JP7645679B2 - Manufacturing method of resin tube - Google Patents

Description

The present invention relates to a method for producing a resin tube containing a poly(3-hydroxyalkanoate)-based resin component.

In recent years, the separate collection and composting of food waste has been promoted, particularly in Europe, and there is a demand for plastic products that can be composted together with food waste. Furthermore, marine pollution caused by microplastics has come under scrutiny, and there are hopes for the development of plastics that decompose in seawater.

Poly(3-hydroxyalkanoate) resins are thermoplastic polyesters that are produced and accumulated as energy storage substances within the cells of many microbial species, and because they are capable of biodegrading not only in soil but also in seawater, they have attracted attention as a material that can solve the above problems.

Patent Document 1 discloses a resin tube with a wall thickness of 0.1 to 0.6 mm that is made of poly(3-hydroxyalkanoate) resin, is flexible, and can be used effectively as a straw.

International Publication No. 2020/040093

Until now, resin tubes made from poly(3-hydroxyalkanoate) resins have been thick in relation to their outer diameter, but when such resin tubes are used as straws, for example, straws with thinner walls in relation to their outer diameter are required to further improve the mouthfeel. For this reason, it is necessary to mold straws with thinner walls in relation to their outer diameter, but when shaping them into a tube in a water bath, the thin walls tend to give way to the water pressure and become flattened.

In view of the above-mentioned current situation, the present invention aims to provide a method for manufacturing a resin tube that contains a poly(3-hydroxyalkanoate)-based resin component and has a thinner wall thickness relative to its outer diameter than conventional tubes.

The inventors conducted extensive research to solve the above problems, and discovered that in a method for producing a resin tube containing a resin composition containing a poly(3-hydroxyalkanoate)-based resin component, it is possible to produce a resin tube with a thinner wall thickness relative to its outer diameter by setting the degree of vacuum in the box, the residence time in the box, and the temperature of the water tank within specific ranges, particularly when the resin tube is placed in a water tank equipped with a box capable of reducing pressure and cooled to solidify, and thus completing the present invention.

That is, the present invention provides a method for producing a resin tube containing a resin composition containing a poly(3-hydroxyalkanoate)-based resin,
The method includes a step of melting the resin composition in an extruder, extruding the resin composition from a circular die, and introducing the extruded resin composition into a water tank having a box capable of reducing pressure.
The degree of vacuum in the box is -0.5 kPa (G) or less,
The present invention relates to a method for manufacturing a resin tube, characterized in that the resin tube is retained in the box for 0.1 seconds or more and the temperature of the water tank is 30°C or more.
Preferably, the temperature of the water bath is 60° C. or less.
Preferably, the ratio of the wall thickness to the outside diameter of the resin tube is equal to or greater than 0.01 and less than 0.05.
In addition, preferably, the resin composition containing the poly(3-hydroxyalkanoate) resin includes a resin composition containing at least two types of poly(3-hydroxyalkanoate) resins differing from each other in the types of constituent monomers and/or the content ratios of the constituent monomers.

The present invention provides a method for manufacturing a resin tube with a thinner wall thickness relative to its outer diameter.

The following describes an embodiment of the present invention, but the present invention is not limited to the following embodiment.

One embodiment of the present invention relates to a method for producing a resin tube containing a poly(3-hydroxyalkanoate)-based resin component.

(Poly(3-hydroxyalkanoate)-based resin component)
The poly(3-hydroxyalkanoate) resin component is preferably a polymer having a 3-hydroxyalkanoate unit, specifically a polymer containing a unit represented by the following general formula (1).
[-CHR-CH ₂ -CO-O-] (1)
In general formula (1), R represents an alkyl group represented by C _p H _2p+1 , and p represents an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, methylpropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. p is preferably an integer of 1 to 10, and more preferably an integer of 1 to 8.

The poly(3-hydroxyalkanoate) resin preferably contains 3-hydroxyalkanoate units (particularly units represented by general formula (1)) in an amount of 50 mol% or more of all constituent units, more preferably 60 mol% or more, and even more preferably 70 mol% or more. The poly(3-hydroxyalkanoate) resin may contain only one or more types of 3-hydroxyalkanoate units as the constituent units of the polymer, or may contain other units (e.g., 4-hydroxyalkanoate units, etc.) in addition to one or more types of 3-hydroxyalkanoate units.

The poly(3-hydroxyalkanoate) resin is preferably a homopolymer or copolymer containing 3-hydroxybutyrate (hereinafter sometimes referred to as 3HB) units. In particular, it is preferable that all of the 3-hydroxybutyrate units are (R)-3-hydroxybutyrate units. In addition, the poly(3-hydroxyalkanoate) resin is preferably a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units.

Specific examples of poly(3-hydroxyalkanoate) resins include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH). , poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), etc. In particular, from the viewpoint of productivity and mechanical properties of the resin tube, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is more preferred.

When the poly(3-hydroxyalkanoate) resin component contains a copolymer of 3-hydroxybutyrate units and other hydroxyalkanoate units, the average content ratio of 3-hydroxybutyrate units and other hydroxyalkanoate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin component is preferably 3-hydroxybutyrate units/other hydroxyalkanoate units=95/5 to 80/20 (mol %/mol %), more preferably 94/6 to 82/18 (mol %/mol %), and even more preferably 93/7 to 84/16 (mol %/mol %), from the viewpoint of achieving both practical usability and productivity of the resin tube.

The average content ratio of each monomer unit in all monomer units constituting the poly(3-hydroxyalkanoate)-based resin component can be determined by a method known to those skilled in the art, for example, the method described in paragraph [0047] of WO 2013/147139. The average content ratio means the molar ratio of each monomer unit in all monomer units in the entire poly(3-hydroxyalkanoate)-based resin component, and means the molar ratio of each monomer unit contained in the entire mixture of two or more poly(3-hydroxyalkanoate)-based resins constituting the poly(3-hydroxyalkanoate)-based resin component.

The weight average molecular weight of the poly(3-hydroxyalkanoate) resin component is not particularly limited, but from the viewpoint of achieving both practical usability and productivity of the resin tube, it is preferably 200,000 to 2,000,000, more preferably 250,000 to 1,500,000, and even more preferably 300,000 to 1,000,000.

The weight average molecular weight of each poly(3-hydroxyalkanoate) resin constituting the poly(3-hydroxyalkanoate) resin component is not particularly limited. However, for example, when blending a highly crystalline poly(3-hydroxyalkanoate) resin and a low crystalline poly(3-hydroxyalkanoate) resin as described below, the weight average molecular weight of the highly crystalline poly(3-hydroxyalkanoate) resin is preferably 200,000 to 1,000,000, more preferably 220,000 to 800,000, and even more preferably 250,000 to 600,000, from the viewpoint of achieving both practical usability and productivity of the resin tube. On the other hand, the weight average molecular weight of the low crystalline poly(3-hydroxyalkanoate) resin is preferably 200,000 to 2,500,000, more preferably 250,000 to 2,300,000, and even more preferably 300,000 to 2,000,000, from the viewpoint of achieving both practical usability and productivity of the resin tube.

The weight average molecular weight of the poly(3-hydroxyalkanoate) resin or poly(3-hydroxyalkanoate) resin component can be measured in terms of polystyrene using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) using a chloroform solution. A column suitable for measuring the weight average molecular weight can be used as the column for the gel permeation chromatography.

The method for producing the poly(3-hydroxyalkanoate) resin is not particularly limited, and may be a chemical synthesis method or a microbial production method.

In order to achieve the required productivity and mechanical strength, it is preferable to mix at least two types of poly(3-hydroxyalkanoate) resins. In this case, it is more preferable to combine and mix at least one type of highly crystalline poly(3-hydroxyalkanoate) resin with at least one type of low-crystalline poly(3-hydroxyalkanoate) resin. In general, highly crystalline poly(3-hydroxyalkanoate) resins have excellent productivity but poor mechanical strength, while low-crystalline poly(3-hydroxyalkanoate) resins have poor productivity but excellent mechanical properties. It is presumed that when the two resins are mixed, the highly crystalline poly(3-hydroxyalkanoate) resin forms fine resin crystal particles, and the low-crystalline poly(3-hydroxyalkanoate) resin forms tie molecules that crosslink the resin crystal particles. By using these resins in combination, the mechanical strength of the resin tube can be significantly improved.

When the highly crystalline poly(3-hydroxyalkanoate) resin contains 3-hydroxybutyrate units, it is preferable that the content of 3-hydroxybutyrate units contained in the highly crystalline poly(3-hydroxyalkanoate) resin is higher than the average content of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin component.

When a highly crystalline poly(3-hydroxyalkanoate) resin contains 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of the other hydroxyalkanoate units in the highly crystalline resin is preferably 1 to 10 mol%, more preferably 1 to 8 mol%, and even more preferably 1 to 6 mol%.

The highly crystalline poly(3-hydroxyalkanoate) resin component is preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

In addition, when the low-crystalline poly(3-hydroxyalkanoate) resin contains 3-hydroxybutyrate units, it is preferable that the content of 3-hydroxybutyrate units contained in the low-crystalline poly(3-hydroxyalkanoate) resin is lower than the average content of 3-hydroxybutyrate units in all monomer units constituting the poly(3-hydroxyalkanoate) resin component.

When a low-crystalline poly(3-hydroxyalkanoate) resin contains 3-hydroxybutyrate units and other hydroxyalkanoate units, the content of the other hydroxyalkanoate units in the low-crystalline resin is preferably 24 to 99 mol%, more preferably 24 to 50 mol%, even more preferably 24 to 35 mol%, and particularly preferably 24 to 30 mol%.

The low-crystalline poly(3-hydroxyalkanoate) resin is preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate), more preferably poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

When a highly crystalline poly(3-hydroxyalkanoate) resin and a low crystalline poly(3-hydroxyalkanoate) resin are used in combination, the proportion of each resin relative to the total amount of both resins is not particularly limited, but it is preferable that the former is 35% by weight or more and 90% by weight or less, and the latter is 10% by weight or more and 65% by weight or less, and it is even more preferable that the former is 45% by weight or more and 80% by weight or less, and the latter is 20% by weight or more and 55% by weight or less.

The method for obtaining a blend of two or more poly(3-hydroxyalkanoate) resins is not particularly limited, and may be a method for obtaining a blend by microbial production or a method for obtaining a blend by chemical synthesis. In addition, a blend may be obtained by melt-kneading two or more resins using an extruder, kneader, Banbury mixer, roll, etc., or a blend may be obtained by dissolving two or more resins in a solvent, mixing, and drying.

(Other resins)
The resin tube according to one embodiment may contain other resins besides poly(3-hydroxyalkanoate)-based resins, as long as the effects of the invention are not impaired. Examples of such other resins include aliphatic polyester-based resins such as polybutylene succinate adipate, polybutylene succinate, polycaprolactone, and polylactic acid, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate, polybutylene sebacate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

The content of the other resin is not particularly limited, but is preferably 60 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 45 parts by weight or less, per 100 parts by weight of the total poly(3-hydroxyalkanoate) resin components. There is no particular lower limit to the content of the other resin, and it may be 0 parts by weight.

(Additives)
The resin tube according to one embodiment may contain additives within a range that does not impair the effects of the invention. Examples of additives that can be used depending on the purpose include crystallization nucleating agents, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, crosslinking agents, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, organic fillers, and hydrolysis inhibitors. Additives that are biodegradable are particularly preferred.

Examples of crystallization nucleating agents include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride.

Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauramide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide and erucamide are preferred because of their particularly excellent lubricant effect on poly(3-hydroxyalkanoate)-based resin components. The amount of lubricant used is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and even more preferably 0.1 to 1.5 parts by weight, per 100 parts by weight of the total of poly(3-hydroxyalkanoate)-based resin components. In addition, one type of lubricant may be used, or two or more types may be used, and the ratio of use can be adjusted appropriately depending on the purpose.

Examples of plasticizers include glycerin ester compounds, citrate ester compounds, sebacic acid ester compounds, adipate ester compounds, polyether ester compounds, benzoic acid ester compounds, phthalic acid ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds.

As inorganic fillers, for example, inorganic particles such as silica, talc, calcium carbonate, barium sulfate, magnesium silicate, etc. are usable. From the viewpoint of dispersibility, the silica is preferably wet silica. As organic fillers, for example, starches such as corn starch (also called cornstarch), wheat starch, rice starch, broad bean starch, mung bean starch, adzuki bean starch, potato starch, sweet potato starch, tapioca starch, etc., chemically modified starches made from these, cellulose fibers, etc. are mentioned.

(Resin tube and its manufacturing method)
In this specification, a tube refers to a long, thin cylindrical molded product having a substantially uniform thickness, a substantially circular cross-sectional shape, and a hollow interior. The tube can be used as a straw or a pipe, but is not limited to these uses.

In the method for producing a resin tube according to the present invention, it is preferable to melt the resin using a known method. Specifically, poly(3-hydroxyalkanoate) resin is fed into a single-screw extruder or a twin-screw extruder and melt-kneaded. The temperature during melt-kneading is preferably, for example, 140°C to 180°C, more preferably 140°C to 175°C, and even more preferably 140°C to 170°C. If the temperature is less than 140°C, the resin cannot be melted sufficiently, and unmelted resin will get mixed into the resin tube, causing a deterioration in appearance and holes, making molding difficult. If the temperature is 180°C or higher, the viscosity tends to decrease, making molding difficult.

In one embodiment, the process of extruding a resin tube into a tube involves connecting an annular die to the outlet of the extruder where the melt-kneading has been performed, and extruding the molten resin from there to produce a tube. The diameter and clearance of the annular die can be selected as desired depending on the diameter and wall thickness of the resin tube, but generally a diameter or clearance larger than the desired tube diameter or wall thickness is selected.

The method for producing a resin tube according to the present invention includes a step of cooling and solidifying the extruded tubular resin in a water tank in which a box capable of reducing pressure is installed. Specifically, the tubular resin extruded from the annular die is cooled and solidified by passing it through a water tank filled with water, but preferably, in order to obtain a tube with a desired outer diameter, air is blown into the tube from the center of the annular die, and then the resin tube is passed through a box capable of reducing pressure installed in the water tank. The inlet of the box capable of reducing pressure may be located anywhere in the water tank, but it is preferably located in the front half of the annular die side relative to the entire length of the water tank. The box capable of reducing pressure may extend over the entire water tank, or may be a part of the water tank. This makes it easier to shape the resin into a uniform cylinder.

The degree of vacuum inside the vacuum box is preferably -0.5 kPa (G) or less, more preferably -1.0 kPa (G) or less, and even more preferably -2.0 kPa (G) or less. A degree of vacuum in this range is preferable because it tends to result in a uniform cylindrical shape, as described below. (G) indicates gauge pressure, and 0 kPa (G) means atmospheric pressure. For example, a degree of vacuum of -0.5 kPa (G) means that the pressure has decreased by 0.5 kPa from atmospheric pressure (0 kPa (G)).

The time it takes for the tubular resin to pass through the vacuum box is preferably 0.1 to 15 seconds, more preferably 0.1 to 12 seconds, and even more preferably 0.1 to 10 seconds. This range is preferable because the resin tube tends to become a uniform cylindrical shape.

In order to adequately cool and solidify the resin tube, the lower limit of the temperature of the water in the vacuum box and in the areas other than the vacuum box is 30°C or higher, preferably 35°C or higher, and more preferably 40°C or higher. The upper limit of the water temperature is preferably 60°C or lower, and even more preferably 55°C or lower. Furthermore, the temperature of the water in the vacuum box and the temperature of the water in the areas other than the vacuum box may be set to the same temperature or different temperatures. Furthermore, two or more water tanks may be provided, and each may be set to the same temperature or different temperatures.

When the resin tube according to one embodiment is used as a straw, the thickness of the resin tube is preferably 0.01 mm or more and 0.6 mm or less, more preferably 0.05 mm or more and 0.5 mm or less, and even more preferably 0.1 mm or more and 0.4 mm or less, because the tube feels good when used as a straw to drink a beverage, is moderately flexible and therefore unlikely to break, is unlikely to cause injury when poking a fingertip, and is rapidly biodegradable even in seawater. The thickness of the resin tube can be measured, for example, using a digital caliper for pipes (NTD-16-P15M, manufactured by Mitutoyo Corporation).

When the resin tube according to one embodiment is used as a straw, the outer diameter of the resin tube is not particularly limited, but is preferably 2 to 10 mm, more preferably 4 to 8 mm, and even more preferably 5 to 7 mm, from the viewpoint of ease of use when using the tube as a straw to drink a beverage. The outer diameter of the resin tube can be calculated by adding the wall thickness to the inner diameter, which is regarded as equivalent to a perfect circle using a cylindrical taper gauge (manufactured by Niigata Seiki Co., Ltd.), for example.

When the resin tube according to one embodiment is used as a straw, the ratio of the wall thickness to the outer diameter of the resin tube is preferably 0.01 or more and less than 0.05, more preferably 0.02 or more and less than 0.05, and even more preferably 0.02 or more and less than 0.04, since the tube feels good when used as a straw to drink from, is moderately flexible and therefore unlikely to break, is unlikely to cause injury when poking a fingertip, and is rapidly biodegradable even in seawater.

The cross-sectional shape of the resin tube according to one embodiment is approximately circular, but from the viewpoint of usability as a straw or pipe, the closer to a perfect circle the better. Therefore, the flatness of the cross-sectional shape of the tube [100 x (maximum outer diameter - minimum outer diameter) / maximum outer diameter] is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less. A flatness of 0% means that the cross-sectional shape is a perfect circle.

The length of the resin tube according to one embodiment is not particularly limited. However, when the resin tube is used as a straw, the length of the resin tube is preferably 50 to 350 mm, more preferably 70 to 300 mm, and even more preferably 90 to 270 mm, in order to facilitate ease of use when using the tube as a straw to drink beverages.

When the resin tube according to one embodiment is used as a pipe, the thickness of the resin tube can be set as appropriate by a person skilled in the art, but is preferably 0.7 mm or more and 10 mm or less, and more preferably 1 mm or more and 8 mm or less. The pipe can be suitably used in marine product farming and fishing. The thickness of the resin tube can be measured, for example, using a digital caliper for pipes (NTD-16-P15M, manufactured by Mitutoyo Corporation).

The resin tube used as a straw may be a tube that has not been subjected to secondary processing, or may be a tube that has been subjected to secondary processing such as the formation of a stopper portion or a bellows portion. The secondary processing can be performed while heating the resin tube, but is preferably performed at room temperature.

The present invention will be described in detail below with reference to examples, but the technical scope of the present invention is not limited to these examples.

The substances used in the examples and comparative examples are listed below.

[Poly(3-hydroxyalkanoate) resin]
P3HB3HH-1: P3HB3HH (average content ratio 3HB/3HH=95.4/4.6 (mol%/mol%), weight average molecular weight is 660,000 g/mol)
Produced according to the method described in Example 2 of WO 2019/142845.
P3HB3HH-2: P3HB3HH (average content ratio 3HB/3HH=71.8/28.2 (mol%/mol%), weight average molecular weight is 660,000 g/mol)
Produced according to the method described in Example 9 of WO 2019/142845.
P3HB3HH-3: P3HB3HH (average content ratio 3HB/3HH=94/5.4 (mol%/mol%), weight average molecular weight is 620,000 g/mol)
Raw material A-6 described in WO 2013/147139 was used.

When a mixture of two or more poly(3-hydroxyalkanoate) resins is used as the poly(3-hydroxyalkanoate) resin component, the average HH ratio in Table 1 is the average value calculated from the HH ratio in each poly(3-hydroxyalkanoate) resin and the weight ratio of each poly(3-hydroxyalkanoate) resin.

[Other resins]
Polybutylene succinate adipate (PBSA FD92PM PPT MCC Biochem BioPBS (registered trademark))

[Additives]
Additive: Behenamide (Nippon Fine Chemicals Co., Ltd.: BNT-22H)
The evaluation methods used in the examples and comparative examples are described below.

[Tube molding]
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 each set to 165°C, the resin composition pellets were charged, and the extruded tube was passed through a water tank equipped with a vacuum box located 100 mm away from the annular die to form a tube.

[Evaluation of roundness]
The maximum and minimum values of the outer diameter at a certain position of the obtained resin tube were measured with a vernier caliper and the arithmetic average was calculated. The deviation was evaluated as follows: 5% or less was marked "○", more than 5% but less than 10% was marked "△", and more than 10% was marked "X".

Example 1
3.75 kg of P3HB3HH-1, 3.75 kg of P3HB3HH-2, and 17.5 kg of P3HB3HH-3 were blended to obtain the resin composition shown in Table 1, and 250 g of additives were added and dry blended. The obtained resin material (resin mixture) was put into a φ26 mm co-rotating twin-screw extruder with a cylinder temperature set to 150 ° C. and a die temperature set to 150 ° C. and extruded. 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.

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 165°C, and the resin composition pellets were added and extruded into a tube at a screw rotation speed of 18 rpm. The extruded tube was passed through a water bath (water temperature 40°C) located 100 mm away from the annular die, and the resin tube was taken so that it passed through a vacuum box with a vacuum degree of -2.0 kPa (G) in 0.7 seconds, obtaining a resin tube with an outer diameter of 5.8 mm and a wall thickness of 0.2 mm (wall thickness/outer diameter ratio 0.034). The roundness of the obtained resin tube is evaluated in Table 1.

Example 2
The same procedure as in Example 1 was carried out except that the degree of vacuum in the vacuum box was set to -1.0 kPa (G). Table 1 shows the evaluation of the roundness of the obtained resin tube.

Example 3
The same procedure as in Example 1 was carried out except that the temperature of the water bath was set to 55° C. Table 1 shows the evaluation of the roundness of the obtained resin tube.

Example 4
The same procedure as in Example 1 was carried out except that the temperature of the water bath was set to 35° C. Table 1 shows the evaluation of the roundness of the obtained resin tube.

(Comparative Example 1)
The same procedure as in Example 1 was carried out except that the pressure in the vacuum box was not reduced but was set to atmospheric pressure (0.0 kPa (G)). Table 1 shows the evaluation of the roundness of the obtained resin tube.

(Comparative Example 2)
The same procedure as in Example 1 was carried out except that the temperature of the water bath was set to 25° C. Table 1 shows the evaluation of the roundness of the obtained resin tube.

(Example 7)
The same procedure as in Example 1 was carried out except that 30 parts of polybutylene succinate adipate was dry-blended with 70 parts of the resin composition pellets obtained in Example 1. Table 1 shows the evaluation of the roundness of the obtained resin tube.

From Table 1, Examples 1 and 2 and Comparative Example 1, by lowering the degree of vacuum in the vacuum box, the flattening ratio becomes 5% or less, and when atmospheric pressure is used, the flattening ratio exceeds 10%, so it can be seen that the roundness is improved by lowering the degree of vacuum in the vacuum box. Furthermore, from Examples 1, 3, 4 and Comparative Example 2, when the water temperature in the water tank is 30°C or higher, the flattening ratio becomes 10% or less, and when the water temperature in the water tank is 25°C, the flattening ratio exceeds 10%, so it can be seen that by making the water tank temperature 30°C or higher, the roundness is greatly improved. Furthermore, from Examples 1, 5, and 6, it can be seen that if the time of passing through the vacuum box is 0.1 seconds or more, the flattening ratio becomes 5% or less, and good roundness is obtained. Furthermore, from Example 7, good roundness can be obtained even if resins other than poly(3-hydroxyalkanoate)-based resins are included.

Claims (4)

A method for producing a resin tube containing a resin composition containing a poly(3-hydroxyalkanoate)-based resin, comprising:
The method includes a step of melting the resin composition in an extruder, extruding the resin composition from a circular die, and introducing the extruded resin composition into a water tank having a box capable of reducing pressure.
The resin tube is a cylindrical molded product having a wall surface with a substantially constant thickness and a hollow interior,
The ratio of the wall thickness to the outer diameter of the resin tube (wall thickness/outer diameter ratio) is 0.01 or more and 0.04 or less,
The degree of vacuum in the box is -0.5 kPa (G) or less,
The resin tube is retained in the box for 0.1 seconds or more;
A method for manufacturing a resin tube, characterized in that the temperature of the water bath is 30°C or higher. The method according to claim 1, wherein the temperature of the water bath is 60° C. or less. The method according to claim 1 or 2, wherein the temperature of the water bath is 40° C. or higher. The method according to any one of claims 1 to 3, wherein the resin composition containing the poly(3-hydroxyalkanoate) resin includes a resin composition containing at least two types of poly(3-hydroxyalkanoate) resins that differ from each other in the type of constituent monomer and/or the content ratio of the constituent monomer.