Waterborne epoxy modified polyurethane coating for flexibly bonding neodymium-iron-boron magnet

Abstract

The invention discloses a waterborne epoxy modified polyurethane coating for flexibly bonding a neodymium-iron-boron magnet. The waterborne epoxy modified polyurethane coating is prepared from the following components in parts by weight: 70 to 80 parts of waterborne epoxy modified polyurethane dispersion and 1.1 to 5.0 parts of auxiliaries. Wherein the water-based epoxy modified polyurethane dispersoid comprises an epoxy resin component and a polyurethane component, the ratio of the epoxy resin component to the polyurethane component is 5.0-25.0%, the acid value of the water-based epoxy modified polyurethane dispersoid is 19-29 KOH / mg, and the solid content of the water-based epoxy modified polyurethane dispersoid is 34.0-44.0%. Compared with a common waterborne epoxy coating, the waterborne epoxy modified polyurethane coating has the advantages that the flexibility of a coating formed by the waterborne epoxy modified polyurethane coating can be improved by 84 times at most, and compared with the common waterborne polyurethane coating, the corrosion resistance and salt spray resistance of the coating formed by the waterborne epoxy modified polyurethane coating are improved by 6-9 times.

Description

Technical Field

[0001] The invention relates to the field of water-based industrial coatings for bonding neodymium iron boron magnets for protection and decorative coating, and in particular to a water-based epoxy-modified polyurethane coating for flexible bonding of neodymium iron boron magnets. Background Art

[0002] In the past, bonded NdFeB magnets were usually bonded and cured with epoxy resin to form NdFeB particles. After forming, epoxy coating was used for corrosion protection, such as CN108624188A and CN108912942A. The shape of such bonded NdFeB and its coating was fixed and hard, and not easy to deform.

[0003] With the expansion of bonded NdFeB applications and technological advancements, flexible bonded NdFeB magnets, bonded with materials such as rubber, polyurethane, or nylon, have emerged. These magnets can be bent or even folded in half without cracking or breaking. However, the epoxy coating commonly used for these bonded NdFeB magnets is hard, which can make the magnets harder and reduce their flexibility. Furthermore, the epoxy coating can crack and break when the bonded NdFeB magnets are bent. Of course, flexible magnets existed before flexible bonded NdFeB magnets, but they were not as strong as NdFeB magnets. Instead, they were common magnets with weaker magnetic properties, such as traditional ferroferric oxide magnets. Fiberferric oxide has a certain degree of corrosion resistance, so it does not require coating protection. However, compared to NdFeB magnets, ferroferric oxide magnets are easily demagnetized and have weaker magnetic properties, making them inadequate for the flexible magnets required by modern high-end devices. Therefore, flexible bonded NdFeB must be developed, and then corresponding protective coatings must be developed.

[0004] In order to meet the requirements of flexible bonding of NdFeB magnets and take into account environmental protection requirements, the key film-forming material of the coating needs to adopt a relatively flexible system such as water-based polyurethane. However, due to the high corrosion activity of "neodymium" in the "neodymium-rich phase" of NdFeB, the current water-based polyurethane coatings do not meet the use requirements of flexible bonding of NdFeB in terms of salt spray corrosion resistance. Rusting and blistering will occur after a few hours of neutral salt spray resistance testing. Moreover, the current general water-based polyurethane coatings are not specially designed for protective coating of flexible bonding of NdFeB. Even if the polyurethane material is flexible, it cannot meet the requirements of flexible bonding of NdFeB. At present, there is no water-based coating that can be used for flexible bonding of NdFeB and can meet the requirements of flexibility and corrosion resistance at the same time. Summary of the Invention

[0005] The invention provides a water-based epoxy-modified polyurethane coating for flexible bonding of NdFeB magnets, which can solve the protective coating problem of flexible bonding of NdFeB magnets.

[0006] An embodiment of the present invention provides a waterborne epoxy-modified polyurethane coating for flexible bonding of NdFeB magnets, comprising the following components, measured in parts by weight: 70-80 parts by weight of a waterborne epoxy-modified polyurethane dispersion and 1.1-5.0 parts by weight of an additive. The waterborne epoxy-modified polyurethane dispersion comprises an epoxy resin component and a polyurethane component, with the ratio of the epoxy resin component to the polyurethane component being 5.0-25.0%. The waterborne epoxy-modified polyurethane dispersion has an acid value of 19-29 KOH / mg and a solids content of 34.0-44.0%.

[0007] Furthermore, the waterborne epoxy-modified polyurethane coating further comprises the following components in parts by weight: 0-35 parts by weight of a pigment and 0-0.8 parts by weight of a dispersant.

[0008] Furthermore, the auxiliary agent includes: 1.0-4.5 parts by weight of an anti-settling agent.

[0009] Furthermore, the auxiliary agent includes: 0.1-0.5 parts by weight of a wetting agent.

[0010] Furthermore, the waterborne epoxy modified polyurethane coating further comprises: 0-5.0 parts by weight of partially methylated amino resin.

[0011] Furthermore, the waterborne epoxy-modified polyurethane coating further comprises: 0-2.5 parts by weight of a polycarbodiimide cross-linking agent.

[0012] Furthermore, the dispersant includes a polyether-modified styrene-maleic anhydride copolymer dispersant.

[0013] Furthermore, the anti-settling agent includes a fumed silica anti-settling agent.

[0014] Furthermore, the wetting agent includes a polyether siloxane-based substrate wetting agent.

[0015] Furthermore, a method for preparing a water-based epoxy-modified polyurethane dispersion is as follows: 50-60 parts by weight of polypropylene glycol is added to a three-necked flask with a vertical condenser, stirred, and heated to 110-130°C, then vacuumed for 30-40 minutes. The temperature is then lowered to 60-70°C, and 8-16 parts by weight of hexamethylene diisocyanate is slowly added dropwise. The temperature is then maintained at 75-85°C for 1-1.5 hours. Then, 4-5 parts by weight of dimethylolpropionic acid are slowly added, and the temperature is maintained. Next, 3-10 parts by weight of a mixed epoxy resin of bisphenol F and bisphenol A with an epoxy equivalent weight of less than 500 is slowly added dropwise, with the ratio of bisphenol F epoxy resin to bisphenol A epoxy resin being 1:1-2, until all the resin is added. Once the NCO% reaction reaches the appropriate range, add 5-6 parts by weight of dimethylethanolamine to the flask and stir thoroughly. Then slowly add 70-80 parts by weight of pure water dropwise. Then, continue to add a mixture of 8-10 parts by weight of butanediamine and 8-10 parts by weight of water dropwise to the flask to extend the chain. After all the additions are complete, stir for 1-1.5 hours to obtain a waterborne epoxy-modified polyurethane dispersion.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] Compared with ordinary water-based epoxy coatings, the flexibility (coil-around test) of the coating formed by the water-based epoxy-modified polyurethane coating of the present invention can be increased by up to 84 times. Compared with ordinary water-based polyurethane coatings, the corrosion resistance of the coating formed by the water-based epoxy-modified polyurethane coating of the present invention is increased by 6-9 times in the salt spray test. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be described in further detail. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] An embodiment of the present invention provides a waterborne epoxy-modified polyurethane coating for flexible bonding of NdFeB magnets, comprising the following components in parts by weight: 70-80 parts by weight of a waterborne epoxy-modified polyurethane dispersion and 1.1-5.0 parts by weight of an additive.

[0020] The amount of the aqueous epoxy-modified polyurethane dispersion can be 70 parts by weight, 75 parts by weight, 80 parts by weight, etc., preferably 75 parts by weight. The aqueous epoxy-modified polyurethane dispersion comprises an epoxy resin component and a polyurethane component. The ratio of the epoxy resin component to the polyurethane component is 5.0 to 25.0%, such as 5.0%, 8%, 10%, 14%, 20%, 25.0%, etc., preferably 8.0 to 14.0%, and more preferably 14.0%. The acid value of the aqueous epoxy-modified polyurethane dispersion is 19 to 29 KOH / mg, such as 19 KOH / mg, 22 KOH / mg, 25 KOH / mg, 29 KOH / mg, etc., preferably 22 to 25 KOH / mg, and more preferably 25 KOH / mg. The solid content of the waterborne epoxy-modified polyurethane dispersion is 34.0-44.0%, such as 34.0%, 36.0%, 38.0%, 40.0%, 44.0%, preferably 36.0-38.0%, more preferably 38.0%.

[0021] The preparation method of the waterborne epoxy-modified polyurethane dispersion comprises the following steps:

[0022] (1) Place 50-60 parts by weight of polypropylene glycol in a three-necked flask with a vertical condenser, stir, heat to 110-130°C, and evacuate for 30-40 minutes. The amount of polypropylene glycol used can be 50 parts by weight, 55 parts by weight, 60 parts by weight, etc. The heating temperature can be 110°C, 120°C, 130°C, etc. The evacuation time can be 30 minutes, 35 minutes, 40 minutes, etc.

[0023] (2) Then, the temperature is lowered to 60-70°C, and 8-16 parts by weight of hexamethylene diisocyanate is slowly added dropwise. The temperature is controlled at 75-85°C and kept warm for 1-1.5 hours. The cooling temperature can be 60°C, 65°C, 70°C, etc. The amount of hexamethylene diisocyanate can be 8 parts by weight, 12 parts by weight, 16 parts by weight, etc. The controlled temperature can be 75°C, 80°C, 85°C, etc. The holding time can be 1 hour, 1.2 hours, 1.5 hours, etc.

[0024] (3) Then, 4-5 parts by weight of dimethylolpropionic acid are slowly added, and the temperature is kept constant. The amount of dimethylolpropionic acid can be 4 parts by weight, 4.5 parts by weight, 5 parts by weight, etc.

[0025] (4) Then, 3-10 parts by weight of a mixed epoxy resin of bisphenol F and bisphenol A with an epoxy equivalent weight of less than 500 is slowly added dropwise, wherein the ratio of bisphenol F epoxy resin to bisphenol A epoxy resin in the mixed epoxy resin is 1:1-2, until all the epoxy resin is added. The amount of the mixed epoxy resin of bisphenol F and bisphenol A is 3 parts by weight, 7 parts by weight, 10 parts by weight, etc. The ratio of bisphenol F epoxy resin to bisphenol A epoxy resin is 1:1, 1:1.5, 1:2, etc.

[0026] (5) When the NCO% reaction reaches the appropriate range, add 5-6 parts by weight of dimethylethanolamine to the three-necked flask and stir evenly, then slowly add 70-80 parts by weight of pure water dropwise. The amount of dimethylethanolamine used is 5 parts by weight, 5.5 parts by weight, 6 parts by weight, etc. The amount of pure water used is 70 parts by weight, 75 parts by weight, 80 parts by weight, etc.

[0027] (6) Then, a mixture of 8-10 parts by weight of dibutylene glycol and 8-10 parts by weight of water is added dropwise to the three-necked flask for chain extension. After all the addition is complete, the mixture is stirred for 1-1.5 hours to obtain a waterborne epoxy-modified polyurethane dispersion. The amount of dibutylene glycol used is 8 parts by weight, 9 parts by weight, 10 parts by weight, etc. The amount of water used is 8 parts by weight, 9 parts by weight, 10 parts by weight, etc. The stirring time is 1 hour, 1.2 hours, 1.5 hours, etc.

[0028] The auxiliary agent may include 1.0-4.5 parts by weight of an anti-settling agent. The amount of the anti-settling agent can be 1.0 part by weight, 2.5 parts by weight, 3.5 parts by weight, 4.5 parts by weight, etc., preferably 2.5-3.5 parts by weight, more preferably 3 parts by weight. The anti-settling agent can be a fumed silica anti-settling agent.

[0029] The auxiliary agent may further include 0.1-0.5 parts by weight of a wetting agent. The amount of the wetting agent may be 0.1 parts by weight, 0.2 parts by weight, 0.5 parts by weight, etc., preferably 0.2 parts by weight. The wetting agent may be a polyether siloxane-based substrate wetting agent.

[0030] The waterborne epoxy-modified polyurethane coating may further include the following components in parts by weight: 0-35 parts by weight of a pigment, and 0-0.8 parts by weight of a dispersant. It should be noted that when the coating includes a pigment and a dispersant, the amounts of the pigment and the dispersant are not zero.

[0031] The amount of the pigment can be 0 parts by weight, 3 parts by weight, 10 parts by weight, 20 parts by weight, 30 parts by weight, 35 parts by weight, etc., preferably 3-30 parts by weight, more preferably 20 parts by weight. The pigment can include at least one of an ion-exchange silica type anti-rust pigment, a medium-pigment carbon black pigment, and a titanium dioxide pigment. The pigment can be an ion-exchange silica type anti-rust pigment, such as GRACE AC3, Lingwei LM-30. These pigments improve salt spray resistance and do not contain any heavy metals or phosphates, making them non-toxic to water ecosystems.

[0032] The amount of the dispersant can be 0 parts by weight, 0.4 parts by weight, 0.6 parts by weight, 0.8 parts by weight, etc., preferably 0.6 parts by weight. The dispersant can be a polyether-modified styrene maleic anhydride copolymer dispersant.

[0033] The waterborne epoxy modified polyurethane coating may further include: 0-5.0 parts by weight of partially methylated amino resin. It should be noted that when the coating includes the partially methylated amino resin, the amount of the partially methylated amino resin is not zero.

[0034] The partially methylated amino resin can be used in an amount of 1.0 parts by weight, 3.0 parts by weight, 4.0 parts by weight, 5.0 parts by weight, etc., preferably 4.0 parts by weight. The partially methylated amino resin reacts with the carboxyl hydrophilic groups in the waterborne epoxy-modified polyurethane dispersion to reduce the hydrophilicity of the coating and slow the penetration of corrosive salt water into the coating, thereby improving the salt spray and corrosion resistance.

[0035] The waterborne epoxy modified polyurethane coating may further include: 0-2.5 parts by weight of a polycarbodiimide crosslinking agent. It should be noted that when the coating includes the polycarbodiimide crosslinking agent, the amount of the polycarbodiimide crosslinking agent is not zero.

[0036] The polycarbodiimide crosslinking agent can be used in an amount of 0.5 parts by weight, 1.0 parts by weight, 2.0 parts by weight, 2.5 parts by weight, etc., preferably 1.0 parts by weight. The polycarbodiimide crosslinking agent reacts with the carboxyl hydrophilic groups in the aqueous epoxy-modified polyurethane dispersion to reduce the hydrophilicity of the coating and slow the penetration of corrosive salt water into the coating, thereby improving the salt spray and corrosion resistance.

[0037] An embodiment of the present invention provides a construction method of the above-mentioned water-based epoxy-modified polyurethane coating, comprising the following steps:

[0038] Under stirring conditions, a dispersant, an anti-settling agent, a wetting agent, and a pigment are sequentially added to a waterborne epoxy-modified polyurethane dispersion and uniformly dispersed to obtain a mixture. The mixture is ground using a sand mill to a fineness of ≤5 μm, and then a portion of a methyl etherified amino resin or a polycarbodiimide crosslinking agent is slowly added under stirring conditions and uniformly mixed to obtain a waterborne epoxy-modified polyurethane coating.

[0039] Dilute the water-based epoxy-modified polyurethane coating with deionized water, apply it to the workpiece (magnetic strip or ring) using an air spray gun, and bake it at 80-140°C for 30 minutes. Then, flip the workpiece (magnetic strip or ring), spray the back, and bake it again to obtain a fully coated flexible bonded NdFeB magnet. The baking temperature can be 80°C, 100°C, 120°C, 140°C, etc.

[0040] The coating formed by the water-based epoxy-modified polyurethane coating of the present invention meets the flexibility requirements of flexible bonding of NdFeB magnets, and its neutral salt spray resistance test is significantly better than that of ordinary water-based polyurethane coatings that have not been epoxy-modified. At the same time, since water is used as a diluent, the content of volatile organic compounds (VOCs) in the coating is reduced, and the coating has good environmental protection.

[0041] The following is a detailed description with reference to specific embodiments:

[0042] Dispersion Examples

[0043] Place 60 parts by weight of polypropylene glycol in a three-necked flask with a vertical condenser, stir, and heat to 120°C under vacuum for 30 minutes. Then, cool to 70°C and slowly dropwise add 16 parts by weight of hexamethylene diisocyanate. Maintain the temperature at 80°C for 1 hour. Then, slowly add 5 parts by weight of dimethylolpropionic acid and continue to heat. Next, slowly dropwise add 10 parts by weight of a mixed epoxy resin of bisphenol F and bisphenol A with an epoxy equivalent weight of less than 500, in a 1:1 ratio, until all the mixture is added. Once the NCO% reaction reaches the appropriate range, add 6 parts by weight of dimethylethanolamine to the flask, stir thoroughly, and slowly add 70 parts by weight of pure water. Subsequently, a mixture of 10 parts by weight of butanediamine and 10 parts by weight of water was added dropwise to the three-necked flask for chain extension. After all the mixture was added dropwise, stirring was performed for 1 hour to obtain a waterborne epoxy-modified polyurethane dispersion.

[0044] The waterborne epoxy-modified polyurethane dispersion has a ratio of epoxy resin component to polyurethane component of 14.0%, an acid value of 25 KOH / mg, and a solid content of 38.0%.

[0045] Coating Example 1

[0046] The preparation process is as follows:

[0047] Under stirring conditions, 0.6 parts by weight of a polyether-modified styrene-maleic anhydride copolymer dispersant, 2.5 parts by weight of a fumed silica anti-settling agent, 0.2 parts by weight of a polyether siloxane substrate wetting agent, and 3.0 parts by weight of a medium-pigment carbon black pigment were added sequentially to 75.0 parts by weight of the waterborne epoxy-modified polyurethane dispersion of Dispersion Example 1 and uniformly dispersed to obtain a mixture. The mixture was then ground using a sand mill to a fineness of ≤5 μm to produce a waterborne epoxy-modified polyurethane coating.

[0048] The construction process is as follows:

[0049] After diluting the above coating with 11.0 parts by weight of deionized water, spray it onto the magnetic strip with an air spray gun and bake it at 80-140°C for 30 minutes. Then, reverse the magnetic strip, spray the back of the strip and bake it again to obtain a flexible bonded NdFeB magnet covered with a complete coating with a film thickness of 20μm.

[0050] Coating Example 2

[0051] The preparation process is as follows:

[0052] Under stirring conditions, 0.6 parts by weight of a polyether-modified styrene-maleic anhydride copolymer dispersant, 3.5 parts by weight of a fumed silica anti-settling agent, 0.2 parts by weight of a polyether siloxane-based substrate wetting agent, and 3.0 parts by weight of a medium-pigment carbon black pigment were added sequentially to 75.0 parts by weight of the waterborne epoxy-modified polyurethane dispersion of Dispersion Example 1 and uniformly dispersed to obtain a mixture. The mixture was then ground using a sand mill to a fineness of ≤5 μm, and then 1.0 parts by weight of a polycarbodiimide crosslinking agent was slowly added under stirring and uniformly mixed to produce a waterborne epoxy-modified polyurethane coating.

[0053] The construction process is as follows:

[0054] After diluting the above coating with 11.0 parts by weight of deionized water, spray it onto the magnetic strip with an air spray gun and bake it at 80-140°C for 30 minutes. Then, reverse the magnetic strip, spray the back of the strip and bake it again to obtain a flexible bonded NdFeB magnet covered with a complete coating with a film thickness of 20μm.

[0055] Coating Example 3

[0056] The preparation process is as follows:

[0057] Under stirring conditions, 0.6 parts by weight of a polyether-modified styrene-maleic anhydride copolymer dispersant, 2.5 parts by weight of a fumed silica anti-settling agent, 0.2 parts by weight of a polyether siloxane substrate wetting agent, and 30.0 parts by weight of a titanium dioxide pigment were added sequentially to 75.0 parts by weight of the waterborne epoxy-modified polyurethane dispersion of Dispersion Example 1 and uniformly dispersed to obtain a mixture. The mixture was then ground using a sand mill to a fineness of ≤5 μm, and then 1.0 parts by weight of a polycarbodiimide crosslinking agent was slowly added under stirring and uniformly mixed to obtain a waterborne epoxy-modified polyurethane coating.

[0058] The construction process is as follows:

[0059] After diluting the above coating with 18.0 parts by weight of deionized water, spray it onto the magnetic strip with an air spray gun and bake it at 80-140°C for 30 minutes. Then, reverse the magnetic strip, spray the back of the strip and bake it again to obtain a flexible bonded NdFeB magnet covered with a complete coating with a film thickness of 20μm.

[0060] Coating Example 4

[0061] The preparation process is as follows:

[0062] Under stirring conditions, 0.6 parts by weight of a polyether-modified styrene-maleic anhydride copolymer dispersant, 3.5 parts by weight of a fumed silica anti-settling agent, 0.2 parts by weight of a polyether siloxane substrate wetting agent, 0.5 parts by weight of a medium-pigment carbon black pigment, and 25.0 parts by weight of a titanium dioxide pigment were added sequentially to 75.0 parts by weight of the waterborne epoxy-modified polyurethane dispersion of Dispersion Example 1 and uniformly dispersed to obtain a mixture. The mixture was then ground using a sand mill to a fineness of ≤5 μm, and then 4.0 parts by weight of a partially methylated amino resin was slowly added under stirring and uniformly mixed to produce a waterborne epoxy-modified polyurethane coating.

[0063] The construction process is as follows:

[0064] After diluting the above coating with 18.0 parts by weight of deionized water, spray it onto the magnetic strip with an air spray gun and bake it at 80-140°C for 30 minutes. Then, reverse the magnetic strip, spray the back of the strip and bake it again to obtain a flexible bonded NdFeB magnet covered with a complete coating with a film thickness of 20μm.

[0065] Test example

[0066] The waterborne polyurethane coating of Comparative Example 1 and the waterborne epoxy magnetic coating of Comparative Example 2 were subjected to the same construction process as that of Coating Example 1, and the properties of the coatings obtained from Coating Examples 1-4 and Comparative Examples 1-2 were tested. The results are as follows:

[0067]

[0068]

[0069] Compared with ordinary water-based epoxy coatings, the flexibility (coil-around test) of the coating formed by the water-based epoxy-modified polyurethane coating of the present invention can be increased by up to 84 times. Compared with ordinary water-based polyurethane coatings, the corrosion resistance of the coating formed by the water-based epoxy-modified polyurethane coating of the present invention is increased by 6-9 times in the salt spray test.

[0070] In addition, the coating of Comparative Example 3 was prepared. The preparation process differed from that of Coating Example 1 only in that an existing waterborne epoxy-modified polyurethane dispersion was used. The coating of Comparative Example 3 was applied in the same manner as Coating Example 1. The properties of the resulting coating were as follows:

[0071]

[0072] Compared to the coating in Comparative Example 3, the coating obtained in the present invention exhibits superior performance. This is because the epoxy resin used in the waterborne epoxy-modified polyurethane dispersion is a mixed epoxy resin of bisphenol F and bisphenol A, which reduces the regularity and crystallinity of the epoxy molecular segments and improves the flexibility of the epoxy segments, thereby reducing the negative impact of epoxy resin modification on the flexibility of the system. The ratio of epoxy resin component to polyurethane component is 5.0-25.0%. Within this ratio range, the coating exhibits good flexibility and significantly improved salt spray resistance. The acid value is 19-29 KOH / mg, and the solids content is 34.0-44.0%. Within this range, the waterborne epoxy-modified polyurethane dispersion obtained exhibits good dispersibility and stability in water, resulting in a uniform and stable aqueous dispersion with a blue appearance. Using an epoxy resin with an equivalent weight of 500 or less, the waterborne epoxy-modified polyurethane dispersion exhibits good storage stability.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A water-based epoxy-modified polyurethane coating for flexible bonding of NdFeB magnets, characterized in that: It comprises the following components in parts by weight: 70-80 parts by weight of waterborne epoxy modified polyurethane dispersion, 1.1-5.0 parts by weight of additives; The waterborne epoxy-modified polyurethane dispersion comprises an epoxy resin component and a polyurethane component, the ratio of the epoxy resin component to the polyurethane component is 5.0-25.0%, the acid value of the waterborne epoxy-modified polyurethane dispersion is 19-29 KOH / mg, and the solid content is 34.0-44.0%.

2. The waterborne epoxy modified polyurethane coating according to claim 1, characterized in that: Also includes the following components by weight: Pigment 0-35 parts by weight, dispersant 0-0.8 parts by weight.

3. The waterborne epoxy modified polyurethane coating according to claim 1, wherein The auxiliary agent includes: 1.0-4.5 parts by weight of anti-settling agent.

4. The waterborne epoxy modified polyurethane coating according to claim 1, wherein The auxiliary agent includes: Wetting agent 0.1-0.5 parts by weight.

5. The waterborne epoxy modified polyurethane coating according to claim 1, wherein Also includes: 0-5.0 parts by weight of partially methylated amino resin.

6. The waterborne epoxy modified polyurethane coating according to claim 1, wherein Also includes: 0-2.5 parts by weight of polycarbodiimide crosslinking agent.

7. The waterborne epoxy modified polyurethane coating according to claim 2, characterized in that: The dispersant includes a polyether-modified styrene-maleic anhydride copolymer dispersant.

8. The waterborne epoxy modified polyurethane coating according to claim 2, wherein: The anti-settling agent includes a fumed silica anti-settling agent.

9. The waterborne epoxy modified polyurethane coating according to claim 1, wherein The wetting agent includes a polyether siloxane-based substrate wetting agent.

10. The waterborne epoxy modified polyurethane coating according to claim 1, characterized in that: The preparation method of the waterborne epoxy-modified polyurethane dispersion comprises the following steps: adding 50-60 parts by weight of polypropylene glycol into a three-necked flask with a vertical condenser, stirring the mixture, heating the mixture to 110-130° C., and evacuating the mixture for 30-40 minutes; then cooling the mixture to 60-70° C., slowly adding 8-16 parts by weight of hexamethylene diisocyanate dropwise, and maintaining the temperature at 75-85° C. for 1-1.5 hours; then slowly adding 4-5 parts by weight of dimethylolpropionic acid, and continuing to maintain the temperature; and then slowly adding 3-10 parts by weight of bisphenol F and bisphenol A with an epoxy equivalent weight of less than 500 dropwise. A phenol A mixed epoxy resin and a bisphenol F and bisphenol A mixed epoxy resin in a ratio of 1:1-2 are added until all the epoxy resins are added. When the NCO% reaction reaches an appropriate range, 5-6 parts by weight of dimethylethanolamine are added to a three-necked flask and stirred evenly, and 70-80 parts by weight of pure water are slowly added dropwise. Subsequently, a mixed solution of 8-10 parts by weight of butanediamine and 8-10 parts by weight of water is added dropwise to the three-necked flask for chain extension. After all the epoxy resins are added dropwise, stirring is performed for 1-1.5 hours to obtain a waterborne epoxy-modified polyurethane dispersion.

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