UV-thermal dual-curing waterborne polyurethane emulsion and preparation method thereof

Abstract

The invention discloses a UV (ultraviolet)-heat dual-curing waterborne polyurethane emulsion and a preparation method thereof. According to the UV-thermal dual-curing waterborne polyurethane emulsion, the heat resistance, the water resistance and the mechanical property of UV-WPUA can be improved, and meanwhile, the storage stability and the yellowing problem of the UV-WPUA can be improved; the polyurethane foam is prepared from the following components in parts by weight: 60-70 parts of binary isocyanate; 35 to 45 parts of polypropylene carbonate; 0 to 12 parts of 1, 4-butanediol; 50 to 55 parts of an acrylate monomer; 0.1 to 0.2 part of p-hydroxyanisole; 0 to 18 parts of sulfydryl silane; 0.1 to 0.3 part of an organic tin catalyst; 5-10 parts of a solvent; 100 to 150 parts of deionized water; belongs to the technical field of coatings.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a UV-thermal dual-curing waterborne polyurethane emulsion and its preparation method. Background Technology

[0002] With increasing environmental awareness and stricter regulations, water-based coatings are gaining popularity in the coatings industry due to their low volatile organic compound (VOC) content and environmental friendliness. UV-curable water-based coatings (UV-WPUA), as a novel coating system, are becoming an important alternative to traditional solvent-based coatings due to their high efficiency, energy saving, and environmental friendliness. UV-WPUA is typically prepared using raw materials such as diisocyanates, diols, and acrylate monomers, through steps including prepolymerization, emulsification, and UV curing.

[0003] However, current UV-WPUA still faces several unresolved issues. First, the lack of high-bond-energy stabilizing groups, such as Si-O bonds, in the UV-WPUA molecular chain leads to insufficient heat resistance. The thermal decomposition temperature of the cured film is typically below 260°C, making it prone to weight loss and deformation at high temperatures, thus limiting its application in heat-resistant environments. Second, traditional UV-WPUA has a high content of hydrophilic groups, resulting in poor water resistance of the cured film, with water contact angles often below 70°. Furthermore, increasing the crosslinking density to improve water resistance leads to increased coating brittleness and decreased elongation at break. In addition, the UV-WPUA curing process is susceptible to oxygen inhibition, resulting in incomplete curing. Long-term exposure to UV light or high temperatures can cause yellowing of the cured film, and the thermal stability of the emulsion typically depends on low-temperature storage, increasing storage costs.

[0004] To address these issues, researchers have been exploring new modification methods. Organosilicon modification is a commonly used technique, but its application in UV-WPUA still faces many limitations. For example, imbalances in the interfacial interactions between organosilicon and the polyurethane matrix, and uneven distribution of active groups in the cured system, make it difficult to simultaneously achieve optimal thermal stability, water resistance, and mechanical properties. Therefore, developing a modified resin composition that can simultaneously improve the heat resistance, water resistance, and mechanical properties of UV-WPUA, while also improving its storage stability and reducing yellowing, is of great significance. CN111718647A discloses an environmentally friendly waterborne UV coating and its preparation method. This coating comprises a UV-curable waterborne polyurethane dispersion, an acrylate emulsion, a photoinitiator, a silane coupling agent, a surfactant, additives, a light stabilizer, and water. This coating exhibits strong weather resistance and adhesion; its viscosity is adjusted with water, eliminating the need for reactive diluents and addressing VOC, toxicity, and irritation issues. However, further optimization of the coating's formulation is still needed to improve its performance and environmental friendliness. CN118755343A discloses a photocurable silicone-modified waterborne acrylic coating and its preparation method. The coating is prepared by preparing a silane-modified acrylic ester, which is then reacted with polyglycerol-2-dipolyhydroxystearate, siloxane, isocyanate, and a catalyst. After chain extension, a capping agent containing the modified acrylic ester is added dropwise at a lower temperature to seal the end-capping, resulting in a waterborne polyurethane emulsion. This coating exhibits advantages such as good adhesion, good chemical resistance, and rapid UV curing, with significantly improved resistance to photoaging and water resistance. However, further research and development of novel photocurable resins and photoinitiators are needed to improve the curing speed, curing degree, and mechanical properties of the coating.

[0005] Therefore, developing a modified resin composition that can improve the heat resistance, water resistance, and mechanical properties of UV-WPUA while simultaneously addressing its storage stability and yellowing issues has become a key research focus and challenge. These problems can be effectively solved by optimizing the UV-WPUA molecular chain design, employing organosilicon modification processes, and further optimizing the curing system design, thus promoting the application of UV-WPUA in the coatings industry. Summary of the Invention

[0006] To address the aforementioned problems, the first objective of this invention is to provide a UV-thermal dual-curing waterborne polyurethane emulsion that can improve the heat resistance, water resistance, and mechanical properties of UV-WPUA while simultaneously improving its storage stability and reducing yellowing issues.

[0007] The second objective of this invention is to provide a method for preparing a UV-thermal dual-curing aqueous polyurethane emulsion, which is simple and easy to industrialize.

[0008] Therefore, the first technical solution provided by this invention is as follows:

[0009] A UV-thermal dual-curing waterborne polyurethane emulsion is prepared from the following components:

[0010]

[0011]

[0012] Furthermore, in the aforementioned UV-thermal dual-curing aqueous polyurethane emulsion, the diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated phenylmethane diisocyanate, and toluene diisocyanate.

[0013] Furthermore, in the aforementioned UV-thermal dual-curing waterborne polyurethane emulsion, the acrylate monomer is one or more of pentaerythritol triacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxybutyl acrylate.

[0014] Furthermore, in the aforementioned UV-thermal dual-curing aqueous polyurethane emulsion, the mercaptosilane is one or both of γ-mercaptopropylmethyldimethoxysilane and γ-mercaptopropyltrimethoxysilane.

[0015] Furthermore, in the aforementioned UV-thermal dual-curing aqueous polyurethane emulsion, the organotin catalyst is one or more of dibutyltin dilaurate, stannous octoate, dioctyltin dilaurate, dibutyltin diacetate, and dioctyltin diacetate.

[0016] Furthermore, in the aforementioned UV-thermal dual-curing aqueous polyurethane emulsion, the solvent is NMP.

[0017] The second technical solution provided by this invention is a method for preparing the above-mentioned UV-thermal dual-curing waterborne polyurethane emulsion, which includes the following steps in sequence:

[0018] (1) Weigh each substance and pre-treat and dehydrate the weighed polypropylene carbonate;

[0019] (2) Add the diisocyanate, dehydrated polypropylene carbonate, NMP, and organotin catalyst weighed in step (1) to a three-necked flask, heat to 80-90℃, and stir for 0.4-0.6h; add 1,4-butanediol, maintain 80-90℃ and continue stirring for 1.4-1.6h to extend the chain and form a long-chain prepolymer; add acrylate monomer and p-hydroxyanisole, maintain 80-90℃ and stir for 2.4-2.6h to obtain a transparent and viscous polyurethane prepolymer;

[0020] (3) Cool the prepolymer prepared in step (2) to 40-50°C, add mercaptosilane, and stir for 0.4-0.6 h to obtain crude Si-WPUA resin.

[0021] (4) Slowly add deionized water to the crude resin while increasing the stirring speed to 500-800 r / min and emulsify for 10-15 min until a uniform and stable milky white or bluish emulsion is formed, thus obtaining a UV-thermal dual-curing waterborne polyurethane emulsion.

[0022] Furthermore, in the above-mentioned method for preparing UV-thermal dual-curing waterborne polyurethane emulsion, the pretreatment and dehydration method for polypropylene carbonate involves placing the weighed polypropylene carbonate in a three-necked flask, heating and stirring at 115–125°C while simultaneously performing vacuum dehydration for 1.5–2.5 hours, then cooling to room temperature, sealing and storing for later use.

[0023] Furthermore, in the above-mentioned method for preparing UV-thermal dual-curing waterborne polyurethane emulsion, the deionized water droplet acceleration is 1-2 mL / min.

[0024] Another object of the present invention is to provide the application of the above-mentioned UV-thermal dual-curing waterborne polyurethane emulsion as a coating additive.

[0025] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0026] 1. The UV-thermal dual-curing waterborne polyurethane emulsion provided by this invention has significantly improved heat resistance after film formation: by introducing high bond energy Si-O bonds (bond energy 452kJ / mol, much higher than the 347kJ / mol of C-C bonds) through KH590, the T5% of the Si-WPUA2 cured film modified by 5% KH590 reaches 276.23℃ (7.8% higher than the unmodified WPUA), and the residual rate at 800℃ reaches 27.9%, which can withstand short-term high temperature environment of 200℃;

[0027] 2. The UV-thermal dual-curing waterborne polyurethane emulsion provided by this invention achieves synergistic optimization of storage properties and mechanical properties after film formation: tensile strength is increased from 1.93MPa to 4.93MPa (10% KH590 modification), while elongation at break remains above 25%, solving the industry pain point of "increased water resistance leads to decreased toughness"; all formulations show no stratification or precipitation after one week of heat storage at 50℃, corresponding to a room temperature storage stability period of ≥6 months, eliminating the need for low-temperature storage and reducing industrialization costs;

[0028] 3. The UV-thermal dual-curing waterborne polyurethane emulsion film-forming process provided by this invention is simple and easy to mass-produce: no special equipment is required (conventional oil bath, stirring, and UV curing machine are sufficient), the reaction time of each step is short (total preparation cycle ≤ 6h); the amount of KH590 can be flexibly adjusted according to performance requirements (2%~10%), taking into account the requirements of hardness and gloss in different scenarios (e.g., gloss of 85.7 at 5% dosage, meeting decorative requirements; hardness B at 10% dosage, meeting wear resistance requirements);

[0029] 4. The UV-thermal dual-curing waterborne polyurethane emulsion provided by this invention improves the yellowing resistance after film formation: After the cured film modified with 5% KH590 is baked at 100℃ for 2 hours, the visible light transmittance retention rate reaches 88% (unmodified WPUA is only 85%), thus extending the service life of the coating. Attached Figure Description

[0030] Figure 1 These are the emulsion particle size test results for the examples and comparative examples;

[0031] Figure 2 These are the TG test results for Examples 1-4 and the comparative example;

[0032] Figure 3 These are the DSC test results of Examples 1-4 and the comparative example;

[0033] Figure 4 These are the results of yellowing resistance tests for Examples 1-4 and the comparative examples. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] Isophorone diisocyanate (IPDI) was heated and stirred at 120°C, vacuum dehydrated for 2 hours to remove trace amounts of moisture, cooled and sealed, and then placed in a dry glass container for later use. 66.7g of IPDI, 39.44g of polypropylene carbonate (PPC), 5.3g of N-methylpyrrolidone (NMP) solvent, and 0.12g of organotin catalyst DBTDL were placed in a four-necked flask and reacted at 85℃ for 0.5h. Then, 10.81g of chain extender 1,4-butanediol (BDO) was added, and the reaction was continued for 1.5h. Next, 53.64g of pentaerythritol triacrylate (PETA) and 0.15g of p-hydroxyanisole (MEHQ) were added, and the reaction was continued for 2.5h. The temperature was lowered to 45℃, and 120g of deionized water and 3.42g of KH590 were added. After stirring for 0.5h, the temperature was raised to 85℃, and the reaction was continued for 1h. The mixture was then cooled and discharged for later use, and named Si-WPUA 1-2%. (Solid content 32.18%, density 0.9710g / cm³) 3 (Refractive index 1.3931).

[0037] Si-WPUA 1-2% 1 The characteristic peaks were determined by H NMR detection and are assigned as follows: 1 ¹H NMR (400MHz, CDCl₃): δ = -0.01–0.12 (s, 3H, Si-OCH₃, Si-CH₃), 2.20–2.31 (d, 3H, -CH₃ directly attached to the six-membered ring in TDI), 6.50–8.51 (s, H, H on the benzene ring of TDI), 3.68–3.75 (s, 2H, -OC₃). H 2CH2C H 2O-), 3.75~3.92(s,2H,-OC H2C H 2CH2O-), 4.10~4.21(m,2H,IPDI-NHOCO-C H 2), 4.61~4.72 (m,2H,IPDI-N) H OCO-CH2), 5.75~6.53(m,2H,-OOCCH=CH2), 7.26(s,H,CDCl3).

[0038] Preparation of the coating film: 2 wt% photoinitiator 184 (1-hydroxycyclohexylphenyl ketone) was added to a 1-2% Si-WPUA sample, and then diluted with distilled water to a suitable viscosity. The solution was then evenly sprayed onto the surface of a PC board using a spray gun to form a coating film. After drying in a 70℃ constant temperature drying oven for 7 minutes, it was then cured in a UV machine and cooled in a desiccator to obtain the final coating film.

[0039] Example 2

[0040] 2,6-Toluene diisocyanate (TDI) was heated and stirred at 110°C, and then vacuum dehydrated for 2 hours to remove trace amounts of moisture. After cooling and sealing, it was placed in a dry glass container and sealed for later use. 66.7g of TDI, 39.44g of polypropylene carbonate (PPC), 5.5g of N-methylpyrrolidone (NMP) solvent, and 0.14g of organotin catalyst DBTDL were placed in a four-necked flask and reacted at 85℃ for 0.5h. Then, 10.81g of chain extender 1,4-butanediol (BDO) was added, and the reaction was continued for 1.5h. Next, 53.64g of PETA and 0.15g of p-hydroxyanisole (MEHQ) were added, and the reaction was continued for 2.5h. The temperature was lowered to 45℃, and 125g of deionized water and 3.42g of KH970 were added. After stirring for 0.5h, the temperature was raised to 85℃, and the reaction was continued for 1h. The mixture was then cooled and discharged for later use, and named Si-WPUA 2-5%. (Solid content 32.59%, density 0.9905g / cm³) 3 (Refractive index 1.3931).

[0041] The characteristic peaks are assigned as follows: 1 H NMR (400MHz, CDCl3): δ=0~0.12(s,3H,Si-OCH3), -0.80~1.13(d,3H, The -CH3 group directly connected to the six-membered ring has a concentration of 1.32–1.44 (s,H). The six-membered ring ), 1.64~1.77 (s, 2H, The six-membered ring (methylene), 2.91–2.93 (d,2H, (Directly linked methylene group of a six-membered ring), 3.70–3.77 (s, 2H, -OC) H 2CH2C H 2O-), 3.75~3.93(s,2H,-OCH2C H 2CH2O-), 4.11~4.23(m,2H,IPDI-NHOCO-C H 2), 4.61~4.76 (m,2H,IPDI-N) H OCO-CH2), 5.77~6.56(m,2H,-OOCCH=CH2), 7.26(s,H,CDCl3).

[0042] Preparation of the coating film: 2 wt% photoinitiator 184 (1-hydroxycyclohexylphenyl ketone) was added to a 2-5% Si-WPUA sample, and then diluted with distilled water to a suitable viscosity. The solution was then evenly sprayed onto the surface of a PC board using a spray gun to form a coating film. After drying in a 70℃ constant temperature drying oven for 7 minutes, it was then cured in a UV machine and cooled in a desiccator to obtain the final coating film.

[0043] Example 3

[0044] IPDI was heated and stirred at 120℃, then vacuum dehydrated for 2 hours to remove trace amounts of moisture. After cooling, it was sealed and stored in a dry glass container for later use. 66.7g of IPDI, 39.44g of polypropylene carbonate (PPC), and N-methylpyrrolidone solvent were then added.

[0045] 5.5g of N-methylpyrrolidone (NMP) and 0.20g of organotin catalyst DBTDL were placed in a four-necked flask and reacted at 85℃ for 0.5h. Then, 10.81g of chain extender 1,4-butanediol (BDO) was added, and the reaction was continued for 1.5h. Next, 53.64g of PETA and 0.15g of p-hydroxyanisole (MEHQ) were added, and the reaction was continued for 2.5h. The temperature was lowered to 45℃, and 119g of deionized water and 11.94g of KH590 were added. After stirring for 0.5h, the temperature was raised to 85℃, and the reaction was continued for 1h. The mixture was then cooled and discharged for later use, and named Si-WPUA3-7%. (Solid content 33.94%, density 1.1468g / cm³) 3 (Refractive index 1.3958).

[0046] The characteristic peaks are assigned as follows: 1 HNMR (400MHz, CDCl3): δ=0~0.12(s,3H,Si-OCH3), -0.80~1.13(d,3H, The -CH3 group directly connected to the six-membered ring has a concentration of 1.32–1.44 (s,H). The six-membered ring ), 1.64~1.77 (s, 2H, The six-membered ring (methylene), 2.91–2.93 (d,2H, (Directly linked methylene group of a six-membered ring), 3.70–3.77 (s, 2H, -OC) H 2CH2C H 2O-), 3.75~3.93(s,2H,-OCH2C H 2CH2O-), 4.11~4.23(m,2H,IPDI-NHOCO-C H 2), 4.61~4.76 (m,2H,IPDI-N) HOCO-CH2), 5.77~6.56(m,2H,-OOCCH=CH2), 7.26(s,H,CDCl3).

[0047] Preparation of the coating film: 2 wt% photoinitiator 184 (1-hydroxycyclohexylphenyl ketone) was added to a 3-7% Si-WPUA sample, and then diluted with distilled water to a suitable viscosity. The solution was then evenly sprayed onto the surface of a PC board using a spray gun to form a coating film. After drying in a 70℃ constant temperature drying oven for 7 minutes, it was then cured in a UV machine and cooled in a desiccator to obtain the final coating film.

[0048] Example 4

[0049] IPDI was heated and stirred at 120℃, then vacuum dehydrated for 2 hours to remove trace amounts of moisture. After cooling, it was sealed and placed in a dry glass container for later use. 66.7g of IPDI, 39.44g of polypropylene carbonate (PPC), 5.5g of N-methylpyrrolidone (NMP) solvent, and 0.45g of stannous octoate were placed in a four-necked flask and reacted at 85℃ for 0.5 hours. Then, 10.81g of 1,4-butanediol (BDO) chain extender was added, and the reaction was continued for 1.5 hours. Next, 53.64g of PETA and 0.15g of p-hydroxyanisole (MEHQ) were added, and the reaction was continued for 2.5 hours. The temperature was lowered to 45℃, and 119g of deionized water and 11.94g of KH590 were added. After stirring for 0.5 hours, the temperature was raised to 85℃, and the reaction was continued for 1 hour. The mixture was then cooled and discharged for later use, and named Si-WPUA4-10%. (Solid content 34.45%, density 1.1651 g / cm³) 3 (Refractive index 1.3954).

[0050] The characteristic peaks are assigned as follows: 1 HNMR (400MHz, CDCl3): δ=-0.03~0.11(s,3H,Si-OCH3,Si-CH3), -0.90~1.15(d,3H, The -CH3 group directly connected to the six-membered ring, 1.34–1.45 (s, H, The six-membered ring ), 1.66~1.77 (s, 2H, The six-membered ring (methylene), 2.93–2.96 (d,2H, (Directly linked methylene group of a six-membered ring), 3.70–3.77 (s, 2H, -OC) H 2CH2C H 2O-), 3.78~3.95(s,2H,-OCH2C H2CH2O-), 4.11~4.20(m,2H,IPDI-NHOCO-C H 2), 4.65~4.78 (m, 2H, IPDI-N) H OCO-CH2), 5.77~6.56(m,2H,-OOCCH=CH2), 7.26(s,H,CDCl3).

[0051] Preparation of the coating film: 2 wt% photoinitiator 184 (1-hydroxycyclohexylphenyl ketone) was added to the Si-WPUA4-10% sample, and then diluted with distilled water to a suitable viscosity. The solution was then evenly sprayed onto the surface of the PC board using a spray gun to form a coating film. After drying in a 70℃ constant temperature drying oven for 7 minutes, it was then cured in a UV machine and cooled in a desiccator to obtain the final coating film.

[0052] Comparative Example 1

[0053] IPDI was heated and stirred at 120℃, then vacuum dehydrated for 2 hours to remove trace amounts of moisture. After cooling, it was sealed and stored in a dry glass container for later use. 66.7g of IPDI, 39.44g of polypropylene carbonate (PPC), 5.3g of N-methylpyrrolidone (NMP) solvent, and 0.12g of organotin catalyst DBTDL were placed in a four-necked flask and reacted at 85℃ for 0.5 hours. Then, 10.81g of chain extender 1,4-butanediol (BDO) was added, and the reaction was continued for 1.5 hours. Next, 53.64g of PETA and 0.15g of p-hydroxyanisole (MEHQ) were added, and the reaction was continued for 2.5 hours. The mixture was then cooled to 45℃, 120g of deionized water was added, and the mixture was discharged after cooling. This product was named WPUA-0%. (Solid content 32.18%, density 0.9710g / cm³) 3 (Refractive index 1.3931).

[0054] The characteristic peaks are assigned as follows: 1 HNMR (400MHz, CDCl3): δ=0.85~1.00(d,3H, The -CH3 group directly connected to the six-membered ring has a concentration of 1.32–1.44 (s,H). The six-membered ring ), 1.63~1.75 (s, 2H, The six-membered ring (methylene), 2.91–2.95 (d,2H, (Directly linked methylene group of a six-membered ring), 3.70–3.77 (s, 2H, -OC) H 2CH2C H 2O-), 3.78~3.95(s,2H,-OCH2C H2CH2O-), 4.10~4.21(m,2H,IPDI-NHOCO-C H 2), 4.65~4.78 (m, 2H, IPDI-N) H OCO-CH2), 5.75~6.55(m,2H,-OOCCH=CH2), 7.26(s,H,CDCl3).

[0055] Preparation of the coating film: WPUA-0% sample was mixed with 2wt% photoinitiator 184 (1-hydroxycyclohexylphenyl ketone), diluted with distilled water to a suitable viscosity, and then evenly sprayed onto the surface of the PC board using a spray gun to form a coating film. After drying in a 70℃ constant temperature drying oven for 7 minutes, it was then cured in a UV machine and cooled in a desiccator to obtain the coating film.

[0056] To verify the advantages of the technical solution provided in this application, the following specific verification experiments, including the embodiments and comparative examples, are given.

[0057] I. Test methods and standards are as follows:

[0058] (1) Density test: Tested according to GB / T6750-2007; the density of the liquid was determined using a density cup at 25℃.

[0059] (2) Refractive index: The refractive index of the liquid was measured by Abbe refractometer at 25℃ according to GB / T6448-2008. Each sample was tested 3 times and the average value was taken.

[0060] (3) Emulsion particle size test: The LS-POP(9) laser particle size analyzer of Zhuhai Omec Instrument Co., Ltd. was used for the test. Before the test, the resin was diluted to a solid mass fraction of 0.3wt% and ultrasonically dispersed. Each sample was tested 3 times at 25℃.

[0061] (4) Gloss test: The gloss of the UV-cured film was measured using a gloss meter JB / WGG-60 with a geometric angle of 60°, in accordance with GB / T9754-2007 standard.

[0062] (5) Adhesion test: According to GB / T9286-1998 standard, the Huaguo adhesion tester was used. The paint film was cut into 100 small squares with a cross-cutting tool, then firmly glued with tape and then peeled off. The squares on the sample were observed to see if they had fallen off. The adhesion rating is 0-5, that is, level 5 means that no squares were glued off, and level 0 means that 65% of the squares were glued off.

[0063] (6) Hardness test: According to GB / T 6793-2006 standard, on the dried and cured film on the PC board, use a pencil of fixed hardness to press the film at a 45° angle, gradually increasing the pencil hardness until the film is scratched. The hardness of the pencil used before scratching is the hardness of the film.

[0064] (7) TG: According to GB / T 33047.1-2016 standard, weigh 3 to 8 mg of sample, the nitrogen flow rate is 50 mL / min, the heating rate is set to 10℃ / min, and the temperature range is 30 to 800℃.

[0065] (8) DSC: According to GB / T 19466.2-2004 standard, weigh 3 to 10 mg of sample, cool it down mechanically under nitrogen flow, keep it at -65℃ for 10 min, the heating rate is 5 K / min, and the temperature range is -65 to 100℃.

[0066] (9) Yellowing test: The paint film was continuously baked at 100℃, and the decay rate of visible light transmittance before and after aging was measured by a Shimadzu UV-2600i UV spectrophotometer.

[0067] (10) Thermal storage stability: The resin emulsion was continuously baked at 50°C for 168 hours. If there was no obvious sedimentation after baking, it was considered that the storage period at room temperature could exceed 6 months.

[0068] (11) Tensile property test: According to ASTM D412-2023, a certain amount of UV-cured waterborne polyurethane sample was poured into a PTFE mold coated with a release agent in three stages to obtain dumbbell-shaped strips. The total length of the strips was 105 mm, the thickness was 1.6 mm, and the width of the narrow parallel section was 5 mm. The tensile properties of the cured film were tested using a tensile testing machine at room temperature. The tensile rate was 50 mm / min, and the gauge length was 45 mm.

[0069] (12) Water contact angle: Deionized water was used as the test liquid. 5 μL of the liquid was dropped onto the paint film, left to stand for 30 seconds, and then photographed and the water contact angle was calculated using protractor software.

[0070] (13) Solid content: Place the waterborne UV resin sample with mass m0 on a clean tin foil tray and bake it at 120℃ for 2 hours. Weigh it and determine its mass m1. The solid content W of the sample is then determined. t It is calculated from Equation 1.

[0071]

[0072] Second test results

[0073] 1. Emulsion particle size and thermal storage stability testing

[0074] The emulsion particle size test results for each embodiment and comparative example are as follows: Figure 1 As shown in Table 1.

[0075] Table 1 Results of emulsion average particle size test

[0076]

[0077] pass Figure 1 As shown in Table 1, the particle size of the emulsion in the prepared examples gradually increased with the increase of mercaptosilane content, and then showed a decreasing trend. This is because the increased mercaptosilane content leads to an increase in hydrophobic groups in the system, resulting in a larger emulsion particle size. Due to the strong hydrophobicity of mercaptosilane, when it is coated by the polyurethane macromolecular chains, it reduces the moisture content inside the polyurethane particles, thereby reducing the particle size of the emulsion. Table 1 also shows that the Si-WPUA resin exhibits good storage stability at room temperature and can be stored stably without the need for low temperature or drying conditions.

[0078] 2. Tests on film hardness, adhesion, and gloss

[0079] The test results of hardness, adhesion and gloss of the cured films of Examples 1-4 and the comparative examples are shown in Table 2.

[0080] Table 2. Test results of paint film hardness, adhesion, and gloss.

[0081]

[0082] As shown in Table 2, with the increase of mercaptosilane content, the hardness of the cured film in the examples increased, adhesion improved, but gloss decreased. Generally, hardness is mainly determined by the content of the hard component and the cross-linking structure of the resin. The increased number of siloxane groups introduced by mercaptosilane enhances the hydrophobicity of the system, leading to increased cross-linking density, increased hardness, and decreased gloss of the cured film. Furthermore, the increased content of mercapto (-SH) groups in the dispersion, a highly polar group, can significantly improve the adhesion of the coating. Therefore, the adhesion performance of Examples 1-4 is significantly better than that of the comparative examples.

[0083] 3. Thermal stability test

[0084] The TG test results of Examples 1-4 and the comparative examples are as follows: Figure 2 And as shown in Table 3

[0085]

[0086] pass Figure 2As shown in Table 3, the thermal stability of the resin-cured film initially increases and then decreases with increasing mercaptosilane content. Mercaptosilane is introduced into the resin system as a hard segment component, and the heat resistance of hard segments is lower than that of soft segments. When the mercaptosilane content continues to increase, the heat resistance of the UV-cured film weakens accordingly. This phenomenon is limited by the structural characteristics of Si-WPUA and the crosslinking density of the system. Generally, under the same crosslinking density conditions, increasing the crosslinking density can significantly enhance the thermal stability of the cured product. Furthermore, the thermal decomposition temperatures of Si-WPUA 2-5% and Si-WPUA 4-10% are higher than those of Si-WPUA 1-2% and Si-WPUA 3-7%, respectively, further confirming that the benzene ring of TDI contributes to improving the thermal stability of the resin.

[0087] The DSC test results of Examples 1-4 and the comparative examples are as follows: Figure 3 As shown.

[0088] Depend on Figure 3 As can be seen, all four embodiments have only one glass transition temperature, which is 66.4℃, 61.8℃, 66.2℃, and 86.3℃, respectively. The glass transition temperature of the resin-cured film first decreases and then increases, which is because organosilicon itself has a low glass transition temperature. When organosilicon is added to the polymer, it may initially lower the overall glass transition temperature of the material because the introduction of organosilicon increases the flexibility of the molecular chains, making them easier to move. As the organosilicon content increases, the interaction between the organosilicon and the matrix polymer may gradually strengthen. This interaction may lead to a decrease in the flexibility of the molecular chains, thereby increasing the glass transition temperature.

[0089] The results of the yellowing resistance test (change in light transmittance) of Examples 1-4 and the comparative examples are as follows: Figure 4 As shown, the visible light transmittance of the cured film decreases with increasing mercaptosilane content, indicating a gradual weakening of its resistance to yellowing. This is because the silicone-modified waterborne polyurethane contains mercapto groups, which are easily oxidized under ultraviolet light. Simultaneously, with increasing baking time, the yellowing resistance of each cured film gradually decreases, and the visible light transmittance also gradually decreases. This is because ultraviolet light exposure may cause the formate groups in the polyurethane structure to break, producing colored groups that cause the material to yellow and darken.

[0090] 4. Tensile property test

[0091] The tensile properties of Examples 1-4 and the comparative examples are shown in Table 4.

[0092] Table 4

[0093]

[0094] As shown in Table 4, the tensile strength of the samples gradually increased while the elongation at break gradually decreased with the increase of mercaptosilane content. This is because after the siloxane group is introduced into the polyurethane backbone, the bond energy of the Si-O bond in the resin is higher than that of the unmodified C-C bond. Therefore, the modification will cause an increase in the tensile strength of the cured film. Due to the addition of KH590, the degree of crosslinking of the cured film gradually increases, which leads to a significant restriction on the movement of molecular chains during tensile deformation, resulting in a decrease in the elongation at break.

[0095] The tensile strength of Si-WPUA2-5% is only slightly improved compared to Si-WPUA1-2% because KH970 has a lower alkoxy content, resulting in a lower crosslinking density of the resin at the same dosage, which in turn has a weaker impact on tensile strength.

Claims

1. A UV-thermal dual-curable waterborne polyurethane emulsion, characterized in that, are prepared from the following components: 60-70 parts of diisocyanate; 35-45 parts of polypropylene carbonate; 10-12 parts of 1,4-butanediol; 50-55 parts of acrylic ester monomer; 0.1-0.2 parts of p-hydroxyanisole; 0-18 parts of mercapto silane; 0.1-0.3 parts of organic tin catalyst; 5-10 parts of solvent; 100-150 parts of deionized water.

2. The UV-thermal dual curable waterborne polyurethane emulsion according to claim 1, characterized in that, The diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated phenylmethane diisocyanate, and toluene diisocyanate.

3. The UV-thermal dual curable waterborne polyurethane emulsion according to claim 1, characterized in that, The acrylic ester monomer is one or more of pentaerythritol triacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxybutyl acrylate. 4.The UV-thermal dual-curable waterborne polyurethane emulsion of claim 1, wherein, The mercapto silane is one or both of γ-mercaptopropyl methyl dimethoxy silane and γ-mercaptopropyl trimethoxy silane. 5.The UV-thermal dual-curable waterborne polyurethane emulsion of claim 1, wherein, The organic tin catalyst is one or more of dibutyl tin dilaurate, stannous octoate, dioctyl tin dilaurate, dibutyl tin diacetate, and dioctyl tin diacetate. 6.The UV-thermal dual-curable waterborne polyurethane emulsion of claim 1, wherein, The solvent is NMP.

7. The process for the preparation of UV-thermal dual curable waterborne polyurethane emulsion as claimed in claim 1, wherein, The method comprises the following steps in sequence: (1) The components are weighed according to claim 1, and the weighed polypropylene carbonate is pretreated and dehydrated; (2) The diisocyanate, dehydrated polypropylene carbonate, NMP, and organic tin catalyst weighed in step (1) are added to a three-necked flask, heated to 80-90°C, and stirred for 0.4-0.6 h; 1,4-butanediol is added, the temperature is maintained at 80-90°C, and the stirring is continued for 1.4-1.6 h to form a long-chain prepolymer by chain extension; the acrylic ester monomer and p-hydroxyanisole are added, the temperature is maintained at 80-90°C, and the stirring is continued for 2.4-2.6 h to obtain a transparent viscous polyurethane prepolymer; (3) The prepolymer prepared in step (2) is cooled to 40-50°C, the mercapto silane is added, and the stirring is continued for 0.4-0.6 h to obtain a Si-WPUA resin crude product. (4) The deionized water is slowly added to the resin crude product, the stirring speed is increased to 500-800 r / min, and the emulsification is continued for 10-15 min until a uniform, stable milky white or bluish emulsion is formed, and a UV-thermal dual-cured waterborne polyurethane emulsion is obtained.

8. The method for preparing UV-thermal dual-curable waterborne polyurethane emulsion according to claim 7, characterized in that, The method for pretreating and dehydrating the polypropylene carbonate is to place the weighed polypropylene carbonate in a three-necked flask, heat and stir at 115-125°C, and open the vacuum for dehydration for 1.5-2.5 h, and then cool to room temperature, seal, and store for use.

9. The method for preparing the UV-thermal dual-curing aqueous polyurethane emulsion according to claim 7, characterized in that, The deionized water is added at a speed of 1-2 mL / min.

10. The UV-thermal dual-cured waterborne polyurethane emulsion of claim 1 as a coating additive.

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