JP5713346B2 - Mold structure for cap molding made of synthetic resin - Google Patents

Description

  The present invention relates to a mold structure for screw-type synthetic resin cap molding, and more particularly to the structure of the stripper.

  The mold for injection molding or compression molding of a screw type synthetic resin cap having a tamper evident band (hereinafter referred to as TE band) consists of an upper mold, a lower mold and a stripper. Generally, the lower mold is the inner circumference of the cap. It is comprised from the core type | mold which is a surface shaping | molding die, and the band core which is a shaping | molding die of TE band part outer peripheral surface. The core type differs depending on the shape of the screw type synthetic resin cap (hereinafter simply referred to as a cap), and includes, for example, a cooling core at the center, an inner ring core, and a screw core. Since the screw forming portion of the screw core is undercut, if the mold is not split, it will be forcibly removed when releasing. In many cases, the forcible removal reduces the resistance due to the elastic deformation of the cap and allows the mold to be released without damaging the screw. Damage occurs. Therefore, in order to alleviate the unreasonable pulling conventionally, the screw shape of the cap is devised (Patent Documents 1 to 3), or the material of the mold is devised (see Patent Document 4), and the mold structure is devised Various proposals have been made (for example, Patent Document 5), but no fundamental solution has been found yet.

  When the cap is a cap having an engaging protrusion 103 that can be engaged with the stripper on the outer peripheral portion near the lower end of the skirt wall 101 near the TE band 102 as shown in FIG. 7, the stripper 110 protrudes so that the inner periphery of the top surface of the stripper engages with the engagement protrusion 103 on the outer periphery of the skirt wall, and the cap is moved in the axial direction of the screw core 120 to release. In that case, the undercut portion 121 of the screw core is forcibly removed from the screw thread 106 of the cap 100.

  In the above-described forced removal, when the conventional stripper is engaged at an engagement position having a sufficient distance from the effective screw start portion, the upper outer peripheral surface is not restrained in a free state from the engagement position. As shown in FIG. 7, the outer peripheral portion of the skirt wall is slightly deformed radially outward with respect to the engagement resistance with the screw portion 106, thereby alleviating excessive pulling and causing the cap to droop. It can be released without any problems. However, when the stripper is engaged with the outer peripheral surface of the skirt wall, the stripper engagement position is constrained by the stripper and the outward deformation is prevented, so that the axial direction distance between the effective screw start portion and the stripper engagement position is prevented. Is short, there is almost no outward deformation of the effective screw starting portion of the skirt wall, and the forcible removal by the undercut of the core type becomes strong, and as shown schematically in FIG. 108 tends to occur.

JP 2005-112444 A JP 2006-117290 A Japanese Patent Laid-Open No. 08-34455 JP 2008-246724 A JP-A-10-16017

  According to the inventor's experiment, the drooping of thread that occurs when the above-mentioned force is removed is, in the case of the cap having the above-mentioned shape having an engaging protrusion on the outer peripheral portion of the skirt wall, the location where the stripper engages and the effective screw starting portion are 3.2 mm. In many cases, drooping occurs at the beginning of the effective screw when it is smaller. Therefore, the axial distance t between the engagement position of the stripper and the effective screw start portion must be 3.2 mm or more. That is, in order to be able to remove the mold without causing the conventional screw dripping, it is necessary to secure the axial length of the engagement position of the stripper and the effective screw start portion corresponding position of the screw core at a predetermined distance t or more, This put various restrictions on the structural design of the skirt wall. For example, if there is no such limitation, even if the cap has a constant axial height from the top wall of the cap to the lower end of the TE band, it is possible to form a screw with the full axial length of the skirt wall. Depending on the application, the axial length of the TE band portion can be increased. Furthermore, it is possible to provide a lightweight cap by reducing the height of the entire cap.

  By increasing the axial length of the screw part of the cap, in the case of a cap having an inner ring, the inner ring can be fitted after the screw has been bitten, and the inner ring biting phenomenon does not occur and is stable. There is an advantage that can be capped. That is, normal sealing by the inner ring is possible. On the other hand, by increasing the length of the TE band, it is difficult for the cap to tilt during capping, and the TE band is locked to the chin of the bottle evenly in the circumferential direction, and good TE properties can be obtained. On the other hand, if the TE band is capped in a tilted state and the locking is biased, the weakened part does not break when opening the plug, and there is a possibility that a spot drop phenomenon may occur.

As described above, with conventional molds, the distance between the position where the stripper engages and the start of the effective screw during molding is used to prevent screw dripping due to undercutting of the screw-type synthetic resin bottle when it is released. There is a problem that it is necessary to secure a predetermined amount or more that allows the vicinity of the effective screw start portion of the skirt wall to bulge outward, and the structure of the cap is limited.
Therefore, the present invention molds a synthetic resin bottle without causing screw dripping even when the position where the stripper is locked and the position of the effective screw start portion are shorter than before when molding the synthetic resin bottle. An object of the present invention is to provide a mold structure for forming a synthetic resin bottle.

The mold structure of the synthetic resin cap of the invention according to claim 1 for solving the above problem is a mold structure for screw type synthetic resin cap molding in which a screw is formed on the inner peripheral surface of the skirt wall, It has a stripper that engages with the outer periphery of the skirt wall of the synthetic resin cap after molding and releases the synthetic resin cap, and faces directly below a predetermined range including the position corresponding to the effective screw start portion of the screw core of the stripper A notch is formed in the inner peripheral portion of the top surface.
According to the above configuration of the first aspect, the mold release can be performed satisfactorily regardless of the position of the engagement protrusion on the outer peripheral surface of the stripper cap. The distance between the predetermined range position including the position where the stripper engages can be reduced. As a result, in a cap having a constant axial height from the top wall of the cap to the lower end of the TE band, it is possible to form a screw with the full axial length of the skirt wall. It is possible to increase the axial length of the portion. Furthermore, it is possible to provide a lightweight cap by reducing the height of the entire cap. The predetermined range including the effective screw start portion corresponding position refers to a predetermined range including at least the position of the screw forming core where the screw thread starts to act as an effective screw, and when acting as an effective screw from the screw cutting start position, A predetermined range including a position corresponding to the threading direction including the threading start part, or when the threading start part does not act as an effective screw, the thread gradually increases from the threading start position and acts as an effective screw. The predetermined range including the position corresponding to the threading direction from the position where the screw is formed is a range corresponding to the lower position where the drooping is most likely to occur when the molded synthetic resin cap is released.

According to a second aspect of the present invention, there is provided a synthetic resin cap mold structure according to the first aspect, wherein the notch is formed in a range of 90 ° to 20 ° of the inner peripheral portion of the top surface. It is characterized by being.
If the range of the notch is larger than 90 °, the non-engagement range of the stripper with respect to the engagement protrusion of the cap becomes large, and an uneven load acts on the push-up of the cap at the time of mold release, so that good mold release cannot be performed. On the other hand, when the angle is less than 20 °, the non-restraining range is small and the deformation effect of the skirt wall is small. Desirably, it is in the range of 50 ° to 90 °.

Furthermore, the invention according to claim 3 is the mold structure of the synthetic resin cap according to claim 1 or 2, wherein the notch portion has the multi-thread screw when the screw core has a multi-thread thread. A plurality of these are formed so as to face each other directly below a predetermined range including positions corresponding to the effective screw start portions.
In the case of a multi-thread screw, by providing a notch according to the number of threads, even a multi-thread screw can be satisfactorily released without causing screw droop.

According to a fourth aspect of the present invention, there is provided a synthetic resin cap mold structure according to any one of the first to third aspects of the present invention, in a predetermined range including a position corresponding to an effective screw start portion of the screw core from the top surface of the stripper. The axial distance to the lower undercut position is 3.2 mm or less.
By setting the axial direction distance t to 3.2 mm or less, the thread forming region of the skirt wall can be made longer than the conventional one. In an extreme case, even if t = 0, the effective screw starting portion position is not constrained, so that the deformation effect of the portion can be achieved.

  According to each of the first to fourth aspects of the present invention, the notch portion is formed in the inner peripheral portion of the top surface facing directly below a predetermined range including the position corresponding to each effective screw start portion. The cap outer surface directly below the portion where the screw droop is likely to occur is released from the restriction by the stripper. Therefore, the skirt wall located in the upper part where the notch is formed is easily deformed outward when the engagement part is pushed up by the stripper and the skirt wall is most likely to hang down. Can be easily removed, and the occurrence of screw dripping can be effectively prevented. As a result, the skirt wall is less prone to screw dripping even if the stripper engages with the effective screw start even in the axial direction, so it is possible to reduce the distance and free the structural design of the cap. The degree spreads.

It is a front longitudinal cross-sectional view of the metal mold | die structure which concerns on embodiment of this invention. (A) is front sectional drawing of the state which excluded the upper type | mold and the lower type | mold core type | mold in the metal mold | die structure of FIG. 1, (b) is the enlarged view of the B section. It is an AA arrow line view of a stripper and a band core in Drawing 2 (a). It is CC arrow line view in FIG. It is drawing corresponding to FIG. 4 which concerns on other embodiment. It is a principal part front longitudinal cross-sectional view in the middle of mold release. It is explanatory drawing of the mold release state in the conventional metal mold structure. It is principal part sectional drawing of the cap which the screw droop produced | generated with the conventional metal mold | die structure generate | occur | produced. It is sectional drawing of the cap shape | molded by the metal mold | die structure of this invention.

Embodiments of a synthetic resin cap mold structure according to the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view of an essential part of the mold structure of the present invention. The mold structure 1 according to this embodiment includes an upper mold 10, a lower mold 20, and a stripper 30. The upper mold is a cavity mold and has a gate in the case of injection molding. The lower mold 20 includes a core mold assembly 21 and a band core 28. The core assembly 21 includes a cooling core 22, an inner ring core 23, and a screw core 24 sequentially from the center to the outside. In the screw core 24, a screw mold for forming a screw is formed as an undercut portion 25 on the inner peripheral surface of the skirt wall of the cap to be formed. The mold structure in this embodiment is for molding a synthetic resin cap 100 having the shape shown in FIG. 9, and the screw of the synthetic resin cap has a thread 106 cut in the axial direction over a predetermined range. There are multiple jump screws.

  In the above-described mold structure, in the present invention, the stripper 30 is specially devised to prevent the cap from drooping due to unreasonable punching as shown in FIGS. That is, as shown in FIG. 3, the stripper 30 according to the present embodiment has a predetermined thickness so as to face a portion located directly below a predetermined range including the position corresponding to the effective screw start portion of the screw core 24 on the inner peripheral edge portion 31 of the top surface. A circular arc-shaped notch 32 was formed. Correspondingly, the upper surface of the band core 28 forming the skirt portion (TE band) of the cap is notched so as to fit into the notched portion 32 of the stripper as shown in FIGS. An arc-shaped protrusion 29 is formed in conformity with the shape of FIG. 2, and as shown in an enlarged view in FIG. 2 (b), there is no gap between the molded product when combined with the stripper.

  In the present embodiment, the notch 32 is directly below the second to fourth jump screws including the effective screw starting portion 106-2 except the screw cutting starting portion 106-1 which has a low screw core thread and does not act as an effective screw. The stripper was cut out in an arc shape with a width of about 1.5 mm in the radial direction. The width in the radial direction of the notch 32 is desirably equal to or greater than the width at which the notch engages with the engaging protrusion 103 of the synthetic resin cap when the stripper is protruded at the time of mold release. It is desirable that the circumferential range of the notch 32 corresponds to the lower position of the range in which undercut resistance is large and mold sag is liable to occur at the time of mold release, and is not limited to the above range. For example, as shown in FIG. In addition, when acting as the effective screw start portion from the thread cutting start portion, if the optimum range is selected depending on the type and size of the screw cap, such as providing a predetermined range from the portion corresponding to the lower position of the screw cutting start portion. Good. In the case of a single thread, it is desirable to form the range of the notch portion from 30 to 90 ° from the effective screw start portion or from the upper portion near the screw cut start portion. In the range smaller than 30 °, the effect of outward spreading of the skirt wall at the time of mold release is weak as will be described later, and when it exceeds 90 °, the engaging portion of the stripper on the outer periphery of the skirt wall is biased in the axial direction. Due to the unbalanced load, the cap is not properly tilted.

  Further, when the screw formed on the inner peripheral surface of the skirt wall of the synthetic resin cap is a multi-threaded screw, a predetermined range including each effective screw start portion corresponding position, that is, including an effective screw start portion or starting screw cutting. It is desirable to form over a range of 20 to 80 ° on the upper side in the vicinity.

The mold according to the present embodiment is configured as described above, and the mold release is performed as follows from the state shown in FIG. 1 after the molding of the synthetic resin cap is completed.
When the mold structure is an injection mold, first, the upper mold 10 is removed, and then the inner ring core 23 and the band core 28 of the core assembly 21 are pulled out almost simultaneously. Next, by pulling out the screw core 24 and protruding the stripper 30, the stripper 30 and the screw core 28 are displaced relative to each other in the opposite direction, so that the engagement protrusion 103 of the molded synthetic resin cap 100 forms the inner peripheral edge 31 of the stripper. , The screw part comes out of the undercut part 25 and is released (see FIG. 2). At this time, the engagement position of the stripper 30 is determined by the pressing force applied to the engagement protrusion 103 of the cap and the resistance caused by the engagement between the thread 105 of the cap and the undercut portion 25 of the screw core 24 on the inner peripheral edge 31 of the stripper. And the undercut portion 25 of the screw core 24 (especially the effective screw start portion), the compressive load acts on the skirt wall of the cap, so that the skirt wall tends to bulge outward. Since a large force is required to swell, an excessive force acts on the undercut portion, resulting in screw dripping.

  However, in the present embodiment, the inner peripheral edge 31 of the stripper 30 located at the lower part of the position where screw drooping is likely to occur is the notch 32 as described above. 103 is not engaged and is not restrained by the stripper 30, so that the skirt wall is allowed to deform outward even at a position where the distance between the engaging position of the stripper 30 and the effective screw start portion is short. As a result, the skirt wall 101 at the portion with the greatest die-cutting resistance is easily expanded outward as schematically shown in FIG. 6, and engagement between the predetermined range including the effective screw start portion corresponding position and the undercut portion 25 is achieved. Relaxed and can be released without screw dripping. Although the above embodiment has been described with respect to the case where the screw thread of the cap is a jump screw, the mold structure of the present invention is effective even if it is a continuous screw thread.

  The mold structure of the above embodiment is an injection mold, but in the case of a compression mold, the upper mold does not have a sprue runner gate through which the molten resin passes. Except for this point, the same mold structure can be adopted. In the case of compression molding, the mold release is performed in the order of the upper mold 10, the inner ring core 23, the band core 28, the screw core 24, and the stripper 30.

Example 1
9 is a synthetic resin cap having a shape shown in FIG. 9 and having a single jump screw formed on the inner peripheral portion of the skirt wall for the bottle diameter of 28 mm, and an effective screw from the lower surface of the engaging protrusion formed on the outer peripheral portion of the skirt wall. The following mold structure was formed by injection molding a 2.6 mm cap having a shorter distance to the beginning than before. The mold structure shown in FIG. 1 was formed so that the distance in the axial direction from the top surface of the stripper at the time of molding to the position corresponding to the effective screw start portion of the undercut of the screw core was 2.6 mm. Then, an arc-shaped cutout portion having a width of 1.5 mm in the radial direction was formed on the inner periphery of the top surface of the stripper of the mold in a range of 90 ° from the position corresponding to the effective screw start portion of the screw core.
100 of the above synthetic resin caps were injection molded by the mold formed as described above. As a result, in all the caps, it was confirmed that the screws formed on the inner peripheral surface of the skirt wall were free from screw dripping and could be released satisfactorily.

Comparative Example 1
Example 1 except that the stripper is formed with a uniform radius without providing a notch at the top inner periphery of the stripper, and correspondingly formed with a uniform inner periphery without providing a convex portion on the inner periphery of the band core. Using a similar mold structure, 100 caps similar to those in Example 1 were injection molded.
As a result, 100 caps in which screw drooping occurred at the beginning of the effective screw were observed.

Example 2
In the same mold structure as in Example 1, the notch portion was formed to a width of 1.5 mm in the radial direction within a range of 70 ° from the position corresponding to the effective screw start portion of the screw core. 100 caps similar to those in Example 1 were molded using the mold. As a result, it was possible to mold satisfactorily without causing dripping.

Example 3
9 is a synthetic resin cap having a shape shown in FIG. 9 and having a single jump screw formed on the inner peripheral portion of the skirt wall for the bottle diameter of 28 mm, and an effective screw from the lower surface of the engaging protrusion formed on the outer peripheral portion of the skirt wall. The following mold structure was formed by injection molding a 3.0 mm cap with a shorter distance to the start. The mold structure shown in FIG. 1 was formed so that the distance in the axial direction from the top surface of the stripper at the time of molding to the position corresponding to the effective screw start portion of the undercut of the screw core was 3.0 mm. Then, an arc-shaped notch portion having a width of 1.5 mm in the radial direction was formed on the inner periphery of the top surface of the stripper of the mold within a range of 20 ° from the position corresponding to the effective screw start portion of the screw core.
100 of the above synthetic resin caps were injection molded by the mold formed as described above. As a result, in all the caps, it was confirmed that the screws formed on the inner peripheral surface of the skirt wall were free from screw dripping and could be released satisfactorily.

Comparative Example 2
In the mold structure of Example 3, the notch was formed with a width of 1.5 mm in the radial direction within a range of 15 ° from the position corresponding to the effective screw start of the screw core. 100 caps similar to those of Example 2 were molded using the mold. As a result, the caps were tilted at the time of mold release, and all the caps were defective in mold release, and the skirt wall was deformed.

  The mold structure for molding a synthetic resin cap according to the present invention generates screw dripping even when the position where the stripper is locked and the position of the effective screw start portion are shorter than before when molding a synthetic resin bottle. Since the mold can be released without any problem, the degree of freedom in structural design of the cap is expanded, and the industrial applicability is high.

DESCRIPTION OF SYMBOLS 1 Mold structure for synthetic resin cap molding 10 Upper mold | type 20 Lower mold | type 21 Core type | mold assembly 22 Cooling core 23 Inner ring core 24 Screw core 25 Undercut part 26 Threading start part 28 Band core 29 Protrusion part 30 Stripper 31 Inner periphery Portion 32 Notch portion 100 Cap made of synthetic resin 101 Skirt wall 102 Tamper evidence (TE) band 103 Engagement protrusion 106 Thread 106-1 Thread cutting start portion 106-2 Effective screw start portion 108 Screw droop

Claims (4)

  A synthetic resin cap molding mold structure for molding a synthetic resin cap having a screw formed on the inner peripheral surface of a skirt wall, which is engaged with the outer peripheral portion of the skirt wall of the synthetic resin cap after molding. It has a stripper for releasing the cap made of synthetic resin, and the stripper is formed by forming a notch in the inner peripheral portion of the top surface facing directly below a predetermined range including the position corresponding to the effective screw start portion of the screw core. Mold structure of synthetic resin cap.   The synthetic resin cap mold structure according to claim 1, wherein the notch is formed in a range of 20 ° to 90 ° of the inner peripheral portion of the top surface.   The said notch part is formed in multiple numbers facing directly under the predetermined range containing each effective screw start part corresponding position of the said multi-thread screw, when the said screw core has a multi-thread thread. The mold structure of the synthetic resin cap described in 2.   The axial distance from the top surface of the stripper to the lowest undercut position in a predetermined range including the position corresponding to the effective screw start portion of the screw core is 3.2 mm or less. A mold structure of the synthetic resin cap according to any one of the above.

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