Lightweight powder coating based on furfural-fluorocarbon modified polyester resin and preparation method thereof

Abstract

The invention discloses a light-weight powder coating based on furfural-fluorocarbon modified polyester resin and a preparation method of the light-weight powder coating. The powder coating takes furfural-fluorocarbon modified polyester resin and organic silicon modified polyester resin as composite film forming base materials, and adopts a composite curing agent of blocked polyisocyanate and beta-hydroxyalkylamide. By means of collaborative optimization of resin molecule design and a curing system, the paint can achieve the adhesive force of 0 grade, the impact resistance of 50 cm, the salt mist resistance of more than 10000 hours and the damp heat resistance and ultraviolet aging resistance of 3000 hours under the condition of an ultrathin coating of about 50 micrometers, and the comprehensive performance is excellent. The product is particularly suitable for long-term protection of extreme corrosion environments such as ocean tidal energy equipment, offshore wind power and cross-sea bridges.

Description

Technical Field

[0001] This invention belongs to the field of marine engineering coatings technology, and specifically relates to a high-performance lightweight powder coating based on furfural-fluorocarbon modified polyester resin and its preparation method for use in harsh conditions such as marine corrosive environments, tidal power generation equipment, and offshore wind power equipment. Background Technology

[0002] In the acquisition of marine energy, tidal energy utilization mainly involves converting the kinetic energy generated by ocean tides into electricity, thereby providing a boost to the development of coastal countries. Tidal power generation equipment, such as tidal generators, operates in harsh environments characterized by high salinity, high humidity, strong ultraviolet radiation, and temperature fluctuations, placing extremely high demands on the protective performance of coatings. Currently, traditional protective systems widely used in marine engineering, such as solvent-based epoxy resin coatings and chlorinated rubber coatings, suffer from problems such as high volatile organic compound (VOC) emissions, thick cured film layers, increased equipment load, long construction cycles, and difficulties in recoating and maintenance.

[0003] Powder coatings, as a representative of environmentally friendly coatings, have outstanding advantages such as being solvent-free, recyclable, and highly efficient, making them one of the best alternatives to traditional solvent-based coatings. However, conventional outdoor polyester powder coatings are insufficient to meet the marine environment's protection life requirements of over 20 years in terms of long-term salt spray resistance, damp heat resistance, and UV aging resistance. Furthermore, traditional petroleum-based polyester resins also face the challenges of depleting non-renewable resources and increasing carbon emission pressures.

[0004] Furfural, as an important bio-based platform compound, can be produced on a large scale from agricultural and forestry wastes such as corn cobs and sugarcane bagasse. Its downstream product, 2,5-furandicarboxylic acid (FDCA), is an ideal bio-based alternative to terephthalic acid (PTA). The rigid furan ring structure of FDCA can endow polyester resins with higher glass transition temperatures, mechanical strength, and chemical resistance. Combining FDCA with fluorocarbon units, which have extremely low surface energy and excellent weather resistance, through molecular design holds promise for creating a new generation of bio-based high-performance polyester resins.

[0005] Meanwhile, the curing system of powder coatings plays a decisive role in their final performance. A single curing agent system often cannot meet multiple performance requirements: although β-hydroxyalkylamide (HAA) curing agents are non-toxic and have good weather resistance, their fast curing speed can easily lead to poor leveling and pinhole defects; blocked polyisocyanate curing agents can provide excellent chemical resistance, high hardness and flexibility, but their unblocking temperature is high, their curing speed is slow, and their cost is high.

[0006] Therefore, developing a powder coating based on bio-based polymer resin, through innovative resin synthesis and curing agent compounding technology, to achieve ultra-long durability and excellent comprehensive performance under thin coating is not only of great technical significance, but also has significant economic and social benefits. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a lightweight powder coating based on furfural-fluorocarbon modified polyester resin, which has good overall performance, thin film, lightweight, excellent curing characteristics, and is environmentally friendly, as well as its preparation method. The powder coating of this invention can maintain or even exceed the protective effect of conventional thick coatings even with a coating thickness as thin as 50 μm.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides a lightweight powder coating comprising the following raw materials in parts by weight: 40-60 parts furfural-fluorocarbon modified polyester resin, 10-20 parts organosilicon modified polyester resin, 5-10 parts curing agent, 0.5-2 parts leveling agent, 0.3-1 parts defoamer, 1-3 parts dispersant, 15-25 parts titanium dioxide, 5-10 parts zinc phosphate, 3-8 parts silicon carbide, 10-20 parts lightweight filler, 0.5-2 parts benzotriazole ultraviolet absorber, and 5-10 parts aluminum powder (added through bonding process).

[0009] The curing agent is prepared by compounding a blocked polyisocyanate curing agent and a β-hydroxyalkylamide curing agent in a weight ratio of 1 to 3:1, preferably 1.5 to 2:1.

[0010] Furthermore, the weight ratio of furfural-fluorocarbon modified polyester resin to organosilicon modified polyester resin is 2~6:1, preferably 2~3:1.

[0011] Further, the furfural-fluorocarbon modified polyester resin is prepared by the following method: 2,5-furandicarboxylic acid (FDCA), fluorinated diol, terephthalic acid (PTA), isophthalic acid (IPA), neopentyl glycol (NPG), trimethylolpropane (TMP), and catalyst monobutyltin oxide are subjected to an esterification reaction under nitrogen protection by stepwise temperature increase, followed by a polycondensation reaction under high vacuum until the acid value is ≤5 mgKOH / g, thus obtaining the resin.

[0012] The mass ratio of 2,5-furandicarboxylic acid, fluorinated diol, terephthalic acid, isophthalic acid, neopentyl glycol, trimethylolpropane, and esterification catalyst is 20-40:5-15:25-40:5-15:30-45:1-3:0.3-0.8. The fluorinated diol is preferably a perfluoropolyether diol with a number-average molecular weight (Mn) of 500-10000.

[0013] The stepwise heating process involves uniformly raising the temperature from room temperature to 180°C over 2 hours and holding it at 180°C for 1 hour; then raising the temperature to 220°C over 1.5 hours and maintaining the reaction at 220°C for 3-5 hours.

[0014] The polycondensation reaction is carried out under a vacuum of -0.05 to -0.1 MPa and a temperature of 230-250℃ for 1-2 hours.

[0015] The preparation method of the furfural-fluorocarbon modified polyester resin further includes: after the reaction is completed, cooling the reactants to below 190°C, adding an antioxidant, stirring and mixing thoroughly, pouring out, cooling to form solid flakes, and then crushing into uniform particles with a particle size of less than 5 mm to obtain the furfural-fluorocarbon modified polyester resin. The mass ratio of the antioxidant to neopentyl glycol is 0.1-0.5:30-45.

[0016] Furthermore, the organosilicon-modified polyester resin is prepared by the following method: first, a hydroxyl-terminated polyester intermediate is synthesized, and then the hydroxyl-terminated intermediate is used to undergo a ring-opening grafting reaction with the silane coupling agent γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) under the action of a catalyst to introduce organosilicon functional groups into the polyester chain.

[0017] A second aspect of the present invention provides a method for preparing the above-mentioned lightweight powder coating, comprising the following steps: a) All raw materials except aluminum powder are mixed at high speed, melt-extruded, cooled and pressed into sheets, crushed and finely ground and sieved to obtain base powder; b) Add the base powder into the bonding machine, add aluminum powder at 35-45°C and low speed stirring, and then switch to high speed stirring for 8-12 minutes for bonding. c) Cool the bonded powder to below 30°C and sieve it to obtain the lightweight powder coating.

[0018] The lightweight powder coating provided by this invention can achieve adhesion grade 0, impact resistance of 50cm, and salt spray resistance of over 10,000 hours and resistance to damp heat and ultraviolet aging of over 3,000 hours with an ultra-thin coating of about 50μm. It has excellent comprehensive performance and is particularly suitable for long-term protection in extreme corrosive environments such as marine tidal energy equipment, offshore wind power, and cross-sea bridges.

[0019] This invention utilizes the rigid furan ring structure of FDCA derived from furfural to effectively improve the heat resistance, mechanical strength, and hydrolysis resistance of the resin. Furthermore, by combining furfural-fluorocarbon resin with organosilicon-modified resin, the rigid framework based on bio-based materials and fluorocarbon materials synergistically modify the coating's weather resistance, chemical resistance, and low surface energy characteristics. Simultaneously, the organosilicon-modified resin, through its soft Si-O-Si backbone and reactive silane groups, effectively improves the coating's flexibility and adhesion, enabling the coating to maintain high hardness and strength while possessing excellent impact resistance and adhesion.

[0020] Furthermore, this invention combines blocked polyisocyanates with β-hydroxyalkylamides. β-hydroxyalkylamides provide a rapid curing reaction initiation rate, which is beneficial for melt leveling. Blocked polyisocyanates contribute high crosslinking density, giving the coating corrosion resistance and excellent long-term durability.

[0021] Through the comprehensive design of the above-mentioned resin and curing agent system, the coating of the present invention can achieve protective performance far exceeding that of conventional thick coatings with a thin coating of about 50μm, such as adhesion grade 0, impact resistance of 50cm, and salt spray resistance of more than 10,000 hours and resistance to damp heat and ultraviolet aging of more than 3,000 hours, thus achieving lightweight and efficient protection. Detailed Implementation

[0022] The present invention will be described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0023] Unless otherwise specified, the reagents and raw materials used in the following embodiments of the present invention are all common reagents and raw materials that are readily available in the art.

[0024] The synthesis method of furfural-fluorocarbon modified polyester resin in the following embodiments of the present invention is as follows: In a 10-liter stainless steel reactor equipped with a stirrer, fractionating column, condenser, thermometer, and high-purity nitrogen inlet pipe, 3000 g of 2,5-furandicarboxylic acid (FDCA, purity ≥99.5%), 3000 g of PTA, 1000 g of IPA, 4000 g of NPG, 200 g of TMP, 1000 g of perfluoropolyether glycol (Mn≈1000, fluorine content ~50%), and 50 g of esterification catalyst monobutyltin oxide were added. High-purity nitrogen (99.999% purity) was introduced to maintain the reaction system in an inert atmosphere at a flow rate of 200 mL / min for 15 minutes. Subsequently, slow heating was started, and after the reactants melted, stirring was initiated, with the initial stirring speed set at 50 rpm and gradually increased to 100 rpm. The esterification reaction was carried out using a stepped temperature ramping program: the temperature was uniformly increased from room temperature to 180°C over 2 hours and held at 180°C for 1 hour; then the temperature was increased to 220°C over 1.5 hours and maintained at 220°C. The temperature at the top of the distillation column was precisely controlled to not exceed 102°C, and the water produced in the reaction was collected. The esterification stage ended when the amount of water produced reached more than 92% of the theoretical value, and the acid value of the reactants decreased to 10-12 mgKOH / g as measured by acid-base titration.

[0025] Polycondensation reaction: The polycondensation reaction was carried out for approximately 1.5 hours under a vacuum of -0.1 MPa and a temperature of 240℃. Samples were taken periodically during the reaction, and the acid value of the resin was determined according to GB / T 6743-2008 standard. The reaction endpoint was reached when the acid value dropped to 4.2 mgKOH / g. Heating and vacuuming were stopped, and nitrogen was introduced into the reactor to restore atmospheric pressure. The reactants were cooled to below 190℃, and 30 g of antioxidant 1010 was added. The mixture was stirred thoroughly for 30 minutes to ensure uniform dispersion. Finally, the molten resin was quickly poured onto a water-cooled stainless steel belt to cool into solid sheets, which were then crushed into uniform particles with a particle size of less than 5 mm to obtain furfural-fluorocarbon modified polyester resin.

[0026] In the following embodiments of the present invention, the organosilicon-modified polyester resin can be prepared by methods known in the art. For example, the present invention provides a method for synthesizing organosilicon-modified polyester resin as follows: In a 5-liter four-necked flask, 2000 g PTA, 750 g IPA, 2400 g NPG, 150 g TMP, and 25 g monobutyltin oxide were added. Under nitrogen protection, the esterification polycondensation reaction was carried out using a stepwise temperature increase procedure similar to that used in the synthesis of furfural-fluorocarbon modified polyester resin: the temperature was raised to 240°C and maintained until the acid value of the reactants decreased to 3.8 mgKOH / g, as determined by titration. At this point, the polyester chain ends were mainly composed of primary hydroxyl groups, exhibiting high reactivity. The mixture was then cooled to 180°C, discharged, cooled, and crushed to obtain a hydroxyl-terminated polyester intermediate.

[0027] 4650 g of hydroxyl-terminated polyester intermediate (theoretical hydroxyl value approximately 35 mgKOH / g) was added to a reaction vessel and heated to 180°C until completely melted, while maintaining nitrogen protection. At a stirring speed of 100 rpm, a premixed solution of 350 g of γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) and 5 g of dibutyltin dilaurate (DBTDL) catalyst was slowly added dropwise through a constant-pressure dropping funnel, controlling the addition time to be completed within 1 hour. After the addition was complete, the reaction was maintained at 180-185°C for 2.5 hours. During this process, the epoxy groups of the KH-560 molecule underwent a ring-opening etherification reaction with the terminal hydroxyl groups of the polyester intermediate, forming stable COC covalent bonds, thereby chemically grafting the propyltrimethoxysilane segment to the end of the polyester molecular chain. After the reaction was completed, any remaining low-molecular-weight volatiles were removed under a vacuum of -0.1 MPa for 30 minutes. The material is discharged, cooled, and crushed to obtain silicone-modified polyester resin.

[0028] The powder coatings of Examples 1-5 and Comparative Examples 1-3 are shown in Table 1 below.

[0029] Table 1: Powder Coating Formulations (parts by weight) for Examples 1-5 and Comparative Examples 1-3

[0030] Powder coating preparation process: Premixing: According to the formula shown in Table 1, furfural-fluorocarbon resin, organosilicon modified resin, composite curing agent, leveling agent (MODAFLOW Powder 6000 from Guangzhou Fangxin), defoamer (benzoin), dispersant (BYK-2164), titanium dioxide (DuPont R-706), zinc phosphate, silicon carbide (800 mesh), light filler (precipitated barium sulfate), and ultraviolet absorber (BASF Tinuvin 405) are all put into a high-speed mixer (Henschel type) and mixed at 800 rpm for 3 minutes to ensure that the materials are initially uniform.

[0031] Melt extrusion: The premixed material is fed into a co-rotating twin-screw extruder (model SLJ-40, L / D ratio 40:1). The extruder temperature is precisely controlled at 105℃ in zone I, 115℃ in zone II, 110℃ at the die head, and the screw speed at 350 rpm. The material, in a molten state, undergoes kneading, shearing, and mixing to achieve full dispersion and partial pre-reaction of the components.

[0032] Tableting and Crushing: The molten material extruded from the extruder die is immediately passed through a double-roll cooling tablet press, where it is pressed into continuous sheets of approximately 1.2 mm thickness and cooled to room temperature (25°C) by a stainless steel cooling belt. The cooled, hard, and brittle sheets are then fed into a jaw crusher for primary crushing to obtain flaky particles with a particle size of less than 5 mm.

[0033] Fine grinding and sieving: The primary crushed material is fed into an ACM micro grinder for fine grinding. By adjusting the rotation speed of the classifying wheel, the particle size distribution of the powder is controlled, ensuring that the median particle size D50 is between 35-40 μm. The ground powder is then sieved through an 180-mesh (80 μm) vibrating screen to remove any coarse particles and impurities, yielding the base powder.

[0034] Metal Powder Bonding: The above-mentioned base powder is fed into a metal bonding mixer (Henschel type). First, under low-speed (300 rpm) stirring, the material temperature is slowly and evenly raised to 40°C through jacket hot water circulation. Then, while maintaining low-speed stirring and temperature, a specified amount of silver-coin type glitter aluminum powder (grade PC101, DSM) is slowly and evenly sprinkled in through the side feed port. After the aluminum powder is added, the stirring speed is quickly increased to high speed (1000 rpm) and run at this state for 10 minutes, utilizing high-speed shear force and frictional heat to firmly and evenly adhere (bond) the aluminum powder to the surface of the powder particles. After bonding is complete, the jacket is immediately switched to cooling water, and the material is cooled to below 30°C under continuous low-speed stirring.

[0035] Finished product sieving and packaging: The cooled bonding powder is passed through a 180-mesh vibrating screen again to remove any small amount of agglomerates that may be generated during the bonding process, thus obtaining the lightweight powder coating product of the present invention, which is then bagged and sealed for storage.

[0036] Performance testing and results analysis: All powder coatings prepared in the above examples and comparative examples were electrostatically sprayed and cured under the same process conditions. Specifically, using a Gema electrostatic spray gun at 70kV and 0.6MPa, the powder was sprayed onto a clean and dry Q235 carbon steel plate (150mm×70mm×1mm) that had undergone rigorous sandblasting treatment (Sa 2.5 grade). The dry film thickness was controlled to be 50±3 μm using a film thickness gauge. The samples were then cured in a forced-air oven at 180℃ for 15 minutes after reaching the set temperature. After curing, the samples were cured under standard conditions (temperature 23±2℃, relative humidity 50±5%) for 24 hours, followed by comprehensive performance testing. The test results are detailed in Table 2.

[0037] Table 2: Results of Comprehensive Coating Performance Tests

[0038] As can be seen from Table 2, the coatings prepared in all examples achieved the highest adhesion level of 0, indicating that the organosilicon-modified resin significantly enhanced the adhesion and impact resistance of the coating through the cross-linking effect of its reactive silane groups with the substrate surface and the interior of the resin.

[0039] The coatings prepared by the powder coatings in Examples 1-5 all exhibited excellent resistance to salt spray corrosion, damp heat, and weathering. This invention utilizes the synergistic effect of furfural-fluorocarbon modified polyester resin and organosilicon modified polyester resin, combined with a composite curing agent, to improve the coating's corrosion resistance, adhesion, and weather resistance, achieving optimal coating performance and meeting the requirements of coatings for marine corrosive environments, tidal power generation equipment, and offshore wind power equipment.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A lightweight powder coating, characterized in that, The components include the following parts by weight: 40-60 parts of furfural-fluorocarbon modified polyester resin; 10-20 parts of silicone-modified polyester resin; 5-10 parts of curing agent; Leveling agent 0.5-2 parts; 0.3-1 part defoamer; 1-3 parts dispersant; 15-25 parts titanium dioxide; 5-10 parts zinc phosphate; 3-8 parts of silicon carbide; 10-20 parts of lightweight filler; 0.5-2 parts of benzotriazole UV absorber; 5-10 parts aluminum powder; The curing agent is composed of a blocked polyisocyanate curing agent and a β-hydroxyalkylamide curing agent in a weight ratio of 1-3:1; the weight ratio of furfural-fluorocarbon modified polyester resin to organosilicon modified polyester resin is 2-4:

1.

2. The lightweight powder coating according to claim 1, characterized in that, The preparation method of the furfural-fluorocarbon modified polyester resin is as follows: 2,5-furandicarboxylic acid, fluorinated diol, terephthalic acid, isophthalic acid, neopentyl glycol, trimethylolpropane and esterification catalyst are subjected to esterification reaction by stepwise heating under nitrogen protection, followed by polycondensation reaction under high vacuum to obtain the resin.

3. The lightweight powder coating according to claim 2, characterized in that, The mass ratio of 2,5-furandicarboxylic acid, fluorinated diol, terephthalic acid, isophthalic acid, neopentyl glycol, trimethylolpropane, and esterification catalyst is 20-40:5-15:25-40:5-15:30-45:1-3:0.3-0.

8.

4. The lightweight powder coating according to claim 2, characterized in that, The stepped heating process is as follows: the temperature is uniformly increased from room temperature to 180°C within 2 hours and held at 180°C for 1 hour; then the temperature is increased to 220°C within 1.5 hours and the reaction is maintained at 220°C for 3-5 hours.

5. The lightweight powder coating according to claim 2, characterized in that, The polycondensation reaction is carried out under a vacuum of -0.05 to -0.1 MPa and a temperature of 230-250℃.

6. The lightweight powder coating according to claim 2, characterized in that, The preparation method of the furfural-fluorocarbon modified polyester resin further includes: after the reaction is completed, cooling the reaction material to below 190°C, adding an antioxidant, stirring and mixing thoroughly, pouring out, cooling into solid flakes, and then crushing into uniform particles with a particle size of less than 3 mm to obtain furfural-fluorocarbon modified polyester resin.

7. The lightweight powder coating according to claim 1, characterized in that, The organosilicon-modified polyester resin is prepared by a ring-opening grafting reaction between a hydroxyl-terminated polyester intermediate and a silane coupling agent.

8. A method for preparing a lightweight powder coating as described in any one of claims 1-7, characterized in that, Includes the following steps: a) The raw materials, excluding aluminum powder, in claim 1 are subjected to high-speed mixing, melt extrusion, cooling and pressing, crushing and fine grinding and sieving to obtain base powder; b) Add the base powder into the bonding machine, add aluminum powder at 35-45°C and low speed stirring, and then switch to high speed stirring for 8-12 minutes for bonding. c) Cool the bonded powder to below 30°C and sieve it to obtain the lightweight powder coating.

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