Coating material for steel sheet, and steel sheet having an electron beam cured coating layer formed therefrom

Abstract

An electron beam curable coating material for steel sheet, comprising the following active ingredients: 40 to 60 parts by weight of a composite matrix resin A, 3 to 10 parts by weight of an organosilicon compound B, 15 to 25 parts by weight of a monofunctional ethylenically unsaturated polymerizable monomer C, 5 to 15 parts by weight of an acrylic acid phosphate ester compound D, and 0.3 to 2.0 parts by weight of an acrylic acid titanium salt or zirconium salt compound E, wherein A comprises an aliphatic polyurethane acrylate oligomer A1 and an amine-modified epoxy diacrylate oligomer A2, and the weight ratio of A1 to A2 is 1.0 to 5.0, and A1 contains 20 to 30 wt % of isobornyl acrylate, based on the weight of A1, and 30 to 40 wt % of dipropylene glycol diacrylate, based on the weight of A2. Also provided is a steel sheet comprising a steel substrate, a plating layer on the surface of the steel substrate, and an electron beam curable coating layer applied to the surface of the plating layer.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a coating material, and more particularly to an electron beam curable coating material for steel sheets. [Background technology]

[0002] Background technology Coated steel sheets, also known as pre-coated steel sheets, are steel sheets manufactured by applying one or more layers of organic coating to the surface of a metal coil (e.g., cold-rolled sheet, hot-dip galvanized sheet, aluminum-coated sheet, zinc-aluminum-magnesium alloy-coated sheet) used as the base material, followed by a hardening process to form the coating.

[0003] The traditional manufacturing process for pre-coated steel sheets involves applying a water-based or organic solvent-based coating to the surface of a steel strip, followed by drying or curing the coating through thermal curing to form a film. This manufacturing method has long been the first choice in the steel coil industry due to its mature process and stable quality. However, the curing speed of the thermal curing coating and the limited space required for the equipment make it difficult to further improve the production efficiency of traditional pre-coated steel sheets. Furthermore, the thermal curing method consumes a lot of energy, resulting in high infrastructure costs and high operating costs. Furthermore, the evaporation of the solvent causes environmental pollution, and combustion emits large amounts of CO2.

[0004] To overcome these problems, low-energy, fast-curing, and solvent-free technologies are currently the trend of development, with electron beam (EB) curing being the most promising. EB curing is a process that uses electron beams as an excitation source in the coating curing process, achieving instantaneous curing and film formation of solvent-free coatings at room temperature. Compared with traditional heat curing, EB curing offers many advantages, including environmental protection, energy efficiency, high productivity, and low carbon emissions. Currently, EB curing is being applied in industries such as wood, paper, and optical fiber. EB-cured coatings in these fields generally do not require further processing, and the working environment is relatively mild.

[0005] However, in the field of steel sheet coating, the cured coating still requires subsequent processing procedures such as rolling and stamping, and must also withstand harsh outdoor conditions. Therefore, the EB-cured coating layer on the metal substrate must have excellent adhesion properties, especially adhesion properties after formation, wet adhesion properties after water penetration, and corrosion resistance. However, existing EB-cured coating layers cannot achieve these properties on metal substrates. Summary of the Invention

[0006] Summary of the Invention One object of the present invention is to provide a coating material for steel sheets, and an electron beam-cured coating layer formed by applying the coating material to a steel sheet has excellent dry and wet adhesion properties and good underfilm corrosion resistance.

[0007] In order to achieve the above object, the present invention provides a coating material for steel sheets, wherein the coating material comprises the following active ingredients: Composite matrix resin A: 40 to 60 parts by weight; Organosilicon compound B: 3 to 10 parts by weight; Monofunctional ethylenically unsaturated polymerizable monomer C: 15 to 25 parts by weight; Acrylic acid phosphate ester compound D: 5 to 15 parts by weight; Acrylic acid titanium salt or zirconium salt compound E: 0.3 to 2.0 parts by weight; Including, The composite matrix resin A comprises an aliphatic polyurethane acrylate oligomer A1 and an amine-modified epoxy diacrylate oligomer A2, and the weight ratio of A1 to A2 is 1.0-5.0; based on the weight of A1, A1 comprises 20-30 wt% isobornyl acrylate, and based on the weight of A2, A2 comprises 30-40 wt% dipropylene glycol diacrylate.

[0008] The present application further provides a coating material for steel sheets, wherein the active ingredients of the coating material are: Composite matrix resin A: 40 to 60 parts by weight; Organosilicon compound B: 3 to 10 parts by weight; Monofunctional ethylenically unsaturated polymerizable monomer C: 15 to 25 parts by weight; Acrylic acid phosphate ester compound D: 5 to 15 parts by weight; Acrylic acid titanium salt or zirconium salt compound E: 0.3 to 2.0 parts by weight; It consists of The composite matrix resin A comprises an aliphatic polyurethane acrylate oligomer A1 and an amine-modified epoxy diacrylate oligomer A2, and the weight ratio of A1 to A2 is 1.0-5.0; based on the weight of A1, A1 comprises 20-30 wt% isobornyl acrylate, and based on the weight of A2, A2 comprises 30-40 wt% dipropylene glycol diacrylate.

[0009] Preferably, in addition to the active ingredient, the balance of the coating material of the present invention is other unavoidable impurities.

[0010] The coating material of the present invention is applied to the surface of a steel sheet having a plating layer and then forms an electron beam-cured (EB-cured) coating layer through an electron beam curing process. Preferably, a top coat is further applied to the surface of the electron beam-cured coating layer to optimize the appearance of the steel sheet and / or to enhance protection of the substrate and the plating layer surface on the coating layer. The flexibility of the electron beam-cured coating layer, as well as its dry and wet adhesion properties to a metal substrate (specifically, a steel sheet having a plating layer in this invention), and its adhesion properties to the top coat, are all closely related to the specific type of composite matrix resin A. Dry adhesion properties refer to the adhesion properties between the coating layer and the metal substrate when the coated steel sheet is in a dry state, and wet adhesion properties refer to the adhesion properties between the coating layer and the metal substrate when the coated steel sheet is in a wet state.

[0011] In the present invention, the composite matrix resin A comprises an aliphatic polyurethane acrylate oligomer A1 and an amine-modified epoxy diacrylate oligomer A2. Based on the weight of A1, A1 contains 20-30 wt% isobornyl acrylate, whose polyurethane segments provide excellent flexibility to the coating. Based on the weight of A2, A2 contains 30-40 wt% dipropylene glycol diacrylate, which provides the coating with excellent adhesion to the metal substrate surface and compatibility with the topcoat.

[0012] In the coating material of the present invention, the weight ratio A1 / A2 of A1 to A2 is 1.0 to 5.0. If this ratio is less than 1.0, the flexibility of the coating may decrease, and if this ratio is greater than 5.0, the adhesion between the coating and both the metal substrate and the top coat may decrease. Preferably, A1 / A2 is 1.5 to 4.0, which allows for excellent coating adhesion performance.

[0013] Furthermore, based on 100 parts by weight of the total coating material, the composite matrix resin A accounts for 40 to 60 parts by weight of the coating material. If the content is less than 40 parts by weight, the flexibility of the coating and adhesion to the top coat and the metal substrate surface may decrease. If the content is more than 60 parts by weight, adhesion to the subsequent top coat and wet adhesion to the metal substrate may decrease.

[0014] In the present invention, the aliphatic polyurethane acrylate oligomer A1 preferably has the following properties: a viscosity at 25°C of 15,000 to 25,000 mPa·s, a molecular weight of 2,000 to 4,000, a functionality of 2, and a viscosity of 1.0 to 1.2 g / m 2 and a glass transition temperature (Tg) of 35 to 55°C.

[0015] In the present invention, the amine-modified epoxy diacrylate oligomer A2 preferably has the following properties: a viscosity at 25°C of 500 to 1500 mPa·s, a functionality of 2, and a viscosity of 1.0 to 1.2 g / m 2 It has a density of 1000 MPa, a glass transition temperature (Tg) of 70-90°C, and an acid value of 2-4 mgKOH / g.

[0016] The role of organosilicon compound B in this invention is to further improve the wet adhesion and underlayer corrosion resistance of the EB-cured coating layer and the metal substrate. Meanwhile, the vinyl groups in the organosilicon compound can participate in reactions during radiation curing, combining with the composite matrix resin A. Meanwhile, when water or water vapor, including corrosive agents (oxygen, carbon dioxide, etc.), penetrates the coating and reaches the substrate interface, organosilicon compound B in the cured coating undergoes hydrolysis in the presence of water to generate Si-OH groups. These Si-OH groups then undergo dehydration condensation with Me-OH groups (Me = metal) on the metal surface, forming strong Si-O-Me covalent bonds at the metal interface. This mechanism prevents further diffusion of corrosive agents, thereby reducing underlayer corrosion and further improving wet adhesion between the coating and the metal substrate interface. Another role of organosilicon compound B is to improve the bond strength between the EB-cured coating layer and the topcoat (such as a solvent-based topcoat or a radiation-cured topcoat).

[0017] Preferably, the content of organosilicon compound B in the coating material is 3 to 10 parts by weight. If the content is less than 3 parts by weight, sufficient wet adhesion and under-film corrosion resistance may not be achieved. If the content is more than 10 parts by weight, the surface energy of the cured coating may decrease, resulting in shrinkage defects during the topcoat application or curing process and reduced adhesion between the EB-cured coating layer and the topcoat.

[0018] In the present invention, the monofunctional ethylenically unsaturated polymerizable monomer C is a monofunctional reactive acrylic monomer with a relatively high Tg. The monofunctional ethylenically unsaturated polymerizable monomer C participates in a crosslinking reaction during the electron beam curing process, and the reactivity of its monofunctional group reduces the shrinkage of the coating during the curing process, thereby ensuring the adhesion performance of the formed coating to metal substrates. Preferably, the weight ratio of the monofunctional ethylenically unsaturated polymerizable monomer C in the coating material is 15 to 25 parts by weight. If the content is less than 15 parts by weight, the degree of curing of the coating is insufficient, and the dry and wet adhesion properties of the coating are reduced. If the content is more than 25 parts by weight, the cure shrinkage of the coating increases, which may adversely affect the dry adhesion performance of the coating to metal substrates.

[0019] In the present invention, acrylic acid phosphate ester compound D functions as an adhesion promoter. The adhesion promoter can significantly improve the dry and wet adhesion of the EB-cured coating to the metal substrate through fine phosphorylation with the metal surface. Preferably, the amount of acrylic acid phosphate ester compound D in the coating material is 5 to 15 parts by weight. If the content is less than 5 parts by weight, the dry and wet adhesion between the cured coating and the metal substrate may be reduced. If the content is more than 15 parts by weight, the adhesion between the cured coating and the top coat may be reduced.

[0020] In the present invention, the titanium or zirconium acrylic acid compound E functions as an interfacial corrosion inhibitor. The primary function of the interfacial corrosion inhibitor is to improve the coating's resistance to subsurface corrosion. Meanwhile, the acrylic acid component is involved in film formation during the electron beam curing process. Meanwhile, when water or water vapor, especially water or water vapor containing corrosive agents (oxygen, carbon dioxide, etc.), penetrates the coating or reaches the interface between the coating and the metal substrate through defects, the metal salt compound in the coating undergoes a passivation reaction with the metal substrate surface in the presence of water, thereby preventing further diffusion of water or other corrosive agents. Preferably, the titanium or zirconium acrylic acid compound E in the coating material is 0.3 to 2.0 parts by weight. If the content is less than 0.3 parts by weight, the effect of subsurface corrosion resistance is not significant. If the content is greater than 2.0 parts by weight, the flexibility of the cured coating may be affected.

[0021] Preferably, in some embodiments of the present invention, the active ingredient of the coating material is one of the following ingredients: Anti-rust pigment F: 2 to 5 parts by weight; hiding pigment G: 5 to 10 parts by weight; Additive H: 0.2 to 1 part by weight The present invention further includes at least one selected from the following:

[0022] The rust prevention mechanism of anti-corrosion pigments is that when corrosive agents (such as water and oxygen) penetrate the interface between the cured coating and the metal substrate, a corrosion reaction occurs. The metal atoms at the interface are oxidized, losing electrons to form metal ions, and oxygen gains electrons to form OH. - ions, thus creating an alkaline environment at the interface between the cured coating and the metal substrate. Preferably, the anti-rust pigment in the coating is 2.0 to 5.0 parts by weight. If the content is less than 2.0 parts by weight, the anti-rust effect is not significant. If the content is more than 5.0 parts by weight, the flexibility of the cured coating may be adversely affected.

[0023] The purpose of the hiding pigment is to provide a certain degree of hiding power to the metal substrate, which is beneficial for the uniformity of the appearance after the subsequent application of a top coat. Preferably, the hiding pigment content in the coating material is 5.0 to 10.0 parts by weight. If the content is less than 5.0 parts by weight, the hiding effect is not significant. If the content is more than 10 parts by weight, the adhesion of the cured coating may be reduced.

[0024] Preferably, in the coating material of the present invention, the weight ratio of A1 to A2 is 1.5 to 4.0.

[0025] Preferably, in the coating material of the present invention, the organosilicon compound B comprises at least one selected from the following: vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltriisopropoxysilane, methylvinyldimethoxysilane, vinyltriacetoxysilane, (methacryloxy)propyltriacetoxysilane, (triethoxysilyl)propyl methacrylate, and triethoxysilane methacrylate.

[0026] Preferably, in the coating material of the present invention, the monofunctional ethylenically unsaturated polymerizable monomer C comprises at least one selected from the following: hydroxypropyl methacrylate, cyclic trimethylolpropane formal acrylate, cyclic trimethylolpropane formal monoacrylate, isobornyl acrylate, lauryl acrylate, lauryl methacrylate, and octyl / decyl acrylate.

[0027] Preferably, in the coating material of the present invention, the acrylic acid phosphate ester compound D comprises at least one selected from the following: polyethylene glycol methacrylate phosphate, bis(hydroxyethyl acrylate) phosphate, 2-hydroxyethyl methacrylate phosphate, and bis(methacryloyloxyethyl) hydrogen phosphate.

[0028] Preferably, in the coating material of the present invention, the titanium or zirconium salt of acrylic acid compound E comprises at least one selected from the following: titanium triisopropoxide methacrylate, zirconium acrylate, and zirconium tetrakis(methacrylate).

[0029] Preferably, in the coating material of the present invention, the rust-preventive pigment F contains an ion-exchange alkaline silica powder.

[0030] Ion-exchange alkaline silica powder has a low density (e.g., 0.15 g / cm 3 bulk density below 80 m 2 / g or more). In an alkaline environment, it can dissolve into silicic acid or silicate ions. These soluble components can react with metal ions at the interface between the coating and the metal to form a protective layer of metal silicate, thereby preventing further corrosion of the metal at the interface.

[0031] More preferably, the ion-exchange alkaline silica powder in the coating material of the present invention has an average particle size of 2-6 μm and a pH of 8-10.

[0032] Preferably, in the coating material of the present invention, the hiding pigment G comprises titanium dioxide. Preferably, in the coating material of the present invention, additive H includes at least one selected from a leveling agent, a wetting agent, and an anti-settling agent.

[0033] Another object of the present invention is to provide a steel sheet having an electron beam cured coating layer that exhibits excellent dry and wet adhesion and underfilm corrosion resistance. The steel sheet can be used independently while satisfying subsequent processing and use conditions, or it can be used as a primer-coated substrate to which a topcoat can be applied to form a double-coated color-coated steel sheet characterized by good adhesion and overall corrosion resistance.

[0034] In order to achieve the above object, the present invention provides a steel sheet comprising a steel substrate, a plating layer on a surface of the steel substrate, and an electron beam hardened coating layer on the surface of the plating layer, wherein the electron beam hardened coating layer is formed by applying the coating material onto the surface of the plating layer and hardening it by electron beam irradiation.

[0035] It should be noted that the coating material of the present invention is solvent-free and the coating formed by electron beam curing retains the same composition as the coating material, i.e., the active ingredients and their proportions in the electron beam cured coating are exactly the same as those in the coating material.

[0036] Preferably, in the steel sheet of the present invention, the electron beam hardened coating layer has a single layer structure. Preferably, the thickness of the electron beam cured coating layer in the steel sheet of the present invention is 3 to 30 μm, preferably 3 to 10 μm. When the metal substrate has only an electron beam cured coating, the thickness of the coating can be 3 to 30 μm to ensure sufficient protection. When a top coat is applied after forming the electron beam cured coating on the metal substrate, the thickness of the electron beam cured coating is preferably 3 to 10 μm, and the top coat can also provide some protective effect.

[0037] Preferably, the plating layer in the steel sheet of the present invention includes a hot-dip zinc layer, a hot-dip aluminum-zinc layer, a hot-dip zinc-aluminum-magnesium layer, and an electrogalvanized zinc layer.

[0038] Preferably, the steel sheet of the present invention is subjected to electron beam hardening under the following conditions: in a protective atmosphere of a mixture of nitrogen and oxygen with an oxygen content ≦200 ppm, an electron beam voltage of 90-150 kV, and an electron dose of 10-60 kGy.

[0039] The present invention makes it possible to form an electron beam cured coating layer having excellent dry and wet adhesion properties and underfilm corrosion resistance by applying the above coating material to a steel sheet and curing it via electron beam irradiation. DETAILED DESCRIPTION OF THE INVENTION

[0040] Detailed Description The coating material and steel sheet according to the present invention will be further described and illustrated with reference to the following specific embodiments, but these descriptions and illustrations should not be construed as excessively limiting the technical solutions of the present invention.

[0041] Examples 1 to 9 and Comparative Examples 1 to 9 In order to demonstrate the effects of the present invention, the inventors prepared coil coating materials for forming electron beam curable coatings of Examples 1 to 9 and coil coating materials of Comparative Examples 1 to 9.

[0042] These coating materials were applied to cold-rolled steel strips having a plating layer, and then subjected to an electron beam hardening process to form a single-layer electron beam hardened coating layer on the steel strip surface.

[0043] Here, the electron beam curing was carried out under the following conditions: in a mixed protective atmosphere of nitrogen and oxygen with an oxygen content of ≦200 ppm, an electron beam voltage of 90-150 kV, and an electron beam dose of 10-60 kGy.

[0044] Table 1 lists the compositions of the plating layer and electron beam hardened coating of the steel sheets of Examples 1 to 9 and Comparative Examples 1 to 9. It should be noted that the composition of the electron beam hardened coating is the same as that of the coil coating material.

[0045] [Table 1]

[0046] Note: A1 in Table 1 is an aliphatic polyurethane acrylate oligomer containing 30 wt% isobornyl acrylate (IBOA), with a viscosity of 21000 mPa s at 25 °C, a molecular weight of 2700 g / mol, a functionality of 2, and a density of 1.1 g / m. 2 , and the glass transition temperature is 46° C. Each example listed in Table 1 uses an aliphatic polyurethane acrylate oligomer containing 30 wt % isobornyl acrylate (IBOA), although other aliphatic polyurethane acrylate oligomers containing 20-30 wt % isobornyl acrylate are also viable.

[0047] A2 in Table 1 is an amine-modified epoxy diacrylate oligomer containing 35 wt% dipropylene glycol diacrylate (DPGDA), with a viscosity of 1100 mPa s at 25 °C, a functionality of 2, and a density of 1.14 g / m 2 , a glass transition temperature of 80°C, and an acid value of 3 mgKOH / g. Each example listed in Table 1 uses an amine-modified epoxy diacrylate oligomer containing 35 wt% dipropylene glycol diacrylate (DPGDA), although other amine-modified epoxy diacrylate oligomers containing 30-40 wt% dipropylene glycol diacrylate are also feasible.

[0048] The specific types of organosilicon compounds (B) in Table 1 are as follows:

[0049] JPEG2026506325000002.jpg53112

[0050] Specific types of the monofunctional ethylenically unsaturated polymerizable monomer (C) in Table 1 are as follows:

[0051] JPEG2026506325000003.jpg48125

[0052] The specific types of adhesion promoters (D) in Table 1 are as follows:

[0053] JPEG2026506325000004.jpg31118

[0054] The specific types of interfacial corrosion inhibitors (E) in Table 1 are as follows:

[0055] JPEG2026506325000005.jpg26101

[0056] Anti-rust pigment F in Table 1 is an ion-exchange alkaline silica powder having an average particle size of 3 μm and a pH of 8.5. It should be noted that an ion-exchange alkaline silica powder having an average particle size of 2-6 μm and a pH of 8-10 is also acceptable. Furthermore, other pigments known in the art that can achieve the anti-rust function are also acceptable as long as they satisfy the anti-rust function.

[0057] The hiding pigment G in Table 1 is titanium dioxide. It should be noted that other pigments known in the art that can achieve the hiding effect are also feasible and fall within the protection scope of the present invention.

[0058] Additive H in Table 1 is selected from a leveling agent, a wetting agent, an anti-settling agent, or a combination thereof. If a leveling agent is used, it can be an acrylic leveling agent or a silicone-based leveling agent. If a wetting agent is used, it can be a surfactant commonly used in existing coating materials. If an anti-settling agent is used, it can be a stearic acid derivative or fumed silica. In actual operation, it can be adjusted based on the type of steel sheet to be coated.

[0059] The types of additives used in the coating of the present invention are not significantly different from those used in existing coatings. The objective of the present invention is to tailor the active ingredients of the coating to achieve effective protection of the substrate during use of the steel sheet.

[0060] It should be noted that while Table 1 lists single substances for components B, C, D, and E in each example, mixtures are also possible. For example, component B can be a mixture of B1 and B2, component C can be a mixture of C2, C4, and C7, etc.

[0061] The solution of the present invention is to demonstrate the excellent performance of the electron beam cured coating layer formed by the designed coil coating material, and it should be noted that there is no particular limitation on the type of steel substrate used, so in practical application, those skilled in the art can select an appropriate steel substrate according to specific requirements.

[0062] Table 2 lists the parameters of the electron beam curing process used to form the electron beam cured coating layers of Examples 1-9 and Comparative Examples 1-9.

[0063] [Table 2]

[0064] NOTE: Electron beam curing was performed in a nitrogen protective atmosphere with an oxygen content ≤ 200 ppm.

[0065] Therefore, in order to confirm the beneficial effects of the coating material designed according to the present invention and the electron beam cured coating formed therefrom, the coated steel sheets of Examples 1 to 9 and Comparative Examples 1 to 9 were sampled and tested as follows, and the test data obtained are listed in Table 3. Specific test items and test methods are as follows:

[0066] 1.Dry adhesion 1.1 T-bend test: The test was conducted according to Section 7 Bending Test of GB / T 13448-2019. The evaluation criteria are as follows: ◎: No peeling of coating and substrate, T-bending level ≦ 3T ○: No peeling of coating-substrate, T-bending level = 4T Δ: No peeling of coating-substrate, T-bending level = 5T ×: T-bending level ≧ 6T with no peeling of coating-substrate

[0067] 1.2 Cross-cut test: The test was conducted in accordance with Section 13 Cross-cut Adhesion Test of GB / T 13448-2019, and the results were scored according to the cross-cut adhesion test score table shown in Table 1 of GB / T 13448-2019. The evaluation criteria were as follows: ◎:Grade 0 ○: Grade 1~2 Δ: Grade 3~4 ×: Grade 5

[0068] 1.3 Impact test: The test was conducted according to Section 8 Reverse Impact Test of GB / T 13448-2019. The test evaluation criteria are as follows: ◎: Impact energy ≥ 9J for no peeling between coating and substrate ○: No peeling between the coating and the substrate, impact energy = 7 to 9 J (excluding 9 J) Δ: Impact energy = 6 to 7 J (excluding 7 J) for no peeling between the coating and the substrate ×: Impact energy <6J for no peeling between coating and substrate

[0069] 2. Wet adhesion 2.1 Boiling test: Steel plate samples were immersed in boiling water for 2 hours. After removal, the coating appearance was visually evaluated for blistering or peeling, and then a cross-cut test was performed according to Section 13 Cross-cut Adhesion Test of GB / T 13448-2019. The evaluation was performed according to the cross-cut adhesion test scoring table shown in Table 1 of GB / T 13448-2019: ◎: No blistering or peeling is observed visually; Cross-cut test score = Grade 0 ○: No peeling and slight swelling (swelling area <50%); Cross-cut test score = Grade 1-2 Δ: No peeling and significant swelling (swelling area ≧50%); Cross-cut test score = Grade 3 to 4 ×: Peeling of the coating is observed; cross-cut test score = grade 5

[0070] 2.2 Saltwater immersion test: The sample was immersed in a 5 wt% NaCl aqueous solution for 72 hours. After removal, the appearance of the coating was visually evaluated for blistering or peeling. The evaluation criteria were as follows: ◎: No swelling or peeling is observed ○: No peeling and slight swelling (swelling area <50%) Δ: No peeling and significant swelling (swelling area ≧50%) ×: Peeling of coating is observed

[0071] 3. Undercoat corrosion resistance test: Before the test, a straight line parallel to the long side of the sample was scribed at the neutral position using a knife. The scribed line had a length of ≥ 50 mm, penetrated completely through the coating, and was positioned ≥ 30 mm from the edge of the sample. Then, a salt spray test was performed according to ASTM B117 for 1000 hours. The evaluation criteria were as follows: ◎: Average one-sided corrosion width of the scribed line ≦ 3 mm ○: Average one-sided corrosion width in the scribed line > 3 mm and ≦ 10 mm Δ: Average one-sided corrosion width in the scribed line > 10 mm and ≦ 15 mm ×: Average one-sided corrosion width in the scribed line > 15 mm

[0072] 4. Testing topcoat adhesion and overall corrosion resistance of coated steel sheets For Examples 1-9 and Comparative Examples 1-9, a conventional solvent-based polyester topcoat (15 μm film thickness) was applied to an EB-cured coated steel panel having an electron beam cured coating layer and cured for 20-30 seconds at a panel metal temperature (PMT) of 241-254° C. The fully coated samples were then subjected to the following tests to evaluate the adhesion between the EB-cured coating and the topcoat, and the overall corrosion protection provided by the combined coating system.

[0073] 4.1 T-bend test: The test was conducted according to Section 7 Bending Test of GB / T 13448-2019. The test evaluation criteria are as follows: ◎: No peeling between the EB-cured coating and the top coat, T-bend level ≦ 3T ○: No delamination between the EB-cured coating and the top coat, T-bend level = 4T Δ: T-bend level = 5T for no delamination between the EB-cured coating and the top coat ×: No peeling between the EB-cured coating and the top coat, T-bend level ≧6T

[0074] 4.2 Cross-cut test: The test was conducted in accordance with Section 13 Cross-cut Adhesion Test of GB / T 13448-2019, and the results were scored according to the cross-cut adhesion test score table shown in Table 1 of GB / T 13448-2019. The evaluation criteria were as follows: ◎: No peeling between the EB cured coating and the top coat, cross-cut test score = Grade 0 ○: No peeling between the EB cured coating and the top coat, cross-cut test score = grade 1 to 2 Δ: No peeling between the EB cured coating and the top coat, cross-cut test score = grade 3-4 ×: No peeling between the EB cured coating and the top coat, cross-cut test score = grade 5

[0075] 4.3 Impact test: The test was conducted according to Section 8 Reverse Impact Test of GB / T 13448-2019. The test evaluation criteria are as follows: ◎: Impact energy ≥ 9J for no peeling between EB cured coating and top coat ○: No peeling between the EB-cured coating and the top coat, impact energy = 7 to 9 J (excluding 9 J) Δ: Impact energy = 6 to 7 J (excluding 7 J) for no peeling between the EB-cured coating and the top coat ×: Impact energy <6J for no delamination between EB-cured coating and top coat

[0076] 4.4 Topcoat corrosion resistance test The flat panels were subjected to a 1000-hour neutral salt spray test in accordance with ASTM B117. The evaluation was based on the overall rating of the aging performance level of the protective coating as shown in Table 23 of GB / T 1766-2008: ◎: Swelling density rating and swell size ≦ Grade 2 ○: Swelling density rating and swell size ≦ grade 3 Δ: Swelling density rating and swell size ≦ grade 4 ×: Swelling density rating and swell size ≦ grade 5

[0077] Table 3 lists the test data of the steel sheets having electron beam cured coating layers in Examples 1 to 9 and Comparative Examples 1 to 9 after the above tests.

[0078] [Table 3]

[0079] Combining Tables 1 and 3, it can be seen that in Comparative Example 1, the content of composite matrix resin A was insufficient and the content of monofunctional ethylenically unsaturated polymerizable monomer C was excessive, which did not promote the dry adhesion performance of the electron beam cured coating layer on the steel sheet, and the insufficient dry adhesion directly affected the wet adhesion and underfilm corrosion resistance.

[0080] In Comparative Example 2, the content of organosilicon compound B was too high, which reduced the surface energy of the electron beam cured coating layer and reduced the adhesion performance between the electron beam cured coating layer and the subsequent top coat, while the excessive content of hiding pigment G adversely affected the dry adhesion performance of the coating.

[0081] In Comparative Example 3, the content of acrylic acid phosphate ester compound D (as an adhesion promoter) was excessive, resulting in poor adhesion between the coating and the subsequent top coat. Also, the content of anti-rust pigment F was insufficient, resulting in insignificant anti-rust effect, which was manifested in poor under-film corrosion resistance of the electron beam cured coated steel sheet and poor corrosion resistance when combined with a top coat.

[0082] In Comparative Example 4, the ratio of A1 to A2 in the composite matrix resin A was excessive, resulting in an insufficient content of the amine-modified epoxy diacrylate oligomer, which primarily provides adhesive properties in the coating, adversely affecting both dry and wet adhesion. In addition, the excessive content of the titanium salt or zirconium salt compound E of acrylic acid affected the flexibility of the coating, thereby affecting the dry adhesion performance of the coating.

[0083] In Comparative Example 5, the content of composite matrix resin A was excessive, which resulted in a relatively low proportion of components providing adhesion, corrosion inhibition, and other functions, and did not contribute to the dry and wet adhesion of the coating.The content of monofunctional ethylenically unsaturated polymerizable monomer C was insufficient, which resulted in incomplete crosslinking and reduced dry adhesion of the coating.

[0084] In Comparative Example 6, the content of organosilicon compound B was insufficient, so the coating did not have sufficient wet adhesion and under-film corrosion resistance.

[0085] In Comparative Example 7, the insufficient content of titanium or zirconium salt of acrylic acid compound E (as an interfacial corrosion inhibitor) resulted in an insignificant under-film corrosion resistance effect, and the insufficient content of hiding pigment G resulted in an insufficient covering effect of the coating.

[0086] In Comparative Example 8, the content of acrylic acid phosphate ester compound D (as an adhesion promoter) was low, resulting in poor dry and wet adhesion performance of the coating. Excessive addition of anti-rust pigment F impaired the flexibility of the coating, thereby affecting the dry adhesion performance.

[0087] In Comparative Example 9, the absence of aliphatic polyurethane acrylate oligomer A1 affected the flexibility of the coating, which in turn affected the dry adhesion performance of the coating. Furthermore, the thickness of the coating was smaller than the average particle size of the anti-corrosion pigment silica in the coating, which reduced the wet adhesion performance of the coating and reduced the overall corrosion resistance when combined with a top coat.

[0088] In contrast, the electron beam cured coated steel sheets of Examples 1 to 9 of the present invention all exhibited excellent dry and wet adhesion, as well as undercoat corrosion resistance, and were able to form good adhesion with the top coat and overall corrosion resistance.

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

Claims

1. A coating material for steel sheets, the coating material comprising the following active ingredients: Composite matrix resin A: 40 to 60 parts by weight; Organosilicon compound B: 3 to 10 parts by weight; Monofunctional ethylenically unsaturated polymerizable monomer C: 15 to 25 parts by weight; Acrylic acid phosphate ester compound D: 5 to 15 parts by weight; Acrylic acid titanium salt or zirconium salt compound E: 0.3 to 2.0 parts by weight; Including, The composite matrix resin A comprises an aliphatic polyurethane acrylate oligomer A1 and an amine-modified epoxy diacrylate oligomer A2, and the weight ratio of A1 to A2 is 1.0 to 5.0; based on the weight of A1, A1 comprises 20 to 30 wt % of isobornyl acrylate, and based on the weight of A2, A2 comprises 30 to 40 wt % of dipropylene glycol diacrylate. Coating material for steel plates.

2. The active ingredient of the coating material is one of the following: Composite matrix resin A: 40 to 60 parts by weight; Organosilicon compound B: 3 to 10 parts by weight; Monofunctional ethylenically unsaturated polymerizable monomer C: 15 to 25 parts by weight; Acrylic acid phosphate ester compound D: 5 to 15 parts by weight; Acrylic acid titanium salt or zirconium salt compound E: 0.3 to 2.0 parts by weight; It consists of The composite matrix resin A comprises an aliphatic polyurethane acrylate oligomer A1 and an amine-modified epoxy diacrylate oligomer A2, and the weight ratio of A1 to A2 is 1.0 to 5.0; based on the weight of A1, A1 comprises 20 to 30 wt % of isobornyl acrylate, and based on the weight of A2, A2 comprises 30 to 40 wt % of dipropylene glycol diacrylate. The coating material for steel sheet according to claim 1.

3. The active ingredient of the coating material is one of the following: Anti-rust pigment F: 2 to 5 parts by weight; Hiding pigment G: 5 to 10 parts by weight; Additive H: 0.2 to 1.0 parts by weight The coating material for steel sheet according to claim 1, further comprising at least one selected from the following:

4. 4. The coating material for steel sheets according to claim 1, wherein the weight ratio of A1 to A2 is 1.5 to 4.

0.

5. 4. The coating material for steel sheet according to claim 1, wherein the organosilicon compound B comprises at least one selected from the group consisting of vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltriisopropoxysilane, methylvinyldimethoxysilane, vinyltriacetoxysilane, (methacryloxy)propyltriacetoxysilane, (triethoxysilyl)propyl methacrylate, and triethoxysilane methacrylate.

6. 4. The coating material for steel sheet according to claim 1, wherein the monofunctional ethylenically unsaturated polymerizable monomer C comprises at least one selected from the following: hydroxypropyl methacrylate, cyclic trimethylolpropane formal acrylate, cyclic trimethylolpropane formal monoacrylate, isobornyl acrylate, lauryl acrylate, lauryl methacrylate, and octyl / decyl acrylate.

7. 4. The coating material for steel sheet according to claim 1, wherein the acrylic acid phosphate ester compound D comprises at least one selected from the following: polyethylene glycol methacrylate phosphate, bis(hydroxyethyl acrylate) phosphate, 2-hydroxyethyl methacrylate phosphate, and bis(methacryloyloxyethyl) hydrogen phosphate.

8. The coating material for steel sheet according to any one of claims 1 to 3, wherein the titanium salt or zirconium salt compound E of acrylic acid comprises at least one selected from the following: titanium triisopropoxide methacrylate, zirconium acrylate, and zirconium tetrakis(methacrylate).

9. 4. The coating material for steel sheets according to claim 3, wherein the anti-rust pigment F contains an ion-exchange alkaline silica powder.

10. 10. The coating material for steel sheets according to claim 9, wherein the ion-exchange alkaline silica powder has an average particle size of 2 to 6 μm and a pH of 8 to 10.

11. 4. The coating material for steel sheets according to claim 3, wherein the hiding pigment G contains titanium oxide.

12. 4. The coating material for steel sheets according to claim 3, wherein the additive H comprises at least one selected from the group consisting of a leveling agent, a wetting agent, and an anti-settling agent.

13. A steel sheet comprising a steel substrate, a plating layer on a surface of the steel substrate, and an electron beam hardened coating layer on the surface of the plating layer, The coating material according to any one of claims 1 to 12 is applied onto the surface of the plating layer, and then the electron beam cured coating layer is formed by electron beam curing. steel plate.

14. The steel sheet according to claim 13, wherein the electron beam cured coating layer has a single layer structure.

15. The steel sheet according to claim 13, wherein the thickness of the electron beam cured coating layer is 3 to 30 μm, preferably 3 to 10 μm.

16. The steel sheet according to claim 13, wherein the plating layer comprises a hot-dip zinc layer, a hot-dip aluminum-zinc layer, a hot-dip zinc-aluminum-magnesium layer, and an electrogalvanized zinc layer.

17. The steel sheet according to claim 13, wherein the electron beam hardening is carried out under the following conditions: in a mixed protective atmosphere of nitrogen and oxygen with an oxygen content of ≦200 ppm, an electron beam voltage of 90-150 kV, and an electron beam dose of 10-60 kGy.

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