JP2025153874A - Fiber and its manufacturing method, and fiber structure and its manufacturing method - Google Patents

Abstract

The present invention provides a fiber containing a poly(3-hydroxyalkanoate) resin, which can provide a fiber structure that combines low fluffing with excellent filter performance.
[Solution] The present invention relates to a fiber containing a resin composition, wherein the resin composition contains 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 40 to 95 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin combined, and the crystallization temperature of the fiber is 85°C or lower.
[Selection diagram] None

Description

The present invention relates to fibers and their manufacturing methods, as well as fiber structures and their manufacturing methods.

In recent years, with the increasing use of fiber structures (nonwoven fabrics, woven fabrics, knitted fabrics, etc.) such as disposable masks, environmental pollution caused by 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).
Furthermore, poly(3-hydroxyalkanoate)-based resins (abbreviated as P3HA-based resins) have attracted attention due to their advantages such as home compostability and excellent marine biodegradability, and nonwoven fabrics using P3HA-based resins have also been proposed (Patent Document 2).

Patent No. 5356960 International Publication No. 2019/142920

Meanwhile, fiber structures are required to have low fluffing and excellent filtering performance.
However, a fiber structure using fibers containing a poly(3-hydroxyalkanoate) resin, which has little fluffing and excellent filter performance, has not yet been sufficiently investigated.

The present invention aims to provide a fiber containing a poly(3-hydroxyalkanoate) resin that can provide a fiber structure that combines low fuzzing with excellent filtering performance, and a fiber structure containing the fiber.

After extensive research, the inventors discovered that by constructing a fiber structure using fibers containing a poly(3-hydroxyalkanoate) resin and a polylactic acid resin in a specified ratio and having a crystallization temperature of 85°C or less, the fiber structure exhibits both low fuzzing and excellent filtering performance, leading to the completion of the present invention.

That is, the present invention provides a fiber containing a resin composition,
the resin composition contains a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin;
The poly(3-hydroxyalkanoate) resin is contained in an amount of 40 to 95 parts by weight per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin,
The present invention relates to a fiber having a crystallization temperature of 85°C or less.
The present invention also relates to a fiber structure comprising the fiber.
Furthermore, the present invention provides a method for producing fibers by melt spinning, comprising the steps of:
The method includes a step of melting a raw material composition containing a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin,
the raw material composition contains 40 to 95 parts by weight of the poly(3-hydroxyalkanoate)-based resin relative to 100 parts by weight in total of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin;
The present invention also relates to a method for producing fibers, wherein the crystallization temperature of the fibers is 85°C or less.
The present invention also provides a fiber structure comprising the fibers produced by the fiber production method,
The present invention also relates to a method for producing a fiber structure, wherein the melt spinning method is a melt blown method or a spunbond method.

The present invention provides fibers containing poly(3-hydroxyalkanoate) resins that can provide fiber structures that combine low fuzzing with excellent filtering performance, as well as fiber structures containing such fibers.

Schematic diagram of a fiber manufacturing device. FIG. FIG. 4 is a schematic cross-sectional view of a nozzle hole and a conveyor belt. Photographs of the surface of the fiber structure of Example 1 after the evaluation test for fluff grade. Photograph of the surface of the sample of the fiber structure of Example 2 after the evaluation test for fluff grade. Photographs of the surface of the sample of the fiber structure of Example 3 after the evaluation test for fluff grade. Photographs of the surface of the fiber structure of Example 4 after the evaluation test for fluff grade. Photograph of the surface of the sample of the fiber structure of Comparative Example 2 after the fluff grade evaluation test. Photograph of the surface of the sample of the fiber structure of Comparative Example 3 after the evaluation test for fluff grade. Photograph of the surface of the sample of the fiber structure of Comparative Example 4 after the fluff grade evaluation test.

One embodiment of the present invention will now be described with reference to the accompanying drawings.

<Fiber>
The fiber according to this embodiment contains a resin composition.
The resin composition contains a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin.
The fiber according to this embodiment contains 40 to 95 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.
The crystallization temperature of the fibers is 85°C or less.

A fiber structure with less fluffing can be obtained by setting the crystallization temperature of the fiber to 85° C. or less. It is believed that when the crystallization temperature of the fiber is 85° C. or less, it becomes easier to adequately fuse the crossing points of the fibers in the fiber structure, resulting in less fluffing.
Furthermore, the resin composition contains 40 to 95 parts by weight of a poly(3-hydroxyalkanoate)-based resin per 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin combined, thereby improving home compostability.
Furthermore, since the fibers contain a polylactic acid-based resin, the fibers can be continuously processed even when the crystallization temperature is 85°C or lower, and a fiber structure can be obtained that combines low fuzzing with excellent filter performance.

(Poly(3-hydroxyalkanoate)-based resin)
The poly(3-hydroxyalkanoate) resin is a polyester containing 3-hydroxyalkanoic acid as a monomer.
That is, the poly(3-hydroxyalkanoate) resin is a resin containing 3-hydroxyalkanoic acid as a constituent unit.
The poly(3-hydroxyalkanoate) resin can be produced from a microorganism.
The poly(3-hydroxyalkanoate) resin is a biodegradable polymer.
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 suitable for 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. In addition, the decomposition ability of microorganisms in seawater can be evaluated by measuring biochemical oxygen demand.

The poly(3-hydroxyalkanoate) resin preferably includes a poly(3-hydroxybutyrate) resin (abbreviated as P3HB resin), and more preferably is a P3HB resin.

The P3HB-based resin is a resin containing a 3-hydroxybutyrate unit as a constituent unit.
The P3HB-based resin is a concept that includes poly(3-hydroxybutyrate) (abbreviated as P3HB), which is a homopolymer, and copolymers having 3-hydroxybutyrate units.
Examples of the copolymerization type of the copolymer include random copolymerization, alternating copolymerization, and graft copolymerization.

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.
Examples of hydroxyalkanoate units other than 3-hydroxybutyrate units include 3-hydroxyhexanoate, 3-hydroxyoctanoate, 3-hydroxyoctadecanoate, 3-hydroxyvalerate (also called "3-hydroxyvalerate"), and 4-hydroxybutyrate.

Examples of the P3HB-based resin include poly(3-hydroxybutyrate) (abbreviation: P3HB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviation: P3HB4HB), and poly(3-hydroxybutyrate-co- Poly(3-hydroxybutyrate-co-3-hydroxyoctanoate) (abbreviation: P3HB3HO), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate) (abbreviation: P3HB3HOD), poly(3-hydroxybutyrate-co-3-hydroxydecanoate) (abbreviation: P3HB3HD), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (abbreviation: P3HB3HV3HH), and the like.
Among these, P3HB, P3HB3HH, P3HB3HV, and P3HB4HB are preferred because they are easy to produce industrially.
Also, P3HB3HH and/or P3HB4HB are more preferred, with P3HB3HH being particularly preferred.

The P3HB-based resin is preferably at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

Examples of poly(3-hydroxyalkanoate) resins other than the P3HB resin include poly(3-hydroxyvalerate) and poly(3-hydroxyhexanoate).

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

The content of the 3-hydroxybutyrate unit (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 unit 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 is less likely to break. When the content of the 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin is 92 mol % or less, the fiber structure is less likely to fluff and is even more unlikely to break.
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.

The content of 3-hydroxybutyrate units in the poly(3-hydroxyalkanoate) resin can be determined by the method described in the examples below.

(Polylactic acid resin)
The polylactic acid resin is a polyester containing lactic acid as a constituent monomer.

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

The lactic acid constituting the polylactic acid-based 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-based 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%.
When the proportion of the D-isomer in the polylactic acid resin is 1.0% or more and 99.0% or less, the melting point of the polylactic acid resin can be lowered, and the poly(3-hydroxyalkanoate) resin can be processed at a temperature at which it is less likely to decompose.
Furthermore, when the proportion of D-isomer in the polylactic acid resin is 1.0% or more, biodegradability can be improved.
The polylactic acid resin may be any of poly(L-lactic acid) resin, poly(D-lactic acid) resin, and poly(DL-lactic acid) resin, or may be a blend of these.

Examples of other monomers that may be contained in polylactic acid-based resins include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polycarboxylic acids, and polyfunctional polysaccharides.

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

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, 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 can be suitably used.
The method for producing the polylactic acid resin is not particularly limited, and known methods such as dehydration condensation polymerization and ring-opening polymerization can be used.

From the viewpoint of improving home compostability, the fiber contains 40 to 95 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, preferably 45 to 93 parts by weight, more preferably 50 to 95 parts by weight, and even more preferably 55 to 95 parts by weight.
From the viewpoint of further suppressing fuzzing, the fiber preferably contains 65 to 95 parts by weight, and particularly preferably 75 to 95 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 in total. On the other hand, from the viewpoint of further improving filtering properties, the fiber preferably contains 40 to 75 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 in total.

The fibers are primarily composed of poly(3-hydroxyalkanoate) resin and polylactic acid resin. The total proportion of poly(3-hydroxyalkanoate) resin and polylactic acid resin in the total amount of fiber 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 also be 95% by weight or more, 98% by weight or more, or 100% by weight.

(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 sebatate terephthalate, and polybutylene azelate terephthalate. Only one type of other resin may be contained, or two or more types may be contained.

The content of the other resin is not particularly limited, but is preferably 100 parts by weight or less, more preferably 50 parts by weight or less, and even more preferably 30 parts by weight or less, per 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. There is no particular lower limit for the content of the other resin, and it may be 0 parts by weight or more.

The resin composition may contain additives that can be used together with the poly(3-hydroxyalkanoate) resin and the polylactic acid resin, as long as they do not impair the effects of the invention.

Additives include, for example, nucleating agents, lubricants, stabilizers (antioxidants, UV absorbers, etc.), colorants (dyes, pigments, etc.), plasticizers, inorganic fillers, organic fillers, antistatic agents, etc.

The resin composition may contain a crystal nucleating agent.
The nucleating agent is a compound that can promote the crystallization of the poly(3-hydroxyalkanoate) resin, and has a melting point higher than that of the poly(3-hydroxyalkanoate) resin.
By including a crystal nucleating agent in the resin composition, crystallization of the poly(3-hydroxyalkanoate) resin is promoted during fiber production, making it difficult for adjacent fibers to fuse together, and as a result, a fiber structure with a homogeneous structure can be easily obtained.
Examples of the crystal nucleating agent include sugar alcohols such as pentaerythritol, galactitol, and mannitol; orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, boron nitride, etc. Among these, sugar alcohols are preferred, and pentaerythritol is particularly preferred, because they are particularly effective in promoting the crystallization of poly(3-hydroxyalkanoate).
The poly(3-hydroxyalkanoate) resin P3HB can also be used as a crystal nucleating agent.
These may be used alone or in combination of two or more.

When a nucleating agent is used, the amount thereof is not particularly limited, but is preferably 0.1 to 2.5 parts by weight, more preferably 0.3 to 2.0 parts by weight, and even more preferably 0.5 to 2.0 parts by weight, per 100 parts by weight of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin combined.
By including 0.1 parts by weight or more of a crystal nucleating agent per 100 parts by weight of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin in total, there is an advantage in that the crystallization of the poly(3-hydroxyalkanoate) resin is more easily promoted when producing fibers.
When the content of the crystal nucleating agent is 2.5 parts by weight or less per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin, there is an advantage in that fibers can be easily obtained.
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.

However, the fiber according to this embodiment may be substantially free of pentaerythritol. "Substantially free of pentaerythritol" means that the amount of pentaerythritol is less than 0.1 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin and polylactic acid resin combined. It may also be less than 0.01 parts by weight. In an embodiment in which pentaerythritol is substantially not added, the crystallization temperature of the fiber can be lowered, making it less likely to fluff when made into a fiber structure. In addition, bleed-out of pentaerythritol from the fiber can be suppressed, reducing process contamination, etc.

The resin composition may contain the lubricant.
When the fibers are produced, the fibers contain a lubricant, which improves the lubricity of the fibers and makes it possible to prevent the fibers from fusing together.
On the other hand, when the resin composition does not contain a lubricant or contains only a trace amount of a lubricant, there are advantages, for example, in that the tape adhesiveness of the fibers and fiber structures is improved, making them easier to handle 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 fiber.
The lubricant may be, for example, a compound having an amide bond.
The compound having an amide bond preferably includes at least one selected from lauric acid amide, myristic acid amide, stearic acid amide, behenic acid amide, and erucic acid amide.

The content of the lubricant in the resin composition is preferably 0.2 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, even more preferably 0.5 to 3 parts by weight, and most preferably 0.5 to 2 parts by weight, relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin.
By setting the content of the lubricant in the resin composition to 0.2 parts by weight or more per 100 parts by weight of the poly(3-hydroxyalkanoate) resin, there is an advantage in that fusion of fibers to each other can be further suppressed when producing fibers.
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.
On the other hand, when the content of the lubricant in the resin composition is 0 parts by weight or more and less than 0.2 parts by weight relative to 100 parts by weight of the poly(3-hydroxyalkanoate) resin, there is an advantage that the tape adhesiveness of the fibers and the fiber structure is improved, making it easier to handle in the production process.

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. It may be 95% by weight or more, 98% by weight or more, or even 100% by weight.

The crystallization temperature of the fiber according to this embodiment is 85°C or lower, preferably 20 to 80°C, more preferably 25 to 75°C, even more preferably 30 to 70°C, and particularly preferably 35 to 65°C.
When the crystallization temperature of the fiber is 85° C. or less, a fiber structure with little fluffing can be obtained.
When the crystallization temperature of the fiber is 20° C. or higher, the fiber is less likely to stick to a collector or the like during spinning, making it easier to obtain fibers and fiber structures. In addition, excessive fusion between fibers can be suppressed, which is advantageous in that the filter performance of the fiber structure can be easily improved.
The crystallization temperature can be measured by the method described in the Examples below.

The crystallization temperature of the fiber is thought to reflect the temperature at which the poly(3-hydroxyalkanoate) resin crystallizes.
Possible methods for lowering the crystallization temperature of the fiber to 85°C or lower include, for example, reducing the amount of an additive that increases the crystallization temperature of the fiber (for example, a crystal nucleating agent such as pentaerythritol), or increasing the ratio of monomers other than the main monomer (the monomer with the highest molar ratio) in the poly(3-hydroxyalkanoate)-based resin (increasing the ratio of copolymerizable monomer components).

The melt flow rate (hereinafter also referred to as "MFR" or "MFR (190°C, 2.16 kg)") of the fiber according to this embodiment 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, even more preferably 50 to 1300 g/10 min, and particularly preferably 100 to 1200 g/10 min.

When the MFR (190° C., 2.16 kg) of the fiber according to this embodiment is 20 to 1500 g/10 min, the fiber can be easily produced.
When the MFR (190° C., 2.16 kg) of the fiber according to this embodiment is 1500 g/10 min or less, the strength and elongation of the fiber are increased.
When the MFR (190°C, 2.16 kg) of the fiber according to this embodiment is 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 fibers. As a result, it is easier to improve the particle collection efficiency of the fiber structure.

In this embodiment, the melt flow rate (MFR) at 190°C and a load of 2.16 kg can be determined by the method described in the Examples below.

The weight-average molecular weight of the fibers according to this embodiment is preferably 50,000 to 350,000, more preferably 70,000 to 300,000, even more preferably 80,000 to 250,000, and particularly preferably 100,000 to 200,000.

When the weight average molecular weight of the fiber according to this embodiment is 50,000 to 350,000, the fiber according to this embodiment can be easily produced.
When the weight average molecular weight of the fiber according to this embodiment is 50,000 or more, the strength and elongation of the fiber are increased.
By setting the weight average molecular weight of the fiber according to this embodiment to 350,000 or less, the tension applied to the fibrous melt during drawing can be reduced, making it easier to thin the resulting fibers, and as a result, it is easier to improve the particle collection efficiency of the fiber structure.

In this embodiment, the weight average molecular weight can be determined by the method described in the examples below.

The upper limit of the fiber diameter of the fibers is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, still more preferably 15 μm or less, and particularly preferably 8 μm or less.
The lower limit of the fiber diameter of the fibers is preferably 0.5 μm or more, more preferably 0.8 μm or more, and even more preferably 1.0 μm or more.

By making the fiber diameter of the fibers 100 μm or less, the rigidity of the fibers can be reduced, which results in improved texture (e.g., feel to the skin, touch, etc.) when made into a fiber structure, and also improves particle collection efficiency when made into a fiber structure.
When the fiber diameter of the fibers is 0.5 μm or more, the strength and elongation of the fibers and the fiber structure are increased, and productivity is also increased.
When the fiber diameter is within the above range (0.5 μm or more and 100 μm or less), the effect as a mask or various filters for beverages can be sufficiently obtained.

The fiber diameter of the fiber can be determined as follows: First, a photograph (1700x magnification) of the fiber is taken with a scanning electron microscope. Then, the diameter (width) of the fiber is measured, and this diameter is defined as the fiber diameter of the fiber.
In the present embodiment, the "fiber diameter of the fiber" means the "fiber diameter of a single fiber of the fiber."

<Fiber structure>
The fiber structure according to this embodiment contains 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 fabric, thermally bonded nonwoven fabric, needle-punched nonwoven fabric, water-punched nonwoven fabric, stitch-bonded nonwoven fabric, air-laid nonwoven fabric, spunlace nonwoven fabric, spunbonded nonwoven fabric, melt-blown nonwoven fabric, flash-spun nonwoven fabric, electrospun nonwoven fabric, and papermaking nonwoven fabric.
The nonwoven fabric is preferably a direct-spun nonwoven fabric.
The directly spun nonwoven fabric means "a nonwoven fabric obtained by entangling raw yarns obtained by melt spinning to form a sheet directly, and then solidifying the raw yarns." Note that "entangling raw yarns to form a sheet directly" means "entangling raw yarns to form a sheet before solidifying the raw yarns."
Examples of the direct spun nonwoven fabric include meltblown nonwoven fabric, spunbond nonwoven fabric, flash spun nonwoven fabric, and electrospun nonwoven fabric.
The meltblown nonwoven fabric is a concept that also includes nonwoven fabrics obtained by the spunblown (registered trademark) method.
The fiber structure according to this embodiment is more preferably a meltblown nonwoven fabric or a spunbonded nonwoven fabric, and even more preferably a meltblown nonwoven fabric.

The fiber structure according to this embodiment preferably has a basis weight of 10 to 150 g/m ² , more preferably 15 to 100 g/m ² , even more preferably 20 to 80 g/m ² , and particularly preferably 20 to 60 g/m ² .
The fiber structure according to this embodiment has a basis weight of 10 g/ ^m2 or more, which increases the strength and elongation, and also increases the efficiency of capturing particles (for example, particles with blood cells, pollen, coffee powder, tea leaves, viruses, etc.) attached thereto.
Furthermore, since the fiber structure according to this embodiment has a basis weight of 150 g/m ² or less, it has high liquid permeability (water permeability, etc.) or breathability.

The basis weight of the fiber structure according to this embodiment can be determined by the method described in the examples below.

The thickness of the fiber structure according to this embodiment is preferably 0.05 to 0.80 mm, more preferably 0.06 to 0.60 mm, even more preferably 0.07 to 0.50 mm, and particularly preferably 0.08 to 0.40 mm.
When the thickness of the fiber structure according to this embodiment is 0.05 to 0.80 mm, a uniform fiber structure can be easily obtained when the fiber structure is produced.
Furthermore, 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 (water permeability, etc.) or air permeability of the fiber structure can be improved.

The thickness of the fiber structure according to this embodiment can be determined by the method described in the examples below.

The upper limit of the average fiber diameter of the fibers in the fiber structure is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, still more preferably 15 μm or less, and particularly preferably 8 μm or less.
The lower limit of 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, and even more preferably 1.0 μm or more.
The coefficient of variation of the fiber diameter of the fibers in the fiber structure is preferably 0.00 to 0.50, more preferably 0.00 to 0.40, even more preferably 0.00 to 0.30, and particularly preferably 0.00 to 0.20. The coefficient of variation of the fiber diameter of the fibers in the fiber structure is, for example, 0.05 or more.

When the average fiber diameter of the fibers in the fiber structure is 100 μm or less, the rigidity of the fibers can be reduced, the texture (e.g., feel to the skin, touch, etc.) of the fiber structure is improved, and the particle collection efficiency is increased.
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, and productivity is also increased.
When the coefficient of variation of the fiber diameter of the fibers in the fiber structure is 0.50 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 improved.

The average fiber diameter and coefficient of variation of the fibers in the fiber structure can be determined by the method described in the examples below.

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. It may be 95% by weight or more, 98% by weight or more, or even 100% by weight.

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" is intended to encompass 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 collect blood cells, and filters for beverage extraction (e.g., coffee drip filters, tea bags, etc.).

<Method for producing fiber and method for producing fiber structure>
The fiber manufacturing method according to this embodiment can manufacture the fiber.
The method for producing fibers according to this embodiment is a method for producing fibers by melt spinning.
The method for producing fibers according to this embodiment also includes a step (A) of melting a raw material composition containing a poly(3-hydroxyalkanoate) resin and a polylactic acid resin.
The raw material composition contains 40 to 95 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.
The crystallization temperature of the fibers is 85°C or less.

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

In the method for producing a fiber structure according to this 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.

The raw material composition contains poly(3-hydroxyalkanoate) resin and polylactic acid resin.

The raw material composition contains 40 to 95 parts by weight, preferably 45 to 93 parts by weight, more preferably 50 to 95 parts by weight, and even more preferably 55 to 95 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.
From the viewpoint of further suppressing fuzzing, the raw material composition preferably contains 65 to 95 parts by weight, and particularly preferably 75 to 95 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 in total. On the other hand, from the viewpoint of further improving filterability, the raw material composition preferably contains 40 to 75 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 in total.

The raw material composition is primarily composed of poly(3-hydroxyalkanoate) resin and polylactic acid resin. The total proportion of poly(3-hydroxyalkanoate) resin and 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, 98% by weight or more, or even 100% by weight.

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

The weight average molecular weight of the polylactic acid resin is preferably 20,000 to 120,000, more preferably 40,000 to 110,000, and even more 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-based resin is 120,000 or less, one of the polylactic acid-based resin and the poly(3-hydroxyalkanoate)-based resin is more finely dispersed and mixed with the other in the fiber, and the fiber structure is more resistant to tearing when made into a fiber structure.

The crystallization temperature of the fibers is 85°C or lower, preferably 20 to 80°C, more preferably 25 to 75°C, even more preferably 30 to 70°C, and particularly preferably 35 to 65°C.
When the crystallization temperature of the fiber is 20° C. or higher, the fiber is less likely to stick to a collector during spinning, making it easier to obtain a fiber structure. In addition, excessive fusion between fibers can be suppressed, which is advantageous in that the filter performance of the fiber structure can be easily improved.
When the crystallization temperature of the fiber is 85° C. or less, a fiber structure with little fluffing can be obtained.

In the following, a method for producing fibers according to this embodiment and a method for producing a fiber structure according to this embodiment will be described, taking as a specific example a method for obtaining fibers and a fiber structure by a meltblown method.
The meltblown method is a concept that also includes the spunblown (registered trademark) method.

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

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

Furthermore, the fiber manufacturing apparatus 1 may include a gear pump 4 for supplying the melt to a kneader 6, if necessary.
The fiber manufacturing apparatus 1 is provided with the gear pump 4, thereby making it possible to suppress fluctuations in the amount of molten material supplied to the kneader 6.

Furthermore, the fiber manufacturing apparatus 1 may be equipped with a filter 5 upstream of the kneader 6 to remove foreign matter from the molten material, if necessary.

In step (A), the raw material composition is supplied to extruder 3 via hopper 2, and the raw material composition is melted to obtain a molten material.

The raw material composition supplied to the extruder 3 is preferably in a solid state, more preferably in pellet form.

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, and a multi-screw extruder.

In addition, in step (A), the molten material is supplied to kneader 6 via filter 5 by gear pump 4, and the molten material is kneaded in kneader 6.

In step (B), the molten material is extruded in the form of fibers from nozzle 7.

2, the nozzle 7 has a plurality of nozzle holes 7a for discharging the melt in a fibrous form. As shown in FIG. 2, the nozzle 7 discharges a plurality of fibrous melt A (also referred to as "raw yarn A").
The nozzle 7 may have only one nozzle hole 7a (the "nozzle hole" may also be simply referred to as "hole"). That is, the nozzle 7 may discharge only one yarn A.

The opening diameter of the nozzle hole 7a is appropriately selected depending on the fiber diameter of the fibers of the fiber structure.
The opening diameter of the nozzle hole 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 "pore diameter") means the arithmetic mean value of the opening diameter.

The nozzle 7 has a plurality of nozzle holes 7a arranged in a row at intervals.
In FIG. 2, a plurality of nozzle holes 7a are arranged in a row.
The number of rows of the nozzle holes 7a may be two or more. 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 setting the distance (spacing) between adjacent nozzle holes 7a to 0.05 mm or more, it is possible to prevent adjacent fibers from fusing together, and as a result, it is possible to reduce the coefficient of variation of the fiber diameter of the fibers.
The distance (interval) 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 it is preferable that the distances are uniform in order to easily produce 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.

The collector 8 has a collecting surface for collecting the fibrous melt A.
The collector 8 is a conveyor.
The conveyor includes a conveyor belt 8a having the collecting surface, and a plurality of rollers 8b for driving the conveyor belt 8a.
The collection surface is disposed directly below the nozzle hole 7a.
The conveyor belt 8a is breathable. Specifically, the conveyor belt 8a is made of a mesh material. That is, the collection surface of the conveyor belt 8a is mesh-like.

The distance between the nozzle hole 7a and the collection surface (hereinafter also referred to as "DCD") 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 holes 7a and the conveyor belt 8a serving as the collecting section is preferably 300 mm or less, more preferably 250 mm or less.
The distance (DCD) between the nozzle hole 7a and the collection surface means the arithmetic mean value of the distance (DCD) between the nozzle hole 7a and the collection surface.

As shown in Figure 3, the fiber manufacturing apparatus 1 is configured to stretch the fibrous molten material A by blowing high-temperature gas C onto the fibrous molten material A.

In the step (B), a high-temperature gas C is blown onto the fibrous melt A, and the high-temperature gas C blown onto the melt A is passed through a mesh conveyor belt 8a.
In the step (B), it is preferable to suck the high-temperature gas C by suction (not shown) so that the high-temperature gas C sprayed 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 fiber structure B in which the fibers are well fused together.

In step (B), the stretched fibrous molten material A is collected by the conveyor belt 8a and cooled while being transported by the conveyor belt 8a, thereby obtaining fibers. Furthermore, a fiber structure containing the fibers is obtained.

The material that constitutes the mesh-like collection surface is not particularly limited, as long as it is heat-resistant to the temperature conditions involved in the production of fiber structure B, does not excessively fuse with fiber structure B, and allows fiber structure B to be peeled off.

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

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 12,000 NL/min or less, and more preferably 10,000 NL/min or less.

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

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

Note that the present invention is not limited to the above-described embodiment. Furthermore, the present invention is not limited by the above-described effects. Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention.

The above describes the fiber manufacturing method according to this embodiment and the fiber structure according to this embodiment, using the meltblown method as an example to obtain the fibers and the fiber structure, but various modifications are possible within the scope of the present invention.
For example, in the fiber manufacturing method according to this embodiment and the fiber structure manufacturing method according to this embodiment, the fiber and the fiber structure may be manufactured by a spunbonding method, a flash spinning method, or an electrospinning method.
In the method for producing a fiber according to this embodiment and the method for producing a fiber structure according to this embodiment, the nonwoven fabric is preferably produced by a meltblown method or a spunbond method.

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, gas is blown onto the raw yarn to stretch the raw yarn.
In the spunbonding method, the raw yarn may be drawn using a drawing roll. In step (B) of the spunbonding method, the fiber is drawn using a suction device such as an ejector. When an ejector is used, the spinning speed can be adjusted by adjusting the pressure of the air drawing. Increasing the volume of the blown air (increasing the air pressure) increases the spinning speed and the fiber is drawn further.
In step (B), before the raw yarn extruded from the spinning nozzle in step (A) is pulled and attenuated, a device for applying rectifying air such as quench air may be used to apply rectifying air to the raw yarn. The rectifying air is also called quench air and serves to stabilize the flow of the raw yarn, which is a thread. It is also possible to cool the raw yarn, which is a spun filament, by using cooled gas. The quench air is preferably discharged through a net or mesh and sent uniformly to the thread. The rectifying air may be blown against the thread from one or both sides of the entangled threads, or may be blown circumferentially.

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.
Next, the molten material under high temperature and pressure is discharged from the nozzle hole under normal temperature and pressure to obtain the raw yarn, and the obtained raw yarn is drawn.
Examples of the solvent include alcohol (e.g., methanol, ethanol, etc.), acetone, and the like.

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 ejected from the nozzle hole to obtain a raw yarn. The raw yarn is then stretched using electrostatic force.

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

[Item 1]
A fiber comprising a resin composition,
the resin composition contains a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin;
The poly(3-hydroxyalkanoate) resin is contained in an amount of 40 to 95 parts by weight per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin,
A fiber having a crystallization temperature of 85°C or less.
[Item 2]
Item 2. The fiber according to item 1, wherein the melt flow rate of the fiber at 190°C and a load of 2.16 kg is 20 to 1500 g/10 min.
[Item 3]
3. The fiber according to item 1 or 2, having a fiber diameter of 8 μm or less.
[Item 4]
4. The fiber according to any one of items 1 to 3, which is substantially free of pentaerythritol.
[Item 5]
5. The fiber according to any one of items 1 to 4, wherein the poly(3-hydroxyalkanoate)-based resin comprises a poly(3-hydroxybutyrate)-based resin.
[Item 6]
Item 6. The fiber according to Item 5, wherein the poly(3-hydroxybutyrate)-based resin is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).
[Item 7]
7. The fiber according to item 6, wherein the poly(3-hydroxybutyrate)-based resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and/or poly(3-hydroxybutyrate-co-4-hydroxybutyrate).
[Item 8]
8. The fiber according to item 7, wherein the poly(3-hydroxybutyrate)-based resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).
[Item 9]
Item 9. A fiber structure comprising the fiber according to any one of items 1 to 8.
[Item 10]
10. The fibrous structure of item 9, which is a spunbond or meltblown nonwoven.
[Item 11]
A method for producing fibers by melt spinning, comprising:
The method includes a step of melting a raw material composition containing a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin,
the raw material composition contains 40 to 95 parts by weight of the poly(3-hydroxyalkanoate)-based resin relative to 100 parts by weight in total of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin;
A method for producing a fiber, wherein the fiber has a crystallization temperature of 85°C or less.
[Item 12]
Item 12. A fiber structure containing the fiber is produced by the fiber production method according to item 11.
The method for producing a fiber structure, wherein the melt spinning method is a melt blown method or a spunbond method.

Next, the present invention will be explained in more detail using examples and comparative examples. However, the present invention is not limited to these examples in any way.

The following materials were prepared.

(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).

(Polylactic acid resin (PLA resin))
Using a highly accelerated life testing machine (ESPEC, EHS-222MD), a PLA-based resin (LX-175, Total Energies Corbion) was hydrolyzed for 3.5 hours under high temperature and humidity conditions (temperature: 105°C, humidity: 100%), and then dried overnight at 80°C to produce a PLA-based resin (melting point: 152°C, melt flow rate (190°C, 2.16 kg) = 317 g/10 min, weight average molecular weight: 74,000).

The physical properties of the above resin were measured using the following methods.

<Melting point>
The melting point was determined by differential scanning calorimetry (DSC). That is, a DSC curve was obtained by DSC measurement, and the peak-top temperature Tm of the crystalline melting peak in the DSC curve was taken as the melting point. 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.

<Melt flow rate (MFR)>
The melt flow rate (190° C., 2.16 kg) was measured as follows.
The melt volume flow rate (MVR) of the test object was determined using a melt flow rate tester (G-02, manufactured by Toyo Seiki Seisakusho) in accordance with Method B of ASTM-D1238 (ISO1133-1, JIS K7210-1:2011), and the melt mass flow rate (MFR) of the test object was determined from the melt volume flow rate (MVR) of the test object and the density of the test object. The melt volume flow rate (MVR) of the test object was measured by heating 3 to 8 g of the test object at 190°C for 4 minutes, and then applying a load of 2.16 kg to the heated test object.

<Weight average molecular weight>
The weight average molecular weight (Mw) of the measurement object was determined by differential scanning calorimetry (DSC measurement).
First, the substance to be measured was dissolved in chloroform and heated in a hot water bath at 60°C for 0.5 hours. The soluble matter was filtered through a disposable PTFE filter with a 0.45 µm pore size. The filtrate was then measured by GPC under the following conditions, and the weight average molecular weight was determined from the polystyrene equivalent molecular weight distribution.
GPC measurement device: High-performance liquid chromatograph 20A system manufactured by Shimadzu Corporation Column: K-G 4A (1 column), K-806M (2 columns) manufactured by Showa Denko K.K.
Sample concentration: 1 mg/ml
Release solution: chloroform solution Release solution flow rate: 1.0 ml/min Sample injection volume: 10 μL
Column temperature: 40°C
Analysis time: 30 minutes Standard sample: standard polystyrene Detector: IR detector

<3HB Unit Content and 3HH Unit Content of Poly(3-hydroxyalkanoate) Resin>
The content of 3-hydroxybutyrate units (3HB units) and the content of 3-hydroxyhexanoate units (3HH units) in the poly(3-hydroxyalkanoate) resin were measured by the following method.
A sample obtained by adding 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 20 mg of poly(3-hydroxyalkanoate) resin was sealed, and the sample was 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.
Next, the first reaction liquid was cooled, and 1.5 g of sodium hydrogen carbonate was added little by little to the cooled first reaction liquid to neutralize it, and the mixture was left to stand until the evolution of carbon dioxide gas stopped, thereby obtaining a second reaction liquid.
Furthermore, the second reaction solution was thoroughly mixed with 4 mL of diisopropyl ether to obtain a mixture, and the mixture was centrifuged to obtain a supernatant.
The monomer unit composition of the decomposition product in the supernatant was analyzed by capillary gas chromatography under the conditions below to calculate the content of 3-hydroxybutyrate units (3HB units) and 3-hydroxyhexanoate units (3HH units) in the poly(3-hydroxyalkanoate) resin.
Gas chromatograph: Shimadzu GC-17A
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 volume: 1 μL
As for the temperature conditions, the temperature was raised at a rate of 8°C/min from 100 to 200°C, and further raised at a rate of 30°C/min from 200 to 290°C.

(Crystal nucleating agent)
PETL: Pentaerythritol (manufactured by Taisei Kayaku Co., Ltd., Neuraizer P)

Example 1
The above materials were fed to a twin-screw extruder in the formulation shown in Table 1 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 raw material composition in the form of pellets.
Next, using the fiber production apparatus shown in FIGS. 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: 15 rpm).
Then, a gas (air) at a set temperature of 185° C. was blown onto the fibrous melt-kneaded material at a rate of 6140 NL/min to produce a melt-blown nonwoven fabric, which is a fiber structure containing fibers.
To produce the fiber structure, a nozzle with a width of 600 mm, a hole diameter of 0.15 mm, a hole spacing of 0.35 mm, and 1,207 holes was used. The flow path width (the distance between the nozzle surface and the lip surface, also called the lip width) when spraying gas (air) was 0.25 mm. The distance (DCD) between the nozzle hole and the collection surface of the collector (conveyor belt) was 225 mm. The room temperature around the fiber production apparatus was 22°C.

(Examples 2 to 4, Comparative Example 3)
A meltblown nonwoven fabric was produced as a fiber structure in the same manner as in Example 1, except that the composition of the above materials was changed to the composition shown in Table 1 below.

(Comparative Example 1)
An attempt was made to produce a meltblown nonwoven fabric as a fiber structure in the same manner as in Example 1, except that the composition of the above materials was changed to the composition shown in Table 1 below. However, the fiber structure stuck to the collecting surface of the conveyor belt like gum, and could not be separated from the collecting surface of the conveyor belt. In other words, a fiber structure could not be produced.

(Comparative Examples 2 and 4)
A meltblown nonwoven fabric as a fiber structure was produced in the same manner as in Example 1, except that the composition of the above materials was changed to the composition shown in Table 1 below and the distance (DCD) between the nozzle hole and the collection surface of the collector (conveyor belt) was changed to 175 mm.

The physical properties of the fabricated fiber structure (meltblown nonwoven fabric) were measured using the following methods.

<Weight of fiber structure>
The basis weight of the fiber structure (meltblown nonwoven fabric) was measured by the following method. The measured values are shown in Table 1 below.
A test piece (size: 100 mm x 100 mm, 200 mm x 200 mm, etc.) was prepared from the fiber structure, the weight of the test piece was measured using an electronic balance, and the weight of the test piece was divided by the area of the test piece to calculate the basis weight.

<Thickness of fiber structure>
The thickness of the fiber structure (meltblown nonwoven fabric) was measured by the following method. The measured values are shown in Table 1 below.
Test pieces (size: 100 mm x 100 mm, 200 mm x 200 mm, etc.) were prepared from the fiber structure, and the thicknesses of the test pieces were measured at three or more points using a thickness meter ("PEACOCK" manufactured by Ozaki Seisakusho Co., Ltd.), and the arithmetic mean value was taken as the thickness of the fiber structure.

<Weight average molecular weight of fiber>
The weight average molecular weight of the fibers in the fiber structure (meltblown nonwoven fabric) was measured in the same manner as for the weight average molecular weight of the resin. The measured values are shown in Table 1.

<MFR of fiber>
The MFR of the fibers in the fibrous structure (meltblown nonwoven fabric) was measured in the same manner as in the above-mentioned resin MFR measurement method. The measured values are shown in Table 1.

<Fiber diameter>
The average value and coefficient of variation of the fiber diameter of the fiber structure (meltblown nonwoven fabric) were measured by the following method. The measured values are shown in Table 1 below.
First, a test specimen was obtained from the fiber structure.
Next, photographs (1700x magnification) were taken of five points on the surface of the test piece using a scanning electron microscope.
Then, the diameters (widths) of 20 or more randomly selected fibers per photograph were measured.
Next, the arithmetic mean value and coefficient of variation (=standard deviation/arithmetic mean value) were calculated from the diameter (width) values of all the measured fibers.

<Maximum load, elongation at maximum load, and elongation at break in the CD and MD directions of the fiber structure>
The fiber structure (meltblown fiber) was measured for maximum load, elongation at maximum load, and elongation at break in the CD and MD directions.
The maximum load in the CD direction and the MD direction, the tensile elongation at the maximum load, and the tensile elongation at break were measured using a constant-speed extension tensile tester in accordance with JIS B7721:2018 "Tensile tester/compression tester - Calibration and verification methods for force measurement systems."
As a constant-speed extension type tensile tester, a universal testing machine (RTG-1210 manufactured by A&D Co., Ltd.) or the like was used.
First, a test piece (width: 8 mm, length: 40 mm) was cut out from the fiber structure.
Next, the test piece was attached to a tensile tester with an initial load and a grip distance of 20 mm. In other words, the grip distance when the initial load was applied to the test piece was 20 mm. However, under the initial load, the test piece was pulled by hand to such an extent that no slack occurred.
A load was applied at a tensile speed of 20 mm/min until the test piece broke, and the maximum load in the CD and MD directions was measured.
Further, the elongation at maximum load in the CD direction and the MD direction 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 is applied to test piece) / Grip spacing when initial load is applied to test piece] x 100 (%)
Elongation at break (%) = [(grip spacing at break - grip spacing when initial load is applied to test piece) / grip spacing when initial load is applied to test piece] x 100 (%)
The measured values are shown in Table 1 below.

<Crystallization temperature of fiber>
The crystallization temperature of the fiber was determined by differential scanning calorimetry (DSC measurement).
That is, the crystallization temperature was measured by the following method using a differential scanning calorimeter (DSC25, manufactured by TA Instruments). The measured values are shown in Table 1.
A sample amount of 5 to 10 mg was weighed out, the weighed sample was placed in an aluminum pan, and the pan was kept at -30°C until the apparatus stabilized. The pan was then heated to 200°C at a heating rate of 10°C/min and held at 200°C for 1 minute.
Subsequently, the sample was cooled to −30° C. at a cooling rate of 10° C./min, and the peak top of the crystallization peak was taken as the crystallization temperature. When two or more crystallization peaks appeared independently, the peak top of the crystallization peak with the largest crystallization enthalpy was taken as the crystallization temperature.

<Virus droplet collection efficiency (VFE) of fiber structures>
The viral droplet collection efficiency (VFE) was measured in accordance with JIS T9001:2021 "Performance requirements and test methods for medical masks and general masks." The measured values are shown in Table 1 below.
The virus droplet collection efficiency means the collection efficiency of viruses attached to particles.

<Pressure loss of fibrous structure>
The pressure loss of the fiber structure (meltblown nonwoven fabric) was measured.
The pressure loss was measured in accordance with JIS T9001:2021 "Performance requirements and test methods for medical masks and general masks."
The measured values are shown in Table 1 below.

<Fluffing grade>
The fluffing grade of the produced fiber structure (meltblown nonwoven fabric) was evaluated by the following method.
A friction test was carried out using a static and dynamic friction tester (TL201Tt, manufactured by Trinity Labs) under the following conditions: test piece size 70 mm × 150 mm, load 200 g, friction speed 50 mm/min, friction distance 70 mm, number of reciprocations 100, contactor: tactile contactor (finger model), and the fluff grade was determined according to the following evaluation criteria.
1.0: Fibers were torn off so severely that the specimen broke.
2.0: The thinner the specimen, the more fibers are peeled off.
2.5: Hairballs are found in 10 or more places.
3.0: Hairballs are found in 1 to 9 places.
3.5: No pilling is observed, but fluffing is observed in 80% or more of the friction area.
4.0: Fuzzing is observed in 20% or more but less than 80% of the friction area.
5.0: No fuzzing or fuzzing is observed in less than 20% of the friction area.
The fluffing grades were determined for MD (collector face), MD (nozzle face), CD (collector face), and CD (nozzle face), respectively, and these values are shown in Table 1 below.
The average fluff grade was calculated from these four values. The average fluff grade is also shown in Table 1 below. An average fluff grade of 3.0 or more was considered to be acceptable.

Figures 4 to 10 show photographs of the sample surfaces of Examples 1 to 4 and Comparative Examples 2 to 4 after the fluff grade evaluation test (CD (nozzle surface)) for the fiber structures.

As shown in Table 1, Examples 1 to 4 within the scope of the present invention had higher fluff grades than Comparative Examples 2 and 3, which had higher crystallization temperatures, and Comparative Example 4, which did not use a poly(3-hydroxyalkanoate)-based resin.
Furthermore, as shown in Table 1, Examples 1 to 4, which are within the scope of the present invention, had higher VFE than Comparative Examples 2 and 3.
Furthermore, in Comparative Example 1, in which no polylactic acid resin was used, it was not possible to produce a nonwoven fabric.
Therefore, it is clear that the present invention can provide a fiber structure that has both low fluffing and excellent filtering performance.

Furthermore, when comparing the Examples, as shown in Table 1, Examples 1 and 2, which contained a large amount of poly(3-hydroxyalkanoate) resin, had a higher fluffing grade than Examples 3 and 4.
On the other hand, in Examples 3 and 4, which contained a large amount of polylactic acid resin, the VFE was higher than in Examples 1 and 2.

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: fibrous structure, C: gas

Claims (12)

A fiber comprising a resin composition,
the resin composition contains a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin;
The poly(3-hydroxyalkanoate) resin is contained in an amount of 40 to 95 parts by weight per 100 parts by weight of the total of the poly(3-hydroxyalkanoate) resin and the polylactic acid resin,
A fiber having a crystallization temperature of 85°C or less. The fiber according to claim 1, wherein the melt flow rate of the fiber at 190°C and a load of 2.16 kg is 20 to 1500 g/10 min. The fiber according to claim 1 or 2, having a fiber diameter of 100 μm or less. The fiber described in claim 1 or 2, which is substantially free of pentaerythritol. The fiber according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate)-based resin includes a poly(3-hydroxybutyrate)-based resin. The fiber according to claim 5, wherein the poly(3-hydroxybutyrate)-based resin is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). The fiber described in claim 6, wherein the poly(3-hydroxybutyrate)-based resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and/or poly(3-hydroxybutyrate-co-4-hydroxybutyrate). The fiber described in claim 7, wherein the poly(3-hydroxybutyrate)-based resin is poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). A fiber structure comprising the fiber according to claim 1 or 2. The fiber structure according to claim 9, which is a spunbond nonwoven fabric or a meltblown nonwoven fabric. A method for producing fibers by melt spinning, comprising:
The method includes a step of melting a raw material composition containing a poly(3-hydroxyalkanoate)-based resin and a polylactic acid-based resin,
the raw material composition contains 40 to 95 parts by weight of the poly(3-hydroxyalkanoate)-based resin relative to 100 parts by weight in total of the poly(3-hydroxyalkanoate)-based resin and the polylactic acid-based resin;
A method for producing a fiber, wherein the fiber has a crystallization temperature of 85°C or less. A fiber structure containing the fibers is produced by the fiber production method according to claim 11,
The method for producing a fiber structure, wherein the melt spinning method is a melt blown method or a spunbond method.