JP5812607B2 - Split type composite fiber and fiber assembly using the same - Google Patents

Description

  The present invention relates to a polyolefin-based split composite fiber and a fiber assembly including the same. In detail, it is related with the split type composite fiber containing the segment containing a polypropylene resin, and the segment containing a polyolefin resin, and a fiber assembly containing the same.

  Originally, split type composite fibers in which homologous resins such as polyolefin resins are combined with each other are highly compatible with each other, so that the resin components are easily bonded to each other at the interface. Therefore, splitting composite fibers combining incompatible polymers, such as splitting composite fibers combining polyester resins and polyolefin resins, and splitting composite fibers combining polyester resins and polyamide resins, are split. Inferior. In order to solve this problem, various attempts have been made to improve the division property. For example, the present applicant has proposed a polyolefin-based split composite fiber made of polyolefin-based resins having Rockwell hardness of 60 or more in Patent Document 1. Patent Document 2 discloses a polyolefin-based split type composite fiber in which at least one component is mixed with a hydrophilic component. Patent Document 3 includes a different polyolefin-based resin. A polyolefin-based split composite fiber in which a component containing a salt and a component not containing a (meth) acrylic acid metal salt are adjacent to each other in the fiber cross section is disclosed. In Patent Document 4, the hollowness is 5 to 40%, and the ratio of the average length W of the one-component fiber outer peripheral arc to the average thickness L from the hollow portion to the fiber outer peripheral portion is 0.25 to 2. And a polyolefin-based split type composite fiber having a two-component melt flow rate ratio (MFR ratio) is disclosed. Patent Document 5 discloses a polyolefin-based split composite fiber in which the cross section of the composite fiber is made into a specific flat shape by external stress.

Japanese Examined Patent Publication No. 6-63129 JP-A-8-311717 JP 2001-49529 A JP 2000-328367 A JP 2001-32138 A JP 2001-192936 A JP 2002-220740 A

  In order to solve the above-mentioned conventional problems, the present invention provides a split type composite fiber excellent in splittability, a fiber assembly including the split type composite fiber, and a method for manufacturing the same.

  The present inventor manufactured split type composite fibers using a polypropylene resin having a Q value of 5 or more and a polyolefin resin as described in Patent Document 6 and Patent Document 7, and confirmed the splitting property. . And the combination which can acquire the further outstanding splitting property, especially the polypropylene resin were examined.

  The present inventor has found that when a specific resin component is used as the polypropylene resin among the segments constituting the split-type conjugate fiber, excellent splitting properties can be obtained, and the present invention has been completed.

  The split-type conjugate fiber of the present invention is a split-type conjugate fiber containing at least one segment A containing a polypropylene resin, and the segment A has a z-average molecular weight Mz of 1,000,000 or more, And the polypropylene resin whose weight average molecular weight Mw is 800,000 or less is included as a main component, It is characterized by the above-mentioned.

  The present invention is also characterized by containing ultrafine fibers formed by splitting the split type composite fiber at a ratio of 5 mass% or more.

  The present invention can provide a split type composite fiber that is excellent in chemical resistance and excellent in splitting properties.

It is sectional drawing which shows typically an example of the fiber cross section of the split type composite fiber of this invention. It is sectional drawing which shows typically another example of the fiber cross section of the split type composite fiber of this invention. It is sectional drawing which shows typically another example of the fiber cross section of the split type composite fiber of this invention.

  The split type composite fiber of the present invention includes a segment A. The split type composite fiber of the present invention will be described.

(Segment A)
The segment A contains as a main component a polypropylene resin (hereinafter also referred to as a specific polypropylene resin) having a z-average molecular weight Mz of 1,000,000 or more and a weight-average molecular weight Mw of 800,000 or less. Here, the “main component” means that 50% by mass or more is contained with respect to the entire segment A, and the same applies to the following.

  The segment A preferably contains 80% by mass or more of the above-described specific polypropylene resin, and particularly preferably substantially consists of the specific polypropylene resin. Here, the term “substantially” means that a specific polypropylene resin is usually used because a resin provided as a product contains additives such as a stabilizer and / or various additives are added during fiber production. It is used in consideration of the fact that it is not possible to obtain a fiber having a form containing no other components at all. Usually, the content of the additive is a maximum of 15% by mass.

  The specific polypropylene resin is not particularly limited as long as it is a polypropylene resin, and for example, a homopolymer, a random copolymer, a block copolymer, or a mixture thereof can be used. Examples of the random copolymer and block copolymer include a copolymer of propylene and 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, but examples thereof include 1-butene, 1-pentene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, and 4,4-dimethyl. Examples include -1-pentene, 1-decene, 1-dodecene, 1-tetradecene, and 1-octadecene. The propylene content in the copolymer is preferably 50% by mass or more. Among the polypropylene resins, a propylene homopolymer is particularly preferable in consideration of processability and economy (manufacturing cost). These may be used alone or in combination of two or more.

  The specific propylene resin has a z-average molecular weight Mz of 1,000,000 or more and a weight-average molecular weight Mw of 800,000 or less. Preferably, the z average molecular weight Mz is 1,000,000 to 5,000,000, and the weight average molecular weight Mw is 200,000 to 800,000. A polypropylene resin having a z-average molecular weight of 1,000,000 or more imparts rigidity to the segment A due to the relatively high molecular weight. And the segment A excellent in rigidity hardly absorbs an impact caused by an external force, and the applied external force acts efficiently as a force for splitting the segment A and other segments, so that the splitting property is improved. However, on the other hand, a resin containing a relatively large amount of high molecular weight has low fluidity and may be difficult to spin. With such a configuration, it is possible to obtain excellent resolution due to the z average molecular weight Mz being 1,000,000 or more, and the weight average molecular weight Mw being 800,000 or less. Thus, the fluidity is good and the fiber can be spun without breakage.

  Moreover, since the split-type composite fiber containing a polypropylene resin having a z-average molecular weight Mz of 1,000,000 or more contains a high molecular weight polypropylene molecule, it tends to be crystallized in the spinning process. The crystallinity becomes high at a stage. And a fiber with few amorphous area | regions can be obtained by performing an extending | stretching process further. Fibers with high crystallinity and few amorphous regions were added to the joint surface due to the fact that there are few amorphous regions that absorb and attenuate the applied impact when performing a split treatment by physical impact. Since the force is transmitted to each segment without lowering, the splitting property is improved.

  The specific polypropylene resin preferably has a number average molecular weight Mn of 10,000 to 80,000, and more preferably a number average molecular weight Mn of 20,000 to 50,000. When the number average molecular weight Mn is in the range of 10,000 to 80,000, the amorphous region tends to be further reduced, and the action of absorbing and attenuating the impact when an external force is applied to the resin can be suppressed. A repulsive force is likely to be generated at the joint surface of the split-type conjugate fiber, and a split-type conjugate fiber excellent in easy splitting can be obtained.

  The specific polypropylene resin preferably has a weight average molecular weight Mw of 200,000 to 800,000, and more preferably a weight average molecular weight Mw of 300,000 to 500,000. When the weight average molecular weight Mw is in the range of 200,000 to 800,000, the fluidity of the resin becomes high, and it becomes a split type composite fiber that is hard to break and is easy to spin.

  The specific polypropylene resin preferably has a z-average molecular weight Mz of 1,000,000 to 5,000,000, and more preferably a z-average molecular weight Mz of 2,000,000 to 4,000,000. When the z-average molecular weight Mz is in the range of 1,000,000 to 5,000,000, it is easy to crystallize at the time of stretching due to the high rigidity and the high molecular weight easily crystallizing component, and the splitting property is improved. Excellent fiber. In addition, a polymer having a large molecular weight is excellent in rigidity, and it is possible to obtain split type composite fibers and / or ultrafine fibers excellent in rigidity. A fiber assembly using such fibers is excellent in puncture strength.

  The specific polypropylene resin preferably has a Q value (hereinafter simply referred to as Q value) of 8 or more, more preferably 8 to 15, which is a ratio between the weight average molecular weight Mw and the number average molecular weight Mn. More preferably, it is 9-12. When the specific polypropylene resin has a Q value of 8 or more, a nonwoven fabric having excellent puncture strength can be obtained when processed into a nonwoven fabric (particularly a wet nonwoven fabric). Moreover, the composite split type fiber using such a specific polypropylene resin has more excellent drawability and splitting property.

  Among general polypropylene resins, a polypropylene resin having a large Q value has a large molecular weight distribution and a large Q value because many high molecular weight polypropylene molecules remain inside the resin. On the other hand, a polypropylene resin having a small Q value cuts a high molecular weight molecular chain generated by polymerization and aligns the length of the molecular chain, so that the remaining amount of high molecular weight molecules is reduced and the molecular weight distribution width is reduced. It is getting smaller. When polypropylene resin is melt-spun, if a polypropylene resin-based resin having a small molecular weight distribution, that is, a small Q value is used, many amorphous regions (tie molecules) exist in the unstretched fiber bundle (unstretched tow). The amorphous region tends to remain even after the stretching treatment. On the other hand, when a polypropylene resin having a large molecular weight distribution in which high molecular weight polypropylene molecules remain, that is, a polypropylene resin having a large Q value, is used, the spinnability is inferior to a resin having a small Q value. However, high-molecular-weight polypropylene molecules tend to be crystallized, and the crystallinity becomes high at the stage of unstretched fiber bundles. By performing a stretching process at a high stretching ratio, the fibers have few amorphous regions.

  The specific polypropylene resin has a melt flow rate according to JIS-K-7210 (hereinafter also referred to as MFR230; measurement temperature 230 ° C., load 2.16 kgf (21.18 N)) in the range of 5 g / 10 min to 23 g / 10 min. It is preferable that it is in the range of 5 to 20 g / 10 minutes, more preferably in the range of 5 to 16 g / 10 minutes, and particularly preferably in the range of 8 to 12 g / 10 minutes. . If the MFR230 of the specific polypropylene resin is less than 5 g / 10 minutes, the stretchability of the polypropylene resin becomes extremely low, and it may not be sufficiently stretched, or there may be frequent stretching breaks in the stretching treatment. On the other hand, when the MFR230 of the specific polypropylene resin is less than 23 g / 10 minutes, a polyolefin-based split composite fiber excellent in stretchability is obtained, and the bonding interface between the specific polypropylene resin and the polyolefin resin does not adhere strongly, Splitting is easy and fibers with high splitting properties can be obtained.

  When using a polypropylene resin having a high MFR as the polypropylene resin in the polyolefin-based splitting composite fiber containing a polypropylene resin as a component, a thermoplastic resin that has a low viscosity when melted and is easier to stretch is used. As a result, the stretchability of the obtained unstretched fiber bundle is increased. However, when the MFR is high, the adhesion at the interface between the polypropylene resin component and the other polyolefin resin component tends to be strong, and the action of the high-pressure water flow and the partitioning property in the mixer process in the papermaking process are likely to deteriorate. . Therefore, in the present invention, it is desirable that the polypropylene resin has a low MFR within a range that does not adversely affect the processability, particularly the stretchability, and the MFR230 is preferably within a range of 5 g / 10 min or more and less than 23 g / 10 min. It is said.

  The specific polypropylene resin preferably has a tensile modulus measured according to JIS-K-7161 of 1700 MPa or more, more preferably 1900 MPa or more, and particularly preferably 2000 MPa or more. If the tensile modulus of the specific polypropylene resin is 1700 MPa or more, the nonwoven fabric has a further excellent puncture strength when processed into a nonwoven fabric due to excellent rigidity. In addition, even if the drawing process is performed under conditions of high temperature and high draw ratio, it is difficult to cause drawing breakage. There is a tendency that fibers or fiber aggregates that are sufficiently divided into each component are easily obtained. The upper limit of the tensile modulus of the specific polypropylene resin is not particularly limited, but the tensile modulus is preferably 3000 MPa or less, and particularly preferably 2700 MPa or less. When the tensile modulus is 3000 MPa or less, the film can be sufficiently stretched in the stretching process, and the occurrence of stretch breakage is small.

  The specific polypropylene resin preferably has a Q value of 9 or more, an MFR230 of 16 g / 10 min or less, and a tensile elastic modulus of 2000 MPa or more. When the Q value, MFR230, and tensile modulus of the specific polypropylene resin satisfy the above ranges, the split-type composite fiber comes to have high stretchability and easy splitting property, and ultrafine fibers can be easily obtained from the split-type composite fiber. Thus, a fiber aggregate having a high content of ultrafine fibers and a low content of undivided split composite fibers can be easily obtained.

  The segment A may contain other polypropylene resins in addition to the specific polypropylene resin as long as the effects of the present invention are not impaired. Other polypropylene-type resin is not specifically limited, For example, a homopolymer, a random copolymer, a block copolymer, or mixtures thereof can be used. Examples of the random copolymer and block copolymer include a copolymer of propylene and 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, but examples thereof include 1-butene, 1-pentene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, and 4,4-dimethyl. Examples include -1-pentene, 1-decene, 1-dodecene, 1-tetradecene, and 1-octadecene. The propylene content in the copolymer is preferably 50% by mass or more. Among the polypropylene resins, a propylene homopolymer is particularly preferable in consideration of processability and economy (manufacturing cost).

  In the segment A, a known splitting accelerator may be added as long as the stretchability, easy splitting property and chemical resistance of the split composite fiber of the present invention are not lost. Examples of known splitting accelerators include silicon compound-based splitting accelerators, unsaturated carboxylic acid-based splitting accelerators, and (meth) acrylic acid-based compound splitting accelerators. From the viewpoint of improvement, a (meth) acrylic acid compound splitting accelerator is preferred, and a (meth) acrylic acid metal salt is more preferred. When the (meth) acrylic acid metal salt is contained in the segment A as a splitting accelerator, the (meth) acrylic acid metal salt may be contained in an amount of 1 to 10% by mass with respect to the entire segment A.

(Segment B)
In addition to the segment A, the split-type conjugate fiber of the present invention preferably further includes a segment B containing a polyolefin-based resin. The segment B is derived from the segment B by splitting the split-type conjugate fiber. It is preferable to form the ultrafine fiber B.

  The split composite fiber preferably includes a segment B containing a polyolefin resin. The segment B more preferably contains 50 mass% or more of polyolefin resin, more preferably 80 mass% or more of polyolefin resin, and particularly preferably substantially consists of polyolefin resin. Polyolefin resins have good compatibility with polypropylene resins, and split composite fibers that combine these resins generally have low splitting properties. In the present invention, even when the combination is a polypropylene resin and a polyolefin resin, an excellent splitting property can be obtained. Moreover, since polyolefin resin is excellent in stability with respect to electrolyte, it is suitable as resin which comprises a battery separator. When the resin component constituting the segment B contains a polyolefin resin in an amount of 80% by mass or more, a battery separator that hardly deteriorates over a long period of time can be obtained even in an electrolytic solution that is an alkaline aqueous solution.

  The polyolefin resin is not particularly limited, but polyethylene, polypropylene, polybutene, polymethylpentene, ethylene vinyl alcohol copolymer, ethylene propylene copolymer, or the like may be used alone or in combination of two or more. These polyolefin resins are preferable as battery separators because of their excellent chemical resistance.

  The segment B is preferably a core-sheath type composite segment in which the polyolefin resin is a sheath component. With such a configuration, the core-sheath ultrafine composite fiber is formed by splitting the split composite fiber. Then, by melting only the polyolefin resin that is the sheath component of the core-sheath type ultrafine composite fiber, the ultrafine fibers formed by splitting the split type composite fiber can be thermally bonded to each other, and the puncture strength and tensile strength can be increased. A fiber assembly having excellent strength can be obtained.

  When segment B is a core-sheath type composite segment, the core component is preferably a specific polypropylene resin. With such a configuration, the split-type conjugate fiber is constituted by two resin components, and the nozzle design and the composite spinning become easier. In addition, you may use another polyolefin resin for a core component, and in that case, you may use it individually or in combination of 2 or more types from the above-mentioned polyolefin resin.

  When segment B is a core-sheath type composite segment, the cross-sectional shape of the core component of segment B is not particularly limited. 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 component B, or may not be located at the center and may be eccentric.

  When segment B is a core-sheath type, in segment B, the polyolefin resin constituting the sheath component preferably has a melting point lower than the melting point of the resin component constituting the core component. In that case, the melting point of the sheath component is preferably 10 ° C. or more lower than the melting point of the core component, more preferably 20 ° C. or more. Alternatively, the melting point of the resin component constituting the sheath component may be higher than the melting point of the resin component constituting the core component. For example, as will be described later, the sheath component may be composed of an ethylene vinyl alcohol copolymer (melting point of about 171 ° C.), and the core component may be composed of polypropylene (melting point of about 165 ° C.). The sheath component may be composed of a resin component that is more easily softened by heat or the like than the core component.

  When the sheath component of segment B is polyethylene, the core-sheath-type ultrafine composite fiber derived from segment B exhibits good thermal adhesiveness, and increases the strength of the fiber assembly after thermal bonding. A fiber assembly having excellent puncture strength is obtained. Moreover, when this combination is used, a fiber assembly suitable for hydrophilization treatment such as sulfonation can be obtained.

  When the sheath component of segment B is an ethylene vinyl alcohol copolymer, the ethylene vinyl alcohol copolymer functions as a thermal adhesive component. Since the ethylene vinyl alcohol copolymer has hydrophilicity and imparts high liquid retention to the fiber assembly, it is preferably used as a battery separator. The ethylene vinyl alcohol copolymer gels when heated in a high humidity state, and exhibits thermal adhesiveness at a temperature lower than the melting point. Therefore, when an ethylene vinyl alcohol copolymer is used as a heat bonding component, the fibers may be heat bonded by wet heat treatment. In addition, a split type composite fiber having a configuration in which polypropylene and an ethylene vinyl alcohol copolymer are adjacent to each other is preferably used from the viewpoint of high splittability.

(Split type composite fiber)
The split type composite fiber includes a segment A containing a polypropylene resin, and preferably further includes a segment B containing a polyolefin resin.

  The split type composite fiber includes a segment A, preferably includes a segment B, and may include other segments made of resin components other than these. When other segments are included, the resin component constituting the other segments is not particularly limited, and polyethylene, polypropylene, polybutene, polymethylpentene, ethylene vinyl alcohol copolymer, ethylene propylene copolymer, polyethylene terephthalate, polybutylene You may use terephthalate, nylon 6, nylon 66, etc. individually or in combination of 2 or more types. The other segment may be one type or two or more types.

  In the split type composite fiber, it is preferable that the segments 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. For example, the number of divisions is preferably 4 to 30, more preferably 6 to 24, and most preferably 8 to 16. Splitting composite fibers tend to improve splitting properties when the number of splits is small, but if the number of splits is too small, it is necessary to reduce the fineness of the splitting composite fibers in order to obtain ultrafine fibers of a predetermined fineness. In some cases, the productivity of the fiber is deteriorated or spinning becomes difficult. If the number of divisions is too large, the division property may deteriorate.

  The split-type conjugate fiber preferably has a hollow portion at the center of the fiber as viewed from the fiber cross section. When the structure has a hollow portion at the fiber center portion, the puncture strength of the fiber assembly can be further increased as compared to a split type composite fiber that does not have a hollow portion at the fiber center portion. 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. In addition, such a configuration can suppress yarn breakage during spinning of the split composite fiber.

  When the split composite fiber has a hollow portion, the hollow ratio may be determined according to the split ratio, the cross-sectional shape of the ultrafine fiber, and the like. 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 division number is 6 to 10, the hollow ratio is preferably 5% to 20%, and when the division number is 12 to 20, the hollow ratio is 15% to 20%. It is preferably 40%. If the hollow ratio is too small, it is difficult to obtain the effect when the hollow portion is provided, and if the hollow ratio is too large, the split-type composite fiber is split in the stretching process or the opening process of the split-type composite fiber. There is a risk that handling will be reduced.

  In the fiber cross section of the split type composite fiber, the segment A preferably occupies 20% to 80% by volume, and more preferably 40% to 60% by volume. When the segment A has a volume of 20% to 80% in the fiber cross section of the split composite fiber, the split property of the split composite fiber is less likely to deteriorate, and the ultrafine fiber A can be easily formed.

  When the split composite fiber includes segment A and segment B, the volume ratio of segment A and segment B constituting the split composite fiber is not particularly limited, and one component can be split into at least two segments. If there is no amount. For example, the ratio of the volume of segment A to segment B (the volume combining the core component and the sheath component) is preferably 2/8 to 8/2 (component A / component B), preferably 4/6 to 6 / 4 is more preferable. When the volume ratio is out of the range of 2/8 to 8/2, the spinnability is lowered, and good splitting properties may not be obtained.

  When segment B is a core-sheath type composite segment, the volume ratio of [segment A + segment B core component] / [segment B sheath component] is preferably 2/8 to 8/2, more preferably 4. It is preferable to design the fiber cross section so that / 6 to 6/4. If the volume ratio of the two resin components is outside the range of 2/8 to 8/2, the spinnability is lowered, and good splitting properties may not be obtained. For example, when the volume ratio of [segment A + segment B core component] / [segment B sheath component] is 5/5, the volume of segment A is smaller than the volume of segment B as a whole. Should.

  The fineness before splitting of the split composite fiber is not particularly limited, but is preferably in the range of 0.1 dtex to 8 dtex, more preferably in the range of 0.6 dtex to 6 dtex, and in the range of 1 dtex to 4 dtex. More preferably, it is within. If the fineness before division is less than 0.1 dtex, the spinning becomes unstable, and the productivity of the fibers, and consequently the fiber aggregates, may be reduced. Similarly, spinning may become unstable even if the fineness before division exceeds 8 dtex.

(Extra fine fiber)
The split-type composite fiber is split to form the ultrafine fiber A derived from the segment A. When the segment B is included, the ultrafine fiber B derived from the segment B is formed. When the other segment is included, another ultrafine fiber derived from another segment is formed. That is, the segments constituting the split-type conjugate fiber become independent with the splitting of the split-type conjugate fiber, and form ultrafine fibers.

  The ultrafine fiber A and / or the ultrafine fiber B is a circle having an area equal to the cross-sectional area of the ultrafine fiber, where L is the longest line segment connecting any two points on the outer periphery (contour of the fiber cross section) in the fiber cross section. The cross-sectional shape satisfying 1 ≦ L / D ≦ 2 is preferable, where D is the diameter. When the ultrafine fiber A has a cross-sectional shape satisfying 1 ≦ L / D ≦ 2, the cross-sectional shape becomes a shape closer to a circle, so that the fiber assembly is compared with the ultrafine fiber having a flat cross-sectional shape. Increase the puncture strength of objects.

  From the viewpoint of obtaining a fiber aggregate having particularly excellent puncture strength, the ultrafine fiber A is more preferably a cross-sectional shape satisfying 1 ≦ L / D ≦ 1.8, and L / D is 1.6 or less. The cross-sectional shape is more preferable, and the ultrafine fiber B is more preferably a cross-sectional shape satisfying 1 ≦ L / D ≦ 1.4, and the cross-sectional shape having L / D of 1.2 or less is preferable. Further preferred.

  The ultrafine fiber having such a cross-sectional shape is provided, for example, by adjusting the fiber cross-sectional structure of the split-type composite fiber to a fiber cross-sectional structure in which the segments are alternately arranged in a radial pattern. Furthermore, in the split type composite fiber, by forming a fiber cross-sectional structure having a hollow portion at the fiber center portion, the ultrafine fiber having the specific shape can be easily obtained.

  The ultrafine fiber A and / or the ultrafine fiber B 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, it becomes easy to obtain a fiber assembly having a small thickness. The fineness of the ultrafine fibers A and B may be different from each other, and the lower limit of the fineness is preferably 0.006 dtex for any of the ultrafine fibers.

  In particular, when the ultrafine fiber B is a core-sheath type, the fineness of the ultrafine fiber is preferably less than 0.4 dtex. When the core-sheath type composite fiber is included in the fiber assembly, 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 machine of the fiber assembly after thermal bonding The mechanical strength becomes higher. Therefore, when the ultrafine fiber B is a core-sheath type ultrafine composite fiber, it is particularly preferable to have a smaller fineness.

(Manufacturing method of split type composite fiber)
The split-type composite fiber may be composite-spun using a conventional melt-spinning machine using an appropriate composite-spinning nozzle so that a desired fiber cross-sectional structure is obtained. The spinning temperature (nozzle temperature) is selected according to the resin component to be used, and may be, for example, 220 ° C. or higher and 320 ° 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 200 to 200 so that the segment A and the segment B are adjacent to each other in the fiber cross section and are divided from each other. At 360 ° C., the specific polypropylene resin constituting the segment A and the polyolefin resin constituting the segment B are extruded and melt-spun to obtain a spun filament (unstretched fiber bundle). Since the split type conjugate fiber of the present invention uses a specific polypropylene resin having a large z-average molecular weight Mz as the segment A, the segment A is preferably melt-spun at a higher temperature, and the spinning temperature of the segment A is 250. -360 degreeC is preferable, 280-360 degreeC is more preferable, 300-350 degreeC is more preferable, 320-350 degreeC is especially preferable. The spinning temperature of the segment B containing the polyolefin-based resin is not particularly limited as long as it is within a range in which the spinnability is lowered and the cross-sectional shape of the split composite fiber is not broken, and is preferably 245 to 350 ° C. 250 to 330 ° C. is more preferable.

  The fineness of the spinning filament may be in the range of 1 dtex to 30 dtex. If the fineness of the spinning filament is less than 1 dtex, yarn breakage may occur frequently during spinning. When the fineness of the spun filament exceeds 30 dtex, a high degree of drawing is required, or the fineness after division becomes large and it is difficult to obtain ultrafine fibers. When the spinning filament is highly stretched to improve the splitting property, the fineness of the spinning filament is preferably 4 to 15 dtex, more preferably 6 to 12 dtex, and 8 to 12 dtex. More preferred is 9 to 11 dtex.

  Next, the spinning filament is drawn using a known drawing processor to obtain a drawn filament. The stretching treatment is preferably performed by setting the stretching temperature to a temperature within the range of 40 ° C. or higher and 150 ° C. or lower. 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, and further preferably 2 to 8 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. As the stretching method, either a wet stretching method performed in warm water or hot water or a dry stretching method is selected according to the resin component to be used. In the case of the wet stretching method, the stretching temperature may be in the range of 40 ° C. to 95 ° C., and in the case of the dry stretching method, the stretching temperature may be in the range of 80 ° C. to 150 ° C.

  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. The number of crimps is preferably within a range of 5 peaks / 25 mm to 30 peaks / 25 mm, and more preferably within a range of 10 peaks / 25 mm to 20 peaks / 25 mm. When the number of crimps is 5 peaks / 25 mm or more, the splitting property is improved due to the external force applied by the crimper, and when the number of crimps is 30 peaks / 25 mm or less, the fibers aggregate and become lumpy. Little or no.

  After the fiber treatment agent is applied (or the fiber treatment agent is not applied but is in a wet state), the filament is subjected to a drying treatment for several seconds to about 30 minutes at a temperature within the range of 80 ° C. to 110 ° C., 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 a nonwoven fabric is produced by a wet papermaking method, the shorter the fiber length, the higher the splitting rate of the split-type composite fiber. Or when manufacturing a nonwoven fabric by the card method, it is more preferable that fiber length shall be 20 mm-100 mm. In addition, when forming a fiber assembly by the spunbond method, the cutting process of the filament may be omitted.

(Fiber assembly)
The fiber assembly of the present invention will be described. Although it does not specifically limit as a form of a fiber assembly, For example, a woven fabric, a knitted fabric, a nonwoven fabric etc. are mentioned. Also, the fiber web form of the nonwoven fabric is not particularly limited. For example, a card web formed by a card method, an air lay web formed by an air lay method, a wet paper making web formed by a wet paper making method, and a spun bond method. Examples thereof include a spunbond web formed.

  It is preferable that the fiber aggregate includes ultrafine fibers formed by dividing the split type composite fiber at a ratio of 5 mass% or more. That is, the fiber aggregate may contain the ultrafine fiber A and the ultrafine fiber B in a ratio of 5 mass% or more. The fiber assembly preferably contains ultrafine fibers in a proportion of 10 mass% or more, more preferably contains 20 mass% or more, and most preferably contains 35 mass% or more. A preferable upper limit is 100 mass%. When the proportion of the split composite fibers in the fiber assembly is large, a dense nonwoven fabric tends to be obtained.

The fiber aggregate is a fiber aggregate for various wipings such as interpersonal / objective wipers, a fiber aggregate for battery separators used in various secondary batteries such as lithium ion batteries and nickel metal hydride batteries, and various filters such as cartridge filters and multilayer filters. In the case of a fiber aggregate for a filtration layer, and a fiber aggregate that requires a certain amount of gaps between constituent fibers and the air permeability and liquid permeability associated therewith, the content of split-type composite fibers in the entire fiber aggregate is , Preferably 90% by mass or less, more preferably 75% by mass or less, and particularly preferably 50% by mass or less. When the proportion of the above-mentioned polyolefin-based segmented composite fibers contained in the fiber assembly such as dry nonwoven fabric and wet nonwoven fabric is 90% by mass or less, the ultrafine fibers generated from the segmented composite fibers in the obtained fiber assembly The ratio does not become too large, and there is no fear that the fiber aggregate becomes a non-woven fabric denser than necessary.

  In particular, when the ultrafine fiber B is a core-sheath type ultrafine composite fiber, the fiber aggregate preferably includes the ultrafine fiber B at a rate of 10 mass% or more, and includes the ultrafine fiber B at a rate of 20 mass% or more. More preferably, it is most preferable that the ultrafine fiber B is contained in a proportion of 35 mass% or more. 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 B, the core-sheath type composite fiber with a small fineness (less than 0.6 dtex) is included. Compared with the non-woven fabric containing the amount, it has higher mechanical strength. In addition, a thin fiber assembly having excellent mechanical strength can be obtained.

  As long as the ultrafine fibers are contained in an amount of 5 mass% or more, the fiber aggregate may contain other fibers other than the ultrafine fibers formed from the split composite fibers in an amount of 95 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 aggregate is composed of only fibers derived from the split-type composite fibers (extra-fine fibers composed of component A, ultra-fine fibers composed of component B, and fibers having high fineness generated because the splitting did not completely proceed and Including a fiber in which branching occurs in one fiber), or only an ultrafine fiber formed from the split composite fiber.

  The total amount of fibers having a small fineness (less than 0.6 dtex) in the fiber aggregate is preferably 10 mass% or more, more preferably 20 mass% or more, and more preferably 50 mass% or more. Even more preferably, it is most preferably 70 mass% or more. 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 aggregate is within the above range, a thin fiber aggregate can be easily obtained. The fibers having a small fineness (less than 0.6 dtex) in the fiber aggregate may be only the ultrafine fibers A, the ultrafine fibers A and the ultrafine fibers B, or may be composed of these and other ultrafine fibers. .

  In the fiber assembly, 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 producing a nonwoven fabric by the wet papermaking method, it should be carried out using the impact received during the disaggregation treatment during papermaking. Can do.

  As the hydroentanglement treatment, a columnar water stream having a water pressure of 3 to 20 MPa is sprayed once or more 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. Good. And if it is the split type composite fiber of the present invention, 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 by 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 at a water pressure of 8 MPa or less, and it is possible to divide even at a water pressure of 6 MPa or less.

  A method for producing a fiber assembly will be described by 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.

  The fibrous web may then be subjected to a thermal bonding process. 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, when the ultrafine fiber B is included and the ultrafine fiber B is a core-sheath type ultrafine composite fiber, the fibers may be bonded to each other by the sheath component of the core-sheath type ultrafine composite fiber. 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 (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 100 to 160 ° C when polyethylene is the sheath component. It is preferable.

  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 assembly of the present invention, the fibers may be entangled. As a method for entanglement of fibers, a water entanglement process in which fibers are entangled 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. In addition, by the hydroentanglement process, entanglement between the ultrafine fibers generated by the division and division of the split composite fibers can be advanced simultaneously with the entanglement of the fibers.

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 such as a plain weave structure of about 70 to 100 mesh, and the pore diameter is 0.05 to 0. A columnar water flow having a water pressure of 1 to 15 MPa, more preferably 2 to 10 MPa is sprayed 1 to 10 times each on one or both sides of the fiber web from a nozzle having 3 mm orifices provided at intervals of 0.5 to 1.5 mm. Good. The fiber web after the hydroentanglement treatment is subjected to a drying treatment as necessary.

  The fiber aggregate 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 assembly preferably has a basis weight within the range of 2 g / m ² or more 100 g / m ² or less, more preferably it has a basis weight within the range of 10 g / m ² or more 100 g / m ² or less, More preferably, it has a basis weight in the range of 20 g / m ² or more and 80 g / m ² or less, and particularly preferably a basis weight in the range 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 aggregate are well formed, and the fiber aggregate tends to have high strength and piercing strength. When the basis weight of the fiber web is 100 g / m ² or less, the air permeability of the fiber aggregate does not decrease, and each component of the polyolefin-based split composite fiber of the present invention contained in the fiber web is subjected to hydroentanglement treatment described later. When dividing into two, the high-pressure water stream tends to act uniformly on the entire fiber web, and it becomes easy to sufficiently divide the polyolefin-based split composite fibers.

In the present invention, the segment B is a core-sheath type composite segment, and the ultrafine fibers can be bonded to each other by the sheath component of the core-sheath type ultrafine composite fiber formed from the segment B. Bonded fiber aggregates can be formed. Such a fiber assembly is preferably in the form of a nonwoven fabric, for example, and can be used as a battery separator. In such a case, the basis weight of the fiber aggregate preferably has a basis weight within a range of 5 g / m ^{2 to} 50 g / m ² , and particularly preferably within a range of 10 g / m ^{2 to} 30 g / m ² . Has a basis weight.

  The split type composite fiber of the present invention has excellent splitting properties as described above, and can produce a fiber assembly such as a dense nonwoven fabric having good texture. The fiber assembly containing the split composite fiber of the present invention has high tensile strength and puncture strength, and is extremely useful as a separator for secondary batteries such as lithium ion batteries and nickel metal hydride batteries.

Moreover, the fiber assembly using the split-type composite fiber of the present invention can realize high puncture strength due to the fact that it contains a polypropylene resin having a large z-average molecular weight and excellent rigidity. For example, when the fiber aggregate is a non-woven fabric and the non-woven fabric has a basis weight of about ² to 50 g / m ^2, it is preferable to have a puncture strength of 0.02 N or more per unit basis weight. When the nonwoven fabric has a basis weight of about 50 to 100 g / m ^2, it preferably has a puncture strength of 0.04 N or more per unit basis weight. The upper limit of the puncture strength per unit basis weight is not particularly limited, but is preferably 1N or less.

  First, the measurement method and the evaluation method used in the examples will be described.

(Number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), Q value)
Number average molecular weight (Mn) from gel permeation chromatography (GPC) using ortho-dichlorobenzene (ODCB) as a measurement solvent using a cross fractionator (CFC) and Fourier transform infrared absorption spectrum analysis (FT-IR) The weight average molecular weight (Mw), the z average molecular weight (Mz), and the weight average molecular weight / number average molecular weight ratio (Mn / Mw: Q value) were measured.

(Melt flow rate, MFR)
In accordance with JIS-K-7210, the melt flow rate was measured at 230 ° C. and a load weight of 21.18 N.

(Tensile modulus)
The tensile modulus of the resin was measured according to the measurement method described in JIS-K-7161.

(Split type composite fiber 1)
1 having a fiber cross-sectional shape shown in FIG. 1 and having a Q value of 10.2, Mn = 32600, Mw = 333000, Mz = 2340000, MFR230 of 10 g / 10 min, and tensile modulus as the core component of segment A and segment B Is a homopolypropylene resin having a viscosity of 2400 MPa, a high-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd., trade name HE481) is used as the sheath component of segment B, the number of divisions is 16, and the hollow ratio is 20% at the center. A split type composite fiber 1 having a hollow portion was produced.

  The split type composite fiber 1 is manufactured using a split type composite nozzle having 205 nozzle holes, and the volume ratio of polypropylene / polyethylene is 5/5 (volume ratio of segment A / segment B = 2.5 / 7. 5), melt extrusion was carried out at a spinning temperature of 290 ° C., a discharge rate of 0.35 g / hole, a take-up speed of 880 m / min, and a spun filament having a fineness of 4 dtex was obtained. Subsequently, the obtained spinning filament was dry-drawn 2.105 times at 105 ° C. to obtain a drawn filament having a fineness of 2 dtex. A fiber treating agent was applied to the obtained drawn filament, and then cut to a fiber length of 3 mm to obtain a split composite fiber 1 in the form of a short fiber.

(Split type composite fiber 2)
When the split type composite fiber 1 is manufactured except that the volume ratio of polypropylene / polyethylene is changed to 7/3 (volume ratio of segment A / segment B = 3.5 / 6.5) to produce a spun filament. According to the same procedure as that adopted in the above, split-type conjugate fiber 2 was obtained in the form of short fibers having a fiber length of 3 mm.

(Split type composite fiber 3)
The split composite nozzle is changed so as to have the fiber cross-sectional shape shown in FIG. 3 and melt extruded at a spinning temperature of 290 ° C., a discharge rate of 0.53 g / hole and a take-up speed of 880 m / min to obtain a spinning filament having a fineness of 6 dtex. Then, the obtained spinning filament was dry-drawn 3.6 times at 105 ° C. to obtain a drawn filament having a fineness of 2 dtex, and the procedure similar to the procedure adopted when manufacturing the split-type composite fiber 1 was followed. The split type composite fiber 3 was obtained in the form of a short fiber having a fiber length of 3 mm.

(Split type composite fiber 4)
The segmented composite fiber 4 was produced using the polypropylene used in the segmented conjugate fiber 1 as the segment A and the polyethylene used in the segmented conjugate fiber 1 as the segment B so as to have the fiber cross-sectional shape shown in FIG. . For the production of the split composite fiber 4, a split composite nozzle having 300 nozzle holes is used, and the volume ratio of polypropylene / polyethylene is 5/5 (volume ratio of segment A / segment B = 5/5). A melt extrusion was performed at a spinning temperature of 290 ° C., a discharge rate of 0.36 g / hole, and a take-up speed of 600 m / min to obtain a spun filament having a fineness of 6 dtex. Subsequently, the obtained spinning filament was dry-drawn 3.6 times at 105 ° C. to obtain a drawn filament having a fineness of 2 dtex. A fiber treatment agent was applied to the obtained drawn filaments, and then cut into 3 mm fiber lengths to obtain split-type composite fibers 4 in the form of short fibers.

(Split type composite fiber 5)
As a core component of segment A and segment B, a polypropylene resin (manufactured by Nippon Polypro Co., Ltd.) having a Q value of 5.3, Mn = 32000, Mw = 171000, Mz = 7000000, MFR230 of 26 g / 10 min, and tensile modulus of 1600 MPa Except for using “SA03A”), the split-type conjugate fiber 5 was obtained in the form of a short fiber having a fiber length of 3 mm according to the same procedure as that employed when the split-type conjugate fiber 1 was produced.

(Split type composite fiber 6)
As a core component of segment A and segment B, a polypropylene resin (manufactured by Nippon Polypro Co., Ltd.) having a Q value of 5.3, Mn = 32000, Mw = 171000, Mz = 7000000, MFR230 of 26 g / 10 min, and tensile modulus of 1600 MPa Except for using “SA03A”), the split-type conjugate fiber 6 was obtained in the form of a short fiber having a fiber length of 3 mm according to the same procedure as that employed when the split-type conjugate fiber 2 was produced.

(Split type composite fiber 7)
As a core component of segment A and segment B, a polypropylene resin (manufactured by Nippon Polypro Co., Ltd.) having a Q value of 5.3, Mn = 32000, Mw = 171000, Mz = 7000000, MFR230 of 26 g / 10 min, and tensile modulus of 1600 MPa Except for using “SA03A”), a split-type conjugate fiber 7 was obtained in the form of a short fiber having a fiber length of 3 mm according to a procedure similar to the procedure adopted when manufacturing the split-type conjugate fiber 3.

(Split type composite fiber 8)
For segment A, use is made of a polypropylene resin (“SA03A” manufactured by Nippon Polypro Co., Ltd.) having a Q value of 5.3, Mn = 32000, Mw = 171000, Mz = 7000000, MFR230 of 26 g / 10 min, and a tensile elastic modulus of 1600 MPa. Except for the above, according to a procedure similar to that employed when the split-type conjugate fiber 4 was produced, the split-type conjugate fiber 8 was obtained in the form of a short fiber having a fiber length of 3 mm.

  Table 1 shows the configurations, finenesses, and the like of the split-type conjugate fibers 1-8.

(Nonwoven fabric 1)
A fiber web was produced using the split type composite fiber 1 by a wet papermaking method. Specifically, the slurry is prepared so that the fiber concentration becomes 0.01 mass%, and stirred with a pulper at a rotation speed of 2000 rpm for 5 minutes to dissociate the fiber and split the split-type composite fiber. Extra fine fibers A and extra fine fibers B were formed. Thereafter, wet paper making was performed using a circular net type wet paper machine so that a web having a basis weight of 80 g / m ² was obtained. Then, the paper web was transported by a transport support and heated to 140 ° C. using a cylinder dryer for 45 seconds to heat the web and dry the wet paper web. The fibers were bonded with a sheath component to obtain a nonwoven fabric. In addition, L / D of the fiber cross section of the ultrafine fiber A was 1.7, and L / D of the fiber cross section of the ultrafine fiber B was 1.0.

(Nonwoven fabric 2)
A nonwoven fabric 2 was obtained according to the same procedure as that adopted when the nonwoven fabric 1 was produced except that the split conjugate fiber 2 was used. In addition, L / D of the fiber cross section of the ultrafine fiber A was 1.5, and L / D of the fiber cross section of the ultrafine fiber B was 1.1.

(Nonwoven fabric 3)
The nonwoven fabric 3 was obtained according to the procedure similar to the procedure employ | adopted when manufacturing the nonwoven fabric 1, except having used the split type composite fiber 3. FIG. In addition, L / D of the fiber cross section of the ultrafine fiber A was 2.9, and L / D of the fiber cross section of the ultrafine fiber B was 1.6.

(Nonwoven fabric 4)
The nonwoven fabric 4 was obtained according to the procedure similar to the procedure employ | adopted when manufacturing the nonwoven fabric 1, except having used the split type composite fiber 4. FIG. In addition, L / D of the fiber cross section of the ultrafine fiber A was 2.0, and L / D of the fiber cross section of the ultrafine fiber B was 2.0.

(Nonwoven fabric 5)
The nonwoven fabric 5 was obtained according to the procedure similar to the procedure employ | adopted when manufacturing the nonwoven fabric 1, except having used the split type composite fiber 5. FIG. In addition, L / D of the fiber cross section of the ultrafine fiber A was 1.7, and L / D of the fiber cross section of the ultrafine fiber B was 1.0.

(Nonwoven fabric 6)
A nonwoven fabric 6 was obtained according to the same procedure as that adopted when the nonwoven fabric 1 was produced except that the split conjugate fiber 6 was used. In addition, L / D of the fiber cross section of the ultrafine fiber A was 1.5, and L / D of the fiber cross section of the ultrafine fiber B was 1.1.

(Nonwoven fabric 7)
A nonwoven fabric 7 was obtained according to the same procedure as that adopted when the nonwoven fabric 1 was produced except that the split conjugate fiber 7 was used. In addition, L / D of the fiber cross section of the ultrafine fiber A was 2.9, and L / D of the fiber cross section of the ultrafine fiber B was 1.6.

(Nonwoven fabric 8)
A nonwoven fabric 8 was obtained according to the same procedure as that adopted when the nonwoven fabric 1 was produced except that the split conjugate fiber 8 was used. In addition, L / D of the fiber cross section of the ultrafine fiber A was 2.0, and L / D of the fiber cross section of the ultrafine fiber B was 2.0.

  The division ratio, thickness, tensile strength, and puncture strength of the obtained nonwoven fabric were evaluated. The evaluation results are shown in Table 2. The evaluation method of the division ratio, thickness, tensile strength and puncture strength is as follows.

(Split rate)
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 fibers consisting of the ultrafine fibers A and the number of fibers consisting of the ultrafine fibers B were counted. Further, the number of constituent components of the undivided fibers is determined by observing the number of components (for example, when having the fiber cross section of FIGS. 1 to 3, the number of constituent components of the fibers not divided at all is 16 and half The number of constituent components of the fibers divided into 8 is 8), and the number of constituent components was counted as the number of undivided fibers. Therefore, for example, if there is one undivided fiber and the number of constituent components 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 fibers made of component A + number of fibers made of component B] / [number of fibers made of component A + number of fibers made of component B + total number of undivided fibers] × 100

(Thickness of nonwoven fabric)
The thickness of the non-woven fabric after heat treatment was measured using a thickness measuring device (trade name: TICHKNESS GAUGE model CR-60A, manufactured by Daiei Kagaku Seisakusho Co., Ltd.) with a load of 2.94 cN per 1 cm ^{2 of} sample. did.

(Tensile strength)
In accordance with JIS L 1096 6.12.1 A method (strip method), using a constant-speed tension type tensile tester, tension was performed under the conditions of a sample piece width of 5 cm, a grip interval of 10 cm, and a tensile speed of 30 ± 2 cm / min. It was attached to the test, the load value at the time of cutting was measured, and it was set as the tensile strength. The tensile test was implemented about the vertical direction (machine direction) of the nonwoven fabric.

(Puncture strength)
A non-woven fabric cut to a size of 30 mm length and 100 mm width was prepared as a sample. This sample is 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.), and further 46 mm in length, 86 mm in width, and thickness. A pressing plate having a hole with a diameter of 11 mm at the center of a 7 mm aluminum plate was placed so that the hole coincided with the cylindrical through hole of the support. Next, the load was measured when a cone-shaped needle having a height of 18.7 mm, a bottom surface diameter of 2.2 mm, and a tip shape of 1 mm was stabbed vertically at the center of the holding plate at a speed of 2 mm / second. Of the measured loads, the maximum load (N) was defined as the puncture strength. The puncture strength was obtained by collecting four samples from one battery separator, measuring the samples at 15 different locations, and calculating the average value of the values measured at a total of 60 locations.

  When the nonwoven fabric 1 and the nonwoven fabric 5 were compared with each other, the nonwoven fabric 1 showed higher puncture strength, although there was no difference in the splitting ratio of the split-type composite fibers and the fineness of the ultrafine fibers after splitting. The same can be said from the comparison between the nonwoven fabric 2 and the nonwoven fabric 6, the comparison between the nonwoven fabric 3 and the nonwoven fabric 7, and the comparison between the nonwoven fabric 4 and the nonwoven fabric 8. This is because the z average molecular weight Mz of the polypropylene used in the nonwoven fabrics 1 to 4 is 2340000.

  The nonwoven fabrics 1 to 3 showed higher tensile strength than the nonwoven fabric 4. This is because the ultrafine fibers B constituting the nonwoven fabrics 1 to 3 are core-sheath type ultrafine composite fibers, and the ultrafine fibers are more strongly bonded to each other by the sheath component of the ultrafine fibers B.

  Moreover, another nonwoven fabric can also be obtained using the split type composite fibers 1-8. For example, the nonwoven fabric can also be obtained according to the same procedure as adopted when the nonwoven fabric 1 is manufactured except that the rotation speed of the pulper is slower than 2000 rpm or the stirring time is shorter than 5 minutes.

  The split type composite fibers 1 to 4 can be split by a relatively weak external force (for example, the pulper rotational speed is made slower or the stirring time is made shorter) compared to the split type composite fibers 5 to 8. it can. This is because the polypropylene resin constituting the split-type composite fibers 1 to 4 has a z-average molecular weight Mz of 2340000, and the segment A made of polypropylene having excellent rigidity hardly absorbs an impact caused by an external force, and during stirring with a pulper. This is because the external force applied to the split type composite fiber acts efficiently as a force for splitting the segment A and the segment B.

  Since the split-type conjugate fiber of the present invention contains ultrafine fibers mainly composed of a specific polypropylene resin, it has high splittability and is used as a material constituting a fiber assembly such as a nonwoven fabric. The fiber assembly using the split composite fiber of the present invention can be used for various wiping products such as interpersonal / objective wipers, artificial leather, sanitary materials, filters, battery separators and the like. In particular, it is suitably used as a separator for nickel metal hydride secondary batteries and lithium ion secondary batteries.

A Segment A
B Segment B
2 core component 4 sheath component 6 hollow part 10 split type composite fiber 12 core component 14 sheath component 20 split type composite fiber

Claims (6)

The segment A containing polypropylene resin, a segment B comprising a polyolefin-based resin 50% by mass or more a including splittable conjugate fibers,
Wherein segment A is, z-average molecular weight Mz is 1,000,000 or more on 5,000,000, and a weight average molecular weight Mw as main components a polypropylene resin is more than 200,000 8 00,000 or less A split type composite fiber characterized by that. The segmented composite fiber according to claim 1, wherein the segment B is a core-sheath composite segment, and the sheath component of the segment B is a polyolefin resin . The segment B is a core-sheath type composite segment, and in the core-sheath type composite segment, the core component is a polypropylene resin contained in the segment A, and the polyolefin resin constituting the segment B is a sheath component. Item 3. The split type composite fiber according to Item 2. The split type composite fiber according to any one of claims 1 to 3, wherein the polyolefin resin contained in the segment B is polyethylene or an ethylene vinyl alcohol copolymer. The split-type conjugate fiber according to any one of claims 1 to 4, wherein the fiber has a hollow portion at the center. Splittable conjugate fiber according to any one of claims 1 to 5 is formed by Wari繊, to include very fine fibers of less fineness than 0.006Dtex 0.6 dtex at a ratio of 5 mass% or more Characteristic fiber assembly.