Dip-coating paint for complex pipeline and preparation method of dip-coating paint

Abstract

The invention belongs to the technical field of dip-coating paint, and particularly relates to dip-coating paint for complex pipelines and a preparation method thereof.The dip-coating paint for the complex pipelines comprises emulsion and color paste, and the emulsion comprises modified epoxy resin and a totally-closed curing agent; the weight part ratio of the emulsion to the color paste is (2.9-3.1): 1; the weight part ratio of the modified epoxy resin to the totally-enclosed curing agent is (1.6-1.8): 1. According to the dip-coating paint for the complex pipeline and the preparation method of the dip-coating paint, a coating formed after the dip-coating paint is coated has excellent adhesive force, chemical stability, good corrosion resistance and excellent heat resistance, aging resistance and moisture resistance, so that the corrosion resistance and reliability of the complex pipeline are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of dip coatings, and in particular relates to a dip coating for complex pipelines and a preparation method thereof. Background Art

[0002] With the development and utilization of marine resources, complex pipelines are often needed to assist equipment to achieve related functions. However, the marine environment is harsh. After long-term erosion by seawater, complex pipelines will be corroded and produce corrosion products, which will affect the geometric dimensions of the complex pipelines and cause varying degrees of damage to the operating reliability of key equipment.

[0003] At present, the treatment of internal corrosion of complex pipelines mainly adopts sacrificial anodes for cathodic protection, enamel, chemical plating, paint coating and other means for the internal corrosion protection of complex steel pipelines under different temperatures, various corrosive media and working conditions. Among the internal corrosion protection of complex steel pipelines, coating corrosion protection is the most effective means. The coating must meet the working conditions of complex pipelines and the construction properties of special structures of complex pipelines, and must have the following properties: (1) excellent resistance to seawater, temperature and chemical media; (2) maintain high adhesion under hydraulic conditions; (3) have good resistance to water erosion and wear; (4) have little effect on the heat transfer efficiency of the workpiece; (5) have good scale inhibition performance.

[0004] However, it is difficult for coating products to meet the above conditions at the same time, resulting in serious corrosion problems for complex pipelines in marine environments and special working conditions.

[0005] Therefore, the prior art needs to be improved. Summary of the invention

[0006] In order to solve the above problems of the prior art, the present invention provides a dip coating for complex pipelines and a preparation method thereof. The coating formed after the dip coating has excellent adhesion, chemical stability, good corrosion resistance, excellent heat resistance, aging resistance and moisture resistance, thereby improving the anti-corrosion performance and reliability of complex pipelines. The amount of materials used and maintenance costs are significantly saved, the protection problem of complex pipelines in marine environments and special working conditions is solved, and the safety and service life of equipment operation are improved.

[0007] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0008] According to a first aspect of the present invention: a dip coating for complex pipes, comprising an emulsion and a color paste, wherein the emulsion comprises a modified epoxy resin and a fully enclosed curing agent;

[0009] By weight:

[0010] The weight ratio of emulsion to color paste is 2.9-3.1:1;

[0011] The weight ratio of modified epoxy resin to fully enclosed curing agent is 1.6-1.8:1;

[0012] in:

[0013] The preparation method of modified epoxy resin is as follows:

[0014] S1: Add epoxy resin, bisphenol A, dodecylphenol and propylene glycol methyl ether into a clean reactor, heat to 118-122° C., and stir until bisphenol A is completely dissolved to obtain reactant 1;

[0015] S2: adding dimethylethanolamine to reactant 1, and reacting at 140-150°C for 1-1.5h to obtain reactant 2;

[0016] S3: When the temperature of reactant 2 is lowered to 132-138°C, propylene glycol phenyl ether and ethylene glycol butyl ether are added, and when the temperature is further lowered to 124-126°C, propylene glycol methyl ether is added, and then the temperature is lowered to below 100°C, butanone is added, and then the mixture is stirred at a constant temperature of 90-100°C for 30-60 minutes to obtain reactant 3;

[0017] S4: When the temperature of reactant 3 is lowered to 88-92°C, diethanolamine and isopropanol are added, and the mixture is reacted at 88-92°C for 1.5-2h to obtain reactant 4;

[0018] S5: When the temperature of reactant 4 is lowered to 79-81°C, the lid of the reactor is opened and stirring is stopped. p-Aminodimethylaniline and isopropanol are added to reactant 4, followed by stirring for 10-15 minutes. The temperature is raised to 88-90°C and the reaction is carried out at a constant temperature for 2-2.5 hours to obtain a modified epoxy resin.

[0019] Preferably, in step S1, the epoxy resin is one or more of E44, E51 and epoxy resin 128, and the weight ratio of epoxy resin, bisphenol A and dodecylphenol is (5.2-5.4):(1.35-1.45):1.

[0020] Preferably, the weight ratio of the total amount of epoxy resin, bisphenol A and dodecylphenol to diethanolamine is (13.75-13.85):1, and the weight ratio of diethanolamine to p-aminodimethylaniline is (3.21-3.30):1.

[0021] Preferably, the weight ratio of reactant 2, reactant 3, reactant 4 and epoxy resin is 1:(1.17-1.20):(1.29-1.32):(1.33-1.38).

[0022] Preferably, the preparation of the fully enclosed curing agent comprises the following steps:

[0023] A1: adding isocyanate and butanone into a reaction kettle and then sealing and stirring to obtain a mixture 1;

[0024] A2: When the mixture 1 is heated to 70-75°C, diethylene glycol ethyl ether is added dropwise, and the temperature is controlled at 78-80°C during the addition. After the addition is completed, the mixture is kept at 78-80°C for 3-4 hours to obtain a mixture 2;

[0025] A3: Add the catalyst to the mixture 2, and after the addition is complete, react at a constant temperature of 78-80°C for 15-30 minutes, then cool to below 50°C and discharge to obtain a fully enclosed curing agent.

[0026] Preferably, the isocyanate is diphenylmethane diisocyanate;

[0027] The catalyst is dibutyltin dilaurate;

[0028] The weight ratio of isocyanate to diethylene glycol ethyl ether is 1:1.

[0029] Preferably, the emulsion further comprises deionized water and lactic acid, and the ratio of the total weight of the modified epoxy resin and the blocked curing agent to the weight of the lactic acid is (42-43):1.

[0030] Preferably, the preparation of the emulsion comprises the following steps:

[0031] B1: Add the fully enclosed curing agent to the modified epoxy resin at 118-122°C and stir for 1-1.5 hours to obtain a resin liquid;

[0032] B2: Add deionized water and lactic acid into the emulsification tank, start stirring at a speed of 1200-1400r / min, add the resin liquid dropwise into the emulsification tank, add deionized water twice during the addition of the resin liquid, after the addition of the resin liquid is completed, control the temperature below 30°C and continue stirring for 45-60 minutes to obtain an emulsion.

[0033] Preferably, in step B2, the dripping speed of the resin liquid is 190-210 kg / 30 min, the weight ratio of deionized water to lactic acid is 34-34.7:1, and the viscosity of the emulsion is 40-50 mPa·s.

[0034] According to a second aspect of the present invention, a method for preparing a dip coating for a complex pipeline, for preparing the above-mentioned dip coating for a complex pipeline, comprises the following steps:

[0035] The color paste is directly added into the emulsion and dispersed and stirred for 1-2 hours to make the color paste and the emulsion completely mixed and uniform, thereby obtaining a dip coating for complex pipelines.

[0036] The beneficial effects of the present invention are:

[0037] (1) Bisphenol A and dodecylphenol are used to co-extend the bisphenol A type small molecule epoxy resin, and the dodecylphenol chain segment with emulsification function is introduced into the epoxy resin, which can improve the self-emulsification function of the epoxy resin and reduce the use of emulsifiers; by extending the chain of the low molecular weight epoxy resin to form a high molecular weight epoxy resin, the crosslinking degree of the coating can be improved, thereby improving the corrosion resistance of the coating; first, more than half of the epoxy groups are opened by the monoamine diethanolamine, and then the epoxy groups are opened by the polyamine p-aminodimethylaniline with a tertiary amine at one end and a primary amine at the other end, which can not only achieve the full opening of the epoxy groups, but also introduce strongly hydrophilic hydroxyl and tertiary amine groups, and the tertiary amine groups can react with lactic acid to neutralize the epoxy resin to ionize the epoxy resin, further improving the hydrophilicity of the resin; a fully enclosed curing agent is used, which can be stably stored with the fully opened epoxy resin and with deionized water, so that the prepared coating only needs to be packaged in a single component, which is convenient for storage and construction;

[0038] (2) After coating with the dip coating of the present invention, the formed coating has excellent adhesion, chemical stability, good corrosion resistance, excellent heat resistance, aging resistance and moisture resistance, thereby improving the anti-corrosion performance and reliability of complex pipelines. It significantly saves the amount of materials used and maintenance costs, solves the protection problem of complex pipelines in marine environments and special working conditions, and improves the safety and service life of equipment operation. DETAILED DESCRIPTION

[0039] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods.

[0040] In order to illustrate the scheme and technical advancement of the present invention, the technical scheme and technical application designed are as follows:

[0041] According to a first aspect of the present invention, a dip coating for complex pipes comprises an emulsion and a color paste, wherein the emulsion comprises a modified epoxy resin and a fully enclosed curing agent;

[0042] By weight:

[0043] The weight ratio of emulsion to color paste is 2.9-3.1:1;

[0044] The weight ratio of modified epoxy resin to fully enclosed curing agent is 1.6-1.8:1;

[0045] in:

[0046] The preparation method of modified epoxy resin is as follows:

[0047] S1: Add epoxy resin, bisphenol A, dodecylphenol and propylene glycol methyl ether into a clean reactor, heat to 118-122° C., and stir until bisphenol A is completely dissolved to obtain reactant 1;

[0048] S2: adding dimethylethanolamine to reactant 1, and reacting at 140-150°C for 1-1.5h to obtain reactant 2;

[0049] S3: When the temperature of reactant 2 is lowered to 132-138° C., propylene glycol phenyl ether and ethylene glycol butyl ether are added, and when the temperature is further lowered to 124-126° C., propylene glycol methyl ether is added, and then the temperature is lowered to below 100° C., propylene glycol methyl ether is added, and then the mixture is stirred at a constant temperature of 90-100° C. for 30-60 min to obtain reactant 3;

[0050] S4: When the temperature of reactant 3 is lowered to 88-92°C, diethanolamine and isopropanol are added, and the mixture is reacted at 88-92°C for 1.5-2h to obtain reactant 4;

[0051] S5: When the temperature of reactant 4 is lowered to 79-81°C, the lid of the reactor is opened and stirring is stopped. p-Aminodimethylaniline and isopropanol are added to reactant 4, followed by stirring for 10-15 minutes. The temperature is raised to 88-90°C and the reaction is carried out at a constant temperature for 2-2.5 hours to obtain a modified epoxy resin.

[0052] According to the technical scheme of the present invention, bisphenol A and dodecylphenol are used to jointly extend the chain of bisphenol A type small molecule epoxy resin, and dodecylphenol chain segments with emulsification function are introduced into the epoxy resin, so that the self-emulsification function of the epoxy resin can be improved and the use of emulsifier can be reduced; by extending the chain of the low molecular weight epoxy resin to form a high molecular weight epoxy resin, the crosslinking degree of the coating can be improved, and then the corrosion resistance of the coating can be improved; first, more than half of the epoxy groups are opened by diethanolamine of a monoamine, and then the epoxy groups are opened by aminodimethylaniline, a polyamine with a tertiary amine at one end and a primary amine at the other end, so that all the epoxy groups can be opened, and strongly hydrophilic hydroxyl groups and tertiary amine groups can be introduced, and the tertiary amine groups can react with lactic acid to ionize the epoxy resin, so as to further improve the hydrophilicity of the epoxy resin; a fully enclosed curing agent is used, which can be stably stored with the fully opened epoxy resin and with deionized water, so that the prepared coating only needs to be packaged in a single component, and is convenient for storage and construction.

[0053] Preferably, in step S1, the epoxy resin is one or more of E44, E51 and epoxy resin 128, and the weight ratio of epoxy resin, bisphenol A and dodecylphenol is (5.2-5.4):(1.35-1.45):1.

[0054] Preferably, the weight ratio of the total amount of epoxy resin, bisphenol A and dodecylphenol to diethanolamine is (13.75-13.85):1, and the weight ratio of diethanolamine to p-aminodimethylaniline is (3.21-3.30):1.

[0055] Preferably, the weight ratio of reactant 2, reactant 3, reactant 4 and epoxy resin is 1:(1.17-1.20):(1.29-1.32):(1.33-1.38).

[0056] Through the above technical scheme, in the present invention, (1) the weight ratio of epoxy resin to bisphenol A is preferably selected because, in the epoxy chain extension, if more bisphenol A is used, the average molecular weight of the epoxy resin after chain extension is likely to be too large, and the excessive viscosity of the system affects the subsequent ring-opening reaction; if less bisphenol A is used, the average molecular weight of the epoxy resin after chain extension is likely to be too small, affecting the final curing and cross-linking of the coating, and further affecting the corrosion resistance and other properties of the coating. (2) Since the technical scheme uses diethanolamine and p-aminodimethylaniline for two-step ring opening, and the ring opening rate of diethanolamine is preferably more than 70%, in the diethanolamine-modified epoxy resin molecule, either the epoxy groups at both ends are ring-opened or only the epoxy groups at one end are not ring-opened. When p-aminodimethylaniline is further used for ring opening, only the unopened epoxy groups in the diethanolamine-modified epoxy resin molecule will be opened. After the ring opening of diethanolamine and p-aminodimethylaniline, the epoxy groups in the epoxy resin are basically all ring-opened. Therefore, when a fully enclosed curing agent is added, a curing cross-linking reaction will not occur, and when deionized water is subsequently added, it will not react with the fully enclosed curing agent. The dip coating for complex pipelines prepared by the technical scheme can be packaged in a single component and stably stored.

[0057] Preferably, the preparation of the fully enclosed curing agent comprises the following steps:

[0058] A1: adding isocyanate and butanone into a reaction kettle and then sealing and stirring to obtain a mixture 1;

[0059] A2: When the mixture 1 is heated to 70-75°C, diethylene glycol ethyl ether is added dropwise, and the temperature is controlled at 78-80°C during the addition. After the addition is completed, the mixture is kept at 78-80°C for 3-4 hours to obtain a mixture 2;

[0060] A3: Add the catalyst to the mixture 2, and after the addition is complete, react at a constant temperature of 78-80°C for 15-30 minutes, then cool to below 50°C to obtain a fully enclosed curing agent. In the fully enclosed curing agent, the NCO value is less than or equal to 0.1.

[0061] Preferably, the isocyanate is diphenylmethane diisocyanate;

[0062] The catalyst is dibutyltin dilaurate;

[0063] The weight ratio of isocyanate to diethylene glycol ethyl ether is 1:1.

[0064] Preferably, the emulsion further comprises deionized water and lactic acid, and the ratio of the total weight of the modified epoxy resin and the blocked curing agent to the weight of the lactic acid is (42-43):1.

[0065] Preferably, the preparation of the emulsion comprises the following steps:

[0066] B1: Add the fully enclosed curing agent to the modified epoxy resin at 118-122°C and stir for 1-1.5 hours to obtain a resin liquid;

[0067] B2: Add deionized water and lactic acid into the emulsification tank, start stirring at a speed of 1200-1400r / min, add the resin liquid dropwise into the emulsification tank, add deionized water twice during the addition of the resin liquid, after the addition of the resin liquid is completed, control the temperature below 30°C and continue stirring for 45-60 minutes to obtain an emulsion.

[0068] Preferably, in step B2, the dripping speed of the resin liquid is 190-210 kg / 30 min, the weight ratio of deionized water to lactic acid is 34-34.7:1, and the viscosity of the emulsion is 40-50 mPa·s.

[0069] According to a second aspect of the present invention, a method for preparing a dip coating for a complex pipeline, for preparing the above-mentioned dip coating for a complex pipeline, comprises the following steps:

[0070] The color paste is directly added into the emulsion and dispersed and stirred for 1-2 hours to make the color paste and the emulsion completely mixed and uniform, thereby obtaining a dip coating for complex pipelines.

[0071] Through the above technical solution, after coating with the dip coating of the present invention, the formed coating has excellent adhesion, chemical stability, good corrosion resistance, excellent heat resistance, aging resistance and moisture resistance, thereby improving the anti-corrosion performance and reliability of complex pipelines. It significantly saves the amount of materials used and maintenance costs, solves the protection problem of complex pipelines in marine environments and special working conditions, and improves the safety and service life of equipment operation.

[0072] Embodiment 1:

[0073] A dip coating for complex pipes, comprising an emulsion and a color paste, wherein the emulsion comprises a modified epoxy resin and a fully enclosed curing agent;

[0074] The preparation method of modified epoxy resin is as follows:

[0075] S1: Add epoxy resin, bisphenol A, dodecylphenol and propylene glycol methyl ether into a clean reactor, heat to 118-122° C., and stir until bisphenol A is completely dissolved to obtain reactant 1;

[0076] S2: adding dimethylethanolamine to reactant 1, and reacting at 140-150°C for 1-1.5h to obtain reactant 2;

[0077] S3: When the temperature of reactant 2 is lowered to 132-138°C, propylene glycol phenyl ether and ethylene glycol butyl ether are added, and when the temperature is further lowered to 124-126°C, propylene glycol methyl ether is added, and then the temperature is lowered to below 100°C, butanone is added, and then the mixture is stirred at a constant temperature of 90-100°C for 30-60 minutes to obtain reactant 3;

[0078] S4: When the temperature of reactant 3 is lowered to 88-92°C, diethanolamine and isopropanol are added, and the mixture is reacted at 88-92°C for 1.5-2h to obtain reactant 4;

[0079] S5: When the temperature of reactant 4 is lowered to 79-81°C, the lid of the reactor is opened and stirring is stopped. p-Aminodimethylaniline and isopropanol are added to reactant 4, followed by stirring for 10-15 minutes. The temperature is raised to 88-90°C and the reaction is carried out at a constant temperature for 2-2.5 hours to obtain a modified epoxy resin.

[0080] The preparation of the fully enclosed curing agent includes the following steps:

[0081] A1: adding isocyanate and butanone into a reaction kettle and then sealing and stirring to obtain a mixture 1;

[0082] A2: When the mixture 1 is heated to 70-75°C, diethylene glycol ethyl ether is added dropwise, and the temperature is controlled at 78-80°C during the addition. After the addition is completed, the mixture is kept at 78-80°C for 3-4 hours to obtain a mixture 2;

[0083] A3: Add the catalyst to the mixture 2, and after the addition is complete, react at a constant temperature of 78-80°C for 15-30 minutes, then cool to below 50°C and discharge to obtain a fully enclosed curing agent.

[0084] The preparation of the emulsion comprises the following steps:

[0085] B1: Add the fully enclosed curing agent to the modified epoxy resin at 118-122°C and stir for 1-1.5 hours to obtain a resin liquid;

[0086] B2: Add deionized water and lactic acid into the emulsification tank, start stirring at a speed of 1200-1400r / min, add the resin liquid dropwise into the emulsification tank, add deionized water twice during the addition of the resin liquid, after the addition of the resin liquid is completed, control the temperature below 30°C and continue stirring for 45-60 minutes to obtain an emulsion.

[0087] A method for preparing a dip coating for complex pipes comprises the following steps:

[0088] The color paste is directly added into the emulsion and dispersed and stirred for 1-2 hours to make the color paste and the emulsion completely mixed and uniform, thereby obtaining a dip coating for complex pipelines.

[0089] Among them: the weight ratio of emulsion to color paste is 3:1, the weight ratio of modified epoxy resin to fully enclosed curing agent is 1.6:1, the epoxy resin is epoxy resin 128, the weight ratio of epoxy resin, bisphenol A and dodecylphenol is 5.4:1.45:1, the weight ratio of the total amount of epoxy resin, bisphenol A and dodecylphenol to diethanolamine is 13.85:1, the weight ratio of diethanolamine to p-aminodimethylaniline is 3.30:1. : 1, the weight ratio of reactant 2, reactant 3, reactant 4 and epoxy resin is 1:1.17:1.29:1.33, the isocyanate is diphenylmethane diisocyanate, the catalyst is dibutyltin dilaurate, the weight ratio of isocyanate to diethylene glycol ethyl ether is 1:1, the ratio of the total weight of modified epoxy resin and blocked curing agent to the weight of lactic acid is 42:1, and the weight ratio of deionized water to lactic acid is 34.5:1.

[0090] Embodiment 2:

[0091] Different from Example 1, this embodiment adopts: the weight ratio of emulsion to color paste is 2.9:1, the weight ratio of modified epoxy resin to fully enclosed curing agent is 1.8:1, the epoxy resin is E44 and epoxy resin 128, the weight ratio of epoxy resin, bisphenol A and dodecylphenol is 5.3:1.4:1, the weight ratio of the total amount of epoxy resin, bisphenol A and dodecylphenol to diethanolamine is 13.80:1, and the weight ratio of diethanolamine and p-aminodimethylaniline is 1:1. The weight ratio of reactant 2, reactant 3, reactant 4 and epoxy resin is 3.26:1, the weight ratio of reactant 2, reactant 3, reactant 4 and epoxy resin is 1:1.18):1.30:1.35, the isocyanate is diphenylmethane diisocyanate, the catalyst is dibutyltin dilaurate, the weight ratio of isocyanate to diethylene glycol ethyl ether is 1:1, the total weight ratio of modified epoxy resin and blocked curing agent to lactic acid is 43:1, and the weight ratio of deionized water to lactic acid is 34:1.

[0092] Embodiment 3:

[0093] Different from Example 1, this embodiment adopts: the weight ratio of emulsion to color paste is 3.1:1, the weight ratio of modified epoxy resin to fully enclosed curing agent is 1.7:1, the epoxy resins are E44, E51 and epoxy resin 128, the weight ratio of epoxy resin, bisphenol A and dodecylphenol is 5.2:1.35:1, the weight ratio of the total amount of epoxy resin, bisphenol A and dodecylphenol to diethanolamine is 13.75-13.85:1, and the weight ratio of diethanolamine and p-aminodiethanolamine is 1:1. The weight ratio of methylaniline is 3.21:1, the weight ratio of reactant two, reactant three, reactant four and epoxy resin is 1:1.20:1.32:1.38, the isocyanate is diphenylmethane diisocyanate, the catalyst is dibutyltin dilaurate, the weight ratio of isocyanate to diethylene glycol ethyl ether is 1:1, the total weight ratio of modified epoxy resin and blocked curing agent to lactic acid is 42.5:1, and the weight ratio of deionized water to lactic acid is 34.7:1.

[0094] The dip coatings for complex pipelines prepared in Example 1, Example 2 and Example 3 were subjected to coating tests on complex steel pipelines and test plates:

[0095] The painting steps are as follows:

[0096] Surface treatment: thoroughly remove foreign matter such as oil and rust from the substrate, and perform phosphating treatment to improve the adhesion and corrosion resistance of the coating. Since the workpiece is a sealed inner cavity with only inlet and outlet, the solution is in a static state in the inner cavity during the degreasing, degreasing and derusting, surface conversion and water washing processes. In order to achieve better results, the workpiece needs to be oriented and swung in each of the above processes.

[0097] Coating steps: inject the paint into the steel pipe manually or mechanically, pour out the remaining paint later, and send it to an oven or drying tunnel for drying after it is dried naturally, and the drying condition is 100℃ for 20min; then paint according to the above steps, and the drying condition is 160℃ for 40min to obtain the coating. For the coating of the test plate, dip coating or spray coating is adopted, and then it is taken out and sent to an oven or drying tunnel for drying after it is dried naturally, and the drying condition is 160℃ for 20min to obtain the coating.

[0098] The coating was tested and the test results are shown in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] Through the coating test of the dip coating for complex pipes of Example 1, Example 2 and Example 3, it can be known that the coating formed after the dip coating of the present invention is used for coating complex pipes has excellent adhesion, chemical stability, good corrosion resistance, excellent heat transfer performance, heat resistance, moisture resistance, and has a good anti-corrosion effect.

[0103] In summary, the technical solution of the present invention can improve the anti-corrosion performance and reliability of complex pipelines, significantly save the amount of materials used and maintenance costs, solve the protection problem of complex pipelines in marine environments and special working conditions, and improve the safety and service life of equipment operation.

[0104] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dip coating for complex pipes, characterized in that: It includes emulsion and color paste, and the emulsion includes modified epoxy resin and fully enclosed curing agent; By weight: The weight ratio of emulsion to color paste is 2.9-3.1:1; The weight ratio of modified epoxy resin to fully enclosed curing agent is 1.6-1.8:1; in: The preparation method of modified epoxy resin is as follows: S1: Add epoxy resin, bisphenol A, dodecylphenol and propylene glycol methyl ether into a clean reactor, heat to 118-122° C., and stir until bisphenol A is completely dissolved to obtain reactant 1; S2: adding dimethylethanolamine to reactant 1, and reacting at 140-150°C for 1-1.5h to obtain reactant 2; S3: When the temperature of reactant 2 is lowered to 132-138°C, propylene glycol phenyl ether and ethylene glycol butyl ether are added, and when the temperature is further lowered to 124-126°C, propylene glycol methyl ether is added, and then the temperature is lowered to below 100°C, butanone is added, and then the mixture is stirred at a constant temperature of 90-100°C for 30-60 minutes to obtain reactant 3; S4: When the temperature of reactant 3 is lowered to 88-92°C, diethanolamine and isopropanol are added, and the mixture is reacted at 88-92°C for 1.5-2h to obtain reactant 4; S5: When the temperature of reactant 4 is lowered to 79-81°C, the lid of the reactor is opened and stirring is stopped. p-Aminodimethylaniline and isopropanol are added to reactant 4, followed by stirring for 10-15 minutes. The temperature is raised to 88-90°C and the reaction is carried out at a constant temperature for 2-2.5 hours to obtain a modified epoxy resin.

2. A dip coating for complex pipes according to claim 1, characterized in that: In step S1, the epoxy resin is one or more of E44, E51 and epoxy resin 128, and the weight ratio of epoxy resin, bisphenol A and dodecylphenol is (5.2-5.4):(1.35-1.45):

1.

3. A dip coating for complex pipes according to claim 2, characterized in that: The weight ratio of the total amount of epoxy resin, bisphenol A and dodecylphenol to diethanolamine is (13.75-13.85):1, and the weight ratio of diethanolamine to p-aminodimethylaniline is (3.21-3.30):

1.

4. The dip coating for complex pipes according to claim 3, characterized in that: The weight ratio of reactant 2, reactant 3, reactant 4 and epoxy resin is 1:(1.17-1.20):(1.29-1.32):(1.33-1.38).

5. The dip coating for complex pipes according to claim 4, characterized in that: The preparation of the fully enclosed curing agent includes the following steps: A1: adding isocyanate and butanone into a reaction kettle and then sealing and stirring to obtain a mixture 1; A2: When the mixture 1 is heated to 70-75°C, diethylene glycol ethyl ether is added dropwise, and the temperature is controlled at 78-80°C during the addition. After the addition is completed, the mixture is kept at 78-80°C for 3-4 hours to obtain a mixture 2; A3: Add the catalyst to the mixture 2, and after the addition is complete, react at a constant temperature of 78-80°C for 15-30 minutes, then cool to below 50°C and discharge to obtain a fully enclosed curing agent.

6. A dip coating for complex pipes according to claim 5, characterized in that: The isocyanate is diphenylmethane diisocyanate; The catalyst is dibutyltin dilaurate; The weight ratio of isocyanate to diethylene glycol ethyl ether is 1:

1.

7. A dip coating for complex pipes according to claim 6, characterized in that: The emulsion also includes deionized water and lactic acid, and the total weight ratio of the modified epoxy resin and the closed curing agent to the weight ratio of the lactic acid is (42-43):

1.

8. The dip coating for complex pipes according to claim 7, characterized in that: The preparation of the emulsion comprises the following steps: B1: Add the fully enclosed curing agent to the modified epoxy resin at 118-122°C and stir for 1-1.5 hours to obtain a resin liquid; B2: Add deionized water and lactic acid into the emulsification tank, start stirring at a speed of 1200-1400r / min, add the resin liquid dropwise into the emulsification tank, add deionized water twice during the addition of the resin liquid, after the addition of the resin liquid is completed, control the temperature below 30°C and continue stirring for 45-60 minutes to obtain an emulsion.

9. A dip coating for complex pipes according to claim 8, characterized in that: In step B2, the dripping speed of the resin liquid is 190-210 kg / 30 min, the weight ratio of deionized water to lactic acid is 34-34.7:1, and the viscosity of the emulsion is 40-50 mPa·s.

10. A method for preparing a dip coating for complex pipelines, characterized in that: The method for preparing the dip coating for complex pipelines according to any one of claims 1 to 9 comprises the following steps: The color paste is directly added into the emulsion and then dispersed and stirred for 1-2 hours to completely mix the color paste and the emulsion to obtain a dip coating for complex pipelines.

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