Bottle can with cap

Abstract

To reduce cap-opening torque while maintaining a sealing performance of a cap itself, and increase a freedom of choice of paint, etc.SOLUTION: A cap is attached to a mouth of a bottle can, and the cap has a top surface portion and a peripheral wall portion formed integrally therewith, and a female screw portion is formed on the peripheral wall portion to engage with a male screw portion on an outer periphery of the mouth portion, and the peripheral wall portion is formed to have a Vickers hardness higher than that of the top surface portion, and a difference in Vickers hardness between the peripheral wall portion and the top surface portion is 3 HV or more and 25 HV or less, and preferably 5 HV or more and 20 HV or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a bottle can with a cap, in which the mouth of a bottle can having a bottle-shaped body is sealed with a cap.

Background Art

[0002] As containers for various carbonated beverages, alcoholic beverages, etc., bottle cans with a structure in which a cap is attached to and seals the mouth of a bottle-shaped body (bottle-shaped body) are widespread. As this bottle can cap, conventionally, for example, the one described in Patent Document 1 is known. This cap includes a cap body made of aluminum or an aluminum alloy in which a top surface portion and a peripheral wall portion are integrally formed, and a resin disc-shaped liner disposed on the inner surface of the top surface portion. Further, at a portion of the peripheral wall portion near the top surface portion, a knurl portion that bulges outward and a groove that is continuous with the lower end of the knurl portion and has a smaller diameter than the knurl portion are formed. At the lower end portion of the peripheral wall portion, a bead that bulges outward, an easily breakable portion having a smaller diameter than this bead, and a cylindrical skirt portion (open end portion) that has a larger diameter than this easily breakable portion and extends to the lower end of the cap body are formed.

[0003] By the way, in recent years, due to the disruption of the distribution network, for example, epoxy paint is in short supply, and a polyester-based inner surface paint of the cap may be used as an alternative paint. However, when using a polyester paint on the inner surface of the cap, the opening torque tends to increase. Also, depending on whether the outer surface paint of the bottle can is an aqueous paint or the selection of the combination of the outer surface paint of the bottle can and the inner surface paint of the cap, the opening torque may become high. From the perspective of procurement, a new technology for reducing the opening torque is required to make the selection of paints more flexible.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of such circumstances, and an object thereof is to reduce the opening torque while maintaining the original sealing performance of the cap and to increase the degree of freedom in the selection of paints.

Means for Solving the Problems

[0006] The bottle can with a cap of the present invention has a cap attached to the mouth portion of the bottle can. The cap has a top surface portion and a peripheral wall portion integrally formed, and a female screw portion that engages with a male screw portion on the outer periphery of the mouth portion is formed on the peripheral wall portion. The Vickers hardness of the peripheral wall portion is formed higher than that of the top surface portion, and the difference in Vickers hardness between the peripheral wall portion and the top surface portion is 3 HV or more and 25 HV or less.

[0007] The cap body is formed into a cup shape composed of a top surface portion and a peripheral wall portion by drawing an aluminum plate material. The peripheral wall portion of the cap body is processed with a knurled portion or the like and is also screw-processed by capping. On the other hand, the top surface portion of the cap is formed with a stepped portion by drawing the peripheral edge portion thereof during capping. Since the peripheral wall portion is processed a plurality of times in this way, the Vickers hardness of the peripheral wall portion tends to be higher than that of the top surface portion. In a well-known cap, the difference is 2 HV or less. In the present invention, by setting the difference in Vickers hardness to 3 HV or more and 25 HV or less, a cap can be obtained that is less likely to deform the screw, has a low opening torque, and has good sealing performance as compared with a conventional cap.

[0008] If the difference in Vickers hardness is less than 3 HV, when selecting a Vickers hardness that allows drawing (in other words, selecting a Vickers hardness in consideration of the drawability of the top surface portion of the cap), the Vickers hardness of the peripheral wall portion also becomes low, so that it becomes impossible to sufficiently prevent the screw from deforming and the opening torque cannot be lowered. Alternatively, if the Vickers hardness of the peripheral wall portion is increased, the Vickers hardness of the top surface portion also increases, so that the drawability decreases and the sealing performance decreases.

[0009] On the other hand, if the difference in Vickers hardness exceeds 25 HV, even when a material with a Vickers hardness of the top surface portion that can be drawn is selected, the Vickers hardness of the peripheral wall portion becomes too high, resulting in poor thread formability and a risk of deteriorating the sealing performance. Or, when a material with a small Vickers hardness and good thread processability is selected for the peripheral wall portion, the Vickers hardness of the top surface portion also further decreases. Therefore, due to the influence of the internal pressure of the can, the top surface portion may bulge too much, risking deterioration of the transportability of the can. Also, the pressure resistance strength decreases.

[0010] The difference in Vickers hardness is more preferably 5 HV or more and 20 HV or less, and even more preferably 10 HV or more and 16 HV or less.

[0011] In the capped bottle can of the present invention, it is preferable that the Vickers hardness of the top surface portion of the cap is 60 HV or more and 75 HV or less, and the Vickers hardness of the peripheral wall portion is 70 HV or more and 86 HV or less.

Advantages of the Invention

[0012] According to the present invention, the Vickers hardness of the peripheral wall portion is formed to be greater than that of the top surface portion, and the difference in Vickers hardness is 3 HV or more and 25 HV or less. As a result, the Vickers hardness of the peripheral wall portion is sufficiently greater than that of the top surface portion, so that the amount of deformation of the thread due to the influence of the internal pressure of the can is reduced, and the initial opening torque can be lowered. Also, since the Vickers hardness of the top surface portion is smaller than that of the peripheral wall portion, the drawing forming of the peripheral edge portion of the cap top surface portion is good, and drawing forming to a predetermined depth is possible with a low load, resulting in good sealing performance. Furthermore, the doming of the top surface portion due to the internal pressure of the can becomes an appropriate amount, and increasing the surface pressure on the liner and the curled portion also contributes to improving the sealing performance.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0014] 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. 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 aluminum or an aluminum alloy, and a resin liner 30 provided inside 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 around the cap central axis C from the outer periphery of the top surface portion 21 toward the lower end side (the lower side in FIG. 2) via a bent portion 21a.

[0015] On the peripheral wall portion 22 of the cap body 20, near the upper end portion closer to the top surface portion 21, there are a narl portion 23 that bulges radially outward with respect to the cap central axis C toward the lower end side, a groove 24 that is recessed inwardly continuous with the lower end of this narl portion 23, a thread forming planned portion 25, a bead 26 that bulges outwardly, a breakable portion 28 in which a plurality of slits 27 are formed at intervals in the circumferential direction with a smaller diameter than this bead 26, 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.

[0016] The composition of the aluminum alloy plate constituting the cap body 20 is not necessarily limited. For example, by mass%, it contains 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%, and the balance consists of inevitable impurities and Al, and such an alloy can be used.

[0017] For this aluminum alloy of this composition, recycled materials of used aluminum cans (UBC: Used Beverage Can) can be used. The recycled material of UBC means an aluminum alloy obtained by casting from a UBC melt obtained by melting UBC as it is, or from a melt obtained by mixing UBC, high-purity raw materials or master alloys, and aluminum scraps such as process end materials generated in the manufacturing process of aluminum alloy plates and the can manufacturing process.

[0018] To manufacture this aluminum alloy plate, an ingot is made from a melt satisfying the above composition, and after performing a homogenization treatment and a soaking treatment by holding at, for example, 560 to 610°C for 4 hours or more and 10 hours or less, hot rolling is performed, followed by cold rolling. After obtaining the target plate thickness, a stabilizing final annealing is performed. In hot rolling, a rolling mill (both not shown) equipped with a pair of upper and lower work rolls and backup rolls is used, and the plate material is reciprocated between the work rolls a plurality of times to roll it to the required thickness. Intermediate annealing may be performed during cold rolling and final cold rolling may be performed. In the final cold rolling, an aluminum alloy plate with a rolling ratio of 20 to 45% and a plate thickness of 0.20 to 0.51 mm can be obtained.

[0019] The aluminum alloy plate manufactured in this way is coated with paint and baked by holding at, for example, 190°C for 10 minutes to 1 hour. The mechanical properties after baking are, for example, tensile strength: 200 to 230 MPa, yield strength: 140 to 200 MPa, elongation: 4% or more, ear rate: 5.5% or less, and the average value of the work hardening index (n value defined in JIS Z2253) at angles of 0°, 45°, and 90° with respect to the rolling direction is 0.15 or less, and the difference between the maximum value and the minimum value of these n values is 0.005 or less.

[0020] In order to manufacture the cap body 20 using the aluminum alloy sheet as described above, the aluminum alloy sheet is press-formed to form a cap shell 43 in which a disk-shaped top surface portion 41 and a peripheral wall portion 42 extending cylindrically through a bent portion 41a from the outer periphery of the top surface portion 41 are integrally formed as shown in FIG. 3, a peripheral wall portion processing step of processing the peripheral wall portion 42 of the cap shell 43, and a liner mounting step are carried out. These steps will be briefly described below.

[0021] [Cap Shell Forming Step] The aluminum alloy sheet is sandwiched between an upper die and a lower die and punched into a disk-shaped blank, and while holding the peripheral edge portion of the blank, it is drawn and trimmed by a die and a punch (both not shown) to form the cap shell 43 as shown in FIG. 3. In this cap shell 43, the peripheral wall portion 42 is a straight cylindrical shape.

[0022] [Peripheral Wall Portion Processing Step] In the peripheral wall portion processing step, the peripheral wall portion 42 of the cap shell 43 is sandwiched between an inner molding tool (not shown) disposed inside the cap shell 43 and a relatively large arc-shaped outer molding tool (not shown) disposed outside the cap shell 43, and while rotating the inner molding tool, the cap shell 43 is rolled along the arc of the outer molding tool, so that a breakage prone portion 27 having a knurl portion 23, a groove 24, a bead 25, a plurality of slits 26, and a skirt portion 28 is formed on the peripheral wall portion 42 of the cap shell 43, thereby forming the cap body 20.

[0023] Then, the cap 10 is manufactured by attaching a separately prepared liner 30 to the cap body 20 thus produced. This liner 30 is, for example, made of a hard resin mainly composed of polyethylene or polypropylene and has a large-diameter sliding layer 31 disposed in a non-adhesive state on the top surface side, and a resin such as an elastomer resin softer than the sliding layer 31 disposed directly or via an intermediate layer such as a barrier layer on the side opposite to the top surface 21 of the sliding layer 31, and a small-diameter sealing layer 32. It has a multi-layer structure.

[0024] On the other hand, the bottle can 50 to which the cap 10 is attached is made of a thin sheet metal of aluminum or an aluminum alloy, and as shown in FIG. 4, it has a bottomed cylindrical body portion 51, and a tapered shoulder portion 52 that bends radially inward at the upper end of the body portion 51 and gradually reduces in diameter upward in the can axis direction, and a mouth portion 53 continuous with the upper end of the shoulder portion 52. Further, the mouth portion 53 has a bulging portion 54 formed at the upper end of the shoulder portion 52, a male screw portion 55 continuous with the upper end of the bulging portion 54, and a curled portion 56 in which the opening end portion is rounded so as to fold back radially outward at the upper end of the male screw portion 55.

[0025] Then, at the filling factory, the cap 10 is placed over the mouth portion 53 of the bottle can 50 filled with beverage, and by performing screw processing or the like, it is attached to the mouth portion 53 (capping). As shown in FIG. 5, this capping device 60 has a placement plate 61 on which the bottle can 50 is placed, a presser block 62 that presses the cap 10 placed over the mouth portion 53 of the bottle can 50 downward in the can axis C direction from above, and a plurality of capping rolls (first roll 63 and second roll 64) that perform screw processing or the like while pressing the peripheral wall portion 22 of the cap 10 radially inward.

[0026] The pressure block 62 is relatively movable in the can axis direction, and the inner side of the lower end portion is a drawing type 62a, and the peripheral edge portion of the cap 10 can be drawn. By this drawing, a stepped portion 75 is formed on the peripheral edge portion of the cap 10. When the peripheral edge portion of the cap 10 is drawn and the stepped portion 75 is formed, the area where the liner 30 disposed on the inner surface of the cap 10 is pressed against the curled portion 56 of the bottle can 50 increases and the surface pressure also increases, so the sealing performance is improved. Further, a cylindrical cavity is formed inside the pressure block 62, and the cap retainer 66 is inserted. A spring 67 is provided between the pressure block 62 and the cap retainer 66, and the cap 10 can be pressed against the bottle can 50 with a predetermined pressing force. Further, the first roll 63 and the second roll 64 are supported so as to be rotatable around the cap 10 and movable in the can axis direction.

[0027] Then, with the cap 10 covering the mouth portion 53 of the bottle can 50, the cap retainer 66 presses the top surface portion 21 of the cap 10, and in that state, the pressure block 62 performs drawing on the peripheral edge portion of the top surface portion 21, so that the peripheral edge portion is annularly crushed to form a stepped portion 75 having a drawing depth H (see FIG. 1). Further, the screw forming planned portion 25 between the groove 24 and the bead 26 is pressed against the mouth portion 53 of the bottle can 50 from the radially outer side by the first roll 63, so that a female screw portion 76 is formed following the male screw portion 55 formed on the mouth portion 53. Also, the skirt portion 29 is caught by the lower surface of the bulging portion 54 by the second roll 64, so that the cap 10 is attached to the mouth portion 53.

[0028] By being capped in this way, the cap 10 is deformed by the pressure block 62 and the two rolls 63 and 64, and the deformed cap 70 presses the inner liner 30 not only on the upper surface of the curled portion 56 of the mouth portion 53 of the bottle can 50 but also on the outer peripheral surface of the curled portion 56 at the stepped portion 65. Further, the female screw portion 66 is engaged with the male screw portion 55 in a screwed state to seal the inside of the bottle can 50 as shown in FIG. 1.

[0029] When the cap 70 is attached to the bottle can 50, the top surface portion 73 has an annular stepped portion 75 formed at its peripheral edge, and the portion radially inside the stepped portion 75 is formed as a substantially flat surface. On the other hand, the peripheral wall portion 72 is formed to extend downward from a position one step lower from the top surface portion 73 by the stepped portion 75 through the bent portion 75a on the outer periphery of the stepped portion 75. In the cap 10 before capping, as shown in FIG. 2, a substantially flat disc-shaped top surface portion 21 was continuous with the peripheral wall portion 22 through the bent portion 21a. However, after capping, as shown in FIG. 1, the top surface portion 73 is no longer a flat disc shape due to the presence of the stepped portion 75, and the top surface portion 73 and the peripheral wall portion 72 are continuous through the bent portion 75a on the outer periphery of the stepped portion 75.

[0030] In this capped bottle can 71, for the cap 70, its top surface portion 73 has its peripheral edge processed into the stepped portion 75 by the pressure block 62 and is not processed at the central portion during both cap forming and capping. Therefore, its Vickers hardness remains substantially in the state of an aluminum alloy plate.

[0031] On the other hand, for the peripheral wall portion 72, in its manufacturing process, it is drawn in the cap shell forming process, the knurl portion 23 etc. are processed in the peripheral wall portion processing process, and also screw processing etc. are performed during capping. Therefore, its Vickers hardness has increased. The difference in Vickers hardness between the peripheral wall portion 72 and the top surface portion 73 is larger than the difference in Vickers hardness between the peripheral wall portion 22 and the central portion (the portion excluding the vicinity of the stepped portion 75) of the top surface portion 21 in the cap 10 before capping, and is formed to be 3 HV or more and 25 HV or less. In a conventional general capped bottle can, the difference in Vickers hardness is about 2 HV or less, and there may be almost no difference in some cases.

[0032] In the capped bottle can 71 of the present embodiment, the cap 10 is formed using the above-described materials and capped onto the bottle can 50. As a result, the Vickers hardness of the peripheral wall portion 72 is formed higher than that of the top surface portion 73 in the range of 3 HV or more and 25 HV or less. When the top surface is lifted by the internal pressure of the can, a tensile force is generated in the thread. Due to this tensile force, the amount of deformation of the thread is considered to become smaller and the opening torque is considered to decrease. On the other hand, since the Vickers hardness is high and the amount of deformation of the thread is small, even if the groove depth of the female thread portion 66 is formed shallow, the pressure resistance is sufficiently high and the sealing performance is not impaired. Forming the thread shallowly is also considered to contribute to a decrease in the opening torque.

[0033] According to the present invention, the Vickers hardness of the peripheral wall portion 72 is formed larger than that of the top surface portion 73, and the difference in Vickers hardness is 3 HV or more and 25 HV or less. Therefore, the Vickers hardness of the peripheral wall portion 72 is sufficiently large compared to the top surface portion. Due to the influence of the internal pressure of the can, the amount of deformation of the thread becomes smaller, and the opening torque can be reduced. In addition, since the workability of the top surface portion is relatively good, the drawing forming of the peripheral edge portion of the cap is good, and drawing forming with a low load and a predetermined depth H is possible, so the sealing performance is improved. If the difference in Vickers hardness is less than 3 HV, when selecting the Vickers hardness that allows drawing (in other words, selecting the Vickers hardness in consideration of the draw formability of the cap top surface portion), the Vickers hardness of the peripheral wall portion 72 also becomes low, so that the deformation of the thread cannot be sufficiently prevented and the opening torque cannot be reduced. Alternatively, if the Vickers hardness of the peripheral wall portion 72 is increased, the Vickers hardness of the top surface portion 73 also increases, so the draw formability decreases and the sealing performance decreases.

[0034] On the other hand, if the difference in Vickers hardness exceeds 25 HV, even when the Vickers hardness of the top surface portion that can be drawn is selected, the Vickers hardness of the peripheral wall portion 72 becomes too high, resulting in poor thread formability and possibly even deteriorating the sealing performance. Conversely, if the Vickers hardness within the range where threading is possible is selected for the peripheral wall portion 72, the Vickers hardness of the top surface portion 73 decreases. As a result, due to the influence of the internal pressure of the can, the top surface portion 73 may bulge too much, potentially impairing the transportability of the can. Also, the pressure resistance strength decreases.

[0035] The difference in Vickers hardness between this peripheral wall portion 72 and the top surface portion 73 is more preferably 5 HV or more and 20 HV or less, and even more preferably 10 HV or more and 16 HV or less. Also, the optimal Vickers hardness of the top surface portion 73 is 60 HV or more and 75 HV or less, and the optimal Vickers hardness of the peripheral wall portion 72 (especially the female thread portion 76) is 70 HV or more and 86 HV or less.

[0036] Note 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 present invention. For example, as the aluminum alloy plate used for the cap, one with a specific composition was exemplified, but it is not limited thereto, and JIS 3000 series, 5000 series, and other aluminum alloy plates can be used. By appropriately controlling this material, the forming of the cap, and the capping, the difference in Vickers hardness between the peripheral wall portion and the top surface portion can be formed high within the range of 3 HV or more and 25 HV or less.

[0037] In recent years, for the purpose of reducing energy consumption related to the product life cycle, greenhouse gas emissions, etc., and reducing the environmental load, as the composition of the aluminum alloy plate, the proportion of recycled raw materials is increased and the proportion of using new ingots is decreased, and it is also possible to apply an aluminum alloy plate manufactured using such recycled materials.

Examples

[0038] Two types were prepared: a conventional product made of a 5000 series aluminum alloy with a thickness of 0.230 mm in accordance with JIS standards, and an example product of the present embodiment made of an aluminum alloy manufactured by the method of the foregoing embodiment. A polyester-based paint was applied to both sides thereof, and a cap body was produced by press forming. A liner was attached to the inner surface of the cap body, and the bottle can was capped. The cap body before capping and the threaded cap removed from the bottle can after capping were each embedded in resin, and a cross-sectional sample was produced by cutting vertically through the center.

[0039] Among the obtained cross-sectional samples, Vickers hardness was measured at two points near the center of the top surface portion and at any 12 points of the threaded portion of the peripheral wall portion, and the average value was obtained for each of the top surface portion and the peripheral wall portion. The measurement of Vickers hardness was carried out in accordance with Japanese Industrial Standard (JIS) Z 2244:2009 at a load of 100 gf and a holding time of 15 seconds. The measurement results are shown in Table 1.

[0040]

Table 1

[0041] In addition, a plurality of cap bodies of the conventional product and the example product manufactured as described above were each produced, the bottle can was filled with gas water to a predetermined internal pressure of the can, and the cap was screwed onto the bottle can. Then, the bottle can with the cap was retort sterilized under predetermined conditions. Next, for the conventional product and the example product of the present embodiment, the draw depth H (average value of 10 cans) at the stepped portion of the top surface portion, the female thread depth (average value of 10 cans), and the opening torque at 5°C, 20°C, and 60°C (average value of 10 cans each) were measured. In this case, the opening torque was measured as the maximum torque (first torque: denoted as "1st") when the cap starts to rotate at the time of opening, and the maximum torque (second torque: denoted as "2nd") when the bridge is broken thereafter. These results are shown in Table 2.

[0042]

Table 2

[0043] As is clear from Table 2, the product of this example has a larger draw depth on the top surface and a smaller depth of the female screw portion compared to the conventional product. And it can be seen that the opening torque is smaller than that of the conventional product at any temperature, and in particular, the first torque is small, making it easy to open the cap.

[0044] Next, a plurality of types of aluminum alloy plates as the cap material were prepared. After applying a polyester-based paint to both sides of each aluminum alloy plate, a cap body was produced, a liner was attached, and the bottle can was capped at the mouth portion. Then, a cross-sectional sample was produced in the same manner as above, and the Vickers hardness was measured. In this case, the cross-sectional sample was produced by cutting along the rolling direction (0° - 180°) of the aluminum alloy plate.

[0045] In addition, the aluminum alloy plates used were of three types with a tensile strength after paint baking of 208 MPa (Examples 1, 2), 218 MPa (Examples 3, 4), and 222 MPa (Examples 5, 6). Also, when the tensile strength of the conventional product was measured, it was 212 MPa, so the Vickers hardness was measured again.

[0046] The results were as shown in Table 3. Note that the conventional product is described as Conventional Example 1 in Table 3.

[0047]

Table 3

[0048] As shown in this Table 3, in Examples 1 and 2 where the tensile strength of the aluminum alloy plate was small, the difference in Vickers hardness between the top surface portion and the peripheral wall portion was large, and in Examples 5 and 6 where the tensile strength was large, the difference in Vickers hardness between the top surface portion and the peripheral wall portion was small. However, the difference in Vickers hardness was a large value compared to Conventional Example 1.

[0049] Next, the bottle cans were filled with carbonated water to a predetermined can internal pressure, and the caps of Examples 1, 3, and 5 were wound around the bottle cans. After subjecting the bottle cans with caps to retort sterilization under predetermined conditions, the drawing depth H, female thread depth, and opening torque at 5°C, 20°C, and 60°C were measured using a pressure block.

[0050] The results are shown in Table 4.

[0051]

Table 4

[0052] As shown in this Table 4, in Example 1, the drawing depth H was larger than that of the conventional product in Table 2, and the female thread depth was approximately the same. Since the Vickers hardness of the top surface portion in Example 1 was smaller than that of the conventional product, the drawing depth H increased. On the other hand, the female thread depth did not increase compared to the conventional product because the Vickers hardness of the peripheral wall portion was larger than that of the top surface portion, resulting in a female thread depth approximately the same as that of the conventional product. This is considered to be because an aluminum alloy plate with a lower tensile strength than the conventional product was used. In Example 3, the drawing depth H was approximately the same as that of the conventional product, but the female thread depth was smaller than that of the conventional product.

[0053] In Examples 1 and 3, due to the large drawing depth H, good sealing performance can be exhibited. Also, the opening torque was lower than that of the conventional product in both Example 1 and Example 3, except that the 2nd torque at 5°C was slightly higher than that of the conventional product. The difference in the 2nd torque at 5°C from the conventional product was also less than several N·cm, and it is hard to say that it impairs the opening performance. In Example 5, both the drawing depth and the female thread depth were smaller than those of the conventional product, and the opening torque was smaller than that of the conventional product in all cases. From these results, although there are some variations, it can be said that the examples generally have a low opening torque and are easy to open.

Explanation of Signs

[0054] 10 Cap 20 Cap body 21 Top surface part 22 Peripheral wall part 23 Narl part 24 Groove 25 Thread forming planned part 26 Bead 27 Slit 28 Easy break part 29 Skirt part 30 Liner 31 Sliding layer 32 Sealing layer 43 Cap shell 50 Bottle can 53 Mouth part 54 Bulging part 55 Male screw part 56 Curling part 60 Capping device 62 Pressure block 63 First roll 64 Second roll 70 Cap 71 Bottle can with cap 72 Peripheral wall part 73 Top surface part 75 Step part 76 Male screw part

Claims

1. A bottle-can with a cap is attached to the mouth of a bottle-can, the cap having a top surface and a peripheral wall portion formed integrally therewith, the peripheral wall portion having a female thread portion formed therein for engaging with a male thread portion on the outer periphery of the mouth portion, the peripheral wall portion having a higher Vickers hardness than the top surface, and the difference in Vickers hardness between the peripheral wall portion and the top surface being 3 HV or more and 25 HV or less.

2. 2. The bottle-shaped can with a cap according to claim 1, wherein the difference in Vickers hardness is 5 HV or more and 20 HV or less.

3. 2. The bottle-shaped can with a cap according to claim 1, wherein the difference in Vickers hardness is 10 HV or more and 16 HV or less.

4. 2. The bottle-shaped can with a cap according to claim 1, wherein the top surface portion of the cap has a Vickers hardness of 60 HV or more and 75 HV or less, and the peripheral wall portion has a Vickers hardness of 70 HV or more and 86 HV or less.

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