UV-cured waterborne polyurethane acrylate resin as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer material synthesis, and particularly relates to UV-cured waterborne polyurethane acrylate resin as well as a preparation method and application thereof. The method comprises the following steps: preparing a disulfide bond and imine bond series dynamic bond monomer based on a Schiff base reaction of disulfide; a series dynamic bond monomer is introduced into waterborne polyurethane acrylate resin as a functional chain extender, and compared with light-cured resin with a single dynamic bond and a simple mixed dynamic bond, the series dynamic bond has lower activation energy, so that the light-cured coating based on the series dynamic bond is endowed with more excellent self-repairing performance; and meanwhile, the good mechanical property and excellent metal base material adhesive force of the coating are kept. The multiple dynamic bonds also enable the photocuring coating to have a multi-mode self-repairing capability, and the UV curing coating has excellent self-repairing performance under the stimulation of heat and ultraviolet.

Description

Technical Field

[0001] This application belongs to the technical field of polymer material synthesis, and specifically relates to a UV-curable waterborne polyurethane acrylate resin, its preparation method and application. Background Art

[0002] As a new type of environmentally friendly material, UV-curable waterborne polyurethane acrylate resin has attracted much attention due to its low VOC emissions, rapid curing and excellent properties. However, in practical applications, such resins still face several challenges, which limit their wider application and development. UV-curable waterborne polyurethane acrylate resin has high hardness and excellent mechanical properties. However, when microcracks or other damages appear on its surface, due to the rigidity of the material itself and the lack of an effective self-healing mechanism, these damages are difficult to recover by themselves, thus significantly reducing the service life of the coating and causing waste of resources. Secondly, the existing UV-curable waterborne polyurethane acrylate resins perform poorly on metal substrates. This makes it mainly applied to substrates such as plastic plates and wooden boards, and the application scenarios are greatly limited. Reports on self-healing waterborne UV resins in China have been relatively common, and the current major problems are poor repair efficiency and narrow applicable scenarios. Summary of the Invention

[0003] In view of the above problems, the present invention aims to develop a highly efficient self-healing UV-curable waterborne polyurethane acrylate resin for metal substrates. This resin can not only provide excellent self-healing performance under the action of ultraviolet and heat, but also has excellent basic properties on metal substrates by introducing a large number of hydrogen bonds, solving the key problems in the prior art.

[0004] Specifically, the following technical solutions are adopted: In the first aspect, the present invention provides a preparation method of a UV-curable waterborne polyurethane acrylate resin, which is characterized by including the following steps: S1. React p-hydroxybenzaldehyde and 4,4'-dithiobenzidine in a first organic solvent, filter, wash, and dry to obtain a tandem dynamic bond monomer; S2. React a diisocyanate, a macromolecular diol, and a catalyst in a second organic solvent for 1.5 - 2 h, add a hydroxy acid and continue to react for 1 - 3 h, then add the tandem dynamic bond monomer, catalyst and second organic solvent and react for 2 - 4 h. After the reaction is completed, continue to add a hydroxyacrylate monomer, an inhibitor and a catalyst and react until the isocyanate functional group content is less than 0.5% to obtain a mixed solution; the molecular weight of the macromolecular diol is 900 g / moL - 1100 g / moL.

[0005] S3. Cool the mixed solution to room temperature, then add a neutralizing agent and disperse evenly to obtain a polyurethane acrylate prepolymer; S4. Slowly drop hot water into the polyurethane acrylate prepolymer at a rotation speed of 600 rpm - 1200 rpm, then disperse it evenly, and remove the solvent under reduced pressure to obtain the UV-curable waterborne polyurethane acrylate resin.

[0006] In the present invention, a tandem dynamic bond monomer containing disulfide bonds and imine bonds is first synthesized through a simple Schiff base reaction, and then used as a chain extender to be introduced into the polyurethane prepolymer together with hydroxy acid. Then, hydroxyacrylate monomers and polymerization inhibitors are added to continue the reaction. Finally, a neutralizing agent and an appropriate amount of water are added for high-speed dispersion to prepare the waterborne UV resin. Among them, the disulfide bonds and imine bonds in the tandem dynamic bond monomer will produce a synergistic effect. When the disulfide bonds are broken, the mobility of the imine bonds in the molecular chain greatly increases, which enables the imine bonds to undergo exchange reactions without breaking themselves. The extremely low activation energy thus endows the UV-curable waterborne polyurethane acrylate resin with high self-healing efficiency. In addition, due to the photo-thermal dual response of the disulfide bonds, the resin can also exhibit a self-healing effect under ultraviolet stimulation.

[0007] In the above preparation process, the reaction temperature in S1 is 40 - 80 °C and the reaction time is 12 h; In S2, the reaction temperature of the diisocyanate, macromolecular diol, and catalyst in the second organic solvent is 50 - 80 °C; the reaction temperature for adding the tandem dynamic bond monomer, catalyst, and the second organic solvent is 60 - 90 °C; the reaction temperature for continuously adding the hydroxyacrylate monomers, polymerization inhibitors, and catalyst is 50 - 80 °C. In the above preparation process, for the first two reaction temperatures of S1 and S2, too low a temperature will lead to insufficient reaction, while too high a temperature will result in an increase in by-products in the system, thus affecting the performance of the final resin; too low a temperature in the last reaction will also lead to insufficient reaction, and too high a temperature may cause the double bonds in the system to self-polymerize.

[0008] In the above preparation process, 4,4'-dithiobenzanilide is used as the raw material for preparing the tandem dynamic bond monomer. The purpose is that 4,4'-dithiobenzanilide itself contains disulfide bonds, and its amino group can react with the aldehyde group on p-hydroxybenzaldehyde through a Schiff base reaction to form imine bonds. In this way, the prepared tandem dynamic bond contains both disulfide bonds and imine bonds. The disulfide bonds and imine bonds in the tandem dynamic bond monomer will produce a synergistic effect; when the disulfide bonds are broken, the mobility of the imine bonds in the molecular chain greatly increases, which enables the imine bonds to undergo exchange reactions without breaking themselves. The extremely low activation energy thus endows the UV-curable waterborne polyurethane acrylate resin with high self-healing efficiency. In addition, due to the photo-thermal dual response of the disulfide bonds, the resin can also exhibit a self-healing effect at a wavelength of 365 nm.

[0009] As a further preferred embodiment, the mass ratio of p-hydroxybenzaldehyde, 4,4'-dithiobis(phenylamine), and the first organic solvent in S1 is 1:0.98 - 1.08:19.4; the first organic solvent includes at least one of absolute ethanol and methanol; wherein, if the reaction monomers exceed this ratio range, it will cause the monomers in the excessive amount to be unable to react, resulting in waste; if the amount of the first organic solvent is too low, it will lead to a smaller reaction site in the system, and the reaction may not be sufficient; if it is too much, it will cause the reaction to be slow and the reaction time needs to be extended.

[0010] As a further preferred embodiment, the diisocyanate monomer in S2 includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and toluene diisocyanate; The macromolecular diol includes at least one of polytetrahydrofuran, polyethylene glycol, polycaprolactone, and polypropylene glycol.

[0011] As a further preferred embodiment, the catalyst includes at least one of dibutyltin dilaurate, organic bismuth, stannous octoate, and dibutyltin diacetate; The second organic solvent includes at least one of acetone, butanone, ethyl acetate, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0012] As a further preferred embodiment, the hydroxy acid includes at least one of 2,2-dimethylolpropionic acid, dimethylolbutyric acid, and salicylic acid.

[0013] As a further preferred embodiment, the hydroxyacrylate monomer includes at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, pentaerythritol triacrylate, and dipentaerythritol pentaacrylate.

[0014] As a further preferred embodiment, the inhibitor includes at least one of p-methoxyphenol, hydroquinone, and p-tert-butylcatechol.

[0015] As a further preferred embodiment, the neutralizing agent in S3 includes at least one of triethylamine, triethanolamine, N,N-dimethylethanolamine, and ammonia water.

[0016] In a second aspect, the present invention provides a UV-curable waterborne polyurethane acrylate resin, and the UV-curable waterborne polyurethane acrylate resin is prepared by the above preparation method.

[0017] As a further preferred embodiment, in the synthesis formula of the UV-curable waterborne polyurethane acrylate resin, by weight, it includes the following components: 12-15 parts of diisocyanate monomer, 12-15 parts of macromolecular diol, 1-2 parts of hydroxy acid, 5-7 parts of tandem dynamic bond monomer, 9-12 parts of hydroxy acrylate, 1-2 parts of neutralizer, 0.003-0.01 part of catalyst, 0.0001-0.001 part of inhibitor, 8-12 parts of second solvent, and 50-60 parts of water.

[0018] In the third aspect, the present invention provides the application of the above UV-curable waterborne polyurethane acrylate resin in metal surface treatment.

[0019] The beneficial effects of the present invention are as follows: (1) The present invention provides a preparation method of a UV-curable waterborne polyurethane acrylate resin. By introducing a tandem dynamic bond monomer with a lower activation energy as a chain extender into the waterborne polyurethane acrylate resin, the resin is endowed with excellent self-healing performance. In addition, relying on the photothermal dual-stimulus response of disulfide bonds, the resin is also endowed with a self-healing effect under ultraviolet irradiation. At the same time, due to the presence of a large number of hydrogen bonds and an appropriate amount of double bond content in the system, it can be applied to metal substrates and has excellent basic properties.

[0020] (2) The method provided by the present invention is particularly suitable for waterborne polyurethane acrylate coatings with higher hardness, effectively improving their self-healing ability. By precisely regulating the proportion of formula components and specific reaction conditions such as temperature and time, a UV-curable waterborne polyurethane acrylate resin is successfully prepared. This resin not only has excellent basic properties, such as excellent adhesion, pencil hardness, gloss, flexibility and impact resistance, but also the rich polar groups in the system can form a strong interaction with the metal surface, further enhancing the adhesion effect of the coating. In addition, due to its unique self-healing characteristics and good adaptability to various substrates, the resin shows broad application prospects in multiple industries such as household appliances, automobiles, and smartphones. In short, the present invention provides a high-performance environmentally friendly coating solution, which not only meets the requirements of modern industry for material performance but also conforms to the requirements of sustainable development. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 The figure shows the reaction principle diagram for synthesizing highly efficient self-healing UV-curable waterborne polyurethane acrylate. Figure 2 Shown are the infrared spectra of the UV-curable waterborne polyurethane acrylate emulsion (WPUA-SN) in Example 1 and the UV-curable waterborne polyurethane acrylate emulsions (WPUA-CN: Comparative Example 1), (WPUA-SS: Comparative Example 2), (WPUA-MCS: Comparative Example 3) in Comparative Examples 1-3; Figure 3 Shown are the Bode diagrams of the UV-curable waterborne polyurethane acrylate coatings (SN-blank: Example 1, CN-blank: Comparative Example 1, SS-blank: Comparative Example 2, MCS-blank: Comparative Example 3) in Example 1 and Comparative Examples 1-3 before and after damage (blank, cracked) and after repair (SN-healed: Example 1, CN-healed: Comparative Example 1, SS-healed: Comparative Example 2, MCS-healed: Comparative Example 3); Figure 4 Shown are the optical microscope photos of the UV-curable waterborne polyurethane acrylate coatings (a, WPUA-SN: Example 1, c, WPUA-CN: Comparative Example 1, d, WPUA-SS: Comparative Example 2, b, WPUA-MCS: Comparative Example 3) in Example 1 and Comparative Examples 1-3 before and after hot pressing at 110 °C and 8 MPa for 30 min (i, before, ii, after); Figure 5 Shown are the optical microscope photos of the UV-curable waterborne polyurethane acrylate coatings (a, WPUA-SN: Example 1, c, WPUA-CN: Comparative Example 1, d, WPUA-SS: Comparative Example 2, b, WPUA-MCS: Comparative Example 3) in Example 1 and Comparative Examples 1-3 before and after repair at 100 °C for 0 min (i), 30 min (ii), and 120 min (iii); Figure 6 For the UV-curable waterborne polyurethane acrylate coatings (WPUA-SN: Example 1, WPUA-CN: Comparative Example 1, WPUA-SS: Comparative Example 2, WPUA-MCS: Comparative Example 3) in Example 1 and Comparative Examples 1-3, the stress-strain curves at 100 °C for repair times of 3 h, 6 h, 9 h, 12 h, and 24 h; Figure 7 Shown are the optical microscope photos of the UV-curable waterborne polyurethane acrylate coatings (a, WPUA-SN: Example 1, c, WPUA-CN: Comparative Example 1, d, WPUA-SS: Comparative Example 2, b, WPUA-MCS: Comparative Example 3) in Example 1 and Comparative Examples 1-3 before and after repair under ultraviolet lamp irradiation at a wavelength of 365 nm (i, before, ii, after); Figure 8The following are the basic property photos of pencil hardness (i), adhesion (ii), impact resistance (iii), and flexibility (iv) of the UV-curable waterborne polyurethane acrylate coatings (a, WPUA-SN in Example 1, c, WPUA-CN: Comparative Example 1, d, WPUA-SS: Comparative Example 2, b, WPUA-MCS: Comparative Example 3) in Example 1 and Comparative Examples 1-3 when applied to tinplate. Detailed implementation manners

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0024] Example 1 A preparation method of an efficient self-healing UV-curable waterborne polyurethane acrylate resin for metal substrates (the reaction schematic diagram is as shown) specifically includes the following steps: Figure 1 as shown), which specifically includes the following steps: (1) Put 2.442 g of p-hydroxybenzaldehyde and 2.484 g of 4,4'-dithiobisbenzeneamine into a 250 mL three-necked flask, and at the same time add 60 mL of absolute ethanol. After the system reacts at 60 °C for 12 h, a yellow solid powder is obtained. After filtering the yellow solid powder, it is washed with absolute ethanol multiple times, and then washed with deionized water and placed in an oven at 60 °C for drying overnight to obtain a tandem dynamic bond monomer; (2) Add 6 g of isophorone diisocyanate, 5.8 g of polytetrahydrofuran, 0.03 g of dibutyltin dilaurate, and 5 mL of tetrahydrofuran to a 500 mL three-necked flask and react at 75 °C for 1 h. After the reaction is completed, add 0.78 g of 2,2-dimethylolpropionic acid to the system and continue to react for 1.5 h. Then, raise the temperature to 85 °C, add 2.83 g of tandem dynamic bond monomer, 0.03 g of dibutyltin dilaurate, and 5 mL of tetrahydrofuran and react for 3 h; finally, lower the temperature to 70 °C, add 0.01 g of hydroquinone, 4.77 g of pentaerythritol triacrylate, and 0.03 g of dibutyltin dilaurate and react until the content of isocyanate functional groups (NCO%) in the system is lower than 0.5% to obtain a mixed solution; (3) Cool the mixed solution obtained in step (2) to room temperature, add 0.59 g of triethylamine to the system, and stop stirring after uniformly dispersing for 30 min to obtain a polyurethane acrylate prepolymer; (4) To the polyurethane acrylate prepolymer obtained in step (3), hot water at 80 °C was slowly added dropwise at a rotation speed of 1000 rpm. After the addition was completed, high-speed dispersion was continued for 30 min. Finally, the solvent in the system was removed under reduced pressure to obtain the UV-curable waterborne polyurethane acrylate resin.

[0025] Example 2 A preparation method of a highly efficient self-healing UV-curable waterborne polyurethane acrylate resin for metal substrates, which specifically includes the following steps: (1) 2.442 g of p-hydroxybenzaldehyde and 2.484 g of 4,4'-dithiobisbenzeneamine were placed in a 250 mL three-necked flask, and 60 mL of absolute ethanol was added at the same time. After the system reacted at 60 °C for 12 h, a yellow solid powder was obtained. The yellow solid powder was filtered and washed with absolute ethanol multiple times, and then washed with deionized water and placed in an oven at 60 °C for drying overnight to obtain the tandem dynamic bond monomer; (2) 5.56 g of isophorone diisocyanate, 5.2 g of polytetrahydrofuran, 0.03 g of dibutyltin dilaurate, and 5 mL of tetrahydrofuran were added to a 500 mL three-necked flask and reacted at 75 °C for 1 h; after the reaction was completed, 0.7 g of 2,2-dimethylolpropionic acid was added to the system and the reaction continued for 1.5 h. Then the temperature was raised to 85 °C, and 2.83 g of the tandem dynamic bond monomer, 0.03 g of dibutyltin dilaurate, and 5 mL of tetrahydrofuran were added and reacted for 3 h; finally, the temperature was lowered to 70 °C, 0.008 g of hydroquinone, 4.18 g of pentaerythritol triacrylate, and 0.03 g of dibutyltin dilaurate were added and the reaction continued until the content of isocyanate functional groups (NCO%) in the system was lower than 0.5% to obtain a mixed solution; (3) The mixed solution obtained above was cooled to room temperature, 0.53 g of triethylamine was added to the system, and after uniform dispersion for 30 min, stirring was stopped to obtain the polyurethane acrylate prepolymer; (4) To the polyurethane acrylate prepolymer obtained in step (3), hot water at 80 °C was slowly added dropwise at a rotation speed of 1000 rpm. After the addition was completed, high-speed dispersion was continued for 30 min. Finally, the solvent in the system was removed under reduced pressure to obtain the UV-curable waterborne polyurethane acrylate resin.

[0026] Example 3 A preparation method of a highly efficient self-healing UV-curable waterborne polyurethane acrylate resin for metal substrates, which specifically includes the following steps: (1) Place 2.442 g of p-hydroxybenzaldehyde and 2.484 g of 4,4'-dithiobis(aniline) in a 250 mL three-necked flask, and simultaneously add 60 mL of absolute ethanol. After the system reacts at 60 °C for 12 h, a yellow solid powder is obtained. Filter the yellow solid powder and wash it several times with absolute ethanol, then wash it with deionized water and place it in an oven at 60 °C to dry overnight to obtain the tandem dynamic bond monomer; (2) Add 5.56 g of isophorone diisocyanate, 5 g of polytetrahydrofuran, 0.03 g of dibutyltin dilaurate, and 5 mL of butanone to a 500 mL three-necked flask and react at 75 °C for 1 h. After the reaction is completed, add 0.67 g of 2,2-dimethylolpropionic acid to the system and continue to react for 1.5 h; then raise the temperature to 90 °C, add 2.83 g of the tandem dynamic bond monomer, 0.03 g of dibutyltin dilaurate, and 10 mL of butanone and react for 3 h; finally, lower the temperature to 70 °C, add 0.009 g of hydroquinone, 4.47 g of pentaerythritol triacrylate, and 0.03 g of dibutyltin dilaurate and react until the content of isocyanate functional groups (NCO%) in the system is lower than 0.5% to obtain a mixed solution; (3) Cool the above-obtained mixed solution to room temperature, add 0.51 g of triethylamine to the system, stir evenly for 30 min, and then stop stirring to obtain a polyurethane acrylate prepolymer; (4) Slowly add hot water at 80 °C to the polyurethane acrylate prepolymer obtained in step (3) at a rotation speed of 1000 rpm. After the addition is completed, continue to disperse at a high rotation speed for 30 min. Finally, remove the solvent under reduced pressure from the system to prepare a UV-curable waterborne polyurethane acrylate resin.

[0027] Example 4 A preparation method of a highly efficient self-healing UV-curable waterborne polyurethane acrylate resin for metal substrates, which specifically includes the following steps: (1) Place 2.442 g of p-hydroxybenzaldehyde and 2.484 g of 4,4'-dithiobis(aniline) in a 250 mL three-necked flask, and simultaneously add 60 mL of absolute ethanol. After the system reacts at 60 °C for 12 h, a yellow solid powder is obtained. Filter the yellow solid powder and wash it several times with absolute ethanol, then wash it with deionized water and place it in an oven at 60 °C to dry overnight to obtain the tandem dynamic bond monomer; (2) Add 6 g of isophorone diisocyanate, 10 g of polytetrahydrofuran, 0.03 g of dibutyltin dilaurate and 5 mL of butanone to a 500 mL three-necked flask and react at 75 °C for 1 h. After the reaction is completed, add 1.34 g of 2,2-dihydroxymethylpropionic acid to the system and continue to react for 1.5 h. Then raise the temperature to 80 °C, add 2.96 g of tandem dynamic bond monomer, 0.03 g of dibutyltin dilaurate and 5 mL of N,N-dimethylacetamide and react for 3 h; finally, lower the temperature to 70 °C, add 0.006 g of hydroquinone, 2.98 g of pentaerythritol triacrylate and 0.03 g of dibutyltin dilaurate and react until the isocyanate functional group content (NCO%) in the system is less than 0.5%, and obtain a mixed solution; (3) The mixed solution obtained above was cooled to room temperature, 1.02 g of triethylamine was added to the system, and stirring was stopped after uniform dispersion for 30 minutes to obtain a polyurethane acrylate prepolymer; (4) Slowly add 80° C. hot water to the polyurethane acrylate prepolymer obtained in step (3) at a speed of 1000 rpm. After the addition is completed, continue to maintain high speed dispersion for 30 minutes. Finally, reduce the pressure of the system to remove the solvent to obtain a UV-curable waterborne polyurethane acrylate resin.

[0028] Example 5 A method for preparing a highly efficient self-repairing UV-curable waterborne polyurethane acrylate resin for a metal substrate, which specifically comprises the following steps: (1) 2.442 g of p-hydroxybenzaldehyde and 2.484 g of 4,4'-dithiodiphenylamine were placed in a 250 mL three-necked flask, and 60 mL of anhydrous ethanol was added. The system was reacted at 60 °C for 12 h to obtain a yellow solid powder. The yellow solid powder was filtered and washed with anhydrous ethanol for several times, then washed with deionized water and placed in a 60 °C oven to dry overnight to obtain a tandem dynamic bond monomer; (2) Add 7.78 g of isophorone diisocyanate, 10 g of polytetrahydrofuran, 0.03 g of dibutyltin dilaurate and 5 mL of butanone to a 500 mL three-necked flask and react at 75 °C for 1 h. After the reaction is completed, add 1.34 g of 2,2-dihydroxymethylpropionic acid to the system and continue to react for 1.5 h. Then, raise the temperature to 90 °C, add 3.42 g of tandem dynamic bond monomer, 0.03 g of dibutyltin dilaurate and 10 mL of tetrahydrofuran and react for 3 h. Finally, lower the temperature to 70 °C, add 0.01 g of hydroquinone, 4.62 g of pentaerythritol triacrylate and 0.03 g of dibutyltin dilaurate and react until the isocyanate functional group content (NCO%) in the system is less than 0.5%, and obtain a mixed solution. (3) Cool the above-obtained mixed solution to room temperature, add 1.02 g of triethylamine to the system, stop stirring after uniformly dispersing for 30 min to obtain a polyurethane acrylate prepolymer; (4) Slowly add hot water at 80 °C to the polyurethane acrylate prepolymer obtained in step (3) at a rotation speed of 1000 rpm. After the addition is completed, continue to disperse at a high rotation speed for 30 min. Finally, remove the solvent from the system under reduced pressure to obtain a UV-curable waterborne polyurethane acrylate resin.

[0029] Example 6 A preparation method of a highly efficient self-healing UV-curable waterborne polyurethane acrylate resin for metal substrates, which specifically includes the following steps: (1) Place 2.442 g of p-hydroxybenzaldehyde and 2.484 g of 4,4'-dithiobis(aniline) in a 250 mL three-necked flask, and simultaneously add 60 mL of absolute ethanol. After the system reacts at 60 °C for 12 h, a yellow solid powder is obtained. Filter the yellow solid powder, wash it with absolute ethanol multiple times, then wash it with deionized water, and place it in an oven at 60 °C to dry overnight to obtain a tandem dynamic bond monomer; (2) Add 7.78 g of isophorone diisocyanate, 8.5 g of polytetrahydrofuran, 0.03 g of dibutyltin dilaurate, and 5 mL of tetrahydrofuran to a 500 mL three-necked flask and react at 75 °C for 1 h. After the reaction is completed, add 1.34 g of 2,2-dimethylolpropionic acid to the system and continue to react for 1.5 h. Then raise the temperature to 85 °C, add 2.96 g of the tandem dynamic bond monomer, 0.03 g of dibutyltin dilaurate, and 5 mL of tetrahydrofuran and react for 3 h. Finally, lower the temperature to 70 °C, add 0.012 g of hydroquinone, 5.97 g of pentaerythritol triacrylate, and 0.03 g of dibutyltin dilaurate and react until the content of isocyanate functional groups (NCO%) in the system is lower than 0.5% to obtain a mixed solution; (3) Cool the above-obtained mixed solution to room temperature, add 1.01 g of triethylamine to the system, stop stirring after uniformly dispersing for 30 min to obtain a polyurethane acrylate prepolymer; (4) Slowly add hot water at 80 °C to the polyurethane acrylate prepolymer obtained in step (3) at a rotation speed of 1000 rpm. After the addition is completed, continue to disperse at a high rotation speed for 30 min. Finally, remove the solvent from the system under reduced pressure to obtain a UV-curable waterborne polyurethane acrylate resin.

[0030] Comparative Example 1 A preparation method of a UV-curable waterborne polyurethane acrylate resin, the preparation method is similar to that of Example 1, the difference is that in step (1), 4,4'-dithiobenzidine is replaced with 4,4'-diaminodiphenylmethane, and a dynamic bond extender (tandem dynamic bond monomer) containing only imine bonds and no disulfide bonds is prepared, and the other components and steps are the same.

[0031] Comparative Example 2 A preparation method of a UV-curable waterborne polyurethane acrylate resin, the preparation method is similar to that of Example 1, the difference is that the tandem dynamic bond monomer obtained in step (1) of Example 1 is replaced with bis(4-hydroxyphenyl) disulfide, and bis(4-hydroxyphenyl) disulfide is used as the dynamic bond extender, and this extender contains only disulfide bonds and no imine bonds, and the other components and steps are the same.

[0032] Comparative Example 3 A preparation method of a UV-curable waterborne polyurethane acrylate resin, the preparation method is similar to that of Example 1, the difference is that in step (1), 4,4'-dithiobenzidine is replaced with 4,4'-diaminodiphenylmethane, and a dynamic bond extender (tandem dynamic bond monomer) containing only imine bonds and no disulfide bonds is prepared, and at the same time, bis(4-hydroxyphenyl) disulfide is used as the second dynamic bond extender, and these two extenders are used in combination to provide imine bonds and disulfide bonds respectively, and the other components and steps are the same.

[0033] Comparative Example 4 A preparation method of a UV-curable waterborne polyurethane acrylate resin, the preparation method is similar to that of Example 1, the difference is that in step (2), the dosage of the reaction monomers, especially the weight ratio of the tandem dynamic bond in the total formulation and the reaction temperature are reduced. The other steps are the same.

[0034] (2) Add 7.78 g of isophorone diisocyanate, 7 g of polytetrahydrofuran, 0.03 g of dibutyltin dilaurate and 5 mL of tetrahydrofuran to a 500 mL three-necked flask and react at 70 °C for 1 h. After the reaction is completed, add 0.94 g of 2,2-dimethylolpropionic acid to the system and continue to react for 1.5 h. Then add 2.85 g of the tandem dynamic bond monomer, 0.03 g of dibutyltin dilaurate, and 5 mL of tetrahydrofuran and react for 3 h; finally, add 0.01 g of hydroquinone, 5.97 g of pentaerythritol triacrylate and 0.03 g of dibutyltin dilaurate and react until the content of isocyanate functional groups (NCO%) in the system is lower than 0.5% to obtain a mixed solution; The waterborne UV resins prepared by using Example 1 and Comparative Examples 1-4 were applied to tinplates for performance testing, and the test results are shown in Table 1 below: Table 1 As can be seen from Table 1, the waterborne UV resin prepared by this method has excellent adhesion and hardness when applied to tinplate, and the resin state is relatively stable. The self-healing efficiency can reach 92.9% under the irradiation of an ultraviolet lamp with a wavelength of 365 nm, and can also reach 95.2% of the self-healing efficiency in an environment of 100 °C.

[0035] Figure 2 For the infrared spectra of Example 1 and Comparative Examples 1-3, the stretching vibration peak of -NH- (3360 cm -1 ) and the stretching vibration peak of C=O (1720 cm -1 ) can be clearly seen. At the same time, it can also be found that the four groups of samples have an absorption peak of C=C at 1605 cm -1 . Imine bonds are contained in Example 1 and Comparative Example 1, and an absorption peak of C=N can be found at 1535 cm -1 , while the other two groups do not have an absorption peak here. In addition, no absorption peak of NCO is found at 2250 cm -1 for the four groups of samples, which can prove the successful preparation of the UV-cured waterborne polyurethane acrylate emulsion.

[0036] Figure 3 The impedance magnitudes before and after damage and after repair of Example 1 and Comparative Examples 1-3 were tested by an electrochemical workstation. It can be clearly observed that the impedance values of the four groups of coatings decreased significantly after damage. After hot-press repair, the impedance value of the coating repaired in Example 1 was closest to the original value, and the repair efficiency of the other three groups was weaker than that of Example 1.

[0037] Figure 4 Optical microscope photos of Example 1 and Comparative Examples 1-3 before and after hot pressing at 110 °C and 8 MPa for 30 min. It can be clearly observed that except for the scratch marks of Comparative Example 2 still visible, the scratches of other coatings decreased significantly or even disappeared, especially the coating effect of Example 1 was the most obvious.

[0038] Figure 5 Self-healing pictures of Example 1 and Comparative Examples 1-3 at 100 °C with repair times of 0 min, 30 min, and 120 min. It can be found that the self-healing efficiency of Example 1 is significantly higher than that of Comparative Examples 1-3. At 30 min, the scratches almost completely disappeared, showing its rapid self-healing effect.

[0039] Figure 6 Stress-strain curves of Example 1 and Comparative Examples 1-3 at 100 °C for 3 h, 6 h, 9 h, 12 h, and 24 h of repair. The repair efficiency of Example 1 is higher than that of Comparative Examples 1-3 at each time period, which is consistent with Figure 5 the results of the microscope photos.

[0040] Figure 7 Self-healing pictures of Example 1 and Comparative Examples 1-3 under ultraviolet lamp irradiation at a wavelength of 365 nm. It can also be clearly observed here that in Example 1 and Comparative Examples 2-3, the scratches can be reduced or even disappear under ultraviolet lamp irradiation. However, since Comparative Example 1 has no disulfide bonds, only a weak self-healing effect can occur relying on a little heat generated by the ultraviolet lamp.

[0041] Figure 8 Base performance test photos of Example 1 and Comparative Examples 1-3 when applied to tinplate can be found that they all have excellent base performance on tinplate.

[0042] The embodiments of the present application have been described above in conjunction with the accompanying drawings. Specific examples have been used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the core idea of the present application. However, the present application is not limited to the above specific implementation manners. The above specific implementation manners are only illustrative and not restrictive. Under the inspiration of the present application, those of ordinary skill in the art can also make many forms without departing from the purpose of the present application and the scope protected by the claims, and all belong to the protection scope of the present application.

Claims

1. A method for preparing a UV-curable waterborne polyurethane acrylate resin, characterized in that: The following steps are involved: S1, placing p-hydroxybenzaldehyde and 4,4'-dithiodiphenylamine in a first organic solvent for reaction, filtering, washing, and drying to obtain a tandem dynamic bond monomer; S2, reacting a diisocyanate monomer, a macromolecular diol, and a catalyst in a second organic solvent for 1.5-2 h, adding a hydroxy acid and continuing the reaction for 1-3 h, then adding the tandem dynamic bond monomer, the catalyst, and the second organic solvent for 2-4 h, and after the reaction, continuing to add a hydroxyl acrylate monomer, an inhibitor, and a catalyst to react until the isocyanate functional group content is less than 0.5%, to obtain a mixed solution; the macromolecular diol has a molecular weight of 900 g / moL-1100 g / moL; S3, cooling the mixed solution to room temperature, and then adding a neutralizing agent to disperse it evenly to obtain a polyurethane acrylate prepolymer; S4, slowly dripping hot water into the polyurethane acrylate prepolymer at a rotation speed of 600 rpm-1200 rpm, then dispersing it evenly, and removing the solvent under reduced pressure to obtain the UV-curable waterborne polyurethane acrylate resin.

2. The preparation method according to claim 1, characterized in that: The mass ratio of p-hydroxybenzaldehyde, 4,4'-dithiodiphenylamine and the first organic solvent in S1 is 1:0.98-1.08:19.4; the first organic solvent includes at least one of anhydrous ethanol and methanol.

3. The preparation method according to claim 1, characterized in that: The diisocyanate monomer in S2 includes at least one of isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and toluene diisocyanate; The macromolecular diol includes at least one of polytetrahydrofuran, polyethylene glycol, polycaprolactone and polypropylene glycol.

4. The preparation method according to claim 2, characterized in that: The catalyst includes at least one of dibutyltin dilaurate, organic bismuth, stannous octoate, and dibutyltin diacetate; The second organic solvent includes at least one of acetone, butanone, ethyl acetate, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

5. The preparation method according to claim 4, characterized in that: The hydroxy acid includes at least one of 2,2-dihydroxymethylpropionic acid, dihydroxymethylbutanoic acid, and salicylic acid.

6. The preparation method according to claim 5, characterized in that: The hydroxy acrylate monomer includes at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, pentaerythritol triacrylate, and dipentaerythritol pentaacrylate; The polymerization inhibitor includes at least one of p-methoxyphenol, hydroquinone, and p-tert-butylcatechol.

7. The preparation method according to claim 6, characterized in that: The S3 comprises at least one of the neutralizing agents triethylamine, triethanolamine, N,N-dimethylethanolamine and ammonia water.

8. A UV-curable waterborne polyurethane acrylate resin, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 7.

9. The UV curable waterborne polyurethane acrylate resin according to claim 8, characterized in that: The UV curable waterborne polyurethane acrylate resin synthesis formula includes the following components in parts by weight: 12-15 parts of diisocyanate monomer, 12-15 parts of macromolecular diol, 1-2 parts of hydroxy acid, 5-7 parts of tandem dynamic bond monomer, 9-12 parts of hydroxy acrylate, 1-2 parts of neutralizer, 0.003-0.01 parts of catalyst, 0.0001-0.001 parts of inhibitor, 8-12 parts of second solvent, and 50-60 parts of water.

10. Use of the UV-curable waterborne polyurethane acrylate resin according to any one of claims 8 to 9 in metal surface treatment.

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