JPH0588186B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a container with seamless sides (the bottom and the can body are integrated) formed by drawing processing (including multistage drawing) or drawing and ironing processing used for beverage cans, general food cans, etc. The coating layer on the inner surface of the can consists of a thermoplastic resin layer from the steel plate side (lower layer), a corrosion-resistant metal layer on top of the thermoplastic resin layer, and a corrosion-resistant metal layer on top of the thermoplastic resin layer. The present invention relates to a composite steel food and beverage can container with no side seam, which has a three-layer structure including a thermosetting resin layer and a thermosetting resin layer, and a method for manufacturing the same. [Prior art] As is well known, with innovations in can manufacturing technology, the manufacturing technology for beverage cans and food cans has changed from the conventional can manufacturing method with seams on the sides of solder cans, adhesive cans, etc. to drawing or drawing. Containers are now being transformed into containers with seamless sides that are formed by ironing. Since the bottom and can body are molded as one piece and there are no seams, only the can lid body needs to be tightened, making it a highly reliable container with no seam leakage accidents. As containers for filling beer, carbonated drinks, etc.
So-called DI cans (Drawn & Ironed) are used, which are formed by a combination of drawing and ironing.For contents with low internal pressure, the can itself needs strength, so the drawing process (can diameter D and can height When the ratio H/D is large, it is manufactured by 2-stage to 3-stage drawing and some ironing (hereinafter referred to as DRD). In the case of DI cans, tinplate or aluminum alloy is used as the material, and after DI molding, degreasing and chemical treatment are performed, and the inner surface is coated with thermosetting resin once or twice. For DRD cans, tinplate, stain-free steel (chromic acid treated steel plate)
Alternatively, a method is used in which the aluminum alloy is coated in advance with a paint with good workability and then subjected to DRD processing to produce a product. [Problems to be solved by the invention] In the case of can bodies made by such a method, there are problems with corrosion resistance, especially when surface-treated steel sheets such as tinplate and stain-free steel (TFS) are used as materials. Occur. In other words, in the case of the above-mentioned surface-treated steel sheet, the plating film has an average thickness of 1.0μ or less, especially
In the case of TFS, since it is extremely thin (less than 0.1μ), the plating film is destroyed during processing, and protection with an organic coating is essential to maintain corrosion resistance. Therefore, if there is a coating defect, there is a strong possibility that the iron in that area will melt early, resulting in a perforated can. Therefore, in the case of DI cans for carbonated beverages, (painting - baking) - (painting - baking)
Two coats of paint are applied to completely eliminate any defects in the paint film. On the other hand, in the case of DRD cans, the inner coating is damaged during processing, causing problems with corrosion resistance, and a method is used to repaint the highly corrosive contents after drawing. In the case of aluminum cans, the corrosion resistance of aluminum itself is relatively excellent, so even if a slight coating defect occurs, the corrosion resistance of the can can be ensured, so it can be coated only once. An object of the present invention is to provide a steel container such as a DI can or a DRD can that has improved corrosion resistance and can simplify the painting of the inside of the can. [Means for solving the problems] The feature of the present invention is that the film structure on the inner surface of the molded can includes a thermoplastic resin layer with a thickness of 2 to 100 μm from the steel plate side;
Next, a corrosion-resistant metal layer with a thickness of more than 1 μm to 100 μm is provided as an upper layer, and a thermosetting resin layer is further provided as an upper layer. As the base steel plate, a surface-treated steel plate such as tinplate, stain-free steel, or Ni-plated steel plate, or an untreated black plate is used. In particular, when adhesion with the thermoplastic resin layer is important, stain-free steel or chromic acid-treated Ni-plated material is used. Using such a steel plate as a base material, a corrosion-resistant metal is bonded using a thermoplastic resin having adhesive strength as a binder. As the thermoplastic resin having adhesive strength, acid-modified polyolefin, polyester ionomer, or polyacid resin is used. Adhesive thickness also provides corrosion resistance2
~100μ, preferably 15-50μ. The lower limit of the adhesive thickness was set from the viewpoint of corrosion resistance effect, and the upper limit was set from the viewpoint of economical efficiency. Next is the corrosion-resistant metal layer, and the types of metals include Al, Al alloys, various stainless steels, Ti, Ti alloys,
Sn, Sn alloys, Ni, Ni alloys, Cr, Cr alloys, etc. can be used, but from the point of view of food storage containers, Al, Al alloys, various stainless steels, Sn, etc., which have a proven track record of use, are particularly desirable. Next, an extremely thin material with a thickness of more than 1μ to 100μ, preferably 5 to 40μ is used. These ultra-thin materials are laminated onto the surface of a steel plate by a pressure bonding method using the above-mentioned thermoplastic resin. Thereafter, process differences arise depending on the can manufacturing method. In the case of DRD cans, a thermosetting resin is applied to a corrosion-resistant metal foil that is thermocompressed, and
After completing the layered structure, it is subjected to can manufacturing processing. As the thermosetting resin, paints normally used for can making such as epoxyphenol can be used, but in the case of cans that are formed by deep drawing and multistage drawing, processable materials such as polyester or vinyl can be used. A relatively good one is desirable. To ensure perfect corrosion resistance, after DRD molding,
It is desirable to heat to a temperature higher than the melting point of the bottom thermoplastic resin layer, preferably about 50°C above the melting point, to recover from damage caused by processing. Next, in the case of a DI can, it is subjected to DI molding with two layers, a thermoplastic resin layer and a corrosion-resistant metal layer. Considering that the lubrication properties of the outer surface are very important in DI molding, there are cases where it is not always appropriate to apply a two-layer structure coating to the outer surface of the can, and in that case, other coatings with good lubricity may be used. (For example, Sn plating, Zn plating, Al plating, or an organic film alone) is used. Since the lubrication conditions on the inner surface of the can are relatively gentle, it is possible to apply the two-layer structure film of the present invention having a thermoplastic resin as the base layer and a corrosion-resistant metal layer as the upper layer. DI molding can be used to mold all can sizes currently on the market, including beer cans (211 diameter) and carbonated cans (202 diameter). Cup forming is usually done through two stages of drawing and three stages of ironing, and after trimming the top of the can, degreasing and chemical treatment are performed using conventional methods, and then painting is printed on the outside of the can, followed by spray painting on the inside of the can. . At this stage 3
A layered structure film is completed, and the thermosetting resin for the third layer is typically epoxyphenol-based, but vinyl-based or the like may also be used. During the baking process of the thermosetting resin, the thermoplastic resin is heated and melted to restore adhesive strength and self-repair defects in the film through processing. As detailed above, in the three-layer structure film according to the present invention, the first layer (thermoplastic resin) provides adhesion and corrosion resistance of the corrosion-resistant metal layer, and the second layer (corrosion-resistant metal layer) provides corrosion resistance as well as DI or DRD. Protection of the first layer during processing (prevention of film tearing and pinhole generation due to processing)
It also has the role of improving mold release from the mold and withstanding high-speed production. If only a thick organic coating is applied, the mold (punch) will not work because the organic resin is soft.
Problems such as surface sticking and extremely inhibiting mold release properties occur, such as tearing of the upper end of the cup (because the upper end of the cup is caught on the claw and released from the mold). The presence of a metal foil layer solves this problem. Also, the presence of the metal foil layer causes the thermoplastic resin layer to melt when heated, but as the temperature rises, the viscosity decreases, resulting in the so-called "sagging" phenomenon. ” can be effectively prevented.
The uppermost thermosetting resin layer prevents the corrosion-resistant metal layer from coming into direct contact with the contents, and also prevents moisture, O ₂ ,
It acts as an ion permeation barrier and improves corrosion resistance. The can body manufactured by the above method has a high degree of corrosion resistance and is therefore applicable to all kinds of contents. [Example] Example 1 Tin plating on one side of a 0.29mm thin steel plate (thickness 0.4μ)
After that, a 1.5μ soft aluminum foil was adhered to the other side via a 20μ modified polyester adhesive layer. 139mm with the tin plated surface facing the outside of the can
Starting from a disc, it was drawn twice and ironed three times to create an outer diameter of 65 mm and an average height of 124 mm.
A can (after flange forming) was created. After degreasing with an alkaline cleaner and passivating the surface with a chemical containing chromic acid and phosphoric acid, the inner surface of the can was spray-painted with 70 to 90 mg of epoxyphenol paint per can, and heated at 205℃ for 10 minutes. I baked it for a minute. Example 2 After applying 7μ of epoxy phenol paint to one side of 0.29mm stain-free steel and baking at 200℃ for 5 minutes, apply 15μ stainless steel (430) foil to the other side through a 25μ modified polypropylene resin layer. was glued. After molding in the same manner as in Example 1 using the surface with the stainless steel foil as the inner surface of the can, 120 mg of modified vinyl paint was applied by spray.
Baking was performed at 175°C for 8 minutes. Example 3 After applying 5 μm of epoxy phenol paint to one side of a 0.16 mm thick tain-free steel plate and baking at 205°C for 10 minutes, the other side was coated with a 7 μm soft coating through an 8 μm modified polyethylene resin layer. Glued aluminum foil. Thereafter, the surface with the aluminum foil was used as the inner surface of the can, and a circular disk blank with a diameter of 180 mm was drawn twice to produce a can with a diameter of 77 mm and a can height of 81.5 mm. Example 4 5μ of epoxy phenol paint was applied to one side of a 0.16mm thick stain-free steel plate, and the coating was heated at 205℃ for 50 minutes.
After baking for a minute, apply 20 μm on the other side.
A 30μ titanium foil (soft material) was bonded through the modified polypropylene resin layer. After that, a modified vinyl paint was applied to the titanium foil with a thickness of 8μ, and then
This surface was used as the inner surface of the can, and by drawing three times and ironing once, a can with an outer diameter of 83 mm and a can height of 139 mm without side wall seam was created. After molding, the can was heated at 185°C for 5 minutes to self-repair defects in the resin layer that occurred during processing. Comparative Example 1 Using double-sided #25 tin plate with a thickness of 0.32 mm, Example 1
Similarly, start from a 139mm disc blank,
The outer diameter is reduced by drawing twice and ironing three times.
Cans with an average can height of 65 mm and 124 mm after flange forming were made. After degreasing and chemical conversion treatment using conventional methods, the inner surfaces of the cans were spray-painted with 70 to 90 mg of epoxyphenol paint per can, and baked at 205°C for 10 minutes. Comparative Example 2 After can manufacturing, degreasing, and chemical conversion treatment in the same manner as Comparative Example 1, 70 to 90 epoxy phenol paint was applied per can.
After spray painting with a coating amount of 70 to 90 mg per can, and baking at 205° C. for 3 minutes, spray painting was performed again with a coating amount of 70 to 90 mg per can, and baking was performed at 205° C. for 10 minutes. Comparative Example 3 5 μ of epoxy phenol paint was applied to one side of a 0.16 mm thick stain-free steel plate and heated at 205℃ for 50 minutes.
After baking for 1 minute, apply vinyl organosol paint to the other side to a thickness of 185 μm.
Baking was performed at ℃ for 10 minutes. Thereafter, a can with a diameter of 77 mm and a can height of 81.5 mm was prepared in the same manner as in Example 3, with the vinyl paint surface placed on the inner surface of the can. Comparative Example 4 Using a sample prepared in the same manner as in Comparative Example 3, a can with an outer diameter of 83 mm and a height of 139 mm was drawn three times in the same manner as in Example 4, with the vinyl paint surface as the inner surface of the can. Created by one ironing process. Among the cans made by the above method, Example 1,
2 and Comparative Examples 1 and 2, the cans were filled with cola-based (trade name: Coca-Cola) and lemon-lime-based (trade name: Mirinda Lemon Lime) carbonated drinks, and the cans were filled with cola-based (trade name: Coca-Cola) and lemon-lime-based (trade name: Mirinda Lemon Lime) carbonated drinks, and when stored for a long period of time (38°C). The incidence of perforated cans and the amount of Fe elution were compared. On the other hand, the cans according to Examples 3 and 4 and Comparative Examples 3 and 4 were filled with clams (flavored with soy sauce), and the corrosion resistance was compared based on the amount of expansion of the cans during long-term storage (38° C.). These characteristic values are summarized in Tables 1 and 2. Table 1 shows that as a result of application to DI cans, in the accelerated test at 38°C, no perforation occurred in the example according to the present invention, and the amount of Fe elution was extremely low compared to the comparative example, making it practical. It has an extremely high level of corrosion resistance with no problems at all. Table 2 shows an example of application to DRD cans, and it is clear that the corrosion resistance level is extremely superior to that of the comparative example (current).

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Claims (1)

[Scope of Claims] 1. A thermoplastic resin having acid-modified polyolefin-based, polyester-based ionomer, or polyacid-based adhesive strength on a steel plate.
Adhesive layer of 100μm and the upper layer is more than 1.0μm ~ 100μm
1. A seamless container for food and beverage cans made of composite steel with excellent corrosion resistance, characterized by having a three-layer structure consisting of a corrosion-resistant metal layer and a thermosetting resin laminated on the upper layer. 2. Made of a thermoplastic resin with acid-modified polyolefin, polyester ionomer, or polyacid adhesive strength on a steel plate.
A 100 μm adhesive layer is formed, a corrosion-resistant metal layer of more than 1.0 μm to 100 μm is laminated by thermocompression bonding via the adhesive layer, and a thermosetting resin is further applied on top of the adhesive layer to form a three-layer coating layer. 1. A method for manufacturing a seamless container for food and beverage cans made of composite steel with excellent corrosion resistance, which comprises forming and then drawing. 3 Made of a thermoplastic resin with acid-modified polyolefin, polyester ionomer, or polyacid adhesive strength on a steel plate.
A 100 μm adhesive layer is formed, a corrosion-resistant metal layer of more than 1.0 μm to 100 μm is laminated by thermocompression bonding via the adhesive layer, and a thermosetting resin is further applied on top of the adhesive layer to form a three-layer coating layer. A side seam for a food and drink can made of composite steel with excellent corrosion resistance, characterized in that after forming a side seam, a side seamless can body is formed by drawing, and the can body is heated to a temperature higher than the melting point of the thermoplastic resin in the bottom layer. Method of manufacturing pear containers. 4 Made of thermoplastic resin with acid-modified polyolefin-based, polyester-based ionomer, or polyacid-based adhesive strength on the steel plate.
After forming an adhesive layer of 100 μm and laminating a corrosion-resistant metal layer of more than 1.0 μm to 100 μm by thermocompression bonding via the adhesive layer, a can body with no side seams is formed by drawing and ironing. A method for producing a seamless container for food and drink cans made of composite steel with excellent corrosion resistance, which comprises applying a thermosetting resin to the inner surface of the can body and heating the can body to a temperature higher than the melting point of the thermoplastic resin in the lowermost layer.