Method for manufacturing preform for biaxial stretch blow molding and method for manufacturing double container

Abstract

To provide a method for manufacturing a preform for biaxial stretch blow molding capable of reducing the nonuniformity of the length in the longitudinal direction of a projecting seal part formed in two preforms when simultaneously forming the two preforms by direct blow molding.SOLUTION: The method for manufacturing a preform for biaxial stretch blow molding includes a blow molding step, in which a molten cylindrical parison is blow molded using a mold unit to form a molded body, wherein the mold unit includes a first mold 32a and a second mold 32b configured to be openable and closable, the mold unit includes a first compression section 32d and a second compression section 32e, the parison has an outer diameter at a first portion facing the first compression section that is larger than an outer diameter at a second portion facing the second compression section, and a first clearance CL1 between the first and second molds in the first compression section is larger than a second clearance CL2 between the first and second molds in the second compression section.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a method for producing a preform for biaxially stretched blow molding, and a method for producing a double-layered container. [Background technology]

[0002] 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 of manufacturing a container body having an inner bag and an outer shell covering it by biaxially stretching blow molding a preform formed by covering an inner preform with an outer preform. Patent Document 1 also discloses a method of simultaneously forming two inner preforms facing each other by direct blow molding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-10741 Summary of the Invention [Problem to be solved by the invention]

[0004] When forming an inner preform 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 relatively low strength, so there is a risk that it will tear 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 to increase the seal strength.

[0005] 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 be non-uniform, so it is desirable that the longitudinal lengths of the protruding seal portions be as uniform as possible.

[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 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. [Means for solving the problem]

[0008] According to the present invention, the following inventions are provided. [1] 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 connecting 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 being parts that constitute 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 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 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] A method as described in [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 the first compression section is arranged upstream of the second compression section in the direction of movement of the parison. [3] A method for manufacturing a double container, comprising a step of biaxially stretching 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 described in [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 the 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 unit described in [4]. [Effects of the Invention]

[0009] 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 lower 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. [Brief explanation of the drawings]

[0010] [Figure 1] This is a perspective view of a double container 1 according to one embodiment of the present invention. The dashed-dotted line in the figure indicates the boundary line where the curvature of the faces that make up the surface shape changes. This is also true for the other figures. [Figure 2] FIG. 2 is a perspective view of the container body 2 in FIG. [Figure 3] FIG. 3 is an exploded perspective view of the vicinity of the mouth portion 5 in FIG. 2. [Figure 4] FIG. 2 is a perspective view of the vicinity of the open end of the outer shell 3. [Figure 5] FIG. 2 is a perspective view showing a state in which the inner preform 14 and the outer preform 13 are separated. [Figure 6] FIG. 1 is a perspective view of a preform 15 formed by covering an outer preform 13 on an inner preform 14. [Figure 7] The figure shows the state in which rotary blow molding is being performed by the rotary blow molding machine 36. [Figure 8] 8A to 8C are a perspective view, a plan view, and a front view, respectively, showing a molded body 34 formed by connecting first and second preform forming parts 34a, 34b with their mouths facing each other via a connecting part 34c. [Figure 9] 9A is a cross-sectional view taken along line AA in FIG. 8B, and FIGS. 9B and 9C are enlarged views of regions B and C in FIG. 9A, respectively. [Figure 10] Fig. 10A is a cross-sectional view of the same cross section as Fig. 9A when the first and second molds 32a, 32b of the mold unit 32 according to the first embodiment of the present invention are closed. Figs. 10B and 10C are enlarged views of regions B and C in Fig. 10A, respectively. Fig. 10D is an enlarged view of region B in Fig. 10B. Fig. 10E is an enlarged view of region E in Fig. 10C. [Figure 11] Fig. 11A is a cross-sectional view of the same cross section as Fig. 9A, showing a state in which the first and second molds 32a and 32b of the mold unit 32 are open. Figs. 11B and 11C are enlarged views of areas B and C in Fig. 11A, respectively. [Figure 12]Fig. 12A is a cross-sectional view of the same cross section as Fig. 9A, showing a state in which a parison 33 is disposed between the first and second molds 32a and 32b of the mold unit 32. Figs. 12B and 12C are enlarged views of areas B and C in Fig. 12A, respectively. [Figure 13] Fig. 13A is a cross-sectional view of a mold unit 32 according to a second embodiment of the present invention, corresponding to Fig. 12A, and Fig. 13B is an enlarged view of region B in Fig. 13A. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes embodiments of the present invention. The 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."

[0012] 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. The double container 1 has a container body 2 and a spout attachment member 8. The spout attachment member 8 is made of a polypropylene resin.

[0013] 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.

[0014] The body 6 is disposed adjacent to the mouth 5 on a side farther from the open end 5c than the mouth 5. The body 6 has a larger outer diameter (in this specification, "outer diameter" means the equivalent circular 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 on the bottom 7 side of 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.

[0015] As shown in Fig. 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.

[0016] <Detailed structure of outer shell 3 and inner bag 4> 2 to 4, inner bag 4 has a protruding portion 4c protruding from open end 3a of outer shell 3. Protruding portion 4c has a protruding tube 4c1, an engaging protrusion 4c2, an annular protrusion 4c5, and an abutting protrusion 4v.

[0017] The annular protrusion 4c5 engages with the spout mounting member 8 in the axial direction. The engaging protrusion 4c2 engages with the spout mounting member 8 in the circumferential direction. The engaging protrusion 4c2 and the annular protrusion 4c5 form the 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.

[0018] 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 nozzle mounting member 8 to climb over the annular protrusion 4c5 and the engaging protrusions 4c2.

[0019] The contact protrusions 4v are positioned to contact the open end 3a and protrude radially outward from the protruding tube 4c1. The contact protrusions 4v contact the open end 3a, 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 are portions that 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 susceptible to deformation than the contact protrusions 4va, and therefore providing the intermediate portions 4vb suppresses deformation of the contact protrusions 4va.

[0020] 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 contacting protrusions 4v tends to be insufficient, and cracks tend to occur in the contacting protrusions 4v during a drop test of the double container 1. However, by providing the contacting protrusions 4v with intermediate portions 4vb, deformation of the contacting projections 4va is suppressed, and cracks in the contacting protrusions 4v are suppressed.

[0021] 3, a ridge 4g is provided on the outer peripheral surface of the inner bag 4 (more specifically, the inner bag main 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.

[0022] 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.

[0023] 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 allows it to come 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.

[0024] <Attaching the mouth attachment member 8 and removing 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.

[0025] 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 action of a 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.

[0026] 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.

[0027] 2. Manufacturing method of double container 1 The container body 2 can be manufactured by biaxially stretching and blow molding a preform 15 shown in Fig. 6. In addition, the double container 1 can be manufactured by attaching a mouth attachment member 8 to the container body 2.

[0028] <Configuration of inner preform 14, outer preform 13, and preform 15> As shown in FIG. 5, the preform 15 includes an inner preform 14 that will become the inner bag 4 and an outer preform 13 that will become the outer shell 3.

[0029] As shown in Fig. 5, the inner preform 14 is cylindrical with a bottom and includes a mouth portion 14a, a body portion 14b, and a bottom portion 14c. The mouth portion 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 portion 14c is provided to close the lower end of the body portion 14b.

[0030] 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 make the seal portion 14s protrude from the bottom portion 14c of the inner preform 14 to form a protruding seal portion 14t, 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 making the seal portion 14s protrude as the protruding seal portion 14t, the area of ​​the sealed surface is increased, and the sealing strength of the seal portion 14s is improved.

[0031] 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.

[0032] 6, a preform 15 can be formed by covering an inner preform 14 with an 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.

[0033] 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 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 configuration included in the mouth portion 5 can also be applied to the configuration included in the mouth portion 15a, as long as it is not contrary to the intent thereof.

[0034] <Materials and manufacturing methods for inner preform 14, outer preform 13, and 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 inner preform 14 can be formed by direct blow molding. The outer preform 13 can be formed by direct blow molding or injection molding.

[0035] <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 facilitates thinner wall thickness compared to injection molding, so forming the inner preform 14 by direct blow molding allows for 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, the resin constituting the gas barrier layer may not reach the open end of the inner preform 14, potentially reducing its 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, direct blow molding uses a cylindrical parison having structures corresponding to the inner layer, gas barrier layer, and outer layer, making it easy to form a gas barrier layer over the entire inner preform 14.

[0036] 3. Manufacturing method of preform for biaxial stretch blow molding Next, a method for manufacturing 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 an 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, an outer preform 13 or a single-layer preform) as long as it does not contradict the spirit of the description.

[0037] The method of this embodiment includes a blow molding step. In this blow molding step, 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 that are concentrically arranged and revolvable. 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.

[0038] 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 produced.

[0039] 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.

[0040] 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 parts 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 are the portions that become 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 a pressurized fluid (e.g., air) into the parison 33 through the connecting part 34c.

[0041] 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.

[0042] 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 the second mold 32b rotating about a 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 second mold 32b may be configured to move parallel to the first mold 32a in the opening and closing direction. Note that, for convenience of illustration, in the figures other than FIG. 7, the first and second molds 32a and 32b are shown to open and close by the parallel movement of the second mold 32b.

[0043] 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.

[0044] 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 portions 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 portion 35h of the cavity 35 other than the compression portions 32d and 32e is disposed between the compression portions 32d and 32e.

[0045] 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 by the first and second compression sections 32d, 32e at the same pressure 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.

[0046] 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, resulting in a non-uniform outer shape of the inner preforms 14. If the outer shape of the inner preforms 14 is non-uniform, the appearance of the inner preforms 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 preforms 14.

[0047] 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 is 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 abutted at the pinch-off sections 32f and 32g, as shown in Figure 10.

[0048] The thickness of the parison 33 is, for example, 0.5 to 2.0 mm (1.0 mm in this embodiment), and preferably 0.7 to 1.5 mm. Specifically, 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), and preferably 0.3 to 0.7 mm, and more preferably 0.4 to 0.6 mm. Specifically, 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.

[0049] 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 within 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, specifically, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and may be in a range between any two of the numerical values ​​exemplified here.

[0050] 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 positioned downstream of the second compression section 32e in the direction of movement of the parison 33 to reduce non-uniformity in the longitudinal length of the protruding seal portion 14t.

[0051] Incidentally, in normal blow molding (e.g., blow molding of containers) that is not a preform, it is possible to reduce unevenness in the longitudinal length of the protruding seal portion 14t by selecting the material, but because the preform is intended to be biaxially stretched blow molded, there are restrictions on the selection of materials for molding the preform. For this reason, the technique of reducing unevenness in the longitudinal length of the protruding seal portion 14t by making the first and second clearances CL1, CL2 different is particularly useful in molding preforms.

[0052] As shown in FIG. 10, the mold unit 32 includes first and second pinch-off portions 32f and 32g. A cavity 35 is disposed between the first and second pinch-off portions 32f and 32g. The first pinch-off portion 32f is disposed adjacent to the first compression portion 32d, and the second pinch-off portion 32g is disposed adjacent to the second compression portion 32e. At the pinch-off portions 32f and 32g, the parison 33 is compressed with a stronger pressure than at the compression portions 32d and 32e, forming a cutting line. The cutting line is thinner than the protruding seal portions 34d and 34e, and can be easily cut. By cutting along the cutting line, the molded body 34 can be separated from the flash 37.

[0053] 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 the first compression section 32d and the first pinch-off section 32f. The second protrusions 32a3 and 32b3 form the second compression section 32e and the second pinch-off section 32g.

[0054] 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. FIG. 12 shows the mold unit 32 in the position indicated by arrow P in FIG. 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 facing portion 33c of the parison 33 facing the first mold 32a is lower than that of the second facing portion 33d facing the second mold, increasing the viscosity and making it more difficult to stretch during blow molding, and in the formed inner preform 14, the wall thickness of the portion formed from the first facing portion 33c is greater than the wall thickness of the portion formed from the second facing portion 33d, resulting in the wall thickness of the inner preform 14 being 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, so 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.

[0055] 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.

[0056] 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).

[0057] The distances D1 and D2 between the bases 32d1 and 32e1 of the compressed portions 32d and 32e and the plane of symmetry 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 have the same value, but D1 and D2 may also have 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.

[0058] The compressed portions 32d, 32e have inclined portions 32d2, 32e2 that incline toward the plane of symmetry 35k as they move away from the bases 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.

[0059] 7, the parison 33 is preferably supplied between the molds 32a, 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, 32b can be accelerated compared to when the parison 33 is supplied between the molds 32a, 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.

[0060] On the other hand, when the mold unit 32 is positioned diagonally upward as viewed 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 come into contact with 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 within a range between any two of the values ​​exemplified here.

[0061] 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 step 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.

[0062] 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 flash 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 flash 37 and connecting portions 34c can be cut off from the molded body unit 39, thereby obtaining the inner preforms 14.

[0063] 4. Mold unit 32 of the second embodiment A mold unit 32 according to a second embodiment of the present invention will be described with reference to Fig. 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 are not contrary to the spirit of the first embodiment. The following description will focus on the differences from the first embodiment.

[0064] 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.

[0065] 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 likely to come into contact with the first mold 32a first at the second protrusion 32a3 and be cooled.

[0066] On the other hand, in this embodiment, the first mold 32a is provided with a third protruding portion 32a4 that is higher than the second protruding portion 32a3 and is located 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.

[0067] Although the third opposing portion 33e of the parison 33 that faces 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.

[0068] The second mold 32b is preferably provided with a recess 32b4 at a position facing the third protruding portion 32a4 to avoid interference with the third protruding portion 32a4. [Explanation of symbols]

[0069] 1:Double container 2: Container body 3: Outer shell 3a: Open end 3l: Cam rail 3m: Concave 4: Inner bag 4c:Protrusion 4c1:Protruding tube 4c2: Engagement convex part 4c5: Circular convex part 4c8: Tapered surface 4d: Inner bag body 4g: Convex strip 4m: Engagement part 4v: Contact convex part 4va: Contact protrusion 4vb: middle part 5: Mouth 5b: Flange 5c: Open end 6: Body 6b:Shoulder 6c: Body 7: Bottom 8: Mouth attachment member 8a: Cap 13: Outer preform 13a: Mouth 13b: Torso 13c: Bottom 13d: Annular convex part 13e: Flange part 13m: Concave 14: Inner preform 14a: Mouth 14b: Torso 14c: Bottom 14d:Protrusion 14g: Convex strip 14m: Engagement part 14s: Seal part 14t: Protruding seal part 14v: Contact convex part 15: Preform 15a: Mouth 15b: Body 15c: bottom 31: Cam mechanism 32: Mold unit 32a: First mold 32a1: First cavity 32a2: 1st protrusion 32a3: Second protrusion 32a4: Third protrusion 32a5: Gap 32b: Second mold 32b1: Second cavity 32b2: 1st protrusion 32b3: Second protrusion 32b4: recess 32d: First compression section 32d1 : Root 32d2: Inclined part 32d3: Tip 32e: Second compression section 32e1 : Root 32e2: Inclined part 32e3 : Tip 32f: First pinch-off section 32g: Second pinch-off section 32h: Hinge part 33: Parison 33a: First compressed part 33b: 2nd compressed part 33c: First opposing part 33d: Second opposing part 33e: Third opposing part 34: Molded body 34a: First preform component 34a1: Mouth 34b: second preform component 34b1: Mouth 34c: Connecting part 34d: First protruding seal portion 34e: Second protruding seal portion 35: Cavity 35f: Bottom forming part 35g: Bottom forming part 35h: Main unit 35i: Body forming section 35j: Body forming section 35k: Symmetry plane 35l: Mouth forming part 35m: Mouth formation part 35n: Cavity central axis 36: Rotary blow molding machine 36a: Central axis 36b: Post 36c: Rotating base 37: Bali 38: Head 39: Molded body unit C: Central axis CL1: First clearance CL2: Second clearance D1: Distance D2 :Distance Di1: Outer diameter Di2: Outer diameter

Claims

1. A method for producing a preform for biaxial stretch blow molding, comprising: A blow molding process is provided. In the blow molding step, a tubular parison in a molten state is blow-molded using a mold unit to form a molded body, The molded body is configured by connecting the first and second preform constituent parts by a connecting part so that the mouth portions of the first and second preform constituent parts face each other, the first and second preform forming parts are parts that form the preform, the preform includes a protruding seal portion protruding from a bottom of the preform; the mold unit includes first and second molds configured to be openable and closable; The parison is fed between a first mold and a second mold; The first mold has a first cavity, and the second mold has a second cavity; the first and second cavities combine to form an outer surface of the cavity having a shape corresponding to the outer surface of the molded body; the die unit includes first and second compression sections; the first and second compression sections are configured to sandwich and compress the parison between the first and second molds to close the parison and form a portion that becomes the protruding seal portion; The parison has an outer diameter at a first portion facing the first compression section that is larger than an outer diameter at a second portion facing the second compression section, The method, wherein a first clearance between the first and second dies in the first compression section is greater than a second clearance between the first and second dies in the second compression section.

2. 10. The method of claim 1, The blow molding is rotary blow molding in which a molten parison is blow-molded while the plurality of mold units are revolved, the parison is continuously supplied to the plurality of mold units along the circumferential direction of the circle formed by the revolution locus; The method, wherein the first compression section is disposed upstream of the second compression section in the direction of movement of the parison.

3. A method for manufacturing a double container, comprising a step of biaxially stretching 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, The inner preform is produced by the method of claim 1 or claim 2.

4. A mold unit for blow molding a molten cylindrical parison to form a molded article, the mold unit includes first and second molds configured to be openable and closable; the first and second molds each having a first and second cavity; the first and second cavities combine to form an outer surface of the cavity that corresponds to the outer surface of the molded body; The molded body is configured by connecting the first and second preform constituent parts by a connecting part so that the mouth portions of the first and second preform constituent parts face each other, the first and second preform forming parts are parts that form a preform for biaxial stretch blow molding, the preform includes a protruding seal portion protruding from a bottom of the preform; the die unit includes first and second compression sections; the first and second compression sections are configured to sandwich and compress the parison between the first and second molds to close the parison and form a portion that becomes the protruding seal portion; The mold unit, wherein a first clearance between the first and second molds in the first compression section is greater than a second clearance between the first and second molds in the second compression section.

5. A rotary blow molding machine, A plurality of mold units are arranged concentrically and configured to be revolvable, A rotary blow molding machine, wherein the mold unit is the mold unit according to claim 4.

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