Polyurethane finish paint and preparation method thereof

Abstract

The invention discloses a polyurethane finish paint and a preparation method thereof, and belongs to the technical field of polyurethane finish paints.The polyurethane finish paint comprises a component A and a component B according to the mass ratio of 5-20: 1; the component A is prepared from the following components in parts by weight: 40 to 50 parts of hydroxyl acrylic acid dispersion, 8 to 15 parts of polyaspartic acid ester resin, 0.5 to 2 parts of defoaming agent, 1 to 3 parts of dispersing agent, 1 to 3 parts of rheological additive, 10 to 15 parts of pigment, 10 to 15 parts of filler and 15 to 20 parts of first solvent; the component B comprises 70-90 parts of an aliphatic isocyanate curing agent and 10-30 parts of a second solvent; the preparation method comprises the following steps: firstly treating a component A: firstly dispersing a first solvent, a hydroxy acrylic acid dispersion and polyaspartic acid ester resin, then dispersing a dispersing agent and a defoaming agent, then dispersing a pigment and a filler, and then adjusting the viscosity; the curing agent and the second solvent are dispersed, finally, the component A and the component B are mixed, and the ultra-fast-drying polyurethane finish paint is obtained.Compared with the prior art, the finish paint obtained through the method has the advantages that the drying speed is increased, the hardness and the corrosion resistance are improved, the adhesive force is enhanced, and the adaptation period is prolonged.

Description

Technical Field

[0001] The invention belongs to the field of polyurethane topcoat, and in particular relates to a polyurethane topcoat and a preparation method thereof. Background Art

[0002] Polyurethane topcoats are suitable for exterior coatings on construction machinery, effectively protecting against UV rays, rain, and mechanical wear, enhancing the durability and aesthetics of the equipment. However, conventional polyurethane topcoats are prone to brittle cracking in cold and humid environments, and their surface and through-drying times are significantly prolonged. During application in these conditions, slow drying can lead to blistering and decreased adhesion, severely impacting the coating's protective properties. Furthermore, the highly reactive isocyanates in the coating system not only rapidly crosslink with the hydroxyl groups in the film-forming substances but also react with ambient moisture to form urea polymers and release CO2. This can lead to pinholes and an orange peel effect in the paint film, affecting its appearance. Furthermore, the viscosity of the paint increases dramatically after mixing, significantly shortening its pot life. Existing technologies, to accelerate drying, often add organotin catalysts or alcohol chain extenders. These can easily cause blistering, false drying, internal stress concentration, and cracking, compromising the overall performance and service life of the paint film. Summary of the Invention

[0003] In response to the shortcomings of existing polyurethane topcoats in terms of drying speed, pot life, and paint film performance, the present invention aims to develop a new polyurethane topcoat that can ensure rapid drying while improving the gloss, adhesion, impact resistance, and corrosion resistance of the paint film, ensuring a reasonable pot life, and meeting the requirements for the use of construction machinery in complex environments. The specific features are as follows: A polyurethane topcoat, comprising component A and component B, wherein the mass ratio of component A to component B is 5-20:1; component A comprises, calculated by weight, 40-50 parts of a hydroxylated acrylic dispersion, 8-15 parts of a polyaspartic acid ester resin, 0.5-2 parts of a defoamer, 1-3 parts of a dispersant, 1-3 parts of a rheological additive, 10-15 parts of a pigment, 10-15 parts of a filler, and 15-20 parts of a first solvent; The B component includes, calculated by weight, 70-90 parts of an aliphatic isocyanate curing agent and 10-30 parts of a second solvent; the hydroxylated acrylic dispersion is selected from one or more of BS-965 and BS-960; the polyaspartic acid resin is selected from one or more of Desmophen® NH 1520, Desmophen® NH 1420, or Zhuhai Feiyang Chemical F421; the hydroxylated acrylic dispersion has a solid content of 59-66%, a hydroxyl value of 51-56 mg KOH / g, and an amino equivalent weight of the polyaspartic acid resin of 270-290 g / mol.

[0004] As a preferred embodiment, the defoaming agent is a compound of a non-silicone polymer and dodecylglycerol itaconate; the weight ratio of the non-silicone polymer to dodecylglycerol itaconate is 3:1~2; the non-silicone polymer is one or more of EFKA 2020, YCK-655, and BYK-011.

[0005] As a preferred embodiment, the dispersant is a compound of a polyurethane dispersant and a dithiane organosulfur compound; the weight ratio of the polyurethane dispersant to the dithiane organosulfur compound is 3 to 5:1; the polyurethane dispersant is selected from Efka PU4061 and / or KEPERDISP®-639, and the dithiane organosulfur compound is selected from 2,5-dimethyl-2,5-dihydroxy-1,4-dithiane and / or 2,5-dimethylmercapto-1,4-dithiane.

[0006] As a preferred embodiment, the rheological additive is a compound of polyamide wax and oleic acid metal soap; the weight ratio of the polyamide wax to the oleic acid metal soap is 5 to 10:1; the polyamide wax is selected from one or more of THIXATROL® PM 8056, THIXATROL MAX, and BYK 440 RC-820, and the oleic acid metal soap is selected from one or more of zinc oleate, magnesium oleate, and calcium oleate.

[0007] As a preferred embodiment, the aliphatic isocyanate curing agent is selected from one or more of Desmodur® N75 MPA / X, Hafotex® SH-2836, Desmodur® N75 BA, and Hafotex® SH-3592.

[0008] As a preferred embodiment, the pigment is selected from one or more of rutile titanium dioxide, red iron oxide, carbon black, phthalocyanine blue, and phthalocyanine green; and the filler is selected from one or more of nano zinc oxide, mica powder, talc, kaolin, and bentonite.

[0009] As a preferred embodiment, the first solvent and the second solvent are both volatile organic solvents, and the first solvent and the second solvent are respectively selected from one or more of n-butanol, isobutanol, xylene, butyl acetate, ethylene glycol diacetate, and 1,2-propylene glycol.

[0010] As a preferred embodiment, the polyaspartic acid ester resin is selected from one or more of Desmophen® NH 1520, Desmophen® NH 1420 or Zhuhai Feiyang Chemical F421.

[0011] A method for preparing a polyurethane topcoat comprises the following steps: S1: First, the first solvent, hydroxylated acrylic acid dispersion, and polyaspartic acid ester resin are sequentially added into a dispersion kettle and dispersed for 10 to 30 minutes; S2: Add the dispersant and defoamer into the dispersion kettle in sequence and disperse for 10 to 30 minutes; S3: Add the rheological additive into the dispersion kettle and disperse for 10 to 30 minutes; S4: Add pigment and filler into the dispersion kettle in sequence, disperse for 30-60 minutes, and grind to a fineness of ≤40μm in a grinder; S5: Using the first solvent again to adjust the viscosity to 90-100 KU, and filtering to obtain component A; S6: Then, the aliphatic isocyanate curing agent and the second solvent are sequentially added to the dispersion kettle, stirred evenly, and dispersed for 15 to 30 minutes to obtain component B; S7: Finally, add component B to component A and mix evenly to obtain the polyurethane topcoat.

[0012] As a preferred embodiment, the dispersant in step S2 is a mixture obtained by dispersing a polyurethane dispersant and a dithiane organic sulfur compound in a weight ratio of 3 to 5:1 for 10 to 20 minutes; the defoaming agent in step S2 is a mixture obtained by dispersing a non-silicone polymer and dodecylglycerol itaconate in a weight ratio of 3:1 to 2 for 10 to 20 minutes; and the rheological additive in step S3 is a mixture obtained by dispersing polyamide wax and oleic acid metal soap in a weight ratio of 5 to 10:1 for 10 to 20 minutes.

[0013] Compared with the prior art, the present invention has the following advantages: 1. By using a compound of a non-silicone polymer and dodecylglycerol itaconate as a defoamer, the defoaming and anti-foaming effects are enhanced by disrupting the stability of the bubble film, the associative network formed during the film-forming process, and the microporous channels. This avoids the "stuffy bubbles" caused by rapid surface drying, as well as poor corrosion resistance and stability. Dodecylglycerol itaconate can wrap around the aliphatic isocyanate curing agent molecules, acting as a barrier, hindering direct contact between the isocyanate groups of the aliphatic isocyanate curing agent and the hydroxyl groups in the film-forming substance. At the same time, dodecylglycerol itaconate can undergo controlled, low-speed crosslinking with the aliphatic isocyanate curing agent. These two effects work synergistically to significantly reduce the curing reaction rate between the isocyanate groups and the film-forming substance, thereby extending the pot life of the coating. After the paint is applied, the solvent in the wet film gradually evaporates, and dodecylglycerol itaconate migrates to the surface of the paint film due to the repulsion between the hydrophilic group and the internal hydrophobic environment. The barrier that originally wrapped the aliphatic isocyanate curing agent was broken, releasing the "shielded" isocyanate group, which indirectly improves the contact efficiency between the isocyanate group and the film-forming substance, effectively improving the drying speed of the polyurethane coating in a low-temperature and high-humidity environment, and forming a hydrophobic layer on the coating surface through the hydrophobic group of dodecylglycerol itaconate, thereby improving the water resistance and corrosion resistance of the paint film. Due to its hydrophobicity, it reduces the penetration of moisture in the paint film in a humid environment, reduces the side reaction of isocyanate and water to generate CO2 from the source, inhibits the generation of bubbles, reduces the interference of moisture on the coating curing process, and significantly improves defects such as pinholes and orange peel in the paint film. In addition, dodecylglycerol itaconate is embedded in the curing network through intermolecular interaction to form elastic buffer points, which disperses the internal stress generated by the rapid cross-linking of the film-forming substance and the aliphatic isocyanate curing agent, improves the impact resistance of the paint film, and effectively solves the problem of brittle cracking of traditional polyurethane paint films at low temperatures; at the same time, when non-silicone polymers are compounded with dodecylglycerol itaconate, the wetting properties of pigments and fillers can be improved, thereby improving the gloss of the paint film.

[0014] 2. The present invention introduces a dithiane organic sulfur compound and a polyurethane dispersant as a dispersant, which not only improves the dispersion stability of pigments and fillers but also improves the uniformity of stress distribution on the surface of the paint film through the combined effect of surface adsorption and steric hindrance; and through the multi-scale interface reinforcement formed by the dithiane organic sulfur compound and the polar substances in the substrate to form coordination bonds or hydrogen bond bridges and cross-linked network anchoring, the adhesion of the paint film is improved, so that the coating still maintains a high adhesion after aging in a low-temperature and humid environment; at the same time, in a humid environment, the active groups (such as hydroxyl groups) released by the dithiane organic sulfur compound After the coordination of the hydroxy acrylic dispersion (or mercapto group) with the aliphatic isocyanate curing agent, the reaction activation energy is reduced, the curing speed of the hydroxy acrylic dispersion and the aliphatic isocyanate curing agent is accelerated, thereby improving the drying speed of the paint film in a low-temperature and high-humidity environment, avoiding blistering caused by moisture retention and decreased adhesion caused by incomplete curing; the slow-release catalysis of the dithiane organic sulfur compound and the steric hindrance of the polyurethane dispersant work together to achieve gradient curing of the paint film, achieving a balance between construction and low-temperature fast drying, avoiding both "bubbling" caused by rapid surface sealing and the "false drying" problem, and improving the mechanical properties and corrosion resistance of the paint film. DETAILED DESCRIPTION

[0015] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0016] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0017] The present invention provides a polyurethane topcoat, comprising a component A and a component B, wherein the mass ratio of the component A to the component B is 5 to 20:1; The component A comprises, by weight, 40-50 parts of hydroxy acrylic dispersion, 8-15 parts of polyaspartic acid resin, 0.5-2 parts of defoamer, 1-3 parts of dispersant, 1-3 parts of rheological additive, 10-15 parts of pigment, 10-15 parts of filler, and 15-20 parts of the first solvent; The B component includes, by weight, 70 to 90 parts of an aliphatic isocyanate curing agent and 10 to 30 parts of a second solvent. The defoaming agent is a compound of a non-silicone polymer and lauryl glycerol itaconate.

[0018] In the present invention, the hydroxyl value of the hydroxylated acrylic dispersion has a significant impact on its reactivity with the aliphatic isocyanate curing agent. A higher hydroxyl value means that there are more active sites for cross-linking reactions with the curing agent, increasing the crosslinking density of the paint film, thereby enhancing the hardness and wear resistance of the coating, but at the same time also reducing the flexibility of the coating. To ensure the hardness and flexibility of the coating, the hydroxylated acrylic dispersion used in the present invention has a hydroxyl value of 51-56 mg KOH / g. A hydroxylated acrylic dispersion with a higher solid content can form a thicker coating under the same construction conditions, thereby reducing solvent volatilization and improving the chemical resistance of the coating. However, a hydroxylated acrylic dispersion with too high a solid content will reduce the overall flexibility of the paint film and cause the paint film to crack when the substrate deforms. To ensure the chemical resistance and flexibility of the paint film, the hydroxylated acrylic dispersion used in the present invention has a solid content of 59-66%, and the hydroxylated acrylic dispersion is selected from BS-965 and / or BS-960.

[0019] In the present invention, the amino equivalent of the polyaspartic acid ester resin has a significant effect on its reactivity with the aliphatic isocyanate curing agent and the coating performance: the lower the amino equivalent, the more active hydrogen contained in the resin, the higher the reactivity with the aliphatic isocyanate curing agent, and the faster the curing speed. However, too high a reactivity will shorten the pot life of the coating and reduce the convenience of construction operation; the higher the amino equivalent, the less active hydrogen contained in the resin, the lower the reactivity, the slower the curing speed, and thus prolong the construction time, but this may also lead to slower development of the hardness and wear resistance of the coating. In order to ensure the curing speed, pot life and coating performance of the coating, the amino equivalent of the polyaspartic acid ester resin is 270-290 g / mol, and the polyaspartic acid ester resin is selected from one or more of Desmophen® NH 1520, Desmophen® NH 1420, and Zhuhai Feiyang Chemical F421; the aliphatic isocyanate curing agent is selected from Desmodur® N75 MPA / X, Hafotex® One or more of SH-2836, Desmodur® N75 BA, and Hafotex® SH-3592.

[0020] After compounding the polyaspartic acid ester resin and hydroxy acrylic acid dispersion in the present invention, low-temperature curing is achieved. However, rapid surface drying will hinder the volatilization of the solvent inside the coating, resulting in "bubbling" or internal stress concentration, thereby affecting the mechanical strength. In addition, rapid curing will also lead to incomplete cross-linking reaction of the coating. Especially in solvent-based systems, residual solvent or incompletely reacted groups will also reduce chemical corrosion resistance and long-term stability.

[0021] During the application process such as brushing or spraying, or during the film-forming process, gases such as air and CO2 can mix into the coating system, causing bulges on the coating surface. After the paint film dries, pinholes and orange peel phenomena will form on the paint film surface, thus affecting the appearance of the paint film. The present invention has found that by compounding a non-silicone polymer with dodecylglycerol itaconate, the compound will adsorb at the gas-liquid interface, thereby reducing the stability of bubbles. In addition, during the film-forming process, the intermolecular forces of dodecylglycerol itaconate and the micro-void channels formed by its arrangement provide a path for gas escape. This mechanism not only inhibits foam regeneration but also achieves rapid degassing, effectively solving the problems of "stuffy bubbles" caused by rapid surface drying, as well as poor corrosion resistance and stability. Dodecylglycerol itaconate can wrap around the aliphatic isocyanate curing agent molecules, playing a barrier role, hindering the isocyanate group of the aliphatic isocyanate curing agent from directly contacting the hydroxyl group in the film-forming substance. At the same time, dodecylglycerol itaconate can undergo controllable low-speed cross-linking with the aliphatic isocyanate curing agent. The two effects work synergistically to significantly reduce the curing reaction rate between the isocyanate group and the film-forming substance, thereby extending the application life of the coating. After the paint is applied, the solvent in the wet film gradually evaporates, and dodecylglycerol itaconate migrates to the surface of the paint film due to the repulsion between the hydrophilic group and the internal hydrophobic environment. The barrier that originally wrapped the aliphatic isocyanate curing agent was broken, releasing the "shielded" isocyanate group, which indirectly improves the contact efficiency between the isocyanate group and the film-forming substance, effectively improving the drying speed of the polyurethane coating in a low-temperature and high-humidity environment, and forming a hydrophobic layer on the coating surface through the hydrophobic group of dodecylglycerol itaconate, thereby improving the water resistance and corrosion resistance of the paint film. Due to its hydrophobicity, it reduces the penetration of moisture in the paint film in a humid environment, reduces the side reaction of isocyanate and water to generate CO2 from the source, inhibits the generation of bubbles, reduces the interference of moisture on the coating curing process, and significantly improves defects such as pinholes and orange peel in the paint film. In addition, dodecylglycerol itaconate is embedded in the curing network through intermolecular interaction to form elastic buffer points, which disperses the internal stress generated by the rapid cross-linking of the film-forming substance and the aliphatic isocyanate curing agent, improves the impact resistance of the paint film, and effectively solves the problem of brittle cracking of traditional polyurethane paint films at low temperatures; at the same time, when non-silicone polymers are compounded with dodecylglycerol itaconate, the wetting properties of pigments and fillers can be improved, thereby improving the gloss of the paint film.

[0022] In the topcoat system of the present invention, the pigment is selected from one or more of rutile titanium dioxide, red iron oxide, carbon black, phthalocyanine blue, and phthalocyanine green; the filler is selected from one or more of nano zinc oxide, mica powder, talc, kaolin, and bentonite.

[0023] In order to ensure the low-temperature curing performance of the topcoat produced by crosslinking the hydroxyl acrylic resin with polyaspartic acid ester and aliphatic isocyanate curing agent, while solving the problem of too fast curing speed resulting from the composite of the two, which makes it difficult for the solvent in the coating to volatilize, and to avoid the curing speed of the entire paint film being too low due to the low-speed crosslinking between dodecylglycerol itaconate and the aliphatic isocyanate curing agent, the weight ratio of the non-silicone polymer to dodecylglycerol itaconate is controlled to be 3:1-2. The non-silicone polymer is selected from one or more of EFKA 2020, YCK-655, and BYK-011. Dodecylglycerol itaconate is mainly polymerized by polyol, itaconic anhydride, and glycidol or a glycidol derivative.

[0024] In the topcoat system of the present invention, the dispersant is a compound of a polyurethane dispersant and a dithiane organic sulfur compound. Studies have found that the introduction of a dithiane organic sulfur compound and a polyurethane dispersant in combination not only comprehensively improves the dispersion stability of pigments and fillers through surface adsorption and steric hindrance effects, but also improves the uniformity of the distribution of surface stress of the paint film. In addition, the dithiane organic sulfur compound forms coordination bonds or hydrogen bond bridges with polar substances in the substrate and cross-linked network anchoring to form multi-scale interface reinforcement, thereby improving the adhesion of the paint film to the substrate, so that the coating maintains a high adhesion after aging in a low-temperature and humid environment. The study also found that in a humid environment, the active groups released by the dithiane organic sulfur compound can act as a catalyst to accelerate the curing speed of the hydroxyl acrylic dispersion and the aliphatic isocyanate curing agent, further improving the drying speed of the paint film in a low-temperature and high-humidity environment, and avoiding blistering caused by water retention and a decrease in adhesion caused by incomplete curing. The slow-release catalysis of dithiane organic sulfur compounds and the steric hindrance of polyurethane dispersants work together to achieve gradient curing of the paint film, achieving a balance between construction and low-temperature quick drying. It not only avoids the "bubbling" caused by rapid surface sealing, but also avoids the "false drying" problem, and also improves the mechanical properties and corrosion resistance of the paint film.

[0025] In order to strike a balance between construction properties such as anti-sagging, drying time, and leveling and low-temperature quick-drying performance, while improving the dispersion stability of pigments and fillers as well as the adhesion and corrosion resistance of the paint film, the weight ratio of the polyurethane dispersant to the dithiane organic sulfur compound is 3 to 5:1. The polyurethane dispersant is selected from Efka PU4061 and / or KEPERDISP®-639, and the dithiane organic sulfur compound is selected from 2,5-dimethyl-2,5-dihydroxy-1,4-dithiane and / or 2,5-dimethylmercapto-1,4-dithiane.

[0026] In the present invention, the rheological modifier is a combination of polyamide wax and oleic acid metal soap. The polyamide wax swells in the solvent and forms a network structure between its molecules. The carboxylate groups of the oleic acid metal soap adsorb on the pigment surface, forming a negatively charged layer on the pigment surface. Through the dual mechanisms of "charge stabilization + network locking," this not only prevents pigment and filler agglomeration and sedimentation, but also improves the coating's storage stability and anti-sagging properties and coating gloss. By forming a dense protective layer and inhibiting corrosion of the pigment and filler, the coating's hardness, wear resistance, and corrosion resistance are enhanced. The weight ratio of the polyamide wax to the oleic acid metal soap is 5 to 10:1. The polyamide wax is selected from one or more of THIXATROL® PM8056, THIXATROL MAX, and BYK 440 RC-820, and the oleic acid metal soap is selected from one or more of zinc oleate, magnesium oleate, and calcium oleate.

[0027] In the present invention, the first solvent and the second solvent are volatile organic solvents, and the first solvent and the second solvent are respectively selected from one or more of n-butanol, isobutanol, xylene, butyl acetate, ethylene glycol diacetate, and 1,2-propylene glycol.

[0028] A method for preparing a polyurethane topcoat comprises the following steps: S1: First, the first solvent, hydroxylated acrylic acid dispersion, and polyaspartic acid ester resin are sequentially added into a dispersion kettle and dispersed for 10 to 30 minutes; S2: Add the dispersant and defoamer into the dispersion kettle in sequence and disperse for 10 to 30 minutes; S3: Add the rheological additive into the dispersion kettle and disperse for 10 to 30 minutes; S4: Add pigment and filler into the dispersion kettle in sequence, disperse for 30-60 minutes, and grind to a fineness of ≤40μm in a grinder; S5: Using the first solvent again to adjust the viscosity to 90-100 KU, and filtering to obtain component A; S6: Then, the aliphatic isocyanate curing agent and the second solvent are sequentially added to the dispersion kettle, stirred evenly, and dispersed for 15 to 30 minutes to obtain component B; S7: Finally, add component B to component A and mix evenly to obtain the polyurethane topcoat.

[0029] The dispersant in step S2 is a mixture obtained by dispersing a polyurethane dispersant and a dithiane organic sulfur compound in a weight ratio of 3 to 5:1 for 10 to 20 minutes.

[0030] The defoaming agent in step S2 is a mixture obtained by dispersing a non-silicone polymer and lauryl glycerol itaconate in a weight ratio of 3:1-2 for 10-20 minutes.

[0031] In step S3, the rheological additive is a mixture obtained by dispersing polyamide wax and oleic acid metal soap in a weight ratio of 5 to 10:1 for 10 to 20 minutes. Example 1

[0032] This embodiment provides a polyurethane topcoat, which includes component A and component B, wherein the mass ratio of component A to component B is 5:1; The component A includes, by weight, 40 parts of hydroxy acrylic dispersion, 8 parts of polyaspartic acid ester resin, 0.5 parts of defoamer, 1 part of dispersant, 1 part of rheological additive, 10 parts of pigment, 10 parts of filler, and 15 parts of the first solvent; The B component includes, calculated by weight, 70 parts of an aliphatic isocyanate curing agent and 10 parts of a second solvent.

[0033] A preparation method of polyurethane topcoat: Step 1: Place 12 parts of n-butanol (the first solvent), 40 parts of BS-965 (a hydroxylated acrylic acid dispersion), and 8 parts of Desmophen® NH 1520 (a polyaspartic acid resin) into a dispersion kettle and disperse for 10 minutes. Step 2: A mixture of 0.75 parts of Efka PU4061 (polyurethane dispersant) and 0.25 parts of 2,5-dimethyl-2,5-dihydroxy-1,4-dithiane (dithiane organic sulfur compound) dispersed for 10 minutes and a mixture of 0.3 parts of EFKA 2020 (non-silicone polymer) and 0.2 parts of dodecylglycerol itaconate dispersed for 10 minutes were added to the dispersion kettle in sequence and dispersed for 10 minutes. Step 3: Add the mixture of 0.9 parts of THIXATROL® PM 8056 (polyamide wax) and 0.1 parts of zinc oleate (oleic acid metal soap) dispersed for 10 minutes into a dispersion kettle and disperse for 10 minutes; Step 4: Put 10 parts of rutile titanium dioxide (pigment) and 10 parts of mica powder (filler) into the dispersion kettle in sequence, disperse at high speed for 30 minutes, and then grind them into a grinder to a fineness of ≤40μm; Step 5: Use 3 parts of n-butanol (first solvent) to adjust the viscosity to 90 KU, and obtain component A after filtration; Step 6: Add 70 parts of Desmodur® N75 MPA / X (aliphatic isocyanate curing agent) and 10 parts of isobutanol (second solvent) into a dispersion kettle, stir evenly, and disperse for 15 minutes to obtain component B. Step 7: Add component B to component A, with the mass ratio of component A to component B being 5:1, and mix well to obtain the polyurethane topcoat. Example 2

[0034] This embodiment provides a polyurethane topcoat, which includes component A and component B, wherein the mass ratio of component A to component B is 10:1; The component A includes, by weight, 45 parts of hydroxy acrylic dispersion, 10 parts of polyaspartic acid ester resin, 1.3 parts of defoamer, 2 parts of dispersant, 1.1 parts of rheological additive, 12 parts of pigment, 12 parts of filler, and 16 parts of the first solvent; The B component includes, calculated by weight, 80 parts of an aliphatic isocyanate curing agent and 20 parts of a second solvent.

[0035] A preparation method of polyurethane topcoat: Step 1: Place 14 parts xylene (first solvent), 45 parts BS-960 (hydroxylated acrylic acid dispersion), and 10 parts Desmophen® NH 1420 (polyaspartic acid resin) into a dispersion kettle in sequence and disperse for 30 minutes. Step 2: A mixture of 1.6 parts of KEPERDISP®-639 (polyurethane dispersant) and 0.4 parts of 2,5-dimethylmercapto-1,4-dithiane (dithiane organic sulfur compound) dispersed for 20 minutes, and a mixture of 0.8 parts of YCK-655 (non-silicone polymer) and 0.5 parts of dodecylglycerol itaconate dispersed for 20 minutes were added to a dispersion kettle in sequence and dispersed for 30 minutes. Step 3: Disperse 0.5 parts of THIXATROL MAX (polyamide wax), 0.5 parts of RC-820 (polyamide wax), and 0.1 parts of magnesium oleate (oleic acid metal soap) for 10 minutes, then add the mixture to a dispersion kettle and disperse for 30 minutes. Step 4: Add 6 parts of iron oxide red (pigment), 6 parts of phthalocyanine blue (pigment), and 12 parts of nano zinc oxide (filler) into the dispersion kettle in sequence, disperse for 60 minutes, and grind in a grinder to a fineness of ≤40μm; Step 5: Use 2 parts of xylene (first solvent) to adjust the viscosity to 100 KU, and obtain component A after filtration; Step 6: Add 80 parts of Hafotex® SH-2836 (aliphatic isocyanate curing agent) and 20 parts of xylene (second solvent) into the dispersion kettle, stir evenly, and disperse for 30 minutes to obtain component B; Step 7: Add component B to component A, with the mass ratio of component A to component B being 10:1, and mix well to obtain the polyurethane topcoat. Example 3

[0036] The present invention provides a polyurethane topcoat, comprising a component A and a component B, wherein the mass ratio of the component A to the component B is 20:1; The component A comprises, by weight, 50 parts of hydroxy acrylic dispersion, 15 parts of polyaspartic acid ester resin, 2 parts of defoamer, 3 parts of dispersant, 3 parts of rheological additive, 15 parts of pigment, 15 parts of filler, and 20 parts of the first solvent; The B component includes, calculated by weight, 90 parts of an aliphatic isocyanate curing agent and 30 parts of a second solvent.

[0037] A preparation method of polyurethane topcoat: Step 1: Place 18 parts of ethylene glycol diacetate (the first solvent), 25 parts of BS-960 (a hydroxylated acrylic dispersion), 25 parts of BS-965 (a hydroxylated acrylic dispersion), 7 parts of Desmophen® NH 1520 (a polyaspartic acid resin), and 8 parts of Zhuhai Feiyang Chemical F421 (a polyaspartic acid resin) into a dispersion kettle in sequence and disperse for 30 minutes. Step 2: A mixture of 1.5 parts of Efka PU4061 (polyurethane dispersant), 1 part of KEPERDISP®-639 (polyurethane dispersant), 0.3 parts of 2,5-dimethyl-2,5-dihydroxy-1,4-dithiane (dithiane organic sulfur compound), and 0.2 parts of 2,5-dimethylmercapto-1,4-dithiane (dithiane organic sulfur compound) dispersed for 20 minutes, and a mixture of 0.5 parts of YCK-655 (non-silicone polymer), 1 part of BYK-011 (non-silicone polymer), and 0.5 parts of dodecylglycerol itaconate dispersed for 20 minutes were sequentially added into a dispersion kettle and dispersed for 30 minutes. Step 3: Add the mixture obtained by dispersing 2.5 parts of RC-820 and 0.5 parts of calcium oleate (oleic acid metal soap) for 10 minutes into a dispersion kettle and disperse for 30 minutes; Step 4: Put 15 parts of phthalocyanine green (pigment), 8 parts of talc powder (filler), and 7 parts of kaolin (filler) into the dispersion kettle in sequence, disperse for 60 minutes, and then grind in a grinder to a fineness of ≤40μm; Step 5: Use 2 parts of ethylene glycol diacetate (first solvent) to adjust the viscosity to 100 KU, and obtain component A after filtering; Step 6: Place 45 parts of Desmodur® N75 BA (aliphatic isocyanate curing agent), 45 parts of Hafotex® SH-3592 (aliphatic isocyanate curing agent), and 30 parts of 1,2-propylene glycol (second solvent) into a dispersion kettle, stir evenly, and disperse for 30 minutes to obtain component B. Step 7: Add component B to component A, with the mass ratio of component A to component B being 20:1, and mix well to obtain the polyurethane topcoat.

[0038] Comparative Example 1 The preparation method of this comparative example is the same as that of Example 1, except that an equal amount of non-silicone polymer EFKA 2020 is used to replace dodecylglycerol itaconate.

[0039] Comparative Example 2 The preparation method of this comparative example is the same as that of Example 1, except that an equal amount of polyurethane dispersant Efka PU 4061 is used to replace 2,5-dimethyl-2,5-dihydroxy-1,4-dithiane.

[0040] Comparative Example 3 The preparation method of this comparative example is the same as that of Example 1, except that an equal amount of polyamide wax THIXATROL® PM 8056 is used to replace zinc oleate.

[0041] Comparative Example 4 The preparation method of this comparative example is the same as that of Example 1, except that the weight ratio of the non-silicone polymer to laurylglycerol itaconate is 4:1.

[0042] Comparative Example 5 The preparation method of this comparative example is the same as that of Example 1, except that the hydroxylated acrylic dispersion BS-965 is replaced by an equal amount of BS-8170 having a solid content of 70% and a hydroxyl value of 70 mg KOH / g, the polyaspartic acid ester resin Desmophen® NH 1520 is replaced by an equal amount of polyaspartic acid ester resin F220 having an amino equivalent weight of 230 g / mol, the lauryl glycerol itaconate is replaced by an equal amount of the non-silicone polymer EFKA 2020, the 2,5-dimethyl-2,5-dihydroxy-1,4-dithiane is replaced by an equal amount of the polyurethane dispersant Efka PU 4061, and the zinc oleate is replaced by an equal amount of the polyamide wax THIXATROL® PM 8056.

[0043] The performance of the polyurethane topcoats prepared in Examples 1 to 3 and Comparative Examples 1 to 5 was tested (the product implementation standard was combined with "HG / T 2454-2014 Solvent-based Polyurethane Coatings (Two-Component)"). The test results are shown in Table 1: Table 1 Performance test indicators of coatings and performance test results of polyurethane topcoat

[0044] The test results in Table 1 show that the polyurethane topcoats obtained in Examples 1 to 3 all meet the technical requirements of Type II exterior topcoat Category 2 products in the standard "HG / T 2454-2014 Solvent-based polyurethane coatings (two-component)".

[0045] Compared with Comparative Example 1, Example 1 uses a non-silicone polymer compounded with dodecylglycerol itaconate, which improves the gloss of the paint film, accelerates the drying speed in a low-temperature and high-humidity environment, enhances the impact resistance, water resistance, and corrosion resistance of the paint film, reduces defects such as bubbles, pinholes, and orange peel in the paint film, and extends the applicability of the coating.

[0046] Compared with Comparative Example 2, Example 1 uses a specific ratio of polyurethane dispersant and dithiane organic sulfur compound to enhance the adhesion of the paint film and increase the drying speed of the paint film in a low-temperature and high-humidity environment, achieving a balance between construction and low-temperature fast drying, and significantly improving the corrosion resistance of the paint film.

[0047] Compared with Comparative Example 3, Example 1 not only improves the anti-sagging property of the coating, improves the glossiness of the coating, but also improves the hardness and corrosion resistance of the coating by using a specific ratio of polyamide wax and oleic acid metal soap.

[0048] Compared with Comparative Example 4, Example 1 controls the weight ratio of the non-silicone polymer to dodecylglycerol itaconate within the range of 3:1~2, which not only further improves the gloss of the paint film and accelerates the drying speed in a low-temperature and high-humidity environment, but also enhances the impact resistance, water resistance and corrosion resistance of the paint film, further reduces the occurrence of bubbles in the paint film, and at the same time extends the application period of the coating.

[0049] Compared with Comparative Example 5, Example 1 achieves the synergistic effect of multiple additives by compounding a non-silicone polymer with dodecylglycerol itaconate as a defoaming agent, a polyurethane dispersant with a dithiane organic sulfur compound as a dispersant, and a polyamide wax with oleic acid metal soap as a rheological additive, thereby obtaining a fast-drying polyurethane topcoat while effectively improving the corrosion resistance, adhesion and gloss of the paint film and extending the application period.

[0050] The foregoing description is intended only to provide specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the embodiments described herein, but rather to be construed in the broadest manner consistent with the principles and novel features disclosed herein.

Claims

1. A polyurethane topcoat, characterized in that: The invention comprises component A and component B, wherein the mass ratio of component A to component B is 5-20:1; component A comprises, calculated by weight, 40-50 parts of hydroxy acrylic dispersion, 8-15 parts of polyaspartic acid resin, 0.5-2 parts of defoamer, 1-3 parts of dispersant, 1-3 parts of rheological additive, 10-15 parts of pigment, 10-15 parts of filler, and 15-20 parts of first solvent; The B component includes, calculated by weight, 70-90 parts of an aliphatic isocyanate curing agent and 10-30 parts of a second solvent; the hydroxylated acrylic dispersion is selected from BS-965 and / or BS-960; the solid content of the hydroxylated acrylic dispersion is 59-66%, the hydroxyl value is 51-56 mg KOH / g, and the amino equivalent of the polyaspartic acid ester resin is 270-290 g / mol; the defoamer is a compound of a non-silicone polymer and dodecylglycerol itaconate.

2. A polyurethane topcoat according to claim 1, characterized in that, The weight ratio of the non-silicone polymer to dodecylglycerol itaconate is 3:1-2; the non-silicone polymer is selected from one or more of EFKA 2020, YCK-655, and BYK-011.

3. A polyurethane topcoat according to claim 1, characterized in that, The dispersant is a compound of a polyurethane dispersant and a dithiane organosulfur compound; the weight ratio of the polyurethane dispersant to the dithiane organosulfur compound is 3 to 5:1; the polyurethane dispersant is selected from Efka PU4061 and / or KEPERDISP®-639, and the dithiane organosulfur compound is selected from 2,5-dimethyl-2,5-dihydroxy-1,4-dithiane and / or 2,5-dimethylmercapto-1,4-dithiane.

4. A polyurethane topcoat according to claim 1, characterized in that, The rheological additive is a compound of polyamide wax and oleic acid metal soap; the weight ratio of the polyamide wax to the oleic acid metal soap is 5 to 10:1; the polyamide wax is selected from one or more of THIXATROL® PM 8056, THIXATROL MAX, and BYK 440 RC-820, and the oleic acid metal soap is selected from one or more of zinc oleate, magnesium oleate, and calcium oleate.

5. A polyurethane topcoat according to claim 1, characterized in that, The aliphatic isocyanate curing agent is selected from one or more of Desmodur® N75 MPA / X, Hafotex® SH-2836, Desmodur® N75 BA, and Hafotex® SH-3592.

6. A polyurethane topcoat according to claim 1, characterized in that: The pigment is selected from one or more of rutile titanium dioxide, red iron oxide, carbon black, phthalocyanine blue, and phthalocyanine green; and the filler is selected from one or more of nano zinc oxide, mica powder, talc, kaolin, and bentonite.

7. A polyurethane topcoat according to claim 1, characterized in that: The first solvent and the second solvent are both volatile organic solvents, and the first solvent and the second solvent are respectively selected from one or more of n-butanol, isobutanol, xylene, butyl acetate, ethylene glycol diacetate, and 1,2-propylene glycol.

8. A polyurethane topcoat according to claim 1, characterized in that, The polyaspartic acid ester resin is selected from one or more of Desmophen® NH 1520, Desmophen® NH 1420, and Zhuhai Feiyang Chemical F421.

9. A method for preparing a polyurethane topcoat according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1: First, the first solvent, hydroxylated acrylic acid dispersion, and polyaspartic acid ester resin are sequentially added into a dispersion kettle and dispersed for 10 to 30 minutes; S2: Add the dispersant and defoamer into the dispersion kettle in sequence and disperse for 10 to 30 minutes; S3: Add the rheological additive into the dispersion kettle and disperse for 10 to 30 minutes; S4: Add pigment and filler into the dispersion kettle in sequence, disperse for 30-60 minutes, and grind to a fineness of ≤40μm in a grinder; S5: Using the first solvent again to adjust the viscosity to 90-100 KU, and filtering to obtain component A; S6: Then, the aliphatic isocyanate curing agent and the second solvent are sequentially added to the dispersion kettle, stirred evenly, and dispersed for 15 to 30 minutes to obtain component B; S7: Finally, add component B to component A and mix evenly to obtain the polyurethane topcoat.

10. The method for preparing a polyurethane topcoat according to claim 9, wherein: The dispersant in step S2 is a mixture obtained by dispersing a polyurethane dispersant and a dithiane organic sulfur compound in a weight ratio of 3 to 5:1 for 10 to 20 minutes; the defoamer in step S2 is a mixture obtained by dispersing a non-silicone polymer and dodecylglycerol itaconate in a weight ratio of 3:1 to 2 for 10 to 20 minutes; the rheological additive in step S3 is a mixture obtained by dispersing polyamide wax and oleic acid metal soap in a weight ratio of 5 to 10:1 for 10 to 20 minutes.

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