Preparation method of anti-sagging polyurea dispersion

Abstract

The invention belongs to the technical field of coatings, in particular to a preparation method of an anti-sagging polyurea dispersion, which is characterized in that the resin is a polyurea dispersion formed by in-situ synthesis of polyisocyanate A and unit primary amine B in a coating resin medium, and the polyisocyanate A and the unit primary amine B are added into a coating resin medium in a simultaneous dropwise adding manner. Therefore, the dispersity of polyurea particles in a resin medium can be remarkably improved, so that the anti-sagging property of the SCA resin is improved, and the SCA resin is suitable for manufacturing automobile varnish, colored paint and the like.

Description

Technical Field

[0001] The invention belongs to the field of coating technology, and in particular to a method for preparing an anti-sagging polyurea dispersion. Background Art

[0002] In recent years, with the rapid development of the automobile industry, the competition in the automobile market has become increasingly fierce. While the requirements for various aspects of automobile performance are getting higher and higher, the requirements for the decorativeness of automobile coatings are also getting higher and higher. Improving the construction performance of automobile coatings is an important part of improving automobile decorativeness, and the construction performance of coatings mainly depends on the structure of the resin. At present, the development trend of automobile coating resins is to reduce the molecular weight and increase the content of active functional groups on the molecular chain segments. The advantages of coatings prepared with this type of resin are good leveling, high gloss, and full paint film, but its disadvantage is that it is easy to sag, especially in the spraying, flash drying and drying processes. This phenomenon is more obvious. In order to prevent sag during coating, anti-sagging agents (such as modified organic bentonite and fumed silica, etc.) are usually used in the design of coating formulas, but these anti-sagging agents will remain in the coating after the coating film is dried, which will have adverse effects on the appearance of the coating, especially the appearance of the varnish, such as gloss and distinctness of image. Therefore, in order to overcome these problems of traditional physically added anti-sagging agents, chemical modification methods have become the best choice to make the coating resin itself have anti-sagging (i.e., thixotropy) function.

[0003] This kind of coating resin with anti-sagging or thixotropic function is also called SCA (Sag Control Agent) resin. There are usually several methods for preparing SCA resin:

[0004] One is to directly graft the functional monomer (or structure) onto the coating resin to obtain a copolymer. As reported in CN110776815, maleic anhydride (double bond) is grafted onto the alkyd resin to obtain an alkyd resin containing an APAO structure.

[0005] One is to generate functional groups (or structures) on the resin structure through chemical reactions to obtain adducts. As reported in USP4965317, isocyanate groups (NCO) are first introduced into the resin structure, and then react with amino groups to generate urea groups, thereby obtaining SCA coating resins containing urea structures.

[0006] Another method is to use the coating resin as a medium, and then synthesize the monomer (or structure) with anti-sagging function in situ in the medium and disperse it therein to obtain a dispersion. As reported in CN101213230, diisocyanate and primary amine (or diprimary amine and monoisocyanate) are simultaneously synthesized and dispersed in a resin medium to obtain an SCA resin (dispersion) containing a diurea structural component.

[0007] As we all know, the product form of urea-based structure is anisotropic colloidal particles, which have strong hydrogen bonding and can build a three-dimensional network structure through hydrogen bonding between particles and between particles and resin. When the resin is subjected to high shear force, the three-dimensional network structure is quickly destroyed and the viscosity of the system decreases immediately; when the shear force is reduced or cancelled, the three-dimensional network structure is quickly rebuilt and the viscosity of the system is restored immediately. This provides construction rheological properties for coating products.

[0008] Research and application in recent years have found that the diurea molecular particles obtained by the polymerization of diisocyanate and unit primary amine (or diprimary amine and monoisocyanate) are actually dispersed in the resin medium in the form of short rods or fibrous microscopic forms in a layered stacking manner, and the resin is constructed into a controlled-flocculation state through hydrogen bonding. Among them, the diurea molecular particles obtained by the reaction of hexamethylene diisocyanate (HDI) and benzylamine are the most suitable because they have a moderate molecular weight, and as long as the particle size is made smaller and the aspect ratio is larger, the network structure (flocculation state) formed thereby is more rigid, the storage stability is also better, and thus the anti-sagging performance of the SCA resin is better. On the other hand, due to the simple process route and low production cost of this preparation method, this type of diurea structure (hereinafter referred to as polyurea) dispersion has become the focus of SCA resin research and application in recent years.

[0009] From the above, it can be seen that under certain raw material composition conditions, the size (particle size) and morphology (aspect ratio) of the polyurea particles in the dispersion become important factors to ensure the anti-sagging performance of the SAC resin.

[0010] CN101213230 describes a method for preparing a polyurea dispersion, which is divided into two steps: the first step is to synthesize a first polyurea particle by HDI and a chiral amine, and the second step is to react HDI and benzylamine and precipitate on the first polyurea particle, thereby forming a so-called polyurea template. It is reported that the characteristic of this template is that the first polyurea particle is used as a nucleation seed, and the second polyurea is deposited and grown on the seed to form a more refined structure similar to a core-shell structure. Obviously, the purpose of this patent is to obtain polyurea particles with a specific morphology through a stepwise reaction method, thereby improving the anti-sagging performance of SCA resin.

[0011] US4677028 describes a method for preparing an SCA composition, which is to first react isocyanate with amine under vigorous stirring to form polyurea particles, and then grind the resin containing the polyurea particles to obtain an SCA resin with a particle size of less than 15 μm. The purpose of this patent is to reduce the particle size of polyurea particles by secondary processing, thereby improving the anti-sagging performance of CSA resin.

[0012] CN109923144 describes a method for controlling the particle size of polyurea particles by ultrasound. The patent claims that if ultrasonic oscillation treatment is maintained during the polyurea particle generation process and during the post-dispersion process for at least 20 minutes after the reaction, the fineness of the polyurea particles of the SCA resin can be guaranteed to be ≤15 μm.

[0013] The above patents all use the control of the morphology or particle size of polyurea particles as a means to ensure the anti-sagging performance of SCA resin. Although the means are different, the mode of promoting the reaction between polyisocyanate and primary amine is the same, that is, the primary amine is first mixed with the coating resin or other medium, and then the polyisocyanate is added, or the polyisocyanate is first mixed with the coating resin or other medium, and then the primary amine is added. In short, a polyurea reactant is first dissolved in the medium to form a continuous distribution, and then the second polyurea reactant reacts with this continuous distribution to form polyurea particles. It is well known that the reaction between isocyanate and primary amine is a very violent exothermic reaction, and polyurea particles are immediately formed once the two come into contact. Therefore, it is not difficult to understand that in the above mode, when the continuously distributed reactant contacts another non-continuous reactant, due to the extremely fast reaction rate, the dispersibility (i.e., the degree of uniform distribution) of the polyurea particles formed as the dispersed phase is uncontrollable, so the morphology and size of the particles must also be uncontrollable and very complicated. However, if the above polyurea reaction mode is changed to a reaction of two non-continuous reactants in a medium, that is, polyisocyanate and primary amine are simultaneously added to the medium for reaction, then the dispersibility of the obtained polyurea particles as the dispersed phase will be much more controllable. In fact, as far as the in-situ polymerized SCA polyurea dispersion is concerned, the morphology and size of the polyurea particles are closely related to the environmental conditions of the polyurea reaction. Therefore, as long as the dispersibility of the polyurea particles as the dispersed phase in the medium (i.e., the degree of uniform distribution) is effectively controlled, the uniform size and regular morphology of the particles can be ensured. However, in the relevant literature that has been reported so far, it is rare to propose that the dispersibility of the polyurea dispersed phase is improved by simultaneously adding isocyanate and primary amine to the medium, thereby improving the anti-sagging property of the SCA resin. Summary of the invention

[0014] Purpose of the Invention

[0015] In view of the defects of the current SCA resin preparation method based on polyurea dispersion, a method for preparing an anti-sagging polyurea dispersion is invented, that is, by simultaneously adding isocyanate and primary amine into the coating resin medium, so that they are contacted and reacted in a discontinuous state, thereby improving the dispersibility of the polyurea dispersed phase, ensuring the uniformity of the size and regularity of the morphology of the polyurea particles, and thus improving the anti-sagging property of the polyurea dispersion.

[0016] Technical Solution

[0017] A method for preparing an anti-sagging polyurea dispersion, characterized in that polyisocyanate A and a unit primary amine B are simultaneously added dropwise to a coating resin medium at a specific flow rate and under specific conditions; wherein:

[0018] The specific flow rate refers to the entire dripping process needs to meet:

[0019] (1) The equivalent ratio of polyisocyanate A and primary amine B per unit time is [NCO] / [NH]=1:1;

[0020] (2) the sum of the weight of the polyisocyanate A and the unit primary amine B (i.e., the weight of the polyurea or SCA) accounts for 2% to 7%, preferably 2% to 4.5%, of the total weight of the coating resin;

[0021] (3) The entire dropwise addition time is controlled within 5 min-40 min, preferably within 10 min-30 min;

[0022] (4) The polyisocyanate A and the monoamine B must be diluted with a suitable solvent before being added, so that the concentration of each solution after dilution is 20%-60%, preferably 30%-50%, and the weight of the A and B solutions is equal to ensure that they can be added simultaneously at the same time.

[0023] The suitable solvent includes, but is not limited to, ethyl acetate, butyl acetate, hexyl acetate, xylene, etc. They can be used alone or mixed in any proportion. The solvents used to dilute A and B can be the same or different.

[0024] The specific conditions are:

[0025] (1) polyisocyanate A and primary amine B are added to the coating resin medium through at least two dropping ports respectively;

[0026] (2) The entire reaction process needs to be carried out under high-speed dispersion conditions and requires nitrogen protection;

[0027] (3) After the addition of materials A and B, they need to be dispersed for at least 30 minutes;

[0028] (4) The material temperature during the entire dropwise addition and post-dispersion process needs to be controlled between 10°C and 25°C.

[0029] The A and B dropping materials are added through at least two dropping ports, respectively, which means that the polyisocyanate A and the primary amine B need to be added to the coating resin medium through at least two syringes or constant flow pumps, and the dropping ports of the A and B materials need to be on the same plane and cross-distributed (see Figure 1 ).

[0030] The rotation speed of the high-speed dispersion is 3000rpm-6000rpm, preferably 3000rpm-4000rpm.

[0031] The post-dispersion means that after the material is added, the original speed needs to be maintained to continue high-speed dispersion for 30 minutes to 90 minutes, preferably 60 minutes.

[0032] The material temperature control refers to the need to promptly remove the heat released by the dropwise addition reaction and the heat released by high-speed dispersion to keep the system in a low temperature state of 10°C-25°C.

[0033] The coating resins include, but are not limited to, general resins or special resins used in the coating field for preparing coatings, such as alkyd resins, amino resins, epoxy resins, acrylic resins, polyol resins, aspartic acid ester resins, etc. They can be solvent-based, and the type and content of the solvent depend on the supply form of the product.

[0034] The coating resin medium refers to that according to the present invention, an appropriate amount of solvent can be added to the coating resin used so that the total content of the solvent in the reactant system (including the inherent solvent in the coating resin and the dilution solvent of the above-mentioned A and B droplets) meets the solid content requirements of the final product. The solid content of the final product can be 40%-65%, preferably 50%-60%. The present invention relates to a SCA resin based on polyurea dispersion; the present invention further relates to a method for preparing a SCA resin based on polyurea dispersion; the present invention also relates to a coating application composed of a SCA resin based on polyurea dispersion.

[0035] The invention relates to a SCA resin based on polyurea dispersion, characterized in that the resin is a polyurea dispersion formed by in-situ synthesis of polyisocyanate A and unit primary amine B in a coating resin medium, and the polyisocyanate A and unit primary amine B are added to the coating resin medium by simultaneous dropwise addition.

[0036] The reaction process of its polyurea structure is shown in Formula 1:

[0037]

[0038] The polyisocyanate A includes, but is not limited to, aliphatic polyisocyanates, alicyclic polyisocyanates, aralkylene polyisocyanates, and arylene polyisocyanates. Preferably, substituted or unsubstituted straight-chain aliphatic polyisocyanates and isocyanurates, biuret and uretdione thereof, and substituted or unsubstituted aralkylene, arylene and cyclohexylene polyisocyanates are used.

[0039] The number of NCO groups of the polyisocyanate is no more than 3, preferably 2. The above polyisocyanates can be used alone or mixed with each other in any proportion.

[0040] The primary amine B includes but is not limited to substituted or unsubstituted aliphatic primary amines, such as cyclohexylamine, butylamine, hexylamine, laurylamine and 3-methoxypropylamine, or substituted or unsubstituted aromatic amines, such as 2-phenylethylamine, benzylamine (BA), and 3-aminomethylpyridine. In order to obtain better anti-sagging (thixotropy), chiral monoamines such as S-(-)-α-methylbenzylamine can also be used. The primary amines can be used alone or mixed in any proportion.

[0041] The present invention also involves the application of a coating composed of a SCA resin based on a polyurea dispersion. According to the different properties of the coating resin used in the polyurea dispersion, the SCA resin involved in the present invention can be used for automobile varnish, automobile metallic paint, automobile solid color paint and automobile primer, etc. The coating formula and preparation process are implemented according to the existing technology and traditional experience in the current coating field.

[0042] Beneficial Effects

[0043] Based on the fact that the reaction rate of polyisocyanate and primary amino group is extremely fast and the resultant polyurea is a solid, the patent of the present invention proposes a method of simultaneously adding polyisocyanate and primary amine when preparing SCA resin based on polyurea dispersion, and limiting them to be simultaneously added to the coating resin medium at a specific flow rate and under specific conditions, so that the two materials are mixed and reacted in a discontinuous state in the coating medium, thereby avoiding the mixing and reaction between discontinuous materials and continuous materials in the traditional preparation process.

[0044] The beneficial effects obtained are: 1. The dispersion of the polyurea dispersed phase obtained by the reaction is better, thereby ensuring that the polyurea particles have a smaller particle size and a more regular particle morphology; 2. The anti-sagging property (i.e., thixotropy) of the SCA resin obtained by the reaction is better;

[0045] 3. The method of simultaneously dropping the reaction materials makes the preparation process of the SCA resin simpler and more efficient, avoiding other physical processing methods that may be taken to improve the performance of the SCA resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 , A, B material drop port distribution diagram;

[0047] Figure 2, schematic diagram of a SCA resin synthesis device based on a polyurea dispersion; wherein 1 is a stirring drive mechanism, 2 is a bearing transmission chamber, 3 is a B2 inlet (connected to a constant flow pump), 4 is an A2 inlet (connected to a constant flow pump), 5 is a vacuum valve, 6 is a jacket cooling water outlet, 7 is a sight glass lamp, 8 is a temperature meter, 9 is a sight glass port, 10 is an agitator, 11 is an A1 inlet (connected to a constant flow pump), 12 is a B2 inlet (connected to a constant flow pump), 13 is a nitrogen inlet, 14 is a vent valve, and 15 is a jacket cooling water inlet;

[0048] Figure 3 , optical microscopy image of SCA-A;

[0049] Figure 4 , optical microscopy image of SCA-B;

[0050] Figure 5 , optical microscope image of SCA-C;

[0051] Figure 6 , optical microscope image of R-1;

[0052] Figure 7 , optical microscope image of R-2;

[0053] Figure 8 , rheological curve comparison chart. DETAILED DESCRIPTION

[0054] Experimental equipment and analytical instruments

[0055] 1Polyurea dispersion synthesis dispersion device 3L (self-made)

[0056] 2 Rheometer MCR102 (Annto Paar Austria)

[0057] 3. Optical microscope MSD1125 (Murzider)

[0058] 4 Medium pressure constant flow pump MP0502C (Shanghai Sanwei Scientific Instrument Co., Ltd.)

[0059] 5 Fineness scraper BGD241 / single groove 0-50μm (Biaogeda)

[0060] 6 Iwata viscosity cup NK-2 (Shanghai Meiyu Experimental Instrument Co., Ltd.)

[0061] 7QAG sag tester QAG (Shanghai Hongfu Instrument Co., Ltd.)

[0062] The main raw materials are shown in Table 1

[0063] Table 1 List of main raw materials used in the experiment

[0064]

[0065] Example 1 Preparation of SCA-A

[0066] In such Figure 2 In the 3L reaction device shown, 1399g Setal 1715 and 423g xylene were added and mixed evenly. 29g HDI was diluted with 60g xylene to obtain 89g HDI solution, which was recorded as A; 36g benzylamine was diluted with 53g xylene to obtain 89g benzylamine solution, which was recorded as B. Then A and B were divided into two equal parts A1 and A2 and B1 and B2 respectively, and the mixture was stirred at room temperature for 2 hours. Figure 2 A1, A2 and B1, B2 are loaded into the liquid storage bottles of four constant flow pumps in order as shown. The output flow rate of the constant flow pump is uniformly set to 3ml / min. Turn on the cooling water to keep the material in the kettle at about 10°C. Under low-speed stirring, use vacuum to replace the air in the kettle with nitrogen, and then open the vent valve to keep the nitrogen unobstructed. Increase the speed to 4000rpm, and then turn on the four constant flow pumps at the same time to start dripping, control the stable temperature between 10℃-25℃, and complete the dripping after about 15 minutes, and turn off the constant flow pump. Continue to pass nitrogen and disperse at high speed at 4000rpm for 45 minutes, controlling the temperature between 10℃-25℃. After the post-dispersion is completed, turn off the stirring motor, nitrogen valve and cooling water valve. Discharge the material to obtain SCA-A. The measured fineness is <10μm, see the microscope picture Figure 3 , rheological curve see Figure 8 .

[0067] The experimental formulas and related data parameters of Example 1, Example 2, 3 and Comparative Examples 1 and 2 are shown in Table 2

[0068] Table 2 Experimental formula and related data parameters

[0069]

[0070]

[0071] Example 2 Preparation of SCA-B

[0072] According to the formula and process parameters of SCA-B in Table 2, the steps of Example 1 were followed to obtain SCA-B. The fineness was measured to be less than 10 μm, and the microscopic image was shown in FIG. Figure 4 , rheological curve see Figure 8 .

[0073] Example 3 Preparation of SCA-C

[0074] According to the formula and process parameters of SCA-C in Table 2, the steps of Example 1 were followed to obtain SCA-C. The fineness was measured to be less than 10 μm, and the microscopic image was shown in FIG. Figure 5 , rheological curve see Figure 8 .

[0075] Preparation of Control Example 1R-1

[0076] In such Figure 2 In the 3L reaction device shown, 1399g Setal 1715, 476g xylene and 36g benzylamine were added and mixed evenly. 29g HDI was diluted with 60g xylene to obtain 89g HDI solution, which was recorded as A. Then A was charged into Figure 1 The liquid is stored in the liquid storage bottle of the A1 constant flow pump shown. Set the output flow rate of the A1 constant flow pump to 3ml / min. Turn on the cooling water to keep the material in the kettle at about 10°C. Use vacuum to replace the air in the kettle with nitrogen under low-speed stirring, and then open the vent valve to keep the nitrogen unobstructed. Increase the speed to 4000rpm, then turn on the A1 constant flow pump to start dripping, control the stable temperature between 10℃-25℃, and complete the dripping after about 30min, and turn off the constant flow pump. Continue to pass nitrogen and disperse at high speed at 4000rpm for 45min, controlling the temperature between 10℃-25℃. After the post-dispersion is completed, turn off the stirring motor, nitrogen valve and cooling water valve. Discharge the material to obtain R-1. The measured fineness is >50μm, see the microscope picture Figure 6 , rheological curve see Figure 8 .

[0077] Preparation of Control Example 2R-2

[0078] According to the formula and process parameters of R-2 in Table 2, the steps of comparative example 1 were followed to obtain R-2. The measured fineness was > 50 μm, and the microscopic image was shown in Figure 7 , rheological curve see Figure 8 .

[0079] Compare Figure 3-Figure 7 From the microscopic image, it can be clearly seen that the distribution state of the polyurea particles in the SCAS resin prepared according to the present invention is much better than that of R- and R-2 prepared according to conventional methods, that is, the dispersibility of the polyurea dispersion is much better. This ensures that the particle size is smaller and the particle shape is more regular.

[0080] Comparing the fineness of SCA-A, SCA-B, and SCA-C (all ≤10 μm) and the fineness of R-1 and R-2 (all >50 μm), it can be clearly seen that the polyurea particles of the SCA resin prepared by the present invention have better dispersibility, so their particles are smaller.

[0081] Compare Figure 8From the rheological curve, it can be clearly seen that the polyurea particles of the SCA resin prepared by the patent of the present invention have better dispersibility. Therefore, compared with R-1 and R-2 prepared by conventional preparation methods, the slopes of SCA-A, SCA-B and SCA-C are significantly larger, that is, the time to restore the high viscosity state after the shear stress is removed is shorter. This shows that the SCA resin of the patent of the present invention has better anti-sagging performance (thixotropic performance).

[0082] In order to determine and compare the anti-sagging properties of varnishes prepared by SCA-A and SCA-B, varnishes were prepared according to the formulas listed in Tables 3 and 4, among which R-2K and R-1K were control examples of two-component and one-component varnishes.

[0083] Table 3 Two-component varnish

[0084]

[0085]

[0086] Table 4 One-component varnish

[0087] Serial number Components SCA-1K R-1K 1 SCA-B g 30 -- 2 R-2g --- 30 3 Setal 1795g 31 31 4 Setamin us138 g 25 25 5 Leveling agent g 1.0 1.0 6 Wetting agent g 0.5 0.5 7 Defoaming agent 0.5 0.5 8 Solvent g 12 12 9 Total g 100 100 10 Average solid content% 59 59 11 SCA as a percentage of solids 1.4 1.4

[0088] Example 4 SCA-2K varnish preparation

[0089] According to the formula of SCA-2K in Table 3, according to the conventional experience in the field of coating technology, SCA-2K is obtained.

[0090] Comparative Example 3R-2K Varnish Preparation

[0091] According to the formula of R-2K in Table 3, according to the conventional experience in the field of coating technology, R-2K is obtained.

[0092] Example 5 SCA-1K varnish preparation

[0093] According to the formula of SCA-1K in Table 4, operations were performed based on conventional experience in the field of coating technology to obtain SCA-1K.

[0094] Comparative Example 4R-1K Varnish Preparation

[0095] According to the formula of R-1K in Table 4, operations were performed based on conventional experience in the field of coating technology to obtain R-1K.

[0096] The varnishes prepared in Example 4, Comparative Example 3, Example 5 and Comparative Example 4 were subjected to anti-sagging test, and the test method and evaluation standard were implemented in accordance with GB / T 9264-2012 "Evaluation of Anti-sagging Property of Paints and Varnishes". The coating film application method was implemented in accordance with method a) in the standard, that is, a sag applicator with a scale was used to scrape the horizontally placed test plate, and then the test plate was placed vertically. The anti-sagging performance (sag limit) of each varnish is listed in Table 5 and Table 6 respectively.

[0097] Table 5 Comparison of sagging limits of two-component varnishes

[0098] Xylene dilution ratio / % Viscosity (NK-2@25℃) / s Sagging limit / μm SCA-2K 25 8 42.3 R-2K 20 8 28.8

[0099] Table 6 Comparison of sagging limits of single-component varnishes

[0100] Xylene dilution ratio / % Viscosity (NK-2@25℃) / s Sagging limit / μm SCA-1K 30 7 36.1 R-1K 26 7 22.3

[0101] It can be clearly seen from the data in Tables 5 and 6 that compared with the two-component varnish R-2K and the one-component varnish R-1K, the two-component varnish SCA-2K and the one-component varnish SCA-1K prepared using SCA-A and SCA-B prepared by the invention patent have significantly larger sag limits, which means that the two varnishes SCA-2K and SCA-1K have better anti-sag properties, that is, the SCA resin prepared according to the invention patent has better anti-sag properties (thixotropic properties).

Claims

1. A method for preparing an anti-sagging polyurea dispersion, characterized in that: The polyisocyanate A and the primary amine B are simultaneously added dropwise into the coating resin medium at a specific flow rate and under specific conditions; The specific flow rate refers to the entire dripping process needs to meet: (1) The equivalent ratio of polyisocyanate A and primary amine B per unit time is [NCO] / [NH]=1:1; (2) the sum of the weight of the polyisocyanate A and the unit primary amine B accounts for 2% to 7% of the total weight of the coating resin; (3) The entire dropwise addition time is controlled within 5 min-40 min; (4) Before adding, polyisocyanate A and primary amine B must be diluted with appropriate solvents to make the concentration of each solution after dilution 20%-60%, and the weight of A and B solutions must be equal to ensure that they can be added simultaneously at the same time; The specific conditions are: (1) polyisocyanate A and primary amine B are added to the coating resin medium through at least two dropping ports respectively; (2) The entire reaction process needs to be carried out under high-speed dispersion conditions and requires nitrogen protection; (3) After the addition of materials A and B, they need to be dispersed for at least 30 minutes; (4) The material temperature during the entire dropwise addition and post-dispersion process needs to be controlled between 10°C and 25°C.

2. The method according to claim 1, characterized in that The suitable solvent includes ethyl acetate, butyl acetate, hexyl acetate or xylene; they can be used alone or mixed in any proportion; the solvents used to dilute A and B can be the same or different.

3. The method according to claim 1, characterized in that The polyisocyanate A and the primary amine B are added to the coating resin medium through at least two dropping ports, respectively, which means that the polyisocyanate A and the primary amine B need to be added to the coating resin medium through at least two syringes or constant flow pumps, respectively, and the dropping ports of the A and B materials need to be on the same plane and cross-distributed; the speed of the high-speed dispersion is 3000rm-6000rpm; Post-dispersion means that after the material is added, it is necessary to maintain the original speed and continue to disperse at high speed for 30min-90min; The material temperature control refers to the need to promptly remove the heat released by the dropwise addition reaction and the heat released by high-speed dispersion to keep the system in a low temperature state of 10°C-25°C.

4. The method according to any one of claims 1 to 3, characterized in that: The coating resin includes a general resin or a special resin, which is an alkyd resin, an amino resin, an epoxy resin, an acrylic resin, a polyol resin or an aspartic acid ester resin.

5. The method according to claim 4, characterized in that The polyisocyanate A includes aliphatic polyisocyanate, alicyclic polyisocyanate, aralkylene polyisocyanate or arylene polyisocyanate.

6. The method according to claim 5, characterized in that The polyisocyanate A is a substituted or unsubstituted straight-chain aliphatic polyisocyanate and its isocyanurate, biuret and uretdione, as well as a substituted or unsubstituted aralkylene, arylene and cyclohexylene polyisocyanate; the number of NCO groups of the polyisocyanate A is not more than 3; the polyisocyanate A is used alone or mixed with each other in any proportion.

7. The method according to claim 4, characterized in that The primary amine B includes substituted or unsubstituted aliphatic primary amines and substituted or unsubstituted aromatic amines.

8. The method according to claim 7, characterized in that The primary amine B is cyclohexylamine, butylamine, hexylamine, laurylamine, or 3-methoxypropylamine; the substituted or unsubstituted aromatic amine is 2-phenylethylamine, benzylamine, 3-aminomethylpyridine, or S-(-)-α-methylbenzylamine; the primary amines are used alone or mixed in any proportion.

Images