EP4692434A1

EP4692434A1 - Core-sheath composite fiber and nonwoven fabric formed therefrom

Info

Publication number: EP4692434A1
Application number: EP24778675.9A
Authority: EP
Inventors: Tsukasa Yoshikawa; Yumin Li; Yusuke KOJO; Shinichi JIZODO; Shinichi KOBUCHI
Original assignee: Toyobo MC Corp
Current assignee: Toyobo MC Corp
Priority date: 2023-03-31
Filing date: 2024-02-02
Publication date: 2026-02-11
Also published as: JPWO2024202530A1; WO2024202530A1; CN120958184A; KR20250166204A; TW202441044A

Abstract

It is an object of the present invention to provide a core-sheath conjugate fiber that exhibits excellent white opacity without using titanium oxide. The core-sheath conjugate fiber of the present invention includes a core component containing a polyester resin; and a sheath component containing a polyolefin resin having a melting point that is lower than a melting point of the polyester resin by 20°C or more, wherein either or both of the core component and the sheath component contain calcium carbonate in an amount of more than 1.0% by mass and 30.0% by mass or less based on 100% by mass of each component, the core component has a maximum peak temperature of crystal melting of lower than 255°C, as measured with a differential scanning calorimeter, and the fiber has an L* value of 91 or more and a b* value of 5.0 or less, which indicate a hue of the fiber.

Description

TECHNICAL FIELD

The present invention relates to a heat-bondable conjugate fiber that exhibits enhanced safety, high opacity, and improved sustainability, while maintaining processability into nonwoven fabrics, and to a nonwoven fabric formed therefrom, which are available in applications such as absorbent articles for sanitary materials including diapers, napkins, and pads; medical sanitary materials; life-related materials; general medical materials; bedding materials; filter materials; nursing care products; and pet supplies.

BACKGROUND ART

Some nonwoven fabrics used in sanitary applications, such as diapers and napkins, are produced by thermally bonding fiber stock that have a core-sheath structure formed from two resin components, using an air-through method. These fabrics are required to have a white appearance that gives a clean impression, and sufficient opacity to conceal the color of absorbed blood and urine.
Titanium oxide has generally been incorporated into resins to improve the opacity of fibers forming nonwoven fabrics. However, titanium oxide was classified as a Category 2 carcinogen (inhalation) under the EU CLP Regulation in October 2021. As a result, products containing more than 1% by mass of titanium oxide are required to carry specific warning statements or labeling, raising concerns regarding its safety.
Since titanium oxide has a high refractive index and excellent stability, it has been widely used as a white pigment by incorporating it into resins, accounting for 70% of the white pigments currently in use. Although other white pigments, such as zinc oxide, are also available, zinc oxide is inferior to titanium oxide in terms of safety and stability, and it is considered that zinc oxide cannot be used as an alternative to titanium dioxide in applications such as sanitary materials. Furthermore, since titanium oxide is an underground resource (mineral resource), it is less sustainable compared with biological resources, which are environmentally recyclable materials.
On the other hand, many studies have reported the incorporation of inorganic particles excluding titanium oxide and zinc oxide, or talc into resins to modify the translucency and the softness of fibers and nonwoven fabrics. However, these inorganic particles and talc have low refractive indices, which are close to that of polyester resin. Hence, it has been thought difficult to achieve white appearance and opacity comparable to those imparted by titanium oxide, simply by incorporating these inorganic particles or talc into a resin.
For example, in Patent Document 1, a soft touch and high stiffness are imparted to a nonwoven fabric by calcium carbonate; however, neither the opacity nor the hue of the fiber is examined.
Patent Document 2 discloses a multifilament fiber in which the mechanical stiffness and the thermal conductivity are improved, and the opacity is enhanced by incorporating calcium carbonate; however, neither the opacity nor the hue is examined.
In Patent Document 3, inorganic particles are incorporated into a bicomponent core-sheath conjugate fiber to improve its anti-show-through property (opacity), wherein the content of the inorganic particles in the core is from 0.10% by mass to 10% by mass, and the content of the inorganic particles in the sheath is from 0.050% by mass to 1.0% by mass. In other words, the functionality is achieved by incorporating inorganic particles into both the core and the sheath, with titanium oxide being primarily used as an inorganic particle. In one example, calcium carbonate is used in the core and aluminum oxide is used in the sheath; however, no investigation is conducted on whether the use of calcium carbonate alone can enhance the anti-show-through property.
In Patent Document 4, recycled PET is used in the core of a recycled polyester core-sheath conjugate fiber, and the hue (L* and b* values) is improved by adding 3% by mass or more of titanium oxide; however, no examination is conducted using other inorganic particles and talc.
As shown in Patent Documents 3 and 4, titanium oxide is not suitable for plastic volume reduction by reducing the amount of resin through high-concentration incorporation.

CITATION LIST

PATENT DOCUMENT

Patent Document 1: JP-A-2020-90771
Patent Document 2: JP-A-2019-112759
Patent Document 3: JP-A-2021-55231
Patent Document 4: JP-A-2006-328600

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

Accordingly, in order to overcome the drawbacks of titanium oxide as a conventional white pigment, such as safety concerns, sustainability issues, and difficulties in reducing plastic volume by high-concentration incorporation of titanium oxide, it is desirable to use inorganic particles in place of titanium oxide to provide a fiber capable of reducing resin usage and contributing to lowering environmental impact, while maintaining post-processability into nonwoven fabrics, without significantly compromising fiber quality. Furthermore, it is also desirable to provide a safe and sustainable fiber by using an inorganic substance which allows for the use of biological resources as environmentally recyclable materials.
It is an object of the present invention to provide a core-sheath conjugate fiber that exhibits excellent white opacity without using titanium oxide, and a nonwoven fabric formed therefrom.

SOLUTION TO THE PROBLEMS

The core-sheath conjugate fiber of the present invention, which achieves the above-mentioned objectives, has the following features.
A core-sheath conjugate fiber comprises:

a core component containing a polyester resin; and
a sheath component containing a polyolefin resin having a melting point that is lower than a melting point of the polyester resin by 20°C or more,
wherein either or both of the core component and the sheath component contain calcium carbonate in an amount of more than 1.0% by mass and 30.0% by mass or less based on 100% by mass of each component,
wherein the core component has a maximum peak temperature of crystal melting of lower than 255°C, as measured with a differential scanning calorimeter, and
wherein the fiber has an L* value of 91 or more and a b* value of 5.0 or less, which indicate a hue of the fiber.

The core component preferably has a crystallization peak temperature on cooling of from 190°C to 220°C, as measured with a differential scanning calorimeter.
The polyester resin preferably contains polyethylene terephthalate, and the polyolefin resin preferably contains polyethylene.
The content of the polyester resin is preferably 40% by mass or more of a total fiber.
The fiber preferably has a concentric, eccentric, or hollow cross-sectional shape.
The fiber preferably has a tensile strength of from 0.80 cN/dtex to 5.00 cN/dtex, as measured in accordance with JIS L 1013 8.5.1, and an elongation rate of from 30% to 200%, as measured in accordance with JIS L 1013 8.5.1.
The present invention includes a nonwoven fabric formed from the core-sheath conjugate fibers.

EFFECTS OF THE INVENTION

According to the present invention, a core-sheath conjugate fiber exhibiting excellent white opacity without using titanium oxide, and a nonwoven fabric formed therefrom, can be provided.
Thus, the core-sheath conjugate fiber of the present invention exhibits enhanced safety and improved sustainability in the environment while maintaining opacity, flexibility, bulkiness, and bulkiness recovery characteristics comparable to those of a fiber containing a conventional white pigment, primarily represented by titanium oxide. Furthermore, the core-sheath conjugate fiber of the present invention enables the production of a nonwoven fabric that contributes to reducing the environmental impact through plastic volume reduction.
Furthermore, titanium oxide has high Mohs hardness and tends to cause metallic wear. As a result, fibers containing titanium oxide on their surfaces may abrade the metal rollers of processing machines, particularly during the crimping process, making it difficult to maintain a long-term stable crimping process. In the present invention, the use of calcium carbonate in the sheath component not only reduces conventional problems such as wear of yarn guides and travelers during drawing, which are problems observed in fibers with titanium oxide on their surfaces, but also improves the white opacity of the fiber. Also, in the present invention, the white opacity of the fiber is improved by using calcium carbonate in the core component. Thus, a bicomponent conjugate fiber for a nonwoven fabric that exhibits white appearance, opacity, and flexibility comparable to those of a conventional fiber containing titanium oxide can be obtained, while exhibiting a smooth fiber surface.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] FIG. 1 shows the measurement result obtained by measuring, with a differential scanning calorimeter, the polyester resin containing calcium carbonate used as the core component in Comparative Example 3.
[FIG. 2] FIG. 2 shows the measurement result obtained by measuring, with a differential scanning calorimeter, the polyester resin containing calcium carbonate used as the core component in Example 1.
[FIG. 3] FIG. 3 shows the measurement result obtained by measuring, with a differential scanning calorimeter, the polyester resin containing calcium carbonate used as the core component in Example 5.
[FIG. 4] FIGs. 4(a) to (c) are schematic diagrams illustrating the orientation of polymer chains contained in an undrawn resin, the presence or absence of added calcium carbonate, and the mechanism by which the degree of whiteness (opacity) of the fiber is developed through the orientation of polymer chains contained in the resin, induced by drawing.

DESCRIPTION OF EMBODIMENTS

[Core-Sheath Conjugate Fiber]

The core-sheath conjugate fiber of the present invention includes a core component containing a polyester resin and a sheath component containing a polyolefin resin having a melting point that is lower than the melting point of the polyester resin by 20°C or more, wherein either or both of the core component and the sheath component contain calcium carbonate in an amount of more than 1.0% by mass and 30.0% by mass or less based on 100% by mass of each component; the core component has a maximum peak temperature of crystal melting lower than 255°C, as measured with a differential scanning calorimeter; and the fiber has an L* value of 91 or more and a b* value of 5.0 or less, which indicate the hue of the core-sheath conjugate fiber.
The fiber contains calcium carbonate in either or both of the core component and the sheath component. By drawing the fiber, the orientation of the polyester resin is enhanced and the crystal size of the polyester resin increases in the presence of calcium carbonate. As a result, the degree of whiteness (opacity) of the core-sheath conjugate fiber can be improved.
The present invention includes (i) a core-sheath conjugate fiber containing calcium carbonate only in the core component (first embodiment), (ii) a core-sheath conjugate fiber containing calcium carbonate only in the sheath component (second embodiment), and (iii) a core-sheath conjugate fiber containing calcium carbonate in both of the core component and the sheath component (third embodiment). Unless otherwise specified as the first embodiment, the second embodiment, or the third embodiment, the following description shall be deemed to refer to all these embodiments.

The core component contains the polyester resin.
The polyester resin is not particularly limited as long as it exhibits strength and low shrinkage as the core component. Examples of the polyester resin include polyethylene terephthalate (melting point: 255°C), polybutylene terephthalate (melting point: 230°C), polytrimethylene terephthalate (melting point: 230°C), polyethylene naphthalate (melting point: 265°C), polybutylene naphthalate (melting point: 243°C), polyhydroxyalkanoate (melting point: approximately 180°C), polyhydroxybutyrate (melting point: 175°C), and polylactic acid (melting point: from 170°C to 175°C).
Among these, from the viewpoint of strength, low shrinkage, and ensuring a melting point at least 20°C higher than that of the polyolefin resin used in the sheath component, the polyester resin preferably contains a polyester resin having a melting point of 200°C or higher (preferably 210°C or higher, more preferably 220°C or higher and 280°C or lower). The polyester resin more preferably contains polyethylene terephthalate (melting point: 255°C), polybutylene terephthalate (melting point: 230°C), polytrimethylene terephthalate (melting point: 230°C), polyethylene naphthalate (melting point: 265°C), and/or polybutylene naphthalate (melting point: 243°C), further preferably contains polyethylene terephthalate (melting point: 255°C), polyethylene naphthalate (melting point: 265°C), and/or polybutylene naphthalate (melting point: 243°C), and particularly preferably contains polyethylene terephthalate (melting point: 255°C). These polyester resins may be used alone or in combination with two or more types.
The polyester resin may have a predetermined intrinsic viscosity. The intrinsic viscosity (IV) of the polyester resin is preferably from 0.3 dl/g to 2.0 dl/g, more preferably from 0.5 dl/g to 1.5 dl/g, and further preferably from 0.55 dl/g to 0.80 dl/g.
The intrinsic viscosity (IV) of the polyester resin is determined by crushing and drying the sample, dissolving it in a 6/4 (mass ratio) mixed solvent of phenol/1,1,2,2-tetrachloroethane, subjecting the resulting solution to centrifugation to remove inorganic particles, and then measuring it at 30°C using an Ubbelohde viscometer.
The content of the polyester resin having a melting point of 200°C or higher is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, further more preferably 97% by mass or more, particularly preferably 99% by mass or more, and most preferably 100% by mass, based on 100% by mass of the polyester resin.
When the content of the polyester resin having a melting point of 200°C or higher falls within the above range, drawing of the fiber containing calcium carbonate can promote crystallization of the polyester resin, thereby enhancing the degree of whiteness of the fiber.
In each of the first and third embodiments, the content of the polyester resin is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, further more preferably 95% by mass or more, and preferably less than 99% by mass, more preferably 98% by mass or less, further preferably 97% by mass or less, further more preferably 96% by mass or less, based on 100% by mass of the core component.
When the content of the polyester resin is less than 70% by mass, the strength of the core may be reduced, thereby potentially lowering the adhesion between the core and the sheath. When the content of the polyester resin is 99% by mass or more, the crystallization of the polyester resin may not be promoted, and a high degree of whiteness may not be achieved.
In the second embodiment, the content of the polyester resin is preferably 100% by mass, based on 100% by mass of the core component.
The content of the polyester resin is, from the viewpoint of the strength of the core, preferably 40% by mass or more, more preferably 45% by mass or more and 75% by mass or less, further preferably 50% by mass or more and 70% by mass or less, and further more preferably 55% by mass or more and 65% by mass or less of a total fiber.
In each of the first and third embodiments, the calcium carbonate contained in the core component may be heavy calcium carbonate, light calcium carbonate, or a mixture thereof.
The heavy calcium carbonate may be obtained by grinding and classifying a natural material such as limestone, marble, calcite, or chalk. The heavy calcium carbonate is also referred to as natural calcium carbonate.
The light calcium carbonate may be produced by precipitating crystals in a liquid through a chemical reaction (for example, a precipitate formed by the reaction of calcium hydroxide with carbon dioxide), and is also referred to as synthetic calcium carbonate or precipitated calcium carbonate.
The calcium carbonate may be surface-treated with a fatty acid, siloxane, or resin.
Examples of the fatty acid include stearic acid, palmitic acid, myristic acid, and lauric acid, and the fatty acid may be used in the form of a salt or an ester.
Examples of the resin include polyacrylate and polydiallyldimethylammonium chloride.
The calcium carbonate preferably has a predetermined average particle size d50 and a predetermined top cut particle size d90. The average particle size d50 is the particle size at which 50% by mass of the total particles are smaller than d50 in particle size, and the top cut particle size d90 is the particle size at which 90% by mass of the total particles are smaller than d90 in particle size.
The calcium carbonate used in the core has an average particle size d50 of preferably from 0.02 µm to 3.0 µm, more preferably from 0.35 µm to 1.75 µm, further preferably from 0.40 µm to 1.50 µm, and, further more preferably from 0.45 µm to 1.25 µm.
The calcium carbonate has a top cut particle size d90 of preferably 5.0 µm or less, more preferably 4.0 µm or less, further preferably 3.0 µm or less, further more preferably 2.0 µm or less, particularly preferably 1.0 µm or less, and is preferably 0.3 µm or more or 0.5 µm or more.
In each of the first and third embodiments, the content of the calcium carbonate in the core component is preferably more than 1.0% by mass and 30.0% by mass or less, more preferably 2.0% by mass or more and 25.0% by mass or less, further preferably 3.0% by mass or more and 20.0% by mass or less, and further more preferably 4.0% by mass or more and 15.0% by mass or less, based on 100% by mass of the core component. When the content of the calcium carbonate is 1.0% by mass or less, the crystallization of the polyester resin may not be promoted, and the obtained fiber may have a reduced L* value. On the other hand, if the content of the calcium carbonate is more than 30.0% by mass, the pressure rise rate in the filter used during spinning may increase. In addition, the interfacial adhesion between the core and the sheath may be reduced, leading to fuzz or breakage.
The core component may contain a component other than the polyester resin and the calcium carbonate, provided that the effects of the present invention are not impaired. Examples of such a component include additives such as an antioxidant, an antistatic agent, an anti-blocking agent, a pigment, a heat stabilizer, an ultraviolet absorber, and a lubricant. These additives may be added to the extent that they do not adversely affect the effects of the present invention.
In each of the first and third embodiments, the content of the polyester resin and the calcium carbonate in the core component is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 97% by mass or more, further more preferably 99% by mass or more, and particularly preferably 100% by mass, based on 100% by mass of the core component.
Preferably, the core component is substantially free of titanium oxide. The content of the titanium oxide is more preferably 0.5% by mass or less, further preferably 0.1% by mass or less, and further more preferably 0% by mass, based on 100% by mass of the core component.
In each of the first to third embodiments, the core component (preferably the polyester resin containing the calcium carbonate or a polyester resin free of the calcium carbonate) may have a predetermined maximum peak temperature of crystal melting, as measured by a differential scanning calorimeter. The maximum peak temperature of crystal melting of the core component is preferably lower than 255°C, more preferably from 243°C to 254°C, further preferably from 244°C to 253°C, and further more preferably from 245°C to 252°C.
The maximum peak temperature of crystal melting is observed within the above range when the core component is subjected to drawing, regardless of the presence or absence of the calcium carbonate, thereby promoting the crystallization of the polyester resin and thus enhancing the degree of whiteness of the fiber. In the case of an undrawn fiber, the maximum peak temperature of crystal melting of the core component is observed at 255°C or higher. This means that the crystallization of the polyester resin is not promoted, and the degree of whiteness of the fiber cannot be enhanced.
When the content of the calcium carbonate in the core component increases within the above range, the maximum peak temperature of crystal melting tends to increase within the above temperature range.
As a differential scanning calorimeter, for example, one manufactured by TA Instruments may be used.
The peak temperature of crystal melting is measured, for example, under the condition of a heating rate of 10°C/min, and a temperature at which a maximum appears on the measured melting endothermic curve is defined as the maximum peak temperature of crystal melting.
The crystallization peak temperature on cooling, as described later, is measured, for example, under the condition of a cooling rate of 10°C/min, and a temperature at which a maximum appears on the measured exothermic crystallization curve is defined as the crystallization peak temperature on cooling.
In each of the first to third embodiments, the core component may have a predetermined crystallization peak temperature on cooling, as measured with a differential scanning calorimeter. The crystallization peak temperature on cooling of the core component is preferably from 200°C to 220°C, more preferably from 202°C to 218°C, further preferably from 204°C to 216°C, and further more preferably from 206°C to 214°C. When the crystallization peak temperature on cooling falls within the above range, fine unoriented crystals tend to be formed, promoting the crystallization of the polyester resin.

The sheath component contains the polyolefin resin having a melting point that is lower than the melting point of the polyester resin by 20°C or more.
The polyolefin resin may be either a polyolefin homopolymer or a polyolefin copolymer.
The number of carbon atoms in the olefin monomer constituting the polyolefin resin is, for example, from 2 to 20, preferably from 2 to 15, more preferably from 2 to 10, and further preferably from 2 to 5.
Examples of the olefin monomer include ethylene, propylene, butene, pentene, hexene, heptene, octene, nonene, and decene.
Among these, the polyolefin resin contains an olefin monomer, such as ethylene, propylene, butene, pentene, or hexene as a main constitutional unit (in an amount of preferably 60 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, further more preferably 90 mol% or more, particularly preferably 95 mol% or more, preferably 100 mol% or less or 99 mol% or less, based on 100 mol% of the total constitutional units).
Examples of the polyolefin resin include polyethylenes such as a low-density polyethylene (melting point: from 100°C to 115°C), a high-density polyethylene (melting point: from 125°C to 137°C), and an ultra-high-molecular-weight polyethylene (melting point: from 135°C to 140°C); polypropylene (melting point: 165°C); polybutene-1 (melting point: from 126°C to 128°C); and 1,2-polybutadiene (melting point: from 71°C to 105°C).
When a polyolefin copolymer is used, it may be a copolymer in which a small amount of an α-olefin such as ethylene, propylene, butene, hexene, or octene is copolymerized, as a copolymerization component, with at least one of those described above.
Among these, the polyolefin resin preferably has a melting point of 180°C or lower (preferably 170°C or lower and 70°C or higher), and more preferably contains polyethylene or polypropylene, further preferably polyethylene. These polyolefin resins may be used alone or in combination with two or more types.
The polyolefin resin may have a predetermined melt flow rate (MFR), as measured in accordance with JIS K 6922-2. The melt flow rate (MFR) of the polyolefin resin, under conditions of a load of 2.16 kg and a temperature of 190°C, is preferably from 8 g/10 min to 25 g/10 min, and more preferably from 9 g/10 min to 21 g/10 min.
The polyolefin resin may have a predetermined density. The low-density polyethylene has a density of from 0.91 g/cm³ to 0.92 g/cm³; the high-density polyethylene has a density of from 0.94 g/cm³ to 0.965 g/cm³; and the polypropylene has a density of from 0.90 g/cm³ to 0.91 g/cm³.
The content of the polyolefin resin having a melting point of 180°C or lower is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, further more preferably 99% by mass or more, and particularly preferably 100% by mass, based on 100% by mass of the polyolefin resin. When the content of the polyolefin resin falls within the above range, a nonwoven fabric that has high inter-fiber adhesion due to thermal bonding can be produced.
In each of the second and third embodiments, the content of the polyolefin resin is preferably 70% by mass or more, more preferably 75% by mass or more, further preferably 80% by mass or more, further more preferably 85% by mass or more, and preferably 99% by mass or less, more preferably 98% by mass or less, further preferably 97% by mass or less, further more preferably 96% by mass or less, based on 100% by mass of the sheath component.
In the first embodiment, the content of the polyolefin resin is preferably 100% by mass, based on 100% by mass of the sheath component.
The content of the polyolefin resin is preferably at least 20% by mass or more, more preferably 25% by mass or more and 55% by mass or less, further preferably 30% by mass or more and 50% by mass or less, and further more preferably 35% by mass or more and 45% by mass or less of a total fiber.
In each of the second and third embodiments, the calcium carbonate contained in the sheath component may be heavy calcium carbonate, light calcium carbonate, or a mixture thereof, similarly to the calcium carbonate used in the core component.
The heavy calcium carbonate may be obtained by grinding and classifying a natural material such as limestone, marble, calcite, or chalk. The heavy calcium carbonate is also referred to as natural calcium carbonate.
The light calcium carbonate may be produced by precipitating crystals in a liquid through a chemical reaction (for example, a precipitate formed by the reaction of calcium hydroxide with carbon dioxide), and is also referred to as synthetic calcium carbonate or precipitated calcium carbonate.
The calcium carbonate may be surface-treated with a fatty acid, siloxane, or resin.
Examples of the fatty acid include stearic acid, palmitic acid, myristic acid, and lauric acid, and the fatty acid may be used in the form of a salt or an ester.
Examples of the resin include polyacrylate and polydiallyldimethylammonium chloride.
The calcium carbonate used in the sheath component preferably has an average particle size d50 of from 0.02 µm to 3.0 µm, more preferably from 0.10 µm to 2.0 µm, and further preferably from 0.20 µm to 1.0 µm. The top cut particle size d90 of the calcium carbonate used in the sheath component is preferably 5.0 µm or less, more preferably 4.0 µm or less, further preferably 3.0 µm or less, further more preferably 2.0 µm or less, particularly preferably 1.0 µm or less, and preferably 0.3 µm or more or 0.5 µm or more.
In each of the second and third embodiments, the content of the calcium carbonate in the sheath component is preferably more than 1.0% by mass and 30.0% by mass or less, more preferably 2.0% by mass or more and 25.0% by mass or less, further preferably 3.0% by mass or more and 20.0% by mass or less, and further more preferably 4.0% by mass or more and 15.0% by mass or less, based on 100% by mass of the sheath component. When the content of the calcium carbonate is 1.0% by mass or less, the crystallization of the polyolefin resin may not be promoted, and the obtained fiber may have a reduced L* value. On the other hand, if the content of the calcium carbonate is more than 30.0% by mass, the pressure rise rate in the filter used during spinning may increase. In addition, the interfacial adhesion between the core and the sheath may be reduced, leading to fuzz or breakage.
The calcium carbonate used in the core component and the calcium carbonate used in the sheath component may be the same or different.
The sheath component may contain a component other than the polyolefin resin and the calcium carbonate, provided that the effects of the present invention are not impaired. Examples of such a component include additives such as an antioxidant, an antistatic agent, an anti-blocking agent, a pigment, a heat stabilizer, an ultraviolet absorber, and a lubricant. These additives may be added to the extent that they do not adversely affect the effects of the present invention.
In each of the second and third embodiments, the content of the polyolefin resin and the calcium carbonate in the sheath component is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 97% by mass or more, further more preferably 99% by mass or more, and particularly preferably 100% by mass, based on 100% by mass of the sheath component.
Preferably, the sheath component is substantially free of titanium oxide. The content of the titanium oxide in the sheath component is more preferably 0.5% by mass or less, further preferably 0.1% by mass or less, and further more preferably 0% by mass, based on 100% by mass of the sheath component.
The content of the calcium carbonate is preferably from 1% by mass to 25% by mass, more preferably from 1.5% by mass to 20% by mass, and further preferably from 2.0% by mass to 15% by mass, based on 100% by mass of the core-sheath conjugate fiber. When the content of the calcium carbonate in the core-sheath conjugate fiber is adjusted within the above range, the volume reduction of the polyester resin and the polyolefin resin can be facilitated. Furthermore, the degree of whiteness of the core-sheath conjugate fiber can be enhanced by drawing.
In the core-sheath conjugate fiber of the present invention, the mass ratio of the core component to the sheath component (core component/sheath component) is preferably less than 7.0, more preferably 5.0 or less, further preferably 4.0 or less, further more preferably 3.0 or less, particularly preferably 2.0 or less, and preferably 0.2 or more or 0.3 or more.
By adjusting the mass ratio of the core component to the sheath component (core component/sheath component) to fall within the above range, the fiber can have appropriate strength and elongation for use in a nonwoven fabric.
The polyester resin, the polyolefin resin, or both resins used in the present invention may contain the calcium carbonate in an amount of more than 1.0% by mass (based on the mass of each resin). The calcium carbonate is incorporated into those resins to improve the opacity, in other words, the degree of whiteness, of the fiber, by controlling the size of the crystals formed by the resins. If the calcium carbonate content is 1.0% by mass or less, the degree of whiteness of the fiber may not be sufficiently improved for use in a nonwoven fabric.
The single-filament fineness of the core-sheath conjugate fiber is preferably from 0.1 dtex to 8.0 dtex, more preferably from 0.2 dtex to 4.8 dtex, further preferably from 0.5 dtex to 4.6 dtex, further more preferably from 1.0 dtex to 4.4 dtex, and particularly preferably from 1.5 dtex to 4.2 dtex.
The single-filament fineness of the core-sheath conjugate fiber can be measured in accordance with JIS L 1095 9.4.1.
The core-sheath conjugate fiber preferably has a concentric, eccentric, or hollow cross-sectional shape, with the concentric cross-section being more preferred.
In the concentric cross-section, the centroids of the core and the sheath coincide. In the eccentric cross-section, the centroids of the core and the sheath do not coincide. In the hollow cross-section, the fiber includes both a core and a sheath, and the core has a hollow structure.
The core-sheath conjugate fiber of the present invention has predetermined L* and b* values, as determined based on the Hunter's color difference formula, which indicate the appropriateness in the degree of whiteness for appearance quality.
Thus, the core-sheath conjugate fiber exhibits a color tone characterized by an L* value of 91 or more and a b* value of 5.0 or less.
The L* value is preferably 91.5 or more, more preferably 92 or more, further preferably 92.5 or more, further more preferably 93 or more, and preferably 99 or less or 98 or less. When the L* value is less than 91, the resulting nonwoven fabric becomes unsuitable for use in sanitary materials.
The b* value is preferably 4.5 or less, more preferably 4.0 or less, further preferably 3.5 or less, further more preferably 3.0 or less, particularly preferably 2.5 or less, and most preferably 2.0 or less. When the b* value of the core-sheath conjugate fiber is more than 5.0, the color tone becomes yellowish, and the resulting nonwoven fabric becomes unsuitable for use in sanitary materials.
The L* and b* values can be measured, for example, using a colorimeter (spectrophotometer CM-3700d manufactured by Minolta Co., Ltd,) with a sample of the core-sheath conjugate fiber that is visually confirmed to have no show-through of the black winding board when wound onto the board.
The core-sheath conjugate fiber of the present invention may have a predetermined strength and a predetermined elongation.
The fiber strength, as the tensile strength measured in accordance with JIS L 1013 8.5.1, is preferably from 0.80 cN/dtex to 5.00 cN/dtex, more preferably from 0.85 cN/dtex to 4.80 cN/dtex, further preferably from 0.90 cN/dtex to 4.60 cN/dtex, further more preferably from 0.95 cN/dtex to 4.40 cN/dtx, and particularly preferably from 1.00 cN/dtex to 4.20 cN/dtx.
The elongation of the fiber, expressed as the elongation rate measured in accordance with JIS L 1013 8.5.1, is preferably from 30% to 200%, more preferably from 35% to 190%, further preferably from 40% to 180%, further more preferably from 45% to 170%, and particularly preferably from 50% to 160%. The core-sheath conjugate fiber of the present invention exhibits an elongation rate comparable to that of typical fibers.

[Method for Preparing Core-Sheath Conjugate Fiber]

The method for producing the core-sheath conjugate fiber of the present invention preferably includes at least the following steps: the step of preparing an undrawn filament yarn by melt spinning the polyester resin as the core component and the polyolefin resin as the sheath component, with the calcium carbonate used in either or both of the core component and the sheath component, into the core-sheath shape; and the step of drawing the undrawn filament yarn under heating conditions.
The polyester resin, the polyolefin resin, the calcium carbonate, and their respective amounts to be used are as described above.
The calcium carbonate may be added in a predetermined amount and stirred during or immediately after the resin polymerization, and then dispersed either by extruding the mixture using an extruder into a chip-shape or by spinning the resin in a molten state.
Methods for uniformly dispersing the calcium carbonate in the resin include a circulation type dispersion method and a masterbatch method.
In the circulation type dispersion method, a predetermined amount of the calcium carbonate may be added immediately after the resin polymerization, and the calcium carbonate may be dispersed by circulating the molten resin.
In the masterbatch method, a predetermined amount of the calcium carbonate is preliminarily wetted with water or a solvent, then mixed with a predetermined resin using a pressure kneader, and the calcium carbonate may be dispersed while separating the water or the solvent.

Preferably, with the calcium carbonate being incorporated in either or both of the polyester resin and the polyolefin resin, each of the polyester resin and the polyolefin resin is separately melted and discharged as a molten resin from a core-sheath type spinneret via a spinning pack. The molten resin is spun from a spinneret that preferably has from 10 to 1000 orifices, more preferably from 50 to 800 orifices, further preferably from 100 to 600 orifices, and further more preferably from 200 to 400 orifices, at a spinning temperature that is 10°C to 30°C higher than the melting point of the polyester resin. The resulting spun filament may be then cooled by applying air at a temperature of preferably from 10°C to 25°C at an airflow velocity of preferably from 50 m/min to 100 m/min, and, subsequently, spinning oil may be applied to the spun filament. The resulting undrawn filament yarn may then be taken up into a container (e.g., a can) at a take-up speed of preferably from 1000 m/min to 1500 m/min.

The obtained undrawn filament yarn is drawn using a liquid or gas phase preferably at a temperature of from 60°C to 130°C at a drawing ratio of preferably from 1.5 times to 6.0 times, more preferably from 1.5 times to 5.0 times, further preferably from 1.5 times to 4.0 times, and further more preferably from 1.5 times to 3.0 times.
In particular, from the viewpoint of further increasing the L* value and further lowering the maximum peak temperature of crystal melting, the undrawn filament yarn is drawn at a drawing ratio of preferably from 1.55 times to 3.0 times, more preferably from 1.60 times to 2.9 times, and further preferably from 1.70 times to 2.8 times.
The drawing may be conducted in a single stage or in two or more stages. In the case of two-stage drawing, the drawing is preferably conducted, for example, at a temperature of from 60°C to 90°C (preferably from 60°C to 80°C) with a drawing ratio of preferably from 2.0 times to 4.0 times (preferably 3.6 times or less, more preferably 3.2 times or less) in the first-stage.
In the second-stage, the drawing is preferably conducted, for example, at a temperature of from 90°C to 130°C (preferably from 100°C to 120°C) with a drawing ratio of from 0.8 times to 1.2 times (preferably from 0.9 times to 1.1 times).
Methods for producing the core-sheath conjugate fiber of the present invention may further include a crimping process, a post-heat treatment process, and/or a cutting process, in addition to the above-mentioned processes.
In the crimping process, crimping may be carried out using a crimping machine, such as a stuffer box crimper.
In the post-heat treatment process, for example, the resulting filament may be treated at a temperature of from 90°C to 140°C (preferably from 100°C to 130°C), without tension.
When the core-sheath conjugate fiber is cut into staple fibers, the staple fibers preferably have the average length of from 30 mm to 80 mm, more preferably from 31 mm to 70 mm, and further preferably from 32 mm to 60 mm.
The core-sheath conjugate fiber may be surface-treated with a spinning oil exhibiting hydrophilic or water-repellent properties, and the spinning oil may be applied in an optional step, for example, after cutting or drying.
The core-sheath conjugate fiber that exhibits a sufficient degree of whiteness (including white appearance, opacity, and anti-show-through property), as well as the mechanical properties required for nonwoven fiber stock, can be produced by controlling the crystalline structure of the drawn filament yarn through the addition of calcium carbonate to the polyester resin, followed by drawing and crystallization treatment. The mechanism by which the degree of whiteness is improved in the first and third embodiments of the present invention is illustrated in FIGs. 4(a) to (c). As shown in FIG. 4(a), the polymer chains contained in the undrawn polyester resin exhibit a random orientation. In the absence of inorganic particles such as calcium carbonate, as shown in FIG. 4(b), unoriented crystals (spherulites, and the like) grow and act as factors that inhibit the orientation of the polymer chains contained in the polyester resin, during the process of necking deformation of the undrawn filament yarn caused by drawing.
When inorganic particles such as calcium carbonate is added, as shown in FIG. 4(c), the calcium carbonate functions as a nucleating agent for the PET resin, enabling the formation of fine unoriented crystals with reduced size in the system (the effect of the calcium carbonate as a nucleating agent promotes the crystallization as fine unoriented crystals). Accordingly, a linear and uniform stress can be applied to the undrawn filament yarn unlike the system free of calcium carbonate, thereby promoting oriented crystallization. As a result, a drawn filament yarn containing crystals having a size sufficient to scatter visible light can be obtained (crystals of larger size exhibit higher visible light scattering properties, resulting in a higher degree of whiteness). The phenomenon in which the calcium carbonate acts as a nucleating agent for PET can be inferred from the crystallization peak temperature on cooling, as measured by differential scanning calorimetry (DSC) (FIGs. 2 and 3). As the concentration of the calcium carbonate increases, the crystallization peak temperature on cooling shifts to a higher temperature, indicating that the effect of the calcium carbonate as a nucleating agent promotes the formation of fine unoriented crystals.
In a system where calcium carbonate is added, the phenomenon in which the crystal size increases depending on the drawing and crystallization conditions can be inferred from the measurement results of differential scanning calorimetry (DSC). In the DSC curve (FIG. 1) of Comparative Example 3, in which the polyester resin was not subjected to drawing after the addition of the calcium carbonate, a crystal melting curve derived from PET appears as a single broad endothermic curve with a peak at around 255°C. This crystal melting curve originates from unoriented crystals (spherulites) that are not associated with the orientation of polymer chains contained in the polyester resin. In contrast, the DSC curve (FIG. 2) of Example 1, in which the polyester resin containing the calcium carbonate was subjected to drawing, shows another endothermic curve with a maximum peak at around 250°C, as well as the above broad endothermic curve with a peak at around 255°C. The former endothermic curve appears because of drawing and corresponds to a crystal melting curve originating from oriented crystals of polymer chains contained in the polyester resin. If the drawing ratio is increased up to around the breaking region, the broad endothermic curve with a peak at around 255°C attenuates, and a peak at around 255°C will be no longer observed (only an endothermic curve with a maximum peak at around 250°C will be observed). Although a drawn filament yarn in this state exhibits a high degree of whiteness, this drawn filament yarn is not suitable for use in nonwoven fabrics due to significantly reduced elongation. Accordingly, in order to obtain a drawn filament yarn that exhibits both a high degree of whiteness and excellent mechanical properties, it is important that the maximum peak temperature of crystal melting of the drawn filament yarn is observed at a temperature lower than 255°C.
The degree of whiteness can be improved by increasing the concentration of the calcium carbonate and promoting the formation of oriented crystals. On the DSC curve (FIG. 2) of Example 1 in which the polyester resin containing the calcium carbonate was subjected to drawing, the maximum peak temperature of crystal melting originating from the oriented crystals (crystals with high visible light scattering properties) is observed at 250°C, while a maximum peak temperature of crystal melting originating from the oriented crystals is observed at 252°C on the DSC curve (FIG. 3) of Example 5 in which the polyester resin containing the calcium carbonate in a higher concentration was subjected to drawing. Since the peak temperature of crystal melting is shifted to a higher temperature, it is considered that the size of oriented crystals is increased with an increase in the concentration of added calcium carbonate.
The core-sheath conjugate fiber of the present invention may be a long fiber (a filament), a short fiber (a staple fiber), or a combination thereof.
The present invention includes a nonwoven fabric formed from the core-sheath conjugate fibers.
The nonwoven fabric is preferably formed by a conventionally known fleece formation technique and a conventionally known fleece bonding technique.
Examples of the fleece formation technique include a dry-laid method, a wet-laid method, a spunbond method, and a meltblown method. Examples of the fleece bonding technique include thermal bonding method, chemical bonding method, needle punching method, spunlace method, stitch bonding method, and steam jet method.
Appropriate fleece formation and fleece bonding methods may be selected from those described above based on the desired nonwoven fabrics.
The present application claims benefit of priority to Japanese Patent Application No. 2023- 058130 filed on March 31, 2023 , and Japanese Patent Application No. 2023-162951 filed on September 26, 2023 . The entire contents of the specifications of Japanese Patent Application No. 2023-058130 filed on March 31, 2023 , and Japanese Patent Application No. 2023-162951 filed on September 26, 2023 , are incorporated herein by reference.

EXAMPLES

The present invention will now be described in more detail with examples. However, the scope of the present invention is not limited to these examples. The present invention may be carried out with various modifications within a range conforming to the gist described above and/or below, all of which are included within the technical scope of the present invention. Unless otherwise stated, throughout the following description, "part(s)" refers to "part(s) by mass", and "%" refers to "% by mass". The standard sample sizes used for measurement are those specified below. However, if the sample was insufficient, the measurement was conducted using a sample of an available size.

(1) Materials

Polyethylene terephthalate (PET) having an intrinsic viscosity IV of 0.63 dl/g was used as the core component, and high-density polyethylene (HDPE) having an MFR of 20 g/10min (load: 2.16 kg, temperature: 190°C) was used as the sheath component to form a bi-component core-sheath conjugate fiber. Calcium carbonate KRS1 manufactured by Maruo Calcium Co., Ltd. was added to the PET of the core component, and calcium carbonate YM10 manufactured by Maruo Calcium Co., Ltd. was added to the PE of the sheath component.

(2) Color Tone Measurement

The L* and b* values were measured using a colorimeter CM-3700d manufactured by Minolta Co., Ltd, under a setting excluding reflected light. In the present invention, the L* and b* values were measured using the obtained fiber sample which was visually confirmed to have no show-through of the black winding board when wound onto the winding board. The L* value indicates the degree of whiteness of a color, while the b* value indicates the yellowness of a color. If the fiber has an L* value of less than 85, or the b* value of more than 5.0, a nonwoven fabric formed from such fibers has an undesirable appearance in terms of color tone, resulting in a nonwoven fabric of poor quality with insufficient opacity. Although the anti-show-through property can be achieved even when the L* value is 90 or less, the L* value is desirably 91 or more for use in nonwoven fabrics for sanitary materials.

(3) Differential Scanning Calorimetry

The peak temperature of crystal melting was measured at a heating rate of 10°C/min using a differential scanning calorimeter manufactured by TA Instruments. The temperature at which the maximum appeared on the measured melting endothermic curve was determined as the maximum peak temperature of crystal melting.
The crystallization peak temperature on cooling was measured at a cooling rate of 10°C/min.

(4) Fineness and Single-Filament Fineness

The fineness was measured in accordance with the method described in JIS L 1095 9.4.1. The single-filament fineness was calculated by dividing the fineness by the number of filaments.

(5) Maximum Point Stress (Also Referred to as Tensile Strength and Shown as "Strength" in Table 1) and Maximum Point Elongation (Also Referred to as Elongation Rate and Shown as "Elongation" in Table 1)

The measurement was conducted in accordance with JIS L 1013 8.5.1. The stress at the maximum load was determined as the maximum point stress, and the elongation rate at the maximum load was determined as the maximum point elongation.

[Example 1]

Polyethylene terephthalate (PET) as a polyester resin was dried by a conventional method. Subsequently, calcium carbonate was blended with the PET so that the calcium carbonate content became 4.0% by mass. Separately, high-density polyethylene (HDPE) as a polyolefin resin was prepared, and the PET containing calcium carbonate and the HDPE were independently fed into a conjugate fiber spinning machine. The PET containing calcium carbonate and the HDPE were then melt extruded at 285°C using an extruder attached to the conjugate fiber spinning machine, and conjugate spinning was performed by spinning the molten resins into a core-sheath structure using a spinneret having multiple orifices, with the PET disposed on the core side and the HDPE on the sheath side in a concentric configuration at a mass ratio of both components of 40/60 (sheath/core). The spun yarn stream was then cooled with an air flow, treated with spinning oil using an oiling guide, and bundled using a bundle-guide. The bundled yarn was then taken up by rollers at a spinning speed of 1240 m/min and wound by a winder. The resulting fiber (undrawn filament yarn) had a single-filament fineness of 5.0 dtex. The resulting fiber was then drawn using a drawing device at a speed of 40 m/min, first at a drawing temperature of 70°C with a drawing ratio of 2.4 times, subsequently at a drawing temperature of 110°C with a drawing ratio of 0.95 times, followed by heat setting at 120°C. As a result of the spinning and the drawing processes, a core-sheath conjugate fiber with a single-filament fineness of 2.2 dtex was obtained, with the PET disposed on the core side and the HDPE on the sheath side in a concentric configuration at a mass ratio of 40/60 (sheath/core).

[Example 2]

Example 2 was conducted in the same manner as in Example 1, except that the resulting core-sheath conjugate fiber was adjusted to have a single-filament fineness of 2.8 dtex by drawing the undrawn filament yarn at a different drawing ratio.

[Example 3]

Example 3 was conducted in the same manner as in Example 1, except that the resulting core-sheath conjugate fiber was adjusted to have a single-filament fineness of 3.3 dtex by drawing the undrawn filament yarn at a different drawing ratio.

[Example 4]

Example 4 was conducted in the same manner as in Example 1, except that the content of the calcium carbonate in PET was adjusted to 8.0% by mass.

[Example 5]

Example 5 was conducted in the same manner as in Example 1, except that the content of the calcium carbonate in PET was adjusted to 15.0% by mass.

[Example 6]

The calcium carbonate content in PET was adjusted to 10% by mass, and the calcium carbonate content in HDPE was adjusted to 10% by mass. The PET containing the calcium carbonate and the HDPE containing the calcium carbonate were then melt extruded at 285°C using an extruder attached to the conjugate fiber spinning machine, and conjugate spinning was performed by spinning the molten resins into a core-sheath structure using a spinneret having multiple orifices, with the PET disposed on the core side and the HDPE on the sheath side in a concentric configuration at a mass ratio of both components of 40/60 (sheath/core). The spun yarn stream was then cooled with an air flow, treated with spinning oil using an oiling guide, and bundled using a bundle-guide. The bundled yarn was then taken up by rollers at a spinning speed of 1240 m/min and dropped and stored in a can. The obtained undrawn filament yarn was then drawn at a drawing temperature of 70°C with a drawing ratio of 2.7 times using a drawing device, subjected to mechanical crimping, and heat set at 120°C with no tension. The resulting core-sheath conjugate fiber was then subjected to a cutting process to obtain a staple fiber (a short fiber) having a single-filament fineness of 2.4 dtex.

[Example 7]

Polyethylene terephthalate (PET) as a polyester resin was dried by a conventional method. Separately, high-density polyethylene (HDPE) as a polyolefin resin was prepared, and calcium carbonate was blended with the HDPE so that the calcium carbonate content became 5.0% by mass. The PET and the HDPE containing calcium carbonate were independently fed into a conjugate fiber spinning machine. Subsequently, the PET and the HDPE containing calcium carbonate were melt extruded at 285°C using an extruder attached to the conjugate fiber spinning machine, and conjugate spinning was performed by spinning the molten resins into a core-sheath structure using a spinneret having multiple orifices, with the PET disposed on the core side and the HDPE on the sheath side in a concentric configuration at a mass ratio of both components of 40/60 (sheath/core). The spun yarn stream was then cooled with an air flow, treated with spinning oil using an oiling guide, and bundled using a bundle-guide. The bundled yarn was then taken up by rollers at a spinning - speed fineness of 5.0 dtex. The resulting fiber was then drawn using a drawing device at a speed of 40 m/min, first at a drawing temperature of 70°C with a drawing ratio of 2.4 times, subsequently at a drawing temperature of 110°C with a drawing ratio of 0.95 times, followed by heat setting at 120°C. As a result of the spinning and the drawing processes, a core-sheath conjugate fiber with a single-filament fineness of 2.3 dtex was obtained, with the PET disposed on the core side and the HDPE on the sheath side in a concentric configuration at a mass ratio of 40/60 (sheath/core).

[Example 8]

Example 8 was conducted in the same manner as in Example 7, except that the content of the calcium carbonate in HDPE was adjusted to 20.0% by mass.

[Comparative Example 1]

Comparative Example 1 was conducted in the same manner as in Example 1, except that the content of the calcium carbonate was adjusted to 1.0% by mass, and drawing and heat-treatment were not performed.

[Comparative Example 2]

Comparative Example 2 was conducted in the same manner as in Example 1, except that the content of the calcium carbonate was adjusted to 1.0% by mass.

[Comparative Example 3]

Comparative Example 3 was conducted in the same manner as in Example 1, except that drawing and heat-treatment were not performed.

[Comparative Example 4]

Comparative Example 4 was conducted in the same manner as in Example 7, except that drawing and heat-treatment were not performed.

[Table 1]

		Core Component (PET)	Sheath Component (PE)	Fiber Form	Drawing + Heat-Setting (120°C)	Total Drawing Ratio (times)	Fineness (dtex)	Strength (cN/dtex)	Elongation (%)	Crystallization Peak Temperature on Cooling (°C)	Maximum Peak Temperature of Crystal Melting (°C)	Color Tone
		Calcium Carbonate Content (% by mass)	Calcium Carbonate Content (% by mass)	Fiber Form	Drawing + Heat-Setting (120°C)	Total Drawing Ratio (times)	Fineness (dtex)	Strength (cN/dtex)	Elongation (%)	Crystallization Peak Temperature on Cooling (°C)	Maximum Peak Temperature of Crystal Melting (°C)	L* value	b* value
Examples	1	4.0	0.0	Filament	Applied	2.29	2.2	2.75	55.9	207	250.4	95.9	-0.1
	2	4.0	0.0	Filament	Applied	1.80	2.8	1.62	79.6	200	250.2	95.4	-0.1
	3	4.0	0.0	Filament	Applied	1.53	3.3	1.09	132.1	200	252.3	94.5	-0.2
	4	8.0	0.0	Filament	Applied	2.29	2.2	2.42	54.6	208	251.2	96.1	-0.1
	5	15.0	0.0	Filament	Applied	2.29	2.2	1.94	52.6	210	252.1	96.9	0.3
	6	10.0	10.0	Staple	Applied	2.70	2.4	2.22	54.1	199	245.5	95.3	0.2
	7	0.0	5.0	Filament	Applied	2.29	2.3	3.06	83.1	204	249.7	95.3	0.2
	8	0.0	20.0	Filament	Applied	2.29	2.3	2.91	69.8	207	250.2	96.1	0.1
Comparative Examples	1	1.0	0.0	Filament	Not Applied	-	5.0	-	-	-	255.2	90.2	-0.1
	2	1.0	0.0	Filament	Applied	2.29	2.2	-	-	-	-	89.8	0.5
	3	4.0	0.0	Filament	Not Applied	-	5.0	-	-	-	255.2	89.8	0.6
	4	0.0	5.0	Filament	Not Applied	-	5.0	-	-	202	255.0	89.0	-0.5

INDUSTRIAL APPLICABILITY

The core-sheath conjugate fiber of the present invention can be suitably used in applications such as absorbent articles for sanitary materials including diapers, napkins, and pads; medical sanitary materials; life-related materials; general medical materials; bedding materials; filter materials; nursing care products; and pet supplies.

Claims

A core-sheath conjugate fiber comprising:
a core component containing a polyester resin; and

a sheath component containing a polyolefin resin having a melting point that is lower than a melting point of the polyester resin by 20°C or more,

wherein either or both of the core component and the sheath component contain calcium carbonate in an amount of more than 1.0% by mass and 30.0% by mass or less based on 100% by mass of each component,

wherein the core component has a maximum peak temperature of crystal melting of lower than 255°C, as measured with a differential scanning calorimeter, and

wherein the fiber has an L* value of 91 or more and a b* value of 5.0 or less, which indicate a hue of the fiber.
The core-sheath conjugate fiber according to Claim 1, wherein the core component has a crystallization peak temperature on cooling of from 190°C to 220°C, as measured with a differential scanning calorimeter.
The core-sheath conjugate fiber according to Claim 1 or 2, wherein the polyester resin contains polyethylene terephthalate, and the polyolefin resin contains polyethylene.
The core-sheath conjugate fiber according to Claim 1 or 2, wherein a content of the polyester resin is 40% by mass or more of a total fiber.
The core-sheath conjugate fiber according to Claim 1 or 2, wherein the fiber has a concentric, eccentric, or hollow cross-sectional shape.
The core-sheath conjugate fiber according to Claim 1 or 2, wherein the fiber has a tensile strength of from 0.80 cN/dtex to 5.00 cN/dtex, as measured in accordance with JIS L 1013 8.5.1.
The core-sheath conjugate fiber according to Claim 1 or 2, wherein the fiber has an elongation rate of from 30% to 200%, as measured in accordance with JIS L 1013 8.5.1.
A nonwoven fabric formed from the core-sheath conjugate fiber according to Claim 1 or 2.