A water-based coating composition, preparation method thereof, and application thereof

Abstract

The present invention provides a water-based coating composition, a preparation method, and an application thereof, belonging to the field of coating technology. The water-based coating composition comprises the following components, by weight: 100 parts of a nano-SiO2-polyurethane-polyacrylate composite dispersion, 0.5-0.8 parts of a defoamer, 0.4-0.6 parts of a leveling agent, 0.2-0.4 parts of a wetting agent, and 0.6-1 parts of a film-forming aid. The present invention improves the physical and mechanical properties of the coating film and enhances the water resistance of the coating film, while also improving the storage stability of the water-based coating.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and in particular relates to a water-based coating composition, a preparation method and an application thereof. Background Art

[0002] Global environmental regulations are tightening limits on volatile organic compound (VOC) emissions. Water-based paints, which use water as a diluent, have VOC levels as low as one-tenth that of traditional solvent-based paints, significantly reducing environmental pollution. Furthermore, many regions have implemented "oil-to-water" policies, mandating the use of water-based paints in industries such as furniture, automotive manufacturing, and packaging and printing. Subsidies and technical support are also being used to promote industrial upgrading.

[0003] In existing waterborne polyurethane coatings, the introduction of inorganic nanoparticles can improve the coating's physical and mechanical properties, providing both reinforcement and toughness. They can also enhance the coating's scratch and water resistance. However, due to the high surface energy and significant agglomeration of inorganic nanoparticles, direct addition of inorganic nanoparticles to waterborne coatings can lead to stability issues after dispersion, impacting the coating's storage stability. Summary of the Invention

[0004] To solve the problems existing in the background technology, the present invention provides a water-based coating composition and its preparation method and application, which improves the physical and mechanical properties of the coating film (increases tensile strength) and the water resistance of the coating film (reduces water absorption), while improving the storage stability of the water-based coating.

[0005] In order to achieve the above-mentioned object, the present invention provides a water-based coating composition in a first aspect, comprising the following components, by weight: 100 parts of nano-SiO2-polyurethane-polyacrylate composite dispersion, 0.5-0.8 parts of defoaming agent, 0.4-0.6 parts of leveling agent, 0.2-0.4 parts of wetting agent and 0.6-1 parts of film-forming aid;

[0006] The preparation method of the nano-SiO2-polyurethane-polyacrylate composite dispersion is as follows:

[0007] A1. Add polyether polyol, trimethyl phosphate, isocyanate, and perfluorooctyl ethyl acrylate to a reactor, with the mass of trimethyl phosphate being 11%-13% of the mass of the polyether polyol, the NCO / OH molar ratio being 1.5-1.8, and the mass of perfluorooctyl ethyl acrylate being 4%-5% of the mass of the polyether polyol. React at 75-80°C until the NCO content reaches the standard (the reaction is considered to be terminated when the fluctuation of the NCO content results of two consecutive tests at an interval of 30 minutes is less than 0.2%) to obtain a prepolymer.

[0008] A2. Add 5%-7% by weight of epoxy resin E-20 to the prepolymer obtained in A1, raise the temperature to 80°C, react for 2 hours, and add acetone to adjust the viscosity to 400-450 mPa·s to obtain an epoxy-modified prepolymer;

[0009] A3. Cool the epoxy-modified prepolymer obtained in A2 to below 40°C, neutralize it with a neutralizer to a pH of 7.5-8.0, and slowly add deionized water dropwise with stirring at 1500-2000 rpm, wherein the mass of the deionized water is 0.8-1 times the mass of the prepolymer to form a primary dispersion. Methyl methacrylate is added in an amount of 22%-26% of the mass of the prepolymer, and acetone is added in an amount of 5%-7% of the mass of the prepolymer to stabilize the emulsion. The mixture is heated to 72-76°C, and ammonium persulfate is added in an amount of 0.8%-1.0% of the mass of the methyl methacrylate to initiate polymerization. The mixture is kept warm for 2.8-3.2 hours, cooled to 30°C, and the pH is adjusted to 7.0-8.0. Residual acetone is removed in vacuo to obtain a polyurethane-polyacrylate dispersion.

[0010] A4. Add 9%-10% by weight of hydrophobically modified nano-SiO2 to the polyurethane-polyacrylate dispersion obtained in A3, and physically blend to obtain the nano-SiO2-polyurethane-polyacrylate composite dispersion.

[0011] Furthermore, the preparation method of the hydrophobically modified nano-SiO2 is as follows: nano-SiO2 and γ-(methacryloyloxy)propyltrimethoxysilane (KH-570) are hydrolyzed and condensed in an acidic ethanol solution at 55-60°C for 2-2.5 hours, centrifuged, washed, and dried to obtain the hydrophobically modified nano-SiO2.

[0012] Furthermore, the pH of the acidic ethanol solution is 4-5.

[0013] Furthermore, in A1, the isocyanate is isophorone diisocyanate or toluene diisocyanate.

[0014] Furthermore, in A1, dibutyltin dilaurate is also added, and its mass is 0.03%-0.05% of the mass of the polyether polyol.

[0015] Furthermore, in A3, the neutralizing agent is prepared by compounding triethylamine and glacial acetic acid in a molar ratio of 1:1.

[0016] Furthermore, in A3, the specific operation of vacuum removal of residual acetone is: using a rotary evaporator, controlling the temperature to 40-50°C to avoid high temperature-induced emulsion demulsification, the vacuum degree to -0.08 to -0.1 MPa, the removal time to 1-2 hours, and the residual acetone content to ≤0.5%.

[0017] Furthermore, in A4, the specific operation of physical blending is: 8000-10000 rpm high-speed shearing treatment for 30-35 min, and 35-40 kHz ultrasonic dispersion for 1-1.5 h.

[0018] In a second aspect, the present invention provides a method for preparing the above-mentioned water-based coating composition, comprising the following steps: adding nano-SiO2-polyurethane-polyacrylate composite dispersion, defoaming agent, leveling agent, wetting agent and film-forming aid into a container, stirring and mixing to obtain the water-based coating composition.

[0019] In a third aspect, the present invention provides an application of the above-mentioned aqueous coating composition for packaging printing.

[0020] This application has the following beneficial effects:

[0021] In the preparation of the nano-SiO2-polyurethane-polyacrylate composite dispersion of the present invention, after the nano-SiO2 reaches a certain amount, the latex particles can no longer coat more nano-SiO2, the particle size of the latex particles will no longer increase, and the nano-SiO2 will be dispersed in the aqueous phase, which will lead to the formation of precipitation and a decrease in storage stability. On this basis, perfluorooctyl ethyl acrylate is added in the prepolymer synthesis stage. On the one hand, the perfluoroalkyl chain (-CF2-CF3) in perfluorooctyl ethyl acrylate has extremely low surface energy, which significantly reduces the surface tension of the polyurethane soft segment. The reduced surface tension causes the latex particles to shrink, forming a denser coating layer. The low surface tension soft shell preferentially wraps the nano-SiO2 during the dispersion process, reducing the contact time between the particles and the aqueous phase, thereby inhibiting the agglomeration of free particles. On the other hand, after the introduction of perfluorooctyl ethyl acrylate, the free volume of the polyurethane soft segment molecular chain increases, forming a thicker coating layer that can accommodate more nanoparticles. The rigid structure of the perfluoro segment forms a three-dimensional barrier on the surface of the latex particles, preventing the already coated SiO2 from detaching, thereby improving the coating strength and coating amount of nano-silica.

[0022] Nano-SiO2 is modified with KH-570 silane coupling agent. After modification, the hydrophobic groups on the SiO2 surface match the polarity of the polyurethane soft shell layer, reducing the interfacial energy difference between the two and promoting particle embedding. At the same time, the reduction of surface hydroxyl groups inhibits the hydrogen bond agglomeration of SiO2, making it easier to disperse evenly, thereby increasing the coating amount.

[0023] The perfluorinated chain segments produce hydrophobic-hydrophobic interactions with the SiO2 surface modified with KH-570 silane coupling agent (containing methacrylate groups), further reducing the interfacial energy difference, promoting particle embedding, and thereby synergistically increasing the coating amount of nano-silica.

[0024] In summary, the present invention increases the amount of nano-SiO2, ensuring that the tensile strength of the coating strips and the water resistance of the coating film are improved, while also improving the storage stability of the resulting water-based coating composition. Furthermore, the water-based coating composition of the present invention has excellent alkali resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 , a comparative trend chart of the precipitation data in the storage stability test of the water-based coating compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 5 in Test Example 1 of the present invention;

[0026] Figure 2 , a comparative trend chart of tensile strength test data of the coating film specimens of the water-based coating compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 5 in Test Example 2 of the present invention;

[0027] Figure 3 , a comparative trend chart of the test data of water absorption rate of the coating films of the water-based coating compositions prepared in Examples 1 to 5 and Comparative Examples 1 to 5 in Test Example 3 of the present invention. DETAILED DESCRIPTION

[0028] The present application is further described in detail below with reference to the embodiments.

[0029] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0030] Example 1: (1) Preparation of hydrophobically modified nano-SiO2: Nano-SiO2 and γ-(methacryloyloxy)propyltrimethoxysilane (KH-570) were hydrolyzed and condensed in an acidic ethanol solution with a pH of 4.5 at 58°C for 2.2 hours, centrifuged, washed, and dried to obtain the hydrophobically modified nano-SiO2.

[0031] Specific raw materials: Nano-SiO2 powder (particle size 20-50nm, specific surface area ≥200m 2 / g), γ-(methacryloyloxy)propyltrimethoxysilane (KH-570), anhydrous ethanol (purity ≥99.7%), glacial acetic acid, and deionized water. Equipment: Constant temperature magnetic stirrer (with heating function, temperature control accuracy ±1°C), ultrasonic disperser (power ≥500W), centrifuge (speed ≥8000rpm), vacuum drying oven.

[0032] Specific preparation steps: ① Place the nano-SiO2 powder in a vacuum drying oven at 105℃ for 2 hours to remove adsorbed moisture; weigh 10g of the dried SiO2 powder, add it to 200mL of anhydrous ethanol, and ultrasonically disperse it for 30 minutes until a uniform suspension is obtained to obtain a SiO2 suspension.

[0033] ② Take 500 mL of anhydrous ethanol, add glacial acetic acid, and adjust the pH to about 4.5 to obtain an acidic ethanol solution; add KH-570 to the acidic ethanol solution in an amount of 9% of the mass of SiO2, i.e. 0.9 g, to obtain a KH-570 solution.

[0034] ③ Slowly add the SiO2 suspension dropwise to the KH-570 solution while stirring, maintaining the system temperature at around 58°C. After 2.2 hours of reaction with continuous mechanical stirring (800 rpm), stop heating, transfer the mixture to a centrifuge tube, and centrifuge at 8000 rpm for 10 minutes to collect the precipitate. Wash the mixture three times with anhydrous ethanol and then deionized water to remove unreacted KH-570 and by-products. Dry the precipitate in a vacuum drying oven at 60°C for 6-8 hours, grind it, and pass it through a 200-mesh sieve to obtain hydrophobically modified nano-SiO2.

[0035] (2) Preparation of nano-SiO2-polyurethane-polyacrylate composite dispersion, the preparation method is as follows:

[0036] A1. Add polyether polyol, trimethyl phosphate, isocyanate, and perfluorooctyl ethyl acrylate into a reactor, wherein the mass of trimethyl phosphate is 12% of the mass of the polyether polyol, the NCO / OH molar ratio is 1.6, the mass of perfluorooctyl ethyl acrylate is 4.5% of the mass of the polyether polyol, and dibutyltin dilaurate is added, the mass of which is 0.04% of the mass of the polyether polyol. The reaction is carried out at about 78°C until the NCO content reaches the standard (the reaction is considered to be terminated when the fluctuation of the NCO content test results at an interval of 30 minutes is less than 0.2%), to obtain a prepolymer.

[0037] Among them, polyether polyol gpe-3000 was purchased from Haian Petrochemical Plant in Jiangsu Province. Isocyanate was isophorone diisocyanate.

[0038] A2: Add 6% by weight of epoxy resin E-20 to the prepolymer obtained in A1, raise the temperature to 80°C, and react for 2 hours. Add acetone to adjust the viscosity to 420 mPa·s to obtain an epoxy-modified prepolymer.

[0039] A3. Cool the epoxy-modified prepolymer obtained in A2 to below 40°C and neutralize it to pH 7.8 with a neutralizer (prepared by mixing triethylamine and glacial acetic acid in a molar ratio of 1:1). Slowly add deionized water dropwise with stirring at 1800 rpm, with the mass of deionized water being 0.9 times the mass of the prepolymer, to form a primary dispersion. Add methyl methacrylate (24% of the mass of the prepolymer) and acetone (6% of the mass of the prepolymer) to stabilize the emulsion. Raise the temperature to approximately 74°C and add ammonium persulfate (0.9% of the mass of methyl methacrylate) to initiate polymerization. Keep the reaction warm for 3 h. Cool to 30°C and adjust the pH to approximately 7.5. Remove the residual acetone in vacuo. Specific steps are as follows: Use a rotary evaporator with the temperature controlled at 45°C to prevent emulsion demulsification caused by high temperature. The vacuum degree is -0.09 MPa, removal time 1.5h‌, residual acetone content ≤0.5%, and polyurethane-polyacrylate dispersion was obtained.

[0040] A4. Add 9.5% by weight of hydrophobically modified nano-SiO2 to the polyurethane-polyacrylate dispersion obtained in A3 and physically blend. The specific operations are: high-speed shear treatment at 9000 rpm for 32 minutes (temperature controlled at ≤45°C to avoid emulsion breakage due to shear heat), and ultrasonic dispersion at 40 kHz for 1.2 hours to obtain a nano-SiO2-polyurethane-polyacrylate composite dispersion.

[0041] (3) Prepare a water-based coating composition, the preparation method of which is as follows: add 100 parts by weight of nano-SiO2-polyurethane-polyacrylate composite dispersion, 0.6 parts by weight of defoamer, 0.5 parts by weight of leveling agent, 0.3 parts by weight of wetting agent and 0.8 parts by weight of film-forming aid into a container and stir to mix. Specifically, stir at 500 rpm for 1 hour, then increase the speed to 1000 rpm for 15 minutes, and then increase the speed to 1500 rpm for 15 minutes. The total stirring time is 1.5 hours. During the stirring process, monitor the system temperature (≤45°C) in real time to avoid emulsion demulsification caused by shear heat. After stirring, the water-based coating composition is obtained. The water-based coating composition can be used for packaging printing and can meet the core requirements of packaging printing for adhesion, wear resistance and environmental protection.

[0042] The defoamer is BKY-019, the leveling agent is BKY-349, the wetting agent is nonionic surfactant wetting agent X-405, and the film-forming aid is ethylene glycol butyl ether.

[0043] Example 2: The difference between this example and Example 1 is that a nano-SiO2-polyurethane-polyacrylate composite dispersion is prepared, and the preparation method is as follows:

[0044] A1. Add polyether polyol, trimethyl phosphate, isocyanate, and perfluorooctyl ethyl acrylate to a reactor. The mass of trimethyl phosphate is 11% of the mass of the polyether polyol, the NCO / OH molar ratio is 1.5, and the mass of perfluorooctyl ethyl acrylate is 4% of the mass of the polyether polyol. Dibutyltin dilaurate is also added at a mass of 0.03% of the mass of the polyether polyol. The reaction is continued at approximately 78°C until the NCO content reaches the specified value (the reaction is considered to be terminated when the fluctuation of the NCO content results between two consecutive tests 30 minutes apart is less than 0.2%) to obtain a prepolymer. Polyether polyol GPE-3000 was purchased from Hai'an Petrochemical Plant in Jiangsu Province. Isocyanate is isophorone diisocyanate.

[0045] A2: Add 5% by weight of epoxy resin E-20 to the prepolymer obtained in A1, raise the temperature to 80°C, and react for 2 hours. Add acetone to adjust the viscosity to approximately 420 mPa·s to obtain an epoxy-modified prepolymer.

[0046] A3. The epoxy-modified prepolymer obtained in A2 was cooled to below 40°C and neutralized to pH 7.8 using a neutralizer (prepared by mixing triethylamine and glacial acetic acid in a molar ratio of 1:1). Deionized water was slowly added dropwise with stirring at 1500 rpm, with the mass of deionized water being 0.8 times the mass of the prepolymer, to form a primary dispersion. Methyl methacrylate was added at a mass of 22% of the mass of the prepolymer, and acetone was added at a mass of 5% of the mass of the prepolymer to stabilize the emulsion. The temperature was raised to 72°C, and ammonium persulfate was added at a mass of 0.8% of the mass of methyl methacrylate to initiate polymerization. The reaction was kept warm for 3.2 h. After cooling to 30°C, the pH was adjusted to approximately 7.5. Residual acetone was removed in vacuo to obtain a polyurethane-polyacrylate dispersion.

[0047] A4. Add 9% by weight of hydrophobically modified nano-SiO2 to the polyurethane-polyacrylate dispersion obtained in A3 and physically blend. The specific operation is: high-speed shear treatment at 8000 rpm for 35 minutes and ultrasonic dispersion at 40 kHz for 1.5 hours to obtain a nano-SiO2-polyurethane-polyacrylate composite dispersion.

[0048] Example 3: The difference between this example and Example 1 is that a nano-SiO2-polyurethane-polyacrylate composite dispersion is prepared, and the preparation method is as follows:

[0049] A1. Add polyether polyol, trimethyl phosphate, isocyanate, and perfluorooctyl ethyl acrylate to a reactor. The mass of trimethyl phosphate is 13% of the mass of the polyether polyol, with an NCO / OH molar ratio of 1.8, and the mass of perfluorooctyl ethyl acrylate is 5% of the mass of the polyether polyol. Dibutyltin dilaurate is also added at a mass of 0.05% of the mass of the polyether polyol. The reaction is continued at approximately 78°C until the NCO content reaches the specified value (the reaction is considered to be terminated when the fluctuation of the NCO content results between two consecutive tests 30 minutes apart is less than 0.2%), to obtain a prepolymer. Polyether polyol GPE-3000 was purchased from Hai'an Petrochemical Plant in Jiangsu Province. Isocyanate is isophorone diisocyanate.

[0050] A2. Add 7% by weight of epoxy resin E-20 to the prepolymer obtained in A1, raise the temperature to 80°C, react for 2 hours, and add acetone to adjust the viscosity to about 420 mPa·s to obtain an epoxy-modified prepolymer;

[0051] A3. The epoxy-modified prepolymer obtained in A2 was cooled to below 40°C and neutralized to pH 7.8 using a neutralizer (prepared by mixing triethylamine and glacial acetic acid in a molar ratio of 1:1). Deionized water was slowly added dropwise with stirring at 2000 rpm, with the mass of the deionized water being equal to the mass of the prepolymer, to form a primary dispersion. Methyl methacrylate was added at a mass of 26% of the mass of the prepolymer, and acetone was added at a mass of 7% of the mass of the prepolymer to stabilize the emulsion. The emulsion was heated to 75°C and ammonium persulfate was added at a mass of 1.0% of the mass of the methyl methacrylate to initiate polymerization. The reaction was kept warm for 2.8 h. After cooling to 30°C, the pH was adjusted to 7.5. The residual acetone was removed in vacuo to obtain a polyurethane-polyacrylate dispersion.

[0052] A4. Add 10% by weight of hydrophobically modified nano-SiO2 to the polyurethane-polyacrylate dispersion obtained in A3 and physically blend. The specific operation is: high-speed shear treatment at 10,000 rpm for 30 minutes and ultrasonic dispersion at 40 kHz for 1.2 hours to obtain a nano-SiO2-polyurethane-polyacrylate composite dispersion.

[0053] Example 4: The difference between this example and Example 1 is that: a water-based coating composition is prepared, and its preparation method is as follows: 100 parts of nano-SiO2-polyurethane-polyacrylate composite dispersion, 0.5 parts of defoaming agent, 0.4 parts of leveling agent, 0.2 parts of wetting agent and 0.6 parts of film-forming aid are added to a container by weight, and stirred to mix to obtain a water-based coating composition.

[0054] Example 5: The difference between this example and Example 1 is that: a water-based coating composition is prepared, and its preparation method is as follows: 100 parts of nano-SiO2-polyurethane-polyacrylate composite dispersion, 0.8 parts of defoaming agent, 0.6 parts of leveling agent, 0.4 parts of wetting agent and 1 part of film-forming aid are added to a container by weight, and stirred to mix to obtain a water-based coating composition.

[0055] Comparative Example 1: The only difference between this comparative example and Example 1 is that in the preparation of the nano-SiO2-polyurethane-polyacrylate composite dispersion, perfluorooctyl ethyl acrylate is not added, and 9.5% of the hydrophobically modified nano-SiO2 is replaced by 7.5% of nano-SiO2 powder.

[0056] Comparative Example 2: The only difference between this comparative example and Example 1 is that perfluorooctyl ethyl acrylate is not added in the preparation of the nano-SiO2-polyurethane-polyacrylate composite dispersion, and 9.5% of the hydrophobically modified nano-SiO2 is replaced by 8.5% of nano-SiO2 powder.

[0057] Comparative Example 3: The only difference between this comparative example and Example 1 is that perfluorooctyl ethyl acrylate is not added in the preparation of the nano-SiO2-polyurethane-polyacrylate composite dispersion, and 9.5% of the hydrophobically modified nano-SiO2 is replaced by 9.5% of nano-SiO2 powder.

[0058] Comparative Example 4: The only difference between this comparative example and Example 1 is that in the preparation of the nano-SiO2-polyurethane-polyacrylate composite dispersion, 9.5% of the hydrophobically modified nano-SiO2 is replaced by 9.5% of nano-SiO2 powder.

[0059] Comparative Example 5: The only difference between this comparative example and Example 1 is that perfluorooctyl ethyl acrylate is not added in the preparation of the nano-SiO2-polyurethane-polyacrylate composite dispersion.

[0060] Test Example 1: Test Subjects: Water-based coating compositions prepared using Examples 1-5 and Comparative Examples 1-5. Test Item: Storage Stability - Referring to HG / T 3828-2006, at 50°C for 30 days, the smaller the amount of sedimentation, the better the storage stability. The test results are shown in Table 1.

[0061] Test Example 2: Test subjects: Water-based coating compositions prepared from Examples 1 to 5 and Comparative Examples 1 to 5. Test item: Tensile strength - in accordance with ASTM D638, with a tensile rate of 5 mm / min at room temperature and standard specimens. Test results are shown in Table 1.

[0062] Test Example 3: Water-based coating compositions were prepared using Examples 1-5 and Comparative Examples 1-5. Test Item: Water Resistance - Films were cast onto polytetrafluoroethylene sheets, dried naturally, and then placed in a 105°C oven for 3 hours. The films were then placed in a silica gel drying oven, weighed, and removed to produce a 1mm thick film. The film was then immersed in deionized water for 24 hours and removed. The surface water was wiped off with filter paper, and the mass was weighed as W2. Water absorption = (W2 - W1) / W1 × 100%. Lower water absorption indicates better water resistance. The test results are shown in Table 1.

[0063] Table 1. Test data statistics of Test Examples 1-3

[0064]

[0065] Result analysis: Analyze Example 1-Example 5 and combine the data in Table 1 and Figure 1-Figure 3 It can be seen that the water-based coating composition prepared in the present invention (Example 1-Example 3) has excellent storage stability; the tensile strength of the coating film strip is as high as 21.4 MPa or more; the water absorption rate of the coating film is as low as 3.86% or less, and the water resistance is excellent.

[0066] Analyze Example 1 and Comparative Examples 1-5 and combine the data in Table 1 and Figure 1-Figure 3 By comparing Comparative Examples 1, 2, and 3, it can be seen that with the increase in the amount of nano-SiO2 powder (7.5% in Comparative Example 1, 8.5% in Comparative Example 2, and 9.5% in Comparative Example 3), the tensile strength of the coating strips increased from 19.1 MPa (Comparative Example 1) to 19.8 MPa (Comparative Example 2), and then to 20.9 MPa (Comparative Example 3); the water absorption rate of the coating decreased from 4.47% (Comparative Example 1) to 4.14% (Comparative Example 2), and then to 3.88% (Comparative Example 3); and the storage precipitation amount increased from no precipitation (Comparative Example 1) to 0.8% (Comparative Example 2), and then to 1.4% (Comparative Example 3). This shows that with the increase in the amount of nano-SiO2 powder (7.5%-9.5%), the tensile strength of the coating strips increased, the water absorption rate of the coating decreased (i.e., the water resistance improved), but the storage stability of the obtained water-based coating composition decreased.

[0067] This is because, after mechanical and ultrasonic dispersion, nano-SiO2 passes through the waterborne polyurethane soft shell layer and enters the polyacrylate hard core layer, increasing the proportion of the hard core phase, which means that the proportion of the polyurethane phase containing hydrophilic groups is relatively reduced, reducing the surface tension of the coating, thereby improving the water resistance of the coating (reducing water absorption). However, when the nano-SiO2 powder reaches a certain dosage (maximum dosage), the latex particles can no longer coat more nano-SiO2, the particle size of the latex particles will no longer increase, and the nano-SiO2 will be dispersed in the water phase, which will lead to the formation of precipitation and a decrease in storage stability.

[0068] By comparing Comparative Examples 3 and 4, it can be seen that when the dosage of nano-SiO2 is 9.5%, adding perfluorooctyl ethyl acrylate in the prepolymer synthesis stage can improve the storage stability of the prepared water-based coating composition.

[0069] This is because the addition of perfluorooctyl ethyl acrylate during the prepolymer synthesis stage, on the one hand, has an extremely low surface energy of the perfluoroalkyl chains (-CF2-CF3) in the acrylate, significantly reducing the surface tension of the polyurethane soft segment. This reduced surface tension causes the latex particles to shrink, forming a denser coating. Furthermore, this low-surface-tension soft shell preferentially encapsulates the nano-SiO2 during dispersion, reducing the contact time between the particles and the aqueous phase and thus inhibiting the agglomeration of free particles. Furthermore, the introduction of perfluorooctyl ethyl acrylate increases the free volume of the polyurethane soft segment molecular chain, forming a thicker coating layer that can accommodate more nanoparticles. Furthermore, the rigid structure of the perfluoro chain forms a three-dimensional barrier on the latex particle surface, preventing the detachment of already encapsulated SiO2. This, in turn, increases the coating strength and amount of the nano-SiO2, achieving the desired storage stability when the nano-SiO2 dosage reaches 9.5% (exceeding the original maximum dosage).

[0070] By comparing Comparative Example 3 and Comparative Example 5, it can be seen that when the dosage of nano-SiO2 is 9.5%, the storage stability of the prepared water-based coating composition can be improved by preparing the hydrophobically modified nano-SiO2 of the present invention from nano-SiO2 powder.

[0071] This is because the nano-SiO2 is modified with KH-570 silane coupling agent. After modification, the hydrophobic groups on the surface of the SiO2 match the polarity of the polyurethane soft shell layer, reducing the interfacial energy difference between the two and promoting particle embedding. At the same time, the reduction of surface hydroxyl groups inhibits the hydrogen bond agglomeration of SiO2, making it easier to disperse evenly, thereby increasing the coating amount and achieving the effect of improving the storage stability of the obtained water-based coating composition when the nano-SiO2 dosage is 9.5% (exceeding the original maximum dosage).

[0072] By comparison with Example 1, it can be seen that when the amount of nano-SiO2 is 9.5%, perfluorooctyl ethyl acrylate is added in the prepolymer synthesis stage, and the nano-SiO2 powder is made into the hydrophobically modified nano-SiO2 of the present invention, the two can produce a synergistic effect and synergistically improve the storage stability of the obtained water-based coating composition.

[0073] This is because the perfluorinated chain segments produce hydrophobic-hydrophobic interactions with the SiO2 surface modified by KH-570 silane coupling agent (containing methacrylate groups), further reducing the interfacial energy difference, promoting particle embedding, and thereby synergistically increasing the coating amount of nano-silica.

[0074] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0075] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A water-based coating composition, characterized in that The composition comprises the following components by weight: 100 parts of nano-SiO2-polyurethane-polyacrylate composite dispersion, 0.5-0.8 parts of defoaming agent, 0.4-0.6 parts of leveling agent, 0.2-0.4 parts of wetting agent and 0.6-1 parts of film-forming aid; The preparation method of the nano-SiO2-polyurethane-polyacrylate composite dispersion is as follows: A1. Add polyether polyol, trimethyl phosphate, isocyanate and perfluorooctyl ethyl acrylate into a reactor, wherein the mass of trimethyl phosphate is 11%-13% of the mass of the polyether polyol, the NCO / OH molar ratio is 1.5-1.8, and the mass of perfluorooctyl ethyl acrylate is 4%-5% of the mass of the polyether polyol. The reaction is completed at 75-80°C to obtain a prepolymer. A2. Add 5%-7% by weight of epoxy resin to the prepolymer, react at 80° C. for 2 h, and add acetone to adjust the viscosity to 400-450 mPa·s to obtain an epoxy-modified prepolymer; A3, using a neutralizer to neutralize the epoxy-modified prepolymer to a pH of 7.5-8.0, stirring and adding water, the mass of which is 0.8-1 times the mass of the prepolymer, adding methyl methacrylate, the mass of which is 22%-26% of the mass of the prepolymer, adding acetone, the mass of which is 5%-7% of the mass of the prepolymer, raising the temperature to 72-76 ° C, adding ammonium persulfate, the mass of which is 0.8%-1.0% of the mass of methyl methacrylate, keeping the temperature for 2.8-3.2 hours, cooling to 30 ° C, adjusting the pH to 7.0-8.0, and removing residual acetone in vacuo to obtain a polyurethane-polyacrylate dispersion; A4. Add 9% to 10% by weight of hydrophobically modified nano-SiO2 into the polyurethane-polyacrylate dispersion, and physically blend to obtain the product.

2. The water-based coating composition according to claim 1, wherein The preparation method of the hydrophobically modified nano-SiO2 is as follows: nano-SiO2 and γ-(methacryloyloxy)propyltrimethoxysilane are hydrolyzed and condensed in an acidic ethanol solution at 55-60°C for 2-2.5 hours, centrifuged, washed, and dried to obtain the hydrophobically modified nano-SiO2.

3. The aqueous coating composition according to claim 2, wherein The pH of the acidic ethanol solution is 4-5.

4. The water-based coating composition according to claim 1, wherein In A1, the isocyanate is isophorone diisocyanate or toluene diisocyanate.

5. The water-based coating composition according to claim 1, wherein In A1, dibutyltin dilaurate is further added, and its mass is 0.03%-0.05% of the mass of the polyether polyol.

6. The water-based coating composition according to claim 1, characterized in that In A3, the neutralizing agent is prepared by mixing triethylamine and glacial acetic acid in a molar ratio of 1:

1.

7. The water-based coating composition according to claim 1, wherein In A3, the specific operation of vacuum removal of residual acetone is: using a rotary evaporator, controlling the temperature at 40-50°C, the vacuum degree at -0.08 to -0.1 MPa, the removal time at 1-2 hours, and the residual acetone content at ≤0.5%.

8. The water-based coating composition according to claim 1, wherein In A4, the specific operation of physical blending is: high-speed shearing treatment at 8000-10000 rpm for 30-35 min, and ultrasonic dispersion at 35-40 kHz for 1-1.5 h.

9. A method for preparing the water-based coating composition according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: adding nano-SiO2-polyurethane-polyacrylate composite dispersion, defoamer, leveling agent, wetting agent and film-forming aid into a container, and stirring and mixing to obtain the product.

10. Use of the water-based coating composition according to any one of claims 1 to 8, characterized in that: Used for packaging printing.

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