1. The modified sericite-epoxy resin composite coating is characterized by comprising the following components in parts by mass: 10-15 parts of epoxy resin, 1-15 parts of modified sericite and 70-89 parts of deionized water, wherein the epoxy resin is a water-based cathode epoxy resin electrophoretic emulsion, and the modified sericite is modified sericite modified by KH 550.

2. The modified sericite-epoxy resin composite coating according to claim 1, wherein the solid content of the epoxy resin is 36%.

3. The method for preparing the modified sericite-epoxy resin composite coating according to claim 1, comprising the steps of:

step S10, heating the ground natural sericite in air, and furnace-cooling to obtain activated sericite powder;

step S11, mixing the activated sericite powder and nitric acid according to a first preset proportion, heating, stirring and filtering, washing the filtrate with deionized water to neutrality, and drying to obtain acidified sericite;

step S12, mixing the acidified sericite and a saturated NaCl solution according to a second preset proportion, heating, stirring and filtering, washing a filtrate by using deionized water, and drying to obtain sodium-modified sericite;

step S13, mixing the sodium-modified sericite, hexadecyltrimethylammonium bromide and deionized water according to a third preset proportion, heating and stirring, washing with deionized water and drying to obtain intercalated sericite;

step S14, dissolving intercalated sericite in deionized water, performing magnetic stirring and ultrasonic treatment to obtain an exfoliated sericite suspension, diluting the dispersed sericite suspension into ethanol, adding KH550, refluxing and continuously stirring to obtain a mixed solution, washing and drying the mixed solution with water and ethanol for multiple times respectively, and then heating and drying to obtain a modified sericite suspension modified by KH 550;

and step S15, mixing the suspension of the modified sericite with the epoxy resin electrophoretic emulsion, and then stirring, ultrasonically treating and vacuum defoaming to obtain the modified sericite-epoxy resin composite coating.

4. The production method according to claim 3, wherein in step S10, the heating temperature is 800 ℃ and the heating time is 1 h;

in step S11, the first preset ratio is 1: 40 to 45, HNO₃The concentration is 5.0mol/L, the heating temperature is 95 ℃, the stirring time is 5h, the temperature of deionized water is 80 ℃, and the drying temperature is 80 ℃;

in step S12, the third preset ratio is 1: 40-45, heating at 95 ℃, stirring for 3h, deionized water at 80 ℃, and drying at 80 ℃;

in step S13, the third preset ratio is 1.5: 4.6: 150, stirring at 80 ℃, stirring for 24 hours, deionized water at 80 ℃ and drying at 80 ℃;

in the step S14, the ultrasonic time is 2-6 h, and the mass concentration of the sericite in the suspension is 1 g/mL; the ratio of deionized water, KH550 and ethanol is 1: 1: 15, refluxing at 80 ℃, continuously stirring for 5-8 h, washing and drying for at least three times, wherein the drying temperature is 80 ℃, and the drying time is 24 h;

in step S15, the ultrasonic time is 0.5-1 h, and the vacuum defoaming time is 10 min.

5. The method for preparing a composite coating layer by using the modified sericite-epoxy resin composite paint according to claim 1, which comprises the following steps:

step S20, placing the prepared modified sericite-epoxy resin composite coating into a container;

step S21, immersing the base material with the surface polished step by step, cleaned and air-dried as a cathode into the composite coating, forming a loop with an anode immersed into the composite coating, and performing electrophoretic deposition treatment under the action of an external voltage to form a modified sericite-epoxy resin composite coating sample on the surface of the base material;

and step S22, cleaning the matrix containing the modified sericite-epoxy resin composite coating sample by using ionized water, and then curing at high temperature to form the modified sericite-epoxy resin composite coating on the surface of the base material.

6. The method of claim 5, wherein the substrate is made of one of carbon steel, alloy steel, titanium alloy, aluminum alloy, or magnesium alloy.

7. The method according to claim 5, wherein in step S21, the steps of polishing the surface step by step and cleaning and air drying comprise;

the SiC sand paper of 400#, 1200# and 2000# is adopted to gradually grind and polish the base material;

cleaning the polished substrate with deionized water and ethanol for 15min by ultrasonic wave;

the cleaned substrate was air-dried in the air.

8. The method of claim 5, wherein in step S21, the anode material is made of platinum or copper sheet.

9. The method of claim 5, wherein in step S21, the electrophoretic deposition is performed in a constant voltage mode, the applied voltage is 20-100V, the deposition temperature is room temperature, and the deposition time is 5-30 min.

10. The method as claimed in claim 5, wherein the high temperature curing temperature is 150 ℃ for 30 to 90min in step S22, and the modified sericite sheets are closely arranged in parallel in the epoxy resin.

Background

Epoxy resin coatings are widely used because of their environmental protection properties. The cured epoxy resin coating has good physical and chemical properties, excellent bonding strength to the surfaces of metal and non-metal materials, good flexibility and stability to alkali and most solvents, so that the epoxy resin coating has a wide market in the fields of priming paint, floor paint, anticorrosive paint and the like. However, a single epoxy coating can present significant challenges in harsh corrosive environments, such as poor weatherability, low structural strength, etc. Meanwhile, in the film forming process, bubbles and pinholes are easily formed along with the volatilization of the solvent, so that the barrier property of the coating is reduced, and the further practical application of the coating as a corrosion protection coating is limited. In order to improve the organization structure and the barrier property of the epoxy resin coating, researches show that the defect of the epoxy resin coating can be made up and the compactness of the epoxy resin coating is improved by adding two-dimensional nanosheet materials such as graphene and molybdenum disulfide with a layered structure into the epoxy resin coating, but the corrosion resistance and the flame retardance of the epoxy resin coating are not enough.

Sericite is a silicate mineral material with a natural two-dimensional lamellar structure, and is widely used as a high-quality filler in the industries of plastics, rubber, papermaking and cosmetics due to good physical stability, wear resistance, ageing resistance and low cost. However, the nanosheet layer in the natural sericite structure is stacked one on another and is not easily separated directly by a mechanical method, and thus it is difficult to exert the advantages of the nanosheet layer structure when used as a filler. In addition, sericite is hydrophilic and oleophobic, and the dispersibility of sericite is poor and the lamella is easy to agglomerate when sericite which is not modified is directly added into an organic coating, so that the interface problem caused by the agglomeration leads to formation of a large number of pores and cracks after the coating is formed into a film, thereby being difficult to play a role in enhancing the compactness of the coating and shielding a corrosive medium, and limiting the further application of the sericite in a polymer coating.

Disclosure of Invention

Based on the above, the invention aims to provide a modified sericite-epoxy resin composite coating, a preparation method thereof and a preparation method of a composite coating thereof, wherein the dispersibility and the interface compatibility of sericite in epoxy resin are improved by performing nano-lamellar separation and surface modification treatment on sericite, the advantages of a two-dimensional lamellar structure of sericite are fully exerted, and the structural compactness and the corrosion resistance of the whole composite coating are improved.

In a first aspect, the invention provides a modified sericite-epoxy resin composite coating, which comprises the following components in parts by mass: 10-15 parts of epoxy resin, 1-15 parts of modified sericite and 70-89 parts of deionized water, wherein the epoxy resin is a water-based cathode epoxy resin electrophoretic emulsion, and the modified sericite is modified sericite modified by KH 550.

Further, the solid content of the epoxy resin was 36%.

In a second aspect, the invention also provides a preparation method of the modified sericite-epoxy resin composite coating, which comprises the following steps:

step S10, heating the ground natural sericite in air, and furnace-cooling to obtain activated sericite powder;

step S11, mixing the activated sericite powder and nitric acid according to a first preset proportion, heating, stirring and filtering, washing the filtrate with deionized water to neutrality, and drying to obtain acidified sericite;

step S12, mixing the acidified sericite and a saturated NaCl solution according to a second preset proportion, heating, stirring and filtering, washing a filtrate by using deionized water, and drying to obtain sodium-modified sericite;

step S13, mixing the sodium-modified sericite, hexadecyltrimethylammonium bromide and deionized water according to a third preset proportion, heating and stirring, washing with deionized water and drying to obtain intercalated sericite;

step S14, dissolving intercalated sericite in deionized water, performing magnetic stirring and ultrasonic treatment to obtain a stripped sericite suspension, diluting the dispersed sericite suspension into ethanol, adding KH550, refluxing and continuously stirring to obtain a mixed solution, washing and drying the mixed solution with water and ethanol for multiple times respectively, and then heating and drying to obtain a modified sericite suspension modified by KH 550;

and step S15, mixing the suspension of the modified sericite with the epoxy resin electrophoretic emulsion, and then stirring, ultrasonically treating and vacuum defoaming to obtain the modified sericite-epoxy resin composite coating.

Further, in step S10, the heating temperature is 800 ℃, and the heating time is 1 h;

in step S11, the first preset ratio is 1: 40 to 45, HNO₃The concentration is 5.0mol/L, the heating temperature is 95 ℃, the stirring time is 5h, the temperature of deionized water is 80 ℃, and the drying temperature is 80 ℃;

in step S12, the third preset ratio is 1: 40-45, heating at 95 ℃, stirring for 3h, deionized water at 80 ℃, and drying at 80 ℃;

in step S13, the third preset ratio is 1.5: 4.6: 150, stirring at 80 ℃, stirring for 24 hours, deionized water at 80 ℃ and drying at 80 ℃;

in the step S14, the ultrasonic time is 2-6 h, and the mass concentration of the sericite in the suspension is 1 g/mL; the ratio of deionized water, KH550 and ethanol is 1: 1: 15, refluxing at 80 ℃, continuously stirring for 5-8 h, washing and drying for at least three times, wherein the drying temperature is 80 ℃, and the drying time is 24 h;

in step S15, the ultrasonic time is 0.5-1 h, and the vacuum defoaming time is 10 min.

In a third aspect, the invention also provides a method for preparing a composite coating by using the modified sericite-epoxy resin composite coating, which comprises the following steps:

step S20, placing the prepared modified sericite-epoxy resin composite coating into a container;

step S21, immersing the base material with the surface polished step by step, cleaned and air-dried as a cathode into the composite coating, forming a loop with an anode immersed into the composite coating, and performing electrophoretic deposition treatment under the action of an external voltage to form a modified sericite-epoxy resin composite coating sample on the surface of the base material;

and step S22, cleaning the matrix containing the modified sericite-epoxy resin composite coating sample by using ionized water, and then curing at high temperature to form the modified sericite-epoxy resin composite coating on the surface of the base material.

Further, the base material is made of one of carbon steel, alloy steel, titanium alloy, aluminum alloy or magnesium alloy.

Further, in step S21, the step of polishing the surface step by step, cleaning and air drying includes the specific steps;

the SiC sand paper of 400#, 1200# and 2000# is adopted to gradually grind and polish the base material;

cleaning the polished substrate with deionized water and ethanol for 15min by ultrasonic wave;

the cleaned substrate was air-dried in the air.

Further, in step S21, the anode material is made of a platinum sheet or a copper sheet.

Further, in step S21, the electrophoretic deposition is performed in a constant voltage mode, the applied voltage is 20-100V, the deposition temperature is room temperature, and the time is 5-30 min.

Further, in step S22, the high temperature curing temperature is 150 ℃ and the time is 30-90 min, and the modified sericite sheet layers are closely arranged in the epoxy resin in a parallel shape.

Compared with the prior art, the invention has the following advantages:

firstly, in the composite coating prepared by the invention, the introduction of hexadecyl trimethyl ammonium bromide improves the interlayer spacing of the sericite through intercalation, so that the sericite is very easy to disperse into a single-sheet layer structure under the mechanical action, and the dispersion and regular arrangement of the single-sheet layer of the sericite in the composite coating are promoted;

secondly, in the composite coating prepared by the invention, the introduction of the modified sericite lamella can make up for the defects in the epoxy resin coating structure, the two-dimensional lamella structure of the modified sericite and the epoxy resin are crosslinked through chemical bonding to form a physical barrier layer in the composite coating and prevent the permeation of corrosive media and oxygen, so that the mechanical property, the corrosion resistance and the flame retardant property of the composite coating are improved, and the composite coating prepared by the invention is expected to be widely applied in the fields of aviation, aerospace, machinery, automobiles, medical treatment, electronics and the like;

thirdly, the solvent of the invention adopts water-based epoxy resin, is green and environment-friendly, and reduces environmental pollution compared with organic solvent;

fourthly, the preparation method of the invention is simple, does not need complex equipment, has huge stock of sericite in China, is widely and easily available, has low cost and is suitable for industrial production.

Drawings

FIG. 1 is a flow chart of a method for preparing a modified sericite-epoxy resin composite coating according to the invention;

FIG. 2 is a FT-IR chart of sericite modified with cetyltrimethylammonium bromide and sericite modified with KH550 according to the present invention;

FIG. 3 is a diagram of the anti-corrosion and flame-retardant mechanism of the modified sericite-epoxy resin composite coating according to the invention;

FIG. 4 is a TEM image of a sericite nanosheet modified with cetyltrimethylammonium bromide according to the present invention;

FIG. 5(a) is a Nyquist plot of a composite coating and a neat epoxy coating prepared in the present invention after soaking in 3.5 wt% NaCl solution for 7 days, respectively;

FIG. 5(b) is a bode impedance plot of the composite coating and the pure epoxy coating prepared in the present invention after soaking in 3.5 wt% NaCl solution for 7 days, respectively.

The following detailed description will further illustrate the invention in conjunction with the above-described figures.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Several embodiments of the invention are presented in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Referring to fig. 1, the invention provides a modified sericite-epoxy resin composite coating, which comprises the following components in parts by mass: 10-15 parts of epoxy resin, 1-15 parts of modified sericite and 70-89 parts of deionized water, wherein the epoxy resin is a water-based cathode epoxy resin electrophoretic emulsion, and the modified sericite is modified sericite modified by KH 550.

Further, the solid content of the epoxy resin was 36%. And the adopted epoxy resin is water-based epoxy resin, so that the epoxy resin is green and environment-friendly, and compared with an organic solvent, the environmental pollution is reduced.

In a second aspect, the invention also provides a preparation method of the modified sericite-epoxy resin composite coating, which comprises the following steps:

step S10, heating the ground natural sericite in air, and furnace-cooling to obtain activated sericite powder;

specifically, in the step, the heating temperature is 800 ℃, and the heating time is 1 h.

Step S11, mixing the activated sericite powder and nitric acid according to a first preset proportion, heating, stirring and filtering, washing the filtrate with deionized water to neutrality, and drying to obtain acidified sericite;

in this step, washing is performed to remove excess nitric acid. Specifically, the first preset ratio is 1: 40 to 45, HNO₃The concentration is 5.0mol/L, the heating temperature is 95 ℃, the stirring time is 5h, the temperature of the deionized water is 80 ℃, and the drying temperature is 80 ℃.

Step S12, mixing the acidified sericite and a saturated NaCl solution according to a second preset proportion, heating, stirring and filtering, washing a filtrate by using deionized water, and drying to obtain sodium-modified sericite;

in this step, washing was performed to remove excess NaCl (AgNO was added)₃No precipitation occurs). Specifically, the third preset ratio is 1: 40-45, heating temperature is 95 ℃, stirring time is 3h, temperature of deionized water is 80 ℃, and drying temperature is 80 ℃.

Step S13, mixing the sodium-modified sericite, hexadecyltrimethylammonium bromide and deionized water according to a third preset proportion, heating and stirring, washing with deionized water and drying to obtain intercalated sericite;

in this step, the washing is performed to remove the excess hexadecyltrimethylammonium bromide (AgNO added)₃No precipitation occurs). Specifically, the third preset ratio is 1.5: 4.6: 150, the stirring temperature is 80 ℃, the stirring time is 24 hours, the temperature of the deionized water is 80 ℃, and the drying temperature is 80 ℃.

Referring to fig. 2, a TEM image of the intercalated sericite is prepared by using a transmission electron microscope, and a significant lamella spacing is observed, which indicates that the intercalated sericite has an increased lamella spacing and is successfully dissociated into a double-layer structure from the original multi-layer structure.

Step S14, dissolving intercalated sericite in deionized water, performing magnetic stirring and ultrasonic treatment to obtain a stripped sericite suspension, diluting the dispersed sericite suspension into ethanol, adding KH550, refluxing and continuously stirring to obtain a mixed solution, washing and drying the mixed solution with water and ethanol for multiple times respectively, and then heating and drying to obtain a modified sericite suspension modified by KH 550;

in this step, washing is performed for the purpose of removing residual silane. Specifically, the ultrasonic time is 2-6 h, and the mass concentration of sericite in the suspension is 1 g/mL; the ratio of deionized water, KH550 and ethanol is 1: 1: 15, refluxing at 80 ℃, continuously stirring for 5-8 h, washing and drying for at least three times, wherein the drying temperature is 80 ℃, and the drying time is 24 h.

And step S15, mixing the suspension of the modified sericite with the epoxy resin electrophoretic emulsion, and then stirring, ultrasonically treating and vacuum defoaming to obtain the modified sericite-epoxy resin composite coating.

Specifically, in the step, the ultrasonic time is 0.5-1 h, and the vacuum defoaming time is 10 min.

In a third aspect, the invention also provides a method for preparing a composite coating by using the modified sericite-epoxy resin composite coating, which comprises the following steps:

step S20, placing the prepared modified sericite-epoxy resin composite coating into a container;

step S21, immersing the base material with the surface polished step by step, cleaned and air-dried as a cathode into the composite coating, forming a loop with an anode immersed into the composite coating, and performing electrophoretic deposition treatment under the action of an external voltage to form a modified sericite-epoxy resin composite coating sample on the surface of the base material;

in the step, the base material is made of one of carbon steel, alloy steel, titanium alloy, aluminum alloy or magnesium alloy, and the anode material is made of a platinum sheet or a copper sheet.

Further, in step S21, the electrophoretic deposition is performed in a constant voltage mode, the applied voltage is 20-100V, the deposition temperature is room temperature, and the time is 5-30 min.

Further, in step S21, the step of polishing the surface step by step, cleaning and air drying includes the specific steps;

the SiC sand paper of 400#, 1200# and 2000# is adopted to gradually grind and polish the base material;

cleaning the polished substrate with deionized water and ethanol for 15min by ultrasonic wave;

the cleaned substrate was air-dried in the air.

And step S22, cleaning the matrix containing the modified sericite-epoxy resin composite coating sample by using ionized water, and then curing at high temperature to form the modified sericite-epoxy resin composite coating on the surface of the base material.

In this step, the washing is performed to wash off the residual electrophoretic emulsion on the surface of the composite coating sample. Specifically, the high-temperature curing temperature is 150 ℃, the time is 30-90 min, and sericite lamella is closely arranged in the epoxy resin in a parallel shape.

In conclusion, the invention has the following advantages:

firstly, in the composite coating prepared by the invention, the introduction of hexadecyl trimethyl ammonium bromide improves the interlayer spacing of the sericite through intercalation, so that the sericite is very easy to disperse into a single-sheet layer structure under the mechanical action, and the dispersion and regular arrangement of the single-sheet layer of the sericite in the composite coating are promoted;

secondly, in the composite coating prepared by the invention, the introduction of the modified sericite sheet layer can make up for the defects in the epoxy resin coating structure, and simultaneously, the two-dimensional sheet layer structure of the modified sericite and the epoxy resin are crosslinked through chemical bonding to form a physical barrier layer in the composite coating and prevent the permeation of corrosive media and oxygen (as shown in figure 3), so that the mechanical property, the corrosion resistance and the flame retardant property of the composite coating are improved, and the composite coating prepared by the invention is expected to be widely applied in the fields of aviation, aerospace, machinery, automobiles, medical treatment, electronics and the like;

thirdly, the solvent of the invention adopts water-based epoxy resin, is green and environment-friendly, and reduces environmental pollution compared with organic solvent;

fourthly, the preparation method of the invention is simple, does not need complex equipment, has huge stock of sericite in China, is widely and easily available, has low cost and is suitable for industrial production.

The invention is illustrated below by means of specific examples.

In each example, the sericite raw material used was 800-mesh sericite powder, and the epoxy resin was a water-based cathodic epoxy resin electrophoretic emulsion with a solid content of 36%.

Example 1:

in this example, an electrophoresis apparatus shown in fig. 1 was used to prepare a modified sericite-epoxy resin composite coating on the surface of 2024 aluminum alloy by electrophoretic deposition, which was performed by the following steps:

the method comprises the following steps: intercalation separation of sericite

20g of ground sericite was heated at 800 ℃ for 1 hour in the air and furnace-cooled. After annealing, mixing mica powder and nitric acid according to the ratio of 1: 45 in a proportion of HNO₃At a concentration of 5.0mol/L, stirred at 95 ℃ for 5h, filtered and washed several times with deionized water at 80 ℃ to neutrality and then dried at 80 ℃. The acidified sericite and a saturated NaCl solution were mixed according to the ratio of 1: 45, stirred at 95 ℃ for 3h, filtered and washed several times with 80 ℃ deionized water to remove excess NaCl (AgNO added)₃No precipitate was generated), and then dried at 80 ℃. Subsequently, the sodium-modified sericite, cetyltrimethylammonium bromide and deionized water were mixed in a ratio of 1.5: 4.6: 150, stirred at 80 ℃ for 24h and washed several times with deionized water at 80 ℃ to remove excess cetyltrimethylammonium bromide (AgNO added)₃No precipitate was generated), and then dried at 80 ℃.

Step two: preparation of modified sericite

Dissolving intercalated sericite in deionized water, magnetically stirring and ultrasonically treating for 2 hours to obtain an exfoliated sericite suspension, wherein the mass concentration of the sericite in the suspension is 1 g/mL; diluting the dispersed suspension into ethanol, and adding KH550, wherein the ratio of deionized water to KH550 to ethanol is 1: 1: 15. reflux and continuous stirring at 80 ℃ for 5h, followed by three washes of the dried material with water and ethanol, respectively, to remove residual silane. Drying at 80 deg.C for 24h to obtain KH550 modified sericite.

Step three: preparation of modified sericite-epoxy resin composite coating

Adding 2g of prepared KH550 modified sericite into a 250mL beaker, dispersing the prepared KH550 modified sericite into 52.5mL of deionized water, stirring at the rotating speed of 3000rmp at room temperature and performing ultrasonic treatment for 1h to obtain KH550 modified sericite suspension, finally adding 37.5g of epoxy resin, mixing with the KH550 modified sericite suspension, stirring at the rotating speed of 3000rmp at room temperature and performing ultrasonic treatment for 0.5h, and performing vacuum deaeration for 10min to obtain the modified sericite-epoxy resin composite coating.

Step four: pretreatment of substrates

The base material was 2024 aluminum alloy (40 mm. times.20 mm. times.1.5 mm). Before the coating is deposited, gradually grinding and polishing the base material by using 400#, 1200# and 2000# SiC sand paper, and ultrasonically cleaning the polished base material for 15min by using deionized water and ethanol; and dried in air. And connecting the polished aluminum sheet with a lead. All metal parts were hermetically immersed in the composite coating except for a 10mm by 10mm surface area exposed to air.

Step five: electrophoretic deposition modified sericite-epoxy resin composite coating

A platinum sheet electrode is used as an anode, 2024 aluminum alloy is used as a cathode, a power supply is externally connected, and the coating is deposited for 5 minutes by electrophoresis under the voltage of 60V in a constant voltage mode. The coated sample was rinsed several times with deionized water to remove the residual emulsion on the surface. And finally drying the mixture at 150 ℃ for 30min to obtain the modified sericite-epoxy resin composite coating.

Referring to FIG. 4, FT-IR images were prepared for cetyltrimethylammonium bromide modified sericite and KH550 modified sericite, respectively. As can be seen, the comparative sericite uses cetyltrimethylammonium bromide to sericiteAfter intercalation treatment of mica, CTAB-sericite is 2918cm^-1And 2849cm^-1Two new bands appear, which are assigned to-CH₂Asymmetric and symmetric stretching vibration is a characteristic peak of CTAB, which indicates successful intercalation; compared with CTAB-sericite, KH 550-sericite was found at 3440cm after KH550 treatment^-1The absorption band appeared here is enhanced compared to before, and is related to-OH stretching and bending frequency, indicating that the modification is successful; and 1025cm^-1Is a Si-O-Si stretching vibration characteristic peak, and the absorption peak is obviously widened, so that residual-OH on the surface of the intercalated sericite reacts with Si-OH hydrolyzed by silane to generate Si-O-Si covalent bonds, and KH550 is successfully grafted to the surface hydroxyl of the sericite.

Referring to fig. 5(a), after the modified sericite-epoxy resin composite coating and the pure epoxy resin coating prepared in the present example are respectively soaked in a 3.5 wt% NaCl solution for 1 week, a Nyquist diagram is prepared, and it can be seen that the impedance arc of the modified sericite-epoxy resin composite coating is significantly increased compared with that of the pure epoxy resin coating.

Referring to fig. 5(b), after the modified sericite-epoxy resin composite coating and the pure epoxy resin coating prepared in the present embodiment are respectively soaked in a 3.5 wt% NaCl solution for 1 week, a bode impedance diagram is prepared, and it can be seen from the bode impedance diagram that the impedance value of the modified sericite-epoxy resin composite coating is improved by one order of magnitude compared with that of the pure epoxy resin coating.

Further, sericite modified with cetyltrimethylammonium bromide and sericite modified with KH550 were analyzed using a zeta potential and a particle size analyzer, respectively, and compared with sericite without any treatment, and the results are shown in table 1.

TABLE 1 zeta potential and particle size analysis of cetyltrimethylammonium bromide, KH550 modified sericite

Solutions of	Zeta potential/mV	Average size/nm
			Sericite aqueous solution	-28.1	2950.88
CTAB sericite aqueous solution	-23.6	843.97
			KH 550-CTAB-sericite-water solution	45.3	599.66

As can be seen from table 1, the sericite modified with cetyltrimethylammonium bromide had a significantly reduced lamella diameter, indicating that the lamella had been effectively dissociated, and the surface of the lamella had a negative charge; after the sericite is modified by KH550, the diameter of the lamella is further reduced, and the surface of the lamella is positively charged, which shows that the dispersibility of the sericite lamella is improved and the sericite lamella is easily coupled with epoxy resin.

Example 2:

in this example, an electrophoresis apparatus shown in fig. 1 was used to prepare a modified sericite-epoxy resin composite coating on the surface of 2024 aluminum alloy by electrophoretic deposition, which was carried out according to the following steps:

in this embodiment, in step three: in the preparation process of the modified sericite-epoxy resin composite coating,

adding 0.5g of prepared KH550 modified sericite into a 250mL beaker, dispersing the prepared sericite into 61.5mL of deionized water, stirring at the rotating speed of 3000rmp at room temperature, performing ultrasonic treatment for 1h to obtain KH550 modified sericite suspension, finally adding 37.5g of epoxy resin, mixing with the sericite suspension, stirring at the rotating speed of 3000rmp at room temperature, performing ultrasonic treatment for 0.5h, and performing vacuum defoamation for 10min to obtain the sericite-epoxy resin composite coating. The rest is the same as in embodiment 1.

In the embodiment, the doping amount of the sericite is less, a small amount of pinholes are formed on the surface of the coating, the anti-corrosion effect of the coating is not good as that of the coating in embodiment 1, but the anti-corrosion effect of the coating is still enhanced to a certain extent compared with that of a pure epoxy resin coating.

Example 3:

in this example, an electrophoresis apparatus shown in fig. 1 was used to prepare a modified sericite-epoxy resin composite coating on a 304 stainless steel surface by electrophoretic deposition, which was carried out according to the following steps:

in this embodiment, step three: in the preparation process of the modified sericite-epoxy resin composite coating,

adding 5g of prepared KH550 modified sericite into a 250mL beaker, dispersing the prepared sericite into 52.5mL of deionized water, stirring at the rotating speed of 3000rmp at room temperature, performing ultrasonic treatment for 1h to obtain KH550 modified sericite suspension, finally adding 37.5g of epoxy resin, mixing with the sericite suspension, stirring at the rotating speed of 3000rmp at room temperature, performing ultrasonic treatment for 0.5h, and performing vacuum defoamation for 10min to obtain the sericite-epoxy resin composite coating.

Step four: in the preparation process of the base material pretreatment,

the base material was 304 stainless steel (Φ 15mm × 1 mm). Before the coating is deposited, gradually grinding and polishing the base material by using 400#, 1200# and 2000# SiC sand paper, and ultrasonically cleaning the polished base material for 15min by using deionized water and acetone; and dried in air. And connecting the polished aluminum sheet with a lead. All metal parts were sealed in the composite coating except for the 10mm x 10mm surface area exposed to air.

Step five: in the preparation process of the electrophoretic deposition modified sericite-epoxy resin composite coating,

a platinum sheet electrode is selected as an anode, 304 stainless steel is selected as a cathode, an external power supply is connected, and the coating is deposited for 5 minutes by electrophoresis under the voltage of 50V in a constant voltage mode. The coated sample was rinsed several times with deionized water to remove the residual emulsion on the surface. And finally drying at 150 ℃ for 30min to obtain the modified sericite-epoxy composite coating.

The rest is the same as in embodiment 1.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.