An ultra-low voc waterborne coating and a preparation method thereof

Abstract

The present application relates to a kind of ultra-low VOC water-based paint and its preparation method, belong to paint technical field, and paint component includes modified acrylic-polyurethane hybrid emulsion, methyl linoleate, choline chloride-glycerol complex, modified nano titanium dioxide photocatalyst, PEG-40 stearate, thickening agent, preservative, pH regulator etc..The present application is prepared by special method modified acrylic-polyurethane hybrid emulsion, modified nano titanium dioxide photocatalyst, then with methyl linoleate, PEG-40 stearate, choline chloride-glycerol complex and other additives are prepared according to certain proportion Cooperation preparation paint, with the effect of fast curing and not cracking, very low VOC volatility, and good water resistance and acid and alkali resistance, strong adhesion.

Description

Technical Field

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

[0002] Traditional solvent-based paints release large amounts of VOCs during production and use. These VOCs include not only harmful substances like benzene, toluene, and xylene, but may also contain carcinogens like formaldehyde. Long-term exposure to these harmful substances can damage the respiratory, nervous, and immune systems, causing symptoms such as headaches, dizziness, coughing, asthma, allergies, and even cancer in severe cases. VOC emissions are also a major factor in the formation of photochemical smog and acid rain, causing severe atmospheric pollution.

[0003] Water-based paints emerged to address the environmental and health concerns associated with traditional solvent-based paints. Using water as its primary solvent, water-based paints significantly reduce VOC emissions. Water, as a solvent, is non-toxic, odorless, and non-flammable, making it safer and more environmentally friendly to use. However, early water-based paints had performance limitations, such as inferior coating film resistance to water, abrasion, and chemicals compared to traditional solvent-based paints. This limited their application, particularly in industrial applications requiring high-performance coatings.

[0004] In recent years, the performance of low-VOC water-based coatings has been significantly improved with the advancement of materials science and nanotechnology. New water-based resins, such as waterborne polyurethanes, waterborne acrylates, and waterborne epoxies, offer improved film-forming properties, adhesion, and weather resistance. The introduction of nanomaterials, such as nano-titanium dioxide and nano-zinc oxide, not only improves the hardness, abrasion resistance, and chemical resistance of coatings but also imparts special features such as self-cleaning, antibacterial, and antifouling properties.

[0005] As consumers become more environmentally conscious and more concerned about their health, the demand for low-VOC water-based coatings continues to grow. Low-VOC water-based coatings are increasingly used in industries such as construction, furniture, and automobiles. However, low-VOC water-based coatings still have the following problems:

[0006] (1) Although water-based paints with some additives are advertised as low VOC, some water-based paint formulas may still contain potentially hazardous chemicals, such as detectable isothiazolinone preservatives, which are associated with skin irritation and asthma symptoms, and may also contain some phthalate replacement chemicals.

[0007] (2) Slow drying speed: It usually takes longer to dry than solvent-based paint, which will extend the coating project cycle.

[0008] (3) Insufficient water resistance: Some water-based paints are prone to whitening and peeling in humid environments. The coating film is more susceptible to moisture than solvent-based paints. Long-term contact with water or high humidity environments may lead to performance degradation. Summary of the Invention

[0009] To address the aforementioned performance issues of existing water-based coatings, the present invention provides an ultra-low VOC water-based coating and its preparation method. A modified acrylic-polyurethane hybrid emulsion and a modified nano-titanium dioxide photocatalyst are prepared using a special method. These are then combined with methyl linoleate, PEG-40 stearate, a choline chloride-glycerol complex, and other additives in a specific proportion to prepare the coating. The coating exhibits rapid curing without cracking, extremely low VOC volatility, good water resistance, acid and alkali resistance, and strong adhesion. The specific technical solution is as follows:

[0010] An ultra-low VOC water-based paint comprises the following raw materials in parts by weight: 40-50 parts of modified acrylic-polyurethane hybrid emulsion, 3-5 parts of methyl linoleate, 8-12 parts of choline chloride-glycerol complex, 1-2 parts of modified nano-titanium dioxide photocatalyst, 3-5 parts of PEG-40 stearate, 0.5-1 part of thickener, 0.1-0.3 part of preservative, 0.5-1 part of dispersant, 6-12 parts of pigment, 0.3-0.6 part of defoamer, 0.1-0.3 part of pH regulator, and the balance is deionized water. The solid content is 40-50 wt%. The modified nano-titanium dioxide photocatalyst is a nano-titanium dioxide photocatalyst whose surface is coated with silicon dioxide and aluminum oxide.

[0011] In the above-mentioned coating, the mass ratio of the components of the choline chloride-glycerol complex is choline chloride:glycerol=(1-1.5):(3-4).

[0012] In the above-mentioned coating, the preparation method of the modified acrylic-polyurethane hybrid emulsion comprises the following steps: in parts by mass: under nitrogen protection, 75°C to 80°C, and continuous stirring, to 340 parts to 345 parts of polycarbonate diol, add 130 parts to 135 parts of isophorone diisocyanate, add 0.20 parts to 0.25 parts of dibutyltin dilaurate, heat to 84°C to 88°C, and react for 2.5h to 3h to obtain a polyurethane prepolymer; at room temperature and continuous stirring, add 400 parts to 430 parts of deionized water and 12 parts to 18 parts of dimethylethanolamine to the polyurethane prepolymer, heat to 75°C to 80°C, add 20 parts to 25 parts of potassium persulfate aqueous solution, and react for 1.5h to 2h to obtain a polyurethane core layer emulsion; 175 parts to 180 parts of methyl methacrylate, 140 parts to 145 parts of butyl acrylate, and 11 parts of 1-13 parts of methacrylic acid, 18-20 parts of vinyltriethoxysilane and 12-15 parts of N-hydroxymethyl acrylamide are uniformly mixed to obtain a shell emulsion; 20-25 parts of γ-methacryloxypropyltriethoxysilane, 0.5-0.8 parts of acetic acid and 20-25 parts of deionized water are uniformly mixed to obtain a pre-hydrolysis solution; 5-8 parts of panthenyl hydroxypropyl stearyl dimethyl ammonium chloride, the shell emulsion and 30-35 parts of potassium persulfate aqueous solution are sequentially added to the polyurethane core emulsion at 75-80° C. under continuous stirring, and the mixture is reacted for 3-4 hours, the pre-hydrolysis solution is added, the temperature is raised to 84-88° C., the mixture is reacted for 1.5-2 hours, 5-10 parts of polycarbonate diol are added, the mixture is reacted for 1-1.5 hours, vacuum treatment is performed, the solid content is adjusted with deionized water, and the mixture is filtered to obtain a modified acrylic-polyurethane hybrid emulsion.

[0013] In the preparation method of the modified acrylic-polyurethane hybrid emulsion, the mass concentration of the potassium persulfate aqueous solution is 10% to 12%. The solid content is adjusted to 45% to 50% by weight with deionized water. The stirring speed is 300 to 500 rpm. The vacuum treatment is performed at 50°C to 60°C and -0.08 MPa to -0.09 MPa for 10 to 20 minutes. The filtration mesh size is 100 to 150 mesh.

[0014] The preparation method of the modified nano titanium dioxide photocatalyst in the coating comprises the following steps: preparing a mixed solution of tetraethyl orthosilicate, anhydrous ethanol and deionized water in a volume ratio of (1-1.5):(4-6):(4-6), adjusting the pH to 2-3 with hydrochloric acid, and stirring to obtain a silica sol; stirring and dissolving aluminum isopropylate and anhydrous ethanol in a mass ratio of (1-1.2):(10-12) at 60-80°C, adding deionized water 2-3 times the mass of aluminum isopropylate, adding nitric acid to adjust the pH to 3-4, and stirring to obtain an alumina sol; stirring and mixing the silica sol and the alumina sol in a volume ratio of (1-2):(1-1.2) to obtain a mixed sol; mixing and dispersing the nano titanium dioxide photocatalyst and the mixed sol in a mass ratio of 1:(10-12) uniformly, evaporating the solvent under reduced pressure to form a gel-photocatalyst complex coated with SiO2-Al2O3, drying, calcining, and making Si The O2-Al2O3 coating layer is further densified and firmly bonded to the TiO2 surface to obtain a modified nano-titanium dioxide photocatalyst.

[0015] In the preparation method of the above-mentioned modified nano-titanium dioxide photocatalyst, the silica sol is stirred at a speed of 400r / min to 600r / min for 30min to 60min; the alumina sol is stirred at a speed of 400r / min to 600r / min for 2h to 3h; the temperature of the reduced pressure evaporation is 60℃ to 70℃; the drying temperature is 80℃ to 100℃, and the drying time is 12h to 24h; the calcination temperature is 400℃ to 500℃, and the calcination time is 2h to 3h.

[0016] The above-mentioned method for preparing an ultra-low VOC water-based paint comprises the following steps: mixing the raw materials according to their mass fractions, adjusting the solid content to 40wt% to 50wt%, homogenizing, filtering, and obtaining the water-based paint.

[0017] In the coating preparation method, the homogenization is carried out at 1500 rpm to 2000 rpm for 10 min to 15 min; and the mesh size of the filtration is 100 mesh to 150 mesh.

[0018] The present invention provides an ultra-low VOC water-based paint and a preparation method thereof, which have the following beneficial effects:

[0019] 1. Modified acrylic-polyurethane hybrid emulsion: With polycarbonate diol as the soft segment and isophorone diisocyanate as the hard segment, this highly cross-linked polyurethane prepolymer imparts excellent mechanical strength and chemical resistance to the coating. Methyl methacrylate provides rigidity, butyl acrylate provides flexibility, and N-methylol acrylamide and vinyl triethoxysilane introduce cross-linking sites, enhancing the coating's water resistance and adhesion. The core-shell interface is chemically bonded via the hydrolysis-condensation reaction of siloxane (γ-methacryloxypropyltriethoxysilane), eliminating interfacial defects associated with traditional physical blending and significantly improving the coating's density and water resistance. This modified acrylic-polyurethane hybrid emulsion combines the advantages of acrylic and polyurethane. Polyurethane offers excellent flexibility, abrasion resistance, and chemical resistance, while acrylic offers excellent weather resistance and gloss retention. Through hybridization, the complementary properties of these two materials complement each other, resulting in a coating with excellent mechanical properties, water resistance, weather resistance, and adhesion, overcoming the limitations of conventional water-based film-forming agents with their single-property properties.

[0020] 2. Panthenol Hydroxypropyl Stearyl Dimethyl Ammonium Chloride is a quaternary ammonium salt functional monomer with both surface activity and reactivity. Its long-chain hydrophobic group (stearyl group) adsorbs at the core-shell interface, reducing interfacial tension and promoting uniform dispersion of the core polyurethane and the shell acrylic monomer. The quaternary ammonium cation in the molecule electrostatically bonds with the carboxylic acid group (derived from methacrylic acid) in the acrylic shell, while the hydroxypropyl group reacts with the isocyanate group of the polyurethane prepolymer to form a covalent cross-linked network. In addition, its long-chain alkyl structure enhances the water resistance of the coating, while the cationic group interacts with other components in the coating to enhance adhesion. This comprehensively improves the various properties of the modified acrylic-polyurethane hybrid emulsion coating.

[0021] The present invention rationally controls the amount of panthenol hydroxypropyl stearyl dimethyl ammonium chloride added based on the reaction characteristics of each component. Too little addition increases interfacial tension, uneven dispersion of the core-shell structure, decreased emulsion stability, and increased coating porosity, leading to deterioration of water resistance, acid and alkali resistance, and adhesion. Too much addition disrupts the micellar equilibrium of the emulsion, causing emulsion demulsification, increasing residual unreacted monomers, and excessive crosslinking, resulting in increased coating brittleness, poor flexibility, and intensified hard segment phase separation, leading to decreased chemical resistance.

[0022] Third, adding polycarbonate diol (chain extender) to the core-shell emulsion polymerization stage achieves "gradient chain extension" of the molecular chain. The hydroxyl groups of the polycarbonate diol further react with unreacted isocyanate (-NCO) groups to extend the polyurethane chain segments, increase molecular weight and crosslink density, and enhance the tensile strength of the coating. The chain extension reaction repairs chain breaks caused by free radical polymerization at the core-shell interface, reduces microcracks, improves water resistance, and improves acid and alkali resistance, resulting in superior performance of the coating formed by the hybrid emulsion.

[0023] Fourth, the modified acrylic-polyurethane hybrid emulsion undergoes vacuum treatment to efficiently remove residual small-molecule monomers such as isophorone diisocyanate (IPDI) and methyl methacrylate (MMA), effectively reducing VOCs. Polar solvents introduced during the reaction, such as acetic acid and potassium persulfate decomposition products, are also removed, preventing "fish-eye" defects caused by residual solvents after the coating dries and improving surface smoothness.

[0024] 5. A SiO2-Al2O3 composite layer is coated on the TiO2 surface through a sol-gel method to achieve "controllable photocatalytic activity." The SiO2-Al2O3 coating layer acts as a physical barrier, limiting direct contact between TiO2 and the resin matrix, preventing photocatalytic oxidation and resin degradation. The microporous structure of the coating layer allows small molecule VOCs to pass through and contact the TiO2 surface, where they are degraded into CO2 and H2O under light, achieving a "self-cleaning" function while protecting the resin matrix. The modified nano-titanium dioxide photocatalyst forms a dense structure by coating with SiO2-Al2O3. This not only improves the dispersibility of nano-titanium dioxide and prevents its agglomeration, but also enhances its compatibility with other ingredients in the coating. At the same time, the SiO2-Al2O3 coating layer can improve the weather resistance and chemical stability of nano-titanium dioxide, allowing it to better exert its photocatalytic properties in the coating.

[0025] PEG-40 stearate has a dual function: the PEG segments (hydrophilic) and stearate (hydrophobic) form an amphiphilic structure, reducing the coating's surface tension and promoting uniform spreading on the substrate, avoiding craters. It also prevents the aggregation of pigments (such as red iron oxide) and nano-TiO2 through steric hindrance, ensuring uniform coating color and consistent photocatalytic activity. It also improves the coating's rheological properties, ensuring good fluidity and leveling during application.

[0026] 7. Methyl linoleate and PEG-40 stearate are used in combination in a certain ratio. The two optimize the film-forming process through "polar-non-polar synergy": methyl linoleate, as a low-polarity film-forming aid, penetrates into the interior of the acrylic-polyurethane hybrid latex particles, lowers the glass transition temperature, promotes the fusion of particles during the drying process, and shortens the surface drying time. PEG-40 stearate stabilizes the emulsion and regulates the water evaporation rate, avoiding cracking of the coating caused by drying too quickly (flexibility is achieved). The hydrophobicity of methyl linoleate balances the hydrophilicity of PEG, forming a gradient evaporation system to achieve "quick drying without cracking." The synergistic effect of the two can not only better disperse and mix the ingredients in the coating, but also make the coating have good flexibility and mechanical properties after film formation, thereby improving the overall performance of the coating. DETAILED DESCRIPTION

[0027] Example 1

[0028] An ultra-low VOC water-based paint comprises the following raw materials in parts by weight: 40 parts of a modified acrylic-polyurethane hybrid emulsion, 3 parts of methyl linoleate, 8 parts of a choline chloride-glycerol complex, 1 part of a modified nano-titanium dioxide photocatalyst, 3 parts of PEG-40 stearate, 0.5 parts of a thickener, 0.1 parts of a preservative, 0.5 parts of a dispersant, 6 parts of a pigment, 0.3 parts of a defoamer, 0.1 parts of a pH adjuster, and the balance being deionized water. The paint has a solid content of 40 wt%. The choline chloride-glycerol complex has a mass ratio of choline chloride to glycerol of 1:3.

[0029] The preparation method of the modified acrylic-polyurethane hybrid emulsion includes the following steps: in parts by mass: under nitrogen protection, 75°C, and continuous stirring at 300r / min, 130 parts of isophorone diisocyanate and 0.20 parts of dibutyltin dilaurate are added to 340 parts of polycarbonate diol, the temperature is raised to 84°C, and the reaction is carried out for 2.5 hours to obtain a polyurethane prepolymer; under normal temperature and continuous stirring at 300r / min, 400 parts of deionized water and 12 parts of dimethylethanolamine are added to the polyurethane prepolymer, the temperature is raised to 75°C, 20 parts of potassium persulfate aqueous solution (mass concentration is 10%) are added dropwise, and the reaction is carried out for 1.5 hours to obtain a polyurethane core layer emulsion; 175 parts of methyl methacrylate, 140 parts of butyl acrylate, 11 parts of methacrylic acid, and 18 parts of vinyl triethylamine are added to the prepolymer; the mixture is stirred for 1 hour. The invention relates to a method for preparing a modified acrylic-polyurethane hybrid emulsion comprising: uniformly mixing oxysilane and 12 parts of N-hydroxymethyl acrylamide to obtain a shell emulsion; uniformly mixing 20 parts of γ-methacryloyloxypropyl triethoxysilane, 0.5 parts of acetic acid and 20 parts of deionized water to obtain a pre-hydrolyzed liquid; and sequentially adding 5 parts of panthenyl hydroxypropyl stearyl dimethyl ammonium chloride and a shell emulsion to the polyurethane core emulsion at 75° C. and 300 r / min under continuous stirring, and dropwise adding 30 parts of an aqueous potassium persulfate solution (mass concentration of 10%), reacting for 3 h, adding the pre-hydrolyzed liquid, heating to 84° C., reacting for 1.5 h, adding 5 parts of polycarbonate diol, reacting for 1 h, vacuum treating at 50° C. and -0.08 MPa for 10 min, adjusting the solid content to 45 wt% with deionized water, and filtering through a 100-mesh filter to obtain a modified acrylic-polyurethane hybrid emulsion.

[0030] The preparation method of the modified nano-titanium dioxide photocatalyst includes the following steps: preparing a mixed solution of ethyl orthosilicate, anhydrous ethanol and deionized water in a volume ratio of 1:4:4, adjusting the pH to 2 with hydrochloric acid, and stirring at a speed of 400 r / min for 30 minutes to obtain a silica sol; stirring and dissolving aluminum isopropoxide and anhydrous ethanol in a mass ratio of 1:12 at 60°C, adding deionized water with a mass of 2 times that of aluminum isopropoxide, adding nitric acid to adjust the pH to 3, and stirring at a speed of 400 r / min for 2 hours to obtain an alumina sol; stirring and mixing the silica sol and the alumina sol in a volume ratio of 1:1 to obtain a mixed sol; mixing and uniformly dispersing the nano-titanium dioxide photocatalyst and the mixed sol in a mass ratio of 1:10, evaporating the solvent under reduced pressure at 60°C to form a gel-photocatalyst complex coated with SiO2-Al2O3, drying at 80°C for 12 hours, and calcining at 400°C for 2 hours to further densify the SiO2-Al2O3 coating layer and combine it with Ti O2 is firmly bonded to the surface to obtain a modified nano-titanium dioxide photocatalyst.

[0031] The above-mentioned method for preparing an ultra-low VOC water-based paint comprises the following steps: mixing the raw materials according to their mass fractions, adjusting the solid content to 40wt%, homogenizing at 1500rpm for 10min, and filtering through a 100-mesh filter to obtain a water-based paint.

[0032] Example 2

[0033] An ultra-low VOC water-based paint comprises the following raw materials in parts by weight: 45 parts of a modified acrylic-polyurethane hybrid emulsion, 4 parts of methyl linoleate, 10 parts of a choline chloride-glycerol complex, 1.5 parts of a modified nano-titanium dioxide photocatalyst, 4 parts of PEG-40 stearate, 0.8 parts of a thickener, 0.2 parts of a preservative, 0.8 parts of a dispersant, 8 parts of a pigment, 0.5 parts of a defoamer, 0.2 parts of a pH adjuster, and the balance being deionized water. The paint has a solid content of 48 wt%. The choline chloride-glycerol complex has a mass ratio of choline chloride to glycerol of 1.2:3.5.

[0034] Among them, the preparation method of the modified acrylic-polyurethane hybrid emulsion includes the following steps: in parts by mass: under nitrogen protection, 78°C, 400r / min continuous stirring, adding 133 parts of isophorone diisocyanate to 342 parts of polycarbonate diol, adding 0.22 parts of dibutyltin dilaurate, heating to 86°C, reacting for 2.5 hours to obtain a polyurethane prepolymer; under room temperature and 400r / min continuous stirring, adding 420 parts of deionized water and 15 parts of dimethylethanolamine to the polyurethane prepolymer, heating to 78°C, adding 22 parts of potassium persulfate aqueous solution (mass concentration of 11%) dropwise, reacting for 1.5 hours to obtain a polyurethane core layer emulsion; adding 178 parts of methyl methacrylate, 142 parts of butyl acrylate, 12 parts of methacrylic acid, 19 parts of vinyl triethoxycaprylate, and the like; The invention relates to a method for preparing a modified acrylic-polyurethane hybrid emulsion comprising: uniformly mixing 14 parts of 1,2-dimethyl-1,2-diol-1,2-diol-2 and 1,2-diol-3,2-diol-4,2-diol-5,2-diol-6,2-diol-7,2-diol-8,2-diol-9,2-diol-10,2-diol-11,2-diol-12,2-diol-13,2-diol-14,2-diol-15,2-diol-16,2-diol-17,2-diol-28,2-diol-18,2-diol-29,2-diol-21,2-diol-30,2-diol-31,2-diol-19,2-diol-22,2-diol-32,2-diol-33,2-diol-34,2-diol-16,2-diol-17,2-diol-29,2-diol-35,2-diol-36,2-diol-37,2-diol-38,2-diol-39,2-diol-40,2-diol-50,2-diol-30,2-diol-31,2-diol-32,2-diol-36,2-diol-41,2-diol-37,2-diol-38,2-diol-39,2-diol-42,2-diol-30,2-diol-31,2-diol-32,2-diol-33,2-diol-34,2-diol-35,2-diol-36,2-diol-37,2-diol-38,2-diol-39,2-diol-41,2-diol-30,2-diol-3

[0035] The preparation method of the modified nano-titanium dioxide photocatalyst includes the following steps: preparing a mixed solution of ethyl orthosilicate, anhydrous ethanol and deionized water in a volume ratio of 1.2:5:5, adjusting the pH to 2.5 with hydrochloric acid, and stirring at a speed of 500 r / min for 50 minutes to obtain a silica sol; stirring and dissolving aluminum isopropoxide and anhydrous ethanol in a mass ratio of 1.1:10.5 at 70°C, adding deionized water 2.5 times the mass of aluminum isopropoxide, adding nitric acid to adjust the pH to 3.5, and stirring at a speed of 500 r / min for 2.5 hours. , obtaining alumina sol; silica sol and alumina sol in a volume ratio of 1.5:1.1, stirred and mixed to obtain a mixed sol; nano-titanium dioxide photocatalyst and mixed sol in a mass ratio of 1:11, mixed and dispersed uniformly, the solvent was evaporated under reduced pressure at 65°C to form a gel-photocatalyst complex coated with SiO2-Al2O3, dried at 90°C for 18h, and calcined at 450°C for 2.5h to further densify the SiO2-Al2O3 coating layer and firmly bonded to the TiO2 surface to obtain a modified nano-titanium dioxide photocatalyst.

[0036] The above-mentioned method for preparing an ultra-low VOC water-based paint comprises the following steps: mixing the raw materials according to their mass fractions, adjusting the solid content to 48 wt %, homogenizing at 1800 rpm for 12 minutes, and filtering through a 120-mesh filter to obtain a water-based paint.

[0037] Example 3

[0038] An ultra-low VOC water-based paint comprises the following raw materials in parts by weight: 50 parts of a modified acrylic-polyurethane hybrid emulsion, 5 parts of methyl linoleate, 12 parts of a choline chloride-glycerol complex, 2 parts of a modified nano-titanium dioxide photocatalyst, 5 parts of PEG-40 stearate, 1 part of a thickener, 0.3 parts of a preservative, 1 part of a dispersant, 12 parts of a pigment, 0.6 parts of a defoaming agent, and 0.3 parts of a pH adjuster, with the balance being deionized water. The paint has a solid content of 50 wt%. The mass ratio of the choline chloride-glycerol complex is 1.5:4.

[0039] Among them, the preparation method of the modified acrylic-polyurethane hybrid emulsion includes the following steps: in parts by mass: under nitrogen protection, 80°C, 500r / min continuous stirring, adding 135 parts of isophorone diisocyanate to 345 parts of polycarbonate diol, adding 0.25 parts of dibutyltin dilaurate, heating to 88°C, reacting for 3 hours to obtain a polyurethane prepolymer; under room temperature and 500r / min continuous stirring, adding 430 parts of deionized water and 18 parts of dimethylethanolamine to the polyurethane prepolymer, heating to 80°C, adding 25 parts of potassium persulfate aqueous solution (mass concentration of 12%) dropwise, reacting for 2 hours to obtain a polyurethane core layer emulsion; adding 180 parts of methyl methacrylate, 145 parts of butyl acrylate, 13 parts of methacrylic acid, 20 parts of vinyltriethoxysilane, stirring at room temperature, stirring at 500r / min, stirring at room temperature, stirring at ... stirring at room temperature, stirring at 500r / min, stirring at room temperature, stirring at 500r / min, stirring at room temperature, stirring at 500r / min, stirring at room temperature, stirring at 500r / min, stirring at room temperature, stirring at 500r / min, stirring at room temperature, stirring at 500r / min, stirring at room temperature, stirring at 500r / min, stirring at room temperature, The invention relates to a method for preparing a modified acrylic-polyurethane hybrid emulsion comprising: uniformly mixing alkyl and 15 parts of N-hydroxymethyl acrylamide to obtain a shell emulsion; uniformly mixing 25 parts of γ-methacryloyloxypropyl triethoxysilane, 0.8 parts of acetic acid and 25 parts of deionized water to obtain a pre-hydrolyzed liquid; and sequentially adding 8 parts of panthenyl hydroxypropyl stearyl dimethyl ammonium chloride and the shell emulsion to the polyurethane core emulsion at 80° C. and 500 r / min under continuous stirring, and dropwise adding 35 parts of an aqueous potassium persulfate solution (mass concentration of 12%), reacting for 4 h, adding the pre-hydrolyzed liquid, heating to 88° C., reacting for 2 h, adding 10 parts of polycarbonate diol, reacting for 1.5 h, and vacuum treating at 60° C. and -0.09 MPa for 20 min, adjusting the solid content to 50 wt % with deionized water, and filtering through a 150-mesh filter to obtain a modified acrylic-polyurethane hybrid emulsion.

[0040] The preparation method of the modified nano-titanium dioxide photocatalyst comprises the following steps: preparing a mixed solution by mixing ethyl orthosilicate, anhydrous ethanol and deionized water at a volume ratio of 1.5:6:6, adjusting pH to 3 by hydrochloric acid, stirring at a speed of 600 r / min for 60 min to obtain a silica sol; dissolving aluminum isopropylate and anhydrous ethanol at a mass ratio of 1.2:10 at 80°C, adding 3 times the mass of deionized water of the aluminum isopropylate, adjusting pH to 4 by adding nitric acid, and stirring at a speed of 600 r / min for 3 h to obtain an alumina sol; mixing the silica sol and the alumina sol at a volume ratio of 2:1.2 to obtain a mixed sol; mixing and uniformly dispersing the nano-titanium dioxide photocatalyst and the mixed sol at a mass ratio of 1:12, evaporating the solvent at 70°C under reduced pressure to form a gel-photocatalyst composite coated with SiO2-Al2O3, drying at 100°C for 24 h, and calcining at 500°C for 3 h to further densify the SiO2-Al2O3 coating layer and firmly combine the TiO2 surface, thereby obtaining the modified nano-titanium dioxide photocatalyst.

[0041] The preparation method of the above-mentioned ultra-low VOC water-based paint comprises the following steps: mixing raw materials according to mass fractions, adjusting the solid content to 50 wt%, homogenizing at 2000 rpm for 15 min, filtering through a 150-mesh filter screen, and obtaining a water-based paint.

[0042] Example 4

[0043] An ultra-low VOC water-based paint comprises the following raw materials by mass fraction: modified acrylic-polyurethane hybrid emulsion 50 parts, methyl linoleate 3 parts, choline chloride-glycerol complex 12 parts, modified nano-titanium dioxide photocatalyst 1 part, PEG-40 stearate 5 parts, thickening agent 0.5 part, preservative 0.2 part, dispersant 0.5 part, pigment 10 parts, defoaming agent 0.3 part, pH adjuster 0.3 part, and the balance is deionized water, with a solid content of 42 wt%. The mass ratio of components of the choline chloride-glycerol complex is choline chloride: glycerol = 1.5:3.2.

[0044] The preparation method of the modified acrylic-polyurethane hybrid emulsion includes the following steps: in parts by mass: under nitrogen protection, 80°C, and continuous stirring at 300r / min, 130 parts of isophorone diisocyanate and 0.25 parts of dibutyltin dilaurate are added to 345 parts of polycarbonate diol, the temperature is raised to 84°C, and the reaction is carried out for 3 hours to obtain a polyurethane prepolymer; under normal temperature and continuous stirring at 300r / min, 430 parts of deionized water and 12 parts of dimethylethanolamine are added to the polyurethane prepolymer, the temperature is raised to 80°C, 20 parts of potassium persulfate aqueous solution (mass concentration is 12%) are added dropwise, and the reaction is carried out for 1.5 hours to obtain a polyurethane core layer emulsion; 180 parts of methyl methacrylate, 140 parts of butyl acrylate, 13 parts of methacrylic acid, and 18 parts of vinyl triethoxy acrylate are added to the prepolymer. Silane and 15 parts of N-hydroxymethyl acrylamide are uniformly mixed to obtain a shell emulsion; 20 parts of γ-methacryloyloxypropyl triethoxysilane, 0.8 parts of acetic acid and 20 parts of deionized water are uniformly mixed to obtain a pre-hydrolyzed solution; 8 parts of panthenyl hydroxypropyl stearyl dimethyl ammonium chloride and the shell emulsion are sequentially added to the polyurethane core emulsion under continuous stirring at 80° C. and 300 r / min, 30 parts of potassium persulfate aqueous solution (mass concentration of 12%) are dropwise added, the reaction is carried out for 3 hours, the pre-hydrolyzed solution is added, the temperature is raised to 88° C., the reaction is carried out for 1.5 hours, 10 parts of polycarbonate diol are added, the reaction is carried out for 1 hour, and the mixture is vacuum treated at 60° C. and -0.08 MPa for 20 minutes. The solid content is adjusted to 46 wt% with deionized water and the mixture is filtered through a 150-mesh filter to obtain a modified acrylic-polyurethane hybrid emulsion.

[0045] The preparation method of the modified nano-titanium dioxide photocatalyst comprises the following steps: preparing a mixed solution of ethyl orthosilicate, anhydrous ethanol and deionized water in a volume ratio of 1:6:4, adjusting the pH to 3 with hydrochloric acid, stirring at 400 r / min for 60 min to obtain a silica sol; stirring and dissolving aluminum isopropoxide and anhydrous ethanol in a mass ratio of 1:12 at 60°C, adding deionized water 3 times the mass of aluminum isopropoxide, adding nitric acid to adjust the pH to 3, stirring at 600 r / min for 2 h, and obtaining an oxide. Aluminum sol; silica sol and alumina sol are stirred and mixed in a volume ratio of 2:1 to obtain a mixed sol; nano-titanium dioxide photocatalyst and the mixed sol are mixed and dispersed uniformly in a mass ratio of 1:12, the solvent is evaporated under reduced pressure at 60°C to form a gel-photocatalyst complex coated with SiO2-Al2O3, dried at 100°C for 12h, and calcined at 500°C for 2h to further densify the SiO2-Al2O3 coating layer and firmly bonded to the TiO2 surface to obtain a modified nano-titanium dioxide photocatalyst.

[0046] The above-mentioned method for preparing an ultra-low VOC water-based paint comprises the following steps: mixing the raw materials according to their mass fractions, adjusting the solid content to 42 wt%, homogenizing at 2000 rpm for 15 minutes, and filtering through a 150-mesh filter to obtain a water-based paint.

[0047] Description of the raw materials in the above examples: Polycarbonate diol with an average molecular weight of 2000 was sourced from Guangzhou Rongyu Trading Co., Ltd., model PH-200. Isophorone diisocyanate was sourced from Jinan Huifengda Chemical Co., Ltd. Dibutyltin dilaurate was sourced from Jinan Haiyuan Chemical Co., Ltd., model 037. Dimethylethanolamine was sourced from Jinan Liyang Chemical Co., Ltd. Methyl methacrylate was sourced from Shandong Ruigang Chemical Co., Ltd. Butyl acrylate was sourced from Chuangyida (Shandong) Biotechnology Co., Ltd. Methacrylic acid was sourced from Jinan Zhiyuancheng Chemical Co., Ltd. Vinyltriethoxysilane was sourced from Jining Hongming Chemical Reagent Co., Ltd., model A-151. N-Hydroxymethylacrylamide was sourced from Shanghai Gaoming Chemical Co., Ltd. γ-Methacryloxypropyltriethoxysilane was sourced from Tianmen Hengchang Chemical Co., Ltd. Panthenylhydroxypropyl stearyldimonium chloride was sourced from Guangzhou Youbao Chemical Co., Ltd. Methyl linoleate was sourced from Jiangsu Leien Environmental Protection Technology Co., Ltd., model 112-63-0. Choline chloride was sourced from Jiangsu Xiangjia Biotechnology Co., Ltd. Glycerin was sourced from Shandong Ruiwang Chemical Technology Co., Ltd., with a glycerol content of 99.5%. Ethyl orthosilicate was sourced from Hubei Xinrunde Chemical Co., Ltd., along with tetraethyl silicate. Aluminum isopropylate was sourced from Shandong Maofa Chemical Co., Ltd. Nano-titanium dioxide photocatalyst, model J25VK-TG01, was sourced from Xuancheng Jingrui New Materials Co., Ltd. PEG-40 stearate was sourced from Shanghai Huijun Chemical Co., Ltd. The thickener was TT-935 thickener, sourced from Wuxi Henderson Chemical Products Co., Ltd. The preservative was BIT-20 preservative, sourced from Foshan Liyuan Chemical Co., Ltd. The dispersant was TEGO Dispers 755W dispersant, sourced from Shanghai Sangjing Chemical Co., Ltd. The pigment was red iron oxide. The defoamer was AKN-3324 defoamer, sourced from Foshan Qianyou Chemical Co., Ltd. The pH adjuster was AMP-95 acid-base adjuster, sourced from Zhengzhou Guangjie Chemical Co., Ltd.

[0048] Comparative Example 1

[0049] In the preparation method of the modified acrylic acid-polyurethane hybrid emulsion, panthenol hydroxypropyl stearyl dimethyl ammonium chloride is not added; other parameters and methods are the same as in Example 1.

[0050] Comparative Example 2

[0051] In the preparation method of the modified acrylic acid-polyurethane hybrid emulsion, the added amount of panthenol hydroxypropyl stearyl dimethyl ammonium chloride is 2 parts; other parameters and methods are the same as in Example 1.

[0052] Comparative Example 3

[0053] In the preparation method of the modified acrylic acid-polyurethane hybrid emulsion, the added amount of panthenol hydroxypropyl stearyl dimethyl ammonium chloride is 15 parts; other parameters and methods are the same as in Example 1.

[0054] Comparative Example 4

[0055] In the preparation method of the modified acrylic-polyurethane hybrid emulsion, no polycarbonate diol is added after the reaction; other parameters and methods are the same as in Example 1.

[0056] Comparative Example 5

[0057] In the preparation method of the modified acrylic acid-polyurethane hybrid emulsion, no vacuum treatment is performed; other parameters and methods are the same as in Example 1.

[0058] Comparative Example 6

[0059] The modified nano-titanium dioxide photocatalyst is replaced by a nano-titanium dioxide photocatalyst; other parameters and methods are the same as in Example 1.

[0060] Comparative Example 7

[0061] PEG-40 stearate was replaced by PEG-100 stearate (raw materials from the same manufacturer); other parameters and methods were the same as in Example 1.

[0062] Comparative Example 8

[0063] PEG-40 stearate was replaced by PEG-10 stearate (raw materials from the same manufacturer); other parameters and methods were the same as in Example 1.

[0064] Comparative Example 9

[0065] No PEG-40 stearate was added; other parameters and methods were the same as in Example 1.

[0066] Comparative Example 10

[0067] No methyl linoleate was added; other parameters and methods were the same as in Example 1.

[0068] Comparative Example 11

[0069] At the same time, PEG-40 stearate and methyl linoleate were not added; other parameters and methods were the same as in Example 1.

[0070] The coatings from each example and comparative example were applied to a clean glass plate measuring 150 mm × 75 mm × 1 mm. A wet film applicator was used to evenly apply the coating to a wet film thickness of 100 μm. After application, the coatings were dried in a constant temperature and humidity chamber at 25°C and 50% relative humidity. The surface set and through-set times were measured according to the drying time test. The through-set coatings were then used for other performance tests.

[0071] 1. VOC Content: Volatile organic compound content was determined using gas chromatography-mass spectrometry (GC-MS), with reference to GB 18582, "Limits of Hazardous Substances in Architectural Wall Coatings." A 5.00 g sample of paint was placed in a 250 mL sealed glass container. The container was heated in a 60°C constant temperature drying oven for 24 hours to allow the volatile compounds to evaporate completely. Volatile compounds were analyzed using GC-MS using an HP-5MS column (30 m × 0.25 mm × 0.25 μm), an inlet temperature of 250°C, and a temperature program (initial temperature of 40°C for 5 minutes, then increasing at 10°C / min to 280°C for 10 minutes). Helium was used as the carrier gas (flow rate of 1.0 mL / min). The injection volume was 1 μL. The mass spectrometer scan range was 35-500 m / z. Total VOC content (g / L) was calculated using the external standard method.

[0072] 2. Drying Time: Surface-free time is measured using the finger touch method and through-dry time is measured using the filter paper method in accordance with GB / T 1728, "Determination of Drying Time of Paint and Putty Films." Surface-free time: After application, test the coating using the finger touch method every 5 minutes. The surface-free time (min) is measured when the coating surface is tack-free and free of fingerprints. Through-dry time: After application, test the coating using the filter paper method (pressing a 500g weight for 30 seconds) every 10 minutes. The through-dry time (min) is measured when the filter paper does not fall off and the coating shows no signs of wear.

[0073] 3. Water resistance: In accordance with GB / T 1733 "Determination of water resistance of paint films", immerse the coating film in deionized water and observe the changes in the coating film. Immerse the dried coating film in 25°C deionized water for 24 hours, remove it, dry it with filter paper, and observe the coating film. Surface change assessment level: Level 1: No changes on the paint film surface. Level 2: Slight gloss loss, discoloration, small bubbles, and slight whitening are allowed on the paint film surface. Level 3: The paint film surface has obvious gloss loss, discoloration, dense small bubbles, obvious whitening, and wrinkling. Level 4: The paint film surface has serious damage such as discoloration, large bubbles, peeling, and dissolution.

[0074] 4. Acid resistance: Refer to GB / T 9274 "Determination of resistance of paints and varnishes to liquid media" and use 5% hydrochloric acid solution to immerse the coating film and evaluate its acid resistance. Prepare a 5% hydrochloric acid solution and completely immerse the dry coating film in it. After soaking at 25°C for 24 hours, remove it, rinse with clean water, dry the moisture, and observe the condition of the coating film. Paint film damage degree level: Level 1: The paint film is intact, and slight discoloration and gloss loss are allowed. Level 2: The paint film is allowed to have slight discoloration, gloss loss, small bubbles, slight wrinkling, etc. Level 3: The paint film has obvious discoloration, gloss loss, dense small bubbles, wrinkling, and shedding. Level 4: The paint film has serious damage such as discoloration, large bubbles, peeling, and dissolution.

[0075] 5. Alkali resistance: According to GB / T 9274 "Determination of resistance of paints and varnishes to liquid media", 5% sodium hydroxide solution is used to immerse the coating film to determine its alkali resistance. Prepare a 5% sodium hydroxide solution and completely immerse the dried coating film. After soaking for 24 hours at 25°C, remove it, rinse with clean water, dry the moisture, and observe the condition of the coating film. Paint film damage degree level: Level 1: The paint film is intact, and slight discoloration and gloss loss are allowed. Level 2: The paint film is allowed to have slight discoloration, gloss loss, small bubbles, slight wrinkling, etc. Level 3: The paint film has obvious discoloration, gloss loss, dense small bubbles, wrinkling, and falling off. Level 4: The paint film has serious damage such as discoloration, large bubbles, peeling, and dissolution.

[0076] 6. Adhesion: Adhesion is assessed using the cross-cut method combined with tape stripping in accordance with GB / T 9286, "Cross-cut Test for Paints and Varnishes." A polypropylene plastic plate with a coating thickness of 100 μm is used. A 10×10 grid of 1 mm squares is scratched on the coating surface, extending to the base plate. 3M tape is firmly applied to the cross-cut area, compacted, and then quickly peeled off at a 90° angle. Adhesion is assessed based on the area of ​​peeling (Grade 0: 0% peeling; Grade 1: ≤5% peeling; Grade 2: >5 to ≤15% peeling; Grade 3: >15 to ≤35% peeling; Grade 4: >35 to ≤65% peeling; Grade 5: >65% peeling).

[0077] 7. Flexibility: Refer to GB / T 1731, "Determination of Flexibility of Paint Films," and evaluate flexibility by bending the coating film around mandrels of varying diameters to observe whether cracking occurs. For metal sheets with a coating thickness of 100 μm, bend the coating film around mandrels of varying diameters (1 mm, 2 mm, 3 mm, and 5 mm). Flexibility is measured as the minimum mandrel diameter (mm) that does not cause cracking.

[0078] Table 1 Test results of each embodiment and each comparative example

[0079]

[0080] From the above results, it can be seen that the coatings of Examples 1 to 4 have extremely low VOC volatility, can dry quickly, have good water resistance and salt and alkali resistance, strong adhesion, good flexibility, and are not easy to crack.

[0081] Comparative Example 1 results show that panthenol hydroxypropyl stearyl dimethyl ammonium chloride can improve acrylic acid-polyurethane hybrid characteristics, reduce surface tension in the emulsion film forming process, promote the close arrangement and fusion between emulsion particles, and form a continuous and dense coating structure. When the substance is not added, the interaction force between the emulsion particles weakens, and the particles are difficult to be closely packed in the film forming process, resulting in more pores and channels inside the coating. These pores and channels provide convenient conditions for the volatilization of volatile organic compounds (VOCs), making it easier for VOCs to escape from the coating during the drying process and subsequent use of the coating, thereby causing the total VOC content to increase. The dense coating structure contributes to the uniform volatilization of moisture and the rapid solidification of the coating. Due to the lack of panthenol hydroxypropyl stearyl dimethyl ammonium chloride, the coating is loose in structure during film formation, and the diffusion path of moisture inside the coating becomes tortuous, making it difficult to discharge quickly. Simultaneously, the fusion efficiency between the emulsion particles is reduced, delaying the curing process of the coating, so the surface dry time and the actual drying time are significantly extended. A loose coating structure cannot effectively block the penetration of water molecules and acid and alkali solutions. When the coating is immersed in water or exposed to acid or alkali solutions, water and acid / alkali molecules can enter the coating through pores and defects, chemically reacting with or swelling the coating components, causing whitening, blistering, and shedding, significantly reducing its water resistance and acid and alkali resistance. Good adhesion between the coating and the substrate depends on the dense structure of the coating and the intermolecular forces between the coating and the substrate surface. The loose structure of the coating reduces the contact area with the substrate surface, weakening the intermolecular forces. Furthermore, the loose structure makes the coating more susceptible to damage and peeling when subjected to external forces, resulting in reduced adhesion, manifested as a higher shedding rating in the cross-cut test. Panthenyl Hydroxypropyl Stearyl Dimonium Chloride participates in the construction of the cross-linked network of the coating, increasing the flexibility and elasticity between the molecular chains. The absence of this substance results in an incomplete cross-linking network in the coating, weakening the interactions between the molecular chains. This makes it difficult for the coating to elastically deform when subjected to external forces such as bending, making it prone to cracking and significantly reducing its flexibility. Although water resistance is in the second range, acid and alkali resistance is in the third range, adhesion is in the first range, and flexibility is the same at 2mm, it is worse than that of Comparative Examples 2 and 3.

[0082] Comparative Example 2 and Comparative Example 3 results show that when panthenol hydroxypropyl stearyl dimethyl ammonium chloride addition is not enough (Comparative Example 2), its effect degree on emulsion particles is limited, it is impossible to fully reduce surface tension and promote interparticle fusion, and film formation process is slow, and water volatilization is hindered, causing drying time to be extended.And when addition is too much (Comparative Example 3), excessive this material can form micelle, agglomerate in emulsion system, interferes with the normal arrangement and the motion of emulsion particles, hinders the volatilization of moisture and the solidification process of film, and equally increases drying time.When addition is not enough, the crosslinking degree and the compactness of film cannot reach optimal state, and there are more micropores, and water and acid, alkaline solution easily penetrate into film inside, cause destruction.When addition is too much, the existence of micelle, agglomerate destroys the uniformity of film structure, forms weak area, and these regions become the breakthrough point that water and acid, alkali erosion cause the water resistance and acid and alkali resistance of film to reduce. If the dosage is insufficient, the bonding between the coating and the substrate is weak, and the cross-linking network within the coating is imperfect, resulting in reduced adhesion and flexibility. If the dosage is excessive, abnormal molecular chain entanglement and aggregation lead to poor mechanical properties of the coating. The molecular chain mobility is restricted, making it difficult to adapt to external forces and deformation, thus reducing adhesion and flexibility. In adhesion tests, this manifests as the coating being more likely to fall off after cross-cutting; in flexibility tests, a larger diameter mandrel is required to prevent cracking of the coating.

[0083] The results of Comparative Example 4 show that polycarbonate diol, as the soft segment in the synthesis of modified acrylic-polyurethane hybrid emulsions, plays a key role in regulating the length and flexibility of the molecular chain. Failure to add polycarbonate diol results in shorter emulsion molecular chains, weakened intermolecular interactions, and reduced crosslinking density. During film formation, a tight network structure cannot form, resulting in numerous voids within the coating, which provide pathways for VOC volatilization and increase the total VOC content. Due to insufficient molecular chain length and low crosslinking density, the emulsion particles struggle to rapidly intertwine and crosslink to form a stable coating structure during film formation. This slows water volatilization and coating curing, resulting in extended surface-drying and curing times. The low crosslinking density and incomplete molecular chain structure weaken the coating's barrier properties against water, acids, and alkalis. Water and acid and alkali solutions easily penetrate the coating, disrupting its chemical structure, causing swelling and shedding, and reducing its water resistance and acid and alkali resistance. The crosslinking density and molecular chain structure of the coating directly influence its adhesion to the substrate and its flexibility. The low cross-linking density reduces the chemical bonds and intermolecular forces between the coating and the substrate, resulting in a decrease in adhesion. At the same time, the molecular chains lack sufficient flexibility and elasticity, and are easily broken when subjected to external forces, resulting in poor flexibility. The adhesion level is low in the cross-cut test, and a larger diameter mandrel is required in the flexibility test to ensure that the coating does not crack.

[0084] The results of Comparative Example 5 show that the purpose of vacuum treatment is to remove residual low-boiling VOCs, air and other substances in the emulsion system. Without vacuum treatment, these residual VOCs will gradually volatilize during the drying process of the coating film; in addition, air holes and cavities are formed inside the coating film, destroying the continuity and density of the coating film. These pores provide more paths for the volatilization of VOCs, making it easier for VOCs in the coating to be released into the environment, resulting in an increase in total VOC content. The presence of air holes and cavities hinders the uniform volatilization of moisture in the coating film, and moisture needs to be discharged from the coating film through more complex paths, at the same time, these defects also affect the curing speed of the coating film, making the drying process slower, and the dry time and dry time increase. The loose and porous structure of the coating film cannot effectively block the invasion of water and acid, alkali solutions. When the coating film contacts water or acid, alkali solution, the solution will quickly penetrate into the pores inside the coating film and react with the coating film components, causing the coating film to appear whitening, swelling, peeling and other phenomena, and the water resistance and acid and alkali resistance are significantly reduced. The air holes and cavities in the coating film weaken the bonding force between the coating film and the substrate, reducing the adhesion. At the same time, these defects destroy the mechanical properties of the coating film, making the coating film more likely to start from the defects when subjected to external force, and the flexibility is poor. In the adhesion test, the coating film is more likely to fall off when the tape is peeled off; in the flexibility test, the coating film is more likely to crack when bending.

[0085] The results of Comparative Example 6 show that the SiO2-Al2O3 coating layer on the surface of the modified nano-titanium dioxide photocatalyst can effectively improve the dispersity and stability of the nanoparticles in the coating system. After using ordinary nano-titanium dioxide photocatalyst instead of the modified product, the nanoparticles are prone to agglomeration, forming larger particles. These agglomerates will form voids and defects in the coating film, creating conditions for the volatilization of VOCs, resulting in an increase in total VOC content. The agglomerated nanoparticles hinder the normal arrangement and fusion of emulsion particles, affecting the formation process of the coating film. The volatilization path of moisture in the coating film becomes complex due to the presence of agglomerates, at the same time, the curing reaction of the coating film is also disturbed, resulting in an increase in drying time. The defects caused by the agglomeration of nanoparticles reduce the density of the coating film, which cannot effectively block the penetration of water and acid, alkali solutions. Water and acid, alkali molecules can enter the interior of the coating film through these defects, destroy the structure of the coating film, and cause the water resistance and acid and alkali resistance of the coating film to deteriorate, and the coating film is more likely to appear whitening, peeling and other phenomena in the immersion test. The bonding force between the agglomerated nanoparticles and the coating film matrix is weak, and the presence of agglomerates destroys the uniformity and continuity of the coating film, reducing the mechanical properties of the coating film. In the adhesion test, the coating film around the agglomerates is prone to separate from the substrate, resulting in a decrease in adhesion; in the flexibility test, the coating film is more likely to crack at the agglomerates when bending, reducing the flexibility.

[0086] Comparative Example 7 and Comparative Example 8 results show that PEG-40 stearate plays the role of dispersion and adjustment film-forming properties in coating. When substituted with PEG-100 stearate (Comparative Example 7), its molecular weight is larger, and molecular chain is longer, easily entangled with each other in coating system, and fluidity deteriorates, causing the dispersion efficiency of each component in coating to reduce, and the motion and fusion of emulsion particles are hindered, and water volatilization is slow, and drying time is extended. And when substituted with PEG-10 stearate (Comparative Example 8), its molecular weight is smaller, and emulsification and dispersion ability are relatively weak, and it is impossible to effectively stabilize the coating system, and the formation process of film is also affected, and drying time is increased. After the PEG stearate of different molecular weight replaces, the stability of the coating system and the structure of film change. Molecular chain entanglement or dispersion deficiency can cause more defects and weak areas in film, and water and acid and alkali solution easily penetrate into these areas, destroy the structure of film, reduce the water resistance and acid and alkali resistance of film, and film is more prone to damage phenomenon in immersion test. Due to the change of film structure, the bonding force between film and substrate is affected, causing adhesion to decline. At the same time, the abnormal state of the molecular chains reduces the flexibility of the coating, making it difficult to elastically deform when subjected to external forces and prone to cracking. In adhesion tests, the coating is more likely to fall off when the tape is peeled off; in flexibility tests, a larger diameter mandrel is required to ensure that the coating does not crack.

[0087] Comparative Example 9 The results show that PEG-40 stearate, as an important auxiliary agent, can participate in the film-forming process of the coating and improve the structure of the coating. Without the addition of PEG-40 stearate, the solid particles such as the pigment and filler in the coating cannot be effectively dispersed and stabilized and are prone to agglomeration. These agglomerates form gaps and defects in the coating, increase the volatilization channel of VOC, make the VOC in the coating more easily released into the environment, and cause the total VOC content to increase. The agglomeration of solid particles hinders the normal arrangement and fusion of emulsion particles, affecting the formation process of the coating. The volatilization of moisture in the coating is hindered. At the same time, the presence of agglomerates also interferes with the curing reaction of the coating, slowing down the drying process, and significantly extending the surface dry time and actual dry time. The gaps and defects formed by agglomeration reduce the compactness of the coating and cannot effectively block the penetration of water and acid and alkali solutions. When the coating comes into contact with water or acid or alkali solutions, the solutions easily enter the coating and react with the coating components, causing the coating to turn white, swell, and fall off, significantly reducing its water resistance and acid and alkali resistance. The bonding between the agglomerated solid particles and the coating matrix is ​​weak, and the presence of agglomerates disrupts the uniformity and continuity of the coating, reducing the mechanical properties of the coating. In adhesion tests, the coating around the agglomerates easily separates from the substrate, resulting in decreased adhesion. In flexibility tests, the coating is more likely to crack at the agglomerates when bent, resulting in reduced flexibility, which is manifested as a lower adhesion grade and poorer flexibility index.

[0088] As can be seen from the results of Comparative Example 10, methyl linoleate contains unsaturated double bonds, which can participate in crosslinking reactions during the film-forming process of the coating, increasing the crosslinking density and compactness of the coating film. Without the addition of methyl linoleate, the crosslinking degree of the coating film is reduced, the intermolecular interaction is weakened, the structure of the formed coating film is relatively loose, and there are more pores. These pores provide conditions for the volatilization of VOC, leading to an increase in the total VOC content. The reduction of crosslinking reactions makes it difficult for emulsion particles to quickly form a stable network structure during the film-forming process, and the water evaporation and coating film curing process is slow, thus leading to an increase in the surface dry time and the real dry time. The coating film with low crosslinking density has weak resistance to acid and alkali solutions. Acid and alkali molecules can easily penetrate into the interior of the coating film, destroying the chemical structure of the coating film, leading to swelling, peeling and other phenomena, and reducing the acid and alkali resistance. The crosslinking density of the coating film directly affects its adhesion to the substrate and its flexibility. Low crosslinking density reduces the chemical bonds and intermolecular forces between the coating film and the substrate, resulting in a decrease in adhesion; at the same time, the molecular chains lack sufficient crosslinking and interaction, and are prone to relative sliding and rupture under external force, leading to poor flexibility, low adhesion grade in the cross-hatch test, and the need for a larger diameter shaft rod to ensure that the coating film does not crack in the flexibility test.

[0089] As can be seen from the results of Comparative Example 11, without the addition of PEG-40 stearate and methyl linoleate, the coating system loses two important film-forming additives. On the one hand, solid particles such as pigments and fillers cannot be effectively dispersed, forming a large number of agglomerates, increasing the volatilization channels of VOC; on the other hand, the crosslinking reaction of the coating film is severely hindered, and a dense structure cannot be formed. Under the action of the double factors, a large amount of VOC in the coating volatilizes, and the total VOC content increases significantly, far higher than the level of the examples. The combination of solid particle agglomeration and low crosslinking density greatly hinders the arrangement and fusion of emulsion particles and the curing process of the coating film. Water evaporation becomes extremely slow, and the coating film needs a longer time to reach a dry state, resulting in a significant increase in the surface dry time and the real dry time. The loose and porous structure of the coating film and the severely damaged crosslinking network make the coating film completely unable to resist the erosion of water and acid and alkali solutions. In the immersion test, the coating film will quickly appear white, swelling, and large-area peeling. The adhesion between the coating film and the substrate is almost lost due to structural defects, and in the adhesion test, the coating film peels off in large areas when the tape is peeled off, and the adhesion grade is extremely low. At the same time, the molecular chains of the coating film lack crosslinking and support, and are prone to rupture under external force, resulting in poor flexibility. Even if a larger diameter shaft rod is used for bending test, the coating film will easily crack. Although the water resistance is in the second level interval, the adhesion is in the first level interval, and the flexibility is also 2 mm, it is worse than Comparative Examples 10 and 9.

Claims

1. An ultra-low VOC water-based paint, characterized in that: The invention comprises the following raw materials in parts by weight: 40 to 50 parts of modified acrylic-polyurethane hybrid emulsion, 3 to 5 parts of methyl linoleate, 8 to 12 parts of choline chloride-glycerol complex, 1 to 2 parts of modified nano-titanium dioxide photocatalyst, 3 to 5 parts of PEG-40 stearate, 0.5 to 1 part of thickener, 0.1 to 0.3 parts of preservative, 0.5 to 1 part of dispersant, 6 to 12 parts of pigment, 0.3 to 0.6 parts of defoaming agent, 0.1 to 0.3 parts of pH regulator, and the balance is deionized water. The solid content is 40 wt% to 50 wt%; the modified nano-titanium dioxide photocatalyst is a nano-titanium dioxide photocatalyst whose surface is coated with silicon dioxide and aluminum oxide; The preparation method of the modified acrylic acid-polyurethane hybrid emulsion comprises the following steps: In parts by mass: under nitrogen protection, at 75°C to 80°C and with continuous stirring, add 130 parts to 135 parts of isophorone diisocyanate to 340 parts to 345 parts of polycarbonate diol, add 0.20 parts to 0.25 parts of dibutyltin dilaurate, raise the temperature to 84°C to 88°C, and react for 2.5h to 3h to obtain a polyurethane prepolymer; under normal temperature and with continuous stirring, add 400 parts to 430 parts of deionized water and 12 parts to 18 parts of dimethylethanolamine to the polyurethane prepolymer, raise the temperature to 75°C to 80°C, add 20 parts to 25 parts of potassium persulfate aqueous solution, and react for 1.5h to 2h to obtain a polyurethane core layer emulsion; add 175 parts to 180 parts of methyl methacrylate, 140 parts to 145 parts of butyl acrylate, 11 parts to 13 parts of methacrylic acid, 18 parts to 2 0 parts of vinyl triethoxysilane and 12 parts to 15 parts of N-hydroxymethyl acrylamide are uniformly mixed to obtain a shell emulsion; 20 parts to 25 parts of γ-methacryloxypropyl triethoxysilane, 0.5 parts to 0.8 parts of acetic acid and 20 parts to 25 parts of deionized water are uniformly mixed to obtain a pre-hydrolysis solution; 5 parts to 8 parts of panthenyl hydroxypropyl stearyl dimethyl ammonium chloride, the shell emulsion and 30 parts to 35 parts of potassium persulfate aqueous solution are sequentially added to the polyurethane core emulsion at 75° C. to 80° C. under continuous stirring, and the mixture is reacted for 3 h to 4 h, the pre-hydrolysis solution is added, the mixture is heated to 84° C. to 88° C., the mixture is reacted for 1.5 h to 2 h, 5 parts to 10 parts of polycarbonate diol are added, the mixture is reacted for 1 h to 1.5 h, vacuum treated, the solid content is adjusted with deionized water, and the mixture is filtered to obtain a modified acrylic-polyurethane hybrid emulsion.

2. An ultra-low VOC water-based paint according to claim 1, characterized in that: The mass ratio of the components of the choline chloride-glycerol complex is choline chloride:glycerol=(1-1.5):(3-4).

3. An ultra-low VOC water-based paint according to claim 1, characterized in that: In the preparation method of the modified acrylic acid-polyurethane hybrid emulsion, the mass concentration of the potassium persulfate aqueous solution is 10% to 12%.

4. The ultra-low VOC water-based paint according to claim 1, characterized in that: In the preparation method of the modified acrylic acid-polyurethane hybrid emulsion, the deionized water is used to adjust the solid content to 45wt% to 50wt%.

5. The ultra-low VOC water-based paint according to claim 1, characterized in that: In the preparation method of the modified acrylic-polyurethane hybrid emulsion, the stirring speed is 300r / min to 500r / min; the vacuum treatment is carried out at 50°C to 60°C and -0.08MPa to -0.09MPa for 10min to 20min; and the mesh number of the filtration is 100mesh to 150mesh.

6. The ultra-low VOC water-based paint according to claim 1, characterized in that: The preparation method of the modified nano titanium dioxide photocatalyst comprises the following steps: preparing a mixed solution by mixing ethyl orthosilicate, anhydrous ethanol and deionized water in a volume ratio of (1-1.5):(4-6):(4-6), adjusting the pH value to 2-3 with hydrochloric acid, and stirring to obtain a silicon dioxide sol; stirring and dissolving aluminum isopropoxide and anhydrous ethanol in a mass ratio of (1-1.2):(10-12) at 60-80° C., adding deionized water with an amount of 2-3 times the mass of aluminum isopropoxide, adding nitric acid to adjust the pH value to 3-4, and stirring to obtain an aluminum oxide sol; stirring and mixing the silicon dioxide sol and the aluminum oxide sol in a volume ratio of (1-2):(1-1.2) to obtain a mixed sol; mixing and uniformly dispersing the nano titanium dioxide photocatalyst and the mixed sol in a mass ratio of 1:(10-12), evaporating the solvent under reduced pressure to form a gel-photocatalyst complex coated with SiO2-Al2O3, and drying and calcining to obtain the modified nano titanium dioxide photocatalyst.

7. The ultra-low VOC water-based paint according to claim 6, characterized in that: The silica sol is stirred at a speed of 400 r / min to 600 r / min for 30 min to 60 min; the alumina sol is stirred at a speed of 400 r / min to 600 r / min for 2 h to 3 h; the temperature of the reduced pressure evaporation is 60°C to 70°C; the temperature of the drying is 80°C to 100°C, and the drying time is 12 h to 24 h; the temperature of the calcination is 400°C to 500°C, and the calcination time is 2 h to 3 h.

8. A method for preparing the ultra-low VOC water-based coating according to claim 1, characterized in that: The method comprises the following steps: mixing raw materials according to weight fractions, adjusting the solid content to 40wt% to 50wt%, homogenizing, filtering, and obtaining the coating.

9. The method for preparing an ultra-low VOC water-based paint according to claim 8, characterized in that: The homogenization is carried out at 1500 rpm to 2000 rpm for 10 min to 15 min; the mesh number of the filtration is 100 mesh to 150 mesh.

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