Chromium-free inorganic surface treatment agent for galvanized steel sheets, finished galvanized steel sheets and their manufacturing method

Abstract

The present invention discloses a chromium-free inorganic surface treatment agent. The surface treatment agent has a total solids content of 11.5 to 15% by weight, with the remainder being water. The total solids content includes the following components by weight: compounded silane coupling agent A: 45 to 65%; surface-modified aqueous silica sol B: 25 to 45%; water-soluble phosphorus-containing compound C: 0.5 to 1% by weight of elemental phosphorus; water-soluble fluorine-containing compound D: 1 to 6% by weight of elemental fluorine; and lubricant additive E: 1 to 10%. The compounded silane coupling agent A is formed by compounding the following four silane coupling agent monomers: silane A1 having an epoxy group, silane A2 having a monoamino group, silane A3 having an alkyl group, and silane A4 having a vinyl group.

Description

[Technical Field]

[0001] Technical Field The present invention relates to a surface treatment agent, particularly a surface treatment agent for galvanized steel sheets, a finished galvanized steel sheet, and a method for producing the same. [Background technology]

[0002] background In recent years, galvanized steel sheets have become popular and are widely used in industries such as automobiles, home appliances, and construction.

[0003] Research has shown that anti-rust oil is typically applied to the surface of galvanized steel sheets during production to improve their performance during storage, processing, and service, and to prevent white rust from forming during transportation and storage. To reduce friction between the galvanized steel sheet and the die during stamping and forming, and to prevent cracking and wear of the zinc layer, lubricating oil is applied to the die surface during forming, and the die surface is then cleaned with a solvent- or alkaline-based degreaser. However, the use of anti-rust oil, lubricating oil, and degreasers throughout the entire process places a significant burden on the environment and costs.

[0004] To address this issue, the prior art has improved methods of passivating galvanized steel sheets with chromate or further coating the surface of the chromate passivation film with an organic resin containing a lubricant to achieve a balance between corrosion resistance and processability. However, in response to increasing demands for environmental protection, chromium-containing post-treatments of galvanized steel sheets are gradually being replaced by more environmentally friendly post-treatment methods.

[0005] Currently, environmentally friendly chromium-free galvanized steel products feature surface lubricating coatings that are generally classified into inorganic and organic / inorganic hybrid types. Among these, inorganic lubricating coatings are primarily composed of inorganic compounds containing elements such as silicon, manganese, and phosphorus. Galvanized steel products with such lubricating coatings exhibit good appearance after deep drawing, but struggle to balance corrosion resistance and coating performance during use.

[0006] In contrast, organic / inorganic composite lubricating coatings are thin films that contain resins, rust inhibitors, silane coupling agents, silica colloids, and solid lubricant additives. These coatings have excellent lubricity, corrosion resistance, and resistance to various chemicals, such as fingerprint resistance and alkali resistance.

[0007] Currently, most galvanized surface treatments utilize organic / inorganic composite systems that meet the requirements of most processing and service scenarios. However, in some specific scenarios (such as high-speed continuous stamping and forming, high-temperature coating, and high-temperature environments), galvanized steel sheets coated with these organic / inorganic composite surface treatments often suffer from problems such as surface darkening during high-speed continuous forming, poor coating performance after high-temperature drying, and discoloration under heat due to the presence of organic components in the surface treatments.

[0008] For example, during high-speed progressive stamping of motor housings, some of the surface film or coating layer of galvanized steel sheets inevitably peels off. Continuous high-speed stamping increases the temperature of the stamping die, and the peeled debris accumulates in the lubricating oil. The accumulated debris particles re-adhere to the surface of the formed parts under high-temperature conditions, leading to surface darkening and damaging the appearance of the parts.

[0009] Similarly, in the production of LCD panels, which require high strength, good heat dissipation, anti-static properties, and a good appearance, the process involves cutting, stamping, cleaning, spraying, and baking. To improve production efficiency, the drying temperature after cleaning is actually continuously increased. Conventional post-processing products do not meet the coating performance requirements under these conditions.

[0010] Furthermore, galvanized steel sheets are used in high-temperature environments, such as air conditioning tube sheets for fixing copper pipes to outdoor units of air conditioners. When brazing copper pipes, the galvanized steel tube sheets are inevitably exposed to the flame of a burner. If conventional organic / inorganic composite surface-treated steel sheets are used in such situations, the organic resin coating will undergo thermal decomposition, causing discoloration and surface cracks, which will damage the appearance.

[0011] At present, many researchers have been researching surface treatment agents for galvanized steel sheets, and have achieved some technical results, but the practical application effects are still not satisfactory. For example,

[0012] A Chinese patent document entitled "Treatment Agent and Treatment Method for Surface Lubrication of Galvanized Steel Sheet," publication number CN101376859A and publication date March 4, 2009, discloses an inorganic treatment agent containing manganese, nickel, phosphate ions, and silane, which can form a transparent inorganic coating on the surface of galvanized steel sheet, thereby improving the stamping and formability of the galvanized steel sheet and eliminating or reducing the problems of zinc adhesion and powdering during the forming process. While this technical solution provides the steel sheet with good lubrication processability, its corrosion resistance is inferior to that of chromate-passivated products, and the coating is easily corroded by alkaline solutions, significantly reducing its corrosion resistance under alkaline conditions.

[0013] A Chinese patent document, Publication Number CN101787527A, published July 28, 2010, entitled "Galvanized Steel Sheet and Surface Treatment Agent with Excellent Workability and Alkali and Solvent Resistance," discloses a galvanized steel sheet with excellent workability and alkali and solvent resistance, the surface of which is covered with an organic / inorganic composite coating. The protective coating is primarily composed of an aqueous cationic polyurethane resin and contains one or more organic silane coupling agents, a corrosion inhibitor, and polyethylene oxide particles. This protective coating imparts excellent stamping and formability, solvent resistance, and alkali resistance to the surface of the galvanized steel sheet, while also ensuring good corrosion resistance and paint adhesion. However, this technical solution does not address corrosion resistance after cleaning, making it difficult to ensure corrosion resistance under alkaline conditions for bare components such as home appliance parts and micromotors.

[0014] A Chinese patent document entitled "Surface Treatment Composition and Surface-Treated Steel Sheet" with publication number CN102666921A and publication date September 12, 2012, discloses a post-treatment agent containing titanate, zirconium carbonate, and phosphate as its main components. Galvanized steel sheets obtained using this surface treatment composition have good heat discoloration resistance, but their corrosion resistance is significantly insufficient. Summary of the Invention [Means for solving the problem]

[0015] overview To solve the technical problems of the prior art, one objective of the present invention is to provide a chromium-free inorganic surface treatment agent for galvanized steel sheet. This chromium-free inorganic surface treatment agent has excellent storage stability and, after application to the surface of the galvanized steel sheet, can form a coating on the surface of the galvanized steel sheet. As a result, the finished galvanized steel sheet (including the galvanized steel sheet and the coating on its surface) has an excellent formed appearance, excellent coating performance after high-temperature drying, and high heat resistance. Furthermore, it provides good corrosion resistance, alkali washing resistance, abrasion resistance, and formability. Therefore, the chromium-free inorganic surface treatment agent has good promotion prospects and application value.

[0016] In order to achieve the above object, a first aspect of the present invention provides a chromium-free inorganic surface treatment agent having a total solid content of 11.5 to 15% by mass, the remainder being water, the total solid content consisting of the following components by mass: Silane coupling agent (A): 45-65%; Surface-modified aqueous silica sol (B): 25%~45%; Water-soluble phosphorus-containing compounds (C): 0.5%-1% by mass of elemental phosphorus; Water-soluble fluorine-containing compounds (D): 1% to 6% by mass of elemental fluorine; and Lubricant additive (E): 1%~10%; Here, the compounded silane coupling agent (A) is a compound of the following four types of silane coupling agent monomers: epoxy-containing silane (A1), monoamino-containing silane (A2), alkyl-containing silane (A3), and vinyl-containing silane (A4).

[0017] To address this issue, the inventors have ingeniously designed a chromium-free inorganic surface treatment agent that is suitable for the surface treatment of galvanized steel sheets. When the chromium-free inorganic surface treatment agent is applied to the surface of galvanized steel sheets, a coating is formed on the surface of the galvanized steel sheets. This coating ensures that the galvanized steel sheets have excellent appearance quality after continuous high-speed forming and also allows the galvanized steel sheets to maintain excellent coating performance after high-temperature baking. Furthermore, this coating also allows the galvanized steel sheets to have good corrosion resistance, alkali washability, and high heat resistance.

[0018] In the present invention, the various excellent properties of the chromium-free inorganic surface treatment agent blended in the present invention are closely related to the blended silane coupling agent A. In its design, the mass percentage of the blended silane coupling agent A in the total solids content must be within the range of 45.0 to 65.0%. If the mass percentage of the blended silane coupling agent A is less than 45.0%, the corrosion resistance of the coating will be insufficient. On the other hand, if the mass percentage of the blended silane coupling agent A is more than 65.0%, the adhesion performance of the coating will be excessive, resulting in excessive adhesion of foreign matter to the surface of the molded part, which will deteriorate the appearance of stamping and molding, and will cause deterioration of the appearance under high-temperature use conditions.

[0019] Furthermore, in the present invention, when designing the chromium-free inorganic surface treatment agent, it is also necessary to specifically control the mass percentage of the surface-modified aqueous silica sol B relative to the total solid content to 25.0% to 45.0%. If the mass percentage of the surface-modified aqueous silica sol B relative to the total solid content is less than 25.0%, the appearance quality of the formed galvanized steel product will be reduced, affecting the subsequent coating performance. On the other hand, if the mass percentage of the surface-modified aqueous silica sol B relative to the total solid content is more than 45.0%, the overall density of the coating will be insufficient, resulting in insufficient corrosion resistance of the processed parts.

[0020] Furthermore, in the present invention, the mass percentage of phosphorus in the water-soluble phosphorus-containing compound C in the total solid content is controlled to be 0.5% to 1.0%. If the mass percentage of phosphorus element is less than 0.5%, the passivation layer at the interface between the substrate and the coating will be incomplete, resulting in a decrease in the corrosion resistance of the coating. If the mass percentage of phosphorus element is more than 1.0%, excessive deposition of the passivation layer at the interface will reduce the adhesion of the coating.

[0021] In the present invention, the mass percentage of fluorine in the water-soluble fluorine-containing compound D in the total solid content is controlled to be 1.0% to 6.0%. If the mass percentage of fluorine element is less than 1.0%, the reactivity between the surface treatment agent and the surface of the steel sheet substrate becomes insufficient, resulting in a thin surface conversion layer with insufficient corrosion resistance. If the mass percentage of fluorine element exceeds 6.0%, the stability of the surface treatment solution decreases.

[0022] Therefore, in the technical solution of the present invention, the mass percentage of Lubricant Additive E in the total solid content is controlled to be 1.0% to 10.0%. If the mass percentage of Lubricant Additive E is less than 1.0%, the lubricity and wear resistance of the formed film may be insufficient. If the mass percentage of Lubricant Additive E is more than 10.0%, the excess solid lubricant particles in the film will create too many interface channels, allowing corrosive media to penetrate and reducing the corrosion resistance of the film.

[0023] Preferably, in some embodiments, the size of the lubricant additive particles is controlled to be 0.2 to 0.5 microns. If the size of the lubricant additive particles is less than 0.2 microns, the wear resistance of the coating is insufficient. If the size of the lubricant additive particles is greater than 0.5 microns, the processability of the coating is deteriorated.

[0024] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the epoxy-containing silane A1 comprises at least one of the following: 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, and 3-glycidyloxypropylmethyldiethoxysilane.

[0025] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the monoamino-containing silane A2 comprises at least one of the following: 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

[0026] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the alkyl-containing silane A3 comprises at least one of the following: triethoxysilylethane, trimethoxysilylethane, and tetraethylsilicate.

[0027] In certain embodiments according to the present invention, the alkyl-containing silane A3 can be: 1,2-bis(triethoxysilyl)ethane, 1,2-bis(trimethoxysilyl)ethane, and tetraethylsilicate.

[0028] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the vinyl-containing silane A4 comprises at least one of the following: vinyltriacetoxysilane, vinyltriisopropenoxysilane, vinyltriisopropoxysilane, vinyltrisilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0029] In certain embodiments according to the present invention, the vinyl-containing silane A4 can be: vinyltriacetoxysilane, vinyltriisopropenoxysilane, vinyltriisopropoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0030] Preferably, the compounded silane coupling agent is prepared by the following steps: Hydrolyzing and mixing epoxy-containing silane A1 and alkyl-containing silane A3; After the epoxy-containing silane A1 and the alkyl-containing silane A3 are mixed uniformly, the monoamino-containing silane A2 is added; After forming a homogeneous mixture of epoxy-containing silane A1, monoamino-containing silane A2, and alkyl-containing silane A3, vinyl-containing silane A4 is added to the mixture.

[0031] More preferably, in the preparation process of the compounded silane coupling agent: During hydrolysis and mixing of the epoxy-containing silane A1 and the alkyl-containing silane A3, the mass percentage ratio of A3 to A1 satisfies: A3 / A1= 0.2-0.6; The amount of monoamino-containing silane A2 added satisfies: A2 / A1=0.3-0.7, where A1 and A2 respectively represent the mass percentages of the corresponding silanes; The amount of vinyl-containing silane A4 added satisfies: A4 / A1=0.1-0.4, where A1 and A4 each represent the mass percentage of the corresponding silane.

[0032] In the above technical solution of the present invention, the various excellent properties exhibited by the formulation of the chromium-free inorganic surface treatment agent of the present invention are closely related to the silane coupling agent A contained therein.

[0033] In the process of preparing compounded silane coupling agent A, the hydrolysis and mixing of epoxy-containing silane A1 and alkyl-containing silane A3 must be controlled so that the mass percent ratio of A3 to A1 satisfies A3 / A1 = 0.2 to 0.6. The reason for controlling A3 / A1 to 0.2 to 0.6 is that if the A3 / A1 ratio is less than 0.2, the amount of hydrolyzed silanol groups will be insufficient, weakening the chemical bond with the steel substrate and reducing coating adhesion and corrosion resistance during molding. If A3 / A1 exceeds 0.6, the designed surface treatment agent will be prone to layer separation, reducing its storage stability.

[0034] Therefore, in the present invention, after mixing the epoxy-containing silane A1 and the alkyl-containing silane A3, the monoamino-containing silane A2 is added in an amount that satisfies A2 / A1 = 0.3 to 0.7. This is because if the A2 / A1 value is less than 0.3, the crosslink density of the coating will be insufficient, resulting in reduced corrosion resistance. If the A2 / A1 value exceeds 0.7, the excess residual amino groups will increase the hydrophilicity of the coating, thereby reducing its corrosion resistance.

[0035] After the three silanes are mixed uniformly, vinyl-containing silane A4 is added to the mixture, and the amount of vinyl-containing silane A4 added is controlled so that A4 / A1 is 0.1 to 0.4. If the A4 / A1 ratio is less than 0.1, the coating performance of the film is reduced. If the A4 / A1 ratio is greater than 0.4, the corrosion resistance of the film is reduced.

[0036] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the surface-modified aqueous silica sol B is a silica sol modified with an organic compound containing epoxy, amino, and methyl groups. These silica sols can further crosslink with the active groups (amino, hydroxyl, etc.) in the silane coupling agent to improve the durability of the coating. Furthermore, these silica sols can reduce the adhesion of coating particles peeled off during molding to the surface of the molded part, improving the surface quality of the molded part.

[0037] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the water-soluble phosphorus-containing compound C comprises a phosphate and / or phosphoric acid.

[0038] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the water-soluble fluorine-containing compound D contains a fluorine-containing salt and / or a fluorine-containing acid.

[0039] Preferably, in the chromium-free inorganic surface treatment agent according to the present invention, the lubricating additive E comprises a lubricating additive consisting of high-density polyethylene particles and high-density polytetrafluoroethylene particles. In the present invention, the high-density lubricating additive (e.g., a lubricating additive based on polyethylene particles or polytetrafluoroethylene particles) has a density of >0.96 g / cm 3 It has a density of

[0040] Therefore, another object of the present invention is to produce a finished galvanized steel sheet comprising a galvanized steel sheet and a coating formed by applying the above-mentioned surface treatment agent on the surface of the galvanized steel sheet.

[0041] Preferably, in the finished galvanized steel sheet according to the present invention, the coating has a thickness of 0.3 to 1.5 microns.

[0042] In the present invention, an environmentally friendly inorganic surface treatment coating can be formed on the surface of a galvanized steel sheet by applying the above-mentioned surface treatment agent to the surface of the galvanized steel sheet. This coating can have a single-layer structure. The thickness of the coating is controlled to be 0.3 to 1.5 microns, because if the thickness is less than 0.3 microns, the coating is too thin and has insufficient scratch resistance and rust prevention properties. If the thickness of the coating exceeds 1.5 microns, the cost of the surface treatment becomes high. Preferably, the thickness of the coating is 0.7 to 1.3 microns.

[0043] Another object of the present invention is to provide a method for manufacturing the above-mentioned finished galvanized steel sheet, which is characterized by a simple process flow and effectively produces the above-mentioned finished galvanized steel sheet according to the present invention.

[0044] The method for producing a finished galvanized steel sheet according to the present invention comprises the following steps: Apply the above surface treatment agent to the surface of the galvanized steel sheet; The surface treatment agent is cured by heating and drying, forming a film on the surface of the galvanized steel sheet.

[0045] Preferably, in the above-mentioned manufacturing method, the surface treatment agent is applied to the surface of the galvanized steel sheet by roller coating.

[0046] In the above technical solution of the present invention, the above surface treatment agent can be roller coated on both the upper and lower surfaces of the galvanized steel sheet, and after curing, the thickness of the coating on the upper and lower surfaces of the galvanized steel sheet is controlled to be 0.3 to 1.5 microns.

[0047] Preferably, in the above production method, the heating and drying temperature is 80 to 180°C.

[0048] If the heating and drying temperature is lower than 80°C, the cross-linking of the coating will be insufficient, resulting in a decrease in coating performance. If the heating and drying temperature is higher than 180°C, the properties of some of the components in the surface treatment agent will change, affecting coating formation.

[0049] It should be noted that the present invention has no special requirements for the heating and drying method, and the method includes hot air heating, induction heating, infrared heating, or a combination thereof.

[0050] In addition, in the present invention, there are no particular limitations on the size or shape of the galvanized steel sheet.

[0051] Compared with the prior art, the chromium-free inorganic surface treatment agent, finished galvanized steel sheet and manufacturing method according to the present invention provide the following advantages and beneficial effects: The present invention provides a chromium-free inorganic surface treatment agent for galvanized steel sheet. This surface treatment agent has excellent storage stability and, when applied to the surface of galvanized steel sheet, can form a film on the surface of the galvanized steel sheet. This film imparts to the galvanized steel sheet product an excellent formed appearance, excellent coating performance after high-temperature drying, high heat resistance, as well as good corrosion resistance, alkali cleaning resistance, wear resistance, and formability, offering great prospects for promotion and application value.

[0052] The coating formed on the surface of a galvanized steel sheet by the chromium-free inorganic surface treatment agent according to the present invention not only ensures the scratch resistance and rust prevention of the galvanized steel sheet during processing, but also enables the formed parts to have excellent appearance quality after the galvanized steel sheet undergoes continuous high-speed forming. Furthermore, this coating enables the galvanized steel sheet to maintain excellent coating performance after high-temperature baking.

[0053] Detailed explanation The following embodiments provide further explanation and illustration of the above-mentioned surface treatment agent, finished galvanized steel sheet, and manufacturing method thereof, but these explanations and illustrations are not intended to unduly limit the scope of the present invention.

[0054] Examples 1 to 42 and Comparative Examples 1 to 9 The aqueous solutions of the chromium-free inorganic surface treatment agents of Examples 1 to 42 and Comparative Examples 1 to 9 all contain a certain total solid content. The total solid content specifically includes: a compounded silane coupling agent A, a surface-modified aqueous silica sol B, a water-soluble phosphorus-containing compound C, a water-soluble fluorine-containing compound D, and a lubricant additive E.

[0055] The silane coupling agent A added to the chromium-free inorganic surface treatment agents of Examples 1 to 42 and the surface treatment agents of Comparative Examples 1 to 9 was prepared by the following steps: (1) Hydrolyze and mix epoxy-containing silane A1 and alkyl-containing silane A3, and control the mass ratio thereof to satisfy: A3 / A1 = 0.2 to 0.6. (2) After the epoxy-containing silane A1 and the alkyl-containing silane A3 are uniformly mixed, the monoamino-containing silane A2 is added so that the amount of the monoamino-containing silane A2 satisfies A2 / A1=0.3-0.7, where A1 and A2 respectively represent the mass percentages of the corresponding silanes. (3) After the above three types of silanes are uniformly mixed, vinyl-containing silane A4 is added so that the amount of vinyl-containing silane A4 added satisfies: A4 / A1 = 0.1 to 0.4, where A1 and A4 respectively represent the mass percentages of the corresponding silanes.

[0056] That is, in the solution of the present invention, the compounded silane coupling agent A is composed of the following four types of silane coupling agent monomers: epoxy-containing silane A1, monoamino-containing silane A2, alkyl-containing silane A3, and vinyl-containing silane A4. The types and amounts of the silane coupling agent monomers designed for the compounded silane coupling agents A of Examples 1 to 42 and Comparative Examples 1 to 9 are shown in Table 1.

[0057] [Table 1-1]

[0058] [Table 1-2]

[0059] Note: In the calculations, for "A3 / A1," "A2 / A1," and "A4 / A1" in Table 1 above, A1, A2, A3, and A4 are replaced with the mass percent of the corresponding silane, respectively.

[0060] In Table 1, "A1-1" is 3-glycidyloxypropyltrimethoxysilane and "A1-2" is 3-glycidyloxypropyltriethoxysilane. Indeed, in some other embodiments, silane A1 can also be 3-glycidyloxypropylmethyldimethoxysilane, or 3-glycidyloxypropylmethyldiethoxysilane.

[0061] "A2-1" is 3-aminopropyltrimethoxysilane, and "A2-2" is 3-aminopropyltriethoxysilane. Indeed, in some other embodiments, silane A2 can also be 3-aminopropylmethyldimethoxysilane, or 3-aminopropylmethyldiethoxysilane.

[0062] "A3-1" is 1,2-bis(triethoxysilyl)ethane and "A3-2" is tetraethylsilicate. Indeed, in some other embodiments, silane A3 can also be 1,2-bis(trimethoxysilyl)ethane.

[0063] "A4-1" is vinyltrimethoxysilane, and "A4-2" is vinyltriacetoxysilane. Indeed, in some other embodiments, silane A4 can also be at least one selected from vinyltriisopropenoxysilane, vinyltriisopropoxysilane, vinyltri(2-methoxyethoxy)silane, and vinyltriethoxysilane.

[0064] The chromium-free inorganic surface treatment agents of Examples 1 to 42 and the surface treatment agents of Comparative Examples 1 to 9 were prepared based on the compounded silane coupling agent A in Table 1, and the proportion of each component in the total solid content added to these surface treatment agents is shown in Table 2 below.

[0065] Table 2 shows the components and the proportion of each component in the total solid content of the surface treatment agents of Examples 1 to 42 and Comparative Examples 1 to 9.

[0066] [Table 2-1]

[0067] [Table 2-2]

[0068] [Table 2-3]

[0069] The surface-modified aqueous silica sol B is a silica sol modified with an organic compound containing an epoxy functional group, an amino functional group, and a methyl functional group. The water-soluble phosphorus-containing compound C contains a phosphate and / or phosphoric acid. The water-soluble fluorine-containing compound D contains a fluorine-containing salt and / or a fluorine-containing acid. The lubricity additive E is a high-density (density > 0.96 g / cm 3 ) Polyethylene particles and high density (density > 0.96 g / cm 3 ) includes a lubricant additive comprised of polytetrafluoroethylene particles.

[0070] In Table 2 above, the specific types of surface-modified aqueous silica sol B are: "B1" is silver-rich water-soluble silica sol SW-101, "B2" is silver-rich water-soluble silica sol SC-101, and "B3" is Akzo Nobel water-soluble silica sol CC301.

[0071] Specific types of water-soluble phosphorus-containing compounds C are: "C1" is zinc dihydrogen phosphate, "C2" is ammonium phosphate, and "C3" is hydroxyethylidene diphosphonic acid.

[0072] Specific types of water-soluble fluorine-containing compound D are: "D1" is ammonium fluorotitanate, "D2" is ammonium fluorozirconate, and "D3" is hexafluorotitanic acid.

[0073] The specific types of lubricant additive E are: "E1" is high density (density > 0.96 g / cm 3 ) polyethylene wax, and "E2" is a mixture of polyethylene wax and polytetrafluoroethylene wax (trade name ULTRALUBE E-801).

[0074] In the present invention, the galvanized steel sheet was treated with the above-mentioned surface treatment agent using the following steps: (1) After wiping the surface of the hot-dip galvanized steel sheet with n-heptane / butanone, the hot-dip galvanized steel sheet is placed in ultrasonic cleaning ethanol for 20 minutes, and then the hot-dip galvanized steel sheet is taken out and washed with pure water, and then spray-dried for later use. (2) Using a wire rod, the surface treatment agent of each Example and Comparative Example was applied to the surface of the corresponding galvanized steel sheet by roller coating. The steel sheet was heated and dried at a temperature of 80 to 180°C to harden the surface treatment agent and form a coating on the surface of the galvanized steel sheet. This process resulted in the finished galvanized steel sheets of Examples 1 to 42 and Comparative Examples 1 to 9, which are post-treated products covered with a protective coating. The thickness of the coating formed by the surface treatment agent is shown in Table 3 below.

[0075] It should be noted that in the present invention, there is no particular limitation on the galvanized steel sheet used to form the finished galvanized steel sheet (including the galvanized steel sheet and the coating on its surface), and those skilled in the art can select a desired galvanized steel sheet according to specific needs.

[0076] Table 3 shows the thickness of the surface film and the heating and drying temperatures of the finished galvanized steel sheets of Examples 1 to 42 and Comparative Examples 1 to 9.

[0077] [Table 3-1]

[0078] [Table 3-2]

[0079] In order to confirm the effect of the surface treatment agent of the present invention, the finished galvanized steel sheets of Examples 1 to 42 and Comparative Examples 1 to 9 were sampled and cut to sizes that met the corresponding standards, and the following tests were carried out to evaluate the various performances of these finished galvanized steel sheets. The specific test items and test methods were as follows:

[0080] 1) Corrosion resistance test of sample plates: According to the test standard ASTM B117, the sample plates were subjected to a salt spray test for 72 hours, and the evaluation criteria were as follows: ◎: White rust area ratio 5% or less; ○: White rust area ratio is greater than 5% and less than 10%; △: White rust area ratio is greater than 10% and less than 50%; ×: White rust area ratio is greater than 50%.

[0081] 2) Corrosion resistance test after alkaline cleaning: The sample is cleaned by spraying with a mild alkaline degreaser (pH 9-11) at 50°C for 3 minutes. After cleaning, the sample is subjected to a salt spray test for 72 hours according to the ASTM B117 test standard. The evaluation criteria are as follows: ◎: White rust area ratio 5% or less; ○: White rust area ratio is greater than 5% and less than 10%; △: White rust area ratio is greater than 10% and less than 50%; ×: White rust area ratio is greater than 50%.

[0082] 3) Coating performance test after high temperature drying: After degreasing and cleaning the sample plate, it is baked in an oven at 200°C for 15 minutes, and then the coating performance test is carried out. The specific test conditions are: select Akzo Nobel powder coating with the trade name EA05BH, apply it to a thickness of 60-80 microns, and bake it at 200°C for 10 minutes. After hardening, use a cutter knife to apply 1mm of 2 The coating layer is peeled off with adhesive tape and the remaining grids are observed. The more grids that remain, the better the coating performance of the powder coating steel sheet. The specific evaluation criteria are as follows: ◎: The film does not peel off; ○: 0<coating peeling≦5%; △: 5%<coating peeling≦15%; ×: 15% or more of the film peeled off.

[0083] 4) Heat resistance test: The sample plate is placed in a muffle furnace at 1000°C for 15 seconds, and then removed. After cooling, a visual inspection is carried out. The evaluation criteria are: ◎: No cracks on the surface; ○: Minor cracks on the surface (0<the ratio of the crack area to the total area of ​​the sample plate≦15%); △: Significant cracks on the surface (ratio of crack area to total area of ​​sample plate >15%).

[0084] 5) Abrasion resistance test: The eraser abrasion test was performed using a rubber eraser (diameter Φ10mm), a load of 500g, a stroke of 20mm, and a travel speed of 300mm / min. The test was repeated 50 times. The specific evaluation criteria were: ◎: No change on the film surface; ○: slight scratches on the coating surface (0 < the ratio of the worn area to the total area of ​​the sample plate ≦ 10%); △: Significant scratches on the coating (10%<the ratio of the worn area to the total area of ​​the sample plate≦60%); ×: The coating was almost completely peeled off (the ratio of the worn area to the total area of ​​the sample plate was >60%).

[0085] 6) Compression bending test: The sample plate is compressed in the bending mold and the surface condition of the bent surface is evaluated. The evaluation criteria are: ◎: No dark spots on the bent surface; ○: slight black spots on the bent surface (0 < the ratio of the blackened area to the total area of ​​the sample plate ≤ 10%); △: Significant black spots on the bent surface (proportion of blackened area to total area of ​​sample plate >10%).

[0086] 7) Drawbead friction test: The draw bead friction test is carried out with a fixed bead downward pressure of 3KN, a pressure head diameter of 9.6mm, and a drawing speed of 200mm / min. The appearance after drawing is observed, and the evaluation criteria are: ◎: No change in appearance; ○: slight black spots on the appearance (0<the ratio of the blackened area to the total area of ​​the sample plate≦20%); △: Visible black streaks on the surface (20%<the ratio of the blackened area to the total area of ​​the sample plate≦80%); ×: Almost completely blackened (ratio of blackened area to total area of ​​sample plate >80%).

[0087] 8) Storage stability test: The treatment solution is stored at room temperature and the changes in the solution are observed after 90 days. The evaluation criteria are: ◎: no change; ○: Slightly thickened (still usable) (8MPa.s<viscosity<12MPa.s); △: Severe thickening (0<(weight of solids in the surface treatment agent) / (total weight of the surface treatment agent)<1); ×: Gelation ((weight of solids in the surface treatment agent) / (total weight of the surface treatment agent)=1).

[0088] If thickening or gelation occurs excessively, the presence of solids will prevent the treatment agent from spreading uniformly over the surface of the galvanized steel sheet, affecting its usability.

[0089] Table 4 lists the relevant performance of the finished galvanized steel sheets of Examples 1 to 42 and Comparative Examples 1 to 9 that underwent the above tests.

[0090] [Table 4-1]

[0091] [Table 4-2]

[0092] It can be seen from Table 4 that the evaluation results for the various performances described above for the finished galvanized steel sheets produced using the chromium-free inorganic surface treatment agents of Examples 1 to 42 of the present invention were all rated as "◎" or "◯." This indicates that the chromium-free inorganic surface treatment agents of Examples 1 to 42 of the present invention have excellent storage stability. When the above surface treatment agents are used on galvanized steel sheets, the galvanized steel sheets after surface treatment all exhibit good corrosion resistance, coating performance, heat resistance, and formability.

[0093] Furthermore, analysis of the finished galvanized steel sheets of Comparative Examples 1-9, taken together with Tables 1, 2, 3, and 4, reveals the following: Compared with Examples 1 to 42, in Comparative Examples 1 to 4, the ratios of the blended silane components (A2 / A1, A3 / A1, A4 / A1) do not satisfy the requirements of the present invention, and the total amount of blended silane (A) is insufficient in Comparative Example 5. This results in an insufficient crosslink density in the coating, and the corrosion resistance of the coating is insufficient.

[0094] In Comparative Example 6, the amount of surface-modified aqueous silica sol B added to the surface treatment agent was insufficient, so the coating performance and formability of the final coating were deteriorated, and the test sample after the coating performance test after high-temperature drying was evaluated as "Δ", and the test sample after the compression bending test and the drawbead friction test were also evaluated as "Δ".

[0095] In Comparative Example 7, the amount of water-soluble phosphorus-containing compound C added to the surface treatment agent was insufficient, resulting in poor corrosion resistance of the final coating. The test sample was evaluated as "X" in both the corrosion resistance test of the plate and the corrosion resistance test after alkaline washing.

[0096] In Comparative Example 8, the solution stability is rapidly reduced due to the excessive addition of water-soluble fluorine-containing compound D in the surface treatment agent. The test sample is evaluated as "Δ" after the storage stability test.

[0097] In Comparative Example 9, the content of lubricating additive E added to the surface treatment agent was insufficient, resulting in insufficient wear resistance of the final coating. The test sample is evaluated as "Δ" after the wear resistance test.

[0098] In summary, the present invention provides a chromium-free inorganic surface treatment agent for galvanized steel sheet. This surface treatment agent itself has excellent storage stability, and the coating formed by applying it to the surface of galvanized steel sheet gives the finished galvanized steel sheet an excellent formed appearance, excellent coating performance after high-temperature drying, and high heat resistance. Furthermore, the treated steel sheet product exhibits good corrosion resistance, alkali washing resistance, abrasion resistance, and formability.

[0099] In practice, the coating formed on the surface of a galvanized steel sheet by the surface treatment agent of the present invention not only ensures scratch resistance and rust prevention during processing of the galvanized steel sheet, but also enables the formed parts to have excellent appearance quality after the galvanized steel sheet undergoes continuous high-speed forming, and enables the galvanized steel sheet to have excellent coating performance even after high-temperature baking, making the surface treatment agent highly valuable for promotion and application.

[0100] It should be noted that the above embodiments are merely specific examples of the present invention. It is clear that the present invention is not limited to the above embodiments. Any similar variations or modifications that can be directly derived or easily conceived by those skilled in the art based on the disclosure of the present invention should fall within the protection scope of the present invention.

Claims

1. A chromium-free inorganic surface treatment agent comprising, by weight percent, 11.5 to 15% total solids, the remainder being water; and wherein the total solids consist of, by weight percent, the following components: Silane coupling agent (A): 45-65%; Surface-modified aqueous silica sol (B): 25%-45%; Water-soluble phosphorus-containing compounds (C): 0.5% to 1% based on the mass of the phosphorus element contained therein; Water-soluble fluorine-containing compounds (D): 1% to 6% by mass of elemental fluorine contained therein; and Lubricant additive (E): 1%-10%; Here, the compounded silane coupling agent (A) is obtained by compounding the following four types of silane coupling agent monomers: epoxy-containing silane (A1), monoamino-containing silane (A2), alkyl-containing silane (A3), and vinyl-containing silane (A4).

2. 2. The chromium-free inorganic surface treatment agent of claim 1, wherein the epoxy-containing silane (A1) comprises at least one of the following: 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, and 3-glycidyloxypropylmethyldiethoxysilane.

3. 2. The chromium-free inorganic surface treatment agent of claim 1, wherein the monoamino-containing silane (A2) comprises at least one of the following: 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

4. 2. The chromium-free inorganic surface treatment agent of claim 1, wherein the alkyl-containing silane (A3) comprises at least one of the following: triethoxysilylethane, trimethoxysilylethane, and tetraethylsilicate.

5. 2. The chromium-free inorganic surface treatment agent of claim 1, wherein the vinyl-containing silane (A4) comprises at least one of the following: vinyltriacetoxysilane, vinyltriisopropenoxysilane, vinyltriisopropoxysilane, vinyltrisilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

6. 2. The chromium-free inorganic surface treatment agent according to claim 1, wherein the compounded silane coupling agent is prepared by the following steps: Hydrolyzing and mixing epoxy-containing silane (A1) and alkyl-containing silane (A3); After the epoxy-containing silane (A1) and the alkyl-containing silane (A3) are mixed uniformly, the monoamino-containing silane (A2) is added; After the epoxy-containing silane (A1), the monoamino-containing silane (A2), and the alkyl-containing silane (A3) are mixed uniformly to form a mixture, the vinyl-containing silane (A4) is added to the mixture.

7. When the epoxy-containing silane (A1) and the alkyl-containing silane (A3) are hydrolyzed and mixed, the ratio of the mass percent of the epoxy-containing silane (A1) to the mass percent of the alkyl-containing silane (A3) satisfies: A3 / A1=0.2-0.6; The amount of monoamino-containing silane (A2) added satisfies: A2 / A1=0.3-0.7, where A1 and A2 respectively represent the mass percent of the corresponding silane; A vinyl-containing silane (A4) is added in a ratio of: A4 / A1 = 0.1 to 0.4, where A1 and A4 represent the weight percent of their respective silanes; The chromium-free inorganic surface treatment agent according to claim 6.

8. 2. The chromium-free inorganic surface treatment agent according to claim 1, wherein the surface-modified aqueous silica sol (B) is a silica sol modified with an organic compound containing an epoxy functional group, an amino functional group, and a methyl functional group.

9. 2. The chromium-free inorganic surface treatment agent according to claim 1, wherein the water-soluble phosphorus-containing compound (C) comprises a phosphate and / or phosphoric acid.

10. 2. The chromium-free inorganic surface treatment agent according to claim 1, wherein the water-soluble fluorine-containing compound (D) comprises a fluorine-containing salt and / or a fluorine-containing acid.

11. 2. The chromium-free inorganic surface treatment agent of claim 1, wherein the lubricating additive (E) comprises a lubricating additive comprised of high-density polyethylene particles and high-density polytetrafluoroethylene particles.

12. A finished galvanized steel sheet comprising a galvanized steel sheet and a coating formed by applying the chromium-free inorganic surface treatment agent according to any one of claims 1 to 11 to the surface of the galvanized steel sheet.

13. 13. The finished galvanized steel sheet of claim 12, wherein the coating has a thickness of 0.3 to 1.5 microns.

14. 13. A method for producing a finished galvanized steel sheet according to claim 12, comprising the steps of: Applying a chromium-free inorganic surface treatment agent to the surface of galvanized steel sheet; The chromium-free inorganic surface treatment agent is heated and dried to harden, forming a coating on the surface of the galvanized steel sheet.

15. 15. The method according to claim 14, wherein the chromium-free inorganic surface treatment agent is applied to the surface of the galvanized steel sheet by roller coating.

16. 15. The method of claim 14, wherein the heating and drying is carried out at a temperature of 80 to 180°C.

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