Modified curing agent and preparation method thereof, and waterborne polyurethane coating

Abstract

The present application is applicable to the field of material technology, and provides a modified curing agent and its preparation method, waterborne polyurethane coating, including: 70-80 parts of waterborne isocyanate curing agent, 5-10 parts of silane prepolymer, 0.5-2 parts of dehydrating agent and 10-30 parts of cosolvent; wherein, the silane prepolymer is obtained by reacting the polyether polyol after dehydration with 3-isocyanate propyl triethoxysilane. The present application prepares the silane prepolymer by using a polyether polyol and 3-isocyanate propyl triethoxysilane with a specific functional group ratio, and then adds it to the waterborne isocyanate curing agent system to modify it, and the obtained modified curing agent is added to the waterborne coating, which can effectively avoid the direct addition of silicone resin / silicone auxiliary agent in the coating, resulting in phase separation / migration problems in the coating curing process, improving the physical and chemical properties of the coating, and increasing the scratch resistance, weather resistance, heat resistance, chemical resistance and bonding performance of the coating.

Description

Technical Field

[0001] The present application belongs to the field of material technology, and in particular relates to a modified curing agent and a preparation method thereof, and a waterborne polyurethane coating. Background Art

[0002] Traditional polyurethane (PU), unsaturated polyester (PE), and nitrocellulose (NC) coatings typically release a certain amount of volatile organic compounds (VOCs) or free TDI into the air during the manufacturing, construction, drying, curing, and film-forming processes. These releases pose a serious threat to human health and the environment. Consequently, countries around the world have enacted environmental regulations to limit VOC emissions from coatings. With rapid economic development, the country's advocacy for green, low-carbon, and environmentally friendly products, and consumers' increasing demands for environmental safety, water-based coatings, as non-toxic and odorless environmentally friendly coatings, are becoming increasingly popular among consumers. Because they meet the requirements of national environmental protection policies, they are listed as one of the three major environmentally friendly coatings.

[0003] However, existing waterborne polyurethane coatings generally have defects such as poor adhesion to complex substrates, poor scratch resistance, weather resistance, and heat resistance, which limit their promotion and application. Summary of the Invention

[0004] The purpose of the embodiments of the present application is to provide a modified curing agent, aiming to solve the problems of existing water-based polyurethane coatings such as poor adhesion to complex substrates, poor scratch resistance, weather resistance, and heat resistance.

[0005] The embodiment of the present application is implemented as follows: a modified curing agent includes the following raw materials in parts by weight:

[0006] 70-80 parts of water-based isocyanate curing agent, 5-10 parts of silane prepolymer, 0.5-2 parts of dehydrating agent and 10-30 parts of cosolvent;

[0007] The silane prepolymer is obtained by reacting a dehydrated polyether polyol with 3-isocyanate propyltriethoxysilane; the molar ratio of the active functional groups of the polyether polyol and 3-isocyanate propyltriethoxysilane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3).

[0008] Another object of the embodiments of the present application is a method for preparing the above-mentioned modified curing agent, comprising:

[0009] 100 parts of polyether polyol and 0.5-2 parts of dehydrating agent are added to a reaction device by weight, and dehydrated at 40-80° C. for 0.5-2 hours. Then, 15-35 parts of 3-isocyanatepropyltriethoxysilane are added and reacted at 80-120° C. for 4-6 hours to obtain a silane prepolymer;

[0010] 5-10 parts of the silane prepolymer, 70-80 parts of an aqueous isocyanate curing agent, 0.5-2 parts of a dehydrating agent, and 10-30 parts of a cosolvent are uniformly mixed to obtain a modified curing agent.

[0011] Another object of an embodiment of the present application is a water-based polyurethane coating, comprising a base coating and the above-mentioned modified curing agent; wherein the amount of the modified curing agent is 10%-15% of the mass of the base coating.

[0012] The modified curing agent provided in the embodiments of the present application is prepared by using a polyether polyol and 3-isocyanatepropyltriethoxysilane with a specific functional group ratio to prepare a silane prepolymer, which is then added to a water-based isocyanate curing agent system to modify it. The obtained modified curing agent is added to a water-based coating. This can effectively avoid the phase separation / migration problem during the coating curing process caused by directly adding silicone resin / silicone additives to the coating, improve the physical and chemical properties of the coating, and increase the coating's scratch resistance, weather resistance, heat resistance, chemical resistance and adhesion properties. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0014] In order to solve the problems of poor adhesion, scratch resistance, weather resistance, heat resistance and other properties commonly found in existing water-based polyurethane coatings on complex substrates, the embodiments of the present application provide a modified curing agent. A silane prepolymer is prepared by using polyether polyol and 3-isocyanatepropyltriethoxysilane with a specific functional group ratio, and then added to a water-based isocyanate curing agent system to modify it. The obtained modified curing agent is added to the water-based coating, which can effectively avoid the phase separation / migration problem in the coating curing process caused by directly adding silicone resin / silicone additives to the coating, thereby improving the physical and chemical properties of the coating and increasing the coating's scratch resistance, weather resistance, heat resistance, chemical resistance and adhesion properties.

[0015] The present invention provides a modified curing agent, comprising the following raw materials in parts by weight:

[0016] 70-80 parts of water-based isocyanate curing agent, 5-10 parts of silane prepolymer, 0.5-2 parts of dehydrating agent and 10-30 parts of cosolvent.

[0017] In the embodiment of the present application, the silane prepolymer is obtained by reacting a dehydrated polyether polyol with 3-isocyanatepropyltriethoxysilane.

[0018] Optionally, the silane prepolymer is obtained by reacting a dehydrated polyether polyol with 3-isocyanate propyltriethoxysilane at 80-120°C for 4-6 hours. Specifically, 1% of a dehydrating agent is added to the polyether polyol, and after dehydration at 40-80°C for 0.5-2h, 3-isocyanate propyltriethoxysilane is added and reacted at 80-120°C for 4-6 hours to obtain a silane prepolymer. Increasing the dehydration temperature can reduce the viscosity of the polyether polyol, which is beneficial to improving the dehydration efficiency. Similarly, extending the dehydration time can ensure that the water in the system is completely removed. Among them, the reaction temperature should not be higher than 120°C. Too fast a reaction speed will cause the viscosity of the system to increase rapidly, the reaction to be uneven, and may also cause gelation; too short a reaction time will lead to insufficient reaction, which may lead to poor subsequent membrane performance.

[0019] Among them, the molar ratio of the active functional groups of the polyether polyol and 3-isocyanate propyltriethoxysilane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3); preferably, the molar ratio of the active functional groups of the polyether polyol and 3-isocyanate propyltriethoxysilane participating in the reaction is n(OH):n(NCO)=1:1.1.

[0020] In the embodiments of the present application, the water-based isocyanate curing agent has a balance between moderate hydrophilicity and high functionality. The prepared water-based coating has the characteristics of fast drying and fast hardening. The formed film has the characteristics of high final hardness and good chemical resistance. Specifically, the water-based isocyanate curing agent can be Bayhydur2655, but is not limited thereto.

[0021] In the embodiment of the present application, the dehydrating agent can effectively eliminate trace moisture in the raw materials and prevent the moisture from reacting with isocyanate to generate carbon dioxide. Specifically, the dehydrating agent can be INCOZOL2, but is not limited thereto.

[0022] In the examples of the present application, the 3-isocyanatepropyltriethoxysilane (IPES) is used as a crosslinker and adhesion promoter in adhesives and sealants, and can adhere to a variety of common and uncommon substrates.

[0023] In the embodiments of the present application, the polyether polyol has three functional groups. Specifically, the polyether polyol can be trihydroxy polyoxypropylene ether (PPG-2000), but is not limited thereto. The molar ratio of the active functional groups of the trihydroxy polyoxypropylene ether and 3-isocyanate propyltriethoxysilane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3). Further preferably, in some embodiments, the molar ratio of the active functional groups of the trihydroxy polyoxypropylene ether and 3-isocyanate propyltriethoxysilane is n(-OH):n(-NCO)=1:1.1.

[0024] As a further preferred solution, trihydroxy polyoxypropylene ether is used. The trifunctional group can increase the silane content of the system. Because the reaction of the prepolymer is affected by molecular weight, the molecular weight of the trihydroxy polyoxypropylene ether is preferably 1000-8000, more preferably 3000. The molecular weight of the trihydroxy polyoxypropylene ether used in the specific examples of this application is 3000. A molecular weight that is too high will result in excessive viscosity, making it unsuitable for production and use, and low activity. A molecular weight that is too low will result in excessive hardness and brittleness.

[0025] In the embodiments of the present application, the co-solvent has good dilutability and volatility. Specifically, the co-solvent may be propylene glycol methyl ether acetate, but is not limited thereto.

[0026] The present invention also provides a method for preparing the modified curing agent, comprising:

[0027] 100 parts of polyether polyol and 0.5-2 parts of dehydrating agent are added to a reaction device by weight, and dehydrated at 40-80° C. for 0.5-2 hours. Then, 15-35 parts of 3-isocyanatepropyltriethoxysilane are added and reacted at 80-120° C. for 4-6 hours to obtain a silane prepolymer;

[0028] 5-10 parts of the silane prepolymer, 70-80 parts of an aqueous isocyanate curing agent, 0.5-2 parts of a dehydrating agent, and 10-30 parts of a cosolvent are uniformly mixed to obtain a modified curing agent.

[0029] Furthermore, an embodiment of the present application also provides a water-based polyurethane coating, comprising a base coating and the above-mentioned modified curing agent; wherein the amount of the modified curing agent is 10%-15% of the mass of the base coating.

[0030] The water-based polyurethane coating for wood provided in this application is obtained by mixing the above-mentioned base coating and modified curing agent in proportion, adding deionized water and stirring to mix evenly. It can effectively improve the defects of water-based polyurethane coatings such as poor adhesion and poor performance on complex substrates, and has excellent adhesion tolerance and water and pollution resistance.

[0031] Optionally, the base coating comprises the following raw materials in parts by weight:

[0032] 20-60 parts of water-based high-hydroxyl acrylic emulsion, 5-30 parts of water-based low-hydroxyl acrylic emulsion, 0.2-1.5 parts of defoaming agent, 0.2-0.5 parts of wetting agent, 0-0.3 parts of leveling agent, 0.1-0.3 parts of dispersant, 1-3 parts of wax dispersion, 0-10 parts of film-forming aid, 0.1-1 part of thickener, 1-3 parts of matting powder, 15-20 parts of titanium dioxide and 3-20 parts of water.

[0033] As an improvement to the above technical solution, the water-based high-hydroxyl acrylic emulsion has a non-volatile content of 40-42%, a viscosity of ≤1000 cps, and a hydroxyl value of 2.8%. Specifically, Houxian2018 can be selected as the water-based high-hydroxyl acrylic emulsion, but is not limited thereto. The water-based low-hydroxyl acrylic emulsion has a non-volatile content of 39-41%, a viscosity of <1000 cps, and a hydroxyl value of 1.5%. Specifically, JFQ3603 can be selected as the water-based low-hydroxyl acrylic emulsion, but is not limited thereto.

[0034] The defoamer is an organosilicon defoamer and / or an organic gemini surfactant. Specifically, the organosilicon defoamer may be, but is not limited to, BYK-024. The organic gemini surfactant may be, but is not limited to, Evonik AD01, which is suitable for water-based formulations and has both dynamic wetting and molecular defoaming properties, with good compatibility.

[0035] The wetting agent is a siloxane twin surfactant, which can wet the substrate, prevent craters, promote flow, and defoam. Specifically, Evonik TEGO Twin 4100 can be used, but is not limited thereto.

[0036] The leveling agent is a silicone leveling agent, which can reduce surface tension, prevent craters, and increase the scratch resistance of the coating. Specifically, the leveling agent can be Evonik TEGO Glide 496, but is not limited thereto.

[0037] The dispersant is a high molecular weight block copolymer solution containing pigment-affinity groups. It can deflocculate the powder through electrostatic stabilization and possesses hydrophobic properties, improving the coating's stain resistance and corrosion resistance. Specifically, BYK-190 is used as the dispersant, but is not limited thereto.

[0038] The wax dispersion is a water-washable dispersion of micronized polytetrafluoroethylene wax, which helps improve the smoothness of the paint film surface and enhances stain resistance. Specifically, the wax dispersion can be Tianshi PTFE-1005, but is not limited thereto.

[0039] Wherein, the film-forming aid is dipropylene glycol methyl ether and / or dipropylene glycol butyl ether;

[0040] The thickener is a nonionic associative thickener having anti-sagging properties, good fluidity, leveling and glossiness. Specifically, the thickener may be French Cotek XS71, but is not limited thereto.

[0041] The matting agent is organically treated silica (i.e., fumed silica). Specifically, Grace 7000 can be used as the matting agent.

[0042] The titanium dioxide is a multi-purpose rutile titanium dioxide pigment produced by the chlorination process. Specifically, DuPont R-706 can be used as the titanium dioxide.

[0043] The modified curing agent and waterborne polyurethane coating are described in detail below using specific examples. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available unless otherwise specified.

[0044] The raw material information used for the base coating in the following examples is as follows:

[0045] The water-based high-hydroxyl acrylic emulsion is Houxian2018; the water-based low-hydroxyl acrylic emulsion is JFQ3603; the defoaming agent is Evonik AD01; the wetting agent is Evonik TEGO Twin4100; the matting agent is Grace 7000; the titanium dioxide is DuPont R-706; the film-forming agent is dipropylene glycol methyl ether; the thickener can be French Coatex XS71; and the dispersant is BYK-190.

[0046] Example 1: Preparation of modified curing agent and base coating

[0047] The base coating of the waterborne polyurethane coating comprises the following raw materials in parts by weight:

[0048] 45 parts of water-based high-hydroxyl acrylic emulsion, 15 parts of water-based low-hydroxyl acrylic emulsion, 0.2 parts of defoaming agent, 0.2 parts of wetting agent, 0.2 parts of dispersant, 2 parts of matting agent, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0049] The preparation method of the base coating of the waterborne polyurethane coating comprises the following steps:

[0050] 1) Weigh each raw material according to the above weight fraction;

[0051] 2) adding the aqueous high-hydroxyl acrylic emulsion and the aqueous low-hydroxyl acrylic emulsion to a mixing device and stirring at a speed of 1000 r / min for 5 minutes, then sequentially adding the defoaming agent and stirring at a speed of 1200 r / min for 5 minutes, then adding the wetting agent and dispersant respectively and stirring at a speed of 1400 r / min for 5 minutes, reducing the stirring speed to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 minutes, and then accelerating to 1600 r / min and stirring for 20 minutes to obtain a first slurry;

[0052] 3) mixing the film-forming aid and water in a mass ratio of 1:1 to obtain a first mixed solution; adding the first mixed solution to the first slurry and stirring at a speed of 1200 r / min for 15 minutes, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 minutes to obtain a second slurry;

[0053] 4) The viscosity of the second slurry was adjusted to 65s, and the slurry was allowed to stand for 1 hour before filtering. During the filtering process, the slurry was first filtered once with a 200-mesh filter and then filtered once with a 250-mesh filter to make the fineness of the base coating less than 25 μm to obtain a finished product.

[0054] The preparation method of the modified curing agent comprises the following steps:

[0055] 1) Add 100 parts by weight of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction flask and dehydrate at 60°C for 1 hour;

[0056] 2) Add 22.23 parts of 3-isocyanatepropyltriethoxysilane to the reaction system in 1) and react at 90° C. for 5 hours to obtain a silane prepolymer.

[0057] 3) 60 parts of Bayhydur 2655, 8 parts of silane prepolymer, 30 parts of propylene glycol methyl ether acetate and 2 parts of BF-5 dehydrating agent were dispersed at a low speed for 10 minutes to obtain a modified curing agent.

[0058] Example 2: Preparation of modified curing agent and base coating

[0059] The base coating of the waterborne polyurethane coating comprises the following raw materials in parts by weight:

[0060] 45 parts of water-based high-hydroxyl acrylic emulsion, 15 parts of water-based low-hydroxyl acrylic emulsion, 0.2 parts of defoaming agent, 0.2 parts of wetting agent, 0.2 parts of dispersant, 2 parts of matting agent, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0061] The preparation method of the base coating of the waterborne polyurethane coating comprises the following steps:

[0062] 1) Weigh each raw material according to the above weight fraction;

[0063] 2) adding the aqueous high-hydroxyl acrylic emulsion and the aqueous low-hydroxyl acrylic emulsion to a mixing device and stirring at a speed of 1000 r / min for 5 minutes, then sequentially adding the defoaming agent and stirring at a speed of 1200 r / min for 5 minutes, then adding the wetting agent and dispersant respectively and stirring at a speed of 1400 r / min for 5 minutes, reducing the stirring speed to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 minutes, and then accelerating to 1600 r / min and stirring for 20 minutes to obtain a first slurry;

[0064] 3) mixing the film-forming aid and water in a mass ratio of 1:1 to obtain a first mixed solution; adding the first mixed solution to the first slurry and stirring at a speed of 1200 r / min for 15 minutes, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 minutes to obtain a second slurry;

[0065] 4) The viscosity of the second slurry was adjusted to 65s, and the slurry was allowed to stand for 1 hour before filtering. During the filtering process, the slurry was first filtered once with a 200-mesh filter and then filtered once with a 250-mesh filter to make the fineness of the base coating less than 25 μm to obtain a finished product.

[0066] The preparation method of the modified curing agent comprises the following steps:

[0067] 1) Add 100 parts by weight of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction flask and dehydrate at 60°C for 1 hour;

[0068] 2) Add 24.7 parts of 3-isocyanatepropyltriethoxysilane to the reaction system in 1) and react at 90° C. for 5 hours to obtain a silane prepolymer.

[0069] 3) 60 parts of Bayhydur 2655, 8 parts of silane prepolymer, 30 parts of propylene glycol methyl ether acetate and 2 parts of BF-5 dehydrating agent were dispersed at a low speed for 10 minutes to obtain a modified curing agent.

[0070] Example 3: Preparation of modified curing agent and base coating

[0071] The base coating of the waterborne polyurethane coating comprises the following raw materials in parts by weight:

[0072] 45 parts of water-based high-hydroxyl acrylic emulsion, 15 parts of water-based low-hydroxyl acrylic emulsion, 0.2 parts of defoaming agent, 0.2 parts of wetting agent, 0.2 parts of dispersant, 2 parts of matting agent, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0073] The preparation method of the base coating of the waterborne polyurethane coating comprises the following steps:

[0074] 1) Weigh each raw material according to the above weight fraction;

[0075] 2) adding the aqueous high-hydroxyl acrylic emulsion and the aqueous low-hydroxyl acrylic emulsion to a mixing device and stirring at a speed of 1000 r / min for 5 minutes, then sequentially adding the defoaming agent and stirring at a speed of 1200 r / min for 5 minutes, then adding the wetting agent and dispersant respectively and stirring at a speed of 1400 r / min for 5 minutes, reducing the stirring speed to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 minutes, and then accelerating to 1600 r / min and stirring for 20 minutes to obtain a first slurry;

[0076] 3) mixing the film-forming aid and water in a mass ratio of 1:1 to obtain a first mixed solution; adding the first mixed solution to the first slurry and stirring at a speed of 1200 r / min for 15 minutes, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 minutes to obtain a second slurry;

[0077] 4) The viscosity of the second slurry was adjusted to 65s, and the slurry was allowed to stand for 1 hour before filtering. During the filtering process, the slurry was first filtered once with a 200-mesh filter and then filtered once with a 250-mesh filter to make the fineness of the base coating less than 25 μm to obtain a finished product.

[0078] The preparation method of the modified curing agent comprises the following steps:

[0079] 1) Add 100 parts by weight of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction flask and dehydrate at 60°C for 1 hour;

[0080] 2) Add 27.17 parts of 3-isocyanatepropyltriethoxysilane to the reaction system in 1) and react at 90° C. for 5 hours to obtain a silane prepolymer.

[0081] 3) 60 parts of Bayhydur 2655, 8 parts of silane prepolymer, 30 parts of propylene glycol methyl ether acetate and 2 parts of BF-5 dehydrating agent were dispersed at a low speed for 10 minutes to obtain a modified curing agent.

[0082] Example 4: Preparation of modified curing agent and base coating

[0083] The base coating of the waterborne polyurethane coating comprises the following raw materials in parts by weight:

[0084] 45 parts of water-based high-hydroxyl acrylic emulsion, 15 parts of water-based low-hydroxyl acrylic emulsion, 0.2 parts of defoaming agent, 0.2 parts of wetting agent, 0.2 parts of dispersant, 2 parts of matting agent, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0085] The preparation method of the base coating of the waterborne polyurethane coating comprises the following steps:

[0086] 1) Weigh each raw material according to the above weight fraction;

[0087] 2) adding the aqueous high-hydroxyl acrylic emulsion and the aqueous low-hydroxyl acrylic emulsion to a mixing device and stirring at a speed of 1000 r / min for 5 minutes, then sequentially adding the defoaming agent and stirring at a speed of 1200 r / min for 5 minutes, then adding the wetting agent and dispersant respectively and stirring at a speed of 1400 r / min for 5 minutes, reducing the stirring speed to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 minutes, and then accelerating to 1600 r / min and stirring for 20 minutes to obtain a first slurry;

[0088] 3) mixing the film-forming aid and water in a mass ratio of 1:1 to obtain a first mixed solution; adding the first mixed solution to the first slurry and stirring at a speed of 1200 r / min for 15 minutes, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 minutes to obtain a second slurry;

[0089] 4) The viscosity of the second slurry was adjusted to 65s, and the slurry was allowed to stand for 1 hour before filtering. During the filtering process, the slurry was first filtered once with a 200-mesh filter and then filtered once with a 250-mesh filter to make the fineness of the base coating less than 25 μm to obtain a finished product.

[0090] The preparation method of the modified curing agent comprises the following steps:

[0091] 1) Add 100 parts by weight of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction flask and dehydrate at 60°C for 1 hour;

[0092] 2) Add 29.64 parts of 3-isocyanatepropyltriethoxysilane to the reaction system in 1) and react at 90° C. for 5 hours to obtain a silane prepolymer.

[0093] 3) 60 parts of Bayhydur 2655, 8 parts of silane prepolymer, 30 parts of propylene glycol methyl ether acetate and 2 parts of BF-5 dehydrating agent were dispersed at a low speed for 10 minutes to obtain a modified curing agent.

[0094] Example 5: Preparation of modified curing agent and base coating

[0095] The base coating of the waterborne polyurethane coating comprises the following raw materials in parts by weight:

[0096] 45 parts of water-based high-hydroxyl acrylic emulsion, 15 parts of water-based low-hydroxyl acrylic emulsion, 0.2 parts of defoaming agent, 0.2 parts of wetting agent, 0.2 parts of dispersant, 2 parts of matting agent, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0097] The preparation method of the base coating of the waterborne polyurethane coating comprises the following steps:

[0098] 1) Weigh each raw material according to the above weight fraction;

[0099] 2) adding the aqueous high-hydroxyl acrylic emulsion and the aqueous low-hydroxyl acrylic emulsion to a mixing device and stirring at a speed of 1000 r / min for 5 minutes, then sequentially adding the defoaming agent and stirring at a speed of 1200 r / min for 5 minutes, then adding the wetting agent and dispersant respectively and stirring at a speed of 1400 r / min for 5 minutes, reducing the stirring speed to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 minutes, and then accelerating to 1600 r / min and stirring for 20 minutes to obtain a first slurry;

[0100] 3) mixing the film-forming aid and water in a mass ratio of 1:1 to obtain a first mixed solution; adding the first mixed solution to the first slurry and stirring at a speed of 1200 r / min for 15 minutes, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 minutes to obtain a second slurry;

[0101] 4) The viscosity of the second slurry was adjusted to 65s, and the slurry was allowed to stand for 1 hour before filtering. During the filtering process, the slurry was first filtered once with a 200-mesh filter and then filtered once with a 250-mesh filter to make the fineness of the base coating less than 25 μm to obtain a finished product.

[0102] The preparation method of the modified curing agent comprises the following steps:

[0103] 1) Add 100 parts by weight of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction flask and dehydrate at 60°C for 1 hour;

[0104] 2) 32.11 parts of 3-isocyanatepropyltriethoxysilane were added to the reaction system in 1) and reacted at 90° C. for 5 hours to obtain a silane prepolymer.

[0105] 3) 60 parts of Bayhydur 2655, 8 parts of silane prepolymer, 30 parts of propylene glycol methyl ether acetate and 2 parts of BF-5 dehydrating agent were dispersed at a low speed for 10 minutes to obtain a modified curing agent.

[0106] Comparative Example 1: Preparation of modified curing agent and base coating

[0107] The base coating of the waterborne polyurethane coating comprises the following raw materials in parts by weight:

[0108] 45 parts of water-based high-hydroxyl acrylic emulsion, 15 parts of water-based low-hydroxyl acrylic emulsion, 0.2 parts of defoaming agent, 0.2 parts of wetting agent, 0.2 parts of dispersant, 2 parts of matting agent, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0109] The preparation method of the base coating of the waterborne polyurethane coating comprises the following steps:

[0110] 1) Weigh each raw material according to the above weight fraction;

[0111] 2) adding the aqueous high-hydroxyl acrylic emulsion and the aqueous low-hydroxyl acrylic emulsion to a mixing device and stirring at a speed of 1000 r / min for 5 minutes, then sequentially adding the defoaming agent and stirring at a speed of 1200 r / min for 5 minutes, then adding the wetting agent and dispersant respectively and stirring at a speed of 1400 r / min for 5 minutes, reducing the stirring speed to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 minutes, and then accelerating to 1600 r / min and stirring for 20 minutes to obtain a first slurry;

[0112] 3) mixing the film-forming aid and water in a mass ratio of 1:1 to obtain a first mixed solution; adding the first mixed solution to the first slurry and stirring at a speed of 1200 r / min for 15 minutes, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 minutes to obtain a second slurry;

[0113] 4) The viscosity of the second slurry was adjusted to 65s, and the slurry was allowed to stand for 1 hour before filtering. During the filtering process, the slurry was first filtered once with a 200-mesh filter and then filtered once with a 250-mesh filter to make the fineness of the base coating less than 25 μm to obtain a finished product.

[0114] The preparation method of the modified curing agent is as follows: by weight, 60 parts of Bayhydur2655, 8 parts of 3-isocyanatepropyltriethoxysilane, 30 parts of propylene glycol methyl ether acetate and 2 parts of BF-5 dehydrating agent are dispersed at a low speed for 10 minutes to obtain the modified curing agent.

[0115] Comparative Example 2: Preparation of modified curing agent and base coating

[0116] The base coating of the waterborne polyurethane coating comprises the following raw materials in parts by weight:

[0117] 45 parts of water-based high-hydroxyl acrylic emulsion, 15 parts of water-based low-hydroxyl acrylic emulsion, 0.2 parts of defoaming agent, 0.2 parts of wetting agent, 0.2 parts of dispersant, 2 parts of matting agent, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0118] The preparation method of the base coating of the waterborne polyurethane coating comprises the following steps:

[0119] 1) Weigh each raw material according to the above weight fraction;

[0120] 2) adding the aqueous high-hydroxyl acrylic emulsion and the aqueous low-hydroxyl acrylic emulsion to a mixing device and stirring at a speed of 1000 r / min for 5 minutes, then sequentially adding the defoaming agent and stirring at a speed of 1200 r / min for 5 minutes, then adding the wetting agent and dispersant respectively and stirring at a speed of 1400 r / min for 5 minutes, reducing the stirring speed to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 minutes, and then accelerating to 1600 r / min and stirring for 20 minutes to obtain a first slurry;

[0121] 3) mixing the film-forming aid and water in a mass ratio of 1:1 to obtain a first mixed solution; adding the first mixed solution to the first slurry and stirring at a speed of 1200 r / min for 15 minutes, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 minutes to obtain a second slurry;

[0122] 4) The viscosity of the second slurry was adjusted to 65s, and the slurry was allowed to stand for 1 hour before filtering. During the filtering process, the slurry was first filtered once with a 200-mesh filter and then filtered once with a 250-mesh filter to make the fineness of the base coating less than 25 μm to obtain a finished product.

[0123] The preparation method of the water-based isocyanate curing agent is as follows: 68 parts of Bayhydur 2655, 30 parts of propylene glycol methyl ether acetate and 2 parts of BF-5 dehydrating agent are dispersed at a low speed for 10 minutes to obtain the water-based isocyanate curing agent.

[0124] The curing agents prepared in Examples 1 to 5 and Comparative Examples 1 to 2 were tested. Specifically, the test was performed according to Type I in HG / T5063-2016. The specific test data are shown in Table 1 below:

[0125] Table 1

[0126]

[0127]

[0128] According to Table 1 above, it can be seen from the data of Examples 1 to 5 of the present application and Comparative Examples 1 to 2 that 3-isocyanate propyl triethoxysilane must first be prepolymerized to be stable in the curing agent system. The molar ratio of the active functional groups of trihydroxy polyoxypropylene ether and 3-isocyanate propyl triethoxysilane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3). As the amount of n(-NCO) increases, the state of the silane-modified isocyanate water-based curing agent in the container becomes increasingly unstable; as the amount of n(-NCO) increases, the viscosity of the silane-modified isocyanate water-based curing agent becomes increasingly stable.

[0129] Furthermore, the base coatings of Examples 1-5 and Comparative Examples 1-2 were mixed with a curing agent to prepare a waterborne polyurethane topcoat, which was then tested. Specifically, the base coating: curing agent: water was prepared in a mass ratio of 100:10:10. The paint film performance was then tested according to the Class B standard of GB / T 23999-2009 (adhesion was tested at the corner of the door, with PVC edge banding and PUR adhesive edge banding, and a UV primer on the front). Specific test data are shown in Table 2 below:

[0130] Table 2

[0131]

[0132] According to Table 2 above, it can be seen from the data of Examples 1 to 5 and Comparative Examples 1 to 2 that the introduction of 3-isocyanatepropyltriethoxysilane into the system can effectively improve the adhesion and pollution resistance of the paint film; the molar ratio of the active functional groups of trihydroxy polyoxypropylene ether and 3-isocyanatepropyltriethoxysilane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3). As the amount of n(-NCO) increases, the performance of the paint film is significantly improved, and the best effect is achieved when n(-OH):n(-NCO)=1:1.1.

[0133] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0134] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A waterborne polyurethane coating, characterized in that: It comprises a base coating and a modified curing agent; wherein the amount of the modified curing agent is 10%-15% of the mass of the base coating; The base coating comprises the following raw materials in parts by weight: 20-60 parts of water-based high-hydroxyl acrylic emulsion, 5-30 parts of water-based low-hydroxyl acrylic emulsion, 0.2-1.5 parts of defoaming agent, 0.2-0.5 parts of wetting agent, 0-0.3 parts of leveling agent, 0.1-0.3 parts of dispersant, 1-3 parts of wax dispersion, 0-10 parts of film-forming aid, 0.1-1 parts of thickener, 1-3 parts of matting powder, 15-20 parts of titanium dioxide, and 3-20 parts of water; The modified curing agent comprises the following raw materials in parts by weight: 70-80 parts of water-based isocyanate curing agent, 5-10 parts of silane prepolymer, 0.5-2 parts of dehydrating agent and 10-30 parts of cosolvent; The silane prepolymer is obtained by reacting a dehydrated polyether polyol with 3-isocyanate propyltriethoxysilane; the molar ratio of the active functional groups of the polyether polyol and 3-isocyanate propyltriethoxysilane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3).

2. The waterborne polyurethane coating according to claim 1, characterized in that The molar ratio of the active functional groups of the polyether polyol and 3-isocyanate propyltriethoxysilane participating in the reaction is n(OH):n(NCO)=1:1.

1.

3. The waterborne polyurethane coating according to claim 1, characterized in that The silane prepolymer is obtained by reacting dehydrated polyether polyol with 3-isocyanate propyltriethoxysilane at 80-120° C. for 4-6 hours.

4. The waterborne polyurethane coating according to claim 1, characterized in that The polyether polyol is trihydroxy polyoxypropylene ether.

5. The waterborne polyurethane coating according to claim 4, characterized in that: The molecular weight of the trihydroxy polyoxypropylene ether is 1000-8000.

6. The waterborne polyurethane coating according to claim 1, characterized in that: It is characterized by: The preparation method of the modified curing agent comprises: 100 parts of polyether polyol and 0.5-2 parts of dehydrating agent are added to a reaction device by weight, and dehydrated at 40-80° C. for 0.5-2 hours. Then, 15-35 parts of 3-isocyanatepropyltriethoxysilane are added and reacted at 80-120° C. for 4-6 hours to obtain a silane prepolymer; 5-10 parts of the silane prepolymer, 70-80 parts of an aqueous isocyanate curing agent, 0.5-2 parts of a dehydrating agent, and 10-30 parts of a cosolvent are uniformly mixed to obtain a modified curing agent.

7. The waterborne polyurethane coating according to claim 1, characterized in that: The non-volatile matter content of the water-based high-hydroxyl acrylic emulsion is 40-42%, the viscosity is ≤1000cps, and the hydroxyl value is 2.8%; the non-volatile matter content of the water-based low-hydroxyl acrylic emulsion is 39-41%, the viscosity is <1000cps, and the hydroxyl value is 1.5%.

8. The waterborne polyurethane coating according to claim 1, characterized in that: The defoaming agent is an organosilicon defoaming agent and / or an organic gemini surfactant; the wetting agent is a siloxane gemini surfactant; the leveling agent is an organosilicon leveling agent; the dispersant is a high molecular weight block copolymer solution containing pigment-affinity groups; the wax dispersion is a water-washable dispersion of polytetrafluoroethylene micronized wax; the film-forming aid is dipropylene glycol methyl ether and / or dipropylene glycol butyl ether; the thickener is a non-ionic associative thickener; the matting powder is organically treated silica; and the titanium dioxide is a multi-purpose rutile titanium dioxide pigment produced by the chlorination process.

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