Manufacturing method of screw cap

Abstract

To provide a screw cap moldable by heat-molding from a resin sheet, that is capable of exhibiting liquid-tightness while having resealability through screw engagement.SOLUTION: A drop-lid type screw cap comprising a top surface, an inner wall extending upward from an outer peripheral edge of the top surface, and a skirt portion provided with a screw portion, the skirt portion being connected to the inner wall via an annular portion extending outward from an upper end of the inner wall, is characterized in that the inner wall has an annular protruding portion whose outer diameter is larger than an inner diameter of a container mouth to which the cap is applied, and is elastically deformable in a radial direction of the cap.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a screw cap, and more particularly to a method for manufacturing a screw cap that can be formed by thermoforming from a resin sheet, is lightweight, and yet can reliably exhibit liquid-tightness. [Background technology]

[0002] BACKGROUND ART Resin screw caps, which are formed by integral molding of plastic and can exhibit liquid-tightness without using liners or packing, are widely used as screw caps applied to containers such as polyester bottles. For example, Patent Document 1 listed below proposes an example of such a resin cap. This closure cap is made of a plastic material and is used to close the mouth of a container. The closure cap consists of a substantially cylindrical cap side wall with an internal thread and a cap top equipped with a ring-shaped sealing lip that abuts against the outside of the mouth of the container to seal the area of ​​the mouth of the container. The inside diameter (A) of the sealing lip (5) before the closure cap (1) is screwed on is dimensioned to be larger than the outside diameter (B) of the container (2). The cap top (4) is equipped with a fastening means that engages with the mouth of the container, so that when the closure cap is screwed on, the container top performs a concentric pressing action. At least the cap top is made elastic, so that as the fastening means is inserted into the mouth of the container, it presses against the container top, and the outside diameter of the container top reduces, allowing the sealing lip to abut and press against the outside of the mouth of the container.

[0003] Furthermore, Patent Document 2 listed below describes a resin screw cap in which the top surface and a skirt hanging down from the periphery of the top surface are integrally molded from plastic, and threads are provided on the inner peripheral surface of the skirt, in which an inner ring and an outer ring hanging down from the inner surface of the top surface adhere closely to the inner and outer surfaces of the container mouth, ensuring liquid-tightness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 58-216552 [Patent Document 2] Patent No. 3872546 Summary of the Invention [Problem to be solved by the invention]

[0005] The screw caps described in Patent Documents 1 and 2 above have high sealing properties and are reliably liquid-tight, but because their structure is complex, they are generally molded by injection molding or compression molding, and it has been difficult to easily mold thin-walled, lightweight screw caps. Furthermore, when a multi-layered cap is formed by injection molding or compression molding, it is not easy to spread the intermediate layer uniformly over the entire cap. Therefore, with such conventional screw caps, it is difficult to improve the gas barrier properties of the cap by adding a gas barrier intermediate layer, thereby making it difficult to reduce the cap's thickness, and it is also difficult to further reduce the cap's weight. Furthermore, since conventional screw caps have an inner ring or the like, reducing the thickness of the top surface inevitably reduces the sealing performance, making it difficult to further reduce the weight of the cap.

[0006] Therefore, an object of the present invention is to provide a screw cap that can be formed by thermoforming from a resin sheet, has resealability through thread engagement, and is capable of exhibiting liquid-tightness. Another object of the present invention is to provide a screw cap that can be made thin and lightweight even when formed by injection molding or compression molding. [Means for solving the problem]

[0007] According to the present invention, a manufacturing method for a screw cap having a drop-lid shape, which consists of a top surface, an inner wall extending upward from the outer peripheral edge of the top surface, and a skirt portion equipped with a screw portion that is connected to the inner wall via an annular portion extending outward from the upper end of the inner wall, is provided by thermoforming a synthetic resin sheet, wherein the inner wall has a dogleg-shaped annular protrusion that is bent radially outward from the cap and is elastically deformable in the radial direction of the cap.

[0008] In the method for manufacturing a screw cap of the present invention, (1) A recess corresponding to the screw portion is formed on the outer surface of the skirt portion at a location where the screw portion is located. (2) A countersink portion is formed on the outer periphery of the top surface. (3) The top surface has an upper dome shape or a lower dome shape; (4) A seal portion that fits tightly against the outer surface of the container mouth is formed at the upper part of the skirt portion. (5) A screw cap applied to a bottle; is preferred. [Effects of the Invention]

[0009] In the screw cap of the present invention, the inner wall has an annular protrusion whose outer diameter is larger than the inner diameter of the container mouth to which it is applied and is elastically deformable in the radial direction of the cap.When applied to a container, the annular protrusion presses the inner surface of the container mouth radially outward due to elastic deformation, thereby achieving excellent sealing properties. In addition, by making the top surface dome-shaped, it is possible to make it pressure-resistant and prevent a decrease in sealing performance due to deformation.Furthermore, by making it a drop-lid shape, it is possible to reduce the head space. Furthermore, by thermoforming a resin sheet, it is possible to easily form a thin and lightweight screw cap. Also, by using a thin screw cap, the flexibility of the cap is improved, and elastic deformation of the annular protrusion and countersink portion is facilitated. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a side cross-sectional view of an example of a screw cap of the present invention. [Figure 2] 2 is a partially enlarged side cross-sectional view showing the screw cap of FIG. 1 applied to the opening of a container. FIG. [Figure 3] FIG. 4 is a partially enlarged side cross-sectional view showing another example of the screw cap of the present invention. [Figure 4] 10 is a partially enlarged side cross-sectional view illustrating another embodiment of the annular protrusion in the screw cap of the present invention. FIG. [Figure 5] FIG. 3 is a partially enlarged side cross-sectional view showing the embodiment shown in FIG. 2 in which a countersink portion is not formed. DETAILED DESCRIPTION OF THE INVENTION

[0011] The screw cap of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a side cross-sectional view of an example of a screw cap of the present invention. The screw cap, generally designated 1, is generally composed of a top surface 2 that covers the container opening, an inner wall 3 that extends upward from the outer periphery of the top surface 2, and a skirt portion 6 that is connected to the inner wall via an annular portion 4 that extends outward from the upper end of the inner wall 3 and has a threaded portion 5. In the screw cap shown in Figures 1 and 2, the inner wall 3 is formed of an upper inner wall 3a that is in a dogleg shape, i.e., an inversely tapered shape in which the outer diameter of the inner wall increases downward, and a tapered lower inner wall 3b that has an outer diameter that decreases downward. The bent portion that is the boundary between the upper inner wall 3a and the lower inner wall 3b is formed as an annular protrusion 7, and the inner wall 3 can elastically deform radially inward with the annular protrusion 7 as its apex. That is, as shown in Figure 2, the maximum outer diameter L1 of the annular protrusion 7 when not applied to a container is larger than the inner diameter L2 of the container mouth 20 to which it is applied.Therefore, when the screw cap 1 is applied to the container mouth 20 and the cap is screw-engaged to the bottom dead center in a sealed state, the annular protrusion 7 and the inner surface 20 of the container mouth are radially pressed against each other, thereby enabling excellent liquid-tightness to be achieved.

[0012] In addition, in the specific example shown in Figures 1 and 2, the top surface 2 is lower than the annular portion 4, so it has a so-called drop lid shape, and the head space is small, which makes it possible to suppress decompression deformation when the product is cooled after hot filling. FIG. 3 illustrates another embodiment of the top surface 2 of the screw cap of the present invention. In the embodiment shown in FIG. 3(A), the top surface 2 is domed upward. In the embodiment shown in FIG. 3(B), the top surface 2 is domed downward. For example, when applied to a container filled with a self-generating content such as a carbonated beverage, upward pressure on the top surface 2 causes the annular protrusion 7 to press more strongly against the inner surface of the container's mouth, improving the sealing performance. Furthermore, by adjusting the shape, it is possible to maintain the pressing force of the annular protrusion 7 on the inner surface of the container's mouth even when the internal pressure increases. In this case, the sealing performance is maintained while the ease of opening is not impaired. As shown in the specific example shown in FIGS. 1 and 2, when the top surface 2 has a flat shape, it deforms into a dome shape when the internal pressure increases, reducing the pressing force of the annular discharge portion 7 on the inner surface of the container's mouth, providing a vent function that allows the internal pressure to be released. In this way, the shape of the top surface 2 can be adjusted to suit the contents.

[0013] Furthermore, in the specific example shown in Figures 1 and 2, a contact ring 9 is formed on the inner surface of the annular portion 4, which is pressed against the tip of the container mouth portion 20 when the cap reaches the bottom dead center due to screw engagement, further improving the sealing performance of the cap. Furthermore, by forming the portion of the skirt portion 6 that connects to the annular portion 4 above the screw portion 5 (hereinafter referred to as the "upper skirt portion 10") in an inverted tapered shape in which the outer diameter of the skirt portion decreases as it goes downward, the tip of the container mouth portion 20 is fastened from the radial outside, forming a seal between the outer surface of the container mouth portion and the inner surface of the upper skirt portion 10, further improving the sealing performance of the cap.

[0014] FIG. 4 is a partially enlarged view illustrating another embodiment of the inner wall and the annular protrusion in the screw cap of the present invention. 1 and 2, the inner wall 3 is composed of an inversely tapered upper inner wall 3a whose outer diameter increases downward and a tapered lower inner wall 3b whose outer diameter decreases downward, and the bent portion at the boundary between the upper inner wall 3a and the lower inner wall 3b is the annular protrusion 7. However, in the embodiment shown in Fig. 4(A), the upper inner wall 3a is inversely tapered as in Fig. 1 and 2, and the lower inner wall 3b is formed as an arc whose apex faces diagonally downward, and the boundary between the upper inner wall 3a and the lower inner wall 3b is the annular protrusion 7. In this embodiment, the inversely tapered upper inner wall 3a ensures liquid-tightness by elastic deformation of the annular protrusion 7 outward in the radial direction.

[0015] 4(B), the upper inner wall 3a is a straight side wall with no inclination, the lower inner wall 3b is an arc-shaped wall with an apex pointing radially outward and positioned radially outward of the upper inner wall 3a, and the point of contact of this arc with the container opening forms an annular protrusion 7. In this embodiment, liquid-tightness is ensured by the elastic deformation of the annular protrusion 7 in the radially outward direction caused by the arc-shaped lower inner wall 3b.

[0016] The screw cap of the present invention is not limited to the specific example described above and can take various forms, as long as an annular protrusion whose outer diameter is larger than the inner diameter of the container mouth to which it is applied is formed on the inner wall. 1, the countersink portion 8 is formed, and as described above, when applied to a container, the countersink portion can also be elastically deformed in the radial direction of the cap. This, combined with the fact that the elastic deformation of the annular protrusion increases the radially outward pressing force on the inner surface of the container opening, making this a preferred embodiment because it can provide excellent sealing. However, depending on the wall thickness and top surface size of the screw cap, excellent sealing can also be achieved even if a countersink portion is not formed. That is, as shown in FIG. 5, excellent sealing can be achieved even without a countersink portion, by the radially outward pressing force of the annular protrusion 7 alone.

[0017] In the screw cap of the present invention, the relationship between the outer diameter (L1) of the annular protrusion and the inner diameter (L2) of the container mouth to which it is applied can be changed as appropriate depending on the degree of elastic deformation of the annular protrusion, such as the diameter of the container, the thickness of the cap, and the presence or absence of a countersink portion, but it is preferable that the difference between L1 and L2 is in the range of 0.1 to 1.0 mm. Furthermore, when the upper inner wall is formed in a reverse tapered shape, the taper angle can be changed as appropriate depending on the length of the upper inner wall and the difference between L1 and L2 described above, but it is preferable to form it in the range of 0.1 to 45° with respect to the cap axial direction. Similarly, when the upper skirt portion is formed in a reverse tapered shape, this can be appropriately changed depending on the length of the upper skirt portion, etc., but it is preferable to form it in the range of 0.1 to 45° with respect to the axial direction of the cap.

[0018] The screw cap of the present invention may be made of either resin or metal as long as it can be molded into the above-mentioned shape that allows elastic deformation of the annular protrusion, but a resin cap is preferred because it is easy to mold and its flexibility allows it to exhibit reliable elastic deformation. In the case of a resin cap, a conventionally known thermoplastic resin such as an olefin resin or a polyester resin, which has been conventionally used for molding a resin cap, can be used, but an olefin resin is particularly preferable. In the case of a metal cap, a metal such as aluminum, which has conventionally been used for molding a metal cap, can be used.

[0019] In addition, in the case of a resin cap, the cap can be formed using a conventionally known forming method such as compression molding or injection molding, but it is preferable to use a resin sheet and form it by thermoforming such as vacuum pressure forming or plug-assisted pressure forming. This makes it possible to easily form a thin-walled screw cap and achieve weight reduction. Furthermore, by using a multilayer sheet with a gas barrier intermediate layer made of a gas barrier resin such as an ethylene-vinyl alcohol copolymer or aluminum foil, it is possible to provide a resin cap that is thin but has excellent gas barrier properties. When the screw cap of the present invention is molded by thermoforming, it is preferable to use a sheet made of an olefin resin such as polyethylene or polypropylene with a thickness of 0.1 to 1.5 mm, although this will vary depending on the type of resin. Metal caps can be formed by press-molding a metal sheet, and conventional shapes can be used, such as forming a liner material in the annular portion or forming a tamper-evident band at the bottom end of the skirt via a breakable weakened portion.

[0020] The screw cap of the present invention can be used for containers that are known in the art, such as metal, glass, and resin containers, but when using a resin cap in particular, it is suitable for containers with a diameter of 100 mm or less, particularly 15 to 50 mm. If the diameter is larger than the above range, sufficient sealing performance against the impact of a drop may not be achieved compared to containers within the above range, and the amount of elastic deformation of the top surface is small, which may make it difficult to further improve the liquid-tightness of the annular protrusion. [Industrial Applicability]

[0021] The screw cap of the present invention can be formed by thermoforming from a resin sheet, has resealability through screw engagement, and can exhibit liquid-tightness, so it can be used as a cap for beverage containers such as small-diameter polyester bottles. [Explanation of symbols]

[0022] 1 screw cap, 2 top surface, 3 inner wall, 4 annular portion, 5 screw portion, 6 skirt portion, 7 annular protrusion portion, 8 countersink portion, 9 contact ring, 10 upper skirt portion, 20 container mouth portion.

Claims

1. A manufacturing method for forming a drop-lid-shaped screw cap, which comprises a top surface, an inner wall extending upward from the outer periphery of the top surface, and a skirt portion having a threaded portion connected to the inner wall via an annular portion extending outward from the upper end of the inner wall, by thermoforming a synthetic resin sheet, comprising: A method for manufacturing a screw cap, wherein the inner wall has a dogleg-shaped annular protrusion bent radially outwardly of the cap and is elastically deformable in the radial direction of the cap.

2. 2. The method for manufacturing a screw cap according to claim 1, wherein a recess corresponding to the screw portion is formed on the outer surface of the skirt portion at a location where the screw portion is located.

3. 3. The method for manufacturing a screw cap according to claim 1, wherein a countersink portion is formed on the outer periphery of the top surface.

4. 3. The method for manufacturing a screw cap according to claim 1, wherein the top surface has an upper dome shape or a lower dome shape.

5. 3. The method for manufacturing a screw cap according to claim 1, wherein a seal portion is formed on an upper portion of the skirt portion to fit tightly against the outer surface of the mouth of the container.

6. 3. The method for manufacturing a screw cap according to claim 1, wherein the screw cap is applied to a bottle.

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