JP7576608B2 - Core-sheath composite fiber for artificial hair, head accessory product containing same, and method for manufacturing same - Google Patents

Description

The present invention relates to core-sheath composite fibers for artificial hair that can be used as a substitute for human hair, head accessories containing the same, and a method for producing the same.

Traditionally, human hair has been used in head accessories such as wigs, hairpieces, false hair, hair bands, and doll hair. However, in recent years, it has become difficult to obtain human hair, and there has been an increasing demand for artificial hair as an alternative to human hair.

Such artificial hair is required to have a texture and appearance similar to that of human hair, and examples of synthetic fibers used as materials for the hair include acrylic fibers, vinyl chloride fibers, vinylidene chloride fibers, polyester fibers, polyamide fibers, polyolefin fibers, etc. Among these, a core-sheath composite fiber with polyester as the core component and polyamide as the sheath component has been developed as a core-sheath composite fiber for artificial hair that has a texture similar to that of human hair and is excellent in durability and heat resistance (Patent Document 1).

In Patent Document 1, the viscosity ratio a/b of the melt viscosity a of the polyester to the melt viscosity b of the polyamide at 285°C is set to 0.5 to 2.5, thereby improving the durability and heat resistance of the core-sheath composite fiber for artificial hair.

International Publication No. 2017/187843

As mentioned above, the fiber described in Patent Document 1 is a core-sheath composite fiber with polyester as the core component and polyamide as the sheath component. However, the polyamide used as the sheath component has poorer curl setting properties than polyester when curled with a hair iron or the like, so the curl setting properties are insufficient for use as a core-sheath composite fiber for artificial hair, and further improvement is required.

The present invention provides a core-sheath composite fiber for artificial hair that has a feel similar to human hair, excellent combability, and good curl setting properties, as well as a head accessory product containing the same and a method for manufacturing the same.

In one or more embodiments, the present invention relates to a sheath-core composite fiber for artificial hair, comprising a core and a sheath, the core-sheath composite fiber for artificial hair having a flattened bilobal or elliptical cross-sectional shape, a core-sheath ratio in the fiber cross-section being 3:7 to 8:2 in terms of area ratio, the sheath being made of a polyamide-based resin composition containing a polyamide-based resin, and the core being characterized in that it has a deformed flattened bilobal or deformed elliptical cross-sectional shape having a pair of convex portions protruding from the center side toward the outer periphery along the minor axis direction of the fiber cross-section.

In one or more embodiments, the present invention also relates to a head accessory product comprising the core-sheath composite fiber for artificial hair.

In one or more embodiments, the present invention also relates to a method for producing the core-sheath composite fiber for artificial hair, which includes a step of melt-spinning a core resin composition and a sheath resin composition using a core-sheath composite nozzle.

The core-sheath composite fiber for artificial hair of the present invention not only has a feel similar to human hair and excellent combability, but also has sufficiently excellent curl setting properties, making it suitable as a material for head decoration products.

The manufacturing method of the present invention makes it possible to obtain core-sheath composite fibers for artificial hair that not only have a feel similar to human hair and excellent combability, but also have sufficiently excellent curl setting properties.

FIG. 1 is a schematic diagram showing a fiber cross section of a core-sheath composite fiber for artificial hair according to one or more embodiments of the present invention. FIG. 2 is a laser microscope photograph of the cross section of the fiber of Example 1. FIG. 3 is a laser microscope photograph of the cross section of the fiber of Comparative Example 1. FIG. 4 is a laser microscope photograph of the cross section of the fiber of Comparative Example 3.

The present invention has been made to solve the problems of the prior art described above, namely, to provide a core-sheath composite fiber for artificial hair with excellent curl set properties (hereinafter also referred to simply as "core-sheath composite fiber"). It has been found that it is difficult to obtain a core-sheath composite fiber for artificial hair with sufficiently excellent curl set properties with conventional fibers having a core-sheath structure in which the core and sheath (fiber) are similar in shape, and it has been found that by giving the fiber and core a specific cross-sectional shape, it is possible to impart sufficiently excellent curl set properties.

(Shape of core-sheath composite fiber)
In one or more embodiments of the present invention, the core-sheath composite fiber for artificial hair has a cross-sectional shape that is flattened bilobal or elliptical, preferably a flattened bilobal shape, and the core has a cross-sectional shape that is modified flattened bilobal with a pair of convex parts protruding from the center to the outer periphery along the minor axis direction of the fiber cross section, or a modified elliptical with a pair of convex parts protruding from the center to the outer periphery along the minor axis direction of the fiber cross section, preferably a modified flattened bilobal cross-sectional shape.

A flat bilobe is formed by joining two lobe shapes selected from the group consisting of circles and ellipses via a recess. The circle or ellipse shape referred to here does not necessarily have to be a continuous arc, and also includes a roughly circle or ellipse with some deformation as long as it does not have an acute angle.

A deformed flat bilobe is a deformed flat bilobe, which has a pair of convex parts protruding from the center toward the outer periphery along the minor axis of the fiber cross section. In a flat bilobe, two lobes selected from the group consisting of circles and ellipses are joined via a concave part, whereas in a deformed flat bilobe, two lobes selected from the group consisting of circles and ellipses are joined via a convex part.

Regarding the cross-sectional shape, irregularities of 2 μm or less that may occur on the outer periphery of the fiber and core due to additives, etc., which may be contained in the core-sheath composite fiber for artificial hair of the present invention, shall not be taken into consideration.

Figure 1 is a schematic diagram showing a fiber cross section of a sheath-core composite fiber for artificial hair according to one or more embodiments of the present invention. The sheath-core composite fiber for artificial hair 1 of the embodiment includes a sheath portion 10 and a core portion 20, and has a cross-sectional shape of a flat bilobe in which two ellipses are joined via a recess.

In the fiber cross section of a core-sheath composite fiber for artificial hair, among the line symmetry axis and the straight lines connecting any two points on the circumference of the fiber cross section parallel to the line symmetry axis, the straight line with the greatest length corresponds to the long axis of the fiber cross section, and the direction of the line and the direction parallel to it correspond to the long axis direction. In addition, when any two points on the circumference of the fiber cross section are connected perpendicular to the long axis of the fiber cross section, the straight line connecting the two points with the greatest length corresponds to the short axis of the fiber cross section, and the direction of the line and the direction parallel to it correspond to the short axis direction.

It is preferable that the length of the long axis of the fiber cross section (referred to as L) and the length of the short axis of the fiber cross section (referred to as S) satisfy the following formula (1).

L/S=1.1 or more and 2.0 or less (1)

As shown in Figure 1, the core 20 is a deformed flattened bilobe shape having a pair of convex parts 30 protruding from the center toward the outer periphery along the minor axis direction of the fiber cross section, and two ellipses are connected via the convex parts 30. Alternatively, the core 20 can be said to be a deformed ellipse having a pair of convex parts 30 protruding from the center toward the outer periphery along the minor axis direction of the fiber cross section.

In the core cross section, it is preferable that the length of the long axis of the core cross section (referred to as Lc), which is the longest line among the line symmetry axis and lines connecting any two points on the periphery of the core cross section parallel to the line symmetry axis, and the length of the short axis of the core cross section (referred to as Sc), which is the longest line among the line symmetry axis and lines connecting any two points on the periphery of the fiber cross section perpendicular to the long axis of the core cross section, satisfy the following formula (2).

Lc/Sc<L/S (2)

In one or more embodiments of the present invention, the sheath-core composite fiber for artificial hair has a flat bilobal fiber cross-sectional shape, which reduces flat areas on the fiber surface, reduces significant light reflection in the flat areas, and tends to produce a luster similar to that of human hair. In addition, the sheath-core composite fiber for artificial hair in one or more embodiments of the present invention preferably has a surface, i.e., the outer peripheral shape of the fiber cross-section, that is composed of smooth irregularities, which reduces the contact area between the fibers or when a comb is passed through them, thereby achieving a feel similar to human hair and good combability.

One of the features of the present invention is that the core has a pair of convex parts along the minor axis of the fiber in the cross section, which improves curl settability. Here, when the cross section of the fiber, i.e., the outer peripheral shape of the sheath, has a flattened bilobal cross section, which is the preferred form, the connecting line connecting the opposing concave parts of the fiber cross section and the connecting line connecting the pair of convex parts of the core overlap, thereby improving curl settability.

In one or more preferred embodiments of the present invention, the core-sheath composite fiber for artificial hair has a flat bilobal fiber cross section, and therefore the bending moment in the direction of the connecting line connecting the recesses and the direction parallel to it, i.e., the short axis direction of the fiber, tends to be smaller than the bending moment in the long axis direction of the fiber that intersects, preferably perpendicular to, the connecting line, and therefore it is easy to bend in the short axis direction when bending deformation is applied. Therefore, by having a pair of convex parts in the cross section of the core that protrude from the center side to the outer periphery in opposite directions along the short axis direction of the fiber, the fiber has a substantially large core line fraction of the core-sheath line ratio, which indicates the ratio of the line fraction occupied by the core and the sheath in the short axis direction of the fiber, and therefore even if the polyamide resin content of the entire fiber is high, the properties of the core, such as polyester resin, become prominent in the short axis direction of the fiber, and the properties of the polyamide resin with low curl set property can be compensated for, resulting in a fiber with extremely high curl set property.

The core-sheath ratio of core:sheath composite fibers for artificial hair is in the area ratio of 3:7 to 8:2, preferably 4:6 to 7:3. When the core-sheath ratio is in the above-mentioned range, the bending moment, which is a physical property related to the touch and texture, becomes close to that of human hair, making it easier to obtain artificial hair of the same quality as human hair.

When the ratio of the core is small, the bending moment tends to be smaller than that of human hair. On the other hand, when the ratio of the core is large, the bending rigidity value tends to be large, and the thickness of the sheath as a layer in the cross section becomes extremely thin, making the core more likely to be exposed. In such cases, there is a risk of the sheath peeling off from the core. It is preferable that the core is not exposed on the fiber surface and is completely covered by the sheath.

The cross-sectional shapes of the fibers and cores, as well as the core-sheath ratio, described above, can be controlled by using a nozzle (hole) having a shape close to the desired cross-sectional shape.

From the viewpoint of suitability for artificial hair, the core-sheath composite fiber for artificial hair preferably has a single fiber fineness of 10 dtex or more and 150 dtex or less, more preferably 30 dtex or more and 120 dtex or less, even more preferably 40 dtex or more and 100 dtex or less, and particularly preferably 50 dtex or more and 90 dtex or less.

In one or more embodiments of the present invention, the core-sheath composite fiber for artificial hair is a fiber aggregate, for example a fiber bundle, in which not all of the fibers necessarily have the same fineness or cross-sectional shape, and fibers of different finenesses and cross-sectional shapes may be mixed.

(Composition of core-sheath composite fiber)
In one or more embodiments of the present invention, the sheath is made of a polyamide-based resin composition containing a polyamide-based resin, i.e., a polyamide-based resin composition mainly composed of a polyamide-based resin, so that the touch is good. In one or more embodiments of the present invention, the "polyamide-based resin composition mainly composed of a polyamide-based resin" means that, when the total weight of the polyamide-based resin composition is taken as 100% by weight, the polyamide-based resin composition contains 67% by weight or more, preferably 75% by weight or more, more preferably 85% by weight or more, even more preferably 90% by weight or more, and even more preferably 95% by weight or more.

Polyamide resin refers to a nylon resin obtained by polymerizing one or more selected from the group consisting of lactams, aminocarboxylic acids, mixtures of dicarboxylic acids and diamines, mixtures of dicarboxylic acid derivatives and diamines, and salts of dicarboxylic acids and diamines.

Specific examples of lactams include, but are not limited to, 2-azetidinone, 2-pyrrolidinone, δ-valerolactam, ε-caprolactam, enantholactam, capryllactam, undecalactam, and laurolactam. Of these, ε-caprolactam, undecalactam, and laurolactam are preferred, and ε-caprolactam is particularly preferred. These lactams may be used alone or in a mixture of two or more.

Specific examples of aminocarboxylic acids include, but are not limited to, 6-aminocaproic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid. Of these, 6-aminocaproic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid are preferred, with 6-aminocaproic acid being particularly preferred. These aminocarboxylic acids may be used alone or in a mixture of two or more.

Specific examples of dicarboxylic acids used in the mixture of dicarboxylic acids and diamines, the mixture of dicarboxylic acid derivatives and diamines, or the salts of dicarboxylic acids and diamines include, but are not limited to, aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecane diacid, dodecane diacid, brassicic acid, tetradecane diacid, pentadecanedioic acid, and octadecanedioic acid, alicyclic dicarboxylic acids such as cyclohexane dicarboxylic acid, and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Among these, adipic acid, sebacic acid, dodecane diacid, terephthalic acid, and isophthalic acid are preferred, and adipic acid, terephthalic acid, and isophthalic acid are particularly preferred. These dicarboxylic acids may be used alone or in a mixture of two or more.

It is used in a mixture of dicarboxylic acid and diamine, a mixture of dicarboxylic acid derivative and diamine, or a salt of dicarboxylic acid and diamine. Specific examples of diamines include, but are not limited to, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 2-methyl-1,5-diaminopentane (MDP), 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, 1,14-diamino Examples of the diamine include aliphatic diamines such as tetradecane, 1,15-diaminopentadecane, 1,16-diaminohexadecane, 1,17-diaminoheptadecane, 1,18-diaminooctadecane, 1,19-diaminononadecane, and 1,20-diaminoeicosane; alicyclic diamines such as cyclohexanediamine and bis-(4-aminohexyl)methane; and aromatic diamines such as m-xylylenediamine and p-xylylenediamine. Among these, aliphatic diamines are particularly preferred, and hexamethylenediamine is particularly preferred. These diamines may be used alone or in a mixture of two or more.

The polyamide resin (sometimes called nylon resin) is not particularly limited, but it is preferable to use, for example, nylon 6, nylon 66, nylon 11, nylon 12, nylon 6.10, nylon 6.12, semi-aromatic nylon containing nylon 6T and/or 6I units, and copolymers of these nylon resins. In particular, nylon 6, nylon 66, and copolymers of nylon 6 and nylon 66 are more preferable.

Polyamide resins can be produced, for example, by a polyamide resin polymerization method in which polyamide resin raw materials are heated in the presence or absence of a catalyst. The polymerization may or may not be performed with stirring, but stirring is preferred to obtain a homogeneous product. The polymerization temperature can be set arbitrarily depending on the polymerization degree, reaction yield, and reaction time of the desired polymer, but a low temperature is preferred in terms of the quality of the final polyamide resin. The reaction rate can also be set arbitrarily. There are no restrictions on pressure, but it is preferable to reduce the pressure in the system in order to efficiently extract volatile components from the system.

The polyamide resin used in the present invention may be end-blocked with an end-blocking agent such as a carboxylic acid compound or an amine compound, if necessary. When the ends are blocked by adding a monocarboxylic acid or a monoamine, the concentration of the terminal amino group or terminal carboxyl group in the resulting nylon resin is lower than when the end-blocking agent is not used. On the other hand, when the ends are blocked with a dicarboxylic acid or a diamine, the sum of the terminal amino group and terminal carboxyl group concentrations does not change, but the concentration ratio of the terminal amino group and terminal carboxyl group changes.

Specific examples of carboxylic acid compounds include, but are not limited to, aliphatic monocarboxylic acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, myristoleic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, and arachic acid; alicyclic monocarboxylic acids such as cyclohexane carboxylic acid and methylcyclohexane carboxylic acid; benzoic acid, toluic acid, and ethylbenzoic acid. aromatic monocarboxylic acids such as phenylacetic acid; aliphatic dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassicic acid, tetradecanedioic acid, pentadecanedioic acid, and octadecanedioic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid.

Specific examples of amine compounds include, but are not limited to, aliphatic monoamines such as butylamine, pentylamine, hexylamine, heptylamine, octylamine, 2-ethylhexylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, octadecylamine, nonadecylamine, and icosylamine; alicyclic monoamines such as cyclohexylamine and methylcyclohexylamine; aromatic monoamines such as benzylamine and β-phenylethylamine; 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminopentane, and 1,7-diaminopentane; aliphatic diamines such as diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, 1,14-diaminotetradecane, 1,15-diaminopentadecane, 1,16-diaminohexadecane, 1,17-diaminoheptadecane, 1,18-diaminooctadecane, 1,19-diaminononadecane, and 1,20-diaminoeicosane; alicyclic diamines such as cyclohexanediamine and bis-(4-aminohexyl)methane; and aromatic diamines such as xylylenediamine.

The terminal group concentration of the polyamide resin is not particularly limited, but when it is necessary to improve dyeability in fiber applications or when designing a material suitable for alloying in resin applications, a high terminal amino group concentration is preferable. Conversely, when it is desired to suppress coloration or gelation under long-term aging conditions, a low terminal amino group concentration is preferable. Furthermore, when it is desired to suppress lactam regeneration during remelting, thread breakage during melt spinning due to oligomer generation, mold deposits during continuous injection molding, and die marks during continuous extrusion of a film, it is preferable that both the terminal carboxyl group concentration and the terminal amino group concentration are low. The terminal group concentration may be adjusted depending on the application, and both the terminal amino group concentration and the terminal carboxyl group concentration are preferably 1.0×10 ⁻⁵ to 15.0×10 ⁻⁵ eq/g, more preferably 2.0×10 ⁻⁵ to 12.0×10 ⁻⁵ eq/g, and particularly preferably 3.0×10 ⁻⁵ to 11.0×10 ⁻⁵ eq/g.

Methods for adding the end-capping agent include adding it simultaneously with raw materials such as caprolactam at the beginning of polymerization, adding it during polymerization, or adding it when the nylon resin is passed through a vertical agitation-type thin-film evaporator in a molten state. The end-capping agent may be added as is, or dissolved in a small amount of solvent.

From the viewpoints of resin properties, versatility, and cost, the polyamide-based resin is preferably a polyamide-based resin mainly composed of at least one selected from the group consisting of nylon 6 and nylon 66. In one or more embodiments of the present invention, "a polyamide-based resin mainly composed of at least one selected from the group consisting of nylon 6 and nylon 66" means a polyamide-based resin containing 80 mol % or more of nylon 6 and/or nylon 66.

The polyamide resin composition constituting the sheath may contain other resins in addition to the polyamide resin. Examples of the other resins include polyamide resins, vinyl chloride resins, modacrylic resins, polycarbonate resins, polyolefin resins, and polyphenylene sulfide resins. These may be used alone or in combination of two or more.

In one or more embodiments of the present invention, from the viewpoint of improving curl set properties, the core is preferably composed of a polyester resin composition containing a polyester resin, i.e., a polyester resin composition mainly composed of a polyester resin. In one or more embodiments of the present invention, the term "polyester resin composition mainly composed of a polyester resin" means that the polyester resin composition contains 67% by weight or more of polyester resin when the total weight of the polyester resin composition is taken as 100% by weight, and preferably contains 75% by weight or more, more preferably contains 85% by weight or more, even more preferably contains 90% by weight or more, and even more preferably contains 95% by weight or more.

From the viewpoints of physical properties, versatility, and cost, the polyester-based resin is preferably one or more selected from the group consisting of polyalkylene terephthalate and copolymer polyesters mainly composed of polyalkylene terephthalate. In one or more embodiments of the present invention, "copolymer polyesters mainly composed of polyalkylene terephthalate" refers to copolymer polyesters containing 80 mol % or more of polyalkylene terephthalate.

Examples of polyalkylene terephthalates include, but are not limited to, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polycyclohexanedimethylene terephthalate, etc.

Copolymer polyesters mainly composed of polyalkylene terephthalate are not particularly limited, but examples include copolymer polyesters mainly composed of polyalkylene terephthalate, such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polycyclohexanedimethylene terephthalate, and containing other copolymerization components.

Other copolymerization components include, for example, polycarboxylic acids and derivatives thereof, such as isophthalic acid, orthophthalic acid, naphthalenedicarboxylic acid, paraphenylenedicarboxylic acid, trimellitic acid, pyromellitic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; dicarboxylic acids and derivatives thereof, including sulfonates, such as 5-sodium sulfoisophthalic acid and 5-sodium dihydroxyethyl sulfoisophthalate; 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, diethylene glycol, polyethylene glycol, trimethylolpropane, pentaerythritol, 4-hydroxybenzoic acid, ε-caprolactone, and ethylene glycol ether of bisphenol A.

From the viewpoint of stability and ease of operation, it is preferable to produce the copolymerized polyester by reacting the main polyalkylene terephthalate with a small amount of other copolymerization components. As the polyalkylene terephthalate, a polymer of terephthalic acid and/or its derivatives (e.g., methyl terephthalate) and alkylene glycol can be used. The copolymerized polyester may be produced by polymerizing a mixture of terephthalic acid and/or its derivatives (e.g., methyl terephthalate) used in the polymerization of the main polyalkylene terephthalate and alkylene glycol, which contains a small amount of other copolymerization components, such as monomers or oligomers.

Copolymer polyesters are those in which the above-mentioned other copolymer components are polycondensed onto the main chain and/or side chain of the main polyalkylene terephthalate, and there are no particular limitations on the copolymerization method, etc.

Specific examples of copolymer polyesters mainly composed of polyalkylene terephthalate include polyesters mainly composed of polyethylene terephthalate copolymerized with a compound selected from the group consisting of ethylene glycol ether of bisphenol A, 1,4-cyclohexadimethanol, isophthalic acid, and 5-dihydroxyethyl sodium sulfoisophthalate.

Polyalkylene terephthalate and copolymer polyesters mainly composed of polyalkylene terephthalate may be used alone or in combination of two or more. Among them, it is preferable to use polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyester mainly composed of polyethylene terephthalate and copolymerized with ethylene glycol ether of bisphenol A, polyester mainly composed of polyethylene terephthalate and copolymerized with 1,4-cyclohexanedimethanol, polyester mainly composed of polyethylene terephthalate and copolymerized with isophthalic acid, and polyester mainly composed of polyethylene terephthalate and copolymerized with 5-sodium dihydroxyethyl sulfoisophthalate, alone or in combination of two or more.

The intrinsic viscosity of the polyester resin (sometimes referred to as IV value) is not particularly limited, but is preferably 0.3 to 1.2, more preferably 0.4 to 1.0. If the intrinsic viscosity is 0.3 or more, the mechanical strength of the resulting fiber will not decrease, and there will be no risk of dripping during a combustion test. Also, if the intrinsic viscosity is 1.2 or less, the molecular weight will not increase too much, the melt viscosity will not become too high, melt spinning will be easy, and the fineness will tend to be uniform.

The polyester resin composition constituting the core may contain other resins in addition to the polyester resin which is the main component resin. Examples of other resins include polyamide resins, vinyl chloride resins, modacrylic resins, polycarbonate resins, polyolefin resins, and polyphenylene sulfide resins. These may be used alone or in combination of two or more.

In order to make the feel and appearance of the core-sheath composite fiber for artificial hair more similar to that of human hair and to further improve curling properties and curl retention, it is preferable that the core be composed of a polyester-based resin composition mainly composed of one or more polyester-based resins selected from the group consisting of polyalkylene terephthalate and copolymer polyesters mainly composed of polyalkylene terephthalate, and it is even more preferable that the sheath be composed of a polyamide-based resin composition mainly composed of at least one polyamide-based resin selected from the group consisting of nylon 6 and nylon 66.

In one or more embodiments of the present invention, a flame retardant may be used in combination from the viewpoint of flame retardancy. Examples of the flame retardant include bromine-containing flame retardants and phosphorus-containing flame retardants. Examples of the phosphorus-containing flame retardant include, for example, phosphoric acid ester amide compounds and organic cyclic phosphorus compounds. Examples of the bromine-containing flame retardant include, but are not limited to, brominated epoxy flame retardants; bromine-containing phosphate esters such as pentabromotoluene, hexabromobenzene, decabromodiphenyl, decabromodiphenyl ether, bis(tribromophenoxy)ethane, tetrabromophthalic anhydride, ethylene bis(tetrabromophthalimide), ethylene bis(pentabromophenyl), octabromotrimethylphenylindane, and tris(tribromoneopentyl)phosphate; brominated polystyrenes; brominated polybenzyl acrylates; brominated Examples of suitable flame retardants include phenoxy resins, brominated polycarbonate oligomers, tetrabromobisphenol A derivatives such as tetrabromobisphenol A, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(allyl ether), and tetrabromobisphenol A-bis(hydroxyethyl ether), bromine-containing triazine compounds such as tris(tribromophenoxy)triazine, and bromine-containing isocyanuric acid compounds such as tris(2,3-dibromopropyl)isocyanurate. Among these, from the viewpoints of heat resistance and flame retardancy, it is preferable to use a brominated epoxy flame retardant.

Brominated epoxy flame retardants having molecular terminals of epoxy groups or tribromophenol can be used as raw materials for the brominated epoxy flame retardant, but the structure of the brominated epoxy flame retardant after melt-kneading is not particularly limited, and when the total number of the structural units shown in the following formula (1) and the structural units obtained by modifying at least a part of the following formula (1) is taken as 100 mol%, it is preferable that 80 mol% or more are structural units shown in the following formula (1). The structure of the brominated epoxy flame retardant may change at the molecular terminal after melt-kneading. For example, the molecular terminal of the brominated epoxy flame retardant may be substituted with a hydroxyl group, a phosphoric acid group, a phosphonic acid group, etc. other than an epoxy group or tribromophenol, and the molecular terminal may be bonded to a polyester component by an ester group.

In addition, a part of the structure of the brominated epoxy flame retardant other than the molecular terminal may change. For example, a secondary hydroxyl group and an epoxy group of the brominated epoxy flame retardant may be bonded to form a branched structure, and a part of the bromine in the above formula (1) may be eliminated or added, as long as the bromine content in the brominated epoxy flame retardant molecule does not change significantly.

As the brominated epoxy flame retardant, for example, a polymeric brominated epoxy flame retardant as shown in the following formula (2) is preferably used. In the following formula (2), m is 1 to 1000. As the polymeric brominated epoxy flame retardant as shown in the following formula (2), for example, a commercially available product such as the brominated epoxy flame retardant (product name "SR-T2MP") manufactured by Sakamoto Yakuhin Kogyo Co., Ltd. may be used.

The brominated epoxy flame retardant is not particularly limited, but is preferably contained in the core and/or sheath in an amount of, for example, 5 to 40 parts by weight per 100 parts by weight of the main component resin. For example, from the viewpoint of heat resistance and flame retardancy, the core is preferably composed of 100 parts by weight of one or more polyester-based resins selected from the group consisting of polyalkylene terephthalate and copolymer polyesters mainly composed of polyalkylene terephthalate, and a polyester-based resin composition containing 5 to 40 parts by weight of a brominated epoxy flame retardant, and the sheath is preferably composed of 100 parts by weight of a polyamide-based resin mainly composed of at least one selected from the group consisting of nylon 6 and nylon 66, and a polyamide-based resin composition containing 5 to 40 parts by weight of a brominated epoxy flame retardant.

In one or more embodiments of the present invention, a flame retardant auxiliary may be used in combination. The flame retardant auxiliary is not particularly limited, but from the viewpoint of flame retardancy, it is preferable to use an antimony-based compound or a composite metal containing antimony. Examples of antimony-based compounds include antimony trioxide, antimony tetraoxide, antimony pentoxide, sodium antimonate, potassium antimonate, and calcium antimonate. In terms of the flame retardancy improving effect and the influence on the touch, one or more selected from the group consisting of antimony trioxide, antimony pentoxide, and sodium antimonate are more preferable.

The flame retardant auxiliary is not particularly limited, but it is preferable to include, for example, 0.1 parts by weight or more and 10 parts by weight or less per 100 parts by weight of the main component resin in the core and/or sheath.

In particular, by incorporating a flame retardant auxiliary into the polyamide resin composition that constitutes the sheath, appropriate surface irregularities are formed on the fiber surface, resulting in a core-sheath composite fiber for artificial hair that is flame retardant as well as has a low gloss appearance similar to that of human hair.

If necessary, the core-sheath composite fiber for artificial hair may contain various additives such as heat resistance agents, stabilizers, fluorescent agents, antioxidants, and antistatic agents within the range that does not impair the effects of the present invention.

(Method of manufacturing core-sheath composite fiber)
In one or more embodiments of the present invention, the core-sheath composite fiber for artificial hair can be produced by melt-kneading the resin compositions constituting the core and the sheath separately using various general kneading machines, and then melt-spinning the resin compositions using a core-sheath composite nozzle.

For example, a polyester resin composition obtained by dry-blending the above-mentioned polyester resin, brominated epoxy flame retardant, and other components can be melt-kneaded using various general kneading machines to form the core component that constitutes the core portion, while a polyamide resin composition obtained by dry-blending the above-mentioned polyamide resin, brominated epoxy flame retardant, and other components can be melt-kneaded using various general kneading machines to form the sheath component that constitutes the sheath portion, and the sheath component can be melt-spun using a composite spinning nozzle to produce the product.

Examples of kneading machines include single-screw extruders, twin-screw extruders, rolls, Banbury mixers, kneaders, etc. Among these, twin-screw extruders are preferred from the standpoint of adjusting the degree of kneading and ease of operation.

In the melt spinning method, for example, in the case of a polyester-based resin composition, the temperature of the extruder, gear pump, nozzle, etc. is set to 250°C or higher and 300°C or lower, and in the case of a polyamide-based resin composition, the temperature of the extruder, gear pump, nozzle, etc. is set to 260°C or higher and 320°C or lower, and melt spinning is performed. The spun yarn is passed through a heating barrel, cooled to below the glass transition point of each resin, and taken up at a speed of 50 m/min to 5,000 m/min to obtain a spun yarn (undrawn yarn).

Specifically, during melt spinning, the polyester resin composition constituting the core is fed by a core extruder of the melt spinning machine, and the polyamide resin composition constituting the sheath is fed by a sheath extruder of the melt spinning machine, and the molten polymer is extruded through a core-sheath composite spinning nozzle (hole) having a specified shape to obtain a spun yarn (undrawn yarn).

It is preferable that the spun yarn (undrawn yarn) is hot drawn. The drawing may be performed by either a two-step method in which the spun yarn is once wound and then drawn, or a direct spin-drawing method in which the spun yarn is continuously drawn without being wound. Hot drawing is performed by a one-stage drawing method or a multi-stage drawing method having two or more stages. Heating means for hot drawing include a heated roller, a heat plate, a steam jet device, a hot water bath, etc., and these can also be used in combination as appropriate.

In one or more embodiments of the present invention, the core-sheath composite fiber for artificial hair may be treated with oils such as fiber treatment agents and softeners to make the feel and texture closer to that of human hair.

Examples of fiber treatment agents include silicone-based fiber treatment agents and non-silicone-based fiber treatment agents to improve the feel and combability.

In one or more embodiments of the present invention, the core-sheath composite fiber for artificial hair may be processed by gear crimping. This gives the fiber a gentle bend, giving it a natural appearance, and improving combability by reducing adhesion between the fibers.

In gear crimp processing, the fiber is generally heated above its softening temperature and passed between two meshing gears, and the shape of the gears is transferred to the fiber to create a bent fiber. If necessary, the core-sheath composite fiber for artificial hair can be heat-treated at different temperatures during the fiber manufacturing stage to create curls of different shapes.

(Headwear products)
In one or more embodiments of the present invention, the core-sheath composite fiber for artificial hair can be suitably used for head decoration products. The head decoration product is not particularly limited, but is preferably one selected from the group consisting of hair wigs, hairpieces, weaving, hair extensions, braided hair, hair accessories, and doll hair, and from the viewpoint of more effectively exerting the sufficiently excellent curl setting property according to the present invention, hair wigs and weaving are more preferred.

Head ornament products may be composed solely of the core-sheath composite fiber for artificial hair of the present invention, or may be composed in combination with other core-sheath composite fibers for artificial hair and natural fibers such as human hair or animal hair.

The present invention will be described in more detail below with reference to examples. Note that the present invention is not limited to these examples.

The measurement and evaluation methods used in the examples and comparative examples are as follows.

(Single fiber fineness)
Measurements were made using an auto-blow type fineness meter "DENIER COMPUTER Type DC-11" (manufactured by Search Co., Ltd.), and the average value of the measurements for 30 samples was calculated to determine the single fiber fineness.

(Curl setting ability)
The filament was wound around a φ32 mm pipe at room temperature (23° C.), curl-set at 120° C. for 60 minutes, and aged at room temperature (23° C.) for 60 minutes. One end of the curled filament was then fixed and hung down, and the length of the filament after setting was measured. This length was used as an index of curl setting ability, and it was determined that curl setting was possible when it was 17 cm or less.

(Exposed core)
At room temperature (23° C.), the fibers were bundled and fixed with a shrink tube so that the fiber bundle (total fineness 550 dtex) would not shift, and then the bundle was cut with a cutter. The presence or absence of exposure of the core was evaluated by visual inspection, or the cross section of the cut fiber was observed and evaluated with a laser microscope (manufactured by Keyence Corporation, "VK-9500").

(Fiber Cross-Sectional Shape)
At room temperature (23°C), the fibers were bundled and fixed with a shrink tube so that the fiber bundle (total fineness 550 dtex) would not shift, and then cut into rings with a cutter to prepare a fiber bundle for cross-sectional observation. This fiber bundle was photographed with a laser microscope (manufactured by Keyence Corporation, "VK-9500") at a magnification of 500 times to obtain a fiber cross-sectional photograph. Based on the fiber cross-sectional photograph, the core-sheath ratio, L/S, and Lc/Sc were determined.

(Tactile sensation)
A sensory evaluation was conducted by a professional hairdresser and rated according to the following four-level scale.
A: Very good feel equivalent to human hair B: Good feel, but slightly inferior to human hair C: Poor feel, inferior to human hair D: Poor feel, significantly inferior to human hair

(Combability)
The curls were completely straightened, and the fibers were cut to a length of 63.5 cm. 5.0 g of the fibers with a fiber length of 63.5 cm were bundled. The fiber bundle was then tied in the center with a string, folded in half, and the string portion was fixed to prepare a fiber bundle for hair iron processing. Next, a hair iron (manufactured by IZUNAMI.INC., USA, "IZUNAMI ITC450 flat iron") heated to 180°C was used to press and heat the fiber bundle from the root to the tip, five times, to prepare a fiber bundle for combability evaluation. Then, a comb (manufactured by Germany, "MATADOR PROFESSIONAL386.81/2F") was used to comb the fiber bundle for combability evaluation from the root to the tip 100 times, and the combability was evaluated based on the number of deformed or split fibers according to the following criteria.
A: Less than 10 fibers are deformed or split after 100 passes, and the comb can be passed through without resistance to the end. B: Between 10 and 30 fibers are deformed or split after 100 passes, and the resistance increases slightly along the way, but the comb can be passed through. C: Between 30 and 100 fibers are deformed or split after 100 passes, and the resistance increases along the way, with a probability of the comb not being able to pass through with 1 or more but less than 20 passes. D: More than 100 fibers are deformed or split after 100 passes, and the resistance increases along the way, with a probability of the comb not being able to pass through with 20 or more passes.

Example 1
To 100 parts by weight of polyethylene terephthalate pellets (manufactured by East West Chemical Private Limited, EastPET product name "A-12", hereinafter also referred to as "PET"), 20 parts by weight of a brominated epoxy flame retardant (manufactured by Sakamoto Yakuhin Kogyo, product name "SR-T2MP") and 2 parts by weight of sodium antimonate (manufactured by Nippon Seiko, product name "SA-A") were added, dry blended, and then fed to a twin-screw extruder, melt-kneaded at a barrel setting temperature of 280°C, and pelletized to obtain a polyester resin composition.

Next, 20 parts by weight of a brominated epoxy flame retardant (manufactured by Sakamoto Yakuhin Kogyo, product name "SR-T2MP") and 2 parts by weight of sodium antimonate (manufactured by Nippon Seiko, product name "SA-A") were added to 100 parts by weight of nylon 6 (manufactured by Unitika, product name "A1030BRL", hereafter also referred to as "PA6"), dry-blended, and then fed into a twin-screw extruder, melt-kneaded at a barrel setting temperature of 260°C, and pelletized to obtain a polyamide resin composition.

Next, the polyester resin composition and polyamide resin composition in pellet form were each fed into an extruder, extruded from a core-sheath type composite spinning nozzle (hole) having the flattening ratio and shape shown in Table 1 below, and wound up at a speed of 40 to 200 m/min to obtain an undrawn yarn of a core-sheath composite fiber having the polyester resin composition as the core and the polyamide resin composition as the sheath, a core-sheath ratio of 5:5 in terms of area ratio, and a cross-sectional shape shown in Table 1 below. The nozzle flattening ratio is the ratio of the length of the major axis, which is the longest line segment among the line segments connecting any two points on the periphery of the cross section parallel to the axis of linear symmetry and the axis of linear symmetry in the nozzle cross section, to the length of the minor axis, which is the longest line segment among the line segments connecting any two points on the periphery of the fiber cross section perpendicular to the major axis.

The resulting undrawn yarn was drawn using a heated roll at 85°C while being taken up at a speed of 45 m/min to produce a 3x drawn yarn, which was then continuously taken up at a speed of 45 m/min using a heated roll heated to 200°C and heat-treated. A polyether-based oil agent (Marubishi Chemical Industries, product name "KWC-Q") was then applied to the yarn to a concentration of 0.20% omf (pure oil agent weight percentage relative to the dry fiber weight), and the yarn was then dried to obtain a core-sheath composite fiber having the single fiber fineness shown in Table 1 below.

Example 2
A core-sheath composite fiber was obtained in the same manner as in Example 1, except that the resin used for the sheath was nylon 66 (manufactured by Toray Industries, Inc., product name "Amilan CM3001"), the barrel temperature during pelletization was set to 280°C, and the core-sheath ratio was set to 7:3 in terms of area ratio.

Example 3
A core-sheath composite fiber was obtained in the same manner as in Example 1, except that the core-sheath ratio was set to 8:2 in terms of area ratio.

Example 4
A core-sheath composite fiber was obtained in the same manner as in Example 1, except that the nozzle flatness ratio was set to 1.4.

(Comparative Example 1)
Core-sheath composite fibers were obtained in the same manner as in Example 1, except that the nozzle shape was changed to the shape shown in Table 1 below.

(Comparative Example 2)
Core-sheath composite fibers were obtained in the same manner as in Example 2, except that the nozzle shape was changed to the shape shown in Table 1 below.

(Comparative Example 3)
Core-sheath composite fibers were obtained in the same manner as in Example 1, except that the nozzle shape was changed to the shape shown in Table 1 below.

(Comparative Example 4)
Core-sheath composite fibers were obtained in the same manner as in Example 1, except that the core-sheath ratio was set to 2:8 in terms of area ratio and the nozzle shape was set to the shape shown in Table 1 below.

(Comparative Example 5)
A core-sheath composite fiber was obtained in the same manner as in Example 1, except that the core-sheath ratio was set to 9:1 in terms of area ratio.

(Comparative Example 6)
Core-sheath composite fibers were obtained in the same manner as in Example 4, except that the nozzle shape was changed to the shape shown in Table 1 below.

The presence or absence of exposed cores and cross-sectional shapes of the fibers of the Examples and Comparative Examples were evaluated and observed as described above. The curl setting properties, touch, and combability of the fibers of the Examples and Comparative Examples were also evaluated as described above. These results are shown in Table 1.

Figure 2 is a laser microscope photograph of the fiber cross section of the fiber of Example 1. As can be seen from Figure 2, in the sheath-core composite fiber for artificial hair, the fiber has a flattened bilobal cross section, and the core has a modified flattened bilobal cross section with a pair of convex parts protruding from the center side to the outer periphery along the short axis direction of the fiber cross section. Figure 3 is a laser microscope photograph of the fiber cross section of the fiber of Comparative Example 1. As shown in Figure 3, in the sheath-core composite fiber for artificial hair, both the fiber and the core have a flattened bilobal cross section. Figure 4 is a laser microscope photograph of the fiber cross section of the fiber of Comparative Example 3. As shown in Figure 4, in the sheath-core composite fiber for artificial hair, both the fiber and the core have an approximately circular cross section.

As can be seen from Table 1, the fibers of Examples 1 to 4 had good curl setting properties, no exposed core, a feel similar to human hair, and were easy to comb.

On the other hand, the fibers of Comparative Examples 1, 2, and 6, which do not have a pair of convex portions in the cross-sectional shape of the core, had poor curl set properties. The fiber of Comparative Example 3, which has a circular fiber cross-section, had an unnatural appearance because it did not have any unevenness on the fiber surface, and the fiber did not have good touch or combability. The fiber of Comparative Example 4, in which the core-sheath ratio was 2:8 by area, had poor curl set properties because the core was too small. The fiber of Comparative Example 5, in which the core-sheath ratio was 9:1 by area, had a sheath that was too thin, exposing the core, and had very poor touch and combability.

The present invention is not particularly limited, but may include, for example, the following embodiments.
[1] A core-sheath composite fiber for artificial hair, comprising a core and a sheath,
The core-sheath composite fiber for artificial hair has a flat bilobal or elliptical cross-sectional shape, and the core-sheath ratio in the fiber cross-section is 3:7 to 8:2 in terms of area ratio,
the sheath is made of a polyamide-based resin composition containing a polyamide-based resin,
The core portion has a cross-sectional shape of a deformed flat biloba or a deformed ellipse having a pair of convex portions protruding from the center side toward the outer periphery along the minor axis of the fiber cross section.
[2] The sheath-core composite fiber for artificial hair according to [1], wherein the sheath-core composite fiber for artificial hair has a flattened bilobal cross-sectional shape, and the core portion has a modified flattened bilobal cross-sectional shape.
[3] The core-sheath composite fiber for artificial hair according to [1] or [2], wherein the core is composed of a polyester-based resin composition containing one or more polyester-based resins selected from the group consisting of polyalkylene terephthalates and copolymer polyesters mainly composed of polyalkylene terephthalates.
[4] The core-sheath composite fiber for artificial hair according to any one of [1] to [3], wherein the sheath is composed of a polyamide-based resin composition containing a polyamide-based resin mainly composed of at least one type selected from the group consisting of nylon 6 and nylon 66.
[5] A head accessory comprising the core-sheath composite fiber for artificial hair according to any one of [1] to [4].
[6] The head accessory product according to [5], which is one selected from the group consisting of hair wigs, hairpieces, weaving, hair extensions, braided hair, hair accessories and doll hair.
[7] A method for producing a sheath-core composite fiber for artificial hair according to any one of [1] to [4], comprising a step of melt-spinning a core resin composition and a sheath resin composition using a core-sheath type composite nozzle.

1. Core-sheath composite fiber for artificial hair (cross section)
10: Sheath portion 20: Core portion 30: Protruding portion

Claims (6)

A core-sheath composite fiber for artificial hair, comprising a core and a sheath,
The core-sheath composite fiber for artificial hair has a flat bilobal cross-sectional shape, and the core-sheath ratio in the fiber cross-section is 3:7 to 8:2 in terms of area ratio,
the sheath is made of a polyamide-based resin composition containing a polyamide-based resin,
the core portion has a cross-sectional shape formed by a shape formed by the four tangents to the ellipse and the curved portions on both sides of the long axis of the ellipse when two perpendicular lines are drawn from both sides equidistant from the center of the long axis of the ellipse and four tangents to the ellipse from two intersections of the two perpendicular lines and the long axis of the ellipse toward the center,
a long axis direction of the core cross section substantially coincides with a long axis direction of the fiber cross section, and a short axis direction of the core cross section substantially coincides with a short axis direction of the fiber cross section,
The sheath-core composite fiber for artificial hair is a concentric sheath-core type. The core-sheath composite fiber for artificial hair according to claim 1, wherein the core is composed of a polyester-based resin composition containing one or more polyester-based resins selected from the group consisting of polyalkylene terephthalates and copolymer polyesters mainly composed of polyalkylene terephthalates. The core-sheath composite fiber for artificial hair according to claim 1 or 2, wherein the sheath portion is composed of a polyamide-based resin composition containing at least one polyamide-based resin selected from the group consisting of nylon 6 and nylon 66. A head accessory comprising the core-sheath composite fiber for artificial hair according to any one of claims 1 to 3. The head accessory product according to claim 4, which is one selected from the group consisting of hair wigs, hairpieces, weaving, hair extensions, braided hair, hair accessories and doll hair. A method for producing the core-sheath composite fiber for artificial hair according to any one of claims 1 to 5, comprising the steps of:
A method for producing a core-sheath composite fiber for artificial hair, comprising the step of melt-spinning a core resin composition and a sheath resin composition using a core-sheath composite nozzle.

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