CN113045982A

CN113045982A - Self-repairing waterborne polyurethane coating composition and coating

Info

Publication number: CN113045982A
Application number: CN202110401735.5A
Authority: CN
Inventors: 张烨
Original assignee: Jiutianqihong Jiangsu Testing Co ltd
Current assignee: Jiutianqihong Jiangsu Testing Co ltd
Priority date: 2020-07-30
Filing date: 2020-07-30
Publication date: 2021-06-29
Also published as: CN111690318A; CN111690318B; CN113045981A; CN113234389A

Abstract

The invention relates to a waterborne polyurethane coating composition with self-repairing performance, which comprises the following components in percentage by weight: (a) 35-50 wt% of polyisocyanate; (b) 15-20 wt% of a polyol; (c) 5-10 wt% of dimethylolpropionic acid; (d) 3-8 wt% of polyurethane microcapsule modified by nano Co particles; the balance of water. The waterborne polyurethane coating composition with the self-repairing performance can excite the rapid rupture of the microcapsules when a coating layer is ruptured, so that the self-repairing sensitivity is improved, the self-repairing process is accelerated, the performance degradation of a coating film is avoided, and the quality of the coating film is ensured.

Description

Self-repairing waterborne polyurethane coating composition and coating

The application has the following application numbers: 2020107484716, the name is: the divisional application of the invention patent application of 'a self-repairing aqueous polyurethane coating composition and coating', the filing date of which is: year 2020, month 07, and 30 days.

Technical Field

The invention relates to a polyurethane coating composition, in particular to a self-repairing aqueous polyurethane coating composition and a coating.

Background

The water-based paint is a paint which takes water as a diluent and does not contain an organic solvent, and compared with an oil paint prepared by using the organic solvent, the water-based paint does not contain free TDI toxic heavy metal, benzene, formaldehyde and other substances, is nontoxic and has no pungent smell, is harmless to a human body and has no pollution to the environment. Among them, the aqueous polyurethane coating has the advantages of good film-forming property, strong covering power, firm adhesion and the like, and has received more and more extensive attention in recent years.

In order to make the application of the waterborne polyurethane coating more extensive and safer, the functional modification of the waterborne polyurethane coating is needed to meet the requirements of people on the waterborne polyurethane coating in various fields. The microcapsule self-repairing coating is one of the functional modifications which are researched widely in recent years. Referring to fig. 1, the specific principle is as follows: the microcapsule 1 is embedded into a polymer matrix in the preparation process of the coating film, when the polymer matrix is damaged and has cracks 3, the microcapsule is broken, the repairing reagent in the microcapsule is released to reach the cracks through capillary action, and the polymer 4 with the repairing action is generated through the catalytic action of the catalyst 2, so that the self-repairing of the coating film is realized. Wherein, fine microcracks are generated in the step (a), the microcracks are continuously expanded in the step (b) and extend to the microcapsules to cause the microcapsules to break, and the repairing agent in the microcapsules in the step (c) generates polymers under the action of the catalyst so as to realize self-repairing.

The prior document CN101215408 discloses a high-temperature self-repairing epoxy resin material, which comprises an epoxy resin matrix, a curing agent for the epoxy resin matrix, a capsule containing liquid epoxy resin, and a catalyst, wherein when the material is subjected to an external force during use to generate micro cracks therein, the micro cracks are expanded through the microcapsule, the liquid epoxy resin in the microcapsule is released and filled into cracks, and the liquid epoxy resin and an imidazole compound dissociated from the catalyst undergo addition and catalytic reactions at a high temperature, so that the liquid epoxy resin is cured, the cracks are bonded, and the purpose of repairing is achieved.

The prior document CN102719184 discloses a self-repairing anticorrosive coating which comprises hydroxyacrylic acid-containing resin, pigment, corrosion inhibition pigment, corrosion inhibitor benzotriazole, polyurethane microcapsule, organic solvent, dispersant, defoaming agent, leveling agent and ultraviolet absorber. If the coating film is broken and damaged, the microcapsule is broken, the polyurethane in the capsule flows out and reacts with water in the air under the action of the auxiliary corrosion inhibition pigment to form a new coating film, and the self-repairing function of the coating film is realized.

Prior document US7108913 discloses a self-healing polymer composition comprising microcapsules; a flowable polymerizable material within said microcapsules; and at least one polymerization agent associated with the outer surface of said microcapsules, said polymerization agent effective to initiate polymerization of said flowable polymerizable material upon rupture of said microcapsules and contact of said polymerization agent with said flowable polymerizable material.

However, in the self-repairing coating, the self-repairing process has a certain hysteresis, and only when cracks are accumulated to a sufficient level and extend to the microcapsules, the microcapsules can be broken to excite the self-repairing process, and the more severe the cracking degree of the coating film is, the greater the breaking tendency of the coating film is, the greater the difficulty of the self-repairing process is, and the tendency that the self-repairing process cannot delay the further breaking of the coating film is often caused, so that the self-repairing failure is caused. In order to improve the excitability of the microcapsules, a feasible method is to increase the content of the microcapsules in the self-repairing coating, but this in turn causes the deterioration of the coating film, and cannot give consideration to the various properties of the coating film and the sensitivity of self-repairing.

Disclosure of Invention

Based on the defects of the prior art, the invention provides an aqueous polyurethane coating composition which can give consideration to both the performance of a coating film and improve the self-repairing sensitivity, and the self-repairing aqueous polyurethane coating composition comprises the following components in percentage by weight:

(a) 35-50 wt% of polyisocyanate; (b) 15-20 wt% of a polyol; (c) 5-10 wt% of dimethylolpropionic acid; (d) 3-8 wt% of polyurethane microcapsule modified by nano Co particles; the balance of water.

Further, the polyisocyanate is specifically one or more of diphenylmethane diisocyanate, isophorone diisocyanate and hexamethylene diisocyanate.

Further, the polyhydric alcohol is one or more of polyhexamethylene glycol, 1, 4-butanediol, dihexylene glycol and trihydroxypropane.

Further wherein the content ratio of the components (a) and (b) is 2: 1 to 4: 1.

Furthermore, the core material of the polyurethane microcapsule is isophorone diisocyanate, and the wall material is urea resin.

Further, the nano Co particles in the polyurethane microcapsule modified by the nano Co particles are uniformly distributed in the urea formaldehyde resin shell of the microcapsule.

Further, the preparation process of the polyurethane microcapsule modified by the nano Co particles comprises the following steps:

(1) weighing a proper amount of urea and formaldehyde, adding the urea into a formaldehyde aqueous solution, adding a certain amount of water, stirring until the urea is completely dissolved, then adjusting the pH value of the solution to 8-9, stirring for reaction to obtain a urea-formaldehyde prepolymer solution, then adding a certain weight part of nano Co particles into the urea-formaldehyde prepolymer solution, and performing ultrasonic oscillation to obtain a wall material solution for later use.

(2) And then adding a proper amount of isophorone diisocyanate into water to prepare a core material solution, adding a Tween-80 emulsifier, continuously stirring and dispersing, and homogenizing for 2 times by using a high-pressure homogenizer at the pressure of 30MPa to form a core material pre-emulsion.

(3) Slowly dripping the obtained core material pre-emulsion into the wall material solution, adjusting the pH value of the mixed solution to 4-5, and stirring for reacting for a certain time to obtain the nano Co particle modified polyurethane microcapsule.

Further, the particle size of the nanometer Co particles in the step (1) is 20-100 nm.

Further, the composition further comprises: (f) 1-5 wt% of a dispersant; (g) 1-5 wt% of colorant.

Another aspect of the present invention relates to a coated article comprising a substrate and a coating film applied on the substrate, the coating film being prepared according to the self-healing aqueous polyurethane coating composition described above.

Further, the coating is applied to a substrate by any one of dipping, spraying, and brushing to form the coating layer.

The principle of the self-repairing aqueous polyurethane coating composition of the invention for realizing high self-repairing sensitivity is as follows:

compared with the pure polyurethane microcapsule, the polyurethane microcapsule modified by the nano Co particles has the advantages that the shell wall of the polyurethane microcapsule modified by the nano Co particles is in an irregular shape, so that the thickness of the urea-formaldehyde resin wall material is uneven, and the coating is more easily broken at a thin wall part after the coating is subjected to external force to generate micro cracks in the coating during processing or use, so that the self-repairing process is more efficiently and quickly initiated;

in addition, on one hand, after the coating layer is subjected to external force to generate micro-cracks in the coating layer in the processing or using process, due to the fact that the environment in the coating layer generates corresponding changes, the interaction generated among the nanometer Co particles provides certain rupture tendency force for the wall material of the urea resin, and the rupture of the wall material of the microcapsule after the cracks are generated on the film is accelerated to release the self-repairing material in the coating layer, so that the problem of hysteresis in the self-repairing process in the prior art is solved, and the self-repairing sensitivity is improved.

Compared with the prior art, the invention has the following beneficial effects:

1. the polyurethane microcapsule modified by the nano Co particles is used as a component of the self-repairing aqueous polyurethane coating composition, and can stimulate the rapid rupture of the microcapsule when a coating layer is ruptured, so that the self-repairing sensitivity is improved, and the self-repairing process is accelerated;

2. the self-repairing aqueous polyurethane coating composition has the advantages that the self-repairing process is started faster, microcracks do not need to trigger, and the problem of self-repairing failure caused by too serious cracking degree of the coating cracks is solved;

3. the invention can realize better rupture triggering performance only by needing lower microcapsule content, and can not cause the performance degradation of the coating film because of lower microcapsule content, thereby ensuring the quality of the coating film.

Drawings

Fig. 1 illustrates the action principle of the microcapsule self-repairing coating.

Fig. 2 shows SEM photographs of the polyurethane microcapsule (a) not modified with the nano Co particles and the polyurethane microcapsule (b) modified with the nano Co particles.

Fig. 3 illustrates the results of the number of cold and hot cycle tests on microcracks for example 1, comparative example 1, and comparative example 2.

Detailed Description

I. Self-repairing aqueous polyurethane coating composition

In one embodiment of the present invention, there is provided a self-healing aqueous polyurethane coating composition comprising:

(a) a polyisocyanate; the polyisocyanate is used as a curing agent component, can react with the polyol to generate polyurethane resin, and is a main film-forming substance of the coating. In the present invention, the polyisocyanate is preferably one or more of diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate. The content of the polyisocyanate is 35-50 wt%, and in the content range, better film-forming performance can be guaranteed.

(b) A polyol; mainly for providing active hydrogen, and can react with polyisocyanate to generate polyurethane resin. In the present invention, the polyhydric alcohol is preferably one or more of polyhexamethylene glycol, 1, 4-butanediol, dihexylene glycol, and trimethylolpropane. The content of the polyol is 15-20 wt%, and within the content range, sufficient reaction of polyisocyanate can be ensured, so that a polyurethane resin coating film with excellent performance is obtained.

(c) Dimethylolpropionic acid; as a hydrophilic chain extender, hydrophilic groups can be introduced into the macromolecular main chain of the polyurethane, so that the waterborne polyurethane has good water dispersibility and is beneficial to promoting the formation of a coating film in the curing process. In the invention, the content of dimethylolpropionic acid is preferably 5-10 wt%, when the content is less than 5 wt%, the hydrophilization of polyurethane macromolecules is not enough, and the film forming performance is reduced, and when the content exceeds 10 wt%, the excessive dimethylolpropionic acid can cause the poor water resistance of a coating layer and is unfavorable for the film performance.

(d) Polyurethane microcapsule modified by nanometer Co particle; the wall material is an outer shell of the microcapsule, the material coated inside the wall material is called the core material, the wall material is used for protecting and maintaining the form of the microcapsule, and the core material is used for repairing cracks of the coating layer after the wall material is broken. In the invention, the core material is isophorone diisocyanate, and the wall material is urea resin. When the coating layer is cracked, isophorone diisocyanate can react with invaded moisture to react at the crack part and be crosslinked and cured, so that the crack is repaired. The urea resin has stable property when the coating layer is normally used, and can well keep the microcapsule. The polyurethane microcapsule is modified by the nano Co particles, and in the preparation process, the nano Co particles are uniformly distributed in the urea resin shell of the microcapsule, so that the obtained polyurethane microcapsule presents an irregular shape and uneven thickness, and compared with a simple urea resin shell, the polyurethane microcapsule is easier to break when being invaded by external force, thereby improving the self-repairing sensitivity. In addition, when the coating layer cracks, the internal environment of the coating layer changes, and the interaction of magnetic Co particles is caused, so that a certain rupture tendency force is provided for the urea-formaldehyde resin wall material, and the rupture sensitivity of the urea-formaldehyde resin wall material is increased. In the invention, the content of the polyurethane microcapsule modified by the nano Co particles is preferably 3-8 wt%, and in the content range, the degradation of the performance of the polyurethane resin coating film is not caused, and the good self-repairing performance can be met.

In a specific embodiment of the present invention, the aqueous polyurethane coating composition further comprises: (f) a dispersant and (parts by weight) a colorant. In particular, the choice may be made among the dispersants and colorants commonly found in the prior art, and the present invention is not to be unduly limited.

II.Coated article

Specifically, the self-healing aqueous polyurethane coating composition may be used to prepare coated articles provided by the present invention by applying to a substrate by any method known to those skilled in the art, including, but not limited to, any of dipping, spraying, and brushing. In one embodiment of the invention, the coating composition is applied to the substrate by brushing.

Specifically, the film thickness of the self-healing aqueous polyurethane coating composition is specifically 1 to 200 μm, more preferably 10 to 100 μm.

Specifically, the film layer of the self-healing aqueous polyurethane coating composition may be obtained by heat curing at a temperature of 50 ℃ to 300 ℃ for about 5min to 12 min.

Examples

The following examples illustrate specific aspects of the invention and are not intended to limit the scope of the invention in any respect and should not be construed as limiting the scope of the invention. The following examples illustrate specific aspects of the self-healing aqueous polyurethane coating compositions of the present invention. These examples are merely illustrative and should not be construed as limiting the scope of the claimed subject matter based on the present disclosure.

Example 1

A self-repairing waterborne polyurethane coating composition is prepared by the following steps:

preparing a polyurethane microcapsule modified by nano Co particles: adding 5 parts by weight of urea into 22 parts by weight of 37% formaldehyde aqueous solution for three times, adding a certain amount of water, stirring until the urea is completely dissolved, then adjusting the pH value of the solution to 8-9, placing the solution at the temperature of 70 ℃ for stirring and reacting for 1h to obtain a urea-formaldehyde prepolymer solution, then adding 0.16 part by weight of nano Co particles into the urea-formaldehyde prepolymer solution, and performing ultrasonic oscillation for 1.5h to obtain a wall material solution for later use. And then adding 5.6 parts by weight of isophorone diisocyanate into water to prepare a core material solution, adding 0.5 part by weight of tween-80 emulsifier, continuously stirring and dispersing, and homogenizing for 2 times by using a high-pressure homogenizer at the pressure of 30MPa to form a core material pre-emulsion. Slowly dripping the obtained core material pre-emulsion into the wall material solution, adjusting the pH value of the mixed solution to 4-5, and stirring for reacting for a certain time to obtain the nano Co particle modified polyurethane microcapsule.

Then, 35 parts by weight of diphenylmethane diisocyanate and 3 parts by weight of nano Co particle-modified polyurethane microcapsule were mixed, and a certain amount of water was added thereto, and 5 parts by weight of dimethylolpropionic acid was added thereto under continuous stirring. After the uniform mixing, 15 parts by weight of the polyhexamethylene glycol was added thereto, and the resulting mixture was stirred using a mechanical mixer until a uniform mixture was obtained, thereby obtaining the self-repairing aqueous polyurethane coating composition of this example.

The self-repairing aqueous polyurethane coating composition is coated on the surface of a substrate by brushing, and is cured for 10min at the temperature of 200 ℃ to obtain a coating layer. The resulting coating was tested for corrosion resistance, adhesion and cold and hot cracking.

Example 2

Then, 35 parts by weight of isophorone diisocyanate and 5 parts by weight of polyurethane microcapsule modified by nano Co particles were mixed, and a certain amount of water was added, and 5 parts by weight of dimethylolpropionic acid was added under continuous stirring. After the uniform mixing, 15 parts by weight of the polyhexamethylene glycol was added thereto, and the resulting mixture was stirred using a mechanical mixer until a uniform mixture was obtained, thereby obtaining the self-repairing aqueous polyurethane coating composition of this example.

The self-repairing aqueous polyurethane coating composition is coated on the surface of a substrate by brushing, and is cured for 10min at the temperature of 200 ℃ to obtain a coating layer. The resulting coating was tested for corrosion resistance, adhesion and cold-hot cycle cracking.

Example 3

Subsequently, 35 parts by weight of hexamethylene diisocyanate and 8 parts by weight of nano Co particle-modified polyurethane microcapsule were mixed, and a certain amount of water was added, and 5 parts by weight of dimethylolpropionic acid was added under continuous stirring. After the uniform mixing, 15 parts by weight of dihexylene glycol and 1.2 parts by weight of NMMO were added thereto, and the resulting mixture was stirred using a mechanical mixer until a uniform mixture was obtained, thereby obtaining the self-repairing aqueous polyurethane coating composition of this example.

Example 4

Next, 50 parts by weight of diphenylmethane diisocyanate and 5 parts by weight of nano Co particle-modified polyurethane microcapsule were mixed and a certain amount of water was added, and 5 parts by weight of dimethylolpropionic acid was added under continuous stirring. After the uniform mixing, 20 parts by weight of polyethylene glycol and 5 parts by weight of NMMO were added thereto, and the resultant mixture was stirred using a mechanical mixer until a uniform mixture was obtained, thereby obtaining the self-repairing aqueous polyurethane coating composition of this example.

Comparative example 1

preparation of polyurethane microcapsules: adding 5 parts by weight of urea into 22 parts by weight of 37% formaldehyde aqueous solution for three times, adding a certain amount of water, stirring until the urea is completely dissolved, then adjusting the pH value of the solution to 8-9, and stirring and reacting at 70 ℃ for 1h to obtain a urea-formaldehyde prepolymer solution, thereby obtaining a wall material solution for later use. And then adding 5.6 parts by weight of isophorone diisocyanate into water to prepare a core material solution, adding 0.5 part by weight of tween-80 emulsifier, continuously stirring and dispersing, and homogenizing for 2 times by using a high-pressure homogenizer at the pressure of 30MPa to form a core material pre-emulsion. Slowly dripping the obtained core material pre-emulsion into the wall material solution, adjusting the pH value of the mixed solution to 4-5, and stirring for reacting for a certain time to obtain the polyurethane microcapsule.

Subsequently, 35 parts by weight of diphenylmethane diisocyanate and 3 parts by weight of polyurethane microcapsules were mixed and a certain amount of water was added, and 5 parts by weight of dimethylolpropionic acid was added under continuous stirring. After the uniform mixing, 15 parts by weight of polyethylene glycol was added thereto, and the resulting mixture was stirred using a mechanical mixer until a uniform mixture was obtained, thereby obtaining the self-repairing aqueous polyurethane coating composition of this example.

The self-repairing aqueous polyurethane coating composition is coated on the surface of a substrate by brushing, and is cured for 10min at the temperature of 200 ℃ to obtain a coating layer. The resulting coating was tested for hardness, corrosion resistance, adhesion and cold-hot cycle cracking.

Comparative example 2

Subsequently, 35 parts by weight of diphenylmethane diisocyanate and 12 parts by weight of polyurethane microcapsules were mixed and a certain amount of water was added, and 5 parts by weight of dimethylolpropionic acid was added under continuous stirring. After the uniform mixing, 15 parts by weight of the polyhexamethylene glycol and 0.1 part by weight of NMMO were added thereto, and the resulting mixture was stirred using a mechanical mixer until a uniform mixture was obtained, thereby obtaining the self-repairing aqueous polyurethane coating composition of this example.

Test method

Hardness test

The hardness of the resulting coating film was measured according to parts by weight B/T6739 "pencil hardness test with paint film", pencils of different hardness being moved over the coating under a fixed pressure and at a fixed angle. The hardness of the pencil scratched through the coating film was recorded.

Corrosion resistance test

The test is carried out by adopting a cross method neutral salt fog test, the model of a salt fog box is a Q-Fo weight part circulating salt fog test machine, and the test conditions are as follows: electrolyte 5% sodium chloride solution, ambient temperature 35 ℃, spray pressure 8 psi. The sample plate uses a cutter to mark two lines which intersect at an angle of 30 degrees on the surface of the coating, the sample plate is placed in a salt spray box in an inclined way at an angle of 15 degrees, and the corrosion condition of the sample plate is periodically checked.

Adhesion test

The obtained coating film was subjected to adhesion test in accordance with parts by weight of B9286 "paint film adhesion test method", and adhesion was tested by 3M test grade tape adhesion test. First, a grid pattern of 1mm cutting spaces was applied on the coating layer. Then, 3M 616 tape was placed on the coating, covering the cut pattern, and slowly pulled back on itself at an angle of about 180 ℃.

Cold thermal cycle crack test

And (3) placing the coating at-10 ℃ for 20min, then placing at 80 ℃ for 20min, then placing in a natural environment for 1h to perform self-repairing of the coating film, circulating for a certain number of times, and observing the number and self-repairing conditions of microcracks with the diameter of more than 1 mu m on the surface of the coating layer through a microscope.

TABLE 1 Performance test results of examples 1-4 and comparative examples 1-2

Examples	Adhesion test	Hardness test	Corrosion resistance test
				Example 1	Level 0	3H	NA
Example 2	Level 0	3H	NA
				Example 3	Level 0	2H	NA
Example 4	Level 0	3H	NA
				Comparative example 1	Level 0	3H	NA
Comparative example 2	Stage 2	1H	YB

Note: n indicates no leak, Y indicates leak detected by the leak detector, A indicates good appearance of the coating and no blistering or peeling off, and B indicates slight blistering of the coating.

It can be seen from the performance test results in table 1 that the polyurethane microcapsules modified by nano Co particles in examples 1 to 4 of the present application have substantially no influence on the performance of the coating film, and can still maintain good hardness, corrosion resistance and adhesion performance, compared with the common polyurethane microcapsules in comparative example 1. In contrast, in comparative example 2, when the content of the polyurethane microcapsules in the coating film reached 10%, the content of the polyurethane microcapsules was too high, which resulted in deterioration of certain properties of the coating film.

SEM photographs of the polyurethane microcapsule (a) not modified with nano Co particles and the polyurethane microcapsule (b) modified with nano Co particles are shown in fig. 2. The polyurethane microcapsules without Co nanoparticles modification in fig. 1 have a substantially spherical appearance and are uniform as a whole, while the polyurethane microcapsules with Co nanoparticles modification have an irregular shape and have a non-uniform wall thickness as a whole, and thus have a higher sensitivity to external forces when the coating film is broken.

Fig. 3 shows the results of the cold thermal cycle crack test of example 1, comparative example 1, and comparative example 2. Compared with example 1 in which unmodified polyurethane microcapsules are used in comparative example 1, cracks are gradually generated after 9 times of circulation, the number of cracks is gradually reduced after 21 times of circulation, and the number of microcracks is continuously increased between 9 and 21 times of circulation, which indicates that the self-repairing process has certain hysteresis. In comparative example 2, cracks begin to generate in the coating layer after about 3 times of circulation, and the number of cracks begins to obviously decrease after about 6 times of circulation, which shows that in comparative example 2, the addition of too many polyurethane microcapsules has a good self-repairing process, but the same film performance also brings adverse effects, and the deterioration of the performance of the coating film is caused.

In conclusion, the self-repairing aqueous polyurethane coating composition provided by the invention has the advantages that through reasonable collocation of the components, the self-repairing sensitivity is improved on the basis of ensuring the performance of a coating film, and the polyurethane microcapsule modified by adding the nano Co particles in the composition can excite the rapid rupture of the microcapsule when the coating layer is ruptured, so that the self-repairing process is accelerated; the self-repairing aqueous polyurethane coating composition has the advantages that the self-repairing process is started faster, microcracks do not need to trigger, and the problem of self-repairing failure caused by too serious cracking degree of the coating cracks is solved; the invention can realize better rupture triggering performance only by needing lower microcapsule content, and can not cause the performance degradation of the coating film because of lower microcapsule content, thereby ensuring the quality of the coating film.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. A self-healing aqueous polyurethane coating composition comprising, in weight percent: (a) 35-50 wt% of polyisocyanate; (b) 15-20 wt% of a polyol; (c) 5-10 wt% of dimethylolpropionic acid; (d) 3-8 wt% of polyurethane microcapsule modified by nano Co particles; the balance of water;

the core material of the polyurethane microcapsule is isophorone diisocyanate, and the wall material is carboxymethyl cellulose;

the polyalcohol is one or more of polyhexamethylene glycol, 1, 4-butanediol, dihexylene glycol and trihydroxypropane;

the content ratio of the components (a) and (b) is 2: 1 to 4: 1;

the composition further comprises: (f) 1-5 wt% of a dispersant; (g) 1-5 wt% of colorant.

2. The self-repairing aqueous polyurethane coating composition of claim 1, wherein the nano-Co particles in the nano-Co particle modified polyurethane microcapsule are uniformly distributed in a urea formaldehyde resin shell of the microcapsule.

3. The self-repairing aqueous polyurethane coating composition as claimed in claim 2, wherein the polyurethane microcapsule modified by the nano Co particles is prepared by the following steps:

(1) weighing a proper amount of urea and formaldehyde, adding the urea into a formaldehyde aqueous solution, adding a certain amount of water, stirring until the urea is completely dissolved, then adjusting the pH value of the solution to 8-9, stirring for reaction to obtain a urea-formaldehyde prepolymer solution, then adding a certain weight part of nano Co particles into the urea-formaldehyde prepolymer solution, and performing ultrasonic oscillation to obtain a wall material solution for later use;

(2) adding a proper amount of isophorone diisocyanate into water to prepare a core material solution, adding a Tween-80 emulsifier, continuously stirring and dispersing, and homogenizing for 2 times by using a high-pressure homogenizer at the pressure of 30MPa to form a core material pre-emulsion;

4. A self-healing aqueous polyurethane coating film comprising a substrate and a coating film applied on the substrate, the coating film being prepared from the self-healing aqueous polyurethane coating composition of claims 1 to 7.