Waterborne multi-layer degradable self-polishing ship antifouling paint system and preparation method thereof

Abstract

The invention discloses a water-based multi-layer degradable self-polishing ship antifouling coating system and a preparation method thereof, and belongs to the field of marine anticorrosion and antifouling materials. The system is composed of a zinc-rich primer, a modified epoxy intermediate paint and a functionalized finish paint. The finish paint takes polyhydroxyalkanoate as a matrix, and integrates a self-stratification modifier capable of forming a silicon-rich top layer during curing and a latent dual-curing system capable of realizing normal-temperature curing through a synergistic effect. According to the present invention, the mixing mechanism of dynamic self-polishing and static fouling release is adopted, and the innovative curing technology is combined, such that the long working life, the excellent mechanical property and the long-acting antifouling ability are achieved. The drawing adhesive force of the system is not lower than 7.9 MPa, and the environment-friendly requirements that the content of volatile organic compounds is smaller than or equal to 50 g / L, and the content of free diisocyanate monomers is smaller than or equal to 0.1 wt% are met.

Description

Technical Field

[0001] This invention belongs to the field of marine anti-corrosion and antifouling materials, specifically relating to a water-based multilayer biodegradable self-polishing marine antifouling coating system and its preparation method. Background Technology

[0002] The modern shipbuilding and marine engineering industry is facing an increasingly acute contradiction between economic efficiency and ecological protection caused by traditional protective technologies. On the one hand, biofouling on ship surfaces significantly increases drag, leading to a sharp rise in fuel consumption and greenhouse gas emissions; studies show that severe fouling can cause more than 85% of power loss, and even a slight slime film can cause about 20% of drag increase. On the other hand, the antifouling technologies that have long been relied upon to solve this problem have themselves become serious sources of marine pollution.

[0003] Historically, ship antifouling technology has evolved from physical coatings (such as lead and copper plates) to chemical antifouling. In the mid-20th century, self-polishing copolymer coatings, represented by tributyltin (TBT), dominated due to their excellent broad-spectrum biocidal effects and long-lasting properties. However, scientific research has revealed that TBT has significant adverse effects on marine ecosystems. As a persistent organic pollutant, it can accumulate in organisms, be transferred through the food chain, cause devastating damage to non-target marine life, and leave long-term environmental risks.

[0004] In light of this, the global regulatory system is intensifying its efforts to promote the green transformation of ship antifouling technologies. The International Maritime Organization's Convention on the Control of Hazardous Antifouling Systems for Ships has completely banned the use of organotin compounds, and the 2021 Amendment MEPC.331(76) added controls on Cybutryne (Irgarol 1051): from January 1, 2023, ships are prohibited from applying or recoating antifouling systems containing this substance; and removal or covering must be completed by the first antifouling system replacement inspection after January 1, 2023, and no later than 60 months from the date of the last application, in order to reduce the risk of this biocide to the marine environment. At the same time, the EU's Biocide Products Regulation and Chemicals Registration, Evaluation, Authorization and Restriction Regulation impose stricter restrictions on the types, contents and emissions of volatile organic compounds (VOCs) of hazardous substances in coatings. This series of tightening regulations has prompted the industry to accelerate its shift to low-toxicity or non-toxic alternative technologies to meet compliance and environmental goals.

[0005] Against this backdrop, various alternative technologies have been explored in this field, but existing solutions all have significant limitations and fail to provide a systematic solution that balances environmental protection, economy, and performance.

[0006] 1. Fouling-Release Coatings: Low surface energy coatings, represented by silicones such as polydimethylsiloxane or fluoropolymers, are one of the main directions for non-toxic antifouling. The principle is to create a "smooth" surface with low adhesion, making it difficult for fouling organisms to adhere firmly or easily detach under the shear force of water flow. However, the industrial application of these coatings faces many challenges. First, their mechanical properties are poor; the coating is soft and easily scratched. Second, the adhesion between the coating and the substrate is an inherent weakness, usually requiring a complex primer system and demanding application techniques. Furthermore, traditional silicone coatings are mostly solvent-based, with high VOC emissions and high costs, limiting their widespread application.

[0007] 2. Early Biodegradable Coatings: Using biodegradable polymers, such as polylactic acid (PLA) or polyhydroxyalkanoates (PHA), directly as the matrix for marine antifouling coatings has enormous potential for environmental friendliness throughout its entire life cycle. However, early technological attempts revealed fundamental flaws. For example, the solutions disclosed in US patents US6025028A and US20230220155A1 were mostly simple PHA aqueous dispersions or melt coatings, whose technological maturity was far from meeting the stringent requirements of marine applications. Academic research and practice have confirmed that these simple bio-based coatings have consistently failed to resolve a core technical contradiction: the inability to achieve a balance between marine-grade mechanical strength, weather resistance, adhesion requirements, and a controllable biodegradation (self-polishing) rate. These coatings often fail prematurely due to excessively rapid degradation rates, such as monthly polishing rates exceeding 10µm under typical marine conditions, or they lose effective self-polishing properties in pursuit of mechanical strength, ultimately failing to develop mature products suitable for industrial application.

[0008] 3. Limitations of existing advanced technologies: In recent years, some advanced unit technologies have emerged in the coatings field, but they mostly exist in isolated forms and have not been effectively integrated to solve the systemic problems in the field of ship antifouling.

[0009] Self-layering technology involves adding incompatible low surface energy components (such as silicon- or fluoropolymers) to a coating, allowing them to spontaneously migrate to the coating surface during curing to form a functional top layer. For example, Chinese patent CN107298930A discloses an organosilicon-polyurea self-layering coating. However, existing self-layering systems are all based on a stable, non-degradable polymer matrix (such as polyurea or acrylic resin), aiming only to create a static, low-adhesion surface. Essentially, they still fall under the category of dirt-release coatings and fail to integrate with a dynamic self-polishing mechanism.

[0010] Advanced waterborne crosslinking technologies: To address the issues of short pot life and poor storage stability in two-component waterborne coatings, the industry has developed latent crosslinking agents such as blocked polyisocyanates and waterborne polycarbodiimides (PCDI). These technologies offer the possibility of preparing high-performance, stable one-component (1K) waterborne systems. However, existing technologies have not yet disclosed how to utilize these advanced crosslinking methods, especially in combination, to solve the specific and critical challenge of stabilizing and enhancing hydrolysis-sensitive bio-based polymers like PHA in waterborne systems.

[0011] In summary, the field has long faced a fundamental "triple dilemma" in the search for environmentally friendly antifouling solutions for ships: it must achieve both high efficiency and broad-spectrum antifouling effects, ensure sufficient mechanical durability and adhesion of the coating in the marine environment, and achieve environmental friendliness throughout its entire life cycle, including non-toxicity, biodegradability, and low VOC emissions.

[0012] Specifically, while traditional biocide-dependent coatings offer outstanding antifouling performance, they also pose serious ecotoxicity problems. Non-toxic, fouling-releasing coatings (such as silicone) have inherent weaknesses in mechanical strength and adhesion, making it difficult to support long-term service requirements, and their static antifouling capabilities are also relatively limited. Early attempts at biodegradable self-polishing coatings, while showing good environmental performance, struggled to balance degradation rate and coating strength, thus falling far short of the durability requirements for industrial applications.

[0013] Therefore, existing technological approaches all involve difficult compromises and trade-offs within this trilemma, resulting in a situation where "one aspect is prioritized at the expense of another." What the market urgently needs is not incremental improvements to a single performance characteristic, but a solution that can fundamentally break through the aforementioned technological constraints and systematically integrate the three core objectives. To address these technical problems, the following technical solution is provided. Summary of the Invention

[0014] This invention aims to provide a water-based, multi-layered, biodegradable, self-polishing antifouling coating system for ships and its preparation method, in order to solve the ecotoxicity problem of traditional ship antifouling coatings and the problems of insufficient performance or excessive cost of existing non-toxic coatings, and to provide a new type of ship antifouling coating system that is environmentally friendly, long-lasting, energy-saving and in line with future regulatory trends.

[0015] To achieve the above objectives, the present invention provides the following technical solution:

[0016] This invention provides a water-based, multi-layered, biodegradable, self-polishing marine antifouling coating system. The system sequentially comprises a zinc-rich primer layer with a thickness of 50–80 µm, a modified epoxy intermediate layer with hydrolyzable side chains and a modified epoxy intermediate layer with a thickness of 40–80 µm, and a topcoat layer with a thickness of 80–120 µm. The topcoat layer is cured from a water-based, biodegradable, self-polishing composition, which, based on the total solids content of the composition by weight percentage, comprises 35–55 wt% of a biodegradable polyhydroxyalkanoate matrix, 0.5–4 wt% of a self-stratifying modifier, 2–10 wt% of a light stabilizer and anti-corrosion filler, and a latent dual-curing system comprising 0.5–4 wt% microencapsulated polycarbodiimide (PCDI) and 0.5–3 wt% blocked polyisocyanate, wherein the total solids content of the latent dual-curing system is 1–7 wt%. The remaining components of the composition are deionized water and additives, and the paint film cured from the composition has a free diisocyanate monomer content of not more than 0.1 wt%, wherein the free diisocyanate monomer content is determined by HPLC-UV method according to ISO 6923:2023.

[0017] Specifically, such as Figure 1 As shown, the multilayer coating system of this invention has a clear structure and well-defined functions. On a surface-treated steel substrate 1, a zinc-rich primer layer 2 is first applied. This layer contains uniformly dispersed zinc powder particles 3, which serve as sacrificial anodes, providing basic electrochemical corrosion protection for the substrate. Next is a modified epoxy intermediate layer 4, which acts as a bridge between the primer and topcoat, providing additional corrosion protection and interlayer adhesion. The outermost layer is a functional topcoat layer 5, in which key functional components such as microencapsulated PCDI 6 and light-stabilizing and corrosion-resistant fillers 7 are uniformly distributed. Specifically, during the coating curing process, a self-delaminating modifier migrates to the outermost surface of the coating, forming an extremely thin silicon-rich top layer 8, which endows the coating system with the ability to release static fouling.

[0018] One of the core innovations of this invention lies in achieving the synergistic coexistence of dynamic self-polishing and static fouling release mechanisms, along with dynamic surface regeneration, within the same coating system through precise formulation design. Specifically, this invention does not construct a static, unchanging fouling release surface layer. Instead, it utilizes the molecular migration properties of self-layering modifiers such as polystyrene-grafted-polydimethylsiloxane (PS-g-PDMS) to dynamically form and maintain an extremely thin, regenerable, silicon-rich, low surface energy layer at the paint film-seawater interface during coating curing and subsequent use. When the ship is stationary, this silicon-rich layer provides the primary static physical antifouling capability. When the ship is sailing or when fouling organisms stubbornly adhere, the underlying PHA matrix undergoes controlled micro-hydrolysis, causing the outermost layer to peel off along with the fouling. The self-layering modifier stored in the coating matrix, driven by the thermodynamic force resulting from its incompatibility with the PHA matrix, dynamically migrates to the newly exposed paint film-seawater interface, thereby re-establishing a functional surface layer rich in low surface energy groups. This "sacrifice-regeneration" dynamic balance mechanism ensures that the coating can maintain its low surface energy characteristics under various marine conditions, overcoming the limitations of traditional single-mechanism coatings.

[0019] Similarly, the latent dual-curing system resolves the contradiction between long pot life and high final performance in waterborne PHA systems through an innovative synergistic curing mechanism. Specifically, the system comprises two latent crosslinking agents activated under different conditions: First curing: After coating film formation and water evaporation, microencapsulated PCDI is released first, reacting with the carboxyl groups (-COOH) inherent in the PHA matrix or generated by hydrolysis to form a preliminary crosslinking network. Second curing: Blocked polyisocyanate undergoes a second crosslinking reaction with the hydroxyl groups (-OH) in the PHA matrix. The core innovation of this invention lies in discovering and utilizing the positive synergistic effect between these two curing reactions. Experiments show that when the two latent curing agents coexist, the system can cure at ambient temperature to form a dense interpenetrating network structure with good mechanical properties; for example, the pull-out adhesion in the embodiment can reach 8.9 MPa. However, if blocked polyisocyanate is used alone, it cannot cure effectively at the same ambient temperature; if PCDI is used alone, the same level of mechanical strength cannot be achieved. This synergistic effect ensures the high performance of the final coating film. Based on the experimental results, the mechanism of this synergistic effect can be explained as follows: the first reaction between PCDI and carboxylic acid alters the chemical properties of the local microenvironment, generating in situ catalytic conditions that effectively promote the deblocking and reaction of the blocked polyisocyanate at ambient temperature. This sequential mechanism, where the first reaction creates favorable activation conditions for the second reaction, allows the entire dual curing process to be completed efficiently at room temperature, thereby endowing the coating with excellent mechanical strength while ensuring a long pot life.

[0020] The additive may be one or more coating additives conventionally used in the art, such as, but not limited to, wetting and dispersing agents, defoamers, leveling agents, and rheology modifiers.

[0021] In the above technical solution, the content of each component can be selected to optimize specific performance. For example:

[0022] The solid content of the biodegradable polyhydroxy fatty acid ester matrix is ​​preferably 35%, 38%, 40%, 43%, 46%, 48%, 50%, 52%, or 55%.

[0023] The solid content of the self-stratifying modifier is preferably 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or 4.0%.

[0024] The solid content of the light-stabilizing and corrosion-resistant filler is preferably 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0025] The solid content of the latent dual-curing system is preferably 1%, 2%, 3%, 4%, 5%, 6%, or 7%. The content of microencapsulated PCDI is preferably 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or 4.0%. The content of blocked polyisocyanate is preferably 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, or 3.0%.

[0026] The biodegradable polyhydroxy fatty acid ester matrix is ​​selected from one or more of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and their terminal hydroxyl-modified derivatives or polydimethylsiloxane-grafted derivatives. In one specific example, the matrix may contain 20–30% PHBH, 8–15% terminal hydroxyl-modified PHBV, and 7–10% polydimethylsiloxane-grafted poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PDMS-g-PHBH).

[0027] The self-stratification modifier is polystyrene-grafted polydimethylsiloxane, which forms a silicon-rich, low surface energy layer on the surface of the topcoat layer after curing. The static water contact angle of the topcoat layer after forming the silicon-rich, low surface energy layer is ≥105°.

[0028] The encapsulation efficiency of the microencapsulated PCDI in the latent dual-curing system is no less than 85%. 50 It is 0.5–5µm.

[0029] The water-based biodegradable self-polishing composition has a solid content of 40–80 wt%. For example, the solid content can be 40%, 55%, 70%, or 80%.

[0030] The modified epoxy intermediate coating containing hydrolyzable side chains is cured from a composition comprising 40–60% β-betaine ester modified epoxy emulsion and 15–25% aqueous fatty amine curing agent. The cured film has an aerobic biodegradation rate of over 25% after 180 days of testing in a simulated marine environment according to ASTM D6691-24a standard.

[0031] The present invention also provides a method for preparing the above-mentioned water-based biodegradable self-polishing composition, comprising the following steps:

[0032] Step 1. The biodegradable polyhydroxy fatty acid ester matrix, self-stratification modifier, light stabilizer and anti-corrosion filler and additives are sequentially dispersed in deionized water to form main agent A, wherein, based on the total solid content of the composition, main agent A contains 35–55 wt% biodegradable polyhydroxy fatty acid ester matrix, 0.5–4 wt% self-stratification modifier, and 2–10 wt% light stabilizer and anti-corrosion filler;

[0033] Step 2. Mix microencapsulated PCDI with blocked polyisocyanate to form curing agent B, wherein curing agent B comprises 0.5–4 wt% microencapsulated polycarbodiimide and 0.5–3 wt% blocked polyisocyanate based on the total solid content of the composition;

[0034] Step 3. Mix the main agent A and the curing agent B before construction, so that the mass ratio of the solid content of the main agent A to the curing agent B is 100:2.5–3.5.

[0035] Furthermore, when tested according to ASTM D4541-22, the pull-out adhesion of the system is not less than 7.9 MPa; and the content of volatile organic compounds (VOCs) in the system, as determined according to ISO 11890-2:2020 / Amd 1:2024, is not higher than 50 g / L.

[0036] Compared with the prior art, the following significant advantages can be obtained by using the present invention:

[0037] Environmentally friendly design throughout the entire life cycle: This invention uses biodegradable PHA as the core of the topcoat and innovatively designs the modified epoxy intermediate coat to be biodegradable (tested according to ASTM D6691 standard, the degradation rate exceeds 25% within 180 days), laying the foundation for achieving environmental friendliness of the entire coating system.

[0038] Precisely addressing current regulations and offering advantages in use: Through an innovative latent dual-curing system, the free diisocyanate monomer content in the final product is strictly controlled to below 0.1%, complying with the EU REACH directive (EU) 2020 / 1149. Simultaneously, the biocide-free / degradable design of this invention aligns with the restrictions on Cybutryne (Irgarol 1051) under the International Convention for the Control of Hazardous Antifouling Systems on Ships (AFS) from January 1, 2023. In the current market environment, this design helps reduce compliance costs and operational risks associated with free isocyanates, and under certain conditions, can simplify some safety management processes, thereby enhancing the convenience of practical applications and market competitiveness.

[0039] Reducing long-term ecological risks: Functional nanofillers are firmly anchored in the matrix by forming a dense interpenetrating polymer network. These fillers peel off from the matrix as a whole at a micron-scale rate rather than leaching out, thereby greatly reducing the potential risk of free nanoparticles entering the marine environment and reinforcing the "safe design" concept of this invention.

[0040] Innovative Hybrid Antifouling Mechanism and Significant Economic Benefits: This invention creatively combines the controlled hydrolytic self-polishing of a PHA matrix with the ultra-low surface energy physical antifouling formed by self-layering. This hybrid antifouling mechanism of "dynamic polishing + static release" ensures that ships can effectively resist biofouling during both high-speed navigation and long-term berthing, thereby significantly saving fuel by maintaining the hydrodynamic smoothness of the hull over a long period.

[0041] Key Breakthrough for Industrial Application: This invention effectively solves the critical challenges of the pot life and storage stability of high-performance waterborne coatings by introducing a latent dual-curing system. The application period of the coating system described in this invention is no less than 60 minutes, far longer than many traditional high-performance two-component systems; simultaneously, its viscosity change rate after accelerated aging at 50°C for 30 days can be controlled within 15%, exhibiting excellent storage stability. These characteristics significantly reduce the requirements for application conditions and improve the feasibility of industrial application of the technical solution of this invention.

[0042] A systematic integrated protection solution and proven physical properties: The three-layer coating system proposed in this invention exhibits high overall performance through the scientific matching of the functions of each layer. This system achieves a pull-out adhesion of up to 8.9 MPa, can withstand 1000 hours of salt spray testing without blistering or corrosion, and successfully passes a harsh low-temperature impact test at -40°C. These properties fully demonstrate that the system of this invention has the ability to provide long-term protection in harsh marine environments. Attached Figure Description

[0043] Figure 1: Schematic diagram of the hull steel substrate and multi-layer antifouling coating and their microstructure of the present invention.

[0044] In the diagram, 1. Steel substrate; 2. Zinc-rich primer layer; 3. Zinc powder particles; 4. Modified epoxy intermediate layer; 5. Topcoat layer; 6. Microencapsulated PCDI; 7. Light-stabilizing and anti-corrosion filler; 8. Silicon-rich top layer. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention. Unless otherwise stated, the raw materials used in this embodiment are commercially available industrial products or can be prepared by conventional methods. Unless otherwise specified, performance testing methods are performed according to the standards described in the invention summary section.

[0046] In all embodiments and comparative examples of the present invention, unless otherwise expressly stated, all parts mentioned in the component content refer to parts by mass.

[0047] Table 1. Primer component names, product models / codes, and suppliers:

[0048]

[0049] Table 2. Names, product models / codes, and suppliers of intermediate paint components:

[0050]

[0051] Table 3. Topcoat component names, product models / codes, and suppliers:

[0052]

[0053] Table 4 Comparative Example Raw Material Names, Product Models / Codes, and Suppliers:

[0054]

[0055] Table 5. Names, product models / codes, and suppliers of titration reagents for analytical testing:

[0056]

[0057] Table 6. Names, Product Models / Codes, and Suppliers of Common Pharmaceutical Raw Materials and Solvents:

[0058]

[0059] Table 7 lists the names, models, and manufacturers of the main analytical instruments:

[0060]

[0061] Table 8. Main Test Items and Test Standards:

[0062]

[0063] * Note: The dry film thickness loss was periodically measured using a rotating cylinder method with a surface profilometer, referring to the equipment in ASTM D6442-06R20 and measuring the dry film thickness with a micrometer according to ASTM D1005-95(2024).

[0064] Preparation of general analytical reagents and pharmaceuticals:

[0065] 1. Preparation and standardization of ethylenediaminetetraacetic acid (EDTA) standard solution.

[0066] Accurately weigh EDTA-2Na, dissolve it in deionized water, and dilute to the required concentration (e.g., 0.05 mol / L). Standardize using ZnO dried to constant weight at 110℃. Accurately weigh three portions of standard zinc oxide, dissolve them in dilute hydrochloric acid, adjust the pH with buffer solution, and titrate with the prepared EDTA solution using Eriochrome Black T as an indicator until the solution color changes from wine red to pure blue. Calculate and determine the accurate concentration of the EDTA standard solution based on the mass of zinc oxide and the volume of EDTA consumed. The relative deviation of three parallel experiments should not exceed 0.2%.

[0067] 2. Preparation of microencapsulated PCDI.

[0068] Step 1 (Core Material Preparation): Dissolve 100 parts of liquid PCDI in 200 parts of ethyl acetate to form a homogeneous oil phase solution.

[0069] Step 2 (Emulsion Preparation): Dissolve 10 parts of polyvinyl alcohol (PVA-1788) in 900 parts of deionized water as a protective colloid for the aqueous phase. Under high-speed shear (8000 rpm), slowly add the oil phase obtained in Step 1 to the aqueous phase and continue emulsifying for 30 minutes to form a stable O / W type emulsion.

[0070] Step 3 (Interfacial Polymerization and Coating): A mixture of 15 parts TDI and 5 parts TMP is slowly added dropwise to the above emulsion. The temperature is raised to 70°C, and the mixture is stirred at 500 rpm for 4 hours. TDI polymerizes with water and TMP at the oil-water interface to form a polyurethane-urea wall material, which encapsulates PCDI.

[0071] Step 4 (Post-processing and characterization): After the reaction was completed, the mixture was cooled to room temperature, centrifuged, washed three times with deionized water, and then vacuum dried at 60°C for 24 hours to obtain a white powdery microencapsulated PCDI product. The encapsulation efficiency was determined using Soxhlet extraction, and the average particle size was measured using a laser particle size analyzer according to ISO 13320 standard.

[0072] Table 9. Characterization results of microencapsulated PCDI:

[0073]

[0074] Table 9 shows that PCDI has an encapsulation rate of up to 88.5%, indicating that the core material is effectively coated by the wall material, which is key to its "latency" in water-based systems. Meanwhile, its moderate average particle size of 3.2µm is beneficial for its stable dispersion in coatings without premature sedimentation.

[0075] 3. Preparation of graphene-zinc phosphate nanosheets (GO-ZP).

[0076] Step 1 (GO Preparation): Graphene oxide (GO) was prepared using a modified Hummers method. 5g of natural graphite powder was added to 120mL of concentrated sulfuric acid, and 15g of potassium permanganate was slowly added under ice bath cooling, with stirring for 2 hours. The temperature was then raised to 35℃ and the reaction proceeded for 12 hours. The reaction mixture was poured into 400mL of ice water, and 30mL of hydrogen peroxide solution was added dropwise until the solution turned golden yellow. After centrifugation and washing until neutral, GO powder was obtained by freeze-drying.

[0077] Step 2 (GO-ZP Composite): 1g of GO powder was ultrasonically dispersed in 500mL of deionized water. 20g of zinc nitrate and 15g of ammonium dihydrogen phosphate were added and stirred to dissolve. Ammonia was added dropwise at 80℃ to adjust the pH to 7.0, and the reaction was continued for 3 hours. During this process, zinc phosphate precipitated in situ on the surface of the GO sheets.

[0078] Step 3 (Post-processing and Characterization): After the reaction, the product was centrifuged, washed several times alternately with deionized water and ethanol, and finally dried under vacuum at 80℃ for 12 hours to obtain gray-black graphene-zinc phosphate nanosheets (GO-ZP) powder. The dried GO-ZP powder was dissolved in dilute hydrochloric acid at 60℃, and then subjected to complexometric titration with EDTA standard solution to determine the zinc ion content, thereby calculating the zinc phosphate loading in the composite material.

[0079] Table 10 Characterization results of GO-ZP:

[0080]

[0081] Note: Zinc phosphate loading is calculated using the following formula:

[0082] Load (wt%) = (C EDTA ×V EDTA ×M 磷酸锌 ) / (3×M Zn ×m 样品 )×100%, where C EDTA V represents the concentration of the EDTA standard solution. EDTA To determine the volume consumed in the titration, M 磷酸锌 and M Zn The molar masses of zinc phosphate and zinc are respectively, m 样品 For sample quality.

[0083] Table 10 shows that the zinc phosphate loading in the GO-ZP samples prepared in different batches remained stable at approximately 22 wt%, with minimal batch-to-batch variation. This indicates that the in-situ precipitation method has good reproducibility and can stably prepare composite anti-corrosion fillers with the target composition.

[0084] 4. Preparation of β-betaine ester modified epoxy emulsion.

[0085] Step 1 (synthesis of β-amino acid esters): 1 mole of N,N-dimethylethylenediamine and 1.1 moles of methyl acrylate were reacted in methanol solvent at 50°C for 6 hours to obtain N,N-dimethyl-N'-(2-methoxycarbonylethyl)ethylenediamine.

[0086] Step 2 (Epoxy Grafting): Dissolve 1 mole of bisphenol A type epoxy resin (E-51) in xylene, add 0.2 moles of the product obtained in Step 1, and react at 120°C for 4 hours to graft the side links containing tertiary amine groups onto the epoxy backbone.

[0087] Step 3 (Quercing and Emulsification): The grafted epoxy resin was cooled to 80°C, and 0.2 mol of chloroacetic acid was added to initiate a quaternization reaction for 4 hours, forming an amphoteric β-betaine ester structure. After the reaction was completed, a measured amount of deionized water was added under high-speed stirring, while xylene solvent was distilled off. A stable β-betaine ester modified epoxy emulsion with a solid content of approximately 50% was obtained by phase inversion.

[0088] Step 4 (Product Characterization): After the reaction is complete, samples are taken. The change in epoxy value before and after the grafting reaction is determined by potentiometric titration using the ASTM D1652 standard method, and the conversion rate of epoxy groups is calculated. After the quaternization reaction, the content of tertiary amine groups in the product is determined by potentiometric titration, and the quaternization rate is calculated.

[0089] Table 11 Characterization results of β-betaine ester modified epoxy emulsion:

[0090]

[0091] Table 11 shows that the conversion rate of epoxy groups and the quaternization rate of tertiary amine groups, as determined by potentiometric titration, both exceeded 95%. Such high reaction efficiency confirms that the target chemical structure—an epoxy resin containing β-betaine ester side chains—has been successfully synthesized.

[0092] 5. Preparation of hydroxyl-terminated modified PHBV-OH emulsion.

[0093] Step 1 (Synthesis of PHBV-diol): 20 parts of PHBV were dissolved in 200 parts of chloroform and heated to reflux. Then, 20 parts of ethylene glycol and 0.5 parts of p-toluenesulfonic acid were added as catalysts. The reaction was carried out at 60°C for 24 hours. After the reaction was complete, the product was precipitated in a large amount of diethyl ether, filtered, and vacuum dried to obtain a white hydroxyl-terminated modified PHBV oligomer (PHBV-diol).

[0094] Step 2 (Product Characterization): The hydroxyl value of the PHBV-diol was determined by titration using the ASTM E222-23 standard method.

[0095] Step 3 (Emulsification): Heat the qualified PHBV-diol to a molten state, and slowly add it to 10 parts of deionized water containing 0.5 parts SDS under high-speed shear at 5000 rpm. Continue emulsification for 20 minutes to obtain a stable aqueous emulsion with a solid content of about 50%.

[0096] Table 12 Characterization results of hydroxyl-terminated modified PHBV-OH emulsion:

[0097]

[0098] The results in Table 12 show that the measured hydroxyl values ​​of the products prepared by transesterification are in high agreement with the theoretical calculations, proving that the PHBV macromolecular chains have been successfully cleaved and terminal hydroxyl groups have been introduced, providing active sites for subsequent cross-linking reactions.

[0099] 6. Preparation of PS-g-PDMS.

[0100] A "graft-then-polymerization" method was employed. First, 10 parts of PDMS-OH and 1.2 parts of chloromethylstyrene were reacted in toluene to prepare a PDMS macromonomer with polymerizable vinyl groups. Subsequently, this macromonomer was reacted with 90 parts of styrene monomer in toluene using AIBN as an initiator, and a free radical polymerization reaction was carried out at 70°C for 12 hours. After the reaction, the product was precipitated in methanol, purified, and dried to obtain the PS-g-PDMS graft copolymer.

[0101] The grafting rate was determined using chemical analysis. A precise amount of the dried product was placed in a crucible and ashed in a muffle furnace at 600°C to completely decompose the organic components, leaving silicon dioxide (SiO2) as the residue. The content of polydimethylsiloxane in the copolymer was calculated by weighing the silicon dioxide, thus determining the grafting rate.

[0102] Table 13 Characterization results of PS-g-PDMS:

[0103]

[0104] The gravimetric analysis results in Table 13 show that the PDMS content in the final product remained stable at approximately 10 wt%, consistent with the feed ratio. This confirms that the PDMS macromonomer with polymerizable groups has been successfully grafted onto the polystyrene backbone, forming the target composition of the PS-g-PDMS self-stratifying modifier.

[0105] 7. Preparation and characterization of PDMS-g-PHBH.

[0106] Grafting free radical polymerization was employed: 10 parts of hydroxyl-terminated PDMS-OH were reacted with 1.2 parts of chloromethylstyrene in toluene to prepare a PDMS macromonomer with polymerizable vinyl groups. Subsequently, this monomer was reacted with 90 parts of PHBH in toluene, using AIBN as an initiator, and subjected to free radical polymerization at 70°C for 12 hours. After the reaction, the product was precipitated in methanol, purified, and dried to obtain the PDMS-g-PHBH graft copolymer.

[0107] The extent of the grafting reaction was characterized by acid value titration. Precisely weighed PHBH starting material before the reaction and PDMS-g-PHBH product after the reaction were dissolved separately in a chloroform-ethanol mixed solvent and titrated with a standardized potassium hydroxide-ethanol standard solution, using phenolphthalein as an indicator. The acid value was calculated based on the volume of titrant consumed. The grafting reaction consumes the terminal carboxyl groups of PHBH, leading to a significant decrease in acid value.

[0108] Table 14 Characterization results of PDMS-g-PHBH:

[0109]

[0110] The titration results in Table 14 clearly show that, compared with the PHBH raw material, the acid value of the grafted product PDMS-g-PHBH decreased significantly from 2.0 mg KOH / g to approximately 0.5 mg KOH / g. This significant decrease in acid value demonstrates that the active sites (terminal carboxyl groups) on the PHBH molecular chain have undergone an effective grafting reaction with the PDMS macromonomer, forming the target product. This method provides direct chemical quantitative evidence for the successful synthesis of graft copolymers.

[0111] 8. Preparation of core-shell structured titanium dioxide.

[0112] The sol-gel method was employed. Step 1 (Al₂O₃ coating): 10 parts of titanium dioxide nanoparticles were ultrasonically dispersed in 200 parts of anhydrous ethanol. Under nitrogen protection, a solution containing 5 parts of aluminum isopropoxide and 50 parts of isopropanol was added dropwise to the suspension, and a small amount of water was added to initiate hydrolysis. The reaction was stirred at 50°C for 6 hours, and after centrifugation, washing, and drying, the intermediate product—aluminum oxide-coated titanium dioxide—was obtained.

[0113] Step 2 (CeO2 Coating): The product obtained in Step 1 was redispersed in ethanol, and an ethanol solution containing 2 parts of cerium(III) nitrate hexahydrate was added dropwise. The pH was adjusted to 9-10 by adding ammonia to initiate the precipitation of cerium hydroxide. After stirring continuously for 4 hours, the product was centrifuged, washed, and calcined at 500°C for 2 hours to obtain the final core-shell structure, namely a multi-layered core-shell composite particle with titanium dioxide as the core, and sequentially coated with an aluminum oxide intermediate layer and a cerium dioxide outer shell.

[0114] Step 3 (Product Characterization): The content of the coating layer was determined by selective acid dissolution and gravimetric analysis. A certain mass of the final product was taken, and the outermost CeO2 layer was first dissolved in an acid solution of a specific concentration under mild conditions. The content was calculated by the mass difference before and after dissolution. Subsequently, the acid concentration or temperature was increased to dissolve the Al2O3 layer, and the content was calculated again by the mass difference, thereby verifying the formation of the core-shell structure and the proportion of each layer.

[0115] Table 15 Characterization results of core-shell structured titanium dioxide:

[0116]

[0117] Table 15 shows the precise determination of the contents of the outer CeO2 layer and the middle Al2O3 layer through selective dissolution and gravimetric analysis, and the results are completely consistent with the design values. These results support the formation and functional characterization of the core-shell structure, which is a prerequisite for ensuring its photostable function.

[0118] 9. Preparation of zinc-rich primer.

[0119] Add 30 parts waterborne epoxy resin, 5 parts conductive mica, 1 part graphene, 10 parts deionized water, and appropriate additives such as dispersants and defoamers to a dispersion vessel and disperse evenly under high-speed stirring to form component A. Premix 15 parts waterborne epoxy curing agent with 39 parts zinc powder evenly to form component B. Before construction, mix components A and B evenly according to the specified ratio.

[0120] To verify the technical effects of the present invention, the following examples and comparative examples were set up. The modified epoxy intermediate paint used in the test was cured from the following components: 50% β-betaine ester modified epoxy emulsion (prepared according to Preparation Example 3) and 20% Anquamine 287 waterborne fatty amine curing agent, with the remainder being water and additives. The topcoats of all examples and comparative examples were applied in conjunction with the primer and intermediate paint of the present invention to form a complete coating system. The dry film thickness of each layer was specifically controlled as follows: zinc-rich primer layer 65±15µm, modified epoxy intermediate paint layer 60±20µm, and topcoat layer 100±20µm. Performance tests were conducted after curing at 25℃ and 65%RH for 7 days. Among them, the low-temperature impact test involved placing the cured complete three-layer system sample in a low-temperature test chamber at -40℃ for at least 4 hours, and then completing the impact test within 10 seconds after removal. The dynamic antifouling performance test was strictly performed in accordance with the ASTM D4939-89R20 standard. The test conditions are as follows: The painted sample is installed on the rotating device of the institution that meets the aforementioned standard requirements and exposed to natural seawater at a surface linear velocity of 15 knots (7.7 m / s); the total test period is 90 days, during which the ship will run dynamically for 12 hours and be stationary for 12 hours each day to simulate the actual operation mode of the ship.

[0121] Table 16 Topcoat Formulations for Examples and Comparative Examples (Based on Solid Content wt%):

[0122]

[0123] Note: The remaining components of Examples 1-5 and Comparative Examples 1-6 are solvents and additives used to adjust the total solids content to approximately 60 wt%. Specifically, Comparative Example 1 removed the self-stratifying agent; Comparative Example 2 used ordinary TiO2 without a core-shell structure; Comparative Example 3 was an optimized pure self-polishing coating; and Comparative Example 4 was a solvent-based system, a typical high-performance silicone fouling-releasing coating. To verify the synergistic effect of the dual-curing system, Comparative Examples 5 and 6 were also set up: the formulation of Comparative Example 5 was similar to that of Example 1, but only microencapsulated PCDI was used as the curing agent; the formulation of Comparative Example 6 was similar to that of Example 1, but only blocked polyisocyanate was used as the curing agent.

[0124] Table 17. Overall performance test results of the coating systems in the examples and comparative examples:

[0125]

[0126] * Note: The fouling level assessment is based on ASTM D3623-78A (2020), where Level 1 represents no fouling, Level 2 represents slight slime, Level 3 represents significant slime or a small amount of algae, Level 4 represents a large amount of algae or a small amount of hard fouling organisms, and Level 5 represents severe hard fouling.

[0127] ** Note: The aerobic biodegradation rate test in the marine environment was only conducted on the intermediate coating cured film.

[0128] Experimental Results and Analysis:

[0129] Validation of the potential environmental degradability of the intermediate coating: To verify the environmental compatibility of the intermediate coating of this invention, the aerobic biodegradability of the cured film of the intermediate coating in a simulated marine environment containing natural seawater inoculum was tested according to ASTM D6691-24a standard. This standard is an internationally recognized authoritative method for evaluating the biodegradability of plastic materials in marine environments, and its test conditions can scientifically reflect the behavior of materials in real marine environments. As shown in Table 17, after 180 days of testing, the biodegradation rate of the intermediate coating of this invention exceeded 25%, while the degradation rate of conventional epoxy coatings under the same conditions is usually much lower than 5%. This result strongly proves that the modified epoxy intermediate coating designed in this invention has significantly higher potential marine environmental degradability than traditional epoxy resins, thus supporting the technical claim of this invention to improve the environmental friendliness of the entire life cycle. The mechanism of the improved biodegradability exhibited by the intermediate coating of this invention can be explained as follows: the introduced β-betaine ester side chain, as an amphoteric structure, not only enhances the hydrophilicity of the polymer chain, but also plays a catalytic role when water molecules attack the epoxy backbone, thereby accelerating the hydrolytic chain-breaking process under the action of marine microorganisms.

[0130] Quantitative Verification of Self-Layering Effect: To verify the effectiveness of the self-layering modifier PS-g-PDMS, the surface properties of the cured coating of Example 1 were quantitatively characterized. As shown in Table 17, its surface water contact angle reached 108°, far exceeding that of Comparative Example 1 (85°) without the modifier, indicating that the coating surface exhibits significant hydrophobicity. This hydrophobicity is due to the enrichment of low surface energy polydimethylsiloxane (PDMS) segments at the coating-air interface. Furthermore, the surface roughness of the coating was measured using a surface profilometer to be extremely low. These quantitative results collectively confirm that PS-g-PDMS successfully migrated to the surface during the curing process, forming the functional silicon-rich top layer structure defined in this invention, providing a physical basis for achieving static fouling release.

[0131] Furthermore, the thickness of the silicon-rich top layer described in this invention can be verified through theoretical calculations. Taking Example 1 as an example, the dry film thickness of the topcoat is controlled at 100µm, and the proportion of the self-stratifying modifier PS-g-PDMS in the solid content is 2.5wt%. Based on typical empirical data of composite coatings containing polyester, epoxy, and inorganic fillers, the average density of the dry film of the topcoat is 1.3g / cm³. 3 The density of PS-g-PDMS is 1.0 g / cm³. 3 Calculations were performed based on these parameters, at 1cm 2Within the coated area, the total mass and volume of PS-g-PDMS can be determined. Based on the migration patterns of the self-layering system and experimental data analysis, approximately 60% of the PS-g-PDMS effectively migrates to the surface during curing and forms a uniform top layer. Therefore, the thickness of the formed silicon-rich top layer is calculated to be 1.92 µm. Combining the measured performance data of high surface contact angle with this theoretical calculation result confirms that the present invention forms a functional silicon-rich top layer within the stated thickness range.

[0132] Verification of the hybrid mechanism: The core innovation of this invention lies in the effective combination of self-polishing (SP) and fouling release (FR) mechanisms. To verify the superiority of this hybrid mechanism, Example 1 was compared with Comparative Example 3, representing a pure SP mechanism, and Comparative Example 4, representing a pure FR mechanism.

[0133] Static antifouling performance: As shown in Table 17, Example 1 exhibited the best Class 1 antifouling performance in the 90-day static immersion test. Comparative Example 3 (pure SP) showed severe fouling under static conditions due to its high surface energy (contact angle 86°), resulting in a Class 3 rating. Comparative Example 4 (pure FR), although exhibiting extremely low surface energy (contact angle 112°), showed excellent Class 1-2 antifouling performance, but was slightly inferior to Example 1.

[0134] Dynamic antifouling performance: In a 90-day dynamic test, all coatings based on the SP mechanism (Example 1 and Comparative Example 3) achieved the best Grade 1 antifouling performance through surface renewal. Comparative Example 4 (pure FR), lacking surface renewal capability, performed slightly worse, achieving Grade 2, when the shear force of the water flow was insufficient to remove all adhesion germination points.

[0135] Overall performance: Comparative Example 4, as a typical silicone coating, exhibits a pull-out adhesion of only 5.1 MPa to the substrate, significantly lower than the system of this invention. In summary, only the hybrid mechanism coating of this invention (Example 1) can achieve optimal Grade 1 antifouling performance under both static and dynamic conditions, while maintaining excellent adhesion, demonstrating its comprehensive advantages over high-performance single-mechanism coatings.

[0136] Analysis of the influence trends of key components:

[0137] Impact of the biodegradable PHA matrix: The PHA matrix is ​​the core component for achieving the self-polishing function. Comparing the data from Example 4 (PHA content 35%), Example 1 (46%), and Example 5 (55%), it is clear that the self-polishing rate increases linearly from 4.1 µm / month to 6.0 µm / month with the increase in the total amount of PHA matrix. This is because the higher content of the hydrolyzable skeleton accelerates the stable peeling of the coating surface. However, this is also accompanied by a slight decrease in pull-out adhesion from a maximum of 8.9 MPa (Example 4) to 7.9 MPa (Example 5), indicating that excessively high biodegradable components slightly sacrifice the mechanical cohesive strength of the coating. Therefore, the 35-55% range defined in this invention is an optimized range for achieving a controllable polishing rate while ensuring sufficient mechanical properties.

[0138] The Influence of Light Stabilizing and Corrosion-Resistant Fillers: These fillers are crucial for the long-term durability and adhesion of the coating. Comparing Example 5 (filler content 2%), Example 1 (4%), and Example 4 (10%), the weather resistance of the coating was significantly enhanced with increasing filler content, as evidenced by a significant decrease in the color difference ΔE value after 1000 hours of QUV accelerated aging from 2.8 (Example 5) to 1.6 (Example 4); simultaneously, the pull-out adhesion also increased from 7.9 MPa (Example 5) to 8.9 MPa (Example 4). This indicates that the filler effectively enhances the density of the coating film and its adhesion to the substrate. However, excessively high filler content can also hinder the hydrolysis of the PHA matrix to some extent, resulting in a decrease in the self-polishing rate from 6.0 µm / month (Example 5) to 4.1 µm / month (Example 4). Therefore, a range of 2-10% is the optimal choice for balancing durability and antifouling efficiency.

[0139] The impact of the latent dual-curing system: This system is crucial for ensuring the mechanical and application properties of the coating film. Comparing Examples 5, 1, and 4, it can be seen that increasing the content of the crosslinking system effectively improves the mechanical strength of the coating, increasing adhesion from 7.9 MPa to 8.9 MPa. Simultaneously, an appropriate amount of crosslinking agent is essential for achieving a long pot life; for example, a 3% content in Examples 1, 2, and 3 yields a pot life of at least 70 minutes. However, excessively high crosslinking agent content slightly shortens the pot life (≥60 minutes). Therefore, a range of 1-7% is an effective range for balancing high mechanical properties with a good application window.

[0140] The necessity of self-layering modifier: Compared with Comparative Example 1, after removing the self-layering modifier PS-g-PDMS, the contact angle of the coating surface dropped sharply from 108° to 85°, and the hydrophobicity was lost. As a result, the static antifouling level after 90 days deteriorated from level 1 (no adhesion) to level 3-4 (a lot of adhesion). This proves that the low surface energy top layer formed by self-layering is the key to achieving physical antifouling.

[0141] The necessity of core-shell structured light stabilizers: Comparing Example 1 and Comparative Example 2, after replacing the core-shell structured light stabilizer with ordinary anatase TiO2, the color difference ΔE of the coating after 1000 hours of QUV accelerated aging increased sharply from an imperceptible 1.8 to over 6.0 (severe discoloration and chalking). This result clearly reveals the inherent defects of ordinary TiO2: as a highly efficient photocatalyst, it generates reactive oxygen free radicals under UV excitation, thereby catalyzing the degradation of the adjacent PHA polymer matrix. The core-shell structure used in this invention physically isolates the photocatalytically active TiO2 core from the PHA matrix through an inert oxide shell, effectively suppressing this catalytic degradation effect while retaining the excellent UV shielding ability of TiO2. Therefore, this core-shell structure is a key and necessary technology for protecting the hydrolysis-sensitive PHA matrix and maintaining the long-term outdoor durability of the coating. Its excellent results provide strong evidence for the long-term durability of the coating system.

[0142] Verification of the synergistic effect of the dual-curing system: To directly verify the synergistic effect of the latent dual-curing system described in this invention, Comparative Examples 5 and 6 were specifically set up. As shown in Table 17, after curing for 7 days at 25°C and 65%RH, the paint film of Comparative Example 6 remained liquid and could not form an effective coating, confirming that the blocked polyisocyanate alone could not be effectively cured at room temperature. This is because the unblocking temperature of the selected blocked polyisocyanate is much higher than the ambient temperature, and its crosslinking reaction cannot be initiated without the synergistic catalytic effect generated by the PCDI reaction. Although Comparative Example 5 could cure into a film, its key mechanical properties were far inferior to those of Example 1. Its pull-out adhesion was only 4.2 MPa, far lower than the 8.5 MPa of Example 1, and it also performed poorly in low-temperature impact and salt spray tests. The results of these two comparative examples contrast sharply with the excellent performance of Example 1. The results show that there is a significant positive synergistic effect between microencapsulated PCDI and blocked polyisocyanate in the system of the present invention. This effect is the key to achieving a balance between room temperature curing and good mechanical properties, and is not a simple superposition of the effects of the two curing agents.

[0143] Verification of the universality of PHA types: Comparing Examples 1, 2, and 3, despite the different PHA types, the core performance indicators of the final coatings, such as adhesion, antifouling rating, and weather resistance, all remained at a very similar excellent level. This demonstrates that the technical framework of this invention, particularly the self-layering, latent crosslinking, and light-stabilized system, has broad applicability to different types of PHA substrates. From a chemical structure perspective, the various PHA types (including PHB, PHBH, PHBV, etc.) share the same polyester backbone and hydrolyzable ester bonds, which is the basis for achieving the self-polishing function of this invention. Simultaneously, they also have similar end groups (hydroxyl and / or carboxyl groups) to participate in the dual curing reaction of this invention. Therefore, the technical solution of this invention is universally applicable to all the various PHA substrates listed in this invention.

[0144] In summary, this invention, through the systematic and innovative design of multi-layer structure, topcoat matrix, functional additives, and crosslinking system, has successfully prepared a marine antifouling coating system that combines high-efficiency antifouling, long-lasting durability, easy application, and significantly improved environmental friendliness. It solves many pain points of existing technologies and has good feasibility for industrial application.

[0145] Those skilled in the art should understand that the above embodiments are merely exemplary and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the technical solutions of the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-based, multi-layered, biodegradable, self-polishing antifouling coating system for ships, characterized in that: The system comprises, in sequence, a zinc-rich primer layer with a thickness of 50–80 µm, a modified epoxy intermediate layer with a thickness of 40–80 µm containing hydrolyzable side chains, and a topcoat layer with a thickness of 80–120 µm. The topcoat layer is cured from an aqueous, biodegradable, self-polishing composition comprising, by weight percentage of total solids, 35–55 wt% of a biodegradable polyhydroxyalkanoate matrix, 0.5–4 wt% of a self-stratifying modifier, 2–10 wt% of a light stabilizer and corrosion inhibitor, and a latent dual-curing system comprising 0.5–4 wt% of microencapsulated polycarbodiimide and 0.5–3 wt% of a blocked polyisocyanate, wherein the total solids content of the latent dual-curing system is 1–7 wt%. The composition further comprises deionized water and additives, and the paint film cured from the composition has a free diisocyanate monomer content of not more than 0.1 wt%.

2. The system according to claim 1, characterized in that, The biodegradable polyhydroxy fatty acid ester matrix is ​​selected from one or more of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and their terminal hydroxyl-modified derivatives or polydimethylsiloxane grafted derivatives.

3. The system according to claim 1, characterized in that, The biodegradable polyhydroxy fatty acid ester matrix specifically comprises 20–30% poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), 8–15% hydroxyl-terminated modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and 7–10% polydimethylsiloxane grafted poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

4. The system according to claim 1, characterized in that, The self-stratification modifier is polystyrene-grafted polydimethylsiloxane, which forms a silicon-rich, low surface energy layer on the surface of the topcoat layer after curing. The static water contact angle of the topcoat layer after forming the silicon-rich, low surface energy layer is ≥105°.

5. The system according to claim 1, characterized in that, The encapsulation efficiency of the microencapsulated polycarbodiimide in the latent dual-curing system is not less than 85%. 50 It is 0.5–5µm.

6. The system according to claim 1, characterized in that, The solid content of the water-based biodegradable self-polishing composition is 40–80 wt%.

7. The system according to claim 1, characterized in that, The modified epoxy intermediate coating containing hydrolyzable side chains is cured from a composition comprising 40–60% β-betaine ester modified epoxy emulsion and 15–25% aqueous fatty amine curing agent. The cured film has an aerobic biodegradation rate of over 25% after 180 days of testing in a simulated marine environment according to ASTM D6691-24a standard.

8. The system according to claim 1, characterized in that, When tested according to ASTM D4541-22 standard, the pull-out adhesion of the system is not less than 7.9 MPa.

9. The system according to claim 1, characterized in that, The volatile organic compound content of the system, as determined according to ISO 11890-2:2020 / Amd 1:2024, is not higher than 50 g / L.

10. A method for preparing an aqueous biodegradable self-polishing composition, characterized in that, It includes the following steps: Step 1. The biodegradable polyhydroxy fatty acid ester matrix, self-stratification modifier, light stabilizer and anti-corrosion filler and additives are sequentially dispersed in deionized water to form main agent A, wherein, based on the total solid content of the composition, main agent A contains 35–55 wt% biodegradable polyhydroxy fatty acid ester matrix, 0.5–4 wt% self-stratification modifier, and 2–10 wt% light stabilizer and anti-corrosion filler; Step 2. Mix microencapsulated polycarbodiimide with blocked polyisocyanate to form curing agent B, wherein curing agent B comprises 0.5–4 wt% microencapsulated polycarbodiimide and 0.5–3 wt% blocked polyisocyanate based on the total solid content of the composition; Step 3. Mix the main agent A and the curing agent B before construction, so that the mass ratio of the solid content of the main agent A to the curing agent B is 100:2.5–3.5.

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