Double container, preform assembly, and method for manufacturing double container

Abstract

To provide a double container whose inner layer and outer layer can be easily separated from each other, a preform assembly capable of forming the double container, and a manufacturing method of the double container.SOLUTION: A double container 1 made of a synthetic resin and formed by blow-molding a preform assembly 30 has a bottle shape having an outer layer 2 and an inner layer 3. The inner layer 3 comprises: a cap attachment part 11a protruding from an upper end of the outer layer 2; a spiral projection 20 extending spirally; and a stopper projection 21 extending downward from an end of the lower side of the spiral projection 20. The outer layer 2 comprises: a spiral passage 22 which extends spirally, has the spiral projection 20 disposed therein, and has a width allowing the spiral projection 20 and the stopper projection 21 to pass therethrough; and a stopper passage 23 which includes a locking surface 23a extending downward from an end of the lower side of the spiral passage 22 and facing a stopper surface 21a, and has the stopper projection 21 provided therein.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a double container, a preform assembly and a method for manufacturing the double container. [Background technology]

[0002] A double container made of synthetic resin is known which comprises an outer layer and an inner layer detachably laminated inside the outer layer, and which is formed into a bottle shape with a mouth, a body, and a bottom (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2009-518245 Summary of the Invention [Problem to be solved by the invention]

[0004] Recycling and reusing containers with environmental considerations in mind is an important issue.

[0005] In the above-mentioned conventional double-layered containers, depending on the contents stored in the container, the contents may adhere to each other, making recycling or reuse difficult. Therefore, from the perspective of recycling and reuse, it is desirable if the inner layer can be easily separated from the outer layer.

[0006] The present invention has been made in consideration of such problems, and its purpose 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 such a double container, and a method for manufacturing such a double container. [Means for solving the problem]

[0007] The double container of the present invention is a synthetic resin double container having an outer layer body and an inner layer body separably laminated inside the outer layer body, formed in a bottle shape with a mouth part, a body part, and a bottom part, by blow molding a preform assembly made of synthetic resin in which an inner preform formed separately from the outer preform is assembled inside the outer preform. The inner layer body has a cap mounting part of the mouth part protruding from the upper end of the outer layer body, a spiral protrusion provided on the outer peripheral surface of a part between the body part and the cap mounting part and extending spirally around the axis of the cap mounting part, and a stopper protrusion having a stopper surface extending downward along the axis from the lower end of the spiral protrusion. The outer layer body has a spiral passage extending spirally around the axis, having a width through which the spiral protrusion is disposed and through which the spiral protrusion and the stopper protrusion can pass, and a stopper passage extending downward along the axis from the lower end of the spiral passage and having a locking surface facing the stopper surface, where the stopper protrusion is disposed.

[0008] In the double container of the present invention, in the above configuration, it is preferable that the spiral passage and the stopper passage are notches penetrating the outer layer body in the radial direction.

[0009] In the double container of the present invention, in the above configuration, it is preferable that the spiral passage and the stopper passage are grooves provided on the inner surface of the outer layer body.

[0010] In the double container of the present invention, in the above configuration, it is preferable that a male screw to which a cap is screwed is provided on the cap mounting part, and the spiral protrusion and the spiral passage are inclined in a direction opposite to that of the male screw.

[0011] In the double container of the present invention, in the above configuration, it is preferable that the outer layer body is made of polyethylene terephthalate and the inner layer body is made of polypropylene.

[0012] The preform assembly of the present invention is a bottomed cylindrical preform assembly made of synthetic resin, having an outer preform and an inner preform formed separately from the outer preform and assembled inside the outer preform. The inner preform has a cap mounting portion protruding from the upper end of the outer preform, a spiral protrusion provided on the outer peripheral surface of a portion between the bottomed cylindrical extending portion and the cap mounting portion, and extending spirally around the axis of the cap mounting portion, and a stopper protrusion having a stopper surface extending downward along the axis from the lower end of the spiral protrusion. The outer preform has a spiral passage extending spirally around the axis, having a width through which the spiral protrusion is disposed and through which the spiral protrusion and the stopper protrusion can pass, and a locking surface extending downward along the axis from the lower end of the spiral passage and facing the stopper surface, and a stopper passage in which the stopper protrusion is disposed.

[0013] The method for manufacturing a double container of the present invention is characterized by having a step of forming the above preform assembly and a step of blow-molding the preform assembly.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide a double container in which an inner layer can be easily separated from an outer layer, a preform assembly capable of forming the double container, and a method for manufacturing the double container.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0016] Hereinafter, with reference to the drawings, the configuration of a double container 1 made of synthetic resin according to an embodiment of the present invention will be exemplified and described in detail.

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

[0018] The double container 1 has a double structure having an outer layer body 2 and an inner layer body 3, and its outer shape is a bottle shape having a mouth portion 11, a body portion 12, and a bottom portion 13. The body portion 12 has a shoulder-shaped portion 12a that expands in diameter downward from the lower end of the mouth portion 11, and the portion between the shoulder-shaped portion 12a and the bottom portion 13 is cylindrical.

[0019] As shown in FIG. 2, the mouth portion 11 has a cap mounting portion 11a to which a cap (not shown) is mounted. In this embodiment, the cap mounting portion 11a is cylindrical, and a male screw 11b to which the cap is screwed is integrally provided on its outer peripheral surface. Instead of the male screw 11b, an annular protrusion for mounting the cap by caulking may be provided.

[0020] As the cap to be mounted on the cap mounting portion 11a, for example, a hinge cap, a mounting cap that supports a pump, etc., which are preferably configured to be able to discharge the contents while being attached to the cap mounting portion 11a, but are not limited thereto.

[0021] As shown in Fig. 1, the outer layer body 2 constitutes the outer contour of the portion of the double container 1 excluding the cap mounting portion 11a, and has an outer cylindrical portion 2a located below the cap mounting portion 11a. Further, at the lower end of the outer cylindrical portion 2a, an outer body portion 2c corresponding to the body portion 12 is integrally provided via a cylindrical portion 2b constituting the lower side portion of the mouth portion 11, and at the lower end of the outer body portion 2c, an outer bottom portion 2d corresponding to the bottom portion 13 is integrally provided.

[0022] The inner layer body 3 is separably laminated inside the outer layer body 2. The separation of the inner layer body 3 from the outer layer body 2 may be any of separation from an adhesive state, separation from a pseudo-adhesive state in the case of a resin laminate with no compatibility, and separation from a close contact state.

[0023] As shown in Fig. 2, the upper end portion of the inner layer body 3 protrudes upward from the upper end of the outer layer body 2, and the protruding portion constitutes the cap mounting portion 11a of the mouth portion 11. That is, the cap mounting portion 11a is constituted only by the inner layer body 3.

[0024] As shown in Fig. 3, the lower side portion of the cap mounting portion 11a of the inner layer body 3 is an inner cylindrical portion 3a constituting the lower side portion of the mouth portion 11, and the inner cylindrical portion 3a is disposed overlappingly inside the outer cylindrical portion 2a of the outer layer body 2. Below the inner cylindrical portion 3a, a storage portion 3b connected to the opening of the mouth portion 11, that is, the cap mounting portion 11a, is integrally provided. The storage portion 3b is separably laminated on the inner peripheral surfaces of the outer body portion 2c and the outer bottom portion 2d of the outer layer body 2. The inside of the storage portion 3b is a storage space S, and contents can be stored in this storage space S.

[0025] The cap mounting portion 11a has an outer diameter larger than that of the inner cylindrical portion 3a, and the lower end portion of the cap mounting portion 11a is in contact with the upper end portion of the outer cylindrical portion 2a from above. Also, the inner cylindrical portion 3a has an outer diameter larger than that of the upper end portion of the storage portion 3b, and the lower end portion of the inner cylindrical portion 3a is in contact with the upper end portion of the cylindrical portion 2b of the outer layer body 2 from above. By these, the cap mounting portion 11a is positioned in the vertical direction with respect to the outer cylindrical portion 2a. Note that the cap mounting portion 11a may be configured to be positioned in the vertical direction with respect to the outer cylindrical portion 2a by only one of the contact between the lower end portion of the cap mounting portion 11a and the upper end portion of the outer cylindrical portion 2a and the contact between the lower end portion of the inner cylindrical portion 3a and the upper end portion of the cylindrical portion 2b of the outer layer body 2, or a configuration may be adopted in which neither of these contacts is provided.

[0026] In the present embodiment, the outer layer body 2 is made of polyethylene terephthalate (PET), and the inner layer body 3 is made of polypropylene (PP). Note that various materials can be used as the materials constituting the outer layer body 2 and the inner layer body 3. Also, the outer layer body 2 and the inner layer body 3 may be made of the same material, for example, both made of polyethylene terephthalate. Further, the peelability of the inner layer body 3 with respect to the outer layer body 2 may be enhanced by applying a release agent such as silicon between the outer layer body 2 and the inner layer body 3. Furthermore, the outer layer body 2 and the inner layer body 3 may each have a single-layer structure or a laminated structure.

[0027] As shown in FIG. 1, the double container 1 has an engagement mechanism M in order to be able to easily separate the inner layer body 3 from the outer layer body 2. In the present embodiment, the double container 1 has a pair of engagement mechanisms M symmetrically with respect to the axis O, but hereinafter, only one of the engagement mechanisms M will be described. Note that the double container 1 only needs to have at least one engagement mechanism M, and the number thereof can be arbitrarily changed.

[0028] As shown in FIGS. 2 and 3, the engagement mechanism M has a spiral protrusion 20 provided integrally on the outer peripheral surface of the inner cylindrical portion 3a, which is a portion between the body portion 12 of the inner layer body 3 and the cap mounting portion 11a. The spiral protrusion 20 protrudes radially outward from the outer peripheral surface of the inner cylindrical portion 3a and extends spirally about the axis O of the mouth portion 11 or the cap mounting portion 11a. The length of the spiral protrusion 20 is shorter than the entire circumference of the inner cylindrical portion 3a.

[0029] In the present embodiment, the spiral protrusion 20 is inclined in a direction opposite to that of the male thread 11b provided on the cap mounting portion 11a. That is, the spiral protrusion 20 is inclined in a so-called reverse thread direction with respect to the circumferential direction.

[0030] The engagement mechanism M also has a stopper protrusion 21 provided integrally on the outer peripheral surface of the inner cylindrical portion 3a. The stopper protrusion 21 protrudes downward from the lower end portion along the spiral direction of the spiral protrusion 20. The stopper protrusion 21 has a substantially rectangular block shape, and the circumferential side surface of the stopper protrusion 21 facing the spiral protrusion 20 is a stopper surface 21a that extends downward along the axis O from the lower end portion of the spiral protrusion 20.

[0031] Furthermore, the engagement mechanism M has a spiral passage 22 that extends spirally about the axis O in the outer cylindrical portion 2a of the outer layer body 2. In the present embodiment, the spiral passage 22 is formed as a notch that penetrates the outer cylindrical portion 2a of the outer layer body 2 in the radial direction.

[0032] The spiral passage 22 is inclined at the same angle in the same direction as the spiral protrusion 20, and the spiral protrusion 20 is disposed inside thereof. Also, the width (vertical width) of the spiral passage 22 in the direction along the axis O is such that the spiral protrusion 20 and the stopper protrusion 21 can pass through.

[0033] In the present embodiment, an introduction path 24 whose width gradually widens upward is provided continuously at the upper end portion along the spiral of the spiral passage 22. The introduction path 24 opens on the upper surface of the outer cylindrical portion 2a.

[0034] Furthermore, the engagement mechanism M has a stopper passage 23 that continues to the lower end of the spiral passage 22. In the present embodiment, the stopper passage 23 is also formed as a notch that radially penetrates the outer cylindrical portion 2a of the outer layer body 2, similar to the spiral passage 22.

[0035] The stopper passage 23 has a rectangular shape with a size corresponding to the stopper projection 21, and is arranged with the stopper projection 21 fitted inside thereof. The stopper passage 23 has a locking surface 23a that extends downward along the axis O from the lower end of the spiral passage 22. The locking surface 23a faces the stopper surface 21a in a contacting state. Note that the stopper passage 23 can be formed to have the same shape and the same size as the stopper projection 21 so that the stopper projection 21 fits without a gap, as in the present embodiment, but it may also be formed larger than the stopper projection 21 to have a gap between the stopper projection 21.

[0036] The surface facing the lower side of the spiral projection 20 is in contact with the inner surface on the lower side of the spiral passage 22, and a vertical interval equal to or greater than the vertical length of the stopper surface 21a is provided between the surface facing the upper side of the spiral projection 20 and the inner surface on the upper side of the spiral passage 22.

[0037] The double container 1 having the above-described configuration is used by filling the contents into the storage space S through the mouth portion 11 and then screwing the cap onto the male screw 11b and attaching it to the cap mounting portion 11a. At this time, when the cap is screwed onto the cap mounting portion 11a, a rotational force about the axis O acts on the outer cylindrical portion 2a of the outer layer body 2. However, since the stopper projection 21 fits into the stopper passage 23 and the stopper surface 21a is locked to the locking surface 23a, rotation about the axis O with respect to the outer cylindrical portion 2a of the cap mounting portion 11a is restricted. Therefore, it is possible to prevent the inner layer body 3 from idling with respect to the outer layer body 2 when the cap is attached, and to facilitate the cap attachment operation to the cap mounting portion 11a. Further, when the cap attached to the cap mounting portion 11a is rotated in the loosening direction, the spiral projection 20 is locked to the side wall end of the spiral passage 22. Therefore, when the cap is unscrewed from the cap mounting portion 11a, it is possible to prevent the inner layer body 3 from idling with respect to the outer layer body 2 and to facilitate the removal operation of the cap from the cap mounting portion 11a.

[0038] When a cap having a configuration in which the contents can be discharged while being attached to the cap mounting portion 11a, such as a hinge cap or a mounting cap that supports a pump, is used, a rotational force in the rotational direction about the axis O acts on the cap mounting portion 11a only when the cap is attached to the cap mounting portion 11a. After attachment, the contents can be discharged while the cap is attached to the cap mounting portion 11a without detaching the cap from the cap mounting portion 11a. Therefore, the stopper projection 21 does not detach from the stopper passage 23 or the engagement mechanism M is not damaged.

[0039] On the other hand, in the double container 1 having the above-described configuration, the inner layer body 3 can be easily separated from the outer layer body 2 when the contents are used up.

[0040] When the double container 1 stores contents containing, for example, oil, even if the inner layer body 3 after use is soiled to the extent that it cannot be recycled due to the adhesion of the contents, the clean outer layer body 2 can be easily separated from the soiled inner layer body 3, and only the outer layer body 2 can be sorted and recycled or reused.

[0041] More specifically, the user first grips the cap mounting portion 11a and pulls it upward with respect to the outer layer body 2, or grips the cap mounted on the cap mounting portion 11a and pulls the cap mounting portion 11a upward with respect to the outer layer body 2 together with the cap, thereby disengaging the stopper projection 21 upward from the stopper passage 23 and releasing the circumferential engagement centered on the axis O with the locking surface 23a of the stopper surface 21a. At this time, since the inner layer body 3 engages with the outer layer body 2 from below at the shoulder portion 12a of the body portion 12 and the upward relative movement with respect to the outer layer body 2 is restricted, the cap mounting portion 11a is pulled upward with respect to the outer layer body 2 while slightly deforming the portion corresponding to the shoulder portion 12a of the inner layer body 3.

[0042] Next, the cap mounting portion 11a or the cap is rotated in the tightening direction to move the spiral projection 20 and the stopper projection 21 along the spiral passage 22. Since the spiral passage 22 is inclined in the reverse screw direction with respect to the male screw 11b, by rotating the cap in the tightening direction and moving the spiral projection 20 and the stopper projection 21 along the spiral passage 22, the inner layer body 3 moves upward with respect to the outer layer body 2. In this way, by rotating the cap mounting portion 11a or the cap in the tightening direction, the inner layer body 3 can be moved upward with respect to the outer layer body 2 while deforming the portion corresponding to the shoulder portion 12a of the inner layer body 3 to an extent that it can be pulled out of the container through the outer cylindrical portion 2a. At this time, the force for rotating the cap mounting portion 11a or the cap in the tightening direction is increased by the movement of the spiral projection 20 with respect to the spiral passage 22 and becomes the force for moving the inner layer body 3 upward with respect to the outer layer body 2. Therefore, compared with the case of simply pulling the inner layer body 3 straight upward with respect to the outer layer body 2, the operating force for pulling the inner layer body 3 upward with respect to the outer layer body 2 can be reduced.

[0043] Then, after rotating the cap mounting portion 11a or the cap in the tightening direction until the spiral protrusion 20 and the stopper protrusion 21 reach the introduction path 24, the cap mounting portion 11a or the cap is pulled upward with respect to the outer layer body 2. As a result, the entire inner layer body 3 can be sequentially pulled out of the container through the outer cylindrical portion 2a of the outer layer body 2, and the inner layer body 3 can be separated from the outer layer body 2.

[0044] Thus, since the double container 1 of the present embodiment has the engagement mechanism M configured as described above, by pulling the cap mounting portion 11a or the cap mounted on the cap mounting portion 11a upward, then rotating it in the circumferential direction, and then further pulling it upward, the inner layer body 3 can be easily separated from the outer layer body 2 with a smaller operating force.

[0045] Further, in the double container 1 of the present embodiment, since the spiral protrusion 20 and the spiral passage 22 are inclined in a direction opposite to the male screw 11b provided on the cap mounting portion 11a and to which the cap is screw-coupled, when performing an operation of separating the inner layer body 3 from the outer layer body 2 by gripping the cap mounted on the cap mounting portion 11a, the operation can be performed by rotating the cap in the tightening direction with respect to the cap mounting portion 11a. Therefore, it is possible to prevent the cap from detaching from the cap mounting portion 11a during the operation, and to make the operation easier to perform.

[0046] Furthermore, in the double container 1 of the present embodiment, since the outer layer body 2 is made of polyethylene terephthalate and the inner layer body 3 is made of polypropylene, the inner layer body 3 can be made more easily deformable, and the operation of separating the inner layer body 3 from the outer layer body 2 can be made easier to perform.

[0047] Furthermore, in the double container 1 of the present embodiment, even when the outer layer 2 is made of polyethylene terephthalate and the inner layer 3 is made of polypropylene, by having the engaging mechanism M configured as described above, the inner layer 3 can be easily peeled off from the outer layer 2 by an easy operation, and the operation of separating the inner layer 3 from the outer layer 2 can be easily performed.

[0048] The double container 1 having the above configuration can be formed by blow molding a synthetic resin preform assembly 30 according to an embodiment of the present invention shown in FIG. 4.

[0049] The preform assembly 30 has an outer preform 31 and an inner preform 32 assembled inside the outer preform 31, and has a bottomed cylindrical shape as a whole.

[0050] The outer preform 31 corresponds to the outer layer 2, and includes an outer cylindrical portion 31a and a bottomed cylindrical outer extension portion 31b integrally connected to the lower end of the outer cylindrical portion 31a. The outer cylindrical portion 31a is a portion that is not stretched by blow molding and has the same shape as the outer cylindrical portion 2a of the double container 1. In the outer cylindrical portion 31a, similar to the outer cylindrical portion 2a of the double container 1, a spiral passage 33 having the same shape as the spiral passage 22, a stopper passage 34 having the same shape as the stopper passage 23, and an introduction passage 35 having the same shape as the introduction passage 24 are provided, and the stopper passage 34 has a locking surface 34a having the same shape as the locking surface 23a.

[0051] The outer preform 31 is made of polyethylene terephthalate, like the outer layer 2, and is formed into the above shape by injection molding using polyethylene terephthalate.

[0052] The inner preform 32 corresponds to the inner layer body 3 and includes a cap mounting portion 32a, an inner cylindrical portion 32b, and a bottomed cylindrical inner extension portion 32c integrally connected to the lower end of the inner cylindrical portion 32b. The cap mounting portion 32a is integrally provided with a male screw 32d corresponding to the male screw 11b. The cap mounting portion 32a and the inner cylindrical portion 32b are portions that are not stretched by blow molding and have the same shape as the cap mounting portion 11a and the inner cylindrical portion 3a of the double container 1, respectively. The inner cylindrical portion 32b is provided with a spiral protrusion 36 having the same shape as the spiral protrusion 20 and a stopper protrusion 37 having the same shape as the stopper protrusion 21, and the stopper protrusion 37 has a stopper surface 37a having the same shape as the stopper surface 21a.

[0053] The inner preform 32 is made of polypropylene, similar to the inner layer body 3, and is formed into the above shape by injection molding using polypropylene separately from the outer preform 31.

[0054] The preform assembly 30 is formed by assembling an inner preform 32, which is formed into the above shape by injection molding separately from the outer preform 31, inside the outer preform 31, which is formed into the above shape by injection molding.

[0055] Here, in the above assembly, first, the inner extension 32c of the inner preform 32 is inserted from the outer cylindrical portion 31a of the outer preform 31 toward the inside of the outer extension 31b. When the stopper projection 37 reaches the outer cylindrical portion 31a, the stopper projection 37 and then the spiral projection 20 are sequentially introduced from the introduction path 35 into the spiral passage 33. Next, the inner preform 32 is inserted further toward the outer preform 31 while being rotated with respect to the outer preform 31. Then, the spiral projection 36 and the stopper projection 37 move along the spiral passage 33. When the stopper projection 37 reaches the lower end portion of the spiral passage 33, next, the inner preform 32 is pushed downward along the axis O with respect to the outer preform 31. As a result, the stopper projection 37 fits into the stopper passage 34, and the inner layer body 3 is prevented from rotating in the circumferential direction with respect to the outer layer body 2. Also, the lower end portion of the cap mounting portion 32a abuts against the upper end portion of the outer cylindrical portion 31a in the axial direction, and the lower end portion of the inner cylindrical portion 32b abuts against the step at the upper end portion of the inner circumferential surface of the outer extension 31b in the axial direction, so that the inner preform 32 is positioned in the vertical direction with respect to the outer preform 31.

[0056] In this way, the inner preform 32 can be easily assembled to the outer preform 31. Also, the configuration of the preform assembly 30 for forming the double container 1 provided with the engagement mechanism M can be made simple, and its cost can be reduced.

[0057] Next, a method for manufacturing a double container according to an embodiment of the present invention will be described.

[0058] The method for manufacturing a double container according to this embodiment can be performed using the preform assembly 30 having the above configuration.

[0059] First, the inner preform 32 is assembled inside the outer preform 31 by the method as described above.

[0060] Next, the preform assembly 30 is blow-molded. As the blow molding, for example, biaxial stretch blow molding using a stretch rod can be employed. Note that as the pressurizing medium in the blow molding, pressurized air, pressurized liquid, or the like can be used. In this way, the double container 1 having the above configuration is formed. When the double container 1 is blow-shaped, a shoulder portion 12a that expands in diameter is formed, thereby preventing the inner layer body 3 from slipping upward with respect to the outer layer body 2 and determining the relative positions of the outer layer body 2 and the inner layer body 3.

[0061] Then, after filling the storage space S inside the double container 1 with the contents, a cap is attached to the cap attachment portion 11a of the mouth portion 11.

[0062] Thus, according to the manufacturing method of the preform assembly 30 to the double container 1 according to the present embodiment, in a simple process of only blow-molding the preform assembly 30 formed by assembling the inner preform 32 having the spiral protrusion 36 and the stopper protrusion 37 inside the outer preform 31 having the spiral passage 33 and the stopper passage 34, a double container 1 in which the outer layer body 2 and the inner layer body 3 can be easily separated can be manufactured easily and inexpensively.

[0063] As shown as a modification in FIGS. 5 and 6, the double container 1 may be such that the spiral passage 22 and the stopper passage 23 are each formed as grooves provided on the inner surface of the outer layer body 2. That is, the spiral passage 22 and the stopper passage 23 can be formed as concave grooves that are recessed from the inner peripheral surface of the outer cylindrical portion 2a of the outer layer body 2 toward the radially outer side with a predetermined depth without penetrating the outer cylindrical portion 2a in the radial direction.

[0064] In this way, when the spiral passage 22 and the stopper passage 23 are each formed as grooves provided on the inner surface of the outer layer body 2, the spiral passage 22, the stopper passage 23, the spiral protrusion 20, and the stopper protrusion 21 are not exposed on the outer peripheral surface of the outer cylindrical portion 2a, so that the engagement mechanism M is not visually recognized from the outside, and the appearance of the double container 1 can be enhanced.

[0065] The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist thereof.

Explanation of Reference Numerals

[0066] 1 Double container 2 Outer layer body 2a Outer cylindrical portion 2b Cylindrical portion 2c Outer barrel portion 2d Outer bottom portion 3 Inner layer body 3a Inner cylindrical portion 3b Storage portion 11 Mouth portion 11a Cap mounting portion 11b Male screw 12 Barrel portion 12a Shoulder-like portion 13 Bottom portion 20 Spiral protrusion 21 Stopper protrusion 21a Stopper surface 22 Spiral passage 23 Stopper passage 23a Locking surface 24 Introduction path 30 Preform assembly 31 Outer preform 31a Outer cylindrical portion 31b Outer extension 32 Inner preform 32a Cap mounting portion 32b Inner cylindrical portion 32c Inner extension 32d Male screw 33 Spiral passage 34 Stopper passage 34a Locking surface 35 Introduction path 36 Spiral protrusion 37 Stopper protrusion 37a Stopper surface S Storage space M Engagement mechanism

Claims

1. By blow molding a preform assembly made of synthetic resin in which an inner preform formed separately from the outer preform is assembled inside the outer preform, a double container made of synthetic resin is provided, which comprises an outer layer and an inner layer separably laminated inside the outer layer, and is formed in a bottle shape having a mouth portion, a body portion, and a bottom portion, wherein the inner layer has, a cap mounting portion of the mouth portion protruding from the upper end of the outer layer, a spiral protrusion provided on the outer peripheral surface of a portion between the body portion and the cap mounting portion and extending spirally around the axis of the cap mounting portion, and a stopper protrusion having a stopper surface extending downward along the axis from the lower end of the spiral protrusion, and the outer layer has, a spiral passage extending spirally around the axis, having a width through which the spiral protrusion is disposed and through which the spiral protrusion and the stopper protrusion can pass, and a stopper passage extending downward along the axis from the lower end of the spiral passage and having a locking surface facing the stopper surface, where the stopper protrusion is disposed. The double container is characterized by the above.

2. The double container according to claim 1, wherein the spiral passage and the stopper passage are notches penetrating the outer layer in the radial direction.

3. The double container according to claim 1, wherein the spiral passage and the stopper passage are grooves provided on the inner surface of the outer layer.

4. A male screw to which a cap is screwed is provided on the cap mounting portion, and the double container according to any one of claims 1 to 3, wherein the spiral protrusion and the spiral passage are inclined in a direction opposite to that of the male screw.

5. The double container according to claim 1, wherein the outer layer is made of polyethylene terephthalate and the inner layer is made of polypropylene.

6. An outer preform and, an inner preform formed separately from the outer preform and assembled inside the outer preform, a bottomed cylindrical preform assembly made of synthetic resin, wherein the inner preform has, a cap mounting portion protruding from the upper end of the outer preform, a spiral protrusion provided on the outer peripheral surface of a portion between the bottomed cylindrical extension portion and the cap mounting portion and extending spirally around the axis of the cap mounting portion, and a stopper protrusion having a stopper surface extending downward along the axis from the lower end of the spiral protrusion, and the outer preform has, A spiral passage that extends spirally about the axis, in which the spiral protrusions are disposed and which has a width through which the spiral protrusions and the stopper protrusions can pass; A preform assembly, comprising: a stopper passage that extends downward along the axis from a lower end of the spiral passage and that has a locking surface facing the stopper surface, in which the stopper protrusions are disposed. **Claim 7** A step of forming the preform assembly according to claim 6; A method for manufacturing a double container, comprising: a step of blow-molding the preform assembly.

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