JP3027059B2 - Method for producing easy-open lid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal container lid, and more particularly to an easy-open lid which can be easily opened manually or partially on the entire surface of a can lid. Used for applications.

[0002]

2. Description of the Related Art An easy-open can lid, which can easily open a part or substantially the entire surface of a container lid by hand, is of a tear-off type in which a handle and an opening piece are torn off and separated from a can body, and both a handle and an opening piece are opened. A stay-on tub method that remains fixed to the can body after the can has been put to practical use. In either system, most easy-open can lids are manufactured from aluminum plates for manufacturing technology reasons, and steel plates are currently used for some limited applications.

[0003] As a typical example of the prior art, a coated aluminum plate or a steel plate is used as a material, and after punching into a basic lid shape, the lid body is placed on a flat lower mold, and a required contour shape is formed from the upper surface thereof. By pressing a sharp blade having the cutting edge into the lid body, an opening piece surrounded by a cutting guide groove having a V-shaped cross section is formed as shown in FIG.

[0004] With regard to the formation of the cutting guide groove, it is necessary to sharply press the sharp blade to reach about half to 2/3 of the plate thickness before processing, and the depth of the cutting guide groove is very important. That is, if the depth of the cutting guide groove is too shallow, the can opening property is poor, and if it is too deep, the impact strength against external shocks is insufficient, so that considerable accuracy is required.

[0005] Therefore, although a considerable precision is required for a machining tool, a sharp pressing of a sharp blade is required, so that the tool life is a problem. In particular, a steel sheet has a drawback that the tool life cannot be maintained. In addition, in order to ensure corrosion resistance to the contents or to prevent the occurrence of rust on the outer surface, repair painting is required for portions where the metal surface is exposed by processing the cutting guide grooves.

As a measure for extending the life of a tool, Japanese Unexamined Patent Publication No.
As disclosed in JP-A-70434 and JP-A-57-175034, a method of forming a cutting guide groove by composite extrusion has been proposed. This known method was premised on the use of a steel sheet, and was an effective measure for extending the life of the tool.However, since the cross-sectional structure of the cutting guide groove was complicated, cutting was not performed by a normal spray coating method. There was a drawback that the paint did not spread to all parts in the guide groove and that sufficient corrosion resistance could not be obtained even if repair painting was performed.

[0007]

As described above, the easily openable lid used is a pre-painted one, regardless of whether an aluminum plate or a steel plate is used as the material. Further, after the processing, it is necessary to perform repair painting on a portion where the metal surface is exposed by the processing.

[0008] In the coating, not only the baking process is complicated, but also a long heating time is required for baking, and a large amount of solvent contained in the paint is discharged during the baking process. However, there is a problem that the solvent discharged from the surface must be incinerated in a special incinerator. Furthermore, heating and solvent incineration in paint baking are also problems from the global environment because carbon dioxide is emitted.

Further, there are the following major problems in the recycling process. It is a material for the current easy-open lid,
For both aluminum and steel sheets, vinyl chloride paints, especially vinyl chloride organosols, are widely used as paints because of their excellent workability, corrosion resistance, retention of content flavor, and price. In addition, a coating film made of a vinyl chloride-based paint generates extremely toxic dioxin by heating and burning. Therefore, in an easy-opening lid using a vinyl chloride-based paint at present, it is necessary to consider the generation of dioxin when the used metal can is recovered and incinerated or re-melted. At present, research and development of paints to replace vinyl chloride paints seems to be proceeding enthusiastically, but there is no promising thing that can be used for a wide range of contents.

Regarding recycling, a so-called “monometal can” in which a metal body and a can lid are formed of the same material can be said to be a product suitable for recycling. The open lid is mostly made of aluminum. On the other hand, most of the can lid except the can body and the easy-open can lid are made of steel plate. For this reason, it has excellent openability,
There is a strong need for a method that can produce not only aluminum easy-open can lids that require no painting and excellent corrosion resistance but also steel plate easy-open can lids with high productivity.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the shoulder radii of the upper and lower dies for forming the cutting guide grooves forming the opening piece shape have a shoulder radius of 0.1 to 1 mm. .
Using a mold having a thickness of 0 mm, a steel plate or an aluminum plate having a resin film having a thickness of 10 to 100 μm and a breaking elongation of 100% or more on both surfaces is formed by pressing at the shoulder radius portions of the upper and lower molds. The cutting guide groove is formed by reducing the metal thickness of the thin portion to 1/2 or less of the metal thickness before processing, and the resin film present on both surfaces of the steel plate or aluminum plate used is made of polyethylene. , A polypropylene, a polyester, an ionomer, or another thermoplastic resin.

Hereinafter, the present invention will be described in detail. The present invention is an invention achieved by combining a material and a processing method. First, the material will be described.

The steel sheet used in the present invention usually has a thickness t.
₀ : It is in the range of _{0.150 to} 0.300 mm, and has mechanical properties such as hardness ( _HR30T ) of 54 to 68 and elongation of about 10 to 40%.

On the surface of this steel sheet, Sn, Cr, Ni, A
One or two or more metals of l and Zn are plated, and a resin film with excellent adhesion, workability, and corrosion resistance is formed on the chromate-treated film to eliminate the need for repair painting after lid manufacturing. It is laminated.

Examples of the steel sheet to be used specifically, the adhesion amount of 0.5 to 3.0 g / m ² tin-plated steel sheet after subjected to chemical conversion treatment tin plating, the coating weight 0.3 to 2.0 g / m ² Nickel-plated steel sheet subjected to chemical treatment after nickel plating, Sn
And 0.5 to 2.0 g / m ² , respectively,
Sn / Ni-plated steel sheet subjected to chemical conversion treatment after plating in the order of 0.01 to 0.5 g / m ² with Ni and Sn, 50 to 200 mg / m ^{2 of} metal Cr adhesion, 5 to 30 mg / m ^{2 of} Cr oxide
² There is a chromium-chromate treated steel plate which is usually called TFS (Tin Free Steel).

The aluminum plate used in the present invention usually has a plate thickness t _{0 of} 0.150 to 0.300 mm and an elongation of about 5 to 30% having mechanical properties. Is done.

The aluminum plate is subjected to electrolytic chromic acid treatment and immersion chromic acid treatment, and has an adhesive property on the chromate-treated film in order to eliminate the need for repair coating after lid manufacturing.
A resin film with excellent workability and corrosion resistance is laminated. The chromium adhesion amount is preferably in the range of 3 to 50 mg / m ² of Cr oxide, more preferably 5 to 30 mg / m ² . The amount of chromium metal is preferably in the range of 10 to ²⁰⁰ mg / m2.

The resin laminated on both sides of the above-mentioned steel plate or aluminum plate has a breaking elongation of 100% or more and a thickness of 10% or more.
~ 100μ is required. This resin film completely adheres to the substrate even after processing, because the resin film follows the substrate with good adhesion and has excellent workability when processing the cutting guide groove by press molding. It is an important entity that does not require repair painting.

As the physical properties of the resin film, the elongation at break is 100%
If it is less than 1, it is not preferable because a large number of defects are generated in the resin film due to insufficient elongation with respect to the molding of the thin portion at the time of the press working described later. Therefore, the lower limit is 100%. Preferably, it is 200% or more. The elongation characteristics of the laminated resin film were determined by peeling the resin film from the substrate
A value measured by a method according to SC2318 is employed.

When the thickness of the resin film to be laminated is too thin, the film is liable to be broken by processing.
In particular, when the film has a thickness of 80 μ or more, the corrosion resistance after processing proceeds in a better direction. However, when the cutting guide groove is broken (when the can is opened), the film elongates long before the breaking, and the film remains phenomenon ( Adopting an excessively thick film is disadvantageous because it easily causes feathering. Therefore, it is set in the range of 10 to 100 μ. Considering performance stability and economics, 16 to
Those in the 60 μ range are particularly effective.

In the present invention, a resin film composed of one or more of thermoplastic resins such as polyethylene, polypropylene, polyester, polyamide, and ionomer is used in view of performance such as food hygiene, corrosion resistance, and processability. Some of the above resins will be supplementarily described below.

The polyester resin in the present invention is a linear thermoplastic polyester obtained by polycondensation of a dicarboxylic acid and a diol, and is represented by polyethylene terephthalate. As the dicarboxylic acid component, terephthalic acid, isophthalic acid, phthalic acid, adipic acid, sebacic acid, azelaic acid, 2,6-naphthalenedicarboxylic acid,
It is a single or mixture of decanedicarboxylic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid and the like, and the diol component is a single or mixture of ethylene glycol, butanediol, decanediol, hexanediol, cyclohexanediol, neopentyl glycol and the like. It may be a copolymer of two or more dicarboxylic acid components or diol components, or a copolymer with another monomer or polymer such as diethylene glycol or triethylene glycol.

The polyamide resin is a single or a mixture of nylon 6, nylon 7, nylon 11, nylon 66, nylon 610, nylon 612, polym-phenylene isophthalamide and the like.

The ionomer resin is a resin in which a copolymer of an α-olefin and an unsaturated carboxylic acid is cross-linked between molecular chains with metal ions, and the α-olefin component is a homopolymer such as ethylene, propylene, butene and pentene. Or a mixture, wherein the unsaturated carboxylic acid is acrylic acid,
It is a single or a mixture of methacrylic acid and the like, and the metal ion component is a single or a mixture of sodium, zinc and the like.

Further, additives such as a plasticizer, an antioxidant, a heat stabilizer, an inorganic particle, a pigment, and an organic lubricant are added to the resin film used in the present invention, if necessary.

The resin film is laminated on both sides of the metal plate by bonding the film itself by heat or applying a thermosetting adhesive.

Next, a working method will be described. The formation of the cutting guide groove as shown in FIG. 6 by the conventional sharp blade pressing method is not preferable because the resin film is broken and repair coating after molding is required.

The present inventors have proposed a method of forming a cutting guide groove which ensures easy opening without breaking the resin film by using a shoulder radius of an upper and lower mold for forming a cutting guide groove which forms an opening piece. Using a mold that is 0.1 to 1.0 mm,
As shown in FIG. 2, a steel plate or an aluminum plate whose both surfaces are coated with a resin is pressed and formed at the shoulder radius portions of the upper and lower molds, and the metal thickness of the thinnest part is set to one of the metal thickness before processing. It has been found that the method of forming the cutting guide groove by reducing the thickness to / 2 or less is optimal.

The shoulder radius of the upper and lower molds for forming the cutting guide grooves is
The reason for setting the thickness to 0.1 to 1.0 mm will be described. If the shoulder radius is smaller than 0.1 mm, the portion of the shoulder radius is sharp, so that the laminated resin film of the workpiece is scratched or broken during processing. When pressing is performed under a condition of more than 1.0 mm, the material is pressed in a wide range. In this pressed portion, the adhesion between the metal and the resin is deteriorated by the processing. Forming a poor adhesion portion more than necessary causes feathering. Further, the poor adhesion portion of the coating film is not preferable from the viewpoint of corrosion resistance.

During processing, the peripheral edge of the opening piece is pressed between the upper and lower dies so as to reach a desired thickness, thereby forming a thin portion having a gently changing plate thickness. The metal thickness of the thinnest part should be 以下 or less, more preferably 以下 or less of the metal thickness before processing from the openability side.

By this processing, the breaking position at the time of opening the can is determined. However, in order to improve the openability and to make the shape of the opening after opening the can desirable, the opening piece portion which is extruded upward or downward is used. Is pushed back to a position close to the previous level. There are various processing methods for the push-back processing. As one example, as shown in FIG. 3, there is a method of bending a thin portion having a gradual change in plate thickness formed by the above-mentioned pressing process into a V-shaped cross section to form a thin cutting guide groove. Further, there is a method of forming a desired shape of the opening by inserting a bead or a step near a thin portion having a gradual change in plate thickness formed by the above-mentioned pressing.

The depth or the thickness of the thinnest portion of the cutting guide groove can be set to a desired value according to the workability of the material by setting the processing conditions as required. Processing conditions are selected according to the workability of the plate and the laminate film.

In a series of these processing steps, the resin film having the above-mentioned properties is uniformly stretched together with the base material, and no processing defects are generated. Therefore, there is no need for repair coating after processing, and good corrosion resistance is ensured. Can be. Further, according to the method of the present invention, since the processing is based on press working such as extrusion or push-back by a shoulder radius portion having a smooth curved surface that is convex to each other, the tool life seen in the pressing method of the sharp blade is reduced. There are no problems, and excellent productivity is guaranteed.

The present invention is characterized mainly by optimizing a cutting guide groove present at a peripheral portion of an opening piece. A tear-off system in which a handle and an opening piece are separated from a can body, a handle and an opening are provided. It is possible to apply both types of the stay-on tub method in which both pieces remain fixed to the can body even after the can is opened.

[0035]

Embodiments of the present invention will be described below.

Example 1 A thin steel plate having a thickness of 0.250 mm and a hardness of 62 (H _R30-T ) was subjected to electrotin plating with an adhesion amount of 2.8 g / m ² . After tin is heated and melted to obtain a surface having a specular gloss, an electrolytic post-treatment is carried out in a treatment bath mainly composed of chromic acid, and metallic chromium 12 mg / m ² and a hydrated chromium oxide 12 mg / m 2 A chromate film having ² (as Cr) was formed. After washing and drying, the steel sheet is heated to obtain a two-layer polyester resin having a different melting point, the upper layer having a thickness of 37 μm, the lower layer having a thickness of 3 μm, and the lower layer resin having a lower melting point than the upper layer resin and containing the ionomer.
A resin film of 0μ was laminated on both sides of the steel sheet. The elongation of the film measured by peeling after lamination was 450%.

When a steel plate having a polyester resin film on both sides is formed into an easy-open can lid as shown in FIG. 1, as shown in FIG. A portion corresponding to the opening piece 2 was extruded upward by pressing a key portion of the lid body with a press using upper and lower dies A5 and A6 of 5 mm.

At this time, the connecting piece 7 connecting the opening piece 2 and the lid main body 1 was processed so as to form a thin portion having a gentle change in plate thickness by pressing.

Next, as shown in FIG. 3, the processed lid main body 1 is placed on a lower mold B11 having a convex portion 13 so that the continuous piece 7 and the convex portion 13 overlap with each other. B1
Pressed at zero.

As a result of this operation, the continuous piece 7 having a gradual change in plate thickness as shown in FIG. 4 is bent downward in a V-shape from a substantially middle portion and protrudes into the concave groove 12. Thus, a thin cutting guide line 4 having a V-shaped cross section is formed at the peripheral edge of the opening piece 2 on the lower surface of the lid main body 1.

In the present embodiment, the thickness of the thinnest steel plate is 48
μ. The resin film was formed in the same manner as the steel plate, and the film thickness remaining on the surface of the thinnest portion was about 8 μm on both surfaces.

The easy-open can lid thus formed was subjected to an evaluation of the openability by measuring the tearing force of the opening piece and an electric current test for examining the degree of destruction of the resin film on the inner and outer surfaces of the can. . The can openability (the force to raise the handle and the force to tear off the opening piece) is excellent at 1.7 kg or less. there were. Further, there was no visually noticeable feather around the cut end of the broken cutting guide groove.

Example 2 A 20 μm nylon 6 film was laminated on both sides of the same steel plate as in Example 1 using a 50 μm modified polypropylene-polyethylene copolymer resin film as an adhesive layer. The thickness of the resin film was 70 μ. The elongation of the film measured by peeling after lamination was 350%.

A steel plate having a resin film on both sides is formed by using upper and lower molds A5 and A6 having a shoulder radius of 0.2 mm as shown in FIG.
As shown in (1), a portion corresponding to the opening piece 2 was extruded upward by pressing.

At this time, the peripheral portion of the opening piece 2, the lid main body 1 and the connecting piece 7 were processed so as to form a thin portion having a gentle change in plate thickness by pressing.

Next, as shown in FIG. 5, a lower mold C15 having convex portions 18 at portions corresponding to both sides of the connecting piece 7 of the opening piece 2 is provided.
The upper die C having the concave portion 17 corresponding to the convex portion 18 of the lower die C15 is placed on the lid main body 1 while the lid main body 1 is placed in the state of the downwardly expanding inclination.
Pressed at 14.

By this operation, beads were formed inside and outside the opening guide groove, and the lid main body 1 and the opening piece 2 became the same height except for this bead portion. A thin cutting guide line 4 is formed on the upper surface of the main body 1 at the periphery of the opening piece 2.

In the present embodiment, the thickness of the steel plate at the thinnest portion is 55
Adjusted to μ. The resin film was formed in the same manner as the steel plate, and the film thickness remaining on the surface of the thinnest portion was about 15 μm on both surfaces.

The can openability was 1.8 kg or less and the can was opened without any problem. The energization value of the resin film was 0.2 mA on the inner surface and 0.1 mA on the outer surface.
2 mA was practically satisfactory. Further, there was no visually noticeable feather around the cut end of the broken cutting guide groove.

Example 3 The surface of an aluminum plate made of alloy of type H39 having a thickness of 0.280 mm and having a thickness of 0.280 mm was subjected to an electrolytic post-treatment in a treatment bath mainly composed of chromic acid to form 12 mg / m ^{2 of} metallic chromium and an upper layer thereof. A chromate film having a hydrated chromium oxide of 12 mg / m ² (as Cr) was formed. After washing and drying, this aluminum plate is heated and the upper layer contains a 20 μm thick ionomer with a two-layer polyester resin having different melting points, the lower layer has a lower melting point than the 20 μm thick upper layer resin, and a total thickness of 40 μm. Resin films were laminated on both sides of the aluminum plate. The elongation of the film measured by peeling after lamination was 200%.

An aluminum plate having a resin film on both sides was processed in the same manner as in Example 1 by using upper and lower dies A5 and A6 each having a shoulder radius of 0.6 mm. In this embodiment,
The thickness of the thinnest aluminum plate was adjusted to be 95 μm. The resin film was formed in the same manner as the aluminum plate, and the film thickness remaining on the surface of the thinnest portion was about 14 μm.

The can opening property was 1.7 kg or less and the can was opened without any problem. The energization value of the resin film was 0.3 mA on the inner surface and 0.1 mA on the outer surface.
3 mA was practically satisfactory. Further, there was no visually noticeable feather around the cut end of the broken cutting guide groove.

Example 4 The same aluminum plate as in Example 3 was coated with a thermosetting polyester paint and baked. The thickness of the paint film is 1
The elongation of the film measured at 5 µm after peeling after lamination is 120
%Met.

An aluminum plate having a resin film on both sides was processed in the same manner as in Example 1 using upper and lower dies A5 and A6 each having a shoulder radius of 0.8 mm. In this embodiment,
The thickness of the thinnest part of the aluminum plate was adjusted to 100 μ. The resin film is molded in the same way as an aluminum plate,
The thickness remaining on the surface of the thinnest portion was about 6 μm.

The can openability was 1.8 kg or less and the can was opened without any problem. The energization value of the resin film was 0.8 mA on the inner surface and 0.1 mA on the outer surface.
9 mA was satisfactory enough for practical use. Further, there was no visually noticeable feather around the cut end of the broken cutting guide groove.

Comparative Example 1 On the same plated steel sheet as in Example 1, a two-layer polyester resin having a different melting point was used. The upper layer had a thickness of 20 μm, the lower layer had a thickness of 20 μm, and the lower layer resin had a lower melting point than the upper layer resin. Was laminated on both sides of the steel sheet. The elongation of the film measured by peeling after lamination was 350%.

A steel plate having a resin film on both sides was processed in the same manner as in Example 1 by using upper and lower dies A5 and A6 each having a shoulder radius of 0.08 mm. In this comparative example, the thickness of the steel plate at the thinnest part was adjusted to be 57 μm.

The can openability was 1.8 kg or less, and the can was opened without any problem. However, the energization value of the resin film was very large at 104.8 mA on the inner surface and 95.6 mA on the outer surface. Many defects were found in the film, and even if the shoulder radius was too small, a practically usable one could not be obtained.

Comparative Example 2 On the same plated steel sheet as in Example 1, a two-layer polyester resin having a different melting point, the upper layer having a thickness of 20 μm, the lower layer having a thickness of 20 μm, and the lower resin having a lower melting point than the upper resin was an ionomer. Was laminated on both sides of the steel sheet. The elongation of the film measured by peeling after lamination was 310%.

A steel plate having a resin film on both sides was processed in the same manner as in Example 1 by using upper and lower molds A5 and A6 each having a shoulder radius of 1.2 mm. In this comparative example, the thickness of the steel plate at the thinnest part was adjusted to be 57 μm. The resin film is formed in the same manner as a steel plate, and the film thickness remaining on the thinnest part surface is about 6
μ.

The openability was excellent at 2.0 kg or less, and the current value of the resin film was 1.2 mA on the inner surface and 1.4 mA on the outer surface. There was severe film residue around the periphery, giving an uncomfortable appearance. Even if the shoulder radius was too large, there was still a problem in practicality.

Comparative Example 3 The same aluminum plate as in Example 3 was coated with a thermosetting polyester paint and baked. The thickness of the paint film is 8
μ, the elongation of the film measured after peeling after lamination is 120%
Met.

An aluminum plate having a resin film on both sides was processed in the same manner as in Example 1 by using upper and lower molds A5 and A6 each having a shoulder radius of 0.5 mm. In this comparative example,
The thickness of the thinnest part of the aluminum plate was adjusted to 100 μ.

The can openability was 1.8 kg or less, and the can was opened without any problem. The current value of the resin film was very large at 100.8 mA on the inner surface and 112.9 mA on the outer surface, and the resin film of the cutting guide portion was very large. Many defects were observed and were not practically usable.

Comparative Example 4 A 60 μm nylon 6 film was laminated on both sides of the same steel plate as in Example 1 using a 60 μm modified polypropylene-polyethylene copolymer resin film as an adhesive layer. The thickness of the resin film was 120 μ. The elongation of the film measured by peeling after lamination was 450%.

A steel plate having a resin film on both surfaces was processed in the same manner as in Example 1 by using upper and lower dies A5 and A6 each having a shoulder radius of 0.5 mm. In this comparative example, the thickness of the steel plate at the thinnest portion was adjusted to be 55 μm. The resin film was formed in the same manner as the steel plate, and the film thickness remaining on the surface of the thinnest portion was about 26 μm on both surfaces.

The openability of the molded product (the force for raising the handle and the force for tearing off the opening piece) is excellent at 2.0 kg or less, and the amount of electricity supplied to the resin film is about 1.5 mA, which is practical in terms of corrosion resistance. However, it was found that the film was severely left around the cut edge of the cutting guide groove that was broken at the time of opening, giving an uncomfortable appearance, and there was a problem in practicality.

Comparative Example 5 On the surface of the same aluminum plate as in Example 3, a two-layer polyester resin having a different melting point and an upper layer having a thickness of 2
A resin film having a thickness of 0 µm, a lower layer having a thickness of 20 µm, and a lower layer resin having a lower melting point than the upper layer resin and having a total thickness of 40 µm containing an ionomer was laminated on both sides of the aluminum plate. The elongation of the film measured by peeling after lamination was 85%.

An aluminum plate having a resin film on both sides was processed in the same manner as in Example 1 by using upper and lower molds A5 and A6 each having a shoulder radius of 0.5 mm. In this comparative example,
The thickness of the thinnest part of the aluminum plate was adjusted to 100 μ.

The can openability was 1.8 kg or less and the can was opened without any problem. The energization value of the resin film was very large at 104.8 mA on the inner surface and 98.9 mA on the outer surface. Many defects were observed and were not practically usable.

[0071]

As described above, the method for manufacturing an easily-openable lid according to the present invention uses a material obtained by laminating a resin film on a steel plate or aluminum, and presses the thin portion by pressing without using a sharp blade. By adopting the method of forming the cutting guide groove by the forming method, there is no need to perform any painting in the manufacturing process, and the major problems of the prior art, such as the problem of the tool life of the machining tool and the uneasiness of the corrosion resistance, etc. It can be completely eliminated.

In particular, if a steel easy-open can lid is put to practical use, it will be possible to convert it into a “monometal can”, thereby providing the market with products suitable for recycling in response to recent global environmental problems. Is possible. Naturally, the steel sheet itself is excellent in economic efficiency, and it is expected that by using steel plates for both the can body and the can lid, the product will be more economical and easy to reuse as resources.

[Brief description of the drawings]

FIG. 1 is a perspective view of an example of a can lid according to the present invention.

FIG. 2 is a longitudinal sectional view showing an embodiment of the present invention in the order of steps.

FIG. 3 is a longitudinal sectional view showing an embodiment of the present invention in the order of steps.

FIG. 4 is a longitudinal sectional view showing an embodiment of the present invention in the order of steps.

FIG. 5 is a longitudinal sectional view showing a state where beads are formed on both sides of a cutting guide groove.

FIG. 6 is a partially enlarged view showing a cutting guide groove having a V-shaped cross section according to the related art.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 lid body 2 opening piece 4 cutting guide line 5 upper mold A 6 lower mold A 7 continuous piece 8 upper mold R section 9 lower mold R section 10 upper mold B 11 ... lower mold B 12 ... concave groove 13 ... convex part 14 ... upper mold C 15 ... lower mold C 16 ... bead 17 ... concave part 18 ... convex part

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-124551 (JP, A) JP-A-4-91834 (JP, A) JP-A-58-171339 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B21D 51/44

Claims (2)

(57) [Claims] An upper and lower mold for forming a cutting guide groove forming an opening piece has a shoulder radius of 0.1 to 1.0 mm. 10 to 100
Cutting guide groove by pressing and forming a steel plate or an aluminum plate having a resin film with a μ, elongation at break of 100% or more on both sides, and reducing the metal thickness of the thinnest part to 1/2 or less of the metal thickness before processing. Forming a readily openable lid. 2. A resin film present on both surfaces of a steel plate or an aluminum plate, comprising one or more of thermoplastic resins such as polyethylene, polypropylene, polyamide, polyester, and ionomer. 2. The method for producing an easily openable lid according to 1.