Protective coating for zinc-plated cathode protection iron material

Abstract

The invention discloses a protective coating for galvanization cathode protection iron materials. The protective coating comprises (45-65)% of polyfunctional group acrylic resin, (0.8-1.6)% of strontium chrome yellow nano mixed liquid, (0.02-0.05)% of graphene nano mixed liquid and (5-8.4)% of isocyanate curing agent, 7%-12% of cellulose resin, 6%-12% of silver powder, 5%-8% of solvent, 1%-3% of auxiliaries and the balance of diluent, wherein the content ratio of the polyfunctional group acrylic resin to the strontium chrome yellow nano mixed liquid to the graphene nano mixed liquid to the isocyanate curing agent is (45-65)%: (0.8-1.6)%: (0.02-0.05)%: (5-8.4)%. Strontium chrome yellow nanoparticles form anchoring points on the surface of an iron material, and meanwhile, the strontium chrome yellow nanoparticles are complexed with the polyfunctional group acrylic resin and the cellulose resin, so that the adhesive force of the coating to a zinc coating is enhanced to 10-12N / mm. The graphene nanosheets form a barrier for corrosive substances between the polyfunctional group acrylic resin and the cellulose resin, so that the corrosion resistance of the coating is enhanced. The protective coating disclosed by the invention is simple and convenient to construct, and provides excellent anti-corrosion and anti-aging capabilities for galvanized cathode protection iron materials.

Description

Technical Field

[0001] This invention relates to the field of paints, and more specifically to a protective coating for galvanized cathodic protection of iron materials. Background Technology

[0002] Concrete guardrails are a crucial component of highway guardrails and an essential part of highway bridge and tunnel sections. Due to the natural characteristics and porous surface of concrete, it is prone to pollution and weathering in long-term exposed environments. Water molecules penetrate and combine with chloride ions within the concrete to produce sodium chloride (a soluble salt), further causing internal expansion and accelerating damage to the concrete's strength and lifespan. Currently, most highway guardrails are galvanized. While galvanizing offers good corrosion resistance, zinc oxidizes in the air, causing the guardrails to lose color and luster after a period of time. Subsequently, under the influence of pollution and exhaust fumes, they gradually darken, affecting their visual appearance. Currently, a nationwide program is underway to replace two-wave guardrails with three-wave guardrails, resulting in a large number of two-wave guardrails being left idle. The issue of reusing these remaining two-wave guardrails is becoming increasingly prominent. Due to the actual working conditions on site, concrete guardrails are usually poured directly on site without additional anti-corrosion and waterproof layers for further protection. Ordinary paint often fades, loses its gloss, and peels after a few months. Since highways are frequently maintained, there are significant safety hazards and costs involved. Therefore, high-quality coatings and construction plans are particularly important for surface protection.

[0003] Currently, there are generally two types of paint commonly used on concrete surfaces: one is conventional acrylic and alkyd paints, which come in many varieties, but the quality of most of them does not meet the requirements. In the environment of highway traffic, they generally lose color and gloss after 6 months, and peel off in some areas after 1 year. The surface is also corroded by moisture and pollutants, gradually becoming ineffective. The second type is higher-end fluorocarbon paint, which performs well in terms of aging resistance and gloss, but it is expensive. Fluorocarbon paint has high requirements, is difficult to apply, and is not easy to recoat. That is, it is very difficult to apply new paint later, the adhesion is very poor, and the old coating is difficult to be compatible with the new coating. In the existing technology, solvent-based coatings and water-based coatings have poor adhesion to galvanized highway guardrails, are prone to cracking and peeling due to large temperature differences between the north and south, have poor stain resistance and corrosion resistance, and have a short service life. Powder coatings have poor stain resistance, cannot be applied and maintained on-site, have high energy consumption, and have high maintenance costs. Hot-melt coating has poor corrosion resistance and fails to meet requirements for artificial aging. It is prone to powdering and discoloration within two years, making on-site painting and maintenance impossible. It also has high energy consumption and high maintenance costs. Currently available renovation paints do not meet technical requirements for surface adhesion, have poor corrosion resistance, are prone to peeling, have poor stain resistance, and do not have on-site renovation and maintenance functions, thus lacking the value for large-scale promotion. Summary of the Invention

[0004] The technical concept of this invention is divided into two aspects: first, by designing anchoring points that connect the macromolecules in the galvanized layer and the coating, the adhesion between the protective coating and the galvanized iron is enhanced; second, by increasing the corrosion path for corrosive substances to enter the galvanized iron and shielding corrosive substances as much as possible, the corrosion barrier and anti-corrosion capabilities of the protective coating are enhanced.

[0005] Adhesion occurs when two objects are placed together, achieving close molecular contact at the interface, thus forming a new interfacial layer. Adhesion involves the physical effects and chemical reactions of the "interface." Adhesion is generated when a coating is applied to a substrate and during the drying and curing process. The magnitude of these forces depends on the properties of the surface and the binder (resin, polymer, binder), and can be divided into primary and secondary valence forces. Chemical bonds are the primary valence forces, possessing much higher adhesion than secondary valence forces, which are based on much weaker physical forces, such as hydrogen bonds. The types of bonds and bond energies / strengths / types / energy (kcal / mol) are shown in the table below:

[0006]

[0007] The inventors used a mechanical connection theory to study the adhesion of coatings. This coating mechanism applies when the coating is applied to a substrate containing holes, cavities, fissures, or voids, allowing the coating to penetrate. In this case, the coating acts like a nail in a wooden frame, providing mechanical anchoring. When the substrate has grooves filled with cured coating, removing the coating becomes more difficult due to mechanical action, similar to joining two mortise-and-tenon pieces of wood. Instrumental analysis and mapping of various surfaces show that the coating can indeed penetrate complex "tunnel"-shaped grooves or cracks, providing mechanical adhesion during curing. Galvanized cathodic protection iron has a large contact area with the coating, thus improving adhesion and corrosion resistance. Increasing surface roughness is only beneficial when the coating completely penetrates irregular surfaces; if it cannot penetrate completely, the contact area between the coating and the surface will be smaller than the corresponding geometric area, leaving gaps between the coating and the substrate. Air bubbles trapped in these gaps can lead to moisture accumulation, ultimately resulting in a loss of adhesion.

[0008] As long as the coating has some fluidity, shrinkage, uneven thickness, and changes in three-dimensional dimensions will rarely generate unreleased stress. However, as viscosity and coating rigidity increase, and adhesion to the substrate gradually forms, a significant amount of stress will be generated and remain in the dried paint film. Clearly, with fixed application parameters (wet and dry film thicknesses), the coating thickness in raised areas is smaller than in recessed areas, resulting in different physical properties. This uneven coating has high internal stress, and when applied, it will be further affected by the erosion or aging of the repair paint solvent. Occasionally, this stress may exceed the coating's stress-bearing capacity, leading to cracks, peeling, or other reductions in coating integrity.

[0009] Zinc ions in galvanized materials are relatively small ions, while resin macromolecules in coatings are relatively large molecules. Due to this significant size difference, they cannot be chemically bonded together at the microscopic level. Therefore, the inventors chose to add an intermediary substance that can connect the resin macromolecules and zinc ions. From a microscopic volume perspective, this intermediary substance needs to be between the volume range of zinc ions and resin macromolecules. From a microscopic chemical force perspective, this intermediary substance can form metallic bonds with zinc ions, thus binding them, and simultaneously form ionic bonds with inorganic resin molecules, thus connecting the resin macromolecules. Furthermore, to achieve the optimal binding state of resin molecules, the intermediary substance, and zinc ions at the microscopic level, their mass percentage can be adjusted to the optimal value, thereby obtaining excellent adhesion between the protective coating and the galvanized iron. The inventors chose strontium chrome yellow as the intermediary substance, and multifunctional acrylic resin and cellulose resin as the resin macromolecules. The small size of the chromate ions in strontium chromium yellow and the spatial structure formed by its four chromium-oxygen double bonds provide stable support for anchoring. Meanwhile, multifunctional acrylic and cellulose resins possess numerous protective oxygen atoms that can form a network of complexes with zinc atoms. See also... Figure 8 After forming a complex, chromium ions enter the lattice of zinc atoms (the volume of chromium ions is smaller than that of zinc atoms), forming a homogeneous, single-phase solid solution. Subsequently, as the coating dries, stable co-crystallization occurs (see "Study on the Presence and Stability of Trace Hexagonal Lattice Nickel in Nickel Plating," Ge Fuyun, Yao Shibing, Xu Shukai, Zhou Shaomin, et al., *Journal of Chemical Research in Chinese Universities*, 1994-11-15; and "Ordered Structure of Hexagonal Close-Packed Binary Alloys," Song Qinggong, Dai Zhanhai, Cong Xuanzhong, Wei Huan, Zhang Qingjun, et al., *Acta Physica Sinica*, 2000-11-12). Therefore, compared to traditional resin-based coatings that anchor the coating to iron through a curing agent to provide adhesion, the coating of this invention, by using strontium chromium yellow as an intermediate medium to tightly connect the multifunctional acrylic resin, cellulose resin, and zinc plating layer, can additionally form stronger adhesion.

[0010] In protective coatings, resin molecules cross-link with a curing agent to form a network structure. Because resin molecules are relatively large, there are significant gaps between them. Small molecules, such as corrosive substances, can penetrate these gaps layer by layer and eventually reach the galvanized layer, causing corrosion. (See also...) Figure 6The inventors designed a barrier material to extend the corrosion path, slow down the corrosion rate, and increase the corrosion resistance of the galvanized layer. This barrier material can insert between resin macromolecules and be densely and parallelly arranged without disrupting the cross-linking between resin molecules or affecting the chemical forces between other molecules. Furthermore, the mass percentage of the barrier material to the resin molecules can be optimally adjusted to increase the flexural strength and color retention of the protective coating. The barrier material chosen in this invention is a graphene nanosolution. The graphene nanosheets are arranged parallel to each other in the gaps between the cross-linked resin molecules, increasing the path length for corrosive substances to penetrate into the galvanized iron material through the protective coating, thereby enhancing the barrier and shielding function and corrosion resistance of the protective coating. The above explains the principle behind the excellent adhesion and corrosion resistance of the protective coating for galvanized cathodic protection iron materials of this invention. Next, to achieve the above effects, the inventors explored the optimal ratio range between the various components of the protective coating.

[0011] First, the proportions of the multifunctional acrylic resin, cellulose resin, strontium chrome yellow nano-mixture, graphene nano-mixture, and isocyanate curing agent need to be designed as a whole.

[0012] Multifunctional acrylic resin and cellulose resin serve as film-forming substances in the coatings of this invention. Their function is to bind pigments and fillers together and form a uniform and dense film on the substrate, which, after curing, forms a coating layer. Simultaneously, they determine the coating's toughness, adhesion to the substrate, and the physicochemical and mechanical properties of the coating. The isocyanate curing agent reacts with the active hydrogen (OH) in the multifunctional acrylic resin and cellulose resin to form urea bonds and urea acid bonds, promoting cross-linking between resin molecules and forming a high-molecular polymer. This further provides the coating with high strength, high heat resistance, and chemical corrosion resistance. Therefore, the ratio of multifunctional acrylic resin, cellulose resin, and isocyanate curing agent needs to be designed based on the degree of cross-linking reaction between them.

[0013] See Figure 1 The carboxylic acid hydroxyl group in the multifunctional acrylic resin molecule a can form a complex c with the chromium (IV) group of the chromate anion b in the strontium chromate molecule. Due to the weak coordination ability of chromium (VI), it will slowly reduce and eventually form a chromium (III) complex. See also Figure 2 and Figure 3 Subsequently, the complexation form of complex c will be divided into two types. Figure 2 In the process, complex d is a chromium (V) complex formed by the spontaneous reduction of chromium (IV) in complex c to adjacent carboxylic acid hydroxyl groups in a polyfunctional acrylic resin. Subsequently, chromium (V) complex d is further reduced to chromium (IV) complex e, and then chromium (IV) complex e is further reduced to chromium (III) complex f. Figure 3In this context, complex g is a chromium (VI) complex formed by the chromium (IV) in complex c bonded to a carboxylic acid hydroxyl group in another acrylic acid molecule. Subsequently, chromium (VI) complex g is further reduced to chromium (V) complex h, which in turn is further reduced to chromium (III) complex i. See also... Figure 4 Chromium(III) complex f and chromium(III) complex i further complex to obtain stable chromium(III) complex j. Therefore, one strontium chromium yellow molecule can stably complex three multifunctional acrylic resin molecules (refer to "Mechanism Study on the Enhanced Visible Light Reduction of Hexavalent Chromium by the Formation of Coordination Complexes between Oxalic Acid and Chromate", Energy and Environmental Protection, Vol. 38, No. 1, February 2024).

[0014] See below. Figure 5 In the chromium(III) complex j, the chromium is in a fully electron-rich state, which can form a stable metallic bond with the zinc atoms in the zinc plating layer. Thus, strontium chromium yellow can be anchored to the zinc plating layer through the metallic bond with the zinc atoms.

[0015] In summary, each strontium chromium yellow molecule acts as an anchor point, anchoring 3 to 7 acrylic acid molecules onto the zinc plating layer. This indicates that the complexation between strontium chromium yellow and acrylic acid preliminarily provides a range for the ratio of strontium chromium yellow to acrylic acid, i.e., the molar ratio of multifunctional acrylic resin to strontium chromium yellow is approximately between 7:1 and 3:1. Converted to mass fraction, the mass ratio of multifunctional acrylic resin to strontium chromium yellow is approximately (7×72):(1×203)~(3×72):(1×203)=2.5:1~1:1=(2.5~1):1 (ratio 1).

[0016] It should be noted that the above description refers to the formation of stable chromium complexes by Cr(III) and Cr(VI) with multifunctional acrylic resins and cellulose resins. When corrosion is expected in the iron, Fe(III) and Fe(II) can also form more stable iron complexes with multifunctional acrylic resins and cellulose resins. Because a greater amount of chromium complexes are formed than iron complexes, they provide stronger anchoring force to the protective coating for galvanized cathodic protection of iron in this invention. Therefore, whether before or after corrosion, the protective coating can form stable anchoring points on the galvanized iron, thereby improving the adhesion of the protective coating to the iron.

[0017] Graphene nanosheets are used to form sheet-like barriers between resin molecular layers, so it is necessary to calculate the specific surface area of ​​graphene. The specific steps are as follows.

[0018] (1) See Figure 7 The inventors calculated the area based on a single-layer regular polygon of graphene. The formula for the area of ​​a regular polygon is as follows: Referring to the figure, the number of sides of the regular hexagon is n=6, α=360 / 6=60 (degrees); in the regular polygon, |OA|=|OC|=r, ∠AOC=α=60º, therefore ΔAOC is an equilateral triangle. From this, we can calculate the radius of the regular hexagon r=|AC|=the length of the carbon-carbon bond in graphene=0.142nm. Substituting this into formula (1), we can calculate the area of ​​a single regular hexagon in graphene as 5.24×10-20 (m²). 2 ).

[0019] (2) Each regular hexagon receives only 1 / 3 of a carbon atom (similar to the conclusion that "each corner of a cubic crystal contributes 1 / 8 of a particle to the entire unit cell"). Therefore, each regular hexagon actually contains 6 × 1 / 3 = 2 carbon atoms. Thus, the mass (m) of each regular hexagon is equal to the mass of two carbon atoms. Where mc represents the mass of a single carbon atom, and M represents the molar mass of carbon. Let m be Avogadro's constant, from which the mass of each regular hexagon is calculated to be m = 3.99 × 10⁻⁶. -23 (g)

[0020] (3) According to the specific surface area formula Based on the calculated S and m above, calculate =1314.(m 2 / g). For monolayer graphene, both the upper and lower surfaces of the regular hexagons are exposed, therefore the actual theoretical specific surface area of ​​each regular hexagon should be . Twice that, that is, 2628.8m 2 / g, approximately equal to 2630m 2 / g.

[0021] The graphene nanosheets used in this invention contain 5-10 layers of monolayer graphene. The graphene nanosheet coverage in the coating is 40-50%. Based on the specific surface area calculated from the monolayer graphene nanosheets, the estimated mass of simulated nanosheets per square meter is (1÷2630)×(5-10)×(40%~50%)=0.0008~0.0019. 1kg of dry coating film can cover 6-9 square meters. Based on the average mass of 10%~30% of multifunctional acrylic resin per kilogram of coating, the mass ratio of multifunctional acrylic resin to graphene nanosheets is 1000×(10%~30%)÷(6-9):(0.08~0.19)%=(33~50):(0.08~0.19)% (ratio 2).

[0022] The inventors designed the composition ratio of the coating by using a mass ratio of approximately 4:1 (ratio 3) of multifunctional acrylic resin and isocyanate curing agent, which is commonly used in the art.

[0023] Therefore, based on the mass of polyfunctional acrylic resin, which accounts for approximately 40% of the coating per kilogram, and according to proportions 1, 2, and 3, the inventors calculated the theoretical mass ratio of polyfunctional acrylic resin, strontium chromium yellow nano-mixture, graphene nanosheets, and isocyanate curing agent to be (99–150)%:(13.2–50)%::(0.08–0.19)%:(8.25–12.25)% (proportion 4).

[0024]

[0025] It should be noted that the theoretical quality above does not take into account the mixing of other coating components. Therefore, based on the above theoretical proportions, the inventors added other components such as cellulose resin (which dries too quickly and is not suitable for anchoring and complexing), silver powder, etc., and appropriately adjusted the overall component proportions of the protective coating based on proportion 4 to obtain the coating formulation and proportion with the highest adhesion and strongest corrosion resistance. These component proportion adjustments may include adding an appropriate amount of cellulose resin to reduce the amount of multifunctional acrylic resin; adding solvents and additives to increase the flatness probability of graphene nanosheets to 70%-80%, thereby reducing the amount of graphene nanosheets; and reducing the amount of multifunctional acrylic resin to increase the content of chromium(III) complex j, resulting in a significant reduction in the amount of strontium chrome yellow, etc.

[0026] Based on the above technical concept, the present invention provides the following technical solution.

[0027] A protective coating for galvanized cathodic protection of iron materials, comprising, by weight percentage:

[0028] The content ratio of multifunctional acrylic resin, strontium chrome yellow nano-mixture, graphene nano-mixture, and isocyanate curing agent is (45-65)%:(0.8-1.6)%:(0.02-0.05)%:(5-8.4)%, cellulose resin: 7%-12%, silver powder: 6%-12%, solvent: 5%-8%, additives: 1%-3%, and the remainder is diluent.

[0029] Strontium chromium yellow nanoparticles form anchoring points on the iron surface and simultaneously complex with multifunctional acrylic and cellulose resins, thereby enhancing the adhesion of the coating to the iron to 10-12 N / mm.

[0030] Graphene nanosheets form a barrier against corrosive substances between multifunctional acrylic resins and cellulose resins, thereby enhancing the corrosion resistance of the coating.

[0031] According to embodiments of the present invention, the additives include at least one of thickeners, toughening agents, alignment agents, leveling agents, and wetting and dispersing agents.

[0032] According to embodiments of the present invention, the graphene nanosheets are at least one of reduced graphene, graphene oxide, and physically exfoliated graphene.

[0033] According to embodiments of the present invention, the solvent is selected from butyl acetate or xylene.

[0034] Compared with existing guardrail paints, the protective coating of this invention for galvanized cathodic protection iron has the following advantages:

[0035] First, it has excellent adhesion to the galvanized layer (10-12 MPa), which solves the industry problem of poor adhesion between conventional coatings and galvanized layers, and will not be troubled by coating peeling in the future.

[0036] Second, it has excellent weather resistance and will not fade or lose its luster within 5-8 years. The surface of the guardrail will basically maintain its appearance when it was first installed.

[0037] Third, easy to clean. Due to the nano-tension of the coating surface, the adhesion between contaminants and the coating surface is poor, so it is easy to clean and can reduce the cleaning frequency of the original high-speed maintenance.

[0038] Fourth, it greatly enhances the corrosion resistance of the original galvanized layer, perfectly integrates with the galvanized layer, and more than doubles the salt spray resistance of the conventional galvanized layer (from the original 1,000 hours of neutral salt spray resistance to more than 2,000 hours). Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the complex c formed by the carboxylic acid hydroxyl group in polyfunctional acrylic resin molecule a and the chromium(IV) in chromate ion b of strontium chromate molecule.

[0040] Figure 2 This is a schematic diagram of chromium (V) complex d, which is formed by the automatic reduction of chromium (IV) in complex c to adjacent carboxylic acid hydroxyl groups in a polyfunctional acrylic resin.

[0041] Figure 3 This is a schematic diagram of a chromium (VI) complex g, in which chromium (IV) in complex c is bonded to a carboxylic acid hydroxyl group in another acrylic acid molecule.

[0042] Figure 4 This is a schematic diagram showing the further complexation of chromium(III) complex f and chromium(III) complex i to obtain stable chromium(III) complex j.

[0043] Figure 5 This is a schematic diagram showing the formation of stable metallic bonds between chromium(III) complex j and zinc atoms in the zinc plating layer.

[0044] Figure 6 This is a schematic diagram illustrating the principle of the barrier and shielding function and anti-corrosion effect of the coating-enhanced protective coating of the present invention.

[0045] Figure 7 This is a schematic diagram illustrating the principle of calculating the area of ​​a single-layer regular polygon in graphene.

[0046] Figure 8 This is a schematic diagram showing chromium ions entering the hexagonal unit cell of zinc atoms to form a common crystal. Detailed Implementation

[0047] 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 and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0048] The inventors prepared 10 coating samples based on the formulation ratio of the coating components, and the components and ratios are shown in the table below:

[0049]

[0050] Then, the protective coating of this invention used for galvanized cathodic protection of iron was subjected to various performance tests by the National Railway Product Quality Supervision and Inspection Center:

[0051] I. Artificial Climate Aging Test - Based on GB / T865-2009 Artificial Climate Aging and Artificial Radiation Exposure of Paints and Varnishes (Filtered Xenon Radiation)

[0052] The thermal stress failure mechanism involves internal stress cracking caused by differences in thermal expansion coefficients, resulting in damage. The seven-temperature cycle ranges from 40 to 120°C. The aging test chamber must achieve spectral matching (e.g., the spectrum after xenon lamp filtration must match the ultraviolet region of sunlight by >85%). It adopts the ASTM standard system, and the light source type is a fluorescent ultraviolet lamp (UVA-340, 295-365nm, matching the ultraviolet cutoff point of sunlight) / xenon lamp (power: 6.5kW; Daylight Filter: simulating surface sunlight, such as borosilicate glass + soda-lime glass). Environmental control is: irradiance 0.3-1.5W / m². 2 @340nm, blackboard temperature 40-120℃, chamber humidity 10%-98%RH, spray water volume 0.1-1.5L / min•m 2 The formula for calculating the acceleration factor is: Where AF: acceleration factor; Q: total ultraviolet radiation (kJ / m³) 2 ); E aActivation energy (e.g., 80 kJ / mol for PP plastic); T: Absolute temperature (K). The results of the aging test are determined by color difference. The color data of the sample after the accelerated aging test under artificial climate is measured according to GB / T11942, and the color difference before and after aging is calculated based on the color data measured before aging. The average color difference of two samples with similar aging degrees is taken as the color difference before and after aging of the sample.

[0053] II. Non-volatile content - According to GB / T1725-2007 Determination of non-volatile content in paints, varnishes and plastics.

[0054] According to GB / T1725-2007, the mass of galvanized cathodic protection iron is tested in air and water (or other suitable liquids of known density). (g) and (g) Coating the paint receiver with the test paint product and testing the quality of the wet-coated paint receiver in air. (g); After the coating product has dried, test the quality of the protective coating on the iron material in air and in the same liquid. (g) and (g); using these measurements and the density of the impregnating liquid and liquid coating at the test temperature (g / ml) and (g / ml), the dry coating density can be obtained using formulas (1), (2), and (3) respectively. (g / ml), percentage of nonvolatile matter (%) and volume percentage of nonvolatile matter %)

[0055]

[0056] III. Impact Resistance - According to GB / T1732-2020 Test Method for Impact Resistance of Coating Films

[0057] Under the environmental conditions specified in GB / T9278, place the impact tester (4.1) on a stable platform, with the guide tube perpendicular to the horizontal plane. Adjust the weight of the impact tester to a certain height using the weight controller. Place the test panel with the paint film facing upwards (forward impact) or downwards (backward impact) on the base. The distance between the impacted edge and the edge of the test panel should not be less than 10 mm, and the distance between adjacent impact points should not be less than 10 mm. Press the control button on the weight controller, and the weight will fall freely onto the punch. Remove the test panel and observe the paint film for cracks, wrinkles, and pineapple-like phenomena under natural or artificial sunlight as specified in GB / T37356. If necessary, a 4x magnifying glass (4.2) can be used for observation. If no cracks, wrinkles, or peeling are observed, repeat the test at higher positions until cracks, wrinkles, and peeling are observed, with each increase in height being 10 cm. If cracks, wrinkles, and peeling are observed, repeat the experiment at the same location on the cultivated land until no cracks, wrinkles, or peeling are observed. Each drop should be 5 cm. Perform the experiment three times at the same height. The result is expressed as the maximum height (in cm) at which no cracks, wrinkles, or peeling are observed in all three experiments.

[0058] IV. Bending Test - According to GB / T6742-2007 Bending Test of Paints and Varnishes

[0059] One end of the specimen is fixed, and it is bent around a bending indenter, bypassing the indenter, until a specified bending angle is reached. The displacement rate of the bending indenter is (1.0±0.2) mm / s. For the test where the specimen is bent until both arms are parallel, the specimen is first bent, then placed between two parallel pressure plates, and continuous pressure is applied to both ends to further bend it until the arms are parallel. A shim is added during the test. The shim thickness is 3 cm. For the test where the specimen is bent until the arms are in direct contact, the specimen is first pre-bent, then placed between two parallel pressure plates, and continuous pressure is applied to both ends to further bend it until the arms are in direct contact.

[0060] V. Cross-cut test - According to GB / T9286-1998 Cross-cut test for paint and varnish films

[0061] Hold the cutting tool with the blade perpendicular to the test panel surface. Using a suitable spacing guide, apply even pressure to the cutting tool and make six cuts on the coating at a uniform speed. The minimum cut length should be significantly longer than the width of the multi-blade tool. All cuts should leave marks or scratches on the substrate. Repeat the above operation, making six more parallel cuts, intersecting the original cuts at 90° angles to form a grid pattern. Remove any loose coating from the cut areas. Under good lighting conditions as specified in ISO 13076, and as agreed by both parties, carefully examine the cut areas of the test coating visually using a magnifying glass. During observation, rotate the test panel appropriately to ensure that the observation and lighting of the test area are not limited to one direction, and rate the test area. All showed a grade of 0, with completely smooth cut edges and no peeling within the grid. The results showed that all 10 coating samples were grade 0.

[0062] VI. Pull-off Adhesion Test - According to GB / T5210-2006=3204 Paint and Varnish Pull-off Adhesion Test

[0063] Test conditions: Tensile testing machine: stress 0.6 MPa / s, from application of force to failure should be completed in 90s; Test column: composed of steel or aluminized cylinders, each test column has a hard, flat surface for bonding adhesive / coating at one end and a device for connecting to the tensile testing machine at the other end, the standard diameter of each test column is 20 mm and the height is not less than half the diameter; Centering device: ensures that the test specimens are concentrically arranged; Adhesive: two-component fast-drying epoxy adhesive; Conditioning: after drying under specified conditions, the test plates are placed for a specified time. Unless otherwise agreed, before the test, the test plates are conditioned for 16 hours at a temperature of (23±2)℃ and a relative humidity of (50±5)%. Test procedure: only test columns are used, one of which is used as the painted substrate. Test results and representation: failure type is assessed by visual inspection: A-cohesive failure of the substrate; A / B-adhesion failure between the first coating and the substrate; B-cohesive failure of the first coating. n / m - Adhesion failure between the nth and mth layers of the composite coating; Y - Cohesive failure of the adhesive; YIZ - Bond failure between the adhesive and the test column. Breaking strength: =F / AF: Force required to pull apart; A: Area of ​​the test column. The final result is expressed as... For example, when the pull-off force is 3 MPa, the average cohesive failure area of ​​the first coating is 20%, and the adhesion failure area between the first and second coatings is 80%. The results are expressed as 3 MPa, 20%B, and 80%B / C. The results show that the average adhesion of all 10 coating samples is 12.9 MPa.

[0064] VII. Pencil Hardness - Determination of paint film hardness according to GB / T6739-2006 Pencil Method for Coloring and Varnishing

[0065] 1. Place the hardness tester flat on the protective coating. If the protective coating is smaller than the hardness tester, place the protective coating in front of the hardness tester and place the shim under the front of the hardness tester to keep the hardness tester horizontal.

[0066] 2. Use a pencil sharpener to trim the pencil lead, leaving a protruding portion of about 5-6mm. Smooth the lead with 400-grit sandpaper, ensuring the edges are smooth and free of chips. Insert the pencil into the instrument, ensuring the lead contacts the protective coating and locks it in place. (It is recommended to use a hexagonal pencil. When fixing, choose one plane, test, rotate both planes, and then test again. Repeat this process, rotating both planes three times per circumference.) Remove the shim before each test. Repeat this smoothing step before each use of the pencil.

[0067] 3. Begin moving the hardness tester as soon as the pencil touches the paint film. Hold the tester between the two wheels with your thumb and middle finger and push it forward at a steady pace a sufficient distance. Then remove the hardness tester and erase the pencil marks with an eraser. (Do not apply any pressure when pushing the hardness tester).

[0068] 4. Determine the hardness by checking for scratches on the protective coating. It is recommended to test the protective coating at least three times and take the average value. Hardness grades from softest to hardest are: 6B, 5B, 4B, 3B, 2B, B, HB, FH, 2H, 3H, 4H, 5H, 6H, 7H, 8H, and 9H, a total of 17 grades. For example, if an H pencil leaves no scratches and a 2H pencil also leaves no scratches, but a 3H pencil leaves scratches, then the hardness grade of the protective coating is 2H. The results showed that all 10 coating samples had a hardness grade of 2H.

[0069] 8. Drying time - According to GB / T1728-1979(89) Determination of drying time of paint film and putty film

[0070] The surface drying time is determined using the finger-touch method: The sample to be tested is evenly coated onto a clean, flat substrate (such as a glass or metal plate). The sample is placed at 20°C and 40% relative humidity. A finger stylus is used to gently touch the surface of the paint or putty film, repeating this process at regular intervals (e.g., every 5 minutes). The time when the surface of the paint or putty film is no longer sticky after the finger stylus touches it is recorded; this is the surface drying time.

[0071] The drying time is determined using the filter paper pressing method: The sample to be tested is evenly coated on a clean, flat substrate. The sample is placed at 25℃ and 45% relative humidity. A clean filter paper is placed over the surface of the paint or putty film, and then a weight (such as a counterweight) is placed on top, ensuring close contact between the filter paper and the paint film. At regular intervals (e.g., every 15 minutes), the weight and filter paper are removed, and the surface of the paint or putty film is observed for any obvious marks. When no obvious marks are left on the filter paper, the time at which this occurs is recorded as the drying time.

[0072] The results for all 10 paint samples are shown in the table below:

[0073]

[0074] According to the results in the table above, the protective coating for galvanized cathodic protection of iron materials of the present invention, tested by the National Railway Product Quality Supervision and Inspection Center, shows better performance than ordinary coating products in all test items.

[0075] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A protective coating for galvanized cathodic protection of iron materials, comprising, by weight percentage: The content ratio of multifunctional acrylic resin, strontium chrome yellow nano-mixture, graphene nano-mixture, and isocyanate curing agent is (45-65)%:(0.8-1.6)%:(0.02-0.05)%:(5-8.4)%, cellulose resin: 7%-12%, silver powder: 6%-12%, solvent: 5%-8%, additives: 1%-3%, and the remainder is diluent. The strontium chromium yellow nanoparticles form anchoring points on the iron surface and simultaneously complex with the multifunctional acrylic resin and the cellulose resin, thereby enhancing the adhesion of the coating to the iron to 10-12 N / mm. The graphene nanosheets form a barrier against corrosive substances between the multifunctional acrylic resins, thereby enhancing the corrosion resistance of the coating.

2. The protective coating according to claim 1, characterized in that, The additives include at least one of thickeners, toughening agents, alignment agents, leveling agents, and wetting and dispersing agents.

3. The protective coating according to claim 1, characterized in that, The graphene nanosheets are at least one of reduced graphene, graphene oxide, and physically exfoliated graphene.

4. The protective coating according to claim 1, characterized in that, The solvent is selected from butyl acetate or xylene.

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