Threaded cap

Abstract

The present invention relates to a screw cap which can be molded by thermal molding of a resin sheet, has resealing properties by screw engagement, and can exhibit liquid-tight properties, the screw cap having a drop cap shape and comprising a top surface, an inner side wall extending upward from the outer peripheral edge of the top surface, and a skirt section, the threaded cap is characterized in that the inner side wall is provided with an annular protruding part, the outer diameter of which is larger than the inner diameter of an opening part of a container to which the inner side wall is applied, and the inner side wall is elastically deformable in the radial direction of the cap, and the skirt part is connected with the inner side wall through an annular part extending outwards from the upper end of the inner side wall and is provided with a threaded part.

Description

Technical Field

[0001] The present invention relates to a screw cap, and more particularly, to a screw cap that can be formed by thermoforming a resin sheet, is lightweight, and can reliably exhibit liquid tightness. Background Art

[0002] As a screw cap applied to containers such as polyester bottles, a resin screw cap is widely used. The resin screw cap is formed by integral molding of plastic and can exhibit liquid tightness without using a gasket or a sealing washer.

[0003] As such a resin cap, for example, in Patent Document 1 below, a closure cap is proposed. The closure cap is composed of a substantially cylindrical cap side wall portion having an internal thread and a cap top portion. The cap top portion has an annular sealing lip that abuts against the outer side of the mouth of the container and performs a sealing function in the region of the mouth of the container. The closure cap is made of a plastic material for closing the mouth of the container. Among them, the inner diameter (A) dimension of the sealing lip (5) before screwing the closure cap (1) is set to be larger than the outer diameter (B) of the container (2). The cap top portion (4) has a fixing and holding unit that engages with the mouth of the container. When the closure cap is screwed, the top of the container is pressed concentrically. At least the cap top portion is made elastic. As the fixing and holding unit is inserted into the mouth of the container, the top of the container is pressed, and the outer diameter of the top of the container decreases. Thus, the sealing lip can abut against the outer side of the mouth of the container and perform pressing.

[0004] In addition, in Patent Document 2 below, a screw cap is described. The screw cap is a resin screw cap formed by integrally molding a top surface and a skirt portion hanging down from the periphery of the top surface, and a screw stripe is provided on the inner peripheral surface of the skirt portion. Among them, liquid tightness is ensured by the inner ring and the outer ring hanging down from the inner surface of the top surface being in close contact with the inner surface and the outer surface of the mouth portion of the container.

[0005] In addition, a synthetic resin cap formed by thermoforming such as vacuum forming a synthetic resin sheet has been proposed. For example, in Patent Document 3 below, a method of forming a screw cap by thermoforming a synthetic resin sheet is proposed.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Laid-Open No. 58-216552

[0009] Patent Document 2: Japanese Invention No. 3872546

[0010] Patent Document 3: Japanese Patent Publication No. 5-57097 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] The screw caps described in Patent Document 1 and Patent Document 2 above have high sealing performance and reliable liquid tightness. However, due to their complex structures, they are generally formed by injection molding or compression molding, and it is difficult to easily form a thin-walled and lightweight screw cap.

[0013] In addition, when forming a multi-layer structure cap by injection molding or compression molding, it is not easy to uniformly stretch the intermediate layer over the entire cap. Therefore, in such conventional screw caps, it is also difficult to improve the gas barrier property of the cap by providing a gas barrier intermediate layer and to pursue thinning, and it is difficult to further reduce the weight of the cap.

[0014] Moreover, since conventional screw caps have an inner ring or the like, if the top surface is thinned, it is inevitable to reduce the sealing performance, and it is difficult to further reduce the weight of the cap.

[0015] In Patent Document 3 above, which proposes to form a cap by thermoforming a synthetic resin sheet, the following main idea is described: compared with a cap formed by injection molding or the like, it has the advantage of being able to reduce the amount of material used.

[0016] However, since the cap having a sealing portion and a threaded portion has a portion that protrudes radially inward of the cap and forms an undercut, when demolding the cap formed by thermoforming, the core mold located inside the cap is forcibly demolded. As a result, the cap made of a thin-walled synthetic resin sheet is likely to elongate when forcibly demolded, and may undergo plastic deformation due to excessive elongation. If the sealing portion and the threaded portion of the cap are deformed, it is difficult to obtain the desired sealing performance.

[0017] On the other hand, it is also considered to suppress the deformation of the undercut portion by rotating the core mold for demolding or the like, but such a method reduces the productivity and does not meet the intention of providing a cap that is easy to form and has excellent economy.

[0018] Therefore, an object of the present invention is to provide a screw cap that can be formed by thermoforming a resin sheet, has re-sealing performance based on screw engagement, and can exhibit liquid tightness.

[0019] In addition, another object of the present invention is to provide a screw cap that can be thinned and lightweight even when formed by injection molding or compression molding.

[0020] Moreover, another object of the present invention is to provide a screw cap that is formed by thermoforming a resin sheet and can effectively prevent plastic deformation even when demolded by forced demolding from a mold.

[0021] Solutions to the Problems

[0022] According to the present invention, there is provided a screw cap which is a drop cap-shaped screw cap composed of a top surface, an inner wall extending upward from the outer peripheral edge of the top surface, and a skirt portion. The skirt portion is connected to the inner wall via an annular portion extending outward from the upper end of the inner wall and has a thread portion. The screw cap is characterized in that the inner wall has an annular protrusion with an outer diameter larger than the inner diameter of the mouth portion of the applicable container and can be elastically deformed in the lid radius direction.

[0023] In the screw cap of the present invention, it is preferable that:

[0024] (1) The inner wall has a shape of an inequality sign curved outward in the lid radius direction, and the annular protrusion is a curved portion of the inequality sign shape;

[0025] (2) A buried head portion is formed on the outer peripheral edge of the top surface;

[0026] (3) The top surface has an upper dome shape or a lower dome shape;

[0027] (4) A sealing portion that closely adheres to the outer surface of the mouth portion of the container is formed on the upper part of the skirt portion;

[0028] (5) It is made of synthetic resin;

[0029] (6) In the skirt portion, a plurality of convex portions are arranged circumferentially on the inner surface of the skirt portion. The amount of protrusion of the convex portion in the radial direction is less than the height of the thread tooth. Through the circumferential unevenness formed by the plurality of convex portions in the skirt portion, the skirt portion can be elastically deformed in the radial direction;

[0030] (7) The convex portion is a convex portion extending along the axial direction or extending obliquely with respect to the axial direction;

[0031] (8) A concave portion corresponding to the convex portion is formed on the outer surface of the skirt portion

[0032] (9) The synthetic resin is polyethylene terephthalate;

[0033] (10) It is a screw cap applicable to a bottle.

[0034] According to the present invention, there is also provided a method for manufacturing a screw cap, which is a method for manufacturing the above screw cap, characterized in that a synthetic resin sheet is formed into a cap shape by thermoforming.

[0035] In the method for manufacturing a screw cap of the present invention, it is preferable that after the synthetic resin sheet is shaped into a cap shape by the thermoforming, demolding is performed from the inside of the cap by forced demolding.

[0036] Advantages of the Invention

[0037] In the screw cap of the present invention, the inner wall has an annular protrusion with an outer diameter larger than the inner diameter of the mouth of the applicable container and can be elastically deformed in the radial direction of the cap. Thus, when applied to the container, the annular protrusion presses the inner surface of the container mouth outward in the radial direction through elastic deformation, and therefore excellent sealing performance can be exhibited.

[0038] In addition, by setting the top surface to a dome shape, pressure resistance can be imparted, and a reduction in sealing performance due to deformation can be suppressed. Moreover, by forming it in a drop - cap shape, the headspace can be reduced.

[0039] Moreover, by thermoforming a resin sheet material, a thin - walled and lightweight screw cap can be easily formed. In addition, by making the screw cap thin - walled, the flexibility of the cap is improved, and the elastic deformation of the annular protrusion and the buried head part becomes easier.

[0040] Furthermore, as described later, even when the lower part of the skirt is slightly expanded in diameter due to forced demolding of the mold, since an annular protrusion capable of exhibiting sealing is formed on the inner wall far from the skirt, the possibility of damage to the sealing performance is small.

[0041] In addition, in the screw cap of the present invention, by forming a plurality of convex parts on the inner surface of the cap skirt in the circumferential direction with a radial protrusion amount smaller than the height of the thread tooth, the space between adjacent convex parts becomes a concave part, and unevenness is formed in the circumferential direction on the inner surface of the skirt. As a result, when a force acting radially outward is applied to the skirt, it elongates in the circumferential direction in a manner that eliminates the unevenness, and thus can elastically deform in a manner that expands the inner diameter of the skirt. In particular, in a cap formed by thermoforming a synthetic resin sheet material, since corresponding shapes are imparted to the inner and outer surfaces of the skirt, a concave part is formed on the corresponding outer surface at the part where the convex part is formed on the inner surface of the skirt. As a whole, the skirt forms a substantially corrugated shape with unevenness arranged in the circumferential direction, and thus the inner diameter of the skirt can be expanded in a manner that can be restored to its original shape.

[0042] Therefore, in the screw cap of the present invention, during molding, even when the core mold located inside the cap is forcibly demolded after shaping, the cap skirt easily expands in diameter radially outward. Thus, the core mold easily passes through the undercut parts such as the thread part and the sealing part, and after the core mold passes through the undercut part, the cap skirt can easily return radially inward, and the thread part and the sealing part maintain the desired shape, effectively preventing the elongation of the thread part and the sealing part due to plastic deformation and thus damaging the desired sealing performance.

[0043] Moreover, since it can be formed by thermoforming a resin sheet material and the mold can be removed by forced demolding after shaping, a thin - walled and lightweight screw cap can be molded with good productivity.

[0044] In the screw cap of the present invention, the above-described effects obtained by forming the convex portion in the skirt portion are also clear from the results of the following embodiments. That is, a screw cap (Experimental Example 1) obtained by thermoforming with the mold of (A) of Figure 11 and having convex portions extending axially and having a height lower than that of the thread teeth evenly arranged in the circumferential direction on the inner surface of the cap skirt is compared with a screw cap (Experimental Example 2) obtained by thermoforming with a mold that is the same except that no convex portion is formed on the inner surface of the cap skirt ( Figure 11 (B)). It can be seen that the skirt portion of Experimental Example 1 has a substantially vertical shape, but the inner diameter of the lower part of the skirt portion of Experimental Example 2 is enlarged and the skirt portion becomes a conical shape. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a side cross-sectional view of an example of the screw cap of the present invention.

[0046] Figure 2 is a partial enlarged side cross-sectional view showing a state where the Figure 1 screw cap is applied to the mouth portion of the container.

[0047] Figure 3 is a partial enlarged side cross-sectional view showing another example of the screw cap of the present invention.

[0048] Figure 4 is a partial enlarged side cross-sectional view for explaining another embodiment of the annular protrusion of the screw cap of the present invention.

[0049] Figure 5 is a partial enlarged side cross-sectional view showing a case where no buried head portion is formed in the embodiment shown in Figure 2 .

[0050] Figure 6 is a side cross-sectional view (right side) and a side view (left side) of another example of the screw cap of the present invention.

[0051] Figure 7 is a partial enlarged side cross-sectional view showing a state where the Figure 6 screw cap is applied to the mouth portion of the container.

[0052] Figure 8 is a partial cross-sectional view showing only the left half portion at the X-X line cross-section of the Figure 6 screw cap.

[0053] Figure 9 is a partial cross-sectional view for explaining a state where pressure acts radially outward on the cap for a part of the cross-section shown in Figure 8 . (a) is a partial cross-sectional view showing the state before diameter expansion, and (b) is a partial cross-sectional view showing the state after diameter expansion.

[0054] Figure 10The figure shows a side sectional view (right side) and a side view (left side) of another example of the screw cap of the present invention.

[0055] Figure 11 1 and 2 are perspective views showing molds used in Examples. (A) is a mold used in Experimental Example 1, and (B) is a mold used in Experimental Example 2. DETAILED DESCRIPTION

[0056] The screw cap of the present invention will be described with reference to the drawings.

[0057] Figure 1 1 is a side sectional view of an example of a screw cap of the present invention. In general, the screw cap, which is indicated as a whole by 1, is composed of a top surface 2 covering a container opening, an inner wall 3 extending upward from the outer peripheral edge of the top surface 2, and a skirt 6, wherein the skirt 6 is connected to the inner wall via an annular portion 4 extending outward from the upper end of the inner wall 3 and has a threaded portion 5.

[0058] exist Figure 1 and Figure 2 In the threaded cap shown, the inner wall 3 is composed of an inequality symbol "<" (the shape of the Hiragana character "ㄑ"), that is, an inverted tapered upper inner wall 3a whose outer diameter increases as it goes downward, and a tapered lower inner wall 3b whose outer diameter decreases as it goes downward. The curved portion serving as 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 be elastically deformed inward in the radial direction with the annular protrusion 7 as the vertex.

[0059] That is, Figure 2 As shown, the maximum outer diameter L1 of the annular protrusion 7 when not applied to the container is formed to be larger than the inner diameter L2 of the container mouth 30 to which it is applied. Therefore, when the threaded cap 1 is applied to the container mouth 30 and the cap thread is engaged to the lower dead point in a sealed state, the annular protrusion 7 is in radial compression contact with the inner surface of the container mouth 30, thereby exhibiting excellent liquid tightness.

[0060] In addition, Figure 1 and Figure 2 In the specific example shown, the top surface 2 is located below the annular portion 4, which is a so-called drop lid shape. The top space is reduced, and decompression deformation can be suppressed during cooling after hot filling.

[0061] Figure 3 2 is a diagram for explaining other solutions of the top surface 2 in the screw cap of the present invention. Figure 3 In the scheme shown in (A), the top surface 2 is dome-shaped upward. Figure 3In the scheme shown in (B), on the contrary, the top surface 2 is dome-shaped downward. For example, in the case of a container filled with a content such as a carbonated beverage with self-generated pressure, by applying pressure upward to the top surface 2, the annular protrusion 7 presses the inner surface of the container mouth more strongly, thereby improving the sealing performance. In addition, even if the internal pressure is increased by designing the shape, the pressing force of the annular protrusion 7 on the inner surface of the container mouth can be kept unchanged. In this case, the ease of opening is not impaired while maintaining the sealing performance. Figure 1 and Figure 2 As shown in the specific example, when the top surface 2 is flat, if the internal pressure increases, the top surface 2 is deformed into a dome shape, reducing the pressing force of the annular discharge portion 7 on the inner surface of the container mouth, and providing a venting function that can release the internal pressure. In this way, the shape of the top surface 2 can be used to provide a function corresponding to the content.

[0062] Moreover, in Figure 1 and Figure 2 In the specific example shown, a contact ring 9 is formed on the inner surface of the annular portion 4. When the cap reaches the bottom dead point by screwing, the contact ring 9 comes into pressure contact with the top end of the container mouth 30, thereby further improving the sealing performance of the cap.

[0063] Furthermore, by forming the portion of the skirt 6 connected to the annular portion 4 above the threaded portion 5 (hereinafter referred to as the "upper skirt 10") into an inverted cone shape in which the outer diameter of the skirt decreases as it goes downward, the container mouth 30 is tightened from the outside in the radial direction near the top, and a sealing portion is formed between the outer surface of the container mouth and the inner surface of the upper skirt 10, the sealing performance of the lid can be further improved.

[0064] Figure 4 It is a partially enlarged view for explaining another embodiment of the inner wall and the annular protrusion of the screw cap of the present invention.

[0065] exist Figure 1 and Figure 2 In the embodiment shown, the inner wall 3 is composed of an upper inner wall 3a of an inverted cone shape whose outer diameter increases as it goes downward and a lower inner wall 3b of a cone shape whose outer diameter decreases as it goes downward, and the boundary between the upper inner wall 3a and the lower inner wall 3b, i.e., the curved portion, is formed as an annular protrusion 7, but Figure 4 In the scheme shown in (A), Figure 1 and Figure 2 Similarly, the upper inner wall 3a is formed into an inverted cone shape, and the lower inner wall 3b is formed into an arc shape with the vertex of the arc facing obliquely downward, and the boundary between the upper inner wall 3a and the lower inner wall b is formed into an annular protrusion 7. In this scheme, liquid tightness is ensured by elastic deformation of the annular protrusion 7 in the radial direction outside by the inverted cone-shaped upper inner wall 3a.

[0066] In addition, in the solution shown in (B) of Figure 4 , the upper inner wall 3a is a straight side wall without inclination, the lower inner wall 3b is an arc-shaped side wall with the vertex of the arc facing outward in the radial direction and located outside the upper inner wall 3a in the radial direction, and the contact point of the arc with the container mouth is the annular protrusion 7. In this solution, the liquid tightness is ensured by the elastic deformation of the annular protrusion 7 realized by the arc-shaped lower inner wall 3b outward in the radial direction.

[0067] In the screw cap of the present invention, as long as an annular protrusion having an outer diameter larger than the inner diameter of the applicable container mouth is formed on the inner side wall, it is not limited to the above specific examples, and various solutions can be adopted.

[0068] For example, in the specific example shown in Figure 1 , by forming a countersink portion 8, as described above, when applied to a container, the countersink portion can also be elastically deformed in the radial direction of the cap. In combination with this, the pressing force of the inner surface of the container mouth generated by the elastic deformation of the annular protrusion becomes higher in the radial direction, so excellent sealing performance can be exhibited, and thus it is a preferred solution. However, depending on the wall thickness of the screw cap, the size of the top surface, etc., excellent sealing performance can also be exhibited even when the countersink portion is not formed. That is, as shown in Figure 5 , without forming a countersink portion, excellent sealing performance can also be exhibited only by the pressing force generated by the annular protrusion 7 outward in the radial direction.

[0069] 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 be applied can be appropriately changed according to the caliber of the container, the wall thickness of the cap, the presence or absence of the countersink portion, etc., and the degree of elastic deformation of the annular protrusion. However, the difference between L1 and L2 is preferably in the range of 0.1 mm to 1.0 mm.

[0070] In addition, when the upper inner wall is formed into an inverted conical shape, the cone angle can be appropriately changed according to the length of the upper inner wall, the difference between L1 and L2, etc., but it is preferably formed in the range of 0.1° to 45° with respect to the cap axis.

[0071] Similarly, when the upper skirt is formed into an inverted conical shape, it can also be appropriately changed according to the length of the upper skirt, etc., but it is preferably formed in the range of 0.1° to 45° with respect to the cap axis.

[0072] In Figure 6 and Figure 7 showing other solutions of the screw cap of the present invention, the basic structure of the cap is the same as that in Figure 1The threaded cap shown is the same, but in this solution, the important feature is that: the cap is made of synthetic resin, and on the inner surface of the skirt portion 6, a plurality of convex portions 20, 20,... are formed at equal intervals in the circumferential direction, extending along the axial direction of the cap and protruding inward in the radial direction of the cap.

[0073] Since the amount of protrusion of the convex portions 20, 20,... inward in the radial direction is less than the height of the threaded portion 5, the rotation of the thread is not impaired. On the other hand, as Figure 8 shown, the same concave-convex shapes are respectively formed on the inner surface and the outer surface of the cap, that is, a spiral concave portion 21 that is recessed inward in the radial direction corresponding to the shape of the threaded portion 5 is formed on the outer surface of the skirt portion 6 of the cap, and a plurality of axial concave portions 22, 22,... that extend along the axial direction and are recessed in the radial direction corresponding to the shape of the convex portions 20, 20,... are formed at equal intervals in the circumferential direction. The skirt portion 6 has a substantially corrugated shape in the horizontal cross-section.

[0074] Thus, as Figure 9 shown in (a), when a pressure acting from the inner surface of the skirt portion to the outside in the radial direction acts on the convex portions 20, 20, 20,..., the convex portions 20, 20, 20,... are stretched in the circumferential direction, whereby the skirt portion 6 expands in diameter ( Figure 9 shown in (b)). Then, when the pressure is removed, the skirt portion 6 can easily return to the original concave-convex shape.

[0075] Therefore, in the threaded cap of the solution shown above, as described above, at the time of demolding during molding, it is possible to easily perform forced demolding of the undercut portions such as the sealing portion and the threaded portion, and effectively prevent plastic deformation of the sealing portion and the threaded portion from impairing their functions. Figure 6

[0076] In addition, in the threaded cap of this solution, a plurality of convex portions with a protrusion amount in the radial direction less than the height of the threaded portion are arranged in the circumferential direction on the inner surface of the skirt portion. Thus, for example, when it is placed in a bag or the like in a state of being fastened to the mouth portion of the container, even if a force is applied to the outer surface of the skirt portion of the cap, the convex portions on the inner surface of the skirt portion can be brought into contact with the thread teeth of the mouth portion of the container to suppress the deformation of the cap and prevent the cap from loosening. In particular, compared with the caps formed by compression molding and injection molding, the cap formed by thermoforming using a synthetic resin sheet is thin-walled, and the skirt portion is easily deformed by an external force, so this effect is high.

[0077] In the threaded cap of this solution, as described above, as long as a plurality of convex portions with a protrusion amount in the radial direction less than the height of the threaded portion are arranged in the circumferential direction on the inner surface of the skirt portion, whereby the skirt portion can elastically deform in the radial direction, various solutions can be adopted.

[0078] Figure 6 That is, in Figure 7 and Figure 7In the specific example shown, axial concave portions 22, 22, 22... corresponding to convex portions 20, 20, 20... formed on the inner surface of the skirt portion 6 are formed on the outer surface of the skirt portion 6, and the skirt portion becomes substantially bellows-shaped. Thus, when pressure is applied from the inner surface of the skirt portion toward the radially outer side during demolding or the like, the skirt portion can be easily expanded in diameter, and can easily recover when the pressure is released. However, depending on the amount of undercut, it is not necessarily required to form concave portions corresponding to the convex portions on the outer surface of the skirt portion. In this way, even when no concave portions are formed on the outer surface of the skirt portion, since the region between adjacent convex portions 20, 20 is in a state of being recessed radially inward compared to the convex portion 20, unevenness is formed on the inner surface of the skirt portion. Therefore, when pressure is applied to the radially outer side, the thin concave portions are easily elongated, while the convex portions are difficult to elongate. Thus, the inner diameter of the skirt portion expands within the elastic region and can recover when the pressure is released.

[0079] In Figure 6 and Figure 7 the specific example shown, the convex portions formed on the inner surface of the skirt portion are convex portions that extend straight along the lid axis, but the convex portions may be inclined with respect to the axis. For example, as Figure 10 shown, convex portions inclined with respect to the axis are formed on the inner surface of the lid skirt portion, concave portions inclined with respect to the axis are formed on the outer surface of the lid skirt portion, and spiral-shaped unevenness is formed on the entire skirt portion of the lid. It should be noted that from the viewpoint of expansion and recovery of the skirt portion, the inclination angle in the case where the convex portions are inclined with respect to the axis is preferably 85° or less, more preferably 10° or less.

[0080] Furthermore, as long as the skirt portion can be expanded and recovered during demolding, the convex portions formed on the inner surface of the skirt portion do not necessarily need to be convex portions of the same shape formed at equal intervals in the circumferential direction. For example, the convex portions may be circular, elliptical, triangular, trapezoidal, rectangular, or may be a combination of convex portions having different axial lengths, widths, or heights arranged, arranged in such a way that the intervals between adjacent convex portions are different, or convex portions are formed only on a part of the inner surface of the skirt portion, the height or shape of the convex portions changes up and down, a shape that bends with a change in the inclination angle midway, or a meandering shape such as an S shape.

[0081] In the screw cap of the present invention, the height of the screw portion (the amount of protrusion from the inner surface of the skirt portion) can be appropriately changed according to the height of the screw portion of the mouth portion of the container to which the cap is applied and the synthetic resin sheet material used. However, in a cap with a diameter of 28 mm suitable for a container having a general bottle shape, a height in the range of 0.4 mm to 1.5 mm is preferred. In addition, the height of the convex portions can be appropriately changed according to the thickness of the skirt portion, the width, length, or arrangement (interval, number) of the convex portions, etc., but a height of 10% to 80% of the height of the above screw portion is preferred, and a height of 30% to 50% is more preferred.

[0082] In addition, as described above, convex portions or the like can be locally used on the inner surface of the skirt portion. However, for uniform diameter expansion, it is ideal to uniformly form convex portions on the inner surface of the skirt portion. Although not limited thereto, in the case of a cap applicable to a bottle with a diameter of 28 mm, it is ideal to uniformly form convex portions with a height of 0.2 mm to 5.0 mm at intervals of 0.2 mm to 5.0 mm. In addition, the axial length of the convex portion can be appropriately changed according to the positions of the threaded portion and the sealing portion that become the undercut portion. However, as in the specific examples shown in Figure 6 and Figure 7 , it is ideal to have a length extending from a position above the upper dead point of the threaded portion to a position below the lower dead point.

[0083] The threaded cap of the present invention can be made of either resin or metal as long as it can be formed into the above-described shape in which the annular protrusion can be elastically deformed. However, from the viewpoints of easy molding and reliable elastic deformation due to flexibility, a resin cap is preferred.

[0084] In the case of a resin cap, conventionally known thermoplastic resins such as olefin resins and polyester resins that have been used in the molding of resin caps can be used. However, a polyester resin is particularly preferred, and polyethylene terephthalate is preferably used.

[0085] In addition, in the case of a metal cap, metals such as aluminum that have been used in the molding of metal caps can be used.

[0086] In addition, regarding its molding method, in the case of a resin cap, it can also be molded by conventionally known molding methods such as compression molding and injection molding. However, it is ideal and preferably a resin sheet is used and molded by thermoforming such as vacuum pressure forming and plug assist pressure forming.

[0087] In addition, in the case of a metal cap, it can be molded by stamping a metal sheet. In the case of a metal cap, conventionally known shapes such as forming a liner material in the annular portion or forming a tamper-evident band via a breakable weakening portion at the lower end of the skirt portion can also be adopted.

[0088] As described above, the threaded cap of the present invention is particularly preferably molded by thermoforming such as vacuum pressure forming and plug assist pressure forming using a synthetic resin sheet. Thereby, a thin-walled threaded cap can be easily molded, and weight reduction can be achieved.

[0089] In addition, a lid obtained by thermoforming using a synthetic resin sheet is thin-walled compared to lids formed by compression molding or injection molding, so it can be easily expanded in diameter. On the other hand, it is easily plastically deformed. However, by forming protrusions on the inner surface of the skirt and corresponding recesses on the outer surface of the skirt, as described above, a skirt having a substantially corrugated shape can be formed. Therefore, especially in the case of a lid with a thin-walled skirt, it can be deformed in the elastic region, elastically deformed during demolding, easily expanded in diameter and restored, and the undercut sealing portion and threaded portion will not be plastically deformed, and it can be molded to the desired dimensions.

[0090] The thickness of the synthetic resin sheet that can be used for molding the threaded lid of the present invention varies depending on the synthetic resin used. However, in the case of being made of a polyester resin such as polyethylene terephthalate, a thickness of 0.5 mm to 1.2 mm is preferred, and in the case of being made of an olefin resin such as polypropylene, a thickness of 0.5 mm to 1.5 mm is preferred.

[0091] In addition, for example, by using a multilayer sheet having a gas barrier intermediate layer composed of a gas barrier resin such as ethylene-vinyl alcohol copolymer and aluminum foil, etc., a resin lid that is thin-walled and has excellent gas barrier properties can also be provided.

[0092] Moreover, by using a multilayer sheet having recycled materials in the intermediate layer and virgin materials in the inner and outer layers, on the basis that there is no problem with the hygiene of the parts in contact with food and people, a lid with an increased utilization rate of recycled materials can also be provided.

[0093] In addition, the threaded lid of the present invention is provided with a plurality of protrusions arranged circumferentially on the inner surface of the skirt, and the amount of protrusion in the radial direction is less than the height of the thread teeth. During demolding, the skirt can be expanded in diameter and restored by elastic deformation. Therefore, even by molding methods such as compression molding and injection molding, the demolding property can be improved. That is, by compression molding and injection molding, using the protrusions formed on the inner surface of the skirt and corresponding recesses formed on the outer surface of the skirt through the mold, the same as the thermoformed lid using the above synthetic resin sheet, a skirt having a substantially corrugated shape can be formed. Therefore, it can be deformed in the elastic region, and the functions of the sealing portion and threaded portion can be effectively prevented from being damaged during demolding.

[0094] Containers that can be applied with the threaded lid of the present invention can use all conventionally known containers such as metal, glass, and resin. The applicable diameter is not limited, but it is preferably applicable to containers with a diameter of 100 mm or less, especially 15 mm to 50 mm.

[0095] As described above, the threaded cap of the present invention can also be formed by compression molding or injection molding. However, in the case of forming a large-diameter cap, it is particularly preferably formed by thermoforming. That is, in compression molding, large molds and pressing forces are required, and in injection molding, the projected area of the molded product becomes larger, and the necessary clamping force also increases. Therefore, in either method, the equipment becomes large-sized. However, in thermoforming, not only such problems do not occur, but also the sheet utilization rate becomes high, so it is efficient.

[0096] Example (Experimental Example 1)

[0097] A commercially available 1.0 mm thick A-PET sheet was heated to about 110 °C. As Figure 11 shown in (A) of

[0098] After vacuum pressure forming using a resin mold in which convex portions extending axially and having a height lower than that of the thread teeth are circumferentially and evenly arranged on the inner surface of the cap skirt after molding, the mold was demolded by forced demolding, and the portion other than the cap portion was cut off with scissors to obtain a sample.

[0099] (Experimental Example 2)

[0100] As Figure 11 shown in (B) of Figure 11 After using the same resin mold as (A) of

[0101] except that no convex portion was formed on the inner surface of the molded cap skirt, samples were obtained in the same manner as in Experimental Example 1.

[0102] [Table 1]

[0103] Experimental Example 1 Experimental Example 2 Inner surface diameter at the lower part of the skirt 28.682 mm 29.752 mm Inner surface cone angle of the skirt 0.2° 1.3°

[0104] Since the resin mold is not designed with a draft taper, the taper angle of the inner surface of the skirt portion is 0°. However, as shown in Table 1, after forced extraction in Experimental Example 2, the diameter of the lower part of the skirt portion expands, and it can be confirmed that a taper angle of 1.3° is present in the skirt portion. In contrast, it can be seen that in Experimental Example 1, the diameter is approximately 1 mm smaller than that in Experimental Example 2, and the taper angle of the skirt portion is approximately the same as that of the resin mold. The difference between the two is whether a convex portion is formed on the inner surface of the skirt portion or not. Therefore, it is speculated that in Experimental Example 1, the boundary region elastically deformed by the convex portion on the inner surface of the skirt portion expands, and the final deformation is suppressed.

[0105] Industrial availability

[0106] The screw cap of the present invention can be formed by thermoforming a synthetic resin sheet, has re-sealability based on screw engagement, and can exhibit liquid tightness. Therefore, it can be used as a cap for beverage containers such as polyester bottles.

[0107] Explanation of reference numerals

[0108] 1: Screw cap; 2: Top surface; 3: Inner side wall; 4: Annular portion; 5: Thread portion; 6: Skirt portion; 7: Annular protrusion; 8: Embedded head portion; 9: Contact ring; 10: Upper skirt portion; 20: Convex portion; 21: Spiral concave portion; 22: Axial concave portion; 30: Container mouth portion.

Claims

1. A screw cap which is a drop - cap - shaped screw cap composed of a top surface, an inner wall extending upward from the outer peripheral edge of the top surface, and a skirt portion. Among them, The skirt portion is connected to the inner wall via an annular portion extending outward from the upper end of the inner wall and has a thread portion. The screw cap is characterized in that The inner wall has an annular protrusion with an outer diameter larger than the inner diameter of the mouth portion of the applicable container and can be elastically deformed in the lid - radius direction.

2. The screw cap according to claim 1, Among them, The inner wall is in the shape of a greater - than - sign that bends outward in the lid - radius direction, and the annular protrusion is the bent portion of the greater - than - sign shape.

3. The screw cap according to claim 1 or 2, Among them, A buried head portion is formed on the outer peripheral edge of the top surface.

4. The screw cap according to any one of claims 1 to 3, Among them, The top surface is in an upper - domed shape or a lower - domed shape.

5. The screw cap according to any one of claims 1 to 4, Among them, A sealing portion that closely adheres to the outer surface of the container mouth portion is formed on the upper part of the skirt portion.

6. The screw cap according to any one of claims 1 to 5, Among them, The screw cap is made of synthetic resin.

7. The screw cap according to claim 6, Among them, In the skirt portion, a plurality of convex portions are circumferentially arranged on the inner surface of the skirt portion. Among them, the protruding amount of the convex portion in the radial direction is less than the height of the thread tooth. Through the circumferential unevenness formed by the plurality of convex portions in the skirt portion, the skirt portion can be elastically deformed in the radial direction.

8. The screw cap according to claim 7, Among them, The convex portion is a convex portion that extends along the axial direction or extends obliquely with respect to the axial direction.

9. The screw cap according to claim 7 or 8, Among them, A concave portion corresponding to the convex portion is formed on the outer surface of the skirt portion.

10. The screw cap according to any one of claims 6 to 9, Among them, The synthetic resin is polyethylene terephthalate.

11. The screw cap according to any one of claims 1 to 10, Among them, The screw cap is a screw cap applicable to a bottle.

12. A manufacturing method of a screw cap, which is a manufacturing method of the screw cap according to any one of claims 1 to 11, Characterized in that A synthetic resin sheet is formed into a cap shape by thermoforming.

13. The manufacturing method of the screw cap according to claim 12, Among them, After the synthetic resin sheet is shaped into a cap shape by the thermoforming, demolding is performed from the inside of the cap by forced demolding.

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