Corrosion resistant metal can

Abstract

This disclosure relates to a corrosion-resistant metal can, including a can body and a bottom cover disposed at the bottom of the can body. The bottom cover is connected to the bottom of the can body by a double-sealed method. The can body, from top to bottom, consists of an unsealed area, a first sealed area, and a second sealed area. The first sealed area is the region from the groove formed by the bottom cover and the can body to the bend at the bottom of the can body. The second sealed area is the region from the bend at the bottom of the can body to the end of the can body. A powder coating is disposed at the bottom of the can body, and the powder coating is disposed in any of the following ways: the powder coating covers the first sealed area, the second sealed area, and part of the unsealed area; or the powder coating covers the first sealed area and part of the unsealed area, and the second sealed area has no powder coating. This disclosure improves the internal corrosion resistance of the metal can by disposing of a powder coating between the bottom of the can body and the bottom cover.

Description

Technical Field

[0001] This disclosure relates to a corrosion-resistant metal can, belonging to the field of metal can technology. Background Technology

[0002] Currently, the shelf life of three-piece welded metal cans used for acidic beverages on the market is insufficient due to environmental temperature and humidity factors, as well as impacts during transportation and handling, making it difficult to meet the 18-month shelf-life safety requirement. The bottom of the metal cans is prone to corrosion and leakage. After the product is filled with acidic contents, the longer it is stored, the more complex electrochemical and oxidation reactions occur between the tinplate metal material at the bottom of the can and the acidic contents, forming rust (Fe2O3). This affects the flavor of the beverage, giving it a rusty taste. Although the beverage may be within its shelf life, it is no longer safe to drink or sell, posing a food safety risk. Furthermore, with increasing storage time, the corrosion points will become larger, eventually leading to complete corrosion or even perforation of the iron wall at the bottom of the can, resulting in leakage.

[0003] Analysis revealed several possible causes of corrosion at the bottom of beverage metal cans. These include: the beverage's ingredients being acidic, with acidic components like citric acid reacting with the can's metal, leading to corrosion; the sugar content increasing electrolyte concentration, accelerating electrochemical corrosion; the can being made of tinplate, with defects in the substrate material and tin plating increasing the probability of reaction with acidic beverages; environmental factors such as temperature and humidity, with high temperature and humidity accelerating corrosion; and oxygen entering the can promoting oxidation reactions, resulting in corrosion.

[0004] In existing technologies, an inner coating is formed inside the metal can using a full-spray process, isolating the beverage from direct contact with the metal and providing protection. This process can improve the lifespan of the metal can and reduce the probability of corrosion. However, the following problems still exist: The existing full-spray process for the bottom grooves is prone to air bubbles during spraying or drying, which cannot be completely eliminated. These bubbles become the weakest points in the coating, making them susceptible to corrosion; the inner coating at the bottom of the can is deformed by mold pressure during the necking and flanging process, inevitably causing damage or impact, increasing the risk of corrosion; damage during transportation, collisions, or compression can damage the coating, leading to corrosion; aluminum cans are generally stored upright (bottom down) in warehouses and on shelves, and after long-term storage, acidic substances tend to settle at the bottom, with higher concentrations in the bottom grooves, increasing the probability of corrosion. Utility Model Content

[0005] To overcome the above problems, this disclosure provides a corrosion-resistant metal can.

[0006] The technical solution disclosed herein is as follows:

[0007] This disclosure provides a corrosion-resistant metal can, including a can body and a bottom cover disposed at the bottom of the can body, wherein the bottom cover is connected to the bottom of the can body by a double roll seal.

[0008] The can body consists of an unsealed area, a first sealed area, and a second sealed area from top to bottom. The first sealed area is the region from the groove formed by the bottom cover and the can body to the bend at the bottom of the can body. The second sealed area is the region from the bend at the bottom of the can body to the end of the can body.

[0009] The bottom of the can body is provided with a powder coating, which is provided in any of the following ways:

[0010] The powder coating covers the first roll sealing area, the second roll sealing area, and part of the unsealed area;

[0011] The powder coating covers the first roll-sealed area and a portion of the unsealed area, while the second roll-sealed area is free of the powder coating.

[0012] Furthermore, the powder coating is a continuous area.

[0013] Furthermore, the powder coating is a ring-shaped coating.

[0014] Furthermore, the material of the powder coating is a thermoplastic polymer powder.

[0015] Furthermore, the thickness of the powder coating is 40-120 μm.

[0016] This disclosure has the following beneficial effects:

[0017] This disclosure describes a powder coating applied to the bottom of a metal can, covering at least the area from the groove formed by the can's bottom cover and body to the bend at the bottom of the can. Existing technologies only use an internal spraying machine to cover the inner wall of the metal can; however, uneven spraying can lead to incomplete coverage of the groove area at the bottom. After filling, beverages may seep into the incompletely covered groove, posing a risk of corrosion to the inner wall. This new method precisely and evenly coats the bottom groove with powder, forming a complete insulating layer that completely prevents direct contact between the contents and the metal substrate, effectively avoiding corrosion problems.

[0018] Powder coating offers superior thickness and corrosion resistance, with a coating thickness exceeding 40µm, fully meeting the acid and corrosion resistance requirements of the necked area at the bottom of beverage cans. Currently available technologies for protecting the interior of metal cans (including the necked area) employ an inner epoxy / polyester resin coating followed by a full vinyl ester spray, resulting in a total coating thickness of only 10-20µm. This coating thickness and density are insufficient to meet the requirements for corrosion resistance and extended shelf life of highly acidic beverage cans.

[0019] The ring-shaped powder coating process is highly environmentally friendly, with a powder solid content generally exceeding 99% and containing no organic solvents (VOC emissions are close to zero), reducing harm to the environment and human health. Oversprayed powder is not recyclable (recovery rate can reach over 95%), minimizing waste.

[0020] Powder coating offers superior performance: uniform film thickness, high mechanical strength (wear-resistant, impact-resistant), good chemical corrosion resistance (such as acids and alkalis), and good weather resistance. It can effectively improve the coating protection effect after metal can transportation and handling collisions and adapt to changes in temperature and humidity in different sales and storage areas. Even when the metal can is deformed by external force collision, compression, or thermal expansion and contraction, the inner coating and inner full-coat of the groove are prone to tearing due to stress concentration. However, the powder coating can still adhere tightly to the groove surface and is not easily torn, maintaining the integrity and isolation effect of the coating. It effectively blocks the contact between the contents and the metal substrate, thereby avoiding the risk of corrosion. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of an embodiment of the present disclosure.

[0022] Figure 2 This is a schematic diagram of the powder coating according to an embodiment of the present disclosure.

[0023] Figure 3 This is a schematic diagram of a powder coating according to another embodiment of the present disclosure.

[0024] Figure 4 This is a schematic diagram of the roll-sealing structure according to an embodiment of the present disclosure.

[0025] Figure 5 This is a schematic diagram of the roll-sealing structure according to another embodiment of the present disclosure.

[0026] Figure 6 The manufacturing process of the metal can is an embodiment of this disclosure.

[0027] Figure 7 This is a schematic diagram of a three-piece welded metal can structure in the existing technology.

[0028] Figure 8 This is a schematic diagram of a three-piece welded metal can structure according to an embodiment of the present disclosure.

[0029] The reference numerals in the figure are as follows:

[0030] 100. Can body; 101. Unsealed area; 102. First roll section; 103. Second roll sealed area; 200. Bottom cover; 300. Powder coating; 400. Groove. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0032] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described object changes. To keep the following description of the embodiments of this disclosure clear and concise, detailed descriptions of some known functions and components are omitted.

[0033] The present disclosure will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 As shown, this disclosure provides a corrosion-resistant metal can, including a can body 100 and a bottom cover 200 disposed at the bottom of the can body 100, wherein the bottom cover 200 is connected to the bottom of the can body 100 by a double roll seal.

[0035] The can body 100 consists of an unsealed area 101, a first sealed area 102, and a second sealed area 103 from top to bottom. The first sealed area 102 is the area from the groove 400 formed by the bottom cover 200 and the can body 100 to the bottom bend of the can body 100. The second sealed area 103 is the area from the bottom bend of the can body 100 to the end of the can body 100.

[0036] The bottom of the can body 100 is provided with a powder coating 300, which is provided in any of the following ways:

[0037] like Figure 2 As shown, the powder coating 300 covers the first roll-sealed area 102, the second roll-sealed area 103, and a portion of the unsealed area 101;

[0038] like Figure 3 As shown, the powder coating 300 covers the first roll-sealed area 102 and part of the unrolled area 101, while the second roll-sealed area 103 is not covered by the powder coating 300.

[0039] like Figure 7 As shown, the existing three-piece welded metal can includes thin steel, coating 1 and coating 2, and an inner coating is also provided inside the three-piece welded metal can through an internal full spraying process.

[0040] like Figure 8 As shown, the three-piece welded metal can of this disclosure has a powder coating 300 between layer 2 and the inner full spray coating process.

[0041] like Figure 4-5 As shown, in both powder coating 300 configurations, the powder coating 300 covers the groove 400 and the areas above and below it. Therefore, even if there are bubbles in the inner coating at the groove 400 or damage for other reasons after the subsequent full inner spraying process, it can still prevent corrosion of the metal can.

[0042] Figure 3 Compared to the solution Figure 2 The solution has the following advantages:

[0043] Fewer materials are required;

[0044] When the can body 100 is transferred on the conveyor, it may be moved upright (bottom of the can facing down) to avoid the powder coating 300 coming into contact with the conveyor and damaging the powder coating 300, and also to avoid the problem of powder falling and contaminating the metal can and the production environment.

[0045] The second section 103 (also known as the can body hook) is rolled into the roll-sealing structure. The absence of powder coating 300 in the second section 103 can reduce the thickness of the entire roll-sealing structure to 40-120μm.

[0046] When the second volume section 103 has a sealing structure with powder coating 300, the sealing structure is thicker. When the second volume section 103 does not have a sealing structure with powder coating 300, the sealing structure is thinner.

[0047] In one embodiment of this disclosure, the powder coating 300 is a continuous region.

[0048] In one embodiment of this disclosure, the powder coating 300 is an annular coating.

[0049] In one embodiment of this disclosure, the powder coating 300 is made of thermoplastic polymer powder.

[0050] In one embodiment of this disclosure, the thickness of the powder coating 300 is specified.

[0051] The metal can disclosed herein can be manufactured by the following method:

[0052] A powder coating 300 is applied to the bottom of the can body 100;

[0053] The bottom cover 200 is connected to the bottom of the can body 100 by a double roll seal.

[0054] In this method, the metal can is sealed by double roll sealing. After double roll sealing, the powder coating 300 is rolled into the roll sealing structure at the hook part of the can body, so that the junction of the necking groove at the bottom of the can body and the double roll sealing (i.e., groove 400) can also be well protected by the powder coating.

[0055] Specifically, the can body 100 consists of an unsealed area 101, a first sealed area 102, and a second sealed area 103 from top to bottom. The first sealed area 102 is the area from the groove 400 formed by the bottom cover 200 and the can body 100 to the area where the bottom of the can body 100 bends. The second sealed area 103 is the area from the bottom bend of the can body 100 to the end of the can body 100.

[0056] When a powder coating 300 is provided at the bottom of the can body 100, the powder coating 300 is provided in any of the following ways:

[0057] The powder coating covers the first roll-sealed area 102, the second roll-sealed area 103, and a portion of the unsealed area 101;

[0058] The powder coating covers the first roll-sealed area 102 and part of the unsealed area 101, while the second roll-sealed area 103 is free of the powder coating 300.

[0059] Specifically, a powder coating 300 is applied to the bottom of the can body 100, including:

[0060] The bottom of the can body 100 is locally heated so that the temperature of the bottom of the can body is close to the melting point of the thermoplastic polymer powder;

[0061] After applying voltage to the thermoplastic polymer powder, it is sprayed onto the bottom of the can body 100 to form a powder coating 300;

[0062] The powder coating 300 is dried and cooled. The drying temperature can be 232-300℃.

[0063] Specifically, when the bottom of the tank body 100 is locally heated, an alternating magnetic field is generated by an electromagnetic coil, causing eddy currents to be generated at the bottom of the tank body 100.

[0064] Specifically, the bottom of the can body 100 is heated to 139-170°C.

[0065] Figure 6 In order to incorporate the above-mentioned method for manufacturing corrosion-resistant metal cans into existing metal can manufacturing processes.

[0066] Specifically, it also includes visual inspection. The visual inspection step uses a visual inspection system to remove defects in the appearance of the ring-shaped powder coating, such as missing spray, insufficient spray, loose powder, foreign matter, etc.

[0067] To verify whether the metal cans manufactured by this method meet the requirements of the national standard GBT 14251-2017 General Technical Requirements for Metal Containers of Canned Food, the applicant poured a mixed solution of 20% copper sulfate and 10% hydrochloric acid into the metal cans manufactured by the new process for a 4-minute stringent test (the national standard requires 2 minutes). The test results showed no corrosion spots and the pass rate was 100%.

[0068] To verify the impact of the new double-sealing process on the sealing performance of metal cans, the applicant conducted a tightened test using a metal can sealing leak detector. The test conditions were a negative pressure of 300 kPa (the national standard is 150 kPa) for 2 minutes. The test results showed no leakage, with a pass rate of 100%. The overlap rate test results were all qualified.

[0069] The test results are shown in Table 1. Among them, Scheme A is that the second roll sealing area 103 contains powder coating 300, and Scheme B is that the second roll sealing area 103 does not contain powder coating 300.

[0070] Table 1. Experimental results of powder coating repair integrity, sealing performance, and overlap rate.

[0071]

[0072] To verify whether canned acidic beverages produced using the method disclosed herein meet the requirements for can bottom corrosion resistance, the applicant compared the same acidic beverage in metal cans made using existing processes and those made using the method disclosed herein through an accelerated corrosion resistance test. The specific test conditions and methods are as follows: the temperature was maintained at 40±1℃ in an insulated chamber. Cans were then opened as required to inspect the corrosion inside, and the test results were recorded. After 60 days of accelerated insulation testing, both schemes of this disclosure showed no corrosion points in the bottom necking and bottom grooves during a two-month insulation test, achieving a 100% pass rate. In contrast, the pass rate for the existing process during the two-month accelerated insulation test was only 70-90%. The experimental results are shown in Table 2.

[0073] Table 2. Results of accelerated corrosion test at 40°C for metal cans containing acidic beverages with a pH of 3.5, manufactured using prior art and the method of this disclosure.

[0074]

[0075] To simulate the most stringent transportation and handling collision and drop conditions, the applicant conducted extreme drop tests to examine the impact and corrosion resistance of the metal-filled acidic beverages disclosed in this invention. The tests showed that the pass rate for the 40-day accelerated insulation test of both can bottom necking and bottom groove designs was 90-100%. Even under the condition of increased extreme drop impact deformation, the corrosion resistance pass rate of the new process was still much higher than the 70% pass rate of the existing process in the 40-day insulation test, demonstrating that the new process has excellent impact and corrosion resistance. The experimental results are shown in Table 3.

[0076] Table 3. Results of the extreme drop test and +40℃ heat preservation accelerated test of acidic beverages with pH 3.5 in metal cans manufactured according to this disclosure.

[0077]

[0078] The following points should be noted regarding this disclosure:

[0079] (1) The accompanying drawings of the embodiments of this disclosure only involve the structures involved in the embodiments of this disclosure. Other structures can be referred to the general design.

[0080] (2) Where there is no conflict, the embodiments of this disclosure and the features in the embodiments can be combined with each other to obtain new embodiments.

[0081] The above description is merely an embodiment of this disclosure and does not limit the patent scope of this disclosure. Any equivalent structure made using the content of this disclosure and its drawings, or directly or indirectly applied to other related technical fields, is similarly included within the patent protection scope of this disclosure.

Claims

1. A corrosion resistant metal can characterized by, It includes a can body (100) and a bottom cover (200) disposed at the bottom of the can body (100), wherein the bottom cover (200) is connected to the bottom of the can body (100) by a double roll seal; The can body (100) consists of an unsealed area (101), a first sealed area (102), and a second sealed area (103) from top to bottom. The first sealed area (102) is the area from the groove (400) formed by the bottom cover (200) and the can body (100) to the area where the bottom of the can body (100) bends. The second sealed area (103) is the area from the bottom bend of the can body (100) to the end of the can body (100). The bottom of the can body (100) is provided with a powder coating (300), which is provided in any of the following ways: The powder coating (300) covers the first roll-sealed area (102), the second roll-sealed area (103), and a portion of the unsealed area (101); The powder coating (300) covers the first roll-sealed area (102) and a portion of the unrolled area (101), while the second roll-sealed area (103) is free of the powder coating (300).

2. The corrosion resistant metal canister of claim 1, wherein, The powder coating (300) is a continuous area.

3. The corrosion-resistant metal can according to claim 1, characterized in that, The powder coating (300) is a ring-shaped coating.

4. The corrosion-resistant metal can according to claim 1, characterized in that, The powder coating (300) is made of thermoplastic polymer powder.

5. The corrosion-resistant metal can according to claim 1, characterized in that, The thickness of the powder coating (300) is 40-120 μm.

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