Carbonated beverage in a bottle with a cap

Abstract

The present invention provides a bottle can with a cap for carbonated beverages that ensures high airtightness and high gas barrier properties, while also being able to be opened with a small opening torque, which is a contradiction to these properties. [Solution] A cap is fitted to the mouth of a bottle can. The cap consists of a cap body made of aluminum alloy and a liner provided inside the cap body. The cap body is integrally formed with a top surface and a peripheral wall. A female thread is formed on the peripheral wall that engages with the male thread on the outer circumference of the mouth. The Vickers hardness of the top surface of the cap is 60 HV to 75 HV, and the Vickers hardness of the peripheral wall is 70 HV to 86 HV. The Vickers hardness of the peripheral wall is formed to be 3 HV to 25 HV higher than that of the top surface. The bottle can is filled with a carbonated beverage.

Description

Technical Field

[0001] The present invention relates to a bottle can filled with a carbonated beverage, having a bottle-shaped body formed in a bottle shape and sealed at its mouth with a cap, and a bottle can with a cap containing a carbonated beverage.

Background Art

[0002] As various beverage containers, bottle cans having a structure in which a cap is attached to and sealed at the mouth of a bottle-shaped body (bottle-shaped body) are widespread.

[0003] As this cap for a bottle can, conventionally, for example, the one for a carbonated beverage described in Patent Document 1 is known. This cap is a cap with a liner for sealing the mouth of the bottle body, and includes a cap body composed of a top plate portion (top surface portion) and a cylindrical peripheral wall portion hanging down from the periphery of the top plate portion, and a liner provided on the inner surface of the top plate portion. The liner includes a sliding layer arranged in contact with the inner surface of the top plate portion, a sealing layer composed of an elastomer laminated on the sliding layer and softer than the sliding layer, an intermediate layer arranged between the sliding layer and the sealing layer and having gas barrier properties, and an adhesive layer provided between the intermediate layer and the sliding layer or the sealing layer for bonding them.

[0004] For this type of cap for a carbonated beverage, high sealing performance and high gas barrier properties are required. Also, as a cap that is easy to open, it is naturally required to have a small opening torque. In this case, if the number of turns of the thread is increased, the sealing performance improves, but the opening torque also increases and it becomes difficult to open. Also, if the diameter of the cap is reduced, the sealing performance improves, but the opening diameter becomes small and it becomes difficult to drink. If the sealing layer of the liner is thickened, or the elastic force of the elastomer of the sealing layer is increased, the sealing performance improves, but the opening torque also becomes high.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] This invention has been made in view of these circumstances, and aims to provide a bottle can with a cap for carbonated beverages that ensures high airtightness and high gas barrier properties, while also being able to be opened with a small opening torque, which is a trade-off between these two requirements. [Means for solving the problem]

[0007] The carbonated beverage bottle can of the present invention comprises a cap fitted to the mouth of the bottle can, the cap comprising a cap body made of an aluminum alloy and a liner provided inside the cap body, the cap body having a top surface and a peripheral wall integrally formed, the peripheral wall having a female screw portion that engages with the male screw portion on the outer circumference of the mouth, the Vickers hardness of the top surface of the cap being 60 HV or more and 75 HV or less, the Vickers hardness of the peripheral wall being 70 HV or more and 86 HV or less, the Vickers hardness of the peripheral wall being formed to be 3 HV or more and 25 HV or less higher than that of the top surface, and the bottle can being filled with a carbonated beverage.

[0008] The cap body is formed into a cup shape consisting of a top surface and a peripheral wall by drawing an aluminum sheet. The peripheral wall of the cap body is processed with knurling and other features, and is also threaded by capping. On the other hand, the top surface of the cap has its peripheral edge drawn during capping to form a stepped section. Because the peripheral wall undergoes multiple processing steps in this way, the Vickers hardness of the peripheral wall tends to be higher than that of the top surface. In this case, by setting the Vickers hardness of the top surface of the cap to 60 HV to 75 HV and the Vickers hardness of the peripheral wall to 70 HV to 86 HV, a cap is obtained that is less prone to screw deformation, has a lower opening torque, and has better sealing performance compared to conventional caps.

[0009] If the Vickers hardness of the top surface is less than 60 Hv, the top surface will have good drawability, but the Vickers hardness of the surrounding wall will also be low, making the screw prone to deformation. Conversely, if the Vickers hardness of the top surface is increased to more than 75 Hv, the Vickers hardness of the surrounding wall will become too high, which may impair the screw formability and compromise the sealing performance. If the Vickers hardness of the peripheral wall is less than 70 Hv, thread machinability improves, but the compression strength decreases due to the decrease in Vickers hardness of the top surface. Conversely, if the Vickers hardness of the peripheral wall is increased to more than 86 HV, the draw-formability of the top surface decreases, resulting in poor sealing performance.

[0010] If the difference in Vickers hardness is less than 3HV, selecting a Vickers hardness that allows for deep drawing (in other words, selecting a Vickers hardness that takes into account the deep drawing formability of the cap's top surface) will also result in a lower Vickers hardness in the peripheral wall, making it impossible to adequately prevent screw deformation and thus preventing a reduction in the opening torque. Alternatively, increasing the Vickers hardness of the peripheral wall will also increase the Vickers hardness of the top surface, reducing its deep drawing formability and thus its sealing performance.

[0011] On the other hand, if the difference in Vickers hardness exceeds 25 HV, even if a material with a Vickers hardness suitable for deep drawing is selected for the top surface, the Vickers hardness of the peripheral wall may become too high, resulting in poor thread formability and potentially compromising the sealing performance. Alternatively, if a material with a low Vickers hardness value suitable for thread machinability is selected for the peripheral wall, the Vickers hardness of the top surface will also decrease further, potentially causing the top surface to bulge excessively due to the internal pressure of the can, thus impairing the can's transportability. Furthermore, the pressure resistance strength will also decrease.

[0012] In the carbonated beverage bottle can with cap of the present invention, the liner comprises a sliding layer disposed in contact with the inner surface of the top surface of the cap body, and a sealing layer made of elastomer laminated on the sliding layer, wherein the sliding layer consists of multiple layers, and at least one layer is a gas barrier layer.

[0013] In typical liners, polyethylene or polypropylene is used as the sliding layer, and an elastomer resin softer than the sliding layer is used as the sealing layer. However, when carbonated beverages are filled and sealed, gas permeation may occur. In the present invention, the sliding layer is composed of multiple layers, and at least one of these layers is formed as a gas barrier layer, thereby suppressing gas permeation to carbonated beverages and providing excellent sealing performance.

[0014] In the carbonated beverage bottle can with a cap of the present invention, it is preferable that the aluminum alloy contains recycled material from used aluminum beverage cans. By using recycled materials from used aluminum beverage cans, the amount of CO2 emitted can be significantly reduced compared to using new aluminum ingots, thereby lowering the environmental impact. [Effects of the Invention]

[0015] According to the present invention, the Vickers hardness of the top surface and peripheral wall of the cap is set to a predetermined value, so that the peripheral edge of the top surface is drawn to a predetermined depth, the deformation of the threads due to the internal pressure of the can is small, and it has excellent sealing properties for carbonated beverages. [Brief explanation of the drawing]

[0016] [Figure 1] This is a front view showing a cross-section of the right half of the central axis of a capped bottle can according to one embodiment of the present invention. [Figure 2] Figure 1 is a front view showing the state before the cap is attached, with the right half of the central axis in cross-section. [Figure 3] Figure 2 is a magnified cross-sectional view of the liner inside the cap. [Figure 4] Figure 1 is a front view showing a cross-section of the right half of the press-formed cap shell, which will become the cap, from the central axis. [Figure 5] Figure 1 is a front view showing a cross-section of the right half of the bottle can, before the cap is attached, from the central axis. [Figure 6] This is a front view of the main components of an example of a capping device.

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described. As shown in FIG. 1, the cap 70 of one embodiment is in a form attached to the bottle can 50. The bottle can 50 is filled with a carbonated beverage. First, the cap before being attached to the bottle can 50 will be described. As shown in FIG. 2, this cap 10 has a cap body 20 made of an aluminum alloy and a liner 30 provided in the cap body 20. The cap body 20 is integrally formed with a disk-shaped top surface portion 21 and a peripheral wall portion 22 that extends in a cylindrical shape centered on the cap central axis C toward the lower end side (the lower side in FIG. 2) via a bent portion 21a from the outer periphery of the top surface portion 21.

[0018] [Cap Body] On the peripheral wall portion 22 of the cap body 20, on the upper end portion side near the top surface portion 21, there is a knurl portion 23 that bulges toward the outer peripheral side in the radial direction with respect to the cap central axis C toward the lower end side, a groove 24 that is recessed toward the inner peripheral side connected to the lower end of this knurl portion 23, a thread forming planned portion 25, a bead 26 that bulges toward the outer peripheral side, a breakable portion 28 having a smaller diameter than this bead 26 and formed with a plurality of slits 27 spaced apart in the circumferential direction, and a cylindrical skirt portion (open end portion) 29 that extends to the lower end of the cap body 20, are formed so as to go around the peripheral wall portion 22 around the cap central axis C.

[0019] The composition of the aluminum alloy plate constituting the cap body 20 is not necessarily limited, but for example, in mass %, Mn: 0.85 to 1.1%, Mg: 0.85 to 1.35%, Si: 0.2 to 0.4%, Fe: 0.35 to 0.60%, Cu: 0.20 to 0.35%, Zn: 0.1 to 0.3% are contained, and the balance is composed of inevitable impurities and Al, and such a material can be used.

[0020] Aluminum alloys of this composition can utilize recycled materials from used aluminum beverage cans (UBCs). Recycled UBCs refer to aluminum alloys obtained by casting from molten UBCs, either by melting UBCs directly, or by mixing UBCs with high-purity raw materials or a master alloy, along with aluminum scrap such as process offcuts generated during the manufacturing process of aluminum alloy sheets and can manufacturing.

[0021] To manufacture this aluminum alloy sheet, an ingot is prepared from molten metal satisfying the above composition, followed by a homogenization treatment and soaking treatment, for example, holding at 560-610°C for 4 to 10 hours. After that, hot rolling is performed, followed by cold rolling to the desired thickness, and then final stabilization annealing is performed. In hot rolling, a rolling mill (not shown) equipped with a pair of upper and lower work rolls and a backup roll is used, and the sheet material is passed back and forth multiple times between the work rolls to roll it to the required thickness. Intermediate annealing may be performed during cold rolling, followed by final cold rolling. In the final cold rolling, an aluminum alloy sheet with a rolling ratio of 20-45% and a thickness of 0.20-0.51 mm is obtained.

[0022] The aluminum alloy sheets produced in this way are then coated with paint and baked, for example, by being held at 190°C for 10 minutes to 1 hour. The mechanical properties after hardening are, for example, tensile strength: 200-230 MPa, yield strength: 140-200 MPa, elongation: 4% or more, ear ratio: 5.5% or less, the average value of the work hardening index (n value as defined in JIS Z 2253) at angles of 0°, 45°, and 90° with respect to the rolling direction is 0.15 or less, and the difference between the maximum and minimum values ​​of these n values ​​is 0.005 or less.

[0023] To manufacture the cap body 20 using the aluminum alloy sheet described above, the following steps are performed: a cap shell forming step in which the aluminum alloy sheet is press-formed to integrally form a cap shell 43, as shown in Figure 4, in which a disc-shaped top surface portion 41 and a peripheral wall portion 42 extending cylindrically from the outer circumference of the top surface portion 41 via a bent portion 41a are formed; a peripheral wall processing step in which the peripheral wall portion 42 of the cap shell 43 is processed; and a liner mounting step. These steps are briefly described below.

[0024] (Cap shell formation process) An aluminum alloy sheet is sandwiched between an upper and lower die and punched out into a disc-shaped blank. At the same time, the periphery of the blank is pressed down and trimmed by drawing using a die and a punch (neither of which are shown in the figure), thereby forming a cap shell 43 as shown in Figure 4. In this cap shell 43, the peripheral wall portion 42 is a straight cylindrical shape.

[0025] (Peripheral wall processing process) In the peripheral wall processing step, the peripheral wall portion 42 of the cap shell 43 is sandwiched between an inner forming tool (not shown) positioned inside the cap shell 43 and a relatively large arc-shaped outer forming tool (not shown) positioned outside the cap shell 43. By rotating the inner forming tool while rolling the cap shell 43 along the arc of the outer forming tool, knurled portions 23, grooves 24, beads 26, easily breakable portions 28 with multiple slits 27, and a skirt portion 29 are formed on the peripheral wall portion 42 of the cap shell 43, thereby forming the cap body 20. Then, by attaching a separately prepared liner 30 to the cap body 20 manufactured in this manner, the cap 10 is produced.

[0026] [liner] As shown in Figure 3, the liner 30 comprises a sliding layer 31 disposed on the inner surface of the top surface 21 of the cap body 20, and a sealing layer 32 laminated on the sliding layer 31 and more flexible than the sliding layer 31. The sliding layer 31 further consists of multiple layers and has a five-layer structure in which a surface resin layer 33 that can slide in contact with the inner surface of the top surface 21, an adhesive layer 34, an intermediate layer 35 having gas barrier properties, an adhesive layer 36, and a surface resin layer 37 (on the back side) are laminated in this order. The surface resin layer 33 is slidably in contact with the inner surface of the top surface 21 and is made of a polyolefin resin such as polyethylene or polypropylene. The surface resin layer 37 on the back side is made of the same material as the surface resin layer 33 on the front side, but it may be made of a different material. This surface resin layer 37 on the back side also has the function of adhering the sealing layer 32. The two adhesive layers 34 and 36 are used to bond the front and back surface resin layers 33 and 37 to the intermediate layer 35, and modified olefin resin is used for this purpose.

[0027] The intermediate layer 35 is formed of a material having higher gas barrier properties than the surface resin layers 33, 37 and the sealing layer 32, such as metal foil or a gas barrier resin. Examples of metal foils used as the intermediate layer 35 include aluminum, iron, and tin. As the barrier resin, organic gas barrier resins such as EVOH resin (ethylene-vinyl alcohol copolymer resin), PA (nylon), and PAN (polyacrylonitrile) are preferred.

[0028] In this case, when metal foil is used as the intermediate layer 35, suitable materials for lamination on both sides include heat-resistant PET film, polypropylene film, and baking paint such as epoxy phenol. Alternatively, for metal foils such as aluminum, iron, and tin, synthetic resin paints such as epoxy phenol may be applied as surface resin layers 33 and 37. In this case, it is preferable that a surface resin layer 37, either a paint that adheres to the sealing layer 32 or a paint with added adhesive components, be formed on the surface facing the sealing layer 32 for adhesion to the sealing layer 32. When surface resin layers 33 and 37 are directly applied to the intermediate layer 35 using paint, the adhesive layers 34 and 36 can be omitted.

[0029] Furthermore, the sealing layer 32 is formed by mold molding on top of the sliding layer 31 (on top of the surface resin layer 37 on the back side), and various elastomers are suitable, but olefin-based elastomers and styrene-based elastomers are suitable in terms of cost, heat resistance, adhesion to the sliding layer, moldability, etc. In particular, when retort processing is performed, a styrene-based elastomer, which is a blend of styrene block copolymer, polypropylene resin, and a flexible material such as liquid paraffin, is preferred. The outer periphery of the sealing layer 32 that comes into contact with the curled portion 56 of the bottle can 50 is formed as a thicker portion 32a than the central portion.

[0030] The SBC (hydrogenated styrene-conjugated diene block copolymer rubber) used in this elastomer is a low MFR (less than 0.01 g / 10 min at 230°C-5 kg) SEBS (styrene-ethylene-butylene-styrene: hydrogenated styrene-butadiene block copolymer rubber) or SEPS (styrene-ethylene-propylene-styrene: hydrogenated styrene-isoprene block copolymer rubber using isoprene polymer blocks). Other SBCs such as SIS, SBS, and SIBS have insufficient heat resistance and cannot withstand retort processing. Liquid paraffin is commonly used as a flexuring agent for this retortable styrene-based elastomer, but polybutene and other materials can also be used.

[0031] [Bottle can] On the other hand, the bottle can 50 to which this cap 10 is attached is made of thin sheet metal of aluminum or aluminum alloy, and as shown in Figure 5, is formed by a bottomed cylindrical body 51, a tapered shoulder 52 that bends radially inward at the upper end of the body 51 and gradually decreases in diameter upward in the direction of the can axis, and a mouth 53 that is continuous with the upper end of the shoulder 52. The mouth 53 also has a bulge 54 formed at the upper end of the shoulder 52, a male threaded portion 55 that is continuous with the upper end of the bulge 54, and a curled portion 56 in which the opening end of the male threaded portion 55 is rounded so as to be folded radially outward.

[0032] [Filling and capping] Then, at the filling plant, after the carbonated beverage is filled into the bottle can 50, the cap 10 is placed over the mouth 53 of the bottle can 50 and attached to the mouth 53 by threading or other means (capping). This carbonated beverage may include carbonated water, sodas with added fruit juice or flavorings / colors, cider, cola, ginger ale, tonic water, etc., or it may be a canned alcoholic beverage, so-called RTD (Ready to Drink), that has been diluted with water or carbonated water. These are filled with a gas volume of 2.0 GV to 4.0 GV. As shown in Figure 6, the capping device 60 includes a mounting plate 61 on which the bottle can 50 is placed, a pressure block 62 that presses the cap 10 placed over the mouth 53 of the bottle can 50 from above in the direction of the can axis C, and a plurality of capping rolls (first roll 63 and second roll 64) that perform screw threading or the like while pressing the peripheral wall portion 22 of the cap 10 radially inward.

[0033] The pressure block 62 is movable relative to the can axis, and its lower end has a draw-shaped inner surface 62a, allowing it to draw-form the periphery of the cap 10. This drawing process forms a stepped portion 75 on the periphery of the cap 10. When the periphery of the cap 10 is drawn and the stepped portion 75 is formed, the area in which the liner 30, which is positioned on the inner surface of the cap 10, is pressed against the curl portion 56 of the bottle can 50 increases, and the surface pressure also increases, thus improving the sealing performance. The inside of the pressure block 62 is formed into a cylindrical cavity into which the cap retainer 66 is inserted. A spring 67 is provided between the pressure block 62 and the cap retainer 66, allowing the cap 10 to be pressed against the bottle can 50 with a predetermined pressing force. The first roll 63 and the second roll 64 are supported so as to be able to pivot around the cap 10 and move in the can axis direction.

[0034] Then, with the cap 10 placed over the mouth 53 of the bottle can 50, the cap holder 66 presses down on the top surface 21 of the cap 10, and in that state, the pressure block 62 performs drawing on the periphery of the top surface 21, so that the periphery is crushed into an annular shape and a stepped portion 75 with a drawing depth H (see Figure 1) is formed. In addition, the thread forming portion 25 between the groove 24 and the bead 26 is pressed radially outward by the first roll 63 against the mouth 53 of the bottle can 50, so that a female thread portion 76 is formed following the male thread portion 55 formed on the mouth 53, and the skirt portion 29 is wrapped around the lower surface of the bulge portion 54 by the second roll 64, so that the cap 10 is attached to the mouth 53.

[0035] By capping in this manner, the cap 10 is deformed by the pressure block 62 and the two rolls 63 and 64, and the deformed cap 70 presses the internal liner 30 not only against the upper surface of the curled portion 56 of the mouth 53 of the bottle can 50, but also against the outer surface of the curled portion 56 at the stepped portion 65, and the female threaded portion 76 engages with the male threaded portion 55 in a screwed state, thereby sealing the inside of the bottle can 50 as shown in Figure 1.

[0036] When the cap 70 is attached to the bottle can 50, the top surface 73 has an annular stepped portion 75 at its peripheral edge, and the area radially inward from the stepped portion 75 is formed as a nearly flat surface. On the other hand, the peripheral wall portion 72 is formed by extending downward from a point one step below the top surface 73 by the stepped portion 75, via a bent portion 75a on the outer circumference of the stepped portion 75. Before capping, as shown in Figure 2, the cap 10 had a nearly flat, disc-shaped top surface 21 that was continuous with the peripheral wall 22 via a bent portion 21a. However, after capping, as shown in Figure 1, the top surface 73 is no longer a flat disc shape due to the presence of a stepped portion 75, and the top surface 73 and the peripheral wall 72 are continuous via a bent portion 75a on the outer circumference of the stepped portion 75.

[0037] In this capped bottle can 71, the cap 70 has a top surface 73 whose peripheral edge is processed into a stepped portion 75 by a pressure block 62, and the central portion is not processed during cap formation or capping. Therefore, its Vickers hardness is almost the same as that of an aluminum alloy sheet, and is between 60HV and 75HV.

[0038] In contrast, the peripheral wall portion 72 undergoes drawing in the cap shell forming process, knurled sections 23 and the like in the peripheral wall processing process, and is also subjected to threading during capping, resulting in a higher Vickers hardness of 70 HV to 86 HV. In this case, the Vickers hardness of the peripheral wall portion 72 is higher than that of the top surface portion 73, and moreover, the difference in Vickers hardness between the peripheral wall portion 72 and the top surface portion 73 is greater than the difference in Vickers hardness between the peripheral wall portion 22 and the central part of the top surface portion 21 (excluding the area near the stepped portion 75) of the cap 10 before capping, and is formed to be, for example, 3 HV to 25 HV. In conventional bottle cans with caps, the difference in Vickers hardness is usually around 2HV or less, and in some cases, there is almost no difference at all.

[0039] The optimal Vickers hardness of the top surface 73 is 68 HV to 73 HV, and the optimal Vickers hardness of the peripheral wall 72 (especially the female thread portion 76) is 70 HV to 75 HV. Furthermore, the difference in Vickers hardness between the peripheral wall 22 and the central part of the top surface 21 is more preferably 5 HV to 20 HV, and even more preferably 10 HV to 16 HV.

[0040] In the carbonated beverage bottle can 71 with a cap of this embodiment, the cap 10 is molded using the aforementioned material and capped onto the bottle can 50. Since it is screw-fitted by the peripheral wall portion 72 with high Vickers hardness, the airtightness is enhanced. Furthermore, the Vickers hardness of the top portion 73 is lower than that of the peripheral wall portion 72, and it has good workability, so the deep drawing of the cap periphery is good, and deep drawing to a predetermined depth H is possible with low load, resulting in good airtightness. Furthermore, since the liner 30 is provided with an intermediate layer 35 that has gas barrier properties, it suppresses the permeation of gas into carbonated beverages and has excellent sealing properties.

[0041] On the other hand, the peripheral wall portion 72 of the cap 70 has a high Vickers hardness and the amount of screw deformation is small, so even if the groove depth of the female thread portion 76 is formed shallowly, the pressure resistance is sufficiently high and the sealing performance is not impaired. It is thought that forming the female thread portion 76 shallowly contributes to a reduction in the opening torque. In addition, the top portion 73 is lifted by the internal pressure of the can due to the carbonated beverage, which generates a tensile force in the female thread portion 76. It is thought that this tensile force reduces the amount of deformation of the female thread portion 76, and thus the opening torque also decreases.

[0042] In this case, by setting the Vickers hardness of the top surface 73 of the cap 70 to 60HV or more and 75HV or less, and the Vickers hardness of the peripheral wall 72 to 70HV or more and 86HV or less, a cap is obtained that is less prone to screw deformation, has a lower opening torque, and has better sealing performance compared to conventional caps.

[0043] If the Vickers hardness of the top surface 73 is less than 60 Hv, the top surface 73 will have good drawability, but the peripheral wall 72 will also have a low Vickers hardness, making it prone to screw deformation. Conversely, if the Vickers hardness of the top surface 73 is increased to more than 75 Hv, the Vickers hardness of the peripheral wall 72 will become too high, which may impair screw formability and compromise sealing performance. If the Vickers hardness of the peripheral wall portion 72 is less than 70 Hv, the thread machinability improves, but the pressure resistance decreases due to the decrease in the Vickers hardness of the top surface portion 73. Conversely, if the Vickers hardness of the peripheral wall portion 72 is increased to more than 86 HV, the draw-formability of the top surface portion 73 decreases, resulting in poor sealing performance.

[0044] If the difference in Vickers hardness is less than 3HV, selecting a Vickers hardness that allows for deep drawing (in other words, selecting a Vickers hardness considering the deep drawing formability of the cap top surface 73) will also result in a lower Vickers hardness of the peripheral wall 72, making it impossible to adequately prevent screw deformation and thus impossible to reduce the opening torque. Alternatively, increasing the Vickers hardness of the peripheral wall 72 will also increase the Vickers hardness of the top surface 73, reducing its deep drawing formability and thus its sealing performance.

[0045] On the other hand, if the difference in Vickers hardness exceeds 25 HV, even if a material with a Vickers hardness suitable for deep drawing is selected for the top surface 73, the Vickers hardness of the peripheral wall 72 may become too high, resulting in poor thread formability and potentially compromising sealing performance. Alternatively, if a material with a low Vickers hardness value suitable for thread machinability is selected for the peripheral wall 72, the Vickers hardness of the top surface 73 will also decrease further, potentially causing the top surface to bulge excessively due to internal pressure, impairing the can's transportability. Furthermore, the pressure resistance will also decrease.

[0046] It should be noted that the present invention is not limited to the configuration of the above-described embodiment, and various modifications can be made without departing from the spirit of the invention. For example, while a specific composition of aluminum alloy sheet was given as an example for use in the cap, it is not limited to this, and JIS 3000 series, 5000 series, or other aluminum alloy sheets can be used. [Examples]

[0047] Two types of aluminum alloys were prepared: a conventional product with a thickness of 0.230 mm made from JIS standard 5000 series aluminum alloy, and an embodiment product made from aluminum alloy manufactured by the method of the embodiment described above. Paint was applied to both sides of the conventional product, and the cap body was manufactured by press molding. In this case, the inner coating of the conventional product was epoxy resin, and the inner coating of the embodiment product was polyester resin. Then, a liner was attached to the inside of the cap body, and after filling the bottle can with a carbonated beverage with a gas volume of GV3.0, the opening was capped. After capping, it was sterilized by passing it through a pasteurizer at 70°C for 10 minutes. Cross-sectional samples were prepared by embedding the cap body before capping and the threaded cap removed from the bottle after capping into resin, and then cutting vertically through the center.

[0048] Of the obtained cross-sectional samples, Vickers hardness was measured at two points near the center of the top surface and at 12 arbitrary points in the threaded portion of the peripheral wall. The average value was calculated for both the top surface and the peripheral wall. Vickers hardness was measured according to Japanese Industrial Standard (JIS) Z 2244:2009, with a load of 100 gf and a holding time of 15 seconds. The measurement results are shown in Table 1.

[0049] [Table 1]

[0050] Furthermore, for both the conventional product and this embodiment, the constriction depth H (average value of 10 cans), the female thread depth (average value of 10 cans), and the opening torque at 5°C and 20°C (average value of 10 cans each) were measured. In this case, the opening torque was measured as the maximum torque when the cap begins to rotate during opening (1st torque: denoted as "1st") and the maximum torque when the bridge breaks thereafter (2nd torque: denoted as "2nd"). These results are shown in Table 2.

[0051] [Table 2]

[0052] Furthermore, with this embodiment, five bottle cans cooled to 5°C were dropped in an inverted position from a height of 30 cm above a steel plate tilted at 10° to the horizontal, and the change in weight was measured. The results are shown in Table 3.

[0053] [Table 3]

[0054] Based on the results above, when carbonated beverages are filled into bottle cans using the cap of this embodiment, the 1st opening torque is reduced, making them easier to open, as shown in Table 2. As mentioned earlier, the inner coating of the conventional product is epoxy resin, while the inner coating of this embodiment is polyester resin, so a direct comparison is not possible. Even if polyester resin has a greater effect in reducing opening torque, this embodiment has an even greater effect in reducing opening torque (1st torque). The 2nd torque is considered to be about the same for both the conventional product and this embodiment. In this case, although the drawing depth of the top surface of this embodiment is greater than that of the conventional product, the thread depth of the peripheral wall is considered to be approximately the same. However, since the Vickers hardness of the peripheral wall of this embodiment is high, it is assumed that the thread depth will often be shallower. Furthermore, as shown in Table 3, this embodiment exhibits excellent drop resistance, and together with the results in Table 2, it can be seen that it is easy to open and has excellent sealing properties. [Explanation of Symbols]

[0055] 10 caps 20 Cap body 21 Top section 22 Peripheral wall section 23 Naru Department 24 Grooves 25 Thread forming section 26 Bead 27 slits 28. Easily breakable portion 29 Skirt section 30 Liner 31 Sliding layer 32 Sealing layer 32a Thick wall part 33,37 Surface resin layer 34,36 Adhesive layer 35. Intermediate layer (gas barrier layer) 43 Cap Shell 50 bottle cans 53 Mouth 54 Bulge 55 Male threaded section 56 Curl section 60 Capping device 62 Pressure Block 63 Roll 1 64. Second Roll 70 caps 71 Bottle cans with caps 72 Peripheral wall part 73 Top section 75 Step part 76 Female thread section

Claims

1. A bottle can with a cap for carbonated beverages, characterized in that a cap is fitted to the mouth of the bottle can, the cap comprises a cap body made of an aluminum alloy and a liner provided inside the cap body, the cap body has a top surface and a peripheral wall integrally formed, and a female screw portion is formed on the peripheral wall that engages with the male screw portion on the outer circumference of the mouth, the Vickers hardness of the top surface of the cap is 60 HV or more and 75 HV or less, and the Vickers hardness of the peripheral wall is 70 HV or more and 86 HV or less, and the Vickers hardness of the peripheral wall is formed to be 3 HV or more and 25 HV or less higher than that of the top surface, and the bottle can is filled with a carbonated beverage.

2. The liner comprises a sliding layer disposed in contact with the inner surface of the top surface of the cap body, and a sealing layer made of elastomer laminated on the sliding layer, wherein the sliding layer consists of multiple layers, and at least one layer is a gas barrier layer, as described in claim 1.

3. The carbonated beverage bottle can with a cap according to claim 1 or 2, characterized in that the aluminum alloy contains recycled material from used aluminum beverage cans.

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