A metal sheet coating pretreatment process

Abstract

The present application relates to the technical field of metal material pretreatment, and specifically discloses a metal plate coating pretreatment process, comprising the following steps: (1) continuously stirring a pretreatment liquid and spraying the metal plate surface with the pretreatment liquid; in this step, the pretreatment liquid comprises the following components in parts by weight: 100-120 parts of water and 8-12 parts of abrasive powder; the abrasive powder is an inorganic powder with an acrylic copolymer grafted on the surface; (2) spraying the metal plate surface with a degreasing liquid, and then spraying and washing the metal plate surface with water after the spraying is completed; in this step, the degreasing liquid comprises an anionic surfactant; (3) spraying a coating liquid onto the metal plate surface, and then baking the metal plate after the spraying is completed. After the baking is completed, the metal plate coating pretreatment is completed. The present application reduces the residue of oil and dust particles on the metal plate surface, enhances the film-forming effect of the coating liquid, and improves the corrosion resistance of the coating.

Description

Technical Field

[0001] The present application relates to the technical field of metal material pretreatment, and more specifically, to a metal sheet coating pretreatment process. Background Art

[0002] The corrosion of metal materials causes enormous losses to the national economy annually. According to statistics, annual losses due to corrosion in my country account for 4% of GDP. The promotion of metal corrosion protection technology is crucial to reducing these losses. Coating protection is currently the most widely used corrosion protection method, which provides protection by forming a coating on the metal surface. Before coating, the metal needs to undergo pre-treatment. The purpose of pre-treatment is to remove oil and dirt, while also forming a corrosion-resistant protective film on the metal surface to improve adhesion between the base metal and the coating.

[0003] In the related art, there is a metal plate pre-treatment process, which includes the following steps: (1) spraying the metal plate with industrial tap water; (2) spraying the surface of the metal plate with a degreasing liquid, and after the spraying is completed, the surface of the metal plate is sprayed and washed with water; in this step, the degreasing liquid includes the following components in parts by weight: 100-120 parts of water and 6.2-6.6 parts of a surfactant; (3) spraying a coating liquid on the surface of the metal plate, and after the spraying is completed, the metal plate is baked. After the baking is completed, the metal plate pre-treatment of the coating is completed. In this step, the components of the coating liquid include a silane coupling agent, water and ethanol.

[0004] Regarding the aforementioned related art, the inventors believe that while the degreasing fluids described in the related art are somewhat effective in removing oil stains from metal surfaces, when the oil stains on the metal surfaces contain dust, the dust absorbs the oil and becomes highly hydrophobic, making the water flow less effective in cleaning the dust particles contained in the oil stains. When the degreasing fluid is sprayed, the surfactant is adsorbed by the dust, which impairs the degreasing fluid's ability to clean the oil stains. Residual oil and dust can also impair the film-forming properties of the coating solution, resulting in a decrease in the coating's corrosion resistance. Summary of the Invention

[0005] In related technologies, when dust is present in the oil stains on the surface of metal sheets, the degreasing solution's ability to clean the oil stains is reduced, which can easily lead to incomplete degreasing of the metal sheet surface. The residual oil stains and dust can affect the film-forming effect of the coating solution, resulting in a decrease in the corrosion resistance of the coating. To address this shortcoming, the present application provides a metal sheet coating pretreatment process.

[0006] This application provides a metal sheet coating pretreatment process, which adopts the following technical solutions:

[0007] A metal sheet coating pretreatment process comprises the following steps:

[0008] (1) Continuously stirring the pretreatment liquid and spraying the surface of the metal plate with the pretreatment liquid; in this step, the pretreatment liquid includes the following components in parts by weight: 100-120 parts of water and 8-12 parts of polishing powder; the polishing powder is an inorganic powder with an acrylic copolymer grafted on its surface;

[0009] (2) Spraying the metal plate surface with a degreasing liquid, and then washing the metal plate surface with water after spraying; in this step, the degreasing liquid comprises an anionic surfactant.

[0010] (3) Spraying the coating liquid onto the surface of the metal plate, and baking the metal plate after the spraying is completed. After the baking is completed, the pre-treatment of the metal plate for coating is completed.

[0011] By adopting the above technical solution, the present application first uses a pretreatment liquid to spray the surface of the metal plate. The grinding powder in the pretreatment liquid can physically flush the dust particles in the oil stain, reducing the adsorption force between the dust particles and the metal matrix. At the same time, when a portion of the grinding powder that enters the oil stain comes into contact with the dust particles, the acrylic copolymer on the surface of these grinding powders adsorbs the dust particles through the carboxyl groups, thereby reducing the adsorption of the dust particles to anions. When a degreasing agent containing anionic surfactants is used for degreasing and cleaning, the carboxyl groups on the surface of the residual grinding powder and the anionic surfactant compete for adsorption on the surface of the dust particles, and the anionic surfactant and the acrylic copolymer on the surface of the grinding powder undergo electrostatic repulsion, making it difficult for the dust particles to adsorb the anionic surfactant. Since the adsorption of dust particles on the anionic surfactant is weakened, the degreasing effect of the degreasing liquid is reduced, the residue of oil stains and dust particles is reduced, the film-forming effect of the coating liquid is enhanced, and the corrosion resistance of the coating is improved.

[0012] Preferably, the pretreatment liquid comprises the following components in parts by weight: 105-115 parts of water and 9-11 parts of polishing powder.

[0013] By adopting the above technical solution, the raw material ratio of the pretreatment liquid is optimized, which helps to reduce the residue of oil and dust particles on the surface of the metal substrate and improves the corrosion resistance of the coating.

[0014] Preferably, in step (1) of the metal sheet coating pretreatment process, the spraying pressure adopted when spraying the pretreatment liquid is 0.8-0.92 MPa.

[0015] By adopting the above technical solution, the spraying pressure adopted when spraying the pretreatment liquid is optimized, which helps to reduce the residue of oil and dust particles on the surface of the metal substrate and improves the corrosion resistance of the coating.

[0016] Preferably, the polishing powder is prepared according to the following method:

[0017] (1) Mixing inorganic powder, silane coupling agent, water, and ethanol, heating at 70-80° C. for 60-80 min, and then filtering and drying to obtain silanized inorganic powder; in this step, the silane coupling agent is vinyltriethoxysilane;

[0018] (2) The silanized inorganic powder, acrylic acid, water, and thermal initiator are mixed, heated at 70-90° C. for 40-60 minutes, and then filtered and dried to obtain a polished powder.

[0019] By adopting the above technical solution, the present application first modifies the surface of the inorganic powder by vinyltriethoxysilane, grafts an organic chain segment containing vinyl onto the surface of the inorganic powder, and then initiates the copolymerization of acrylic acid, grafts the acrylic acid copolymer onto the surface of the inorganic powder to obtain a polished powder.

[0020] Preferably, in step (1) of preparing the polishing powder, silica sol is mixed with inorganic powder, silane coupling agent, water and ethanol.

[0021] By adopting the above technical solution, the silicon dioxide particles in the silica sol can combine with the surface of the inorganic powder, thereby increasing the surface area of ​​the inorganic powder, helping to increase the density of the grafted acrylic copolymer on the surface of the inorganic powder, improving the adsorption effect between the polishing powder and the dust particles, and helping to reduce the interference of dust particles on the degreasing performance of the degreasing liquid.

[0022] Preferably, the inorganic powder includes at least one of silica sand and steel slag powder.

[0023] By adopting this technical solution, both silica sand and steel slag powder possess high hardness, effectively flushing dust particles from oily contaminants. The dissolution of free calcium oxide in the steel slag upon contact with water accelerates the hydrolysis of the silane coupling agent, helping to shorten the production cycle of the polished powder.

[0024] Preferably, the coating liquid includes component A and component B, the component A includes silica sol and lithium silicate, and the component B includes aluminum sol. When spraying the coating liquid onto the surface of the metal plate, the component A of the coating liquid is sprayed first, and then the component B of the coating liquid is sprayed.

[0025] By employing this technical solution, lithium silicate hydrolyzes in the silica sol, raising the pH of the sol and rendering it alkaline. Mixing the alkaline silica sol with the alumina sol produces a silica-alumina gel, which accelerates the film formation rate of the coating solution. Furthermore, when the silica-alumina gel produced by the silica sol and alumina sol solidifies, the lithium silicate forms a water-insoluble dry film, which helps to hinder the spread of salt spray and improve the coating's corrosion resistance.

[0026] Preferably, component A of the coating solution includes ethyl orthosilicate.

[0027] By adopting the above technical solution, ethyl orthosilicate can be dehydrated in the silica sol, and the dehydration product can condense with the original silicon dioxide particles in the silica sol, thereby increasing the density of the silica-alumina gel after curing, helping to hinder the diffusion of salt spray on the metal surface, and improving the corrosion resistance of the coating.

[0028] Preferably, component A of the coating solution further comprises sodium methyl silicate.

[0029] By adopting the above technical solution, sodium methyl silicate can introduce a hydrophobic chain segment of methyl into the silica-alumina gel, thereby producing a partial hydrophobic area in the film layer formed by the curing of the silica-alumina gel, which helps to hinder the diffusion of salt mist on the metal surface and improve the corrosion resistance of the coating.

[0030] Preferably, component A of the coating solution further comprises isopropyl titanate.

[0031] By employing this technical solution, isopropyl titanate can form a gel with silica sol and aluminum sol and solidify to form a titanium hybrid coating. The newly doped titanium-oxygen bond in the titanium hybrid coating increases the average bond energy within the coating, thereby improving the coating's salt spray isolation and enhancing the coating's corrosion resistance.

[0032] In summary, this application has the following beneficial effects:

[0033] 1. The present application physically flushes the dust particles through the polishing powder in the pretreatment liquid, and adsorbs the dust particles through the acrylic copolymer on the surface of the polishing powder, thereby reducing the adsorption of dust particles on anionic surfactants, reducing the impact of the degreasing effect of the degreasing liquid, reducing the residue of oil and dust particles, enhancing the film-forming effect of the coating liquid, and improving the corrosion resistance of the coating.

[0034] 2. In this application, the preferred coating solution A component includes isopropyl titanate. Isopropyl titanate can form a gel with silica sol and alumina sol and solidify to form a titanium hybrid coating. The titanyl bonds in the titanium hybrid coating increase the average bond energy of the chemical bonds within the coating, improving the coating's isolation from salt spray and enhancing the coating's corrosion resistance. DETAILED DESCRIPTION

[0035] The present application is further described in detail below with reference to the Examples, Preparation Examples and Comparative Examples. The raw materials involved in the present application can all be obtained commercially.

[0036] Preparation example of grinding powder

[0037] The following is an explanation using Preparation Example 1.

[0038] Preparation Example 1

[0039] In this preparation example, the grinding powder was prepared according to the following method:

[0040] (1) 15 kg of inorganic powder, 2 kg of silane coupling agent, 30 kg of water, and 20 kg of ethanol were mixed, heated at 75° C. for 70 min, filtered, and then dried at 105° C. to obtain silanized inorganic powder; in this step, the silane coupling agent was vinyltriethoxysilane and the inorganic powder was silica sand with an average particle size of 200 μm;

[0041] (2) The silanized inorganic powder, 10 kg of acrylic acid, 80 kg of water, and 0.05 kg of a thermal initiator were mixed, heated at 70° C. for 45 min, and then filtered and dried to obtain a polished powder; in this step, the thermal initiator was azobisisobutylamidine hydrochloride.

[0042] Preparation Example 2

[0043] The difference between this preparation example and preparation example 1 is that in step (1) of preparing the polishing powder, silica sol is mixed with inorganic powder, silane coupling agent, water and ethanol, the amount of silica sol used is 20% by weight of water, and the water content of the silica sol is 75%.

[0044] Preparation Example 3

[0045] The difference between this Preparation Example and Preparation Example 1 is that the inorganic powder is steel slag powder with an average particle size of 200 μm.

[0046] Preparation Example 4

[0047] The difference between this preparation example and preparation example 3 is that in step (1) of preparing the polished powder, the inorganic powder, silane coupling agent, water and ethanol are mixed and then heated at 75° C. for 60 minutes.

[0048] Preparation Example 5

[0049] The difference between this preparation example and preparation example 3 is that in step (1) of preparing the polished powder, the inorganic powder, silane coupling agent, water and ethanol are mixed and then heated at 75° C. for 50 minutes.

[0050] Preparation Example 6

[0051] The difference between this preparation example and preparation example 3 is that in step (1) of preparing the polished powder, the inorganic powder, silane coupling agent, water and ethanol are mixed and then heated at 75° C. for 40 minutes.

[0052] Example

[0053] Examples 1-5

[0054] The following description will be given using Example 1 as an example.

[0055] Example 1

[0056] In this embodiment, the metal sheet pre-coating treatment process includes the following steps:

[0057] (1) The pretreatment liquid is continuously stirred at a rate of 260 r / min, and at the same time, the 40°C pretreatment liquid is sprayed on the surface of the metal plate at a spray pressure of 0.74 MPa for 120 s; in this step, the pretreatment liquid comprises the following components in parts by weight: 100 kg of water and 8 kg of polishing powder, and the pretreatment liquid is recycled after recovery; the polishing powder is an inorganic powder with an acrylic copolymer grafted on the surface;

[0058] (2) Spraying the metal sheet surface with a degreasing liquid at 35°C at a spray pressure of 0.12 MPa. After the spraying is completed, the metal sheet surface is sprayed with industrial tap water at 35°C at a spray pressure of 0.12 MPa. In this step, the degreasing liquid comprises 5 kg of anionic surfactant and 95 kg of industrial tap water, and the anionic surfactant is sodium lauryl sulfate.

[0059] (3) The surface of the metal plate is sprayed with a coating liquid at 35°C at a spraying pressure of 0.12 MPa. After the spraying, the metal plate is baked at 173°C. After baking for 5 minutes, the pre-treatment of the metal plate is completed. In this step, the components of the coating liquid include component A and component B. Component A is a mixture of 80% water-containing silica sol and lithium silicate in a weight ratio of 40:1. Component B is an 80% water-containing aluminum sol. When spraying the coating liquid on the surface of the metal plate, first use component A of the coating liquid to spray for 60 seconds, and then spray component B of the coating liquid for 60 seconds. The spraying pressure is 0.12 MPa.

[0060] As shown in Table 1, the difference between Examples 1-5 is mainly due to the different ratios of raw materials.

[0061] Table 1

[0062] sample Water / kg Grinding powder / kg Example 1 100 8 Example 2 105 9 Example 3 110 10 Example 4 115 11 Example 5 120 12

[0063] Examples 6-9

[0064] As shown in Table 2, the difference between Examples 6-9 and Example 5 is that different spraying pressures are used when spraying the pretreatment liquid.

[0065] Table 2

[0066] sample Example 5 Example 6 Example 7 Example 8 Example 9 Spray pressure / MPa 0.74 0.80 0.86 0.92 0.98

[0067] Examples 10-14

[0068] As shown in Table 3, the difference between Examples 10-14 and Example 5 is that the preparation examples of the polishing powder are different.

[0069] Table 3

[0070] sample Preparation example of grinding powder Example 5 Preparation Example 1 Example 10 Preparation Example 2 Example 11 Preparation Example 3 Example 12 Preparation Example 4 Example 13 Preparation Example 5 Example 14 Preparation Example 6

[0071] Example 15

[0072] The difference between this embodiment and embodiment 5 is that component A of the coating solution further includes tetraethyl orthosilicate, and the weight ratio of tetraethyl orthosilicate to silica sol is 1:12.

[0073] Example 16

[0074] The difference between this embodiment and embodiment 5 is that component A of the coating solution further includes sodium methyl silicate, and the weight ratio of sodium methyl silicate to silica sol is 1:12.

[0075] Example 17

[0076] The difference between this embodiment and embodiment 5 is that component A of the coating solution further includes isopropyl titanate, and the weight ratio of isopropyl titanate to silica sol is 1:12.

[0077] Comparative Example

[0078] Comparative Example 1

[0079] The pre-treatment process for metal sheet coating includes the following steps:

[0080] (1) Spray the metal sheet surface with 40°C industrial tap water at a spray pressure of 0.12 MPa for 120 seconds;

[0081] (2) Spraying the metal sheet surface with a degreasing liquid at 35°C at a spray pressure of 0.12 MPa. After the spraying is completed, the metal sheet surface is sprayed with industrial tap water at 35°C at a spray pressure of 0.12 MPa. In this step, the degreasing liquid comprises 5 kg of anionic surfactant and 95 kg of industrial tap water, and the anionic surfactant is sodium lauryl sulfate.

[0082] (3) Spray the surface of the metal plate with a coating liquid at 35°C at a spraying pressure of 0.12 MPa. After spraying, bake the metal plate at 173°C. After baking for 5 minutes, the pre-treatment of the metal plate is completed. In this step, the coating liquid is composed of 5 kg of silane coupling agent KH-570, 70 kg of industrial tap water, and 50 kg of anhydrous ethanol. The spraying time is 120 seconds and the spraying pressure is 0.12 MPa.

[0083] Comparative Example 2

[0084] The difference between this embodiment and comparative example 1 is that the spraying pressure in step (1) is 0.74 MPa.

[0085] Comparative Example 3

[0086] The difference between this comparative example and Example 5 is that the grinding powder in the pretreatment liquid is replaced with silica sand of the same weight.

[0087] Comparative Example 4

[0088] This comparative example is different from Example 5 in that sodium lauryl sulfate as a surfactant is replaced by hexadecyltrimethylammonium chloride of the same weight.

[0089] Performance testing methods

[0090] Kaolin particles and lubricating oil were mixed and stirred in a weight ratio of 1:10, and then the mixture was applied to the surface of a Q215 steel plate until the lubricating oil stopped dripping. The steel plate was then subjected to the coating pretreatment described in the above embodiments and comparative examples, and then electrostatic powder coating was applied. The electrostatic powder coating used for the coating was commercially available AkzoNobel RAL9010. The coating and curing processes were carried out in accordance with GB 15607-2020 Safety Regulations for Coating Operations - Safety of Powder Electrostatic Spraying Processes. After spraying, a sample was obtained.

[0091] A scalpel was used to create a 1 cm long and 50 μm wide scratch on the sample surface, extending to the depth of an artificial defect in the substrate. Steel plates with defective coatings were subjected to a 500-hour neutral salt spray test in accordance with GB / T 1771-2007 Paints and varnishes — Determination of resistance to neutral salt spray. After the salt spray period expired, the steel plates were removed, and any corrosion products on the surface were cleaned. The plates were then rinsed with tap water and acetone, and dried. After 24 hours, the corroded areas were pulled with 3M No. 600 tape. The maximum corrosion extension width on both sides of the scratch was measured. The results are shown in Table 4.

[0092] Table 4

[0093]

[0094]

[0095] Combining Examples 1-5 and Comparative Example 1 and Table 4, it can be seen that as the proportion of grinding powder in the pretreatment liquid of Examples 1-5 increases, the cleaning effect on the metal plate is also improved, and the corrosion expansion width measured in Examples 1-5 is smaller than that in Comparative Example 1, indicating that the pretreatment process of the present application cleans oil and dust more thoroughly, thereby enhancing the film-forming effect of the coating liquid and improving the corrosion expansion resistance of the coating.

[0096] Combining Example 3 and Comparative Example 2 with Table 4, it can be seen that increasing the flushing water pressure in step (1) has limited improvement on the flushing effect and is not enough to significantly enhance the film-forming effect of the coating liquid. Therefore, the improvement in the corrosion resistance of the coating is limited.

[0097] Combining Example 3 and Comparative Example 3 with Table 4, it can be seen that there are no groups on the surface of silica sand to adsorb dust, so it can only play a physical scouring role, resulting in limited removal effect of dust and oil stains, which is not enough to significantly enhance the film-forming effect of the coating liquid. Therefore, the improvement value of the corrosion resistance of the coating is limited.

[0098] Combining Example 3 and Comparative Example 4 with Table 4, it can be seen that when a cationic surfactant is used, the cationic surfactant is adsorbed by the acrylic copolymer that washes the surface of the powder, affecting the degreasing effect of the cationic surfactant and is insufficient to significantly enhance the film-forming effect of the coating liquid. Therefore, the improvement in the corrosion resistance of the coating is limited.

[0099] Combining Example 5, Examples 6-9 and Comparative Example 2 with Table 4, it can be seen that increasing the spray pressure has a more obvious effect on the pretreatment liquid of the present application.

[0100] From Example 5, Example 10 and Table 4, it can be seen that the silica sol increases the surface area of ​​the inorganic powder, helps to increase the density of the grafted acrylic copolymer on the surface of the inorganic powder, improves the adsorption effect between the polishing powder and the dust particles, helps to reduce the interference of dust particles on the degreasing performance of the degreasing liquid, thereby enhancing the film-forming effect of the coating liquid and improving the corrosion resistance of the coating.

[0101] As can be seen from Examples 11-14 and Table 4, the hydrolysis time of the silane coupling agent is significantly shortened with the presence of steel slag powder. This indicates that after the steel slag comes into contact with water, the dissolution of free calcium oxide in the steel slag creates an alkaline environment, which accelerates the hydrolysis of the silane coupling agent and helps shorten the production cycle of the polished powder.

[0102] It can be seen from Example 5, Example 15 and Table 4 that ethyl orthosilicate helps to hinder the diffusion of salt mist on the metal surface and improves the corrosion resistance of the coating.

[0103] It can be seen from Example 5, Example 16 and Table 4 that sodium methyl silicate helps to hinder the diffusion of salt mist on the metal surface and improves the corrosion resistance of the coating.

[0104] It can be seen from Example 5, Example 17 and Table 4 that isopropyl titanate improves the isolation effect of the coating film against salt spray and improves the corrosion resistance of the coating.

[0105] 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 non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A metal sheet coating pretreatment process, characterized in that: The following steps are involved: (1) Continuously stirring the pretreatment liquid and spraying the surface of the metal plate with the pretreatment liquid; in this step, the pretreatment liquid includes the following components in parts by weight: 100-120 parts of water and 8-12 parts of polishing powder; the polishing powder is an inorganic powder with an acrylic copolymer grafted on the surface; (2) spraying the surface of the metal plate with a degreasing liquid, and then washing the surface of the metal plate with water after the spraying is completed; in this step, the degreasing liquid includes an anionic surfactant; (3) Spraying the coating liquid onto the surface of the metal sheet, and baking the metal sheet after the spraying is completed. After the baking is completed, the pre-treatment of the metal sheet for coating is completed; The polished powder is prepared according to the following method: (1) Mixing inorganic powder, silane coupling agent, water, and ethanol, heating at 70-80°C for 60-80 minutes, and then filtering and drying to obtain silanized inorganic powder; in this step, the silane coupling agent is vinyltriethoxysilane; (2) Mix the silanized inorganic powder, acrylic acid, water, and thermal initiator, heat at 70-90°C for 40-60 minutes, and then filter and dry to obtain a polished powder.

2. The metal sheet coating pretreatment process according to claim 1, characterized in that: The pretreatment liquid includes the following components in parts by weight: 105-115 parts of water and 9-11 parts of polishing powder.

3. The metal sheet coating pretreatment process according to claim 1, characterized in that: In step (1) of the metal plate coating pretreatment process, the spraying pressure adopted when spraying the pretreatment liquid is 0.8-0.92 MPa.

4. The metal sheet coating pretreatment process according to claim 1, characterized in that: In the step (1) of preparing the polishing powder, silica sol is mixed with inorganic powder, silane coupling agent, water and ethanol.

5. The metal sheet coating pretreatment process according to claim 1, characterized in that: The inorganic powder includes at least one of silica sand and steel slag powder.

6. The metal sheet coating pretreatment process according to claim 1, characterized in that: The coating liquid includes component A and component B, wherein component A includes silica sol and lithium silicate, and component B includes aluminum sol. When spraying the coating liquid onto the surface of the metal plate, component A of the coating liquid is sprayed first, and then component B of the coating liquid is sprayed.

7. The metal sheet coating pretreatment process according to claim 6, characterized in that: Component A of the coating solution includes ethyl orthosilicate.

8. The metal sheet coating pretreatment process according to claim 6, characterized in that: Component A of the coating solution also includes sodium methyl silicate.

9. The metal sheet coating pretreatment process according to claim 6, characterized in that: Component A of the coating solution further comprises isopropyl titanate.

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