JP2008002037A - Fibrous structure containing ethylene-vinyl alcohol-based copolymer nano-fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fibrous structure containing an ethylene-vinyl alcohol-based copolymer nano-fiber excellent in hydrophilicity, water absorbability, liquid retainability, biocompatibility and the like. <P>SOLUTION: The fibrous structure contains the ethylene-vinyl alcohol-based copolymer nano-fiber having 25-70 mol% ethylene unit content and has ≤800 nm maximum diameter, ≤100 nm minimum diameter and ≥10 branch units/25μm<SP>2</SP>of the fibrous structure, wherein the branch unit expresses the unit from where the nano-fibers extend arbitrary at least 3 directions from an adhesion point. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fibrous structure containing nanofibers made of an ethylene-vinyl alcohol copolymer. More specifically, the present invention relates to a fibrous structure having a three-dimensional network structure composed of nanofibers made of an ethylene-vinyl alcohol copolymer, and the fibrous structure of the present invention has extremely high water absorption. It has properties such as liquid retention and biocompatibility.

Filters that require high filtration performance and thinning because fabrics and paper made of ultrafine fibers are superior in filtration performance, wiping performance, water absorption, and feel compared to fabrics made of non-fine fibers It is used in various applications such as materials, water-absorbing materials that require high water-absorbing performance, and clothing that requires a soft touch and a natural texture.
Typical production methods for products made of ultrafine fibers include a method of mechanically dividing sheets and fabrics formed from split-type composite fibers into ultrafine fibers, and chemicals such as sheets and fabrics formed from composite fibers. And a method of removing one of a plurality of polymer components forming a composite fiber by processing to make ultrafine fibers, a method of producing by direct melt spinning such as a melt blow method, and the like.

As a conventional technique for mechanically dividing a fabric or sheet formed from split-type composite fibers into ultrafine fibers, for example, a sheet made of split-type composite fibers composed of a polycapramide polymer and a polyester polymer, There is known a technique for producing a water-absorbing material by splitting and exfoliating at the boundary between a polycapramide polymer and a polyester polymer constituting a split-type conjugate fiber by processing with a water jet punch machine (Patent Literature). 1).
In addition, as one of the conventional techniques for removing one component of a plurality of polymer components constituting a composite fiber to form an ultrafine fiber, for example, a fabric formed from a composite fiber made of specific polyvinyl alcohol and a thermoplastic polymer is used. A method for producing a fabric made of ultrafine fibers by treating with water to dissolve and remove polyvinyl alcohol is known (see Patent Document 2).

In recent years, fiber products having higher performance than fiber products made of ultrafine fibers have been demanded. For example, fibers that are superior in performance such as filtration performance, wiping performance, water absorption, hydrophilicity, and liquid retention capability. There is a demand for products and fiber products with excellent biocompatibility.
From this point of view, so-called nanofiber-related technologies with smaller fiber diameters than ultrafine fibers are attracting attention all over the world, and nanofiber manufacturing methods and application development utilizing the characteristics of nanofibers are proceeding. It has been.

As a conventional technique related to nanofibers, for example, nanofiber aggregates made of thermoplastic polymers such as polyester, polyamide, and polyolefin and used as clothing fabrics and polishing fabrics are known (see Patent Document 3).
However, the nanofiber aggregate described in Patent Document 3 does not have sufficient physical properties such as hydrophilicity, liquid retention, and biocompatibility, and has high hydrophilicity, liquid retention, and biocompatibility. It is not effective for applications that require the above.

  Further, as a method for producing a nonwoven fabric composed of nanofibers, an electrospinning method using a solution of a fiber-forming polymer is known. However, the apparatus is large and a polymer and a solvent for producing nanofibers are used. Therefore, it is very difficult to put it into practical use.

On the other hand, fibers made of an ethylene-vinyl alcohol copolymer have high biocompatibility, good hydrophilicity and liquid retention, and fiber products made of these fibers are easy to touch. (See Patent Document 4).
In fibrous structures composed of ethylene-vinyl alcohol copolymer fibers, the finer the fiber structure, the more biocompatible, hydrophilic, moisture retention, etc., are the characteristics of ethylene-vinyl alcohol copolymers. Since the properties can be improved, the development of the microstructure has been studied using various methods, but the fibrous structure having excellent physical properties composed of nano-order ethylene-vinyl alcohol copolymer fibers, And a method capable of stably producing the same has not been developed yet.

JP 2004-100057 A JP 2000-239926 A JP 2004-162244 A JP 2004263331 A

An object of the present invention is to provide a fibrous structure composed of ethylene-vinyl alcohol copolymer nanofibers and excellent in properties such as biocompatibility, hydrophilicity, liquid retention, and touch.
Furthermore, an object of the present invention is to provide a method capable of reliably and stably producing a fibrous structure composed of ethylene-vinyl alcohol copolymer nanofibers by an industrially simple technique. .

The present inventors have made various studies in order to achieve the above object. As a result, an ethylene-vinyl alcohol copolymer containing a specific proportion of structural units derived from ethylene, and a water-soluble thermoplastic polyvinyl alcohol having a specific degree of polymerization, saponification degree, melting point and alkali metal ion content When a water-based polymer is melt-mixed at a specific mass ratio, a water-soluble thermoplastic polyvinyl alcohol polymer is used as a sea component, and an island component composed of an ethylene-vinyl alcohol copolymer is included in the sea component. It was found that a polymer alloy finely dispersed by number was formed. Therefore, based on such knowledge, a fiber containing at least one component of the polymer alloy is manufactured, and the fiber or a fibrous base material manufactured using the fiber is treated with water to form water-soluble thermoplastic polyvinyl in the polymer alloy. When the alcohol-based polymer (sea component) is dissolved and removed, the ethylene-vinyl alcohol-based copolymer in the polymer alloy exists in the form of nano-sized fibers, and tertiary due to branching, crossing, bonding, etc. of the nanofibers. An unprecedented fibrous structure having an original network structure was obtained.
And when the present inventors investigated the physical properties of this fibrous structure, it was found to be extremely excellent in hydrophilicity, liquid retention, biocompatibility, tactile sensation, etc., and also excellent in shape retention. I found it.

  Furthermore, the inventors of the present invention, in the production of a fiber comprising the above polymer alloy as at least one component, is a single fiber of a polymer alloy, a core-sheath type having a polymer alloy as a sheath component and another thermoplastic polymer as a core component. Various kinds of composite fiber, sea-island type composite fiber with polymer alloy as sea component and other thermoplastic polymer as island component, and bonded type composite fiber in which polymer alloy and other thermoplastic polymer are laminated in layers When composite fibers can be produced, and the water-soluble thermoplastic polyvinyl alcohol polymer in the polymer alloy is dissolved and removed by treating the composite fiber or the fibrous base material formed using the same with water. Based on their knowledge, we found that various fibrous structures containing ethylene-vinyl alcohol copolymer nanofibers can be produced according to their composite form. And it completed the present invention.

That is, the present invention
(1) An ethylene-vinyl alcohol copolymer (A) in which the content ratio of structural units derived from ethylene (hereinafter referred to as “ethylene units” in the same manner for other structural units) is 25 to 70 mol%. An ethylene-vinyl alcohol copolymer comprising a nanofiber comprising the following [this may be referred to as “ethylene-vinyl alcohol copolymer nanofiber” hereinafter), and the ethylene-vinyl alcohol copolymer contained in the fiber structure A fibrous structure having a forked portion in which the nanofiber has a maximum diameter of 800 nm or less and a minimum diameter of 100 nm or less, and the ethylene-vinyl alcohol copolymer nanofiber extends in three or more directions starting from an adhesion point It is a fibrous structure characterized by having 10 or more per 25 μm ² .

And this invention,
(2) The fibrous structure according to (1) above, wherein the average fiber diameter of the ethylene-vinyl alcohol copolymer nanofibers is 20 to 500 nm; and
(3) Including ethylene-vinyl alcohol copolymer nanofibers and other thermoplastic polymer fibers having a fineness of 0.001 to 20 dtex, the surface of the other thermoplastic polymer fibers is covered with an ethylene-vinyl alcohol copolymer fiber. (1) or (2) the fibrous structure coated with polymer nanofibers;
It is.

Furthermore, the present invention provides:
(4) an ethylene-vinyl alcohol copolymer (A) having an ethylene unit content of 25 to 70 mol%, a viscosity average polymerization degree of 200 to 500, and a saponification degree of 95 to 99.99 mol%, A water-soluble thermoplastic polyvinyl alcohol polymer (B) having a melting point of 160 to 230 and containing an alkali metal ion in a proportion of 0.0003 to 1% by mass in terms of sodium is represented by (A) :( B) = It is composed of an ethylene-vinyl alcohol copolymer (A) in a sea component composed of a water-soluble thermoplastic polyvinyl alcohol polymer (B) obtained by melt mixing at a mass ratio of 2:98 to 30:70. the fibrous substrate island component to form a polymer alloy dispersed in two or more number of islands per 1 [mu] m ² by using a fiber or the fiber and at least one component is treated with water, Porimaa Method for producing a water-soluble thermoplastic polyvinyl alcohol polymer constituting the sea component (B) to the dissolving and removing fibrous structures, wherein in b; and,
(5) A fiber having at least one component of a polymer alloy is a single fiber of a polymer alloy, a core-sheath type composite fiber having a polymer alloy as a sheath component and another thermoplastic polymer as a core component, and a polymer alloy as a sea component. The production method according to (4) above, which is a sea-island type composite fiber having an island component of the above-mentioned thermoplastic polymer, or a bonded type composite fiber in which a polymer alloy and another thermoplastic polymer are bonded together in a layer form;
It is.

And this invention,
(6) An ethylene-vinyl alcohol copolymer (A) having a content ratio of ethylene units of 25 to 70 mol%, a viscosity average polymerization degree of 200 to 500, a saponification degree of 95 to 99.99 mol%, A water-soluble thermoplastic polyvinyl alcohol polymer (B) having a melting point of 160 to 230 and containing an alkali metal ion in a proportion of 0.0003 to 1% by mass in terms of sodium is represented by (A) :( B) = It is composed of an ethylene-vinyl alcohol copolymer (A) in a sea component composed of a water-soluble thermoplastic polyvinyl alcohol polymer (B) obtained by melt mixing at a mass ratio of 2:98 to 30:70. A fiber comprising at least one polymer alloy in which the island component is finely dispersed in the number of islands of 2 or more per 1 μm ² or a fibrous base material formed using the fiber;
(7) A fiber having a polymer alloy as at least one component is a single fiber of a polymer alloy, a core-sheath type composite fiber having a polymer alloy as a sheath component and another thermoplastic polymer as a core component, and a polymer alloy as a sea component. The fiber or fibrous base material according to the above (6), which is a sea-island type composite fiber comprising the above-mentioned thermoplastic polymer as an island component, or a laminated type composite fiber in which a polymer alloy and another thermoplastic polymer are laminated in layers. ;and,
(8) A fiber product using the fibrous structure according to any one of (1) to (3);
It is.

The fibrous structure of the present invention containing nanofibers composed of an ethylene-vinyl alcohol copolymer (A) having an ethylene unit content of 25 to 70 mol% is extremely high in water absorption, hydrophilicity, and liquid retention. (Especially moisture retention) and also excellent in terms of biocompatibility and tactile sensation. Therefore, taking advantage of these excellent properties, binder fibers, paper cutting fibers, dry nonwoven staples, spinning staples , Multifilaments for textiles, Multifilaments for knitting, Cement reinforcements, Rubber reinforcements, Packaging materials, Sanitary materials, Medical disposable products, Agricultural footwear, Filters, Wipers, Insulating paper, Battery separators, Artificial leather It can be effectively used for various applications such as.
In the case of the production method of the present invention, a fibrous structure having the above-described excellent characteristics and containing ethylene-vinyl alcohol copolymer nanofibers is reliably and stably produced by an industrially simple technique. can do.

The present invention is described in detail below.
The fibrous structure of the present invention comprises an ethylene-vinyl alcohol copolymer nanofiber, that is, a nanofiber made of an ethylene-vinyl alcohol copolymer (A) having an ethylene unit content of 25 to 70 mol%. It is a fibrous structure containing.

  The ethylene unit content in the ethylene-vinyl alcohol copolymer (A) forming the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure of the present invention is as follows. It is necessary that it is 25-70 mol% with respect to all the structural units of a polymer (A). In the ethylene-vinyl alcohol copolymer (A) forming the nanofiber, when the ethylene unit content is too high (when the vinyl alcohol unit content is too low), ethylene is reduced due to the reduction of hydroxyl groups. -The water-absorbing property, hydrophilicity, liquid retention, biocompatibility, and the like of the fibrous structure containing vinyl alcohol copolymer nanofibers are reduced, and the tactile sensation becomes poor. On the other hand, if the ethylene unit content in the ethylene-vinyl alcohol copolymer (A) forming the nanofiber is too small (if the vinyl alcohol unit content is too high), the ethylene-vinyl alcohol type The thermal stability of the copolymer (A) is lowered, making it difficult to form a fiber by melt spinning, and moreover, single yarn breakage and yarn breakage increase during spinning or drawing. Ethylene-vinyl alcohol copolymer nanofibers, and thus the hydrophilicity, water absorption, liquid retention, biocompatibility of the fibrous structure containing the nanofibers, and processability when manufacturing the fibrous structure (especially melting) In consideration of a balance such as spinnability and thermal stability, the ethylene unit content in the ethylene-vinyl alcohol copolymer (A) forming the nanofiber is preferably 30 to 55 mol%. .

  The ethylene-vinyl alcohol copolymer (A) forming the nanofiber is generally a vinyl carboxylate obtained by saponifying a copolymer of ethylene and vinyl carboxylate such as ethylene-vinyl acetate copolymer. It can be obtained by changing the unit to a vinyl alcohol unit, and the saponification degree of the vinyl alcohol unit in the ethylene-vinyl alcohol copolymer (A) is preferably 95% or more, particularly preferably 97% or more. When the saponification degree of the vinyl alcohol unit is lower than 95%, the crystallinity of the ethylene-vinyl alcohol copolymer (A) is lowered, and not only physical properties such as strength are lowered, but also softening is facilitated. Trouble may occur in the fiber forming step of the polymer alloy described later for producing the fibrous structure of the present invention.

  The ethylene-vinyl alcohol copolymer nanofiber contained in the fibrous structure of the present invention has an ethylene-melt flow rate (MFR) of 0.1 to 200 g / 10 min, particularly 0.2 to 100 g / 10 min. It is preferable that it is formed from the vinyl alcohol copolymer (A) from the viewpoint of thermal stability and spinning processability. The melt flow rate (MFR) of the ethylene-vinyl alcohol copolymer (A) here refers to the melt flow rate measured at 190 ° C. under a load of 2160 g. However, in the case where the melting point is around 190 ° C. or exceeds 190 ° C., the melt flow rate is measured by measuring at a plurality of temperatures equal to or higher than the melting point under a load of 2160 g, the reciprocal absolute temperature is shown on the horizontal axis, The melt flow rate is plotted as the vertical axis (logarithm), and the value extrapolated to 190 ° C. is defined as the melt flow rate (MFR).

  The production method of the ethylene-vinyl alcohol copolymer (A) forming the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure of the present invention is not limited at all, and is produced by a known method. be able to. For example, ethylene and vinyl acetate are radically polymerized in a polymerization solvent such as methanol in the presence of a radical polymerization catalyst, and then unreacted monomers are driven out, followed by saponification with sodium hydroxide to produce an ethylene-vinyl alcohol system. The copolymer (A) can be obtained by pelletizing in water, washing with water and drying. At that time, the washing treatment of the pellets may be performed using pure water only, or may be performed by a method of further washing only with a large excess of pure water after washing the pellets with a large amount of pure aqueous solution containing acetic acid. Good.

In the fibrous structure of the present invention, the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure are generally uneven in thickness, and one ethylene-vinyl alcohol copolymer nanofiber. There are also thick and thin parts. In the fibrous structure of the present invention, the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure have a maximum diameter of 800 nm or less and a minimum diameter of 100 nm or less, and the ethylene-vinyl alcohol copolymer The diameter of the fiber made of the polymer (A) is a nano-order size.
When the maximum diameter of the ethylene-vinyl alcohol copolymer nanofiber is larger than 800 nm, the difference from a normal ultrafine fiber is reduced, and the water absorption, hydrophilicity, liquid retention, biocompatibility of the fibrous structure, The tactile sensation is likely to be lowered.
If the minimum diameter of the ethylene-vinyl alcohol copolymer nanofibers is larger than 100 nm, the water absorption, hydrophilicity, liquid retention, biocompatibility, tactile sensation, etc. of the fibrous structure are likely to decrease.

In the fibrous structure of the present invention, when the maximum diameter of the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure is 800 nm or less, the strength, water absorption, hydrophilicity of the fibrous structure, It is excellent in liquid retainability, biocompatibility, tactile sensation, and the like, and the maximum diameter of the nanofiber is preferably 50 to 600 nm.
Further, in the fibrous structure of the present invention, the minimum diameter of the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure is 100 nm or less, so that the water absorption, hydrophilicity, and liquid of the fibrous structure are reduced. It is excellent in retainability, biocompatibility, tactile sensation, and the like, and the minimum diameter of the nanofiber is particularly preferably 5 to 80 nm.
In the fibrous structure of the present invention, the minimum diameter of the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure is ¼ or less, more preferably 径 or less of the maximum diameter, In particular, it is preferable that it is 1/6 or less because a finer nano-order fibrous structure is obtained and performance such as liquid retention is improved.
Here, the “maximum diameter” and “minimum diameter” of the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure in this specification are the surface of the fibrous structure (or a cut parallel to the surface). Based on a photograph obtained by photographing a surface with a scanning electron microscope (SEM), a linear portion of the ethylene-vinyl alcohol copolymer nanofiber (formed by branching, crossing, adhesion, etc. of the nanofiber) In the linear portion that is not the fork-like portion, it means the thickest portion of the fiber diameter and the smallest portion of the fiber diameter, and the detailed method is as described in the section of the following examples.

In the fibrous structure of the present invention, the average fiber diameter of the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure is 20 to 500 nm, particularly 50 to 350 nm. It is preferable from the viewpoint that the fibrous structure can be easily manufactured and the strength, water absorption, hydrophilicity, liquid retention, biocompatibility, touch and the like of the fibrous structure become better.
If the average fiber diameter of the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure is less than 20 nm, the strength of the fibrous structure is insufficient, making it difficult to obtain a practical product. On the other hand, when the thickness exceeds 500 nm, the fiber structure is not sufficiently fiberized, so that the water absorption, hydrophilicity, liquid retention, biocompatibility, and feel of the fibrous structure are likely to deteriorate.
Here, the “average fiber diameter” of the nanofiber (ethylene-vinyl alcohol copolymer nanofiber) made of the ethylene-vinyl alcohol copolymer (A) contained in the fibrous structure in the present specification is: Based on the photograph obtained by photographing the surface of the fibrous structure (or the cut surface parallel to the surface) with a scanning electron microscope (SEM), the linear portion (fork) of the ethylene-vinyl alcohol copolymer nanofiber is selected. The fiber diameters of the linear portions that are not the shape portions) were measured and the average values thereof were taken, and the detailed method for obtaining them was as described in the following Examples section.

Furthermore, in the fibrous structure of the present invention, the number of forked parts in which the ethylene-vinyl alcohol copolymer nanofibers extend in any three directions starting from the adhesion point is 25 μm in the fibrous structure. ^The number needs to be 10 or more per ² and is preferably 40 or more, particularly 50 or more.
The fibrous structure of the present invention comprises ethylene-vinyl alcohol copolymer nanofiber branches, ethylene-vinyl alcohol copolymer nanofiber bonds, and ethylene-vinyl alcohol copolymer nanofiber crossings. The ethylene-vinyl alcohol copolymer nanofibers have a number of forked portions extending in any three or more directions centering on the adhesion point, whereby ethylene-vinyl alcohol is contained in the fibrous structure. A three-dimensional network structure (network structure) is formed by the copolymer nanofibers.
One of the reasons why the fibrous structure of the present invention has very high hydrophilicity and liquid retention is presumed to be due to the three-dimensional network structure of the above-described ethylene-vinyl alcohol copolymer nanofibers. That is, when an aqueous substance is incorporated into the network structure of the ethylene-vinyl alcohol copolymer nanofiber, the hydroxyl group in the ethylene-vinyl alcohol copolymer (A) and the hydroxyl group of the incorporated aqueous substance are hydrogenated. Since it is retained by forming a bond, it is considered that high hydrophilicity and liquid retention are exhibited.

In the fibrous structure, when the number of the forked portions in the ethylene-vinyl alcohol copolymer nanofiber is less than 10 per 25 μm ^{2 of the} fibrous structure, 3 by the ethylene-vinyl alcohol copolymer nanofiber. The dimension network structure is not sufficiently formed, and the intended functions (particularly high hydrophilicity and liquid retention) are not exhibited.
The mechanism by which the above-described three-dimensional network structure is formed by the ethylene-vinyl alcohol copolymer nanofibers in the fibrous structure of the present invention is not necessarily clear, but according to the method of the present invention described later, a specific structure can be obtained. A polymer in which islands made of an ethylene-vinyl alcohol copolymer (A) having an ethylene unit content of 25 to 70 mol% are finely dispersed in a sea component made of water-soluble thermoplastic polyvinyl alcohol (B) When a fiber is produced by melt spinning using an alloy, the ethylene-vinyl alcohol copolymer (A) is nano-sized with irregular thickness in the fiber, and in some cases, the fibers are adhered to each other in some cases. When the water-soluble thermoplastic polyvinyl alcohol (B) is dissolved and removed from the fiber with water, the ethylene- Alkenyl alcohol copolymer nano fibers is considered to adhere further cross-shaped or branched.

Here, “the forked portion in which the ethylene-vinyl alcohol copolymer nanofibers extend in any three or more directions starting from the adhesion point” in this specification refers to the ethylene-vinyl alcohol copolymer nanofiber. The ethylene-vinyl alcohol-based copolymer nanofibers are formed by fiber branching, adhesion (bonding) between the ethylene-vinyl alcohol-based copolymer nanofibers, crossing of the ethylene-vinyl alcohol-based copolymer nanofibers, and the like. It extends in any three or more directions starting from the adhesion point (branch point, bond point, intersection point, etc.), thereby forming a forked portion (non-linear) on the ethylene-vinyl alcohol copolymer nanofiber. A branched portion of the shape).
The “forked part” is illustrated in FIG. 1 (schematic diagram). In FIG. 1, in the parts (locations) a to k surrounded by circles, the ethylene-vinyl alcohol-based copolymer nanofibers have their adhesion points ( Branching points, connecting points, intersections, etc.), and extending in three or more directions. Therefore, the portions (locations) a to k surrounded by circles are all referred to as “forks” in this specification. Part.
As used herein, “the number of forks in the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure” is the scanning type of the surface of the fibrous structure (or a cut surface parallel to the surface). Based on a photograph taken with an electron microscope (SEM), the number of forked portions was counted and obtained as an average value per 25 μm ² , and the detailed calculation method is described in the section of the following examples. As explained in the above.

The fibrous structure of the present invention may be composed of ethylene-vinyl alcohol copolymer nanofibers alone, or may be composed of ethylene-vinyl alcohol copolymer nanofibers and other fibers.
When the fibrous structure of the present invention is composed of ethylene-vinyl alcohol copolymer nanofibers alone, it has extremely high properties such as hydrophilicity, water absorption, liquid retention, biocompatibility, and smooth touch.
In addition, when the fibrous structure of the present invention is composed of ethylene-vinyl alcohol copolymer nanofibers and other fibers, the excellent hydrophilicity, water absorption, and liquid retention of the ethylene-vinyl alcohol copolymer nanofibers. It can be made into the fibrous structure which has the characteristic and function which other fiber has with characteristics, such as property and biocompatibility. When the fibrous structure of the present invention is formed from ethylene-vinyl alcohol copolymer nanofibers and other fibers, the ratio of the other fibers is 100 parts by mass of ethylene-vinyl alcohol copolymer nanofibers. 50-1000 parts by mass, especially 100-900 parts by mass, the ethylene-vinyl alcohol copolymer nanofibers exhibit high water absorption, hydrophilicity, liquid retention, biocompatibility and other properties of the fibrous structure It is preferable for fully expressing the product.

In particular, the fibrous structure of the present invention contains other thermoplastic polymer fibers as other fibers, and the surfaces of the thermoplastic polymer fibers are covered with ethylene-vinyl alcohol copolymer nanofibers. In the case of a fibrous structure, the presence of thermoplastic polymer fibers often reinforces the fibrous structure and strengthens the structure.
At that time, the fineness (single fiber fineness) of the other thermoplastic polymer fibers is preferably 0.001 to 20 dtex, particularly preferably 0.01 to 15 dtex. When the fineness of the other thermoplastic polymer fiber is less than 0.001 dtex, it may not contribute to the improvement of the structural reinforcement of the fibrous structure. On the other hand, when the fineness exceeds 20 dtex, the ethylene-vinyl alcohol copolymer nanofiber Other thermoplastic polymer fibers cannot be covered smoothly with the fibers, and the ethylene-vinyl alcohol copolymer nanofibers have sufficient functions such as high water absorption, hydrophilicity, liquid retention, and biocompatibility. It may not develop.

Other thermoplastic polymer fibers that can be contained in the fibrous structure together with the ethylene-vinyl alcohol copolymer nanofibers include thermoplastic heavy fibers having a melting point of 150 ° C. or higher from the viewpoint of heat resistance and dimensional stability. A fiber made of a coalescence is preferable, and examples thereof include a polyester fiber, a polyamide fiber, and a polyolefin fiber.
Polyester fibers include terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, phthalic acid, 痾, 竈-(4-carboxyphenoxy) ethane, 4,4'-dicarboxydiphenyl, 5-sodium sulfoisophthalic acid Aromatic dicarboxylic acids such as these or their esters, ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexane-1,4-dimethanol, polyethylene glycol, polytetramethylene Examples thereof include polyesters synthesized from diols such as glycols or ester-forming derivatives thereof, and fibers made from polyesters such as polylactic acid. Among them, 80% or more of the structural units are ethylene terephthalate units or The fiber which consists of polyester which is a tylene terephthalate unit is preferable.

Polyamide fibers include nylon 4, nylon 6, nylon 7, nylon 11, nylon 12, nylon 66, nylon 6,10, polymetaxylene adipamide, polyparaxylene decanamide, polybiscyclohexylmethane decanamide and their components. And fibers made of aliphatic polyamide, semi-aromatic polyamide, and the like. Among these, nylon 6 and fibers made of polyamide mainly composed of nylon 6 are preferable. Moreover, the fiber which consists of polyamide containing a small amount of 3rd components may be sufficient.

  Other thermoplastic polymer fibers include polyolefin resins such as polyethylene, polypropylene, and polymethylpentene, acrylic acid resins, vinyl acetate resins, diene resins, polyurethane resins, polycarbonate resins, polyarylate, and polyphenylene. Examples thereof include fibers made of sulfide, polyetheresterketone, fluororesin, and semi-aromatic polyesteramide.

  Other thermoplastic polymer fibers are within the range not impairing the effects of the present invention, if necessary, inorganic substances such as titanium oxide, silica, barium oxide, carbon black, colorants such as dyes and pigments, antioxidants, You may contain a ultraviolet absorber, a light stabilizer, a fluorescent whitening agent, etc.

The shape and structure of the fibrous structure of the present invention are not particularly limited, and include nanofibers of an ethylene-vinyl alcohol copolymer (A) having an ethylene unit content of 25 to 70 mol%, and the nanofibers The fibrous structure has a maximum diameter of 800 nm or less and a minimum diameter of 100 nm or less, and the number of forked parts made of ethylene-vinyl alcohol copolymer nanofibers is 10 or more per 25 μm ² of the fibrous structure. Any object can be used.
The fibrous structure of the present invention includes, for example, short fibers, filaments, cotton-like materials, spun yarns, perlock yarns, slabs, woven and knitted fabrics, nonwoven fabrics, sheet-like materials, paper-like materials, block-like materials, and artificial leather substrates. Any of these may be used.

The fibrous structure of the present invention has an ethylene-vinyl alcohol copolymer (A) having a content ratio of ethylene units of 25 to 70 mol%, a viscosity average polymerization degree of 200 to 500, and a saponification degree of 95 to 95. A water-soluble thermoplastic polyvinyl alcohol polymer (B) containing 99.99 mol%, a melting point of 160 to 230, and containing an alkali metal ion in a proportion of 0.0003 to 1% by mass in terms of sodium, (A ): (B) = 2: 98 to 30:70 obtained by melt mixing at a mass ratio of water-soluble thermoplastic polyvinyl alcohol polymer (B) [hereinafter referred to as “water-soluble thermoplastic PVA polymer” (B) ")] in a sea component consisting of an ethylene-vinyl alcohol copolymer (A) and dispersed in an island component of 2 or more islands per 1 μm ² as at least one component. By treating the fiber to be made or the fibrous base material formed using the fiber with water and dissolving and removing the water-soluble thermoplastic polyvinyl alcohol polymer (B) forming the sea component in the polymer alloy Can be manufactured.

A fiber comprising at least one component of a polymer alloy in which an island made of an ethylene-vinyl alcohol copolymer (A) is finely dispersed in a sea component made of a water-soluble thermoplastic PVA polymer (B) or the fiber The fibrous base material formed by use corresponds to a precursor for producing the fibrous structure of the present invention.
As the ethylene-vinyl alcohol copolymer (A) constituting the island component in the polymer alloy, the ethylene-vinyl alcohol copolymer nanofibers contained in the fibrous structure of the present invention are formed, as described above. The same ethylene-vinyl alcohol copolymer (A) having an ethylene unit content of 25 to 70 mol% is used.

Further, the water-soluble thermoplastic PVA polymer (B) constituting the sea component in the polymer alloy can be obtained by saponifying the vinyl ester unit in the vinyl ester polymer to change it to a vinyl alcohol unit. .
Examples of the vinyl ester (vinyl carboxylate) used for the production of the vinyl ester polymer that is a precursor of the water-soluble thermoplastic PVA polymer (B) include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, Examples thereof include vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and one or more of these can be used. Among them, vinyl acetate is preferably used because it can produce a pinyl ester polymer and a water-soluble thermoplastic PVA polymer (B) obtained by saponifying it with high productivity.
The vinyl ester polymer can be produced by a known method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, or an emulsion polymerization method. Among them, a bulk polymerized without solvent or in a solvent such as alcohol is used. A polymerization method or a solution polymerization method is usually employed. Examples of alcohol used as a solvent during solution polymerization include lower alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol. Examples of the initiator used for the polymerization include α, α′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethyl-valeronitrile), benzoyl peroxide, n-propyl peroxycarbonate, etc. And known initiators such as azo initiators and peroxide initiators. Although there is no restriction | limiting in particular about superposition | polymerization temperature, The range of 0-200 degreeC is suitable.

In addition, as a water-soluble thermoplastic PVA polymer (B) which is obtained by saponifying a vinyl ester polymer and forms a sea component in the polymer alloy, a viscosity average polymerization degree (hereinafter simply referred to as “polymerization degree”) is used. Is abbreviated as 200 to 500), and a polymerization degree of 250 to 420, particularly 320 to 390 is preferably used.
If the degree of polymerization of the water-soluble thermoplastic PVA polymer (B) is less than 200, the melt viscosity becomes remarkably low and it may be difficult to spin stably, while if it exceeds 500, the melt viscosity is too high. As a result, the polymer cannot be discharged from the spinning nozzle, and it may be difficult to perform stable spinning.
Since higher strength fibers are obtained as the degree of polymerization is higher, PVA polymers having a degree of polymerization of 1500 or more are usually used for fibers. Generally, those having a degree of polymerization of about 1700 or about 2100 are used. Things are universal. In view of that, it can be said that the water-soluble thermoplastic PVA polymer (B) used in the present invention has an extremely low degree of polymerization of 200 to 500.

Here, the polymerization degree (P) of the water-soluble thermoplastic PVA polymer (B) and the PVA polymer in this specification refers to the viscosity average polymerization degree measured according to JIS K6726. That is, the polymerization degree (P) (viscosity average polymerization degree) of the water-soluble thermoplastic PVA polymer (B) or PVA polymer referred to in the present specification is determined by completely re-saponifying and purifying the polymer. It is a polymerization degree calculated | required by following formula (1) from intrinsic viscosity [(eta)] (dl / g) measured in 30 degreeC water.
P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)} (1)

  The saponification degree of the water-soluble thermoplastic PVA polymer (B) constituting the sea component in the polymer alloy constituting the fiber is 95 to 99.99 mol%, preferably 98 to 99.7 mol%. 98.3 to 99.5 mol% is more preferable. When the saponification degree of the water-soluble thermoplastic PVA polymer (B) is less than 95 mol%, the thermal stability at the time of melting becomes very low, and gelation and decomposition are likely to occur, and stable spinning. On the other hand, if it is larger than 99.99 mol%, it becomes difficult to stably produce the water-soluble thermoplastic PVA polymer (B) itself.

The melting point of the water-soluble thermoplastic PVA polymer (B) constituting the sea component in the polymer alloy constituting the fiber is 160 to 230 ° C, preferably 200 to 220 ° C, and preferably 205 to 212 ° C. It is more preferable.
When the melting point of the water-soluble thermoplastic PVA polymer (B) is within the above range, the ethylene-vinyl alcohol copolymer (A) is contained in the sea component composed of the water-soluble thermoplastic PVA polymer (B). The polymer alloy in which the island component is finely dispersed at the number of islands of 2 or more per 1 μm ² can be smoothly prepared by melt mixing, and the fiber containing the polymer alloy as at least one component can be prepared by melt spinning. It can be manufactured smoothly.
If the melting point of the water-soluble thermoplastic PVA polymer (B) is lower than 160 ° C, the viscosity becomes too low to be suitable for melt spinning, while if it is higher than 230 ° C, the water-soluble thermoplastic PVA polymer (B) It becomes close to the decomposition point, and gelation decomposition is likely to occur during melt spinning.

The water-soluble thermoplastic PVA polymer (B) that constitutes the sea component in the polymer alloy is based on the mass of the water-soluble thermoplastic PVA polymer (B), and alkali metal ions are converted into sodium ions in an amount of 0.0003 to It is preferably contained at a rate of 0.0003 to 0.8% by mass, more preferably at a rate of 0.0005 to 0.6% by mass. More preferably, it is contained in a proportion of 0005 to 0.5% by mass. When the content of alkali metal ions in the water-soluble thermoplastic PVA polymer (B) is less than 0.0003% by mass, the water-soluble thermoplastic PVA polymer (B ) May not exhibit sufficient water solubility, and undissolved materials may remain. On the other hand, when the content of alkali metal ions in the water-soluble thermoplastic PVA polymer (B) is more than 1% by mass, it decomposes and gels during melt spinning to produce fibers containing at least one polymer alloy. Becomes remarkable and fiberization becomes difficult.
Examples of the alkali metal ions contained in the water-soluble thermoplastic PVA polymer (B) include potassium ions and sodium ions.
In addition, the content of alkali metal ions in the PVA polymer in the present specification is determined by an atomic absorption method, and details thereof are as described in the section of Examples below.

The production method of the water-soluble thermoplastic PVA polymer (B) containing the alkali metal ion in the above-mentioned specific amount is not particularly limited. For example, (i) a water-soluble thermoplastic PVA polymer containing no alkali metal ion is used. (Ii) saponifying a vinyl ester polymer in a solvent to change the vinyl ester unit to a vinyl alcohol unit to produce a water-soluble thermoplastic PVA-based polymer. When producing a coalescence, an alkali substance containing an alkali ion is used as a saponification catalyst, and after the alkali metal ion is contained in the PVA polymer, the content of the alkali metal ion in the PVA polymer May be a method of cleaning with a cleaning liquid while controlling so as to be within the above range defined in the present invention.
Among these, the method (ii) is preferable because the production process can be simplified.

  A saponification catalyst (alkaline substance) used when the water-soluble thermoplastic PVA polymer (B) having an alkali metal ion content within the above range defined in the present invention is produced by the method (ii). Examples thereof include potassium hydroxide and sodium hydroxide, among which sodium hydroxide is preferably used. The amount of the alkaline substance (saponification catalyst) used is preferably 0.004 to 0.5 mol, preferably 0.005 to 0.05 mol, per 1 mol of vinyl ester unit in the vinyl ester polymer. More preferably. The saponification catalyst may be added all at once in the initial stage of the saponification reaction, or may be added sequentially during the saponification reaction.

  Examples of the solvent used in the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, dimethylformamide, etc. Among them, methanol is preferably used. In the case of using methanol, it is preferable to use methanol whose water content is controlled to 0.001 to 1% by mass, further 0.003 to 0.9% by mass, and particularly 0.005 to 0.8% by mass. Examples of the cleaning solution used after the saponification reaction include methanol, acetone, methyl acetate, ethyl acetate, hexane, and water. Among them, methanol, methyl acetate, or water can be used alone, or the above-described liquid can be used. It is preferable to use a mixed solution. The washing temperature is preferably 5 to 80 ° C., particularly 20 to 70 ° C., and the washing time is preferably 20 minutes to 100 hours, particularly 1 to 50 hours.

  The water-soluble thermoplastic PVA polymer (B) constituting the sea component in the polymer alloy may be a PVA homopolymer consisting only of vinyl alcohol units, or a modified PVA polymer introduced with copolymer units. Any of them may be used, and among them, a modified PVA polymer into which copolymer units are introduced is preferable from the viewpoint of good thermal stability during melting. Examples of the monomer constituting the copolymer unit in this case include α-olefins such as ethylene, propylene, 1-butene, isobutene, and 1-hexene; acrylic acid and salts thereof, methacrylic acid and salts thereof (Meth) methacrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate ; (Meth) acrylamides such as acrylamide, N-methylacrylamide, N-ethylacrylamide, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl Vinyl ethers such as ether and n-butyl vinyl ether; vinyl ethers containing hydroxy groups such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether and 1,4-butanediol vinyl ether; allyl acetate, propyl allyl ether, butyl allyl ether, Allyl ethers such as hexyl allyl ether; unsaturated monomers having an oxyalkylene group such as polyoxyethylene group, polyoxypropylene group and polyoxybutylene group; vinyl silanes such as vinyltrimethoxysilane; isopropenyl acetate, 3 -Buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decene-1-ol, 3-methyl-3-buten-1-ol Hide Α-olefins containing an xyl group or esterified products thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; fumaric acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride Unsaturated monomers having a carboxyl group such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, unsaturated monomers having a sulfonic acid group such as 2-acrylamido-2-methylpropane sulfonic acid; vinyloxy Ethyltrimethylammonium chloride, vinyloxybutyltrimethylammonium chloride, vinyloxyethyldimethylamine, vinyloxymethyldiethylamine, N-acrylamidomethyltrimethylammonium chloride, N-acrylamidoethyltrimethylammonium And unsaturated monomers having a cationic group such as um chloride, N-acrylamidodimethylamine, allyltrimethylammonium chloride, methallyltrimethylammonium chloride, dimethylallylamine, and allylethylamine. The coalescence (B) can have a copolymer unit derived from one or more of the aforementioned unsaturated monomers.

  The content ratio of the copolymer unit in the water-soluble thermoplastic PVA polymer (B) is 0.01 to 20 mol% with respect to the total structural units of the water-soluble thermoplastic PVA polymer (B). Preferably, it is 0.1 to 20 mol%, more preferably 0.5 to 18 mol%. If the proportion of the copolymerized unit exceeds 20 mol%, the solubility of the water-soluble thermoplastic PVA polymer (B) in water tends to be reduced, whereas if it is less than 0.01 mol%, the copolymerized unit is reduced. It tends to be difficult to bring out the merits of the introduction.

  Among the above copolymerized units, α-olefins such as ethylene, propylene, 1-butene, isobutene, 1-hexene; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i -Vinyl ethers such as propyl vinyl ether and n-butyl vinyl ether; Hydroxy group-containing vinyl ethers such as ethylene glycol vinyl ether, 1,3-propanediol vinyl ether and 1,4-butanediol vinyl ether; Allyl esters represented by allyl acetate , Allyl ethers such as propyl allyl ether, butyl allyl ether and hexyl allyl ether; N-vinyl amides such as N-vinylformamide, N-vinylacetamide and N-vinylpyrrolidone; Unsaturated monomer having a xyalkylene group; 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol, 7-octen-1-ol, 9-decene-1-ol Copolymer units derived from hydroxy group-containing α-olefins such as 3-methyl-3-buten-1-ol are preferred.

In particular, from the viewpoint of availability of raw materials, thermal stability at the time of melting, and balance of physical properties of the obtained fibrous structure, the copolymer unit in the water-soluble thermoplastic PVA polymer (B) is ethylene, Α-olefins having 4 or less carbon atoms of propylene, 1-butene, and isobutene; copolymer units derived from vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, and n-butyl vinyl ether. It is more preferable.
When the copolymerized unit is a unit derived from α-olefins having 4 or less carbon atoms and / or vinyl ethers, the content ratio of these copolymerized units is the total amount of the water-soluble thermoplastic PVA polymer (B). It is preferable that it is 0.1-20 mol% with respect to a structural unit, especially 0.5-18 mol%.
Among them, the production rate of the vinyl ester polymer (modified vinyl ester polymer), which is a precursor of the water-soluble thermoplastic PVA polymer (B), is high and the productivity is high. The water-soluble thermoplastic PVA polymer (B) obtained by saponifying the polymer is excellent in thermal stability at the time of melting, and the water-soluble thermoplastic PVA polymer (B) formed using a polymer alloy As a water-soluble thermoplastic PVA polymer (B) that forms a sea component in a polymer alloy from the viewpoint of excellent strength properties, tensile properties, etc. of the fiber structure before being dissolved and removed with water) Water-soluble thermoplastic PVA polymer (B) having ethylene units as copolymerized units, water-soluble thermoplastic PVA system containing ethylene units in a proportion of 3 to 20 mol%, particularly 5 to 18 mol%. Polymer (B) is preferably used.

  In addition, the water-soluble thermoplastic PVA polymer (B) that constitutes a sea component in the polymer alloy is adjusted as necessary with respect to the melting point and melt viscosity of the polymer as long as the objects and effects of the present invention are not impaired. A plasticizer may be contained for the purpose. A conventionally well-known thing can be used as a plasticizer, As a preferable example, what added ethylene oxide and propylene oxide to diglycerol, polyglycerol alkyl monocarboxylic acid ester, glycols can be mentioned. Among these, the compound which added 1-30 mol of ethylene oxide with respect to 1 mol of sorbitol is used preferably from points, such as availability.

A polymer alloy in which an island component composed of an ethylene-vinyl alcohol copolymer (A) is finely dispersed in a sea component composed of a water-soluble thermoplastic PVA polymer (B) is an ethylene-vinyl alcohol copolymer ( A) and a water-soluble thermoplastic PVA polymer (B) are mixed at a mass ratio of (A) :( B) = 2: 98-30: 70, preferably 5: 95-20: 80. It can be obtained by melt-kneading with the same extruder.
The ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) are dissolved because the main structural units constituting the polymer are vinyl alcohol units and have similar structures to each other. Solubility Parameter values are close and easily distributed to each other. For this reason, the mixing ratio of the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) is set within the above range, and the ethylene-vinyl alcohol copolymer ( By further adjusting the content of ethylene units in A) and the water-soluble thermoplastic PVA polymer (B), an ethylene-vinyl alcohol system is contained in the sea component comprising the water-soluble thermoplastic PVA polymer (B). A polymer alloy in which island components made of the copolymer (A) are finely dispersed can be obtained.

When the proportion of the ethylene-vinyl alcohol copolymer (A) exceeds 30% by mass based on the total mass of the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) [ When the proportion of the water-soluble thermoplastic PVA polymer (B) is less than 70% by mass], the phase inversion of the sea-island structure occurs, and the ethylene-vinyl alcohol copolymer (A) is a sea component and water-soluble heat. The plastic PVA polymer (B) becomes an island component.
On the other hand, the proportion of the ethylene-vinyl alcohol copolymer (A) based on the total mass of the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) is less than 2% by mass. If [the ratio of the water-soluble thermoplastic PVA polymer (B) exceeds 98% by mass], the water-soluble thermoplastic PVA polymer (B) constitutes a sea component, and an ethylene-vinyl alcohol copolymer. Although (A) forms an island component, a fibrous form containing an ethylene-vinyl alcohol copolymer (A) fiber obtained after dissolving and removing the water-soluble thermoplastic PVA polymer (B) forming a sea component with water The structure becomes very fragile, and the fibrous structure may collapse due to mechanical external force during the dissolution treatment with water, or the product made of the fibrous structure may collapse due to light frictional force, etc. For practical use It can not be.

Then, the above-described polymer alloy [that is, a molten mixture of the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B)] is used as at least one component and melted and discharged from the spinneret. Thus, a fiber having a polymer alloy as at least one component, which is a precursor for producing the fibrous structure of the present invention, is formed.
In a fiber comprising at least one polymer alloy in which an island component composed of an ethylene-vinyl alcohol copolymer (A) is finely dispersed in a sea component composed of a water-soluble thermoplastic PVA polymer (B), For each 1 μm ² of the constituent polymer alloy (polymer alloy portion), it is necessary that the island component made of the ethylene-vinyl alcohol copolymer (A) is finely dispersed with the number of islands of two or more. The number of islands is preferably finely dispersed, and more preferably 4 to 10 islands. When the number of islands made of the ethylene-vinyl alcohol copolymer (A) in the polymer alloy portion constituting the fiber is less than ² per 1 μm ² of the polymer alloy, the sea component in the polymer alloy [water-soluble thermoplastic PVA The ethylene-vinyl alcohol copolymer (A) fiber obtained by dissolving and removing the system polymer (B)] with water becomes thicker but less likely to become nanofibers. On the other hand, if the number of islands in the polymer alloy portion is too large, the water-soluble thermoplastic PVA polymer (B) constituting the sea component may not be dissolved and removed smoothly.
Here, “the number of islands per 1 μm ^{2 of the} polymer alloy constituting the fiber is obtained by observing the cross section of the fiber with a scanning electron microscope (SEM) and counting the actual number of islands”. The detailed measurement method is as described in the section of the following examples.

Further, the diameter of the island made of the ethylene-vinyl alcohol copolymer (A) present in the polymer alloy part constituting at least one component of the fiber is preferably 800 nm or less, more preferably 600 nm or less, More preferably, it is 5-400 nm, and it is especially preferable that it is 10-100 nm. If the island diameter exceeds 800 nm, the island fineness increases, and it becomes difficult to obtain a fibrous structure containing the intended ethylene-vinyl alcohol copolymer nanofibers. On the other hand, if the island diameter becomes too small, the fibrous structure obtained after dissolving and removing the water-soluble thermoplastic PVA polymer (B) constituting the sea component from the polymer alloy constituting the fiber and the fiber product comprising the same The mechanical strength of the steel is reduced, and the utility is easily lost.
Here, the “diameter of the island existing in the polymer alloy part constituting the fiber” as used in this specification is a photograph of a cross section of the fiber taken by a scanning electron microscope (SEM), and the diameter of the island in the photograph is Measured. In some polymer alloys constituting the fiber, two or more islands are bonded to each other to form a dumbbell shape or an elongated cross-sectional shape. In such a case, before bonding, Treat the object as one island and measure the island diameter. Also in this case, the island is not completely circular, but may be elliptical or deformed. In such an island, it is converted to the diameter of a circle with the same area as the island. And “the diameter of the island”.

  The cross-sectional shape of the fiber comprising the above polymer alloy as at least one component is not particularly limited. For example, round shape, flat shape, saddle shape, hollow shape, T shape, triangle shape, square shape, multi-leaf shape, dog bone shape, etc. Any shape can be used.

As a method for producing a fiber comprising the above polymer alloy as at least one component, a fiberizing method involving a melt mixing extrusion process is preferably employed. In carrying out the fiberization method involving the melt mixing extrusion step, the melt-kneaded body is obtained by melt-kneading the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) with the same extruder. The melt-kneaded body is discharged from a predetermined spinneret alone, and stretched as necessary, and scraped off, or the melt-kneaded body is made of another thermoplastic polymer (especially other fiber-forming thermoplastic). A method in which the polymer is discharged together with a polymer from a predetermined spinneret and is drawn as necessary is preferably employed.
In melt-kneading the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B), the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer are used. (B) may be either powdery or granular, and among these, from the viewpoint of easy availability and ease of handling, it is preferably in the form of chips or pellets.

The ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) can be mixed by pre-blending both chips (chip blend), or a chip feeder in a melt kneader. It may be carried out by any of the methods of attaching and mixing while simultaneously supplying both chips to the melt-kneader.
In the case of chip blending, it is important to uniformly mix the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) at the specific mass ratio defined in the present invention. is there. Even when mixing at a mass ratio specified in the present invention, if the mixing state is non-uniform, the mixing ratio changes during melt-kneading, and not only stably melt-extrusion, but also the structure of the polymer alloy changes, The target fiber cannot be obtained, and as a result, the fibrous structure of the present invention cannot be obtained. In order to uniformly mix the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) by chip blending, the ethylene-vinyl alcohol copolymer (A) chip and water It is preferable that the shape and size of the chip of the thermoplastic thermoplastic PVA polymer (B) are completely matched or substantially the same. In the case where it is difficult to completely match, the chip of the ethylene-vinyl alcohol copolymer (A) and the volume occupied by a certain mass and the chip of the water-soluble thermoplastic PVA polymer (B) having the same mass It is preferable that the difference in volume occupied by be within 30%.
Moreover, when mixing using a chip feeder, it is preferable to manage the discharge accuracy of the chip feeders of both polymer chips within ± 1% using a high-performance feeder.

  When the mixture of the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) is melt-extruded, the above-mentioned polymer alloy can be obtained in an industrially stable and homogeneous manner. It is desirable to use an extruder, and it is preferable to use a single screw extruder or a twin screw extruder equipped with a screw having a high melt-kneading effect. In the case of using a single screw extruder, it is also effective to perform dull mage processing or the like to improve the kneading effect at the tip of the screw. When a twin-screw extruder is used, the screw shaft rotation speed is preferably 100 rotations / minute or more, particularly preferably 150 rotations / minute or more. In this case, the ethylene-vinyl alcohol copolymer (A) and In order to suppress thermal decomposition of the water-soluble thermoplastic PVA polymer (B), it is preferable to set the shaft rotational speed of the screw to 400 revolutions / minute or less.

In the production of a polymer alloy composed of an ethylene-vinyl alcohol copolymer (A) and a water-soluble thermoplastic PVA polymer (B), the temperature at the time of melt-kneading / extrusion has a great influence on the phase structure. Therefore, it is necessary to appropriately manage the temperature conditions during melt kneading and extrusion. In order to obtain a fiber comprising at least one polymer alloy having the specific structure described above as defined in the present invention, an ethylene-vinyl alcohol copolymer (A) or a water-soluble thermoplastic PVA polymer (B) Depending on the type and combination thereof, the melt-kneading and extrusion of the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) are carried out by the following formulas (2) and (3 ) At the same time satisfying the temperature T ₁ (° C.).
It consists of a water-soluble thermoplastic PVA polymer (B) by adjusting the temperature at the time of melt-kneading and extrusion within the range of temperature T ₁ (° C.) that simultaneously satisfies the following formulas (2) and (3). It becomes possible to adjust the number of islands of the island component made of the ethylene-vinyl alcohol copolymer (A) in the sea component to a range specified in the present invention. Since both the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) have relatively low thermal stability, the upper limits of the following formulas (2) and (3) It is necessary to avoid melting and kneading / extrusion at temperatures exceeding the above as much as possible.

T _A +30 <T ₁ <T _A +80 (2)
T _B +5 <T ₁ <T _B +30 (3)

[In the above formula, T _A represents the melting point (° C.) of the ethylene-vinyl alcohol copolymer (A), and T _B represents the melting point (° C.) of the water-soluble thermoplastic PVA polymer (B). ]

In the present invention, a spinneret in which a melt-kneaded product of an ethylene-vinyl alcohol copolymer (A) and a water-soluble thermoplastic PVA polymer (B) melt-kneaded by the above method is attached to the tip of an extruder or the like. It is possible to produce a single fiber of only the polymer alloy described above by discharging it alone and scraping it at a constant speed.
In the present invention, the melt-kneaded product of the ethylene-vinyl alcohol copolymer (A) and the water-soluble thermoplastic PVA polymer (B) melt-kneaded by the above method is supplied to the spinneret by an extruder. Other thermoplastic polymers (especially other fiber-forming thermoplastic polymers) are melt-kneaded with another extruder, supplied to the spinneret, and simultaneously discharged from the spinneret, and scraped at a constant speed. The composite fiber which consists of an above-described polymer alloy and another thermoplastic polymer can be manufactured.
In manufacturing the above-described single fiber or composite fiber, the fiber is preferably stretched. The stretching process may be performed by a two-step division method in which the fiber wound after winding is rewound, or when the fiber discharged from the spinneret is heated by a heating means such as a heat tube before stretching. You may carry out by the 1 step system wound up simultaneously.
In the case of the two-step division method, it is desirable to perform a fiber drawing process by a hot drawing facility using a non-aqueous medium such as a hot air furnace or a dry heat furnace. The reason is that the water-soluble thermoplastic PVA polymer (B) that forms the sea component of the polymer alloy swells or melts due to contact with moisture. The stretching treatment is preferably performed in a temperature range of 80 to 200 ° C. in order to adjust the strength physical properties after stretching of the fiber and the elongation physical properties, and the stretching ratio is 1.5 to 8 times, particularly 2 to 2. Five times is preferable.

  A fiber comprising at least one polymer alloy obtained by the above, in which an island component composed of an ethylene-vinyl alcohol copolymer (A) is finely dispersed in a sea component composed of a water-soluble thermoplastic PVA polymer (B). Single fiber fineness (single fiber of polymer alloy or composite fiber of polymer alloy and other thermoplastic polymer) is the stability in spinning process, stability in drawing process, handling and strength of fiber, the fiber concerned Alternatively, from the viewpoint of dissolution and removal processability when the fibrous base material formed using the fiber is treated with water to dissolve and remove the water-soluble thermoplastic PVA polymer (B) in the polymer alloy, it is preferable to add 0.00. It is preferably about 01 to 40 dtex, more preferably about 0.1 to 30 dtex, and particularly preferably about 0.5 to 10 dtex.

  When the fiber having the polymer alloy as at least one component is a composite fiber of a polymer alloy and another thermoplastic polymer, at least a part of the polymer alloy is exposed on the surface of the composite fiber. A composite form is desirable. A composite form in which the polymer alloy is not exposed on the fiber surface and is completely encapsulated in the fiber (for example, a core-sheath composite fiber in which the polymer alloy is the core component and the other thermoplastic polymer is the sheath component, etc. In the case of a sea-island type composite fiber in which an island component composed of a polymer alloy is present on the surface without being exposed to the surface, the thermoplastic polymer of Fiber containing water-soluble thermoplastic PVA polymer (B), which is a sea component of polymer alloy by treating water with water, is not smoothly removed and contains the desired ethylene-vinyl alcohol copolymer nanofibers It becomes difficult to obtain a structure.

  In composite fibers composed of polymer alloy and other thermoplastic polymer, the composite ratio of polymer alloy and other thermoplastic polymer can be adjusted according to the type of other thermoplastic polymer, etc. Polymer alloy: other thermoplastic polymer = 5: 95 to 70:30 mass ratio, particularly 10:90 to 60:40 mass ratio, ease of production of composite fiber, water solubility in polymer alloy Properties of fibrous structures containing ethylene-vinyl alcohol copolymer nanofibers obtained by dissolving and removing water-soluble thermoplastic PVA polymer (B) with water (particularly hydrophilicity, water absorption, liquid retention, biological (Compatibility, strength, etc.) are preferable from the viewpoint of good.

In a composite fiber composed of a polymer alloy and another thermoplastic polymer, the composite form is not particularly limited as long as it is a composite fiber in which at least a part of the polymer alloy is exposed on the fiber surface. Any of a sea-island type, a side-by-side type, a multilayer laminated type, and the like may be used. Further, as described above, the cross-sectional shape of the fiber is not particularly limited.
In the case of a composite fiber composed of a polymer alloy and another thermoplastic polymer, the water-soluble thermoplastic PVA-based heavy polymer in the polymer alloy that constitutes the fiber by treating the composite fiber or a fibrous base material composed thereof with water. When the polymer (B) is dissolved and removed, a fiber made of another thermoplastic polymer becomes a base fiber, and the base fiber is covered or surrounded by an ethylene-vinyl alcohol copolymer nanofiber having a three-dimensional network structure. Often becomes.
In particular, when the composite fiber is a core-sheath type composite fiber in which another thermoplastic polymer forms a core component and the polymer alloy forms a sheath component, the water-soluble thermoplastic PVA polymer (B) in the polymer alloy is used. By dissolving and removing with water, a fibrous structure in which ethylene-vinyl alcohol copolymer nanofibers having a three-dimensional network structure are surrounded and coated around fibers made of another thermoplastic polymer is obtained. .
In the fibrous structure after dissolving and removing the water-soluble thermoplastic PVA polymer (B) in the polymer alloy, the fineness (single fiber fineness) of the fiber made of the other thermoplastic polymer is as described above. It is preferably 0.001 to 20 dtex, particularly 0.01 to 15 dtex.

When the fiber comprising a polymer alloy as at least one component is a composite fiber of a polymer alloy and another thermoplastic polymer, it has a melting point as another thermoplastic polymer from the viewpoint of heat resistance and dimensional stability. A thermoplastic polymer of 150 ° C. or higher is preferred. Preferable examples of other thermoplastic polymers include polyesters, polyamides, and polyolefins having a melting point of 150 ° C. or higher.
Specifically, examples of the polyester include terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, phthalic acid, 痾, 竈-(4-carboxyphenoxy) ethane, 4,4′-dicarboxydiphenyl, Aromatic dicarboxylic acids such as 5-sodiumsulfoisophthalic acid or esters thereof, ethylene glycol, diethylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexane-1,4-dimethanol, Examples thereof include polyesters synthesized from diols such as polyethylene glycol and polytetramethylene glycol or ester-forming derivatives thereof, and polyesters such as polylactic acid. Of these, polyesters in which 80% or more of the structural units are ethylene terephthalate units or butylene terephthalate units are preferably used.

  Examples of polyamides include nylon 4, nylon 6, nylon 7, nylon 11, nylon 12, nylon 66, nylon 6,10, polymetaxylene adipamide, polyparaxylene decanamide, polybiscyclohexylmethane decanamide and the like. Examples thereof include aliphatic polyamides and semi-aromatic polyamides. Among these, nylon 6 or polyamide mainly composed of nylon 6 is preferable.

Examples of polyolefins include polyolefin resins such as polypropylene and polymethylpentene.
Examples of other thermoplastic polymers include acrylic acid resin, vinyl acetate resin, diene resin, polyurethane resin, polycarbonate resin, polyarylate, polyphenylene sulfide, polyetheresterketone, fluororesin, semi-aromatic Examples include polyester amide.

  Other thermoplastic polymers that form the composite fiber are within the range that does not impair the effects of the present invention, if necessary, inorganic substances such as titanium oxide, silica, barium oxide, colorants such as carbon black, dyes and pigments, You may contain 1 type, or 2 or more types, such as antioxidant, a ultraviolet absorber, a light stabilizer, and a fluorescent whitening agent.

  In particular, in the present invention, as a composite fiber composed of a polymer alloy and another thermoplastic polymer, a core-sheath composite fiber having another thermoplastic polymer as a core component and a polymer alloy as a sheath component, and a polymer alloy as a sea component Sea-island type composite fibers containing other thermoplastic polymers as island components are preferably used. When these composite fibers are used, the water-soluble thermoplastic PVA polymer (B) in the polymer alloy can be easily dissolved and removed with water, and the water-soluble thermoplastic PVA polymer (B) can be dissolved and removed. Later, ethylene-vinyl alcohol copolymer nanofibers are present on the surface of the fibrous structure in a state in which the base fiber made of another thermoplastic polymer is coated. Therefore, the nanofiber has high hydrophilicity and water absorption. Functions such as property, liquid retention, and biocompatibility are expressed in the fibrous structure, and the base fiber made of another thermoplastic polymer serves to reinforce the fibrous structure or the textile product.

A fiber (single fiber of a polymer alloy, a composite fiber of a polymer alloy and another thermoplastic polymer) containing at least one component as described above, or a fibrous substrate formed using these fibers is treated with water. Then, the water-soluble thermoplastic PVA polymer (B) in the polymer alloy constituting the fiber is dissolved and removed.
The dissolution / removal of the water-soluble thermoplastic PVA polymer (B) in the polymer alloy may be performed using the fiber itself (fiber itself before forming the fibrous base material) containing the polymer alloy as at least one component. Alternatively, it may be carried out after producing a non-woven fabric, woven or knitted fabric, paper, other sheet-like or other shape fibrous substrate using the fiber.

After manufacturing a non-woven fabric, woven or knitted fabric, paper, or other sheet-like fibrous base material using a fiber containing at least one component of the polymer alloy, the water-soluble thermoplastic PVA polymer (B) in the polymer alloy is washed with water. When dissolving and removing, a sheet-like fibrous base material can be produced by a known method.
For example, using a rapier, gripper, air jet, water jet, sulzer or other loom, a weft knitting machine such as a circular knitting machine, or a warp knitting machine such as tricot, russell, or miranese, a woven or knitted fabric is prepared. It is possible to dissolve and remove the water-soluble thermoplastic PVA polymer (B) in the polymer alloy.
In addition, the fiber containing at least one component of the polymer alloy is cut or crimped and cut into a cotton form, carded and entangled to produce a nonwoven fabric, and the nonwoven fabric is treated with water to form a polymer alloy. The water-soluble thermoplastic PVA polymer (B) may be dissolved and removed. At that time, other binder fiber raw cotton may be blended depending on the purpose at the time of carding. Examples of the entanglement method for producing the nonwoven fabric include a method by needle punching and an entanglement method by high-pressure water flow. When the entanglement treatment by high-pressure water flow is performed with hot water, the water-soluble thermoplastic PVA polymer (B) in the polymer alloy is dissolved and removed and the fibers are entangled at the same time. A high-strength nonwoven fabric containing fibers can be obtained.
When the fibrous base material is in the form of paper, a water-soluble thermoplastic PVA polymer (B) is used when disaggregating short fibers formed by cutting fibers containing at least one polymer alloy in water. ) May be simultaneously dissolved and removed to make paper.

  A method for dissolving and removing the water-soluble thermoplastic PVA polymer (B) with water from a fiber comprising at least one component of a polymer alloy or a fibrous substrate formed using the fiber is not particularly limited. A fiber itself comprising at least one component of an alloy, or a non-woven sheet, woven or knitted fabric, paper, or other fibrous base material made from the fiber, and a dyeing machine such as a circular, a beam, a zicker, or a Wiens, a vibratory washer, a relaxer, etc. The method of processing using a hot water treatment facility, the method of processing by jetting a high-pressure water stream, and the like can be mentioned. The water for dissolving and removing the water-soluble thermoplastic PVA polymer (B) may be any of neutral water, alkaline aqueous solution, acidic aqueous solution, aqueous solution to which a surfactant is added.

The treatment temperature at the time of dissolving and removing the water-soluble thermoplastic PVA polymer (B) with water may be appropriately adjusted according to the purpose, but when it is dissolved using hot water, 40 to 120 ° C, Furthermore, it is preferable to perform the treatment at a temperature of 60 to 110 ° C., particularly 80 to 100 ° C., since a fibrous structure composed of ethylene-vinyl alcohol copolymer nanofibers can be maintained in a more complete form. If the treatment temperature is lower than 40 ° C., dissolution / removal of the water-soluble thermoplastic PVA polymer (B) becomes insufficient, or it takes time to dissolve / remove the water-soluble thermoplastic PVA polymer (B). Productivity may be reduced.
The treatment time for dissolving and removing the water-soluble thermoplastic PVA polymer (B) can be appropriately adjusted according to the purpose, the apparatus to be used, and the treatment temperature, but considering production efficiency, stability, etc. In general, when batch processing is performed, the total time is preferably 10 to 200 minutes, and in the case of continuous processing, generally 1 to 20 minutes is preferable.

  The dissolution and removal rate of the water-soluble thermoplastic PVA polymer (B) from the fiber comprising at least one component of polymer alloy or the fibrous base material formed from the fiber is preferably 50% or more, and 70% or more. Is more preferable. When the dissolution removal rate of the water-soluble thermoplastic PVA polymer (B) is less than 50%, the ethylene-vinyl alcohol copolymer (A) does not have a sufficiently fine nanofiber structure, and has high hydrophilicity. The water-soluble thermoplastic PVA polymer (B) remaining in the fibrous structure may not be exhibited in the actual use of the product using the fibrous structure. ) May elute due to moisture.

By dissolving and removing the water-soluble thermoplastic PVA polymer (B) with water as described above, a fibrous structure containing ethylene-vinyl alcohol copolymer nanofibers, which is contained in the fibrous structure, The maximum diameter of the vinyl alcohol copolymer nanofibers is 800 nm or less and the minimum diameter is 100 nm or less, and the ethylene-vinyl alcohol copolymer nanofibers extend in three or more directions starting from the adhesion point. The fibrous structure of the present invention having 10 or more parts per 25 μm ² of fibrous structure can be obtained.

  The fibrous structure of the present invention comprises a binder fiber, a cut fiber for papermaking, a staple for dry nonwoven fabric, a staple for spinning, a multifilament for woven fabric, a multifilament for knitting, a cement reinforcing material, a rubber reinforcing material, a packaging material, and a sanitary material. It can be used for medical disposable products, agricultural footwear, filters, wipers, insulating paper, battery separators, artificial leather and the like. Examples of applications that make use of particularly high hydrophilicity, liquid retention, and biocompatibility include chemical liquid pasting substrates, battery separators, capacitor separators, and high-functional filters.

The present invention will be described more specifically with reference to examples and the like. However, the present invention is not limited to the following examples.
In the following example, a fiber comprising a water-soluble thermoplastic PVA polymer (B) having a polymerization degree, an ethylene unit content, a saponification degree, a melting point and an alkali metal ion content, and a polymer alloy as at least one component is produced. Fiber formation process, measurement of the number of islands in the polymer alloy part constituting the fiber, and fibrous structure obtained by removing sea components from the polymer alloy part constituting the fiber (ethylene-vinyl alcohol-based copolymer) The measurement and evaluation of the structure and physical properties of the fibrous structure containing the combined nanofibers were performed as follows.

(1) Degree of polymerization of water-soluble thermoplastic PVA polymer (B):
As described above, the degree of polymerization (viscosity average degree of polymerization) (P) of the water-soluble thermoplastic PVA polymer (B) was determined from the above formula (1) according to JIS K6726.

(2) Content of ethylene unit in water-soluble thermoplastic PVA polymer (B):
Using an NMR apparatus (“JEOL GX-500” manufactured by JEOL Ltd., 500 MHz), ¹ H-NMR measurement was performed under the condition of 80 ° C., and the ethylene unit in the water-soluble thermoplastic PVA polymer (B) The content (mol%) of was measured.

(3) Saponification degree of water-soluble thermoplastic PVA polymer (B):
It measured according to JIS K6726.

(4) Melting point of water-soluble thermoplastic PVA polymer (B):
Using DSC (“TA3000” manufactured by Perkin Elmer), a 10 mg sample of a water-soluble thermoplastic PVA polymer (B) was heated to 300 ° C. at a heating rate of 10 ° C./min in a nitrogen atmosphere, Then, the temperature was raised again to 300 ° C. at a temperature rising rate of 10 ° C./min, and the peak top of the endothermic peak at that time was defined as the melting point (° C.) of the water-soluble thermoplastic PVA polymer (B).

(5) Content of alkali metal ion of water-soluble thermoplastic PVA polymer (B):
A part of the water-soluble thermoplastic PVA polymer (B) is sampled, completely ashed, the ashed sample is dissolved in nitric acid, and the solution is used to prepare an atomic absorption photometer (Hitachi Co., Ltd.). The content (mass%) of alkali metal ions (sodium ions) was measured using “Z-5300” manufactured by Seisakusho.

(6) Evaluation of fiberizing process property:
Depending on how many times the fiber was cut when spinning 100 kg of fiber, the evaluation was as follows.
○: The number of yarn breaks is 3 or less, and the fiberizing processability is good.
(Triangle | delta): The frequency | count of a thread breakage is 4 times or more and 9 times or less, and a fiberization process is a little inferior.
X: The number of yarn breakage is 10 times or more, and substantially no spinning is possible.

(7) Measurement of the number of islands in the polymer alloy part constituting the fiber:
(I) Photographing was performed using a scanning electron microscope (SEM) (manufactured by JEOL Ltd.) (hereinafter the same) for each of the five portions of the fiber cross-section obtained by cutting the fiber along the length direction at intervals of 50 cm. Then, the number of islands in the polymer alloy is counted by the following method based on the obtained photograph, the number of islands per 1 μm ^{2 of} the polymer alloy is obtained, the average value of the five locations is taken, and the number of islands in the polymer alloy portion constituting the fiber is obtained. (Pieces / μm ² ).
That is, when the cross section of the fiber is circular or nearly circular, the photographed circular fiber cross section is divided into 100 equal parts by drawing a straight line passing through the center of the circle, and the central angle is 100. Divided into individual sectors, for 5 out of 100 sectors (taken every 20 along the circumference of the circle), count the number of islands in the polymer alloy part within each sector and count the islands in the sector 5 The total number was multiplied by 20 to obtain the total number of islands in the polymer alloy portion within the circular fiber cross section. The total number of islands was divided by the area (μm ² ) occupied by the polymer alloy portion in the circular fiber cross section to determine the number of islands per 1 μm ^{2 of} polymer alloy. The number of islands per 1 μm ^{2 of} polymer alloy is determined by performing the same operation as described above for the fiber cross-sections at 5 locations, and the average value of 5 locations is taken to determine the number of islands in the polymer alloy portion constituting the fibers (pieces / μm ² ) It was.
In the polymer alloy in the fiber cross-sectional photograph, there may be a plurality of islands connected together with islands that are separated and independent separately. Those that can be determined to be connected are counted by the number of islands involved in the connection, and those that cannot be determined to be connected by multiple islands are counted as one island.

(Ii) If the fiber cross section has a shape other than a circle, divide the photographed fiber cross section into 100 parts so as to be as uniform as possible, and perform the same operation as in (i) above. The number of islands (pieces / μm ² ) in the polymer alloy part constituting the fiber is obtained.
(Iii) The area of the polymer alloy part in the fiber cross section is, for example, a predetermined area (Sa) from a photograph taken at the same magnification as above using the same scanning electron microscope (SEM) as in (i) above. By cutting out a circle or a square and measuring its mass (Wa), while cutting out a polymer alloy part from a fiber cross-sectional photograph and measuring its mass (Wb), it can be determined from the following equation (4). .

Area of polymer alloy part in fiber cross section (Sb) = Sa × (Wb / Wa) (4)

(8) Dissolution removal rate of hydrophilic thermoplastic PVA polymer in polymer alloy in fibrous structure:
The dissolution removal rate of the hydrophilic thermoplastic PVA polymer in the polymer alloy was determined from the mass change after the dissolution treatment.

(9) Maximum diameter and minimum diameter of nanofibers contained in the fibrous structure:
A test piece of length × width = 10 cm × 10 cm is cut out from a fibrous structure (nonwoven fabric) containing ethylene-vinyl alcohol copolymer nanofibers, and the surface of the test piece (from the surface it is difficult to understand the nanofiber content state) In the thing, a total of five places of the central part (part centering on the intersection of diagonal lines) and four corners in the cut surface parallel to the surface are photographed at a magnification of 5000 times using a scanning electron microscope (SEM), From the five photographs, the thickest part of the fiber diameter and the thinnest part of the fiber diameter were searched for and set as the maximum diameter (nm) and the minimum diameter (nm). If it is difficult to measure the minimum diameter (such as when it is difficult to find where the minimum diameter is, or if it is too thin to measure), measure the diameter near the minimum diameter, The minimum diameter was displayed as “XX nm or less”.
In the measurement of the maximum diameter and the minimum diameter, the nanofibers are in any three or more directions centering on the bonding point by branching of the ethylene-vinyl alcohol copolymer nanofibers, bonding or crossing of the nanofibers. The diameter at the “forked part” extending in the figure was not the maximum diameter, and the maximum diameter at the linear part other than the forked part was measured. The photo also shows the nanofibers located on the innermost side of the specimen, as well as the nanofibers located on the innermost surface of the test piece. Since it is quite difficult to discriminate the fibers, the maximum diameter and the minimum diameter were obtained by measuring all of the nanofibers shown in the photograph without measuring whether they are located on the outermost surface or on the inner side.

(10) Average fiber diameter of nanofibers contained in the fibrous structure:
(I) A test piece of length × width = 5 cm × 5 cm from a fibrous structure (nonwoven fabric) containing ethylene-vinyl alcohol copolymer nanofibers with an interval of 50 cm in the length direction of the fibrous structure. Three pieces were cut out, and the center part (part centering on the intersection of the diagonal lines) at the surface of each test piece (the cut surface parallel to the surface if the inclusion state of the nanofiber is difficult to understand from the surface) was scanned with an electron microscope (SEM). ) Was taken at a magnification of 5000 times.
(Ii) A square having a side of 5 μm (25 μm) in a total of three locations, the central portion (portion centering on the intersection of diagonal lines) and two left and right portions separated by 5 μm from the central portion in each photograph obtained in (i) above ² ) was drawn with a pen, the fiber diameter was measured for substantially all of the nanofibers present in the square part, and the average value of the nanofibers present in the three squares was taken. The same operation was performed on the three test pieces, and the average value of the nanofibers was taken. Then, the average value of the nanofibers (average value of the mean values) in the three test pieces was taken, and the nanofibers contained in the fibrous structure The average fiber diameter (nm).
In the measurement of the fiber diameter of the nanofiber, the nanofiber is in any three or more directions around the adhesion point by branching of the ethylene-vinyl alcohol copolymer nanofiber, bonding or crossing of the nanofibers, and the like. The diameter of the intermediate position of the linear portion between the “fork portion” and the “fork portion” (the fork portions adjacent to each other) extending in the cross section was measured. Moreover, in measuring the fiber diameter, both the nanofibers located on the outermost surface and the nanofibers located behind the nanofibers (all nanofibers shown in the measurement target area of the photograph) were used as measurement targets.

(11) Measurement of the number of forks in the fibrous structure:
In (ii) of (9) above, a forked part [ethylene-vinyl alcohol copolymer nanoparticle present in a square part (center, left and right, 25 μm ² each) drawn with a pen in the SEM photograph of the test piece The ethylene-vinyl alcohol-based copolymer nanofibers are formed by fiber branching, adhesion (bonding) between the ethylene-vinyl alcohol-based copolymer nanofibers, crossing of the ethylene-vinyl alcohol-based copolymer nanofibers, and the like. Count all three points (adhesive points that form starting points in any part extending in any of three or more directions from the starting point (branch point, connecting point, intersection point)) (three squares) The average value was taken for each of the above, and the average value of the forked portions in the three test pieces (average value of the average values) was taken as the number of forked portions in the fibrous structure. In measuring the number of forks, both the fork located at the outermost surface and the fork located at the back (all forks shown in the measurement area of the photograph) were measured. .

(12) Water absorption rate (%):
A test piece (50 mm × 50 mm) [mass = W ₀ (g)] was collected from the fibrous structure (nonwoven fabric), immersed in distilled water at a temperature of 20 ° C. at a bath ratio of 1/100 for 30 minutes, and then taken out. The solution was allowed to stand for 30 seconds on the plate and drained naturally. The mass [W ₁ (g)] at that time was measured, and the water absorption was determined from the following equation (5).
Water absorption (%) = {(W ₁ −W ₀ ) / W ₀ } × 100 (5)

(13) Water retention:
A test piece (150 mm × 150 mm) [mass = W ₀ (g)] was collected from the fibrous structure (nonwoven fabric), immersed in distilled water at a temperature of 20 ° C. for 30 minutes at a bath ratio of 1/100, and then immediately centrifuged. Using a machine (manufactured by Kokusan Co., Ltd.), the dehydration treatment was performed for 1 minute (the rotational speed of the dewatered basket was 3000 rpm). Thereafter, it is naturally dried in a temperature-controlled room at a temperature of 20 ° C. and a humidity of 65% RH. At that time, the mass [W ₁ (g)] is measured every 5 minutes, and the water absorption of the test piece is reduced to 20% by mass. The measurement time was measured (measured from the time when it was placed in a temperature-controlled room) and used as an index of water retention. It shows that water retention (liquid holding power) is so high that the time required for water absorption to fall to 20 mass% is long. In addition, the water absorption of the test piece was calculated | required from said Formula (5).

  The contents of the PVA polymers (B-1) to (B-7) used in the following examples or comparative examples are as shown in Table 1 below.

Example 1
(1) Ethylene-vinyl alcohol copolymer (A) (ethylene content 44 mol%) (“Eval E112Y” manufactured by Kuraray Co., Ltd.) and PVA polymer (B-1) B-1) = 20: 80 The mass ratio was mixed using a screw feeder and supplied to a twin-screw extruder (manufactured by Kobe Steel, screw rotation = 100 times / min) and melt-kneaded at 215 ° C. Then, the polymer alloy is melt-extruded while being supplied and supplied to the core-sheath type composite spinneret, and at the same time, isophthalic acid-modified polyethylene terephthalate (hereinafter sometimes referred to as “modified PET”) (isophthalic acid-modified amount = 10 mol%, Inc. Kuraray's “Kurapet”) was melted and extruded at an extrusion temperature of 280 ° C. with another twin-screw extruder (manufactured by Kobe Steel Co., Ltd., screw rotation = 100 times / minute). A core-sheath type, which is supplied to a sheath-type composite spinneret and uses a polymer alloy of an ethylene-vinyl alcohol copolymer (A) and a PVA polymer (B-1) as a sheath component and a modified PET as a core component. Composite fiber (Sheath component: mass ratio of core component = 50/50, discharge temperature at base temperature = 250 ° C. and wound into a spinning yarn. The fiber forming processability when producing this spinning yarn is as follows. As shown in Table 2, it was good.
(2) After spinning the spinning yarn obtained in (1) 1.5 times in a first stage furnace (temperature = 90 ° C.) using a two-stage hot air furnace (length: 3 m) The filament was stretched twice in the second stage furnace (temperature = 90 ° C.) to produce a multifilament of 120 dtex / 24f (single fiber fineness = 5 dtex) of core-sheath composite fiber. At this time, the continuous running property and stretchability were good, and there was no problem at all.

(3) The fineness of the core component (modified PET) in the stretched core-sheath composite fiber obtained in (2) above is 2.5 dtex, and a cross section of the core-sheath composite fiber is photographed with an SEM. The area ratio of the polymer alloy (sheath component) occupying the entire fiber cross section was determined from the photograph to be 56%.
Further, when the number of island components made of the ethylene-vinyl alcohol copolymer (A) in the polymer alloy (sheath component) in the cross section of the core-sheath composite fiber after stretching was measured by the above-described method, the polymer alloy was measured. The number was 3.3 per 1 μm ² .
(4) The stretched core-sheath composite fiber multifilament obtained in (2) was cut to 51 mm to obtain a raw cotton for a nonwoven fabric. 80 parts by weight of this raw cotton and 20 parts by weight of binder fiber (binder fiber whose core component is PET and sheath component is polyethylene (manufactured by Kuraray Co., Ltd., “N-710”, 2.2 dtex × 51 mm)) A web of 70 g / m ² was produced with a card machine, and the web was calendered with a calender roll at 115 ° C. and a linear pressure of 40 kg / cm to produce a nonwoven fabric.

(5) The nonwoven fabric obtained in (4) above is treated in an aqueous solution (containing 1 g of sodium dodecylbenzenesulfonate in 1 L) at a bath temperature of 85 ° C. and a bath ratio of 100: 1 for 120 minutes, By dissolving and removing the sea component [PVA polymer (B-1)] in the polymer alloy part constituting the fiber, it contains an ethylene-vinyl alcohol copolymer nanofiber, and the nanofiber is a modified PET fiber. The fibrous structure shown in FIG. 2 (SEM photograph) covering the periphery was obtained.
(6) About the fibrous structure obtained by said (5), when the dissolution removal rate of the PVA-type polymer (B-1) was measured by the above-mentioned method, it was 83 mass%.
Further, when the maximum diameter, the minimum diameter, the average fiber diameter, and the number of forked portions of the nanofibers contained in the fibrous structure were measured using the SEM, the maximum diameter was 465 nm, the minimum diameter was 63 nm, The average fiber diameter was 321 nm, and the number of forked portions was 54/25 μm ² .
Furthermore, when the water absorption and water retention of the obtained fibrous structure were measured by the above-described method, the water absorption was 147%, and the water retention (drying time required for the water absorption to decrease to 20%) was It was 75 minutes and was very hydrophilic.

Example 2
(1) Using a sea-island type composite spinneret instead of a core-sheath type composite spinneret, a polymer alloy composed of an ethylene-vinyl alcohol copolymer (A) and a PVA polymer (B-1) is used as a sea component, Example 1 After producing sea-island type composite fibers (sea component: mass ratio of island components = 50/50, number of islands = 16) containing modified PET as island components in the same manner as in Example 1 (1), Example 1 In the same manner as in (2), a sea filament type multifilament of 120 dtex / 24 f (single fiber fineness = 5 dtex) was produced. At this time, the continuous running property and stretchability were good, and there was no problem at all.
(2) The fineness of the island component (modified PET) in the stretched sea-island composite fiber obtained in (1) was 0.16 dtex. The cross section of the sea-island composite fiber was photographed with an SEM, and the area ratio of the polymer alloy (sea component) occupying the fiber cross section was determined from the photograph and found to be 56%.
Moreover, ethylene in the polymer alloy portion in the cross section of the sea-island type composite fiber after stretching - vinyl alcohol copolymer where the number of island component made of (A) was measured by the method described above, polymer alloy 1 [mu] m ² per 3. There were six.

(3) The stretched sea-island composite fiber multifilament obtained in (1) above is cut to 51 mm to obtain a raw cotton for nonwoven fabric, and the nonwoven fabric is used in the same manner as in (4) of Example 1 using this raw cotton. The non-woven fabric is produced and immersed in an aqueous solution in the same manner as in Example 1 (5) to dissolve and remove the sea component [PVA polymer (B-1)] in the polymer alloy constituting the fiber. Thus, a fibrous structure composed of ethylene-vinyl alcohol copolymer nanofibers and modified PET fibers was obtained.
(4) About the fibrous structure obtained by said (3), when the dissolution removal rate of the PVA polymer (B-1) was measured by the above-mentioned method, it was 78 mass%.
Further, when the maximum diameter, the minimum diameter, the average fiber diameter, and the number of forked portions of the nanofibers contained in the fibrous structure were measured using the SEM, the maximum diameter was 475 nm, the minimum diameter was 58 nm, The average fiber diameter was 309 nm, and the number of forked portions was 67 pieces / 25 μm ² .
Further, when the water absorption and water retention of the obtained fibrous structure were measured by the above-described method, the water absorption was 206%, and the water retention (drying time required for the water absorption to decrease to 20%) was It was 87 minutes and was very hydrophilic.

Example 3
(1) In Example 1 (1), an ethylene-vinyl alcohol copolymer (A) and a PVA polymer (B-1) were used by using a single fiber spinneret instead of the core-sheath type composite spinneret. After melt-discharging the single fiber made of polymer alloy consisting of the above, it was stretched in the same manner as in (2) of Example 1 to produce a multifilament of single fiber of 120 dtex / 24f (single fiber fineness = 5 dtex). At this time, the continuous running property and stretchability were good, and there was no problem at all.
(2) The cross-section of the stretched polymer alloy single fiber obtained in (1) above is photographed with an SEM, and from the photograph, it is composed of an ethylene-vinyl alcohol copolymer (A) in the fiber cross-section. When the number of island components was measured by the method described above, it was 3.9 per 1 μm ^{2 of} polymer alloy.

(3) The stretched polymer alloy single fiber multifilament obtained in the above (1) is cut into 51 mm to obtain a raw cotton for a nonwoven fabric. The non-woven fabric is produced and immersed in an aqueous solution in the same manner as in Example 1 (5) to dissolve and remove the sea component [PVA polymer (B-1)] in the polymer alloy constituting the fiber. As a result, a fibrous structure composed of ethylene-vinyl alcohol copolymer nanofibers alone was obtained.
(4) About the fibrous structure obtained by said (3), it was 74 mass% when the dissolution removal rate of the PVA-type polymer (B-1) was measured by the above-mentioned method.
Moreover, when the maximum diameter, the minimum diameter, the average fiber diameter, and the number of forked parts of the nanofibers constituting the fibrous structure using SEM were measured by the method described above, the maximum diameter was 389 nm, and the minimum diameter was The average fiber diameter was 66 nm, the average fiber diameter was 313 nm, and the number of forked portions was 58 pieces / 25 μm ² .
Furthermore, when the water absorption and water retention of the obtained fibrous structure were measured by the above-described method, the water absorption was 213%, and the water retention (drying time required for the water absorption to decrease to 20%) was It was 78 minutes and was very hydrophilic.

Example 4
(1) Except for using an ethylene-vinyl alcohol copolymer (“Eval F110Y” manufactured by Kuraray Co., Ltd.) having an ethylene unit content of 32 mol% as the ethylene-vinyl alcohol copolymer (A). After producing a core-sheath-type conjugate fiber in the same manner as (1) of Example 1, the core-sheath type of 120 dtex / 24f (single fiber fineness = 5 dtex) was drawn in the same manner as in (2) of Example 1. A multifilament of composite fiber was produced. At this time, the continuous running property and stretchability were good, and there was no problem at all.
(2) The fineness of the core component (modified PET) in the stretched core-sheath composite fiber obtained in (1) above was 2.5 dtex. A cross section of the core-sheath composite fiber was photographed with an SEM, and the area ratio of the polymer alloy (sheath component) occupying the fiber cross section was determined from the photograph and found to be 56%.
Further, when the number of island components made of the ethylene-vinyl alcohol copolymer (A) in the polymer alloy (sheath component) in the cross section of the core-sheath composite fiber after stretching was measured by the above-described method, the polymer alloy was measured. The number was 5.7 per 1 μm ² .

(3) The stretched core-sheath composite fiber multifilament obtained in (1) above is cut to 51 mm to obtain a raw cotton for a nonwoven fabric, and the nonwoven fabric is used in the same manner as in (4) of Example 1 using this raw cotton. This nonwoven fabric is immersed in an aqueous solution in the same manner as in Example 1 (5) to dissolve and remove the sea component [PVA polymer (B-1)] in the polymer alloy constituting the fiber. As a result, a fibrous structure in which ethylene-vinyl alcohol copolymer nanofibers surround the modified PET fibers was obtained.
(4) About the fibrous structure obtained by said (3), when the dissolution removal rate of the PVA polymer (B-1) was measured by the above-mentioned method, it was 81 mass%.
Further, when the maximum diameter, the minimum diameter, the average fiber diameter, and the number of forked portions of the nanofibers contained in the fibrous structure were measured by the SEM, the maximum diameter was 231 nm, the minimum diameter was 23 nm, The average fiber diameter was 89 nm, and the number of forked portions was 89/25 μm ² .
Furthermore, when the water absorption and water retention of the obtained fibrous structure were measured by the methods described above, the water absorption was 186%, and the water retention (drying time required for the water absorption to decrease to 20%) was It was 96 minutes and was very hydrophilic.

Example 5
(1) After producing a core-sheath type composite fiber in the same manner as (1) of Example 1 except that the PVA polymer (B-2) was used instead of the PVA polymer (B-1). Then, stretching was carried out in the same manner as in (2) of Example 1 to produce a multifilament of a core-sheath composite fiber of 120 dtex / 24f (single fiber fineness = 5 dtex). At this time, the continuous running property and stretchability were good, and there was no problem at all.
(2) The fineness of the core component (modified PET) in the stretched core-sheath composite fiber obtained in (1) above was 2.5 dtex. A cross section of the core-sheath composite fiber was photographed with an SEM, and the area ratio of the polymer alloy (sheath component) occupying the fiber cross section was determined from the photograph and found to be 56%.
Further, when the number of island components made of the ethylene-vinyl alcohol copolymer (A) in the polymer alloy (sheath component) in the cross section of the core-sheath composite fiber after stretching was measured by the above-described method, the polymer alloy was measured. The number was 4.2 per μm ² .

(3) The stretched core-sheath composite fiber multifilament obtained in (1) above is cut to 51 mm to obtain a raw cotton for a nonwoven fabric, and the nonwoven fabric is used in the same manner as in (4) of Example 1 using this raw cotton. This nonwoven fabric is immersed in an aqueous solution in the same manner as in Example 1 (5) to dissolve and remove the sea component [PVA polymer (B-1)] in the polymer alloy constituting the fiber. As a result, a fibrous structure in which ethylene-vinyl alcohol copolymer nanofibers surround the modified PET fibers was obtained.
(4) About the fibrous structure obtained by said (3), when the dissolution removal rate of the PVA polymer (B-1) was measured by the above-mentioned method, it was 84 mass%.
Further, when the maximum diameter, the minimum diameter, the average fiber diameter, and the number of forked portions of the nanofibers contained in the fibrous structure were measured using the SEM, the maximum diameter was 373 nm, the minimum diameter was 57 nm, The average fiber diameter was 237 nm, and the number of forked portions was 51/25 μm ² .
Furthermore, when the water absorption rate and water retention of the obtained fibrous structure were measured by the methods described above, the water absorption rate was 136%, and the water retention rate (drying time required for the water absorption rate to decrease to 20%) was It was 65 minutes and was very hydrophilic.

Example 6
(1) In preparation of the polymer alloy, (1) of Example 1 except that the ethylene-vinyl alcohol copolymer (A) and the PVA polymer (B-1) were used at a mass ratio of 10:90. After producing a core-sheath type composite fiber in the same manner as in Example 1, the core-sheath type composite fiber multifilament of 120 dtex / 24f (single fiber fineness = 5 dtex) was produced by stretching in the same manner as in Example 2 (2). . At this time, the continuous running property and stretchability were good, and there was no problem at all.
(2) The fineness of the core component (modified PET) in the stretched core-sheath composite fiber obtained in (1) above was 2.5 dtex. A cross section of the core-sheath composite fiber was photographed with an SEM, and the area ratio of the polymer alloy (sheath component) occupying the fiber cross section was determined from the photograph and found to be 56%.
Further, when the number of island components made of the ethylene-vinyl alcohol copolymer (A) in the polymer alloy (sheath component) in the cross section of the core-sheath composite fiber after stretching was measured by the above-described method, the polymer alloy was measured. The number was 5.2 per 1 μm ² .

(3) The stretched core-sheath composite fiber multifilament obtained in (1) above is cut to 51 mm to obtain a raw cotton for a nonwoven fabric, and the nonwoven fabric is used in the same manner as in (4) of Example 1 using this raw cotton. This nonwoven fabric is immersed in an aqueous solution in the same manner as in Example 1 (5) to dissolve and remove the sea component [PVA polymer (B-1)] in the polymer alloy constituting the fiber. As a result, a fibrous structure in which ethylene-vinyl alcohol copolymer nanofibers surround the modified PET fibers was obtained.
(4) About the fibrous structure obtained by said (3), when the dissolution removal rate of the PVA polymer (B-1) was measured by the above-mentioned method, it was 84 mass%.
Further, when the maximum diameter, the minimum diameter, the average fiber diameter, and the number of forked portions of the nanofibers contained in the fibrous structure were measured using the SEM, the maximum diameter was 345 nm, the minimum diameter was 46 nm, The average fiber diameter was 189 nm, and the number of forks was 68/25 μm ² .
Furthermore, when the water absorption and water retention of the obtained fibrous structure were measured by the above-described method, the water absorption was 129%, and the water retention (drying time required for the water absorption to decrease to 20%) was It was 68 minutes and was very hydrophilic.

<< Comparative Example 1 >>
(1) The same procedure as in (1) of Example 1 except that an ethylene-vinyl alcohol copolymer having an ethylene unit content of 75 mol% was used as the ethylene-vinyl alcohol copolymer (A). After producing the core-sheath type composite fiber, the core-sheath type composite fiber multifilament of 120 dtex / 24f (single fiber fineness = 5 dtex) was produced in the same manner as (2) of Example 1. At this time, continuous running property and stretchability were good.
(2) The fineness of the core component (modified PET) in the stretched core-sheath composite fiber obtained in (1) above was 2.5 dtex. A cross section of the core-sheath composite fiber was photographed with an SEM, and the area ratio of the polymer alloy (sheath component) occupying the fiber cross section was determined from the photograph and found to be 56%.
Further, when the number of island components made of the ethylene-vinyl alcohol copolymer (A) in the polymer alloy (sheath component) in the cross section of the core-sheath composite fiber after stretching was measured by the above-described method, the polymer alloy was measured. The number was 0.4 per 1 μm ² .

(3) The stretched core-sheath composite fiber multifilament obtained in (1) above is cut to 51 mm to obtain a raw cotton for a nonwoven fabric, and the nonwoven fabric is used in the same manner as in (4) of Example 1 using this raw cotton. This nonwoven fabric is immersed in an aqueous solution in the same manner as in Example 1 (5) to dissolve and remove the sea component [PVA polymer (B-1)] in the polymer alloy constituting the fiber. As a result, a fibrous structure in which the ethylene-vinyl alcohol copolymer (A) fibers surround the modified PET fibers was obtained.
(4) About the fibrous structure obtained by said (3), when the dissolution removal rate of the PVA polymer (B-1) was measured by the above-mentioned method, it was 73 mass%.
Moreover, when the maximum diameter, the minimum diameter, and the average fiber diameter of the ethylene-vinyl alcohol copolymer (A) fibers contained in the fibrous structure were measured by the above-described method using SEM, the maximum diameter was 4120 nm, the maximum diameter. The small diameter was 160 nm and the average fiber diameter was 3430 nm. Most of the fibers were μm-sized fibers, and could not be said to be fibrous structures containing nanofibers. The number of forked portions of the ethylene-vinyl alcohol copolymer fiber per 25 μm ² in the fibrous structure is 6/25 μm ² , and the degree of reticulation of the ethylene-vinyl alcohol copolymer fiber is It was low.
Further, when the water absorption and water retention of the obtained fibrous structure were measured by the above-described method, the water absorption was 89%, and the water retention (drying time required for the water absorption to decrease to 20%) was It was 28 minutes, and its hydrophilicity was significantly lower than the fibrous structures obtained in Examples 1 to 6.

<< Comparative Example 2 >>
(1) As the ethylene-vinyl alcohol copolymer (A), an ethylene-vinyl alcohol copolymer having an ethylene unit content of 20 mol% is used, and the ethylene-vinyl alcohol copolymer (A) is used. Example 1 After producing the core-sheath type composite fiber in the same manner as in (1) of Example 1 except that the ratio of use of the PVA polymer (B-1) was changed to a mass ratio of 10:90, Example 1 In the same manner as in (2), a multifilament of 120 dtex / 24 f (single fiber fineness = 5 dtex) core-sheath composite fiber was produced. At this time, continuous running property and stretchability were good.
(2) The fineness of the core component (modified PET) in the stretched core-sheath composite fiber obtained in (1) above was 2.5 dtex. A cross section of the core-sheath composite fiber was photographed with an SEM, and the area ratio of the polymer alloy (sheath component) occupying the fiber cross section was determined from the photograph and found to be 56%.
Further, when the number of island components made of the ethylene-vinyl alcohol copolymer (A) in the polymer alloy (sheath component) in the cross section of the core-sheath composite fiber after stretching was measured by the above-described method, the polymer alloy was measured. The number was 9.2 per 1 μm ² .

(3) The stretched core-sheath composite fiber multifilament obtained in (1) above is cut to 51 mm to obtain a raw cotton for a nonwoven fabric, and the nonwoven fabric is used in the same manner as in (4) of Example 1 using this raw cotton. This nonwoven fabric is immersed in an aqueous solution in the same manner as in Example 1 (5) to dissolve and remove the sea component [PVA polymer (B-1)] in the polymer alloy constituting the fiber. As a result, the dissolution removal rate of the PVA polymer (B-1) exceeds 103% of the theoretical value and is 103%, and a part of the ethylene-vinyl alcohol copolymer (A) is dissolved and removed. In the obtained fibrous structure, the ethylene-vinyl alcohol copolymer nanofibers were easily collapsed or damaged, and had low practical value. When the water absorption and water retention of the fibrous structure obtained were measured by the methods described above, the water absorption was 66%, and the water retention (drying time required for the water absorption to decrease to 20%) was 30 minutes. It was inferior in hydrophilicity.

<< Comparative Examples 3-7 >>
Instead of the PVA polymer (B-1), the PVA polymers (B-3) to (B-7) are used, and the core-sheath type is obtained by melt spinning in the same manner as (1) of Example 1. When trying to manufacture the composite fiber, the yarn breakage occurred frequently, the fiberization processability was poor, and the manufacture of the core-sheath type composite fiber was difficult.

<< Comparative Example 8 >>
(1) Using the same modified PET (modified by isophthalic acid = 8 mol%) as used in (1) of Example 1 alone, spinning at 280 ° C. using a twin screw extruder, spinning A modified PET multifilament was produced by discharging from the die at 260 ° C. and then wound up to obtain a spinning yarn.
(2) After spinning the spinning yarn obtained in (1) 1.5 times in a first stage furnace (temperature = 90 ° C.) using a two-stage hot air furnace (length: 3 m) A modified PET multifilament of 60 dtex / 24f (single fiber fineness = 2.5 dtex) was produced by stretching twice in a second stage furnace (temperature = 90 ° C.). At this time, continuous running property and stretchability were good.
(3) After the stretched modified PET multifilament obtained in (1) above was crimped, it was cut into 51 mm to obtain a raw cotton for nonwoven fabric. For 80 parts by mass of the raw cotton, binder fibers (“N-710” manufactured by Kuraray Co., Ltd., core-sheath type composite fiber whose core component is made of PET and sheath component of polyethylene, single fiber fineness = 2.2 dtex, fiber length = 51 mm) was blended at a ratio of 20 parts by mass, and a nonwoven web having a basis weight of 70 g / m ² was produced using a roller card machine. This web was calendered at 115 ° C. with a calender roll having a linear pressure of 40 kg / cm to produce a nonwoven fabric. When the water absorption and water retention of this nonwoven fabric were measured by the methods described above, the water absorption was 52%, and the water retention (drying time required for the water absorption to decrease to 20%) was 8 minutes, which is hydrophilic. It was inferior to.

  The results of Examples 1 to 6 are summarized in Table 2 below, and the results of Comparative Examples 1 to 8 are summarized in Table 3 below.

  The fibrous structure of the present invention containing nanofibers composed of an ethylene-vinyl alcohol copolymer (A) having an ethylene unit content of 25 to 70 mol% is extremely high in water absorption, hydrophilicity, and liquid retention. (Especially moisture retention) and excellent in biocompatibility and tactile sensation, so binder fibers, papermaking cut fibers, dry nonwoven staples, spinning staples, woven multifilaments, knitted multifilaments , Cement reinforcement, rubber reinforcement, packaging material, sanitary material, medical disposable products, agricultural footwear, filters, wipers, insulating paper, battery separator, artificial leather, etc. In the case of the production method of the present invention, the fibrous structure having the above-mentioned excellent characteristics can be reliably reduced by an industrially simple method. It is possible to manufacture with the present invention is industrially useful.

It is a schematic diagram for demonstrating the "forked part" in a fibrous structure. It is the photograph which image | photographed the fibrous structure containing the ethylene-vinyl alcohol-type copolymer nanofiber obtained in Example 1 with the scanning electron microscope (SEM).

Claims (8)

A fibrous structure containing nanofibers made of an ethylene-vinyl alcohol copolymer (A) having a content ratio of structural units derived from ethylene of 25 to 70 mol%, and ethylene contained in the fibrous structure -The maximum diameter of the nanofiber made of the vinyl alcohol copolymer (A) is 800 nm or less and the minimum diameter is 100 nm or less, and the nanofiber made of the ethylene-vinyl alcohol copolymer (A) starts from the adhesion point. A fibrous structure characterized by having 10 or more fork portions extending in three or more directions per 25 μm ² of the fibrous structure.   The fibrous structure according to claim 1, wherein the average fiber diameter of the nanofiber made of the ethylene-vinyl alcohol copolymer (A) is 20 to 500 nm.   In addition to nanofibers made of an ethylene-vinyl alcohol copolymer (A), other thermoplastic polymer fibers having a fineness of 0.001 to 20 dtex are included, and the surface of the other thermoplastic polymer fibers is made of ethylene-vinyl alcohol. The fibrous structure according to claim 1 or 2, which is coated with nanofibers made of a copolymer (A). An ethylene-vinyl alcohol copolymer (A) in which the content ratio of structural units derived from ethylene is 25 to 70 mol%, a viscosity average polymerization degree of 200 to 500, and a saponification degree of 95 to 99.99 mol%. A water-soluble thermoplastic polyvinyl alcohol polymer (B) having a melting point of 160 to 230 and containing an alkali metal ion in a proportion of 0.0003 to 1% by mass in terms of sodium, (A): (B) = From the ethylene-vinyl alcohol copolymer (A) in the sea component consisting of a water-soluble thermoplastic polyvinyl alcohol polymer (B) obtained by melt mixing at a mass ratio of 2:98 to 30:70. A fiber comprising at least one polymer alloy in which two or more islands are dispersed per 1 μm ² or a fibrous base material formed using the fiber is treated with water, A method for producing a fibrous structure, comprising dissolving and removing a water-soluble thermoplastic polyvinyl alcohol polymer (B) constituting a sea component in a mar alloy.   A fiber having at least one component of polymer alloy is a single fiber of polymer alloy, a core-sheath type composite fiber having a polymer alloy as a sheath component and another thermoplastic polymer as a core component, and a polymer alloy as a sea component and other thermoplastics The method for producing a fibrous structure according to claim 4, which is a sea-island type composite fiber having a polymer as an island component, or a bonded type composite fiber in which a polymer alloy and another thermoplastic polymer are bonded in layers. An ethylene-vinyl alcohol copolymer (A) in which the content ratio of structural units derived from ethylene is 25 to 70 mol%, a viscosity average polymerization degree of 200 to 500, and a saponification degree of 95 to 99.99 mol%. A water-soluble thermoplastic polyvinyl alcohol polymer (B) having a melting point of 160 to 230 and containing an alkali metal ion in a proportion of 0.0003 to 1% by mass in terms of sodium, (A): (B) = From the ethylene-vinyl alcohol copolymer (A) in the sea component consisting of a water-soluble thermoplastic polyvinyl alcohol polymer (B) obtained by melt mixing at a mass ratio of 2:98 to 30:70. A fiber base material formed by using a fiber containing at least one component of a polymer alloy in which the island component is finely dispersed with 2 or more islands per 1 μm ² .   A fiber having at least one component of polymer alloy is a single fiber of polymer alloy, a core-sheath type composite fiber having a polymer alloy as a sheath component and another thermoplastic polymer as a core component, and a polymer alloy as a sea component and other thermoplastics The fiber or the fibrous base material according to claim 6, which is a sea-island type composite fiber having a polymer as an island component, or a bonded type composite fiber in which a polymer alloy and another thermoplastic polymer are bonded in layers. A textile product using the fibrous structure according to any one of claims 1 to 3.