Water-based polyvinylidene chloride rust-conversion antirust resin coating with rust and preparation method of water-based polyvinylidene chloride rust-conversion antirust resin coating

Abstract

The invention relates to a water-based polyvinylidene chloride rust-to-rust resin coating and a preparation method thereof, and belongs to the technical field of anticorrosive coatings. The coating is composed of a bottom coating and a surface coating, and both the bottom coating and the surface coating take a water-based polyvinylidene chloride resin emulsion from the same source as a film-forming binder. A stabilizer ethylene diamine tetraacetic acid salt is added in advance in the polymerization process of the water-based polyvinylidene chloride resin emulsion; tannic acid is particularly added into the primer as a rust conversion agent. The preparation method of the coating comprises the following steps: respectively preparing a primer slurry containing tannic acid and an anti-rust pigment and a finish slurry containing a finish pigment filler, respectively mixing the primer slurry and the finish slurry with the water-based polyvinylidene chloride resin emulsion, and filtering to obtain the coating. Through the synergistic effect of the stabilizer and the tannic acid, the obtained coating system has excellent storage stability, physical and mechanical properties and excellent anti-rust and anti-corrosion properties.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coatings, and in particular to a water-based polyvinylidene chloride rust-inhibiting resin coating and its preparation method. Background Technology

[0002] Steel materials are widely used in various fields, but they are prone to electrochemical corrosion in the atmosphere and water, causing huge economic losses and safety hazards. Applying anti-rust coatings is one of the commonly used and effective protective measures. Traditional solvent-based coatings have excellent performance, but they release a large amount of VOCs during production and construction, which harms the environment and human health. Water-based coatings use water as a dispersion medium, have low VOCs, and are safe and environmentally friendly, but they are difficult to match solvent-based coatings in terms of corrosion resistance, drying speed, and substrate compatibility.

[0003] Currently, common water-based anti-rust coating bases, such as acrylic emulsions and epoxy ester emulsions, still have room for improvement in terms of corrosion barrier properties, film density, and chemical resistance. Water-based polyvinylidene chloride (PVDC) resin, due to its high chlorine content, exhibits excellent barrier and corrosion resistance, making it a potential high-performance base. However, it is prone to decomposition during storage, releasing hydrogen chloride, leading to performance degradation and coating system instability, severely limiting its application. Furthermore, in the field of metal repair, an ideal anti-rust coating should be capable of application on rust-covered substrates, meaning it can be directly coated onto substrates with simple surface treatment and loose rust, transforming the rust into a stable protective layer through chemical conversion, thereby simplifying pretreatment processes and reducing construction costs. However, existing water-based rust-covered coatings generally suffer from limited rust-transfer capabilities, low tolerance to residual rust layers, and unsatisfactory long-term rust prevention effects. Therefore, developing an environmentally friendly water-based anti-rust coating that combines excellent storage stability, efficient rust-transfer function, rapid drying, and superior comprehensive protective performance has significant practical importance and application value.

[0004] CN108300096A discloses a rust-proof and cold-resistant coating, which comprises the following raw materials in parts by weight: polyvinylidene chloride resin, polyvinyl chloride resin, ABS resin, phenolic resin, light calcium carbonate, diatomaceous earth, dioctyl phthalate, bentonite, iron oxide, titanium dioxide, mica powder, antimony trioxide, and lithium silicate. This coating has good corrosion resistance and rust prevention capabilities, is inexpensive, and maintains good performance in low-temperature environments, resisting cracking at low temperatures. However, it has limited ability to prevent rust from forming, low tolerance for residual rust layers, and unsatisfactory long-term rust prevention effect.

[0005] CN113773705A discloses a water-based polyvinylidene chloride (PVDC) one-component anti-rust primer and its preparation method. The primer comprises: water-based PVDC resin, pigments and fillers, additives, co-solvents, and an appropriate amount of water. This coating has a very low VOC content, uses water as the diluent, and exhibits extremely low VOC emissions during the coating process. The coating film demonstrates excellent water resistance, salt water resistance, and salt spray resistance, as well as strong adhesion and good flexibility. However, the water-based PVDC resin in this anti-rust primer contains a large amount of Cl, which often detaches from the resin in the form of HCl, leading to unstable coating performance and poor storage stability. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, the present invention provides a water-based polyvinylidene chloride resin coating, which is environmentally friendly, fast-drying, has excellent physical and mechanical properties, and excellent rust-transfer function.

[0007] To achieve the above objectives, the present invention provides an aqueous polyvinylidene chloride resin coating, which consists of a primer and a topcoat, both of which use an aqueous polyvinylidene chloride resin emulsion from the same source as a film-forming binder.

[0008] Preferably, the primer, by weight, comprises 148-152 parts of water-based polyvinylidene chloride resin emulsion, 5.5-6.5 parts of tannic acid, 105-128 parts of coloring and rust-preventing pigment, 18-20 parts of talc, and 178-258 parts of water. Alternatively, 148-152 parts of water-based polyvinylidene chloride resin emulsion, 5.5-6.5 parts of tannic acid, 105-128 parts of coloring and rust-preventing pigments, 18-20 parts of talc, 12-13 parts of silica, and 178-258 parts of water.

[0009] Preferably, the topcoat comprises, by weight, 190-210 parts of waterborne polyvinylidene chloride resin emulsion and 1-3 parts of dipropylene glycol monobutyl ether.

[0010] Preferably, the preparation method of the aqueous polyvinylidene chloride resin emulsion includes the following steps, in parts by weight: S1. Add 85-95 parts water and 2.4-3.6 parts emulsifier to a reaction vessel, purge with nitrogen to remove oxygen, and stir at 100-200 rpm for 8-15 min; in an ice-water bath, shear emulsify 33-36 parts vinylidene chloride, 2.5-3.5 parts acrylic acid, and 10-13 parts butyl acrylate at 8000-1000 rpm for 3-6 min to obtain a seed pre-emulsion; separately, add 0.8-1.2 parts sodium persulfate to 18-22 parts water and mix. Dissolve 1.3-1.7 parts of sodium thiosulfate in 18-22 parts of water to prepare oxidant and reducing agent solutions respectively; control the reactor temperature at 20-22℃, first add 4-6 parts of oxidant solution and 4-6 parts of reducing agent solution to the reactor, then add the seed pre-emulsion dropwise into the reactor over 20-30 minutes; after the addition is complete, maintain the reaction at 45-60℃ and 0.2-0.5MPa for 1-2 hours to obtain the seed emulsion; S2. In an ice-water bath, separately emulsify 133-138 parts of vinylidene chloride, 33-36 parts of butyl methacrylate, 18-22 parts of butyl acrylate, 3-5 parts of 2-hydroxyethyl methacrylate, 0.4-0.6 parts of β-phosphate methacrylate, 68-72 parts of water, 0.8 parts of stabilizer, and 4 parts of emulsifier at 8000 rpm for 15 min to obtain a shell pre-emulsion; then separately dissolve 1.1-1.3 parts of sodium persulfate in 28-32 parts of water, and 0.6-1... 0 parts of sodium thiosulfate were added to 28-32 parts of water and dissolved to prepare oxidant and reducing agent solutions respectively. The reactor temperature was controlled at 45-60℃ and the reactor pressure at 0.2-0.5MPa. The shell pre-emulsion, oxidant solution and reducing agent solution were added dropwise simultaneously over 1-2 hours. The reaction was then kept at the temperature for 3-5 hours. After that, the temperature was lowered to 30-35℃ and degassed at -0.09MPa to -0.08MPa for 20-30 minutes. The mixture was filtered through a 200-250 mesh filter to obtain an aqueous polyvinylidene chloride resin emulsion.

[0011] Preferably, the emulsifier is selected from one of the following: a composite emulsifier and ethoxylated cashew phenol sulfosuccinate disodium salt.

[0012] Preferably, the composite emulsifier is composed of sodium dodecylbenzenesulfonate and nonylphenol polyoxyethylene ether mixed in a mass ratio of 1:1-2.

[0013] Preferably, the stabilizer is sodium ethylenediaminetetraacetate.

[0014] Preferably, the coloring and rust-preventing pigment comprises, by weight, 48-94 parts iron oxide red, 11-18 parts zinc phosphate, 9-28 parts iron phosphate powder, and 13-14 parts mica iron oxide.

[0015] This invention also provides a method for preparing the above-mentioned waterborne polyvinylidene chloride rust-inducing and rust-preventing resin coating, comprising the following steps, in parts by weight: Step 1: Mix water and tannic acid at 400-600 rpm. Then, while stirring, add iron oxide red, zinc phosphate, iron phosphate powder, mica iron oxide, talc powder, and silica in sequence to obtain slurry A. Increase the stirring speed to 1200-1500 rpm for high-speed dispersion until the slurry fineness is ≤25μm. Then, reduce the stirring speed to 400-600 rpm and add water-based polyvinylidene chloride resin emulsion to the slurry. Stir evenly to obtain a mixed slurry. Filter the mixed slurry through a 200-300 mesh sieve to obtain the primer coating. Alternatively, mix water and tannic acid at 400-600 rpm, then add iron oxide red, zinc phosphate, iron phosphate powder, mica iron oxide, and talc powder sequentially while stirring to obtain slurry A. Increase the stirring speed to 1200-1500 rpm for high-speed dispersion until the slurry fineness is ≤25μm. Then reduce the stirring speed to 400-600 rpm and add water-based polyvinylidene chloride resin emulsion to the slurry, stirring until homogeneous to obtain a mixed slurry. Filter the mixed slurry through a 200-300 mesh sieve to obtain the primer coating. Step 2: Stir the water-based polyvinylidene chloride resin emulsion and dipropylene glycol monobutyl ether evenly at 400-600 rpm, then filter through a 200-300 mesh sieve to obtain the topcoat. Step 3: Separate the primer from Step 1 and the topcoat from Step 2 into separate containers to obtain the water-based polyvinylidene chloride rust-inhibiting resin coating.

[0016] Preferably, during the application of the water-based polyvinylidene chloride rust-preventing resin coating, after cleaning the rusted metal surface, the primer is first sprayed, and then the topcoat is sprayed.

[0017] The beneficial effects of this invention are: 1. Compared with existing technologies, the coating of this invention uses water as the continuous phase, has a near-zero VOC content, and is non-toxic and harmless during production and use, meeting stringent environmental protection requirements. This invention effectively inhibits the release of chlorine atoms and HCl by pre-adding the stabilizer sodium ethylenediaminetetraacetate during the resin polymerization stage, fundamentally solving the problem of performance degradation of the resin and coating during storage, exhibiting excellent long-term storage stability. Furthermore, by introducing tannic acid as a rust-transfer agent and its synergistic effect with PVDC resin and various rust-inhibiting pigments, the coating possesses excellent rust-transfer capabilities, allowing direct application to properly treated rusted steel surfaces. Through a chemical reaction, loose rust is transformed into a stable chelate layer, which, together with other components, forms a dense, strongly adhesive composite protective coating, resulting in outstanding long-term rust prevention. The waterborne polyvinylidene chloride resin coating prepared by this invention achieves rapid curing at room temperature, with surface drying in 25 minutes and complete drying in 2 hours, which greatly improves construction efficiency. Furthermore, the resulting coating film has excellent physical and mechanical properties, with adhesion reaching grade 0, and excellent flexibility, impact resistance, hardness, and other indicators. It also has outstanding resistance to water, salt spray, and acid and alkali corrosion.

[0018] 2. Compared with the prior art, the present invention uses ethoxylated cashew phenol sulfosuccinate half ester disodium salt, an emulsifier with a specific structure, in the preparation method of waterborne polyvinylidene chloride resin emulsion. By utilizing the internal plasticizing effect generated by the long-chain alkanes in its molecule in the resin phase, the deformation and fusion ability of the resin at low temperature is significantly improved. This allows the coating to form a smooth and complete film without any microcracks, even after application and surface drying at low temperature, thus completely overcoming the inherent defect of easy cracking during low-temperature application in the prior art. Detailed Implementation

[0019] The parameters and sources of the specific chemical substances used are as follows: Iron oxide red, Fe2O3≥98%, oil absorption 18g / 100g, mesh size: 325 mesh, commercially available; Zinc phosphate, mesh size: 1250, commercially available; Ferrophosphate powder, mesh size: 600 mesh, commercially available; Mica iron oxide, Fe2O3≥90%, mesh size: 600 mesh, commercially available; Silica, particle size: 12nm, commercially available; Talc powder, mesh size: 3000 mesh, commercially available; Ethoxylated cashew phenol sulfosuccinate disodium salt, model: CPE-1035Y, is sourced from Guangzhou Shuangjian Trading Co., Ltd. Example

[0020] A method for preparing a water-based polyvinylidene chloride (PVDC) rust-inducing and rust-preventing resin coating includes the following steps: Step 1: Mix 257.7g of deionized water and 6.0g of tannic acid at 500rpm. Then, while stirring, add 93.2g of iron oxide red, 11.2g of zinc phosphate, 9.52g of iron phosphate powder, 13.14g of mica iron oxide, 18.6g of talc powder, and 12.3g of silica in sequence to obtain slurry A. Then, increase the stirring speed to 1400rpm for high-speed dispersion until the slurry fineness is ≤25μm. After that, reduce the stirring speed to 500rpm and add 150g of water-based polyvinylidene chloride resin emulsion to the slurry, and stir evenly to obtain a mixed slurry. Filter the mixed slurry through a 250-mesh sieve to obtain the primer coating. Step 2: Stir 200g of water-based polyvinylidene chloride resin emulsion and 2g of dipropylene glycol monobutyl ether at 500rpm until homogeneous, then filter through a 250-mesh sieve to obtain the topcoat. Step 3: Separate the primer from Step 1 and the topcoat from Step 2 into separate containers to obtain the water-based polyvinylidene chloride rust-inhibiting resin coating.

[0021] The preparation method of the aqueous polyvinylidene chloride resin emulsion in steps one and two includes the following steps: S1. Add 90g of deionized water and 3g of emulsifier to the reactor, purge with nitrogen to remove oxygen, and stir at 100rpm for 10min. In an ice-water bath, shear emulsify 34g of vinylidene chloride, 3g of acrylic acid, and 12g of butyl acrylate at 8000rpm for 5min to obtain a seed pre-emulsion. Separately, dissolve 1g of sodium persulfate in 20g of deionized water and dissolve 1.5g of sodium thiosulfate in 20g of deionized water to prepare oxidizing and reducing agent solutions, respectively. Controlling the reactor temperature at 20℃, first add 5g of oxidizing agent solution and 5g of reducing agent solution to the reactor, then add the seed pre-emulsion dropwise to the reactor over 20min. After the addition is complete, maintain the reaction at 55℃ and 0.3MPa for 1h to obtain a seed emulsion. S2. In an ice-water bath, 136g of vinylidene chloride, 35g of butyl methacrylate, 20g of butyl acrylate, 4g of 2-hydroxyethyl methacrylate, 0.5g of β-ethyl methacrylate, 70g of deionized water, 0.8g of sodium ethylenediaminetetraacetate, and 4g of emulsifier were sheared and emulsified at 8000rpm for 15min to obtain a shell pre-emulsion. Then, 1.2g of sodium persulfate and 0.8g of sodium thiosulfate were dissolved in 30g of deionized water to prepare oxidizing and reducing agent solutions, respectively. The shell pre-emulsion, oxidizing agent solution, and reducing agent solution were added dropwise simultaneously at a controlled temperature of 55℃ over 1.5h. The reaction was then maintained at this temperature for 4h. Afterward, the temperature was lowered to 35℃, and the mixture was degassed at -0.09MPa for 30min. The mixture was then filtered through a 200-mesh filter to obtain an aqueous polyvinylidene chloride resin emulsion.

[0022] The emulsifier is composed of sodium dodecylbenzenesulfonate and nonylphenol polyoxyethylene ether mixed in a mass ratio of 1:2.

[0023] Example 1 A method for preparing a water-based polyvinylidene chloride rust-inducing and rust-preventing resin coating differs from Example 1 only in step one, which specifically involves: 178.4g of deionized water and 6.0g of tannic acid were mixed and stirred at 500rpm. Then, while stirring, 48.0g of iron oxide red, 18.0g of zinc phosphate, 27.7g of iron phosphate powder, 13.0g of mica iron oxide, and 19.3g of talc powder were added sequentially to obtain slurry A. The stirring speed was then increased to 1400rpm for high-speed dispersion until the slurry fineness was ≤25μm. After that, the stirring speed was reduced to 500rpm, and 150g of water-based polyvinylidene chloride resin emulsion was added to the slurry and stirred evenly to obtain a mixed slurry. The mixed slurry was filtered through a 250-mesh sieve to obtain the primer coating.

[0024] The preparation method of the aqueous polyvinylidene chloride resin emulsion is the same as that in Example 1.

[0025] Example 2 A method for preparing a waterborne polyvinylidene chloride rust-inducing and rust-preventing resin coating differs from Example 1 only in that the emulsifier used in the preparation of the waterborne polyvinylidene chloride resin emulsion is ethoxylated cashew phenol sulfosuccinate half ester disodium salt.

[0026] Comparative Example 1 A method for preparing a water-based polyvinylidene chloride rust-inhibiting resin coating includes the following steps; Step 1: Mix 257.7g of deionized water and 6.0g of tannic acid at 500rpm. Then, while stirring, add 93.2g of iron oxide red, 11.2g of zinc phosphate, 9.52g of iron phosphate powder, 13.14g of mica iron oxide, 18.6g of talc powder, and 12.3g of silica in sequence to obtain slurry A. Then, increase the stirring speed to 1400rpm for high-speed dispersion until the slurry fineness is ≤25μm. After that, reduce the stirring speed to 500rpm, add 150g of water-based polyvinylidene chloride resin emulsion and 0.4g of sodium ethylenediaminetetraacetate to the slurry, and stir evenly to obtain a mixed slurry. Filter the mixed slurry through a 250-mesh sieve to obtain the primer coating. Step 2: At 500 rpm, 200 g of waterborne polyvinylidene chloride resin emulsion, 2 g of dipropylene glycol monobutyl ether and 0.4 g of sodium ethylenediaminetetraacetate are stirred evenly and then filtered through a 250-mesh sieve to obtain the topcoat. Step 3: Separate the primer from Step 1 and the topcoat from Step 2 into separate containers to obtain the water-based polyvinylidene chloride rust-inhibiting resin coating.

[0027] The preparation method of the aqueous polyvinylidene chloride resin emulsion in steps one and two includes the following steps: S1. Add 90g of deionized water and 3g of emulsifier to the reactor, purge with nitrogen to remove oxygen, and stir at 100rpm for 10min. In an ice-water bath, shear emulsify 34g of vinylidene chloride, 3g of acrylic acid, and 12g of butyl acrylate at 8000rpm for 5min to obtain a seed pre-emulsion. Separately, dissolve 1g of sodium persulfate in 20g of deionized water and dissolve 1.5g of sodium thiosulfate in 20g of deionized water to prepare oxidizing and reducing agent solutions, respectively. Controlling the reactor temperature at 20℃, first add 5g of oxidizing agent solution and 5g of reducing agent solution to the reactor, then add the seed pre-emulsion dropwise to the reactor over 20min. After the addition is complete, maintain the reaction at 55℃ and 0.3MPa for 1h to obtain a seed emulsion. S2. In an ice-water bath, 136g of vinylidene chloride, 35g of butyl methacrylate, 20g of butyl acrylate, 4g of 2-hydroxyethyl methacrylate, 0.5g of β-phosphate methacrylate, 70g of deionized water, and 4g of emulsifier were sheared and emulsified at 8000rpm for 15min to obtain a shell pre-emulsion. Then, 1.2g of sodium persulfate and 0.8g of sodium thiosulfate were dissolved in 30g of deionized water to prepare oxidizing and reducing agent solutions, respectively. The shell pre-emulsion, oxidizing agent solution, and reducing agent solution were added dropwise simultaneously at a controlled temperature of 55℃ over 1.5h. The reaction was then maintained at this temperature for 4h. Afterward, the temperature was lowered to 35℃, and the mixture was degassed at -0.09MPa for 30min. The mixture was then filtered through a 200-mesh filter to obtain an aqueous polyvinylidene chloride resin emulsion.

[0028] The emulsifier is composed of sodium dodecylbenzenesulfonate and nonylphenol polyoxyethylene ether mixed in a mass ratio of 1:2.

[0029] Comparative Example 2 A method for preparing a water-based polyvinylidene chloride (PVDC) rust-inducing and rust-preventing resin coating differs from Example 1 only in that the method for preparing the water-based PVDC resin emulsion includes the following steps: S1. Add 90g of deionized water and 3g of emulsifier to the reactor, purge with nitrogen to remove oxygen, and stir at 100rpm for 10min. In an ice-water bath, shear emulsify 34g of vinylidene chloride, 3g of acrylic acid, and 12g of butyl acrylate at 8000rpm for 5min to obtain a seed pre-emulsion. Separately, dissolve 1g of sodium persulfate in 20g of deionized water and dissolve 1.5g of sodium thiosulfate in 20g of deionized water to prepare oxidizing and reducing agent solutions, respectively. Controlling the reactor temperature at 20℃, first add 5g of oxidizing agent solution and 5g of reducing agent solution to the reactor, then add the seed pre-emulsion dropwise to the reactor over 20min. After the addition is complete, maintain the reaction at 55℃ and 0.3MPa for 1h to obtain a seed emulsion. S2. In an ice-water bath, 136g of vinylidene chloride, 35g of butyl methacrylate, 20g of butyl acrylate, 4g of 2-hydroxyethyl methacrylate, 0.5g of β-phosphate methacrylate, 70g of deionized water, and 4g of emulsifier were sheared and emulsified at 8000rpm for 15min to obtain a shell pre-emulsion. Then, 1.2g of sodium persulfate and 0.8g of sodium thiosulfate were dissolved in 30g of deionized water to prepare oxidizing and reducing agent solutions, respectively. The shell pre-emulsion, oxidizing agent solution, and reducing agent solution were added dropwise simultaneously at a controlled temperature of 55℃ over 1.5h. The reaction was then maintained at this temperature for 4h. Afterward, the temperature was lowered to 35℃, and the mixture was degassed at -0.09MPa for 30min. The mixture was then filtered through a 200-mesh filter to obtain an aqueous polyvinylidene chloride resin emulsion.

[0030] The emulsifier is composed of sodium dodecylbenzenesulfonate and nonylphenol polyoxyethylene ether mixed in a mass ratio of 1:2.

[0031] The aqueous polyvinylidene chloride resin emulsion prepared in this comparative example needs to be filtered through a 250-mesh sieve before use to remove the fine aggregated particles after a period of storage.

[0032] Comparative Example 3 A method for preparing a water-based polyvinylidene chloride rust-inducing and rust-preventing resin coating differs from Example 1 only in that 6.0g of tannic acid is replaced with 6.0g of phosphoric acid in step one.

[0033] Comparative Example 4 A method for preparing a water-based polyvinylidene chloride rust-inducing and rust-preventing resin coating differs from Example 1 only in that tannic acid is not added in step one.

[0034] Comparative Example 5 A method for preparing a waterborne polyvinylidene chloride rust-inducing and rust-preventing resin coating differs from Example 1 only in that the emulsifier used in the preparation of the waterborne polyvinylidene chloride resin emulsion is sodium dodecyl sulfate.

[0035] Stability: The stability of the coatings was tested in accordance with the standard GB / T 6753.3-1986 Test method for storage stability of coatings. The waterborne polyvinylidene chloride resin coatings obtained in Examples 1-3 and Comparative Examples 1-5 were sealed and stored at natural conditions (23±2)℃ for 12 months, and the condition was observed and evaluated. Low-temperature film-forming properties and micro-crack resistance: At 5°C, waterborne polyvinylidene chloride resin coatings obtained in Examples 1-3 and Comparative Examples 1-5 were sprayed onto rusted tinplate to prepare samples. During application, the surface of the rusted tinplate was first cleaned to remove loose dust and rust. At 5°C, a primer layer was sprayed with a thickness of 70 μm, allowing it to surface dry for 25 minutes and then fully dry for 2 hours. Then, at 5°C, a topcoat layer was sprayed with a thickness of 90 μm. After 25 minutes of surface drying, observation and evaluation were conducted. A control group was also established, where the coating from Example 1 was applied at 23°C and allowed to surface dry for 25 minutes. Specifically, the surface of the rusted tinplate was first cleaned to remove loose dust and rust. At 23°C, a primer layer was sprayed with a thickness of 70 μm, allowing it to surface dry for 25 minutes and then fully dry for 2 hours. Then, at 23°C, a topcoat layer was sprayed with a thickness of 90 μm, allowing it to surface dry for 25 minutes. Observations and comparisons were then conducted. The observations and evaluations are as follows: Visual inspection: Under a standard light source, observe whether there are network-like, hairline-like, or tortoise-crack-like microcracks on the surface of the coating.

[0036] Instrument inspection: A digital microscope (300x) is used to scan the microscopic morphology of the coating surface to look for microcracks that are difficult to detect with the naked eye.

[0037] Quantitative rating: Grade 0: Smooth surface, no cracks visible under a microscope.

[0038] Level 1: Invisible to the naked eye, but very few, discontinuous, fine cracks can be seen under a microscope.

[0039] Level 2: Localized microcrack networks are faintly visible to the naked eye.

[0040] Level 3: Large areas of continuous microcracks are clearly visible to the naked eye.

[0041] The specific test results are shown in Table 1 below: Table 1

[0042] As shown in Table 1, after 12 months of storage, the coatings of Examples 1-3 remained in good condition, were easily re-stirred, and showed no irreversible hard sedimentation or gelation. This indicates that pre-adding the stabilizer sodium ethylenediaminetetraacetate during the emulsion polymerization of waterborne polyvinylidene chloride resin significantly improves the storage stability of the waterborne coating system. In contrast, Comparative Example 1, where the stabilizer was added later, although it could be used after filtration, showed an increase in fine particles, indicating that the later addition method could not completely compensate for the slight degradation of the resin during storage. Comparative Example 2, lacking a stabilizer, could not be stirred evenly and therefore failed the evaluation.

[0043] As shown in Table 1, the coatings of Examples 1-2 were prone to microcracks during surface drying at 5°C. However, Example 3, by introducing ethoxylated cashew phenol sulfosuccinate disodium salt as a key emulsifier, exhibited a smooth and intact coating with no microcracks after application at 5°C and surface drying for 25 minutes, demonstrating better low-temperature film-forming properties and resistance to microcracks. The reason for this may be that the ethoxylated cashew phenol sulfosuccinate disodium salt, through the internal plasticizing effect provided by its long-chain alkanes, fundamentally improves the film-forming behavior of the resin at low temperatures, effectively releasing internal stress during surface drying. This solves the defects of poor film-forming properties and easy microcrack formation in the waterborne polyvinylidene chloride resin coating of this invention during low-temperature application.

[0044] Physical and mechanical property testing Adhesion: The test was conducted in accordance with the standard GB / T 9286-2021 "Cross-cut Adhesion Test for Paints and Varnishes". The test plates were standard tinplate and rusted tinplate. When testing the cross-cut adhesion of rusted tinplate, rusted tinplate was selected. No excessive surface treatment was required for the test sample. Only the surface rust needed to be removed. Impact resistance: Tested according to the standard GB / T 1732-2020 Test Method for Impact Resistance of Coating Film, the test board is standard tinplate; Flexibility: The test is conducted in accordance with the standard GB / T 1731-2020 Test Method for Flexibility of Paint Film and Putty Film. The test board is a standard tinplate, and the flexibility is expressed by the radius (R, mm) of the smallest shaft that does not cause damage to the paint film after bending. Hardness: The test was conducted in accordance with the standard GB / T 6739-2022 "Determination of Hardness of Paint and Varnish Film by Pencil Method". The test board was a standard tinplate. The application method for the waterborne polyvinylidene chloride resin coating in this test case was as follows: At room temperature, a layer of primer was first sprayed onto the test panel, with the primer thickness controlled at 70 μm. The surface drying time was 25 min, followed by a complete drying time of 2 h. Then, at room temperature, a layer of topcoat was sprayed, with the topcoat thickness controlled at 90 μm. The surface drying time was 25 min, followed by a complete drying time of 2 h. Specific test data are shown in Table 2 below: Table 2

[0045] As shown in Table 2, Examples 1-3 exhibited excellent performance with adhesion grade 0, impact resistance >56cm, flexibility ≤1.0mm, and hardness H, demonstrating good physical and mechanical properties. In contrast, Comparative Example 1 showed slight decreases in adhesion grade 1, impact resistance >52cm, and flexibility 2.0mm, while Comparative Example 2 showed significant deterioration in all mechanical properties. The test results indicate that the waterborne polyvinylidene chloride resin coating prepared in this application possesses good flexibility and impact resistance, high bonding strength with the substrate, and excellent adhesion.

[0046] On rusted iron plates simulating real-world applications, the cross-cut adhesion of Examples 1-3 remained at grade 0, indicating that the tannic acid component in the primer could effectively transform the rust layer, achieving a strong chemical-physical bond between the coating and the rusted substrate. Conversely, Comparative Example 2, without a stabilizer, showed comprehensive deterioration in all mechanical properties; while the experimental groups using phosphoric acid as a substitute in Comparative Example 3 or completely omitting tannic acid in Comparative Example 4 all experienced a significant decrease in rust adhesion to grade 2 or worse, indicating that tannic acid can effectively improve the rust-preventive ability of the coating and help maintain excellent mechanical properties.

[0047] Rust and corrosion resistance performance test Salt water resistance: The test was conducted in accordance with the standard GB / T 9274-1988 "Determination of resistance to liquid media for paints and varnishes". The test plate was a standard tinplate, which was soaked in a 3wt% NaCl aqueous solution for 700 hours. Salt spray resistance: The test was conducted in accordance with the standard GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test. The test plate was a standard tinplate, and the neutral salt spray test (NSS) lasted for 240 hours. Weather resistance of rusted construction samples: Rusted tinplate with surface rust removed was selected as test samples. The water-based polyvinylidene chloride resin coatings obtained in Examples 1-3 and Comparative Examples 1-5 were sprayed onto the test samples respectively. After that, they were stored in a 40°C, RH≥95% humidity chamber for 30 days. The appearance of the coating was observed to determine whether there were signs of rust re-emergence (i.e. no reddish-brown rust stains seeped out from under the coating). The application method for the waterborne polyvinylidene chloride resin coating in this test case was as follows: At room temperature, a layer of primer was first sprayed onto the test panel, with the primer thickness controlled at 70 μm. The surface drying time was 25 min, followed by a complete drying time of 2 h. Then, at room temperature, a layer of topcoat was sprayed, with the topcoat thickness controlled at 90 μm. The surface drying time was 25 min, followed by a complete drying time of 2 h.

[0048] The test results are shown in Table 3 below; Table 3

[0049] As shown in Table 3, after immersion in 3wt% NaCl aqueous solution for 700 h, neutral salt spray for 240 h, and humid heat storage of rusted samples for 30 days in Examples 1-3, the coatings remained intact, without blistering, rusting, or rust recurrence. This indicates that the dense topcoat coating composed of stabilized waterborne polyvinylidene chloride resin emulsion provides an excellent physical barrier, while the tannic acid-converted undercoat effectively blocks the further development of the original rust, and the two work synergistically to achieve excellent protective effects. Comparative Example 1, due to incomplete stabilization, showed localized early defects during long-term testing; while Comparative Examples 3 and 4 exhibited typical interface failure modes, i.e., corrosive media penetrated along the interface between the coating and the rust layer, leading to early blistering, rust recurrence, and protective failure. The test results show that the waterborne polyvinylidene chloride resin coating prepared in this application has good and durable rust prevention and corrosion resistance effects.

Claims

1. An aqueous polyvinylidene chloride rusted rust-preventive resin paint characterized by, The primer and the topcoat are both prepared by using the same source of water-based polyvinylidene chloride resin emulsion as the film-forming binder; the preparation method of the water-based polyvinylidene chloride resin emulsion comprises the following steps: ice-water emulsification of reaction monomers to obtain a seed pre-emulsion, then adding an oxidizing agent, a reducing agent solution and the seed pre-emulsion into water containing an emulsifier to obtain a seed emulsion, and then ice-water emulsification of a shell layer polyvinylidene chloride formula containing a stabilizer, and synchronous dropwise addition of an oxidizing agent and a reducing agent solution for mixed reaction to obtain the water-based polyvinylidene chloride resin emulsion.

2. The aqueous polyvinylidene chloride rusted-to-rust rust-preventive resin paint according to claim 1, characterized by, The primer comprises, by weight, 148-152 parts of the water-based polyvinylidene chloride resin emulsion, 5.5-6.5 parts of tannic acid, 105-128 parts of colored anti-rust pigment, 18-20 parts of talc, 12-13 parts of silicon dioxide, and 178-258 parts of water. Alternatively, the primer comprises, by weight, 148-152 parts of the water-based polyvinylidene chloride resin emulsion, 5.5-6.5 parts of tannic acid, 105-128 parts of colored anti-rust pigment, 18-20 parts of talc, and 178-258 parts of water.

3. The aqueous polyvinylidene chloride rusted-to-rust rust-preventive resin paint according to claim 1, characterized by, The topcoat comprises, by weight, 190-210 parts of the water-based polyvinylidene chloride resin emulsion, 1-3 parts of dipropylene glycol monobutyl ether.

4. The aqueous polyvinylidene chloride rusted-to-rust rust-preventive resin paint according to any one of claims 1 to 3, characterized by, The preparation method of the water-based polyvinylidene chloride resin emulsion comprises the following steps, by weight: S1, adding 85-95 parts of water and 2.4-3.6 parts of emulsifier into a reaction kettle, purging oxygen with nitrogen, stirring at 100-200 rpm for 8-15 min; ice-water bath shearing emulsification of 33-36 parts of vinylidene chloride, 2.5-3.5 parts of acrylic acid and 10-13 parts of butyl acrylate at 8000-10000 rpm for 3-6 min to obtain a seed pre-emulsion; separately dissolving 0.8-1.2 parts of sodium persulfate in 18-22 parts of water and 1.3-1.7 parts of sodium thiosulfate in 18-22 parts of water to prepare an oxidizing agent solution and a reducing agent solution; controlling the kettle temperature at 20-22℃, first adding 4-6 parts of the oxidizing agent solution and 4-6 parts of the reducing agent solution into the reaction kettle, then dropping the seed pre-emulsion into the reaction kettle, and completing the dropping within 20-30 min; after the dropping is completed, reacting at a kettle temperature of 45-60℃ and a kettle pressure of 0.2-0.5 MPa for 1-2 h to obtain a seed emulsion; S2, ice-water bath shearing emulsification of 133-138 parts of vinylidene chloride, 33-36 parts of butyl methacrylate, 18-22 parts of butyl acrylate, 3-5 parts of 2-hydroxyethyl methacrylate, 0.4-0.6 parts of beta-phosphoethyl methacrylate, 68-72 parts of water, 0.8 parts of stabilizer and 4 parts of emulsifier at 8000 rpm for 15 min to obtain a shell layer pre-emulsion; Then 1.1-1.3 parts of sodium persulfate is added into 28-32 parts of water to dissolve, 0.6-1.0 parts of sodium thiosulfate is added into 28-32 parts of water to dissolve, respectively, to prepare oxidant and reducing agent solutions; the temperature of the reactor is controlled at 45-60℃, the pressure of the reactor is controlled at 0.2-0.5 MPa, the shell pre-emulsion, the oxidant solution and the reducing agent solution are added dropwise synchronously, the dropping is completed in 1-2 hours, then the reaction is carried out for 3-5 hours, then the temperature is decreased to 30-35℃, the pressure is decreased to -0.09 MPa to -0.08 MPa, the degassing is carried out for 20-30 minutes, the product is filtered out through a 200-250 mesh screen, and a water-based polyvinylidene chloride resin emulsion is obtained.

5. The aqueous polyvinylidene chloride rusted-to-rust rust-preventive resin paint according to claim 4, characterized by, The emulsifier is selected from one of a composite emulsifier and ethoxylated cardanol sulfosuccinic acid half ester disodium salt; the composite emulsifier is composed of sodium dodecyl benzene sulfonate and nonylphenol polyoxyethylene ether at a mass ratio of 1:1-2.

6. The aqueous polyvinylidene chloride rusted-to-rust rust-preventive resin paint according to claim 4, characterized by, The stabilizer is sodium salt of ethylenediamine tetraacetate.

7. The method of preparing a waterborne polyvinylidene chloride rusted-to-rust rust-preventive resin paint according to claim 2, characterized by, The coloring and rust-proof pigment comprises, by weight, 48-94 parts of red iron oxide, 11-18 parts of zinc phosphate, 9-28 parts of phosphorus iron powder and 13-14 parts of mica iron oxide.

8. A process for preparing the aqueous polyvinylidene chloride rusted-to-rusted rust-preventive resin paint as claimed in any one of claims 1 to 7, characterized by, The method comprises the following steps: Step one, water and tannic acid are mixed and stirred at 400-600 rpm, then red iron oxide, zinc phosphate, phosphorus iron powder, mica iron oxide, talc powder and silicon dioxide are added in sequence under stirring to obtain slurry A; the stirring speed is then increased to 1200-1500 rpm for high-speed dispersion until the fineness of the slurry is less than or equal to 25 μm; the stirring speed is then decreased to 400-600 rpm, and the water-based polyvinylidene chloride resin emulsion is added to the slurry and stirred uniformly to obtain a mixed slurry; the mixed slurry is filtered through a 200-300 mesh screen to obtain a base coating; Or, water and tannic acid are mixed and stirred at 400-600 rpm, then red iron oxide, zinc phosphate, phosphorus iron powder and mica iron oxide are added in sequence under stirring to obtain slurry A; the stirring speed is then increased to 1200-1500 rpm for high-speed dispersion until the fineness of the slurry is less than or equal to 25 μm; the stirring speed is then decreased to 400-600 rpm, and the water-based polyvinylidene chloride resin emulsion is added to the slurry and stirred uniformly to obtain a mixed slurry; the mixed slurry is filtered through a 200-300 mesh screen to obtain a base coating; Step two, the water-based polyvinylidene chloride resin emulsion and dipropylene glycol monobutyl ether are stirred uniformly at 400-600 rpm and then filtered through a 200-300 mesh screen to obtain a top coating; Step three, the base coating of step one and the top coating of step two are independently packaged to obtain the water-based polyvinylidene chloride rusted surface conversion rust-proof resin coating.

9. The aqueous polyvinylidene chloride rusted-to-rust rust-preventive resin paint according to any one of claims 1 to 7, characterized by, The water-based polyvinylidene chloride rusted surface conversion rust-proof resin coating is used by first spraying the base coating on the cleaned rusted metal surface and then spraying the top coating.

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