A coating for the inner wall of a polyethylene pipe used in gas fields and its preparation method

Abstract

This invention relates to a coating for the inner wall of polyethylene pipes used in gas fields and its preparation method, belonging to the field of coating technology. The coating comprises, by weight, 100 parts epoxy resin, 3-6 parts silica powder, 5-8 parts ceramic microspheres, 15-18 parts latent curing agent, 6.5-9 parts crosslinking fluorinated modifier, 0.8-1.2 parts accelerator, 0.3-0.5 parts wetting agent, 0.2-0.3 parts defoamer, and 0.3-0.5 parts leveling agent. The crosslinking fluorinated modifier is prepared in three steps: substitution of bromoethanol with KH-550, esterification with tetrafluorosuccinyl chloride, end-capping with ethylene glycol, and ring-opening and ring-closing with epichlorohydrin. It works synergistically with inorganic fillers to construct a molecular-level bridging network between the filler, modifier, and resin matrix within the epoxy resin matrix, achieving a systematic improvement in the overall performance of the coating at multiple levels.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a coating for the inner wall of a polyethylene pipe used in gas fields and its preparation method. Background Technology

[0002] Gas field water refers to the water that is brought to the surface from the gas reservoir along with the natural gas during the natural gas extraction process. It has a high mineralization and contains corrosive media, so the inner wall of the pipeline transporting this medium usually needs to be coated. At present, the inner wall coating used for this type of pipeline is mostly epoxy resin system. Its coating molding process is relatively simple, the coating has excellent adhesion, relatively high hardness and certain corrosion resistance. However, like other polymer coatings, it has similar defects: gas field water contains a large number of solid impurities. During transportation, these impurities erode the coating and damage the surface smoothness of the coating. In addition, the high mineralization of gas field water makes it easy to form scale at the erosion points, leading to pipeline blockage.

[0003] To address the aforementioned issues, various improvement studies have been conducted in existing technologies. One common improvement strategy is to introduce high-hardness fillers (such as ceramic microspheres, alumina, and silicon carbide) into the epoxy coating system. The dispersion strengthening effect of these fillers improves the coating's hardness and erosion resistance. However, these high-density fillers are prone to gravity settling and segregation during coating application and curing, resulting in uneven filler distribution along the coating thickness. This makes it difficult to achieve a uniform strengthening effect across the entire coating, leaving erosion-prone areas still present. Another improvement strategy is to introduce fluoride components into the coating. The extremely low surface energy of fluorides reduces the adhesion between the coating surface and minerals, thereby mitigating scaling tendency. Studies have shown that the surface enrichment effect of fluoroalkyl chains can form a hydrophobic barrier, enhancing the coating's barrier ability against corrosive media. However, conventional physical blending methods for fluorides struggle to achieve stable dispersion of fluorine components in the coating. Fluorides easily form agglomeration defects in the coating, becoming weak points for erosion damage and reducing the overall erosion resistance of the coating.

[0004] Therefore, how to synergistically improve the coating's resistance to solid particle erosion and scaling while ensuring good adhesion and anti-corrosion performance of epoxy coatings, and at the same time avoid the adverse effects of filler segregation and fluoride agglomeration, is a technical problem that urgently needs to be solved in the field of coatings for the inner walls of gas field water transportation pipelines. Summary of the Invention

[0005] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a coating for the inner wall of a polyethylene pipe for gas field water use and a method for preparing the same.

[0006] The objective of this invention can be achieved through the following technical solutions: A coating for the inner wall of a polyethylene pipe used in gas fields comprises, by weight: 100 parts epoxy resin, 3-6 parts silica powder, 5-8 parts ceramic microspheres, 15-18 parts latent curing agent, 6.5-9 parts cross-linking fluorinated modifier, 0.8-1.2 parts accelerator, 0.3-0.5 parts wetting agent, 0.2-0.3 parts defoamer, and 0.3-0.5 parts leveling agent.

[0007] The cross-linked fluorinated modifier is prepared by the following method: Step A1: Under a dry inert gas atmosphere, silane coupling agent KH-550, bromoethanol and anhydrous tetrahydrofuran were premixed, heated to 60±2℃, triethylamine was slowly added dropwise and the reaction was stirred for 5.5h. After the reaction was completed, the mixture was cooled, filtered to remove salt and removed tetrahydrofuran by rotary evaporation to obtain diol silane monomer. Furthermore, the ratio of silane coupling agent KH-550, bromoethanol, triethylamine, and anhydrous tetrahydrofuran is 0.1 mol: 0.2 mol: 15 mL: 100 mL. Bromoethanol reacts with the amino substitution of silane coupling agent KH-550 to prepare a compound containing a triethoxysilane structure and a bibranched alcohol structure.

[0008] Step A2: Under a dry inert gas atmosphere, diol silane monomer and anhydrous dichloromethane are premixed, cooled in an ice-water bath, and tetrafluorosuccinyl chloride is slowly added and stirred for 0.5-0.8 h. After returning to room temperature, ethylene glycol and 4-dimethylaminopyridine are added and the reaction continues for 1.5-2 h. After the reaction is complete, dichloromethane is removed by rotary evaporation to obtain the fluorinated block intermediate. Furthermore, the ratio of diol silane monomer, tetrafluorosuccinyl chloride, ethylene glycol, 4-dimethylaminopyridine, and anhydrous dichloromethane is 0.1 mol: 0.12-0.14 mol: 80-100 mmol: 1.5-2 g: 350-400 mL. A slight excess of tetrafluorosuccinyl chloride undergoes an esterification reaction with the diol silane monomer, followed by end-capping with ethylene glycol to prepare an oligomer with a fluorinated structure and a side-chain triethoxysilane block, with the molecular chain end-capped with hydroxyl groups.

[0009] Step A3: Mix the fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide and anhydrous dioxane, heat to 80-95℃ and stir for 4-5 hours, then cool down and control the temperature in a water bath at 35-45℃, add potassium tert-butoxide solution and continue the reaction for 2.5-3 hours. After the reaction is complete, remove dioxane by rotary evaporation under reduced pressure to obtain the cross-linked fluorinated modification. Furthermore, the ratio of the fluoroblock intermediate, epichlorohydrin, tetrabutylammonium bromide, potassium tert-butoxide, and anhydrous dioxane is 50g:15-22mmol:0.4-0.6g:0.9-1.2g:150-200mL. Epichlorohydrin ring-opens with the terminal hydroxyl group of the fluoroblock intermediate, and then ring-closes under the strong alkalinity of potassium tert-butoxide to form an epoxy-terminated modification.

[0010] Preferably, the epoxy resin is a bisphenol A type liquid resin, which has high curing hardness and is easy to apply as a coating.

[0011] Preferably, the fineness of the silicon micro powder is not less than 800 mesh, and the fineness of the ceramic microspheres is not less than 500 mesh. Under these specifications, a certain degree of dispersibility is maintained, while also meeting the requirements for internal coating construction.

[0012] Preferably, the latent curing agent and accelerator result in a curing temperature for the coating not exceeding 90°C, thus having minimal impact on the base polyethylene pipe.

[0013] A method for preparing a coating for the inner wall of a polyethylene pipe used in gas fields includes: premixing epoxy resin, cross-linking fluorinated modifier, wetting agent, defoamer and leveling agent, then adding silica powder and ceramic microspheres for mixing, vacuum degassing, and then adding latent curing agent and accelerator for mixing to obtain the coating for the inner wall of the polyethylene pipe.

[0014] The beneficial effects of this invention are: This invention provides a coating for the inner wall of polyethylene pipes used in gas fields and its preparation method. By introducing a cross-linking fluorinated modifier into a single-component latent curing epoxy system and synergistically working with inorganic fillers, a molecular-level bridging network is constructed between the filler, modifier, and resin matrix within the epoxy resin matrix. This achieves a systematic improvement in the overall performance of the coating at multiple levels, as detailed below: The cross-linked fluorinated modifier of this invention features a unique multifunctional block molecular design. The molecular backbone of this modifier is formed by esterification of tetrafluorosuccinyl chloride with intermediate 1 followed by ethylene glycol end-capping, with fluorinated alkyl segments embedded in the main chain. Due to the strong electronegativity and low polarizability of fluorine atoms, the CF bond has extremely high bond energy and extremely low surface energy, causing the fluorinated segments to tend to migrate to the coating surface during the coating curing process. This characteristic endows the coating surface with excellent hydrophobic and oleophobic properties, effectively reducing the adhesion tendency and scaling rate of scale-forming ions in gas field water on the coating surface. More importantly, the fluorinated modifier of this invention is not doped into the coating in a free form, but rather forms a covalent coupling with the inorganic filler surface through the triethoxysilane structure of the side chain, using the filler as an anchoring site to stably fix the fluorinated segments in a specific region. This anchoring mechanism solves the problem of fluorine components easily agglomerating inside the coating or excessively migrating to the coating surface in conventional fluoride doping methods, leading to surface "softening". The term "softening" refers to the phenomenon where a large amount of low surface energy fluorides accumulate disorderly on the coating surface. Although a hydrophobic interface is formed, this disrupts the cross-linking density and mechanical integrity of the coating surface, making the surface layer softer and more susceptible to abrasion by solid particles. The anchoring design of this invention allows fluorinated segments to gain surface migration capability while being restrained by the filler, achieving a gradient and orderly distribution of fluorine components along the coating thickness direction. Fluorinated segments are moderately enriched on the surface to achieve anti-fouling function, without excessive segregation that would compromise surface hardness and wear resistance.

[0015] More importantly, the cross-linking fluorinated modifier of this invention constructs a true molecular bridge between the epoxy resin matrix and the inorganic filler. One end of the modifier's molecular chain undergoes a condensation reaction with the silanol groups on the surface of fillers such as silica powder and ceramic microspheres through a triethoxysilyl group, forming a strong Si-O-Si covalent bond; the other end of the modifier participates in the cross-linking and curing reaction of the epoxy resin through the epoxy end group, forming a chemical bond with the resin matrix. This chemical bridging structure of "filler-modifier-resin" is completely different from the traditional physical blending reinforcement method. In traditional filler reinforcement systems, the filler and resin are only bonded by van der Waals forces and mechanical interlocking, resulting in limited interfacial bonding strength. Under the continuous erosion of solid particles, the filler is easily pulled out and detached from the resin matrix, causing a rapid decay of the reinforcement effect. However, this invention firmly anchors the filler in the three-dimensional cross-linked network through chemical bridging, significantly improving the interfacial bonding strength between the filler and the matrix, allowing the filler's load-bearing and stress-dispersing effects to be fully utilized, thereby greatly improving the overall hardness and erosion resistance of the coating.

[0016] Furthermore, the cross-linked fluorinated modifier of this invention also has a positive synergistic effect on the dispersion stability of fillers in coatings. In traditional filler-reinforced coatings, high-density fillers are prone to sedimentation and segregation due to gravity during construction and curing, resulting in an uneven distribution of filler enrichment at the bottom of the coating and a lack of filler on the surface. This uneven distribution severely compromises the erosion resistance of the coating surface. In this invention, the molecular chain of the cross-linked fluorinated modifier contains both organophilic epoxy and inorganic silane segments, exhibiting structural characteristics similar to amphiphilic surfactants. This effectively reduces the interfacial tension between the filler and the resin matrix, improving the wetting and dispersion of the filler in the coating. Simultaneously, the introduction of fluorinated segments into the modifier molecular chain further reduces the overall surface energy of the system, creating a certain steric hindrance effect during coating curing. This effectively inhibits the gravitational sedimentation and agglomeration of filler particles, resulting in a more uniform distribution of fillers along the coating thickness direction. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: Preparation of a coating for the inner wall of a polyethylene pipe used in gas field water supply. The specific implementation method is as follows: I. Preparation of Crosslinked Fluorinated Modifiers Step A1: Dry nitrogen gas is introduced into the reactor for protection. Silane coupling agent KH-550, bromoethanol, and anhydrous tetrahydrofuran are added and premixed by stirring. The temperature is raised to 60±2℃, and triethylamine is slowly added dropwise while stirring for 5.5 h. The ratio of silane coupling agent KH-550, bromoethanol, triethylamine, and anhydrous tetrahydrofuran is 0.1 mol: 0.2 mol: 15 mL: 100 mL. After the reaction is complete, the mixture is cooled, filtered to remove salts, and rotary evaporated to remove tetrahydrofuran, yielding a diol silane monomer.

[0019] Step A2: Dry nitrogen gas is introduced into the reactor for protection. Diol silane monomer and anhydrous dichloromethane are stirred and premixed. The temperature is controlled at 10°C in an ice-water bath. Tetrafluorosuccinyl chloride is slowly added and stirred for 0.5 h. After returning to room temperature, ethylene glycol and 4-dimethylaminopyridine are added and the reaction continues for 1.5 h. The ratio of diol silane monomer, tetrafluorosuccinyl chloride, ethylene glycol, 4-dimethylaminopyridine and anhydrous dichloromethane is 0.1 mol: 0.14 mol: 100 mmol: 2 g: 400 mL. After the reaction is complete, dichloromethane is removed by rotary evaporation to obtain the fluorinated block intermediate.

[0020] Step A3: Add the fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide, and anhydrous dioxane to the mixture and stir. Heat to 95°C and stir for 4 hours. Then cool down and control the temperature at 45°C in a water bath. Dissolve potassium tert-butoxide in DMF and add it to the mixture to continue the reaction for 2.5 hours. The ratio of the amount of fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide, potassium tert-butoxide, and anhydrous dioxane is 50g:22mmol:0.6g:1.2g:200mL. After the reaction is complete, remove the dioxane by rotary evaporation under reduced pressure to obtain the cross-linked fluorinated modified product.

[0021] II. Preparation of coating for the inner wall of polyethylene pipes The composition information for the coating is as follows: 100 parts epoxy resin, E-51 type bisphenol A liquid resin raw material, epoxy equivalent 240 g / mol; 3 parts silica powder, industrial grade raw material, fineness 800 mesh, SiO2≥99; 7 parts ceramic microspheres, industrial grade raw material, true density 2.5 g / cm³. 3 Mohs hardness ≥7; 15 parts latent curing agent, modified amine curing agent, model JTN-1020; 7.2 parts crosslinking fluorinated modifier, self-made in this embodiment; 0.9 parts accelerator, substituted urea accelerator, model PDU-250M; 0.4 parts wetting agent, polyether siloxane preparation, model TEGO Wet 500; 0.2 parts defoamer, model BYK-A530; 0.3 parts leveling agent, model BYK-320.

[0022] Coating preparation: Epoxy resin, cross-linking fluorinated modifier, wetting agent, defoamer and leveling agent are added and premixed at 120 rpm for 10 min. Then, silica powder and ceramic microspheres are added and mixed at 600 rpm for 5 min. Vacuum degassing is performed for 30 min. Then, latent curing agent and accelerator are slowly added under low speed stirring at 30 rpm and mixed for 15 min to obtain the coating for the inner wall of polyethylene pipe.

[0023] Example 2: Preparation of a coating for the inner wall of a polyethylene pipe used in gas field water supply. The specific implementation method is as follows: I. Preparation of Crosslinked Fluorinated Modifiers Step A1: Dry nitrogen gas is introduced into the reactor for protection. Silane coupling agent KH-550, bromoethanol, and anhydrous tetrahydrofuran are added and premixed by stirring. The temperature is raised to 60±2℃, and triethylamine is slowly added dropwise while stirring for 5.5 h. The ratio of silane coupling agent KH-550, bromoethanol, triethylamine, and anhydrous tetrahydrofuran is 0.1 mol: 0.2 mol: 15 mL: 100 mL. After the reaction is complete, the mixture is cooled, filtered to remove salts, and rotary evaporated to remove tetrahydrofuran, yielding a diol silane monomer.

[0024] Step A2: Dry nitrogen gas is introduced into the reactor for protection. Diol silane monomer and anhydrous dichloromethane are premixed by stirring. The temperature is controlled at 10°C in an ice-water bath. Tetrafluorosuccinyl chloride is slowly added and the reaction is stirred for 0.8 h. After returning to room temperature, ethylene glycol and 4-dimethylaminopyridine are added and the reaction is continued for 2 h. The ratio of diol silane monomer, tetrafluorosuccinyl chloride, ethylene glycol, 4-dimethylaminopyridine and anhydrous dichloromethane is 0.1 mol: 0.12 mol: 80 mmol: 1.5 g: 350 mL. After the reaction is complete, dichloromethane is removed by rotary evaporation to obtain the fluorinated block intermediate.

[0025] Step A3: Add the fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide, and anhydrous dioxane to the mixture and stir. Heat the mixture to 80°C and stir for 5 hours. Then cool the mixture and control the temperature at 35°C using a water bath. Dissolve potassium tert-butoxide in DMF and add it to the mixture to continue the reaction for 3 hours. The ratio of the amount of fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide, potassium tert-butoxide, and anhydrous dioxane is 50 g: 15 mmol: 0.4 g: 0.9 g: 150 mL. After the reaction is complete, remove the dioxane by rotary evaporation under reduced pressure to obtain the cross-linked fluorinated modified product.

[0026] II. Preparation of coating for the inner wall of polyethylene pipes The composition information for the coating is as follows: 100 parts epoxy resin, E-51 type bisphenol A liquid resin raw material, epoxy equivalent 240 g / mol; 5 parts silica powder, industrial grade raw material, fineness 800 mesh, SiO2≥99; 5 parts ceramic microspheres, industrial grade raw material, true density 2.5 g / cm³. 3 Mohs hardness ≥7; 16 parts latent curing agent, modified amine curing agent, model JTN-1020; 6.5 parts crosslinking fluorinated modifier, self-made in this embodiment; 0.8 parts accelerator, substituted urea accelerator, model PDU-250M; 0.3 parts wetting agent, polyether siloxane preparation, model TEGO Wet 500; 0.2 parts defoamer, model BYK-A530; 0.4 parts leveling agent, model BYK-320.

[0027] Coating preparation: Epoxy resin, cross-linking fluorinated modifier, wetting agent, defoamer and leveling agent are added and premixed at 120 rpm for 10 min. Then, silica powder and ceramic microspheres are added and mixed at 600 rpm for 5 min. Vacuum degassing is performed for 30 min. Then, latent curing agent and accelerator are slowly added under low speed stirring at 30 rpm and mixed for 15 min to obtain the coating for the inner wall of polyethylene pipe.

[0028] Example 3: Preparation of a coating for the inner wall of a polyethylene pipe used in gas field water supply. The specific implementation method is as follows: I. Preparation of Crosslinked Fluorinated Modifiers Step A1: Dry nitrogen gas is introduced into the reactor for protection. Silane coupling agent KH-550, bromoethanol, and anhydrous tetrahydrofuran are added and premixed by stirring. The temperature is raised to 60±2℃, and triethylamine is slowly added dropwise while stirring for 5.5 h. The ratio of silane coupling agent KH-550, bromoethanol, triethylamine, and anhydrous tetrahydrofuran is 0.1 mol: 0.2 mol: 15 mL: 100 mL. After the reaction is complete, the mixture is cooled, filtered to remove salts, and rotary evaporated to remove tetrahydrofuran, yielding a diol silane monomer.

[0029] Step A2: Dry nitrogen gas is introduced into the reactor for protection. Diol silane monomer and anhydrous dichloromethane are stirred and premixed. The temperature is controlled at 10°C in an ice-water bath. Tetrafluorosuccinyl chloride is slowly added and the reaction is stirred for 0.6 h. After returning to room temperature, ethylene glycol and 4-dimethylaminopyridine are added and the reaction is continued for 1.7 h. The ratio of diol silane monomer, tetrafluorosuccinyl chloride, ethylene glycol, 4-dimethylaminopyridine and anhydrous dichloromethane is 0.1 mol: 0.13 mol: 90 mmol: 1.8 g: 380 mL. After the reaction is complete, dichloromethane is removed by rotary evaporation to obtain the fluorinated block intermediate.

[0030] Step A3: Add the fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide, and anhydrous dioxane to the mixture and stir. Heat to 90°C and stir for 4.5 hours. Then cool down and control the temperature at 40°C in a water bath. Dissolve potassium tert-butoxide in DMF and add it to the mixture to continue the reaction for 3 hours. The ratio of the amount of fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide, potassium tert-butoxide, and anhydrous dioxane is 50 g: 20 mmol: 0.5 g: 1.1 g: 170 mL. After the reaction is complete, remove the dioxane by rotary evaporation under reduced pressure to obtain the cross-linked fluorinated modified product.

[0031] II. Preparation of coating for the inner wall of polyethylene pipes The composition information for the coating is as follows: 100 parts epoxy resin, E-51 type bisphenol A liquid resin raw material, epoxy equivalent 240 g / mol; 6 parts silica powder, industrial grade raw material, fineness 800 mesh, SiO2≥99; 8 parts ceramic microspheres, industrial grade raw material, true density 2.5 g / cm³. 3 Mohs hardness ≥7; 18 parts latent curing agent, modified amine curing agent, model JTN-1020; 9 parts crosslinking fluorinated modifier, self-made in this embodiment; 1.2 parts accelerator, substituted urea accelerator, model PDU-250M; 0.5 parts wetting agent, polyether siloxane preparation, model TEGO Wet 500; 0.3 parts defoamer, model BYK-A530; 0.5 parts leveling agent, model BYK-320.

[0032] Coating preparation: Epoxy resin, cross-linking fluorinated modifier, wetting agent, defoamer and leveling agent are added and premixed at 120 rpm for 10 min. Then, silica powder and ceramic microspheres are added and mixed at 600 rpm for 5 min. Vacuum degassing is performed for 30 min. Then, latent curing agent and accelerator are slowly added under low speed stirring at 30 rpm and mixed for 15 min to obtain the coating for the inner wall of polyethylene pipe.

[0033] Comparative Example 1, as a blank control, was carried out in accordance with the specific implementation process of Example 3, except that no cross-linking fluorine modifier was added to the components, and the rest were the same.

[0034] Comparative Example 2 follows the same procedure as Example 3, except that the cross-linking fluorinated modifier was replaced with 5.5 parts of silane coupling agent KH-560 and 3 parts of fluorinated surfactant FC-4430, while the rest remained the same.

[0035] The coatings prepared above were sprayed onto the surfaces of polyethylene sheets and pipes, preheated at 60°C for 10 min, and then heated to 85°C for 30 min to obtain samples. The coating hardness was tested according to ASTM D3363-22 standard; The adhesion of the coating was tested according to GB / T 9286-2021 standard; The erosion resistance of the coating was tested in accordance with GB / T 43498-2023 standard. The simulated gas field water parameters were controlled as follows: mineralization 60000mg / L, pH=6.0, containing 5wt% quartz sand with a particle size of 80-120 mesh as erosion particles, with a flow velocity of 5m / s, an erosion angle of 90°, and an erosion time of 72h. Preparation of supersaturated scaling solution (Ca 2+ Concentration 2000 mg / L, HCO3 - (Concentration 3000 mg / L) The coating sample was vertically immersed in the scaling solution and placed in an 80℃ constant temperature water bath for 72 hours to allow the scale layer to deposit and grow on the coating surface. After the test, the coating sample was removed, the surface was gently rinsed with deionized water, dried, and the weight gain of the coating sample was measured. The amount of scaling per unit area was calculated. The surface water contact angle of the coating was tested in accordance with GB / T 30693-2014 standard.

[0036] The specific test results are shown in Table 1: Table 1

[0037] As can be seen from the test results in Table 1, the coating prepared in the example has high surface hardness, is erosion resistant, scale resistant, and has stable adhesion after curing, effectively protecting the inner wall of polyethylene pipes.

[0038] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A coating for the inner wall of a polyethylene pipe used in gas fields, characterized in that, The composition by weight is as follows: 100 parts epoxy resin, 3-6 parts silica powder, 5-8 parts ceramic microspheres, 15-18 parts latent curing agent, 6.5-9 parts cross-linking fluorinated modifier, 0.8-1.2 parts accelerator, 0.3-0.5 parts wetting agent, 0.2-0.3 parts defoamer, and 0.3-0.5 parts leveling agent; The cross-linked fluorinated modifier is prepared by the following method: Step A1: Under a dry inert gas atmosphere, silane coupling agent KH-550, bromoethanol and anhydrous tetrahydrofuran were premixed, heated to 60±2℃, and triethylamine was slowly added dropwise while stirring for 5.5h. After treatment, diol silane monomer was obtained. Step A2: Under a dry inert gas atmosphere, diol silane monomer and anhydrous dichloromethane are premixed, cooled in an ice-water bath, and tetrafluorosuccinyl chloride is slowly added and stirred for 0.5-0.8 h. After returning to room temperature, ethylene glycol and 4-dimethylaminopyridine are added and the reaction continues for 1.5-2 h. After treatment, a fluorinated block intermediate is obtained. Step A3: Mix the fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide and anhydrous dioxane, heat to 80-95℃ and stir for 4-5 hours, then cool down and control the temperature in a water bath at 35-45℃, add potassium tert-butoxide solution and continue the reaction for 2.5-3 hours. After treatment, a cross-linked fluorinated modifier is obtained.

2. The coating for the inner wall of a polyethylene pipe for gas field water supply according to claim 1, characterized in that, The ratio of silane coupling agent KH-550, bromoethanol, triethylamine and anhydrous tetrahydrofuran is 0.1 mol: 0.2 mol: 15 mL: 100 mL.

3. The coating for the inner wall of a polyethylene pipe for gas field water use according to claim 2, characterized in that, The ratio of diol silane monomer, tetrafluorosuccinyl chloride, ethylene glycol, 4-dimethylaminopyridine and anhydrous dichloromethane is 0.1 mol: 0.12-0.14 mol: 80-100 mmol: 1.5-2 g: 350-400 mL.

4. The coating for the inner wall of a polyethylene pipe for gas field water supply according to claim 3, characterized in that, The ratio of fluorinated block intermediate, epichlorohydrin, tetrabutylammonium bromide, potassium tert-butoxide, and anhydrous dioxane is 50g: 15-22mmol: 0.4-0.6g: 0.9-1.2g: 150-200mL.

5. The coating for the inner wall of a polyethylene pipe for gas field water supply according to claim 1, characterized in that, The epoxy resin is a bisphenol A type liquid resin.

6. The coating for the inner wall of a polyethylene pipe for gas field water supply according to claim 1, characterized in that, The fineness of the silicon micro powder is not less than 800 mesh, and the fineness of the ceramic microspheres is not less than 500 mesh.

7. The coating for the inner wall of a polyethylene pipe for gas field water supply according to claim 1, characterized in that, Latent curing agents and accelerators should not increase the curing temperature of coatings above 90°C.

8. A method for preparing a coating for the inner wall of a polyethylene pipe for gas field water use according to any one of claims 1-7, characterized in that, Specifically, epoxy resin, cross-linking fluorinated modifier, wetting agent, defoamer and leveling agent are premixed, then silica powder and ceramic microspheres are added and mixed. After vacuum degassing, latent curing agent and accelerator are added and mixed evenly to obtain a polyethylene pipe inner wall coating.

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