Preparation method of zip-top can cover

Abstract

The invention discloses a preparation method of a ring-pull can cover. The preparation method comprises the steps that an aluminum-containing metal base material is pretreated to obtain a can cover blank, the surface of the can cover blank is coated with water-based epoxy paint to obtain a pre-coated blank, the pre-coated blank is cured, the water-based epoxy paint is cured to form a water-based epoxy paint film, and the ring-pull can cover is obtained. The curing treatment comprises the steps that the pre-coated blank is sequentially subjected to volatilization treatment and cross-linking treatment, the volatilization temperature of the volatilization treatment is T1, the cross-linking temperature of the cross-linking treatment is T2, and T1 < lt >; t1 is larger than or equal to 120 DEG C and smaller than or equal to 180 DEG C, the highest plate temperature of the precoated blank is PMTm, and PMTm is larger than or equal to 220 DEG C and smaller than or equal to 240 DEG C. The paint film on the surface layer of the ring-pull can cover adopts the environment-friendly water-based epoxy coating, the process requirement that the gold surface of the aluminum-containing metal base material is evenly coated with the water-based epoxy coating is met, the painting quality of the can cover of the aluminum alloy ring-pull can is more stable, and the machining process is safer.

Description

Technical Field

[0001] The present application relates to the technical field of roller manufacturing, and in particular to a method for preparing a can lid. Background Art

[0002] In the 1960s, aluminum cans emerged in the United States. Due to their excellent performance such as easy to carry, safe to use, and high recyclable value, they quickly became popular all over the world, which gave rise to and expanded a new aluminum product - aluminum strip for cans (also known as "can material"). Aluminum cans are the main metal packaging products and are widely used as food packaging for beer, carbonated beverages, juices, etc. The production of aluminum cans in my country began in the 1980s. Due to the difficulty of production, can materials are considered to be the four major high-precision aluminum strip products today, along with aerospace plates, PS and CTP plates, and passenger car body plates.

[0003] The all-aluminum can is mainly composed of two parts, one is the can body (a barrel body that is integrated with the bottom surface, and patterns can be printed on its side), and the other is the can cover (a cover with an easy-open system and connected to the barrel body, and the surface is painted). The can cover needs to have good corrosion resistance and excellent formability. Among them, the materials used to make the can cover include blanks and anti-corrosion coating layers. For example, the blanks may include 5182 aluminum alloy, 3104 aluminum alloy, etc. The current production process of blanks for making can covers includes: smelting → refining → casting → sawing and milling → heating → hot rolling (rough rolling, finishing rolling) → cold rolling (middle trimming) → bending and straightening → coating. The production process is complicated, the construction period is long, the technical requirements are high, and the index control is difficult.

[0004] The anti-corrosion coating layer is coated on the inner and outer wall surfaces of the blank. At present, most domestic companies use solvent-based epoxy resin coatings as the material for the anti-corrosion coating layer. This type of material uses organic solvents. During the production and coating process of solvent-based epoxy resin coatings, volatile organic compounds (VOC, volatile organic compounds, including acetone, toluene, butanol, etc.) are easily generated, causing environmental pollution and bringing occupational health hazards to operators. With the continuous improvement of environmental protection laws and regulations and the increasingly stringent restrictions on atmospheric emissions, solvent-based epoxy resin coatings have been difficult to meet the use needs. Summary of the invention

[0005] This application complies with the new development concept and environmental protection requirements. The anti-corrosion coating layer of the can lid uses a water-based epoxy coating that is more environmentally friendly. In addition, this application also has the advantages of reducing production and storage costs, high production efficiency, and saving diluent usage.

[0006] The present application provides a method for preparing a can cover, which can improve the stability problem of the coating on the surface of the can cover.

[0007] The method for preparing an aluminum can lid provided by this application includes the following steps:

[0008] Provide an aluminum-containing metal substrate, and perform pretreatment on the aluminum-containing metal substrate to obtain a lid blank;

[0009] Provide a waterborne epoxy coating and apply it to the surface of the lid blank to obtain a pre-coated blank;

[0010] Perform a curing treatment on the pre-coated blank to cure the waterborne epoxy coating to form a waterborne epoxy paint film and obtain an aluminum can lid;

[0011] Wherein, the curing treatment includes: sequentially performing a volatilization treatment and a crosslinking treatment on the pre-coated blank, the volatilization temperature of the volatilization treatment is T1, and the crosslinking temperature of the crosslinking treatment is T2, wherein, T1 < T2, 120°C ≤ T1 ≤ 180°C, and when performing the crosslinking treatment, the highest plate temperature of the pre-coated blank is PMT m , PMT m Satisfies: 220°C ≤ PMT m ≤ 240°C.

[0012] In some exemplary embodiments, the volatilization treatment includes sequentially performing a first volatilization treatment, a second volatilization treatment, and a third volatilization treatment on the pre-coated blank; the volatilization temperature T1 includes T11, T12, and T13, T11 is the temperature of the first volatilization treatment, T12 is the temperature of the second volatilization treatment, and T13 is the temperature of the third volatilization treatment, wherein, T11 < T12 < T13.

[0013] In some exemplary embodiments, T11 satisfies: 115°C ≤ T11 ≤ 125°C.

[0014] In some exemplary embodiments, T12 satisfies: 140°C ≤ T12 ≤ 150°C.

[0015] In some exemplary embodiments, T13 satisfies: 170°C ≤ T13 ≤ 180°C.

[0016] In some exemplary embodiments, T2 satisfies: 215°C ≤ T2 ≤ 260°C,

[0017] In some exemplary embodiments, the crosslinking treatment includes sequentially performing a first crosslinking treatment, a second crosslinking treatment, and a third crosslinking treatment on the pre-coated blank after performing the crosslinking treatment; the volatilization temperature T2 includes T21, T22, and T23, T21 is the temperature of the first crosslinking treatment, T22 is the temperature of the second crosslinking treatment, and T23 is the temperature of the third crosslinking treatment, wherein, T21 < T22 ≤ T23.

[0018] In some exemplary embodiments, T21 satisfies: 215°C≤T21≤225°C.

[0019] In some exemplary embodiments, T22 satisfies: 250°C≤T22≤265°C.

[0020] In some exemplary embodiments, T23 satisfies: 250°C≤T23≤265°C.

[0021] In some exemplary embodiments, the waterborne epoxy coating includes a waterborne epoxy material and an aqueous solvent; the waterborne epoxy material includes at least one of Valspar 13Q80CA, Valspar 13Q80AG, Valspar 28Q, and Valspar 4000W; and the aqueous solvent is deionized water.

[0022] In some exemplary embodiments, the can cover blank includes an inner surface and an outer surface, and the water-based epoxy coating is applied to the inner surface and the outer surface of the can cover blank.

[0023] In some exemplary embodiments, using Ford No. 4 Cup as the mark, the viscosity of the water-based epoxy coating applied to the inner surface of the tank cover blank is P11, and the viscosity of the water-based epoxy coating applied to the outer surface of the tank cover blank is P12, 15S≤P11≤16S, 80S≤P12≤90S.

[0024] In some exemplary embodiments, using Ford No. 2 Cup as the mark, the viscosity of the water-based epoxy coating applied to the inner surface of the can cover blank is P21, and the viscosity of the water-based epoxy coating applied to the outer surface of the can cover blank is P22, 12S≤P21≤13S, 47S≤P22≤53S.

[0025] In some exemplary embodiments, applying the water-based epoxy coating to the surface of the can cover blank includes: using a first coating roller to reversely apply the water-based epoxy coating to the surface of the can cover blank, and the speed ratio of the first coating roller is r, and r satisfies: 105%≤r≤125 ％ The roughness of the surface of the first coating roller is S, and S satisfies: 2.0μm≤S≤3.0μm. The pressure exerted by the first coating roller on the surface of the can cover blank is P, and P satisfies: 3.0kN≤P≤7.0kN.

[0026] In some exemplary embodiments, the pretreatment includes sequentially performing shear straightening treatment, surface degreasing treatment and passivation treatment on the aluminum-containing metal substrate.

[0027] In some exemplary embodiments, the shear straightening process is used to make the straightness of the aluminum-containing metal substrate M, where M satisfies: 5I≤M≤10I;

[0028] In some exemplary embodiments, the surface degreasing treatment is used to remove oil and aluminum ash on the surface of the aluminum-containing metal substrate.

[0029] In some exemplary embodiments, the passivation treatment includes: forming a passivation film on the surface of the aluminum-containing metal substrate, wherein the chromium content of the passivation film is B, and B satisfies: 10 mg / m 2 ≤B≤30mg / m 2 .

[0030] In some exemplary embodiments, the mass percentage of each element of the aluminum-containing metal substrate is: Si 0.075% to 0.08%, Fe 0.2% to 0.25%, Cu 0.05% to 0.07%, Mn: 0.33% to 0.39%, Mg 4.6% to 5.0%, Cr 0.01% to 0.05%, Zn 0.013% to 0.015%, other single impurities ≤ 0.03%, total impurities ≤ 0.15%, and the balance is Al.

[0031] In some exemplary embodiments, the aluminum-containing metal substrate has a thickness H, and H satisfies: 0.208 μm≤H≤0.224 μm.

[0032] The present application provides a method for preparing a can lid, which has at least the following beneficial effects:

[0033] This application overturns the original production process and material application scheme of the can lid. The paint film on the surface of the can lid uses environmentally friendly water-based epoxy paint, which meets the process requirement of using water-based epoxy paint to evenly coat the gold surface of the aluminum-containing metal substrate, thereby obtaining a solid and continuous water-based epoxy paint film, making the paint quality of the aluminum alloy can lid more stable and the processing process safer.

[0034] In addition, during the production of can lids, the emission indicators are more environmentally friendly and meet the diversified use needs of different scenarios. At the same time, it can also reduce the production and storage costs of enterprises, improve production efficiency, and ensure the mechanical properties of aluminum-containing metal substrates and the lubricity of water-based epoxy paint films. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1Flow chart of the preparation method of an aluminum can lid according to an embodiment of the present application;

[0037] Figure 2 Film coating diagram formed on the inner surface of the can lid blank according to Embodiment 1 of the present application;

[0038] Figure 3 Film coating diagram formed on the inner surface of the can lid blank according to Comparative Example 1 of the present application;

[0039] Figure 4 Film coating diagram formed on the inner surface of the can lid blank according to Comparative Example 2 of the present application. Detailed implementation manners

[0040] In order to make the objectives, technical solutions and advantages of the present application clearer and more understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0041] As Figure 1 shown, it is a flow chart of the preparation method of an aluminum can lid according to an embodiment of the present application. The preparation method of the aluminum can lid provided by the present application includes the following steps:

[0042] Step S110: Provide an aluminum-containing metal substrate, and perform pretreatment on the aluminum-containing metal substrate to obtain a can lid blank.

[0043] Step S120: Provide a waterborne epoxy coating and coat it on the surface of the can lid blank to obtain a pre-coated blank.

[0044] Step S130: Perform a curing treatment on the pre-coated blank to cure the waterborne epoxy coating to form a waterborne epoxy film coating, and obtain an aluminum can lid.

[0045] In step S130, the curing treatment includes: successively performing a volatilization treatment and a crosslinking treatment on the pre-coated blank. The volatilization temperature of the volatilization treatment is T1, and the crosslinking temperature of the crosslinking treatment is T2, where T1 < T2, 120°C ≤ T1 ≤ 180°C, and when performing the crosslinking treatment, the maximum plate temperature of the pre-coated blank is PMT m , PMT m satisfies: 220°C ≤ PMT m ≤ 240°C.

[0046] In the preparation method of the aluminum can lid according to the embodiment of the present application, the volatilization treatment stage is the stage where a large amount of waterborne solvent in the waterborne epoxy coating volatilizes. After entering the crosslinking treatment process, the amount of waterborne solvent in the waterborne epoxy coating is small and continues to volatilize, enabling other components in the waterborne epoxy coating to crosslink and cure with the can lid blank to form a film coating connected to the can lid blank, and this film coating has corrosion resistance.

[0047] The waterborne epoxy coating of the embodiment of the present application has excellent wear resistance compared with the oil-based coating film. The coating film formed by the wax-free waterborne epoxy coating has good foam retention performance for liquids such as beer and soda water. The total volatile organic compounds (TVOC, Total Volatile Organic Compounds) released during the film-forming process are greatly reduced. In addition, the waterborne coating is more suitable for the production process of high-speed lines, and the film control is more stable, improving the production efficiency. It is superior to ordinary epoxy oil-based coatings in terms of production efficiency, environmental friendliness, and use performance. However, in the prior art, the waterborne coating is prone to skin formation during the film-forming process, which affects the surface quality of the coating film. In this application, the temperature in the volatilization stage and the crosslinking and curing stage is optimized and adjusted according to the characteristics of the waterborne coating. Since the solvent of the waterborne coating volatilizes more slowly than that of the oil-based coating, if the same curing method is adopted, in the intermediate stage, the waterborne epoxy coating of the embodiment of the present application will cause premature curing and crosslinking of the coating film at the same curing temperature, and the solvent of the waterborne epoxy coating cannot be fully volatilized. After crosslinking and curing into a film, the film layer will limit the volatilization of the solvent of the waterborne epoxy coating, resulting in defects such as bubbles and fisheyes. By controlling T1 < T2, 120°C ≤ T1 ≤ 180°C, the temperature in the volatilization treatment stage is reduced, and the crosslinking and curing process is postponed, so that the solvent in the waterborne epoxy coating is fully volatilized and then cured into a film, preventing the generation of defects such as bubbles and fisheyes.

[0048] Among them, the volatilization temperature T1 and the crosslinking temperature T2 are both the temperatures of the environment where the pre-coated blank is located. In the embodiment of the present application, the maximum plate temperature of the pre-coated blank is also controlled to be PMT m , PMT m satisfies: 220°C ≤ PMT m ≤ 240°C. The waterborne epoxy coating film formed under this temperature condition has good stability and uniformity. Preferably, PMT m is 232°C. Compared with the film layer formed by the oil-based coating at the maximum plate temperature PMT of 249°C, it has better flexibility. After laminating, the product can reach 0T without any film damage when compared with the oil-based coating film in mechanical bending. In addition, compared with the film layer formed by curing the oil-based coating, the temperature during the entire curing process of forming the film layer with the waterborne epoxy coating of the embodiment of the present application is lower, which can reduce energy consumption.

[0049] In some exemplary embodiments, in step S120, after the waterborne epoxy coating is applied to the surface of the can lid blank, it further includes leveling the waterborne epoxy coating and then performing a curing treatment. Among them, the waterborne epoxy coating after leveling treatment can be more evenly distributed on the surface of the can lid blank, making the formed waterborne epoxy coating film more uniform and delicate.

[0050] In some exemplary embodiments, during the curing process, the volatilization treatment includes performing multiple volatilization treatments with gradually increasing temperatures on the pre-coated blank in sequence, so that the waterborne epoxy coating cures to form a waterborne epoxy paint film. In this way, the uniformity and gloss quality of the formed waterborne epoxy paint film are better, and further prevent surface defects such as bubbles and fisheyes from forming on the waterborne epoxy paint film.

[0051] In some exemplary embodiments, the volatilization treatment includes performing a first volatilization treatment, a second volatilization treatment, and a third volatilization treatment on the pre-coated blank in sequence. The volatilization temperature T1 includes T11, T12, and T13. T11 is the temperature of the first volatilization treatment, T12 is the temperature of the second volatilization treatment, and T13 is the temperature of the third volatilization treatment. Among them, T11 < T12 < T13. By adopting the method of gradually adjusting the temperature, the solvent in the waterborne epoxy coating volatilizes more fully. While volatilizing and removing the solvent in the waterborne epoxy coating, the plate temperature of the pre-coated blank is gradually increased, preventing the phenomenon that the paint film cures and crosslinks prematurely due to too rapid temperature change, and avoiding defects such as bubbles appearing on the surface of the paint film due to incomplete solvent volatilization, which affects the use of the lid making.

[0052] In some exemplary embodiments, T11 satisfies: 115°C ≤ T11 ≤ 125°C. For example, T11 can be 115°C, 117°C, 119°C, 121°C, 123°C, 125°C, or any range between the two.

[0053] In some exemplary embodiments, T12 satisfies: 140°C ≤ T12 ≤ 150°C. For example, T12 can be 140°C, 142°C, 144°C, 146°C, 148°C, 150°C, or any range between the two.

[0054] In some exemplary embodiments, T13 satisfies: 170°C ≤ T13 ≤ 180°C. For example, T13 can be 170°C, 172°C, 174°C, 176°C, 178°C, 180°C, or any range between the two.

[0055] In some exemplary embodiments, the crosslinking temperature T2 of the crosslinking treatment satisfies: 215°C ≤ T2 ≤ 260°C. In this temperature range, it is convenient to control the maximum plate temperature PMT of the pre-coated blank m satisfies: 220°C ≤ PMT m ≤ 240°C.

[0056] In some exemplary embodiments, during the curing process, the crosslinking process includes performing a first crosslinking process, a second crosslinking process, and a third crosslinking process on the pre-coated blank after the crosslinking process in sequence. The volatilization temperature T2 includes T21, T22, and T23. T21 is the temperature of the first crosslinking process, T22 is the temperature of the second crosslinking process, and T23 is the temperature of the third crosslinking process. Among them, T21 < T22 ≤ T23. From the first crosslinking process to the second crosslinking process, the pre-coated blank is still heated up to raise the plate temperature of the pre-coated blank to PMT m From the second crosslinking process to the third crosslinking process, the temperature remains unchanged to stabilize the plate temperature of the pre-coated blank at PMT m to make the crosslinking and curing more complete. At the same time, it can ensure that the mechanical properties of the product after laminating meet the usage requirements.

[0057] In some exemplary embodiments, T21 satisfies: 215°C ≤ T21 ≤ 225°C. For example, T21 can be 215°C, 217°C, 219°C, 221°C, 223°C, 225°C, or any range between the two.

[0058] In some exemplary embodiments, T22 satisfies: 250°C ≤ T22 ≤ 265°C. For example, T22 can be 250°C, 254°C, 256°C, 260°C, 262°C, 265°C, or any range between the two.

[0059] In some exemplary embodiments, T23 satisfies: 250°C ≤ T23 ≤ 265°C. For example, T23 can be 250°C, 254°C, 257°C, 260°C, 263°C, 265°C, or any range between the two.

[0060] In some exemplary embodiments, the curing process includes multiple volatilization processes and multiple crosslinking processes. The multiple volatilization processes and multiple crosslinking processes can be carried out in multiple independent spaces. For example, the pre-coated blank is placed in a curing furnace, and the pre-coated blank is sequentially transferred to six zones of the curing furnace for curing treatment. Specifically, the pre-coated blank is placed in the first zone of the curing furnace for the first volatilization process, placed in the second zone of the curing furnace for the second volatilization process, placed in the third zone of the curing furnace for the third volatilization process, placed in the fourth zone of the curing furnace for the first crosslinking process, placed in the fifth zone of the curing furnace for the second crosslinking process, and placed in the sixth zone of the curing furnace for the third crosslinking process. The above is only an exemplary introduction, and any solution in the art that can cure the waterborne epoxy coating is applicable to this application.

[0061] In some exemplary embodiments, the time of each zone for the multiple volatilization processes and multiple crosslinking processes in the curing process is the same and is Q. Q satisfies: 12s ≤ Q ≤ 16s.

[0062] In some exemplary embodiments, the waterborne epoxy coating includes a waterborne epoxy material and an aqueous solvent; the waterborne epoxy material includes at least one of Valspar 13Q80CA, Valspar 13Q80AG, Valspar 28Q, and Valspar 4000W; and the aqueous solvent is deionized water.

[0063] The present application can directly use deionized water as an aqueous solvent to adjust the viscosity of the waterborne epoxy coating, and no diluent is required to adjust the viscosity of the waterborne epoxy coating, which not only reduces the health hazards to personnel, but also saves the diluent procurement costs and on-site storage costs. The solvent removed during the curing process is also deionized water, and the emission of volatile organic substances (VOC) is reduced, which is more environmentally friendly. Compared with oil-based coatings, the viscosity of waterborne epoxy coatings is more stable, and the paint film formed by curing is more uniform, reducing the time for adjusting the viscosity and improving production efficiency.

[0064] In some exemplary embodiments, the can lid is used to be mounted on the can body, the can lid and the can body together define a closed cavity, the can lid blank includes an inner surface facing the bottom of the can body and an outer surface facing away from the bottom of the can body, and the water-based epoxy coating is applied to at least one of the inner surface and the outer surface of the can lid blank.

[0065] In some exemplary embodiments, the viscosity of the water-based epoxy coating applied to the inner surface of the can cover blank is greater than the viscosity of the water-based epoxy coating applied to the outer surface of the can cover blank, so that a denser and thicker water-based epoxy paint film is formed on the inner surface of the can cover blank, so that the water-based epoxy paint film on the inner surface of the can cover blank has better anti-corrosion performance.

[0066] The present application example adopts the method of "GB / T 1723-1993 Coating Viscosity Determination Method" to detect the viscosity of water-based epoxy coatings.

[0067] In some exemplary embodiments, using Ford No. 4 Cup as the gauge, the viscosity of the water-based epoxy coating applied on the inner surface of the can cover blank is P11, and the viscosity of the water-based epoxy coating applied on the outer surface of the can cover blank is P12, 15S≤P11≤16S, 80S≤P12≤90S.

[0068] In some exemplary embodiments, using Ford No. 2 Cup as the gauge, the viscosity of the water-based epoxy coating applied on the inner surface of the can cover blank is P21, and the viscosity of the water-based epoxy coating applied on the outer surface of the can cover blank is P22, 12S≤P21≤13S, 47S≤P22≤53S.

[0069] In some exemplary embodiments, applying the waterborne epoxy coating to the surface of the can cover blank includes: using a first coating roller to reversely apply the waterborne epoxy coating to the surface of the can cover blank.

[0070] In some exemplary embodiments, the speed ratio of the first coating roller is r, and r satisfies: 105%≤r≤125%. For example, r can be 105 ％ , 109 ％ , 114 ％ , 118 ％ , 120 ％ , 125 ％ Or any range of the above two. Specifically, the conveying speed of the can cover blank on the production line is r0, the actual rotation speed of the first coating roller is r1, and the rotation speed ratio of the first coating roller is r=r1 / r0*100%. For example, the conveying speed r0 of the can cover blank on the production line is 100m / min, and r is selected as 105%, then the actual rotation speed r1 of the first coating roller is 105m / min. By selecting r in the range of 105% to 125%, the moving speed of the can cover blank and the rotation speed of the first coating roller can be controlled in a suitable range, so that the water-based epoxy coating can be evenly coated on the surface of the can cover blank.

[0071] In some exemplary embodiments, the roughness of the surface of the first coating roller is S, and S satisfies: 2.0 μm≤S≤3.0 μm. For example, S may be 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, or any range thereof.

[0072] In some exemplary embodiments, the first coating roller is made of polyurethane material, for example, a polyurethane coating roller with a diameter of φ400 mm provided by Nanjing Qihang Rubber Co., Ltd. is selected.

[0073] In some exemplary embodiments, the pressure applied by the first coating roller on the surface of the can cover blank is P, and P satisfies: 3.0kN≤P≤7.0kN. For example, P can be 3.0kN, 4.0kN, 5.0kN, 6.0kN, 7.0kN or any range of the above two.

[0074] In some exemplary embodiments, before applying the water-based epoxy coating to the surface of the can cover blank, the water-based epoxy coating is also stirred evenly, and deionized water is used as a diluent to adjust the viscosity of the water-based epoxy coating to be uniform. For example, an agitator is installed and the stirring speed is controlled to make the viscosity and liquid level of the water-based epoxy coating more uniform, thereby preventing defects such as longitudinal flowering caused by insufficient neutralization of the water-based epoxy material. In this way, the water-based epoxy coating can be more evenly attached to the surface of the first coating roller, and the viscosity of the water-based epoxy coating attached to the surface of the first coating roller is uniform.

[0075] In some exemplary embodiments, pre-treating the aluminum-containing metal substrate includes: sequentially performing shear straightening treatment, surface degreasing treatment and passivation treatment on the aluminum-containing metal substrate to improve the stability of the water-based epoxy paint film bonding to the can cover blank.

[0076] The mass percentage of each element of the aluminum-containing metal substrate is: Si 0.075% to 0.08%, Fe 0.2% to 0.25%, Cu 0.05% to 0.07%, Mn: 0.33% to 0.39%, Mg 4.6% to 5.0%, Cr 0.01% to 0.05%, Zn 0.013% to 0.015%, other single impurities ≤ 0.03%, total impurities ≤ 0.15%, and the balance is Al. For example, the aluminum-containing metal substrate can be 5182 aluminum alloy, 3104 aluminum alloy, etc.

[0077] In some exemplary embodiments, the thickness of the aluminum-containing metal substrate is H, and H satisfies: 0.208 μm≤H≤0.224 μm.

[0078] In some exemplary embodiments, the shear straightening process is used to make the aluminum-containing metal substrate have a straightness M, where M satisfies: 5I≤M≤10I. Specifically, the shear straightening process includes: cutting the aluminum-containing metal substrate to a preset width and then sizing it. To ensure the shearing quality, the horizontal gap of the shearing tool is controlled at 8%-10% of the thickness H of the aluminum-containing metal substrate, and the overlap is controlled at 30%-50%. After shearing, there are no burrs, the surface is flat and there is no scratch on the coating roller. Then, the plate is straightened by a stretch bending straightening machine, and the straightness M satisfies: 5I≤M≤10I, ensuring that the aluminum-containing metal substrate has a good edge after straightening, no ruffles, good lubrication, and no straightening roller marks, so as to prevent subsequent coating of water-based epoxy coatings from leaking and other surface defects.

[0079] In some exemplary embodiments, the surface degreasing treatment includes: multiple alkaline solution cleaning and multiple deionized water rinsing of the aluminum-containing metal substrate. Wherein, the free alkali concentration point of the alkaline solution is A, A satisfies: 12≤A≤15, the temperature of the surface degreasing treatment is Tx, Tx satisfies: 50℃≤Tx≤60℃, the alkaline solution and deionized water are respectively applied to the aluminum-containing metal substrate by spraying, and the spraying direction is an acute angle with the plate surface of the aluminum-containing metal substrate, and the spraying pressure is Pt, Pt satisfies: 1bar≤Pt≤2bar. The surface degreasing treatment is used to remove oil stains and aluminum ash on the surface of the aluminum-containing metal substrate, and through the dyne test, the dyne value of the surface of the aluminum-containing metal substrate after the surface degreasing treatment reaches more than 40, and the oil stains on the surface of the aluminum material are thoroughly cleaned, which is conducive to the subsequent formation of the surface passivation film, and improving the surface adhesion is conducive to coating.

[0080] In some exemplary embodiments, the passivation treatment includes: applying a passivation solution to the surface of the aluminum-containing metal substrate, drying and curing to form a passivation film, wherein the chromium content of the passivation film is B, and B satisfies: 10 mg / m 2 ≤B≤30mg / m 2It is beneficial to improve the adhesion between the water-based epoxy paint film and the passivation film and enhance the stability of the water-based epoxy paint film.

[0081] In some exemplary embodiments, the passivation solution includes a passivator and deionized water, with the passivation solution as the reference, the mass percentage of the passivator is C, C satisfies: 30%≤C≤50%, and the passivator includes at least one of a chromium phosphate passivator or a zirconium-based passivator. Among them, the chromium phosphate passivator includes at least one of chromium aluminum phosphate and calcium chromium aluminum phosphate, and the zirconium-based passivator includes at least one of fluorozirconic acid, zirconium tetrafluoride, and potassium zirconate.

[0082] In some exemplary embodiments, the passivation treatment is carried out by roller reverse coating, and the second coating roller of the passivation treatment is made of materials such as Haibolun, polyurethane, nitrile rubber, etc. The passivation liquid is applied to the surface of the aluminum-containing metal substrate after surface degreasing treatment by roller coating. The aluminum-containing metal substrate undergoes a passivation reaction after contacting the passivation liquid, and then immediately enters the curing furnace for baking. Hot air at 150°C to 200°C is passed through the furnace for 3s to 5s. Preferably, hot air at 180°C is passed through the furnace for 4.5s. After drying, a dense passivation film is formed on the surface of the aluminum-containing metal substrate to obtain a can cover blank.

[0083] The preparation method of the can lid in the present application is introduced below in conjunction with specific embodiments.

[0084] Example 1

[0085] (1) Pretreatment

[0086] 5182 aluminum alloy is selected as the aluminum-containing metal substrate and cut into coils with a diameter of 200cm×240cm. A sewing machine is used to overlap and sew the tail of the product on the line with the head of the new coil. The seams are then cleaned and high-temperature resistant tape is pasted on them for head-to-tail sewing to ensure production continuity.

[0087] The aluminum alloy substrate is placed in a washing tank and is rinsed with the first alkaline solution and the first deionized water in a self-circulating overflow pipe spray mode. After drying, it is straightened by a stretch straightening machine to achieve a straightness M of 7.5I. Then, the first looper treatment is carried out to achieve the effect of caching the pre-cleaned coil in the looper to ensure production continuity, and then two alkaline solution cleanings and four deionized water rinses are carried out in sequence.

[0088] The specific process is: alkaline washing 1→rinsing 1→drying→straightening→loop 1→alkaline washing 2→alkaline washing 3→rinsing 2→rinsing 3→rinsing 4→rinsing 5.

[0089] The spray pressure of the alkaline solution cleaning and deionized water rinsing is 1 bar to 2 bar, the temperature of the alkaline solution and the deionized water is 53°C to 57°C, and the oil and aluminum ash on the surface of the aluminum-containing metal substrate are removed. The dyne value of the surface of the aluminum-containing metal substrate after surface degreasing treatment is 41. The alkaline solution is a mixed alkaline solution with a free alkali concentration point of 12.5.

[0090] Passivation treatment: dissolve the passivator (model Henkel 6207RT) in deionized water and stir evenly, and obtain a passivation solution with a concentration of 50% by mass ratio of 1:1. Use a coating roller made of Haibolun to reversely apply the passivation solution to the surface of the aluminum-containing metal substrate after degreasing treatment, and then immediately enter the curing furnace for baking. The furnace is passed with hot air at a temperature of 180°C. After drying, a dense passivation film is formed on the surface of the aluminum-containing metal substrate after degreasing treatment, and the can cover blank is obtained. The chromium content in the passivation film is detected to be 18.0 mg / m 2 .

[0091] (2) Paint

[0092] The water-based epoxy materials Valspar 13Q80CA and Valspar 13Q80AG are dissolved in aqueous solvent deionized water to obtain a water-based epoxy coating, and the water-based epoxy coating is reversely coated on the inner surface and the outer surface of the can cover blank by using a first coating roller made of polyurethane.

[0093] Among them, deionized water was used to regulate the viscosity of the water-based epoxy coating, and Ford No. 4 cup was used to test the viscosity. The viscosity P11 of the water-based epoxy coating coated on the inner surface of the can cover blank was 15.6S, and the viscosity P12 of the water-based epoxy coating coated on the outer surface of the can cover blank was 12.5S.

[0094] The speed of the first coating roller is 110 ％ (ie 110 m / min), the roughness S of the surface of the first coating roller is 2.7 μm, and the pressure P of the first coating roller on the surface of the can cover blank is 6.0 kN.

[0095] (3) Curing treatment

[0096] The pre-coated blank is placed in a curing furnace, and volatilization treatment and cross-linking treatment are carried out in sequence. The volatilization treatment includes placing the pre-coated blank in the first zone of the curing furnace for the first volatilization treatment, placing it in the second zone of the curing furnace for the second volatilization treatment, and placing it in the third zone of the curing furnace for the third volatilization treatment. The cross-linking treatment includes placing the pre-coated blank in the fourth zone of the curing furnace for the first cross-linking treatment, placing it in the fifth zone of the curing furnace for the second cross-linking treatment, and placing it in the sixth zone of the curing furnace for the third cross-linking treatment. The treatment time of zones 1 to 6 in the curing furnace is 4S. Among them, the maximum plate temperature PMT of the pre-coated blank is controlled m It is 232℃.

[0097] After the curing treatment is completed, the pre-coated blank is subjected to looping, wax coating, electrostatic oiling and coiling processes to be processed into the desired shape of the can lid.

[0098] Specifically, the process flow of Example 1 is as follows:

[0099] Uncoiler → disc shear → stitching machine → alkali cleaning 1 → rinsing 1 → drying machine → straightening machine → looper 1 → alkali cleaning 2 → alkali cleaning 3 → rinsing 2 → rinsing 3 → rinsing 4 → rinsing 5 → chemical coating machine → drying box → cooling box → coating machine No. 1 → coating machine No. 2 → curing furnace 1-6 zone → looper 2 → wax coating machine → electrostatic oiling machine → coiler.

[0100] Example 2-Example 3: The difference from Example 1 is that the curing treatment temperature is different. The specific parameters are shown in Table 1.

[0101] Comparative Example 1-Comparative Example 2: The difference from Example 1 is that the curing treatment temperature is different. The specific parameters are shown in Table 1.

[0102] Comparative Example 3: The difference from Example 1 is that in Comparative Example 3, oil-based coating is applied to the surface of the can cover blank, the oil-based coating includes Valspar 92X205B material + diluent butanone solvent, and the viscosity of the oil-based coating is 17s for inner coating and 14.5s for outer coating.

[0103] The parameters in Example 1 and Comparative Examples 1 to 3 are shown in Table 1.

[0104] Table 1

[0105]

[0106] Figure 2 : is a picture of the paint film formed on the inner surface of the can cover blank in Example 1, Figure 3 The middle is a picture of the paint film formed on the inner surface of the can cover blank in Comparative Example 1, Figure 4 The figure in FIG. 2 is a paint film formed on the inner surface of the can cover blank in comparative example 2. Figures 2 to 4 It can be seen that the flexibility and gloss quality of the paint film on the surface of the can lid of Example 1 are significantly improved compared with the flexibility and gloss quality of the paint films prepared in Comparative Examples 1 and 2. This is because, in Comparative Examples 1 and 2, during the volatilization treatment stage, the water-based epoxy material undergoes cross-linking and curing prematurely, intercepting the volatilization of deionized water. The intercepted deionized water is completely volatilized during the cross-linking treatment stage at a higher temperature, resulting in surface defects such as bubbles and fish eyes on the surface of the paint film.

[0107] In Comparative Example 3, under the same processing conditions, the paint film surface has surface defects such as bubbles due to the low furnace temperature and fast process speed, and the solvent has solidified before it is fully volatilized. At the same time, the paint film has poor adhesion due to the short curing time and insufficient strength of the paint film.

[0108] The applicant declares that the present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing an easy-pull can lid, characterized in that: include: Providing an aluminum-containing metal substrate, and pretreating the aluminum-containing metal substrate to obtain a can cover blank; Providing a water-based epoxy coating and applying it on the surface of the can cover blank to obtain a pre-coated blank; The pre-coated blank is subjected to a curing treatment to cure the waterborne epoxy coating to form a waterborne epoxy paint film, thereby obtaining a can lid; Wherein, the curing treatment includes: performing a volatilization treatment and a crosslinking treatment on the pre-coated blank in sequence. The volatilization temperature of the volatilization treatment is T1, and the crosslinking temperature of the crosslinking treatment is T2, where T1 < T2, 120°C ≤ T1 ≤ 180°C, and when performing the crosslinking treatment, the maximum plate temperature of the pre-coated blank is PMT m , PMT m satisfies: 220°C ≤ PMT m ≤ 240°C.

2. The method for preparing an easy-open can lid according to claim 1, characterized in that: The volatilization treatment includes sequentially performing a first volatilization treatment, a second volatilization treatment and a third volatilization treatment on the pre-coated blank; The volatilization temperature T1 includes T11, T12 and T13, T11 is the temperature of the first volatilization treatment, T12 is the temperature of the second volatilization treatment, and T13 is the temperature of the third volatilization treatment, wherein T11 <T12<T13。 3. The method for preparing an easy-open can lid according to claim 2, characterized in that: T11 meets: 115℃≤T11≤125℃; T12 meets: 140℃≤T12≤150℃; T13 satisfies: 170℃≤T13≤180℃.

4. The method for preparing an easy-open can lid according to claim 1, characterized in that: The cross-linking treatment comprises sequentially performing a first cross-linking treatment, a second cross-linking treatment and a third cross-linking treatment on the pre-coated blank after the cross-linking treatment; T2 satisfies: 215°C≤T2≤260°C, the volatilization temperature T2 includes T21, T22 and T23, T21 is the temperature of the first cross-linking treatment, T22 is the temperature of the second cross-linking treatment, and T23 is the temperature of the third cross-linking treatment, wherein T21 <T22≤T23。 5. The method for preparing an easy-open can lid according to claim 4, characterized in that: T21 meets: 215℃≤T21≤225℃; T22 meets: 250℃≤T22≤265℃; T23 satisfies: 250℃≤T23≤265℃.

6. The method for preparing an easy-open can lid according to claim 1, characterized in that: The can lid blank comprises an inner surface and an outer surface; Using Ford No. 4 cup as the gauge, the viscosity of the waterborne epoxy coating applied to the inner surface of the can cover blank is P11, and the viscosity of the waterborne epoxy coating applied to the outer surface of the can cover blank is P12, 15S≤P11≤16S, 80S≤P12≤90S; Using Ford No. 2 Cup as the gauge, the viscosity of the waterborne epoxy coating applied to the inner surface of the can cover blank is P21, and the viscosity of the waterborne epoxy coating applied to the outer surface of the can cover blank is P22, 12S≤P21≤13S, 47S≤P22≤53S.

7. The method for preparing an easy-open can lid according to claim 1, characterized in that: Applying the water-based epoxy coating to the surface of the can cover blank comprises: using a first coating roller to reversely apply the water-based epoxy coating to the surface of the can cover blank; The speed ratio of the first coating roller is r, and r satisfies: 105 ％ ≤r≤125 ％ ; The roughness of the surface of the first coating roller is S, and S satisfies: 2.0 μm ≤ S ≤ 3.0 μm; The pressure exerted by the first coating roller on the surface of the can cover blank is P, and P satisfies: 3.0 kN≤P≤7.0 kN.

8. The method for preparing an easy-open can lid according to claim 1, characterized in that: The pretreatment comprises sequentially performing shear straightening treatment, surface degreasing treatment and passivation treatment on the aluminum-containing metal substrate; The shear straightening treatment is used to make the straightness of the aluminum-containing metal substrate M, where M satisfies: 5I≤M≤10I; The surface degreasing treatment is used to remove oil stains and aluminum ash from the surface of the aluminum-containing metal substrate; The passivation treatment comprises: forming a passivation film on the surface of the aluminum-containing metal substrate, wherein the chromium content of the passivation film is B, and B satisfies: 10 mg / m 2 ≤B≤30mg / m 2 .

9. The method for preparing an easy-open can lid according to claim 1, characterized in that: The mass percentage of each element of the aluminum-containing metal substrate is: Si 0.075% to 0.08%, Fe 0.2% to 0.25%, Cu 0.05% to 0.07%, Mn: 0.33% to 0.39%, Mg 4.6% to 5.0%, Cr 0.01% to 0.05%, Zn 0.013% to 0.015%, other single impurities ≤ 0.03%, total impurities ≤ 0.15%, and the balance is Al; The thickness of the aluminum-containing metal substrate is H, and H satisfies: 0.208 μm≤H≤0.224 μm.

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