A zinc-aluminum-magnesium coated steel sheet suitable for electron beam coating and its manufacturing method

Abstract

This invention discloses a zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating, comprising a zinc-aluminum-magnesium coated steel sheet with a composite coating on its surface. The composite coating contains the following effective components: polymer resin A, with a weight of 50-80 parts; a compounded organosilane coupling agent B, with a weight of 10-35 parts; the compounded organosilane coupling agent B is formed by the mixed hydrolysis and condensation of at least one organosilane coupling agent B1 containing epoxy functional groups and at least one organosilane coupling agent B2 containing amino functional groups; resin C containing unsaturated bonds, with a weight of 3-10 parts; a water-soluble fluorine-containing compound D, wherein the weight of fluorine is 1.5-5 parts; and a water-soluble phosphorus-containing compound E, wherein the weight of phosphorus is 2-5 parts. This invention also discloses a surface treatment agent for zinc-aluminum-magnesium coated steel sheets adapted for electron beam coating and a method for manufacturing zinc-aluminum-magnesium coated steel sheets.

Description

Technical Field

[0001] This invention relates to a steel sheet with a surface coating, and more particularly to a zinc-aluminum-magnesium coated steel sheet with a surface coating. Background Technology

[0002] Zinc-aluminum-magnesium coatings, by adding aluminum and magnesium elements to traditional zinc coatings, form a more stable structure and significantly improve corrosion resistance.

[0003] Radiation-cured color-coated steel sheets produced using zinc-aluminum-magnesium coated steel sheets as the substrate not only have stronger corrosion resistance but also exhibit greater durability in humid or corrosive environments. Furthermore, compared to traditional thermosetting processes, the production technology of radiation-cured color-coated steel sheets is environmentally friendly, energy-saving, and highly efficient, and is considered the future direction of color-coated steel sheet manufacturing. This technology utilizes the energy of ultraviolet light (UV) or electron beam (EB) irradiation as the excitation source for coating curing during the production of color-coated steel sheets, enabling instantaneous curing of solvent-free coatings at room temperature.

[0004] In the production process of radiation-cured color-coated steel sheets, it is difficult to achieve full curing of the topcoat coating within the specified board time using UV curing. Therefore, EB curing has become the mainstream process choice.

[0005] While EB energy can achieve cross-linking and curing of radiation-cured topcoat coatings, excessive EB energy can damage the chemical bonds in most non-radiation-cured coatings, leading to coating degradation and failure. If traditional pretreatment methods for color coatings are continued, such as curing to a solvent-based primer coating, the primer coating cannot form an effective bond with the subsequent EB-cured topcoat, resulting in decreased adhesion and corrosion resistance between the substrate and the color coating, severely impacting product quality. Conversely, if coating and curing are performed directly, the untreated substrate surface also struggles to ensure good adhesion and corrosion resistance to the radiation-cured coating. Furthermore, zinc-aluminum-magnesium plating, due to the addition of aluminum and magnesium, has slightly lower plasticity than traditional zinc plating. During the production of color-coated steel sheets, the interface between the plating and coating is more prone to cracking during processing and deformation, leading to loss of interfacial adhesion and corrosion resistance. Existing patent literature addresses these areas, for example:

[0006] Chinese patent document CN113522706A, published on October 22, 2021, entitled "Surface-treated color-coated substrate suitable for radiation-cured color-coated steel sheet production process," discloses a surface-treated color-coated substrate suitable for radiation-cured color-coated steel sheet production process. This product possesses excellent surface wear resistance and rust prevention properties and can be directly used in the production of radiation-cured color coating processes. During the EB curing process of the color coating layer, its surface composite protective film effectively resists damage from electron beam irradiation and effectively improves the adhesion and corrosion resistance between the substrate and the radiation-cured coating. However, this surface-treated color-coated substrate does not optimize the deformation and impact resistance of zinc-aluminum-magnesium radiation-cured color-coated steel sheets, nor can it simultaneously provide sufficient corrosion resistance and adhesive bonding performance, thus failing to meet the functional requirements for use as a back coating for color-coated steel sheets. Summary of the Invention

[0007] One of the objectives of this invention is to provide a zinc-aluminum-magnesium coated steel sheet adapted to electron beam coating, wherein the composite coating of the steel sheet is adapted to EB radiation curing process and has excellent corrosion resistance and adhesion properties.

[0008] To achieve the above objectives, the present invention provides a zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating, comprising a zinc-aluminum-magnesium coated steel sheet, wherein the surface of the zinc-aluminum-magnesium coated steel sheet has a composite coating, the composite coating containing the following effective components:

[0009] Polymer resin A, in parts by weight of 50-80 parts;

[0010] The compounded organosilane coupling agent B has a weight of 10-35 parts; the compounded organosilane coupling agent B is formed by the mixed hydrolysis and condensation of at least one organosilane coupling agent B1 containing an epoxy functional group and at least one organosilane coupling agent B2 containing an amino functional group.

[0011] Resin C containing unsaturated bonds, in parts by weight of 3-10;

[0012] Water-soluble fluorine-containing compound D, wherein the fluorine element is 1.5-5 parts by weight;

[0013] Water-soluble phosphorus-containing compound E, wherein the phosphorus element is present in 2-5 parts by weight.

[0014] In this manner, the zinc-aluminum-magnesium coated steel sheet of the present invention comprises, from the core outwards: a steel substrate, a zinc-aluminum-magnesium coating, and an organic-inorganic composite coating. This composite coating not only ensures excellent inter-process surface damage resistance and rust prevention of the color-coated substrate, but also participates in the cross-linking and curing process of the upper paint film during the subsequent electron beam (EB) radiation curing process, effectively improving the adhesion, processability, and corrosion resistance between the zinc-aluminum-magnesium substrate and the radiation-cured coating. Furthermore, the composite coating on the surface of this zinc-aluminum-magnesium surface-treated steel sheet can also be directly used as the back paint for color-coated steel sheets, exhibiting certain corrosion resistance and adhesion properties.

[0015] In this invention, the inventors control the weight of polymer resin A in the coating to be between 50 and 80 parts because: when the weight of polymer resin A is less than 50 parts, the cohesive force of the composite coating will decrease, and it will be unable to effectively suppress the influence of microcracks in the zinc-aluminum-magnesium coating process on the interface adhesion; while when the weight of polymer resin A is greater than 80 parts, the relative proportion of the silane skeleton formed by the compounded organosilane coupling agent B, which plays an electrochemical anti-corrosion role on the surface of the zinc-aluminum-magnesium plate, will decrease, affecting the corrosion resistance of the zinc-aluminum-magnesium surface-treated steel plate.

[0016] In this invention, the inventors control the weight of the compounded organosilane coupling agent B in the coating to be between 10 and 35 parts because: when the weight of the compounded organosilane coupling agent B is less than 10 parts, the corrosion resistance of the composite coating will decrease; while when the weight of the compounded organosilane coupling agent B is greater than 35 parts, the relative proportion of the waterborne cationic polymer resin A, which increases the flexibility of the coating, will decrease, resulting in poor T-bend adhesion and impact resistance of the radiation-cured color-coated steel sheet prepared on the galvanized aluminum-magnesium surface-treated steel sheet.

[0017] In this invention, the inventors control the weight percentage of resin C containing unsaturated bonds in the coating to 3-10 parts because: the unsaturated bonds on the resin participate in the subsequent EB irradiation crosslinking and curing process of the upper radiation-cured coating film, while the remaining resin segments form a certain degree of interpenetration and interconnection with the polymer resin A, which is the main component. This reduces the decrease in plasticity of the organic-inorganic composite coating caused by the crosslinking and curing of unsaturated bonds, allowing the organic-inorganic composite coating to form good interlayer adhesion with the upper radiation-cured coating film while maintaining relatively good plasticity. When the weight percentage of resin C containing unsaturated bonds is less than 3 parts, the relative content of at least one resin containing unsaturated bonds is low, which cannot enable the composite coating to form sufficient adhesion with the upper radiation-cured coating film. When the weight percentage of resin C containing unsaturated bonds is greater than 10 parts, the crosslinking polymerization into a brittle resin polymer will reduce the plasticity of the composite coating, thereby worsening the T-bend adhesion and impact resistance of the radiation-cured color-coated steel sheet prepared on the galvanized aluminum-magnesium surface-treated steel sheet.

[0018] In this invention, the inventors controlled the fluorine compound D in the coating, by weight, to be between 1.5 and 5 parts based on elemental fluorine because: if the weight of elemental fluorine is less than 1.5 parts, that is, when there is less fluorine compound, the corrosion resistance of the composite coating may decrease, thereby reducing the resistance of the radiation-cured color-coated steel sheet prepared on the galvanized aluminum-magnesium surface-treated steel sheet to under-film corrosion; while if the weight of elemental fluorine is greater than 5 parts, that is, when there is too much fluorine compound, due to the water-soluble nature of fluorine compound, residual fluorine compound that has not fully reacted with the galvanized aluminum-magnesium interface may reduce the water resistance of the composite coating, affecting its resistance to damp heat and other properties, thereby reducing the water boiling resistance of the radiation-cured color-coated steel sheet prepared on the galvanized aluminum-magnesium surface-treated steel sheet.

[0019] In this invention, the inventors control the water-soluble phosphorus compound E in the coating to be 2-5 parts by weight of phosphorus element because: if the weight of phosphorus element is less than 2 parts, that is, when there is less phosphorus compound, there is no additive effect, and the corrosion resistance of the composite coating may decrease, thereby making the radiation-cured color-coated steel plate prepared on the zinc-aluminum-magnesium surface-treated steel plate less resistant to under-film corrosion; while if the weight of phosphorus element is greater than 3 parts, that is, when there is too much acidic phosphorus compound, it will lead to poor stability of the composite coating treatment solution.

[0020] Furthermore, in the zinc-aluminum-magnesium coated steel sheet of the present invention, the polymer resin A is selected from: acrylic resin, epoxy resin, polyurethane, polyester resin and alkyd resin, and the resin dry film formed by compounding at least one of the above resins with copolymerized modified resins, the 100% modulus can be 50-600MPa, and the elongation at break can be 100-400%.

[0021] Furthermore, in the zinc-aluminum-magnesium coated steel sheet of the present invention, the organosilane coupling agent B1 containing epoxy functional groups is selected from one or more of the following: 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0022] Furthermore, in the zinc-aluminum-magnesium coated steel sheet of the present invention, the organosilane coupling agent B2 containing an amino functional group is selected from one or more of the following: 3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, and bis(3-triethoxysilylpropyl)amine.

[0023] Furthermore, in the zinc-aluminum-magnesium coated steel sheet of the present invention, the unsaturated bonds in the resin C are one or more of acrylic, vinyl, and epoxy groups.

[0024] Furthermore, in the zinc-aluminum-magnesium coated steel sheet of the present invention, the water-soluble fluorine-containing compound D is selected from at least one of fluorine-containing metal acids, fluorine metal salts, or fluorides.

[0025] Furthermore, in the zinc-aluminum-magnesium coated steel sheet of the present invention, the water-soluble phosphorus-containing compound E is selected from at least one of: ammonium dihydrogen phosphate, zinc dihydrogen phosphate, manganese dihydrogen phosphate, phosphoric acid, phytic acid, and hydroxyethylidene diphosphonic acid.

[0026] Furthermore, in the zinc-aluminum-magnesium coated steel sheet of the present invention, the film weight of the composite coating is 1.0-3 g / m³. 2 .

[0027] In this invention, when the film weight of the composite coating is less than 1.0 g / m³ 2 When the coating is thin, the corrosion resistance of the composite coating may decrease, and the processing plasticity may be insufficient. This, in turn, will worsen the corrosion resistance, T-bend adhesion, and impact resistance of the radiation-cured color-coated steel sheet prepared on the zinc-aluminum-magnesium surface-treated steel sheet. When the film weight of the composite coating exceeds 3 g / m²... 2 On the one hand, this will increase the surface treatment cost per unit area. On the other hand, due to the thicker coating, the coating may not cure and cross-link completely under the same conditions, resulting in decreased cohesion and reduced wear resistance.

[0028] In this invention, the zinc-aluminum-magnesium coating can be: a low-aluminum-content zinc-aluminum-magnesium coating (aluminum content ≤ 3%), a medium-aluminum-content zinc-aluminum-magnesium coating (3% < aluminum content ≤ 10%), a medium-high-aluminum-content zinc-aluminum-magnesium coating (10% < aluminum content ≤ 30%), and a high-aluminum-content zinc-aluminum-magnesium coating (aluminum content > 30%).

[0029] Another objective of this invention is to provide a surface treatment agent for zinc-aluminum-magnesium coated steel sheets adapted to electron beam coatings. By applying this surface treatment agent to the surface of the zinc-aluminum-magnesium coated steel sheet, a composite coating with excellent corrosion resistance and adhesion properties can be obtained.

[0030] To achieve the above objectives, the present invention provides a surface treatment agent for zinc-aluminum-magnesium coated steel sheets adapted to electron beam coating, which is an aqueous solution containing solids, wherein the solids contain the following active ingredients in parts by weight:

[0031] Polymer resin A, in parts by weight of 50-80 parts;

[0032] The compounded organosilane coupling agent B has a weight of 10-35 parts; the compounded organosilane coupling agent B is formed by the mixed hydrolysis and condensation of at least one organosilane coupling agent B1 containing an epoxy functional group and at least one organosilane coupling agent B2 containing an amino functional group.

[0033] Resin C containing unsaturated bonds, in parts by weight of 3-10;

[0034] Water-soluble fluorine-containing compound D, wherein the fluorine element is 1.5-5 parts by weight;

[0035] Water-soluble phosphorus-containing compound E, wherein the phosphorus element is present in 2-5 parts by weight.

[0036] Furthermore, in the surface treatment agent of the present invention, the polymer resin A is selected from: acrylic resin, epoxy resin, polyurethane, polyester resin and alkyd resin, and at least one of the copolymerized modified resins of the above resins.

[0037] Furthermore, in the surface treatment agent described in this invention, the epoxy-functionalized organosilane coupling agent B1 is selected from one or more of the following: 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0038] Furthermore, in the surface treatment agent described in this invention, the organosilane coupling agent B2 containing an amino functional group is selected from one or more of the following: 3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, and bis(3-triethoxysilylpropyl)amine.

[0039] Furthermore, in the surface treatment agent described in this invention, the unsaturated bonds in the resin C are one or more of acrylic, vinyl, and epoxy groups.

[0040] Furthermore, in the surface treatment agent described in this invention, the water-soluble fluorinated compound D is selected from at least one of fluorinated metal acids, fluorinated metal salts, or fluorides.

[0041] Furthermore, in the surface treatment agent of the present invention, the water-soluble phosphorus-containing compound E is selected from at least one of: ammonium dihydrogen phosphate, zinc dihydrogen phosphate, manganese dihydrogen phosphate, phosphoric acid, phytic acid, and hydroxyethylidene diphosphonic acid.

[0042] Another object of the present invention is to provide a method for manufacturing a zinc-aluminum-magnesium coated steel sheet adapted to electron beam coating, which can obtain a zinc-aluminum-magnesium coated steel sheet adapted to electron beam coating.

[0043] To achieve the above objectives, the present invention provides a method for manufacturing zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating, comprising the following steps:

[0044] The above-mentioned surface treatment agent is applied to the surface of the zinc-aluminum-magnesium coated steel sheet and cured into a film to form a composite coating on the surface of the zinc-aluminum-magnesium coated steel sheet.

[0045] Compared with the prior art, the zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating and its manufacturing method described in this invention have the following advantages and beneficial effects:

[0046] The zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating described in this invention uses polymer resin A and compounded organosilane coupling agent B as the matrix of the composite coating to achieve the effect of preventing physical penetration of corrosive media and inhibiting electrochemical corrosion. This results in a composite coating with excellent corrosion resistance, which can be directly used as the back paint of color-coated steel sheets. It also has certain corrosion resistance and adhesion properties.

[0047] In some preferred embodiments, the zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating of the present invention is selected from a polymer resin system with both high modulus and high elongation, so that the composite coating has both flexibility and hardness, which can further improve the machinability of zinc-aluminum-magnesium surface-treated steel sheet, maintain good corrosion resistance after processing deformation, and thus enable the radiation-cured color-coated steel sheet prepared on the zinc-aluminum-magnesium surface-treated steel sheet to have good formability and corrosion resistance.

[0048] The zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating described in this invention uses resin C containing unsaturated bonds. The unsaturated bonds on resin C participate in the subsequent EB irradiation crosslinking and curing process of the upper radiation-cured coating film, while the remaining resin segments form a certain degree of interpenetration and interconnection with the polymer resin A, which is the main component. This reduces the decrease in plasticity of the organic-inorganic composite coating caused by the crosslinking and curing of unsaturated bonds, so that the composite coating and the upper radiation-cured coating film form good interlayer adhesion, while maintaining better processing plasticity. Detailed Implementation

[0049] The following will further explain and illustrate the zinc-aluminum-magnesium coated steel sheet adapted to electron beam coating, its manufacturing method, and surface treatment agent described in this invention with reference to specific embodiments. However, this explanation and illustration do not constitute an improper limitation on the technical solution of this invention.

[0050] Examples 1-21 and Comparative Examples 1-8

[0051] The zinc-aluminum-magnesium coated steel sheets adapted for electron beam coating in Examples 1-21 and Comparative Examples 1-6 of this invention were all prepared using the following steps:

[0052] (1) Apply the surface treatment agent to the surface of zinc-aluminum-magnesium coated steel sheet by roller coating or spraying.

[0053] (2) A composite coating is formed on the surface of zinc-aluminum-magnesium coated steel sheet by blowing or drying to cure the film.

[0054] In some specific embodiments, the obtained zinc-aluminum-magnesium coated steel sheet includes, from the core outwards: a cold-rolled substrate, front and back zinc-aluminum-magnesium coatings, and a composite coating on the front and back.

[0055] It should be noted that Comparative Example 7 is a hot-dip zinc-aluminum-magnesium coated steel plate with medium aluminum content without any surface treatment. The steel plate consists of the following components from the core outward: cold-rolled substrate, front and back hot-dip zinc-aluminum-magnesium coating with medium aluminum content, and does not have a composite coating.

[0056] In addition, Comparative Example 8 shows a pretreated hot-dip galvanized zinc-aluminum-magnesium color-coated substrate with a medium aluminum content, prepared using a conventional color coating pretreatment process. The conventional pretreatment process involves spraying a composite film-forming agent with Co and Ni as film-forming elements onto the substrate surface, followed by spraying a chromate passivating agent to seal the pretreated layer. The Co and Cr content in the pretreated layer is Co: 3-7 mg / m³. 2 Cr: 15-25 mg / m³ 2 .

[0057] Furthermore, it should be noted that the effective components of the composite coating of the present invention are the same as the effective components of the solid components of the surface treatment agent aqueous solution, therefore the two will not be described separately.

[0058] Table 1-1 lists the composite coatings of zinc-aluminum-magnesium coated steel sheets in Examples 1-21 and Comparative Examples 1-6, as well as the types and contents of active ingredients in the surface treatment agents used in them.

[0059] Table 1-1.

[0060]

[0061]

[0062]

[0063] *Note: In Table 1-1, A1 is polycarbonate-modified polyurethane, A2 is acrylic resin, A3 is epoxy resin, A4 is alkyd resin, and A5 is polyester resin; B1-1 is 3-glycidyl etheroxypropyltriethoxysilane, B1-2 is 3-glycidyl etheroxypropylmethyldiethoxysilane, B1-3 is 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, B1-4 is 3-glycidyl etheroxypropyltrimethoxysilane, B1-5 is 3-glycidyl etheroxypropylmethyldimethoxysilane, and B1-6 is 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; B2-1 is 3-aminopropyltriethoxysilane, and B2-2 is 3-aminopropyltriethoxysilane. The composition of the styrene is as follows: B2-3 is N-2-aminoethyl-3-aminopropyltriethoxysilane, B2-4 is bis(3-triethoxysilylpropyl)amine, B2-5 is 3-aminopropyltrimethoxysilane, B2-6 is N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, and B2-7 is N-(n-butyl)-3-aminopropyltrimethoxysilane; C1 is polyurethane acrylate, C2 is vinyl ester resin, and C3 is epoxy acrylate; D1 is fluorotitanic acid, D2 is ammonium fluorotitanate, and D3 is ammonium fluorozirconate; E1 is ammonium dihydrogen phosphate, E2 is phytic acid, E3 is hydroxyethylidene diphosphonic acid, E4 is zinc dihydrogen phosphate, E5 is manganese dihydrogen phosphate, and E6 is phosphoric acid.

[0064] It should be noted that although B1, B2, D, and E in the above embodiments all use a single substance, it is also feasible to use multiple substances that meet the requirements in combination in other embodiments.

[0065] Table 1-2 lists the coating types and composite coating film weights of the galvanized aluminum-magnesium surface-treated steel sheets in Examples 1-21 and Comparative Examples 1-6.

[0066] Table 1-2.

[0067]

[0068]

[0069] Accordingly, to verify the superiority of the zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating designed in this invention, samples of the zinc-aluminum-magnesium coated steel sheets prepared in Examples 1-21 and Comparative Examples 1-8 were taken, cut into standard-sized samples, and subjected to the following tests to obtain test data for evaluating various properties. The evaluation results are listed in Tables 2-1 and 2-2. The specific test items and methods are as follows:

[0070] (1) Plate corrosion resistance test:

[0071] The plate was subjected to a salt spray test according to ASTM B117, with a test duration of 120 hours. The evaluation criteria are as follows:

[0072] ◎: White rust area ratio is less than or equal to 5%

[0073] ○: White rust area ratio greater than 5% and less than or equal to 10%

[0074] Δ: White rust area ratio greater than 10% and less than or equal to 50%

[0075] ×: White rust area ratio greater than 50%

[0076] (2) Moisture and heat resistance test:

[0077] The stacked wet heat method was used, in which two samples were stacked and a torque of 30 N·m was applied. They were then placed in a wet heat chamber at a temperature of 49℃ and a humidity of 98% for 120 hours. The evaluation criteria are as follows:

[0078] ◎: White rust area ratio is less than or equal to 5%

[0079] ○: White rust area ratio greater than 5% and less than or equal to 5%

[0080] Δ: White rust area ratio greater than 10% and less than or equal to 30%

[0081] ×: White rust area ratio greater than 30%

[0082] (3) Wear resistance test:

[0083] Using the rubber method, a Φ10mm flat rubber sheet is repeatedly rubbed against the surface under a load of 500g, a friction speed of 300m / min, a friction distance of 20mm, and 50 cycles of reciprocating friction. The evaluation criteria are as follows:

[0084] ◎: No change in the surface protective film

[0085] ○: Minor scratches on the protective film

[0086] Δ: Multiple scratches on the protective film

[0087] ×: Protective film completely peeled off

[0088] (4) Adhesion test:

[0089] To determine the bonding performance between the backing paint and the adhesive, the test specimen was cut to a length of 205 mm and a width of 25 mm. At a distance of 50 mm from the end along the length, it was T-bent at a 90-degree right angle. The upper surface of the remaining 155 mm of the specimen at the bend was wiped with a small amount of ethanol using a cotton swab and thoroughly dried. Then, the adhesive (Henkel Microplast UK8103 / UK5400 two-component polyurethane adhesive, mixed in a 5:1 ratio) was evenly applied over the entire width (25 mm). Another specimen with the same 50 mm T-bent was taken, and the remaining 155 mm of the specimen was aligned and attached to the adhesive area. The positions of the upper and lower specimens were adjusted to prevent misalignment, forming a T-shaped test specimen. Pressure (0.7 kPa) was maintained in the fixed mold for 72 hours. The specimen was then removed, and the adhesive on the edges of the specimen was scraped off with a utility knife. At least three parallel specimens were prepared for each sample.

[0090] Adjust the clamped portion of the specimen to be perpendicular to the bonded portion, and then place it in the tensile testing machine clamps for fixation. According to GB / T 2791, set the tensile testing machine parameters, including a tensile rate of 100±10 mm / min, a specimen width of 25 mm, and a peel length of 155 mm. Set the data for the peel length range before and after removal, within 25 mm increments. Start the tensile test. The tensile testing machine recording device records the peel load curve and automatically calculates the peel strength of the specimen.

[0091] The percentage of cohesive failure area is observed, i.e., the percentage of cohesive failure area S = 100% - (percentage of interlaminar failure area of ​​upper sample + percentage of interlaminar failure area of ​​lower sample). The final evaluation criteria for adhesion are as follows:

[0092] ◎: Cohesive failure area S≥80%, and peel strength σ≥4.0 (N / mm)

[0093] ○: 80% > cohesive failure area S ≥ 60%, and peel strength σ ≥ 4.0 (N / mm)

[0094] Δ: 60% > cohesive failure area S ≥ 40%, and peel strength σ ≥ 4.0 (N / mm)

[0095] ×: Cohesive area S < 40%

[0096] (5) Compatibility test with electron beam (EB) cured coating:

[0097] Radiation-cured color-coated topcoat was applied and cured on galvanized aluminum-magnesium alloy (GAMA) substrates. The topcoat used was an electron beam (EB) cured coating with a film thickness of 15 μm. Curing conditions included a maximum EB dose of 100 KGy and a maximum voltage of 200 KV. The coated samples were then subjected to the following adhesion tests: T-bend, cross-cut adhesion, impact, and boiling water tests, as well as corrosion resistance tests: salt spray and under-film corrosion tests. The adhesion and corrosion resistance test results directly reflect the compatibility of the galvanized color-coated substrate with the electron beam radiation curing process and the coating. Among these tests:

[0098] 5.1T Bending Adhesion Performance Test: Conducted according to GB / T 13448, section 7. Bending Test standard, with the following evaluation criteria:

[0099] ◎:≤3T

[0100] ○: 4T

[0101] Δ: 5T

[0102] ×:≥6T

[0103] 5.2 Cross-cut adhesion performance test: Conducted according to the cross-cut test standard in GB / T 13448, section 13. The evaluation criteria are as follows:

[0104] ◎: The cross-cut test rating is level 0 as specified in Table 1 of GB / T13448.

[0105] ○: Cross-cut test rating is level 1-2 as specified in Table 1 of GB / T13448.

[0106] Δ: Cross-cut test rating is level 3-4 as specified in Table 1 of GB / T13448.

[0107] ×: The cross-cutting test rating is Level 5 as specified in Table 1 of GB / T13448.

[0108] 5.3 Impact Adhesion Performance Test: Conducted according to GB / T 13448, section 8. Reverse Impact Test standard, with the following evaluation criteria:

[0109] ◎: The maximum impact energy that causes the coating to not crack or peel off is ≥9J

[0110] ○: The maximum impact energy that causes the coating to not crack or peel off is ≥7-8J.

[0111] Δ: The cross-cut test rating is level 6-7 as specified in Table 1 of GB / T13448.

[0112] ×: The cross-cutting test rating is ≤6 as specified in Table 1 of GB / T13448.

[0113] 5.4 Water Adhesion Resistance Test: Immerse the sample in boiling water for 2 hours. After removal, first evaluate the appearance of blistering or peeling of the coating, then conduct a cross-cut adhesion test according to GB / T 13448, section 13. The evaluation criteria are as follows:

[0114] ◎: The coating shows no blistering or peeling, and its cross-cut test rating is grade 0 as specified in Table 1 of GB / T13448.

[0115] ○: The coating has minor blistering but no peeling, and the cross-cut test rating is level 1-2 as specified in Table 1 of GB / T13448.

[0116] Δ: The coating exhibits extensive blistering without peeling, and its cross-cut test rating is 3-4 as specified in Table 1 of GB / T13448.

[0117] ×: Extensive coating peeling, cross-cut test rating is level 5 as specified in Table 1 of GB / T13448.

[0118] 5.5 Planar Salt Spray Corrosion Resistance Test: Conducted according to ASTM B117, duration 1000 hours, evaluation criteria are as follows:

[0119] ◎: The bubble density grade and bubble size should not exceed grade 2 as specified in Table 21 of GB / T1766.

[0120] ○: The bubble density grade and bubble size should not exceed grade 3 as specified in Table 21 of GB / T1766. Δ: The bubble density grade and bubble size should not exceed grade 4 as specified in Table 21 of GB / T1766.

[0121] ×: The bubble density grade and bubble size should not exceed grade 5 as specified in Table 21 of GB / T1766.

[0122] 5.6 Under-film corrosion resistance test: Before the test, use a knife to draw a single straight line parallel to the long side of the sample on the central part of the sample. The line should be no less than 50 mm long and penetrate the coating. The line should be no less than 30 mm from the edge. Then, conduct a salt spray test according to ASTM B117 for 1000 hours. The evaluation criteria are as follows:

[0123] ◎: The average erosion width on one side of the marked area is less than or equal to 5mm

[0124] ○: The average erosion width on one side of the marked area is greater than 5mm and less than or equal to 10mm.

[0125] Δ: The average erosion width on one side of the scribed area is greater than 10mm and less than or equal to 15mm.

[0126] ×: The average erosion width on one side of the marked area is greater than 15mm.

[0127] Tables 2-1 and 2-2 list the evaluation results of various performance tests on the zinc-aluminum-magnesium coated steel sheet samples of Examples 1-21 and Comparative Examples 1-8 of the present invention.

[0128] Table 2-1.

[0129]

[0130]

[0131] Table 2-2.

[0132]

[0133]

[0134] As can be seen from Tables 2-1 and 2-2 above, the galvanized aluminum-magnesium plates in Examples 1-21 prepared by the present invention all received “◎” and “○” after the above tests. When used as a back coating, they all exhibited good corrosion resistance, wear resistance and adhesion. As a pretreatment layer, they can form good adhesion and corrosion resistance with electron beam (EB) cured coating.

[0135] In summary, the zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating described in this invention can effectively adhere to the electron beam (EB) cured coating. Radiation-cured color-coated steel sheets produced using this zinc-aluminum-magnesium surface-treated steel sheet can meet the requirements for stamping performance, corrosion resistance, and overall resistance. Furthermore, its superior corrosion resistance, abrasion resistance, and adhesion can meet the requirements for back-side coating, reducing the number of back-side coating steps.

[0136] It should 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 zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating, comprising a zinc-aluminum-magnesium coated steel sheet, characterized in that, The zinc-aluminum-magnesium coated steel sheet has a composite coating on its surface, and the composite coating contains the following active ingredients: Polymer resin A, in parts by weight of 50-80 parts; The compounded organosilane coupling agent B has a weight of 10-35 parts; the compounded organosilane coupling agent B is formed by the mixed hydrolysis and condensation of at least one organosilane coupling agent B1 containing an epoxy functional group and at least one organosilane coupling agent B2 containing an amino functional group. Resin C containing unsaturated bonds, in parts by weight of 3-10; Water-soluble fluorine-containing compound D, wherein the fluorine element is 1.5-5 parts by weight; Water-soluble phosphorus-containing compound E, wherein the phosphorus element is present in 2-5 parts by weight.

2. The zinc-aluminum-magnesium coated steel sheet as described in claim 1, characterized in that, The polymer resin A is selected from at least one of the following: acrylic resin, epoxy resin, polyurethane, polyester resin and alkyd resin, and copolymerized modified resins of the above resins.

3. The zinc-aluminum-magnesium coated steel sheet as described in claim 1, characterized in that, The organosilane coupling agent B1 containing an epoxy functional group is selected from one or more of the following: 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

4. The zinc-aluminum-magnesium coated steel sheet as described in claim 1, characterized in that, The amino-functionalized organosilane coupling agent B2 is selected from one or more of the following: 3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, and bis(3-triethoxysilylpropyl)amine.

5. The zinc-aluminum-magnesium coated steel sheet as described in claim 1, characterized in that, The unsaturated bonds in resin C are one or more of acrylic, vinyl, and epoxy groups.

6. The zinc-aluminum-magnesium coated steel sheet as described in claim 1, characterized in that, The water-soluble fluorinated compound D is selected from at least one of the following: fluorinated metal acids, fluorinated metal salts, or fluorides.

7. The zinc-aluminum-magnesium coated steel sheet as described in claim 1, characterized in that, The water-soluble phosphorus-containing compound E is selected from at least one of: ammonium dihydrogen phosphate, zinc dihydrogen phosphate, manganese dihydrogen phosphate, phosphoric acid, phytic acid, and hydroxyethylidene diphosphonic acid.

8. The zinc-aluminum-magnesium coated steel sheet as described in claim 1, characterized in that, The composite coating has a film weight of 1.0-3 g / m³. 2 .

9. A surface treatment agent for zinc-aluminum-magnesium coated steel sheets adapted for electron beam coating, characterized in that, It is an aqueous solution containing solids, wherein the solids contain the following active ingredients in parts by weight: Polymer resin A, in parts by weight of 50-80 parts; The compounded organosilane coupling agent B has a weight of 10-35 parts; the compounded organosilane coupling agent B is formed by the mixed hydrolysis and condensation of at least one organosilane coupling agent B1 containing an epoxy functional group and at least one organosilane coupling agent B2 containing an amino functional group. Resin C containing unsaturated bonds, in parts by weight of 3-10; Water-soluble fluorine-containing compound D, wherein the fluorine element is 1.5-5 parts by weight; Water-soluble phosphorus-containing compound E, wherein the phosphorus element is present in 2-5 parts by weight.

10. The surface treatment agent as described in claim 9, characterized in that, The polymer resin A is selected from at least one of the following: acrylic resin, epoxy resin, polyurethane, polyester resin and alkyd resin, and copolymerized modified resins of the above resins.

11. The surface treatment agent as described in claim 9, characterized in that, The organosilane coupling agent B1 containing an epoxy functional group is selected from one or more of the following: 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, 3-glycidyl etheroxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

12. The surface treatment agent as described in claim 9, characterized in that, The amino-functionalized organosilane coupling agent B2 is selected from one or more of the following: 3-aminopropylmethyldimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(n-butyl)-3-aminopropyltrimethoxysilane, and bis(3-triethoxysilylpropyl)amine.

13. The surface treatment agent as described in claim 9, characterized in that, The unsaturated bonds in resin C are one or more of acrylic, vinyl, and epoxy groups.

14. The surface treatment agent as described in claim 9, characterized in that, The water-soluble fluorinated compound D is selected from at least one of the following: fluorinated metal acids, fluorinated metal salts, or fluorides.

15. The surface treatment agent as described in claim 9, characterized in that, The water-soluble phosphorus-containing compound E is selected from at least one of: ammonium dihydrogen phosphate, zinc dihydrogen phosphate, manganese dihydrogen phosphate, phosphoric acid, phytic acid, and hydroxyethylidene diphosphonic acid.

16. A method for manufacturing a zinc-aluminum-magnesium coated steel sheet adapted for electron beam coating, characterized in that, Including the following steps: The surface treatment agent as described in any one of claims 9-15 is applied to the surface of a zinc-aluminum-magnesium coated steel sheet and cured into a film to form a composite coating on the surface of the zinc-aluminum-magnesium coated steel sheet.

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