Biodegradable fiber manufacturing method

Abstract

The purpose of the present invention is to provide a method for manufacturing biodegradable fibers containing a PHA. The abovementioned problem is solved by providing a method for manufacturing biodegradable fibers containing PHA, the method including a discharge step in which a resin composition containing the PHA is heated to a temperature greater than or equal to the melting point of the resin composition containing the PHA and less than or equal to the thermal decomposition temperature thereof, and the resin composition is then discharged from a spinning nozzle. The weight average molecular weight of the resin composition when discharged from the spinning nozzle is greater than or equal to 120,000 or greater, and the melt flow rate is greater than or equal to 150.

Description

[Technical Field]

[0001] The present invention relates to a method for producing biodegradable fibers containing polyhydroxyalkanoic acid. [Background technology]

[0002] Meltblown nonwoven fabrics are nonwoven fabrics made from fibers obtained by the meltblowing method, in which a polymer and hot air are extruded together from a spinneret. Meltblown nonwoven fabrics have a microporous structure, are finely textured, and have excellent flexibility, so they are used as raw materials for masks, disposable diapers, sound-absorbing materials, oil absorbents, heat insulating materials, filters, etc., and demand for them has been growing significantly in recent years.

[0003] As an example of a meltblown nonwoven fabric, Patent Document 1 describes a meltblown nonwoven fabric made of thermoplastic resin fibers, which has a low bulk density and excellent breathability.

[0004] Patent Document 2 describes fine fibers containing a thermoplastic aliphatic polyester and a specific viscosity modifier, and a method for producing the same.

[0005] Patent Document 3 describes a method for producing biodegradable fibers, characterized in that when a resin made of a thermoplastic aliphatic polyester is subjected to hot melt spinning, water is added before or during the melting to adjust the moisture content in the molten polymer, and then the resin is spun.

[0006] Polyhydroxyalkanoates (hereinafter sometimes referred to as "PHAs") are known to be biodegradable. Among them, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter sometimes referred to as "PHBH" or "P3HB3HH") has excellent seawater degradability and is considered a promising material that can solve the environmental problems caused by discarded plastics. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2014 / 030730 [Patent Document 2] International Publication No. 2009 / 152349 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-84118 Summary of the Invention [Problem to be solved by the invention]

[0008] However, no technology has been developed to date for producing meltblown nonwoven fabrics using PHA (for example, PHBH) as a material.

[0009] Therefore, an object of the present invention is to provide a method for producing a biodegradable fiber containing PHA. [Means for solving the problem]

[0010] As a result of intensive research to solve the above-mentioned problems, the present inventors have found for the first time that biodegradable fibers containing PHA can be obtained by controlling the weight average molecular weight and melt flow rate of a resin composition discharged from a spinning nozzle within specific ranges in a manufacturing process in which PHA (e.g., PHBH) is molded by a melt-blowing method, and have thus completed the present invention.

[0011] Therefore, one aspect of the present invention is a method for producing a biodegradable fiber containing a PHA, which includes a discharge step of heating a resin composition containing the PHA to a temperature above the melting point and below the thermal decomposition temperature of the resin composition containing the PHA, and discharging the resin composition from a spinning nozzle, wherein the resin composition has a weight average molecular weight of 120,000 or more and a melt flow rate of 150 or more when discharged from the spinning nozzle (hereinafter referred to as "this production method").

[0012] Another aspect of the present invention is a biodegradable fiber containing polyhydroxyalkanoic acid (hereinafter referred to as "the present biodegradable fiber"), which has a weight-average molecular weight of 120,000 or more, a melt flow rate of 150 or more, a fineness of 5.0 dtex or less, and a fiber diameter of 22.6 μm or less. [Effects of the Invention]

[0013] According to one aspect of the present invention, a biodegradable fiber containing PHA can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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 and B or less." In addition, all documents described in this specification are incorporated herein by reference.

[0015] 1. Overview of the Invention As described above, no method for producing a meltblown nonwoven fabric using a PHA has been developed to date. While investigating melt-blowing molding using PHBH as an example of a PHA, the present inventors first focused on the viscosity of the resin composition discharged from the spinning nozzle. In melt-blowing molding, it is generally required to maintain a low viscosity of the resin composition discharged from the spinning nozzle. Therefore, the present inventors investigated (i) heating and (ii) adding a plasticizer to reduce the viscosity of the resin composition containing PHBH. As a result, the following new problems were discovered.

[0016] In the case of (i), the temperature characteristics of PHBH (melting point 145°C, thermal decomposition temperature 180°C) cause thermal decomposition and thermal degradation (reduction in molecular weight), which causes problems with the quality of the resulting fiber. Specifically, to reduce the viscosity, it is necessary to increase the temperature of the resin composition, but if the temperature becomes too high, the resin will thermally decompose.

[0017] In the case of (ii), if a non-volatile plasticizer whose boiling point is equal to or higher than the temperature of the spinning nozzle is used, the plasticizer will remain in the resulting fiber, resulting in unstable quality. Furthermore, if a sufficient plasticizing effect is desired, the plasticizer content in the resin composition will exceed 1% by weight. If the plasticizer is a non-biodegradable substance, the advantage of biodegradability will be diminished. Furthermore, the manufacturing process will be lengthened, resulting in reduced productivity.

[0018] Therefore, the present inventors conducted extensive research to solve the above problems and discovered for the first time that biodegradable fibers containing PHA can be obtained by controlling the weight-average molecular weight and melt flow rate of the resin composition discharged from a spinning nozzle within specific ranges during the melt-blowing process of PHBH. Furthermore, the present inventors also discovered for the first time that the weight-average molecular weight and melt flow rate of the resin composition can be controlled by adding a supercritical fluid to the resin composition. This technology based on this concept is unprecedented and surprising.

[0019] The inventors speculate that the effect of the supercritical fluid is as follows: By adding a supercritical fluid to the resin composition, an increase in the temperature of the resin composition can be prevented, and the residence time of the resin composition in the spinning machine can be shortened. As a result, a decrease in the weight-average molecular weight of the resin composition can be suppressed, and a melt flow rate suitable for extrusion can be achieved.

[0020] Therefore, according to the present production method, it is possible to obtain a biodegradable fiber containing PHA. Furthermore, according to the present production method, it is possible to obtain a high-quality, ultrafine biodegradable fiber containing PHA.

[0021] Furthermore, the above-mentioned configuration can suppress marine pollution caused by waste, thereby contributing 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." The configuration of this manufacturing method will be described in detail below.

[0022] 2. Method for producing biodegradable fibers This manufacturing method includes a discharge step of heating a resin composition containing PHA to a temperature above the melting point and below the thermal decomposition temperature of the resin composition containing PHA, and discharging the resin composition from a spinning nozzle, wherein the weight average molecular weight of the resin composition when discharged from the spinning nozzle is 120,000 or more, and the melt flow rate is 150 or more.

[0023] As used herein, the term "biodegradable fiber" refers to a fiber that is biodegradable, preferably marine degradable. The biodegradable fiber in this specification mainly contains PHA, preferably PHBH. Furthermore, the biodegradable fiber in this specification does not contain 1% by weight or more of non-biodegradable substances.

[0024] In this specification, "melt flow rate (hereinafter also referred to as "MFR")" refers to the flow rate of a resin composition containing a PHA per 10 minutes at 165°C, expressed in weight (g). The melt flow rate is an index of viscosity; the higher the melt flow rate value, the lower the viscosity and the higher the fluidity of the resin composition.

[0025] <Discharge process> This manufacturing method includes a step of heating a PHA-containing resin composition to a temperature above the melting point and below the thermal decomposition temperature of the PHA-containing resin composition, and discharging the composition through a spinning nozzle. In the discharging step, the PHA-containing resin composition is heated and then discharged through a spinning nozzle, whereby the composition is processed into fibers. The spinning nozzle is preferably a meltblown nozzle.

[0026] In one embodiment of the present invention, the weight-average molecular weight of the resin composition containing the PHA when discharged from the spinning nozzle is 120,000 or more, preferably 130,000 or more, and more preferably 140,000 or more. When the weight-average molecular weight of the resin composition is 120,000 or more, the mechanical strength of the resulting fibers and nonwoven fabric is improved. Furthermore, the increased solidification rate improves fiber productivity. The upper limit of the weight-average molecular weight of the resin composition is not particularly limited, but is, for example, 1,000,000 or less. A weight-average molecular weight of 1,000,000 or less has the advantage that the melting point of the resin composition is below the thermal decomposition temperature, making it easier to adjust the temperature of the spinning nozzle. The weight-average molecular weight of the resin composition can be determined by gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko) using a polystyrene gel (Shodex K-804 manufactured by Showa Denko) as a column and chloroform as the mobile phase, and is expressed as the molecular weight in terms of polystyrene.

[0027] In one embodiment of the present invention, the melt flow rate of the resin composition containing the PHA when discharged from the spinning nozzle is 150 or more, preferably 180 or more, and more preferably 200 or more. When the melt flow rate of the resin composition is 150 or more, it is possible to produce finer fibers and reduce variation in fineness. Furthermore, productivity is improved by reducing the load on the device. Furthermore, the frequency of thread breakage and poor appearance is reduced by reducing nozzle clogging and reducing foreign matter (unmelted material). The upper limit of the melt flow rate of the resin composition is not particularly limited, but is, for example, 2000 or less. When the melt flow rate of the resin composition is 2000 or less, acceleration and orientation due to high-speed airflow can be easily achieved when the resin composition is discharged from the meltblown nozzle, resulting in the advantageous result of producing a meltblown nonwoven fabric with excellent physical properties. The melt flow rate is measured by the method described in the Examples.

[0028] The temperature at which the resin composition is heated in the spinning machine (referred to as the "nozzle temperature" in the examples) is equal to or higher than the melting point and equal to or lower than the thermal decomposition temperature of the resin composition. The temperature is preferably lower than 180°C, more preferably lower than 179°C, and even more preferably lower than 178°C. A temperature lower than 180°C can prevent thermal decomposition of the PHA and prevent a decrease in the weight-average molecular weight of the resin composition. The lower limit of the temperature is not particularly limited as long as it is a temperature at which the resin composition can be melted, but is, for example, 145°C or higher, preferably 150°C or higher, and more preferably 155°C or higher. Furthermore, if the resin composition contains a chemical foaming agent described below, a temperature of 145°C or higher can easily cause the chemical foaming agent to decompose and generate a supercritical fluid. The temperature can be controlled, for example, by a cylinder heater of a device that heats the resin composition, such as an extruder, or a nozzle heater that discharges the resin composition.

[0029] In one embodiment of the present invention, the resin composition is pressurized in the spinning machine and / or when being discharged from the spinning nozzle. The pressurization causes the gas generated by decomposition of the chemical foaming agent to become a supercritical fluid. The pressure applied during pressurization (referred to as "nozzle pressure" in the examples) is equal to or higher than the critical pressure of the substance to be converted into a supercritical fluid, for example, 3.4 MPa or higher for nitrogen, 7.4 MPa or higher for carbon dioxide, and 22.1 MPa or higher for water. The upper limit of the pressure is not particularly limited, but is, for example, 50 MPa or lower. The pressurization method is not particularly limited, and any method can be used.

[0030] The rotation speed of the gear pump (hereinafter also referred to as "GP") in the spinning machine is, for example, 3 to 50 rpm, preferably 5 to 50 rpm, and more preferably 10 to 40 rpm. When the rotation speed of the GP in the spinning machine is 3 to 50 rpm, the flow state of the resin composition in the spinning machine is stable, and the discharge rate from the spinning machine is stable, which reduces variation in fiber thickness and makes it possible to obtain fibers with stable physical properties.

[0031] In one embodiment of the present invention, the PHA-containing resin composition may be retained in a spinning machine before being discharged. The retention time is not particularly limited as long as the weight-average molecular weight of the resin composition is not excessively reduced, but is, for example, 1 to 30 minutes, preferably 2 to 28 minutes, and more preferably 3 to 25 minutes.

[0032] In the discharging step, the resin composition containing PHA is preferably discharged from the spinning nozzle onto a conveyor located below the spinning nozzle. By discharging the resin composition directly from the spinning nozzle onto the conveyor, fibers are accumulated on the conveyor surface to form a nonwoven web, which is then moved and collected to obtain a nonwoven fabric. During the collection of the nonwoven web, the web surface may be shaped, decorated, or thermally bonded, for example, by passing it through a calendar roll, or a composite sheet structure may be formed by laminating fibers, nonwoven webs, etc. obtained through a different process onto the surface of the nonwoven web.

[0033] In the discharging step, the hole shape of the spinning nozzle that discharges the resin composition can be set appropriately depending on the purpose, but when a meltblown nozzle is used, one having multiple circular holes with a diameter of φ0.05 to φ0.5 mm is usually used.

[0034] <Resin composition> In this production method, the resin composition discharged from the spinning nozzle contains PHA.

[0035] (PHA) As used herein, "PHA" refers to a compound represented by the following formula (1): [-O-CHR-CH2-CO-] (1) (Wherein R is C n H 2n+1 and n is an integer of 1 to 15. The term "aromatic group" refers to a general term for polymers or copolymers comprising one or more units represented by the following formula:

[0036] In one embodiment of the present invention, the PHA may be poly(3-hydroxybutyrate) having only 3-hydroxybutyrate as a repeating unit, or may be a copolymer of 3-hydroxybutyrate and another hydroxyalkanoate.

[0037] In one embodiment of the present invention, the PHA may be a mixture of a homopolymer and one or more copolymers, or a mixture of two or more copolymers. The type of copolymerization is not particularly limited and may be random copolymerization, alternating copolymerization, block copolymerization, graft copolymerization, etc.

[0038] In one embodiment of the present invention, examples of PHA include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxypropionate) (P3HB3HP), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) ( Examples include poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (P3HB3HO), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (P3HB3HOD), poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (P3HB3HD), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH). From the viewpoints of being able to adjust the melting point low and widen the processing range, P3HB3HH, P3HB4HB, and P3HB3HP are preferred. Among these, P3HB3HH and P3HB4HB are particularly preferred due to their ease of industrial production. From the viewpoint of industrial productivity, in addition to the above, P3HB and P3HB3HV are also preferred.

[0039] PHA is preferably produced by a microorganism. The microorganism that produces PHA is not particularly limited as long as it is capable of producing PHA. For example, the first P3HB3HH-producing bacterium was Bacillus megaterium, discovered in 1925. Other examples include naturally occurring microorganisms such as Cupriavidus necator (formerly classified as Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. It is known that P3HB3HH accumulates intracellularly in these microorganisms.

[0040] In addition, the P3HB3HH-producing bacterium Aeromonas kayae (Aeromonas viridis) is known to produce copolymers of hydroxybutyrate and other hydroxyalkanoates. Examples of microorganisms known for producing P3HB3HH include Alcaligenes caviae and Alcaligenes eutrophus, a P3HB4HB-producing bacterium. In particular, for P3HB3HH, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)), into which genes encoding P3HB3HH synthases have been introduced, are preferred for increasing P3HB3HH productivity. These microorganisms are cultured under appropriate conditions to allow P3HB3HH to accumulate within the cells. Alternatively, genetically modified microorganisms into which various PHA synthesis-related genes have been introduced may be used depending on the PHA to be produced, or the culture conditions, including the type of substrate, may be optimized.

[0041] PHA can also be produced by the method described in, for example, WO 2010 / 013483. Commercially available PHA products include Kaneka Biodegradable Polymer PHBH (registered trademark) (e.g., X131A, X151A, X331N) manufactured by Kaneka Corporation.

[0042] In one embodiment of the present invention, the weight-average molecular weight of the PHA is not particularly limited. From the viewpoint of molding processability, the weight-average molecular weight is preferably 120,000 to 3,000,000, more preferably 120,000 to 2,500,000, and even more preferably 150,000 to 1,000,000. A weight-average molecular weight of 120,000 or more of the PHA provides sufficient mechanical properties, while a weight-average molecular weight of 3,000,000 or less facilitates molecular weight and viscosity adjustment of the resin composition in a spinning machine, achieving good molding processability. The weight-average molecular weight of the PHA can be determined by gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko) using a polystyrene gel (Shodex K-804 manufactured by Showa Denko) as a column and chloroform as the mobile phase, and is expressed as the molecular weight in terms of polystyrene.

[0043] When the PHA used in this production method is PHBH, the composition ratio of 3HB units / 3HH units in PHBH is preferably 89 / 11 to 99.5 / 0.5 (mol / mol), more preferably 90 / 10 to 99 / 1 (mol / mol), and even more preferably 91 / 9 to 98 / 2 (mol / mol). When the composition ratio of 3HB units / 3HH units is 99.5 / 0.5 (mol / mol) or less, good moldability and sufficient hardness are obtained, and when it is 89 / 11 (mol / mol) or more, sufficient flexibility is obtained.

[0044] (supercritical fluid) In one embodiment of the present invention, the resin composition when discharged from the spinning nozzle preferably contains a supercritical fluid.

[0045] As used herein, "supercritical fluid" refers to a fluid at or above its critical temperature and critical pressure. Because the diffusion rate of a supercritical fluid is comparable to that of a gas and its mass is comparable to that of a liquid, a large amount of the supercritical fluid dissolves uniformly within the resin composition. In other words, the inclusion of a supercritical fluid in the resin composition makes the resin composition more likely to be plasticized. This improves the fluidity during discharge from the spinning nozzle, allowing for a lower heating temperature. Furthermore, because the resin composition can be melted even with a short heating time, a decrease in the weight-average molecular weight of the resin composition can also be suppressed.

[0046] In addition, since the supercritical fluid vaporizes immediately after being discharged from the spinning nozzle, it is unlikely to remain in products such as nonwoven fabrics obtained from the fibers. Therefore, compared with the case where a conventional plasticizer is used, it has the advantage that the biodegradability of the fibers is less likely to be impaired. Furthermore, the inclusion of a supercritical fluid improves productivity and quality.

[0047] In one embodiment of the present invention, the supercritical fluid is not particularly limited as long as it falls within the above definition, and examples thereof include supercritical carbon dioxide, supercritical nitrogen, supercritical carbon monoxide, supercritical propane, and supercritical butane. Supercritical nitrogen is most preferred because it has a low critical pressure, requires low pressure resistance for the spinning machine and spinning nozzle, is non-flammable, and has low toxicity. These may be used alone or in combination of two or more.

[0048] In one embodiment of the present invention, a supercritical fluid can be obtained by pressurizing a desired substance above its critical pressure and heating it above its critical temperature. The pressurizing and heating methods are not particularly limited, and any method can be used. In one embodiment of the present invention, for example, a PHA-containing biodegradable fiber is produced by heating a desired substance to above its critical temperature in a spinning machine and then pressurizing it to above its critical pressure when it is discharged from the spinning machine or spinning nozzle.

[0049] Examples of methods for incorporating the supercritical fluid into the resin composition include a method of mixing a chemical foaming agent capable of generating a supercritical fluid into the resin composition, and a method of directly injecting the supercritical fluid into the resin composition in a molten state in a spinning machine.

[0050] (chemical foaming agent) In one embodiment of the present invention, the supercritical fluid is preferably derived from a chemical foaming agent.

[0051] As used herein, "chemical blowing agent" means a chemical composition that evolves a gas upon decomposition.

[0052] In one embodiment of the present invention, examples of chemical foaming agents include azodicarbonamide (ADCA), sodium bicarbonate (NaHCO3, sodium bicarbonate), N,N'-dinitrosopentamethylenetetramine (DPT), and 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH). ADCA, NaHCO3, and OBSH are preferred because their decomposition temperatures are close to the molding temperature of PHA and facilitate uniform dispersion of the generated gas in the molten resin composition. Foaming aids such as urea, zinc compounds, and citric acid can also be added to adjust the decomposition temperature of the chemical foaming agent and improve gas generation efficiency. Primary antioxidants such as phenolic antioxidants and secondary antioxidants such as phosphoric acid antioxidants, sulfur-based antioxidants, and sulfur-based antioxidants can also be used to adjust the weight-average molecular weight. These may be used alone or in combination.

[0053] In one embodiment of the present invention, the amount of chemical foaming agent added is not particularly limited, but is preferably 1.0 part by weight or less, more preferably 0.9 part by weight or less, and even more preferably 0.8 part by weight or less, per 100 parts by weight of PHA in the resin composition. The lower limit of the amount of chemical foaming agent added is not particularly limited, but is, for example, 0.1 part by weight or more, preferably 0.2 part by weight or more, and more preferably 0.3 part by weight or more, per 100 parts by weight of PHA in the resin composition. By adjusting the amount of chemical foaming agent added within the above range, it is possible to adjust the amount of supercritical fluid generated and independently adjust the weight average molecular weight and melt flow rate of the resin composition when it is discharged from the spinning nozzle.

[0054] In one embodiment of the present invention, the discharging step may include a step of adding 1 part by weight or less of the chemical foaming agent to 100 parts by weight of the PHA to generate the supercritical fluid.

[0055] (Other ingredients) In one embodiment of the present invention, the resin composition may contain additives commonly used in the relevant technical field, as long as the effects of the present invention are achieved. Examples of such additives include 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, crystal nucleating agents, lubricants, mold release agents, water repellents, antibacterial agents, and sliding properties improvers. In particular, the addition of a crystal nucleating agent can significantly improve processability. Examples of such crystal nucleating agents that can be used include pentaerythritol, mica, talc, and boron nitride. Furthermore, the inclusion of a lubricant has the effect of improving the surface smoothness of molded articles. Examples of such lubricants that can be used include fatty acid amides such as erucic acid amide, behenic acid amide, stearic acid amide, and oleic acid amide. The additives may be used alone or in combination. The content of these additives can be appropriately determined by those skilled in the art depending on the intended use. In the case of non-biodegradable additives, the amount is preferably less than 1% by weight from the viewpoint of maintaining the biodegradability of the resin composition, fiber, and nonwoven fabric.

[0056] <Other processes> In one embodiment of the present invention, the production method may include a step of preparing a resin composition containing a PHA before the discharge step.

[0057] The resin composition is prepared, for example, by mixing the components described above under "Other Components" together with PHA. There are no particular limitations on the mixing method, and any method can be used.

[0058] The method may further include a step of melt-kneading the mixed resin composition and pelletizing it. Pelletization has the advantage of facilitating processing in the next step. The resin composition is prepared, for example, by the method described in the Examples.

[0059] In one embodiment of the present invention, the manufacturing method may include, after the discharging step, a step of accumulating the biodegradable fibers on a conveyor and winding the accumulated biodegradable fiber group (web) around a paper tube to obtain a meltblown nonwoven fabric.

[0060] In another embodiment of the present invention, the present production method is a method for producing a biodegradable fiber containing a PHA, characterized in that the temperature and residence time of the spinning machine are set so that the weight-average molecular weight of the resin composition when discharged from the spinning nozzle is 120,000 or more and the melt flow rate is 150 or more. The PHA is preferably PHBH. Furthermore, the composition ratio of 3HB units / 3HH units of the PHBH is preferably 91 / 9 to 98 / 2 (mol / mol).

[0061] In another embodiment of the present invention, the present invention provides a method for producing a biodegradable fiber containing a PHA, which comprises adding 1 part by weight or less of a chemical foaming agent per 100 parts by weight of the PHA to a resin composition supplied to a spinning machine, heating the resin composition to a temperature equal to or higher than the decomposition temperature of the chemical foaming agent to generate gas within the spinning machine, and then uniformly dispersing the gas throughout the resin composition as it is discharged from a spinning nozzle. The PHA is preferably PHBH. The PHBH preferably has a 3HB unit / 3HH unit ratio of 91 / 9 to 98 / 2 (mol / mol).

[0062] [3. Biodegradable Fibers] In one embodiment of the present invention, there is provided a biodegradable fiber containing a polyhydroxyalkanoic acid, having a weight-average molecular weight of 120,000 or more, a melt flow rate of 150 or more, a fineness of 5.0 dtex or less, and a fiber diameter of 22.6 μm or less. In one embodiment of the present invention, the biodegradable fiber is obtained by the production method of the present invention.

[0063] The weight-average molecular weight of the biodegradable fiber is 120,000 or more, preferably 130,000 or more, and more preferably 140,000 or more. If the weight-average molecular weight of the biodegradable fiber is 120,000 or more, the strength and elongation of the nonwoven fabric are improved. There is no particular upper limit for the weight-average molecular weight of the biodegradable fiber, but it is, for example, 1,000,000 or less. If it is 1,000,000 or less, there is an advantage that it is easier to adjust the temperature of the spinning nozzle during the production of the nonwoven fabric.

[0064] The melt flow rate of the biodegradable fiber is 150 or more, preferably 180 or more, and more preferably 200 or more. When the melt flow rate of the biodegradable fiber is 150 or more, the flexibility of the biodegradable fiber is improved. There is no particular upper limit for the melt flow rate of the biodegradable fiber, but it is, for example, 2000 or less. When the melt flow rate of the biodegradable fiber is 2000 or less, there is an advantage that a nonwoven fabric with good physical properties can be obtained.

[0065] The fineness of the present biodegradable fiber is 5.0 dtex or less, preferably 3.0 dtex or less, more preferably 1.0 dtex or less, and even more preferably 0.5 dtex or less. In other words, when the present biodegradable fiber has a circular cross section, the fiber diameter (cross-sectional diameter) is 22.6 μm or less, preferably 17.5 μm or less, more preferably 10.1 μm or less, and even more preferably 7.1 μm or less. The lower limit of the fineness is not particularly limited, but is preferably 0.00015 dtex or more. The lower limit of the fiber diameter is also not particularly limited, but is preferably 0.1 μm or more. If the fineness is 0.00015 dtex or more and the fiber diameter is 0.1 μm or more, the fiber will have sufficient thickness and will be less likely to break, and will have sufficient strength when processed into nonwoven fabrics, etc. If the fineness of the present biodegradable fiber is within the above ranges, the resulting feel and filtering properties will be improved. In this specification, the term "fineness" means "single fineness."

[0066] The non-biodegradable substance contained in the present biodegradable fiber is preferably less than 1% by weight, more preferably 0.5% by weight or less, and even more preferably substantially free of the non-biodegradable substance. By containing the non-biodegradable substance in the present biodegradable fiber within this range, the biodegradability of the present biodegradable fiber is improved.

[0067] [4. Nonwoven fabric] In one embodiment of the present invention, a nonwoven fabric containing the present biodegradable fiber (hereinafter referred to as "the present nonwoven fabric") is provided.

[0068] The thickness of the nonwoven fabric varies depending on the application and size. When used as a single layer for a separator or liquid filter, the thickness is, for example, 0.01 to 1.5 mm, preferably 0.03 to 1.0 mm, and more preferably 0.05 to 0.50 mm. A thickness of 0.01 mm or more can maintain appropriate breathability and liquid permeability. Furthermore, a thickness of 1.5 mm or less prevents excessively high airflow resistance and liquid permeation resistance, allowing the separator and filter performance to be maintained. The thickness of the nonwoven fabric is measured by the method described in the Examples.

[0069] The basis weight of the nonwoven fabric is determined in various ways depending on the application and size. When used as a single layer filter, it is usually, for example, 1 to 500 g / m 2 and 3 to 200 g / m 2 It is preferable that the density is 4 to 100 g / m 2 More preferably, it is 5 to 50 g / m 2 It is more preferable that the basis weight is 1 g / m 2 If the weight is 500g / m or more, it is possible to maintain a suitable strength for processing. 2 The basis weight of the nonwoven fabric is measured by the method described in the Examples.

[0070] The tensile strength of the nonwoven fabric varies depending on the application and size. When used as a filter, the tensile strength of the nonwoven fabric in the machine direction (MD) is, for example, 2.0 N or more, preferably 2.2 N or more, more preferably 2.5 N or more, and even more preferably 2.8 N or more. The tensile strength of the nonwoven fabric in the cross direction (CD) is, for example, 0.8 N or more, preferably 1.0 N or more, more preferably 1.2 N or more, and even more preferably 1.3 N or more. When the tensile strength of the nonwoven fabric is within the above range, the strength is excellent. There are no particular limitations on the upper limit of the tensile strength of the nonwoven fabric, but it may be, for example, 15.0 N or less in the MD direction and 8.0 N or less in the CD direction. The tensile strength of the nonwoven fabric is measured in accordance with JIS 1913:2010.

[0071] In one embodiment of the present invention, the nonwoven fabric preferably has a uniform thickness. "Uniform thickness" means that the variation in thickness measurements across the entire nonwoven fabric is no more than the average value ±20%.

[0072] The method for producing the nonwoven fabric is not particularly limited, and it can be produced by a known method. For example, it can be produced by the method described above in "2. Method for producing biodegradable fibers." The shape of the nonwoven fabric is also not particularly limited, and can be appropriately determined depending on the application and size.

[0073] As described above, the nonwoven fabric is made of the biodegradable fibers and is therefore biodegradable. Furthermore, the nonwoven fabric may contain various components other than the biodegradable fibers that are generated or not removed during the manufacturing process, as long as the biodegradability is not impaired.

[0074] This nonwoven fabric can be used for a variety of purposes, including masks, disposable diapers, sanitary products, sound absorbers, oil absorbents, heat insulators, filters, and separators.

[0075] 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.

[0076] That is, one embodiment of the present invention is as follows. <1> A method for producing a biodegradable fiber containing polyhydroxyalkanoic acid, a discharge step of heating the resin composition containing the polyhydroxyalkanoic acid to a temperature equal to or higher than the melting point of the resin composition containing the PHA and equal to or lower than the thermal decomposition temperature of the resin composition, and discharging the resin composition from a spinning nozzle; The method for producing biodegradable fibers, wherein the resin composition when discharged from the spinning nozzle has a weight average molecular weight of 120,000 or more and a melt flow rate of 150 or more. <2> The resin composition when discharged from the spinning nozzle contains a supercritical fluid. <1> A method for producing a biodegradable fiber according to claim 1. <3> The supercritical fluid is at least one selected from the group consisting of supercritical carbon dioxide and supercritical nitrogen. <1> or <2> A method for producing a biodegradable fiber according to claim 1. <4> The supercritical fluid is derived from a chemical foaming agent. <2> or <3> A method for producing a biodegradable fiber according to claim 1. <5> The chemical blowing agent is at least one selected from the group consisting of azodicarbonamide, sodium bicarbonate, N,N'-dinitrosopentamethylenetetramine, and 4,4'-oxybis(benzenesulfonylhydrazide). <4> A method for producing a biodegradable fiber according to claim 1. <6> In the discharging step, the chemical foaming agent is added in an amount of 1 part by weight or less relative to 100 parts by weight of the polyhydroxyalkanoic acid, thereby generating the supercritical fluid. <4> or <5> A method for producing a biodegradable fiber according to claim 1. <7> In the discharging step, the heating temperature of the polyhydroxyalkanoic acid is less than 180°C. <1> ~ <6> A method according to any one of the preceding claims. <8> The polyhydroxyalkanoic acid is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). <1> ~ <7> 1. A method for producing a biodegradable fiber according to any one of the preceding claims. <9> The spinning nozzle is a meltblown nozzle. <1> ~ <8> 1. A method for producing a biodegradable fiber according to any one of the preceding claims. <10> The fineness of the obtained biodegradable fiber is 5.0 dtex or less, and the fiber diameter is 22.6 μm or less. <1> ~ <9> 1. A method for producing a biodegradable fiber according to any one of the preceding claims. <11> A biodegradable fiber containing polyhydroxyalkanoic acid, having a weight average molecular weight of 120,000 or more, a melt flow rate of 150 or more, a fineness of 5.0 dtex or less, and a fiber diameter of 22.6 μm or less. <12> <11> A nonwoven fabric comprising the biodegradable fiber according to claim 1. [Example]

[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] [Measurement and evaluation methods] Measurements and evaluations in the examples and comparative examples were carried out by the following methods.

[0079] (Weight average molecular weight (Mw)) The Mw of the obtained resin composition and biodegradable fiber was determined as a polystyrene-equivalent molecular weight by gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko) using a polystyrene gel (Shodex K-804 manufactured by Showa Denko) as a column and chloroform as a mobile phase.

[0080] (Melt flow rate (MFR)) The MFR of the obtained resin composition and biodegradable fiber was measured using a Melt Indexer G-01 manufactured by Toyo Seiki Seisaku-sho, Ltd., at 165°C and 5 kg, measuring the outflow amount (g) for 10 seconds from 5 minutes of preheating, and converted to a 10-minute value (however, the MFR was expressed as the average of three measurements).

[0081] (fiber diameter) The fiber diameter of the obtained biodegradable fiber was measured using a digital microscope VHX-5000 manufactured by Keyence Corporation (however, the diameter was expressed as the average value of 10 samples).

[0082] (fineness) The fineness of the obtained biodegradable fiber was calculated from the results of the fiber diameter measurement, assuming a fiber specific gravity of 1.25, and the mass (g) per 10,000 m of length was calculated.

[0083] (Metsuke) The basis weight of the obtained nonwoven fabric was measured by sampling an area of ​​100 mm in the machine direction (MD) x 100 mm in the cross direction (CD) (however, the weight was expressed as the average value of 10 samples).

[0084] (Thickness) The thickness of the obtained nonwoven fabric was measured at the center of the sample for measuring the basis weight using a dial gauge (however, the thickness was expressed as the average value of 10 samples).

[0085] (tensile strength) The tensile strength of the obtained nonwoven fabric was measured in both the machine direction (MD) and the cross direction (CD) in accordance with JIS1913:2010. The maximum load was determined with a sample width of 50 mm, a grip distance of 200 m, and a pulling speed of 100 mm / min.

[0086] Example 1 100 parts by weight of a (3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resin (3HB unit / 3HH unit composition ratio of 95:5, Mw = 320,000, MFR (165°C, 5 kg) = 12 g / 10 min) as the resin, 1 part by weight of pentaerythritol ("Neuriser P" manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) as the crystal nucleating agent, 0.5 parts by weight of erucic acid amide and 0.5 parts by weight of behenic acid amide as the lubricant, and 0.6 parts by weight of azodicarbonamide ("Vinihol FE-788" manufactured by Eiwa Chemical Industry Co., Ltd., containing urea and a zinc compound as the foaming aid) as the chemical foaming agent were dry-blended, and the mixture was melt-kneaded at 150°C and pelletized using an extruder to obtain resin composition pellets. The Mw of the obtained pellets was 300,000, the MFR (165°C, 5 kg) was 16.7 g / 10 min, the melting point was 145°C, and the thermal decomposition temperature was 180°C.

[0087] Biodegradable fibers and nonwoven fabrics were produced from the resin composition pellets according to the following process. First, the resulting pellets were melted in a single-screw extruder with a cylinder diameter of 32 mm. Next, biodegradable fibers were obtained by discharging the pellets from a meltblown nozzle with a hole diameter of 0.20 mm and 620 holes at a gear pump rotation speed of 6 rpm, a nozzle temperature of 175°C, and a nozzle pressure of 8.2 MPa. The residence time in the spinning machine was 10 minutes, and the resin composition at the time of nozzle discharge had an Mw of 180,000 and an MFR of 202 g / 10 min. Furthermore, during the nozzle discharge, high-speed airflows at 175°C were discharged from both sides of the circular nozzle row at an angle of 90° in a direction that accelerated the flow rate of the resin composition.

[0088] The obtained biodegradable fiber mass was accumulated on a conveyor located 200 mm below the nozzle, and the conveyor was moved at a speed of 6.0 m / min in a direction perpendicular to the direction of travel of the biodegradable fiber mass. The biodegradable fiber mass (nonwoven web) accumulated on the conveyor was then wound onto a paper tube to obtain a meltblown nonwoven fabric. The fineness of the biodegradable fibers constituting the obtained nonwoven fabric was 0.27 dtex, the fiber diameter was 5.2 μm, the Mw was 180,000, and the MFR was 202 g / 10 min. The basis weight of the nonwoven fabric was 15 g / m 2 The nonwoven fabric had a thickness of 0.14 mm. The tensile strength of the nonwoven fabric was 8.0 N in the MD direction and 3.8 N in the CD direction.

[0089] Example 2 Biodegradable fibers and meltblown nonwoven fabrics were obtained in the same manner as in Example 1, except that the nozzle temperature was 178°C, the nozzle pressure was 7.4 MPa, and the high-velocity air temperature was 178°C. The residence time in the spinning machine was 10 minutes, and the Mw of the resin composition when discharged from the nozzle was 156,000, and the MFR was 262 g / 10 min. The fineness of the biodegradable fibers constituting the obtained nonwoven fabric was 0.18 dtex, the fiber diameter was 4.3 μm, the Mw was 156,000, and the MFR was 262 g / 10 min. The basis weight of the nonwoven fabric was 15 g / m 2 The nonwoven fabric had a thickness of 0.14 mm and a tensile strength of 7.1 N in the MD direction and 3.4 N in the CD direction.

[0090] Example 3 Biodegradable fibers and meltblown nonwoven fabrics were obtained in the same manner as in Example 1, except that the gear pump rotation speed was 3 rpm, the nozzle temperature was 170°C, the nozzle pressure was 3.5 MPa, the high-velocity air temperature was 170°C, and the residence time in the spinning machine was 20 minutes. The residence time in the spinning machine was 20 minutes, and the Mw of the resin composition when discharged from the nozzle was 150,000 and the MFR was 285 g / 10 min. The fineness of the biodegradable fibers constituting the obtained nonwoven fabric was 0.11 dtex, the fiber diameter was 3.4 μm, the Mw was 150,000, and the MFR was 285 g / 10 min. The basis weight of the nonwoven fabric was 7 g / m 2The nonwoven fabric had a thickness of 0.09 mm. The tensile strength of the nonwoven fabric was 3.7 N in the MD direction and 2.0 N in the CD direction.

[0091] Comparative Example 1 A resin composition was obtained in the same manner as in Example 1, except that the chemical foaming agent "Vinihol FE-788" containing a foaming aid was not added. Then, a biodegradable fiber and a meltblown nonwoven fabric were obtained in the same manner as in Example 1. The residence time in the spinning machine was 10 minutes, and the resin composition had an Mw of 180,000 and an MFR of 126 g / 10 min when discharged from the nozzle. The nozzle pressure fluctuated between 10 and 12 MPa and was not stable. The biodegradable fiber constituting the obtained nonwoven fabric had an Mw of 180,000 and an MFR of 126 g / 10 min. The fineness of the biodegradable fiber constituting the obtained nonwoven fabric was 0.09 to 9.1 dtex, and the fiber diameter was nonuniform, ranging from 3.0 to 30.4 μm. The basis weight of the nonwoven fabric was 17 (±40%) g / m 2 The thickness was 0.13 (±15%) mm.

[0092] Comparative Example 2 Biodegradable fibers and meltblown nonwoven fabrics were obtained in the same manner as in Comparative Example 1, except that the gear pump rotation speed was 3 rpm and the residence time in the spinning machine was 20 minutes. The residence time in the spinning machine was 20 minutes, the nozzle pressure was 2.1 MPa, and the Mw of the resin composition when discharged from the nozzle was 117,000 and the MFR was 376 g / 10 min. The biodegradable fiber group (web) accumulated on the conveyor stuck to the conveyor, making it difficult to collect samples for measurement. Therefore, it was not possible to measure the fineness of the obtained biodegradable ultrafine fibers, or the basis weight and thickness of the nonwoven fabric.

[0093] Comparative Example 3 Biodegradable fibers and meltblown nonwoven fabrics were obtained in the same manner as in Example 1, except that the nozzle temperature was set to 185°C. The residence time in the spinning machine was 10 minutes, and the nozzle pressure was varied from 0.2 to 0.6 MPa. The Mw of the resin composition when discharged from the nozzle was 41,000, and the MFR was 1,500 g / 10 min or more. Decomposition gas was generated from the nozzle, and the biodegradable fibers were fused together on the conveyor, preventing the formation of a good web. In addition, they stuck to the conveyor, making it difficult to collect samples for measurement. Therefore, it was not possible to measure the fineness of the obtained biodegradable ultrafine fibers, or the basis weight and thickness of the nonwoven fabric.

[0094] 〔result〕 The production conditions for Examples 1 to 3 and Comparative Examples 1 to 3, and the physical properties of the resulting biodegradable fibers and nonwoven fabrics are shown in Table 1. In the table, "-" means that the measurement could not be performed.

[0095] [Table 1] From Table 1, it was found that when the weight average molecular weight of the resin composition when discharged from the nozzle is 120,000 or more and the melt flow rate is 150 or more, biodegradable ultrafine fibers containing PHBH can be obtained by spinning through a melt-blown nozzle (Examples 1 to 3).

[0096] On the other hand, in Comparative Example 1, the melt flow rate during nozzle discharge was low, resulting in large fluctuations in nozzle pressure and instability. Consequently, only biodegradable fibers and nonwoven fabrics with insufficient physical properties were obtained, with large fluctuations in fineness, fiber diameter, basis weight, and thickness. In Comparative Example 2, the residence time was extended to 20 minutes, resulting in a high melt flow rate, but a significant decrease in weight average molecular weight. This resulted in increased adhesion of the biodegradable fibers and reduced strength, making it impossible to obtain a nonwoven fabric with a good appearance. The results of Comparative Examples 1 and 2 are presumably due to the absence of a supercritical fluid in the resin composition. Furthermore, in Comparative Example 3, the temperature was increased above the thermal decomposition temperature of the resin composition, resulting in a high melt flow rate. However, the decomposition gas of the resin composition was generated, causing the biodegradable fibers to fuse together, making it impossible to obtain a nonwoven fabric with a good appearance. [Industrial Applicability]

[0097] According to the present invention, biodegradable fibers and nonwoven fabrics containing PHA can be produced, and therefore the fibers and nonwoven fabrics can be suitably used in masks, disposable diapers, sanitary products, sound absorbing materials, oil absorbents, heat insulating materials, filters, separators, and other fields.

Claims

1. A method for producing a biodegradable fiber containing polyhydroxyalkanoic acid, a discharge step of heating the resin composition containing the polyhydroxyalkanoic acid to a temperature equal to or higher than the melting point of the resin composition containing the polyhydroxyalkanoic acid and equal to or lower than the thermal decomposition temperature of the resin composition, and discharging the resin composition from a spinning nozzle; the weight average molecular weight of the resin composition when discharged from the spinning nozzle is 120,000 or more and the melt flow rate is 150 or more; Here, the melt flow rate is a value measured under conditions of 165°C and 5 kg. The method for producing biodegradable fibers, wherein the resin composition when discharged from the spinning nozzle contains a supercritical fluid.

2. 2. The method for producing biodegradable fibers according to claim 1, wherein the supercritical fluid is at least one selected from the group consisting of supercritical carbon dioxide and supercritical nitrogen.

3. The method for producing a biodegradable fiber according to claim 1 or 2, wherein the supercritical fluid is derived from a chemical foaming agent.

4. The method for producing biodegradable fibers according to claim 3, wherein the chemical foaming agent is at least one selected from the group consisting of azodicarbonamide, sodium bicarbonate, N,N'-dinitrosopentamethylenetetramine, and 4,4'-oxybis(benzenesulfonylhydrazide).

5. 5. The method for producing a biodegradable fiber according to claim 3, further comprising the step of adding 1 part by weight or less of the chemical foaming agent to 100 parts by weight of the polyhydroxyalkanoic acid in the discharging step to generate the supercritical fluid.

6. The method for producing a biodegradable fiber according to any one of claims 1 to 5, wherein the polyhydroxyalkanoic acid is heated to a temperature of less than 180°C in the discharging step.

7. The method for producing a biodegradable fiber according to any one of claims 1 to 6, wherein the polyhydroxyalkanoic acid is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

8. The method for producing a biodegradable fiber according to any one of claims 1 to 7, wherein the spinning nozzle is a meltblown nozzle.

9. The method for producing a biodegradable fiber according to any one of claims 1 to 8, wherein the resulting biodegradable fiber has a fineness of 5.0 dtex or less and a fiber diameter of 22.6 µm or less.

10. A biodegradable fiber containing polyhydroxyalkanoic acid, having a weight average molecular weight of 120,000 or more, a melt flow rate of 150 to 285, wherein the melt flow rate is a value measured under conditions of 165°C and 5 kg, a fineness of 5.0 dtex or less, and a fiber diameter of 22.6 μm or less.

11. A nonwoven fabric comprising the biodegradable fiber according to claim 10.

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