WO2009101888A1 - Fiber and process for producing the same - Google Patents

Abstract

A fiber characterized by comprising: a core resin layer having voids in inner parts thereof and having an almost circular section perpendicular to the lengthwise direction; and one or more resin layers formed on the core resin layer and having an almost annular section perpendicular to the lengthwise direction. It is preferable that with respect to directions perpendicular to the lengthwise direction for the core resin layer, the proportion of the sectional area of the voids (Y, µm2) to the sectional area of the fiber (X, µm2), Y/X, be 5-40% on the average. When the average dimension of the voids in a diameter direction perpendicular to the direction of orientation for the voids is expressed by r (µm) and the average dimension of the voids in the direction of orientation for the voids is expressed by L (µm), then the L/r ratio is preferably 10-100.

Description

Fiber and method for producing the same

The present invention relates to a fiber having excellent durability and having a cavity inside, and a method for producing the same.

In recent years, various efforts have been made to improve the functionality and aesthetics of fibers. For example, by changing the cross-sectional shape of the fiber, improving water absorption, or modifying the polymer, the lightness is improved, the fibrillation is improved, or the deep color is improved (for example, , See Patent Document 1).
On the other hand, in order to improve the aesthetics of the fiber, various composite fibers having an optical interference function in which two kinds of polymers having different refractive indexes are alternately laminated and covered with a protective layer have been proposed (for example, Patent Document 2).

However, the hollow fiber-making method described in Patent Document 1 is a technique for laminating a polymer that is melted and discharged from a discharge hole of a die in order to achieve a high hollow ratio in order to reduce the weight of the fiber. Is necessary and the process is complicated.
In addition, voids are formed in order to increase the hollow ratio while maintaining the strength of the fibers. These voids contain inorganic fine particles and the like, and the inorganic fine particles and the resin interface are formed during the resin film formation. Is formed inside by peeling off. In addition, a resin (eg, polyester) that is a main component is added with another resin that is incompatible with the resin (incompatible) and kneaded to form a two-phase structure (eg, sea-island structure). It is formed by exfoliation of the interface between the resin which is the main component at the time of film formation and another resin added and kneaded therewith.

However, according to such a method of forming voids, voids may be formed up to the vicinity of the surface of the fiber, and the smoothness of the surface is impaired. As a result, when a fiber is bent for use in a woven fabric or the like, a stress is easily applied to a void formed on the surface (near), a crack is generated, and the fiber is damaged by expanding it. there were.
In addition, the presence of voids inside the fiber contributes greatly to the improvement of the heat insulation properties of the fiber, so that cracks and breakage of the fiber due to voids formed in the vicinity of the surface and on the surface have a heat insulation effect. It will be significantly reduced.
In addition, the technique described in Patent Document 1 is a method in which a different component is mixed in a main component, and a void is expressed using the component as a nucleus. Therefore, the different component remains in the void, which is reflected by the reflectance. In some cases, the improvement was hindered. In addition, since the resin and inorganic materials, or different types of resins are used, the problem of difficulty in recycling is becoming apparent.

JP 2005-256243 A Japanese Patent No. 3356438

This invention makes it a subject to solve the said conventional problems and to achieve the following objectives. That is, an object of the present invention is to provide a fiber having high recyclability and durability and having a cavity inside and an efficient manufacturing method thereof.

Means for solving the problems are as follows. That is,
<1> On a resin layer of a core material having a cavity inside and having a substantially circular cross-sectional shape orthogonal to the length direction, a resin layer having a substantially annular cross-sectional shape orthogonal to the length direction It is a fiber characterized by having at least one layer.
<2> The average of the ratio (Y / X) of the cross-sectional area Y (μm ² ) of the cavity to the cross-sectional area X (μm ² ) of the fiber in the direction perpendicular to the length direction of the resin layer of the core material is 5% or more The fiber according to <1>, which is 40% or less.
<3> L / r when the average length of the cavity in the diameter direction perpendicular to the orientation direction of the cavity is r (μm) and the average length of the cavity in the orientation direction of the cavity is L (μm) The fiber according to any one of <1> to <2>, wherein the ratio is 10 or more and 100 or less.
<4> The fiber according to any one of <1> to <3>, wherein the resin layer of the core material is made of only a crystalline polymer.
<5> Permeation of a fiber having the same crystallinity as that of the polymer having the crystallinity of the fiber, and having the same fineness as the fiber and having no cavity, where the transmittance of the fiber is M (%) The fiber according to <4>, wherein the M / N ratio when the rate is N (%) is 0.2 or less, and the glossiness of the fiber is 50 or more.
<6> The average number of cavities in an arbitrary cross section in the diameter direction perpendicular to the orientation direction of the cavities is P, the refractive index of the crystalline polymer portion is N1, the refractive index of the cavities is N2, and N1 and N2 Is a fiber according to any one of <4> to <5>, wherein a product of ΔN and P is 3 or more, where ΔN (= N1−N2).
<7> The fiber according to any one of <4> to <6>, wherein the polymer having crystallinity includes only one kind.
<8> The fiber according to any one of <4> to <7>, wherein the polymer having crystallinity is a polyolefin, a polyester, or a polyamide.
<9> The resin layer of the core material is obtained by melt spinning a resin composition composed only of a polymer having crystallinity,
At a speed of 10 to 36,000 mm / min, and
When the stretching temperature is T (° C.) and the glass transition temperature of the crystalline polymer is Tg (° C.),
(Tg-30) ≦ T ≦ (Tg + 50)
The fiber according to any one of <1> to <8>, obtained by stretching at a stretching temperature T (° C.) represented by:
<10> The method for producing a fiber according to any one of <1> to <9>, wherein a plurality of resin layers are laminated and spun on a resin layer of a core material made only of a crystalline polymer. A lamination spinning process, and a stretching process of stretching in the length direction of the resin layer of the core material,
The stretching step includes
At a speed of 10 to 36,000 mm / min, and
When the stretching temperature is T (° C.) and the glass transition temperature of the crystalline polymer is Tg (° C.),
(Tg-30) ≦ T ≦ (Tg + 50)
It is the manufacturing method of the fiber characterized by extending | stretching with the extending | stretching temperature T (degreeC) represented by these.

According to the present invention, it is possible to solve conventional problems, provide a fiber having high recyclability and durability, and having a cavity inside, and an efficient manufacturing method thereof.

FIG. 1 is a cross-sectional view showing the structure of the fiber of the present invention. FIG. 2A is a diagram illustrating an example of a spinning step in the fiber manufacturing method of the present invention. FIG. 2B is a diagram illustrating an example of a spinning step in the fiber manufacturing method of the present invention. FIG. 3A is a diagram for explaining an aspect ratio and is a perspective view of a fiber. FIG. 3B is a diagram for explaining the aspect ratio, and is a cross-sectional view taken along the line A-A ′ of the fiber in FIG. 3A. FIG. 3C is a diagram for explaining the aspect ratio, and is a cross-sectional view taken along the line B-B ′ of the fiber in FIG. 3A. FIG. 4 is a schematic view of a coating line. FIG. 5 is a photographic image of the cross section of the fiber of Example 1.

(fiber)
FIG. 1 is a cross-sectional view in a direction orthogonal to the length direction of a fiber as an example of the present invention. As shown in FIG. 1, the fiber 10 of the present invention includes a core resin layer 11 having a cavity 100 therein, and one or more resin layers 12 laminated so as to cover the core resin layer 11 ( Hereinafter, it may be referred to as a coating resin layer 12).
Here, the resin layer located in the outermost layer of the cross section in the direction orthogonal to the length direction of the fiber 10 of this invention among the resin layers which comprise the coating resin layer 12 is set as the protective layer 12a.
The diameter of the cross section in the direction perpendicular to the length direction of the fiber of the present invention is not generally known, but is preferably 0.1 μm to 200 μm, more preferably 1 μm to 100 μm, and particularly preferably 1 μm to 80 μm. When the diameter of the cross section is less than 0.1 μm, it may be cut at the time of stretching, and when it exceeds 200 μm, the flexibility and texture of the fiber may be inferior, and the productivity may be lowered.

<Glossiness of fiber>
The glossiness of the fiber of the present invention is preferably 60 or more, more preferably 70 or more, and still more preferably 80 or more.
Here, the glossiness can be measured by a variable glossmeter.

<Insulation of fiber>
As the heat insulating property of the fiber of the present invention, the larger the cavity cross-sectional area of the core material layer, the more the still air layer is formed and the better the heat insulating property. However, as the cavity cross-sectional area of the core material layer increases, the mechanical properties as fibers deteriorate. Therefore, the ratio of the cavity cross-sectional area of the core layer is preferably 5% to 40%, more preferably 8% to 40%, and most preferably 12% to 40%. The thickness of the coating resin layer is appropriately selected depending on the purpose, and for example, it is preferably 3% or more and 30% or less of the radius in the cross section of the resin layer of the core material. It is more preferably 3% or more and 25% or less, and most preferably 3% or more and 20% or less.

<Durability of fiber>
As the durability of the fiber of the present invention, basically, a fiber having a cavity has low mechanical durability. However, the provision of the sheath material layer can greatly increase the mechanical durability. In addition, a resin different from the resin of the core material layer can be applied to the sheath material layer. For example, by forming a sheath material layer such as polypropylene on the polyester core material layer, the water resistance and the like can be improved.

<Resin layer of core material>
The resin layer of the core material is not particularly limited as long as it has a cavity inside when it is made of fibers, and is appropriately selected according to the purpose. For example, it is disclosed in JP-A-2005-256243. It may be formed by a resin composition or a resin composition made of a crystalline polymer. Among these, a resin composition consisting only of a crystalline polymer is particularly preferable in that cavities are efficiently formed inside without using inorganic fine particles or an incompatible polymer.
The resin layer of the core material is produced by melt spinning a resin composition composed only of a crystalline polymer (hereinafter also referred to as a core resin composition) and drawing at high speed. Specifically, the core resin composition is dried, melted with an extruder, melted and discharged from a melt spinneret, cooled with cooling air, and then wound up and subjected to high-speed stretching. Is done.
The resin composition of the core material is formed of a crystalline polymer, and the polymer component is only the crystalline polymer, but the component other than the polymer includes additive components appropriately selected as necessary. May be.
There is no restriction | limiting in particular as a shape of the resin composition of the said core material, According to the objective, it can select suitably, For example, a film form and a sheet form are mentioned.
Further, the structure of the resin composition of the core material may be a single material or a composite material of two or more materials. As an example, a section of the resin composition of the core material is incorporated into another sheet and integrated. It is good also as a resin composition.

<< Crystalline polymer >>
In general, polymers are divided into crystalline polymers and amorphous (amorphous) polymers. The crystalline polymer is not usually 100% crystalline, a crystalline region in which long chain molecules are regularly arranged in a molecular structure, and an amorphous region that is not regularly arranged. Is included.
In the present invention, the crystalline polymer only needs to include at least the crystalline region in a molecular structure, and a crystalline region and an amorphous region may be mixed.

The crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include high-density polyethylene, polyolefin (for example, polypropylene), polyamide (PA) (for example, nylon-6), Polyacetal (POM), polyester (for example, PET, PEN, PTT, PBT, PBN, etc.), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), liquid crystal polymer (LCP), And fluororesin. Among these, polyester, syndiotactic polystyrene (SPS), and liquid crystal polymer (LCP) are preferable from the viewpoint of mechanical strength and production, and polyester is more preferable. Two or more of these polymers may be blended or copolymerized.

The melt viscosity of the crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 50 to 700 Pa · s, more preferably 70 to 500 Pa · s, and more preferably 80 to 300 Pa · s. Further preferred. The melt viscosity of 50 to 700 Pa · s is preferable in that the shape of the melt film discharged from the die head during melt film formation is stable and uniform film formation is facilitated. In addition, when the melt viscosity is 50 to 700 Pa · s, the viscosity at the time of melt film formation becomes appropriate and the extrusion becomes easy, or the melt film at the time of film formation is leveled to reduce unevenness. Is preferable.
Here, the melt viscosity can be measured by a plate type rheometer or a capillary rheometer.

The intrinsic viscosity (IV: Intrinsic Viscosity) of the crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.4 to 1.2, preferably 0.6 to 1.0. Is more preferable, and 0.7 to 0.9 is even more preferable. When the IV is 0.4 to 1.2, the strength of the film formed becomes high and the film can be efficiently stretched.

The melting point (Tm) of the crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 40 to 350 ° C, more preferably 100 to 300 ° C, and further preferably 150 to 260 ° C. preferable. The melting point is preferably from 40 to 350 ° C. in that it is easy to maintain the shape in the temperature range expected for normal use, even without using special techniques required for processing at high temperatures. It is preferable at the point which can form a uniform film.
Here, the melting point can be measured by a differential thermal analyzer (DSC).

The weight average molecular weight of the crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 5,000 to 2,000,000, and 10,000 to 1,500,000. More preferred is 20,000 to 1,200,000. The weight average molecular weight is preferably 5,000 to 2,000,000 from the viewpoints of cavitation in drawing and mechanical stability as a fiber.
Here, the weight average molecular weight can be measured by a gel permeation chromatography (GPC Gel Permeation Chromatography) method.

-polyester-
Here, among the crystalline polymers, polyesters that are particularly preferably used in the present invention will be described from the viewpoint of mechanical strength and production.
The polyester is a polymer having an ester bond as a main bond chain of the main chain. Therefore, examples of the polyester suitable as the crystalline polymer include the exemplified PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PTT (polytrimethylene terephthalate), PBT (polybutylene terephthalate), and PBN (polyethylene). Not only butylene naphthalate) but also all polymer compounds obtained by polycondensation reaction of a dicarboxylic acid component and a diol component.

The dicarboxylic acid component is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, oxycarboxylic acids, and polyfunctional acids. Among them, aromatic dicarboxylic acids are preferable.

Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, diphenyldicarboxylic acid, diphenylsulfone dicarboxylic acid, naphthalenedicarboxylic acid, diphenoxyethanedicarboxylic acid, and 5-sodium sulfoisophthalic acid. Acid, diphenyldicarboxylic acid, and naphthalenedicarboxylic acid are preferable, and terephthalic acid, diphenyldicarboxylic acid, and naphthalenedicarboxylic acid are more preferable.

Examples of the aliphatic dicarboxylic acid include oxalic acid, succinic acid, eicoic acid, adipic acid, sebacic acid, dimer acid, dodecanedioic acid, maleic acid, and fumaric acid. Examples of the alicyclic dicarboxylic acid include cyclohexyne dicarboxylic acid. Examples of the oxycarboxylic acid include p-oxybenzoic acid. Examples of the polyfunctional acid include trimellitic acid and pyromellitic acid.

The diol component is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include aliphatic diols, alicyclic diols, aromatic diols, diethylene glycol, and polyalkylene glycols. Aliphatic diols are preferred.

Examples of the aliphatic diol include ethylene glycol, propane diol, butane diol, pentane diol, hexane diol, neopentyl glycol, and triethylene glycol. Among them, propane diol, butane diol, pentane diol, and hexane diol are exemplified. Particularly preferred. Examples of the alicyclic diol include cyclohexanedimethanol. Examples of the aromatic diol include bisphenol A and bisphenol S.

The melt viscosity of the polyester is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 50 to 700 Pa · s, more preferably 70 to 500 Pa · s, and still more preferably 80 to 300 Pa · s. . When the melt viscosity is higher, cavities are more likely to be generated during stretching. However, when the melt viscosity is 50 to 700 Pa · s, it is easier to extrude during film formation, and the resin flow is stable and retention is less likely to occur. It is preferable in that the quality is stable. Further, the melt viscosity of 50 to 700 Pa · s is preferable in that the stretching tension is appropriately maintained at the time of stretching, so that uniform stretching is facilitated and breakage is difficult. Furthermore, when the melt viscosity is 50 to 700 Pa · s, it is easy to maintain the form of the melt film discharged from the die head during film formation, and it is possible to form stably and the product is difficult to break. , Which is preferable in terms of enhancing physical properties.

The intrinsic viscosity (IV) of the polyester is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.4 to 1.2, more preferably 0.6 to 1.0, 7 to 0.9 is more preferable. When the IV is larger, cavities are more likely to appear during stretching. However, when the IV is 0.4 to 1.2, extrusion becomes easier during film formation, and the resin flow becomes stable and stays. This is preferable in that the quality becomes stable. Further, when the IV is 0.4 to 1.2, even when a molten resin filter is installed at the time of film formation, it is difficult to apply a load to the filter, and the resin flow is stable and stagnation occurs. It is preferable in that it becomes difficult to do. Further, when the IV is 0.4 to 1.2, the stretching tension is appropriately maintained at the time of stretching, so that it is easy to stretch uniformly and it is preferable in that a load is not easily applied to the apparatus. In addition, when the IV is 0.4 to 1.2, the product is less likely to be damaged, which is preferable in terms of improving physical properties.

The melting point of the polyester is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 150 to 300 ° C., more preferably 180 to 270 ° C. from the viewpoints of heat resistance and film forming properties.

In addition, as said polyester, the said dicarboxylic acid component and the said diol component may each superpose | polymerize, and the polymer may be formed, and the said dicarboxylic acid component and / or the said diol component are copolymerized by 2 or more types. Thus, a polymer may be formed. Further, two or more kinds of polymers may be blended and used as the polyester resin.

In the blend of two or more polymers, the polymer added to the main polymer has a melt viscosity and an intrinsic viscosity that are close to those of the main polymer, and the addition amount is smaller when the film is formed or melted. It is preferable in that the physical properties are enhanced during extrusion and the extrusion becomes easy.

In addition, for the purpose of improving the flow characteristics of the polyester resin, controlling light transmittance, and improving the adhesion with the coating solution, a resin other than polyester may be added to the polyester resin.

As described above, the resin layer of the core material can form cavities in a simple process even without adding a cavity forming agent such as inorganic fine particles or incompatible resins added in the prior art. it can. Furthermore, no special equipment for dissolving the inert gas in the resin in advance is required. The fiber manufacturing method will be described later.

Here, as long as the resin layer of the core material is a component that does not contribute to the development of the cavity, it may contain other components as necessary. Examples of the other components include fillers, heat stabilizers, antioxidants, ultraviolet absorbers, organic lubricants, nucleating agents, dyes, pigments, flame retardants, mold release agents, dispersants, and coupling agents. . Whether or not the other component contributes to the development of the cavity can be determined by whether or not a component other than the crystalline polymer (for example, each component described later) is detected in the cavity or at the interface portion of the cavity.

There is no restriction | limiting in particular as said antioxidant, According to the objective, it can select suitably, For example, a phenolic compound, a sulfur type compound, a phosphorus type compound is mentioned, Especially, a well-known hindered phenol is mentioned. . Examples of the hindered phenol include antioxidants commercially available under trade names such as Irganox 1010, Sumilyzer BHT, Sumilyzer GA-80.
Further, the antioxidant can be used as a primary antioxidant and further combined with a secondary antioxidant. Examples of the secondary antioxidant include antioxidants commercially available under trade names such as Sumilizer TPL-R, Sumilizer TPM, Sumilizer TP-D, and the like.

Examples of the release agent include plant waxes such as carnauba wax, animal waxes such as beeswax and lanolin, mineral waxes such as montan wax, petroleum waxes such as paraffin wax and polyethylene wax, castor oil and derivatives thereof, fatty acids and Examples of the fatty acid derivatives include esters of higher fatty acids such as lauric acid, stearic acid, and montanic acid, and monohydric or dihydric or higher alcohols.

The flame retardant is not particularly limited and may be appropriately selected depending on the purpose, but a brominated flame retardant is particularly preferable. As brominated flame retardants, organic halogen flame retardants such as high molecular weight organic halogen compounds and low molecular weight organic halogen compounds may be used alone or in combination of two or more. Moreover, you may use flame retardants, such as a phosphorus type and an inorganic type.

<Cavity>
The resin layer of the core material has a cavity and is characterized by an aspect ratio of the cavity.
The cavity means a vacuum domain or a gas phase domain existing inside the resin molded body.

3A to 3C are diagrams for explaining the aspect ratio. FIG. 3A is a perspective view of the resin layer of the core material, and FIG. 3B is an A− of the resin layer of the core material in FIG. 3A. FIG. 3C is a cross-sectional view taken along line A ′, and FIG. 3C is a cross-sectional view taken along line BB ′ of the resin layer of the core material in FIG. 3A.

The aspect ratio is defined as an average length of the cavity 100 in a direction orthogonal to the surface 10a of the fiber 10 and orthogonal to the orientation direction of the cavity, r (μm) (see FIG. 3B), and the core material. L / r ratio when the average length of the cavity 100 in the orientation direction of the cavity is L (μm) (see FIG. 3C).
The aspect ratio is not particularly limited as long as the effect of the present invention is not impaired, can be appropriately selected according to the purpose, and is preferably 10 or more and 100 or less, more preferably 15 or more and 100 or less, and 20 More preferred is 100 or less.

The orientation direction of the cavities indicates the uniaxial stretching direction (first stretching direction) when stretching is uniaxial. Usually, since longitudinal stretching is performed along the direction in which the molded body flows during production, this longitudinal stretching direction corresponds to the orientation direction of the cavities (first stretching direction).
Moreover, when extending | stretching is biaxial or more, at least one direction is shown among the extending directions aiming at cavity formation. Usually, even in the case of biaxial or more stretching, longitudinal stretching is performed along the flow direction of the molded body during production, and a cavity can be formed by this longitudinal stretching. It corresponds to the orientation direction of the cavity (first stretching direction).

<Occupied area of core layer cavity>
In the fiber of the present invention, the cross-sectional area of the fiber core layer in an arbitrary cross section orthogonal to the length direction is X (μm ² ), and the cross-sectional area of the cavity in the cross-section is Y (μm ² ). In this case, the average of these ratios (Y / X) is preferably 0.05 or more and 0.4 or less.
In addition, each cross-sectional area in the said cross section can be measured with the image of an optical microscope or an electron microscope.

In addition, the resin layer of the core material is characterized by an average number P of cavities in the film thickness direction, a refractive index difference ΔN between the crystalline polymer portion and the cavities, and a product of the ΔN and the P. ing.
The number of cavities in the film thickness direction is a plane (AA ′ cross section in FIG. 3A) including a direction orthogonal to the surface 10a of the resin layer 10 of the core material and orthogonal to the alignment direction of the cavities. This means the number of cavities 100 included in the film thickness direction.
The crystalline polymer portion refers to a portion (a portion made of a crystalline polymer) other than a cavity in the fiber.
The average number P of cavities in the film thickness direction is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the purpose, preferably 5 or more, more preferably 10 or more. Preferably, 15 or more are more preferable.
Here, the number of cavities in the film thickness direction can be measured by an image of an optical microscope or an electron microscope.

The refractive index difference ΔN between the crystalline polymer portion and the cavity is specifically the difference between N1 and N2 when the refractive index of the crystalline polymer portion is N1 and the refractive index of the cavity is N2. It means a value of ΔN (= N1−N2).
Here, the refractive indexes N1 and N2 of the crystalline polymer portion and the cavity can be measured by an Abbe refractometer or the like.
The product of the ΔN and the P is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the purpose, but is preferably 3 or more, more preferably 5 or more, and 7 or more. Is more preferable.

Thus, the resin layer of the core material has various excellent characteristics in, for example, reflectivity and glossiness due to the hollow inside. In other words, characteristics such as reflectance and gloss can be adjusted by changing the shape of the cavity inside the resin layer of the core material.

-Glossiness-
The glossiness of the resin layer of the core material is preferably 60 or more, more preferably 70 or more, and still more preferably 80 or more.
Here, the glossiness can be measured by a variable glossmeter.

<Coating resin layer>
In this invention, a sheath material is the said coating resin layer.
The material of the coating resin layer is not particularly limited as long as the function of the cavity in the resin layer of the core material is not significantly impaired, and is appropriately selected according to the purpose. For example, durability, particularly water resistance, In view of hydrolyzability, tensile modulus, and bendability, hydrophobic polymers such as polyolefins and fluororesins are preferred. Further, from the viewpoint of adhesion with the core material layer, the same resin as the core material layer is preferable. Here, the function of the cavity in the resin layer of the core material is an interference color, reflection, and heat insulation that are manifested by light refraction at the interface of the cavity. That is, it is preferable that the coating resin layer has light transmittance and heat insulation properties that do not hinder the expression of the interference color and reflection.
The thickness of the coating resin layer is appropriately selected depending on the purpose, and for example, it is preferably 3% or more and 30% or less of the radius in the cross section of the resin layer of the core material. If the thickness of the coating resin layer is less than 3% of the radius of the cross section of the resin layer of the core material, sufficient mechanical properties may not be imparted, and the thickness of the coating resin layer may be the resin layer of the core material. If it exceeds 30% or less of the radius in the cross section, there may be a decrease in heat insulation, a lack of flexibility and touch as a fiber, or a decrease in productivity.

<< Protective layer >>
In the present invention, it is preferable that the resin layer located in the outermost layer of the cross section in the direction orthogonal to the length direction of the fiber of the present invention among the resin layers constituting the coating resin layer is a protective layer. In particular, since the coating resin layer often serves as a protective layer, the protective layer may not be provided.

(Coating resin / Protective layer resin)
When selecting the coating resin composition that is the above-described coating material, it is important that the wire does not damage the strands (the core layer may be called in this way) during and after the production. When coating by the melt extrusion method, heat applied to the coating material by melting the resin propagates to the strands in the coating step and adversely affects the strands. Therefore, the thermoplastic resin constituting the composition It is preferable that the flow start temperature falls within a certain range.

The thermoplastic resin having a preferable flow start temperature used in the present invention is not particularly limited as long as it has the above-described characteristics. Examples include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, nylon (nylon-6, nylon-66, nylon-11, etc.), polyvinyl chloride, ethylene ethyl acrylate copolymer, polyester compound, etc. Of these, polyethylene, polypropylene, and polyester are preferable. These thermoplastic resins exhibit various melting behaviors by changing the molecular weight, molecular weight distribution, branching degree, crosslinking degree, type of terminal functional group, and the like, and the value of the flow start temperature can be controlled.
Further, these resins may be mixed as appropriate to adjust to a preferable flow start temperature range. Similarly, in order to lower the flow start temperature, a copolymer of the aforementioned polymer may be used, or a vinyl acetate component may be copolymerized. Alternatively, the flow start temperature may be controlled by adjusting the amount of an additive such as a plasticizer.

Here, regardless of whether or not the covering resin layer is the protective layer, in order to protect the resin layer of the core material, it is preferable that the coating resin layer does not break even when pulled as a fiber. High adhesion to the resin layer is required.
Therefore, the difference between the solubility parameter of the resin composition of the coating resin layer and the solubility parameter of the resin composition of the resin layer of the core material is preferably 7 (cal / cm ³ ) ^1/2 or less. .
Here, the solubility parameter is a characteristic value that is a measure of the mixing property between substances, the solubility parameter is δ, the solidification energy (molar evaporation energy) of the substance is E, and the molecular volume. When (molar volume) is V, it is represented by the following formula (x).
δ = (E / V) ^1/2 Equation (x)
As for the solubility parameter, for example, J. Org. Brandrup, E.I. H, “Polymer Handbook (4th edition), VII / 671 to VII / 714”.

(Fiber manufacturing method)
Hereinafter, the manufacturing method of the fiber of this invention is demonstrated.
The fiber production method of the present invention includes a preform production step (melt spinning) for producing a preform (precursor) in which the coating resin layer is coated on the resin layer of the core material so as to have a concentric cross section. Step) and a drawing step for expressing a cavity in the core resin layer, a spinning step for melt spinning the resin layer of the core material, and drawing the melt-spun undrawn yarn into the inside And a method having a stretching step for developing a cavity and a coating step for forming one or more coating resin layers on the surface of the stretched fiber. Among these, the former method for forming a preform (melt spinning step) and a method having a drawing step are preferable in terms of production efficiency. Moreover, as long as the effect of this invention is not impaired, you may combine another process as needed.

[Preform production process (melt spinning process)]
The melt spinning step is a step of producing a cylindrical preform in which each resin layer is laminated concentrically. Examples of the melt spinning step include a coating method and a melt composite spinning method. Among these, the melt composite spinning method is preferable.
The coating method is a manufacturing method in which the resin composition of the coating resin layer is dissolved in a solvent, applied to the core resin layer, and then dried to evaporate the solvent.
Examples of the melt composite spinning method further include a ram extrusion composite spinning method and a continuous composite spinning method.

In the ram extrusion compound spinning method, a resin layer of a core material and a polymer rod constituting a plurality of coating resin layers are formed, inserted into a cylinder, and melted at one end of the cylinder by a piston. Pressing and extruding from the other end, into the inflow hole 1 of the core resin layer material formed on the composite spinning die (see FIG. 2A), and the respective inflow holes 2 to 7 of the plurality of coating resin layer materials, respectively The polymer is quantitatively supplied so as to have a predetermined thickness, sequentially laminated to form a multilayer structure, and then discharged from the discharge port isolated by the guide pipe 8. The discharged filament is fixed. It is cooled while being taken up at a high speed to produce a preform.

In the continuous composite spinning method, the polymer constituting each layer is continuously melted by an extruder, and after devolatilization as necessary, the composite spinning die as shown in FIG. In the same manner as the spinning method, quantitative supply is performed, and a multi-layered structure is sequentially laminated, and then discharged from the die. The discharged filament is cooled while being drawn at a constant speed to produce a preform. .

In particular, the continuous composite spinning method is easy to consistently and continuously perform spinning from polymer polymerization to spinning, and is excellent in productivity, and by introducing a continuous devolatilization process before the spinning process, Since monomers and impurities can be sufficiently removed, a fiber having high permeability and excellent optical durability is preferable.

[Stretching process]
As shown in FIG. 2B, the preform 21 obtained as described above is inserted into, for example, a heating furnace 30 adjusted to 220 to 260 ° C., and the winding machine 32 is passed through an annealing treatment device 31. The fiber of the present invention is produced by being subjected to a heat stretching process while being wound around the fiber.
Specifically, the preform (undrawn yarn) is drawn at least uniaxially. Then, the preform (undrawn yarn) is drawn by the drawing step, and a cavity having a major axis in the first drawing direction is formed therein, whereby the fiber of the present invention is obtained.
In addition, in FIG. 2B, 21a shows an extending | stretching start point.

The reason why cavities are formed by stretching is that the polymer having at least one crystallinity constituting the resin layer of the core material is in a phase containing a crystal in which a microcrystalline nucleus state is formed and hardly stretched during stretching, It is considered that a cavity is formed by peeling and stretching in such a manner that the amorphous phase resin between hard microcrystals is torn off.
Such void formation by stretching is possible not only when there is only one kind of crystalline polymer, but also when two or more kinds of crystalline polymers are blended or copolymerized. is there.

The stretching method is not particularly limited as long as the effects of the present invention are not impaired, and examples thereof include uniaxial stretching, sequential biaxial stretching, and simultaneous biaxial stretching. In any stretching method, molding is performed during production. Longitudinal stretching is preferably performed along the direction of body flow.

In general, in the longitudinal stretching, the number of longitudinal stretching stages and the stretching speed can be adjusted by the combination of rolls and the speed difference between the rolls.
The number of stages of the longitudinal stretching is not particularly limited as long as it is one or more, but it is preferable to perform longitudinal stretching in two or more stages in that it can be more stably stretched at a high speed. Further, longitudinal stretching in two or more stages is advantageous in that a cavity can be formed by second-stage stretching after confirming the occurrence of necking by first-stage stretching.
Here, the necking means a constricted deformation that occurs when the preform is stretched, and it is confirmed that the thickness of the preform decreases discontinuously during the stretching. Is expressed ".

--Stretching speed--
The stretching speed of the longitudinal stretching is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected according to the purpose, but is preferably 10 to 36,000 mm / min, and preferably 800 to 24,000 mm. / Min is more preferable, and 1200 to 12,000 mm / min is still more preferable. When the stretching speed is 10 mm / min or more, it is preferable in that sufficient necking can be easily expressed. Further, when the stretching speed is 36,000 mm / min or less, uniform stretching is facilitated, and the resin is not easily broken. In particular, a large stretching apparatus for high-speed stretching is not required, and the cost is reduced. Is preferable in that it can be reduced.

In addition, examples of the stretching method include single-stage stretching and two-stage stretching, and any of them can be suitably applied to the present invention, but two-stage stretching is more preferable from the viewpoint of manufacturing yield and machine restrictions. .
More specifically, the stretching speed in the case of single-stage stretching is preferably 1,000 to 36,000 mm / min, more preferably 1,100 to 24,000 mm / min, and 1,200 to 12,000 mm / min. Is more preferable.

In the case of two-stage stretching, it is preferable that the first-stage stretching is a preliminary stretching whose main purpose is to develop necking. The stretching speed of the preliminary stretching is preferably 10 to 300 mm / min, more preferably 40 to 220 mm / min, and further preferably 70 to 150 mm / min.

In the two-stage stretching, the second-stage stretching speed after the necking is expressed by the preliminary stretching (first-stage stretching) is preferably changed from the preliminary stretching speed. The second stage stretching speed after causing necking by the preliminary stretching is preferably 600 to 36,000 mm / min, more preferably 800 to 24,000 mm / min, and 1,200 to 15,000 mm. / Min is more preferable.

--Extension temperature--
The temperature during stretching is not particularly limited and can be appropriately selected according to the purpose.
When the stretching temperature is T (° C) and the glass transition temperature is Tg (° C),
(Tg-30) ≦ T ≦ (Tg + 50)
It is preferable to stretch at a stretching temperature T (° C.) in the range indicated by
(Tg−25) ≦ T ≦ (Tg + 45)
It is more preferable to stretch at a stretching temperature T (° C.) in the range indicated by
(Tg−20) ≦ T ≦ (Tg + 40)
More preferably, the film is stretched at a stretching temperature T (° C.) in the range indicated by.

In general, the higher the stretching temperature (° C.), the lower the stretching tension, and the easier it can be stretched. However, when the stretching temperature (° C.) is {glass transition temperature (Tg) +50} ° C. or less, cavities are formed. The volume ratio is high, and the aspect ratio is preferably 10 or more. Further, it is preferable that the stretching temperature (° C.) is {glass transition temperature (Tg) −30} ° C. or more from the standpoint that cavities are sufficiently developed.

Here, the stretching temperature T (° C.) can be measured with a non-contact thermometer. The glass transition temperature Tg (° C.) can be measured by a differential thermal analyzer (DSC).

In the drawing step, the drawn fiber may be further subjected to heat shrinkage by applying heat or treatment such as tension for the purpose of shape stabilization.

Moreover, the preparation of the preform may be performed independently of the stretching step or may be performed continuously.

The core layer of the present invention can be obtained by stretching the preform. The fiber of the present invention is formed through the coating step described below on the core layer.
As the coating line used for producing the fiber of the present invention, a coating line similar to a conventionally known electric cable or quartz glass optical fiber can be used.

FIG. 4 shows a schematic diagram of the coating line. The strands (core fibers having cavities) 110 are fed from the feeder 120 and cooled to a temperature of 5 to 35 ° C. by the cooling device 130 in order to suppress damage to the strands 110 during coating. However, the cooling device 130 can be omitted. After that, the cable 150 is obtained by covering the wire 110 with the covering material by the covering device 140. After the cable 150 is cooled with cold water in the water tank 160, the moisture on the surface thereof is removed by the moisture removing device 170. The cooling of the cable 150 is not limited to the water tank, and other devices may be used. And it is conveyed by the roller 180 and wound up by the winder 190.
In addition, as a coating method, a melt extrusion method, a method of obtaining a coating layer by applying and curing using an active energy ray curable resin, and the like can be used. In the present invention, it is preferable to use a melt extrusion method.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
<Formation of preform (unstretched fiber)>
<< Core resin layer composition >>
Polybutylene terephthalate 100% resin PBT1 (manufactured in-house at Fujifilm) was employed as a resin composition (core resin composition) constituting the core resin layer. It was 0.72 (Pa * s) when the intrinsic viscosity (IV) of this composition was measured with the Ubbelohde viscometer (made by Asahi Seisakusho). Further, the glass transition temperature Tg (° C.) and the melting point Tm (° C.) of the PBT 1 were measured with a differential thermal analyzer (manufactured by Seiko II).

<Extension process>
Next, the preform obtained was uniaxially stretched at a speed of 120 mm / min in a heated atmosphere at 40 ° C., and after confirming that necking had occurred, it was the same as the beginning at a speed of 6,000 mm / min. A fiber (also referred to as a strand) corresponding to a core material layer containing a cavity was further uniaxially stretched in the direction.

<Coating process>
As a coating resin, PBT1 pellets used for preform production were coated with a cross extrusion head (die diameter 1.5 mm, nipple diameter 0.5 mm) using a coating line (see FIG. 4) of the strand 110. Coating was carried out at a conveyance speed of 500 m / min to obtain a fiber of the present invention having a coating layer having a thickness of 5 μm.
A photographic image of a cross section of the fiber of Example 1 is shown in FIG.

(Example 2)
<Preform production>
A preform was produced in the same manner as in Example 1 except that the resin layer composition of the core material was changed to 100% polybutylene terephthalate resin PBT2 (produced in-house by Fuji Film).
The intrinsic viscosity (IV) of the PBT2 was measured in the same manner as in Example 1, and found to be 0.86 (Pa · s). Further, the glass transition temperature Tg (° C.) and the melting point Tm (° C.) of the PBT 2 were measured in the same manner as in Example 1. The measurement results are shown in Table 1.

<Extension process>
Next, the preform obtained is uniaxially stretched in a single step at a speed of 2400 mm / min in a heated atmosphere at 40 ° C. to produce a fiber (also referred to as a strand) corresponding to a core material layer containing a cavity. did.

<Coating process>
Coating was performed in the same manner as in Example 1 except that the coating resin was changed to PET (produced in-house at Fuji Film).
In addition, it was 0.6 (Pa * s) when the intrinsic viscosity (IV) of the said PET was measured like Example 1. FIG. Further, the glass transition temperature Tg (° C.) and the melting point Tm (° C.) of the PET were measured in the same manner as in Example 1. The measurement results are shown in Table 1.
A fiber of the present invention having a coating layer with a thickness of 3 μm was obtained.

(Example 3)
<Preform production>
A preform was produced in the same manner as in Example 1, except that the resin layer composition of the core material was changed to 100% polybutylene terephthalate resin PHT (produced in-house by Fuji Film).
The intrinsic viscosity (IV) of the PHT was measured in the same manner as in Example 1, and found to be 0.7 (Pa · s). The glass transition temperature Tg (° C.) and melting point Tm (° C.) of the PHT were measured in the same manner as in Example 1. The measurement results are shown in Table 1.

<Extension process>
Next, the preform obtained was uniaxially stretched at a speed of 100 mm / min in a heated atmosphere at 30 ° C., and after confirming that necking had occurred, it was the same as the beginning at a speed of 6,000 mm / min. A fiber (also referred to as a strand) corresponding to a core material layer containing a cavity was further uniaxially stretched in the direction.

<Coating process>
Example 1 except that the coating resin was changed to isotactic polypropylene (manufactured by Aldrich, weight average molecular weight 190,000, number average molecular weight 50,000, glass transition temperature -13 ° C., Tm: 170 to 175 ° C.) Coating was carried out. A fiber of the present invention having a coating layer with a thickness of 5 μm was obtained.

Example 4
<Preform production>
In Example 1, the core resin layer composition was changed to isotactic polypropylene (manufactured by Aldrich, weight average molecular weight 190,000, number average molecular weight 50,000, glass transition temperature −13 ° C., Tm: 170 to 175 ° C.). A preform was produced in the same manner as in Example 1 except that.

<Extension process>
Next, the preform obtained was uniaxially stretched at a speed of 100 mm / min in a heated atmosphere at 35 ° C., and after confirming that necking occurred, the same as the beginning at a speed of 6,000 mm / min. A fiber (also referred to as a strand) corresponding to a core material layer containing a cavity was further uniaxially stretched in the direction.

<Primary coating process>
Example 1 except that the coating resin was changed to isotactic polypropylene (manufactured by Aldrich, weight average molecular weight 190,000, number average molecular weight 50,000, glass transition temperature -13 ° C., Tm: 170 to 175 ° C.) Coating was carried out. A fiber of the present invention having a coating layer with a thickness of 5 μm was obtained.

<Secondary coating process>
Coating was carried out in the same manner as in Example 1 except that LDPE (manufactured by Aldrich, weight average molecular weight is unknown, MI value was 25 g / 10 min, glass transition temperature −125 ° C., Tm: 146 ° C.) was used as the coating resin. Went. A fiber of the present invention having a coating layer with a thickness of 3 μm was obtained.

(Comparative Example 1)
<Production of fiber>
<Formation of preform (unstretched fiber)>
<< Core resin layer composition >>
Polybutylene terephthalate 100% resin PBT1 (manufactured in-house at Fujifilm) was employed as a resin composition (core resin composition) constituting the core resin layer. It was 0.72 (Pa * s) when the intrinsic viscosity (IV) of this composition was measured with the Ubbelohde viscometer (made by Asahi Seisakusho). Further, the glass transition temperature Tg (° C.) and the melting point Tm (° C.) of the PBT 1 were measured with a differential thermal analyzer (manufactured by Seiko II).

<Extension process>
Next, the preform obtained was uniaxially stretched at a speed of 120 mm / min in a heated atmosphere at 100 ° C., and after confirming that necking occurred, it was the same as the beginning at a speed of 6,000 mm / min. A fiber (also referred to as a strand) corresponding to the core material layer was produced by further uniaxially stretching in the direction. However, the cavity did not develop.

<Coating process>
As a coating resin, the PBT1 pellets used for preform production were coated with a coating extruder (die diameter: 1.5 mm, nipple diameter: 0.5 mm) with a cross die head. Coating was carried out at a conveyance speed of 500 m / min to obtain a fiber of the present invention having a coating layer having a thickness of 5 μm.

(Comparative Example 2)
<Production of fiber>
The fibers of Comparative Example 2 were prepared in the same manner as in Example 4 until the wires were prepared and the coating step was not performed.

Table 1 summarizes the fibers produced in Examples 1 to 4 and Comparative Examples 1 and 2.

<Measurement and evaluation>
The fibers of Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated as follows. The measurement results are shown in Table 2, and the evaluation results are shown in Table 3.

<< Measurement of transmittance >>
The transmittance was measured using a spectrophotometer U-4100 manufactured by Hitachi, Ltd. Light was incident at an angle of 5 degrees from the normal direction of the surface of the obtained fiber, and the intensity of light transmitted through the fiber was compared with the value of a blank that did not transmit the fiber. A wavelength of 550 nm was used.
Moreover, the transmittance | permeability was measured similarly to the measurement of the transmittance | permeability of the said resin composition also with respect to the obtained fiber.
Regarding the ratio between the transmittance of the resin composition and the transmittance of the fiber, the transmittance of the resin composition is converted into the same dimension as the thickness (cross-sectional diameter) of the fiber according to Lambert-Beer's law. And calculated.

<< Aspect ratio measurement >>
A cross section perpendicular to the surface of the fiber and perpendicular to the longitudinal stretching direction (see FIG. 3B) and a cross section perpendicular to the surface of the fiber and parallel to the longitudinal stretching direction (see FIG. 3C) are scanned. Using an electron microscope, the microscope was examined at an appropriate magnification of 300 to 3,000 times, and a measurement frame was set in each cross-sectional photograph. This measurement frame was set so that 50 to 100 cavities were included in the measurement frame.
Next, the number of cavities included in the measurement frame is measured, and the number of cavities included in the measurement frame (see FIG. 3B) of the cross section orthogonal to the longitudinal stretching direction is m, and the cross section parallel to the longitudinal stretching direction. The number of cavities included in the measurement frame (see FIG. 3C) was n.
Then, the longitudinal stretching direction orthogonal cross section of the measurement frame determined (Fig. 3B see) on one by one the length of the cavity included a (r _i), and the length of the average and r. Further, the length (L _i ) of each cavity included in the measurement frame (see FIG. 3C) having a cross section parallel to the longitudinal stretching direction was measured, and the average length was defined as L.
That is, r and L can be represented by the following formulas (1) and (2), respectively.
r = (Σr _i ) / m (1)
L = (ΣL _i ) / n (2)
Then, L / r was calculated as an aspect ratio.

<< Average number of cavities P >>
First, a cross section perpendicular to the longitudinal stretching direction was photographed with a scanning electron microscope.
Then, in the cross-sectional photograph, a straight line was drawn in the fiber diameter direction, and the number of cavities in contact with the straight line was measured. This operation was performed for 20 straight lines, and the average was obtained.

<< Refractive index difference ΔN between crystalline polymer part and cavity >>
The refractive index N1 of the polymer part having crystallinity was measured with an Abbe refractometer by separately preparing a film. The refractive index N2 of the cavity is set such that the refractive index of the air is equal to the refractive index N2 of the cavity because the cavity is separately air. The measurement wavelength is 589 nm. Then, the difference ΔN (= N1−N2) was calculated.

<< Cavity cross-sectional area ratio >>
Image processing was performed using a photograph of the cross-sectional SEM of the core material layer, and the overall cross-sectional area and the cross-sectional area of the cavity portion were separately obtained using all the cavities, and the cross-sectional area ratio of the cavities was calculated and evaluated.

<Evaluation of heat retention>
For evaluation of heat retention, the woven or knitted fabric of the present invention was manufactured and evaluated by five skilled workers based on the following evaluation criteria.
[Evaluation criteria]
○: Feels warm △: Feels warm ×: No change

<< Durability Evaluation >>
The woven or knitted fabric used in the evaluation of heat retention was placed in a water bath set at a constant temperature of 40 ° C. and stirred for 1 hour at a rotation speed of 30 rpm. Once taken out, the water was removed with a dehydrator and dried with a dryer at 50 ° C. for 1 hour. This cycle was performed 100 times. And durability was evaluated based on the following evaluation criteria.

[Evaluation criteria]
○: 100 cycles before and no change Δ: Compared to 100 cycles before, the touch feels worse, but there is not much change in appearance.
X: Compared with 100 cycles before, the touch and the appearance were clearly changed.

As shown in Table 3, Examples 1 to 4 were confirmed to exhibit performance such as high recyclability and durability.

Claims (10)

1. One or more resin layers having a hollow inside and a resin layer having a substantially circular cross section perpendicular to the length direction as a sheath material on the resin layer of the core material having a substantially circular cross section perpendicular to the length direction A fiber characterized by comprising.
2. Average ratio (Y / X) of the cross-sectional area Y (μm ² ) of the cavity to the cross-sectional area X (μm ² ) of the fiber in the direction perpendicular to the length direction of the resin layer of the core material is 5% or more and 40% The fiber according to claim 1, wherein:
3. The L / r ratio is 10 when the average length of the cavity in the diameter direction perpendicular to the orientation direction of the cavity is r (μm) and the average length of the cavity in the orientation direction of the cavity is L (μm). The fiber according to claim 1, wherein the fiber is 100 or less.
4. The fiber according to any one of claims 1 to 3, wherein the resin layer of the core material is composed only of a polymer having crystallinity.
5. The transmittance of the fiber is M (%), and the transmittance of a fiber made of a polymer having the same crystallinity as the polymer having the crystallinity of the fiber and having the same fineness as that of the fiber and having no cavity is N. The fiber according to claim 4, wherein the M / N ratio is 0.2 or less and the glossiness of the fiber is 50 or more.
6. The average number of cavities in an arbitrary cross section in the diameter direction perpendicular to the orientation direction of the cavities is P, the refractive index of the crystalline polymer part is N1, the refractive index of the cavities is N2, and the difference between N1 and N2 is 6. The fiber according to claim 4, wherein the product of ΔN and P is 3 or more when ΔN (= N1−N2).
7. The fiber according to any one of claims 4 to 6, wherein the polymer having crystallinity comprises only one kind.
8. The fiber according to any one of claims 4 to 7, wherein the polymer having crystallinity is a polyolefin, a polyester or a polyamide.
9. The resin layer of the core material is obtained by melt spinning a resin composition composed only of a crystalline polymer,
   At a speed of 10 to 36,000 mm / min, and
   When the stretching temperature is T (° C.) and the glass transition temperature of the crystalline polymer is Tg (° C.),
   (Tg-30) ≦ T ≦ (Tg + 50)
   The fiber according to any one of claims 1 to 8, obtained by stretching at a stretching temperature T (° C) represented by:
10. A method for producing a fiber according to any one of claims 1 to 9, wherein a plurality of resin layers are laminated and spun on a resin layer of a core material made of only a crystalline polymer, A stretching step of stretching in the length direction of the resin layer of the core material,
    The stretching step includes
    At a speed of 10 to 36,000 mm / min, and
    When the stretching temperature is T (° C.) and the glass transition temperature of the crystalline polymer is Tg (° C.),
    (Tg-30) ≦ T ≦ (Tg + 50)
    A method for producing a fiber, wherein the fiber is drawn at a drawing temperature T (° C.) represented by:

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