CN118755373A - A water-based two-component polyurethane topcoat and its application - Google Patents

Abstract

The present invention relates to the technical field of automotive coatings, and specifically discloses a water-based two-component polyurethane topcoat and its application. The water-based two-component polyurethane topcoat selects a hydroxyl-containing water-based dispersion and a high glass transition temperature water-based polycarbonate-containing aliphatic anionic polyurethane dispersion for compounding as a film-forming resin, and selectively adds a low glass transition temperature water-based aliphatic anionic polyurethane dispersion, and through a specific ratio and the synergistic effect of each component, the characteristics of different types of water-based resins are brought into play to the best state, so that the water-based two-component polyurethane topcoat has excellent leveling, thixotropy, elasticity and interlayer adhesion, no fly ash, and excellent mechanical properties and weather resistance. It can be constructed on a large area under high temperature, low temperature or high humidity environment, and cooperates well with non-polished mid-coat coating. The topcoat after coating does not need to be covered with a clear varnish, and the appearance is glossy and vivid, and has high practical value and promotion value.

Description

A water-based two-component polyurethane topcoat and its application

Technical Field

The invention relates to the technical field of automotive coatings, and in particular to a water-based two-component polyurethane topcoat and application thereof.

Background Art

Rail transit vehicles are a major means of transportation for the public. Rail transit vehicles are mostly manufactured using lightweight aluminum alloys instead of steel. With the change in the material of the carriage, the type and quality of coatings also change. Rail transit vehicles operate in various environments from C2 to C5, which determines that their coatings must take into account both anti-corrosion and decorative effects.

Topcoat is a coating used on top of primer or midcoat, which mainly plays the role of coloring, covering and decoration. The traditional rail transit vehicle topcoat coating system consists of solvent-based 1K basecoat + clearcoat. Due to their low solid content, clearcoat and basecoat have VOC (volatile organic compound) emissions accounting for more than 60% of the total coating, which not only wastes resources, but also pollutes the environment, and also poses a fire hazard. In addition, the basecoat + clearcoat system coating adopts a two-coat and one-bake (i.e. 2C1B) coating method. Although the gloss, distinctness and other properties are very excellent, the raw material cost and labor cost are very high, and the work efficiency is relatively low. At present, there is no water-based topcoat that does not require clearcoat.

Water-based topcoats for rail transit vehicles have high requirements for the construction environment, and the construction area of rail transit vehicle body painting is large. For example, the length of a typical EMU body is between 24.5m and 27m, and the height is about 3.3m. When the construction environment temperature is too high, too low, or the humidity is high, there are spray sags, fly ash, and difficulty in connecting the gun. In order to solve the problem of harsh construction conditions for water-based topcoats, it is urgent to find a water-based topcoat to replace the "base paint and clear varnish" coating system. It can be constructed in high temperature, low temperature or high humidity environments. At the same time, the paint film has excellent anti-sag, anti-prickly heat, anti-orange peel, anti-dark bubble and other characteristics. When spraying over a large area, the transition of the paint film joint is smooth, the surface is flat and smooth, and the interlayer adhesion with the base coat applied in the previous process is excellent, so as to meet the actual needs of the application of water-based topcoats in rail transit vehicle painting.

Summary of the invention

In view of the above problems, the present invention provides a water-based two-component polyurethane topcoat and its application. Through the synergistic effect of various raw material components, large-area construction can be carried out in high temperature, low temperature or high humidity environments. The water-based two-component polyurethane topcoat is used in conjunction with a sanding-free base coat, has excellent interlayer adhesion, and does not require compounding of clear varnish. It has excellent gloss and image clarity, and can be comparable to the paint film appearance of a "solvent-based 1K basecoat + clear varnish" coating system, and has excellent comprehensive performance.

In order to solve the above technical problems, the technical solution provided by the present invention is:

In a first aspect, the present invention provides a water-based two-component polyurethane topcoat, which is composed of component A and component B in a mass ratio of 2:1 to 6.5:1; wherein

The component A comprises the following raw material components in percentage by mass: 40% to 45% of a hydroxyl-containing aqueous dispersion, 5% to 17% of an aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, 0 to 17% of an aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, 0.2% to 1% of a first surfactant, 0.2% to 1% of a first defoamer, 0.2% to 1% of a substrate wetting agent, 0.1% to 1% of a leveling agent, 0.1% to 1% of an aqueous ultraviolet absorber, 15% to 45% of an aqueous color paste, 3% to 6% of a first cosolvent, 1% to 3% of a neutralizer, 0.2% to 0.5% of a thickener, and 5% to 10% of water;

The hydroxyl content of the hydroxyl-containing aqueous dispersion is 3.5% to 5%, and the solid content of the hydroxyl-containing aqueous dispersion is 35% to 50%; the aqueous color paste comprises water, a dispersant, a second defoamer, a second surfactant, a pigment, a color paste stabilizer and a neutralizer;

The B component includes the following raw material components in percentage by mass: 70% to 80% of a curing agent and 20% to 30% of a second co-solvent; the curing agent is at least one of hexamethylene diisocyanate or a hydrophilic aliphatic polyisocyanate.

Compared with the prior art, the water-based two-component polyurethane topcoat provided by the present invention comprises component A as a main paint component and component B as a curing component; component A is compounded with a hydroxyl-containing water-based dispersion and a water-based polycarbonate-containing aliphatic anionic polyurethane dispersion with a high glass transition temperature as a film-forming resin, and a water-based aliphatic anionic polyurethane dispersion with a low glass transition temperature is selectively added, the film-forming resins have good compatibility, and the characteristics of different types of water-based resins are brought into play to an optimal state through a specific ratio and the synergistic effect of each component, so that the finally obtained water-based two-component polyurethane topcoat has a higher solid content, and the coating film has excellent leveling, stone chip resistance, chemical resistance and weather resistance, high toughness, good elasticity, and gloss (60°) and distinctness of image (DOI) both reach above 95, having excellent hiding power and fullness, and no haze, and the finished paint film does not need to be covered, and can achieve the gloss and distinctness of image after being coated with a clear varnish. In addition, the coating film does not need to be polished when used in conjunction with the base coating (epoxy, polyurethane), and the interlayer adhesion is excellent, which can reach level 0. Even when large-scale construction is carried out under high temperature, low temperature or high humidity weather, the coating film joint of the water-based two-component polyurethane topcoat provided by the present invention has a smooth transition, no sagging or "flying ash" during spraying, no traces of lapsing, and the overall surface of the coating film is flat and smooth, and the interlayer adhesion with the midcoat is excellent, and the thixotropic index is increased from the existing 2.5 to more than 4.8. At the same time, it can also balance the flexibility and hardness of the cured film, so that its hardness is increased from the conventional HB to more than H, which can fully meet the needs of large-area spraying of the whole body of rail transit vehicles.

The paint film prepared by the waterborne polyurethane dispersion is soft, has good thixotropic index and anti-sagging properties, and has a moderate drying speed; at the same time, the permeability is very good, and different spraying technologies have little effect on the color effect of the two-component polyurethane topcoat, the coating efficiency is high, and the bonding force with the middle coating is also strong, which can ensure good interlayer adhesion. The flexibility of the molecular chain is the most important factor determining the glass transition temperature (Tg, referred to as the glass transition temperature) of the polymer. The better the flexibility of the main chain, the lower the glass transition temperature. The present invention has found through a large number of experiments that the waterborne polyurethane dispersion with a low glass transition temperature can still maintain good flexibility under low temperature conditions, and can improve the film-forming property under low temperature conditions; the waterborne polyurethane dispersion with a high glass transition temperature can improve the adaptability of the coating under high temperature environments and enhance its high temperature resistance; the waterborne polyurethane dispersions with different glass transition temperatures are compounded to adapt to and improve the paint film construction under various complex conditions such as high temperature and low temperature, and can form a smooth and bright coating.

In addition, the hydroxyl-containing aqueous dispersion is a secondary dispersion with the characteristics of high solid content (35% to 50%), high hydroxyl content (3% to 5%) and low volatile organic compound (VOC) content. The hydroxyl-containing aqueous dispersion and polyisocyanate curing agent are used in a two-component polyurethane topcoat with excellent reactivity and film-forming properties, which can make the two-component polyurethane topcoat have good adhesion, durability, water resistance, solvent resistance and thermal stability, improve the flexibility and hardness of the coating (above pencil hardness H), and make the coating have high gloss (60° gloss is 95%), high fullness, and high distinctness of image (DOI is above 95). Compared with low-hydroxyl acrylic resin, the hydroxyl value of the hydroxyl-containing aqueous dispersion is higher, and the number of hydroxyl groups in the film-forming resin will also increase accordingly, thereby improving the reactivity of the resin, so that the crosslinking speed and degree of crosslinking of the film-forming resin are significantly improved during curing. Due to the shortcomings of hydroxyl-containing aqueous dispersions, such as fast drying, fast shrinkage of the paint film, many pits in the paint film, and obvious particles, the water-based two-component polyurethane topcoat prepared by hydroxyl-containing aqueous dispersions will have blue or white light on the side, which is difficult to adjust the color. Therefore, the use of hydroxyl-containing aqueous dispersions alone as film-forming resins cannot meet the requirements of large-area spraying of rail transit vehicle bodies and rapid color adjustment of later repair paints. Compounding a specific proportion of hydroxyl-containing aqueous dispersions in hydroxyl-free aqueous polyurethane dispersions can further enhance the adhesion of the paint film through chemical cross-linking of hydroxyl (-OH) and isocyanate (-NCO) curing agents; the synergistic effect of aqueous polyurethane dispersions and hydroxyl-containing aqueous dispersions can make up for the shortcomings of the single film-forming resins (single aqueous polyurethane dispersions have poor self-thickening properties, low solid content, and poor water resistance, heat resistance and gloss of the paint film; single aqueous acrylic resin emulsions are hot and viscous, cold and brittle, have poor flexibility, are not solvent-resistant, and are difficult to adjust the color).

The present invention obtains a water-based two-component polyurethane topcoat with excellent comprehensive performance through the synergistic effect of each raw material component and a specific ratio content. The results of the embodiments show that the water-based two-component polyurethane topcoat provided by the present invention can be constructed on a large area under high temperature, low temperature or high humidity environment, and cooperates well with the unpolished mid-coat. Under the premise of not affecting the construction fluidity, it has excellent anti-sagging, color joint ability and interlayer adhesion, no fly ash, and at the same time has excellent mechanical properties and corrosion resistance. The topcoat after coating does not need to be covered with a clear varnish, and the appearance is glossy and vivid, which is comparable to the appearance of the paint film of the "solvent-based 1K base paint + clear varnish" coating system, and has high practical value and promotion value.

It should be noted that the hydroxyl content of the hydroxyl-containing aqueous dispersion is calculated based on the calculated value of the solid resin.

Preferably, the viscosity of the hydroxyl-containing aqueous dispersion is 100 mPa·s to 3000 mPa·s.

Preferably, the solid content of the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C. and the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature ≤ 5° C. are both 33% to 40%.

Preferably, the hydroxyl-containing aqueous dispersion is at least one of Bayhydrol A 2470 (Covestro), Bayhydrol A2770 (Covestro) or Bayhydrol U XP 2766 (Covestro).

Preferably, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion having a glass transition temperature of 40 to 50° C. is Bayhydol UH 2606 produced by Covestro.

Preferably, the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5° C. is at least one of Bayhydrol UH 2648/1, Bayhydrol UH 2110, Bayhydrol UH 2621 or Bayhydrol UH 2952/1.

In the present invention, the aliphatic anionic polyurethane dispersion has the advantages of light color, high transparency, good compatibility, slightly slow drying speed, softer paint film, moderate film volume shrinkage, strong corrosion resistance and strong interlayer adhesion, etc., which can minimize the interference with the color of the wet film state of the paint, have the fast color matching required by the repair paint, have excellent leveling, chemical resistance and weather resistance after film formation, and have high toughness and good elasticity. Among them, the water-based aliphatic anionic polyurethane dispersion with low glass transition temperature (especially Covestro Bayhydrol UH 2952/1) and the water-based polycarbonate-containing aliphatic anionic polyurethane dispersion with high glass transition temperature (Covestro Bayhydol UH 2606) can be attached to the body surface (or OEM product surface) without polishing, and have excellent adhesion and chemical resistance, which can not only meet the needs of large-area spraying of the whole vehicle body of rail transit vehicles, but also cooperate well with the mid-coat paint coating, and are also suitable for repair paint under infrared baking lamps (without clear varnish). Hydroxyl-containing aqueous dispersions have more hydroxyl groups inside the molecules, fewer chemical bonds between molecules, and more orderly arrangement between molecules, resulting in lower viscosity; in addition, the higher the hydroxyl value, the better the reaction activity with polyisocyanate curing agent, the greater the crosslinking density, and the better the adhesion and hardness after film formation. Adding a certain amount of high hydroxyl value resin to the film-forming resin and compounding it with waterborne polyurethane dispersion can not only improve the thixotropic index and anti-sagging properties of the coating, but also synergistically improve the flexibility and hardness of the coating, so that the coating has high gloss, high fullness, high distinctness, and excellent water resistance, solvent resistance and thermal stability.

Preferably, the pigment is an organic pigment or an inorganic pigment.

Preferably, when the pigment is an organic pigment, the component A comprises: 10% to 20% of the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion having a glass transition temperature of 40 to 50° C. and 15% to 25% of the aqueous color paste;

When the pigment is an inorganic pigment, the component A comprises: 5% to 12% of the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C., 0 to 12% of the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5° C., and 25% to 45% of the aqueous color paste.

Further preferably, when the pigment is an inorganic pigment, the component A comprises 25% to 35% of the aqueous color paste.

Preferably, based on 100% of component A, the aqueous color paste includes 5% to 10% water, 0.8% to 1.4% dispersant, 0.2% to 0.5% second defoamer, 0.2% to 1% second surfactant, 5% to 13% organic pigment, 0.9% to 4.5% color paste stabilizer and 0.1% to 0.3% neutralizer.

Preferably, based on 100% of component A, the aqueous color paste includes 7% to 12% water, 1.2% to 1.8% dispersant, 0.2% to 0.5% second defoamer, 0.2% to 0.5% second surfactant, 15% to 25% inorganic pigment, 1.5% to 5.4% color paste stabilizer and 0.1% to 0.3% neutralizer.

Preferably, the dispersant is at least one of a nonionic wetting dispersant or an anionic wetting dispersant.

Further preferably, the nonionic wetting and dispersing agent is at least one of BYK DISPERBYK-190, BYK DISPERBYK-LPN 23160, BYK DISPERBYK-2010, BYK DISPERBYK-2012, allnex VXW6208-60 or BASF DispexUltra PX 4585.

Further preferably, the anionic wetting and dispersing agent is at least one of TEGO Dispers 747W, TEGO Dispers 757W, TEGO Dispers 750W or TEGO Dispers 755W.

Further preferably, the dispersant comprises a nonionic wetting dispersant and an anionic wetting dispersant in a mass ratio of 1:1 to 2.5:1.

Preferably, the mass ratio of the non-volatile matter of the dispersant to the organic pigment is 0.02:1 to 0.2:1.

Preferably, the mass ratio of the non-volatile matter of the dispersant to the inorganic pigment is 0.03:1 to 0.05:1.

Preferably, the second defoaming agent is at least one of BYK-011, BYK-024, BYK-1711 or TEGO-810.

Preferably, the second surfactant is at least one of an acetylenic glycol surfactant or an alcohol alkoxy compound.

More preferably, the second surfactant is at least one of Surfynol AD01, Surfynol 440, Surfynol 104BC or BYK-DYNWET 800.

In the present invention, Surfynol AD01 is a Gemini acetylene glycol surfactant, HLB value (hydrophile-lipophile balance) = 4, has defoaming and wetting functions, can provide defoaming, dynamic wetting and help film-forming effects; Surfynol 440 is a nonionic acetylene glycol ethoxy compound, has low dynamic tension, good compatibility, HLB value = 8, has Gemini wetting and low foaming effects, can reduce the dynamic and static surface tension of the system, and prevent the occurrence of shrinkage holes, pinholes and fish eyes; Surfynol 104BC is a Gemini tetramethyldecynediol nonionic surfactant, has wetting, leveling, defoaming and other functions; BYK-DYNWET 800 is an alcohol alkoxy compound, has a slight foam stabilizing function, can reduce the dynamic surface tension of the system, and is particularly suitable for high-speed construction grinding slurry.

Preferably, the organic pigment is at least one of bright chestnut red, phthalocyanine green, phthalocyanine blue, organic yellow or carbon black.

Preferably, the inorganic pigment is titanium dioxide.

Preferably, the color paste stabilizer includes at least three of water-based fumed silica, modified urea rheological additive, resin-free color paste moisturizer or anti-drying agent for water-based pigment concentrate.

More preferably, the color paste stabilizer includes at least three of Degussa AEROSIL R972, BYK RHEOBYK-420, TEGO Humectant 7005 or BYKETOL-PC.

More preferably, the color paste stabilizer includes Degussa AEROSIL R972, BYK RHEOBYK-420 and TEGO Humectant 7005 in a mass ratio of 1:1:8 to 1:1:12.

More preferably, the color paste stabilizer includes Degussa AEROSIL R972, BYK RHEOBYK-420 and BYKETOL-PC in a mass ratio of 1:1:8 to 1:1:12.

In the present invention, AEROSILR972 is a water-based fumed silica, which contains silanol groups on its surface. After being fully stirred and dispersed, hydrogen bonds are formed between the silanol groups to produce a three-dimensional network structure, thereby increasing the viscosity of the dispersion system, producing thixotropic flow properties, and playing an anti-settling role, thereby improving the stability, corrosion resistance and thixotropy of the pigment; RHEOBYK-420 is a modified urea rheological additive, which has anti-settling and anti-sagging effects and can produce a thixotropic effect; TEGO Humectant 7005 is a resin-free color paste moisturizer; BYKETOL-PC is an anti-drying agent for water-based pigment concentrates, which is also a modified urea solution. Based on a specific molecular structure, water evaporation can be optimally controlled to ensure that the water-based pigment concentrate does not dry too quickly.

Preferably, the neutralizing agent is an 8 wt % to 12 wt % aqueous solution of dimethylethanolamine.

Preferably, the method for preparing the water-based color paste comprises the following steps:

Add the dispersant, the second defoamer and the second surfactant into water, mix them evenly, add the pigment and the color paste stabilizer, grind them, add the neutralizer, and obtain the water-based color paste.

For example, the preparation method of the water-based color paste comprises the following steps:

Add water to a clean container, stir at 280rpm-320rpm, add dispersant and second defoamer in sequence, adjust the speed to 800rpm-1500rpm, add second surfactant, stir for 5min-10min to make it uniform; adjust the speed to 1500rpm-2000rpm, add pigment and color paste stabilizer in sequence, adjust the speed to 2000rpm-3000rpm, disperse and stir for 25min-40min; grind with horizontal grinder or basket grinder; finally add neutralizer, mix well to obtain water-based color paste.

Since the second surfactant has low solubility in water (such as Surfynol AD01's HLB=4, solubility in water is 0.1%), low molecular weight, and is volatile, in order to fully adsorb it onto various particles in the system to achieve good compatibility, it needs to be fully dispersed. It is recommended that the dispersion speed be no less than 800rpm to avoid water sensitivity problems.

More preferably, the pH of the aqueous color paste is 8 to 8.5.

More preferably, the fineness of the water-based color paste is 10 μm to 20 μm.

It should be noted that there is no need to adjust the pH before and during grinding, and no other components such as resins, amines, organic co-solvents, thickeners, etc. are added, otherwise the grinding effect of the pigment slurry will be affected.

Preferably, the first surfactant is a gemini acetylenic diol surfactant.

Further preferably, the first surfactant is at least one of Surfynol AD01, Surfynol 104BC or Surfynol 440 manufactured by Air Chemicals.

More preferably, the first surfactant is at least two of Surfynol AD01, Surfynol 104BC or Surfynol 440.

For example, the first surfactant is Surfynol AD01, Surfynol 104BC and Surfynol 440 of Air Chemicals in a mass ratio of 2:1:1.

In the present invention, Surfynol AD01 is a Gemini acetylene glycol surfactant, HLB value (hydrophile-lipophile balance) = 4, has defoaming and wetting functions, can provide defoaming, dynamic wetting and help film formation effects; Surfynol 104BC is a Gemini tetramethyldecynediol nonionic surfactant, the dynamic surface tension of the wet film is slightly lower than the surface tension of the substrate, can well wet the substrate, form a continuous and stable paint film, has low water sensitivity, has wetting, leveling, defoaming, improves dispersibility, reduces surface tension and stabilizes consistency and viscosity and other functions; Surfynol 440 is a nonionic acetylene glycol ethoxylate, low dynamic tension, good compatibility, HLB value = 8, has Gemini wetting and low foaming effects, can reduce the dynamic and static surface tension of the system, and prevent the occurrence of shrinkage holes, pinholes and fish eyes.

Preferably, the first defoaming agent is at least one of BYK-093, BYK-011 or TEGO-830.

Preferably, the substrate wetting agent is a polyether-modified silicone surfactant.

Further preferably, the substrate wetting agent is at least one of BYK-345, BYK-346, BYK-347, Tego-4100, Tego-280 or Surfynol 104BC.

The preferred substrate wetting agent of the present invention can effectively reduce the surface tension of the system, significantly improve the substrate wettability of the system, and at the same time has good recoatability without increasing the surface smoothness, and is suitable for all water-based systems without cosolvents.

Preferably, the leveling agent is at least one of BYK-378, BYK-381, BYK-333, BYK-331, Tego-4100 or Surfynol 104BC.

The paint molecules are constantly moving during the leveling process. As the viscosity of the paint gradually increases during the leveling process, the system molecules gradually form Bénard vortices, which leads to defects such as pinholes and sagging in the film-forming process. Among the preferred leveling agents of the present invention, BYK-378 is a polyether-modified dimethyl polysiloxane, which can significantly reduce the surface tension of the system, improve the surface smoothness, and thus improve the anti-scratch performance of the coating. It also has excellent substrate wettability and good anti-shrinkage effect, and has a good effect even at a low addition amount. It also has low foam stability, good compatibility, and is easy to re-coat without causing oil spots; BYK-381 is an ionic polyacrylate solution type surface additive, which can improve the leveling and substrate wettability of the system and prevent surface defects (shrinkage and pinholes); Tego-4100 is a leveling agent with a twin structure, which has high activity and unstable foam. Even at extremely low concentrations, it can effectively reduce surface tension and improve wettability and leveling performance.

The dynamic surface tension of the wet film needs to be slightly lower than the surface tension of the substrate, so that the paint film can wet the substrate well and form a continuous and stable paint film. The preferred surfactants, substrate wetting agents and leveling agents of the present invention have low water sensitivity, which can effectively reduce the surface tension and achieve a balance between static and dynamic surface tensions. The special structure enables it to have wetting and defoaming effects, which can improve the dispersibility of the system, improve fluidity and leveling, control foam, and stabilize consistency and viscosity.

Preferably, the aqueous ultraviolet absorber is at least one of BASF Tinuvin 5151, Zhonghao Chemical UV-DL2, Everlight Chemical EVERSORB AQ1, Everlight Chemical EVERSORB AQ2 or Everlight Chemical EVERSORB AQ3.

In the present invention, Tinuvin 5151 light stabilizer is a synergistic mixture of hydrophilic 2-(2-hydroxyphenyl)-benzotriazole ultraviolet light absorber (UVA) and alkaline hindered amine radical scavenger (HALS), has excellent spectral coverage in the ultraviolet light region, and the hydroxyl-containing ultraviolet light absorber can react with isocyanate and melamine crosslinking agent to reduce migration; UV-DL2 is a compound product of a high-efficiency ultraviolet light absorber and a light stabilizer, which can slow down the aging phenomena of the coating such as discoloration, gloss loss, cracking, detachment, etc. caused by light, improve the gloss retention rate, and thus improve the durability of the coating; EVERSORB AQ1, EVERSORBAQ2 and EVERSORB AQ3 are high-efficiency light stabilizers, which can inhibit the aging of the coating film and are suitable for transparent varnish.

Preferably, the first co-solvent includes at least three of propylene glycol methyl ether propionate, propylene glycol butyl ether, dipropylene glycol dimethyl ether, ethylene glycol butyl ether, dipropylene glycol methyl ether, dimethyl sulfoxide, N-methylpyrrolidone, dipropylene glycol butyl ether or diethylene glycol monobutyl ether.

Further preferably, based on the A component as 100%, the first co-solvent includes 1% to 2% of a first solvent, 0.75% to 1.5% of a second solvent and 1.25% to 2.5% of a third solvent; the first solvent includes at least one of propylene glycol methyl ether propionate (PMP), dipropylene glycol dimethyl ether (DMM) or propylene glycol butyl ether (PNB), the second solvent includes at least one of ethylene glycol butyl ether (BCS), dipropylene glycol methyl ether (DPM) or dimethyl sulfoxide (DMSO), and the third solvent includes at least one of N-methylpyrrolidone (NMP), diethylene glycol monobutyl ether (BDG) or dipropylene glycol butyl ether (DPNB).

More preferably, the first co-solvent comprises propylene glycol methyl ether propionate (PMP), dipropylene glycol methyl ether (DPM) and N-methylpyrrolidone (NMP) in a mass ratio of 1:1:1.

The present invention controls the boiling point (gradient boiling point) and solubility of the first cosolvent miscible with water (including the solubility of the solvent in water and the solubility of water in the solvent), which is beneficial to balancing the volatilization rate during the film-forming process, improving the solubility in water, and is more conducive to coating the paint film under high temperature or high humidity, with a moderate drying speed, no fly ash, no sagging, and no obvious traces of grabbing. As long as the ventilation conditions on site are good, normal coating can be performed. The specific first cosolvent can couple different phases, has a strong solubility for both polar and non-polar substances, interacts with the solution system in the water-based paint, causes it to produce a slight phase separation, helps to reduce the surface tension of the water-based system, enhances the fluidity of the paint, thereby adjusting its paint performance, increasing the viscosity of the water-based paint, changing the drying time of the paint, improving the wettability and coating effect of the paint, and improving the elasticity, wear resistance, water resistance, solvent resistance and mechanical strength of the paint film. The preferred first co-solvent can also be used as a film-forming aid. Its unique hydrophilic and lipophilic balance properties enable it to exert different film-forming effects on different resins, helping the coating to form a uniform and smooth coating. In particular, it can significantly reduce the surface tension of the system, assist in leveling, and prevent cracking and orange peel.

Preferably, the neutralizing agent is an 8 wt % to 12 wt % aqueous solution of dimethylethanolamine.

Preferably, the thickener is a polyurethane associative thickener.

Further preferably, the thickener is at least one of Hemmings RHEOLATE 299, BYK RHEOBYK-H 7625VF, Rohm and Haas RM5000 or Rohm and Haas RM-8W.

More preferably, the thickener is at least two of Hemmings RHEOLATE 299, BYK RHEOBYK-H 7625VF, Rohm and Haas RM5000 or Rohm and Haas RM-8W.

In the present invention, RHEOLATE 299, RHEOBYK-H 7625VF and RM5000 are the same type of polyurethane associative thickeners and are not affected by pH value; RHEOLATE 299 can provide efficient thickening in the medium and low shear rate range, RHEOBYK-H 7625VF can sharply increase the viscosity under low shear, and RM5000 can increase the viscosity in the high shear rate range, and the three play a complementary role; RM-8W is a low-odor, solvent-free, hydrophobically modified polyurethane nonionic associative thickener with excellent flow and leveling properties, uniform film-forming properties, glossiness and high thickening efficiency.

Preferably, the solid content of component A is 35% to 45%.

In the present invention, the solid content of component A refers to the mass ratio of all solid components in component A (including resin dispersion and pigment).

Preferably, the mass ratio of the component A to the component B is 2.2:1 to 5.7:1, and more preferably 3:1 to 5:1.

Preferably, based on 100% of the B component, the curing agent includes 25% to 30% of low-viscosity hydrophobic hexamethylene diisocyanate, 25% to 30% of high-viscosity hydrophilic hexamethylene diisocyanate and 18% to 22% of hydrophilic modified isophorone diisocyanate.

It should be noted that the hydrophilic modified isophorone diisocyanate in the present invention refers to a hydrophilic modified aliphatic polyisocyanate based on isophorone diisocyanate (IPDI).

Further preferably, the low-viscosity hydrophobic hexamethylene diisocyanate is at least one of Covestro Desmodur N3900, Covestro Desmodur N3600 or Wanhua WANNATE HT-600.

Further preferably, the high-viscosity hydrophilic hexamethylene diisocyanate is at least one of Bayhydrol XP2655, Bayhydur XP 2547, Bayhydur XP 2487/1, Bayhydur 304 or Bayhydur 305.

Preferably, the solid content of the hydrophilic aliphatic polyisocyanate is 60% to 70%.

Preferably, the -NCO content of the hydrophilic aliphatic polyisocyanate is 8.5% to 12%.

Further preferably, the hydrophilic aliphatic polyisocyanate is at least one of Covestro Bayhydur 401-70, Covestro Bayhydur 401-60 or Evonik Vestanat T1890E.

The present invention can further enhance the curing effect and improve the construction fluidity, viscosity and glossiness of the coating by limiting the type of the curing agent.

Preferably, the second co-solvent is at least two of propylene glycol methyl ether acetate (PMA), propylene glycol methyl ether acrylate (PMP), propylene glycol diacetate (PGDA), ethylene glycol butyl ether acetate (BGA), dipropylene glycol dimethyl ether (DMM), propylene carbonate (PC) or dibasic acid ester (DBE).

Further preferably, based on 100% of the B component, the second co-solvent includes 6% to 9% of a fourth solvent, 8% to 12% of a fifth solvent and 6% to 9% of a sixth solvent; the fourth solvent includes at least one of propylene glycol methyl ether acetate (PMA) or propylene glycol methyl ether propionate (PMP), the fifth solvent includes at least one of propylene glycol diacetate (PGDA), ethylene glycol butyl acetate (BGA) or dipropylene glycol dimethyl ether (DMM), and the sixth solvent includes at least one of propylene carbonate (PC) or dibasic acid ester (DBE).

Table 1 Summary of the physicochemical properties of the second co-solvent

In the present invention, a certain amount of the second co-solvent is added to the curing component, which can not only improve the compatibility of the curing agent with the hydroxyl-containing aqueous dispersion, but also prolong the open time of the paint film, which is beneficial to leveling. The specific second co-solvents are all environmentally friendly solvents (see Table 1 for specific properties) with the following characteristics: (1) They contain multiple functional groups and have strong solubility for both polar and non-polar substances, which can improve the strength of the coating film; (2) They have low surface tension, strong solvent power, low viscosity and good volatility, which can provide good solubility and fluidity, ensure uniform coating and easy construction, and at the same time improve the adhesion and durability of the coating, adjust the volatilization rate of the entire system, adjust the drying speed of the paint film, reduce pinholes and fish eyes, and increase gloss, wetting, leveling and re-leveling; (3) Propylene carbonate has good film-forming properties and strong carbon dioxide absorption capacity. When used with a hydrophilic isocyanate curing agent, the effect is excellent, which can improve prickly heat and reduce bubbles; (4) The use of multiple second co-solvents can complement each other to achieve a better comprehensive effect. In addition, by compounding second co-solvents with different boiling points (gradient boiling points), it is beneficial to balance the volatilization rate during the film-forming process and improve the solubility in water. For example, the synergy of propylene glycol methyl ether propionate (PMP), propylene glycol diacetate (PGDA), and propylene carbonate (PC) can not only improve the strength of the coating film, but also facilitate the stable storage of the coating. It can also absorb carbon dioxide during the coating and film-forming process, and is extremely effective in diluting water-based isocyanate curing agents.

Preferably, the molar ratio of -NCO in the B component to -OH in the A component is 1.4:1 to 1.6:1, and more preferably 1.5:1.

The preferred molar ratio of -NCO to -OH in the present invention can not only satisfy the combined application of component A and component B, but also, after adding a specific activated diluent during subsequent use, the ratio of -NCO to -OH in the system is more conducive to the formation of a paint film.

In a second aspect, the present invention provides a method for preparing a water-based two-component polyurethane topcoat, comprising the following steps:

S1, weighing each raw material according to the designed ratio, adding a hydroxyl-containing aqueous dispersion, an aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, and an aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C into water, mixing evenly, adding a first surfactant, a first defoamer, a substrate wetting agent, a leveling agent, an aqueous ultraviolet absorber, an aqueous color paste, and a first cosolvent, mixing evenly, and then adding a neutralizer and a thickener in sequence, mixing evenly, to obtain component A;

S2, adding the second co-solvent into the curing agent, mixing evenly, to obtain component B.

It should be noted that there is no order of precedence for steps S1 and S2.

The preparation method of the water-based two-component polyurethane topcoat provided by the invention does not require special treatment of the raw materials and is simple and easy to implement.

Exemplarily, the preparation method of component A comprises the following steps:

Weigh the raw materials according to the designed ratio, add the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, and the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C into a clean container, add water at 600 rpm to 800 rpm, and stir for 4 to 6 minutes; then add the first surfactant, the first defoamer, the substrate wetting agent, the leveling agent, the aqueous ultraviolet absorber, the aqueous color paste and the first cosolvent in sequence, and continue to stir at 600 rpm to 800 rpm for 10 to 15 minutes; then add the neutralizer to adjust the pH of the system to 8 to 8.5; finally add the thickener, mix well, and obtain component A.

In a third aspect, the present invention provides the use of the above-mentioned water-based two-component polyurethane topcoat in automotive coatings.

Preferably, the vehicle coating is a coating for rail transit vehicles.

In a fourth aspect, the present invention provides a method for using the above-mentioned water-based two-component polyurethane topcoat, comprising the following steps:

Mix component A and component B evenly, add activation diluent, mix evenly to obtain construction coating, and evenly apply it on the mid-coat paint;

The activated diluent includes a hydroxyl-containing aqueous dispersion, an aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C., an aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5° C., a water-based synthetic sheet silicate solution, a water-based modified urea solution, a first cosolvent, a stabilizer, a first defoamer, a leveling agent and water.

In the method for using a waterborne two-component polyurethane topcoat, a unique activated diluent is used to dilute the waterborne two-component polyurethane topcoat (component A + component B), which has the following beneficial effects: (1) improving the system's tolerance to high levels of surfactants or extreme pH values; (2) preventing the coating from sagging or miscibility; and (3) accelerating the formation of the structure after construction during large-area spraying, thereby improving the adhesion of vertical surfaces (improving the interlayer adhesion between the waterborne midcoat and the waterborne two-component polyurethane topcoat).

Preferably, the activated diluent comprises the following raw material components in percentage by mass: 8% to 11.5% of an aqueous hydroxyl-containing dispersion, 3% to 4.5% of an aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, 3% to 4.5% of an aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, 25% to 33.5% of a water-based synthetic sheet silicate solution, 0.5% to 0.7% of a water-based modified urea solution, 7.5% to 8.5% of a first cosolvent, 7.5% to 8.5% of a stabilizer, 0.5% to 0.7% of a first defoamer, 0.5% to 0.7% of a leveling agent and 27% to 42% of water, and the sum of each component is 100%.

Preferably, the mass ratio of the component A to the activated diluent is 100:(20-30).

The present invention adopts the above mass ratio to ensure the solid content of the construction coating. The specific amount of the activated diluent can be adjusted according to the ambient temperature and humidity and whether the construction spraying sags. Generally, the higher the temperature or humidity, the more the activated diluent is added; the more serious the sag phenomenon is, the more the activated diluent is added.

Preferably, the hydroxyl content of the hydroxyl-containing aqueous dispersion is 3.5% to 5%.

Preferably, the viscosity of the hydroxyl-containing aqueous dispersion is 100 mPa·s to 3000 mPa·s.

Preferably, the solid content of the hydroxyl-containing aqueous dispersion is 35% to 50%.

Preferably, the solid content of the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C. and the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature ≤ 5° C. are both 33% to 40%.

Preferably, the hydroxyl-containing aqueous dispersion is at least one of Bayhydrol A 2470 (Covestro), Bayhydrol A2770 (Covestro) or Bayhydrol U XP 2766 (Covestro).

Preferably, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion having a glass transition temperature of 40 to 50° C. is Bayhydol UH 2606 produced by Covestro.

Preferably, the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5° C. is at least one of Bayhydrol UH 2648/1, Bayhydrol UH 2110, Bayhydrol UH 2621 or Bayhydrol UH 2952/1.

Preferably, the water-based synthetic sheet silicate solution comprises the following raw material components in percentage by mass: 1.5% to 2.5% of organic modified synthetic layer silicate, 1.5% to 2.5% of emulsifying dispersant and 95% to 97% of water, and the sum of the components is 100%.

More preferably, the organic-modified synthetic layered silicate is at least one of BYK Laponite-RD or BYK Laponite-RDS.

Laponite-RD and Laponite-RDS are synthetic sheet silicates that are insoluble in water but can hydrate and swell in water to form a colorless and transparent colloid. When the concentration in water is above 2%, a colloid with improved thixotropy can be formed, which plays an activation and regulating role in anti-sagging. The present invention utilizes the synergistic effect of the compounding of LAPONITE and polymer to improve the tolerance of the system to high content of surfactants, electrolytes or extreme pH values.

Further preferably, the emulsifying dispersant is at least one of polyethylene glycol and polypropylene glycol. If the emulsifying dispersant includes polyethylene glycol and polypropylene glycol, the mass ratio of polyethylene glycol to polypropylene glycol may be 1:1.

More preferably, the emulsifying dispersant is at least one of PEG-1000, PEG-1500, PPG-200, PPG-400 or PPG-600.

Preferably, the method for preparing the water-based synthetic sheet silicate solution comprises the following steps:

The emulsifying dispersant is added into water and mixed evenly, and then the organic modified synthetic layered silicate is added and mixed evenly to obtain a water-based synthetic sheet silicate solution.

For example, under stirring at 400 rpm to 600 rpm, an emulsifying dispersant is added to water, the rotation speed is adjusted to 1000 rpm to 1500 rpm, and the organic modified synthetic layered silicate is slowly added, and stirring is continued until the solution is clear and no dissolved particles are seen, thereby obtaining a water-based synthetic sheet silicate solution.

Preferably, the water-based modified urea solution is at least one of BYK RHEOBYK-7420CA, BYK RHEOBYK-7420ET or BYK RHEOBYK-7420ES.

In the present invention, the water-based modified urea solution is a liquid rheological agent, and a specific amount of the water-based modified urea solution can produce a strong thixotropic effect, thereby improving the anti-settling and anti-sagging properties of the system.

Preferably, the first co-solvent includes at least three of propylene glycol methyl ether propionate, propylene glycol butyl ether, dipropylene glycol dimethyl ether, ethylene glycol butyl ether, dipropylene glycol methyl ether, dimethyl sulfoxide, N-methylpyrrolidone, dipropylene glycol butyl ether or diethylene glycol monobutyl ether.

Further preferably, based on the A component as 100%, the first co-solvent includes 1% to 2% of a first solvent, 0.75% to 1.5% of a second solvent and 1.25% to 2.5% of a third solvent; the first solvent includes at least one of propylene glycol methyl ether propionate (PMP), dipropylene glycol dimethyl ether (DMM) or propylene glycol butyl ether (PNB), the second solvent includes at least one of ethylene glycol butyl ether (BCS), dipropylene glycol methyl ether (DPM) or dimethyl sulfoxide (DMSO), and the third solvent includes at least one of N-methylpyrrolidone (NMP), diethylene glycol monobutyl ether (BDG) or dipropylene glycol butyl ether (DPNB).

Preferably, the stabilizer is at least one of propylene glycol methyl ether acetate (PGMEA) or propylene glycol methyl ether propionate (PMP).

In the present invention, the preferred stabilizer can provide good solubility and fluidity, ensure uniform coating and easy construction, and improve the adhesion and durability of the coating.

Preferably, the first defoaming agent is at least one of BYK-093, BYK-011 or TEGO-830.

Preferably, the leveling agent is at least one of BYK-378, BYK-381, BYK-333, BYK-331, Tego-4100 or Surfynol 104BC.

For example, the preparation method of the activated diluent comprises the following steps:

Weigh the raw materials according to the designed ratio, add a hydroxyl-containing aqueous dispersion, an aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, an aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, a first defoamer, a leveling agent, a first cosolvent, a stabilizer, a water-based synthetic sheet silicate solution and a water-based modified urea solution into water at 400 rpm to 600 rpm, and continue stirring at 600 rpm to 800 rpm for 8 min to 12 min to obtain an activated diluent.

The corresponding film-forming resin in component A is added to the activated diluent of the present invention, which increases the solid content of the construction and the hydroxyl content, further promotes the reaction activity of the film-forming resin and the isocyanate curing agent, thereby enhancing the adhesion and improving the gloss, distinctness and fullness of the paint film; through the synergistic effect of compounding the hydroxyl-containing aqueous dispersion and the aqueous polyurethane dispersion with different glass transition temperatures, the tolerance of the system to the limit film thickness of the two-component polyurethane topcoat is improved, and an ideal paint film surface state can be formed after accelerated construction, which is particularly suitable for large-area construction spraying of rail transit vehicle bodies, and can be smoothly constructed under high temperature, low temperature or high humidity environments. The water-based modified urea solution is a liquid rheological agent, which can produce a strong thixotropic effect and can improve the anti-settling and anti-sagging properties of water-based and high-polarity systems. In addition, the stabilizer is a high-grade industrial solvent with excellent performance. It has strong solubility and fluidity for both polar and non-polar substances, which can ensure uniform coating and easy construction, further improve the adhesion and durability of the coating, and at the same time improve the solubility of the water-based synthetic sheet silicate solution, ensuring that the coating can be stored for a long time without flocculation and agglomeration. During construction, by adding an activated diluent, the interlayer adhesion can be greatly improved and the rheological properties can be accurately adjusted, thereby improving the interlayer adhesion of the two-component polyurethane topcoat and the water-based midcoat.

The water-based synthetic sheet silicate solution and the water-based modified urea solution can form a synergistic effect, increase the low shear viscosity of the coating, prevent the coating from sagging or mixing during construction, improve the construction and storage stability of the coating, and effectively prevent the sedimentation and dehydration shrinkage of solid matter in the water-based coating system, thereby accelerating the formation of the structure after construction. The present invention has found through a large number of experiments that when the rheological additive water-based synthetic sheet silicate solution and the surfactant water-based modified urea solution are compounded, if the rheological additive is used in too much amount, it will cause the activation dilution to be unable to be stored for a long time (caking and flocculation will occur after long storage), and it will also cause the water resistance of the water-based two-component polyurethane topcoat to deteriorate; if the surfactant is used in too much amount, it will cause the paint film to have defects such as shrinkage cavities, prickly heat, and orange peel. Therefore, the rheological additive is compounded with the surface additive, stabilizer and other additives and part of the film-forming resin in a specific ratio, which further improves the storage stability and water resistance of the coating, and makes the appearance of the paint film reach the best state.

DETAILED DESCRIPTION

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

The water used in the embodiments of the present invention is deionized water.

The test instrument used in the present invention comprises:

Grid marker, Guangzhou Biaogeda;

Pencil hardness tester, impact instrument, bending tester, cupping tester, distinctness of image tester, BYK, Germany;

MA85 multi-angle wind photometer, X-Rite, USA;

ISO No. 6 cup, Tu-4# cup, solvent resistance wiper, pH meter, film thickness meter, Shanghai Modern Environmental Engineering Technology Co., Ltd.;

Salt spray resistance test equipment, artificial weathering resistance (QUA/SPARY), Q-Lab, USA.

In order to better illustrate the present invention, further examples are given below.

Example 1

This embodiment provides a water-based two-component polyurethane topcoat, which is composed of component A and component B in a mass ratio of 4.5:1.

Component A is composed of the following raw material components in percentage by mass: 44% hydroxyl-containing aqueous dispersion, 11% aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C (denoted as PUD with Tg=40-50), 12% aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C (denoted as PUD with Tg≤5), 0.4% first surfactant, 0.4% first defoamer, 0.4% substrate wetting agent, 0.3% leveling agent, 0.3% aqueous ultraviolet absorber, 19.1% aqueous color paste (including 7% water, 1% dispersant, 0.3% second defoamer, 0.6% second surfactant, 8% organic pigment, 2% color paste stabilizer and 0.2% neutralizer), 3.5% first cosolvent, 1.3% neutralizer, 0.3% thickener and 7% water.

Component B is composed of the following raw material components in percentage by mass: 75% of curing agent (28% of low viscosity hydrophobic hexamethylene diisocyanate, 27% of high viscosity hydrophilic hexamethylene diisocyanate and 20% of hydrophilic modified isophorone diisocyanate) and 25% of the second cosolvent.

The specific components of the above raw materials are shown in Table 2. After calculation, the solid content of component A is 37.9%.

The preparation method of the above-mentioned water-based two-component polyurethane topcoat comprises the following steps:

S1, weigh the raw materials according to the designed ratio, add the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C, and the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C into a clean container, add water at 700rpm, and stir for 5min; then add the first surfactant, the first defoamer, the substrate wetting agent, the leveling agent, the aqueous ultraviolet absorber, the aqueous color paste and the first cosolvent in sequence, and continue to stir at 700rpm for 13min; then add the neutralizer to adjust the pH of the system to 8.5; finally add the thickener, mix well, and obtain component A.

S2, adding the second co-solvent into the curing agent, mixing evenly, to obtain component B.

Example 2

This embodiment provides a water-based two-component polyurethane topcoat, which is composed of component A and component B in a mass ratio of 4.9:1.

Component A is composed of the following raw material components in percentage by mass: 40% of hydroxyl-containing aqueous dispersion, 12% of aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C (denoted as PUD with Tg=40-50), 20% of aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C (denoted as PUD with Tg≤5), 0.2% of a first surfactant, 0.2% of a first defoamer, 0.2% of a substrate wetting agent, 0.1% of a leveling agent, 0.1% of an aqueous ultraviolet absorber, 18% of an aqueous color paste (including 10% water, 0.8% dispersant, 0.2% of a second defoamer, 1% of a second surfactant, 5% of an organic pigment, 0.9% of a color paste stabilizer and 0.1% of a neutralizer), 3% of a first cosolvent, 1% of a neutralizer, 0.2% of a thickener and 5% of water.

Component B is composed of the following raw material components in percentage by mass: 73% of curing agent (30% of low viscosity hydrophobic hexamethylene diisocyanate, 25% of high viscosity hydrophilic hexamethylene diisocyanate and 18% of hydrophilic modified isophorone diisocyanate) and 27% of the second cosolvent.

The specific components of the above raw materials are shown in Table 2. After calculation, the solid content of component A is 35.5%.

The preparation method of the above-mentioned water-based two-component polyurethane topcoat comprises the following steps:

S1, weigh the raw materials according to the designed ratio, add the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C, and the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C into a clean container, add water at 800rpm, and stir for 4min; then add the first surfactant, the first defoamer, the substrate wetting agent, the leveling agent, the aqueous ultraviolet absorber, the aqueous color paste and the first cosolvent in sequence, and continue to stir at 800rpm for 10min; then add the neutralizer to adjust the pH of the system to 8.5; finally add the thickener, mix well, and obtain component A.

S2 is the same as in Example 1 and will not be described in detail.

Example 3

This embodiment provides a water-based two-component polyurethane topcoat, which is composed of component A and component B in a mass ratio of 4.3:1.

Component A is composed of the following raw material components in percentage by mass: 45% of hydroxyl-containing aqueous dispersion, 20% of aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C (denoted as PUD with Tg=40-50), 0.3% of a first surfactant, 0.2% of a first defoamer, 0.2% of a substrate wetting agent, 0.1% of a leveling agent, 0.1% of an aqueous ultraviolet absorber, 24.9% of an aqueous color paste (including 5% water, 1.4% dispersant, 0.5% of a second defoamer, 0.2% of a second surfactant, 13% of an organic pigment, 4.5% of a color paste stabilizer and 0.3% of a neutralizer), 3% of a first cosolvent, 1% of a neutralizer, 0.2% of a thickener and 5% of water.

Component B is composed of the following raw material components in percentage by mass: 80% of curing agent (28% of low viscosity hydrophobic hexamethylene diisocyanate, 30% of high viscosity hydrophilic hexamethylene diisocyanate and 22% of hydrophilic modified isophorone diisocyanate) and 20% of the second cosolvent.

The specific components of the above raw materials are shown in Table 2. After calculation, the solid content of component A is 42.8%.

The preparation method of the above-mentioned water-based two-component polyurethane topcoat comprises the following steps:

S1, weigh the raw materials according to the designed ratio, add the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C, and the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C into a clean container, add water at 600rpm, and stir for 6min; then add the first surfactant, the first defoamer, the substrate wetting agent, the leveling agent, the aqueous ultraviolet absorber, the aqueous color paste and the first cosolvent in sequence, and continue to stir at 600rpm for 15min; then add the neutralizer to adjust the pH of the system to 8; finally add the thickener, mix well, and obtain component A.

S2 is the same as in Example 1 and will not be described in detail.

Example 4

This embodiment provides a water-based two-component polyurethane topcoat, which is composed of component A and component B in a mass ratio of 4.4:1.

Component A is composed of the following raw material components in percentage by mass: 43% hydroxyl-containing aqueous dispersion, 8% aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C (denoted as PUD with Tg=40-50), 8% aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C (denoted as PUD with Tg≤5), 0.2% first surfactant, 0.2% first defoamer, 0.2% substrate wetting agent, 0.1% leveling agent, 0.1% aqueous ultraviolet absorber, 30.8% aqueous color paste (including 8% water, 1.5% dispersant, 0.3% second defoamer, 0.3% second surfactant, 18% inorganic pigment, 2.5% color paste stabilizer and 0.2% neutralizer), 3% first cosolvent, 1% neutralizer, 0.2% thickener and 5.2% water.

Component B is composed of the following raw material components in percentage by mass: 75% of curing agent (55% of high viscosity hydrophobic hexamethylene diisocyanate and 20% of hydrophilic modified isophorone diisocyanate) and 25% of the second co-solvent.

The specific components of the above raw materials are shown in Table 2. After calculation, the solid content of component A is 44.9%.

The preparation method of the above-mentioned water-based two-component polyurethane topcoat is the same as that in Example 1 and will not be repeated herein.

Example 5

This embodiment provides a water-based two-component polyurethane topcoat, which is composed of component A and component B in a mass ratio of 5.6:1.

Component A is composed of the following raw material components in percentage by mass: 43% hydroxyl-containing aqueous dispersion, 6% aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C (denoted as PUD with Tg=40-50), 6% aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C (denoted as PUD with Tg≤5), 0.2% first surfactant, 0.2% first defoamer, 0.2% substrate wetting agent, 0.1% leveling agent, 0.1% aqueous ultraviolet absorber, 32.4% aqueous color paste (including 10% water, 1.5% dispersant, 0.2% second defoamer, 0.2% second surfactant, 15% inorganic pigment, 5.4% color paste stabilizer and 0.1% neutralizer), 5.6% first cosolvent, 1% neutralizer, 0.2% thickener and 5% water.

Component B is composed of the following raw material components in percentage by mass: 75% of curing agent (75% of high viscosity hydrophilic hexamethylene diisocyanate) and 25% of the second co-solvent.

The specific components of the above raw materials are shown in Table 2. After calculation, the solid content of component A is 41.2%.

The preparation method of the above-mentioned water-based two-component polyurethane topcoat is the same as that in Example 1 and will not be repeated herein.

Example 6

This embodiment provides a water-based two-component polyurethane topcoat, which is composed of component A and component B in a mass ratio of 2.3:1.

Component A is composed of the following raw material components in percentage by mass: 43% hydroxyl-containing aqueous dispersion, 12% aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40-50°C (denoted as PUD with Tg=40-50), 1% first surfactant, 1% first defoamer, 1% substrate wetting agent, 1% leveling agent, 1% aqueous ultraviolet absorber, 25.2% aqueous color paste (including 7% water, 1.2% dispersant, 0.2% second defoamer, 0.2% second surfactant, 15% inorganic pigment, 1.5% color paste stabilizer and 0.1% neutralizer), 3% first cosolvent, 3% neutralizer, 0.5% thickener and 8.3% water.

Component B is composed of the following raw material components in percentage by mass: 75% of curing agent (75% of hydrophilic modified isophorone diisocyanate) and 25% of the second co-solvent.

The specific components of the above raw materials are shown in Table 2. After calculation, the solid content of component A is 41.8%.

The preparation method of the above-mentioned water-based two-component polyurethane topcoat is the same as that in Example 1 and will not be repeated herein.

Table 2 Specific raw material components of water-based two-component polyurethane topcoat in Examples 1 to 6

Comparative Example 1

This comparative example provides a water-based two-component polyurethane topcoat, which is similar to Example 1, except that Covestro Bayhydrol A2470 is replaced with Covestro Bayhydol UH 2606 of equal quality (i.e., the water-based resin does not include a hydroxyl-containing aqueous dispersion). The remaining components are the same as those in Example 1 and are not described in detail.

Comparative Example 2

This comparative example provides a water-based two-component polyurethane topcoat, which is similar to Example 1, except that Covestro Bayhydol UH 2606 is replaced with Covestro Bayhydrol A 2470 of equal quality (i.e., the water-based resin does not contain a water-based polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C.). The remaining components are the same as those in Example 1 and are not described in detail.

Comparative Example 3

This comparative example provides a water-based two-component polyurethane topcoat, which is similar to Example 1, except that Covestro Bayhydol UH 2606 and Bayhydrol UH 2952/1 are replaced with Covestro Bayhydrol A 2470 of equal quality (i.e., the water-based resin contains only a hydroxyl-containing aqueous dispersion). The remaining components are the same as those in Example 1 and are not described in detail.

Comparative Example 4

This comparative example provides a water-based two-component polyurethane topcoat, which is similar to Example 1, except that Covestro Bayhydrol A 2470 and Bayhydrol UH 2952/1 are replaced with Covestro Bayhydol UH 2606 of equal quality (i.e., the water-based resin contains only a water-based polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C.). The remaining components are the same as those in Example 1 and are not described in detail.

Comparative Example 5

This comparative example provides a water-based two-component polyurethane topcoat, which is similar to Example 1, except that Covestro Bayhydol UH 2606 and Bayhydrol A 2470 are replaced with Covestro Bayhydrol UH2952/1 of equal quality (i.e., the water-based resin contains only a water-based polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C). The remaining components are the same as those in Example 1 and are not described in detail.

Comparative Example 6

This comparative example provides a water-based two-component polyurethane topcoat, which is similar to Example 1, except that the water-based resin (Covestro Bayhydol UH 2606, Bayhydrol A 2470 and Bayhydrol UH 2952/1) is replaced with Liangu Uacryl 4219 (acrylic emulsion). The remaining components are the same as those in Example 1 and are not described in detail.

Comparative Example 7

This comparative example provides a water-based two-component polyurethane topcoat, which is similar to Example 1, except that Covestro Bayhydol UH 2606 and Bayhydrol UH 2952/1 are replaced by allnex of equal quality. 6803 (water-based acrylic resin emulsion). The remaining components are the same as those in Example 1 and will not be described in detail.

Application Example 1

This application embodiment provides a method for using a water-based two-component polyurethane topcoat, comprising the following steps:

The components A and B of Example 1 were mixed evenly, and an activated diluent was added and mixed evenly to obtain a construction coating. The mass ratio of the component A to the activated diluent was 100:25.

The activated diluent is composed of the following raw material components in percentage by mass: 10% of a hydroxyl-containing aqueous dispersion, 4% of an aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, 4% of an aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, 29% of a water-based synthetic sheet silicate solution, 0.6% of a water-based modified urea solution, 8% of a first cosolvent, 8% of a stabilizer, 0.6% of a defoamer, 0.6% of a leveling agent and 35.2% of water.

The water-based synthetic sheet silicate solution is composed of the following raw materials in percentage by mass: 2% of organic modified synthetic layer silicate, 2% of emulsifying dispersant and 96% of water.

It should be noted that the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C., the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5° C., the first cosolvent, the first defoamer and the leveling agent in the activated diluent are the same as the corresponding raw material components in component A of Example 1. The specific components of the remaining raw materials are shown in Table 3.

Application Example 2

This application embodiment provides a method for using a water-based two-component polyurethane topcoat, comprising the following steps:

The components A and B of Example 2 were mixed evenly, and an activated diluent was added and mixed evenly to obtain a construction coating. The mass ratio of the component A to the activated diluent was 100:20.

The activated diluent is composed of the following raw material components in percentage by mass: 11.5% of hydroxyl-containing aqueous dispersion, 4.5% of aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, 4.5% of aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, 33.5% of water-based synthetic sheet silicate solution, 0.7% of water-based modified urea solution, 8.4% of a first cosolvent, 8.5% of a stabilizer, 0.7% of a defoamer, 0.7% of a leveling agent and 27% of water.

The water-based synthetic sheet silicate solution is composed of the following raw materials in percentage by mass: 1.5% of organic modified synthetic layer silicate, 1.5% of emulsifying dispersant and 97% of water.

It should be noted that the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C., the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5° C., the first cosolvent, the defoamer and the leveling agent in the activated diluent are the same as the corresponding raw material components in component A of Example 2. The specific components of the remaining raw materials are shown in Table 3.

Application Example 3

This application embodiment provides a method for using a water-based two-component polyurethane topcoat, comprising the following steps:

The components A and B of Example 3 were mixed evenly, and an activated diluent was added and mixed evenly to obtain a construction coating. The mass ratio of the component A to the activated diluent was 100:30.

The activated diluent is composed of the following raw material components in percentage by mass: 8.1% of aqueous dispersion containing hydroxyl groups, 3.1% of aqueous aliphatic anionic polyurethane dispersion containing polycarbonate with a glass transition temperature of 40 to 50°C, 3.1% of aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, 27% of water-based synthetic sheet silicate solution, 0.5% of water-based modified urea solution, 7.6% of a first cosolvent, 7.6% of a stabilizer, 0.5% of a defoamer, 0.5% of a leveling agent and 42% of water.

The water-based synthetic sheet silicate solution is composed of the following raw materials in percentage by mass: 2.5% of organic modified synthetic layer silicate, 2.5% of emulsifying dispersant and 95% of water.

It should be noted that the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C., the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5° C., the first cosolvent, the defoamer and the leveling agent in the activated diluent are the same as the corresponding raw material components in the A component of Example 3. The specific components of the remaining raw materials are shown in Table 3.

Application Example 4

This application embodiment provides a method for using a water-based two-component polyurethane topcoat, comprising the following steps:

The components A and B of Example 4 were mixed evenly, and an activated diluent was added and mixed evenly to obtain a construction coating. The mass ratio of the component A to the activated diluent was 100:25.

The raw material ratio of the activated diluent and the raw material ratio of the water-based synthetic sheet silicate solution are the same as those in Application Example 1; the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, the first cosolvent, the defoamer and the leveling agent in the activated diluent are the same as the corresponding raw material components in component A of Example 4. The specific components of the remaining raw materials are shown in Table 3.

Application Example 5

This application embodiment provides a method for using a water-based two-component polyurethane topcoat, comprising the following steps:

The components A and B of Example 5 were mixed evenly, and the activated diluent was added and mixed evenly to obtain a construction coating. The mass ratio of the component A to the activated diluent was 100:25.

The raw material ratio of the activated diluent and the raw material ratio of the water-based synthetic sheet silicate solution are the same as those in Application Example 1; the hydroxyl-containing aqueous dispersion, the aqueous polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50°C, the aqueous aliphatic anionic polyurethane dispersion with a glass transition temperature of ≤5°C, the first cosolvent, the defoamer and the leveling agent in the activated diluent are the same as the corresponding raw material components in component A of Example 5. The specific components of the remaining raw materials are shown in Table 3.

Application Example 6

This application embodiment provides a method for using a water-based two-component polyurethane topcoat, comprising the following steps:

The components A and B of Example 6 were mixed evenly, and an activated diluent was added and mixed evenly to obtain a construction coating. The mass ratio of the component A to the activated diluent was 100:25.

The raw material ratio and components of the activated diluent are the same as those in Application Example 1 and will not be described in detail.

Table 3 Specific raw material components of the activated diluent in application examples 1 to 5

Application Comparative Examples 1 to 7

Comparative Examples 1 to 7 provide a method for using a water-based two-component polyurethane topcoat, respectively, comprising the following steps:

Components A and B of Comparative Examples 1 to 7 were mixed evenly, and activated diluent was added and mixed evenly to obtain 7 groups of construction coatings. The mass ratio of component A to activated diluent was 100:25. The raw material components and proportions of the activated diluent were the same as those of Application Example 1, and will not be described in detail.

Application Comparative Example 8

This application comparative example provides a method for using a water-based two-component polyurethane topcoat, comprising the following steps:

The components A and B of Example 1 were mixed evenly, and water was added and mixed evenly to obtain a construction coating. The mass ratio of the component A to water was 100:25.

Application Comparative Example 9

This comparative application example provides a method for using a water-based two-component polyurethane topcoat, which is similar to Application Example 1, except that the water-based polycarbonate-containing aliphatic anionic polyurethane dispersion with a glass transition temperature of 40 to 50° C. in the activated diluent is replaced with an equal amount of a hydroxyl-containing water-based dispersion. The remaining conditions are the same as those in Application Example 1 and are not described in detail.

Application Comparative Example 10

This comparative application example provides a method for using a water-based two-component polyurethane topcoat, which is similar to Application Example 1, except that the water-based modified urea solution in the activated diluent is replaced with an equal amount of water-based synthetic sheet silicate solution. The remaining conditions are the same as those in Application Example 1 and are not described in detail.

Performance Testing

The performance tests were conducted on the construction coatings provided in Application Examples 1 to 6 and Application Comparative Examples 1 to 10.

(1) The tinplate was polished with 400-500 mesh sandpaper, and the surface oil was removed with ethanol, and then the construction coatings provided in application examples 1-6 and application comparative examples 1-10 were applied, such as: the construction coatings provided in application examples 1-2, 6 and application comparative examples 1-4 were applied at high temperature and high humidity (38°C, RH=85%), and the construction coatings provided in application examples 3-5 and application comparative examples 5-10 were applied at low temperature and high humidity (0°C, RH=85%); the film thickness was 25μm-35μm, and the coating was baked at 60°C for 2h. The paint film color and appearance, drying time, impact resistance, bending test and cupping test of the obtained test sample were tested respectively, and the test standards are shown in Table 4, and the test results are shown in Tables 5-6.

(2) Coat a WB07-1 midcoat (purchased from Beijing Yulin Chemical Co., Ltd.) on a steel plate coated with a cathode electrophoretic paint (CED, model EcoTa8500, purchased from Shanghai Jinlitai Chemical Co., Ltd.) with a film thickness of 55 μm to 66 μm and bake at 60°C for 2 h; then coat the construction coatings provided in Application Examples 1 to 6 and Application Comparative Examples 1 to 10 on the WB07-1 midcoat, such as: coating the construction coatings provided in Application Examples 3 to 5 and Application Comparative Examples 1 to 4 at high temperature and high humidity (38°C, RH=85%), and coating the construction coatings provided in Application Examples 1 to 2, 6 and Application Comparative Examples 5 to 10 at low temperature and high humidity (0°C, RH=85%); spray 2 to 3 coats, flash dry each coat for 3 min to 5 min, and pre-bake at 60°C for 10 min (the paint film is surface dry). The solvent wiping resistance, water resistance, gasoline resistance, acid resistance, acid resistance, alkali resistance and artificial climate accelerated aging resistance of the obtained test samples were tested respectively. The test standards are shown in Table 4, and the test results are shown in Tables 5-6.

Table 4 Performance test standards and requirements of the construction coatings provided in the application examples and comparative examples

Note: For any undated referenced standards, the latest version shall apply to this invention.

Table 5 Performance test results of the construction coating provided by the application example

In the table:

Thixotropic index: measured using NDJ-1 rotational viscometer; the viscosity of component A (ISO6 ^# ) was adjusted to about 70s by the amount of thickener, and its low rotation (6r/min) viscosity and high rotation (60r/min) viscosity were measured. The calculation formula of the thixotropic index is: Thixotropic index (DI) = low rotation viscosity / high rotation viscosity.

Appearance effect evaluation: 0 is "excellent", 1 is "qualified", and the larger the number is, the worse it is. 0-smooth and delicate; 1-not delicate enough; 2-slightly orange peel; 3-rough paint film with many pits; 4-obvious orange peel, paint film sagging, dark.

Construction performance: 0 is "excellent", 1 is "qualified", and the larger the number is, the worse it is. 0-the paint film is smooth and flat, without sagging; 1-slight orange peel; 2-slight sagging; 3-slight orange peel and slight sagging; 4-fly ash, particles, poor fluidity; 5-severe orange peel and severe sagging.

Cross-cut test: 0 means "excellent", 1 means "qualified", and the larger the number is, the worse it is. 0-The substrate is not polished, and the adhesion is excellent; the rest is based on the cross-cut test standard GB/T9286-1998 "Cross-cut test for paint and varnish film".

Table 6 Performance test results of the construction coating provided by the comparative example

In summary, the water-based two-component polyurethane topcoat provided by the present invention, component A selects a hydroxyl-containing water-based dispersion and a high glass transition temperature water-based polycarbonate-containing aliphatic anionic polyurethane dispersion for compounding as a film-forming resin, and a low glass transition temperature water-based aliphatic anionic polyurethane dispersion is selectively added, and the characteristics of different types of water-based resins are brought into play to the best state through a specific ratio and the synergistic effect of each component, so that the final water-based two-component polyurethane topcoat has good thixotropy, and the paint film has excellent characteristics such as high gloss, high distinctness, high fullness and small orange peel, and no fly ash is produced when spraying on a large area, the gun is well mounted, the thixotropy is improved, and the flexibility and hardness of the cured film are balanced at the same time, and large-area construction can be carried out in high temperature, low temperature or high humidity environments. Through the synergistic effect of various raw material components and specific proportions and contents, the base intermediate paint does not need to be polished, and the water-based two-component polyurethane topcoat of the present invention can be directly sprayed. After the coating is completed, there is no need to cover with a clear varnish. The paint film has excellent gloss and image clarity, and can be comparable to the paint film appearance of a "solvent-based 1K base paint + clear varnish" coating system, and has high practical value and promotion value.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The aqueous double-component polyurethane finish paint is characterized by comprising a component A and a component B in a mass ratio of 2:1-6.5:1; wherein,

The component A comprises the following raw material components in percentage by mass: 40-45% of hydroxyl-containing aqueous dispersion, 5-20% of aqueous polycarbonate-containing aliphatic anion polyurethane dispersion with a glass transition temperature of 40-50 ℃, 0-20% of aqueous aliphatic anion polyurethane dispersion with a glass transition temperature of less than or equal to 5 ℃, 0.2-1% of first surfactant, 0.2-1% of first defoamer, 0.2-1% of substrate wetting agent, 0.1-1% of leveling agent, 0.1-1% of aqueous ultraviolet absorbent, 15-45% of aqueous color paste, 3-6% of first cosolvent, 1-3% of neutralizing agent, 0.2-0.5% of thickener and 5-10% of water;

the hydroxyl content of the hydroxyl-containing aqueous dispersion is 3.5-5%, and the solid content of the hydroxyl-containing aqueous dispersion is 35-50%; the water-based color paste comprises water, a dispersing agent, a second defoaming agent, a second surfactant, pigment, a color paste stabilizer and a neutralizer;

The component B comprises the following raw material components in percentage by mass: 70-80% of curing agent and 20-30% of second cosolvent; the curing agent is at least one of hexamethylene diisocyanate or hydrophilic aliphatic polyisocyanate.

2. The aqueous two-component polyurethane topcoat as set forth in claim 1 wherein the hydroxyl-containing aqueous dispersion has a viscosity of from 100 mPa-s to 3000 mPa-s;

the solid content of the aqueous polyurethane dispersion containing polycarbonate and aliphatic anions with the glass transition temperature of 40-50 ℃ and the solid content of the aqueous polyurethane dispersion containing aliphatic anions with the glass transition temperature of less than or equal to 5 ℃ are 33-40 percent.

3. The aqueous two-component polyurethane topcoat as set forth in claim 1 wherein the hydroxyl-containing aqueous dispersion is at least one of Bayhydrol a 2470, bayhydrol a 2770 or Bayhydrol U XP 2766;

The aqueous polyurethane dispersion containing polycarbonate aliphatic anions with the glass transition temperature of 40-50 ℃ is kesi chuang Bayhydol UH 2606;

The aqueous aliphatic anionic polyurethane dispersion with the glass transition temperature less than or equal to 5 ℃ is at least one of Colorado Bayhydrol UH 2648/1, colorado Bayhydrol UH 2110, colorado Bayhydrol UH 2621 or Colorado Bayhydrol UH 2952/1.

4. The aqueous two-component polyurethane finish according to claim 1, wherein the aqueous color paste comprises, based on 100% of the component A, 5% -10% of water, 0.8% -1.4% of a dispersing agent, 0.2% -0.5% of a second defoaming agent, 0.2% -1% of a second surfactant, 5% -13% of an organic pigment, 0.9% -4.5% of a color paste stabilizer and 0.1% -0.3% of a neutralizing agent; or (b)

Based on 100% of the component A, the aqueous color paste comprises 7% -12% of water, 1.2% -1.8% of dispersing agent, 0.2% -0.5% of second defoaming agent, 0.2% -0.5% of second surfactant, 15% -25% of inorganic pigment, 1.5% -5.4% of color paste stabilizer and 0.1% -0.3% of neutralizer.

5. The aqueous two-component polyurethane topcoat as set forth in claim 1 wherein said curing agent comprises, based on 100% of said B component, 25% to 30% of a low viscosity hydrophobic hexamethylene diisocyanate, 25% to 30% of a high viscosity hydrophilic hexamethylene diisocyanate and 18% to 22% of a hydrophilic modified isophorone diisocyanate; wherein,

The solid content of the hydrophilic aliphatic polyisocyanate is 60% -70%, and the-NCO content of the hydrophilic aliphatic polyisocyanate is 8.5% -12%.

6. The aqueous two-component polyurethane topcoat as set forth in claim 5 wherein the low viscosity hydrophobic hexamethylene diisocyanate is at least one of cosmeceutical Desmodur N3900, cosmeceutical Desmodur N3600, or vancomic WANNATE HT-600;

The high-viscosity hydrophilic hexamethylene diisocyanate is at least one of kestose Bayhydrol XP 2655, kestose Bayhydur XP 2547, kestose Bayhydur XP 2487/1, kestose Bayhydur 304 or kestose Bayhydur 305;

the hydrophilic aliphatic polyisocyanate is at least one of Colorgeable Bayhydur 401-70 or Colorgeable Bayhydur 401-60.

7. The aqueous two-component polyurethane topcoat of any one of claims 1 to 6 wherein the first co-solvent comprises at least 3 of propylene glycol methyl ether propionate, propylene glycol butyl ether, dipropylene glycol dimethyl ether, ethylene glycol butyl ether, dipropylene glycol methyl ether, dimethyl sulfoxide, N-methylpyrrolidone, dipropylene glycol butyl ether, or diethylene glycol monobutyl ether;

the second cosolvent is at least 2 of propylene glycol methyl ether acetate, propylene glycol methyl ether acrylate, propylene glycol diacetate, ethylene glycol butyl ether acetate, dipropylene glycol dimethyl ether, propylene carbonate or dibasic ester;

the dispersing agent is at least one of nonionic wetting dispersing agent or anionic wetting dispersing agent;

the second surfactant is at least one of an acetylenic diol surfactant or an alcohol alkoxy compound;

The color paste stabilizer comprises at least 3 of water-type fumed silica, a modified urea rheological aid, a resin-free color paste humectant or an anti-drying agent for water-based pigment concentrated paste;

The neutralizer is an 8-12 wt% dimethyl ethanolamine aqueous solution;

The first surfactant is a gemini alkyne diol surfactant;

the substrate wetting agent is a polyether modified organosilicon surfactant;

The water-based ultraviolet absorbent is at least one of Pasteur Tinuvin 5151, medium-high-frequency chemical UV-DL2, immortalized chemical EVERSORB AQ, immortalized chemical EVERSORB AQ or immortalized chemical EVERSORB AQ;

The thickener is polyurethane associative thickener.

8. Use of the aqueous two-component polyurethane top-coat as claimed in any one of claims 1 to 7 in automotive coatings.

9. The method of using the aqueous two-component polyurethane topcoat as set forth in any one of claims 1 to 7, comprising the steps of:

uniformly mixing the component A and the component B, adding an activating diluent, uniformly mixing to obtain a construction paint, and uniformly coating the construction paint on the water-based base paint;

The activating diluent comprises hydroxyl-containing aqueous dispersion, aqueous polycarbonate-containing aliphatic anion polyurethane dispersion with a glass transition temperature of 40-50 ℃, aqueous aliphatic anion polyurethane dispersion with a glass transition temperature of less than or equal to 5 ℃, water-based synthetic sheet silicate solution, water-based modified urea solution, first cosolvent, stabilizer, first defoamer, leveling agent and water.

10. The method of using a waterborne two-component polyurethane topcoat as set forth in claim 9, wherein the activating diluent comprises the following raw material components in mass percent: 8 to 11.5 percent of hydroxyl-containing aqueous dispersion, 3 to 4.5 percent of aqueous polycarbonate-containing aliphatic anion polyurethane dispersion with the glass transition temperature of 40 to 50 ℃,3 to 4.5 percent of aqueous aliphatic anion polyurethane dispersion with the glass transition temperature of less than or equal to 5 ℃,25 to 33.5 percent of water-based synthetic sheet silicate solution, 0.5 to 0.7 percent of water-based modified urea solution, 7.5 to 8.5 percent of first cosolvent, 7.5 to 8.5 percent of stabilizer, 0.5 to 0.7 percent of first defoamer, 0.5 to 0.7 percent of flatting agent and 27 to 42 percent of water, and the sum of the components is 100 percent;

The mass ratio of the component A to the activating diluent is 100: (20-30);

The water-based synthetic sheet silicate solution comprises the following raw material components in percentage by mass: 1.5 to 2.5 percent of organic matter modified synthetic phyllosilicate, 1.5 to 2.5 percent of emulsifying dispersant and 95 to 97 percent of water, wherein the sum of the components is 100 percent;

The water-based modified urea solution is at least one of Pick RHEOBYK-7420CA, pick RHEOBYK-7420ET or Pick RHEOBYK-7420 ES.