JP2005254627A - Laminated metal sheet for can lid and can lid manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated metal sheet for a can lid excellent not only in general processability such as score processing or the like but also in processability in local bending processing performed after heat treatment. <P>SOLUTION: The laminated metal sheet for the can lid has an organic resin layer formed by superposing a main layer comprising a polyester resin and a sub-layer comprising a resin with a glass transition point (Tg) of 5°C or below one upon another in a laminar state directly or through an adhesive layer. Since the organic resin layer is formed by superposing the main layer comprising the resin satisfying general processability such as rivet processing or score processing and the sub-layer comprising a resin excellent in local bending processability one upon another, excellent local bending processability is obtained almost without damaging general processability when the organic resin layer is adapted to an easy open end type can lid material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated metal plate that is used as a can lid material for beverage cans, food cans, and the like, and particularly suitable for an easy open end type can lid, and a method for producing a can lid using the laminated metal plate.

  In recent years, the resin coating of can materials has been laminated, and for example, for beverage cans, the bottom and can body of a two-piece can and the can body of a three-piece can have been laminated. Reasons for the lamination of can materials in this way include rationalization of manufacturing processes by omitting painting and baking, lower environmental impact by omitting solvent drying processes (baking processes), and inclusion in paints And avoidance of elution of environmental hormones such as BPA. In particular, regarding environmental hormones, there is a report that a very small amount of BPA affects the human body. In general, food cans have more BPA elution than beverage cans, and it is expected that laminating will continue in the field of food cans.

However, in the actual market, for example, in the case of beverage cans, the lamination of the bottom part of the two-piece can and the can body part is proceeding, whereas the lamination of the top lid and the bottom cover of the three-piece can is proceeding. Not. Similarly, food can laminate lids are not common. It is considered that the reason why the laminating of the lid material does not proceed in this way is because the problems unique to the can lid have not been solved.
There may be various reasons for preventing the laminating of the lid, but one of the most difficult issues when laminating the lid is that severe processing may be performed after the printing process. is there. In recent years, the top lid for beverage cans is mainly a steion tab type easy open end lid, and for food cans, easy open end lids that do not require can openers are increasing. Most of the easy open end type lids for food cans are printed with instructions on how to open the lid. Usually, this printing is performed before processing of the lid, and thereafter, it is formed into a lid shape (cover manufacturing). However, since heat is applied during printing in the printing process, the laminate film (resin layer) deteriorates, and the film cannot follow the processing in the subsequent lid making process, resulting in film breakage, resulting in deterioration in corrosion resistance. End up.

  As mentioned above, laminating of the lid material in the market has not progressed, but many proposals have been made on this, and this indicates that there is a big problem that remains unresolved compared to the size of demand. . In particular, many proposals have been made regarding a manufacturing method of an easy open-end lid that does not require repair coating, which is considered to be the biggest problem, and a laminated steel sheet for the lid used therefor. For example, in Patent Document 1, the polyester resin is applied only to the inner surface side to achieve non-repair of the inner surface. However, this method requires not only the exterior surface to be repaired, but also does not take into account film degradation due to the printing process after lamination, and is not applicable to lids that are printed after lamination. difficult.

Patent Document 2 discloses an easy-to-end easy-open-end lid film in which the degree of biaxial orientation of the polyester film is controlled, but this also takes into account the deterioration of the film due to the printing process after lamination. Not. In addition, the biaxially oriented film has no provisions regarding the state after lamination, despite the fact that the orientation state after lamination largely dominates the properties, and a specific lid-making method such as a score processing method is also specified. It has not been.
In addition, Patent Document 3 and Patent Document 4 define film physical properties (such as plane orientation) after lamination, and there are disclosures that take into consideration the workability after heat treatment. The lid making method is not specified, and according to the investigation by the present inventors, it has been found that sufficient corrosion resistance cannot be obtained when general score processing is performed. Furthermore, Patent Document 5 has provisions relating to a score processing method and a resin film, but this also does not take into account deterioration of the film due to a printing process after lamination.

JP 2001-122258 A JP-A-9-309146 JP-A-5-77358 JP-A-5-77359 JP 2000-301268 A

  When the plate thickness distribution after the lid making process in the easy open end lid was examined, the largest change in the plate thickness occurred in a portion of a breaking groove called a score (hereinafter referred to as a score portion). This score part is usually repaired by repair coating, but there is also a method of avoiding repair coating by devising the score processing method and the configuration of the laminated steel plate as disclosed in Patent Document 5 and the like. However, according to the results of the investigation by the present inventors, even if the film (resin layer) breakage at the score part is eliminated by using a specific laminated steel sheet and the score processing method, the film breaks at other processed parts. Has been found to occur. When the rupture site was examined in detail, the film rupture occurred on the yama side of the locally bent processed portion, where there was almost no change in the plate thickness. In lid manufacturing, it is widely used to provide bent parts (for example, beads and embosses) in the flat plate part (panel part) for the purpose of increasing the rigidity of the lid or absorbing the surplus due to score processing. However, it has been found that film breakage tends to occur on the yama side of the processed part with such bending deformation even if the degree of processing is slight. This phenomenon is a peculiar phenomenon seen in laminated steel sheets after heat treatment (for example, laminated steel sheets that have been baked in the printing process after lamination), and it is clearly different from the processing behavior of unheated laminated steel sheets. understood. Therefore, it is considered that the processing characteristics after the heat treatment are indispensable for the lid material that requires the printing process, and a coating film specific to the lid corresponding to this is necessary. Hereinafter, this special processing is referred to as “local bending processing”, and other processing is referred to as “general processing” to be distinguished.

The object of the present invention is a laminated metal for can lids that is excellent not only in general processability such as score processing but also in local bending performed after heat treatment when applied to an easy open end type can lid material. To provide a board.
Another object of the present invention is to provide a can lid manufacturing method capable of manufacturing an easy open-end can lid of good quality using the laminated metal plate as described above.

  As mentioned above, it was thought that the film breakage in the locally bent portion of the laminated steel sheet was caused by the deterioration of the film during heat treatment, so a detailed investigation and examination of the cause using polyethylene terephthalate resin laminated steel sheet Went. As a result, it was found that spherulites were formed during the heat treatment in the polyethylene terephthalate resin. In general, it is known that when spherulites are formed, the film becomes brittle, and the formation of such spherulites degrades the film, and the film is broken during lid-making after heat treatment (printing process). Estimated. It has also been found that it is difficult to suppress the formation of spherulites in a general polyethylene terephthalate resin even if the baking conditions in the printing process are slightly changed.

  Therefore, the present inventors have made the following investigations in order to obtain a film structure that can be made with a lid without causing film breakage even when spherulites are formed. In laminated steel sheets of polyethylene terephthalate resin, since it is known that the degree of crystal orientation has a great influence on the film properties, the present inventors first tried to solve the problem by adjusting the degree of crystal orientation. investigated. By controlling the lamination conditions of the biaxially stretched polyethylene terephthalate, polyethylene terephthalate films having various orientations can be prepared. Based on this, various laminated steel sheets having different orientations were produced. The laminated steel sheet was subjected to a heat treatment equivalent to a printing and baking process to form an easy open end lid. As a result, it was found that a high degree of orientation shows a good result for the local bending workability in question. In general processing, the lower the orientation, the better the workability, but in this local bending, the opposite result was obtained. This means that if the processing of the lid is only the local bending process in question, or if the processing level is sufficiently small even when other general processing is involved, the degree of orientation is appropriately set by the above-described method. This means that lid molding is possible. In fact, it has been found that there are cases where this coating design can adequately handle the bottom lid. However, the present invention is not intended to cover materials with such a processing level, but to process under severe processing conditions such as local open processing and general processing with a large degree of processing, such as an easy open end cover. It is also intended for lids to which a non-repair type score processing with a high degree of processing (for example, score processing using a curved mold) is applied.

Except for the local bending part, especially difficult parts in the lid making process of the easy open-end lid, when applying non-repair type score processing (for example, score processing with a curved die), the score processing part and rivet processing Part. The effect of spherulite generation by heat treatment is not negligible for score processing, but the effect of the amount of oriented crystals is still much greater. Therefore, the score processing can be sufficiently handled by appropriately setting the amount of oriented crystals. The rivet processing portion is a processing portion to which rivet processing (processing to crush the overhang portion) is applied after the overhang processing is performed. The overhanging process shows the same tendency as the score process, and can be handled by appropriately setting the amount of oriented crystals. In general, it can be said that the processing is easier than the score processing. On the other hand, in the subsequent rivet processing, since an element of bending is added, the influence of spherulite generation by heat treatment cannot be ignored. However, the degree of processing tends to be lighter than the deformed portion of local bending. Therefore, the rivet processing has both a general processing element and a local bending process element, but it can be said that it is a mild process compared to the processing of the score part and the local bending part.
On the other hand, the effect of spherulites is very large for local bending. For this reason, by simply adjusting the amount of oriented crystals, it is not possible to achieve both the workability of a general processed portion and a locally bent portion that are severely processed.

  In view of the above problems, the present inventors pay attention to the fact that the local bending process has a very small deformation amount, and the sublayer (resin layer) made of a resin having excellent local bending deformability. If the film structure is attached to the main layer (resin layer), even if the bulk part (main layer part) of the film does not follow the local bending deformation, the resin in the sub layer part exhibits local bending deformability. I got the idea that the workability as a whole could be secured by supplementing. Of course, if the degree of local bending is large, it is difficult to compensate for the entire deformation only by deformation of the sub-layer part, and there is a possibility of rupture. There is little fear. In other words, if the local bending process is small, even if the local bending workability of the bulk part (main layer part) deteriorates due to the formation of spherulites, the sub-layer part with excellent local bending workability I thought it could be supplemented.

As a result of repeated experiments and examinations based on the above ideas, it has been found that the above-described processing characteristics can be realized by forming a film structure including the following specific sublayer and main layer.
The sub-layer portion may be a layer having excellent local bending deformability, but should not inhibit general workability such as rivet workability and score workability at the same time. As a result of investigating a resin suitable for the sub-layer portion from such a viewpoint, it was found that one having a low glass transition point (one sufficiently lower than the processing temperature) is excellent in local bending deformability. Such a resin having a low glass transition point cannot follow general processing such as rivet processing or score processing due to insufficient strength by itself, but when arranged as a sublayer, the main layer supplements the strength, so that the above It was found that general processing can be followed. In addition, as the main layer, it has been found that a polyester-based resin is suitable because it has a good balance between strength and extensibility and is excellent in general workability such as rivet workability and score workability.

The present invention has been made on the basis of the above findings, and the features thereof are as follows.
[1] A laminated metal plate having a multilayer organic resin layer on at least one side of the metal plate, wherein a part of the multilayer organic resin layer has a thickness of 9 to 25 μm made of a polyester resin. The other resin layer is a sublayer having a glass transition point (Tg) of 5 to 10 ° C. and having a thickness of 1 to 10 μm, and the main layer and the sublayer are directly or bonded. A laminated metal plate for can lids, characterized in that it has a film structure laminated in layers via layers.
[2] The laminated metal plate for can lids according to [1], wherein the main layer is made of a resin having polyethylene terephthalate as a basic skeleton, and the sub-layer is made of polyolefin.

[3] In the laminated metal plate for can lids according to [1] or [2], the main layer was obtained by condensation polymerization of a dicarboxylic acid component composed of terephthalic acid or / and isophthalic acid and a diol component composed of ethylene glycol. A laminated metal plate for a can lid, comprising a polyester resin, wherein the sub-layer is made of at least one selected from polyethylene, polypropylene, and ionomer.
[4] A method for producing an easy open end type can lid using the laminated metal plate for can lids according to any one of [1] to [3] above, wherein the radius of curvature of the tip is 0. A method for producing a can lid, wherein a fracture groove is formed using a curved mold having a curved surface of 1 to 1.0 mm.
[5] The method for producing a can lid according to the above [4], wherein the outer surface of the can lid material is printed before the lid making process.

In the laminated metal plate for can lids of the present invention, the laminated organic resin layer has a main layer composed of a resin that satisfies general processability such as rivet processing and score processing, and a sublayer composed of a resin excellent in local bending workability. Since the layers are stacked in layers, when applied to an easy open end type can lid material, excellent local bending workability can be obtained without substantially impairing general workability. For this reason, even when the lid is processed through the printing process, a can lid having excellent corrosion resistance can be produced without causing film breakage.
Further, according to the method for producing a can lid of the present invention, in the lid making process of an easy open end type can lid, it is possible to appropriately perform the processing of the score portion having the largest plate thickness change without causing film breakage. it can.

  The laminated metal plate for can lids of the present invention is a laminated metal plate having a multilayer organic resin layer on at least one side of the metal plate, and a part of the resin layer of the multilayer organic resin layer is made of polyester. A main layer of 9 to 25 μm thick made of a resin, and another part of the resin layer is a sublayer of 1 to 10 μm thick made of a resin having a glass transition point (Tg) of 5 ° C. or less, It has a film structure in which a main layer and a sub layer are layered directly or via an adhesive layer. In the present invention, the resin layer responsible for the original function of the film is referred to as a “main layer”, and the resin layer responsible for an additional function is referred to as a “sub-phase”. It is not related to the size of.

  The main function of the main layer is to ensure general workability such as rivet workability and score workability (particularly, workability in score processing using a curved mold). From the viewpoint of securing the property, a polyester resin is used as the resin constituting the main layer. This is because, for general processability such as rivet processability and score processability, an appropriate balance between stretchability and strength is important, but polyester resins are excellent in balance. The polyester resin of the main layer has a glass transition point (Tg) exceeding 5 ° C. for the purpose of the present invention. In the present invention, since the polyester resin as the main layer is inferior in local bending workability, a sublayer is provided as a means to compensate for this, and it is bothered if the glass transition point of the polyester resin layer is 5 ° C. or less. There is no point in providing a sublayer.

  As the polyester-based resin, a polyethylene terephthalate-based resin is preferable because it has a good balance of stretchability and strength for processing and is suitable for food hygiene. In lid processing, it is desirable that the film has a good balance between extensibility and strength. However, in general, elongation and strength are contradictory properties. When the elongation is good, the strength is low, and when the strength is high, the elongation tends to be poor. Among resins suitable for food hygiene, polyethylene terephthalate polyester resin is excellent in the balance between elongation and strength for lid processing. Specifically, a polyester resin obtained by condensation polymerization of a diol component composed of polyethylene terephthalate, terephthalic acid or / and isophthalic acid and a diol component composed of ethylene glycol, an ethylene terephthalate-butylene terephthalate copolymer, etc. are balanced. It is mentioned as good resin and these 1 type (s) or 2 or more types can be used.

The amount of oriented crystals of the resin constituting the main layer may be appropriately set according to the processing level of general processing, but may of course be non-oriented. Rather, since it becomes unnecessary to use a stretched film by selecting a non-oriented system, the direct laminating method by extrusion can be applied, which may be desirable in laminating.
The thickness of the main layer is 9-25 μm. The thickness of the main layer is appropriately selected according to the degree of general processing required, but if it is less than 9 μm, the function of the main layer, that is, the function of maintaining a balance between stretchability and strength (insufficient strength) is sufficient. Therefore, the film may be broken during score processing. On the other hand, if the thickness exceeds 25 μm, characteristics such as workability are saturated and the cost is increased, which is not preferable.

  As the resin constituting the sublayer, it is necessary that the local bending workability is excellent and that general workability such as rivet workability and score workability is not hindered. It can be satisfied by using a resin having a low (Tg) (a temperature sufficiently lower than the temperature at the time of lid processing), specifically, a resin having a glass transition point (Tg) of 5 ° C. or lower. Such a resin having a low glass transition point tends to not be able to follow rivet processing or score processing by itself due to insufficient strength, but when placed as a sub-layer, the main layer supplements the strength, so the general workability is low. It will not be damaged.

Here, the glass transition point (Tg) of the resin was determined by a DSC method using Q100 manufactured by TA Instruments. That is, 5 mg of a sample resin or film was sampled and measured under the conditions of a temperature rising rate of 10 ° C./min and a nitrogen gas flow rate of 50 ml / min, and the intersection was determined by the tangent method to determine Tg.
The resin constituting the sublayer is preferably a polyolefin resin. Examples of the polyolefin-based resin include polyethylene, polypropylene, and ionomer, and one or more of these can be used.
The thickness of the sublayer is 1 to 10 μm, preferably 2 to 4 μm. If the thickness of the sublayer is less than 1 μm, the local bending workability is inferior. On the other hand, if it exceeds 10 μm, the effect on the workability is saturated and the cost is increased.

A plurality of main layers and sub-layers may be provided. For example, a layer structure in which a sublayer is sandwiched between two main layers may be used.
The arrangement relationship between the main layer and the sub layer may be either the upper layer or the lower layer, and may be an intermediate layer as in the case of the sandwich structure described above, depending on various required characteristics. Selection is possible. For example, when emphasizing the flavor characteristics due to dye adsorption of the contents, the upper layer is preferably a polyester-based main layer, while the upper layer is a sub-layer when the contents are required to be taken out. Is generally preferable.
The main layer and sublayer may be directly stacked, but in cases where there is a risk of delamination between the main layer and sublayer due to the required processing, an adhesive layer may be provided between the main layer and sublayer. Good. Further, the sublayer may be made of a modified resin having good adhesiveness and may be directly stacked on the main layer.

The organic resin layer laminated on the metal plate may be composed of only the main layer / sublayer. However, as long as the effect of the present invention is not impaired, other resin layers (for example, the uppermost resin layer, metal An adhesive layer with a plate or the like may be provided. In this case, the sublayer or the main layer may be an intermediate layer.
The main layer and sublayer may contain additives such as an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a pigment, an antistatic agent, a lubricant, and a crystal nucleating agent as necessary. Also, a wax component or the like can be added to the surface layer of the upper layer side.
The main layer and the sublayer may be formed by a film lamination method (thermocompression bonding of a film sheet), or may be formed by a coextrusion method or a direct lamination method.
There is no special restriction | limiting in the base metal plate of the laminated metal plate of this invention. Tin-free steel is preferable in terms of being inexpensive and excellent in adhesion, but other surface-treated steel plates such as tinplate, aluminum plates, and the like may be used.

Next, a method for producing a can lid using the laminated metal plate of the present invention will be described.
When manufacturing a can lid using the laminated metal plate of the present invention, especially when manufacturing a can lid that does not require repair coating, the score portion with the largest plate thickness change is processed by the following specific method. It turned out to be preferable.
That is, in the lid making process, it is desirable to perform score processing using a curved mold having a radius of curvature R at the tip of 0.1 to 1.0 mm. If the radius of curvature of the curved mold is too small, the film may be broken due to insufficient strength. On the other hand, if the radius of curvature is too large, the degree of processing tends to be large, and molding tends to be difficult. In the above-described score processing using a curved mold having a tip radius of curvature R of 0.1 to 1.0 mm, for example, one of a pair of upper and lower molds has a tip radius of curvature R of 0.1 to 1. When the curved mold is 0.0 mm and the other is a flat mold, the pair of upper and lower molds are both curved molds having a tip radius of curvature R of 0.1 to 1.0 mm, etc. Any of these may be used, and the fracture groove is formed by press molding with such a mold.

As the base metal plate, a tin-free steel original plate having a thickness of 0.20 mm and a hardness of T4 was used. The base metal plate was laminated with an organic resin layer using a film laminating method or a direct laminating method to produce a laminated steel plate for a can lid.
A method for measuring the plane orientation coefficient of the obtained laminated steel sheet and a method for evaluating the lid-making characteristics are shown below.
(1) Measurement of plane orientation coefficient Using an Abbe refractometer, light source: sodium / D line, intermediate solution: methylene iodide, temperature: 25 ° C., the refractive index Nx in the longitudinal direction of the film surface, the lateral direction of the film surface The refractive index Ny in the direction and the refractive index Nz in the thickness direction of the film were measured, respectively, and the plane orientation coefficient Ns was calculated by the following equation.
Planar orientation coefficient (Ns) = (Nx + Ny) / 2−Nz

(2) Lid making property evaluation The laminated steel plate was heat-treated at 210 ° C for 10 minutes, and then subjected to easy open-end lid making. The score part was a non-repair type score process, and was molded using a 0.3 mmR curved mold. The corrosion resistance of the locally bent portion, the rivet portion, and the score portion of the formed lid was evaluated. Corrosion resistance is evaluated by measuring the current value when applying a voltage of 6.0 V with a sponge containing an electrolytic solution in close contact with the measurement part of the processed part of the lid after the lid making process. Based on the evaluation. In addition, as electrolyte solution, what added 2 drops of surfactant to 200 mass of 1mass% KCl aqueous solution was used.
○: Current value of 0.1 mA or less ×: Current value of more than 0.1 mA

Tables 1 to 3 show the coating structure and lamination method of the laminated steel sheet of each example, and Table 4 shows the results of the lid-making characteristic evaluation of each example.
In Tables 1 to 4, Invention Examples 1 to 4 are those in which the main layer is arranged in the upper layer and the sub layer is arranged in the lower layer, and the thickness of the sub layer is variously changed. It is good. Invention Example 5 has a sub-layer on the upper layer and a main layer on the lower layer, but, as in Examples 1 to 4, the corrosion resistance of any processed part is good, regardless of the position at which the sub-layer is arranged. It can be seen that the sublayer functions effectively. In Invention Example 6, the sub-layer is arranged as an intermediate layer between the two main layers. In this case, the corrosion resistance of any processed part is also good.

  Inventive Examples 7 and 8 are obtained by variously changing the plane orientation coefficient of the main layer, but the corrosion resistance of any processed part is good. The plane orientation coefficient is appropriately selected according to the degree of processing in the score processing, etc. From these invention examples, the lid making process can be performed without any problem if the plane orientation coefficient is approximately 0.04 or less. I understand that. Inventive Examples 9 to 11 are obtained by using a polyethylene terephthalate-polyethylene isophthalate copolymer in the main layer and changing the copolymerization ratio, but the corrosion resistance of any processed part is also good. Inventive Examples 12 to 14 are obtained by variously changing the resin type of the sublayer, but the glass transition point satisfies the conditions of the present invention, so that the corrosion resistance of any processed part is good. Invention Examples 15 and 16 use polybutylene terephthalate or polyethylene terephthalate-polybutylene terephthalate copolymer for the main layer, but the corrosion resistance of any processed part is also good. Invention Example 17 is an ethylene propylene rubber sub-layer superposed on the main layer via an adhesive layer, but the corrosion resistance of any processed part is also good.

  In Comparative Example 1, the thickness of the sublayer is less than the lower limit of the present invention. In Comparative Example 1, the rivet-processed portion has good corrosion resistance, and although the effect of the sublayer is slightly seen, the corrosion resistance of the local bending deformation portion is inferior. In Comparative Example 2, the glass transition point of the resin constituting the sublayer is 77 ° C., which does not satisfy the conditions of the present invention, and therefore the corrosion resistance is inferior in both the locally bent portion and the rivet portion. Comparative Example 3 is an example in which the resin layer is a single layer of polyethylene terephthalate, and the corrosion resistance of a portion having a bending element such as a locally bent portion or a rivet portion is inferior. In Comparative Example 4, the resin layer is composed only of the resin used for the sublayer of the present invention, but the score processing part and the rivet processing part are inferior in corrosion resistance. In this comparative example, film damage was already confirmed in the rivet portion overhanging process. In Comparative Example 5, polyvinyl acetate was used for the sublayer, and the glass transition point of this resin was 32 ° C. For this reason, both a local bending process part and a rivet process part are inferior in corrosion resistance. In Comparative Example 6, polycarbonate was used for the sublayer, but since the glass transition point of this resin is 140 ° C., both the locally bent portion and the rivet portion are inferior in corrosion resistance.

Claims (5)

  A laminated metal plate having a multilayer organic resin layer on at least one side of the metal plate, wherein a main resin layer having a thickness of 9 to 25 μm, wherein a part of the multilayer organic resin layer is made of a polyester resin. And the other resin layer is a sublayer having a glass transition point (Tg) of 5 to 10 ° C. and having a thickness of 1 to 10 μm, and the main layer and the sublayer are directly or via an adhesive layer. A laminated metal plate for can lids, characterized in that it has a film structure laminated in layers.   The laminated metal plate for can lid according to claim 1, wherein the main layer is made of a resin having polyethylene terephthalate as a basic skeleton, and the sublayer is made of polyolefin.   The main layer is composed of a polyester resin obtained by condensation polymerization of a dicarboxylic acid component composed of terephthalic acid or / and isophthalic acid and a diol component composed of ethylene glycol, and the sublayer is selected from polyethylene, polypropylene, and ionomer. It consists of seed | species or more, The laminated metal plate for can lids of Claim 1 or 2 characterized by the above-mentioned.   It is a manufacturing method of an easy open end type can lid using the laminated metal plate according to any one of claims 1 to 3, wherein a curved surface having a radius of curvature of a tip of 0.1 to 1.0 mm in the lid making process A method for manufacturing a can lid, comprising forming a breaking groove using a metal mold.   5. The method for producing a can lid according to claim 4, wherein printing is performed on the outer surface of the can lid material before the lid making process.