Double container, preform assembly, and method for manufacturing a synthetic resin container

Abstract

To provide a double container in which an inner layer body can be easily separated from an outer layer body, a preform assembly capable of forming the double container, and a method for manufacturing the double container.SOLUTION: Provided is a synthetic resin double container 1 formed in a bottle shape, including an outer layer body 2 and an inner layer body 3 separably laminated inside the outer layer body 2, by blow molding a preform assembly 40 in which an inner preform 42 is assembled inside an outer preform 41, and including a mouth part 11, a body part 12 and a bottom part 13, wherein a band-shaped sheet 20 formed in a belt shape by a synthetic resin material different from at least an inner surface of the outer layer body 2 or an outer surface of the inner layer body 3 and extending upward from the bottom part 13 is arranged between the outer layer body 2 and the inner layer body 3. Also provided are the preform assembly 40 for forming the double container 1 by blow molding, and a method for manufacturing the double container 1.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a double container, a preform assembly, and a synthetic resin container.

Background Art

[0002] There is known a synthetic resin double container having an outer layer and an inner layer separably laminated inside the outer layer, and formed in a bottle shape having a mouth portion, a body portion, and a bottom portion (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Regarding the double container as described above, from the viewpoint of recyclability and the like, it is desirable that the inner layer can be easily separated from the outer layer.

[0005] The present invention has been made in view of such problems, and an object thereof is to provide a double container in which the inner layer can be easily separated from the outer layer, a preform assembly capable of forming the double container, and a method for manufacturing the double container.

Means for Solving the Problems

[0006] The double-walled container of the present invention is a double-walled container made of synthetic resin, formed in the shape of a bottle having a mouth, a body, and a bottom, by blow molding a synthetic resin preform assembly in which an inner preform formed separately from the outer preform is assembled inside an outer preform, and comprising an outer layer and an inner layer separated and laminated inside the outer layer, wherein a strip-shaped sheet is disposed between the outer layer and the inner layer, formed in the shape of a strip of synthetic resin material different from at least the inner surface of the outer layer or the outer surface of the inner layer, and extending upward from the bottom.

[0007] In the double-walled container of the present invention, it is preferable that the strip-shaped sheet has a bottom strip portion that straddles the bottom portion and a pair of vertical strip portions that extend upward from the ends of the bottom strip portion.

[0008] In the double-walled container of the present invention, it is preferable that at least one end of the strip-shaped sheet is exposed to the outside at the opening.

[0009] The double-walled container of the present invention, in the above configuration, has a cap attached to the opening, It is preferable that the end of the strip-shaped sheet that is exposed to the outside at the opening is covered by the peripheral wall of the cap.

[0010] In the double-walled container of the present invention, it is preferable that the outer layer and the inner layer are made of polyethylene terephthalate, and the strip-shaped sheet is made of polyolefin.

[0011] The present invention provides a preform assembly made of synthetic resin, having a bottomed cylindrical shape, comprising an outer preform and an inner preform formed separately from the outer preform and assembled inside the outer preform, characterized in that a strip-shaped sheet material is disposed between the outer preform and the inner preform, formed in a strip shape from a synthetic resin material different from at least the inner surface of the outer preform or the outer surface of the inner preform, and extending upward from the bottom.

[0012] The present invention provides a method for manufacturing a double-walled container, comprising the steps of: assembling an inner preform, formed separately from the outer preform, inside an outer preform; arranging a strip-shaped sheet material, formed from a synthetic resin material different from at least the inner surface of the outer preform or the outer surface of the inner preform and extending upward from the bottom, between the outer preform and the inner preform to form a synthetic resin preform assembly; and blow-molding the preform assembly. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a double-walled container in which the inner layer can be easily separated from the outer layer, a preform assembly capable of forming the double-walled container, and a method for manufacturing the double-walled container. [Brief explanation of the drawing]

[0014] [Figure 1] This is a front view of a semi-cross-sectional view of a double container according to one embodiment of the present invention. [Figure 2] Figure 1 is a magnified view of a partially cutaway section of the upper part of the double-walled container shown in Figure 1. [Figure 3] Figure 1 is a side view of the double-walled container. [Figure 4] This is a semi-cross-sectional view of a preform assembly according to one embodiment of the present invention. [Figure 5] This is a front view cross-sectional view of a double container according to another embodiment of the present invention. [Figure 6] Figure 5 is an enlarged cross-sectional view of the upper portion of the double-walled container. [Modes for carrying out the invention]

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] As shown in Fig. 1, a double container 1 made of synthetic resin according to an embodiment of the present invention has a double structure including an outer layer 2 and an inner layer 3, and its outer shape is a bottle shape having a mouth portion 11, a body portion 12, and a bottom portion 13.

[0017] In this specification and the claims, the up-and-down direction means upward and downward along the axis O in the state where the double container 1 is in a upright posture as shown in Fig. 1.

[0018] The outer layer 2 constitutes the outer contour of the double container 1 and has a cylindrical outer mouth portion 2a that constitutes the mouth portion 11. An annular neck ring 4 is integrally provided on the outer mouth portion 2a. Further, at the lower end of the outer mouth portion 2a, an outer body portion 2b corresponding to the body portion 12 is integrally provided in series, and at the lower end of the outer body portion 2b, an outer bottom portion 2c corresponding to the bottom portion 13 is integrally provided in series.

[0019] The inner layer 3 is separably laminated inside the outer layer 2. The separation of the inner layer 3 from the outer layer 2 may be any of separation from an adhesive state, separation from a pseudo-adhesive state in the case of a resin laminate having no compatibility, and separation from a close contact state.

[0020] As shown in Fig. 2, the inner layer 3 has a cylindrical inner mouth portion 3a that is disposed inside the outer mouth portion 2a and whose upper portion protrudes above the outer mouth portion 2a. A flange 3b is integrally provided on the inner mouth portion 3a, and the inner mouth portion 3a is positioned in the up-and-down direction with respect to the outer mouth portion 2a by the flange 3b being supported by the upper end of the outer mouth portion 2a.

[0021] Below the inner mouth portion 3a, a storage portion 3c connected to the opening of the mouth portion 11 is integrally provided. The storage portion 3c is laminated on the inner peripheral surfaces of the outer body portion 2b and the outer bottom portion 2c of the outer layer 2. The inside of the storage portion 3c is a storage space S, and the content can be stored in this storage space S.

[0022] In this embodiment, both the outer layer 2 and the inner layer 3 are made of polyethylene terephthalate (PET). Alternatively, the outer layer 2 may be made of polyethylene terephthalate and the inner layer 3 may be made of polypropylene (PP). Furthermore, the outer layer 2 and the inner layer 3 may be made of the same material or different materials, and release properties may be improved by applying a release agent such as silicone between them. Also, the outer layer 2 and the inner layer 3 may be single layers or laminated layers.

[0023] As shown in Figures 1 and 3, a strip-shaped sheet 20 extending upward from the bottom 13 is placed between the outer layer 2 and the inner layer 3.

[0024] In this embodiment, the strip-shaped sheet 20 has a bottom strip portion 21 that straddles the bottom portion 13 so as to extend from one edge to the other edge of the axis O of the bottom portion 13 between the outer layer 2 and the inner layer 3, and a pair of vertical strip portions 22 that are integrally connected to the ends of the bottom strip portion 21 and extend upward from those ends. The pair of vertical strip portions 22 extend from the bottom portion 13 through the body portion 12 to the opening portion 11 between the outer layer 2 and the inner layer 3, and are pulled out to the outside of the opening portion 11 from between the upper end of the outer opening portion 2a and the flange 3b provided on the inner opening portion 3a, and are exposed to the outside. As shown in Figure 2, the ends 23 of the pair of vertical strip portions 22, i.e., both ends 23 of the strip-shaped sheet 20, are each pulled out to the outside of the opening portion 11, then bent downward and arranged along the outer surface of the outer opening portion 2a.

[0025] The strip-shaped sheet 20 is formed in a strip shape from a synthetic resin material that is at least different from the inner surface of the outer layer 2 or the outer surface of the inner layer 3. In this embodiment, the strip-shaped sheet 20 is made of polyolefin (specifically polyethylene (PE)).

[0026] Furthermore, the strip-shaped sheet 20 is not limited to polyethylene; it can also be formed from other synthetic resin materials such as polypropylene (PP), as long as it is a synthetic resin material different from at least the inner surface of the outer layer 2 or the outer surface of the inner layer 3.

[0027] In this embodiment, both ends 23 of the strip-shaped sheet 20 are exposed to the outside at the opening 11, but it is also possible to have only one end 23 of the strip-shaped sheet 20 exposed to the outside at the opening 11.

[0028] Alternatively, the end portions 23 of the strip-shaped sheet 20 can be configured so that they are not exposed to the outside at the opening 11. In this case, the end portions 23 of the strip-shaped sheet 20 can be placed at any location between the bottom portion 13 and the opening 11, but it is preferable that they reach the opening 11.

[0029] Furthermore, the strip-shaped sheet 20 can be configured without a bottom strip portion 21 that straddles the bottom portion 13, as long as it extends upward from the bottom portion 13. In this case, it is sufficient that at least a portion of the strip-shaped sheet 20 is placed on the bottom portion 13, but it is preferable that it extends to the center of the bottom portion 13.

[0030] The double-walled container 1 can be configured with a cap 30 attached to the opening 11. In this embodiment, as shown in Figure 2, the cap 30 is a hinged cap in which an upper lid 33 is connected to a cap body 32 having a peripheral wall 31 via a hinge (not shown), and is attached to the upper end portion of the inner opening 3a that constitutes the opening 11 by pressing it in.

[0031] The cap 30 is positioned above the flange 3b of the inner layer 3, and both ends 23 of the strip-shaped sheet 20 that are exposed to the outside at the opening 11 are exposed to the outside without being covered by the peripheral wall 31 of the cap 30.

[0032] The double-walled container 1 having the above configuration allows for easy separation of the inner layer 3 from the outer layer 2 when the contents have been used up.

[0033] Even if the inner layer 3 of the double-walled container 1 becomes too dirty to recycle after use, for example, when it stores contents containing oil, the clean outer layer 2 can be easily separated from the dirty inner layer 3, allowing only the outer layer 2 to be separated and recycled.

[0034] More specifically, the user can separate the inner layer 3 from the outer layer 2 by grasping the inner opening 3a or the cap 30 attached to the inner opening 3a and pulling it upward relative to the outer layer 2, or by cutting off the outer opening 2a of the outer layer 2 and directly grasping the inner layer 3 and pulling it upward relative to the outer layer 2.

[0035] In this case, since the bottom 13 of the double-walled container 1 is thick and has an uneven shape, the adhesion force of the inner layer 3 to the outer layer 2 is large in the central part of the bottom 13, which can be an obstacle when separating the inner layer 3 from the outer layer 2. In contrast, in the double-walled container 1 of this embodiment, a strip-shaped sheet 20 extending upward from the bottom 13 is placed between the outer layer 2 and the inner layer 3. Therefore, when pulling the inner layer 3 upward from the outer layer 2 to separate it from the outer layer 2, pulling the strip-shaped sheet 20 upward makes it easier to release the adhesion force of the inner layer 3 to the outer layer 2 at the bottom 13, and the inner layer 3 can be easily separated from the outer layer 2.

[0036] Furthermore, since the strip-shaped sheet 20 is formed in a strip shape from a synthetic resin material different from at least the inner surface of the outer layer 2 or the outer surface of the inner layer 3, when the strip-shaped sheet 20 is pulled upward, the strip-shaped sheet 20 will easily peel off from either the outer layer 2 or the inner layer 3. As a result, the tensile force can be transmitted by the strip-shaped sheet 20 as a force that separates the inner layer 3 from the outer layer 2 at the bottom 13.

[0037] The strip-shaped sheet 20 may be lifted together with the inner layer 3, or it may be lifted before the inner layer 3. If the strip-shaped sheet 20 is configured not to be exposed to the outside at the opening 11, the inner opening 3a or the cap 30 attached to the inner opening 3a may be grasped and lifted upward relative to the outer layer 2 to lift the inner layer 3 relative to the outer layer 2 to the extent that the strip-shaped sheet 20 is exposed to the outside, and then the strip-shaped sheet 20 may be lifted.

[0038] Thus, in the double-walled container 1 of this embodiment, a strip-shaped sheet 20 is placed between the outer layer 2 and the inner layer 3, formed from a synthetic resin material different from at least the inner surface of the outer layer 2 or the outer surface of the inner layer 3, and extending upward from the bottom 13. Therefore, when pulling the inner layer 3 upward from the outer layer 2 to separate it from the outer layer 2, the inner layer 3 can be easily separated from the outer layer 2 by pulling the strip-shaped sheet 20 upward.

[0039] Furthermore, in the double-walled container 1 of this embodiment, the strip-shaped sheet 20 is configured to have a bottom strip portion 21 that straddles the bottom portion 13, and a pair of vertical strip portions 22 that extend upward from the ends of the bottom strip portion 21. Therefore, when pulling the inner layer 3 upward from the outer layer 2 to separate it from the outer layer 2, by grasping the pair of vertical strip portions 22 and pulling upward, an upward force is applied to the inner layer 3 from both sides of the axis O of the bottom portion 13, thereby more effectively separating the inner layer 3 from the outer layer 2 at the bottom portion 13. This makes it even easier to separate the inner layer 3 from the outer layer 2.

[0040] Furthermore, in the double-walled container 1 of this embodiment, at least one end 23 of the strip-shaped sheet 20 is exposed to the outside at the opening 11. This allows the strip-shaped sheet 20 to be pulled upward by grasping the exposed end 23 without having to perform preparatory work such as cutting off the outer opening 2a of the outer layer 2. This makes it even easier to separate the inner layer 3 from the outer layer 2.

[0041] In the double-walled container 1 of this embodiment, when both ends 23 of the strip-shaped sheet 20 are exposed to the outside at the opening 11, the inner layer 3 can be separated from the outer layer 2 even more easily.

[0042] Furthermore, in the double-walled container 1 of this embodiment, the outer layer 2 and the inner layer 3 are made of polyethylene terephthalate, and the strip-shaped sheet 20 is made of polyethylene. This allows the double-walled container 1 to be made of polyethylene terephthalate, which is transparent and has high strength, while when the inner layer 3 is pulled upward from the outer layer 2 to separate it from the outer layer 2, the strip-shaped sheet 20 can be easily peeled off from the outer layer 2 and the inner layer 3, making it even easier to separate the inner layer 3 from the outer layer 2.

[0043] The double-walled container 1 having the above configuration can be formed by blow molding a synthetic resin preform assembly 40 according to one embodiment of the present invention shown in Figure 4.

[0044] The preform assembly 40 has an outer preform 41, an inner preform 42 assembled inside the outer preform 41, and a strip-shaped sheet material 43 positioned between the outer preform 41 and the inner preform 42, and is shaped as a bottomed cylinder overall.

[0045] The outer preform 41 corresponds to the outer layer 2 and comprises an outer opening 41a and a bottomed cylindrical outer extension 41b integrally connected to the lower end of the outer opening 41a. The outer opening 41a is a portion that is not stretched by blow molding and has the same shape as the outer opening 2a of the double-walled container 1.

[0046] The outer preform 41 is made of polyethylene terephthalate, similar to the outer layer 2, and is formed into the above shape by injection molding using polyethylene terephthalate.

[0047] The inner preform 42 corresponds to the inner layer 3 and includes an inner opening 42a and a bottomed cylindrical inner extension 42b integrally connected to the lower end of the inner opening 42a. The inner opening 42a is a portion that is not stretched by blow molding and has the same shape as the inner opening 3a of the double container 1, and includes a flange 42c corresponding to the flange 3b.

[0048] The inner preform 42 is made of polyethylene terephthalate, similar to the inner layer 3, and is formed into the above shape separately from the outer preform 41 by injection molding using polyethylene terephthalate.

[0049] The strip-shaped sheet material 43 is formed in a strip shape from a synthetic resin material that is different from at least the inner surface of the outer preform 41 or the outer surface of the inner preform 42. In this embodiment, the strip-shaped sheet material 43 is made of polyethylene. The strip-shaped sheet material 43 is positioned between the outer preform 41 and the inner preform 42 and extends upward from the bottom 44 of the preform assembly 40.

[0050] In this embodiment, the strip-shaped sheet material 43 includes a bottom strip forming portion 43a that straddles the bottom portion 44, and a pair of vertical strip forming portions 43b that extend upward from the ends of the bottom strip forming portion 43a (in Figure 4, only one vertical strip forming portion 43b is shown for convenience, but identical vertical strip forming portions 43b are provided symmetrically on both sides). The bottom strip forming portion 43a is the portion that is stretched by blow molding to become the bottom strip portion 21, and the vertical strip forming portions 43b are the portions that are stretched by blow molding to become the vertical strip portion 22.

[0051] Each of the pair of vertical strip-forming portions 43b extends from the bottom portion 44 to the space between the outer opening portion 41a and the inner opening portion 42a, and is pulled out to the outside of the outer opening portion 41a from between the upper end of the outer opening portion 41a and the flange 42c provided on the inner opening portion 42a, and is exposed to the outside. The ends 43c of the pair of vertical strip-forming portions 43b, i.e., both ends 43c of the strip-shaped sheet material 43, are each pulled out to the outside of the outer opening portion 41a, then bent downward and positioned along the outer surface of the outer opening portion 41a.

[0052] Next, a method for manufacturing a double-walled container according to one embodiment of the present invention will be described.

[0053] The method for manufacturing a double-walled container according to this embodiment can be carried out using a preform assembly 40 having the above configuration.

[0054] First, the inner preform 42 with the above configuration is assembled inside the outer preform 41 with the above configuration. At this time, the strip-shaped sheet material 43 with the above configuration is placed between the outer preform 41 and the inner preform 42 so as to extend upward from the bottom 44. In this embodiment, the bottom strip forming portion 43a straddles the bottom 44, the pair of vertical strip forming portions 43b extend upward from both ends of the bottom strip forming portion 43a, and the strip-shaped sheet material 43 is placed between the outer preform 41 and the inner preform 42 so as to be exposed to the outside from between the upper end of the outer opening portion 41a and the flange 42c. In this way, a preform assembly 40 having the above configuration is formed.

[0055] Here, the strip-shaped sheet material 43 may be positioned between the outer preform 41 and the inner preform 42 by inserting it between the outer preform 41 and the inner preform 42 when assembling the outer preform 41 and the inner preform 42, or the strip-shaped sheet material 43 may be integrated with the outer preform 41 or the inner preform 42 by in-mold molding when molding the outer preform 41 or the inner preform 42. When in-mold molding is performed, the preform material and the material of the strip-shaped sheet material 43 are made of different materials that do not weld to each other.

[0056] Next, the preform assembly 40 is blow-molded. For blow molding, for example, biaxial stretch blow molding using a stretching rod can be employed. Pressurized air, pressurized liquid, etc., can be used as the pressurizing medium in blow molding. In this way, a double-walled container 1 having the above configuration is formed.

[0057] Then, after filling the contents into the double container 1, the cap 30 is attached to the opening 11 by pressing it in.

[0058] Thus, according to the manufacturing method of the preform assembly 40 or double-walled container 1 according to this embodiment, a double-walled container 1 in which the outer layer 2 and inner layer 3 can be easily separated can be manufactured easily and inexpensively by simply blow-molding a preform assembly 40 in which a strip-shaped sheet material 43 is arranged between the outer preform 41 and the inner preform 42.

[0059] As shown in Figures 5 and 6 as another embodiment, the double-walled container 1 can also be configured as a laminated peel-off container in which the storage section 3c constituting the inner layer 3 is peelably laminated on the inner surfaces of the outer body 2b and outer bottom 2c of the outer layer 2.

[0060] In this case, as shown in Figure 6, the outer layer 2 is configured to have an outside air inlet 2d that communicates between the outer layer 2 and the inner layer 3. In this embodiment, the outer opening 2a is provided with a pair of outside air inlets 2d that have the form of through holes that penetrate the outer opening 2a radially.

[0061] Furthermore, the pair of outside air inlets 2d are positioned at a 90-degree angle in the circumferential direction around the axis O relative to the strip-shaped sheet 20.

[0062] Furthermore, the cap 30 is provided with a first check valve 35 that opens and closes the discharge port 34 connected to the storage space S. The first check valve 35 operates to allow the flow of contents from the storage space S through the discharge port 34 toward the outside of the container, and to block the flow of contents and air from the outside of the container through the discharge port 34 toward the storage space S. In addition, the fitted cap 30 is provided with a vent 36 connected to the outside air inlet 2d, and below the vent 36 is a second check valve 37 that opens and closes the vent 36. The second check valve 37 operates to allow the flow of air from the vent 36 toward the outside air inlet 2d, and to block the flow of air from the outside air inlet 2d toward the vent 36. Note that the pair of outside air inlet holes 2d are not limited to being positioned 90 degrees circumferentially relative to the strip-shaped sheet 20, as long as they do not overlap the strip-shaped sheet 20.

[0063] According to this other embodiment of the double-walled container 1, squeezing the outer shell 2b opens the first check valve 35, allowing the contents stored in the storage space S to be discharged to the outside through the discharge port 34. After the contents are discharged, releasing the squeeze of the outer shell 2b closes the discharge port 34 by the first check valve 35, and the second check valve 37 opens, allowing outside air to be introduced between the outer layer 2 and the inner layer 3 through the vent 36 and the outside air inlet 2d as the outer shell 2b returns to its original shape. This prevents outside air from being introduced into the storage space S, as the storage portion 3c of the inner layer 3 is separated from the inner surface of the outer shell 2b and deformed to reduce its volume as the contents are discharged. Therefore, it is possible to prevent the contents stored in the storage space S from coming into contact with the outside air, thereby preventing deterioration or loss of freshness of the contents.

[0064] Furthermore, by positioning a vertically extending strip-shaped sheet 20 between the outer body 2b and the storage section 3c, the storage section 3c becomes more easily flattened starting from the strip-shaped sheet 20 after the contents are dispensed. This allows the storage section 3c to easily detach from the outer body 2b, thereby enhancing its function as a laminated peel-off container.

[0065] In the double-walled container 1 according to this other embodiment, when recycling after use when all the contents have been emptied, the inner layer 3 can be easily separated from the outer layer 2 by pulling the strip-shaped sheet 20 upwards relative to the outer layer 2 together with the inner layer 3, and these can be separated for disposal or recycling.

[0066] As shown in Figure 6, in the double-walled container 1 according to another embodiment, the peripheral wall 31 extends below the outside air inlet 2 in order to partition a flow path that connects the outside air introduction d and the ventilation passage 36 between the peripheral wall 31 and the mouth 11. As a result, the cap 30 is configured such that the peripheral wall 31 covers the end portion 23 of the strip-shaped sheet 20 that is exposed to the outside at the mouth 11.

[0067] In this way, by covering the end 23 of the strip-shaped sheet 20 that is exposed to the outside at the opening 11 with the peripheral wall 31 of the cap 30, it is possible to prevent the end 23 from being accidentally pulled during use.

[0068] The present invention is not limited to the embodiments described above, and can be modified in various ways without departing from its spirit. [Explanation of Symbols]

[0069] 1 double container 2 Outer body 2a External opening 2b Outer body 2c outer bottom 2d Outside air intake 3. Inner layer 3a Inner mouth 3b Flange 3c Storage compartment 4 Neck Rings 11 Mouth 12 Torso 13 Bottom 20 Strip-shaped sheets 21 Bottom band 22 Vertical band 23 End 30 caps 31 Peripheral wall 32 Cap body 33 Top lid 34 Discharge port 35 First check valve 36 Ventilation holes 37. Second check valve 40 preform assemblies 41 External preform 41a External opening 41b Outer extension 42 Internal preform 42a Inner mouth 42b Inner extension 42c flange 43 Strip-shaped sheet material 43a Bottom band forming part 43b Vertical band forming section 43c end O axis S storage space

Claims

1. A synthetic resin double container is formed into a bottle shape having an outer layer body and an inner layer body separably stacked inside the outer layer body, and having a mouth, a body, and a bottom, by blow molding a synthetic resin preform assembly in which an inner preform formed separately from the outer preform is assembled inside the outer preform, A double container characterized in that a strip-shaped sheet is disposed between the outer layer and the inner layer, the strip-shaped sheet being made of a synthetic resin material different from at least the inner surface of the outer layer or the outer surface of the inner layer, and extending upward from the bottom.

2. The double container according to claim 1, wherein the belt-like sheet has a bottom belt portion that straddles the bottom portion and a pair of vertical belt portions that each extend upward from an end of the bottom belt portion.

3. 3. The double container according to claim 1, wherein at least one end of the strip-shaped sheet is exposed to the outside at the opening.

4. a cap attached to the mouth portion, 4. The double container according to claim 3, wherein an end of the strip-shaped sheet exposed to the outside at the mouth is covered by the peripheral wall of the cap.

5. The double container according to any one of claims 1 to 4, wherein the outer layer and the inner layer are each made of polyethylene terephthalate, and the strip-shaped sheet is made of polyolefin.

6. Outer preform and an inner preform formed separately from the outer preform and assembled inside the outer preform; and A preform assembly characterized in that a strip-shaped sheet material is disposed between the outer preform and the inner preform, the strip-shaped sheet material being made of a synthetic resin material different from at least the inner surface of the outer preform or the outer surface of the inner preform, and extending upward from the bottom.

7. a step of assembling an inner preform formed separately from the outer preform inside the outer preform, and disposing a strip-shaped sheet material formed in a strip shape from a synthetic resin material different from at least the inner surface of the outer preform or the outer surface of the inner preform and extending upward from the bottom between the outer preform and the inner preform to form a synthetic resin preform assembly; and a step of blow molding the preform assembly.

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