JP2002193255A - Laminated can cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated can cover consisting of a laminated plate 15 made by integrally laminating a polyester film 13 at least on one face of a metal plate 14, and excellent in contents protecting property, cover opening property and anticorrosive property by improving the flavor property, the processing property and the cutting property of the polyester film. SOLUTION: A thickness of the polyester film 13 is set to 8-15.8 μm. A value of the thickness of the film multiplied by the tensile strength is made in a range of 1500-3900 μm.MPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated can lid using a laminated plate composed of a metal plate and a polyester film.

[0002]

2. Description of the Related Art As containers for storing beverages such as juices, soft drinks, and beers, so-called easy-open cans having a can lid having a simple opening structure attached to an opening of a can body made of a metal material such as aluminum. Commonly used. Above all, easy-open cans using a stay-tab type (hereinafter referred to as "SOT type") can lid, in which tabs and opening pieces are held on the can lid even after the can lid is opened, are highly evaluated from the environmental point of view and widely used. Used.

FIG. 3 and FIG. 4 show an example of such a SOT type can lid. The can lid 10 has a top plate 1, a peripheral groove 2 provided on a peripheral portion of the top plate 1, and a winding portion 3 that is wound around a can body (not shown). A panel deboss 4 having a concave cross section is formed in a vertical direction of a plane of the plate portion 1 in the drawing. A rivet 5 is protrudingly provided at the center of the top plate 1 in the panel deboss 4, and a main score as a notch groove is provided between the rivet 5 and the lower edge of the panel deboss 4 in the drawing. 6 is engraved so as to surround the opening piece 9, and an auxiliary score 7 formed in a groove shape shallower than the main score 6 is engraved along the inside of the main score 6. The auxiliary score 7 has a function of suppressing movement of the metal in the vicinity of the main score 6 during processing, and in particular, reducing the remaining thickness of the metal immediately below the main score 6 so as not to cause constriction. On the opposite side of the portion where the main score 6 is formed in the panel deboss 4, a tab 8 is fixedly accommodated by the rivet 5. This tab 8
It comprises an opening 8c fixed to the rivet 5, a finger rest 8a and a pressing portion 8b.

[0004] In such a can lid 10,
By pulling up the finger hook 8c of the tab 8,
The main score 6 is broken by pressing the opening piece 9 downward while the pressing portion 8b of the tab 8 is in contact with the rivet 5 side portion of the opening piece 9, and the opening piece 9 is further pushed into the can to open the opening. It is supposed to.

Conventionally, a metal plate made of aluminum or an aluminum alloy or the like is coated with an epoxy or vinyl chloride paint to protect the corrosion-resistant contents. . However, in recent years, there has been a concern about the effects of bisphenol A, vinyl chloride, and the like contained in these paints on the environment. Therefore, measures to reduce the environmental impact of using such paints are required. As a substitute for the metal plate coated with the paint, a laminated metal plate (laminate plate) in which a thermoplastic resin film is adhered to a surface serving as an inner surface of the metal plate has attracted attention. As the thermoplastic resin film, in particular, a polyester film, corrosion resistance,
It is widely used because it is relatively excellent in mechanical strength, moldability, heat resistance, etc., is inexpensive and easily available.

[0006]

However, in the case of a polyester film, the main score is 6 due to the problem that damage is easily caused by various stresses generated at the time of can lid processing and the like, and the adhesion to a metal plate is not sufficient. When the can lid 10 is opened due to breakage of the polyester film, the cutability of the polyester film is poor, and the polyester film remains at the cut portion of the main score 6 or the polyester film peels off from the metal plate (hereinafter, referred to as “feathering”). ).

In order to prevent such a polyester film from being damaged at the time of can lid processing, a method using an amorphous polyester film has been proposed. Since the amorphous polyester film is in a state where the polyester is not crystallized (or the degree of crystallinity is 20% or less), a film crack along a crystal grain boundary which is a problem in a crystalline polyester film does not occur. In addition, the film is hardly damaged even when subjected to various stresses such as when processing a can lid or when impacting, and is excellent in workability. However, the amorphous polyester film still has a problem in openability and has a property of adsorbing an aromatic component of the can contents. Therefore, when used as a can lid, the flavor of the contents is impaired. That is, there are problems such as inferior content protection (flavor suitability) and inferior stability with time of the film.

[0008] In order to solve such problems as the suitability of flavor and stability over time in such an amorphous polyester film, a method of forming a polyester film of the above-mentioned amorphous polyester film in which stretch is left (Japanese Patent Laid-Open No. No. 7-507515). With the polyester film having the above-mentioned stretching remaining, a normal biaxially stretched polyester film is subjected to lamination, and the stretching of the polyester film is fixed by the heat of lamination while the polyester film is being melted. The crystallinity (stretching amount) of is adjusted.

[0009] However, such a polyester film has a problem that although it is excellent in the above-mentioned flavor aptitude, it is inferior in can lid processability as compared with an amorphous polyester film. In a laminate plate using, there was a tendency that the enamellator value (ERV) indicating the quality of the film deteriorated after the can lid processing. In addition, control of temperature management also poses a major problem in process management.
The ERV refers to a current value flowing between the electrolytic solution and the sample when the sample is immersed in the electrolytic solution. The smaller the value is, the smaller the breakage of holes and cracks in the film, and the better the state. It can be said that.

As described above, the polyester film used for the laminated can lid has processability (less damage during can lid processing) and cutability (feathering does not occur when the can is opened as a can lid). At present, it has not yet been obtained that satisfies all the properties required for use in a laminated can lid, such as the suitability for flavor and the like. The present invention has been made in order to solve such a problem, and is excellent in flavor suitability, hardly causes damage to a film at the time of can lid processing and the like, and has a high ERV even after can lid processing.
And a polyester film that is excellent in openability (cutting property) when used as a can lid and does not cause feathering, and is excellent in content protection, openability, and corrosion resistance The purpose is to obtain.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention examines the film thickness and the tensile strength of a polyester film in which the above-mentioned stretch is left, and satisfies the workability. The present inventors have found an optimum region of the above value that can obtain a laminated can lid having excellent can-opening properties. That is, the laminated can lid of the present invention is a can lid made of a laminated plate obtained by laminating and integrating a polyester film on a surface serving as an inner surface of a metal plate, wherein the polyester film has a thickness of 8 to 15.8 μm. Yes, the value of (film thickness × film tensile strength) is 1500 to 3900 (μm · MP
a).

The polyester film includes a base layer of biaxially stretched polyester film or modified polyester film having a thickness of 6 to 15 μm and an amorphous modified polyester film having a thickness of 0.5 to 3 μm.
m, and has a crystallinity of 45 to 60%. Further, the base layer is polyethylene terephthalate or a modified polyethylene terephthalate containing 3 mol% or less of isophthalic acid, and the adhesive layer is formed of 15 to 22 mol of isophthalic acid.
Preferably, the modified polyethylene terephthalate contains 1% by weight.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The feature of the laminated can lid of the present invention resides in the polyester film on the inner surface side, and any other known configuration can be applied to the structure and manufacturing method of the other laminated can lid. Therefore, the polyester film used in the laminated can lid of the present invention will be described in detail below, and the detailed description of the other components will be omitted.

The laminated can lid of the present invention is obtained by processing a laminated plate in which a polyester film is laminated on the inner surface of a metal plate such that the laminated surface of the polyester film is the inner surface of the can lid. . As the polyester film, a biaxially stretched polyester film is preferably used because of its excellent strength, and its thickness (μ
m) and the product of tensile strength (MPa) are 1500 to 3900
μm · MPa, more preferably 1900 to 3000 μm
-Desirably, it is MPa. Here, the tensile strength
Average value of tensile strength in the longitudinal direction (TD) and tensile strength in the transverse direction (MD) of the polyester film, that is, (tensile strength = (tensile strength in TD direction + tensile strength in MD direction) / 2)
The measurement method is based on JIS C-2318. When the value of (thickness × tensile strength) in the above polyester film is less than 1500 μm · MPa, the processability of the polyester film is reduced, and the film is damaged at the time of can lid processing or the like, and the film quality is reduced. Would. When the above value exceeds 3900 μm · MPa,
The cutting property is deteriorated, and feathering occurs when the can lid is opened.

[0015] The thickness and tensile strength of the polyester film are appropriately adjusted so as to have the above-mentioned values.
8μm to obtain the required workability and openability when making a can lid
As described above, the thickness is preferably 8 to 15.8 μm. Further, the tensile strength of the polyester film is controlled by the method of producing the film, the method of attaching the polyester film to the metal plate, the resin mixing ratio and a small amount of additives in the polyester film, and can be appropriately adjusted. 150-300MP as tensile strength of polyester film
It can be adjusted to the range of a.

As the polyester film, for example, a polyester film having a two-layer structure comprising a base layer and an adhesive layer is exemplified. FIG. 1 is a sectional view showing an example of the two-layer polyester film. This two-layer polyester film 1
3 is composed of a base layer 11 and an adhesive layer 12;
It is used by being adhered to a metal plate through. From the viewpoint of strength, the base layer 11 is preferably a polyester film or a modified polyester film having a thickness of 6 to 15 μm obtained by biaxial stretching. Among them,
A film made of a modified PET containing 3 mol% or less of polyethylene terephthalate (PET) or isophthalic acid (IPA) is preferable because of relatively excellent workability, corrosion resistance, flavor suitability, and the like. Also,
The melting point (Tm) of the PET or modified PET film is preferably 245 to 260 ° C. Here, the melting point is defined by using a differential calorimeter (“SS580 DSC20” manufactured by Seiko Instruments Inc.), placing 10 mg of a film serving as a sample on a suggestive calorimeter, and heating the sample at a rate of 10 ° C./min. And the temperature at the top of the obtained crystal melting.

The adhesive layer 12 is preferably an amorphous polyester film having a thickness of 0.5 to 3 μm because of its excellent adhesiveness to a metal plate and excellent workability. Among them, a film made of a modified polyethylene terephthalate containing 15 to 22 mol% of IPA is preferable. PET containing IPA in an amount of 15 to 22 mol% has excellent adhesiveness to a metal plate, makes it difficult for the film to be damaged at the time of can lid processing, easily breaks the score, and easily opens the laminated can lid. improves.

Such a base layer 11 and an adhesive layer 12
A polyester film made of is excellent in adhesiveness to a metal plate, and is excellent in flavor suitability, workability, openability, and the like.

FIG. 2 shows the two-layer polyester film 1 described above.
3 shows an example of a laminated plate using No. 3. Such a laminate plate 15 is made of a polyester film 1 comprising a base layer 11 and an adhesive layer 12 on both sides of a metal plate 14.
3 is laminated and integrated such that the adhesive layer 12 is on the metal plate 14 side. In the laminated plate 15, a polyester film is laminated on both sides. As the laminated plate used for the laminated can lid of the present invention, at least the polyester film is laminated on the inner side of the laminated can lid. Anything is acceptable.

As the metal plate 14, various steel plates or light metal plates such as aluminum or aluminum alloy can be used. In addition, it is preferable to use a metal plate surface that has been subjected to a surface treatment by a known method such as a chromate treatment in order to enhance the adhesiveness to the polyester film. At this time, the thickness of the aluminum plate is usually 0.3
mm.

As a method of laminating the metal plate 14 and the two-layer polyester film 13, there is a thermocompression method in which the metal plate 14 is heated and a two-layer polyester film is pressure-bonded thereto. At this time, the temperature at which the polyester film 13 is attached to the metal plate 14 is appropriately adjusted according to the characteristics of the polyester film 13. For example, when a two-layer polyester film made of PET is used, the attachment temperature is set to (Tm-55) ~
(Tm-18) ° C., and preferably cooled by air cooling or water cooling after application. In such a case, the crystallinity of the two-layer PET film is in the range of 45 to 60%, and a polyester film having more excellent flavor aptitude can be obtained. In order to enhance the adhesion between the polyester film 13 and the metal plate 14, an epoxy or polyester adhesive may be applied to the metal plate 14 in advance, and the polyester film 13 may be bonded thereon.

Here, the crystallinity of the above-mentioned polyester film refers to that measured as follows. First, a standard density float is placed in a density gradient tube having a density gradient with a mixture of n-heptane and carbon tetrachloride, and the density of the sample is defined as ρ depending on the position of the sample relative to the float, Substituting the obtained density ρ into the following equation, the crystallinity X
Obtain c. X _c = (ρ-1.335) × 100 / (1.
455-1.335) Further, for the film after lamination, the crystallinity X _{c ′} can be determined by the X-ray diffraction method. (1) The X-ray diffraction intensity of the film before lamination is measured in the range of 2θ = 20 to 30 °. (2) X-ray diffraction intensity curves at 2θ = 20 ° and 2θ = 30 ° are connected by a straight line, and this is set as a baseline. (3) The height of a sharp peak appearing around 2θ = 26 ° is measured based on the baseline. (4) Assuming that the peak height of the film before lamination is Ia and the peak height of the film after lamination is Ib, _{Xc '} is calculated by the following equation. X _{c ′} = Ib / Ia × X _c

The thus obtained laminate plate 15
Is punched and formed into a can lid shape, a score is formed by an ordinary method, and a tab is fixed with a rivet to obtain a laminated can lid. The structure and manufacturing method of the laminated can lid are not particularly limited, and for example, an SOT type can lid shown in FIGS. 3 and 4 is exemplified. The laminated can lid thus obtained is provided with a polyester film having good ERV, excellent cuttability, and excellent flavor suitability on its inner surface side, so that it is excellent in corrosion resistance, content protection and the like. . Further, feathering does not occur at the time of opening the can, and the can opening property is excellent.

[0024]

The present invention will be described below in detail with reference to examples. Laminated plates were manufactured using a two-layer polyester film having the values of (thickness × tensile strength) shown in Table 1, and the ERV of each laminated plate was measured. A can lid having the structure shown in FIGS. 3 and 4 was manufactured using the obtained laminate plate, and the can-opening property of this can lid was evaluated. At this time, the tensile strength was measured using a measurement method defined by JIS C-2318.
It was determined by applying the following formula. Film tensile strength = (T
Table 1 shows the results of (D-direction tensile strength + MD-direction tensile strength) / 2.

The ERV was obtained by immersing a sample in an aqueous solution of sodium chloride (concentration: 1%) and measuring the current flowing through the sample. When the flowing current was 1 mA or less, ◎ was evaluated when the current was 10 mA or less, and X when the flowing current exceeded 10 mA. Regarding the can opening property, the presence or absence of feathering at the time of opening the can was visually evaluated. Those with no feathering are excellent ◎, those with little feathering are good ○, those with much feathering Was evaluated as poor.

[0026]

[Table 1]

From the results shown in Table 1, the value of (thickness × tensile strength) of the two-layer polyester film was 1500 to 3%.
In the range of 900 μm · MPa, ER
Since V was good and feathering did not occur, it was found that the material had excellent workability and openability.

Next, laminates were manufactured using two-layer polyester films having different degrees of crystallinity of the polyester films, and the flavor property of each laminate was evaluated. At this time, the crystallinity of the polyester film was prepared by changing the laminating conditions at the time of laminating, and the crystallinity was changed. Then, the crystallinity of the obtained two-layer polyester film was measured. The crystallinity at this time was measured by the method described above.

Flavor properties were evaluated according to the crystallinity of the polyester film. Table 2 shows the results. At this time, those having no problem in flavor were evaluated as ○, those having some problem were evaluated as Δ, and those having problem were evaluated as ×.

[0030]

[Table 2]

From the results shown in Table 2, it was found that those having a crystallinity of 45% or more had no problem in flavor.

Next, in the two-layer polyester film, a modified polyethylene terephthalate containing IPA was used for the base layer 11 and the adhesive layer 12, and each of the base layers 11 and the adhesive layer 12 was used for the respective layers.
A two-layer polyester film was prepared by changing the amount of PA, and a laminate was produced using the two-layer polyester film, and the flavor and feathering properties of each laminate were evaluated. At this time, the thickness of the two-layer polyester film was adjusted to 8.8 to 9.6 μm, and the thickness of the adhesive layer was adjusted to 0.7 to 1.2 μm. The flavor property was the same as the evaluation method in Table 2 above. The feathering property was the same as the evaluation method in Table 1.

[0033]

[Table 3]

From Table 3, it can be seen that the base layer has an IPA
The amount is 3 mol% or less, and the amount of IPA in the adhesive layer is 1
It can be seen that the use of a two-layer polyester film in the case of a modified polyethylene terephthalate containing 5 to 22 mol% for a laminated can lid is excellent in both flavor and feathering properties and suitable as a film for a laminated can lid.

[0035]

As described above, in the laminated can lid of the present invention, the polyester film used on the inner surface side is excellent in flavor suitability, and the film is hardly damaged at the time of processing the can lid. Since a high ERV value is obtained even after processing, and it has excellent cutability when used as a can lid and does not cause feathering,
It has excellent content protection, can openability, corrosion resistance, and the like.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a polyester film used for a laminated can lid of the present invention.

FIG. 2 is a cross-sectional view showing an example of a laminate plate used for a laminate can lid of the present invention.

FIG. 3 is a plan view showing an example of a SOT type can lid.

FIG. 4 is a perspective view showing an example of a SOT type can lid.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Base layer 12 Adhesive layer, 13 Polyester film 14 Metal plate 15 Laminate plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3E093 AA13 BB06 CC09 EE20 4F100 AB01A AK41B AK41C AK42B AK42C AL06B AL06C BA02 BA03 BA07 BA10A BA10B EH23 EH232 EJ38B GB16 GB18 JA12C JB02 JK02B JB11Y

Claims (3)

[Claims] 1. A laminated can lid comprising a laminated plate in which a polyester film is laminated and integrated on an inner surface of a metal plate, wherein the polyester film has a film thickness of 8
A laminated can lid, wherein the thickness of the film × the tensile strength of the film is 1500 to 3900 μm · MPa. 2. A base layer having a thickness of 6 to 15 μm, wherein the polyester film is formed of a biaxially stretched polyester film or a modified polyester film, and an adhesive layer having a thickness of 0.5 to 3 μm, which is formed of an amorphous modified polyester film. 2. The aluminum can lid according to claim 1, wherein the laminate has a crystallinity of 45 to 60%. 3. 3. The method according to claim 1, wherein the base layer is polyethylene terephthalate or modified polyethylene terephthalate containing 3% by mole or less of isophthalic acid, and the adhesive layer is a modified polyethylene terephthalate containing 15 to 22% by mole of isophthalic acid. The laminated can lid according to claim 2.