Environmentally friendly solvent-free coating composition for metal surfaces and preparation method thereof

Abstract

The present invention belongs to the technical field of coatings, and provides an environmentally friendly solvent-free coating composition for metal surfaces and a preparation method thereof. Through the synergistic effect of fluoropolymers, fluorinated polyesters and modified polyurethanes, the coating composition improves the anti-corrosion performance and environmental stability of the coating. First, a fluoropolymer is prepared by reacting perfluoromethyl vinyl ether with triethanolamine under the action of a catalyst, and its three-dimensional cross-linked network structure imparts hydrophobicity and chemical inertness to the coating; secondly, a fluorinated polyester is prepared by free radical polymerization, and the perfluorinated chain segments reduce the surface energy; finally, a modified polyurethane is prepared by using polycaprolactone diol, mono-terminal dihydroxy polydimethylsiloxane, etc., and its siloxane chain segments reduce the surface energy, and the thioether bonds improve the antioxidant performance. This coating composition exhibits excellent waterproof, antioxidant and chemical corrosion resistance capabilities, and at the same time has excellent mechanical properties and adhesion, and is suitable for protecting metal substrates in long-term harsh environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and relates to an environmentally friendly solvent-free coating composition for metal surfaces and a preparation method thereof. Background Art

[0002] Metal materials are widely used in fields such as construction, transportation, and machinery. However, due to their easy oxidation and corrosion, the development of effective anti-corrosion coatings is of great significance for extending the service life of metal products and reducing maintenance costs. Traditional anti-corrosion coatings mainly include solvent-based coatings. Since such coatings contain volatile organic compounds (VOCs), they are released into the air during the coating process, causing environmental pollution and health risks. Solvent-free coatings, because they do not contain organic solvents, reduce the impact on the environment and become an ideal choice. Solvent-free coatings are cured by physical or chemical methods and have excellent adhesion, corrosion resistance, and weather resistance, and are suitable for various metal surfaces. Chinese Patent with the authorized announcement number CN103421420B discloses a solvent-free polyurethane weather-resistant anti-corrosion coating for storage tanks. The film-forming resin in its A component has poor weather resistance; and when reacting with a polyisocyanate polymer curing agent, the reaction rate is slow, and a curing accelerator needs to be added, otherwise the cured coating contains more bubbles. Therefore, it is necessary to develop a new type of environmentally friendly solvent-free coating composition to provide excellent anti-corrosion effects for metal surfaces. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an environmentally friendly solvent-free coating composition for metal surfaces and a preparation method thereof. A fluoropolymer is prepared by reacting perfluoromethyl vinyl ether with triethanolamine under the action of a catalyst, and its three-dimensional cross-linked network structure endows the coating with hydrophobicity and chemical inertness; fluorinated polyacrylate is prepared by free radical polymerization, and the perfluorinated chain segments reduce the surface energy; modified polyurethane is prepared by polycaprolactone diol, mono-terminal dihydroxy polydimethylsiloxane, etc., and its siloxane chain segments reduce the surface energy, so as to meet the actual production needs.

[0004] To achieve this purpose, the present invention adopts the following technical solutions:

[0005] In the first aspect, the present invention provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces, and the preparation method includes:

[0006] Step S1, mixing perfluoromethyl vinyl ether with triethanolamine, adding a catalyst, heating to a first temperature under a N2 atmosphere for sufficient reaction, and after the reaction is completed, cooling to room temperature, washing, and then drying under vacuum at a second temperature to obtain a fluoropolymer;

[0007] Step S2: Mix acrylate, perfluorobutyl methacrylate, benzyl methacrylate and 2-hydroxyethyl acrylate, add methyl ethyl ketone thereto, stir evenly at the first stirring speed, add di-tert-butyl peroxide, heat to the second temperature under N2 atmosphere and continue the reaction, then add di-tert-butyl peroxide and continue the reaction. After the reaction is completed, rotary evaporation is performed to obtain fluorinated polyacrylate;

[0008] Step S3: Mix polycaprolactone diol, mono-terminal dihydroxy polydimethylsiloxane, glycerol and isophorone diisocyanate, heat to the second temperature under N2 atmosphere and continue the reaction, then add 3,3'-dithiobispropionic acid and continue the reaction, then add 1,6-hexanediol, continuously stir and react, adjust the temperature to the third temperature, and then add 3-aminopropyltrimethoxysilane and stir to react to generate modified polyurethane;

[0009] Step S4: Mix the modified polyurethane, fluoropolymer, fluorinated polyacrylate and crosslinking agent evenly, add polyethylene glycol diglycidyl ether and dibutyltin dilaurate, and stir evenly to obtain an environmentally friendly solvent-free coating composition for metal surfaces.

[0010] Perfluoromethyl vinyl ether is a fluorinated unsaturated compound, whose structure contains a carbon-carbon double bond and an ether group. Due to the strong electron-withdrawing effect of the perfluoro part on the perfluoromethyl vinyl ether molecule, the electron cloud density of the double bond is greatly reduced, making the double bond exhibit obvious electrophilic characteristics. This characteristic makes perfluoromethyl vinyl ether more likely to accept the attack of nucleophiles (such as triethanolamine) in the reaction. Triethanolamine is a multi-functional group compound, containing three hydroxyl groups in its molecule. The lone pair electrons on its oxygen atom have strong nucleophilicity. In addition, the molecular structure of triethanolamine has a certain flexibility, which helps it connect with multiple perfluoromethyl vinyl ether molecules in the reaction, thus forming a crosslinked three-dimensional network structure. Under heating conditions, the hydroxyl group in the triethanolamine molecule attacks the double bond of perfluoromethyl vinyl ether through the lone pair electrons on its oxygen atom. This nucleophilic addition reaction causes the double bond to break and generates a new carbon-oxygen bond and a new carbon-hydrogen bond. Each triethanolamine molecule contains three hydroxyl groups, so it can react with multiple perfluoromethyl vinyl ether molecules, thus forming a highly crosslinked three-dimensional network structure through multi-point connection. This crosslinking behavior significantly enhances the mechanical properties and chemical stability of the polymer. The crosslinked three-dimensional network structure not only improves the strength and toughness of the material, but also significantly reduces the penetration rate of external corrosive media (such as moisture, oxygen, chloride ions, etc.) in the material, thus forming an effective physical barrier on the surface of the substrate.

[0011] A large number of fluorine-containing groups in fluoropolymers greatly reduce the surface free energy of the material. Low-surface-energy materials have extremely strong hydrophobicity and can effectively repel water molecules, thereby reducing the adhesion of water on the coating surface. The hydrophobic property not only prevents the accumulation of water on the substrate surface but also reduces the infiltration rate of corrosive ions (such as chloride ions and sulfate ions) carried by water, thus reducing the possibility of electrochemical corrosion. At the same time, the bond dissociation energy of the carbon-fluorine bond in fluoropolymers is relatively high and is very difficult to be destroyed by chemical substances. This chemical inertness enables the coating to remain stable in corrosive chemical environments such as strong acids, strong bases, and oxidants. The perfluorinated chain segment structure of fluoropolymers also has extremely strong ultraviolet radiation resistance, which can avoid aging and degradation caused by long-term exposure to sunlight. The highly cross-linked polymer structure endows the material with excellent mechanical properties, including high strength, high toughness, and good crack resistance. These mechanical properties make the coating less likely to crack or peel when subjected to external mechanical stresses (such as impact and friction). The integrity of the coating is one of the key factors for anti-corrosion performance. Any crack or peel will significantly increase the penetration risk of corrosive media. Therefore, the improvement of mechanical properties also indirectly enhances the anti-corrosion performance of the coating.

[0012] Polycaprolactone diol is a bifunctional compound with flexible chain segments and contains multiple hydroxyl active sites in its molecule. Polycaprolactone diol provides the flexible chain segments of polyurethane, endowing the material with excellent toughness and elasticity. In addition, its linear structure helps to form a uniform polyurethane network, which is suitable for constructing a dense coating. Mono-terminal dihydroxy polydimethylsiloxane is a low-surface-energy silicone compound, and its chain segments contain Si−O−Si bonds. The introduction of polydimethylsiloxane significantly reduces the surface energy of the coating, endowing the material with excellent hydrophobicity and weather resistance. At the same time, its hydroxyl groups can undergo chemical reactions with isocyanates and be incorporated into the polyurethane system. Glycerol is a small-molecule trifunctional compound and contains three hydroxyl groups in its molecule. The polyhydroxyl structure of glycerol can provide additional cross-linking points, making the polyurethane network denser and improving the mechanical properties and anti-permeability of the coating. 3,3'-Dithiobis(propionic acid) contains two mercapto groups, which can undergo chemical reactions with isocyanate groups to form thioether bonds. Thioether bonds have excellent antioxidant properties and can effectively inhibit the oxidation reaction on the surface of metal substrates and delay the corrosion process. 3-Aminopropyltrimethoxysilane contains both amino and methoxysilyl groups in its molecule. The amino group can react with isocyanate, while the methoxysilyl group undergoes hydrolysis in the presence of water to generate silanol, and then forms siloxane bonds through a condensation reaction. This chemical structure enhances the adhesion and weather resistance of the coating.

[0013] Sulfide bonds can effectively capture free radicals, thereby preventing the chain extension of corrosive oxidation reactions. This capture mechanism can reduce the formation rate of oxides on the surface of the metal substrate and delay the occurrence of the corrosion process. In addition, the chemical stability of sulfide bonds enables them to play a role in high-temperature, humid, and strongly oxidizing environments for a long time, thereby significantly improving the durability of the coating. The introduction of a single-terminal dihydroxy polydimethylsiloxane segment significantly reduces the surface energy of the coating, making it exhibit excellent hydrophobicity. This hydrophobic property can effectively repel water molecules, reduce the attachment of water on the coating surface, and lower the penetration rate of corrosive media. At the same time, the dense cross-linked network of polyurethane enhances the barrier effect of the coating, thereby effectively preventing the penetration of corrosive media and further protecting the metal substrate. The flexible segments of polyurethane endow the coating with excellent toughness and elasticity, enabling it to withstand mechanical stress. The multi-hydroxy structure of glycerol further enhances the mechanical strength of the coating by increasing the cross-linking points. The chemical inertness of silicon-oxygen bonds and C-F bonds enhances the stability of the coating in chemical environments such as acids, alkalis, and oxidants.

[0014] As a preferred technical solution of the present invention, in step S1, the mass ratio of perfluoromethyl vinyl ether, triethanolamine, and 1,4-diazacycloheptane is (30-50):(90-100):(4-6).

[0015] In some alternative examples, the first temperature is 100-110 °C, for example, it can be 100 °C, 101 °C, 102 °C, 103 °C, 104 °C, 105 °C, 106 °C, 107 °C, 108 °C, 109 °C, or 110 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0016] In some alternative examples, the reaction time at the first temperature is 6-8 h, for example, it can be 6.0 h, 6.2 h, 6.4 h, 6.6 h, 6.8 h, 7.0 h, 7.2 h, 7.4 h, 7.6 h, 7.8 h, or 8.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0017] In some alternative examples, the second temperature is 40-50 °C, for example, it can be 40 °C, 41 °C, 42 °C, 43 °C, 44 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, or 50 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0018] In some alternative examples, the time for the first temperature vacuum drying is 8 - 10 h. For example, it can be 8.0 h, 8.2 h, 8.4 h, 8.6 h, 8.8 h, 9.0 h, 9.2 h, 9.4 h, 9.6 h, 9.8 h or 10 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0019] As a preferred technical solution of the present invention, in step S2, the mass ratio of the acrylate, perfluorobutyl methacrylate, benzyl methacrylate, 2 - hydroxyethyl acrylate, methyl ethyl ketone, di - tert - butyl peroxide and the additionally added di - tert - butyl peroxide is (30 - 40):(60 - 70):(5 - 10):(20 - 30):(40 - 50):(5 - 6):(2 - 3).

[0020] In some alternative examples, the first stirring speed is 300 - 400 rpm. For example, it can be 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm or 400 rpm. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0021] In some alternative examples, the second temperature is 80 - 90 °C. For example, it can be 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C or 90 °C. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0022] In some alternative examples, the reaction time at the second temperature is 2 - 3 h. For example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] In some alternative examples, the reaction time for the additionally added di - tert - butyl peroxide is 5 - 6 h. For example, it can be 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h or 6.0 h. However, it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] As a preferred technical solution of the present invention, in step S3, the mass ratio of the polycaprolactone diol, mono-terminal dihydroxy polydimethylsiloxane, glycerol, isophorone diisocyanate, 3,3'-dithiobispropionic acid, 1,6-hexanediol to 3-aminopropyltrimethoxysilane is (30-40):(5-10):(10-20):(50-60):(4-7):(20-30):(60-70).

[0025] In some alternative examples, the second temperature is 80-90 °C, for example, it can be 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C or 90 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] In some alternative examples, the reaction time at the second temperature is 1-2 h, for example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0027] In some alternative examples, the reaction time for adding 3,3'-dithiobispropionic acid is 1-2 h, for example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] In some alternative examples, the reaction time for adding 1,6-hexanediol is 2-3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] In some alternative examples, the third temperature is 70-80 °C, for example, it can be 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C or 80 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] In some alternative examples, the reaction time for adding 3-aminopropyltrimethoxysilane is 2 - 3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but it is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] As a preferred technical solution of the present invention, in step S4, the mass ratio of the modified polyurethane, fluoropolymer, crosslinking agent, fluorinated polyacrylate, polyethylene glycol diglycidyl ether to dibutyltin dilaurate is (70 - 90) : (20 - 30) : (5 - 8) : (20 - 30) : (5 - 10) : (3 - 5).

[0032] In some alternative examples, the crosslinking agent is 3-(2-aminoethylamino)propyltrimethoxysilane.

[0033] In the second aspect, there is provided an environment-friendly solvent-free coating composition for metal surfaces obtained by using the preparation method described in the first aspect.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention adopts a solvent-free formulation, significantly improving the environmental friendliness of the coating. Currently, many anti-corrosion coatings still rely on solvent-based formulations, and these solvents not only cause pollution of volatile organic compounds to the environment but also pose a potential threat to human health. The solvent-free system not only reduces environmental pollution but also improves the safety of the coating, meeting the requirements of green chemistry and sustainable development; (2) The hydrophobicity and chemical stability of the fluoropolymer can effectively improve the corrosion resistance of the coating. Compared with traditional anti-corrosion coatings, the strong electronegativity of fluorine atoms and their stability with the carbon chain endow the coating with durability in acidic, alkaline, and high-humidity environments; (3) By means of various chemical modification methods, the polyurethane-based coating system is optimized. Using raw materials such as polycaprolactone diol, glycerol, and isophorone diisocyanate, a polyurethane network structure with high toughness and weather resistance is formed through crosslinking reactions. This modification not only improves the mechanical properties of the coating but also effectively enhances its chemical corrosion resistance and thermal stability, and the polyurethane-based coating can provide a long protection period. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of a preparation method of an environment-friendly solvent-free coating composition for metal surfaces provided by Embodiments 1 - 6 of the present invention;

[0036] Figure 2 It is a SEM image of the coating composition prepared in Example 1 of the present invention;

[0037] Figure 3 It is the contact angle between the coating composition prepared in Example 1 of the present invention and water. Detailed implementation manners

[0038] The technical solutions of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific implementation manners of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary and should not be construed as limiting the implementation manners of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims of this application and its specification, and these technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0039] The chemical reagents used in the embodiments and comparative examples of the present invention are all commercially available products, and their brand names, specifications and manufacturer information are as follows:

[0040] Perfluoromethyl vinyl ether, purity ≥ 99%, Tianmen Hengchang Chemical Co., Ltd.;

[0041] Triethanolamine, purity ≥ 99%, Henan Anno Chemical Technology Co., Ltd.;

[0042] 1,4-Diazacycloheptane, purity ≥ 99%, Guangdong Wengjiang Chemical Reagent Co., Ltd.;

[0043] N2, purity ≥ 99%, Nanjing Special Gas Factory Co., Ltd.;

[0044] Acrylate, purity ≥ 99%, Shandong Derui High Polymer Materials Co., Ltd.;

[0045] Perfluorobutyl methacrylate, purity ≥ 98%, Fuxin Ruifeng Fluorochemical Co., Ltd.;

[0046] Benzyl methacrylate, purity ≥ 98%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0047] 2-Hydroxyethyl acrylate, purity ≥ 99%, Heze Changshengyuan Technology Co., Ltd.;

[0048] Methyl ethyl ketone, purity ≥ 99%, Wuxi Tensheng Chemical Co., Ltd.;

[0049] Di-tert-butyl peroxide, purity ≥ 98%, Jiangsu Qinrui Chemical Co., Ltd.;

[0050] Polycaprolactone diol, purity ≥ 99%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0051] Mono-terminal dihydroxy polydimethylsiloxane, purity ≥ 99%, Merck Group, Darmstadt, Germany;

[0052] Glycerol, purity ≥ 98%, Nanjing Yongdu Chemical Co., Ltd.;

[0053] Isophorone diisocyanate, purity ≥ 99%, Xiamen Greenda Chemical Co., Ltd.;

[0054] 3,3'-Dithiodipropionic acid, purity ≥ 99%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0055] 1,6-Hexanediol, purity ≥ 99%, Zhejiang Boju New Materials Co., Ltd.;

[0056] 3-Aminopropyltrimethoxysilane, purity ≥ 97%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0057] 3-(2-Aminoethylamino)propyltrimethoxysilane, purity ≥ 95%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0058] Polyethylene glycol glycidyl ether, purity ≥ 99%, Liaoning Kelong Fine Chemical Co., Ltd.;

[0059] Dibutyltin dilaurate, purity ≥ 99%, Changzhou Yurong Chemical Co., Ltd.;

[0060] Other raw materials can be purchased on the market.

[0061] Example 1

[0062] This example provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces, as Figure 1 shown, the preparation method specifically includes the following steps:

[0063] Step S1, Mix 39 g of perfluoromethyl vinyl ether with 92 g of triethanolamine, add 4.5 g of 1,4-diazacycloheptane, and under a N2 atmosphere, heat to 102 °C and react fully for 6.5 h. After the reaction is completed, cool to room temperature, wash, and then place in a vacuum dryer at 42 °C for 9 h to obtain a fluoropolymer;

[0064] Step S2, Mix 31 g of acrylate, 65 g of perfluorobutyl methacrylate, 6.3 g of benzyl methacrylate, and 25 g of 2-hydroxyethyl acrylate, then add 42 g of butanone. After stirring evenly at a speed of 330 rpm, add 5.3 g of di-tert-butyl peroxide, and under a N2 atmosphere, heat to 84 °C and react continuously for 2.5 h. Then add 2.5 g of di-tert-butyl peroxide and continue to react for 5.3 h. After the reaction is completed, perform rotary evaporation to obtain a fluorinated polyacrylate;

[0065] Step S3: Mix 32 g of polycaprolactone diol, 6.7 g of mono-terminal dihydroxy polydimethylsiloxane, 12 g of glycerol, and 54 g of isophorone diisocyanate. Heat the mixture to 85 °C in an N2 atmosphere and react for 1.5 h. Then add 5.2 g of 3,3'-dithiobispropionic acid and continue to react for 1.3 h. Next, add 23 g of 1,6-hexanediol and continuously stir and react for 2.5 h. Adjust the temperature to 73 °C, then add 64 g of 3-aminopropyltrimethoxysilane and stir and react for 2.3 h to produce a modified polyurethane.

[0066] Step S4: Mix 73 g of the modified polyurethane, 23 g of the fluoropolymer, 22 g of the fluorinated polyacrylate, and 45 g of 3-(2-aminoethylamino)propyltrimethoxysilane uniformly. Then add 6 g of polyethylene glycol diglycidyl ether and 3.8 g of dibutyltin dilaurate, and stir evenly to obtain an environmentally friendly solvent-free coating composition for metal surfaces.

[0067] Figure 2 SEM image of the coating composition prepared in this example. The coating presents a smooth and dense surface with a low porosity and no obvious cracks or bubbles on the surface. Figure 3 Contact angle between the coating composition prepared in this example and water. The contact angle is 130°, indicating that the coating has good hydrophobic effect.

[0068] Example 2

[0069] This example provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces, as Figure 1 shown. The preparation method specifically includes the following steps:

[0070] Step S1: Mix 33 g of perfluoromethyl vinyl ether and 95 g of triethanolamine, add 5.2 g of 1,4-diazacycloheptane. Under an N2 atmosphere, heat to 104 °C and react fully for 7.2 h. After the reaction, cool to room temperature, wash, and then place in a vacuum dryer at 46 °C for 8.5 h to obtain a fluoropolymer.

[0071] Step S2: Mix 35 g of acrylate, 67 g of perfluorobutyl methacrylate, 8 g of benzyl methacrylate, and 27 g of 2-hydroxyethyl acrylate, then add 45 g of butanone. Stir evenly at a speed of 360 rpm, add 5.7 g of di-tert-butyl peroxide, heat to 88 °C in an N2 atmosphere and react for 2.2 h. Then add 2.2 g of di-tert-butyl peroxide and continue to react for 5.7 h. After the reaction, perform rotary evaporation to obtain a fluorinated polyacrylate.

[0072] Step S3: Mix 37 g of polycaprolactone diol, 8.2 g of mono-terminal dihydroxy polydimethylsiloxane, 18 g of glycerol, and 58 g of isophorone diisocyanate. Heat the mixture to 82 °C under a nitrogen atmosphere and react for 1.9 h. Then add 6.5 g of 3,3'-dithiobispropionic acid and continue to react for 1.7 h. Next, add 27 g of 1,6-hexanediol and continuously stir and react for 2.7 h. Adjust the temperature to 78 °C, then add 68 g of 3-aminopropyltrimethoxysilane and stir and react for 2.7 h to produce a modified polyurethane.

[0073] Step S4: Mix 81 g of the modified polyurethane, 28 g of the fluoropolymer, 28 g of fluorinated polyacrylate, and 42 g of 3-(2-aminoethylamino)propyltrimethoxysilane uniformly. Then add 9.2 g of polyethylene glycol diglycidyl ether and 4.2 g of dibutyltin dilaurate, and stir evenly to obtain an environmentally friendly solvent-free coating composition for metal surfaces.

[0074] Example 3

[0075] This example provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces. As Figure 1 shown, the preparation method specifically includes the following steps:

[0076] Step S1: Mix 41 g of perfluoromethyl vinyl ether and 97 g of triethanolamine, add 4.3 g of 1,4-diazacycloheptane. Under a nitrogen atmosphere, heat to 108 °C and fully react for 6.8 h. After the reaction ends, cool to room temperature, wash, and then place in a vacuum dryer at 45 °C for 9.3 h to obtain a fluoropolymer.

[0077] Step S2: Mix 33 g of acrylate, 62 g of perfluorobutyl methacrylate, 7.5 g of benzyl methacrylate, and 22 g of 2-hydroxyethyl acrylate, then add 44 g of butanone. Stir evenly at a speed of 310 rpm, add 5.2 g of di-tert-butyl peroxide, heat to 82 °C under a nitrogen atmosphere and react for 2.7 h. Then add 2.7 g of di-tert-butyl peroxide and continue to react for 5.2 h. After the reaction ends, perform rotary evaporation to obtain a fluorinated polyacrylate.

[0078] Step S3: Mix 36 g of polycaprolactone diol, 7.5 g of mono-terminal dihydroxy polydimethylsiloxane, 15 g of glycerol, and 58 g of isophorone diisocyanate. Heat the mixture to 88 °C under a nitrogen atmosphere and react for 1.3 h. Then add 4.3 g of 3,3'-dithiobispropionic acid and continue to react for 1.5 h. Next, add 25 g of 1,6-hexanediol and continuously stir and react for 2.9 h. Adjust the temperature to 74 °C, then add 63 g of 3-aminopropyltrimethoxysilane and stir and react for 2.5 h to produce a modified polyurethane.

[0079] Step S4: After uniformly mixing 88 g of modified polyurethane, 26 g of fluoropolymer, 29 g of fluorinated polyacrylate and 48 g of 3-(2-aminoethylamino)propyltrimethoxysilane, add 7.5 g of polyethylene glycol diglycidyl ether and 4.6 g of dibutyltin dilaurate, and stir evenly to obtain an environmentally friendly solvent-free coating composition for metal surfaces.

[0080] Example 4

[0081] This example provides a preparation method for an environmentally friendly solvent-free coating composition for metal surfaces, as Figure 1 shown, the preparation method specifically includes the following steps:

[0082] Step S1: Mix 35 g of perfluoromethyl vinyl ether with 94 g of triethanolamine, add 5.8 g of 1,4-diazacycloheptane, heat to 103 °C under N2 atmosphere and react for 7.5 h. After the reaction, cool to room temperature, wash and then place in a vacuum dryer at 48 °C for 10 h to obtain a fluoropolymer.

[0083] Step S2: Mix 37 g of acrylate, 64 g of perfluorobutyl methacrylate, 6.8 g of benzyl methacrylate and 22 g of 2-hydroxyethyl acrylate, add 48 g of butanone, stir evenly at a speed of 350 rpm, then add 5.9 g of di-tert-butyl peroxide, heat to 89 °C under N2 atmosphere and react for 2.3 h, then add 2.3 g of di-tert-butyl peroxide and continue to react for 5.5 h. After the reaction, perform rotary evaporation to obtain fluorinated polyacrylate.

[0084] Step S3: Mix 33 g of polycaprolactone diol, 5.9 g of mono-terminal dihydroxypolydimethylsiloxane, 13 g of glycerol and 53 g of isophorone diisocyanate, heat to 84 °C under N2 atmosphere and react for 1.8 h), then add 6.1 g of 3,3'-dithiobispropionic acid and continue to react for 1.9 h, then add 29 g of 1,6-hexanediol and continuously stir and react for 2.3 h, adjust the temperature to 74 °C, then add 69 g of 3-aminopropyltrimethoxysilane and stir and react for 2.9 h to generate modified polyurethane.

[0085] Step S4: After uniformly mixing 78 g of modified polyurethane, 24 g of fluoropolymer, 24 g of fluorinated polyacrylate and 41 g of 3-(2-aminoethylamino)propyltrimethoxysilane, add 5.3 g of polyethylene glycol diglycidyl ether and 3.4 g of dibutyltin dilaurate, and stir evenly to obtain an environmentally friendly solvent-free coating composition for metal surfaces.

[0086] Example 5

[0087] This example provides a preparation method for an environmentally friendly solvent-free coating composition for metal surfaces, as Figure 1As shown, the preparation method specifically includes the following steps:

[0088] Step S1: Mix 46 g of perfluoromethyl vinyl ether with 91 g of triethanolamine, add 5.6 g of 1,4-diazacycloheptane, heat to 106 °C under a N2 atmosphere and react fully for 6.3 h. After the reaction ends, cool to room temperature, wash, and then place in a vacuum dryer at 41 °C for 8.2 h to obtain a fluoropolymer;

[0089] Step S2: Mix 38 g of acrylate, 69 g of perfluorobutyl methacrylate, 9 g of benzyl methacrylate, and 24 g of 2-hydroxyethyl acrylate, then add 41 g of methyl ethyl ketone. After stirring evenly at a speed of 370 rpm, add 5.5 g of di-tert-butyl peroxide, heat to 80 °C under a N2 atmosphere and react continuously for 2.9 h. Then add 2.9 g of di-tert-butyl peroxide and continue to react for 6.0 h. After the reaction ends, perform rotary evaporation to obtain a fluorinated polyacrylate;

[0090] Step S3: Mix 39 g of polycaprolactone diol, 6.3 g of mono-terminal dihydroxypolydimethylsiloxane, 17 g of glycerol, and 56 g of isophorone diisocyanate, heat to 81 °C under a N2 atmosphere and react continuously for 1.7 h. Then add 4.9 g of 3,3'-dithiobispropionic acid and continue to react for 1.2 h. Then add 24 g of 1,6-hexanediol and continuously stir and react for 2.2 h. Adjust the temperature to 79 °C, then add 61 g of 3-aminopropyltrimethoxysilane and stir and react for 2.6 h to produce a modified polyurethane;

[0091] Step S4: Mix 80 g of modified polyurethane, 29 g of fluoropolymer, 25 g of fluorinated polyacrylate, and 47 g of 3-(2-aminoethylamino)propyltrimethoxysilane evenly, then add 8 g of polyethylene glycol diglycidyl ether and 4.8 g of dibutyltin dilaurate, and stir evenly to obtain an environmentally friendly solvent-free coating composition for metal surfaces.

[0092] Example 6

[0093] This example provides a preparation method for an environmentally friendly solvent-free coating composition for metal surfaces, as Figure 1 shown, the preparation method specifically includes the following steps:

[0094] Step S1: Mix 44 g of perfluoromethyl vinyl ether with 98 g of triethanolamine, add 5.1 g of 1,4-diazacycloheptane, heat to 107 °C under a N2 atmosphere and react fully for 7.1 h. After the reaction ends, cool to room temperature, wash, and then place in a vacuum dryer at 49 °C for 8.9 h to obtain a fluoropolymer;

[0095] Step S2: Mix 36 g of acrylate, 68 g of perfluorobutyl methacrylate, 7.2 g of benzyl methacrylate, and 26.3 g of 2-hydroxyethyl acrylate, then add 49 g of methyl ethyl ketone. After stirring evenly at a speed of 340 rpm, add 5.8 g of di-tert-butyl peroxide. Heat to 83 °C under a nitrogen atmosphere and react for 2.6 h. Then add 2.8 g of di-tert-butyl peroxide and continue to react for 5.4 h. After the reaction is completed, rotary evaporation is carried out to obtain fluorinated polyacrylate;

[0096] Step S3: Mix 38 g of polycaprolactone diol, 7.9 g of mono-terminal dihydroxy polydimethylsiloxane, 19.5 g of glycerol, and 57 g of isophorone diisocyanate. Heat to 83 °C under a nitrogen atmosphere and react for 1.4 h. Then add 6.2 g of 3,3'-dithiobispropionic acid and continue to react for 1.8 h. Then add 28 g of 1,6-hexanediol and continuously stir and react for 2.6 h. Adjust the temperature to 77 °C, then add 66 g of 3-aminopropyltrimethoxysilane and stir and react for 2.4 h to generate modified polyurethane;

[0097] Step S4: Mix 85 g of modified polyurethane, 27 g of fluoropolymer, 26 g of fluorinated polyacrylate, and 46 g of 3-(2-aminoethylamino)propyltrimethoxysilane evenly, then add 9 g of polyethylene glycol diglycidyl ether and 3.9 g of dibutyltin dilaurate, and stir evenly to obtain an environmentally friendly solvent-free coating composition for metal surfaces.

[0098] Comparative Example 1

[0099] This comparative example provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces. The difference from Example 1 is that the mass fraction of polycaprolactone diol in Step S3 is adjusted to 47 g, which is 15 g more than that in Example 1. The increased mass is proportionally deducted from mono-terminal dihydroxy polydimethylsiloxane, glycerol, isophorone diisocyanate, 3,3'-dithiobispropionic acid, 1,6-hexanediol, and 3-aminopropyltrimethoxysilane, so that the mass ratio between other components except polycaprolactone diol remains unchanged. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0100] Comparative Example 2

[0101] This comparative example provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces. The difference from Example 1 is that in step S3, the mass portion of polycaprolactone diol is adjusted to 17 g, which is 15 g less than that in Example 1. The reduced mass is supplemented proportionally to mono-terminal dihydroxy polydimethylsiloxane, glycerol, isophorone diisocyanate, 3,3'-dithiodipropionic acid, 1,6-hexanediol, and 3-aminopropyltrimethoxysilane, so that the mass ratio between other components except polycaprolactone diol remains unchanged. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0102] Comparative Example 3

[0103] This comparative example provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces. The difference from Example 1 is that in step S3, the mass portion of 3-aminopropyltrimethoxysilane is adjusted to 84 g, which is 20 g more than that in Example 1. The increased mass is deducted proportionally from polycaprolactone diol, mono-terminal dihydroxy polydimethylsiloxane, glycerol, isophorone diisocyanate, 3,3'-dithiodipropionic acid, and 1,6-hexanediol, so that the mass ratio between other components except 3-aminopropyltrimethoxysilane remains unchanged. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0104] Comparative Example 4

[0105] This comparative example provides a preparation method of an environmentally friendly solvent-free coating composition for metal surfaces. The difference from Example 1 is that in step S3, the mass portion of 3-aminopropyltrimethoxysilane is adjusted to 44 g, which is 20 g less than that in Example 1. The reduced mass is supplemented proportionally to polycaprolactone diol, mono-terminal dihydroxy polydimethylsiloxane, glycerol, isophorone diisocyanate, 3,3'-dithiodipropionic acid, and 1,6-hexanediol, so that the mass ratio between other components except 3-aminopropyltrimethoxysilane remains unchanged. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0106] In the present invention, the test standards for the weather resistance of the prepared coating composition are GB / T 14522 - 2008; the test standards for adhesion are GB / T 9286 - 2021; the test standards for coating hardness are GB / T 6739 - 2022; the test standards for resistance to cyclic corrosion environment are GB / T 31588.1 - 2015. The test results are shown in Table 1.

[0107] Table 1 Test Results of Environmentally Friendly Solvent-Free Coating Compositions for Metal Surfaces Prepared in Examples 1 - 6 and Comparative Examples 1 - 4

[0108]

[0109] It can be obtained from the data in Table 1 that, compared with Example 1, the adhesion of Comparative Example 1 remains unchanged, while the hardness, weather resistance and cyclic corrosion resistance all decrease; the hardness and cyclic corrosion resistance of Comparative Example 2 remain unchanged, while the adhesion and weather resistance decrease. This is because in Comparative Example 1, the polycaprolactone diol is in excess. Polycaprolactone diol is a diol with a long-chain flexible structure. The proportion of flexible segments in the modified polyurethane chain increases significantly, the soft segment content of the coating increases, and the hardness of the coating decreases. The long-chain flexible structure can provide a certain stretchability for the coating, and the adhesion remains basically unchanged; a large number of ester groups in polycaprolactone diol may undergo oxidative degradation reactions under strong ultraviolet radiation, resulting in a decrease in weather resistance; due to the increase in the proportion of flexible segments, the number of ester groups relatively increases, making the coating more susceptible to chemical erosion. In Comparative Example 2, the polycaprolactone diol is insufficient, the flexible segments in the coating decrease, and the overall toughness of the coating decreases. At the bonding interface between the coating and the substrate, the proportion of rigid segments is relatively high, which may cause stress concentration on the substrate surface of the coating, thereby reducing the adhesion, and the hardness remains basically unchanged; the flexible segments in the polyurethane chain decrease, and the proportion of rigid segments relatively increases, resulting in the coating being more likely to crack under ultraviolet exposure; the proportion of rigid segments increases, and the crosslinking density of the coating increases. The coating with a high crosslinking density has a denser structure, which can effectively prevent the penetration of corrosive media.

[0110] It can be obtained from the data in Table 1 that, compared with Example 1, the adhesion of Comparative Example 3 remains unchanged, the hardness increases, the weather resistance decreases, and the cyclic corrosion resistance remains unchanged; the adhesion, hardness, weather resistance and cyclic corrosion resistance of Comparative Example 4 all decrease. This is because the amino group in the excessive 3-aminopropyltrimethoxysilane in Comparative Example 3 can form hydrogen bonds with the oxide layer on the surface of the metal substrate. At the same time, the silanol generated after hydrolysis of the methoxysilyl group can also form a chemical bond with the metal surface through a condensation reaction, ensuring the adhesion of the coating. The excessive 3-aminopropyltrimethoxysilane will increase the density of silicon-oxygen bonds. The strength and hardness of silicon-oxygen bonds are relatively high, so the hardness of the coating increases; the excessive 3-aminopropyltrimethoxysilane may cause some unreacted methoxysilyl groups to remain, resulting in hydrolysis of the coating during use, thus affecting the weather resistance; the excessive 3-aminopropyltrimethoxysilane increases the density of silicon-oxygen bonds in the coating, and silicon-oxygen bonds have high chemical inertness and can effectively resist the erosion of corrosive media. When the amount of 3-aminopropyltrimethoxysilane in Comparative Example 4 is insufficient, the number of amino groups and siloxy groups decreases, the chemical bonding force between the coating and the metal substrate decreases significantly, the adhesion decreases, the content of silicon-oxygen bonds is low, and the polyurethane coating is mainly composed of flexible segments, resulting in a decrease in the hardness of the coating; the density of silicon-oxygen bonds decreases, the network structure of the coating is not dense enough, and the weather resistance decreases; the density of silicon-oxygen bonds in the coating is low, the chemical inertness and compactness decrease, and the corrosive medium is more likely to penetrate into the interior of the coating, resulting in a decrease in cyclic corrosion resistance.

[0111] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing an environmentally friendly solvent-free coating composition for metal surfaces, characterized in that, The preparation method includes: Step S1: Mix perfluoromethyl vinyl ether with triethanolamine, add 1,4-diazepane, and heat and react under a nitrogen atmosphere to obtain a fluoropolymer. Step S2: Mix acrylate, perfluorobutyl methacrylate, benzyl methacrylate, and 2-hydroxyethyl acrylate, add methyl ethyl ketone and stir evenly, then add di-tert-butyl peroxide, heat and react under a nitrogen atmosphere, add di-tert-butyl peroxide again and continue to react. After the reaction is completed, rotary evaporation is carried out to obtain a fluorinated polyacrylate. Step S3: Mix polycaprolactone diol, mono-terminal dihydroxypolydimethylsiloxane, glycerol, and isophorone diisocyanate, heat and react under a nitrogen atmosphere, then add 3,3'-dithiodipropionic acid, 1,6-hexanediol, and 3-aminopropyltrimethoxysilane to generate a modified polyurethane. Step S4: Mix the modified polyurethane, fluoropolymer, fluorinated polyacrylate, and crosslinking agent evenly, add polyethylene glycol diglycidyl ether and dibutyltin dilaurate, and stir evenly to obtain an environment-friendly solvent-free coating composition for metal surfaces. The mass ratio of the polycaprolactone diol, mono-terminal dihydroxypolydimethylsiloxane, glycerol, isophorone diisocyanate, 3,3'-dithiodipropionic acid, 1,6-hexanediol, and 3-aminopropyltrimethoxysilane is (30-40):(5-10):(10-20):(50-60):(4-7):(20-30):(60-70). The mass ratio of the modified polyurethane, fluoropolymer, crosslinking agent, fluorinated polyacrylate, polyethylene glycol diglycidyl ether, and dibutyltin dilaurate is (70-90):(20-30):(5-8):(20-30):(5-10):(3-5).

2. The preparation method of the environment-friendly solvent-free coating composition for metal surfaces according to claim 1, characterized in that, Step S1 The mass ratio of the perfluoromethyl vinyl ether, triethanolamine, and 1,4-diazepane is (30-50):(90-100):(4-6). The heating reaction time is 6-8 h.

3. The preparation method of the environment-friendly solvent-free coating composition for metal surfaces according to claim 1, characterized in that, Step S2 The mass ratio of the acrylate, perfluorobutyl methacrylate, benzyl methacrylate, 2-hydroxyethyl acrylate, methyl ethyl ketone, di-tert-butyl peroxide, and the added di-tert-butyl peroxide is (30-40):(60-70):(5-10):(20-30):(40-50):(5-6):(2-3).

4. The preparation method of the environment-friendly solvent-free coating composition for metal surfaces according to claim 1, characterized in that, Step S2 The reaction time for adding the added di-tert-butyl peroxide is 5-6 h.

5. The preparation method of the environment-friendly solvent-free coating composition for metal surfaces according to claim 1, characterized in that, Step S3 The reaction time for adding 3,3'-dithiodipropionic acid is 1-2 h.

6. The preparation method of the environment-friendly solvent-free coating composition for metal surfaces according to claim 1, characterized in that, Step S4 The crosslinking agent is 3-(2-aminoethylamino)propyltrimethoxysilane.

7. An environment-friendly solvent-free coating composition for metal surfaces obtained by the preparation method according to any one of claims 1-6.

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