A bio-based epoxy resin anticorrosive powder coating and a preparation method thereof

Abstract

The present application relates to the technical field of powder coating, in particular to a bio-based epoxy resin anticorrosive powder coating and a preparation method thereof.The present application overcomes the problem that high bio-based content and corrosion resistance cannot be considered in the prior art.The powder coating of the present application is composed of modified epoxy resin, rosin-based epoxy resin, modified bio-based phenolic amine curing agent and titanate modified composite filler;the long chain structure of dimer acid and the rigid skeleton of rosin are used to achieve the rigid and tough balance of the coating;the curing agent modified by amino-terminated silicone oil is used to endow the coating surface with low surface energy and hydrophobic characteristics;the biochar loaded graphene and the in-situ grafting technology in the step temperature control extrusion process are combined to build a dense anticorrosive barrier;the problem of large brittleness and poor water resistance of bio-based coating is solved, and the present application is suitable for heavy anti-corrosion fields such as pipelines and marine facilities.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, specifically to a bio-based epoxy resin anti-corrosion powder coating and its preparation method. Background Technology

[0002] Powder coatings are widely used in industrial coatings due to their environmental friendliness, high utilization rate, and excellent performance. As a high-efficiency, economical, ecological, and energy-efficient environmentally friendly coating, powder coatings are widely used in heavy-duty corrosion protection fields such as pipeline anti-corrosion, marine facilities, and engineering machinery. To reduce dependence on fossil resources, utilizing renewable biomass resources, including vegetable oils, rosin, and cashew nut shell extract, to replace traditional petroleum-based bisphenol A epoxy resins has become a research hotspot in the field of polymer materials. However, in existing technologies, there is an irreconcilable technical contradiction between high bio-based content and high-performance corrosion protection, which severely limits the large-scale application of fully bio-based powder coatings.

[0003] First, bio-based epoxy resins often have an inherent defect in their molecular structure, which makes it difficult to balance rigidity and flexibility. Although long-chain aliphatic epoxy resins derived from vegetable oils give the coating excellent flexibility, their lack of a rigid skeleton results in an excessively low glass transition temperature, insufficient coating hardness, and the powder is prone to cold flow and clumping during storage and transportation, leading to poor storage stability. Conversely, bio-based resins derived from rosin or furan have rigid fused ring or heterocyclic structures and high modulus, but after curing, the crosslinking network is too dense and rigid, with high internal stress, making them prone to brittle fracture and unable to meet the impact resistance requirements of heavy-duty anti-corrosion applications.

[0004] Secondly, biomass raw materials are inherently rich in polar oxygen-containing groups such as hydroxyl, carboxyl, and ester bonds. In formulation systems with high bio-based content, the accumulation of these groups significantly increases the surface energy and water absorption rate of the coating, resulting in a coating with strong hydrophilicity. Consequently, in humid or salt spray environments, water molecules and corrosive ions can easily penetrate into the interior of the coating and the metal interface through polar channels, causing failure phenomena such as blistering and delamination. Its salt spray resistance is far inferior to that of petroleum-based coatings.

[0005] In summary, existing technologies mostly maintain anti-corrosion performance by sacrificing bio-based content, failing to achieve high performance at high bio-based content. In addition, the introduction of nanofillers such as graphene for reinforcement has the problem of poor compatibility, which further affects the overall performance. Therefore, there is an urgent need to develop a powder coating that balances high bio-based content with anti-corrosion performance.

[0006] To this end, a bio-based epoxy resin anti-corrosion powder coating and its preparation method are proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a bio-based epoxy resin anti-corrosion powder coating and its preparation method. The powder coating of this invention is composed of modified epoxy resin, rosin-based epoxy resin, modified bio-based phenolic amine curing agent, and titanate-modified composite filler. This invention achieves a balance between the rigidity and toughness of the coating through the long-chain structure of dimer acid and the rigid skeleton of rosin; it utilizes an amino-terminated silicone oil-modified curing agent to impart low surface energy hydrophobic properties to the coating surface; and it constructs a dense anti-corrosion barrier by loading graphene onto biochar and combining it with in-situ grafting technology in a stepwise temperature-controlled extrusion process. This solves the problems of high brittleness and poor water resistance in bio-based coatings, making it suitable for heavy-duty anti-corrosion applications such as pipelines and marine facilities.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing a bio-based epoxy resin anti-corrosion powder coating, comprising the following steps: adding 50-60 parts by weight of modified epoxy resin, 10-15 parts by weight of rosin-based epoxy resin, 18-25 parts by weight of modified curing agent, 2-4 parts by weight of modified composite filler, 20 parts by weight of precipitated barium sulfate, 1.0 part by weight of solid acrylate leveling agent, 0.5 parts by weight of benzoin, and 0.2 parts by weight of 2-methylimidazole accelerator to a high-speed premixer, maintaining a speed of 1500-2000 rpm, a mixing time of 3-5 minutes, and controlling the temperature of the discharged material to be below 40℃ to prevent early gelation of the material during the premixing stage; using a twin-screw extruder with a length-to-diameter ratio of 40:1 for further processing. The process involves melt mixing, with the screw speed set at 350-450 rpm and the feed rate adjusted to maintain the screw torque within 70%-85% of the load range to ensure sufficient shearing process and control the material residence time to less than 40 seconds to obtain the molten system. The molten system is then pressed into thin sheets using a tablet press, cooled to room temperature by a water-cooled stainless steel conveyor belt, and then crushed into smaller pieces. These smaller pieces are then fed into an ACM grinding system for air classifying and milling, with 0.2% fumed silica added as a dry mixing flow aid. The auxiliary mill speed is adjusted to 2500-3200 rpm, and the main mill speed to 6000-8000 rpm. The mixture is then filtered through a 140-mesh screen, and iron is removed by magnetic separation to obtain the anti-corrosion powder coating. The finished powder has a particle size distribution (D50) of 30-35 μm, and a maximum particle size (D98) of less than 90 μm.

[0010] Preferably, in this invention, the temperature of the first zone (feeding zone) is 80℃-85℃, which is preheated by mechanical friction to prevent bridging at the feed inlet due to material melting; the temperature of the second zone (melt dispersion zone) is 95℃-100℃ to ensure that the resin is completely melted and wetted with filler; the temperature of the third zone (reaction grafting zone) is 100℃-115℃, at which temperature and under the high shear action of the twin screw, the titanate coupling agent is activated to form a chemical bond with the resin matrix; and the temperature of the fourth zone (cooling homogenization zone) is 90℃-95℃ to reduce the melt temperature and prevent excessive curing reaction.

[0011] Preferably, the preparation of the modified epoxy resin includes the following steps: 30 parts of high-purity dimer acid are added to a four-necked reactor, nitrogen is introduced to purge oxygen for 5 minutes, stirring is started at a speed of 300-500 rpm, the temperature is raised to 100°C, and vacuum dehydration is carried out at this temperature for 30 minutes to obtain a dehydrated system; 100 parts of bisphenol A type epoxy resin are added to the dehydrated system, the temperature is raised to 120°C, and the mixture is stirred until homogeneous; then 0.08 parts of triphenylphosphine are added as a catalyst, and the temperature is slowly increased at a rate of 1°C / min. The temperature is raised to 145℃-155℃ and the esterification reaction is maintained for 3-4 hours to obtain the reaction system. During the reaction, the acid value is measured every 30 minutes until the acid value drops below 0.5 mg KOH / g. The reaction system is degassed under vacuum for 10 minutes, discharged while hot, and crushed after natural cooling to obtain modified epoxy resin. The modified epoxy resin has an epoxy equivalent of 580-620 g / eq, a melt viscosity of 2500-3500 mPa·s at 150℃, and a softening point of 88℃-95℃.

[0012] Preferably, the preparation of the modified curing agent includes the following steps: In a reaction vessel equipped with a dropping funnel, a water separator, and a reflux condenser, 100 parts of cashew phenol are added to the reaction vessel; 10-15 parts of terminal amino silicone oil are added after stirring evenly, and the mixture is heated to 70°C at a speed of 400-600 rpm to obtain a mixed system; 25 parts of paraformaldehyde (96% purity) are added to the mixed system, and the mixture is kept at this temperature for 30 minutes to obtain a homogeneous system; the temperature of the homogeneous system is controlled to not exceed 90°C, and 45 parts of tetraethylenepentamine are slowly added dropwise through the dropping funnel at a time of 45-60 minutes. After the addition is complete, the temperature is raised to 100°C-110°C, and the mixture is refluxed for 2-3 hours; in the later stage of the reaction, the temperature is raised to 130°C and a vacuum pump is connected to dehydrate and remove unreacted small molecules under a vacuum of -0.095 MPa until no fraction is distilled off, and the mixture is cooled and discharged to obtain the modified curing agent. The modified curing agent is a reddish-brown viscous liquid with an amine value of 350-450 mgKOH / g and a viscosity of 2000-5000 mPa·s at 25℃.

[0013] Preferably, the preparation of the modified composite filler includes the following steps: pulverizing coconut shell powder and passing it through a 200-mesh sieve; then dispersing it in an aqueous solution of graphene oxide and ultrasonically treating it to obtain a mixed slurry; wherein the ultrasonic power is 800W, the ultrasonic frequency is 20-40KHz, and the ultrasonic time is 60min; placing the mixed slurry in a vacuum drying oven and drying it at 105℃ to constant weight; then placing it in a tube furnace and heating it to 800℃ at a rate of 5℃ / min under nitrogen protection, holding it at that temperature for 2h for carbonization, and cooling it to room temperature with the furnace to obtain the loaded filler; adding the loaded filler to a high-speed mixer with a heating jacket, heating it to 100-110℃, and uniformly spraying a solution of 2% by weight of the titanium ester coupling agent in isopropanol in the form of a spray while the mixer speed is set to 2000-2500rpm, wherein the titanium ester coupling agent is diluted with isopropanol, and treating it with high-speed stirring for 10-15min to obtain the modified composite filler.

[0014] This invention also provides a bio-based epoxy resin anti-corrosion powder coating, the raw materials of which include rosin-based epoxy resin, dimer acid, epoxy resin E51, cashew nut shell, amino-terminated silicone oil, tetraethylenepentamine, coconut shell powder, graphene oxide and precipitated barium sulfate.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1. This invention sets up a specific reaction grafting zone during the melt extrusion process and uses a titanate coupling agent to achieve in-situ chemical bonding between inorganic fillers and organic resin matrix. Through chemical bonding, microscopic defects at the inorganic-organic interface are eliminated, preventing orange peel or sand-like phenomena caused by filler agglomeration, and ensuring the firm adhesion and leveling of the coating on the metal substrate.

[0017] 2. This invention employs a compound system of dimer acid-modified epoxy and rosin-based epoxy. The long aliphatic chains of dimer acid form a micro-phase separation structure in the solidified network, effectively dissipating impact energy. At the same time, the fused ring structure of rosin-based epoxy ensures high pencil hardness, resolving the contradiction that traditional bio-based materials become softer when toughened and brittle when hardened.

[0018] 3. This invention utilizes biochar as a carrier to disperse graphene oxide, and after high-temperature carbonization and organic treatment, constructs a highly efficient labyrinth barrier network. The graphene sheets maintain a high aspect ratio under the support of biochar, extending the diffusion path of corrosive media. At the same time, titanate coupling agent repairs the structural defects on the filler surface, blocks the capillary penetration of water molecules along the filler interface, and significantly improves the heavy-duty anti-corrosion capability.

[0019] 4. This invention synthesizes a cashew phenol aldehyde amine curing agent modified with amino-terminated silicone oil. Utilizing the low surface energy of the organosilicon segments and the surface enrichment effect during curing, a dense hydrophobic film is formed on the coating surface. This active water-repellent mechanism reduces water molecule adsorption and penetration into the coating from the source, significantly delaying substrate corrosion.

[0020] 5. The system of the present invention achieves rapid curing while maintaining high storage stability. The phenolic amine system of the present invention utilizes the autocatalytic effect of phenolic hydroxyl groups to achieve high activity at low temperature. It utilizes the high glass transition temperature characteristics of rosin-based resin and the steric hindrance effect of the long chain of modified resin to effectively prevent cold flow agglomeration of powder during storage and transportation, thus taking into account both energy-saving production and the convenience of practical application. Attached Figure Description

[0021] Figure 1 The graphs show the changes in the anti-corrosion and waterproof performance of the coatings obtained in Examples 1-3 and Comparative Examples 8-12 of this invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the present invention, the dimer acid is a high-purity dimer acid with a dimer content ≥98%, a monomer acid content ≤1%, an acid value of 194-198 mgKOH / g, and a CAS number of 61788-89-4; the epoxy resin is a bisphenol A type epoxy resin E-51 with an epoxy equivalent of 184-195 g / eq and a viscosity of 11000-14000 mPa·s at 25℃; the amino-terminated silicone oil is a polydimethylsiloxane main chain with amino groups at both ends, a viscosity of 50-100 cSt at 25℃, and an amino value of 0.6-0.8 mmol. / g; the graphene oxide sheet diameter is 5-10μm, and the mass concentration of graphene oxide in aqueous solution is 2mg / mL; the titanate coupling agent is isopropyl tris(dioctyl pyrophosphate) titanate, model number NDZ-201, CAS number 61417-49-0; the rosin-based epoxy resin is glycidyl rosinate, with an epoxy equivalent of 450-500g / eq, a softening point of 95-105℃, CAS number 13411-54-6; the benzoin is diphenylethanol ketone, CAS number 579-44-2.

[0023] Please see Figure 1 This invention provides a bio-based epoxy resin anti-corrosion powder coating and its preparation method, the technical solution of which is as follows:

[0024] Example 1

[0025] Add 30 parts of high-purity dimer acid to a four-necked reactor, purge with nitrogen for 5 minutes to remove oxygen, start stirring at 400 rpm, heat to 100°C and dehydrate under vacuum for 30 minutes at this temperature to obtain a dehydrated system, wherein the vacuum degree is controlled at 0.09 MPa; add 100 parts of bisphenol A type epoxy resin to the dehydrated system, heat to 120°C and stir evenly; then add 0.08 parts of triphenylphosphine as a catalyst, slowly heat to 150°C at a heating rate of 1°C / min, and maintain the temperature for esterification reaction for 4 hours to obtain a reaction system; during the reaction, sample and test the acid value every 30 minutes until the acid value drops below 0.5 mg KOH / g; degas the reaction system under vacuum for 10 minutes, discharge while hot, and crush after natural cooling to obtain modified epoxy resin.

[0026] Add 100 parts of cashew phenol to a reaction vessel; stir evenly and add 12 parts of terminal amino silicone oil, stir and heat to 70℃, and rotate at 500 rpm to obtain a mixed system; add 25 parts of paraformaldehyde to the mixed system, keep it at the temperature for 30 min to obtain a homogeneous system; control the temperature of the homogeneous system to not exceed 90℃, slowly add 45 parts of tetraethylenepentamine through a dropping funnel, control the dropping time to 60 min, after the dropping is completed, heat to 100℃, and reflux for 3 h; in the later stage of the reaction, heat to 130℃ and connect a vacuum pump, dehydrate and remove unreacted small molecules under a vacuum of -0.095 MPa until no fraction is distilled out, cool down and discharge to obtain the modified curing agent.

[0027] Coconut shell powder was pulverized and passed through a 200-mesh sieve; then dispersed in an aqueous solution of graphene oxide, and ultrasonically treated to obtain a mixed slurry; the ultrasonic power was 800W, the ultrasonic frequency was 30KHz, and the ultrasonic time was 60min; the mixed slurry was placed in a vacuum drying oven and dried at 105℃ to constant weight; then placed in a tube furnace, and heated to 800℃ at a rate of 5℃ / min under nitrogen protection, and carbonized at that temperature for 2h, and cooled to room temperature with the furnace to obtain the loaded filler; the loaded filler was added to a high-speed mixer with a heating jacket, heated to 110℃, and sprayed uniformly with 2% of the weight of the composite titanate coupling agent in the form of a spray while the mixer speed was set to 2500rpm, and treated with high-speed stirring for 15min to obtain the modified composite filler.

[0028] By weight, 55 parts modified epoxy resin, 15 parts rosin-based epoxy resin, 22 parts modified curing agent, 3 parts modified composite filler, 20 parts precipitated barium sulfate, 1.0 part solid acrylate leveling agent, 0.5 parts benzoin, and 0.2 parts 2-methylimidazole accelerator were added to a high-speed premixer, maintaining a speed of 2000 rpm and a mixing time of 5 minutes. The temperature of the discharged material was controlled below 40℃ to prevent early gelation of the material during the premixing stage. A twin-screw extruder with a length-to-diameter ratio (L / D) of 40:1 was used for melt mixing to obtain the melt system. The temperature of zone one (feed zone) was 85℃; the temperature of zone two (melt dispersion zone) was... The temperature is 100℃ in zone 3 (reaction grafting zone); 110℃ in zone 4 (cooling and homogenization zone); and 95℃ in zone 5 (cooling and homogenization zone). The screw speed is 400 rpm, and the feeding speed is set to keep the screw torque at 80%. The molten system is pressed into thin sheets by a tablet press and cooled to room temperature by a water-cooled stainless steel conveyor before being crushed into small pieces. The sheets are then fed into an ACM grinding system for air classifying milling, and 0.2% of the total amount of fumed silica (as a dry mixing flow aid) is added. The speed of the auxiliary mill (classifying wheel) is adjusted to 3000 rpm, and the speed of the main mill is 8000 rpm. The mixture is then filtered through a 140-mesh screen, and iron is removed by magnetic separation to obtain an anti-corrosion powder coating.

[0029] Examples 2-5 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 1.

[0030] Table 1. Parameter variations in Examples 1-5

[0031] Example Example 1 Example 2 Example 3 Example 4 Example 5 Synthesis temperature of modified epoxy resin / ℃ 150 145 155 148 152 Mass of amino-terminated silicone oil (parts) 12 10 11 15 13 Titanate coupling agent mass dosage / % 2 1.5 2.5 1.8 2.2 Modified epoxy resin mass dosage / part 55 60 50 52 58 rosin-based epoxy resin mass dosage / part 15 10 20 18 12 Modified curing agent mass dosage / part 22 20 25 24 21 Modified composite filler mass dosage / part 3 2 2.5 3.5 4 Extruder three-zone temperature / ℃ 110 100 115 105 110 Curing time at 160℃ / min 15 20 12 18 16

[0032] Comparative Example 1 is the same as Example 1, except that dimer acid-modified epoxy resin is not used, but an equal amount of monomer acid is used for modification.

[0033] Comparative Example 2 is the same as Example 1, except that dimethyl silicone oil was used for physical blending in the preparation of the modified curing agent, and amino-terminated silicone oil was not used, while the amounts of the other components remained unchanged.

[0034] Comparative Example 3 is the same as Example 1, except that the temperature of the three melting zones is set to 130°C, while the other parameters remain unchanged.

[0035] Comparative Example 4 is the same as Example 1, except that in the preparation of the modified composite filler, no titanate coupling agent is used for surface treatment, and the carbonized product is used directly.

[0036] Comparative Example 5 is the same as Example 1, except that rosin-based epoxy resin is not added, but an equal amount of modified epoxy resin is added to supplement it.

[0037] Comparative Example 6 is the same as Example 1, except that no modified epoxy resin is used, and an equal amount of epoxy resin E51 is used instead.

[0038] Comparative Example 7 is the same as Example 1, except that in the synthesis of the modified resin, equimolar adipic acid is used instead of dimer acid.

[0039] Comparative Example 8 is the same as Example 1, except that only graphene oxide is used and coconut shell powder is not used as a carrier, but is added directly.

[0040] Comparative Example 9 is the same as Example 1, except that the temperature of the three melting zones is set to 90°C, while the other parameters remain unchanged.

[0041] Comparative Example 10 is the same as Example 1, except that unmodified common cashew phenol aldehyde amine curing agent is used and no terminal amino silicone oil is added during the preparation process.

[0042] Comparative Example 11 is the same as Example 1, except that only coconut shell powder is used to provide biochar, and no graphene oxide is added, while other processing techniques remain unchanged.

[0043] Comparative Example 12 is the same as Example 1, except that the preparation process of the modified composite filler is adjusted, and the carbonization temperature is reduced from 800°C to 400°C.

[0044] Comparative Example 13 is the same as Example 1, except that an equal amount of polyamide curing agent is used instead of the modified curing agent, while the other parameters remain unchanged.

[0045] Experimental Example 1: Coating Appearance and Basic Physical Properties

[0046] The powder coatings prepared in Examples 1-5 and Comparative Examples 1-5 were applied using an electrostatic powder spray gun with a voltage set to 70kV and a powder supply pressure of 0.2MPa. The powder coatings were uniformly sprayed onto phosphated metal substrates. The workpieces were then placed in a curing oven and cured at 160℃ (workpiece surface temperature) for 15 minutes to form an anti-corrosion coating. For Examples 2-5, the anti-corrosion coatings were tested for appearance and basic physical properties according to the spraying times in Table 1. The coating's 60° gloss was tested according to GB / T 9754-2007; its scratch resistance and pencil hardness were tested according to GB / T 6739-2022; and its adhesion was tested according to GB / T 9286-2021, with grade 0 being the best and grade 5 the worst. The test results are shown in Table 2.

[0047] Table 2 Test Results of Examples and Comparative Examples

[0048] Example 60° gloss / % Pencil hardness Adhesion / Grade Coating appearance description Example 1 92.4 3H 0 Smooth and flat, without defects Example 2 90.1 3H 0 Flat, slightly low hardness Example 3 93.5 4H 0 High gloss, high hardness Example 4 91.8 3H 0 Smooth Example 5 86.2 3H 0 Slightly matte finish, slightly lower hardness Comparative Example 1 15.3 <6B 5 The surface is sticky, does not harden, and can be easily wiped off. Comparative Example 2 55.6 2H 4 Numerous shrinkage pores, interlayer peeling Comparative Example 3 35.8 3H 2 Poor leveling, feels gritty. Comparative Example 4 72.1 2H 1 The surface is matte and has fine particles. Comparative Example 5 91.7 HB 0 It is flat, but the surface is extremely soft and not scratch-resistant.

[0049] As shown in Table 2, the basic physical properties of the anti-corrosion powder coating obtained in the comparative examples, through adjustments to the components and processes, are significantly different from those in the examples. Comparative Example 1 shows that the dimer acid contains two carboxyl groups, enabling it to undergo chain extension reactions with epoxy resin, increasing molecular weight and forming long-chain polymers. The monomeric acid, containing only one carboxyl group, acts as a capping agent in the reaction. After reacting with epoxy groups, the molecular chain stops growing, resulting in a low-molecular-weight oligomer that cannot form a three-dimensional network structure and therefore cannot form a film. Comparative Example 2 uses dimethyl silicone oil for physical blending instead of chemically grafted terminal amino silicone oil. Dimethyl silicone oil has extremely low surface tension and poor compatibility with the epoxy resin system. Without chemical bonding, free silicone oil molecules migrate uncontrollably during curing. Some aggregate on the coating surface, forming a surface tension gradient, leading to film rupture and pinholes; others migrate to the interface between the coating and the substrate, forming an oil film isolation layer, causing the coating to completely lose adhesion to the metal substrate. In Comparative Example 3, at 130℃... When the curing temperature of the system was approached or reached, some of the resin and hardener reacted prematurely, forming an unmeltable cured product. This product could not melt and level during subsequent spraying and baking, hindering the flow of the coating and resulting in a rough appearance and severe orange peel effect. It also affected melt wettability, leading to decreased adhesion. In Comparative Example 4, graphene and biochar are both inorganic carbon materials with poor compatibility with the organic epoxy resin matrix. Without the use of titanate coupling agents, the filler surface lacks active groups that react with the resin, making chemical bonding impossible and easily causing the filler to break down in the matrix. Aggregation occurs, which easily scatters light, leading to a decrease in gloss. At the same time, the bonding force between the filler and the resin interface is weak, and interface peeling is easily caused under stress, resulting in a significant reduction in adhesion. The results of Comparative Example 5 show that dimer acid modified epoxy resin uses long aliphatic chains to provide flexibility, while rosin-based epoxy resin contains a fused ring rigid skeleton to provide hardness and glass transition temperature. Without the addition of rosin-based resin, the proportion of flexible chain segments in the system is too high, and the rigid support is insufficient. As a result, although the cured coating is smooth, it is soft in texture, and its scratch resistance and mechanical strength are greatly reduced.

[0050] Experiment Example 2: Mechanical Performance Testing

[0051] The powder coatings of Examples 1-5 and Comparative Examples 6-9 were sprayed according to the method of Experimental Example 1. The coatings were tested according to GB / T1732-2020, and the work corresponding to the maximum height at which the coating did not crack or peel off when impacted by a 1kg hammer was recorded. The coatings were tested according to GB / T 30791-2014 to evaluate their crack resistance under bending deformation. 0T represents no cracking when folded in half, and the smaller the value, the better the toughness. The test results are shown in Table 3.

[0052] Table 3 Test Results of Examples and Comparative Examples

[0053] Example Impact resistance / kg·cm T-bend test / T Example 1 62.5 1T Example 2 66.8 0T Example 3 54.2 2T Example 4 61.3 1T Example 5 63.7 1T Comparative Example 6 25.2 4T Comparative Example 7 35.4 3T Comparative Example 8 48.3 2T Comparative Example 9 42.6 2T

[0054] As shown in Table 3, the mechanical properties of the anti-corrosion coatings obtained by adjusting the components and processes in the comparative examples are significantly different from those in the examples. In Comparative Example 6, the ordinary E51 epoxy resin contains a large number of rigid benzene rings in its molecular structure. The network structure formed after cross-linking and curing is dense, but too rigid, lacking flexible segments that can deform to absorb energy. When subjected to high-speed impact or large-angle bending, the molecular chains cannot dissipate energy through conformational adjustment, exhibiting brittle fracture. In contrast, the dimer acid modified resin in Example 1 introduces long aliphatic chains, forming a micro-phase separation structure. The soft segments play a toughening role similar to rubber when subjected to stress. The results of Comparative Example 7 show that although adipic acid can also introduce ester bonds and has flexibility, its carbon chain length is much shorter than that of dimer acid. The shorter chain segments provide limited free volume, and the molecular chain mobility is weak, making it unable to effectively reduce energy like long-chain dimer acid. The local modulus of the cross-linked network does not hinder crack propagation; in addition, the excessively high ester group density caused by short-chain acids may also increase intermolecular forces, restrict chain segment movement, and affect the overall mechanical properties; in Comparative Example 8, only graphene oxide was added, and without biochar as a protective support, it was very easy for irreversible stacking and aggregation to occur in the resin matrix. These aggregates were no longer reinforcing phases, but instead became defect points and stress concentration points inside the coating. When the coating was impacted, cracks were easy to initiate and rapidly propagate at the edges of these aggregates, leading to a decrease in mechanical properties; the results of Comparative Example 9 show that the present invention uses titanate coupling agent to achieve in-situ chemical grafting between filler and resin. The temperature of 90°C is insufficient to activate the chemical reaction, resulting in only a weak physical bond between the filler and resin. When subjected to external impact, the interface between the inorganic filler and the organic matrix is ​​prone to debonding, which cannot effectively transfer stress, leading to premature coating failure.

[0055] Experiment Example 3: Corrosion Resistance and Chemical Resistance Test

[0056] The powder coatings of Examples 1-5 and Comparative Examples 8-12 were sprayed according to the method of Experimental Example 1. Tests were conducted according to GB / T 10125-2021, recording the maximum tolerance time for a single-sided erosion width of less than 2 mm. The static contact angle of deionized water on the coating surface was tested using a contact angle meter according to GB / T 30693-2014 (a larger value indicates better hydrophobicity). The cured coating was boiled in boiling water for 24 hours according to GB / T 1034-2008, and the weight gain percentage was calculated. The test results are shown in Table 4. The changes in the anti-corrosion and waterproof performance of the coatings obtained in Examples 1-3 and Comparative Examples 8-12 are as follows: Figure 1 As shown.

[0057] Table 4 Test Results of Examples and Comparative Examples

[0058] Example Neutral salt spray test / h Water contact angle / ° Water absorption rate / % Example 1 1280 105.4 0.28 Example 2 1215 104.1 0.32 Example 3 1325 105.6 0.24 Example 4 1260 107.2 0.29 Example 5 1310 105.9 0.25 Comparative Example 8 885 101.5 0.46 Comparative Example 9 855 96.2 0.42 Comparative Example 10 765 76.9 0.68 Comparative Example 11 625 100.8 0.45 Comparative Example 12 200 56.2 2.87

[0059] As shown in Tables 4 and 1, the protective performance of the powder coating obtained in the comparative examples, through adjustments to the components and processes, is significantly different from that in the examples. In Comparative Example 8, graphene oxide has an extremely high specific surface area and interlayer van der Waals forces. Without biochar particles as a dispersion medium, graphene sheets easily undergo irreversible stacking in the epoxy resin matrix, forming a graphite-like blocky structure. This not only significantly reduces the effective barrier path length but also results in poor interfacial bonding between the aggregates and the resin, easily becoming defect points for rapid penetration of corrosive media, leading to a deterioration in overall mechanical properties. In Comparative Example 9, based on the above description, an extrusion temperature of 90°C can only achieve physical mixing of the filler and cannot trigger in-situ chemical grafting. Therefore, only physical adsorption exists between the inorganic filler and the organic resin, resulting in weak interfacial bonding and the presence of microscopic interfacial pores. These micropores become transport channels for water molecules and chloride ions, further accelerating corrosion. In Comparative Example 10, the modified amino silicone oil with missing ends resulted in a coating surface rich in... Containing polar hydrophilic groups such as phenolic hydroxyl and amino groups, the water film easily spreads on the surface and penetrates into the interior, increasing the water absorption rate and corrosion rate of the coating. In Example 1, the low surface energy polydimethylsiloxane segments spontaneously migrate to the coating surface, forming a dense hydrophobic layer, thereby improving the overall hydrophobic properties. Coconut shell biochar is a porous carbon material; graphene oxide sheets adsorb onto the surface of the biochar or fill its pores, acting as a pore blocker and extending the barrier pathway. In Comparative Example 11, without the addition of graphene oxide, the biochar... The microporous structure itself may become a channel for the penetration of corrosive media, failing to provide an effective physical shield and resulting in poor corrosion resistance. In Comparative Example 12, 400℃ is only in the initial stage of biomass pyrolysis, and the carbonization of cellulose and lignin is incomplete. A large number of oxygen-containing hydrophilic functional groups remain in the product. These polar groups not only make the filler itself very easy to absorb water, but also interfere with the curing network of epoxy resin. In high humidity or water immersion environments, the filler absorbs water and swells, causing the coating to blister and crack, thus losing its corrosion resistance.

[0060] Experiment Example 4 Storage Stability

[0061] The powder coatings prepared in Examples 1-5 were not cured and compared with the powder coatings of Comparative Example 5 and Comparative Example 13. The gelation time was tested according to GB / T 16995-1997, with the test temperature set at 180℃ (the industry standard test temperature; although the curing temperature is 160℃, 180℃ better standardizes the reactivity data). The lower the value, the higher the reactivity. Storage stability was tested according to GB / T 21782-2008. The powder samples were placed in a 40℃ constant temperature oven for 72 hours, then cooled to room temperature. The powder state was observed and rated: Grade 1: Loose powder, no lumps; Grade 2: Slight lumps, easily crushed; Grade 3: Lumps present, requires force to crush; Grade 4: Severely lumpy, difficult to crush; Grade 5: Completely hardened. The test results are shown in Table 5.

[0062] Table 5 Test Results of Examples and Comparative Examples

[0063] Example gelation time at 180℃ / s Storage stability Example 1 135 Level 1 Example 2 132 Level 2 Example 3 141 Level 1 Example 4 128 Level 1 Example 5 138 Level 1 Comparative Example 5 125 Level 4 Comparative Example 13 385 Level 2

[0064] As shown in Table 5, the powder coatings obtained in the comparative examples, through adjustments to the components and processes, exhibit significantly different storage stability compared to the examples. The modified curing agents in Examples 1-5 of this invention contain phenolic hydroxyl groups, exhibiting a self-catalytic effect on epoxy ring-opening. Therefore, rapid gelation can be achieved at 180°C for approximately 130 seconds, ensuring sufficient cross-linking under a curing process of 160°C / 15 minutes. Furthermore, the introduction of rosin-based epoxy resin effectively increases the glass transition temperature of the powder coating system. Combined with the steric hindrance effect generated by the long-chain structure of the self-synthesized resin, the molecular chain movement of the powder coating is restricted at 40°C, preventing cold flow adhesion and maintaining good looseness. In Comparative Example 5, the main characteristic of the dimer acid-modified epoxy resin is the presence of long aliphatic chains, belonging to typical flexible soft segments. Although it provides excellent impact resistance, its own glass transition temperature is relatively low. The rosin-based... The addition of resin as a rigid hard segment can increase the glass transition temperature of the overall system; however, removing the rigid rosin-based resin may cause the glass transition temperature of the powder system to drop to around 40°C or below. In the test environment, the resin molecular chain segments gain enough energy to begin moving, the powder particle surface softens and becomes sticky, and they fuse together under gravity, resulting in severe agglomeration and affecting stability. In Comparative Example 13, conventional polyamide curing agents usually require high activation energy to react with epoxy groups, and their reaction rate constant is much lower than that of the phenolic amine system, resulting in a prolonged gelation time. A gelation time of 385s means that the resin does not crosslink for a long time during the melt leveling stage after extrusion and spraying. Although this is beneficial for leveling, the coating cannot be cured at all under the curing process of 160°C / 15min, resulting in poor mechanical properties and corrosion resistance. This further illustrates that the modified curing agent of the present invention achieves low-temperature rapid curing.

[0065] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a bio-based epoxy resin anti-corrosion powder coating, characterized in that, The powder coating preparation includes the following steps: premixing modified epoxy resin, rosin-based epoxy resin, modified curing agent, modified composite filler, precipitated barium sulfate, solid acrylate leveling agent, benzoin, and 2-methylimidazole in a premixer; then melt extruding to obtain a melt system; cooling and crushing the melt system into flakes, adding fumed silica, grinding and filtering, and magnetically separating to remove iron to obtain the anti-corrosion powder coating; wherein, the modified epoxy resin is obtained by esterification reaction of dimer acid and epoxy resin E51; the modified curing agent is obtained by stepwise mixing of cashew nut shell powder, amino-terminated silicone oil, paraformaldehyde, and tetraethylenepentamine, followed by reflux reaction; Coconut shell powder is crushed and sieved; it is dispersed in an aqueous solution of graphene oxide and ultrasonically treated to obtain a mixed slurry; the mixed slurry is vacuum dried, placed in a tube furnace, heated to 800°C at a rate of 5°C / min under nitrogen protection, carbonized at that temperature for 2 hours, and then cooled to room temperature with the furnace to obtain the loaded filler; the loaded filler is added to a high-speed mixer with a heating jacket, and a titanate coupling agent is uniformly sprayed in the form of a spray, and stirred to obtain the modified composite filler; The melt extrusion process includes: the temperature of the feeding zone is 80℃-85℃, the temperature of the melt dispersion zone is 95℃-100℃, the temperature of the reaction grafting zone is 100℃-115℃, and the temperature of the homogenization zone is 90℃-95℃.

2. The method for preparing a bio-based epoxy resin anti-corrosion powder coating according to claim 1, characterized in that: The preparation of the modified epoxy resin includes the following steps: The dimer acid was added to a four-necked reactor, oxygen was removed by nitrogen, and the system was dehydrated under vacuum to obtain a dehydrated system. The epoxy resin E51 was added to the dehydrated system and stirred evenly. Triphenylphosphine was then added, and an esterification reaction was carried out to obtain a reaction system. The material was discharged while hot, and after natural cooling, it was crushed to obtain the modified epoxy resin.

3. The method for preparing a bio-based epoxy resin anti-corrosion powder coating according to claim 1, characterized in that, The preparation of the modified curing agent includes the following steps: adding cashew phenol to a reaction vessel, stirring evenly, adding the terminal amino silicone oil, and stirring to obtain a mixed system; adding paraformaldehyde to the mixed system, keeping it at a constant temperature to obtain a homogeneous system; adding tetraethylenepentamine dropwise through a dropping funnel, refluxing, vacuum dehydrating, cooling and discharging to obtain the modified curing agent.

4. A bio-based epoxy resin anti-corrosion powder coating, characterized in that, The raw materials for preparation include rosin-based epoxy resin, dimer acid, epoxy resin E51, cashew phenol, amino-terminated silicone oil, tetraethylenepentamine, coconut shell powder, graphene oxide, and precipitated barium sulfate; the anti-corrosion powder coating is prepared by the preparation method according to any one of claims 1-3.

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