Method of manufacturing double container

Abstract

To provide a method of manufacturing a double container, capable of curbing shrinking of an inner bag in cooling after molding.SOLUTION: A method of manufacturing a double container uses a preform configured by overlaying an outer preform onto an inner preform, wherein: the inner preform includes a polyolefin layer consisting of polyolefin resin containing polyolefin; the outer preform includes an amorphous PET layer consisting of amorphous PET-based resin containing amorphous PET; a temperature range between a crystallization peak temperature and a melting peak temperature of the polyolefin resin is a first temperature range; a temperature range between a softening completion temperature and a crystallization start temperature of the amorphous PET-based resin is a second temperature range; and the preform is heated to an overlapping temperature where the first temperature range and the second temperature range overlap with each other so as to perform biaxial drawing blow molding.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a double container. [Background technology]

[0002] Patent Document 1 discloses a method for producing a double-layered container by biaxially stretching and blow molding an inner preform and an outer preform in a stacked state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2004 / 071887 Summary of the Invention [Problem to be solved by the invention]

[0004] In a reference example in which the inventors used homopolypropylene as the material for the inner preform and amorphous PET as the material for the outer preform, they found that when a double container was produced by biaxially stretching blow molding the inner and outer preforms stacked on top of each other, the inner bag of the double container could shrink when cooled, causing a gap to form between the inner bag and the outer shell, resulting in the content of the inner bag being less than the specified amount.

[0005] The present invention has been made in consideration of the above circumstances, and provides a method for manufacturing a double-layered container that makes it possible to prevent the inner bag from shrinking when cooled after molding. [Means for solving the problem]

[0006] According to the present invention, there is provided a method for manufacturing a double-layered container using a preform formed by covering an inner preform with an outer preform, the inner preform having a polyolefin layer formed of a polyolefin-based resin containing polyolefin, the polyolefin including a propylene-ethylene random copolymer which is a random copolymer of propylene and ethylene, or a homopolypropylene and a low-density polyethylene or a linear low-density polyethylene, the outer preform having an amorphous PET layer formed of an amorphous PET-based resin including amorphous PET, the first temperature range being a temperature range between the crystallization peak temperature and the melting peak temperature of the polyolefin-based resin, and the second temperature range being a temperature range between the softening completion temperature and the crystallization start temperature of the amorphous PET-based resin, the preform is heated to a temperature within an overlapping temperature range where the first temperature range and the second temperature range overlap, and biaxially stretched blow molding is performed.

[0007] In the above Reference Example, an analysis was conducted to determine why the inner bag was prone to shrinkage during cooling after molding, and it was found that this was because, at the molding temperature in the Reference Example, the amorphous PET was in a softened state suitable for molding, but the homopolypropylene was not in a sufficiently softened state. In other words, it was found that molding was performed in a state where the homopolypropylene that constitutes the inner preform was not sufficiently softened, which caused the inner bag to be prone to shrinkage during cooling after molding.

[0008] Further analysis revealed that polyolefins such as homopolypropylene are in a softened state suitable for molding in a first temperature range, amorphous PET is in a softened state suitable for molding in a second temperature range, and both polyolefins and amorphous PET are in a softened state suitable for molding within the overlapping temperature range where the first and second temperature ranges overlap. Furthermore, it was found that because the overlapping temperature range of homopolypropylene and amorphous PET is a very narrow temperature range of about 1°C, it is not easy to mold them at a temperature suitable for both.

[0009] On the other hand, in the method for producing a double layered container of the present invention, the polyolefin contains a propylene-ethylene random copolymer, which is a random copolymer of propylene and ethylene, or a homopolypropylene and a low density polyethylene or a linear low density polyethylene. This allows the overlapping temperature range to be widened by shifting the first temperature range to the lower temperature side. Therefore, compared to the above-mentioned reference example, it is easier to mold at a molding temperature that can bring both the polyolefin and the amorphous PET into a softened state suitable for molding, and as a result, it is possible to suppress the shrinkage of the inner bag during cooling after molding.

[0010] Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other. Preferably, in the method for producing a double container described above, the polyolefin contains a propylene copolymer which is a random copolymer of propylene and ethylene. Preferably, in the method for producing a double container described above, the polyolefin contains homopolypropylene and low-density polyethylene or linear low-density polyethylene. Preferably, in the method for producing a double container described above, the overlapping temperature range is 10°C or higher. [Brief description of the drawings]

[0011] [Figure 1] 1 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. [Diagram 2] FIG. 2 is a perspective view showing a state in which the inner preform 14 and the outer preform 13 are separated. [Diagram 3] FIG. 3A is a perspective view of a preform 15 formed by covering an outer preform 13 on an inner preform 14, and FIG. 3B is a perspective view of FIG. 3A as seen from a different angle. [Figure 4]FIG. 4A is a graph showing the results of differential scanning calorimetry for the propylene-ethylene random copolymer in Example 1, and FIG. 4B is a graph showing the results of differential scanning calorimetry for the amorphous PET in Example 1. [Diagram 5] FIG. 2 is a cross-sectional view showing a state in which a preform 15 is attached to a mouth support mold 21 and brought close to a heater 31. [Figure 6] 6 is a cross-sectional view showing the state after mouth support mold 21 with preform 15 attached thereto has been moved from the state shown in FIG. 5 to a position between molding molds 23 and 24. FIG. [Figure 7] 7 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. 6. FIG. [Figure 8] FIG. 8 is a cross-sectional view showing a state after the support rods 25 are extended and the bottom support mold 22 is retracted from the state shown in FIG. 7 to longitudinally stretch the preform 15. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described. Various features shown in the following embodiments can be combined with each other. Also, each feature can be an invention independently.

[0013] 1. Double container 1 and preform 15 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. 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.

[0014] As shown in FIG. 1, the container body 2 has a mouth 5, a body 6, and a bottom 7. The mouth 5 is a tubular (preferably cylindrical) part having an open end 5c. The mouth 5 has an engagement part 5a to which a mouth attachment member such as a cap or a pump can be attached. The engagement part 5a is a male thread part 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 plug 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 with a flange 5b. The flange 5b can be used to support the mouth 5 when the mouth attachment member is attached to the mouth 5.

[0015] The body 6 is disposed adjacent to the mouth 5 on the side farther from the open end 5c than the mouth 5. In other words, the mouth 5 is provided so as to extend from the upper end 6a of the body 6. 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 body 6 has a shoulder 6b whose outer diameter increases with increasing distance from the mouth 5, and a body main body 6c which is provided on the bottom 7 side of the shoulder 6b and has a substantially constant outer diameter.

[0016] 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 is housed within the outer shell 3 except for the flange 4b. The inner bag 4 is prevented from slipping down into the outer shell 3 by the flange 4b ​​abutting against the open end of the outer shell 3.

[0017] An outside air introduction hole (not shown) is provided in the outer shell 3. The outside air introduction hole is a through hole that penetrates the outer shell 3, and as the inner bag 4 shrinks, outside air is introduced into the intermediate space between the outer shell 3 and the inner bag 4 through the outside air introduction hole, making it possible to shrink the inner bag 4 without shrinking the outer shell 3. The outside air introduction hole may be provided in any of the mouth portion 5, the body portion 6, or the bottom portion 7.

[0018] As shown in Figures 2 to 8, the container body 2 can be formed by covering an inner preform 14, which will become the inner bag 4, with an outer preform 13, which will become the outer shell 3, to form a preform 15, and then heating the inner preform 14 and the outer preform 13 and biaxially stretching blow molding them.

[0019] 2, 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.

[0020] As shown in Fig. 2, the outer preform 13 is a bottomed cylindrical shape, and includes an opening 13a, a body 13b, and a bottom 13c. A positioning hole 13c2 and a through hole 17 are provided in the bottom 13c. As shown in Fig. 3B, an annular protrusion 13c4 is provided on the outer surface of the bottom 13c. The positioning hole 13c2 and the through hole 17 are disposed in the inner region of the annular protrusion 13c4. The outer preform 13 has a size that allows the inner preform 14 to be inserted therein. The through hole 17 serves as an outside air introduction hole for the container body 2.

[0021] 3, when forming the preform 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.

[0022] 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. As shown in Fig. 5, the body portion 15b and the bottom portion 15c become the stretched portion 15d that will be stretched in the molding process described below.

[0023] The inner preform 14 and the outer preform 13 can be formed by direct blow molding, injection molding, or the like of a thermoplastic resin.

[0024] The inner preform 14 includes a polyolefin layer made of a polyolefin-based resin containing polyolefin. The content of polyolefin in the polyolefin-based resin is, for example, 60 to 100% by mass, specifically, for example, 60, 70, 80, 90, or 100% by mass, and may be within a range between any two of the values ​​exemplified here. Examples of polyolefin include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), homopolypropylene (PP), propylene copolymer, cyclic polyolefin (COP), and mixtures thereof.

[0025] The propylene copolymer is a copolymer between propylene and another monomer, and may be a random copolymer or a block copolymer, but is preferably a random copolymer. The propylene copolymer can be obtained by copolymerizing a monomer mixture. The content of propylene in the monomer mixture is, for example, 60 to 99.5 mol%, specifically, for example, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5 mol%, and may be within a range between any two of the numerical values ​​exemplified here. As the monomer to be copolymerized with propylene, ethylene is particularly preferred.

[0026] The inner preform 14 may have a single layer structure or a multilayer structure. In the case of a single layer structure, the inner preform 14 has only the above-mentioned polyolefin layer. In the case of a multilayer structure, the inner preform 14 has a laminated structure of the above-mentioned polyolefin layer and another layer. Examples of the other layer include a gas barrier resin layer and an adhesive resin layer. The adhesive resin layer is used to increase the adhesion between the polyolefin layer and the gas barrier resin layer.

[0027] The gas barrier resin layer is a layer made of a gas barrier resin. In this specification, the gas barrier resin is a resin having an oxygen permeability of 50 cc / (m2) in an environment of 20°C and 65% RH when made into a film having a thickness of 20 μm. 2The oxygen permeability is, for example, 0 to 49 cc / (m 2 ·24 hours ·atm), specifically, for example, 0.01, 0.1, 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 49cc / (m 2 24 hours atm), and may be within a range between any two of the values ​​given as examples here, or any of the values ​​below.

[0028] The gas barrier resin may be composed solely of a resin having high gas barrier properties, such as EVOH or polyamide, or may be a mixed resin of the above resin with another resin.

[0029] The adhesive resin layer is a layer made of an adhesive resin, such as an acid-modified polyolefin resin (e.g., maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene).

[0030] At the center of the inner preform 14 in the longitudinal direction, the ratio of the thickness of the polyolefin layer to the entire wall thickness of the inner preform 14 is, for example, 50 to 100%, specifically, for example, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100%, and may be within a range between any two of the numerical values ​​exemplified here.

[0031] The outer preform 13 has an amorphous PET layer made of an amorphous PET-based resin containing amorphous PET. Amorphous PET is obtained by quenching molten PET (polyethylene terephthalate) to solidify it without crystallizing it. The PET constituting the outer preform 13 can be made amorphous by molding the outer preform 13 at a temperature equal to or higher than the melting peak temperature (about 270 to 280°C) by injection molding or the like, and then quenching it. The content of amorphous PET in the amorphous PET-based resin is, for example, 60 to 100% by mass, specifically, for example, 60, 70, 80, 90, or 100% by mass, and may be within a range between any two of the numerical values ​​exemplified here.

[0032] The outer preform 13 may have a single layer structure or a multi-layer structure. In the case of a single layer structure, the outer preform 13 has only the amorphous PET layer. In the case of a multi-layer structure, the outer preform 13 has a laminated structure of the amorphous PET layer and another layer. Examples of the other layer include the gas barrier resin layer and the adhesive resin layer.

[0033] In this embodiment, the temperature range between the crystallization peak temperature and melting peak temperature of the polyolefin-based resin is defined as a first temperature range, and the temperature range between the softening completion temperature and crystallization start temperature of the amorphous PET-based resin is defined as a second temperature range, and the overlap temperature range where the first temperature range and the second temperature range overlap is 2°C or more.

[0034] FIG. 4A shows an example of a graph obtained by carrying out differential scanning calorimetry (DSC) on a polyolefin resin (graph obtained in Example 1). DSC can be carried out in accordance with JIS K 7121:2012. The horizontal axis of this graph indicates temperature, and the vertical axis indicates endothermic or exothermic amounts. In the first run, the measurement is carried out while raising the temperature of the sample. Polyolefin resins are in a crystalline state at low temperatures, and a melting peak is observed during heating. The temperature of this melting peak is the "melting peak temperature."

[0035] Above the melting peak temperature, the polyolefin resin becomes a liquid state with a very low viscosity. Next, in the second run, the temperature of the liquid polyolefin resin is gradually lowered. At this time, a crystallization peak is observed. The temperature of this crystallization peak is the "peak crystallization temperature." Polyolefin resins tend to become excessively softened at temperatures higher than the peak melting temperature, and tend to be insufficiently softened at temperatures lower than the peak crystallization temperature. For this reason, in the temperature range between the peak crystallization temperature and the peak melting temperature, the polyolefin resin becomes softened and suitable for molding. This temperature range is the first temperature range.

[0036] The crystallization peak temperature of the polyolefin resin is, for example, 80 to 117°C, preferably 90 to 110°C. Specifically, this temperature may be, for example, 80, 85, 90, 95, 100, 105, 110, 115, 116, or 117°C, and may be within a range between any two of the numerical values ​​exemplified here. The melting peak temperature of the polyolefin resin is, for example, 90 to 145°C, preferably 115 to 135°C. Specifically, this temperature may be, for example, 90, 100, 110, 115, 120, 125, 130, 135, 140, or 145°C, and may be within a range between any two of the numerical values ​​exemplified here. The first temperature range is, for example, 5 to 50° C., specifically, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50° C., and may be within a range between any two of the numerical values ​​exemplified here.

[0037] The crystallization peak temperature and melting peak temperature of the polyolefin resin can be adjusted by changing the composition of the polyolefin resin. For example, since the crystallization peak temperature and melting peak temperature of the propylene-ethylene random copolymer are lower than those of homopolypropylene, the crystallization peak temperature and melting peak temperature can be lowered by increasing the content of the propylene-ethylene random copolymer contained in the polyolefin resin.

[0038] When a polyolefin-based resin is a mixture of multiple polyolefins, the peak crystallization temperature and peak melting temperature of the polyolefin-based resin will be values ​​reflecting the peak crystallization temperature and peak melting temperature of each of the multiple polyolefins. For example, when a polyolefin-based resin contains a polyolefin with a low peak crystallization temperature and peak melting temperature, such as LLDPE or LDPE, and homopolypropylene, the peak crystallization temperature and peak melting temperature will be lower than those of homopolypropylene.

[0039] Fig. 4B shows an example of a graph obtained by performing DSC on an amorphous PET resin (graph obtained in Example 1). The explanation of the DSC and the graph is the same as that of Fig. 4A.

[0040] Amorphous PET resins are in an amorphous state at low temperatures, and when heated, the softening onset, softening completion, crystallization onset, and crystallization peak appear in that order. The temperatures at which the softening onset, softening completion, crystallization onset, and crystallization peak appear are the "softening onset temperature," "softening completion temperature," "crystallization onset temperature," and "crystallization peak temperature," respectively.

[0041] The softening onset appears at the temperature equivalent to the glass transition temperature (Tg), and from this point onwards the amount of heat absorbed increases (the negative slope of the DSC curve becomes larger). The softening completion point appears at the temperature at which the amount of heat absorbed stops increasing (in other words, the temperature at which the slope of the DSC curve goes from negative to zero). Between the softening onset and softening completion points, the amorphous PET resin gradually softens. At the softening completion temperature, the amorphous PET resin is in a sufficiently softened state.

[0042] When the amorphous PET resin is further heated, a crystallization onset and a crystallization peak appear. The crystallization onset appears at the temperature at which the amorphous PET resin starts to crystallize, and the slope of the DSC curve increases beyond the crystallization onset. The crystallization peak appears at the temperature at which the crystallization of the amorphous PET resin is completed. At temperatures higher than the crystallization onset temperature, the degree of crystallization of the amorphous PET resin increases, causing it to lose flexibility and resulting in insufficient softening of the amorphous PET resin. For this reason, in the temperature range between the softening completion temperature and the crystallization onset temperature, the amorphous PET resin is in a softened state suitable for molding. This temperature range is the second temperature range.

[0043] The softening completion temperature of the amorphous PET resin is, for example, 70 to 90°C, preferably 75 to 85°C. This temperature is, for example, 70, 75, 80, 85, 90°C, and may be within a range between any two of the numerical values ​​exemplified here. The crystallization start temperature of the amorphous PET resin is, for example, 110 to 130°C, preferably 115 to 125°C. This temperature is, for example, 110, 115, 120, 125, 130°C, and may be within a range between any two of the numerical values ​​exemplified here. The second temperature range is, for example, 30 to 50°C, preferably 35 to 45°C. This temperature is, for example, 30, 35, 40, 45, 50°C, and may be within a range between any two of the numerical values ​​exemplified here.

[0044] In a reference example, the polyolefin resin is made of homopolypropylene, and the amorphous PET resin is made of amorphous PET. In one example, the homopolypropylene has a crystallization peak temperature of about 119°C and a melting peak temperature of about 149°C, so the first temperature range is 119 to 149°C. In one example, the amorphous PET has a softening completion temperature of about 81°C and a crystallization start temperature of about 120°C, so the second temperature range is 81 to 120°C. The overlapping temperature range where the first temperature range and the second temperature range overlap is about 1°C.

[0045] Within the overlap temperature range, both polyolefin resins and amorphous PET resins reach a softened state suitable for molding, so it is desirable to perform molding at a temperature within this overlap temperature range. However, with homopolypropylene and amorphous PET, the overlap temperature range is a very narrow range of approximately 1°C, so it is not easy to mold at a temperature suitable for both.

[0046] The reason why the overlapping temperature range is narrow is that the first temperature range is located on the higher temperature side than the second range, and the overlapping temperature range can be widened by shifting the first temperature range to the lower temperature side. As described above, the crystallization peak temperature and melting peak temperature of the propylene-ethylene random copolymer are lower than those of homopolypropylene, so that the first temperature range can be shifted to the lower temperature side by including the propylene-ethylene random copolymer in the polyolefin resin, thereby widening the overlapping temperature range. The first temperature range may also be shifted to the lower temperature side by adding a polyolefin having a low crystallization peak temperature and melting peak temperature, such as LLDPE or LDPE.

[0047] In the preform 15 of this embodiment, a polyolefin resin is selected so that the overlapping temperature range is 2° C. or more (preferably 10° C.) Therefore, compared to the above-mentioned reference example, it is easier to mold at a molding temperature at which both the polyolefin resin and the amorphous PET resin are in a softened state suitable for molding, and as a result, it is possible to suppress shrinkage of the inner bag 4 during cooling after molding.

[0048] The overlap temperature range is, for example, 2 to 40° C., and preferably 4 to 40° C. This overlap temperature range is specifically, for example, 2, 4, 5, 10, 15, 20, 25, 30, 35, or 40° C., and may be within a range between any two of the numerical values ​​exemplified here, or equal to or greater than any one of them.

[0049] 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.

[0050] As shown in FIGS. 5 to 8, the manufacturing apparatus 40 includes a mold unit 20 and a plurality of heaters 31.

[0051] The heaters 31 are arranged so as to be aligned along the longitudinal direction of the preform 15 at positions adjacent to the side surfaces of the preform 15 when the preform 15 approaches the heaters 31. The outputs of the heaters 31 can be controlled independently of one another. Each heater 31 is preferably rod-shaped and extends in a direction perpendicular to the plane of FIG.

[0052] The mold unit 20 includes a mouth support mold 21, a bottom support mold 22, and molding molds 23 and 24.

[0053] 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).

[0054] The mouth support mold 21 is configured to be movable between position A close to the heater 31 as shown in FIG. 5 and position B between the molding molds 23 and 24 as shown in FIG. 6. Therefore, after performing a heating step of heating the preform 15 at position A, it is possible to perform a molding step of molding the preform 15 at position B. The mouth support mold 21 is configured to rotate the preform 15 around the central axis of the mouth 13a. By moving the preform 15 close to the heater 31 while rotating the preform 15, it is possible to heat the entire circumference of the preform 15 uniformly. Instead of moving the mouth support mold 21, the heater 31 may be moved.

[0055] 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 Figs. 6 to 8). The forming molds 23 and 24 are openable and closable, 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.

[0056] 3. Manufacturing method of double container 1 The method for manufacturing 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.

[0057] <Heating process> In the heating step, the preform 15 is heated and softened to a softened state. The heating step can be performed by heating the preform 15 with a plurality of heaters 31 while rotating the preform 15.

[0058] In one example, as shown in Fig. 5, the preform 15 can be heated by placing the preform 15 close to a heater 31 while the preform 15 is attached to a mouth support mold 21. Since the mouth 15a of the preform 15 is covered by the mouth support mold 21, the body 15b and bottom 15c (i.e., the stretched portion 15d) are heated. Note that, before the heating step, the tip of the support rod 25 may be brought into contact with the inner bottom surface of the inner preform 14. This prevents the softened preform 15 from shaking.

[0059] The heating temperature of the preform 15 is preferably set to a temperature within the above-mentioned overlapping temperature range, which allows both the outer preform 13 and the inner preform 14 to be in a softened state suitable for molding.

[0060] <Bottom support process> In the bottom support step, as shown in Figs. 6 to 7, 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. 7 shows a state in which the molding dies 23, 24 are closed, 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.

[0061] <Longitudinal stretching process> In the longitudinal stretching step, as shown in Figs. 7 and 8, the support rod 25 is pressed against the inner bottom surface of the inner preform 14 to stretch the preform 15 in the longitudinal direction (the vertical direction in Fig. 8). At this time, it is preferable to move the bottom support mold 22 backward in synchronization with the stretching of the support rod 25. This allows the preform 15 to be stably stretched. 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.

[0062] <Blow molding process> In the blow molding process, air is blown into the inner preform 14 from the state shown in Fig. 8 to stretch (i.e. expand) the preform 15 laterally 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.

[0063] In this embodiment, air is blown into the outer preform 13 while the bottom portion 13c is supported by the bottom support mold 22, so that the extension of the bottom portion 13c of the outer preform 13 is suppressed.

[0064] The blow molding process can be performed simultaneously with the longitudinal stretching process. That is, air may be blown into the inner preform 14 while stretching the preform 15 in the longitudinal direction. Also, the longitudinal stretching process may be omitted, and air may be blown into the preform 15 after the bottom supporting process without stretching it in the longitudinal direction.

[0065] The preform 15 expands by blow molding to obtain the container body 2 shown in Fig. 1. The mouth parts 13a, 14a become the mouth part 5, the body parts 13b, 14b become the body part 6, and the bottom parts 13c, 14c become the bottom part 7. During blow molding, the mouth parts 13a, 14a and the annular convex part 13c4 and its inner area are hardly deformed, and other parts are mainly deformed. 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 Fig. 1A. EXAMPLES

[0066] <Reference example 1> According to the above-mentioned method, the container body 2 (capacity 300 mL) shown in FIG. 1 was manufactured by biaxially stretching and blow molding the preform 15 shown in FIG. 2-FIG. 3 using the manufacturing apparatus 40 shown in FIG. 5-FIG. 8. The inner preform 14 was manufactured by injection molding homopolypropylene (type: Novatec, manufactured by Japan Polypropylene Corporation). The outer preform 13 was manufactured by injection molding PET (type: titanium catalyst grade, manufactured by Teijin Ltd.) at 300°C to form the shape of the outer preform, and then quenching to 20°C. The PET in the molten state was made into an amorphous state by quenching.

[0067] Since homopolypropylene has a crystallization peak temperature of about 119°C and a melting peak temperature of about 149°C, the first temperature range was 119 to 149°C. Since amorphous PET has a softening completion temperature of about 81°C and a crystallization onset temperature of about 120°C, the second temperature range was 81 to 120°C. The overlapping temperature range where the first temperature range and the second temperature range overlap was about 1°C.

[0068] Such a preform 15 was heated to 110° C. (the temperature at the center of the preform 15 in the longitudinal direction) and then subjected to biaxial stretch blow molding to obtain the container body 2.

[0069] After the container body 2 was cooled to room temperature, the condition of the inner bag 4 was checked at the bottom of the container body 2, and it was found that a gap of about 2 mm had opened between the inner bag 4 and the outer shell 3 due to shrinkage of the inner bag 4.

[0070] <Example 1> A container body 2 was produced in the same manner as in Reference Example 1, except that the material of the inner preform 14 was changed.

[0071] In Example 1, the inner preform 14 was manufactured by injection molding a propylene-ethylene random copolymer (type: Wintec, manufactured by Japan Polypropylene Corporation). Since the crystallization peak temperature of the propylene-ethylene random copolymer is about 100°C and the melting peak temperature is about 125°C, the first temperature range was 100 to 125°C. The overlapping temperature range where the first temperature range and the second temperature range overlap was 20°C.

[0072] Such a preform 15 was heated to 110° C. (the temperature at the center of the preform 15 in the longitudinal direction) and then subjected to biaxial stretch blow molding to obtain the container body 2.

[0073] After cooling the container body 2 to room temperature, the state of the inner bag 4 was checked at the bottom of the container body 2, and the gap between the inner bag 4 and the outer shell 3 was 1 mm or less due to shrinkage of the inner bag 4. This result shows that in Example 1, shrinkage of the inner bag 4 during cooling after molding was suppressed compared to Reference Example 1.

[0074] (Additional Note) Below is an outline of the invention in the original application.

[0075] (Item 1) A preform constructed by covering an inner preform with an outer preform, the inner preform comprising a polyolefin layer comprised of a polyolefin-based resin containing polyolefin, the outer preform comprising an amorphous PET layer comprised of an amorphous PET-based resin containing amorphous PET, the temperature range between the crystallization peak temperature and melting peak temperature of the polyolefin-based resin being defined as a first temperature range, and the temperature range between the softening completion temperature and crystallization start temperature of the amorphous PET-based resin being defined as a second temperature range, the overlapping temperature range of the first temperature range and the second temperature range being 2°C or more.

[0076] According to the present invention, the overlapping temperature range is 2° C. or more. Therefore, compared to the above-mentioned Reference Example, it is easier to mold at a molding temperature that can bring both the polyolefin and the amorphous PET into a softened state suitable for molding, and as a result, it is possible to suppress shrinkage of the inner bag during cooling after molding.

[0077] Various embodiments of the present invention will be described below. The embodiments described below can be combined with each other.

[0078] (Item 2) The preform according to item 1, The preform, wherein the polyolefin comprises a propylene copolymer, which is a copolymer between propylene and another monomer.

[0079] (Item 3) The preform according to item 1, The polyolefin comprises homopolypropylene and low density polyethylene or linear low density polyethylene.

[0080] (Item 4) A preform according to any one of items 1 to 3, The overlapping temperature range is 10° C. or greater.

[0081] (Item 5) A method for producing a double container using the preform according to any one of items 1 to 4, and heating the preform to a temperature within the overlap temperature range to effect biaxial stretch blow molding. [Explanation of symbols]

[0082] 1:Double container 2: Container body 3: Outer shell 4: Inner bag 4b: Flange 5: Mouth 5a: Engagement part 5b: Flange 5c: Open end 6: Torso 6a: Upper end 6b:Shoulder 6c: Body 7: Bottom 13: Outer preform 13a: Mouth 13b: Torso 13c: Bottom 13c2: Positioning hole 13c4: Annular protrusion 14: Inner preform 14a: Mouth 14a1: Flange 14b: Torso 14c: Bottom 14c1: Locating pin 15: Preform 15a: Mouth 15b: Torso 15c: bottom 15d: Stretched part 17:Through hole 20: Mold unit 21: Mouth support type 21a: Insertion hole 22: Bottom support type 22a: Recess 22b: Recess 22c: Drive mechanism 23: Molding mold 23a: Cavity surface 24: Molding mold 24a: Cavity surface 25: Support rod 26: Air passage 31: Heater 40: Manufacturing equipment

Claims

1. A method for manufacturing a double container using a preform configured by covering an outer preform with an inner preform, The inner preform includes a polyolefin layer made of a polyolefin-based resin containing a polyolefin, The polyolefin includes a propylene-ethylene random copolymer, which is a random copolymer of propylene and ethylene, or includes a homopolypropylene and a low density polyethylene or a linear low density polyethylene; The outer preform includes an amorphous PET layer made of an amorphous PET-based resin including amorphous PET, A temperature range between a crystallization peak temperature and a melting peak temperature of the polyolefin resin is defined as a first temperature range, If a temperature range between the softening completion temperature and the crystallization initiation temperature of the amorphous PET resin is defined as a second temperature range, The method further comprises heating the preform to a temperature within an overlapping temperature range where a first temperature range and a second temperature range overlap, to perform biaxial stretch blow molding.

2. A method for manufacturing a double container using a preform configured by covering an outer preform with an inner preform, The inner preform includes a polyolefin layer made of a polyolefin-based resin containing a polyolefin, The outer preform includes an amorphous PET layer made of an amorphous PET-based resin including amorphous PET, A temperature range between a crystallization peak temperature and a melting peak temperature of the polyolefin resin is defined as a first temperature range, If a temperature range between the softening completion temperature and the crystallization initiation temperature of the amorphous PET resin is defined as a second temperature range, and heating the preform to a temperature within an overlapping temperature range in which a first temperature range and a second temperature range overlap, and performing biaxial stretch blow molding (excluding a method in which the inner preform and the outer preform are sealably bonded at the bottom and top of the preform).

3. 3. The method of claim 1 or claim 2, The method of claim 1, wherein the polyolefin comprises a propylene copolymer which is a random copolymer of propylene and ethylene.

4. 3. The method of claim 1 or claim 2, The method of claim 1, wherein the polyolefin comprises homopolypropylene and low density polyethylene or linear low density polyethylene.

5. The method according to any one of claims 1 to 4, The method, wherein the overlap temperature range is 10° C. or greater.

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