Preform for double container forming and double container

Abstract

To provide a preform of double container molding and a double container that easily secure an air path of outside air between the inner container and the outer container of the double container.SOLUTION: It includes an inner preform P2, an outer preform P1, and a thermoplastic resin plate material 30 disposed between the inner preform P2 and the outer preform P1, an outside air introduction hole 17 is provided at the mouth part of the double container, the plate material 30 is arranged in the circumferential direction of the preform P with respect to the outside air introduction hole 17, the plate member 30 straddles a part P2c, which is the boundary between the mouth part and a shoulder part of the double container, in the axial direction of the preform P among the outer preform P1, a part P1c that serves as a boundary between the mouth and the shoulder of the double container, and among the inner preform P2, the plate material 30 is a thermoplastic synthetic resin material whose compatibility is low with at least either the thermoplastic synthetic resin material forming the outer peripheral surface of the inner preform P2 or the thermoplastic synthetic resin material forming the inner peripheral surface of the outer preform P1.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a preform for forming a double container and a double container.

Background Art

[0002] As a double container, a configuration is known that includes an inner container that undergoes volume reduction deformation as the content to be contained decreases, and an outer container in which the inner container is installed. At the mouth of the double container, an outside air introduction hole for introducing outside air between the inner container and the outer container is provided as the content decreases. The double container is formed, for example, by blow molding a preform for double container molding in which a preform for an inner container and a preform for an outer container, which are individually molded, are assembled. In the double container formed by this method, the inner container and the outer container may stick together, and the air that should be introduced from the outside air introduction hole may not be supplied between the inner container and the outer container. For example, during the above-mentioned blow molding, due to differences in heating temperature during molding, differences in melting points of materials, etc., one of the inner container and the outer container may extend and swell with respect to the other, and there is also a risk that the outside air introduction hole and the air passage connected to the outside air introduction hole may be blocked. As a countermeasure, a method of thermally crystallizing (whitening) a predetermined region at the mouth of the preform is known as described in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional method, management of the degree and range of thermal crystallization becomes complicated. Further, if thermal crystallization is essential, it cannot be applied to resins that cannot be thermally crystallized.

[0005] The present invention has been made in view of the above-described circumstances, and aims to provide a preform and a double container that utilize a method different from thermal crystallization and, in some cases, use thermal crystallization in combination, and that facilitate securing an air passage for outside air between an inner container and an outer container in the double container.

Means for Solving the Problems

[0006] A preform according to one aspect of the present invention includes an inner container that decreases in volume and deforms as the content accommodated therein decreases, and an outer container in which the inner container is housed. The preform is for molding a double container provided with an outside air introduction hole for introducing outside air between the inner container and the outer container as the content decreases. The preform includes a bottomed cylindrical inner preform for molding the inner container, a bottomed cylindrical outer preform for molding the outer container, and a plate material made of a thermoplastic resin disposed between the inner preform and the outer preform. The outside air introduction hole is provided in a portion that becomes the mouth portion of the double container, and the plate material is arranged in the circumferential direction of the preform with respect to the outside air introduction hole. At least a part of the plate material is at a height overlapping the outside air introduction hole. The plate material straddles, in the axial direction of the preform, a portion that becomes the boundary between the mouth portion and the shoulder portion of the double container in the outer preform and a portion that becomes the boundary between the mouth portion and the shoulder portion of the double container in the inner preform. The plate material is a thermoplastic resin material having low compatibility with at least one of the thermoplastic synthetic resin material constituting the outer peripheral surface of the inner preform and the thermoplastic synthetic resin material constituting the inner peripheral surface of the outer preform. In the preform, "low compatibility" means that in a double container formed by heating a preform for a double container to an extensible temperature and performing biaxial stretch blow molding, the plate material and at least one of the inner container and the outer container are laminated so as to be separable (including adhesion and pseudo-adhesion). As a combination of thermoplastic synthetic resin materials with low compatibility, for example, there is a combination of polyethylene terephthalate and polypropylene. The above-mentioned "low compatibility" may also be expressed as incompatibility. Depending on the degree of incompatibility, the bonding strength (peel strength) between the plate material and the inner container or the outer container can be appropriately adjusted.

[0007] The plate materials are arranged in the circumferential direction of the preform with respect to the outside air introduction holes. Therefore, at the portion communicating with the outside air introduction holes, the distance corresponding to the thickness of the plate material can be provided between the inner surface of the outer preform and the inner surface of the inner preform. Thereby, even when the inner preform or the outer preform expands during blow molding, it is difficult to block the outside air introduction holes and the air passages connected to the outside air introduction holes, and it becomes easy to secure the air passages. Here, the inventor of the present application has found that when the inner preform or the outer preform expands, the air passage is likely to be blocked at the boundary between the mouth portion and the shoulder portion in the double container. Therefore, the plate material straddles in the axial direction of the preform the portion that becomes the boundary between the mouth portion and the shoulder portion of the double container in the outer preform and the portion that becomes the boundary between the mouth portion and the shoulder portion of the double container in the inner preform, respectively. Therefore, it becomes easy to secure an air passage at the portion that becomes the boundary between the mouth portion and the shoulder portion in the double container, and the effect is remarkably achieved. Furthermore, the plate material is a thermoplastic synthetic resin material having low compatibility with at least one of the thermoplastic synthetic resin material constituting the outer peripheral surface of the inner preform and the thermoplastic synthetic resin material constituting the inner peripheral surface of the outer preform. Therefore, the plate material is likely to peel off from at least one of the inner container and the outer container. Thereby, it is also possible to easily secure the air passage generated at the time of peeling.

[0008] The plate material may be disposed on both sides in the circumferential direction with respect to the outside air introduction hole.

[0009] The plate material is disposed on both sides in the circumferential direction with respect to the outside air introduction hole. Thereby, in the portion communicating with the outside air introduction hole, the distance corresponding to the thickness of the plate material can be surely set between the inner surface of the outer preform and the inner surface of the inner preform. Therefore, it is easier to secure an air passage.

[0010] An outside air introduction flow path communicating with the outside air introduction hole is provided on the outer peripheral surface of the inner preform or the inner peripheral surface of the outer preform. The flow path is (1) a groove provided on the outer peripheral surface of the inner preform or the inner peripheral surface of the outer preform, or (2) defined by a protrusion provided on the outer peripheral surface of the inner preform or the inner peripheral surface of the outer preform. The compatibility between the plate material and the preform provided with the flow path among the outer peripheral surface of the inner preform and the inner peripheral surface of the outer preform may be low.

[0011] A double container according to an aspect of the present invention includes an inner container that is reduced in volume and deformed as the content to be accommodated decreases, and an outer container in which the inner container is installed. An outside air introduction hole for introducing outside air is provided between the inner container and the outer container as the content decreases. The double container includes a mouth portion, a shoulder portion, a body portion, and a bottom portion. The outside air introduction hole is provided in the mouth portion of the double container, and a plate material made of a thermoplastic resin is disposed in a range from the outside air introduction hole to the shoulder portion between the inner container and the outer container. The plate material is arranged in the circumferential direction of the double container with respect to the outside air introduction hole, and at least a part of the plate material is at a height overlapping the outside air introduction hole. The plate material has low compatibility with at least one of the thermoplastic synthetic resin material constituting the outer peripheral surface of the inner container and the thermoplastic synthetic resin material constituting the inner peripheral surface of the outer container. In the double container, "low compatibility" means that the plate material and at least one of the inner container and the outer container are laminated so as to be separable (including adhesion and pseudo-adhesion).

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a preform and a double container that utilize a method different from thermal crystallization and, in some cases, use thermal crystallization in combination, and can secure an air passage for outside air between the inner container and the outer container in the double container.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0014] Hereinafter, with reference to FIGS. 1 and 2, an embodiment of the present invention will be described. First, a double container formed from the preform according to an embodiment of the present invention will be described. As shown in FIG. 1, the double container 1 includes an inner container 12 that decreases in volume and deforms as the content stored therein decreases, and an outer container 11 in which the inner container 12 is installed. The outer surface of the inner container 12 is provided on the inner surface of the outer container 11 so as to be separable.

[0015] The materials of the inner container 12 and the outer container 11 are synthetic resin materials, and they may be of the same material or different materials from each other. Examples of synthetic resin materials include, for example, PET (polyethylene terephthalate), PP (polypropylene), PE (polyethylene), nylon (polyamide), and EVOH (ethylene-vinyl alcohol copolymer).

[0016] The double container 1 includes a mouth portion 13, a shoulder portion 15, a body portion 16, and a bottom portion 14. The mouth portion 13, the shoulder portion 15, the body portion 16, and the bottom portion 14 are arranged in this order coaxially with a common axis. Hereinafter, this common axis is referred to as the bottle axis O. The mouth portion 13 side of the double container 1 along the bottle axis O is the upper side, and the bottom portion 14 side of the double container 1 is the lower side. When viewed from the bottle axis O direction, the direction intersecting the bottle axis O is the radial direction, and the direction of orbiting around the bottle axis O is the circumferential direction.

[0017] The mouth portion 13 of the double container 1 is formed by laminating the mouth portion of the inner container 12 and the mouth portion of the outer container 11. The shoulder portion 15 of the double container 1 is formed by laminating the shoulder portion of the inner container 12 and the shoulder portion of the outer container 11. The body portion 16 of the double container 1 is formed by laminating the body portion of the inner container 12 and the body portion of the outer container 11. The bottom portion 14 of the double container 1 is formed by laminating the bottom portion of the inner container 12 and the bottom portion of the outer container 11. In the following description, unless otherwise specified, it is assumed that both the inner container 12 and the outer container 11 have the same form.

[0018] The mouth portion 13 of the double container 1 is formed in a cylindrical shape extending upward from the upper end portion of the shoulder portion 15. At the upper end portion of the mouth portion of the inner container 12, a flange portion that protrudes outward in the radial direction and continuously extends over the entire circumferential length is formed. The flange portion is placed on the upper end opening edge of the mouth portion of the outer container 11.

[0019] On the outer peripheral surface of the mouth portion of the outer container 11, a locking protrusion 18 into which the peripheral wall portion of a cap (not shown) is undercut-fitted and a sealing protrusion 19 onto which the lower end portion of the peripheral wall portion of a cap (not shown) is externally fitted are formed in this order from above downward. The locking protrusion 18 and the sealing protrusion 19 protrude outward in the radial direction from the mouth portion of the outer container 11 and continuously extend over the entire circumferential length. An airtight seal is provided between the outer peripheral surface of the sealing protrusion 19 and the inner peripheral surface of the lower end portion of the peripheral wall portion of a cap (not shown). Note that the cap (not shown) may be screwed onto the mouth portion of the outer container 11. An outside air introduction hole 17 for introducing outside air between the inner container 12 as the content decreases is formed in the mouth portion of the outer container 11. The outside air introduction hole 17 is located above the locking protrusion 18.

[0020] The shoulder portion 15 extends radially outward as it extends downward from the lower end portion of the mouth portion 13. The lower portion of the body portion 16 extends straight in the direction of the bottle axis O. Among the body portion 16, the portion located above the lower portion forms a constricted portion 21 that extends radially inward as it extends from the outside to the inside along the direction of the bottle axis O. A circumferential groove 21a that continuously extends over the entire circumferential length is formed in the portion of the constricted portion 21 that is located at the central portion in the direction of the bottle axis O and is located most radially inward.

[0021] At least the body portion of the outer container 11 is capable of being squeezed and deformed (elastically deformed), and the inner container 12 is squeezed and deformed as the outer container 11 is squeezed and deformed. In the illustrated example, the shoulder portion of the outer container 11 is also capable of being squeezed and deformed. Note that the outer container 11 may be applied as a rigid body that is substantially incapable of being squeezed and deformed, and the double container 1 may be applied as a discharge container that discharges the contents using a pump or the like. Also, in the present embodiment, both the outer container 11 and the inner container 12 have a single-layer structure, but they may have a laminated structure.

[0022] And in the present embodiment, the double container 1 further includes a plate material 30 made of a thermoplastic resin. The plate material 30 is disposed between the inner container 12 and the outer container 11. In the double container 1, the portion where the plate material 30 is disposed has a triple structure in which the inner container 12, the plate material 30, and the outer container 11 are laminated. The plate materials 30 are arranged side by side in the circumferential direction with respect to the outside air introduction holes 17. The plate materials 30 are disposed on both sides in the circumferential direction with respect to the outside air introduction holes 17. For example, the circumferential distance between the plate material 30 and the outside air introduction holes 17 may be smaller than the circumferential size of the outside air introduction holes 17. The plate material 30 is plate-shaped and extends in the circumferential direction. The plate material 30 is C-shaped in a top view.

[0023] The plate member 30 is disposed from the mouth portion 13 to the shoulder portion 15. The upper end of the plate member 30 is located at the mouth portion 13. In the present embodiment, the upper end of the outside air introduction hole 17 coincides with the upper end of the plate member 30. The upper end of the plate member 30 may be located at the upper end of the mouth portion 13, or may be located below the upper end of the mouth portion 13. Note that it is preferable that at least a part of the plate member 30 is at a height overlapping the outside air introduction hole 17, and it is more preferable to arrange it up to a height equal to or higher than the upper end of the outside air introduction hole 17. However, the plate member 30 may be at a height (position in the bottle axis O direction) that does not completely overlap the outside air introduction hole 17. In other words, the plate member 30 and the outside air introduction hole 17 do not necessarily have to be aligned in a cross section orthogonal to the bottle axis O direction. The lower end of the plate member 30 is located at the shoulder portion 15. The lower end of the plate member 30 may be located at the lower end of the shoulder portion 15, or may be located above the lower end of the shoulder portion 15. The plate member 30 straddles the boundary 20 (hereinafter, also simply referred to as the boundary 20) between the mouth portion 13 and the shoulder portion 15 in the bottle axis O direction. By making the plate member 30 a thermoplastic resin, the outer preform P1 and the plate member 30 can be stretched together with the outer preform P1, which will be described later.

[0024] The compatibility of the plate member 30 with at least one of the thermoplastic synthetic resin material constituting the outer peripheral surface of the inner container 12 and the thermoplastic synthetic resin material constituting the inner peripheral surface of the outer container 11 is low. For example, when the inner container 12 is made of PP and the outer container 11 is made of PET, PET can be adopted as the plate member 30. Further, for example, when both the inner container 12 and the outer container 11 are made of PET, PP can be adopted as the plate member 30.

[0025] In the double container 1, "low compatibility" means that the plate material 30 and at least one of the inner container 12 and the outer container 11 are laminated so as to be separable (including adhesion and pseudo-adhesion). As a combination of thermoplastic synthetic resin materials with low compatibility, for example, there is a combination of polyethylene terephthalate and polypropylene. The above-mentioned "low compatibility" may also be expressed as incompatibility. Depending on the degree of incompatibility, the bonding strength (peel strength) between the plate material 30 and the inner container 12 or the outer container 11 can be adjusted as appropriate. Furthermore, the plate material 30 and a release agent may be used in combination. For example, when the inner container 12 and the outer container 11 are made of the same material, a release agent may be applied at least in a portion where the plate material 30 is not arranged (as an example, the region below the plate material 30) to adjust the bonding strength (peel strength) between the inner container 12 and the outer container 11.

[0026] Also, when the inner container 12 has a laminated structure, the "thermoplastic synthetic resin material constituting the outer peripheral surface of the inner container 12" is the outermost thermoplastic synthetic resin material in the inner container 12. Furthermore, when the outer container 11 has a laminated structure, the "thermoplastic synthetic resin material constituting the inner peripheral surface of the outer container 11" is the innermost thermoplastic synthetic resin material in the outer container 11.

[0027] The above double container 1 is formed from a preform P for forming a double container as shown in FIG. 2. The preform P includes a bottomed cylindrical outer preform P1, a bottomed cylindrical inner preform P2, and the aforementioned plate material 30. The inner preform P2 is a preform for forming the inner container 12. The outer preform P1 is a preform for forming the outer container 11. The plate material 30 is disposed between the inner preform P2 and the outer preform P1.

[0028] The double container 1 is formed by blow molding the preform P in a state where the inner preform P2 is fitted inside the outer preform P1 and the plate material 30 is sandwiched between the outer preform P1 and the inner preform P2. Note that the plate material 30 may be integrally formed with the inner preform P2 or the outer preform P1 in advance, or may be formed separately from the inner preform P2 and the outer preform P1 and then incorporated into the inner preform P2 or the outer preform P1.

[0029] Here, in the outer preform P1, the portion that becomes the mouth portion 13 of the double container 1 is referred to as the outer mouth portion P1a, the portion that becomes the shoulder portion 15 is referred to as the outer shoulder portion P1b, and the portion that becomes the boundary 20 is referred to as the outer boundary P1c. In the inner preform P2, the portion that becomes the mouth portion 13 of the double container 1 is referred to as the inner mouth portion P2a, the portion that becomes the shoulder portion 15 is referred to as the inner shoulder portion P2b, and the portion that becomes the boundary 20 is referred to as the inner boundary P2c. The outer shoulder portion P1b and the inner shoulder portion P2b are stretched significantly more during blow molding than the outer mouth portion P1a and the inner mouth portion P2a. In principle, the outer mouth portion P1a and the inner mouth portion P2a are not stretched.

[0030] The outer mouth portion P1a is provided with an outside air introduction hole 17, a locking projection 18, and a sealed projection 19. In this embodiment, both the outer preform P1 and the inner preform P2 have a single-layer structure, but they may have a laminated structure.

[0031] The plate material 30 is arranged in the circumferential direction of the preform P with respect to the outside air introduction hole 17. The plate material 30 is arranged on both sides in the circumferential direction with respect to the outside air introduction hole 17. For example, the circumferential distance between the plate material 30 and the outside air introduction hole 17 may be smaller than the circumferential size of the outside air introduction hole 17. The plate material 30 is plate-shaped and extends in the circumferential direction. The plate material 30 is C-shaped in top view. The plate material 30 is arranged from the portion of the preform P that becomes the mouth portion 13 of the double container 1 to the portion that becomes the shoulder portion 15. The plate material 30 straddles the outer boundary P1c and the inner boundary P2c in the axial direction of the preform P, respectively.

[0032] The plate material 30 is a thermoplastic synthetic resin material having low compatibility with at least one of the thermoplastic synthetic resin material constituting the outer peripheral surface of the inner preform P2 and the thermoplastic synthetic resin material constituting the inner peripheral surface of the outer preform P1. The inner preform P2 is made of the same material as the inner container 12. The outer preform P1 is made of the same material as the outer container 11.

[0033] In the preform P, "low compatibility" means that in a double container formed by heating the double container preform P to a stretchable temperature and performing biaxial stretch blow molding, the plate material 30 and at least one of the inner container 12 and the outer container 11 can be separated (including adhesion and pseudo-adhesion) and laminated.

[0034] When the inner preform P2 has a laminated structure, the "thermoplastic synthetic resin material constituting the outer peripheral surface of the inner preform P2" is the outermost layer thermoplastic synthetic resin material in the inner preform P2. Further, when the outer preform P1 has a laminated structure, the "thermoplastic synthetic resin material constituting the inner peripheral surface of the outer preform P1" is the innermost layer thermoplastic synthetic resin material in the outer preform P1.

[0035] As described above, according to the preform P according to the present embodiment, the plate materials 30 are arranged in the circumferential direction of the preform P with respect to the outside air introduction holes 17. Therefore, in the portion communicating with the outside air introduction holes 17, the outer preform P1 and the inner preform P2 can be separated by a distance corresponding to the thickness of the plate material 30. Thereby, even when the inner preform P2 or the outer preform P1 expands during blow molding, the outside air introduction holes 17 and the air passages 17a connected to the outside air introduction holes 17 are less likely to be blocked, and the air passages 17a are easily secured.

[0036] Here, the inventor of the present application has found that when the inner preform P2 or the outer preform P1 expands, the air passage 17a is likely to be blocked at the boundary 20 between the mouth portion 13 and the shoulder portion 15 in the double container 1. Therefore, the plate member 30 straddles the outer boundary P1c and the inner boundary P2c in the axial direction of the preform P, respectively. Thus, it becomes easier to secure the air passage 17a at the portion that becomes the boundary 20 between the mouth portion 13 and the shoulder portion 15 in the double container 1, and the effect is remarkably achieved.

[0037] Furthermore, it is a thermoplastic resin material having low compatibility with at least one of the thermoplastic resin material constituting the outer peripheral surface of the inner preform P2 and the thermoplastic resin material constituting the inner peripheral surface of the outer preform P1. Therefore, the plate member 30 is easily peeled off from at least one of the inner container 12 and the outer container 11. Thereby, the air passage 17a generated at the time of peeling can also be easily secured.

[0038] The plate member 30 is disposed on both circumferential sides of the outside air introduction hole 17. Thereby, in the portion communicating with the outside air introduction hole 17, the distance corresponding to the thickness of the plate member 30 can surely separate the space between the outer preform P1 and the inner preform P2. Therefore, the air passage 17a is more easily secured.

[0039] Note that the technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0040] As in the preform PA according to the modified example shown in FIG. 3, an air passage 17a (flow path) for introducing outside air and communicating with the outside air introduction hole 17 may be provided on the outer peripheral surface of the inner preform P2 or the inner peripheral surface of the outer preform P1. In the illustrated example, the air passage 17a is a groove 17b provided on the inner peripheral surface of the outer preform P1. However, the air passage 17a may be defined by a protrusion provided on the outer peripheral surface of the inner preform P2 or the inner peripheral surface of the outer preform P1. In the illustrated example, four grooves 17b are arranged on the outer preform P1 at equal intervals in the circumferential direction. Among the four grooves 17b, the outside air introduction holes 17 are provided in two grooves 17b facing each other in the radial direction. On the other hand, the outside air introduction holes 17 are not provided in the remaining two grooves 17b. In this case, it is preferable that the compatibility between the plate material 30 and the inner peripheral surface of the outer preform P1, which is the preform provided with the air passage 17a among the outer peripheral surface of the inner preform P2 and the inner peripheral surface of the outer preform P1, is low. Note that the air passage 17a (groove 17b) may be provided on the outer peripheral surface of the inner preform P2.

[0041] The plate material 30 does not have to be C-shaped in a top view. For example, two plate materials 30 may be arranged with the outside air introduction hole 17 interposed therebetween in the circumferential direction. In the preform P or the double container 1, the plate material 30 does not have to be arranged on both sides in the circumferential direction with respect to the outside air introduction hole 17, and may be arranged only on one side in the circumferential direction with respect to the outside air introduction hole 17. The outside air introduction hole 17 does not have to be provided in the outer container 11. For example, the outside air introduction hole 17 may be the boundary (gap) between the inner container 12 and the outer container 11.

[0042] In addition, within the scope not departing from the gist of the present invention, it is possible to appropriately replace the components in the above-described embodiment with well-known components, and the above-described modified examples may be appropriately combined.

Explanation of Reference Numerals

[0043] 1 Double container 11 Outer container 12 Inner container 13 Mouth part 15 Shoulder part 17 Outside air introduction hole 20 Boundary 30 Plate material P Preform P1 Outer preform P2 Inner preform

Claims

1. A preform for forming a double container including an inner container that decreases in volume and deforms as the content to be contained decreases, and an outer container in which the inner container is housed, and an outside air introduction hole for introducing outside air between the inner container and the outer container as the content decreases, comprising: A bottomed cylindrical inner preform for forming the inner container; A bottomed cylindrical outer preform for forming the outer container; A plate material made of a thermoplastic resin disposed between the inner preform and the outer preform; The outside air introduction hole is provided in a portion that becomes the mouth portion of the double container; The plate material is arranged in the circumferential direction of the preform with respect to the outside air introduction hole; At least a part of the plate material has a height overlapping the outside air introduction hole; The plate material straddles in the axial direction of the preform, respectively, a portion that becomes a boundary between the mouth portion and the shoulder portion of the double container in the outer preform, and a portion that becomes a boundary between the mouth portion and the shoulder portion of the double container in the inner preform; The plate material is a thermoplastic resin material having low compatibility with at least one of the thermoplastic synthetic resin material constituting the outer peripheral surface of the inner preform and the thermoplastic synthetic resin material constituting the inner peripheral surface of the outer preform.

2. The preform according to claim 1, wherein the plate material is disposed on both sides in the circumferential direction with respect to the outside air introduction hole.

3. An outside air introduction flow path communicating with the outside air introduction hole is provided on the outer peripheral surface of the inner preform or the inner peripheral surface of the outer preform; The flow path is (1) a groove provided on the outer peripheral surface of the inner preform or the inner peripheral surface of the outer preform, or (2) defined by a protrusion provided on the outer peripheral surface of the inner preform or the inner peripheral surface of the outer preform; The preform according to claim 1 or 2, wherein the compatibility between the plate material and the preform provided with the flow path among the outer peripheral surface of the inner preform and the inner peripheral surface of the outer preform is low.

4. A double container including an inner container that decreases in volume and deforms as the content to be contained decreases, and an outer container in which the inner container is housed, and an outside air introduction hole for introducing outside air between the inner container and the outer container as the content decreases, the double container having a mouth portion, a shoulder portion, a body portion, and a bottom portion, comprising: The outside air introduction hole is provided in the mouth portion of the double container. Between the inner container and the outer container, a plate material made of a thermoplastic resin is disposed in a range extending from the outside air introduction hole to the shoulder portion. The plate materials are arranged in the circumferential direction of the double container with respect to the outside air introduction hole. At least a part of the plate material has a height overlapping with the outside air introduction hole. The double container in which the plate material has low compatibility with at least one of the thermoplastic synthetic resin material constituting the outer peripheral surface of the inner container and the thermoplastic synthetic resin material constituting the inner peripheral surface of the outer container.

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