Weather-resistant waterborne polyurethane composite coating and preparation method thereof

Abstract

The invention provides a weather-resistant waterborne polyurethane composite coating and a preparation method thereof. The weather-resistant waterborne polyurethane composite coating comprises the following components in parts by weight: 100 parts of a waterborne polyurethane emulsion; 30 to 50 parts of siloxane modified epoxy acrylic resin; 15 to 25 parts of hydroxyl terminated hyperbranched polycarbosilane; 20 to 35 parts of a flame retardant synergist containing phosphorus and nitrogen; 2-6 parts of a polyacrylate dispersant; 3-8 parts of a polyether modified organic silicon defoaming agent; 4 to 12 parts of a fluorine-containing modified polysiloxane flatting agent; 3-8 parts of a modified cellulose thickening agent; 5 to 15 parts of amino silane modified reduced graphene oxide; and 10-30 parts of a water dispersible isocyanate curing agent. The water resistance, the mechanical strength, the weather resistance and the flame retardant property of the coating are remarkably improved.

Description

Technical Field

[0001] The invention relates to a polyurethane coating, in particular to a weather-resistant waterborne polyurethane composite coating and a preparation method thereof, belonging to the technical field of functional coatings. Background Art

[0002] Waterborne polyurethane is a polyurethane system that uses water instead of organic solvents as a dispersion medium. It uses water as a solvent, is safe and environmentally friendly, and has excellent wear resistance, acid and alkali resistance, and weather resistance after film formation. The hardness and other properties of the film are highly controllable, and it is widely used in many fields. The application of waterborne polyurethane coatings also includes being used as a coating layer for polyester base fabrics in tarpaulins to form a paint film on the surface of the tarpaulin, thereby making the tarpaulin water-resistant, weather-resistant, and flame-retardant. However, due to the presence of hydrophilic groups in waterborne polyurethane coatings and the low cross-linking density of the film after film formation, existing waterborne polyurethane coatings generally have the problems of poor water resistance and low mechanical strength of the film after film formation, making it difficult to fully meet the requirements of the actual application of tarpaulins. Summary of the invention

[0003] Based on the above background, the purpose of the present invention is to provide a weather-resistant waterborne polyurethane composite coating and a preparation method thereof, so as to solve the problems described in the background technology.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] A weather-resistant waterborne polyurethane composite coating comprises the following components in parts by weight:

[0006] Water-based polyurethane emulsion: 100 parts;

[0007] Siloxane modified epoxy acrylic resin: 30-50 parts;

[0008] Hydroxyl terminated hyperbranched polycarbosilane: 15-25 parts;

[0009] Phosphorus- and nitrogen-containing flame retardant synergist: 20-35 parts;

[0010] Polyacrylate dispersant: 2-6 parts;

[0011] Polyether modified silicone defoamer: 3-8 parts;

[0012] Fluorine-containing modified polysiloxane leveling agent: 4-12 parts;

[0013] Modified cellulose thickener: 3-8 parts;

[0014] Aminosilane-modified reduced graphene oxide: 5-15 parts;

[0015] Water-dispersible isocyanate curing agent: 10-30 parts.

[0016] Preferably, the aqueous polyurethane emulsion is a hydroxyl-modified polycarbonate-polyurethane dispersion emulsion with a solid content of 35%-45% and a hydroxyl value of 40-60 mgKOH / g.

[0017] Preferably, the siloxane-modified epoxy acrylic resin is prepared by a mixed reaction of epoxy resin, acrylic acid, γ-glycidyl ether propyl trimethoxy silane and a catalyst.

[0018] Preferably, the hydroxyl-terminated hyperbranched polycarbosilane is prepared by a mixed reaction of silicon tetrachloride, trichloromethylsilane, polyol, catalyst and ethylene glycol, the molar ratio of silicon tetrachloride, trichloromethylsilane and polyol is 1:2:3-5, and the catalyst is tetrabutyl titanate.

[0019] Preferably, the phosphorus- and nitrogen-containing flame retardant synergist is at least one of phosphazene derivatives, nitrogen-containing phosphates, and phosphorus-containing triazine compounds; the polyether-modified silicone defoamer is a composite defoamer containing polydimethylsiloxane and polyether-modified polysiloxane; the fluorine-containing modified polysiloxane leveling agent is a block copolymer containing perfluoroalkyl and polydimethylsiloxane; and the modified cellulose thickener is hydrophobically modified hydroxyethyl cellulose.

[0020] Preferably, the aminosilane-modified reduced graphene oxide is prepared by a mixed reaction of graphene oxide, γ-aminopropyltriethoxysilane and ascorbic acid, and the weight ratio of the graphene oxide, γ-aminopropyltriethoxysilane and ascorbic acid is 1:20-40:10-20.

[0021] Preferably, the water-dispersible isocyanate curing agent is hexamethylene diisocyanate trimer with an isocyanate content of 15%-20%.

[0022] A method for preparing a weather-resistant waterborne polyurethane composite coating, the method comprising the following steps:

[0023] In parts by weight, 30-50 parts of siloxane-modified epoxy acrylic resin, 15-25 parts of hydroxyl-terminated hyperbranched polycarbosilane, 20-35 parts of phosphorus-containing and nitrogen-containing flame retardant synergist, 2-6 parts of polyacrylate dispersant, 3-8 parts of polyether-modified silicone defoamer, 4-12 parts of fluorine-modified polysiloxane leveling agent, and 3-8 parts of modified cellulose thickener are sequentially added into a dispersion kettle, and dispersed at a rotation speed of 600-800 rpm for 30-60 minutes;

[0024] Add 100 parts of aqueous polyurethane emulsion into the dispersion kettle, continue to disperse for 20-40 minutes, then filter through a 200-mesh filter to obtain component A;

[0025] Ultrasonic dispersion of 5-15 parts of aminosilane-modified reduced graphene oxide in deionized water, followed by mixing with 10-30 parts of a water-dispersible isocyanate curing agent and stirring to obtain component B;

[0026] Mix component A and component B, stir evenly, let stand for 10-20 minutes, and then use for coating.

[0027] Preferably, the preparation method of the aqueous polyurethane emulsion comprises the following steps:

[0028] 250 g of poly-1,6-hexanediol carbonate diol, 25 g of 1,4-butanediol and 0.5 g of dibutyltin dilaurate were added to a reaction kettle, heated to 120° C. under nitrogen protection, stirred and reacted for 4 hours, cooled to 80° C., 100 g of isophorone diisocyanate was added, and reacted at 80° C. for 2.5 hours to obtain a polyurethane prepolymer with an isocyanate content of 3.8%;

[0029] Add 15 g of N-methyldiethanolamine to the polyurethane prepolymer, react at 75° C. for 1.5 hours, cool to 55° C., add 12 g of ethylenediamine for chain extension reaction, then add 10 g of acetic acid for neutralization, and stir evenly;

[0030] The neutralized polyurethane prepolymer was slowly added to 700 g of deionized water under strong stirring to form a stable aqueous dispersion. Trimethylolpropane was added to the aqueous dispersion and stirred for reaction at 60° C. for 1 hour to make the hydroxyl value 40-60 mgKOH / g. After that, deionized water was added to adjust the solid content of the aqueous dispersion to 35%-45%.

[0031] Preferably, the preparation method of the siloxane-modified epoxy acrylic resin comprises the following steps:

[0032] 100 g of bisphenol A epoxy resin, 30 g of acrylic acid, 20 g of γ-glycidyl ether propyl trimethoxy silane and 1.5 g of tetrabutyl titanate were added to a reaction kettle, and the temperature was slowly raised to 90° C. under a nitrogen atmosphere, and the temperature was maintained constant and stirred for 6 hours;

[0033] When the acid value of the mixture in the reactor drops below 5 mgKOH / g, the reaction is stopped, the reaction product is cooled to room temperature, and 0.1 g of hydroquinone is added as an inhibitor to obtain a siloxane-modified epoxy acrylic resin.

[0034] Preferably, the preparation method of the hydroxyl-terminated hyperbranched polycarbosilane comprises the following steps:

[0035] 34 g of silicon tetrachloride, 60 g of trichloromethylsilane, 68 g of pentaerythritol and 2 g of tetrabutyl titanate were added to the reaction kettle, and the temperature was slowly raised to 160° C. under a nitrogen atmosphere, and the temperature was maintained constant and stirred for reaction for 8 hours;

[0036] After the reaction was completed, the temperature was lowered to 120°C and distilled under reduced pressure for 2 hours to remove volatile components;

[0037] Ethylene glycol was added to the reactor, the temperature was raised to 140° C., the reaction was carried out for 3 hours, the reaction product was cooled to room temperature, washed with ethanol, filtered, and vacuum dried for 12 hours to obtain hydroxyl-terminated hyperbranched polycarbosilane.

[0038] Preferably, the method for preparing the aminosilane-modified reduced graphene oxide comprises the following steps:

[0039] 1 g of graphene oxide and 5 g of γ-aminopropyltriethoxysilane were added to a mixed solvent of 100 mL of ethanol and 100 mL of deionized water, and ultrasonically dispersed for 30 minutes. 5 g of ascorbic acid was added, and the temperature was raised to 80°C. The mixture was stirred and reacted for 14 hours under a nitrogen atmosphere.

[0040] After the reaction is completed, the mixture is cooled to room temperature, and the precipitate is collected by centrifugation, washed, centrifuged and then dried in vacuum to obtain aminosilane-modified reduced graphene oxide.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] The invention discloses a weather-resistant waterborne polyurethane composite coating, wherein the siloxane-modified epoxy acrylic resin provides fast curing performance and excellent weather resistance, the hydroxyl-terminated hyperbranched polycarbosilane can improve the crosslinking density and chemical resistance of the coating, and the aminosilane-modified reduced graphene oxide not only enhances the mechanical properties of the coating but also provides thermal conductivity and electromagnetic shielding functions, and the three synergistically form an organic-inorganic hybrid network structure, significantly improving the water resistance, mechanical strength, weather resistance and flame retardancy of the coating, and in addition, the water-dispersible isocyanate curing agent also has a synergistic effect with the hydroxyl-terminated hyperbranched polycarbosilane and the waterborne polyurethane emulsion to form a highly crosslinked three-dimensional network structure, which also improves the mechanical strength and weather resistance of the coating to a certain extent. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the protection scope of the present invention.

[0044] In the present invention, unless otherwise specified, all parts and percentages are weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. The components or equipment in the following embodiments, unless otherwise specified, are universal standard parts or components known to those skilled in the art, and their structures and principles are known to those skilled in the art through technical manuals or conventional experimental methods.

[0045] Example 1

[0046] Preparation of waterborne polyurethane emulsion:

[0047] 250 g of poly-1,6-hexanediol carbonate diol, 25 g of 1,4-butanediol and 0.5 g of dibutyltin dilaurate were added to a reaction kettle, heated to 120° C. under nitrogen protection, stirred and reacted for 4 hours, cooled to 80° C., 100 g of isophorone diisocyanate was added, and reacted at 80° C. for 2.5 hours to obtain a polyurethane prepolymer with an isocyanate content of 3.8%;

[0048] Add 15 g of N-methyldiethanolamine to the polyurethane prepolymer, react at 75° C. for 1.5 hours, cool to 55° C., add 12 g of ethylenediamine for chain extension reaction, then add 10 g of acetic acid for neutralization, and stir evenly;

[0049] The neutralized polyurethane prepolymer was slowly added to 700 g of deionized water under strong stirring to form a stable aqueous dispersion. Trimethylolpropane was added to the aqueous dispersion and stirred for reaction at 60° C. for 1 hour to make the hydroxyl value 40-60 mgKOH / g. After that, deionized water was added to adjust the solid content of the aqueous dispersion to 35%-45%.

[0050] Preparation of siloxane-modified epoxy acrylic resin:

[0051] 100 g of bisphenol A epoxy resin, 30 g of acrylic acid, 20 g of γ-glycidyl ether propyl trimethoxy silane and 1.5 g of tetrabutyl titanate were added to a reaction kettle, and the temperature was slowly raised to 90° C. under a nitrogen atmosphere, and the temperature was maintained constant and stirred for 6 hours;

[0052] When the acid value of the mixture in the reactor drops below 5 mgKOH / g, the reaction is stopped, the reaction product is cooled to room temperature, and 0.1 g of hydroquinone is added as an inhibitor to obtain a siloxane-modified epoxy acrylic resin.

[0053] Preparation of hydroxyl terminated hyperbranched polycarbosilane:

[0054] 34 g of silicon tetrachloride, 60 g of trichloromethylsilane, 68 g of pentaerythritol and 2 g of tetrabutyl titanate were added to the reaction kettle, and the temperature was slowly raised to 160° C. under a nitrogen atmosphere, and the temperature was maintained constant and stirred for reaction for 8 hours;

[0055] After the reaction was completed, the temperature was lowered to 120°C and distilled under reduced pressure for 2 hours to remove volatile components;

[0056] Ethylene glycol was added to the reactor, the temperature was raised to 140° C., the reaction was carried out for 3 hours, the reaction product was cooled to room temperature, washed with ethanol, filtered, and vacuum dried for 12 hours to obtain hydroxyl-terminated hyperbranched polycarbosilane.

[0057] Preparation of component A:

[0058] 40 parts of siloxane-modified epoxy acrylic resin, 20 parts of hydroxyl-terminated hyperbranched polycarbosilane, 30 parts of phosphorus- and nitrogen-containing flame retardant synergist (hexa(2-hydroxyethyl)cyclotriphosphazene), 4 parts of polyacrylate dispersant, 5 parts of polyether-modified organosilicon defoamer, 8 parts of fluorine-modified polysiloxane leveling agent, and 5 parts of modified cellulose thickener (hydroxyethyl cellulose) were added to a dispersion kettle in sequence and dispersed at a speed of 700 rpm for 45 minutes. Then 100 parts of aqueous polyurethane emulsion (solid content 40%, hydroxyl value 50 mg KOH / g) were slowly added and dispersed for 30 minutes. Finally, the mixture was filtered through a 200-mesh filter to obtain component A.

[0059] Preparation of aminosilane-modified reduced graphene oxide:

[0060] 1 g of graphene oxide and 5 g of γ-aminopropyltriethoxysilane were added to a mixed solvent of 100 mL of ethanol and 100 mL of deionized water, and ultrasonically dispersed for 30 minutes. 5 g of ascorbic acid was added, and the temperature was raised to 80°C. The mixture was stirred and reacted for 14 hours under a nitrogen atmosphere.

[0061] After the reaction is completed, the mixture is cooled to room temperature, and the precipitate is collected by centrifugation, washed, centrifuged and then dried in vacuum to obtain aminosilane-modified reduced graphene oxide.

[0062] Preparation of component B:

[0063] 10 parts of aminosilane-modified reduced graphene oxide were ultrasonically dispersed in 50 g of deionized water, and then mixed with 20 parts of a water-dispersible isocyanate curing agent (NCO content 18%), and stirred evenly to obtain component B.

[0064] Preparation of coating:

[0065] Mix components A and B, stir evenly, and let stand for 15 minutes before use.

[0066] Example 2

[0067] The coating was prepared according to the method of Example 1, wherein the amount of siloxane-modified epoxy acrylic resin in component A was 35 parts, the amount of hydroxyl-terminated hyperbranched polycarbosilane was 25 parts, and the amount of phosphorus-containing and nitrogen-containing flame retardant synergist was 25 parts; the amount of aminosilane-modified reduced graphene oxide in component B was 8 parts, and the amount of water-dispersible isocyanate curing agent was 25 parts.

[0068] Example 3

[0069] The coating was prepared according to the method of Example 1, wherein the amount of siloxane-modified epoxy acrylic resin in component A was 45 parts, the amount of hydroxyl-terminated hyperbranched polycarbosilane was 18 parts, and the amount of phosphorus-containing and nitrogen-containing flame retardant synergist was 35 parts; the amount of aminosilane-modified reduced graphene oxide in component B was 12 parts, and the amount of water-dispersible isocyanate curing agent was 15 parts.

[0070] Example 4

[0071] The coating was prepared according to the method of Example 1, wherein the amount of siloxane-modified epoxy acrylic resin in component A was 50 parts, the amount of hydroxyl-terminated hyperbranched polycarbosilane was 15 parts, and the amount of phosphorus-containing and nitrogen-containing flame retardant synergist was 32 parts; the amount of aminosilane-modified reduced graphene oxide in component B was 15 parts, and the amount of water-dispersible isocyanate curing agent was 30 parts.

[0072] Comparative Example 1

[0073] The coating was prepared according to the method of Example 1, but without adding the siloxane-modified epoxy acrylic resin and the hydroxyl-terminated hyperbranched polycarbosilane, and the amount of the aqueous polyurethane emulsion was increased to 160 parts.

[0074] Comparative Example 2

[0075] The coating was prepared according to the method of Example 1, but without adding the phosphorus- and nitrogen-containing flame retardant synergist and the aminosilane-modified reduced graphene oxide, and at the same time increasing the amount of the aqueous polyurethane emulsion to 130 parts.

[0076] Comparative Example 3

[0077] The coating was prepared according to the method of Example 1, except that the aqueous polyurethane emulsion was replaced by a commercially available ordinary aqueous acrylic emulsion.

[0078] The coatings prepared in Examples 1-4 and Comparative Examples 1-3 were coated on the pretreated polyester fabric surface, and the coating dry film thickness was controlled at 100±5μm. Under standard conditions (temperature 23±2℃, relative humidity 50±5%), the polyester fabric coated with the coating was cured for 7 days, and the performance test was performed on the polyester fabric. The test items and test methods are as follows:

[0079] Water resistance test: refer to GB / T 1733-1993, soak the coated fabric in deionized water at 23±2℃ for 168h, observe the coating state after taking it out, and test the adhesion according to GB / T 9286-1998.

[0080] Weathering test: Refer to GB / T 1865-2009, use xenon arc lamp aging test chamber for testing, observe the coating state after aging for 1000h, and test the gloss retention rate.

[0081] Flame retardancy test: Refer to GB / T 5455-2014 to test the burning rate of the coated fabric.

[0082] Anti-corrosion test: Referring to GB / T 1771-2007, a cross scratch was made on the coating surface. After a 5% NaCl salt spray test for 1000 hours, the coating state was observed and the rust extension width was measured.

[0083] Tensile strength and elongation at break test: refer to GB / T 1040.3-2006, use universal testing machine for testing.

[0084] The test results are shown in Table 1.

[0085] Table 1 Test results

[0086]

[0087]

[0088] From Table 1 we can see that:

[0089] In terms of water resistance, the coatings of Examples 1-4 had no significant change in appearance after 168 hours of immersion in water, and the adhesion remained at level 0-1, showing excellent water resistance. In contrast, the coatings of Comparative Examples 1-3 had varying degrees of blistering, discoloration or shedding after immersion in water, and the adhesion was significantly reduced. This shows that the siloxane-modified epoxy acrylic resin and hydroxyl-terminated hyperbranched polycarbosilane introduced in the present invention significantly improve the water resistance of the coating.

[0090] In terms of weather resistance, the gloss retention of the coatings of Examples 1 to 4 after 1000 hours of xenon lamp aging is all above 90%, which is much higher than that of Comparative Examples 1 to 3. This shows that the coating of the present invention has excellent weather resistance, which is mainly due to the introduction of siloxane-modified epoxy acrylic resin, hydroxyl-terminated hyperbranched polycarbosilane and aminosilane-modified reduced graphene oxide, which forms an organic-inorganic hybrid network structure.

[0091] In terms of flame retardancy, the coatings of Examples 1-4 exhibited excellent flame retardancy, and the burning rates were all lower than 25 mm / min. The burning rates of Comparative Examples 1-3 were significantly higher. This indicates that the phosphorus- and nitrogen-containing flame retardant synergist and the aminosilane-modified reduced graphene oxide in the present invention have a synergistic effect, forming multiple flame retardant barriers in the gas phase and the condensed phase, significantly improving the flame retardancy of the coating.

[0092] In terms of corrosion resistance, the rust extension widths of the coatings of Examples 1 to 4 after 1000 hours of salt spray testing were all less than 1.5 mm, which was significantly less than the rust extension widths of Comparative Examples 1 to 3. The siloxane-modified epoxy acrylic resin also improved the corrosion resistance of the coating.

[0093] In terms of mechanical properties, the coatings of Examples 1-4 exhibited higher tensile strength and elongation at break due to the highly cross-linked three-dimensional network structure formed by the synergistic effect of the organic-inorganic hybrid network structure and the water-dispersible isocyanate curing agent, hydroxyl-terminated hyperbranched polycarbosilane and aqueous polyurethane emulsion.

[0094] The introduction of siloxane-modified epoxy acrylic resin, hydroxyl-terminated hyperbranched polycarbosilane and aminosilane-modified reduced graphene oxide, as well as the reaction of water-dispersible isocyanate curing agent with these components, together form a highly cross-linked organic-inorganic hybrid network structure, and its mechanism of action is analyzed as follows:

[0095] The epoxy groups in the siloxane-modified epoxy acrylic resin can react with isocyanate to form urethane bonds, the acrylic groups can undergo free radical polymerization to form a cross-linked network, and the siloxane groups can form Si-O-Si bonds through hydrolysis condensation reactions to construct an inorganic network structure;

[0096] The terminal hydroxyl groups in the hydroxyl-terminated hyperbranched polycarbosilane can react with isocyanate to form urethane bonds. The Si-C skeleton provides a rigid structure, and the highly branched structure provides a large number of reaction sites, thereby facilitating the formation of a dense network.

[0097] The graphene sheets in the aminosilane-modified reduced graphene oxide provide mechanical strength, the amino groups can react with isocyanate to form urea bonds, the silane groups can hydrolyze to form silanols and then condense with other siloxane groups to form Si-O-Si bonds, and the residual oxygen-containing functional groups can also react with isocyanate;

[0098] The formation of organic-inorganic hybrid network structure mainly includes:

[0099] Siloxane network formation:

[0100] The reactions between the siloxane-modified epoxy acrylic resin, the hydroxyl-terminated hyperbranched polycarbosilane and the aminosilane-modified reduced graphene oxide are mainly:

[0101] Si-OR+H2O→Si-OH+ROH

[0102] Si-OH+HO-Si→Si-O-Si+H2O

[0103] Through the above reaction, an inorganic Si-O-Si network is formed;

[0104] Isocyanate cross-linking reaction:

[0105] Reaction with hydroxyl group: R-OH+OCN-R'→RO-CO-NH-R'

[0106] Reaction with amino group: R-NH2+OCN-R'→R-NH-CO-NH-R'

[0107] Reaction with epoxy groups:

[0108] Through the above reaction, the organic component and the inorganic component are connected by covalent bonds;

[0109] Free radical polymerization of acrylic acid groups:

[0110] CH2=CH-COO-R→[-CH2-CH(COO-R)-]n

[0111] Through the above reactions, an organic polymer network is formed, further increasing the cross-linking density.

[0112] The water-dispersible isocyanate curing agent reacts with hydroxyl-terminated hyperbranched polycarbosilane to form urethane bonds to connect highly branched molecules, reacts with the hydroxyl ends of the polyurethane in the waterborne polyurethane emulsion to increase the crosslinking density, reacts with the epoxy and hydroxyl groups of the siloxane-modified epoxy acrylic resin to connect the macromolecular monomers into a network structure, and reacts with the amino groups and residual oxygen-containing groups of the aminosilane-modified reduced graphene oxide to integrate the graphene sheets into the network structure.

[0113] The above reactions work together to form a complex multi-scale cross-linked network.

[0114] Therefore, in the present invention, the siloxane-modified epoxy acrylic resin provides fast curing performance and excellent weather resistance, the hydroxyl-terminated hyperbranched polycarbosilane can improve the crosslinking density and chemical resistance of the coating, and the aminosilane-modified reduced graphene oxide enhances the mechanical properties of the coating, and the three synergistically form an organic-inorganic hybrid network structure, which significantly improves the water resistance, mechanical strength, weather resistance and flame retardancy of the coating. In addition, the water-dispersible isocyanate curing agent also has a synergistic effect with the hydroxyl-terminated hyperbranched polycarbosilane and the waterborne polyurethane emulsion to form a highly crosslinked three-dimensional network structure, which also improves the mechanical strength and weather resistance of the coating to a certain extent.

[0115] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A weather-resistant waterborne polyurethane composite coating, characterized in that: The weather-resistant waterborne polyurethane composite coating comprises the following components in parts by weight: Water-based polyurethane emulsion: 100 parts; Siloxane modified epoxy acrylic resin: 30-50 parts; Hydroxyl terminated hyperbranched polycarbosilane: 15-25 parts; Phosphorus- and nitrogen-containing flame retardant synergist: 20-35 parts; Polyacrylate dispersant: 2-6 parts; Polyether modified silicone defoamer: 3-8 parts; Fluorine-containing modified polysiloxane leveling agent: 4-12 parts; Modified cellulose thickener: 3-8 parts; Aminosilane-modified reduced graphene oxide: 5-15 parts; Water-dispersible isocyanate curing agent: 10-30 parts.

2. The weather-resistant waterborne polyurethane composite coating according to claim 1, characterized in that: The aqueous polyurethane emulsion is a hydroxyl-modified polycarbonate-polyurethane dispersion emulsion with a solid content of 35%-45% and a hydroxyl value of 40-60 mgKOH / g.

3. The weather-resistant waterborne polyurethane composite coating according to claim 1, characterized in that: The hydroxyl-terminated hyperbranched polycarbosilane is prepared by mixed reaction of silicon tetrachloride, trichloromethylsilane, polyol, catalyst and ethylene glycol, wherein the molar ratio of silicon tetrachloride, trichloromethylsilane and polyol is 1:2:3-5, and the catalyst is tetrabutyl titanate.

4. The weather-resistant waterborne polyurethane composite coating according to claim 1, characterized in that: The aminosilane-modified reduced graphene oxide is prepared by a mixed reaction of graphene oxide, γ-aminopropyltriethoxysilane and ascorbic acid, and the weight ratio of the graphene oxide, γ-aminopropyltriethoxysilane and ascorbic acid is 1:20-40:10-20.

5. The weather-resistant waterborne polyurethane composite coating according to claim 1, characterized in that: The water-dispersible isocyanate curing agent is a hexamethylene diisocyanate trimer with an isocyanate content of 15%-20%.

6. The method for preparing a weather-resistant waterborne polyurethane composite coating according to claim 1, characterized in that: The method comprises the following steps: In parts by weight, 30-50 parts of siloxane-modified epoxy acrylic resin, 15-25 parts of hydroxyl-terminated hyperbranched polycarbosilane, 20-35 parts of phosphorus-containing and nitrogen-containing flame retardant synergist, 2-6 parts of polyacrylate dispersant, 3-8 parts of polyether-modified silicone defoamer, 4-12 parts of fluorine-modified polysiloxane leveling agent, and 3-8 parts of modified cellulose thickener are sequentially added into a dispersion kettle, and dispersed at a rotation speed of 600-800 rpm for 30-60 minutes; Add 100 parts of aqueous polyurethane emulsion into the dispersion kettle, continue to disperse for 20-40 minutes, then filter through a 200-mesh filter to obtain component A; Ultrasonic dispersion of 5-15 parts of aminosilane-modified reduced graphene oxide in deionized water, followed by mixing with 10-30 parts of a water-dispersible isocyanate curing agent and stirring to obtain component B; Mix component A and component B, stir evenly, let stand for 10-20 minutes, and then use for coating.

7. The method for preparing a weather-resistant waterborne polyurethane composite coating according to claim 6, characterized in that: The preparation method of the aqueous polyurethane emulsion comprises the following steps: 250 g of poly-1,6-hexanediol carbonate diol, 25 g of 1,4-butanediol and 0.5 g of dibutyltin dilaurate were added to a reaction kettle, heated to 120° C. under nitrogen protection, stirred and reacted for 4 hours, cooled to 80° C., 100 g of isophorone diisocyanate was added, and reacted at 80° C. for 2.5 hours to obtain a polyurethane prepolymer with an isocyanate content of 3.8%; Add 15 g of N-methyldiethanolamine to the polyurethane prepolymer, react at 75° C. for 1.5 hours, cool to 55° C., add 12 g of ethylenediamine for chain extension reaction, then add 10 g of acetic acid for neutralization, and stir evenly; The neutralized polyurethane prepolymer was slowly added to 700 g of deionized water under strong stirring to form a stable aqueous dispersion. Trimethylolpropane was added to the aqueous dispersion and stirred for reaction at 60° C. for 1 hour to make the hydroxyl value 40-60 mgKOH / g. After that, deionized water was added to adjust the solid content of the aqueous dispersion to 35%-45%.

8. The method for preparing a weather-resistant waterborne polyurethane composite coating according to claim 6, characterized in that: The preparation method of the siloxane-modified epoxy acrylic resin comprises the following steps: 100 g of bisphenol A epoxy resin, 30 g of acrylic acid, 20 g of γ-glycidyl ether propyl trimethoxy silane and 1.5 g of tetrabutyl titanate were added to a reaction kettle, and the temperature was slowly raised to 90° C. under a nitrogen atmosphere, and the temperature was maintained constant and stirred for 6 hours; When the acid value of the mixture in the reactor drops below 5 mgKOH / g, the reaction is stopped, the reaction product is cooled to room temperature, and 0.1 g of hydroquinone is added as an inhibitor to obtain a siloxane-modified epoxy acrylic resin.

9. The method for preparing a weather-resistant waterborne polyurethane composite coating according to claim 6, characterized in that: The preparation method of the hydroxyl-terminated hyperbranched polycarbosilane comprises the following steps: 34 g of silicon tetrachloride, 60 g of trichloromethylsilane, 68 g of pentaerythritol and 2 g of tetrabutyl titanate were added to the reaction kettle, and the temperature was slowly raised to 160° C. under a nitrogen atmosphere, and the temperature was maintained constant and stirred for reaction for 8 hours; After the reaction was completed, the temperature was lowered to 120°C and distilled under reduced pressure for 2 hours to remove volatile components; Ethylene glycol was added to the reactor, the temperature was raised to 140° C., the reaction was carried out for 3 hours, the reaction product was cooled to room temperature, washed with ethanol, filtered, and vacuum dried for 12 hours to obtain hydroxyl-terminated hyperbranched polycarbosilane.

10. The method for preparing a weather-resistant waterborne polyurethane composite coating according to claim 6, characterized in that: The preparation method of the aminosilane-modified reduced graphene oxide comprises the following steps: 1 g of graphene oxide and 5 g of γ-aminopropyltriethoxysilane were added to a mixed solvent of 100 mL of ethanol and 100 mL of deionized water, and ultrasonically dispersed for 30 minutes. 5 g of ascorbic acid was added, and the temperature was raised to 80°C. The mixture was stirred and reacted for 14 hours under a nitrogen atmosphere. After the reaction is completed, the mixture is cooled to room temperature, and the precipitate is collected by centrifugation, washed, centrifuged and then dried in vacuo to obtain aminosilane-modified reduced graphene oxide.

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