Water-based cardanol-based epoxy resin anticorrosive coating

Abstract

The invention relates to a water-based cardanol-based epoxy resin anticorrosive coating, and belongs to the technical field of water-based epoxy resin coatings. The paint is prepared by adopting the following method: carrying out epoxidation on anacardol by adopting a method for generating peroxyformic acid in situ to prepare anacardol-based epoxy resin; preparing a water-based cardanol-based epoxy resin emulsion by a phase inversion method; and mixing the water-based cardanol-based epoxy resin emulsion with a curing agent, and curing to obtain the water-based cardanol-based epoxy resin anticorrosive coating. According to the method, cardanol is adopted as a raw material, the raw material is a natural renewable resource and is low in price, petrochemical resources can be protected, sustainable development of the resources can be achieved, and high-value utilization of agricultural by-products is achieved; the aqueous cardanol-based epoxy resin emulsion is prepared by adopting a phase inversion method for the first time, and the emulsion has the characteristics of good stability, long preservation time, small emulsion particle size, narrow particle size distribution, high cost performance and the like; and water is used as a solvent, so that the coating is environment-friendly and can be stably stored for a relatively long time.

Description

Technical Field

[0001] The invention relates to a water-based cardanol-based epoxy resin anti-corrosion coating, belonging to the technical field of water-based epoxy resin coatings. Background Art

[0002] Metal corrosion is the phenomenon of performance degradation caused by electrochemical or chemical reactions between metal materials and environmental media. This process can significantly reduce the material's mechanical properties (such as strength, plasticity, and toughness), destroy the structural integrity of metal components, and affect their electrical, optical, and other physical properties. Currently, metal corrosion protection mainly relies on three methods: electrochemical protection, the addition of corrosion inhibitors, and coating protection. Among them, organic coatings have become the most widely used protection method due to their excellent physical barrier effect, effectively preventing contact between corrosive media and metal substrates.

[0003] Epoxy resin coatings occupy an important position in the field of protective coatings due to their excellent corrosion resistance, mechanical strength and high adhesion to metal substrates. However, approximately 90% of epoxy resins on the market are still synthesized from petroleum-based raw materials, with bisphenol A diglycidyl ether (DGEBA) prepared using bisphenol A (BPA) as a precursor being the main product. Numerous studies have shown that BPA has estrogenic activity and can endanger human health through endocrine disruption, and its ecotoxicity has attracted global attention. At the same time, the non-renewable nature of petrochemical resources also restricts the sustainable development of traditional epoxy resins. Therefore, the development of environmentally friendly and renewable bio-based epoxy resins has become an important research direction for achieving green manufacturing.

[0004] Among numerous biomass raw materials, cardanol has attracted considerable attention due to its unique chemical structure. A byproduct of cashew nut processing, cardanol is primarily composed of meta-substituted phenolic hydroxyl groups, aromatic rings, and long-chain unsaturated alkyl groups. This structure endows it with three active sites: a phenolic hydroxyl group, a benzene ring, and a side double bond, making it an ideal raw material for the preparation of bio-based epoxy resins. In particular, the unsaturated double bonds in its side chains can be directly converted into epoxy groups through epoxidation, offering new avenues for the development of high-performance bio-based materials. However, existing epoxy resin technology still faces significant challenges. Firstly, traditional solvent-based epoxy resins contain large amounts of organic solvents, which release volatile organic compounds (VOCs) during production and use, posing a threat to the environment and human health. Secondly, existing water-based technologies have significant drawbacks. For example, mechanically prepared emulsions have poor stability and are prone to delamination and aggregation. Chemical modification methods require complex synthesis steps and poor process controllability. Furthermore, curing agent emulsification methods are limited by the reactivity of the curing agent. In contrast, although the phase inversion method can prepare nanoemulsions with better stability, the waterborne epoxy resins reported so far are still mainly based on petroleum-based raw materials. Therefore, it is urgent to develop a waterborne bio-based epoxy resin system that is both environmentally friendly and stable. Summary of the Invention

[0005] In order to overcome the defects of the prior art, the object of the present invention is to provide a water-based cardanol-based epoxy resin anti-corrosion coating. The raw materials of the coating are easily available and environmentally friendly, contain a curing agent, and have good mechanical properties and anti-corrosion capabilities. The coating preparation method is simple to operate and adopts a phase inversion method to obtain a water-based cardanol-based epoxy resin emulsion with good stability and small particle size.

[0006] To achieve the purpose of the present invention, the following technical solutions are provided.

[0007] A water-based cardanol-based epoxy resin anti-corrosion coating, wherein the coating is prepared by the following method:

[0008] (1) Cardanol is epoxidized by in-situ generation of peroxyformic acid to prepare a cardanol-based epoxy resin, as follows:

[0009] Formic acid and cardanol were mixed in a mass ratio of 1:3 and stirred uniformly at room temperature, hydrogen peroxide was added dropwise within 30 minutes, and the mixture was stirred at a constant temperature of 60°C to 70°C for 2 hours to 3 hours to obtain a crude product; the crude product was then purified by solvent extraction, neutralized, and the organic phase was collected, dried, and concentrated to obtain a reddish-brown viscous liquid, which was a cardanol-based epoxy resin;

[0010] The mass of hydrogen peroxide is 75% to 80% of the mass of cardanol.

[0011] Further, the reaction was carried out at a constant temperature of 60° C. to 70° C. for 2 h to 3 h under magnetic stirring;

[0012] Further, the mixture was neutralized with a saturated sodium bicarbonate solution, and the organic phase was collected, dried over anhydrous sodium sulfate and concentrated under reduced pressure.

[0013] (2) Preparation of water-based cardanol-based epoxy resin emulsion by phase inversion method

[0014] The cardanol-based epoxy resin prepared in step (1) and the composite emulsifier are stirred and mixed uniformly, and then the temperature is raised to 60° C. to 70° C. for emulsification reaction. Water is slowly added dropwise while stirring. After all the water is added, stirring is continued until the system is stable to obtain a water-based cardanol-based epoxy resin emulsion.

[0015] During the water addition process, the emulsion changes from oil-in-water type (W / O) to water-in-oil type (O / W), and a phase reversal occurs. The viscosity of the system shows a trend of first decreasing, then increasing, and then decreasing. When a sharp decrease in viscosity is observed, it indicates that the system has completed the phase transition.

[0016] The composite emulsifier is composed of emulsifier Span 80 (Span80) and sodium dodecyl sulfate (SDS) in a mass ratio of 1:3 to 4.

[0017] The mass of the composite emulsifier is 10% to 15% of the mass of the cardanol-based epoxy resin.

[0018] The mass of the added water is 40% to 50% of the mass of the water-based cardanol-based epoxy resin emulsion; further, the mass of the added water is 40% of the mass of the water-based cardanol-based epoxy resin emulsion.

[0019] The water is water with a purity higher than that of deionized water, such as deionized water, ultrapure water, etc.

[0020] Furthermore, the stirring speed is 2000 r / min to 3000 r / min.

[0021] Furthermore, after all the water was added, stirring was continued for 30 min to ensure that the system was fully stable.

[0022] (3) Preparation of water-based cardanol-based epoxy resin anti-corrosion coating

[0023] The water-based cardanol-based epoxy resin emulsion prepared in step (2) is mixed with a curing agent and then cured to obtain a water-based cardanol-based epoxy resin anti-corrosion coating;

[0024] Further, the curing agent is isophorone diamine (IPDA);

[0025] Furthermore, the mass ratio of the water-based cardanol-based epoxy resin to isophorone diamine is 6 to 4:1; furthermore, the mass ratio of the water-based cardanol-based epoxy resin to isophorone diamine is 6:1.

[0026] The coating can be applied to the surface of a low-carbon steel substrate using a thin film coater, and after drying and curing, a water-based cardanol-based epoxy resin anti-corrosion coating is formed.

[0027] Beneficial effects

[0028] (1) The present invention provides a water-based cardanol-based epoxy resin anti-corrosion coating, which needs to be prepared by a specific preparation method, wherein step (1) uses cardanol as a raw material to replace petrochemical raw materials. Cardanol is a by-product of the cashew nut processing industry. It is a natural renewable resource and is inexpensive. It can protect petrochemical resources to achieve sustainable development of resources and also realize the high-value utilization of agricultural by-products. Cardanol is epoxidized by a method of in-situ generating peroxyformic acid to prepare a cardanol-based epoxy resin.

[0029] (2) The present invention provides a water-based cardanol-based epoxy resin anti-corrosion coating, which needs to be prepared by a specific preparation method. In step (2), through creative research, it is achieved for the first time to prepare a water-based cardanol-based epoxy resin emulsion by a phase inversion method; and the emulsion has the characteristics of good stability, long shelf life, small emulsion particle size, narrow particle size distribution, and high cost performance.

[0030] (3) The present invention provides a water-based cardanol-based epoxy resin anti-corrosion coating, which is prepared by a specific preparation method. No organic solvent is added during the entire process. Water is used as a solvent to replace the volatile organic solvents used in most epoxy resins, thereby greatly reducing VOC emissions, protecting the environment and human health, and avoiding the risks of fire and explosion. At the same time, since water, which is cheap and easily available, is used as a diluent, it replaces solvents such as xylene in oil-based coatings, thereby greatly saving energy. The coating is both environmentally friendly and can be stably preserved for a long time.

[0031] (4) The present invention provides a water-based cardanol-based epoxy resin anti-corrosion coating, which is prepared by a specific preparation method. The method is simple, the conditions are easy to control, the product is easy to separate, no special instruments and equipment are required, the operability is strong, and it is suitable for large-scale industrial production.

[0032] (5) The present invention provides a water-based cardanol-based epoxy resin anti-corrosion coating, which has good anti-corrosion performance and better safety and environmental protection than oil-based coatings. It also has less VOC emissions, meets the demand for green and environmentally friendly coatings, and provides a new solution for the sustainable development of the anti-corrosion coating industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the hydrogen nuclear magnetic resonance spectrum of the cardanol-based epoxy resin prepared in Example 1.

[0034] Figure 2 This is a Fourier transform infrared spectrum of the cardanol-based epoxy resin prepared in Example 1.

[0035] Figure 3 The electrochemical impedance spectroscopy diagram of the coating prepared in Example 1 at different immersion times.

[0036] Figure 4 The electrochemical impedance spectroscopy diagram of the coating prepared in Comparative Example 1 at different immersion times.

[0037] Figure 5 The electrochemical impedance spectroscopy diagram of the coating prepared in Comparative Example 2 at different immersion times.

[0038] Figure 6The electrochemical impedance spectroscopy diagram of the coating prepared in Comparative Example 3 at different immersion times. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but this does not limit the present invention.

[0040] Example 1

[0041] A water-based cardanol-based epoxy resin anti-corrosion coating, wherein the coating is prepared by the following method:

[0042] (1) 3.33 g of anhydrous formic acid and 10.0 g of cardanol were mixed in a flask and stirred at room temperature. 25.0 g of a 30% hydrogen peroxide solution was added dropwise within 30 min so that the mass ratio of formic acid to cardanol was 1:3 and the mass of hydrogen peroxide was 75% of the mass of cardanol. After the addition of the hydrogen peroxide solution, the mixture was kept at 60 ° C for 2 h under magnetic stirring. After the reaction was completed, the crude product was purified by solvent extraction and neutralized with 40 ml of a saturated sodium bicarbonate solution. The organic phase was collected, dried with anhydrous sodium sulfate and concentrated under reduced pressure to obtain 9.0 g of cardanol-based epoxy resin.

[0043] (2) 6.0 g of the cardanol-based epoxy resin prepared in step (1) was added, and a composite emulsifier consisting of 0.225 g of Span80 and 0.675 g of SDS was added, the mass ratio of Span80 to SDS was 1:3, and the mass of the composite emulsifier was 15% of the cardanol-based epoxy resin. The mixture was stirred and mixed evenly, and then heated to 60° C. and mechanically stirred at a stirring speed of 2000 r / min. At the same time, 4.6 g of deionized water was slowly added dropwise to the reaction system at a rate of 1 second / drop. After all the deionized water was added, stirring was continued for 30 min to ensure that the system was fully stable, and a water-based cardanol-based epoxy resin emulsion with a solid content mass fraction of 60% was obtained;

[0044] During the water addition process, the emulsion changes from oil-in-water type to water-in-oil type, and a phase reversal occurs. The viscosity of the system shows a trend of first decreasing, then increasing, and then decreasing. When a sharp decrease in viscosity is observed, it indicates that the system has completed the phase transition.

[0045] (3) 5 g of the water-based cardanol-based epoxy resin emulsion prepared in step (2) was taken, 0.5 g of IPDA was added, so that the mass ratio of the cardanol-based epoxy resin to the IPDA was 6:1, and the mixture was stirred for 20 min to fully mix and solidify to prepare a water-based cardanol-based epoxy resin anti-corrosion coating.

[0046] A water-based cardanol-based epoxy resin anti-corrosion coating prepared in Example 1 was evenly coated on the surface of a mild steel substrate using a thin film coater. After drying and curing at room temperature for 3 days, a water-based cardanol-based epoxy resin anti-corrosion coating was obtained with a dry film thickness of 100 μm.

[0047] Example 2

[0048] A water-based cardanol-based epoxy resin anti-corrosion coating, wherein the coating is prepared by the following method:

[0049] (1) 3.33 g of anhydrous formic acid and 10.0 g of cardanol were mixed in a flask and stirred at room temperature. 29.3 g of a 30% hydrogen peroxide solution was added dropwise within 30 min so that the mass ratio of formic acid to cardanol was 1:3 and the mass of hydrogen peroxide was 80% of the mass of cardanol. After the addition of the hydrogen peroxide solution was completed, the mixture was kept at 70 ° C. for 3 h under magnetic stirring. After the reaction was completed, the crude product was purified by solvent extraction and neutralized with 40 ml of saturated sodium bicarbonate solution. The organic phase was collected, dried with anhydrous sodium sulfate and concentrated under reduced pressure to obtain 8.6 g of cardanol-based epoxy resin.

[0050] (2) 6.0 g of the cardanol-based epoxy resin prepared in step (1) was added, and a composite emulsifier consisting of 0.12 g of Span80 and 0.48 g of SDS was added, so that the mass ratio of Span80 to SDS was 1:4, and the mass of the composite emulsifier was 10% of the cardanol-based epoxy resin. The mixture was stirred and mixed evenly, and then the temperature was raised to 70° C. and mechanically stirred at a stirring speed of 3000 r / min. At the same time, 4.6 g of deionized water was slowly added dropwise at a rate of 1 second / drop. After all the deionized water was added, stirring was continued for 30 min to ensure that the system was fully stable, and a water-based cardanol-based epoxy resin emulsion with a solid content mass fraction of 60% was obtained;

[0051] During the water addition process, the emulsion changes from oil-in-water type to water-in-oil type, and a phase reversal occurs. The viscosity of the system shows a trend of first decreasing, then increasing, and then decreasing. When a sharp decrease in viscosity is observed, it indicates that the system has completed the phase transition.

[0052] (3) 5 g of the water-based cardanol-based epoxy resin emulsion prepared in step (2) was taken, 0.5 g of IPDA was added, so that the mass ratio of the cardanol-based epoxy resin to the IPDA was 6:1, and the mixture was stirred for 20 min to fully mix and solidify to prepare a water-based cardanol-based epoxy resin anti-corrosion coating.

[0053] A water-based cardanol-based epoxy resin anti-corrosion coating prepared in Example 2 was evenly coated on the surface of a mild steel substrate using a thin film coater. After drying and curing at room temperature for 3 days, a water-based cardanol-based epoxy resin anti-corrosion coating was obtained with a dry film thickness of 100 μm.

[0054] Comparative Example 1

[0055] A water-based cardanol-based epoxy resin anti-corrosion coating, wherein the coating is prepared by the following method:

[0056] (1) 2.0 g of anhydrous formic acid and 10.0 g of cardanol were mixed in a flask and stirred uniformly at room temperature. 20.0 g of a 30% hydrogen peroxide solution was added dropwise over 30 min, such that the mass ratio of formic acid to cardanol was 1:5 and the mass of hydrogen peroxide was 60% of the mass of cardanol. After the addition of the hydrogen peroxide solution, the mixture was kept at 60° C. for 1 h under magnetic stirring. After the reaction was completed, the crude product was purified by solvent extraction and neutralized with 40 ml of saturated sodium bicarbonate solution. The organic phase was collected, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to obtain 6.0 g of cardanol-based epoxy resin.

[0057] (2) Take 4.0 g of the cardanol-based epoxy resin prepared in step (1), add 0.2 g of Span80 and 0.2 g of SDS composed of a composite emulsifier, the mass ratio of Span80 to SDS is 1:1, the mass of the composite emulsifier is 10% of the mass of the cardanol-based epoxy resin, stir and mix evenly, then heat to 60 ° C, mechanically stir at a stirring speed of 2000 r / min, and slowly add 3.0 g of deionized water to the reaction system at a rate of 1 second / drop. After all the deionized water is added, continue stirring for 30 min to ensure that the system is fully stable, and obtain a water-based cardanol-based epoxy resin emulsion with a solid content mass fraction of 60%.

[0058] (3) 5 g of the water-based cardanol-based epoxy resin emulsion prepared in step (2) was taken, 0.5 g of IPDA was added, so that the mass ratio of the cardanol-based epoxy resin to the IPDA was 6:1, and the mixture was stirred for 20 min to fully mix and solidify to prepare a water-based cardanol-based epoxy resin anti-corrosion coating.

[0059] A water-based cardanol-based epoxy resin anti-corrosion coating prepared in Comparative Example 1 was evenly coated on the surface of a mild steel substrate using a thin film coater. After drying and curing at room temperature for 3 days, a water-based cardanol-based epoxy resin anti-corrosion coating was obtained with a dry film thickness of 100 μm.

[0060] Comparative Example 2

[0061] A water-based cardanol-based epoxy resin anti-corrosion coating, wherein the coating is prepared by the following method:

[0062] (1) 2.5 g of anhydrous formic acid and 10.0 g of cardanol were mixed in a flask and stirred at room temperature. 20.0 g of a 30% hydrogen peroxide solution was added dropwise within 30 min so that the mass ratio of formic acid to cardanol was 1:4 and the mass of hydrogen peroxide was 60% of the mass of cardanol. After the addition of the hydrogen peroxide solution, the mixture was kept at 80 ° C. for 4 h under magnetic stirring. After the reaction was completed, the crude product was purified by solvent extraction and neutralized with 40 ml of saturated sodium bicarbonate solution. The organic phase was collected, dried with anhydrous sodium sulfate and concentrated under reduced pressure to obtain 8.0 g of cardanol-based epoxy resin.

[0063] (2) Take 6.0 g of the cardanol-based epoxy resin prepared in step (1), add 0.3 g of Span80 and 0.9 g of SDS composed of a composite emulsifier, the mass ratio of Span80 to SDS is 1:3, the mass of the composite emulsifier is 20% of the cardanol-based epoxy resin, stir and mix evenly, then heat to 70 ° C, mechanically stir at a stirring speed of 1000 r / min, and slowly add 4.8 g of deionized water to the reaction system at a rate of 1 second / drop. After all the deionized water is added, continue stirring for 30 min to ensure that the system is fully stable, and obtain a water-based cardanol-based epoxy resin emulsion with a solid content mass fraction of 60%.

[0064] (3) 5 g of the water-based cardanol-based epoxy resin emulsion prepared in step (2) was taken, 0.5 g of IPDA was added, so that the mass ratio of the cardanol-based epoxy resin to the IPDA was 6:1, and the mixture was stirred for 20 min to fully mix and solidify to prepare a water-based cardanol-based epoxy resin anti-corrosion coating.

[0065] A water-based cardanol-based epoxy resin anti-corrosion coating prepared in Comparative Example 2 was evenly coated on the surface of a mild steel substrate using a thin film coater. After drying and curing at room temperature for 3 days, a water-based cardanol-based epoxy resin anti-corrosion coating was formed with a dry film thickness of 100 μm.

[0066] Comparative Example 3

[0067] A water-based cardanol-based epoxy resin anti-corrosion coating, wherein the coating is prepared by the following method:

[0068] (1) 3.33 g of anhydrous formic acid and 10.0 g of cardanol were mixed in a flask and stirred at room temperature. 20.0 g of a 30% hydrogen peroxide solution was added dropwise within 30 min so that the mass ratio of formic acid to cardanol was 1:3 and the mass of hydrogen peroxide was 60% of the mass of cardanol. After the addition of the hydrogen peroxide solution was completed, the mixture was kept at 50 ° C. for 2 h under magnetic stirring. After the reaction was completed, the crude product was purified by solvent extraction and neutralized with 40 ml of a saturated sodium bicarbonate solution. The organic phase was collected, dried with anhydrous sodium sulfate and concentrated under reduced pressure to obtain 8.0 g of cardanol-based epoxy resin.

[0069] (2) Take 6.0 g of the cardanol-based epoxy resin prepared in step (1), add 0.3 g of Span80 and 0.6 g of SDS composed of a composite emulsifier, the mass ratio of Span80 to SDS is 1:2, the mass of the composite emulsifier is 15% of the cardanol-based epoxy resin, stir and mix evenly, then heat to 60 ° C, mechanically stir at a stirring speed of 1000 r / min, and slowly add 4.8 g of deionized water to the reaction system at a rate of 1 second / drop. After all the deionized water is added, continue stirring for 30 min to ensure that the system is fully stable, and obtain a water-based cardanol-based epoxy resin emulsion with a solid content mass fraction of 60%.

[0070] (3) 5 g of the water-based cardanol-based epoxy resin emulsion prepared in step (2) was taken, 0.6 g of IPDA was added, so that the mass ratio of the cardanol-based epoxy resin to the IPDA was 5:1, and the mixture was stirred for 20 min to fully mix and solidify to prepare a water-based cardanol-based epoxy resin anti-corrosion coating.

[0071] A water-based cardanol-based epoxy resin anti-corrosion coating prepared in Comparative Example 3 was evenly coated on the surface of a mild steel substrate using a thin film coater. After drying and curing at room temperature for 3 days, a water-based cardanol-based epoxy resin anti-corrosion coating was formed with a dry film thickness of 100 μm.

[0072] Test and analysis experiments

[0073] The cardanol-based epoxy resin, water-based cardanol-based epoxy resin emulsion, water-based cardanol-based epoxy resin anti-corrosion coating and water-based cardanol-based epoxy resin anti-corrosion coating prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were tested as follows:

[0074] (1) Determination of epoxy value of cardanol-based epoxy resin

[0075] The epoxy value was determined using the hydrochloric acid acetone method described in "Determination of Epoxy Value of Plasticizers" (GB / T1677-2008). Approximately 0.5 g of cardanol-based epoxy resin was weighed to the nearest 1 mg as a sample into a conical flask. 20 mL of a hydrochloric acid acetone solution (composed of concentrated hydrochloric acid and acetone in a volume ratio of 1:40) was pipetted into the flask. Seal the flask with a rubber stopper and shake well. Once the sample was completely dissolved, place it in a dark corner for 1.5 hours. Add 3 to 5 drops of phenolphthalein indicator and titrate with 0.1 mol / L NaOH standard solution until the solution turns pink. If the solution does not return to its original color within 30 seconds, this is the titration endpoint. Record the volume of NaOH consumed.

[0076] Results and Analysis:

[0077] From the comparison of Examples 1 and 2 and Comparative Examples 1 and 2, it can be seen that the amount of raw materials added, the reaction temperature and the reaction time in the synthesis reaction of the cardanol-based epoxy resin will affect the formation of epoxy groups in the product cardanol-based epoxy resin, affect the properties of the cardanol-based epoxy resin and ultimately affect the properties of the coating.

[0078] Excessive addition of formic acid will promote the ring-opening reaction of the epoxy group, thereby reducing the epoxy value; when the hydrogen peroxide exceeds a certain amount, it will lead to an increase in the water content in the reaction system, reduce the concentration of the reactants, and at the same time promote the hydrolysis of the product, destroying the formation of the epoxy group, thereby reducing the epoxy value; if the reaction time in the reaction system is too long, the hydrogen peroxide concentration will decrease and it will be difficult to continue the epoxidation reaction, and in the presence of formic acid, a ring-opening reaction will occur, causing the epoxy value to decrease; when the temperature is too high, it will promote the decomposition of hydrogen peroxide, and peroxyformic acid is unstable and easy to decompose at high temperatures, and the generated epoxy compound will also undergo a ring-opening side reaction, thereby reducing the epoxy value.

[0079] Table 1 Epoxy value test results of cardanol-based epoxy resins prepared in Examples and Comparative Examples

[0080]

[0081] (2) Structural test of cardanol-based epoxy resin

[0082] The cardanol-based epoxy resin structures prepared in Examples 1 and 2 were tested and characterized. Figure 1 Comparing the H NMR spectra of cardanol before and after the reaction, the peaks between 5.3 ppm and 5.5 ppm (protons m and n) representing hydrogen on the internal double bonds of the long carbon chains have almost disappeared, indicating that the internal double bonds of the side chains were converted into epoxy groups during the epoxidation reaction. In addition, a new peak between 2.9 ppm and 3.2 ppm (protons h) appears, representing hydrogen on the oxirane ring, indicating the successful formation of epoxy groups.

[0083] Figure 2 The Fourier transform infrared spectra of cardanol before and after reaction. After epoxidation modification, cardanol showed a peak at 825 cm -1 At 3010 cm -1 The carbon-hydrogen bond absorption peak of the unsaturated double bond disappeared; the infrared results showed that the epoxidation reaction occurred successfully, the epoxy group was introduced, and the skeleton structure of the original cardanol was not changed.

[0084] (3) Characterization of waterborne cardanol-based epoxy resin emulsion

[0085] The following tests were performed on the water-based cardanol-based epoxy resin emulsions prepared in Examples 1 and 2 and Comparative Examples 1, 2, and 3:

[0086] Determination of emulsion particle size: The emulsion was diluted 1000 times with deionized water, ultrasonicated in an ultrasonic cleaner for 15 min, and the particle size of the emulsion was measured at 25° C. using a nanoparticle size zeta potential analyzer.

[0087] Emulsion mechanical stability test: The mechanical stability of the emulsion was measured by centrifugal stratification method, which was divided into 5 levels. The effect of level 1 to level 5 increased in sequence, and level 5 was the best. Specifically:

[0088] Level 5: 3000r / min×20min without delamination,

[0089] Level 4: 2500r / min×20min without stratification,

[0090] Level 3: 2000r / min×20min without stratification,

[0091] Level 2: 1500r / min×20min without stratification,

[0092] Level 1: 1000r / min×20min without stratification.

[0093] Storage stability: The emulsion was sealed in a transparent centrifuge tube and placed in a dark place at room temperature. The time for the occurrence of stratification, coagulation and solidification of the fat emulsion was observed and recorded.

[0094] Results and Analysis:

[0095] The performance test results of the water-based cardanol-based epoxy resin emulsions prepared in Examples 1 and 2 and Comparative Examples 1, 2, and 3 are shown in Table 1. It can be found that the average particle size of the emulsions prepared in Comparative Examples 1 to 3 is larger than that of the emulsion prepared in Example 1, resulting in poor mechanical stability and a short storage life. The average particle size of the emulsion prepared in Example 1 is only 325 nm, and the average particle size of the emulsion prepared in Example 2 is only 255 nm. They also have good mechanical stability, are not prone to delamination, and can be stored for more than 3 months without delamination.

[0096] Table 2 Performance test results of water-based cardanol-based epoxy resin emulsions prepared in Examples and Comparative Examples

[0097]

[0098] (1) Coating mechanical properties test

[0099] The water-based cardanol-based epoxy resin anti-corrosion coatings prepared in Examples 1 and 2 and Comparative Examples 1, 2, and 3 were subjected to the following tests:

[0100] Test method: Refer to the standard "GB / T31586.1-2015 Paint film pull-off test" to test the coating adhesion; refer to the standard "GB / T1732-2020 Paint film impact resistance test" to test the coating impact resistance; refer to the standard "GBT / 1731-1993 Paint film flexibility test method" to test the coating flexibility.

[0101] Results and Analysis:

[0102] From the comparison of the examples and the comparative examples, it can be seen that the water-based cardanol-based epoxy resin anti-corrosion coating prepared by the method of the present invention has good mechanical properties, and the adhesion, impact resistance and flexibility of Examples 1 and 2 are better than those of Comparative Examples 1, 2 and 3. It can be seen that the water-based cardanol-based epoxy properties of the resin and the properties of the emulsion will affect the mechanical properties of the coating. The higher the epoxy value of the water-based cardanol-based epoxy value and the better the performance of the water-based cardanol-based epoxy resin emulsion, the better the mechanical properties of the water-based cardanol-based epoxy resin anti-corrosion coating.

[0103] Table 3 Mechanical properties test results of water-based cardanol-based epoxy resin anti-corrosion coatings prepared in Examples and Comparative Examples

[0104]

[0105] (3) Corrosion resistance test of water-based cardanol-based epoxy resin anti-corrosion coating

[0106] The water-based cardanol-based epoxy resin anti-corrosion coatings prepared in the examples and comparative examples were tested to examine their anti-corrosion properties and to conduct electrochemical performance tests on the coatings. The electrolyte used was simulated seawater, i.e., a 3.5% NaCl solution by mass. A standard three-electrode system was employed, with a platinum sheet as the counter electrode, a saturated calomel electrode as the reference electrode, and the coating sample as the working electrode. The electrodes were placed 1 cm apart. All electrochemical test processes were measured at open circuit potential, with an excitation voltage of 10 mv / s and a frequency range of 100 kHz to 0.01 Hz. The anti-corrosion performance of the coatings was evaluated using electrochemical impedance spectroscopy obtained from a simulated seawater immersion test.

[0107] Results and Analysis:

[0108] The electrochemical impedance spectroscopy of the coatings prepared in Example 1 and Comparative Examples 1, 2, and 3 is shown in Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 The results show that the coatings prepared in Comparative Examples 1, 2, and 3, i.e. Figure 4 、 Figure 5 、 Figure 6 The coating has an impedance of 10 at the beginning of immersion. 7 Ωcm 2 , 10 7 Ωcm 2 and 10 6 Ωcm 2 The coating impedance dropped significantly compared with that of Example 1. Double arcs appeared after 25 days of immersion, indicating poor corrosion resistance. Figure 3 The low frequency impedance of the coating reaches 10 8 Ωcm 2 The double arcs only appeared after the coating was immersed for 30 days, indicating that the coating prepared in Example 1 has good anti-corrosion performance. The results of Example 2 are similar to those of Example 1.

[0109] It can be seen from this that the performance of the cardanol-based epoxy resin and the performance of the emulsion will affect the anti-corrosion performance of the coating. The higher the epoxy value of the resin and the better the performance of the water-based cardanol-based epoxy resin emulsion, the better the anti-corrosion performance of the coating.

[0110] Although the above embodiments provide a detailed description of the present invention, they are only part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on the embodiments of the present invention without creative work, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A water-based cardanol-based epoxy resin anti-corrosion coating, characterized in that: The coating is prepared by the following method: (1) Formic acid and cardanol are mixed in a mass ratio of 1:3 and stirred at room temperature, hydrogen peroxide is added dropwise within 30 minutes, and the mixture is stirred and reacted at a constant temperature of 60°C to 70°C for 2 hours to 3 hours to obtain a crude product; the crude product is purified by solvent extraction, neutralized, and the organic phase is collected, dried and concentrated to obtain a cardanol-based epoxy resin; the mass of hydrogen peroxide is 75% to 80% of the mass of cardanol; (2) Stirring and mixing the cardanol-based epoxy resin and the composite emulsifier uniformly, heating to 60°C to 70°C for reaction, adding water dropwise while stirring, and continuing to stir until the system is stable after the water is added to obtain a water-based cardanol-based epoxy resin emulsion; the composite emulsifier is composed of emulsifier Span 80 and sodium lauryl sulfate in a mass ratio of 1:3 to 4; the mass of the composite emulsifier is 10% to 15% of the mass of the cardanol-based epoxy resin; the mass of the added water is 40% to 50% of the mass of the water-based cardanol-based epoxy resin emulsion; (3) The water-based cardanol-based epoxy resin emulsion is mixed with a curing agent and then cured to obtain a water-based cardanol-based epoxy resin anti-corrosion coating.

2. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 1, characterized in that: In step (2), the mass of water added is 40% of the mass of the water-based cardanol-based epoxy resin emulsion.

3. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 1 or 2, characterized in that: In step (2), the stirring speed is 2000 r / min to 3000 r / min.

4. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 1 or 2, characterized in that: In step (2), after all the water is added, stirring is continued for 30 minutes.

5. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 1 or 2, characterized in that: In step (2), the water is water with a purity higher than that of deionized water.

6. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 1 or 2, characterized in that: In step (3), the curing agent is isophorone diamine, and the mass ratio of the water-based cardanol-based epoxy resin to isophorone diamine is 6 to 4:

1.

7. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 6, characterized in that: In step (3), the mass ratio of water-based cardanol-based epoxy resin to isophorone diamine is 6:

1.

8. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 1 or 2, characterized in that: In step (1), the reaction is carried out at a constant temperature of 60° C. to 70° C. for 2 h to 3 h under magnetic stirring.

9. A water-based cardanol-based epoxy resin anti-corrosion coating according to claim 1 or 2, characterized in that: In step (1), the mixture is neutralized with a saturated sodium bicarbonate solution, and the organic phase is collected, dried over anhydrous sodium sulfate, and concentrated under reduced pressure.

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