JP5147045B2 - Mold for cap molding made of synthetic resin - Google Patents

Description

  The present invention relates to a synthetic resin cap, and more particularly, to a mold for molding a synthetic resin cap having an inner ring integrally with a top wall.

  Conventionally, in a one-piece type synthetic resin cap 15 as shown in FIG. 3 (hereinafter simply referred to as a cap), an inner ring 17 that hangs downward from the inner surface of the top wall 16 of the cap body is connected to the inner peripheral surface of the bottle mouth. In order to improve the sealing performance, the diameter is increased downward. In the cap shown in FIG. 3, the screw 20 is formed on the skirt wall 19 and the tamper evidence band 21 is formed on the lower end, but the shape of the cap is not necessarily limited to this shape. When such a cap is molded by compression molding or injection molding, the inner ring diameter-expanded portion 18 and the screw 20 are undercut, which causes unreasonable punching. Conventionally, a mold 30 for molding such a cap is schematically shown in FIG. 4. As shown in FIG. 4, the core mold has an inner head 31 that forms a mold part that molds the top wall of the cap and the inner surface of the inner ring. From the outer peripheral surface of the ring 17 through the outer ring 22 to the inner peripheral surface of the skirt wall and the outer ring core 33 that constitutes the mold part that molds the thread, and from the TE band core 34 that constitutes the mold part that molds the tamper-evident band part It is configured. In the figure, 35 is an upper mold (cavity mold), and 36 is a lower mold.

  When the above-described cap is formed by the mold having the above-described configuration, the inner ring 17 and the screw 20 are undercut at the time of mold release, so that there is a risk that the cap will be deformed or damaged. In order to avoid this, it is conceivable that the inner ring is not sufficiently cooled and solidified, that is, the die is removed in a short time. However, in this case, the inner ring can be punched well, but there is a problem that sink marks 25 as shown in FIG. On the other hand, when the ceiling wall is sufficiently cooled, the inner ring in the vicinity is cooled more than necessary, and the releasability is deteriorated, and the ceiling wall 16 is pulled in a circular shape from the base portion of the inner ring 17. There is a problem that a circular recess 26 as shown in FIG. When such depressions and sink marks are generated on the top wall surface, the sealing performance is affected, and a non-uniform flat surface is produced at the time of printing on the top wall surface.

As a solution to such a problem, it can be solved by improving the cooling structure of the mold so that the part that contacts the top wall is well cooled and the part that contacts the inner ring is not cooled. The internal cooling water circulation path must be a separate path between the top wall and the inner ring contact area, which is physically difficult with a small mold for bottle caps, and is not easy to adopt. Not. The mold temperature control is controlled by cooling water, but there is a lower limit of the low temperature setting because of the risk of condensation on the mold. Conventionally, there is no literature showing a solution to the above problem in the formation of a cap having an undercut-shaped inner ring, but a measure to prevent the occurrence of sink marks and dents caused by forcibly removing the undercut part during cap molding. In general, it has been proposed to improve the shape of the undercut portion (see, for example, Patent Document 1) or to devise the shape of the cap and the mold so as to absorb the volume change during cooling ( For example, Patent Documents 2 and 3).
JP 2005-112444 A JP 2001-180706 A JP-A-10-16017

As a means for solving the above problems, the present inventor has made various studies focusing on changing the cooling mechanism depending on the material of the mold so as to solve the problem without particularly changing the cap shape and the mold shape. The above problem does not occur if the die is removed while the inner ring is still solidified and the top wall is sufficiently solidified. At the same time, the conflicting problem of slowing the cooling rate and conversely increasing the cooling rate of the ceiling wall must be solved.
As a solution to this problem, in the mold structure shown in FIG. 4, the inner head 31 is made of a copper alloy having a high thermal conductivity for the purpose of cooling the top wall as much as possible, and the outer ring core 33 is made of a copper alloy. An experiment was conducted using iron alloy steel having a thermal conductivity inferior to that of the alloy. However, the inner ring cooled more than necessary, resulting in dents that deteriorated the releasability and pulled the top wall. On the contrary, if both the inner head 31 and the outer ring core 33 are made of iron alloy steel, the inner ring was released properly by appropriate cooling, but sinking occurred on the top wall due to insufficient cooling of the top wall. The above problems were not solved.

  Therefore, the present invention more effectively prevents the formation of dents and sink marks that occur on the top wall in the molding of a cap having an undercut inner ring, without particularly changing the conventional cap shape and mold shape. A second object of the present invention is to provide a synthetic resin cap mold that can be formed, and a second object of the present invention is to provide a synthetic resin cap that does not have a thread shape defect (screw droop). And

A mold for molding a synthetic resin according to the present invention that achieves the first object is a mold for molding a synthetic resin cap having an inner ring that is integrally suspended from a top wall. The mold that forms the surface has an undercut shape, and the inner head that forms the core mold on the inner surface of the inner ring has a thermal conductivity between the top wall mold surface and the inner ring mold surface. Composed of two members made of different materials ,
The portion of the top wall mold surface relationship between the thermal conductivity kappa ₂ parts of the thermal conductivity kappa ₁ and the inner ring mold surface becomes satisfies κ _1> κ _2, of the top wall mold surface The portion is formed of a copper-based or aluminum-based material, and the portion of the inner ring mold surface is formed of an iron-based material .

In the mold for the synthetic resin cap molding, the ceiling wall mold surface of a portion of the thermal conductivity kappa ₁ and the inner ring mold surface of a portion of the thermal conductivity kappa ₂ and the relationship κ _1> κ ₂ By constructing so as to satisfy, the part that contacts the inner ring is not cooled very much, the part that contacts the top wall is cooled well, and the ceiling wall that occurs by pulling the top wall when releasing the inner ring The occurrence of sink marks caused by dents and insufficient cooling of the ceiling wall is eliminated, and a flat ceiling wall cap can be formed. Said portion of the top wall mold surface is formed of copper based or aluminum-based material, the portion serving as the inner ring mold surface that is formed of a ferrous material.

In the synthetic resin cap molding die, the material having a thermal conductivity κ _{3 in which} the outer head constituting the core die on the outer peripheral surface side of the inner ring is lower than the portion of the top wall molding die surface of the inner head. It is desirable that the inner ring and the outer ring can be more excellently punched by forming. Furthermore, the screw core constituting the thread-side core mold is formed of a material having a thermal conductivity κ ₄ that is higher or equivalent to that of the outer head, so that the occurrence of screw droop can be effectively prevented. The relationship between the thermal conductivity κ ₁ and κ _{2 of} the material constituting the inner head, the thermal conductivity κ ₃ of the material constituting the outer head, and the thermal conductivity κ ₄ of the material constituting the screw core is κ _1. With the cooling structure such that ≧ κ ₄ > κ ₃ ≧ κ ₂ , the first and second objects can be effectively achieved by claim 5. With such a cooling structure, the ceiling wall, the inner ring, and the threaded portion have an appropriate cooling relationship, and the production speed can be increased.

  According to the synthetic resin cap molding die of the present invention according to claims 1 to 6, it is very difficult to construct an ideal cooling structure with cooling water due to space problems. Molds with an ideal cooling structure that cools the ceiling wall and lowers the cooling efficiency of the inner ring by forming the inner head with two types of materials having different thermal conductivities. I was able to. Furthermore, according to the invention of claim 2, the inner head having the above cooling structure can be easily configured. According to the invention of claim 3, since the copper-based or aluminum-based material has a thermal conductivity that is 3 to 5 times or more higher than that of an iron-based material such as stainless steel, the above effect can be more effectively achieved. Can do. According to the invention of claim 4, the cooling efficiency of the outer peripheral surface of the inner ring is particularly lowered, and the outer head can be more easily punched. According to the invention of claim 5 and claim 6, the cooling efficiency of the screw portion is improved, the occurrence of screw dripping can be prevented at the time of die cutting, and both the top wall and the screw portion are good even if the production speed is increased. Can be molded.

Hereinafter, a synthetic resin cap according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a schematic cross-sectional view of a mold for molding a synthetic resin cap according to an embodiment of the present invention. As in the conventional mold, the mold has a cooling water passage formed inside the core mold, but is omitted in the drawing. The mold 1 of the present embodiment is generally composed of an upper mold (cavity mold) 6, a lower mold 7 and a core mold. The core mold molds the cap top wall and the inner ring inner surface. An inner head 2 constituting a part, an outer head 3 constituting a mold part for molding an inner ring outer peripheral surface and an outer ring inner peripheral surface, a screw core 4 constituting a mold part for molding a skirt wall inner peripheral surface and a thread, And a TE band core 5 constituting a mold part for forming the tamper evident band part.

The mold 1 of the present embodiment is particularly characterized in that the inner head 2 is composed of two members having different thermal conductivities as shown in FIG. That is, the inner ring inner mold surface 12 in which the main body portion 11 including the portion where the top portion becomes the ceiling wall mold surface 10 is formed of a copper-based or aluminum-based material having high thermal conductivity and the inner peripheral surface of the inner ring 17 contacts. The outer peripheral portion 13 is formed of an iron-based material having a lower thermal conductivity than the main body portion 11 having the ceiling wall surface 10. Therefore, when the thermal conductivity κ ₁ of the main body portion 11 and the thermal conductivity of the outer peripheral portion 13 are κ ₂ , the body portion 11 is formed to satisfy the relationship κ ₁ > κ ₂ . In addition, as an iron-type material, although normal carbon steel and steel for metal mold | die can be employ | adopted, stainless steel can be employ | adopted as a material with worse thermal conductivity. In the case of this embodiment, stainless steel is desirable to effectively delay the cooling of the inner ring.

In the present embodiment, the outer head 3 is separately provided as a core mold that forms a mold part for molding the inner ring outer peripheral surface and the outer ring inner peripheral surface. It was formed by an iron-based material having a low thermal conductivity kappa _3. Thereby, the cooling of the inner ring and the outer ring was delayed, and the mold could be removed without being sufficiently solidified, and the inner ring and the outer ring mold surface could be easily removed. As the iron-based material constituting the outer head 3, ordinary carbon steel or mold steel can be adopted, and preferably the thermal conductivity is higher than the thermal conductivity κ ₂ of the outer peripheral portion 13 that becomes the inner ring inner mold surface 12. A high iron-based material is desirable. If the thermal conductivity of the outer head 3 is too low, cooling of the top wall surface and the outer ring with which the outer head comes into contact will occur. Therefore, the inner ring inner mold surface 12 is lower than the portion that becomes the top wall mold surface 10. It is desirable to be lower than the part.

Further, the screw core 4 can be formed of an iron-based material having a low thermal conductivity like the outer head 3, but a so-called screw dripping phenomenon occurs when the screw portion is not sufficiently cooled. Therefore, in order to solve this problem, it is desirable that the screw core 4 is made of a material having a thermal conductivity κ ₄ that is substantially the same as that of the top wall surface of the inner head 2. A copper-based or aluminum-based material can be suitably used as the material. From the above, the relationship among the thermal conductivity κ ₁ and κ _{2 of} the material constituting the inner head, the thermal conductivity κ ₃ of the material constituting the outer head, and the thermal conductivity κ ₄ of the material constituting the screw core is as follows. , Κ ₁ ≧ κ ₄ > κ ₃ ≧ κ ₂ is desirable. By adopting such a cooling structure, the ceiling wall, the inner ring, and the screw part have an appropriate cooling relationship, and in the case of the embodiment described later, the production speed is increased by nearly 30% compared to the conventional case. Became possible. The thermal conductivity of each of the above materials is preferably in the range of κ ₁ , κ ₄ = 100 W / m · K or more, κ ₂ = 10 to 60 W / m · K, and κ ₃ = 30 to 60 W / m · K.

  The mold 1 for cap molding made of synthetic resin according to the embodiment is configured as described above, and the inner head 2 has a body portion 11 having a top wall surface 10 at the top, and a copper-based or aluminum-based thermal conductivity. The outer peripheral portion 13 which is the inner ring inner mold surface 12 which is made of a material having a high thermal conductivity and is in contact with the inner ring is formed of an iron-based material having a thermal conductivity lower than that of the main body portion 11 and has a different thermal conductivity. Since it is formed of various types of materials, the cooling efficiency of the inner ring can be lowered while the top wall is well cooled. As a result, the inner ring can be released smoothly while it is soft, and the top wall is well cooled, so a flat top wall cap can be molded without sinking. be able to.

In the mold structure shown in FIG. 1, the materials of the inner head 2, the outer head 3, and the screw core 4 are configured by combining the materials of Example 1 and Example 2 shown in Table 1, and the structure as shown in FIG. A synthetic resin cap (material: polypropylene, outer diameter: 28 mm, top wall thickness: 1.4 mm) was compression-molded under high-speed conditions corresponding to an increase of about 30% with respect to the current production rate. The following judgment method examined the presence or absence of the screw cap of the obtained cap, the hollow of the top wall, and the sink of the top wall.
<Criteria>
Screw dripping: Two points of the thread diameter were measured and visually checked.
○: Both screw dimensions and visual inspection are within the standard range.
Δ: The screw dimension is within the standard range, but there is some screw droop.
X: Screw size out of standard range Dimple: Visually confirmed whether there was a dimple on the top wall.
○: No depression is observed on the top wall
X: Circumferential depression is observed on the top wall. Sink: The size of the sink on the top wall was measured to confirm the sink.
○: Within the standard range of sink dimensions
×: Outside the standard range of sink dimensions

なお、上記実施例及び比較例で使用した材料は、次の熱伝導率を有するものを使用した。
銅系合金：１２１Ｗ／ｍ・Ｋ
ステンレス鋼：１６Ｗ／ｍ・Ｋ
鉄系合金：５３Ｗ／ｍ・Ｋ

In addition, the material used by the said Example and comparative example used what has the following heat conductivity.
Copper alloy: 121 W / m · K
Stainless steel: 16W / m · K
Iron-based alloy: 53 W / m · K

  As Comparative Examples 1 to 4, when the inner head is composed of one piece of a single material, the inner head and outer head screw core materials are combined using the materials shown in Table 1 to form a mold. Then, it was compression molded at a high production rate in the same manner as in the examples. As a result, the results shown in Table 1 were obtained regarding the presence or absence of screw sagging, depressions on the top wall, and sink marks on the top wall.

  As shown in Table 1, a portion that becomes the top wall type surface of the top of the inner head is formed of a copper-based material having high thermal conductivity, and a portion that becomes the inner ring type surface that the inner ring contacts is a top wall type surface. In the case of Example 1 and Example 2 formed of two kinds of materials having different thermal conductivity, which are formed of an iron-based material having a lower thermal conductivity than the portion, both the dent and sink on the top wall are generated. It was confirmed that a very ideal cooling efficiency can be obtained. In particular, in the case of Example 1, no screw sagging occurred at all by forming the screw core with a material having high thermal conductivity. As described above, in the conventional mold, high-speed production is impossible and the production speed is limited, but in the case of Example 1, high-speed production is possible, and the production speed can be improved by about 30%. The effectiveness was confirmed.

  On the other hand, in Comparative Example 1, there was no occurrence of screw sagging, but depressions and sink marks on the top wall were observed. Moreover, in the case of the comparative example 2, although the screw sagging and the hollow of the ceiling wall surface were not observed, generation | occurrence | production of sink marks was observed. This is considered to be caused by the shrinkage of the cooling after the mold is released because the cooling of the top wall is insufficient. Furthermore, in Comparative Example 3, it is thought that screw sagging and sink marks on the top wall are observed, and cooling of the screw portion and the top wall surface is insufficient. Further, in the case of Comparative Example 4, screw dripping, a dent on the top wall, and sink marks were observed. This is considered to be due to insufficient cooling of the screw portion in addition to Comparative Example 1.

  The mold for molding a synthetic resin cap according to the present invention is particularly suitable for the production of a synthetic resin cap in which an undercut inner ring is formed integrally with the top wall, and there is no generation of a dent or sink on the top wall. Caps with a uniform flat surface and excellent printability can be formed, and high-speed production of synthetic resin caps without screw sagging is possible, and industrial applicability is high.

It is a schematic sectional drawing of the metal mold | die for synthetic resin cap shaping | molding concerning embodiment of this invention. It is a partial cross section front view of the inner head in the metal mold | die of FIG. It is sectional drawing of the synthetic resin cap shape | molded by the metal mold | die for synthetic resin cap shaping | molding of this invention. It is a schematic sectional drawing of the metal mold | die for conventional synthetic resin cap shaping | molding. It is sectional drawing of the synthetic resin caps of the state which the hollow has generate | occur | produced in the top wall. It is sectional drawing of the synthetic resin caps in the state where sink marks are generated on the top wall.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mold for synthetic resin cap molding 2 Inner head 3 Outer head 4 Screw core 5 TE band core 6 Upper mold 7 Lower mold 10 Top wall mold surface 11 Body portion 12 Inner ring inner mold surface 13 Outer peripheral portion 15 Made of synthetic resin Cap 16 Top wall 17 Inner ring 18 Expanded portion 19 Skirt wall 20 Screw 21 Tamper-evident band 22 Outer ring

Claims (4)

A mold for molding a synthetic resin cap that has an inner ring that hangs down from the top wall, and the mold that forms the outer peripheral surface of the inner ring has an undercut shape,
And the inner head which comprises the core metal mold | die of the inner surface side of an inner ring is comprised by two members formed with the material from which a heat conductivity differs in the part of a top wall shaping | molding die surface, and the part of an inner ring shaping | molding die surface ,
Wherein the ceiling wall mold surface thermal conductivity kappa ₁ part of the relationship between the thermal conductivity kappa ₂ parts of the inner ring mold surface becomes satisfies κ _1> κ _2,
A synthetic resin cap molding die, wherein the top wall molding die surface portion is formed of a copper-based or aluminum-based material, and the inner ring molding die surface portion is formed of an iron-based material. . Outer head constituting the core mold of the inner ring outer peripheral surface side, made of a synthetic resin according to claim 1 which is formed of a material of the top wall mold lower thermal conductivity than the portion of the surface kappa ₃ of the inner head Mold for cap molding. The synthetic resin cap molding according to claim 2 , wherein a screw core constituting a mold part for molding the inner peripheral surface of the skirt wall and the thread is made of a material having a higher thermal conductivity κ ₄ than the outer head. Mold. The relationship among the thermal conductivity κ ₁ , κ _{2 of} the material constituting the inner head, the thermal conductivity κ ₃ of the material constituting the outer head, and the thermal conductivity κ ₄ of the material constituting the screw core is κ ₁ ≧ κ _4> mold for synthetic resin cap forming according to claim 3 kappa is ₃ ≧ kappa _2.

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