Method for coating steel coils with highly chemical-resistant coating structures

Abstract

The present invention discloses a coating method for a coiled steel with a high chemical resistance coating structure, comprising step S1: performing surface decontamination treatment on the coiled steel product to be processed, removing oil stains on the surface of the coiled steel product, and removing moisture on the surface of the coiled steel product and then drying it with wind; step S2: performing passivation treatment on the surface of the coiled steel product and then drying it; step S3: rolling at least one layer of PVDF primer on the surface of the coiled steel product, and after each layer of PVDF primer is applied, baking at a temperature of 235°C-245°C for more than 50s to complete curing to form a primer layer, and the thickness of each primer layer is 7μm-20μm; step S4: applying one or two layers of PVF coating on the primer layer. The coating structure prepared on the surface of the coiled steel according to the above method forms a smoother, uniform, dense and strong surface layer, has a better protective effect, can extend the service life of the substrate, and the coating structure on the surface of the substrate can be flexibly adjusted as needed.

Description

Technical Field

[0001] The invention relates to the field of coil steel surface treatment, and in particular to a coating method for a coil steel with a high chemical resistance coating structure. Background Art

[0002] In order to protect coiled steel products and improve their chemical resistance, corrosion resistance and weather resistance, the traditional treatment method is to attach a protective film to the surface of the coiled steel substrate. However, the processing cost of attaching the protective film is high, and the weather resistance and wear resistance of the protective film are inferior to those of the protective coating. The protective film is not easy to recycle and is likely to cause environmental pollution.

[0003] The existing processing method is to form a protective coating after coating the paint film on the surface of the coil substrate and curing it, thereby replacing the protective film. Since the protective structure on the surface of the coil product needs to have a certain thickness, and the surface of the coil product needs to be coated with color to improve the decorative performance, the coating structure on the surface of the coil usually includes a primer layer, a color paint layer and a topcoat layer. Common coating materials include epoxy primer, polyurethane (polyester-amino) primer, water-soluble acrylic primer, polyester resin coating, PVC plastisol, PVDF coating, PVF coating, etc.

[0004] Among them, the production process of coatings using epoxy resin as the main resin, such as the invention patent with authorization announcement number CN115260853B, the prepared coil coating has good adhesion and chemical resistance, but relatively poor flexibility; the construction process of polyurethane coating is relatively complicated, and the requirements for the construction environment are high. During the construction process, it is necessary to ensure that the substrate is dry and clean. When it is used in a humid environment, it may encounter the problem of moisture causing blistering of the paint film. In addition, over time, the paint film may become powdery, and long-term exposure to sunlight may cause aging and fading of the coating, affecting the appearance and service life; water-soluble acrylic primer has good water resistance and weather resistance, but poor chemical resistance, and its physical indicators such as hardness and wear resistance are low; polyester coatings, such as the invention patent with publication number CN103965749A, have excellent weather resistance, but poor environmental performance and high hardness, and are prone to cracking; PVC plastisol has good mechanical properties and chemical resistance, but poor adhesion and flow characteristics, and is prone to release toxic gases during the molding process. The coating prepared with PVF fluorocarbon resin as film-forming resin is called PVF fluorocarbon coating. It has good weather resistance, chemical resistance, solvent resistance, salt spray resistance, anti-fouling and impact resistance. However, due to the film-forming characteristics of PVF, when it is affected by the solvent volatilization rate, film-forming rate, film-forming temperature, etc. in the actual production process, the leveling performance of the coating is extremely poor, which greatly affects the density of the paint film. Therefore, it is necessary to provide a coil surface protection structure that has the advantages of the above materials. Summary of the invention

[0005] Therefore, in order to solve the above problems, the present invention provides a method for coating a steel coil having a high chemical resistance coating structure.

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

[0007] A method for coating a steel coil having a highly chemical resistant coating structure comprises the following steps:

[0008] Step S0: pre-preparing PVF colored topcoat and PVF clearcoat;

[0009] The preparation steps of the PVF colored topcoat include:

[0010] Step 1) Prepare the following raw materials by mass:

[0011] Pre-mixed PVF 58-70 parts;

[0012] 6-10 parts of acrylic resin;

[0013] Propylene carbonate 2-7 parts;

[0014] 10-20 parts of titanium dioxide;

[0015] 0.5-2 parts of methylated amino resin;

[0016] Dispersant II 0.2-0.4 parts;

[0017] 0.1-0.6 parts of antioxidant additives;

[0018] 0.5 to 1 part of ultraviolet absorbing agent;

[0019] 3-8 parts of diluent;

[0020] Matting powder 0.1-1 part;

[0021] The particle size of the titanium dioxide is 8 μm, and the premixed PVF is formed by mixing PVF resin and propylene carbonate solvent in a mass ratio of 45:55;

[0022] Step 2) grinding the acrylic resin, propylene carbonate and titanium dioxide until the dispersion fineness reaches 10 μm to obtain a mixed solution;

[0023] Step 3) mixing the premixed PVF with the mixed solution and the remaining raw materials at a speed of ≥1000 rpm for more than 2 hours, filtering and packaging to obtain the PVF colored topcoat;

[0024] The preparation steps of the PVF varnish include:

[0025] Step a) Prepare the following raw materials by mass:

[0026] Pre-mixed PVF 58-85 parts;

[0027] 6-10 parts of acrylic resin;

[0028] Dispersant I 0.1 part - 0.4 part;

[0029] Propylene carbonate 2-7 parts;

[0030] 0.5-2 parts of methylated amino resin;

[0031] Dispersant II 0.2-0.4 parts;

[0032] 0.1-0.6 parts of antioxidant additives;

[0033] Matting powder 0.1-1 part;

[0034] The premixed PVF is formed by mixing PVF resin and propylene carbonate solvent in a mass ratio of 45:55;

[0035] Step b) mixing the above raw materials together, mixing at a rotation speed of ≥1000 rpm for more than 2 hours, filtering and packaging to obtain the PVF varnish;

[0036] Step S1: performing surface decontamination treatment on the coiled steel product to be processed to remove oil stains on the surface of the coiled steel product, remove moisture on the surface of the coiled steel product, and then blow dry;

[0037] Step S2: performing passivation treatment on the surface of the coiled steel product and then drying it;

[0038] Step S3: Roll-coating at least one layer of PVDF primer on the surface of the coiled steel product, and after each layer of PVDF primer is coated, baking is performed at a temperature of 235° C.-245° C. for more than 50 seconds to complete curing to form a primer layer, and the thickness of each primer layer is 7 μm-20 μm;

[0039] Step S4: applying one or two layers of PVF coating on the primer layer;

[0040] When only one layer of PVF coating is applied on the primer layer, the PVF coating is a PVF colored topcoat, and a layer of PVF colored topcoat is rolled on the primer layer and then baked at a temperature of 235° C.-245° C. for 50 seconds to cure, thereby forming a colored topcoat layer;

[0041] When two layers of PVF coating are applied on the primer layer, the first layer of PVF coating is a PVF colored topcoat, and the second layer of PVF coating is a PVF colored topcoat or a varnish; after the first layer of PVF coating is roller-coated on the primer layer, it is baked at a temperature of 230°C-240°C for more than 50 seconds to complete curing, forming a colored topcoat layer, and then a second layer of PVF coating is applied on the colored topcoat layer, and baked at a temperature of 235°C-245°C for more than 50 seconds to complete curing, forming a second layer of colored topcoat layer or a varnish layer.

[0042] Preferably, the dispersant I is an alkylhydroxyl ammonium salt of a copolymer containing an acidic group, and the dispersant II is a high molecular weight block copolymer solution containing a pigment affinity group.

[0043] Preferably, the premixed PVF used in the PVF colored topcoat and PVF varnish is prepared by stirring a PVF resin and a propylene carbonate solvent in a mass ratio of 45:55 at a speed of 1000 rpm to make a premixed PVF for standby use after the dispersion fineness reaches less than 10 μm. During the mixing and use process, the overall temperature needs to be controlled not to exceed 45°C.

[0044] Preferably, a primer layer is formed on the surface of the steel coil, the primer layer has a thickness of 7 μm, a 20 μm colored topcoat layer is formed on the primer layer, or two 15 μm colored topcoat layers are formed, or a 15 μm colored topcoat layer and a 15 μm clear varnish layer are formed.

[0045] Preferably, 2-4 primer layers are formed on the surface of the steel coil, each primer layer is 20 μm thick, the primer layer also includes a colored topcoat layer and a clearcoat layer, and the thickness of the PVF colored topcoat layer and the clearcoat layer are both 15 μm.

[0046] Preferably, in step S2, the passivation treatment of the surface of the steel coil product includes: using a chromium-free passivation liquid to roller-coat the surface of the steel coil product, after passivation for 10s-20s, drying the surface of the steel coil product at a temperature of 80°C-90°C.

[0047] Preferably, step S1 comprises the following steps:

[0048] S11: Use water or alkaline cleaning solution with a pH value of 7-11 and a concentration of 3%-5% to pre-clean the surface of the coil and then rinse the surface of the coil with clean water;

[0049] S12: placing the steel coil in a pickling tank containing a pickling solution, pickling at a temperature of 60° C. to 80° C. for 1 min to 5 min, and taking out the steel coil after observing that the oxide layer on the surface of the steel coil is removed, wherein the pickling solution is one of hydrochloric acid, sulfuric acid or nitric acid with a concentration of 10%;

[0050] S13: Rinse the coil with clean water twice or more;

[0051] S14: Use hot air at 80℃-120℃ to dry the surface of the steel coil for 1h-3h to ensure that the surface of the steel coil is completely dry.

[0052] The beneficial effects of the technical solution of the present invention are mainly reflected in:

[0053] 1. Provide a method for preparing a steel coil with a high chemical resistance coating structure, so that the surface of the steel coil has a primer layer made of PVDF primer, and a colored topcoat layer formed of PVF colored topcoat is further formed on the primer layer, or a varnish layer made of PVF varnish is further formed on the colored topcoat layer. The multi-layer structure is used in combination to form a more comprehensive and excellent protection structure. Since the main resin of the PVDF primer is PVDF, it has high strength and high toughness under low temperature conditions. At the same time, its excellent adhesion can be closely attached to the substrate to provide strong Adhesion ensures that the coating is not easy to fall off. The main resin of PVF colored topcoat and PVF varnish is PVF. Since the main resin component in the PVF colored topcoat layer is a mixture of PVF resin and propylene carbonate solvent, it has good weather resistance, corrosion resistance, flexibility and impact resistance. At the same time, its adhesion on PVDF primer is extremely high, and the decorative layer of PVF coating has good isolation and density, so it has better protection effect. The combination of the two coating structures can form a smoother, more uniform, dense and solid surface layer, thereby extending the service life of the substrate.

[0054] 2. Coiled steel products usually include galvanizing, aluminum zinc plating, zinc aluminum magnesium plating, etc. Before processing the surface structure on the coiled steel products, the coiled steel products are surface treated. The surface treatment includes pickling and alkali washing to remove oil stains on the surface of the coiled steel products to ensure the cleanliness and flatness of the surface of the coiled steel products. Subsequently, the coiled steel products are purified by purification liquid to form a layer of purification film on the surface of the coiled steel substrate, further improving the strength, wear resistance and corrosion resistance of the substrate surface, and at the same time improving the adhesion of the coating on the substrate surface. In addition, when the PVF coating has multiple layers, the curing temperature is strictly controlled to ensure that the curing temperature of the first layer of PVF coating is 5℃-10℃ lower than that of the second layer of PVF coating, and the curing temperature of the second layer of PVF coating does not exceed 245℃, so as to avoid the first layer of PVF coating being affected by reheating when the second layer of PVF coating is cured, resulting in uneven coating or bubbling.

[0055] 3. The surface coating of the steel coil products can be flexibly arranged according to actual needs. It is suitable for the main resin as the topcoat. Since PVF resin can effectively maintain the stability and durability of the color, that is, it has good color fixing performance, it can meet the requirements of substrate protection and surface color fixing without coating varnish on the surface of the colored topcoat layer in an environment with low requirements for chemical corrosion resistance; if the use environment of the steel coil products has high requirements for the color fixing effect, PVF varnish can be further coated on the PVF colored topcoat layer; if there are certain requirements for the hardness and thickness of the surface protection structure of the steel coil products, multiple layers of PVDF primer can be applied to increase the primer thickness and the hardness of the steel coil substrate surface structure, and further PVF colored topcoat layer and varnish layer can be coated on the outside of the PVDF primer. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is a schematic diagram of the coating structure when a primer layer and a PVF colored topcoat layer are provided on a coiled steel product;

[0057] Figure 2 It is a schematic diagram of the coating structure when a primer layer and two PVF colored topcoat layers are provided on a coiled steel product;

[0058] Figure 3 It is a schematic diagram of the coating structure when a primer layer, a PVF colored topcoat layer and a clearcoat layer are provided on a coiled steel product;

[0059] Figure 4 It is a schematic diagram of the coating structure when four primer layers, one PVF colored topcoat layer and one clear varnish layer are provided on the coiled steel product. DETAILED DESCRIPTION

[0060] In order to make the purpose, advantages and features of the present invention more clearly and in detail, the following preferred embodiments are used for illustration and explanation. The embodiments are only typical examples of the application of the technical solution of the present invention. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection claimed by the present invention.

[0061] The present invention discloses a method for coating a steel coil having a high chemical resistance coating structure, comprising the following steps:

[0062] Step S0: pre-preparing PVF colored topcoat and PVF clearcoat;

[0063] Step S1: performing surface decontamination treatment on the coiled steel product to be processed to remove oil stains on the surface of the coiled steel product, remove moisture on the surface of the coiled steel product, and then blow dry;

[0064] Step S2: performing passivation treatment on the surface of the coiled steel product and then drying it;

[0065] Step S3: Roll-coating at least one layer of PVDF primer on the surface of the coiled steel product, and after each layer of PVDF primer is coated, baking is performed at a temperature of 235° C.-245° C. for more than 50 seconds to complete curing to form a primer layer, and the thickness of each primer layer is 7 μm-20 μm; in some embodiments, the PVDF primer adopts a fluorocarbon primer product produced by Yongji Paint Industry (Kunshan) Co., Ltd., such as: Hong brand Yongflon primer;

[0066] Step S4: applying one or two layers of PVF coating on the primer layer;

[0067] When only one layer of PVF coating is applied on the primer layer, the PVF coating is a PVF colored topcoat, and a layer of PVF colored topcoat is rolled on the primer layer and then baked at a temperature of 235° C.-245° C. for 50 seconds to cure, thereby forming a colored topcoat layer;

[0068] When two layers of PVF coating are applied on the primer layer, the first layer of PVF coating is a PVF colored topcoat, and the second layer of PVF coating is a PVF colored topcoat or a varnish; after the first layer of PVF coating is roller-coated on the primer layer, it is baked at a temperature of 230°C-240°C for more than 50 seconds to complete curing to form a colored topcoat layer, and then a second layer of PVF coating is applied on the colored topcoat layer, and baked at a temperature of 235°C-245°C for more than 50 seconds to complete curing to form a second layer of colored topcoat layer or a varnish layer, wherein the curing temperature of the first layer of PVF coating should be 5°C-10°C lower than the curing temperature of the second layer of PVF coating so that it is not completely cured, thereby ensuring that when the second layer of PVF coating is cured, the first layer of colored topcoat layer will not be affected by reheating and produce defects.

[0069] PVF colored topcoat, PVF varnish, PVDF primer, polyester coating and epoxy modified coating were coated on the PVDF primer respectively, and each was cured (baked at 235℃-245℃ for more than 50s to complete the curing) to form the coating to be tested. The coating to be tested formed after the curing of the above coatings was tested by the national standard GB / T 9286-98. The adhesion test results are shown in the following figure 1:

[0070] Table 1: Adhesion test results of PVF colored topcoat, PVDF primer, polyester coating and epoxy modified coating on primer layer;

[0071]

[0072] As shown in Table 1 above, PVF colored topcoat and PVDF primer have good adhesion on the PVDF primer layer, while polyester coating and epoxy modified coating have poor adhesion and compatibility on the PVDF primer layer and cannot be used in combination with the PVDF primer layer.

[0073] like Figure 1 As shown, in one embodiment, a primer layer 2 is formed on the surface of the steel coil product 1, the thickness of the primer layer 2 is 7 μm, a 20 μm PVF colored topcoat layer 3 is formed on the primer layer 2, and the primer layer 2 and the PVF colored topcoat layer 3 together form the coating structure on the surface of the steel coil product 1 in this embodiment; Figure 2 As shown, in one embodiment, a primer layer 2 is formed on the surface of the coiled steel product 1, the thickness of the primer layer 2 is 7 μm, and two 15 μm colored topcoat layers 3 are formed on the primer layer 2. The primer layer 2 and the PVF colored topcoat layer 3 together form the coating structure on the surface of the coiled steel product 1 in this embodiment; at this time, since the PVF colored topcoat has a good color fixing effect and decorative layer isolation, it is not necessary to apply PVF varnish on the colored topcoat layer.

[0074] like Figure 3 As shown, in one embodiment, a primer layer 2 is formed on the surface of the coiled steel product 1, and the thickness of the primer layer 2 is 7 μm. A 15 μm colored topcoat layer 3 and a 15 μm clearcoat layer 4 are formed on the primer layer 2. The primer layer 2, the PVF colored topcoat layer 3 and the clearcoat layer 4 together form a coating structure on the surface of the coiled steel product 1 in this embodiment, and the coating structure can be applied to a use environment with high requirements for chemical resistance.

[0075] like Figure 4 As shown, in one embodiment, 2-4 primer layers are formed on the surface of the steel coil, and the thickness of each primer layer is 20 μm. The primer layer also includes a colored topcoat layer and a varnish layer. The thickness of the PVF colored topcoat layer and the varnish layer are both 15 μm. The primer layer 2, the PVF colored topcoat layer 3 and the varnish layer 4 together form a coating structure on the surface of the steel coil product 1 in this embodiment. The coating structure can be applied to use environments with high requirements for chemical resistance and impact resistance.

[0076] As can be seen from Table 1 above, since both the PVF colored topcoat and the PVDF primer have good adhesion on the PVDF primer layer, when the PVF colored topcoat is applied on the PVDF primer layer and multiple layers of PVDF primer are repeatedly applied, the bonding degree between the two adjacent coating layers is extremely high, which can ensure excellent protection performance for the coiled steel products.

[0077] In some embodiments, in step S2, the passivation treatment of the surface of the steel coil product includes: using a chromium-free passivation liquid roller to apply to the surface of the steel coil product, after passivation for 10s-20s, using a temperature of 80°C-90°C to dry the surface of the steel coil product. In one embodiment, the chromium-free passivation liquid is a chromium-free passivation liquid produced by Shanghai Chemetall Chemical Co., Ltd., such as: a chromium-free passivation liquid with a product brand of Gardobond D6800.

[0078] In some embodiments, step S1 comprises the following steps:

[0079] S11: using water or an alkaline cleaning solution with a pH value of 7-11 and a concentration of 3%-5% to pre-clean the surface of the steel coil for degreasing, and then rinsing the surface of the steel coil with clean water; in one embodiment, the pre-cleaning refers to fully immersing the steel coil in the alkaline cleaning solution or hot water at 70° C.-80° C. for 5 min-15 min;

[0080] S12: placing the steel coil in a pickling tank containing a pickling solution, pickling at a temperature of 60° C. to 80° C. for 1 min to 5 min, and taking out the steel coil after observing that the oxide layer on the surface of the steel coil is removed, wherein the pickling solution is one of hydrochloric acid, sulfuric acid or nitric acid with a concentration of 10%;

[0081] S13: Rinse the steel coil with clean water for two or more times; in one embodiment, a multi-stage water washing tank is provided, and the steel coil is sequentially placed in each water washing tank for soaking and rinsing for 10 minutes to 30 minutes, until there is no residue on the surface of the steel coil and the cleaning is completed;

[0082] S14: Use hot air at 80℃-120℃ to dry the surface of the steel coil for 1h-3h to ensure that the surface of the steel coil is completely dry.

[0083] The preparation steps of the PVF colored topcoat include:

[0084] Step 1) Prepare the following raw materials by mass:

[0085] Pre-mixed PVF 58-70 parts;

[0086] 6-10 parts of acrylic resin;

[0087] Propylene carbonate 2-7 parts;

[0088] 10-20 parts of titanium dioxide;

[0089] 0.5-2 parts of methylated amino resin;

[0090] Dispersant II 0.2-0.4 parts;

[0091] 0.1-0.6 parts of antioxidant additives;

[0092] 0.5 to 1 part of ultraviolet absorbing agent;

[0093] 3-8 parts of diluent;

[0094] Matting powder 0.1-1 part;

[0095] The particle size of the titanium dioxide is 8 μm, and the premixed PVF is formed by mixing PVF resin and propylene carbonate solvent in a mass ratio of 45:55;

[0096] Step 2) grinding the acrylic resin, propylene carbonate and titanium dioxide until the dispersion fineness reaches 10 μm to obtain a mixed solution;

[0097] Step 3) The premixed PVF is mixed with the mixed solution and the remaining raw materials at a speed of ≥1000 rpm for more than 2 hours to ensure that the coating has no defects such as shrinkage cavities, pinholes, and bubbles. The PVF colored topcoat is obtained after filtering and packaging.

[0098] The preparation steps of the PVF varnish include:

[0099] Step a) Prepare the following raw materials by mass:

[0100] Pre-mixed PVF 58-85 parts;

[0101] 6-10 parts of acrylic resin;

[0102] Dispersant I 0.1 part - 0.4 part;

[0103] Propylene carbonate 2-7 parts;

[0104] 0.5-2 parts of methylated amino resin;

[0105] Dispersant II 0.2-0.4 parts;

[0106] 0.1-0.6 parts of antioxidant additives;

[0107] Matting powder 0.1-1 part;

[0108] The premixed PVF is formed by mixing PVF resin and propylene carbonate solvent in a mass ratio of 45:55;

[0109] Step b) Mix the above raw materials together, mix at a speed of ≥1000 rpm for more than 2 hours, so that the coating has no defects such as shrinkage cavities, pinholes, and bubbles, and obtain the PVF varnish after filtering and packaging.

[0110] In some embodiments, the dispersant I is an alkylhydroxyl ammonium salt of a copolymer containing an acidic group, such as EFKA-4060 dispersant, which helps to improve the transparency of transparent pigments and the hiding power of opaque pigments; the dispersant II is a high molecular weight block copolymer solution containing pigment-affinity groups, such as BYK-163, HY-161 and BYK-164, etc. This type of additive deflocculates the pigment through steric stabilization. Since the deflocculated pigment has a small particle size, high gloss can be obtained and color intensity can be enhanced. In addition, due to the reduction in viscosity, the flowability is improved and the pigment content is increased, the transparency of transparent pigments and the hiding power of opaque pigments can also be improved. In addition, dispersant II has a particularly high molecular weight, thereby showing excellent stability to inorganic and organic pigments.

[0111] The premixed PVF used in the PVF colored topcoat and PVF varnish is prepared by stirring a PVF resin and a propylene carbonate solvent in a mass ratio of 45:55 at a speed of 1000 rpm to disperse the fineness to less than 10 μm to prepare the premixed PVF for standby use. During the mixing and use process, the overall temperature needs to be controlled not to exceed 45°C.

[0112] According to the ratio and preparation method of the above-mentioned PVF colored topcoat and PVF varnish, embodiments 1 and 2 of PVF varnish and embodiments 3-5 of PVF colored topcoat are provided. At the same time, a comparative example 1 of a transparent varnish not using premixed PVF and a comparative example 2 of a colored topcoat not using premixed PVF are provided. The raw material ratios of each embodiment and comparative example are shown in Table 2 below:

[0113] Table 2: Raw material ratios of Examples 1-5 and Comparative Examples 1 and 2;

[0114]

[0115] The varnish and colored topcoat prepared in the above examples and comparative examples were cured at 235°C-245°C for 50s, with a coating thickness of 7 μm to form coatings. The appearance of each coating was observed, and then each coating was immersed in 5% NaOH, 5% HCl, and 5% H 2 SO 4 The results are shown in Table 3 below:

[0116] Table 3: Appearance and chemical test results of Examples 1-5 and Comparative Examples 1 and 2;

[0117]

[0118] According to the above test results, the coating prepared by adding PVF resin and propylene carbonate solvent to the raw materials after premixing in a specific ratio can have better film-forming properties and chemical resistance.

[0119] The present invention further discloses a coating for coiled steel products, including a colored topcoat and a clearcoat, wherein the colored topcoat and the clearcoat are respectively prepared by the following preparation methods:

[0120] The preparation steps of the colored topcoat include:

[0121] Step I: Prepare the following raw materials by mass:

[0122] Pre-mixed PVF 58-70 parts;

[0123] 6-10 parts of acrylic resin;

[0124] Propylene carbonate 2-7 parts;

[0125] 10-20 parts of titanium dioxide;

[0126] 0.5-2 parts of methylated amino resin;

[0127] Dispersant II 0.2-0.4 parts;

[0128] 0.1-0.6 parts of antioxidant additives;

[0129] 0.5 to 1 part of ultraviolet absorbing agent;

[0130] 3-8 parts of diluent;

[0131] Matting powder 0.1-1 part;

[0132] The particle size of the titanium dioxide is 8 μm. In some embodiments, the diluent is propylene carbonate diluent;

[0133] Step II: Grind the acrylic resin, propylene carbonate and titanium dioxide until the dispersion fineness reaches 10 μm to obtain a mixed solution;

[0134] Step III: mixing the premixed PVF with the mixed solution and the remaining raw materials at a speed of ≥1000 rpm for more than 2 hours, filtering and packaging to obtain the PVF colored topcoat;

[0135] The preparation steps of the varnish include:

[0136] Step A: Prepare the following raw materials by mass:

[0137] Pre-mixed PVF 58-85 parts;

[0138] 6-10 parts of acrylic resin;

[0139] Dispersant I 0.1 part - 0.4 part;

[0140] Propylene carbonate 2-7 parts;

[0141] 0.5-2 parts of methylated amino resin;

[0142] Dispersant II 0.2-0.4 parts;

[0143] 0.1-0.6 parts of antioxidant additives;

[0144] Matting powder 0.1-1 part;

[0145] Step B: mixing the above raw materials together, mixing at a rotation speed of ≥1000 rpm for more than 2 hours, filtering and packaging to obtain the PVF varnish;

[0146] The premixed PVF used in the PVF colored topcoat and PVF varnish is prepared by stirring a PVF resin and a propylene carbonate solvent in a mass ratio of 45:55 at a speed of 1000 rpm to disperse the fineness to less than 10 μm to prepare the premixed PVF for standby use. During the mixing and use process, the overall temperature needs to be controlled not to exceed 45°C.

[0147] There are many implementation methods of the present invention, and all technical solutions formed by equivalent transformation or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for coating a steel coil having a highly chemical resistant coating structure, characterized in that: The steps include: Step S0: pre-preparing PVF colored topcoat and PVF clearcoat; The preparation steps of the PVF colored topcoat include: Step 1) Prepare the following raw materials by mass: Pre-mixed PVF 58-70 parts; 6-10 parts of acrylic resin; Propylene carbonate 2-7 parts; 10-20 parts of titanium dioxide; 0.5-2 parts of methylated amino resin; Dispersant II 0.2-0.4 parts; 0.1-0.6 parts of antioxidant additives; 0.5 to 1 part of ultraviolet absorbing agent; 3-8 parts of diluent; Matting powder 0.1-1 part; The particle size of the titanium dioxide is 8 μm, and the premixed PVF is formed by mixing PVF resin and propylene carbonate solvent in a mass ratio of 45:55; Step 2) grinding the acrylic resin, propylene carbonate and titanium dioxide until the dispersion fineness reaches 10 μm to obtain a mixed solution; Step 3) mixing the premixed PVF with the mixed solution and the remaining raw materials at a speed of ≥1000 rpm for more than 2 hours, filtering and packaging to obtain the PVF colored topcoat; The preparation steps of the PVF varnish include: Step a) Prepare the following raw materials by mass: Pre-mixed PVF 58-85 parts; 6-10 parts of acrylic resin; Dispersant I 0.1 part - 0.4 part; Propylene carbonate 2-7 parts; 0.5-2 parts of methylated amino resin; Dispersant II 0.2-0.4 parts; 0.1-0.6 parts of antioxidant additives; Matting powder 0.1-1 part; The premixed PVF is formed by mixing PVF resin and propylene carbonate solvent in a mass ratio of 45:55; Step b) mixing the above raw materials together, mixing at a rotation speed of ≥1000 rpm for more than 2 hours, filtering and packaging to obtain the PVF varnish; Step S1: performing surface decontamination treatment on the coiled steel product to be processed to remove oil stains on the surface of the coiled steel product, remove moisture on the surface of the coiled steel product, and then blow dry; Step S2: performing a passivation treatment on the surface of the coiled steel product and then drying it; Step S3: Roll-coating at least one layer of PVDF primer on the surface of the coiled steel product, and after each layer of PVDF primer is coated, baking is performed at a temperature of 235° C.-245° C. for more than 50 seconds to complete curing to form a primer layer, and the thickness of each primer layer is 7 μm-20 μm; Step S4: coating one or two layers of PVF coating on the primer layer; When only one layer of PVF coating is applied on the primer layer, the PVF coating is the PVF colored topcoat prepared in step S0, a layer of PVF colored topcoat is rolled on the primer layer and then baked at a temperature of 235° C.-245° C. for 50 seconds to cure, to form a colored topcoat layer; When two layers of PVF coating are applied on the primer layer, the first layer of PVF coating is the PVF colored topcoat prepared in step S0, and the second layer of PVF coating is the PVF colored topcoat or varnish prepared in step S0; after the first layer of PVF coating is roller-coated on the primer layer, it is baked at a temperature of 230° C.-240° C. for more than 50 seconds to complete curing, forming a colored topcoat layer, and then a second layer of PVF coating is applied on the colored topcoat layer, and is baked at a temperature of 235° C.-245° C. for more than 50 seconds to complete curing, forming a second layer of colored topcoat layer or varnish layer.

2. The method for coating a steel coil having a high chemical resistance coating structure according to claim 1, characterized in that: The dispersant I is an alkylhydroxyl ammonium salt of a copolymer containing an acidic group, and the dispersant II is a high molecular weight block copolymer solution containing a pigment affinity group.

3. The method for coating a steel coil having a high chemical resistance coating structure according to claim 1, characterized in that: The premixed PVF used in the PVF colored topcoat and PVF varnish is prepared by stirring a PVF resin and a propylene carbonate solvent in a mass ratio of 45:55 at a speed of 1000 rpm to disperse the fineness to less than 10 μm to prepare the premixed PVF for standby use. During the mixing and use process, the overall temperature needs to be controlled not to exceed 45°C.

4. The method for coating a steel coil having a high chemical resistance coating structure according to claim 3, characterized in that: A primer layer is formed on the surface of the steel coil, the thickness of the primer layer is 7 μm, a 20 μm colored topcoat layer is formed on the primer layer, or two 15 μm colored topcoat layers are formed, or a 15 μm colored topcoat layer and a 15 μm clear varnish layer are formed.

5. The method for coating a steel coil having a high chemical resistance coating structure according to claim 3, characterized in that: The surface of the steel coil is formed with 2-4 primer layers, each of which is 20 μm thick. The primer layer also includes a colored topcoat layer and a clearcoat layer, and the thickness of the PVF colored topcoat layer and the clearcoat layer are both 15 μm.

6. The method for coating a steel coil having a high chemical resistance coating structure according to claim 1, characterized in that: In step S2, the passivation treatment of the surface of the steel coil product includes: using a chromium-free passivation liquid to roll on the surface of the steel coil product, after passivation for 10s-20s, using a temperature of 80°C-90°C to dry the surface of the steel coil product.

7. The method for coating a steel coil having a high chemical resistance coating structure according to claim 1, characterized in that: The step S1 comprises the following steps: S11: Use water or alkaline cleaning solution with a pH value of 7-11 and a concentration of 3%-5% to pre-clean the surface of the coil and then rinse the surface of the coil with clean water; S12: placing the steel coil in a pickling tank containing a pickling solution, pickling at a temperature of 60° C. to 80° C. for 1 min to 5 min, and taking out the steel coil after observing that the oxide layer on the surface of the steel coil is removed, wherein the pickling solution is one of hydrochloric acid, sulfuric acid or nitric acid with a concentration of 10%; S13: Rinse the coil with clean water twice or more; S14: Use hot air at 80℃-120℃ to dry the surface of the steel coil for 1h-3h to ensure that the surface of the steel coil is completely dry.

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