JP2807941B2 - Method for forming can body of highly corrosion resistant metal container - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a can body of a highly corrosion-resistant metal container using a steel sheet coated with a polyolefin-based thermoplastic resin. The metal container manufactured by the method of the present invention has a problem of corrosion in a metal container manufactured from a conventional coated steel plate, and can be applied to contents in which cans exclusively containing plastic bags are used.

[0002]

2. Description of the Related Art Conventionally, as a container which can be filled with a highly corrosive content, for example, an aqueous solution containing a strong acid such as hydrochloric acid, sulfuric acid, and sodium hydroxide, and a strong alkali, the metal material itself is extremely excellent in corrosion resistance like stainless steel. Or an Atron can having a plastic bag such as polypropylene, polyethylene, or polyethylene terephthalate inside a normal metal can. Conventionally, attempts have been made to produce a highly corrosion-resistant can using a laminated steel sheet, but Japanese Patent Publication No. 64-139 discloses an adhesive tape on a side seam portion in order to secure the adhesiveness of a joint. Then, a method of performing lock seam processing after sticking is proposed.

[0003]

A problem arises when a steel sheet coated on at least one side with a polyolefin-based thermoplastic resin such as PE (polyethylene) or PP (polypropylene) is used for manufacturing a highly corrosion-resistant metal container. Is
This is a joining method of joining the resin-coated steel sheets to form a can. For example, in the case of a small can such as a 200 ml or 350 ml beverage can, a two-piece can manufacturing method of forming a can by squeezing and ironing can be applied. In the case of a large can such as an 18 l can, such a two-piece can is used. It is difficult to apply the manufacturing method. Therefore, as in the conventional can-making method, it is necessary to join the can body by a welding method or an adhesive method after forming and processing a cut plate, but the welding method needs to remove the resin film of the welded portion. Even if welding can be performed, the film is removed near the welded portion, and it is necessary to repair the portion from which the film has been removed by some method. Such partial repair is not only complicated in the can manufacturing process, but even if it is possible, it is quite difficult to secure the corrosion resistance of the repaired part. In addition, in the method of joining the can body by self-fusion of polyolefin resin, it is necessary to heat the steel sheet to a temperature higher than the melting point of the polyolefin resin coated on the steel sheet. In such cases, crystallization of the polyolefin proceeds and the impact resistance of the resin deteriorates. For this reason, crystallization of the bonded portion is suppressed by a method of rapidly cooling at a cooling rate of 10 ° C./sec or more immediately after the heat fusion. As a method for solving this problem, a method in which a polyethylene-based tape having a melting point lower than the melting point of the polyolefin-based resin laminated on the steel sheet is applied to the lock seam portion, lock seam processing is performed, and heating is performed to perform joining. It is proposed in Japanese Patent Publication No. 64-139. However, the method of controlling the cooling rate has problems such as the necessity of new equipment in the canning line and the difficulty of controlling the cooling rate. In the method using a tape, it is necessary to accurately adhere the tape to the lock seam portion of the joint at the correct position, and it is very difficult to thermo-compress a tape as thin as about 30 μm and as narrow as about 10 mm. there were. It is possible to solve the problem by installing a dedicated tape-attaching facility, but it requires considerable capital investment and has the disadvantage of increasing the cost of can production.Therefore, a method for forming a can body with a simple method is desired. I was In addition, the upper and lower parts of the can body, which has been cut off from the end of the can body part that has been cut into steel plates in order to smoothly perform the tightening, become an obstacle when tightening the can bottom and can lid. There were also problems such as impairing airtightness.

[0004]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a resin composite steel sheet in which at least one surface of a steel sheet is coated with a thermoplastic resin containing polyolefin as a main component in a thickness of 30 μm or more and 120 μm or less by side seam by a rock seam method. In a method for forming a can body by heat fusion, an adhesive obtained by dispersing an amorphous polyolefin-based resin having a melting point lower than the melting point of a thermoplastic resin containing polyolefin as a main component coated on a steel sheet in a solvent is used. The coating is applied to the place where the rock seam of the steel sheet is to be applied, the solvent is removed by heating, and the rock seam processing is performed. ° C
A method for forming a can body of a highly corrosion-resistant metal container, comprising heating at the above-mentioned temperature for 2 seconds or more to fuse and bond the lock seam portion.

[0005]

The present inventors have used an adhesive obtained by dispersing an amorphous polyolefin resin having a melting point lower than that of a thermoplastic resin containing polyolefin as a main component coated on a steel sheet in a solvent. For example, it has been found that by selecting the melting point of the adhesive resin, it is possible to produce a can having sufficient adhesive strength and airtightness as a can body. That is, instead of a method of applying a tape, an adhesive in which an amorphous polyolefin resin is dispersed in a solvent is applied to a rock seam portion of a steel plate for a can body, and a rock seam process is performed after removing the solvent, It adheres by heating, ensuring airtightness.

The most important method for obtaining a metal container having high corrosion resistance is to use a resin-coated steel sheet having excellent corrosion resistance. In addition, it is important to apply a joining method suitable for a resin composite steel sheet having excellent corrosion resistance.

First, a method of joining resin-coated steel sheets is adopted. In the present invention, an adhesive method using an adhesive is adopted. The can joint is formed by the rock seam method as in the conventional solder can method and the adhesive can method. Before performing rock seam processing, an amorphous polyolefin-based thermoplastic resin is used as a solid in a place to be a rock seam portion of a steel plate for a can body.
Then, the organic solvent as a solvent or a dispersant is volatilized by heating. After that, lock seam processing is performed. After the lock seam processing, the polyolefin resin coated on the steel sheet is heated at a temperature of not higher than T ° C. and not lower than T-50 ° C. for 2 seconds or more to bond the rock seam portion. Next, a can lid and a can base plate formed using the same polyolefin resin-coated steel sheet as the can body steel sheet are wound around the can body in a usual manner.
Heat at 2 ° C. or more for 2 seconds or more to cause self-fusion of the polyolefin resin coated on the steel sheet. Also, the wound portion can be joined by using the same polyolefin-based adhesive used for forming the can body. At this time, bonding can be performed by heating at a temperature of T ° C. or lower and T−50 ° C. or higher for 2 seconds or more as in the method of forming the can body.

[0008] The points of the present invention are that an amorphous polyolefin adhesive is used as an adhesive for joining the rock seam portion of the can body, and that the joining of the can body steel sheet to the resin coated steel sheet is performed. This is two points of performing the heat fusion of the adhesive at a melting temperature or lower. According to this method, it is possible to produce a metal container excellent in corrosion resistance without impairing the properties of the resin film coated on the steel sheet at all.

Hereinafter, the contents of the present invention will be described in detail.

First, the steel plate used in the present invention is not particularly limited, and an electric tinplate (Sn containing 0.5 to 12 g / m ^2, which has conventionally been often used as a material for cans) is used.
Electroplated steel sheets), TFS (a steel sheet obtained by electroplating chromium on a tin-free steel sheet at 30 to 120 mg / m ² ), and the like, and Ni-plated steel sheets and the like can also be used. TFS is the best in terms of adhesion to polyolefin resin, but even in the case of electric tinting, chromate treatment is strengthened and the amount of chromium adhered is 20 mg / m ^2.
By doing so, adhesion close to TFS can be ensured.

Next, the resin to be coated on the steel plate is PE, PP
Are most excellent in terms of corrosion resistance, workability, and resin price. Of course, PE, PP, and copolymer resins of these resins can also be used. Other α-olefin resins and copolymer resins of PE and PP with other α-olefin resins are also applicable. As described above, in the present invention, the thermoplastic resin for coating the steel sheet used is limited to a mixed resin or copolymer resin of various polyolefins, but the acid modification for improving the adhesion to the steel sheet, and the resin is colored. For example, a polyolefin to which a titanium oxide or the like is added for addition of an inorganic compound for enhancing the resin strength can be used.

In the present invention, the structure of the resin layer is not particularly limited. As will be described in detail in Examples, as for the actual coating composition, considering the adhesion between the steel sheet and the resin layer and the corrosion resistance of the resin layer, first, the steel sheet side is subjected to acid modification to secure the adhesiveness. It is preferable to form a two-layer structure in which a polyolefin resin layer containing a type carboxyl group and a layer of ordinary PE, PP, other α-olefin resin, and a copolymer of these resins are disposed on the upper layer.

Next, the thickness of the coated polyolefin resin is limited to 30 μm or more and 120 μm or less. If it is less than 30 μm, the corrosion resistance of the highly corrosion-resistant metal container aimed at by the present invention is insufficient. If it is more than 120 μm, the resin film is thick, so that the lock seam is formed after applying the adhesive resin to the lock seam portion. In this case, the thickness of the lock seam portion becomes large, and processing becomes difficult. Adhesive thickness is 1
When about 0μ, the thickness of the polyolefin resin is 140
Although lock seam processing could be performed even with μ, when a large adhesive force is required, the adhesive needs to be about 30 μ. In this case, the total thickness of the resin layer becomes 170 μ, and lock seam processing cannot be performed. For the above reasons, the thickness of the polyolefin resin is limited to 30 μm or more and 120 μm or less.

Although the resin-coated surface of the inner surface of the can has been described above, the surface treatment of the surface to be the outer surface of the can is not limited at all in the present invention. Hereinafter, a processing example on the side to be the outer surface of the can will be described. The properties required for the outer surface of the can include good appearance and excellent rust resistance in the air or in a humid atmosphere. Used in. However, when TFS, thin Sn-plated steel sheet, thin nickel-plated steel sheet, or the like is used, bare use is difficult in terms of rust resistance, and painting or resin lamination is required. As the coating, 3 to 10 μm of a coating resin such as ordinary epoxy phenol, polyester and polyurea can be used. As the resin laminate, a laminate of a polyolefin resin can be used as in the case of the inner surface of the can, and other thermoplastic resins such as polyamide and polyester can also be used. When painting or resin laminating on the outer surface of the can,
It is necessary to select a material having good adhesion to the amorphous polyolefin resin used as the adhesive.

Next, in the method of making cans, the above-mentioned polyolefin-coated steel sheet is first cut to fit the size of the can.
Use a cutting board. Then, after cutting the upper and lower corners of the lock seam joint so that it can be easily tightened, and after framed, the side seam part and, if necessary, the solvent-type A polyolefin adhesive is applied, and the solvent is removed by heating. Thereafter, the cut plate is subjected to goby folding and then rock seam forming. FIG. 1 shows a cross section of a lock seam portion employed in the present invention. Although this cross section is not particularly different from ordinary lock seam forming, unlike a case of solder can, it is necessary to minimize the gap between each plate as much as possible.

After processing into a rock seam shape, the amorphous polyolefin resin applied as an adhesive is self-fused by heating. In the case of self-fusion, when the melting temperature of the polyolefin resin coated on the steel sheet is T ° C., T-50 or less is T-50.
Hold at a temperature of not less than 2 ° C. for not less than 2 seconds.

The reason why the temperature is set to T ° C. or lower is that, when the temperature exceeds T ° C., the polyolefin resin coated on the steel sheet is melted. This changes the properties of the polyolefin and deteriorates the adhesion to steel sheets, impact resistance, and the like. The reason why the heating temperature is set to T-50 ° C or higher is that if the heating temperature is lower than this temperature, the softening of the polyolefin resin coated on the steel sheet is insufficient even if the polyolefin resin for bonding is softened or molten, and This is because the adhesiveness with the polyolefin resin cannot be ensured. For the above reasons, the heating temperature during bonding was T to T-50 ° C.

The reason why the time required for bonding is 2 seconds or more is as follows.
If the time is shorter than this, excellent adhesive strength cannot be secured. Further, the reason why the upper limit of the bonding time is not particularly limited in the present invention is that even if heating is performed for a considerably long time, if the temperature is equal to or lower than T ° C., deterioration in quality of the polyolefin resin coated on the steel sheet is not recognized. The upper limit of the bonding time may be appropriately determined in consideration of the productivity of the can manufacturing equipment.

Next, the reason why the adhesive is limited to an amorphous polyolefin resin is that a crystalline polyolefin resin can also be used, but a crystalline one has a melting point or higher and has a low adhesive strength unless melted once. In order to ensure a sufficient adhesive force at a temperature lower than the melting point of the polyolefin resin coated on the steel sheet, it was limited to an amorphous thermoplastic polyolefin resin.

The can body joined by the rock seam method is
Similarly, it is processed from a steel sheet coated with a polyolefin resin, and is joined to a can bottom plate and a can lid plate by double winding. Subsequently, the double-sealed portion is bonded by heat treatment. The heating conditions at this time are as follows: when the adhesive is also applied to the double tightened portion, T to T-50 as in the can body bonding.
Although it is good to adhere at ℃, if the adhesive is not applied, it is necessary to seal by self-fusion of the polyolefin resin coated on the steel plate, so it is heated for 2 seconds or more in the range of T + 10 ℃ ~ T + 50 ℃. Need to be joined. Unlike the rock seam part, the double wound part is extremely strong at the joint, so after the contents are filled, the adhesion between the polyolefin coated on the steel sheet and the steel sheet deteriorates, and the impact resistance is reduced. Even if it deteriorates, no particular problem occurs. Therefore, the limitation such as the lock seam portion of the can body is not performed. That is, the adhesive may be applied to the double-sealed portion, which is the junction between the can lid or can bottom and the can body, as necessary, and is not particularly limited.

[0021]

EXAMPLE After a low-carbon cold-rolled steel sheet of 0.32 mm was subjected to thin chromium plating at 100 mg / m ² , first, a water-dispersible acrylic modified epoxy resin (Dai Nippon Ink Chemical Industry Co., Ltd., trade name: T -154) was painted and baked in 5μ.
After that, the other side is PP-extruded by T-die extrusion.
Was laminated. At this time, a PP-PE copolymer resin (Mitsui Petrochemical Industry Co., Ltd., trade name: ADMER QE-050) modified with maleic acid to improve the adhesiveness is applied to the steel sheet side.
Is extruded at a thickness of 20 μm, and PP (Mitsui Petrochemical Industry Co., Ltd., trade name PP L-840) is applied to the
Coextruded in the range of 100μ thickness. An 18-liter can was manufactured using this PP laminated steel sheet. After blanking, slicing, and framed, a polyolefin-based thermoplastic elastomer (Mitsui Petrochemical Co., Ltd., trade name P401) is applied to the side seam in terms of resin solid content of 20 to 50 μm.
Applied. Thereafter, the mixture was heated to 100 to 130 [deg.] C. to remove the solvent, and then rock seamed by a usual method.
Subsequently, after the lock seam portion was heated and joined under various conditions, the can lid and the can bottom plate were double-wrapped to obtain an 18-liter can. The adhesive was not applied to the double wound portion of the can lid and the can bottom plate, and airtightness was secured by a self-fusion method of the resin coated on the steel plate. The wound portion was heated at 170 ° C. for 5 seconds after the wound. The airtightness of the obtained cans and the adhesive strength of the side seam portions were investigated. Table 1 shows the results.

[0022]

[Table 1]

* 1 Resin thickness indicates the total thickness of the lower resin and the upper resin (the value obtained by subtracting 20 μ from the total thickness is the upper resin thickness). The melting point of the lower layer PP-PE copolymer resin is 1
53 ° C., the melting point of the upper layer PP is 162 ° C., and T is 162 ° C.
° C.

* 2 The thickness of the adhesive after heating and drying was indicated. After the bonding, the resin is melted, so that the thickness is slightly reduced.

* 3 The temperature measured by attaching a thermocouple to the inner surface of the can at the lock seam portion is displayed.

* 4 Adhesive strength was measured by setting the rock seam part to width 1
It was cut to 0 mm and the shear strength was measured. 50 kg or more was judged to be acceptable.

* 5 An 18-liter can is filled with 5% saline,
After being lifted by 15 cm, it was dropped on a concrete floor. Thereafter, the can lid was removed, a stainless steel rod of 10 mmφ was placed in the center, and a voltage of about 6 V was applied using the stainless rod as a cathode and the can body as an anode. At this time, the current flowing between the electrodes was measured. 0.1 mA or less was regarded as a pass.

* 6 Water Detection Test Method (Pressure Leak Test) After manufacturing an 18-liter can, high-pressure air at a pressure of 3.0 kg / cm ² was injected from the mouthpiece. The can was submerged in a state where high-pressure air was injected thereinto, and leakage of the can body and the can lid tightly tightened portion was inspected.

[0029]

The can made by the method of the present invention has excellent airtightness, and is excellent in corrosion resistance because the inner surface is coated with a thermoplastic resin containing polyolefin as a main component. It is possible.

In this method, an adhesive resin dispersed in a solvent is used, so that a conventional adhesive can manufacturing equipment using a solvent-type adhesive can be used as it is. Instead, a highly corrosion-resistant metal container can be manufactured simply by applying a laminated steel sheet.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a lock seam portion.

FIG. 2 is a view showing a metal container.

[Explanation of symbols]

 1 Metal container A Steel plate B Thermoplastic resin containing polyolefin as main component C Adhesive X Double tightening part Y Lock seam part

Claims (1)

(57) [Claims] 1. A method for forming a can body by side-seaming a resin composite steel sheet coated with a thermoplastic resin containing polyolefin as a main component at a thickness of 30 μm or more and 120 μm or less on at least one surface of the steel sheet by a rock seam method and heat-fusing the same. Applying an adhesive made by dispersing an amorphous polyolefin resin with a melting point lower than the melting point of the thermoplastic resin containing polyolefin as the main component, which is coated on the steel sheet, to the place where the rock seam of the steel sheet for can body is used After the solvent is removed by heating, a lock seam process is performed, and the lock seam portion is heated at a temperature of not higher than T-50 ° C or higher for a thermoplastic resin having a polyolefin as a main component and having the lock seam portion coated on the steel plate for 2 seconds or more. A method for forming a can body of a highly corrosion-resistant metal container, wherein the lock seam portion is fusion-bonded.