Surface treatment agent for galvanized steel sheet and preparation process thereof

Abstract

The present invention provides a surface treatment agent for galvanized steel sheets and a preparation process thereof. In the presence of a linear polysiloxane resin and modified nanoparticles, in-situ polymerization of acrylate monomers is carried out to form an IPN structure, thereby improving the internal density of a composite resin protective film layer. Simultaneously, diacetone acrylamide is introduced to react with a primary amine to produce a Schif base, thereby imparting a self-repairing function to the composite resin protective film layer, thereby achieving excellent mechanical strength, scratch resistance, corrosion resistance, heat resistance, and self-repairing function.

Description

Technical Field

[0001] The invention belongs to the technical field of surface treatment agents, and in particular relates to a surface treatment agent for galvanized steel plates and a preparation process thereof. Background Art

[0002] Galvanized steel sheet is a welded steel sheet with a hot-dip or electroplated zinc layer on its surface. It exhibits excellent corrosion resistance and is widely used in various fields, including automobiles, home appliances, and construction, primarily as components for automobiles, home appliances, and micromotors. Steel sheets often have residual oil and adhesive impurities on their surfaces, or after prolonged exposure to the atmosphere, various oxide films and rust stains will form on the surface, making them impractical for direct galvanizing. Furthermore, because elemental zinc is susceptible to corrosion and white rust in high-humidity atmospheric environments, passivation treatment is required. Surface treatment agents for galvanized steel sheets are chemical agents used to treat the surface of galvanized steel sheets to improve their corrosion resistance, adhesion, and coating properties.

[0003] Common surface treatment agents for galvanized steel sheets include phosphate treatment agents, silane treatment agents, organic coating agents, and passivation treatment agents. Traditional post-galvanizing metal surface treatment agents typically contain chromic acid and chromates as their primary ingredients. These agents form a dense chromate conversion film on the surface of the galvanized part, thereby improving its corrosion resistance. However, chromate-based metal surface treatment agents are subject to restrictions due to the significant environmental pollution caused by wastewater discharge after treatment, and the presence of hexavalent chromium in these agents is highly toxic and can cause cancer. Currently, organic / inorganic composite systems are the predominant surface treatment agent solution for galvanizing, meeting most processing requirements. However, in certain applications, such as high-speed continuous stamping, high-pressure water jet coating, and high-temperature environments, galvanized steel sheets coated with these organic / inorganic composite surface treatment agents often exhibit surface blackening during high-speed continuous stamping, poor performance during high-pressure water jet coating, and thermal discoloration due to the presence of organic components.

[0004] Chromium-free surface treatment agents have become a more popular development trend. Chromium-free surface treatment agents include phosphates, rare earth salts, silanes, and resin mixed treatment agents. Among them, resin mixed treatment agents are mainly water-based resins, and organic or inorganic fillers with anti-corrosion effects are added to improve the corrosion resistance. Their performance is relatively complete and is currently a hot research topic that has attracted much attention. However, there are still some problems, such as the tendency of internal defects and cracks to occur in the coating film during the formation process, insufficient hardness and impact resistance, which affect its surface corrosion resistance effect on galvanized parts, and the chromium-free galvanized steel plate surface treatment agent may turn black or discolor due to heat in special scenarios such as high-speed continuous stamping, high-water cutting and high-temperature environments. Therefore, it is urgent to develop a new galvanized steel plate surface treatment agent that can take into account multiple excellent properties. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the purpose of the present invention is to provide a surface treatment agent for galvanized steel sheets. In the presence of linear polysiloxane resin and modified nanoparticles, in-situ polymerization of acrylate monomers is carried out to form an IPN structure, thereby improving the density of the internal layer of the composite resin protective film. At the same time, diacetone acrylamide is introduced to react with primary amines to produce a Schif base, thereby giving the composite resin protective film layer a self-repairing function, so that the composite resin protective film layer has excellent mechanical strength, scratch resistance, corrosion resistance, heat resistance and self-repairing function.

[0006] The object of the present invention is achieved through the following technical solutions:

[0007] A surface treatment agent for galvanized steel sheets has an IPN structure and comprises 1-10% linear polysiloxane resin, 15-20% isooctyl acrylate, 15-20% butyl acrylate, 5-15% methyl methacrylate, 5-15% styrene, 0.5-2% methacrylic acid, 0.5-2% hydroxyethyl methacrylate, 0.5-3% diacetone acrylamide, 0.5-2% modified nanoparticles, 0.2-1.5% primary amine, 0.2-1.5% emulsifier, 0.01-0.05% initiator, and the balance deionized water.

[0008] Preferably, the linear polysiloxane resin is a polysiloxane resin containing amino, epoxy or hydroxyl reactive groups.

[0009] Preferably, the linear polysiloxane resin is a polysiloxane resin containing amino reactive groups.

[0010] Preferably, the modified nanoparticles are nanoparticles having amino active groups on their surfaces.

[0011] Preferably, the nanoparticles containing amino active groups on the surface are nanoparticles modified with an aminosilane coupling agent, and the nanoparticles are one or more of nano-silicon dioxide, nano-bentonite, nano-silicon carbide, nano-calcium carbonate, and rare earth nanoparticles.

[0012] Preferably, the aminosilane coupling agent is KH550.

[0013] Preferably, the preparation method of the modified nanoparticles is wet modification, wherein the silane coupling agent and nanoparticles are dispersed in water, stirred to form a suspension, and then stirred and heated to 35-75° C. for 1-1.5 hours, filtered, washed, and dried to obtain the modified nanoparticles.

[0014] Preferably, the primary amine is one or more of ethylenediamine, propylenediamine, hexamethylenediamine, p-phenylenediamine, and cyclohexylamine.

[0015] Preferably, the emulsifier includes one or more of sodium lauryl sulfate, sodium dodecylbenzene sulfonate, Tween, sodium stearate, and Span.

[0016] Preferably, the initiator is one or more of ammonium persulfate, potassium persulfate, sodium persulfate, dicumyl peroxide, AIBN, AIVN, and a redox initiator.

[0017] A preparation process for a surface treatment agent for galvanized steel sheets, comprising the following steps:

[0018] Step 1, weigh each component according to mass ratio;

[0019] Step 2: linear polysiloxane resin, diacetone acrylamide, isooctyl acrylate, methyl methacrylate, modified nanoparticles, 1 / 3 emulsifier, and 1 / 4 initiator are sequentially mixed and stirred until uniformly dispersed to prepare pre-emulsion 1;

[0020] Step 3: butyl acrylate, styrene, methacrylic acid, hydroxyethyl methacrylate, 1 / 3 emulsifier, and 1 / 4 initiator are mixed in sequence, and stirred until uniformly dispersed to prepare pre-emulsion 2;

[0021] Step 4: Add 1 / 3 of the emulsifier and deionized water to a four-necked flask equipped with a thermometer, a stirrer, a condenser, and a constant pressure funnel, start stirring, add 1 / 4 of the pre-emulsion 1 under stirring, heat to 55-75°C, and react for 10-30 minutes;

[0022] Step 5: Then, add the remaining pre-emulsion 1 and pre-emulsion 2 to the four-necked flask dropwise at the same rate, complete the addition within 2-4 hours, add the remaining initiator, and continue to keep warm for 0.5-1.5 hours;

[0023] Step 6: add primary amine dropwise, keep warm for 0.5-1h after the addition is complete, cool to room temperature, adjust the pH to neutral with a pH adjuster, and filter the material.

[0024] The beneficial effects of the present invention are:

[0025] 1) In the presence of linear polysiloxane resin and modified nanoparticles, acrylate monomers are in situ polymerized to form an IPN structure. The cross-linked structure formed by the interaction with polar groups such as carboxyl, hydroxyl, siloxane, ester, amino, and imine groups has a synergistic effect, further improving the density of the composite resin protective film layer, preventing the corrosive medium in the air from diffusing to the galvanized steel plate substrate, inhibiting electrochemical corrosion, and at the same time improving the mechanical strength, toughness, scratch resistance, and corrosion resistance of the composite resin protective film layer. The presence of modified nanoparticles can improve the heat resistance of the composite resin protective film layer.

[0026] 2) In the presence of linear polysiloxane resin and modified nanoparticles, in-situ polymerization of acrylic monomers is carried out to form a composite resin. As a surface treatment agent, the presence of polar groups such as carboxyl, hydroxyl, siloxane, ester, amino, and imine groups in the composite resin can improve the adsorption of the composite resin protective film to the galvanized steel plate substrate and enhance the adhesion.

[0027] 3) The ketone group of diacetone acrylamide can react with the amino group of linear polysiloxane resin, the amino group on the surface of modified nanoparticles, and the amino group of ethylenediamine to produce a reversible imine bond through a Schif base reaction, which gives the composite resin protective film a self-repairing function. When the composite resin protective film is scratched or damaged, it can achieve self-repair through the Schif base reaction. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] The present invention will be further explained below with reference to specific embodiments.

[0030] Example 1

[0031] A surface treatment agent for galvanized steel sheets having an IPN structure comprises 6% linear polysiloxane resin, 15% isooctyl acrylate, 15% butyl acrylate, 8% methyl methacrylate, 5% styrene, 0.5% methacrylic acid, 1.5% hydroxyethyl methacrylate, 1.5% diacetone acrylamide, 2% modified nanoparticles, 0.8% ethylenediamine, 0.8% emulsifier, 0.03% initiator, and the balance deionized water. The linear polysiloxane resin is X-22-161A, an amino-modified polydimethylsiloxane. The modified nanoparticles are nanosilica modified with the aminosilane coupling agent KH550. The emulsifier is sodium dodecylbenzenesulfonate, and the initiator is AIBN.

[0032] The preparation method thereof comprises the following reaction steps:

[0033] Step 1, weigh each component according to mass ratio;

[0034] Step 2: linear polysiloxane resin X-22-161A, diacetone acrylamide, isooctyl acrylate, methyl methacrylate, KH550-modified nano-silica, 1 / 3 emulsifier, and 1 / 4 initiator are sequentially mixed and stirred until uniformly dispersed to prepare pre-emulsion 1;

[0035] Step 3: butyl acrylate, styrene, methacrylic acid, hydroxyethyl methacrylate, 1 / 3 emulsifier, and 1 / 4 initiator are mixed in sequence, and stirred until uniformly dispersed to prepare pre-emulsion 2;

[0036] Step 4: Add 1 / 3 of the emulsifier and deionized water to a four-necked flask equipped with a thermometer, a stirrer, a condenser, and a constant pressure funnel, start stirring, add 1 / 4 of the pre-emulsion 1 under stirring, heat to 65°C, and react for 15 minutes;

[0037] Step 5: Then, add the remaining pre-emulsion 1 and pre-emulsion 2 to the four-necked flask dropwise at the same rate, complete the addition within 3 hours, add the remaining initiator, and continue to keep warm for 1 hour;

[0038] Step 6: add ethylenediamine dropwise, keep warm for 1 hour after the addition is complete, cool to room temperature, adjust the pH to neutral with a pH adjuster, and filter the material.

[0039] Comparative Example 1

[0040] A surface treatment agent for galvanized steel sheets was prepared according to the method of Example 1, with the only difference being that the linear polysiloxane resin X-22-161A was replaced by KH550-modified nano-silica.

[0041] Comparative Example 2

[0042] A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, except that the amino-containing linear polysiloxane resin X-22-161A is replaced by the epoxy-containing linear polysiloxane resin X-22-169A, and the aminosilane coupling agent KH550-modified nanosilica is replaced by the epoxysilane coupling agent KH560-modified nanosilica.

[0043] Comparative Example 3

[0044] A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, with the only difference being that diacetone acrylamide is replaced by N,N-methylenebisacrylamide.

[0045] Comparative Example 4

[0046] A surface treatment agent for galvanized steel sheets was prepared according to the method of Example 1, with the only difference being that the KH550-modified nano-silica was replaced by an amino-containing linear polysiloxane resin X-22-161A.

[0047] Comparative Example 5

[0048] A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, with the only difference being that methacrylic acid and hydroxyethyl methacrylate are replaced by butyl acrylate.

[0049] Performance Testing

[0050] The surface treatment agents obtained in Example 1 and Comparative Examples 1-5 were respectively applied to the surface of galvanized steel sheets to form composite resin protective films, and the performance was characterized. The specific coating method is as follows:

[0051] (1) Cutting and trimming of galvanized steel sheets, using 0.5mm galvanized steel sheets with a zinc layer weight of 40 / 40g / m 2 ;

[0052] (2) Use a 1% alkalinity degreasing agent solution (pH 11-12) to spray clean the galvanized steel sheet at 45°C, then rinse with pure water to remove the alkaline components remaining on the surface, and dry for use;

[0053] (3) Roll-coating the surface treatment agents obtained in Example 1 and Comparative Examples 1-5 onto the galvanized steel sheets treated in step 2;

[0054] (4) The galvanized steel sheet coated with the surface treatment agent is placed in an oven at 80°C for drying to form a composite resin protective film with a thickness of 1 μm on the surface of the galvanized steel sheet.

[0055] The test method is as follows:

[0056] 1) Corrosion resistance: According to the test standard GB / T6461-2002, a neutral salt spray test was conducted in a DCTC1200P artificial atmosphere salt spray test chamber. After 96 hours, photos were taken with a digital camera and the corrosion area was measured.

[0057] 2) Self-repairing property: Use a cutting knife to cut through the composite resin protective film to the galvanized layer, immerse it in a 5% salt water solution at room temperature, and observe the time it takes for rust to appear at the scratch.

[0058] 3) Adhesion: According to the test standard GB / T 9286-2021, the 6×6 cross-hatch method is used for testing. The adhesion of the coating is divided into different levels from 0 to 5, with level 0 indicating the best adhesion and level 5 indicating the worst adhesion.

[0059] 4) Heat resistance: Place the sample in a muffle furnace at 1000°C for 15 seconds, then take it out and evaluate it. The evaluation criteria are as follows:

[0060] ◎: No surface cracks; ○: Minor surface cracks; △: Numerous surface cracks.

[0061] Table 1 Properties of surface treatment agents for galvanized steel sheets

[0062]

[0063] From the comparison of Example 1, Comparative Example 1, and Comparative Example 4, it can be seen that the composite resin protective film formed on the surface of the galvanized steel plate by the surface treatment agent prepared in Example 1 of the present application has better effects in terms of corrosion resistance, adhesion, heat resistance and self-repairing properties. This may be because in Example 1, in the presence of linear polysiloxane resin and modified nanoparticles, in-situ polymerization of acrylate monomers is carried out to form an IPN structure. On this basis, polar groups such as carboxyl groups, hydroxyl groups, siloxane groups, ester groups, amino groups, and imine groups in the polyacrylic resin, linear polysiloxane resin, and modified nanoparticles interact to form a re-crosslinked structure. The two work synergistically to further improve the density of the composite resin protective film layer, prevent corrosive media in the air from diffusing to the galvanized steel plate substrate, inhibit electrochemical corrosion, and at the same time improve the mechanical strength, scratch resistance, corrosion resistance, and heat resistance of the composite resin protective film layer.

[0064] From the comparison of Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that the composite resin protective film formed on the surface of the galvanized steel plate by the surface treatment agent prepared in Example 1 of the present application has better effects in terms of corrosion resistance, adhesion, heat resistance and self-repairing properties. This may be because in Example 1, the ketone group of diacetone acrylamide can react with the amino group of the linear polysiloxane resin, the amino group on the surface of the modified nanoparticles, and the amino group of ethylenediamine to undergo a Schiff base reaction to generate a reversible imine bond, so that the composite resin protective film layer has a self-repairing function, and can achieve self-repair through the Schiff base reaction when the composite resin protective film is scratched or damaged.

[0065] From the comparison of Example 1 and Comparative Example 5, it can be seen that the composite resin protective film formed on the surface of the galvanized steel plate by the surface treatment agent prepared in Example 1 of the present application has better effects in terms of corrosion resistance, adhesion, heat resistance and self-repairing. This may be because in Example 1, in the presence of linear polysiloxane resin and modified nanoparticles, the in-situ polymerization of acrylate monomers is carried out to form a composite resin, and in the polymerization process, 1 / 3 of pre-emulsion 1 (linear polysiloxane resin X-22-161A, diacetone acrylamide, isooctyl acrylate, methyl methacrylate, KH550 modified nano-silica) is first polymerized, and then the remaining pre-emulsion 1 and pre-emulsion 2 (acrylic acid) are added dropwise to the four-necked flask at the same speed. The invention discloses a novel polysiloxane copolymer comprising diacetone acrylamide, diacetone acrylamide, linear polysiloxane resin X-22-161A ...

[0066] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A surface treatment agent for galvanized steel sheets, characterized in that: The invention has an IPN structure, comprising 1-10% linear polysiloxane resin, 15-20% isooctyl acrylate, 15-20% butyl acrylate, 5-15% methyl methacrylate, 5-15% styrene, 0.5-2% methacrylic acid, 0.5-2% hydroxyethyl methacrylate, 0.5-3% diacetone acrylamide, 0.5-2% modified nanoparticles, 0.2-1.5% primary amine, 0.2-1.5% emulsifier, 0.01-0.05% initiator, and the balance deionized water; The linear polysiloxane resin is a linear polysiloxane resin containing amino active groups; the modified nanoparticles are nanoparticles modified with an aminosilane coupling agent, and the nanoparticles are one or more of nanosilicon dioxide, nanobentonite, nanosilicon carbide, nanocalcium carbonate, and rare earth nanoparticles; The preparation process of the surface treatment agent for galvanized steel sheets comprises the following reaction steps: Step 1, weigh each component according to mass ratio; Step 2: linear polysiloxane resin, diacetone acrylamide, isooctyl acrylate, methyl methacrylate, modified nanoparticles, 1 / 3 emulsifier, and 1 / 4 initiator are sequentially mixed and stirred until uniformly dispersed to prepare pre-emulsion 1; Step 3: butyl acrylate, styrene, methacrylic acid, hydroxyethyl methacrylate, 1 / 3 emulsifier, and 1 / 4 initiator are mixed in sequence, and stirred until uniformly dispersed to prepare pre-emulsion 2; Step 4: Add 1 / 3 of the emulsifier and deionized water to a four-necked flask equipped with a thermometer, a stirrer, a condenser, and a constant pressure funnel, start stirring, add 1 / 4 of the pre-emulsion 1 under stirring, heat to 55-75°C, and react for 10-30 minutes; Step 5: Then, add the remaining pre-emulsion 1 and pre-emulsion 2 to the four-necked flask dropwise at the same rate, complete the addition within 2-4 hours, add the remaining initiator, and continue to keep warm for 0.5-1.5 hours; Step 6: add primary amine dropwise, keep warm for 0.5-1 hour after the addition is complete, cool to room temperature, adjust the pH to neutral with a pH adjuster, and filter the material.

2. The surface treatment agent for galvanized steel sheet according to claim 1, characterized in that The primary amine is one or more of ethylenediamine, propylenediamine, hexamethylenediamine, p-phenylenediamine, and cyclohexylamine.

3. The surface treatment agent for galvanized steel sheet according to claim 1, characterized in that The emulsifier includes one or more of sodium lauryl sulfate, sodium dodecylbenzene sulfonate, Tween, sodium stearate, and Span.

4. A process for preparing the surface treatment agent for galvanized steel sheets according to any one of claims 1 to 3, comprising the following reaction steps: Step 1, weigh each component according to mass ratio; Step 2: linear polysiloxane resin, diacetone acrylamide, isooctyl acrylate, methyl methacrylate, modified nanoparticles, 1 / 3 emulsifier, and 1 / 4 initiator are sequentially mixed and stirred until uniformly dispersed to prepare pre-emulsion 1; Step 3: butyl acrylate, styrene, methacrylic acid, hydroxyethyl methacrylate, 1 / 3 emulsifier, and 1 / 4 initiator are mixed in sequence, and stirred until uniformly dispersed to prepare pre-emulsion 2; Step 4: Add 1 / 3 of the emulsifier and deionized water to a four-necked flask equipped with a thermometer, a stirrer, a condenser, and a constant pressure funnel, start stirring, add 1 / 4 of the pre-emulsion 1 under stirring, heat to 55-75°C, and react for 10-30 minutes; Step 5: Then, add the remaining pre-emulsion 1 and pre-emulsion 2 to the four-necked flask dropwise at the same rate, complete the addition within 2-4 hours, add the remaining initiator, and continue to keep warm for 0.5-1.5 hours; Step 6: add primary amine dropwise, keep warm for 0.5-1h after the addition is complete, cool to room temperature, adjust the pH to neutral with a pH adjuster, and filter the material.

Images