Bottom mold used when blow molding a synthetic resin container

Abstract

To provide a bottom forming mold capable of sufficiently cooling a bottom of a container evenly and uniformly when blow molding a synthetic resin container having an uneven bottom.SOLUTION: There is provided a bottom forming mold that comprises a coolant flow path 34 to be displaced in a central axis direction along a bottom defined surface 16 defining a bottom 106 of a container 102.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] The present invention relates to a bottom forming die used when blow molding a synthetic resin container having irregularities on the bottom surface.

Background Art

[0002] As a beverage container, a synthetic resin container molded from an appropriate synthetic resin such as polyethylene terephthalate is widely used in practice. As is well known to those skilled in the art, such a synthetic resin container is molded by a process of molding a preform (preformed body) by injection molding or compression molding and a process of blow molding the preform. The preform consists of a mouth portion, a neck portion, and a blow molding portion, and the blow molding portion is stretched into a predetermined shape in the blow molding process to form the body portion and the bottom portion of the container. As an example of an apparatus for blow molding a preform, Patent Document 1 below discloses a molding apparatus including a body die for molding the body portion of the container and a bottom forming die for molding the bottom portion of the container.

[0003] The container immediately after blow molding is relatively soft at a high temperature, and the container is taken out of the molding apparatus after being cooled and sufficiently cured. In particular, if there is uneven cooling at the bottom of the container, the container is likely to shrink or deform during demolding, and cracks or so-called sink marks are likely to occur in the shrunk or deformed portion after demolding. For this reason, it is a commonly used technique to dispose a coolant flow path in the mold and cool the mold with a coolant to accelerate the cooling of the container and shorten the molding time.

[0004] On the one hand, the bottom of the container formed in Patent Document 1 has a central bottom valley portion, and a plurality of valley portions and leg portions alternately arranged around the central bottom valley portion, and has a complicated shape with unevenness, a so-called petaloid shape. Thus, when unevenness is formed on the bottom, it is difficult to sufficiently cool the bottom of the container in a short time only with the cooling liquid flowing through the cooling liquid flow path formed on the plane, which is provided in a general bottom forming die. Therefore, in the molding apparatus of Patent Document 1, a cooling liquid flow path is provided in the bottom forming die, and a nozzle is provided at the tip of the stretching rod, and the bottom is also cooled by injecting cooling air from the nozzle toward the inner surface of the bottom of the container after blow molding.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above facts, and its main technical problem is to provide a novel and improved bottom forming die that can cool the bottom of a synthetic resin container with unevenness on the bottom uniformly and sufficiently without unevenness when blow molding.

Means for Solving the Problems

[0007] As a result of intensive studies, the present inventors have found that the above main technical problem can be achieved by providing a cooling liquid flow path that is displaced in the central axis direction along the bottom defining surface that defines the bottom of the container in the bottom forming die.

[0008] That is, according to the first aspect of the present invention, as a bottom forming die that achieves the above main technical problem, it is a bottom forming die used when blow molding a synthetic resin container having unevenness on the bottom, A first member having a bottom defining surface that defines the bottom of the container provided on one side surface, and a second member laminated on the other side surface of the first member. A groove that is displaced in the central axis direction along the bottom defining surface is formed on the other side surface of the first member, and one side surface of the second member that faces the other side surface of the first member corresponds to the shape of the bottom defining surface of the first member. Between the first member and the second member, a cooling liquid flow path that is displaced in the central axis direction along the bottom defining surface is defined by the groove formed on the other side surface of the first member and the one side surface of the second member. Cold A bottom forming mold is provided, which is characterized in that. Further, according to a second aspect of the present invention, as a bottom forming mold for achieving the above main technical problem, it is a bottom forming mold used when blow molding a synthetic resin container having unevenness on the bottom, A first member having a bottom defining surface that defines the bottom of the container provided on one side surface, and a second member laminated on the other side surface of the first member. A groove that is displaced in the central axis direction along the bottom defining surface is formed on one side surface of the second member that faces the other side surface of the first member, and the other side surface of the first member corresponds to the shape of the bottom defining surface of the first member. Between the first member and the second member, a cooling liquid flow path that is displaced in the central axis direction along the bottom defining surface is defined by the groove formed on the one side surface of the second member and the other side surface of the first member. Cold A bottom forming mold is provided, which is characterized in that. Furthermore, according to a third aspect of the present invention, as a bottom forming mold for achieving the above main technical problem, it is a bottom forming mold used when blow molding a synthetic resin container having unevenness on the bottom, A bottom forming mold is provided, which is characterized by including a cooling liquid flow path that is displaced in the central axis direction along the bottom defining surface that defines the bottom of the container, and the cooling liquid flow path extends in a spiral shape in the circumferential direction.

[0009] In a first aspect of the present invention, it is preferable that the coolant flow path extends in a circumferential spiral shape. In this case and in a second aspect of the present invention, it is suitable that the coolant flows in from the center of the coolant flow path extending in a spiral shape and flows out from the radially outer end. The bottom of the container may be petaloid in shape.。

Advantages of the Invention

[0010] In the bottom forming die of the present invention, since a coolant flow path is provided which is displaced in the central axis direction along the bottom defining surface that defines the bottom of the container, when blow molding a synthetic resin container having irregularities on the bottom, the distance between the bottom of the container and the coolant flow path has no portion that is too far apart to cause insufficient cooling. Further, even when there is a locally thick-walled portion on the bottom of the container, if the coolant flow path is locally brought close to the bottom defining surface for such a portion, cooling of the thick-walled portion can be locally promoted. Thereby, even only with the coolant flowing through the coolant flow path, the bottom of the container can be uniformly and sufficiently cooled without unevenness. That is, by using the bottom forming die in the present invention, the quality of the container can be improved, the speed of the production line can be increased, and the productivity can be improved.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, with reference to the accompanying drawings, a preferred embodiment of the bottom forming die configured according to the present invention will be described in more detail.

[0013] For the sake of convenience, prior to the description of the preferred embodiment of the bottom forming die configured according to the present invention, a molding apparatus including the same and a synthetic resin container molded by this molding apparatus will be described. In Fig. 1, a typical example of a container molded by a molding apparatus including the bottom forming die of the present invention is shown. This container, indicated as a whole by reference numeral 102, is formed by blow molding a preform made of an appropriate synthetic resin such as polyethylene terephthalate, and has a main part 104 including a body part and a part above this, and a bottom part 106 located below the main part 104. Referring to Fig. 2 together with Fig. 1 for explanation, there are irregularities on the bottom part 106 of the container 102. In the illustrated embodiment, such irregularities are of a petaloid shape well-known to those skilled in the art, and the bottom part 106 includes a bottom central valley part 108, and a plurality of valley parts 110 and leg parts 112 alternately arranged at equal angular intervals in the circumferential direction around the bottom central valley part 108. As described above, the petaloid shape is the most common as a container having a complex concavo-convex structure on the bottom, and since it is the shape for which the solution of the present problem is required, this shape is adopted in the present embodiment.

[0014] FIG. 3 shows a molding apparatus 202 for blow-molding the container 102. The molding apparatus 202 includes a main part forming die 204 that forms the main part 104 of the container 102 and a bottom part forming die 2 that forms the bottom part 106. A molding space part 206 is defined by the inner surfaces of the respective forming dies within the molding apparatus 202. The container 102 is formed by blow-molding a preform (not shown) in this molding space part 206. The above-described bottom part forming die 2 is supported by a bottom part forming die support base 208, and an intermediate flow path 210 is formed inside the bottom part forming die support base 208. The bottom part forming die 2 is provided with a coolant flow path 34, and coolant is supplied to this coolant flow path 34 from a circulation-type coolant supply source (not shown) via the intermediate flow path 210, and the bottom part forming die 2 is cooled.

[0015] As shown in FIG. 3, the bottom part forming die 2 includes a first member 4 and a second member 6. Hereinafter, the bottom part forming die 2 configured according to the present invention will be mainly described with reference to the drawings from FIG. 4 onwards.

[0016] Referring to FIGS. 7 to 9 together with FIGS. 4 to 6, the first member 4 includes an annular flange 8 that extends substantially horizontally, a cylindrical side wall 10 that hangs downward from the inner peripheral edge of the flange 8, and a closing wall 12 that closes the lower end of the side wall 10. A plurality of screw holes 14 are formed at intervals in the circumferential direction on the lower surface of the flange 8. A bottom defining surface 16 that defines the bottom 106 of the container 102 is provided on one side surface of the first member 4. In the illustrated embodiment, the bottom defining surface 16 is defined by the inner peripheral surface of the side wall 10 and the upper surface of the closing wall 12. In the illustrated embodiment, since the bottom 106 of the container 102 is petaloid in shape, the bottom defining surface 16 is also made to have the same petaloid shape as the shape of the bottom 106 of the container 102. As can be understood by also referring to FIG. 10, on the other side surface of the first member 4, in the illustrated embodiment, on the lower surface of the closing wall 12, a groove 18 is formed that extends in a spiral shape in the circumferential direction while being displaced in the central axis direction along the bottom defining surface 16. Regarding the lower surface of the closing wall 12 and the groove 18, referring to FIGS. 7 to 9 together with FIG. 10, the lower surface of the closing wall 12 is originally displaced in the central axis direction along the bottom defining surface 16, and this is shown by a two-dot chain line as a virtual lower surface 20 in FIGS. 7 to 9. Such a virtual lower surface 20 also corresponds to the upper surface of a bulging portion 24 of the second member 6 described later. And the groove 18 extends in a spiral shape in the circumferential direction while being displaced in the central axis direction along the bottom defining surface 16 with a certain depth in the central axis direction along the virtual lower surface 20. Note that the depth of the groove 18 in the central axis direction does not necessarily have to be constant and may be appropriately displaced.

[0017] The second member 6 is laminated on the other side surface (the lower surface in the illustrated embodiment) of the first member 4. Continuing the description with reference to FIGS. 11 to 14 as well, the second member 6 includes a disk-shaped base portion 22 that extends substantially horizontally as a whole, and a bulging portion 24 of a required shape that bulges upward is provided at the center of the base portion 22. The upper surface of the bulging portion 24, that is, one side surface of the second member 6 that faces the other side surface of the first member 4, corresponds to the shape of the bottom defining surface 16 of the first member 4. As can be understood by referring to FIG. 6 together with FIGS. 13 and 14, an inflow channel 26 having a circular cross-section that linearly extends in the central axis direction and penetrates the entire second member 6 is formed at the center of the bulging portion 24, and an outflow channel 28 having a circular cross-section that linearly extends along the central axis and penetrates the entire second member 6 is formed at required angular positions of the outer peripheral edge portion in a plan view (bottom view). An annular auxiliary groove 30 that surrounds this is formed outside the bulging portion 24 on one side surface of the base portion 22. A plurality of mounting holes 32 having a circular cross-section that penetrate in the central axis direction are formed at the outer peripheral edge portion of the base portion 22 at intervals in the circumferential direction corresponding to the screw holes 14 of the first member 4. With the second member 6 and the first member 4 combined such that the upper surface of the bulging portion 24 of the second member 6 faces the lower surface of the first member 4, a fastening tool such as a bolt is passed through the mounting holes 32 and screwed into the screw holes 14 of the first member 4, whereby the first member 4 and the second member 6 are fastened (the above-mentioned fastening tool is shown in FIG. 3).

[0018] When the first member 4 and the second member 6 are combined as described above, as shown in FIGS. 7 to 9, a coolant flow path 34 that is displaced in the central axis direction along the bottom defining surface 16 is defined between the first member 4 and the second member 6. In the illustrated embodiment, since the coolant flow path 34 is defined by the combination of the first member 4 and the second member 6, it is easier to manufacture than the case where the bottom forming die to be mentioned later is composed of a single member and a coolant flow path is provided inside it. Therefore, the manufacturing cost can be reduced. Since the bottom defining surface 16 is displaced in the central axis direction along the shape of the bottom 106 of the container 102, as shown in FIG. 15, the coolant flow path 34 is displaced in the central axis direction along the shape of the bottom 106 of the container 102 (petaloid shape in the illustrated embodiment) indicated by the two-dot chain line in the figure. In the illustrated embodiment, the coolant flow path 34 extends in a spiral shape in the circumferential direction. By making the flow path shape spiral, the flow path is constituted by a gentle curve, so that the coolant can flow easily, and since the flow path can be evenly arranged with respect to the bottom surface of the bottom 106, the bottom 106 can be cooled uniformly. In the illustrated embodiment, the distance between the coolant flow path 34 and the bottom defining surface 16 is constant, but the above distance does not necessarily have to be constant, and it may be locally reduced as appropriate, that is, the coolant flow path 34 may be brought closer to the bottom defining surface 16 as needed. For example, the central portion of the bottom 106, that is, the bottom central valley portion 108, is relatively thick and prone to cooling unevenness for the reasons described above. Therefore, in the central portion of the coolant flow path 34, the distance may be locally reduced to bring it closer to the bottom defining surface 16. Then, the intermediate flow path 210 formed on the bottom forming die support base 208 is aligned with the inflow flow path 26 and the outflow flow path 28 formed on the second member 6, respectively (see FIG. 3), and coolant is supplied from a circulation type coolant supply means (not shown) to the coolant flow path 34 of the bottom forming die 2 through the intermediate flow path 210. In the illustrated embodiment, the coolant flows in from the center of the coolant flow path 34 that extends in a spiral shape and flows out from the radially outer end.

[0019] Therefore, according to the bottom forming die configured according to the present invention, when blow molding a synthetic resin container having unevenness on the bottom of the container, the bottom of the container can be uniformly and sufficiently cooled without unevenness only by the cooling liquid flowing through the cooling liquid flow path.

[0020] <ESC resistance evaluation> As an example, the container shown in FIG. 1 with a maximum outer diameter of 67 mm and a height of 206 mm in the body part was formed using a bottom forming die configured according to the present invention, that is, in the form shown in FIGS. 4 to 14, with a bottom forming die in which the cooling liquid flow path extends in a spiral shape in the circumferential direction while being displaced in the central axis direction along the bottom defining surface. In such a bottom forming die, the distance between the cooling liquid flow path and the bottom defining surface at the center of the spiral-shaped cooling liquid flow path was 3 mm. As a comparative example, a container having the same shape as the above-described example was formed using a bottom forming die in which the cooling liquid flow path is planar and extends in a spiral shape in the circumferential direction. In such a bottom forming die, the distance between the cooling liquid flow path and the bottom defining surface at the center of the spiral-shaped cooling liquid flow path was 3 mm. The configuration of the molding apparatus for molding the containers of the example and the comparative example is the same except for the above-described bottom forming die. The containers of the example and the comparative example were each molded 10 or 5 at a time at the temperatures shown in the molding temperature column of Table 1 (number of evaluations). Then, each molded container was filled with carbonated water adjusted to the gas volume value shown in the GV column of the same table, sealed with a container lid, and the filled containers were stored under the conditions shown in the storage conditions column of the same table. Thereafter, each filled container was immersed in a citric acid aqueous solution at 22 degrees, and the number of containers that cracked within 15 minutes from the start of immersion was used as the measurement result of the ESC resistance evaluation (environmental stress cracking resistance evaluation).

[0021]

Table 1

[0022] As can be understood by referring to the column of the number of containers in which cracks occurred in Table 1, at the same level, the number of containers in the examples in which cracks occurred is less than that in the comparative examples, and the ESC resistance performance is improved. Therefore, the containers of the examples are less likely to crack or have so-called sink marks than the containers of the comparative examples, and it can be seen that the cooling efficiency of the bottom forming die in the present invention is high.

[0023] As described above, the bottom forming die of the present invention has been described in detail with reference to the attached drawings. However, the bottom forming die of the present invention is not limited to the above-described embodiments, and various modifications can be considered without departing from the scope of the present invention. For example, in the illustrated embodiment, the bottom forming die includes a first member having a bottom defining surface provided on one side surface, and a second member laminated on the other side surface of the first member, and a coolant flow path is defined between the first member and the second member. However, according to a molding method such as so-called stereolithography, the coolant flow path can also be formed inside after integrally molding the first member and the second member or simultaneously with the molding. Further, in the illustrated embodiment, a groove extending in a spiral shape in the circumferential direction while being displaced in the central axis direction along the bottom defining surface is formed on the other side surface of the first member. However, such a groove may be formed on one side surface of the second member. In that case, the other side surface of the first member corresponds to the shape of the bottom defining surface. Furthermore, in the illustrated embodiment, the coolant flows in from the center of the coolant flow path extending in a spiral shape and flows out from the radially outer end. However, the coolant may flow in from the radially outer end and flow out from the center. The coolant flow path does not necessarily have to extend in a spiral shape in the circumferential direction, and may have an arbitrary shape as long as it is displaced in the central axis direction along the bottom of the container. In the illustrated embodiment, the central axis direction is the vertical direction and the first member and the second member are laminated in the vertical direction. However, the central axis direction may be the horizontal direction. When the central axis direction is the horizontal direction, the first member and the second member will be laminated in the left-right direction. Furthermore, the bottom of the container does not necessarily have to be petaloid in shape, and it is sufficient that there are simply irregularities on the bottom of the container.

[0024] As described above, the bottom forming die of the present invention has high cooling efficiency and can cool the bottom of the container uniformly and sufficiently without unevenness. However, separate cooling means may be used in combination. For example, cooling by cooling air as in Patent Document 1 can be used in combination, or a method such as directly spraying a coolant onto the inner surface of the bottom can be used in combination. By using these means in combination, it is also possible to further increase the production speed.

Explanation of Signs

[0025] 2: Bottom forming die 4: First member 6: Second member 16: Bottom defining surface 34: Coolant flow path 102: Container 106: (Bottom of the) container

Claims

1. A bottom forming mold used when blow molding a synthetic resin container having unevenness on the bottom, comprising a first member having a bottom defining surface that defines the bottom of the container provided on one side surface, and a second member laminated on the other side surface of the first member, a groove that is displaced in the central axis direction along the bottom defining surface is formed on the other side surface of the first member, and one side surface of the second member facing the other side surface of the first member corresponds to the shape of the bottom defining surface of the first member, a coolant flow path that is displaced in the central axis direction along the bottom defining surface is defined by the groove formed on the other side surface of the first member and the one side surface of the second member between the first member and the second member. A bottom forming mold characterized by this.

2. A bottom forming mold used when blow molding a synthetic resin container having unevenness on the bottom, comprising a first member having a bottom defining surface that defines the bottom of the container provided on one side surface, and a second member laminated on the other side surface of the first member, a groove that is displaced in the central axis direction along the bottom defining surface is formed on one side surface of the second member facing the other side surface of the first member, and the other side surface of the first member corresponds to the shape of the bottom defining surface of the first member, a coolant flow path that is displaced in the central axis direction along the bottom defining surface is defined by the groove formed on the one side surface of the second member and the other side surface of the first member between the first member and the second member. A bottom forming mold characterized by this.

3. A bottom forming mold used when blow molding a synthetic resin container having unevenness on the bottom, comprising a coolant flow path that is displaced in the central axis direction along the bottom defining surface that defines the bottom of the container, and the coolant flow path extends in a spiral shape in the circumferential direction. A bottom forming mold characterized by this.

4. The bottom forming mold according to claim 1 or 2, wherein the coolant flow path extends in a spiral shape in the circumferential direction.

5. The bottom forming mold according to claim 3 or 4, wherein the coolant flows in from the center of the coolant flow path extending in a spiral shape and flows out from the radially outer end.

6. The bottom forming mold according to any one of claims 1 to 5, wherein the bottom of the container has a petaloid shape.

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