JP2022092962A - Bottom forming mold used when blow molding synthetic resin container - Google Patents

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

The present invention relates to a bottom forming mold used for blow molding a synthetic resin container having an uneven bottom.

As a beverage container, a synthetic resin container molded from an appropriate synthetic resin such as polyethylene terephthalate is widely used in practical use. As is well known to those skilled in the art, such a synthetic resin container is molded by a step of molding a preform (preform) by injection molding or compression molding and a step 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 a body portion and a 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 mold for molding the body of a container and a bottom forming die for molding the bottom of the container. There is.

Immediately after blow molding, the container is relatively soft at high temperature, and the container is cooled and sufficiently cured before being removed from the molding apparatus. In particular, if the bottom of the container is unevenly cooled, the container is likely to shrink or deform at the time of mold release, and cracks or so-called sink marks are likely to occur at the shrunk or deformed portion after mold release. For this reason, it is a commonly used method to accelerate the cooling of the container and shorten the molding time by arranging the cooling liquid flow path in the molding mold and cooling the mold with the cooling liquid. ..

On the other hand, the bottom of the container molded in Patent Document 1 is provided with a bottom central valley and a plurality of valleys and legs alternately arranged around the bottom center valley, and has a complicated shape having irregularities. , So-called petaloid shape. In this way, when unevenness is formed on the bottom, the cooling liquid flowing through the cooling liquid flow path formed on the flat surface, which is provided in the general bottom forming mold, is sufficient for the bottom of the container in a short time. It is difficult to cool. Therefore, in the molding apparatus of Patent Document 1, a cooling liquid flow path is provided in the bottom forming mold, a nozzle is provided at the tip of the drawing rod, and after blow molding, cooling air is provided from the nozzle toward the inner surface of the bottom of the container. The bottom is also cooled by injecting.

Japanese Unexamined Patent Publication No. 2000-343590

The present invention has been made in view of the above facts, and its main technical problem is that when a synthetic resin container having an uneven bottom is blow-molded, the bottom of the container is uniformly and sufficiently cooled. It is to provide a new and improved bottom forming mold that can be used.

As a result of diligent studies, the present inventors have solved the above-mentioned main technical problems by providing the bottom forming mold with a coolant flow path that is displaced in the direction of the central axis along the bottom defining surface that defines the bottom of the container. Found to be achieved.

That is, according to the present invention, as a bottom forming mold that achieves the above-mentioned main technical problem, it is a bottom forming mold used when blow molding a synthetic resin container having an uneven bottom, and the container. Provided is a bottom forming mold comprising a coolant flow path that is displaced in the central axis direction along a bottom defining surface that defines the bottom.

Preferably, the bottom defining surface comprises a first member provided on one side surface and a second member laminated on the other side surface of the first member, the first member and the second member. The coolant flow path is defined between the member and the member. In this case, 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 the other of the first member in the second member. It is preferable that one side surface facing the side surface corresponds to the shape of the bottom defined surface of the first member. The bottom of the container may be petaloid shaped. Preferably, the coolant flow path extends in a spiral direction in the circumferential direction. In this case, the cooling liquid may flow in from the center of the cooling liquid flow path extending in a spiral shape and flow out from the radial outer end.

In the bottom forming mold of the present invention, since the cooling liquid flow path that is displaced in the central axis direction is provided along the bottom defining surface that defines the bottom of the container, the synthetic resin container having an uneven bottom is provided. The distance between the bottom of the container and the coolant flow path is not too far apart for insufficient cooling when blow molding. Further, even if there is a local thick portion at the bottom of the container, if the coolant flow path is locally brought close to the bottom regulation surface for such a portion, the cooling of the thick portion can be locally performed. Can be promoted to. As a result, the bottom of the container can be cooled evenly and uniformly with only the coolant flowing through the coolant flow path. That is, by using the bottom forming mold 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.

Front view showing an example of a synthetic resin container having a petaloid-shaped bottom. A perspective view of the bottom of the container shown in FIG. 1 as viewed from below. The figure which shows typically the structure of the molding apparatus for blow molding the container shown in FIG. 1. FIG. 3 is a front view of a preferred embodiment of a bottom forming die that is a part of the molding apparatus shown in FIG. 3 and is configured according to the present invention. The plan view of the bottom forming mold shown in FIG. The bottom view of the bottom forming mold shown in FIG. FIG. 5 is a sectional view taken along line AA of the bottom forming mold shown in FIG. FIG. 5 is a sectional view taken along line BB of the bottom forming mold shown in FIG. FIG. 5 is a sectional view taken along line CC of the bottom forming mold shown in FIG. The bottom view of the first member constituting the bottom forming mold shown in FIG. FIG. 3 is a perspective view of a second member constituting the bottom forming mold shown in FIG. The front view of the second member shown in FIG. The plan view of the second member shown in FIG. FIG. 13 is a sectional view taken along line AA of the second member shown in FIG. FIG. 3 is a perspective view showing a coolant flow path defined in the bottom forming mold shown in FIG.

Hereinafter, preferred embodiments of the bottom forming mold configured according to the present invention will be described in more detail with reference to the accompanying drawings.

For convenience, prior to the description of the preferred embodiment of the bottom forming mold configured according to the present invention, a molding apparatus including the molding apparatus and a synthetic resin container formed by the molding apparatus will be described. FIG. 1 shows a typical example of a container molded by a molding apparatus including the bottom forming mold of the present invention. This container, which is indicated by reference numeral 102 in its entirety, is formed by blow molding a preform made of an appropriate synthetic resin such as polyethylene terephthalate, and includes a main portion 104 including a body portion and a portion above the main portion 104, and a main portion 104. It has a bottom 106 located below. Explaining with reference to FIG. 2 together with FIG. 1, there are irregularities on the bottom 106 of the container 102. In the illustrated embodiment, the unevenness is a petaloid shape well known to those skilled in the art, and the bottom 106 is spaced at equal angles in the circumferential direction around the bottom central valley 108 and the bottom center valley 108. , A plurality of alternately arranged valleys 110 and legs 112. As described above, the petaloid shape is the most common container having a complicated uneven structure at the bottom, and the shape is required to solve the problem. Therefore, this shape is adopted in the present embodiment.

FIG. 3 shows a molding apparatus 202 for blow molding the container 102. The molding apparatus 202 includes a main portion forming mold 204 for forming the main portion 104 of the container 102 and a bottom forming mold 2 for forming the bottom portion 106. The inner surface defines the molding space 206. The container 102 is formed by blow molding a preform (not shown) in the molding space 206. The bottom forming mold 2 described above is supported by the bottom forming mold support base 208, and an intermediate flow path 210 is formed inside the bottom forming mold support base 208. The bottom forming mold 2 is provided with a coolant flow path 34, and the coolant is supplied from a circulating coolant supply source (not shown) to the coolant flow path 34 via an intermediate flow path 210 to form the bottom. The mold 2 is cooled.

As shown in FIG. 3, the bottom forming mold 2 includes a first member 4 and a second member 6. In the following, the bottom forming mold 2 configured according to the present invention will be described mainly with reference to the drawings after FIG.

Explaining with reference to FIGS. 7 to 9 together with FIGS. 4 to 6, the first member 4 has an annular flange 8 extending substantially horizontally and a cylinder hanging downward from the inner peripheral edge of the flange 8. It is provided with a side wall 10 having a shape and a closing wall 12 that closes the lower end of the side wall 10. A plurality of screw holes 14 are formed on the lower surface of the flange 8 at intervals in the circumferential direction. A bottom defining surface 16 defining the bottom 106 of the container 102 is provided on one side surface of the first member 4. In the illustrated embodiment, the bottom defined surface 16 is defined by the inner peripheral surface of the side wall 10 and the upper surface of the closed wall 12. In the illustrated embodiment, since the bottom 106 of the container 102 has a petaloid 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 referring to FIG. 10, the other side surface of the first member 4, in the illustrated embodiment, the lower surface of the closed wall 12 is displaced in the central axis direction along the bottom defined surface 16 in the circumferential direction. A groove 18 extending in a spiral shape is formed in the groove 18. Explaining the lower surface of the closed wall 12 and the groove 18 with reference to FIGS. 7 to 9, the lower surface of the closed wall 12 is originally displaced in the central axis direction along the bottom defined surface 16. , This is shown by a two-dot chain line as a virtual lower surface 20 in FIGS. 7 to 9. The virtual lower surface 20 also corresponds to the upper surface of the bulging portion 24 described later of the second member 6. The groove 18 extends in a spiral direction in the circumferential direction while being displaced in the central axis direction along the bottom defined surface 16 at a constant depth in the central axis direction along the virtual lower surface 20. The depth of the groove 18 in the central axis direction does not necessarily have to be constant and may be appropriately displaced.

The second member 6 is laminated on the other side surface (lower surface in the illustrated embodiment) of the first member 4. Continuing the description with reference to FIGS. 11 to 14, the second member 6 has a disk-shaped base 22 extending substantially horizontally as a whole, and bulges upward in the center of the base 22. A bulging portion 24 having a required shape is provided. The upper surface of the bulging portion 24, that is, one side surface of the second member 6 facing the other side surface of the first member 4, corresponds to the shape of the bottom defined surface 16 of the first member 4. As will be understood by referring to FIG. 6 together with FIGS. 13 and 14, an inflow flow path having a circular cross section extending linearly in the central axis direction and penetrating the entire second member 6 at the center of the bulging portion 24. 26 is formed at a required angle position of the outer peripheral edge portion in a plan view (bottom view), and an outflow flow path 28 having a circular cross section extending linearly along the central axis and penetrating the entire second member 6 is formed. There is. An annular-shaped auxiliary groove 30 surrounding the bulging portion 24 on one side surface of the base portion 22 is formed. A plurality of mounting holes 32 having a circular cross section penetrating in the central axis direction are formed on 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. In a state where the second member 6 and the first member 4 are combined so that the upper surface of the bulging portion 24 of the second member 6 faces the lower surface of the first member 4, the mounting hole 32 is like a bolt. The first member 4 and the second member 6 are fastened by screwing the fastener into the screw hole 14 of the first member 4 through the fastener (the fastener is shown in FIG. 3). Yes).

When the first member 4 and the second member 6 are combined as described above, as shown in FIGS. 7 to 9, there is a bottom specification between the first member 4 and the second member 6. A coolant flow path 34 that is displaced in the central axis direction along the surface 16 is defined. In the illustrated embodiment, since the coolant flow path 34 is defined by combining the first member 4 and the second member 6, the bottom forming mold described later is composed of a single member. Therefore, it is easier to manufacture than the case where the coolant flow path is provided inside, and therefore the manufacturing cost can be reduced. Since the bottom regulation 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 the container 102 shown by the alternate long and short dash line in the figure. It is displaced in the direction of the central axis along the shape of the bottom 106 (the petaloid shape in the illustrated embodiment). In the illustrated embodiment, the coolant flow path 34 extends in a spiral shape in the circumferential direction. By making the flow path spiral, the flow path is formed by a gentle curve, so that the cooling liquid can easily flow, and the flow path can be evenly arranged with respect to the bottom surface of the bottom 106. The 106 can be cooled uniformly. In the illustrated embodiment, the distance between the coolant flow path 34 and the bottom defined surface 16 is constant, but the distance does not necessarily have to be constant, and is appropriately reduced locally as necessary. The coolant flow path 34 may be brought close to the bottom defined surface 16. For example, the central portion of the bottom portion 106, that is, the bottom central valley portion 108 is relatively thick for the reason described above, and cooling unevenness is likely to occur. Therefore, in the central portion of the coolant flow path 34, the above distance is localized. It may be brought close to the bottom regulation surface 16 in order to reduce it. Then, the intermediate flow path 210 formed in the bottom forming mold support base 208 is aligned with the inflow flow path 26 and the outflow flow path 28 formed in the second member 6, respectively (see FIG. 3). The coolant is supplied from the circulating coolant supply means (not shown) to the coolant flow path 34 of the bottom forming mold 2 via the intermediate flow path 210. In the illustrated embodiment, the cooling liquid flows in from the center of the cooling liquid flow path 34 extending in a spiral shape and flows out from the radial outer end.

Therefore, according to the bottom forming mold configured according to the present invention, when blow molding a synthetic resin container having irregularities on the bottom of the container, the bottom of the container is evenly distributed only by the cooling liquid flowing through the cooling liquid flow path. It can be cooled uniformly and sufficiently.

<ESC resistance evaluation>
As an example, the container shown in FIG. 1, which has a maximum outer diameter of 67 mm and a height of 206 mm, has a bottom forming mold configured according to the present invention, that is, in the form as shown in FIGS. 4 to 14. , The cooling liquid flow path was formed by using a bottom forming mold extending in a spiral shape in the circumferential direction while being displaced in the central axis direction along the specified bottom surface. In such a bottom forming mold, the distance between the cooling liquid flow path and the bottom defined surface in the central portion of the cooling liquid flow path extending in a spiral shape was 3 mm. As a comparative example, a container having the same shape as that of the above-described embodiment was formed by using a bottom forming mold having a planar coolant flow path extending in a spiral shape in the circumferential direction. In such a bottom forming mold, the distance between the cooling liquid flow path and the bottom defined surface in the central portion of the cooling liquid flow path extending in a spiral shape was 3 mm. The configuration of the molding apparatus for molding the containers of the examples and the comparative examples is the same except for the bottom forming mold described above. The containers of Examples and Comparative Examples were each molded into 10 or 5 containers at the temperature shown in the column of molding temperature in Table 1 (evaluation number). Then, each molded container is filled with carbonated water adjusted to the gas volume value shown in the GV column of the same table, and the filled container created by sealing with the container lid is the condition shown in the storage condition column of the same table. Stored in. After that, each filled container was immersed in a citric acid aqueous solution at 22 degrees Celsius, and the number of containers in which cracks occurred within 15 minutes from the start of immersion was measured as the measurement result of ESC resistance evaluation (environmental stress crack resistance evaluation). did.

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

Although the bottom forming mold of the present invention has been described in detail with reference to the attached drawings, the bottom forming mold of the present invention is not limited to the above-described embodiment and does not deviate from the scope of the present invention. Various modifications can be considered. For example, in the illustrated embodiment, the bottom forming mold comprises a first member having a bottom defined surface on one side surface and a second member laminated on the other side surface of the first member. , A coolant flow path was defined between the first member and the second member, but according to a molding method such as so-called stereolithography, the first member and the second member are integrally formed. It is also possible to form a coolant flow path inside after or at the same time as 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 defined surface is formed on the other side surface of the first member. 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 defined surface. Furthermore, in the illustrated embodiment, the coolant flows in from the center of the spirally extending coolant flow path and flows out from the radial outer end, but the coolant flows in from the radial outer end. And it may 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 any 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 stacked in the vertical direction. However, the central axis direction may be the horizontal direction, and the center may be the horizontal direction. When the axial direction is the horizontal direction, the first member and the second member are laminated in the left-right direction. Further, the bottom of the container does not necessarily have to be petaloid-shaped, and the bottom of the container may simply have irregularities.

As described above, the bottom forming mold of the present invention has high cooling efficiency and can sufficiently cool the bottom of the container evenly and uniformly, but a separate cooling means may be used in combination. For example, cooling with cooling air can be used in combination as in Patent Document 1, or a method such as spraying a cooling liquid directly on the inner surface of the bottom can also be used in combination. By using these means together, it is possible to further increase the production speed.

2: Bottom forming mold 4: First member 6: Second member 16: Bottom specified surface 34: Coolant flow path 102: Container 106: Bottom (of container)

Claims (6)

A bottom forming mold used when blow molding a synthetic resin container with uneven bottom.
A bottom forming mold comprising a coolant flow path that is displaced in the central axis direction along a bottom defined surface that defines the bottom of the container. A first member having the bottom defining surface provided on one side surface and a second member laminated on the other side surface of the first member are provided.
The bottom forming mold according to claim 1, wherein the coolant flow path is defined between the first member and the second member. A groove is formed on the other side surface of the first member so as to be displaced in the central axis direction along the bottom defined surface, and a piece of the second member facing the other side surface of the first member. The bottom forming mold according to claim 2, wherein the side surface corresponds to the shape of the bottom regulation surface of the first member. The bottom forming mold according to any one of claims 1 to 3, wherein the bottom of the container has a petaloid shape. The bottom forming mold according to any one of claims 1 to 4, wherein the coolant flow path extends in a spiral shape in the circumferential direction. The bottom forming mold according to claim 5, wherein the coolant flows in from the center of the coolant flow path extending in a spiral shape and flows out from the radial outer end.

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