Packaging container and method for manufacturing a packaging container

Abstract

To provide a packaging container that ensures transparency. [Solution] The packaging container 10 is a packaging container formed from a resin sheet 20. The resin sheet 20 comprises a recycled polyester layer 21 containing recycled polyester made from used polyester, and a virgin polyester layer 22 laminated on one or both sides of the recycled polyester layer 21, which does not contain recycled polyester and contains unused virgin polyester. The recycled polyester is washed with a weakly alkaline detergent. The haze value of the packaging container 10 formed from the resin sheet 20 is less than 3%.

Description

Technical Field

[0001] The present invention relates to a packaging container and a method for producing the packaging container.

Background Art

[0002] For example, Patent Document 1 discloses a packaging container obtained by collecting and reusing a food container. The packaging container disclosed in Patent Document 1 includes a container body for containing food and having an opening upward, and a lid body attached to the container body for closing the opening of the container body.

[0003] The container body and the lid body are formed of a resin sheet in which a polyester layer and a recycled polyester layer are laminated. The polyester layer is a layer formed of unused (i.e., not recycled) polyester. The recycled polyester layer is a layer obtained by reusing used polyester containers.

[0004] For example, Patent Document 2 discloses a biaxially oriented polyester film using a PET bottle recycling raw material. In the production of the PET bottle recycling raw material used for the biaxially oriented polyester film, for example, after washing away foreign substances such as the remaining beverage from a beverage PET bottle, it is pulverized to obtain flakes. Then, the flakes are subjected to detergent washing under stirring using an aqueous sodium hydroxide solution.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0006] Incidentally, when manufacturing a packaging container as described in Patent Document 1, for example, it is conceivable to crush used polyester containers to produce a crushed material, and then clean the crushed material with a strong alkaline cleaning agent, such as an aqueous sodium hydroxide solution, as disclosed in Patent Document 2. For example, Patent Document 3 discloses that PET resin recovered from the market deteriorates due to alkaline cleaning agents, and therefore it is important to select a cleaning agent that does not easily degrade the resin. Alkaline cleaning agents can be broadly divided into two types: strong alkaline cleaning agents and weak alkaline cleaning agents. Strong alkaline cleaning agents have a pH value of 11 or higher, while weak alkaline cleaning agents have a pH value of around 7.1 to 10.9. Strong alkaline cleaning agents have higher cleaning ability compared to weak alkaline cleaning agents, but they also have the characteristic of easily degrading PET resin.

[0007] Furthermore, during the processes of preparing and washing the crushed material, and during the thermoforming process, cracks and fractures (also called mechanical racks) occur due to physical forces and stresses from the crusher, etc., and cracks (also called chemical racks) occur due to the cleaning agent or additives. For example, Patent Document 4 discloses that cracks occur when PET resin is washed with alkali. Strong alkaline cleaning agents have a higher degree of ionization than weak alkaline cleaning agents and contain a larger amount of ions dissolved in the aqueous solution, so it is thought that cracks are more likely to occur in PET resin. From these points, it is thought that when PET resin is thermoformed after washing, mechanical racks occur due to physical forces, and it is presumed that strong alkaline cleaning agents are more likely to cause cracks than weak alkaline cleaning agents, resulting in a deterioration of the transparency of the packaging container.

[0008] Furthermore, the sodium hydroxide aqueous solution mentioned above is a strongly alkaline cleaning agent, known for its high cleaning power and used in cleaning glass bottles and other items, but it also has the characteristic of easily foaming. Therefore, air bubbles may easily adhere to the crushed material during detergent cleaning. If a packaging container is made using crushed material to which air bubbles have adhered, it may become difficult to ensure the transparency of the packaging container because light is scattered due to the air bubbles.

[0009] The present invention has been made in view of the above, and its object is to provide a packaging container that can ensure transparency and a method for manufacturing a packaging container. [Means for solving the problem]

[0010] The packaging container according to the present invention is a packaging container formed from a resin sheet. The resin sheet comprises a recycled polyester layer containing recycled polyester made from used polyester, and a virgin polyester layer laminated on one or both sides of the recycled polyester layer, which does not contain recycled polyester and contains unused virgin polyester. The recycled polyester is washed with a weakly alkaline detergent. The haze value of the packaging container formed from the resin sheet is less than 3%.

[0011] According to the aforementioned packaging container, a weakly alkaline detergent is considered to be safer to use and less prone to foaming compared to, for example, a strongly alkaline detergent. Therefore, by using recycled polyester that has been cleaned with a weakly alkaline detergent, it is possible to prevent bubbles from the weakly alkaline detergent from adhering to the recycled polyester. Thus, a packaging container can be formed from a resin sheet equipped with a recycled polyester layer containing recycled polyester that is less prone to bubble adhesion. As a result, a packaging container with a haze value of less than 3.0% and ensured transparency can be provided.

[0012] According to one preferred embodiment of the present invention, the flexural modulus of the resin sheet is 2,700 MPa or higher.

[0013] According to the above embodiment, since a packaging container can be formed using a resin sheet with sufficient strength, the strength of the packaging container can be ensured.

[0014] According to another preferred embodiment of the present invention, the virgin polyester includes petroleum-derived polyester or plant-derived polyester.

[0015] According to the above embodiment, virgin polyester becomes more easily mixed with recycled polyester. For example, when a resin sheet is made in multiple layers, differences in the fluidity of the resin between adjacent layers are less likely to occur during molding, thus reducing the likelihood of defects in the appearance of the packaging container. Furthermore, the adhesion between layers is also excellent, making it less likely for the layers to peel off.

[0016] According to another preferred embodiment of the present invention, the weakly alkaline cleaning agent is an aqueous solution of sodium carbonate or an aqueous solution of sodium bicarbonate.

[0017] According to the above embodiment, even when recycled polyester is washed with a detergent using a weakly alkaline cleaning solution such as an aqueous sodium carbonate solution or an aqueous sodium bicarbonate solution, a packaging container with guaranteed transparency can be provided.

[0018] The present invention relates to a method for manufacturing a packaging container, which involves manufacturing a packaging container using a resin sheet. The resin sheet comprises a recycled polyester layer containing recycled polyester made from used polyester, and a virgin polyester layer laminated on one or both sides of the recycled polyester layer, which does not contain recycled polyester but contains virgin polyester. In the method for manufacturing the packaging container, the recycled polyester is washed with a weakly alkaline detergent, and the resin sheet is manufactured using the recycled polyester that has been washed with the detergent.

[0019] According to the method for producing the packaging container, since the recycled polyester is washed with a weakly alkaline detergent, a resin sheet including a recycled polyester layer containing recycled polyester to which bubbles hardly adhere is used to form the packaging container. Therefore, a packaging container with ensured transparency can be produced.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a packaging container capable of ensuring transparency and a method for producing the packaging container.

Brief Description of the Drawings

[0021] [Figure 1] It is a perspective view showing the packaging container according to the embodiment. [Figure 2] It is a cross-sectional view showing a part of the packaging container and is also a cross-sectional view of the resin sheet. [Figure 3] It is a flowchart showing the procedure for producing the recycled pellets. [Figure 4] It is a diagram schematically showing the extrusion device used in the extrusion molding. [Figure 5] It is a diagram schematically showing the mold and the plug used in the thermoforming.

Embodiments for Carrying Out the Invention

[0022] Hereinafter, embodiments of the packaging container according to the present invention will be described with reference to the drawings. Note that the embodiments described here are not intended to limit the present invention. In addition, members and parts having the same function are denoted by the same reference numerals, and duplicate explanations are omitted or simplified as appropriate.

[0023] Figure 1 is a perspective view showing a packaging container 10 according to this embodiment. The packaging container 10 is, for example, a container for holding food. However, the packaging container 10 is not limited to a container for holding food. The packaging container 10 may be a container that is heated in a microwave oven or the like, or it may be a container that is not heated (for example, a container for non-heated food).

[0024] As shown in Figure 1, the packaging container 10 comprises a container body 11 and a lid 15. In this embodiment, the packaging container 10 includes both the container body 11 and the lid 15. However, the packaging container 10 may comprise at least one of the container body 11 and the lid 15. For example, the packaging container 10 may comprise the container body 11 but not the lid 15. Alternatively, the packaging container 10 may comprise the lid 15 but not the container body 11. In the following description, the packaging container 10 can be appropriately replaced with the container body 11 and the lid 15. In this embodiment, the packaging container 10, i.e., the container body 11 and the lid 15, is formed from a resin sheet 20. The type, use, and shape of the packaging container 10 are not particularly limited as long as it is formed from a resin sheet 20. The configuration and shape of the container body 11 and the lid 15 will be described below, but the forms described below are merely examples, and the packaging container according to the present invention is not limited to the forms described below.

[0025] As shown in Figure 1, the container body 11 has a bottom portion 12 and side wall portions 13. The bottom portion 12 constitutes the bottom part of the container body 11. The side wall portions 13 rise up from the bottom portion 12. The side wall portions 13 extend upward from, for example, the circumferential edge of the bottom portion 12. In a plan view, the side wall portions 13 are arranged to surround the bottom portion 12. The side wall portions 13 extend diagonally outward and upward relative to the bottom portion 12. In other words, the side wall portions 13 incline outward from the bottom portion 12 as they move away upward from the bottom portion 12. However, the side wall portions 13 may extend perpendicularly to the bottom portion 12. The bottom portion 12 and the side wall portions 13 may have flat surfaces, or they may be provided with protrusions or recesses (not shown) or so-called ribs to increase rigidity. Here, food or the like is contained in the space enclosed by the bottom portion 12 and the side wall portions 13.

[0026] The bottom portion 12 is, for example, circular in shape. However, the shape of the bottom portion 12 is not particularly limited. Also, the shape of the container body 11 is not particularly limited. Here, the container body 11 has a container opening (not shown) surrounded by a side wall portion 13. This container opening is formed, for example, by the upper end of the side wall portion 13 and opens upward.

[0027] As shown in Figure 1, the lid 15 is attachable to the container body 11. Here, the lid 15 is attached to the container body 11 so that the container opening of the container body 11 can be opened and closed. The lid 15 fits onto the upper end of the container body 11. The lid 15 closes the container opening by being attached to the upper end of the side wall portion 13 of the container body 11.

[0028] The lid 15 comprises a top surface portion 16 and a fitting portion 17. The top surface portion 16 constitutes the top surface of the lid 15. When the lid 15 is attached to the container body 11, the top surface portion 16 faces the bottom portion 12. The fitting portion 17 is the portion that fits into the container body 11 when the lid 15 is attached to the container body 11. In this embodiment, the fitting portion 17 can be fitted into the upper end of the side wall portion 13 of the container body 11. In a plan view, the fitting portion 17 is provided on the circumferential edge of the top surface portion 16. In a plan view, the fitting portion 17 is provided so as to surround the top surface portion 16. Here, the fitting portion 17 protrudes upward from the top surface portion 16. The specific configuration of the fitting portion 17 is not particularly limited. The fitting portion 17 may be provided with a recess into which, for example, the upper end of the side wall portion 13 of the container body 11 is fitted. The recess is provided, for example, so as to surround the top surface portion 16 in a plan view, and is configured to be recessed upward in the fitting portion 17.

[0029] In this embodiment, as shown in Figure 1, an opening valve 18 is formed on the top surface 16 of the lid 15, allowing gas or liquid to enter and exit. For example, if the packaging container 10 is a container that is heated in a microwave oven or the like while containing food, when the packaging container 10 is heated, steam (e.g., water vapor) is generated as the food is heated. The opening valve 18 is closed before heating in a microwave oven, for example. When the packaging container 10 is heated in a microwave oven, the opening valve 18 opens as the steam generated by the heating of the food is discharged to the outside of the lid 15, and the steam passes through the opening valve 18. After the steam has passed, the opening valve 18 returns to its original closed state. The number and position of the opening valves 18 formed on the top surface 16 are not particularly limited. In this embodiment, there are two opening valves 18 formed on the top surface 16 of the lid 15. The opening valves 18 are formed in the central part of the top surface 16.

[0030] As shown in Figure 1, the opening valve 18 has an opening 19a formed in the top surface 16 and a valve body 19b that can open and close the opening 19a. Gas and liquid pass through the opening 19a. The valve body 19b is connected to the top surface 16. In this embodiment, the opening valve 18 is formed by making a cut in the top surface 16. The cut portion of the top surface 16 becomes the opening 19a and also the valve body 19b. Therefore, the valve body 19b has a shape that matches the opening 19a. The valve body 19b is formed integrally with the top surface 16. The shape of the valve body 19b is, for example, U-shaped. However, the shape of the valve body 19b is not particularly limited. In this embodiment, the opening valve 18 is formed on the lid 15, but the opening valve 18 may not be formed. A packaging container 10 equipped with a lid 15 that does not have an opening valve 18 is, for example, a container for non-heated food.

[0031] As shown in Figure 1, the packaging container 10, that is, the container body 11 and the lid 15, is formed from a resin sheet 20 as described above. Next, the resin sheet 20 will be described. The resin sheet 20 is a sheet formed from polyester (in other words, polyester resin), and is a so-called polyester sheet. The resin sheet 20 is formed from, for example, polyethylene terephthalate (hereinafter also referred to as PET or PET resin). However, the material used to form the resin sheet 20 is not limited to PET resin, and may be, for example, polylactic acid (hereinafter also referred to as PLA). PLA is a type of biodegradable plastic made from agricultural products such as corn, potatoes, sugarcane, and beets.

[0032] Figure 2 is a cross-sectional view of the resin sheet 20 of the packaging container 10. As shown in Figure 2, the resin sheet 20 is formed from multiple layers. The number of layers forming the resin sheet 20 is not particularly limited. Below, as an example of the resin sheet 20, a resin sheet 20 formed from five layers will be described.

[0033] In this embodiment, the resin sheet 20 comprises a recycled polyester layer 21 and a virgin polyester layer 22. The resin sheet 20 is a sheet formed by laminating the recycled polyester layer 21 and the virgin polyester layer 22. Here, three layers are formed by the recycled polyester layer 21 and two layers are formed by the virgin polyester layer 22.

[0034] The recycled polyester layer 21 is a layer containing recycled polyester. Here, recycled polyester is made from used polyester. Used polyester is polyester obtained from used polyester products. Used polyester products are, for example, used polyester products collected from the market. Here, polyester products refer to, for example, PET bottles (hereinafter also called PET bottles) and PET trays. Recycled polyester is polyester obtained by collecting used polyester products, and is recycled polyester. Furthermore, recycled polyester is polyester obtained by collecting used polyester products according to a predetermined recycling method.

[0035] In this embodiment, recycled polyester made from used PET bottles is referred to as bottle recycling material. Recycled polyester includes bottle recycling material. Bottle recycling material refers to polyester obtained from used PET bottles collected from the market. Here, the recycled polyester layer 21 contains bottle recycling material. Note that recycled polyester may also contain polyester other than bottle recycling material, for example, container recycling material obtained from used food containers made of PET resin.

[0036] For example, methods for recycling polyester products such as PET bottles include material recycling, chemical recycling, and mechanical recycling. Material recycling involves crushing collected used polyester products, then performing alkaline washing to reuse them as fibers, etc. Chemical recycling involves chemically decomposing collected used polyester products, returning them to the raw material level, and then repolymerizing the PET resin. Mechanical recycling involves thoroughly removing dirt from collected used polyester products by performing alkaline washing more rigorously than in the material recycling method described above, or by vacuum drying at high temperatures, in order to reuse the polyester products. Here, polyester reused through mechanical recycling is called mechanically recycled polyester. In this embodiment, recycled polyester is, for example, mechanically recycled polyester.

[0037] In this embodiment, as will be described in detail later, in mechanical recycling, the recycled polyester is washed with a weakly alkaline detergent. The detergent washing referred to here is the alkaline washing described above. Here, used polyester products are crushed to produce crushed material. Since this crushed material is obtained from used polyester products, it is recycled polyester. In this embodiment, this crushed material is washed with a weakly alkaline detergent. Here, a weakly alkaline detergent refers to, for example, one with a pH value of about 7.1 to 10.9. Examples of weakly alkaline detergents include sodium carbonate (Na2CO3) aqueous solution or baking soda (sodium bicarbonate (NaHCO3) aqueous solution). In addition, weakly alkaline detergents may include sodium sesquicarbonate, sodium citrate, borax (sodium tetraborate), sodium percarbonate, potassium carbonate, sodium phosphate, sodium metasilicate, sodium silicate, sodium pyrophosphate, etc.

[0038] The recycled polyester layer 21 may also contain polyesters other than recycled polyester (for example, PET resin). Examples of polyesters other than recycled polyester included in the recycled polyester layer 21 include virgin polyester, which will be described later. In this embodiment, the recycled polyester content in the recycled polyester layer 21 is 50% by mass or more.

[0039] Furthermore, the recycled polyester layer 21 may include manufacturing process losses such as selvage loss and skeleton generated during the production of the resin sheet 20 and the packaging container 10, to the extent that it does not significantly impair moldability.

[0040] The virgin polyester layer 22 is a layer that does not contain recycled polyester. The virgin polyester layer 22 is a layer that contains so-called virgin polyester. The virgin polyester layer 22 is formed of virgin polyester. Here, virgin polyester refers to unused polyester that does not contain recycled polyester. Also, virgin polyester refers to unused (in other words, not recycled) polyester. Virgin polyester is a new material. The virgin polyester layer 22 is a layer formed of unused polyester, and is not formed from recycled polyester containing bottle recycling material. Virgin polyester is different from recycled polyester obtained from used polyester products recovered from the market.

[0041] For example, virgin polyester may contain plant-derived polyester. Examples of plant-derived polyester include plant-derived PET. Plant-derived polyester refers to polyester made using plant-derived raw materials such as corn, potatoes, sugarcane, and beets. Plant-derived PET refers to PET made using the above-mentioned plant-derived raw materials. Virgin polyester may also contain petroleum-derived polyester. Petroleum-derived polyester (e.g., petroleum-derived PET) refers to polyester (e.g., PET) made from petroleum. In this embodiment, virgin polyester may contain either plant-derived or petroleum-derived polyester, or both plant-derived and petroleum-derived polyester.

[0042] Furthermore, the virgin polyester layer 22 may contain other components besides polyester (e.g., PET) as needed, to the extent that transparency and functionality are not significantly impaired. Examples of such other components include additives used in known resin sheets (e.g., flame retardants, ultraviolet absorbers, fluorescent whitening agents, antistatic agents, anti-fogging agents, lubricants (e.g., lubricant MB (masterbatch)), antiblocking agents, flow modifiers, plasticizers, dispersants, and antibacterial agents).

[0043] In this embodiment, as shown in Figure 2, the recycled polyester layer 21 is composed of three layers. Here, the recycled polyester layer 21 has a first outer recycled polyester layer 21a, a second outer recycled polyester layer 21b, and an inner recycled polyester layer 21c. In the recycled polyester layer 21, the first outer recycled polyester layer 21a, the inner recycled polyester layer 21c, and the second outer recycled polyester layer 21b are laminated in order. In this embodiment, the first outer recycled polyester layer 21a is provided on one side surface (the wider surface) of the inner recycled polyester layer 21c. The second outer recycled polyester layer 21b is provided on the other side surface (the wider surface) of the inner recycled polyester layer 21c, that is, the surface opposite to the first outer recycled polyester layer 21a.

[0044] In this embodiment, the proportion of recycled polyester (e.g., bottle recycling material) contained in the inner recycled polyester layer 21c and the first outer recycled polyester layer 21a and the second outer recycled polyester layer 21b differs. Here, the inner recycled polyester layer 21c contains a larger proportion of recycled polyester than the first outer recycled polyester layer 21a and a larger proportion of recycled polyester than the second outer recycled polyester layer 21b. For example, the inner recycled polyester layer 21c contains 80% by mass of recycled polyester and 20% by mass of virgin polyester. The first outer recycled polyester layer 21a and the second outer recycled polyester layer 21b both contain 50% by mass of recycled polyester and 50% by mass of virgin polyester. In this embodiment, the first outer recycled polyester layer 21a and the second outer recycled polyester layer 21b have the same proportion of recycled polyester and the same proportion of virgin polyester. However, the first outer recycled polyester layer 21a and the second outer recycled polyester layer 21b may have different proportions of recycled polyester, and may also have different proportions of virgin polyester. Furthermore, the proportions of recycled polyester contained in the first outer recycled polyester layer 21a, the second outer recycled polyester layer 21b, and the inner recycled polyester layer 21c may all be different or all be the same. Moreover, the proportion of recycled polyester contained in the first outer recycled polyester layer 21a, the second outer recycled polyester layer 21b, and the inner recycled polyester layer 21c should be greater than 0% and less than 100%. In other words, at least recycled polyester is contained in the first outer recycled polyester layer 21a, the second outer recycled polyester layer 21b, and the inner recycled polyester layer 21c.

[0045] In this embodiment, as shown in Figure 2, the virgin polyester layer 22 is composed of two layers. The virgin polyester layer 22 is laminated on both sides of the recycled polyester layer 21. The virgin polyester layer 22 is provided on both sides (the top and bottom surfaces in Figure 2) of the wide surface of the recycled polyester layer 21. The recycled polyester layer 21 is sandwiched between the two virgin polyester layers 22. Here, the virgin polyester layer 22 has a first virgin polyester layer 22a and a second virgin polyester layer 22b. The first virgin polyester layer 22a is provided on the surface of the first outer recycled polyester layer 21a of the recycled polyester layer 21. The second virgin polyester layer 22b is provided on the surface of the second outer recycled polyester layer 21b of the recycled polyester layer 21. In the resin sheet 20, the layers are laminated in the following order: first virgin polyester layer 22a, first outer recycled polyester layer 21a, inner recycled polyester layer 21c, second outer recycled polyester layer 21b, and second virgin polyester layer 22b.

[0046] In this embodiment, the overall thickness of the resin sheet 20 (in other words, the thickness of the container body 11 and lid 15) is 1.0 mm or less, preferably 0.6 mm or less, and particularly preferably 0.4 mm or less. Here, the thickness of the resin sheet 20 refers to the total thickness of the recycled polyester layer 21 and the virgin polyester layer 22 combined (in the example in Figure 2, the total thickness of all five layers). In this embodiment, of the recycled polyester layer 21 and the virgin polyester layer 22 of the resin sheet 20, the overall thickness of the recycled polyester layer 21 is greater than the overall thickness of the virgin polyester layer 22. Here, the overall thickness of the recycled polyester layer 21 refers to the sum of the thickness of the first outer recycled polyester layer 21a, the second outer recycled polyester layer 21b, and the inner recycled polyester layer 21c. The overall thickness of the virgin polyester layer 22 refers to the sum of the thickness of the first virgin polyester layer 22a and the second virgin polyester layer 22b.

[0047] For example, the ratio of the total thickness of the recycled polyester layer 21 to the total thickness of the resin sheet 20 is 50% or more and 98% or less, preferably 70% or more and 98% or less, and particularly preferably 80% or more and 98% or less. For example, the ratio of the total thickness of the recycled polyester layer 21 to the virgin polyester layer 22 is 92:8, but it is not limited to this ratio.

[0048] In the recycled polyester layer 21, the thickness of the inner recycled polyester layer 21c is greater than the thickness of the first outer recycled polyester layer 21a and also greater than the thickness of the second outer recycled polyester layer 21b. Furthermore, the thickness of the first outer recycled polyester layer 21a is the same as the thickness of the second outer recycled polyester layer 21b. However, the thickness of the first outer recycled polyester layer 21a may be greater than or less than the thickness of the second outer recycled polyester layer 21b. For example, the ratio of the thicknesses of the first outer recycled polyester layer 21a, the inner recycled polyester layer 21c, and the second outer recycled polyester layer 21b could be 1st outer recycled polyester layer:inner recycled polyester layer:2nd outer recycled polyester layer = 6:80:6, but this ratio is not limited to this.

[0049] In this embodiment, the thickness of the first virgin polyester layer 22a and the thickness of the second virgin polyester layer 22b are the same. However, the thickness of the first virgin polyester layer 22a may be greater than or less than the thickness of the second virgin polyester layer 22b.

[0050] The resin sheet 20 according to this embodiment has been described above. Here, as shown in Figure 2, the packaging container 10 (in other words, the container body 11 and lid 15) comprises an inner layer 31, an outer layer 32, an inner intermediate layer 33, an outer intermediate layer 34, and a central layer 35. In Figure 2, the upper side shows the inside of the container body 11 and lid 15, and the lower side shows the outside of the container body 11 and lid 15. The inner layer 31 is the innermost layer among the multiple layers that make up the container body 11 and lid 15. The inner layer 31 is a layer that makes up the inner circumferential surface of the packaging container 10. The inner layer 31 is the layer that food directly touches when food is contained in the packaging container 10. The outer layer 32 is the outermost layer among the multiple layers that make up the container body 11 and lid 15, and is a layer that makes up the outer circumferential surface of the packaging container 10. The outer layer 32 is the layer that a user's hand directly touches when they hold the packaging container 10 in their hand.

[0051] The central layer 35 is a layer positioned between the inner layer 31 and the outer layer 32. As shown in Figure 2, the central layer 35 is sandwiched between the inner layer 31 and the outer layer 32. The inner intermediate layer 33 is positioned between the inner layer 31 and the central layer 35. The inner intermediate layer 33 is sandwiched between the inner layer 31 and the central layer 35. The outer intermediate layer 34 is positioned between the outer layer 32 and the central layer 35. The outer intermediate layer 34 is sandwiched between the outer layer 32 and the central layer 35. The inner intermediate layer 33, outer intermediate layer 34, and central layer 35 can be layers that do not come into direct contact with food or users. Note that the inner layer 31, outer layer 32, inner intermediate layer 33, outer intermediate layer 34, and central layer 35 may each be a single layer or a layer formed by stacking multiple layers.

[0052] In this embodiment, as shown in Figure 2, the inner layer 31 and outer layer 32 of the container body 11 and lid 15 of the packaging container 10 are formed from the virgin polyester layer 22 of the resin sheet 20. Specifically, the inner layer 31 is formed from the first virgin polyester layer 22a, and the outer layer 32 is formed from the second virgin polyester layer 22b. Furthermore, the inner intermediate layer 33, outer intermediate layer 34, and central layer 35 of the container body 11 and lid 15 of the packaging container 10 are formed from the recycled polyester layer 21 of the resin sheet 20. Specifically, the inner intermediate layer 33 is formed from the first outer recycled polyester layer 21a, the outer intermediate layer 34 is formed from the second outer recycled polyester layer 21b, and the central layer 35 is formed from the inner recycled polyester layer 21c.

[0053] In this embodiment, the packaging container 10, i.e., the container body 11 and the lid 15 (in other words, the resin sheet 20), is transparent. In this embodiment, the haze value of the packaging container 10 (in other words, the container body 11 and the lid 15) is less than 3.0%, preferably less than 2.9%, particularly preferably less than 2.8%, and for example less than 2.7%.

[0054] In this embodiment, the intrinsic viscosity IV value of the packaging container 10 (here, the container body 11 and the lid 15) is 0.61 dl / g or more and 0.90 dl / g or less, preferably 0.63 dl / g or more and 0.88 dl / g or less, and particularly preferably 0.65 dl / g or more and 0.86 dl / g or less.

[0055] In this embodiment, the flexural modulus of the resin sheet 20 is 2,700 MPa or higher, preferably 2,800 MPa or higher. Here, the flexural modulus includes the flexural modulus in the MD direction relative to the resin sheet 20 and the flexural modulus in the TD direction perpendicular to the MD direction. Here, both the flexural modulus in the MD direction and the flexural modulus in the TD direction of the resin sheet 20 are 2,700 MPa or higher, preferably 2,800 MPa or higher.

[0056] In this embodiment, the buckling strength of the packaging container 10 is 8.5 kgf or more, preferably 8.8 kgf or more, particularly preferably 9.0 kgf or more, for example 9.2 kgf or more.

[0057] Next, a method for producing the resin sheet 20 and the packaging container 10 according to this embodiment, that is, a method for producing the packaging container 10, will be described. The method for producing the packaging container 10 includes a preparation step of preparing pellets, an extrusion step of performing extrusion molding, and a thermoforming step of performing thermoforming. Here, pellets are prepared, and the resin sheet 20 is produced by extrusion molding of the pellets. Then, the packaging container 10, that is, the container body 11 and the lid 15, can be produced by thermoforming the resin sheet 20.

[0058] In the preparation process, two types of pellets are prepared: virgin pellets formed from virgin polyester and recycled pellets formed from recycled polyester (in this case, bottle recycling material). The recycled pellets are made from recycled polyester, for example, from used polyester resin molded products (in other words, used polyester products) recovered from the market. Used polyester products refer to used PET containers such as used PET bottles and used PET trays. In this case, the recycled pellets are pellets formed from bottle recycling material consisting of used PET bottles.

[0059] Figure 3 is a flowchart showing the procedure for producing recycled pellets. As shown in Figure 3, the method for producing recycled pellets includes a first water washing step S11, a crushing step S12, a detergent washing step S13, a second water washing step S14, a drying step S15, and a polymerization step S16.

[0060] First, in the first water washing step S11 shown in Figure 3, used polyester products (for example, used PET bottles) recovered from the market are washed with water. Used polyester products may have foreign matter attached to them, including liquids such as juice and tea (in this case, liquids other than water). Therefore, in the first water washing step S11, water is used to remove the foreign matter attached to the used polyester product. Here, the foreign matter is removed by pouring water onto the used polyester product. In the first water washing step S11, for example, the used polyester product is immersed in water and rotated (in other words, agitated) for a predetermined first water washing time to perform one first water washing. In the first water washing step S11, the first water washing is performed a predetermined number of times. The above first water washing time and the number of first water washings are set appropriately according to the type of used polyester product recovered from the market and the type of contents, such as food, that were contained in the used polyester product.

[0061] Next, the crushing process S12 shown in Figure 3 is performed. The crushing process S12 crushes the water-washed used polyester product. Here, the crushed used polyester product is called the crushed material. The crushed material is recycled polyester. In the crushing process S12, for example, a crusher (not shown) is used to crush the used polyester product and produce the crushed material. The type of crusher is not particularly limited, and a conventionally known crusher used when crushing used polyester products may be used. If dirt remains on the crushed material after it has been produced, the crushed material may be washed with water as needed prior to the detergent washing process S13 shown in Figure 3.

[0062] After the grinding process S12 is performed, the detergent washing process S13 shown in Figure 3 is carried out. In the detergent washing process S13, the ground material is washed with a detergent. In other words, the recycled polyester is washed with a detergent. For example, since the ground material is made by grinding used polyester products that have been washed with water in the first water washing process S11, there may be deposits that cannot be removed by water washing alone (for example, oil used in food) attached to the ground material. The detergent washing process S13 is mainly carried out to remove deposits attached to the ground material.

[0063] In this embodiment, when cleaning the crushed material with detergent, a weakly alkaline detergent is used. In other words, recycled polyester is cleaned with a weakly alkaline detergent. A weakly alkaline detergent is a detergent with a pH value of approximately 7.1 to 10.9, as described above. Examples of weakly alkaline detergents include aqueous sodium carbonate solution and baking soda (aqueous sodium bicarbonate solution).

[0064] For example, conventionally, in the detergent cleaning process, strongly alkaline detergents were used when cleaning crushed materials with detergent. Here, a strongly alkaline detergent is a detergent with a pH value of 11 or higher. Examples of strongly alkaline detergents include aqueous solutions of sodium hydroxide (NaOH) and potassium hydroxide (KOH). Strongly alkaline detergents have higher cleaning power and are more effective at removing dirt compared to weakly alkaline detergents. Therefore, strongly alkaline detergents are used, for example, when cleaning drain pipes, and are so-called industrial detergents. Strongly alkaline detergents have a high degree of ionization and dissociate almost completely when dissolved in water. Thus, because strongly alkaline detergents have high cleaning power, they have conventionally been used as detergents for cleaning crushed materials with detergent. However, the stronger the alkalinity of a strongly alkaline detergent (in other words, the higher the pH value), the more easily the surfactant is activated, and the stronger the ability to emulsify and disperse oily dirt, so it tends to foam easily. Therefore, if a strongly alkaline detergent remains, it is likely to leave behind bubbles. If a resin sheet is manufactured using crushed material that has air bubbles attached to it, the transparency of the resin sheet may deteriorate.

[0065] Therefore, in this embodiment, in the detergent washing step S13 shown in Figure 3, the crushed material (recycled polyester) is washed with a weakly alkaline detergent. Here, weakly alkaline detergents can be used more safely than strongly alkaline detergents and can therefore be used, for example, as household detergents or food additives. Furthermore, weakly alkaline detergents have a low degree of ionization and only partially ionize when dissolved in water. Weakly alkaline cleaning solutions have little chemical impact on PET resin. Weakly alkaline cleaning solutions are considered to have a low burden on the global environment. In addition, weakly alkaline detergents do not foam as easily as strongly alkaline detergents. Since weakly alkaline detergents have inferior cleaning power against stubborn oil stains, the cleaning ability can be improved even with weakly alkaline detergents by increasing the number of washes, extending the immersion time, or raising the washing temperature. Therefore, in this embodiment, by washing the crushed material with a weakly alkaline detergent, it is possible to prevent air bubbles from adhering to the crushed material. Therefore, since the resin sheet 20 is manufactured in a state where air bubbles are less likely to adhere, it is easier to ensure the transparency of the resin sheet 20.

[0066] In this embodiment, the detergent washing step S13 involves immersing the crushed material in an aqueous solution containing, for example, a weakly alkaline detergent, and rotating (in other words, stirring) the crushed material for a predetermined detergent washing time. The detergent washing step S13 is performed a predetermined number of times. The detergent washing time and the number of detergent washing cycles are set appropriately according to the size of the crushed material and the amount of deposits expected to be attached to the crushed material. The detergent washing time is longer than, for example, the first water washing time in the first water washing step S11 in Figure 3. The number of detergent washing cycles is also greater than, for example, the first water washing cycle in the first water washing step S11. However, the detergent washing time may be shorter than or the same as the first water washing time. The number of detergent washing cycles may be less than or the same as the first water washing cycles.

[0067] After the detergent washing process S13 is performed, the second water washing process S14 shown in Figure 3 is carried out. In the second water washing process S14, the crushed material that has been washed with detergent is washed with water. When the crushed material is washed with detergent, detergent residue adheres to it. Therefore, in the second water washing process S14, the detergent residue is washed off the crushed material using water. Here, the detergent residue is removed, for example, by pouring water onto the crushed material (or by putting the crushed material into a tank of water). In the second water washing process S14, one second water washing is performed, for example, by immersing the crushed material in water and rotating (in other words, stirring) the crushed material for a predetermined second water washing time. In the second water washing process S14, the second water washing is performed a predetermined number of times. The above second water washing time and the number of second water washings are set appropriately according to the size of the crushed material and the amount of detergent residue expected to adhere to the crushed material. In this embodiment, the second water washing time is the same as, for example, the first water washing time in the first water washing step S11 in Figure 3. Also, the number of second water washing cycles is the same as, for example, the number of first water washing cycles in the first water washing step S11. However, the second water washing time may be longer or shorter than the first water washing time. The number of second water washing cycles may be more or fewer than the number of first water washing cycles. Also, the second water washing time may be longer or shorter than the detergent washing time, or it may be the same as the detergent washing time. The number of second water washing cycles may be more or fewer than the number of detergent washing cycles, or it may be the same as the number of detergent washing cycles.

[0068] Next, the drying process S15 shown in Figure 3 is performed. In the drying process S15, the pulverized material is dried. Here, the pulverized material has water adhering to it because it was washed with water in the second water washing process S14. In the drying process S15, the water is removed from the pulverized material by drying it. For example, PET resin such as pulverized material is a so-called crystalline resin. PET resin has an amorphous part in which water molecules can penetrate relatively easily and a crystalline part in which water molecules cannot penetrate easily. When pulverized material, which is PET resin, is washed with detergent and water, some water molecules may penetrate into the amorphous part. When PET resin is melted with water adhering to it, the molecular chains are broken by hydrolysis, the molecular weight decreases, and the intrinsic viscosity decreases. Here, for example, if recycled pellets are made using pulverized material with water adhering to it, and then a resin sheet is made, the PET resin becomes more susceptible to degradation. As a result, since packaging containers are made from resin sheets that are easily degraded, the intrinsic viscosity tends to decrease. Therefore, in this embodiment, a drying step S15 is performed to remove water from the pulverized material and make the PET resin less susceptible to deterioration. In the drying step S15, the drying time for drying the pulverized material is not particularly limited. It is preferable to ensure a drying time sufficient to remove the water adhering to the pulverized material.

[0069] Next, the polymerization step S16 shown in Figure 3 is performed. In the polymerization step S16, the pulverized material is polymerized to re-pelletize it. By polymerizing the pulverized material, recycled pellets are produced. The specific method of polymerization in the polymerization step S16 is not particularly limited, and conventionally known methods can be used. As described above, recycled pellets can be produced. Therefore, recycled pellets and virgin pellets can be prepared in the preparation step.

[0070] After virgin pellets and recycled pellets are prepared in this manner, an extrusion process is carried out. In the extrusion process, a resin sheet 20 is produced by extruding the virgin pellets and recycled pellets. Figure 4 is a schematic diagram of an extruder 50 used in extrusion molding. In this embodiment, an extruder 50 as shown in Figure 4 is used in extrusion molding. As shown in Figure 4, the extruder 50 has a first hopper 51A, a first screw 52A, a second hopper 51B, a second screw 52B, a feed block 58, a confluence die 53, a cooling roll 54, and a winding machine 55.

[0071] In this embodiment, the first hopper 51A and the first screw 52A are for virgin pellets (hereinafter referred to as "virgin pellets"). The second hopper 51B and the second screw 52B are for recycled pellets (hereinafter referred to as "recycled pellets"). The first hopper 51A is connected to the first screw 52A, and a first heater 57A is provided around the first screw 52A. The second hopper 51B is connected to the second screw 52B, and a second heater 57B is provided around the second screw 52B. The first screw 52A and the second screw 52B are connected to a feed block 58. The feed block 58 is connected to a merging die 53.

[0072] In the extrusion process, virgin pellets 40A are first placed in the first hopper 51A. For virgin pellets, the virgin pellets 40A placed in the first hopper 51A are flowed into the first screw 52A and mixed by the rotation of the first screw 52A while being heated by the first heater 57A. The virgin pellets 40A mixed by the first screw 52A are then flowed toward the narrow feed block 58. Similarly, for recycled pellets, recycled pellets 40B are placed in the second hopper 51B. The recycled pellets 40B placed in the second hopper 51B are flowed into the second screw 52B and mixed by the rotation of the second screw 52B while being heated by the second heater 57B. The recycled pellets 40B mixed by the second screw 52B are then flowed toward the feed block 58.

[0073] In the feed block 58, virgin pellets 40A and recycled pellets 40B merge and flow to the merging die 53. In the merging die 53, the virgin pellets 40A and recycled pellets 40B form a layer and are pushed out (co-extruded in this case) by the feed block 58 and discharged. Here, the layer of virgin pellets 40A pushed out of the merging die 53 by the feed block 58 becomes the virgin polyester layer 22 (specifically, the first virgin polyester layer 22a and the second virgin polyester layer 22b) (see Figure 2). The layer containing recycled pellets 40B and virgin pellets 40A pushed out of the merging die 53 by the feed block 58 becomes the recycled polyester layer 21 (specifically, the first outer recycled polyester layer 21a, the second outer recycled polyester layer 21b, and the inner recycled polyester layer 21c) (see Figure 2).

[0074] In this embodiment, although detailed illustrations are omitted, when heated, the virgin polyester layer 22, recycled polyester layer 21, and virgin polyester layer 22 are stacked in order (more specifically, the first virgin polyester layer 22a, the first outer recycled polyester layer 21a, the inner recycled polyester layer 21c, the second outer recycled polyester layer 21b, and the second virgin polyester layer 22b) to form a sheet which is then discharged from the confluence die 53. At this time, the virgin polyester layer 22 and the recycled polyester layer 21 are bonded together to form a resin sheet 20.

[0075] In this embodiment, as shown in Figure 4, a cooling roll 54 and a winding machine 55 are arranged in order downstream of the confluence die 53, that is, where the resin sheet 20 discharged from the confluence die 53 goes. The resin sheet 20 discharged from the confluence die 53 passes through the cooling roll 54. Here, since the resin sheet 20 discharged from the confluence die 53 is in a heated state, it is cooled as it passes through the cooling roll 54. The resin sheet 20 that has passed through the cooling roll 54 is conveyed toward the winding machine 55 and wound into a roll by the winding machine 55. The resin sheet 20 is manufactured by the above procedure.

[0076] In the resin sheet 20 produced in the extrusion process, the recycled polyester (e.g., bottle recycling material) contained in the recycled polyester layer 21 is made from recycled pellets obtained by re-pelletizing crushed material that has been washed with a weakly alkaline detergent, as described above. Therefore, the recycled polyester has been washed with a weakly alkaline detergent. In the method for producing the packaging container 10 in this embodiment, the recycled polyester is washed with a weakly alkaline detergent, and the resin sheet 20 is produced using the detergent-washed recycled polyester.

[0077] After the resin sheet 20 is produced in the extrusion process, a thermoforming process is performed. In the thermoforming process, the resin sheet 20 is thermoformed to produce a packaging container 10, that is, a container body 11 and a lid 15. Here, thermoforming can also be described as vacuum forming, pressure forming, or a combination of vacuum forming and pressure forming. Figure 5 is a schematic diagram showing the mold 60 and plug 65 used in thermoforming. As shown in Figure 5, the mold 60 and plug 65 are used in the thermoforming process. The mold 60 has a recess 61 formed therein. The plug 65 has a protrusion 66 that is inserted into the recess 61 of the mold 60. Here, during thermoforming, the mold 60 and plug 65 are positioned spaced apart so that the recess 61 and the protrusion 66 face each other. Then, the heated resin sheet 20 is placed between the mold 60 and plug 65. At this time, the resin sheet 20 is positioned such that one of the two virgin polyester layers 22 of the resin sheet 20 (in this case, the first virgin polyester layer 22a) is located on the plug 65 side, and the other of the two virgin polyester layers 22 (in this case, the second virgin polyester layer 22b) is located on the mold 60 side.

[0078] Subsequently, as shown by the arrow in Figure 5, the mold 60 or plug 65 is moved to insert the protrusion 66 of the plug 65 into the recess 61 of the mold 60. As a result, the resin sheet 20 is thermoformed between the recess 61 and the protrusion 66, following the shapes of the recess 61 and the protrusion 66. After thermoforming, the resin sheet 20 is cut as appropriate to produce the packaging container 10 (in this case, the container body 11 and the lid 15).

[0079] In this embodiment, a mold 60 and plug 65 for manufacturing the container body 11 and a mold 60 and plug 65 for manufacturing the lid 15 are provided. For manufacturing the container body 11, the recess 61 of the mold 60 and the protrusion 66 of the plug 65 have shapes corresponding to the shape of the container body 11. For manufacturing the lid 15, the recess 61 of the mold 60 and the protrusion 66 of the plug 65 have shapes corresponding to the shape of the lid 15.

[0080] Next, an evaluation test was conducted to assess the packaging container 10 according to this embodiment. For this evaluation test, the following three samples of packaging containers, Samples 1 to 3, were prepared. In Samples 1 to 3, the overall thickness of the resin sheet was 0.4 mm. In Samples 1 to 3, the dimensions of the container body of the packaging container were 175 mm in length, 175 mm in width, and 60 mm in height.

[0081] <Sample 1> Sample 1 is a packaging container formed from a resin sheet according to this embodiment. In Sample 1, the ratio of the thicknesses of the inner layer, inner intermediate layer, center layer, outer intermediate layer, and outer layer in the packaging container (hereinafter also referred to as the layer ratio) is inner layer:inner intermediate layer:center layer:outer intermediate layer:outer layer = 4:6:80:6:4.

[0082] In Sample 1, the recycled polyester layers (here, the inner intermediate layer, outer intermediate layer, and core layer) are composed of virgin polyester and recycled polyester. The ratio of virgin polyester to recycled polyester differs between the inner intermediate layer, outer intermediate layer, and core layer. In Sample 1, the inner intermediate layer and outer intermediate layer contain 50% by mass of virgin polyester (petroleum-derived PET) and 50% by mass of recycled polyester (bottle recycling material). The core layer contains 20% by mass of virgin polyester and 80% by mass of recycled polyester. In Sample 1, the virgin polyester layers (here, the inner and outer layers) are composed of virgin polyester and lubricant MB (masterbatch). The inner and outer layers contain 94% by mass of virgin polyester and 6% by mass of lubricant MB.

[0083] In Sample 1, mechanically recycled polyester, i.e., bottle recycling material, made from PET bottles collected from the market, was used as the recycled polyester. In Sample 1, PET bottles collected from the market were first washed with water and then crushed to produce crushed material. Next, the crushed material was subjected to detergent washing, water washing, drying, and polymerization to produce re-pelletized recycled polyester (bottle recycling material). In Sample 1, when washing the crushed material obtained from crushed PET bottles collected from the market with detergent, a weakly alkaline detergent, an aqueous sodium carbonate solution, was used. In Sample 1, the crushed material was immersed in a sodium carbonate solution with a concentration of 3% and a temperature of 85 degrees Celsius and stirred for 30 minutes to perform detergent washing.

[0084] In this study, the virgin polyester for Sample 1 was "YS-H01," a PET resin manufactured by Hainan Yisheng Petrochemical Co., Ltd., China. The intrinsic viscosity (IV) of this virgin polyester was 0.78 dl / g. The lubricant MB for Sample 1 was "RE555," manufactured by Toyobo Co., Ltd. This lubricant MB was a polyester resin containing fine particles, with an intrinsic viscosity (IV) of 0.62 dl / g, mixed with 7000 ppm of spherical silica with an average particle size of 2.4 μm during polymerization (see, for example, Japanese Patent Publication No. 2008-30282).

[0085] Subsequently, in Sample 1, resin sheets and packaging containers were manufactured as follows: First, 94% by mass of virgin polyester and 6% by mass of lubricant MB were mixed to prepare a virgin polyester layer mixture for the inner and outer layers. Next, 50% by mass of virgin polyester and 50% by mass of recycled polyester (bottle recycling material) were mixed to prepare an intermediate layer mixture for the inner and outer intermediate layers. Furthermore, 20% by mass of virgin polyester and 80% by mass of recycled polyester (bottle recycling material) were mixed to prepare a core layer mixture for the core layer.

[0086] Subsequently, extrusion molding was performed using a twin-screw extruder (extruder in this case) of model "SBIN-42-S2-30-L" manufactured by Plastics Engineering Laboratory Co., Ltd. Here, the virgin polyester layer mixture, intermediate layer mixture, and core layer mixture were supplied to the extruder, and melt-mixed extrusion was performed at a processing temperature of 280 degrees Celsius to produce a resin sheet with a thickness of approximately 0.20 mm to 1.00 mm (here, a resin sheet consisting of five layers: inner layer, inner intermediate layer, core layer, outer intermediate layer, and outer layer).

[0087] Next, the above resin sheet was formed into a container by vacuum pressure molding to create the packaging container for Sample 1.

[0088] <Sample 2> The packaging container for Sample 2 was manufactured using the same configuration and procedure as Sample 1, except that baking soda (aqueous solution of sodium bicarbonate), a weakly alkaline detergent, was used as the detergent agent in the detergent washing of the crushed material when producing recycled polyester (bottle recycling material).

[0089] <Sample 3> The packaging container of Sample 3 is a packaging container manufactured using the same configuration and manufacturing procedure as Sample 1, except that a sodium hydroxide aqueous solution, a strongly alkaline detergent, was used as the detergent agent in the detergent washing of the crushed material when producing recycled polyester (bottle recycling material).

[0090] Table 1 below shows the formulations of the packaging containers for Samples 1-3, as well as the detergents used for washing the crushed material.

[0091] [Table 1]

[0092] The flexural modulus of the resin sheets of the packaging containers Samples 1-3, prepared as described above, was measured. Specifically, the flexural modulus in the MD direction and the TD direction were measured for the resin sheets of Samples 1-3. Here, using the "Autograph AGS-X" manufactured by Shimadzu Corporation, the flexural modulus of the resin sheets of Samples 1-3 was measured under measurement conditions in accordance with JIS K7171, with a support distance of 30 mm and a bending speed of 20 mm / min. The measurement of the flexural modulus was performed in an environment of 23 degrees Celsius in accordance with JIS K7203. The flexural modulus of the resin sheets of the packaging containers Samples 1-3 (specifically, the flexural modulus in the MD direction and the flexural modulus in the TD direction) is shown in Table 1 above.

[0093] Next, the intrinsic viscosity IV (dl / g) was measured for the packaging containers of Samples 1 to 3. In accordance with JIS K7367-5, a mixed solvent of phenol / 1,1,2,2-tetrachloroethane (weight ratio 3 / 1) was used to measure the intrinsic viscosity IV. The intrinsic viscosity IV values ​​for the packaging containers of Samples 1 to 3 are shown in Table 1 above.

[0094] Next, transparency evaluation tests were conducted on the packaging containers of samples 1 to 3. In the transparency evaluation tests, the total light transmittance (Tt) (%) and diffuse transmittance (Td) (%) were measured for the packaging containers of samples 1 to 3 in accordance with JIS K7136. Then, the haze value (%) of the packaging containers of samples 1 to 3 was calculated using the measured total light transmittance and diffuse transmittance. The haze value is calculated using, for example, the formula 100 × Td / Tt. The haze values ​​for the packaging containers of samples 1 to 3 are shown in Table 1 above. Note that a lower haze value indicates better transparency.

[0095] Next, the buckling strength of the packaging containers for samples 1 to 3 was measured. Here, using the "Autograph AGS-X" manufactured by Shimadzu Corporation, the packaging containers were placed on the compression test stand with the opening of the packaging container (in this case, the opening of the container body) facing downwards. Then, the packaging containers were compressed from above at a speed of 10 m / min. The load at which the side of the packaging container deformed during compression was measured as the buckling strength (kgf). The buckling strengths of the packaging containers for samples 1 to 3 are shown in Table 1 above.

[0096] Next, drop tests were conducted on the packaging containers of samples 1 to 3. In the drop tests, multiple packaging containers for each of samples 1 to 3, along with a 100g weight, were first left undisturbed for more than 12 hours in a constant temperature chamber set to -5 degrees Celsius. After that, the 100g weight was placed inside the packaging containers of samples 1 to 3. Then, the packaging containers of samples 1 to 3, with the weights inside, were free-dropped onto a steel plate from a height of 1.0m. Here, 10 drop tests were conducted for each sample. In the drop tests, the packaging containers of samples 1 to 3 were visually inspected to see if any cracks had occurred after free-dropping, and the number of cracked packaging containers for samples 1 to 3 was investigated. The results of the drop tests on the packaging containers of samples 1 to 3 are shown in Table 1 above.

[0097] As shown in Table 1 above, in samples 1 and 2, using a weakly alkaline detergent when washing the crushed material resulted in a haze value of less than 3%. On the other hand, in sample 3, using a strongly alkaline detergent when washing the crushed material resulted in a haze value of 3% or more. Therefore, the packaging containers of samples 1 and 2 were found to be more transparent than the packaging container of sample 3. This is thought to be because using a weakly alkaline detergent during washing makes it difficult for air bubbles to adhere to the crushed material, and as a result, transparency can be ensured for the recycled pellets (in other words, recycled polyester) produced by polymerizing the crushed material. Furthermore, since the resin sheet is made using recycled polyester with ensured transparency, it is thought that the transparency of the packaging container formed from the resin sheet can be ensured.

[0098] As shown in Table 1 above, the flexural modulus in the MD direction and the flexural modulus in the TD direction were 2,700 MPa or higher for samples 1 and 2, which was higher than that of sample 3. In addition, the intrinsic viscosity IV value for samples 1 and 2 was 0.65 dl / g or higher, which was higher than that of sample 3. Furthermore, the buckling strength for samples 1 and 2 was 9.0 kgf or higher, which was higher than that of sample 3, and there were 0 cracks in the drop test. These results indicate that, even when a weakly alkaline cleaning agent is used as a cleaning agent for the crushed material in samples 1 and 2, the strength of the packaging container can be ensured.

[0099] In this embodiment, as shown in Figure 1, the packaging container 10 is formed from a resin sheet 20. As shown in Figure 2, the resin sheet 20 comprises a recycled polyester layer 21 and a virgin polyester layer 22. The recycled polyester layer 21 contains recycled polyester made from used polyester. The virgin polyester layer 22 is laminated on one or both sides of the recycled polyester layer 21, does not contain recycled polyester, and contains unused virgin polyester. The recycled polyester is washed with a weakly alkaline detergent. The haze value of the packaging container 10 formed from the resin sheet 20 is less than 3%. In this embodiment, the method for manufacturing the packaging container 10 is a method for manufacturing the packaging container 10 using a resin sheet 20. In the method for manufacturing the packaging container 10, recycled polyester is washed with a weakly alkaline detergent, and the resin sheet 20 is manufactured using the recycled polyester that has been washed with the detergent.

[0100] Thus, by using recycled polyester that has been cleaned with a weakly alkaline detergent, it is possible to prevent bubbles from the weakly alkaline detergent from adhering to the recycled polyester. Therefore, a packaging container 10 can be formed from a resin sheet 20 equipped with a recycled polyester layer 21 containing recycled polyester that is resistant to bubble adhesion. Consequently, a packaging container 10 with a haze value of less than 3.0% and ensuring transparency can be provided.

[0101] In this embodiment, the flexural modulus of the resin sheet 20 is 2,700 MPa or higher. This ensures that the strength of the packaging container 10 can be ensured by using a resin sheet 20 with sufficient strength.

[0102] In this embodiment, the virgin polyester includes petroleum-derived polyester or plant-derived polyester. This improves the ease with which the virgin polyester mixes with recycled polyester. For example, when the resin sheet 20 is made in multiple layers as in this embodiment, differences in the fluidity of the resin between adjacent layers during molding (for example, between the inner layer 31 and the inner intermediate layer 33, between the inner intermediate layer 33 and the central layer 35, between the central layer 35 and the outer intermediate layer 34, and between the outer intermediate layer 34 and the outer layer 32) are less likely to occur, thus reducing the likelihood of defects in the appearance of the packaging container 10. Furthermore, the adhesion between the layers of the resin sheet 20 is also excellent, making it less likely for the layers to peel off.

[0103] In this embodiment, the weakly alkaline cleaning agent used when washing recycled polyester (in other words, pulverized material) with detergent is an aqueous sodium carbonate solution or an aqueous sodium bicarbonate solution. In this way, even when recycled polyester is washed with a detergent using an aqueous sodium carbonate solution or an aqueous sodium bicarbonate solution as the weakly alkaline cleaning solution, a transparent packaging container 10 can be provided.

[0104] In the above embodiment, as shown in Figure 2, the virgin polyester layer 22 was laminated on both sides of the recycled polyester layer 21. In other words, the virgin polyester layer 22 was arranged on both sides of the wide surface of the recycled polyester layer 21, and there were two virgin polyester layers 22: a first virgin polyester layer 22a and a second virgin polyester layer 22b. However, the virgin polyester layer 22 may be laminated on only one side of the recycled polyester layer 21. That is, the virgin polyester layer 22 may be arranged on only one side of the wide surface of the recycled polyester layer 21, and there may be only one virgin polyester layer 22. In the virgin polyester layer 22, for example, the second virgin polyester layer 22b may be omitted. In this case, the outer layer 32 may be omitted in the packaging container 10. In this case, the recycled polyester layer 21 may consist of two layers, and for example, the second outer recycled polyester layer 21b may be omitted. In this case, the outer intermediate layer 34 may be omitted in the packaging container 10.

[0105] In the above embodiment, as shown in Figure 2, the recycled polyester layer 21 was composed of three layers: a first outer recycled polyester layer 21a, a second outer recycled polyester layer 21b, and an inner recycled polyester layer 21c. However, the recycled polyester layer 21 may be composed of only one layer. In this case, for example, any two of the first outer recycled polyester layer 21a, the second outer recycled polyester layer 21b, and the inner recycled polyester layer 21c may be omitted. For example, the first outer recycled polyester layer 21a and the second outer recycled polyester layer 21b of the recycled polyester layer 21 may be omitted. In this case, the inner intermediate layer 33 and the outer intermediate layer 34 may be omitted in the packaging container 10. [Explanation of Symbols]

[0106] 10 Packaging containers 11 Container body 15 Lid 20 resin sheets 21 Recycled polyester layer 22 Virgin polyester layer

Claims

1. A packaging container formed from a resin sheet, The aforementioned resin sheet is A recycled polyester layer containing recycled polyester made from used polyester, A virgin polyester layer laminated on one or both sides of the recycled polyester layer, which does not contain the recycled polyester and contains unused virgin polyester, Equipped with, The recycled polyester mentioned above has been washed with a weakly alkaline detergent. A packaging container formed from the aforementioned resin sheet, wherein the haze value of the packaging container is less than 3%.

2. The packaging container according to claim 1, wherein the flexural modulus of the resin sheet is 2,700 MPa or more.

3. The packaging container according to claim 1, wherein the virgin polyester includes petroleum-derived polyester or plant-derived polyester.

4. The packaging container according to any one of claims 1 to 3, wherein the weakly alkaline cleaning agent is an aqueous solution of sodium carbonate or an aqueous solution of sodium bicarbonate.

5. A method for manufacturing a packaging container using a resin sheet, The aforementioned resin sheet is A recycled polyester layer containing recycled polyester made from used polyester, A virgin polyester layer laminated on one or both sides of the recycled polyester layer, comprising a virgin polyester layer that does not contain the recycled polyester, Equipped with, A method for manufacturing a packaging container, comprising washing the recycled polyester with a weakly alkaline detergent, and then manufacturing the resin sheet using the recycled polyester that has been washed with the detergent.

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