Preform, method for manufacturing a container

Abstract

To provide a preform in which cracking of a pinch-off portion is suppressed during biaxial stretch blow molding.SOLUTION: A preform has a cylindrical trunk portion and a bottom portion that closes a lower end of the trunk portion. The bottom portion is provided with a pinch-off portion. The preform satisfies T2 / T1>1, where T1 denotes a wall thickness of the trunk portion at a central surface in a height direction of the preform, and T2 denotes a wall thickness of the bottom portion at a middle point between a center and an end in a lengthwise direction of the pinch-off portion when the preform is viewed from a bottom portion side in the lengthwise direction of the preform.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a preform and a method for manufacturing a container using the same.

Background Art

[0002] Patent Document 1 discloses a method for manufacturing a double container by loading a tubular molded body inside a preform and performing biaxial stretch blow molding in that state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the tubular molded body is formed by direct blow molding, it has a pinch-off portion at the bottom. Since the strength of the pinch-off portion is relatively weak, when biaxial stretch blow molding is performed with such a tubular molded body loaded inside the preform, if the pinch-off portion of the tubular molded body is stretched vigorously, the pinch-off portion may crack.

[0005] The present invention has been made in view of such circumstances, and provides a preform in which the pinch-off portion is suppressed from cracking during biaxial stretch blow molding.

Means for Solving the Problems

[0006] According to the present invention, there is provided a preform having a cylindrical body portion and a bottom portion closing the lower end of the body portion, the bottom portion being provided with a pinch-off portion. Let the wall thickness of the body portion at the central plane in the height direction of the preform be T1, and let the wall thickness of the bottom portion at the midpoint between the longitudinal center and the end of the pinch-off portion when the preform is viewed along the longitudinal direction of the preform from the bottom side be T2. Then, T2 / T1>1, and a preform is provided.

[0007] In the preform of the present invention, since the wall thickness of the bottom portion is larger than the wall thickness of the body portion, stretching of the bottom portion of the preform is suppressed during biaxial stretch blow molding. When the stretching of the bottom portion is suppressed, the stretching at the pinch-off portion provided at the bottom portion is also suppressed, and the cracking of the pinch-off portion is suppressed.

[0008] Hereinafter, various embodiments of the present invention will be exemplified. The embodiments shown below can be combined with each other. Preferably, the preform is the preform described above, and T2 / T1≧1.2. Preferably, the preform is the preform described above, and includes an innermost layer, a gas barrier layer, and an outermost layer in order from the inside of the preform. Preferably, the preform is configured by covering an inner preform with an outer preform, and the inner preform is the preform described above. Preferably, the preform is the preform described above, and the outer preform is provided with an annular convex portion at the bottom portion of the outer preform, and the end of the pinch-off portion is located outside the outer edge of the annular convex portion. Preferably, it is a method for manufacturing a container, including a biaxial stretch blow molding step. In the biaxial stretch blow molding step, air is blown into the preform in a state where the preform described above is heated and softened to biaxially stretch the preform.

Brief Description of the Drawings

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Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described. Various characteristic matters shown in the following embodiments can be combined with each other. Also, an invention can be established independently for each characteristic.

[0011] 1. Double container 1 First, the double container 1 that can be manufactured by the manufacturing method of the double container according to an 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 such that the inner bag 4 contracts as the content decreases.

[0012] As shown in FIG. 1, the container body 2 includes a mouth part 5, a body part 6, and a bottom part 7. The mouth part 5 includes an engaging part 5a to which a mouth part mounting member such as a cap or a pump can be mounted. The engaging part 5a is a male screw part when the mouth part mounting member is screw-type, and an annular protrusion protruding in the circumferential direction when the mouth part mounting member is a stopper type. The mouth part mounting member preferably has a check valve and is configured such that the content can be discharged but outside air does not flow into the container body 2. The mouth part 5 is provided so as to extend from the upper end 6a of the body part 6. The mouth part 5 is cylindrical. The outer diameter of the body part 6 is larger than that of the mouth part 5 (in this specification, the "outer diameter" means the circumscribed circle diameter when the cross-section is not circular).

[0013] The body part 6 is cylindrical, and the bottom part 7 is provided at the lower end of the body part 6 and closes the lower end of the body part 6. The bottom part 7 includes a central recess 7a provided at the center of the bottom part 7 and a peripheral edge part 7b surrounding the central recess 7a.

[0014] As shown in FIG. 2A, the fovea 7a is provided with a locking portion 7a1, an outside air introduction hole 16, an annular convex portion 7a3, and a positioning recess 7a4. As shown in FIG. 3A, the locking portion 7a1 is configured by inserting a locking projection 4a provided on the inner bag 4 into an insertion hole 3a provided in 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 penetrating 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 disposed within the annular convex portion 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.

[0015] The peripheral portion 7b is provided with a grounding portion 7b1 and a peripheral recess 7b2. The grounding portion 7b1 is a portion that contacts the placement surface on which the container body 2 is placed when the container body 2 is erected. If the entire peripheral portion 7b is used as the grounding portion 7b1, when the container body 2 is erected, the fovea 7a may become a sealed space between the container body 2 and the placement surface, and the introduction of outside air through the outside air introduction hole 16 may be inhibited. Therefore, the peripheral recess 7b2 is provided as a ventilation path so that the inside of the fovea 7a does not become a sealed space.

[0016] When the content in the inner bag 4 is discharged by a pump attached to the mouth portion 5, the inner bag 4 contracts and tries to separate 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 in the vicinity of 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 the present embodiment, a spacer 9 is disposed between the outer shell 3 and the inner bag 4. In the present embodiment, as the spacer 9, a projection 3b protruding from the outer shell 3 toward the inner bag 4 is provided. 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.

[0017] As shown in FIGS. 4 to 9, the container body 2 can be formed by heating a preform 15, which is configured by covering an inner preform 14 serving as an inner bag 4 with an outer preform 13 serving as an outer shell 3, and performing biaxial stretch blow molding.

[0018] As shown in FIG. 4, the inner preform 14 has a bottomed cylindrical shape and includes a mouth portion 14a, a body portion 14b, and a bottom portion 14c. A flange 14a1 is provided at the open end of the mouth portion 14a. The bottom portion 14c is provided so as to close the lower end of the body portion 14b. A positioning pin 14c1 is provided on the bottom portion 14c.

[0019] As shown in FIG. 4, the outer preform 13 has a bottomed cylindrical shape and includes a mouth portion 13a, a body portion 13b, and a bottom portion 13c. The bottom portion 13c is provided so as to close the lower end of the body portion 13b. As shown in FIG. 8, protrusions 13c1 arranged radially are provided on the inner surface of the bottom portion 13c of the outer preform 13. A positioning hole 13c2 and a through hole 17 are provided in the bottom portion 13c. As shown in FIG. 9B, an annular convex portion 13c4 is provided on the outer surface of the bottom portion 13c. The positioning hole 13c2 and the through hole 17 are arranged in a region inside the annular convex portion 13c4. The outer preform 13 is sized such that the inner preform 14 can be inserted therein. Since the through hole 17 serves as the outside air introduction hole 16 of the container body 2, the portion where the through hole 17 is provided becomes the outside air introduction hole forming portion 41.

[0020] When forming the preform 15, the flange 14a1 is brought into contact with the open end of the mouth portion 13a, and the positioning pin 14c1 is inserted into the positioning hole 13c2. Thereby, the inner preform 14 and the outer preform 13 are positioned relative to each other. In this state, the mouth portion 14a and the mouth portion 13a face each other, and the body portion 14b and the body portion 13b face each other.

[0021] The mouth parts 13a and 14a become the mouth part 15a of the preform 15, the body parts 13b and 14b become the body part 15b of the preform 15, and the bottom parts 13c and 14c become the bottom part 15c of the preform 15. Also, as shown in FIG. 10, the body part 15b and the bottom part 15c become the stretched part 15d to be stretched in the molding process described later.

[0022] The inner preform 14 and the outer preform 13 can be formed by direct blow molding or injection molding of a thermoplastic resin such as polyester (e.g., PET) or polyolefin (e.g., polypropylene, polyethylene). The inner preform is preferably composed 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, facilitating the introduction of outside air into the intermediate space between the outer shell 3 and the inner bag 4.

[0023] In one example, the inner preform 14 is composed of polyolefin (e.g., polypropylene), and the outer preform 13 is composed of PET. Since polyolefin has a larger molding shrinkage rate than PET, such a resin configuration makes it easier to form a gap between the outer shell 3 and the inner bag 4. Also, by using different materials for the inner preform 14 and the outer preform 13, welding between them during blow molding is suppressed.

[0024] The inner preform 14 is preferably formed by direct blow molding. According to direct blow molding (blow molding using a tubular parison in a molten state), the inner preform 14 with a laminated structure can be easily formed. The outer preform 13 is preferably formed by injection molding. In this case, since the through hole 17 can be formed during injection molding, the labor for post-processing can be saved.

[0025] 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 at the position where the parison is closed. Since the strength of the pinch-off portion 14h is relatively weak, when the portion near the pinch-off portion 14h is stretched vigorously during biaxial stretch blow molding, the pinch-off portion 14h may crack.

[0026] In one example, as shown in FIGS. 5 to 7, the inner preform 14 has a multi-layer structure and includes, in order from the inside, the innermost layer 14d, a gas barrier layer (e.g., EVOH layer) 14e, and the 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 FIG. 7B, in the pinch-off portion 14h, the gas barrier layer 14e is very thin. When the portion 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 be formed in the gas barrier layer 14e, resulting in problems such as a decrease in gas barrier properties.

[0027] In order to solve the above problems, in this embodiment, the wall thickness of the body portion 14b at the central plane C in the height direction of the inner preform 14 shown in FIG. 6 is defined as T1, and as shown in FIG. 5B, when the inner preform 14 is viewed from the bottom 14c side, the wall thickness of the bottom 14c at the midpoint 14h3 between the longitudinal center 14h1 and the end 14h2 of the pinch-off portion 14h (in FIG. 7B, the wall thickness of the portion where the pinch-off portion 14h is provided) is defined as T2. Then, a configuration is adopted in which T2 / T1 > 1 (preferably T2 / T1 ≥ 1.2). This configuration means that the wall thickness of the bottom 14c of the inner preform 14 is larger than the wall thickness of the body portion 14b. By increasing the wall thickness of the bottom 14c, the stretching of the bottom 14c is suppressed, and as a result, the stretching of the portion near the pinch-off portion 14h is also suppressed, and the above problems are solved.

[0028] The central plane C is a plane passing through the longitudinal center 14h1 of the pinch-off portion 14h as shown in FIG. 6 and passing through the centers of the upper end surface 14i and the lower end 14j of the inner preform 14 in a cross-section perpendicular to the longitudinal direction of the pinch-off portion 14h and parallel to the upper end surface 14i. The wall thickness T1 is the wall thickness of the inner preform 14 at the central plane C, and is preferably the average value of the wall thicknesses at a plurality of points in the circumferential direction. For example, the wall thickness T1 is the average value at points P1 and P2 arranged on the extension line of the pinch-off portion 14h in the bottom view shown in FIG. 5B and at points P3 and P4 arranged in a direction passing through the center 14h1 and perpendicular to the longitudinal direction of the pinch-off portion 14h.

[0029] T2 / T1 is, for example, 1.05 to 3, and 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 the range between any two of the numerical values exemplified herein.

[0030] The above configuration can be realized, for example, by making the wall thickness of the portion constituting the bottom 14c of the parison formed when directly blow-molding the inner preform 14 larger than that of other portions.

[0031] At the intermediate point 14h3, when the protruding amount of the pinch-off portion 14h from the bottom 14c is T3, T3 / T2 is preferably 0.5 or less. If this value is too large, the pinch-off portion 14h may contact the inner surface of the outer preform 13, increasing the distance between the inner preform 14 and the outer preform 13, and the heating of the inner preform 14 in the heating step during biaxial stretch blow molding may become uneven, or an air pocket may easily form 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, 0.50, and may be within the range between any two of the numerical values exemplified herein or less than any of the values.

[0032] The end 14h2 of the pinch-off part 14h is preferably located outside the outer edge of the annular convex part 13c4. Since the region outside the outer edge of the annular convex part 13c4 is not affected by the effect of suppressing the stretching by the annular convex part 13c4, in this region, the inner preform 14 is likely to be stretched vigorously, and therefore, the pinch-off part 14h is likely to crack. Accordingly, when the end 14h2 of the pinch-off part 14h is located outside the outer edge of the annular convex part 13c4, the technical effect of increasing the wall thickness of the bottom part 14c and suppressing the stretching of the bottom part 14c is remarkable.

[0033] 2. Manufacturing apparatus 40 Next, a manufacturing apparatus 40 that can be used in the manufacturing method of the double container 1 according to an embodiment of the present invention will be described.

[0034] As shown in FIGS. 10 to 13, the manufacturing apparatus 40 includes a mold unit 20 and a plurality of heaters 31.

[0035] The plurality of heaters 31 are arranged so as to be aligned along the longitudinal direction of the preform 15 at positions adjacent to the side surface of the preform 15 when the preform 15 approaches the heaters 31. The outputs of the plurality of heaters 31 can be controlled independently of each other. Each heater 31 is preferably in the shape of a rod extending in the direction perpendicular to the plane of FIG. 10.

[0036] The mold unit 20 includes a mouth support mold 21, a bottom support mold 22, and molding molds 23, 24.

[0037] The mouth support mold 21 is configured to be able to support the mouth part 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 through the insertion hole 21a. The support rod 25 can be expanded and contracted by a drive mechanism (not shown).

[0038] The mouth support 21 is configured to be movable between a position A close to the heater 31 as shown in FIG. 10 and a position B between the mold forms 23 and 24 as shown in FIG. 11. Therefore, after performing a heating step of heating the preform 15 at position A, it is possible to perform a molding step of molding the preform 15 at position B. The mouth support 21 is capable of rotating the preform 15 about the central axis of the mouth portion 13a. By bringing the preform 15 close to the heater 31 while rotating the preform 15, it is possible to uniformly heat the entire circumference of the preform 15. Note that instead of moving the mouth support 21, the heater 31 may be moved.

[0039] The bottom support 22 is driven by a drive mechanism 22c and is configured to be movable in the longitudinal stretching direction (the vertical direction in FIGS. 11 to 13). The mold forms 23 and 24 are openable and closable, and each includes a cavity surface 23a and 24a. When the cavity surfaces 23a and 24a are combined, a cavity having a shape corresponding to the outer shape of the container body 2 is formed.

[0040] 3. Manufacturing method of the double container 1 The manufacturing method of the double container 1 according to an embodiment of the present invention includes a biaxial stretch blow molding step. In the biaxial stretch blow molding step, air is blown into the preform 15 in a state where the preform 15 is heated and softened to biaxially stretch the preform 15. This step preferably includes a heating step, a bottom support step, a longitudinal stretching step, and a blow step.

[0041] <Heating step> 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.

[0042] In one example, as shown in FIG. 10, with the preform 15 mounted on the mouth support type 21, the preform 15 can be heated by bringing it close to the heater 31. Since the mouth portion 15a of the preform 15 is covered by the mouth support type 21, the body portion 15b and the bottom portion 15c (that is, the portion to be stretched 15d) are heated. Note that before the heating step, the tip of the support rod 25 may be brought into contact with the inner bottom surface of the inner preform 14. Thereby, the softened preform 15 is suppressed from swaying.

[0043] <Bottom support step> In the bottom support step, as shown in FIGS. 11 to 12, the bottom support type 22 moves toward the bottom portion 13c of the outer preform 13 and supports the bottom portion 13c of the outer preform 13 with the bottom support type 22. The bottom support type 22 is provided with a concave portion 22a capable of accommodating the annular convex portion 13c4, and it is preferable that the bottom support type 22 supports the bottom portion 13c such that the annular convex portion 13c4 is accommodated in the concave portion 22a. Thereby, the annular convex portion 13c4 and the region inside thereof are suppressed from being stretched during the biaxial stretch blow molding step. The concave portion 22a is preferably annular. Further, the bottom support type 22 is provided with a concave portion 22b capable of accommodating the positioning pin 14c1, and it is preferable that the bottom support type 22 supports the bottom portion 13c so as to accommodate the positioning pin 14c1 in the concave portion 22b. Thereby, the positioning pin 14c1 is suppressed from interfering with the bottom support type 22. FIG. 12 shows a state where the mold forms 23 and 24 are closed, but the mold forms 23 and 24 may be closed at any point in time before the biaxial stretch blow molding step, so they may be closed after the longitudinal stretch step.

[0044] <Longitudinal stretch step> In the longitudinal stretching process, as shown in FIGS. 12 to 13, the preform 15 is stretched in the longitudinal direction (the vertical direction in FIGS. 12 to 13) by pressing the support rod 25 against the inner bottom surface of the inner preform 14 and stretching it. At this time, it is preferable to retract the bottom support mold 22 in synchronization with the stretching of the support rod 25. Thereby, the preform 15 can be stably stretched. In addition, since the longitudinal stretching process can also be performed in a state where the bottom 13c is not supported by the bottom support mold 22, the bottom support process may be performed after the longitudinal stretching process. Further, a recess into which the support rod fits may be provided on the inner bottom surface of the inner preform 14 so that the support rod can be easily fixed to the inner preform 14.

[0045] <Blowing Process> In the blowing process, the preform 15 is stretched laterally (i.e., expanded) from the state of FIG. 13 by blowing air into the inner preform 14 to form it into the shape of the cavity surfaces 23a, 24a. The air can be blown through the air passage 26 between the mouth support mold 21 and the support rod 25. For example, an air passage may be provided in the support rod 25 so that air is blown out from the side surface of the support rod 25.

[0046] In this embodiment, since air is blown in a state where the bottom 13c of the outer preform 13 is supported by the bottom support mold 22, the stretching of the bottom 13c of the outer preform 13 is suppressed.

[0047] Note that the blowing process can also be performed simultaneously with the longitudinal stretching process. That is, air may be blown into the inner preform 14 while stretching the preform 15 in the longitudinal direction. Further, the longitudinal stretching process may be omitted, and after the bottom support process, air may be blown without stretching the preform 15 in the longitudinal direction.

[0048] By biaxial stretch blow molding, the preform 15 expands to obtain the container body 2 shown in FIGS. 1 to 3. The mouth portions 13a and 14a become the mouth portion 5, the body portions 13b and 14b become the body portion 6, and the bottom portions 13c and 14c become the bottom portion 7. The protrusion 13c1, the annular convex portion 13c4, and the through hole 17 become the protrusion 3b, the annular convex portion 7a3, and the outside air introduction hole 16, respectively. During blow molding, the mouth portions 13a and 14a, the annular convex portion 13c4, and the region inside thereof hardly deform, and the other portions mainly deform. Since the through hole 17 is disposed in the region inside the annular convex portion 13c4, it is suppressed from deforming and closing during blow molding. Further, since the wall thickness of the bottom portion 14c of the inner preform 14 is large, the stretching of the bottom portion 14c of the inner preform 14 is suppressed, and the cracking of the pinch-off portion 14h is suppressed. The flange 14a1 becomes the flange 4b that covers the open end of the mouth portion 5 of the container body 2 as shown in FIG. 1A.

[0049] 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. Thereafter, the positioning pin 14c1 is deformed (that is, crushed or bent) to form the locking projection 4a shown in FIG. 3A. Thereby, the locking portion 7a1 of the container body 2 is configured.

[0050] 4. Other Embodiments · In the above embodiment, the through hole 17 provided in the outer preform 13 is configured to become the outside air introduction hole 16 after blow molding. However, in the outer preform 13, a through hole may not be provided at the portion that becomes the outside air introduction hole 16, and the outside air introduction hole 16 may be formed by perforating the perforated portion of the outer shell 3 after blow molding. In this case, the outside air introduction hole forming portion 41 is the portion that becomes the perforated portion of the outer shell 3. · In the above embodiment, the outside air introduction hole 16 is formed in the bottom portion 7 of the container body 2, but the outside air introduction hole 16 may be formed in the body portion 6. · In the above embodiment, the spacers 9 are provided radially, but the spacers 9 may have another shape. The spacers 9 may be constituted by protrusions protruding from the inner bag 4 or by separate members. The spacers 9 may be omitted. ·In the above embodiment, the inner preform 14 has a multi-layer structure, but it may also have a single-layer structure. ·The preform 15 has a two-piece structure of the outer preform 13 and the inner preform 14, but it may also have an integral structure. In that case, the preform 15 can have, for example, the same manufacturing method and wall thickness structure as the inner preform 14 and the same mouth part 13a as the outer preform 13. In this case, a single-layer container can be obtained.

Explanation of Reference Numerals

[0051] 1: Double-layer container 2: Container body 3: Outer shell 3a: Insertion hole 3b: Protrusion 4: Inner bag 4a: Locking protrusion 4b: Flange 5: Mouth part 5a: Engaging part 6: Barrel part 6a: Upper end 7: Bottom part 7a: Central recess 7a1: Locking part 7a3: Annular convex part 7a4: Positioning recess 7b: Peripheral part 7b1: Grounding part 7b2: Peripheral recess 8: Gap 9: Spacer 13: Outer preform 13a: Mouth part 13b: Barrel part 13c: Bottom part 13c1: Protrusion 13c2: Positioning hole 13c4: Annular convex part 14: Inner preform 14a: Mouth part 14a1: Flange 14b: Barrel part 14c: Bottom part 14c1: Positioning pin 14d: Innermost layer 14e: Gas barrier layer 14f: Outermost layer 14h: Pinch-off part 14h1: Center 14h2: End 14h3: Intermediate point 14i: Upper end face 14j: Lower end 15: Preform 15a: Mouth part 15b: Barrel part 15c: Bottom part 15d: Part to be stretched 16: Outer air introduction hole 17: Through hole 20: Mold unit 21: Mouth part support mold 21a: Insertion hole 22: Bottom part support mold 22a: Recess 22b: Recess 22c: Driving mechanism 23: Forming mold 23a: Cavity surface 24: Forming mold 24a: Cavity surface 25: Support rod 26: Vent passage 31: Heater 40: Manufacturing apparatus 41: Outer air introduction hole forming part C: Central plane

Claims

1. A method for manufacturing a container, comprising: a biaxial stretch blow molding step; in the biaxial stretch blow molding step, air is blown into the preform in a state where the preform formed by covering an inner preform with an outer preform is heated and softened to biaxially stretch the preform; the inner preform has a cylindrical body portion and a bottom portion that closes the lower end of the body portion; the inner preform is provided with a pinch-off portion at the bottom portion; let the wall thickness of the body portion at the central plane in the height direction of the inner preform be T1; when viewing the inner preform from the bottom side along the longitudinal direction of the inner preform, let the wall thickness of the bottom portion at the midpoint between the longitudinal center and the end of the pinch-off portion be T2; T2 / T1 > 1; the wall thickness of the portion of the bottom portion other than the pinch-off portion is larger than the wall thickness of the body portion; a method in which a gap is provided between the outer preform and the body portion.

2. The method according to claim 1, wherein: the outer preform is provided with an annular convex portion at the bottom of the outer preform.

3. The method according to claim 2, wherein: the biaxial stretch blow molding step includes a bottom support step and a longitudinal stretch step; in the bottom support step, the bottom of the preform is supported by a bottom support mold provided with a recess capable of accommodating the annular convex portion so that the annular convex portion is accommodated in the recess; in the longitudinal stretch step, the preform is stretched while the bottom support mold is retracted.

4. The method according to claim 2, wherein: the biaxial stretch blow molding step includes a bottom support step and a blow step; in the bottom support step, the bottom of the preform is supported by a bottom support mold provided with a recess capable of accommodating the annular convex portion so that the annular convex portion is accommodated in the recess; in the blow step, air is blown while the bottom of the outer preform is supported by the bottom support mold.

5. The method according to any one of claims 1 to 4, wherein: the biaxial stretch blow molding step includes a longitudinal stretch step and a blow step; in the longitudinal stretch step, the preform is stretched in the longitudinal direction; in the blow step, the preform is stretched in the lateral direction by blowing air into the preform. The blowing step is performed simultaneously with the longitudinal stretching step, and air is blown into the preform while stretching the preform in the longitudinal direction. **Claim 6**: The method according to any one of Claims 1 to 5, wherein the biaxial stretch blow molding step includes a longitudinal stretching step, and in the longitudinal stretching step, the preform is stretched by pressing the support rod against the inner bottom surface of the preform such that the convex portion at the tip of the support rod fits into the concave portion provided on the inner bottom surface of the preform. **Claim 7** The method according to any one of Claims 1 to 6, comprising, in order from the inside of the inner preform, an innermost layer, a gas barrier layer, and an outermost layer. **Claim 8** The method according to any one of Claims 1 to 7, wherein the outer preform includes an annular convex portion at the bottom thereof, and the end of the pinch-off portion is located outside the outer edge of the annular convex portion. **Claim 9** The method according to any one of Claims 1 to 8, wherein at the intermediate point, when the protruding amount of the pinch-off portion from the bottom is T3, T3 / T2 ≤ 0.

40. **Claim 10** The method according to any one of Claims 1 to 9, where T2 / T1 ≥ 1.2, and at the intermediate point, when the protruding amount of the pinch-off portion from the bottom is T3, T3 / T2 ≤ 0.

15. **Claim 11** The method according to any one of Claims 1 to 9, where T2 / T1 ≥ 1.2.

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