An ultra-low voc baking type quick-drying paint and a preparation method thereof

Abstract

The present application relates to a kind of ultra-low VOC baking type quick-drying paint and its preparation method, belong to paint technical field, and paint component includes composite hybrid resin, methyl etherified melamine formaldehyde resin, neopentyl glycol diglycidyl ether, trimethylolpropane triacrylate, composite filler, zinc fatty acid, fumed silica, silane coupling agent KH-560, aminoethyl aminopropyl polydimethylsiloxane etc..The present application is prepared using special method to obtain composite hybrid resin;Composite hybrid resin is used with methyl etherified melamine formaldehyde resin, neopentyl glycol diglycidyl ether, trimethylolpropane triacrylate, composite filler, zinc fatty acid, fumed silica, silane coupling agent KH-560, aminoethyl aminopropyl polydimethylsiloxane etc.composition is used according to certain proportion, with low VOC emission, baking fast drying, while having good adhesion, balanced hardness and flexibility, and excellent chemical resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coatings, and particularly relates to an ultra-low VOC baking type fast-drying coating and a preparation method thereof. BACKGROUND

[0002] Coatings are a class of widely used materials that play important roles in protection and decoration. However, traditional coatings have problems of volatile organic compound (VOC) emissions during use, some of which are toxic and harmful to human health. With the increasing awareness of environmental protection and the increasingly stringent environmental protection regulations, the limitation on VOC emissions in coatings is becoming more and more stringent. Under such a background, the research and development of low VOC coatings have become an important development direction of the coating industry. Low VOC coatings not only help to improve indoor and outdoor air quality and reduce potential threats to human health, but also conform to the concept of sustainable development, can reduce negative impacts on the environment, and promote the transformation and upgrading of the coating industry towards green and environmentally friendly direction.

[0003] In the research and development process of low VOC coatings, baking type fast-drying coatings have attracted much attention due to their unique advantages. Traditional coatings have a slow drying speed, which not only prolongs the construction period and increases the time cost, but also is easily affected by external factors during drying, resulting in film defects such as sagging, dust adhesion, and reduced coating quality. Baking type fast-drying coatings can be cured and formed through baking in a relatively short time, greatly improving the construction efficiency and being suitable for large-scale industrial production scenarios. Moreover, fast drying can effectively reduce various problems caused by excessive drying time, ensuring the quality and performance stability of the coating.

[0004] However, it is not easy to develop ultra-low VOC baking type fast-drying coatings, and there are many technical challenges. On the one hand, it is necessary to reduce VOC content while ensuring good film-forming performance, adhesion, hardness, corrosion resistance and other key properties of the coating, and maintaining its effective protection and decoration function for the coated object. For example, many manufacturers use a large amount of small molecule resins and active diluents in the formulation to reduce the viscosity of the coating in order to achieve low VOC, which results in short mixing use period of the coating and reduced water and salt mist resistance. On the other hand, the applicability of the coating on different substrates and the compatibility with existing coating equipment and processes also need to be considered to ensure its smooth application in actual production.

[0005] Therefore, it is an urgent problem to be solved in the coating industry to develop an ultra-low VOC baking type fast-drying coating that can significantly reduce VOC emissions, meet the requirements of fast drying, and perform well in performance and applicability, which has important practical significance and market value. SUMMARY

[0006] In order to significantly reduce VOC emissions, meet the requirements of rapid drying of baking, ensure the use performance and applicability of the paint film, the present application provides a kind of ultra-low VOC baking type fast drying coating and its preparation method, which is prepared by special method, and is used with methoxylated melamine formaldehyde resin, neopentyl glycol diglycidyl ether, trimethylolpropane triacrylate, composite filler, zinc fatty acid, silane coupling agent KH-560, aminoethyl aminopropyl polydimethylsiloxane and other ingredients in a certain proportion, with low VOC emissions, baking and rapid drying, while having good adhesion, balanced hardness and flexibility, and excellent chemical resistance.The specific technical scheme is as follows:

[0007] An ultra-low VOC baking type fast drying coating, the coating includes the following mass fractions of raw materials: composite hybrid resin 45-50 parts, methoxylated melamine formaldehyde resin 15-20 parts, neopentyl glycol diglycidyl ether 5-7 parts, trimethylolpropane triacrylate 3-5 parts, composite filler 8-10 parts, zinc fatty acid 1-1.5 parts, fumed silica 0.5-0.8 parts, silane coupling agent KH-560 0.5-0.8 parts, polyacrylic acid sodium salt dispersant 1-1.5 parts, polyether modified silicone defoamer 0.1-0.3 parts, aminoethyl aminopropyl polydimethylsiloxane 2-3 parts, fluorocarbon modified polyether leveling agent 0.6-1 part, and the balance is deionized water, the coating viscosity is 1500-2000 mPa·s.

[0008] In the above-mentioned coating, the preparation method of the composite hybrid resin includes: under nitrogen protection, 20-25 parts of isophthalic acid, 10-15 parts of adipic acid, 15-20 parts of neopentyl glycol, 5-8 parts of propylene glycol, 10-15 parts of propylene glycol butyl ether, 15-20 parts of dimethyl carbonate, 10-12 parts of dipropylene glycol butyl ether and 0.2-0.3 parts of tetrabutyl titanate are mixed uniformly, refluxed at 180-200℃, and the water generated in the reaction is collected through a water trap, when the acid value of the reaction system is reduced to 5-7 mgKOH / g, the temperature is reduced to 70-80℃, 8-10 parts of methyl methacrylate, 6-8 parts of butyl acrylate, 4-6 parts of trimethylolpropane triacrylate, 3-8 parts of ethylene-vinyl acetate copolymer, 5-8 parts of polyester polyurethane prepolymer I, 3-5 parts of polyester polyurethane prepolymer II and 1-2 parts of silane coupling agent KH-560 are added and mixed uniformly, 0.8-1.2 parts of dibenzoyl peroxide is added, and refluxed at 130-140℃ for 4-5 h, then dimethyl carbonate is removed by reduced pressure distillation, and impurities are removed by screen mesh filtration to obtain the composite hybrid resin.

[0009] In the preparation method of the composite hybrid resin, the polyester polyurethane prepolymer I is polyester polyurethane prepolymer T80; and the polyester polyurethane prepolymer II is polyester polyurethane prepolymer T100.

[0010] In the preparation method of the composite hybrid resin, the dibenzoyl peroxide is diluted with 10-15 times of dipropylene glycol butyl ether by mass before being added, and is evenly divided into 3-4 parts by volume, and 1 part by volume is added every 30-40 min.

[0011] In the preparation method of the composite hybrid resin, the nitrogen protection is 0.02-0.05 MPa of micro-positive pressure nitrogen protection.

[0012] In the preparation method of the composite hybrid resin, the temperature of the reduced pressure distillation is 50-60 DEG C.

[0013] In the preparation method of the composite hybrid resin, the mesh number of the screen is 150-200 meshes.

[0014] In the coating, the D90 particle size of the fumed silica is 15 μm or less.

[0015] In the coating, the mass ratio of the components of the composite filler is (3-4) : (7-9) of mica powder : modified barium sulfate. The D90 particle size of the mica powder and the modified barium sulfate is 15 μm or less.

[0016] The preparation method of the one kind of ultra-low VOC baking type quick-drying coating comprises the following steps:

[0017] S1: according to the mass fraction, the composite hybrid resin, neopentyl glycol diglycidyl ether and 10-15 parts of deionized water are uniformly mixed, and the polyacrylic acid sodium salt dispersant, fumed silica and composite filler are sequentially added and uniformly mixed and dispersed to form a homogeneous base;

[0018] S2: according to the mass fraction, the methoxylated melamine formaldehyde resin and zinc fatty acid are sequentially added to the homogeneous base and uniformly mixed, and then ground by a sand mill to a fineness of ≤15 μm to obtain a ground material;

[0019] S3: according to the mass fraction, the trimethylolpropane triacrylate, silane coupling agent KH-560, polyether modified silicone defoaming agent, aminoethyl aminopropyl polydimethylsiloxane and fluorocarbon modified polyether leveling agent are sequentially added to the ground material, stirred at a low speed, the coating viscosity is adjusted to 1500-2000 mPa·s by deionized water, filtered by a screen, and the filtrate is obtained to obtain the coating.

[0020] In the preparation method, the low-speed stirring is at 300-350 rpm for 20-30 min; and the mesh number of the screen is 150-200 meshes.

[0021] The present application provides an ultra-low VOC baking type fast-drying paint and a preparation method thereof, which has the following advantages:

[0022] I. In the paint system, zinc fatty acid has the dual advantages of drying and cross-linking promotion, and surface property adjustment. The metal zinc ions of zinc fatty acid can form a complex with carboxyl groups and other groups in the composite hybrid resin, accelerating the cross-linking process between the composite hybrid resin and the methylated melamine formaldehyde resin. Zinc fatty acid has an irreplaceable role in promoting drying and cross-linking. The improvement of cross-linking degree helps to form a more compact coating structure, thereby improving the hardness, adhesion and corrosion resistance of the coating. Zinc fatty acid can also effectively reduce the surface tension of the paint system, making the paint have better wettability and leveling on the surface of the substrate. This helps to form a smooth and smooth paint film during the construction process, reduces surface defects such as shrinkage and orange peel caused by uneven surface tension, and ensures the appearance quality of the coating.

[0023] II. In the paint system, the advantages of the controlled addition amount of aminoethyl aminopropyl polydimethylsiloxane are reflected in performance optimization and avoidance of negative effects. The appropriate addition of aminoethyl aminopropyl polydimethylsiloxane can fully play the role of improving the leveling and low-temperature flexibility of the paint. The organic silicon structure can reduce the surface tension of the paint, making the paint spread better during the baking process to form a smooth coating surface; at the same time, the flexibility of its molecular chain helps to improve the deformation ability of the coating in a low-temperature environment, avoiding the cracking of the coating due to low temperature brittleness. When the addition amount is too high, the compatibility of the paint system will be damaged. Excessive organic silicon segments will accumulate on the surface of the coating, hindering the cross-linking reaction between the composite hybrid resin and the methylated melamine formaldehyde resin, resulting in a decrease in cross-linking density, which in turn weakens the adhesion between the coating and the substrate, and reduces the hardness, corrosion resistance and other properties of the coating. Therefore, precise control of the addition amount can ensure the improvement of the performance of the paint while avoiding the performance degradation caused by excessive addition.

[0024] III. In the preparation method of the composite hybrid resin, ethylene-vinyl acetate copolymer mainly plays a role in improving flexibility, improving filler wettability and enhancing coating density in the paint system. The ethylene segments in its molecular chain endow the material with good flexibility, and the vinyl acetate segments provide polar groups. In the composite hybrid resin, intermolecular forces (including hydrogen bonds and van der Waals forces) are formed with other components to improve the overall flexibility of the resin. Ethylene-vinyl acetate copolymer can improve the compatibility of polyester polyurethane prepolymer with other components, improve the uniformity of the reaction, and help to improve the coating density of the composite hybrid resin after cross-linking, reduce porosity, reduce the penetration of corrosive media (water, acid and alkali, etc.), improve the chemical resistance and water resistance of the coating, and dense coating can also improve other comprehensive performance.

[0025] Ethylene-vinyl acetate copolymer is used in combination with silane coupling agent KH-560 to improve the performance of the coating from three aspects of enhancing interface bonding, improving crosslinking effect and optimizing overall performance. The siloxane group at one end of silane coupling agent KH-560 can condense with the hydroxyl group on the surface of the substrate to form Si-O-M (M is the metal atom of the substrate or other hydroxyl-containing materials) chemical bond, and the active group such as epoxy group at the other end reacts with the active group in the composite hybrid resin; ethylene-vinyl acetate copolymer combines with resin and filler through intermolecular forces, and the two work together to form a firm chemical and physical bond between resin-filler-substrate, significantly enhancing the adhesion of the coating to the substrate. Ethylene-vinyl acetate copolymer improves the flexibility of the resin and the dispersibility of the filler, creating a more uniform environment for crosslinking reaction; silane coupling agent KH-560 promotes the perfection of the resin crosslinking network, and the two work together to make the crosslinking of the composite hybrid resin more sufficient, forming a more dense three-dimensional network structure, improving the hardness, corrosion resistance and water resistance of the coating. When the two work together, they can effectively make up for the shortcomings of each other, complement each other's performance, and improve the overall performance of the coating.

[0026] Four, the polyester polyurethane prepolymer I in the molecular structure contains active groups such as isocyanate groups, which can rapidly react with hydroxyl groups and other groups in the system when the composite hybrid resin is blended and baked with methoxylated melamine formaldehyde resin, increasing the crosslinking points, improving the crosslinking density, and accelerating the film forming process. The rigid urethane groups of polyester polyurethane prepolymer I are embedded in the crosslinking network, limiting the movement of molecular segments and increasing the intermolecular force, thereby improving the hardness of the coating. The composite hybrid resin has good tensile strength, wear resistance and other mechanical properties, so that the coating can better resist deformation and wear when subjected to external force, and is suitable for application scenarios with high mechanical property requirements.

[0027] Polyester polyurethane prepolymer II contains flexible polyester segments, which can increase the flexibility of the composite hybrid resin, allowing the coating to deform to a certain extent without breaking when subjected to external force, improving the impact resistance of the coating. It effectively improves the low temperature resistance of the composite hybrid resin, maintains the movement ability of the molecular chain in low temperature environment, prevents the coating from cracking due to low temperature brittleness, and expands the use temperature range of the coating.

[0028] The polyester polyurethane prepolymer II cooperates with the polyester polyurethane prepolymer I, balances the rigidity and flexibility of the crosslinking network, and the combination of the two makes the crosslinking network have sufficient strength and proper flexibility, realizes the advantages of performance complementation, optimized crosslinking network and broadened application range. The combination of the two makes the composite hybrid resin have good hardness, tensile strength and flexibility at the same time, overcomes the performance limitations of a single prepolymer. The active groups of the two prepolymers and the composite hybrid resin and the methylated melamine formaldehyde resin undergo multiple crosslinking reactions to form a more complex and stable three-dimensional crosslinking network structure. This network structure makes the coating have better integrity and improves the comprehensive performance of the coating, such as hardness, adhesion and chemical resistance.

[0029] The addition amount of the polyester polyurethane prepolymer I and the polyester polyurethane prepolymer II is controlled to ensure the stability of the system and optimize the cost benefit, and the addition amount and ratio of the two are designed to realize the performance of the composite hybrid resin. Ensure that the prepolymer is uniformly dispersed and fully reacted in the composite hybrid resin system, avoid excessive addition amount which leads to excessive viscosity and uneven dispersion of the system, affecting the subsequent film forming performance; at the same time, when the addition amount is too low, the expected crosslinking effect and performance improvement cannot be achieved.

[0030] Five, the prepared coating has the following comprehensive advantages:

[0031] (1) Low VOC emission: dimethyl carbonate is removed by vacuum distillation at the later stage of the synthesis of the composite hybrid resin, reducing the VOC emission of the solvent type. At the same time, the crosslinking density of the composite hybrid resin is improved, and the three-dimensional network structure formed physically wraps the residual solvent molecules, and the active groups are consumed by reaction during the crosslinking process, further reducing VOC emission.

[0032] (2) Fast drying: the multi-polymer structure of the composite hybrid resin forms multiple crosslinking reaction paths when it is blended and baked with the methylated melamine formaldehyde resin, greatly accelerating the formation of the crosslinking network, and the crosslinking speed is significantly improved compared with the single resin system, greatly shortening the film forming time.

[0033] (3) Good adhesion: silane coupling agent KH-560 forms a firm chemical connection between the resin and the substrate, and the dense network structure formed by the crosslinking of the composite hybrid resin and the methylated melamine formaldehyde resin further enhances the adhesion to the substrate through mechanical interlocking.

[0034] (4) High hardness: the highly crosslinked network structure restricts the movement of molecular segments, and the rigid urethane groups of the polyester polyurethane prepolymer are embedded in the crosslinking network, further enhancing the rigidity and hardness of the network.

[0035] (5) Excellent chemical resistance: The dense crosslinking network increases the difficulty of corrosive medium molecules penetrating into the interior of the coating, the high crosslinking density makes the pore size extremely small and tortuous, prolonging the diffusion path, while the chemical bonds and intermolecular forces can interact with the medium molecules, consuming the penetration energy of the medium molecules. DETAILED DESCRIPTION

[0036] Example 1

[0037] An ultra-low VOC baking type fast-drying paint, the paint comprises the following mass fractions of raw materials: composite hybrid resin 45 parts, methyl etherified melamine formaldehyde resin 15 parts, neopentyl glycol diglycidyl ether 5 parts, trimethylolpropane triacrylate 3 parts, composite filler 8 parts, zinc fatty acid 1 part, fumed silica 0.5 part, silane coupling agent KH-560 0.5 part, polyacrylic acid sodium salt dispersant 1 part, polyether modified silicone defoamer 0.1 part, aminoethyl aminopropyl polydimethylsiloxane 2 parts, fluorocarbon modified polyether leveling agent 0.6 part, and the balance is deionized water, the viscosity of the paint is 1500 mPa·s.

[0038] The preparation method of the composite hybrid resin comprises the following steps: under the protection of nitrogen gas with a floating micro-positive pressure between 0.02 MPa and 0.03 MPa, 20 parts of isophthalic acid, 10 parts of adipic acid, 15 parts of neopentyl glycol, 5 parts of propylene glycol, 10 parts of propylene glycol butyl ether, 15 parts of dimethyl carbonate, 10 parts of dipropylene glycol butyl ether and 0.2 parts of tetrabutyl titanate are uniformly mixed, and then refluxed at 180℃, the water generated in the reaction is collected through a water trap, when the acid value of the reaction system is reduced to 5 mgKOH / g, the temperature is reduced to 70℃, 8 parts of methyl methacrylate, 6 parts of butyl acrylate, 4 parts of trimethylolpropane triacrylate, 3 parts of ethylene-vinyl acetate copolymer, 5 parts of polyester polyurethane prepolymer I, 3 parts of polyester polyurethane prepolymer II and 1 part of silane coupling agent KH-560 are added in sequence and uniformly mixed, 0.8 parts of dibenzoyl peroxide is diluted with 10 times mass of dipropylene glycol butyl ether, and then divided into 3 parts by volume, 1 part by volume is added every 30 min, and then refluxed at 130℃ for 4 h, and then distilled at 50℃ under reduced pressure to remove dimethyl carbonate (residual amount below 1%), and then filtered through a 150 mesh screen to remove impurities, to obtain the composite hybrid resin.

[0039] The mass ratio of the components of the composite filler is mica powder: modified barium sulfate = 3:7; the D90 particle size of the mica powder and the modified barium sulfate is 13 μm. The D90 particle size of the fumed silica is 10 μm.

[0040] The preparation method of the above-mentioned ultra-low VOC baking type fast-drying paint comprises the following steps:

[0041] S1: according to mass fraction, the composite hybrid resin, neopentyl glycol diglycidyl ether and 10 parts of deionized water were mixed at 300 rpm for 10 min, and then polyacrylic acid sodium salt dispersant, fumed silica and composite filler were added in turn, and stirred and mixed at 500 rpm for 20 min to form a homogeneous base;

[0042] S2: according to mass fraction, the methoxylated melamine formaldehyde resin and zinc fatty acid were added in turn to the homogeneous base, and stirred and mixed at 400 rpm for 15 min, and then ground by a sand mill at 1000 rpm for 30 min to a fineness of ≤15 μm to obtain a ground material;

[0043] S3: according to mass fraction, trimethylolpropane triacrylate, silane coupling agent KH-560, polyether modified silicone defoamer, aminoethyl aminopropyl polydimethylsiloxane and fluorocarbon modified polyether leveling agent were added in turn to the ground material, and stirred at low speed at 300 rpm for 20 min, and then the coating viscosity was adjusted to 1500 mPa·s with deionized water, filtered through a 150 mesh screen, and the filtrate was obtained to obtain the coating.

[0044] Example 2

[0045] An ultra-low VOC baking type fast-drying coating, the coating comprises the following mass fraction of raw materials: composite hybrid resin 48 parts, methoxylated melamine formaldehyde resin 18 parts, neopentyl glycol diglycidyl ether 6 parts, trimethylolpropane triacrylate 4 parts, composite filler 9 parts, zinc fatty acid 1.2 parts, fumed silica 0.7 parts, silane coupling agent KH-560 0.7 parts, polyacrylic acid sodium salt dispersant 1.2 parts, polyether modified silicone defoamer 0.2 parts, aminoethyl aminopropyl polydimethylsiloxane 2.5 parts, fluorocarbon modified polyether leveling agent 0.8 parts, and the balance is deionized water, and the coating viscosity is 1800 mPa·s.

[0046] The preparation method of the composite hybrid resin comprises the following steps: under the protection of nitrogen gas with a floating micro-positive pressure between 0.03 MPa and 0.04 MPa, 23 parts of isophthalic acid, 12 parts of adipic acid, 18 parts of neopentyl glycol, 6 parts of propylene glycol, 12 parts of propylene glycol butyl ether, 16 parts of dimethyl carbonate, 11 parts of dipropylene glycol butyl ether and 0.25 parts of tetrabutyl titanate are uniformly mixed, and then refluxed at 190 ℃, and the water generated in the reaction is collected through a water trap; when the acid value of the reaction system is reduced to 6 mgKOH / g, the temperature is reduced to 75 ℃, and 9 parts of methyl methacrylate, 7 parts of butyl acrylate, 5 parts of trimethylolpropane triacrylate, 5 parts of ethylene-vinyl acetate copolymer, 6 parts of polyester polyurethane prepolymer I, 4 parts of polyester polyurethane prepolymer II and 1.5 parts of silane coupling agent KH-560 are uniformly mixed; 1 part of dibenzoyl peroxide is diluted with 12 times the mass of dipropylene glycol butyl ether, and then divided into 3 parts by volume; 1 part by volume is added every 40 min; refluxed at 135 ℃ for 4.5 h; dimethyl carbonate is removed by distillation under reduced pressure at 55 ℃ (residual amount less than 1%); impurities are removed by filtering through a 200-mesh screen to obtain the composite hybrid resin.

[0047] The mass ratio of the components of the composite filler is mica powder: modified barium sulfate = 3.5:8; the D90 particle size of the mica powder and the modified barium sulfate is 11 μm; and the D90 particle size of the fumed silica is 12 μm.

[0048] The preparation method of the above-mentioned ultra-low VOC baking type quick-drying paint comprises the following steps:

[0049] S1: 15 min of 400 rpm stirring and mixing of the composite hybrid resin, neopentyl glycol diglycidyl ether and 12 parts of deionized water by mass fraction, and then 25 min of 600 rpm stirring and mixing and dispersion of the polyacrylic acid sodium salt dispersant, fumed silica and composite filler in sequence to form a homogeneous base;

[0050] S2: 20 min of 500 rpm stirring and mixing of the methoxylated melamine formaldehyde resin and zinc fatty acid into the homogeneous base by mass fraction, and then 35 min of 1200 rpm grinding of the grinding material to a fineness of ≤15 μm to obtain the ground material;

[0051] S3: 20 min of 350 rpm low-speed stirring of the trimethylolpropane triacrylate, silane coupling agent KH-560, polyether modified silicone defoaming agent, aminoethyl aminopropyl polydimethylsiloxane and fluorocarbon modified polyether leveling agent into the ground material by mass fraction, and then adjustment of the paint viscosity to 1800 mP a·s with deionized water, filtration through a 200-mesh screen and collection of the filtrate to obtain the paint.

[0052] Example 3

[0053] An ultra-low VOC baking type fast-drying paint, the paint comprises the following raw materials in mass fraction: composite hybrid resin 50 parts, methyl etherified melamine formaldehyde resin 20 parts, neopentyl glycol diglycidyl ether 7 parts, trimethylolpropane triacrylate 5 parts, composite filler 10 parts, zinc fatty acid 1.5 parts, fumed silica 0.8 parts, silane coupling agent KH-560 0.8 parts, polyacrylic acid sodium salt dispersant 1.5 parts, polyether modified silicone defoamer 0.3 parts, aminoethyl aminopropyl polydimethylsiloxane 3 parts, fluorocarbon modified polyether leveling agent 1 part, and the balance is deionized water, the viscosity of the paint is 2000 mPa·s.

[0054] The preparation method of the composite hybrid resin comprises the following steps: under the protection of nitrogen with a floating micro-positive pressure of 0.04 MPa-0.05 MPa, 25 parts of isophthalic acid, 15 parts of adipic acid, 20 parts of neopentyl glycol, 8 parts of propylene glycol, 15 parts of propylene glycol butyl ether, 20 parts of dimethyl carbonate, 12 parts of dipropylene glycol butyl ether and 0.3 parts of tetrabutyl titanate are uniformly mixed, and then refluxed at 200 DEG C to collect the water generated in the reaction through a water trap; when the acid value of the reaction system is reduced to 7 mgKOH / g, the temperature is reduced to 80 DEG C, and 10 parts of methyl methacrylate, 8 parts of butyl acrylate, 6 parts of trimethylolpropane triacrylate, 8 parts of ethylene-vinyl acetate copolymer, 8 parts of polyester polyurethane prepolymer I, 5 parts of polyester polyurethane prepolymer II and 2 parts of silane coupling agent KH-560 are added in sequence and uniformly mixed; 1.2 parts of dibenzoyl peroxide is diluted with 15 times the mass of dipropylene glycol butyl ether, and then divided into 4 parts by volume; 1 part by volume is added every 40 min; refluxed at 140 DEG C for 5 h; dimethyl carbonate is removed by distillation under reduced pressure at 60 DEG C (residual amount is less than 1%); impurities are removed by filtering through a 200 mesh screen to obtain the composite hybrid resin.

[0055] The mass ratio of the components of the composite filler is mica powder: modified barium sulfate = 4:9; the D90 particle size of the mica powder and the modified barium sulfate is 8 mu m; and the D90 particle size of the fumed silica is 14 mu m.

[0056] The preparation method of the above-mentioned ultra-low VOC baking type fast-drying paint comprises the following steps:

[0057] S1: according to mass fraction, the composite hybrid resin, neopentyl glycol diglycidyl ether and 15 parts of deionized water are mixed by stirring at 500 rpm for 10 min, and then the polyacrylic acid sodium salt dispersant, fumed silica and composite filler are added in sequence and mixed and dispersed by stirring at 600 rpm for 30 min to form a homogeneous base;

[0058] S2: In the homogeneous base, add methoxylated melamine formaldehyde resin and zinc fatty acid in mass fraction, stir for 15 min at 600 rpm, then grind for 30 min at 1500 rpm by sand mill, grind to fineness ≤15 μm, to obtain ground material;

[0059] S3: In the ground material, add trimethylolpropane triacrylate, silane coupling agent KH-560, polyether modified silicone defoamer, aminoethyl aminopropyl polydimethylsiloxane and fluorocarbon modified polyether leveling agent in mass fraction, stir for 30 min at 350 rpm, adjust the viscosity of the coating to 2000 mPa·s with deionized water, filter through 200 mesh screen, take the filtrate, to obtain the coating.

[0060] Example 4

[0061] An ultra-low VOC baking type fast-drying coating, the coating comprises the following raw materials in mass fraction: composite hybrid resin 50 parts, methoxylated melamine formaldehyde resin 15 parts, neopentyl glycol diglycidyl ether 7 parts, trimethylolpropane triacrylate 3 parts, composite filler 10 parts, zinc fatty acid 1 part, fumed silica 0.8 part, silane coupling agent KH-560 0.5 part, polyacrylic acid sodium salt dispersant 1.5 parts, polyether modified silicone defoamer 0.1 part, aminoethyl aminopropyl polydimethylsiloxane 3 parts, fluorocarbon modified polyether leveling agent 0.6 part, and the balance is deionized water, the viscosity of the coating is 2000 mPa·s.

[0062] The preparation method of the composite hybrid resin comprises the following steps: under the protection of nitrogen gas with a floating micro-positive pressure between 0.03 MPa and 0.04 MPa, 20 parts of isophthalic acid, 15 parts of adipic acid, 15 parts of neopentyl glycol, 8 parts of propylene glycol, 10 parts of propylene glycol butyl ether, 20 parts of dimethyl carbonate, 10 parts of dipropylene glycol butyl ether and 0.3 parts of tetrabutyl titanate are uniformly mixed, and then refluxed at 180℃, the water generated in the reaction is collected through a water trap, when the acid value of the reaction system is reduced to 6.5 mgKOH / g, the temperature is reduced to 70℃, 10 parts of methyl methacrylate, 6 parts of butyl acrylate, 6 parts of trimethylolpropane triacrylate, 3 parts of ethylene-vinyl acetate copolymer, 8 parts of polyester polyurethane prepolymer I, 3 parts of polyester polyurethane prepolymer II and 2 parts of silane coupling agent KH-560 are sequentially added and uniformly mixed, 0.8 parts of dibenzoyl peroxide is diluted with 15 times mass of dipropylene glycol butyl ether, and then divided into 3 parts by volume, 1 part by volume is added every 40 min, and then refluxed at 130℃ for 5 h, and then distilled at 50℃ under reduced pressure to remove dimethyl carbonate (residual amount less than 1%), and then filtered through a 200 mesh screen to remove impurities, to obtain the composite hybrid resin.

[0063] The component mass ratio of the composite filler is mica powder: modified barium sulfate = 3:9, and the D90 particle size of the mica powder and the modified barium sulfate is 12 μm. The D90 particle size of the fumed silica is 9 μm.

[0064] The preparation method of the above-mentioned ultra-low VOC baking type quick-drying paint includes the following steps:

[0065] S1: According to the mass fraction, 10 parts of deionized water is mixed with the composite hybrid resin, neopentyl glycol diglycidyl ether, and 500 rpm stirring for 15 min. Then, the polyacrylic acid sodium salt dispersant, fumed silica, and composite filler are added in sequence, and 500 rpm stirring and mixing are carried out for 30 min to form a homogeneous base;

[0066] S2: According to the mass fraction, the homogeneous base is sequentially added with methyl etherified melamine formaldehyde resin and zinc fatty acid, and 500 rpm stirring and mixing are carried out for 20 min. Then, the material is ground by a sand mill at 1200 rpm for 40 min until the fineness is ≤15 μm to obtain a ground material;

[0067] S3: According to the mass fraction, the ground material is sequentially added with trimethylolpropane triacrylate, silane coupling agent KH-560, polyether modified silicone defoaming agent, aminoethyl aminopropyl polydimethylsiloxane, and fluorocarbon modified polyether leveling agent, and 350 rpm low-speed stirring is carried out for 20 min. Then, the paint viscosity is adjusted to 2000 mP a·s by deionized water, filtered by a 200 mesh screen, and the filtrate is obtained to obtain the paint.

[0068] The paint recommended baking parameters of each of the above embodiments are as follows: the construction is carried out by spraying or brushing, the ambient temperature is controlled at 15℃-30℃, and the relative humidity is controlled at 40%-70%. After construction, the coated workpiece is placed in an oven, pre-baked at 60℃-70℃ for 5-10 min, then heated to 120℃-140℃ for baking, and at the same time, the appropriate intensity of ultraviolet light irradiation (the power is adjusted according to the actual situation) can be selected to realize the rapid curing of the coating and form a paint film with excellent performance.

[0069] The raw material sources in the above embodiments: methyl etherified melamine formaldehyde resin is from Jining Oligon Chemical Co., Ltd., model 2526. Neopentyl glycol diglycidyl ether is from Wuhan Chengtian Fine Chemical Co., Ltd., model 17557-23-2. Trimethylolpropane triacrylate is from Wuhan Chengtian Fine Chemical Co., Ltd., model TMPTA. Zinc fatty acid is from Jinan Jinyu Chemical Co., Ltd., model ZnFA. Fumed silica is from Shandong Casone New Material Co., Ltd. Silane coupling agent KH-560 is from Jinan Yunuo Chemical Co., Ltd. Sodium polyacrylate dispersant is from Guangdong Zhongtai Lianhua New Material Co., Ltd., model AG-22. Polyether modified silicone defoamer is from Dongguan Haoyoudu New Material Co., Ltd., model D-001. Amine ethyl amine propyl polydimethylsiloxane is from Guangzhou Youbao Chemical Co., Ltd., model GY22. Fluorocarbon modified polyether leveling agent is from Kunshan Luolisi High Polymer Material Co., Ltd., model LS3024. Isophthalic acid is from Shandong Wuyang Biological Technology Co., Ltd. Adipic acid is from Shandong Wuyang Biological Technology Co., Ltd. Neopentyl glycol is from Shanghai Gaoming Chemical Co., Ltd. Propylene glycol is from Tianjin Zhonghe Shengtai Chemical Co., Ltd., 1,2-propylene glycol. Propylene glycol butyl ether is from Jinan Shengda Chemical Co., Ltd., model 416, propylene glycol monobutyl ether. Dimethyl carbonate is from Shandong Chuangying Chemical Co., Ltd. Dipropylene glycol butyl ether is from Guangzhou Honghai Chemical Co., Ltd. Tetrabutyl titanate is from Jinan Jiayi New Material Co., Ltd. Methyl methacrylate is from Shandong Yansuo Chemical Co., Ltd. Butyl acrylate is from Chuangyida (Shandong) Biological Technology Co., Ltd. Ethylene-vinyl acetate copolymer is from Dongguan Yuehaoxuan Plastic Co., Ltd., model 7470M. Polyester polyurethane prepolymer I is polyester polyurethane prepolymer T80, from Jiangsu Qianmei Polyurethane New Material Co., Ltd., model K1235, MOCA dosage 10.5 g / 100 g of prepolymer. Polyester polyurethane prepolymer II is polyester polyurethane prepolymer T100, from Jiangsu Qianmei Polyurethane New Material Co., Ltd., model K1150, MOCA dosage 14.5 g / 100 g of prepolymer. Diphenyl peroxide is from Jiangyin Jianheng Chemical Co., Ltd. Mica powder is from Lingshou Chuankai Mineral Products Co., Ltd. Modified barium sulfate is from Guangzhou Xianwan Chemical Co., Ltd., model 1336.

[0070] Comparative Example 1

[0071] The composite hybrid resin was replaced by acrylic resin (water-based silicone modified acrylic resin, from Qingdao Wanjia Huxin Surface Material Technology Co., Ltd., model S-611, content 40%); and additional isocyanate curing agent (isocyanate curing agent from Shanghai Kaizhi New Material Technology Co., Ltd., model N3300) of 10% of the mass of acrylic resin was added, and the curing agent was added after the defoaming agent in S3; other parameters and methods were the same as in Example 1.

[0072] Comparative Example 2

[0073] The composite hybrid resin was replaced by epoxy resin (from Qingdao Jinwanli Fine Chemical Co., Ltd., content 70%, model J-990); and additional N-(2-hydroxyethyl) ethylenediamine curing agent (from Guangzhou Jiangshun Chemical Technology Co., Ltd., model HS0595) of 8% of the mass of epoxy resin was added, and the curing agent was added after the defoaming agent in S3; other parameters and methods were the same as in Example 1.

[0074] Comparative Example 3

[0075] The methylolated melamine formaldehyde resin was replaced by acrylic resin (water-based silicone modified acrylic resin, from Qingdao Wanjia Huxin Surface Material Technology Co., Ltd., model S-611, content 40%); and additional isocyanate curing agent (isocyanate curing agent from Shanghai Kaizhi New Material Technology Co., Ltd., model N3300) of 12% of the mass of acrylic resin was added, and the curing agent was added after the defoaming agent in S3; other parameters and methods were the same as in Example 1.

[0076] Comparative Example 4

[0077] The methylolated melamine formaldehyde resin was replaced by epoxy resin (from Qingdao Jinwanli Fine Chemical Co., Ltd., content 70%, model J-990); and additional N-(2-hydroxyethyl) ethylenediamine curing agent (from Guangzhou Jiangshun Chemical Technology Co., Ltd., model HS0595) of 7% of the mass of epoxy resin was added, and polyamide curing agent (from Shanghai Yunhe Material Technology Co., Ltd., model 8115) of 3% of the mass of epoxy resin was added, and the curing agents were added after the defoaming agent in S3; other parameters and methods were the same as in Example 1.

[0078] Comparative Example 5

[0079] The zinc fatty acid was replaced by sodium dodecylbenzenesulfonate; other parameters and methods were the same as in Example 1.

[0080] Comparative Example 6

[0081] The amount of aminoethyl aminopropyl polydimethylsiloxane added was 10 parts; other parameters and methods were the same as in Example 1.

[0082] Comparative Example 7

[0083] The preparation method of the composite hybrid resin does not add ethylene-vinyl acetate copolymer; other parameters and methods are the same as in Example 1.

[0084] Comparative Example 8

[0085] The preparation method of the composite hybrid resin does not add silane coupling agent KH-560; other parameters and methods are the same as in Example 1.

[0086] Comparative Example 9

[0087] The preparation method of the composite hybrid resin does not add both ethylene-vinyl acetate copolymer and silane coupling agent KH-560; other parameters and methods are the same as in Example 1.

[0088] Comparative Example 10

[0089] The preparation method of the composite hybrid resin replaces ethylene-vinyl acetate copolymer with silane coupling agent KH-560; other parameters and methods are the same as in Example 1.

[0090] Comparative Example 11

[0091] The preparation method of the composite hybrid resin does not add polyester polyurethane prepolymer I; other parameters and methods are the same as in Example 1.

[0092] Comparative Example 12

[0093] The preparation method of the composite hybrid resin does not add polyester polyurethane prepolymer II; other parameters and methods are the same as in Example 1.

[0094] Comparative Example 13

[0095] The preparation method of the composite hybrid resin does not add both polyester polyurethane prepolymer I and polyester polyurethane prepolymer II; other parameters and methods are the same as in Example 1.

[0096] Comparative Example 14

[0097] The preparation method of the composite hybrid resin replaces polyester polyurethane prepolymer I with polyester polyurethane prepolymer II; other parameters and methods are the same as in Example 1.

[0098] Comparative Example 15

[0099] The preparation method of the composite hybrid resin replaces polyester polyurethane prepolymer II with polyester polyurethane prepolymer I; other parameters and methods are the same as in Example 1.

[0100] Comparative Example 16

[0101] The preparation method of the composite hybrid resin adds 15 parts of polyester polyurethane prepolymer I; other parameters and methods are the same as in Example 1.

[0102] Comparative Example 17

[0103] In the preparation method of the composite hybrid resin, 10 parts of polyester polyurethane prepolymer II were added; other parameters and methods were the same as in Example 1.

[0104] Comparative Example 18

[0105] In the preparation method of the composite hybrid resin, 12 parts of polyester polyurethane prepolymer I and 8 parts of polyester polyurethane prepolymer II were added; other parameters and methods were the same as in Example 1.

[0106] I. Baking film forming time detection: air spraying method was used, a spray gun with a caliber of 1.5 mm was used, the distance between the spray gun and the test plate (a standard tin plate with a size of 150 mm x 70 mm x 1 mm) was kept at 20 cm, so that the final coating thickness reached 80 ± 2 μm, and several parallel samples were prepared.

[0107] Several parallel samples were set at different baking times at 120 °C, and the baking time was set to increase by 1 min every 1 min after 10 min of 120 °C baking. The preconditions of the parallel samples were consistent, and the coated workpieces were quickly placed in a preheated to 60 °C air drying oven, and pre-baked for 8 min. After pre-baking, the temperature of the drying oven was raised to 120 °C within 3 min, and the timing started, and the baking time was set to increase by 1 min every 1 min after 10 min, the coating surface was detected until the coating surface of the removed sample had no obvious scratches and was not sticky, and the time was recorded as the baking film forming time.

[0108] II. VOC emission detection: according to GB / T 23986 “Determination of the content of volatile organic compounds (VOC) in color paints and varnishes by gas chromatography”, the total volatile VOC content at 150 °C for 30 min was determined.

[0109] III. Adhesion detection: according to GBT 9286 “Color paints and varnishes cross-hatch test”, the coating thickness was 80 ± 2 μm, the spacing was 1 mm, and the adhesion grade was evaluated: 0 grade was the best, and 5 grade was the worst.

[0110] IV. Hardness detection: according to GB / T 6739 “Pencil method for determining the hardness of paint film for color paints and varnishes”, the coating thickness was 100 ± 2 μm, the pencil was at an angle of 45 ° to the coating surface, a pressure of 1 kg was applied, and the pencil was pushed forward at a speed of 0.5 cm / s. Each hardness grade was tested 3 times, and the hardest pencil hardness without scratching the coating was taken as the coating hardness.

[0111] V. Low temperature flexibility detection: the PET thin substrate coating thickness was 80 ± 2 μm, and after being placed at -25 °C for 2 h, the sample plate was bent on a 3 mm diameter shaft within 10 s, and the cracking, peeling and other phenomena of the coating were observed.

[0112] Six, water resistance: glass plate coating thickness 80±2 μm, immersed in 40 °C deionized water for 240 h, observe the blistering, peeling, discoloration, etc.

[0113] Evaluation grade: 1st grade: no change on the surface of the paint film. 2nd grade: slight gloss loss, discoloration, small bubbles, slight whitening, etc. on the surface of the paint film are allowed. 3rd grade: obvious gloss loss, discoloration, dense small bubbles, obvious whitening, wrinkling, etc. on the surface of the paint film. 4th grade: serious discoloration, large bubbles, peeling, dissolution, etc. on the surface of the paint film.

[0114] Seven, acid resistance: glass plate coating thickness 80±2 μm, immersed in 5wt% hydrochloric acid solution at room temperature, take out and observe once every 2h, record the time when corrosion phenomenon (any one of small bubbles, wrinkling, peeling, etc.) appears on the coating.

[0115] Eight, alkali resistance: glass plate coating thickness 80±2 μm, immersed in 5wt% sodium hydroxide solution at room temperature, take out and observe once every 2h, record the time when corrosion phenomenon (any one of small bubbles, wrinkling, peeling, etc.) appears on the coating.

[0116] Table 1 test data results of each example and comparative example

[0117]

[0118] From the above results, the comprehensive performance of Examples 1 to 4 is obviously superior, and the multi-polymer structure of the composite hybrid resin is the key factor. During the synthesis of the composite hybrid resin, the polyester segments generated in the early stage of the polyesterization reaction provide a large number of active groups such as hydroxyl groups, the monomers such as methyl methacrylate and butyl acrylate introduced in the middle stage are polymerized by free radicals to introduce a large number of carbon-carbon double bonds into the molecular chain, and the addition of polyester polyurethane prepolymers I and II in the later stage further introduces active groups such as isocyanate groups, thereby synthesizing a special four-component composite hybrid resin. When the four-component composite hybrid resin is blended with the methyl etherified melamine formaldehyde resin and baked, multiple crosslinking reaction paths are formed: the ether exchange reaction of the hydroxyl groups of the polyester segments with the methoxyl groups of the methyl etherified melamine formaldehyde resin to form a methylene bridge; the free radical-nucleophilic substitution synergistic reaction of the acrylate double bonds with the active groups of the methyl etherified melamine formaldehyde resin; and the rapid reaction of the isocyanate groups of the polyurethane prepolymer with the hydroxyl groups in the system. Multiple reactions occur simultaneously, greatly accelerating the formation of the crosslinking network, and the crosslinking speed is significantly improved compared with single resin systems (Comparative Examples 1 and 2), thereby greatly shortening the film forming time. Trimethylolpropane triacrylate acts as an active diluent, and its three acrylate double bonds act as a "crosslinking node amplifier" in the system. After the decomposition of the initiator dibenzoyl peroxide generates free radicals, the double bonds of trimethylolpropane triacrylate are quickly opened, not only participating in self-polymerization, but also acting as a connection point to promote the crosslinking between the composite hybrid resin and the methyl etherified melamine formaldehyde resin, making the construction of the crosslinking network more efficient.

[0119] The root cause of VOC emission reduction: Most of the residual solvent is effectively removed by reduced pressure distillation during the late stage of the synthesis of the composite hybrid resin, which greatly reduces the solvent VOC emission compared with traditional high VOC solvents (such as toluene and xylene). At the resin structure level, as the crosslinking density of the composite hybrid resin increases, the three-dimensional network structure formed physically encapsulates the small amount of residual solvent molecules in the network pores, limiting VOC volatilization; at the same time, the reaction of active groups in the crosslinking process consumes volatile monomers that exist in free state, further reducing VOC emission.

[0120] The silane coupling agent KH-560 plays a "molecular bridge" role in the synthesis of the composite hybrid resin and the film forming process of the coating. The siloxane group at one end of KH-560 can undergo condensation reaction with the hydroxyl groups on the surface of the substrate in a humid environment or high temperature baking to form a Si-O-M (M is a substrate metal atom or other hydroxyl-containing material) chemical bond; the active groups such as epoxy groups at the other end of KH-560 undergo chemical reaction with the active groups in the composite hybrid resin, thereby forming a firm chemical connection between the resin and the substrate. In addition, the dense network structure formed by the crosslinking of the composite hybrid resin and the methyl etherified melamine formaldehyde resin further enhances the adhesion to the substrate through mechanical interlocking.

[0121] The highly crosslinked network structure greatly limits the movement of molecular segments. When subjected to external force, the crosslinking points hinder the relative sliding of molecular chains, and higher energy is required to deform the coating, which macroscopically manifests as an increase in hardness. The addition of polyester type polyurethane prepolymers I and II, with their rigid urethane groups embedded in the crosslinked network, further enhances the rigidity and hardness of the network.

[0122] Improved chemical resistance: The dense crosslinked network acts as a "molecular fence", significantly increasing the difficulty of corrosive medium molecules such as water, acid, and base penetrating into the coating. On the one hand, medium molecules need to diffuse through the pores of the crosslinked network, and high crosslinking density makes the pore size extremely small and tortuous, prolonging the diffusion path. On the other hand, the chemical bonds and intermolecular forces in the crosslinked network can interact with the medium molecules, consuming the penetration energy of the medium molecules. For example, in the water resistance test, water molecules penetrating into the coating will cause the resin to swell and the crosslinking points to be destroyed, while the high crosslinking density coating in the examples can effectively resist the erosion of water molecules, prolonging the water resistance time.

[0123] Acrylic resin substitution (Comparative Example 1, Comparative Example 3): The molecular chain of acrylic resin is mainly composed of carbon-carbon single bond and ester group, and its crosslinking mode mainly depends on the free radical polymerization of acrylic ester double bond, forming a relatively loose crosslinked network. When synergized with methylated melamine formaldehyde resin, due to the lack of active groups (such as insufficient number of hydroxyl groups) in acrylic resin that can react efficiently with methylated melamine formaldehyde resin, not enough methylene bridge bonds and other crosslinking structures can be formed, resulting in low crosslinking density. This makes the hardness, adhesion, and corrosion resistance of the coating decrease, and at the same time, the loose structure is not conducive to the wrapping and fixation of solvents, increasing the VOC emission.

[0124] Epoxy resin substitution (Comparative Example 2, Comparative Example 4): The curing of epoxy resin mainly depends on the reaction of epoxy group with amine, acid anhydride, etc. curing agent, but it does not match the reaction with methylated melamine formaldehyde resin in this system. The reactivity of the epoxy group of the epoxy resin with the methoxy group of the methylated melamine formaldehyde resin is low, making it difficult to form a stable crosslinking structure. In addition, although the crosslinked network formed after the curing of the epoxy resin has high hardness, it has poor flexibility and is prone to cracking due to internal stress concentration at low temperatures (such as low temperature flexibility test). At the same time, due to insufficient crosslinking, there is more solvent residue, and the VOC emission increases.

[0125] Zinc fatty acid salt substitution (Comparative Example 5): Zinc fatty acid salt not only has the function of air drying in the coating system, but also participates in the crosslinking reaction. Its metal zinc ion can form a complex with the carboxyl group in the resin, promote the crosslinking between the resin molecules, and at the same time, reduce the surface tension of the system, which is conducive to the leveling and drying of the coating. Sodium dodecyl benzene sulfonate as a surfactant, mainly functions to reduce surface tension and disperse pigments, and cannot replace the functions of zinc fatty acid salt in crosslinking and air drying, resulting in slower drying speed of the coating, reduced crosslinking degree, and further affecting the adhesion, hardness, and corrosion resistance, etc.

[0126] Excessive addition of aminoethyl aminopropyl polydimethylsiloxane (Comparative Example 6): Although this substance can improve the leveling property, low-temperature flexibility, and other properties of the coating, it is essentially an organic silicon polymer, and excessive addition will destroy the compatibility of the coating system. Excessive organic silicon segments will accumulate on the surface of the coating, hindering the crosslinking reaction between the composite hybrid resin and the methoxylated melamine formaldehyde resin, resulting in a decrease in crosslinking density. At the same time, the accumulation of organic silicon segments will also weaken the adhesion between the coating and the substrate, because it reduces the polarity matching degree between the coating surface and the substrate.

[0127] Absence of ethylene-vinyl acetate copolymer (Comparative Example 7): Ethylene-vinyl acetate copolymer has good flexibility and polarity, and the ethylene segments in its molecular chain provide flexibility, and the vinyl acetate segments provide polar groups. In the composite hybrid resin, it can form intermolecular forces (such as hydrogen bonds, van der Waals forces) with other components, improving the flexibility of the resin and the wettability of the filler. After the absence of this component, the molecular chain segment movement ability of the coating at low temperature (low-temperature flexibility test) is weakened, and the internal stress cannot be effectively released, which is prone to cracking.

[0128] Absence of silane coupling agent KH-560 (Comparative Example 8): Silane coupling agent KH-560 is a key bridge connecting the resin and the substrate. After its absence, the resin and the substrate mainly rely on physical adsorption, which is far less firm than chemical bonds, and the coating is prone to fall off from the substrate surface, resulting in poor performance.

[0129] Comparative Example 9 does not add ethylene-vinyl acetate copolymer and silane coupling agent KH-560 at the same time, and Comparative Example 10 lacks the synergistic effect of ethylene-vinyl acetate copolymer and silane coupling agent KH-560, and the fusion of each component is poor, the reaction synthesis rate is reduced, and the performance is poor.

[0130] Polyester polyurethane prepolymer absence or substitution or increment (comparative example 11-comparative example 18): Polyester polyurethane prepolymers I and II introduce rigid urethane groups and flexible polyester segments into the complex hybrid resin, playing a role in adjusting the balance of hardness and flexibility of the resin. When one of them is absent or both are absent (comparative example 11-comparative example 13), the structural balance of the resin is destroyed, and both hardness and flexibility are affected. When the prepolymers are substituted or incremented (comparative example 14-comparative example 18), the composition and structure of the crosslinking network are changed, and too high a content will lead to too high a crosslinking density, uneven dispersion, insufficient emulsion dispersion fusion, poor compatibility, and difficulty in achieving good homogenization after dilution, affecting the performance of subsequent film formation.

[0131] In addition, VOC volatilization analysis: Comparative Example 1 and Comparative Example 3 contain VOC volatile solvents in the acrylic resin, and volatile substances containing additional curing agents. Comparative Example 2 and Comparative Example 4 contain VOC volatile solvents in the epoxy resin, and volatile substances containing additional curing agents, releasing benzene series and small molecule amines. Comparative Example 5 has no metal passivation effect, and the porosity of the coating increases, and the VOC penetration increases slightly. Comparative Example 6 releases a small amount of siloxane small molecules due to the self-polymerization of excess aminoethyl aminopropyl polydimethylsiloxane. Comparative Example 7 has no ethylene-vinyl acetate copolymer, resulting in a decrease in coating density, poor fusion of polar components, and accelerated solvent residue volatilization. Comparative Example 8 has no silane coupling agent, poor filler-resin interface bonding, increased porosity, and increased VOC release. Comparative Example 9 lacks both ethylene-vinyl acetate copolymer and silane coupling agent, resulting in a loose coating structure and a significant increase in VOC release. Comparative Example 10 replaces the ethylene-vinyl acetate copolymer with a silane coupling agent, resulting in poor fusion of polar components and insufficient flexibility, but the interface bonding is improved, partially offsetting the increase in VOC. Comparative Example 11 lacks Prepolymer I, resulting in a decrease in crosslinking density and a slight increase in unreacted monomer residue. Comparative Example 12 lacks Prepolymer II, resulting in a slight increase in unreacted monomer residue and a decrease in flexibility, but the crosslinking degree is still high and the VOC release is slightly lower. Comparative Example 13 lacks both Prepolymers I and II, resulting in a poor crosslinking network and a significant increase in solvent and monomer residue. Comparative Example 14 and Comparative Example 15 exchange Prepolymers I and II, resulting in similar crosslinking degrees and VOC releases close to those of Example 1. Comparative Example 16-Comparative Example 18 have excessive Prepolymer I, resulting in high viscosity, uneven dispersion, and a slight increase in residue.

Claims

1. An ultra-low VOC baking-type quick-drying coating, characterized in that, The coating comprises the following raw materials in parts by weight: 45-50 parts of composite hybrid resin, 15-20 parts of methylated melamine-formaldehyde resin, 5-7 parts of neopentyl glycol diglycidyl ether, 3-5 parts of trimethylolpropane triacrylate, 8-10 parts of composite filler, 1-1.5 parts of zinc fatty acid, 0.5-0.8 parts of fumed silica, 0.5-0.8 parts of silane coupling agent KH-560, 1-1.5 parts of sodium polyacrylate dispersant, 0.1-0.3 parts of polyether-modified silicone defoamer, 2-3 parts of aminoethylaminopropyl polydimethylsiloxane, 0.6-1 part of fluorocarbon-modified polyether leveling agent, with the balance being deionized water. The coating viscosity is 1500 mPa·s to 2000 mPa·s. The preparation method of the composite hybrid resin includes: under nitrogen protection, mixing 20-25 parts by mass of isophthalic acid, 10-15 parts by mass of adipic acid, 15-20 parts by mass of neopentyl glycol, 5-8 parts by mass of propylene glycol, 10-15 parts by mass of propylene glycol butyl ether, 15-20 parts by mass of dimethyl carbonate, 10-12 parts by mass of dipropylene glycol butyl ether, and 0.2-0.3 parts by mass of tetrabutyl titanate, and refluxing at 180℃-200℃. Water generated during the reaction is collected using a water separator. When the acid value of the reaction system drops to 5 mg KOH / g-7 mg KOH / g, the temperature is lowered. At 70℃~80℃, 8~10 parts of methyl methacrylate, 6~8 parts of butyl acrylate, 4~6 parts of trimethylolpropane triacrylate, 3~8 parts of ethylene-vinyl acetate copolymer, 5~8 parts of polyester-type polyurethane prepolymer I, 3~5 parts of polyester-type polyurethane prepolymer II and 1~2 parts of silane coupling agent KH-560 are added and mixed evenly. Then, 0.8 parts~1.2 parts of benzoyl peroxide are added and the mixture is refluxed at 130℃~140℃ for 4h~5h. Dimethyl carbonate is removed by vacuum distillation and impurities are removed by sieve filtration to obtain composite hybrid resin. The polyester-type polyurethane prepolymer I is polyester-type polyurethane prepolymer T80; the polyester-type polyurethane prepolymer II is polyester-type polyurethane prepolymer T100.

2. The ultra-low VOC baking-type fast-drying coating according to claim 1, characterized in that, The benzoyl peroxide was diluted with 10 to 15 times its mass of dipropylene glycol butyl ether before being added, and divided into 3 to 4 volume portions. One volume portion was added every 30 to 40 minutes.

3. The ultra-low VOC baking-type fast-drying coating according to claim 1, characterized in that, The nitrogen protection is a slightly positive pressure nitrogen protection of 0.02MPa to 0.05MPa; the temperature of the vacuum distillation is 50℃ to 60℃; and the mesh size of the sieve is 150 mesh to 200 mesh.

4. The ultra-low VOC baking-type fast-drying coating according to claim 1, characterized in that, The fumed silica has a D90 particle size of less than 15 μm.

5. The ultra-low VOC baking-type quick-drying coating according to claim 1, characterized in that, The mass ratio of the components of the composite filler is mica powder: modified barium sulfate = (3-4): (7-9).

6. The ultra-low VOC baking-type quick-drying coating according to claim 5, characterized in that, The mica powder and modified barium sulfate have a D90 particle size of less than 15 μm.

7. The method for preparing an ultra-low VOC baking-type fast-drying coating according to claim 1, characterized in that, Includes the following steps: S1: Mix the composite hybrid resin, neopentyl glycol diglycidyl ether and 10 to 15 parts of deionized water evenly according to the mass fraction, then add sodium polyacrylate dispersant, fumed silica and composite filler in sequence, mix and disperse evenly to form a homogeneous base material; S2: Add methylated melamine-formaldehyde resin and zinc fatty acid to the homogeneous base material in parts by mass, mix evenly, and then grind it to a fineness of ≤15μm using a sand mill to obtain the ground material. S3: According to the mass fractions, add trimethylolpropane triacrylate, silane coupling agent KH-560, polyether modified silicone defoamer, aminoethylaminopropyl polydimethylsiloxane and fluorocarbon modified polyether leveling agent to the ground material in sequence, stir at low speed, adjust the viscosity of the coating to 1500mPa·s~2000mPa·s with deionized water, filter through a sieve, and take the filtrate to obtain the coating.

8. The method for preparing an ultra-low VOC baking-type fast-drying coating according to claim 7, characterized in that, The low-speed stirring is performed at 300 rpm to 350 rpm for 20 to 30 minutes; the mesh size of the sieve is 150 to 200 mesh.

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