A fluorocarbon powder coating and its preparation method

Abstract

The present invention discloses a fluorocarbon powder coating and a preparation method thereof, belonging to the technical field of powder coatings, which comprises the following steps: premixing methyl methacrylate, 2-hydroxyethyl methacrylate, 1H,1H,2H,2H-hexafluorobutyl methacrylate and methyl p-coumarate to obtain a premixed solution; transferring the premixed solution to a reaction kettle, heating up, adding an initiator, carrying out a reaction, filtering, and drying to obtain a modified acrylic resin, then carrying out melt mixing and extrusion to obtain material A; putting PVDF fluorocarbon resin and a filler into a reaction kettle, heating up and stirring to obtain material B, adding material A and modified PMMA, stirring, cooling and pressing into tablets to obtain the powder coating. The fluorocarbon powder coating of the present invention can maintain the advantage of high weather resistance, while also improving the internal compatibility and anti-ultraviolet performance, and enhancing the internal bonding effect of the double-layer powder body.

Description

Technical Field

[0001] The present invention relates to the technical field of powder coatings, and particularly relates to a fluorocarbon powder coating and a preparation method thereof. Background Art

[0002] Fluorocarbon coatings are a general term for a series of coatings with fluororesin as the main film-forming substance. It is a new type of coating material modified and processed on the basis of fluororesin. The main feature is that a large number of F-C bonds are contained in the resin, and the bond energy is 485 kJ / mol -1 , with high bond energy, thus showing extremely long weather resistance and resistance to chemical medium corrosion. With the global climate change, the demand for building and transportation facilities to withstand extreme climate conditions is increasing continuously, and super weather-resistant fluorocarbon coatings also have good market adaptability.

[0003] Although fluorocarbon resins have high weather resistance, such as PVDF (polyvinylidene fluoride) fluorocarbon resin, their own adhesion is very low and their compatibility is poor, resulting in affecting the overall mechanical properties. To solve this problem, the existing technology mainly modifies PVDF by introducing highly reactive functional groups into the molecular chain. For example, by the grafting method, one or more graft monomers are introduced into the PVDF molecular chain. Although this improves the adhesion of the modified PVDF fluorocarbon resin powder coating to some extent, the high stability, antioxidant property and weather resistance of the PVDF fluorocarbon resin itself also decrease significantly, and the reaction is complex and difficult.

[0004] In addition, the adhesion of the coating can also be improved by adding acrylic resin for blending, but the ultraviolet resistance of acrylic resin is relatively low and its weather resistance is poor. The addition of acrylic resin will also affect the overall weather resistance, resulting in an impact on the ultraviolet resistance and weather resistance. To improve the ultraviolet resistance of acrylic resin, metal oxides are generally added as fillers, but the addition of metal oxides is likely to affect the overall compatibility effect. Therefore, how to make the added acrylic resin not affect the weather resistance, while maintaining good compatibility and improving the ultraviolet resistance as much as possible is also a major problem at present.

[0005] In addition, with the global high attention to environmental protection, relevant policies have been introduced everywhere to promote the use of low-VOC and environmentally friendly products. Therefore, powder coatings have emerged as the times require. Powder coatings, without solvents, are more environmentally friendly while the coating is more convenient and cost-saving during storage, transportation and use, but the compatibility of the coating is more difficult to grasp, and phase separation and other situations are likely to occur, especially for PVDF fluorocarbon powder coatings. Also, the current double-layer powder technology can improve the adhesion and weather resistance of the coating, but there has been no suitable bonding aid, resulting in poor bonding effect between layers. After a long time, local layer separation, bubbles or cracking and other problems may occur. Summary of the Invention

[0006] In view of this, the present invention provides a fluorocarbon powder coating and a preparation method thereof, which can maintain the advantages of high weather resistance, improve the internal compatibility and anti-ultraviolet performance, and enhance the internal bonding effect of the double-layer powder body.

[0007] In order to achieve the above object, the present invention provides a preparation method of a fluorocarbon powder coating, which includes the following steps:

[0008] S1: Premix methyl methacrylate, 2-hydroxyethyl methacrylate, 1H,1H,2H,2H-hexafluorobutyl methacrylate, methyl p-coumarate and a solvent to obtain a premixed solution;

[0009] S2: Transfer the premixed solution to a reaction kettle, raise the temperature, add an initiator, carry out a reaction, filter, and dry to obtain a modified acrylic resin;

[0010] S3: Mix the modified acrylic resin and a filler evenly, carry out melt mixing and extrusion to obtain material A;

[0011] S4: Put PVDF fluorocarbon resin and a filler into a reaction kettle, raise the temperature, stir to obtain material B, add material A and modified PMMA, mix evenly, cool and press into tablets to obtain a powder coating;

[0012] The modified PMMA is obtained by modifying PMMA with 2,2,3,3,3-pentafluoropropyl acrylate;

[0013] The mass ratio of material A to material B is (2-3):(7-8);

[0014] In the premixed solution, the mass proportion of 1H,1H,2H,2H-hexafluorobutyl methacrylate is 3-8%.

[0015] By adopting the above technical solution, the obtained modified acrylic resin can not only improve its own anti-ultraviolet performance and weather resistance, but also improve the adhesion of the fluorocarbon powder coating; and by adopting the double-layer powder technology, the film formed after coating tends to gather a large amount of fluorocarbon resin layer (material B) with hydrophobicity and greater surface tension on the surface layer, and a relatively larger amount of modified acrylic resin layer (material A) with smaller surface tension and greater viscosity at the bottom. Moreover, by using modified PMMA as a bonding aid, it can not only play a bonding role, but also improve the compatibility between material A and material B, and better avoid the occurrence of layer separation phenomenon.

[0016] By using methyl p -coumarate to modify acrylic resin, methyl p -coumarate has good antioxidant properties. It can form resonance - stabilized phenolic free radicals, absorb part of the energy in ultraviolet light, and when some free radicals are generated by ultraviolet radiation, it can capture and neutralize these free radicals, thereby improving the ultraviolet resistance of acrylic resin. At the same time, methyl p -coumarate itself contains double bonds and ester groups, which have a high degree of matching with acrylic monomers, and can undergo free - radical copolymerization to form a random copolymer, improving the ultraviolet resistance without causing problems such as compatibility. Moreover, methyl p -coumarate is derived from biobased lignin, which is environmentally friendly and easy to obtain. At the same time, in acrylic resin, hexafluorobutyl methacrylate is also introduced. The introduction of C - F bonds can improve the weather resistance of acrylic resin, but attention should be paid to the dosage, and its mass ratio should not exceed 8% to avoid affecting the viscosity and adhesion of acrylic resin.

[0017] By using 2,2,3,3,3 - pentafluoropropyl acrylate to modify the adhesion promoter PMMA (polymethyl methacrylate), while improving the chemical resistance, the bonding strength between the PMMA adhesion promoter and the PVDF fluorocarbon resin layer is enhanced. The molecular chain of PVDF contains -CF 2 - groups, and 2,2,3,3,3 - pentafluoropropyl acrylate contains pentafluoropropyl (-CF 2 CF 2 CF 3 ), which has a similar polarity to the fluorocarbon chain of PVDF. The pentafluoropropyl group introduced into the PMMA chain segment through copolymerization modification can form a stronger intermolecular bonding force with PVDF through fluorine - fluorine interaction, effectively reducing phase separation. And 2,2,3,3,3 - pentafluoropropyl acrylate contains acrylate groups, which can copolymerize highly with PMMA, and the obtained modified PMMA can also maintain a high bonding effect with the acrylic resin layer. Therefore, the introduction of 2,2,3,3,3 - pentafluoropropyl acrylate not only improves the chemical resistance of the PMMA adhesion promoter, but also enhances the bonding effect inside the double - layer powder coating, laying a solid foundation for the large - scale popularization and application of the double - layer powder coating market.

[0018] Preferably, the methyl p -coumarate is prepared by the following method:

[0019] a. Clean and crush the raw material bagasse, use the Soxhlet extraction method to extract lignin, then carry out alkaline hydrolysis in a high - pressure reactor, and then carry out acid precipitation treatment and purification to obtain p -coumaric acid;

[0020] b. Add thionyl chloride and DMF to the obtained p -coumaric acid, heat and stir the reaction until the solid is completely dissolved, carry out reduced - pressure distillation to obtain p -coumaroyl chloride, dissolve it in methanol, cool in an ice bath, dropwise add methanol, slowly warm up to room temperature for reaction, after the reaction is completed, carry out reduced - pressure distillation, extraction, and recrystallization to obtain methyl p -coumarate.

[0021] By adopting the above scheme, methyl p - coumarate can be extracted and prepared from waste sugarcane bagasse. The raw materials are easily available, the preparation method is concise, and the ultraviolet resistance of the modified acrylic resin can be significantly improved.

[0022] Preferably, 3%wt sodium hydroxide and antioxidant Na 2 SO 3 Perform alkaline hydrolysis in a high - pressure reactor, then adjust the pH to 2.2 with 18%wt hydrochloric acid, let it stand and precipitate for 10 - 15 h, centrifuge and purify to obtain p - coumaric acid;

[0023] In step b, heat to 50 - 60 °C, stir and react for 3 hours until the solid is completely dissolved, then perform vacuum distillation to obtain p - coumaroyl chloride, dissolve it in methanol, cool it to 0 - 5 °C in an ice bath, and then dropwise add methanol and slowly warm up to room temperature and react for 5 h;

[0024] The molar ratio of p - coumaric acid, thionyl chloride, DMF, and methanol is 1:1.3:0.1:5.

[0025] Preferably, the modified PMMA is prepared by the following method: Mix MMA and 2,2,3,3,3 - pentafluoropropyl acrylate evenly, add tetrahydrofuran, then add an initiator, stir until completely dissolved, purge with nitrogen to remove oxygen, raise the temperature, keep it warm, carry out the reaction, lower the temperature, add methanol, filter, wash, and vacuum dry to obtain granular modified PMMA.

[0026] Preferably, the mass of 2,2,3,3,3 - pentafluoropropyl acrylate added accounts for 0.5 - 3% of the total mass of the modified PMMA.

[0027] The above preparation method is concise and efficient. The addition amount of 2,2,3,3,3 - pentafluoropropyl acrylate is appropriate, and using tetrahydrofuran as a solvent can improve the dispersion effect of 2,2,3,3,3 - pentafluoropropyl acrylate, making the bonding effect of the prepared modified PMMA better.

[0028] Preferably, in the preparation process of the modified PMMA, the initiator added is azobisisobutyronitrile, purge with nitrogen for 20 min to remove oxygen, slowly raise the temperature to 60 - 65 °C, keep it warm for 1 - 2 hours, then raise the temperature to 75 - 80 °C, carry out a constant - temperature reaction for 6 - 8 hours, lower the temperature to below 38 °C, add methanol, filter, wash with methanol 2 - 4 times, and vacuum dry at 50 °C for 24 h to obtain granular modified PMMA.

[0029] Preferably, in step S2, transfer the premixed solution to the reactor, introduce N 2Exhaust the air completely, heat up to 80 - 88 °C, slowly dropwise add the initiator, keep the temperature for 4 - 6 h, then cool down to 50 - 60 °C, add the neutralizing agent ammonia water, adjust the pH to 7 - 8, filter to remove unreacted impurities, and then carry out drying and pulverization to obtain the modified acrylic resin.

[0030] Preferably, in the premixed solution, the mass proportion of methyl p - coumarate is 5 - 15%.

[0031] Preferably, in step S3, mix the modified acrylic resin, curing agent, surface smoothing agent and filler evenly, and carry out melt mixing and extrusion using a melt extruder. The temperature of zone I of the melt extruder is set at 105 °C, and the temperature of zone II of the melt extruder is set at 95 °C. This is the preferred temperature, and the temperatures of zones I and II of the extruder can also be adjusted according to the proportion of the materials.

[0032] Preferably, in step S4, put the PVDF fluorocarbon resin and filler into a reaction kettle, stir for 15 min, heat up to 95 - 120 °C, keep stirring for 10 - 20 min, adjust the temperature to 80 - 100 °C, add the surface smoothing agent and accelerator, keep stirring for 10 - 20 min to obtain material B, then adjust the temperature to 60 - 80 °C, add material A and modified PMMA, keep stirring for 20 - 40 min, feed it into a feeder, mix evenly, cool and press into sheets, carry out multi - stage pulverization, control the nitrogen pressure at 0.7 MPa, and the flow rate at 5 - 10 m 2 / min, screen to obtain powder particles with a particle size of 5 - 35 microns, and carry out spheroidization treatment to obtain the powder coating.

[0033] By adopting multi - stage pulverization and controlling the nitrogen pressure at 0.7 MPa and the flow rate at 5 - 10 m 2 / min, further better control the particle size and distribution of the coating, improve the filling density of the double - layer powder, improve the leveling property, and enhance the mixing effect.

[0034] Preferably, in step S1, the solvent added is one of propylene glycol methyl ether acetate, toluene, and xylene.

[0035] Preferably, in step S2, the initiator added is azobisisobutyronitrile or benzoyl peroxide.

[0036] Preferably, the curing agent is one of self - blocking isophorone diisocyanate and caprolactam - blocked isophorone diisocyanate, the surface smoothing agent is polytetrafluoroethylene, the filler is one of nano - silica and mica powder, and the accelerator is dibutyltin dilaurate.

[0037] The present invention also provides a fluorocarbon powder coating, which is prepared by the above-mentioned preparation method of the fluorocarbon powder coating. The coating comprises the following components in parts by weight: 20-30 parts of PVDF fluorocarbon resin, 1-8 parts of curing agent, 5-30 parts of filler, 0.2-2 parts of surface smoothing agent, 0.5-5 parts of accelerator, 70-80 parts of modified acrylic resin, and 5-10 parts of modified PMMA;

[0038] The modified acrylic resin comprises the following raw materials in parts by weight: 40-65 parts of methyl methacrylate, 10-20 parts of butyl acrylate, 4-10 parts of 2-hydroxyethyl methacrylate, 1-6 parts of hexafluorobutyl methacrylate, 3-10 parts of methyl p-coumarate, 70-100 parts of solvent, and 0.5-1 part of initiator;

[0039] The modified PMMA comprises the following raw materials in parts by weight: 90-99 parts of MMA, 0.5-3 parts of 2,2,3,3,3-pentafluoropropyl acrylate, 50-100 parts of tetrahydrofuran, and 0.1-0.6 part of initiator.

[0040] The above technical solutions of the present invention at least include the following beneficial effects:

[0041] (1) In the present invention, methyl p-coumarate is used to modify the acrylic resin. Methyl p-coumarate has good antioxidant properties, can form resonance-stabilized phenolic radicals, absorb part of the energy in ultraviolet light, capture and neutralize free radicals, thereby improving the ultraviolet resistance of the acrylic resin. At the same time, methyl p-coumarate itself contains double bonds and ester groups, which has a high matching degree with acrylate monomers, and can carry out free radical copolymerization to form a random copolymer, so as to improve the ultraviolet resistance without causing problems such as compatibility. Moreover, methyl p-coumarate is derived from biobased lignin, which is environmentally friendly and easy to obtain.

[0042] (2) In the present invention, the powder coating is prepared by using the double-layer powder technology, so that the film formed after coating tends to aggregate a large amount of fluorocarbon resin layer (material B) with more hydrophobicity and greater surface tension on the surface layer, and a relatively larger amount of modified acrylic resin layer (material A) with smaller surface tension and greater viscosity at the bottom. And modified PMMA is used as a bonding aid, which not only plays a bonding role but also can improve the compatibility between material A and material B, and better avoid the occurrence of layer separation phenomenon.

[0043] (3) By using 2,2,3,3,3-pentafluoropropyl acrylate to modify PMMA, taking advantage of the fact that 2,2,3,3,3-pentafluoropropyl acrylate contains pentafluoropropyl (-CF 2 CF 2 CF 3It has a similar polarity to the fluorocarbon chain of PVDF. The pentafluoropropyl group introduced into the PMMA segment through modified copolymerization can form a stronger intermolecular binding force with PVDF through fluorine-fluorine interaction, effectively reducing phase separation. Moreover, 2,2,3,3,3-pentafluoropropyl acrylate contains acrylate groups and can copolymerize highly with PMMA. The obtained modified PMMA can also maintain a high bonding effect with the acrylic resin layer. Therefore, the introduction of 2,2,3,3,3-pentafluoropropyl acrylate not only improves the chemical resistance of the PMMA adhesion promoter but also enhances the bonding effect inside the double-layer powder coating, laying a solid foundation for the large-scale popularization and application of the double-layer powder coating market. Detailed Embodiments

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0045] The following are preparation examples of methyl p-coumarate.

[0046] Preparation Example 1

[0047] Wash and crush 10 parts of bagasse as raw materials. Using the Soxhlet extraction method, add 50 parts of a mixed solvent of toluene and ethanol mixed in a ratio of 2:1 for lignin extraction for 6 hours to remove fat-soluble impurities. Add 3%wt sodium hydroxide according to a solid-liquid ratio of 1:15 (w / v), and add 2 parts of Na 2 SO 3 , carry out alkaline hydrolysis in a high-pressure reactor for 3 hours, then adjust the pH to 2.2 with 18%wt hydrochloric acid, let it stand and precipitate for 10 hours, centrifuge, and purify to obtain p-coumaric acid. Then prepare the corresponding reagents according to the molar ratio of p-coumaric acid to thionyl chloride, DMF, and methanol of 1:1.3:0.1:5. Add thionyl chloride and DMF (N,N-dimethylformamide) to the obtained p-coumaric acid, heat to 50°C, stir and react for 3 hours until the solid is completely dissolved, distill off the excess thionyl chloride under reduced pressure to obtain p-coumaroyl chloride, dissolve it in part of methanol, cool it to 0°C in an ice bath, and slowly add dropwise the remaining methanol solution, slowly raise the temperature to room temperature and react for 5 hours. After the reaction, distill off methanol under reduced pressure, extract with ethyl acetate, and recrystallize to obtain methyl p-coumarate.

[0048] Preparation Example 2

[0049] Wash and crush 10 parts of bagasse as raw material. Using the Soxhlet extraction method, add 60 parts of a mixed solvent of toluene and ethanol mixed in a ratio of 2:1, and extract lignin for 6 hours. Remove fat-soluble impurities. Add 3% wt sodium hydroxide according to a solid-liquid ratio of 1:15 (w / v), and add 1.5 parts of Na 2 SO 3 , and carry out alkaline hydrolysis in a high-pressure reactor for 3 hours. Then adjust the pH to 2.2 with 18% wt hydrochloric acid, let it stand and precipitate for 15 hours, centrifuge and purify to obtain p-coumaric acid. Then prepare the corresponding reagents according to a molar ratio of p-coumaric acid, thionyl chloride, DMF, and methanol of 1:1.3:0.1:5. Add thionyl chloride and DMF (N,N-dimethylformamide) to the obtained p-coumaric acid, heat to 60 °C, stir and react for 3 hours until the solid completely dissolves. Distill off the excess thionyl chloride under reduced pressure to obtain p-coumaroyl chloride, dissolve it in part of methanol, cool it to 5 °C in an ice bath, and slowly add dropwise the remaining methanol solution, and slowly warm up to room temperature and react for 5 hours. After the reaction, distill off methanol under reduced pressure, extract with ethyl acetate, and recrystallize to obtain methyl p-coumarate.

[0050] Preparation Example 3

[0051] Compared with Preparation Example 2, this preparation example is only different in that: let it stand and precipitate for 13 hours, and add thionyl chloride and DMF (N,N-dimethylformamide) to the obtained p-coumaric acid, heat to 58 °C, stir and react for 3 hours until the solid completely dissolves. Distill off the excess thionyl chloride under reduced pressure to obtain p-coumaroyl chloride, dissolve it in part of methanol, cool it to 2 °C in an ice bath, and keep other steps the same to prepare methyl p-coumarate.

[0052] Methyl p-coumarate can be prepared in situ using sugarcane waste residue, or it can be directly purchased, and its CAS number is 19367-38-5.

[0053] The following are examples of fluorocarbon powder coatings. Among them, the CAS number of 2,2,3,3,3-pentafluoropropyl acrylate is 356-86-5; the CAS number of MMA (hexafluorobutyl methacrylate) is 36405-47-7.

[0054] Example 1

[0055] Mix 65 parts of methyl methacrylate, 10 parts of butyl acrylate, 10 parts of 2-hydroxyethyl methacrylate, 6 parts of hexafluorobutyl methacrylate and 10 parts of methyl p-coumarate evenly, add 100 parts of the solvent propylene glycol monomethyl ether acetate, and stir for 10 min to obtain a premixed solution; then transfer the premixed solution to a reaction kettle, and introduce N 2Evacuate the air completely, heat up to 88 °C, slowly add 1 part of initiator benzoyl peroxide (BPO), keep the temperature for 6 h. When the conversion rate is greater than 95%, terminate the reaction, cool down to 60 °C, add neutralizing agent ammonia water, adjust the pH to 8, filter to remove unreacted impurities, obtain a transparent resin solution, dry and crush it to obtain the modified acrylic resin. Among them, methyl p - coumarate is prepared according to Preparation Example 1.

[0056] Mix 99 parts of methyl methacrylate (MMA) and 3 parts of 2,2,3,3,3 - pentafluoropropyl acrylate evenly, add 100 parts of tetrahydrofuran (THF), then add 0.5 part of initiator azobisisobutyronitrile (AIBN), stir until completely dissolved, purge with nitrogen for 20 min to remove oxygen, slowly heat up to 60 °C, keep the temperature for 2 h, then heat up to 75 °C, carry out a constant - temperature reaction for 8 h. When the conversion rate > 95%, terminate the reaction, cool down to below 38 °C, add methanol to precipitate the polymer, filter, wash with methanol 4 times to remove unreacted monomers and solvents, and dry in vacuum at 50 °C for 24 h to obtain granular modified PMMA.

[0057] Mix 80 parts of the modified acrylic resin, 6 parts of self - blocking isophorone diisocyanate, 1.5 parts of polytetrafluoroethylene, and 20 parts of nano - silica evenly, put them into a melt extruder for melt mixing and uniform dispersion, then melt - extrude, press into sheets, cool, and finely crush to obtain Material A. Put 30 parts of PVDF fluorocarbon resin and 8 parts of nano - silica into a reaction kettle, stir for 15 min, heat up to 120 °C, keep the temperature and stir for 10 min, adjust the temperature to 100 °C, add 0.5 part of polytetrafluoroethylene and 5 parts of dibutyltin dilaurate, keep the temperature and stir for 10 min, adjust the temperature to 80 °C, add 10 parts of modified PMMA, then add Material A, keep the temperature and stir for 20 min, feed it into a forced feeder, mix evenly, cool and press into sheets, cool to room temperature, carry out multi - stage crushing, control the nitrogen pressure at 0.7 MPa, flow rate 10 m 2 / min, carry out standard screening to obtain powder particles with a particle size of 5 - 35 microns, and carry out spheroidization treatment to obtain powder coatings.

[0058] Example 2

[0059] Mix 40 parts of methyl methacrylate, 20 parts of butyl acrylate, 6 parts of 2 - hydroxyethyl methacrylate, 3 parts of 2,2,3,3,3 - hexafluorobutyl methacrylate and 7 parts of methyl p - coumarate evenly, add 70 parts of solvent xylene, stir for 10 min to obtain a premixed solution; then transfer the premixed solution to a reaction kettle, and introduce N 2Evacuate the air completely, heat up to 80 °C, slowly add 0.5 parts of initiator azobisisobutyronitrile (AIBN), keep the temperature for 4 h, terminate the reaction when the conversion rate is greater than 95%, cool down to 50 °C, add neutralizer ammonia water, adjust the pH to 7, filter to remove unreacted impurities, obtain a transparent resin solution, dry and pulverize to obtain the modified acrylic resin. Among them, methyl p -coumarate is prepared by Preparation Example 2.

[0060] Mix 90 parts of methyl methacrylate (MMA) and 0.5 parts of 2,2,3,3,3 - pentafluoropropyl acrylate evenly, add 50 - 100 parts of tetrahydrofuran (THF), then add 0.1 part of initiator azobisisobutyronitrile (AIBN), stir until completely dissolved, purge with nitrogen for 20 min to remove oxygen, slowly heat up to 65 °C, keep the temperature for 1 h, then heat up to 80 °C, carry out a constant - temperature reaction for 6 h, terminate the reaction when the conversion rate > 95%, cool down to below 38 °C, add methanol to precipitate the polymer, filter, wash with methanol twice to remove unreacted monomers and solvents, dry in vacuum at 50 °C for 24 h to obtain granular modified PMMA.

[0061] Mix 70 parts of the modified acrylic resin, 1 part of ε - caprolactam - blocked isophorone diisocyanate, 0.1 part of polytetrafluoroethylene, and 3 parts of mica powder evenly, put them into a melt extruder for melt mixing and uniform dispersion, then melt - extrude, press into sheets, cool, and finely pulverize to obtain Material A. Put 20 parts of PVDF fluorocarbon resin and 2 parts of filler mica powder into a reaction kettle, stir for 15 min, heat up to 85 °C, keep stirring for 20 min, adjust the temperature to 100 °C, add 0.1 part of polytetrafluoroethylene and 1 part of dibutyltin laurate, keep stirring for 20 min, adjust the temperature to 50 °C, add 5 parts of modified PMMA, then add Material A, keep stirring for 40 min, feed into a forced feeder, mix evenly, cool and press into sheets, cool to room temperature, carry out multi - stage pulverization, control the nitrogen pressure at 0.7 MPa, flow rate 5 m 2 / min, perform standard screening to obtain powder particles with a particle size of 5 - 35 microns, and carry out spheroidization treatment to obtain the powder coating.

[0062] Example 3

[0063] Mix 50 parts of methyl methacrylate, 15 parts of butyl acrylate, 8 parts of 2 - hydroxyethyl methacrylate, 4 parts of 1H,1H,2H,2H - hexafluorobutyl methacrylate and 8 parts of methyl p -coumarate evenly, add 80 parts of solvent toluene, stir for 10 min to obtain a premixed solution; then transfer the premixed solution to a reaction kettle, and introduce N 2Evacuate the air completely, heat up to 85 °C, slowly add 0.6 parts of initiator azobisisobutyronitrile (AIBN), keep the temperature for 5 h. When the conversion rate is greater than 95%, terminate the reaction, cool down to 55 °C, add neutralizer ammonia water, adjust the pH to 8, filter to remove unreacted impurities, obtain a transparent resin solution, dry and crush it to get the modified acrylic resin. Among them, methyl p -coumarate is prepared by Preparation Example 3.

[0064] Mix 95 parts of methyl methacrylate (MMA) and 2 parts of 2,2,3,3,3 - pentafluoropropyl acrylate evenly, add 90 parts of tetrahydrofuran (THF), then add 0.3 parts of initiator azobisisobutyronitrile (AIBN), stir until completely dissolved, purge with nitrogen for 20 min to remove oxygen, slowly heat up to 60 °C, keep the temperature for 1.5 h, then heat up to 76 °C, carry out a constant - temperature reaction for 6 h. When the conversion rate > 95%, terminate the reaction, cool down to below 38 °C, add methanol to precipitate the polymer, filter, wash with methanol 3 times to remove unreacted monomers and solvents, and dry in vacuum at 50 °C for 24 h to obtain granular modified PMMA.

[0065] Mix 75 parts of modified acrylic resin, 5 parts of ε - caprolactam - blocked isophorone diisocyanate, 0.6 part of polytetrafluoroethylene, and 10 parts of nano - silica evenly, put them into a melt extruder for melt - mixing and uniform dispersion, then melt - extrude, press into sheets, cool, and finely crush to obtain Material A. Put 25 parts of PVDF fluorocarbon resin and 3 parts of filler nano - silica into a reaction kettle, stir for 15 min, heat up to 110 °C, keep stirring for 15 min, adjust the temperature to 90 °C, add 0.3 part of polytetrafluoroethylene and 2 parts of dibutyltin dilaurate, keep stirring for 15 min, adjust the temperature to 60 °C, add 8 parts of modified PMMA, then add Material A, keep stirring for 30 min, feed it into a forced feeder, mix evenly, cool and press into sheets, cool to room temperature, carry out multi - stage crushing, control the nitrogen pressure at 0.7 MPa, flow rate 6 m 2 / min, perform standard screening to obtain powder particles with a particle size of 5 - 35 microns, and carry out spheroidization treatment to obtain powder coatings.

[0066] Example 4

[0067] Mix 55 parts of methyl methacrylate, 15 parts of butyl acrylate, 8 parts of 2 - hydroxyethyl methacrylate, 3 parts of 1H,1H,2H,2H - hexafluorobutyl methacrylate and 8 parts of methyl p -coumarate evenly, add 80 parts of solvent toluene, stir for 10 min to obtain a premixed solution; then transfer the premixed solution to a reaction kettle, and introduce N 2Evacuate the air completely, heat up to 85 °C, slowly add 0.6 parts of initiator azobisisobutyronitrile (AIBN), keep the temperature for 5 h. When the conversion rate is greater than 95%, terminate the reaction, cool down to 55 °C, add neutralizing agent ammonia water, adjust the pH to 8, filter to remove unreacted impurities, obtain a transparent resin solution, dry and crush it to obtain the modified acrylic resin. Among them, methyl p -coumarate is prepared according to Preparation Example 3.

[0068] Mix 96 parts of methyl methacrylate (MMA) and 2 parts of 2,2,3,3,3 - pentafluoropropyl acrylate evenly, add 90 parts of tetrahydrofuran (THF), then add 0.3 parts of initiator azobisisobutyronitrile (AIBN), stir until completely dissolved, purge with nitrogen for 20 min to remove oxygen, slowly heat up to 60 °C, keep the temperature for 1.5 h, then heat up to 78 °C, carry out a constant - temperature reaction for 6 h. When the conversion rate > 95%, terminate the reaction, cool down to below 38 °C, add methanol to precipitate the polymer, filter, wash with methanol 3 times to remove unreacted monomers and solvents, and dry in vacuum at 50 °C for 24 h to obtain granular modified PMMA.

[0069] Mix 76 parts of the modified acrylic resin, 5 parts of self - blocking isophorone diisocyanate, 0.6 part of polytetrafluoroethylene, and 10 parts of nano - silica evenly, put them into a melt extruder for melt mixing and uniform dispersion, then melt - extrude, press into sheets, cool, and finely crush to obtain Material A. Put 25 parts of PVDF fluorocarbon resin and 3 parts of filler nano - silica into a reaction kettle, stir for 15 min, heat up to 110 °C, keep stirring for 15 min, adjust the temperature to 90 °C, add 0.3 part of polytetrafluoroethylene and 2 parts of dibutyltin dilaurate, keep stirring for 15 min, adjust the temperature to 60 °C, add 7 parts of modified PMMA, then add Material A, keep stirring for 30 min, feed it into a forced feeder, mix evenly, cool and press into sheets, cool to room temperature, carry out multi - stage crushing, control the nitrogen pressure at 0.7 MPa, the flow rate at 8 m 2 / min, carry out standard screening to obtain powder particles with a particle size of 5 - 35 microns, and carry out spheroidization treatment to obtain powder coatings.

[0070] Example 5

[0071] Mix 55 parts of methyl methacrylate, 12 parts of butyl acrylate, 8 parts of 2 - hydroxyethyl methacrylate, 2 parts of 2,2,3,3,3 - hexafluorobutyl methacrylate and 8 parts of methyl p -coumarate evenly, add 80 parts of solvent toluene, stir for 10 min to obtain a premixed solution; then transfer the premixed solution to a reaction kettle, and introduce N 2Evacuate the air completely, heat up to 85 °C, slowly add 0.6 parts of initiator azobisisobutyronitrile (AIBN), keep the temperature for 5 h. When the conversion rate is greater than 95%, terminate the reaction, cool down to 55 °C, add neutralizing agent ammonia water, adjust the pH to 8, filter to remove unreacted impurities, obtain a transparent resin solution, dry and crush it to get the modified acrylic resin. Among them, methyl p - coumarate is prepared according to Preparation Example 2.

[0072] Mix 97 parts of methyl methacrylate (MMA) and 2 parts of 2,2,3,3,3 - pentafluoropropyl acrylate evenly, add 92 parts of tetrahydrofuran (THF), then add 0.3 parts of initiator azobisisobutyronitrile (AIBN), stir until completely dissolved, purge with nitrogen for 20 min to remove oxygen, slowly heat up to 60 °C, keep the temperature for 1.5 h, then heat up to 78 °C, carry out a constant - temperature reaction for 6 h. When the conversion rate > 95%, terminate the reaction, cool down to below 38 °C, add methanol to precipitate the polymer, filter, wash with methanol 3 times to remove unreacted monomers and solvents, dry in vacuum at 50 °C for 24 h to obtain granular modified PMMA.

[0073] Mix 75 parts of the modified acrylic resin, 4 parts of self - blocking isophorone diisocyanate, 0.8 parts of polytetrafluoroethylene, and 10 parts of nano - silica evenly, put them into a melt extruder for melt mixing and uniform dispersion, then melt - extrude, press into sheets, cool, and finely crush to obtain Material A. Put 26 parts of PVDF fluorocarbon resin and 3 parts of filler nano - silica into a reaction kettle, stir for 15 min, heat up to 110 °C, keep stirring for 15 min, adjust the temperature to 93 °C, add 0.3 parts of polytetrafluoroethylene and 2 parts of dibutyltin dilaurate, keep stirring for 15 min, adjust the temperature to 60 °C, add 8 parts of modified PMMA, then add Material A, keep stirring for 30 min, feed it into a forced feeder, mix evenly, cool and press into sheets, cool to room temperature, carry out multi - stage crushing, control the nitrogen pressure at 0.7 MPa, the flow rate at 6 m 2 / min, carry out standard screening to obtain powder particles with a particle size of 5 - 35 microns, and carry out spheroidization treatment to obtain powder coatings.

[0074] The present invention also carried out the following comparative examples and related tests

[0075] Comparative Example 1

[0076] The difference from Example 4 is only that methyl methacrylate is used instead of methyl p - coumarate, that is, the addition amount of methyl methacrylate is 63 parts in the process of preparing the modified acrylic resin, and other components and preparation processes are the same as those in Example 4, and powder coatings are prepared.

[0077] Comparative Example 2

[0078] The difference from Example 4 is only that traditional nano-zinc oxide is used instead of methyl p-coumarate, and other components and the preparation process are the same as those in Example 4, and a powder coating is prepared.

[0079] Comparative Example 3

[0080] The difference from Example 4 is only that the preparation of modified PMMA is not carried out, but conventional PMMA is used instead, and other components and the preparation process are the same as those in Example 4, and a powder coating is prepared.

[0081] Performance detection test

[0082] According to the following standards, the powder coatings obtained in Examples 1-5 and Comparative Examples 1-3 were tested for weather resistance, salt spray resistance, adhesion, hardness, ultraviolet light resistance and antioxidant performance.

[0083] (I) Weather resistance test

[0084] The detection method refers to the standard GB / T 1865-2009, artificial weathering for 1000H, irradiance: 0.51 (W / m 2 @340nm), BST: 65 °C, temperature inside the chamber: 38 °C, humidity inside the chamber: 50%RH, stage 1: light exposure, 102 min, stage 2: light exposure, 18 min, spray the front of the specimen, total test time: 1000h; result requirement: color change ≤ 2 levels, loss of gloss ≤ 2 levels, no abnormal phenomena such as powdering, bubbling, cracking, peeling, etc. The final test results are summarized in Table 1 below.

[0085] (II) Salt spray resistance test

[0086] The detection method refers to the standard GB / T 10125-2021, and the salt spray resistance is detected for 900H. An intelligent salt spray corrosion test chamber is used, and the instrument number is E-033-011TD. The result requirement: at the scribed line: unidirectional rust ≤ 2.0 mm, in the non-scribed area: no abnormality. The final test results are summarized in Table 1 below.

[0087] Table 1

[0088]

[0089] From the test results in Table 1 above, it can be clearly seen that the powder coating products obtained in Examples 1-5 prepared by the present invention have excellent artificial weathering resistance and salt spray resistance, and can meet the requirements of high weather resistance and salt spray resistance for high-end buildings and ships.

[0090] From the test results of Comparative Examples 2-3, it can be seen that the powder coatings obtained in Comparative Example 2 should be resistant to salt rust after adding metal oxides. However, due to poor compatibility and poor adhesion, there is a slight peeling in some parts; the powder coatings obtained in Comparative Example 3 have insufficient binding force of the bonding aid, cannot withstand long-term weather resistance and salt spray resistance tests, are prone to local aging and delamination, and there are slight blisters or even cracks, which cannot meet the requirements of high-performance coating products.

[0091] (III) Adhesion Test

[0092] The adhesion test was carried out with reference to the standard GB / T 9286-2021. A coating adhesion tester was used, with the instrument number E-008-011TD. The test conditions were: (23±2) °C, (50±5) %, 16 h. A square grid was drawn, the grid spacing was 2 mm, the number of grid lines in each direction was 6, the tape type was 3M 600, the tape peeling angle was 60°, and the material type was hard; the result requirement was: ≤1 level. The final test results are summarized in Table 2 below.

[0093] (IV) Hardness (Scratch) Test

[0094] The hardness (scratch) test was carried out with reference to the standard GB / T 6739-2022, and the detection was carried out before 1000 h of artificial weathering and after 1000 h of artificial weathering of the fluorocarbon powder coating. The technical requirement was: hardness >1H. The final test results are summarized in Table 2 below.

[0095] (V) UV Resistance Test

[0096] The test method was carried out with reference to the standard GB / T 1865-2009. The evaluation standard of the test result was whether there was color change. The technical requirement was: no color change. The final test results are summarized in Table 2 below.

[0097] (VI) Antioxidation Test

[0098] The test method was carried out with reference to the standard GB / T 1766-2008. The evaluation standard of the test result was whether there was powdering phenomenon. The technical requirement was: no powdering. The final test results are summarized in Table 2 below.

[0099] Table 2

[0100]

[0101] From the test results in Table 2 above, it can be clearly seen that the powder coating products obtained in Examples 1-5 prepared by the present invention have excellent adhesion, hardness, UV resistance and antioxidant properties, and can meet the requirements of high-performance powder coatings.

[0102] From the test results of Comparative Examples 1-2, it can be seen that although the powder coating obtained in Comparative Example 1 has excellent adhesion performance, its ultraviolet resistance and antioxidant properties are poor, and the hardness after aging also decreases. This shows that the modification of methyl p-coumarate on acrylic resin can significantly improve the ultraviolet resistance and oxidation resistance, and thus also affect the hardness performance during long-term aging. The powder coating of Comparative Example 2, due to the addition of metal oxides, although it can improve the ultraviolet resistance, has poor compatibility, which will affect the adhesion of the product and cannot meet the requirements of high-performance coating products.

[0103] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a fluorocarbon powder coating, characterized in that: The following steps are involved: S1: premixing methyl methacrylate, hydroxyethyl methacrylate, hexafluorobutyl methacrylate, methyl p-coumarate and a solvent to obtain a premixed solution; S2: transferring the premixed liquid to a reaction kettle, heating it, adding an initiator, reacting it, filtering it, and drying it to obtain a modified acrylic resin; S3: uniformly mixing the modified acrylic resin and the filler, performing melt kneading, and extruding to obtain material A; S4: Put PVDF fluorocarbon resin and filler into a reaction kettle, heat up, stir to obtain material B, add material A and modified PMMA, mix evenly, cool and tablet to obtain powder coating; The modified PMMA is obtained by copolymerizing 2,2,3,3,3-pentafluoropropyl acrylate with MMA; The mass ratio of material A to material B is (2-3): (7-8); In the premixed liquid, the mass proportion of hexafluorobutyl methacrylate is 3-8%.

2. The method for preparing a fluorocarbon powder coating according to claim 1, characterized in that: The methyl p-coumarate is prepared by the following method: a. The raw material bagasse is washed and crushed, and lignin is extracted by Soxhlet extraction, and then alkaline hydrolysis is performed in a high pressure reactor, followed by acid precipitation and purification to obtain p-coumaric acid; b. Add thionyl chloride and DMF to the obtained p-coumaric acid, heat and stir to react until the solid is completely dissolved, and distill under reduced pressure to obtain p-coumaryl chloride, which is dissolved in methanol, placed in an ice bath, and methanol is added dropwise. The temperature is slowly raised to room temperature for reaction. After the reaction is completed, distill under reduced pressure, extract, and recrystallize to obtain methyl p-coumarate.

3. The method for preparing a fluorocarbon powder coating according to claim 2, characterized in that: In the step a, 3%wt sodium hydroxide and an antioxidant Na2SO3 are used to perform alkaline hydrolysis in a high-pressure reactor, and then 18%wt hydrochloric acid is used to adjust the pH to 2.2, and the mixture is allowed to stand for precipitation for 10-15h, centrifuged, and purified to obtain p-coumaric acid; In the step b, heating to 50-60°C, stirring and reacting for 3 hours until the solid is completely dissolved, distilling under reduced pressure to obtain p-coumaroyl chloride, dissolving in methanol, cooling to 0-5°C in an ice bath, then dropping methanol, slowly heating to room temperature and reacting for 5 hours; The molar ratio of p-coumaric acid to thionyl chloride, DMF and methanol is 1:1.3:0.1:

5.

4. The method for preparing a fluorocarbon powder coating according to claim 1, characterized in that: The modified PMMA is prepared by the following method: MMA and 2,2,3,3,3-pentafluoropropyl acrylate are uniformly mixed, tetrahydrofuran is added, and then an initiator is added, and the mixture is stirred until completely dissolved, nitrogen is passed through for deoxygenation, the mixture is heated, kept warm, reacted, cooled, methanol is added, filtered, washed, and vacuum dried to obtain granular modified PMMA; the mass of the added 2,2,3,3,3-pentafluoropropyl acrylate accounts for 0.5-3% of the mass of the total modified PMMA.

5. The method for preparing a fluorocarbon powder coating according to claim 4, characterized in that: In the preparation process of the modified PMMA, an initiator is added, azobisisobutyronitrile is passed through nitrogen for 20 minutes for deoxygenation, the temperature is slowly raised to 60-65°C, kept warm for 1-2 hours, then raised to 75-80°C, kept at a constant temperature for 6-8 hours, cooled to below 38°C, methanol is added, filtered, washed with methanol for 2-4 times, and vacuum dried at 50°C for 24 hours to obtain granular modified PMMA.

6. The method for preparing a fluorocarbon powder coating according to claim 1, characterized in that: In the step S2, the premixed liquid is transferred to a reactor, N2 is introduced to remove the air, the temperature is raised to 80-88°C, an initiator is slowly added dropwise, the temperature is kept for 4-6 hours, the temperature is lowered to 50-60°C, ammonia water as a neutralizing agent is added, the pH is adjusted to 7-8, the mixture is filtered, dried, and crushed to obtain a modified acrylic resin.

7. The method for preparing a fluorocarbon powder coating according to claim 1, characterized in that: In the step S3, the modified acrylic resin, the curing agent, the surface lubricant and the filler are uniformly mixed, and a melt extruder is used for melt mixing and extrusion. The temperature of the melt extruder zone I is set to 105° C., and the temperature of the melt extruder zone II is set to 95° C.; the curing agent is one of self-sealed isophorone diisocyanate and caprolactam-sealed isophorone diisocyanate, and the surface lubricant is polytetrafluoroethylene.

8. The method for preparing a fluorocarbon powder coating according to claim 1, characterized in that: In the step S4, PVDF fluorocarbon resin and filler are placed in a reaction kettle, stirred for 15 minutes, heated to 95-120°C, kept warm and stirred for 10-20 minutes, the temperature is adjusted to 80-100°C, a surface lubricant and an accelerator are added, kept warm and stirred for 10-20 minutes to obtain material B, the temperature is adjusted to 60-80°C, material A and modified PMMA are added, kept warm and stirred for 20-40 minutes, fed into a feeder, mixed evenly, cooled and tableted, multi-stage crushing is performed, and the nitrogen pressure is controlled to be 0.7MPa and the flow rate is 5-10m 2 / min, sieving to obtain powder particles with a particle size of 5-35 microns, and spheroidizing to obtain powder coating; the accelerator is dibutyltin laurate.

9. The method for preparing a fluorocarbon powder coating according to claim 1, characterized in that: The solvent added in step S1 is one of propylene glycol methyl ether acetate, toluene and xylene; in step S2, the initiator added is azobisisobutyronitrile or benzoyl peroxide; and the filler is one of nano-silicon dioxide and mica powder.

10. A fluorocarbon powder coating, characterized in that: The fluorocarbon powder coating is prepared by the preparation method of any one of claims 1 to 9, comprising the following components in parts by weight: 20-30 parts of PVDF fluorocarbon resin, 1-8 parts of curing agent, 5-30 parts of filler, 0.2-2 parts of surface smoothing agent, 0.5-5 parts of accelerator, 70-80 parts of modified acrylic resin, and 5-10 parts of modified PMMA; The modified acrylic resin includes the following raw materials in parts by weight: 40-65 parts of methyl methacrylate, 10-20 parts of butyl acrylate, 4-10 parts of hydroxyethyl methacrylate, 1-6 parts of hexafluorobutyl methacrylate, 3-10 parts of methyl p-coumarate, 70-100 parts of solvent, and 0.5-1 part of initiator; The modified PMMA comprises the following raw materials in parts by weight: 90-99 parts of MMA, 0.5-3 parts of 2,2,3,3,3-pentafluoropropyl acrylate, 50-100 parts of tetrahydrofuran, and 0.1-0.6 parts of initiator.

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