Manufacturing method for straw

Abstract

To achieve a manufacturing method for a straw excellent in processability of a bellows structure when the bellows structure is formed in a straw body including an aliphatic polyester resin.SOLUTION: In a bellows structure forming step in a straw manufacturing method, a straw body has an elastic modulus of 1300 MPa to 2200 MPa and breaking strain of 200% to 600%.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Aliphatic polyester resins are used for various purposes. Among them, biodegradable resins such as poly(3-hydroxyalkanoate) resins have been attracting attention as environmentally friendly resins due to their biodegradability. Attempts have been made to develop straws using such biodegradable resins as raw materials.

[0003] Patent Document 1 discloses a resin tube containing a poly(3-hydroxyalkanoate) resin component having the following characteristics: (1) The P3HA resin component contains at least two types of poly(3-hydroxyalkanoate) resins differing from each other in the type of constituent monomer and / or the content ratio of the constituent monomer. (2) The 50% breaking energy of the resin tube measured by an impact resistance test is 0.2 J or more. Patent Document 1 also discloses straws as an application of the resin tube. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2022 / 009717 Summary of the Invention [Problem to be solved by the invention]

[0005] The resin tube disclosed in Patent Document 1 has excellent impact resistance. However, when forming a bellows structure in the resin tube in order to use the resin tube as a straw with a bellows structure, there is room for improvement in terms of workability of the bellows structure.

[0006] One aspect of the present invention aims to realize a manufacturing method for a straw that has excellent workability when forming a bellows structure in a straw body containing an aliphatic polyester resin. [Means for solving the problem]

[0007] In order to solve the above problems, one embodiment of the present invention relates to a method for manufacturing a straw, which includes a bellows structure forming step of forming a bellows structure in a straw body containing an aliphatic polyester resin, and in the bellows structure forming step, the straw body has an elastic modulus of 1300 MPa to 2200 MPa and a breaking strain of 200% to 600%. Effect of the Invention

[0008] According to one aspect of the present invention, when a bellows structure is formed in a straw body containing an aliphatic polyester resin, the bellows structure has excellent processability. [Brief description of the drawings]

[0009] [Figure 1] 1001 to 1003 are diagrams illustrating an example of a bellows structure forming step in the method for producing a straw according to an embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view mainly showing the schematic configuration of a bellows structure of a straw manufactured by a straw manufacturing method according to an embodiment of the present invention. FIG. [Diagram 3] 2 is a side view showing an example of the configuration of a first concave-convex portion of an inner mold of a mold set used in a straw manufacturing method according to an embodiment of the present invention. FIG. [Figure 4] 4 is a side view showing an example of the configuration of a second concave-convex portion of an outer mold of a mold set used in a straw manufacturing method according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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.

[0011] [Technical philosophy] The technique for forming a bellows structure in a straw body uses a mold set including an inner mold and an outer mold. The inner mold is inserted into the straw body and has a concave-convex part that forms the mountain folds of the bellows structure. The outer mold presses the straw body from the outside and has a concave-convex part that forms the valley folds of the bellows structure.

[0012] The bellows structure is then formed in the straw body through the following steps: a molding step in which the above-mentioned mold set is set on the straw body and mountain folds and valley folds of the bellows structure are molded 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 parts of the straw body are compressed and folded from both sides.

[0013] Therefore, the inventors of the present application found that when a straw body made of aliphatic polyester resin such as biodegradable resin is used, the following problems occur when the bellows structure is molded using the above mold set, resulting in poor workability of the bellows structure: (1) In the above molding process, the bent portions of the straw body (valley folds or mountain folds) are crushed. (2) In the above folding process, the ridges of the bent portions of the straw body are torn.

[0014] Therefore, the inventors of the present application have been working hard to develop a manufacturing method that is excellent in workability of the bellows structure when forming the bellows structure in the straw body containing an aliphatic polyester resin. As a result, the inventors of the present application have focused on the elastic modulus and breaking strain of the straw body to which the bellows structure is applied. They have found that the workability of the bellows structure is excellent by setting the elastic modulus and breaking strain of the straw body to a specific range, and have arrived at the manufacturing method of the straw according to the present embodiment.

[0015] In other words, the straw manufacturing method according to this embodiment (hereinafter sometimes referred to as this manufacturing method) is a straw manufacturing method that includes a bellows structure forming process of forming a bellows structure in a straw body containing an aliphatic polyester resin, and 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%.

[0016] According to this manufacturing method, in the bellows structure forming step, the straw body has an elastic modulus of 1300MPa to 2200MPa and a breaking strain of 200% to 600%, so that the bellows structure has excellent workability. Hereinafter, this manufacturing method will be described in detail.

[0017] (Aliphatic polyester resin) In this manufacturing method, an aliphatic polyester resin is used as the raw material for the straw body. The aliphatic polyester resin is not particularly limited, but is preferably biodegradable. 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 3-hydroxyalkanoic acid repeating unit represented by the general formula: [-CHR-CH2-CO-O-] (wherein R is C n H 2n+1 where n is an integer of 1 or more and 15 or less.) is a polyhydroxyalkanoate containing this as a repeating unit.

[0018] More specifically, the P3HA resin preferably contains 3-hydroxybutyrate (3HB) units. The P3HA resin is preferably one or more 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.

[0019] 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, and P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are more preferred, in terms of ease of industrial production.

[0020] The P3HA resin can also be produced by, for example, the method described in International Publication No. 2010 / 013483. Commercially available P3HA resins include Kaneka Biodegradable Polymer PHBH (registered trademark) manufactured by Kaneka Corporation.

[0021] The P3HA resin also contains at least one copolymer of 3HB units and other hydroxyalkanoate units, and the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin account 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 %).

[0022] When the composition ratio of the 3HB repeating unit is 90.0 mol% or more, the rigidity of the P3HA resin is improved, the crystallization speed 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 lower than the thermal decomposition temperature, so stable and continuous production is possible. The monomer composition ratio of the P3HA resin can be measured by gas chromatography or the like (see, for example, International Publication No. 2014 / 020838).

[0023] The molecular weight of the P3HA resin is not particularly limited as long as it shows substantially sufficient physical properties for the intended use. 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, further 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. In addition, when the molecular weight is 1,000,000 or less, the increase in melt viscosity can be suppressed, and the moldability is excellent.

[0024] The weight average molecular weight can be measured by gel permeation chromatography (GPC) (Shodex GPC-101, manufactured by Showa Denko K.K.), using a polystyrene gel (Shodex K-804, manufactured by Showa Denko K.K.) as a column, and using chloroform as a mobile phase, and can be calculated as a molecular weight converted into polystyrene. 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.

[0025] In addition, the material of the straw body used in this manufacturing method may contain additives that can be used with the aliphatic polyester 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 absorbents such as activated carbon and zeolite, fragrances such as vanillin and dextrin, plasticizers, antioxidants, weather resistance improvers, ultraviolet absorbers, crystal nucleating agents, lubricants, release agents, water repellents, antibacterial agents, and sliding improvers. Only one type of additive may be included. Two or more types may be included. The content of these additives can be appropriately set by a person skilled in the art depending on the purpose of use.

[0026] According to this embodiment, when P3HA-based resin is used as the raw material for the 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."

[0027] The aliphatic polyester resin is not limited to a P3HA resin, and may be, for example, at least one selected from the group consisting of polybutylene succinate (PBS), polybutylene succinate-co-butylene adipate (PBSA), and polylactic acid.

[0028] 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 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 resin is melted in an extruder. After the melting step, the resin composition is extruded from a circular die connected to the outlet of the extruder, poured into water, and solidified to form into a tube.

[0029] (Bellows structure forming process) The bellows structure forming process is a process of forming a bellows structure in the straw body containing the above-mentioned aliphatic polyester resin. The bellows structure forming process is not particularly limited as long as it can form a bellows structure in the straw body.

[0030] From the viewpoint of workability of the bellows structure, the bellows structure forming step preferably includes a molding step and a folding step. In the molding step, a mountain fold and a valley fold of the bellows structure are molded into the straw body using a mold set. In the folding step, the straw body molded in the molding step is compressed, and the mountain fold and the valley fold are folded to form the bellows structure.

[0031] 1001 to 1003 in Fig. 1 are diagrams showing an example of a bellows structure forming step in the present manufacturing method. The bellows structure forming step includes a preparation step shown in 1001 in Fig. 1, a shaping step shown in 1002 in Fig. 1, and a folding step shown in 1003 in Fig. 1. As shown in the drawings, in this specification, the length direction (axial direction) of the straw body is referred to as the LD direction, and in the LD direction, one side (front side) is the LDa side, and the other side (rear side) is the LDb side.

[0032] As shown in 1001 of FIG. 1, in the preparation step, the mold set 100 is set on the cylindrical straw body 31. Here, the mold set 100 includes a rod-shaped inner mold 10 and a rod-shaped outer mold 20. The inner mold 10 is inserted into the straw body 31. The outer mold 20 presses the straw body 31 from the outside. The inner mold 10 has an uneven portion 12 (first uneven portion). The uneven portion 12 forms the mountain fold portion 32F of the bellows structure 32 (see 1002 of FIG. 1). The outer mold 20 has an uneven portion 22 (second uneven portion). The uneven portion 22 forms the valley fold portion 32E of the bellows structure 32 (see 1002 of FIG. 1). In the preparation step, the outer mold 20 is arranged to face the uneven portion 12 of the inner mold 10. The straw body 31 is attached to the inner mold 10 arranged in this way. Specifically, the straw body 31 is attached so that the inner mold 10 is inserted inside the straw body 31.

[0033] Then, as shown in 1002 of FIG. 1, in the molding process, the inner mold 10 and the outer mold 20 are rotated in opposite directions to each other while pressing the outer mold 20 against the straw body 31 with the inner mold 10 attached thereto. This rotation and pressing molds the valley folds 32E and mountain folds 32F of the bellows structure 32 against the straw body 31. Then, the ridge 32c of the valley folds 32E is formed at the contact portion between the straw body 31 and the apex 14c of the inner mold 10. Also, the ridge 32d of the mountain folds 32F is formed at the contact portion between the straw body 31 and the apex 24c of the outer mold 20. Through the molding process, the valley folds 32E and mountain folds 32F are alternately formed in the LD direction on the straw body 31. The ridgelines 32c and 32d can be expressed as the bending or folding lines of the valley fold portion 32E and the mountain fold portion 32F in the bellows structure 32. The "mountain fold portion" here means a bending portion of the bellows structure where the ridgeline is located on the outside. The "valley fold portion" here means a bending portion of the bellows structure where the ridgeline is located on the inside.

[0034] Here, in the molding process, the rotation speed and rotation time of the inner mold 10 and the outer mold 20 may be any rotation speed at which the ridges 32c and 32d are formed on the straw body 31, and may be appropriately set according to 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, and 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, and 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.

[0035] 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 number of rotations at which the ridges 32c and 32d are formed on the straw body 31, and may be appropriately set according to the thickness, material, etc. of the straw body 31. For example, for a straw body 31 with a 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.

[0036] As shown in 1003 of Fig. 1, in the folding process, the inner mold 10 and the outer mold 20 are removed from the straw body 31 that has been shaped in the shaping process. Then, the straw body 31 is compressed from both sides. This causes the valley folds 32E and the mountain folds 32F to be compressed, forming the bellows structure 32 in the straw body 31.

[0037] (Straw body 31) According to this manufacturing method, in the above-mentioned 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%. Since the elastic modulus and breaking strain of the straw body 31 are within a specific numerical range, the bellows structure 32 has excellent workability. Specific effects are, for example, as follows. (1) In the above-mentioned shaping process, the bent portion of the straw body 31 (the valley fold portion 32E or the mountain fold portion 32F) is not crushed. (2) In the above-mentioned folding process, cracks are not generated at the ridges 32c and 32d of the bent portion of the straw body 31 (the bellows structure 32 is not torn at the ridges 32c or 32d).

[0038] The elastic modulus and breaking strain are calculated based on an SS curve obtained by performing a tensile test on a dumbbell-shaped film obtained by cutting 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.

[0039] The elastic modulus is preferably 1400 MPa to 2100 MPa, and more preferably 1500 MPa to 2000 MPa. The breaking strain is preferably 200% to 500%, and more preferably 240% to 500%.

[0040] This manufacturing method preferably 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 values ​​of the elastic modulus and breaking strain 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. Also, the longer the curing time, the smaller the breaking strain tends to be.

[0041] 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 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.

[0042] 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.

[0043] (straw) Fig. 2 is a cross-sectional view showing an example of a schematic configuration of a bellows structure 32 of a straw 30 manufactured by this manufacturing method. As shown in Fig. 2, the straw 30 has a configuration in which the bellows structure 32 is formed on a tubular straw body 31 containing an aliphatic polyester resin.

[0044] The bellows structure 32 includes a plurality of valley folds 32E and a plurality of mountain folds 32F, and the valley folds 32E and the mountain folds 32F are alternately arranged in the axial direction of the straw body 31. In the cross-sectional shape along the axial direction of the straw body 31, i.e., the cross-sectional shape shown in FIG. 2, the bellows structure 32 has a wavy wall portion in which the long side portions 32a and the short side portions 32b are alternately connected. Both the valley folds 32E and the mountain folds 32F are composed of the long side portions 32a and the 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 the 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.

[0045] Here, the thickness T1 of the straw body 31 is 0.180mm to 0.220mm, and more preferably 0.185mm to 0.205mm. By having the thickness of the straw body 31 within the above numerical range, it is possible to realize a straw 30 that can maintain the bellows structure 32 without cracks on the ridges 32c and 32d. Therefore, when manufacturing a straw with a bellows structure using an aliphatic polyester resin such as a biodegradable resin as a raw material, the bellows structure 32 is excellent in processability.

[0046] In addition, in the cross-sectional shape along the axial direction of the straw body 31, i.e., the cross-sectional shape shown in Fig. 2, the ratio of the length of the long side portion 32a to the length of the short side portion 32b is preferably 1.50 to 2.50, and more preferably 1.70 to 2.30. By having the ratio of the length of the long side portion 32a to the length of the short side portion 32b within the above numerical range, the bellows structure 32 can be maintained without cracks in the ridges 32c and 32d.

[0047] Furthermore, the thickness T2 of the ridges 32c and 32d, i.e., the connecting portions between the long side portions 32a and the short side portions 32b, is preferably 0.040 mm to 0.120 mm, and more preferably 0.070 mm to 0.110 mm. When the thickness of the connecting portions between the long side portions 32a and the short side portions 32b is within the above numerical range, the bellows structure 32 can be maintained without cracks in the ridges 32c and 32d.

[0048] (Mold set 100 used in this manufacturing method) The mold set 100 used in this manufacturing method is not particularly limited as long as it is capable of forming a bellows structure on the straw body 31 having the elastic modulus and breaking strain in the above-mentioned numerical range. Preferably, the mold set 100 includes the inner mold 10 and the outer mold 20 described above.

[0049] Fig. 3 is a side view showing an example of the configuration of the concave-convex portion 12 of the inner mold 10 shown in Fig. 1. As shown in Fig. 3, the concave-convex portion 12 has a shaft portion 13 and a plurality of ridge portions 14.

[0050] In the uneven portion 12, the mountain portion 14 has one apex 14c and an inclined surface 14a extending from the apex 14c to the LDa side. More specifically, the mountain portion 14 has a truncated cone shape with the axis X of the shaft portion 13 as its axis, and is composed of the inclined surface 14a, the rear end surface 14b, and the front end surface 14d. The inclined surface 14a is a surface inclined with respect to the axis X1 of the shaft portion 13, and is inclined so that the distance from the shaft portion 13 becomes smaller as it goes from the LDb side to the LDa side. In addition, 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 side and the LDa side of the mountain portion 14, respectively. Moreover, the apex 14c is a connecting portion between the inclined surface 14a and the rear end surface 14b, and is the portion of the peak 14 that is the farthest from the shaft portion 13. The apex 14c can be said to be an edge portion of the truncated cone shape of the peak 14 described above.

[0051] The surface of the uneven portion 12 is a surface in which a surface 13a of the shaft portion 13, a rear end face 14b of the mountain portion 14, an inclined surface 14a, and a front end face 14d are alternately repeated from the LDb side to the LDa side.

[0052] At the mountain-folded portion of the bellows structure of the straw body, the apex 14c of the uneven portion 12 forms a ridgeline. The apex 14c of each mountain portion 14 has an R surface. Therefore, even if the inner surface of the straw body strongly abuts against the uneven portion 12 due to the pressure from the outer mold 20, cracks are unlikely to occur at the ridgeline portion of the bellows structure. Therefore, in order to form the bent portion of the bellows structure without cracks, the apex 14c of the uneven portion 12 can be abutted against the inner surface of the straw body with a strong force.

[0053] From the viewpoint of abutting the apex 14c of the uneven portion 12 with a strong force, the radius of curvature of the R 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 R surface of the apex 14c is, for example, 0.10 mm.

[0054] In the mold set 100, the length L1 of each mountain portion 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 having the length L1 within the above numerical range, even if the thickness of the mountain-folded portion is relatively large, a mountain fold that can be folded at the ridge line can be realized. A bellows structure can be formed even for a straw body with a relatively thick wall. The length L1 is, for example, 1.64 mm.

[0055] Furthermore, the larger the inclination angle θ1 of the inclined surface 14a with respect to the shaft portion 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°.

[0056] Furthermore, the greater the distance H1 between the apex 14c and the shaft 13, the deeper the concave groove formed by two adjacent peaks 14. If the concave groove is deep, the apex 14c of the uneven portion 12 can be abutted against the inner surface of the straw body with a strong force. From this perspective, the distance H1 between the apex 14c and the shaft 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.

[0057] 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 at the ridge line. From this viewpoint, 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. The distance P1 between two adjacent peaks 14 refers to the distance between two apexes 14c of the two adjacent peaks 14. The distance P1 is, for example, 2.3 mm.

[0058] In addition, in 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 having the distance D1 within the above numerical range, the contact area between the straw body and the parts of the uneven portion 12 other than the apex 14c can be reduced, which has the effect of improving the appearance of the bellows structure. The distance D1 is, for example, 0.6 mm.

[0059] Fig. 4 is a side view showing an example of the configuration of concave-convex portion 22 of outer mold 20 shown in Fig. 1. As shown in Fig. 4, concave-convex portion 22 has a shaft portion 23 and a plurality of ridge portions 24.

[0060] In the uneven portion 22, the mountain portion 24 has one apex 24c (second apex) and an inclined surface 24a extending from the apex 24c to the LDb side. More specifically, the mountain portion 24 has a truncated cone shape with the axis X2 of the shaft portion 23 as its axis, and is composed of the inclined surface 24a, the front end surface 24b, and the rear end surface 24d. The inclined surface 24a is a surface inclined with respect to the axis X2 of the shaft portion 23, and is inclined so that the distance from the shaft portion 23 becomes smaller as it goes from the LDa side to the LDb side. In addition, 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 side and the LDb side of the mountain portion 24, respectively. Moreover, the apex 24c is a connecting portion between the inclined surface 24a and the front end surface 24b, and is the portion of the peak 24 that is farthest from the shaft portion 23. The apex 24c can be said to be an edge portion of the truncated cone shape of the peak 24 described above.

[0061] 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 mountain portion 24, the inclined surface 14a, and the front end surface 24b are alternately repeated from the LDb side to the LDa side.

[0062] Furthermore, when viewed from a direction perpendicular to the axes X1 and X2, in a state in which the peak portion 24 is inserted between two adjacent peak portions 14, the inclined surfaces 14a and 24a are preferably parallel to each other. The various dimensions of the peak portion 24 are preferably the same as the various dimensions of the peak portion 14 of the inner mold 10. Here, "the same" means that the dimensions of the peak portion 24 are the same as the dimensions of the peak portion 14 within the measurement limits or design limits.

[0063] At the valley fold of the bellows structure of the straw body, the apex 24c of the mountain portion 24 forms a ridgeline. The apex 24c of each mountain portion 24 has an R surface. Therefore, even if the outer surface of the straw body abuts strongly against the uneven portion 22 due to the pressure from the outer mold 20, cracks are unlikely to occur at the ridgeline portion of the bellows structure. Therefore, in order to form the bent portion of the bellows structure without cracks, the apex 24c of the uneven portion 22 can be abutted strongly against the outer surface of the straw body.

[0064] From the viewpoint of abutting the apex 24c of the uneven portion 22 with a strong force, the radius of curvature of the R-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 R-surface of the apex 24c is preferably the same as the radius of curvature of the R-surface of the apex 14c. The radius of curvature of the R-surface of the apex 24c is, for example, 0.10 mm.

[0065] 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 realized 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 thick wall. The length L2 is, for example, 1.64 mm.

[0066] 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, it is preferable that the inclination angle θ2 is the same as the inclination angle θ1. The inclination angle θ2 is, for example, 31.07°.

[0067] Furthermore, the greater the distance H2 between the apex 24c and the shaft 23, the deeper the concave groove formed by two adjacent peaks 24. If the depth of the concave groove is deep, the apex 24c of the uneven portion 22 can be abutted against the outer surface of the straw body with a strong force. From this point of view, the distance H2 between the apex 24c and the shaft 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.

[0068] Furthermore, if the distance (pitch) P2 between two adjacent peaks 24 in the uneven portion 22 is large, the valley bend portion, which has a relatively large thickness, can be folded at the ridge line. From this viewpoint, 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 two apexes 24c in two adjacent peaks 24. The distance P2 is, for example, 2.30 mm.

[0069] In addition, in two adjacent peaks 24, 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 having the distance D2 within the above numerical range, the contact area between the straw body and the parts of the uneven portion 22 other than the apex 24c can be reduced, and the appearance of the bellows structure can be improved. The distance D2 is, for example, 0.6 mm.

[0070] 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.

[0071] That is, one embodiment of the present invention is as follows.

[0072] <1> A method for manufacturing a straw 30, comprising a bellows structure forming step of forming a bellows structure 32 on a straw body 31 containing an aliphatic polyester resin, In the bellows structure forming step, the straw body 31 has an elastic modulus of 1300 MPa to 2000 MPa and a breaking strain of 200% to 600%.

[0073] <2> The bellows structure forming step includes: A molding process of molding the mountain fold portion 32F and the valley fold portion 32E of the bellows structure 32 to the straw body 31 using a mold set 100; A folding process of compressing the straw body 31 shaped by the shaping process and folding the mountain fold portion 32F and the valley fold portion 32E to form the bellows structure 32. <1> A method for manufacturing straws 30.

[0074] <3> The mold set 100 includes: A rod-shaped inner mold 10 that is inserted into the straw body 31; and a rod-shaped outer mold 20 that presses the straw body 31 from the outside. The inner mold 10 has a first uneven portion (uneven portion 12) that forms the mountain-folded portion 32F of the bellows structure 32, The outer mold 20 has a second uneven portion (uneven portion 22) that forms the valley fold portion 32E of the bellows structure 32, The molding step includes: The method includes a pressing step of pressing the outer mold 20 from the outside against the straw body 31 with the inner mold 10 attached thereto while rotating the inner mold 10 and the outer mold 20 in opposite directions to each other. <2> A method for manufacturing straws 30.

[0075] <4> The aliphatic polyester resin is a poly(3-hydroxyalkanoate) resin. <1> ~ <3> A method for manufacturing any one of the straws 30.

[0076] <5> The poly(3-hydroxyalkanoate) resin is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxydecanoate). <4> A method for manufacturing straws 30. EXAMPLES

[0077] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0078] The substances used in the examples and comparative examples are shown below.

[0079] [Poly(3-hydroxyalkanoate) resin] PHB: Poly(3-hydroxybutyrate) (weight average molecular weight is 300,000 g / mol) It was produced according to 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 is 300,000 g / mol) It was 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 is 330,000 g / mol) P3HB3HH-30: P3HB3HH (average content ratio 3HB / 3HH = 70.5 / 29.5 (mol% / mol%), weight average molecular weight is 640,000 g / mol) It was produced in accordance with the method described in Example 9 of WO 2019 / 142845.

[0080] [Additives] Additive-1: Behenamide (Nippon Fine Chemicals: BNT-22H) Additive-2: Erucic acid amide (Neutron-S, manufactured by Nippon Fine Chemicals) [Plasticizer] Plasticizer: Glycerin diacetomonolaurate (manufactured by Riken Vitamin Co., Ltd.: BIOCIZER) [others] Polybutylene succinate (PBS) and cellulose acetate tubes were obtained and used as the straw bodies. Both tubes had an outer diameter of 6 mm and a wall thickness of 0.2 mm.

[0081] 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 further blended 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.

[0082] 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 at 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, and cut with a pelletizer to obtain resin composition pellets.

[0083] 2. Forming the 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 a speed of 30 m / min with a take-up machine. As a result, a tube with an outer diameter of 6 mm, a wall thickness of 0.2 mm, and a length of 200 mm was obtained as the straw body.

[0084] 3. Processing the bellows structure To process the bellows structure, a pair of mold sets (see Figures 1, 3, and 4) were used to place the straw body on the inside and outside.

[0085] Preparation step: The tube prepared in step 2 was inserted into a rod-shaped inner mold (see Figure 3), and a movable outer mold (see Figure 4) having the same shape as the inner mold was pressed against the outside of the tube.

[0086] Molding process: The outer mold is movable in a direction perpendicular to the longitudinal direction of the tube. After the outer mold comes into contact with the outer surface of the tube, it is pressed further in. In this state, the outer mold and the inner mold are rotated in opposite directions at 300 rpm for 5 seconds to mold a bellows structure into the tube. After the rotation of the inner mold and the outer mold is completed, the outer mold is removed from the tube, and the tube is removed from the inner mold. The condition for the amount of pressing of the outer mold after it comes into contact with the outer surface of the tube was 0.6 mm.

[0087] Folding process: 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.

[0088] 4. Dimensions of the mold set to be used The dimensions of the die set used in machining the bellows structure will be described with reference to Figs.

[0089] Inner mold 10: The length L1 of the ridge 14 is 1.64 mm. The inclination angle θ1 of the inclined surface 14a with respect to the shaft 13 is 31.07°. The distance H1 between the apex 14c and the shaft 13 is 1.20 mm. The distance P1 between two adjacent ridges 14 is 2.30 mm. The apex 14c is rounded with a radius of curvature of 0.1 mm.

[0090] Outer mold 20: Length L2 of ridge 24 is 1.64 mm. Incline angle θ2 of inclined surface 24a with respect to shaft 23 is 31.07°. Distance H2 between apex 24c and shaft 23 is 1.20 mm. Distance P2 between two adjacent ridges 24 is 2.30 mm. Apex 24c is rounded with a radius of curvature of 0.1 mm.

[0091] The evaluation methods used in the examples and comparative examples are described below.

[0092] [Tensile test: Calculation of elastic modulus and breaking strain] The prepared tube was cut into a film, which was then cut into a No. 8 dumbbell shape conforming to JIS K 6251. The cut film was subjected to a tensile test at a tensile speed of 100 mm / min using a tensile tester (Shimadzu Corporation: EZ-LX 1kN) conforming to JIS K 7127. The tensile modulus and breaking strain were calculated based on the SS curve obtained by the tensile test.

[0093] [Evaluation of workability of bellows structure] The evaluation of the workability of the bellows structure is as follows. "Crushing": During the folding process, the bellows structure breaks at a portion other than the ridge lines of the mountain folds and valley folds. "Cracks": Cracks are observed on the ridges of the mountain folds and valley folds during the shaping process or the folding process. "No problem": In the above folding process, the mountain folds and the valley folds are folded at their ridges, a bellows structure is formed, and no cracks are observed at the ridges.

[0094] Example 1 The straw body was made from the tube prepared in 2., which had been cured for one hour. The straw body was processed into a bellows structure according to 3., and the workability 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.

[0095] The evaluation results of the elastic modulus and breaking strain of the straw body, as well as the workability of the bellows structure, are shown in Table 1.

[0096] (Examples 2 to 4, Comparative Examples 1 to 3) A bellows structure was processed in the same manner as in Example 1, except that the tube prepared in 2 was cured for the time shown in Table 1. A tensile test was performed on the straw body, and the elastic modulus and breaking strain were calculated.

[0097] The evaluation results of the elastic modulus and breaking strain of the straw body, as well as the workability of the bellows structure, are shown in Table 1.

[0098] Example 5 A bellows structure was processed in the same manner as in Example 1, except that a polybutylene succinate tube was used as the straw body and the curing time was set to the time shown in Table 1. A tensile test was performed on the straw body, and the elastic modulus and breaking strain were calculated.

[0099] The evaluation results of the elastic modulus and breaking strain of the straw body, as well as the workability of the bellows structure, are shown in Table 1.

[0100] Comparative Example 4 A bellows structure was fabricated in the same manner as in Example 1, except that a cellulose acetate tube was used as the straw body and the curing time was set to the time shown in Table 1. A tensile test was performed on the straw body, and the elastic modulus and breaking strain were calculated.

[0101] Table 1 shows the evaluation results of the elastic modulus and breaking strain of the straw body, as well as the workability of the bellows structure.

[0102] [Table 1]

[0103] The results in Table 1 show that when the elastic modulus of the straw body is 1300 MPa to 2000 MPa and the breaking strain of the straw body 3 is 200% to 600%, there is no problem with the workability of the bellows structure. [Industrial Applicability]

[0104] The present invention can be used in the field of straw manufacturing. [Explanation of symbols]

[0105] 10 Inner mold 12 Uneven part (first uneven part) 20 Outer mold 22 Concave and convex portion (second concave and convex portion) 30 Straws 31 Straw body 32 Bellows structure 32E Valley fold 32F Mountain fold 100 mold sets

Claims

1. A method for manufacturing a straw, comprising a bellows structure forming step of forming a bellows structure on a straw body containing an aliphatic polyester resin, In the bellows structure forming step, the straw body has an elastic modulus of 1300 MPa to 2200 MPa and a breaking strain of 200% to 600%.

2. The bellows structure forming step includes: A molding process of molding mountain folds and valley folds of the bellows structure into the straw body using a mold set; The method for manufacturing a straw according to claim 1, further comprising a folding step of compressing the straw body shaped by the shaping step, and folding the mountain folds and the valley folds to form the bellows structure.

3. The mold set includes: A rod-shaped inner mold inserted into the straw body; A rod-shaped outer mold that presses the straw body from the outside, the inner mold has a first concave-convex portion that forms the mountain-folded portion of the bellows structure, the outer mold has a second concave-convex portion that forms the valley fold portion of the bellows structure, The molding step includes:

3. The method for manufacturing a straw according to claim 2, further comprising a pressing step of pressing the outer mold from the outside against the straw body with the inner mold attached thereto while rotating the inner mold and the outer mold in opposite directions.

4. The method for manufacturing a straw according to any one of claims 1 to 3, wherein the aliphatic polyester resin is a poly(3-hydroxyalkanoate) resin.

5. The method for producing a straw according to claim 4, wherein the poly(3-hydroxyalkanoate)-based resin is one or more selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxydecanoate).

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