Modified curing agent, preparation method thereof and waterborne polyurethane coating

Abstract

The invention is applicable to the technical field of materials, and provides a modified curing agent, a preparation method thereof and a waterborne polyurethane coating, the modified curing agent comprises 70-80 parts of a waterborne isocyanate curing agent, 5-10 parts of a silane prepolymer, 0.5-2 parts of a dehydrating agent and 10-30 parts of a cosolvent; wherein the silane prepolymer is obtained by carrying out a reaction on polyether polyol subjected to dehydration treatment and 3-isocyanate propyl triethoxy silane. The preparation method comprises the following steps: carrying out a reaction on polyether polyol subjected to dehydration treatment and 3-isocyanate propyl triethoxy silane; the silane prepolymer is prepared from polyether polyol and 3-isocyanate propyl triethoxy silane with a specific functional group ratio, then the silane prepolymer is added into a water-based isocyanate curing agent system to modify the water-based isocyanate curing agent system, and the obtained modified curing agent is added into the water-based paint. The organic silicon resin / organic silicon auxiliary agent can effectively avoid the phase separation / migration problem in the coating curing process when the organic silicon resin / organic silicon auxiliary agent is directly added into the coating, the physical and chemical properties of the coating are improved, and the scratch resistance, weather resistance, heat resistance, chemical resistance and adhesive property of the coating are improved.

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) coatings, unsaturated polyester (PE) coatings and nitro (NC) coatings usually emit a certain amount of volatile organic compounds (VOC) or free TDI into the air during the manufacturing, construction drying, curing and film-forming processes, which pose serious pollution and threats to human health and the environment. For this reason, countries around the world have formulated corresponding environmental protection laws and regulations to limit the emission of VOCs in coatings. With the rapid development of the economy and the country's advocacy of green, low-carbon and environmentally friendly products, as well as the continuous improvement of consumers' requirements for product environmental safety, water-based coatings, as a non-toxic and odorless environmentally friendly coating, are increasingly popular among consumers, and 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 poor adhesion to complex substrates, and poor scratch resistance, weather resistance, and heat resistance, which limits 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, which aims to solve the problems of poor adhesion, poor scratch resistance, weather resistance, heat resistance and other properties commonly found in existing water-based polyurethane coatings when facing complex substrates.

[0005] The embodiment of the present application is implemented as follows: a modified curing agent comprises 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 propyl triethoxy silane; the molar ratio of the active functional groups of the polyether polyol and 3-isocyanate propyl triethoxy silane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3).

[0008] Another object of the embodiment 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 after dehydration treatment at a temperature of 40-80° C. for 0.5-2 hours, 15-35 parts of 3-isocyanate propyl triethoxysilane 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 co-solvent are uniformly mixed to obtain a modified curing agent.

[0011] Another object of an embodiment of the present application is a waterborne 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 with a specific functional group ratio and 3-isocyanatepropyltriethoxysilane to prepare a silane prepolymer, which is then added to an aqueous isocyanate curing agent system to modify it. The obtained modified curing agent is added to an aqueous 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, thereby improving the physical and chemical properties of the coating and increasing the scratch resistance, weather resistance, heat resistance, chemical resistance and adhesion properties of the coating. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0014] In order to solve the problems that existing water-based polyurethane coatings generally have in the face of complex substrates, such as poor adhesion, poor scratch resistance, weather resistance, and heat resistance, the embodiment of the present application provides a modified curing agent, which is prepared by using polyether polyols 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 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 scratch resistance, weather resistance, heat resistance, chemical resistance and adhesion properties of the coating.

[0015] The present application 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-isocyanate propyltriethoxysilane.

[0018] Optionally, the silane prepolymer is obtained by reacting a dehydrated polyether polyol with 3-isocyanate propyl triethoxy silane at 80-120°C for 4-6 hours. Specifically, 1% of a dehydrating agent is added to the polyether polyol, and after dehydration treatment at a temperature of 40-80°C for 0.5-2h, 3-isocyanate propyl triethoxy silane 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 will be uneven, and it 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, and the prepared water-based coating has the characteristics of fast drying and fast hardening, and the formed film has the characteristics of high final hardness and good chemical resistance. Specifically, the water-based isocyanate curing agent can be selected from Bayhydur2655, but is not limited thereto.

[0021] In the embodiments 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 may be INCOZOL2, but is not limited thereto.

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

[0023] In the embodiment of the present application, the polyether polyol has three functional groups. Specifically, the polyether polyol can be selected from 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 propyl triethoxysilane 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 propyl triethoxysilane is n(-OH):n(-NCO)=1:1.1.

[0024] As a further preferred solution, trihydroxy polyoxypropylene ether is used, and the trifunctional group can increase the content of silane in the system. Since the reaction of the prepolymer is affected by the molecular weight, preferably, the molecular weight of the trihydroxy polyoxypropylene ether is 1000-8000, more preferably 3000; the molecular weight of the trihydroxy polyoxypropylene ether used in the specific embodiments of the present application is 3000. Among them, too high a molecular weight will lead to excessive viscosity, which is not suitable for production and use, and low activity, and too low a molecular weight will lead to 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 application 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 after dehydration treatment at a temperature of 40-80° C. for 0.5-2 hours, 15-35 parts of 3-isocyanate propyl triethoxysilane 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 co-solvent are uniformly mixed to obtain a modified curing agent.

[0029] Furthermore, an embodiment of the present application also provides a waterborne 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 the present 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 coating such as poor adhesion and poor performance on complex substrates, and has excellent adhesion tolerance and water and stain resistance.

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

[0032] 20-60 parts of water-based high-hydroxy acrylic emulsion, 5-30 parts of water-based low-hydroxy 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.

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

[0034] The defoamer is selected from silicone defoamers and / or organic twin surfactants; specifically, the silicone defoamer can be selected from BYK-024, but is not limited thereto. The organic twin surfactant can be selected from Evonik AD01, but is not limited thereto, which is suitable for water-based formulations and has both dynamic wetting and molecular defoaming properties and good compatibility.

[0035] The wetting agent is a siloxane twin surfactant, which can wet the substrate, prevent craters, and promote flow and defoaming. 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 has hydrophobicity, which can improve the stain resistance and corrosion resistance of the coating. Specifically, the dispersant is BYK-190, but is not limited thereto.

[0038] The wax dispersion is a polytetrafluoroethylene micronized wax water-washable dispersion, which is beneficial to improving the smoothness of the paint film surface and improving the 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, which has anti-sagging properties, good fluidity, leveling properties and glossiness. Specifically, the thickener can be French Coatex XS71, but is not limited thereto.

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

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

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

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

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

[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 powder, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0049] The method for preparing a base coating of a 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 into a mixing device and stirring at a speed of 1000 r / min for 5 min, then sequentially adding the defoamer and stirring at a speed of 1200 r / min for 5 min, then respectively adding the wetting agent and dispersant and stirring at a speed of 1400 r / min for 5 min, after the stirring speed is reduced to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 min, and then accelerating to 1600 r / min and stirring for 20 min 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 min, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 min to obtain a second slurry;

[0053] 4) The viscosity of the second slurry is adjusted to 65s, and the slurry is filtered after standing for 1 hour. During the filtering process, the slurry is 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 of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction bottle by weight, 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 powder, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0061] The method for preparing a base coating of a 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 into a mixing device and stirring at a speed of 1000 r / min for 5 min, then sequentially adding the defoamer and stirring at a speed of 1200 r / min for 5 min, then respectively adding the wetting agent and dispersant and stirring at a speed of 1400 r / min for 5 min, after the stirring speed is reduced to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 min, and then accelerating to 1600 r / min and stirring for 20 min 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 min, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 min to obtain a second slurry;

[0065] 4) The viscosity of the second slurry is adjusted to 65s, and the slurry is filtered after standing for 1 hour. During the filtering process, the slurry is 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 of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction bottle by weight, 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 powder, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0073] The method for preparing a base coating of a 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 into a mixing device and stirring at a speed of 1000 r / min for 5 min, then sequentially adding the defoamer and stirring at a speed of 1200 r / min for 5 min, then respectively adding the wetting agent and dispersant and stirring at a speed of 1400 r / min for 5 min, after the stirring speed is reduced to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 min, and then accelerating to 1600 r / min and stirring for 20 min 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 min, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 min to obtain a second slurry;

[0077] 4) The viscosity of the second slurry is adjusted to 65s, and the slurry is filtered after standing for 1 hour. During the filtering process, the slurry is 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 of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction bottle by weight, 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 powder, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0085] The method for preparing a base coating of a 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 into a mixing device and stirring at a speed of 1000 r / min for 5 min, then sequentially adding the defoamer and stirring at a speed of 1200 r / min for 5 min, then respectively adding the wetting agent and dispersant and stirring at a speed of 1400 r / min for 5 min, after the stirring speed is reduced to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 min, and then accelerating to 1600 r / min and stirring for 20 min 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 min, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 min to obtain a second slurry;

[0089] 4) The viscosity of the second slurry is adjusted to 65s, and the slurry is filtered after standing for 1 hour. During the filtering process, the slurry is 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 of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction bottle by weight, 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 powder, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0097] The method for preparing a base coating of a 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 into a mixing device and stirring at a speed of 1000 r / min for 5 min, then sequentially adding the defoamer and stirring at a speed of 1200 r / min for 5 min, then respectively adding the wetting agent and dispersant and stirring at a speed of 1400 r / min for 5 min, after the stirring speed is reduced to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 min, and then accelerating to 1600 r / min and stirring for 20 min 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 min, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 min to obtain a second slurry;

[0101] 4) The viscosity of the second slurry is adjusted to 65s, and the slurry is filtered after standing for 1 hour. During the filtering process, the slurry is 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 of trihydroxy polyoxypropylene ether and 1 part of dehydrating agent INCOZOL 2 into a reaction bottle by weight, dehydrate at 60°C for 1 hour;

[0104] 2) Add 32.11 parts of 3-isocyanatepropyltriethoxysilane to the reaction system in 1) and react 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 powder, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0109] The method for preparing a base coating of a 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 into a mixing device and stirring at a speed of 1000 r / min for 5 min, then sequentially adding the defoamer and stirring at a speed of 1200 r / min for 5 min, then respectively adding the wetting agent and dispersant and stirring at a speed of 1400 r / min for 5 min, after the stirring speed is reduced to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 min, and then accelerating to 1600 r / min and stirring for 20 min 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 min, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 min to obtain a second slurry;

[0113] 4) The viscosity of the second slurry is adjusted to 65s, and the slurry is filtered after standing for 1 hour. During the filtering process, the slurry is 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: according to weight fraction, 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 powder, 18 parts of titanium dioxide, 4 parts of film-forming aid, 16.5 parts of water, and 0.1 parts of thickener;

[0118] The method for preparing a base coating of a 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 into a mixing device and stirring at a speed of 1000 r / min for 5 min, then sequentially adding the defoamer and stirring at a speed of 1200 r / min for 5 min, then respectively adding the wetting agent and dispersant and stirring at a speed of 1400 r / min for 5 min, after the stirring speed is reduced to 600 r / min, adding the matting powder and titanium dioxide, stirring for 5 min, and then accelerating to 1600 r / min and stirring for 20 min 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 min, reducing the stirring speed to 1000 r / min, and then adding the thickener and stirring for 8 min to obtain a second slurry;

[0122] 4) The viscosity of the second slurry is adjusted to 65s, and the slurry is filtered after standing for 1 hour. During the filtering process, the slurry is 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 Bayhydur2655, 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 the above 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 triethoxy silane must first be prepolymerized to be stable in the curing agent system, and the molar ratio of the active functional groups of trihydroxy polyoxypropylene ether and 3-isocyanate propyl triethoxy silane 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] Further, the base coatings in the above-mentioned Examples 1 to 5 and Comparative Examples 1 to 2 were mixed with a curing agent to prepare a waterborne polyurethane topcoat and tested. Specifically, the base coating: curing agent: water = 100:10:10 was prepared, and then the paint film performance was tested according to the Class B standard in the standard GB / T 23999-2009 (adhesion was tested at the corner of the door, the edge sealing was PVC edge sealing strips and PUR glue edge sealing, and the front was UV primer.). The 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), and 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-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached 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 substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A modified curing agent, characterized in that: The invention 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 propyl triethoxy silane; the molar ratio of the active functional groups of the polyether polyol and 3-isocyanate propyl triethoxy silane participating in the reaction is n(-OH):n(-NCO)=1:(0.8-1.3).

2. The modified curing agent 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 modified curing agent according to claim 1, characterized in that The silane prepolymer is obtained by reacting the dehydrated polyether polyol with 3-isocyanate propyl triethoxy silane at 80-120° C. for 4-6 hours.

4. The modified curing agent according to claim 1, characterized in that The polyether polyol is trihydroxy polyoxypropylene ether.

5. The modified curing agent according to claim 4, characterized in that The molecular weight of the trihydroxy polyoxypropylene ether is 1000-8000.

6. A method for preparing the modified curing agent according to any one of claims 1 to 5, characterized in that: include: 100 parts of polyether polyol and 0.5-2 parts of dehydrating agent are added to a reaction device by weight, and after dehydration treatment at a temperature of 40-80° C. for 0.5-2 hours, 15-35 parts of 3-isocyanate propyl triethoxysilane 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 co-solvent are uniformly mixed to obtain a modified curing agent.

7. A waterborne polyurethane coating, characterized in that: It comprises a base coating and the modified curing agent according to any one of claims 1 to 5; wherein the amount of the modified curing agent is 10% to 15% of the mass of the base coating.

8. The waterborne polyurethane coating according to claim 7, characterized in that: The base coating comprises the following raw materials in parts by weight: 20-60 parts of water-based high-hydroxy acrylic emulsion, 5-30 parts of water-based low-hydroxy 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.

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

10. The waterborne polyurethane coating according to claim 7, 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-washed 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 silicon dioxide; and the titanium dioxide is a multi-purpose rutile titanium dioxide pigment produced by the chlorination process.

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