A weather-resistant, high-hardness composite anti-corrosion coating and its preparation method

Abstract

This invention discloses a weather-resistant, high-hardness composite anti-corrosion coating and its preparation method, belonging to the field of anti-corrosion coating technology. The preparation method includes: firstly, synthesizing an epoxy resin containing dynamic disulfide bonds by reacting dithiodibenzoic acid and epichlorohydrin in an alkaline aqueous phase; secondly, constructing a low surface energy siloxane network using hydroxyl-terminated polydimethylsiloxane and methyltriethoxysilane; subsequently, introducing chlorzoxazone and N-acetyl-p-aminophenol as composite organic corrosion inhibitors, blending them with the resin to obtain a composite base material; finally, adding graphene, carbon nanotubes, and inorganic anti-corrosion fillers, and cross-linking and curing to form a film using a polyamine curing agent. This invention suppresses microcracks through the dynamic stress relief of disulfide bonds, combined with the weather-resistant barrier of the siloxane network, the active interface passivation of the heteroatom corrosion inhibitor, and the three-dimensional synergistic mechanical bonding of carbon-based nanomaterials, achieving a perfect unity of ultra-strong corrosion resistance, excellent weather resistance, and high mechanical hardness in the coating.

Description

Technical Field

[0001] This invention belongs to the field of anti-corrosion coating technology, specifically, it relates to a weather-resistant, high-hardness composite anti-corrosion coating and its preparation method. Background Technology

[0002] Anti-corrosion coatings are widely used for metal protection in fields such as steel metallurgy, marine engineering, and chemical infrastructure. Epoxy resin, due to its dense cross-linked network and good adhesion to the metal substrate, has become the mainstream matrix resin in heavy-duty anti-corrosion applications. However, with the increasing demands for long-term protection and structural integrity in complex service environments, existing conventional epoxy anti-corrosion coatings have gradually revealed the following systemic defects: First, the high rigidity of the cross-linked network and the problem of microcrack propagation. Conventional bisphenol A and other traditional epoxy resins, after curing, have high cohesive energy and poor chain segment flexibility in their three-dimensional cross-linked network. When subjected to external mechanical impact, alternating loads, or temperature stress, they are prone to localized stress concentration and the initiation of microcracks. These microscopic physical defects directly evolve into short-circuit channels for water molecules, oxygen, and corrosive ions to penetrate into the metal substrate, thus causing the coating system to fail covertly. Second, the inherent inadequacy of UV aging (weather resistance) performance. Conventional epoxy resin backbones contain a large number of aromatic ether bonds and polar groups. Under outdoor high-frequency ultraviolet radiation and oxygen, they are prone to photo-oxidative degradation and chain scission reactions, which macroscopically manifest as severe chalking, loss of gloss, and weight loss on the coating surface, thereby losing the physical coating and shielding function against the underlying anti-corrosion medium. Thirdly, the limitations of single anti-corrosion mechanisms and unstable interface passivation. Current heavy-duty anti-corrosion systems usually rely heavily on the "sacrificial anode" cathodic protection effect of zinc-rich primers. However, during long-term corrosion, the insulating zinc salts generated by zinc powder oxidation will block the conductive path, leading to a sharp decline in the effective utilization rate of zinc powder. At the same time, traditional single-component organic small molecule corrosion inhibitors have low binding energy to the metal surface in complex electrolyte solutions, are prone to desorption, and are difficult to maintain a long-term chemical adsorption passivation layer at the coating-metal interface. Fourthly, the aggregation and mechanical conduction faults of two-dimensional nanofillers. In recent years, two-dimensional carbon-based materials such as graphene have been introduced into coatings due to their extremely high aspect ratio in order to construct physical maze barriers. However, due to the extremely strong interlayer interactions, single graphene sheets are prone to self-aggregation and layering within the resin matrix. More critically, the two-dimensional filler lacks mechanical overlap (intercalation and anchoring) in the thickness direction within the matrix, resulting in significant interlayer slippage defects when subjected to normal stress. This severely restricts the overall hardness modulus and impact resistance of the coating. In summary, developing a composite anti-corrosion coating that combines dynamic stress relief, high weather resistance, strong interfacial passivation, and excellent mechanical properties through interventions from multiple dimensions, including resin molecular structure design, low surface energy interface modification, multi-dimensional nanofiller gradation, and synergistic electrochemical active and passive corrosion protection, is a key technical challenge urgently needing to be solved in this field. Summary of the Invention

[0003] To address the technical problems of traditional epoxy anticorrosion coatings, such as high rigidity of the crosslinked network leading to stress microcracks, susceptibility to photo-oxidative degradation under high-frequency ultraviolet irradiation (poor weather resistance), easy desorption of the interfacial chemical adsorption passivation layer, and easy agglomeration of single two-dimensional carbon-based fillers leading to mechanical conduction fracture, resulting in long-term protective failure and low mechanical modulus, the primary objective of this invention is to provide a weather-resistant, high-hardness composite anticorrosion coating and its preparation method. This invention is based on molecular-level network design and a multi-dimensional interfacial electrochemical anticorrosion synergistic mechanism. It aims to fundamentally reconstruct the stress dissipation capacity, thermodynamic stability, and long-term electrochemical barrier microenvironment of the composite coating by introducing dynamic covalent disulfide bonds, constructing a low-surface-energy siloxane isolation defense line, incorporating trace amounts of highly efficient heteroatom organic composite corrosion inhibitors, and graded to construct a one-dimensional / two-dimensional interpenetrating carbon-based heterostructure. This achieves a closed-loop technology for high cohesive hardness, resistance to impact microcracks, long-term weather resistance, and comprehensive active passivation of the anticorrosion coating.

[0004] The present invention adopts the following technical solution: a method for preparing a weather-resistant, high-hardness composite anti-corrosion coating, comprising the following steps: Step A: dithiobenzoic acid and epichlorohydrin undergo an epoxidation reaction under alkaline aqueous conditions to synthesize dithiobenzoic acid-based epoxy resin; Step B: in a mixed organic solvent, hydroxyl-terminated polydimethylsiloxane and methyltriethoxysilane are mixed to construct a low surface energy siloxane network; Step C: an organic corrosion inhibitor is added to the system of Step B, wherein the organic corrosion inhibitor is a mixture of chlorzoxazone and N-acetyl-p-aminophenol, and then blended with the dithiobenzoic acid-based epoxy resin prepared in Step A to obtain a composite resin base; Step D: carbon-based nanofillers and inorganic anti-corrosion fillers are added to the composite resin base, wherein the carbon-based nanofillers include graphene and carbon nanotubes; after uniform dispersion, a polyamine curing agent is added for cross-linking and curing.

[0005] Preferably, in step A, after dithiobenzoic acid and epichlorohydrin undergo a preliminary reaction at 60-70°C, sodium hydroxide is added and the reaction continues at 60-70°C for 9-10 hours. Subsequently, the dithiobenzoic acid-based epoxy resin is obtained by vacuum distillation.

[0006] Preferably, in step B, the mass ratio of terminal hydroxyl polydimethylsiloxane to methyltriethoxysilane is 10:(1~5); the mixed organic solvent is selected from one or more combinations of ethyl acetate, butanol and xylene.

[0007] Preferably, in step C, the sum of the mass percentages of chlorzoxazone and N-acetyl-p-aminophenol accounts for 0.005% to 0.04% of the total mass of the liquid system; and the mass ratio of chlorzoxazone to N-acetyl-p-aminophenol is 1:1.

[0008] Preferably, in step D, based on a total mass of 100 parts by mass of the composite resin base, the amount of graphene added is 0.5 to 2.0 parts by mass, and the amount of carbon nanotubes is 0.01 to 0.1 parts by mass; the lateral dimension of the graphene is 1 to 10 μm, and the diameter of the carbon nanotubes is 5 to 50 nm.

[0009] Preferably, in step D, the inorganic anti-corrosion filler includes titanium dioxide powder, zinc phosphate, talc powder, and calcium carbonate; the total amount of inorganic anti-corrosion filler added is 100-300 parts by weight, calculated based on 100 parts by weight of the total composite resin base material.

[0010] Preferably, the inorganic anti-corrosion filler also includes a zinc-rich primer component containing 40% to 42% zinc powder by mass.

[0011] Preferably, in step D, the polyamine curing agent is an aromatic polyamine adduct or polyamide 651; the mass ratio of the composite resin base to the polyamine curing agent is (3~5):1.

[0012] A weather-resistant, high-hardness composite anti-corrosion coating, wherein the weather-resistant, high-hardness composite anti-corrosion coating is obtained by the preparation method described above.

[0013] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Constructing a dynamic stress relief mechanism to inhibit the initiation of microcracks: The present invention utilizes dithiodibenzoic acid and epichlorohydrin to synthesize a special epoxy resin, introducing disulfide bonds (-SS-) into the polymer backbone system. When the coating is subjected to mechanical impact, thermal stress or alternating load, the dynamic covalent characteristics of disulfide bonds endow the crosslinking system with adaptive stress dissipation and topological reconstruction capabilities, fundamentally avoiding the physical defects of traditional high-rigidity epoxy resins that are prone to micro-brittle cracks, and blocking the short-circuit channels for the penetration of corrosive media (water, oxygen, chloride ions). (2) Constructing a low surface energy siloxane network to overcome the bottleneck of weather resistance: The present invention generates a Si-O-Si hybrid network in situ in the coating system through the co-crosslinking of hydroxyl-terminated polydimethylsiloxane and methyltriethoxysilane. Since the Si-O bond energy is much higher than that of conventional carbon-carbon bonds and surface ultraviolet photons, this network effectively resists polymer chain breakage caused by photo-oxidative degradation. At the same time, the low surface energy siloxane segments accumulate on the coating surface, forming a highly hydrophobic physical defense line, which greatly improves the coating's gloss retention rate and long-term outdoor service stability. (3) Inducing multi-point chemical adsorption to achieve active passivation closed loop at the interface: This invention uses a micro-graded chlorzoxazone and N-acetyl-p-aminophenol composite organic corrosion inhibitor, which utilizes the N, O heteroatoms and aromatic ring system in its structure to provide lone pair electrons and π electrons to the metal substrate (such as empty d orbitals), resulting in strong coordination chemical adsorption at the metal-coating micro-interface. The in-situ generated monomolecular passivation film complements the "sacrificial anode" effect of the inorganic zinc-rich primer, constructing a dual anti-corrosion closed loop of "active interface repair + passive electrochemical protection". (4) Constructing a cross-scale heterogeneous structure to synergistically enhance mechanical modulus and physical barrier: This invention overcomes the self-aggregation and interlayer slip defects that are prone to occur in single two-dimensional nanomaterials by using a specific ratio of graphene (2D) and carbon nanotubes (1D). The micro- and nano-scale carbon nanotubes are interspersed between the graphene sheets as interlayer "rivets" to construct a long-range ordered three-dimensional spatial mechanical conduction network. This not only geometrically amplifies the physical "maze effect" of the diffusion of corrosive media, but also significantly improves the cohesive hardness (pencil hardness) and mechanical puncture (impact) resistance of the coating from a macroscopic perspective. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments. However, these embodiments are only for illustrating the present invention and do not constitute any limitation on the scope of protection of the present invention. For those skilled in the art, simple deductions or substitutions made without departing from the concept of the present invention should be considered as falling within the scope of protection defined by the claims of the present invention. In the present invention, unless otherwise specified, intermediate values ​​are used for undefined parameter ranges by default.

[0015] Example 1

[0016] A method for preparing a weather-resistant, high-hardness composite anti-corrosion coating includes the following steps: Step A: Synthesis of dithiodibenzoic acid-based epoxy resin (resin A liquid). In a 500mL three-necked flask equipped with a mechanical stirrer, reflux condenser, and constant-temperature water bath, 30.0g of dithiodibenzoic acid (CAS: 119-80-2) and 150mL of deionized water are added, and stirring is started (300rpm). Then, 60.0g of epichlorohydrin (CAS: 106-89-8) is added, and the temperature is raised to 65℃ for initial isothermal reaction for 3 hours. After the reaction is complete, 40.0g of a 10% sodium hydroxide aqueous solution and 5g of tetrabutylammonium bromide (CAS: 1643-19-2) are slowly added dropwise through a constant-pressure dropping funnel, and the reaction is maintained at 65℃ for another 9.5 hours. After the reaction was completed, the system was transferred to a rotary evaporator and vacuum distilled at -0.09 MPa and 80 °C to remove unreacted epichlorohydrin and water. After extraction with dichloromethane and drying, dithiodibenzoic acid-based epoxy resin (referred to as resin A solution) was obtained.

[0017] Step B: Construction of a low surface energy siloxane network (siloxane B solution). In 37.0 g of a mixed organic solvent (ethyl acetate:butanol:xylene = 1:1:1, mass ratio), 10.0 g of hydroxyl-terminated polydimethylsiloxane (CAS: 70131-67-8) and 3.0 g of methyltriethoxysilane (CAS: 2031-67-6) were added. After stirring until homogeneous, 2.0 g of deionized water and 0.1 g of dibutyltin dilaurate (CAS: 77-58-7) catalyst were added. The mixture was heated to 60 °C and stirred for 4 hours to allow the alkoxysilanes to fully hydrolyze and condense to form a Si-O-Si hybrid network, thus obtaining siloxane B solution.

[0018] Step C: Preparation of composite resin base material. Add 0.010g of chlorzoxazone (CAS: 95-25-0) and 0.010g of N-acetyl-p-aminophenol (CAS: 103-90-2) (mass ratio of the two is 1:1) to 50.0g of the above siloxane B solution, stir until completely dissolved, and then mix with 50.0g of resin A solution prepared in step A, disperse at high speed for 30 minutes to obtain composite resin base material (total mass adjusted to 100.0g).

[0019] Step D: Formulation and curing of the composite anti-corrosion coating. Based on 100.0g of the above composite resin base, add 1.0g of graphene (CAS: 1034343-98-0, thickness 0.55~3.74nm, lateral dimension 0.5~3μm, number of layers less than 10), 0.05g of single-walled carbon nanotubes (CAS: 308068-56-6, purity ≥99.7%, diameter 0.75~3nm, length 1~50μm), 110.0g of inorganic anti-corrosion filler (titanium dioxide powder, zinc phosphate, talc powder (CAS: 14807-96-6), and calcium carbonate mixed in equal mass ratio), and 50.0g of zinc-rich primer component (Jotun's Barrier 77 CN) containing 40%~42% zinc powder by mass. Disperse in a high-speed disperser for 2 hours to ensure uniform distribution of the filler. Then add 25.0g of polyamide 651 curing agent (CAS: 63428-84-2, composite resin base to curing agent mass ratio 4:1), and continue stirring for 15 minutes to obtain a weather-resistant, high-hardness composite anti-corrosion coating.

[0020] The obtained coating was sprayed onto a 304 stainless steel test plate that had been sanded and degreased with acetone. The dry film thickness was controlled to be about 80 μm. After curing at room temperature for 24 hours, the performance was tested.

[0021] This invention comprises three exemplary embodiments and four comparative embodiments. The detailed formulations of each component are shown in Tables 1 to 3 below. Process parameters not listed are consistent with those in Example 1.

[0022] Table 1: Core Raw Material Formulas for Steps A and B (mass / g)

[0023] Group Dithiodibenzoic acid epichlorohydrin Hydroxyl-terminated polydimethylsiloxane Methyltriethoxysilane Mixed solvent (ethyl acetate:butanol:xylene = 1:1:1) Example 1 30.0 60.0 10.0 3.0 37.0 Example 2 30.0 60.0 10.0 5.0 37.0 Example 3 30.0 60.0 10.0 1.0 37.0 Comparative Example 1 0.0 (equivalent E-44 replacement) 0.0 10.0 3.0 37.0 Comparative Example 2 30.0 60.0 0.0 0.0 37.0 Comparative Example 3 30.0 60.0 10.0 3.0 37.0 Comparative Example 4 30.0 60.0 10.0 3.0 37.0

[0024] Table 2: Raw material formulation for liquid phase mixing in step C (mass / g)

[0025] Group Amount of resin A solution Siloxane B solution (product of step B) Chlorzoxazone N-acetyl-p-aminophenol Example 1 50.0 50.0 0.010 0.010 Example 2 50.0 50.0 0.020 0.020 Example 3 50.0 50.0 0.0025 0.0025 Comparative Example 1 0 50.0 0.010 0.010 Comparative Example 2 50.0 37.0 (pure solvent) 0.010 0.010 Comparative Example 3 50.0 50.0 0.0 0.0 Comparative Example 4 50.0 50.0 0.010 0.010

[0026] Table 3: Formulation of solid-phase nanomaterials and core inorganic fillers in step D (mass / g)

[0027] Group Composite base material graphene carbon nanotubes <![CDATA[Total inorganic fillers (TiO2 / zinc phosphate / talc / CaCO3)]]> Zinc-rich primer curing agent Example 1 100.0 1.0 0.05 110.0 50.0 25.0 Example 2 100.0 2.0 0.10 150.0 60.0 33.3 Example 3 100.0 0.5 0.01 80.0 40.0 20.0 Comparative Example 1 100.0 1.0 0.05 110.0 50.0 25.0 Comparative Example 2 100.0 1.0 0.05 110.0 50.0 25.0 Comparative Example 3 100.0 1.0 0.05 110.0 50.0 25.0 Comparative Example 4 100.0 1.0 0.0 110.0 50.0 25.0

[0028] The test results are shown in Table 4.

[0029] Table 4: Test Results of Comprehensive Performance of Samples | Group | Low-Frequency Impedance Modulus

[0030] Group Low-frequency impedance modulus | Gloss retention rate (%) Adhesion (Grade) Pencil hardness Impact strength (kg⋅cm) Example 1 <![CDATA[5.6×10 8 ]]> 86.4 0 4H 50 Example 2 <![CDATA[6.2×10 8 ]]> 89.2 0 5H 48.5 Example 3 <![CDATA[3.5×10 8 ]]> 81.5 0 3H 50 Comparative Example 1 <![CDATA[8.2×10 6 ]]> 85 1 4H 30.5 Comparative Example 2 <![CDATA[2.1×10 7 ]]> 45.2 0 3H 49 Comparative Example 3 <![CDATA[4.5×10 6 ]]> 86 0 4H 50 Comparative Example 4 <![CDATA[1.8×10 8 ]]> 85.8 0 2H 35

[0031] Test Results and Mechanism Analysis: Dynamic Stress Relief Mechanism of Disulfide Bonds (Comparative Example 1 vs. Comparative Example 1): Comparative Example 1 uses conventional bisphenol A epoxy resin, which lacks the dynamic covalent properties of disulfide bonds, resulting in an impact strength of only 30.5 kg·cm. The -SS- bonds introduced in this invention effectively alleviate stress concentration within the coating through dynamic reconstruction under impact stress, maintaining the coating's density and corrosion barrier properties. Weather Barrier Effect of Siloxane Network (Comparative Example 1 vs. Comparative Example 2): Comparative Example 2, without the addition of terminal hydroxyl polydimethylsiloxane and methyltriethoxysilane, has a gloss retention rate of only 45.2%. The Si-O-Si low surface energy network constructed in this invention effectively prevents UV degradation of the base material, significantly improving the coating's outdoor weather resistance. Active Protection of Heteroatom Corrosion Inhibitors (Comparative Example 1 vs. Comparative Example 3): The lack of synergistic interaction between chlorzoxazone and N-acetyl-p-aminophenol leads to a significant decrease in corrosion resistance (impedance modulus drops to 10). 6 (Orders in magnitude). This hybrid corrosion inhibitor utilizes the lone pair electrons in its molecules to undergo chemical adsorption on the metal substrate, forming a synergistic anti-corrosion mechanism with the physical shielding layer. The synergistic bonding mechanism of carbon-based materials (Comparative Example 1 and Comparative Example 4): Carbon nanotubes act as "bridging rivets" connecting two-dimensional graphene, significantly enhancing the matrix strength. Comparative Example 4 lacks carbon nanotubes, resulting in a missing internal mechanical conduction network in the coating, and a significant degradation in pencil hardness and impact resistance, confirming the crucial role of the synergistic effect of 1D and 2D carbon materials in improving the high hardness and high impact resistance of the composite coating.

Claims

1. A method for preparing a weather-resistant, high-hardness composite anti-corrosion coating, characterized in that: The process includes the following steps: Step A: Dithiobenzoic acid and epichlorohydrin undergo an epoxidation reaction under alkaline aqueous conditions to synthesize dithiobenzoic acid-based epoxy resin; Step B: Hydroxyl-terminated polydimethylsiloxane and methyltriethoxysilane are mixed in a mixed organic solvent to construct a low surface energy siloxane network; Step C: An organic corrosion inhibitor, a mixture of chlorzoxazone and N-acetyl-p-aminophenol, is added to the system of Step B, and then blended with the dithiobenzoic acid-based epoxy resin prepared in Step A to obtain a composite resin base; Step D: Carbon-based nanofillers and inorganic anti-corrosion fillers are added to the composite resin base, the carbon-based nanofillers including graphene and carbon nanotubes; after uniform dispersion, a polyamine curing agent is added for cross-linking and curing.

2. The preparation method of the weather-resistant high-hardness composite anti-corrosion coating according to claim 1, characterized in that: In step A, after dithiobenzoic acid and epichlorohydrin undergo a preliminary reaction at 60-70°C, sodium hydroxide is added and the reaction continues at 60-70°C for 9-10 hours. Subsequently, the dithiobenzoic acid-based epoxy resin is obtained by vacuum distillation.

3. The preparation method of the weather-resistant high-hardness composite anti-corrosion coating according to claim 1, characterized in that: In step B, the mass ratio of hydroxyl-terminated polydimethylsiloxane to methyltriethoxysilane is 10:(1~5); the mixed organic solvent is selected from one or more combinations of ethyl acetate, butanol and xylene.

4. The preparation method of the weather-resistant high-hardness composite anti-corrosion coating according to claim 1, characterized in that: In step C, the sum of the mass percentages of chlorzoxazone and N-acetyl-p-aminophenol accounts for 0.005% to 0.04% of the total mass of the liquid phase system; and the mass ratio of chlorzoxazone to N-acetyl-p-aminophenol is 1:

1.

5. The preparation method of the weather-resistant high-hardness composite anti-corrosion coating according to claim 1, characterized in that: In step D, based on a total mass of 100 parts by mass of the composite resin base, the amount of graphene added is 0.5 to 2.0 parts by mass, and the amount of carbon nanotubes is 0.01 to 0.1 parts by mass; the lateral dimension of the graphene is 1 to 10 μm, and the diameter of the carbon nanotubes is 5 to 50 nm.

6. The preparation method of the weather-resistant high-hardness composite anti-corrosion coating according to claim 1, characterized in that: In step D, the inorganic anti-corrosion filler includes titanium dioxide powder, zinc phosphate, talc powder, and calcium carbonate; the total amount of inorganic anti-corrosion filler added is 100-300 parts by mass, calculated based on 100 parts by mass of the total composite resin base.

7. The preparation method of the weather-resistant high-hardness composite anti-corrosion coating according to claim 1, characterized in that: The inorganic anti-corrosion filler also includes a zinc-rich primer component containing 40% to 42% zinc powder by mass.

8. The preparation method of the weather-resistant high-hardness composite anti-corrosion coating according to claim 1, characterized in that: In step D, the polyamine curing agent is an aromatic polyamine adduct or polyamide 651; the mass ratio of the composite resin base to the polyamine curing agent is (3~5):

1.

9. A weather-resistant, high-hardness composite anti-corrosion coating, characterized in that, The weather-resistant, high-hardness composite anti-corrosion coating is obtained by the preparation method according to any one of claims 1-8.