JP7395101B2 - Splitable composite fiber, short fiber nonwoven fabric using the same, and method for producing the same - Google Patents

Description

The present invention relates to a splittable conjugate fiber, a short fiber nonwoven fabric using the same, and a method for producing the same.

In order to obtain ultrafine fibers and short fiber nonwoven fabrics containing ultrafine fibers, a plurality of thermoplastic resins are used, and when the fiber cross section is observed, it is found that the cross section has two or more resin segments (hereinafter simply referred to as segments). A method using a splittable conjugate fiber composed of: When splittable composite fibers are used, ultrafine fibers can be easily obtained by dividing the fibers into segments.

For example, splittable composite fibers can be split into resin segments by applying external force such as splitting with high-pressure water jets or high-speed stirring of slurry dispersed in water, and ultrafine fibers can be easily obtained. , Patent Documents 1 and 2 propose the use as fibers constituting wet-laid nonwoven fabrics used in battery separators and microfiltration membranes that require a dense structure.

In addition, when splittable composite fibers are used as fibers constituting dry nonwoven fabrics using short fibers such as spunlace nonwoven fabrics, the generated ultrafine fibers not only give the nonwoven fabric a soft texture, but also the cross-section of the ultrafine fibers. Patent Documents 2 and 3 disclose that dry nonwoven fabrics containing splittable composite fibers are used for cosmetic impregnated sheets, personal/objective wiping sheets, etc. because they are not circular and have excellent dirt wiping properties. is proposed.

International Publication No. 2011/122657 Japanese Patent Application Publication No. 2012-142235 Japanese Patent Application Publication No. 2006-000625 JP 2015-148023 Publication

However, Patent Documents 1 and 2 are based on the premise that a fibrous web is obtained by a wet nonwoven fabric, that is, a papermaking method. Therefore, when attempting to obtain a dry nonwoven fabric containing short fiber nonwoven fabric by cutting the fibers described in the patent document into short fibers of about 25 to 75 mm, the fibers are divided into resin segments during the opening and carding processes. As a result, the generated ultrafine fibers become entangled with each other to form a fiber mass (nep), or the ultrafine fibers become entangled inside the carding machine, resulting in a failure to form a well-formed fiber web. Furthermore, in Patent Documents 3 and 4, a fiber web containing splittable conjugate fibers is hydroentangled, and among the generated ultrafine fibers, ultrafine fibers generated from a low melting point resin segment are melted and thermally bonded. In order to improve the splittability of the splittable conjugate fibers used in the production of nonwoven fabrics, it is necessary to split and entangle the fibers using a high-pressure water stream during hydroentanglement. In particular, splittable conjugate fibers made by combining polyolefin resins such as polypropylene resin and polyethylene resin, and splittable conjugate fibers made by combining polyester resins, have strong adhesion between resin segments, so they are split using high water pressure. There is a need for improvement.

In order to solve the above-mentioned problems, the present invention provides a splittable composite fiber that has a core-sheath structure for some of the segments constituting the splittable composite fiber, improves card passability, and can be suitably used for short fiber nonwoven fabrics. Provided are fibers, short fiber nonwoven fabrics containing the same, and methods for producing the same.

The present invention is a splittable conjugate fiber including a first segment and a second segment, the first segment being a resin segment made of a first component, and the second segment having a cross-sectional structure including the first component. A core-sheath type resin segment having a core component and a second component as a sheath component, the first component being a resin component containing 50% by mass or more of polypropylene resin, and the second component containing 50% by mass of polyethylene resin. % or more, and the splittable composite fiber has a single fiber strength of 1.8 cN/dtex or more and 4.2 cN/dtex or less, an elongation of 30% or more and 200% or less, and an apparent young The present invention relates to a splittable composite fiber having a ratio of 700 N/mm ² to 4000 N/mm ² .

The present invention also relates to a short fiber nonwoven fabric containing 20% by mass or more of the above-mentioned splittable conjugate fibers.

The present invention also provides a method for producing the splittable conjugate fiber, wherein the first component is a resin component containing 50% by mass or more of polypropylene resin, and the second component is a resin component containing 50% by mass or more of polyethylene resin. The first segment is a resin segment made of the first component, the cross-sectional structure is the first component as the core component, and the second component is melt-spun using a melt-spinning machine equipped with a split type composite nozzle. A step of obtaining a spun filament including a second segment which is a core-sheath type resin segment as a sheath component, and a temperature of 60° C. or higher and 100° C. or lower, and a drawing ratio of 0.58 times or more and 0.88 times or less of the maximum drawing ratio. The present invention relates to a method for producing a splittable conjugate fiber, including a step of wet-drawing the spun filament.

FIG. 1 schematically shows a cross section of a splittable conjugate fiber according to one embodiment of the present invention. FIG. 2 schematically shows a cross section of a splittable conjugate fiber according to another embodiment of the present invention. FIG. 3 schematically shows a cross section of the splittable composite fiber of Comparative Example 3. FIG. 4 schematically shows a cross section of the splittable composite fiber of Comparative Example 4.

The inventors of the present invention have made extensive studies on making some of the segments constituting the splittable conjugate fibers have a core-sheath structure and improving the card passability. As a result, in a splittable composite fiber including a first segment and a second segment, the first segment is a resin segment made of a first component, the second segment has a cross-sectional structure in which the first component is a core component, and the second component is a resin segment. A core-sheath type resin segment having a sheath component of By setting the single fiber strength to 1.8 cN/dtex or more and 4.2 cN/dtex or less, the elongation to 30% or more and 200% or less, and the apparent Young's modulus to 700 N/mm ² or more and 4000 N/mm ² or less. , without reducing the generation rate of ultrafine fibers (meaning the rate at which ultrafine fibers are generated after the splitting treatment, generally also referred to as the splitting rate) in the dry nonwoven fabric containing the splittable conjugate fibers. It was discovered that the card passing property of splittable composite fibers was improved. That is, the splittable composite fiber has the above-mentioned resin composition, strength and elongation, and apparent Young's modulus, so that it is not divided into each resin segment until the carding process, and can be processed into a nonwoven fabric, such as a hydroentangling process, etc. It can be divided and made into ultra-fine fibers in the process of

FIGS. 1 and 2 schematically show cross sections of splittable conjugate fibers (10, 20) of one embodiment of the present invention, respectively. Both include a first segment (1) and a second segment (2), and the first segment (1) is a unitary structure segment, but the second segment (2) is a core-sheath type segment (Fig. 1 and Figure 2). A core-sheath segment can have a core component (4, 14) and a sheath component (6, 16). Furthermore, the splittable composite fiber may have a hollow (8) (FIG. 1).

<1st segment>
The first segment is a resin segment made of the first component. The first segment forms the ultrafine fiber 1 by splitting the splittable conjugate fiber. In other words, the first segment is composed of the first component and is a unitary segment with a unitary 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 polypropylene resin in an amount of 75% by mass or more, more preferably 80% by mass or more.

It is particularly preferred that the first component consists essentially of polypropylene resin. Here, the term "substantially" is used because the polypropylene resin provided as a product usually contains additives such as stabilizers, and/or various additives are added during the production of fibers. , it is taken into consideration that it is impossible to obtain a fiber in which the first component consists only of polypropylene resin and does not contain any other thermoplastic resin. Typically, the first component may contain up to 15% by weight of additives.

In the present invention, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw/Mn) (hereinafter also referred to as "Q value") of the polypropylene resin measured after spinning is preferably 6 or less. It is preferably 2 or more and 5.5 or less, even more preferably 2.2 or more and less than 5, particularly preferably 2.3 or more and 4.5 or less, and 2.4 or more and 4.2. The following are most preferred. By having a Q value of 6 or less, the polypropylene resin after spinning has the same size (length of polypropylene molecular chain) of the polypropylene molecules contained therein, and the width of the distribution is narrower, so the polypropylene molecules The behavior of is easy to match. As a result, in the splittable conjugate fiber, not only the cross-sectional shape of the fiber and the cross-sectional shape of each segment can be easily arranged, but also fibers with high productivity that are less likely to break during spinning and drawing can be easily obtained. Since the fiber productivity is good, the physical properties of the obtained splittable conjugate fiber and short fiber nonwoven fabric using the same are further improved.

The weight average molecular weight (Mw) of the polypropylene resin measured after spinning is preferably 750,000 or less, more preferably 150,000 or more and 700,000 or less, and 200,000 or more and 500,000 or less. More preferably, it is 230,000 or more and 400,000 or less. Further, the number average molecular weight (Mn) of the polypropylene resin measured after spinning is preferably 43,000 or more and 150,000 or less, more preferably 48,000 or more and 120,000 or less, and 55,000 or more. It is particularly preferable that the number is greater than or equal to 100,000. The methods for measuring the weight average molecular weight (Mw) and number average molecular weight (Mn) of polypropylene resin are described in Examples.

The polypropylene resin may be a propylene homopolymer (a homopolymer containing propylene as a monomer) or a copolymer containing propylene as a monomer (hereinafter referred to as polypropylene resin). The polypropylene resin is not particularly limited as long as it can obtain the splittable conjugate fiber aimed at by the present invention. 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 copolymers, block copolymers, and graft copolymers include copolymers with at least one α-olefin selected from the group consisting of ethylene and α-olefins having 4 or more carbon atoms.

The α-olefin having 4 or more carbon atoms is not particularly limited as long as it can obtain the splittable conjugate fiber aimed at by the present invention, but examples include 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, and 1-octadecene. The content of propylene in the copolymer is preferably more than 50% by mass. As the first component, a homopolymer of propylene or the above polypropylene resin can be used, but a homopolymer of propylene is particularly preferable in consideration of ease of manufacture and economy (manufacturing cost). These may be used alone or in combination of two or more.

The polypropylene resin has a melt mass flow rate (hereinafter also referred to as "MFR230"; measurement temperature 230°C, load 2.16 kgf (21.18 N)) according to JIS K 7210 of 8 g/10 minutes or more and 60 g/10 minutes or less. It is preferably 15 g/10 minutes or more and 60 g/10 minutes or less, particularly preferably 20 g/10 minutes or more and 45 g/10 minutes or less, and 25 g/10 minutes or more and 40 g/10 minutes or less. is most preferable.

The first component may contain known additives as long as the card passability and splittability of the splittable conjugate fiber of the present invention are not impaired. Known additives include splitting accelerators such as silicon compounds, unsaturated carboxylic acid compounds, and (meth)acrylic acid compounds; hydrophilic agents such as polyglycerin compounds in which multiple glycerins are polymerized; and carbonic acid. Crystallizing agents such as calcium and talc, antistatic agents, matting agents, heat stabilizers, light stabilizers, flame retardants, antibacterial agents, lubricants, plasticizers, softeners, etc., with the mass of the first component being 100% by mass. In this case, it may be contained in an amount of 0.1 to 10% by mass. In particular, white inorganic powders (inorganic fillers) such as titanium oxide and zinc oxide can adjust the transparency (transparency) of nonwoven fabrics containing splittable composite fibers, so they can be used as cosmetic-impregnated skin covering sheets such as face masks. The splittable composite fiber to be used contains 0.1 to 3% by mass of an inorganic filler such as titanium oxide or zinc oxide when the mass of the first component is 100% by mass, or It is preferable not to intentionally add inorganic fillers such as titanium oxide or zinc oxide. On the other hand, when the splittable conjugate fiber of the present invention is used in a nonwoven fabric used for various absorbent articles that require the nonwoven fabric to have a white appearance or the color of the absorbed liquid to be difficult to see, the splittable conjugate fiber is , it is preferable to contain an inorganic filler such as titanium oxide or zinc oxide in an amount of 1 to 10% by mass when the mass of the first component is 100% by mass.

<Second segment>
It is preferable that the second segment forms ultrafine fibers 2 derived from the second segment by splitting the splittable conjugate fiber. The second segment is a core-sheath type resin segment with a cross-sectional structure in which the first component is the core component and the second component is the 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 polyethylene resin. Here, the term "substantially" is used because the polyethylene resin provided as a product usually contains additives such as stabilizers, and/or because various additives are added during the production of fibers. , it is taken into consideration that it is not possible to obtain fibers in the form of polyethylene resins alone and without any other components. Typically, the second component may contain up to 15% by weight of additives.

Polyethylene resin has good compatibility with polypropylene resin, and splittable composite fibers made by combining these resins generally have low splittability. In the present invention, even when a polypropylene resin and a polyethylene resin are combined, the splittable conjugate fiber has the above-mentioned strength and elongation characteristics, so that excellent splittability can be obtained in the process of making a nonwoven fabric.

The polyethylene resin may be an ethylene homopolymer (a homopolymer containing ethylene as a monomer) or a copolymer containing ethylene as a monomer (hereinafter referred to as polyethylene resin). good. Due to differences in density and/or molecular structure, the ethylene homopolymers include high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene (general linear low-density polyethylene) as a copolymer containing ethylene as a monomer. Chain low-density polyethylene is produced by combining ethylene and α-olefins such as 1-butene (4 carbon atoms), 1-hexene (6 carbon atoms), and 1-octene (8 carbon atoms) using a metallocene catalyst or a Ziegler-Natta catalyst. It is an ethylene/α-olefin copolymer obtained by copolymerizing using The polyethylene resin is not particularly limited as long as it can obtain the splittable conjugate fiber aimed at by the present invention. 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 copolymers, block copolymers, and graft copolymers include copolymers with at least one α-olefin selected from the group consisting of ethylene and α-olefins having 3 or more carbon atoms.

The α-olefin having 3 or more carbon atoms is not particularly limited as long as it can obtain the splittable conjugate fiber aimed at by the present invention, but examples include propylene, 1-butene, 1-pentene, 3 , 3-dimethyl-1-butene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-decene, 1-dodecene, 1-tetradecene, 1-octadecene, and the like. The content of ethylene in the copolymer is preferably 50% by mass or more. As the second component, an ethylene homopolymer or the above-mentioned polyethylene resin can be used, but an ethylene homopolymer is particularly preferable in consideration of ease of production and economy (production cost). These may be used alone or in combination of two or more.

Polyethylene resin has a melt mass flow rate (hereinafter also referred to as "MFR190"; measurement temperature: 190°C, load: 2.16 kgf (21.18 N)) according to JIS K 7210 of 5 g/10 minutes or more and less than 30 g/10 minutes. It is preferably 8 g/10 minutes or more and less than 28 g/10 minutes, and particularly preferably 10 g/10 minutes or more and less than 25 g/10 minutes. When the MFR190 of the polyethylene resin is in the range of 5 g/10 minutes or more and less than 30 g/10 minutes, the productivity of the splittable composite fiber is further improved.

The second segment is a core-sheath type resin segment with a cross-sectional structure in which the first component is the core component and the second component is the sheath component. Since the second segment is a core-sheath type resin segment, by splitting the splittable conjugate fiber in a process of forming a nonwoven fabric, such as a hydroentangling process, the conjugate fiber has a core-sheath type fiber cross section. Ultrafine fibers (core-sheath type ultrafine composite fibers) are formed. By melting only the second component (containing 50% by mass 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 splittable composite fiber are thermally bonded together. be able to. Therefore, a short fiber nonwoven fabric with good texture can be obtained.

The second segment is a core-sheath type resin segment, and the core component is the same first component as the resin component constituting the first segment, so the splittable composite fiber is composed of two types of resin components. , the nozzle design and composite spinning become 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 splittable conjugate fiber targeted 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. Also, the core component may be located at the center of the second segment, or may be off-center and eccentric.

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

<Splitable composite fiber>
The splittable conjugate fiber in one or more embodiments of the present invention includes a first segment and a second segment, but may also include other resin segments, such as a third segment. Other resin segments are not particularly limited as long as the splittable conjugate fibers targeted by the present invention can be obtained. As resin components constituting other segments, for example, polybutene-1, polymethylpentene, ethylene vinyl alcohol copolymer, ethylene propylene copolymer, polyethylene terephthalate, polybutylene terephthalate, nylon 6, and nylon 66 may be used alone or , two or more types may be used in combination. The number of other segments may be one or more.

It is preferable that the segments of the splittable conjugate fiber are mutually arranged. For example, it may be radial, multilayered, cross-shaped, etc. Among these, from the viewpoint of further improving the splittability of the splittable conjugate fiber, it is preferable that the segments of the splittable conjugate fiber be arranged in a radial pattern.

In the splittable conjugate fiber, the number of divisions (total number of segments) may be determined depending on the fineness of the splittable conjugate fiber, the fineness of the ultrafine fiber to be obtained, and the like. The number of divisions is, for example, preferably 4 or more and 30 or less, more preferably 6 or more and 24 or less, even more preferably 8 or more and 18 or less, and particularly preferably 8 or more and 16 or less. When the number of divisions is 4 or less and 30 or less, the productivity of the fiber can be moderate, and even though it is easier to spin, the divisibility can also be kept moderate.

It is preferable that the splittable conjugate fiber has a hollow portion at the center of the fiber when viewed from a fiber cross section. When the fiber has a hollow part in the center, the contact area between adjacent resin segments is smaller compared to a split type composite fiber that does not have a hollow part in the center of the fiber, so that the distance between the resin segments is moderate. By adhering, the fibers are easily split when subjected to entanglement treatment using high-pressure water jets, and unsplit conjugate fibers are less likely to remain in the nonwoven fabric. Furthermore, yarn breakage during spinning of the splittable conjugate fiber can be suppressed.

When the splittable conjugate fiber has a hollow portion, the hollowness ratio can be determined depending on the splitting 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 to the cross section of the fiber. For example, the hollowness ratio is preferably about 1% or more and 50% or less, and preferably about 5% or more and 40% or less. More specifically, when the number of divisions is 6 or more and 10 or less, the hollowness ratio is preferably 5% or more and 20% or less, and when the number of divisions is 12 or more and 20 or less, the hollowness ratio is 15% or more and 40% or less. % or less. When the hollowness ratio is about 1% or more and 50% or less, it is preferable because it is easy to obtain the effect of providing the hollow portion and the splittable conjugate fiber is difficult to split during the manufacturing process, so it is easy to handle.

In the fiber cross section of the splittable composite fiber, the first segment preferably occupies 20% or more and 80% or less in area, and more preferably 40% or more and 60% or less in area. When the first segment of the splittable conjugate fiber occupies 20% or more and 80% or less in terms of area, the splittability of the splittable conjugate fiber is unlikely to decrease and is easily split to form the ultrafine fiber 1 derived from the first segment. can.

As long as the splittable conjugate fiber targeted by the present invention can be obtained, the volume ratio of the first segment and the second segment constituting the splittable conjugate fiber is not particularly limited. For example, the volume of the first segment and the volume of the second segment (because the cross-sectional structure of the second segment is a core-sheath type resin segment in which the first component is the core component and the second component is the sheath component, the second segment The ratio of the combined volume of the core component and the sheath component is preferably 2/8 or more and 8/2 or less (volume of first segment/volume of second segment), and preferably 4/6 or more and 6/4. It is more preferable that it is below. When the volume ratio is 2/8 or more and 8/2 or less, spinnability is further improved, which is preferable.

The second segment is a core-sheath type resin segment, and the volume ratio of [first segment + second segment core component]/[sheath component of second segment] in the fiber cross section is 2/8 or more and 8/2 or less. It is preferably 4/6 or more and 6/4 or less. When the volume ratio is 2/8 or more and 8/2 or less, spinnability is further improved, which is preferable. For example, if 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 smaller than the volume of the entire second segment. It should be noted that this will also be smaller.

The volume ratio of the first component and the second component is not particularly limited as long as the splittable conjugate fiber targeted by the present invention can be obtained. For example, the ratio of the volume of the first component to the volume of the second component (the combined volume of the core component and sheath component) is 8/2 or more and 3/7 or less (volume of the first component/volume of the second component). The ratio is preferably 75/25 or more and 35/65 or less, and particularly preferably 70/30 or more and 40/60 or less. When the volume ratio is 8/2 or more and 3/7 or less, spinnability is further improved, which is preferable.

From the viewpoint of further improving spinnability, card passability when making a fiber web, and splittability when making a nonwoven fabric, the volume ratio of the first component and the second component (first component/second component) is ) is preferably 8/2 or more and 3/7 or less, and the volume ratio of the first segment and the second segment (first segment/second segment) is preferably 2/8 or more and 8/2 or less, and the first The volume ratio of the component and the second component (first component/second component) is 70/30 or more and 40/60 or less, and the volume ratio of the first segment and the second segment (first segment/second segment) More preferably, it is 4/6 or more and 6/4 or less.

The fineness of the splittable conjugate fiber before splitting is not particularly limited as long as the splittable conjugate fiber targeted by the present invention can be obtained, but it is preferably 0.5 dtex or more and 4.8 dtex or less. , more preferably 0.8 dtex or more and 3.6 dtex or less. When the fineness of the splittable conjugate fiber before splitting is 0.5 dtex or more and 4.8 dtex or less, spinnability is improved and productivity is further improved, which is preferable.

The single fiber strength of the splittable composite fiber before splitting is 1.8 cN/dtex or more and 4.2 cN/dtex or less, the elongation is 30% or more and 200% or less, and the apparent Young's modulus is 700 N/mm ² It is above 4000N/mm ² or below. When the strength and elongation and apparent Young's modulus are within the above-mentioned ranges, card passability when forming a fibrous web becomes good, and divisibility when forming a nonwoven fabric also becomes good.

The single fiber strength of the splittable composite fiber before splitting is preferably 1.8 cN/dtex or more and 4.0 cN/dtex or less, more preferably 1.9 cN/dtex or more and 3.8 cN/dtex or less, More preferably, it is 2.0 cN/dtex or more and 3.6 cN/dtex or less. Single fiber strength is measured by the method described in Examples.

The elongation of the splittable composite fiber before splitting is preferably 40% or more and 190% or less, more preferably 50% or more and 180% or less, even more preferably 60% or more and 170% or less, It is particularly preferably 70% or more and 160% or less. Elongation is measured by the method described in Examples.

The apparent Young's modulus of the splittable composite fiber before splitting is preferably 800 N/mm ² or more and 3800 N/mm ² or less, more preferably 900 N/mm ² or more and 3600 N/mm ² or less, and even more preferably It is 1000 N/mm ² or more and 3500 N/mm ² or less. When the apparent Young's modulus is within the above range, the card passability when forming a fibrous web becomes better, and the divisibility when forming a nonwoven fabric also becomes better. The apparent Young's modulus is measured by the method described in Examples.

The fiber length of the splittable composite fiber is not particularly limited, but is preferably, for example, 25 mm or more and 75 mm or less, more preferably 30 mm or more and 70 mm or less. From the viewpoint of better card passing properties, it is particularly preferable that the fiber length is 35 mm or more and 65 mm or less.

<Ultra-fine fiber>
The splittable composite fiber is split to form ultrafine fibers 1 originating from the first segment and ultrafine fibers 2 originating 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 splittable composite fiber is preferably a fiber cross-sectional structure in which each segment is arranged alternately in a radial manner. Furthermore, in the splittable conjugate fiber, it is also preferable to have a fiber cross-sectional structure having a hollow portion at the center of the fiber.

The fineness of the ultrafine fibers 1 and/or the ultrafine fibers 2 is preferably less than 0.6 dtex, more preferably less than 0.4 dtex. When the fineness of the ultrafine fibers is less than 0.6 dtex, a thin short fiber nonwoven fabric 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 of any of the ultrafine fibers is preferably 0.006 dtex.

In particular, since the ultrafine fibers 2 are of a core-sheath type, the fineness of the ultrafine fibers 2 is preferably less than 0.4 dtex. When a core-sheath composite fiber is included in a short fiber nonwoven fabric, the smaller the fineness of the composite fiber, the larger the surface area of the composite fiber, which increases the thermal bonding area and increases the mechanical strength of the short fiber nonwoven fabric after thermal bonding. becomes higher. When the ultrafine fiber 2 is a core-sheath type ultrafine conjugate fiber, it is particularly preferable to have a smaller fineness.

The method for producing the above-described splittable conjugate fiber of one or more embodiments of the present invention is not particularly limited as long as the desired splittable conjugate fiber can be obtained, but preferably, the first component and the first component are Melt-spinning the two components using a melt-spinning machine equipped with a split-type composite nozzle to obtain a spun filament including a first segment and a second segment, and at a temperature of 60°C or more and 100°C or less and a maximum draw ratio. It is preferable to include a step of wet-stretching the spun filaments at a stretching ratio of 0.58 times or more and 0.88 times or less.

The splittable composite fibers can be composite spun using a conventional melt spinning machine using a suitable composite spinning nozzle to obtain the desired fiber cross-sectional structure. The spinning temperature (nozzle temperature) is selected depending on the resin component used, and may be, for example, 200°C or more and 360°C or less.

Specifically, a split-type composite nozzle that obtains a predetermined fiber cross section is installed on the melt spinning machine, and the spinning temperature is adjusted so that the first segment and the second segment are adjacent to each other in the fiber cross section and have a structure in which they are separated from each other. The first component (resin component containing polypropylene resin) and the second component (resin component containing polypropylene resin) are extruded and melt-spun at a temperature of 200° C. or higher and 360° C. or higher, and the first segment (resin segment consisting of the first component) and A spun filament (undrawn fiber bundle) containing the second segment (core-sheath type resin segment in which the first component is the core component and the second component is the sheath component) can be obtained.

The fineness of the spun filament (undrawn fiber bundle) may be within the range of 1 dtex or more and 30 dtex or less. When the fineness of the spun filament is 1 dtex or more and 30 dtex or less, spinning can be made easier. The fineness of the spun filaments is preferably 2.0 dtex or more and 15 dtex or less, from the viewpoint of further improving card passability when making a fiber web and divisibility when making a nonwoven fabric by appropriately drawing the spun filaments. , more preferably 2.5 dtex or more and 12 dtex or less, further preferably 3 dtex or more and 10 dtex or less, particularly preferably 4.0 dtex or more and 8.0 dtex or less.

Next, the spun filaments can be drawn using a known drawing machine to obtain drawn filaments. The stretching process is performed at a temperature of 60°C or higher and 100°C or lower, and from 0.58 times to 0.88 times the maximum stretching ratio (Vmax), from the viewpoint of easily obtaining splittable conjugate fibers having the above-mentioned strength and elongation characteristics. It is preferable to carry out wet stretching at a stretching ratio of Stretching ratio/Vmax=0.58 or more and 0.88 or less).

The stretching method may be wet stretching, and is preferably carried out in warm water, hot water, or steam depending on the resin component used. The stretching temperature may be in the range of 60°C or more and 98°C or less, 60°C or more and 95°C or less, 70°C or more and 95°C or less, or 80°C or more and 95°C or less. Good too. When the stretching temperature satisfies the above range, it is preferable to carry out the stretching process by wet stretching which not only facilitates stretching but also allows uniform heating of the fibers.

The stretching ratio is preferably 0.60 times or more and 0.88 times or less of the maximum stretching ratio, more preferably 0.60 times or more and 0.85 times or less, and 0.62 times or more and 0.85 times. It is even more preferably the following, and particularly preferably 0.65 times or more and 0.82 times or less. The maximum stretching ratio is determined by the method described in Examples.

It is preferable that the ratio of the stretching ratio to the maximum stretching ratio satisfies the above range, and that the stretching ratio is 2 times or more and less than 5 times. By performing the stretching process at the above stretching ratio, the unstretched fibers can be sufficiently stretched, and the resulting splittable composite fibers can have sufficient single fiber strength as fibers constituting various nonwoven fabrics. In addition, the possibility of excessive crystallization is low. The stretching ratio is preferably 2.5 times or more and 4.5 times or less, more preferably 2.8 times or more and less than 4 times, and particularly preferably 3 times or more and 3.8 times or less.

A predetermined amount of a fiber treatment agent is attached to the obtained drawn filament, if necessary, and further mechanically crimped with a crimper (crimping device), if necessary. The fiber treatment agent suppresses the generation of static electricity during the carding process and improves the card passability. Furthermore, when the fibers are cut into fiber lengths of less than 20 mm to form a wet-laid nonwoven fabric, the fibers can be easily dispersed in water or the like.

Drying the filament after applying the fiber treatment agent (or not applying the fiber treatment agent but in a wet state) at a temperature within the range of 80 ° C. to 110 ° C. for several seconds to about 30 minutes, Dry the fibers. The drying process may be omitted depending on the case. Thereafter, the filament is cut so that the fiber length is preferably 1 mm or more and 100 mm or less, more preferably 2 mm or more and 70 mm or less. When producing a nonwoven fabric by a card method, the fiber length is more preferably 25 mm or more and 75 mm or less.

<Short fiber nonwoven fabric>
Short fiber nonwoven fabrics of one or more embodiments of the present invention will be explained. The form of the fiber web of the short fiber nonwoven fabric is not particularly limited, and examples thereof include a carded web formed by a carding method, an air-lay web formed by an air-laying method, and the like.

From the perspective of improving texture, short fiber nonwoven fabrics are splittable conjugate fibers (including ultrafine fibers formed by splitting and unsplit conjugate fibers that have not been split even after splitting treatment such as high-pressure water jets). The content is preferably 15% by mass or more, more preferably 20% by mass or more, and particularly preferably 25% by mass or more. The short fiber nonwoven fabric preferably contains 10% by mass or more of ultrafine fibers formed by splitting splittable conjugate fibers. That is, the short fiber nonwoven fabric may contain the ultrafine fibers 1 and 2 in a total proportion of 10% by mass or more. The short fiber nonwoven fabric preferably contains ultrafine fibers in a proportion of 15% 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. In the short fiber nonwoven fabric using the splittable conjugate fibers of the present invention, the upper limit of the proportion of ultrafine fibers is not particularly limited, and the short fiber nonwoven fabric contains 100% by mass of ultrafine fibers formed by splitting the splittable conjugate fibers. It may also be a nonwoven fabric made of ultrafine fibers formed by splitting. When the ratio of the splittable conjugate fibers in the short fiber nonwoven fabric is high, the texture is good and a dense nonwoven fabric tends to be easily obtained.

Short fiber nonwoven fabrics are used for cosmetic-impregnated skin covering sheets such as face masks; for absorbent articles such as top sheets, second sheets, and back sheets that constitute absorbent articles such as infant diapers, nursing care diapers, and sanitary napkins. In the case of a sheet nonwoven fabric, a short fiber nonwoven fabric in which the proportion of the splittable conjugate fibers is 100% by mass may be used. If a certain degree of voids between the constituent fibers and associated air permeability and liquid permeability are required for the short fiber nonwoven fabric containing the above-mentioned splittable conjugate fibers, the content of the splittable conjugate fibers in the entire short fiber nonwoven fabric is , may be 90% by mass or less, 80% by mass or less, or 75% by mass or less. When the proportion of the splittable conjugate fibers contained in the short fiber nonwoven fabric such as the dry-laid nonwoven fabric is 90% by mass or less, the proportion of the ultrafine fibers generated from the splittable conjugate fibers in the obtained short fiber nonwoven fabric is moderate, Depending on the use, the structure becomes a suitably dense nonwoven fabric, which is preferable.

The short fiber nonwoven fabric preferably contains ultrafine fibers 2 in a proportion of 5% by mass or more, more preferably in a proportion of 8% by mass or more, particularly preferably in a proportion of 10% by mass or more, and 12% by mass. It is most preferable to include it in the above ratio. A preferable upper limit is 50% by mass. When the non-woven fabric contains core-sheath type ultrafine conjugate fibers as the ultra-fine fibers 2 in a ratio within this range, since core-sheath type conjugate fibers with a small fineness (less than 0.6 dtex) are included, core-sheath type conjugate fibers with a large fineness are included in the same proportion. It has higher mechanical strength compared to non-woven fabrics containing Moreover, a short fiber nonwoven fabric that is thin and has excellent mechanical strength can be obtained.

When the ultrafine fibers are contained in an amount of 10% by mass or more, the short fiber nonwoven fabric may contain fibers other than the ultrafine fibers formed from the splittable conjugate fibers in an amount of 90% by mass or less. The other fibers may be natural or regenerated fibers, or may be monofilaments and composite fibers of synthetic resins. Alternatively, other fibers may include microfibers formed from other splittable composite fibers. Alternatively, the other fibers may not be ultrafine fibers formed from splittable conjugate fibers, but may be ultrafine fibers manufactured by a single spinning method and having a fineness of less than 0.6 dtex. Alternatively, the short fiber nonwoven fabric is made up of only fibers originating from the splittable conjugate fibers (ultrafine fibers 1 originating from the first segment, ultrafine fibers 2 originating from the second segment, and fibers originating from the splittable conjugate fibers due to the splitting not proceeding completely. (including fibers with large fineness and fibers in which branching occurs in a single fiber, etc.), or may be composed only of ultrafine fibers formed from the splittable conjugate fibers.

The short fiber nonwoven fabric preferably has a total amount of small fineness (less than 0.6 dtex) fibers in the short fiber nonwoven fabric of preferably 10% by mass or more, more preferably 20% by mass or more, and 50% by mass. % or more is even more preferred, and most preferably 70% by mass or more. Note that a preferable upper limit is 100% by mass. When the total amount of fibers with a small fineness (less than 0.6 dtex) in the short fiber nonwoven fabric is within the above range, a thin short fiber nonwoven fabric can be easily obtained. The fibers with a small fineness (less than 0.6 dtex) that occupy the short fiber nonwoven fabric may be only the ultrafine fiber 1, or only the ultrafine fiber 1 and the ultrafine fiber 2, or may be composed of these and other ultrafine fibers. .

In the short fiber nonwoven fabric, the splittable conjugate fibers of one or more embodiments of the present invention can be split by applying a physical impact. For example, it can be carried out by hydroentangling treatment (injecting high-pressure water jets).

The short fiber nonwoven fabric is produced by producing a fibrous web according to a known method, and then, if necessary, subjecting it to heat treatment to thermally bond the fibers together. Furthermore, the fibrous web may be subjected to fiber entanglement treatment, if necessary. The fibrous web is produced, for example, by a dry method such as a card method or an airlay method using splittable conjugate fibers having a fiber length in a range of 25 mm or more and 75 mm or less. When used in fields such as personal/objective wipers and filters, it is preferable to use a nonwoven fabric produced by a dry method such as a card method or an airlay method. This is because the nonwoven fabric produced by the dry method has a soft texture and an appropriate density.

The fibrous web may then be subjected to a thermal bonding treatment. For example, since the ultrafine fiber 2 is a core-sheath type ultrafine conjugate fiber, the fibers may be adhered to each other by a sheath component of the core-sheath type ultrafine conjugate fiber. Alternatively, core-sheath type conjugate fibers may be added to the splittable conjugate fibers, and the fibers may be adhered to each other by the sheath component of the core-sheath type conjugate fibers. The conditions for the thermal bonding treatment are appropriately selected depending on the basis weight of the fiber web, the cross-sectional form of the core-sheath type ultrafine conjugate fiber, the type of resin constituting the fibers contained in the nonwoven fabric, and the like. For example, as the heat treatment machine, a cylinder dryer, a hot air blowing machine, a hot roll machine, a hot embossing machine, or the like can be used. The thermal bonding treatment is selected depending on the intended use of the obtained short fiber nonwoven fabric. If short fiber nonwoven fabrics are used for applications that require soft, bulky nonwoven fabrics, such as wiping sheets for people/objects or surface sheets for absorbent articles, air-through processing using a hot air blowing processing machine that does not apply pressure is the heat treatment process. It is preferable to do this. If the short fiber nonwoven fabric is used for applications requiring hardness and stiffness, such as polishing cloth, it is preferable that the thermal bonding treatment be performed with a cylinder dryer or hot roll processing machine that applies pressure to the fiber web. The temperature at which the thermal bonding treatment is performed is not particularly limited, but is preferably 100°C or more and 150°C or less, more preferably 120°C or more and 145°C or less.

As described below, when the fibrous web is subjected to hydroentangling treatment, it is preferable to carry out the thermal bonding treatment before hydroentangling treatment. If the fibers of the fiber web are joined together in advance and then hydroentangled, the fibers are less likely to escape when the fibers are exposed to a high-pressure water stream, and the fibers can be tightly entangled with each other. Fiber division is further promoted. Of course, the thermal bonding treatment may be performed after the fibers are entangled with each other. That is, the order of thermal bonding treatment and hydroentangling treatment is not particularly limited as long as a desired nonwoven fabric can be obtained.

In the short fiber nonwoven fabric, the fibers may be entangled with each other. As the treatment for entangling the fibers, a hydroentanglement treatment in which the fibers are entangled with each other by the action of a high-pressure water stream is preferably used. According to the hydroentangling treatment, fibers can be firmly entangled with each other without impairing the density of the entire nonwoven fabric. In addition, by the hydroentangling treatment, it is possible to simultaneously advance the intertwining of the fibers and the intertwining of the ultrafine fibers generated by the splitting and splitting of the splittable conjugate fibers.

Conditions for the hydroentangling treatment are appropriately selected depending on the type and basis weight of the fibrous web used, the type and proportion of fibers contained in the fibrous web, and the like. For example, when a fibrous web with a basis weight of 10 g/m ² or more and 120 g/m ² or less is subjected to hydroentangling treatment, the fibrous web is preferably placed on a support such as a plain weave structure with a pore size of 70 mesh or more and 100 mesh or less. From a nozzle in which orifices of 0.05 mm or more and 0.3 mm or less are provided at intervals of 0.5 mm or more and 1.5 mm or less, a columnar water stream with a water pressure of 1 MPa or more and 20 MPa or less is applied to one or both sides of the fiber web 1 to 10 times each. Can be injected. The water pressure of the columnar water stream is more preferably 1.5 MPa or more and 15 MPa or less, and even more preferably 2 MPa or more and 10 MPa or less. The fibrous web after the hydroentanglement treatment is subjected to a drying treatment, if necessary.

The short fiber nonwoven fabric may be subjected to a hydrophilic treatment if necessary. The hydrophilic treatment may be carried out using any method such as fluorine gas treatment, vinyl monomer graft polymerization treatment, sulfonation treatment, electric discharge treatment, surfactant treatment, or hydrophilic resin imparting treatment.

The short fiber nonwoven fabric preferably has a basis weight of 10 g/m ² or more and 120 g/m ² or less, more preferably 15 g/m ² or more and 100 g/m ² or less, and even more preferably 20 g/m ² or more. It has a basis weight of 80 g/m ² or less, particularly preferably 25 g/m ² or more and 60 g/m ² or less. When the basis weight of the fibrous web is 2 g/m ² or more, the resulting fibrous web and short fiber nonwoven fabric will have good texture, and the short fiber nonwoven fabric will tend to have high strength and puncture strength. When the basis weight of the fibrous web is 100 g/m ² or less, the air permeability of the short fiber nonwoven fabric does not decrease, and the splittable conjugate fibers of one or more embodiments of the present invention contained in the fibrous web can be subjected to the hydroentangling treatment described below. This makes it easier for the high-pressure water stream to act uniformly on the entire fiber web when dividing it into each component, making it easier to sufficiently divide the splittable conjugate fibers.

Furthermore, the present invention allows the ultrafine fibers to be bonded to each other by the sheath component of the core-sheath type ultrafine conjugate fiber formed from the second segment. I can do it.

The short fiber nonwoven fabric can be used as a dry wiping sheet. In that case, liquid paraffin or the like may be attached as necessary. Dry wiping sheets may be used to remove dirt or liquids from surfaces, or may be used to apply wax to furniture, floors, or automobiles, or to apply cosmetics to the skin. .

Further, the short fiber nonwoven fabric can be used as a wet wiping sheet by attaching a wetting agent to the short fiber nonwoven fabric by methods such as impregnation, spraying, and coating. Here, the wetting agent refers to a liquid that wets the wiping sheet, such as water, alcohol, various functional agents (e.g., surfactants, detergents, preservatives, antifogging agents, cosmetics, etc.), or any of these. A mixture, etc. The wetting agent may be attached in an amount of 1000 parts by mass or less, preferably in an amount of 50 parts by mass or more and 500 parts by mass or less, and 50 parts by mass or more, per 100 parts by mass of the short fiber nonwoven fabric. It is more preferable to deposit it in an amount within a range of 300 parts by mass or less. Wet wiping sheets may also be used as wiping sheets or to apply impregnated liquids to objects (including people).

More specifically, when using a wet wiping sheet as a wiping sheet for OA equipment, alcohol (especially ethanol) should be contained in an amount of 1% by mass or more and 30% by mass or less, and a cleaning agent should be contained in an amount of 0.1% by mass or more and 1% by mass or less. It is preferable to attach a wetting agent containing 0.0% by mass or less, a preservative (especially paraben) of 0.3% by mass or more and 1.0% by mass or less, and purified water as the balance. When using a wet wiping sheet as a wiping sheet for cleaning window glass, the alcohol (especially ethanol) should be 5% by mass or more and 30% by mass or less, and the cleaning agent should be 0.1% by mass or more and 1.0% by mass or less. , preservatives (especially industrial preservatives) from 0.5% by mass to 2.0% by mass, chelating agents from 0.05% by mass to 0.2% by mass, humectants from 1.0% by mass to 5 It is preferable to attach a wetting agent containing .0% by mass or less, and the balance containing purified water.

More specifically, wet wiping sheets for personal use are provided as, for example, hand wipes, baby wipes, menstrual blood wipes, makeup remover sheets, facial cleansing sheets, antiperspirant sheets, and nail removers.

When providing a wet wiping sheet as a liquid-impregnated skin covering sheet for personal use such as a personal face mask, a keratin care sheet, and a decolletage sheet, a liquid containing an active ingredient (for example, a cosmetic) is added to 100 parts by mass of the nonwoven fabric. The impregnation amount may be 150 parts by mass or more and 2500 parts by mass or less. The active ingredients are not particularly limited, but include, for example, a moisturizing ingredient, a keratin softening ingredient, a cleansing ingredient, an antiperspirant ingredient, a fragrance ingredient, a whitening ingredient, a blood circulation promoting ingredient, an ultraviolet ray prevention ingredient, and a slimming ingredient.

A face mask has a shape suitable for covering the face, and is further provided with openings or notches formed by punching as necessary, for example, in areas corresponding to the eyes, nose, and mouth. can be provided. Alternatively, the face mask may be shaped to cover only a portion of the face (eg, around the eyes, mouth, nose, or cheeks). Alternatively, the face mask may be provided as a set consisting of a sheet that covers the area around the eyes and a sheet that covers the area around the mouth. Alternatively, it may be provided as a set of sheets that separately cover three or more parts.

A keratin care sheet is a skin covering sheet used on heels, elbows, knees, etc. where the keratin is thick and hardens easily.It moisturizes and softens the keratin by impregnating it with a liquid containing keratin softening ingredients and moisturizing ingredients. It is a sheet that promotes the removal of excess dead skin and a sheet that promotes the removal of excess dead skin. The short fiber nonwoven fabric of one or more forms of the present invention can be used as a base material in a keratin care sheet that exhibits any effect or efficacy. A keratin care sheet, for example, a keratin care sheet for heels, has notches and/or notches, and/or a part of the sheet is punched out to form an opening so that the sheet can easily match the curve of the heel when pasted. Provided in a form with

Liquid-impregnated skin covering sheets are used to moisturize or otherwise care for any part of the body (for example, the neck, the back of the hand, or the area from the neck to the chest (also called the décolletage)). It may also be a moisturizing sheet impregnated with a liquid containing other benefits. Alternatively, the liquid-impregnated skin covering sheet may be a slimming sheet impregnated with a liquid containing a slimming component. The slimming sheet is used by being attached to the thigh or abdomen, for example.

A dry wiping sheet for personal use or a wet wiping sheet for personal use may be provided with a nonwoven fabric as a base material folded. Since the short fiber nonwoven fabric of one or more embodiments of the present invention is easy to unfold from a wet and folded state, it may be provided in a state of being folded multiple times in order to be stored in a predetermined packaging bag or container. suitable for The folding may be carried out only in one direction of the non-woven fabric, or may be carried out one or more times in each different direction of the non-woven fabric. For example, a liquid-impregnated nonwoven fabric is folded one or more times in a direction parallel to the machine direction (i.e., the folds are parallel to the machine direction), and then folded in a direction parallel to the transverse direction (i.e., the folds are parallel to the machine direction). may be folded one or more times (parallel to) to provide a wet wiping sheet or a liquid-impregnated skin covering sheet.

The present invention will be explained below using Examples and Comparative Examples, but these examples are for illustrating the present invention and are not intended to limit the present invention in any way.

The components used to produce the nonwoven fabrics of Examples and Comparative Examples are shown below.
<First component: polypropylene (PP)>
PP1: Mn after spinning = 9.6 x 10 ⁴ , Mw after spinning = 2.5 x 10 ⁵ , Mz after spinning = 5.3 x 10 ⁵ , Q value after spinning = 2.63, MFR230 (g/10 min) = 30, Japan Polypropylene Co., Ltd. SA03 (product name) manufactured by
The number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz) after spinning, and Q value after spinning were measured using a resin strand taken as a sample during melt spinning.
PP2: Prime Polymer Co., Ltd. Mn after spinning = 5.3 x 10 ⁴ , Mw after spinning = 2.8 x 10 ⁵ , Mz after spinning = 8.3 x 10 ⁵ , Q value after spinning = 5.21, MFR230 (g/10 min) = 30 S105HG (product name) manufactured by
The number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz) after spinning, and Q value after spinning were measured using a resin strand taken as a sample during melt spinning.

<Second component: polyethylene (PE)>
PE1: High-density polyethylene, HE490 (product name) manufactured by Japan Polyethylene Co., Ltd. with MFR190 (g/10 minutes) = 20
PE2: Linear low-density polyethylene, 431GD (product name) manufactured by Ube Maruzen Polyethylene Co., Ltd. with MFR190 (g/10 minutes) = 20

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

Weigh 5 mg of a sample containing polypropylene resin, and weigh 5 mL of 1,2,4-trichlorobenzene (TCB) containing 0.1% by mass of butylated hydroxytoluene (BHT) as a stabilizer and antioxidant to this sample. 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 substances such as undissolved sample from the solution in which the sample was dissolved, this solution was filtered through a metal filter to obtain a sample solution for measurement. The obtained measurement sample solution was injected into the gel permeation chromatography device at a flow rate of 1.0 mL/min and an injection volume of 0.2 mL (200 μL) to determine the number average molecular weight (Mn) and weight average molecular weight. (Mw) and z-average molecular weight (Mz) were measured. When measuring, TCB containing 0.1% by mass of BHT was used as the measurement solvent, and one column of Shodex (registered trademark) manufactured by Showa Denko K.K., product number HT-G, and Shodex (registered trademark) manufactured by Showa Denko K.K. were used as columns. The measurement was carried out using two columns of product number HT-806M and setting the temperature of the column constant temperature bath to 145°C.

In the present invention, the number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), and Q value of the polypropylene resin are measured using the polypropylene resin after spinning. The average molecular weight (namely, Mn, Mw, and Mz) and Q value of the polypropylene resin may differ before and after spinning. This is because the bonds between the molecules that make up relatively high molecular weight polypropylene molecules are broken by the heat during spinning, or because some of the relatively high molecular weight polypropylene molecules are chain-transferred to low molecular weight polypropylene molecules. It is assumed that.

When measuring the number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), and Q value (Mw/Mn) of the polypropylene resin after spinning, the sample used is the polypropylene resin to be measured. When performing melt spinning, the temperature of the extruder is set to 290°C, and the polypropylene resin is melted and extruded from the extruder without a spinning nozzle attached, and then cooled in the air to form a rod-shaped resin with a diameter of 5 to 8 mm. You can prepare a strand, cut this rod-shaped resin strand into a length of about 3 mm, and use it as a sample for measurement, or use the obtained split composite fiber as a sample for gel permeation chromatography or FT-IR analysis. The ratio of the two components at each molecular weight may be determined, and the weight average molecular weight (Mw), number average molecular weight (Mz), and Mw/Mn (Q value) of each component may be calculated by GPC curve fitting.

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

<Manufacture of splittable composite fiber of Example 1>
The fibers have the cross-sectional shape shown in FIG. 1, and PP1, a propylene homopolymer, is used as the core component of the first segment and the core-sheath type second segment, and high-density polyethylene is used as the sheath component of the core-sheath type second segment. Using PE1, the splittable composite fiber of Example 1 having 16 divisions was produced.

The splittable conjugate fiber of Example 1 was produced under the following spinning and drawing conditions. Using a split-type composite nozzle in which the cross-sectional structure of the extruded molten resin is as shown in Figure 1, propylene homopolymer (PP1) and high-density polyethylene (PE1) are charged into separate extruders and thoroughly melted. I let it happen. The discharge amount of the molten homopolypropylene resin and high-density polyethylene resin is at a ratio of PP1/PE1 volume ratio = 5/5 (first segment / second segment volume ratio = 2.5/7.5). The molten resin is extruded from each extruder so that the fineness is A spun filament of 6.0 dtex was obtained. Next, the spun filament was wet-stretched at 80°C using a water bath filled with 80°C warm water at a draw ratio of 3.1 times to obtain a drawn filament with a fineness of 2.14 dtex.

In order to evaluate the drawability of the spun filaments, the maximum draw ratio (Vmax) was measured by the following method. First, the obtained spun filament was set in a drawing device adjusted to a predetermined drawing temperature. At this time, the feeding speed (V ₁ ) of the roll feeding out the spun filament was set to 5 m/sec, and the winding speed (V ₂ ) of the metal roll on the winding side was gradually increased from 5 m/sec. Then, the winding speed of the metal roll on the winding side when the spun filament breaks is taken as the maximum drawing speed, and the ratio of the maximum drawing speed to the feed-out speed of the roll that sends out the undrawn fiber bundle (V ₂ /V ₁ ) was determined, and the obtained speed ratio was taken as the maximum stretching ratio (Vmax). It is preferable that the maximum draw ratio is 3 or more, since the drawing process can be carried out at a high draw ratio and a splittable conjugate fiber with a small fineness can be easily obtained.

When the maximum draw ratio of the spun filament of Example 1 was measured using the above method, the maximum draw ratio (Vmax) was 4.6 times. Therefore, the stretching ratio was 0.68 times the maximum stretching ratio (stretching ratio/Vmax=0.68). A fiber treatment agent containing an anionic surfactant as a main component is attached to the drawn filament so that the active ingredient is 0.3% by mass based on the mass of the fiber, and excess fiber treatment agent is dehydrated using nip rolls. The material was mechanically crimped using a stuffing box type crimper to give 15 crimps/25 mm. Then, the mechanically crimped drawn filament was simultaneously subjected to an annealing treatment and a drying treatment in a relaxed state for about 15 minutes using a hot air blowing device set at 100°C. The sufficiently dried drawn filament was cut into fiber lengths of 45 mm to obtain the splittable conjugate fiber of Example 1 in the form of short fibers. The production, structure, fineness, etc. of the splittable composite fiber of Example 1 are shown in Table 1 below.

<Production of splittable composite fibers of Examples 2 to 5 and Comparative Examples 1 and 2>
The splittable conjugate fibers of Examples 2 to 5 and Comparative Examples 1 and 2 were prepared according to the same method as the method for producing the splittable conjugate fiber of Example 1, except that the components, spinning conditions, and drawing conditions listed in Table 1 were used. The fibers were obtained in the form of short fibers with a fiber length of 45 mm. The production, structure, fineness, etc. of the splittable composite fibers of Examples 2 to 5 and Comparative Examples 1 to 2 are shown in Tables 1 and 2 below.

<Manufacture of splittable composite fibers of Comparative Examples 3 and 4>
Using a hollow 16-split spinning nozzle in which the cross-sectional structure of the extruded molten resin becomes the cross-section shown in FIG. 3 and a hollow part is formed in the center of the fiber cross-section, the components, spinning conditions, and stretching conditions listed in Table 2 were applied. Fibers were produced in the same manner as the method for producing the splittable conjugate fiber of Example 1, except that the splittable conjugate fiber of Comparative Example 3 (fiber length: 45 mm) was obtained.
In addition, using a solid 8-segment spinning nozzle in which the cross-sectional structure of the extruded molten resin becomes the cross-section shown in FIG. 4 and in which no hollow part is formed in the center of the fiber cross-section, Fibers were produced in the same manner as the method for producing the splittable conjugate fiber of Example 1, except that the stretching conditions were used, and the splittable conjugate fiber of Comparative Example 4 (fiber length: 45 mm) was obtained.

<Measurement of single fiber strength and elongation>
According to JIS L 1015 (2010), using a tensile tester, the sample grip interval was 20 mm, the load value when the fiber was cut was taken as the single fiber strength, and the elongation when the fiber was cut was taken as the elongation.

<Apparent Young's modulus>
Perform a tensile test using the above method, draw a load-elongation curve, determine the maximum slope up to the first yield point (initial tensile resistance) according to JIS L 1015 (2010) 8.11, and calculate the initial tensile strength. The apparent Young's modulus was determined from the resistance.

<Production of short fiber nonwoven fabric of Example 1>
Using the splittable composite fiber of Example 1, a carded web with a basis weight of about 50 g/m ² was produced using a parallel carding machine. Next, the carded web was placed on an 80-mesh plain weave transport support with a warp diameter of 0.2 mm and a weft diameter of 0.2 mm, and an orifice with a hole diameter of 0.12 mm was formed on the card web. A water stream with a water pressure of 2.5 MPa was injected twice from nozzles arranged in a straight line in the width direction of the web at 1 mm intervals, and the web was turned over and a water stream with a water pressure of 4 MPa was injected twice from the same nozzle to perform hydroentangling treatment. did. Next, the hydroentangled short fiber nonwoven fabric was dried and heat-treated at 45° C. for 45° C. using a hot air processing machine set at a temperature of 140° C., so that the sheath components of the ultrafine fibers 2 bonded the fibers together. , the short fiber nonwoven fabric of Example 1 was obtained. All of the splittable composite fibers of Example 1 had good card passability, and the texture of the obtained fiber web and hydroentangled nonwoven fabric was uniform.

(Production of short fiber nonwoven fabrics of Examples 2 to 5)
Nonwoven fabrics of Examples 2 to 5 were obtained using the same method as described in Example 1, except that the splittable conjugate fibers of Examples 2 to 5 were used. The splittable conjugate fibers of Examples 2 to 5 all had good card passability, and the resulting fiber webs and hydroentangled nonwoven fabrics had uniform texture.

(Manufacture of short fiber nonwoven fabric of Comparative Example 1)
Using the splittable composite fiber of Comparative Example 1, an attempt was made to produce a carded web with a basis weight of approximately 50 g/m ² using a parallel carding machine, but the fibers frequently wound around the inside of the carding machine. I couldn't.

(Manufacture of short fiber nonwoven fabrics of Comparative Examples 2 to 4)
Nonwoven fabrics of Comparative Examples 2 to 4 were obtained using the same method as described in Example 1, except that the splittable conjugate fibers of Comparative Examples 2 to 4 were used.

<Evaluation of card passability>
When a card web was produced using a parallel card machine, the card passageability was evaluated as follows.
A: A fibrous web with good texture can be obtained without the raw cotton wrapping around the carding machine or with neps.
B: A fibrous web is obtained, but the fibers are wrapped around the carding machine and neps are generated, resulting in poor texture of the fibrous web. C: The raw cotton often gets wrapped around the inside of the carding machine, making it difficult to produce a fibrous web. It's impossible.

<Evaluation of divisibility of hydroentangled nonwoven fabric>
When producing a hydroentangled nonwoven fabric using the above method, the fibrous web that has been entangled and divided by high-pressure water jets is taken out, thoroughly dried at room temperature, and the cross section of the dried fibrous web is examined using a scanning electron microscope (SEM). ), and the divisibility of the hydroentangled nonwoven fabric obtained from the splittable composite fibers was evaluated as follows.
A: In the cross section of the fibrous web, there are almost no fibers that maintain the fiber cross-sectional shape before the splitting treatment.
B: In the cross section of the fibrous web, there are a plurality of fibers that maintain the fiber cross-sectional shape before the splitting treatment.
C: In the cross section of the fibrous web, there are many fibers that maintain the fiber cross-sectional shape before the splitting treatment.

The splittable composite fibers of Examples 1 to 5 have a single fiber strength of 1.8 cN/dtex or more and 4.2 cN/dtex or less, an elongation of 30% or more and 200% or less, and an apparent Young's modulus of 700N. /mm ² or more and 4000 N/mm ² or less, the fibers did not split when passing through the card, and the card passing property was good, and the splitting property after hydroentangling was also good, and a high percentage of splitting occurred. The ultra-fine fibers create a hydroentangled nonwoven fabric that is smooth to the touch. On the other hand, the splittable conjugate fiber of Comparative Example 1 had poor card passability, and a fiber web could not be produced. The splittable composite fiber of Comparative Example 1 has the same fiber cross-sectional structure, first component, and second component as Example 1, but in the drawing process, dry drawing was performed to promote crystallization of the thermoplastic resin. In addition, dry stretching was carried out at a draw ratio close to the maximum draw ratio, which caused the first component, polypropylene, to crystallize and become too divisible, causing it to split inside the card machine when passing through the card. It is presumed that the object became entangled inside the aircraft or became stuck inside the aircraft. Similarly, the splittable conjugate fiber of Comparative Example 2 was drawn at a draw ratio close to the maximum draw ratio, although it was wet drawn, and as in Comparative Example 1, crystallization of the polypropylene proceeded too much and the splittability became too high. It is presumed that this caused the card to wrap around the inside of the card machine and cause nip.

The splittable conjugate fiber of Comparative Example 3 had good card passability, but when the cross section of the obtained hydroentangled nonwoven fabric was observed, it was found that the unsplit conjugate fiber was better compared to the nonwoven fabrics of Examples 1 to 5. There were many. The splittable conjugate fibers of Examples 1 to 5 have a structure in which segments of the fiber cross section are made of the first component and segments of a core-sheath structure in which the first component is the core component and the second component is the sheath component are arranged alternately. It has become. The first component is a resin component containing 50% by mass or more of polypropylene, and the second component is a resin component containing 50% by mass or more of polyethylene, and the polypropylene resin, which is harder than polyethylene resin, contains polyethylene resin. Because it is placed not only on both sides of the second segment, but also at the center of the second segment (i.e., the core component), it is easier for shocks such as high-pressure water to pass through the polypropylene resin and act on the polyethylene resin. Since the second segment has a core-sheath structure, strain caused by the difference in stretchability of the two resin components during the stretching process is not only caused between the first and second segments, but also between the core component of the second segment. Since this strain also occurs between the sheath component and the sheath component, it is presumed that this strain acts to be released during the splitting process, thereby increasing the splitting properties of hydroentangling. Unlike the splittable conjugate fibers of Examples 1 to 5, the above effect did not occur in the splittable conjugate fiber of Comparative Example 3 in which the first segment made of the first component and the second segment made of the second component were arranged alternately. Although it was not divided inside the card machine, it is thought that it was not divided sufficiently even after the hydroentangling treatment. Furthermore, like the splittable conjugate fiber of Comparative Example 3, the splittable conjugate fiber of Comparative Example 4 has a fiber cross-sectional structure in which first segments made of the first component and second segments made of the second component are arranged alternately. In addition, since the cross-sectional structure has no hollow portions, the contact area of the first and second segments is large, resulting in strong adhesion between the segments, and they are not sufficiently divided in the hydroentangling process. It is thought that there was no such thing.

This specification includes the following forms.
1.
A splittable composite fiber including a first segment and a second segment,
The first segment is a resin segment made of a first component,
The second segment is a core-sheath type resin segment with a cross-sectional structure in which the first component is a core component and the second component is 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 polyethylene resin,
The splittable composite fiber has a single fiber strength of 1.8 cN/dtex or more and 4.2 cN/dtex or less, an elongation of 30% or more and 200% or less, and an apparent Young's modulus of 700 N/mm ² or more and 4000 N. /mm ² or less, a splittable composite fiber.
2.
The ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polypropylene resin measured after spinning is 6 or less, and the weight of the polypropylene resin measured after spinning. The splittable conjugate fiber according to 1 above, which has an average molecular weight (Mw) of 750,000 or less.
3.
The splittable conjugate fiber according to 1 or 2 above, wherein the splittable conjugate fiber has a fiber length of 25 mm or more and 75 mm or less.
4.
In the splittable composite fiber, the volume ratio of the first component and the second component (first component/second component) is 8/2 or more and 3/7 or less, and the first segment and the second segment The splittable composite fiber according to any one of 1 to 3 above, wherein the volume ratio (first segment/second segment) is 2/8 or more and 8/2 or less.
5.
The polyethylene resin is one or more selected from the group consisting of high-density polyethylene resin and linear low-density polyethylene resin, and the polyethylene resin conforms to JIS K 7210 (measurement temperature 190°C, load 2.16 kgf (21.18 N)). )) The splittable conjugate fiber according to any one of 1 to 4 above, which has a melt mass flow rate of 5 g/10 minutes or more and less than 30 g/10 minutes.
6.
A short fiber nonwoven fabric containing 20% by mass or more of the splittable conjugate fibers according to any one of 1 to 5 above.
7.
A method for producing a splittable conjugate fiber according to any one of 1 to 5 above, comprising:
A resin component containing 50% by mass or more of polypropylene resin is used as the first component, a resin component containing 50% by mass or more of polyethylene resin is used as the second component, melt-spun with a melt-spinning machine equipped with a split type composite nozzle, and the above-mentioned A spun filament comprising a first segment that is a resin segment made of a first component, and a second segment that is a core-sheath type resin segment whose cross-sectional structure includes the first component as a core component and the second component as a sheath component. The process of obtaining
A method for producing a splittable conjugate fiber, comprising the step of wet-drawing the spun filament at a temperature of 60° C. or higher and 100° C. or lower, and at a draw ratio of 0.58 times or more and 0.88 times or less of the maximum draw ratio.

The splittable conjugate fiber of one or more embodiments of the present invention is a splittable conjugate fiber that can bond between ultrafine fibers by heating by making one of the resin segments a core-sheath type resin segment, and has good card passability. , a short fiber nonwoven fabric with a soft texture can be produced. Examples of the short fiber nonwoven fabric of one or more embodiments of the present invention include various wiping sheets for personal and/or objective wipers, cosmetic-impregnated skin covering sheets such as face masks, disposable baby diapers, nursing care diapers, sanitary napkins, etc. It is useful as a sheet for absorbent articles such as a top sheet, a second sheet, and a back sheet constituting an absorbent article.

1: First segment 2: Second segment 4, 14: Core component 6, 16: Sheath component 8: Hollow 10, 20, 30, 40: Split type composite fiber

Claims (6)

A splittable composite fiber including a first segment and a second segment,
The first segment is a resin segment made of a first component,
The second segment is a core-sheath type resin segment with a cross-sectional structure in which the first component is a core component and the second component is 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 polyethylene resin,
The volume ratio of the first component and the second component (first component/second component) is 8/2 or more and 3/7 or less, and the volume ratio of the first segment and the second segment (first segment /2nd segment) 2/8 or more and 8/2 or less,
the first segments and the second segments are arranged alternately and radially;
The splittable composite fiber has a single fiber strength of 1.8 cN/dtex or more and 4.2 cN/dtex or less, an elongation of 30% or more and 200% or less, and an apparent Young's modulus of 700 N/mm ² or more and 4000 N. / ^mm2 or less,
A splittable conjugate fiber, wherein 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 2 or more and less than 5. 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 2 or more and 4.5 or less, and the The splittable conjugate fiber according to claim 1, wherein the polypropylene resin has a weight average molecular weight (Mw) of 150,000 or more and 750,000 or less. The splittable conjugate fiber according to claim 1 or 2, wherein the splittable conjugate fiber has a fiber length of 25 mm or more and 75 mm or less. The polyethylene resin is one or more selected from the group consisting of high-density polyethylene resin and linear low-density polyethylene resin, and the polyethylene resin is measured according to JIS K 7210 at a temperature of 190°C and a load of 2.16 kgf (21.18 N). ) The splittable conjugate fiber according to any one of claims 1 to 3 , which has a melt mass flow rate of 5 g/10 minutes or more and less than 30 g/10 minutes. A short fiber nonwoven fabric containing 20% by mass or more of the splittable conjugate fiber according to any one of claims 1 to 4 . A method for producing a splittable conjugate fiber according to any one of claims 1 to 5 , comprising:
A resin component containing 50% by mass or more of polypropylene resin is used as the first component, a resin component containing 50% by mass or more of polyethylene resin is used as the second component, melt-spun with a melt-spinning machine equipped with a split type composite nozzle, and the above-mentioned A spun filament comprising a first segment that is a resin segment made of a first component, and a second segment that is a core-sheath type resin segment whose cross-sectional structure includes the first component as a core component and the second component as a sheath component. The process of obtaining
A method for producing a splittable conjugate fiber, comprising the step of wet-drawing the spun filament at a temperature of 60° C. or higher and 100° C. or lower, and at a draw ratio of 0.58 times or more and 0.88 times or less of the maximum draw ratio.

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