JP3420803B2 - Method and apparatus for forming container with hanger - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a container with a hanger, such as an infusion bottle used as a drip container, which is formed with a hanger for hanging the container upside down, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In forming a container with a lifting tool of this kind, in addition to injection molding of a preform (also called a parison) and subsequent stretch blow molding, as in the case of molding a normal container, a suspension is also used. There is a demand for facilitating the manufacturing method of the container with a hanging tool because it requires a step of forming the tool and reduces the cost of the container with a hanging tool. On the other hand, since this type of container with a hanging device is used for medical purposes such as a container for drip,
High reliability is required for the hanging equipment. That is, if the container is detached from the hanger, a serious accident related to human life will be triggered.

The following proposals have been made regarding a method of manufacturing a container with a hanging tool of this type.

Japanese Unexamined Patent Publication No. 63-11324 discloses a manufacturing method in which a hanging device with a hole is integrally molded with the bottom portion of a parison at the stage of the injection molding process of pasolin.

On the other hand, in Japanese Patent Laid-Open No. 63-21804, stretch blow molding of a container is performed with the gate runner portion remaining at the bottom portion of the parison, and then molding is performed using another injection molding die. There is disclosed a manufacturing method in which the hole portion of the hanging device is inserted into the gate runner portion and the gate runner portion and the hanging device are heat-welded.

[0006]

This type of container with a hanging tool is often used for medical purposes, and therefore it is necessary to make it easy to hang the hanging tool in case of an emergency. Is required to be a certain size or more. In this respect, as in the manufacturing method described in JP-A-63-11324,
In the case of integrally molding a hanger having a relatively large hole by injection molding of a parison, the existence of this hanger does not simply mold a cylindrical parison, and its injection molding becomes more difficult than necessary. . Furthermore, in the case of the hot parison type in which the parison injection molding, blow molding and eject operation are performed in one stage, the temperature distribution of the parison cannot be obtained as desired due to the presence of a relatively large hanger, and the parison has an unbalanced temperature. The molded product also has a problem that the resin wall thickness varies.

On the other hand, the container with a lifting tool formed by the manufacturing method disclosed in Japanese Patent Laid-Open No. 63-218045 is inferior in reliability to the lifting tool. According to this manufacturing method,
After inserting the hole of the hanger into the gate runner part, the head part of the gate runner part protruding like a rivet from this hanger is welded to join the two. In this case, if the container is hung upside down, a large load is applied to the head of the rivet-shaped gate runner, and the rivet shaft, which has a relatively small outer diameter composed of the gate runner, has to be damaged, causing the hanger to fall off. There is a high risk that it will end up. If the rivet-shaped shaft portion is thickened, the parison shape becomes special, and the same problem as in the technique of JP-A-63-11324 occurs.

Furthermore, according to this manufacturing method, it is necessary to heat-weld the gate runner portion and the hanger in a separate step, and it takes time and labor to heat-weld the container once cooled and solidified. There is also a problem that a container with a tool cannot be manufactured inexpensively.

In order to solve the above-mentioned problems, the applicant of the present invention does not impair the quality of the container as the final product by performing the injection molding process in the parison injection molding process under the same injection molding condition as that of the ordinary cylindrical parison. Moreover, by connecting the bottom part of the container and the hanger within the stretch blow molding die, the container with the hanger capable of improving the reliability of the hanger and reducing the manufacturing cost is provided. Proposed (JP-A-4-174668).

According to this proposal, a suspender having a hole formed therein is inserted into a stretch blow molding die, and by stretch blow molding a preform, a part of the bottom wall of the container is formed into a hollow ring-shaped cross section. By projecting from the hole of the hanging tool and forming the area of this projecting part larger than the opening area of the hole,
It forms a flange-shaped head for holding the hanging equipment.

The present invention is a further improvement of the above-mentioned proposal, in which the center of the flange-shaped head portion formed at the tip of the shaft portion having a hollow ring-shaped cross section is always aligned with the hole center of the suspender. The purpose is to further reduce the fall of the tool from the bottom wall of the container.

[0012]

SUMMARY OF THE INVENTION The method of the present invention is a method for producing a container with a hanging tool, which comprises a hanging tool for hanging a container upside down on the bottom wall of the container formed by stretch blow molding of a preform. In, the hanger in which the hole is formed is inserted at a position corresponding to the container bottom wall of the stretch blow molding die, and the bottom wall of the preform is extended to the vicinity of the hanger using a stretch rod. By stretching, then by driving the shaft portion on the center side of the stretching rod to project from the hole of the suspender,
While centering the central region of the bottom wall, the bottom wall is formed by the blow fluid so as to project from the hole in a hollow ring shape in cross section, and the area of the projecting portion is larger than the opening area of the hole. It is characterized in that a flange-shaped head portion for holding the hanging tool is formed by molding.

At this time, while the center of the flange-shaped head is centered by the protruding shaft portion on the center side of the stretching rod, the flange-shaped head is pushed back toward the bottom wall of the container, It is also possible to increase the area and to make close contact with the facing surface of the hanger.

In the blow molding apparatus of the present invention for carrying out the above-mentioned molding method, the stretching rod comprises a concentric double shaft,
The tip of the hollow rod on the outside has a tip that faces the inner surface of the bottom wall of the preform, and a centering rod that can project from the tip is arranged inside the hollow shaft. When the bottom wall is extended to the vicinity of the suspender, the end face of the centering rod is substantially flush with the tip and the hollow shaft and the centering rod are simultaneously driven in the vertical direction, and then the centering rod is used. It is characterized in that it has a rod driving unit for driving only the rod to project from the hole of the suspender.

[0015]

[Function] Since the shaft portion connecting the flange-shaped head portion and the bottom wall has a hollow ring shape in cross section by stretch blow molding, its outer diameter is relatively larger than that which can be realized by injection molding such as a gate runner. It becomes possible to form thick. Therefore, even if a considerable amount of weight acts on the flange-shaped head when the container is suspended upside down, the durability against tensile stress and bending stress is further improved than when the shaft is formed by the gate runner itself. It is possible to configure a highly safe container with a hanging tool that does not fall off.

In the method of the present invention for molding such a structure, when the bottom wall of the preform projects as a shaft portion having a hollow ring-shaped cross section from the hole of the hanger, and further by the action of blow pressure, When the protrusion expands laterally on the outer surface side of the hanger to form a flange-shaped head for holding the hanger, the shaft and the head are driven by a part of the extension rod to drive. Can be centered. As a result, the peripheral portion of the flange-shaped head, which has a diameter larger than the hole diameter of the hanger and is in contact with the surface of the hanger, can be reliably secured over the entire circumference of the hole of the hanger. Further, since the flange-shaped head portion is expanded while being centered, the thickness of the peripheral portion can be ensured substantially even in the circumferential direction.

Even if a step of pushing back the flange-shaped head toward the bottom wall of the container is added after this step, the flange-shaped head is pushed back while being centered for a more reliable fastening. Can be realized.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a method for forming an infusion bottle with a hanging tool will be specifically described with reference to the drawings.

5 (A) and 5 (B) show an infusion solution bottle 10 with a hanging tool formed by the method of this embodiment. In the figure, this infusion bottle 10 has a side wall 12 with a rectangular ring-shaped cross section.
The bottom wall 14 has, for example, four leg portions 16 at four corners which serve as a grounding surface when the infusion bottle 10 is in an upright state. A step surface 18 lower than the four leg portions 16 is formed in another region of the bottom wall 14, and a hanging tool 20 is fixed to the center thereof. The suspending tool 20 is formed by integrally forming a base 24 having a hole 22 and a hook 26. The suspending tool 20 can always be stored in the plane connecting the leg portions 16, and the ring-shaped hook portion 26 can be used only when suspending.
May be elastically deformed in a direction away from the bottom wall of the infusion bottle 10.

The hanger 20 is formed by injection molding of, for example, a resin material, but may be formed of elastically deformable metal or other material.

The suspending tool 20 is connected to the bottom wall 14 of the infusion bottle 10 by being sandwiched between the step surface 18 of the bottom wall 14 and the flange-shaped head 30. Flange head 30
Is integrally connected to the step surface 18 by a shaft portion 32 having a hollow ring-shaped cross section which is inserted through the hole portion 22 of the hanging device 20, and the flange area of the flange-shaped head portion 30 is an opening of the hole portion 22 of the hanging device 20. It is larger than the area. As a result, the step surface 1
The shape from 8 to the flange-shaped head portion 30 is an undercut shape. It should be noted that the size of the hole portion 22 may be any size as long as it is commensurate with the diameter of the shaft portion 32 that can withstand the weight of the infusion bottle 10 suspended upside down, and the shaft portion 32 is formed by stretch blow molding. The molding is performed only depending on the diameter of the portion 22, and the outer diameter can be increased regardless of the injection molding conditions of the parison 40.

As a molding material for the container 10 and the parison 40 as a preform thereof, when the final product is an infusion bottle used for a drip container or the like,
Polypropylene is the most suitable, but as the other thermoplastic resin, for example, a thermoplastic polyester resin such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene, polyarylate, or a polyamide (nylon) resin, polyvinyl chloride or the like is used. You can also

FIG. 1 shows a method of manufacturing the infusion bottle 10 with a hanging tool, particularly a stretch blow molding step having a characteristic step.
~ It demonstrates with reference to FIG. In this embodiment, the injection molding of the parison 40, which is a preformed product for stretch blow molding the infusion bottle 10, is carried out under the same injection molding conditions as the ordinary bottomed parison molding. This parison 40
Although the gate runner portion 44 remains on the bottom wall 42 of the above, this is not essential for fastening the hanger 20. In addition, the method of this embodiment includes an injection molding process of the parison 40,
Either the so-called one-stage type in which the temperature control step, the stretch blow molding step and the eject step of the parison 40 thereafter are performed in series, or the so-called two-stage type in which those steps are performed in another stage may be used.

FIG. 4 shows a mold clamped state in which the parison 40 as a preform of the infusion bottle 10 is set inside the blow mold 50 and the suspending tool 20 is used as an inserter on the bottom wall side.

In the stretch blow molding process of the parison 40,
A blow cavity mold 5 composed of two split molds that can be opened and closed in the direction of the back surface of FIG. 4 and that defines the outer wall of the infusion bottle 10.
2 and a bottom mold 54 that can move up and down to define the bottom wall of the infusion bottle 10.
And a neck mold 56 that holds the neck of the parison 40.
A blow core mold 58 that is fitted inside the neck portion of the parison 40 to introduce blow air, and a stretch rod 60 that extends the parison 40 in the vertical axis are used. The suspending tool 20 formed in advance by injection molding or the like is placed on the bottom mold 54 as shown in FIG. It should be noted that it is also possible to adopt a configuration for positioning the suspension 20 with respect to the bottom mold 54.

Here, the extending rod 60 comprises a concentric double shaft, an outer hollow rod 62, a tip tip 64 fixed to the tip of the hollow rod 62, and an insert tip disposed inside the hollow rod 62. And a centering rod 66 capable of projecting below 64. In addition, above the neck die 56, the first movable plate 10 is arranged in order from above.
0, a second movable plate 102, and a blow core type elevating plate 110 are arranged. The first movable plate 100 is one in which the upper end of the centering rod 66 is fixed and is driven up and down by a rod driving cylinder (not shown). The second movable plate 102 fixes the upper end of the hollow shaft 62. The first and second movable plates 100 and 102 are connected by a spring 104 composed of a compression coil spring, for example. This spring 1
The spring constant of 04 is not compressed by the stretching resistance force received as a reaction force from the parison 40 when the stretching rod 60 is driven in the vertical axis. In addition, the lower surface and the upper surface of the second movable plate 102 respectively have the first and second
The second stopper pins 106 and 108 are fixed. These stopper pins 106 and 108 are for determining respectively a stroke at the time of integral drive of the hollow rod 62 and a distal ring rod 66, and a single driving stroke of the sensor Tali ring rod 66.

FIG. 1 shows the stretch blow molding process of the parison 40. In order to perform this step, the blow cavity mold 52 composed of a split mold is closed and driven, and the blow cavity mold 52 and the bottom mold 54 form a cavity that defines the outer wall of the infusion bottle 10. Then, the stretching rod 60
Is driven downward, the tip 64 of the tip extends the parison 40 in the axial direction, and blow air is introduced into the parison 40 through the blow core mold 58.

At this time, the longitudinal rod of the stretching rod 60 is driven by a hollow rod 62 and a centering rod 66.
And are integrally driven downward. That is, the driving force from the rod driving cylinder (not shown) is transmitted to the first movable plate 100, and the first movable plate 1
00 through the spring 104 to the second movable plate 102
Be transmitted to. At this time, if the spring constant of the spring 104 is set as described above, the spring 104 can be driven when the rod is driven.
Is not compressed, the first and second movable plates 100, 1
In the case of 02, the parison 40 is vertically driven while being vertically extended. Therefore, the centering rod 6
6 is a tip 6 fixed to the tip of the hollow rod 62.
While being flush with the surface of No. 4, the parison 40 is driven vertically. This stretch rod 60
By the vertical axis drive and the introduction of blow air, the blow molding of the infusion bottle 10 having the side wall 12 and the bottom wall 14 is biaxially stretched axially and laterally until the outer wall of the parison 40 reaches the cavity surface. It This hollow rod 62
In order to integrally drive the centering rod 66, the first stopper pin 106 fixed to the lower surface of the second movable plate 102 causes the blow core lifting plate 110 to move.
Until the upper surface is reached, and the driving stroke is the length L1 in FIG.

FIG. 1 shows a stretched state of the parison 40 at this time. The bottom wall 42 of the parison 40 is substantially in contact with the cavity surface of the bottom mold 54 due to the vertical drive of the stretching rod 60.

FIG. 2 shows the blow molding process subsequent to FIG. When the rod driving cylinder is subsequently driven from the state of FIG. 1, the downward movement of the second movable plate 102 is restricted by the first stopper pin 106, while only the first movable plate 100 compresses the spring 104. While being driven downward. Therefore, the spring 104 is set to have a spring constant that is compressed by the direct application of the cylinder driving force. First movable plate 10 described above
Only the centering rod 66 inside the extension rod 60 is driven downward by the independent driving of only 0, and the rod 66 is driven to project toward the hole 22 of the hanging tool 20 mounted on the bottom mold 54. become.

Meanwhile, after the state shown in FIG. 1, blow air is introduced into the parison 40 from the blow core mold 56. Therefore, the bottom wall portion of the parison 40 that has reached the cavity surface of the bottom mold 54 is further attached to the hanging tool 20.
It will be extended toward the side of the hole 22 formed in the. Then, the shaft portion 32 having a hollow ring-shaped cross section is formed in the hole portion 22 of the suspender 20. In the present embodiment, in the process of forming the shaft portion 32 having the hollow ring cross section, the centering rod 66 can center the shaft portion 32 so that the shaft center of the shaft portion 32 coincides with the shaft center of the parison 40. When the protrusion of the centering rod 66 is driven, the first movable plate 100 moves to the second
It is carried out until it comes into contact with the second stopper pin 108 formed on the upper surface of the movable plate 102, and its driving stroke is the length L2 in FIG.

In order to secure the centering action of the centering rod 66, a recess 66a is formed at the tip thereof, and the parison 40 is placed in the recess 66a .
The inner wall of the bottom wall 42 may be made to bite.

The shaft portion 32 having a hollow ring-shaped cross section, which is centered and guided by the centering rod 66 and which is formed to project from the hole portion 22 of the hanger 20 by the blow pressure,
Thus, the flange-shaped head portion 30 whose end portion has an area larger than the opening area of the hole 22 is formed. Therefore, the hanger 20 includes the step surface 18 and the peripheral edge portion 3 of the flange-shaped head portion 30.
It is sandwiched and held by 0a.

In the process of forming the flange-shaped head portion 30, the shaft portion 32 having a hollow ring-shaped cross section is centered by the centering rod 66. Therefore, the peripheral edge portion 30 a of the flange-shaped head portion 30 that is expanded in diameter larger than the diameter of the hole portion 22 of the hanging device 20 and contacts the base 24 of the hanging device 20.
Can be reliably secured over the entire circumference of the hole 22 of the hanging device 20. Further, since the flange-shaped head portion 30 is expanded while being centered, the wall thickness of the peripheral edge portion 30a can be substantially uniform in the circumferential direction.

A plurality of vertical grooves (not shown) are formed in the distal end tip 64 of the extending rod 60 in the circumferential direction to increase the blow pressure near the bottom wall 14 to form a hollow ring-shaped shaft portion in cross section. Blow molding of 32 and the flange-shaped head 30 can be performed more reliably. There is. Further, in order to ensure the molding of the shaft portion 32 and the head portion 30, the hole portion 22 of the hanger 20 has a tapered guide surface for guiding the lateral migration of the resin protruding from the hole portion 22. It is preferable to provide 22a.

In the present embodiment, the additional step shown in FIG. 3 is adopted in order to further firmly attach the suspending tool 20 to the bottom wall 14 of the infusion bottle 10.

FIG. 3 shows a step of pushing back the flange-shaped head portion 30 toward the bottom wall 14 side of the infusion bottle 10 by the head pressing elevating pin 70 provided at the center of the bottom mold 54.
Even when the push-back operation is performed by the upward drive of the head pressing lift pin 70, the bottom wall 14 by the tip 64 of the stretching rod 60 is also used.
Either one or both of the pressing operation and the blow air blowing operation are maintained. As a result,
It is possible to prevent the flange-shaped head portion 30 from escaping upward due to the buckling of the infusion bottle 10, and it is possible to ensure a reliable pushing back operation of the flange-shaped head portion 30.

The flange-shaped head portion 30 is crushed by the flat tip surface 72 of the head-pressing lifting pin 70 to increase the flange area, and the inner surface of the flange is hung by the hanging tool 22.
It is in close contact with the base 24 of. Such an operation can be easily realized because the bottom wall 14 still retains heat inside the blow mold 50. Further, the flange-shaped head portion 30 whose flange area is increased by being crushed by the head pressing elevating pin 70 has a uniform wall thickness in the circumferential direction thereof in advance. However, a portion where the wall thickness is extremely thin is not formed. As a result, the hanger 20 can be fastened more securely and reliably. The tip surface 72 is not necessarily flat. If the recess 72a is also formed in the tip surface 72, the misalignment of the flange-shaped head portion 30 when the gate runner 44 is crushed can be prevented.

In this embodiment, the stretching rod 60 is used.
The reason for having a double axis structure is as follows. If the tip tip 62 of the extension rod 60 is too small in area, the bottom wall 14 of the infusion bottle 10 is easily stretched, and the bottom wall 1
4 is thinner than the target thickness. Therefore, when the parison 40 is longitudinally stretched, the tip tip 64 should have an area capable of ensuring a desired wall thickness in the bottom wall 14, and then the tip tip 62 should be placed in the hole 22 of the lifting device 20. Is virtually impossible to insert into.

For this reason, a centering rod 66 is provided which protrudes from the tip 64 after the parison 40 is stretched and which can be inserted into the hole 22 of the hanger 20.
In addition, if the structure is such that the centering rod can project from the tip 64 of the parison 40 after being stretched, it is not always necessary to have the double shaft structure.

The head pressing lift pin 70 has a tip surface 72.
Since the bulging portion 74 is provided at a position lower than that of the bottom die 54, the stopper surface 54b for restricting the upper limit position of the upper end surface 74a of the bulging portion 74 is formed in the pin elevating / lowering guide portion 54a of the bottom mold 54. If the rising drive pressure of the head-pressing lifting pin is made constant by, for example, cylinder drive, a uniform pressing force can be applied at all times, and a suspending tool holding structure having a constant quality can be realized. After that, the stretching rod 60 moves backward, the supply of blow air is stopped, and the infusion bottle 10 is opened after the mold is opened.
The neck portion 58 that has held is conveyed to the eject stage, and one cycle of the molding process is completed by the eject operation.

As described above, by carrying out the step of connecting the suspender 20 to the bottom wall 14 inside the mold in the stretch blow molding step, it is possible to easily realize a suspender holding structure having stable quality and to manufacture the suspension. Cost can be reduced. Since the shaft portion 32, which is the rivet shaft of the suspension structure formed by this manufacturing method, has a hollow ring-shaped cross section, the infusion bottle 10 is filled with contents and suspended upside down, and a weight equivalent to that of the flange-shaped head 30 is obtained. Even if the above action occurs, the risk of the lifting device 20 coming off the infusion bottle 10 can be sufficiently reduced, and the reliability of the infusion bottle used for medical purposes can be greatly improved. Further, particularly when used for medical purposes, it is necessary to secure a large size of the hole of the ring-shaped hook portion 26 serving as a hanging portion of the hanging tool 20, but regardless of the molding process of the infusion bottle 10. ,
In other words, it is also excellent in that such a large hole can be formed without affecting the molding quality of the infusion bottle 10.

Further, the molding conditions are almost equivalent to the molding conditions for molding the conventional ordinary bottomed cylindrical parison, and the molding process of the parison 40 is not complicated. Further, even when compared with the manufacturing method disclosed in Japanese Patent Laid-Open No. 63-11324, the shape of the bottom portion of the parison 40 near the gate opening does not become complicated, so that the flow of resin in the parison is not deteriorated. It is also possible to prevent an adverse effect that uneven temperature of the parison 40 causes uneven thickness in the final product after blow molding.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention.

[0045]

As described above, according to the method of the present invention, a shaft portion having a hollow ring-shaped cross section which is inserted into a hole of a hanging tool, and a flange formed by expanding the end portion of the shaft portion. The head portion can be formed while centering it so that it coincides with the central axis of the hole portion of the hanging device, so that the peripheral portion of the flange head portion is
It is possible to surely secure the entire circumference of the hole of the hanging tool, and it is possible to secure the thickness of the peripheral portion of the flange-shaped head portion to be substantially uniform in the circumferential direction. Therefore, even when it is used particularly for medical purposes, it is possible to form a highly reliable container with a lifting tool that can reliably prevent the lifting tool and the container from coming off.

[Brief description of drawings]

FIG. 1 is a schematic enlarged cross-sectional view showing a blow molding step in an embodiment of the method of the present invention.

FIG. 2 is a schematic enlarged cross-sectional view showing a molding process of a shaft portion and a flange-shaped head portion having a hollow ring-shaped cross section, which is performed subsequent to the step of FIG.

3 is a schematic enlarged cross-sectional view showing a step of pushing back the head, which is performed subsequent to the step of FIG.

FIG. 4 is a schematic cross section of a blow molding process part in which an embodiment of the method of the present invention is carried out.

5 (A) and 5 (B) are a schematic cross-sectional view and a bottom view of a bottom wall portion of an infusion bottle with a lifting tool formed by the manufacturing method of FIG. 1.

[Explanation of symbols]

10 container (infusion bottle) 14 bottom wall 20 Hanging equipment 22 holes 30 flange head 32 hollow shaft 40 parison 50 blow type 60 Stretching rod 62 hollow rod 64 tip 66 Centering rod 70 Lifting pin for pressing head

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) B29C 49/12 B29C 49/20 B65D 1/02 B65D 1/09 B65D 25/22

Claims (3)

(57) [Claims] 1. A method for manufacturing a container with a hanging tool, comprising a hanging tool for hanging a container upside down on a bottom wall of the container molded by stretch blow molding of a preformed product, wherein a hanging hole is formed. The tool is inserted at a position corresponding to the container bottom wall of the stretch blow molding mold, and the bottom wall of the preform is stretched to the vicinity of the hanging tool by using a stretch rod, and then the center of the stretch rod. By driving the shaft part on the side to project from the hole of the hanging tool, the center wall of the bottom wall is centered, and the bottom wall is molded by the blow fluid so as to project from the hole in a hollow ring shape in cross section. A method for forming a container with a lifting tool, characterized in that a flange-shaped head for holding the lifting tool is formed by molding the area of the projecting portion larger than the opening area of the hole. 2. The flange-shaped head according to claim 1, wherein the flange-shaped head is pushed back toward the container bottom wall side while centering the flange-shaped head by the protruding shaft portion on the center side of the stretching rod. Thus, the method for forming a container with a hanging tool is characterized in that the area of the hanging tool is increased and the surface is brought into close contact with the facing surface of the hanging tool. 3. A blow molding apparatus for carrying out the molding method according to claim 1, wherein the stretch rod comprises a concentric double shaft, and the hollow rod on the outside has a tip and an inner surface of the bottom wall of the preform. A centering rod that has opposed tip tips and is capable of projecting from the tip tips is disposed inside the hollow shaft. When the bottom wall of the preform is extended to the vicinity of the hanger, the centering rod is formed. A rod driving section for driving the hollow shaft and the centering rod at the same time in a vertical axis with the end surface of the working rod substantially flush with the tip, and thereafter driving only the centering rod to project from the hole of the suspender. A blow molding device characterized in that