Composite coating, and method of making and use thereof

Abstract

The application relates to the coating technical field and discloses a composite coating as well as a preparation method and application of the composite coating. The composite coating comprises an inner layer, an outer layer and a bonding layer arranged between the inner layer and the outer layer; the outer layer is a basalt fiber cloth; and the preparation raw materials of the inner layer comprise 100 parts by weight of a first epoxy resin, 10-40 parts by weight of chopped basalt fibers, 5-30 parts by weight of hexagonal boron nitride, 0.5-5 parts by weight of a coupling agent, 1-3 parts by weight of a surfactant, 0.5-2.5 parts by weight of an antioxidant and 1-15 parts by weight of a curing agent. The composite coating provided in the application can significantly enhance the bonding strength between the composite coating and a base body through the interaction between the various components, can avoid the falling-off of the composite coating, can significantly improve the acid resistance and halogen water corrosion resistance of the composite coating, and is suitable for industrial popularization.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and more specifically to a composite coating, a method for preparing the composite coating, and its application. Background Technology

[0002] Drilling instruments play a crucial role in drilling operations, typically used for measuring downhole information (inclination, azimuth, etc.). The conventional materials for the casing of drilling instruments are beryllium copper, titanium alloys, and other metals. During use, these instruments must withstand the high-speed erosion of drilling fluid; solid particles in the drilling fluid can easily corrode the casing, causing wear. Particularly, when drilling encounters special situations, such as stuck pipe that cannot be released by conventional methods, acid injection is often used to release the stuck pipe. This involves injecting a mixture of hydrofluoric acid and hydrochloric acid into the well. This mixture of hydrofluoric acid and hydrochloric acid can easily cause chemical corrosion of the instrument casing, leading to damage to the delicate and expensive electronic components inside the instrument.

[0003] Therefore, there is an urgent need to develop a composite coating that can be used on drilling instruments, has good acid resistance and wear resistance, and is not easy to peel off. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of easy detachment, acid corrosion, and wear of the housing of drilling instruments during use, and to provide a composite coating, a method for preparing the composite coating, and its application.

[0005] To achieve the above objectives, a first aspect of the present invention provides a composite coating comprising: an inner layer, an outer layer, and an adhesive layer disposed between the inner layer and the outer layer; wherein the outer layer is basalt fiber cloth, and the raw materials for preparing the inner layer include: 100 parts by weight of a first epoxy resin, 10-40 parts by weight of chopped basalt fiber, 5-30 parts by weight of hexagonal boron nitride, 0.5-5 parts by weight of a coupling agent, 1-3 parts by weight of a surfactant, 0.5-2.5 parts by weight of an antioxidant, and 1-15 parts by weight of a curing agent.

[0006] A second aspect of the present invention provides a method for preparing the composite coating described in the first aspect of the present invention, wherein the method includes the following steps:

[0007] (1) Mix the first epoxy resin, chopped basalt fiber, hexagonal boron nitride, coupling agent, surfactant and antioxidant evenly, and then add curing agent and continue mixing to obtain inner coating; apply the obtained inner coating evenly to the substrate and let it stand at room temperature for 18-24 hours to obtain inner layer;

[0008] (2) The second epoxy resin is uniformly coated on the inner layer, and then basalt fiber cloth is covered on the second epoxy resin. The mixture is left to stand at room temperature for 18-24 hours to obtain a composite coating.

[0009] The third aspect of the present invention provides an application of the composite coating described in the first aspect of the present invention or the composite coating prepared by the preparation method described in the second aspect of the present invention on the housing of an instrument or device.

[0010] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0011] 1) The composite coating provided in this invention has interactions between its components, which can significantly enhance the bonding strength between the composite coating and the substrate (instrument or equipment housing) and the wear resistance of the composite coating, prevent the composite coating from falling off, and improve the erosion resistance of the composite coating.

[0012] 2) The composite coating provided in this invention can significantly improve the acid resistance and brine corrosion resistance of the composite coating, and can better protect the instrument and extend its service life without affecting the normal use of the instrument.

[0013] 3) The composite coating preparation method provided in this invention can prepare the composite coating by coating at room temperature without thermal spraying, which can avoid the internal stress caused by thermal spraying and further improve the mechanical properties of the composite coating. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] A first aspect of the present invention provides a composite coating comprising: an inner layer, an outer layer, and an adhesive layer disposed between the inner layer and the outer layer; wherein the outer layer is basalt fiber cloth, and the raw materials for preparing the inner layer include: 100 parts by weight of a first epoxy resin, 10-40 parts by weight of chopped basalt fiber, 5-30 parts by weight of hexagonal boron nitride, 0.5-5 parts by weight of a coupling agent, 1-3 parts by weight of a surfactant, 0.5-2.5 parts by weight of an antioxidant, and 1-15 parts by weight of a curing agent.

[0016] In this invention, the inventors discovered through research that adding short-cut basalt fibers to the inner layer can significantly improve the erosion resistance of the composite coating, preventing it from peeling off or being scratched during use. The synergistic effect of the short-cut basalt fibers with other components also enhances the corrosion resistance of the composite coating, making it more resistant to acid and brine corrosion. The composite coating exhibits optimal overall performance when the content of short-cut basalt fibers is within the aforementioned defined range.

[0017] In a preferred embodiment, the raw materials for preparing the inner layer include: 100 parts by weight of a first epoxy resin, 20-30 parts by weight of chopped basalt fiber, 10-20 parts by weight of hexagonal boron nitride, 2.5-3.5 parts by weight of a coupling agent, 1.5-2.5 parts by weight of a surfactant, 0.8-1.8 parts by weight of an antioxidant, and 5-12 parts by weight of a curing agent.

[0018] In a preferred embodiment, the raw materials for preparing the inner layer include: 100 parts by weight of a first epoxy resin, 24-26 parts by weight of chopped basalt fiber, 14-16 parts by weight of hexagonal boron nitride, 2.8-3.2 parts by weight of a coupling agent, 1.8-2.2 parts by weight of a surfactant, 1.4-1.6 parts by weight of an antioxidant, and 7-8 parts by weight of a curing agent.

[0019] In a preferred embodiment, the first epoxy resin is selected from one or more of alicyclic epoxy resins, bisphenol A epoxy resins, and phenolic epoxy resins.

[0020] In this invention, there is no particular limitation on alicyclic epoxy resins, alicyclic epoxy resins and phenolic epoxy resins. Commonly used alicyclic epoxy resins, alicyclic epoxy resins and phenolic epoxy resins in the art can all be used in this invention.

[0021] In a preferred embodiment, the first epoxy resin is an alicyclic epoxy resin and a bisphenol A epoxy resin, or the first epoxy resin is an alicyclic epoxy resin and a phenolic epoxy resin.

[0022] In this invention, compared with a single type of epoxy resin, the synergistic effect of alicyclic epoxy resin and bisphenol A epoxy resin or phenolic epoxy resin can further improve the bonding strength of the composite coating and enhance its erosion resistance.

[0023] In a preferred embodiment, the mass ratio of the alicyclic epoxy resin to the bisphenol A epoxy resin is 1:2-8, preferably 1:4-6; the mass ratio of the alicyclic epoxy resin to the phenolic epoxy resin is 1:2-8, preferably 1:4-6.

[0024] In a preferred embodiment, the monomer of the aliphatic epoxy resin is selected from one or more of bis((3,4-epoxycyclohexyl)methyl) adipate, 3,4-epoxycyclohexanecarboxylic acid-3',4'-epoxycyclohexane methyl ester, 3,4-epoxy-6-methylcyclohexanecarboxylic acid-3',4'-epoxy-6-methylcyclohexane methyl ester, dicyclopentadiene dioxide, and dicyclopentyl ether dioxide.

[0025] In this invention, the aliphatic epoxy resin can be a commercially available product, or it can be prepared according to conventional methods in the art based on the monomers described above. Among them, the domestic model of the aliphatic epoxy resin corresponding to the monomer of 3,4-epoxycyclohexanecarboxylic acid-3',4'-epoxycyclohexanemethyl ester is 6221221, and the foreign model is ERL-4221Unox 221; the domestic model of the aliphatic epoxy resin corresponding to the monomer of 3,4-epoxy-6-methylcyclohexanecarboxylic acid-3',4'-epoxy-6-methylcyclohexanemethyl ester is H-71 201 6201, and the foreign model is Unox 201ERL-4201; the domestic model of the aliphatic epoxy resin corresponding to the monomer of dicyclopentadiene dioxide is R-122207 6207, and the foreign model is Unox 207ERL-4207; the domestic model of the aliphatic epoxy resin corresponding to the monomer of dicyclopentyl ether dioxide is 6300, and the foreign model is ERR-4205.

[0026] In a preferred embodiment, the length of the chopped basalt fiber is 10μm-3mm, preferably 0.2-2mm; the average diameter is 0.5-50μm, preferably 1-20μm.

[0027] The chopped basalt fibers used in this invention can be commercially available products, or commercially available products can be processed using conventional secondary processing to obtain chopped basalt fibers of the aforementioned dimensions. When the dimensions of the chopped basalt fibers are within the aforementioned limits, the surface area of ​​the chopped basalt fibers is large, resulting in a large contact area with the inner resin layer and high bonding strength. This can more effectively improve the strength of the composite coating and enhance its mechanical properties.

[0028] In a preferred embodiment, the hexagonal boron nitride has a lamellar structure with an average particle size of 100nm-10μm, preferably 100nm-500nm.

[0029] In this invention, the hexagonal boron nitride with a lamellar structure can effectively improve the self-lubricating properties of the composite coating, thereby improving the wear resistance and erosion resistance of the composite coating.

[0030] In a preferred embodiment, the coupling agent is selected from one or more of vinyltriethoxysilane, aminopropyltriethoxysilane, aminopropyltrimethoxysilane, and propyltrimethoxysilane.

[0031] In this invention, under the action of a coupling agent, hexagonal boron nitride can be coupled with chopped basalt fibers, which can increase the roughness of the chopped basalt fibers, thereby enhancing the bonding strength between the inner layer and the bonding layer and improving the erosion resistance of the fiber cloth.

[0032] In a preferred embodiment, the surfactant comprises 10-30 parts by weight, preferably 15-25 parts by weight of dimethyl sulfoxide, 5-15 parts by weight, preferably 8-12 parts by weight of fatty alcohol polyoxyethylene ether (MOA-9), 5-15 parts by weight, preferably 8-12 parts by weight of bisphenol A diglycidyl ether, and 35-55 parts by weight, preferably 40-50 parts by weight of water.

[0033] In this invention, by adding surfactants, the toughness of the composite coating can be improved, the erosion resistance of the composite coating can be further improved, and the mechanical strength of the composite coating can be enhanced.

[0034] In a preferred embodiment, the antioxidant is selected from one or more of phenolic antioxidants, phosphite antioxidants, and organosulfur antioxidants.

[0035] In this invention, no particular limitation is made to the antioxidants used; conventional phenol-inhibiting antioxidants, phosphite antioxidants, and organosulfur antioxidants in the art can all be used in this invention. For example, the antioxidant can be one or more of diphenyl isooctyl phosphite, trioctyl phosphite, and triisodecyl phosphite.

[0036] In a preferred embodiment, the curing agent is an amine curing agent, selected from one or more of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and diethylaminopropylamine.

[0037] In this invention, the curing agent works synergistically with hexagonal boron nitride, which has excellent thermal conductivity, to enable the epoxy resin to crosslink and cure at room temperature, saving time and facilitating large-scale construction and repair.

[0038] In a preferred embodiment, the basalt fiber cloth is a basalt fiber yarn cloth. Specifically, in this invention, basalt fiber yarn cloth refers to a cloth woven from basalt fiber yarn with a density of less than 150 TEX, or a cloth woven from basalt fiber yarn and fine nylon rope. The basalt fiber cloth in this invention is a conventional commercially available product, and this invention does not impose any special limitations on it.

[0039] In a preferred embodiment, the adhesive layer is made of a second epoxy resin, preferably the same as the first epoxy resin.

[0040] In this invention, the second epoxy resin is the same as the first epoxy resin, which can further increase the bonding force between the inner and outer layers and improve the erosion resistance and corrosion resistance of the composite coating.

[0041] In a preferred embodiment, the thickness of the inner layer is 150-400 μm, preferably 250-350 μm; the thickness of the adhesive layer is 25-75 μm, preferably 35-50 μm; and the thickness of the outer layer is 300-700 μm, preferably 450-550 μm.

[0042] In a preferred embodiment, the thickness of the composite coating is 500-1000 μm, preferably 780-870 μm.

[0043] The composite coating provided in this invention can be used on the housing of instruments or equipment, such as the housing of a drilling instrument. It can significantly improve the bonding strength between the composite coating and the housing, and significantly improve the wear resistance and corrosion resistance of the composite coating. It can extend the service life of the instrument or equipment without affecting its normal use.

[0044] A second aspect of the present invention provides a method for preparing the composite coating described in the first aspect of the present invention, wherein the method includes the following steps:

[0045] (1) Mix the first epoxy resin, chopped basalt fiber, hexagonal boron nitride, coupling agent, surfactant and antioxidant evenly, and then add curing agent and continue mixing to obtain inner coating; apply the obtained inner coating evenly to the substrate and let it stand at room temperature for 18-24 hours to obtain inner layer;

[0046] (2) The second epoxy resin is uniformly coated on the inner layer, and then basalt fiber cloth is covered on the second epoxy resin. The mixture is left to stand at room temperature for 18-24 hours to obtain a composite coating.

[0047] In this invention, room temperature has a generally accepted meaning, and the invention does not specifically limit room temperature. The method for preparing the composite coating provided in this invention can prepare the composite coating by coating at room temperature, without the need for thermal spraying, thus avoiding the internal stress caused by thermal spraying and improving the mechanical properties of the composite coating.

[0048] The third aspect of the present invention provides an application of the composite coating described in the first aspect of the present invention or the composite coating prepared by the preparation method described in the second aspect of the present invention on the housing of an instrument or device.

[0049] The composite coating in this invention is particularly suitable for use on the housings of instruments or equipment that need to operate in abrasion-resistant and acid-resistant environments, such as drilling instruments in the drilling field.

[0050] The present invention will be described in detail below through embodiments.

[0051] Aliphatic epoxy resin A was purchased from Wuhan Xinyang Ruihe Chemical Technology Co., Ltd., with the domestic model number 6221221 and the international model number ERL-4221Unox 221. The monomer is 3,4-epoxycyclohexanecarboxylic acid-3',4'-epoxycyclohexane methyl ester.

[0052] The aliphatic epoxy resin B was purchased from Wuhan Xinyang Ruihe Chemical Technology Co., Ltd., with the domestic model number H-71 2016201 and the international model number Unox 201ERL-4201. The monomer is 3,4-epoxy-6-methylcyclohexanecarboxylic acid-3',4'-epoxy-6-methylcyclohexane methyl ester.

[0053] The aliphatic epoxy resin C was purchased from Wuhan Xinyang Ruihe Chemical Technology Co., Ltd., with the domestic model number R-1222076207 and the international model number Unox 207ERL-4207. The monomer is dicyclopentadiene dioxide.

[0054] The bisphenol A epoxy resin was purchased from Shanghai Jizhi Biochemical Technology Co., Ltd., product model: Lutai Deyuan Epoxy Resin 99% E44 E51.

[0055] The phenolic epoxy resin was purchased from Wuxi Xinyehao Chemical Co., Ltd., product model: phenolic epoxy resin F-51.

[0056] The chopped basalt fibers were purchased from Haining Anjie Composite Materials Co., Ltd., and were processed in the laboratory into chopped basalt fibers with a length of 0.5-2 mm and an average diameter of 1-20 μm.

[0057] Hexagonal boron nitride was purchased from Zhejiang Manli Nanotechnology Co., Ltd. Hexagonal boron nitride A: ML-BN-500, average particle size 500nm; Hexagonal boron nitride B: ML-BN-100, average particle size 100nm; Hexagonal boron nitride C: ML-BN-W01, average particle size 1μm; Hexagonal boron nitride D: ML-BN-W10, average particle size 10μm.

[0058] The fatty alcohol polyoxyethylene ether was purchased from Haian Petrochemical Plant in Jiangsu Province. Product model: fatty alcohol polyoxyethylene ether MOA-9.

[0059] The basalt fiber cloth was purchased from Yixing Xinli Weaving Co., Ltd., and the thickness of the fiber cloth is 0.5mm.

[0060] The substrate is a sample of the outer shell of a drilling instrument.

[0061] Example 1

[0062] (1) Mix 100g of first epoxy resin (the mass ratio of aliphatic epoxy resin A and bisphenol A epoxy resin is 1:4), 25g of short-cut basalt fiber, 15g of hexagonal boron nitride (average particle size 500nm), 3g of coupling agent aminopropyltrimethoxysilane, 2g of surfactant (the mass ratio of dimethyl sulfoxide: fatty alcohol polyoxyethylene ether: bisphenol A diglycidyl ether: water is 20:8:8:45) and 1.5g of diphenyl isooctyl phosphite evenly, and then add 8g of curing agent ethylenetriamine and continue mixing to obtain an inner layer coating; coat the obtained inner layer coating evenly on the substrate and let it stand at room temperature for 24h to obtain a substrate with an inner layer; wherein, the thickness of the inner layer is 180μm;

[0063] (2) The second epoxy resin (the mass ratio of aliphatic epoxy resin A and bisphenol A epoxy resin is 1:5) is uniformly coated on the inner layer, and then covered with basalt fiber cloth. The coating is left to stand at room temperature for 24 hours to obtain a composite coating; wherein the thickness of the adhesive layer formed by the second epoxy resin is 40 μm.

[0064] Examples 2-5

[0065] Similar to Example 1, except that the types and / or contents of each component are different, as shown in Table 1:

[0066] Table 1

[0067]

[0068] Table 1 (continued)

[0069]

[0070] Example 6

[0071] Similar to Example 5, except that the aliphatic epoxy resin is omitted and the first epoxy resin is 100g of bisphenol A epoxy resin.

[0072] Example 7

[0073] Similar to Example 5, except that the mass ratio of aliphatic epoxy resin to bisphenol A epoxy resin is 1:4.

[0074] Comparative Example 1

[0075] Similar to Example 5, except that the amount of chopped basalt fiber used is 5g.

[0076] Comparative Example 2

[0077] Similar to Example 5, except that the short-cut basalt fibers are omitted.

[0078] Comparative Example 3

[0079] Same as Example 5, except that hexagonal boron nitride is omitted.

[0080] Comparative Example 4

[0081] Same as Example 5, except that the antioxidant is omitted.

[0082] Test Example 1

[0083] The thickness of the composite coatings in Examples 1-7 and Comparative Examples 1-4 was tested, and the results are shown in Table 2.

[0084] Table 2

[0085]

[0086]

[0087] Test Example 2

[0088] The resistance to brine corrosion, erosion, acid and wear of the composite coatings in Examples 1-7 and Comparative Examples 1-4 were tested, and the results are shown in Table 3.

[0089] The test method for resistance to brine corrosion involves immersing the sample in a 5 wt% CaCl solution at 80°C for 120 hours. The test method for resistance to erosion involves preparing a simulated erosion solution using quartz sand with an average particle size of 1-1.2 mm and water at a mass ratio of 1:9. The flow rate of the simulated erosion solution is 22 m / s, and the erosion experiment is conducted at a 60° angle. The erosion rate is calculated based on the mass difference before and after the experiment. The test method for acid resistance involves immersing the sample in 20 wt% HCl at room temperature and observing any changes on the sample surface.

[0090] Table 3

[0091]

[0092]

[0093] As shown in Table 3, the composite coating provided in this invention has various components that interact with each other, which can significantly enhance the bonding strength between the composite coating and the substrate, prevent the composite coating from falling off, improve the erosion resistance of the composite coating, greatly improve the corrosion resistance and wear resistance of the composite coating, better protect the instrument, and extend the service life of the instrument.

[0094] Comparing Example 5 and Comparative Example 1, it is evident that insufficient use of chopped basalt fibers reduces the erosion resistance of the composite coating, resulting in slight corrosion in acidic environments. Comparing Example 5 and Comparative Example 2, it is clear that the interaction of chopped basalt fibers with other components significantly improves the erosion and corrosion resistance of the composite coating.

[0095] Comparative Examples 5 and 3 show that hexagonal boron nitride helps improve the erosion resistance and brine corrosion resistance of the composite coating. Comparative Examples 5 and 4 show that the antioxidant, in conjunction with other components, helps improve the erosion resistance and acid resistance of the coating.

[0096] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite coating, characterized in that, The coating comprises: an inner layer, an outer layer, and an adhesive layer disposed between the inner layer and the outer layer; The outer layer is basalt fiber cloth, and the raw materials for preparing the inner layer include: 100 parts by weight of first epoxy resin, 10-40 parts by weight of chopped basalt fiber, 5-30 parts by weight of hexagonal boron nitride, 0.5-5 parts by weight of coupling agent, 1-3 parts by weight of surfactant, 0.5-2.5 parts by weight of antioxidant and 1-15 parts by weight of curing agent; The hexagonal boron nitride has a lamellar structure with an average particle size of 100nm-500nm; The surfactant comprises 10-30 parts by weight of dimethyl sulfoxide, 5-15 parts by weight of fatty alcohol polyoxyethylene ether, 5-15 parts by weight of bisphenol A diglycidyl ether, and 35-55 parts by weight of water. The chopped basalt fibers have a length of 10μm-3mm and an average diameter of 0.5-50μm.

2. The composite coating according to claim 1, wherein, The first epoxy resin is selected from one or more of alicyclic epoxy resins, bisphenol A epoxy resins, and phenolic epoxy resins.

3. The composite coating according to claim 2, wherein, The first epoxy resin is an alicyclic epoxy resin and a bisphenol A epoxy resin, or the first epoxy resin is an alicyclic epoxy resin and a phenolic epoxy resin.

4. The composite coating according to claim 3, wherein, The mass ratio of the alicyclic epoxy resin to the bisphenol A epoxy resin is 1:2-8; the mass ratio of the alicyclic epoxy resin to the phenolic epoxy resin is 1:2-8.

5. The composite coating according to claim 4, wherein, The mass ratio of the alicyclic epoxy resin to the bisphenol A epoxy resin is 1:4-6; the mass ratio of the alicyclic epoxy resin to the phenolic epoxy resin is 1:4-6.

6. The composite coating according to claim 1, wherein, The chopped basalt fibers have a length of 0.2-2 mm and an average diameter of 1-20 μm.

7. The composite coating according to claim 1, wherein, The coupling agent is selected from one or more of vinyltriethoxysilane, aminopropyltriethoxysilane, aminopropyltrimethoxysilane, and propyltrimethoxysilane.

8. The composite coating according to claim 1, wherein, The surfactant comprises 15-25 parts by weight of dimethyl sulfoxide, 8-12 parts by weight of fatty alcohol polyoxyethylene ether, 8-12 parts by weight of bisphenol A diglycidyl ether, and 40-50 parts by weight of water.

9. The composite coating according to claim 1, wherein, The curing agent is an amine-based curing agent.

10. The composite coating according to claim 9, wherein, The curing agent is selected from one or more of ethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and diethylaminopropylamine.

11. The composite coating according to claim 1, wherein, The adhesive layer is made of a second epoxy resin.

12. The composite coating according to claim 11, wherein, The second epoxy resin is the same as the first epoxy resin.

13. The composite coating according to any one of claims 1-12, wherein, The thickness of the inner layer is 150-400 μm; the thickness of the adhesive layer is 25-75 μm; and the thickness of the outer layer is 300-700 μm.

14. The composite coating according to claim 13, wherein, The thickness of the inner layer is 250-350 μm; the thickness of the adhesive layer is 35-50 μm; and the thickness of the outer layer is 450-550 μm.

15. The composite coating according to any one of claims 1-12, wherein, The thickness of the composite coating is 500-1000 μm.

16. The composite coating according to claim 15, wherein, The thickness of the composite coating is 780-870 μm.

17. A method for preparing a composite coating according to any one of claims 1-16, characterized in that, The method includes the following steps: (1) Mix the first epoxy resin, chopped basalt fiber, hexagonal boron nitride, coupling agent, surfactant and antioxidant evenly, and then add curing agent and continue mixing to obtain inner coating; coat the obtained inner coating evenly on the substrate and let it stand at room temperature for 18-24 hours to obtain inner layer; (2) The second epoxy resin is uniformly coated on the inner layer, and then basalt fiber cloth is covered on the second epoxy resin. The mixture is left to stand at room temperature for 18-24 hours to obtain a composite coating. The hexagonal boron nitride has a lamellar structure with an average particle size of 100nm-500nm; The surfactant comprises 10-30 parts by weight of dimethyl sulfoxide, 5-15 parts by weight of fatty alcohol polyoxyethylene ether, 5-15 parts by weight of bisphenol A diglycidyl ether, and 35-55 parts by weight of water. The chopped basalt fibers have a length of 10μm-3mm and an average diameter of 0.5-50μm.

18. The application of the composite coating according to any one of claims 1-16 or the composite coating prepared by the preparation method according to claim 17 on the housing of an instrument or device.

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