JP7698182B2 - Manufacturing method of preforms and containers - Google Patents

Description

The present invention relates to a preform and a method for manufacturing a container using the preform.

Patent Document 1 discloses a method for producing a double-walled container by loading a tubular molded body inside a preform and performing biaxial stretch blow molding in that state.

JP 2017-94677 A

Since the tubular molded body is formed by direct blow molding, it has a pinch-off part at the bottom. The strength of the pinch-off part is relatively weak, so if such a tubular molded body is loaded inside a preform and biaxial stretch blow molding is performed, there is a risk that the pinch-off part of the tubular molded body will break if it is stretched too vigorously.

The present invention was made in consideration of these circumstances, and provides a preform that prevents the pinch-off portion from tearing during biaxial stretch blow molding.

According to the present invention, there is provided a preform having a cylindrical body and a bottom that closes the lower end of the body, the bottom being provided with a pinch-off portion, in which T2/T1>1 is satisfied, where T1 is the thickness of the body at the center plane in the height direction of the preform, and T2 is the thickness of the bottom at the midpoint between the center and end in the longitudinal direction of the pinch-off portion when the preform is viewed from the bottom side along the longitudinal direction of the preform.

In the preform of the present invention, the thickness of the bottom part is greater than the thickness of the body part, so that stretching of the bottom part of the preform is suppressed during biaxial stretch blowing. When stretching of the bottom part is suppressed, stretching at the pinch-off part provided at the bottom part is also suppressed, and the pinch-off part is prevented from cracking.

Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other.
Preferably, the preform is as described above, in which T2/T1≧1.2.
Preferably, the preform described above comprises, in order from the inside of the preform, an innermost layer, a gas barrier layer, and an outermost layer.
Preferably, the preform is configured by covering an inner preform with an outer preform, and the inner preform is the preform described above.
Preferably, in the preform described above, the outer preform has an annular protrusion at the bottom of the outer preform, and an end of the pinch-off portion is located outside the outer edge of the annular protrusion.
Preferably, the method for manufacturing a container includes a biaxially stretching blow molding step, in which the preform described above is heated and softened, and air is blown into the preform to biaxially stretch the preform.

FIG. 1A shows a container body 2 of a double container 1 that can be manufactured by a double container manufacturing method according to one embodiment of the present invention, and FIG. 1B is a bottom view. 2A is a perspective view of the container body 2 of FIG. 1 as viewed from the bottom 7 side, and FIG. 2B is a cross-sectional perspective view of the vicinity of the bottom 7 of the outer shell 3 as viewed from the inside of the container. 3A is a cross-sectional view taken along line AA in FIG. 1B, and FIG. 3B is a cross-sectional view taken along line BB in FIG. 3A. FIG. 2 is a perspective view showing a state in which the inner preform 14 and the outer preform 13 are separated. FIG. 5A is a perspective view of the inner preform 14 as viewed from the bottom 14c side, and FIG. 5B is an enlarged bottom view of the inner preform 14 (as viewed from the bottom 14c side along the longitudinal direction of the inner preform 14). 5B (a cross-sectional view passing through the longitudinal center 14h1 of the pinch-off portion 14h and perpendicular to the longitudinal direction of the pinch-off portion 14h). 7A is a cross-sectional view taken along line BB in FIG. 5B (a cross-sectional view passing through the midpoint 14h3 and perpendicular to the longitudinal direction of the pinch-off portion 14h), and FIG. 7B is an enlarged view of a region D in FIG. 7A. 5 is a cross-sectional perspective view of the vicinity of a bottom portion 13c of the outer preform 13 of FIG. 4, as viewed from the inside of the outer preform 13. FIG. FIG. 9A is a perspective view of a preform 15 formed by covering an inner preform 14 with an outer preform 13, and FIG. 9B is a perspective view of FIG. 9A as seen from a different angle. 1 is a cross-sectional view showing a state in which a preform 15 is attached to a mouth support mold 21 and brought close to a heater 31. FIG. 11 is a cross-sectional view showing the state after the mouth support mold 21 with the preform 15 attached thereto has been moved to a position between the molding molds 23 and 24 from the state shown in FIG. 10. FIG. 12 is a cross-sectional view showing a state after the molding dies 23, 24 are closed and the bottom support die 22 supports the bottom 13c of the outer preform 13 from the state shown in FIG. 11. FIG. 13 is a cross-sectional view showing the state after the support rod 25 is extended and the bottom support mold 22 is retracted from the state shown in FIG. 12 to longitudinally stretch the preform 15. FIG.

The following describes the embodiments of the present invention. The various features shown in the embodiments below can be combined with each other. In addition, each feature can be an invention independently.

1. double container 1
First, a double container 1 that can be manufactured by the manufacturing method of a double container according to one embodiment of the present invention will be described. As shown in Fig. 1, the double container 1 that can be manufactured by the method of the present invention includes a container body 2. As shown in Fig. 3A, the container body 2 has an outer shell 3 and an inner bag 4, and is configured so that the inner bag 4 shrinks as the content decreases.

As shown in FIG. 1, the container body 2 has a mouth 5, a body 6, and a bottom 7. The mouth 5 has an engagement portion 5a to which a mouth attachment member such as a cap or a pump can be attached. The engagement portion 5a is a male thread portion when the mouth attachment member is a screw type, and is an annular projection protruding in the circumferential direction when the mouth attachment member is a stopper type. The mouth attachment member preferably has a check valve, which allows the contents to be discharged but prevents outside air from flowing into the container body 2. The mouth 5 is provided to extend from the upper end 6a of the body 6. The mouth 5 is cylindrical. The body 6 has a larger outer diameter (in this specification, "outer diameter" means the circumscribed circle diameter when the cross section is not circular) than the mouth 5.

The body 6 is cylindrical, and the bottom 7 is provided at the lower end of the body 6 and closes the lower end of the body 6. The bottom 7 has a central recess 7a provided at the center of the bottom 7 and a peripheral portion 7b surrounding the central recess 7a.

2A, the central recess 7a is provided with a locking portion 7a1, an outside air introduction hole 16, an annular protrusion 7a3, and a positioning recess 7a4. As shown in FIG. 3A, the locking portion 7a1 is formed by inserting a locking protrusion 4a provided on the inner bag 4 into an insertion hole 3a provided on the outer shell 3. The locking portion 7a1 prevents the inner bag 4 from coming off the outer shell 3. The outside air introduction hole 16 is a through hole that penetrates the outer shell 3, and as the inner bag 4 contracts, outside air is introduced into the intermediate space between the outer shell 3 and the inner bag 4 through the outside air introduction hole 16. The locking portion 7a1 and the outside air introduction hole 16 are arranged in the annular protrusion 7a3. The positioning recess 7a4 is used to position the container body 2 in the circumferential direction when printing or the like is performed on the container body 2.

The peripheral portion 7b is provided with a grounding portion 7b1 and a peripheral recess 7b2. The grounding portion 7b1 is the portion that comes into contact with the mounting surface on which the container body 2 is placed when the container body 2 is erected. If the entire peripheral portion 7b were to be the grounding portion 7b1, the central recess 7a would become an airtight space between the container body 2 and the mounting surface when the container body 2 is erected, and there is a risk that the introduction of outside air through the outside air inlet 16 would be hindered. Therefore, the peripheral recess 7b2 is provided as an air passage to prevent the inside of the central recess 7a from becoming an airtight space.

When the contents in the inner bag 4 are discharged by the pump attached to the mouth 5, the inner bag 4 contracts and tries to move away from the outer shell 3. At this time, outside air is introduced into the space between the inner bag 4 and the outer shell 3 through the outside air introduction hole 16. If the outer shell 3 and the inner bag 4 are in close contact near the outside air introduction hole 16, it is difficult for outside air to be introduced into the intermediate space between the outer shell 3 and the inner bag 4. For this reason, in this embodiment, a spacer 9 is placed between the outer shell 3 and the inner bag 4. In this embodiment, the spacer 9 is a protrusion 3b that protrudes from the outer shell 3 toward the inner bag 4. When the spacer 9 is provided, a gap 8 is formed between the outer shell 3 and the inner bag 4 at a position adjacent to the spacer 9, and the gap 8 makes it easier for outside air to be introduced.

As shown in Figures 4 to 9, the container body 2 can be formed by heating and biaxially stretching and blow molding a preform 15 that is made by covering an inner preform 14 that will become the inner bag 4 with an outer preform 13 that will become the outer shell 3.

As shown in FIG. 4, the inner preform 14 is a bottomed cylinder having a mouth 14a, a body 14b, and a bottom 14c. A flange 14a1 is provided at the open end of the mouth 14a. The bottom 14c is provided so as to close the lower end of the body 14b. A positioning pin 14c1 is provided at the bottom 14c.

As shown in FIG. 4, the outer preform 13 is a bottomed tubular member, and includes a mouth 13a, a body 13b, and a bottom 13c. The bottom 13c is provided to close the lower end of the body 13b. As shown in FIG. 8, the inner surface of the bottom 13c of the outer preform 13 is provided with radially arranged protrusions 13c1. The bottom 13c is provided with positioning holes 13c2 and through holes 17. As shown in FIG. 9B, the outer surface of the bottom 13c is provided with an annular protrusion 13c4. The positioning holes 13c2 and through holes 17 are arranged in the inner region of the annular protrusion 13c4. The outer preform 13 is sized to allow the inner preform 14 to be inserted. The through holes 17 become the outside air introduction holes 16 of the container body 2, so the portion where the through holes 17 are provided becomes the outside air introduction hole forming portion 41.

When forming the preform 15, the flange 14a1 is abutted against the open end of the mouth portion 13a, and the positioning pin 14c1 is inserted into the positioning hole 13c2. This positions the inner preform 14 and the outer preform 13 relative to each other. In this state, the mouth portion 14a faces the mouth portion 13a, and the body portion 14b faces the body portion 13b.

The mouth portions 13a and 14a become the mouth portion 15a of the preform 15, the body portions 13b and 14b become the body portion 15b of the preform 15, and the bottom portions 13c and 14c become the bottom portion 15c of the preform 15. As shown in FIG. 10, the body portion 15b and the bottom portion 15c become the stretched portion 15d that will be stretched in the molding process described below.

The inner preform 14 and the outer preform 13 can be formed by direct blow molding, injection molding, or the like, of thermoplastic resins such as polyester (e.g., PET) or polyolefin (e.g., polypropylene, polyethylene). The inner preform is preferably made of a material with a larger molding shrinkage rate than the outer preform. In this case, a gap is formed between the outer shell 3 and the inner bag 4 due to molding shrinkage, making it easier to introduce outside air into the intermediate space between the outer shell 3 and the inner bag 4.

In one example, the inner preform 14 is made of polyolefin (e.g., polypropylene), and the outer preform 13 is made of PET. Since polyolefin has a larger molding shrinkage rate than PET, this type of resin configuration makes it easier for a gap to form between the outer shell 3 and the inner bag 4. In addition, by making the inner preform 14 and the outer preform 13 from different materials, welding to each other during blow molding is suppressed.

The inner preform 14 is preferably formed by direct blow molding. Direct blow molding (blow molding using a molten cylindrical parison) makes it easy to form the inner preform 14 with a laminated structure. The outer preform 13 is preferably formed by injection molding. In this case, the through holes 17 can be formed during injection molding, eliminating the need for post-processing.

When the inner preform 14 is formed by direct blow molding, a pinch-off portion 14h is formed at the bottom 14c of the inner preform 14 where the parison is closed. Since the strength of the pinch-off portion 14h is relatively weak, there is a risk that the pinch-off portion 14h will rupture if the area near the pinch-off portion 14h is stretched too vigorously during biaxial stretch blow molding.

In one example, as shown in Figures 5 to 7, the inner preform 14 has a multi-layer structure, and includes, from the inside, an innermost layer 14d, a gas barrier layer (e.g., an EVOH layer) 14e, and an outermost layer 14f. The innermost layer 14d and the outermost layer 14f are made of polyolefin (e.g., polyethylene, polypropylene), PET, or the like. As shown in Figure 7B, the gas barrier layer 14e is very thin at the pinch-off portion 14h. If the area near the pinch-off portion 14h is stretched during biaxial stretch blow molding, the gas barrier layer 14e may become even thinner or pinholes may form in the gas barrier layer 14e, resulting in problems such as a decrease in gas barrier properties.

In order to solve the above problem, in this embodiment, the thickness of the body 14b at the center plane C in the height direction of the inner preform 14 shown in FIG. 6 is T1, and the thickness of the bottom 14c at the midpoint 14h3 between the center 14h1 and the end 14h2 in the longitudinal direction of the pinch-off portion 14h when the inner preform 14 is viewed from the bottom 14c side as shown in FIG. 5B (the thickness of the portion where the pinch-off portion 14h is provided in FIG. 7B) is T2, so that T2/T1>1 (preferably T2/T1≧1.2) is adopted. This configuration means that the thickness of the bottom 14c of the inner preform 14 is greater than the thickness of the body 14b. By increasing the thickness of the bottom 14c, the elongation of the bottom 14c is suppressed, and as a result, the elongation of the portion near the pinch-off portion 14h is also suppressed, solving the above problem.

The central plane C is a plane that passes through the center 14h1 of the pinch-off portion 14h in the longitudinal direction and is parallel to the upper end surface 14i in a cross section perpendicular to the longitudinal direction of the pinch-off portion 14h, as shown in FIG. 6. The thickness T1 is the thickness of the inner preform 14 at the central plane C, and is preferably the average value of the thicknesses at multiple points in the circumferential direction. For example, the thickness T1 is the average value of the thicknesses at points P1 and P2, which are located on the extension line of the pinch-off portion 14h in the bottom view shown in FIG. 5B, and the thicknesses at points P3 and P4, which pass through the center 14h1 and are located perpendicular to the longitudinal direction of the pinch-off portion 14h.

T2/T1 is, for example, 1.05 to 3, specifically, for example, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, and may be within a range between any two of the numerical values exemplified here.

The above configuration can be achieved, for example, by making the thickness of the part of the parison that forms the bottom 14c greater than the other parts when direct blow molding the inner preform 14.

If the amount of protrusion of the pinch-off portion 14h from the bottom 14c at the midpoint 14h3 is T3, then T3/T2 is preferably 0.5 or less. If this value is too large, the pinch-off portion 14h abuts against the inner surface of the outer preform 13, increasing the gap between the inner preform 14 and the outer preform 13, which can lead to uneven heating of the inner preform 14 during the heating process in biaxial stretch blow molding, or air pockets being formed between the inner bag 4 and the outer shell 3 of the container body 2 obtained by molding. T3/T2 is, for example, 0.01 to 0.5, and specifically, for example, 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, or 0.50, and may be within a range between any two of the numerical values exemplified here, or may be less than any of the values.

The end 14h2 of the pinch-off portion 14h is preferably located outside the outer edge of the annular protrusion 13c4. The area outside the outer edge of the annular protrusion 13c4 is not affected by the annular protrusion 13c4 in suppressing elongation, so the inner preform 14 is likely to be stretched vigorously in this area, which makes it easy for the pinch-off portion 14h to rupture. Therefore, when the end 14h2 of the pinch-off portion 14h is located outside the outer edge of the annular protrusion 13c4, the technical effect of increasing the thickness of the bottom portion 14c and suppressing the elongation of the bottom portion 14c is significant.

2. Manufacturing equipment 40
Next, a manufacturing apparatus 40 that can be used in the manufacturing method of the double container 1 according to one embodiment of the present invention will be described.

As shown in Figures 10 to 13, the manufacturing apparatus 40 includes a mold unit 20 and multiple heaters 31.

The heaters 31 are arranged so as to be aligned along the longitudinal direction of the preform 15 at positions adjacent to the side of the preform 15 when the preform 15 approaches the heaters 31. The output of the heaters 31 can be controlled independently of each other. Each heater 31 is preferably rod-shaped and extends in a direction perpendicular to the plane of the paper in FIG. 10.

The mold unit 20 includes a mouth support mold 21, a bottom support mold 22, and molding molds 23 and 24.

The mouth support mold 21 is configured to be able to support the mouth 13a of the outer preform 13. An insertion hole 21a is provided in the mouth support mold 21, and a support rod 25 is inserted into the insertion hole 21a. The support rod 25 can be extended and retracted by a drive mechanism (not shown).

The mouth support mold 21 is configured to be movable between position A close to the heater 31 as shown in FIG. 10 and position B between the molding molds 23 and 24 as shown in FIG. 11. Therefore, after performing a heating process to heat the preform 15 at position A, it is possible to perform a molding process to mold the preform 15 at position B. The mouth support mold 21 is configured to rotate the preform 15 around the central axis of the mouth 13a. By bringing the preform 15 close to the heater 31 while rotating it, it is possible to heat the entire circumference of the preform 15 uniformly. Note that instead of moving the mouth support mold 21, the heater 31 may be moved.

The bottom support mold 22 is driven by a drive mechanism 22c and configured to be movable in the vertical stretching direction (the up and down direction in Figures 11 to 13). The molding molds 23 and 24 can be opened and closed, and each have a cavity surface 23a and 24a. The cavity surfaces 23a and 24a come together to form a cavity having a shape corresponding to the outer shape of the container body 2.

3. Manufacturing method of the double container 1 The manufacturing method of the double container 1 according to one embodiment of the present invention includes a biaxial stretch blow molding process. In the biaxial stretch blow molding process, the preform 15 is heated and softened, and air is blown into the preform 15 to biaxially stretch the preform 15. This process preferably includes a heating process, a bottom supporting process, a longitudinal stretching process, and a blowing process.

<Heating process>
In the heating step, the preform 15 is heated and softened to a softened state. The heating step can be performed by heating the preform 15 with a plurality of heaters 31 while rotating the preform 15.

In one example, as shown in FIG. 10, the preform 15 can be heated by placing the preform 15 close to a heater 31 while the preform 15 is attached to a mouth support mold 21. Since the mouth 15a of the preform 15 is covered by the mouth support mold 21, the body 15b and bottom 15c (i.e., the stretched portion 15d) are heated. Note that, before the heating step, the tip of the support rod 25 may be abutted against the inner bottom surface of the inner preform 14. This prevents the softened preform 15 from shaking.

<Bottom support process>
In the bottom support step, as shown in Figs. 11 and 12, the bottom support mold 22 moves toward the bottom 13c of the outer preform 13, and supports the bottom 13c of the outer preform 13 with the bottom support mold 22. The bottom support mold 22 is provided with a recess 22a capable of accommodating the annular convex portion 13c4, and the bottom support mold 22 preferably supports the bottom 13c so that the annular convex portion 13c4 is accommodated in the recess 22a. This prevents the annular convex portion 13c4 and its inner region from being stretched during the biaxial stretch blow molding step. The recess 22a is preferably annular. In addition, the bottom support mold 22 preferably includes a recess 22b capable of accommodating the positioning pin 14c1, and supports the bottom 13c so that the positioning pin 14c1 is accommodated in the recess 22b. This prevents the positioning pin 14c1 from interfering with the bottom support mold 22. FIG. 12 shows the molding dies 23, 24 in a closed state, but the molding dies 23, 24 may be closed at any time before the biaxial stretch blow molding process, and may be closed after the longitudinal stretching process.

<Longitudinal Stretching Process>
In the longitudinal stretching step, as shown in Figures 12 to 13, the support rod 25 is pressed against the inner bottom surface of the inner preform 14 to stretch it, thereby stretching the preform 15 in the longitudinal direction (the vertical direction in Figures 12 to 13). At this time, it is preferable to move the bottom support mold 22 backward in synchronization with the extension of the support rod 25. This allows the preform 15 to be stably stretched. Note that the longitudinal stretching step can also be performed in a state in which the bottom 13c is not supported by the bottom support mold 22, so the bottom support step may be performed after the longitudinal stretching step. Also, a recess into which the support rod fits may be provided on the inner bottom surface of the inner preform 14 to make it easier to fix the support rod to the inner preform 14.

<Blow process>
In the blowing process, air is blown into the inner preform 14 from the state shown in Fig. 13 to stretch (i.e. expand) the preform 15 laterally and shape it into the shape of the cavity surfaces 23a, 24a. The air can be blown in through the air passage 26 between the mouth support mold 21 and the support rod 25, but for example, an air passage may be provided in the support rod 25 so that the air can be blown out from the side of the support rod 25.

In this embodiment, air is blown in while the bottom 13c of the outer preform 13 is supported by the bottom support mold 22, so stretching of the bottom 13c of the outer preform 13 is suppressed.

The blowing process can also be performed simultaneously with the vertical stretching process. That is, air can be blown into the inner preform 14 while the preform 15 is being stretched in the vertical direction. Also, the vertical stretching process can be omitted, and air can be blown into the preform 15 after the bottom support process without stretching it in the vertical direction.

The preform 15 expands by biaxial stretch blow molding to obtain the container body 2 shown in Figures 1 to 3. The mouth parts 13a and 14a become the mouth part 5, the body parts 13b and 14b become the body part 6, and the bottom parts 13c and 14c become the bottom part 7. The protrusions 13c1, the annular protrusions 13c4, and the through holes 17 become the protrusions 3b, the annular protrusions 7a3, and the outside air introduction holes 16, respectively. During blow molding, the mouth parts 13a and 14a, the annular protrusions 13c4, and the area inside them are hardly deformed, and the other parts are mainly deformed. Since the through holes 17 are arranged in the area inside the annular protrusions 13c4, they are prevented from being deformed and blocked during blow molding. In addition, since the thickness of the bottom part 14c of the inner preform 14 is large, the extension of the bottom part 14c of the inner preform 14 is suppressed, and the cracking of the pinch-off part 14h is suppressed. As shown in FIG. 1A, the flange 14a1 becomes the flange 4b that covers the open end of the mouth 5 of the container body 2.

After blow molding, the positioning hole 13c2 becomes the insertion hole 3a shown in FIG. 3A, and the positioning pin 14c1 is inserted into the insertion hole 3a. The positioning pin 14c1 is then deformed (i.e., crushed or bent) to become the locking protrusion 4a shown in FIG. 3A. This forms the locking portion 7a1 of the container body 2.

4. Other embodiments: In the above embodiment, the through holes 17 provided in the outer preform 13 are configured to become the outside air introduction holes 16 after blow molding, but the outside air introduction holes 16 may be formed by perforating the perforated portion of the outer shell 3 after blow molding without providing a through hole in the outer preform 13 at the portion that will become the outside air introduction hole 16. In this case, the outside air introduction hole formation portion 41 is the portion of the outer shell 3 that will become the perforated portion.
In the above embodiment, the outside air introduction hole 16 is formed in the bottom 7 of the container body 2 . However, the outside air introduction hole 16 may be formed in the trunk portion 6 .
In the above embodiment, the spacers 9 are provided radially, but the spacers 9 may have a different shape. The spacers 9 may be configured by protrusions protruding from the inner bag 4 or may be configured by a separate member. The spacers 9 may be omitted.
In the above embodiment, the inner preform 14 has a multi-layer structure. However, the inner preform 14 may have a single layer structure.
The preform 15 is made up of two bodies, the outer preform 13 and the inner preform 14, but may be made up of one body. In this case, the preform 15 may have, for example, the same manufacturing method and wall thickness configuration as the inner preform 14, and may have the same mouth portion 13a as the outer preform 13. In this case, a single-layer container is obtained.

1: Double container 2: Container body 3: Outer shell 3a: Insertion hole 3b: Protrusion 4: Inner bag 4a: Locking protrusion 4b: Flange 5: Mouth 5a: Engagement portion 6: Body 6a: Upper end 7: Bottom 7a: Central recess 7a1: Locking portion 7a3: Annular protrusion 7a4: Positioning recess 7b: Peripheral portion 7b1: Grounding portion 7b2: Peripheral recess 8: Gap 9: Spacer 13: Outer preform 13a: Mouth 13b: Body 13c: Bottom 13c1: Protrusion 13c2: Positioning hole 13c4: Annular protrusion 14: Inner preform 14a: Mouth 14a1: Flange 14b: Body 14c: Bottom 14c1: Positioning pin 14d: Innermost layer 14e: Gas barrier layer 14f : outermost layer 14h : pinch-off portion 14h1 : center 14h2 : end 14h3 : midpoint 14i : upper end surface 14j : lower end 15 : preform 15a : mouth portion 15b : body portion 15c : bottom portion 15d : stretched portion 16 : outside air introduction hole 17 : through hole 20 : mold unit 21 : mouth support mold 21a : insertion hole 22 : bottom support mold 22a : recess 22b : recess 22c : drive mechanism 23 : molding mold 23a : cavity surface 24 : molding mold 24a : cavity surface 25 : support rod 26 : ventilation path 31 : heater 40 : manufacturing device 41 : outside air introduction hole forming portion C : center surface

Claims (11)

A method for manufacturing a container, comprising the steps of:
A biaxial stretch blow molding process is provided,
In the biaxial stretch blow molding process, a preform formed by covering an outer preform with an inner preform is heated and softened, and air is blown into the preform to biaxially stretch the preform,
The inner preform has a cylindrical body portion and a bottom portion closing a lower end of the body portion,
the inner preform has a pinch-off portion at the bottom;
The wall thickness of the body portion at the center plane in the height direction of the inner preform is T1,
When the inner preform is viewed from the bottom side along the longitudinal direction of the inner preform, the thickness of the bottom portion at the midpoint between the center and the end of the pinch-off portion in the longitudinal direction is defined as T2.
T2/T1>1 ,
The thickness of the bottom portion other than the pinch-off portion is greater than the thickness of the body portion,
A gap is provided between the outer preform and the body . 2. The method of claim 1 ,
The method of claim 1, wherein the outer preform comprises an annular protrusion at a bottom of the outer preform. 3. The method of claim 2,
The biaxial stretch blow molding process includes a bottom supporting process and a longitudinal stretching process,
In the bottom supporting step, a bottom support mold is provided with a recess capable of accommodating the annular protrusion, and supports a bottom of the preform so that the annular protrusion is accommodated within the recess;
In the longitudinal stretching step, the preform is stretched while the bottom support mold is retracted. 3. The method of claim 2,
The biaxial stretch blow molding process includes a bottom supporting process and a blowing process,
In the bottom supporting step, a bottom support mold is provided with a recess capable of accommodating the annular protrusion, and supports a bottom of the preform so that the annular protrusion is accommodated within the recess;
In the blowing step, air is blown into the outer preform while the bottom of the outer preform is supported by the bottom support mold. The method according to any one of claims 1 to 4,
The biaxial stretch blow molding process includes a longitudinal stretching process and a blowing process,
In the longitudinal stretching step, the preform is stretched in the longitudinal direction,
In the blowing step, the preform is stretched in a lateral direction by blowing air into the preform,
The blowing step is carried out simultaneously with the longitudinal stretching step, and the air is blown into the preform while the preform is being stretched in the longitudinal direction. The method according to any one of claims 1 to 5,
The biaxial stretch blow molding process includes a longitudinal stretching process,
In the longitudinal stretching step, the support rod is pressed against the inner bottom surface of the preform so that a convex portion at the tip of the support rod fits into a concave portion provided in the inner bottom surface of the preform, thereby stretching the preform. The method according to any one of claims 1 to 6 ,
The method comprises providing, in order from the inside of the inner preform, an innermost layer, a gas barrier layer, and an outermost layer. A method according to any one of claims 1 to 7, comprising:
The outer preform has an annular protrusion at a bottom portion of the outer preform,
An end of the pinch-off portion is located outside an outer edge of the annular protrusion. The method according to any one of claims 1 to 8 ,
If the amount of protrusion of the pinch-off portion from the bottom at the midpoint is T3,
A method, wherein T3/T2≦0.40. A method according to any one of claims 1 to 9 , comprising:
T2/T1≧1.2,
If the amount of protrusion of the pinch-off portion from the bottom at the midpoint is T3,
The method, wherein T3/T2≦0.15. A method according to any one of claims 1 to 9 , comprising:
The method, wherein T2/T1 >= 1.2.