JP7614489B2 - Double container - Google Patents

Description

The present invention relates to a double container.

Patent document 1 discloses a method for producing a double-walled container by blow molding an inner preform and an outer preform in a stacked state.

WO2004/071887

The inner bag is made up of the inner preform, and the outer shell is made up of the outer preform. As the contents inside the inner bag decrease, the inner bag shrinks, but the outer shell maintains its original state by introducing outside air into the intermediate space between the inner bag and the outer shell through an air inlet hole in the outer shell.

It has been found that in such double-walled containers, it can sometimes be difficult to introduce outside air into the intermediate space between the inner bag and the outer shell.

The present invention was made in consideration of these circumstances, and provides a double container that allows outside air to be smoothly introduced into the intermediate space between the inner bag and the outer shell.

According to the present invention, there is provided a method for manufacturing a double-walled container, the double-walled container comprising a container body having an outer shell and an inner bag, the inner bag being configured to shrink as the content decreases, the outer shell being provided with an air inlet hole for introducing air between the outer shell and the inner bag, the method comprising a heating step and a molding step, in which the heating step heats and softens an assembly formed by covering an inner preform with an outer preform to a softened state, the molding step comprising a blow molding step of blowing air into the inner preform in the softened state, the heating step heating the assembly with a plurality of heaters while rotating the assembly, the plurality of heaters heating the assembly, The method provides a method in which the heaters are arranged in a line along the longitudinal direction of the assembly at a position adjacent to the side, the part of the assembly where the outside air inlet hole is formed is the outside air inlet hole forming part, the heater closest to the outside air inlet hole forming part among the plurality of heaters is the nearest heater, and the heaters other than the nearest heater among the plurality of heaters are other heaters, the output of the nearest heater is divided by the square of the distance from the nearest heater to the outside air inlet hole forming part as V, and the maximum value among the values obtained by dividing the output of each of the other heaters by the square of the distance to the assembly as Wa, where V/Wa is 0.60 or less.

After careful consideration, the inventors found that in the area surrounding the air inlet hole, the outer shell made of the outer preform and the inner bag made of the inner preform are tightly adhered to each other, preventing the smooth introduction of air into the intermediate space between the inner bag and the outer shell. Based on this knowledge, the inventors found that when they reduced the value of V to weaken the heating of the area where the air inlet hole is formed, the adhesion between the outer shell and the inner bag decreased and the introduction of air became easier, leading to the completion of the present invention. It is also possible to reduce the adhesion between the outer shell and the inner bag by weakening the heating of the entire assembly, but in that case, there is a problem that the entire inner bag shrinks after molding, making it easier for the content to decrease. According to the present invention, it is possible to smoothly introduce air into the intermediate space while suppressing the shrinkage of the inner bag.

Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other.
Preferably, the method is as described above, in which V/Wb is 0.70 or less, where Wb is the average of the values obtained by dividing the output of each of the other heaters by the square of the distance to the assembly.
Preferably, the method is as described above, in which V/Wc is 0.95 or less, where Wc is the smallest value obtained by dividing the output of each of the other heaters by the square of the distance to the assembly.
Preferably, in the method described above, the inner preform is made of a material having a larger molding shrinkage rate than the outer preform.
Preferably, in the above-described method, a through hole provided in the outer preform is the outside air introduction hole formation site.
Preferably, in the method described above, the outer preform does not have a through hole that serves as the outside air introduction hole, and the method includes a step of forming an outside air introduction hole by perforating a perforated portion of the outer shell of the container body obtained by the molding step, and the outside air introduction hole formation portion is the portion that will become the perforated portion.
Preferably, in the method described above, the assembly includes a stretched portion that is stretched in the molding process, and the heating is performed so that the temperature of the outside air inlet hole formation portion is lower than the temperature of the portion of the stretched portion that has the highest temperature.

FIG. 1A shows a container body 2 of a double container 1 that can be manufactured by a double container manufacturing method according to one embodiment of the present invention, and FIG. 1B is a bottom view. 2A is a perspective view of the container body 2 of FIG. 1 as viewed from the bottom 7 side, and FIG. 2B is a cross-sectional perspective view of the vicinity of the bottom 7 of the outer shell 3 as viewed from the inside of the container. 3A is a cross-sectional view taken along line AA in FIG. 1B, and FIG. 3B is a cross-sectional view taken along line BB in FIG. 3A. FIG. 2 is a perspective view showing a state in which the inner preform 14 and the outer preform 13 are separated. 5 is a cross-sectional perspective view of the vicinity of a bottom portion 13c of the outer preform 13 of FIG. 4, as viewed from the inside of the outer preform 13. FIG. FIG. 6A is a perspective view of an assembly 15 formed by covering an outer preform 13 on an inner preform 14, and FIG. 6B is a perspective view of FIG. 6A seen from a different angle. 1 is a cross-sectional view showing a state in which an assembly 15 is attached to a mouth support mold 21 and brought close to a heater 31. FIG. 8 is a cross-sectional view showing the state after the mouth support mold 21 with the assembly 15 attached thereto has been moved from the state shown in FIG. 7 to a position between the molding molds 23 and 24. FIG. 9 is a cross-sectional view showing a state after the molding dies 23, 24 are closed and the bottom support die 22 supports the bottom 13c of the outer preform 13 from the state shown in FIG. 8. FIG. 10 is a cross-sectional view showing the state after the support rod 25 is extended and the bottom support mold 22 is retracted from the state shown in FIG. 9 to longitudinally stretch the assembly 15. FIG.

The following describes the embodiments of the present invention. The various features shown in the embodiments below can be combined with each other. In addition, each feature can be an invention independently.

1. Double container 1
First, a double container 1 that can be manufactured by the manufacturing method of a double container according to one embodiment of the present invention will be described. As shown in Fig. 1, the double container 1 that can be manufactured by the method of the present invention includes a container body 2. As shown in Fig. 3A, the container body 2 has an outer shell 3 and an inner bag 4, and is configured so that the inner bag 4 shrinks as the content decreases.

As shown in FIG. 1, the container body 2 has a mouth 5, a body 6, and a bottom 7. The mouth 5 has an engagement portion 5a to which a mouth attachment member such as a cap or a pump can be attached. The engagement portion 5a is a male thread portion when the mouth attachment member is a screw type, and is an annular projection protruding in the circumferential direction when the mouth attachment member is a stopper type. The mouth attachment member preferably has a check valve, which allows the contents to be discharged but prevents outside air from flowing into the container body 2. The mouth 5 is provided to extend from the upper end 6a of the body 6. The mouth 5 is cylindrical. The body 6 has a larger outer diameter (in this specification, "outer diameter" means the circumscribed circle 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 bottom 7 has a central recess 7a provided at the center of the bottom 7 and a peripheral portion 7b surrounding the central recess 7a.

2A, the central recess 7a is provided with a locking portion 7a1, an outside air introduction hole 16, an annular protrusion 7a3, and a positioning recess 7a4. As shown in FIG. 3A, the locking portion 7a1 is formed by inserting a locking protrusion 4a provided on the inner bag 4 into an insertion hole 3a provided on the outer shell 3. The locking portion 7a1 prevents the inner bag 4 from coming off the outer shell 3. The outside air introduction hole 16 is a through hole that penetrates the outer shell 3, and as the inner bag 4 contracts, outside air is introduced into the intermediate space between the outer shell 3 and the inner bag 4 through the outside air introduction hole 16. The locking portion 7a1 and the outside air introduction hole 16 are arranged in the annular protrusion 7a3. The positioning recess 7a4 is used to position the container body 2 in the circumferential direction when printing or the like is performed on the container body 2.

The peripheral portion 7b is provided with a grounding portion 7b1 and a peripheral recess 7b2. The grounding portion 7b1 is the portion that comes into contact with the mounting surface on which the container body 2 is placed when the container body 2 is erected. If the entire peripheral portion 7b were to be the grounding portion 7b1, the central recess 7a would become an airtight space between the container body 2 and the mounting surface when the container body 2 is erected, and there is a risk that the introduction of outside air through the outside air inlet 16 would be hindered. Therefore, the peripheral recess 7b2 is provided as an air passage to prevent the inside of the central recess 7a from becoming an airtight space.

When the contents in the inner bag 4 are discharged by the pump attached to the mouth 5, the inner bag 4 contracts and tries to move away from the outer shell 3. At this time, outside air is introduced into the space between the inner bag 4 and the outer shell 3 through the outside air introduction hole 16. If the outer shell 3 and the inner bag 4 are in close contact near the outside air introduction hole 16, it is difficult for outside air to be introduced into the intermediate space between the outer shell 3 and the inner bag 4. For this reason, in this embodiment, a spacer 9 is placed between the outer shell 3 and the inner bag 4. In this embodiment, the spacer 9 is a protrusion 3b that protrudes from the outer shell 3 toward the inner bag 4. When the spacer 9 is provided, a gap 8 is formed between the outer shell 3 and the inner bag 4 at a position adjacent to the spacer 9, and the gap 8 makes it easier for outside air to be introduced.

However, even when the spacer 9 is provided, the outer shell 3 and the inner bag 4 may come into close contact with each other near the air inlet 16, making it difficult for outside air to be introduced into the intermediate space. Therefore, in the manufacturing method described below, the manufacturing conditions are devised to prevent the outer shell 3 and the inner bag 4 from coming into close contact with each other near the air inlet 16.

As shown in Figures 4 to 6, the container body 2 can be formed by heating the inner preform 14, which will become the inner bag 4, and the outer preform 13, which will become the outer shell 3, to form an assembly 15, and then performing biaxial stretch blow molding on the inner preform 14 and the outer preform 13.

As shown in FIG. 4, the inner preform 14 is a cylindrical member with a bottom, and includes a mouth portion 14a, a body portion 14b, and a bottom portion 14c. A flange 14a1 is provided at the open end of the mouth portion 14a. A positioning pin 14c1 is provided at the bottom portion 14c.

As shown in FIG. 4, the outer preform 13 is a bottomed tubular shape, and includes a mouth portion 13a, a body portion 13b, and a bottom portion 13c. As shown in FIG. 5, the inner surface of the bottom portion 13c of the outer preform 13 is provided with radially arranged protrusions 13c1. The bottom portion 13c is provided with positioning holes 13c2 and through holes 17. As shown in FIG. 6B, the outer surface of the bottom portion 13c is provided with an annular protrusion 13c4. The positioning holes 13c2 and through holes 17 are arranged in the inner region of the annular protrusion 13c4. The outer preform 13 is sized to allow the inner preform 14 to be inserted. The through holes 17 become the outside air introduction holes 16 of the container body 2, so the area where the through holes 17 are provided becomes the outside air introduction hole forming area 41.

When forming the assembly 15, the flange 14a1 is abutted against the open end of the mouth portion 13a, and the positioning pin 14c1 is inserted into the positioning hole 13c2. This positions the inner preform 14 and the outer preform 13 relative to each other. In this state, the mouth portion 14a faces the mouth portion 13a, and the body portion 14b faces the body portion 13b.

The mouth portions 13a and 14a become the mouth portion 15a of the assembly 15, the body portions 13b and 14b become the body portion 15b of the assembly 15, and the bottom portions 13c and 14c become the bottom portion 15c of the assembly 15. As shown in FIG. 7, the body portion 15b and the bottom portion 15c become the stretched portion 15d that will be stretched in the molding process described below.

The inner preform 14 and the outer preform 13 can be formed by direct blow molding, injection molding, or the like, of thermoplastic resins such as polyester (e.g., PET) or polyolefin (e.g., polypropylene, polyethylene). The inner preform is preferably made of a material with a larger molding shrinkage rate than the outer preform. In this case, a gap is formed between the outer shell 3 and the inner bag 4 due to molding shrinkage, making it easier to introduce outside air into the intermediate space between the outer shell 3 and the inner bag 4.

The molding shrinkage rate of the material constituting the inner preform 14 is, for example, 0.5 to 6%, e.g., 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0%, and may be within a range between any two of the numerical values exemplified here. The molding shrinkage rate of the material constituting the outer preform 13 is, for example, 0.1 to 3%, e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, 3.0%, and may be within a range between any two of the numerical values exemplified here. The difference in molding shrinkage is, for example, 0.1 to 5.5%, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5%, and may be within a range between any two of the values exemplified here. The molding shrinkage can be measured in accordance with JIS K7152-4.

In one example, the inner preform 14 is made of polyolefin (e.g., polypropylene), and the outer preform 13 is made of PET. Since polyolefin has a larger molding shrinkage rate than PET, this type of resin configuration makes it easier for a gap to form between the outer shell 3 and the inner bag 4. In addition, by making the inner preform 14 and the outer preform 13 from different materials, welding to each other during blow molding is suppressed.

The inner preform 14 is preferably formed by direct blow molding. Direct blow molding (blow molding using a molten cylindrical parison) makes it easy to form the inner preform 14 with a laminated structure. The outer preform 13 is preferably formed by injection molding. In this case, the through holes 17 can be formed during injection molding, eliminating the need for post-processing.

2. Manufacturing Equipment 40
Next, a manufacturing apparatus 40 that can be used in the manufacturing method of the double container 1 according to one embodiment of the present invention will be described.

As shown in Figures 7 to 10, the manufacturing apparatus 40 includes a mold unit 20 and multiple heaters 31.

The heaters 31 are arranged so as to be aligned along the longitudinal direction of the assembly 15 at positions adjacent to the side of the assembly 15 when the assembly 15 approaches the heater 31. The output of the heaters 31 can be controlled independently of each other. Each heater 31 is preferably rod-shaped and extends in a direction perpendicular to the paper surface of FIG. 7. Of the heaters 31, the one closest to the outside air introduction hole formation portion 41 is referred to as the closest heater 31a, and the remaining heaters are referred to as other heaters 31b (31b1, 31b2, 31b3).

The mold unit 20 includes a mouth support mold 21, a bottom support mold 22, and molding molds 23 and 24.

The mouth support mold 21 is configured to be able to support the mouth 13a of the outer preform 13. An insertion hole 21a is provided in the mouth support mold 21, and a support rod 25 is inserted into the insertion hole 21a. The support rod 25 can be extended and retracted by a drive mechanism (not shown).

The mouth support mold 21 is configured to be movable between position A close to the heater 31 as shown in FIG. 7 and position B between the molding molds 23, 24 as shown in FIG. 8. This makes it possible to carry out a heating process to heat the assembly 15 at position A, and then a molding process to mold the assembly 15 at position B. The mouth support mold 21 is configured to rotate the assembly 15 around the central axis of the mouth 13a. By bringing the assembly 15 close to the heater 31 while rotating it, it is possible to heat the entire circumference of the assembly 15 uniformly. Note that instead of moving the mouth support mold 21, the heater 31 may be moved.

The bottom support mold 22 is driven by a drive mechanism 22c and configured to be movable in the vertical stretching direction (the up and down direction in FIG. 7). The molding molds 23 and 24 can be opened and closed, and each have a cavity surface 23a and 24a. The cavity surfaces 23a and 24a come together to form a cavity having a shape corresponding to the outer shape of the container body 2.

3. Manufacturing Method of Double Container 1 The manufacturing method of the double container 1 according to one embodiment of the present invention includes a heating step and a molding step. The molding step includes a bottom supporting step, a stretching step, and a blow molding step.

<Heating process>
In the heating step, the assembly 15 is heated and softened to a softened state. The heating step can be performed by heating the assembly 15 with a plurality of heaters 31 while rotating the assembly 15.

In one example, as shown in FIG. 7, the assembly 15 can be heated by placing the assembly 15 close to a heater 31 while the assembly 15 is attached to the mouth support mold 21. Since the mouth 15a of the assembly 15 is covered by the mouth support mold 21, the body 15b and bottom 15c (i.e., the stretched portion 15d) are heated.

Here, the output Pa of the nearest heater 31a divided by the square of the distance Da from the nearest heater 31a to the outside air introduction hole formation site 41 (=Pa/(Da) ² ) is defined as V, and the output Pb (Pb1-Pb3) of each of the other heaters 31b1-31b3 is divided by the square of the distance Db (Db1-Db3) to the assembly 15 to obtain values W1-W3 (=Pb/(Db) ² ), with the maximum of W1-W3 being Wa, the average of W1-W3 being Wb, and the minimum of W1-W3 being Wc. Since the density of the radiant energy from a heater is inversely proportional to the square of the distance, the indices V and W1-W3 indicating the degree to which the assembly 15 is heated are calculated by dividing the heater output by the square of the distance.

In this embodiment, the value of V is reduced to make V/Wa 0.60 or less so that the heating of the assembly 15 at the outside air inlet hole formation portion 41 is weakened. Methods for reducing V include reducing the output Pa and increasing the distance Da. When V/Wa is 0.60 or less, the heating of the assembly at the outside air inlet hole formation portion 41 and its vicinity is weakened, so that the degree of adhesion between the outer shell 3 and the inner bag 4 near the outside air inlet hole 16 is reduced, and outside air is smoothly introduced into the intermediate space through the outside air inlet hole 16. In addition, the degree of adhesion between the outer shell 3 and the inner bag 4 is not reduced except in the vicinity of the outside air inlet hole 16, so the reduction in the content volume due to the contraction of the inner bag 4 is suppressed. V/Wa is, for example, 0.10 to 0.60, e.g., 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, and may be within a range between any two of the numerical values exemplified here.

From another perspective, it is preferable that V/Wb is 0.70 or less. In this case, too, the effect of smoothly introducing outside air into the intermediate space while suppressing the contraction of the inner bag 4 is achieved. V/Wb is, for example, 0.10 to 0.70, e.g., 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, and may be within a range between any two of the numerical values exemplified here.

From another perspective, it is preferable that V/Wc is 0.95 or less. In this case, too, the effect of smoothly introducing outside air into the intermediate space while suppressing the contraction of the inner bag 4 is achieved. V/Wc is, for example, 0.10 to 0.95, e.g., 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, and may be within a range between any two of the numerical values exemplified here.

As described above, when the value of V is reduced, the temperature of the outside air inlet hole formation portion 41 decreases. The temperature of the outside air inlet hole formation portion 41 is preferably lower than the temperature of the portion of the stretched portion 15d that has the highest temperature, and more preferably lower than the average temperature of the entire stretched portion 15d.

In addition, before the heating step, the tip of the support rod 25 may be abutted against the inner bottom surface of the inner preform 14. This prevents the softened assembly 15 from shaking.

<Bottom support process>
In the bottom support step, as shown in FIG. 8, the bottom support mold 22 moves toward the bottom 13c of the outer preform 13, and supports the bottom 13c of the outer preform 13 with the bottom support mold 22. The bottom support mold 22 is provided with a recess 22a capable of accommodating the annular convex portion 13c4, and the bottom support mold 22 preferably supports the bottom 13c so that the annular convex portion 13c4 is accommodated in the recess 22a. This prevents the annular convex portion 13c4 and its inner region from being stretched during the blow molding step. The recess 22a is preferably annular. In addition, the bottom support mold 22 preferably includes a recess 22b capable of accommodating the positioning pin 14c1, and supports the bottom 13c so that the positioning pin 14c1 is accommodated in the recess 22b. This prevents the positioning pin 14c1 from interfering with the bottom support mold 22. FIG. 8 shows the molding dies 23, 24 in a closed state, but the molding dies 23, 24 may be closed at any time before the blow molding step, and may be closed after the longitudinal stretching step.

<Longitudinal Stretching Process>
In the longitudinal stretching step, as shown in Figures 8 to 9, the support rod 25 is pressed against the inner bottom surface of the inner preform 14 to stretch it, thereby stretching the assembly 15 in the longitudinal direction (the vertical direction in Figure 9). At this time, it is preferable to move the bottom support mold 22 backward in synchronization with the extension of the support rod 25. This allows the assembly 15 to be stably stretched. Note that the longitudinal stretching step can also be performed in a state in which the bottom 13c is not supported by the bottom support mold 22, so the bottom support step may be performed after the longitudinal stretching step. Also, a recess into which the support rod fits may be provided on the inner bottom surface of the inner preform 14 to make it easier to fix the support rod to the inner preform 14.

<Blow molding process>
In the blow molding process, air is blown into the inner preform 14 from the state shown in Fig. 9 to stretch (i.e. expand) the assembly 15 in the lateral direction and shape it into the shape of the cavity surfaces 23a, 24a. The air can be blown in through the air passage 26 between the mouth support mold 21 and the support rod 25, but for example, an air passage may be provided in the support rod 25 so that the air can be blown out from the side of the support rod 25.

In this embodiment, air is blown in while the bottom 13c of the outer preform 13 is supported by the bottom support mold 22, so stretching of the bottom 13c of the outer preform 13 is suppressed.

The blow molding process can also be performed simultaneously with the vertical stretching process. That is, air can be blown into the inner preform 14 while the assembly 15 is being stretched in the vertical direction. Also, the vertical stretching process can be omitted, and air can be blown in after the bottom support process without stretching the assembly 15 in the vertical direction.

By blow molding, the assembly 15 expands to obtain the container body 2 shown in Figures 1 to 3. The mouth parts 13a and 14a become the mouth part 5, the body parts 13b and 14b become the body part 6, and the bottom parts 13c and 14c become the bottom part 7. The protrusion 13c1, the annular protrusion 13c4, and the through hole 17 become the protrusion 3b, the annular protrusion 7a3, and the outside air introduction hole 16, respectively. During blow molding, the mouth parts 13a and 14a, the annular protrusion 13c4, and the area inside it are hardly deformed, and other parts are mainly deformed. Since the through hole 17 is located in the area inside the annular protrusion 13c4, it is suppressed from being deformed and blocked during blow molding. The flange 14a1 becomes the flange 4b that covers the open end of the mouth part 5 of the container body 2, as shown in Figure 1A.

After blow molding, the positioning hole 13c2 becomes the insertion hole 3a shown in FIG. 3A, and the positioning pin 14c1 is inserted into the insertion hole 3a. The positioning pin 14c1 is then deformed (i.e., crushed or bent) to become the locking protrusion 4a shown in FIG. 3A. This forms the locking portion 7a1 of the container body 2.

4. Other embodiments: In the above embodiment, the through holes 17 provided in the outer preform 13 are configured to become the outside air introduction holes 16 after blow molding, but the outside air introduction holes 16 may be formed by perforating the perforated portion of the outer shell 3 after blow molding without providing a through hole in the outer preform 13 at the portion that will become the outside air introduction hole 16. In this case, the outside air introduction hole formation portion 41 is the portion of the outer shell 3 that will become the perforated portion.
In the above embodiment, the outside air introduction hole 16 is formed in the bottom 7 of the container body 2, but the outside air introduction hole 16 may be formed in the body 6. In this case, the outside air introduction hole formation site 41 is located in the body 13b of the outer preform 13. Also, like heaters 31b1 to 31b3, one of the heaters arranged adjacent to the body 13b of the outer preform 13 becomes the closest heater, and the rest become the other heaters. In this case, the body 13b may or may not have a through hole 17 that becomes the outside air introduction hole 16. Also, it is preferable that a spacer 9 is provided in a position adjacent to the outside air introduction hole formation site 41.
In the above embodiment, the spacers 9 are provided radially, but the spacers 9 may have a different shape. The spacers 9 may be configured by protrusions protruding from the inner bag 4 or may be configured by a separate member. The spacers 9 may be omitted.

According to the above-mentioned method, the outer preform 13 and the inner preform 14 shown in Figs. 4 to 6 were biaxially stretch-blow molded using the manufacturing apparatus 40 shown in Figs. 7 to 10 to produce the container body 2 (capacity 300 mL) shown in Figs. 1 to 3. The heater outputs Pa, Pb and distances Da, Db in the heating process were set as shown in Table 1 to produce the container bodies 2 of the examples and comparative examples. The rotation speed of the assembly 15 in the heating process was 70 rpm. The cross-sectional diameter of each heater was 15 mm, the vertical pitch between adjacent heaters was 17.5 mm, and the diameter of the body 15b of the assembly 15 was 30 mm.

Next, after the container body 2 was filled with the content (water), a pump having a check valve was attached to the mouth portion 5, and the content was discharged by operating the pump. When 30 mL of the content had been discharged, the state of the outer shell 3 was visually observed, and the outside air introduction property was evaluated according to the following criteria.
○: The outer shell 3 does not shrink. ×: The outer shell 3 shrinks.

As shown in Table 1, in the double container of the embodiment in which V/Wa is 0.60 or less, outside air was smoothly introduced into the intermediate space between the outer shell 3 and the inner bag 4. On the other hand, in the double container of the comparative example in which V/Wa is more than 0.60, outside air was not smoothly introduced into the intermediate space between the outer shell 3 and the inner bag 4.

1: Double container 2: Container body 3: Outer shell 3a: Insertion hole 3b: Protrusion 4: Inner bag 4a: Locking protrusion 4b: Flange 5: Mouth 5a: Engagement portion 6: Body 6a: Upper end 7: Bottom 7a: Central recess 7a1: Locking portion 7a3: Annular protrusion 7a4: Positioning recess 7b: Peripheral portion 7b1: Grounding portion 7b2: Peripheral recess 8: Gap 9: Spacer 13: Outer preform 13a: Mouth 13b: Body 13c: Bottom 13c1: Protrusion 13c2: Positioning hole 13c4: Annular protrusion 14: Inner preform 14a: Mouth 14a1: Flange 14b: Body 14c: Bottom 14c1: Positioning pin 15: Assembly 15a: Mouth 15b : Body 15c : Bottom 15d : Stretched portion 16 : Outside air introduction hole 17 : Through hole 20 : Mold unit 21 : Mouth support mold 21a : Insertion hole 22 : Bottom support mold 22a : Recess 22b : Recess 22c : Drive mechanism 23 : Mold 23a : Cavity surface 24 : Mold 24a : Cavity surface 25 : Support rod 26 : Air passage 31 : Heater 31a : Closest heater 31b : Other heaters 31b1 : Other heaters 31b2 : Other heaters 31b3 : Other heaters 40 : Manufacturing device 41 : Outside air introduction hole forming portion

Claims (7)

A method for manufacturing a double container, comprising the steps of:
The double container includes a container body having an outer shell and an inner bag, the inner bag being configured to shrink as the contents decrease ,
The outer shell has an outside air introduction hole for introducing outside air between the outer shell and the inner bag,
The method includes a heating step and a molding step,
In the heating step, an assembly formed by covering the inner preform with the outer preform is heated and softened to a softened state,
the molding step includes a blow molding step of blowing air into the inner preform in the softened state,
In the heating step, the assembly is heated by a plurality of heaters while rotating the assembly;
the heaters are arranged adjacent to the side surfaces of the assembly and aligned along the longitudinal direction of the assembly;
a portion of the assembly where the outside air inlet is formed is defined as an outside air inlet forming portion, and among the plurality of heaters, the heater closest to the outside air inlet forming portion is defined as a nearest heater, and among the plurality of heaters, heaters other than the nearest heater are defined as other heaters,
The output of the nearest heater is divided by the square of the distance from the nearest heater to the outside air introduction hole formation portion, and the value is defined as V.
The maximum value among the values obtained by dividing the output of each of the other heaters by the square of the distance to the assembly is defined as Wa.
A method in which V/Wa is 0.48 or more and 0.53 or less. 2. The method of claim 1 ,
Let Wb be the average of the output of each of the other heaters divided by the square of the distance to the assembly,
A method wherein V/Wb is 0.70 or less. 3. The method of claim 1 or claim 2,
Let Wc be the minimum value among the values obtained by dividing the output of each of the other heaters by the square of the distance to the assembly,
The method wherein V/Wc is 0.95 or less. The method according to any one of claims 1 to 3,
The method of claim 1, wherein the inner preform is made of a material that has a higher mold shrinkage than the outer preform. The method according to any one of claims 1 to 4,
The method, wherein a portion of the outer preform in which a through hole is provided is the outside air introduction hole formation portion. The method according to any one of claims 1 to 4,
The outer preform does not have a through hole serving as the outside air introduction hole, and a process for forming an outside air introduction hole by perforating a perforated portion of the outer shell of the container body obtained by the molding process is provided,
The method, wherein the outside air introduction hole formation portion is a portion that will become the perforated portion. The method according to any one of claims 1 to 6,
The assembly includes a stretched portion that is stretched in the molding process,
The heating is performed so that the temperature of the portion where the outside air introduction hole is formed is lower than the temperature of a portion of the stretched portion that has the highest temperature.