Environment-friendly powder coating as well as preparation method and application thereof

Abstract

The invention discloses an environment-friendly powder coating as well as a preparation method and application thereof, belongs to the technical field of powder coating processing, and is used for solving the technical problem that the wear resistance, impact resistance and ultraviolet aging resistance of a powder coating in the prior art need to be further improved. The composite material comprises the following components in parts by weight: 70-80 parts of polyolefin resin, 15-25 parts of epoxy resin, 5-6 parts of a curing agent and 3-5 parts of an auxiliary additive, the polyolefin resin is prepared by reinforcing an unsaturated monomer through activated filler and olefin-terminated polysiloxane, and then the polyolefin resin is reinforced by the epoxy resin. According to the present invention, the wear resistance and the impact resistance of the paint film layer sample are effectively improved, the adhesion and the ultraviolet resistance of the paint film are improved, and the production process has low harm to the environment and the human health, and is environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of powder coating processing, and particularly relates to an environmentally friendly powder coating and its preparation method and application. Background Art

[0002] Powder coatings are solid powder synthetic resin coatings composed of solid resins, pigments, fillers, and additives. Different from ordinary solvent-based coatings and water-based coatings, their dispersion medium is air rather than solvents and water. With the tightening of global environmental protection policies and the promotion of the "dual carbon" goal, traditional solvent-based coatings are gradually replaced by environmentally friendly coatings due to their high volatile organic compound (VOCs) emissions and serious pollution.

[0003] The coating hardness and impact resistance of the existing powder coatings are poor, and scratches are easily generated under mechanical friction, resulting in a decline in the durability of mechanical equipment and making it difficult to meet the requirements of high-wear scenarios such as outdoor equipment and heavy-duty machinery. To improve the wear resistance of the material, fillers such as nano-silica and alumina are usually added to the powder coating. However, nano-fillers are prone to agglomeration, resulting in poor coating leveling and insufficient compatibility with the resin matrix, and are likely to fall off after long-term use. Moreover, the existing powder coatings formed have poor aging resistance. When used outdoors, they are easily affected by ultraviolet radiation, resulting in coating aging, coating discoloration, or powdering.

[0004] In view of the technical defects in this regard, a solution is now proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide an environmentally friendly powder coating and its preparation method and application, aiming to solve the technical problems that the wear resistance, impact resistance, and ultraviolet aging resistance of the existing powder coatings need to be further improved.

[0006] The purpose of the present invention can be achieved through the following technical solutions: An environmentally friendly powder coating comprises the following components by weight: 70 - 80 parts of polyolefin resin, 15 - 25 parts of epoxy resin, 5 - 6 parts of curing agent, and 3 - 5 parts of auxiliary additive; The preparation method of the polyolefin resin is as follows: Under the protection of inert gas, a solvent and an emulsifier are mixed and stirred, and an activated filler, an olefin-capped polysiloxane, glycidyl methacrylate, styrene, and butyl acrylate are added to the reaction system. After stirring and dispersing for 30 - 50 min, the temperature of the reaction system is raised to 70 - 80 °C, and an initiator solution is added dropwise to the reaction system. After the addition is completed, the reaction is carried out under insulation for 4 - 6 h, and then post-treatment is carried out to obtain the polyolefin resin.

[0007] The synthesis reaction formula of the polyolefin resin is:

[0008] In the formula: .

[0009] The synthesis reaction mechanism of the polyolefin resin is as follows: During the reaction process, the initiator decomposes to generate active free radicals. The active free radicals catalyze and activate the opening of the unsaturated double bonds on the filler, olefin-terminated polysiloxane, glycidyl methacrylate, styrene, and butyl acrylate molecules to form macromolecular free radicals, and then through random copolymerization, a multi-block copolymer sequence is formed to prepare the polyolefin resin.

[0010] Furthermore, the epoxy resin is bisphenol A epoxy resin E-12, the curing agent is polyetheramine, and the auxiliary additive is composed of a pigment, a leveling agent, a curing accelerator, and a slip agent in a weight ratio of 5:1.5:0.6:2. Among them, the pigment is a phthalocyanine pigment, the leveling agent is an acrylate leveling agent, the curing accelerator is 2-methylimidazole, and the slip agent is polypropylene wax.

[0011] Furthermore, the dosage ratio of the solvent, emulsifier, activated filler, olefin-terminated polysiloxane, glycidyl methacrylate, styrene, butyl acrylate, and initiator solution is 150 mL:4 g:5 - 7 g:10 - 15 g:4 - 6 g:2 - 3 g:5 - 6 g:10 mL. The solvent is composed of deionized water and absolute ethanol in a volume ratio of 2:1. The emulsifier is composed of sodium dodecylbenzenesulfonate, sodium oleate, and Tween-80 in a weight ratio of 5:3:2. The initiator solution is composed of azobisisobutyronitrile and deionized water in a ratio of 1 g:20 mL. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, suction filtration is carried out, the filter cake is washed 3 - 5 times with purified water and then dried by suction, the filter cake is transferred to an oven at 60 - 70 °C and dried to a constant weight to obtain the polyolefin resin.

[0012] Furthermore, the olefin-terminated polysiloxane is prepared by the following steps: A1. Under the protection of an inert gas, 3,5-ditert-butyl-4-hydroxybenzyl alcohol and tetrahydrofuran are mixed and stirred, the temperature of the reaction system is raised to 40 - 50 °C, 3-isocyanatopropylmethyldiethoxysilane is added to the reaction system, and the reaction is carried out at a constant temperature for 60 - 70 min, followed by post-treatment to obtain diethoxysilane-modified butylated hydroxytoluene; A2. D4, diethoxysilane-modified butylated hydroxytoluene, diphenyldiethoxysilane, and a catalyst are mixed and stirred. After the reaction system is sealed, the temperature of the reaction system is raised to 120 - 130 °C, and the reaction is carried out at a constant temperature for 3 - 4 h. Diallyltetramethyldisiloxane is added to the reaction system, and the reaction is carried out at a constant temperature for 2 - 3 h, followed by post-treatment to obtain the olefin-terminated polysiloxane.

[0013] The synthesis reaction formula of the olefin-capped polysiloxane is as follows:

[0014] In the formula: .

[0015] The synthesis reaction mechanism of the olefin-capped polysiloxane is as follows: During the reaction, the hydroxyl group of the 3,5-di-tert-butyl-4-hydroxybenzyl alcohol molecule undergoes a condensation reaction with the isocyanate group on the 3-isocyanatopropylmethyldiethoxysilane molecule to modify the diethoxysilane on the 3,5-di-tert-butyl-4-hydroxybenzyl alcohol molecule, and diethoxysilane-modified butylated hydroxytoluene is prepared. Under the action of a catalyst, while D4 undergoes ring-opening to form a siloxane chain, the siloxane bonds on the diethoxysilane-modified butylated hydroxytoluene and diphenyldiethoxysilane molecules hydrolyze to form silanol groups, and dehydration condensation occurs between the silanol groups to form a long polysiloxane chain. Diallyltetramethyldisiloxane hydrolyzes under the action of a catalyst to form an allylsilane modified with a single silanol group, which acts as a capping agent to condense with the silanols at both ends of the long polysiloxane chain to form an olefin double bond modification, and the olefin-capped polysiloxane is prepared.

[0016] Furthermore, in step A1, the dosage ratio of the 3,5-di-tert-butyl-4-hydroxybenzyl alcohol to the 3-isocyanatopropylmethyldiethoxysilane is 1 mol:1 mol, the dosage ratio of the 3,5-di-tert-butyl-4-hydroxybenzyl alcohol to tetrahydrofuran is 1 g:7 mL, and the post-treatment includes: after the reaction is completed, low-boiling substances are removed under reduced pressure to obtain diethoxysilane-modified butylated hydroxytoluene.

[0017] Furthermore, in step A2, the dosage ratio of D4, diethoxysilane-modified butylated hydroxytoluene, diphenyldiethoxysilane, the catalyst, and diallyltetramethyldisiloxane is 10 g:2 g:3 g:0.2 g:0.8 g, the catalyst is a 60-75 wt% sulfuric acid solution, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, purified water is added to the reaction system, and stirred for 20-30 min. A 0.5 mol / L sodium carbonate aqueous solution is added to the reaction system to adjust the system pH to 7, allowed to stand for liquid separation, the upper layer liquid is washed 3 times with purified water and then transferred to a rotary evaporator at a temperature of 80-90 °C, and low-boiling substances are removed under reduced pressure to obtain the olefin-capped polysiloxane.

[0018] Furthermore, the preparation method of the activated filler is: mixing nano-titanium dioxide, nano-silica, absolute ethanol, and KH-570, ultrasonically dispersing for 80-120 min, raising the temperature of the reaction system to 50-60 °C, adding a catalyst to the reaction system, holding the reaction for 40-60 min, and performing post-treatment to obtain the activated filler.

[0019] The synthesis reaction formula of the activated filler is as follows:

[0020] In the formula: is nano-titanium dioxide or nano-silicon dioxide particles.

[0021] The synthesis reaction mechanism of the activated filler is as follows: During the reaction process, the catalyst catalyzes the hydrolysis of the siloxane bond on the KH-570 molecule to form silanol, and the silanol bonds with the siloxane bond on the surface of the nano-silicon dioxide or nano-titanium dioxide particles to form an unsaturated double bond modification, and the activated filler is prepared.

[0022] Furthermore, the dosage ratio of the nano-titanium dioxide, nano-silicon dioxide, absolute ethanol, KH-570 and the catalyst is 2g:3g:30mL:1g:8mL. The catalyst is 2mol / L sodium hydroxide solution. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, suction filtration is carried out, the filter cake is washed with purified water until neutral and then dried by suction, the filter cake is transferred to a drying oven at 65-75 °C and dried to constant weight to obtain the activated filler.

[0023] A preparation method of an environment-friendly powder coating, the preparation method of the environment-friendly powder coating is: adding a polyolefin resin, an epoxy resin, a curing agent and an auxiliary additive into a high-speed crusher, crushing and passing through a 200-300 mesh sieve to obtain the powder coating.

[0024] An application of an environment-friendly powder coating, applying the powder coating prepared according to the preparation method of an environment-friendly powder coating to the surface coating of metal products.

[0025] The present invention has the following beneficial effects: The environment-friendly powder coating of the present invention, in a water-emulsified environment, promotes the polymerization of activated fillers, olefin-terminated polysiloxane, glycidyl methacrylate, styrene, and butyl acrylate through free radical polymerization to form a polyolefin resin. Then, it is enhanced with bisphenol A epoxy resin and cooperates with a curing agent and auxiliary additives to prepare the powder coating. During the preparation process, raw materials containing primary flammable solvents such as benzene, toluene, and ethylbenzene that can release a large amount of volatile organic compounds are avoided, reducing the harm to the environment and human health. The benzene ring and ether bond in the molecular structure of bisphenol A epoxy resin can effectively absorb the energy of ultraviolet rays and form a chemical bonding effect with the substrate surface, enhancing the adhesion and anti-ultraviolet performance of the coating. The saturated single-bond structure in the molecular chain of the polyolefin resin endows it with high chemical stability and mechanical strength. The polysiloxane enhances the flexibility of the powder coating. After the powder coating is cured, the polar groups in its coating can form intermolecular forces such as hydrogen bonds and van der Waals forces with the substrate surface, significantly enhancing the adhesion grade of the coating film. The flexibility of the powder coating helps the coating film to form a continuous and uniform coating on the substrate surface, increasing the contact area between the coating film and the substrate, thereby enhancing the adhesion grade. Moreover, the filler particles cooperate with the polyolefin to build a good wear-resistant enhancement system, improving the wear resistance of the powder coating film.

[0026] The environment-friendly powder coating of the present invention modifies the olefin double bond on the polysiloxane molecular chain. The olefin-terminated polysiloxane undergoes free radical copolymerization with the double bond in the polyolefin resin through the terminal olefin group to form an organic-inorganic hybrid crosslinked network, thereby significantly improving the hardness and anti-deformation ability of the coating. The polysiloxane chain segments are uniformly dispersed in the resin matrix, and the external force impact is dispersed through the Si-O bond, reducing local stress concentration and lowering the wear rate. The bond energy of the Si-O bond in the main chain of the polysiloxane is much higher than that of the C-C bond, and the Si-O bond is less sensitive to UV radiation. By introducing butylated hydroxytoluene as an ultraviolet absorber on the polysiloxane chain, it can effectively resist the chain-breaking reaction induced by ultraviolet rays and delay the aging of the coating. By introducing a benzene ring structure on the polysiloxane chain, the energy is dispersed and absorbed through the π-electron conjugate system, reducing the impact of ultraviolet rays on the coating. Moreover, the benzene ring increases the rigidity of the polysiloxane chain, forming a rigid support on the polysiloxane chain, enabling it to better absorb and disperse energy when subjected to an impact force, thereby improving the impact resistance.

[0027] The environmentally friendly powder coating of the present invention modifies and activates the surfaces of nano-silica and nano-titanium dioxide particles, modifies olefin double bonds on their surfaces, can increase the dispersibility of the activated filler during the synthesis of polyolefin resin, improve its surface activity at the same time, and uses the olefin double bonds modified on the activated filler particles as active reaction sites to increase the crosslinking degree of the polyolefin resin. The three-dimensional network structure formed by the crosslinking bonding can effectively dissipate impact energy. When the material is impacted, the crosslinking points can prevent the expansion of cracks. At the same time, the bridging effect of the nano-fillers can further absorb energy, improving the wear resistance and impact resistance of the powder coating specimen. Nano-titanium dioxide in the activated filler has excellent light shielding performance, can effectively absorb and reflect ultraviolet rays, reduce the direct irradiation of ultraviolet rays on the polyolefin resin, thereby reducing the photo-oxidative degradation rate, and its synergistic cooperation with olefin-capped polysiloxane improves the anti-ultraviolet aging performance of the material. Detailed implementation manners

[0028] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] In this application, D4 is octamethylcyclotetrasiloxane, and its CAS number is 556-67-2; In this application, the nano-titanium dioxide is selected from Qinghe County Chaotai Metal Materials Co., Ltd., the effective ingredient content is 99%, and the particle size is 2000 mesh; In this application, the nano-silica is selected from Qinghe County Chaotai Metal Materials Co., Ltd., the silicon content is ≥99.9%, the particle size is 2000 mesh, and the purity is 99.9%; In this application, the acrylate leveling agent is octadecyl acrylate, and the effective ingredient content is 99%; In this application, the polypropylene wax is selected from Shanghai Hongzhuang Chemical Technology Co., Ltd., the effective ingredient content is 99%, and the model is CS-52NC; In this application, the polyetheramine is selected from Shanghai Yushicheng Chemical Technology Co., Ltd., the product name is BASF polyetheramine D230, and the model is BASGU EC301.

[0030] Example 1. This example provides a preparation method of an environmentally friendly powder coating, including the following steps: S1. Prepare diethoxysilane-modified butylated hydroxytoluene; Weigh: 23.6 g of 3,5 - di - tert - butyl - 4 - hydroxybenzyl alcohol and 165.2 mL of tetrahydrofuran and add them to a 500 - mL reaction flask protected by nitrogen and stir. Raise the temperature of the reaction flask to 40 °C, add 21.7 g of 3 - isocyanatopropylmethyldiethoxysilane to the reaction flask, keep the temperature for reaction for 60 min, evacuate the reaction flask to a negative pressure of 0.1 MPa, and remove the low - boiling substances under reduced pressure to obtain diethoxysilane - modified butylated hydroxytoluene.

[0031] S2. Prepare olefin - terminated polysiloxane; Weigh: 200 g of D4, 40 g of diethoxysilane - modified butylated hydroxytoluene, 60 g of diphenyldiethoxysilane, and 4 g of 60 wt% sulfuric acid solution and add them to a 500 - mL reaction flask and stir. After closing the reaction flask, raise the temperature of the reaction flask to 120 °C, keep the temperature for reaction for 3 h, add 16 g of diallyltetramethyldisiloxane to the reaction flask, keep the temperature for reaction for 2 h, lower the temperature of the reaction flask to room temperature, add 200 mL of purified water to the reaction flask, stir for 20 min, add 0.5 mol / L sodium carbonate aqueous solution to the reaction system to adjust the pH of the system to 7, let it stand and separate the liquid. Wash the upper layer liquid with purified water 3 times and then transfer it to a rotary evaporator at 80 °C, and remove the low - boiling substances under reduced pressure to obtain olefin - terminated polysiloxane.

[0032] S3. Prepare activated filler; Weigh: 10 g of nano - titanium dioxide, 15 g of nano - silicon dioxide, 150 mL of absolute ethanol, and 5 g of KH - 570 and add them to a 500 - mL reaction flask, ultrasonically disperse for 80 min, fix the reaction flask in a water bath with mechanical stirring and stir. Raise the temperature of the reaction flask to 50 °C, add 40 mL of 2 mol / L sodium hydroxide solution to the reaction flask, keep the temperature for reaction for 40 min, lower the temperature of the reaction flask to room temperature, filter by suction, wash the filter cake with purified water until neutral and then dry it by suction, transfer the filter cake to a drying oven at 65 °C, and dry it to a constant weight to obtain activated filler.

[0033] S4. Prepare polyolefin resin; Mix deionized water and absolute ethanol evenly according to a volume ratio of 2:1 to obtain a solvent; Mix sodium dodecylbenzenesulfonate, sodium oleate, and Tween - 80 evenly according to a weight ratio of 5:3:2 to obtain an emulsifier; Mix azobisisobutyronitrile and deionized water at 1 g:20 mL and stir until the system is dissolved to obtain an initiator solution; Under the protection of inert gas, Weigh: 1500 mL of solvent and 40 g of emulsifier are added to a 3 L reaction flask and stirred. Set the stirring speed to 600 r / min. Then, 50 g of activated filler, 100 g of olefin-terminated polysiloxane, 40 g of glycidyl methacrylate, 20 g of styrene, and 50 g of butyl acrylate are successively added to the reaction flask and stirred for dispersion for 30 min. The temperature of the reaction flask is raised to 70 °C, and 100 mL of initiator solution is added dropwise to the reaction flask. After the addition is complete, keep the temperature for reaction for 4 h. Then, the temperature of the reaction flask is lowered to room temperature, and filtration is carried out. The filter cake is washed 3 times with purified water and then dried by suction. The filter cake is transferred to an oven at 60 °C and dried to a constant weight to obtain polyolefin resin.

[0034] S5. Prepare powder coating; Mix phthalocyanine pigment, acrylate leveling agent, curing accelerator 2-methylimidazole, and slip agent polypropylene wax evenly according to the weight ratio of 5:1.5:0.6:2 to obtain auxiliary additive; Weigh by weight: 70 parts of polyolefin resin, 15 parts of bisphenol A epoxy resin E-12, 5 parts of curing agent polyetheramine, and 3 parts of auxiliary additive are added to a high-speed grinder, pulverized, and passed through a 200-mesh sieve to obtain powder coating.

[0035] Example 2. This example provides a preparation method of an environment-friendly powder coating, including the following steps: S1. Prepare diethoxysilane-modified butylated hydroxytoluene; Weigh: 23.6 g of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 165.2 mL of tetrahydrofuran are added to a 500 mL reaction flask under nitrogen protection and stirred. The temperature of the reaction flask is raised to 45 °C, and 21.7 g of 3-isocyanatopropylmethyldiethoxysilane is added to the reaction flask. Keep the temperature for reaction for 65 min. The reaction flask is evacuated to 0.1 MPa, and low-boiling substances are removed by reduced pressure distillation to obtain diethoxysilane-modified butylated hydroxytoluene.

[0036] S2. Prepare olefin-terminated polysiloxane; Weigh: 200 g of D4, 40 g of diethoxysilane-modified butylated hydroxytoluene, 60 g of diphenyldiethoxysilane, and 4 g of 68 wt% sulfuric acid solution are added to a 500 mL reaction flask and stirred. After the reaction flask is sealed, the temperature of the reaction flask is raised to 125 °C, and keep the temperature for reaction for 3.5 h. Then, 16 g of diallyltetramethyldisiloxane is added to the reaction flask, and keep the temperature for reaction for 2.5 h. The temperature of the reaction flask is lowered to room temperature, 200 mL of purified water is added to the reaction flask, and stirred for 25 min. Then, 0.5 mol / L sodium carbonate aqueous solution is added to the reaction system to adjust the pH of the system to 7. Let it stand for liquid separation. The upper layer liquid is washed 3 times with purified water and then transferred to a rotary evaporator at 85 °C, and low-boiling substances are removed by reduced pressure distillation to obtain olefin-terminated polysiloxane.

[0037] S3. Prepare activated filler; Weigh: 10 g of nano-titanium dioxide, 15 g of nano-silica, 150 mL of absolute ethanol, and 5 g of KH-570 and add them to a 500 mL reaction flask. Ultrasonically disperse for 100 min, fix the reaction flask in a water bath with mechanical stirring, raise the temperature of the reaction flask to 55 °C, add 40 mL of 2 mol / L sodium hydroxide solution to the reaction flask, keep the temperature for reaction for 50 min, lower the temperature of the reaction flask to room temperature, filter by suction, wash the filter cake with purified water until neutral and then dry by suction. Transfer the filter cake to a drying oven at 70 °C and dry to constant weight to obtain the activated filler.

[0038] S4. Prepare polyolefin resin; Mix deionized water and absolute ethanol evenly according to a volume ratio of 2:1 to obtain a solvent; Mix sodium dodecylbenzenesulfonate, sodium oleate, and Tween-80 evenly according to a weight ratio of 5:3:2 to obtain an emulsifier; Mix azobisisobutyronitrile and deionized water according to 1 g:20 mL and stir until the system is dissolved to obtain an initiator solution; Under the protection of an inert gas, Weigh: 1500 mL of solvent and 40 g of emulsifier and add them to a 3 L reaction flask and stir. Set the stirring speed to 700 r / min. Add 60 g of activated filler, 130 g of olefin-terminated polysiloxane, 50 g of glycidyl methacrylate, 25 g of styrene, and 55 g of butyl acrylate to the reaction flask in sequence, stir and disperse for 40 min, raise the temperature of the reaction flask to 75 °C, add 100 mL of the initiator solution dropwise to the reaction flask. After the dropping is completed, keep the temperature for reaction for 5 h, lower the temperature of the reaction flask to room temperature, filter by suction, wash the filter cake with purified water 4 times and then dry by suction. Transfer the filter cake to a drying oven at 65 °C and dry to constant weight to obtain the polyolefin resin.

[0039] S5. Prepare powder coating; Mix phthalocyanine pigment, acrylate leveling agent, curing accelerator 2-methylimidazole, and slip agent polypropylene wax evenly according to a weight ratio of 5:1.5:0.6:2 to obtain an auxiliary additive; Weigh by weight: 75 parts of polyolefin resin, 20 parts of bisphenol A epoxy resin E-12, 5.5 parts of curing agent polyetheramine, and 4 parts of auxiliary additive and add them to a high-speed grinder, grind and pass through a 250-mesh sieve to obtain the powder coating.

[0040] Example 3. This example provides a preparation method of an environment-friendly powder coating, including the following steps: S1. Prepare diethoxysilane-modified butylated hydroxytoluene; Weigh: 23.6 g of 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 165.2 mL of tetrahydrofuran, add them to a 500 mL reaction flask under nitrogen protection and stir. Raise the temperature of the reaction flask to 50 °C, add 21.7 g of 3-isocyanatopropylmethyldiethoxysilane to the reaction flask, keep the temperature for reaction for 70 min, evacuate the reaction flask to a negative pressure of 0.1 MPa, and remove low-boiling substances under reduced pressure to obtain diethoxysilane-modified butylated hydroxytoluene.

[0041] S2. Prepare olefin-terminated polysiloxane; Weigh: 200 g of D4, 40 g of diethoxysilane-modified butylated hydroxytoluene, 60 g of diphenyldiethoxysilane and 4 g of 75 wt% sulfuric acid solution, add them to a 500 mL reaction flask and stir. After the reaction flask is sealed, raise the temperature of the reaction flask to 130 °C, keep the temperature for reaction for 4 h, add 16 g of diallyltetramethyldisiloxane to the reaction flask, keep the temperature for reaction for 3 h, lower the temperature of the reaction flask to room temperature, add 200 mL of purified water to the reaction flask, stir for 30 min, add 0.5 mol / L sodium carbonate aqueous solution to the reaction system to adjust the pH of the system to 7, let it stand and separate the liquid. The upper layer liquid is washed 3 times with purified water and then transferred to a rotary evaporator at 90 °C to remove low-boiling substances under reduced pressure to obtain olefin-terminated polysiloxane.

[0042] S3. Prepare activated filler; Weigh: 10 g of nano-titanium dioxide, 15 g of nano-silica, 150 mL of absolute ethanol, 5 g of KH-570, add them to a 500 mL reaction flask, ultrasonically disperse for 120 min, fix the reaction flask in a water bath with mechanical stirring and stir. Raise the temperature of the reaction flask to 60 °C, add 40 mL of 2 mol / L sodium hydroxide solution to the reaction flask, keep the temperature for reaction for 60 min, lower the temperature of the reaction flask to room temperature, filter by suction, wash the filter cake with purified water until neutral and then drain it, transfer the filter cake to a drying oven at 75 °C and dry to constant weight to obtain activated filler.

[0043] S4. Prepare polyolefin resin; Mix deionized water and absolute ethanol evenly according to a volume ratio of 2:1 to obtain a solvent; Mix sodium dodecylbenzenesulfonate, sodium oleate and Tween-80 evenly according to a weight ratio of 5:3:2 to obtain an emulsifier; Mix azobisisobutyronitrile and deionized water at 1 g:20 mL and stir until the system is dissolved to obtain an initiator solution; Under the protection of inert gas, Weigh: Add 1500 mL of solvent and 40 g of emulsifier into a 3 L reaction flask and stir. Set the stirring speed to 800 r / min. Add 70 g of activated filler, 150 g of olefin-terminated polysiloxane, 60 g of glycidyl methacrylate, 30 g of styrene, and 60 g of butyl acrylate into the reaction flask in sequence. Stir and disperse for 50 min. Raise the temperature of the reaction flask to 80 °C. Dropwise add 100 mL of initiator solution into the reaction flask. After the addition is complete, keep the reaction at a constant temperature for 6 h. Lower the temperature of the reaction flask to room temperature. Perform suction filtration. Wash the filter cake 5 times with purified water and then drain it. Transfer the filter cake to a drying oven at 70 °C and dry it to a constant weight to obtain polyolefin resin.

[0044] S5. Prepare powder coating; Mix phthalocyanine pigment, acrylate leveling agent, curing accelerator 2-methylimidazole, and slip agent polypropylene wax evenly according to the weight ratio of 5:1.5:0.6:2 to obtain auxiliary additive. Weigh by weight: Add 80 parts of polyolefin resin, 25 parts of bisphenol A epoxy resin E-12, 6 parts of curing agent polyetheramine, and 5 parts of auxiliary additive into a high-speed grinder, crush and pass through a 300-mesh sieve to obtain powder coating.

[0045] Comparative Example 1. The difference between this comparative example and Example 3 is that diphenyldiethoxysilane was not added in step S2.

[0046] Comparative Example 2. The difference between this comparative example and Example 3 is that step S3 was cancelled, and a mixture composed of nano-titanium dioxide and nano-silica in a weight ratio of 2:3 in step S3 was used to replace the activated filler in step S4.

[0047] Comparative Example 3. The difference between this comparative example and Example 3 is that styrene was not added in step S4.

[0048] Comparative Example 4. The difference between this comparative example and Example 3 is that bisphenol A epoxy resin E-12 in step S5 was replaced with diglycidyl ether with equal epoxy equivalent.

[0049] Performance test: Spray the powder coatings prepared in Examples 1-3 and Comparative Examples 1-4 evenly on the polished and degreased tinplate to form a spray coating with a thickness of 100 μm on the tinplate. Then, under the environment of 200 °C, thermally cure for 15 min to obtain the test specimens to be tested; Refer to the standard GB / T 23988-2009 "Determination of coating abrasion resistance - Falling sand method" to determine the abrasion resistance of the test specimens to be tested; Refer to the standard GB / T 9286-2021 "Paints and varnishes - Cross-cut test" to determine the adhesion of the test specimens to be tested; Refer to the standard GB / T 23987-2009 "Paints and varnishes - Artificial weathering of coatings - Exposure to fluorescent ultraviolet light and water", expose the test specimen to ultraviolet light with a wavelength of 300 - 320 nm for cyclic irradiation for 360 h. The cyclic irradiation conditions are: set the blackboard temperature to 50 °C, relative humidity to 15%, dry irradiation for 5 h, then at a black - white temperature of 25 °C, water spray, wet irradiation for 1 h. Refer to the standard GB / T 1766-2008 "Paints and varnishes - Method for rating the degradation of coatings" to evaluate the gloss loss rate of the test specimen; Refer to the standard GB / T 1732-2020 "Method for the determination of impact resistance of film coatings" to determine the maximum height at which the film of the test specimen is damaged; The specific test results are shown in Table 1 below.

[0050] Table 1 - Data sheet for performance detection of specimens

[0051] Data analysis: Compare and analyze the data in Table 1 above. After the powder coating prepared by the present invention is thermally cured, the abrasion resistance of the paint film reaches 5.4 L / μm, the gloss loss rate is reduced to 1.5%, the adhesion grade reaches level 0, and the maximum height at which the paint film is damaged reaches 45 cm. All the performance test data are better than those of the comparative example. This shows that the present invention prepares polyolefin resin by enhancing unsaturated monomers with activated fillers and olefin - terminated polysiloxane, and then enhancing the polyolefin resin with epoxy resin. It not only effectively improves the abrasion resistance and impact resistance of the paint film layer specimens, but also improves the adhesion and anti - ultraviolet performance of the paint film. Moreover, the production process has little harm to the environment and human health and is relatively friendly to the environment.

[0052] The above content is only an example and explanation of the structure of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar ways to replace them. As long as they do not deviate from the structure of the invention or exceed the scope defined by this claim book, they should fall within the protection scope of the present invention.

[0053] In the description of this specification, the description referring to terms such as "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0054] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments only. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. An environmentally friendly powder coating, characterized in that: The invention comprises the following components by weight: 70-80 parts of polyolefin resin, 15-25 parts of epoxy resin, 5-6 parts of curing agent and 3-5 parts of auxiliary additives; The preparation method of the polyolefin resin is as follows: under the protection of inert gas, a solvent and an emulsifier are mixed and stirred, activated filler, olefin-terminated polysiloxane, glycidyl methacrylate, styrene and butyl acrylate are added to the reaction system, stirred and dispersed for 30-50 minutes, the temperature of the reaction system is increased to 70-80°C, an initiator solution is dripped into the reaction system, and after the dripping is completed, the reaction is kept warm for 4-6 hours, and post-processed to obtain the polyolefin resin.

2. An environmentally friendly powder coating according to claim 1, characterized in that: The epoxy resin is bisphenol A epoxy resin E-12, the curing agent is polyetheramine, and the auxiliary additives are composed of pigment, leveling agent, curing accelerator, and slip agent in a weight ratio of 5:1.5:0.6:2, wherein the pigment is a phthalocyanine pigment, the leveling agent is an acrylate leveling agent, the curing accelerator is 2-methylimidazole, and the slip agent is polypropylene wax.

3. An environmentally friendly powder coating according to claim 1, characterized in that: The amount ratio of the solvent, emulsifier, activated filler, olefin-terminated polysiloxane, glycidyl methacrylate, styrene, butyl acrylate and initiator solution is 150mL:4g:5-7g:10-15g:4-6g:2-3g:5-6g:10mL, the solvent is composed of deionized water and anhydrous ethanol in a volume ratio of 2:1, the emulsifier is composed of sodium dodecylbenzene sulfonate, sodium oleate and Tween-80 in a weight ratio of 5:3:2, the initiator solution is composed of azobisisobutyronitrile and deionized water in a weight ratio of 1g:20mL, and the post-treatment comprises: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, suction filtration is performed, the filter cake is washed with purified water for 3-5 times and then dried, the filter cake is transferred to a drying oven with a temperature of 60-70°C, and dried to constant weight to obtain a polyolefin resin.

4. The environmentally friendly powder coating according to claim 1, characterized in that: The olefin-terminated polysiloxane is processed by the following steps: A1. Under the protection of inert gas, 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and tetrahydrofuran are mixed and stirred, the temperature of the reaction system is raised to 40-50° C., 3-isocyanatopropylmethyldiethoxysilane is added to the reaction system, and the reaction is kept warm for 60-70 minutes, and post-processed to obtain diethoxysilane-modified butylated hydroxytoluene; A2. D4, diethoxysilane-modified butylhydroxytoluene, diphenyldiethoxysilane and a catalyst are mixed and stirred. After the reaction system is sealed, the temperature of the reaction system is raised to 120-130°C and the reaction is kept warm for 3-4 hours. Diallyltetramethyldisiloxane is added to the reaction system and the reaction is kept warm for 2-3 hours. After post-treatment, an olefin-terminated polysiloxane is obtained.

5. An environmentally friendly powder coating according to claim 4, characterized in that: In step A1, the amount ratio of the 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and 3-isocyanatopropylmethyldiethoxysilane is 1 mol:1 mol, and the amount ratio of the 3,5-di-tert-butyl-4-hydroxybenzyl alcohol and tetrahydrofuran is 1 g:7 mL. The post-treatment comprises: after the reaction is completed, reducing the pressure to remove the low-boiling substances to obtain diethoxysilane-modified butylhydroxytoluene; in step A2, the amount of D4, diethoxysilane-modified butylhydroxytoluene, diphenyldiethoxysilane, catalyst and diallyltetramethyldisiloxane is The ratio is 10g:2g:3g:0.2g:0.8g, the catalyst is a 60-75wt% sulfuric acid solution, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, purified water is added to the reaction system, and stirred for 20-30min, 0.5mol / L sodium carbonate aqueous solution is added to the reaction system, the pH of the system is adjusted to 7, and the liquid is allowed to stand for separation, the upper layer liquid is washed with purified water 3 times and then transferred to a rotary evaporator with a temperature of 80-90°C, and low boiling points are removed under reduced pressure to obtain olefin-terminated polysiloxane.

6. The environmentally friendly powder coating according to claim 1, characterized in that: The preparation method of the activated filler is as follows: nano titanium dioxide, nano silicon dioxide, anhydrous ethanol and KH-570 are mixed, ultrasonically dispersed for 80-120 minutes, the temperature of the reaction system is increased to 50-60°C, a catalyst is added to the reaction system, the reaction is kept warm for 40-60 minutes, and post-processed to obtain the activated filler.

7. An environmentally friendly powder coating according to claim 6, characterized in that: The dosage ratio of the nano titanium dioxide, nano silicon dioxide, anhydrous ethanol, KH-570 and catalyst is 2g:3g:30mL:1g:8mL, the catalyst is 2mol / L sodium hydroxide solution, and the post-treatment comprises: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, suction filtration is performed, the filter cake is washed with purified water until it is neutral and then dried, the filter cake is transferred to a drying oven at a temperature of 65-75°C, and dried to constant weight to obtain an activated filler.

8. A method for preparing an environmentally friendly powder coating according to any one of claims 1 to 7, characterized in that: Add polyolefin resin, epoxy resin, curing agent and auxiliary additives into a high-speed pulverizer, pulverize through a 200-300 mesh screen to obtain a powder coating.

9. An application of an environmentally friendly powder coating, characterized in that: The powder coating prepared by the method for preparing an environmentally friendly powder coating as described in claim 8 is applied to the surface coating of metal products.

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