A waterborne polyurethane topcoat that does not lose its gloss and its preparation method

Abstract

This application relates to the technical field of waterborne coatings, and particularly to a non-fading waterborne polyurethane topcoat and a preparation method thereof. A non-fading waterborne polyurethane topcoat includes component A and a waterborne curing agent B; by weight, component A includes raw materials in the following mass parts: a waterborne polyurethane emulsion, a graphene-modified filler, a pigment, an antifoaming agent, a dispersant, a waterborne thickener, and a polyethylene wax emulsion. The mass ratio of component A to the waterborne curing agent B is 100:13-15. The non-fading waterborne polyurethane topcoat of this application has performance advantages such as strong adhesion, waterproof, moisture-proof, excellent water resistance, low VOC content, health and environmental protection, etc., can solve the problem of fading that easily occurs in conventional two-component polyurethane topcoats in humid environments, and has a wide range of application prospects.

Description

Technical Field

[0001] This application relates to the technical field of waterborne coatings, and particularly to a waterborne polyurethane topcoat that does not lose gloss and a preparation method thereof. Background Art

[0002] The toy industry has developed rapidly with an increasing variety of toys. Among them, foamed polyurethane toys can be made into various shapes through molds of different shapes to meet consumers' requirements for unique shapes. Moreover, foamed polyurethane toys are soft and safe, and can safely add fun to children's entertainment life.

[0003] Currently, a layer of polyurethane topcoat is added to the surface of foamed polyurethane toys for purposes such as adding different colors to the polyurethane toys. Due to the large voids on the surface of foamed polyurethane toys, the solution absorbs water in humid weather, resulting in the appearance of matte or loss of gloss in the existing polyurethane topcoat.

[0004] Therefore, there is an urgent need to provide a new waterborne polyurethane topcoat to solve the problem of loss of gloss of the polyurethane topcoat on the toy surface. Summary of the Invention

[0005] In order to solve the above existing problems, this application provides a waterborne polyurethane topcoat that does not lose gloss and a preparation method thereof.

[0006] In the first aspect, a waterborne polyurethane topcoat that does not lose gloss provided by this application adopts the following technical solution:

[0007] A waterborne polyurethane topcoat that does not lose gloss includes component A and waterborne curing agent B; by weight, component A includes the following raw materials in the following mass fractions: 60 - 80 parts of waterborne polyurethane emulsion, 11 - 20 parts of graphene-modified filler, 5 - 10 parts of pigment, 0.5 - 0.8 part of defoamer, 2 - 3 parts of dispersant, 0.5 - 1.5 parts of waterborne thickener, 0 - 2 parts of polyethylene wax emulsion, and 10 - 20 parts of water. The mass ratio of component A to waterborne curing agent B is 100:13 - 15.

[0008] By adopting the above technical scheme, water-based polyurethane emulsion: as the main resin matrix, has good adhesion and waterproof performance. It can increase the reaction probability of curing agent and resin, reduce the probability of side reaction between curing agent and amine and water, and solve the problems of loss of gloss and prickly heat that are easy to occur in conventional two-component polyurethane topcoat in humid environment. Graphene modified filler: through the characteristics of graphene, the compatibility of filler and other components is improved, and the water resistance is further improved. By adopting graphene modified filler, the compatibility of filler and other components is improved, and the water resistance is further improved by using the characteristics of graphene, which completely solves the problem of loss of gloss that is easy to occur in conventional two-component polyurethane topcoat in humid environment. Graphene has good anti-penetration and water resistance, which can increase the water resistance of the coating. Pigment: provides color and hiding power of the coating. Defoamer: used to eliminate bubbles on the surface of the coating and improve the flatness of the coating. Dispersant: helps to evenly disperse pigments and fillers, and improve the uniformity and hiding power of the coating. Water-based thickener: Improves the leveling and hiding power of the coating by increasing the viscosity of the coating. Polyethylene wax emulsion: Used to increase the gloss and hardness of the coating. Water: Used to adjust the viscosity of the coating and dilute the coating. Water-based curing agent: Reacts with the water-based polyurethane emulsion to promote rapid curing and drying of the coating. By using a special water-based curing agent, the compatibility of the curing agent and the water-based polyurethane emulsion is further improved, thereby improving the performance of the coating. In summary, the effects and synergistic effects of the various components jointly improve the adhesion, waterproofing, moisture resistance and water resistance of the water-based polyurethane topcoat, achieving a gloss-free effect.

[0009] Preferably, the water-based curing agent B comprises the following raw materials in parts by weight: 34.0-38.0 parts of hydrophilic aliphatic polyisocyanate, 44.0-48.0 parts of lipophilic aliphatic polyisocyanate, and 14.0-22.0 parts of propylene glycol methyl ether acetate.

[0010] By adopting the above technical scheme, the main function of the water-based curing agent B is to react with the water-based polyurethane emulsion to promote the curing and drying of the coating. Specifically, hydrophilic aliphatic polyisocyanate and lipophilic aliphatic polyisocyanate are two polyisocyanates of different properties, which react with the water-based polyurethane emulsion and the water-based thickener respectively. Propylene glycol methyl ether acetate is a solvent used to adjust the curing rate, the drying time of the coating and the hardness of the coating. The reaction of water-based curing agent B with the water-based polyurethane emulsion can enhance the water resistance, chemical resistance and mechanical properties of the coating. By using a special water-based curing agent B, its compatibility with the water-based polyurethane emulsion can be improved to ensure the smooth reaction. Due to the special formula of the water-based curing agent B, the probability of side reactions between the curing agent and amines and water will be reduced, thereby solving the problem of gloss loss that is easy to occur in conventional two-component polyurethane topcoats in humid environments.

[0011] Preferably, the preparation method of the aqueous polyurethane emulsion comprises the following steps:

[0012] S31. By mass parts, in a reactor, under the protection of an inert gas, nitrogen, add 2 - 3 parts of hydroxyl-terminated polybutadiene, heat up to 60 °C, dropwise add 10 parts of hexamethylene diisocyanate, stir and mix evenly, heat up to 85 °C, add 0.05 - 0.1 part of catalyst A, and carry out a constant-temperature reaction for 2 - 3 h;

[0013] S32. By mass parts, in the reactor of step S31, continue to add 2 - 3 parts of poly(propylene carbonate) diol and 3 - 5 parts of N,N-dimethylformamide, stir and mix evenly, heat up to 80 °C, add 0.02 - 0.05 part of p-hydroxyanisole and 0.08 - 0.12 part of catalyst B, carry out a constant-temperature reaction for 2 - 4 h, add 0.2 - 0.3 part of 1,4-butanediol, continue the reaction for 1 h, cool down to 40 °C, add 0.2 - 0.4 part of triethylamine, stir and react for 2 - 4 min, add deionized water, and carry out high-speed stirring emulsification to obtain an aqueous polyurethane emulsion with a solid content of 40 wt% - 45 wt%.

[0014] Preferably, the catalyst A is one or more of stannous octoate, dibutyltin dilaurate, and dimethyltin diacetate, and the catalyst B is one or more of dibutyltin maleate, zinc naphthenate, and zinc octoate.

[0015] By adopting the above technical solution, in the present application, the aqueous polyurethane emulsion plays a role in increasing the reaction probability between the curing agent and the resin and reducing the probability of side reactions between the curing agent and amines or water. This is because the polyurethane resin in the aqueous polyurethane emulsion reacts with the curing agent B to form a network structure, thereby enhancing the performance of the coating. In addition, the optimization of the polyurethane resin formulation in the aqueous polyurethane emulsion can also improve the adhesion and water resistance of the coating film. Meanwhile, the addition of catalyst A and catalyst B during the preparation process plays roles such as catalyzing the reaction and controlling the reaction rate. The addition of p-hydroxyanisole can increase the molecular weight and compatibility of the aqueous polyurethane emulsion, thereby improving its performance. The addition of 1,4-butanediol and triethylamine can adjust the reaction equilibrium and improve the curing effect of the aqueous polyurethane emulsion. In summary, each step and the addition of raw materials in the preparation method of the aqueous polyurethane emulsion play corresponding roles and synergistic effects, thereby obtaining a waterborne polyurethane topcoat with excellent performance and no loss of gloss.

[0016] Preferably, the preparation method of the graphene-modified filler is as follows: By mass, 5-10 parts of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent are added to 100 parts of an aqueous solution with an ethanol mass concentration of 50%, heated to 60°C, and stirred to obtain a hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent. Then, 2-3 parts of graphene are added to the hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent and stirred evenly. Finally, 30-50 parts of filler are added to the above solution and stirred for 15 minutes to obtain the graphene-modified filler.

[0017] Preferably, the filler is one or more of talc powder, calcium carbonate, and kaolin.

[0018] By adopting the above technical solution, the functions and synergistic effects of the preparation method of the graphene-modified filler are as follows: In the preparation method of the graphene-modified filler, the addition of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent and graphene plays the following roles: Role of the coupling agent: 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent can form chemical bonds on the surface of the filler, improve the surface properties of the filler, enhance the compatibility and interfacial adhesion between the filler and the polyurethane matrix, thereby improving the performance of the coating. Role of graphene: Graphene has excellent electrical conductivity, mechanical properties, and thermal stability, which can increase the strength and rigidity of the filler, improve the durability and water resistance of the coating. The addition of graphene can also form a multi-level network structure, increasing the shear resistance and wear resistance of the coating. Role of filler selection: The selection of fillers such as talc powder, calcium carbonate, and kaolin will affect the quality and performance of the coating. The proportion and interaction of different types of fillers in the formulation can control the properties of the coating such as fluidity, gloss, adhesion, and weather resistance. Through the preparation method of the graphene-modified filler, the surface properties and compatibility of the filler can be optimized, enabling it to interact better with other components, improving the dispersibility and stability of the filler. This will further improve the water resistance of the coating and effectively solve the problem of loss of gloss of two-component polyurethane topcoat in a humid environment.

[0019] Preferably, the pigment is a mixture of one or more of titanium dioxide, iron oxide red, phthalocyanine blue, and carbon black.

[0020] Preferably, the dispersant is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, and sodium dodecylbenzenesulfonate in a mass ratio of 5:1 - 3:2 - 4.

[0021] By adopting the above technical solutions, the dispersant can effectively disperse the pigments and fillers evenly, prevent them from aggregating into lumps, and enable them to maintain a stable dispersed state in the coating. This helps to improve the uniformity, transparency, and coating performance of the coating. Vinyltris(β-methoxyethoxy)silane and vinyltrimethoxysilane are surfactants that can act as surface activity and dispersion media in the coating, improve the rheological properties and wettability of the coating, and enhance the contact and adhesion between the coating and the substrate. Sodium dodecylbenzenesulfonate is an anionic surfactant with excellent dispersibility and emulsifying properties. It can promote the compatibility and stability among various components in the coating, and improve the quality and durability of the coating. The compositions of these dispersants have good compatibility and complementary effects, can mutually enhance the dispersion effect on pigments and fillers, and improve the quality and stability of the coating. Their synergistic effect can effectively improve the dispersion of pigments and fillers in the coating and avoid the problems of suspension solid sedimentation and precipitation. In summary, the dispersant has the functions of dispersion, emulsification, and interfacial activity in the non-yellowing waterborne polyurethane topcoat. By using them in combination, the uniformity, transparency, and coating performance of the coating can be improved, and the quality and service performance of the coating can be further enhanced.

[0022] Preferably, the defoamer is one of polyvinyl acetate and dimethyl silicone oil, and the waterborne thickener is one of hydroxypropyl methylcellulose, hydroxyethyl cellulose, and polyurethane associative thickener.

[0023] In a second aspect, a preparation method of a non-yellowing waterborne polyurethane topcoat provided by the present application adopts the following technical solutions:

[0024] A preparation method of a non-yellowing waterborne polyurethane topcoat adopts the raw materials of the above-mentioned non-yellowing waterborne polyurethane topcoat, and includes the following steps:

[0025] S101. By mass parts, in a reactor, sequentially add the waterborne polyurethane emulsion, graphene-modified filler, pigment, defoamer, dispersant, waterborne thickener, polyethylene wax emulsion, and water, mix and stir at a stirring rate of 200 - 300 r / min for 10 - 15 min, and then let it stand to obtain Component A;

[0026] S102. By mass parts, in a reactor, mix the hydrophilic aliphatic polyisocyanate, lipophilic aliphatic polyisocyanate, and propylene glycol methyl ether acetate, stir at a stirring rate of 100 - 200 r / min for 5 - 7 min, and then let it stand to obtain the waterborne curing agent B;

[0027] S103. Mix Component A and the waterborne curing agent B to obtain the non-yellowing waterborne polyurethane topcoat.

[0028] By adopting the above technical solution, the waterborne polyurethane topcoat of the present application without loss of gloss has performance advantages such as strong adhesion, waterproof, moisture-proof, excellent water resistance, low VOC content, health and environmental protection, etc. It can solve the problem of loss of gloss that is prone to occur in conventional two-component polyurethane topcoats in humid environments and has broad application prospects.

[0029] In summary, the beneficial technical effects of the present application are as follows:

[0030] 1. Strong adhesion: The waterborne polyurethane topcoat can firmly adhere to the surface of the substrate, providing excellent adhesion and making the coating not easy to peel off or fall off.

[0031] 2. Waterproof and moisture-proof: The polyurethane topcoat has good waterproof and moisture-proof properties and can effectively protect the substrate from moisture erosion.

[0032] 3. Excellent water resistance: By using special waterborne curing agents and graphene-modified fillers, the topcoat has excellent water resistance and can maintain good gloss and performance for a long time in humid environments.

[0033] 4. Low VOC content: The topcoat uses waterborne polyurethane emulsion as the base material. Compared with traditional solvent-based polyurethane topcoats, it has a lower VOC content and meets environmental protection requirements.

[0034] 5. Health and environmental protection: Due to the low VOC content, the topcoat has no adverse effects on human health and the environment and meets the requirements of health and environmental protection.

[0035] 6. Without loss of gloss: By using the waterborne polyurethane emulsion, the reaction probability between the curing agent and the resin can be effectively increased, and the probability of side reactions between the curing agent and amines and water can be reduced, solving the problems of loss of gloss, prickly heat, etc. that are prone to occur in conventional two-component polyurethane topcoats in humid environments; by using special waterborne curing agents, the compatibility with the waterborne polyurethane emulsion is further improved. Similarly, by using graphene-modified fillers, the compatibility between the fillers and other components is improved, and the water resistance is further enhanced by utilizing the properties of graphene, completely solving the problem of loss of gloss that is prone to occur in conventional two-component polyurethane topcoats in humid environments. Specific embodiments

[0036] The following will describe the implementation solutions of the present application in detail in combination with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0037] Example 1

[0038] A waterborne polyurethane topcoat that does not lose luster, comprising component A and waterborne curing agent B; by weight, said component A comprises raw materials in the following mass parts: 60 g of waterborne polyurethane emulsion, 11 g of graphene-modified filler, 5 g of titanium dioxide, 0.5 g of polyvinyl acetate, 2 g of dispersant, 0.5 g of hydroxypropyl methylcellulose, 10 g of water, and said dispersant is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, and sodium dodecylbenzenesulfonate in a mass ratio of 5:1:2; the mass ratio of said component A to said waterborne curing agent B is 100:13. The waterborne curing agent B, by weight, comprises raw materials in the following weight parts: 34.0 g of hydrophilic aliphatic polyisocyanate, 44.0 g of lipophilic aliphatic polyisocyanate, and 22.0 g of propylene glycol methyl ether acetate.

[0039] The preparation method of the waterborne polyurethane emulsion comprises the following steps:

[0040] S31. By mass parts, in a reactor, under the protection of inert gas nitrogen, add 2 g of hydroxyl-terminated polybutadiene, heat up to 60 °C, dropwise add 10 g of hexamethylene diisocyanate, stir and mix evenly, heat up to 85 °C, add 0.05 g of stannous octoate, and carry out a constant-temperature reaction for 2 h;

[0041] S32. By mass parts, in the reactor of step S31, continue to add 2 g of poly(propylene carbonate) diol and 3 g of N,N-dimethylformamide, stir and mix evenly, heat up to 80 °C, add 0.02 g of p-hydroxyanisole and 0.08 g of dibutyltin maleate, carry out a constant-temperature reaction for 2 h, add 0.2 g of 1,4-butanediol, continue the reaction for 1 h, cool down to 40 °C, add 0.2 g of triethylamine, stir and react for 2 min, add deionized water, and carry out high-speed stirring emulsification to obtain a waterborne polyurethane emulsion with a solid content of 40 wt%.

[0042] The preparation method of the graphene-modified filler is as follows: By mass parts, add 5 g of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent to an aqueous solution with an ethanol mass concentration of 50% in 100 g, heat up to 60 °C, stir to obtain a hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent, then add 2 g of graphene to the hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent, stir evenly, and finally add 30 g of talc powder to the above solution, stir for 15 minutes to obtain the graphene-modified filler.

[0043] A preparation method of a waterborne polyurethane topcoat that does not lose luster, using the raw materials of the above-mentioned waterborne polyurethane topcoat that does not lose luster, comprises the following steps:

[0044] S101. By mass parts, in a reactor, sequentially add aqueous polyurethane emulsion, graphene-modified filler, titanium dioxide, polyvinyl acetate dispersant, hydroxypropyl methylcellulose and water, mix and stir at a stirring rate of 200 r / min for 15 min, then let it stand to obtain Component A;

[0045] S102. By mass parts, in a reactor, mix hydrophilic aliphatic polyisocyanate, lipophilic aliphatic polyisocyanate and propylene glycol methyl ether acetate, stir at a stirring rate of 100 r / min for 7 min, then let it stand to obtain aqueous curing agent B;

[0046] S103. Mix Component A and aqueous curing agent B to obtain a non - glossing aqueous polyurethane topcoat.

[0047] Example 2

[0048] A non - glossing aqueous polyurethane topcoat, comprising Component A and aqueous curing agent B; by weight parts, said Component A comprises raw materials with the following mass parts: 80 g of aqueous polyurethane emulsion, 20 g of graphene - modified filler, 10 g of iron oxide red, 0.8 g of dimethyl silicone oil, 3 g of dispersant, 1.5 g of hydroxyethyl cellulose, 2 g of polyethylene wax emulsion, 20 g of water, and said dispersant is a composition of vinyltris(β - methoxyethoxy)silane, vinyltrimethoxysilane, and sodium dodecylbenzenesulfonate in a mass ratio of 5:3:4; the mass ratio of Component A to said aqueous curing agent B is 100:15. Aqueous curing agent B, by weight parts, comprises raw materials with the following weight parts: 38.0 g of hydrophilic aliphatic polyisocyanate, 48.0 g of lipophilic aliphatic polyisocyanate, 14.0 g of propylene glycol methyl ether acetate.

[0049] The preparation method of said aqueous polyurethane emulsion comprises the following steps:

[0050] S31. By mass parts, in a reactor, under the protection of inert gas nitrogen, add 3 g of hydroxyl - terminated polybutadiene, heat up to 60 °C, dropwise add 10 g of hexamethylene diisocyanate, stir and mix evenly, heat up to 85 °C, add 0.1 g of dibutyltin dilaurate, and react at a constant temperature for 3 h;

[0051] S32. By mass parts, in the reactor of step S31, continue to add 3 g of poly(propylene carbonate)diol and 5 g of N,N - dimethylformamide, stir and mix evenly, heat up to 80 °C, add 0.05 g of p - hydroxyanisole and 0.12 g of zinc naphthenate, react at a constant temperature for 4 h, add 0.3 g of 1,4 - butanediol, continue to react for 1 h, cool down to 40 °C, add 0.4 g of triethylamine, stir and react for 4 min, add deionized water, and stir at high speed for emulsification to obtain an aqueous polyurethane emulsion with a solid content of 45 wt%.

[0052] The preparation method of the graphene-modified filler is as follows: By mass, 10 g of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent is added to 100 g of an aqueous solution with an ethanol mass concentration of 50%, heated to 60 °C, and stirred to obtain a hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent. Then, 3 g of graphene is added to the hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent and stirred evenly. Finally, 50 g of calcium carbonate is added to the above solution and stirred for 15 minutes to obtain the graphene-modified filler.

[0053] A preparation method of a non-fading waterborne polyurethane topcoat, using the raw materials of the above non-fading waterborne polyurethane topcoat, includes the following steps:

[0054] S101. By mass, in a reactor, the waterborne polyurethane emulsion, graphene-modified filler, iron oxide red, dimethyl silicone oil, dispersant, hydroxyethyl cellulose, polyethylene wax emulsion, and water are added in sequence, mixed, and stirred at a stirring rate of 300 r / min for 15 min, and then left standing to obtain Component A;

[0055] S102. By mass, in a reactor, the hydrophilic aliphatic polyisocyanate, lipophilic aliphatic polyisocyanate, and propylene glycol methyl ether acetate are mixed and stirred at a stirring rate of 200 r / min for 5 min, and then left standing to obtain the waterborne curing agent B;

[0056] S103. After mixing Component A and the waterborne curing agent B, the non-fading waterborne polyurethane topcoat is obtained.

[0057] Example 3

[0058] A non-fading waterborne polyurethane topcoat, including Component A and the waterborne curing agent B; by weight, Component A includes the following raw materials in mass parts: 70 g of waterborne polyurethane emulsion, 16 g of graphene-modified filler, 8 g of phthalocyanine blue, 0.7 g of polyvinyl acetate, 2.5 g of dispersant, 1 g of polyurethane associative thickener, 1 g of polyethylene wax emulsion, and 15 g of water. The dispersant is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, and sodium dodecylbenzenesulfonate in a mass ratio of 5:2:3; the mass ratio of Component A to the waterborne curing agent B is 100:14. The waterborne curing agent B, by weight, includes the following raw materials in weight parts: 36.0 g of hydrophilic aliphatic polyisocyanate, 46.0 g of lipophilic aliphatic polyisocyanate, and 18.0 g of propylene glycol methyl ether acetate.

[0059] The preparation method of the waterborne polyurethane emulsion includes the following steps:

[0060] S31. By mass parts, in a reactor, under the protection of inert gas nitrogen, add 2.5 g of hydroxyl-terminated polybutadiene, heat up to 60 °C, dropwise add 10 g of hexamethylene diisocyanate, stir and mix evenly, heat up to 85 °C, add 0.08 g of dimethyltin diacetate, and react at a constant temperature for 2.5 h;

[0061] S32. By mass parts, in the reactor of step S31, continue to add 2.5 g of poly(propylene carbonate) diol and 4 g of N,N-dimethylformamide, stir and mix evenly, heat up to 80 °C, add 0.04 g of p-hydroxyanisole and 0.10 g of zinc octoate, react at a constant temperature for 3 h, add 0.25 g of 1,4-butanediol, continue to react for 1 h, cool down to 40 °C, add 0.2 - 0.4 g of triethylamine, stir and react for 3 min, add deionized water, and stir at high speed for emulsification to obtain an aqueous polyurethane emulsion with a solid content of 43 wt%.

[0062] The preparation method of the graphene-modified filler is as follows: By mass parts, add 8 g of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent to an aqueous solution with an ethanol mass concentration of 50% in 100 g, heat to 60 °C, stir to obtain a hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent, then add 2.5 g of graphene to the hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent, stir evenly, and finally add 40 g of kaolin to the above solution, stir for 15 minutes to obtain the graphene-modified filler.

[0063] A preparation method of a non-discoloring aqueous polyurethane topcoat, using the raw materials of the above-mentioned non-discoloring aqueous polyurethane topcoat, includes the following steps:

[0064] S101. By mass parts, in a reactor, sequentially add the aqueous polyurethane emulsion, graphene-modified filler, phthalocyanine blue, polyvinyl acetate, dispersant, polyurethane associative thickener, polyethylene wax emulsion and water, mix and stir, the stirring rate is 250 r / min, the stirring time is 13 min, and let it stand to obtain component A;

[0065] S102. By mass parts, in a reactor, mix the hydrophilic aliphatic polyisocyanate, lipophilic aliphatic polyisocyanate and propylene glycol methyl ether acetate, stir, the stirring rate is 150 r / min, the stirring time is 6 min, and let it stand to obtain the aqueous curing agent B;

[0066] S103. Mix component A and the aqueous curing agent B to obtain the non-discoloring aqueous polyurethane topcoat.

[0067] Example 4

[0068] A waterborne polyurethane topcoat that does not lose luster, comprising component A and a waterborne curing agent B; by weight, the component A includes the following raw materials in the following mass parts: 70 g of waterborne polyurethane emulsion, 17 g of graphene-modified filler, 7 g of carbon black, 0.6 g of polyvinyl acetate, 2.5 g of dispersant, 1 g of hydroxypropyl methylcellulose, 1 g of polyethylene wax emulsion, and 15 g of water. The dispersant is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, and sodium dodecylbenzenesulfonate in a mass ratio of 5:2:3; the mass ratio of the component A to the waterborne curing agent B is 100:14. The waterborne curing agent B, by weight, includes the following raw materials in the following weight parts: 36.0 g of hydrophilic aliphatic polyisocyanate, 46.0 g of lipophilic aliphatic polyisocyanate, and 18.0 g of propylene glycol methyl ether acetate.

[0069] The preparation method of the waterborne polyurethane emulsion includes the following steps:

[0070] S31. By mass parts, in a reactor, under the protection of an inert gas nitrogen, add 2.5 g of hydroxyl-terminated polybutadiene, heat up to 60 °C, dropwise add 10 g of hexamethylene diisocyanate, stir and mix evenly, heat up to 85 °C, add 0.08 stannous octoate, and react at a constant temperature for 2 h;

[0071] S32. By mass parts, in the reactor of step S31, continue to add 2.8 g of poly(propylene carbonate) diol and 4 g of N,N-dimethylformamide, stir and mix evenly, heat up to 80 °C, add 0.04 g of p-hydroxyanisole and 0.09 g of zinc octoate, react at a constant temperature for 3 h, add 0.25 g of 1,4-butanediol, continue to react for 1 h, cool down to 40 °C, add 0.3 g of triethylamine, stir and react for 3 min, add deionized water, and stir at high speed for emulsification to obtain a waterborne polyurethane emulsion with a solid content of 42 wt%.

[0072] The preparation method of the graphene-modified filler is as follows: By mass parts, add 8 g of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent to an aqueous solution with an ethanol mass concentration of 50% in 100 g of water, heat up to 60 °C, stir to obtain a hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent, then add 2.4 g of graphene to the hydrolysis solution of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent, stir evenly, and finally add 40 g of talc powder to the above solution, stir for 15 minutes to obtain the graphene-modified filler.

[0073] A preparation method of a waterborne polyurethane topcoat that does not lose luster, using the raw materials of the above-mentioned waterborne polyurethane topcoat that does not lose luster, includes the following steps:

[0074] S101. By mass parts, in a reactor, sequentially add aqueous polyurethane emulsion, graphene-modified filler, carbon black, polyvinyl acetate, dispersant, hydroxypropyl methylcellulose polyethylene wax emulsion and water, mix and stir at a stirring rate of 260 r / min for 13 min, then let stand to obtain Component A;

[0075] S102. By mass parts, in a reactor, mix hydrophilic aliphatic polyisocyanate, lipophilic aliphatic polyisocyanate and propylene glycol methyl ether acetate, stir at a stirring rate of 150 r / min for 6 min, then let stand to obtain aqueous curing agent B;

[0076] S103. Mix Component A and aqueous curing agent B to obtain a non-glossy aqueous polyurethane topcoat.

[0077] Comparative Example 1

[0078] Same as Example 4, except that an equal amount of talcum powder is used to replace the graphene-modified filler prepared in this application.

[0079] Comparative Example 2

[0080] Same as Example 4, except that an equal amount of aqueous polyurethane resin is used to replace the aqueous polyurethane emulsion prepared in this application.

[0081] Comparative Example 3

[0082] Same as Example 4, except that an equal amount of vinyltris(β-methoxyethoxy)silane is used to replace the dispersant which is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane and sodium dodecylbenzenesulfonate in a mass ratio of 5:2:3.

[0083] Comparative Example 4

[0084] Same as Example 4, except that an equal amount of vinyltrimethoxysilane is used to replace the dispersant which is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane and sodium dodecylbenzenesulfonate in a mass ratio of 5:2:3.

[0085] Comparative Example 5

[0086] Same as Example 4, except that an equal amount of sodium dodecylbenzenesulfonate is used to replace the dispersant which is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane and sodium dodecylbenzenesulfonate in a mass ratio of 5:2:3.

[0087] Performance Test

[0088] Samples of the non - dulling water - borne polyurethane topcoats obtained from Examples 1 - 4 and Comparative Examples 1 - 5 were taken for performance testing, and the results are shown in Table 1.

[0089] After pretreatment processes such as blowing ash, cleaning, degreasing, water washing, drying, and cooling for the foamed polyurethane toy board (150mm * 70mm * 10mm), the non - dulling water - borne polyurethane topcoats obtained from Examples 1 - 4 and Comparative Examples 1 - 5 were sprayed, with a dry film thickness of 40 - 50μm. The drying conditions were leveling for 15 min (23℃, 80 - 95% RH), and then drying at 50℃ for 70 min. After drying for 7 days at room temperature, various properties were tested.

[0090] Volatile organic compounds (VOCs) test: The test was carried out according to the provisions of GB / T 23985 - 2009 8.4. Three groups of values were tested and then their average value was calculated.

[0091] Water resistance test: The test was carried out according to the provisions of GB / T 1733 - 1993: 3 / 4 of the test panel was immersed in deionized water, the water temperature was adjusted to 23 ± 2℃, and this temperature was maintained throughout the test process.

[0092] Adhesion test: The adhesion test was carried out by the cross - hatch method, with grades from 5 - 1, where 5 is the best and 1 is the worst.

[0093] Gloss loss test: It was carried out according to the visual colorimetry of paints and varnishes in GB / T976l - 2008. Among them, the gloss loss degree was determined by visual inspection to determine the gloss loss ratio grade, from 0 - 5. Grade 0 means no visible difference, and grade 5 means a very large difference.

[0094] Table 1

[0095] Adhesion / level VOC / g / L Water resistance / h Loss of gloss Example 1 5 80 216 0 Example 2 5 75 192 0 Example 3 5 68 200 0 Example 4 5 76 216 0 Comparative example 1 2 169 144 5 Comparative example 2 2 87 156 4 Comparative example 3 3 82 184 1 Comparative example 4 3 84 178 1 Comparative example 5 3 80 188 1

[0096] As can be seen from Table 1, the physical and chemical performance indicators of the water - borne polyurethane topcoats obtained from Examples 1 - 4 are all very good. The adhesion is grade 5, the VOC is between 68 - 80 g / L, the water resistance is 192 - 216 hours, and the gloss loss grade is 0, indicating no visible difference and no gloss loss. By using the water - borne polyurethane emulsion, the reaction probability between the curing agent and the resin can be effectively increased, and the probability of side reactions between the curing agent and amines and water can be reduced, solving the problems such as gloss loss that are prone to occur in conventional two - component polyurethane topcoats in humid environments. By using a special water - borne curing agent, the compatibility with the water - borne polyurethane emulsion is further improved. Similarly, by using graphene - modified fillers, the compatibility between the fillers and other components is enhanced, and by utilizing the properties of graphene, the water resistance performance is further improved, completely solving the problem of gloss loss that is prone to occur in conventional two - component polyurethane topcoats in humid environments.

[0097] As can be seen from Table 1, through the comparative analysis of the performance indicators of the waterborne polyurethane topcoats obtained in Example 4 and Comparative Example 1, the waterborne polyurethane emulsion prepared in this application can effectively increase the reaction probability between the curing agent and the resin, reduce the probability of side reactions between the curing agent and amines or water, and solve the problems such as loss of gloss that easily occur in conventional two-component polyurethane topcoats in humid environments.

[0098] As can be seen from Table 1, through the comparative analysis of the performance indicators of the waterborne polyurethane topcoats obtained in Example 4 and Comparative Example 2, the graphene-modified filler prepared in this application improves the compatibility of the filler with other components. Utilizing the properties of graphene, it further enhances the water resistance performance and completely solves the problem of loss of gloss that easily occurs in conventional two-component polyurethane topcoats in humid environments.

[0099] As can be seen from Table 1, through the comparative analysis of the performance indicators of the waterborne polyurethane topcoats obtained in Example 4 and Comparative Examples 3 - 5, in this application, a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, and sodium dodecylbenzenesulfonate with a mass ratio of 5:2:3 is used as the dispersant and added to the waterborne polyurethane topcoat, and the performance of the obtained coating is relatively good.

[0100] The above embodiments are only used to explain the technical solutions of this application rather than limit them. Although the above embodiments have specifically described this application, those skilled in the art should understand that modifications or equivalent replacements can still be made to the specific implementation manners of this application. Any modification and equivalent replacement that do not depart from the spirit and scope of this application shall be covered by the protection scope of this application.

Claims

1. A waterborne polyurethane topcoat that does not lose its luster, characterized in that, It includes component A and aqueous curing agent B; by weight, component A includes raw materials in the following mass parts: 60 - 80 parts of aqueous polyurethane emulsion, 11 - 20 parts of graphene-modified filler, 5 - 10 parts of pigment, 0.5 - 0.8 parts of defoamer, 2 - 3 parts of dispersant, 0.5 - 1.5 parts of aqueous thickener, 0 - 2 parts of polyethylene wax emulsion, and 10 - 20 parts of water. The mass ratio of component A to aqueous curing agent B is 100:13 - 15; The aqueous curing agent B, by weight, includes raw materials in the following weight parts: 34.0 - 38.0 parts of hydrophilic aliphatic polyisocyanate, 44.0 - 48.0 parts of lipophilic aliphatic polyisocyanate, and 14.0 - 22.0 parts of propylene glycol methyl ether acetate, where the hydrophilic aliphatic polyisocyanate and lipophilic aliphatic polyisocyanate are composed in a mass ratio of 1:0.6 - 0.8; The preparation method of the aqueous polyurethane emulsion includes the following steps: S31. By mass parts, in a reactor, under the protection of inert gas nitrogen, add 2 - 3 parts of hydroxyl-terminated polybutadiene, heat up to 60 °C, dropwise add 10 parts of hexamethylene diisocyanate, stir and mix evenly, heat up to 85 °C, add 0.05 - 0.1 part of catalyst A, and carry out a constant-temperature reaction for 2 - 3 h; S32. By mass parts, in the reactor of step S31, continue to add 2 - 3 parts of poly(propylene carbonate) diol and 3 - 5 parts of N,N-dimethylformamide, stir and mix evenly, heat up to 80 °C, add 0.02 - 0.05 part of p-hydroxyanisole and 0.08 - 0.12 part of catalyst B, carry out a constant-temperature reaction for 2 - 4 h, add 0.2 - 0.3 part of 1,4-butanediol, continue the reaction for 1 h, cool down to 40 °C, add 0.2 - 0.4 part of triethylamine, stir and react for 2 - 4 min, add deionized water, and carry out high-speed stirring emulsification to obtain an aqueous polyurethane emulsion with a solid content of 40wt% - 45wt%; among them, the catalyst A is one or more of stannous octoate, dibutyltin dilaurate, and dimethyltin diacetate, and the catalyst B is one or more of dibutyltin maleate, zinc naphthenate, and zinc octoate; The preparation method of the graphene-modified filler is: by mass parts, add 5 - 10 parts of 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent to an aqueous solution with an ethanol mass concentration of 50% in 100 parts, heat up to 60 °C, stir to obtain a 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent hydrolysis solution, then add 2 - 3 parts of graphene to the 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane coupling agent hydrolysis solution, stir evenly, and finally add 30 - 50 parts of filler to the above solution, stir for 15 minutes to obtain the graphene-modified filler; among them, the filler is one or more of talc powder, calcium carbonate, and kaolin; The dispersant is a composition of vinyltris(β-methoxyethoxy)silane, vinyltrimethoxysilane, and sodium dodecylbenzenesulfonate in a mass ratio of 5:1 - 3:2 - 4.

2. The waterborne polyurethane topcoat without loss of gloss according to claim 1, characterized in that, The pigment is one or a mixture of more than one of titanium dioxide, iron oxide red, phthalocyanine blue, and carbon black.

3. The waterborne polyurethane topcoat without light loss according to claim 1, wherein, The defoamer is one of polyvinyl acetate and dimethyl silicone oil, and the water-based thickener is one of hydroxypropyl methylcellulose, hydroxyethyl cellulose, and polyurethane associative thickener.

4. A preparation method of a non-yellowing aqueous polyurethane topcoat as described in any one of claims 1-3, characterized in that, It includes the following steps: S101. By mass fraction, in a reactor, sequentially add waterborne polyurethane emulsion, graphene-modified filler, pigment, defoamer, dispersant, water-based thickener, polyethylene wax emulsion, and water, mix and stir. The stirring rate is 200 - 300 r / min, the stirring time is 10 - 15 min, and then let it stand to obtain Component A; S102. By mass fraction, in a reactor, mix hydrophilic aliphatic polyisocyanate, lipophilic aliphatic polyisocyanate, and propylene glycol methyl ether acetate, stir. The stirring rate is 100 - 200 r / min, the stirring time is 5 - 7 min, and then let it stand to obtain water-based curing agent B; S103. After mixing Component A and water-based curing agent B, a non - loss of gloss waterborne polyurethane topcoat is obtained.