Corrosion-resistant metal tank and manufacturing method thereof

Abstract

The invention relates to a corrosion-resistant metal can and a manufacturing method thereof.The metal can comprises a can body and a bottom cover arranged at the bottom of the can body, and the bottom cover is connected with the bottom of the can body in a double-rolling-sealing mode; the can body is sequentially provided with a non-seaming area, a first seaming area and a second seaming area from top to bottom, the first seaming area is an area from a groove formed by the bottom cover and the can body to the bottom of the can body in a bent mode, and the second seaming area is an area from the bent position of the bottom of the can body to the tail end of the can body; a powder coating is arranged at the bottom of the can body, and the powder coating is arranged according to any one of the following modes: the powder coating covers the first seaming area, the second seaming area and part of the non-seaming area; the powder coating covers the first seaming area and part of the non-seaming area, and the second seaming area is free of the powder coating. According to the metal tank, the powder coating is arranged between the bottom of the tank body and the bottom cover, so that the internal corrosivity of the metal tank is improved.

Description

Technical Field

[0001] The present disclosure relates to a corrosion-resistant metal can and a manufacturing method thereof, belonging to the technical field of metal cans. Background Art

[0002] At present, three-piece welded metal cans for acidic beverages on the market are affected by factors such as environmental temperature and humidity, transportation and handling collisions, etc. The shelf life is not long enough to meet the safety requirement of 18 months of shelf life. Corrosion and liquid leakage problems are likely to occur at the bottom of the metal can (as Figure 2 shown). After the product is filled with acidic contents, as the storage time increases, a series of complex electrochemical reactions and oxidation reactions are likely to occur between the tinplate metal material of the bottom of the metal can and the acidic contents, forming rust (Fe2O3), resulting in the flavor of the beverage being affected and having a rusty taste. Although the beverage is within the shelf life, it can no longer be normally consumed and sold, posing a food safety risk. In addition, as the storage time increases, the corrosion points will become larger and larger, and finally the iron wall at the bottom of the can body may be completely corroded or even perforated, resulting in liquid leakage.

[0003] Upon analysis, there are many possible reasons for the corrosion of the bottom of the beverage metal can. These include: the beverage components are acidic substances, and acidic components such as citric acid in the beverage will react with the metal of the can body, resulting in corrosion; the sugars in the beverage increase the concentration of electrolytes, accelerating electrochemical corrosion; the can body is made of tinplate metal material. If there are defects in the substrate material and the tin-plated protective layer of the iron material of the can body, the probability of reaction with acidic beverages will be higher; environmental factors such as temperature and humidity, and high-temperature and high-humidity environments will accelerate corrosion; the entry of oxygen into the can will promote oxidation reactions, resulting in corrosion.

[0004] In the prior art, an inner coating is formed on the inner wall of the metal can through an inner full-spray process to isolate the direct contact between the beverage and the metal, achieving a protective effect. The use of the inner full-spray process can increase the lifespan of the metal can and reduce the probability of corrosion. However, there are still the following problems: Bubbles are likely to exist during the spraying or drying process of the bottom groove of the existing inner full-spray process cans and cannot be completely eliminated (as Figure 3 shown). The existence of bubbles becomes the weakest part of the coating and is easily corroded; the inner coating at the bottom of the can is deformed by the extrusion of the mold during the necking and flanging process, and the inner coating is inevitably damaged or affected, increasing the corrosion risk; transportation damage, collision or extrusion may damage the coating, resulting in corrosion; generally, the way of storing and selling canned drinks in the warehouse and on the shelves is to place them upright (the bottom of the can is down). After a long time of storage, acidic substances are likely to precipitate towards the bottom of the can, and the concentration is higher at the bottom groove position of the can, and the probability of corrosion is higher. Summary of the Invention

[0005] In order to overcome the above problems, the present disclosure provides a corrosion-resistant metal can and a manufacturing method thereof.

[0006] The technical solution of the present disclosure is as follows:

[0007] The present disclosure provides a corrosion-resistant metal can, comprising a can body and a bottom cover disposed at the bottom of the can body, and the bottom cover is connected to the bottom of the can body by means of double seam sealing;

[0008] The can body is successively an unsealed area, a first sealed area and a second sealed area from top to bottom. The first sealed area is the area from the groove formed by the bottom cover and the can body to the bent part of the bottom of the can body, and the second sealed area is the area from the bent part of the bottom of the can body to the end of the can body;

[0009] A powder coating is provided on the bottom of the can body, and the powder coating is arranged in any of the following ways:

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

[0011] The powder coating covers the first sealed area and a part of the unsealed area, and there is no powder coating in the second sealed area.

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

[0013] Further, the powder coating is an annular coating.

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

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

[0016] The present disclosure also provides a manufacturing method of a corrosion-resistant metal can, comprising:

[0017] Setting a powder coating on the bottom of the can body;

[0018] Connecting the bottom cover to the bottom of the can body by means of double seam sealing.

[0019] Further, the can body is successively an unsealed area, a first sealed area and a second sealed area from top to bottom. The first sealed area is the area from the groove formed by the bottom cover and the can body to the bent part of the bottom of the can body, and the second sealed area is the area from the bent part of the bottom of the can body to the end of the can body;

[0020] When setting the powder coating on the bottom of the can body, the powder coating is arranged in any of the following ways:

[0021] The powder coating covers the first sealed area, the second sealed area and a part of the unsealed area;

[0022] The powder coating covers the first sealed area and a part of the unsealed area, and there is no powder coating in the second sealed area.

[0023] Furthermore, a powder coating is provided at the bottom of the can body, including:

[0024] Locally heat the bottom of the can body to make the temperature of the bottom of the can body close to the melting point of the thermoplastic polymer powder;

[0025] After applying a voltage to the thermoplastic polymer powder, spray it on the bottom of the can body to form a powder coating;

[0026] Dry and cool the powder coating.

[0027] Furthermore, when locally heating the bottom of the can body, an alternating magnetic field is generated by an electromagnetic coil to generate eddy currents at the bottom of the can body.

[0028] Furthermore, the bottom of the can body is heated to 139 - 160 °C.

[0029] The present disclosure has the following beneficial effects:

[0030] The present disclosure provides a powder coating at the bottom of a metal can, and the powder coating covers at least the area from the groove formed by the bottom cover and the can body to the bending of the bottom of the can body. In the prior art, only the inner wall of the metal can is coated with paint by an internal full-spraying machine. However, if the spraying is uneven, the groove area at the bottom of the can is likely to have an incomplete coverage problem. After filling, the beverage may seep into the incompletely covered groove, leading to the risk of inner wall corrosion. It can accurately and evenly cover the powder to the bottom groove of the can to form a complete isolation layer, completely blocking the direct contact between the content and the metal substrate, thereby effectively avoiding corrosion problems.

[0031] The powder coating is superior in terms of thickness and corrosion resistance. The coating thickness can reach more than 40 μm, which can fully meet the corrosion resistance requirements such as acid resistance at the necking position at the bottom of the beverage can. For the protection of the interior of the metal can (including the necking at the bottom) in the existing market processes, epoxy / polyester resin coatings are used for internal coating + vinyl internal full spraying, and the total coating thickness is generally only 10 - 20 μm. The coating thickness and compactness are difficult to meet the corrosion resistance and long shelf life requirements of high-acid beverage cans.

[0032] The annular powder process has high environmental protection. The solid content of the powder is generally above 99%, and it does not contain organic solvents (VOC emissions are close to zero), reducing the harm to the environment and the human body. The oversprayed powder can be recycled (the recovery rate can reach more than 95%), reducing waste.

[0033] The powder coating has excellent performance: the coating film has a uniform thickness, high mechanical strength (wear-resistant and impact-resistant), good chemical corrosion resistance (such as acids and alkalis) and weather resistance. It can effectively improve the coating protection effect after the metal can is transported, handled and collided, and adapt to the temperature and humidity changes in different sales and storage areas. Even when the metal can body is deformed due to external force collision, extrusion or thermal expansion and contraction, the inner coating film and the inner full-spray coating in the groove area are easily torn due to stress concentration, but 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, effectively blocking the contact between the content and the metal substrate, thus avoiding the corrosion risk. Description of the Drawings

[0034] Figure 1 It is a schematic structural diagram of an embodiment of the present disclosure.

[0035] Figure 2-4 It shows the corrosion condition at the bottom of the metal can body.

[0036] Figure 5 It is the bubbles in the inner full-spray process.

[0037] Figure 6 It is a schematic diagram of the powder coating of an embodiment of the present disclosure.

[0038] Figure 7 It is a schematic diagram of the powder coating of another embodiment of the present disclosure.

[0039] Figure 8 It is a schematic structural diagram of the double-seam structure of an embodiment of the present disclosure.

[0040] Figure 9 It is a schematic structural diagram of the double-seam structure of another embodiment of the present disclosure.

[0041] Figure 10-12 It is the double-seam structure of an embodiment of the present disclosure.

[0042] Figure 13-15 It is the double-seam structure of another embodiment of the present disclosure.

[0043] Figure 16 It is the manufacturing process flow of the metal can of an embodiment of the present disclosure.

[0044] Figure 17 It is a schematic structural diagram of a three-piece welded metal can in the prior art.

[0045] Figure 18 It is a schematic structural diagram of a three-piece welded metal can of an embodiment of the present disclosure.

[0046] The reference numerals in the drawings are shown as:

[0047] 100, can body; 101, un-double-seamed area; 102, first double-seam area; 103, second double-seam area; 200, bottom cover; 300, powder coating; 400, groove. Detailed implementation manners

[0048] In order to make the objectives, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Apparently, the described embodiments are only a part rather than all of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0049] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure shall have the ordinary meanings understood by those of ordinary skill in the art to which the present disclosure pertains. The "first", "second" and similar terms used in the present disclosure do not denote any order, quantity or importance, but are only used to distinguish different components. The terms such as "include" or "comprise" mean that the elements or objects appearing before the term cover the elements or objects listed after the term and their equivalents, without excluding other elements or objects. The terms such as "connect" or "couple" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The terms such as "upper", "lower", "left" and "right" are only used to indicate relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationships may also change accordingly. To keep the following description of the embodiments of the present disclosure clear and concise, detailed descriptions of some known functions and known components are omitted in the present disclosure.

[0050] The present disclosure will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0051] As Figure 1 shown, the present 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, and the bottom cover 200 is connected to the bottom of the can body 100 by means of double seam sealing;

[0052] The can body 100 successively includes an unsealed area 101, a first sealing area 102 and a second sealing area 103 from top to bottom. The first sealing area 102 is the area where the bottom cover 200 and the can body 100 form a groove 400 to the bent area at the bottom of the can body 100, and the second sealing area 103 is the area from the bent portion at the bottom of the can body 100 to the end of the can body 100;

[0053] A powder coating 300 is disposed at the bottom of the can body 100, and the powder coating 300 is disposed in any of the following manners:

[0054] As Figure 6As shown, the powder coating 300 covers the first double-seamed area 102, the second double-seamed area 103, and a part of the unseamed area 101;

[0055] As Figure 7 shown, the powder coating 300 covers the first double-seamed area 102 and a part of the unseamed area 101, and the second double-seamed area 103 has no powder coating 300.

[0056] As Figure 17 shown, a three-piece welded metal can of the prior art includes thin steel, coating 1 and coating 2, and an inner coating is also provided by an inner full-spraying process inside the three-piece welded metal can.

[0057] As Figure 18 shown, a powder coating 300 is provided between coating 2 and the inner full-spraying process in the three-piece welded metal can of the present disclosure.

[0058] As Figure 8-15 shown, in two setting methods of the powder coating 300, the powder coating 300 covers the groove 400 and the areas above and below it. Therefore, after the subsequent inner full-spraying process, even if there are bubbles in the inner coating at the groove 400 or it is damaged for other reasons, the metal can can still be prevented from corrosion.

[0059] Figure 7 The solution compared to Figure 6 the solution has the following advantages:

[0060] Less materials are required;

[0061] When the can body 100 is transferred on the conveying device, it may move in an upright position (the bottom of the can is downward), avoiding the powder coating 300 contacting the conveying device and damaging the powder coating 300, and also avoiding the problem of powder falling and polluting the metal can and the production environment;

[0062] The second double-seamed area 103 (also called the body hook of the can) is double-seamed into the double-seaming structure. Not setting the powder coating 300 in the second double-seamed area 103 can reduce the thickness of the entire double-seaming structure by 40 - 120 μm.

[0063] As Figure 10-15 shown, Figure 10-12 is a double-seaming structure with a powder coating 300 provided for the second double-seamed area 103, and the double-seaming structure is thicker. Figure 13-15 is a double-seaming structure without a powder coating 300 provided for the second double-seamed area 103, and the double-seaming structure is thinner.

[0064] In an embodiment of the present disclosure, the powder coating 300 is a continuous area.

[0065] In an embodiment of the present disclosure, the powder coating 300 is an annular coating.

[0066] In one embodiment of the present disclosure, the material of the powder coating 300 is a thermoplastic polymer powder.

[0067] In one embodiment of the present disclosure, the thickness of the powder coating 300.

[0068] The present disclosure also provides a method for manufacturing a corrosion-resistant metal can, including:

[0069] Providing a powder coating 300 at the bottom of the can body 100;

[0070] Connecting the bottom cover 200 to the bottom of the can body 100 by means of double seam sealing.

[0071] In this embodiment, the metal can is capped by means of double seam sealing. After double seam sealing, the part of the powder coating 300 at the body hook of the can body will be rolled into the double seam structure, so that the necking groove at the bottom of the can body and the joint of the double seam sealing (i.e., the groove 400) can also be well protected by the powder coating.

[0072] In one embodiment of the present disclosure, the can body 100 includes, from top to bottom, an unsealed area 101, a first double seam area 102, and a second double seam area 103. The first double seam area 102 is the area from the groove 400 formed by the bottom cover 200 and the can body 100 to the bend at the bottom of the can body 100, and the second double seam area 103 is the area from the bend at the bottom of the can body 100 to the end of the can body 100;

[0073] When providing the powder coating 300 at the bottom of the can body 100, the powder coating 300 is provided in any of the following manners:

[0074] The powder coating covers the first double seam area 102, the second double seam area 103, and a part of the unsealed area 101;

[0075] The powder coating covers the first double seam area 102 and a part of the unsealed area 101, and there is no powder coating 300 in the second double seam area 103.

[0076] In one embodiment of the present disclosure, providing the powder coating 300 at the bottom of the can body 100 includes:

[0077] Locally heating the bottom of the can body 100 to make the temperature of the bottom of the can body close to the melting point of the thermoplastic polymer powder;

[0078] After applying a voltage to the thermoplastic polymer powder, spraying it on the bottom of the can body 100 to form a powder coating 300;

[0079] Drying and cooling the powder coating 300. When drying and cooling, the drying temperature can be 232 - 300 °C.

[0080] In one embodiment of the present disclosure, when locally heating the bottom of the can body 100, an alternating magnetic field is generated by an electromagnetic coil, causing eddy currents to be generated at the bottom of the can body 100.

[0081] In one embodiment of the present disclosure, the bottom of the can body 100 is heated to 139 - 170 °C.

[0082] Figure 16 To incorporate the manufacturing method of the above corrosion-resistant metal can into the existing metal can manufacturing process.

[0083] In one embodiment of the present disclosure, visual inspection is further included. In the visual inspection step, defects are removed from the appearance of the annular powder coating through a visual inspection system, and abnormal cans such as missed spraying, under-spraying, powder scattering, and foreign objects are removed.

[0084] 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 for Canned Foods, the applicant poured a mixed solution of 20% copper sulfate and 10% hydrochloric acid into the new process metal cans for a 4-minute enhanced test (the national standard requires 2 minutes). The test results showed no corrosion points, and the pass rate was 100%.

[0085] To verify the influence of the new process on the sealing performance of the metal cans after double seam welding, the applicant conducted an enhanced test with a metal can sealing leak detector. The test conditions were a negative pressure of 300 kPa (the national standard is 150 kPa) and a pressure holding time of 2 min. The test results showed no leakage, and the pass rate was 100%. The lap joint rate test results were all qualified.

[0086] The test results are shown in Table 1. Among them, Scheme A is that the second double seam welding area 103 contains a powder coating 300, and Scheme B is that the second double seam welding area 103 does not contain a powder coating 300.

[0087] Table 1 Experimental results of powder coating repair integrity, sealing performance, and lap joint rate

[0088]

[0089] To verify whether the canned acidic beverages produced by applying the method of the present disclosure meet the requirements for the corrosion resistance of the can bottom, the applicant conducted a comparative accelerated corrosion resistance insulation experiment on metal cans of the existing process products and metal cans of the products of the present disclosure canned with the same acidic beverage. The specific test conditions and methods are as follows: Keep the temperature at 40 ± 1 °C in the insulation chamber. Open the cans as required respectively to check the corrosion situation inside the cans and record the test results. Through a 60-day accelerated insulation test, there were no corrosion points in the necking and bottom grooves of the can bottoms of the two schemes of the present disclosure after two months of insulation test, and the pass rate was 100%. While the pass rate of the existing process in the two-month accelerated insulation test was only 70 - 90%. The experimental results are shown in Table 2.

[0090] Table 2 Experimental results of accelerated corrosion test at 40°C for metal cans filled with acidic content beverages with a pH value of 3.5 manufactured by the prior art and the method of the present disclosure

[0091]

[0092] To simulate the most severe conditions of transportation, handling, collision, and dropping, the applicant conducted an extreme drop test to detect the impact resistance and corrosion resistance of the metal cans filled with acidic beverages in the present disclosure. After testing, the passing rates of the necking and bottom groove of the two proposed cans in the present disclosure in the 40-day accelerated heat preservation test were both 90-100%. Even under the condition of adding extreme dropping to deform the cans by collision, the passing rate of the new process in terms of corrosion resistance was still much higher than the 70% passing rate of the existing process in the 40-day heat preservation test, which can reflect that the new process has very excellent impact resistance and corrosion resistance. The experimental results are shown in Table 3.

[0093] Table 3 Experimental results of extreme drop test + 40°C accelerated test for metal cans filled with acidic content beverages with a pH value of 3.5 manufactured by the present disclosure

[0094]

[0095] For the present disclosure, the following points need to be noted:

[0096] (1) The attached drawings of the embodiments of the present disclosure only relate to the structures involved in the embodiments of the present disclosure, and other structures can refer to the general design.

[0097] (2) Without conflict, the embodiments of the present disclosure and the features in the embodiments can be combined with each other to obtain new embodiments.

[0098] The above are only the embodiments of the present disclosure, and do not limit the patent scope of the present disclosure. Any equivalent structures made by using the specification and attached drawings of the present disclosure, directly or indirectly applied in other related technical fields, are equally included in the patent protection scope of the present disclosure.

Claims

1. A corrosion-resistant metal tank, characterized in that, It includes a can body (100) and a bottom cover (200) provided at the bottom of the can body (100), and the bottom cover (200) is connected to the bottom of the can body (100) by means of double seam sealing; The can body (100) is successively an unsealed area (101), a first sealing area (102) and a second sealing area (103) from top to bottom. The first sealing area (102) is the area where the groove (400) formed by the bottom cover (200) and the can body (100) bends to the bottom of the can body (100), and the second sealing area (103) is the area from the bending part of the bottom of the can body (100) to the end of the can body (100); A powder coating (300) is provided at the bottom of the can body (100), and the powder coating (300) is provided in any of the following ways: The powder coating (300) covers the first sealing area (102), the second sealing area (103) and a part of the unsealed area (101); The powder coating (300) covers the first sealing area (102) and a part of the unsealed area (101), and there is no powder coating (300) in the second sealing area (103).

2. The corrosion-resistant metal tank according to claim 1, wherein The powder coating (300) is a continuous area.

3. The corrosion-resistant metal tank according to claim 1, wherein The powder coating (300) is an annular coating.

4. The corrosion-resistant metal tank according to claim 1, wherein The material of the powder coating (300) is thermoplastic polymer powder.

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

6. A manufacturing method of a corrosion-resistant metal can, characterized in that It includes: Setting a powder coating (300) at the bottom of the can body (100); Connecting the bottom cover (200) to the bottom of the can body (100) by means of double seam sealing.

7. The manufacturing method of the corrosion-resistant metal tank according to claim 6, characterized in that, The can body (100) is successively an unsealed area (101), a first sealing area (102) and a second sealing area (103) from top to bottom. The first sealing area (102) is the area where the groove (400) formed by the bottom cover (200) and the can body (100) bends to the bottom of the can body (100), and the second sealing area (103) is the area from the bending part of the bottom of the can body (100) to the end of the can body (100); When setting a powder coating (300) at the bottom of the can body (100), the powder coating (300) is provided in any of the following ways: The powder coating covers the first sealing area (102), the second sealing area (103) and a part of the unsealed area (101); The powder coating covers the first sealing area (102) and a part of the unsealed area (101), and there is no powder coating (300) in the second sealing area (103).

8. The manufacturing method of the corrosion-resistant metal tank according to claim 6, characterized in that, Setting a powder coating (300) at the bottom of the can body (100) includes: Locally heating the bottom of the can body (100) to make the temperature of the bottom of the can body close to the melting point of the thermoplastic polymer powder; After applying a voltage to the thermoplastic polymer powder, spraying it on the bottom of the can body (100) to form a powder coating (300); Drying and cooling the powder coating (300).

9. The manufacturing method of the corrosion-resistant metal tank according to claim 7, characterized in that, When locally heating the bottom of the can body (100), an alternating magnetic field is generated by an electromagnetic coil to generate eddy currents at the bottom of the can body (100).

10. The manufacturing method of the corrosion-resistant metal tank according to claim 7, characterized in that, The bottom of the can body (100) is heated to 139 - 160 °C.

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