JP2002192614A - Manufacturing method of laminated can lid and beverage can using this laminated can lid - Google Patents

Abstract

(57) [Problem] To provide a method for producing a laminated can lid that improves the sensory suitability and corrosion resistance of the laminated can lid. SOLUTION: A metal plate is coated with a polyester resin film having a two-layer structure composed of a base layer having ethylene terephthalate as a main repeating unit and an adhesive layer having ethylene terephthalate as a main repeating unit and having a lower melting point than the base layer. A laminated material was formed, and a can lid was formed using a laminated material having a value of film thickness × film tensile strength at 20 ° C. of the coated polyester resin film at 20 ° C. of 1500 μm · MPa or more. ,
Heat treatment is performed for 10 seconds or more in a temperature range from the glass transition point of the base layer of the polyester resin film + 30 ° C. to the melting point of the adhesive layer of the polyester resin film−40 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a laminated can lid in which a metal plate is coated with a polyester resin film, and more particularly to a laminated can lid having improved flavor characteristics and corrosion resistance by subjecting the can lid to heat treatment. And a method for producing the same.

[0002]

2. Description of the Related Art In general, cans such as beer cans, liquor cans, and juice cans comprise a bottomed cylindrical can body and a can lid for closing an open end of the can body. There are various types of can lids, and the main one is an easy-open type can lid that can be easily opened by attaching a tab or the like. This easy-open type can lid is roughly divided into a pull-top type that removes the opening piece that forms the opening by pulling up the pull tab, and a stay-on tab type that pushes the opening piece into the container and the tab can not be removed from the lid There are things.

In a pull-top type can lid, after opening the can, a score portion and a tab surrounded by a cut line (hereinafter, the score portion and the tab are referred to as "opening pieces") are separated from the lid body and discarded. However, there is a problem that it is difficult to collect the opening pieces. In order to solve such a problem, in recent years, most of the stay-tab types have a can body and an opening piece connected to each other even after the can is opened.

As shown in FIGS. 2 (a), 2 (b) and 3, for example, a simple open can lid 10 of the stained tub type is used.
Are a top plate 1 having a circular shape, a winding portion 2 provided on the periphery of the top plate 1 and wound around a can body (not shown);
An outer peripheral groove 3 provided between the upper plate 1 and the top plate 1, an opening piece 5 connected to the groove-shaped score 4, and a rivet arranged so that a tip thereof overlaps the top plate center CP side of the opening piece 5. 6 and a pull tab 7 connected to the center CP of the top plate. The pull tab 7 has an insertion hole 2 through which the rivet 6 is inserted almost in the center.
b is formed.

When the pull tab 7 is pulled, the tab tip 7a on the score 4 side is the fulcrum, the tab finger hook 7b is the power point, and the rivet 7
c is the point of action, the score is pressed, and FIG.
The first step in which the rivet peripheral portion 4d of the score 4 shown in FIG. 2 (a) is viewed from the back is broken, and the tip 7a of the pull tab 7 is opened with the rivet 6 in FIG. By pressing the base end of the piece 5 on the top plate center CP side, the remaining score 4 is broken by the pressing force, and the second step in which the opening piece 5 is put into the inside of the can main body. It is formed.

[0006] As the can lid 10, a pre-coated material in which an inner surface of the can lid 10 is coated with an epoxy or vinyl chloride paint on one side of a thin aluminum plate is manufactured, and this pre-coated material is molded. The resulting precoated can lid has been developed. Such a precoat material is intended to prevent corrosion and protect contents.

[0007] However, epoxy-based and vinyl chloride-based paints contain bisphenol-A and organic solvents, and thus have a problem in safety. In addition, since it takes a long time to bake and dry the paint, large-scale heating equipment such as an oven is required. Furthermore, low molecular weight components contained in the paint elute into contents such as juices, soft drinks, and beers in cans, and taste and aroma components of such contents (hereinafter, referred to as "flavors"). And other problems.

[0008] In order to solve these problems, a polyester resin film is coated on a metal plate using Japanese Patent Publication No. 3-60735, Japanese Patent Publication No. 7-507525, etc. A method for obtaining an easy open can is shown. However, in this method, since the adhesive is used when the polyester resin film is coated on the metal plate, the elution of the solvent is inevitable as in the case of using the paint. Further, since a step of applying an adhesive to a polyester resin film or a metal plate is added, there is a disadvantage that the steps are complicated and large-scale.

On the other hand, the method described in Japanese Patent Application Laid-Open No. 7-507525 does not use an adhesive, so that no solvent is eluted, and the polyester resin film and the metal plate can be bonded with a relatively simple apparatus. . In this method, when the polyester resin film is bonded to a metal plate in order to prevent tearing of the polyester resin film in a portion of the lid that is subjected to strong processing such as a score, the crystallinity of the polyester resin film is reduced. ing. However, when the crystallinity of the polyester resin film is low, the flavor in the contents of the can is easily adsorbed, and there is a problem in the organoleptic suitability when the beverage is filled. In particular, when a beverage containing alcohol, for example, water-whiskey whiskey or wine is filled, the effect is remarkable.

On the other hand, a polyester resin film having a high crystallinity is less likely to adsorb flavors than a film having a low crystallinity. It is described in JP-T-7-507525 that when a polyester resin film having a high crystallinity is used, the polyester resin film breaks during processing of a score or the like, which is not preferable. Breakage of the polyester resin film in the score or the like can be prevented by reducing the depth of the groove at the time of score processing. According to such a method, a can lid coated with a polyester resin film having high crystallinity and high strength can be obtained.

The can lid produced by the above-described method was evaluated for organoleptic suitability. As a result, despite the high crystallinity of the polyester resin film, the can not sufficiently satisfy the organoleptic suitability. It was found to be significant for beverages containing. In addition, it was found that the flavor was adsorbed on the parts that had been subjected to heavy processing during the manufacture of the can lid, rivets, scores, countersinks, etc.

[0012]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a laminated can lid that improves the sensory suitability and corrosion resistance of the laminated can lid, and a beverage can using the laminated can lid. .

[0013]

In order to solve the above-mentioned problems, a method for producing a laminated can lid according to claim 1 of the present invention comprises a base layer having ethylene terephthalate as a main repeating unit and an ethylene terephthalate as a main repeating unit. A metal sheet is coated with a polyester resin film having a two-layer structure composed of an adhesive layer having a lower melting point than the base material layer to form a laminate, and the thickness of the coated polyester resin film at 20 ° C. × film A can lid is formed using a laminate material having a tensile strength of not less than 1500 μm · MPa, and the can lid is formed by heating the can lid to a glass transition point of the base layer of the polyester resin film + 30 ° C.
Melting point of the adhesive layer of the polyester resin film -40C
The heat treatment is performed for 10 seconds or more in the above temperature range. Further, the beverage can according to the second aspect of the present invention is characterized in that a beverage is filled in a bottomed tubular can body and sealed with the laminated can lid manufactured by the method for producing a laminated can lid according to the first aspect. It is assumed that.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 is a schematic sectional view showing an example of a laminated can lid manufactured by the method for manufacturing a laminated can lid of the present invention.
The laminate can lid 20 has a laminate film 22 coated on the outer surface side of a metal plate 21, and a base layer 24 having ethylene terephthalate as a main repeating unit and an ethylene terephthalate as a main repeating unit on the inner surface side, A polyester resin film 23 having a two-layer structure with an adhesive layer 25 having a lower melting point than the base material layer 24 is covered.

Further, as the metal plate 21, various steel plates or light metal plates such as aluminum or 5000 series aluminum alloy can be used. In addition, it is preferable to use a metal plate surface-treated by a known method such as a chromate treatment in order to enhance the adhesiveness to the polyester resin film.

The polyester resin film 23 has a base layer 24 having a thickness of 5 to 15 μm and an adhesive layer 25 having a thickness of 0.5 μm.
Desirably, the difference between the melting points of the base material layer 24 and the adhesive layer 25 is 10 ° C. or more. If the thickness of the base material layer 24 is less than 5 μm, sufficient corrosion resistance cannot be obtained,
On the other hand, if it exceeds 15 μm, the flavor to be adsorbed increases, and the sensory suitability is impaired. The thickness of the adhesive layer 25 is 0.3 μm
If it is less than m, sufficient adhesive strength cannot be obtained, and a problem occurs in corrosion resistance. On the other hand, if the thickness of the adhesive layer 25 exceeds 4 μm, the film tends to peel off during the heat treatment, which is not desirable.

In the method for manufacturing a laminated can lid according to the present invention, first, the adhesive layer 25 side of the polyester resin film 23 is adhered and coated on the metal plate 21 to form a laminated material. Next, the value of the film thickness at 20 ° C. × the tensile strength of the coated polyester resin film 23 is 15
A laminate can lid 20 is formed using a laminate material having a thickness of at least 00 μm · MPa. Then, laminate can lid 2
0 is heat-treated for 10 seconds or more in a temperature range from the glass transition point of the base layer 24 of the polyester resin film 23 + 30 ° C. to the melting point of the adhesive layer 25 of the polyester resin film 23 −40 ° C.

The polyester resin film 23 is applied to the metal plate 2
As a method for bonding to the first, a method in which the metal plate 21 is heated to a temperature equal to or higher than the melting point of the bonding layer 25 by an oven, a heat roll, or the like, and then the polyester resin film 23 is pressed. Thereafter, in order to sufficiently increase the adhesive strength, it is desirable to heat the substrate layer 24 in a temperature range where the crystallinity of the base layer 24 does not decrease. As a heating method at this time, any means such as an oven, induction heating, and a heat roll may be used.

It is necessary that the polyester resin film 23 of the laminated material produced as described above has a value of film thickness × film tensile strength of not less than 1500 μm · MPa. When the value of the film thickness × the tensile strength of the film has this range, the crystallinity of the polyester resin film 23 is as high as 40 to 60%. The physical properties of the polyester resin film 23 after being covered with the metal plate 21 are determined according to JIS after dissolving the metal plate 23 with dilute hydrochloric acid or the like to obtain the polyester resin film 23 alone.
Measured by the method specified in. When the value of the film thickness × the tensile strength of the film is less than 1500 μm · MPa, the polyester resin film 23 has high water permeability and oxygen permeability, and maintains sufficient corrosion resistance as a can lid for beverages. Can not do.

The laminated material thus produced is processed to obtain a laminated can lid 20. When processing the laminated can lid 20 and processing the simple opening structure, using the same apparatus and processing as in processing the pre-coated material coated with the paint into the can lid for a beverage can, a polyester resin film is obtained. 23 is likely to have defects. Therefore, it is preferable that the degree of processing such as the score is made loose. In addition, it is necessary to maintain the openability of the tub by keeping the strength of the tub high.

The thus obtained laminate can lid 2
0 to the glass transition temperature of the base layer 24 of the polyester resin film 23 + 30 ° C.
Is heated for 10 seconds or more in the temperature range of the melting point of the adhesive layer 25 of −40 ° C. Here, when the heating temperature is lower than the glass transition temperature of the base layer 24 + 30 ° C, the stress of the base layer 24 is not sufficiently relaxed, and the organoleptic suitability is not sufficiently improved. If the heating temperature exceeds the melting point of the adhesive layer 25 −40 ° C., the adhesive layer 25 softens during heating, and the adhesive strength with the metal plate 21 decreases. As a result, the polyester resin film 23 contracts and peels off from the metal plate 21. If the heating time is less than 10 seconds, the organoleptic suitability is not sufficiently improved. In addition,
Although the upper limit of the heating time is not particularly limited, if it exceeds 1 hour, the performance of the sealant applied to the laminate can lid 20 may be impaired, so it is preferably 1 hour or less. Further, even if the heat treatment is performed under the above conditions after the can lid processing, the crystallinity of the polyester resin film 23 is almost the same as the value after the metal plate 21 is covered.

The purpose of this heat treatment is to use a laminate can lid 2
The purpose is to improve the adhesion between the metal plate 21 and the polyester resin film 23 in a score-processed portion of 0, etc., and to enhance the sensory suitability. There is no need for heat treatment for portions that are not subjected to scoring or the like and portions that do not come into contact with the contents. Therefore, it is not necessary to heat-treat the entire can lid in the above-mentioned temperature range, and a sufficient effect can be obtained only by heating the scored portion and the like in the above-mentioned temperature range and heating time. The heating method may be any of batch processing in which a large number of laminated can lids 20 are heated simultaneously in an oven, and continuous processing in which the laminated can lids 20 are passed through the oven one by one and heated. As a heat source for heating, various heating devices such as a gas oven and an electric oven can be used.

Meanwhile, in the case of a can lid processed using a conventional paint, a low molecular weight component is contained in the coating film. The can lid may be heat-treated at a temperature exceeding 100 ° C. for sterilization after filling the beverage, but during the heat treatment, low-molecular components in the coating film may elute and impair the functionality. On the other hand, the polyester resin film has less low molecular weight components than the coating film, so that even if it is sterilized, there is no problem in terms of organoleptic properties.

Further, an alcoholic beverage or the like was filled in a bottomed cylindrical can body (can body) and sealed with the laminated can lid 20 manufactured as described above to obtain a beverage can. In the beverage can of this example, flavor adsorption is suppressed, and the organoleptic suitability is good.

The following is a specific example. First, the thickness 9 μm,
A polyester resin film having a crystallinity of 53 to 56% and having a two-layer structure of a base material layer and an adhesive layer was prepared. This polyester resin film has a thickness of 8.5 μm as a base material layer.
m, a biaxially stretched polyethylene terephthalate film having a melting point of 253 ° C. and an adhesive layer having a thickness of 0.5 μm and a melting point of 2
It is composed of an amorphous film made of a copolymer of polyethylene terephthalate and isophthalic acid containing 15 to 22 mol% of isophthalic acid at 10 ° C. For the measurement of the melting point, a differential scanning calorimeter (DSC) meter (SSC58) was used.
0 DSC20, manufactured by Seiko Denshi Kogyo Co., Ltd.). Biaxially stretched polyester resin film 10m
g was heated at a rate of 10 ° C./min, and the peak temperature due to crystal melting of the film was defined as the melting point.

Next, a chromated aluminum sheet was prepared. Next, the polyester resin film was coated on a chromate-treated aluminum thin plate to produce a laminated material, and the laminated material was processed to produce a laminated can lid. Glass transition point and thickness of the substrate layer of the polyester resin film, melting point and thickness of the adhesive layer,
Several types of can lids were prepared by changing the heat treatment temperature after can lid processing, and the sensory suitability and corrosion resistance were investigated. The sensory aptitude was evaluated after filling various commercially available beverages into a beverage can using various can lids, heat-treating the mixture, and leaving the lid at 37 ° C. with the can lid down for 3 months. Regarding corrosion resistance,
Various commercially available beverages were filled in a beverage can using various can lids, heat-treated, and allowed to stand at 37 ° C. for 3 months with the can lid down, and the elution amount of aluminum was measured and evaluated. Table 1 shows the results.

[0027]

[Table 1]

From the results shown in Table 1, it can be seen that the can lid manufactured by the method for manufacturing a laminated can lid according to the present invention has sufficient organoleptic properties for all kinds of beverages and also has high corrosion resistance.

[0029]

As described above, the laminated can lid manufactured by the method for manufacturing a laminated can lid according to the present invention maintains a high degree of crystallinity of the polyester resin film while maintaining a processed portion such as a score. Has a high film adhesion, so that the adsorption of flavor to the polyester resin film and the adsorption of flavor at the interface between the polyester resin film and the metal plate can be suppressed.
As a result, the organoleptic suitability was improved as compared with a conventional can lid covered with a polyester resin film. This effect is significant for beverages containing alcohols that have a high flavor penetration into the film.

In addition, since the polyester resin film has a high degree of crystallinity, water permeability and oxygen permeability can be kept extremely low, and since the processed parts have high adhesion, sufficient corrosion resistance can be obtained. . Further, when the crystallinity of the polyester resin film is high, the permeability of sulfurous acid gas is low, and the film adhesion of a processed portion such as a score where corrosion generally tends to occur is high. Therefore, it is suitable as a can lid for wine-based beverages containing sulfurous acid gas. Further, since the polyester resin film has less low molecular weight components than the paint, even when sterilized at a temperature exceeding 100 ° C., the low molecular weight components are not eluted and the sensory suitability is not impaired.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a laminated can lid manufactured according to the present invention.

FIG. 2 is a view showing a conventional can lid, wherein (a) is a plan view of the can lid and (b) is a bottom view of the can lid.

FIG. 3 is a sectional view showing a conventional can lid.

[Explanation of symbols]

20: Laminated can lid, 21: Metal plate, 23: Polyester resin film, 24: Base layer, 25: Adhesive layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) // B29L 7:00 B29L 7:00 9:00 9:00 F Term (Reference) 3E093 AA01 BB06 4F100 AA22 AB01C AB10 AK42A AK42B BA03 BA10A BA10C EJ192 EJ413 EJ691 GB18 GB23 JA04B JK02A JK06 JL11B YY00A 4F211 AA24 AD03 AD08 AG01 AG03 AH55 TA01 TC05 TD11 TH02 TH06 TN09 TN16 TN28 TQ03 TW06 TW16

Claims (2)

[Claims] 1. A two-layer polyester resin film comprising a base material layer containing ethylene terephthalate as a main repeating unit and an adhesive layer containing ethylene terephthalate as a main repeating unit and having a lower melting point than the base material layer is formed on a metal plate. A can lid is formed by using a laminated material in which a value of (film thickness at 20 ° C. × film tensile strength of the coated polyester resin film at 20 ° C.) is 1500 μm · MPa or more. To
A method for producing a laminated can lid, wherein a heat treatment is performed for 10 seconds or more in a temperature range from the glass transition point of the base layer of the polyester resin film + 30 ° C to the melting point of the adhesive layer of the polyester resin film-40 ° C. 2. A beverage can, characterized in that a beverage is filled in a bottomed tubular can body and sealed with the laminated can lid produced by the method for producing a laminated can lid according to claim 1.