TWI787248B - Splittable conjugate fiber and fiber structure using the same - Google Patents

Abstract

The present invention discloses a splittable conjugate fiber which comprises a first segment and a second segment, wherein the first segment contains 50% by mass or more of a polypropylene resin and the second segment contains 50% by mass or more of a polyethylene resin, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polypropylene resin measured after spinning is 6 or less, and after spinning, the shape of the melting peak of the polypropylene resin indicated by the DSC curve subjected to differential scanning calorimetry (DSC) based on the method of measuring the transition temperature of plastic in JIS K 7121 (1987) is a double peak shape.

The splittable conjugate fiber can be used in applications requiring denseness of a fiber structure, and in particular productivity at the time of fiber production and splitability are further improved.

Description

Split type composite fiber and fiber structure using the split type composite fiber

The present invention relates to a split type composite fiber and a fiber structure using the split type composite fiber.

In order to obtain ultrafine fibers and fibrous structures containing ultrafine fibers, there is known a method of using split type composite fibers using plural types of thermoplastic resins, and when observing the cross section of the fiber, the cross section is divided into two or more Resin segment (segment; hereinafter, simply referred to as segment) configuration. When split type conjugate fibers are used, ultrafine fibers can be easily obtained by splitting the fibers into individual segments. However, when the division process is incomplete, it is known that there remains an undivided portion, that is, a portion in which the segments remain in a glued state (generally also referred to as undivided fiber).

Also, the segment constituting the segmented composite fiber is generally composed of a single resin component (even if it is a resin component obtained by mixing a plurality of thermoplastic resins, these have been uniformly mixed into a single resin component in the segment), if Ultrafine fibers can be obtained by sufficiently splitting, but when bonding these ultrafine fibers, it is necessary to mix thermal bonding fibers with a fiber diameter larger than that of the ultrafine fibers. A core-sheath composite fiber made of resin. As a result, it is known that the bonded fiber structure obtained by bonding ultrafine fibers using thermally bonded fibers having a larger fiber diameter than the ultrafine fibers reduces the density of the bonded fiber structure.

In addition, for two or more segments constituting the split-type conjugate fiber, polyolefin-based resins such as polypropylene and polyethylene, polyester-based resins such as polyethylene terephthalate and copolymerized polyester, etc. When a thermoplastic resin with high inter-compatibility is used as the thermoplastic resin constituting the adjacent segment, when the split-type composite fiber is obtained by combining the resin with high compatibility, the adhesion between adjacent segments tends to become stronger, and undivided fibers tend to remain in the resulting fiber structure. Parts (undivided fibers) will easily survive.

For example, polypropylene, high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polymethylpentene, ethylene-propylene copolymer, propylene-ethylene-1-butene terpolymer Polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, copolymerized polyester and other polyester resins A segmented composite fiber combined with each other. In order to prevent such split-type composite fibers from remaining undivided parts, it is necessary to perform strong stirring when mixing the fibers in the manufacturing stage of the fiber structure, spray high-pressure water on the obtained fiber structure, and convert the obtained fiber structure. It is divided between two metal rollers and applied with a strong impact such as pressure.

In order to improve the splittability, the obtained fibrous structure is composed only of ultrafine fibers, and the surface of the ultrafine fibers is melted for a part of the ultrafine fibers, so that the ultrafine fibers are interlinked, mechanical properties such as tensile strength and puncture strength An excellent fiber structure has been examined. Among the two or more segments constituting the split-type composite fiber, one segment maintains a single component segment (single segment), and the cross-sectional shape of the other segment is made into a core-sheath-type cross-sectional shape (made into a core sheath segment) etc. (for example, refer to Patent Documents 1 to 4).

Patent Document 1 has reported a split-type composite fiber with excellent splittability, which is a single-component segment (single-type segment), and the core component of the core-sheath segment is composed of an α-olefin polymer component with the same high melting point. The sheath component of the segment is composed of a low-melting α-olefin polymer component, and the total Rockwell hardness R of the low-melting α-olefin polymer component and the high-melting α-olefin polymer component is 60 or more.

Patent Document 2 has reported a split-type conjugate fiber excellent in splittability, in which the cross-section of the core-sheath segment is made into a specific shape. In addition, Patent Documents 3 and 4 have reported a split-type conjugate fiber excellent in splittability, which contains a single segment with a polypropylene resin having a specific z-average molecular weight (Mz) and a specific weight-average molecular weight (Mw) as a main component.

In the split-type composite fibers described in Patent Documents 1 to 4, the segment-to-segment interface is peeled off even without splitting by high-pressure water flow, and ultrafine fibers are produced by splitting at each segment. In addition, it has a core-sheath segment, so even if it is a fiber structure composed of only such split-type composite fibers, thermal bonding between fibers can be performed.

[Prior Art Literature] (patent documents)

[Patent Document 1] Japanese Patent Application Laid-Open No. 4-163315

[Patent Document 2] Japanese Patent Laid-Open No. 2011-9150

[Patent Document 3] Japanese Unexamined Patent Publication No. 2012-142235

[Patent Document 4] Japanese Unexamined Patent Publication No. 2012-140734

However, in applications that require the compactness of the fibrous structure, for example, in various secondary batteries that use the fibrous structure as the isolation chamber between electrodes; filtration of various filters for liquids and gases that require higher fineness material (filter material); as a support for various filtration membranes such as reverse osmosis membrane (RO membrane) or nanofiltration membrane (NF membrane), ultrafiltration membrane (UF membrane), precision filtration membrane (MF membrane), etc. Fibrous structures for various membrane supports used; Wiping materials for people and objects that require less irritation and damage to the wiped part; Skin covering sheets impregnated with cosmetics that must have a soft texture when in contact with the skin (generally also called It is required to improve the performance of split type composite fibers in applications such as sheets for absorbent articles and the like. For the split-type conjugate fibers of Patent Documents 1 to 4, it is also required to further improve the overall performance, especially the productivity during fiber production (for example, it is easy to adjust the shape and arrangement of each segment constituting the split-type conjugate fiber during fiber manufacture, melt It is less likely to cause thread cutting, etc.) and separability during spinning and drawing steps.

The present inventors have surprisingly found that a segmented composite fiber composed of the first section and the second section, wherein the first section is a resin section made of the first component, and the second section has a cross-sectional structure of In the split-type conjugate fiber formed by the core-sheath resin segment with the first component as the core component and the second component as the sheath component, the first segment contains the Q value after spinning (weight average molecular weight (Mw) and number average The ratio of molecular weight (Mn), represented by Mw/Mn) satisfies a specific range of polypropylene resin, and for the obtained split-type conjugate fiber, by using the obtained split-type composite fiber containing In the DSC curve, the shape of the endothermic peak (melting peak of the polypropylene resin) generated by the melting of the polypropylene resin is a specific shape of the resin component of the polypropylene resin, which further improves the productivity and the division obtained during fiber production. Separation of type composite fibers, etc.

Also, the inventors of the present invention have found that in such a split-type conjugate fiber, a nonwoven fabric (fibrous structure) manufactured using the obtained split-type conjugate fiber is a core-sheath type resin segment obtained by splitting the split-type conjugate fiber. The sheath part is melted so that the fibers constituting the nonwoven fabric (for example, ultrafine fibers) can be bonded together. And it was found that such a non-woven fabric is composed of ultrafine fibers as the main fibers, so not only the internal structure is dense, but also the ultrafine fibers are interlinked by the sheath component that constitutes the ultrafine core-sheath composite fibers, and it has excellent tensile strength. Fiber structures with mechanical properties such as strength and puncture strength, thus completing the present invention.

That is, one gist of the present invention is to provide a segmented composite fiber comprising a first segment and a second segment, wherein the first segment is a resin segment made of the first component, and the second segment is a section The structure is a core-sheath type resin segment with the first component as a core component and the second component as a sheath component, the first component is a resin component containing 50% by mass or more of polypropylene resin, and the second component is a resin component containing 50% by mass The ratio (Mw/Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the aforementioned polypropylene resin measured after spinning is 6 or less. The melting peak shape of the polypropylene resin in the DSC curve measured by differential scanning calorimetry (DSC) based on JIS K 7121 (1987) Transition temperature measurement method of plastics is a double peak shape.

Since the present invention has the characteristics as described above, at least one of the problems of productivity and splitability during fiber production is improved. In addition, the nonwoven fabric (fibrous structure) produced using such split-type composite fibers has a dense structure of the fibrous structure and moderate air permeability. Further, by melting the second component (namely, polyethylene resin), the second component is the one whose cross-sectional structure is the sheath component constituting the core-sheath type resin segment of the aforementioned second segment, and then Between the ultrafine fibers, it becomes a non-woven fabric (fibrous structure) with excellent mechanical properties.

In addition, in this specification, the sign of "to" means to use the meaning of both ends.

1‧‧‧paragraph 1

2‧‧‧paragraph 2

4‧‧‧core composition

6‧‧‧sheath composition

8‧‧‧hollow

10‧‧‧Split composite fiber

14‧‧‧core composition

16‧‧‧sheath composition

20‧‧‧Split composite fiber

a‧‧‧The melting peak of polypropylene resin

a ₁ ‧‧‧The first melting peak of polypropylene resin

a ₂ ‧‧‧The second melting peak of polypropylene resin

a ₃ ‧‧‧The valley among the melting peaks of polypropylene resin

T ₁ ‧‧‧The first melting peak temperature of polypropylene resin

T ₂ ‧‧‧The second melting peak temperature of polypropylene resin

W ₂ ‧‧‧Heat flux in the second melting peak of polypropylene resin

W ₃ ‧‧‧The heat flux existing in the valley between the first melting peak and the second melting peak of polypropylene resin

S ₁ ‧‧‧The area of the first endothermic peak of polypropylene resin

S ₂ ‧‧‧The area of the second endothermic peak of polypropylene resin

BL _LT ‧‧‧The baseline of the low temperature side of the DSC curve

BL _HT ‧‧‧The baseline of the high temperature side in the DSC curve

BL _E ‧‧‧DSC curve, the straight line that extends the reference line on the low temperature side from the end of the high temperature side to the end of the low temperature side of the reference line on the high temperature side

Fig. 1 schematically shows a cross section of a split type conjugate fiber according to an embodiment of the present invention.

Fig. 2 schematically shows a cross-section of a split-type conjugate fiber of another embodiment of the present invention.

Fig. 3 schematically shows a cross-section of a split-type conjugate fiber used in a reference example.

Fig. 4 schematically shows that in the endothermic peak of polypropylene resin, after the first melting peak (a ₁ ) clearly appears on the low temperature side, the second melting peak (a ₂ ) appears on the high temperature side.

Fig. 5 schematically shows the extension of the second melting peak (a ₂ ) on the high temperature side among the endothermic peaks of polypropylene resin.

Fig. 6 schematically shows the first melting peak area (S ₁ ) among endothermic peaks of polypropylene resin.

Fig. 7 schematically shows the second melting peak area (S ₂ ) in the endothermic peak of polypropylene resin.

Fig. 8 schematically shows that in the endothermic peak of polypropylene resin, after the first melting peak (a ₁ ) appears as a shoulder on the low temperature side, the second melting peak (a ₂ ) appears on the high temperature side.

Fig. 9 schematically shows the extension of the second melting peak on the high temperature side among the endothermic peaks of polypropylene resin.

Fig. 10 schematically shows the first melting peak area (S ₁ ) among endothermic peaks of polypropylene resin.

Fig. 11 schematically shows the second melting peak area (S ₂ ) among endothermic peaks of polypropylene resin.

Fig. 12 schematically shows that among the endothermic peaks of polypropylene resin, one melting peak clearly appears.

FIG. 13 shows a DSC curve obtained by performing differential scanning calorimetry (DSC) on the split-type conjugate fiber of Example 1. FIG.

Fig. 14 shows a DSC curve obtained by performing differential scanning calorimetry (DSC) on the split-type conjugate fiber of Example 7.

FIG. 15 shows a DSC curve obtained by performing differential scanning calorimetry (DSC) on the split-type conjugate fiber of Comparative Example 1. FIG.

FIG. 16 shows a DSC curve obtained by performing differential scanning calorimetry (DSC) on the split-type conjugate fiber of Comparative Example 3. FIG.

FIG. 17 shows a DSC curve obtained by performing differential scanning calorimetry (DSC) on the split-type conjugate fiber of Comparative Example 5. FIG.

Fig. 18 shows a DSC curve obtained by performing differential scanning calorimetry (DSC) on the split-type conjugate fiber of Comparative Example 6

[Best Mode for Carrying Out the Invention]

Figures 1 to 2 are schematic cross-sections of split type conjugate fibers (10, 20) according to the present invention. Both contain the first paragraph (1) and the second paragraph (2). The first paragraph (1) is a single-structure segment, but the second paragraph (2) is a core-sheath type segment (Fig. 1 and Fig. 2). The core-sheath segment may have a core component (4, 14) and a sheath component (6, 16). Also, the split type conjugate fiber may have a hollow (8) (FIG. 1).

<paragraph 1>

The first stage is a resin stage made of the first component. In the first stage, ultrafine fibers 1 are formed by splitting the split-type composite fibers. In other words, the first section is composed of the first component and has a single section with a single structure. The said 1st component is a resin component containing 50 mass % or more of polypropylene resin. The aforementioned first component preferably contains 75% by mass or more of polypropylene resin, more preferably contains 80% by mass or more.

It is particularly preferable that the first component is substantially composed of polypropylene resin. Here, the term "substantially" is used. Usually, polypropylene resin provided as a product contains additives such as stabilizers, and/or various additives are added at the time of fiber production, so it is considered that it cannot be obtained only by Composed of polypropylene resin, it does not contain fibers in the form of other components. Usually, the first component can contain up to 15% by mass of additives.

In the present invention, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polypropylene resin measured after spinning (hereinafter also referred to as "Q value") is 6 or less, expressed as 2 6 to 6 is better, 2.2 to 5.6 is better, 2.3 to 5.2 is especially good, and 2.4 to 5.0 is the best. The lower limit of the above range of Mw/Mn may be 2 or more, and may be 2.4 or more. For example, it may be 2 to 6, 2.5 to 6, 2.8 to 6, or 3.4 to 6. When the Q value is less than 6, the polypropylene resin after spinning, because the size of the polypropylene molecules contained in it (the length of the polypropylene molecular chain) is neat, and its distribution range is relatively narrow, so the movement of the polypropylene molecules is easy to be neat. As a result, the cross-sectional shape of the fiber in the split-type conjugate fiber and the cross-sectional shape of each segment are not only uniform, but also the yarn breakage is less likely to occur during spinning and stretching, making it easy to obtain highly productive fibers. Since the productivity of the fiber is good, various physical properties of the obtained split-type conjugate fiber and the fiber structure using the split-type conjugate fiber are further improved.

The weight average molecular weight (Mw) of the polypropylene resin measured after spinning is preferably 150,000 to 700,000, more preferably 200,000 to 500,000, and most preferably 230,000 to 400,000. Furthermore, the number average molecular weight (Mn) of the polypropylene resin measured after spinning is preferably 43,000 to 150,000, more preferably 48,000 to 120,000, and most preferably 55,000 to 100,000. The measuring methods of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of a polypropylene resin are described in an Example.

The polypropylene resin may be a homopolymer of propylene (a homopolymer containing propylene as a monomer), or may contain a copolymer containing propylene as a monomer (hereinafter referred to as a polypropylene-based resin). The polypropylene resin is not particularly limited as long as the split-type conjugate fiber which is the object of the present invention can be obtained. As the polypropylene-based resin, a random copolymer, a block copolymer, a graft copolymer or a mixture thereof containing propylene as a monomer can be used. Examples of the aforementioned random copolymer, block copolymer, and graft copolymer include, for example, copolymers of ethylene and at least one α-olefin selected from the group consisting of α-olefins having 4 or more carbon atoms.

The above-mentioned α-olefins having 4 or more carbon atoms are not particularly limited as long as the split-type composite fibers that are the object of the present invention can be obtained, for example: 1-butene, 1-pentene, 3, 3-Dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene , 1-octadecene, etc. The content of propylene in the above-mentioned copolymer is preferably more than 50% by mass. As the first component, a homopolymer of propylene or the above-mentioned polypropylene-based resin can be used, but a homopolymer of propylene is particularly preferable in consideration of easiness of production and economical efficiency (production cost). These may be used alone or in combination of two or more.

Polypropylene resin, according to JIS K 7210, the melt flow rate (hereinafter also referred to as "MFR230"; measurement temperature 230 ℃, load 2.16kgf (21.18N)), is 8g/10 minutes or more and 60g/10 minutes or less Best, more than 15g/10 minutes and less than 60g/10 minutes is better, more than 20g/10 minutes and less than 45g/10 minutes is especially good, more than 25g/10 minutes and less than 40g/10 minutes is the best.

The first stage may contain a known split accelerator as long as the split-type conjugate fiber targeted by the present invention can be obtained. As known split accelerators, for example, silicon compound-based split accelerators, unsaturated carbonic acid-based split accelerators, (meth)acrylic compound split accelerators, etc. In other words, it is preferably a partition accelerator of a (meth)acrylic compound, and more preferably a metal salt of (meth)acrylate. When a (meth)acrylic acid metal salt is contained as a split accelerator in the first stage, the (meth)acrylic acid metal salt may be contained in an amount of 1 to 10% by mass relative to the entire first stage.

<paragraph 2>

The split type conjugate fiber of the present invention includes a second segment. The second stage is preferably one in which ultrafine fibers 2 derived from the second stage are formed by splitting the split-type composite fiber. The second stage is a core-sheath type resin stage having a cross-sectional structure in which the first component is a core component and the second component is a sheath component.

The second component is a resin component containing 50% by mass or more of polyethylene resin. The above-mentioned second component is preferably a resin component containing 75% by mass or more of polyethylene resin, more preferably 80% by mass or more of polyethylene resin. It is particularly preferable that the second component is substantially composed of polyethylene resin. Here, the term "substantially" is generally considered to be unavailable because the polyethylene resin provided as a product contains additives such as stabilizers and/or various additives are added when manufacturing fibers. Made of polyethylene resin, fiber in the form of no other components. Usually, the second component can contain up to 15% by mass of additives.

Polyethylene resins and polypropylene resins have good compatibility, and generally speaking, splittable conjugate fibers obtained by combining them have low splittability. In the present invention, excellent splittability can be obtained even in a combination of a polypropylene resin and a polyethylene resin.

The polyethylene resin can also be a homopolymer of ethylene (the homopolymer of ethylene as a monomer, depending on the density and molecular structure, there are high-density polyethylene, medium-density polyethylene, low-density polyethylene, straight-chain low-density polyethylene, etc. density polyethylene) or a copolymer containing ethylene as a monomer (hereinafter referred to as polyethylene-based resin). The polyethylene resin is not particularly limited as long as the split-type conjugate fiber which is the object of the present invention can be obtained. As the polyethylene-based resin, random copolymers, block copolymers, graft copolymers or mixtures thereof containing ethylene as a monomer can be used. Examples of the aforementioned random copolymers, block copolymers and graft copolymers include copolymers of ethylene and at least one α-olefin selected from the group consisting of α-olefins having 3 or more carbon atoms.

The above-mentioned α-olefins having 3 or more carbon atoms are not particularly limited as long as the split-type conjugate fiber that is the object of the present invention can be obtained, and examples thereof include propylene, 1-butene, 1-pentene, 3,3-Dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-decene, 1-dodecene, 1-deca Tetracene, 1-octadecene, etc. The content of ethylene in the above-mentioned copolymer is preferably at least 50% by mass. As the second component, a homopolymer of ethylene or the above-mentioned polyethylene-based resin can be used, but a homopolymer of ethylene is particularly preferred in consideration of ease of manufacture and economical efficiency (manufacturing cost). These may be used alone or in combination of two or more.

Polyethylene resin, based on JIS K 7210, the melt flow rate (hereinafter also referred to as "MFR190"; measurement temperature 190°C, load 2.16kgf (21.18N)) is defined as 5g/10min or more but less than 3g/10min Better, more than 8g/10 minutes but less than 2g/10 minutes, more preferably 10g/10 minutes but less than 25g/10 minutes. When the MFR190 of the polyethylene resin is in the range of 5 g/10 minutes or more and less than 30 g/10 minutes, the productivity of the split type conjugate fiber is further improved.

The second stage may contain a known split accelerator as long as the split-type conjugate fiber targeted by the present invention can be obtained. As known split accelerators, for example, silicon compound-based split accelerators, unsaturated carbonic acid-based split accelerators, (meth)acrylic compound split accelerators, etc. In other words, a partition accelerator of (meth)acrylic acid compound is preferable, and metal salt of (meth)acrylate is more preferable. When the second stage contains a (meth)acrylic acid metal salt as a split accelerator, the (meth)acrylic acid metal salt may be contained in an amount of 1 to 10% by mass relative to the entire second stage.

The second stage is a core-sheath type resin stage having a cross-sectional structure in which the first component is a core component and the second component is a sheath component. Using the second stage as the core-sheath type resin stage, splitting the split-type composite fiber creates ultra-fine fibers whose cross-section is the core-sheath composite fiber. By melting only the second component (containing 50% by weight or more of polyethylene resin) which is the sheath component of the core-sheath ultrafine composite fiber, the ultrafine fibers formed by splitting the split composite fiber can be thermally bonded to each other. Then, a fiber structure having more excellent mechanical properties such as puncture strength and tensile strength can be obtained.

Since the second stage is a core-sheath type resin stage, and the core component is the first component, the split-type conjugate fiber is composed of two types of resin components, making nozzle design and composite spinning easier.

The second stage is a core-sheath type resin stage, and the cross-sectional shape of the core component of the second stage is not particularly limited as long as the split-type conjugate fiber targeted by the present invention can be obtained. The cross section of the core component may have, for example, an ellipse or a perfect circle. In addition, the core component may be positioned at the center of the second stage, or may be positioned off-center instead of at the center.

The second component (which can constitute the sheath component) preferably has a melting point lower than that of the first component (which can constitute the core component). The melting point of the second component is preferably at least 10°C lower than the melting point of the first component, more preferably at least 20°C lower.

<Split type composite fiber>

The split-type conjugate fiber according to the aspect of the present invention includes a first stage and a second stage, and may contain another resin stage, for example, a third stage. Other resin segments are not particularly limited as long as the split-type conjugate fiber targeted by the present invention can be obtained. As the resin components constituting the other segments, for example, polybutene-1, polymethylpentene, ethylene vinyl alcohol copolymer, ethylene propylene copolymer, polyethylene terephthalate, polyethylene terephthalate Butylene glycol, nylon 6, nylon 66, etc. are used alone or in combination of two or more. The other segments may be one type or two or more types.

In the split-type conjugate fiber, it is preferable to arrange the segments mutually. For example, it may be radial, multi-layered, cross-shaped, or the like. Among them, from the viewpoint of further improving the splittability of the split-type conjugate fiber, it is preferable that the segments of the split-type conjugate fiber are arranged radially.

In split-type composite fibers, the number of splits (total number of segments) can be determined according to the fineness of the split-type composite fibers, the fineness of ultrafine fibers to be obtained, and the like. The number of divisions is, for example, preferably 4 to 30, more preferably 6 to 24, most preferably 8 to 18, and most preferably 8 to 16. When the number of divisions is 4 to 30, moderate fiber productivity can be achieved, and moderate division performance can be maintained even if spinning is easier.

The split-type conjugate fiber preferably has a hollow portion at the center of the fiber when viewed from the cross section of the fiber. When the fiber center has a hollow part, the puncture strength of the fiber structure can be improved compared to the segmented composite fiber without a hollow part in the fiber center. These are presumed to be due to the fact that the fiber cross-section of the ultrafine fibers formed by splitting the split-type conjugate fibers becomes more circular. In addition, it is possible to suppress yarn breakage of the split-type conjugate fiber during the spinning process.

When the split-type conjugate fiber has a hollow portion, the hollow ratio can be determined according to the split ratio and the cross-sectional shape of the microfiber. The hollow ratio is the area ratio occupied by the hollow portion in the cross section of the fiber. For example, the hollow ratio is preferably about 1% to 50%, more preferably about 5% to 40%. More specifically, when the division number is 6 to 10, the hollow rate is preferably 5% to 20%, and when the division number is 12 to 20, the hollow rate is preferably 15% to 40%. When the hollow rate is about 1% to 50%, even if the effect of providing the hollow part is easy to be obtained, the split type composite fiber is not easy to split in the manufacturing process, so it is easy to handle, so it is preferable.

In the fiber cross-section of the segmented composite fiber, the first section preferably occupies 20% to 80% of the area, and more preferably occupies 40% to 60% of the area. When the first stage of the split-type composite fiber occupies 20% to 80% of the area, the splittability of the split-type composite fiber is not easily reduced, and it can be easily split to form ultrafine fibers 1 originating from the first stage.

The volume ratio of the first stage and the second stage constituting the split-type conjugate fiber is not particularly limited as long as the split-type conjugate fiber targeted by the present invention can be obtained. For example, the volume ratio of the first stage to the second stage (since the cross-sectional structure of the second stage is a core-sheath type resin stage in which the first component is the core component and the second component is the sheath component, the second stage The total volume of the core component and the sheath component) is preferably 2/8 to 8/2 (volume of the first section/volume of the second section), more preferably 4/6 to 6/4. When the volume ratio is 2/8 to 8/2, the spinnability and splittability are further improved, so it is preferable.

The second section is a core-sheath type resin section. The volume ratio of [the first section + the second section core component]/[the second section sheath component] of the fiber section is preferably 2/8 to 8/2, and 4 /6 to 6/4 is better. When the volume ratio is 2/8 to 8/2, it is preferable because the spinnability and splitability are improved. Also, for example, when the volume ratio of [the first stage + the core component of the second stage]/[the sheath composition of the second stage] is 5/5, it should be noted that the volume of the first stage will become smaller than that of the entire second stage volume.

The volume ratio of the first component to the second component is not particularly limited as long as the split-type conjugate fiber targeted by the present invention can be obtained. For example, the ratio of the volume of the first component to the volume of the second component (the total volume of the core component and the sheath component) is preferably 8/2 to 3/7 (volume of the first component/volume of the second component), 75/25 to 35/65 is better, and 70/30 to 40/60 is especially good. When the volume ratio is 8/2 to 3/7, the spinnability and splittability are further improved, so it is preferable.

As long as the segmented composite fiber that is the object of the present invention can be obtained, the fineness before splitting of the segmented composite fiber is not particularly limited, but it is preferably 0.5dtex to 4.8dtex, preferably 0.8dtex to 3.6dtex, and 1.1dtex to 2.4dtex is better, and 1.1dtex to 2.0dtex is the best. When the fineness before splitting of the split type conjugate fiber is 0.5 dtex to 4.8 dtex, spinning is easier and productivity is improved, so it is preferable.

The single fiber strength of split type composite fiber before splitting is preferably 2.5 to 7.0cN/dtex, preferably 2.7 to 6.5cN/dtex, more preferably 2.8 to 6.0cN/dtex, and 3.0 to 5.8cN /dtex is preferred. The single fiber strength was measured by the method described in the Examples.

The elongation before splitting of split fibers is preferably 10 to 120%, more preferably 15 to 80%, more preferably 20 to 60%, and most preferably 20 to 55%. The elongation was measured by the method described in the Examples.

DSC (differential scanning calorimetry) is performed on the split type conjugate fiber, and the obtained DSC curve will be described. The DSC curve obtained from the DSC of the entire segmented composite fiber can be based on the melting point, molecular weight distribution, crystallization state, crystallinity, and each of the polypropylene resin and polyethylene resin contained in the segmented composite fiber. The amount contained, and the type, amount, and crystal state of other thermoplastic resins contained in the split type conjugate fiber are changed.

The split-type conjugate fiber of the present invention is subjected to DSC. Among the obtained DSC curves, the shape of the melting peak of the polypropylene resin affects various physical properties of the split-type conjugate fiber, especially the splittability of the split-type conjugate fiber. Hereinafter, the shape of the melting peak of the polypropylene resin shown in the DSC curve obtained by performing DSC on the split-type conjugate fiber of the present invention will be described. In the segmented composite fiber containing polypropylene resin, in the DSC curve, the melting peak of the polypropylene resin has the shape peak shown in Figs. 4 to 11.

The symbols in Figs. 4 to 11 have the following meanings.

a: Melting peak of polypropylene resin contained in split type conjugate fiber

a ₁ : 1st melting peak of polypropylene resin (1st melting peak)

a ₂ : Second melting peak of polypropylene resin (second melting peak)

a ₃ : valley of melting peak of polypropylene resin (valley of melting peak)

T ₁ : the first melting peak temperature (°C) of polypropylene resin (hereinafter, also simply referred to as the first melting peak temperature)

T ₂ : Second melting peak temperature (°C) of polypropylene resin (hereinafter also referred to simply as second melting peak temperature)

W ₂ : heat flux in the second melting peak of polypropylene resin (mW)

W ₃ : heat flux (mW) present in the trough (a ₃ above) between the first melting peak and the second melting peak of the polypropylene resin

S ₁ : The area of the first endothermic peak of polypropylene resin (the area of the first melting peak)

S ₂ : The area of the second endothermic peak of polypropylene resin (the area of the second melting peak)

BL _LT : Baseline on the low temperature side of the DSC curve

BL _HT : Base line on the high temperature side of the DSC curve

BL _E : In the DSC curve, the straight line that extends the reference line on the low temperature side from the end of the high temperature side (the right end of BL _LT ) to the end of the low temperature side of the reference line on the high temperature side (the left end of BL _HT )

In addition, in Figures 4 to 11, the vertical axis represents heat absorption energy corresponding to heat flux (generally, the unit is mW: centimeter watt), and the horizontal axis represents time (generally, the unit is second or minute).

The split type conjugate fiber of the present invention is characterized in that the melting peak shape of the polypropylene resin is a bimodal shape in the DSC curve. When the shape of the melting peak of the polypropylene resin is a bimodal shape, it means any shape corresponding to the following (1) or (2).

(1) Among the endothermic peaks of the polypropylene resin, after the first melting peak (a ₁ ) appears on the low temperature side (in other words, the side where the elapsed time from the temperature rise is short), the melting peak of the polypropylene resin appears clearly After the middle valley (a ₃ ), the second melting peak (a ₂ ) appears on the high temperature side (in other words, the side where the elapsed time from the temperature rise is longer).

(2) Among the melting peaks of the polypropylene resin, the first melting peak appears on the low-temperature side, but the apexes at which the two peaks can be separated do not appear clearly between the first melting peak and the second melting peak, (in other words, there is no clear It is called the valley (a ₃ ) of the melting peak of the polypropylene resin, and presents a shoulder-like shape (shoulder peak) as shown in Figures 8 to 11.

First, the melting peak shape of the polypropylene resin satisfying the above (1) condition will be described.

Figures 4 to 7 show schematic diagrams of melting peak shapes satisfying the condition (1) above. At the melting peak that satisfies the above (1) condition, in DSC, the melting of the polypropylene resin begins at a sample temperature of about 145°C, and the first melting peak (a ₁ ) is measured in the sample temperature range of about 157 to 165°C . As time elapses and the temperature of the sample rises further, the trough (a ₃ ) of the melting peak of the polypropylene resin clearly appears, and then the second melting peak (a ₂ ) appears in the sample temperature range of about 165 to 175°C. Melting of the polypropylene resin was completed when the sample temperature reached 180°C.

Next, the melting peak shape of the polypropylene resin satisfying the condition of (2) above will be described.

Figures 8 to 11 show schematic diagrams of melting peak shapes satisfying the aforementioned condition (2). For the melting peak that satisfies the above (2) condition, in DSC, the melting of the polypropylene resin starts from the sample temperature of about 145°C, but the first melting peak that becomes the minimum value is not measured. , the second melting peak (a ₂ ) appears as the temperature of the sample rises, and the melting of the polypropylene resin is completed when the temperature of the sample reaches 180°C. The shape of such a melting peak is measured when the temperatures of the first melting peak and the second melting peak are close.

In the DSC curve, whether the shape of the melting peak of the polypropylene resin is bimodal, when one of the conditions (1) to (2) above is met, it is a bimodal shape, and when none of them are satisfied, the shape of the melting peak is not bimodal, or That is, it becomes the shape of a single peak (Fig. 12). The single peak shape can be judged by investigating the DSC curve divided by the DDSC curve. The DDSC curve is a curve in which the DSC curve is differentiated with time, and represents the slope of the DSC curve. Therefore, since the slope of the DSC curve becomes zero when it becomes zero, the value of the DDSC curve becomes zero at the maximum or minimum value of the DSC curve.

In the split type conjugate fiber of the present invention, the shape of the melting peak (a) of the polypropylene resin is a bimodal shape, more specifically, as long as any one of the aforementioned conditions (1) to (2) is satisfied, but It is particularly preferable to satisfy the condition of (1) above. When the shape of the endothermic peak resulting from the melting of the polypropylene resin in the DSC curve satisfies the condition (1) above, in other words, in the DSC curve, there are two melting peaks with minimum values, and there is a clear gap between the two melting peaks. At the valley (a ₃ ) of the melting peak, it is estimated that the polypropylene resin contained in the split type conjugate fiber not only has a high degree of crystallinity, but also crystallizes in a lower temperature melting region and a higher temperature melting region. . The reason why the splittability of the obtained split-type conjugate fiber increases when the above-mentioned condition (1) is satisfied is not clear, but it can be estimated as follows from the selected resin properties and the DSC curve of the split-type conjugate fiber.

As described above, in the DSC curve of the split-type conjugate fiber, if the melting peak shape of the polypropylene resin satisfies the above-mentioned (1) condition, it is estimated that the polypropylene resin crystallizes in a lower melting region and a higher melting region.

The region that melts at a lower temperature is an amorphous phase, the crystalline phase that melts at a lower temperature, and the crystallized phase, but a phase with a lower molecular weight is crystallized, but it is presumed to include distortion/cutting in the molecular chain by the elongation step equal.

On the other hand, in the crystalline region melted at a higher temperature, there are no crystallized polypropylene molecules during melt spinning, and as a result of stretching at a high stretching ratio above the glass transition temperature of polypropylene in the stretching step, it is presumed that the polypropylene A region generated by sufficient crystallization of propylene.

In addition, the present invention is presumed to exert an excellent effect due to such a reason, but the present invention is not limited by such a reason.

In order to increase the degree of crystallization of the polypropylene resin contained in the segmented conjugate fiber, it is presumed that most of the polypropylene molecules are crystallized in the stretching step. For this reason, it is presumed that it is preferable to make the size of the polypropylene molecule, that is, the molecular weight of the polypropylene molecule uniform, and to make the motion uniform. Therefore, in the segmented conjugate fiber of the present invention, the polypropylene resin constituting the resin segment contains a resin having a narrow molecular weight distribution, that is, the ratio of the weight average molecular weight to the number average molecular weight after spinning is A polypropylene resin having a Q value of 6 or less. The polypropylene resin whose Q value after spinning is greater than 6 has a relatively large molecular weight range of the polypropylene molecule, that is, there are more polypropylene molecules with too large a molecular weight (too long molecule), and/or the molecular weight is too small ( Molecules are too short) There are many polypropylene molecules, so the former is crystallized in the spinning step, and it becomes difficult to stretch in the stretching step, resulting in the deterioration of the step-by-step process of the stretching step, and the latter is difficult to crystallize even after the stretching step , Therefore, the remaining soft region in the resin segment becomes the cause of the decrease in splittability in the split-type conjugate fiber.

In addition, in the present invention, the differential scanning calorimetry (DSC) of the split type conjugate fiber is measured in accordance with JIS K 7121 (1987) Transition temperature measurement method of plastics.

The split-type conjugate fiber of the aspect of the present invention preferably satisfies at least one of (A) and (B) shown below.

(A) In differential scanning calorimetry (DSC) performed under the aforementioned conditions, the melting peak of the polypropylene resin is divided into a low-temperature side region and a high-temperature side region, and the areas of each region are defined as the first melting peak area, the second melting peak area, and the second melting peak area. For the melting peak area, the ratio of the second melting peak area to the first melting peak area (second melting peak area/first melting peak area) is 0.85 to 3.5, preferably 0.9 to 3.2, more preferably 0.95 or more Below 3.0, more preferably above 1.0 and below 2.5.

(B) In the differential scanning calorimetry (DSC) performed under the aforementioned conditions, for the melting peak in the DSC curve of the aforementioned polypropylene resin, obtained from the values of W ₂ and W ₃ obtained by the method described later The extension of the second peak is at least 0.6, and the extension of the second peak is preferably at least 0.7, more preferably at least 0.8, and still more preferably at least 0.85.

The above-mentioned (A) condition which is a preferable condition in the split type conjugate fiber of this invention is demonstrated.

In the DSC of split-type composite fibers, the measured shape of the melting peak of the polypropylene resin is the valley (a ₃ ) in the melting peak of the polypropylene resin when the melting peak satisfies the above-mentioned (1) condition. A straight line perpendicular to the horizontal axis is drawn, and the straight line is used as a boundary line to divide the melting peak of polypropylene into a low-temperature side region and a high-temperature side region. In this straight line, DSC curve, and melting peak of polypropylene, the reference line (BL _LT ) on the low temperature side is formed by a straight line (BL _E ) extending from the end of the high temperature side to the reference line (BL _HT ) on the high temperature side The area of each surrounded region is referred to as the first melting peak area and the second melting peak area. More specifically, in FIG. 6 , the shaded area S1 is the _first melting peak area, and the hatched area S2 in FIG. ₇ is the second melting peak area.

The above-mentioned (A) condition which is a preferable condition in the split type conjugate fiber of this invention is demonstrated further.

When the measured melting peak shape of the polypropylene resin in the DSC of the segmented conjugate fiber is a melting peak satisfying the condition (2) above, for the shoulder measured in the melting peak (a) of polypropylene, From the point at which the absolute value of the first _- order differential of the DSC curve becomes the minimum between T1 and T2, draw _a straight line perpendicular to the horizontal axis of the graph, and use this straight line as a boundary line to divide the melting peak of polypropylene into low temperature The area on the side, the area on the high temperature side.

In this straight line, DSC curve, and melting peak of polypropylene, the reference line (BL _LT ) on the low temperature side is formed by a straight line (BL _E ) extending from the end of the high temperature side to the reference line (BL _HT ) on the high temperature side The areas of the surrounding regions are referred to as the first melting peak area and the second melting peak area. More specifically, in FIG. 10, the shaded area S1 is the _first melting peak area, and the hatched area S2 in FIG. ₁₁ is the second melting peak area.

When calculating the ratio of the area of the second melting peak to the area of the first melting peak (the area of the second melting peak/the area of the first melting peak), after printing the DSC curve on paper, drawing the boundary line in the above-mentioned method, and cutting out the corresponding The portion of the first melting peak area corresponds to the portion of the second melting peak area and their mass is measured to obtain the ratio of the second melting peak area to the first melting peak area (second melting peak area/first melting peak area) Peak area). Alternatively, the DSC curve can be automatically integrated in any interval using a measuring device (using the function attached to the measuring device), and the area of the first melting peak and the area of the second melting peak can be calculated to calculate the ratio of these.

The aforementioned condition (B) which is a preferable condition in the split type conjugate fiber of the present invention will be described.

(B): In the differential scanning calorimetry (DSC), the melting peak of the bimodal polypropylene resin is divided into a first melting peak and a second melting peak, and the DSC curve value at the temperature of the second melting peak As W ₂ (mW), between the first melting peak and the second melting peak, the value of the DSC curve when the absolute value of the first differential of the DSC curve becomes the minimum is W ₃ (mW), and the value of the second peak defined by the following formula The extension is 0.6 or more.

‧Extension of the second melting peak=(absolute value of W ₂ )-(absolute value of W ₃ )

More specifically, in the melting peak (a) of polypropylene shown in Fig. 5, there are the second melting peak (a ₂ ), the first melting peak (a ₁ ), and the gap between a ₁ and a ₂ When measuring the trough (a ₃ ) of the melting peak of the polypropylene resin, measure the DSC value (W ₂ ) in a ₂ and the DSC value (W ₃ ) when it becomes the trough (a ₃ ) of the melting peak, W ₂ The difference between the absolute values of , W ₃ is the extension of the second melting peak.

The aforementioned condition (B) which is a preferred condition in the split-type conjugate fiber of the present invention will be further described.

When the shape of the melting peak of the polypropylene resin measured by DSC of the split type conjugate fiber satisfies the aforementioned condition (2), the extension of the second melting peak is defined as follows.

That is, (B): In the differential scanning calorimetry (DSC), the melting peak of the bimodal polypropylene resin is divided into a first melting peak and a second melting peak, and the temperature at which the second melting peak becomes The value of the DSC curve is W ₂ (mW), and the value of the DSC curve when the absolute value of the first differential of the DSC curve becomes the minimum between the first melting peak and the second melting peak is W ₃ (mW), defined by the following formula The extension of the second peak is above 0.6

‧Extension of the second melting peak=(absolute value of W ₂ )-(absolute value of W ₃ )

More specifically, as shown in Fig. 9, in the melting peak (a) of polypropylene, there is a second melting peak (a ₂ ) and a shoulder measured on the low temperature side thereof, and the DSC in a ₂ is measured The value (W ₂ ), the DSC value (W ₃ ) measured when the absolute value of the primary differential of the DSC curve between T ₁ and T ₂ becomes the minimum point (W 3 ), the difference between the absolute values of W ₂ and W ₃ is Extension of the second melting peak.

In addition, DSC curves obtained by performing DSC on the split-type conjugate fiber according to the embodiment of the present invention will be described using Figs. 4 to 11, but Figs. 4 to 11 represent only an example. For example, the shape of these DSC curves, that is, the shape of the melting peak of the polypropylene resin is such that the melting peak (first melting peak) on the low temperature side is smaller than the melting peak (second melting peak) on the high temperature side, in other words, the melting peak on the high temperature side The melting peak (second melting peak) is larger than the melting peak (first melting peak) on the low temperature side, but such a shape is not necessary. Therefore, even if the size relationship between the first melting peak and the second melting peak is opposite, and the first melting peak is larger than the second melting peak (the melting peak is sharp and elongated), the aforementioned conditions are still met, that is, the conditions described in the present invention are satisfied. The melting peak shape of polypropylene resin is defined as bimodal, and the split type composite fiber satisfying the ratio of the area of the second melting peak to the area of the first melting peak and the extension of the second melting peak is also included in the present invention. .

<Microfiber>

Split-type composite fibers are split to form ultrafine fibers 1 from the first stage, and to form ultrafine fibers 2 from the second stage. When other segments are contained, other ultrafine fibers originating from other segments are formed.

The fiber cross-sectional structure of the segmented composite fiber is preferably a radial fiber cross-sectional structure in which segments are alternately arranged. Also, in the split-type composite fiber, a fiber cross-sectional structure having a hollow portion at the center of the fiber is also preferable.

The ultrafine fiber 1 and/or ultrafine fiber 2 is preferably one whose fineness is less than 0.6 dtex, more preferably less than 0.4 dtex. When the fineness of the ultrafine fiber is less than 0.6 dtex, a thinner fiber structure can be obtained more easily. In addition, the fineness of the ultrafine fiber 1 and the ultrafine fiber 2 may be the same or different, and the lower limit of the fineness of any ultrafine fiber is preferably 0.006 dtex.

In particular, since the ultrafine fiber 2 is a core-sheath type, the fineness of the ultrafine fiber 2 is preferably less than 0.4 dtex. When the fiber structure contains the core-sheath type composite fiber, the smaller the fineness of the composite fiber is, the larger the surface area of the composite fiber is, so the thermally bonded area becomes larger, and the mechanical strength of the thermally bonded fiber structure becomes higher. When the ultrafine fiber 2 is a core-sheath type ultrafine composite fiber, it is preferable to have a particularly smaller fineness.

<Manufacturing method of split type composite fiber>

Another purpose of the present invention is to provide a novel manufacturing method of split-type composite fibers. The manufacturing method of the split-type composite fibers includes the following steps:

A step of preparing a melt-spinning machine equipped with a split-type composite nozzle for forming a split-type composite fiber, the split-type conjugate fiber being in a fiber cross-section, comprising a first stage and a second stage of the split-type composite fiber, wherein the aforementioned The first section is a resin section made of the first component, and the above-mentioned second section is a core-sheath type resin section with the above-mentioned first component as the core component and the second component as the sheath component; Mw/Mn is used A resin component containing 50% by mass or more of polypropylene resin of 6 or less is used as the first component, and a resin component containing 50% by mass or more of polyethylene resin is used as the second component, and is produced by melt spinning with a melt spinning machine. The step of spinning long fibers; the step of stretching the spun long fibers at a stretching temperature of 60°C to 125°C and a stretching ratio of 1.1 times or more to obtain split type composite fibers.

The above-mentioned split-type composite fiber of the present invention is not particularly limited in its production method as long as the target split-type composite fiber can be obtained. However, the above-mentioned split-type composite fiber can be preferably produced by using the above-mentioned production method of the split-type composite fiber. The split-type composite fiber of the form of the present invention.

Hereinafter, a method for producing split type conjugate fibers will be described in more detail.

The split-type composite fiber can be composite-spun using a conventional melt-spinning machine using an appropriate composite spinning nozzle in order to obtain a desired fiber cross-sectional structure. The spinning temperature (nozzle temperature) is selected in accordance with the resin component used, for example, it can be set at 200°C or higher and 360°C or lower.

Specifically, the melt spinning machine is equipped with a split-type composite nozzle that can obtain a predetermined fiber cross-section, so that the first segment and the second segment are adjacent to each other in the fiber cross-section and form a mutually segmented structure. From 200 to 360°C, the polypropylene resin constituting the first stage and the polyethylene resin constituting the second stage are extruded and melt spun to obtain spun long fibers (unstretched fiber bundles).

The fineness of the spun long fibers (unstretched fiber bundles) can be in the range of 1 dtex to 30 dtex. When the fineness of the spun filament is 1 dtex or more and 30 dtex or less, spinning can be performed more easily. When the spinning long fiber is highly extended to improve splitability, the fineness of the spinning long fiber is preferably 2.0 to 15dtex, more preferably 2.5 to 12dtex, more preferably 3 to 10dtex, and 4.0 to 8.0dtex Very good, with 4.5 to 7.5dtex being the best.

Next, the spun long fibers are drawn using a known drawing machine to obtain drawn long fibers. The stretching treatment is preferably carried out by setting the stretching temperature at a temperature in the range of 60°C to 125°C, more preferably at a temperature in the range of 80°C to 120°C. In addition, the stretching treatment is preferably performed at or below the melting point of the resin having the lowest melting point among the resin components constituting the split type conjugate fiber. The extension ratio is preferably 1.1 times or more, preferably 1.5 times or more, more preferably 2 to 8 times, particularly preferably 3 to 6 times, and most preferably 3.5 to 5.5 times. When the stretching ratio is set to 1.1 times or more, splittability is improved because the molecules constituting the fiber are aligned in the longitudinal direction of the fiber.

Depending on the resin components used, the stretching method can be carried out in warm water or hot water, wet stretching, hot air, dry stretching in a high temperature environment, or in a liquid heat medium other than water such as silicone oil. However, in terms of good thermal efficiency and excellent productivity, dry stretching, wet stretching, and steam stretching are preferred, and dry stretching or wet stretching is more preferred. The stretching method can be selected in consideration of the use of the obtained split-type composite fiber. That is, for applications that can be split at a high rate without being exposed to high-pressure water flow, or that require high single fiber strength, when using the split-type composite fiber of the present invention, the stretching method is preferably dry stretching at a higher temperature or The stretching method of water vapor stretching. Conversely, when using the split-type composite fiber of the present invention as the fiber constituting the hydroentangled nonwoven fabric, if it is used for an application that does not require high single-fiber strength for the obtained split-type composite fiber or the ultrafine fiber obtained after splitting , it is preferable to carry out wet stretching which is easy to stabilize in productivity. In the case of the wet stretching method, the stretching temperature can be set in the range of 60°C to 98°C, or in the range of 60°C to 95°C, or in the range of 70°C to 95°C. It can also be set in the range of 80°C or higher and 95°C or lower. In the case of the dry stretching method, the stretching temperature can be set within the range of 80°C to 125°C, 90°C to 125°C, or 100°C to 125°C. It can be set within the range of 100°C to 120°C.

The extension ratio is preferably 0.7 to 0.98 times the maximum extension ratio (Vmax) (extension ratio/Vmax=0.7 to 0.98), preferably 0.75 to 0.97 times, and 0.8 to 0.96 times More preferably, it is more than 0.85 times but not more than 0.96 times. When the draw ratio is 0.7 to 0.98 times the maximum draw ratio (Vmax) (draw ratio/Vmax = 0.7 to 0.98), the spun long fibers are stretched at a high draw ratio. The polypropylene molecules contained in the polypropylene resin and the polyethylene molecules constituting the polyethylene resin are crystallized by the stretching treatment, or the molecular arrangement is oriented, so the obtained split type conjugate fiber becomes easy to split in each segment the beneficial effect.

The maximum elongation ratio was obtained by the method described in the examples.

A predetermined amount of fiber treatment agent is applied to the obtained elongated long fibers as required, and mechanical crimping is given by a crimping device (a device for imparting crimping) as required. The fiber treatment agent can easily disperse fibers in water or the like when producing a nonwoven fabric by a wet papermaking method as described later. Also, when the fiber treatment agent is dyed into the fiber by applying an external force (external force, such as an external force applied when crimping is applied by a crimper) from the surface of the fiber, the fiber treatment agent can be dyed again. Improves dispersibility to water etc.

The long fibers after adding the fiber treating agent (or in a wet state without adding the fiber treating agent) are subjected to drying treatment at a temperature ranging from 80°C to 110°C for several seconds to about 30 minutes to dry the fibers. The drying treatment can be omitted depending on the occasion. Thereafter, the long fibers are preferably cut so that the fiber length becomes 1 mm to 100 mm, more preferably 2 mm to 70 mm. As will be described later, when the nonwoven fabric is produced by the wet papermaking method, it is more preferable to set the fiber length to 3 mm to 20 mm. When the nonwoven fabric is produced by the wet papermaking method, the shorter the fiber length, the higher the split ratio of the split-type composite fiber. When the nonwoven fabric is produced by the cutting method, it is more preferable to set the fiber length to 20 mm to 100 mm.

<fibrous structure>

The fibrous structure of the present invention will be described. The form of the fibrous structure is not particularly limited, and examples thereof include woven fabrics, knitted fabrics, and nonwoven fabrics. Also, the form of the fiber web of the above-mentioned nonwoven fabric is not particularly limited, and examples thereof include a card web formed by a cutting method, an air lay web formed by an air-flow method, and an air lay web formed by an air-flow method. A wet papermaking wire formed by a wet papermaking method, etc.

The fibrous structure preferably contains ultrafine fibers formed by splitting split-type conjugate fibers in a ratio of 5% by mass or more. That is, the fibrous structure may contain the ultrafine fibers 1 and the ultrafine fibers 2 in a ratio of 5% by mass or more in total. The fibrous structure preferably contains ultrafine fibers at a ratio of 10% by mass or more, more preferably at least 20% by mass, most preferably at least 25% by mass. A preferable upper limit is 100% by mass. When the proportion of split-type conjugate fibers in the fibrous structure is large, it tends to be easy to obtain a dense nonwoven fabric.

Even if the fiber structure is used as a separator in various secondary batteries such as lithium-ion batteries and nickel-metal hydride batteries, various condensers, and various capacitors, it is used to capture and/or capture fluids from liquids and gases. Or the fibrous structure used for the filter layer of various filters such as cartridge filter and laminated filter to remove foreign matter; as reverse osmosis membrane (RO membrane), nanofiltration membrane (NF membrane), ultrafiltration Fibrous structures for various membrane supports used as supports for various filtration membranes such as membranes (UF membranes) and precision filtration membranes (MF membranes); fibrous structures for various wiping cloths for wiping people and/or objects ; Fibrous structures for skin covering films impregnated with cosmetics such as facial masks; surface films, second sheets and back sheets constituting absorbent articles such as disposable diapers for infants, nursing disposable diapers, sanitary pads, etc. In the case of the fibrous structure of the sheet for absorbent articles, a fibrous structure in which the ratio of the aforementioned split-type conjugate fibers is 100% by mass can be used. For the fibrous structure containing the above-mentioned split-type composite fibers, if a certain degree of voids between the constituent fibers or the accompanying air permeability and liquid permeability are required, the content of the split-type composite fibers in the entire fiber structure can be 90% Mass % or less, may be 80 mass % or less, may be 75 mass % or less. In addition, the lower limit of the split-type conjugate fibers contained in the fibrous structure is as described above, and may be 10% by mass or more, may be 20% by mass or more, or may be 25% by mass or more.

When the ratio of the above-mentioned split-type conjugate fibers contained in fiber structures such as dry-laid nonwoven fabrics and wet-laid nonwoven fabrics is 90% by mass or less, the ratio of ultrafine fibers generated from the split-type conjugate fibers occupied in the obtained fiber structure becomes Moderate, depending on the use of the fiber structure, the structure becomes a moderately dense non-woven fabric, so it is preferable.

The fibrous structure preferably contains the ultrafine fiber 2 at a rate of 10% by mass or more, more preferably contains the ultrafine fiber 1 at a rate of 20% by mass or more, and most preferably contains the ultrafine fiber 2 at a rate of 35% by mass or more. A preferable upper limit is 50% by mass. When the non-woven fabric contains the core-sheath type ultra-fine composite fiber as the ultra-fine fiber 2 at the ratio of the above-mentioned range, since the core-sheath type composite fiber with a small fineness (less than 0.6 dtex) is contained, compared with the core containing the same amount of large fineness The non-woven fabric of sheath type composite fiber has higher mechanical strength. In addition, a thin fiber structure with excellent mechanical strength can be obtained.

When the ultrafine fibers are contained in an amount of 5% by mass or more, the fibrous structure may contain fibers other than the ultrafine fibers formed of the aforementioned split-type composite fibers in an amount of 95% by mass or less. Other fibers may be natural fibers or regenerated fibers, or single fibers or composite fibers made of synthetic resins. Alternatively, other fibers may include ultrafine fibers formed from other split-type composite fibers. Alternatively, other fibers may be ultrafine fibers not formed of split-type composite fibers, but ultrafine fibers having a fineness of less than 0.6 dtex produced by a single spinning method. Alternatively, the fibrous structure may be made only of fibers derived from the aforementioned split-type composite fibers (including ultrafine fibers 1 derived from the first step, ultrafine fibers 2 derived from the second step, and fibers produced due to incomplete splitting). Fibers with a large fineness and fibers branched from one fiber, etc.), or may be composed only of ultrafine fibers formed of the aforementioned split-type composite fibers.

For fibrous structures, preferably, the total amount of fibers with small fineness (less than 0.6 dtex) in the fibrous structure is preferably at least 10% by mass, preferably at least 20% by mass, and preferably at least 50% by mass. Better, more than 70% by mass is the best. In addition, a preferable upper limit is 100% by mass. When the total amount of small-denier (less than 0.6 dtex) fibers in the fibrous structure is within the above range, a thinner fibrous structure can be easily obtained. The fibers of small fineness (less than 0.6 dtex) occupied in the fibrous structure may be composed of only the ultrafine fiber 1, only the ultrafine fiber 1 and the ultrafine fiber 2, or these and other ultrafine fibers.

In the above-mentioned fibrous structure, the split-type conjugate fiber of the present invention can be split by imparting a physical impact. For example, it can be implemented by hydroentanglement treatment (jet high-pressure water flow), or when producing nonwoven fabrics by wet papermaking method, it can be implemented by utilizing the impact of dissociation treatment during papermaking.

The water flow interweaving treatment is preferably set up from nozzles with an aperture of 0.05 to 0.5mm at intervals of 0.5 to 1.5mm, spraying a columnar water flow with a water pressure of 3 to 20MPa on the surface and back of the non-woven fabric for more than once. Furthermore, in the case of the split-type conjugate fiber of the present invention, even in the so-called split-type conjugate fiber of the present invention, which is less likely to cause disorder in the texture of the fiber web or the water pressure of the opening through the high-pressure water flow is 10 MPa or less, sufficient split cannot be obtained. It can be divided even under low pressure, and can be divided even if the water pressure is below 8MPa, especially even if the water pressure is below 6MPa.

Regarding the manufacturing method of the fibrous structure, a nonwoven fabric will be described as an example. The nonwoven fabric is produced by producing a fiber web according to a known method, and then, if necessary, applying heat treatment to thermally bond the fibers to each other. In addition, the fiber web may be given fiber intertwining treatment as needed. The fiber web is, for example, a dry method such as a cutting method or an air-flow method using split type composite fibers with a fiber length in the range of 10 mm to 80 mm, or a fiber web with a fiber length in the range of 2 mm to 20 mm. Produced by wet papermaking method of split type composite fiber. When used in the fields of wiping people/objects or filtering, nonwoven fabrics produced by dry methods such as cutting methods or air-flow methods are preferred. This is because the non-woven fabric produced by the dry method has a soft feel and a moderate density. Also, when used in the field of battery separators, etc., a nonwoven fabric made from a wet-type papermaking wire is preferable. This is due to the fact that non-woven fabrics produced using wet-laid papermaking wires are generally dense and have a good texture. Also, in the wet papermaking method, by adjusting the dissociation treatment conditions during paper production, it is possible to divide the split type conjugate fiber at a desired split ratio only by the dissociation treatment.

Second, the fiber web can be given a heat bonding treatment. For example, core-sheath composite fibers are added in addition to split composite fibers, and the fibers can be bonded to each other by the sheath component of the core-sheath composite fibers. Alternatively, if the ultrafine fiber 2 is included, since the ultrafine fiber 2 is a core-sheath type ultrafine composite fiber, the fibers can be bonded to each other by the sheath component of the core-sheath type ultrafine composite fiber. The conditions of the heat bonding treatment can be appropriately selected according to the basis weight of the fiber web, the cross-sectional shape of the core-sheath type ultrafine composite fiber, and the type of resin constituting the fiber contained in the nonwoven fabric. For example, as a heat treatment machine, a roll dryer (Yankee dryer), a processing machine with hot air blowing, a hot roll processing machine, or a hot press processing machine can be used. In particular, a roll dryer (Yankee dryer) is preferable because it can thermally bond fibers to each other while adjusting the thickness of the nonwoven fabric. The heat treatment temperature of the roller dryer is, for example, preferably 80 to 160°C when the sheath component is ethylene-vinyl alcohol copolymer, and 100 to 160°C when the sheath component is polyethylene.

As will be described later, when the fiber web is subjected to hydroentanglement treatment, it is preferable to perform thermal bonding treatment before hydroentanglement treatment. When the fibers of the fiber web are bonded to each other in advance and then subjected to water flow intertwining treatment, it is difficult for the fibers to "escape" when the high-pressure water flow is applied to the fibers, and the fibers can be closely intertwined with each other, which further promotes the splitting of split-type composite fibers. In particular, heat bonding treatment may be performed after fibers are entangled with each other. That is, the order of heat bonding treatment and hydroentanglement treatment is not particularly limited as long as the desired nonwoven fabric is obtained.

In the fibrous structure of the present invention, fibers may be entangled with each other. For the treatment of interlacing the fibers, it is preferable to use a hydroentanglement treatment in which the fibers are intertwined by the action of high-pressure water flow. If the hydroentanglement treatment is performed, the fibers can be strongly intertwined without impairing the overall compactness of the nonwoven fabric. In addition, by the hydroentanglement treatment, the splitting of the split-type composite fibers and the intertwining of ultrafine fibers generated by the splitting can be performed simultaneously with the intertwining of the fibers.

The conditions of hydro-interlacing treatment are appropriately selected according to the type and basis weight of the fiber web to be used, the type and ratio of fibers contained in the fiber web, and the like. For example, when a wet-type papermaking web with a basis weight of 10 to 100 ^g /m2 is subjected to hydroentanglement treatment, the fiber web can be placed on a support such as a plain weave structure with a mesh size of 70 to 100 meshes, and the hole diameter is 0.05 to 0.3 mm. The nozzles are set as nozzles at intervals of 0.5 to 1.5 mm, and the columnar water flow with a water pressure of 1 to 15 MPa, preferably 2 to 10 MPa, is sprayed on one or both sides of the fiber web for 1 to 10 times. The fibrous web after hydroentanglement treatment can be given drying treatment as required.

The fibrous structure can be given a hydrophilic treatment as needed. The hydrophilization treatment can be performed by any method such as fluorine treatment, graft polymerization treatment of vinyl monomers, sulfonation treatment, discharge treatment, surfactant treatment, or hydrophilic resin imparting treatment.

The fibrous structure preferably has a basis weight of 2 g/m ² to 100 g/m ² , more preferably has a basis weight of 10 g/m ² to 100 g/m ² , and more preferably has a basis weight of 20 g/m ² to 80 g/m 2 The basis weight is not more than 30 ^g /m ² and not more than 60 g/m ² . When the basis weight of the fiber web is 2 g/m ² or more, the texture of the obtained fiber web and fiber structure becomes good, and the strength or puncture strength of the fiber structure tends to be higher. When the basis weight of the fiber web is 100 g/m ² or less, the air permeability of the fiber structure does not decrease, and when the split type conjugate fiber of the present invention contained in the fiber web is divided into individual components by the hydroentanglement treatment described later Therefore, the high-pressure water flow becomes easy to uniformly act on the entire fiber web, and it becomes easy to sufficiently divide the above-mentioned split-type composite fibers.

In addition, since the present invention can bond the ultrafine fibers to each other by the sheath component of the core-sheath type ultrafine composite fiber formed in the second stage, it is possible to form a fiber structure in which the fibers are interlinked only by the ultrafine fibers. Such a fibrous structure is preferably in the form of, for example, a nonwoven fabric, and can be used as a battery separator, various filter materials, and various membrane supports. In such a case, the basis weight of the fibrous structure preferably has a basis weight of 5 g/m ² to 80 g/m ² , more preferably has a basis weight of 5 g/m ² to 60 g/m ² , and is particularly preferably It has a basis weight of not less than 5 g/m ² and not more than 50 g/m ² , and preferably has a basis weight of not less than 10 g/m ² and not more than 30 g/m ² .

In the fibrous structure of the present invention, the split ratio of split-type composite fibers is preferably at least 90%, more preferably at least 92%, more preferably at least 95%, and particularly preferably at least 97%.

The fiber structure of the present invention has an air permeability of 5 to 24 cm ³ /cm ² . Second is better, with 8 to 22cm ³ /cm ² . Second is better, with 10 to 20cm ³ /cm ² . Second is better, with 12 to 18cm ³ /cm ² . Seconds are best.

Air permeability was measured by the method described in the examples.

The average pore size of the fibrous structure of the present invention is preferably 1 to 16 μm, more preferably 2 to 15 μm, particularly preferably 3 to 12 μm, most preferably 5 to 10 μm. When the average pore diameter of the fibrous structure is 1 to 16 μm, the pores in the fibrous structure are sufficiently small, and it is estimated that the entire fibrous structure has a dense structure, and it is particularly suitable for the following applications: use in various electrical storage devices Fibrous structures for isolators; fibrous structures for filter layers of various filters; fibrous structures for various membrane supports used as supports for various filtration membranes. Also, the maximum pore size of the fibrous structure of the present invention is preferably 5 to 30 μm, more preferably 8 to 24 μm, particularly preferably 10 to 20 μm, and most preferably 12 to 18 μm. When the maximum pore diameter of the fibrous structure is 5 to 30 μm, it exists in the pores of the fibrous structure, and the diameter of the largest pore becomes sufficiently small, so it becomes especially suitable for the following fibrous structures: It is required to prevent the passage of foreign matter Fibrous structures for separators, fibrous structures for filter layers, and fibrous structures for membrane supports through which impurities pass.

In the fibrous structure of the present invention, the minimum pore diameter is preferably 1 to 10 μm, more preferably 2 to 8 μm, particularly preferably 2.5 to 6 μm, and most preferably 3 to 5 μm. Also, the fibrous structure of the present invention preferably has a maximum pore size of 1 to 15 μm, more preferably 2 to 12 μm, particularly preferably 2.5 to 10 μm, most preferably 3 to 8 μm. When the minimum pore diameter of the fibrous structure is 1 to 10 μm, and the maximum pore diameter of the fibrous structure is 1 to 15 μm, the pores in the fibrous structure become sufficiently small, and not only become a dense structure, but the fibrous structure can also remove water. Substances other than foreign matter such as gas or gas can pass through or be held, so it is especially suitable as a fibrous structure for separators, a fibrous structure for a filter layer, and a fibrous structure for a membrane support. The pore distribution such as average pore diameter, maximum pore diameter, minimum pore diameter, and maximum pore diameter was measured by the method described in Examples.

The fiber structure of the present invention preferably has a puncture strength of 6N or higher, more preferably 8N or higher, particularly preferably 10N or higher, and most preferably 12N or higher. When the puncture strength of the fibrous structure is high, it is not easy to cause damage or rupture caused by contact with foreign matter, and penetration of foreign matter. When a fibrous structure with high puncture strength is used as a separator material, it is less likely to cause needle-like crystals (dendrite) caused by foreign matter mixed in such as metal burrs when the secondary battery is used repeatedly. Short circuit (short), so it is better. In addition, when a fibrous structure with high puncture strength is used as a support for various filter materials for filtering liquid or gas, or various filter membranes such as RO membranes or NF membranes, damage caused by foreign matter during use, and damage due to filtration can be suppressed. The pressure at the time will cause damage to the filter material or filter membrane, so it is better. The upper limit of the puncture strength of the fibrous structure of the present invention is not particularly limited, but considering the productivity and handling of the fibrous structure, it is preferably 30N or less, more preferably 27N or less, and particularly preferably 5N or less.

The puncture strength was measured by the method described in the Examples.

In the fibrous structure of the aspect of the present invention, the puncture strength is controlled by the basis weight of the web structure. That is, the larger the basis weight of the fibrous structure, the larger the puncture strength tends to be. The fibrous structure of the present invention contains split-type composite fibers that are easily split, and preferably contains ultra-fine fibers having a core-sheath cross-sectional structure, so that puncture strength can be easily obtained even if the basis weight of the obtained fibrous structure is small the larger one. The fiber structure of the present invention preferably has a puncture strength (N) per unit basis weight (g/m ² ) of 0.15N or higher, more preferably 0.2N or higher, particularly preferably 0.25N or higher, and 0.3N or higher. The above is the best. Since the puncture strength per unit basis weight becomes large, even a fibrous structure having a low basis weight is less likely to be damaged or broken during use, which is preferable. The upper limit of the puncture strength (N) per unit basis weight (g/m ² ) of the fiber structure of the present invention is not particularly limited, but in consideration of the productivity and handling of the fiber structure, it is preferably 0.8N or less. It is more preferably below 0.7N, especially preferably below 0.65N.

The puncture strength (N) per unit basis weight (g/m ² ) is the puncture strength (N) measured by the method described in the example, divided by the basis weight of the sample used in the measurement (g/m ² ) to obtain.

The split-type composite fiber of the present invention can be used to produce fibrous structures such as non-woven fabrics having excellent splittability, denseness, and good texture as described above. The fibrous structure containing the split-type composite fiber of the present invention can be used, for example, as separators used in various secondary batteries such as lithium-ion batteries and nickel-metal hydride batteries, various condensers, and various capacitors; and gas and other fluids to capture and/or remove foreign matter filter cartridge filter and laminated filter and other filter materials; such as reverse osmosis membrane (RO membrane), nanofiltration membrane (NF membrane), ultrafiltration membrane ( UF membrane), precision filtration membrane (MF membrane) and other fibrous structures used for various membrane supports; constitute various wiping sheets for wiping people and/or objects; masks and other impregnated cosmetics Skin covering sheets; surface protection sheets constituting absorbent articles such as disposable diapers for infants, nursing disposable diapers, and physiological sheets; films for absorbent articles such as copy sheets and back sheets, etc.

[Example]

Hereinafter, the present invention will be described using Examples and Comparative Examples, but these examples are for explaining the present invention and do not limit the present invention in any way.

The components used to manufacture the nonwoven fabrics of Examples and Comparative Examples are shown below.

<the first component: polypropylene (PP)>

PP1: Mn=9.6×10 ⁴ after spinning, Mw=2.5×10 ⁵ after spinning, Mz=5.3×10 ⁵ after spinning, Q value after spinning=2.63, MFR(g/10min)=30 SA03 (trade name) manufactured by Japan Polypropylene Co., Ltd.

PP2: Mn=5.3×10 ⁴ after spinning, Mw=2.8×10 ⁵ after spinning, Mz=8.3×10 ⁵ after spinning, Q value after spinning=5.21, MFR(g/10min)=30 S105 HG (trade name) manufactured by Prime Polymer Co., Ltd.

PP3: Mn=9.5×10 ⁴ after spinning, Mw=3.1×10 ⁵ after spinning, Mz=7.8×10 ⁵ after spinning, Q value after spinning=3.28, MFR(g/10min)=9 SA01A (trade name) manufactured by Japan Polypropylene Co., Ltd.

PP4: Mn=4.3×10 ⁴ after spinning, Mw=2.9×10 ⁵ after spinning, Mz=10.6×10 ⁵ after spinning, Q value after spinning=6.68, MFR(g/10min)=10 CJ700 (trade name) manufactured by Prime Polymer Co., Ltd.

<the second component: Polyethylene (PE)>

PE1: HE490 (trade name) manufactured by Nippon Polyethylene Co., Ltd. of MFR (g/10 minutes)=20

PE2: HE481 (trade name) manufactured by Nippon Polyethylene Co., Ltd. of MFR (g/10 minutes)=10

<Measurement of number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), and Q value>

The number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), and the Q value (Mw/Mn) belonging to the ratio of Mw to Mn of polypropylene resin were analyzed by gel permeation chromatography (GPC) To measure. In the measurement, a gel permeation chromatography analyzer (high temperature GPC apparatus, PL-220 manufactured by Polymer Laboratories) equipped with a differential refractive index detector RI as a detector was used.

Weigh 5 mg of a sample containing polypropylene resin, add 5 mL of 1,2,4-trichlorobenzene (TCB) containing 0.1% butylhydroxytoluene (BHT) as a stabilizer and antioxidant to this sample, and Heat from 160°C to 170°C, and stir for 30 minutes to dissolve the polypropylene resin into the solvent. Next, in order to remove foreign matters such as undissolved samples from the solution in which the samples were dissolved, the solution was filtered with a metal filter to obtain a sample solution for measurement. With the measurement sample solution that obtains, be 1.0mL/min with flow rate, inject the condition of 0.2mL (200 μ L) amount, inject in the aforementioned gel permeation chromatography analyzer, measure number average molecular weight (Mn), weight average molecular weight ( Mw), z average molecular weight (Mz). During the measurement, TCB containing 0.1% BHT was used as the solvent for the measurement, one HT-G made by Shodex and two HT-806M made by Showa Denko Co., Ltd. were used as columns, and the temperature of the column thermostat was set at 145 °C for measurement.

<Measurement of melt flow rate (MFR)>

The melt flow rate of the polypropylene resin is measured at 230° C. under a load of 21.18 N in accordance with JIS K7210. The melt flow rate of the polyethylene resin was measured at 190° C. under a load of 21.18 N in accordance with JIS K 7210.

<Manufacture of split-type composite fiber in Example 1>

The split-type conjugate fiber of Example 1 shown in Fig. 1 was produced, the split-type conjugate fiber had a fiber cross-sectional shape, and PP1 of a homopolypropylene resin was used as the core component of the first stage and the second stage of the core-sheath type, using PE1 of high-density polyethylene is used as the sheath component of the second stage of the core-sheath type, and the number of divisions is 16.

The split-type conjugate fiber of Example 1 was produced under the following spinning conditions and drawing conditions. Homopolypropylene resin (PP1) and high-density polyethylene (PE1) are fed into the extruder separately by using a split-type composite nozzle with 205 nozzle holes, and the cross-section structure of the extruded molten resin is as shown in Fig. 1. , and fully melted. The volume ratio of PP1/PE1 = 5/5 (volume ratio of the first stage/second stage = 2.5/7.5) of the above-mentioned homopolypropylene resin and high-density polyethylene resin after melting is discharged. The methods are respectively extruded from the extruder, and the molten resin is drawn out under the conditions of the spinning temperature of 290°C, the output of each nozzle hole is set to 0.51g/min, and the operating speed is 840m/min, and the fineness is obtained by cooling. 6.0dtex spinning long fiber. Next, the spun filaments were dry-stretched at 105° C. with a draw ratio of 4.2 times to obtain stretched filaments with a fineness of 1.60 dtex.

In order to evaluate the elongation of the spun filaments, the maximum elongation ratio (Vmax) was measured by the following method. First, the obtained spun filaments are attached to a stretching device at a predetermined stretching temperature. At this time, the delivery speed (V ₁ ) of the delivery roll of the spun filament was set at 5 m/sec, and the take-up speed (V ₂ ) of the metal roll on the take-up side was gradually increased from 5 m/s. Then, the take-up speed of the metal roller on the take-up side when the spun filaments are broken is set to the maximum stretching speed, and the ratio (V ₂ / V ₁ ), and set the obtained speed ratio as the maximum elongation ratio (Vmax). When the maximum draw ratio is 3 or more, since the draw treatment can be performed at a high draw ratio, it is easy to obtain a split type conjugate fiber having a small fineness, which is preferable. Even if the maximum stretching ratio is less than 3, the stretching process will not be affected. However, since the maximum stretching ratio is low, it may be difficult to obtain a split-type conjugate fiber having a desired fineness.

When the maximum draw ratio was measured for the spun filament of Example 1 by the method described above, the maximum draw ratio (Vmax) was 4.4 times. Therefore, the stretching ratio is 0.95 times the maximum stretching ratio (stretching ratio/Vmax=0.95). After the fiber-treating agent was applied to the drawn filaments, they were cut to a fiber length of 3 mm to obtain the split-type conjugate fibers of Example 1 in the form of short fibers.

Table 1 shows the production, structure, fineness, etc. of the split-type conjugate fiber of Example 1.

<Manufacture of split-type composite fibers of Examples 2 to 8 and Comparative Examples 1 to 4>

Example 2 was obtained in the form of short fibers with a fiber length of 3 mm in the same manner as the method for producing the split-type composite fiber of Example 1, except that the components, spinning conditions, and drawing conditions described in Tables 1 to 3 were used. to 8 and the split type conjugate fibers of Comparative Examples 1 to 4.

Tables 1 to 3 show the production, configuration, fineness, and the like of the split-type conjugate fibers of Examples 2 to 8 and Comparative Examples 1 to 4.

<Manufacture of Split Conjugate Fiber of Comparative Example 5>

The split-type conjugate fiber of Comparative Example 5 was produced under the following spinning conditions and drawing conditions. Homopolypropylene resin (PP2 ), high-density polyethylene (PE1) resins were put into the extruder respectively, and fully melted. Melt the aforementioned homopolymer polypropylene resin and high-density polyethylene resin so that the discharge amount becomes the ratio of volume ratio of PP2/PE1=5/5 (volume ratio of the first stage/second stage=5/5) The method is respectively extruded from the extruder, with the spinning temperature (the temperature of the spinning head) at 290°C, the discharge rate of each nozzle hole being set at 0.51g/min, and the pulling speed at 840m/min, the molten resin Pulling out, cooling, and melt-extruding PP2 and PE1 to obtain spun long fibers with a fineness of 7.1 dtex. Next, using a warm water bath filled with warm water at 90°C, the spun long fibers were wet-drawn at 90°C with a draw ratio of 5.0 times, and then heat-set at a draw ratio of 1.0 times in a warm water bath at 90°C to obtain Extended long fiber with a fineness of 1.70dtex. The stretched long fibers were given the same fiber treatment agent as that of the split-type conjugate fibers of Example 1, and then cut to a fiber length of 3 mm to obtain split-type conjugate fibers of Comparative Example 5 in the form of short fibers. In addition, the maximum draw ratio of the spun filaments of Comparative Example 5 was 5.9 times.

<Manufacture of Split Conjugate Fiber of Comparative Example 6>

The spun filaments obtained in the same manner as in Comparative Example 5 were dry-drawn using heated metal rolls to produce split-type conjugate fibers. That is, the spun long fibers produced by the same method as in Comparative Example 5 were dry-drawn between metal rolls heated at 105°C so that the draw ratio was 4.95 times, and the fineness was obtained. 1.51dtex extended long fiber. The stretched long fibers were given the same fiber treatment agent as that of the split-type conjugate fibers of Example 1, and then cut to a fiber length of 3 mm to obtain split-type conjugate fibers of Comparative Example 6 in the form of short fibers. In addition, the maximum elongation ratio of the spun filaments of Comparative Example 6 was 5.2 times.

<Measurement of short fiber strength and elongation>

According to JIS L1015 (2010), using a tensile testing machine, set the pinching interval of the sample to 20mm, and let the load value when cutting the fiber be the single fiber strength, and let the elongation at the time of cutting be the elongation.

<Melting peak shape, second melting peak area/first melting peak area, extension of second melting peak of polypropylene resin measured by DSC>

DSC was performed on the split-type conjugate fibers obtained in Examples and Comparative Examples, and the shape of the melting peak of the polypropylene resin was judged according to the above definition, and the area of the second melting peak, the area of the first melting peak, and the area of the second melting peak were determined. Determination of extension. The ratio of the area of the second melting peak to the area of the first melting peak is obtained by enlarging and printing the obtained DSC curve on paper, drawing the boundary line such as the reference line at the melting peak part of the polypropylene resin, and cutting along the boundary line. The mass of the cut out portion was measured at the portion corresponding to the area of the first peak and the portion corresponding to the area of the second peak, and their ratio was obtained. In addition, the differential scanning calorimetry (DSC) of split-type composite fibers is based on JIS K7121 (1987) Transition temperature measurement method of plastics, using a differential scanning calorimeter (manufactured by Seiko Instruments Co., Ltd., trade name "EXSTAR6000/DSC6200") To measure.

<Manufacture of the nonwoven fabric of Example 1>

Using the split-type conjugate fiber of Example 1, a fiber web was produced by a wet papermaking method. Specifically, the slurry was prepared so that the fiber concentration became 0.01% by mass, stirred for 5 minutes at an attritor rotation speed of 2000 rpm, the fibers were dissociated, and the split-type composite fibers were split to form the first-stage ultrafine fibers. Fiber 1 and ultrafine fiber 2 of the second stage. Wet papermaking was carried out using a cylinder wet paper machine to obtain a net with a basis weight of 80 g/m ² . The web is conveyed with a support for transportation, and the web is heat-treated for 45 seconds using a cylinder dryer heated to 140°C. While drying the web, the fibers are bonded to each other by the sheath component of the ultrafine fiber 2. The nonwoven fabric of Example 1.

Nonwoven fabrics of Examples 2 to 8 and Comparative Examples 1 to 6 were obtained in the same manner as in Example 1 except for using the split-type conjugate fibers of Examples 2 to 8 and Comparative Examples 1 to 6.

<Measurement of split ratio>

In the stage before the heat treatment, the wet papermaking web is wrapped as closely as possible in the cylinder so that the cut surface in the thickness direction of the wet papermaking web is exposed. The non-woven fabric wrapped in the tube was magnified 300 times with an electron microscope, and an area of 0.4 mm×0.3 mm was photographed. Confirm each fiber section present in the photographed image, and count the number of ultrafine fibers 1 and the number of ultrafine fibers 2 . In addition, for undivided fibers, measure and calculate the total number of the first and second segments (for example, when there are fiber sections in Figures 1 to 3, the total number of the first and second segments of fibers that are not completely divided) The total number is 16, the total number of the first and second stages of half-divided fibers is 8), and the total number of the first and second stages is taken as the number of each undivided fiber. According to this, for example, if there is one undivided fiber and the total number of the first and second steps is 16, the fiber count is 16. From the counting result, the division ratio was calculated according to the following formula.

Split rate (%)=[number of ultrafine fibers 1 + number of ultrafine fibers 2]÷[number of ultrafine fibers 1+number of ultrafine fibers 2+total number of undivided fibers]×100

The split ratios are shown in Tables 1 to 3.

<breathability>

Measure and evaluate the air permeability and air permeability of non-woven fabrics. The air permeability was measured in accordance with JIS L1096 (2010) 8.26A (Frazir format method).

Since the nonwoven fabrics of Examples 1 to 8 are all obtained by using the split-type composite fibers of Examples 1 to 8, the Mw/Mn of the polypropylene resin is 6 or less, and the melting peak shape of the polypropylene resin shown by the DSC curve is a bimodal shape. , Therefore, at least one of the problems of improving the productivity and splittability during fiber production is raised.

Since the nonwoven fabrics of Examples 1 to 6 and 8 further satisfy (A) the area of the second melting peak/the area of the first melting peak is 0.85 or more and 3.5 or less; and (B) the extension of the second peak is at least one of 0.6 or more, Therefore, it is further excellent in both separability and air permeability.

On the other hand, in the nonwoven fabrics of Comparative Examples 1 to 4, the Mw/Mn of the polypropylene resin was not less than 6, or the shape of the melting peak of the polypropylene resin indicated by the DSC curve was not bimodal, so the productivity during fiber production None of the issues such as segregation and severability were improved. In addition, although the split-type conjugate fibers of Comparative Example 5 and Comparative Example 6 used the same polypropylene resin and polyethylene resin as the split-type conjugate fibers of Example 5, the split ratio of the obtained split-type conjugate fibers was low. It is speculated that in the cross-section of the fiber, the second stage does not become a core-sheath cross-section, so it occurs during the cooling process during melt spinning, the crystallization state of the thermoplastic resin generated during the cooling process, during melt spinning or during stretching. Due to the difference in the skewed state inside the fiber, the resin segments are firmly glued together, or when force is applied to the split type composite fiber, the effect of absorbing the impact becomes high, so it is not easy to split.

<Evaluation of Fibrous Structures>

[Example 9]

In order to investigate various fiber structures of the split-type composite fiber of the present invention, especially for liquid treatment materials such as various battery separator applications requiring mechanical strength and compactness, filter materials, and various membrane supports (for example, RO membrane supports) The adaptability of the application is to produce a heat-bonded nonwoven fabric using the split-type composite fiber of the present invention.

Using the split-type conjugate fiber of Example 5, a slurry was produced under the same slurry concentration and rotation speed as the above-mentioned production conditions, and the split-type conjugate fiber was split to form the first-stage ultrafine fiber 1 and the second-stage ultrafine fiber 2. Wet papermaking was carried out using a cylinder wet paper machine to obtain a net with a basis weight of about 40 g/m ² . The web is conveyed with a support for transportation, and the web is heated for 45 seconds using a cylinder dryer heated to 140°C. While drying the web, the fibers are bonded to each other by the sheath component of the ultrafine fiber 2 to form a heat treatment. Then do not weave.

In the obtained thermally bonded nonwoven fabric, thickness processing was performed using a hot roller under conditions of a temperature of 80° C. and a linear pressure of about 760 N/cm, and the thickness of the thermally bonded nonwoven fabric was adjusted to a thickness of about 120 μm to obtain the thermally bonded nonwoven fabric of Example 9.

The obtained thermal bonding nonwoven fabric of Example 9 was evaluated by the following method.

[thickness]

The thickness of the obtained thermally bonded nonwoven fabric was measured using a micrometer (Mitutoyo Co., Ltd. Micrometer MDC-25MJ), according to JIS B 7502, at 10 points different from each of the three samples so that the load became 175kPa. The thickness is measured by the method, and the average value of a total of 30 points is obtained as the thickness of the sample.

[pore distribution]

The pore size distribution of the thermally bonded nonwoven fabric obtained in Example 9 was measured according to ASTM F316-86 (bubble point method), and the average pore size, maximum pore size, maximum pore size and minimum pore size of the thermally bonded nonwoven fabric were measured.

[tear strength]

According to JIS L1085 5.5.A-1 method (single tongue method (Single tongue method)), the measurement was performed using a tensile tester (Tensilon (registered trademark) UCT-1 (trade name) manufactured by A And D Co., Ltd.). In this embodiment, as the test piece, a slit of 8 cm at right angles to the side is cut in the center of the short side of a rectangular piece cut into a width of 5 cm x length of 15 cm to make two tongue pieces, with a clamping distance of 10 cm , The maximum load at the time of tearing was measured at a tensile speed of 30 cm/min.

[Tensile Strength]

According to JIS L1096 8.12.1 A method (stripe method), using a constant speed tension type tensile testing machine, the specimen piece with a width of 5cm and a length of 30cm is pulled under the conditions of a clamping distance of 10cm and a tensile speed of 30±2cm/min. In the tensile test, the load value at which the load becomes the maximum was measured as the tensile strength. The tensile test was carried out in the longitudinal direction (machine direction) of the nonwoven fabric.

[puncture strength]

The puncture strength refers to the stress at the penetration point (maximum penetration force F) resulting from the measurement of the needle penetration force, and is measured by the method described below. First, a nonwoven fabric cut into a size of 30 mm in length and 100 mm in width was prepared as a sample. This sample was placed on a support having a cylindrical through hole (11 mm in diameter) of a simple compression tester (KES-G5 manufactured by Kyoto Tach Co., Ltd.). Next, on the sample arranged on the support body, a press plate made of an aluminum plate with a length of 46 mm, a width of 86 mm, and a thickness of 7 mm, and a hole with a diameter of 11 mm in the central part is placed so that the hole of the press plate and the cylinder of the support body Shaped through holes are placed in a consistent manner. Next, measure the load when a spherical conical needle with a height of 18.7mm, a bottom surface diameter of 2.2mm, and a tip shape of 1mm pierces the center of the platen vertically at a speed of 2mm/second, and the load obtained by the above-mentioned conical needle is measured. The length of deformation caused by extrusion of the sample, among the measured loads, the stress of the above-mentioned conical needle at the penetration point of the sample is taken as the maximum penetration force F (N), that is, the puncture strength. For the puncture strength, four samples were taken from one nonwoven fabric (battery separator), and the measurement was performed at 5 different points of each sample, and the average value of a total of 20 points was measured. Also, the puncture strength (N) per unit basis weight (g/m ² ) was obtained by dividing this value by the basis weight of the sample.

In the nonwoven fabric of Example 9, in addition to using split-type conjugate fibers, it is estimated that the split-type conjugate fibers used were sufficiently divided by the stirring treatment performed when adjusting the slurry before papermaking, so the obtained nonwoven fabric Most of the fibers become very fine fibers, and become dense non-woven fabrics through thermal bonding and thickness processing.

From the measurement results of the pore distribution, it can be seen that all of the measured average pore diameter, minimum pore diameter, maximum pore diameter, and maximum pore diameter of the nonwoven fabric of Example 9 became small. It is presumed that not only the voids constituting the inside of the nonwoven fabric become smaller, but also the pores formed in the nonwoven fabric become smaller and uniform.

From the mechanical strength (tear strength, tensile strength) of the obtained nonwoven fabric, it can be seen that although the nonwoven fabric of Example 9 is thin, the tear strength and tensile strength are high. This is presumed, because the nonwoven fabric of Example 9 is a nonwoven fabric obtained from a segmented composite fiber with a core-sheath cross section from a resin segment, so half of the fibers constituting the nonwoven fabric become ultrafine fibers that are thermally bonded to each other by moderate heating , By heat-treating the obtained fiber web, the ultrafine fibers are strongly thermally bonded to each other.

This specification includes the following aspects.

1. A segmented composite fiber comprising a segmented composite fiber comprising a first segment and a second segment, wherein the first segment is a resin segment comprising the first component, and the second segment has a cross-sectional structure of the first segment The core component is a core-sheath type resin segment in which the second component is a sheath component, the first component is a resin component containing 50% by mass or more of polypropylene resin, and the second component is a resin component containing 50% by mass or more of polyethylene The resin component of the resin, the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the aforementioned polypropylene resin measured after spinning is 6 or less, after spinning, according to JIS K 7121 (1987 ) The DSC curve of the differential scanning calorimetry (DSC) of the method for measuring the transition temperature of plastics shows that the shape of the melting peak of the aforementioned polypropylene resin is a bimodal shape.

2. The split-type conjugate fiber described in 1 above satisfies at least one of the following (A) and (B).

(A): The bimodal melting peak of the polypropylene resin shown in the DSC curve is divided into a first melting peak and a second melting peak, and the areas of the respective regions are defined as the first melting peak area and the second melting peak area. When melting the peak area, the ratio of the second melting peak area to the first melting peak area (the second melting peak area/the first melting peak area) is more than 0.85 and less than 3.5; and (B): in the aforementioned differential scanning calorimetry (DSC ), the melting peak of the aforementioned bimodal polypropylene resin is divided into a first melting peak and a second melting peak, and the DSC curve value at the second melting peak temperature is defined as W ₂ (mW). Between the second melting peak, the DSC curve value at which the absolute value of the first differential of the DSC curve becomes the minimum is W ₃ (mW), and the extension of the second peak defined by the following formula is 0.6 or more

Extension of the second melting peak=(absolute value of W ₂ )−(absolute value of W ₃ ).

3. The split-type conjugate fiber described in 1 or 2 above, wherein the split-type conjugate fiber has a single fiber strength of 3.0 cN/dtex or more and 8.0 cN/dtex or less, and an elongation of 20% or more and 120% or less.

4. The split-type conjugate fiber according to any one of 1 to 3 above, wherein the ratio of the first component to the second component contained in the split-type conjugate fiber (first component/second component) is 8/2 to 3/7 (volume ratio).

5. A fibrous structure comprising 10% by mass or more of the split-type composite fiber described in any one of 1 to 4 above.

6. The fiber structure described in the above 5 is 8 cm ³ /cm ² in air permeability measured in accordance with JIS L1096 using a Frazier type testing machine. Above 22cm ³ /cm ² . seconds or less.

7. A separator material comprising the fibrous structure described in 5 or 6 above.

8. A filter material comprising the fibrous structure described in 5 or 6 above.

9. A method for producing a split-type composite fiber according to any one of 1 to 4 above, comprising the step of preparing a melt spinning machine equipped with a split-type composite nozzle for forming the split-type composite fiber, wherein , the aforementioned split-type composite fiber is a split-type composite fiber that contains the first segment and the second segment in the fiber section, the aforementioned first segment is a resin segment that includes the first component, and the aforementioned second segment is a cross-sectional structure that combines the aforementioned The first component is a core component, and the second component is a core-sheath type resin segment that is a sheath component; a resin component containing 50% by mass or more of a polypropylene resin with a Mw/Mn of 6 or less is used as the first component, and 50% by mass of polypropylene resin is used as the first component. % or more of the resin component of the polyethylene resin is used as the second component, melt-spun by a melt-spinning machine, and the step of producing spun long fibers; The step of stretching the spun long fibers to obtain split-type composite fibers.

10. The production method described in 9 above, comprising the step of stretching the spun filament at a stretching ratio of 3 times to 8 times.

11. The production method described in 9 or 10 above, comprising the step of wet stretching the spun filaments at a stretching temperature of 60°C to 95°C.

12. The production method described in 9 or 10 above, comprising the step of dry-drawing the spun filaments at a stretching temperature of 80°C to 125°C.

13. The production method described in any one of items 9 to 12 above, comprising the step of stretching the spun filaments at a stretching ratio of 0.7 to 0.98 times the maximum stretching ratio.

14. A split-type composite fiber produced by the production method described in any one of items 9 to 13 above.

15. A fibrous structure comprising 10% by mass or more of the split-type composite fiber described in 14 above.

<Related Application>

This application is based on the application number 2017-72525 filed in Japan on March 31, 2017 as the basic application, and claims priority under Article 4 of the Paris Treaty. The content of this basic application is incorporated in this specification by reference.

[industrial availability]

The split-type conjugate fiber of the present invention has high productivity and excellent splittability. Furthermore, by using one resin segment as a core-sheath type resin segment, it becomes a split-type composite fiber in which ultra-fine fibers can be interlinked by heating. The split-type composite fiber of the present invention can be used in applications requiring a dense fiber structure and a fiber structure with a small fiber diameter, for example, in various secondary batteries such as lithium-ion batteries and nickel-metal hydride batteries, Fibrous structures for separators used in various condensers and various capacitors, etc.; for filter layers of various filters such as filter elements and laminated filters that capture and/or remove foreign matter from fluids such as liquids and gases Various membranes used as supports for various filtration membranes such as reverse osmosis membrane (RO membrane), nanofiltration membrane (NF membrane), ultrafiltration membrane (UF membrane), precision filtration membrane (MF membrane), etc. Fibrous structures for supports; fibrous structures constituting various wiping sheets for wiping people and/or objects; skin covering sheets impregnated with cosmetics such as facial masks; disposable diapers for infants, nursing disposable diapers, cotton for physiological use Surface protection sheets of absorbent articles such as pads; fiber structures of sheets for absorbent articles such as copy sheets and back sheets; fiber structures used in artificial leather.

1‧‧‧paragraph 1

2‧‧‧paragraph 2

4‧‧‧core composition

6‧‧‧sheath composition

8‧‧‧hollow

10‧‧‧Split composite fiber

Claims (13)

A segmented composite fiber, which is a segmented composite fiber comprising a first segment and a second segment, wherein the first segment is a resin segment containing a first component, and the second segment has a cross-sectional structure such that the first component is used as The core component is a core-sheath type resin segment in which the second component is a sheath component, the first component is a resin component containing 50% by mass or more of polypropylene resin, and the second component is a resin component containing 50% by mass or more of polyethylene resin For the resin component, the ratio (Mw/Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the aforementioned polypropylene resin measured after spinning is 5.21 or less. The DSC curve measured by differential scanning calorimetry (DSC) based on the transition temperature measurement method shows that the shape of the melting peak of the aforementioned polypropylene resin is a bimodal shape. The segmented composite fiber described in item 1 of the scope of the patent application satisfies at least one of the following (A) and (B), (A): the bimodal shape of the aforementioned polypropylene resin represented by the aforementioned DSC curve The melting peak is divided into a first melting peak and a second melting peak, and when the respective area areas are defined as the first melting peak area and the second melting peak area, the ratio of the second melting peak area to the first melting peak area (second melting peak area) melting peak area/first melting peak area) is 0.85 to 3.5; and (B): In the above-mentioned differential scanning calorimetry (DSC), the melting peak of the aforementioned bimodal polypropylene resin is divided into the first melting peak and For the second melting peak, the value of the DSC curve at the second melting peak temperature is defined as W ₂ (mW), and the DSC that minimizes the absolute value of the first differential of the DSC curve between the first melting peak and the second melting peak The value of the curve is W ₃ (mW), and the extension of the second peak defined by the following formula is 0.6 or more. The extension of the second melting peak=(absolute value of W ₂ )−(absolute value of W ₃ ). The segmented composite fiber as described in claim 1 or 2 of the patent claims, wherein the single fiber strength of the aforementioned segmented composite fiber is not less than 3.0 cN/dtex and not more than 8.0 cN/dtex, and the elongation is not less than 20% and not more than 120%. The split-type composite fiber according to claim 1 or 2, wherein the ratio of the first component to the second component contained in the split-type composite fiber (first component/second component) is 8/2 to 3/7 (volume ratio). A fibrous structure containing more than 10% by mass of the split-type composite fiber described in any one of claims 1 to 4 of the patent application. The fibrous structure described in claim 5 of the patent application, wherein the air permeability measured by using a Fraser type testing machine according to JIS L1096 is 8cm ³ /cm ² . Above 22cm ³ /cm ² . seconds or less. An isolator material containing the fiber structure described in item 5 or 6 of the scope of application. A kind of filter material, is to contain the 5th or 6th described in the scope of patent application Fibrous structures. A method for producing split composite fibers, which is the method for manufacturing split composite fibers described in item 1 of the scope of patent application, comprising the following steps: preparing a melt-spun yarn equipped with a split composite nozzle for forming split composite fibers The step of machine, wherein the split-type composite fiber is a split-type composite fiber comprising a first segment and a second segment in the fiber section, the first segment is a resin segment containing the first component, and the second segment is The cross-sectional structure is a core-sheath type resin segment in which the aforementioned first component is used as a core component and the second component is used as a sheath component; a resin component containing 50% by mass or more of a polypropylene resin with a Mw/Mn of 5.21 or less is used as the first component. Components, a resin component containing 50% by mass or more of polyethylene resin as the second component, melt spinning with a melt spinning machine to produce spun filaments; The step of stretching the spun long fiber to obtain a segmented composite fiber at a stretching ratio of more than 100 times. The manufacturing method described in claim 9 of the patent application includes the step of stretching the spun long fiber at a stretching ratio of not less than 3 times but not more than 8 times. The manufacturing method described in claim 9 or 10 of the patent application includes the step of wet stretching the spun long fiber at a stretching temperature of 60°C to 95°C. Such as the manufacturing method described in item 9 or 10 of the scope of the patent application, it includes It includes the step of dry stretching the spun long fiber at the stretching temperature of 80°C to 125°C. The manufacturing method as described in claim 9 or 10 of the patent application includes the step of stretching the spun long fiber at a stretching ratio of 0.7 to 0.98 times the maximum stretching ratio.

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