Nonwoven fabric and method for producing the same

Abstract

To provide a nonwoven fabric reduced in unintentionally fused places of fibers, and a method of producing the same.SOLUTION: A nonwoven fabric has a layer including fibers containing a thermoplastic resin, and an electric charge regulator. The electric charge regulator is contained in the fiber by 1 mass% or more and 20 mass% or less. When the constituting fibers in the layer are observed, a percentage of the constituting fibers in which portions where the constituting fibers are fused to join together, are observed along a longitudinal direction of the constituting fibers, is 9% or more and 15% or less, by the number of fibers. The fiber favorably includes a triglyceride. It is also favorable that the triglyceride contains a group derived from a fatty acid, and that the group is a hydrocarbon group having no unsaturated bond.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a nonwoven fabric and a method for manufacturing the same.

Background Art

[0002] The melt blowing method and the electrospinning method are methods suitable for manufacturing nonwoven fabrics made of fine-diameter fibers. Taking advantage of such characteristics, melt blown nonwoven fabrics are used in various fields such as filters, sanitary products, clothing, packaging materials, and battery separators.

[0003]

[0004] For example, Patent Document 1 describes a manufacturing apparatus having a melt blow die in which nozzles for extruding a molten polymer as filaments are arranged in parallel, and a conveyor 1 for collecting and transporting the filaments extruded from the nozzles. Immediately below the melt blow die, a high-voltage applying member for charging the filaments extruded from the nozzles is arranged, and further below that, an electric field generating member for generating an electric field such that the polarities alternate on both sides of the charged filaments is arranged.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the technique described in Patent Document 1, since the melt blowing method is adopted, a nonwoven fabric with a small fiber diameter can be produced with high productivity. However, since the pitch of the nozzles is set narrow for the purpose of increasing productivity and no mention is made of a charge control agent and it is considered that the charge amount is insufficient, the discharged molten polymers are likely to fuse with each other while being stretched. Due to this, fibers having thick portions are likely to be generated, and this is one of the factors that increase the variation in the fiber diameter of the fibers constituting the nonwoven fabric. Since the technique described in Patent Document 2 uses the electrospinning method, it has the advantage that it is easier to make the fibers thinner than the melt blowing method. However, since it is not easy to narrow the pitch of the nozzles, it is not easy to increase the productivity of the nonwoven fabric.

[0007] Therefore, an object of the present invention is to provide a nonwoven fabric in which unintended fused portions of fibers are reduced and a method for manufacturing the same.

Means for Solving the Problems

[0008] The present invention is a nonwoven fabric having a layer containing fibers containing a thermoplastic resin and a charge control agent, wherein the charge control agent is contained in the fibers in an amount of 1% by mass or more and 20% by mass or less, and when observing the constituent fibers of the layer, the ratio of the constituent fibers in which fused portions between the constituent fibers are observed along the longitudinal direction of the constituent fibers is 9% or more and 15% or less on a number basis.

[0009] The present invention is a method for manufacturing a nonwoven fabric in which a melt of a composition containing a thermoplastic resin is discharged from a plurality of nozzles, the discharged melt is stretched by a hot air flow and spun, and the fibers generated by the spinning are deposited on a collector, wherein the pitch between adjacent nozzles is 0.15 mm or more and 2.85 mm or less, A method for manufacturing a non-woven fabric is provided, in which the molten material is discharged from the nozzle to perform spinning under a state where an electric field is generated by a high-voltage application unit installed at a position separated from the opening end of the nozzle by a predetermined distance.

Advantages of the Invention

[0010] The non-woven fabric of the present invention has reduced unintended fiber fusion points. Further, according to the manufacturing method of the present invention, such a non-woven fabric can be manufactured with high productivity.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described based on its preferred embodiments. The present invention relates to a non-woven fabric. The non-woven fabric of the present invention is formed by randomly depositing fibers. The non-woven fabric of the present invention is composed of a single type of fiber or a plurality of types of fibers. When the non-woven fabric of the present invention is composed of a single type of fiber, or when it is composed of a plurality of types of fibers and the plurality of types of fibers are in a mixed state, the non-woven fabric can be a single-layer non-woven fabric. When the nonwoven fabric of the present invention is composed of a plurality of types of fibers, the nonwoven fabric can be a single nonwoven fabric composed of a plurality of layers having at least a first layer containing a first fiber and a second layer containing a second fiber different from the first fiber.

[0013] The nonwoven fabric of the present invention has at least a layer containing fibers containing a thermoplastic resin and a charge control agent (hereinafter, this fiber is also simply referred to as "thermoplastic fiber"). In the following description, when referring to "constituent fibers", it is intended to mean all the fibers contained in the nonwoven fabric of the present invention. Therefore, the above-mentioned "thermoplastic fiber" is included in the category of "constituent fibers". When the nonwoven fabric of the present invention is composed of only one type of fiber, the "constituent fibers" refer to the "thermoplastic fiber" itself. On the other hand, when the nonwoven fabric of the present invention is a blended fabric of "thermoplastic fiber" and a fiber not containing a charge control agent, the "constituent fibers" refer to the general term for "thermoplastic fiber" and a fiber not containing a charge control agent.

[0014] The above-mentioned thermoplastic resin preferably has fiber-forming ability. Various thermoplastic resins having fiber-forming ability are known in the art. For example, polyolefin resins such as polyethylene, polypropylene, and ethylene-α-olefin copolymer; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polylactic acid, and liquid crystal polymer; polyamide resins such as nylon 6 and nylon 66; vinyl-based polymers such as polyvinyl chloride, polyvinylidene chloride, and polystyrene; acrylic-based polymers such as polyacrylic acid, polyacrylate, polymethacrylic acid, and polymethacrylate; polyvinyl acetate and polyvinyl acetate-ethylene copolymer; etc. can be used in the present invention. In particular, using a polyolefin resin as the thermoplastic resin having fiber-forming ability is preferable from the viewpoint of being easy to manufacture fine-diameter fibers.

[0015] As the polyolefin resin, for example, homopolymers or copolymers of lower olefins such as ethylene and propylene can be used. Specifically, polyethylene, polypropylene, and ethylene-α-olefin copolymers can be mentioned. Examples of polyethylene include high-density polyethylene, low-density polyethylene, and linear low-density polyethylene.

[0016] Examples of polypropylene include isotactic polypropylene and syndiotactic polypropylene. Also, as polypropylene, low stereoregular homopolypropylene can be used. Low stereoregular homopolypropylene is a homopolypropylene in which the mesopentad fraction (mmmm [%]) measured by 13C-NMR is 90% or less, which is an index of stereoregularity. 13 It is a homopolypropylene in which the mesopentad fraction (mmmm [%]) measured by 13C-NMR is 90% or less. Examples of the ethylene-α-olefin copolymer include copolymers of α-olefins such as propylene, 1-butene, 1-pentene, and 1-hexene with ethylene. Examples of the copolymer form include random copolymers, block copolymers, and graft copolymers. In particular, it is preferable to use a random copolymer of ethylene and propylene (hereinafter also referred to as "random propylene copolymer").

[0017] Among these polyolefin resins, from the viewpoints of high fiber-forming ability and ease of manufacturing fine-diameter fibers, it is preferable to use polypropylene and polyolefins containing propylene as a copolymer component.

[0018] Further, the polyolefin resin is preferably a blend of homopolypropylene and a random propylene copolymer or a low stereoregular homopolypropylene. In this case, the proportion of the random propylene copolymer or the low stereoregular homopolypropylene is preferably 5% by mass or more based on the polyolefin resin from the viewpoint of further improving the water resistance and anti-seepage of the nonwoven fabric, more preferably 15% by mass or more, still more preferably 20% by mass or more from the viewpoint of further improving the water resistance and anti-seepage. Further, the proportion is preferably less than 60% by mass from the viewpoint of enhancing the spinnability of the fiber, more preferably 55% by mass or less, still more preferably 50% by mass or less from the viewpoint of further enhancing the spinnability.

[0019] The thermoplastic fiber may contain only one kind of the above-described polyolefin resin, or may contain two or more kinds. The thermoplastic fiber may contain only the above-described polyolefin resin, or may contain another thermoplastic resin in addition to the polyolefin resin. In the latter case, it is preferable that the polyolefin resin described above is contained in an amount of 50% by mass or more as the constituent resin of the thermoplastic fiber.

[0020] The thermoplastic fiber preferably contains a charge control agent in addition to the above-described thermoplastic resin. The charge control agent is a substance that can promote the degree of polarization and ionization of the thermoplastic resin when the thermoplastic resin is placed in an electric field, and can charge the thermoplastic resin. For this purpose, it is preferable to use a substance having various salt structures as the charge control agent.

[0021] The charge control agent preferably has a salt structure that melts and ionizes, for example. In particular, the charge control agent is preferably a compound having a salt structure with a melting point at a temperature not higher than the melting point of the thermoplastic resin used in combination therewith. In order to adjust this melting point, it is also preferable to use a mixture of two or more kinds of the compounds. The charge control agent forms an ionized state in the thermoplastic resin, which is preferable in terms of increasing the charge amount of the thermoplastic resin. From the perspective of dispersibility in the thermoplastic resin, the charge control agent is preferably an organic salt, and particularly preferably a salt of an organic acid and an inorganic base. For example, compounds having a quaternary ammonium base structure, metal soaps forming metal salts, etc. are preferred. Further, an organic sulfonate having an alkyl group at the terminal in the molecular structure and a sulfonate group at an arbitrary position in the molecular structure, or an organic sulfonate having an alkylene group in a part of the molecular structure and a sulfonic acid group at an arbitrary position in the molecular structure (hereinafter, these compounds are collectively also referred to as "alkyl sulfonates") are also preferred.

[0022] When using a compound having the above-mentioned quaternary ammonium base structure as the charge control agent, examples of the compound include a styrene acrylic resin having a quaternary ammonium base structure. When using the above-mentioned metal soap as the charge control agent, examples of the metal soap include fatty acid salts of divalent or higher, such as Zn stearate, Mg stearate, Li stearate, Ca stearate, Ba stearate, Zn laurate, Ca laurate, Ba laurate, Ca ricinoleate, Ba ricinoleate, Zn ricinoleate, etc. By using these metal soaps alone or in combination of two or more, the absolute value of the electrical impedance during melting of the thermoplastic resin can be easily reduced, thereby facilitating the spinning of fine-diameter fibers.

[0023] Examples of the alkyl sulfonate include alkylbenzene sulfonate (R-Ph-SO 3 M), higher alcohol sulfate ester salt (R-O-SO 3 M), polyoxyethylene alkyl ether sulfate (R-O-(CH 2 CH 2 O) n -SO 3 M), alkyl sulfosuccinate (R-O-CO-C-C(-SO 3 M)-O-CO-M), dialkyl sulfosuccinate (R-O-CO-C-C(-SO 3 M)-O-CO-R), α-sulfo fatty acid ester (R-CH(-SO 3 M)-COOCH3 ) α-olefin sulfonate (R-CH=CH-(CH 2 ) n -SO 3 M, R-CH(-OH)(CH 2 ) n -SO 3 M), acyl taurine salt (R-CO-NH 2 -(CH 2 ) 2 -SO 3 M), acyl alkyl taurine salt (R-CO-NH(-R’)-(CH 2 ) 2 -SO 3 M), alkane sulfonate (R-SO 3 M), etc. may be mentioned. In these alkyl sulfonates, R represents an alkyl group. The number of carbon atoms of R is preferably 8 or more and 22 or less, more preferably 10 or more and 20 or less, and even more preferably 12 or more and 18 or less. R’ also represents an alkyl group, and the number of carbon atoms thereof is preferably 5 or less. Ph represents a phenyl group which may be substituted. M represents a monovalent cation, preferably a metal ion, and more preferably a sodium ion. n preferably represents a number of 6 or more and 24 or less, more preferably 8 or more and 22 or less, and even more preferably 10 or more and 20 or less. The above alkyl sulfonates may be used alone or as a mixture of two or more. Among the above alkyl sulfonates, from the viewpoint of high charging effect of the resin, acyl taurine salt (R-CO-NH 2 -(CH 2 ) 2 -SO 3 M), acyl alkyl taurine salt (R-CO-NH(-R’)-(CH 2 ) 2 -SO 3 M) and alkane sulfonate (R-SO 3 M) are preferably used. Also, from the viewpoint of heat resistance, acyl taurine salt (R-CO-NH 2 -(CH 2 ) 2 -SO 3 M) and acyl alkyl taurine salt (R-CO-NH(-R’)-(CH2 ) 2 -SO 3 M) is more preferably used.

[0024] From the viewpoint of imparting an appropriate charge amount for spinning to the thermoplastic resin in a molten state, the proportion of the charge control agent in the thermoplastic fiber is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more in the thermoplastic fiber. Further, from the viewpoint of dispersibility in the thermoplastic resin, it is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. From these viewpoints, the charge control agent is preferably contained in the thermoplastic fiber in an amount of 1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less.

[0025] In addition to containing the above-described thermoplastic resin and charge control agent, the thermoplastic fiber can contain triglyceride as necessary. By incorporating triglyceride into the thermoplastic fiber, the surface tension of the thermoplastic fiber can be reduced, and the water resistance and anti-seepage properties of the nonwoven fabric of the present invention can be enhanced. In other words, sufficient water pressure resistance and anti-seepage properties can be imparted to the nonwoven fabric of the present invention. This advantage becomes more prominent as the diameter of the thermoplastic fiber becomes smaller. The triglyceride may be present in a state of adhering to the surface of the thermoplastic fiber, or may be kneaded into the thermoplastic resin constituting the thermoplastic fiber and present therein.

[0026] The triglyceride used in the present invention is preferably represented by the following formula (1).

[0027]

Chemical formula

[0028] In the formula, R 1 to R 3 represent the same or different hydrocarbon groups. R 1 to R 3At least one of them is a group derived from a fatty acid having 16 to 22 carbon atoms, and the group is a hydrocarbon group having no unsaturated bond and no substituent. Note that the number of carbon atoms in the alkyl group of palmitic acid, which is a fatty acid having 16 carbon atoms, is 15. The "hydrocarbon group having no unsaturated bond" means a hydrocarbon group having neither a carbon-carbon double bond nor a triple bond. That is, it is an alkyl group. Further, the "hydrocarbon group having no substituent" means that the hydrogen atoms contained in the hydrocarbon group are not substituted by other atoms or atomic groups (for example, a hydroxyl group). Therefore, the "hydrocarbon group having no unsaturated bond and no substituent" is synonymous with an unsubstituted alkyl group. In the following description, the triglyceride used in the present invention is also conveniently referred to as the "triglyceride of the present invention".

[0029] In the triglyceride represented by the formula (1), from the viewpoint of obtaining a nonwoven fabric having even higher water resistance and anti-bleeding properties, R 1 to R 3 At least one of them is preferably a group derived from a fatty acid having 16 to 20 carbon atoms, and the group is preferably a hydrocarbon group having no unsaturated bond and no substituent, and more preferably a group derived from a fatty acid having 16 to 18 carbon atoms, and the group is preferably a hydrocarbon group having no unsaturated bond and no substituent. Further, in the triglyceride represented by the formula (1), when any one or two of R 1 to R 3 is a group other than a group derived from a fatty acid having 16 to 22 carbon atoms (the group is a hydrocarbon group having no unsaturated bond and no substituent), the type of the group is not particularly limited as long as it is a group derived from a fatty acid, but from the viewpoint of obtaining a nonwoven fabric having even higher water pressure resistance, it is preferable that the group has no unsaturated bond and no substituent.

[0030] The triglyceride of the present invention preferably has the number of carbon atoms of the fatty acid residue adjusted. Specifically, it is preferably the following (a) or (b) as the triglyceride. (a) A triglyceride containing a mixture of a triglyceride containing at least one group derived from a fatty acid having 16 carbon atoms (i.e., palmitic acid) (the group is a hydrocarbon group having no unsaturated bond and no substituent) in one molecule and a triglyceride containing at least one group derived from a fatty acid having 18 carbon atoms (i.e., stearic acid) (the group is a hydrocarbon group having no unsaturated bond and no substituent) in one molecule. (b) A triglyceride containing a triglyceride containing at least one group derived from a fatty acid having 16 carbon atoms and at least one group derived from a fatty acid having 18 carbon atoms in one molecule.

[0031] When the triglyceride of the present invention contains a plurality of types of triglycerides as in the case of (a), at least one type of triglyceride preferably contains at least one group derived from a saturated fatty acid having 16 carbon atoms in one molecule (this triglyceride is also referred to as "triglyceride 16"). Triglyceride 16 may contain one group derived from a saturated fatty acid having 16 carbon atoms in one molecule (this triglyceride is also referred to as "triglyceride P"), two groups (this triglyceride is also referred to as "triglyceride PP"), or three groups (this triglyceride is also referred to as "triglyceride PPP"). In addition, there is no particular limitation on the type of the remaining fatty acid residues in triglyceride P and triglyceride PP, and they can be, for example, residues of saturated fatty acids having 12 to 24 carbon atoms.

[0032] Triglyceride 16 may be composed only of triglyceride P, only of triglyceride PP, or only of triglyceride PPP. Triglyceride 16 may be a combination of two or more selected from triglyceride P, triglyceride PP, and triglyceride PPP. For example, triglyceride 16 may be a combination of triglyceride P and triglyceride PP, a combination of triglyceride P and triglyceride PPP, a combination of triglyceride PP and triglyceride PPP, or a combination of triglyceride P, triglyceride PP, and triglyceride PPP.

[0033] When the triglyceride of the present invention contains a plurality of types of triglycerides as in the case of (a), it is also preferable that at least one type of triglyceride contains at least one group derived from a saturated fatty acid having 18 carbon atoms in one molecule (this triglyceride is also referred to as "triglyceride 18"). Triglyceride 18 may contain one group derived from a fatty acid having 18 carbon atoms in one molecule (this triglyceride is also referred to as "triglyceride S"), may contain two groups (this triglyceride is also referred to as "triglyceride SS"), or may contain three groups (this triglyceride is also referred to as "triglyceride SSS"). Note that there are no particular restrictions on the types of the remaining fatty acid residues in triglyceride S and triglyceride SS, and they can be, for example, residues of saturated fatty acids having 12 to 24 carbon atoms.

[0034] Triglyceride 18 may be composed only of triglyceride S, may be composed only of triglyceride SS, or may be composed only of triglyceride SSS. Triglyceride 18 may be a combination of two or more selected from triglyceride S, triglyceride SS, and triglyceride SSS. For example, triglyceride 18 may be a combination of triglyceride S and triglyceride SS, a combination of triglyceride S and triglyceride SSS, a combination of triglyceride SS and triglyceride SSS, or a combination of triglyceride S, triglyceride SS, and triglyceride SSS.

[0035] In the case of (a), the triglyceride of the present invention may be composed of only triglyceride 16 and triglyceride 18, or may be composed of triglyceride 16 and triglyceride 18 in addition to other triglycerides. Examples of the other triglycerides include triglycerides having no group derived from a fatty acid having 14 to 22 carbon atoms, and triglycerides containing a group derived from a fatty acid having 14 to 22 carbon atoms (excluding triglyceride 16 and triglyceride 18).

[0036] When a group derived from a saturated fatty acid having 16 carbon atoms is designated as "P", a group derived from a saturated fatty acid having 18 carbon atoms is designated as "S", and groups derived from fatty acids other than the saturated fatty acid having 16 carbon atoms and the saturated fatty acid having 18 carbon atoms are designated as "X" and "Y", examples of the combination of aliphatic groups constituting the triglyceride of the present invention include PPP, SSS, PPX, SSX, PXY, SXY, PPS, PSS, and PSX. The structures of the triglycerides represented by PPX, SSX, PXY, SXY, and PSX are as follows (a) to (m). Although the structures of PPS and PSS are not shown, the structure of PPS conforms to the structure of PPX, and the structure of PSS conforms to the structure of SSX.

[0037]

Chemical formula

[0038]

Chemical formula

[0039]

Chemical formula

[0040]

Chemical formula

[0041] [Chemical formula]

[0042] The triglyceride of the present invention can use each of the various triglycerides described above alone. For example, in the case of (b), the triglyceride of the present invention may be composed of a substance that contains at least 1 group derived from a saturated fatty acid having 16 carbon atoms, at least 1 group derived from a saturated fatty acid having 18 carbon atoms, and does not contain groups derived from other fatty acids in one molecule. Alternatively, the triglyceride of the present invention may be composed of a triglyceride that contains 1 group derived from a saturated fatty acid having 16 carbon atoms, 1 group derived from a saturated fatty acid having 18 carbon atoms, and 1 group derived from another fatty acid.

[0043] The triglyceride of the present invention may be a combination of two or more of the various triglycerides described above. For example, the triglyceride of the present invention may be a combination of (a) and (b) described above. Alternatively, it may be a combination of two or more of (b). Furthermore, the triglyceride of the present invention may be a combination of one or two or more of the triglycerides described above and other triglycerides. Examples of other triglycerides include triglycerides containing groups derived from fatty acids having 14 to 22 carbon atoms (excluding triglyceride 16 and triglyceride 18). In the present invention, it is preferable to use each of the various triglycerides described above alone or a combination of two or more of only the various triglycerides described above from the viewpoint of further increasing the water pressure resistance of the nonwoven fabric of the present invention.

[0044] The triglycerides contained in the thermoplastic fibers are preferably 30% by mass or more and 70% by mass or less, particularly 35% by mass or more and 70% by mass or less, especially 50% by mass or more and 70% by mass or less, based on the total amount of groups derived from fatty acids contained in all the triglycerides, and are groups derived from fatty acids having 18 carbon atoms (the group is a hydrocarbon group having no unsaturated bond and no substituent), from the viewpoint of obtaining a nonwoven fabric with even higher water resistance and exudation resistance.

[0045] From the same viewpoint as above, the triglycerides contained in the thermoplastic fibers are preferably 30% by mass or more and 70% by mass or less, based on the total amount of groups derived from fatty acids contained in all the triglycerides, and are groups derived from fatty acids having 18 carbon atoms (the group is a hydrocarbon group having no unsaturated bond and no substituent), and 25% by mass or more and 50% by mass or less are groups derived from fatty acids having 16 carbon atoms (the group is a hydrocarbon group having no unsaturated bond and no substituent), provided that the total of the ratio of the group derived from fatty acids having 18 carbon atoms and the ratio of the group derived from fatty acids having 16 carbon atoms does not exceed 100% by mass. In this case, the ratio of the group derived from fatty acids having 18 carbon atoms is preferably 35% by mass or more and 70% by mass or less, and more preferably 50% by mass or more and 70% by mass or less. On the other hand, the ratio of the group derived from fatty acids having 16 carbon atoms is preferably 25% by mass or more and 45% by mass or less, and more preferably 35% by mass or more and 45% by mass or less.

[0046] The respective ratios of the group derived from fatty acids having 16 carbon atoms and the group derived from fatty acids having 18 carbon atoms, based on the total amount of groups derived from fatty acids contained in all the triglycerides, are measured by the following method. Extract the triglycerides present on the surface of the constituent fibers of the nonwoven fabric using a good solvent for triglycerides, such as toluene. Hydrolyze the ester bonds in the extracted triglycerides with an alkali and quantitatively analyze the methyl esterified fatty acids by gas chromatography.

[0047] Whether or not there are alkyl chains having different numbers of carbon atoms in one molecule of triglyceride can be determined by TOF-MS (time-of-flight mass spectrometry). Specifically, the molecular weight distribution of triglyceride is measured by TOF-MS, and it is discriminated whether or not an alkyl group having a different number of carbon atoms is contained in the molecule from the molecular weight of one molecule. Whether or not there are alkyl chains having different numbers of carbon atoms in one molecule among compounds having the same molecular weight can be determined by a tandem mass spectrometer (MS / MS) as a mass spectrometer. It is discriminated by selecting a specific ion in the first mass separation section, colliding it with an inert gas, separating and detecting the fragment ions generated in the second mass separation section.

[0048] It is preferable that the triglyceride of the present invention does not contain a group derived from an unsaturated fatty acid from the viewpoint of further enhancing the water resistance and anti-seepage properties of the nonwoven fabric of the present invention. Not containing a group derived from an unsaturated fatty acid includes both the case where no group derived from an unsaturated fatty acid is contained at all and the case where an unavoidably small amount of unsaturated fatty acid is contained. The case where an unavoidably small amount of unsaturated fatty acid is contained means, for example, when the proportion of the group derived from an unsaturated fatty acid is 2% by mass or less based on the total amount of the groups derived from fatty acids contained in all the triglycerides contained in the nonwoven fabric.

[0049] Similarly to the above, it is preferable that the triglyceride of the present invention does not contain a group derived from a fatty acid having a hydroxyl group from the viewpoint of further enhancing the water resistance and anti-seepage properties of the nonwoven fabric of the present invention. A fatty acid having a hydroxyl group means a fatty acid in which at least one hydrogen atom in the hydrocarbon group of the fatty acid is substituted with a hydroxyl group. Not containing a group derived from a fatty acid having a hydroxyl group includes both the case where no group derived from a fatty acid having a hydroxyl group is contained at all and the case where an unavoidably small amount of a group derived from a fatty acid having a hydroxyl group is contained. The case where an unavoidably small amount of a group derived from a fatty acid having a hydroxyl group is contained means, for example, when the proportion of the group derived from a fatty acid having a hydroxyl group is 2% by mass or less based on the total amount of the groups derived from fatty acids contained in all the triglycerides contained in the thermoplastic fiber.

[0050] The thermoplastic fiber may contain only triglyceride as the glyceride, or may contain monoglyceride and / or diglyceride in addition to the triglyceride within the range where the intended effect of the present invention can be achieved.

[0051] From the viewpoint of imparting sufficient water pressure resistance and anti-seepage properties to the nonwoven fabric of the present invention, the amount of triglyceride contained in the thermoplastic fiber is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more in the thermoplastic fiber. Further, from the viewpoint of preventing the thermoplastic fiber from becoming sticky, it is preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 15% by mass or less. From these viewpoints, the triglyceride is preferably contained in the thermoplastic fiber in an amount of 1% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 20% by mass or less, still more preferably 10% by mass or more and 15% by mass or less.

[0052] In the nonwoven fabric of the present invention, the layer containing thermoplastic fibers (hereinafter also referred to as "thermoplastic fiber layer") maintains its form as a nonwoven fabric by the fusion of the constituent fibers of the layer (i.e., thermoplastic fibers and, if any, other fibers) at the intersections, which is preferable from the viewpoint of maintaining the strength of the nonwoven fabric. However, if the intersections of the constituent fibers along the longitudinal direction of the constituent fibers are excessively fused, the thickness of the fibers at the fusion sites increases, the average fiber diameter of the constituent fibers tends to increase, and the value of the standard deviation of the fiber diameter with respect to the average fiber diameter also tends to increase. As a result, when comparing nonwoven fabrics with the same level of texture, the nonwoven fabric with excessively fused intersections of the constituent fibers tends to have lower water resistance and anti-seepage properties. From this viewpoint, in the thermoplastic fiber layer, when observing the constituent fibers of the layer, it is preferable that the ratio of the constituent fibers in which fusion sites of the constituent fibers are observed along the longitudinal direction of the constituent fibers is controlled to 15% or less on a number basis (hereinafter, this value is also referred to as "fiber fusion rate"). By controlling the fusion state of the constituent fibers of the thermoplastic fiber layer in this way, the average fiber diameter of the constituent fibers of the nonwoven fabric can be reduced, the value of the standard deviation of the fiber diameter with respect to the average fiber diameter can be decreased, and consequently, the water resistance and anti-seepage properties of the nonwoven fabric can be enhanced. From this viewpoint, it is more preferable that the fiber fusion rate is 15% or less, still more preferable that it is 13% or less, and even more preferable that it is 11% or less.

[0053] The lower the value of the fiber fusion rate, the fewer excessive fusion sites there are in the nonwoven fabric. Therefore, a lower value of the fiber fusion rate is advantageous in terms of reducing the average fiber diameter of the constituent fibers of the nonwoven fabric, decreasing the value of the standard deviation of the fiber diameter with respect to the average fiber diameter, and enhancing the water resistance and anti-seepage properties. However, as a result of the study by the present inventors, it has been confirmed that even when the lower limit value of the fiber fusion rate is about 9%, the average fiber diameter of the constituent fibers of the nonwoven fabric can be reduced, the value of the standard deviation of the fiber diameter with respect to the average fiber diameter can be decreased, and the water resistance and anti-seepage properties of the nonwoven fabric can be maintained at a high level.

[0054] The fiber fusion rate is a value measured by focusing on the fused parts along the longitudinal direction of the fibers among the fused parts of the constituent fibers of the thermoplastic fiber layer. In the present invention, the fiber fusion rate is determined for the parts where the fibers are fused along the longitudinal direction with a length of 10 μm or more (hereinafter, this part is also referred to as the "longitudinal fusion part"). The reason for setting the minimum value of the length of the longitudinal fusion part to 10 μm is based on the fact that the present inventors have found that the fused parts with a length less than this value do not significantly affect the decrease in the water pressure resistance of the nonwoven fabric.

[0055] The specific measurement method of the fiber fusion rate is as described below. When obtaining the nonwoven fabric to be measured from an article such as a diaper, the hot melt adhesive is inactivated with cold spray or an organic solvent, and the nonwoven fabric to be measured is carefully peeled off and isolated. This step is common to all measurements in this specification unless otherwise specified. <Specific Measurement Method of Fiber Fusion Rate> Randomly collect 5 small samples from the nonwoven fabric. When the nonwoven fabric is in the form of a spunbond-meltblown-spunbond composite nonwoven fabric, observe from the upper surface of the nonwoven fabric and measure the fine fibers derived from the meltblown layer. Next, take a photograph magnified 1000 - 10000 times with a scanning electron microscope so that 20 - 60 fibers are reflected in the field of view. Count all the fiber numbers in the field of view. At this time, for the fibers having a longitudinal fusion part, the fiber parts where the constituent fibers are not fused are not counted, and only the longitudinal fusion part is counted as 1 count. Next, count the number of longitudinal fusion parts. Calculate the ratio (%) of the number of longitudinal fusion parts to the number of all counted fiber numbers of 100 or more, and round the value to the first decimal place as the fiber fusion rate.

[0056] From the viewpoints of water pressure resistance and anti-seepage property, the average fiber diameter D of the constituent fibers of the thermoplastic fiber layer is preferably 1.5 μm or less, more preferably 1.2 μm or less, and still more preferably 1.0 μm or less. In particular, from the viewpoints of water pressure resistance and anti-seepage property, it is preferable that the average fiber diameter D of the thermoplastic fibers among the constituent fibers of the thermoplastic fiber layer is not more than the above value. The smaller the value of the average fiber diameter D of the constituent fibers of the thermoplastic fiber layer is, the higher the water pressure resistance and anti-seepage property are. As a result of the study by the present inventors, it has been found that when the average fiber diameter D of the constituent fibers of the thermoplastic fiber layer, particularly the average fiber diameter D of the thermoplastic fibers, is as small as about 0.5 μm, a nonwoven fabric with sufficiently high water resistance and anti-seepage property can be obtained.

[0057] The average fiber diameter D can be determined by the following method. First, five small random samples are collected from the nonwoven fabric. When the nonwoven fabric is in the form of a spunbond-meltblown-spunbond composite nonwoven fabric, thin fibers derived from the meltblown layer are measured by observing from the upper surface of the nonwoven fabric. Next, a photograph is taken at a magnification of 1000 to 10000 times so that 20 to 60 fibers are shown in the field of view with a scanning electron microscope. For all the fibers in the field of view, the fiber diameter is measured so as to count each of them once. For a fiber having a longitudinally fused part, the part is counted as one, and the fiber diameter of the part is measured. The average value of the fiber diameters for 100 or more fibers is calculated in the order of micrometers, and the second decimal place is rounded off for calculation. The value thus obtained is taken as the average fiber diameter D.

[0058] In relation to the above-mentioned average fiber diameter D, when considering the standard deviation σ of the average fiber diameter D of the constituent fibers of the thermoplastic fiber layer, the value of σ / D, which is the ratio of the standard deviation σ to the average fiber diameter D, is preferably 1.8 or less, and the water resistance and anti-seepage property of the nonwoven fabric will be further improved. From the viewpoint of making this advantage more prominent, the value of σ / D is more preferably 1.0 or less, and still more preferably 0.8 or less. The closer the value of σ / D is to zero, the more preferable it is.

[0059] The nonwoven fabric of the present invention contains the above-described charge control agent. Due to the fibers being placed in an electric field and charged during the spinning process, the fibers are scattered due to charge repulsion, resulting in a good texture. The goodness of the texture can be evaluated by the texture index. The smaller the value of the texture index, the better the texture. The texture index of the nonwoven fabric of the present invention is preferably 350 or less, more preferably 330 or less, and even more preferably 320 or less. The value of the above texture index preferably satisfies when the basis weight of the nonwoven fabric is 5 g / m 2 .

[0060] The texture index is determined using a texture meter (Formation Tester "FMT-MIII") manufactured by Nomura Securities Co., Ltd. Specifically, a sample piece collected from the nonwoven fabric is placed on the sample stage, and the transmission image when light is irradiated from one side of the sample piece is captured by a two-dimensional CCD camera. The effective size of 10 cm × 10 cm in the sample piece is decomposed into 320 × 230 pixels, the intensity of light received by each pixel is measured, and the transmittance for each pixel is calculated by the following formula. Transmittance T (%) = [((V T - V R ) / (V 100 - V 0 )) × 100 ··· (1) In the formula, V T is the amount of transmitted light when the light is on (with the sample piece), V R is the amount of transmitted light when the light is off (with the sample piece), V 100 is the amount of transmitted light when the light is on (without the sample piece), and V 0 is the amount of transmitted light when the light is off (without the sample piece). From the obtained transmittance T, the absorbance is calculated according to the following formula (2). Absorbance E = 2 - log T ··· (2) From the obtained absorbance, the texture index is calculated by the following formula (3). Texture index = coefficient of variation of absorbance E × 10 = [standard deviation (σ) of absorbance] / [average value (Eave.) of absorbance] × 10 ··· (3) The measurement is performed on 10 sample pieces, and the average value is taken as the texture index of the nonwoven fabric. When the size of the sample piece is small and an effective size of 10 cm × 10 cm cannot be obtained, place the sample piece at the center of the sample stage, and appropriately specify the effective size to be less than the size of the sample piece and as large an area as possible, and perform measurement to determine the terrain index of the sample piece.

[0061] In the non-woven fabric of the present invention, the above-mentioned thermoplastic fiber layer has a basis weight of 0.5 g / m 2 or more, which is preferable from the viewpoint of being able to exhibit sufficient water pressure resistance and anti-seepage properties. From this viewpoint, the thermoplastic fiber layer preferably has a basis weight of 1.5 g / m 2 or more, more preferably 3 g / m 2 or more. On the other hand, the above-mentioned thermoplastic fiber layer preferably has a basis weight of 15 g / m 2 or less from the viewpoint of being able to exhibit sufficient air permeability and filter characteristics, more preferably 10 g / m 2 or less, and even more preferably 5 g / m 2 or less.

[0062] When the non-woven fabric of the present invention consists of a single layer, it can be, for example, a meltblown non-woven fabric or an electrospinning non-woven fabric. It is preferable that this meltblown non-woven fabric or electrospinning non-woven fabric is the above-mentioned thermoplastic fiber layer, that is, a layer of thermoplastic fibers and fibers containing a charge control agent. The non-woven fabric of the present invention may be a single-layer meltblown non-woven fabric, but is preferably composed of a plurality of layers from the viewpoint of the strength of the non-woven fabric. When the non-woven fabric of the present invention consists of a plurality of layers, the non-woven fabric can be, for example, a meltblown - spunbond composite (hereinafter also referred to as "SM") non-woven fabric or a spunbond - meltblown - spunbond composite (hereinafter also referred to as "SMS") non-woven fabric. It is preferable that the meltblown layer in these composite non-woven fabrics is the above-mentioned thermoplastic fiber layer, that is, a layer of thermoplastic fibers and fibers containing a charge control agent.

[0063] Next, a preferred method for manufacturing the nonwoven fabric of the present invention will be described. FIG. 1 shows an embodiment of a nonwoven fabric manufacturing apparatus by the meltblowing method. The manufacturing apparatus 1 shown in the figure includes a spinning head 10. The spinning head 10 has a longitudinal direction X and a width direction Y orthogonal thereto, and is installed such that the width direction Y coincides with the machine direction MD of the manufacturing apparatus 1. The spinning head 10 is connected to an extruder 12 having a hopper 11. The hopper 11 is filled with pellets of a thermoplastic resin which is a raw material of the nonwoven fabric (this thermoplastic fiber contains a charge control agent and, if necessary, triglyceride). The thermoplastic resin supplied from the hopper 11 becomes a melt that is melt-kneaded in the extruder 12, and the melt is supplied to the spinning head 10.

[0064] A hot air supply unit 13 is connected to the spinning head 10. The supply unit 13 is connected to a hot air supply source (not shown). Air heated to a predetermined temperature is supplied from the hot air supply source. The supplied hot air is supplied to the spinning head 10 after the flow rate is adjusted in the supply unit 13.

[0065] Below the spinning head 10, a fiber collection unit 15 is installed. The collection unit 15 includes an endless belt 16 as a collector made of a material having air permeability. The endless belt 16 is stretched between a pair of rollers 17, 17 and is adapted to move in a circular motion.

[0066] The collection unit 15 includes a suction box 18. The suction box 18 is installed within the circular orbit of the endless belt 16. The suction box 18 is installed at a position corresponding to the fiber spinning line L in the spinning head 10. By operating the suction box 18, the hot air ejected from the spinning head 10 is sucked, and the deposition of fibers on the endless belt 16 is stabilized.

[0067] The collecting section 15 further includes a winder 19. The melt blown nonwoven fabric 2 formed by the deposition of fibers on the endless belt 16 is wound up by the winder 19. When manufacturing SM nonwoven fabric or SMS nonwoven fabric, a nonwoven fabric manufacturing apparatus using the spunbond method may be arranged before and after in the flow direction of the nonwoven fabric manufacturing apparatus using the above-mentioned melt blow method.

[0068] Figures 2 and 3 schematically show the structure in the cross-section in the width direction Y of the spinning head 10. The spinning head 10 includes the divided die bodies 20a and 20b. The die bodies 20a and 20b are joined by fastening means such as bolts (not shown).

[0069] The spinning head 10 has a resin supply port 21 at its upper part, to which a melt of the thermoplastic resin that is the raw material of the melt blown nonwoven fabric is supplied. The melt supplied to the resin supply port 21 is supplied to the spinning die 22 described below. The supply of the melt from the resin supply port 21 to the spinning die 22 is performed via a flow path 21a having a coat hanger shape or a tournament shape.

[0070] The spinning head 10 has a spinning die 22 at its lower part. As shown in FIG. 4, the spinning die 22 has a die nose 22a whose cross-sectional shape in the width direction Y is an isosceles triangle. A plurality of spinning nozzles 23 arranged in series along the longitudinal direction X of the spinning die 22 are formed at the ridge line positions of the die nose 22a. That is, in the spinning head 10, the spinning nozzles 23 are arranged in a row. The melt of the thermoplastic resin is supplied to the spinning nozzles 23 via a die flow path 24 (see FIG. 3) connected to the above-mentioned flow path 21a. The number of the spinning nozzles 23 generally ranges from 300 nozzles / m or more to 4100 nozzles / m or less, depending on the dimensions of the spinning die 22.

[0071] The die bodies 20a and 20b are provided with first manifolds 25a and 25b. The first manifolds 25a and 25b communicate with the hot air supply unit 13 (see FIG. 1) described above. The hot air supplied from the hot air supply unit 13 is ejected from a pair of slits 28a and 28b facing each other via the first manifolds 25a and 25b, the hot air flow paths 26a and 26b, and the buffer spaces 27a and 27b. The hot air ejected from the slits 28a and 28b is blown onto the fiber group discharged from the spinning nozzles 23.

[0072] As shown in FIG. 3, both of the slits 28a and 28b extend along the hypotenuse of the die nozzle 22a in the spinning die 22 and are directed toward the ridge line of the die nozzle 22a. The hot air ejected from the slits 28a and 28b is configured to converge at the ridge line of the die nozzle 22a. The buffer spaces 27a and 27b and the slits 28a and 28b are defined by the spinning die 22 and the plates 29a and 29b.

[0073] Below the plates 29a and 29b, a high voltage application unit 30 is installed at a position separated by a predetermined distance from the open end of the spinning nozzles 23. The high voltage application units 30 are arranged in a pair with the columns of the spinning nozzles 23 as the axis of symmetry. The high voltage application unit 30 has a plate-like shape extending along a direction orthogonal to the plane of the paper in FIG. 3. Although not shown in FIG. 3, the high voltage application unit 30 may have a plate-like shape extending along a direction parallel to the plane of the paper. Also, as shown in FIG. 3, there is a gap S between the plates 29a and 29b and the high voltage application unit 30.

[0074] In order to manufacture a nonwoven fabric using the manufacturing apparatus 1 having the above configuration, first, a thermoplastic resin as a raw material is supplied from the hopper 11 shown in FIG. 1 to the extruder 12, and the thermoplastic resin is melt-kneaded in the extruder 12. The thermoplastic resin melted in the extruder is sent to the spinning head 10. In the spinning head 10, the melt is discharged from a plurality of spinning nozzles 23 (see FIG. 4) arranged in series at intervals. At the same time, hot air flows are ejected from a pair of slits 28a and 28b provided to face each other with the spinning nozzles 23 interposed therebetween, and the hot air flows are blown onto the melt. By blowing the hot air flows, the melt is stretched and formed into fibers. The spinning head 10 may be heated for the purpose of preventing spinning defects caused by a temperature drop of the melt or a temperature drop of the hot air.

[0075] In the above spinning process, spinning is performed by discharging a melt from the spinning nozzle 23 in a state where an electric field is generated by the high-voltage application unit 30. Since a charge control agent is contained in the melt, polarization and ionization occur when the melt passes through the electric field, and the melt is charged and stretched by the hot air flow while being charged to form fibers. Since the fibers formed by stretching the melt remain charged, an electrostatic repulsive action due to Coulomb force occurs between the fibers, and it becomes difficult for the fibers to fuse with each other. Then, while the electrostatic repulsive action due to Coulomb force occurs between the charged fibers, the fibers are deposited on the endless belt 16 which is a collector. As a result, it becomes difficult for the fibers to fuse with each other along the longitudinal direction, and the obtained nonwoven fabric has a good texture. From the viewpoint of making the above advantages more prominent, as shown in FIG. 3, it is preferable to spin the melt with the high-voltage application unit 30 installed between the spinning head 10 and the endless belt 16 which is a collector. In this case, as shown in the figure, a negative potential can be applied relative to the high-voltage application unit 30, a positive potential can be applied relative to the spinning head 10, and the endless belt 16 can be grounded. Alternatively, although not shown, a positive potential can be applied relative to the high-voltage application unit 30 and a negative potential can be applied relative to the spinning head 10.

[0076] In the embodiment shown in FIG. 3, from the viewpoint of sufficiently charging the melt of the thermoplastic fiber, the potential applied to the high voltage application unit 30 is preferably set to 5 kV or more, more preferably 10 kV or more, and still more preferably 20 kV or more, with a negative potential (with respect to ground). Also, from the viewpoint of safety, the potential applied to the high voltage application unit 30 is preferably set to 60 kV or less, more preferably 50 kV or less, and still more preferably 40 kV or less, with a negative potential (with respect to ground).

[0077] When the potential difference between the spinning head 10 and the high voltage application unit 30 is large, there is a possibility of discharge. Therefore, for the purpose of spinning, as the high voltage application unit 30, as shown in FIG. 3, it is preferable to use a member including a conductor member 31 to which a voltage is applied and an insulating member 32 that suppresses discharge of the conductor member 31. In the figure, a state where the entire surface of the conductor member 31 is covered with the insulating member 32 is shown. However, as long as discharge between the spinning head 10 and the high voltage application unit 30 can be prevented, it is not necessary for the entire surface of the conductor member 31 to be covered with the insulating member 32.

[0078] As the insulating member 32, various dielectric materials can be used. For example, ceramic materials such as mica, alumina, zirconia, and barium titanate, and resin-based materials such as bakelite (phenolic resin), nylon (polyamide), vinyl chloride resin, polystyrene, polyester, polypropylene, polytetrafluoroethylene, polyphenylene sulfide, polyetherimide, polyamideimide, polyimide, polyetheretherketone, and polybenzimidazole can be mentioned. Among these, it is preferable to use at least one selected from polyetherimide, polyamideimide, polyimide, polyetheretherketone, and polybenzimidazole resins from the viewpoint of heat resistance, and it is particularly preferable to use polyetheretherketone and polybenzimidazole. An antistatic agent can be contained in the dielectric material used for the insulating member 32. By containing the antistatic agent, when the charged fiber adheres to the insulating member 32, the charging of the insulating member 32 can be reduced. As the antistatic agent, known commercially available products can be used. For example, Perfectron (Sanyo Chemical Industries, Ltd.), Electro Stripper (Kao Corporation), Electro Master (Kao Corporation), Rikemal (Riken Vitamin Co., Ltd.), Rikemaster (Riken Vitamin Co., Ltd.), etc. can be used.

[0079] When charging the melt discharged from the spinning nozzle 23 by the high voltage application unit 30, as shown in FIG. 3, it is preferable to charge and spin the melt with a gap S of 3 mm or more provided between the spinning head 10 provided with the spinning nozzle 23 and the high voltage application unit 30. The reason is as described below. Due to the melt being transported and stretched by the hot air flow, a downward (i.e., the direction of the hot air flow ejection) ambient air flow is generated directly below the spinning nozzle 23. If there is no gap S between the spinning head 10 and the high voltage application unit 30, the downward flow of the ambient air is less likely to occur, and the fiber spinning line L may deflect. On the other hand, by providing a sufficient gap S between the spinning head 10 and the high voltage application unit 30, the downward flow of the ambient air is stably generated, and the fiber spinning line L is stabilized. From this perspective, it is more preferable to set the gap S to 4 mm or more, and even more preferable to set it to 5 mm or more. Also, from the perspective of sufficiently charging the melt before solidification and preventing the molten resin from adhering to the high voltage application unit 30, it is preferable to set the gap S to 25 mm or less, more preferably 20 mm or less, and even more preferably 15 mm or less. From the same perspective, the distance W from the fiber spinning line L to the high voltage application unit 30 is preferably set to 5 mm or more and 30 mm or less, more preferably 10 mm or more and 25 mm or less, and even more preferably 15 mm or more and 20 mm or less.

[0080] Since this manufacturing method is based on the melt blowing method, it is possible to produce nonwoven fabric with high productivity. From this perspective, the total discharge amount of the melt per unit length of the row of spinning nozzles 23 is preferably set to 10 kg / hr / m or more, more preferably 12 kg / hr / m or more, and even more preferably 14 kg / hr / m or more. Also, from the perspective of reducing the fiber diameter, the total discharge amount of the melt per unit length of the row of spinning nozzles 23 is preferably set to 100 kg / hr / m or less, more preferably 75 kg / hr / m or less, and even more preferably 50 kg / hr / m or less.

[0081] Regarding the discharge amount for one spinning nozzle 23, from the perspective of reducing the fiber diameter, it is preferably set to 1.0 g / min / hole or less, more preferably 0.6 g / min / hole or less. Also, from the perspective of improving the productivity of the nonwoven fabric, it is preferably set to 0.04 g / min / hole or more, more preferably 0.06 g / min / hole or more.

[0082] In addition to the above manufacturing conditions, the manufacturing conditions of the nonwoven fabric that can be set include the pore diameter and pitch of the spinning nozzles 23. Regarding the pore diameter of the spinning nozzles 23, from the perspective of reducing the fiber diameter, it is preferably set to 0.5 mm or less, more preferably 0.4 mm or less, and even more preferably 0.35 mm or less. Also, from the perspective of improving the productivity of the nonwoven fabric, it is preferably set to 0.10 mm or more, more preferably 0.13 mm or more, and even more preferably 0.15 mm or more. Regarding the pitch P (see Figure 4) of the spinning nozzles 23, from the perspective of improving the productivity of the nonwoven fabric, it is preferably set to 2.85 mm or less, more preferably 1.45 mm or less, and even more preferably 0.85 mm or less. Also, from the perspectives of stable spinning and sufficient cooling of the fibers, it is preferably set to 0.15 mm or more, more preferably 0.20 mm or more, and even more preferably 0.25 mm or more.

[0083] Regarding the total amount of hot air, from the perspective of reducing the fiber diameter, it is preferably 250 Nm 3Above / hr / m, more preferably 350 Nm 3 Above / hr / m, even more preferably 500 Nm 3 It is set to be above / hr / m. Also, from the viewpoint of preventing yarn breakage of the fiber, it is preferably 1000 Nm 3 Below / hr / m, more preferably 900 Nm 3 Below / hr / m, even more preferably 750 Nm 3 It is set to be below / hr / m. The total amount of hot air is measured by an air flow meter installed in the middle of the supply air pipe.

[0084] The nonwoven fabric of the present invention produced by the above method is excellent in water resistance, anti-seepage property, filter characteristics, etc. The excellent water resistance and anti-seepage property means that when the nonwoven fabric of the present invention is used as, for example, the back sheet of absorbent articles such as sanitary napkins and disposable diapers, or the constituent sheet of leak-proof cuffs arranged at the front and rear ends and sides, there are advantages such as high leak-proof performance. The excellent filter characteristics mean that when the nonwoven fabric of the present invention is used as various separation membranes, sanitary masks, etc., there are advantages such as being able to efficiently collect foreign substances to be removed.

[0085] Absorbent articles are mainly used to absorb and hold liquids excreted from the body such as urine and menstrual blood. Absorbent articles typically include a surface sheet forming a skin-facing surface, a back sheet constituting a non-skin-facing surface, and a liquid-retaining absorbent body interposed between both sheets. Absorbent articles may further include various members according to the specific uses of the absorbent articles. Such members are known to those skilled in the art. For example, when the absorbent article is a disposable diaper, sanitary napkin, or incontinence pad, one or two or more pairs of leak-proof cuffs can be arranged on both sides in the longitudinal direction along the front-rear direction of the wearer. The leak-proof cuff has a fixed end and a free end, and preferably an elastic member is arranged in the vicinity of the free end.

[0086] The nonwoven fabric of the present invention is preferably in the form of a spunbond - meltblown - spunbond composite nonwoven fabric from the viewpoints of improving the strength of the nonwoven fabric and conveyance properties. From this viewpoint, the nonwoven fabric of the present invention is suitably used as a constituent material for a backsheet or a leak - proof cuff that requires water resistance among the constituent members of an absorbent article, or a top sheet that requires color concealment of menstrual blood, urine, etc. When forming the backsheet of an absorbent article from a laminated sheet of a resin film and an exterior nonwoven fabric that covers the non - skin - facing side thereof, the nonwoven fabric of the present invention may be used instead of this resin film, or the nonwoven fabric of the present invention may be used instead of the exterior nonwoven fabric. Alternatively, the nonwoven fabric of the present invention may be used instead of the entire conventional backsheet.

[0087] As described above, the present invention has been described based on its preferred embodiments, but the present invention is not limited to the above - mentioned embodiments. For example, regarding points not particularly described in the above - mentioned manufacturing method, conditions related to the manufacturing method of conventional melt - blown nonwoven fabrics are appropriately applied. Further, the structure of the spinning head 10 is not limited to that shown in the drawings, and the spinning head 10 may have other structures as long as the manufacturing method of the present invention can be implemented. Furthermore, the high - voltage application unit 30 shown in FIG. 5 can also be used. In the high - voltage application unit 30 shown in the figure, the entire surface of the round - bar - shaped conductor member 31 is covered by the insulating member 32. When the heat resistance of the insulating member 32 is low, as shown in the figure, the entire surface of the insulating member 32 can be covered with a heat - resistant material 33, such as a fluorine - based resin, polyetherimide, polyamideimide, polyimide, polyetheretherketone, polybenzimidazole, etc.

Examples

[0088] Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “%” and “parts” mean “mass %” and “parts by mass”, respectively.

[0089] 〔Example 1〕 A nonwoven fabric was manufactured using the manufacturing apparatus shown in FIGS. 1 to 4. The manufacturing conditions are as shown below. <Resin composition> · 95 parts of polypropylene homopolymer (MFR: 1200 g / min) · 5 parts of alkyl sulfonate (Nikkol SMT manufactured by Nikko Chemicals Co., Ltd.) <Manufacturing apparatus> · Spinning nozzle hole diameter: 0.15 mm · Spinning nozzle pitch: 0.25 mm · Resin temperature: 260 °C · Single-hole discharge amount: 0.06 g / min / hole · Total resin discharge amount: 14.4 kg / hr / m · Hot air temperature: 265 °C · Total amount of hot air: 750 Nm 3 / hr / m <High voltage application section> · Applied charge voltage: -20 kV · Installation position Gap S: 13 mm <Nonwoven fabric> · Basis weight: 5 g / m 2

[0090] 〔Example 2〕 A nonwoven fabric was manufactured in the same manner as in Example 1 except that the following conditions were adopted. <Resin composition> · 59.5 parts of polypropylene homopolymer (MFR: 1200 g / min) · 25.5 parts of polypropylene random polymer (MFR: 10000 g / min or more) · 5 parts of alkyl sulfonate (Nikkol SMT manufactured by Nikko Chemicals Co., Ltd.) · 10 parts of palm extreme hardened oil (manufactured by Shioda Oil Co., Ltd.) The palm extreme hardened oil had a group derived from a C14 saturated fatty acid, a group derived from a C16 saturated fatty acid, and a group derived from a C18 saturated fatty acid. The ratio of each group was 1% for the group derived from the C14 saturated fatty acid, 42% for the group derived from the C16 saturated fatty acid, and 57% for the group derived from the C18 saturated fatty acid.

[0091] 〔Example 3〕 A nonwoven fabric was produced in the same manner as in Example 1 except that the following conditions were adopted. <Resin Composition> · 59.5 parts of polypropylene homopolymer (MFR: 1200 g / min) · 25.5 parts of polypropylene random polymer (MFR: 10,000 g / min or more) · 5 parts of alkyl sulfonate (Nikkol SMT manufactured by Nikko Chemicals Co., Ltd.) · 10 parts of glyceryl tristearate technical grade (manufactured by Sigma-Aldrich) Glyceryl tristearate had a group derived from a C16 saturated fatty acid and a group derived from a C18 saturated fatty acid. The ratio of each group was 29% for the group derived from the C16 saturated fatty acid and 62% for the group derived from the C18 saturated fatty acid.

[0092] 〔Comparative Example 1〕 A nonwoven fabric was produced in the same manner as in Example 1 except that the following conditions were adopted. <Resin Composition> · 100 parts of polypropylene homopolymer (MFR: 1200 g / min)

[0093] 〔Evaluation〕 For the nonwoven fabrics obtained in the examples and comparative examples, the fiber fusion rate, average fiber diameter D, σ / D, and fabric texture index were measured by the above-described method. Also, the water pressure resistance was measured in accordance with JIS L1092. Furthermore, the liquid seepage prevention property was evaluated by the following method. The results are shown in Table 1 below.

[0094] 〔Liquid Seepage Prevention Property〕 A nonwoven fabric cut to 8 cm × 8 cm was placed on a filter paper (manufactured by Advantec Toyo Co., Ltd., No. 2, diameter 70 mm). On the placed nonwoven fabric, a dry pulp sheet (manufactured by Lion Corporation, Lead Healthy Cooking Paper Double (trade name), basis weight 40 g / m 2 ) cut to 30 mm × 30 mm was placed. 1.0 g of a wetting tension test solution (surface tension at 25°C: 35 mN / m) was injected into the central part of the dry pulp sheet using a dropper. After injection, an acrylic plate with a diameter of 60 mm was overlaid, and a 2-kg weight was placed on it and pressurized for 60 minutes. After 60 minutes, the weight was removed, and the degree of liquid seepage onto the filter paper was visually observed to determine the presence or absence of seepage. This evaluation was performed in 3 sets for each level, and the degree of seepage was evaluated according to the following criteria. A: None of the three sheets showed seepage. B: Seepage was observed in only 1 sheet. C: Seepage was observed in only 2 sheets. D: Seepage was observed in all three sheets.

[0095]

Table 1

[0096] As is clear from the comparison between Comparative Example 1 and Example 1, by adding a charge control agent to the thermoplastic resin, placing the fibers in an electric field during the spinning process, charging them, and causing the fibers to repel each other by electric charge, the fiber fusion rate decreases and the average fiber diameter becomes thinner. Also, since the fibers are scattered and collected due to the electric charge repulsion, the fabric appearance is improved. As a result, it can be seen that the non-woven fabric of Example 1 has excellent water pressure resistance. Furthermore, for the non-woven fabrics of Examples 2 and 3 to which triglyceride was added, due to the same effect, it can be seen that they have a lower fiber fusion rate and better fabric appearance than Comparative Example 1, and thus have excellent water pressure resistance. In particular, as is clear from the comparison between Example 1 and Examples 2 and 3, it can be seen that when the constituent fibers of the non-woven fabric contain triglyceride, the exudation resistance is increased.

Explanation of Signs

[0097] 10 Spinning head 20a, 20b Die body 22 Spinning die 22a Die nose 23 Spinning nozzle 25a, 25b First manifold 27a, 27b Buffer space 28a, 28b Slit 29a, 29b Plate 30 High voltage application section 31 Conductor member 32 Insulating member

Claims

1. A nonwoven fabric having a layer containing fibers containing a thermoplastic resin and a charge control agent, wherein the charge control agent contains an alkyl sulfonate, and the alkyl sulfonate is contained in the fibers in an amount of 1% by mass or more and 20% by mass or less, and when observing the constituent fibers of the layer, the ratio of the constituent fibers in which fusion sites are observed along the longitudinal direction of the constituent fibers is 9% or more and 15% or less on a number basis as measured by the following method. Nonwoven fabric. <Measurement method> Randomly collect 5 small samples from the nonwoven fabric. When the nonwoven fabric is in the form of a spunbond-meltblown-spunbond composite nonwoven fabric, measure the fine fibers derived from the meltblown layer by observing from the upper surface of the nonwoven fabric. Next, take a photograph magnified 1000 to 10000 times with a scanning electron microscope so that 20 to 60 fibers are reflected in the field of view. Count all the fiber numbers in the field of view. At this time, for fibers having a longitudinal fusion site, only the longitudinal fusion site is counted, and the fiber sites where the constituent fibers are not fused are not counted, and it is counted as 1 count. Next, count the number of longitudinal fusion sites. Calculate the ratio (%) of the number of longitudinal fusion sites to 100 or more of all the counted fiber numbers.

2. A nonwoven fabric having a layer containing fibers containing a thermoplastic resin, a charge control agent, and a triglyceride, wherein the charge control agent is contained in the fibers in an amount of 1% by mass or more and 20% by mass or less, the triglyceride is contained in the fibers in an amount of 1% by mass or more and 30% by mass or less, and when observing the constituent fibers of the nonwoven fabric, the ratio of the constituent fibers in which fusion sites are observed along the longitudinal direction of the constituent fibers is 15% or less on a number basis as measured by the following method. Nonwoven fabric. <Measurement method> Randomly collect five small samples from the non-woven fabric. When the non-woven fabric is in the form of a spunbond-meltblown-spunbond composite non-woven fabric, observe from the upper surface of the non-woven fabric and measure the fine fibers derived from the meltblown layer. Next, take a photograph magnified 1000 to 10000 times with a scanning electron microscope so that 20 to 60 fibers are reflected in the field of view. Count all the fiber numbers in the field of view. At this time, for the fibers having a longitudinal fusion part, the fiber parts where the constituent fibers are not fused are not counted, and only the longitudinal fusion parts are counted as one count. Next, count the number of longitudinal fusion parts. Calculate the ratio (%) of the number of longitudinal fusion parts to 100 or more of all the counted fiber numbers.

3. The non-woven fabric according to claim 2, wherein the triglyceride contains a group derived from a fatty acid, and the group is a hydrocarbon group having no unsaturated bond.

4. The triglyceride is (a) a mixture of a triglyceride containing at least a group derived from a fatty acid having 16 carbon atoms in one molecule and a triglyceride containing at least a group derived from a fatty acid having 18 carbon atoms in one molecule, or (b) a triglyceride containing at least a group derived from a fatty acid having 16 carbon atoms and a group derived from a fatty acid having 18 carbon atoms in one molecule, the non-woven fabric according to claim 2 or 3.

5. The non-woven fabric according to any one of claims 1 to 4, wherein the value of σ / D, which is the ratio of the standard deviation σ of the average fiber diameter D of the constituent fibers of the layer to the average fiber diameter D, is 1.8 or less.

6. The non-woven fabric according to any one of claims 1 to 5, wherein the thermoplastic resin is a polyolefin.

7. The non-woven fabric according to any one of claims 1 to 6, wherein the charge control agent is an organic sulfonate having an alkyl group at the terminal in the molecular structure and a sulfonate group at an arbitrary position in the molecular structure.

8. The non-woven fabric according to any one of claims 1 to 7, wherein the ground contact index is 350 or less.

9. The non-woven fabric according to any one of claims 1 to 8, which is for absorbent articles.

10. An absorbent article having the non-woven fabric according to any one of claims 1 to 9.

Images