WO2018181909A1

WO2018181909A1 - Splittable conjugate fibers and fiber structure using same

Info

Publication number: WO2018181909A1
Application number: PCT/JP2018/013648
Authority: WO
Inventors: 洋志岡屋; 惠介内海; 昂史杉山
Original assignee: ダイワボウホールディングス株式会社; ダイワボウポリテック株式会社
Priority date: 2017-03-31
Filing date: 2018-03-30
Publication date: 2018-10-04
Also published as: TW201842247A; JPWO2018181909A1; JP7364829B2; TWI787248B

Abstract

Disclosed are splittable conjugate fibers each comprising a first segment and a second segment, wherein the first segment contains at least 50% by mass of a polypropylene resin, the second segment contains at least 50% by mass of a polyethylene resin, the ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polypropylene resin measured after spinning is not more than 6, and the shape of melting peaks of the polypropylene resin indicated by a differential scanning calorimetry (DSC) curve obtained through DSC performed according to the plastic transition temperature measurement method defined in JIS K 7121 (1987) after spinning is a double-peak shape. The splittable conjugate fibers can be used in applications where compactness is required in the fiber structure, and, in particular, further improves productivity, splittability, and the like during fiber production.

Description

Split type composite fiber and fiber structure using the same

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

To obtain ultrafine fibers and fiber structures containing ultrafine fibers, a plurality of thermoplastic resins are used, and when the fiber cross section is observed, the cross section is composed of two or more resin segments (hereinafter simply referred to as segments). A method using a split type composite fiber is known. When a split type composite fiber is used, an ultrafine fiber can be easily obtained by dividing the fiber into segments. However, it is known that if the division process is insufficient, a part that is not divided, that is, a part that remains with the segments stuck together (generally referred to as undivided fibers) remains. It has been.

In addition, the segment constituting the split-type conjugate fiber is generally a single resin component (even if a resin component is a mixture of a plurality of types of thermoplastic resins) Component), the fine fibers can be obtained when the splitting process is sufficiently performed. However, when bonding these ultrafine fibers, a heat-bonding fiber having a fiber diameter larger than that of the ultrafine fibers, for example, the surface is the ultrafine fiber. It is necessary to mix a core-sheath type composite fiber composed of a thermoplastic resin having a melting point lower than that of the thermoplastic resin constituting the fiber. As a result, it is known that the denseness of fiber structures obtained by bonding ultrafine fibers using heat-bonded fibers having a fiber diameter larger than that of the ultrafine fibers decreases.

In addition, for two or more segments constituting the split-type conjugate fiber, as thermoplastic resins constituting adjacent segments, polyolefin resins such as polypropylene and polyethylene, and polyester resins such as polyethylene terephthalate and copolyester are used. In the case of a split type composite fiber in which highly compatible resins are combined, sticking between adjacent segments tends to be strong, and an unsplit portion (unsplit fiber) tends to remain in the resulting fiber structure.

For example, a combination of polyolefin resins such as polypropylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polymethylpentene, ethylene-propylene copolymer, propylene-ethylene-1-butene terpolymer. Split type composite fibers; examples include split type composite fibers obtained by combining polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and copolyester. In order to prevent such a split type composite fiber from leaving an undivided part, it is vigorously stirred when mixing the fibers in the manufacturing stage of the fiber structure, and a high-pressure water stream is injected into the obtained fiber structure. It is necessary to perform a splitting process that gives a strong impact such as sandwiching and pressing the obtained fiber structure between two metal rolls.

Splitting is improved, and the resulting fiber structure is composed only of ultrafine fibers. The ultrafine fibers are bonded to each other by melting the surface of some of the ultrafine fibers, resulting in tensile strength and puncture strength. In order to obtain a fiber structure having excellent mechanical properties, one of the two or more segments constituting the split-type composite fiber remains as a single component segment (single-type segment), and the other segment. The cross-sectional shape of the core is made into a core-sheath type cross-sectional shape (a core-sheath type segment) or the like (for example, see Patent Documents 1 to 4).

Patent Document 1 is composed of a single component segment (single-type segment) and an α-olefin polymer component having the same melting point as the core component of the core-sheath segment, and the sheath component of the core-sheath segment has a low melting point. A split-type composite that is excellent in splitting properties because the low-melting α-olefin polymer component and the high-melting α-olefin polymer component both have a Rockwell hardness R of 60 or more. Report fiber.

Patent Document 2 reports a split-type composite fiber that is excellent in splittability by making the cross-section of the core-sheath segment into a specific shape.

Patent Documents

3 and 4 show that the single-type segment includes a polypropylene resin having a specific z-average molecular weight (Mz) and a specific weight-average molecular weight (Mw) as a main component. Report fiber.

In the split-type composite fibers described in Patent Documents 1 to 4, even if the splitting process is not performed by a high-pressure water stream, the interface between the segments is peeled off, and ultrafine fibers are generated by splitting into segments. In addition, since it has a core-sheath type segment, even if it is a fiber structure comprised only of these split type composite fibers, it is possible to heat-bond between the fibers.

JP-A-4-163315 JP 2011-9150 A JP 2012-142235 A JP 2012-140734 A

However, in applications where the denseness of the fiber structure is required, for example, various secondary batteries that use the fiber structure as a separator between electrodes; filter materials for various liquid and gas filters that require higher filtration accuracy ( Filter materials): Various membranes used as a support for various filtration membranes such as reverse osmosis membranes (RO membranes), nanofiltration membranes (NF membranes), ultrafiltration membranes (UF membranes), and microfiltration membranes (MF membranes) Fiber structure for support; Interpersonal and objective wiping materials that are required to irritate the wiped part and reduce scratches; Cosmetic-impregnated skin-covering sheets that require a soft texture when in contact with the skin (generally Are also referred to as face masks); and in applications such as sheets for absorbent articles, further improvements in the performance of split composite fibers are required. Also for the split type composite fibers of Patent Documents 1 to 4, the overall performance, particularly the productivity at the time of fiber production (for example, the shape and arrangement of each segment constituting the split type composite fiber at the time of fiber manufacture is easy, and melt spinning is performed. Further, it is demanded that thread breakage is less likely to occur during the stretching process, and that the splitting property is further improved.

Surprisingly, the inventors of the present invention are split type composite fibers composed of a first segment and a second segment, wherein the first segment is a resin segment composed of the first component, and a cross section of the second segment. In a split type composite fiber having a core-sheath type resin segment in which the first component is a core component and the second component is a sheath component, the first segment has a Q value after spinning (weight average molecular weight (Mw ) And the number average molecular weight (Mn), which is expressed as Mw / Mn), includes a polypropylene resin that satisfies a specific range, and the obtained split type composite fiber was subjected to differential scanning calorimetry (hereinafter simply referred to as DSC). In the DSC curve obtained by performing the process, the endothermic peak generated by melting of the polypropylene resin (polypropylene resin melting peak) has a specific shape. It has been found that by using a resin component containing a propylene resin, productivity at the time of fiber production, splitting property of the obtained split composite fiber, and the like are further improved.

Furthermore, the inventors of the present invention have found that the nonwoven fabric (fiber structure) manufactured using the obtained split composite fiber in such split composite fiber is a core obtained by splitting the split composite fiber. It has been found that fibers (for example, ultrafine fibers) constituting the nonwoven fabric can be bonded together by melting the sheath portion of the sheath type resin segment. Such a non-woven fabric is composed of ultrafine fibers as the main fibers, so that not only the internal structure is dense, but the ultrafine fibers are bonded together by the sheath component constituting the ultrafine core-sheath composite fiber, The inventors have found that the fiber structure is excellent in mechanical properties such as tensile strength and puncture strength, and have completed the present invention.

That is, the present invention in one aspect,
A split-type composite fiber including a first segment and a second segment;
The first segment is a resin segment composed of a first component,
The second segment is a core-sheath resin segment whose cross-sectional structure has a first component as a core component and a second component as a sheath component,
The first component is a resin component containing 50% by mass or more of polypropylene resin,
The second component is a resin component containing 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,
JIS K 7121 (1987) after spinning The split type in which the shape of the melting peak of the polypropylene resin in the DSC curve of differential scanning calorimetry (DSC) measured based on the plastic transition temperature measurement method is a double peak shape Provide composite fiber.

Since the present invention has the features as described above, at least one of the problems such as productivity and splitting at the time of fiber production is improved. Furthermore, the nonwoven fabric (fiber structure) manufactured using such a split type composite fiber has a fine structure of the fiber structure and appropriate air permeability. Further, the second component (that is, polyethylene resin) constituting the sheath component of the core-sheath segment in which the cross-sectional structure of the second segment is a core-sheath resin segment is melted so that the ultrafine fibers are bonded to each other, and mechanical characteristics are obtained. Excellent non-woven fabric (fiber structure).
In the present specification, the symbol “˜” is used to include both end points.

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 another split-type composite fiber according to the present invention. FIG. 3 schematically shows a cross section of the split type composite fiber used in the reference example. FIG. 4 schematically shows that in the endothermic peak of the 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 elongation of the second melting peak (a ₂ ) on the high temperature side in the endothermic peak of the polypropylene resin. FIG. 6 schematically shows the first melting peak area (S ₁ ) in the endothermic peak of the polypropylene resin. FIG. 7 schematically shows the second melting peak area (S ₂ ) in the endothermic peak of the polypropylene resin. FIG. 8 schematically shows that in the endothermic peak of polypropylene resin, the first melting peak (a ₁ ) appears as a shoulder peak on the low temperature side, and then the second melting peak (a ₂ ) appears on the high temperature side. . FIG. 9 schematically shows the elongation of the second melting peak on the high temperature side in the endothermic peak of the polypropylene resin. FIG. 10 schematically shows the first melting peak area (S ₁ ) at the endothermic peak of the polypropylene resin. FIG. 11 schematically shows the second melting peak area (S ₂ ) in the endothermic peak of the polypropylene resin. FIG. 12 schematically shows that one melting peak clearly appears in the endothermic peak of the polypropylene resin. FIG. 13 shows a DSC curve obtained by differential scanning calorimetry (DSC) performed on the split-type conjugate fiber of Example 1. FIG. 14 shows a DSC curve obtained by differential scanning calorimetry (DSC) performed on the split conjugate fiber of Example 7. FIG. 15 shows a DSC curve obtained by differential scanning calorimetry (DSC) performed on the split type conjugate fiber of Comparative Example 1. FIG. 16 shows a DSC curve obtained by differential scanning calorimetry (DSC) performed on the split composite fiber of Comparative Example 3. FIG. 17 shows a DSC curve obtained by differential scanning calorimetry (DSC) performed on the split composite fiber of Comparative Example 5. FIG. 18 shows a DSC curve obtained by differential scanning calorimetry (DSC) performed on the split composite fiber of Comparative Example 6.

1 and 2 schematically show a cross section of a split type composite fiber (10, 20) according to an embodiment of the present invention. Each includes a first segment (1) and a second segment (2). The first segment (1) is a single-structure segment, but the second segment (2) is a core-sheathed segment (FIG. 1). And FIG. 2). The core-sheath type segment can have a core component (4, 14) and a sheath component (6, 16). Furthermore, the split-type conjugate fiber may have a hollow (8) (FIG. 1).

<First segment>
The first segment is a resin segment made of the first component. The first segment forms the ultrafine fiber 1 by splitting the split type composite fiber. In other words, the first segment is a single-type segment that is composed of the first component and has a single structure in cross section. The first component is a resin component containing 50% by mass or more of polypropylene resin. The first component preferably contains 75% by mass or more of polypropylene resin, more preferably 80% by mass or more.

It is particularly preferable that the first component consists essentially of a polypropylene resin. Here, the term “substantially” means that a polypropylene resin provided as a product usually contains an additive such as a stabilizer and / or various additives are added during fiber production. Considering that it is not possible to obtain a fiber composed of only a polypropylene resin and containing no other components. Usually, the first component can contain up to 15% by weight of additives.

In the present invention, the ratio (Mw / Mn) (hereinafter also referred to as “Q value”) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polypropylene resin measured after spinning is 6 or less, 2 to 6, more preferably 2.2 to 5.6, particularly preferably 2.3 to 5.2, and most preferably 2.4 to 5.0. The lower limit of the above range of Mw / Mn may be 2 or more, or may be 2.4 or more. For example, it may be 2 or more, 2.5 or more and 6 or less, 2.8 or more and 6 or less, or 3.4 or more and less than 6. When the Q value is 6 or less, the polypropylene resin after spinning has the same size (the length of the polypropylene molecular chain) of the polypropylene molecules contained therein, and the distribution range is narrower. The behavior of is easy to align. As a result, in the split type composite fiber, not only the cross-sectional shape of the fiber and the cross-sectional shape of each segment are easily adjusted, but also a highly productive fiber that is less likely to break during spinning and drawing. Since the productivity of the fiber is good, various physical properties of the obtained split composite fiber and the fiber structure using the same are further improved.

The weight average molecular weight (Mw) of the polypropylene resin measured after spinning is preferably from 150,000 to 700,000, more preferably from 200,000 to 500,000, and particularly preferably from 230,000 to 400,000. 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 particularly preferably 55,000 to 100,000. The measuring method of the weight average molecular weight (Mw) and number average molecular weight (Mn) of a polypropylene resin was described in the Example.

The polypropylene resin may be a homopolymer of propylene (a homopolymer having propylene as a monomer) or a copolymer containing propylene as a monomer (hereinafter referred to as a polypropylene resin). The polypropylene resin is not particularly limited as long as the split type composite fiber intended by the present invention can be obtained. As the polypropylene 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 random copolymer, block copolymer and graft copolymer include a copolymer with at least one α-olefin selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms.

The α-olefin having 4 or more carbon atoms is not particularly limited as long as the split type composite fiber intended by the present invention can be obtained. For example, 1-butene, 1-pentene, 3, 3 Examples include -dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene, 1-octadecene and the like. The propylene content in the copolymer is preferably more than 50% by mass. As the first component, a homopolymer of propylene or the above-mentioned polypropylene resin can be used, but a propylene homopolymer is particularly preferable in consideration of easiness of production and economy (manufacturing cost). These may be used alone or in combination of two or more.

The polypropylene resin has a melt flow rate (hereinafter also referred to as “MFR230” according to JIS K7210; measurement temperature 230 ° C., load 2.16 kgf (21.18 N)) of 8 g / 10 min or more and 60 g / 10 min or less. It is preferably 15 g / 10 min to 60 g / 10 min, more preferably 20 g / 10 min to 45 g / 10 min, particularly 25 g / 10 min to 40 g / 10 min. Most preferred.

As long as the split type composite fiber targeted by the present invention can be obtained, the first segment can contain a known split accelerator. As a known partition accelerator, for example, a silicon compound-based partition accelerator, an unsaturated carboxylic acid-based partition accelerator, a (meth) acrylic acid-based compound partition accelerator, and the like can be used. Among these, from the viewpoint of improving partitionability. , (Meth) acrylic acid compound splitting accelerators are preferred, and (meth) acrylic acid metal salts are more preferred. When the first segment contains a (meth) acrylic acid metal salt as a splitting accelerator, 1 to 10% by mass of the (meth) acrylic acid metal salt may be contained in the first segment.

<Second segment>
The split type composite fiber of the present invention includes a second segment. The second segment preferably forms the ultrafine fiber 2 derived from the second segment by splitting the split-type composite fiber. The second segment is a core-sheath type resin segment whose cross-sectional structure has a first component as a core component and a second component as a sheath component.

The second component is a resin component containing 50% by mass or more of polyethylene resin. Preferably, the second component is a resin component containing 75% by mass or more of polyethylene resin, and more preferably 80% by mass or more of polyethylene resin. It is particularly preferred that the second component consists essentially of a polyethylene resin. Here, the term “substantially” usually means that polyethylene resins provided as products contain additives such as stabilizers and / or various additives are added during the production of fibers. Considering that it is not possible to obtain a fiber composed of only a polyethylene resin and containing no other components. Usually, the second component can contain up to 15% by weight of additives.

Polyethylene resin has good compatibility with polypropylene resin, and split type composite fibers combining these are generally low in splittability. In the present invention, even if the combination is a polypropylene resin and a polyethylene resin, excellent splitting properties can be obtained.

The polyethylene resin is a homopolymer of ethylene (a homopolymer having ethylene as a monomer, and there are high density polyethylene, medium density polyethylene, low density polyethylene, and linear low density polyethylene due to differences in density and molecular structure). It may be a copolymer containing ethylene as a monomer (hereinafter referred to as polyethylene resin). The polyethylene resin is not particularly limited as long as the split type composite fiber intended by the present invention can be obtained. As the polyethylene resin, a random copolymer, a block copolymer, a graft copolymer or a mixture thereof containing ethylene as a monomer can be used. Examples of the random copolymer, block copolymer and graft copolymer include a copolymer with at least one α-olefin selected from the group consisting of ethylene and an α-olefin having 3 or more carbon atoms.

The α-olefin having 3 or more carbon atoms is not particularly limited as long as the split type composite fiber intended by the present invention can be obtained. For example, propylene, 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 and the like. The ethylene content in the copolymer is preferably 50% by mass or more. As the second component, an ethylene homopolymer or the polyethylene-based resin can be used, but an ethylene homopolymer is particularly preferable in view of ease of manufacture and economy (manufacturing cost). These may be used alone or in combination of two or more.

The polyethylene resin has a melt flow rate (hereinafter also referred to as “MFR190” according to JIS K7210; measurement temperature 190 ° C., load 2.16 kgf (21.18 N)) of 5 g / 10 min or more and less than 30 g / 10 min. It is preferably 8 g / 10 min or more and less than 28 g / 10 min, more preferably 10 g / 10 min or more and less than 25 g / 10 min. When the MFR 190 of the polyethylene resin is in the range of 5 g / 10 min or more and less than 30 g / 10 min, the productivity of the split composite fibers is further improved.

As long as the split type composite fiber targeted by the present invention can be obtained, the second segment can contain a known split accelerator. As a known partition accelerator, for example, a silicon compound-based partition accelerator, an unsaturated carboxylic acid-based partition accelerator, a (meth) acrylic acid-based compound partition accelerator, and the like can be used. Among these, from the viewpoint of improving partitionability. , (Meth) acrylic acid compound splitting accelerators are preferred, and (meth) acrylic acid metal salts are more preferred. When the second segment contains a (meth) acrylic acid metal salt as a splitting accelerator, 1 to 10% by mass of the (meth) acrylic acid metal salt may be contained in the entire second segment.

The second segment is a core-sheath type resin segment whose cross-sectional structure has a first component as a core component and a second component as a sheath component. When the second segment is a core-sheath type resin segment, the split type composite fiber is split to form an ultrafine fiber having a fiber-sheathed core-sheath type 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 type ultrafine composite fiber, the ultrafine fibers formed by splitting the split type composite fiber are thermally bonded to each other. be able to. And the fiber structure which is more excellent in mechanical characteristics, such as puncture strength and tensile strength, can be obtained.

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

The second segment is a core-sheath type resin segment, and the cross-sectional shape of the core component of the second segment is not particularly limited as long as the split type composite fiber intended by the present invention can be obtained. The cross section of the core component may have, for example, an elliptical shape or a perfect circular shape. Further, the core component may be located at the center of the second segment, or may not be located at the center and may be eccentric.

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

<Split type composite fiber>
The split type composite fiber according to the present invention includes the first segment and the second segment, but may further include another resin segment, for example, a third segment. Other resin segments are not particularly limited as long as the split type composite fiber intended by the present invention can be obtained. As the resin component constituting the other segment, for example, polybutene-1, polymethylpentene, ethylene vinyl alcohol copolymer, ethylene propylene copolymer, polyethylene terephthalate, polybutylene terephthalate, nylon 6 or nylon 66 alone or Two or more types may be used in combination. The other segment may be one type or two or more types.

It is preferable that the segments of the split type composite fiber are arranged mutually. For example, it may be a radial shape, a multilayer shape, a cross shape, or the like. Among these, from the viewpoint of further improving the splitting property of the split-type conjugate fiber, the arrangement of the segments of the split-type conjugate fiber is preferably radial.

In the split composite fiber, the number of splits (total number of segments) may be determined according to the fineness of the split composite fiber, the fineness of the ultrafine fiber to be obtained, and the like. The number of divisions is preferably 4 to 30, for example, 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, the productivity of the fibers can be moderate, and the division properties can be kept moderate even though spinning is easier.

The split-type composite fiber preferably has a hollow portion at the center of the fiber as viewed from the fiber cross section. When it has a hollow part in a fiber center part, the puncture strength of a fiber structure can be made higher compared with the split type composite fiber which does not have a hollow part in a fiber center part. This is presumably because the fiber cross section of the ultrafine fiber formed by splitting the split-type composite fiber has a more circular shape. Furthermore, yarn breakage during spinning of the split composite fiber can be suppressed.

When the split-type composite fiber has a hollow portion, the hollow ratio can be determined according to the split ratio and the cross-sectional shape of the ultrafine fiber. The hollow ratio is the ratio of the area of the hollow portion in the fiber cross section. For example, the hollowness is preferably about 1% to 50%, and preferably about 5% to 40%. More specifically, when the number of divisions is 6 to 10, the hollow ratio is preferably 5% to 20%, and when the number of divisions is 12 to 20, the hollow ratio is 15% to 40%. It is preferable. When the hollowness is about 1% to 50%, it is preferable that the split type composite fiber is difficult to split in the manufacturing process, although the effect of providing the hollow portion is easy to obtain.

In the fiber cross section of the split type composite fiber, the first segment preferably occupies 20% to 80% in area, and more preferably occupies 40% to 60% in area. When the first segment of the split-type composite fiber occupies 20% to 80% in area, the splitability of the split-type composite fiber is not easily lowered, and the ultrafine fiber 1 derived from the first segment can be formed easily. .

The volume ratio between the first segment and the second segment constituting the split-type composite fiber is not particularly limited as long as the target split-type composite fiber can be obtained. For example, the volume of the first segment and the volume of the second segment (since the cross-sectional structure of the second segment is a core-sheath resin segment having the first component as the core component and the second component as the sheath component, The ratio of the total volume of the core component and the sheath component is preferably 2/8 to 8/2 (volume of the first segment / volume of the second segment), and is 4/6 to 6/4. More preferably. A volume ratio of 2/8 to 8/2 is preferred because the spinnability and splitting property are further improved.

The second segment is a core-sheath type resin segment, and the volume ratio of [first segment + second segment core component] / [sheath component of the second segment] in the fiber cross section is 2/8 to 8/2 Is preferably 4/6 to 6/4. A volume ratio of 2/8 to 8/2 is preferred because the spinnability and splitting property are further improved. For example, when the volume ratio of [first segment + core component of second segment] / [sheath component of second segment] is 5/5, the volume of the first segment is larger than the volume of the entire second segment. Note that also becomes smaller.

The volume ratio of the first component to the second component is not particularly limited as long as the split type composite 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 volume of the core component and the sheath component) is 8/2 to 3/7 (volume of the first component / volume of the second component). Preferably, the ratio is 75/25 to 35/65, more preferably 70/30 to 40/60. A volume ratio of 8/2 to 3/7 is preferred because the spinnability and splitting properties are further improved.

The fineness before splitting of the split-type composite fiber is not particularly limited as long as the target split-type composite fiber of the present invention can be obtained, but is preferably 0.5 dtex to 4.8 dtex, More preferably, it is 0.8 dtex to 3.6 dtex, more preferably 1.1 dtex to 2.4 dtex, and most preferably 1.1 dtex to 2.0 dtex. When the fineness before splitting of the split-type composite fiber is 0.5 dtex to 4.8 dtex, it is preferable because spinning is easier and productivity is further improved.

The single fiber strength of the split type composite fiber before splitting is preferably 2.5 to 7.0 cN / dtex, more preferably 2.7 to 6.5 cN / dtex, and more preferably 2.8 to 6.c. It is even more preferably 0 cN / dtex, and particularly preferably 3.0 to 5.8 cN / dtex. The single fiber strength is measured by the method described in the examples.

The elongation before splitting of the split-type fiber is preferably 10 to 120%, more preferably 15 to 80%, still more preferably 20 to 60%, and further preferably 20 to 55%. It is particularly preferred. The elongation is measured by the method described in the examples.

DSC (differential scanning calorimetry) is performed on the split type composite fiber, and the resulting DSC curve will be described. The DSC curve by DSC of the entire split type composite fiber is the melting point, molecular weight distribution, crystal state, crystallinity, and amount contained in the split type composite fiber of each of the polypropylene resin and polyethylene resin contained in the split type composite fiber, Moreover, it may change with the kind of other thermoplastic resin contained in a split type composite fiber, quantity, and those crystal | crystallization states.

The split composite fiber of the present invention is subjected to DSC, and the physical properties of the split composite fiber, particularly the split properties of the split composite fiber, are affected by the shape of the melting peak of the polypropylene resin in the obtained DSC curve. Hereinafter, the shape of the melting peak of the polypropylene resin indicated by the DSC curve obtained by performing DSC on the split composite fiber of the present invention will be described. In split type composite fibers containing a polypropylene resin, the melting peak of the polypropylene resin appears as a peak having the shape shown in FIGS. 4 to 11 in the DSC curve.

4 to 11 indicate the following.
a: Melting peak of polypropylene resin contained in split type composite fiber a ₁ : First melting peak of polypropylene resin (first melting peak)
a ₂ : Second melting peak of polypropylene resin (second melting peak)
a ₃ : valley in melting peak of polypropylene resin (valley in melting peak)
T ₁ : First melting peak temperature of polypropylene resin (° C.)
(Hereinafter also simply referred to as the first melting peak temperature)
T ₂ : second melting peak temperature of polypropylene resin (° C.)
(Hereinafter, also simply referred to as the second melting peak temperature)
W ₂ : heat flux (mW) at the second melting peak of polypropylene resin
W ₃ : heat flux (mW) in a valley (a ₃ ) existing between the first melting peak and the second melting peak of the polypropylene resin
S ₁ : area of the first endothermic peak of the polypropylene resin (first melting peak area)
S ₂ : area of the second endothermic peak of the polypropylene resin (second melting peak area)
BL _LT : Base line on the low temperature side in the DSC curve BL _HT : Base line on the high temperature side in the DSC curve BL _E : In the DSC curve, the base line on the low temperature side is moved from the terminal portion on the high temperature side (the right end portion of the BL _LT ). , A straight line extending toward the low temperature side end of the high temperature side base line (the left end of the BL _HT ) In FIGS. 4 to 11, the vertical axis is the heat flux (usually the unit is mW: milliwatt) and absorbs heat. It corresponds to energy, and the horizontal axis indicates time (usually the unit is seconds or minutes).

The split composite fiber of the present invention is characterized in that the shape of the melting peak of the polypropylene resin is a double peak shape in the DSC curve. The fact that the shape of the melting peak of the polypropylene resin is a double peak shape means that the shape corresponds to one of the following (1) or (2).

(1) In the endothermic peak of the polypropylene resin, after the first melting peak (a ₁ ) appears on the low temperature side (in other words, on the side where the time elapsed from the start of temperature increase is short), the valley in the melting peak of the polypropylene resin ( After a ₃ ) clearly appears, the second melting peak (a ₂ ) appears on the high temperature side (in other words, on the side where the time elapsed from the start of temperature increase is long).
(2) In the melting peak of polypropylene resin, the first melting peak appears on the low temperature side, but the first melting peak and the second melting peak do not appear as two vertices that can be clearly separated (in other words, the polypropylene resin A valley (a ₃ ) in the melting peak does not appear clearly), and a shoulder-like shape (shoulder-like peak) appears as shown in FIGS.

First, the melting peak shape of the polypropylene resin that satisfies the condition (1) will be described.
Schematic diagrams of melting peak shapes satisfying the condition (1) are shown in FIGS. In the melting peak satisfying the condition (1), the melting of the polypropylene resin is started from around 145 ° C. in the DSC, and the first melting peak (a ₁ ) is observed in the sample temperature range of about 157 to 165 ° C. It is measured. As time further elapses and the sample temperature further rises, after the valley (a ₃ ) in the melting peak of the polypropylene resin clearly appears, the second melting peak (a ₂ ) is observed when the sample temperature is in the range of about 165 to 175 ° C. ) Appears, and when the sample temperature reaches 180 ° C., the melting of the polypropylene resin is completed.

Next, the melting peak shape of the polypropylene resin that satisfies the condition (2) will be described.
Schematic diagrams of melting peak shapes satisfying the condition (2) are shown in FIGS. At the melting peak satisfying the condition (2), the melting of the polypropylene resin starts from a sample temperature of around 145 ° C. in DSC, but the first melting peak that is the minimum value is not measured, and the shoulder-like peak is measured. Then, as time elapses, the second melting peak (a ₂ ) appears as the temperature of the sample rises, and when the sample temperature reaches 180 ° C., the melting of the polypropylene resin is completed. Such a shape of the melting peak is measured when the temperatures of the first melting peak and the second melting peak are close.

In the DSC curve, whether or not the melting peak shape of the polypropylene resin is a double peak is a double peak shape if one of the above conditions (1) to (2) is satisfied, and none of them is satisfied. Has a so-called single peak shape in which the shape of the melting peak is not a double peak (FIG. 12). The single peak shape can be determined by examining a DDSC curve obtained by differentiating the DSC curve. The DDSC curve is a curve obtained by first differentiating the DSC curve with respect to time, and indicates the slope of the DSC curve. Therefore, when the slope of the DSC curve becomes zero, it becomes zero, and therefore the value of the DDSC curve becomes zero at the maximum value and the minimum value in the DSC curve.

In the split type composite fiber of the present invention, the shape of the melting peak (a) of the polypropylene resin is a double peak shape, more specifically, if any one of the conditions (1) to (2) is satisfied. However, it is particularly preferable that the condition (1) is satisfied. When the shape of the endothermic peak resulting from the melting of the polypropylene resin in the DSC curve satisfies the above condition (1), in other words, there are two melting peaks that are minimal in the DSC curve. When there is a clear melting peak valley (a ₃ ) between them, the polypropylene resin contained in the split-type composite fiber is not only in a high crystallinity state, but also melts at a lower temperature. It is thought that it is crystallized by dividing into regions that melt at higher temperatures. When the condition (1) is satisfied, the reason why the splitting property of the obtained split composite fiber is improved is not clear, but it is considered as follows from the characteristics of the selected resin and the DSC curve of the split composite fiber.

As described above, when the shape of the melting peak of the polypropylene resin satisfies the condition (1) in the DSC curve of the split-type composite fiber, the polypropylene resin has a region that melts at a lower temperature and a region that melts at a higher temperature. It is thought that it has been crystallized separately.
The region that melts at a lower temperature is an amorphous phase, a crystalline phase that melts at a lower temperature, a crystallized phase that has a low molecular weight, or is crystallized. It is presumed that the same level is included.
On the other hand, in the crystalline region that melts at higher temperatures, polypropylene molecules that have not been crystallized during melt spinning are sufficiently crystallized as a result of stretching at a high draw ratio above the glass transition temperature of polypropylene in the stretching process. It is thought that this is the area that occurred in
In addition, although it is thought that this invention has the outstanding effect for such a reason, this invention is not restrict | limited at all for such a reason.

In order to increase the crystallinity of the polypropylene resin contained in the split type composite fiber, it is considered preferable to crystallize most of the polypropylene molecules in the stretching step. Therefore, it is considered that it is preferable that the sizes of the polypropylene molecules, that is, the molecular weights of the polypropylene molecules are made uniform and their behaviors are made uniform. Therefore, in the split-type composite fiber of the present invention, as the polypropylene resin constituting the resin segment, a resin having a narrower molecular weight distribution width, that is, a Q value that is a ratio of the weight average molecular weight to the number average molecular weight after spinning is 6 or less. Of polypropylene resin. Polypropylene resin having a Q value of greater than 6 after spinning has a larger molecular weight range of the polypropylene molecule, that is, the molecular weight is too large (the molecule is too long) and / or the molecular weight is too small (molecular However, since the former is crystallized in the spinning process and becomes difficult to stretch in the stretching process, the process of the stretching process may be deteriorated. Since it is difficult to crystallize, it remains as a soft region in the resin segment, which may cause a decrease in the splitting property in the split composite fiber.

In the present invention, the differential scanning calorimetry (DSC) of the split-type composite fibers is measured based on the plastic transition temperature measurement method of JIS K 7121 (1987).

It is preferable that the split type composite fiber according to the embodiment of the present invention satisfies at least one of the following (A) and (B).
(A) In differential scanning calorimetry (DSC) performed under the above conditions, the melting peak of the polypropylene resin is divided into a low temperature side region and a high temperature side region, and the area of each region is defined as a first melting peak area and a second melting peak. When the area is defined, 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 or more and 3.5 or less, preferably 0.9 or more and 3 .2 or less, more preferably 0.95 or more and 3.0 or less, and even more preferably 1.0 or more and 2.5 or less.
(B) In the differential scanning calorimetry (DSC) performed under the above conditions, the elongation of the second peak obtained from the values of W ₂ and W ₃ obtained by the method described later is obtained for the melting peak in the DSC curve of the polypropylene resin. The elongation of the second peak, which is 0.6 or more, is preferably 0.7 or more, more preferably 0.8 or more, and even more preferably 0.85 or more.

The condition (A), which is a preferable condition in the split type composite fiber of the present invention, will be described.
When the shape of the measured melting peak of the polypropylene resin in the DSC of the split-type composite fiber is a melting peak satisfying the condition (1), it passes through the valley (a ₃ ) in the melting peak of the polypropylene resin, 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 region and a high temperature region. A straight line (BL _E ) obtained by extending the low-temperature side base line (BL _LT ) from the high-temperature side end portion toward the high-temperature side base line (BL _HT ) in this line, the DSC curve, and the melting peak of polypropylene. The area of each region surrounded by is referred to as a first melting peak area and a second melting peak area. More specifically, in FIG. 6, a region S ₁ which is filled with oblique lines is a first melting peak area, the area S ₂ which is filled with oblique lines is a second melting peak area in FIG.

The condition (A), which is a preferable condition for 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 in the DSC of the split type composite fiber is a melting peak satisfying the condition (2) above, the shoulder peak measured in the melting peak (a) of polypropylene, T ₁ and T as the absolute value of the first derivative of the DSC curve points becomes minimum between _2, a straight line is drawn which intersects perpendicularly to the horizontal axis of the graph, the straight line as a boundary line, melting peak of polypropylene Are divided into a low temperature region and a high temperature region.
In this straight line, DSC curve, and melting peak of polypropylene, the low temperature side baseline (BL _LT ) is a straight line (BL _E ) extending from the high temperature side end portion toward the high temperature side base line (BL _HT ). The area of each enclosed region is referred to as a first melting peak area and a second melting peak area. More specifically, in FIG. 10, region S ₁ which is filled with oblique lines is a first melting peak area, the area S ₂ which is filled with oblique lines is a second melting peak area in FIG. 11.

When determining the ratio of the second melting peak area to the first melting peak area (second melting peak area / first melting peak area), after printing the DSC curve on paper and drawing the boundary line by the above method, A portion corresponding to the first melting peak area and a portion corresponding to the second melting peak area are cut out and their masses are measured, and the ratio of the second melting peak area to the first melting peak area (second melting peak area / first Melting peak area). Alternatively, using a measuring instrument that can automatically integrate the DSC curve in an arbitrary interval (using the function attached to the measuring instrument), obtain the first melting peak area and the second melting peak area, and calculate the ratio thereof. You can also

The condition (B), which is a preferable condition for the split conjugate fiber of the present invention, will be described.
(B): In the differential scanning calorimetry (DSC), the melting peak of the double peak-shaped polypropylene resin is divided into a first melting peak and a second melting peak,
The value of the DSC curve when the second melting peak temperature is reached is W ₂ (mW),
The value of the DSC curve that minimizes the absolute value of the first derivative of the DSC curve between the first melting peak and the second melting peak is W ₃ (mW),
Elongation of second melting peak = (Absolute value of W ₂ ) − (Absolute value of W ₃ )
The elongation of the second peak defined by is 0.6 or more.
More specifically, as shown in FIG. 5, in the melting peak (a) of polypropylene, it is measured between the second melting peak (a ₂ ), the first melting peak (a ₁ ), and a ₁ , a _2. If valley in melting peak of the polypropylene resin _{(a 3)} is present, the value of the DSC in _{a 2} _(W _2), measures the value of DSC when a valley of the melting peak _{(a ₃₎} _(W ₃₎ The difference between the absolute values of W ₂ and W ₃ is the elongation of the second melting peak.

The condition (B), which is a preferable condition in the split type composite fiber of the present invention, will be further described.
When the shape of the melting peak of the polypropylene resin measured in the DSC of the split composite fiber satisfies the condition (2), the elongation of the second melting peak is defined as follows.
That is, (B): In the differential scanning calorimetry (DSC), the melting peak of the double peak-shaped polypropylene resin is divided into a first melting peak and a second melting peak,
The value of the DSC curve when the second melting peak temperature is reached is W ₂ (mW),
The value of the DSC curve that minimizes the absolute value of the first derivative of the DSC curve between the first melting peak and the second melting peak is W ₃ (mW),
Elongation of second melting peak = (Absolute value of W ₂ ) − (Absolute value of W ₃ )
The elongation of the second peak defined by is 0.6 or more.
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-like peak measured on its low temperature side, and the DSC value at a ₂ (W ₂ ), the DSC value (W ₃ ) measured at the point where the absolute value of the first derivative of the DSC curve is smallest between T ₁ and T ₂ , and the absolute values of W ₂ and W ₃ The difference in values is the elongation of the second melting peak.

In addition, although DSC was performed on the split-type composite fiber according to the embodiment of the present invention and the obtained DSC curves were described using FIGS. 4 to 11, FIGS. 4 to 11 are merely examples. For example, the shape of these DSC curves, that is, the melting peak shape of polypropylene resin is such that the melting peak on the low temperature side (first melting peak) is smaller than the melting peak on the high temperature side (second melting peak). In other words, the melting peak on the high temperature side (second melting peak) is larger than the melting peak on the low temperature side (first melting peak), but such a shape is not necessarily obtained. Therefore, even if the relationship between the size of the first melting peak and the second melting peak is reversed, the first melting peak is larger than the second melting peak (the melting peak is sharp and elongated). The above-mentioned conditions, that is, satisfying the definition that the shape of the melting peak of the polypropylene resin in the present invention is a double peak, the ratio of the second melting peak area to the first melting peak area, and the elongation of the second melting peak Needless to say, the present invention includes split type composite fibers that satisfy the requirements.

<Ultrafine fiber>
The split-type conjugate fiber is split to form an ultrafine fiber 1 derived from the first segment, and an ultrafine fiber 2 derived from the second segment. When other segments are included, other ultrafine fibers derived from the other segments are formed.

The fiber cross-sectional structure of the split-type composite fiber is preferably a fiber cross-sectional structure in which the segments are arranged alternately in a radial pattern. Furthermore, in the split type composite fiber, it is also preferable to have a fiber cross-sectional structure having a hollow part at the fiber center part.

The ultrafine fiber 1 and / or the ultrafine fiber 2 preferably has a fineness of less than 0.6 dtex, and more preferably less than 0.4 dtex. When the fineness of the ultrafine fiber is less than 0.6 dtex, a thin fiber structure can be obtained more easily. The fineness of the

ultrafine fibers

1 and 2 may be the same or different from each other, and the lower limit of the fineness is preferably 0.006 dtex for any of the ultrafine fibers.

Particularly, 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 core-sheath type composite fiber is included in the fiber structure, the smaller the fineness of the composite fiber, the larger the surface area of the composite fiber, so that the thermal bonding area increases, and the mechanical strength of the fiber structure after thermal bonding Becomes higher. When the ultrafine fiber 2 is a core-sheath type ultrafine composite fiber, it is particularly preferable to have a smaller fineness.

<Method for producing split composite fiber>
In another aspect, the present invention provides a method for producing a new split-type composite fiber,
In a fiber cross section, a split-type conjugate fiber including a first segment and a second segment,
The first segment is a resin segment composed of a first component,
The second segment is a melt spinning machine equipped with a split type composite nozzle that is a split type composite fiber that is a core-sheath type resin segment whose cross-sectional structure is the core component of the first component and the sheath component of the second component. To prepare;
Using a resin component containing 50% by mass or more of a polypropylene resin having an Mw / Mn of 6 or less as a first component and a resin component containing 50% by mass or more of a polyethylene resin as a second component, melt spinning with a melt spinning machine Producing spinning filaments;
This is a method for producing a split-type conjugate fiber, comprising drawing a spun filament at a drawing temperature of 60 ° C. or more and 125 ° C. or less and a draw ratio of 1.1 times or more to obtain a split-type conjugate fiber.

As long as the split-type conjugate fiber according to the embodiment of the present invention can obtain the target split-type conjugate fiber, its production method is not particularly limited, but the above-described split-type conjugate fiber production method is used. Thus, it is possible to preferably manufacture the above-mentioned split type composite fiber according to the present invention.
Hereinafter, the manufacturing method of a split type composite fiber is demonstrated in detail.

The split type composite fiber can be composite-spun using a conventional melt-spinning machine using an appropriate composite spinning nozzle so that a desired fiber cross-sectional structure can be obtained. The spinning temperature (nozzle temperature) is selected according to the resin component used, and may be, for example, 200 ° C. or higher and 360 ° C. or lower.

Specifically, a split type composite nozzle that obtains a predetermined fiber cross section is attached to the melt spinning machine, and the spinning temperature is set so that the first segment and the second segment are adjacent to each other in the fiber cross section and are divided from each other. The polypropylene resin constituting the first segment and the polyethylene resin constituting the second segment can be extruded and melt-spun at 200 to 360 ° C. to obtain a spun filament (unstretched fiber bundle).

The fineness of the spun filament (unstretched fiber bundle) may be in the range of 1 dtex to 30 dtex. When the fineness of the spinning filament is 1 dtex or more and 30 dtex or less, spinning can be facilitated. In the case where the spinning filament is highly stretched to improve the splitting property, the fineness of the spinning filament is preferably 2.0 to 15 dtex, more preferably 2.5 to 12 dtex, and 3 to 10 dtex. More preferably, it is 4.0 to 8.0 dtex, particularly preferably 4.5 to 7.5 dtex.

Next, the drawn filament can be obtained by drawing the spinning filament using a known drawing processor. The stretching treatment is preferably carried out by setting the stretching temperature to a temperature within the range of 60 ° C. to 125 ° C., and more preferably at a temperature within the range of 80 ° C. to 120 ° C. In addition, it is preferable to perform a extending | stretching process below below melting | fusing point of resin with the lowest melting | fusing point among the resin components which comprise split-type composite fiber. The draw ratio is preferably 1.1 times or more, more preferably 1.5 times or more, further preferably 2 to 8 times, particularly preferably 3 to 6 times. Most preferably, the ratio is from 5 to 5.5 times. When the draw ratio is 1.1 times or more, the molecules constituting the fiber are oriented in the length direction of the fiber, so that the splitting property is improved.

Depending on the resin component used, the stretching method may be a wet stretching method performed in warm water or hot water, hot air spraying, a dry stretching method performed in a high temperature atmosphere, or in a liquid heat medium other than water such as silicone oil. However, it is preferable to carry out by a dry stretching method, a wet stretching method, or a steam stretching method because the thermal efficiency is good and the productivity is excellent. More preferred. The drawing method can be selected in consideration of the intended use of the resulting split conjugate fiber. That is, when the split composite fiber of the present invention is used for splitting at a high ratio without being exposed to a high-pressure water stream, or for applications where high single fiber strength is required, the stretching method is a dry process that can be stretched at a higher temperature. It is preferable to perform stretching or steam stretching. On the contrary, when the split-type composite fiber of the present invention is used as a fiber constituting the hydroentangled nonwoven fabric, a high single fiber strength is not required for the obtained split-type composite fiber and the ultrafine fiber obtained after the split. If it is used for an application, it is preferable to perform wet stretching where the productivity is easily stabilized. In the case of the wet stretching method, the stretching temperature may be in the range of 60 ° C. or higher and 98 ° C. or lower, may be in the range of 60 ° C. or higher and 95 ° C. or lower, may be in the range of 70 ° C. or higher and 95 ° C. or lower, and is 80 ° C. or higher. It is good also as a range below 95 degreeC. In the case of the dry stretching method, the stretching temperature may be in the range of 80 ° C. or more and 125 ° C. or less, may be in the range of 90 ° C. or more and 125 ° C. or less, may be in the range of 100 ° C. or more and 125 ° C. or less, It is good also in the range below 120 degreeC.

The draw ratio is preferably 0.7 to 0.98 times the maximum draw ratio (Vmax) (draw ratio / Vmax = 0.7 to 0.98), preferably 0.75 to 0.97. It is more preferable that it is 2 times or less, 0.8 to 0.96 times is even more preferable, and 0.85 to 0.96 times is particularly preferable. 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 spinning filament is stretched at a high draw ratio. Since the crystallization of the polypropylene molecules contained in the polypropylene resin that constitutes the spinning filament and the polyethylene molecules that constitute the polyethylene resin are advanced by the stretching treatment, and the orientation of the molecular arrangement is advanced, the resulting division is obtained. There exists an advantageous effect that a type | mold composite fiber becomes easy to be divided | segmented into each segment.
The maximum draw ratio is determined by the method described in the examples.

A predetermined amount of fiber treatment agent is adhered to the obtained drawn filament as necessary, and further, mechanical crimping is given by a crimper (crimping device) as necessary. As will be described later, the fiber treatment agent facilitates dispersion of fibers in water or the like when a nonwoven fabric is produced by a wet papermaking method. Further, when an external force is applied to the fiber to which the fiber treatment agent is attached from the fiber surface (the external force is a force applied when crimping is applied by a crimper, for example), and the fiber treatment agent is soaked into the fiber, water is further added. The dispersibility to etc. improves.

After the fiber treatment agent is applied (or the fiber treatment agent is not applied but is in a wet state), the cocoon filament is dried at a temperature within the range of 80 ° C. to 110 ° C. for several seconds to about 30 minutes, Allow the fibers to dry. The drying process may be omitted depending on circumstances. Thereafter, the filament is preferably cut so that the fiber length is 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, the fiber length is more preferably 3 mm to 20 mm. When manufacturing a nonwoven fabric by the wet papermaking method, the division | segmentation rate of a split type composite fiber becomes high, so that fiber length is short. When the nonwoven fabric is produced by the card method, the fiber length is more preferably 20 mm to 100 mm.

<Fiber structure>
The fiber structure of the present invention will be described. Although it does not specifically limit as a form of a fiber structure, For example, a woven fabric, a knitted fabric, a nonwoven fabric etc. are mentioned. Moreover, the fiber web form of the nonwoven fabric is not particularly limited, and examples thereof include a card web formed by a card method, an air lay web formed by an air lay method, and a wet paper making web formed by a wet paper making method.

It is preferable that the fiber structure includes 5% by mass or more of ultrafine fibers formed by dividing the split composite fiber. That is, the fiber structure may include the ultrafine fiber 1 and the ultrafine fiber 2 in a proportion of 5% by mass or more. The fiber structure preferably contains ultrafine fibers in a proportion of 10% by mass or more, more preferably in a proportion of 20% by mass or more, and most preferably in a proportion of 25% by mass or more. A preferable upper limit is 100 mass%. When the proportion of the split composite fibers in the fiber structure is large, a dense nonwoven fabric tends to be obtained.

Fiber structure for separators used for various secondary batteries such as lithium ion batteries and nickel metal hydride batteries, various capacitors and various power storage devices such as capacitors; captures foreign substances from fluids such as liquids and gases Fiber structures for filtration layers constituting various filters such as cartridge filters and multilayer filters to be removed; reverse osmosis membrane (RO membrane), nanofiltration membrane (NF membrane), ultrafiltration membrane (UF membrane), precision Fiber structures for various membrane supports used as supports for various filtration membranes such as filtration membranes (MF membranes); fiber structures for various wiping sheets such as interpersonal and / or objective wipers; cosmetics such as face masks Fiber structures for skin-impregnated skin-coated sheets; surface sheets constituting absorbent articles such as infant paper diapers, nursing care paper diapers, sanitary napkins, Even if it is Kandoshito and backsheet fiber structure of the sheet for an absorbent article, such as the proportion of the splittable conjugate fibers may be used fiber structure comprising a 100% by weight. If a certain amount of voids between constituent fibers and the air permeability and liquid permeability associated therewith are required for the fiber structure containing the above-mentioned split type composite fiber, the content of the split type composite fiber in the entire fiber structure is 90 mass% or less, 80 mass% or less, or 75 mass% or less. In addition, as above-mentioned, the minimum of the said splitting type | mold composite fiber contained in a fiber structure may be 10 mass% or more, may be 20 mass% or more, and may be 25 mass% or more.
When the ratio of the above-mentioned split-type composite fibers contained in the fiber structure such as dry nonwoven fabric and wet nonwoven fabric is 90% by mass or less, the ratio of the ultrafine fibers generated from the split-type composite fibers in the obtained fiber structure is Depending on the use of the fiber structure, the structure is preferably a suitably dense non-woven fabric.

The fiber structure more preferably contains the ultrafine fiber 2 in a proportion of 10% by mass or more, more preferably contains the ultrafine fiber 1 in a proportion of 20% by mass or more, and the ultrafine fiber 2 in a proportion of 35% by mass or more. The inclusion is most preferred. A preferable upper limit is 50 mass%. When the core-sheath type ultrafine composite fiber is included in the nonwoven fabric in such a ratio as the ultrafine fiber 2, the core-sheath type composite fiber having a small fineness (less than 0.6 dtex) is included. Compared with the non-woven fabric containing the amount, it has higher mechanical strength. Further, a thin fiber structure having excellent mechanical strength can be obtained.

When the ultrafine fiber is contained in an amount of 5% by mass or more, the fiber structure may contain other fibers other than the ultrafine fiber formed from the split composite fiber in an amount of 95% by mass or less. Other fibers may be natural fibers or regenerated fibers, or may be single fibers and composite fibers made of synthetic resin. Alternatively, the other fiber may include an ultrafine fiber formed from another split type composite fiber. Alternatively, the other fiber may be an ultrafine fiber having a fineness of less than 0.6 dtex manufactured by a single spinning method, rather than an ultrafine fiber formed from a split composite fiber. Alternatively, the fiber structure is generated only because of the fibers derived from the split type composite fibers (the ultrafine fiber 1 derived from the first segment, the ultrafine fiber 2 derived from the second segment, and the division did not proceed completely) Or a fiber having a branching in one fiber, or the like, or may be composed only of ultrafine fibers formed from the split type composite fibers.

The fiber structure preferably has a total amount of fibers having a small fineness (less than 0.6 dtex) in the fiber structure, preferably 10% by mass or more, more preferably 20% by mass or more, and 50% by mass. % Or more is even more preferable, and 70% by mass or more is most preferable. In addition, a preferable upper limit is 100 mass%. When the total amount of fibers having a small fineness (less than 0.6 dtex) in the fiber structure is within the above range, a thin fiber structure can be easily obtained. The fibers having a small fineness (less than 0.6 dtex) in the fiber structure may be only the ultrafine fibers 1 or only the

ultrafine fibers

1 and 2 or may be composed of these and other ultrafine fibers. .

In the above fiber structure, the split composite fiber of the present invention can be split by applying a physical impact. For example, it can be carried out by hydroentanglement treatment (injecting a high-pressure water flow), or when a nonwoven fabric is produced by a wet papermaking method, it can be carried out by using the impact received during the disaggregation treatment during papermaking. .

In the water entangling process, a columnar water flow with a water pressure of 3 to 20 MPa is sprayed at least once on the front and back of the nonwoven fabric from a nozzle in which orifices having a hole diameter of 0.05 to 0.5 mm are provided at intervals of 0.5 to 1.5 mm. It is preferable. If the split type composite fiber of the present invention is used, the conventional split type composite fiber having a water pressure of 10 MPa or less in which the formation of the fiber web is not disturbed and the opening due to the high-pressure water flow is less likely to be sufficiently split. However, it is possible to divide, and further, it is possible to divide even when the water pressure is 8 MPa or less, and it is possible to divide even when the water pressure is 6 MPa or less.

A method for manufacturing a fiber structure will be described taking a nonwoven fabric as an example. The non-woven fabric is produced by producing a fiber web according to a known method and then subjecting the fibers to heat treatment by heat treatment as necessary. Moreover, you may attach | subject a fiber web to a fiber entanglement process as needed. For example, the fiber web is divided by a dry method such as a card method or an air array method using a split type composite fiber having a fiber length in a range of 10 mm to 80 mm, or a fiber length in a range of 2 mm to 20 mm. It is produced by wet papermaking using a mold composite fiber. When used in fields such as interpersonal / objective wipers and filters, nonwoven fabrics produced by dry methods such as the card method or air array method are preferred. This is because the nonwoven fabric produced by the dry method has a soft texture and an appropriate density. Moreover, when using in field | areas, such as a battery separator, it is preferable that it is the nonwoven fabric manufactured from the wet papermaking web. This is because a nonwoven fabric produced using a wet papermaking web is generally dense and has a good texture. Furthermore, according to the wet papermaking method, by adjusting the conditions of the dissociation process during papermaking, it is possible to divide the split-type composite fiber at a desired splitting rate only by the dissociation process.

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

As will be described later, the thermal bonding treatment is preferably performed before the hydroentanglement treatment when the fiber web is subjected to the hydroentanglement treatment. When the hydroentanglement treatment is carried out after the fibers of the fiber web have been joined in advance, the fiber “escape” is less likely to occur when the fibers are subjected to a high-pressure water stream, and the fibers can be closely entangled, and the split composite Fiber splitting is further promoted. However, the thermal bonding treatment may be performed after the fibers are entangled. That is, the order of the thermal bonding treatment and the hydroentanglement treatment is not particularly limited as long as a desired nonwoven fabric is obtained.

In the fiber structure of the present invention, the fibers may be entangled. As a process for entanglement of fibers, a water entanglement process for entanglement of fibers by the action of a high-pressure water flow is preferably used. According to the hydroentanglement process, the fibers can be strongly entangled without impairing the density of the entire nonwoven fabric. Moreover, the entanglement between the ultrafine fibers generated by the splitting and splitting of the split-type composite fibers can be advanced simultaneously with the entanglement of the fibers by the hydroentanglement process.

The conditions for the hydroentanglement treatment are appropriately selected according to the type and basis weight of the fiber web to be used and the type and ratio of the fibers contained in the fiber web. For example, when a wet papermaking web having a basis weight of 10 to 100 g / m ² is subjected to hydroentanglement treatment, the fiber web is placed on a support having a plain weave structure of about 70 to 100 mesh and a pore diameter of 0.05 to 0.3 mm. A columnar water flow having a water pressure of 1 to 15 MPa, more preferably 2 to 10 MPa, may be sprayed 1 to 10 times each on one or both sides of the fiber web from a nozzle provided with an orifice of 0.5 to 1.5 mm. . The fiber web after the hydroentanglement treatment is subjected to a drying treatment as necessary.

The fiber structure may be subjected to a hydrophilization treatment as necessary. The hydrophilization treatment may be performed using any method such as a fluorine gas treatment, a vinyl monomer graft polymerization treatment, a sulfonation treatment, a discharge treatment, a surfactant treatment, or a hydrophilic resin application treatment.

Fiber structure preferably has a 2 g / m ² or more 100 g / m ² or less of the mass per unit area, more preferably has a 10 g / m ² or more 100 g / m ² or less of the mass per unit area, more preferably 20 g / m ² or more It has a basis weight of 80 g / m ² or less, and particularly preferably has a basis weight of 30 g / m ² or more and 60 g / m ² or less. When the basis weight of the fiber web is 2 g / m ² or more, the resulting fiber web and the fiber structure are well formed, and the fiber structure tends to have high strength and high puncture strength. When the basis weight of the fiber web is 100 g / m ² or less, the air permeability of the fiber structure is not lowered, and the split type composite fiber of the present invention contained in the fiber web is divided into each component by hydroentanglement treatment described later. When this is done, the high-pressure water stream tends to act uniformly on the entire fiber web, and it becomes easy to sufficiently divide the split composite fibers.

Moreover, since the present invention can bond ultrafine fibers to each other by the sheath component of the core-sheath type ultrafine composite fiber formed from the second segment, it forms a fiber structure in which the fibers are bonded only by the ultrafine fibers. Can do. Such a fiber structure is preferably in the form of a non-woven fabric, for example, and can be used as a battery separator, various filter media, and various membrane supports. In such a case, the basis weight of the fiber structure preferably has a basis weight of 5 g / m ^{2 to} 80 g / m ² , more preferably 5 g / m ^{2 to} 60 g / m ² , Preferably, it has a basis weight of 5 g / m ² or more and 50 g / m ² or less, and most preferably has a basis weight of 10 g / m ² or more and 30 g / m ² or less.

In the fiber structure in the form of the present invention, the splitting ratio of the split-type composite fiber is preferably 90% or more, more preferably 92% or more, still more preferably 95% or more, 97 % Or more is particularly preferable.

The fiber structure in the form of the present invention preferably has an air permeability of 5 to 24 cm ³ / cm ² · second, more preferably 8 to 22 cm ³ / cm ² · second, and 10 to 20 cm ³ / second. preferably more than that cm is ² · sec, particularly preferably 12 ~ 18cm ³ / cm ² · sec.
The air permeability is measured by the method described in the examples.

The fiber structure in the form of the present invention preferably has an average pore size of 1 to 16 μm, more preferably 2 to 15 μm, particularly preferably 3 to 12 μm, most preferably 5 to 10 μm. preferable. When the average pore size of the fiber structure is 1 to 16 μm, it is considered that the pores present in the fiber structure are sufficiently small and the entire fiber structure has a dense structure. The fiber structure for the filter layer which comprises various filters; It becomes a fiber structure especially suitable for the fiber structure for various membrane supports used as a support body of various filter membranes. The fiber structure of the present invention preferably has a maximum pore size of 5 to 30 μm, more preferably 8 to 24 μm, particularly preferably 10 to 20 μm, and 12 to 18 μm. Is most preferred. If the maximum pore size of the fiber structure is 5 to 30 μm, it can be said that the diameter of the largest pore among the pores existing in the fiber structure is sufficiently small. The fiber structure is particularly suitable for a separator fiber structure, a filtration layer fiber structure, and a membrane support fiber structure that are required to be blocked.

The fiber structure in the form of the present invention preferably has a minimum pore size of 1 to 10 μm, more preferably 2 to 8 μm, particularly preferably 2.5 to 6 μm, and 3 to 5 μm. Is most preferred. The fiber structure of the present invention preferably has a most porous diameter of 1 to 15 μm, more preferably 2 to 12 μm, particularly preferably 2.5 to 10 μm, and 3 to 8 μm. Most preferably it is. If the minimum pore size of the fiber structure is 1 to 10 μm or the maximum pore diameter of the fiber structure is 1 to 15 μm, the pores existing in the fiber structure are sufficiently small and the structure is dense. In particular, since the fiber structure can permeate or hold substances other than foreign matters such as water and gas, it is particularly suitable for a separator fiber structure, a filter layer fiber structure, and a membrane support fiber structure. It becomes a suitable fiber structure. The pore distribution such as the average pore size, the maximum pore size, the minimum pore size, and the maximum pore size is measured by the method described in Examples.

The fiber structure in the form of the present invention preferably has a puncture strength of 6N or more, more preferably 8N or more, particularly preferably 10N or more, and most preferably 12N or more. When the puncture strength of the fiber structure is large, breakage or tear due to contact with the foreign matter and penetration of the foreign matter are difficult to occur. When a fiber structure with high piercing strength is used as a separator material, a short circuit (short) caused by foreign matter, such as metal burrs, or needle-like crystals (dendrites) that occur when secondary batteries are used repeatedly ) Is less likely to occur. In addition, if a fiber structure with high puncture strength is used as a support for various filtration media for filtering liquids and gases, and various filtration membranes such as RO membranes and NF membranes, it may be damaged by foreign substances during use, or the pressure during filtration It is preferable that the filter medium and the filter membrane are prevented from being damaged. The upper limit of the puncture strength of the fiber structure in the form of the present invention is not particularly limited, but is preferably 30 N or less, more preferably 27 N or less, considering the productivity and handleability of the fiber structure, 25 N It is particularly preferred that
The puncture strength is measured by the method described in the examples.

In the fiber structure in the form of the present invention, the puncture strength depends on the basis weight of the fiber structure. That is, the fiber structure having a larger basis weight tends to have higher puncture strength. The fiber structure in the form of the present invention includes split-type composite fibers that can be easily divided, and preferably includes ultrafine fibers having a core-sheath cross-sectional structure, so that the resulting fiber structure has a small basis weight. Products with high puncture strength are easily obtained. The fiber structure in the form of the present invention preferably has a puncture strength (N) per unit basis weight (g / m ² ) of 0.15 N or more, more preferably 0.2 N or more, and 0.25 N or more. It is particularly preferable if it is, and it is most preferable if it is 0.3 N or more. By increasing the puncture strength per unit basis weight, even a low-weight fiber structure is preferable because it is less likely to be broken or torn during use. The upper limit of the puncture strength (N) per unit basis weight (g / m ² ) of the fiber structure in the form of the present invention is not particularly limited, but is 0.8 N or less in consideration of the productivity and handleability of the fiber structure. Preferably, it is 0.7N or less, more preferably 0.65N or less.
Unit basis weight (g / m ²⁾ per puncture strength (N) is dividing the puncture strength was measured by the method described in Example (N), in basis weight of the sample used for the measurement (g / m ²⁾ Is required.

The split type composite fiber of the present invention has excellent splitting properties as described above, and can produce a fiber structure such as a dense and well-woven nonwoven fabric. The fiber structure containing the split composite fiber of the present invention includes, for example, various secondary batteries such as lithium ion batteries and nickel metal hydride batteries, separators used for various power storage devices such as various capacitors and various capacitors, liquids and gases, etc. Filtration materials, reverse osmosis membranes (RO membranes), nanofiltration membranes (NF membranes), ultrafiltration membranes (UF membranes), which constitute various filters such as cartridge filters and laminated filters that capture and / or remove foreign substances from fluids, Used as a support for various filtration membranes such as microfiltration membranes (MF membranes), fiber structures for various membrane supports, various wiping sheets such as interpersonal and / or objective wipers, and cosmetic-impregnated skin coatings such as face masks Sheet, infant paper diaper, nursing paper diaper, surface sheet constituting a absorbent article such as sanitary napkin, second sheet, and the like It is useful as an absorbent article sheet such as Kkushito.

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 component used in order to manufacture the nonwoven fabric of an Example and a comparative example is shown below.
<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 / 10 min) = 30 SA03 (product name)
PP2: After spinning, Mn = 5.3 × 10 ⁴ , After spinning Mw = 2.8 × 10 ⁵ , After spinning Mz = 8.3 × 10 ⁵ , After spinning Q value = 5.21, MFR (g / 10 min) = 30 Made by S105HG (trade name)
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 / 10 min) = 9 SA01A (product name)
PP4: After spinning Mn = 4.3 × 10 ⁴ , after spinning Mw = 2.9 × 10 ⁵ , after spinning Mz = 10.6 × 10 ⁵ , after spinning Q-value = 6.68, MFR (g / 10 min) = 10 Prime Polymer Co., Ltd. CJ700 (product name)

<Second component: Polyethylene (PE)>
PE1: MFR (g / 10min) = 20 HE490 (trade name) manufactured by Nippon Polyethylene Corporation
PE2: MFR (g / 10 min) = 10 HE481 (trade name) manufactured by Japan Polyethylene Corporation

<Measurement of number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), Q value>
The number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), and Q value (Mw / Mn) ratio of Mw and Mn of polypropylene resin were measured by gel permeation chromatographic analysis (GPC). . For the measurement, a gel permeation chromatograph apparatus (PL-220 manufactured by Polymer Laboratories, high temperature GPC apparatus) equipped with a differential refractive index detector RI as a detector was used.

Weigh 5 mg of a sample containing polypropylene resin, and weigh 5 mL of 1,2,4-trichlorobenzene (TCB) containing 0.1% of butylhydroxytoluene (BHT) as a stabilizer and antioxidant. In addition, the polypropylene resin was dissolved in the solvent by stirring for 30 minutes while heating from 160 ° C to 170 ° C. Next, in order to remove foreign matters such as an undissolved sample from the solution in which the sample was dissolved, this solution was filtered with a metal filter to obtain a measurement sample solution. The obtained sample solution for measurement was injected into the gel permeation chromatograph apparatus under the conditions of a flow rate of 1.0 mL / min and an injection amount of 0.2 mL (200 μL), and a number average molecular weight (Mn) and a weight average molecular weight. (Mw), z average molecular weight (Mz) was measured. In the measurement, TCB containing 0.1% BHT was used as a measurement solvent, one Shodex HT-G and two Showa Denko HT-806M were used as columns, and the temperature of the column thermostat was 145. Measured as ° C.

<Measurement of melt flow rate (MFR)>
The melt flow rate of the polypropylene resin was measured at 230 ° C. and a load load of 21.18 N according to JIS K 7210. The melt flow rate of the polyethylene resin was measured according to JIS K 7210 at 190 ° C. and a load load of 21.18 N.

<Manufacture of split type composite fiber of Example 1>
The cross-sectional shape of the fiber shown in FIG. 1, PP1 of homopolypropylene resin is used as the core component of the first segment and the core-sheath type second segment, and PE1 of high-density polyethylene is used as the sheath component of the core-sheath type second segment. Was used to produce the split type conjugate fiber of Example 1 having a split number of 16.

The production of the split type composite fiber of Example 1 was performed under the following spinning conditions and stretching conditions. Using a split type composite nozzle that has 205 nozzle holes and the cross-sectional structure of the extruded molten resin is the cross section shown in FIG. 1, homopolypropylene resin (PP1) and high-density polyethylene (PE1) are put into separate extruders. Fully melted. The discharge rate of the melted homopolypropylene resin and high-density polyethylene resin is such that the volume ratio of PP1 / PE1 = 5/5 (volume ratio of the first segment / second segment = 2.5 / 7.5) By extruding from each extruder so that the spinning temperature is 290 ° C., the discharge amount per nozzle hole is 0.51 g / min, and the molten resin is drawn under the conditions of a take-up speed of 840 m / min and cooled, the fineness A 6.0 dtex spun filament was obtained. Next, the spinning filament was dry-drawn at a draw ratio of 4.2 times at 105 ° C. to obtain a drawn filament having a fineness of 1.60 dtex.

In order to evaluate the drawability of the spinning filament, the maximum draw ratio (Vmax) was measured by the following method. First, the obtained spinning filament is set in a stretching apparatus that matches a predetermined stretching temperature. At this time, the feeding speed (V ₁ ) of the roll for feeding the spinning filament is set to 5 m / second, and the winding speed (V ₂ ) of the metal roll on the winding side is gradually increased from 5 m / second. The winding speed of the metal roll on the winding side when the spinning filament breaks is the maximum drawing speed, and the ratio between the maximum drawing speed and the feed speed of the roll that feeds the unstretched fiber bundle (V ₂ / V ₁ ). And the obtained speed ratio is taken as the maximum draw ratio (Vmax). A maximum draw ratio of 3 or more is preferable because a stretchable treatment can be performed at a high draw ratio, and a split-type composite fiber having a small fineness can be easily obtained. Even if the maximum draw ratio is less than 3, it does not affect the drawing treatment, but since the maximum draw ratio is low, there is a possibility that it is difficult to obtain a split type composite fiber having a desired fineness.

When the maximum draw ratio of the spun filament of Example 1 was measured by the above method, the maximum draw ratio (Vmax) was 4.4 times. Therefore, the draw ratio was 0.95 times the maximum draw ratio (draw ratio / Vmax = 0.95). After the fiber treatment agent was applied to the drawn filament, it was cut into a fiber length of 3 mm to obtain the split type composite fiber of Example 1 in the form of a short fiber.
Table 1 shows the production, configuration, fineness, and the like of the split-type composite fiber of Example 1.

<Manufacture of split type composite fibers of Examples 2 to 8 and Comparative Examples 1 to 4>
The division of Examples 2 to 8 and Comparative Examples 1 to 4 was carried out in the same manner as the production method of 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. Mold composite fibers were obtained in the form of short fibers with a fiber length of 3 mm.
Tables 1 to 3 show the production, configuration, fineness, and the like of the split type composite fibers of Examples 2 to 8 and Comparative Examples 1 to 4.

<Manufacture of split type composite fiber of Comparative Example 5>
The split composite fiber of Comparative Example 5 was produced under the following spinning conditions and stretching conditions. Using a split type composite nozzle having 300 nozzle holes and having a fiber cross section shown in FIG. 3 that is a hollow 16 split type (both the first segment and the second segment are a single type), a homopolypropylene resin ( PP2) and high-density polyethylene (PE1) were put into separate extruders and sufficiently melted. The melted homopolypropylene resin and high-density polyethylene resin have a discharge rate of PP2 / PE1 volume ratio = 5/5 (first segment / second segment volume ratio = 5/5). Extruding from each extruder, spinning temperature (spinning head temperature) 290 ° C, discharge rate per nozzle hole 0.51g / min, taking molten resin under conditions of take-up speed 840m / min and cooling Then, PP2 and PE1 were melt-extruded to obtain a spun filament having a fineness of 7.1 dtex. Next, after using a hot water tank filled with 90 ° C. hot water and spinning the filament at 90 ° C. at a draw ratio of 5.0 times, the draw ratio is 1.0 times in a 90 ° C. hot water tank. Then, heat setting was performed to obtain a drawn filament having a fineness of 1.70 dtex. After applying the same fiber treating agent as that of the split type composite fiber of Example 1 to the drawn filament, it was cut into a fiber length of 3 mm to obtain the split type composite fiber of Comparative Example 5 in the form of short fibers. In addition, the spinning filament of Comparative Example 5 has a maximum draw ratio of 5.9 times.

<Manufacture of split type composite fiber of Comparative Example 6>
The spinning filament obtained by the same method as in Comparative Example 5 was subjected to a dry stretching process using a heated metal roll to produce a split composite fiber. That is, a spun filament was produced by the same method as in Comparative Example 5, and the obtained spun filament was dry-stretched between metal rolls heated to 105 ° C. so that the stretch ratio was 4.95 times. A 51 dtex drawn filament was obtained. After applying the same fiber treating agent as the split type composite fiber of Example 1 to the drawn filament, it was cut into a fiber length of 3 mm to obtain the split type composite fiber of Comparative Example 6 in the form of a short fiber. The spun filament of Comparative Example 6 has a maximum draw ratio of 5.2 times.

<Measurement of short fiber strength and elongation>
In accordance with JIS L 1015 (2010), using a tensile tester, the holding distance of the sample was 20 mm, the load value when the fiber was cut was the single fiber strength, and the elongation when cut was the elongation.

<Measurement of melting peak shape of polypropylene resin by DSC, second melting peak area / first melting peak area, elongation of second melting peak>
About the obtained split type composite fibers of Examples and Comparative Examples, DSC is performed, and the determination regarding the shape of the melting peak of the polypropylene resin, the second melting peak area, the identification of the first melting peak area, and the second melting are performed according to the above definition. The peak elongation was measured. The ratio of the second melting peak area to the first melting peak area is determined by enlarging the DSC curve to be obtained on paper and printing a boundary line such as a baseline on the melting peak portion of the polypropylene resin, and then along the boundary line. A portion corresponding to the first peak area and a portion corresponding to the second peak area were cut out, the mass of the cut out portion was measured, and the ratio was determined. The differential scanning calorimetry (DSC) of the split-type composite fiber is based on JIS K 7121 (1987), a plastic transition temperature measurement method, and a differential scanning calorimeter (trade name “EXSTAR6000 / DSC6200” manufactured by Seiko Instruments Inc.). ).

<Manufacture of the nonwoven fabric of Example 1>
A fiber web was produced by the wet papermaking method using the split type composite fiber of Example 1. Specifically, the slurry is prepared so that the fiber concentration becomes 0.01% by mass, and stirred with a pulper at a rotation speed of 2000 rpm for 5 minutes to dissociate the fibers and split the split-type composite fibers. Thus, the ultrafine fiber 1 of the first segment and the ultrafine fiber 2 of the second segment were formed. Wet paper making was carried out using a circular net type wet paper machine to obtain a web having a basis weight of 80 g / m ² . Using a cylinder dryer heated to 140 ° C. by transporting the web with a support for transportation, the web is heated for 45 seconds to dry the web, and at the same time, the fibers are separated from each other by the sheath component of the ultrafine fibers 2. The nonwoven fabric of Example 1 was obtained by bonding.
The nonwoven fabrics of Examples 2 to 8 and Comparative Examples 1 to 6 were used in the same manner as described in Example 1 except that the split type composite fibers of Examples 2 to 8 and Comparative Examples 1 to 6 were used. Got.

<Measurement of split ratio>
Before the heat treatment, the web was packed into the cylinder as densely as possible so that the cut surface in the thickness direction of the wet papermaking web was exposed. The non-woven fabric packed in a cylinder was magnified 300 times with an electron microscope, and a region of 0.4 mm × 0.3 mm was photographed. The cross sections of the fibers appearing in the photograph taken were confirmed one by one, and the number of ultrafine fibers 1 and the number of ultrafine fibers 2 were counted. For undivided fibers, the total number of the first and second segments is measured (for example, the first segment of fibers that are not divided at all when having the fiber cross section shown in FIGS. 1 to 3). And the total number of the second segment is 16, the total number of the first segment and the second segment of the fiber divided in half is 8, and the total number of the first segment and the second segment is Counted as the number of each undivided fiber. Therefore, for example, when there is one undivided fiber and the total number of the first segment and the second segment is 16, the fiber is counted as 16. From the count result, the division ratio was calculated based on the following formula.
Division ratio (%) = [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 division ratios are shown in Tables 1 to 3.

<Breathability>
The air permeability of the nonwoven fabric was evaluated by measuring the air permeability. The air permeability was measured according to JIS L 1096 (2010) 8.26A (Fragile method).

The nonwoven fabrics of Examples 1 to 8 are all obtained using the split-type composite fibers of Examples 1 to 8, and the Mw / Mn of the polypropylene resin is 6 or less, and the melting peak of the polypropylene resin indicated by the DSC curve Since the shape is a double peak shape, at least one of the problems such as productivity and splitability during fiber production is improved.

In the nonwoven fabrics of Examples 1 to 6 and 8, the (A) second melting peak area / first melting peak area is 0.85 or more and 3.5 or less; and (B) the second peak elongation is 0. Since it satisfies at least one of 6 or more, it is further excellent in both splitting property and air permeability.

On the other hand, in the nonwoven fabrics of Comparative Examples 1 to 4, the Mw / Mn of the polypropylene resin is not 6 or less, or the shape of the melting peak of the polypropylene resin indicated by the DSC curve is not the double peak shape. None of the problems such as separability improve. Further, the split composite fibers of Comparative Example 5 and Comparative Example 6 use the same polypropylene resin and polyethylene resin as the split composite fiber of Example 5, but the split ratio of the obtained split composite fibers was low. . This is because, in the fiber cross section, the second segment is not a core-sheath cross section, so that the cooling process during melt spinning, the crystallization state of the thermoplastic resin generated during the cooling process, the fiber interior during melt spinning and stretching It is estimated that because the strain state generated in the resin is different, the resin segments are firmly adhered to each other, or when the force is applied to the split composite fiber, the effect of absorbing the impact is increased, so that it is difficult to break. Is done.

<Evaluation of fiber structure>
[Example 9]
Various fiber structures of the split-type composite fiber of the present invention, especially liquid treatment materials such as various battery separator applications requiring mechanical strength and denseness, filter media, and various membrane supports (for example, RO membrane supports). In order to examine the adaptability to use, a heat-bonding nonwoven fabric using the split type conjugate fiber of the present invention was produced.

Using the split type composite fiber of Example 5, a slurry was prepared at the same slurry concentration and rotation speed as the above production conditions, and the split type composite fiber was split to obtain the first segment of ultrafine fibers 1 and Two segments of ultrafine fibers 2 were formed. Using a circular net type wet paper machine, wet paper was made to obtain a web having a basis weight of about 40 g / m ² . Using a cylinder dryer heated to 140 ° C. by transporting the web with a support for transportation, the web is heated for 45 seconds to dry the web, and at the same time, the fibers are separated from each other by the sheath component of the ultrafine fibers 2. It was made to adhere and it was set as the heat bonding nonwoven fabric.

Thickness processing using a heat roll was performed on the obtained heat-bonded nonwoven fabric under conditions of a temperature of 80 ° C. and a linear pressure of about 760 N / cm, and the thickness of the heat-bonded nonwoven fabric was adjusted to about 120 μm. A heat bonded nonwoven fabric was obtained.

The obtained heat bonded nonwoven fabric of Example 9 was evaluated by the following method.

[thickness]
Using a micrometer (Micrometer MDC-25MJ manufactured by Mitutoyo Corporation), the thickness of the obtained heat-bonded nonwoven fabric is 175 kPa so that the load is 175 kPa at 10 different points of each of the three samples according to JIS B 7502. Then, the thickness was measured, and the average value of a total of 30 locations was obtained to obtain the thickness of the sample.

[Pore distribution]
The pore size distribution of the obtained heat-bonded nonwoven fabric of Example 9 was measured according to ASTM F 316-86 (bubble point method), and the average pore size, maximum pore size, maximum pore size and minimum pore size of the heat-bonded nonwoven fabric were measured.

[Tear strength]
JIS L 1085 5.5. According to the A-1 method (single tongue method), measurement was performed using a tensile testing machine (A & D Co., Ltd., Tensilon (registered trademark) UCT-1 (trade name)). As the test piece, a rectangular piece cut into a width of 5 cm and a length of 15 cm was cut in the center of the short side with a cut of 8 cm perpendicular to the side to create two tongues. The maximum load when tearing at / min was measured.

[Tensile strength]
In accordance with JIS L 1096 8.12.1 A method (strip method), using a constant speed tension type tensile tester, a sample piece having a width of 5 cm and a length of 30 cm is gripped at a distance of 10 cm and a tensile speed of 30 ± 2 cm / The sample was subjected to a tensile test under the condition of minutes, and the load value when the load reached the maximum was measured to obtain the tensile strength. The tensile test was implemented about the vertical direction (machine direction) of the nonwoven fabric.

[Puncture strength]
The puncture strength refers to the stress (maximum penetration force F) at the penetration point by needle penetration force measurement, and was measured by the following method. First, a nonwoven fabric cut to 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 (diameter 11 mm) of a handy compression tester (KES-G5 manufactured by Kato Tech Co., Ltd.). Next, a pressing plate made of an aluminum plate having a length of 46 mm, a width of 86 mm, and a thickness of 7 mm and having a hole of 11 mm in diameter at the center is placed on the sample placed on the support. It was placed so as to coincide with the cylindrical through hole. Next, the load when a needle of a conical shape with a height of 18.7 mm, a bottom diameter of 2.2 mm, and a tip shape of 1 mm is vertically stabbed into the center of the holding plate at a speed of 2 mm / second, and the above The sample is pushed by the conical needle and the length of the deformation is measured. Of the measured load, the stress at the penetration point where the conical needle penetrates the sample is the maximum penetration force F (N), that is, the puncture strength. It was. The puncture strength was obtained by taking four samples from one non-woven fabric (battery separator), measuring each sample at five different locations, and taking the average of the values measured at a total of 20 locations. The puncture strength (N) per unit basis weight (g / m ² ) was determined by dividing this value by the basis weight of the sample.

In addition to the use of split-type conjugate fibers, the nonwoven fabric of Example 9 constitutes the resulting non-woven fabric because the split-type conjugate fibers used were sufficiently split by the stirring treatment performed when preparing the slurry before papermaking. Most of the fibers became ultrafine fibers, and it was thought that the heat-bonding and thickness processing resulted in a dense nonwoven fabric.

From the measurement results of the pore distribution, the nonwoven fabric of Example 9 has all of the measured average pore diameter, minimum pore diameter, maximum pore diameter, and maximum pore diameter being small. It is considered that not only the void portion formed inside the nonwoven fabric was reduced, but also the pores formed in the nonwoven fabric were small and uniform.

From the mechanical strength (tear strength and tensile strength) of the obtained nonwoven fabric, the nonwoven fabric of Example 9 is thin, but the tear strength and tensile strength are high. This is because the nonwoven fabric of Example 9 is a nonwoven fabric obtained from a split type composite fiber in which one resin segment has a core-sheath cross section. This is thought to be because the ultrafine fibers were bonded to each other by heat, and the resulting fiber web was heat-bonded to each other by heat treatment.

This specification includes the following forms.
1.
A split-type composite fiber including a first segment and a second segment;
The first segment is a resin segment composed of a first component,
The second segment is a core-sheath resin segment whose cross-sectional structure has 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,
The second component is a resin component containing 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,
After spinning, JIS K 7121 (1987) Split type composite in which the shape of the melting peak of the polypropylene resin indicated by the DSC curve obtained by differential scanning calorimetry (DSC) based on the plastic transition temperature measurement method is a double peak shape fiber.
2.
2. The split type composite fiber according to 1 above, which satisfies at least one of the following (A) and (B).
(A): The melting peak of the double peak shape of the polypropylene resin indicated by the DSC curve is divided into a first melting peak and a second melting peak,
When the area of each region is 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 / first melting peak area) is 0.85 or more and 3.5 or less; and (B): the differential scanning calorimetry (DSC). ), The melting peak of the double peak-shaped polypropylene resin is divided into a first melting peak and a second melting peak,
The value of the DSC curve when the second melting peak temperature is reached is W ₂ (mW),
The value of the DSC curve that minimizes the absolute value of the first derivative of the DSC curve between the first melting peak and the second melting peak is W ₃ (mW),
Elongation of second melting peak = (Absolute value of W ₂ ) − (Absolute value of W ₃ )
The elongation of the second peak defined by is 0.6 or more.
3.
3. The split type composite fiber according to 1 or 2 above, wherein the split type composite 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 ratio of the first component to the second component (first component / second component) contained in the split composite fiber is any one of the above items 1 to 3, wherein the ratio is 8/2 to 3/7 (volume ratio) The split type composite fiber as described.
5).
A fiber structure containing 10% by mass or more of the split-type conjugate fiber according to any one of 1 to 4 above.
6).
6. The fiber structure according to 5 above, wherein the air permeability measured according to JIS L 1096 is 8 cm ³ / cm ² · sec or more and 22 cm ³ / cm ² · sec or less using a Frazier type tester.
7).
The separator material containing the fiber structure of said 5 or 6.
8).
A filtration material comprising the fiber structure according to 5 or 6 above.
9.
In a fiber cross section, a split-type conjugate fiber including a first segment and a second segment,
The first segment is a resin segment composed of a first component,
The second segment is a melt spinning machine equipped with a split type composite nozzle that is a split type composite fiber that is a core-sheath type resin segment whose cross-sectional structure is the core component of the first component and the sheath component of the second component. To prepare;
Using a resin component containing 50% by mass or more of a polypropylene resin having an Mw / Mn of 6 or less as a first component and a resin component containing 50% by mass or more of a polyethylene resin as a second component, melt spinning with a melt spinning machine Producing spinning filaments;
5. The division according to any one of 1 to 4 above, comprising drawing a spun filament at a drawing temperature of 60 ° C. to 125 ° C. and a draw ratio of 1.1 times or more to obtain a split type composite fiber A method for producing a mold composite fiber.
10.
10. The production method according to 9 above, comprising drawing the spun filament at a draw ratio of 3 to 8 times.
11.
11. The production method according to 9 or 10 above, comprising wet-drawing a spun filament at a drawing temperature of 60 ° C. or higher and 95 ° C. or lower.
12
11. The production method according to 9 or 10 above, comprising dry-drawing the spun filament at a drawing temperature of 80 ° C or higher and 125 ° C or lower.
13.
13. The production method according to any one of 9 to 12, comprising drawing the spun filament at a draw ratio of 0.7 to 0.98 times the maximum draw ratio.
14
14. A split type composite fiber produced by the production method according to any one of 9 to 13 above.
15.
15. A fiber structure containing 10% by mass or more of the split type composite fiber described in 14 above.

<Related applications>
This application claims priority based on Article 4 of the Paris Convention, which is based on application number 2017-72525 filed in Japan on March 31, 2017. The contents of this basic application are incorporated herein by reference.

The split composite fiber of the present invention has high productivity and excellent splitability. Furthermore, by setting one resin segment as a core-sheath type resin segment, it becomes a split type composite fiber that can bond ultrafine fibers by heating. The split composite fiber of the present invention is used in applications where a dense fiber structure and a fiber structure having a small fiber diameter are required, for example, various secondary batteries such as lithium ion batteries and nickel metal hydride batteries, various capacitors, and various capacitors. Fiber structures for separators used in various power storage devices such as, fiber structures for filtration layers constituting various filters such as cartridge filters and laminated filters that capture and / or remove foreign substances from fluids such as liquids and gases, Fibers for various membrane supports used as supports for various filtration membranes such as reverse osmosis membranes (RO membranes), nanofiltration membranes (NF membranes), ultrafiltration membranes (UF membranes), and microfiltration membranes (MF membranes) Structures, fiber structures for various wiping sheets such as interpersonal and / or objective wipers, fiber structures for cosmetic-impregnated skin-covering sheets such as face masks, To be used for absorbent fabrics such as infant paper diapers, nursing care diapers, sanitary napkins, etc. Can do.

1: first segment, 2: second segment, 4: core component, 6: sheath component, 8: hollow,
10: Split type composite fiber, 14: Core component, 16: Sheath component, 20: Split type composite fiber,
a: melting peak of polypropylene resin, a ₁ : first melting peak of polypropylene resin a ₂ : second melting peak of polypropylene resin, a ₃ : valley in melting peak of polypropylene resin T ₁ : first melting peak temperature of polypropylene resin T ₂ : second melting peak temperature of the polypropylene resin W ₂ : heat flux at the second melting peak of the polypropylene resin, W ₃ : heat flux at the valley existing between the first melting peak and the second melting peak of the polypropylene resin S ₁ : Area of the first endothermic peak of the polypropylene resin, S ₂ : Area of the second endothermic peak of the polypropylene resin BL _LT : Base line on the low temperature side in the DSC curve, BL _HT : Base line on the high temperature side in the DSC curve, BL _E: in the DSC curve, the baseline on the low temperature side, the From the end portion of the hot side, and extended toward the low temperature side end portion of the high temperature side base line linear

Claims

A split-type composite fiber including a first segment and a second segment;
The first segment is a resin segment composed of a first component,
The second segment is a core-sheath resin segment whose cross-sectional structure has 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,
The second component is a resin component containing 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,
After spinning, JIS K 7121 (1987) Split type composite in which the shape of the melting peak of the polypropylene resin indicated by the DSC curve obtained by differential scanning calorimetry (DSC) based on the plastic transition temperature measurement method is a double peak shape fiber.
The split-type conjugate fiber according to claim 1, which satisfies at least one of the following (A) and (B).
(A): The melting peak of the double peak shape of the polypropylene resin indicated by the DSC curve is divided into a first melting peak and a second melting peak,
When the area of each region is 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 / first melting peak area) is 0.85 or more and 3.5 or less; and (B): the differential scanning calorimetry (DSC). ), The melting peak of the double peak-shaped polypropylene resin is divided into a first melting peak and a second melting peak,
The value of the DSC curve when the second melting peak temperature is reached is W 2 (mW),
The value of the DSC curve that minimizes the absolute value of the first derivative of the DSC curve between the first melting peak and the second melting peak is W 3 (mW),
Elongation of second melting peak = (Absolute value of W 2 ) − (Absolute value of W 3 )
The elongation of the second peak defined by is 0.6 or more.
The split composite fiber according to claim 1 or 2, wherein the split composite 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.
The ratio of the first component and the second component (first component / second component) contained in the split-type conjugate fiber is 8/2 to 3/7 (volume ratio). Split type composite fiber as described in 1.
A fiber structure comprising 10% by mass or more of the split-type conjugate fiber according to any one of claims 1 to 4.
6. The fiber structure according to claim 5, wherein the air permeability measured in accordance with JIS L 1096 is 8 cm 3 / cm 2 · second or more and 22 cm 3 / cm 2 · second or less using a Frazier type tester.
Separator material containing the fiber structure according to claim 5 or 6.
A filtration material comprising the fiber structure according to claim 5 or 6.
In a fiber cross section, a split-type conjugate fiber including a first segment and a second segment,
The first segment is a resin segment composed of a first component,
The second segment is a melt spinning machine equipped with a split type composite nozzle that is a split type composite fiber that is a core-sheath type resin segment whose cross-sectional structure is the core component of the first component and the sheath component of the second component. To prepare;
Using a resin component containing 50% by mass or more of a polypropylene resin having an Mw / Mn of 6 or less as a first component and a resin component containing 50% by mass or more of a polyethylene resin as a second component, melt spinning with a melt spinning machine Producing spinning filaments;
Including stretching a spinning filament at a stretching temperature of 60 ° C. or more and 125 ° C. or less and a draw ratio of 1.1 or more to obtain a split-type composite fiber;
The manufacturing method of the split type composite fiber of Claim 1.
The production method according to claim 9, comprising drawing the spun filament at a draw ratio of 3 to 8 times.
The production method according to claim 9 or 10, comprising wet-stretching the spinning filament at a stretching temperature of 60 ° C or higher and 95 ° C or lower.
The production method according to claim 9 or 10, comprising dry-drawing the spun filament at a drawing temperature of from 80 ° C to 125 ° C.
The production method according to any one of claims 9 to 12, comprising drawing the spun filament at a draw ratio of 0.7 to 0.98 times the maximum draw ratio.