Mold set, method for manufacturing straw using mold set, and straw

Abstract

The objective of the present invention is to achieve a mold set that can be used for producing a straw with a bellows structure by using an aliphatic polyester resin as a raw material. In a mold set (100), each peak part (14) of an inner mold (10) has a top part having an R surface, and each peak part (24) of an outer mold (20) has a top part having an R surface. In the LD direction, the length of each peak part (14) is 1.50-1.80 mm, and the length of each peak part (24) is 1.50-1.80 mm.

Description

Mold set, method for manufacturing straws using the mold set, and straws

[0001] The present invention relates to a mold set, a method for manufacturing a straw using the mold set, and a straw.

[0002] To realize a stretchable or bendable straw, a technique for forming a bellows structure as a stretchable or bendable portion on the straw body is known. For example, Patent Document 1 discloses a straw made of thermoplastic resin and having a stretchable portion. The stretchable portion of Patent Document 1 has a small diameter portion, a large diameter portion, and an inclined side portion located between the small diameter portion and the large diameter portion, and the small diameter portion and the large diameter portion are alternately connected via the side portion. When the stretchable portion of Patent Document 1 is in a contracted state, the side portion folds back and overlaps the small diameter portion and the large diameter portion. Patent Document 1 also discloses a mold set for forming the stretchable portion.

[0003] Furthermore, Patent Document 2, although not related to straws made of thermoplastic resin, discloses a technique for forming a bellows by forming an uneven surface on the outer peripheral wall of a thin-walled cylindrical mother tube. The technique in Patent Document 2 uses a mold consisting of a male mold having uneven portions along the circumferential direction on the outer peripheral surface and a female mold that meshes with the uneven surface of the male mold. The outer peripheral wall of the mother tube is then interposed between the male mold and the female mold, and the bellows is formed by pressing the female mold into the male mold while rotating the male mold.

[0004] Aliphatic polyester resins are used in a variety of applications. Among these, biodegradable resins such as poly(3-hydroxyalkanoate) resins (hereinafter sometimes referred to as "P3HA resins") have attracted attention as environmentally friendly resins due to their biodegradability. Attempts have been made to develop straws with bellows structures using such biodegradable resins as raw materials.

[0005] JP-A-59-020120 JP-A-58-131036

[0006] However, when the mold set of Patent Documents 1 or 2 is used to mold the bellows structure of a straw using an aliphatic polyester resin such as a biodegradable resin as a raw material, the bent portion of the bellows structure collapses or breaks, making it impossible to manufacture a practical straw. For this reason, the mold sets of Patent Documents 1 and 2 cannot be used to manufacture straws with a bellows structure using an aliphatic polyester resin such as a biodegradable resin as a raw material, and there is room for improvement.

[0007] One aspect of the present invention aims to provide a mold set that can be used to manufacture straws with bellows structures using aliphatic polyester resins such as biodegradable resins as raw materials, a method for manufacturing straws using the mold set, and the straws themselves.

[0008] In order to solve the above-mentioned problems, a mold set according to one aspect of the present invention is a mold set for forming a bellows structure in a cylindrical straw body, and includes a rod-shaped inner mold that is inserted into the straw body, and a rod-shaped outer mold that presses the straw body from the outside. The inner mold has a first uneven portion that forms the mountain-folded portion of the bellows structure, and the first uneven portion has a first shaft portion that extends in the axial direction of the straw body, and a plurality of first mountain portions that protrude in the radial direction of the inner mold relative to the first shaft portion and are provided at predetermined intervals in the axial direction of the straw body. , the outer mold has a second uneven portion that forms a valley fold portion of the bellows structure, the second uneven portion has a second shaft portion arranged parallel to the first shaft portion, and a plurality of second ridge portions that protrude in the radial direction of the outer mold relative to the second shaft portion and are each inserted between two adjacent first ridge portions, each first ridge portion has a first apex portion with a rounded surface, and each second ridge portion has a second apex portion with a rounded surface, the length of each first ridge portion in the axial direction of the straw body is 1.50 mm to 1.80 mm, and the length of each second ridge portion is 1.50 mm to 1.80 mm.

[0009] In addition, in order to solve the above-mentioned problems, a straw according to another aspect of the present invention is a straw in which a bellows structure is formed in a cylindrical straw body containing an aliphatic polyester resin, and the thickness of the straw body is 0.18 mm to 0.22 mm.

[0010] According to these aspects of the present invention, a mold set that can be used when manufacturing straws with a bellows structure using aliphatic polyester resins such as biodegradable resins as raw materials can be realized.

[0011] 1 shows a schematic configuration of a mold set according to an embodiment of the present invention, with 1001 being a side view and 1002 being a rear view seen from the rear. FIG. 1 is a side view showing a schematic configuration of the concave-convex portion of the inner mold shown in FIG. 1. FIG. 2 is a side view showing a schematic configuration of the concave-convex portion of the outer mold shown in FIG. 1. 4001 to 4003 are diagrams schematically showing an example of a bellows structure forming step in a method for manufacturing a straw according to an embodiment of the present invention. FIG. 2 is a cross-sectional view mainly showing a schematic configuration of the bellows structure of a straw according to an embodiment of the present invention.

[0012] An embodiment of the present invention will be described in detail below. In this specification, unless otherwise specified, "A to B" representing a numerical range means "A or more, B or less." In addition, all documents described in this specification are incorporated herein by reference.

[0013] [Technical Concept] As disclosed in Patent Document 1 and other publications, the technology for forming a bellows structure in a straw body uses a mold set comprising an inner mold and an outer mold. The inner mold is inserted into the straw body and has concave and convex portions that form the mountain folds of the bellows structure. The outer mold presses the straw body from the outside and has concave and convex portions that form the valley folds of the bellows structure.

[0014] The bellows structure is then formed on the straw body through the following steps: a molding step in which the mold set is set on the straw body, and the inner and outer molds are rotated in opposite directions while the outer mold is pressed against the outer surface of the straw body to mold the mountain folds and valley folds of the bellows structure into the straw body; and a folding step in which, after the molding step, the mold set is removed from the straw body, and the molded portions of the straw body are compressed and folded from both sides.

[0015] Therefore, the present inventors discovered that when a straw body made from an aliphatic polyester resin such as biodegradable resin is used to form a bellows structure using the above-mentioned mold set, the ridges of the bent portions of the straw body (valley folds or mountain folds) become white and cracked due to the pressure applied during the shaping process. The present inventors also discovered that the compression of the shaping portion during the folding process whitens and cracks the ridges of the bent portions of the straw body. Therefore, the present inventors have been working diligently to develop a mold set that can be used to manufacture straws with a bellows structure, even when a straw body made from an aliphatic polyester resin such as biodegradable resin is used.

[0016] The present inventors conducted extensive research, believing that a mold set capable of forming a bellows structure in a straw body with a relatively large wall thickness would enable the manufacture of practical straws without cracks at the bends of the bellows structure, and that this mold set could be used to manufacture straws with a bellows structure. As a result, the present inventors discovered that a practical bellows structure straw could be manufactured and used to manufacture straws with a bellows structure by (1) setting the length of each peak (convex portion) of the concave-convex portion of the inner mold and the length of each peak (convex portion) of the concave-convex portion of the outer mold in the axial direction of the straw body to a specific numerical range, and (2) making the tops of each peak (convex portion) of the concave-convex portion of the inner mold and the outer mold rounded, and thus arrived at the present embodiment.

[0017] That is, the mold set according to this embodiment is a mold set for forming a bellows structure in a cylindrical straw body, and includes a rod-shaped inner mold that is inserted into the straw body, and a rod-shaped outer mold that presses the straw body from the outside. The inner mold has a first uneven portion that forms the mountain-folded portion of the bellows structure, and the first uneven portion has a first shaft portion that extends in the axial direction of the straw body, and a plurality of first mountain portions that protrude in the radial direction of the inner mold relative to the first shaft portion and are provided at predetermined intervals in the axial direction of the straw body. The outer mold has a second uneven portion that forms the valley fold portion of the accordion structure, and the second uneven portion has a second shaft portion arranged parallel to the first shaft portion and a plurality of second ridge portions that protrude radially of the outer mold relative to the second shaft portion and are each inserted between two adjacent first ridge portions, each first ridge portion having a first apex with an R-surface and each second ridge portion having a second apex with an R-surface, and the length of each first ridge portion in the axial direction of the straw body is 1.50 mm to 1.80 mm, and the length of each second ridge portion is 1.50 mm to 1.80 mm.

[0018] The straw according to this embodiment is a straw in which a bellows structure is formed in a cylindrical straw body containing an aliphatic polyester resin, and the thickness of the straw body is 0.18 mm to 0.22 mm.

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in the drawings, the longitudinal direction (axial direction) of the straw body is referred to as the LD direction, and one side (front side) in the LD direction is referred to as the LDa side, and the other side (rear side) is referred to as the LDb side.

[0020] (Configuration of mold set) Fig. 1 shows a schematic configuration of a mold set 100 according to this embodiment, where 1001 in Fig. 1 is a side view and 1002 in Fig. 1 is a rear view seen from the LDb side. As shown in 1001 and 1002 in Fig. 1, the mold set 100 includes an inner mold 10 and an outer mold 20.

[0021] The inner mold 10 is a cylindrical rod member that is inserted into the cylindrical straw body. The diameter of the inner mold 10 is slightly smaller than the inner diameter of the straw body. Here, the radial direction of the inner mold 10 is defined as the RD1 direction.

[0022] The inner mold 10 has a cylindrical main body 11 extending in the LD direction, and the main body 11 has an uneven portion 12 (first uneven portion). The uneven portion 12 forms the mountain fold portion of the bellows structure of the straw body. The "mountain fold portion" here refers to the bent portion of the bellows structure where the ridge line is located on the outside.

[0023] The uneven portion 12 has a shaft portion 13 (first shaft portion) and multiple peaks 14 (first peaks). The shaft portion 13 extends in the LD direction and is coaxial with the rest of the body portion 11 except for the uneven portion 12. The peaks 14 protrude in the RD1 direction relative to the shaft portion 13. The peaks 14 have a truncated cone shape with the shaft portion 13 as its axis. The peaks 14 are provided at predetermined intervals in the LD direction.

[0024] The outer mold 20 is a member with a cylindrical side surface that presses the straw body from the outside. The diameter of the outer mold 20 is not particularly limited, but is preferably 5 mm to 60 mm, and more preferably 10 mm to 40 mm. Here, the radial direction of the outer mold 20 is defined as the RD2 direction.

[0025] The outer mold 20 is positioned opposite the concave-convex portion 12 of the inner mold 10 so that the wall of the straw body is sandwiched between the concave-convex portion 12 of the inner mold 10 and the outer mold 20. The outer mold 20 has a concave-convex portion 22 (second concave-convex portion). The concave-convex portion 22 forms the valley fold portion of the bellows structure of the straw body. Here, "valley fold portion" refers to the bent portion of the bellows structure where the ridge line is located on the inside.

[0026] The uneven portion 22 has a shaft portion 23 (second shaft portion) and multiple peaks 24 (second peaks). The shaft portion 23 is arranged parallel to the shaft portion 13. That is, the shaft portion 23 extends in the LD direction. The peaks 24 protrude in the RD2 direction relative to the shaft portion 23. The peaks 24 are frustoconical in shape with the shaft portion 23 as its axis. The peaks 24 are also provided at predetermined intervals in the LD direction. Each peak 24 is configured to be inserted between two adjacent peaks 14 in the uneven portion 12.

[0027] (Configuration of the Concave-Convex Portion of the Inner Mold) FIG. 2 is a side view showing a schematic configuration of the concave-convex portion 12 of the inner mold 10. As shown in FIG. 2, in the concave-convex portion 12, the peak portion 14 has one apex 14c (first apex) and an inclined surface 14a extending from the apex 14c toward the LDa side. More specifically, the peak portion 14 has a truncated cone shape with the axis X of the stem portion 13 as its axis, and is composed of the inclined surface 14a, a rear end surface 14b, and a front end surface 14d. The inclined surface 14a is inclined with respect to the axis X1 of the stem portion 13, and is inclined so that the distance from the stem portion 13 decreases as the inclined surface 14a moves from the LDb side toward the LDa side. The rear end surface 14b and the front end surface 14d are connected to the LDb side and the LDa side of the inclined surface 14a, respectively. The rear end surface 14b and the front end surface 14d are the end surfaces on the LDb and LDa sides, respectively, of the peak portion 14. The apex portion 14c is the connecting portion between the inclined surface 14a and the rear end surface 14b, and is the part of the peak portion 14 that is farthest from the shaft portion 13. The apex portion 14c can be said to be an edge portion of the truncated cone shape of the peak portion 14 described above.

[0028] The surface of the uneven portion 12 is a surface in which the surface 13a of the shaft portion 13, the rear end surface 14b of the peak portion 14, the inclined surface 14a, and the front end surface 14d are alternately repeated from the LDb side to the LDa side.

[0029] At the mountain-folded portions of the bellows structure of the straw body, the apex 14c of the uneven portion 12 forms a ridgeline. In the mold set 100 according to this embodiment, the apex 14c of each mountain portion 14 has a rounded surface. Therefore, even if the inner surface of the straw body abuts strongly against the uneven portion 12 due to pressure from the outer mold 20, cracks are less likely to occur at the ridgeline portion of the bellows structure. Therefore, in order to form the bent portions of the bellows structure without cracks, the apex 14c of the uneven portion 12 can be abutted with a strong force against the inner surface of the straw body.

[0030] From the viewpoint of abutting the apex 14c of the concave-convex portion 12 with a strong force, the radius of curvature of the rounded surface of the apex 14c is preferably 0.01 mm to 1.00 mm, and more preferably 0.05 mm to 0.20 mm. The radius of curvature of the rounded surface of the apex 14c is, for example, 0.10 mm.

[0031] Furthermore, in the mold set 100, the length L1 of each peak 14 of the uneven portion 12 in the LD direction is 1.50 mm to 1.80 mm, preferably 1.55 mm to 1.77 mm, and more preferably 1.60 mm to 1.75 mm. By keeping the length L1 within the above range, a mountain fold that can be folded along the ridge line can be achieved even if the thickness of the peak fold is relatively large. A bellows structure can be formed even for straw bodies with relatively large wall thicknesses. The length L1 is, for example, 1.64 mm.

[0032] Furthermore, the larger the inclination angle θ1 of the inclined surface 14a relative to the stem 13, the stronger the force with which the apex 14c of the uneven portion 12 can abut against the inner surface of the straw body. From this perspective, the inclination angle θ1 is preferably 30.0° to 40.0°, and more preferably 30.0° to 35.0°. The inclination angle θ1 is, for example, 31.07°.

[0033] Furthermore, the greater the distance H1 between the apex 14c and the stem 13, the deeper the groove formed by two adjacent peaks 14. The deeper the groove, the stronger the force with which the apex 14c of the uneven portion 12 can abut against the inner surface of the straw body. From this perspective, the distance H1 between the apex 14c and the stem 13 is preferably 1.10 mm to 1.80 mm, and more preferably 1.30 mm to 1.70 mm. The distance H1 is, for example, 1.49 mm.

[0034] Furthermore, if the distance (pitch) P1 between two adjacent peaks 14 in the uneven portion 12 is large, the relatively thick peak-folded portion can be folded along the ridge line. From this perspective, the distance P1 between two adjacent peaks 14 is preferably 2.20 mm to 2.50 mm, and more preferably 2.25 mm to 2.40 mm. Note that the distance P1 between two adjacent peaks 14 refers to the distance between the two peaks 14c of the two adjacent peaks 14. The distance P1 is, for example, 2.3 mm.

[0035] Furthermore, for two adjacent peaks 14, the distance D1 between the rear end surface 14b of one peak 14 and the front end surface 14d of the other peak 14 is not particularly limited, but is preferably 0.2 mm to 0.8 mm, and more preferably 0.4 mm to 0.7 mm. By keeping the distance D1 within the above range, the contact area between the straw body and parts of the uneven portion 12 other than the apex 14c can be reduced, reducing contact between the mold and the straw other than the ridge 32d of the straw, which improves the appearance of the bellows structure. The distance D1 is, for example, 0.6 mm.

[0036] (Configuration of Concave-Convex Portion of Outer Mold) FIG. 3 is a side view showing a schematic configuration of the concave-convex portion 22 of the outer mold 20. As shown in FIG. 3, in the concave-convex portion 22, the peak portion 24 has one apex 24c (second apex) and an inclined surface 24a extending from the apex 24c toward the LDb side. More specifically, the peak portion 24 has a truncated cone shape with the axis X2 of the stem portion 23 as its axis, and is composed of the inclined surface 24a, a front end surface 24b, and a rear end surface 24d. The inclined surface 24a is inclined with respect to the axis X2 of the stem portion 23, and is inclined so that the distance from the stem portion 23 decreases as the inclined surface 24a moves from the LDa side toward the LDb side. The front end surface 24b and the rear end surface 24d are connected to the LDa side and the LDb side of the inclined surface 24a, respectively. The front end surface 24b and the rear end surface 24d are the end surfaces on the LDa and LDb sides, respectively, of the peak portion 24. The apex portion 24c is the connecting portion between the inclined surface 24a and the front end surface 24b, and is the part of the peak portion 24 that is farthest from the shaft portion 23. The apex portion 24c can be said to be an edge portion of the truncated cone shape of the peak portion 24 described above.

[0037] The surface of the uneven portion 22 is a surface in which the surface 33a of the shaft portion 23, the rear end surface 24d of the peak portion 24, the inclined surface 14a, and the front end surface 24b are alternately repeated from the LDb side to the LDa side.

[0038] 1 (viewed from a direction perpendicular to the axes X1 and X2), when the peak 24 is inserted between two adjacent peaks 14, the inclined surfaces 14a and 24a are preferably parallel to each other. The various dimensions of the peak 24 are preferably the same as the various dimensions of the peak 14 of the inner mold 10. Here, "same" means that the dimensions of the peak 24 are the same as the dimensions of the peak 14 within measurement limits or design limits.

[0039] At the valley-folded portions of the bellows structure of the straw body, the apex 24c of the peaks 24 form ridges. In the mold set 100 according to this embodiment, the apex 24c of each peak 24 has a rounded surface. Therefore, even if the outer surface of the straw body abuts strongly against the uneven portion 22 due to pressure from the outer mold 20, cracks are less likely to occur at the ridges of the bellows structure. Therefore, in order to form the bent portions of the bellows structure without cracks, the apex 24c of the uneven portion 22 can be abutted with a strong force against the outer surface of the straw body.

[0040] From the viewpoint of abutting the apex 24c of the uneven portion 22 with a strong force, the radius of curvature of the rounded surface of the apex 24c is preferably 0.01 mm to 1.00 mm, and more preferably 0.05 mm to 0.20 mm. Furthermore, the radius of curvature of the rounded surface of the apex 24c is preferably the same as the radius of curvature of the rounded surface of the apex 14c. The radius of curvature of the rounded surface of the apex 24c is, for example, 0.10 mm.

[0041] Furthermore, in the mold set 100, the length L2 of each peak 24 of the uneven portion 22 in the LD direction is 1.50 mm to 1.80 mm, preferably 1.55 mm to 1.77 mm, and more preferably 1.60 mm to 1.75 mm. Furthermore, it is preferable that the length L2 is the same as the length L1 of the peak 14. By having the length L2 within the above numerical range, a valley fold that can be folded at the ridge line can be achieved even if the thickness of the valley fold portion is relatively large. A bellows structure can be formed even for a straw body with a relatively large wall thickness. The length L2 is, for example, 1.64 mm.

[0042] Furthermore, the larger the inclination angle θ2 of the inclined surface 24a relative to the shaft portion 23, the stronger the force with which the apex 24c of the uneven portion 22 can abut against the outer surface of the straw body. From this perspective, the inclination angle θ2 is preferably 30.0° to 40.0°, and more preferably 30.0° to 35.0°. Furthermore, the inclination angle θ2 is preferably the same as the inclination angle θ1. The inclination angle θ2 is, for example, 31.07°.

[0043] Furthermore, the greater the distance H2 between the apex 24c and the stem 23, the deeper the groove formed by two adjacent peaks 24. The deeper the groove, the stronger the force with which the apex 24c of the uneven portion 22 can abut against the outer surface of the straw body. From this perspective, the distance H2 between the apex 24c and the stem 23 is preferably 1.10 mm to 1.80 mm, and more preferably 1.30 mm to 1.70 mm. Furthermore, the distance H2 is preferably the same as the distance H1. The distance H2 is, for example, 1.49 mm.

[0044] Furthermore, if the distance (pitch) P2 between two adjacent peaks 24 in the uneven portion 22 is large, the relatively thick valley fold portion can be folded along the ridge line. From this perspective, the distance P2 between two adjacent peaks 24 is preferably 2.20 mm to 2.50 mm, and more preferably 2.25 mm to 2.40 mm. Furthermore, the distance P2 is preferably the same as the distance P1. Note that the distance P2 between two adjacent peaks 24 refers to the distance between the two peaks 24c of the two adjacent peaks 24. The distance P2 is, for example, 2.30 mm.

[0045] Furthermore, for two adjacent peaks 14, the distance D2 between the front end surface 24b of one peak 24 and the rear end surface 24d of the other peak 24 is not particularly limited, but is preferably 0.2 mm to 0.8 mm, and more preferably 0.3 mm to 0.7 mm. Furthermore, it is preferable that the distance D2 is the same as the distance D1. By keeping the distance D2 within the above numerical range, the contact area between the straw body and parts of the uneven portion 22 other than the apex 24c can be reduced, resulting in a better appearance of the bellows structure. The distance D2 is, for example, 0.6 mm.

[0046] As described above, the mold set 100 has the following features (1) and (2). Each ridge 14 has a crest 14c with a rounded surface, and each ridge 24 has a crest 24c with a rounded surface. (2) In the LD direction, the length L1 of each ridge 14 is 1.50 mm to 1.80 mm, and the length L2 of each ridge 24 is 1.50 mm to 1.80 mm. Therefore, the mold set 100 allows the crests 14c and 24c to abut against the straw body with a strong force, and furthermore, it is possible to form a bellows structure even in straw bodies with relatively large wall thicknesses. This makes it possible to realize a straw that maintains its bellows structure without cracks in the ridges, even when the thickness of the bent portion is large. Therefore, the mold set 100 can produce a practical bellows-structured straw, even when the straw body is made from an aliphatic polyester resin such as a biodegradable resin. Therefore, according to this embodiment, a mold set 100 can be realized that can be used when manufacturing straws with a bellows structure using aliphatic polyester resins such as biodegradable resins as raw materials.

[0047] (Straw Manufacturing Method) The straw manufacturing method according to this embodiment (hereinafter sometimes referred to as this manufacturing method) includes a bellows structure forming step of forming a bellows structure in the straw body using the above-described mold set 100. This makes it possible to manufacture a practical straw with a bellows structure even when using a straw body made from an aliphatic polyester resin such as a biodegradable resin.

[0048] The present manufacturing method may be any method as long as it includes the bellows structure forming step. From the viewpoint of the workability of the bellows structure, the bellows structure forming step preferably includes a shaping step and a folding step. In the shaping step, a mold set is used to shaping the mountain folds and valley folds of the bellows structure into the straw body. In the folding step, the straw body shaped in the shaping step is compressed, and the mountain folds and valley folds are folded to form the bellows structure. 4001 to 4003 in Figure 4 are schematic diagrams illustrating an example of the bellows structure forming step in the present manufacturing method. The bellows structure forming step includes a preparation step indicated by 4001 in Figure 4, a shaping step indicated by 4002 in Figure 4, and a folding step indicated by 4003 in Figure 4.

[0049] As shown in 4001 in Figure 4, in the preparation step, the mold set is set on the cylindrical straw body 31. In this preparation step, the outer mold 20 is positioned so as to face the concave-convex portion 12 of the inner mold 10. The straw body 31 is attached to the inner mold 10 thus positioned. Specifically, the straw body 31 is attached so that the inner mold 10 is inserted inside the straw body 31.

[0050] Then, as shown in 4002 in Figure 4, in the shaping process, the inner mold 10 and the outer mold 20 are rotated in opposite directions against the straw body 31 with the inner mold 10 attached thereto, while the outer mold 20 is pressed from the outside. This rotation and pressing force shaping the valley folds 32E and mountain folds 32F of the accordion structure 32 into the straw body 31. Then, at the contact point between the straw body 31 and the apex 14c of the inner mold 10, a ridge line 32c of the valley folds 32E is formed. Furthermore, at the contact point between the straw body 31 and the apex 24c of the outer mold 20, a ridge line 32d of the mountain folds 32F is formed. Through the shaping process, the straw body 31 is formed with valley folds 32E and mountain folds 32F alternately in the LD direction. By using the above-described mold set 100, cracks are prevented from occurring in the ridge lines 32c of the valley folds 32E and the ridge lines 32d of the mountain folds 32F during the molding process. Note that the ridge lines 32c and 32d can be expressed as bending lines or folding lines of the valley folds 32E and the mountain folds 32F in the bellows structure 32.

[0051] Here, in the molding process, the rotation speed and rotation time of the inner mold 10 and the outer mold 20 may be any speed that forms the ridgelines 32c and 32d on the straw body 31, and can be set appropriately depending on the thickness, material, etc. of the straw body 31. For example, the rotation speed of the inner mold 10 and the outer mold 20 is 50 rpm to 1000 rpm, preferably 200 rpm to 600 rpm. The rotation time of the inner mold 10 and the outer mold 20 is 0.5 seconds to 30 seconds, preferably 1.5 seconds to 10 seconds. More specifically, the rotation speed and rotation time of the inner mold 10 and the outer mold 20 are 300 rpm and 5 seconds, respectively.

[0052] Furthermore, the outer mold 20 is pressed against the straw body 31 by, for example, moving the outer mold 20 toward the inner mold 10 while the outer mold 20 is in contact with the outer surface of the straw body 31. The distance the outer mold 20 moves toward the inner mold 10 corresponds to the amount of pressing of the outer mold 20 against the straw body 31. The amount of pressing of the outer mold 20 may be any rotation speed that forms the ridge lines 32c and 32d on the straw body 31, and can be set appropriately depending on the thickness, material, etc. of the straw body 31. For example, for a straw body 31 with a wall thickness of 0.16 mm to 0.20 mm, the amount of pressing of the outer mold 20 is preferably 0.1 mm to 1.0 mm, and more preferably 0.2 mm to 0.8 mm.

[0053] As shown in 4003 in Figure 4, in the folding process, the inner mold 10 and outer mold 20 are removed from the straw body 31 that has been shaped in the shaping process. The straw body 31 is then compressed from both sides. This compresses the valley folds 32E and the mountain folds 32F, forming the bellows structure 32 in the straw body 31. If the mold set 100 described above is used, the compression in the folding process will not cause cracks in the ridge lines 32c of the valley folds 32E or the ridge lines 32d of the mountain folds 32F.

[0054] (Straw body 31) Here, according to this manufacturing method, in the bellows structure forming process described above, it is preferable that the straw body 31 has an elastic modulus of 1300 MPa to 2200 MPa and a breaking strain of 200% to 600%. Because the elastic modulus and breaking strain of the straw body 31 are within specific numerical ranges, the bellows structure 32 has the effect of being excellent in workability. Specific effects are, for example, as follows: (1) In the above-mentioned shaping process, the bent portions of the straw body 31 (valley fold portion 32E or mountain fold portion 32F) are not crushed. (2) In the above-mentioned folding process, cracks do not occur at the ridge lines 32c and 32d of the bent portions of the straw body 31 (the bellows structure 32 does not tear at the ridge lines 32c or 32d).

[0055] The elastic modulus and breaking strain are calculated based on a tensile test performed on a dumbbell-shaped film cut from the straw body 31 using a tensile tester (Shimadzu Corporation: EZ-LX 1kN) in accordance with JIS K 7127 at a tensile speed of 100 mm / min to obtain an S-S curve.

[0056] The elastic modulus is preferably 1400 MPa to 2100 MPa, and more preferably 1500 MPa to 2000 MPa, and the breaking strain is preferably 200% to 500%, and more preferably 240% to 500%.

[0057] Preferably, this manufacturing method further includes a process of forming the straw body 31 (straw body forming process), and a curing process of storing the straw body 31 formed in the straw body forming process under predetermined curing conditions (curing time, curing temperature, etc.) until the bellows structure forming process. The elastic modulus and breaking strain values ​​can be controlled, for example, by adjusting the curing time of the straw body 31 in the curing process. The longer the curing time, the higher the elastic modulus tends to be. Furthermore, the longer the curing time, the smaller the breaking strain tends to be.

[0058] The curing time is not particularly limited as long as it allows the elastic modulus and the breaking strain to fall within the above-mentioned numerical ranges, but is preferably 1 to 24 days, and more preferably 2 to 15 days. The curing temperature is also not particularly limited as long as it allows the elastic modulus and the breaking strain to fall within the above-mentioned numerical ranges, but is preferably −20° C. to 50° C., and more preferably 0° C. to 30° C.

[0059] Furthermore, when the aliphatic polyester resin is a P3HA resin, the elastic modulus and breaking strain can also be controlled, for example, by adjusting the average content ratio of other hydroxyalkanoate units in all monomer units constituting the P3HA resin component.

[0060] 5 is a cross-sectional view mainly showing the schematic configuration of the bellows structure 32 of the straw 30 according to this embodiment. The straw 30 can be manufactured, for example, by this manufacturing method, that is, the method for manufacturing a straw using the mold set 100 described above.

[0061] As shown in Figure 5, the straw 30 has a cylindrical straw body 31 containing an aliphatic polyester resin and a bellows structure 32 formed in the straw body 31. The aliphatic polyester resin contained in the straw body 31 will be described later.

[0062] The bellows structure 32 includes multiple valley folds 32E and multiple mountain folds 32F, with the valley folds 32E and mountain folds 32F arranged alternately in the axial direction of the straw body 31. In a cross-sectional shape along the axial direction of the straw body 31, i.e., the cross-sectional shape shown in FIG. 5, the bellows structure 32 has a wavy wall portion in which long side portions 32a and short side portions 32b are alternately connected. Both the valley folds 32E and the mountain folds 32F are composed of long side portions 32a and short side portions 32b. In the valley folds 32E and the mountain folds 32F, the ridge lines 32c and 32d are both connecting portions between the long side portions 32a and short side portions 32b. In the valley folds 32E, the ridge line 32c is arranged on the outside, while in the mountain folds 32F, the ridge line 32d is arranged on the inside.

[0063] In the straw 30 according to this embodiment, the straw body 31 has a thickness T1 of 0.18 mm to 0.22 mm, and preferably 0.185 mm to 0.205 mm. By ensuring that the straw body 31 has a thickness within the above range, the straw 30 can maintain the bellows structure 32 without cracks along the ridges 32c and 32d. Therefore, the straw 30 can be used to manufacture straws with a bellows structure using aliphatic polyester resins such as biodegradable resins as raw materials.

[0064] Furthermore, in the cross-sectional shape along the axial direction of the straw body 31, i.e., the cross-sectional shape shown in Figure 5, the ratio of the length of the long side 32a to the length of the short side 32b is preferably 1.50 to 2.50, and more preferably 1.70 to 2.30. By having the length of the long side 32a / the length of the short side 32b within the above numerical range, it is possible to realize a straw 30 that can maintain the bellows structure 32 without cracks in the ridges 32c and 32d.

[0065] Furthermore, the thickness T2 of the ridges 32c and 32d, i.e., the connecting portions between the long side 32a and the short side 32b, is preferably 0.040 mm to 0.120 mm, and more preferably 0.070 mm to 0.110 mm. By having the thickness of the connecting portions between the long side 32a and the short side 32b within the above numerical range, the straw 30 can maintain the bellows structure 32 without any cracks along the ridges 32c and 32d.

[0066] (Thermoplastic Resin) The straw body that is the subject of the mold set 100 according to this embodiment, i.e., the straw body used in this manufacturing method, and the straw according to this embodiment, are made of a thermoplastic resin. The thermoplastic resin is not particularly limited. Preferred thermoplastic resins include general-purpose resins such as polypropylene, polyethylene, polyvinyl chloride, polyvinyl acetate, polyacetal, polycarbonate, polyamide, acrylonitrile, butadiene, polystyrene, and acrylic polymers, as well as biodegradable resins such as P3HA resin, polylactic acid, polyglycolic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, and polycaprolactone. Furthermore, the thermoplastic resins can be used alone or in combination of two or more.

[0067] In particular, the straw (straw body) according to this embodiment preferably contains an aliphatic polyester resin. Furthermore, the aliphatic polyester resin is preferably a poly(3-hydroxyalkanoate) resin (hereinafter sometimes referred to as P3HA resin). In this specification, "P3HA resin" refers to a polymer having the general formula: [-CHR-CH２ -CO-O-] (wherein R is C ｎ H ２ｎ＋１ and n is an integer of 1 or more and 15 or less.) as a repeating unit.

[0068] More specifically, the P3HA-based resin preferably contains 3-hydroxybutyrate (3HB) units. The P3HA-based resin containing 3HB units is preferably selected from the group consisting of poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxydecanoate). The P3HA resin may contain only one type, or may contain two or more types.

[0069] The P3HA resin is preferably a P3HA resin produced by a microorganism (a microbially produced P3HA resin). A microbially produced P3HA resin is usually composed only of D-form (R-form) polyhydroxyalkanoate monomer units. Among the microbially produced P3HA resins, P3HB, P3HB3HH, P3HB3HV, P3HB3HV3HH, and P3HB4HB are preferred because of ease of industrial production, with P3HB, P3HB3HH, P3HB3HV, and P3HB4HB being more preferred.

[0070] P3HA-based resins can also be produced by, for example, the method described in International Publication No. 2010 / 013483. Commercially available P3HA-based resins include Kaneka Biodegradable Polymer PHBH (registered trademark) manufactured by Kaneka Corporation.

[0071] The P3HA resin also contains at least one copolymer of a 3HB unit and another hydroxyalkanoate unit, and the 3-hydroxybutyrate unit in the poly(3-hydroxyalkanoate) resin accounts for 65.0 to 99.0 mol %, preferably 68.0 to 98.5 mol %, more preferably 70.0 to 98.5 mol %, and even more preferably 70.0 to 98.0 mol %, of all repeating units (100 mol %).

[0072] When the composition ratio of the 3HB repeating unit is 90.0 mol% or more, the rigidity of the P3HA-based resin is improved, the crystallization rate is accelerated, burrs are reduced, and productivity tends to be improved. On the other hand, when the composition ratio of the 3HB repeating unit is 99.0 mol% or less, the melting point is below the thermal decomposition temperature, making stable and continuous production possible. The monomer composition ratio of the P3HA-based resin can be measured by gas chromatography or the like (see, for example, International Publication No. 2014 / 020838).

[0073] The molecular weight of the P3HA resin is not particularly limited as long as it exhibits substantially sufficient physical properties for the intended application. The weight-average molecular weight of the P3HA resin is preferably in the range of 100,000 to 1,000,000, more preferably 150,000 to 700,000, even more preferably 200,000 to 500,000, and particularly preferably 250,000 to 450,000. When the weight-average molecular weight is 100,000 or more, appropriate mechanical strength is obtained. Furthermore, when the molecular weight is 1,000,000 or less, an increase in melt viscosity can be suppressed, resulting in excellent moldability.

[0074] The weight-average molecular weight can be measured using gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko K.K.) with a polystyrene gel (Shodex K-804 manufactured by Showa Denko K.K.) as a column, chloroform as a mobile phase, and the molecular weight can be calculated as a polystyrene-equivalent. In this case, a calibration curve is prepared using polystyrenes with weight-average molecular weights of 31,400, 197,000, 668,000, and 1,920,000. As the column for the GPC, a column appropriate for measuring the molecular weight may be used.

[0075] The material of the straw (straw body) according to this embodiment may also contain additives that can be used with the thermoplastic resin, as long as they do not impair the effects of the present invention. Examples of such additives include inorganic fillers such as talc, calcium carbonate, mica, and silica; colorants such as pigments and dyes; odor absorbers such as activated carbon and zeolite; fragrances such as vanillin and dextrin; plasticizers; antioxidants; weather resistance improvers; UV absorbers; nucleating agents; lubricants; release agents; water repellents; antibacterial agents; and sliding properties improvers. Only one type of additive may be used, or two or more types may be used. The amount of these additives can be appropriately determined by those skilled in the art depending on the intended use.

[0076] According to this embodiment, when P3HA-based resin is used as the raw material for the straws (straw body), marine pollution due to disposal can be suppressed, which can contribute to the achievement of Sustainable Development Goals (SDGs) such as Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and sustainably use the oceans and marine resources for sustainable development."

[0077] The straw body used in this manufacturing method can be manufactured by a known method using a resin composition containing the above-mentioned aliphatic polyester-based resin. The straw body can be manufactured, for example, by the following method: A melting step in which the resin composition containing the aliphatic polyester-based resin is melted in an extruder. After the melting step, the resin composition is extruded through a circular die connected to the outlet of the extruder, poured into water, and solidified into a tubular shape in a molding step.

[0078] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0079] That is, one embodiment of the present invention is as follows.

[0080] <1> A mold set 100 for forming a bellows structure 32 in a cylindrical straw body 31, comprising: a rod-shaped inner mold 10 inserted into the straw body 31; and a rod-shaped outer mold 20 pressing the straw body 31 from the outside; the inner mold 10 having a first uneven portion (uneven portion 12) that forms a mountain fold portion 32F of the bellows structure 32, the first uneven portion having: a first shaft portion (shaft portion 13) extending in the axial direction of the straw body (LD direction); and a plurality of first peak portions (peak portions 14) that protrude in the radial direction of the inner mold 10 (RD1 direction) relative to the first shaft portion and are provided at predetermined intervals in the axial direction of the straw body 31; the outer mold 20 having a second uneven portion (uneven portion 22) that forms a valley fold portion 32E of the bellows structure 32, the second uneven portion having: The mold set 100 has a second shaft portion (shaft portion 23) arranged parallel to the first shaft portion, and a plurality of second peak portions (peak portions 24) that protrude in the radial direction (RD2 direction) of the outer mold 20 relative to the second shaft portion and are each inserted between two adjacent first peak portions (peak portions 14), each of which has a first apex (apex portion 14c) with an R-surface, and each of which has a second apex (apex portion 24c) with an R-surface, and the length L1 of each of the first peak portions in the axial direction of the straw body 31 is 1.50 mm to 1.80 mm, and the length L2 of each of the second peak portions is 1.50 mm to 1.80 mm.

[0081] <2> The mold set 100 of <1>, wherein each first peak has a first inclined surface (inclined surface 14a) extending from the first apex, and each second peak has a second inclined surface (inclined surface 24a) extending from the second apex, an inclination angle θ1 of the first inclined surface with respect to the first shaft portion is 30.0° to 40.0°, and an inclination angle θ2 of the second inclined surface with respect to the second shaft portion is 30.0° to 40.0°.

[0082] <3> The mold set 100 of <1> or <2>, wherein the distance H1 between the first apex and the first shaft portion is 1.10 mm to 1.80 mm, and the distance H2 between the second apex and the second shaft portion is 1.10 mm to 1.80 mm.

[0083] <4> The mold set 100 according to any one of <1> to <3>, wherein the distance P1 between two adjacent first peaks (peaks 14) is 2.20 mm to 2.50 mm, and the distance P2 between two adjacent second peaks (peaks 24) is 2.20 mm to 2.50 mm.

[0084] <5> The mold set 100 of any one of <1> to <4>, wherein the straw body 31 contains an aliphatic polyester resin.

[0085] <6> The mold set 100 of <5>, wherein the aliphatic polyester-based resin is a poly(3-hydroxyalkanoate)-based resin.

[0086] <7> A method for manufacturing a straw 30, including a bellows structure forming process for forming a bellows structure 32 in a straw body 31 using any one of the mold sets 100 of <1> to <6>.

[0087] <8> The straw manufacturing method of <7>, wherein in the bellows structure forming process, the straw body 31 has an elastic modulus of 1300 MPa to 2200 MPa and a breaking strain of 200% to 600%.

[0088] <9> The method for manufacturing a straw according to <8>, wherein the bellows structure forming step includes: a molding step of molding mountain folds 32F and valley folds 32E of the bellows structure 32 into the straw body 31 using the mold set 100; and a folding step of compressing the straw body 31 molded in the molding step and folding the mountain folds 32F and the valley folds 32E to form the bellows structure 32.

[0089] <10> The method for manufacturing a straw according to <9>, wherein the molding step includes a pressing step of pressing the outer mold 20 from the outside against the straw body 31 with the inner mold 10 attached inside while rotating the inner mold 10 and the outer mold 20 in opposite directions.

[0090] <11> The method for manufacturing a straw according to any one of <7> to <10>, further comprising: a straw body forming step of forming the straw body 31; and a curing step of storing the straw body 31 formed in the straw body forming step under predetermined curing conditions until the bellows structure forming step.

[0091] <12> The method for manufacturing a straw according to <11>, wherein in the curing step, the curing conditions include the following: a curing time of 1 to 24 days, and a curing temperature of -20°C to 50°C.

[0092] <13> A straw 30 in which a bellows structure 32 is formed on a cylindrical straw body 31 containing an aliphatic polyester resin, and the straw body 31 has a wall thickness T1 of 0.18 mm to 0.22 mm.

[0093] <14> The straw 30 of <13>, in which, in a cross-sectional shape along the axial direction (LD direction) of the straw body 31, the bellows structure 32 has a wavy wall portion in which long side portions 32a and short side portions 32b are alternately connected, and the length of the long side portions 32a / the length of the short side portions 32b is 1.50 to 2.50.

[0094] <15> The straw 30 of <14>, wherein the thickness T2 of the connecting portion (the portion of the ridge lines 32c, 32d) between the long side portion 32a and the short side portion 32b is 0.040 mm to 0.120 mm.

[0095] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0096] The substances used in the examples and comparative examples are shown below.

[0097] [Poly(3-hydroxyalkanoate)-based resin] PHB: Poly(3-hydroxybutyrate) (weight average molecular weight: 300,000 g / mol) Produced in accordance with the method described in Comparative Example 1 of WO 2004 / 041936. P3HB3HH-3: P3HB3HH (average content ratio 3HB / 3HH = 97.1 / 2.9 (mol% / mol%), weight average molecular weight: 300,000 g / mol) Produced in accordance with the method described in Example 2 of WO 2019 / 142845. P3HB3HH-13: P3HB3HH (Kaneka Biodegradable Polymer PHBH (registered trademark)) (average content ratio 3HB / 3HH = 87.1 / 12.9 (mol% / mol%), weight average molecular weight 330,000 g / mol) P3HB3HH-30: P3HB3HH (average content ratio 3HB / 3HH = 70.5 / 29.5 (mol% / mol%), weight average molecular weight 640,000 g / mol) Produced in accordance with the method described in Example 9 of WO 2019 / 142845.

[0098] [Additives] Additive-1: Behenic acid amide (Nippon Fine Chemicals: BNT-22H) Additive-2: Erucic acid amide (Nippon Fine Chemicals: Neutron-S) [Plasticizer] Plasticizer: Glycerin diacetomonolaurate (Riken Vitamin: BIOCIZER) [Others] Tubes made of polybutylene succinate (PBS) and cellulose acetate were obtained and used as the straw body. Both tubes had an outer diameter of 6 mm and a wall thickness of 0.2 mm.

[0099] 1. Preparation of Resin Composition Pellets A blend of 12.0 parts by weight of PHB, 52.2 parts by weight of P3HB3HH-3, 22.8 parts by weight of P3HB3HH-30, and 13.0 parts by weight of P3HB3HH-13 was mixed with 1.0 part by weight of Additive-1, 0.5 part by weight of Additive-2, and 4.3 parts by weight of a plasticizer, and further blended.

[0100] The obtained resin material (resin mixture) was fed into a φ26 mm co-rotating twin-screw extruder with the cylinder temperature and die temperature both set to 150°C, and strands of the resin material were extruded at 20 kg / hour. The extruded resin material was passed through a water tank filled with hot water at 40°C to solidify the strands, which were then cut with a pelletizer to obtain resin composition pellets.

[0101] 2. Molding of tube (straw body) The cylinder temperature and die temperature of a φ50 mm single-screw extruder connected to an annular die (outer diameter 15 mm, inner diameter 13.5 mm) were set to 160 ° C., and the resin composition pellets were added and extruded into a tube. The extruded tube was passed through a 40 ° C. water bath located 100 mm away from the annular die and taken up at speeds of 25 m / min, 30 m / min, and 40 m / min. As a result, tubes with an outer diameter of 6 mm and a length of 200 mm, each with a wall thickness of 0.16 mm, 0.18 mm, and 0.20 mm, were obtained.

[0102] 3. Processing the bellows structure To process the bellows structure, a pair of mold sets (see Figure 1) was used, which were placed on the inside and outside of the straw body.

[0103] Preparation step: The tubes with different wall thicknesses prepared in 2 were inserted into a rod-shaped inner mold, and a movable outer mold having the same shape as the inner mold was pressed against the tubes from the outside.

[0104] Shaping process: The outer mold was movable in a direction perpendicular to the longitudinal direction of the tube. After the outer mold contacted the outer surface of the tube, it was further pressed down. Then, in this state, the outer mold and inner mold were rotated in opposite directions at 300 rpm for 5 seconds to form a bellows structure on the tube. After the rotation of the inner mold and outer mold was completed, the outer mold was separated from the tube, and the tube was removed from the inner mold. The conditions for the amount of pressing of the outer mold after contacting the outer surface of the tube were 0.30 mm and 0.60 mm.

[0105] Folding step: Next, the tube was inserted into the compression pin on the cylindrical side, and a force was applied to the tube in the longitudinal direction to compress it, thereby folding the bellows structure.

[0106] 4. Dimensions of the die set used The dimensions of the die set used to process the bellows structure will be described with reference to FIGS. 2 and 3.

[0107] Mold set #1 Inner mold 10: The length L1 of the ridge portion 14 is 1.34 mm. The inclination angle θ1 of the inclined surface 14a relative to the stem portion 13 is 27.18°. The distance H1 between the peak 14c and the stem portion 13 is 1.00 mm. The distance P1 between two adjacent ridge portions 14 is 2.00 mm. No rounded surface is formed on the peak 14c.

[0108] Outer mold 20: The length L2 of the ridge portion 24 is 1.34 mm. The inclination angle θ2 of the inclined surface 24a relative to the shaft portion 23 is 27.18°. The distance H2 between the peak 24c and the shaft portion 23 is 1.00 mm. The distance P2 between two adjacent ridge portions 24 is 2.00 mm. No rounded surface is formed on the peak 24c.

[0109] Mold set #2 Inner mold 10: The length L1 of the ridge portion 14 is 1.64 mm. The inclination angle θ1 of the inclined surface 14a relative to the stem portion 13 is 31.07°. The distance H1 between the peak 14c and the stem portion 13 is 1.20 mm. The distance P1 between two adjacent ridge portions 14 is 2.30 mm. The peak 14c is rounded with a radius of curvature of 0.1 mm.

[0110] Outer mold 20: The length L2 of the ridge portion 24 is 1.64 mm. The inclination angle θ2 of the inclined surface 24a relative to the shaft portion 23 is 31.07°. The distance H2 between the peak 24c and the shaft portion 23 is 1.20 mm. The distance P2 between two adjacent ridge portions 24 is 2.30 mm. The peak 24c is rounded with a radius of curvature of 0.1 mm.

[0111] 5. Evaluation of workability of bellows structure The evaluation of workability of the bellows structure is as follows: "Moldable": In the folding process, the tube can be folded at the ridge lines of the mountain folds and valley folds in the bellows structure. "Not formable": In the folding process, the tube cannot be folded at the ridge lines of the mountain folds and valley folds in the bellows structure. "Crack": Regardless of whether the result is "moldable" or "not formable", cracks occur at the ridge lines of the mountain folds and valley folds in the bellows structure.

[0112] (Example 1) A tube with a wall thickness of 0.16 mm, prepared in 2., was used as the straw body. Using mold set #2, the amount of depression after contact with the outer surface of the tube of the outer mold was set to 0.3 mm, and a bellows structure was processed in accordance with 3. Then, the processability of the bellows structure was evaluated in accordance with 5.

[0113] (Examples 2 to 7, Comparative Examples 1 to 5) The bellows structures were processed in the same manner as in Example 1, except that the wall thickness of the tube used as the straw body, the type of mold set used to process the bellows structure, and the amount of pressure applied after the outer mold contacted the outer surface of the tube were set under the conditions shown in Table 1. Then, the processability of the bellows structures was evaluated according to 5.

[0114] The evaluation results of the workability of the bellows structure are shown in Table 1.

[0115] (Examples 8 to 12, Comparative Examples 6 to 9) The evaluation methods carried out in Examples 8 to 12 and Comparative Examples 6 to 9 will be explained below.

[0116] [Tensile Test: Calculation of Elastic Modulus and Breaking Strain] The produced tube was cut into a film, which was then cut into a No. 8 dumbbell shape in accordance with JIS K 6251. A tensile test was then carried out on the cut film using a tensile tester (Shimadzu Corporation: EZ-LX 1kN) in accordance with JIS K 7127 at a tension speed of 100 mm / min. The tensile modulus and breaking strain were calculated based on the S-S curve obtained from the tensile test.

[0117] [Evaluation of Workability of Bellows Structure] The workability of the bellows structure was evaluated as follows: "Crushed": During the folding process, the bellows structure broke at a portion other than the ridge lines of the mountain folds and valley folds. "Cracked": During the shaping process or the folding process, cracks were observed at the ridge lines of the mountain folds and valley folds. "No problem": During the folding process, the bellows structure broke at the ridge lines of the mountain folds and valley folds, a bellows structure was formed, and no cracks were observed at the ridge lines.

[0118] (Example 8) The straw body was made from the tube prepared in 2., which was cured for one hour. The straw body was processed into a bellows structure according to 3., and the processability of the bellows structure was evaluated. A tensile test was also conducted on the straw body, and the elastic modulus and breaking strain were calculated.

[0119] The evaluation results of the elastic modulus and breaking strain of the straw body, as well as the processability of the bellows structure, are shown in Table 2.

[0120] (Examples 9 to 11, Comparative Examples 6 to 8) A bellows structure was processed in the same manner as in Example 8, except that the tube prepared in 2. was cured for the time shown in Table 2. A tensile test was conducted on the straw body, and the elastic modulus and breaking strain were calculated.

[0121] The evaluation results of the elastic modulus and breaking strain of the straw body, as well as the processability of the bellows structure, are shown in Table 2.

[0122] (Example 12) A bellows structure was fabricated in the same manner as in Example 8, except that a polybutylene succinate tube was used as the straw body and the curing time was set to the time shown in Table 2. A tensile test was performed on the straw body, and the elastic modulus and breaking strain were calculated.

[0123] The evaluation results of the elastic modulus and breaking strain of the straw body, as well as the processability of the bellows structure, are shown in Table 2.

[0124] (Comparative Example 9) A bellows structure was fabricated in the same manner as in Example 8, except that a cellulose acetate tube was used as the straw body and the curing time was set to the time shown in Table 2. A tensile test was also performed on the straw body, and the elastic modulus and breaking strain were calculated.

[0125] The evaluation results of the elastic modulus and breaking strain of the straw body, as well as the processability of the bellows structure, are shown in Table 2.

[0126] The results in Table 2 show that there is no problem with the workability of the bellows structure when the elastic modulus of the straw body is 1300 MPa to 2000 MPa and the breaking strain of the straw body is 200% to 600%.

[0127] The present invention can be used in the field of straw manufacturing.

[0128] REFERENCE SIGNS LIST 10 Inner mold 12 Concave-convex portion (first concave-convex portion) 13 Shaft portion (first shaft portion) 14 Mountain portion (first mountain portion) 14a Inclined surface (first inclined surface) 14c Peak portion (first peak portion) 20 Outer mold 22 Concave-convex portion (second concave-convex portion) 23 Shaft portion (second shaft portion) 24 Mountain portion (second mountain portion) 24a Inclined surface (second inclined surface) 24c Peak portion (second peak portion) 30 Straw 31 Straw body 32 Accordion structure 32a Long side portion 32b Short side portion 32c, 32d Ridge line (connecting portion between long side portion and short side portion) 32E Mountain fold portion 32F Valley fold portion 100 Mold set

Claims

1. A mold set for forming a bellows structure in a cylindrical straw body, comprising: a rod-shaped inner mold inserted into the straw body; and a rod-shaped outer mold pressing the straw body from the outside, wherein the inner mold has a first uneven portion forming a mountain fold of the bellows structure, the first uneven portion having: a first shaft portion extending in the axial direction of the straw body; and a plurality of first peaks protruding from the first shaft portion in the radial direction of the inner mold and provided at predetermined intervals in the axial direction of the straw body; the outer mold has a second uneven portion forming a valley fold of the bellows structure, the second uneven portion having: a second shaft portion arranged parallel to the first shaft portion; and a plurality of second peaks protruding from the radial direction of the outer mold relative to the second shaft portion and inserted between two adjacent first peaks, Each first ridge portion has a first apex having an R-surface, and each second ridge portion has a second apex having an R-surface, and the length of each first ridge portion in the axial direction of the straw body is 1.50 mm to 1.80 mm, and the length of each second ridge portion is 1.50 mm to 1.80 mm.

2. The mold set according to claim 1, wherein each first peak has a first inclined surface extending from the first apex, and each second peak has a second inclined surface extending from the second apex, the inclination angle of the first inclined surface relative to the first axis portion is 30.0° to 40.0°, and the inclination angle of the second inclined surface relative to the second axis portion is 30.0° to 40.0°.

3. A mold set as described in claim 1 or 2, wherein the distance between the first apex and the first shaft portion is 1.10 mm to 1.80 mm, and the distance between the second apex and the second shaft portion is 1.10 mm to 1.80 mm.

4. A mold set as claimed in claim 1 or 2, wherein the distance between two adjacent first ridges is 2.20 mm to 2.50 mm, and the distance between two adjacent second ridges is 2.20 mm to 2.50 mm.

5. The mold set according to claim 1 or 2, wherein the straw body comprises an aliphatic polyester resin.

6. The mold set according to claim 5, wherein the aliphatic polyester resin is a poly(3-hydroxyalkanoate) resin.

7. A method for manufacturing a straw, comprising a bellows structure forming step of forming a bellows structure in a straw body using the mold set according to claim 1 or 2.

8. A method for manufacturing a straw as described in claim 7, wherein in the bellows structure forming process, the straw body has an elastic modulus of 1300 MPa to 2200 MPa and a breaking strain of 200% to 600%.

9. A method for manufacturing a straw as described in claim 8, wherein the bellows structure forming process includes: a molding process for molding mountain folds and valley folds of the bellows structure into the straw body using the mold set; and a folding process for compressing the straw body molded in the molding process and folding the mountain folds and valley folds to form the bellows structure.

10. A method for manufacturing a straw as described in claim 9, wherein the molding process includes a pressing process in which the outer mold is pressed from the outside against the straw body with the inner mold attached inside while rotating the inner mold and the outer mold in opposite directions to each other.

11. The method for manufacturing a straw as described in claim 7, further comprising: a straw body forming process for forming the straw body; and a curing process for storing the straw body formed in the straw body forming process under specified curing conditions until the bellows structure forming process.

12. The method for manufacturing straws according to claim 11, wherein in the curing step, the curing conditions include: the curing time is 1 day to 24 days, and the curing temperature is -20°C to 50°C.

13. A straw having a bellows structure formed in a cylindrical straw body containing an aliphatic polyester resin, the straw body having a wall thickness of 0.18 mm to 0.22 mm.

14. The straw according to claim 13, wherein in a cross-sectional shape along the axial direction of the straw body, the bellows structure has a wavy wall portion in which long sides and short sides are alternately connected, and the ratio of the length of the long sides to the length of the short sides is 1.50 to 2.

50.

15. The straw according to claim 14, wherein the thickness of the connecting portion between the long side and the short side is 0.040 mm to 0.120 mm.

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