Mold and method for manufacturing cap using same

Abstract

To provide a mold capable of improving a cooling performance of a screw core, improving manufacturing efficiency, and preventing defects, and a method for manufacturing a cap using the mold.SOLUTION: A mold used for molding a synthetic resin cap includes: a substantially cylindrical side wall 2 having a female thread 1 formed on an inner peripheral surface; a top wall 3 provided to close one end of the side wall 2; a substantially ring-shaped mid-foot 5 projecting inward from the top wall 3 and having an outer peripheral surface that increases in diameter from its base end toward a maximum outer diameter portion 4 located at a position away from a tip end; a center core 10 that molds an inner peripheral surface of the mid-foot 5; and a screw core 11 that molds a female thread on an outer peripheral surface of the mid-foot 5 and on the side wall 2. The center core 10 and the screw core 11 are slidable relative to each other in an axial direction while in contact with each other, and a small-diameter step 15 is provided on an outer peripheral surface of the center core 10 at a position closer to a tip end of the center core 10 than an area that molds the inner peripheral surface of the mid-foot 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a mold used for molding a synthetic resin cap to be attached to the mouth of a container such as a PET bottle, and a method for manufacturing the cap using the mold. [Background technology]

[0002] 4(A), a conventional synthetic resin cap is a so-called one-piece cap having a generally tubular (approximately cylindrical) side wall 2 with a female thread 1 formed on its inner surface that screws into a male thread provided on the outer surface of a container mouth (not shown), a generally disc-shaped top wall 3 provided to close one end (top end) of the side wall 2, a generally ring-shaped middle leg 5 that protrudes inward from the top wall 3 and expands in diameter toward a sealing portion (maximum outer diameter portion) 4 located away from the base end toward the tip, a tamper evidence band 7 connected to the other end of the side wall 2 via multiple bridges (weakened portions) 6, and multiple flaps 8 connected to the lower end of the tamper evidence band 7 and extending inward. The sealing portion 4 is provided on the middle leg 5 to improve the sealing performance provided by the middle leg 5 that fits into the container mouth when the cap is attached to the container mouth.

[0003] In the synthetic resin cap described above, the female thread 1 and the seal portion 4 are undercut, so when molding is performed by compression molding or injection molding, forced removal occurs during mold release. The greater the resistance during forced removal, the more likely the cap is to be damaged or deformed, so various measures have been taken to reduce this resistance (see Patent Document 1, etc.).

[0004] An example of a mold used to mold the above-mentioned synthetic resin cap is one that has a cavity mold (lower mold) 9 for molding the outer surface of the cap C (the outer surface of the side wall 2 and the upper surface of the top wall 3), a center core 10 for molding the inner surface of the middle leg 5, a screw core 11 for molding the outer surface of the middle leg 5 and the female thread 1 of the side wall 2, an outer core 12 for molding the flap piece 8, and a stripper 13, as shown in Figure 5(A).

[0005] This mold is configured so that the center core 10 and the screw core 11 can slide relatively in the axial direction while in contact with each other (in the illustrated example, the center core 10 does not move, but the screw core 11 moves). More specifically, the center core 10 has a support portion 10a that does not include a molding region for the synthetic resin cap, and a head portion 10b that is connected to the tip side of the support portion 10a and includes a molding region for the synthetic resin cap, with the outer diameter of the head portion 10b being larger than the outer diameter of the support portion 10a. The screw core 11 has a base portion 11a that does not include a molding region for the synthetic resin cap, and a tip portion 11b that is connected to the tip side of the base portion 11a and includes a molding region for the synthetic resin cap, with the inner and outer diameters of the tip portion 11b being larger than the inner and outer diameters of the base portion 11a. Then, the screw core 11 slides (up and down) relative to the center core 10 with the outer peripheral surface of the head 10b of the center core 10 and the inner peripheral surface of the tip 11b of the screw core 11 in contact with each other.

[0006] In the above mold, when the cap C is removed from the mold after molding, the cavity mold 9 is first opened and the stripper 13 is moved downward in Fig. 5(A), causing the screw core 11 and cap C to move downward together with the stripper 13, as shown in Fig. 5(B). At this time, the cap C and the screw core 11 move downward without sliding relative to each other (i.e., they move downward as a unit), while the center core 10 and the outer core 12 are connected to each other and do not move. When the stripper 13 is then moved downward further, the cap C is ejected from the screw core 11, completing the demolding process.

[0007] Here, in the state shown in FIG. 5(B), when the stripper 13 is moved downward to eject the cap C from the screw core 11 and release it from the mold, the undercut female thread 1, the midfoot 5, and the flap piece 8 are forcibly removed. In this mold, a space is provided outside the outer circumferential surface of the side wall 2 (the open cavity mold 9 does not interfere with the side wall 2), so the radial expansion deformation of the side wall 2 is not hindered, and resistance to the forcible removal of the female thread 1, which involves radial expansion deformation of the side wall 2, is reduced. Furthermore, a space is provided inside the inner circumferential surface of the midfoot 5 (the center core 10 does not interfere with the midfoot 5), so the radial contraction deformation of the midfoot 5 is not hindered, and resistance to the forcible removal of the midfoot 5, which involves radial contraction deformation, is reduced. Furthermore, a space is provided outside the flap piece 8 (the outer core 12 does not interfere with the flap piece 8), so the radial expansion deformation of the flap piece 8 is not hindered, and resistance to the forcible removal of the flap piece 8, which involves radial expansion deformation, is reduced. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-246724 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the above mold has the following problem: In the above mold, cooling water W (see FIG. 5(A)) is passed through the center core 10 to cool the core side, and the screw core 11, which does not have a cooling circuit, is indirectly cooled by contacting the center core 10. Therefore, expanding the contact area (heat conduction area) R between the center core 10 and the screw core 11 as much as possible when the cap C shown in FIG. 5(A) is cooled and solidified is advantageous for improving the cooling performance of the screw core 11, improving manufacturing efficiency, and preventing defects such as screw dripping. However, when removing the synthetic resin cap C after molding, in order to slide the screw core 11 and cap C together and move them from the molding position (see Figure 5(A)) where the center core 10 molds the inner surface of the midfoot 5 to a retracted position (see Figure 5(B)) where the center core 10 does not interfere with the inner surface of the midfoot 5 (so that the center core 10 does not interfere with the midfoot 5), a certain amount of stroke (pre-removal stroke) S of the screw core 11 (or center core 10) must be secured (see Figures 5(A) and (B)), and securing this stroke S limits the contact range R.

[0010] In particular, as shown in Figures 4(B), 6(A) and (B), in caps where the distance (height difference) D (see Figure 4(B)) from the inner surface of the top wall 3 connected to the inside of the midfoot 5 to the tip (bottom end) of the midfoot 5 is large, the stroke S needs to be made larger, which in turn makes the contact range R narrower, and there is a risk of a decrease in the cooling performance of the screw core 11 and ultimately a decrease in manufacturing efficiency and the occurrence of defects becoming more pronounced.

[0011] The present invention has been made with the above-mentioned points in mind, and its object is to provide a mold that can improve the cooling performance of the screw core, improve manufacturing efficiency, and prevent defects, as well as a method for manufacturing a cap using the mold. [Means for solving the problem]

[0012] In order to achieve the above object, the mold of the present invention is a mold used to mold a synthetic resin cap having a substantially cylindrical side wall with a female thread formed on its inner surface, a top wall arranged to close one end of the side wall, and a substantially ring-shaped mid-foot that protrudes inward from the top wall and whose outer surface expands in diameter toward its maximum outer diameter located away from its base end toward the tip, and has a center core that molds the inner surface of the mid-foot and a screw core that molds the outer surface of the mid-foot and the female thread on the side wall, the center core and the screw core being able to slide relative to each other in the axial direction while in contact with each other, and a small-diameter step portion is provided on the outer surface of the center core at a position closer to the tip of the center core than the area that molds the inner surface of the mid-foot (Claim 1).

[0013] In the above mold, the center core is connected to the tip side of the support part, which does not include the molding area of ​​the synthetic resin cap, and the outer diameter of the head part, which includes the molding area of ​​the synthetic resin cap, is larger than that of the support part, which does not include the molding area of ​​the synthetic resin cap; the screw core is connected to the tip side of the root part, which does not include the molding area of ​​the synthetic resin cap, and the inner and outer diameters of the tip part, which includes the molding area of ​​the synthetic resin cap, are larger than that of the base part, which does not include the molding area of ​​the synthetic resin cap; and the center core and the screw core may slide relative to each other with the outer surface of the head part of the center core and the inner surface of the tip part of the screw core in contact (Claim 2).

[0014] On the other hand, in order to achieve the above-mentioned object, the method for manufacturing a cap according to the present invention is a method for manufacturing a cap made of synthetic resin using a mold as described in claim 1 or 2, and when removing the synthetic resin cap after molding, the center core and the screw core are slid relative to each other, and the center core is moved from the molding position where the inner surface of the midfoot is molded by the center core to a retracted position where it does not interfere with the inner surface of the midfoot, and then the cap is released from the mold (claim 3). [Effects of the Invention]

[0015] The present invention provides a mold that can improve the cooling performance of the screw core, improve manufacturing efficiency, and prevent defects, as well as a method for manufacturing a cap using the mold.

[0016] In other words, in the mold of the invention according to each claim of this application, by providing a small diameter step portion at the tip side of the center core, it is possible to reduce the stroke of the screw core or the sliding of the center core, which is necessary to prevent the center core from interfering with the midfoot when demolding, and by reducing the stroke, it is possible to expand the contact area between the center core and the screw core when the cap cools and solidifies. As a result, for example, when cooling the screw core indirectly by flowing cooling water through the center core, the cooling performance of the screw core can be improved, which in turn improves manufacturing efficiency and prevents defects. [Brief explanation of the drawings]

[0017] [Figure 1] 1A and 1B are overall longitudinal cross-sectional end views of a mold according to an embodiment of the present invention when cooled and solidified and when demolded. [Figure 2] 10(A) to 10(C) are explanatory views showing a mold of a comparative example, a mold of another comparative example, and a demolding process for the mold. [Figure 3] 10A and 10B are overall longitudinal cross-sectional end views of a mold according to a modified example of the present invention when cooled and solidified and when demolded. [Figure 4] (A) is an explanatory diagram of a conventional synthetic resin cap (the left half is a longitudinal cross-sectional view, and the right half is a front view), (B) is an explanatory diagram of another conventional synthetic resin cap (the left half is a longitudinal cross-sectional view, and the right half is a front view), and (C) is an explanatory diagram of a synthetic resin cap molded by the mold of the present invention (the left half is a longitudinal cross-sectional view, and the right half is a front view). [Figure 5] 1A and 1B are overall longitudinal cross-sectional end views of a conventional mold during cooling and solidification and during demolding. [Figure 6] 10A and 10B are overall longitudinal cross-sectional end views of another conventional mold during cooling and solidification and during demolding. [Figure 7] (A) is an explanatory diagram of a conventional synthetic resin cap with a tapered midfoot (the left half is a longitudinal cross-sectional view, the right half is a front view), and (B) is an explanatory diagram of a conventional synthetic resin cap with another tapered midfoot (the left half is a longitudinal cross-sectional view, the right half is a front view). DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of the present invention will be described below.

[0019] The mold shown in Fig. 1(A) is a mold used to mold the synthetic resin cap shown in Fig. 4(C). The synthetic resin cap shown in Fig. 4(C) differs from the synthetic resin cap shown in Fig. 4(A) in that the central portion of the upper surface of the top wall 3 is raised higher than the peripheral portion (Difference 1) and that an annular step 14 is provided on the inner surface of the top wall 3 at a position that connects to the inside of the midfoot 5 (Difference 2). Other than that, the two caps are generally identical, and a detailed description of these similarities will be omitted to avoid redundancy. The synthetic resin cap shown in Fig. 4(C) and the synthetic resin cap shown in Fig. 4(B) differ only in the presence or absence of the annular step 14.

[0020] Furthermore, the mold shown in Figures 1(A) and (B) for molding the cap of Figure 4(C) differs from the mold shown in Figures 5(A) and (B) for molding the cap of Figure 4(A) in that, in relation to difference 1 above, the shape of the cavity mold 9 differs, and in relation to difference 2 above, the outer surface of the center core 10 has a small diameter step portion 15 located closer to the tip (lower end) of the center core 10 than the area where the inner surface of the midfoot 5 is molded. However, in other respects, such as the basic configuration and operation, the mold and the mold are generally identical, and explanations of these similarities will be omitted to avoid repetition.

[0021] In the mold shown in Figures 1(A) and (B) and the method for manufacturing a cap using the mold, a small-diameter step 15 is provided at the tip side of the center core 10, which makes it possible to reduce the stroke S of the screw core 11 required to prevent the center core 10 from interfering with the midfoot 5 during demolding. Reducing the stroke S makes it possible to expand the contact area R between the center core 10 and the screw core 11 when the cap is cooled and solidified. This improves the cooling performance of the screw core 11 when cooling the screw core 11 indirectly by flowing cooling water through the center core 10, thereby improving manufacturing efficiency and preventing defects.

[0022] Here, Figure 2(A) shows the demolding process of a comparative example mold that does not have a small diameter step portion 15. Before the tip is removed (when the center core 10 is at the most tip end within the screw core 11), the contact range R is sufficiently secured, but after the tip is removed (when the center core 10 is at the most base end within the screw core 11), the tip of the midfoot 5 is in a position that contacts the outer peripheral surface of the head 10b of the center core 10, so there is interference in the subsequent ejection steps 1 to 4, and there is a possibility that the midfoot 5 will be damaged (in the illustrated example, the midfoot 5 is torn off).

[0023] Therefore, as shown in Figure 2(B), if the axial length of the head 10b of the center core 10 is reduced, interference will not occur, but the contact range R before the leading edge removal will be insufficient, and the cooling performance of the screw core 10 will be reduced, increasing the possibility of reduced manufacturing efficiency and defects such as screw dripping.

[0024] In contrast to these, in the mold of this example, which has a small diameter step portion 15 as shown in Figure 2(C), even if the contact range R before the leading-out is sufficiently secured, the small diameter step portion 15 can prevent the middle leg 5 from interfering with the center core 10 in the subsequent process.

[0025] Here, the small diameter step 15 is intended to reduce the diameter of the tip of the center core 10 in order to prevent interference of the center core 10 with the midfoot 5 during demolding as shown in Fig. 1(B). However, excessive reduction in diameter can cause other problems (larger pockets of material, which are unfavorable for cooling and reduce moldability, and the base of the midfoot 5 becomes thicker, reducing mold releasability). Therefore, when the small diameter step 15 is configured as shown in Fig. 1(B) to have a gently sloping portion 15a with a large degree of diameter expansion (nearly horizontal) on the base side (upper side) of the center core 10 and a steeply sloping portion 15b with a small degree of diameter expansion (nearly vertical) on the tip side (lower side), the radial width of the gently sloping portion 15a is preferably determined in accordance with the radial undercut amount of the midfoot 5 (maximum outer diameter of the midfoot minus outer diameter of the base of the midfoot) (for example, 1 to 1.5 times the undercut amount). The height (axial length) of the leg 5 is preferably determined so that when the center core 10 is in a position closest to the base portion 11a within the screw core 11 (the position after the tip is removed) as shown in Figure 1 (B), the tip (upper end) of the middle leg 5 is in a position that overlaps the small diameter step portion 15 (the tip of the middle leg 5 is in a position from the lower end to the upper end of the small diameter step portion 15), and more preferably is determined so that it overlaps the steep slope portion 15b (the tip of the middle leg 5 is in a position from the lower end to the upper end of the steep slope portion 15b).

[0026] It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the following modifications can be mentioned.

[0027] The mold shown in FIGS. 1(A) and (B) is a mold for compression molding, but it may also be configured as a mold for injection molding.

[0028] Furthermore, the mold shown in Figures 1(A) and (B) is for molding a synthetic resin cap as shown in Figure 4(C) in which the central portion of the upper surface of the top wall 3 is raised higher than the peripheral portion, but the mold of the present invention is not limited to this and may have a structure suitable for molding a synthetic resin cap in which the upper surface of the top wall 3 is approximately flush over its entire surface, as shown in Figures 3(A) and (B).

[0029] The midfoot 5 of the cap shown in Figures 4(A) to (C) is a medium-thick type (i.e., the base of the midfoot is thinner than the center) that includes a portion that thickens from the base to the tip. However, in addition to the medium-thick type, there is also a tapered type midfoot 5A that does not include a portion that thickens from the base to the tip (i.e., it maintains the same thickness or becomes thinner from the base to the tip) (see Figures 7(A) and (B)). Even if the midfoot is generally ring-shaped, with its outer diameter expanding from its base to its maximum outer diameter located away from the tip, if it is a tapered type midfoot 5A, it can be released from the cap during molding without the need for a leading edge removal, in which the inner midfoot insert (the mold part corresponding to the center core 10) is removed from the cap before the outer midfoot insert (the mold part corresponding to the screw core 11). In contrast, a medium-thick type midfoot like the midfoot 5 described above would almost certainly tear during release if leading edge removal was not performed. That is, as described above, the mold of the present invention, in which the center core 10 and the screw core 11 are in contact with each other and can slide relative to each other in the axial direction, and which allows for leading-out, and the manufacturing method of the cap using the mold are particularly suitable for use in molding a medium-thick type center foot.

[0030] In the above examples, the relative sliding between the center core 10 and the screw core 11 during die-cutting is performed by (1) moving the screw core 11 downward while keeping the center core 10 stationary, but this is not limited thereto, and for example, (2) moving the center core 10 upward while keeping the screw core 11 stationary, or (3) moving the center core 10 upward while moving the screw core 11 downward, may be performed. Here, the stroke S of the screw core 11 or the center core 10 described above is the relative stroke between them, and in the above (1) it refers to the stroke of the screw core 11, in the above (2) it refers to the stroke of the center core 10, and in the above (3) it refers to the combined stroke of the center core 10 and the screw core 11. [Explanation of symbols]

[0031] 1 female thread 2 side wall 3 Ceiling wall 4 Seal part 5 Medium leg (medium thick type) 5A Midfoot (Tapered) 6 Bridge 7 Tamper Evidence Bands 8 flap pieces 9 Cavity Mold 10 Center Core 10a Support part 10b head 11 Screw Core 11a Base 11b Tip 12 outer core 13 Stripper 14 Annular step 15 Small diameter stepped section 15a Gentle slope section 15b Steep slope section C Cap D distance R Contact Range S stroke W Cooling water

Claims

1. A mold used for molding a synthetic resin cap, the mold having a generally cylindrical side wall with a female thread formed on its inner peripheral surface, a top wall provided to close one end of the side wall, and a generally ring-shaped center leg protruding inward from the top wall and having an outer peripheral surface with a diameter expanding toward a maximum outer diameter portion located away from the base end toward the tip end, The shoe has a center core that forms the inner peripheral surface of the midfoot, and a screw core that forms the outer peripheral surface of the midfoot and the female thread of the side wall, The center core and the screw core are axially slidable relative to each other while in contact with each other, A mold in which a small diameter step is provided on the outer peripheral surface of the center core at a position closer to the tip of the center core than the area where the inner peripheral surface of the midfoot is molded.

2. The center core has a head portion that is connected to the tip end of the support portion and includes the molding region of the synthetic resin cap, and has a larger outer diameter than the support portion that does not include the molding region of the synthetic resin cap; The screw core has a tip end portion, which is connected to the tip end side of the base portion and includes the molding region of the synthetic resin cap, and has larger inner and outer diameters than a root portion, which does not include the molding region of the synthetic resin cap; 2. The mold according to claim 1, wherein the center core and the screw core slide relative to each other with the outer peripheral surface of the head of the center core and the inner peripheral surface of the tip of the screw core in contact with each other.

3. A method for manufacturing a synthetic resin cap using the mold according to claim 1 or 2, comprising the steps of: This method for manufacturing a cap involves relatively sliding a center core and a screw core when removing the synthetic resin cap from a mold after molding, and moving the center core from a molding position where the inner peripheral surface of the middle leg is molded to a retreat position where the center core does not interfere with the inner peripheral surface of the middle leg, and then releasing the cap from the mold.

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