Surface treating agent for galvanized steel sheet and preparation process of surface treating agent

Abstract

According to the surface treating agent for the galvanized steel sheet and the preparation technology of the surface treating agent, in the presence of linear polysiloxane resin and modified nanoparticles, in-situ polymerization of acrylate monomers is carried out, an IPN structure is formed, the compactness of the interior of a composite resin protective film layer is improved, meanwhile, diacetone acrylamide is introduced and subjected to a Schif alkali reaction with primary amine, and therefore the surface treating agent for the galvanized steel sheet is obtained. The composite resin protective film layer has a self-repairing function, and the composite resin protective film layer has excellent mechanical strength, scratch resistance, corrosion resistance, heat resistance and the self-repairing function.

Description

Technical Field

[0001] The invention belongs to the technical field of surface treatment agents, and particularly 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 the surface. It has excellent corrosion resistance and is widely used in various fields such as automobiles, home appliances and construction. It is mostly used as parts for automobiles, home appliances, micromotors, etc. Usually, there are residual oil stains and adhesive impurities on the surface of the steel sheet, or various forms of oxide films and rust spots will form on the surface after being exposed to the atmosphere for a long time, so it cannot be directly galvanized. In addition, because the surface of the zinc layer of single metal zinc is easily corroded and produces white rust in an atmospheric environment with high humidity, it is necessary to passivate the surface of the galvanized steel sheet. The surface treatment agent for galvanized steel sheet is a chemical agent used to treat the surface of galvanized steel sheet to improve its corrosion resistance, adhesion and coating performance.

[0003] Common surface treatment agents for galvanized steel sheets include phosphate treatment agents, silane treatment agents, organic coating treatment agents, and passivation treatment agents. The metal surface treatment agents used in traditional post-galvanizing surface treatment usually use chromic acid and chromate as the main components. After treatment, a dense chromate conversion film is formed on the surface of the galvanized parts, thereby improving the corrosion resistance of the galvanized parts. However, since the wastewater discharged by chromate metal surface treatment agents after treatment causes great pollution to the environment, and the treatment agent containing hexavalent chromium is a very toxic substance that can cause cancer in the human body, its use is restricted. The organic / inorganic composite system is currently the main solution for galvanized surface treatment agents, which can meet most processing requirements. However, in some special scenarios, such as high-speed continuous stamping, high-water-cut coating, and high-temperature environments, galvanized steel sheets coated with these organic / inorganic composite surface treatment agents often have blackening of the surface during high-speed continuous forming, incompatibility with high-water-cut coating, and 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, the resin mixed treatment agent is mainly composed of water-based resins, and organic or inorganic fillers with anti-corrosion effects are added to improve the corrosion resistance. Its performance is relatively complete and it is currently a hot research topic that has attracted much attention. However, there are still some problems, such as the coating film is prone to internal defects and cracks during the formation process, insufficient hardness and impact resistance, which affects its surface anti-corrosion effect on galvanized parts, and the chromium-free galvanized steel plate surface treatment agent appears black or heat-discolored in special scenarios such as high-speed continuous stamping, high-water cutting and coating, and high-temperature environment. 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, which performs in-situ polymerization of acrylate monomers in the presence of linear polysiloxane resins and modified nanoparticles to form an IPN structure, thereby improving the compactness of the interior of the composite resin protective film layer. At the same time, diacetone acrylamide is introduced to react with primary amines to produce a Schif base, so that the composite resin protective film layer has a self-repairing function, and the composite resin protective film layer has excellent mechanical strength, scratch resistance, corrosion resistance, heat resistance and self-repairing function.

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

[0007] Preferably, the linear polysiloxane resin is a polysiloxane resin containing amino, epoxy or hydroxyl active groups.

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

[0009] Preferably, the modified nanoparticles are nanoparticles having amino active groups on their surfaces.

[0010] 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.

[0011] Preferably, the aminosilane coupling agent is KH550.

[0012] Preferably, the preparation method of the modified nanoparticles is wet modification, dispersing the silane coupling agent and nanoparticles in water, stirring to form a suspension, continuing to stir and heating to 35-75° C., reacting for 1-1.5 hours, filtering, washing, and drying to obtain modified nanoparticles.

[0013] Preferably, the primary amine is one or more of ethylenediamine, propylenediamine, hexamethylenediamine, p-phenylenediamine, and cyclohexylamine.

[0014] Preferably, the emulsifier includes one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, Tween, sodium stearate, and Span.

[0015] Preferably, the initiator is one or more of ammonium persulfate, potassium persulfate, sodium persulfate, dicumyl peroxide, AIBN, AIVN, and a redox initiator.

[0016] A preparation process of a surface treatment agent for galvanized steel sheets, comprising the following steps: Step 1, weigh each component according to the 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 a pre-emulsion 1; Step 3, butyl acrylate, styrene, methacrylic acid, hydroxyethyl methacrylate, 1 / 3 of an emulsifier, and 1 / 4 of an initiator are sequentially mixed, and stirred until uniformly dispersed to prepare a 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 at the same speed, finish adding within 2-4 hours, add the remaining initiator, and continue to keep warm for 0.5-1.5 hours; Step six, add primary amine dropwise, keep warm for 0.5-1h after adding, cool to room temperature, adjust to neutral with pH adjuster, and filter out the material.

[0017] The beneficial effects of the present invention are: 1) In the presence of linear polysiloxane resin and modified nanoparticles, the acrylate monomers are in-situ polymerized to form an IPN structure, which interacts with polar groups such as carboxyl, hydroxyl, siloxane, ester, amino, and imine to form a cross-linked structure. The synergistic effect further improves the density of the composite resin protective film layer, prevents the corrosive medium in the air from diffusing into the galvanized steel plate substrate, and inhibits electrochemical corrosion. At the same time, it can improve 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.

[0018] 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, which is used 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 improve the adhesion.

[0019] 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 generate a reversible imine bond through a Schif base reaction, so that the composite resin protective film layer has a self-repairing function. When the composite resin protective film is scratched or damaged, it can achieve self-repair through a Schif base reaction. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The present invention is further explained below in conjunction with specific implementation modes.

[0022] Example 1 A surface treatment agent for galvanized steel sheets, having an IPN structure, includes 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 is deionized water. The linear polysiloxane resin is X-22-161A, amino-modified polydimethylsiloxane. The modified nanoparticles are nano-silica modified by aminosilane coupling agent KH550. The emulsifier is sodium dodecylbenzene sulfonate, and the initiator is AIBN.

[0023] The preparation method thereof comprises the following reaction steps: Step 1, weigh each component according to the mass ratio; 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; Step 3, butyl acrylate, styrene, methacrylic acid, hydroxyethyl methacrylate, 1 / 3 of an emulsifier, and 1 / 4 of an initiator are sequentially mixed, and stirred until uniformly dispersed to prepare a 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 65° C., and react for 15 minutes; Step 5: Then, the remaining pre-emulsion 1 and pre-emulsion 2 are added dropwise to the four-necked flask at the same speed, and the addition is completed within 3 hours. The remaining initiator is added and the temperature is kept warm for another 1 hour. Step six, add ethylenediamine dropwise, keep warm for 1 hour after the addition is complete, cool to room temperature, adjust to neutral with a pH adjuster, and filter out the material.

[0024] Comparative Example 1 A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, the only difference being that the linear polysiloxane resin X-22-161A is replaced by KH550-modified nano-silica.

[0025] Comparative Example 2 A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, the only difference being that the linear polysiloxane resin X-22-161A containing amino groups is replaced by the linear polysiloxane resin X-22-169A containing epoxy groups, and the nano-silica modified by the aminosilane coupling agent KH550 is replaced by the nano-silica modified by the epoxysilane coupling agent KH560.

[0026] Comparative Example 3 A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, the only difference being that diacetone acrylamide is replaced by N,N-methylenebisacrylamide.

[0027] Comparative Example 4 A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, the only difference being that the KH550-modified nano-silica is replaced by an amino-containing linear polysiloxane resin X-22-161A.

[0028] Comparative Example 5 A surface treatment agent for galvanized steel sheets is prepared according to the method of Example 1, the only difference being that methacrylic acid and hydroxyethyl methacrylate are replaced by butyl acrylate.

[0029] Performance Testing The surface treatment agents obtained in Example 1 and Comparative Examples 1-5 were respectively applied to the surface of the galvanized steel plate to form a composite resin protective film, and the performance was characterized. The specific coating method is as follows: (1) Shearing and correction of galvanized steel sheet, using 0.5mm galvanized steel sheet, zinc layer weight is 40 / 40g / m 2 ; (2) Use a 1% alkalinity degreasing agent solution (pH 11-12) to spray clean the galvanized steel sheet at 45°C, then wash it with pure water to remove the alkaline components remaining on the surface, and dry it for later use; (3) Roll-coating the surface treatment agents obtained in Example 1 and Comparative Examples 1-5 on the galvanized steel sheets treated in step 2; (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.

[0030] The test method is as follows: 1) Corrosion resistance: According to the test standard GB / T6461-2002, a neutral salt spray test was carried out in a DCTC1200P artificial atmosphere salt spray test chamber. After 96 hours, photos were taken with a digital camera to measure the corrosion area.

[0031] 2) Self-repairing property: Use a cutting knife to cut the composite resin protective film to the galvanized layer, immerse it in a 5% salt water solution at room temperature, and observe the time when rust begins to appear at the scratch.

[0032] 3) Adhesion: According to the test standard GB / T 9286-2021, the 6×6 cross-cut method is used for testing, and the adhesion of the coating is divided into different levels from 0 to 5. Level 0 indicates the best adhesion and level 5 indicates the worst adhesion.

[0033] 4) Heat resistance: Place the sample in a muffle furnace at 1000°C for 15 seconds, take it out, and evaluate it. The evaluation criteria are as follows: ◎: no cracks on the surface; ○: a few cracks on the surface; △: a lot of cracks on the surface.

[0034] Table 1 Properties of surface treatment agents for galvanized steel sheets 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-healing. 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, the polar groups such as carboxyl, hydroxyl, siloxane group, ester group, amino group, imine group and other polar groups in the polyacrylic acid 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 the corrosive medium in the air from diffusing into 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.

[0035] 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. 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 produce a reversible imine bond by Schiff base reaction, so that the composite resin protective film layer has a self-repairing function, and can achieve self-repair through Schiff base reaction when scratches or damage appear on the composite resin protective film.

[0036] From the comparison between 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 acrylate monomer is polymerized in situ 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 respectively added dropwise to the four-necked flask at the same speed. On the one hand, diacetone acrylamide can form Schiff bonds with the amino groups of linear polysiloxane resin X-22-161A and the amino groups of nano-silica modified by KH550 through its keto group, so that the polymerizable monomer, modified nanoparticles and linear polysiloxane resin are fully dispersed to obtain an IPN structure. On the other hand, methacrylic acid and hydroxyethyl methacrylate monomers containing carboxyl and hydroxyl groups are only added in pre-emulsion 2. The addition method of the present invention can make the polar groups tend to be distributed on the surface of the composite resin, better play the adsorption effect, improve the adhesion of the composite resin protective film formed on the surface of the galvanized steel plate, and show better corrosion resistance, heat resistance and self-repairing properties.

[0037] 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 equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A surface treatment agent for galvanized steel sheet, characterized in that: It has an IPN structure, including 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 is deionized water; The linear polysiloxane resin is a linear polysiloxane resin containing amino reactive groups; The modified nanoparticles are nanoparticles modified by 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.

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 dodecyl sulfate, sodium dodecylbenzene sulfonate, Tween, sodium stearate, and Span.

4. A process for preparing the surface treatment agent for galvanized steel sheet according to any one of claims 1 to 3, comprising the following reaction steps: Step 1, weigh each component according to the 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 a pre-emulsion 1; Step 3, butyl acrylate, styrene, methacrylic acid, hydroxyethyl methacrylate, 1 / 3 of an emulsifier, and 1 / 4 of an initiator are sequentially mixed, and stirred until uniformly dispersed to prepare a 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 at the same speed, finish the dripping within 2-4 hours, add the remaining initiator, and continue to keep warm for 0.5-1.5 hours; Step six, add primary amine dropwise, keep warm for 0.5-1h after adding, cool to room temperature, adjust to neutral with pH adjuster, and filter out the material.

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