Modified epoxy resin and preparation method thereof, modified epoxy polyurethane resin and coating

Abstract

The invention relates to a modified epoxy resin and a preparation method thereof, a modified epoxy polyurethane resin and a coating. The modified epoxy polyurethane resin is composed of bisphenol A epoxy resin, bisphenol AF, epoxy chloropropane, a NaOH aqueous solution, butyl acetate, xylene, small molecule amine and modified isocyanate. The modified epoxy polyurethane resin has high-content hydroxyl groups, and a paint film prepared from the resin is more compact, good in adhesive force and high in hardness and has good stain resistance, corrosion medium resistance, anti-icing agent resistance and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of research and preparation of protective coatings, and more specifically, to a modified epoxy resin with a high hydroxyl content and excellent anti-fouling properties, resistance to corrosion media, and resistance to anti-icing agents, and a preparation method thereof, as well as a modified epoxy polyurethane resin containing the same and a coating prepared thereby. Background Art

[0002] Paint is an indispensable material for protecting infrastructure in daily life. It is widely used in the decoration of buildings and industrial products as well as vehicles, ships, aircraft and other fields. In the past, the requirements of paint for the protective layer of the substrate were often only beautiful appearance and bright gloss, but there were no strict requirements for the media resistance of the coating. With the rapid development of industry, various fields have more different usage requirements for coating performance, especially in the aviation field, which has high standards and strict requirements for coatings on aircraft.

[0003] Protective coatings play a vital role in the safety and reliability of aircraft operations. The corrosion of the local environment of the aircraft's overall fuel tank is an important hidden danger that affects aircraft safety. There is a certain concentration of water dissolved in aviation fuel. When the aircraft is flying at high altitude, the low temperature causes the dissolved water to precipitate and freeze, thereby blocking the valves, pumps, filters and screens of the fuel system, causing the engine combustion chamber to shut down, thus endangering flight safety. Fuel system anti-icing agent is a fuel additive that can prevent or reduce the formation or accumulation of ice in the fuel system in cold weather or at high altitudes. Diethylene glycol methyl ether (DIEGME) is commonly used as an anti-icing agent. When the organic coating is in the anti-icing agent for a long time, the anti-icing agent can attack the free hydroxyl, carboxyl and other polar groups on the surface of the coating, thereby causing the shielding performance of the coating to decrease, and in severe cases, the coating may peel off from the surface of the substrate. During the operation of the aircraft, the DIEGME anti-icing agent may condense in high concentration in the top space of the fuel tank, or be enriched in the residual water at the bottom of the fuel tank. DIEGME, as a solvent for traditional epoxy-based fuel tank coatings, causes the coating to swell or peel off. The peeled fuel tank coating may enter and clog the fuel filter, thereby interrupting the operation of the fuel system and threatening flight safety.

[0004] The development of aircraft fuel tank coatings in my country is carried out synchronously with the changes in fuel tank structure design, aviation fuel application development and aircraft service environment. The design of aircraft fuel tanks has developed from early independent fuel tanks to integrated fuel tanks; the application direction of domestic aviation fuel has never considered the anti-icing problem to the current trend of standardized addition of anti-icing agents; the service environment of aircraft has also changed from conventional continental environment to harsh marine corrosion environment. Therefore, the overall development trend of fuel tank coatings can be summarized into three points: long service life, anti-icing agent tolerance, and broad-spectrum environmental adaptability.

[0005] The fuel tank protective coating is different from the external structure protective coating. It cannot be replaced during its service life. At the beginning of the design, the subsequent use must be considered. Therefore, when choosing the fuel tank protective coating, the aircraft plans to choose the anti-icing agent type protective coating; at the same time, according to the characteristics of the use environment, the seaworthiness requirements of the coating are increased.

[0006] Commonly used protective coating systems include acrylic, polyurethane, and epoxy systems. Acrylic polyurethane coatings are commonly used for various types of transportation vehicles, construction machinery, aircraft skins and other objects that require surface decoration. They have high adhesion and good mechanical properties, excellent water resistance, oil resistance, salt spray resistance, moisture resistance, and chemical resistance. Modified epoxy resin and isocyanate cross-linking and curing are usually used for the interior of aircraft fuel tanks. In addition to having good corrosion resistance, this coating can also help protect the interior of the aircraft fuel tank from corrosion by fuel pollutants, including water, salt water, aircraft fuel, hydraulic fluid, engine oil, and dilute acid solutions. Zhou Yingying, Wang Pinghua, etc. used diethanolamine to modify epoxy resin E-44 and used isocyanate as a curing agent to prepare a film-forming material with good mechanical properties and good adhesion to different substrates. However, due to its low hydroxyl content, the prepared film-forming material has a low degree of crosslinking and its medium resistance is general. Summary of the invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of this application.

[0008] Since epoxy resin contains many hydroxyl groups and ether bonds, it can attract the substrate and has excellent adhesion. Moreover, the epoxy resin forms a dense film after curing with isocyanate, making it an ideal base resin for anti-corrosion primers. However, based on the above shortcomings in the coating design, this application chooses to introduce a fluorinated epoxy resin made from bisphenol AF as a raw material into the bisphenol A epoxy resin. The performance of bisphenol AF fluorinated epoxy resin and bisphenol A epoxy resin is similar. Since bisphenol AF contains FC bonds, the surface has excellent hydrophobicity and anti-fouling properties, which can greatly improve the coating's resistance to corrosion media and anti-icing agents. At the same time, through resin modification, the unreacted groups of the epoxy resin are eliminated to meet the design requirements of the project.

[0009] In view of the shortcomings of the prior art, one object of the present application is to provide a modified epoxy resin and an anti-icing agent-resistant modified epoxy polyurethane resin containing the same. The modified epoxy polyurethane resin is used as a component of the coating, and the prepared paint film has good physical and chemical mechanical properties, long service life, anti-icing agent tolerance, broad-spectrum environmental adaptability, mildew resistance and tolerance to different types of fuel media, and has excellent bonding with the inner and outer walls of the aluminum alloy fuel tank, meeting the protection requirements of the carrier-based aircraft metal fuel tank. Another object of the present application is to use the anti-icing agent-resistant modified epoxy polyurethane resin to prepare a protective coating with excellent anti-icing agent resistance, fuel resistance, mildew resistance, and marine environment adaptability.

[0010] To achieve the above objectives, this application adopts the following technical solutions:

[0011] The first aspect of the present application provides a modified epoxy resin, comprising the following raw materials in parts by weight: 20-25 parts of epoxy resin, 15-20 parts of bisphenol AF, 30-40 parts of epichlorohydrin, 8-12 parts of NaOH aqueous solution, 10-15 parts of butyl acetate, 10-20 parts of xylene, and 10-15 parts of amine modifier.

[0012] In an exemplary embodiment, the epoxy resin is selected from one or a combination of bisphenol A epoxy resin, bisphenol AF fluorinated epoxy resin, hydrogenated bisphenol A epoxy resin, linear phenolic epoxy resin, and glycidylamine multifunctional epoxy resin; preferably, it is bisphenol A epoxy resin.

[0013] Among them, bisphenol AF is introduced into bisphenol A epoxy resin, and the unreacted groups in the epoxy resin are eliminated through resin modification to meet the design requirements.

[0014] In an exemplary embodiment, the modified epoxy resin includes the following raw materials in parts by weight: 20-25 parts of bisphenol A epoxy resin, 15-20 parts of bisphenol AF, 30-40 parts of epichlorohydrin, 8-12 parts of NaOH aqueous solution, 10-15 parts of butyl acetate, 10-20 parts of xylene, and 10-15 parts of amine modifier.

[0015] In an exemplary embodiment, the modified epoxy resin is composed of the following raw materials in parts by weight: 20-25 parts of bisphenol A epoxy resin, 15-20 parts of bisphenol AF, 30-40 parts of epichlorohydrin, 8-12 parts of NaOH aqueous solution, 10-15 parts of butyl acetate, 10-20 parts of xylene, and 10-15 parts of amine modifier.

[0016] In an exemplary embodiment, the modified epoxy resin has a high hydroxyl content, wherein the hydroxyl content is 5-8%.

[0017] In an exemplary embodiment, the NaOH aqueous solution is an aqueous solution with a NaOH mass fraction of 10%.

[0018] In an exemplary embodiment, the amine modifier is a small molecule amine modifier, selected from any one or both of monoethanolamine and diethanolamine; since the epoxy resin modified by diethanolamine has a higher hydroxyl content, the paint film is denser after cross-linking with isocyanate, the coating has good adhesion and high hardness, preferably, the small molecule amine modifier is diethanolamine.

[0019] Among them, the bisphenol A type epoxy resin has a fast drying rate, the functional groups contain phenyl and ether bonds, the active functional groups contain epoxy and hydroxyl groups, and has excellent adhesion, chemical resistance, strength, and heat resistance; the bisphenol AF has a fast drying rate, the functional groups contain phenyl, ether bonds, and FC bonds, the active functional groups contain epoxy and hydroxyl groups, and has excellent anti-fouling, adhesion, chemical resistance, strength, and heat resistance.

[0020] The second aspect of the present application provides a method for preparing the above-mentioned modified epoxy resin, comprising the following steps:

[0021] a) In a four-mouth reactor equipped with a thermometer, a condenser and a stirrer, 15-20 parts of bisphenol AF and 30-40 parts of epichlorohydrin are added in sequence for blending, and then a NaOH aqueous solution is gradually added for polycondensation reaction, and the temperature is controlled at 70°C-75°C for 2-3 hours;

[0022] b) heating to 80-90° C. and maintaining for 2-3 hours, then vacuum removing, adding a mixed solvent of 10-15 parts of butyl acetate and 10-20 parts of xylene to adjust the viscosity, and obtaining a fluorine-containing epoxy resin;

[0023] c) adding 20-25 parts of bisphenol A epoxy resin to the fluorine-containing epoxy resin and stirring, and adding 10-15 parts of amine modifier and stirring, heating to 60-65° C., and then washing with water;

[0024] d) After washing with water, vacuum extraction is performed to adjust the solid, and finally filtering is performed to obtain a modified epoxy resin.

[0025] In an exemplary embodiment, in step b), the temperature is raised to 85° C. and maintained for 2 hours.

[0026] In an exemplary embodiment, in step b), the adjusted viscosity is 500-1500 mPa·s.

[0027] The third aspect of the present application provides a modified epoxy resin prepared by the above method.

[0028] The fourth aspect of the present application provides a modified isocyanate, wherein the modified isocyanate is obtained by reacting a linear diol with an isocyanate monomer.

[0029] In an exemplary embodiment, the modified isocyanate comprises the following raw materials in parts by weight: 15-20 parts of isocyanate monomer and 18-22 parts of linear diol. Here, the modified isocyanate is a toughened isocyanate.

[0030] In an exemplary embodiment, the isocyanate monomer is one or a combination of aromatic isocyanate, aliphatic isocyanate, alicyclic isocyanate, and aromatic isocyanate.

[0031] In an exemplary embodiment, the aromatic isocyanate is one or a combination of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymethylene polyphenyl isocyanate (PAPI).

[0032] In an exemplary embodiment, the aliphatic isocyanate is hexamethylene diisocyanate (HDI).

[0033] In an exemplary embodiment, the alicyclic isocyanate is isophorone diisocyanate (IPDI).

[0034] In an exemplary embodiment, the linear diol is a linear diol selected from one or a combination of polyether diol, polyester diol and alkyl diol.

[0035] In an exemplary embodiment, the polyether diol is one or a combination of diethylene glycol, oligotetramethylene glycol.

[0036] In an exemplary embodiment, the polyester diol is oligomeric 1,4-butanediol adipate.

[0037] In an exemplary embodiment, the alkyl glycol is one or a combination of 1,6-hexanediol and propylene glycol.

[0038] In an exemplary embodiment, the isocyanate monomer and the linear diol are toluene diisocyanate (TDI) and 1,6-hexanediol, respectively.

[0039] The fifth aspect of the present application provides a method for preparing the above-mentioned modified isocyanate, comprising the following steps:

[0040] 1) Add isocyanate monomer into a reaction kettle containing solvent according to the ratio, heat to 20-30°C and stir for 25-35 minutes;

[0041] 2) After mixing evenly, heat the mixed solution to 40-50°C, then dropwise add dehydrated linear diol and raise the temperature to 75-85°C;

[0042] 3) Keep the reaction going for 2.5-3.5 hours, test the NCO% content, when the NCO content tends to be stable and close to the theoretical value, it is the end point of the reaction, and lower the temperature to extract the material.

[0043] In an exemplary embodiment, in step 1), the solvent in the reaction kettle is 22-30 parts of butyl acetate.

[0044] In an exemplary embodiment, in step 1), the temperature is raised to 25° C. and stirred for 30 min.

[0045] In an exemplary embodiment, in step 2), the temperature is raised to 80°C.

[0046] In an exemplary embodiment, in step 3), the reaction is maintained for 3 hours.

[0047] The sixth aspect of the present application provides a modified isocyanate prepared by the above method.

[0048] The seventh aspect of the present application provides a modified epoxy polyurethane resin, which is obtained by cross-linking the above-mentioned amine-modified epoxy resin and the above-mentioned modified isocyanate, wherein -OH / -NCO=1:1 to 1:1.5; for example, 1:1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc. or any two of them as range values ​​between endpoint values, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] In an exemplary embodiment, in the modified epoxy polyurethane resin, -OH / -NCO=1:1 to 1:1.3; preferably, 1:1.3.

[0050] In an exemplary embodiment, the modified epoxy polyurethane resin includes the following raw materials in parts by weight: 20-25 parts of bisphenol A epoxy resin, 15-20 parts of bisphenol AF, 30-40 parts of epichlorohydrin, 8-12 parts of NaOH aqueous solution, 10-15 parts of butyl acetate, 10-20 parts of xylene, 10-15 parts of amine modifier, 15-20 parts of isocyanate monomer, and 18-22 parts of linear diol.

[0051] In an exemplary embodiment, the modified epoxy polyurethane resin includes the following raw materials in parts by weight: 20 parts of bisphenol A epoxy resin, 16 parts of bisphenol AF, 35 parts of epichlorohydrin, 8 parts of NaOH aqueous solution, 11 parts of butyl acetate, 12 parts of xylene, 11 parts of amine modifier, 16 parts of toluene diisocyanate (TDI) and 19 parts of 1,6-hexanediol.

[0052] In an exemplary embodiment, the modified epoxy polyurethane resin includes the following raw materials in parts by weight: 22 parts of bisphenol A epoxy resin, 18 parts of bisphenol AF, 31 parts of epichlorohydrin, 9 parts of NaOH aqueous solution, 12 parts of butyl acetate, 15 parts of xylene, 13 parts of amine modifier, 18 parts of toluene diisocyanate (TDI) and 20 parts of 1,6-hexanediol.

[0053] In an exemplary embodiment, the modified epoxy polyurethane resin includes the following raw materials in parts by weight: 25 parts of bisphenol A epoxy resin, 20 parts of bisphenol AF, 30 parts of epichlorohydrin, 12 parts of NaOH aqueous solution, 15 parts of butyl acetate, 18 parts of xylene, 11 parts of amine modifier, 20 parts of toluene diisocyanate (TDI) and 22 parts of 1,6-hexanediol.

[0054] In an exemplary embodiment, the modified epoxy polyurethane resin has a high hydroxyl content, wherein the hydroxyl content is 5-8%.

[0055] The eighth aspect of the present application provides a coating containing the above-mentioned modified epoxy polyurethane resin.

[0056] Other features and advantages of the present application will be described in the following description, and partly become apparent from the description, or be understood by implementing the present application. Other advantages of the present application can be realized and obtained by the schemes described in the description. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the present application more clear, the embodiments of the present application will be described in detail below. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other arbitrarily without conflict.

[0058] The present application is further described in detail below in conjunction with specific examples, but the examples should not be construed as limiting the present invention.

[0059] Raw materials, unless otherwise specified, are conventional products on the market.

[0060] Example 1

[0061] A modified epoxy resin with a high hydroxyl content comprises the following raw materials in parts by weight: 22 parts of bisphenol A epoxy resin, 17 parts of bisphenol AF, 35 parts of epichlorohydrin, 10 parts of NaOH aqueous solution, 12 parts of butyl acetate, 15 parts of xylene, and 12 parts of amine modifier. The preparation steps are as follows:

[0062] a) In a four-mouth reactor equipped with a thermometer, a condenser and a stirrer, 17 parts of bisphenol AF and 35 parts of epichlorohydrin are added in sequence for blending, and then a NaOH aqueous solution is gradually added for polycondensation reaction, and the temperature is controlled between 70°C and 75°C for 2-3 hours;

[0063] b) heating to 85° C. and maintaining for 2 h, then vacuum removing, adding a mixed solvent of 12 parts of butyl acetate and 15 parts of xylene to adjust the viscosity, and obtaining a fluorine-containing epoxy resin;

[0064] c) adding 22 parts of bisphenol A epoxy resin to the fluorine-containing epoxy resin and stirring, and adding 12 parts of a small molecular amine and stirring, heating to 60-65° C., and then washing with water;

[0065] d) After washing with water, vacuum extraction is performed to adjust the solid, and finally filtering is performed to obtain a modified epoxy resin.

[0066] Example 2

[0067] A toughened modified isocyanate comprises the following raw materials in parts by weight: 17 parts of toluene diisocyanate and 20 parts of 1,6-hexanediol. The preparation steps are as follows:

[0068] a) 17 parts of toluene diisocyanate (TDI) and 26 parts of butyl acetate were added into a reaction kettle, heated to 25°C and stirred for 30 minutes;

[0069] b) After mixing evenly, the mixed solution was heated to 40°C, and then 20 parts of dehydrated 1,6-hexanediol was added dropwise, and the temperature was raised to 80°C;

[0070] c) Keep the reaction going for 3 hours, test the NCO% content, and lower the temperature to extract the material.

[0071] Test 1:

[0072] In Example 1, bisphenol AF and epichlorohydrin are used to prepare a fluorine-containing epoxy resin, which is then blended with a bisphenol A epoxy resin to achieve adjustable fluorine content in the epoxy resin.

[0073] The coating was prepared by curing the modified epoxy resin in Example 1 with the aromatic isocyanate in Example 2, and the coating was preliminarily tested for resistance to 4050 lubricating oil (121°C ± 2°C, 14 days), anti-icing agent resistance (diethylene glycol methyl ether and deionized water were prepared into a test solution in a volume ratio of 80:20, and the test solution temperature was controlled by an oil bath to maintain 74°C ± 3°C, after 60 days of testing), and compatibility with QFS-15 weather-resistant polyurethane enamel (tested according to GB / T 5210 and the pull-off method with QFS-15 coating), etc., to investigate the effect of fluorine content on the performance of the film-forming material, and the results are shown in Table 1. Wherein, -OH / -NCO = 1:1.3; the bisphenol A epoxy resin and the fluorine-containing epoxy resin in test numbers 1-5 are respectively the ratios of the bisphenol A epoxy resin added in step (c) of Example 1 and the bisphenol AF fluorine-containing epoxy resin obtained in step (b).

[0074] Table 1 Effect of fluorine content on resin properties

[0075]

[0076]

[0077] According to Table 1, the increase of F content can greatly improve the corrosion resistance of the coating, but the introduction of too much F element can lead to excessive surface tension of the coating, affecting its compatibility with matching topcoats and sealants. Therefore, it is necessary to design a reasonable F content to take into account the protective performance and matching of the coating.

[0078] Test 2.

[0079] A coating was prepared by curing the modified epoxy resin in Example 1 with the aromatic isocyanate in Example 2 and unmodified toluene diisocyanate, respectively, and the coating was tested for performance, wherein -OH / -NCO=1:1.3; the test results are shown in Table 2 below.

[0080] Table 2

[0081] standard Coatings containing toluene diisocyanate Coating containing toluene diisocyanate modified with 1,6-hexanediol Cross-hatch adhesion ≤1 level Level 2 Level 0 Pull-off adhesion ≥16MPa 20.5MPa 19.8MPa hardness ≥H 3H 2H Flexibility ≤2mm 3mm 1mm Impact resistance 50cm 40cm 50cm

[0082] Summary: Compared with toluene diisocyanate not modified with 1,6-hexanediol, the flexibility and impact resistance of the paint film containing the aromatic isocyanate in Example 2 are significantly improved, indicating that the toughening effect is obvious.

[0083] Test 3.

[0084] The coating was prepared by curing the modified epoxy resin in Example 1 with the aromatic isocyanate in Example 2, and the -OH / -NCO ratio was changed to measure the effect on the coating properties. The test results are shown in Table 3 below.

[0085] Table 3

[0086]

[0087] Summary: By appropriately increasing the amount of NCO functional group, the reaction degree between the OH group and the NCO group in the two components and the density of the coating can be improved to a certain extent without affecting other comprehensive properties of the coating, which is manifested in the gradual enhancement of the coating solubility and the increasing trend of the coating hardness. When the -OH / -NCO theoretical equivalent ratio is 1:1.5, the solvent resistance of the coating decreases and the mechanical properties deteriorate, indicating that there are too many small molecular structures formed by the excess -NCO groups in the system, resulting in poor overall performance.

[0088] The modified epoxy resin of Example 1 and the modified aromatic isocyanate of Example 2 were cross-linked, and -OH / -NCO=1:1.3 was selected for preparation to obtain the anti-icing agent modified epoxy polyurethane resins of Examples 3-5.

[0089] Example 3

[0090] An anti-icing agent modified epoxy polyurethane resin comprises, by weight, 20 parts of bisphenol A epoxy resin, 16 parts of bisphenol AF, 35 parts of epichlorohydrin, 8 parts of NaOH aqueous solution, 11 parts of butyl acetate, 12 parts of xylene, 11 parts of amine modifier, 16 parts of toluene diisocyanate and 19 parts of 1,6-hexanediol.

[0091] Example 4

[0092] An anti-icing agent modified epoxy polyurethane resin comprises, by weight, 22 parts of bisphenol A epoxy resin, 18 parts of bisphenol AF, 31 parts of epichlorohydrin, 9 parts of NaOH aqueous solution, 12 parts of butyl acetate, 15 parts of xylene, 13 parts of amine modifier, 18 parts of toluene diisocyanate and 20 parts of 1,6-hexanediol.

[0093] Example 5

[0094] An anti-icing agent modified epoxy polyurethane resin comprises, by weight, 25 parts of bisphenol A epoxy resin, 20 parts of bisphenol AF, 30 parts of epichlorohydrin, 12 parts of NaOH aqueous solution, 15 parts of butyl acetate, 18 parts of xylene, 11 parts of amine modifier, 20 parts of toluene diisocyanate and 22 parts of 1,6-hexanediol.

[0095] Test 4:

[0096] According to relevant test standards, the anti-icing agent modified epoxy polyurethane resin prepared in Example 3, Example 4, and Example 5 was added to the coating for performance testing. The test results are shown in Table 4.

[0097] Table 4

[0098]

[0099]

[0100] Conclusion: The present application provides a modified epoxy resin and a modified epoxy polyurethane resin containing the same. The modified epoxy polyurethane resin is used as a component of a coating. The prepared paint film has good physical and chemical mechanical properties, long service life, anti-icing agent tolerance, broad-spectrum environmental adaptability, mildew resistance and tolerance to different types of fuel media. It has excellent bonding strength with the inner and outer walls of aluminum alloy fuel tanks, meets the protection needs of carrier-based aircraft metal fuel tanks, and prepares a protective coating with excellent anti-icing agent resistance, fuel resistance, mildew resistance, and marine environment adaptability.

[0101] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A modified epoxy resin, characterized in that: The invention comprises the following raw materials in parts by weight: 20-25 parts of epoxy resin, 15-20 parts of bisphenol AF, 30-40 parts of epichlorohydrin, 8-12 parts of NaOH aqueous solution, 10-15 parts of butyl acetate, 10-20 parts of xylene and 10-15 parts of amine modifier.

2. The modified epoxy resin according to claim 1, characterized in that The epoxy resin is selected from one or a combination of bisphenol A epoxy resin, bisphenol AF fluorinated epoxy resin, hydrogenated bisphenol A epoxy resin, novolac epoxy resin, and glycidylamine multifunctional epoxy resin; Optionally, the epoxy resin is a bisphenol A type epoxy resin.

3. The modified epoxy resin according to claim 2, characterized in that The modified epoxy resin comprises the following raw materials in parts by weight: 20-25 parts of bisphenol A epoxy resin, 15-20 parts of bisphenol AF, 30-40 parts of epichlorohydrin, 8-12 parts of NaOH aqueous solution, 10-15 parts of butyl acetate, 10-20 parts of xylene, and 10-15 parts of amine modifier.

4. The modified epoxy resin according to any one of claims 1 to 3, characterized in that The NaOH aqueous solution is an aqueous solution with a mass fraction of NaOH of 10%; and / or The amine modifier is selected from any one or both of monoethanolamine and diethanolamine.

5. The modified epoxy resin according to claim 4, characterized in that The amine modifier is diethanolamine.

6. A method for preparing the modified epoxy resin according to any one of claims 2 to 5, characterized in that: The following steps are involved: a) In a four-mouth reactor equipped with a thermometer, a condenser and a stirrer, 15-20 parts of bisphenol AF and 30-40 parts of epichlorohydrin are added in sequence for blending, and then a NaOH aqueous solution is gradually added for polycondensation reaction, and the temperature is controlled between 70°C and 75°C for 2-3 hours; b) heating to 80-90° C. and maintaining for 2-3 hours, washing with deionized water for multiple times, then vacuum removing, adding a mixed solvent of 10-15 parts of butyl acetate and 10-20 parts of xylene to adjust its viscosity, and obtaining a fluorine-containing epoxy resin; c) adding 20-25 parts of bisphenol A epoxy resin to the fluorine-containing epoxy resin and stirring, and adding 10-15 parts of amine modifier and stirring, heating to 60-65° C., and then washing with water; d) After washing with water, vacuum extraction is performed to adjust the solid, and finally filtering is performed to obtain a modified epoxy resin.

7. The method according to claim 6, characterized in that In step b), the temperature is raised to 85° C. and maintained for 2 h; and / or In step b), the adjusted viscosity is 500-1500 mpa·s.

8. A modified epoxy resin prepared by the method of claim 6 or 7.

9. A modified epoxy polyurethane resin, characterized in that: The modified epoxy polyurethane resin is obtained by cross-linking the modified epoxy resin according to any one of claims 1 to 5 and 8 with modified isocyanate, wherein -OH / -NCO=1:1 to 1:1.5; the modified isocyanate is obtained by reacting a linear diol with an isocyanate monomer.

10. The modified epoxy polyurethane resin according to claim 9, characterized in that: In the modified epoxy polyurethane resin, -OH / -NCO=1:1 to 1:1.3; and / or The modified isocyanate comprises the following raw materials in parts by weight: 15-20 parts of isocyanate monomer and 18-22 parts of linear diol.

11. The modified epoxy polyurethane resin according to claim 9 or 10, characterized in that: The isocyanate monomer is selected from one or a combination of aromatic isocyanate, aliphatic isocyanate, alicyclic isocyanate, and aromatic isocyanate; Optionally, the aromatic isocyanate is selected from one or a combination of toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl isocyanate; Optionally, the aliphatic isocyanate is selected from hexamethylene diisocyanate; Optionally, the cycloaliphatic isocyanate is isophorone diisocyanate.

12. The modified epoxy polyurethane resin according to claim 9 or 10, characterized in that: The linear diol is a linear diol selected from one or a combination of polyether diols, polyester diols and alkyl diols; Optionally, the polyether diol is one or a combination of diethylene glycol and oligotetrahydrofuran diol; Optionally, the polyester diol is oligomeric 1,4-butanediol adipate; Optionally, the alkyl glycol is one or a combination of 1,6-hexanediol and propylene glycol.

13. The modified epoxy polyurethane resin according to claim 9 or 10, characterized in that: The preparation method of the modified isocyanate comprises the following steps: 1) Add isocyanate monomer into a reaction kettle containing solvent according to the ratio, heat to 20-30°C and stir for 25-35 minutes; 2) After mixing evenly, heat the mixed solution to 40-50°C, then dropwise add dehydrated linear diol and raise the temperature to 75-85°C; 3) Keep the reaction going for 2.5-3.5h, test the NCO% content, when the NCO content tends to be stable and close to the theoretical value, it is the end point of the reaction, and lower the temperature to extract the material.

14. The modified epoxy polyurethane resin according to claim 9 or 10, characterized in that: The modified epoxy polyurethane resin comprises the following raw materials in parts by weight: 20-25 parts of bisphenol A epoxy resin, 15-20 parts of bisphenol AF, 30-40 parts of epichlorohydrin, 8-12 parts of NaOH aqueous solution, 10-15 parts of butyl acetate, 10-20 parts of xylene, 10-15 parts of amine modifier, 15-20 parts of isocyanate monomer, and 18-22 parts of linear diol.

15. The modified epoxy polyurethane resin according to claim 14, characterized in that: The isocyanate monomer and the linear diol are toluene diisocyanate and 1,6-hexanediol respectively.

16. The modified epoxy polyurethane resin according to claim 15, characterized in that: The modified epoxy polyurethane resin comprises the following raw materials in parts by weight: 20 parts of bisphenol A epoxy resin, 16 parts of bisphenol AF, 35 parts of epichlorohydrin, 8 parts of NaOH aqueous solution, 11 parts of butyl acetate, 12 parts of xylene, 11 parts of amine modifier, 16 parts of toluene diisocyanate and 19 parts of 1,6-hexanediol; or The modified epoxy polyurethane resin comprises the following raw materials in parts by weight: 22 parts of bisphenol A epoxy resin, 18 parts of bisphenol AF, 31 parts of epichlorohydrin, 9 parts of NaOH aqueous solution, 12 parts of butyl acetate, 15 parts of xylene, 13 parts of amine modifier, 18 parts of toluene diisocyanate and 20 parts of 1,6-hexanediol; or The modified epoxy polyurethane resin comprises the following raw materials in parts by weight: 25 parts of bisphenol A epoxy resin, 20 parts of bisphenol AF, 30 parts of epichlorohydrin, 12 parts of NaOH aqueous solution, 15 parts of butyl acetate, 18 parts of xylene, 11 parts of amine modifier, 20 parts of toluene diisocyanate and 22 parts of 1,6-hexanediol.

17. A coating comprising the modified epoxy polyurethane resin according to any one of claims 9 to 16.

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