Aqueous acrylate-modified polyurethane dispersions, methods of making and using the same

Abstract

The present application belongs to the technical field of paint, and particularly relates to a water-based acrylic ester modified polyurethane dispersion, a preparation method and application thereof. The water-based acrylic ester modified polyurethane dispersion has a core-shell structure; the core of the core-shell structure comprises modified polyurethane; the shell layer of the core-shell structure comprises polyacrylate; the modified polyurethane is obtained by modifying polyurethane prepolymer with a capping agent 1; the capping agent 1 comprises at least one of linoleic acid and n-octadecanol. The present application takes hydrophobic modified polyurethane as a core, grafts polyacrylate on the core through a free radical polymerization reaction, and obtains the water-based acrylic ester modified polyurethane dispersion with a core-shell structure. The modified polyurethane is connected by hydrogen bonds through the hydrophilic segments of the polyurethane core and the shell layer, forms a transient grid structure, produces thickening and thixotropy, improves the directional arrangement of silver powder in silver powder paint and the flash effect, and improves water resistance.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and specifically relates to a water-based acrylate-modified polyurethane dispersion, its preparation method, and its application. Background Technology

[0002] Traditional solvent-based coatings contain large amounts of volatile organic compounds (VOCs), which do not meet current environmental protection requirements. Waterborne coatings use water as the dispersion medium, replacing organic solvents entirely or mostly, greatly reducing the use and emission of VOCs and mitigating the environmental harm and pollution during coating production and application. This makes it one of the main development directions for green and environmentally friendly coatings. Waterborne acrylic-modified polyurethane dispersions (PUA) are known as "third-generation waterborne polyurethanes." Polyacrylate (PA) has excellent solvent resistance, mechanical properties, water resistance, weather resistance, and gloss and color retention, while polyurethane (PU) has excellent abrasion resistance, cold resistance, and flexibility. However, due to the large amount of hydrophilic monomers introduced into the molecular chain during the waterborne polyurethane process, its water resistance is reduced and its thickening effect is poor, which greatly limits the application range of waterborne polyurethane coatings.

[0003] Water-based two-component metallic paint is favored for its rich colors, excellent angle-dependent color effect, and elegant metallic decorative effect, and is widely used in heating equipment, metal pipes, automotive parts, and plastic panel surfaces. Currently, the coating of metallic surfaces in China mainly adopts a composite coating process of single-component metallic paint and clear topcoat. This coating process is complex and costly, which is not conducive to large-scale promotion and application. Replacing the single-component silver powder paint with a composite coating process of clear topcoat and acrylic modified polyurethane silver powder paint with a two-component water-based acrylic modified polyurethane silver powder paint can simplify the existing construction process to a certain extent and help reduce the coating costs for downstream customers. However, due to the high latent heat of water and slow evaporation rate in the system, water-based two-component silver powder paint is prone to defects such as sagging, silver powder sedimentation, and poor silver powder orientation. This makes it impossible for the flake-like aluminum powder to present a "flat" state in the wet or dry film during spraying or film formation, resulting in the silver powder paint failing to meet the requirements for blackening, mottled appearance, gloss, reflectivity, and metallic feel. In conventional water-based two-component metallic paint formulations, rheology modifiers such as low-shear viscosity thickeners, non-Newtonian pseudoplastic thickeners, and organobentonite thixotropic agents are often used to adjust the viscosity and thixotropy of the water-based metallic paint system, thereby enhancing the orientation, anti-sagging, and anti-settling effects of the metallic powder. However, when the resin system contains a large amount of hydrophilic solvents or hydrophilic groups, the thickening efficiency of water-based rheology modifiers is extremely low, making it impossible for water-based metallic paints to be applied in high-end fields with requirements for high humidity, high film thickness, and strong metallic feel.

[0004] Therefore, there is an urgent need to provide a water-based acrylate-modified polyurethane dispersion that has good thickening, thixotropic and water resistance properties, and the silver powder paint prepared by it has excellent silver powder orientation and glitter effect. Summary of the Invention

[0005] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative or create conditions. Specifically, the present invention provides an aqueous acrylate-modified polyurethane dispersion, which has good thickening properties, thixotropic properties and water resistance, and the silver powder paint prepared from it has excellent water resistance, silver powder directional alignment effect and glitter effect.

[0006] The inventive concept of this invention is as follows: The waterborne acrylate-modified polyurethane dispersion of this invention has a core-shell structure; the core of the core-shell structure includes modified polyurethane; the shell of the core-shell structure includes polyacrylate; the modified polyurethane is obtained by modifying a polyurethane prepolymer with a capping agent 1; the capping agent 1 includes at least one of linoleic acid and n-octadecyl alcohol. This invention modifies polyurethane prepolymers using hydrophobic end-capping agents to synthesize polyurethanes with hydrophobic ends and carbon-carbon double bond structures. In waterborne acrylate-modified polyurethane dispersions, the hydrophobic end structure of the modified polyurethane enables strong association and hydrogen bonding in emulsions and resins. In the core-shell structure of the waterborne acrylate-modified polyurethane dispersion, the hydrophobic ends of the polyurethane core associate with each other to form micelles. Furthermore, the modified polyurethane with hydrophobic ends can be connected to the hydrophilic segments of the polyurethane core and the polyacrylate shell through hydrogen bonds to form a transient network structure, thereby producing thickening and thixotropic properties, and improving water resistance. As a result, the prepared silver powder paint has excellent water resistance, silver powder orientation effect, and glitter effect.

[0007] Therefore, a first aspect of the present invention provides an aqueous acrylate-modified polyurethane dispersion.

[0008] Specifically, the waterborne acrylate-modified polyurethane dispersion has a core-shell structure; the core of the core-shell structure comprises modified polyurethane; and the shell of the core-shell structure comprises polyacrylate.

[0009] The modified polyurethane is obtained by modifying the polyurethane prepolymer with end-capping agent 1;

[0010] The capping agent 1 includes at least one of linoleic acid and n-octadecyl alcohol.

[0011] Specifically, the end-capping agent 1, as a long carbon chain end-capping agent, is mainly used for the hydrophobic modification of polyurethane prepolymers. The waterborne acrylate-modified polyurethane dispersion of this invention is a self-emulsifying, surfactant-free, environmentally friendly waterborne resin that exhibits thixotropy, which facilitates the directional alignment of silver powder.

[0012] Preferably, the method for preparing the modified polyurethane includes the following steps:

[0013] (1) The polymer polyol is dehydrated under vacuum, and catalyst 1 and isocyanate monomer are added to carry out reaction 1 to obtain polyurethane prepolymer I; catalyst 2 and chain extender are added to polyurethane prepolymer I to carry out reaction 2 to obtain polyurethane prepolymer II.

[0014] (2) The end-capping agent 1, end-capping agent 2 and the polyurethane prepolymer II obtained in step (1) are mixed and reacted to obtain the modified polyurethane.

[0015] Preferably, in step (1), the polymer polyol includes at least one of polyether polyol and polyester polyol.

[0016] Preferably, in step (1), both catalysts 1 and 2 comprise dibutyltin dilaurate.

[0017] Preferably, in step (1), the isocyanate monomer includes at least one of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate.

[0018] Preferably, in step (1), the chain extender includes at least one of diethylene glycol, dimethylolpropionic acid, and sodium 1,4-butanediol-2-sulfonate.

[0019] Preferably, in step (1), the vacuum degree of the vacuum dehydration is 0.08-0.095 MPa, the vacuum dehydration temperature is 50-70℃, and the vacuum dehydration time is 0.8-1.2 h; more preferably, in step (1), the vacuum degree of the vacuum dehydration is 0.085-0.095 MPa, the vacuum dehydration temperature is 55-65℃, and the vacuum dehydration time is 0.9-1.1 h; even more preferably, in step (1), the vacuum degree of the vacuum dehydration is 0.09 MPa, the vacuum dehydration temperature is 60℃, and the vacuum dehydration time is 1 h.

[0020] Preferably, in step (1), the reaction temperature of reaction 1 is 75-90℃ and the reaction time of reaction 1 is 1.5-2.5h; more preferably, in step (1), the reaction temperature of reaction 1 is 80-90℃ and the reaction time of reaction 1 is 1.8-2.2h; even more preferably, in step (1), the reaction temperature of reaction 1 is 85℃ and the reaction time of reaction 1 is 2h.

[0021] Preferably, in step (1), the reaction temperature of reaction 2 is 55-75℃ and the reaction time of reaction 2 is 2.5-3.5h; more preferably, in step (1), the reaction temperature of reaction 2 is 60-70℃ and the reaction time of reaction 2 is 2.7-3.3h; even more preferably, in step (1), the reaction temperature of reaction 2 is 65℃ and the reaction time of reaction 2 is 3h.

[0022] Specifically, step (1) yields a polyurethane prepolymer with isocyanate (-NCO) end groups.

[0023] Preferably, in step (2), the capping agent 1 includes at least one of linoleic acid and n-octadecyl alcohol.

[0024] Preferably, in step (2), the capping agent 2 comprises 2-hydroxyethyl methacrylate.

[0025] Preferably, in step (2), the reaction temperature of reaction 3 is 65-85℃ and the reaction time of reaction 3 is 2.0-3.0h; more preferably, in step (2), the reaction temperature of reaction 3 is 70-80℃ and the reaction time of reaction 3 is 2.2-2.8h; even more preferably, in step (2), the reaction temperature of reaction 3 is 75℃ and the reaction time of reaction 3 is 2.5h.

[0026] Specifically, linoleic acid (LA) and n-octadecyl alcohol are used as long-chain end-capping agents, mainly for hydrophobic modification; 2-hydroxyethyl methacrylate (HEMA) is used as an end-capping agent to complete the -NCO end-capping. Because it contains carbon-carbon double bonds, it can form conjugated double bonds with the 8th, 9th, 10th, and 11th carbon atoms of linoleic acid (LA), while providing active reaction sites for subsequent free radical copolymerization reactions.

[0027] Preferably, in the modified polyurethane, the molar ratio of isocyanate group (-NCO) to hydroxyl group (-OH) is 1.0-1.5:1; more preferably, in the modified polyurethane, the molar ratio of -NCO to -OH is 1.05-1.45:1.

[0028] A second aspect of the present invention provides a method for preparing the waterborne acrylate-modified polyurethane dispersion described in the first aspect of the present invention.

[0029] Specifically, the preparation method of the waterborne acrylate-modified polyurethane dispersion includes the following steps:

[0030] (1) Mix acrylate monomers and initiators to obtain a mixture. Take a portion of the mixture and mix it with modified polyurethane and neutralizer, then emulsify it to obtain a mixed emulsion.

[0031] (2) The remaining mixture is mixed with the mixed emulsion obtained in step (1) and reacted to obtain the waterborne acrylate-modified polyurethane dispersion.

[0032] Specifically, step (1) employs a monomer pre-emulsification process. The addition of some acrylate monomers and some initiators reduces the viscosity of the modified polyurethane, increases the success rate of reverse emulsification, acts as both a solvent and a raw material for acrylic modification, avoids the use of emulsifiers, and improves the water resistance of the resin film. This invention uses hydrophobically modified polyurethane as the core, and through free radical polymerization, grafts polyacrylate onto the core to obtain a core-shell structured waterborne acrylate-modified polyurethane dispersion.

[0033] Specifically, step (1) is carried out at room temperature. Therefore, step (1) is merely a physical mixing of the raw material components, and no chemical reaction occurs.

[0034] Preferably, the mass ratio of the acrylate monomer to the modified polyurethane is 4:(4-6); more preferably, the mass ratio of the acrylate monomer to the modified polyurethane is 4:(4.5-5.5); even more preferably, the mass ratio of the acrylate monomer to the modified polyurethane is 4:5.

[0035] Preferably, the emulsification is performed by adding deionized water while the mixture is in a high-speed dispersion state to complete the emulsification treatment of the modified polyurethane.

[0036] Preferably, in step (2), the reaction temperature is 65-85℃ and the reaction time is 1.5-2.5h; more preferably, in step (2), the reaction temperature is 70-80℃ and the reaction time is 1.8-2.2h; even more preferably, in step (2), the reaction temperature is 75℃ and the reaction time is 2h.

[0037] Preferably, the remaining mixture is added dropwise to the mixed emulsion obtained in step (1) for mixing.

[0038] Preferably, the post-initiation reaction is carried out after the reaction is completed.

[0039] Specifically, the post-initiation reaction refers to extending the reaction time or adding an additional initiator (generally 0.1% of the total amount of reaction initiator) to consume the remaining trace amounts of monomer in the reaction system, or to further increase the molecular weight.

[0040] Preferably, the time for the post-initiation reaction is 0.8-1.2 hours; more preferably, the time for the post-initiation reaction is 0.9-1.1 hours; and even more preferably, the time for the post-initiation reaction is 1 hour.

[0041] Preferably, the acrylate monomers include at least one of methacrylic acid, isobornyl methacrylate, isobutyl methacrylate, glycidyl methacrylate, isooctyl methacrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, acrylic acid, n-butyl acrylate, acrylamide, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, cyclohexyl acrylate, styrene, and isobornyl methacrylate.

[0042] Preferably, the initiator includes at least one selected from tert-butyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, di-tert-pentyl peroxide, potassium persulfate, ammonium persulfate, and sodium persulfate.

[0043] Preferably, the neutralizing agent comprises an amine neutralizing agent; more preferably, the neutralizing agent comprises triethylamine.

[0044] A third aspect of the present invention provides a silver powder paint.

[0045] Specifically, the silver powder paint includes the water-based acrylate-modified polyurethane dispersion described in the first aspect of this invention.

[0046] Preferably, the silver powder paint includes component A and component B; component A includes an aqueous acrylate-modified polyurethane dispersion, cosolvent A, and silver powder; component B includes an isocyanate curing agent and cosolvent B.

[0047] More preferably, component A further includes water and additives.

[0048] Preferably, the mass ratio of component A to component B is 4.5-8.5:1; more preferably, the mass ratio of component A to component B is 5-8:1.

[0049] Specifically, components A and B should be stored separately. When needed, components A and B can be mixed according to the above mass ratio.

[0050] Preferably, the isocyanate curing agent comprises a hydrophilic aliphatic polyisocyanate; more preferably, the isocyanate curing agent comprises hexamethylene diisocyanate (HDI).

[0051] Preferably, the cosolvent A and cosolvent B each independently include at least one of ethylene glycol butyl ether, propylene glycol butyl ether, dipropylene glycol butyl ether, dipropylene glycol methyl ether, and propylene glycol methyl ether acetate.

[0052] Preferably, the additive is an aqueous additive.

[0053] Preferably, the additives include at least one of the following: neutralizer, wetting agent, dispersant, leveling agent, rheology modifier, thixotropic modifier, silver powder orientation additive, anti-flash rust agent, and defoamer.

[0054] Preferably, the neutralizing agent includes an organic alcohol amine neutralizing agent.

[0055] Preferably, the wetting agent comprises a fluorosilicone hybrid wetting agent.

[0056] Preferably, the dispersant comprises a polyurethane-modified acrylic copolymer dispersant.

[0057] Preferably, the leveling agent comprises a fluorinated acrylate leveling agent.

[0058] Preferably, the rheology modifier comprises a nonionic polyurethane low-shear thickener.

[0059] Preferably, the thixotropic agent comprises an inorganic colloidal mineral thixotropic agent.

[0060] Preferably, the silver powder orientation aid includes a polyamide wax-based silver powder orientation aid.

[0061] Preferably, the flash rust inhibitor comprises a mixture of phosphate and various organic complex acids.

[0062] Preferably, the defoamer comprises a block copolymer defoamer of polyethylene oxide and polypropylene oxide.

[0063] Preferably, by weight, component A comprises 45-65 parts of waterborne acrylate-modified polyurethane dispersion, 4.5-11 parts of cosolvent A, 4.5-11 parts of silver powder, 0.9-8 parts of additives, and 18-35 parts of water; component B comprises 11-18 parts of isocyanate curing agent and 3.5-6.5 parts of cosolvent B.

[0064] More preferably, by weight, component A comprises 50-60 parts of waterborne acrylate-modified polyurethane dispersion, 5-10 parts of cosolvent A, 5-10 parts of silver powder, 1-5 parts of additives, and 20-32 parts of water; component B comprises 12-17 parts of isocyanate curing agent and 4-6 parts of cosolvent B.

[0065] Specifically, the molecular structure of the waterborne acrylate-modified polyurethane dispersion of the present invention includes a modified polyurethane core with hydrophobic ends and a hydroxyl-containing polyacrylic shell, enabling it to undergo a crosslinking reaction with an isocyanate curing agent, thereby preparing a two-component waterborne coating. Simultaneously, the unique self-thickening and thixotropic properties of the hydrophobic modified polyurethane core are beneficial for improving the directional alignment and shimmering effect of silver powder in waterborne two-component silver powder paint, and can better solve the problems of sagging and poor silver powder orientation in existing waterborne two-component silver powder paints during application.

[0066] Preferably, the method for preparing the silver powder paint includes the following steps:

[0067] (1) Mix the raw material components of component A to obtain component A;

[0068] (2) Mix the raw material components of component B to obtain component B; component A and component B constitute the silver powder paint.

[0069] Preferably, in step (1), the silver powder is first prepared into a silver powder paste, and then mixed with other components to obtain component A.

[0070] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0071] (1) The waterborne acrylate-modified polyurethane dispersion of the present invention is a self-emulsifying and surfactant-free environmentally friendly waterborne resin with thixotropic properties, which helps the directional alignment of silver powder. The present invention modifies the polyurethane prepolymer by using hydrophobic end-capping agents (octadecyl alcohol and / or linoleic acid) to synthesize a modified polyurethane with hydrophobic ends and carbon-carbon double bond structure. In the waterborne acrylate-modified polyurethane dispersion, due to the hydrophobic end structure of the modified polyurethane, the waterborne acrylate-modified polyurethane dispersion can have strong association and hydrogen bonding in the emulsion and resin. In the waterborne acrylate-modified polyurethane dispersion with core-shell structure, the hydrophobic ends of the polyurethane core associate with each other to form micelles. Furthermore, the modified polyurethane with hydrophobic ends can be connected to the hydrophilic segments of the polyurethane core and the polyacrylate shell through hydrogen bonds to further form a transient network structure, thereby producing thickening and thixotropic properties, and improving water resistance and mechanical properties.

[0072] (2) The molecular structure of the waterborne acrylate-modified polyurethane dispersion of the present invention includes a modified polyurethane core with hydrophobic ends and a hydroxyl-containing polyacrylic shell, which allows it to undergo a crosslinking reaction with an isocyanate curing agent to prepare a two-component waterborne coating. Simultaneously, the unique self-thickening and thixotropic properties of the hydrophobic modified polyurethane core are beneficial for improving the directional alignment and glitter effect of silver powder in waterborne two-component silver powder paint, and can better solve the problems of sagging and poor silver powder orientation in existing waterborne two-component silver powder paints during application.

[0073] (3) In the preparation of waterborne acrylate-modified polyurethane dispersion, the present invention adopts a monomer pre-emulsification process. The role of adding some acrylate monomers and some initiators is to reduce the viscosity of modified polyurethane, increase the success rate of reverse emulsification, act as both solvent and raw material for acrylic acid modification, avoid the use of emulsifiers, and improve the water resistance of resin film. Detailed Implementation

[0074] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0075] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0076] The source information of the raw material components in the application examples of this invention is as follows:

[0077] Wetting agent TEGO-245, purchased from Guangzhou Tinci New Materials Co., Ltd.

[0078] Defoamer Surfynol DF110D was purchased from Guangzhou Tinci New Materials Co., Ltd.

[0079] Surfynol 420 defoamer was purchased from Guangzhou Tinci New Materials Co., Ltd.

[0080] Leveling agent BYK-333, purchased from Guangzhou Tinci New Materials Co., Ltd.;

[0081] NALZIN FA 179 anti-flash rust agent was purchased from Deqian (Shanghai) Chemical Co., Ltd.

[0082] Silver powder SR-7010, purchased from Cair New Materials Co., Ltd.

[0083] Dispersant BYK-190 was purchased from Guangzhou Tinci New Materials Co., Ltd.

[0084] PUR64, purchased from Mingling Chemicals, Germany;

[0085] Coapur2025, purchased from Shanghai Lingrui Chemical Co., Ltd.

[0086] The silver powder orientation alignment aid BYK-AQUATIX 8421 was purchased from Guangzhou Tinci New Materials Co., Ltd.

[0087] Waterborne isocyanate curing agent Ultra 2655, purchased from Covestro Polymers (China) Co., Ltd.

[0088] Example 1

[0089] A method for preparing an aqueous acrylate-modified polyurethane dispersion includes the following steps:

[0090] (1) Under dry nitrogen protection, the polyether polyol N210 (M) after vacuum dehydration (vacuum dehydration at 0.09 MPa and 60°C for 1 h) was subjected to further dehydration. n =1000) 60 parts and isophorone diisocyanate (IPDI) 18.34 parts were added to a four-necked flask, and 0.4 parts of dibutyltin dilaurate (T-12) catalyst were added. After mixing evenly, the mixture was heated to 85°C and reacted for 2 hours to obtain polyurethane prepolymer I. Then the reaction system was cooled to 65°C, diluted with a mixed solution of acetone and methyl isobutyl ketone (10.12 parts each of acetone and methyl isobutyl ketone) to reduce the viscosity of the polyurethane oligomer, and 0.2 parts of dibutyltin dilaurate (T-12) and 1.3 parts of diethylene glycol (DEG) were added to carry out a chain extension reaction for 3 hours to obtain polyurethane prepolymer II;

[0091] (2) The polyurethane prepolymer II with -NCO end group synthesized in step (1) was end-capped using 3.27 parts of linoleic acid (LA) and 1.53 parts of 2-hydroxyethyl methacrylate (HEMA); that is, 0.2 parts of butyltin dibutylsilicate (T-12) was dissolved in 3.27 parts of 2-hydroxyethyl methacrylate (HEMA) and 1.53 parts of linoleic acid (LA) and added to the mixed solution of polyurethane prepolymer II obtained in step (1), and the system temperature was raised to 75°C. After stirring and reacting under nitrogen atmosphere for 2.5 h, the temperature was lowered to obtain modified polyurethane.

[0092] (3) At 35°C, 1 / 3 of the total amount of acrylate monomers and initiators used to prepare the waterborne acrylate-modified polyurethane dispersion (i.e., 13.62 parts of methyl methacrylate, 13.33 parts of butyl acrylate (BA), 6.67 parts of isobornyl methacrylate (IBOMA), 5.67 parts of styrene (St), 1.31 parts of 2-hydroxyethyl methacrylate (HEMA), and 0.85 parts of azobisisobutyronitrile (AIBN)) was added to the modified polyurethane obtained in step (2), so that the acrylate monomers and initiator could be used as solvents to further dilute the modified polyurethane obtained in step (2); and after neutralizing the modified polyurethane with 2.64 parts of triethylamine (TEA), 230.23 parts of deionized water were added dropwise at a stirring speed of 800 rpm to reverse emulsify the modified polyurethane, resulting in a milky white modified polyurethane mixed emulsion;

[0093] (4) Under the protection of inert nitrogen gas, the modified polyurethane mixed emulsion obtained in step (3) was heated to 75°C. Under stirring, a mixed solution of 26.38 parts methyl methacrylate, 26.67 parts butyl acrylate, 13.33 parts isobornyl methacrylate, 11.33 parts styrene, 2.63 parts 2-hydroxyethyl methacrylate and 1.29 parts azobisisobutyronitrile was slowly and dropwise added to the reaction system. The dropwise addition lasted for 3 hours. After the dropwise addition was completed, the temperature was maintained for another 2 hours. Then, 1 part potassium persulfate was dissolved in 10 parts deionized water and added to the reaction system. The reaction was carried out at a constant temperature of 75°C for 1 hour and then cooled to room temperature to obtain an aqueous acrylate modified polyurethane dispersion.

[0094] Example 2

[0095] A method for preparing an aqueous acrylate-modified polyurethane dispersion includes the following steps:

[0096] (1) Under dry nitrogen protection, the polyether polyol N210 (M) after vacuum dehydration (vacuum dehydration at 0.09 MPa and 60°C for 1 h) was subjected to further dehydration. n =1000) 60 parts and 4,4'-dicyclohexylmethane diisocyanate (HMDI) 20.46 parts were added to a four-necked flask, and 0.4 parts of dibutyltin dilaurate (T-12) catalyst were added. After mixing evenly, the mixture was heated to 85°C and reacted for 2 hours to obtain polyurethane prepolymer I. Then the reaction system was cooled to 65°C, diluted with a mixed solution of acetone and methyl isobutyl ketone (10.12 parts each of acetone and methyl isobutyl ketone) to reduce the viscosity of the polyurethane oligomer, and 0.2 parts of dibutyltin dilaurate (T-12) and 1.3 parts of diethylene glycol (DEG) were added to carry out a chain extension reaction for 3 hours to obtain polyurethane prepolymer II.

[0097] (2) The polyurethane prepolymer II with -NCO end group synthesized in step (1) was end-capped using 3.27 parts of linoleic acid (LA) and 1.53 parts of 2-hydroxyethyl methacrylate (HEMA); that is, 0.2 parts of butyltin dimethyl methacrylate (T-12) was dissolved in a mixed solution of 3.27 parts of 2-hydroxyethyl methacrylate (HEMA), 1.53 parts of linoleic acid (LA) and the polyurethane prepolymer II obtained in step (1), and the system temperature was raised to 75°C. After stirring and reacting under a nitrogen atmosphere for 2.5 h, the temperature was lowered to obtain the modified polyurethane.

[0098] (3) At 35°C, 1 / 3 of the total amount of acrylate monomers and initiators used to prepare the waterborne acrylate-modified polyurethane dispersion (i.e., 16.44 parts of methyl methacrylate, 14.99 parts of butyl acrylate, 5 parts of isobornyl methacrylate, 3.34 parts of styrene, 1.26 parts of 2-hydroxyethyl methacrylate, and 0.85 parts of azobisisobutyronitrile) were added to the modified polyurethane obtained in step (2) to further dilute the modified polyurethane obtained in step (2) by using the acrylate monomers and initiator as solvents; and after neutralizing the modified polyurethane with 2.64 parts of triethylamine (TEA), 246.35 parts of deionized water were added dropwise at a stirring speed of 800 rpm to reverse emulsify the modified polyurethane to obtain a milky white modified polyurethane mixed emulsion;

[0099] (4) Under the protection of inert nitrogen gas, the modified polyurethane mixed emulsion obtained in step (3) was heated to 75°C. Under stirring, a mixed solution of 32.89 parts methyl methacrylate, 29.97 parts butyl acrylate, 10 parts isobornyl methacrylate, 6.67 parts styrene, 2 parts 2-hydroxyethyl methacrylate and 1.29 parts azobisisobutyronitrile was slowly and dropwise added to the reaction system. The dropwise addition lasted for 3 hours. After the dropwise addition was completed, the temperature was maintained for another 2 hours. Then, 1 part potassium persulfate was dissolved in 10 parts deionized water and added to the reaction system. The reaction was carried out at a constant temperature of 75°C for 1 hour and then cooled to room temperature to obtain an aqueous acrylate modified polyurethane dispersion.

[0100] Example 3

[0101] A method for preparing an aqueous acrylate-modified polyurethane dispersion includes the following steps:

[0102] (1) Under dry nitrogen protection, the polyester polyol PCL (M) after vacuum dehydration (vacuum dehydration at 0.09 MPa and 60℃ for 1 h) was... n =1000) 60 parts and isophorone diisocyanate (IPDI) 18.34 parts were added to a four-necked flask, and 0.4 parts of dibutyltin dilaurate (T-12) catalyst were added. After mixing evenly, the mixture was heated to 85°C and reacted for 2 hours to obtain polyurethane prepolymer I. Then the reaction system was cooled to 65°C, diluted with a mixed solution of acetone and methyl isobutyl ketone (10.12 parts each of acetone and methyl isobutyl ketone) to reduce the viscosity of the polyurethane oligomer, and 0.2 parts of dibutyltin dilaurate (T-12) and 1.3 parts of diethylene glycol (DEG) were added to carry out a chain extension reaction for 3 hours to obtain polyurethane prepolymer II;

[0103] (2) The polyurethane prepolymer II with -NCO end group synthesized in step (1) was end-capped using 3.27 parts of linoleic acid (LA) and 1.53 parts of 2-hydroxyethyl methacrylate (HEMA); that is, 0.2 parts of butyltin dimethyl methacrylate (T-12) was dissolved in a mixed solution of 3.27 parts of 2-hydroxyethyl methacrylate (HEMA), 1.53 parts of linoleic acid (LA) and the polyurethane prepolymer II obtained in step (1), and the system temperature was raised to 75°C. After stirring and reacting under a nitrogen atmosphere for 2.5 h, the temperature was lowered to obtain the modified polyurethane.

[0104] (3) At 35°C, 1 / 3 of the total amount of acrylate monomers and initiators used to prepare the waterborne acrylate-modified polyurethane dispersion (i.e., 13.62 parts of methyl methacrylate, 13.60 parts of butyl acrylate, 5.34 parts of isobornyl methacrylate, 4 parts of styrene, 1.33 parts of 2-hydroxyethyl methacrylate, and 0.85 parts of azobisisobutyronitrile) were added to the modified polyurethane obtained in step (2) to further dilute the modified polyurethane obtained in step (2) by using the acrylate monomers and initiator as solvents; and after neutralizing the modified polyurethane with 2.64 parts of triethylamine (TEA), 234.65 parts of deionized water were added dropwise at a stirring speed of 800 rpm to reverse emulsify the modified polyurethane to obtain a milky white modified polyurethane mixed emulsion;

[0105] (4) Under the protection of inert nitrogen gas, the modified polyurethane mixed emulsion obtained in step (3) was heated to 75°C. While stirring, a mixed solution of 27.24 parts methyl methacrylate, 27.19 parts butyl acrylate, 8 parts isobornyl methacrylate, 10.67 parts styrene, 2.66 parts 2-hydroxyethyl methacrylate, and 1.29 parts azobisisobutyronitrile was slowly and dropwise added to the reaction system for 3 hours. After the addition was complete, the mixture was kept at the same temperature for 2 hours. Then, 1 part potassium persulfate was dissolved in 10 parts deionized water and added to the reaction system. The mixture was reacted at a constant temperature of 75°C for 1 hour and then cooled to room temperature to obtain an aqueous acrylate-modified polyurethane dispersion.

[0106] Example 4

[0107] A method for preparing an aqueous acrylate-modified polyurethane dispersion includes the following steps:

[0108] (1) Under dry nitrogen protection, the polyester polyol PCL (M) after vacuum dehydration (vacuum dehydration at 0.09 MPa and 60℃ for 1 h) was... n=1000) 60 parts and 4,4'-dicyclohexylmethane diisocyanate (HMDI) 20.46 parts were added to a four-necked flask, and 0.4 parts of dibutyltin dilaurate (T-12) catalyst were added. After mixing evenly, the mixture was heated to 85°C and reacted for 2 hours to obtain polyurethane prepolymer I. Then the reaction system was cooled to 65°C, diluted with a mixed solution of acetone and methyl isobutyl ketone (10.12 parts each of acetone and methyl isobutyl ketone) to reduce the viscosity of the polyurethane oligomer, and 0.2 parts of dibutyltin dilaurate (T-12) and 1.3 parts of diethylene glycol (DEG) were added to carry out a chain extension reaction for 3 hours to obtain polyurethane prepolymer II.

[0109] (2) The polyurethane prepolymer II with -NCO end group synthesized in step (1) was end-capped using 3.27 parts of linoleic acid (LA) and 1.53 parts of 2-hydroxyethyl methacrylate (HEMA); that is, 0.2 parts of butyltin dimethyl methacrylate (T-12) was dissolved in a mixed solution of 3.27 parts of 2-hydroxyethyl methacrylate (HEMA), 1.53 parts of linoleic acid (LA) and the polyurethane prepolymer II obtained in step (1), and the system temperature was raised to 75°C. After stirring and reacting under a nitrogen atmosphere for 2.5 h, the temperature was lowered to obtain the modified polyurethane.

[0110] (3) At 35°C, 1 / 3 of the total amount of acrylate monomers and initiators used to prepare the waterborne acrylate-modified polyurethane dispersion (i.e., 12.63 parts of methyl methacrylate, 15.64 parts of butyl acrylate, 4.44 parts of isobornyl methacrylate, 5.96 parts of styrene, 1.29 parts of 2-hydroxyethyl methacrylate, and 0.85 parts of azobisisobutyronitrile) were added to the modified polyurethane obtained in step (2) to further dilute the modified polyurethane obtained in step (2) by using the acrylate monomers and initiator as solvents; and after neutralizing the modified polyurethane with 2.64 parts of triethylamine (TEA), 240.15 parts of deionized water were added dropwise at a stirring speed of 800 rpm to reverse emulsify the modified polyurethane to obtain a milky white modified polyurethane mixed emulsion;

[0111] (4) Under the protection of inert nitrogen gas, the modified polyurethane mixed emulsion obtained in step (3) was heated to 75°C. While stirring, a mixed solution of 25.25 parts methyl methacrylate, 30.27 parts butyl acrylate, 8.89 parts isobornyl methacrylate, 11.93 parts styrene, 2.57 parts 2-hydroxyethyl methacrylate, and 1.29 parts azobisisobutyronitrile was slowly and dropwise added to the reaction system for 3 hours. After the addition was complete, the temperature was maintained for 2 hours. Then, 1 part potassium persulfate was dissolved in 10 parts deionized water and added to the reaction system. The reaction was carried out at a constant temperature of 75°C for 1 hour and then cooled to room temperature to obtain an aqueous acrylate-modified polyurethane dispersion.

[0112] Example 5

[0113] A method for preparing an aqueous acrylate-modified polyurethane dispersion includes the following steps:

[0114] (1) In a three-necked flask equipped with a stirrer, thermometer, and reflux condenser, add polyether polyol N210 (M) that has undergone vacuum dehydration treatment (vacuum dehydration for 1 h under vacuum conditions of 0.09 MPa and 60°C). n =1000) 60 parts and isophorone diisocyanate (IPDI) 18.34 parts, and 0.4 parts dibutyltin dilaurate (T-12) were added to a three-necked flask. The mixture was slowly heated to 85°C under stirring and reacted at a constant temperature for 2 hours to obtain polyurethane prepolymer I. After the constant temperature was completed, 3.5 parts dimethylolpropionic acid (DMPA) were added and reacted at 85°C for 1 hour to complete the chain extension reaction and obtain polyurethane prepolymer II.

[0115] (2) The reaction temperature was lowered to 70°C, and 3.16 parts of n-octadecyl alcohol (C18), 1.53 parts of 2-hydroxyethyl methacrylate (HEMA) and 0.4 parts of dibutyltin dilaurate (T-12) were added to the polyurethane prepolymer II reaction system obtained in step (1) for a 3-hour end-capping reaction to obtain modified polyurethane.

[0116] (3) Cool the temperature to room temperature, and add 1 / 3 of the total amount of acrylate monomers and initiators used to prepare the waterborne acrylate-modified polyurethane dispersion to the reaction system (i.e., 11.21 parts of methyl methacrylate, 13.51 parts of butyl acrylate, 5.21 parts of isobornyl methacrylate, 5.96 parts of styrene, 1.15 parts of 2-hydroxyethyl methacrylate, and 0.85 parts of azobisisobutyronitrile). Use the acrylate monomers and initiator as solvents to further dilute the polyurethane prepolymer. After neutralizing the modified polyurethane with 2.64 parts of triethylamine (TEA), add 225.65 parts of deionized water dropwise under high-speed stirring to reverse emulsify the prepolymer and obtain a milky white modified polyurethane mixed emulsion.

[0117] (4) Under the protection of inert nitrogen gas, the modified polyurethane mixed emulsion obtained in step (3) is heated to 75°C. Under stirring, a mixed solution of 22.41 parts methyl methacrylate, 27.03 parts butyl acrylate, 10.43 parts isobornyl methacrylate, 11.93 parts styrene, 2.29 parts 2-hydroxyethyl methacrylate and 1.94 parts azobisisobutyronitrile is slowly and dropwise added to the reaction system. The dropwise addition lasts for 3 hours. After the dropwise addition is completed, the reaction is kept at a constant temperature for 2 hours. Then, a solution of 1 part potassium persulfate and 10 parts deionized water is added to the reaction system. The temperature is raised to 85°C and the reaction is carried out for 1.5 hours. Then, the aqueous acrylate modified polyurethane dispersion is cooled to room temperature to obtain the aqueous acrylate modified polyurethane dispersion.

[0118] Comparative Example 1

[0119] The only difference between Comparative Example 1 and Example 5 is that in step (2) of Comparative Example 1, an equal amount of 2-hydroxyethyl methacrylate is used to replace n-octadecyl alcohol, that is, n-octadecyl alcohol is not added, and the amount of 2-hydroxyethyl methacrylate is 4.69 parts. The rest is the same as in Example 5.

[0120] Comparative Example 2

[0121] The only difference between Comparative Example 2 and Example 5 is that in step (2) of Comparative Example 2, an equal amount of n-hexadecyl alcohol is used to replace the n-octadecyl alcohol in Example 5, and the rest is the same as in Example 5.

[0122] Comparative Example 3

[0123] Comparative Example 3 used an existing waterborne acrylate-modified polyurethane dispersion, specifically the waterborne hydroxyl acrylic emulsion 154-E0324 purchased from Honeycomb Nanotechnology.

[0124] Comparative Example 4

[0125] Comparative Example 4 used an existing waterborne acrylate-modified polyurethane dispersion, specifically the waterborne hydroxyl acrylic dispersion PA-4570 purchased from Guangzhou Guanzhi New Materials Co., Ltd.

[0126] Comparative Example 5

[0127] Comparative Example 5 used an existing waterborne acrylate-modified polyurethane dispersion, specifically waterborne hydroxyl acrylic emulsion DB3730 purchased from Wuhan Shuangjian New Materials Co., Ltd.

[0128] Comparative Example 6

[0129] Comparative Example 6 used an existing waterborne acrylate-modified polyurethane dispersion, specifically waterborne hydroxyl acrylic dispersion AC-033B purchased from Ward Polymer Materials.

[0130] Application Example 1

[0131] A water-based two-component silver powder paint, by weight, comprises component A and component B; wherein component A comprises 54 parts of water-based acrylate-modified polyurethane dispersion as described in Example 1, 4 parts of cosolvent dipropylene glycol butyl ether (DPNB), 1 part of cosolvent ethylene glycol butyl ether (BCS), 0.3 parts of neutralizing agent N,N-dimethylethanolamine (DMEA), 26 parts of deionized water, 0.2 parts of wetting agent TEGO-245, 0.2 parts of defoamer surfynol DF110D, 0.2 parts of defoamer Surfynol 420, 0.3 parts of leveling agent BYK-333, 0.8 parts of anti-flash rust agent NALZIN FA 179, 6 parts of silver powder SR-7010, and 0.5 parts of dispersant BYK-190;

[0132] Component B includes an aqueous isocyanate curing agent. 14 parts of ultra 2655 and 5 parts of propylene glycol methyl ether acetate (PMA).

[0133] A method for preparing a water-based two-component silver powder paint includes the following steps:

[0134] (1) Add the water-based acrylate-modified polyurethane dispersion to the paint mixing tank, and add the neutralizing agent N,N-dimethylethanolamine, the cosolvent dipropylene glycol butyl ether and ethylene glycol butyl ether in sequence while stirring at 600 rpm. After continuous dispersion for 5 min, add the wetting agent, defoamer, leveling agent and anti-flash rust agent to the paint mixing tank in sequence and disperse for 5 min to obtain a mixed system.

[0135] (2) Add silver powder to another paint mixing tank, along with deionized water and dispersant, and slowly disperse at 200 rpm for 5 minutes to obtain the desired water-based silver powder paste.

[0136] (3) At a stirring speed of 600 rpm, the water-based silver powder paste prepared in step (2) is slowly added to the mixing system in step (1) and dispersed for 20 min to obtain component A of the water-based two-component silver powder paint.

[0137] (4) Hydrophilic aliphatic polyisocyanate of hexamethylene diisocyanate (HDI) Ultra 2655 was dissolved in propylene glycol methyl ether acetate (PMA) and mixed evenly to obtain component B of the water-based two-component silver powder paint.

[0138] During construction, mix components A and B evenly at a mass ratio of 7:1, and dilute the mixture of components A and B at a dilution ratio of 25% to obtain water-based two-component silver powder paint.

[0139] Application Example 2

[0140] The only difference between Application Example 2 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Application Example 2 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Example 2.

[0141] Application Example 3

[0142] The only difference between Application Example 3 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Application Example 3 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Example 3.

[0143] Application Example 4

[0144] The only difference between Application Example 4 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Application Example 4 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Example 4.

[0145] Application Example 5

[0146] The only difference between Application Example 5 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Application Example 5 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Example 5.

[0147] Application Example 6

[0148] The only difference between Application Example 6 and Application Example 1 is that in Application Example 6, component A also includes a rheology modifier. 0.5 parts of PUR64 and 0.5 parts of Coapur2025 were added. In step (1) of the preparation process, after adding wetting agent, defoamer, leveling agent and anti-flash rust agent and dispersing for 5 minutes, the stirring speed was increased to 1200 rpm and the following were added sequentially: PUR64 and Coapur 2025 were stirred for 5 minutes to obtain a mixed system, and the rest was the same as in Application Example 1.

[0149] Application Example 7

[0150] The only difference between Application Example 7 and Application Example 1 is that in Application Example 7, component A also includes 4.5 parts of silver powder orientation aid BYK-AQUATIX 8421, and in step (1) of the preparation process, after adding wetting agent, defoamer, leveling agent and anti-flash rust agent and dispersing for 5 minutes, the stirring speed is increased to 1200 rpm and the silver powder orientation aid is added, and the mixture is stirred for 5 minutes to obtain a mixed system. The rest is the same as in Application Example 1.

[0151] Application Example 8

[0152] The only difference between Application Example 8 and Application Example 1 is that in Application Example 8, component A also includes 4.5 parts of magnesium aluminum silicate dispersion with 20% (mass fraction) silver powder orientation aid. In step (1) of the preparation process, after adding wetting agent, defoamer, leveling agent and anti-flash rust agent and dispersing for 5 min, the stirring speed is increased to 1200 rpm and silver powder orientation aid is added. Stirring for 5 min yields a mixed system. The rest is the same as in Application Example 1.

[0153] Comparative Application Example 1

[0154] The only difference between Comparative Application Example 1 and Application Example 5 is that the waterborne acrylate-modified polyurethane dispersion in Comparative Application Example 1 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Comparative Example 1.

[0155] Comparative Application Example 2

[0156] The only difference between Comparative Application Example 2 and Application Example 5 is that the waterborne acrylate-modified polyurethane dispersion in Comparative Application Example 2 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Comparative Example 2.

[0157] Comparative Application Example 3

[0158] The only difference between Comparative Application Example 3 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Comparative Application Example 3 is the same as that in Comparative Example 3.

[0159] Comparative Application Example 4

[0160] The only difference between Comparative Application Example 4 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Comparative Application Example 4 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Comparative Example 4.

[0161] Comparative Application Example 5

[0162] The only difference between Comparative Application Example 5 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Comparative Application Example 5 is the same as the waterborne acrylate-modified polyurethane dispersion prepared in Comparative Example 5.

[0163] Comparative Application Example 6

[0164] The only difference between Comparative Application Example 6 and Application Example 1 is that the waterborne acrylate-modified polyurethane dispersion in Comparative Application Example 6 is the same as that prepared in Comparative Example 6.

[0165] Performance testing

[0166] 1. Physical performance testing

[0167] The hydroxyl content, viscosity, and solid content of the waterborne acrylate-modified polyurethane dispersions of Examples 1-5 and Comparative Examples 1-6 were tested, and the results are shown in Table 1.

[0168] Table 1: Test results of waterborne acrylate-modified polyurethane dispersions in Examples 1-5 and Comparative Examples 1-6

[0169] Example 1 2.9 900 45±2 Example 2 2.9 960 45±2 Example 3 3.0 1080 45±2 Example 4 3.0 1190 45±2 Example 5 2.9 920 45±2 Comparative Example 1 2.9 540 45±2 Comparative Example 2 2.9 600 45±2 Comparative Example 3 3.0 200 40±2 Comparative Example 4 2.6 500 38±2 Comparative Example 5 3.2 300 40±2 Comparative Example 6 3.3 200 45±1

[0170] As can be seen from Table 1, the viscosity of the waterborne acrylate-modified polyurethane dispersion in the embodiments of the present invention is significantly higher than that of comparative examples 1-6, indicating that its resin molecular weight is larger, resulting in a higher system viscosity. For silver powder paint, the larger the resin molecular weight, the more conducive it is to the arrangement of silver powder.

[0171] 2. Performance testing of water-based two-component silver powder paint

[0172] The substrate was tinplate. After pretreatment such as degreasing and sanding, water-based two-component silver powder paint (Application Examples 1-8 and Comparative Examples 1-6) was sprayed onto the substrate surface using air spraying under a construction environment of 25±5℃ and 65±5% RH humidity. The drying time of the wet film was observed. After it was surface dry, the paint film was baked at 80℃ for 30 minutes to cure and crosslink, resulting in a paint film with a thickness of 20-25μm. The performance of the paint film was then tested. The test items and test methods are as follows:

[0173] Drying time: Refer to GB / T 1728-2020 (Method B);

[0174] Gloss: Refer to GB / T 9754-2007;

[0175] Adhesion: Tested according to GB / T 9286-2021;

[0176] Water resistance: After curing, the paint film is cured at room temperature for 24 hours, and then water resistance is tested according to GB / T 1733-1993;

[0177] Impact resistance: Tested in accordance with GB / T 1732-2020;

[0178] Hardness: Refer to GB / T 6739-2006;

[0179] Flexibility: Refer to GB / T 1731-2020.

[0180] The performance test results of the silver powder paint coatings obtained from the water-based two-component silver powder paints of Application Examples 1-8 and Comparative Examples 1-6 are shown in Table 2.

[0181] Table 2: Performance test results of silver paint coatings obtained from application examples 1-8 and comparative examples 1-6 using water-based two-component silver paints.

[0182]

[0183] As shown in Table 2, the waterborne two-component silver powder paints prepared by the waterborne acrylate-modified polyurethane dispersions in Examples 1-5 of this invention exhibit good gloss, adhesion, impact resistance, and water resistance, meeting the current application requirements of industrial coatings for waterborne two-component silver powder paints. After baking at 80℃ for 30 minutes, the paint films all exhibit excellent flexibility and initial hardness, which is beneficial for the rapid stacking and handling of coated workpieces after production.

[0184] Compared to Application Example 1, the waterborne acrylate-modified polyurethane dispersion was prepared without the addition of n-octadecyl alcohol, resulting in the silver paint of Application Example 1 exhibiting inferior gloss, water resistance, and impact resistance compared to Application Example 5. This indicates that modifying the polyurethane prepolymer with the hydrophobic end-capping agent n-octadecyl alcohol to synthesize a polyurethane with hydrophobic ends and a carbon-carbon double bond structure can improve the water resistance, gloss, and impact resistance of the silver paint.

[0185] In Comparative Application Example 2, an equal amount of n-hexadecyl alcohol was used to replace n-octadecyl alcohol, resulting in the silver paint in Comparative Application Example 2 exhibiting inferior gloss, water resistance, and impact resistance compared to Application Example 5. This demonstrates that specific types of end-capping agents must be added to modify the polyurethane prepolymer in order to improve the water resistance, gloss, and impact resistance of the silver paint.

[0186] Comparative Examples 3-6 all used existing waterborne acrylate-modified polyurethane dispersions to prepare silver powder paint. The gloss, water resistance, and impact resistance of the silver powder paints in Comparative Examples 3-6 were inferior to those in Example 1, and the pencil hardness of Comparative Examples 3-5 was lower than that of Example 1. This demonstrates that by modifying the polyurethane prepolymer with a hydrophobic end-capping agent, the present invention synthesizes a polyurethane with hydrophobic ends and a carbon-carbon double bond structure, thereby obtaining a waterborne acrylate-modified polyurethane dispersion, which can improve the gloss, water resistance, and impact resistance of silver powder paint.

[0187] 3. Viscosity, thixotropic value, and gloss index tests of water-based two-component metallic paint

[0188] The viscosity, thixotropic value, and glitter index of the water-based two-component silver paint corresponding to Examples 1-8 and Comparative Examples 1-6 were tested. The test methods are as follows:

[0189] Viscosity: Measured using an NDJ-1 rotational viscometer;

[0190] Thixotropic value: The viscosity ratio of a water-based two-component silver paint at 60 rpm and 6 rpm on a rotational viscometer;

[0191] Flash index: The SGY-A flash index meter was used to measure the flash index of the paint film at 15° (L) 15° ), 45° (L 45° ), 110° (L 110° The brightness values ​​were measured from three angles and calculated using the Flop index formula.

[0192] Flop index = 2.69 × (L) 15° -L 110° ) 1.11 / L 45° 0.86 .

[0193] The viscosity, thixotropic value, and glitter index test results of the water-based two-component silver powder paints used in Application Examples 1-8 and Comparative Examples 1-6 are shown in Table 3.

[0194] Table 3: Test results of viscosity, thixotropic value and glitter index of water-based two-component silver powder paints in Application Examples 1-8 and Comparative Examples 1-6

[0195]

[0196] As can be seen from Table 3, the water-based two-component silver powder paints of Examples 1-8 of the present invention have good viscosity, thixotropic value and glitter index, indicating that the water-based acrylate-modified polyurethane dispersions prepared in Examples 1-5 of the present invention can improve the thixotropic value and glitter index of the silver powder paint.

[0197] The results from Application Examples 6-8 and Application Example 1 show that the rheology modifier in Application Example 6... The use of PUR 64 and Coapur 2025 has very limited effect on improving the silver powder orientation effect and cannot significantly increase the gloss index of the silver powder paint film. However, the use of silver powder orientation aids BYK-AQUATIX 8421 (a rheology-modified wax emulsion of modified ethylene-vinyl acetate copolymer wax) and magnesium aluminum silicate dispersions can significantly improve the thixotropy and silver powder orientation effect of water-based two-component silver powder paints. Regarding the cost of paint formulations, under the same conditions, magnesium aluminum silicate dispersions can serve as a cost-effective alternative to silver powder orientation aid BYK-AQUATIX 8421.

[0198] The only difference between Comparative Application Example 1 and Application Example 5 is that Comparative Application Example 1 did not use n-octadecyl alcohol to modify the polyurethane prepolymer during the preparation of the waterborne acrylate-modified polyurethane dispersion. As a result, the thixotropic value and gloss index of the silver powder paint prepared in Comparative Application Example 1 were significantly lower than those in Application Example 5. This indicates that the waterborne acrylate-modified polyurethane dispersion obtained by modifying the polyurethane prepolymer with the end-capping agent n-octadecyl alcohol can significantly improve the thixotropic value and gloss index of the silver powder paint when applied to silver powder paint.

[0199] The only difference between Comparative Application Example 2 and Application Example 5 is that Comparative Application Example 2 uses n-hexadecyl alcohol to replace n-octadecyl alcohol in an equal amount, which makes the thixotropic value and flash index of the silver powder paint prepared in Comparative Application Example 2 significantly lower than those in Application Example 5. This shows that the waterborne acrylate-modified polyurethane dispersion obtained by modifying the polyurethane prepolymer with the end-capping agent n-octadecyl alcohol can significantly improve the thixotropic value and flash index of the silver powder paint when applied to silver powder paint.

[0200] As can be seen from the test results of comparative application examples 1 and 2, the present invention requires the use of a specific end-capping agent (octadecyl alcohol or linoleic acid) in the process of preparing waterborne acrylate-modified polyurethane dispersions in order to better improve the thickening and thixotropic properties of the waterborne acrylate-modified polyurethane dispersions, thereby improving the thixotropic value and gloss index of the silver paint.

[0201] Comparative Application Examples 3-6 all used existing waterborne acrylate-modified polyurethane dispersions. The thixotropic value and gloss index of the silver powder paint prepared in Comparative Application Examples 3-6 were significantly lower than those of the silver powder paint in Application Example 1 of this invention. This indicates that the waterborne acrylate-modified polyurethane dispersion with a specific structure prepared in this invention can improve the thixotropic value and gloss index of the silver powder paint.

[0202] In summary, this invention modifies a polyurethane prepolymer using hydrophobic end-capping agents (octadecyl alcohol and / or linoleic acid) to synthesize a modified polyurethane resin with hydrophobic ends and a carbon-carbon double bond structure. Using the hydrophobically modified polyurethane as the core, polyacrylate is grafted onto the core via free radical polymerization to synthesize a waterborne acrylate-modified polyurethane with a core-shell structure. The modified polyurethane with hydrophobic ends further forms a transient network structure through hydrogen bonding between the polyurethane core and the polyacrylate shell, resulting in thickening and thixotropic properties. This improves the directional alignment and glitter effect of silver powder in waterborne two-component silver powder paint, better addressing the problems of sagging and poor silver powder orientation in existing waterborne two-component silver powder paints during application, and also improving water resistance and mechanical properties.

[0203] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silver powder paint, characterized in that, The silver powder paint comprises component A and component B; component A comprises an aqueous acrylate-modified polyurethane dispersion, cosolvent A, and silver powder; component B comprises an isocyanate curing agent and cosolvent B; The aqueous acrylate-modified polyurethane dispersion comprises 45-65 parts by weight. The aqueous acrylate-modified polyurethane dispersion has a core-shell structure; the core of the core-shell structure comprises modified polyurethane; the shell of the core-shell structure comprises hydroxyl-containing polyacrylate. The modified polyurethane is obtained by modifying a polyurethane prepolymer with end-capping agent 1 and end-capping agent 2; The capping agent 1 includes at least one of linoleic acid and n-octadecyl alcohol; The capping agent 2 comprises 2-hydroxyethyl methacrylate; The preparation method of the waterborne acrylate-modified polyurethane dispersion includes the following steps: (1) Mix acrylate monomers and initiators to obtain a mixture, take a portion of the mixture and mix it with modified polyurethane and neutralizer, emulsify it to obtain a mixed emulsion; (2) The remaining mixture is mixed with the mixed emulsion obtained in step (1) and reacted to obtain the waterborne acrylate-modified polyurethane dispersion.

2. The silver powder paint according to claim 1, characterized in that, The method for preparing the modified polyurethane includes the following steps: (1) The polymer polyol was dehydrated under vacuum, and catalyst 1 and isocyanate monomer were added to carry out reaction 1 to obtain polyurethane prepolymer I; catalyst 2 and chain extender were added to polyurethane prepolymer I to carry out reaction 2 to obtain polyurethane prepolymer II. (2) The end-capping agent 1, end-capping agent 2 and the polyurethane prepolymer II obtained in step (1) are mixed and reacted to obtain the modified polyurethane.

3. The silver paint according to claim 2, characterized in that, In step (1), the polymer polyol includes at least one of polyether polyol and polyester polyol; and / or, catalyst 1 and catalyst 2 both include dibutyltin dilaurate; and / or, the isocyanate monomer includes at least one of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate; and / or, the chain extender includes at least one of diethylene glycol, dimethylolpropionic acid, and sodium 1,4-butanediol-2-sulfonate.

4. The silver paint according to claim 2, characterized in that, In step (1), the reaction temperature of reaction 1 is 75-90℃ and the reaction time of reaction 1 is 1.5-2.5h; and / or, the reaction temperature of reaction 2 is 55-75℃ and the reaction time of reaction 2 is 2.5-3.5h; And / or, in step (2), the reaction temperature of reaction 3 is 65-85℃, and the reaction time of reaction 3 is 2.0-3.0h.

5. The silver paint according to claim 1, characterized in that, The acrylate monomers include at least one of methacrylic acid, isobornyl methacrylate, isobutyl methacrylate, glycidyl methacrylate, isooctyl methacrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, acrylic acid, n-butyl acrylate, acrylamide, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, cyclohexyl acrylate, styrene, and isobornyl acrylate; and / or, the initiator includes at least one of tert-butyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, di-tert-amyl peroxide, potassium persulfate, ammonium persulfate, and sodium persulfate; and / or, the neutralizing agent includes an amine neutralizing agent.

6. The silver paint according to claim 1, characterized in that, In step (2), the reaction temperature is 65-85℃ and the reaction time is 1.5-2.5h.

Images