JPH0262092B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a salt-containing beverage can,
More specifically, it consists of a steel can body with an internal coating and an easy-open lid made of internally coated aluminum, and is excellent for handling salt-containing beverage contents without the need for corrective coating on the easy-open lid. This invention relates to a method for producing a salt-containing beverage can that provides pitting prevention properties. (Prior Art) Conventionally, as cans for sports drinks and salt-containing beverages containing relatively high concentrations of salts such as tomato juice, steel cans such as tinplate and tain-free steel have been used because they are corrosion-resistant and resistant. Commonly used due to its pitting properties. Since these beverage cans are heated and sterilized while still in the can, and the internal pressure is reduced during storage, so-called three-piece cans are widely used, consisting of a can body with openings at both ends and a top and bottom lid. As one of the lids, an easy-open lid is used, which can be opened with fingers without using any special equipment. This easy-open lid has an opening section defined by a score (partial cutting line), a rivet is formed in this opening section, and a tension tab is fixed by the rivet. Widely used are devices in which the score is broken by pulling and the opening portion is removed. As an easy-open lid for salt-containing beverage cans,
Products made from tinplate are already in practical use. (Problems to be Solved by the Invention) However, since the rigidity of tinplate as a constituent material is significantly higher than that of aluminum material, the opening force is large, making it difficult to open, especially for small people. Sharp cut edges are formed due to score breakage, which can easily cause cuts to fingers, etc., and iron can be eluted through damaged parts of the inner coating of score processed areas and rivet processed areas, which tends to reduce the flavor of the contents. There are drawbacks. On the other hand, aluminum material has excellent workability and does not have the above-mentioned problems, so it is widely used as an easy-to-open lid for cola, beer, etc. However, aluminum material is corrosive to contents with high salt concentration. Pitting corrosion occurs through the damaged portions of the inner surface coating of the scored and riveted portions mentioned above, and the problems of leakage of contents and bacterial contamination from these through holes are likely to occur. In order to prevent this, it is possible to apply correction coating to the inner surfaces of the score processed parts and rivet processed parts, but this requires an extra process of spraying and baking the paint, which increases the cost and also makes it difficult to apply the correction coating. This causes a problem in that the coated film remains in the form of feathers on the score shearing area (referred to as feathering), impairing the appearance characteristics and commercial value. Therefore, an object of the present invention is to provide a can body made of internally coated steel and an easy-open lid made of internally coated aluminum, and to provide excellent corrosion resistance and pitting corrosion resistance without the need for corrective coating on the easy-open lid. An object of the present invention is to provide a method for producing a salt-containing beverage can. Another object of the present invention is to provide a method for manufacturing an easy-to-open can for salt-containing beverages with excellent pitting corrosion resistance, easy opening, safety, flavor retention, and fading resistance with a small number of steps at a low cost. There is something to do. (Means for Solving the Problems) According to the present invention, in a method for manufacturing a beverage can comprising tightening an easy-open lid made of internally coated aluminum to a steel can body with internal coating, the above-mentioned internally coated steel can body is , an internally coated steel can body with an enamellator value (ERV) of 10 mA or less measured at an applied voltage of 6.3 volts in 1% saline solution, and an easy-open lid made of internally coated aluminum are used in the lid making process and can manufacturing process. Provided is a method for producing a salt-containing beverage can characterized by an easy-open lid made of internally coated aluminum without correction coating. (Function) In a salt-containing beverage can consisting of an inner-coated steel can body and an inner-coated aluminum easy-open lid, the pitting corrosion of the easy-open lid is surprisingly affected by the inner surface. It is the degree of exposure of the steel material of a painted steel can body, and is an internally painted steel can body whose enamelator value (ERV) measured at an applied voltage of 6.3 volts in 1% saline is 10 mA or less, especially 5 mA or less. When using the barrel, pitting corrosion of the aluminum lid can be prevented even if an easy-open lid made of internally coated aluminum is used as an easy-open lid made of internally coated aluminum that has not been subjected to correction coating during the lid making process and can manufacturing process. It is based on discovery. Figures 1 to 6 of the attached drawings show that a steel material and an aluminum material are immersed in an electrolytic solution having the following composition at a fixed area ratio, that is, citric acid 0.6% salt, variable pH 3.5, and temperature 37°C, and a galvanic solution flowing between the two materials is shown. Figures 1 and 2 show the results of measuring the Nikkuppull current and the potential difference with respect to the silver-silver chloride reference electrode.
500ppm, the salt concentration in Figures 3 and 4 is 1750ppm,
Figures 5 and 6 show the case where the salt concentration is 3000 ppm, and Figures 1, 3 and 5 show the case where the Al:Fe area ratio is 1:
Case 1 and Figures 2, 4 and 6 show cases where the area ratio of Al:Fe is 1:9.6, respectively. According to these results, Al is electrochemically less noble than Fe, and therefore, in both systems, corrosion current flows due to the elution of Al into the electrolyte, but this current is caused by the exposed area of Al. Even if it is the same,
It can be seen that the value increases as the exposed area of Fe increases. The present invention applies this principle to the combination of an internally coated steel can body and an internally coated aluminum easy-open lid. If you use a can, it will heat up to 6 at 37℃.
It was found that aluminum pitting corrosion in the score-processed part or the rivet-processed part of the easy-open lid was prevented in several months' storage tests (this corresponds to storage for one to one and a half years at room temperature). It is. According to the present invention, in a salt-containing beverage can, by using an aluminum material as the material for the easy-open lid, the opening force is reduced and easy opening is achieved, and cuts to fingers etc. caused by the cut edge of the score portion are prevented. Furthermore, by preventing metal elution, especially iron elution, the flavor retention of the contents can also be maintained at a high level. Moreover, since there is no need to apply correction coating to the lid during the lid making process or can manufacturing process, the number of processes is reduced, and there are manufacturing advantages such as reducing equipment costs and manufacturing costs. The occurrence of phasing can also be eliminated. (Preferred Embodiment of the Invention) Structure of Beverage Can In FIG. 7 showing an example of the salt-containing beverage can of the present invention, this specific example is a two-piece can, including a seamless can body 1 with an open top end, and a seamless can body 1 with an open top end; and an easy-open lid 3 which is fastened to the top via a seaming part 2. The can body 1 is made of a painted steel material, and consists of a cylindrical body part 4 whose thickness has been reduced by drawing and ironing, and an unthinned bottom part 5 which is seamlessly connected to this body part. The easy-open lid 3 is made of painted aluminum and has the structure shown in FIGS. 8 and 9. In FIG. 8 (top view) and FIG. 9 (side sectional view) showing the structure of the easy-open lid used in the present invention, the easy-open lid 3 has an annular rim that is to be fitted into the inner surface of the side surface of the can body. A sealing groove 11 is provided on the outer circumferential side of the chuck wall 10, and a score 19 is provided on the inside of the annular rim portion 10 to define a portion 12 to be opened (a portion that becomes a drinking spout). ing. A rivet 13 formed by protruding the lid material toward the outer surface of the can lid is formed in this portion 12 to be opened, and a pull tab 14 for opening is formed.
is fixed by the riveting of this rivet 13 as shown below. That is, the unsealing pull tab 14 has an unsealing tip 15 at one end and a gripping ring 16 at the other end, and a fulcrum portion 17 fixed with a rivet 13 is present adjacent to the unsealing tip 15. The pull tab 14 is provided so that its opening tip 15 is close to the opening start side of the score 19. The aforementioned sealing groove 11 is lined with a sealing rubber composition (sealant) 18, and sealing is performed between the can body flange and the can body flange. As shown in FIG. 10, this easy-open lid consists of an aluminum base 20, an inner protective coating 21 applied to the inner surface of the can, and an outer protective coating 22 applied to the outer surface of the can. It is completed. The score 19 is carved so as to reach halfway in the thickness direction of the aluminum base 20 from the outer surface of the can. Of the inner surface protective coating film 21 of the lid, the parts where the score 19 is provided and the part where the rivet 13 is provided are often damaged during processing, but according to the present invention, this can be prevented. It is used for manufacturing beverage cans without applying a correction coat (reveal coat) to the parts. On the other hand, in FIG. 11 showing the cross-sectional structure of the can body, the can body 1 has a steel base 30 and a steel base 3.
It consists of a protective undercoat 31 and a protective topcoat 32 applied to the inner surface of the steel substrate 30, and a printing layer 33 and a clear lacquer 34 applied to the outer surface of the steel base 30. Of course, the salt-containing beverage can of the present invention is not limited to the two-piece can described above, but can also be applied to a so-called three-piece can. In this three-piece glued can, the can body is open at both ends with side seams, the aforementioned easy-open lid is secured to one end, and the easy-open mechanism is attached to the other end. A normal can lid without a lid is sealed. Side seams can be joined using polyamide adhesive or
It can be formed by welding. Can body The can body used in the present invention has an enamel rating value (ERV) of 10 mA or less as determined by the method described above.
The degree of completeness of the steel surface coating shall be such that the current is 5mA or less. There are several limitations that must be adhered to in order to obtain this degree of completeness in coating the steel surface. (i) First, the steel substrate must have a surface with no defects and excellent adhesion to the coating. That is, if the substrate has surface defects, the coating film adhesion will be poor in these areas and the enamel rating will increase. In order to improve the adhesion of the coating film to the substrate, the steel substrate is preferably made of a surface-treated steel plate, particularly electrolytic chromic acid treated steel plate, tin-plated steel plate, chromate-treated tin-plated steel plate, nickel-plated steel plate, chromate-treated steel plate, etc. Nickel-plated steel sheets, nickel-tin-plated steel sheets, chromated nickel-tin steel sheets, etc. are advantageously used. Among these surface-treated steel sheets, tin-plated steel sheets are used for drawing and ironing cans.
In order to further improve the adhesion of the coating film after can manufacturing, phosphoric acid treatment, chromic acid treatment, phosphoric acid/chromic acid treatment, zirconium compound treatment, etc. are used.
Furthermore, electrolytic chromic acid treated steel plates are advantageously used for adhesive cans, and tin-plated steel plates and nickel-tin-plated steel plates are advantageously used for welded cans. (ii) Next, the inner surface protective coating must be free from coating defects, have adhesion to the steel substrate, and have sufficient barrier properties against aqueous electrolyte solutions. From this point of view, an undercoat layer made of paint resin that has excellent adhesion to the steel substrate, and an overcoat layer that adheres well to this undercoat layer and also has an excellent combination of continuous coating film formation and flavor retention. Double coat coatings are preferred. As the inner surface protective coating, thermosetting resin paint,
For example, phenol-formaldehyde resin, furan-formaldehyde resin, xylene-formaldehyde resin, ketone-formaldehyde resin, urea-formaldehyde resin, melamine-formaldehyde resin,
Formaldehyde resins, alkyd resins, unsaturated polyester resins, epoxy resins, bismaleimide resins, triallyl cyanurate resins, thermosetting acrylic resins, silicone resins, oil-based resins, or thermoplastic resin coatings, such as unsaponified or partially saponified vinyl chloride-vinyl acetate copolymers, vinyl chloride-maleic acid copolymers, unsaponified or partially saponified vinyl chloride-maleic acid-vinyl acetate copolymers, acrylic polymers,
Examples include saturated polyester resins, from which an appropriate combination of undercoat and topcoat is selected. For example, epoxy-phenolic paints and epoxy-amino paints are particularly suitable as base coats, while the above-mentioned vinyl paints are particularly suitable as top coats. Of course, different types of epoxy-phenol paints can be provided as a base coat and a top coat. The undercoat film is generally preferably provided to a thickness of 2 to 7 μm, particularly 3 to 6 μm, and the top coat film is generally provided to a thickness of 2 to 7 μm, particularly 3 to 6 μm. For drawn and ironed cans, it is necessary to apply both by spraying, for example, spraying an epoxy-amino paint as an undercoat and then spraying a vinyl paint as a topcoat. Compared to the steel material used in the can,
Both the undercoat and topcoat may be provided by roll coating, or the undercoat may be applied to the steel material by roll coating, and the topcoat may be spray coated after can manufacturing. (iii) In the case of side-seamed can bodies, the paint film may be scratched when it comes into contact with conveying members or tools during the process of transporting the painted steel material for can manufacturing or during the can manufacturing process. In order to prevent this, fatty acids or derivatives thereof, or waxes are contained in the coating film so that the coefficient of dynamic friction of the coating film is 0.20 or less, particularly 0.15 or more. (iv) In the case of side seam can bodies, the steel material inside the seam shall be fully protected so that it is not exposed. The types and methods of applying protective coating resins are already known per se. For example, thermoplastic resins such as polyamides and polyesters, thermosetting resins such as epoxy-phenolic resins, or combinations thereof are coated with coating liquids and coating powders. Apply to the body or in the form of tape, etc. Easy-open lid All aluminum materials used for this type of easy-open lid can be used, such as pure aluminum or aluminum with other alloying metals, especially aluminum containing small amounts of magnesium, manganese, etc. Alloys are used. Ordinary aluminum materials are electrochemically more base than steel, and when both metals coexist in an electrolyte system, corrosion of aluminum progresses. From this point of view, in the present invention, Cu0~
0.8%, Mg0~2.8%, Mn0~1.5%, Fe0~0.5%,
Corrosion in the above system can be effectively prevented by using an aluminum alloy containing 0 to 0.5% Si (% by weight) as the aluminum material. That is, Cu contained as an alloy component is preferably in the range of 0% to 0.8%; particularly, 0.2 to 0.8% from the viewpoint of corrosion resistance. this
Cu acts to bring the aluminum material into an electrochemically noble state, and corrosion of the steel-aluminum system is more effectively prevented. Furthermore, mechanical strength can be improved. Further, Mg is preferably 0% to 2.8% from the viewpoint of corrosion resistance. If it exceeds 2.8%, pitting corrosion tends to occur when combined with steel. From the viewpoint of processability, Mn is preferably 0% to 1.5%. If it exceeds 15%, processing such as riveting becomes difficult. The thickness of the aluminum material varies depending on the size of the lid, etc., but it is generally 0.20 to 0.50 mm, especially 0.23 mm.
It is preferably within the range of 0.30mm to 0.30mm. From the viewpoint of adhesion of the inner material to the aluminum material and corrosion resistance, it is generally desirable to form a chromate treatment film or a phosphate alumite treatment film on the surface of the aluminum material. The chromate treatment film can be formed by means known per se, for example, after degreasing the aluminum material with caustic soda and slightly etching it, CrO ₃ 4
g/, H ₃ PO ₄ 12 g/, F 0.65 g/, and the rest is carried out by chemical treatment by immersion in a treatment liquid such as water. The thickness of the chromate treatment film is
5 to 50 mg/dm ² , expressed in weight of Cr atoms;
In particular, from the viewpoint of adhesion, it is desirable that the content be within the range of 10 to 35 mg/dm ² . In addition, as a means of forming a phosphoric acid alumite treatment film, for example, aluminum material is degreased with caustic soda, washed with water, and then electrolyzed in a phosphoric acid solution (concentration 10 to 50 wt%) using aluminum as an anode (voltage 20 to 40 V, current density 10
~30A/ ^dm2 ) Form an anodic oxide film. Adhesion is determined by the thickness of the film being within the range of 0.1 to 2 μm.
It is preferable from the viewpoint of workability. As an internal protective coating for this aluminum material,
The thermosetting or thermoplastic protective coating mentioned above in the section of the can body is used. Even if the degree of metal exposure (ERV) of the aluminum lid is large, pitting leakage will not occur in the present invention, but there is a problem of expansion can formation due to hydrogen generation. It is necessary to use a paint that has good processability so that the defects in the coating film are not too large. An example of such a paint with good processability is a vinyl chloride resin organosol paint, in which a vinyl chloride paste resin is added to a solution phase of a solvent-soluble vinyl chloride copolymer resin and an epoxy-containing thermosetting paint resin. It is made by dispersing resin particles. In this case, by using a high molecular weight vinyl chloride resin particle, for example, one with an average degree of polymerization of 1500 or more, toughness that can withstand processing can be obtained, and by using an epoxy-phenol type resin as a thermosetting resin. , excellent adhesion to aluminum materials can be obtained, and further, by containing an epoxy plasticizer, workability can be improved by plasticization. Another type of paint that is easy to process is epoxy.
It is a phenolic paint, and excellent processability can be obtained by using an epoxy resin with a particularly high molecular weight, for example, one with an average molecular weight of 25,000 to 35,000. The thickness of the inner coating film is 3 to 12 μm, especially 5 to 12 μm.
A range of 10 μm is appropriate. Sealing According to the present invention, a salt-containing beverage can is manufactured by seaming the above-mentioned easy-open lid to the can body, but in this case, the protective coating of the can body is damaged during seaming. It is important to prevent it from entering. To this end, a sealing rubber composition 18 such as styrene-butadiene rubber is applied at least to the base of the chalk wall 10 of the lid, preferably to 1/5 of the height of the chalk wall 10, as shown in FIG. This prevents the can body coating near the seaming part from being scratched. (Effects of the Invention) According to the present invention, even when using a combination of an inner-coated steel can body and an inner-coated aluminum easy-open lid, the easy-open lid can be easily opened by suppressing metal exposure of the can body. Pitting corrosion of this lid could be prevented without the need for corrective coating of the inner surface coating. In addition, by using aluminum as the material for the easy-open lid of salt-containing beverage cans, the opening force is reduced and easy opening is achieved, and cuts to fingers etc. caused by the cut edge of the score section are prevented. By preventing metal elution, especially iron elution, the flavor retention of the contents could also be maintained at a high level. Furthermore, since there is no need for correction coating in the lid making process or the can production process, the number of processes is reduced, which provides the manufacturing advantage of reducing equipment costs and manufacturing costs, as well as reducing the occurrence of feathering due to the correction coating. It has now become possible to resolve the issue. (Example) Example 1 Toyo Seam Can A TFS material (plate thickness 0.22 mm) with metallic chromium and hydrated chromium oxide on the surface is used as the can body, and epoxy/phenol paint is applied to the inside and outside surfaces. The inner surface is painted with a base coat (thickness: 3 μm), followed by a top coat (thickness: 3 μm), followed by cutting, nylon gluing for side seams, and other processes to create a 250ml can body at a body maker. Next, neck-in processing to reduce the seaming dimensions and flange processing necessary for seaming are performed on both ends of the can body. The aluminum lid is made of aluminum treated with chromic acid phosphate.
-Mg-based alloy 5052 material (plate thickness 0.25 mm) is used, and the inner surface of the lid is coated with one type of epoxy/phenol paint (film thickness 5 μm) and the other type is vinyl organosol paint (film thickness 10 μm). Paint. All exterior surfaces will be painted with epoxy/urea. After that, wax is applied to the surface and cut into a predetermined size.
Next, punch it out with a press to the size of the lid with a diameter of about 51 mm.
Curling process and compound application necessary for seaming are performed. The compound was applied to about 1/5 of the height of the chalk wall. After that, score processing and tab attachment are performed to create an easy-open lid. The can body and aluminum lid created in this way were wrapped with a seamer to form an empty pack can. Table 1 shows the results of hot-packing the exposed metal (ERV) of the can body and lid and the sports drink Pocari Sweat. Note) Pocari Sweat liquid composition NaCl approx. 1000ppm PH 3.5 Example 2 Welded can The can body was made of tin plate (tin adhesion amount 2.8g/m ² ,
Use a plate with a thickness of 0.22mm) and apply epoxy/phenol paint (film thickness 3μm) to the inner surface. Apply a finishing varnish to the outside. After cutting to a specified size, a body maker welds it to create a can body. After welding, apply epoxy/phenol + nylon paint (film thickness 16μm) to the inner surface of the welded area. Next, neck-in processing to reduce the seaming diameter and flange processing necessary for seaming are performed on both ends of the can body. This can body and the aluminum lid described in the section of the Toyo seam can are sealed and used as an empty can for packs. Table 1 shows the metal exposure (ERV) of the can body and the packing results for the sports drink Pocari Sweat. Example 3 Tinplate DI can As the can body, tinplate (tin coating amount 5.6g/ ^m2 ,
Using a plate thickness of 0.30), the cutter is formed into a cutter using a body maker and then ironed. Then wash,
After drying, apply phosphoric acid surface treatment, then paint the outside, then spray paint the inside. The inner surface is coated with epoxy/urea (film thickness 6μm) on the base and vinyl (film thickness 3μm) on the top. After that, neck-in processing to reduce the seaming diameter and flange processing necessary for seaming are performed. This can body is combined with the aluminum lid described in the section on Toyo seam cans to pack. Table 1 shows the metal exposure (ERV) of the can body and the results of packing the sports drink Pocari Sweat with nitrogen. Example 4 A welded can with a copper-containing aluminum lid wrapped around it.The aluminum material was 0.4% Cu, 1.0% Mg,
A lid was manufactured using a material having a plate thickness of 0.32 mm containing 0.8% Mn, 0.09% Si, 0.20% Fe, and 0.02% Ti using the Al lid manufacturing method shown in Example 1. However, the interior paint was only epoxyphenol-based. This Al lid was wrapped around the welded can body shown in Example 2 to form an empty can for a pack. The contents of the pack were 1000ppm NaCl in the sports drinks Pocari Sweat and Pocari Sweat.
There are two types with added. The results are shown in Table 1. No perforation occurred in either the 5052 material or the copper-containing aluminum material, but the corrosion depth of the 5052 material was at its maximum, which was greater than the plate thickness.
In contrast, copper-containing aluminum only accounts for about 6% of the plate thickness at most, reducing the degree of corrosion. No perforation was observed even in a solution containing 1000 ppm of NaCl added to Pocari Sweat. Example 5 Taburiki DI with copper-containing aluminum lid rolled tightly
Can Cu0.4%, Mg2.7%, Si0.05%, Fe0.15%,
The mechanical strength of the 5052 material used in Examples 1 to 4, which is a material with a Ti content of 0.01 (yield strength: 25 Kgf/
mm ² ) is a stronger material (31Kgf/mm ² as yield strength,
A lid was manufactured using the Al lid manufacturing method shown in Example 1 using a plate having a thickness of 0.28 mm. However, the interior paint was only epoxyphenol-based. This aluminum lid was combined with the tin DI can shown in Example 3, and the sports drink Pocari Sweat was packed with nitrogen filling. Table 1 shows the metal exposure (ERV) of the lid and the packaging results for the sports drink Pocari Sweat. Comparative Example Welded Can The can body was manufactured according to the method described in the Examples section, but the film thickness of the welded part correction paint was lowered to 10 μm to manufacture the can body. Table 1 shows the can body metal exposure (ERV) and the sports drink packing results. Tinplate DI can The can body was manufactured according to the method described in the Examples section, but the spray pattern of the inner surface paint was changed and the can body was manufactured. Table 1 shows the can body metal exposure (ERV) and the packing results for the sports drink Pocari Sweat.

【table】

【table】 [Brief explanation of the drawing]

Figures 1, 2, 3, 4, 5, and 6 show the galvanic couple current generated when steel and aluminum materials are immersed in electrolyte solution with different area ratios, and - FIG. 7 is a diagram showing the results of measuring the potential difference with respect to a silver chloride reference electrode; FIG. 7 is a perspective view showing an example of the salt-containing beverage can of the present invention; and FIG. 8 is an easy-open lid used in the present invention. 9 is a side sectional view of the easy-open lid shown in FIG. 8, FIG. 10 is an enlarged sectional view showing the cross-sectional structure of the easy-open lid, and FIG. FIG. 2 is an enlarged cross-sectional view showing the cross-sectional structure of the can body. 1 is a can body, 2 is a sealing part, 3 is an easy-open lid, 20 is an aluminum base, 21 is an inner protective coating film, 30 is a steel base, 31 is a protective undercoat film, 32 is a protective topcoat film .

Claims (1)

[Scope of Claims] 1. A method for manufacturing a beverage can, which comprises wrapping an easy-open lid made of aluminum with an internal coating on an internally coated steel can body, wherein 6.3 bottles of 1% saline solution are applied as the internally coated steel can body. An internally coated steel can body with an enamel rating (ERV) measured by voltage of 10mA or less is used, and the easy-open lid is made of internally coated aluminum with no correction coating applied during the lid making process or the can making process. A method for manufacturing a salt-containing beverage can characterized by an easy-to-open lid.