Method for manufacturing bottomed beverage container

Abstract

To provide a method for manufacturing a container that can ensure a dimensional accuracy of a mouth flange, is less likely to cause thickness deviation even in a container with a step, and can increase a strength of the container.SOLUTION: A method for manufacturing a bottomed beverage container having a coaxial cylindrical shape centered on a vertical axis C and having an opening with a flange that is heat-sealed to a lid material includes forming the container by injection blow molding accompanied by vertical stretching. With this configuration, when a preform made of amorphous plastic is stretched, it undergoes strain hardening, making it possible to mold a container with a uniform wall thickness and good wall thickness accuracy.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a bottomed beverage container, and more particularly to a method for manufacturing a bottomed beverage container with a side wall having high thickness accuracy and good thickness distribution. [Background technology]

[0002] Fermented milk, dairy lactic acid bacteria drinks, and lactic acid bacteria drinks (hereinafter sometimes collectively referred to as "lactic acid bacteria drinks") are commonly sold in small plastic containers of around 100 mL. There are two types of lactic acid bacteria drinks: live bacteria type and sterilized type, and the amount of plastic used varies depending on the type. Specifically, when the weight (g) of plastic used in a live bacteria type container is converted to the amount of plastic used per ml of content, the weight average is 0.0561 (g / ml). In contrast, the weight average for a sterilized type container is 0.109 (g / ml).

[0003] In recent years, the "food functionality" of live-bacterial lactic acid bacteria drinks has attracted attention, and demand for live-bacterial lactic acid bacteria drinks is increasing. As distribution volume increases, the total amount of plastic on the market and the total amount of plastic discarded from the market are also increasing. As the amount of plastic distributed and discarded increases, the amount of carbon dioxide released into the atmosphere also increases. Therefore, even for products that use a small amount of plastic, further reductions in container weight are desired.

[0004] A well-known example of a live-bacteria-type lactic acid bacteria beverage container is one made by injection blow molding a preform made of amorphous high-impact polystyrene (HIPS). Injection blow molding is a manufacturing method suitable for molding containers with a mouth flange that ensures dimensional precision. During manufacturing, the mouth flange of the preform is held, fixed, and cooled in the lip cavity, while the stretching region below the flange is heated to the stretching temperature. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-145560

[0006] However, injection blow molding does not use a rotary heating method to heat the stretching region under the flange to the stretching temperature. This can lead to uneven temperatures around the circumference of the preform, which can lead to problems such as uneven thickness in the molded container. In particular, uneven thickness is likely to occur in stepped containers, leading to a decrease in impact resistance and other properties starting from the thin-walled portion. Furthermore, if the amount of plastic used is reduced to reduce the container weight, uneven thickness tends to become more pronounced, and the thin-walled portion becomes even thinner. This results in a further decrease in impact resistance and other properties. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above problems, and it is an object of the present invention to provide a method for manufacturing a container that ensures dimensional accuracy of the mouth flange, is less likely to cause uneven thickness even in containers with steps, and can increase the strength of the container. [Means for solving the problem]

[0008] The inventors have conducted extensive research into whether there is a method for forming a container with a precise wall thickness by applying a relatively uniform stretching tension in both the vertical and horizontal directions to a preform made of amorphous plastic during stretch molding. They have discovered that blow molding using a combination of vertical stretching and conventional horizontal stretching, which was previously thought to be inapplicable to amorphous plastics, can ensure a stretching tension in the vertical direction as well, thereby enabling the formation of a container with a precise wall thickness, and have completed the present invention.

[0009] To solve the above problems, the present invention provides a method for manufacturing a bottomed beverage container having a coaxial cylindrical shape centered on a vertical axis and having an opening with a flange heat-sealed to a lid, characterized in that the bottomed beverage container is formed by injection blow molding with vertical stretching. Furthermore, in the above configuration, it is preferable that the vertical stretch ratio is 1.3 times or more. It is also preferable that the beverage container is made of PLA.

[0010] According to this configuration, after vertical stretching, the polymer molecular chains can be oriented and distributed in both the vertical and horizontal directions by stretching laterally with blown air. Furthermore, crystalline polylactic acid such as PLA undergoes strain hardening as the vertical stretching tension increases, allowing for the molding of containers with precise wall thickness. [Effects of the Invention]

[0011] According to this invention, it is possible to provide a container that ensures dimensional accuracy of the mouth flange, is less likely to develop thickness unevenness even in containers with steps, and has increased container strength. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic explanatory diagram for explaining the structure of a container according to the present invention. FIG. [Figure 2] FIG. 10 is a diagram summarizing the measurement results of each test example in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Preferred embodiments for carrying out the present invention will be described below. Note that the embodiment described below is an example of a typical embodiment of the present invention, and the scope of the present invention should not be construed as being narrow.

[0014] Materials for the container that can be used in this embodiment include olefin resins such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polypropylene, and polystyrene, ethylene-propylene copolymer resins, and acid-modified olefin resins. Other examples include homopolycondensation polyesters such as polyglycolic acid, polylactic acid, polycaprolactone, and polysuccinate, copolymers such as polybutylene succinate, polybutylene adipate, and adipate terephthalate, and copolymer polyester resins composed of one or more monomers selected from lactic acid, glycolic acid, polylactic acid, malic acid, 3-hydroxybutanoic acid, 3-hydroxyvaleric acid, and 3-hydroxyhexanoic acid. These resins are collectively referred to as resins classified as polyhydroxyalkanoates.

[0015] Polylactic acid (PLA) is a crystalline polyester polymerized from lactic acid, a product of lactic acid fermentation of carbohydrates, and is a 100% biomass plastic. Because it has the same mechanical strength as polystyrene, it is also being marketed as a polystyrene substitute.

[0016] The polylactic acid (PLA) that can be used in this embodiment is composed of a repeating unit represented by formula (I). -[-OC(CH3)H-CO-] (I)

[0017] The structural unit of polylactic acid is essentially L-lactic acid, and in relation to the amount of copolymerized optical isomer D-lactic acid, the optical purity (OP) represented by formula (II) is within the range of 88 to 99%. [OP] =(LD) / (L+D)×100 (%) ···(II)

[0018] The polylactic acid (PLA) preferably has a melt flow rate of 10 g / 10 min or less at a test temperature of 190°C and a load of 2.16 kg. The density is 1.20 to 1.26 g / cm. 3Preferably, the melting point is 160 to 200° C. Two or more different polylactic acids can be used in combination, but it is necessary that the melt flow rate of the mixture after melt mixing is within the above range.

[0019] Depending on the application, the polylactic acid (PLA) used can be compounded with various colorants, fillers, inorganic or organic reinforcing agents, lubricants, antiblocking agents, plasticizers, leveling agents, surfactants, thickeners, viscosity reducers, stabilizers, antioxidants, ultraviolet absorbers, etc. according to known recipes. [Example]

[0020] (Test plastic (HIPS: High Impact Polystyrene)) We prepared HIPS (manufactured by PS Japan Co., Ltd.) containing styrene-butadiene rubber (SBR) with a melt flow rate of 6.0 g / 10 min at a test temperature of 200°C and a load of 5 kg, and ISCC-certified HIPS (manufactured by PS Japan Co., Ltd.).

[0021] (Test plastic (PLA: polylactic acid) Polylactic acid (manufactured by Total Corbion) with a melt flow rate of 3.0 g / 10 min at a test temperature of 190°C, a load of 2.16 kg, and a melting point (Tm (°C)) of 155°C or higher was prepared.

[0022] (Preform injection molding for injection blow molding: HIPS) Using an injection blow molding machine (manufactured by Sumitomo Heavy Industries, Ltd.), the injection molding barrel temperature was set to a range of 200°C to 270°C, and the material was injected into an injection mold with a shell temperature of 50°C and an injection core mold temperature of 150°C, to mold a cylindrical HIPS preform with a bottom and a mouth flange, measuring 78 mm in height, 21 mm in outer diameter, 1.0 mm in thickness, and weighing 3.5 g.

[0023] (Preform for injection blow molding: PLA) The process is the same as for the bottomed HIPS preform for injection blow molding, except that the injection molding barrel temperature is set in the range of 190°C to 230°C, the shell temperature is set to 90°C, and the injection core mold temperature is set to 100°C when the polylactic acid is injected into the injection mold.

[0024] (Preform injection molding for injection stretch blow molding: HIPS) Using an injection stretch blow molding machine (manufactured by Nissei ASB Machinery Co., Ltd.), the barrel temperature was set between 200 and 270°C, and the preforms were injection molded into shell molds and injection core molds set at 20°C. After the mold was cooled, the injection core mold was retracted while the mouth flange was still held and fixed in the lip cavity, and the preform was separated from the injection core mold. The lip cavity mold was opened, yielding HIPS bottomed preforms for injection stretch blow molding. The cylindrical mouth flange measured 49, 56, or 60 mm in height, 21 mm in outer diameter, 1.0 mm in thickness, and weighed 3.5 g.

[0025] (Preform injection molding for injection stretch blow molding: PLA) Except for the barrel temperature of the injection molding machine being in the range of 190°C to 230°C, the process is the same as the HIPS bottomed preform for injection stretch blow molding.

[0026] (Container molding by injection blow molding: HIPS) The mouth flange of a bottomed HIPS preform for injection blow molding was clamped and fixed in a lip cavity mold, and then the body of the preform was moved to the blow station while still clinging (closely attached) to the 150°C injection core mold, where it was blown into a container shape using 1 MPa air pressure using a blow mold set to 50°C.

[0027] (Container molding by injection blow molding: PLA) A PLA bottomed preform for injection stretch blow molding of containers was injection blow molded in the same manner as HIPS, except that the injection core temperature was set to 100°C.

[0028] (Container molding by injection steel toilet blow molding: HIPS) A bottomed HIPS preform with a lip flange for injection stretch blow molding was clamped and fixed in a rotatable lip-cavity mold with a sprocket mechanism. A heating iron core, induction-heated to 400°C, was inserted into the preform's inner surface, and the preform was heated from the inside by rotating it around its upright center axis. Simultaneously, the preform was externally heated with an infrared heater (external heating). The preform was then heated to 150°C and inserted into a blow mold set at 20°C. The bottom of the preform was stretched to the container bottom using a stretch rod. Air at 1.0 MPa pressure was then blown into the preform to form a container. In particular, the area directly below the lip flange of the preform clamped and fixed in the lip cavity was additionally heated by blowing hot air using a spot-type hot air blower.

[0029] (Container molding by injection steel blow molding: PLA) A PLA bottomed preform for injection stretch blow molding was molded into a container in the same manner as for HIPS for injection stretch blow molding, except that the preform was heated to 100°C.

[0030] The shape of a container formed by injection blow molding or injection stretch blow molding is as shown in Figure 1. Specifically, it is a bottomed beverage container that is a coaxial cylinder centered on a vertical axis C. It has an opening with a flange that is heat-sealed to a lid, a neck portion that hangs down from the opening while maintaining the same diameter as the opening, a linear shoulder portion that extends in an inverse tapered manner from the neck portion, a chest portion that hangs down a predetermined width from one end of the shoulder portion opposite the neck portion and then tapers down in diameter, a body portion that hangs down from the reduced-diameter chest portion while maintaining the same diameter, and a foot portion that extends in an inverse tapered manner from the body portion to the maximum diameter of the chest portion and then hangs down to a width equal to or greater than the chest portion. Here, C in the figure represents the vertical center axis of the bottomed beverage container. R2 represents the distance from the center axis C to the body portion. R3 represents the distance from the center axis C to the chest portion. T1 to T3 represent the thickness of the container at the arrows.

[0031] <Test Example 1> A 60 mm high HIPS injection stretch blow molding preform was injection stretch blow molded to a height of 78 mm (vertical stretching equivalent to 1.3 times the original size) with an R3 / R2 ratio of 1.12.

[0032] <Test Example 2> The same as Test Example 1, except that a 56 mm high HIPS injection stretch blow molding preform was injection stretch blow molded to a height of 78 mm (equivalent to a vertical stretch of 1.4 times the size before stretching).

[0033] <Test Example 3> This test was the same as Test Example 1, except that a 49 mm high HIPS injection stretch blow molding preform was injection stretch blow molded to a height of 78 mm (equivalent to a vertical stretch of 1.6 times the size before stretching).

[0034] <Test Example 4> The same as Test Example 1 was performed except that R3 / R2=1.45.

[0035] <Test Example 5> The same as Test Example 3 except that R3 / R2=1.45 was satisfied.

[0036] <Test Example 6> The same as Test Example 2 except that an ISCC-certified HIPS injection stretch blow molding preform was used.

[0037] <Test Example 7> The same as Test Example 1 except that a PLA injection stretch blow molding preform was used.

[0038] <Test Example 8> The same as Test Example 2 except that a PLA injection stretch blow molding preform was used.

[0039] <Test Example 9> The same as Test Example 3 except that a PLA injection stretch blow molding preform was used.

[0040] <Test Example 10> The same as Test Example 4 except that a PLA injection stretch blow molding preform was used.

[0041] <Test Example 11> The same as Test Example 5 except that a PLA injection stretch blow molding preform was used.

[0042] <Test Example 12> A 78 mm high HIPS injection blow molding preform was injection blow molded to a height of 78 mm (equivalent to vertical stretching of 1.0 times the size before stretching) with an R3 / R2 ratio of 1.12.

[0043] <Test Example 13> The same as Test Example 2 except that R3 / R2=1.50 was used.

[0044] <Test Example 14> The same as Test Example 3 except that R3 / R2=1.50 was used.

[0045] <Test Example 15> A 78 mm high PLA injection blow molding preform was injection blow molded to a height of 78 mm (vertical stretching equivalent to 1.0 times the size before stretching) with an R3 / R2 ratio of 1.12.

[0046] <Test Example 16> The same as Test Example 8 except that R3 / R2=1.50 was used.

[0047] <Test Example 17> The same as Test Example 9 except that R3 / R2=1.50 was used.

[0048] Each test example was evaluated according to the following evaluation items, and the results are shown in Figure 2.

[0049] <Evaluation of container formability> If there was one or more blowouts (broken bodies) or defective containers that could not be formed into containers during the molding of 100 containers, the blow molding was judged to be defective and rated as ×. If there was no blowout and all containers were able to be formed, the moldability was judged to be good and rated as ○.

[0050] <Foreign substance inspection evaluation> Using a foreign matter inspection device that measures the dimensional accuracy of the mouth of injection blow or injection stretch blow molded containers and determines whether or not there are any foreign matters mixed in based on the amount of transmitted and reflected light (brightness), if the frequency of defectively molded containers is 100 ppm or more, the container is judged to be poorly molded and rated as X. If the frequency of defective containers is less than 100 ppm, the moldability is judged to be good and rated as O.

[0051] <Evaluation of container vertical compressive strength> The compressive strength of empty containers was measured at a compression speed of 50 mm / min using a V-notched circular flat plate compression test jig on a load testing machine manufactured by Imada Co., Ltd. The measurement was stopped when the container buckled and the compressive load value decreased, and this inflection point was taken as the compressive strength. Containers with a load of 100 N or more were judged to be good containers and marked with a circle. Bottles with a load of less than 100 N were judged to be defective and marked with an X.

[0052] <Thickness measurement evaluation> Using a one-shot 3D shape measuring machine manufactured by Keyence Corporation, a 78mm high cylindrical plastic container section that was vertically divided into two along a vertical plane passing through the central axis C of the container was used, and a white LED was irradiated onto the inside and outside of the cut surface. The shape was measured from the change in the imaging position of the reflected light from the light receiving element, and the container wall thickness was determined from the 3D shape measurement image.

[0053] <Evaluation of container wall thickness distribution> From the container wall thickness obtained using the Keyence one-shot 3D shape measuring machine mentioned above, the thickness distribution of the container chest thickness T1, the container body thickness T3, and the tapered chest thickness T2 is calculated. The case where the annular depression (T3) ≧ the connecting portion (T2) > the annular protrusion (T1) was evaluated as ◯. On the other hand, if the thickness distribution is Annular depression (T3)>Annular protrusion (T1)>>Connection (T2) If the order was as follows, it was marked as ×.

[0054] <Evaluation of container wall thickness accuracy> In the container wall thicknesses determined using a Keyence one-shot 3D shape measuring machine, for the thickness T1 of the container chest, the thickness T3 of the container body, and the thickness T2 of the tapered chest, if the thickness ratio (thickness deviation ratio) of maximum thickness to minimum thickness is 2 or less, it is judged to be a good thickness deviation ratio and marked with a circle, and if it is more than 2, it is considered to be a poor thickness deviation and marked with an ×.

[0055] <Biomass content (C14) measurement using accelerator mass spectrometry> Using an accelerator mass spectrometer (AMS) in accordance with ISO 16620, the concentration of radioactive carbon-14 in the plastic was measured, and the biomass carbon content in the plastic's constituent carbon was calculated, expressed as a percentage (%).

[0056] <Evaluation of carbon dioxide emissions> The amount of carbon dioxide (CO2) emitted during combustion was calculated using the following formula. First, because the weight of the container in this experiment was 3.5 g, the container weight (3.5 g) was divided by the molar mass of styrene (104 g / mol). Next, the number of moles of carbon dioxide generated was calculated by multiplying this by the number of carbon atoms constituting styrene (×8). The amount of carbon dioxide (g) emitted from one container was calculated by multiplying this number of moles of carbon dioxide generated by the molar mass of carbon dioxide (44 g / mol). Furthermore, if a value (%) for the biomass degree (C14) determined by accelerator mass spectrometry (AMS) measurement is present, the amount of carbon dioxide equivalent to the measured biomass degree (%) is derived from biomass and can be excluded from the carbon dioxide released into the atmosphere. (Polystyrene: Biomass content 0%) 3.5(g) / 104(g / mol)×8×44(g / mol)=11.84g (Polystyrene: biomass content 1%) 3.5(g) / 104(g / mol)×8×44(g / mol)×0.99=11.72g (Polystyrene: biomass content 10%) 3.5(g) / 104(g / mol)×8×44(g / mol)×0.90=10.66g

[0057] As can be seen from Figure 2, Test Examples 1 to 11 received favorable ratings in all evaluation criteria. This is believed to be because, even for plastics that do not strain-harden when uniaxially stretched, longitudinal stretching induces molecular orientation in the longitudinal direction, increasing melt tension in the longitudinal direction. This prevents the subsequent transverse stretching from concentrating the strain between the circumferentially formed high-stretch and low-stretch regions at the junction, thereby suppressing selective longitudinal stretching of the junction wall, which would otherwise be dragged by the high-stretch region. As a result, the order of annular depression (T3) ≥ junction (T2) > annular protrusion (T1) is established, presumably enabling the molding of containers with precise wall thickness distribution. This demonstrates that, for all materials, as long as R3 / R2 is less than 1.50, injection stretch blow molding can be used to ensure dimensional accuracy of the neck flange, minimize wall thickness variations even with stepped containers, and increase container strength. Although not shown in the table, in all of Test Examples 1 to 11, the container vertical compressive strength was 100 N or more.

[0058] On the other hand, as is clear from Test Examples 12 and 15, even when R3 / R2 was less than 1.50, injection blow molding was unsatisfactory in all evaluation items. Furthermore, as is clear from Test Examples 13, 14, 16, and 17, when R3 / R2 was 1.50, injection stretch blow molding was also unsatisfactory in all evaluation items. Furthermore, although not shown in the table, the container longitudinal compressive strength was less than 100 N in all Test Examples 12 to 17.

[0059] As described above, according to this embodiment, polylactic acid (PLA) can be used to form containers with reduced thickness variations in the body portion by injection stretch blow molding, similar to high-impact polystyrene, and it has been confirmed that this does not pose any practical problems.

[0060] Furthermore, according to this embodiment, containers that require high dimensional accuracy at the mouth can be molded with high precision and a nearly uniform distribution of wall thickness. As a result, the amount of plastic used for each container can be reduced, and the number of defective containers generated at container production sites can also be reduced, which is thought to contribute to reducing carbon dioxide emissions. [Explanation of symbols]

[0061] C Vertical central axis R2, R3 Distance from each part to the central axis C Thickness of each part from T1 to T3

Claims

1. A method for manufacturing a bottomed beverage container having a coaxial cylindrical shape centered on a vertical axis, the container having an opening with a flange that is heat-sealed to a lid material, comprising: A method for manufacturing a bottomed beverage container, characterized in that the container is formed by injection blow molding accompanied by vertical stretching.

2. 2. The method for producing a bottomed beverage container according to claim 1, wherein the stretching ratio in the vertical direction is 1.3 times or more compared to before stretching.

3. The method for manufacturing a bottomed beverage container according to claim 1, wherein the beverage container is made of PLA.

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