Cold-rolled steel sheet surface treating agent, application method and high-corrosion-resistance and high-cleanness carbon steel sheet

Abstract

The invention discloses a surface treating agent for a cold-rolled steel sheet. The surface treating agent comprises amino-containing organic acid, hydroxyl-containing organic amine and water, wherein the mass percentage content of the organic acid is 0.5-2%, the mass percentage content of the organic amine is 0.5-4%, and the sum of the percentage content of the organic acid and the organic amine is 2-5%. The invention further discloses an application method of the treating agent. The application method comprises the following steps: roller coating: roller coating the cold-roll steel sheet with the cold-roll steel sheet surface treating agent; and drying to form the film. The invention further discloses a high-corrosion-resistance and high-cleanness carbon steel plate which is obtained on the basis that the application method is carried out on the surface of a cold-roll steel plate. The cold-rolled steel sheet surface treating agent does not contain harmful substances; the application method is simple and convenient in process control and easy to realize. A film layer can be formed after surface treatment of the high-corrosion-resistance and high-cleanliness carbon steel plate, and good corrosion resistance can be provided in the storage, transportation and machining processes.

Description

Technical Field

[0001] This invention relates to a surface treatment agent, an application method, and a steel plate, and more particularly to a surface treatment agent for cold-rolled steel plates, an application method, and a carbon steel plate. Background Technology

[0002] Carbon steel has long been used in traditional spray-coating drum manufacturing. During the production, manufacturing, storage, and transportation of cold-rolled carbon steel sheets, a certain thickness of anti-rust oil is applied to the surface to prevent corrosion during storage and transportation. Traditional drum manufacturing processes generate wastewater, waste gas, and waste residue pollution problems during degreasing, pretreatment, and spray coating.

[0003] In recent years, with increasing environmental protection demands, the drum manufacturing industry has developed a new coating process that involves directly applying a PET film to the surface of steel drums. Compared to traditional spraying processes, this coating process offers numerous advantages. It eliminates the need for degreasing, pretreatment, spraying, and baking, saving energy and protecting the environment while significantly improving production efficiency. Furthermore, the surface coating exhibits excellent corrosion resistance, and its scratch and abrasion resistance far surpasses that of traditional sprayed coatings.

[0004] The new coating process places new demands on cold-rolled carbon steel, mainly in terms of excellent corrosion resistance, high surface cleanliness, and excellent coating adhesion performance. First, it requires a high degree of surface cleanliness for the steel plate, free from rust-preventive oil, rolling oil, etc., so that the coating process can be carried out directly after shearing into circles without the need for degreasing and oil removal for subsequent coating performance. Second, cold-rolled carbon steel itself has good corrosion resistance, ensuring that there are no rust spots or rust patches on the surface during storage, transportation, and processing in an unoiled state. At the same time, the coating has good adhesion and can have a good bond with the coating layer.

[0005] In response to industry changes, cold-rolled carbon steel used in the coated drum manufacturing industry can be used in two ways: one is to continue using steel plates coated with anti-rust oil to make drums, but alkaline degreasing and drying must be carried out before coating; the other is to use food-grade DOS oil and strengthen storage and transportation packaging to ensure that the surface is free of rust, but the DOS oil needs to be completely or partially removed by baking before coating.

[0006] In the prior art, some inventions also provide excellent corrosion resistance by preparing an alloy layer or a combination of alloy layer / coating on the surface of cold-rolled sheet.

[0007] For example, Chinese patent document CN1416478A, published on October 26, 2001, entitled "Surface-treated tin-plated steel sheet and chemical treatment liquid", discloses a surface-treated tin-plated steel sheet and chemical treatment liquid, which prepares an alloy layer on the surface of the steel sheet, providing excellent coating adhesion, corrosion resistance after painting, rust resistance and processability.

[0008] For example, Chinese patent document CN1342211A, published on March 27, 2002, entitled "Coated steel with excellent corrosion resistance, coated steel sheet and painted steel sheet and manufacturing method thereof", discloses a coated steel with excellent corrosion resistance, coated steel sheet and painted steel sheet and manufacturing method thereof. The coated steel with excellent corrosion resistance provided has a chromate coating on the coating containing Zn, Mg and Si. Summary of the Invention

[0009] One of the objectives of this invention is to provide a surface treatment agent for cold-rolled steel sheets, which can form a modified film layer on the surface of the steel sheet through a roller coating process, thereby giving the steel sheet the characteristics of strong corrosion resistance, high surface cleanliness, and good coating performance.

[0010] To achieve the above objectives, the present invention provides a surface treatment agent for cold-rolled steel sheets, comprising: an organic acid containing amino groups, an organic amine containing hydroxyl groups, and water; wherein the mass percentage of the organic acid is 0.5-2%, the mass percentage of the organic amine is 0.5-4%, and the total mass percentage of the organic acid and organic amine is 2-5%.

[0011] In this invention, the organic acid containing amino groups has a good adsorption effect on the metal matrix. At the same time, the amino group, as a hydrophobic side chain, can form a relatively dense hydrophobic film on the surface, protecting the metal matrix from corrosion by moisture or humid air in the atmospheric environment.

[0012] Furthermore, the combination of amino-containing organic acids and hydroxyl-containing organic amines in the above proportions can effectively improve the adhesion between the reactive film layer and the coating adhesive. The hydroxyl groups in the organic amines can form a large number of hydrogen bonds with the oxygen atoms in the epoxy resin components of the adhesive through electrostatic interactions. Although this non-bonded interaction does not directly determine the adhesive strength, it has a significant impact on the wettability of the adhesive and the substrate.

[0013] In this invention, when the total percentage of organic acid and organic amine is less than 2%, the resulting treatment film is too thin, significantly reducing its ability to block corrosive ions and failing to effectively inhibit the electrochemical corrosion reaction. Conversely, if the total percentage of organic acid and organic amine is greater than 5%, the resulting treatment film is too thick and will detach due to insufficient cohesion, affecting the cleanliness of the cold-rolled sheet surface and, more importantly, the adhesion of the coating. Therefore, in the surface treatment agent for cold-rolled steel sheets described in this invention, the total percentage of organic acid and organic amine can be controlled to be 2-5%.

[0014] Furthermore, the pH value of the cold-rolled steel sheet surface treatment agent described in this invention is 8 to 9.

[0015] Furthermore, in the surface treatment agent for cold-rolled steel sheets described in this invention, the organic acid includes alanine and / or glutamic acid.

[0016] Alanine and glutamic acid are adsorbent amino acids that exhibit good adsorption properties with the metal matrix. Simultaneously, the amino group, as a hydrophobic side chain, can form a relatively dense hydrophobic film on the surface, protecting the metal matrix from corrosion by moisture or humid air in the atmosphere. Furthermore, the carboxyl group in alanine can form hydrogen bonds and ionic bonds with the hydroxyl and ether groups in the adhesive, further enhancing interfacial adhesion.

[0017] Furthermore, in the surface treatment agent for cold-rolled steel sheets described in this invention, the organic amine includes diethanolamine and / or triethanolamine.

[0018] In this invention, organic amines may include diethanolamine and / or triethanolamine. Their main function is to act as corrosion inhibitors, effectively improving the corrosion resistance of cold-rolled steel sheets. The N and O elements in the polar groups of amines and nitrogen-containing compounds contain highly electronegative lone pairs of electrons, allowing the treatment agent to be firmly adsorbed onto the metal surface, hindering the diffusion of corrosive media into the metal substrate. This effectively enhances the barrier effect of the film-forming system against corrosive media ions and inhibits the electrochemical corrosion reaction. Furthermore, amine compounds also contain π bonds. When nitrogen-containing groups approach π bonds, large π bonds are formed due to conjugation, and this chemisorption greatly enhances the corrosion inhibitor's effectiveness.

[0019] Another objective of this invention is to provide a method for applying a surface treatment agent to cold-rolled steel sheets, which can produce a highly corrosion-resistant and clean carbon steel sheet with strong corrosion resistance, high surface cleanliness, and good coating performance.

[0020] To achieve the above objectives, the present invention provides a method for applying a surface treatment agent to cold-rolled steel sheets, comprising the following steps:

[0021] Roll coating: Roll coating the surface treatment agent for cold-rolled steel sheet as described above onto the cold-rolled steel sheet;

[0022] Dry to form a film.

[0023] Furthermore, in the application method described in this invention, the average surface roughness Ra of the cold-rolled steel sheet is 0.8 to 2.0 μm, and the maximum peak and valley value of the surface roughness Rz is 10 to 20 μm.

[0024] In this invention, the surface roughness Ra of the cold-rolled steel sheet is related to the post-processing performance. If the average surface roughness Ra is too small, it will affect the bonding area of ​​the physical adhesion during coating, and thus the bonding force between the substrate and the coating. If the roughness is too large, especially the maximum peak-to-trough value Rz, it will affect the smoothness of the coating appearance. Therefore, in order to ensure that the produced cold-rolled sheet has good corrosion resistance and to maximize the coating performance of the steel sheet, the average surface roughness Ra of the cold-rolled steel sheet can be controlled at 0.8 to 2.0 μm, and the maximum peak-to-trough value Rz can be controlled at 10 to 20 μm.

[0025] Furthermore, in the roller coating step of the application method described in this invention, the process parameters are controlled to satisfy at least one of the following:

[0026] The running speed of the cold-rolled steel sheet is controlled at 120–250 m / min;

[0027] The speed ratio of the coating roller to the cold-rolled sheet is 1:(1.2~1.4);

[0028] The speed ratio of the conveyor roller to the cold-rolled sheet is 1:(1~1.2);

[0029] The pressure between the conveyor roller and the coating roller is 110-120 kg.

[0030] Furthermore, in the drying and film-forming step of the application method described in this invention, the plate temperature is controlled at 60–80°C.

[0031] In the drying and film-forming step of this invention, when the plate temperature is below 60°C, it is not conducive to the conversion of the post-treatment film with good corrosion resistance, and it affects the thickness of the plate surface treatment film; when the plate temperature is above 80°C, it will lead to the oxidation of the organic chemical conversion film. Therefore, in the drying and film-forming step of this invention, the plate temperature can be controlled at 60-80°C.

[0032] Another objective of this invention is to provide a high-corrosion-resistant and high-cleanliness carbon steel plate, which has the characteristics of strong corrosion resistance, high surface cleanliness, and good coating performance.

[0033] To achieve the above objectives, the present invention provides a high-corrosion-resistant and high-cleanliness carbon steel sheet, which is obtained by applying the above-described method to the surface of a cold-rolled steel sheet.

[0034] Furthermore, in the high-corrosion-resistant and high-cleanliness carbon steel plate described in this invention, the single-sided film thickness is 10–30 mg / m². 2 between.

[0035] Compared with existing technologies, the cold-rolled steel sheet surface treatment agent, application method, and high-corrosion-resistant, high-cleanliness carbon steel sheet described in this invention have the following advantages and beneficial effects:

[0036] The high-corrosion-resistant and clean carbon steel plate described in this invention can form a film layer after surface treatment, which can provide good corrosion resistance during storage, transportation and processing.

[0037] The high-corrosion-resistant and clean carbon steel plate of the present invention has good corrosion resistance, can ensure oil-free storage and transportation, can provide a high-cleanliness, low-carbon and environmentally friendly surface, and can directly enter the coating process without degreasing and cleaning.

[0038] The corrosion-resistant and high-cleanliness carbon steel plate described in this invention has good adhesion to the coating layer. The hydroxyl and carboxyl groups in the treated film can form a large number of hydrogen bonds and ionic bonds with the PET coating adhesive, which can ensure the bonding strength of the coating layer.

[0039] The surface treatment agent and application method of the cold-rolled steel sheet described in this invention are green and environmentally friendly, and do not contain harmful substances; the post-treatment roller coating process is simple to control and easy to implement. Detailed Implementation

[0040] The following will further explain and illustrate the surface treatment agent for cold-rolled steel sheets, the application method, and the high-corrosion-resistant and clean carbon steel sheets described in this invention with reference to specific embodiments. However, this explanation and illustration do not constitute an undue limitation on the technical solution of this invention.

[0041] Examples 1-6 and Comparative Examples 1-4

[0042] The high-corrosion-resistant and high-cleanliness carbon steel plates described in Examples 1-8 of this invention are all prepared using the following steps:

[0043] (1) The base steel is SPC with a specification of 0.8×1340mm. Then, it is uncoiled, straightened, welded, pickled, cold rolled and leveled. The average surface roughness Ra of the obtained cold-rolled plate is 0.8~2.0μm, and the maximum peak and valley value of surface roughness Rz is 10~20μm.

[0044] (2) Roll coating: The surface treatment agent for cold-rolled steel is uniformly coated on the cold-rolled strip. The surface treatment agent contains 0.5-2% by mass of organic acid containing amino groups, 0.5-4% by mass of organic amine containing hydroxyl groups, and a total percentage of 2-5% of organic acid and organic amine. The pH value is 8-9.

[0045] In some embodiments, the coating process parameters can be controlled as follows: the running speed of the cold-rolled steel sheet can be controlled to be 120-250 m / min; the running speed ratio of the coating roller to the cold-rolled sheet can be controlled to be 1:(1.2-1.4); the speed ratio of the strip roller to the cold-rolled sheet can be controlled to be 1:(1-1.2); and the pressure between the strip roller and the coating roller can be controlled to be 110-120 kg.

[0046] (3) Drying and film formation: Hot air is used to dry the cold-rolled sheet to ensure that the surface temperature reaches 60-80℃;

[0047] (4) Cool and roll up directly without oiling.

[0048] It should be noted that the comparative steel plates in Comparative Examples 3-4 of this invention did not use the surface treatment agent for cold-rolled steel plates described in this invention. Instead, rust-preventive oil was directly applied to the cold-rolled steel plates. The rust-preventive oil application rates for Comparative Examples 3 and 4 were 100 mg / m², respectively. 2 / face and 50mg / m 2 / noodle.

[0049] Table 1 lists the component ratios of the surface treatment agents in Examples 1-6 and Comparative Examples 1-2 of the present invention.

[0050] Table 1.

[0051]

[0052]

[0053] Table 2 lists the specific process parameters of the high corrosion resistance and cleanliness carbon steel plates of Examples 1-6 of the present invention and the comparative steel plates of Comparative Examples 1-4.

[0054] Table 2.

[0055]

[0056] The performance of the corrosion-resistant and high-cleanliness carbon steel plates of Examples 1-6 and the comparative steel plates of Examples 1-4 was evaluated, and the performance evaluation results are listed in Table 3. The evaluation methods for each performance item are as follows:

[0057] (1) Corrosion resistance: A laminated damp heat test was conducted. After modification treatment, the sample and the comparative sample were subjected to the laminated damp heat test simultaneously. The test conditions were 49℃, 98%RH, with a pressure of 5kg applied to both laminates, and the test was conducted for 240h. The surface corrosion was then observed.

[0058] When the rust area is less than 5%, it is rated as excellent;

[0059] When the rust area is 5-10%, it is rated as good;

[0060] When the rusted area is 10-50% (excluding the endpoint value), it is rated as average;

[0061] When the rusted area is ≥50%, it is rated as poor.

[0062] (2) Surface Cleanliness Performance: The surface cleanliness of the sample was tested using the surface tension method. The cleanliness of the steel plate surface was evaluated by measuring the contact angle of water on the metal surface.

[0063] When the contact angle is <10°, it is rated as excellent;

[0064] When the contact angle is between 10° and 30°, it is rated as good;

[0065] When the contact angle is between 30° and 90° (excluding the endpoint values), it is rated as average.

[0066] When the contact angle is ≥90°, it is rated as poor.

[0067] (3) Coating adhesion performance: The coating adhesion performance of the steel plates was evaluated using a cross-cut method. After coating the steel plates in the examples and comparative examples using the hot-melt method, parallel lines were drawn at equal intervals of 1 mm to form a 10*10 grid. Then, 3M-610 tape was adhered to the grid and peeled off at the same angle. The number of grids that were peeled off was counted.

[0068] When the number of squares that are glued off is less than 5, it is rated as excellent;

[0069] When 5 to 10 pigeons are successfully caught, it is rated as good.

[0070] When 10 to 20 squares are glued off (excluding endpoint values), it is rated as average.

[0071] When the number of squares that have been glued off is ≥20, the rating is poor.

[0072] (4) Coating Appearance: The surface roughness (Rpc) of the coating was used to evaluate the appearance quality of the steel plate coating. Three conditions were set for Rpc evaluation: reference type, height, and width. The reference type and height were used together, with a height above the average value and a height of 0. That is, the number of peak values ​​per inch of length centered on the centerline was defined as Rpc, where:

[0073] When Rpc < 30, it is rated as excellent;

[0074] When Rpc is between 30 and 50, it is rated as good;

[0075] When Rpc is between 50 and 100 (excluding endpoint values), it is rated as average.

[0076] When Rpc≥100, it is rated as poor.

[0077] Table 3 lists the evaluation results of the high corrosion resistance and cleanliness carbon steel plates of Examples 1-6 of the present invention and the comparative steel plates of Comparative Examples 1-4.

[0078] Table 3.

[0079]

[0080]

[0081] In Table 3, “◎” indicates an excellent rating, “○” indicates a good rating, “Δ” indicates a fair rating, and “×” indicates a poor rating.

[0082] As can be seen from Table 3 above, the surface film weight of the high-corrosion-resistant and high-cleanliness carbon steel plates prepared using the cold-rolled steel plate surface treatment agent and application method described in this invention is all between 10 and 30 mg / m³. 2 Furthermore, as can be seen from Table 3 above, Examples 1 through 6 all exhibited good performance in the aforementioned evaluation items.

[0083] As shown in Table 3, Examples 1 to 6 all exhibited good performance in the above evaluation items, especially the samples in Examples 4 and 5, which showed excellent comprehensive performance in terms of corrosion resistance, surface cleanliness, and film coating. Example 3 was a laboratory bar coating process simulating roller coating, and as shown in Table 3, its coating effect and performance were both good.

[0084] Compared to Comparative Examples 1-2, the corrosion resistance of Examples 1-6 remained at a level comparable to that of the oil-coated comparative examples. Examples 3 and 5-6, with higher treatment solution concentrations, and Comparative Example 2 exhibited excellent corrosion resistance, comparable to that of a single-sided rust-preventive oil coating of 100 mg / m². 2 The corrosion resistance of Examples 1-2, which have lower treatment solution concentrations but higher drying plate temperatures or higher treatment solution concentrations but lower drying plate temperatures, is comparable to that of a single-sided rust-preventive oil coating of 50 mg / m². 2 The treatment agent concentration in Comparative Example 1 was below the lower limit of the control range, and the film thickness was below the lower limit, which affected the corrosion resistance.

[0085] Compared to Comparative Examples 1-2, the surface cleanliness of Examples 1-6 was significantly improved. The rust-preventive oil on the sample surface isolates the substrate from the external atmospheric environment, providing good corrosion protection, but it also affects the surface cleanliness of the steel plate, thus affecting the adhesion of the surface coating. Examples 1-6, due to their oil-free, highly clean surface, exhibited good adhesion to the coating layer. Furthermore, the high hydroxyl content in the treated layer effectively generates hydrogen bonds with the C==O in the adhesive or organic film layer during the coating process, increasing the coating adhesion.

[0086] Compared to Comparative Examples 1-2, the coating adhesion performance of Examples 1-6 was significantly improved. When the concentration and drying temperature were within the relevant range, the film thickness could be kept within a suitable range, which could further ensure the coating adhesion. In Example 1, when the concentration of the treatment solution was low and the drying plate temperature was low, the film thickness was at the lower limit of the control range. Due to the small number of reactive hydroxyl groups in the treated film, the adhesion between the coating and the substrate was generally weak. In Comparative Example 2, when the concentration of the treatment solution was high and the drying plate temperature was high, the film thickness exceeded the upper limit of the control range. The reduced cohesion after the treatment of the film would lead to cohesion failure and affect the coating adhesion.

[0087] Therefore, the high-cleanliness steel plate for the coated drum of the present invention has the characteristics of strong corrosion resistance, high surface cleanliness, and good coating performance. The modified film layer can be formed on the surface of the steel plate through the roller coating process. The modified film layer has good corrosion resistance and ensures that no rust will occur during long-term storage and transportation, replacing the traditional coating of anti-rust oil on the steel plate surface. At the same time, the steel plate has a high-cleanliness surface, and the coating process of oil drums can be carried out without washing, which is economical and environmentally friendly, and has good coating adhesion.

[0088] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0089] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A surface treatment agent for cold-rolled steel sheets, characterized in that, It includes: The mixture comprises an organic acid containing an amino group, an organic amine containing a hydroxyl group, and water; wherein the organic acid has a mass percentage of 0.5-2%, and the organic amine has a mass percentage of 0.5-4%; and the total percentage of the organic acid and organic amine is 2-5%.

2. The surface treatment agent for cold-rolled steel sheets as described in claim 1, characterized in that, The pH value of the surface treatment agent is 8 to 9.

3. The surface treatment agent for cold-rolled steel sheets as described in claim 1, characterized in that, The organic acids include alanine and / or glutamic acid.

4. The surface treatment agent for cold-rolled steel sheets as described in claim 1, characterized in that, The organic amines include diethanolamine and / or triethanolamine.

5. A method for applying a surface treatment agent to cold-rolled steel sheets, characterized in that, Including the following steps: Roll coating: Roll coating a cold-rolled steel sheet with the surface treatment agent as described in any one of claims 1-4; Dry to form a film.

6. The application method as described in claim 5, characterized in that, The average surface roughness Ra of the cold-rolled steel sheet is 0.8 to 2.0 μm, and the maximum peak and valley values ​​of surface roughness Rz are 10 to 20 μm.

7. The application method as described in claim 5, characterized in that, In the roller coating step, the process parameters are controlled to meet at least one of the following conditions: The running speed of the cold-rolled steel sheet is controlled at 120–250 m / min; The speed ratio of the coating roller to the cold-rolled sheet is 1:(1.2~1.4); The speed ratio of the conveyor roller to the cold-rolled sheet is 1:(1~1.2); The pressure between the conveyor roller and the coating roller is 110-120 kg.

8. The application method as described in claim 5, characterized in that, During the drying and film-forming step, the plate temperature is controlled at 60–80°C.

9. A high-corrosion-resistant and high-cleanliness carbon steel plate, characterized in that, It is obtained by applying the method described in any one of claims 5-8 to the surface of a cold-rolled steel sheet.

10. The high-corrosion-resistant and high-cleanliness carbon steel plate as described in claim 9, characterized in that, Its single-sided film thickness is 10-30 mg / m² 2 between.

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