Method for manufacturing preform for biaxial stretch blow molding, method for manufacturing double container, mold unit, rotary blow molding machine, and method for manufacturing container

Abstract

Provided is a technique capable of reducing circumferential non-uniformity of the wall thickness of a preform formed by direct blow molding.　The present invention provides a method for manufacturing a preform for biaxial stretch blow molding, the method comprising a blow molding step. In the blow molding step, a molded body having a preform constituent part that constitutes the preform is molded by blow molding a cylindrical parison in molten state using a mold unit. The preform is provided with a protruding seal part that protrudes from the bottom part of the preform. The mold unit is provided with first and second molds that are configured to be openable and closable. The parison is supplied between the first mold and the second mold. The first mold is provided with a first cavity. The second mold is provided with a second cavity. The first and second cavities are combined to form the outer surface of a cavity having a shape corresponding to the outer surface of the molded body. The mold unit is provided with a compression part. The compression part is configured to form a portion that becomes the protruding seal part, by compressing and sealing the parison between the first and second molds. In the blow molding, the parison comes into contact with the first mold prior to the second mold. In a bottom part formation part of the cavity that forms a portion that becomes the bottom part of the preform, the volume of the first cavity is greater than the volume of the second cavity.

Description

Method for manufacturing a preform for biaxially stretched blow molding, method for manufacturing a double-layered container, mold unit, rotary blow molding machine, and method for manufacturing a container

[0001] The present invention relates to a method for manufacturing a preform for biaxial stretch blow molding, a method for manufacturing a double-layered container, a mold unit, a rotary blow molding machine, and a method for manufacturing a container.

[0002] (First and Second Aspects) Conventionally, double-layered containers having a container body with an outer shell and an inner bag have been known. For example, Patent Document 1 discloses a method for manufacturing a container body having an inner bag and an outer shell covering the inner bag by biaxially stretching blow molding a preform formed by covering an inner preform with an outer preform. Patent Document 1 also discloses a method for simultaneously forming two inner preforms facing each other by direct blow molding, which blow molds a molten cylindrical parison.

[0003] (Third Aspect) Patent Document 2 discloses a method for manufacturing a container by biaxially stretching and blow molding a preform.

[0004] JP 2019-10741 A JP 2019-130735 A

[0005] (First Aspect) Incidentally, it has been found that when an inner preform is formed by direct blow molding, the wall thickness of the inner preform may become non-uniform in the circumferential direction. The inner preform is stretched during biaxial stretch blow molding, and thinner portions of the inner preform are more likely to be stretched. Therefore, if the wall thickness of the inner preform is non-uniform in the circumferential direction, the non-uniformity in the wall thickness becomes even more pronounced in the inner bag formed by stretching the inner preform.

[0006] Such a problem is not limited to the inner preform used to manufacture a double-walled container, but can similarly occur in any preform formed by direct blow molding.

[0007] The present invention has been made in consideration of the above circumstances, and provides a technique that can reduce the circumferential non-uniformity in the wall thickness of a preform formed by direct blow molding.

[0008] (Second Aspect) When the inner preform is formed by direct blow molding, a seal is formed at the bottom of the inner preform by welding the inner surfaces of the cylindrical parison together. This seal has a relatively low strength, and therefore there is a risk that it may rupture during biaxial stretch blow molding of the inner preform, resulting in the formation of a tear in the inner bag. To solve this problem, it is conceivable to form a protruding seal that protrudes from the main body of the inner preform, thereby increasing the seal strength.

[0009] When two inner preforms are formed facing each other simultaneously by direct blow molding as in Patent Document 1, protruding seal portions are formed in each inner preform, but depending on the molding conditions, the longitudinal lengths of the protruding seal portions may differ significantly between the two inner preforms formed simultaneously. If the longitudinal lengths of the protruding seal portions differ, the outer shape of the inner preforms will become non-uniform, so it is desirable that the longitudinal lengths of the protruding seal portions be as uniform as possible.

[0010] Such a problem is not limited to the inner preform used to manufacture a double-walled container, but can similarly occur in any preform formed by direct blow molding.

[0011] The present invention has been made in consideration of these circumstances, and provides a technology that can reduce the unevenness in the longitudinal length of the protruding seal portion formed on two preforms when the two preforms are formed simultaneously by direct blow molding.

[0012] (Third Aspect) In one example, biaxial stretch blow molding is performed by placing a blow core inside a preform and blowing air through through holes provided in the blow core. Conventionally, in order to prevent interference between the blow core and the preform, the outer diameter of the blow core was set to a dimension that did not interfere with the preform, and the blow core was not press-fit into the preform. In biaxial stretch blow molding using preforms formed by injection molding, setting the outer diameter of the blow core as described above did not cause any problems during mass production.

[0013] On the other hand, when mass production trials were carried out using a blow core with an outer diameter designed with a similar concept in biaxial stretch blow molding using a preform formed by direct blow molding, it was found that the incidence of molding defects was significantly higher than when using a preform formed by injection molding.

[0014] The present invention has been made in view of the above circumstances, and provides a technique that can suppress the occurrence of molding defects even when a preform formed by direct blow molding is used.

[0015] (First Aspect) According to the present invention, the following inventions are provided: [1] A method for manufacturing a preform for biaxial stretch blow molding, comprising a blow molding step, in which a molten cylindrical parison is blow molded using a mold unit to form a molded body having a preform constituent part that constitutes the preform, the preform having a protruding seal part that protrudes from a bottom of the preform, the mold unit having first and second molds configured to be openable and closable, the parison being supplied between the first mold and the second mold, the first mold having a first cavity, and the second mold having a second cavity. a first cavity formed by joining the first and second cavities to form an outer surface of the cavity having a shape corresponding to the outer surface of the molded body, the mold unit including a compression section configured to sandwich and compress the parison between the first and second molds to close the parison and form a portion that will become the protruding seal portion, the parison contacts the first mold before the second mold during the blow molding, and in a bottom-forming section of the cavity that forms a portion that will become the bottom of the preform, the volume of the first cavity is larger than the volume of the second cavity. [2] The method according to [1], wherein, when a portion of the cavity that forms a portion that will become the mouth of the preform is defined as a mouth-forming section, the bottom-forming section has a plane of symmetry in a cross section that passes through a cavity central axis that passes through the centers of the bottom-forming section and the mouth-forming section and is perpendicular to the longitudinal direction of the compression section, the bottom-forming section has a plane of symmetry, the compression section is provided so as to protrude from the bottom-forming section, and a base of the compression section is provided on the second mold side relative to the plane of symmetry. [3] The method according to [1] or [2], wherein the blow molding is rotary blow molding in which a molten parison is blown while a plurality of the mold units are revolved, the parison is continuously supplied to the plurality of mold units along the circumferential direction of a circle formed by the locus of the revolution, and when the first and second molds are closed, the first mold is positioned closer to the center of the revolution than the second mold. [4] The method according to any one of [1] to [3], wherein the molded body is configured by connecting a pair of the preform constituent parts with a connecting part so that the mouths of the pair of preform constituent parts face each other.[5] The method according to any one of [1] to [4], wherein the blow molding is performed by injecting a pressurized fluid into the parison while the parison is in close contact with a second mold by vacuum suction. [6] A method for manufacturing a double container, comprising a step of biaxially stretching blow molding a preform formed by covering an outer preform with an inner preform, to manufacture a container body having an inner bag and an outer shell covering the inner bag, wherein the inner preform is manufactured by the method according to any one of [1] to [5].

[0016] (Second Aspect) According to the present invention, the following inventions are provided: [1] A method for manufacturing a preform for biaxial stretch blow molding, comprising a blow molding step, in which a molten cylindrical parison is blow molded using a mold unit to form a molded body, the molded body being configured by connecting first and second preform constituent parts with a connecting part so that mouths of the first and second preform constituent parts face each other, the first and second preform constituent parts respectively being parts that constitute the preform, the preform having a protruding seal part that protrudes from a bottom of the preform, the mold unit comprising first and second molds configured to be openable and closable, the parison being supplied between the first mold and the second mold, the first mold being a a first mold having a first cavity and a second mold having a second cavity, the first and second cavities combined to form an outer surface of the cavity having a shape corresponding to the outer surface of the molded body, the mold unit having first and second compression sections, the first and second compression sections being configured to sandwich and compress the parison between the first and second molds to close and form a portion that becomes the protruding seal portion, the outer diameter of the parison at a first section facing the first compression section being larger than the outer diameter at a second section facing the second compression section, and a first clearance between the first and second molds at the first compression section being larger than a second clearance between the first and second molds at the second compression section. [2] The method according to [1], wherein the blow molding is rotary blow molding in which a molten parison is blown while a plurality of mold units are revolved, the parison is continuously supplied to the plurality of mold units along the circumferential direction of a circle formed by the locus of the revolution, and the first compression section is arranged upstream of the second compression section in the moving direction of the parison. [3] A method for manufacturing a double container, comprising a step of biaxially stretch blow molding a preform formed by covering an outer preform on an inner preform to manufacture a container body having an inner bag and an outer shell covering the inner bag, wherein the inner preform is manufactured by the method according to [1] or [2].[4] A mold unit for blow molding a molten cylindrical parison to form a molded body, the mold unit comprising first and second molds configured to be openable and closable, the first and second molds comprising first and second cavities, respectively, which combine to form an outer surface of the cavity having a shape corresponding to the outer surface of the molded body, the molded body being configured by connecting the first and second preform-forming parts with a connecting part so that the mouths of the first and second preform-forming parts face each other, the first and second preform-forming parts each being a part that constitutes a preform for biaxially stretched blow molding, the preform having a protruding seal part that protrudes from the bottom of the preform, the mold unit comprising first and second compression parts, which are configured to close the first and second compression parts by sandwiching and compressing the parison between the first and second molds to form a part that becomes the protruding seal part, and a first clearance between the first and second molds in the first compression part being larger than a second clearance between the first and second molds in the second compression part. [5] A rotary blow molding machine comprising a plurality of mold units arranged concentrically and configured to be revolvable, the mold units being the mold units described in [4].

[0017] (Third Aspect) The present invention provides the following inventions: [1] A method for manufacturing a container, comprising a biaxially stretch blow molding step of biaxially stretch blow molding a preform to manufacture a container body, wherein in the biaxially stretch blow molding step, the preform is attached to a blow core so that an insert portion of the blow core is disposed within the preform, and the preform is biaxially stretch blow molded into the shape of the container body, wherein a portion of the preform facing the insert portion is a direct blow-molded article, and wherein, at a constituent portion constituting a nearest portion where the distance between the insert portion and the direct blow-molded article is smallest when the preform is attached to the blow core, Db is the outer diameter of the insert portion, where Db > Dmin. [2] The method described in [1], wherein Db ≥ Dmid is the maximum allowable inner diameter of the direct blow-molded article at the constituent portion, and Dmax is the midpoint value Dmid of the average of Dmin and Dmax. [3] The method according to [2], wherein Db≧Dmax. [4] The method according to any one of [1] to [3], wherein, when Di is the inner diameter of the direct blow-molded body at the closest portion, Db>Di, and the insertion portion is press-fitted into the direct blow-molded body. [5] A method for manufacturing a container, comprising a biaxially stretch blow-molding step of manufacturing a container body by biaxially stretch blow-molding a preform, wherein in the biaxially stretch blow-molding step, the preform is attached to a blow core so that an insertion portion of the blow core is positioned within the preform, and the preform is biaxially stretch blow-molded into the shape of the container body, [6] The method according to [5], wherein the insertion section has a tapered section that reduces in diameter toward the tip of the blow core, and the open end of the preform expands in diameter along the tapered section during the press-fitting. [7] The method according to any one of [1] to [6], wherein the direct blow-molded article includes a polyolefin layer.[8] The method according to any one of [1] to [7], wherein the preform is constructed by covering an outer preform on an inner preform, and the inner preform is the direct blow molded article. [9] The method according to [8], wherein the inner preform has a protruding portion protruding from an open end of the outer preform, and a constituent portion constituting a closest portion where the gap between the insertion portion and the direct blow molded article is smallest when the preform is attached to the blow core is provided on the protruding portion.

[0018] (First Aspect) The inventors conducted extensive research and found that in direct blow molding, the parison may contact the first mold before the second mold. In this case, the temperature of the first facing portion of the parison facing the first mold is lower than that of the second facing portion of the parison facing the second mold, resulting in increased viscosity and reduced stretching during blow molding. This results in a preform with a larger wall thickness at the first facing portion than at the second facing portion. As a result, the preform tends to have a non-uniform wall thickness in the circumferential direction. Based on this finding, the inventors came up with the idea of ​​making the volume of the first cavity larger than the volume of the second cavity. This configuration promotes stretching of the first facing portion and reduces non-uniformity in the circumferential wall thickness of the preform.

[0019] (Second Aspect) In direct blow molding, when first and second compression sections are provided along the direction of parison movement, the outer diameter of the parison at the first section facing the first compression section may be larger than the outer diameter at the second section facing the second compression section. In this case, it has been found that if the parison is compressed at the same pressure in the first and second compression sections, the protruding seal portion formed in the first compression section will have a longer longitudinal length than the protruding seal portion formed in the second compression section. Therefore, in the present invention, in the above case, the pressure when compressing the parison in the first compression section is made smaller than the pressure when compressing the parison in the second compression section, thereby reducing the non-uniformity in the longitudinal lengths of the protruding seal portions formed on the two preforms.

[0020] (Third Aspect) The inventors investigated the causes of the high incidence of molding defects in mass-production trials and found that preforms formed by direct blow molding have greater inner diameter variation than preforms formed by injection molding. When the inner diameter of a preform is large, the gap between the inner surface of the preform and the outer surface of the blow core becomes excessively large. The pressurized fluid injected during biaxial stretch blow molding leaks through this gap, resulting in insufficient internal pressure on the preform and molding defects. Based on this finding, the inventors arrived at the idea of ​​increasing the outer diameter of the blow core beyond the dimensions derived from conventional design concepts, thereby allowing the blow core to be pressurized into the preform. Using a blow core designed based on this concept eliminates or reduces the gap between the blow core and the preform, thereby preventing leakage of the pressurized fluid during biaxial stretch blow molding and, as a result, reducing molding defects.

[0021] (First and Second Aspects) A perspective view of a double-walled container 1 according to one embodiment of the present invention. The dashed-dotted lines in the figures represent the boundary lines where the curvature of the surfaces constituting the surface shape changes. This also applies to other figures. This is a perspective view of the container body 2 in FIG. 1. This is an exploded perspective view of the vicinity of the mouth 5 in FIG. 2. This is a perspective view of the vicinity of the open end of the outer shell 3. This is a perspective view showing the inner preform 14 and the outer preform 13 separated from each other. This is a perspective view of a preform 15 formed by covering the inner preform 14 with the outer preform 13. This shows the state in which rotary blow molding is being performed in a rotary blow molding machine 36. FIGS. 8A to 8C are a perspective view, a plan view, and a front view, respectively, showing a molded body 34 formed by connecting the mouths of first and second preform constituent parts 34a, 34b with a connecting part 34c so that they face each other. FIG. 9A is a cross-sectional view taken along the line A-A in FIG. 8B, and FIGS. 9B and 9C are enlarged views of areas B and C in FIG. 9A, respectively. FIG. 10A is a cross-sectional view of the same cross section as FIG. 9A , but with the first and second molds 32a and 32b of the mold unit 32 of the first embodiment of the present invention closed. FIGS. 10B and 10C are enlarged views of regions B and C, respectively, in FIG. 10A . FIG. 10D is an enlarged view of region B in FIG. 10B . FIG. 10E is an enlarged view of region E in FIG. 10C . FIG. 11A is a cross-sectional view of the same cross section as FIG. 9A , but with the first and second molds 32a and 32b of the mold unit 32 open. FIGS. 11B and 11C are enlarged views of regions B and C, respectively, in FIG. 11A . FIG. 12A is a cross-sectional view of the same cross section as FIG. 9A , but with the parison 33 positioned between the first and second molds 32a and 32b of the mold unit 32. FIGS. 12B and 12C are enlarged views of regions B and C, respectively, in FIG. 12A . FIG. 13A is a cross-sectional view of a mold unit 32 of a second embodiment of the present invention, but corresponding to FIG. 12A . Fig. 13B is an enlarged view of region B in Fig. 13A. (Third Viewpoint) A perspective view of the container 10 of the first embodiment of the present invention. A perspective view of the container body 2 in Fig. 14. An exploded perspective view of the vicinity of the opening end 5c in Fig. 15. A perspective view of the vicinity of the opening end 3a of the outer shell 3 in Fig. 16. A perspective view showing a state in which the inner preform 14 and the outer preform 13 are separated. A perspective view of a preform 15 formed by covering the outer preform 13 on the inner preform 14.20A to 20C are a perspective view, a bottom view, and a CC cross-sectional view of the blow core 21 of the first embodiment, respectively. A cross-sectional view of the same cross section as FIG. 20C, showing the blow core 21 and preform 15 of the first embodiment separated. FIG. 22A is a cross-sectional view corresponding to FIG. 21, showing the insert portion 21b of the blow core 21 of the first embodiment press-fitted into the preform 15. FIG. 22B is an enlarged view of region B in FIG. 22A. A cross-sectional view showing the blow core 21 of the first embodiment with the preform 15 attached and brought close to the heater 42. A cross-sectional view showing the state after the preform 15 has been transferred to the molding die 23 from the state of FIG. 23. FIG. 25A is a cross-sectional view showing the state after the bottom support die 22 supports the bottom portion 15c of the preform 15 from the state of FIG. 24. FIG. 25B is an enlarged view of region B in FIG. 25A. This is a cross-sectional view showing the state after the stretch rod 25 is extended and the bottom support mold 22 is retracted from the state shown in FIG. 25 to first-axis stretch the preform 15. FIGS. 27A to 27C are a perspective view, a bottom view, and a CC cross-sectional view, respectively, of the blow core 21 of the second embodiment. This is a cross-sectional view of the same cross section as FIG. 27C, showing the blow core 21 and preform 15 of the second embodiment separated. FIG. 29A is a cross-sectional view corresponding to FIG. 28, showing the tapered portion 21f of the blow core 21 of the second embodiment with the open end 15f of the preform 15 abutting against the tapered portion 21f. FIG. 29B is an enlarged view of region B in FIG. 29A. FIG. 30A is a cross-sectional view corresponding to FIG. 28, showing the insert portion 21b of the blow core 21 of the second embodiment press-fitted into the preform 15. FIG. 30B is an enlarged view of region B in FIG. 30A.

[0022] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently. Furthermore, in the following embodiments, elements not specified in the claims are optional elements and can be omitted. Any number of "0"s (for example, one or two) may be added to the end of numerical values ​​disclosed in the following description. For example, one or two "0"s may be added after "1.4" to make it "1.40" or "1.400".

[0023] (First and Second Aspects) 1. Configuration of Double Container 1 <Basic Configuration> As shown in FIG. 1 , a double container 1 according to one embodiment of the present invention comprises a container body 2 and a spout attachment member 8 .

[0024] As shown in Figures 2 and 3, the container body 2 has a mouth 5, a body 6, and a bottom 7. The mouth 5 is a tubular (preferably cylindrical) portion having an open end 5c. The open end 5c is the open end of the container body 2 and also the open end of the inner bag 4. The mouth 5 has an engaging portion 4m to which a mouth attachment member 8 can be attached. In this embodiment, the mouth attachment member 8 is a cap 8a, but it may also be a pump. The mouth 5 has a flange 5b. The flange 5b can be used to support the mouth 5 when the mouth attachment member 8 is attached to the mouth 5.

[0025] The body 6 is disposed adjacent to the mouth 5 on a side farther from the open end 5c than the mouth 5. In one example, the body 6 is located below the flange 5b. The body 6 has a larger outer diameter (in this specification, "outer diameter" means a circular equivalent diameter when the cross section is not circular) than the mouth 5. The body 6 is cylindrical, and the bottom 7 is provided at the lower end of the body 6 and closes the lower end of the body 6. The body 6 has a shoulder 6b whose outer diameter increases with increasing distance from the mouth 5. The body 6 also has a body main body 6c closer to the bottom 7 than the shoulder 6b. The body main body 6c has a shape in which the outer diameter is approximately constant toward the bottom 7, or a shape in which the diameter decreases toward the bottom 7, for example.

[0026] As shown in Figure 3, the container body 2 includes an inner bag 4 and an outer shell 3 arranged to cover the inner bag 4. The inner bag 4 has an inner bag body 4d other than a protruding portion 4c housed within the outer shell 3. In the following description, the portions of the inner bag 4 that correspond to the mouth 5, body 6, and bottom 7 of the container body 2 will be referred to as the mouth 5, body 6, and bottom 7 of the inner bag 4, respectively. The same applies to the outer shell 3.

[0027] 2 to 4, the inner bag 4 has a protruding portion 4c that protrudes from the open end 3a of the outer shell 3. The protruding portion 4c has a protruding tube 4c1, an engaging protrusion 4c2, an annular protrusion 4c5, and an abutting protrusion 4v.

[0028] The annular protrusion 4c5 engages with the spout attachment member 8 in the axial direction. The engaging protrusion 4c2 engages with the spout attachment member 8 in the circumferential direction. The engaging protrusion 4c2 and the annular protrusion 4c5 form an engaging portion 4m. The engaging portion 4m is positioned closer to the open end 5c of the inner bag 4 than the abutting protrusion 4v. In this specification, the "axial direction" refers to the direction in which the central axis C of the spout 5 extends, in other words, the direction in which the inner bag 4 is pulled out from the container body 2. The "circumferential direction" refers to the direction in which the spout 5 rotates around the central axis C, in other words, the direction in which the inner bag 4 rotates at the spout 5 relative to the outer shell 3.

[0029] The engaging protrusions 4c2 are preferably provided at multiple locations (eight locations in this embodiment) spaced apart in the circumferential direction. The engaging protrusions 4c2 are arranged on the annular protrusion 4c5 and protrude radially outward from the annular protrusion 4c5. The annular protrusion 4c5 and the engaging protrusions 4c2 have tapered surfaces 4c8 on their upper surfaces. This makes it easier for the annular protrusion provided on the opening attachment member 8 to climb over the annular protrusion 4c5 and the engaging protrusions 4c2.

[0030] The contact protrusions 4v are positioned to contact the outer shell 3 (in this embodiment, the opening end 3a) and protrude radially outward from the protruding tube 4c1. The contact protrusions 4v contact the outer shell 3, preventing the inner bag 4 from falling into the outer shell 3. The contact protrusions 4v preferably include a plurality of contact protrusions 4va arranged along the circumferential direction. Intermediate portions 4vb are provided between the plurality of contact protrusions 4va. The intermediate portions 4vb protrude less from the protruding tube 4c1 than the contact protrusions 4va, or do not protrude at all from the protruding tube 4c1. The intermediate portions 4vb are less likely to deform than the contact protrusions 4va, and thus providing the intermediate portions 4vb suppresses deformation of the contact protrusions 4va. The contact protrusions 4v may be annular protrusions.

[0031] The container body 2 is preferably a molded article produced by biaxially stretching blow molding a preform 15 (shown in FIGS. 5 and 6) formed by covering an inner preform 14 formed by direct blow molding with an outer preform 13. When the inner preform 14 is formed by direct blow molding, the strength of the contact convex portions 4v tends to be insufficient, and cracks tend to occur in the contact convex portions 4v during a drop test of the double container 1. However, by providing the contact convex portions 4v with intermediate portions 4vb, deformation of the contact protrusions 4va is suppressed, and cracks in the contact convex portions 4v are suppressed.

[0032] 3, a ridge 4g is provided on the outer peripheral surface of the inner bag 4 (more specifically, the inner bag body 4d). The lower surface of the ridge 4g is inclined counterclockwise when viewed from the opening end 5c of the mouth portion 5 so as to approach the opening end 5c.

[0033] As shown in Figures 3 and 4, a cam rail 3l is provided on the inner peripheral surface of the outer shell 3. A recess 3m that can engage with the protrusion 4g is provided in a portion of the cam rail 3l. The recess 3m is preferably provided at the end of the cam rail 3l. The upper surface of the cam rail 3l is inclined so as to approach the open end 3a as it progresses in the counterclockwise direction. The protrusion 4g and the recess 3m are configured to be engageable with each other by rotating the inner bag 4 clockwise relative to the outer shell 3, and to be disengageable by rotating the inner bag 4 counterclockwise relative to the outer shell 3.

[0034] Before the inner bag 4 is pulled out of the container body 2, the lower surface of the ridge 4g abuts against the upper surface of the cam rail 3l. The ridge 4g and the cam rail 3l form a cam mechanism 31. When the inner bag 4 is rotated counterclockwise relative to the outer shell 3, the cam mechanism 31 causes the inner bag 4 to displace in a direction that pulls it out of the container body 2. At this time, the inner bag 4 is twisted and its diameter is reduced. The cam mechanism 31 has an inclined structure that is inclined in the same direction as a right-handed screw.

[0035] <Attaching the mouth attachment member 8 and pulling out the inner bag 4> The mouth attachment member 8 is preferably of a stopper type and is configured to be attachable to the mouth 5 of the container body 2, and by placing the mouth attachment member 8 over the mouth 5 and pressing the mouth attachment member 8 in the direction of the bottom 7, the mouth attachment member 8 can be engaged with and attached to the mouth 5.

[0036] The mouth attachment member 8 is engaged with the mouth 5 of the inner bag 4 in the circumferential and axial directions, and is configured so that the inner bag 4 rotates relative to the outer shell 3 as the mouth attachment member 8 rotates. The cam mechanism 31 provided between the inner bag 4 and the outer shell 3 causes the inner bag 4 to move in a direction that allows it to come out of the container body 2 as the inner bag 4 rotates.

[0037] With this configuration, by rotating the mouth attachment member 8, the inner bag 4 can be twisted and moved in a direction that allows it to come out of the container body 2, and then by pulling the mouth attachment member 8, the inner bag 4 can be pulled out of the container body 2.

[0038] 2. Manufacturing Method of Double Container 1 The container body 2 can be manufactured by biaxially stretching blow molding a preform 15 shown in Fig. 6. The double container 1 can also be manufactured by attaching a mouth attachment member 8 to the container body 2.

[0039] <Configuration of Inner Preform 14 , Outer Preform 13 , and Preform 15 > As shown in FIG. 5 , the preform 15 includes the inner preform 14 that will become the inner bag 4 and the outer preform 13 that will become the outer shell 3 .

[0040] As shown in Fig. 5, the inner preform 14 is cylindrical with a bottom and includes an opening 14a, a body 14b, and a bottom 14c. The opening 14a is provided with a protrusion 14d and a ridge 14g. The protrusion 14d is provided with an engagement portion 14m and a contact ridge 14v. The engagement portion 14m, the contact ridge 14v, and the ridge 14g become the engagement portion 4m, the contact ridge 4v, and the ridge 4g, respectively, after molding. The bottom 14c is provided to close the lower end of the body 14b.

[0041] The inner preform 14 is formed by direct blow molding using a molten cylindrical parison 33. In this case, a seal portion 14s is formed in the inner preform 14 by welding the inner surfaces of the parison 33 together. The seal portion 14s may not have sufficient strength, so it is preferable to form a protruding seal portion 14t by having the seal portion 14s protrude from the bottom portion 14c of the inner preform 14, as shown in FIG. 5. The protruding seal portion 14t is formed by welding the inner surfaces of the parison 33 together and protrudes from the bottom portion 14c of the inner preform 14. By having the seal portion 14s protrude as the protruding seal portion 14t, the area of ​​the sealing surface is increased, and the sealing strength at the seal portion 14s is improved.

[0042] As shown in Fig. 5, the outer preform 13 is cylindrical with a bottom and includes a mouth portion 13a, a body portion 13b, and a bottom portion 13c. The bottom portion 13c is provided so as to close the lower end of the body portion 13b. The bottom portion 13c is provided with an annular convex portion 13d. The mouth portion 13a is provided with a flange portion 13e. The mouth portion 13a is provided with a groove 13m, which becomes the groove 3m after molding.

[0043] 6, a preform 15 can be formed by covering the inner preform 14 with the outer preform 13. In the preform 15, the mouth portion 14a faces the mouth portion 13a, and the body portion 14b faces the body portion 13b.

[0044] The mouth portions 13a and 14a become the mouth portion 15a of the preform 15, the body portions 13b and 14b become the body portion 15b of the preform 15, and the bottom portions 13c and 14c become the bottom portion 15c of the preform 15. The body portion 15b and the bottom portion 15c are primarily stretched in the biaxially stretch blow molding. The mouth portion 15a is hardly deformed during molding and becomes the mouth portion 5 of the container body 2. The above-described contents regarding the configuration included in the mouth portion 5 can also be applied to the configuration included in the mouth portion 15a, as long as it does not contradict the intent thereof.

[0045] <Materials and manufacturing method of the inner preform 14, outer preform 13, and preform 15> The inner preform 14 and outer preform 13 can be formed from a thermoplastic resin such as polyester (e.g., PET) or polyolefin (e.g., polypropylene, polyethylene). The inner preform 14 can be formed by direct blow molding. The outer preform 13 can be formed by direct blow molding or injection molding.

[0046] <Manufacturing the Inner Preform 14 by Direct Blow Molding> The inner preform 14 is formed by direct blow molding using a molten cylindrical parison. Direct blow molding makes it easier to achieve a thinner wall than injection molding, so forming the inner preform 14 by direct blow molding allows for a thinner inner bag 4. To form a multilayered inner bag 4, the inner preform 14 is preferably configured to include, from the inside out, an inner layer, a gas barrier layer, and an outer layer. However, such an inner preform 14 is not easily formed by multilayer injection molding. Furthermore, if a gate is provided at the bottom 14c of the inner preform 14, for example, the resin constituting the gas barrier layer may not reach the open end of the inner preform 14, resulting in a decrease in gas barrier properties. In particular, the thinner the inner preform 14, the more difficult it is for the resin to flow, making the above problem more pronounced. On the other hand, in direct blow molding, a cylindrical parison having structures corresponding to the inner layer, gas barrier layer, and outer layer is used for molding, so it is easy to provide the gas barrier layer over the entire inner preform 14.

[0047] 3. Manufacturing Method of Preform for Biaxial Stretch Blow Molding Next, a manufacturing method of a preform for biaxial stretch blow molding according to one embodiment of the present invention will be described. Here, the case where the preform is the inner preform 14 will be described as an example, but the following description can be applied to any preform that can be formed by direct blow molding (for example, the outer preform 13 or a single-layer preform) as long as it does not contradict the spirit of the description.

[0048] The method of this embodiment includes a blow molding process. In this blow molding process, as shown in FIG. 7 , a molten cylindrical parison 33 is blow-molded using the mold unit 32 of the first embodiment of the present invention to form a molded article 34. In one example, the blow molding can be performed using a rotary blow molding machine 36 including multiple mold units 32 arranged concentrically and configured to revolve. In this case, the blow molding is rotary blow molding, in which the molten parison is blown while the multiple mold units 32 revolve. In this embodiment, the mold unit 32 revolves clockwise around a central axis 36a. More specifically, the mold unit 32 is fixed to a rotation base 36c via a support 36b. When the rotation base 36c rotates about the central axis 36a, the mold unit 32 revolves about the central axis 36a.

[0049] In rotary blow molding, parisons 33 are continuously supplied to a plurality of mold units 32 along the circumferential direction of the circle formed by the revolution locus. Therefore, the parisons 33 are connected to each other between adjacent mold units 32. Furthermore, molded bodies 34 obtained by rotary blow molding are connected to each other via flash 37, making it easy to continuously remove the molded bodies 34 from the rotary blow molding machine 36. With this configuration, a large number of molded bodies 34 can be efficiently manufactured.

[0050] The following description will be given taking the blow molding as rotary blow molding as an example, but the following description can also be applied to blow molding other than rotary blow molding as long as it does not contradict the spirit of the description.

[0051] As shown in FIG. 8 , the molded body 34 has preform constituent parts 34a and 34b that constitute the inner preform 14. Therefore, the inner preform 14 can be manufactured by cutting away unnecessary portions from the molded body 34. The molded body 34 is preferably configured such that the openings 34a1 and 34b1 of the first and second preform constituent parts 34a and 34b are connected by a connecting part 34c so that they face each other. The openings 34a1 and 34b1 form the openings 14a of the inner preform 14. In this case, two inner preforms 14 can be manufactured in a single molding operation, resulting in high manufacturing efficiency. Furthermore, the parison 33 can be molded into the shape of the molded body 34 by injecting pressurized fluid (e.g., air) into the parison 33 through the connecting part 34c.

[0052] The following explanation will be given using an example in which the molded body 34 has two preform constituent parts 34a, 34b, but the following explanation can also be applied to cases in which the molded body 34 has only one preform constituent part, as long as it does not contradict the intent of the explanation.

[0053] As shown in FIGS. 7 and 10 to 12, the mold unit 32 includes first and second molds 32a and 32b that are configured to be openable and closable. In rotary blow molding, when the first and second molds 32a and 32b are closed, the first mold 32a is positioned closer to the center of revolution than the second mold 32b. The first mold 32a is fixed to a support column 36b. In this embodiment, the first and second molds 32a and 32b are opened and closed by rotating the second mold 32b around the hinge portion 32h. However, the method for opening and closing the first and second molds 32a and 32b is not particularly limited. For example, the first and second molds 32a and 32b may be opened and closed by translating the second mold 32b in the opening and closing direction relative to the first mold 32a. Note that, for convenience of illustration, in figures other than FIG. 7, the first and second molds 32a and 32b are shown as opening and closing by translating the second mold 32b.

[0054] As shown in Figures 7 and 12, the parison 33 is supplied between a first mold 32a and a second mold 32b. As shown in Figure 11, the first mold 32a has a first cavity 32a1. The second mold 32b has a second cavity 32b1. As shown in Figure 10, the first and second cavities 32a1 and 32b1 are combined to form the outer surface of a cavity 35 having a shape corresponding to the outer surface of the molded body 34. The portions of the cavity 35 that form the portion that will become the bottom 14c of the inner preform 14, the portion that will become the body 14b, and the portion that will become the mouth 14a are referred to as bottom forming portions 35f and 35g, body forming portions 35i and 35j, and mouth forming portions 35l and 35m, respectively.

[0055] The mold unit 32 includes first and second compression sections 32d and 32e. The compression sections 32d and 32e are configured to close the parison 33 by sandwiching and compressing it between the first and second molds 32a and 32b. The compression sections 32d and 32e are regions where the clearance between the first and second molds 32a and 32b is smaller than twice the wall thickness of the parison 33. Therefore, the parison 33 is compressed by being sandwiched between the compression sections 32d and 32e. The compression sections 32d and 32e are also configured to protrude from the bottom forming sections 35f and 35g. Therefore, when the parison 33 is compressed in the compression sections 32d and 32e, protruding seal portions 34d and 34e are formed, which become the protruding seal portion 14t protruding from the bottom 14c of the inner preform 14. The compression sections 32d and 32e are disposed at both ends of the cavity 35 in the moving direction of the parison 33. That is, the main body section 35h of the cavity 35 other than the compression sections 32d and 32e is disposed between the compression sections 32d and 32e.

[0056] In rotary blow molding, tension is applied to the parison 33 while it is sandwiched between the revolving mold units 32. As a result, as shown in FIG. 12 , the outer diameter of the parison 33 gradually decreases with increasing distance from the head 38 that injects the parison 33. Therefore, when the first compression section 32d is located upstream of the second compression section 32e in the direction of movement of the parison 33, the outer diameter Di1 of the parison 33 at the first compressed portion 33a facing the first compression section 32d is larger than the outer diameter Di2 of the parison 33 at the second compressed portion 33b facing the second compression section 32e. In this state, if the parison 33 is compressed at the same pressure by the first and second compression sections 32d, 32e to form the first and second protruding seal portions 34d, 34e, the longitudinal length of the first protruding seal portion 34d is likely to be longer than the longitudinal length of the second protruding seal portion 34e.

[0057] In the two inner preforms 14 obtained by cutting out the molded body 34 thus formed, the longitudinal lengths of the protruding seal portions 14t are non-uniform, which results in a non-uniform outer shape of the inner preform 14. If the outer shape of the inner preform 14 is non-uniform, the appearance of the inner preform 14 may be poor, the sealing strength of the protruding seal portions 14t may be non-uniform, and the degree of interference between the protruding seal portions 14t and the outer preform 13 when the outer preform 13 is placed over the inner preform 14 may be non-uniform. For this reason, it is desirable to reduce the non-uniformity in the outer shape of the inner preform 14.

[0058] To solve this problem, as shown in Fig. 10, it is preferable that the first clearance CL1 between the first and second molds 32a and 32b in the first compression section 32d is larger than the second clearance CL2 between the first and second molds 32a and 32b in the second compression section 32e. The larger the clearance between the first and second molds 32a and 32b in the compression sections 32d and 32e, the smaller the pressure applied to the parison 33 in the compression sections 32d and 32e, and the shorter the longitudinal lengths of the protruding seal portions 34d and 34e formed by compressing the parison 33 in the compression sections 32d and 32e. Therefore, by making the first clearance CL1 larger than the second clearance CL2, the longitudinal length of the first protruding seal portion 34d becomes relatively shorter, thereby reducing non-uniformity in the longitudinal length of the protruding seal portion 14t. The first and second clearances CL1 and CL2 refer to the gaps between the first and second molds 32a and 32b at the bases 32d1 and 32e1 of the compression sections 32d and 32e when the first and second molds 32a and 32b are in contact at the pinch-off sections 32f and 32g, as shown in Figure 10.

[0059] The thickness of the parison 33 is, for example, 0.5 to 2.0 mm (1.0 mm in this embodiment), preferably 0.7 to 1.5 mm. This thickness may be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0 mm, or may be within a range between any two of the values ​​exemplified here. The first clearance is, for example, 0.2 to 0.8 mm (0.5 mm in this embodiment), preferably 0.3 to 0.7 mm, and more preferably 0.4 to 0.6 mm. This value may be, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.8 mm, or may be within a range between any two of the values ​​exemplified here.

[0060] The value of {first clearance CL1 / second clearance CL2} is, for example, 1.2 to 3.0 (2.0 in this embodiment), preferably 1.5 to 2.5, and more preferably 1.8 to 2.2. Specific examples of this value include 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, and 3.0, and may be in a range between any two of the values ​​exemplified here. The value of {first clearance CL1 / wall thickness of parison 33} is preferably 0.8 or less, and more preferably 0.6 or less. This value is, for example, 0.1 to 0.8, and specifically, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, or may be in a range between any two of the numerical values ​​exemplified here.

[0061] In blow molding other than rotary blow molding, the outer diameter of the parison 33 may gradually decrease or increase with increasing distance from the head 38. When the outer diameter of the parison 33 gradually decreases, the compression sections 32e, 32e can be provided in the same manner as in rotary blow molding. When the outer diameter of the parison 33 gradually increases, the first compression section 32d can be disposed downstream of the second compression section 32e in the direction of movement of the parison 33, thereby reducing non-uniformity in the longitudinal length of the protruding seal portion 14t.

[0062] In ordinary blow molding (e.g., blow molding of containers) that does not involve preforms, the unevenness of the longitudinal length of the protruding seal portion 14t can be reduced by selecting the material, but because the preform is intended to be biaxially stretched and blow molded, there are restrictions on the selection of materials for molding the preform. For this reason, the technique of reducing the unevenness of the longitudinal length of the protruding seal portion 14t by making the first and second clearances CL1 and CL2 different is particularly useful in molding preforms.

[0063] As shown in FIG. 10 , the mold unit 32 includes first and second pinch-off sections 32f and 32g. A cavity 35 is disposed between the first and second pinch-off sections 32f and 32g. The first pinch-off section 32f is disposed adjacent to the first compression section 32d, and the second pinch-off section 32g is disposed adjacent to the second compression section 32e. At the pinch-off sections 32f and 32g, the parison 33 is compressed with a stronger pressure than at the compression sections 32d and 32e, forming a cutting line. The cutting line is thinner than the protruding seal sections 34d and 34e, allowing for easy cutting. By cutting along the cutting line, the molded body 34 can be separated from the flash 37.

[0064] 11, the first mold 32a is provided with first and second protrusions 32a2 and 32a3, and the second mold 32b is provided with first and second protrusions 32b2 and 32b3. The first protrusions 32a2 and 32b2 form a first compression section 32d and a first pinch-off section 32f. The second protrusions 32a3 and 32b3 form a second compression section 32e and a second pinch-off section 32g.

[0065] 7 and 12, in rotary blow molding, tension is applied to the parison 33 while the parison 33 is sandwiched between the revolving mold units 32, so the parison 33 contacts the first mold 32a, which is located closer to the center of revolution, before the second mold 32b. Figure 12 shows the mold unit 32 in the position indicated by arrow P in Figure 7. In this state, the parison 33 contacts the first mold 32a near the compression section 32e on the downstream side in the direction of revolution of the mold unit 32. As the mold unit 32 continues to revolve, the parison 33 also contacts the first mold 32a near the compression section 32d on the upstream side in the direction of revolution of the mold unit 32. Because the parison 33 is cooled by contact with the first mold 32a, the temperature of the first opposing portion 33c of the parison 33 facing the first mold 32a is lower than that of the second opposing portion 33d facing the second mold, increasing the viscosity and making it more difficult to stretch during blow molding. In the formed inner preform 14, the wall thickness of the portion formed from the first opposing portion 33c is greater than the wall thickness of the portion formed from the second opposing portion 33d. As a result, the wall thickness of the inner preform 14 is likely to be non-uniform in the circumferential direction. The inner preform 14 is stretched during biaxial stretch blow molding, and thinner portions of the inner preform 14 are more likely to be stretched. Therefore, if the wall thickness of the inner preform 14 is non-uniform in the circumferential direction, the non-uniformity in the wall thickness will be more pronounced in the inner bag 4 formed by stretching the inner preform 14.

[0066] To solve this problem, it is preferable to make the volume of the first cavity 32a1 larger than the volume of the second cavity 32b1 in the bottom forming portions 35f, 35g (preferably in the bottom forming portions 35f, 35g and the body forming portions 35i, 35j). With this configuration, the elongation of the first opposing portion 33c is promoted during blow molding, thereby reducing non-uniformity in the circumferential thickness of the inner preform 14.

[0067] 10, in a cross section passing through a cavity central axis 35n that passes through the centers of the bottom-forming portions 35f, 35g and the mouth-forming portions 35l, 35m and perpendicular to the longitudinal direction of the compression portions 32d, 32e, the bottom-forming portions 35f, 35g have a plane of symmetry 35k. It is also preferable that the body-forming portions 35i, 35j are symmetrical about the plane of symmetry 35k. The compression portions 32d, 32e are provided so as to protrude from the bottom-forming portions 35f, 35g, and the bases 32d1, 32e1 of the compression portions 32d, 32e are provided closer to the second mold 32b than the plane of symmetry 35k. With this configuration, it is possible to realize a configuration in which the volume of the first cavity 32a1 is larger than the volume of the second cavity 32b1 in the bottom forming portions 35f, 35g (preferably in the bottom forming portions 35f, 35g and the body forming portions 35i, 35j).

[0068] The distances D1 and D2 between the bases 32d1 and 32e1 of the compressed portions 32d and 32e and the symmetry plane 35k are, for example, 0.2 to 2.0 mm (0.7 mm in this embodiment), preferably 0.5 to 1.5 mm, and more preferably 0.8 to 1.2 mm. In this embodiment, D1 and D2 are the same value, but D1 and D2 may also be different values. Specifically, D1 and D2 are, for example, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0 mm, respectively, and may be in a range between any two of the values ​​exemplified here.

[0069] The compressed portions 32d, 32e have inclined portions 32d2, 32e2 that incline toward the plane of symmetry 35k as they move away from the roots 32d1, 32e1. As a result, an inclined portion is also formed in the protruding seal portion 14t, which prevents the bottom portion 14c of the inner preform 14 from tearing during biaxial stretch blow molding of the inner preform 14. The tips 32d3, 32e3 of the compressed portions 32d, 32e are preferably positioned on the plane of symmetry 35k, and in this case, the pinch-off portions 32f, 32g can also be positioned on the plane of symmetry 35k.

[0070] 7, the parison 33 is preferably supplied between the molds 32a and 32b with the mold unit 32 positioned higher than the central axis 36a and obliquely relative to the central axis 36a (i.e., with the straight line from the central axis 36a to the mold unit 32 pointing obliquely upward). In this case, the timing of closing the molds 32a and 32b can be accelerated compared to when the parison 33 is supplied between the molds 32a and 32b with the mold unit 32 positioned horizontally relative to the central axis 36a (i.e., with the mold unit 32 positioned at the 3 o'clock position). This has the advantage of allowing for a longer time for blow molding after mold closing and for the mold unit 32 to rotate at a higher speed.

[0071] On the other hand, when the mold unit 32 is positioned diagonally upward from the central axis 36a, the parison 33 is supplied between the molds 32a and 32b in an inclined state. In this case, the parison 33 is more likely to contact the first mold 32a before the second mold 32b, making the application of the present invention particularly significant. The inclination of the parison 33 relative to the vertical direction is, for example, 15 to 75 degrees, preferably 30 to 60 degrees, and more preferably 40 to 50 degrees. Specific examples of this inclination include 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, and 75 degrees, and may be in a range between any two of the values ​​exemplified here.

[0072] Blow molding is performed by sandwiching the parison 33 between the first and second molds 32a, 32b, closing the first and second molds 32a, 32b, and then blowing a pressurized fluid (e.g., air) into the parison 33 located in the cavity 35. This process is preferably performed with the parison 33 in close contact with the second mold 32b by vacuum suction. In this case, the parison 33 is expanded by the pressurized fluid while positioned closer to the second mold 32b. This makes the first opposing portion 33c more likely to be stretched than the second opposing portion 33d, further reducing circumferential non-uniformity in the wall thickness of the inner preform 14. The pressurized fluid is preferably blown in by inserting a blow pin (not shown) that penetrates the second mold 32b into the connecting portion 34c and blowing the pressurized fluid through the blow pin.

[0073] After blow molding, the first and second molds 32a, 32b can be opened, and the molded bodies 34 formed by blow molding can be removed from the first and second molds 32a, 32b. Adjacent molded bodies 34 are connected to each other via burrs 37 to form a molded body unit 39, so that by gripping and pulling a part of the molded body unit 39, a large number of molded bodies 34 can be successively removed from the first and second molds 32a, 32b. After removal, the burrs 37 and connecting portions 34c can be cut off from the molded body unit 39, thereby obtaining the inner preforms 14.

[0074] 4. Mold Unit 32 of Second Embodiment A mold unit 32 of a second embodiment of the present invention will be described with reference to Figure 13. This embodiment is similar to the first embodiment, and the details described in the first embodiment can also be applied to this embodiment as long as they do not contradict the spirit of the first embodiment. The following description will focus on the differences from the first embodiment.

[0075] In this embodiment, the first mold 32a is provided with a third protruding portion 32a4. The third protruding portion 32a4 is provided downstream of the second protruding portion 32a3. The third protruding portion 32a4 is higher than the second protruding portion 32a3. A gap 32a5 is provided between the second protruding portion 32a3 and the third protruding portion 32a4.

[0076] In the mold unit 32 of the first embodiment, the parison 33 is supplied between the first and second molds 32a, 32b in an inclined state so that it approaches the first mold 32a as it proceeds downstream, as shown in Figure 12. In this case, the parison 33 is more likely to come into contact with the first mold 32a first at the second protrusion 32a3 and be cooled.

[0077] On the other hand, in this embodiment, the first mold 32a has a third protruding portion 32a4 that is higher than the second protruding portion 32a3 and is provided downstream of the second protruding portion 32a3, so that the parison 33 comes into contact with the third protruding portion 32a4 first. This separates the parison 33 from the first mold 32a, preventing the parison 33 from contacting the second protruding portion 32a3. The third protruding portion 32a4 is preferably higher than the first protruding portion 32a2, which prevents the parison 33 from contacting the first protruding portion 32a2.

[0078] Although the third opposing portion 33e of the parison 33 facing the third protrusion 32a4 is cooled by contact with the third protrusion 32a4, since the third protrusion 32a4 is located outside the pinch-off portion 32g, the impact on molding caused by the cooling of the third opposing portion 33e is relatively small.

[0079] It is preferable that the second mold 32b be provided with a recess 32b4 at a position opposite the third protruding portion 32a4 to avoid interference with the third protruding portion 32a4.

[0080] (Third Aspect) 1. First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

[0081] 1-1. Structure of the container 10 <Basic structure> As shown in Figures 14 to 17, the container 10 of the first embodiment of the present invention includes a container body 2 and a spout attachment member 8. The container 10 is a bottle-shaped container that can hold beverages, seasonings, etc. The container 10 may be a single-walled container or a double-walled container. The description of the structure of the container 10 when the container 10 is a double-walled container is the same as the description in "1. Structure of the double container 1" in the first and second aspects.

[0082] 1-2. Manufacturing Method of Container 10 The container body 2 can be manufactured by a method including a biaxially stretch blow molding process in which a preform 15 shown in Fig. 19 is biaxially stretch blow molded. In addition, the container 10 can be manufactured by attaching the mouth attachment member 8 to the container body 2.

[0083] <Configuration of Inner Preform 14 , Outer Preform 13 , and Preform 15 > The preform 15 includes the inner preform 14 that will become the inner bag 4 and the outer preform 13 that will become the outer shell 3 .

[0084] As shown in Fig. 18, the inner preform 14 is cylindrical with a bottom, and includes a mouth 14a, a body 14b, and a bottom 14c. A protrusion 14d is provided on the mouth 14a. As shown in Fig. 19, the protrusion 14d is a portion of the preform 15 that protrudes from the open end 13f of the outer preform 13. The protrusion 14d does not deform during molding, and becomes the protrusion 4c in its original shape. The protrusion 14d is provided with an engaging portion 14m that becomes the engaging portion 4m. The bottom 14c is provided to close the lower end of the body 14b.

[0085] 18, the outer preform 13 is cylindrical with a bottom and includes a mouth 13a, a body 13b, and a bottom 13c. The bottom 13c is provided so as to close the lower end of the body 13b. The bottom 13c is provided with an annular protrusion 13d.

[0086] 19, a preform 15 can be formed by covering the inner preform 14 with the outer preform 13. In the preform 15, the mouth portion 14a faces the mouth portion 13a, and the body portion 14b faces the body portion 13b.

[0087] The mouth portions 13a and 14a become the mouth portion 15a of the preform 15, the body portions 13b and 14b become the body portion 15b of the preform 15, and the bottom portions 13c and 14c become the bottom portion 15c of the preform 15. The body portion 15b and the bottom portion 15c (in this embodiment, the portion closer to the bottom portion 15c than the flange 15e) are primarily stretched in the biaxial stretch blow molding. The mouth portion 15a is hardly deformed during molding and becomes the mouth portion 5 of the container body 2. The above-described content regarding the configuration included in the mouth portion 5 can also be applied to the configuration included in the mouth portion 15a, as long as it does not contradict the intent thereof.

[0088] <Materials and Manufacturing Methods of the Inner Preform 14, the Outer Preform 13, and the Preform 15> The inner preform 14 and the outer preform 13 can be formed from a thermoplastic resin such as polyester (e.g., PET) or polyolefin (e.g., polypropylene, polyethylene). The outer preform 13 can be formed by direct blow molding or injection molding. The inner preform 14 is formed by direct blow molding using a molten cylindrical parison. Direct blow molding has the advantage of easily achieving thinner walls and multi-layered structures compared to injection molding. A seal portion is formed on the bottom 14c of the inner preform 14 formed by direct blow molding, by welding the inner surfaces of the parison together. This seal portion has relatively low strength and is prone to tearing during biaxial stretch blow molding. Therefore, to increase the strength of the seal portion, it is preferable that the seal portion be a protruding seal portion 14t that protrudes from the bottom 14c of the inner preform 14.

[0089] <Biaxially stretched blow molding process> The biaxially stretched blow molding process will be described using Figures 20 to 26. In the biaxially stretched blow molding process, the preform 15 is attached to the blow core 21 so that the insertion portion 21b of the blow core 21 is positioned within the preform 15, and the preform 15 is then biaxially stretched blow molded into the shape of the container body 2.

[0090] In one example, the biaxial stretch blow molding process includes a mounting step, a heating step, and a stretching step. Each step will be described below.

[0091] <Attachment Process> In the attachment process, as shown in Figures 20 to 22, the preform 15 is attached to the blow core 21 so that the insertion portion 21b of the blow core 21 is positioned within the preform 15. The blow core 21 has a base 21a, an insertion portion 21b, and a through hole 21c. The insertion portion 21b is provided so as to protrude from the base 21a. The insertion portion 21b is inserted into the preform 15. The insertion portion 21b is tapered, making it easier to insert the insertion portion 21b into the preform 15. In addition, the insertion portion 21b is provided with an expanded diameter portion 21e, and the gap between the insertion portion 21b and the preform 15 is narrowed at the expanded diameter portion 21e.

[0092] As shown in Figure 22, the base 21a abuts against the open end 15f of the preform 15. The open end 15f is also the open end of the inner preform 14. As shown in Figure 21, an expanded diameter portion 14n is provided at the open end 15f. The reduced diameter portion 14o between the expanded diameter portion 14n and the engaging portion 14m has a smaller inner diameter than the expanded diameter portion 14n and the engaging portion 14m. The reduced diameter portion 14o has the smallest inner diameter of all the protruding portions 14d.

[0093] In this embodiment, the preform 15 is composed of an inner preform 14 and an outer preform 13 that covers it, and the insertion portion 21b is inserted into the inner preform 14. The inner preform 14 is a direct blow molded article, and the inner preform 14 faces the insertion portion 21b. Therefore, the portion of the preform 15 that faces the insertion portion 21b (i.e., the inner preform 14) is the direct blow molded article. In the following description, the "inner preform 14" can be read as "direct blow molded article" as appropriate.

[0094] Incidentally, when the inner preform 14 is formed by direct blow molding, the outer surface shape of the inner preform 14 is defined by a mold and therefore has high precision, but the inner surface shape of the inner preform 14 is not defined by a mold and therefore tends to vary greatly in the inner surface shape of the inner preform 14. For this reason, the inner diameter of the inner preform 14 also tends to vary greatly.

[0095] Here, the closest portion 41 is the portion where the gap between the insertion portion 21b and the inner preform 14 is smallest when the preform 15 is attached to the blow core 21. The closest portion 41 is made up of a component portion 41a on the inner preform 14 side and a component portion 41b on the blow core 21 side. In this embodiment, as shown in Figures 21 and 22, the closest portion 41 is the portion where the expanded diameter portion 21e and the reduced diameter portion 14o face each other, and the reduced diameter portion 14o and the expanded diameter portion 21e are the component portions 41a and 41b. Unless otherwise specified, the dimensions of the preform 15 and the blow core 21 refer to the dimensions when no external force is applied to the preform 15 and the blow core 21 (that is, when the preform 15 and the blow core 21 are separated, as shown in Figure 21).

[0096] For example, when a large number of inner preforms 14 are manufactured under the condition that the reference dimension of the inner diameter Di of the inner preform 14 in the component portion 41a is 27.5 mm, some inner preforms 14 will be manufactured with Di both smaller and larger than 27.5 mm. Typically, a predetermined tolerance is set so that those with Di that are too small or too large will be deemed defective. Di is measured for each inner preform 14, and those with a deviation from the reference dimension that is within the tolerance range are deemed to be good products, while those outside the tolerance range are deemed to be defective products. While a smaller tolerance has the advantage of increasing the uniformity of good products, it also increases the proportion of products deemed to be defective, thereby reducing the yield. Therefore, the tolerance is set by taking into consideration the balance between the uniformity of good products and the yield.

[0097] In direct blow molding, the variation in Di is likely to be large, so if the tolerance is set to the same level as in injection molding, the yield will be too low, and the tolerance must be set to a certain degree, for example, ±0.2 mm. In this case, the minimum allowable value of the inner diameter Di is 27.3 mm, and the maximum allowable value of the inner diameter Di is 27.7 mm. The minimum allowable value and maximum allowable value are the minimum and maximum values, respectively, when the tolerance is taken into consideration. The minimum allowable value and maximum allowable value of the inner diameter Di will be referred to as Dmin and Dmax hereinafter.

[0098] If the outer diameter of the insertion portion 21b at the component part 41b is Db, in this embodiment, Db is set so that Db > Dmin. In conventional design concepts, the outer diameter of the insertion portion of the blow core is determined so that the blow core does not interfere with the preform, so the outer diameter Db is set so that Db < Dmin. Therefore, the blow core is not press-fitted into the preform.

[0099] On the other hand, when using an inner preform 14 formed by direct blow molding, if Db<Dmin, and Di is close to Dmax, the gap between the constituent parts 41a, 41b becomes too large, and the air blown in during biaxial stretch blow molding leaks out from the gap, making the internal pressure applied to the preform 15 insufficient and causing molding defects. Therefore, in this embodiment, Db is made larger than the dimension derived from conventional design concepts, so that Db>Dmin, thereby suppressing molding defects.

[0100] Among the many non-defective inner preforms 14 manufactured during mass production (hereinafter referred to as "non-defective mass-produced products"), some have Di less than Db, and for such inner preforms 14, the inserting portion 21b is press-fitted into the inner preforms 14. That is, the inserting portion 21b is inserted into the inner preforms 14 while the constituent portion 41b on the blow core 21 side presses and spreads the constituent portion 41a on the inner preform 14 side. On the other hand, when Db < Dmax, the non-defective mass-produced products may include those for which Di > Db. In such cases, the inserting portion 21b is not press-fitted into the inner preforms 14, and a gap is formed between the constituent portions 41a, 41b. In one example, Db = 27.5 mm. In this case, the inserting portion 21b is press-fitted into inner preforms 14 for which Di is 27.4 mm, and the inserting portion 21b is not press-fitted into inner preforms 14 for which Di is 27.6 mm. However, even in this case, the gap between the constituent parts 41a and 41b is small, so molding defects are suppressed.

[0101] If the average value of Dmin and Dmax is the intermediate value Dmid, then Db is preferably set so that Db≧Dmid or Db>Dmid. In the above example, Dmid is 27.5 mm, and Db is set to, for example, 27.6 mm. In this case, even if Di is close to Dmax, the gap between the components 41a and 41b becomes relatively small, further suppressing molding defects.

[0102] Preferably, Db is set so that Db≧Dmax or Db>Dmax. In the above example, Dmax is 27.7 mm, so Db is set to, for example, 27.8 mm. In this case, regardless of the value of Di, no gap is formed between the components 41a and 41b, further suppressing molding defects.

[0103] If (Dmax - Dmin) is the allowable dimensional difference Ddif, Ddif is, for example, 0.20 to 1.0 mm, and preferably 0.30 to 0.60 mm. Specifically, Ddif is, for example, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, or 1.00 mm, or may be in a range between any two of the values ​​exemplified here.

[0104] If (Db - Dmin) is the maximum interference amount Pmax, Pmax is, for example, 0.01 to 1.0 mm. Pmax refers to the amount of interference between the components 41a and 41b when Di is Dmin. Specific examples of Pmax are 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, and 1.00 mm, and may be in a range between any two of the values ​​exemplified here.

[0105] Alternatively, Pmax is α×Ddif. α is, for example, 0.05 to 2. When Db=Dmid, α=0.5, and when Db=Dmax, α=1. Specific examples of α include 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0, and may be in a range between any two of the values ​​exemplified here.

[0106] The inner preform 14 preferably includes a polyolefin layer. If the inner preform 14 is formed of a highly rigid resin such as PET, the inner preform 14 may not deform sufficiently when inserting the insertion portion 21b, making it difficult to insert the insertion portion 21b or to pull out the insertion portion 21b from the inner preform 14. Therefore, it is preferable to provide a layer of a resin with relatively low rigidity such as polyolefin. The polyolefin layer is preferably provided in the innermost layer of the inner preform 14. This is because the innermost layer is the layer that comes into contact with the insertion portion 21b when the insertion portion 21b is press-fitted, and therefore it is desirable for the innermost layer to be easily deformed.

[0107] The ratio of the polyolefin layer (or the total of multiple polyolefin layers if multiple polyolefin layers are provided) to the thickness of the inner preform 14 at the component part 41a is, for example, 50 to 100%, preferably 80 to 100%, and specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100%, or may be in the range between any two of the numerical values ​​exemplified here. Among the layers constituting the inner preform 14, layers other than the polyolefin layer include gas barrier layers such as EVOH and nylon.

[0108] The thickness of the inner preform 14 at the component portion 41a is, for example, 0.40 to 1.20 mm, preferably 0.50 to 1.00 mm, specifically, for example, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, or 1.20 mm, or may be in a range between any two of the values ​​exemplified here.

[0109] The component part 41 a is preferably provided on the protruding part 14 d because the periphery of the protruding part 14 d is not covered by the outer preform 13 and therefore the deformation of the inner preform 14 is not hindered by the outer preform 13.

[0110] <Heating Process> The heating process can be performed using a heating device 45 shown in FIG. 23. In the heating process, the preform 15 is heated and softened to a softened state. In one example, the heating process can be performed by placing the preform 15 in proximity to a heater 42 while the preform 15 is attached to a blow core 21, as shown in FIG. 23. The heating process is performed by heating the body portion 15b and bottom portion 15c while the flange 15e provided on the preform 15 is covered with a heat shield 43. This softens the body portion 15b and bottom portion 15c. On the other hand, the flange 15e and the mouth portion 15a covered with the heat shield 43 receive little or no heat from the heater 42 and are not softened. In one example, the preform 15 can be heated while being rotated. In one example, the heater 42 is composed of multiple rod-shaped heaters arranged along the side of the preform 15, but other configurations are also possible.

[0111] <Stretching Step> The stretching step can be performed using a blow molding device 46 shown in Figures 24 to 26. The blow molding device 46 includes a molding die 23, a bottom support die 22, and a stretching rod 25. In the stretching step, the softened preform 15 is stretched to form the shape of the container body 2. In one example, the stretching step includes a first stretching step and a second stretching step.

[0112] <First Stretching Step> In the first stretching step, the preform 15 is stretched along a first axial direction (i.e., the vertical direction). The first axis is, for example, a direction parallel to the central axis C of the mouth portion 5, i.e., the vertical direction in FIG. 24. In one example, this step can be performed by setting the heated preform 15 in a molding die 23 as shown in FIG. 24, and then, as shown in FIGS. 25 and 26, supporting the bottom 15c of the preform 15 with a bottom support die 22, pressing a stretch rod 25 inserted through a through hole 21c in the blow core 21 against the inner bottom surface of the inner preform 14 to stretch it. At this time, it is preferable to retract the bottom support die 22 in synchronization with the extension of the stretch rod 25. This allows the preform 15 to be stably stretched.

[0113] The preform 15 can be transferred from the heating device 45 to the blow molding device 46 while supported by the blow core 21. The molding die 23 is composed of a split mold that can be opened and closed, and includes a cavity surface 23a that corresponds to the outer surface shape of the container body 2, and a flange accommodating portion 23b that can accommodate the flange 15e. The preform 15 is set in the molding die 23 so that the flange 15e is disposed within the flange accommodating portion 23b. The first stretching step can be performed in a state where the flange 15e is pressed against an opposing surface 23c that faces the flange 15e in the first axial direction.

[0114] <Second Stretching Step> In the second stretching step, air is blown into the inner preform 14 from the state shown in Fig. 26 to stretch (i.e., expand) the preform 15 in the second axial direction (i.e., the lateral direction) and shape it into the shape of the cavity surface 23a, thereby obtaining the container body 2 shown in Fig. 18. Air can be blown in through the through holes 21c provided in the blow core 21.

[0115] 2. Second Embodiment A second embodiment of the present invention will be described using Figures 27 to 30. This embodiment is similar to the first embodiment, and the content described in the first embodiment can also be applied to this embodiment as long as it does not contradict the spirit of the first embodiment. This embodiment differs mainly from the first embodiment in the shape of the blow core 21. The following description will focus on these differences.

[0116] As shown in Figure 27, the blow core 21 of this embodiment has an expanded diameter portion 21e at the base end of the insertion portion 21b. As shown in Figure 30, when the preform 15 is attached to the blow core 21, the gap between the insertion portion 21b and the inner preform 14 is minimized at the expanded diameter portion 21e, so the expanded diameter portion 21e and the portion of the inner preform 14 facing the expanded diameter portion 21e become the constituent portions 41b and 41a that make up the closest portion 41. In this embodiment, the expanded diameter portion 14n of the inner preform 14 faces the expanded diameter portion 21e, so the expanded diameter portion 14n and the expanded diameter portion 21e become the constituent portions 41a and 41b. Because the expanded diameter portion 14n is provided at the open end 15f, the inner diameter Di of the inner preform 14 at the constituent portion 41a matches the inner diameter of the inner preform 14 at the open end 15f. Further, the outer diameter Db of the insertion portion 21b at the component portion 41b coincides with the outer diameter of the expanded diameter portion 21e.

[0117] A tapered portion 21f is provided on the tip side of the expanded diameter portion 21e. The tapered portion 21f is provided so that the expanded diameter portion 21e tapers toward the tip. When the inner diameter at the open end 15f is smaller than the outer diameter of the expanded diameter portion 21e (i.e., when Di<Db), when the insertion portion 21b is inserted into the inner preform 14, the open end 15f abuts against the tapered portion 21f, as shown in Figure 29. When further force is applied to the insertion portion 21b from this state, the opening end 15f is expanded in diameter along the tapered portion 21f, as shown in Figure 30, and the insertion portion 21b is press-fit.

[0118] With this configuration, air leakage from between the component parts 41a, 41b is suppressed, thereby suppressing molding defects. Furthermore, since the component part 41a is located at the opening end 15f, the inner preform 14 is likely to expand in diameter at the component part 41a. Furthermore, since the opening end 15f is expanded in diameter along the tapered portion 21f, the inner preform 14 is likely to expand in diameter at the component part 41a. Therefore, in this embodiment, it is easy to increase the maximum interference amount Pmax defined by (Db - Dmin), thereby further suppressing air leakage.

[0119] The insertion portion 21b can be pressed into the inner preform 14 at any timing before the completion of (preferably before the start of) the step of blowing air into the inner preform 14. In one example, in the first stretching step, as shown in Fig. 25, the insertion portion 21b can be pressed into the inner preform 14, thereby pressing the flange 15e against the opposing surface 23c.

[0120] 3. Other Embodiments In the above embodiment, the preform 15 is a two-body structure of the inner preform 14 and the outer preform 13, but it may also be an integrated structure. In this case, the entire preform 15 is made up of a direct blow molded article. In addition, in this case, the description of the inner preform 14 in the above embodiment can be read as a description of the preform 15, as long as it does not contradict the spirit of the description.

[0121] 1: double container, 2: container body, 3: outer shell, 3a: opening end, 3l: cam rail, 3m: groove, 4: inner bag, 4c: protrusion, 4c1: protruding tube, 4c2: engaging protrusion, 4c5: annular protrusion, 4c8: tapered surface, 4d: inner bag body, 4g: protrusion, 4m: engaging portion, 4v: abutting protrusion, 4va: abutting projection, 4vb: intermediate portion, 5: mouth, 5b: flange, 5c: opening end, 6: body, 6b: shoulder, 6c: body body, 7: bottom, 8: mouth attachment member, 8a: cap, 10: container, 13: outer preform, 13a: mouth, 13b: body, 13c: bottom, 13d: annular protrusion, 13e: flange Langing portion, 13f: opening end, 13m: groove, 14: inner preform, 14a: mouth, 14b: body, 14c: bottom, 14d: protruding portion, 14g: convex rib, 14m: engaging portion, 14n: enlarged diameter portion, 14o: reduced diameter portion, 14s: seal portion, 14t: protruding seal portion, 14v: abutting convex portion, 15: preform, 15a: mouth, 15b: body, 15c: bottom, 15e: flange, 15f: opening end, 21: blow core, 21a: base, 21b: insertion portion, 21c: through hole, 21e: enlarged diameter portion, 21f: tapered portion, 22: bottom support mold, 23: molding mold, 23a: cavity surface, 23b: flange Lunge accommodating portion, 23c: opposing surface, 25: extension rod, 31: cam mechanism, 32: mold unit, 32a: second mold, 32a1: first cavity, 32a2: first protrusion, 32a3: second protrusion, 32a4: third protrusion, 32a5: gap, 32b: second mold, 32b1: second cavity, 32b2: first protrusion, 32b3: second protrusion, 32b4: recess, 32d: second compression portion, 32d1: base, 32d2: inclined portion, 32d3: tip, 32e: second compression portion, 32e1: base, 32e2: inclined portion, 32e3: tip, 32f: first pinch-off portion, 32g: second pinch-off part, 32h: hinge part, 33: parison, 33a: first compressed part, 33b: second compressed part, 33c: first opposed part, 33d: second opposed part, 33e: third opposed part, 34: molded body, 34a: second preform constituent part, 34a1: mouth part, 34b: second preform constituent part, 34 b1: Mouth part, 34c: Connecting part, 34d: First protruding seal part, 34e: Second protruding seal part, 35: Cavity, 35f: Bottom forming part, 35g: Bottom forming part, 35h: Main body part, 35i: Trunk forming part, 35j: Trunk forming part, 35k: Symmetrical surface, 35l: Mouth forming part, 35m: Mouth forming part,35n: cavity central axis, 36: rotary blow molding machine, 36a: central axis, 36b: support, 36c: rotary base, 37: burr, 38: head, 39: molded body unit, 41: closest part, 41a: component part, 41b: component part, 42: heater, 43: heat shield part, 45: heating device, 46: blow molding device, C: central axis, CL1: first clearance, CL2: second clearance, D1: distance, D2: distance, Db: outer diameter, Di: inner diameter, Di1: outer diameter, Di2: outer diameter,

Claims

1. A method for manufacturing a preform for biaxially stretched blow molding, comprising: a blow molding step; in the blow molding step, a molten cylindrical parison is blow molded using a mold unit to form a molded body having a preform component that constitutes the preform; the preform has a protruding seal portion that protrudes from the bottom of the preform; the mold unit comprises first and second molds configured to be openable and closable; the parison is supplied between the first and second molds; the first mold has a first cavity, and the second mold has a second cavity; the first and second cavities are combined to form an outer surface of the cavity having a shape corresponding to the outer surface of the molded body; the mold unit comprises a compression section; the compression section is configured to sandwich and compress the parison between the first and second molds, thereby closing it to form a portion that becomes the protruding seal portion; in the blow molding step, the parison comes into contact with the first mold before the second mold; A method according to claim 1, wherein a volume of a first cavity is larger than a volume of a second cavity in a bottom forming portion of the cavity that forms a portion that will become a bottom of the preform.

2. A method according to claim 1, wherein, if the portion of the cavity that forms the mouth of the preform is defined as the mouth forming portion, in a cross section passing through the cavity central axis that passes through the centers of the bottom forming portion and the mouth forming portion and perpendicular to the longitudinal direction of the compression portion, the bottom forming portion has a plane of symmetry, the compression portion is arranged to protrude from the bottom forming portion, and the base of the compression portion is arranged on the second mold side of the plane of symmetry.

3. A method according to claim 1, wherein the blow molding is rotary blow molding in which a molten parison is blown while a plurality of the mold units are revolved, the parison is continuously supplied to the plurality of mold units along the circumferential direction of a circle formed by the trajectory of the revolution, and when the first and second molds are closed, the first mold is positioned closer to the center of the revolution than the second mold.

4. The method according to claim 1, wherein the molding is constructed by connecting a pair of the preform constituent parts with a connecting part so that the mouths of the preform constituent parts face each other.

5. The method according to claim 1, wherein the blow molding is carried out by injecting pressurized fluid into the parison while the parison is held in close contact with a second mold by vacuum suction.

6. A method for manufacturing a double container, comprising the step of biaxially stretching blow molding a preform formed by placing an outer preform over an inner preform, to manufacture a container body having an inner bag and an outer shell covering the inner bag, wherein the inner preform is manufactured by the method described in any one of claims 1 to 5.

7. A method for manufacturing a preform for biaxially stretched blow molding, comprising a blow molding step, in which a molten cylindrical parison is blow molded using a mold unit to form a molded body, the molded body being configured by first and second preform constituent parts connected by a connecting part so that the mouths of the first and second preform constituent parts face each other, the first and second preform constituent parts each being a part that constitutes the preform, the preform having a protruding seal part that protrudes from the bottom of the preform, the mold unit comprising first and second molds configured to be openable and closable, the parison being supplied between the first mold and the second mold, the first mold having a first cavity and the second mold having a second cavity, the first and second cavities coming together to form an outer surface of the cavity having a shape corresponding to the outer surface of the molded body, the mold unit comprising first and second compression parts, the first and second compression parts being configured to close the parison by sandwiching it between the first and second molds and compressing it to form a part that becomes the protruding seal part, The method, wherein the parison has a larger outer diameter at a first portion facing the first compression section than at a second portion facing the second compression section, and a first clearance between the first and second molds at the first compression section is larger than a second clearance between the first and second molds at the second compression section.

8. A method according to claim 7, wherein the blow molding is rotary blow molding in which a molten parison is blown while a plurality of the mold units are revolved, the parison is continuously supplied to the plurality of mold units along the circumferential direction of a circle formed by the trajectory of the revolution, and the first compression section is positioned upstream of the second compression section in the direction of movement of the parison.

9. A method for manufacturing a double container, comprising a step of biaxially stretching blow molding a preform formed by placing an outer preform over an inner preform, to manufacture a container body having an inner bag and an outer shell covering the inner bag, wherein the inner preform is manufactured by the method described in claim 7 or claim 8.

10. A mold unit for blow molding a molten cylindrical parison to form a molded body, the mold unit comprising first and second molds configured to be able to open and close, the first and second molds comprising first and second cavities, respectively, the first and second cavities coming together to form an outer surface of the cavity having a shape corresponding to the outer surface of the molded body, the molded body being configured by connecting the first and second preform constituent parts with a connecting part so that the mouths of the first and second preform constituent parts face each other, the first and second preform constituent parts each being a part that constitutes a preform for biaxially stretch blow molding, the preform having a protruding seal part protruding from the bottom of the preform, the mold unit comprising first and second compression parts, the first and second compression parts being configured to close the part that becomes the protruding seal part by sandwiching and compressing the parison between the first and second molds, and a first clearance between the first and second molds in the first compression part being larger than a second clearance between the first and second molds in the second compression part.

11. A rotary blow molding machine comprising a plurality of mold units arranged concentrically and configured to be revolvable, wherein the mold units are the mold units described in claim 10.

12. A method for manufacturing a container, comprising a biaxially stretched blow molding process for manufacturing a container body by biaxially stretching blow molding a preform, wherein in the biaxially stretched blow molding process, the preform is attached to a blow core so that an insert portion of the blow core is positioned within the preform, and the preform is biaxially stretched blow molded into the shape of the container body, and the portion of the preform facing the insert portion is a direct blow molded body, and where Dmin is the minimum allowable value of the inner diameter of the direct blow molded body at a constituent part that constitutes the closest part where the gap between the insert portion and the direct blow molded body is smallest when the preform is attached to the blow core, and Db is the outer diameter of the insert portion, Db > Dmin.

13. The method according to claim 12, wherein, when the maximum allowable inner diameter of the direct blow-molded article at the component part is Dmax and the average value of Dmin and Dmax is the midpoint value Dmid, Db≧Dmid.

14. The method of claim 13, wherein Db≧Dmax.

15. A method according to any one of claims 12 to 14, wherein, if the inner diameter of the direct blow molded body at the closest portion is Di, then Db > Di, and the insertion portion is press-fitted into the direct blow molded body.

16. A method for manufacturing a container, comprising a biaxially stretched blow molding step of biaxially stretching a preform to manufacture a container body, wherein in the biaxially stretched blow molding step, the preform is attached to a blow core so that an insert portion of the blow core is positioned within the preform, and the preform is biaxially stretched blow molded into the shape of the container body, and the portion of the preform facing the insert portion is a direct blow molded body, and the insert portion is press-fitted into the direct blow molded body.

17. The method according to claim 16, wherein the insertion section has a tapered section that reduces in diameter toward the tip of the blow core, and the open end of the preform is expanded in diameter along the tapered section during the press-fitting.

18. The method according to claim 12 or claim 16, wherein the direct blow-molded article comprises a polyolefin layer.

19. A method according to claim 12 or 16, wherein the preform is constructed by covering an outer preform on an inner preform, and the inner preform is the direct blow molded article.

20. A method according to claim 19, wherein the inner preform has a protruding portion protruding from the open end of the outer preform, and a component portion constituting the closest portion at which the gap between the insert portion and the direct blow molded article is smallest when the preform is attached to the blow core is provided on the protruding portion.

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