use as an epoxy resin coating.

[0040] Beneficial technical effects: (1) The present invention uses monolithic graphene as raw material and obtains highly dispersed, few-layer graphene dispersion through anode-cathode peeling; (2) By preparing a foamed nickel cage, multiple electrode peeling can be effectively achieved, avoiding large-area peeling or electrode dissociation of electrode materials, thereby obtaining few-layer graphene; (3) By using graphene as a filler in epoxy resin coating, the highly dispersed graphene makes the coating have the characteristics of high corrosion resistance, high density, high bonding force and high hardness. Attached Figure Description

[0041] Appendix Figure 1 TEM and HTEM images of the graphene prepared in Example 4 of this invention.

[0042] Appendix Figure 2 Raman diagrams of Embodiment 4 and Comparative Example 1 of the present invention.

[0043] Appendix Figure 3 SEM images of embodiments and comparative examples of the present invention.

[0044] Appendix Figure 4 Tafel polarization curve test of an embodiment of the present invention.

[0045] Appendix Figure 5 Salt spray corrosion resistance tests of Examples 5-7 of this invention. Detailed Implementation Example 1

[0046] A graphene-based waterborne coating is prepared by the following steps:

[0047] (I) Add the highly dispersed graphene solution to deionized water and ultrasonically disperse for 15 min. Then add waterborne epoxy resin and wetting and dispersing agent, stir for 30 min, and ultrasonically disperse for 30 min.

[0048] (II) Add curing agent, defoamer and film-forming aid, stir for 10 minutes until the system is uniform, and then the graphene / waterborne epoxy resin composite coating is obtained.

[0049] The highly dispersed graphene is prepared by the following steps.

[0050] (1) Preparation of three-dimensional bulk graphene cathode material.

[0051] (a) Preparation of graphene aqueous solution by Hummer method: 25 ml of concentrated sulfuric acid was added to a flask and cooled to 0 °C. 0.5 g of natural flake graphite, 0.5 g of NaNO3, and 3 g of KMnO4 particles were added while stirring and stirred until homogeneous. The flask was then placed in a constant temperature water bath at 35 °C ± 2 °C. When the temperature of the reaction solution rose to 35 ± 2 °C, stirring was continued. 46 ml of deionized water was added to the solution and stirred at 98 ± 2 °C for 15 min. After the high-temperature reaction, 140 ml of deionized water and 3 ml of H2O2 (30 wt.%) were added and reacted for 40 min. Finally, the graphene oxide solution was washed with 2 wt% HCl solution and then washed multiple times with deionized water until neutral to obtain the graphene oxide ink solution.

[0052] (b) Centrifugation to obtain graphene sol: Centrifuge at 2000 rpm for 1.5 min, collect the supernatant, then centrifuge at 9000 rpm for 4 min, collect the undiluted sol to remove incompletely oxidized aggregated graphite and obtain high-quality graphene oxide sol.

[0053] (c) Preparation of bulk graphene by hydrothermal method: The temperature is increased to 150°C at a heating rate of 12.5°C / min and held for 2 hours, then increased to 310°C at a heating rate of 12.5°C / min and held for 35 hours, then cooled to room temperature, filtered, frozen in a refrigerator for 11 hours, and then freeze-dried to remove excess moisture to obtain bulk graphene, wherein the bulk graphene is cylindrical in shape.

[0054] (2) Preparation of graphene cathode nickel foam cage: Nickel foam is cut and bent to obtain nickel foam cylindrical cage. The upper end of the nickel foam cylindrical cage is not closed and is connected to the negative power supply wire. The lower end is closed. The size of the nickel foam cylindrical cage is larger than the size of the block graphene. The block graphene is put into the nickel foam cylindrical cage through the unclosed part of the upper end.

[0055] (3) First anode stripping: The bulk graphene obtained in step (c) is placed in a nickel foam cylindrical cage, and then the upper end is sealed. The nickel foam cylindrical cage sinks to the bottom of the electrolyte. The nickel foam cylindrical cage is connected to the power supply wire as the anode and the platinum electrode as the cathode. The electrolyte is 95wt.%H2SO4, the power supply is DC, the voltage is 5V, and the time is 3min. The cage is then removed and cleaned with deionized water.

[0056] (4) Secondary cathode stripping: Then connect the foamed nickel cylindrical cage to the cathode, Pt sheet as anode, and use tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF as electrolyte, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.3mol / L and the concentration of hexadecyltrimethylammonium chloride is 1g / L, and the cathode stripping is performed at a constant voltage of 5V for 1h.

[0057] (5) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and washing with ethanol, and then disperse the graphene again by alkylphenol polyoxyethylene ether, glycerol and deionized water. The secondary dispersion is carried out by a high shear homogenizer at 10000 rpm for 2 hours at 10℃. The high dispersion graphene solution is obtained. The mass ratio of each component in the high dispersion graphene solution is as follows.

[0058] Graphene 20 wt.%, alkylphenol polyoxyethylene ether 1 wt.%, glycerol 20 wt.%, and balance deionized water. Example 2

[0059] A graphene-based waterborne coating is prepared by the following steps:

[0060] (I) Add the highly dispersed graphene solution to deionized water and ultrasonically disperse for 15 min. Then add waterborne epoxy resin and wetting and dispersing agent, stir for 30 min, and ultrasonically disperse for 30 min.

[0061] (II) Add curing agent, defoamer and film-forming aid, stir for 10 minutes until the system is uniform, and then the graphene / waterborne epoxy resin composite coating is obtained.

[0062] The highly dispersed graphene is prepared by the following steps.

[0063] (1) Preparation of three-dimensional bulk graphene cathode material:

[0064] (a) Preparation of graphene aqueous solution by Hummer method: 25 ml of concentrated sulfuric acid was added to a flask and cooled to 0 °C. 0.5 g of natural flake graphite, 0.5 g of NaNO3, and 3 g of KMnO4 particles were added while stirring and stirred until homogeneous. The flask was then placed in a constant temperature water bath at 35 °C ± 2 °C. When the temperature of the reaction solution rose to 35 ± 2 °C, stirring was continued. 46 ml of deionized water was added to the solution and stirred at 98 ± 2 °C for 15 min. After the high-temperature reaction, 140 ml of deionized water and 3 ml of H2O2 (30 wt.%) were added and reacted for 40 min. Finally, the graphene oxide solution was washed with 2 wt% HCl solution and then washed multiple times with deionized water until neutral to obtain the graphene oxide ink solution.

[0065] (b) Centrifugation to obtain graphene sol: Centrifuge at 2000 rpm for 1.5 min, collect the supernatant, then centrifuge at 9000 rpm for 4 min, collect the undiluted sol to remove incompletely oxidized aggregated graphite and obtain high-quality graphene oxide sol.

[0066] (c) Preparation of bulk graphene by hydrothermal method: The temperature is increased to 150°C at a heating rate of 12.5°C / min and held for 2 hours, then increased to 310°C at a heating rate of 12.5°C / min and held for 35 hours, then cooled to room temperature, filtered, frozen in a refrigerator for 11 hours, and then freeze-dried to remove excess moisture to obtain bulk graphene, wherein the bulk graphene is cylindrical in shape.

[0067] (2) Preparation of graphene cathode nickel foam cage: Nickel foam is cut and bent to obtain nickel foam cylindrical cage. The upper end of the nickel foam cylindrical cage is not closed and is connected to the negative power supply wire. The lower end is closed. The size of the nickel foam cylindrical cage is larger than the size of the block graphene. The block graphene is put into the nickel foam cylindrical cage through the unclosed part of the upper end.

[0068] (3) First anode stripping: The bulk graphene obtained in step (c) is placed in a nickel foam cylindrical cage, and then the upper end is sealed. The nickel foam cylindrical cage sinks to the bottom of the electrolyte. The nickel foam cylindrical cage is connected to the power supply wire as the anode and the platinum electrode as the cathode. The electrolyte is 97wt.%H2SO4, the DC power supply is 6V, and the time is 4min. The cage is then removed and cleaned with deionized water.

[0069] (4) Secondary cathode stripping: Then connect the foamed nickel cylindrical cage to the cathode, Pt sheet as anode, and use tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF as electrolyte, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.5mol / L, the concentration of hexadecyltrimethylammonium chloride is 1.5g / L, and the cathode stripping is performed at a constant voltage of 7.5V for 1.5h.

[0070] (5) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and washing with ethanol, and then disperse the graphene again by alkylphenol polyoxyethylene ether, glycerol and deionized water. The secondary dispersion is carried out by a 12500 high shear homogenizer for 3 hours at a temperature of 15°C. The high-dispersed graphene solution is obtained. The mass ratio of each component in the high-dispersed graphene solution is as follows.

[0071] The composition consists of 30 wt.% graphene, 1.5 wt.% alkylphenol polyoxyethylene ether, 25 wt.% glycerol, and the balance being deionized water. Example 3

[0072] A graphene-based waterborne coating is prepared by the following steps:

[0073] (I) Add the highly dispersed graphene solution to deionized water and ultrasonically disperse for 15 min. Then add waterborne epoxy resin and wetting and dispersing agent, stir for 30 min, and ultrasonically disperse for 30 min.

[0074] (II) Add curing agent, defoamer and film-forming aid, stir for 10 minutes until the system is uniform, and then the graphene / waterborne epoxy resin composite coating is obtained.

[0075] The highly dispersed graphene is prepared by the following steps.

[0076] (1) Preparation of three-dimensional bulk graphene cathode material.

[0077] (a) Preparation of graphene aqueous solution by Hummer method: 25 ml of concentrated sulfuric acid was added to a flask and cooled to 0 °C. 0.5 g of natural flake graphite, 0.5 g of NaNO3, and 3 g of KMnO4 particles were added while stirring and stirred until homogeneous. The flask was then placed in a constant temperature water bath at 35 °C ± 2 °C. When the temperature of the reaction solution rose to 35 ± 2 °C, stirring was continued. 46 ml of deionized water was added to the solution and stirred at 98 ± 2 °C for 15 min. After the high-temperature reaction, 140 ml of deionized water and 3 ml of H2O2 (30 wt.%) were added and reacted for 40 min. Finally, the graphene oxide solution was washed with 2 wt% HCl solution and then washed multiple times with deionized water until neutral to obtain the graphene oxide ink solution.

[0078] (b) Centrifugation to obtain graphene sol: Centrifuge at 2000 rpm for 1.5 min, collect the supernatant, then centrifuge at 9000 rpm for 4 min, collect the undiluted sol to remove incompletely oxidized aggregated graphite and obtain high-quality graphene oxide sol.

[0079] (c) Preparation of bulk graphene by hydrothermal method: The temperature is increased to 150°C at a heating rate of 15°C / min and held for 2 hours. Then the temperature is increased to 320°C at a heating rate of 15°C / min and held for 40 hours. The temperature is then reduced to room temperature, filtered, frozen in a refrigerator for 12 hours, and then freeze-dried to remove excess moisture to obtain bulk graphene.

[0080] (2) Preparation of graphene cathode nickel foam cage: Nickel foam is cut and bent to obtain nickel foam cylindrical cage. The upper end of the nickel foam cylindrical cage is not closed and is connected to the negative power supply wire. The lower end is closed. The size of the nickel foam cylindrical cage is larger than the size of the block graphene. The block graphene is put into the nickel foam cylindrical cage through the unclosed part of the upper end.

[0081] (3) First anode stripping: The bulk graphene obtained in step (c) is placed in a nickel foam cylindrical cage, and then the upper end is sealed. The nickel foam cylindrical cage sinks to the bottom of the electrolyte. The nickel foam cylindrical cage is connected to the power supply wire as the anode and the platinum electrode as the cathode. The electrolyte is 98wt.%H2SO4, the power supply is DC, the voltage is 7V, and the time is 5min. The cage is then removed and cleaned with deionized water.

[0082] (4) Secondary cathode stripping: Then connect the foamed nickel cylindrical cage to the cathode, Pt sheet as anode, and use tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF as electrolyte, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.7mol / L, the concentration of hexadecyltrimethylammonium chloride is 2g / L, and the cathode stripping is performed at a constant voltage of 10V for 2h.

[0083] (5) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and washing with ethanol, and then disperse the graphene a second time using alkylphenol polyoxyethylene ether, glycerol and deionized water. The second dispersion is carried out by a high-shear homogenizer at 15000 rpm for 4 h at 20℃. The resulting highly dispersed graphene solution is as follows:

[0084] The composition consists of 50 wt.% graphene, 2 wt.% alkylphenol polyoxyethylene ether, 30 wt.% glycerol, and the balance being deionized water. Example 4

[0085] A graphene-based waterborne coating is prepared by the following steps:

[0086] (1) Preparation of three-dimensional bulk graphene cathode material:

[0087] (a) Preparation of graphene aqueous solution by Hummer method: 25 ml of concentrated sulfuric acid was added to a flask and cooled to 0 °C. 0.5 g of natural flake graphite, 0.5 g of NaNO3, and 3 g of KMnO4 particles were added while stirring and stirred until homogeneous. The flask was then placed in a constant temperature water bath at 35 °C ± 2 °C. When the temperature of the reaction solution rose to 35 ± 2 °C, stirring was continued. 46 ml of deionized water was added to the solution and stirred at 98 ± 2 °C for 15 min. After the high-temperature reaction, 140 ml of deionized water and 3 ml of H2O2 (30 wt.%) were added and reacted for 40 min. Finally, the graphene oxide solution was washed with 2 wt% HCl solution and then washed multiple times with deionized water until neutral to obtain the graphene oxide ink solution.

[0088] (b) Centrifugation to obtain graphene sol: Centrifuge at 2000 rpm for 1.5 min, collect the supernatant, then centrifuge at 9000 rpm for 4 min, collect the undiluted sol to remove incompletely oxidized aggregated graphite and obtain high-quality graphene oxide sol.

[0089] (c) Preparation of bulk graphene by hydrothermal method: The temperature is increased to 150°C at a heating rate of 12.5°C / min and held for 2 hours, then increased to 310°C at a heating rate of 12.5°C / min and held for 35 hours, then cooled to room temperature, filtered, frozen in a refrigerator for 11 hours, and then freeze-dried to remove excess moisture to obtain bulk graphene, wherein the bulk graphene is cylindrical in shape.

[0090] (2) Preparation of graphene cathode nickel foam cage: Nickel foam is cut and bent to obtain nickel foam cylindrical cage. The upper end of the nickel foam cylindrical cage is not closed and is connected to the negative power supply wire. The lower end is closed. The size of the nickel foam cylindrical cage is larger than the size of the block graphene. The block graphene is put into the nickel foam cylindrical cage through the unclosed part of the upper end.

[0091] (3) First anode stripping: The bulk graphene obtained in step (c) is placed in a nickel foam cylindrical cage, and then the upper end is sealed. The nickel foam cylindrical cage sinks to the bottom of the electrolyte. The nickel foam cylindrical cage is connected to the power supply wire as the anode and the platinum electrode as the cathode. The electrolyte is 97wt.%H2SO4, the DC power supply is 6V, and the time is 4min. The cage is then removed and cleaned with deionized water.

[0092] (4) Secondary cathode stripping: Then connect the foamed nickel cylindrical cage to the cathode, Pt sheet as anode, and use tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF as electrolyte, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.5mol / L, the concentration of hexadecyltrimethylammonium chloride is 1.5g / L, and the cathode stripping is performed at a constant voltage of 7.5V for 1.5h.

[0093] (5) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and washing with ethanol to obtain graphene, named S-4.

[0094] Comparative Example 1.

[0095] A highly dispersed graphene was prepared by the following steps.

[0096] (1) Preparation of graphene cathode nickel foam cage: Nickel foam is cut and bent to obtain nickel foam cylindrical cage. The upper end of the nickel foam cylindrical cage is not closed and is connected to the negative power supply wire. The lower end is closed. The size of the nickel foam cylindrical cage is larger than the size of the block graphene. The carbon rod is placed into the nickel foam cylindrical cage through the unclosed part of the upper end.

[0097] (2) First anode stripping: The nickel foam cylindrical cage is submerged at the bottom of the electrolyte. The nickel foam cylindrical cage is connected to the power supply wire as the anode and the platinum electrode as the cathode. The electrolyte is 97wt.%H2SO4, the power supply is DC, the voltage is 6V, and the time is 4min. The cage is then removed and cleaned with deionized water.

[0098] (3) Secondary cathode stripping: Then connect the foamed nickel cylindrical cage to the cathode, Pt sheet as anode, and use tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF as electrolyte, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.5mol / L, the concentration of hexadecyltrimethylammonium chloride is 1.5g / L, and the cathode stripping is performed at a constant voltage of 7.5V for 1.5h.

[0099] (4) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and ethanol washing, and obtain graphene, named D-1.

[0100] Comparative Example 2.

[0101] A highly dispersed graphene was prepared by the following steps.

[0102] (1) First anode stripping: Graphite is used as the anode and platinum electrode is used as the cathode. The electrolyte is 97wt.%H2SO4, DC power supply, voltage is 6V, time is 4min. Remove and clean the foamed nickel cylindrical cage with deionized water.

[0103] (2) Secondary cathode stripping: A graphite rod is used as the cathode, a Pt sheet is used as the anode, and tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF are used as electrolytes, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.5 mol / L, the concentration of hexadecyltrimethylammonium chloride is 1.5 g / L, and the cathode stripping is performed at a constant voltage of 7.5 V for 1.5 h.

[0104] (3) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and ethanol washing, and obtain graphene, named D-2.

[0105] Comparative Example 3.

[0106] A highly dispersed graphene was prepared by the following steps.

[0107] (1) Secondary cathode stripping: a graphite rod is used as the cathode, a Pt sheet is used as the anode, and tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF are used as electrolytes, wherein the concentration of tetrabutylammonium hexafluorophosphate is 0.5 mol / L, the concentration of hexadecyltrimethylammonium chloride is 1.5 g / L, and the cathode stripping is performed at a constant voltage of 7.5 V for 1.5 h.

[0108] (2) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and washing with ethanol, and obtain graphene, named D-3.

[0109] The graphite rods in Comparative Examples 1-3 all need to undergo degreasing with organic solvents, impurity removal with hydrochloric acid, and deionization cleaning.

[0110] See appendix Figure 1 The graphene images prepared in Example 2 are shown, where A is a bulk transmission electron microscope (TEM) image and (B) is a high-magnification TEM image. It can be observed that the number of graphene layers is approximately 5-8, with a spacing of 0.4 nm between each layer.

[0111] See appendix Figure 2 The graphene obtained in Example 4 and Comparative Example 1 was subjected to Raman testing at 1350 cm⁻¹. -1 1574cm -1 And 2710cm -1 Diffraction peaks appeared at the locations, corresponding to the D, G, and 2D peaks of the carbon material, respectively. The G and 2D peak in Example 4 were significantly stronger than those in Comparative Example 1, indicating that both Example 4 and Comparative Example 1 obtained graphene sheets. However, compared to Comparative Example 1, the graphene in Example 4 had fewer layers and the corresponding sheets were thinner, consistent with the TEM and SEM results.

[0112] See appendix Figure 3 SEM images of graphite rods and graphene blocks clearly show that the graphene blocks obtained through reduction-oxidation-reduction and hydrothermal treatment can maintain the three-dimensional structure of graphene. However, during the hydrothermal process, significant stacking and aggregation occurred between the graphene sheets in order to form the shape. In addition, Comparative Example 1 is a simple graphene electrode, which is different from the graphite raw material in Example 4. Compared with Comparative Example 1 and Example 4, the graphene obtained in Example 2 showed significant expansion, intercalation, and exfoliation. Furthermore, as with Comparative Example 2 and Comparative Example 3, Comparative Example 2 did not have an electrode cage, and the layers were partially exfoliated in sheets. As shown in the SEM of Comparative Example 2, some layers were severely stacked, and some showed signs of separation. Although these sheets also experienced local exfoliation, the overall sheets were thicker and had larger lateral dimensions, resulting in poor overall exfoliation effect. However, as with Comparative Example 3, if only cathode exfoliation was performed, the exfoliation effect was poor. Based on the above, Comparative Example 1 demonstrates the importance of graphite raw material, Comparative Example 2 demonstrates the influence of the electrode cage on multiple exfoliations of the electrochemical cathode, and Comparative Example 3 demonstrates the importance of a single anode exfoliation for electrochemical exfoliation. Example 5

[0113] A graphene-based waterborne coating is prepared by the following steps:

[0114] (I) Add the highly dispersed graphene solution to deionized water and ultrasonically disperse for 15 min. Then add waterborne epoxy resin and wetting and dispersing agent, stir for 30 min, and ultrasonically disperse for 30 min.

[0115] (II) Add curing agent, defoamer and film-forming aid, stir for 10 minutes until the system is uniform, and then the graphene / waterborne epoxy resin composite coating is obtained.

[0116] The highly dispersed graphene was obtained using the preparation method of Example 4. The graphene obtained in Example 4 was then further dispersed using alkylphenol polyoxyethylene ether, glycerol, and deionized water. The secondary dispersion was performed using a 12500 high-shear homogenizer for 3 hours at 15°C. The resulting highly dispersed graphene solution contained the following components by mass: 30 wt.% graphene, 1.5 wt.% alkylphenol polyoxyethylene ether, 25 wt.% glycerol, and the balance deionized water.

[0117] The water-based coating is composed of the following components in parts by weight:

[0118] 40 parts water-based epoxy resin;

[0119] 30 parts curing agent;

[0120] 20 parts of highly dispersed graphene;

[0121] 1.5 parts wetting and dispersing agent;

[0122] 2 parts film-forming aid;

[0123] 0.75% defoamer;

[0124] Deionized water. Example 6

[0125] A graphene-based waterborne coating is prepared by the following steps:

[0126] (I) Add the highly dispersed graphene solution to deionized water and ultrasonically disperse for 15 min. Then add waterborne epoxy resin and wetting and dispersing agent, stir for 30 min, and ultrasonically disperse for 30 min.

[0127] (II) Add curing agent, defoamer and film-forming aid, stir for 10 minutes until the system is uniform, and then the graphene / waterborne epoxy resin composite coating is obtained.

[0128] The highly dispersed graphene was obtained using the preparation method of Example 4. The graphene obtained in Example 4 was then further dispersed using alkylphenol polyoxyethylene ether, glycerol, and deionized water. The secondary dispersion was performed using a 12500 high-shear homogenizer for 3 hours at 15°C. The resulting highly dispersed graphene solution contained the following components by mass: 30 wt.% graphene, 1.5 wt.% alkylphenol polyoxyethylene ether, 25 wt.% glycerol, and the balance deionized water.

[0129] The water-based coating is composed of the following components in parts by weight:

[0130] 40 parts water-based epoxy resin;

[0131] 30 parts curing agent;

[0132] 30 parts of highly dispersed graphene;

[0133] 1.5 parts wetting and dispersing agent;

[0134] 2 parts film-forming aid;

[0135] 0.75% defoamer;

[0136] Deionized water. Example 7

[0137] A graphene-based waterborne coating is prepared by the following steps:

[0138] (I) Add the highly dispersed graphene solution to deionized water and ultrasonically disperse for 15 min. Then add waterborne epoxy resin and wetting and dispersing agent, stir for 30 min, and ultrasonically disperse for 30 min.

[0139] (II) Add curing agent, defoamer and film-forming aid, stir for 10 minutes until the system is uniform, and then the graphene / waterborne epoxy resin composite coating is obtained.

[0140] The highly dispersed graphene was obtained using the preparation method of Example 4. The graphene obtained in Example 4 was then further dispersed using alkylphenol polyoxyethylene ether, glycerol, and deionized water. The secondary dispersion was performed using a 12500 high-shear homogenizer for 3 hours at 15°C. The resulting highly dispersed graphene solution contained the following components by mass: 30 wt.% graphene, 1.5 wt.% alkylphenol polyoxyethylene ether, 25 wt.% glycerol, and the balance deionized water.

[0141] The water-based coating is composed of the following components in parts by weight:

[0142] 40 parts water-based epoxy resin;

[0143] 30 parts curing agent;

[0144] 40 parts of highly dispersed graphene;

[0145] 1.5 parts wetting and dispersing agent;

[0146] 2 parts film-forming aid;

[0147] 0.75% defoamer;

[0148] Deionized water.

[0149] Corrosion resistance tests were conducted on Examples 5, 6, and 7, as well as on the bare patch and the pure epoxy resin coating. The test results are attached. Figure 4 As shown, attached Figure 4 The corresponding table is as follows:

[0150] First, the adhesion of the coatings prepared in Examples 5-7 was tested, with an adhesion range of 7-9 MPa. Regarding hardness, the hardness of pure epoxy resin was only B, while the hardness of Examples 5-7 was H. The anti-corrosion performance of the coatings was evaluated using Tafel polarization curves, with all samples obtained by immersing in a 3.5 wt% NaCl solution. Generally, a higher corrosion potential and lower corrosion current density result in better anti-corrosion performance. Highly dispersed graphene fills the pores in the epoxy coating, making it denser and thus making it difficult for corrosion ions to penetrate the coating and reach the metal layer. In Examples 5-7, as the amount of graphene increased, the corrosion performance only leveled off, without a significant decrease. Figure 5 The consistent corrosion resistance and salt spray test results sufficiently demonstrate that the graphene in the coating of this invention exhibits a highly dispersed state.

[0151] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A graphene-based waterborne coating, characterized in that... The water-based coating is composed of the following components in parts by weight: 20-60 parts water-based epoxy resin; 30-60 parts curing agent; 20-40 parts of highly dispersed graphene solution; 1-2 parts wetting and dispersing agent; 1-5 parts film-forming aid; 0.5-1 defoamer; Deionized water; The highly dispersed graphene solution was prepared through the following steps: (1) Preparation of three-dimensional bulk graphene cathode material: (a) Preparation of graphene aqueous solution by the Hummer method; (b) Centrifugation to obtain graphene sol; (c) Preparation of bulk graphene by hydrothermal method; (2) Preparation of graphene cathode nickel foam cage: cut and bend nickel foam to obtain nickel foam cylindrical cage. The upper end of the nickel foam cylindrical cage is not closed and is connected to the negative power supply wire, while the lower end is closed. (3) Anodic stripping: The block graphene prepared in step (c) is placed in a nickel foam cylinder cage, and then the upper end is sealed. The nickel foam cylinder cage sinks to the bottom of the electrolyte. The nickel foam cylinder cage is connected to the power supply wire as the anode and the platinum electrode as the cathode. Anodic stripping is performed. The cage is then removed and cleaned with deionized water. (4) Secondary cathode stripping: Then connect the foamed nickel cylindrical cage to the cathode, Pt sheet as anode, and use tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF as electrolyte to perform cathode stripping; (5) Collect the graphene that overflows from the foamed nickel cylinder cage, remove excess tetrabutylammonium hexafluorophosphate, hexadecyltrimethylammonium chloride and DMF by vacuum filtration and washing with ethanol, and then disperse the graphene a second time using alkylphenol polyoxyethylene ether, glycerol and deionized water. The second dispersion is carried out by a high shear homogenizer at 10000-15000 rpm for 2-4 hours at a temperature of 10-20℃. The resulting highly dispersed graphene solution is then obtained.

2. The graphene water-based coating as described in claim 1, characterized in that... The mass percentages of each component in the highly dispersed graphene solution are as follows: graphene 5-50 wt.%, alkylphenol polyoxyethylene ether 1-2 wt.%, glycerol 20-30 wt.%, and the balance deionized water.

3. The graphene water-based coating as described in claim 1, characterized in that... The curing agent is selected from at least one of diaminodiphenylmethane, diaminodiphenyl ether, or dicyandiamide.

4. The graphene water-based coating as described in claim 1, characterized in that... The wetting and dispersing agent is BYK-P104 dispersant.

5. A graphene-based waterborne coating as described in claim 1, characterized in that... The film-forming aid is propylene glycol methyl ether.

6. The graphene waterborne coating as described in claim 1, characterized in that... The defoamer is selected from BYK-054 defoamer.

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