Preparation method of PDA modified BI (at) ZIF-8 photocuring composite coating on surface of NdFeB magnet

Abstract

The invention discloses a preparation method of a PDA modified BI (at) ZIF-8 photocuring composite coating on the surface of an NdFeB magnet, and particularly relates to the technical field of magnet coatings, the preparation method comprises six steps of BI (at) ZIF-8 preparation, BI (at) ZIF-8 modification, electrophoresis pretreatment, electrophoresis liquid preparation, NdFeB magnet electrophoresis in the electrophoresis liquid to form an epoxy modified acrylic acid coating, and coating curing. The BI (at) ZIF-8 has strong hydrophobicity and poor dispersibility in an electrophoresis liquid, and the PDA has good hydrophilicity, so that the PDA-BI (at) ZIF-8 composite filler is formed by self-polymerization of the dopamine hydrochloride on the BI (at) ZIF-8, the dispersibility of the BI (at) ZIF-8 in water is greatly improved, and the hydrophobicity of the BI (at) ZIF-8 is improved. Passive protection and active corrosion inhibition effects of PDA-BI-ZIF-8 are combined, so that the corrosion resistance of the epoxy modified acrylic acid light-cured composite coating is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnet coating, more particularly, the present application relates to a preparation method of NdFeB magnet surface PDA modified BI@ZIF-8 photocuring composite coating. BACKGROUND

[0002] Since the emergence of the third generation of NdFeB magnets in 1983, NdFeB magnets have been widely used in new energy, electronic devices and high-end equipment due to their high magnetic energy product, high remanence and high coercivity. However, the multi-phase structure and the difference in chemical properties between the phases in NdFeB make the NdFeB rare earth permanent magnet material exhibit inherent insufficient corrosion resistance, which limits its development.

[0003] Surface protection is the most widely used corrosion protection method, and organic coating is the most convenient and economical surface treatment technology. Traditional organic coating has the disadvantages of long curing time, poor moisture resistance and weak aging resistance, and the generation of organic protective film will produce waste liquid and waste residue, etc. Environmental problems, which further increase the production cost. Therefore, the future research direction should be to develop diversified organic coatings, improve the corrosion resistance and mechanical properties of the coating, and at the same time use materials with little pollution. Photocuring is a kind of "green" new technology, and its development speed is getting faster and faster at present, and its application range is continuously expanding. Compared with thermal curing and room temperature curing, photocuring has the advantages of high efficiency and excellent performance, and the curing time is greatly reduced. However, the pure photocuring of acrylic resin coating has poor adhesion to the substrate, and the photocuring process is accompanied by volume shrinkage. When the crosslinking density is uneven, local stress concentration causes microcracks, resulting in poor corrosion resistance of the coating. SUMMARY

[0004] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present application provide a preparation method of NdFeB magnet surface PDA modified BI@ZIF-8 photocuring composite coating to solve the problems raised in the above background art.

[0005] To achieve the above object, the present application provides the following technical scheme: a preparation method of NdFeB magnet surface PDA modified BI@ZIF-8 photocuring composite coating, comprising the following preparation method:

[0006] A preparation method of NdFeB magnet surface PDA modified BI@ZIF-8 photocuring composite coating, comprising the following preparation method:

[0007] Step S1: preparation of BI@ZIF-8;

[0008] More specifically:

[0009] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2-methylimidazole were added to 20-30 mL of methanol solution, respectively, and were recorded as solution A and solution B. A 20 mL methanol solution of corrosion inhibitor benzimidazole (BI) was prepared, solution B was first added to the methanol solution of BI, stirred for 5-15 min, then solution A was added to the mixed solution, stirred for 1-3 h, and left to stand for 12-24 h. The obtained product was repeatedly washed with methanol several times, and then dried in a 70°C drying oven for 24 h;

[0010] Step S2: Preparation of PDA-BI@ZIF-8

[0011] First, BI@ZIF-8 was dispersed in Tris buffer, then ultrasonic treatment was performed for 1-2 h, then dopamine hydrochloride was added and stirred and ultrasonic treatment was performed again, then the mixed solution was stirred in the dark for 12-24 h, then the black suspension was centrifuged to collect the precipitate, which was washed several times with anhydrous ethanol and deionized water, and dried at 70° for 24 h to obtain PDA-BI@ZIF-8 composite filler;

[0012] Step S3: Preparation of electrophoretic fluid;

[0013] More specifically:

[0014] The epoxy resin and acrylic mixed resin, photoinitiator and deionized water were mixed to prepare the electrophoretic fluid, which was stirred at 25-30° for 1-2 h, then PDA-BI@ZIF-8 composite filler was added and ultrasonic treatment was performed for 1-2 h;

[0015] Step S4: Pretreatment before electrophoresis;

[0016] More specifically:

[0017] The NdFeB magnet was subjected to pickling and drying treatment;

[0018] Step S5: Electrophoresis treatment;

[0019] More specifically:

[0020] The NdFeB magnet was placed in the electrophoretic fluid for treatment;

[0021] Step S6: Coating curing;

[0022] More specifically:

[0023] The NdFeB magnet after electrophoresis was subjected to ultraviolet curing.

[0024] In a preferred embodiment: step S1 includes adding zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2-methylimidazole in amounts of 1.3g to 1.6g and 1.6g to 2g, respectively, and the methanol solution concentration of BI is 2 to 5mg / L.

[0025] In a preferred embodiment: step S2 includes a Tris buffer concentration of 1×10⁻⁶. -5 mol / L, pH 8.5.

[0026] In a preferred embodiment: step S2 further includes that the mass ratio of BI@ZIF-8 to dopamine hydrochloride in the mixed solution is 2:1.

[0027] In a preferred embodiment: step S3 includes the following: the epoxy resin in the mixed resin is 10-20 wt% of the acrylic resin, the photoinitiator is 1-5 wt% of the acrylic resin, and the ratio of acrylic resin to deionized water is 7:43.

[0028] In a preferred embodiment: Step S4 includes placing the NdFeB magnet in a 0.3-6 wt% nitric acid solution for acid washing for 30-60 seconds, then placing it in deionized water for ultrasonic treatment for 1-2 minutes, repeating the above operation once, then placing it in anhydrous ethanol solution for ultrasonic treatment for 1-2 minutes, and finally drying it with a hair dryer using cold air.

[0029] In a preferred embodiment: step S4 further includes adding composite PDA-BI@ZIF-8 composite filler for electrophoresis solution, with a concentration of 1.5 to 2.5 g / L.

[0030] In a preferred embodiment: step S5 includes placing the acid-washed NdFeB magnet in an electrophoresis tank for cathodic electrophoresis to prepare an epoxy-modified acrylic resin photocurable composite coating, and then washing away the residual electrophoretic solution on the surface with deionized water.

[0031] In a preferred embodiment: step S5 further includes: performing cathodic electrophoresis on the acid-washed NdFeB magnet, with a working voltage of 60V to 80V, a working ambient temperature of 25 to 30℃, and an energizing time of 10 to 20s.

[0032] In a preferred embodiment: step S6 includes: pre-drying the electrophoretically treated NdFeB magnet under a fan for 5-15 minutes, then flash-drying it in an 80°C oven for 10-15 minutes, and then irradiating it under an ultraviolet curing lamp.

[0033] In a preferred embodiment: step S6 further includes: the ultraviolet light irradiation time is 30-60s, and the irradiation distance is 5cm.

[0034] The technical effects and advantages of this invention are as follows:

[0035] 1. This invention improves the corrosion resistance of NdFeB magnets by preparing a PDA-BI@ZIF-8 enhanced photocurable composite coating, which is an efficient and environmentally friendly coating protection method.

[0036] 2. The method of PDA modification of BI@ZIF-8 in this invention is simple, the reaction environment is easy to achieve, greatly improves the dispersibility of BI@ZIF-8 in water, and the reaction process is green and environmentally friendly.

[0037] 3. The method of the present invention uses an electrophoretic photocurable coating instead of a traditional electrophoretic thermocurable coating, which is efficient, green and environmentally friendly.

[0038] 4. The method for preparing epoxy-modified acrylic photocurable composite coating in this invention is flexible and simple, has a high utilization rate of raw materials, and is easy to implement mechanized production, which is of great significance to industrial production. Attached Figure Description

[0039] Figure 1 This is a SEM image of the PDA-BI@ZIF-8 prepared in this invention.

[0040] Figure 2 This is a Zeta potential diagram of the original BI@ZIF-8 and the BI@ZIF-8 modified by PDA in water in this invention;

[0041] Figure 3 The EIS curves of NdFeB samples with different filler addition amounts in this invention after soaking in 3.5wt% NaCl solution for 14 days are shown. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0043] Reference Figure 1 , Figure 2 and Figure 3 A method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet.

[0044] Example 1:

[0045] Step S1: Add 1.45g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 1.6g of 2-methylimidazole to 30mL of methanol solution, respectively, and label them solution A and solution B. Prepare 20mL of 3mg / L benzimidazole (BI) methanol solution. First, add solution B to the methanol solution of BI and stir for 10min. Then add solution A to the mixture and stir for 3h. Let it stand for 12h. Wash the obtained product repeatedly with methanol several times, and then dry it in a 70℃ drying oven for 24h.

[0046] Step S2: First, disperse BI@ZIF-8 in Tris buffer (pH=8.5), then sonicate for 2 hours. Next, add dopamine hydrochloride, stir, and sonicate again to form a mixture. The ratio of BI@ZIF-8 to dopamine hydrochloride is 2:1. Stir the mixture in the dark for 12 hours. Then, centrifuge the black suspension using a high-speed centrifuge to collect the precipitate. Wash the precipitate several times with anhydrous ethanol and deionized water, and dry at 70°C for 24 hours to obtain PDA-BI@ZIF-8 composite particles.

[0047] Step S3: Add a photoinitiator to the epoxy resin and acrylic resin mixture. The epoxy resin accounts for 15 wt% of the acrylic resin, and the photoinitiator is added at a rate of 3 wt% of the acrylic resin. Prepare an electrophoresis solution at a ratio of acrylic resin to deionized water of 7:43, stir for 2 hours, then add the composite filler PDA-BI@ZIF-8 at a concentration of 1.5 g / L, and sonicate for 1 hour.

[0048] Step S4: Place the NdFeB magnet in a 3% nitric acid solution for acid washing for 30 seconds. After cleaning, place it in deionized water for ultrasonic treatment for 1 minute. Repeat the above operation once. Then place it in anhydrous ethanol solution for ultrasonic treatment for 1 minute. Finally, dry it with a hair dryer using cold air.

[0049] Step S5: Place the acid-washed NdFeB magnet in an electrophoresis tank for cathodic electrophoresis to prepare an epoxy-modified acrylic resin photocurable composite coating. Electrophoresis parameters: 25°, 60V, 15s. Then wash off the residual electrophoretic solution on the surface with deionized water.

[0050] Step S6: After electrophoresis, the NdFeB magnet is pre-dried under a fan for 10 minutes, then flash-dried in an 80°C oven for 10 minutes, and then irradiated under a UV curing lamp for 30 seconds at a distance of 5 cm.

[0051] In summary, the obtained PDA-modified BI@ZIF-8 photocurable composite coating is deep transparent with uniform color and dense film. After two weeks of full immersion corrosion testing, |Z| 0.01Hz 3.109×10 6 Ω·cm 2 .

[0052] Example 2:

[0053] Step S1: Add 1.45g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 1.6g of 2-methylimidazole to 30mL of methanol solution, respectively, and label them solution A and solution B. Prepare 20mL of 3mg / L benzimidazole (BI) methanol solution. First, add solution B to the methanol solution of BI and stir for 10min. Then add solution A to the mixture and stir for 3h. Let it stand for 12h. Wash the obtained product repeatedly with methanol several times, and then dry it in a 70℃ drying oven for 24h.

[0054] Step S2: First, disperse BI@ZIF-8 in Tris buffer (pH=8.5), then sonicate for 2 hours. Next, add dopamine hydrochloride, stir, and sonicate again to form a mixture. The ratio of BI@ZIF-8 to dopamine hydrochloride is 2:1. Stir the mixture in the dark for 12 hours. Then, centrifuge the black suspension using a high-speed centrifuge to collect the precipitate. Wash the precipitate several times with anhydrous ethanol and deionized water, and dry at 70°C for 24 hours to obtain PDA-BI@ZIF-8 composite particles.

[0055] Step S3: Add a photoinitiator to the epoxy resin and acrylic resin mixture. The epoxy resin accounts for 15 wt% of the acrylic resin, and the amount of photoinitiator added is 3 wt% of the acrylic resin. Prepare an electrophoresis solution at a ratio of acrylic resin:deionized water = 7:43, stir for 2 hours, then add the composite filler PDA-BI@ZIF-8 at a concentration of 2 g / L, and sonicate for 1 hour.

[0056] Step S4: Place the NdFeB magnet in a 3% nitric acid solution for acid washing for 30 seconds. After cleaning, place it in deionized water for ultrasonic treatment for 1 minute. Repeat the above operation once. Then place it in anhydrous ethanol solution for ultrasonic treatment for 1 minute. Finally, dry it with a hair dryer using cold air.

[0057] Step S5: Place the acid-washed NdFeB magnet in an electrophoresis tank for cathodic electrophoresis to prepare an epoxy-modified acrylic resin photocurable composite coating. Electrophoresis parameters: 25°, 60V, 15s. Then wash off the residual electrophoretic solution on the surface with deionized water.

[0058] Step S6: After electrophoresis, the NdFeB magnet is pre-dried under a fan for 10 minutes, then flash-dried in an 80°C oven for 10 minutes, and then irradiated under a UV curing lamp for 30 seconds at a distance of 5 cm.

[0059] In summary, the obtained PDA-modified BI@ZIF-8 photocurable composite coating is deep transparent with uniform color and dense film. After two weeks of full immersion corrosion testing, |Z|0.01Hz It is 1.376×10 7 Ω·cm 2 Example 3:

[0060] Step S1: Add 1.45g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 1.6g of 2-methylimidazole to 30mL of methanol solution, respectively, and label them solution A and solution B. Prepare 20mL of 3mg / L benzimidazole (BI) methanol solution. First, add solution B to the methanol solution of BI and stir for 10min. Then add solution A to the mixture and stir for 3h. Let it stand for 12h. Wash the obtained product repeatedly with methanol several times, and then dry it in a 70℃ drying oven for 24h.

[0061] Step S2: First, disperse BI@ZIF-8 in Tris buffer (pH=8.5), then sonicate for 2 hours. Next, add dopamine hydrochloride, stir, and sonicate again to form a mixture. The ratio of BI@ZIF-8 to dopamine hydrochloride is 2:1. Stir the mixture in the dark for 12 hours. Then, centrifuge the black suspension using a high-speed centrifuge to collect the precipitate. Wash the precipitate several times with anhydrous ethanol and deionized water, and dry at 70°C for 24 hours to obtain PDA-BI@ZIF-8 composite particles.

[0062] Step S3: Add a photoinitiator to the epoxy resin and acrylic resin mixture. The epoxy resin accounts for 15 wt% of the acrylic resin, and the amount of photoinitiator added is 3 wt% of the acrylic resin. Prepare an electrophoresis solution at a ratio of acrylic resin:deionized water = 7:43, stir for 2 hours, then add the composite filler PDA-BI@ZIF-8 with a concentration of 2.5 g / L, and sonicate for 1 hour.

[0063] Step S4: Place the NdFeB magnet in a 3% nitric acid solution for acid washing for 30 seconds. After cleaning, place it in deionized water for ultrasonic treatment for 1 minute. Repeat the above operation once. Then place it in anhydrous ethanol solution for ultrasonic treatment for 1 minute. Finally, dry it with a hair dryer using cold air.

[0064] Step S5: Place the acid-washed NdFeB magnet in an electrophoresis tank for cathodic electrophoresis to prepare an epoxy-modified acrylic resin photocurable composite coating. Electrophoresis parameters: 25°, 60V, 15s. Then wash off the residual electrophoretic solution on the surface with deionized water.

[0065] Step S6: After electrophoresis, the NdFeB magnet is pre-dried under a fan for 10 minutes, then flash-dried in an 80°C oven for 10 minutes, and then irradiated under a UV curing lamp for 30 seconds at a distance of 5 cm.

[0066] In summary, the obtained PDA-modified BI@ZIF-8 photocurable composite coating is deep transparent with uniform color and dense film. After two weeks of full immersion corrosion testing, |Z| 0.01Hz It is 1.161×10 6 Ω·cm 2 .

[0067] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet, characterized in that; The preparation methods include the following: Step S1: Preparation of BI@ZIF-8; More specifically: Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2-methylimidazole were added to 20–30 mL of methanol solution, respectively, and labeled as solution A and solution B. A 20 mL methanol solution of the corrosion inhibitor benzimidazole (BI) was prepared. Solution B was first added to the methanol solution of BI, and the mixture was stirred for 5–15 min. Then, solution A was added to the mixture, and the mixture was stirred for 1–3 h, followed by standing for 12–24 h. The resulting product was washed several times with methanol and then dried in a 70 °C oven for 24 h. Step S2: Preparation of PDA-BI@ZIF-8 First, BI@ZIF-8 was dispersed in Tris buffer, then sonicated for 1-2 hours. Dopamine hydrochloride was added, stirred, and sonicated again to form a mixture. The mixture was stirred in the dark for 12-24 hours. Then, the black suspension was centrifuged using a high-speed centrifuge to collect the precipitate, which was washed several times with anhydrous ethanol and deionized water. The precipitate was dried at 70°C for 24 hours to obtain PDA-BI@ZIF-8 composite particles. Step S3: Electrophoresis buffer preparation; More specifically: An electrophoresis solution was prepared by mixing epoxy resin with acrylic resin, photoinitiator and deionized water, and stirred at 25-30°C for 1-2 hours. Then, PDA-BI@ZIF-8 composite filler was added and ultrasonic treatment was performed for 1-2 hours. Step S4: Pretreatment before electrophoresis; More specifically: The NdFeB magnets were acid-washed and dried. Step S5: Electrophoresis treatment; More specifically: The NdFeB magnet was placed in an electrophoretic solution for treatment; Step S6: Coating curing; More specifically: The electrophoretically coated NdFeB magnets were then cured with ultraviolet light.

2. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: In step S1, the amounts of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and 2-methylimidazole added are 1.3g~1.6g and 1.6~2g, respectively, and the concentration of BI in methanol solution is 2~5mg / L.

3. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: In step S2, the concentration of Tris buffer is 1×10⁻⁶. -5 mol / L, pH 8.

5.

4. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: Step S2 also includes that the mass ratio of BI@ZIF-8 to dopamine hydrochloride in the mixed solution is 2:

1.

5. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: In step S3, the epoxy resin in the mixed resin is 10-20 wt% of the acrylic resin, the photoinitiator is 1-5 wt% of the acrylic resin, and the ratio of acrylic resin to deionized water is 7:

43.

6. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: In step S4, the NdFeB magnet is placed in a 0.6-6 wt% nitric acid solution for acid washing for 30-60 seconds. After washing, it is placed in deionized water for ultrasonic treatment for 1-2 minutes. The above operation is repeated once, and then it is placed in anhydrous ethanol solution for ultrasonic treatment for 1-2 minutes. Finally, it is dried with a hair dryer using cold air.

7. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: Step S4 also includes adding composite PDA-BI@ZIF-8 composite filler to the electrophoresis solution at a concentration of 1.5–2 g / L.

8. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: In step S5, the acid-washed NdFeB magnet is placed in an electrophoresis tank for cathodic electrophoresis to prepare an epoxy-modified acrylic resin photocurable composite coating, and then the residual electrophoretic solution on the surface is washed away with deionized water.

9. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: Step S5 also includes: performing cathodic electrophoresis on the acid-washed NdFeB magnet, with a working voltage of 60V to 80V, a working ambient temperature of 25 to 30℃, and an energizing time of 10 to 20s.

10. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: In step S6: After electrophoresis, the NdFeB magnet is pre-dried under a fan for 5-15 minutes, then placed in an 80°C oven for flash evaporation for 10-15 minutes, and then irradiated under an ultraviolet curing lamp.

11. The method for preparing a PDA-modified BI@ZIF-8 photocurable composite coating on the surface of an NdFeB magnet according to claim 1, characterized in that: Step S6 also includes: the ultraviolet light irradiation time is 30-60 seconds and the irradiation distance is 5 cm.

Images