Chromium-free inorganic surface treatment agent for galvanized steel sheet, galvanized steel sheet, and method for manufacturing same

Abstract

The application discloses a chromium-free inorganic surface treatment agent for galvanized steel plate, which contains 11.5-15% of total solid content in mass percentage in an aqueous solution, and components of the total solid content are as follows: a compounded silane coupling agent A, which accounts for 45-65% of the total solid content in mass percentage; a surface modified water-based silica sol B, which accounts for 25-45% of the total solid content in mass percentage; a water-soluble phosphorus-containing compound C, which accounts for 0.5-1% of the total solid content in mass percentage of phosphorus element; a water-soluble fluorine-containing compound D, which accounts for 1-6% of the total solid content in mass percentage of fluorine element; and a lubricating aid E, which accounts for 1-10% of the total solid content in mass percentage; wherein the compounded silane coupling agent A is compounded by four types of silane coupling agent monomers, i.e., a silane A1 with an epoxy group, a silane A2 with a mono-amino group, a silane A3 with an alkyl group and a silane A4 with a vinyl group.

Description

TECHNICAL FIELD

[0001] The present application relates to a surface treatment agent, in particular to a surface treatment agent for a galvanized steel sheet. BACKGROUND

[0002] In recent years, with the increasing use of galvanized steel sheets, they have been widely used in the automobile, home appliance and construction industries.

[0003] It has been found in research that, in actual use, in order to improve the performance of the galvanized steel sheet during storage, processing and service, and to prevent white rust from occurring on the galvanized steel sheet during transportation and storage, the technical solution in the art often applies rust-proof oil to the surface of the steel sheet when the steel sheet is produced; and in order to reduce the friction between the galvanized steel sheet and the mold during stamping forming, and to prevent the steel sheet from cracking and the zinc layer from being scratched, lubricating oil is applied to the mold, and then the surface is cleaned by a solvent type or alkaline degreasing agent. In the entire process, the use of rust-proof oil, lubricating oil and degreasing agent brings a great burden to the environment and production cost.

[0004] Therefore, the existing technology is to perform chromic acid passivation on the galvanized steel sheet, or to further coat an organic resin containing a lubricant on the surface of the chromate passivation film, so as to achieve the effects of corrosion resistance and processing. However, with the introduction of environmental protection instructions, the galvanized post-processing steel sheet containing chromium has been gradually replaced by an environmentally friendly post-processing.

[0005] At present, the lubricating film covered on the surface of the galvanized steel sheet product designed by the existing technology can be roughly divided into inorganic type and organic / inorganic composite type. Among them, the environmentally friendly inorganic lubricating film mainly includes a thin film containing inorganic compounds such as silicon, manganese and phosphorus. This type of galvanized steel sheet product can obtain a good appearance after deep drawing processing, but it is difficult to achieve compatibility between corrosion resistance and paintability during service.

[0006] The organic / inorganic composite lubricating film is a thin film composed of resin, corrosion inhibitor, silane coupling agent, silica colloid and solid lubricating aid. This film not only has excellent lubricity and corrosion resistance, but also has good comprehensive resistance such as fingerprint resistance and alkali resistance to various chemical media.

[0007] It should be noted that the organic / inorganic composite system is the main scheme currently adopted by the galvanized surface treatment agent. This system can meet most processing and service scenarios. However, in some special scenarios (high-speed continuous stamping forming, high-water-cut coating and high-temperature environment), the galvanized steel sheet coated with these organic / inorganic composite surface treatment agents often has the phenomena of surface blackening during high-speed continuous forming, high-water-cut coating incompatibility and discoloration under heat due to the presence of organic components.

[0008] For example, when a progressive die is used to continuously and rapidly stamp a motor housing, it is inevitable that a portion of the surface film and plating of the galvanized steel sheet will be stripped. The continuous and rapid stamping will cause the temperature of the stamping die to rise, and the stripped debris will accumulate in the lubricating oil. The accumulated debris will adhere to the surface of the formed part again in this harsh environment, causing the part surface to darken (surface blackening) and damaging the appearance of the part.

[0009] For another example, when a liquid crystal module with high water cutting coating is prepared, the liquid crystal module requires high strength, good heat dissipation, anti-static, and good appearance. Therefore, the industry usually uses cutting, stamping, cleaning, spraying, and baking processes. In order to improve production efficiency, the drying temperature after cleaning is continuously increasing. Conventional post-processing products are difficult to meet the coating performance requirements under this process.

[0010] In addition, galvanized steel sheets are also used in high-temperature environments. For example, the air conditioner pipe plate for fixing the copper pipe in the outdoor unit of an air conditioner. When the copper pipe is flame brazed, the pipe plate made of galvanized steel sheet will inevitably be burned by the flame of the burner. When this organic / inorganic composite surface-treated steel sheet of the prior art is applied to this scenario, the film mainly composed of organic resin will discolor due to thermal decomposition, and surface cracks will appear, resulting in poor appearance.

[0011] Therefore, many researchers have studied surface treatment agents for galvanized steel sheets, and have achieved certain technical results, but the actual application effect is still not good:

[0012] Chinese patent document CN101376859A, published on March 4, 2009, entitled "Galvanized steel sheet surface lubricating treatment agent and treatment method", discloses the use of an inorganic treatment agent containing manganese, nickel, phosphate ions, and silane, which can form a transparent inorganic film on the surface of the galvanized steel sheet, thereby improving the stamping forming performance of the galvanized steel sheet and eliminating or reducing the zinc sticking and powdering phenomena during the forming process. Although this technical solution gives the steel sheet good lubrication processing properties, the corrosion resistance is not as good as that of chromate passivation products, and the film is easily cleaned with alkaline solution, and the corrosion resistance after alkaline treatment is significantly insufficient.

[0013] Chinese patent document CN101787527A, published on July 28, 2010, entitled "Galvanized Steel Sheet with Excellent Processability and Alkali and Solvent Resistance and Surface Treatment Agent," discloses a galvanized steel sheet with excellent processability and alkali and solvent resistance. Its surface is covered with an organic / inorganic composite film. This protective film is mainly composed of water-based cationic polyurethane resin and contains one or more organosilane coupling agents, corrosion inhibitors, and oxidized polyethylene particles. This protective film can impart excellent stamping formability, solvent resistance, and alkali resistance to the galvanized steel sheet surface, while also giving it good corrosion resistance and coating adhesion. However, this technical solution does not mention corrosion resistance after cleaning. Generally, household appliance parts, micro-motors, etc., are mostly used bare, and the above surface treatment method is difficult to guarantee corrosion resistance after alkaline treatment.

[0014] Chinese patent document CN102666921A, published on September 12, 2012, entitled "Surface Treatment Composition and Surface-Treatment Steel Sheet," discloses a post-treatment agent mainly composed of titanate, zirconium carbonate, and phosphate. Although the galvanized steel sheet coated with this surface treatment composition has good heat discoloration resistance, its corrosion resistance is still significantly insufficient.

[0015] Based on this, and in view of the technical problems existing in the prior art, the present invention aims to obtain a new chromium-free inorganic surface treatment agent for galvanized steel sheets. This chromium-free inorganic surface treatment agent can be applied to the surface of galvanized steel sheets and form a film on the surface of the galvanized steel sheets, so that the surface-treated galvanized steel sheet products have excellent forming appearance, excellent high-temperature water-cutting coating performance and high heat resistance. It has good prospects for promotion and application value. Summary of the Invention

[0016] The purpose of this invention is to provide a chromium-free inorganic surface treatment agent for galvanized steel sheets. This chromium-free inorganic surface treatment agent exhibits excellent storage stability and can be applied to the surface of galvanized steel sheets to form a film. This results in galvanized steel sheet products with excellent forming appearance, excellent high-temperature water-cutting coating performance, and high heat resistance. It also exhibits good corrosion resistance, alkali washing resistance, wear resistance, and formability, and has good prospects for promotion and application value.

[0017] To achieve the above objectives, the present invention provides a chromium-free inorganic surface treatment agent for galvanized steel sheets, wherein the aqueous solution contains a total solids content of 11.5-15% by mass, and the components of the total solids are as follows:

[0018] The compound silane coupling agent A accounts for 45-65% of the total solid content by mass.

[0019] Surface modified aqueous silica sol B, the mass percentage in total solid content is 25%-45%;

[0020] Water-soluble phosphorus-containing compound C, the mass percentage of phosphorus element in total solid content is 0.5%-1%;

[0021] Water-soluble fluorine-containing compound D, the mass percentage of fluorine element in total solid content is 1%-6%;

[0022] Lubricating aid E, the mass percentage in total solid content is 1%-10%;

[0023] The complex silane coupling agent A is compounded by the following four types of silane coupling agent monomers: silane A1 with epoxy group, silane A2 with mono-amino group, silane A3 with alkyl group and silane A4 with vinyl group.

[0024] In the above scheme, the inventors creatively designed a chromium-free inorganic surface treatment agent for galvanized steel sheet, and the galvanized steel sheet treated with the chromium-free inorganic surface treatment agent forms a film on the surface, which can ensure that the galvanized steel sheet has excellent appearance quality after continuous high-speed forming, and also provides excellent coating performance of the galvanized steel sheet after water cutting high-temperature baking; in addition, the film also makes the galvanized steel sheet have good corrosion resistance, alkali washing resistance and high heat resistance.

[0025] In the present application, the excellent properties of the entire formula system of the chromium-free inorganic surface treatment agent designed by the present application are closely related to the complex silane coupling agent A. In the design, the mass percentage of the complex silane coupling agent A in the total solid content is controlled to be 45-65%. If the mass percentage is less than 45%, the corrosion resistance of the film is insufficient; if the mass percentage exceeds 65%, the adhesion of the film is strong, which causes too much foreign matter to adhere to the surface of the formed part, deteriorates the appearance of the stamping forming, and the appearance deteriorates in high-temperature service environment.

[0026] In addition, in the present application, when designing the chromium-free inorganic surface treatment agent, the mass percentage of the surface modified aqueous silica sol B in the total solid content is also specifically controlled to be 25%-45%, because if the mass percentage of the surface modified aqueous silica sol B in the total solid content is less than 25%, the galvanized steel sheet product formed after the surface treatment agent is coated on the galvanized steel sheet will cause the appearance quality of the formed part to decrease, and affect the paintability of the subsequent part. If the mass percentage is higher than 45%, the overall density of the film is insufficient, which will cause insufficient corrosion resistance of the processed part.

[0027] In addition, in the present application, the mass percentage of phosphorus element in the water-soluble phosphorus-containing compound C is specifically controlled to be 0.5%-1% in the total solid content. If the mass percentage of phosphorus element is less than 0.5%, the passivation layer at the interface between the substrate and the coating is incomplete, and the corrosion resistance of the coating is reduced; if the mass percentage of phosphorus element is higher than 1%, the interface deposition passivation layer is excessive, and the adhesion of the coating is deteriorated.

[0028] In the present application, the mass percentage of fluorine element in the water-soluble fluorine-containing compound D is specifically controlled to be 1%-6% in the total solid content. If the mass percentage of fluorine element is less than 1%, the reactivity of the surface treatment agent to the surface of the steel plate substrate is insufficient, the surface conversion layer is thin, and the corrosion resistance is insufficient; if the mass percentage of fluorine element is greater than 6%, the stability of the surface treatment liquid is reduced.

[0029] Correspondingly, in the technical solution designed in the present application, the mass percentage of the lubrication aid E solid content is specifically controlled to be 1%-10% in the total solid content; if the mass percentage is less than 1%, the lubricity and wear resistance of the formed coating may not be enough; if it exceeds 10%, there are more solid lubricating particles inside the coating, which can cause excessive interface channels of the coating, and the corrosion medium can easily penetrate into the interior along the interface channels, reducing the corrosion resistance of the coating.

[0030] In some embodiments, the particle size of the lubrication aid particles can be further controlled to be between 0.2-0.5 microns. When the particle size of the lubrication aid particles is less than 0.2 microns, the wear resistance of the coating is insufficient; when the particle size of the lubrication aid particles exceeds 0.5 microns, the processing performance of the coating is deteriorated.

[0031] Further, in the chromium-free inorganic surface treatment agent described in the present application, the silane A1 with an epoxy group includes at least one of the following: 3-glycidyloxypropyl triethoxysilane, 3-glycidyloxypropyl trimethoxysilane, 3-glycidyloxypropyl methyl dimethoxysilane, 3-glycidyloxypropyl methyl diethoxysilane.

[0032] Further, in the chromium-free inorganic surface treatment agent described in the present application, the silane A2 with a mono-amino group includes at least one of the following: 3-aminopropyl methyl dimethoxysilane, 3-aminopropyl methyl diethoxysilane, 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane.

[0033] Further, in the chromium-free inorganic surface treatment agent described in the present application, the silane A3 with an alkyl group includes at least one of the following: triethoxysilyl ethane, trimethoxysilyl ethane, tetraethyl silicate.

[0034] In the present application, in some embodiments, the silane A3 having an alkyl group can specifically use: 1,2-bis(triethoxysilyl)ethane, 1,2-bis(trimethoxysilyl)ethane and tetraethyl silicate.

[0035] Further, in the chromium-free inorganic surface treatment agent described in the present application, the silane A4 having a vinyl group includes at least one of the following: vinyltriacetoxysilane, vinyltriisopropenoxysilane, vinyltriisopropoxysilane, vinyltrisilane, vinyltriethoxysilane and vinyltrimethoxysilane.

[0036] In the present application, in some embodiments, the silane A4 having a vinyl group can specifically use: vinyltriacetoxysilane, vinyltriisopropenoxysilane, vinyltriisopropoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltriethoxysilane and vinyltrimethoxysilane.

[0037] Further, the compounded silane coupling agent is prepared by the following steps:

[0038] The silane A1 having an epoxy group and the silane A3 having an alkyl group are first hydrolyzed and mixed;

[0039] After the silane A1 having an epoxy group and the silane A3 having an alkyl group are uniformly mixed, the monoamino silane A2 is added thereto;

[0040] After the three types of silanes are uniformly mixed, the vinyl silane A4 is added to the mixture.

[0041] Further, in the preparation process of the compounded silane coupling agent:

[0042] When the silane A1 having an epoxy group and the silane A3 having an alkyl group are hydrolyzed and mixed, the mass percentage content of the two is controlled to satisfy: A3 / A1: 0.2-0.6;

[0043] The addition amount of the monoamino silane A2 is controlled to satisfy: A2 / A1: 0.3-0.7, wherein A1 and A2 respectively represent the mass percentage content of the corresponding silane;

[0044] The addition amount of the vinyl silane A4 is controlled to satisfy: A4 / A1: 0.1-0.4, wherein A1 and A4 respectively represent the mass percentage content of the corresponding silane.

[0045] In the above technical solutions of the present application, the excellent properties exhibited by the entire formula system of the chromium-free inorganic surface treatment agent designed in the present application are closely related to the compounded silane coupling agent A.

[0046] In the process of preparing the compounded silane coupling agent A, the silane A1 with an epoxy group and the silane A3 with an alkyl group are first hydrolyzed and mixed, and the mass percentage of the two is controlled to satisfy A3 / A1: 0.2-0.6. The A3 / A1 is controlled between 0.2-0.6 because: if the ratio of A3 / A1 is less than 0.2, the number of hydrolyzed silanol groups is insufficient, the degree of chemical bonding between the substrate is weak, and the skin film is prone to fall off during the forming process, and the corrosion resistance of the skin film is reduced; and when the ratio of A3 / A1 exceeds 0.6, the designed surface treatment agent is prone to delamination or reduces the storage of the surface treatment agent.

[0047] Correspondingly, in the present application, after the silane A1 with an epoxy group and the silane A3 with an alkyl group are uniformly mixed, the inventors further add a monoamino silane A2 thereto. The addition amount of the monoamino silane A2 is controlled to satisfy A2 / A1: 0.3-0.7. This is because: if the value of A2 / A1 is less than 0.3, the crosslinking density in the skin film is insufficient, and the corrosion resistance of the skin film is insufficient; and if the value of A2 / A1 exceeds 0.7, the residual amino group is too much, resulting in strong hydrophilicity of the skin film and insufficient corrosion resistance.

[0048] After the above three types of silanes are uniformly mixed, the present application further adds a vinyl silane (A4) to the mixture, and the addition amount of the vinyl silane A4 is controlled to satisfy A4 / A1: 0.1-0.4. If the value of A4 / A1 is less than 0.1, the coating performance of the skin film will be reduced; and if the value of A4 / A1 is higher than 0.4, the corrosion resistance of the skin film will be reduced.

[0049] Further, in the chromium-free inorganic surface treatment agent described in the present application, the surface modified aqueous silica sol B is a silica sol modified by an organic compound containing an epoxy group, an amino group and a methyl functional group.

[0050] In the above technical solution of the present application, the surface modified silica sol B used in the present application can be specifically selected as: a silica sol modified by an organic compound containing an epoxy group, an amino group and a methyl functional group. This type of silica sol can be further crosslinked with active groups (amino, hydroxyl, etc.) in the compounded silane coupling agent to improve the resistance of the skin film. At the same time, this compound can reduce the adhesion of the peeled skin film on the surface of the molded part during the molding process, and improve the surface quality of the molded part.

[0051] Further, in the chromium-free inorganic surface treatment agent described in the present application, the water-soluble phosphorus-containing compound C includes phosphate and / or phosphoric acid.

[0052] Further, in the chromium-free inorganic surface treatment agent described in the present application, the water-soluble fluorine-containing compound D includes fluorine-containing salt and / or fluorine-containing acid.

[0053] Further, in the chromium-free inorganic surface treatment agent according to the present application, the lubricant aid E includes high-density polyethylene particles, polytetrafluoroethylene particle-based lubricant aid.

[0054] Accordingly, another object of the present application is to provide a galvanized steel sheet having a coating film formed by the chromium-free inorganic surface treatment agent according to the present application.

[0055] Further, in the galvanized steel sheet according to the present application, the coating film has a thickness of 0.3 to 1.5 micrometers.

[0056] In the technical solution according to the present application, the chromium-free inorganic surface treatment agent according to the present application is coated on the surface of the galvanized steel sheet to form an environmentally friendly inorganic surface treatment film on the surface of the galvanized steel sheet. The coating film can have a single-layer structure, and the thickness of the coating film can be 0.3 to 1.5 micrometers.

[0057] The thickness of the coating film is controlled to be 0.3 to 1.5 micrometers because, if the thickness of the coating film is less than 0.3 micrometers, the coating film will be too thin to have sufficient scratch resistance and rust resistance, and if the thickness of the coating film is more than 1.5 micrometers, the surface treatment cost will be increased.

[0058] In addition, another object of the present application is to provide a method for manufacturing the galvanized steel sheet according to the present application. The method has a simple process flow, and the galvanized steel sheet according to the present application can be effectively manufactured by using the method.

[0059] To achieve the above objects, the present application provides a method for manufacturing a galvanized steel sheet, which includes the following steps:

[0060] coating the chromium-free inorganic surface treatment agent on the surface of the galvanized steel sheet;

[0061] curing the chromium-free inorganic surface treatment agent by heating and drying to form a coating film on the surface of the galvanized steel sheet.

[0062] Further, in the method according to the present application, the chromium-free inorganic surface treatment agent is coated on the surface of the galvanized steel sheet by roll coating.

[0063] In the technical solution according to the present application, the chromium-free inorganic surface treatment agent is coated on the upper and lower surfaces of the galvanized steel sheet by roll coating, and then the chromium-free inorganic surface treatment agent is cured by heating and drying to control the thickness of the obtained coating film to be 0.3 to 1.5 micrometers.

[0064] Further, in the method according to the present application, the temperature for heating and drying is 80 to 180 degrees Celsius.

[0065] In the above technical solution of the present application, the temperature of the heated drying of the galvanized steel sheet can be preferably controlled between 80-180℃. If the temperature of the heated drying is lower than 80℃, the cross-linking of the film is not sufficient enough, which in turn leads to the decline of the performance of the film; if the temperature of the heated drying is higher than 180℃, the performance of some components in the surface treatment liquid changes, which in turn affects the film forming effect.

[0066] It should be noted that the present application does not have special requirements for the way of heated drying, which can be hot air heating, induction heating, infrared heating, etc. one or a combination of more than one.

[0067] In addition, the present application does not have special limitations on the size and shape of the galvanized steel sheet and other features.

[0068] Compared with the prior art, the chromium-free inorganic surface treatment agent for galvanized steel sheet, galvanized steel sheet and its manufacturing method described in the present application have the following advantages and beneficial effects:

[0069] The present application provides a chromium-free inorganic surface treatment agent for galvanized steel sheet, which itself has excellent storage stability, and which can be applied to the surface of the galvanized steel sheet and form a film on the surface of the galvanized steel sheet, so that the galvanized steel sheet product after surface treatment has excellent forming appearance, excellent high-temperature water cutting coating performance and high heat resistance, and shows good corrosion resistance, alkali washing resistance, wear resistance and formability, which has good popularization prospect and application value.

[0070] In actual use, the film formed on the surface of the galvanized steel sheet by using the chromium-free inorganic surface treatment agent described in the present application can not only ensure the scratch resistance and rust prevention performance of the galvanized steel sheet between processes, but also can make the appearance quality of the formed part excellent after continuous high-speed forming of the galvanized steel sheet, and can also provide the galvanized steel sheet with excellent coating performance after water cutting high-temperature baking. DETAILED DESCRIPTION

[0071] The chromium-free inorganic surface treatment agent for galvanized steel sheet, galvanized steel sheet and its manufacturing method described in the present application will be further explained and described below in conjunction with specific examples, however, the explanation and description do not constitute undue limitation on the technical solution of the present application.

[0072] Examples 1-42 and Comparative Examples 1-9

[0073] In the present application, the inventors correspondingly prepared the chromium-free inorganic surface treatment agents of Examples 1-42 and the comparative surface treatment agents of Comparative Examples 1-9. The aqueous solutions of the chromium-free inorganic surface treatment agents of Examples 1-42 and the comparative surface treatment agents of Comparative Examples 1-9 each added with a certain mass percentage of total solids, which specifically included: compounded silane coupling agent A, surface-modified aqueous silica sol B, water-soluble phosphorus-containing compound C, water-soluble fluorine-containing compound D, and lubricating aid E.

[0074] In the present application, the compounded silane coupling agent A correspondingly added in the chromium-free inorganic surface treatment agents of Examples 1-42 and the comparative surface treatment agents of Comparative Examples 1-9 were each prepared by the following steps:

[0075] (1) The silane A1 with an epoxy group and the silane A3 with an alkyl group were first hydrolyzed and mixed, and the mass percentage of the two was controlled to satisfy: A3 / A1: 0.2-0.6.

[0076] (2) After the silane A1 with an epoxy group and the silane A3 with an alkyl group were uniformly mixed, the monoamino silane A2 was added thereto, and the addition amount of the monoamino silane A2 was controlled to satisfy: A2 / A1: 0.3-0.7, wherein A1 and A2 respectively represented the mass percentage of the corresponding silane.

[0077] (3) After the above three types of silanes were uniformly mixed, the vinyl silane A4 was added to the mixture, and the addition amount of the vinyl silane A4 was controlled to satisfy: A4 / A1: 0.1-0.4, wherein A1 and A4 respectively represented the mass percentage of the corresponding silane.

[0078] It can be seen from the above that, in the technical scheme designed in the present application, the compounded silane coupling agent A is compounded from the following four types of silane coupling agent monomers: silane A1 with an epoxy group, silane A2 with a monoamino group, silane A3 with an alkyl group, and silane A4 with a vinyl group. The composition and content of each type of silane coupling agent monomer added in the compounded silane coupling agent A of Examples 1-42 and Comparative Examples 1-9 are specifically listed in Table 1 below.

[0079] Table 1 lists the composition and content of each type of silane coupling agent monomer added in the compounded silane coupling agent A of Examples 1-42 and Comparative Examples 1-9.

[0080] Table 1.

[0081]

[0082]

[0083] Note: In the above Table 1, A1, A2, A3, and A4 in the formulas “A3 / A1”, “A2 / A1”, and “A4 / A1” each respectively bring in the mass percentage of the corresponding type of silane.

[0084] Note that in the above Table 1, "A1-1" in the silane A1 specifically selected indicates 3-glycidyloxypropyltrimethoxysilane, and "A1-2" indicates 3-glycidyloxypropyltriethoxysilane. Of course, in some other embodiments, the silane A1 can also use 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane.

[0085] Correspondingly, "A2-1" in the silane A2 specifically selected indicates 3- aminopropyltrimethoxysilane, and "A2-2" indicates 3-aminopropyltriethoxysilane. Of course, in some other embodiments, the silane A2 can also use 3- aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane.

[0086] "A3-1" in the silane A3 specifically selected indicates 1,2-bis(triethoxysilyl)ethane, and "A3-2" indicates tetraethyl silicate. Of course, in some other embodiments, the silane A3 can also use 1,2-bis(trimethoxysilyl)ethane.

[0087] "A4-1" in the silane A4 specifically selected indicates vinyltrimethoxysilane, and "A4-2" indicates vinyltriacetoxysilane. Of course, in some other embodiments, the silane A4 can also use vinyltriisopropenoxysilane, vinyltriisopropoxysilane, vinyltri(2-methoxyethoxy)silane and vinyltriethoxysilane.

[0088] In the present application, based on the above design, the compounded silane coupling agent A in Table 1 prepared can correspondingly obtain the chromium-free inorganic surface treatment agent of the designed embodiments 1-42 of the present application and the comparative surface treatment agent of the comparative examples 1-9, and the component allocation ratio of the total solid content added in the aqueous solution is listed in the following Table 2.

[0089] Table 2 lists the specific information of the components and the ratio of each component of the total solid content of the surface treatment agent aqueous solution of the embodiments 1-42 and the comparative examples 1-9.

[0090] Table 2.

[0091]

[0092]

[0093] Note that the surface-modified aqueous silica sol B is a silica sol modified with an organic compound having an epoxy group, an amino group, or a methyl functional group; the water-soluble phosphorus-containing compound C includes a phosphate and / or phosphoric acid; the water-soluble fluorine-containing compound D includes a fluorine-containing salt and / or a fluorine-containing acid; and the lubricating aid E includes a high-density polyethylene particle, a polytetrafluoroethylene particle, or the like.

[0094] In Table 1 above, "B1" in the surface-modified aqueous silica sol B indicates a silver-fortified water-soluble silica sol SW-101, "B2" indicates a silver-fortified water-soluble silica sol SC-101, and "B3" indicates an aqueous silica sol CC301 from Akzo Nobel.

[0095] "C1" in the water-soluble phosphorus-containing compound C indicates zinc dihydrogen phosphate, "C2" indicates ammonium phosphate, and "C3" indicates hydroxyethylidene diphosphonic acid.

[0096] "D1" in the water-soluble fluorine-containing compound D indicates ammonium fluorotitanate, "D2" indicates ammonium fluorozirconate, and "D3" indicates hexafluorotitanic acid.

[0097] "E1" in the lubricating aid E indicates a high-density polyethylene wax, and "E2" indicates a polyethylene wax / polytetrafluoroethylene wax mixture.

[0098] In the present application, based on the chromium-free inorganic surface treatment agents obtained in Examples 1 to 42 and the comparative surface treatment agents of Comparative Examples 1 to 9 described above, the inventors treated galvanized steel sheets in the following manner using the inorganic chromium-free surface treatment agents:

[0099] (1) The surface of a hot-dip galvanized steel sheet was wiped with n-heptane / butyronitrile, and then the hot-dip galvanized steel sheet was placed in alcohol and subjected to ultrasonic cleaning for 20 minutes. The hot-dip galvanized steel sheet was then removed and cleaned with pure water and dried for use.

[0100] (2) The chromium-free inorganic surface treatment agents of the respective examples and comparative examples were applied to the surface of the corresponding galvanized steel sheet by means of a wire bar using a roll coating method, and the inorganic chromium-free aqueous treatment agent was cured by heating and drying at a temperature of 80 to 180°C to form a coating film on the surface of the galvanized steel sheet, thereby obtaining the finished galvanized steel sheet of Examples 1 to 42 and Comparative Examples 1 to 9, which is a post-treatment product having an inorganic chromium-free protective film on the surface. The thickness data of the coating film formed by the relevant surface treatment agent are shown in Table 3 below.

[0101] Note that the present application focuses on the excellent performance of the coating film formed by the designed surface treatment agent, and there is no particular limitation on the galvanized substrate used, and in actual applications, a person skilled in the art can select the desired galvanized steel sheet according to the specific requirements.

[0102] Table 3 lists the surface film thickness and heating drying temperature of the finished galvanized steel sheets of Examples 1-42 and Comparative Examples 1-9.

[0103] Table 3.

[0104]

[0105]

[0106] Accordingly, in order to verify the superiority of the chromium-free inorganic surface treatment agent designed in the present application, the finished galvanized steel sheets of Examples 1-42 and Comparative Examples 1-9 prepared were respectively sampled and cut into standard size sample panels and subjected to the following tests, thereby obtaining test data for evaluating the respective performances, and the specific test items and test methods are as follows:

[0107] 1) Flat plate corrosion resistance test:

[0108] The flat plate was subjected to a salt spray test, the test standard was ASTM B117, the test time was 72 h, and the evaluation standard was as follows:

[0109] ◎: White rust area ratio less than 5%;

[0110] O: White rust area ratio greater than 5% and less than 10%;

[0111] △: White rust area ratio greater than 10% and less than 50%;

[0112] X: White rust area ratio greater than 50%.

[0113] 2) Corrosion resistance test after alkaline cleaning:

[0114] The sample panel was cleaned using a medium alkalinity degreaser (PH: 9-11) at a temperature of 50°C for 3 minutes, and then subjected to a salt spray test, the test standard was ASTM B117, the test time was controlled for 72 h, and the evaluation standard was as follows:

[0115] ◎: White rust area ratio less than 5%;

[0116] O: White rust area ratio greater than 5% and less than 10%;

[0117] △: White rust area ratio greater than 10% and less than 50%;

[0118] X: White rust area ratio greater than 50%.

[0119] 3) High water cutting paintability test:

[0120] After the sample panel was degreased and washed with water, it was baked in an oven at 200°C for 15 min, and then subjected to a paintability test.

[0121] The test conditions are specifically: selecting the powder coating of the product of AkzoNobel Company with the brand of EA05BH, controlling the powder spraying thickness of 60-80 microns, and controlling the baking condition of 200 DEG C for 10 minutes.

[0122] After curing the sample plate coated with the above powder, 100 small grids with the size of 1mm2 are drawn on the surface of the coating film by using a knife, and the depth should be drawn through the paint film layer to reach the surface of the steel plate. After peeling off by using the peeling tape, the residual grid number of the paint film is observed, the more the residual grid number, the more excellent the powder coating performance of the steel plate, and the specific evaluation standard is:

[0123] ◎: no peeling of the paint film;

[0124] O: 0 < peeling degree of the paint film < 5%;

[0125] △: 5% < peeling degree of the paint film < 15%;

[0126] X: 15% < peeling degree of the paint film.

[0127] 4) Heat resistance test:

[0128] The sample plate is placed in a muffle furnace at 1000 DEG C for 15S, and then taken out and evaluated, and the evaluation standard is:

[0129] ◎: no cracking on the surface;

[0130] O: a small amount of cracks on the surface;

[0131] △: a large amount of cracks on the surface.

[0132] 5) Wear resistance test:

[0133] Rubber wear method, rubber diameter Φ10mm, load 500g, stroke 20mm, moving speed 300mm / min, reciprocating friction 50 times, and the evaluation standard is:

[0134] ◎: no change on the surface of the coating film;

[0135] O: a small amount of scratches on the surface of the coating film;

[0136] △: multiple scratches on the surface of the coating film;

[0137] X: complete peeling of the coating film.

[0138] 6) Compaction bending test:

[0139] The sample plate is compacted in a bending mold, and the surface condition of the bending side is evaluated, and the evaluation standard is:

[0140] ◎: no blackening on the bending surface;

[0141] O: sporadic blackening on the bending surface;

[0142] △: a large number of black spots on the bending surface.

[0143] 7) Drawbead friction test:

[0144] The drawbead friction test conditions are as follows: fixed bead pressure 3KN, pressure head diameter 9.6mm, and draw speed 200mm / min. The appearance after drawing is observed, and the evaluation method is as follows:

[0145] ◎: no change in appearance;

[0146] ○: a small amount of black spots on the appearance;

[0147] △: more obvious black stripes on the appearance;

[0148] ×: appearance is completely black.

[0149] 8) Storage stability test:

[0150] The treatment solution is placed at room temperature, and the solution change is observed after 90 days, and the evaluation method is as follows:

[0151] ◎: no change;

[0152] ○: slightly thickened (can be used normally);

[0153] △: severe thickening;

[0154] ×: gel.

[0155] Table 4 lists the relevant performance parameters of the finished galvanized steel sheet after the above tests of Examples 1-42 and Comparative Examples 1-9.

[0156] Table 4.

[0157]

[0158]

[0159] As can be seen from the above Table 4, the finished galvanized steel sheet manufactured by the chromium-free inorganic surface treatment agent based on Examples 1-42 of the present application after the above tests has an evaluation result of "◎" and "O". It can be seen that the chromium-free inorganic surface treatment agent for treating the surface of the galvanized steel sheet in Examples 1-42 of the present application has excellent storage stability, and the chromium-free inorganic surface treatment agent applied to the galvanized steel sheet also has good corrosion resistance, paintability, heat resistance, and formability.

[0160] In addition, by analyzing Comparative Examples 1-9 in combination with Tables 1, 2, 3 and 4, it can be seen that:

[0161] Compared with Examples 1-42, in Comparative Examples 1, 2, 3, 4, and 5, the proportions of the components of the compounded silane (A2 / A1, A3 / A1, A4 / A1) are not appropriate, and the total amount of the compounded silane (A) is insufficient, resulting in insufficient crosslinking density of the coating film, and further causing insufficient corrosion resistance of the coating film.

[0162] In Comparative Example 6, when designing the comparative surface treatment agent, the amount of the surface-modified aqueous silica sol B added in the surface treatment agent is insufficient, resulting in deterioration of the coating property and the forming property of the final coating film, and the evaluation of the test sample after the high-water cutting coating property test is “Δ”, and the evaluations after the compaction bending test and the drawbead friction test are also “Δ”.

[0163] In Comparative Example 7, when designing the comparative surface treatment agent, the amount of the water-soluble phosphorus-containing compound C added in the surface treatment agent is insufficient, resulting in poor corrosion resistance of the final coating film, and the evaluations of the test sample after the flat plate corrosion resistance test and the alkali washing corrosion resistance test are both “×”.

[0164] In Comparative Example 8, when designing the comparative surface treatment agent, the addition of the water-soluble fluorine-containing compound D in a high content leads to a sharp decrease in the stability of the solution, and the evaluation of the test sample after the storage stability test is “Δ”.

[0165] In Comparative Example 9, when designing the comparative surface treatment agent, the content of the lubricating aid E added is insufficient, resulting in insufficient wear resistance of the final coating film, and the evaluation of the test sample after the wear resistance test is “Δ”.

[0166] In summary, the present application provides a chromium-free inorganic surface treatment agent for galvanized steel sheets, which itself has excellent storage stability, and can be applied to the surface of a galvanized steel sheet and form a coating film on the surface of the galvanized steel sheet, so that the galvanized steel sheet product after surface treatment has excellent forming appearance, excellent high-temperature water cutting coating property, and high heat resistance, and also exhibits good corrosion resistance, alkali washing resistance, wear resistance, and formability.

[0167] In actual use, the coating film formed on the surface of a galvanized steel sheet using the chromium-free inorganic surface treatment agent of the present application can not only ensure the scratch resistance and rust resistance of the galvanized steel sheet between processes, but also can make the appearance quality of the formed part excellent after continuous high-speed forming of the galvanized steel sheet, and can also provide the galvanized steel sheet with excellent coating property after high-temperature baking with water cutting, which has good popularization prospect and application value.

[0168] It should be noted that the above-mentioned embodiments are only specific embodiments of the present application. Obviously, the present application is not limited to the above-mentioned embodiments, and similar changes or modifications made in accordance with the disclosure of the present application are directly derived or easily thought of by those skilled in the art, and should all belong to the protection scope of the present application.

Claims

1. A chromium-free inorganic surface treatment agent for galvanized steel sheets, characterized in that, Its aqueous solution contains 11.5-15% total solids by mass, and the components of the total solids are as follows: The compound silane coupling agent A accounts for 45-65% of the total solid content by mass. Surface-modified aqueous silica sol B, which accounts for 25%-45% of the total solid content by mass; Water-soluble phosphorus compound C, with a phosphorus content of 0.5%-1% of the total solids by mass, is present. Water-soluble fluorinated compound D, with a fluorine content of 1%-6% of the total solids by mass (based on elemental fluorine); Lubricating agent E, which accounts for 1%-10% of the total solids by mass; The compounded silane coupling agent A is composed of the following four types of silane coupling agent monomers: silane A1 with an epoxy group, silane A2 with a monoamino group, silane A3 with an alkyl group, and silane A4 with a vinyl group, wherein the amount of vinyl silane A4 added is A4 / A1: 0.1-0.

4. The compounded silane coupling agent is prepared by the following steps: Silane A1 with epoxy groups and silane A3 with alkyl groups are first hydrolyzed and mixed; when silane A1 with epoxy groups and silane A3 with alkyl groups are hydrolyzed and mixed, the mass percentage of the two is controlled to meet the following condition: A3 / A1: 0.2-0.6; After the silane A1 with epoxy groups and the silane A3 with alkyl groups are mixed evenly, monoaminosilane A2 is added to it. The amount of monoaminosilane A2 added is controlled as follows: A2 / A1: 0.3-0.7, where A1 and A2 represent the mass percentage content of the corresponding silanes. After the three types of silanes are mixed evenly, vinyl silane A4 is added to the mixture. The amount of vinyl silane A4 added is controlled as follows: A4 / A1: 0.1-0.4, where A1 and A4 represent the mass percentage content of the corresponding silanes.

2. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The silane A1 having an epoxy group includes at least one of the following: 3-glycidyl etheroxypropyltriethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, 3-glycidyl etheroxypropylmethyldimethoxysilane, and 3-glycidyl etheroxypropylmethyldiethoxysilane.

3. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The silane A2 having a single amino group includes at least one of the following: 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

4. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The silane A3 having an alkyl group includes at least one of the following: triethoxysilyl ethane, trimethoxysilyl ethane, and tetraethyl silicate.

5. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The vinyl silane A4 comprises at least one of the following: vinyltriacetoxysilane, vinyltriisopropoxysilane, vinyltriisopropoxysilane, vinyltrisilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

6. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The surface-modified aqueous silica sol B is a silica sol modified with organic compounds containing epoxy, amino, and methyl functional groups.

7. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The water-soluble phosphorus-containing compound C includes phosphates and / or phosphoric acid.

8. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The water-soluble fluorinated compound D includes fluorinated salts and / or fluorinated acids.

9. The chromium-free inorganic surface treatment agent as described in claim 1, characterized in that, The lubricant E includes high-density polyethylene particles and polytetrafluoroethylene particles.

10. A galvanized steel sheet, characterized in that, The galvanized steel sheet surface has a film formed by coating with the chromium-free inorganic surface treatment agent as described in any one of claims 1-9.

11. The galvanized steel sheet as described in claim 10, characterized in that, The thickness of the membrane is 0.3-1.5 micrometers.

12. The method for manufacturing galvanized steel sheet as described in claim 10 or 11, characterized in that, Including the following steps: The chromium-free inorganic surface treatment agent is coated onto the surface of the galvanized steel sheet; The inorganic chromium-free water-based treatment agent is cured by heating and drying to form a film on the surface of galvanized steel sheet.

13. The manufacturing method as described in claim 12, characterized in that, The chromium-free inorganic surface treatment agent is applied to the surface of the galvanized steel sheet by roller coating.

14. The manufacturing method as described in claim 12, characterized in that, The temperature for heating and drying is 80-180℃.

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