Water-containing alkaline composition for surface pretreatment of metal coil, and use thereof

Abstract

The present invention relates to a water-containing alkaline composition for the surface pretreatment of a metal coil, and the use thereof. Provided in the present invention is a water-containing alkaline composition for the surface pretreatment of a metal coil, which composition comprises 80-400 ppm of ferric ions. The value of the free alkalinity of the water-containing alkaline composition is not lower than 20 (10 mL); and the sum of the concentrations of the elements cobalt, nickel, chromium and phosphorus in the water-containing alkaline composition does not exceed 30 ppm. The water-containing alkaline composition of the present invention has low raw material costs, is more environmentally friendly and applicable to a wider range of substrates, exhibits high efficiency in a surface pretreatment of a metal coil, enables a compact and uniform oxide film to be obtained within a very short treatment time, and is beneficial to the preparation of a pre-coated metal coil having better paint adhesion and corrosion resistance.

Description

A water-containing alkaline composition for surface pretreatment of metal coils and its uses Technical Field

[0001] This invention relates to the field of metal surface treatment, and more specifically to an aqueous alkaline composition for the pretreatment of metal coil surfaces and its uses. Background Technology

[0002] Metal coils are strip-shaped materials made of metal, including coils made by rolling steel, galvanized sheet, or aluminum. The width of metal coil strips is generally about 2000 mm, and the thickness is generally 0.2–2 mm. They are widely used in construction, home appliances, decoration, automobiles, and many other industries. Pre-coated metal coils refer to products made by using metal coils (such as galvanized sheet, aluminized sheet, high-aluminum alloy sheet, stainless steel sheet, etc.) as the base material, and then continuously coating or laminating various organic coatings or plastic films onto the surface after metal surface pretreatment. Because this type of coil is coated at the metallurgical plant, it can be directly used for subsequent processing; therefore, it is also called pre-coated coil, coated steel sheet, pre-coated steel sheet, or color-coated coil.

[0003] Pre-coated metal coils are typically lightweight, aesthetically pleasing, environmentally friendly, and easy to process and shape. Furthermore, because the coating process takes place on the metal coil production line, rather than during the production of individual parts or bodies, costs are significantly reduced.

[0004] However, because pre-coated metal coils are packaged in rolls, these coils require high flexibility and durability in both the substrate and the coating. The quality of the surface pretreatment of pre-coated metal coils directly affects the coating effect. Currently, the most commonly used surface pretreatment methods for metal coils are based on surface treatment agents containing heavy metals such as chromium (VI) compounds, cobalt, and / or nickel, or phosphorus-containing agents. For example, hexavalent chromate passivation solutions are used to form a chemical passivation film on the surface of the metal coil to enhance its corrosion resistance.

[0005] However, considering the toxicological and ecological risks associated with such processes, as well as potential legal restrictions—for example, the widespread use of chromium and nickel has led to environmental and public health concerns, and the use of phosphates can cause eutrophication—there is an urgent need to find more environmentally friendly alternatives. These alternatives should meet the performance requirements of metal coils while exhibiting better environmental friendliness. Patent Document 1 provides a substrate treatment composition for coated steel sheets, comprising an organosilicon compound, a hexafluorometallic acid, a urethane resin with cationic groups, a vanadium compound, and an aqueous medium, providing a substrate treatment layer with good resistance to under-eave corrosion. Patent Document 2 discloses a chromium-free pretreatment liquid for galvanized sheets, which is obtained by mixing specific organosilicones, cerium nitrate, sodium molybdate, hydrogen peroxide, a complexing agent, an inorganic acid, and water. This passivation treatment is performed by chemically degreasing, rinsing, and washing the surface of the galvanized sheet with a degreasing solution. Patent Document 3 discloses an organic-inorganic composite passivation system composed of aqueous polyurethane and fluorotitanic acid. While these chromium-free passivation systems can improve the corrosion resistance of the substrate to some extent, they still lag behind chromates. Furthermore, the currently common process involves directly passivating the metal coil substrate after degreasing. For some substrates, especially galvanized sheets, the bonding strength between the passivation film and the paint is not ideal when using architectural coatings.

[0006] Furthermore, the surface pretreatment and coating processes for metal coils are carried out on continuous production lines. Although some research has been conducted on the surface pretreatment of traditional sheet metal, the pretreatment and coating rates for metal coils are much higher than those for sheet metal, posing a greater challenge to improving the quality of metal coil surface pretreatment. Specifically, the typical operating speed of metal coils on continuous production lines is 50 to 150 meters per minute, which is far higher than the operating speed of pretreated parts in traditional component or vehicle body production processes (e.g., 3 meters per minute). Existing surface pretreatment processes for sheet metal are difficult to directly apply to metal coils to meet their specific surface pretreatment requirements due to their long processing times. To further improve production efficiency, some manufacturers have put forward new requirements for the operating speed of metal coils. How to achieve ideal surface pretreatment results in a shorter processing time has become a major challenge for those skilled in the art.

[0007] Patent Document 1: CN105143513A

[0008] Patent Document 2: CN102070928A

[0009] Patent Document 3: CN101048476A Summary of the Invention

[0010] The purpose of this invention is to solve the above-mentioned problems of the prior art and provide a new metal coil surface pretreatment agent that is low in cost, more environmentally friendly, has a wide range of substrate applications, and has high processing efficiency. It can obtain a dense and uniform oxide film in a short processing time, which helps to prepare pre-coated metal coils with better paint adhesion and corrosion resistance.

[0011] To achieve this objective, the present invention provides the following technical solution:

[0012] An aqueous alkaline composition for surface pretreatment of metal coils, wherein,

[0013] The aqueous alkaline composition contains 80 to 400 ppm of ferric ions, the free alkalinity of the aqueous alkaline composition is not less than 20 (10 mL) points, and the sum of the concentrations of cobalt, nickel, chromium and phosphorus in the aqueous alkaline composition does not exceed 30 ppm.

[0014] Furthermore, the present invention also provides a method for surface pretreatment of metal coils using the aqueous alkaline composition of the present invention, and the metal coils or components thereof obtained therefrom.

[0015] Furthermore, the present invention also provides a pre-coated metal coil comprising an oxide film obtained by treating a metal coil substrate with the aqueous alkaline composition of the present invention.

[0016] Surprisingly, the formulation of this invention, though simple in composition, is environmentally friendly, highly efficient, and fast in film formation. Using this formulation, a dense oxide film can be rapidly generated on the surface of the metal substrate, significantly increasing the specific surface area of ​​the metal substrate and resulting in a more uniform passivation distribution. Combined with chromium-free passivation treatment, it effectively improves the paint adhesion and corrosion resistance of pre-coated metal coils. After undergoing the alkaline oxidation and chromium-free passivation treatment of this invention, the metal coil substrate can achieve the same or better passivation effect as chromate, especially in terms of adhesion performance. In some preferred embodiments of this invention, the pre-coated metal coil obtained by this invention can achieve a T-bend test result of ≤1T (GB / T 13448-2006), a neutral salt spray test (ASTM B117-97) of ≤4mm after 1008h scribing salt spray test, a ≤20mm (preferably ≤14mm) after 1008h tangential salt spray test, and a reverse impact test result of ≥9J (GB / T13448-2006).

[0017] It should be noted that the above description does not disclose all embodiments of the present invention or all advantages of the present invention. Attached Figure Description

[0018] Figure 1 shows a comparison of the appearance SEM results of the board surface treated with the aqueous alkaline composition of the present invention and the untreated board surface (Figure 1(a) is the untreated board surface, Figure 1(b) is the board surface treated with the aqueous alkaline composition prepared in Example 1 of the present invention). Detailed Implementation

[0019] The following describes embodiments of the present invention, but the invention is not limited thereto. The present invention is not limited to the configurations described below; various modifications can be made within the scope of the claims. Embodiments and examples obtained by appropriately combining the disclosed technical means in different embodiments and examples are also included within the technical scope of the present invention. Furthermore, all documents described in this specification are incorporated herein by reference.

[0020] Unless otherwise defined, the technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] In the context of describing this specification (especially in the context of the appended claims), the terms “a,” “an,” and “the,” and similar language will be interpreted to cover both the singular and plural, unless otherwise indicated herein or clearly contradicted by the context.

[0022] In this specification, the range of values ​​referred to as “value A ~ value B” or “value A - value B” refers to the range that includes the endpoint values ​​A and B and all ranges between the endpoints.

[0023] In this specification, the word "may" has both the meaning of performing a certain process and the meaning of not performing a certain process. In this specification, "optional" or "optionally" means that the event or situation described below may or may not occur, and the description includes both the case where the event occurs and the case where the event does not occur.

[0024] In this specification, the terms "some specific / preferred embodiments," "other specific / preferred embodiments," "some specific / preferred technical solutions," and "other specific / preferred technical solutions" refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to the described embodiment that are included in at least one of the embodiments described herein, and may or may not exist in other embodiments. Furthermore, it should be understood that these elements can be combined in any suitable manner in various embodiments.

[0025] In this specification, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that comprises a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0026] In this specification, expressions such as "containing A, B and / or C" or "including A, B and / or C" mean containing A or B or C, or containing any two of A and C, or containing all three of A, B and C.

[0027] In this specification, the term "organic" refers to a carbon-containing compound.

[0028] In this specification, the term "inorganic" refers to compounds that do not contain carbon atoms except for carbonates and oxides of carbon.

[0029] In this specification, phrases such as “does not contain” or “does not include” are used. These phrases are not intended to exclude the presence of trace amounts of related compounds or chemical structures that may be present but were not intentionally used, such as the presence of environmental pollutants.

[0030] In this specification, the term "paint" refers to a colored film-forming material capable of providing a coating on a substrate. Paints include any of primers, intermediate coats, topcoats, dyes, and other coatings that can generally have various functions (e.g., protective, insulating, reflective, or decorative coatings), and include liquid coating compositions and powder coating compositions.

[0031] Aqueous alkaline composition

[0032] The present invention provides an aqueous alkaline composition for surface pretreatment of metal coils, comprising 80 to 400 ppm of ferric ions, with a free alkalinity of not less than 20 (10 mL) points, and the sum of the concentrations of cobalt, nickel, chromium and phosphorus in the aqueous alkaline composition not exceeding 30 ppm.

[0033] In some specific embodiments of the present invention, "alkaline" refers to strong alkalinity, meaning the composition has a pH in the range of 13.0-14.0, preferably greater than 13.0, and more preferably between 13.5 and 13.9. The inventors have discovered that when the pH is <13.0, it is difficult to form a dense iron-containing alloy layer on the substrate surface when the substrate surface comes into contact with the aqueous alkaline composition. The pH described in this invention is determined by potentiometry using a calibrated glass electrode.

[0034] In some preferred embodiments of the present invention, the aqueous alkaline composition of the present invention comprises 100-300 ppm of ferric ions, more preferably 120-200 ppm of ferric ions. By controlling the content of ferric ions in the composition, the present invention helps to form a uniform and dense iron-containing composite oxide film on the surface of metal coils. This composite oxide film has strong adhesion to the substrate, resulting in high bonding strength between the subsequent passivation layer, paint layer, and substrate. If the ferric ion content is too high, it can easily lead to an excessively thick composite oxide film, affecting paint adhesion. Furthermore, a high proportion of complexing agent is also detrimental to subsequent passivation. If the ferric ion content is too low, it will result in insufficient film density, similarly affecting paint adhesion and corrosion resistance.

[0035] In some specific embodiments of the present invention, the ferric ions are provided by water-soluble ferric salts. Preferably, the water-soluble ferric salts include one or more of ferric nitrate, ferric sulfate, ferric chloride, ferric acetate, ferric acetate, and ferric citrate. More preferably, the ferric ions are provided by ferric nitrate (including its hydrate), because nitrate ions have no negative impact on corrosion prevention.

[0036] In industry, free alkalinity and total alkalinity, rather than pH, are typically used to characterize treatment solutions. Controlling free alkalinity is crucial in this invention. Free alkalinity is determined by titrating 10 ml of the treatment solution with a 0.1N acid, such as hydrochloric acid or sulfuric acid, to a pH of 8.5. The volume of acid solution consumed (in ml) indicates the free alkalinity point. Total alkalinity is determined using the same method, by titrating 10 ml of the treatment solution with a 0.1N acid to a pH of 4.0. The inventors have found that when the free alkalinity is less than 20 points, the aqueous alkaline composition cannot sufficiently etch the metal coil substrate, preventing iron from reacting quickly with the substrate surface, affecting the formation of the composite oxide film, and ultimately impacting the paint adhesion and corrosion resistance of the pre-coated metal coil. Therefore, the free alkalinity of the aqueous alkaline composition of this invention needs to be controlled at no less than 20 points, preferably 25 to 60 points, and more preferably 30 to 50 points. In some embodiments of the present invention, the total alkalinity is not less than 25 points, preferably the total alkalinity / free alkalinity ratio is less than 2, and more preferably the total alkalinity / free alkalinity ratio is less than 1.5.

[0037] A significant advantage of this invention is that, while ensuring the effectiveness of pretreatment, it completely avoids the intentional addition of toxic heavy metal ions and phosphate ions used in conventional alkaline compositions for oxidizing metal surfaces. Therefore, the aqueous alkaline composition according to the invention preferably does not contain heavy metals selected from cobalt, nickel, chromium, or phosphorus. However, considering the operation of pretreatment production lines, the presence of small amounts of these heavy metals or phosphorus in the aqueous alkaline composition of the invention cannot be completely avoided. For example, nickel is a common alloying element in steel, and in the case of treatment with the aqueous alkaline composition of the invention, it can enter the aqueous alkaline composition of the invention through partial dissolution of the natural oxide layer, or from impurities and unavoidable pollution from the environment and municipal water sources. Therefore, the aqueous alkaline composition according to the invention contains a total concentration of no more than 30 ppm of cobalt, nickel, chromium, and phosphorus, preferably less than 20 ppm, and more preferably no more than 10 ppm. In some preferred embodiments of the present invention, magnesium and manganese are not intentionally added to the aqueous alkaline composition. Also, considering the substrate, preferably, the sum of the concentrations of magnesium and manganese in the aqueous alkaline composition of the present invention does not exceed 20 ppm; more preferably, the sum of the concentrations of cobalt, nickel, chromium, magnesium, manganese, and phosphorus in the aqueous alkaline composition of the present invention does not exceed 50 ppm. The sum of the concentrations of these elements is so small that the presence of these trace elements does not affect the performance of the aqueous alkaline composition of the present invention and does not cause a corresponding environmental burden.

[0038] In some preferred embodiments of the present invention, to enhance the oxidation performance of the system and promote the reaction of ferric ions on the substrate surface to form a film, the aqueous alkaline composition of the present invention includes molybdate ions. Compared with other metal ions such as magnesium ions, the molybdate ions of the present invention have strong oxidizing and chemical activity, and can better improve the film-forming rate of ferric ions. Molybdate ions can form polymolybdate ions depending on the concentration and pH. In the present invention, molybdate (MoO4) is used to form polymolybdate ions. 2- ) and polymolybdate (e.g., Mo8O) that may exist under certain conditions. 26 4- ), protonated molybdate (HMoO4) 1-These are collectively referred to as molybdate ions. Preferably, the molybdate ions are provided by a water-soluble molybdenum compound; more preferably, the water-soluble molybdenum compound includes one or more of sodium molybdate, ammonium molybdate, potassium molybdate, zinc molybdate, and calcium molybdate. In some specific embodiments of the present invention, the water-soluble molybdenum compound is selected from one or more of sodium molybdate, ammonium molybdate, and potassium molybdate. In some preferred embodiments of the present invention, the concentration of molybdenum in the aqueous alkaline composition of the present invention is not less than 10 ppm, preferably, the concentration of molybdenum is at least 50 ppm, more preferably, at least 100 ppm, and in some cases, the amount present may not exceed 800 ppm based on the total weight of the alkaline composition, for example, not more than 700 ppm.

[0039] In some preferred embodiments of the present invention, to stabilize the system, the aqueous alkaline composition of the present invention further includes a complexing agent. Preferably, the complexing agent includes one or more of aminocarboxylic acid esters or salts, hydroxycarboxylic acid salts, and carboxylic acid esters or salts. For environmental reasons, the present invention preferably does not use complexing agents containing phosphate or phosphonate groups. More preferably, the complexing agent includes one or more of tartrate esters or salts, citrate esters or salts, gluconate esters or salts, glucohepanoate esters or salts, methylaminoacetic acid esters or salts, ethylenediaminetetraacetic acid esters or salts, and hypozoxytriacetic acid esters or salts. In some specific embodiments of the present invention, the effective content of the complexing agent is not less than 1.0 wt.%, preferably not less than 2.0 wt.%, calculated based on the total mass of the aqueous alkaline composition. Considering that commercially available complexing agents are in solution form, the effective content of the complexing agent is obtained by multiplying its solution weight by its mass concentration. Preferably, the preferred content of the aqueous alkaline composition according to the present invention is such that the molar ratio of the complexing agent to ferric ions is greater than 1.5:1, preferably greater than 2:1. Excess complexing agent can inhibit the precipitation of insoluble iron hydroxides.

[0040] To obtain the aqueous alkaline composition of the present invention, an inorganic base needs to be added to the composition to ensure sufficient free alkalinity. There are no specific limitations on the type of inorganic base, as long as it can provide a hydroxide ion source for the aqueous alkaline composition. For example, the inorganic base component can be sodium hydroxide, potassium hydroxide, and similar compounds or combinations thereof. In some specific embodiments of the present invention, the amount of the inorganic base present in the aqueous alkaline composition is sufficient to adjust the free alkalinity of the aqueous alkaline composition to not less than 20. In other specific embodiments of the present invention, the amount of the inorganic base present in the aqueous alkaline composition is sufficient to adjust the pH of the aqueous alkaline composition to at least 13, preferably at least 13.2, and more preferably at least 13.5.

[0041] In some preferred embodiments of the present invention, the aqueous alkaline composition of the present invention may comprise an aqueous medium and optionally other materials, such as commonly used additives. Water with a conductivity of less than 30 μS / cm is preferably used in the present invention. In this aqueous medium, a water-dispersible organic solvent may be present, such as an alcohol having up to about 8 carbon atoms, such as methanol, isopropanol, etc.; or a glycol ether, such as a monoalkyl ether of ethylene glycol, diethylene glycol, or propylene glycol, etc. When present, the water-dispersible organic solvent is typically used in an amount of up to about 2% by volume, based on the total volume of the aqueous medium. Optional commonly used additives include defoamers, surfactants, oxidants, other corrosion inhibitors, etc., provided that the addition of the above additives does not affect the performance of the aqueous alkaline composition of the present invention and does not cause a corresponding environmental burden. To enhance the cleaning ability of the metal coil substrate surface to be treated, the aqueous alkaline composition according to the invention may additionally contain a nonionic surfactant, preferably selected from one or more ethoxylated and / or propoxylated C10 to C18 aliphatic alcohols having at least two but no more than 14 alkoxy groups (particularly ethoxy and / or propoxy), wherein the aliphatic alcohol may be partially end-capped by alkyl, particularly preferably methyl, ethyl, propyl, or butyl residues. For sufficient cleaning and activation of the metal coil substrate surface, the concentration of the nonionic surfactant in the aqueous alkaline composition according to the invention is preferably at least 10 ppm, preferably at least 120 ppm.

[0042] Unexpectedly, it was found that by controlling the content of ferric ions and free alkalinity, and in conjunction with the pretreatment method of this invention, the amount of metals and other additives used can be reduced while achieving good surface pretreatment results. In some preferred embodiments of this invention, the aqueous alkaline composition of this invention is composed only of a water-soluble ferric salt, a water-soluble molybdenum compound, a complexing agent, an inorganic alkali, and water. Specifically, the aqueous alkaline composition of this invention includes:

[0043] (a) 80–400 ppm of ferric ions;

[0044] (b) Molybdenum content of not less than 10 ppm;

[0045] (c) Based on the total mass of the aqueous alkaline composition, at least 1.0 wt% of a complexing agent;

[0046] (d) The sum of the concentrations of cobalt, nickel, chromium and phosphorus does not exceed 30 ppm; preferably, the sum of the concentrations of cobalt, nickel, chromium, magnesium, manganese and phosphorus does not exceed 50 ppm.

[0047] (e) The equivalent counterion of components a), b) and d);

[0048] (f) The residue is water;

[0049] The free alkalinity of the aqueous alkaline composition is not less than 20 (10 mL), and preferably, the pH value of the aqueous alkaline composition is not less than 13.

[0050] In some preferred embodiments of the present invention, the aqueous alkaline composition of the present invention is composed solely of a water-soluble trivalent ferric salt, a water-soluble molybdenum compound, a complexing agent, a nonionic surfactant, an inorganic base, and water. Specifically, the aqueous alkaline composition of the present invention comprises:

[0051] (a) 80–400 ppm of ferric ions;

[0052] (b) Molybdenum content of not less than 10 ppm;

[0053] (c) Based on the total mass of the aqueous alkaline composition, at least 1.0 wt% of a complexing agent;

[0054] (d) Nonionic surfactants of not less than 10 ppm;

[0055] (e) The sum of the concentrations of cobalt, nickel, chromium and phosphorus does not exceed 30 ppm; preferably, the sum of the concentrations of cobalt, nickel, chromium, magnesium, manganese and phosphorus does not exceed 50 ppm.

[0056] (f) is the equivalent counterion of components a), b) and e);

[0057] (g) The residue is water;

[0058] The free alkalinity of the aqueous alkaline composition is not less than 20 (10 mL), and preferably, the pH value of the aqueous alkaline composition is not less than 13.

[0059] The preferred types and amounts of each component are described above. The aqueous alkaline composition of the present invention has significant advantages in raw material cost, is environmentally friendly, and has high efficiency in surface pretreatment of metal coils. It can be used for surface pretreatment of various metal coil substrates (such as hot-dip galvanized HDG, aluminum-magnesium-zinc ZM, aluminum-zinc alloy AZ, and aluminum-magnesium-zinc AM), and is suitable for large-scale industrial applications.

[0060] Concentrate

[0061] In principle, the aqueous alkaline composition of the present invention can be prepared in situ by dissolving individual components in water at the desired concentration. However, in practice, it is common practice to manufacture a concentrate and transport it to a treatment plant, where it can be diluted with water to prepare a ready-to-use treatment tank solution. Therefore, the present invention also provides a concentrate from which the aqueous alkaline composition of the present invention can be obtained by diluting with water and optionally adjusting the pH with a suitable acid or base. In some specific embodiments of the present invention, the concentrated acid is diluted with water to a concentration of 4.0 wt.% to 15.0 wt.% (tank concentration) to obtain the aqueous alkaline composition of the present invention.

[0062] In some specific embodiments of the present invention, in producing these concentrates, a water-soluble molybdenum compound is first dissolved, followed by the sequential addition of a complexing agent, a water-soluble ferric salt, and optionally a nonionic surfactant, and the mixture is stirred until completely dissolved. Finally, an inorganic base (e.g., sodium hydroxide solution) is added to adjust the alkalinity, and the concentrate is obtained by stirring. By diluting with water and optionally adjusting the pH with a suitable acid or base, the aqueous alkaline composition of the present invention can be obtained.

[0063] Methods for surface pretreatment of metal coils

[0064] This invention also provides a method for pretreating the surface of metal coils, wherein the method includes an alkaline oxidation step and a chromium-free passivation step, wherein the alkaline oxidation step uses an aqueous alkaline composition as described in this invention to contact the metal coil substrate for 3 to 15 seconds. The method for pretreating the surface of metal coils of this invention can achieve excellent surface pretreating results in a shorter processing time.

[0065] The "alkaline oxidation" of this invention refers to the formation of an oxide film on the surface of a metal coil under alkaline conditions after treatment with the aqueous alkaline composition of this invention. The processing technology of this invention is designed for processing continuous metal coils or strips. The aqueous alkaline composition of this invention has high surface pretreatment efficiency, thus meeting the requirements of high line speeds and requiring a short contact treatment time. Preferably, the contact treatment time is 4 to 10 seconds, more preferably 5 to 8 seconds. Examples of contact treatments in this invention include immersion treatment, spray treatment (also called spraying treatment), and coating, with immersion treatment being the preferred method. The specific immersion time depends on the line speed and the length of the treatment zone.

[0066] In a preferred embodiment of the present invention, the immersion temperature of the alkaline oxidation step is 40°C to 70°C, preferably 45°C to 65°C, and more preferably 50°C to 60°C. Temperature affects the activation energy of the reaction; higher temperatures result in faster reaction rates and shorter film formation times, but excessively high temperatures can lead to a decrease in film quality. After the immersion treatment of the present invention, rinsing with pure water is preferred.

[0067] The metal coil substrate of this invention requires chromium-free passivation after undergoing an alkaline oxidation step. The alkaline oxidation and chromium-free passivation of this invention exhibit excellent compatibility and synergistic effects. Specifically, after treatment with the aqueous alkaline composition of this invention, the metal coil substrate can form a uniform and dense oxide film, effectively increasing the specific surface area of ​​the metal coil substrate. This helps the passivation film to adhere evenly and firmly to the surface of the metal coil substrate, resulting in good paint adhesion and corrosion resistance in the final pre-coated metal coil product. In some preferred embodiments of this invention, the chromium-free passivating agent used is an acidic, titanium-containing aqueous chromium-free composition. Preferably, based on the amount of titanium, the chromium-free passivating agent of this invention contains at least 10 ppm of a titanium-containing water-soluble inorganic compound, preferably selected from water-soluble inorganic compounds that release fluoride ions. In some cases, titanium-containing fluorine-free compounds such as TiO(SO4) can also be used. In some preferred embodiments of this invention, to obtain a good passivation effect, the titanium film weight on the passivation film surface is preferably controlled at 2–10 mg / m³. 2 Preferred concentration: 3–6 mg / m³ 2 In some preferred embodiments of the present invention, the chromium-free passivating agent of the present invention further contains phosphate. The chromium-free passivating agent of the present invention is commercially available, for example... X-series products. The passivation temperature of the chromium-free passivation step in this invention is not particularly limited; for example, passivation can be carried out in the range of 18–40°C, preferably 20–35°C, and more preferably at room temperature. After passivation, the metal coil will undergo drying treatment and subsequent painting.

[0068] In some specific embodiments, the method for pretreating the surface of the metal coil of the present invention further includes a degreasing and alkaline washing step, the purpose of which is to remove grease or other adhering substances from the metal coil substrate, so as to perform chemical pretreatment on a clean metal surface and generate a stable oxide film and passivation film. In one embodiment of the present invention, the surface pretreatment of the metal coil includes unwinding, degreasing and alkaline washing, alkaline oxidation, water washing, and chromium-free passivation. The degreasing and alkaline washing preferably uses an alkaline degreasing agent containing a nonionic surfactant. The alkaline degreasing agent preferably has a pH range of 9-14, more preferably 10-14. Such degreasing agents can effectively peel and disperse mineral oil on the surface of the metal coil, which helps the aqueous alkaline composition of the present invention to fully contact the substrate surface. The alkaline degreasing agent of the present invention is commercially available, for example... Alkaline degreasing agent. In some specific embodiments of the present invention, the temperature range for degreasing alkaline washing is 40–60°C, preferably 50–50°C, and the free alkalinity of the degreasing alkaline washing bath is preferably 3–7 points, more preferably 4.0–6.5 points. In another embodiment of the present invention, since the aqueous alkaline composition of the present invention may also contain a nonionic surfactant, the degreasing alkaline washing and alkaline oxidation steps of the present invention can be combined into one step, which is also a prominent advantage of the present invention. That is, the surface pretreatment of the metal coil of the present invention includes unwinding, alkaline oxidation, water washing and chromium-free passivation in sequence, which can effectively reduce production energy consumption and is suitable for industrial use and promotion.

[0069] Metal coil products

[0070] The present invention also provides a metal coil or a component thereof whose surface has been pretreated by at least a portion thereof by the metal coil surface pretreatment method according to the present invention.

[0071] According to the present invention, metal coils coated with an aqueous alkaline composition can be painted, formed, printed, glued, welded, riveted, or otherwise joined to other elements. Forming is typically performed only after painting. There are no particular limitations on the substrate material of the metal coils of the present invention, such as hot-dip galvanized steel, electrolytically galvanized steel, aluminum-magnesium-zinc alloy, aluminum-zinc alloy, aluminum-magnesium-zinc alloy, aluminum alloy coated with pure aluminum, etc. The pretreated metal coils or components thereof according to the present invention can be wires, wire windings, wire meshes, steel strips, metal sheets, panels, shields, bodies or parts thereof; parts of vehicles or houses; traffic components, furniture, household appliances or components thereof; frames, profiles, molded parts with complex geometries, crash barriers, radiator or fence elements, bumpers, pipes or components thereof.

[0072] The present invention further provides a pre-coated metal coil, comprising a metal coil substrate, a metal pretreatment layer, and a paint layer, wherein the metal pretreatment layer comprises an oxide film obtained by treating the metal coil substrate with the aqueous alkaline composition of the present invention. Further, the metal pretreatment layer also includes a passivation film. The metal pretreatment layer of the present invention is spaced between the paint layer and the metal coil substrate to improve paint adhesion and the corrosion resistance of the product. In some specific embodiments of the present invention, a primer for metal coils can be applied by roller coating onto the metal coil treated by the pretreatment method described in the present invention. Typically, the primer can be selected from solvent-based primers for metal coils, such as those with polyester, polyurethane, epoxy resin, polyacrylate, and melamine resin as the main adhesive component and / or polyisocyanate as a crosslinking agent component. The dry film thickness of the primer layer is approximately 4–8 μm, and the primer coating is typically cured in an oven at a steel surface peak temperature (PMT) between 220 and 250 °C, wherein the metal strip is quenched by a water curtain and subsequently dried after leaving the oven. A topcoat or varnish can then be applied to the primer-coated metal coil to improve its appearance. The dry film thickness of the topcoat layer is approximately 15–25 μm, and the topcoat coating is typically cured in an oven at a PMT temperature between 220 and 250 °C. The dry film thickness can be measured using a Helmut-Fischer FMP20 instrument according to DIN EN ISO 2808:2007-05 (dated: May 2007), Method 12A - Magnetometer. If necessary, an intermediate coat can be applied between the primer and the topcoat. In some preferred embodiments of the invention, the primer is selected from chromium-free primers, and the topcoat is selected from polyester topcoats. Combined with the metal coil surface pretreatment method of the present invention, pre-coated metal coil products with excellent paint adhesion and corrosion resistance can be obtained.

[0073] The following embodiments are provided to illustrate the invention in more detail.

[0074] Implementation Plan 1:

[0075] An aqueous alkaline composition for surface pretreatment of metal coils, comprising 80-400 ppm of ferric ions, wherein the free alkalinity of the aqueous alkaline composition is not less than 20 (10 mL) points, and the sum of the concentrations of cobalt, nickel, chromium and phosphorus in the aqueous alkaline composition does not exceed 30 ppm.

[0076] Implementation Plan 2:

[0077] According to the aqueous alkaline composition of the first embodiment, wherein,

[0078] The aqueous alkaline composition comprises 100-300 ppm of ferric ions, preferably 120-200 ppm of ferric ions.

[0079] Implementation Plan 3:

[0080] According to the aqueous alkaline composition of the first or second embodiment, wherein,

[0081] The ferric ions are provided by water-soluble ferric salts, preferably, the water-soluble ferric salts include one or more of ferric nitrate, ferric sulfate, ferric chloride, ferric acetate, ferric acetate, and ferric citrate.

[0082] Implementation Plan 4:

[0083] According to any one of the embodiments of 1 to 3, the aqueous alkaline composition, wherein,

[0084] The aqueous alkaline composition further includes molybdate ions. Preferably, the molybdate ions are provided by a water-soluble molybdenum compound. Preferably, the water-soluble molybdenum compound includes one or more of sodium molybdate, ammonium molybdate, potassium molybdate, zinc molybdate, and calcium molybdate.

[0085] Implementation Plan 5:

[0086] According to the aqueous alkaline composition of the fourth embodiment, wherein,

[0087] The concentration of molybdenum in the aqueous alkaline composition is not less than 10 ppm.

[0088] Implementation Plan 6:

[0089] According to any one of the embodiments 1 to 5, the aqueous alkaline composition wherein,

[0090] The aqueous alkaline composition further includes a complexing agent. Preferably, the complexing agent includes one or more of aminocarboxylic acid esters or salts, hydroxycarboxylic acid salts, and carboxylic acid esters or salts. More preferably, the complexing agent includes one or more of tartrate esters or salts, citrate esters or salts, gluconate esters or salts, glucono-p-ethyl esters or salts, methylaminoacetic acid esters or salts, ethylenediaminetetraacetic acid esters or salts, and hypozoxytriacetic acid esters or salts.

[0091] Implementation Plan 7:

[0092] According to any of the embodiments 1 to 6, the aqueous alkaline composition wherein,

[0093] The aqueous alkaline composition comprises a water-soluble ferric salt, a water-soluble molybdenum compound, a complexing agent, an inorganic base, water, and an optional nonionic surfactant.

[0094] Implementation Plan No. 8:

[0095] A concentrate, by diluting it with water and optionally adjusting the pH with a suitable acid or base, yields an aqueous alkaline composition according to any of embodiments 1 to 7.

[0096] Implementation Plan 9:

[0097] A method for surface pretreatment of metal coil, wherein the method includes an alkaline oxidation step and a chromium-free passivation step, wherein the alkaline oxidation step uses an aqueous alkaline composition as described in any of embodiments 1 to 7 to contact the metal coil substrate for 3 to 15 seconds, preferably 4 to 10 seconds, more preferably 5 to 8 seconds.

[0098] Implementation Plan 10:

[0099] According to the method for pretreating the surface of metal coils as described in embodiment 9, wherein...

[0100] The contact treatment is an immersion treatment, preferably at a temperature of 40°C to 70°C, more preferably 45°C to 65°C, and even more preferably 50°C to 60°C.

[0101] Implementation Plan 11:

[0102] According to the method for pretreating the surface of metal coils as described in embodiment 9 or 10, wherein...

[0103] The method for pretreating the surface of the metal coil also includes a degreasing and alkaline washing step.

[0104] Implementation Plan 12:

[0105] At least a portion of the surface of the metal coil or its components has been pretreated by the method for surface pretreatment of metal coils as described in any of embodiments 9 to 11.

[0106] Implementation Plan 13:

[0107] A pre-coated metal coil includes a metal coil substrate, a metal pretreatment layer, and a paint layer, wherein the metal pretreatment layer includes an oxide film obtained by treating the metal coil substrate with the aqueous alkaline composition described in any of embodiments 1 to 7.

[0108] The present invention will be explained in more detail below with reference to embodiments and comparative examples, and it should be understood that the present invention is not limited to these embodiments.

[0109] [Preparation of Aqueous Alkaline Compositions]

[0110] Example 1

[0111] Add pure water to the stirred tank and turn on the stirrer. According to the relative addition amounts (expressed as mass percentages) of each component shown in Table 1, add sodium molybdate and stir until the solution is clear. Then add a 50% solution of sodium gluconate and stir for 5 minutes. Next, add ferric nitrate nonahydrate and stir until completely dissolved. Finally, add solid sodium hydroxide and stir until completely dissolved. Continue stirring until the solution cools to below 40°C, then add water to the required sample volume, i.e., dilute the entire solution to 6.5% (tank concentration) to obtain an aqueous alkaline composition. Take a sample for parameter testing.

[0112] Example 2

[0113] The composition of Example 2 was prepared by changing the composition of each component in Table 1 according to the method of Example 1.

[0114] Comparative Examples 1-3

[0115] According to the method of Example 1, the compositions of each component in Table 1 were changed to prepare the compositions of Comparative Examples 1-3.

[0116] Table 1

[0117] [Appearance and Performance Testing]

[0118] Appearance

[0119] Gardoclean alkaline degreasing agent was used to degrease the hot-dip galvanized substrate. The free alkalinity of the bath solution was 3. The solution was heated to 50°C and sprayed for 6 seconds. The residual degreasing was then rinsed with pure water and dried with hot air. The appearance of the board surface was observed by SEM. The results are shown in Figure 1(a).

[0120] The hot-dip galvanized substrate that has undergone the above treatment was placed in an alkaline oxidation bath prepared with an aqueous alkaline composition prepared in Example 1 of the present invention. The free alkalinity was 35, the Fe ion content was 180 ppm, the temperature was 60°C, and the substrate was immersed for 6 seconds. After removal, the surface was washed with water and then dried with hot air. The appearance of the substrate was observed again by SEM. The results are shown in Figure 1(b).

[0121] A comparison of Figures 1(a) and 1(b) shows that the specific surface area of ​​the board treated with the aqueous alkaline composition prepared in Example 1 of the present invention is significantly higher than that of the untreated board, which is beneficial to improving the adhesion between the substrate and the paint.

[0122] T-bend test and salt spray test cleaning: Gardoclean alkaline degreaser was used to degrease the hot-dip galvanized substrate. The free alkalinity of the bath solution was 3. The solution was heated to 50°C and sprayed for 6 seconds. Then the residual degreaser was rinsed with pure water.

[0123] Alkaline oxidation: Multiple hot-dip galvanized substrates that have undergone the aforementioned treatment are placed in the alkaline oxidation tanks prepared by Examples 1, 2, and Comparative Examples 1-3 of this invention. The temperature of the tank solution is controlled at 60°C. The substrates are immersed for 6 seconds, then rinsed with pure water for 10 seconds and dried with hot air for later use.

[0124] Chromium-free passivation: After alkaline oxidation treatment in the alkaline oxidation tanks prepared according to Examples 1, 2, and Comparative Examples 1-3, the substrate also needs to undergo chromium-free passivation treatment. The chromium-free passivating agent Gardobond X 4802 / 2RFU is applied to the aforementioned alkaline-oxidized substrate using a #3 RDS stainless steel wire rod, with the surface titanium film weight controlled at 3-6 mg / m³. 2 The plate drying temperature (PMT) is 70℃.

[0125] Comparative Example 4 is based on the alkaline oxidation tank configured in Example 1, but without chromium-free passivation.

[0126] Paint application: Primer and topcoat were applied to the hot-dip galvanized substrate after the above treatment. The primer used was Xuanwei's chromium-free white lime primer (PMY0500), applied using a 10# RDS squeegee, with the board drying temperature controlled at 224℃. The topcoat used Xuanwei's polyester paint (PMW0072S-E), applied using a 22# RDS squeegee, with the board drying temperature controlled at 232℃. The dry film thickness of the primer was 5μm, and the dry film thickness of the topcoat was 15μm. Samples were then obtained. The obtained samples were subjected to the following tests, and the experimental results are shown in Tables 2 and 3.

[0127] (1) T-bend test

[0128] The samples obtained in Examples 1 and 2 and Comparative Examples 1-4 were subjected to T-bend tests according to GB / T 13448-2019 standard. After the T-bend test, the degree of paint peeling at the bend was determined by applying adhesive tape. The paint peeling rate is the percentage of peeled paint relative to the strip-like marks on the entire tape.

[0129] (2) Neutral salt spray test

[0130] For the samples obtained in Examples 1 and 2 and Comparative Examples 1-3, neutral salt spray tests (including streaked salt spray test and cut-edge salt spray test) were conducted according to ASTM B117-97 standard. Each test was performed in duplicate, and the results were a set of values ​​from repeated tests or the average value of repeated tests. The test conditions were 5% sodium chloride solution, pH 7.0, continuous spraying, temperature 35°C, and sampling was performed after 1008 hours.

[0131] Table 2

[0132] Table 3

[0133] According to Tables 2 and 3, it can be seen that the pre-coated metal coils treated with the aqueous alkaline composition of the present invention according to the surface pretreatment method of the present invention have excellent paint adhesion and corrosion resistance. In particular, in some preferred embodiments of the present invention, the pre-coated metal coils obtained by the present invention can achieve a T-bend test result of ≤1T while also having very good corrosion resistance.

Claims

1. An aqueous alkaline composition for surface pretreatment of metal coils, characterized in that, The aqueous alkaline composition contains 80 to 400 ppm of ferric ions, the free alkalinity of the aqueous alkaline composition is not less than 20 (10 mL) points, and the sum of the concentrations of cobalt, nickel, chromium and phosphorus in the aqueous alkaline composition does not exceed 30 ppm.

2. The aqueous alkaline composition according to claim 1, characterized in that, The aqueous alkaline composition comprises 100-300 ppm of ferric ions, preferably 120-200 ppm of ferric ions.

3. The aqueous alkaline composition according to claim 1 or 2, characterized in that, The ferric ions are provided by water-soluble ferric salts, preferably, the water-soluble ferric salts include one or more of ferric nitrate, ferric sulfate, ferric chloride, ferric acetate, ferric acetate, and ferric citrate.

4. The aqueous alkaline composition according to any one of claims 1 to 3, characterized in that, The aqueous alkaline composition further includes molybdate ions. Preferably, the molybdate ions are provided by a water-soluble molybdenum compound. Preferably, the water-soluble molybdenum compound includes one or more of sodium molybdate, ammonium molybdate, potassium molybdate, zinc molybdate, and calcium molybdate.

5. The aqueous alkaline composition according to claim 4, characterized in that, The concentration of molybdenum in the aqueous alkaline composition is not less than 10 ppm.

6. The aqueous alkaline composition according to any one of claims 1 to 5, characterized in that, The aqueous alkaline composition further includes a complexing agent. Preferably, the complexing agent includes one or more of aminocarboxylic acid esters or salts, hydroxycarboxylic acid salts, and carboxylic acid esters or salts. More preferably, the complexing agent includes one or more of tartrate esters or salts, citrate esters or salts, gluconate esters or salts, glucono-p-ethyl esters or salts, methylaminoacetic acid esters or salts, ethylenediaminetetraacetic acid esters or salts, and hypozoxytriacetic acid esters or salts.

7. The aqueous alkaline composition according to any one of claims 1 to 6, characterized in that, The aqueous alkaline composition comprises a water-soluble ferric salt, a water-soluble molybdenum compound, a complexing agent, an inorganic base, water, and an optional nonionic surfactant.

8. A concentrate, by diluting it with water and optionally adjusting the pH with a suitable acid or base, yields an aqueous alkaline composition according to any one of claims 1 to 7.

9. A method for surface pretreatment of metal coils, characterized in that, The method includes an alkaline oxidation step and a chromium-free passivation step, wherein the alkaline oxidation step involves contacting the metal coil substrate with an aqueous alkaline composition as described in any one of claims 1 to 7 for 3 to 15 seconds, preferably, the contact treatment time is 4 to 10 seconds, more preferably 5 to 8 seconds.

10. The method for pretreatment of the surface of metal coils according to claim 9, characterized in that, The contact treatment is an immersion treatment. Preferably, the temperature of the immersion treatment is 40℃~70℃, more preferably 45℃~65℃, and even more preferably 50℃~60℃.

11. The method for pretreatment of the surface of metal coils according to claim 9 or 10, characterized in that, The method for pretreating the surface of the metal coil also includes a degreasing and alkaline washing step.

12. At least a portion of the surface of a metal coil or a component thereof has been pretreated by the method according to any one of claims 9 to 11.

13. A pre-coated metal coil comprising a metal coil substrate, a metal pretreatment layer, and a paint layer, wherein the metal pretreatment layer comprises an oxide film obtained by treating the metal coil substrate with the aqueous alkaline composition according to any one of claims 1 to 7.

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