A metal beverage bottom end and a corrosion resistant curl seam formed with a can body

Abstract

The application provides a metal beverage bottom cover and a corrosion-resistant curling seal structure formed by the metal beverage bottom cover and a can body, and belongs to the technical field of metal packaging cans. The circular bottom cover has, from outside to inside, a cover hook part, an outer wrapping curved part, an inner wrapping curved part, a gradual opening part, a cover bottom reinforcing convex part and a cover core part. The cover hook part is in a U shape with an inside opening. The outer wrapping curved part has an inner end with an inclination angle of 12-20 degrees with respect to the axis of the bottom cover. The gradual opening part is flat. The flat surface of the gradual opening part has an inclination angle of 45-55 degrees with respect to the axis of the bottom cover. The corrosion-resistant curling seal structure formed by the metal beverage bottom cover and the can body is a five-layer superimposed structure formed by a can hook inner sealing layer, a can hook outer sealing layer, a cover hook inner sealing layer, a cover hook outer sealing layer and a bottom cover inner sealing layer. The curling part between the cover hook inner sealing layer and the cover hook outer sealing layer is formed by bending and pressing the cover hook part. The gradual opening part and the inner wall of the can body form a 45-55 degree gradual opening inclination angle. The application has the advantages of material saving and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal packaging cans, and relates to a metal beverage bottom cover and a corrosion-resistant curling structure formed by the bottom cover and a can body. BACKGROUND

[0002] The metal can packaging of food and beverages was invented by the British Peter Durand in 1810, and has undergone more than two hundred years of development. Today, it is mainly divided into two-piece cans and three-piece cans according to its structure, and can be used to package various types of food, beverages, and water containing acid, alkali, sulfur and other substances.

[0003] Among them, the three-piece can is composed of a top cover (an aluminum or tinplate cover that can be conveniently opened), a can body (a tinplate middle connecting body), and a bottom cover (an aluminum or tinplate cover). In order to prevent the corrosion of acidic substances to the metal material inside the can body, the three-piece can containing acidic beverages also needs to be fully sprayed with an epoxy phenolic resin inside the semi-finished product after the can cover is combined during the manufacturing process, so as to block the contact between the metal and the acidic beverage, slow down the oxidation and corrosion process, and ensure the shelf life of the product and food safety.

[0004] Through long-term research on the shelf life of metal cans containing acidic beverages (pH < 4.0) and analysis of national and international standards for three-piece cans, it is found that there is still an electrochemical corrosion phenomenon in the existing process technology and manufacturing standards. In order to further improve the shelf life, increase the shelf life of the product content, and improve the flavor of the food, the present application discloses a new type of bottom cover which can effectively slow down the corrosion of acidic beverages to the can body.

[0005] Analysis of the reasons why the existing three-piece can bottom cover curling structure is easily corroded by acidic beverages:

[0006] Based on the analysis of the corrosion position and the double curling forming process, the curling position is tightly combined between the can covers after processing, while the necking position is affected by the tension during the curling process, and the tightness of the combination between the can covers is significantly lower than that of the curling position, thereby forming a small groove-shaped groove at the gradually opening position of the bottom cover and the can body curling, which allows the beverage to penetrate, that is, the corrosion occurs. The corrosion occurs in the following scenarios:

[0007] The inner coating of the can body and the bottom cover curling necking position is tightly combined with the bottom cover shoulder position after the can body is curled, forming a local closed structure. If the bottom groove is not completely covered by the coating, the beverage will penetrate into the groove after filling, causing internal wall corrosion;

[0008] The inner coating of the can body and the bottom cover curling necking position is tightly combined with the bottom cover shoulder position after the can body is curled, forming a local closed structure. If the bottom groove is not completely covered by the coating, the beverage will penetrate into the groove after filling, causing internal wall corrosion;

[0009] The bottom cover sealing position is different from the top cover sealing position, in the process of finished beverage packaging, storage and transportation, the top cover sealing position is not in contact or not often in contact with the beverage, while the bottom cover sealing position is in long-term contact with the beverage, at the same time, under the action of liquid pressure in the tank and pressure fluctuation, the beverage frequently "flushes" at the groove of the bottom cover sealing position, which accelerates the peeling of the damaged protective coating and the corrosion at the peeling position.

[0010] The occurrence time of corrosion and the degree of corrosion directly affect the shelf life, taste stability and quality during the shelf life of the beverage. Delaying corrosion or reducing corrosion is of great help to the extension of shelf life, the maintenance of taste and the stability of quality. SUMMARY

[0011] The purpose of the present application is to solve the above-mentioned problems existing in the prior art, and to provide a metal beverage bottom cover and a corrosion-resistant sealing structure formed by the bottom cover and the can body. The technical problem to be solved by the present application is to reduce the risk of coating film being squeezed and torn at the neck part of the tank bottom during processing.

[0012] The purpose of the present application can be achieved by the following technical scheme: a metal beverage bottom cover and a corrosion-resistant sealing structure formed by the bottom cover and the can body, characterized in that the circular bottom cover has, from outside to inside, a cover hook part, an outer wrapping part, an inner wrapping part, a gradual opening part, a cover bottom reinforcing convex part and a cover core part, the cover hook part is in the form of a U-shaped opening on the inside, the inner end of the outer wrapping part and the bottom cover axis form an inclination angle of 12-20°, the gradual opening part is flat, and the flat surface of the gradual opening part and the bottom cover axis form an inclination angle of 45-55°.

[0013] The corrosion-resistant sealing structure formed by the metal beverage bottom cover and the can body is a five-layer overlapping structure formed by the inner sealing layer of the can hook, the outer sealing layer of the can hook, the inner sealing layer of the cover hook, the outer sealing layer of the cover hook, and the inner sealing layer of the bottom cover. The overlapping order of the five-layer overlapping structure on the finished metal beverage can from outside to inside is: the outer sealing layer of the cover hook, the inner sealing layer of the can hook, the inner sealing layer of the cover hook, the outer sealing layer of the can hook, and the inner sealing layer of the bottom cover. The curved part between the inner sealing layer of the cover hook and the outer sealing layer of the cover hook is formed by bending and pressing the cover hook part, the curved part between the outer sealing layer of the cover hook and the outer sealing layer of the can hook is formed by bending and pressing the outer wrapping part, the inner sealing layer of the bottom cover is formed by bending and pressing the inner wrapping part, and the gradual opening part and the inner wall of the can body form a gradual opening inclination angle of 45-55°.

[0014] Further, the height of the cover hook part is 1.85-2.00 mm.

[0015] Preferably, the height of the cover hook part is 1.91 mm.

[0016] Further, the intersection of the inner curved portion and the involute portion has a kink portion with a radius of 0.3-0.8 mm, and the kink portion has an arc of 0.11π-0.22π.

[0017] Preferably, the radius of the kink portion is 0.5 mm, and the arc of the kink portion is 0.16π.

[0018] Further, the height between the kink portion and the top surface of the outer curved portion is 2.8-2.95 mm.

[0019] Preferably, the height between the kink portion and the top surface of the outer curved portion is 2.9 mm.

[0020] Preferably, the outer curved portion has an inclination of 17° between the inner end and the axis of the bottom cover.

[0021] Preferably, the flat surface of the involute portion has an inclination of 45° with respect to the axis of the bottom cover.

[0022] Preferably, the involute portion forms an involute inclination of 30° with respect to the inner wall of the can body.

[0023] It should be noted that the bottom cover and the top cover are obviously different in a three-piece can. In order to reserve a large opening flat area without affecting the compressive strength, the top cover needs to be involuted immediately after the curling to form a large difference between the top cover opening flat surface and the curling position, thereby forming a large lower convex reinforcing rib close to the inner wall of the can body. The bottom cover is not the same. The bottom cover does not have other accessories, and only needs to provide corresponding mechanical strength. Therefore, under the condition of considering the can height to volume ratio, a large lifting height of the bottom cover is not allowed. In this scheme, two stretching angles are designed, i.e., an inclination of 17° between the inner end of the outer curved portion and the axis of the bottom cover, and an inclination of 40° between the flat surface of the involute portion and the axis of the bottom cover. A flat involute portion is also designed to quickly form a large involute at the end position of the curling and overlapping surface of the can body and the bottom cover, thereby reducing the contact area between the shoulder portion of the bottom cover and the inner wall of the can, and avoiding the generation of a "non-tight overlapping area". The "non-tight overlapping area" refers to a position that is similar to a compression but not a compression due to a small involute angle. This greatly reduces the risk of the inner coating film being squeezed and torn at the neck portion of the can bottom during the processing, thereby maintaining the integrity and coverage effect of the inner coating film, especially the wear of the inner coating film due to the difference in thermal expansion coefficient of the material during hot processing.

[0024] At the same time, the amount of material can be reduced because the rapid opening of the bottom cover and the can body at the end position of the curling reduces the overall amount of the bottom cover compared to the traditional slow opening. In addition, the height between the kink portion and the top surface of the outer curved portion and the height of the cover hook portion are reduced in this scheme, which further reduces the lifting amount of the bottom cover, improves the can height to volume ratio of the packaging can, and makes it easier for full paint spraying to enter due to the large opening angle, thereby achieving better coverage effect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the comparison chart of the existing bottom cover structure and the bottom cover structure of the present application.

[0026] Figure 2 is the size parameter chart of the bottom cover structure of the present application.

[0027] Figure 3 is the schematic diagram of the bottom cover structure of the present application.

[0028] Figure 4 is the schematic diagram of the cross section of the sealing structure of the present application.

[0029] Figure 5 is the anti-electrochemical corrosion test data table.

[0030] Figure 6 is the anti-electrochemical corrosion test flow chart.

[0031] Figure 7 is the schematic diagram of the cross section of the existing bottom cover structure in the embodiment.

[0032] Figure 8 is the data table of each cross section in Figure 7

[0033] Figure 9 is the schematic diagram of the cross section of the bottom cover structure of the present application in the embodiment.

[0034] Figure 10 is the data table of each cross section in Figure 9

[0035] In the figure, 1, cover hook part; 2, outer wrapping curved part; 3, inner wrapping curved part; 4, involute part; 5, cover bottom reinforcing convex part; 6, cover core piece part; 7, folding point part; 1a, inner sealing layer of can hook; 2a, outer sealing layer of can hook; 3a, inner sealing layer of cover hook; 4a, outer sealing layer of cover hook; 5a, inner sealing layer of bottom cover. DETAILED DESCRIPTION

[0036] The following is a specific embodiment of the present application and further describes the technical solution of the present application in combination with the drawings, but the present application is not limited to these embodiments.

[0037] As shown in Figure 1 , A is the existing conventional bottom cover structure, and B is the bottom cover structure mentioned in the present application, as shown in Figures 2 to 4 , the round bottom cover has, from outside to inside, cover hook part 1, outer wrapping curved part 2, inner wrapping curved part 3, involute part 4, cover bottom reinforcing convex part 5, and cover core piece part 6, the cover hook part 1 is in the form of a U-shaped opening on the inside, the outer wrapping curved part 2 has an inclination of 12-20° between the inner end and the bottom cover axis, the involute part 4 is flat, and the flat surface of the involute part 4 has an inclination of 35-45° with the bottom cover axis; ​​

[0038] The corrosion-resistant curling structure of the metal beverage bottom cover and the can body is a five-layer superimposed structure formed by the can hook inner sealing layer 1a, the can hook outer sealing layer 2a, the cover hook inner sealing layer 3a, the cover hook outer sealing layer 4a, and the bottom cover inner sealing layer 5a. The superimposed order of the five-layer superimposed structure from the outside to the inside on the finished metal beverage can is: the cover hook outer sealing layer 4a, the can hook inner sealing layer 1a, the cover hook inner sealing layer 3a, the can hook outer sealing layer 2a, and the bottom cover inner sealing layer 5a. The curling part between the cover hook inner sealing layer 3a and the cover hook outer sealing layer 4a is formed by bending and pressing the cover hook part 1. The curling part between the cover hook outer sealing layer 4a and the bottom cover inner sealing layer 5a is formed by bending and pressing the outer wrapping part 2. The bottom cover inner sealing layer 5a is formed by bending and pressing the inner wrapping part 3. The involute part 4 and the inner wall of the can body form an involute inclination angle of 45-55°.

[0039] The height of the cover hook part 1 is 1.85-2.00 mm. The intersection of the inner wrapping part 3 and the involute part 4 has a fold point part 7 with a radius of 0.3-0.8 mm, and the angle of the fold point part 7 is 20-40°. The height between the fold point part 7 and the top surface of the outer wrapping part 2 is 2.8-2.95 mm.

[0040] Summary of electrochemical corrosion resistance test of strong acid beverage metal can 209 end neck:

[0041] In view of the problem of electrochemical corrosion of the strong acid beverage metal can 209 end neck, on the basis of previous detection and evaluation, the existing technology and resources are further expanded from August 2023 to now, and three improvement factors are tested. A total of 1142 empty cans were tested, including 435 cans tested for 2 hours and 707 cans soaked in copper sulfate for 2 hours.

[0042] Experimental scheme

[0043] 1. Purpose of the experiment

[0044] The purpose of this experiment is to test four single-factor changes and compare the improvement effect of electrochemical corrosion of the strong acid beverage metal can 209 end neck under the same experimental conditions.

[0045] 2. Experimental comparison factors

[0046] From the three improvement factors of new bottom cover, double nozzle, and A brand inner coating color printing iron, three types of empty cans are prepared by changing single factors and tested under the same conditions.

[0047] 3. Experimental materials

[0048] 1) New bottom cover: Increase the gap between the curling shoulder and the can body to improve the adhesion damage caused by thermal expansion and contraction during the curing process of the coating in the groove.

[0049] 2) Double nozzle: under the premise of the same spraying amount, by spraying at two angles (tank body and groove), increase the stability of the groove spraying effect.

[0050] 3) A brand of inner coating printing iron: compare the effects of different suppliers' inner coating against electrochemical corrosion.

[0051] 4, Sample pre-treatment

[0052] 3 types of empty cans are uniformly treated, filled with boiling water, sealed, and then placed in a cold water pool for cooling. The whole box is manually dropped 1 meter high.

[0053] 5, Detection method

[0054] Combine copper sulfate soaking for 2 hours and 2 hours of power-on detection. Open the cover and observe the 209 end groove corrosion.

[0055] 6, Result evaluation criteria

[0056] Evaluate the corrosion resistance of 3 types of empty cans by corrosion grade and number of perforations. From 0, 1-2, 6-7, and perforation, the more 0 and 1-2, the better the anti-electrochemical corrosion effect, and the more 6-7 and perforation, the worse the anti-electrochemical corrosion effect.

[0057] 7, Experimental results

[0058] According to the 2-hour power-on detection results, as shown in Figure 5 The experimental process is shown in Figure 6 .

[0059] Experimental summary

[0060] Combine 3 types of empty cans, compare the 209 end groove corrosion results after soaking in copper sulfate for 2 hours and 2 hours of power-on detection:

[0061] Single factor: the new bottom cover is the best;

[0062] Two detection methods: from the data comparison results, copper sulfate soaking for 2 hours is the reaction of strong acid content with iron. The detection results show that the anti-electrochemical corrosion effect of the empty cans made under the same improvement conditions is significantly worse than that of the 2-hour power-on detection, with a high 6-7 grade corrosion degree and a low 0-2 grade corrosion degree. The 2-hour power-on detection method is closer to the content of normal production filling, and the detection results are more instructive to actual production.

[0063] Seam data and projection:

[0064] The conventional three-piece can bottom cover seam structure selects 5 samples, each sample is cut into 3 planes at different positions, and the projection diagram of the seam part is shown in 7, and the seam data is shown in Figure 8as shown.

[0065] With the three-piece can bottom cover sealing structure described in the present application, five samples are selected, each of which is cut into three planar surfaces at different positions, the projection view of the sealing part is shown in FIG. 9, and the sealing data is shown in Table 1. Figure 10 as shown.

[0066] From the sealing data, both the conventional bottom cover and the new type bottom cover meet the requirements of the national standard for the sealing structure.

[0067] The specific embodiments described herein are merely illustrative of the spirit of the present application. Those skilled in the art of the present application can make various modifications or supplements to the described specific embodiments or replace them with similar ways, without departing from the spirit of the present application or exceeding the scope defined by the appended claims.

Claims

1. A corrosion resistant curl seam structure formed between a metal beverage end and a can body, characterized by, The circular bottom cover has, from outside to inside, a cover hook part (1), an outer wrapping part (2), an inner wrapping part (3), a gradual opening part (4), a cover bottom reinforcing convex part (5) and a cover core part (6), the cover hook part (1) is in U shape with an inside opening, the outer wrapping part (2) has an inner end with an inclination angle of 12-20° between the bottom cover axis, the gradual opening part (4) is flat, and the flat surface of the gradual opening part (4) has an inclination angle of 45-55° between the bottom cover axis; The corrosion-resistant curling structure of the metal beverage bottom cover and the can body is a five-layer superimposed structure formed by the can hook inner sealing layer (1a), the can hook outer sealing layer (2a), the cover hook inner sealing layer (3a), the cover hook outer sealing layer (4a) and the bottom cover inner sealing layer (5a), the superimposed order of the five-layer superimposed structure from outside to inside on the finished metal beverage can is: the cover hook outer sealing layer (4a), the can hook inner sealing layer (1a), the cover hook inner sealing layer (3a), the can hook outer sealing layer (2a) and the bottom cover inner sealing layer (5a), the curling part between the cover hook inner sealing layer (3a) and the cover hook outer sealing layer (4a) is formed by bending and pressing the cover hook part (1), the curling part between the cover hook outer sealing layer (4a) and the bottom cover inner sealing layer (5a) is formed by bending and pressing the outer wrapping part (2), the bottom cover inner sealing layer (5a) is formed by bending and pressing the inner wrapping part (3), and the gradual opening part (4) forms a gradual opening inclination angle of 45-55° with the inner wall of the can body.

2. The corrosion resistant curl seam formed between a metal beverage end and a can body according to claim 1, wherein The height of the cover hook part (1) is 1.85-2.00 mm.

3. The corrosion resistant curl seam formed between a metal beverage end and a can body according to claim 2, wherein, The height of the cover hook part (1) is 1.91 mm.

4. The corrosion resistant curl seam of a metal beverage bottom closure and can body according to claim 1, wherein, The intersection of the inner wrapping part (3) and the gradual opening part (4) has a folding point part (7) with a radius of 0.3-0.8 mm, and the folding point part (7) has an arc of 0.11π-0.22π.

5. The corrosion resistant curl seam formed between a metal beverage end and a can body according to claim 4, wherein The radius of the folding point part (7) is 0.5 mm, and the folding point part (7) has an arc of 0.16π.

6. The corrosion resistant curl seam formed between a metal beverage end and a can body according to claim 5, wherein The height between the folding point part (7) and the top surface of the outer wrapping part (2) is 2.8-2.95 mm.

7. The corrosion resistant curl seam formed between a metal beverage end and a can body according to claim 6, wherein The height between the folding point part (7) and the top surface of the outer wrapping part (2) is 2.9 mm.

8. The corrosion resistant curl seam of a metal beverage bottom closure and can body according to claim 1, wherein, The inner end of the outer wrapping part (2) has an inclination angle of 17° with the bottom cover axis.

9. The corrosion resistant curl seam of a metal beverage bottom closure and can body according to claim 1, wherein, The flat surface of the gradual opening part (4) has an inclination angle of 45° with the bottom cover axis.

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