CX-grade extreme environment corrosion-resistant pre-coating hot-dip coating steel belt with double functions of shielding isolation and cathode protection

Abstract

The invention relates to the technical field of continuous coating of steel strips, and particularly discloses a CX-grade extreme environment corrosion-resistant pre-coating hot-dip coating steel strip with double functions of shielding isolation and cathode protection. The steel substrate is protected through the alloy plating layer, the primer coating and the finish coating together, and it is limited that polyaniline nanoparticles are contained in the primer coating and the finish coating. Within the limited use amount range, polyaniline is added, and the alloy coating, the primer coating and the finish coating are combined within the specific thickness range, so that the protection effect on the steel substrate can be improved jointly, and the influence of an external corrosive medium on the steel substrate is reduced; and the pre-coating hot-dip coating steel strip capable of serving for a long time in a CX-grade extreme corrosion environment is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of continuous coating of steel strips, and more specifically, to a pre-coated hot-dip coated steel strip having the dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environmental corrosion. Background Art

[0002] Steel corrosion refers to the process in which steel is gradually destroyed due to electrochemical reactions between metal and environmental corrosive media in natural or specific environments. It is one of the main causes of metal material failure. According to the ISO9223 standard, the use environment of metal materials was once divided into five levels: C1, C2, C3, C4, and C5. Traditional pre-coated steel strips are also mainly designed around these five levels. In recent years, with the improvement of environmental awareness, industries such as construction, animal husbandry, modern prefabricated construction, and "5G" have put forward new requirements for steel strips that can be used for a long time in extreme environments. The ISO9223 standard has also added the CX level above C1-C5, representing an extremely harsh corrosive environment. In traditional processes, the principles of hot-dip protection and coating protection are cathodic protection and isolation shielding, respectively, which are two relatively basic protection methods.

[0003] For the coated steel plate produced by hot-dip plating on the surface of steel materials, the anti-corrosion principle is the cathodic protection method, that is, the coating and the steel material form a galvanic couple, the coating is corroded first as the anode, and the steel is protected as the cathode. Since the corrosion product of the coating will form a protective film, the life of the coated plate is greatly improved compared with the bare steel plate. However, the coating is also a metal or metal alloy, and the maximum coating adhesion is limited, the corrosion resistance is still limited, and the maximum coating adhesion can only reach 150-550g / m 2 Therefore, the coating alone is not enough to meet the requirements for use in C5 environment, let alone CX environment, so further coating treatment is necessary.

[0004] For the coated steel plate produced by roller coating on the surface of the plated plate, the anti-corrosion principle is shielding protection, that is, the steel plate and the coating are isolated from the external environment by a relatively dense coating. In this way, the corrosive medium in the environment is difficult to contact the coating and the steel plate, so it will not be easily corroded. However, the shielding effect of the coating not only isolates the contact between the coating and the corrosive medium, but also isolates the electron exchange between the coating and the medium. Cathodic protection is based on ionization, which weakens the cathodic protection of the coating under the coating. In this case, a galvanic couple will be formed between different tissues inside the coating itself, causing ineffective coating corrosion. Moreover, the density of the coating prepared by ordinary methods is limited, so it still cannot meet the requirements of use in CX-level extreme environments.

[0005] With respect to the above-mentioned related technologies, the inventors believe that when the steel strip is protected by hot-dip plating plus coating according to the known technology, the anti-corrosion mechanisms of the two conflict with each other and cannot meet the needs of long-term use in CX-level extreme environments. Summary of the invention

[0006] At present, when the steel strip is protected by hot-dip plating and coating, the anti-corrosion mechanisms of the two conflict and cannot meet the needs of long-term use in CX-level extreme environments. In order to improve this defect, the present application provides a pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection, which is resistant to CX-level extreme environment corrosion.

[0007] The present application provides a pre-coated hot-dip coated steel strip having the dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environmental corrosion, adopting the following technical solution: A pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion, comprising a steel substrate and an adhesive weight of 150-550g / m 2 An alloy coating, a primer coating with a thickness of 8-10 μm and a topcoat coating with a thickness of 30-60 μm, wherein the alloy coating is coated on the surface of a steel substrate, the primer coating is coated on the surface of the alloy coating, and the topcoat coating is coated on the surface of the primer coating; the primer coating and the topcoat coating both contain 3-30wt% of polyaniline nanoparticles.

[0008] By adopting the above technical scheme, the core concept of the present application is to play the role of cathodic protection and coating shielding at the same time, that is, while shielding with primer coating and topcoat coating, continue to maintain the conductive effect between the coating and the corrosive medium. In order to achieve this, the present application defines that the primer coating and the topcoat coating contain a certain amount of polyaniline nanoparticles. There are a large number of delocalized bonds in the polyaniline molecule, which can promote the transfer of electrons. The addition of polyaniline nanoparticles not only enhances the shielding effect of the primer coating and the topcoat coating through the filling effect, but also improves the electron transmission effect between the coating and the corrosive medium, making it difficult to form a galvanic couple between different tissues inside the coating, but it is easier to form a galvanic couple with the outside world, thereby reducing invalid coating corrosion. Under the combined effect of factors such as the addition of polyaniline and the combination of alloy coating, primer coating and topcoat coating within a specific thickness range, the steel substrate can obtain the dual protective effect of cathodic protection and coating shielding, thereby reducing the influence of external corrosive media on the steel substrate, and obtaining a pre-coated film hot-dip coated steel strip that can serve for a long time in a CX-level extreme corrosion environment. This technical solution that combines cathodic protection and shielding protection significantly improves the corrosion resistance of the steel strip, allowing the color-coated plates produced using ordinary coatings as the substrate to maintain excellent durability even in CX-level extreme environments, fully overcoming the defects existing in related technologies.

[0009] Preferably, the primer coating and the topcoat coating both contain 5-30 wt % of polyaniline nanoparticles based on the dry weight of the film-forming coating.

[0010] By adopting the above technical solution, the present application optimizes the dosage range of polyaniline nanoparticles, which helps to ensure its conductive performance.

[0011] Preferably, the polyaniline nanoparticles have a D 90 The particle size is 100-300nm.

[0012] By adopting the above technical solution, the present application preferably selects the D of polyaniline nanoparticles. 90 The particle size can prevent the microscopic pores inside the coating from being too large due to the large single particle size of the powder material, which is beneficial to reducing the porosity and the maximum void.

[0013] Preferably, the proportion of the polyaniline nanoparticles existing in the primer coating and the topcoat coating in the form of a single particle is ≥90%, and the proportion of the polyaniline nanoparticles existing in the resin in the form of two or less particles is 100%.

[0014] By adopting the above technical solution, the present application limits the distribution of polyaniline nanoparticles in the primer coating and the topcoat coating, which helps to prevent the microscopic pores inside the coating from being too large due to the mutual aggregation of nano-polyaniline particles, and is beneficial to reducing the porosity and the maximum voids, thereby improving the corrosion resistance of the pre-coated hot-dip coated steel strip.

[0015] Preferably, the alloy coating is an Al-Zn-Mg alloy coating.

[0016] By adopting the above technical solution, the present application uses Al-Zn-Mg alloy coating to protect the steel substrate. During the processing and in the corrosive environment, an oxide film of a certain thickness will be produced on the surface of the Al-Zn-Mg alloy coating, which has the effect of slowing down the corrosion rate of the coating. At the same time, the Al-Zn-Mg alloy coating can also act as a sacrificial anode to reduce the electrochemical corrosion of the substrate, so the Al-Zn-Mg alloy coating can effectively protect the substrate.

[0017] Preferably, the maximum grain size of the alloy coating is ≤0.5 mm.

[0018] By adopting the above technical solution, the present application optimizes the range of the maximum grain size of the alloy coating. Within the above range, the size of the primary Al-rich phase in the alloy coating can be well controlled, and the segregation of the magnesium component can be suppressed to a certain extent, which can minimize the invalid galvanic phenomenon between different structures inside the coating. Therefore, the pre-coated film hot-dip coated steel strip of the present application can also achieve good corrosion resistance when the increase in the thickness of the alloy coating is limited, and can have a long service life in the CX-level extreme corrosion environment.

[0019] Preferably, the maximum grain size of the alloy coating is ≤0.2 mm.

[0020] By adopting the above technical scheme, the present application further limits the maximum grain size of the alloy coating, and more strictly controls the size of the primary Al-rich phase and the segregation of the magnesium component in the alloy coating, thereby improving the protective effect of the alloy coating on the steel substrate, and also making the structure of the alloy coating more compact, thereby obtaining a pre-coated hot-dip coated steel strip with better corrosion resistance and longer service life in CX-level extreme corrosion environment.

[0021] Preferably, the impurity iron-zinc and iron-aluminum compound content of the alloy coating is ≤0.05%.

[0022] By adopting the above technical scheme, the present application limits the impurity content range of the alloy coating, reduces the ineffective galvanic corrosion between the internal coating structure and impurities such as iron-zinc and iron-aluminum compounds caused by impurities, improves the protective effect of the alloy coating on the steel substrate, and extends the service life of the pre-coated hot-dip coated steel strip in the CX-level extreme corrosion environment.

[0023] Preferably, the surface of the alloy coating has an oxide film, and the thickness of the oxide film is ≤0.10 μm.

[0024] By adopting the above technical solution, the present application controls the upper limit of the thickness of the oxide film, so that the aluminum oxide in the oxide film composition increases and the magnesium oxide decreases, the oxide is denser, and the segregation of magnesium is very small, thereby improving the protective effect of the alloy coating on the steel substrate and extending the service life of the pre-coated hot-dip coated steel strip in the CX-level extreme corrosion environment.

[0025] Preferably, the thickness of the oxide film is ≤0.05 μm.

[0026] By adopting the above technical solution, the present application further limits the thickness of the oxide film, making the oxide film denser and the magnesium segregation smaller, improving the protective effect of the alloy coating on the steel substrate, and extending the service life of the pre-coated hot-dip coated steel strip in the CX-level extreme corrosion environment.

[0027] In summary, this application has the following beneficial effects: 1. The present application protects the steel substrate by alloy coating, primer coating and topcoat coating, and limits the polyaniline nanoparticles contained in the primer coating and topcoat coating. Within the dosage range specified in the present application, the addition of polyaniline and the combination of alloy coating, primer coating and topcoat coating within a limited thickness range can jointly improve the protective effect of the steel substrate, reduce the corrosion effect of external corrosive media on the steel substrate, and obtain a pre-coated hot-dip coated steel strip that can serve for a long time in a CX-level extreme corrosion environment.

[0028] 2. In this application, the alloy coating is preferably Al-Zn-Mg alloy coating, and the maximum grain size of the alloy coating is preferably selected. The Al-Zn-Mg alloy coating can be used as an anode to reduce the electrochemical corrosion of the substrate at the expense of the maximum grain size; the limitation of the maximum grain size realizes the control of the size of the primary Al-rich phase and inhibits the segregation of magnesium, which can maximize the reduction of the invalid galvanic phenomenon between different tissues in the coating.

[0029] 3. This application limits the impurity content and oxide film thickness of the alloy coating. By limiting the impurity content, the ineffective galvanic corrosion between the internal coating structure and the iron-zinc and iron-aluminum compounds caused by impurities is reduced; and by limiting the oxide film thickness, the aluminum oxide in the oxide film composition can be increased and the magnesium oxide can be reduced, the oxide is more dense, and the segregation of magnesium is smaller, thereby improving the protective effect of the alloy coating on the steel substrate. Both aspects extend the service life of the pre-coated hot-dip coated steel strip in the CX-level extreme corrosion environment. DETAILED DESCRIPTION

[0030] The present application is further described in detail below in conjunction with embodiments, preparation examples and comparative examples. The raw materials involved in the present application can all be obtained commercially. Example

[0031] Examples 1-5 The following description is given by taking Example 1 as an example.

[0032] Example 1 This embodiment provides a pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environmental corrosion, including a steel substrate, an alloy coating, a primer coating and a topcoat coating. The alloy coating is coated on the surface of the steel substrate, the primer coating is coated on the surface of the alloy coating, and the topcoat coating is coated on the surface of the primer coating. The thickness of the steel substrate is 1 mm, and the adhesion amount of the alloy coating is 150 g / m 2 The thickness of the primer coating is 8 μm (referred to as H1 in Table 1), and the thickness of the topcoat coating is 30 μm (referred to as H2 in Table 1).

[0033] In the pre-coated hot-dip coated steel strip of this embodiment, the steel substrate is a Q235 hot-rolled steel strip, the alloy coating is an Al-Zn-Mg alloy coating, the maximum grain size of the alloy coating is 0.2 mm (abbreviated as Dmax in Table 1), and the content of impurity iron-zinc and iron-aluminum compounds is 0.05% (abbreviated as impurity content in Table 1). The surface of the alloy coating has an oxide film, and the thickness of the oxide film is 0.05 μm (abbreviated as H4 in Table 1).

[0034] Both the primer coating and the topcoat coating are made by curing the film-forming coating. The film-forming coating is composed of a film-forming resin and polyaniline nanoparticles as well as other powder materials such as fillers and pigments. The film-forming resin is a mixture of a fluorocarbon resin with a curing temperature of 220°C and an epoxy resin with a curing temperature of 160°C in a weight ratio of 3:2. 90 The particle size is 300nm (referred to as PANI particle size in Table 1), the weight of polyaniline nanoparticles accounts for 5% of the dry weight of the film-forming coating (referred to as PANI proportion in Table 1), the proportion of polyaniline nanoparticles in the primer coating and the topcoat coating in the form of single particles is 92% (referred to as the first distribution ratio in Table 1) and 95% (referred to as the second distribution ratio in Table 1), respectively, and the proportion of polyaniline nanoparticles in the primer coating and the topcoat coating in the form of two or less particles in the resin is 100%.

[0035] In this embodiment, a pre-coated hot-dip coated steel strip having dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion is prepared according to the following method: The alloy coating is subjected to passivation pretreatment, the contact angle between the alloy coating and the passivation solution is controlled to be 15°, and then the steel substrate is passivated using the passivation solution in a continuous pre-coating film production line, a primer is coated on the surface of the passivated alloy coating, and a primer coating is formed after baking and curing; a topcoat is coated on the surface of the primer coating, and a topcoat coating is formed after baking and curing, thereby completing the preparation of a pre-coated film hot-dip coated steel strip resistant to CX-level extreme environment corrosion and having the dual functions of shielding isolation and cathodic protection; the bonding rate between the primer and the alloy coating is 99.9993%, the porosity of the primer coating and the topcoat coating is 0.0007%, and the maximum gap between the primer coating and the topcoat coating is 40nm.

[0036] In the above method, the passivation solution is a chromium-free passivation solution, and the specific steps of the passivation pretreatment are: alkali washing with a 1wt% (referred to as the alkali concentration in Table 1) sodium hydroxide solution, then rinsing with water, then pickling with a 1wt% (referred to as the acid concentration in Table 1) hydrochloric acid solution, then rinsing again, and finally drying to complete the passivation pretreatment.

[0037] As shown in Table 1, the main difference between Examples 1-5 is that some product performance parameters of the pre-coated hot-dip coated steel strip are different.

[0038] Table 1 Product performance parameters Example 6 The difference between this embodiment and embodiment 1 is that the weight of the polyaniline nanoparticles accounts for 3% of the dry weight of the film-forming coating.

[0039] Example 7 The difference between this embodiment and embodiment 1 is that the average particle size of the polyaniline nanoparticles is 350 nm.

[0040] Example 8 The difference between this embodiment and embodiment 1 is that the proportion of the polyaniline nanoparticles existing in the state of single particles in the primer coating and the topcoat coating is 85% and 88% respectively.

[0041] Example 9 The difference between this embodiment and embodiment 1 is that the maximum grain size of the alloy coating is 0.5 mm.

[0042] Example 10 The difference between this embodiment and embodiment 1 is that the impurity content of the alloy plating layer is 0.06%.

[0043] Embodiment 11 The difference between this embodiment and embodiment 1 is that the thickness of the oxide film is 0.10 μm.

[0044] Comparative Example Comparative Example 1 The difference between this comparative example and Example 1 is that the adhesion amount of the alloy coating is 116 g / m 2 .

[0045] Comparative Example 2 The difference between this comparative example and Example 1 is that the thickness of the primer coating is 5 μm.

[0046] Comparative Example 3 The difference between this comparative example and Example 1 is that the thickness of the topcoat coating is 20 μm.

[0047] Comparative Example 4 The difference between this comparative example and Example 1 is that the weight of the polyaniline nanoparticles accounts for 1% of the dry weight of the film-forming coating.

[0048] Performance testing methods 1. Coating adhesion The weighing method is used to detect the coating adhesion on the surface of the steel strip substrate. The steps are as follows: (1) Before hot-dip plating, measure and record the initial weight of the substrate using an electronic balance; (2) After the hot-dip plating treatment is completed, the total weight of the substrate and the plated layer is measured using a balance.

[0049] (3) The coating adhesion amount was calculated based on the difference between the two measurement results and the substrate area. The results are shown in Table 2.

[0050] 2. Use a coating thickness gauge to measure the thickness of the primer coating and the topcoat coating. The results are shown in Table 2.

[0051] 3. Corrosion resistance Referring to the record of "GB / T 10125-2012 Artificial atmosphere corrosion test salt spray test", the copper accelerated acetate salt spray test was carried out on the steel strip substrate, and the time when red rust appeared in each group of tests was recorded. The results are shown in Table 2.

[0052] Table 2 Combining Examples 1-11 and Comparative Examples 1-4 and Table 2, it can be seen that when the coating adhesion, primer thickness, and topcoat thickness are similar, the corrosion time of each example and comparative example is quite different.

[0053] Combining Examples 1-5 and Comparative Examples 1-4 and Table 2, it can be seen that the corrosion time measured in Examples 1-5 is relatively long, indicating that the present application uses the primer coating and the topcoat coating for shielding, and through the addition of polyaniline nanoparticles, and the combination of the alloy coating, the primer coating and the topcoat coating within a specific process parameter range, the steel substrate can obtain the dual protection of cathodic protection and coating shielding, reducing the impact of external corrosive media on the steel substrate, and obtaining a pre-coated hot-dip coated steel strip that can serve for a long time in a CX-level extreme corrosion environment. This technical solution combining cathodic protection and shielding protection significantly improves the corrosion resistance of the steel strip, so that it can maintain excellent durability even in a CX-level extreme environment, and fully overcomes the defects existing in the relevant technology. When the parameters such as the amount of alloy coating adhesion, the thickness of the primer coating, the thickness of the topcoat coating, and the percentage of the weight of the polyaniline nanoparticles in the dry weight of the film-forming coating do not meet the range specified in the present application, the corrosion resistance of the pre-coated hot-dip coated steel strip is poor.

[0054] It can be seen from Examples 1-5 and Examples 6-11 and Table 2 that when the weight of the polyaniline nanoparticles accounts for less than 5% of the dry weight of the film-forming coating, or the average particle size of the polyaniline nanoparticles, the proportion of the polyaniline nanoparticles in the primer coating and the topcoat coating in the form of single particles, the maximum grain size of the alloy coating, the impurity content of the alloy coating, the thickness of the oxide film and other parameters do not meet the preferred ranges defined in the present application, the corrosion resistance of the pre-coated hot-dip coated steel strip is relatively poor, but is still better than the results of the comparative examples.

[0055] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion, characterized in that: Including steel substrate, adhesion is 150-550g / m 2 An alloy coating, a primer coating with a thickness of 8-10 μm and a topcoat coating with a thickness of 30-60 μm, wherein the alloy coating is coated on the surface of the steel substrate, the primer coating is coated on the surface of the alloy coating, and the topcoat coating is coated on the surface of the primer coating; The primer coating and the topcoat coating both contain 3-30wt% of polyaniline nanoparticles.

2. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 1, characterized in that: The primer coating and the topcoat coating both contain 5-30wt% of polyaniline nanoparticles in the dry weight of the film-forming coating.

3. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 2, characterized in that: The D 90 The particle size is 100-300nm.

4. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 3 is characterized in that: The proportion of the polyaniline nanoparticles existing in the primer coating and the topcoat coating in the form of a single particle is ≥90%, and the proportion of the polyaniline nanoparticles existing in the resin in the form of two or less particles is 100%.

5. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 1, characterized in that: The alloy coating is an Al-Zn-Mg alloy coating.

6. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 5, characterized in that: The maximum grain size of the alloy coating is ≤0.5 mm.

7. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 6, characterized in that: The maximum grain size of the alloy coating is ≤0.2 mm.

8. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 7, characterized in that: The content of impurity iron-zinc and iron-aluminum compounds in the alloy coating is ≤0.05%.

9. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 1, characterized in that: The surface of the alloy coating has an oxide film, and the thickness of the oxide film is ≤0.10 μm.

10. The pre-coated hot-dip coated steel strip with dual functions of shielding isolation and cathodic protection and resistant to CX-level extreme environment corrosion according to claim 5, characterized in that: The thickness of the oxide film is ≤0.05 μm.

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