Fiber, method for producing fiber, fiber structure, and method for producing fiber structure

Abstract

The present invention provides, for example, a poly(3-hydroxyalkanoate)-based resin-containing fiber which can provide a fiber structure that is unlikely to tear. The present invention provides, for example, a fiber comprising a resin composition, wherein: the resin composition contains a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin; the resin composition contains the poly(3-hydroxyalkanoate)-based resin in an amount of 50-99 parts by weight with respect to 100 parts by weight of the total of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin; in a cross section of said fiber, said fiber does not have a sea-island structure that includes an island part, the minimum diameter of which is not less than 100 nm, or has a sea-island structure that includes one or two or more island parts, the total area of which is not more than 5% of the area of the cross section of said fiber; and the average fiber diameter of said fiber is not more than 5 μm.

Description

Fiber and its manufacturing method, and fiber structure and its manufacturing method

[0001] The present invention relates to a fiber and a method for producing the same, and a fiber structure and a method for producing the same.

[0002] In recent years, with the increasing use of fiber structures (nonwoven fabrics, woven fabrics, knitted fabrics, etc.), such as disposable masks, environmental pollution due to the outflow of microfibers into the ocean has become apparent. In response to this, nonwoven fabrics using plant-derived polylactic acid resins (abbreviated as PLA resins) have been proposed (see, for example, Patent Document 1). However, PLA resins have issues such as difficulty in home composting and poor marine biodegradability. In contrast, poly(3-hydroxyalkanoate) resins (abbreviated as P3HA resins) have attracted attention due to their advantages, such as home compostability and excellent marine biodegradability, and nonwoven fabrics using P3HA resins have been proposed (see, for example, Patent Document 2). Furthermore, the use of fibers containing polyhydroxyalkanoate copolymers and polylactic acid polymers in the production of nonwoven fabrics has also been proposed (see, for example, Patent Document 3).

[0003] Patent No. 5356960 International Publication No. 2019 / 142920 Special Publication No. 2004-532360

[0004] However, a fiber structure using fibers containing poly(3-hydroxyalkanoate) resin has a problem specific to poly(3-hydroxyalkanoate) resin, that is, it is prone to tearing.

[0005] Therefore, an object of the present invention is to provide a fiber containing a poly(3-hydroxyalkanoate) resin that can provide a tear-resistant fiber structure, and a fiber structure containing the fiber.

[0006] As a result of intensive research to solve the above problems, the present inventors have found that a fiber structure can be made less prone to tear by constructing it from fibers that contain a poly(3-hydroxyalkanoate) resin and a polylactic acid resin in a predetermined ratio and have a cross-sectional structure with a predetermined structure, and have completed the present invention. Furthermore, the present inventors have found that a fiber structure can be made less prone to tear by constructing it from fibers produced using a raw material composition that contains a poly(3-hydroxyalkanoate) resin and a polylactic acid resin in a predetermined ratio and in which the melt mass flow rate of the polylactic acid resin is within a predetermined range, and have completed the present invention.

[0007] That is, the present invention relates to a fiber comprising a resin composition, wherein the resin composition comprises a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin, and the poly(3-hydroxyalkanoate)-based resin is contained in an amount of 50 to 99 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin combined; the fiber does not have an island-sea structure including islands with a minimum diameter of 100 nm or more in its cross section, or has an island-sea structure including one or more such islands, the total area of ​​which is 5% or less of the area of ​​the cross section of the fiber; and the fiber has an average fiber diameter of 5 μm or less. The present invention also relates to a method for producing fibers by a melt spinning method, comprising the step of melting a raw material composition containing a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin, wherein the raw material composition contains 50 to 99 parts by weight of the poly(3-hydroxyalkanoate)-based resin per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin combined, and the polylactic acid-based resin has a melt mass-flow rate of 40 to 1,500 g / 10 min at 190°C under a load of 2.16 kg.

[0008] According to the present invention, it is possible to provide a poly(3-hydroxyalkanoate) resin-containing fiber that can provide a tear-resistant fiber structure, and a fiber structure containing the fiber.

[0009] Schematic diagram of a fiber manufacturing apparatus. Schematic oblique view of a nozzle. Schematic cross-sectional view of a nozzle hole and a conveyor belt. TEM image of a fiber cross section of Example 3. TEM image of a fiber cross section of Comparative Example 3. SEM image of a fiber structure of Example 3. SEM image of a fiber structure of Comparative Example 3. DSC curve of the fiber of Example 3. DSC curve of the fiber of Comparative Example 3. Results of biodegradation tests in seawater for Examples, Comparative Examples, and Reference Examples.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0011] <Fiber> The fiber according to this embodiment comprises a resin composition. The resin composition comprises a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin, with 50 to 99 parts by weight of the poly(3-hydroxyalkanoate)-based resin per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin combined. The cross section of the fiber does not have a sea-island structure including islands with a minimum diameter of 100 nm or more, or has a sea-island structure including one or more such islands, the total area of ​​which is 5% or less of the cross section of the fiber. The average fiber diameter of the fiber is 5 μm or less.

[0012] The resin composition contains a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin.

[0013] (Poly(3-hydroxyalkanoate)-based resin) The poly(3-hydroxyalkanoate)-based resin is a polyester containing 3-hydroxyalkanoic acid as a monomer. That is, the poly(3-hydroxyalkanoate)-based resin is a resin containing 3-hydroxyalkanoic acid as a structural unit. The poly(3-hydroxyalkanoate)-based resin is also a polymer having biodegradability. Note that, in this embodiment, "biodegradability" refers to the property of being decomposed into low molecular weight compounds by microorganisms in nature. Specifically, the presence or absence of biodegradability can be determined based on tests suited to each environment, such as ISO 14855 (compost) and ISO 14851 (activated sludge) under aerobic conditions, and ISO 14853 (aqueous phase) and ISO 15985 (solid phase) under anaerobic conditions. The decomposition ability of microorganisms in seawater can be evaluated by measuring the biochemical oxygen demand.

[0014] The poly(3-hydroxyalkanoate) resin preferably contains a copolymer having a 3-hydroxybutyrate unit.

[0015] In the copolymer having a 3-hydroxybutyrate unit, examples of the monomer unit other than the 3-hydroxybutyrate unit include a hydroxyalkanoate unit other than the 3-hydroxybutyrate unit, etc. Examples of the hydroxyalkanoate unit other than the 3-hydroxybutyrate unit include 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxyoctadecanoate, 3-hydroxyvalerate, and 4-hydroxybutyrate.

[0016] Examples of copolymers having 3-hydroxybutyrate units include P3HB3HH, P3HB3HV, P3HB4HB, poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Here, P3HB3HH means poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). P3HB3HV means poly(3-hydroxybutyrate-co-3-hydroxyvalerate). P3HB4HB means poly(3-hydroxybutyrate-co-4-hydroxybutyrate). The poly(3-hydroxyalkanoate) resin may contain only one copolymer having 3-hydroxybutyrate units, or may contain two or more copolymers having 3-hydroxybutyrate units. P3HB3HH is preferred as the copolymer having 3-hydroxybutyrate units.

[0017] Examples of poly(3-hydroxyalkanoate) resins other than copolymers having 3-hydroxybutyrate units include P3HB, poly(3-hydroxyvalerate), poly(3-hydroxyhexanoate), etc. Here, P3HB refers to poly(3-hydroxybutyrate) as a homopolymer.

[0018] P3HB has the function of promoting the crystallization of P3HB itself and poly(3-hydroxyalkanoate) resins other than P3HB.

[0019] The content of the 3-hydroxybutyrate units (3HB) in the poly(3-hydroxyalkanoate) resin is preferably 40 mol% or more and 98 mol% or less, more preferably 60 mol% or more and 97 mol% or less, even more preferably 70 mol% or more and 96 mol% or less, and particularly preferably 80 mol% or more and 96 mol% or less. When the content of the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin is 40 mol% or more, the rigidity of the fiber is increased. When the content of the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin is 98 mol% or less, the fiber structure becomes even more resistant to tearing. Furthermore, when the content of the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin is 92 mol% or less, the fiber structure becomes less likely to fluff and becomes even more resistant to tearing. The content ratio of the 3-hydroxybutyrate unit in the poly(3-hydroxyalkanoate) resin means the content ratio of the 3-hydroxybutyrate unit in the entire poly(3-hydroxyalkanoate) resin contained in the fiber.

[0020] The content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin can be determined as follows. First, 20 mg of the dried poly(3-hydroxyalkanoate) resin of the resin composition is added with 2 mL of a mixed solution of sulfuric acid and methanol (volume of sulfuric acid:volume of methanol=15:85) and 2 mL of chloroform to form a sample, which is then sealed. The sample is heated in a sealed state at 100°C for 140 minutes to obtain a first reaction solution containing methyl esters, which are decomposition products of the poly(3-hydroxyalkanoate) resin. The first reaction solution is then cooled, and 1.5 g of sodium bicarbonate is added little by little to neutralize the cooled first reaction solution. The mixture is then left to stand until the evolution of carbon dioxide gas ceases to yield a second reaction solution. The second reaction solution is then thoroughly mixed with 4 mL of diisopropyl ether to obtain a mixture. The mixture is then centrifuged to obtain a supernatant. The monomer unit composition of the decomposition product in the supernatant is then analyzed by capillary gas chromatography under the following conditions to determine the content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin: Gas chromatograph: GC-17A manufactured by Shimadzu Corporation Capillary column: NEUTRA BOND-1 manufactured by GL Sciences (column length: 25 m, column inner diameter: 0.25 mm, liquid film thickness: 0.4 μm) Carrier gas: He Column inlet pressure: 100 kPa Sample amount: 1 μL Temperature conditions include heating at a rate of 8°C / min from 100 to 200°C, and then at a rate of 30°C / min from 200 to 290°C.

[0021] (Polylactic Acid Resin) The polylactic acid resin is a polyester containing lactic acid as a constituent monomer.

[0022] The polylactic acid resin is preferably a homopolymer of lactic acid, but may contain other monomers in addition to lactic acid.

[0023] The lactic acid constituting the polylactic acid resin may be either the L- or D-form, or may contain both. In the latter case, the proportion of the D-form in the polylactic acid resin is preferably 1.0% to 99.0%, more preferably 1.5% to 98.5%, even more preferably 2.0% to 98.0%, and particularly preferably 3.0% to 97.0%. By ensuring that the proportion of the D-form in the polylactic acid resin is 1.0% to 99.0%, the melting point of the polylactic acid resin can be lowered, allowing it to be processed at a temperature at which poly(3-hydroxyalkanoate) resins are less likely to decompose. Furthermore, by ensuring that the proportion of the D-form in the polylactic acid resin is 1.0% or more, biodegradability can be enhanced. The polylactic acid resin may be any of poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin. Blends of these resins may also be used.

[0024] Examples of the other monomers that may be contained in the polylactic acid resin include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polycarboxylic acids, and polyfunctional polysaccharides.

[0025] The polylactic acid resin may be either a crystalline polylactic acid resin or an amorphous polylactic acid resin. From the viewpoint of heat resistance, such as shrinkage upon heating, it is preferable to use a crystalline polylactic acid resin. On the other hand, from the viewpoint of enhancing biodegradability and imparting heat-weldability, it is preferable to use an amorphous polylactic acid resin.

[0026] The lactic acid raw material for producing polylactic acid resins is not particularly limited, and examples thereof include L-lactic acid, D-lactic acid, DL-lactic acid, or a mixture thereof, and L-lactide, D-lactide, meso-lactide, or a mixture thereof. Lactic acid obtained by microbial fermentation from renewable plant-derived raw materials such as starch is preferably used. The method for producing polylactic acid resins is not particularly limited, and known methods such as dehydration condensation polymerization and ring-opening polymerization can be used.

[0027] From the viewpoint of making the fiber structure less likely to break and allowing the resin composition to contain a large amount of poly(3-hydroxyalkanoate)-based resin, which has excellent biodegradability (particularly biodegradability in compost and marine degradability), the resin composition contains 50 to 99 parts by weight, preferably 60 to 98 parts by weight, and more preferably 70 to 97 parts by weight of the poly(3-hydroxyalkanoate)-based resin per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin combined.

[0028] The fibers are primarily composed of poly(3-hydroxyalkanoate) resin and polylactic acid resin. The total proportion of the poly(3-hydroxyalkanoate) resin and polylactic acid resin in the total amount of the fibers may be 50 to 100% by weight, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more. It may be 95% by weight or more, 98% by weight or more, or even 100% by weight.

[0029] (Other Resins) The resin composition may contain other resins in addition to the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin, 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, and polycaprolactone, and aliphatic aromatic polyester-based resins such as polybutylene adipate terephthalate, polybutylene sebate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

[0030] The content of the other resin is not particularly limited, but is preferably 100 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 30 parts by weight or less, relative to 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin. It may be 10 parts by weight or less, 5 parts by weight or less, or 1 part by weight or less. The lower limit of the content of the other resin is not particularly limited, and may be 0 parts by weight or more.

[0031] The resin composition may contain additives that can be used together with the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin, as long as the effects of the invention are not impaired.

[0032] Examples of additives include nucleating agents, lubricants, stabilizers (antioxidants, ultraviolet absorbers, etc.), colorants (dyes, pigments, etc.), plasticizers, inorganic fillers, organic fillers, antistatic agents, etc.

[0033] The resin composition preferably contains a nucleating agent. The nucleating agent is a compound capable of promoting crystallization of the poly(3-hydroxyalkanoate)-based resin. Furthermore, the nucleating agent has a higher melting point than the poly(3-hydroxyalkanoate)-based resin. By including a nucleating agent in the resin composition, crystallization of the poly(3-hydroxyalkanoate)-based resin is promoted during fiber production, making it less likely for adjacent fibers to fuse together. As a result, a fiber structure with a homogeneous structure is more easily obtained. Examples of nucleating agents include sugar alcohols such as pentaerythritol, galactitol, and mannitol; orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. Among these, sugar alcohols are preferred, with pentaerythritol being particularly preferred, due to their particularly excellent effect of promoting the crystallization of poly(3-hydroxyalkanoate). The poly(3-hydroxyalkanoate)-based resin P3HB can also be used as a nucleating agent. These may be used alone or in combination of two or more.

[0034] The resin composition contains a nucleating agent, preferably at least 0.1 parts by weight, more preferably at least 0.3 parts by weight, and even more preferably at least 0.5 parts by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. The inclusion of 0.1 parts by weight or more of the nucleating agent per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin offers the advantage of further accelerating the crystallization of the poly(3-hydroxyalkanoate)-based resin during fiber production. Furthermore, the resin composition contains preferably 2.5 parts by weight or less, more preferably 2.0 parts by weight or less of the nucleating agent per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. The inclusion of 2.5 parts by weight or less of the nucleating agent per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin offers the advantage of making it easier to obtain fibers. It should be noted that P3HB is a poly(3-hydroxyalkanoate)-based resin and can also function as a crystal nucleating agent. Therefore, when the resin composition contains P3HB, the amount of P3HB is included in both the amount of the poly(3-hydroxyalkanoate)-based resin and the amount of the crystal nucleating agent.

[0035] The resin composition may contain the lubricant. When fibers are produced, the lubricant in the fibers improves the lubricity of the fibers, thereby preventing fusion between the fibers. On the other hand, when the resin composition does not contain a lubricant or contains a very small amount of a lubricant, there are advantages, for example, in improving the tape adhesiveness of the fibers and the fiber structure, and making handling easier during the manufacturing process. The presence or absence of a lubricant and the amount of lubricant to be added can be determined appropriately depending on the intended use of the fibers. Examples of the lubricant include compounds having an amide bond. The compound having an amide bond preferably contains one or more selected from lauric acid amide, myristic acid amide, stearic acid amide, behenic acid amide, and erucic acid amide.

[0036] The content of the lubricant in the resin composition is preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. Having a lubricant content of 0.2 parts by weight or more per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin offers the advantage of further suppressing fusion between fibers when producing fibers. On the other hand, having a lubricant content of 0 parts by weight or more and less than 0.2 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin offers the advantage of improving the tape adhesiveness of the fibers and fiber structures, making them easier to handle during the manufacturing process. Furthermore, the content of the lubricant in the resin composition is preferably 10 parts by weight or less, more preferably 5 parts by weight or less, even more preferably 3 parts by weight or less, and most preferably 2 parts by weight or less, per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin. By controlling the content of the lubricant in the resin composition to 10 parts by weight or less per 100 parts by weight of the poly(3-hydroxyalkanoate) resin, there is an advantage in that bleeding out of the lubricant onto the surface of the fibers can be suppressed.

[0037] The melt mass flow rate (hereinafter also referred to as "MFR" or "MFR (190°C, 2.16 kg)") of the resin composition at 190°C and a load of 2.16 kg is preferably 20 to 1500 g / 10 min, more preferably 30 to 1400 g / 10 min, still more preferably 50 to 1300 g / 10 min, particularly preferably 100 to 1200 g / 10 min, and most preferably 300 to 1000 g / 10 min.

[0038] When the resin composition has an MFR (190°C, 2.16 kg) of 20 to 1500 g / 10 min, the fiber according to this embodiment can be easily produced. When the resin composition has an MFR (190°C, 2.16 kg) of 1500 g / 10 min or less, the strength and elongation of the fiber are increased. When the resin composition has an MFR (190°C, 2.16 kg) of 20 g / 10 min or more, the tension applied to the fibrous melt during stretching of the fibrous melt, as described below, can be reduced, making it easier to thin the resulting fiber. As a result, the particle collection efficiency of the fiber structure can be easily improved.

[0039] In this embodiment, the melt mass-flow rate (MFR) at 190°C and a load of 2.16 kg is determined by determining the melt volume flow rate (MVR) of the object using Method B of ASTM-D1238 (ISO1133-1, JIS K7210-1:2011), and then determining the melt mass-flow rate (MFR) of the object from the melt volume flow rate (MVR) and density of the object. A melt flow rate tester (G-02, manufactured by Toyo Seiki Seisakusho) can be used as the measuring device. The melt volume flow rate (MVR) of the object is measured by heating 3 to 8 g of the object at a heating temperature of 190°C for 4 minutes, and then applying a load of 2.16 kg to the heated object.

[0040] The weight average molecular weight of the resin composition is preferably 50,000 to 350,000, more preferably 70,000 to 300,000, still more preferably 80,000 to 250,000 (for example, 80,000 to 150,000), and particularly preferably 100,000 to 200,000.

[0041] When the weight-average molecular weight of the resin composition is 50,000 to 350,000, the fiber according to this embodiment can be easily produced. When the weight-average molecular weight of the resin composition is 50,000 or more, the strength and elongation of the fiber are increased. When the weight-average molecular weight of the resin composition is 350,000 or less, the tension applied to the fibrous melt during stretching can be reduced, making it easier to thin the resulting fiber. As a result, the particle collection efficiency of the fiber structure can be easily increased.

[0042] In this embodiment, the weight-average molecular weight (Mw) refers to a value measured from the polystyrene-equivalent molecular weight distribution using gel permeation chromatography (GPC) with a chloroform eluent. A column suitable for measuring the molecular weight may be used as the column in the GPC. For example, the column temperature is set to 40°C, 10 μl of a solution of 3 mg of the target substance in 2 ml of chloroform (HPLC grade) is injected, and the flow rate of the chloroform eluent (mobile phase) is set to 1.0 ml / min, thereby determining the weight-average molecular weight (Mw). A Shimadzu 20A manufactured by Shimadzu Corporation can be used as the GPC apparatus, a GPCK-806M (manufactured by Showa Denko KK) column, and an RI detector can be used as the detector.

[0043] The proportion of the resin composition in the fibers may be 50 to 100% by weight, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more, and may be 95% by weight or more, 98% by weight or more, or even 100% by weight.

[0044] The fiber does not have an island-sea structure containing islands with a minimum diameter of 100 nm or more in its cross section, or has an island-sea structure containing one or more such islands, the total area of ​​which is 5% or less of the cross-sectional area of ​​the fiber. The total area of ​​the island portions is preferably 3% or less of the cross-sectional area of ​​the fiber, more preferably 2% or less of the cross-sectional area of ​​the fiber, and even more preferably 1% or less of the cross-sectional area of ​​the fiber. The fiber may have a non-island-sea structure or a co-continuous structure.

[0045] The fiber does not have an island-sea structure in its cross section that includes islands with a minimum diameter of 100 nm or more, or has an island-sea structure that includes one or more such islands and the total area of ​​the island portions is 5% or less of the cross-sectional area of ​​the fiber, thereby resulting in a fiber structure in which either the polylactic acid resin or the poly(3-hydroxyalkanoate) resin is finely dispersed and mixed with the other, making the fiber structure less likely to break. Note that the island portions refer to islands consisting only of the P3HA resin or the PLA resin, and the areas of islands of other resins, additives, etc. are not included in the total area of ​​the island portions.

[0046] The ratio of the total area of ​​the islands to the cross-sectional area of ​​the fiber can be calculated as follows: First, the fibers or a fiber structure containing the fibers are infiltrated with a curable resin, cured, and then cut to prepare ultrathin sections. For this cutting, an ultramicrotome (FC6, manufactured by Leica Microsystems) or the like can be used. Next, the ultrathin sections are cut with RuO ４ The fiber is stained with fluorine, and an image of the fiber cross section is taken using a transmission electron microscope (e.g., H-7650 manufactured by Hitachi High-Technologies Corporation) at an accelerating voltage of 100 V. The magnification of the image was 10,000x or 40,000x depending on the size of the fiber cross section. The area ratio of islands (having a minimum diameter of 100 nm or more) consisting only of P3HA-based resin or PLA-based resin in the fiber cross section is then calculated using image analysis software (e.g., Win ROOF manufactured by Mitani Corporation). When determining the ratio from a fiber structure, three or more fiber cross-sectional areas may be randomly selected from the photographed image, and the area ratio of islands (having a minimum diameter of 100 nm or more) consisting only of P3HA-based resin or PLA-based resin in the fiber cross section may be calculated. The minimum diameter (minimum diameter) refers to the shortest line segment passing through the midpoint of the line segment defining the maximum diameter.

[0047] In the fiber, the extrapolated glass transition onset temperature (T ｉｇ (PLA)) and midpoint glass transition temperature (T ｍｇThe difference between the extrapolated glass transition onset temperature (T ｉｇ (PLA)) and midpoint glass transition temperature (T ｍｇ The difference between the midpoint glass transition temperature (T ｍｇ (PLA)) to the extrapolated glass transition onset temperature (T ｉｇ (PLA)) minus the value (T ｍｇ (PLA)-T ｉｇ It is known that in a mixture of a polylactic acid resin and another resin component, when the glass transition peak in the DSC curve derived from the polylactic acid resin component becomes broad, this means that either the polylactic acid resin or the other component is finely dispersed and mixed into the other component. When the difference between the extrapolated glass transition onset temperature and the midpoint glass transition temperature is 4.0°C or more, the peak of the glass transition DSC curve derived from the polylactic acid resin component becomes broad, and in the fiber, either the polylactic acid resin or the poly(3-hydroxyalkanoate) resin is more finely dispersed and mixed with the other, making the fiber structure even more resistant to tearing.

[0048] The extrapolated glass transition temperature (T ｉｇ (PLA)) and midpoint glass transition temperature (T ｍｇ The glass transition temperature (T ) of the polylactic acid-based resin component can be calculated as follows. That is, in accordance with JIS K7121-1987 "Method for measuring transition temperature of plastics," measurements are carried out on the fiber as the object under the conditions of a sample amount of 5 to 10 mg, a measurement temperature range of -30°C to 200°C, and a temperature rise rate of 20°C / min, a DSC curve is obtained, and the extrapolated glass transition temperature (T ) derived from the polylactic acid-based resin component is calculated using analysis software (TRIOS). ｉｇ (PLA)) and midpoint glass transition temperature (T ｍｇ (PLA)) can be calculated. A differential scanning calorimeter (DSC25, manufactured by TA Instruments) can be used as the measuring device.

[0049] The average fiber diameter of the fibers is 5 μm or less, preferably 5.0 μm or less, more preferably 4.9 μm or less, and even more preferably 4.8 μm or less. The average fiber diameter of the fibers is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1.0 μm or more, and particularly preferably 1.5 μm or more. The coefficient of variation of the fiber diameter of the fibers is preferably 0.30 or less, more preferably 0.27 or less, even more preferably 0.25 or less, and particularly preferably 0.20 or less. The coefficient of variation of the fiber diameter of the fibers in the fiber structure is, for example, 0.05 or more.

[0050] When the average fiber diameter of the fibers is 5 μm or less, the rigidity of the fibers can be reduced. As a result, the texture (e.g., feel to the skin, touch, etc.) is improved when the fibers are formed into a fiber structure. In addition, the particle collection efficiency is increased when the fibers are formed into a fiber structure. When the average fiber diameter of the fibers is 0.5 μm or more, the strength and elongation of the fibers and fiber structure are increased, and productivity is also increased. When the fiber diameter coefficient of the fibers is 0.30 or less, the fiber structure formed into a fiber structure has little variation in fiber diameter and is homogeneous, thereby further increasing the particle collection efficiency of the fiber structure. As one of the polylactic acid resin and the poly(3-hydroxyalkanoate) resin becomes finely dispersed and mixed into the other in the fiber, the coefficient of variation of the fiber diameter of the fibers becomes smaller, and the particle collection efficiency is further increased when the fibers are formed into a fiber structure.

[0051] The average value and coefficient of variation of the fiber diameter of the fiber can be determined as follows. When the fiber is a monofilament, first, the diameter (width) is measured at 20 or more randomly selected locations at intervals of 10 cm or more in the fiber axis direction of the fiber. For example, a scanning electron microscope can be used to measure the diameter (width). Next, the average value (arithmetic mean value) and coefficient of variation (= standard deviation / arithmetic mean value) are determined from the arithmetic mean value and standard deviation of all the measured diameters (widths). When the fiber is a multifilament, first, the diameters (widths) of 100 or more randomly selected single fibers are measured. For example, a scanning electron microscope can be used to measure the diameter (width). Next, the average value (arithmetic mean value) and coefficient of variation (= standard deviation / arithmetic mean value) are determined from the arithmetic mean value and standard deviation of all the measured diameters (widths). In addition, in this embodiment, "fiber diameter of the fiber" means "fiber diameter of a single fiber of the fiber."

[0052] <Fiber Structure> The fiber structure according to this embodiment includes the fibers. The fiber structure according to this embodiment is preferably in the form of a sheet. Examples of the fiber structure include fabrics (nonwoven fabrics, woven fabrics, knitted fabrics, etc.). Examples of the nonwoven fabric include chemically bonded nonwoven fabrics, thermally bonded nonwoven fabrics, needle-punched nonwoven fabrics, water-punched nonwoven fabrics, stitch-bonded nonwoven fabrics, air-laid nonwoven fabrics, spunlace nonwoven fabrics, spunbonded nonwoven fabrics, melt-blown nonwoven fabrics, flash-spun nonwoven fabrics, electrospun nonwoven fabrics, and papermaking. The nonwoven fabric is preferably a direct-spun nonwoven fabric. The direct-spun nonwoven fabric refers to a "nonwoven fabric obtained by entangling raw yarns obtained by melt spinning to form a sheet directly, and solidifying the raw yarns." Note that "entangling raw yarns to form a sheet directly" means "entangling raw yarns to form a sheet before the raw yarns are solidified." Examples of the spun nonwoven fabric include meltblown nonwoven fabric, spunbond nonwoven fabric, flash-spun nonwoven fabric, and electrospun nonwoven fabric. The meltblown nonwoven fabric also includes nonwoven fabrics obtained by the Spunblown (registered trademark) method. The fiber structure according to this embodiment is preferably a meltblown nonwoven fabric or a spunbond nonwoven fabric, and more preferably a meltblown nonwoven fabric.

[0053] The basis weight of the fiber structure according to this embodiment is preferably 10 to 150 g / m ２ , more preferably 15 to 100 g / m ２ , more preferably 20 to 80 g / m ２ , particularly preferably 20 to 60 g / m ２ The fiber structure according to this embodiment has a basis weight of 10 g / m ２ By satisfying the above conditions, the strength and elongation are increased, and the efficiency of collecting particles (for example, particles with blood cells, pollen, coffee powder, tea leaves, viruses, etc.) is improved. ２ When the thickness is equal to or less than 100 μm, the liquid permeability (water permeability, etc.) or air permeability is high.

[0054] The basis weight of the fiber structure according to this embodiment can be determined as follows. First, a test piece is obtained from the fiber structure according to this embodiment. The size of the test piece can be, for example, 100 mm x 100 mm, 200 mm x 200 mm, etc. Next, the weight of the test piece is measured using an electronic balance or the like. Then, the basis weight is calculated by dividing the weight of the test piece by the area of ​​the test piece.

[0055] The thickness of the fiber structure according to this embodiment is preferably 0.05 to 0.80 mm, more preferably 0.08 to 0.60 mm, even more preferably 0.10 to 0.50 mm, and particularly preferably 0.10 to 0.40 mm. When the thickness of the fiber structure according to this embodiment is 0.05 to 0.80 mm, a homogeneous fiber structure is more likely to be obtained when the fiber structure is produced. When the thickness of the fiber structure according to this embodiment is 0.05 mm or more, the strength and elongation of the fiber structure are increased, and the particle collection efficiency of the fiber structure is further improved. Furthermore, when the thickness of the fiber structure according to this embodiment is 0.80 mm or less, the liquid permeability (such as water permeability) or breathability of the fiber structure can be improved.

[0056] The thickness of the fiber structure according to this embodiment can be determined by measuring the thickness of the fiber structure at three or more locations using a thickness meter, and averaging the measured values. Examples of thickness meter include "PEACOCK" manufactured by Ozaki Seisakusho Co., Ltd.

[0057] The average fiber diameter of the fibers in the fiber structure is preferably 5 μm or less, more preferably 5.0 μm or less, even more preferably 4.9 μm or less, and even more preferably 4.8 μm or less. The average fiber diameter of the fibers in the fiber structure is preferably 0.5 μm or more, more preferably 0.8 μm or more, even more preferably 1.0 μm or more, and even more preferably 1.5 μm or more. The coefficient of variation of the fiber diameter of the fibers in the fiber structure is preferably 0.30 or less, more preferably 0.27 or less, even more preferably 0.25 or less, and particularly preferably 0.20 or less. The coefficient of variation of the fiber diameter of the fibers in the fiber structure is, for example, 0.05 or more.

[0058] When the average fiber diameter of the fibers in the fiber structure is 5 μm or less, the rigidity of the fibers can be reduced, improving the texture (e.g., feel to the skin, touch, etc.) of the fiber structure and increasing the particle collection efficiency. When the average fiber diameter of the fibers in the fiber structure is 0.5 μm or more, the strength and elongation of the fiber structure are increased. When the coefficient of variation of the fiber diameter of the fibers in the fiber structure is 0.30 or less, the fiber structure becomes a homogeneous fiber structure with little variation in fiber diameter, and the particle collection efficiency of the fiber structure is further increased. As one of the polylactic acid-based resin and the poly(3-hydroxyalkanoate)-based resin becomes finely dispersed and mixed into the other in the fibers of the fiber structure, the coefficient of variation of the fiber diameter of the fibers in the fiber structure becomes even smaller, and the particle collection efficiency of the fiber structure is further increased.

[0059] The average fiber diameter and coefficient of variation of the fibers in the fiber structure can be determined as follows. First, a test piece is obtained from the fiber structure. Next, photographs (1700x magnification) of five or more locations on the surface of the test piece are taken using a scanning electron microscope. Then, the diameters (widths) of 20 or more randomly selected fibers are measured for each photograph. Next, the arithmetic mean value and coefficient of variation (= standard deviation / arithmetic mean value) are determined from the diameter (width) values ​​of all the measured fibers.

[0060] The proportion of the fibers in the total amount of the fiber structure may be 50 to 100% by weight, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more, and may be 95% by weight or more, 98% by weight or more, or even 100% by weight.

[0061] The fiber structure according to this embodiment can be suitably used as a substrate for various products (e.g., masks, filters, disposable diapers, sanitary napkins, taping materials, patches, bandages, gloves, clothing, etc.). The term "substrate" includes a reinforcing material. Examples of the filter include removal filters (e.g., mask filters) that remove particles (e.g., particles with viruses or the like attached, pollen, etc.), blood filters that capture blood cells, and filters for beverage extraction (e.g., coffee drip filters, tea bags, etc.).

[0062] <Method for producing fiber and method for producing fiber structure> The method for producing fiber according to this embodiment can produce the fiber. The method for producing fiber according to this embodiment is a method for producing fiber by melt spinning. The method for producing fiber according to this embodiment also includes a step (A) of melting a raw material composition containing a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin. The raw material composition contains 50 to 99 parts by weight of the poly(3-hydroxyalkanoate)-based resin per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin combined. The polylactic acid-based resin has a melt mass flow rate of 40 to 1,500 g / 10 min at 190°C.

[0063] In the fiber manufacturing method according to the present embodiment, a nozzle having a nozzle hole is used to manufacture a fiber. The fiber manufacturing method according to the present embodiment includes a step (A) of melting a raw material composition containing a poly(3-hydroxyalkanoate) resin and a polylactic acid resin to obtain a melt, and a step (B) of obtaining a fiber from the melt.

[0064] In the method for producing a fiber structure according to the present embodiment, a fiber structure containing the fibers is produced by the fiber production method. Examples of the melt spinning method include a melt blown method, a spunbond method, a flash spinning method, and an electrospinning method. The melt spinning method is preferably a melt blown method or a spunbond method.

[0065] The raw material composition contains a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin.

[0066] The raw material composition contains 50 to 99 parts by weight, preferably 60 to 98 parts by weight, and more preferably 70 to 97 parts by weight of the poly(3-hydroxyalkanoate) resin relative to 100 parts by weight in total of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin.

[0067] The raw material composition is a raw material composition mainly composed of a poly(3-hydroxyalkanoate) resin and a polylactic acid resin. The total proportion of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin in the total amount of the raw material composition may be 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more. It may also be 95% by weight or more, or 98% by weight or more.

[0068] The polylactic acid resin has an MFR (190°C, 2.16 kg) of 40 to 1500 g / 10 min, preferably 50 to 1300 g / 10 min, more preferably 60 to 1200 g / 10 min, even more preferably 80 to 1000 g / 10 min, and particularly preferably 100 to 800 g / 10 min. When the polylactic acid resin has an MFR (190°C, 2.16 kg) of 40 g / 10 min or more, the polylactic acid resin and the poly(3-hydroxyalkanoate) resin are more finely dispersed and mixed in the fiber than the other, making the fiber structure even more resistant to tearing. When the polylactic acid resin has an MFR (190°C, 2.16 kg) of 1500 g / 10 min or less, the strength and elongation of the fiber are increased.

[0069] The MFR (210°C, 2.16 kg) of the polylactic acid resin is preferably more than 80 g / 10 min and not more than 2000 g / 10 min, more preferably 90 to 1800 g / 10 min, even more preferably 90 to 1500 g / 10 min (e.g., 150 to 1500 g / 10 min), still more preferably 100 to 1200 g / 10 min, and particularly preferably 150 to 1000 g / 10 min. When the MFR (210°C, 2.16 kg) of the polylactic acid resin exceeds 80 g / 10 min, one of the polylactic acid resin and the poly(3-hydroxyalkanoate) resin is more finely dispersed and mixed in the fiber than the other, making the fiber structure more resistant to tearing. The MFR (210°C, 2.16 kg) of the polylactic acid resin is 2000 g / 10 min or less, thereby increasing the strength and elongation of the fiber. The MFR (210°C, 2.16 kg) can be measured by the above-mentioned method for measuring the MFR (190°C, 2.16 kg), except that the heating temperature is changed from 190°C to 210°C.

[0070] The weight-average molecular weight of the polylactic acid resin is preferably 20,000 to 120,000, more preferably 40,000 to 110,000, even more preferably 40,000 to 100,000, and particularly preferably 50,000 to 100,000. When the weight-average molecular weight of the polylactic acid resin is 20,000 or more, the strength and elongation of the fiber are increased. When the weight-average molecular weight of the polylactic acid resin is 120,000 or less, one of the polylactic acid resin and the poly(3-hydroxyalkanoate) resin is more finely dispersed and mixed with the other in the fiber, making the fiber structure more resistant to tearing.

[0071] The MFR (190°C, 2.16 kg) of the raw material composition is preferably 1 to 1500 g / 10 min, more preferably 5 to 1200 g / 10 min, even more preferably 10 to 1000 g / 10 min, particularly preferably 20 to 800 g / 10 min, still more preferably 50 to 500 g / 10 min, still more preferably 80 to 400 g / 10 min, and most preferably 90 to 300 g / 10 min.

[0072] When the MFR (190°C, 2.16 kg) of the raw material composition is 1 to 1500 g / 10 min, the fiber according to this embodiment can be easily produced. When the MFR (190°C, 2.16 kg) of the raw material composition is 1500 g / 10 min or less, the strength and elongation of the fiber structure are further increased. When the MFR (190°C, 2.16 kg) of the raw material composition is 1 g / 10 min or more, the tension applied to the fibrous melt during drawing can be reduced, making it easier to reduce the fiber diameter of the resulting fiber. As a result, the particle collection efficiency of the fiber structure is further improved.

[0073] The weight average molecular weight of the raw material composition is preferably 100,000 to 550,000, more preferably 110,000 to 450,000, even more preferably 120,000 to 350,000, and particularly preferably 150,000 to 250,000.

[0074] When the weight-average molecular weight of the raw material composition is 100,000 to 550,000, the fiber according to this embodiment can be easily produced. When the weight-average molecular weight of the raw material composition is 100,000 or more, the strength and elongation of the fiber structure are further increased. When the weight-average molecular weight of the raw material composition is 550,000 or less, the tension applied to the fibrous melt during drawing can be reduced, making it easier to reduce the fiber diameter of the fiber. As a result, the particle collection efficiency of the fiber structure is further increased.

[0075] In the following, as a specific example of the method for producing fibers and the method for producing a fiber structure according to this embodiment, a method for obtaining fibers and a fiber structure by a meltblown method will be described. Note that the meltblown method is a concept that also includes the Spunblown (registered trademark) method.

[0076] In the fiber production method and fiber structure production method according to this embodiment, a fiber production apparatus is used to obtain a fiber structure from the raw material composition.

[0077] As shown in FIG. 1 , the fiber production apparatus 1 includes an extruder 3 that melts a raw material composition to obtain a melt, a hopper 2 that supplies the raw material composition to the extruder 3, a kneader 6 that kneads the melt, a nozzle 7 that discharges the kneaded melt in the form of fibers, a collector 8 that collects and cools the fibrous melt to obtain a first fiber structure B, and a winding device 9 that winds up the first fiber structure B.

[0078] Furthermore, the fiber production apparatus 1 may include, as necessary, a gear pump 4 that supplies the molten material to the kneader 6. By including the gear pump 4, the fiber production apparatus 1 can suppress fluctuations in the amount of molten material supplied to the kneader 6.

[0079] Furthermore, the fiber manufacturing apparatus 1 may include a filter 5 for removing foreign matter from the melt upstream of the kneader 6, if necessary.

[0080] In the step (A), the raw material composition is fed to an extruder 3 via a hopper 2, and the raw material composition is melted to obtain a melt.

[0081] The raw material composition supplied to the extruder 3 is preferably in a solid state, more preferably in a pellet state. The raw material composition supplied to the extruder 3 is preferably dried by heating, from the viewpoint of suppressing hydrolysis of the resin in the raw material composition and suppressing oxidative degradation of the resin in the raw material composition. The moisture content in the raw material composition supplied to the extruder 3 is preferably 1000 ppm or less, more preferably 500 ppm or less, and even more preferably 300 ppm or less. When drying the raw material composition, it is preferable to remove oxygen from the atmosphere or to remove oxygen from the raw material composition. The atmosphere during drying is preferably an inert gas atmosphere (e.g., nitrogen gas). In the step (A), the raw material composition may be dried before being supplied to the hopper 2, or the hopper 2 may be a hopper-type dryer, and the raw material composition may be dried in the hopper 2.

[0082] Examples of the extruder 3 include a single-screw extruder, a co-rotating intermeshing twin-screw extruder, a co-rotating non-intermeshing twin-screw extruder, a counter-rotating non-intermeshing twin-screw extruder, a multi-screw extruder, etc. As the extruder 3, a single-screw extruder is preferred from the viewpoint that thermal deterioration of the raw material composition during extrusion is easily suppressed due to a small resin retention area in the extruder, and from the viewpoint that equipment costs are low.

[0083] In the step (A), the melt is supplied to a kneader 6 via a filter 5 by a gear pump 4 , and the melt is kneaded in the kneader 6 .

[0084] Examples of the filter 5 include a screen mesh, a pleated filter, and a leaf disc filter. From the viewpoints of filtration accuracy, filtration area, and pressure resistance, as well as the fact that clogging due to foreign matter is unlikely to occur, a leaf disc filter is preferred as the filter 5. As the filter material of the filter 5, for example, a sintered nonwoven fabric of metal fibers can be used.

[0085] In the step (B), the melt is discharged from the nozzle 7 in the form of fibers.

[0086] The nozzle 7 is a spinning die head. In Fig. 2, the nozzle 7 has a plurality of nozzle holes 7a that discharge a molten material in a fibrous form. As shown in Fig. 2, the nozzle 7 discharges a plurality of fibrous molten material A (also referred to as "raw yarn A"). The nozzle 7 may have only one nozzle hole 7a ("nozzle hole" may also be simply referred to as "hole"). In other words, the nozzle 7 may discharge only one raw yarn A.

[0087] The plurality of nozzle holes 7a open downward. The shape of the nozzle holes 7a is, for example, circular (a concept including circular, approximately circular, elliptical, and approximately elliptical). The opening diameter of the nozzle holes 7a is appropriately selected depending on the fiber diameter of the fibers of the fiber structure. The opening diameter of the nozzle holes 7a is preferably 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably 0.15 mm or more. The opening diameter is preferably 1.0 mm or less, more preferably 0.5 mm or less, even more preferably 0.4 mm or less, and particularly preferably 0.3 mm or less. The opening diameter (also referred to as "hole diameter") means the arithmetic mean value of the opening diameter.

[0088] In the nozzle 7, a plurality of nozzle holes 7a are arranged in a row with a gap therebetween. In FIG. 2, a plurality of nozzle holes 7a are arranged in a single row. The plurality of nozzle holes 7a may be arranged in two or more rows. In other words, the meltblown method may be a spunblown (registered trademark) method. The distance between adjacent nozzle holes 7a (hereinafter also referred to as "spacing" or "hole spacing") is, for example, preferably 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably 0.25 mm or more. By making the distance (spacing) between adjacent nozzle holes 7a 0.05 mm or more, it is possible to suppress fusion of adjacent fibers, and as a result, it is possible to reduce the coefficient of variation of the fiber diameter of the fibers. Furthermore, the distance (spacing) between adjacent nozzle holes 7a is, for example, preferably 3.0 mm or less, more preferably 2.0 mm or less, and even more preferably 1.0 mm or less. The distance between adjacent nozzle holes 7a may or may not be uniform, but is preferably uniform in that it facilitates the production of a homogeneous fiber structure. The distance (interval) between adjacent nozzle holes 7a means the arithmetic mean value of the distance (interval) between adjacent nozzle holes 7a.

[0089] The collector 8 has a collecting surface that collects the fibrous molten material A. The collector 8 is a conveyor. The conveyor includes a conveyor belt 8a having the collecting surface and a plurality of rollers 8b that drive the conveyor belt 8a. The collecting surface is disposed directly below the nozzle holes 7a. The conveyor belt 8a is breathable. Specifically, the conveyor belt 8a is formed of a mesh-like material. That is, the collecting surface is mesh-like. The collector 8 only needs to have a collecting unit, and may be a collecting drum or a collecting net instead of the conveyor.

[0090] The distance (DCD) between the nozzle hole 7a and the collecting surface is preferably 20 mm or more, more preferably 50 mm or more, and even more preferably 80 mm or more. The distance (DCD) between the nozzle hole 7a and the conveyor belt 8a serving as the collecting section is preferably 300 mm or less, and more preferably 250 mm or less. The distance (DCD) between the nozzle hole 7a and the collecting surface refers to the arithmetic mean value of the distance (DCD) between the nozzle hole 7a and the collecting surface.

[0091] As shown in FIG. 3, the fiber manufacturing apparatus 1 is configured to stretch a fibrous melt A by blowing a high-temperature gas C onto the fibrous melt A.

[0092] In the step (B), a high-temperature gas C is blown onto the fibrous molten material A, and the high-temperature gas C blown onto the molten material A is passed through a mesh conveyor belt 8a. In the step (B), the high-temperature gas C is preferably sucked by suction (not shown) so that the high-temperature gas C blown onto the molten material A can easily pass through the mesh conveyor belt 8a. This makes it easier to prevent the fibers from bouncing off the collection surface of the mesh conveyor belt 8a, and as a result, it becomes easier to form a first fiber structure B in which the fibers are well fused together.

[0093] In the step (B), the drawn fibrous melt A is collected by the conveyor belt 8a and cooled while being conveyed by the conveyor belt 8a to obtain fibers. Also, a first fiber structure containing the fibers is obtained.

[0094] The material constituting the mesh-like collection surface is not particularly limited as long as it has heat resistance to the temperature conditions involved in the production of the first fiber structure B, does not fuse excessively with the first fiber structure B, and is a material that allows the first fiber structure B to be peeled off.

[0095] Examples of the gas C include air and inert gases (nitrogen gas, etc.). Examples of a method for blowing high-temperature gas C include a method in which gas C pressurized by a compressor (not shown) is heated by a heater (not shown).

[0096] The flow rate of the high-temperature gas C blown onto the fibrous melt A is preferably 500 NL / min or more, more preferably 1000 NL / min or more, and even more preferably 2000 NL / min or more. The flow rate of the high-temperature gas C blown onto the fibrous melt A is preferably 12000 NL / min or less, and more preferably 10000 NL / min or less.

[0097] In the step (B), the temperature and flow rate of the high-temperature gas C are appropriately controlled in order to obtain a fiber structure with a high degree of crystallinity.

[0098] In the step (B), the first fiber structure B is transported by the conveyor belt 8a to a winding device 9, and the first fiber structure B is wound into a roll by the winding device 9.

[0099] The method for producing a fiber structure according to this embodiment may include a step (C) of heating the first fiber structure B obtained in the step (B) to obtain a second fiber structure.

[0100] When the method for producing a fiber structure according to this embodiment includes the step (C), the second fiber structure serves as the fiber structure. On the other hand, when the method for producing a fiber structure according to this embodiment does not include the step (C), the first fiber structure serves as the fiber structure.

[0101] In the method for producing a fiber structure according to this embodiment, the fiber structure is less likely to break due to the step (C). Furthermore, in the method for producing a fiber structure according to this embodiment, the tensile elongation at break in the MD and CD directions of the fiber structure can be increased due to the step (C). Furthermore, in the method for producing a fiber structure according to this embodiment, the fibers are partially fused together due to the step (C), which makes it easier to suppress fuzzing of the fiber structure.

[0102] The heating temperature range in step (C) is preferably 80°C to 135°C. The heating time range within the preferred heating temperature range in step (C) is preferably 2 to 300 minutes, more preferably 5 to 100 minutes, and even more preferably 10 to 50 minutes. In step (C), by heating the first fiber structure for 2 minutes or more within the preferred heating temperature range, the tensile elongation at break in the CD and MD directions of the fiber structure can be increased. The MD direction is the direction in which the fiber structure moves during production of the fiber structure (machine direction). The CD direction is the direction perpendicular to the MD direction. Furthermore, in step (C), by heating the first fiber structure for 300 minutes or less within the preferred heating temperature range, the productivity of the second fiber structure is improved.

[0103] In the step (C), the first fiber structure may be heated with a gas within the preferred heating temperature range. Examples of the gas include air and inert gas (nitrogen gas, etc.). Examples of a method for heating the first fiber structure with a gas within the preferred heating temperature range include heating the first fiber structure in a heating furnace with a gas within the preferred heating temperature range and / or heating the first fiber structure by blowing a gas within the preferred heating temperature range onto the first fiber structure.

[0104] In the step (C), the first fiber structure may be sandwiched between a pair of heating rolls to heat the first fiber structure within the preferable heating temperature range.

[0105] In the step (C), it is preferable to heat the first fiber structure without contact within the preferred heating temperature range. In the step (C), if the first fiber structure is heated by being sandwiched between a pair of heating rolls, there is a concern that the first fiber structure may be welded to the heating rolls. In the step (C), by heating the first fiber structure without contact with the heating rolls or the like within the preferred heating temperature range, there is an advantage that the first fiber structure can be prevented from being welded to the heating rolls or the like. Examples of a method for heating the first fiber structure without contact within the preferred heating temperature range include a method of heating the first fiber structure with a gas within the preferred heating temperature range.

[0106] In the step (C), the first fiber structure may be heated in a state where the first fiber structure is wound around a roll.

[0107] In the step (C), the first fiber structure may be formed into a sheet shape and heated without being wound around a roll. For example, the first fiber structure in a long shape may be continuously heated while being transported.

[0108] In the step (C), the heated first fiber structure is cooled to obtain a second fiber structure. The cooling method for the heated first fiber structure may be a method in which the heated first fiber structure is naturally cooled at room temperature and normal pressure, or a method in which the heated first fiber structure is forcedly cooled by blowing a gas (e.g., a gas at room temperature) onto the heated first fiber structure.

[0109] It should be noted that the present invention is not limited to the above-described embodiment. Furthermore, the present invention is not limited to the above-described effects. Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention.

[0110] The above describes the fiber manufacturing method according to the present embodiment and the fiber structure according to the present embodiment, taking as an example a method for obtaining the fibers and the fiber structure by the meltblown method, but various modifications are possible without departing from the spirit and scope of the present invention. For example, in the fiber manufacturing method according to the present embodiment and the fiber structure manufacturing method according to the present embodiment, the fibers and the fiber structure may be manufactured by the spunbond method, the flash spinning method, or the electrospinning method. In the fiber manufacturing method according to the present embodiment and the fiber structure manufacturing method according to the present embodiment, it is preferable to manufacture the nonwoven fabric by the meltblown method or the spunbond method.

[0111] In the spunbonding method, the raw material composition is melted by heating to obtain the melt, and the melt is discharged from the nozzle hole to obtain the raw yarn. Next, the raw yarn is stretched by blowing gas onto the raw yarn. In the spunbonding method, the raw yarn may be stretched using a stretching roll. In step (B) of the spunbonding method, the fiber is stretched using a suction device such as an ejector. When an ejector is used, the spinning speed can be adjusted by adjusting the air traction pressure. Increasing the volume of the blown air (increasing the air pressure) increases the spinning speed and further stretches the fiber. In step (B), before the raw yarn extruded from the spinning nozzle in step (A) is pulled and attenuated, a device that applies rectifying air, such as quenching air, may be used to apply rectifying air to the raw yarn. The rectifying air, also known as quenching air, stabilizes the flow of the raw yarn, which is a thread. It is also possible to cool the raw yarn, which is a spun filament, using cooled gas. The quenching air is preferably discharged through a net or mesh and sent uniformly to the yarns. The rectifying air may be blown onto one or both sides of the entangled yarns, or may be blown circumferentially.

[0112] In the flash spinning method, the raw material composition and a solvent are mixed under high temperature and pressure to obtain a melt under high temperature and pressure. The melt under high temperature and pressure is then discharged from the nozzle hole under normal temperature and pressure to obtain the raw yarn, which is then stretched. Examples of the solvent include alcohol (e.g., methanol, ethanol, etc.) and acetone.

[0113] In the electrospinning method, the raw material composition is heated and melted by irradiating it with laser light while a high voltage is applied. As a result, the molten material is obtained. The molten material is then discharged from the nozzle hole to obtain a raw yarn. The raw yarn is then stretched by electrostatic force.

[0114] Disclosure Items Each of the following items is a disclosure of a preferred embodiment.

[0115] [Item 1] A fiber comprising a resin composition, wherein the resin composition comprises a poly(3-hydroxyalkanoate) resin and a polylactic acid resin, and the poly(3-hydroxyalkanoate) resin is contained in an amount of 50 to 99 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin combined; the fiber does not have a sea-island structure including islands with a minimum diameter of 100 nm or more in its cross section, or has a sea-island structure including one or more such islands, the total area of ​​which is 5% or less of the cross-sectional area of ​​the fiber; and the average fiber diameter of the fiber is 5 μm or less. [Item 2] The fiber according to Item 1, wherein the fiber has a coefficient of variation of fiber diameter of 0.30 or less. [Item 3] The fiber according to Item 1 or 2, wherein the difference between the extrapolated glass transition onset temperature and the midpoint glass transition temperature derived from the polylactic acid resin component is 2.0°C or more. [Item 4] The fiber according to any one of items 1 to 3, wherein the resin composition has a melt mass flow rate of 20 to 1500 g / 10 min at 190°C under a load of 2.16 kg. [Item 5] The fiber according to any one of items 1 to 4, wherein the poly(3-hydroxyalkanoate)-based resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). [Item 6] A fiber structure comprising the fiber according to any one of items 1 to 5. [Item 7] The fiber structure according to item 6, which is a spunbond nonwoven fabric or a meltblown nonwoven fabric. [Item 8] A method for producing fibers by melt spinning, comprising the step of melting a raw material composition containing a poly(3-hydroxyalkanoate) resin and a polylactic acid resin, wherein the raw material composition contains 50 to 99 parts by weight of the poly(3-hydroxyalkanoate) resin per 100 parts by weight of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin combined, and wherein the polylactic acid resin has a melt mass flow rate of 40 to 1,500 g / 10 min at 190°C under a load of 2.16 kg. [Item 9] The method for producing fibers according to item 8, wherein the polylactic acid resin has a weight average molecular weight of 20,000 to 120,000.[Item 10] A method for producing a fiber structure, comprising producing a fiber structure containing the fiber by the method for producing a fiber according to item 8 or 9, wherein the melt spinning method is a meltblown method or a spunbond method.

[0116] Next, the present invention will be described in more detail with reference to examples, although the present invention is not limited to these examples in any way.

[0117] The following materials were prepared.

[0118] (Poly(3-hydroxyalkanoate)-based resin (P3HA-based resin)) A P3HA-based resin, P3HB3HH, was prepared according to the method described in Example 1 of WO 2019 / 142845 (melting point: 145°C, MFR (190°C, 2.16 kg): 65 g / 10 min, 3-hydroxybutyrate unit (3HB unit) content: 94.9 mol%, 3-hydroxyhexanoate unit (3HH unit) content: 5.1 mol%, weight average molecular weight: 240,000).

[0119] The melting point refers to the peak top temperature Tm of the crystalline melting peak in a DSC curve obtained by differential scanning calorimetry (DSC measurement). The DSC curve was obtained by precisely weighing about 5 mg of the resin to be measured and heating it from 0°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter.

[0120] The MFR (190° C., 2.16 kg), 3HB unit content, 3HH unit content, and weight average molecular weight of the poly(3-hydroxyalkanoate) resin were measured by the methods described above.

[0121] (Polylactic Acid Resin (PLA Resin)) Using a highly accelerated life tester (ESPEC, EHS-222MD), the following PLA resins were hydrolyzed for the following times under high temperature and humidity conditions (temperature: 105°C, humidity: 100%), followed by drying overnight at 80°C, to obtain the following PLA-1 to PLA-6. PLA-1 was produced by hydrolyzing a PLA-based resin (LX-175, Total Energy Corbion) for 3.5 hours. PLA-2 was produced by hydrolyzing a PLA-based resin (Ingeo3251D, NatureWorks) for 1.5 hours. PLA-3 was produced by hydrolyzing a PLA-based resin (L-175, Total Energy Corbion) for 5.5 hours. PLA-based resin (LX-175, manufactured by Total Energy Corbion) was hydrolyzed for 1.5 hours to produce PLA-4. PLA-based resin (LX-175, manufactured by Total Energy Corbion) was hydrolyzed for 4.5 hours to produce PLA-5. PLA-based resin (LX-175, manufactured by Total Energy Corbion) was hydrolyzed for 2.5 hours to produce PLA-6.

[0122] The melting point, MFR (190°C, 2.16 kg), MFR (210°C, 2.16 kg), 3HB unit content, 3HH unit content, and weight average molecular weight of the polylactic acid resin were measured by the methods described above. The physical properties of PLA-1 to PLA-6 are shown in Table 1 below.

[0123]

[0124] (Nucleating Agent) PETL: Pentaerythritol (manufactured by Taisei Kayaku Co., Ltd., Neuraizer P)

[0125] (Examples 1 to 10, Comparative Examples 1 to 3, Reference Example 1) The above materials were fed into a twin-screw extruder in the formulations shown in Table 2 below and melt-kneaded at a set temperature of 165°C to obtain pellets. The pellets were then dried overnight at 80°C to obtain a pellet-shaped raw material composition. Next, using the fiber production apparatus shown in Figures 1 to 3, a fibrous melt (fibrous melt-kneaded product) was obtained by kneading the pellet-shaped raw material composition under set conditions of an extruder temperature of 180°C, a nozzle temperature of 192°C, and a single-hole discharge rate of 0.045 g / min / hole (gear pump rotation speed of 15 rpm). Then, a gas (air) at a set temperature of 185°C was blown onto the fibrous melt-kneaded product at a rate of 6140 NL / min to produce a melt-blown nonwoven fabric, which is a fiber-containing fiber structure. Note that a nozzle with a width of 600 mm, a hole diameter of 0.15 mm, a hole spacing of 0.35 mm, and 1207 holes was used to produce the fiber structure. The distance (DCD) between the nozzle hole and the collecting surface of the collector (conveyor belt) was 175 mm. The room temperature around the fiber manufacturing apparatus was 22°C.

[0126] (Example 11) A meltblown nonwoven fabric, which is a fiber structure containing fibers, was produced by the same operation as in Examples 1 to 10, except that the above materials were used in the formulation shown in Table 2 below and gas (air) at a set temperature of 185°C was blown onto the fibrous melt-kneaded material at a rate of 3000 NL / min.

[0127] (Example 12) A meltblown nonwoven fabric, which is a fiber structure containing fibers, was produced by the same operation as in Examples 1 to 10, except that the above materials were used in the formulation shown in Table 2 below and gas (air) at a set temperature of 185°C was blown onto the fibrous melt-kneaded material at a rate of 2000 NL / min.

[0128] The physical properties were measured by the following methods.

[0129] (Physical Properties of Raw Material Composition) The weight average molecular weight and MFR (190° C., 2.16 kg) of the raw material composition were measured by the methods described above.

[0130] (Maximum load, elongation at maximum load, and elongation at break in CD and MD directions of fiber structure) The maximum load, elongation at maximum load, and elongation at break in the CD and MD directions of the fiber structure were measured. The maximum load, tensile elongation at maximum load, and tensile elongation at break in the CD and MD directions were measured using a constant-rate extension tensile tester in accordance with JIS B7721:2018 "Tensile tester / compression tester - Calibration and verification method for force measurement system." As the constant-rate extension tensile tester, a universal testing machine (RTG-1210 manufactured by A&D Co., Ltd.) or the like was used. First, a test specimen (width: 8 mm, length: 40 mm) was cut from the fiber structure. Next, the test specimen was attached to the tensile tester with an initial load and a grip spacing of 20 mm. In other words, the grip spacing when the initial load was applied to the test specimen was 20 mm. However, when the initial load was applied, the test piece was pulled by hand to a degree that did not cause slack. A load was then applied at a tensile rate of 20 mm / min until the test piece broke, and the maximum load in the CD and MD directions was measured. The elongation at maximum load in the CD and MD directions and the tensile strength at break were calculated using the following formulas: Elongation at maximum load (%) = [(Grip spacing at maximum load - Grip spacing when initial load was applied to the test piece) / Grip spacing when initial load was applied to the test piece] x 100 (%) Elongation at break (%) = [(Grip spacing at break - Grip spacing when initial load was applied to the test piece) / Grip spacing when initial load was applied to the test piece] x 100 (%) The measured values ​​are shown in Table 2 below.

[0131] (Other physical properties) The basis weight and thickness of the fiber structure, the weight average molecular weight and MFR (190°C, 2.16 kg) of the resin composition, the average value and coefficient of variation of the fiber diameter of the fibers in the fiber structure, and the extrapolated glass transition onset temperature (T ｉｇ (PLA)) and midpoint glass transition temperature (T ｍｇThe total area of ​​the islands in the cross section of the fiber relative to the area of ​​the cross section of the fiber (also referred to as the "ratio of the total area of ​​the islands in the cross section of the fiber") was measured by the method described above. The ratio of the total area of ​​the islands in the cross section of the fiber was determined from the fiber structure, and three or more fiber cross sections were randomly selected from the photographed image, and the ratio of the area of ​​islands (with a minimum diameter of 100 nm or more) consisting only of P3HA resin or PLA resin in the fiber cross section was calculated. The measured values ​​are shown in Table 2 below. TEM images of the fiber cross sections of Example 3 and Comparative Example 3 are shown in Figures 4 and 5, respectively. SEM images of the fiber structures of Example 3 and Comparative Example 3 are shown in Figures 6 and 7. DSC curves of the fibers of Example 3 and Comparative Example 3 are shown in Figures 8 and 9.

[0132] The evaluation test was carried out in the following manner.

[0133] (Fracture energy in the CD and MD directions of fiber structures: resistance to breakage) Using a universal testing machine (for example, RTG-1210, manufactured by A&D Co., Ltd.) conforming to JIS B7721:2018 "Tensile tester / compression tester - Calibration and verification method for force measurement system," a tensile test was performed on a test piece (fiber structure) having a width of 8 mm and a length of 40 mm under conditions of a gripping distance of 20 mm and a pulling speed of 20 mm / min, and data on the "load (N)-displacement (mm) curve" was obtained. The integral value of the data until the test piece broke was defined as the fracture energy (mJ), and the fracture energy per unit cross-sectional area (mJ / mm) was calculated using the following formula. ２ The breaking energy per unit cross-sectional area (mJ / mm ２ ) = Breaking energy (mJ) / (Width (mm) x Thickness (mm) of test piece) Hereinafter, "breaking energy per unit cross-sectional area" will also be simply referred to as "breaking energy". The breaking energy was measured in each of the CD and MD directions of the fiber structure. The measured values ​​are shown in Table 2 below.

[0134] (Virus droplet collection efficiency of fiber structure) The virus droplet collection efficiency (VFE) of the fiber structure was measured. The virus droplet collection efficiency (VFE) was measured in accordance with JIS T9001:2021 "Performance requirements and test methods for medical masks and general masks." The virus droplet collection efficiency means the collection efficiency of viruses attached to particles. The measured values ​​are shown in Table 2 below.

[0135] (Pressure loss due to fiber structure) The pressure loss due to the fiber structure was measured. The pressure loss was measured in accordance with JIS T9001:2021 "Performance requirements and test methods for medical masks and general-use masks." The measured values ​​are shown in Table 2 below.

[0136] (Home Compostability) The home compostability of the fiber structures was evaluated. The home compostability was evaluated based on the following criteria: ◯: In a composting environment at 28°C, at least one of the biodegradability (absolute value) or biodegradability (relative value) is 90% or more within 12 months. ×: In a composting environment at 28°C, both the biodegradability (absolute value) and the biodegradability (relative value) do not exceed 90% within 12 months. Note that the biodegradability (relative value) refers to the biodegradability when the saturated biodegradability of cellulose, the reference substance, is set to 100. The biodegradability was measured in accordance with JIS K6953-2, except that the biodegradation test temperature was set to 28°C. The results are shown in Table 2 below.

[0137] (Biodegradability in Seawater) The degree of biodegradation of the fiber structure in seawater over time was measured in accordance with ASTM D6691. Note that a cellulose powder was prepared as Reference Example 2, and the degree of biodegradation of the cellulose powder in seawater over time was also measured. The results are shown in Figure 10.

[0138]

[0139] As shown in Table 2, the breaking energy of the fiber structures was high in Examples 1 to 12, which are within the scope of the present invention. On the other hand, the breaking energy was low in Comparative Example 1, which did not contain a polylactic acid resin, and Comparative Examples 2 and 3, which had a sea-island structure in which the total proportions of island portions in the fiber cross section were 8.8% and 15.3%, respectively, of the cross-sectional area of ​​the fiber. Therefore, it is clear that the present invention can provide a fiber structure that is difficult to break.

[0140] In addition, Reference Example 1, which did not contain a poly(3-hydroxyalkanoate)-based resin, had a high breaking energy. This shows that the challenge of providing a tear-resistant fiber structure is a challenge specific to fibers containing a poly(3-hydroxyalkanoate)-based resin.

[0141] Furthermore, as shown in Table 2, Examples 1 to 12 had higher VFE than Comparative Examples 1 to 3. Therefore, it can be seen that the present invention can provide a fiber structure with high particle collection efficiency. Here, as shown in FIG. 6, clean fibers of uniform fineness were obtained in Example 3, while as shown in FIG. 7, nodules were observed in the fibers of Comparative Example 3. It is believed that the fibers according to the present invention are obtained by thoroughly mixing the poly(3-hydroxyalkanoate) resin and the polylactic acid resin to form clean fibers of uniform fineness, and as a result, the fiber structure has high particle collection efficiency.

[0142] Furthermore, as shown in Table 2, Examples 1 to 12 had superior home compostability compared to Reference Example 1. Furthermore, as shown in Figure 10, Examples 2, 3, and 6 to 8 had superior biodegradability in seawater compared to Reference Example 1. Therefore, it can be seen that the present invention can provide a fiber structure with excellent biodegradability.

[0143] 1: fiber manufacturing apparatus, 2: hopper, 3: extruder, 4: gear pump, 5: filter, 6: kneader, 7: nozzle, 7a: nozzle hole, 8: collector, 8a: conveyor belt, 8b: roller, 9: winding device, A: fibrous melt (raw yarn), B: first fiber structure, C: gas

Claims

1. A fiber comprising a resin composition, wherein the resin composition comprises a poly(3-hydroxyalkanoate) resin and a polylactic acid resin, and the poly(3-hydroxyalkanoate) resin is contained in an amount of 50 to 99 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin combined; the fiber does not have an island-sea structure containing islands with a minimum diameter of 100 nm or more in its cross section, or has an island-sea structure containing one or more such islands, the total area of ​​which is 5% or less of the cross-sectional area of ​​the fiber; and the fiber has an average fiber diameter of 5 μm or less.

2. The fiber according to claim 1, wherein the coefficient of variation of the fiber diameter in said fiber is 0.30 or less.

3. The fiber according to claim 1 or 2, wherein the difference between the extrapolated glass transition onset temperature and the midpoint glass transition temperature derived from the polylactic acid resin component is 2.0°C or more.

4. The fiber according to claim 1 or 2, wherein the resin composition has a melt mass flow rate of 20 to 1500 g / 10 min at 190°C under a load of 2.16 kg.

5. The fiber according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate)-based resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

6. A fiber structure comprising the fiber according to claim 1 or 2.

7. The fibrous structure of claim 6, which is a spunbonded nonwoven or a meltblown nonwoven.

8. A method for producing fibers by melt spinning, comprising the step of melting a raw material composition containing a poly(3-hydroxyalkanoate) resin and a polylactic acid resin, wherein the raw material composition contains 50 to 99 parts by weight of the poly(3-hydroxyalkanoate) resin per 100 parts by weight of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin combined, and the polylactic acid resin has a melt mass flow rate of 40 to 1,500 g / 10 min at 190°C under a load of 2.16 kg.

9. The method for producing fibers according to claim 8, wherein the weight-average molecular weight of the polylactic acid resin is 20,000 to 120,000.

10. A method for producing a fiber structure, comprising producing a fiber structure containing the fiber by the method for producing the fiber according to claim 8 or 9, wherein the melt spinning method is a meltblown method or a spunbond method.

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