JP2015212449A - Composite short fiber for absorption article, production method of the same and thermally adhered nonwoven fabric for absorption article containing the same and absorption article - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite short fiber for absorption articles which is suitable for acquisition of a thermally adhered nonwoven fabric for absorption articles having good cardability, smooth touch and high concealing performance, a production method of the fiber and a thermally adhered nonwoven fabric for absorption articles containing the fiber and an absorption article.SOLUTION: A composite short fiber 10 for absorption articles includes a core component 2 and a sheath component 1. The core component 2 contains 50 mass% or more of a polypropylene having a ratio Mw/Mn of the mass average molecular weight Mw to the number average molecular weight Mn after spinning of 3.0-8.0, and the sheath component 1 contains 60 mass% or more of a high-density polyethylene having a melting point 5°C or more lower than the polypropylene, constituting a core-sheath type composite short fiber 10 having a concentric circle structure. The composite short fiber 10 for absorption articles has a composite ratio of the core component 2 and the sheath component 1, in terms of the core component/sheath component vol. ratio, of 52/48 to 73/27 and a fineness of 1.1-2.0 dtex and contains 0.5-10 mass% of an inorganic filler to 100 mass% of the composite short fiber.

Description

  The present invention relates to absorbent articles such as sanitary napkins and paper diapers, composite staple fibers for absorbent articles used in absorbent articles, heat-bonding nonwoven fabrics for absorbent articles, and methods for producing composite staple fibers for absorbent articles. Specifically, the composite staple fiber for absorbent articles whose core component and sheath component are mainly composed of a polyolefin resin, the heat-bonding nonwoven fabric for absorbent articles and the absorbent article containing the same, and the composite staple fiber for absorbent articles It relates to a manufacturing method.

  In absorbent articles such as sanitary napkins and paper diapers, the feel of the surface sheet that directly contacts the wearer's skin and the feel of the back sheet that forms the outer part of the absorbent article such as paper diapers are made smoother and softer. It is requested to do.

  For the surface sheet of the absorbent article, a heat-bonded nonwoven fabric is used in which a fiber web containing heat-bonding fibers is manufactured using a card machine, and a high-temperature air stream is blown onto the fiber web to thermally bond the constituent fibers. . In order to soften the tactile sensation of the heat-bonding nonwoven fabric, it is considered effective to reduce the fineness of the fiber and to make the resin constituting the fiber a softer resin. As a heat-bonding fiber used for the heat-bonding nonwoven fabric, a polyester-based composite fiber containing a polyester resin and a polyolefin-based composite fiber containing a polyolefin resin are known. When comparing polyester-based composite fibers containing polyester resin with polyolefin-based composite fibers containing polyolefin resin, polyolefin resin is softer than polyester resin, so if the fibers are the same thickness, non-woven fabric using polyolefin-based composite fibers It is considered that the touch is softer than the non-woven fabric using the polyester composite fiber. Therefore, by making a heat-bonded nonwoven fabric using polyolefin composite fibers with fineness and using it for the surface sheet and back sheet of the absorbent article, the comfort and tactile sensation when the absorbent article is mounted are further improved. Improvements are being made.

  However, as the fineness of the polyolefin-based composite fiber is reduced, the fiber card passing property is lowered and the productivity of the nonwoven fabric is likely to be lowered. The cause is that the polyolefin resin is soft, so the elasticity of the fiber is lost by making it finer, and when the fiber web is opened and made into a fiber web, the fibers get entangled inside the card machine. It is easy to generate a granular fiber lump called. Also, because the polyolefin resin is soft, the crimped shape cannot be maintained, and when it is opened with a card machine and made into a card web, it tends to be in a so-called “fly” state that does not get entangled with the card wire. Is one of the causes. In particular, since the polyolefin composite short fibers having a fineness are low in strength and elasticity of the fibers, there is a possibility that when the fiber web is produced at high speed, nep and fly occur frequently and the fiber web cannot be produced.

  In addition, the nonwoven fabric used for the absorbent article is required to have a white appearance, that is, a high whiteness. In particular, the surface sheet used on the surface of the non-woven fabric used for absorbent articles that comes in contact with the skin of the wearer is not only white in appearance, but also blood discharged from the body (menstrual blood), urine and fluidity In addition to rapidly absorbing excrement such as stool, so-called concealment is required to make the absorbed blood and excrement difficult to see from the surface. Synthetic fibers used in absorbent articles for the purpose of increasing the apparent whiteness (whiteness) of nonwoven fabrics or improving the concealability of nonwoven fabrics include titanium dioxide (also simply referred to as titanium oxide) and zinc oxide. Inorganic filler is mixed with synthetic resin. Synthetic fibers containing an inorganic filler not only tend to lower the spinnability because the inorganic filler works as a foreign substance, but also the single fiber strength and the elasticity of the fiber decrease. Flying easily occurs. In this way, from the decrease in card permeability due to the fineness and the decrease in card permeability due to the addition of the inorganic filler, the composite short fiber for absorbent articles contains an inorganic filler and has a fineness polyolefin type. It was difficult to obtain composite short fibers.

  As a polyolefin-based composite fiber that can be used for a heat-bonding nonwoven fabric such as a sanitary material surface material such as a sanitary napkin, for example, Patent Document 1 discloses a composite fiber made of polypropylene and polyethylene, and the fiber cross section is an eccentric core-sheath type or a parallel type. A polyolefin-based composite fiber having a single yarn fineness of 1 to 2d and a fiber length of 20 to 40 mm is described.

JP-A-8-60441

  The composite fiber described in Patent Document 1 has an eccentric core-sheath type or a parallel type fiber cross section. In these cross-sectional structures, since there is a thin portion of the sheath component, that is, the heat-bonding component, the strength of the heat-bonded bonding point is insufficient, and the strength of the heat-bonded nonwoven fabric itself may be insufficient, or due to friction during use, the nonwoven fabric The surface may become fuzzy and the surface feel may be deteriorated. In addition, the reduction in card passage due to the inclusion of the inorganic filler is not taken into consideration, and there is a possibility that measures against the reduction in the card passage when the inorganic filler is contained are insufficient.

  The present invention has been made in view of such circumstances, and is suitable for obtaining a heat-bonding nonwoven fabric for absorbent articles that has good card passing properties, smooth tactile sensation, and high concealability. Provided are a composite short fiber, a method for producing the same, a heat-bonding nonwoven fabric for absorbent articles containing the same, and an absorbent article.

  The present invention is a composite short fiber for absorbent articles comprising a core component and a sheath component, wherein the core component has a ratio Mw / Mn of 3.0 or more of the weight average molecular weight Mw and the number average molecular weight Mn after spinning. 0.0 or less of polypropylene is contained in an amount of 50% by mass or more, and the sheath component contains 60% by mass or more of high-density polyethylene having a melting point of 5 ° C. or more lower than that of the polypropylene, and the composite short fiber comprises the core component and the sheath component. Is a core-sheath type composite short fiber in which the composite ratio of the core component and the sheath component is 52/48 to 73/27 in terms of the volume ratio of the core component / sheath component. The short fiber contains 0.5% by mass or more and 10% by mass or less of an inorganic filler with respect to 100% by mass of the composite short fiber, and the fineness of the composite short fiber is 1.1 dtex or more and 2.0 dtex or less. Composite short fiber for absorbent articles About textiles.

  The present invention is also a method for producing the above-described composite short fiber for absorbent articles, wherein 50 mass of polypropylene having a ratio Mw / Mn of mass average molecular weight Mw to number average molecular weight Mn of 3.0 or more and 10.0 or less is 50 mass. A core component containing at least 5% and a sheath component containing at least 60% by mass of a high-density polyethylene having a melting point of 5 ° C. or more lower than that of the polypropylene, the sheath component covering the surface of the composite short fiber in the fiber cross section, and the core component Is supplied to a composite type nozzle arranged so as to have a concentric circular structure in which the center of gravity of the composite short fiber coincides with the center of gravity of the composite short fiber, and the core component is spun at a temperature of 250 ° C. to 350 ° C. The present invention relates to a method for producing a composite staple fiber for absorbent articles, which includes a step of melt spinning at a temperature of 0 ° C. or lower.

  The present invention also relates to a heat-bonding nonwoven fabric for absorbent articles, comprising 20% by mass or more of the above-mentioned composite short fibers for absorbent articles, wherein at least a part of the above-mentioned composite short fibers for absorbent articles is adhered by a sheath component.

  The present invention is also an absorbent article including the heat-adhesive nonwoven fabric for absorbent articles, wherein the heat-adhesive nonwoven fabric for absorbent articles is arranged as a top sheet and / or a back sheet. The present invention relates to an absorbent article.

  The composite short fiber for absorbent articles according to the present invention includes 50% by mass or more of polypropylene whose core component has a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 3.0 or more and 8.0 or less after spinning. The sheath component contains 60% by mass or more of high-density polyethylene whose melting point is 5 ° C. or lower than the polypropylene contained in the core component, and the core component and the sheath component are arranged substantially concentrically. When the composite ratio is 52/48 to 73/27 in the volume ratio of the core component / sheath component, the card passing property is good, and an excellent card web can be provided. Further, in the composite short fiber for absorbent articles of the present invention, since the core component and the sheath component are arranged concentrically, the sheath component having a low melting point is uniformly present on the surface of the composite short fiber, which is easy. The fibers can be thermally bonded to each other to provide a heat-bonded nonwoven fabric having high adhesive strength. Moreover, the composite short fiber for absorbent articles of the present invention contains 0.5% by mass or more and 10% by mass or less of an inorganic filler, and has good card passability even if the fineness is 1.1 dtex or more and 2.0 dtex or less. The heat-bonding nonwoven fabric for absorbent articles and the absorbent article containing the composite short fibers for absorbent articles have a smooth and soft touch. In addition to the fact that the composite staple fiber for absorbent articles of the present invention contains an inorganic filler, the fineness is 2.0 dtex or less, so that the thermal adhesive for absorbent articles containing the composite staple fiber for absorbent articles is included. The nonwoven fabric and the absorbent article have excellent concealability when absorbing blood and excreta.

FIG. 1 is a schematic cross-sectional view showing a fiber cross section of a composite short fiber according to an embodiment of the present invention. 2A and 2B are schematic views showing crimped forms of composite short fibers according to an embodiment of the present invention.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have spun as polypropylene (hereinafter, also referred to as “main component polypropylene”) contained in the core component in a polyolefin-based composite short fiber in an amount of 50% by mass or more. A polypropylene (hereinafter also referred to as PP) having a ratio Mw / Mn (hereinafter also referred to as “Q value”) of the weight average molecular weight Mw and the number average molecular weight Mn (hereinafter also referred to as “Q value”) is used. The sheath component contains 60% by mass or more of high-density polyethylene having a melting point 5 ° C. lower than that of the main component polypropylene, and the composite ratio of the core component to the sheath component in the composite short fiber is 52 by the volume ratio of the core component / sheath component. / 48 to 73/27 increases the ratio of the core component, and the cross-sectional structure in which the core component and the sheath component are arranged substantially concentrically makes the composite short fiber Even if it is a composite short fiber containing a specific amount of inorganic filler, the stiffness of the body is high, the fineness is 2.0 dtex or less, the card passing property is good, and the tactile sensation and adhesive strength when it is made into a heat-bonded nonwoven fabric The present invention was found to be superior to the present invention.

  The composite short fiber for absorbent articles of the present invention is a core-sheath type composite short fiber having a concentric structure in which a core component and a sheath component are arranged substantially concentrically.

(Core component)
The core component of the composite short fiber for absorbent articles of the present invention contains 50% by mass or more of polypropylene having a Q value after spinning of 3.0 or more and 8.0 or less. Polypropylene resins having a large Q value have a large molecular weight distribution because many high molecular weight polypropylene molecules are present inside the resin. On the other hand, a polypropylene resin having a small Q value cuts a high molecular weight molecular chain generated by polymerization and aligns the length of the molecular chain, so that the remaining amount of the high molecular weight polypropylene molecule is reduced and the width of the molecular weight distribution is reduced. Is getting smaller. In addition, by using a polypropylene having a Q value before spinning of 3.0 or more and 10.0 or less, the Q value of polypropylene after spinning can be made 3.0 or more and 8.0 or less.

  When polypropylene is melt-spun, if a polypropylene having a small molecular weight distribution, that is, a small Q value is used, there are many amorphous regions (tie molecules) in unstretched fibers. Tend to remain. In the amorphous region, the polypropylene molecules are often not oriented, or the orientation of the polypropylene molecules is often not uniform, and the more the amorphous region of the polypropylene in the drawn fiber, the lower the strength of the fiber and the card passing property. It is likely to be low. On the other hand, when a polypropylene having a large molecular weight distribution and a large molecular weight distribution, that is, a polypropylene having a large Q value is used, the high molecular weight polypropylene molecule tends to be crystallized, and a high draw ratio is stretched. By performing the treatment, a fiber having a small amorphous region can be obtained. Since the ratio of the amorphous region is small and the fiber has a high degree of crystallinity, it is presumed that the fiber containing polypropylene having a large Q value has a high fiber strength and a high card passing property.

  The Q value after spinning of the main component polypropylene is 3.0 or more and 8.0 or less, preferably 3.0 or more and 6.5 or less, and more preferably 3.2 or more and 6.0 or less. Preferably, it is 3.4 or more and 5.5 or less, more preferably 3.6 or more and 5.2 or less. When the Q value after spinning of the polypropylene is 3.0 or more and 8.0 or less, the composite staple fiber for absorbent articles has excellent card passing properties, and the composite staple fiber for absorbent articles is manufactured. The productivity is also good.

  The Q value before spinning of the main component polypropylene is 3.0 or more and 10.0 or less, preferably 3.0 or more and 8.5 or less, more preferably 3.2 or more and 7.0 or less. Preferably, it is 3.4 or more and 6.5 or less. When the Q value before spinning of the polypropylene is 3.0 or more and 10.0 or less, the composite staple fiber for absorbent articles has excellent card passing properties, and the composite staple fiber for absorbent articles is manufactured. The productivity is also good.

  The main component polypropylene preferably has a mass average molecular weight Mw after spinning of 120,000 or more. A more preferable mass average molecular weight Mw is 140000 or more, and a particularly preferable mass average molecular weight Mw is 150,000 or more. When the weight average molecular weight Mw after spinning of the main component polypropylene is 120,000 or more, the Q value after spinning of the main component polypropylene easily satisfies the above-described range, and the composite staple fiber for absorbent articles has a high molecular weight polypropylene molecule. A lot remains. When the mass average molecular weight Mw of the main component polypropylene is less than 120,000, the Q value after spinning of the main component polypropylene tends to deviate from the above-mentioned range, and the ratio of the high molecular weight polypropylene molecules contained in the polypropylene Therefore, the card passing property of the composite short fiber for absorbent articles may be reduced. The upper limit of the weight average molecular weight Mw after spinning of the main component polypropylene is not particularly limited, but may be 300,000 or less, 240000 or less, or 220,000 or less. If the mass average molecular weight Mw after spinning of the main component polypropylene exceeds 300,000, the spinnability and stretchability may be reduced, and composite short fibers with high productivity may not be obtained.

  The Q value and mass average molecular weight Mw of the main component polypropylene may be different before and after spinning. Particularly, a polypropylene having a Q value after spinning of 3.0 or more and 8.0 or less may have a Q value before spinning of more than 8. This is because the bonds between the molecules constituting the relatively high molecular weight polypropylene molecule are broken by the heat during spinning, or a part of the relatively high molecular weight polypropylene molecule is chain-transferred to the low molecular weight polypropylene molecule. It is guessed that. In the present invention, the value of the Q value is a value after spinning unless otherwise stated as a value before spinning.

  The core component of the composite short fiber for absorbent articles contains 50% by mass or more of the main component polypropylene. In the core component of the composite short fiber for absorbent articles, the content of the main component polypropylene is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, Particularly preferably, in the core component, the resin component excluding the inorganic filler described later is all polypropylene. The main component polypropylene is not particularly limited, and for example, a homopolymer, a random copolymer, a block copolymer, or a mixture thereof can be used. Examples of the random copolymer and block copolymer include a copolymer of propylene and at least one α-olefin selected from the group consisting of ethylene and an α-olefin having 4 or more carbon atoms. The α-olefin having 4 or more carbon atoms is not particularly limited, but examples thereof include 1-butene, 1-pentene, 3,3-dimethyl-1-butene, 4-methyl-1-pentene, and 4,4-dimethyl. Examples include -1-pentene, 1-decene, 1-dodecene, 1-tetradecene, and 1-octadecene. The propylene content in the copolymer is preferably 50% by mass or more. Among these, from the viewpoint of bulk recoverability of the nonwoven fabric containing the composite short fiber for absorbent articles, it is selected from the group consisting of propylene homopolymer, ethylene-propylene copolymer, ethylene-butene-1-propylene terpolymer. In consideration of the productivity, card passability and economy (manufacturing cost) of the resulting composite short fiber for absorbent articles, the core component polypropylene is particularly preferably a propylene homopolymer.

  In the composite short fiber for absorbent articles, the core component may contain a resin other than the main component polypropylene in addition to the main component polypropylene as long as the effects of the present invention are not impaired. Although it does not specifically limit as resin other than the said main component polypropylene, For example, polyolefin resin, polyester resin, polyamide resin, polycarbonate, polystyrene etc. are mentioned. The polyolefin resin is not particularly limited, and examples thereof include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polymethylpentene, polybutene-1, and acrylic acid, methacrylic acid, and maleic acid. Unsaturated carboxylic acid such as acid, unsaturated carboxylic acid such as acrylic acid ester, methacrylic acid ester and maleic acid ester, unsaturated carboxylic acid such as acrylic acid anhydride, methacrylic acid anhydride and maleic acid anhydride Examples thereof include those obtained by copolymerizing at least one selected from the group consisting of products, those obtained by graft polymerization, and elastomers thereof. The polyester resin is not particularly limited, but examples thereof include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and acid components such as isophthalic acid, succinic acid, and adipic acid, and 1 , 4-butanediol, glycol components such as 1,6-hexanediol, copolymers with polytetramethylene glycol, polyoxymethylene glycol and the like, and elastomers thereof. Although it does not specifically limit as said polyamide resin, For example, nylon 6, nylon 66, nylon 11, nylon 12, etc. are mentioned. In addition, various known additives may be added to the core component as long as the effects of the present invention are not hindered and do not affect fiber productivity, nonwoven fabric productivity, thermal adhesiveness, and touch. . Additives that can be added to the core component include known crystal nucleating agents, antistatic agents, pigments, matting agents, heat stabilizers, light stabilizers, flame retardants, antibacterial agents, lubricants, plasticizers, softeners, oxidation agents. Examples thereof include an inhibitor and an ultraviolet absorber.

  In the core component of the composite short fiber for absorbent articles, the melt flow rate of the main component polypropylene is not particularly limited, but the melt flow rate (MFR) measured according to JIS-K-7210 (measurement temperature 230 ° C., load 2) .16 kgf (21.18 N), hereinafter referred to as MFR230) is preferably 10 g / 10 min or more and 50 g / 10 min or less. More preferable MFR230 is 20 g / 10 min or more and 40 g / 10 min or less, and particularly preferable MFR230 is 25 g / 10 min or more and 35 g / 10 min or less. When the MFR230 of the main component polypropylene is within the above range, not only the take-up property and stretchability are improved, but also the core component has sufficient elasticity to pass through the card machine, and the above absorption The card passing property of the composite short fiber for a functional article is improved.

  In the core component of the composite short fiber for absorbent articles, the melting point of the main component polypropylene is not particularly limited, but is preferably 150 ° C or higher, more preferably 152 ° C or higher, and 155 ° C or higher. Is particularly preferred. When the melting point of the main component polypropylene is 150 ° C. or higher, the bulk of the nonwoven fibrous web is less likely to be reduced, and a bulky and soft tactile thermal adhesive nonwoven fabric is easily obtained. The upper limit of the melting point of the main component polypropylene is not particularly limited, but may be 170 ° C. or lower and may be 168 ° C. or lower. In this invention, melting | fusing point says melting peak temperature calculated | required from the DSC curve measured according to JIS-K-7121.

  In the core component of the composite short fiber for absorbent articles, the main component polypropylene preferably has a tensile modulus measured according to JIS-K-7161 of 1600 MPa or more, more preferably 1650 MPa or more. 1680 MPa or more is particularly preferable. When the tensile modulus of the main component polypropylene is 1600 MPa or more, the core component has sufficient elasticity, and the card passing property of the composite short fiber is improved. In addition, since the core component of the composite short fiber has sufficient elasticity, the crimp expression is also improved.

(Sheath component)
In the composite short fiber for absorbent articles, the sheath component contains 60% by mass or more of high-density polyethylene having a melting point of 5 ° C. or more lower than that of the main component polypropylene in the core component. Since high density polyethylene has a higher density than other polyethylenes, the resulting composite short fiber is likely to have high rigidity, and the card passing property and crimp expression of the composite short fiber are improved and obtained. A bulky thermal bonding nonwoven fabric can be easily obtained. The content of the high-density polyethylene contained in the sheath component is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and particularly preferably in the sheath component, The resin component excluding the inorganic filler described later is a high-density polyethylene.

  In the composite short fiber for absorbent articles, the melt flow rate of the high-density polyethylene contained in the sheath component is not particularly limited, but the melt flow rate (MFR measured according to JIS-K-7210; measurement temperature 190 ° C., It is preferable that the load is 2.16 kgf (21.18 N), and hereinafter referred to as MFR190) is 5 g / 10 min or more and 30 g / 10 min or less. More preferred MFR 190 is 8 g / 10 min or more and 23 g / 10 min or less, and particularly preferred MFR 190 is 10 g / 10 min or more and 18 g / 10 min or less. When the MFR 190 of the high-density polyethylene is within the above range, not only the take-up property and drawability are improved, but also the sheath component of the obtained composite short fiber is sufficiently elastic to pass through the card machine. Thus, the card passing property of the composite short fiber is improved.

  Since the surface of the composite short fiber for absorbent articles is substantially composed of a sheath component containing 60% by mass or more of the high density polyethylene, the thermal adhesiveness of the composite short fiber is mainly melted by the high density polyethylene. Depends on the liquidity at the time. In addition, the strength of the heat-bonded nonwoven fabric using the composite staple fiber for absorbent articles mainly depends on the strength of the heat-bonding point between the constituent fibers generated by melting and heat-bonding the sheath component during heat treatment. ing. When the MFR 190 of the high-density polyethylene satisfies the above-described range, the fluidity at the time of melting of the sheath component is appropriately suppressed. As a result, when the fiber web containing the composite short fiber for absorbent articles is heat-treated near the melting point of the high-density polyethylene, the entire sheath component of the composite short fiber is melted, but it is difficult to flow because the fluidity is suppressed. As a result, the thickness of the sheath component is uniform, and thermal bonding points with uniform bonding strength are formed between constituent fibers at any bonding point, and the strength of the obtained thermal bonding nonwoven fabric is sufficient. Presumed to be expensive. When MFR190 of high-density polyethylene exceeds 30 g / 10 min, the sheath component tends to flow during heat treatment, and the thickness of the sheath component is uneven in the composite short fiber, and the adhesive strength is thermally bonded to the thin sheath component. There is a possibility that a low thermal bonding point may be formed inside the nonwoven fabric. As a result, when the nonwoven fabric is pulled in the longitudinal and / or transverse direction, or when friction is applied by rubbing the surface of the nonwoven fabric, the adhesive point with weak adhesive strength is likely to be detached, resulting in insufficient strength of the nonwoven fabric or causing the fluff of the nonwoven fabric. There is a fear. On the other hand, if the MFR 190 of the high-density polyethylene is less than 5 g / 10 minutes, the fluidity of the sheath component is too low, and there is a possibility that the spinning take-up property and stretchability may be lowered.

  In the sheath component of the composite short fiber for absorbent articles, the melting point of the high-density polyethylene is not particularly limited as long as it is 5 ° C. lower than the melting point of the main component polypropylene contained in the core component. Considering the passability and the productivity, strength and heat resistance of the heat-bonded nonwoven fabric, the melting point of the high-density polyethylene is preferably 125 ° C. or higher and 140 ° C. or lower, more preferably 128 ° C. or higher and 138 ° C. or lower. preferable.

  In the composite short fiber for absorbent articles of the present invention, the sheath component may contain a resin other than the above high-density polyethylene as long as the effect of the present invention is not impaired. Although it does not specifically limit as resin other than the said high density polyethylene, For example, polyolefin resin other than high density polyethylene, a polyester resin, a polyamide resin, a polycarbonate, a polystyrene etc. are mentioned. The polyolefin resin other than the high-density polyethylene is not particularly limited. For example, polypropylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, polymethylpentene, polybutene-1, and acrylic acid and methacrylic acid are used. Unsaturated carboxylic acid such as acid, maleic acid, unsaturated carboxylic acid ester such as acrylic acid ester, methacrylic acid ester, maleic acid ester, unsaturated carboxylic acid such as acrylic acid anhydride, methacrylic acid anhydride, maleic acid anhydride Examples include those obtained by copolymerizing at least one selected from the group consisting of acid anhydrides, those obtained by graft polymerization, and elastomers thereof. The polyester resin is not particularly limited, but examples thereof include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and acid components such as isophthalic acid, succinic acid, and adipic acid, and 1 , 4-butanediol, glycol components such as 1,6-hexanediol, copolymers with polytetramethylene glycol, polyoxymethylene glycol and the like, and elastomers thereof. Although it does not specifically limit as said polyamide resin, For example, nylon 6, nylon 66, nylon 11, nylon 12, etc. are mentioned. In addition, various known additives can be added to the sheath component as long as the effects of the present invention are not hindered and the fiber productivity, nonwoven fabric productivity, thermal adhesiveness, and touch are not affected. is there. Additives that can be added to the sheath component include known crystal nucleating agents, antistatic agents, pigments, matting agents, heat stabilizers, light stabilizers, flame retardants, antibacterial agents, lubricants, plasticizers, softeners, oxidation An inhibitor, an ultraviolet absorber, etc. can be contained.

  The said composite short fiber for absorbent articles contains 0.5 mass% or more and 10 mass% or less of inorganic fillers with respect to 100 mass% of composite short fibers. By including the inorganic filler in the above-described range, the apparent whiteness, that is, the whiteness of the heat-bonded nonwoven fabric including the composite short fiber for absorbent articles is increased. In addition, since the fineness of the composite short fiber for absorbent articles is 2.0 dtex or less, if the nonwoven fabric has the same basis weight, the number of fibers constituting the nonwoven fabric increases. It tends to be expensive. When the heat-bonded nonwoven fabric containing the composite short fiber for absorbent articles is used for the surface sheet of the absorbent article, menstrual blood, urine, etc. absorbed by the absorber located under the surface sheet due to high whiteness The so-called concealing property that makes the color of the excrement difficult to see from the surface becomes high. From the viewpoint of enhancing the concealability, the inorganic filler is preferably an inorganic powder having a high whiteness. Specifically, white inorganic powders such as titanium dioxide, zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, silica (silicon dioxide), mica, zeolite, and talc are contained in the composite short fiber as an inorganic filler. The inorganic filler preferably contains at least one selected from the group consisting of titanium dioxide, zinc oxide, calcium carbonate, barium sulfate, silica and talc, more preferably contains at least titanium oxide, substantially. It is particularly preferable that only titanium oxide is contained as an inorganic filler.

  In the composite short fiber for absorbent articles, the content of the inorganic filler may be 0.5% by mass or more and 10% by mass or less with respect to 100% by mass of the composite short fiber, but with respect to 100% by mass of the composite short fiber. It is preferably 0.8% by mass or more and 8% by mass or less, more preferably 1.0% by mass or more and 6.0% by mass or less, and 1.2% by mass or more and 5.0% by mass or less. Is more preferably 1.3% by mass or more and 3.5% by mass or less. The composite short fiber for absorbent articles contains an inorganic filler, so that when the heat-bonded nonwoven fabric containing the composite short fiber is used for an absorbent article, it exhibits excellent concealability and is combined with an inorganic filler. The tactile sensation of the short fiber itself and the heat-bonded nonwoven fabric containing the short fiber also tends to be soft. In addition, the inclusion of the inorganic filler reduces the occurrence of neps during the production of the card web and improves the card passing property. The inorganic filler may be contained in one or both of the sheath component and the core component constituting the composite short fiber. However, it is preferable that at least the core component contains an inorganic filler from the viewpoints of productivity of the composite short fiber for absorbent articles and concealment of the nonwoven fabric produced using the composite short fiber for absorbent articles. Moreover, in the said composite short fiber for absorbent articles, when content of an inorganic filler with respect to 100 mass% of composite short fibers exceeds 4 mass% or 5 mass%, an inorganic filler is only one resin component of a sheath component or a core component. When it is contained, the spinnability of the resin component containing the inorganic filler is extremely lowered. Therefore, it is preferable to contain the inorganic filler in both the sheath component and the core component.

  In the composite short fiber for absorbent articles, the cross-sectional structure is a concentric circular structure in which the position of the center of gravity of the core component substantially coincides with the position of the center of gravity of the composite short fiber. That is, in the fiber cross section, the center of gravity of the core component is not substantially deviated from the center of gravity of the composite short fiber. FIG. 1 is a schematic diagram of a fiber cross section of a composite short fiber for absorbent articles having a concentric structure. The sheath component 1 is disposed around the core component 2, and the sheath component 1 surrounds the periphery of the core component 2, so that the fiber surface other than the cut surface is covered with the sheath component 1 in the composite short fiber 10. Thereby, the surface of the sheath component 1 melt | dissolves at the time of heat-bonding the fiber web comprised with the composite short fiber, and heat-bonds fibers. In the composite short fiber 10, the core component 2 is not decentered, that is, has a concentric circular structure. Therefore, the thickness of the sheath component 1 in the fiber cross section is almost constant in any part of the fiber cross section. As a result, when heat-treating a fiber web composed of composite short fibers, even if any other fiber comes into contact with any portion of the composite short fibers in which the sheath component on the fiber surface is softened and melted, it is uniform. Since a strong heat-bonding point is formed, the heat-bonded nonwoven fabric using the composite short fiber for absorbent articles has a high bond strength and is resistant to friction and hardly fuzzes. The gravity center position 3 of the core component 2 is not substantially deviated from the gravity center position 4 of the composite short fiber 10. The fact that the center of gravity of the core component does not substantially deviate from the position of the center of gravity of the composite short fiber means that the ratio of deviation obtained by the following method (hereinafter also referred to as eccentricity) is 10% or less, preferably 7% or less. , Particularly preferably 5% or less, most preferably 3% or less.

<Eccentricity>
The cross section of the composite short fiber 10 is magnified by a scanning electron microscope or the like, the center of gravity position 3 of the core component 2 is C1, the center of gravity 4 of the composite short fiber 10 is Cf, and the radius 5 of the composite short fiber 10 is rf. Is calculated by the following mathematical formula 1.

[Equation 1]
Eccentricity (%) = [(Cf−C1) / rf] × 100

  In the composite short fiber for absorbent articles, the composite ratio of the core component and the sheath component is 52/48 to 73/27, preferably 55/45 to 70/30, as the volume ratio of the core component / sheath component, More preferably, it is 60 / 40-70 / 30, More preferably, it is 62 / 38-68 / 32. The core component mainly affects the elasticity of the entire composite short fiber, and the sheath component mainly affects the adhesive strength, tactile sensation, and hardness of the heat-bonded nonwoven fabric containing the composite short fiber. When the composite ratio of the core component and the sheath component in the composite short fiber for absorbent articles is 52/48 to 73/27, the card passing property of the composite short fiber and the adhesive strength of the heat-bonding nonwoven fabric containing the composite short fiber Both tactile sensations can be achieved. When the sheath component is too large, for example, when the composite ratio of the core component and the sheath component is 50/50, the strength of the nonwoven fabric increases, but the touch of the nonwoven fabric may be hardened. In addition, since the ratio of the core component is small, the fiber has no elasticity, the card passing property is likely to be lowered, and the crimp developing property is also likely to be lowered. On the other hand, when the core component becomes too large, for example, when the composite ratio of the core component and the sheath component is 80/20, the ratio of the sheath component contributing to the thermal bonding between the constituent fibers is small, and the sheath component is a composite short fiber. Because it exists as a thin layer covering the side surface of the fabric, the thermal bond point is small even when heat-treated to form a thermal bond point between the constituent fibers, and it is easy to come off by external force, so the nonwoven fabric strength is small There is a risk that fluffing may occur easily when friction is applied to the nonwoven fabric.

  In the composite short fiber for absorbent articles, the shape of the core component in the fiber cross section may be elliptical, Y-shaped, X-shaped, well-shaped, polygonal, star-shaped, etc. The shape of the fiber in the fiber cross section may be elliptical, Y-shaped, X-shaped, well-shaped, polygonal, star-shaped, or hollow, as well as circular.

  The composite short fiber for absorbent articles has a fineness of 1.1 dtex to 2.0 dtex. When the fineness is 2.0 dtex or less, the heat-bonded nonwoven fabric containing the composite short fiber for absorbent articles has a smooth touch and becomes a soft nonwoven fabric. In addition, in the case of non-woven fabrics with the same basis weight due to the small fineness, since the number of fibers constituting the non-woven fabric is larger than the non-woven fabric composed of fibers with high fineness, the texture and appearance of the non-woven fabric are fine and the concealment is high Easy to become non-woven fabric. When the fineness of the composite short fiber for absorbent articles exceeds 2.0 dtex, a nonwoven fabric having a soft and smooth feel and high concealability cannot be obtained. The fineness of the composite short fiber for absorbent articles is preferably 1.8 dtex or less, and more preferably 1.7 dtex or less. In the composite short fiber for absorbent articles, when the fineness is 1.1 dtex or more, the card passing property of the composite short fiber is improved, and the productivity is improved. The fineness of the composite short fiber for absorbent articles is more preferably 1.2 dtex or more. The fineness of the composite short fiber for absorbent articles can be adjusted as desired by adjusting the fineness and draw ratio of the spinning filament described later.

  The composite staple fiber for absorbent articles mainly has at least one crimp selected from the group consisting of a serrated crimp (also referred to as a mechanical crimp) shown in FIG. 2A and a corrugated crimp shown in FIG. 2B. The number of crimps is preferably 5/25 mm or more and 25/25 mm or less. A more preferable number of crimps is 8 pieces / 25 mm or more and 22 pieces / 25 mm or less, and a more preferred number of crimps is 10 pieces / 25 mm or more and 20 pieces / 25 mm or less. In addition, the above-mentioned composite short fiber for absorbent articles is crimped from the viewpoint of the card passing property of the composite short fiber for absorbent articles, and the tactile sensation and bulk recovery of the heat-bonded nonwoven fabric containing the composite short fiber for absorbent articles. The rate is preferably 5% or more and 20% or less, more preferably 6% or more and 18% or less, and further preferably 6.5% or more and 16% or less.

  The fiber length of the composite staple fiber for absorbent articles is not particularly limited, but is preferably 25 mm or more and less than 65 mm. This is because, when the fiber length satisfies this range, the composite short fiber for absorbent articles is excellent in card passing property even if it has a fineness and can produce a fiber web (card web) with good formation. If the fiber length is less than 25 mm, the fiber length is too short and does not catch on the card, so that a so-called fly state is likely to occur, and the card web may not be manufactured. When the fiber length is 65 mm or more, the so-called nep occurs frequently because the composite short fibers are too much caught on the wire of the card machine or the composite short fibers are easily entangled with each other, so that so-called nesting occurs frequently. There is a risk that it will not be possible. The fiber length of the composite short fiber for absorbent articles is more preferably 28 mm or greater and 55 mm or less, still more preferably 30 mm or greater and 48 mm or less, and particularly preferably 34 mm or greater and 45 mm or less.

  The single fiber strength of the composite short fiber for absorbent articles is not particularly limited, but the single fiber strength is preferably 2.4 cN / dtex or more and 6.0 cN / dtex or less, more preferably 2.6 cN / dtex or more. 0.6 cN / dtex or less, and more preferably 2.8 cN / dtex or more and 5.4 cN / dtex or less. In addition, the elongation of the composite short fiber for absorbent articles is not particularly limited, but from the viewpoint of card passability of the composite short fiber for absorbent articles, the elongation at break is preferably 20% or more and 120% or less, More preferably, they are 25% or more and 100% or less, More preferably, they are 28% or more and 90% or less, Especially preferably, they are 30% or more and 80% or less.

Young's modulus of the composite staple fibers for the absorbent article is not particularly limited, in view of the card passing property, it is preferable that the apparent Young's modulus is 1500 N / mm ² or more 3200N / mm ² or less, more preferably 1600 N / mm ² or more 3000N / mm ² or less, further preferably 1800 N / mm ² or more 2800N / mm ² or less.

  Hereinafter, the manufacturing method of the composite short fiber for absorbent articles of this invention is demonstrated. Although the said composite staple fiber for absorbent articles is not specifically limited, For example, it can manufacture as follows.

  First, a sheath component containing 60% by mass or more of high-density polyethylene and a core component containing 50% by mass or more of polypropylene having a melting point higher by 5 ° C. than the melting point of the high-density polyethylene are prepared. Next, in the fiber cross section, a composite type nozzle, for example, a concentric circular core, is arranged so that the sheath component covers the surface of the composite short fiber and the center of gravity of the core component is concentric with the center of gravity of the composite short fiber. The sheath component and the core component are supplied to the sheath type composite nozzle, the core component is melt-spun at a spinning temperature of 250 ° C. to 350 ° C., the sheath component is melt-spun at a spinning temperature of 230 ° C. to 330 ° C., and the take-up speed is 500 m / min to 2500 m / Take up in less than a minute to obtain a spun filament. By using polypropylene having a Q value before spinning of 3.0 or more and 10.0 or less as the main component polypropylene contained in the core component, the Q value of the main component polypropylene in the core component after spinning is 3.0 or more and 8.0. Adjust to:

  Next, the obtained spinning filament is stretched at a stretching ratio of not less than 3.0 times and not more than 8.5 times at a stretching temperature of 40 ° C. or higher and lower than the melting point of the sheath component. A more preferable lower limit of the stretching temperature is 60 ° C. or higher. A more preferable upper limit of the stretching temperature is a temperature 5 ° C. lower than the melting point of the sheath component, and a particularly preferable upper limit of the stretching temperature is a temperature 10 ° C. lower than the melting point of the sheath component. When the stretching temperature is less than 40 ° C., the crystallization of the sheath component is difficult to proceed, so that the thermal shrinkage tends to increase and the bulk recovery property tends to decrease. If the stretching temperature is equal to or higher than the melting point of the sheath component, the fibers tend to be fused. A more preferable lower limit of the draw ratio is 3.3 times or more. A more preferable upper limit of the draw ratio is 8.0 times or less. When the draw ratio is 3.0 times or more, crystallization of the sheath component and the core component proceeds, and a fiber having good card passability is obtained. The stretching method is not particularly limited, and wet stretching is performed while being heated with a high-temperature liquid such as high-temperature hot water, dry stretching is performed while being heated in a high-temperature gas or a high-temperature metal roll, and 100 ° C. or higher. A known stretching process such as steam stretching, in which stretching is performed while heating the fiber under normal pressure or pressurized state, can be performed. Among these, wet stretching using hot water or dry stretching using a high-temperature gas or a high-temperature metal roll is preferable. The stretching process may be so-called one-stage stretching in which the stretching process is only one stage, may be two-stage stretching in which the stretching process has two stages, or may be multi-stage stretching in which the stretching process exceeds two stages. Since the composite short fiber for absorbent articles of the present invention has a fineness as small as 2.0 dtex or less, it is often drawn at a high magnification. Therefore, the stretching step is preferably multistage stretching performed in a plurality of times. Moreover, you may perform an annealing process before and after the said extending | stretching process as needed.

  Then, if necessary, crimps of 5 crimps / 25 mm or more and 25/25 mm or less are applied using a known crimping machine such as a stuffing box type crimper. The crimped shape after passing through the crimper may be a serrated crimp and / or a corrugated crimp. When the number of crimps is less than 5 pieces / 25 mm, the card passing property tends to deteriorate, and the initial bulk and bulk recoverability of the nonwoven fabric tend to deteriorate. On the other hand, when the number of crimps exceeds 25 pieces / 25 mm, the number of crimps is too large, so that the card passing property is lowered, and the formation of the nonwoven fabric is deteriorated. Moreover, you may process with a fiber processing agent as needed before or after providing a crimp.

  Furthermore, it is preferable that after the crimping is performed by the crimping machine, an annealing treatment is performed. The annealing treatment is preferably performed in an atmosphere such as dry heat, moist heat, and steam within a temperature range of 80 ° C. to 120 ° C., and more preferably 90 ° C. to 120 ° C. Specifically, after applying the fiber treatment agent to the fiber bundle, crimping is performed with a crimping machine, and the drying process is performed simultaneously with the annealing process in a dry heat atmosphere of 90 ° C. or more and 120 ° C. or less. Can be simplified. When the annealing treatment is performed at a temperature of 90 ° C. or higher, the dry heat shrinkage of the obtained composite short fiber does not increase, and the composite short fiber expresses a clear crimped shape. Become.

  The composite short fiber obtained by the above method mainly has at least one kind of crimp selected from the group consisting of a serrated crimp (also referred to as a mechanical crimp) shown in FIG. 2A and a corrugated crimp shown in FIG. 2B. In addition, since the number of crimps is 5/25 mm or more and 25/25 mm or less, a nonwoven fabric having a soft and smooth texture can be obtained without deteriorating the card passing property, which is preferable. And it cut | disconnects to desired fiber length, and an actual crimpable composite staple fiber is obtained.

  The fineness of the composite short fiber for absorbent articles can be adjusted as desired by adjusting the fineness of the spinning filament and the draw ratio. After the above-described annealing treatment, the composite short fiber for absorbent articles having a predetermined length is obtained by cutting the fiber.

  By containing 20% by mass or more of the composite short fiber for absorbent articles in the nonwoven fabric, a nonwoven fabric having excellent surface tactile sensation, excellent bulkiness, flexibility in the thickness direction, and bulk recoverability is formed.

  Subsequently, as an example of the nonwoven fabric containing the composite short fiber for absorbent articles of the present invention, a thermal bonding nonwoven fabric will be described together with its production method. The heat-bonding nonwoven fabric for absorbent articles of the present invention contains 20% by mass or more of the composite short fibers for absorbent articles, and at least a part of the composite short fibers for absorbent articles is bonded by a sheath component. The heat-bonding nonwoven fabric for absorbent articles is obtained by preparing a fiber web containing 20% by mass or more of the composite short fiber for absorbent articles, thermally bonding the obtained fiber web, and integrating the fibers. be able to. When other fibers are used, for example, natural fibers, regenerated fibers, purified cellulose fibers, semi-synthetic fibers, and synthetic fibers can be used as the other fibers. Examples of the natural fiber include cotton, silk, wool, hemp, and pulp. Examples of the regenerated fiber include rayon and cupra. Examples of the purified cellulose fiber include tencel and lyocell. Examples of the semi-synthetic fiber include acetate and triacetate. Examples of the synthetic fiber include acrylic fiber, polyester fiber, polyamide fiber, polyolefin fiber, and polyurethane fiber. As the other fibers, one type or a plurality of types of fibers can be appropriately selected from the above-described fibers depending on the application. Other fibers may be used by mixing with the composite short fiber for absorbent articles of the present invention, or a fiber web composed of the composite short fiber for absorbent articles of the present invention and a fiber web composed of other fibers are laminated. May be used.

  Examples of the fiber web used when producing the heat-bonding nonwoven fabric for absorbent articles include card webs such as parallel webs, semi-random webs, random webs, cross webs, and cross webs, airlaid webs, and the like. Since the nonwoven fabric used for the absorbent article, particularly the surface sheet of the absorbent article, is required to have bulkiness, flexibility, and a certain amount of voids between the fibers, the fiber web is preferably a card web. As the heat-bonding nonwoven fabric, two or more types of different types of fiber webs may be laminated and used.

  It is preferable to obtain a non-woven fabric in the form of a heat-bonded non-woven fabric in which the fiber web is subjected to a heat treatment to thermally bond the fibers with a sheath component. This is because the heat-bonded nonwoven fabric remarkably exhibits the effects brought about by the composite short fiber of the present invention, such as flexibility in the thickness direction, bulk recoverability, and smooth texture of the nonwoven fabric surface. In order to entangle the fibers, the fiber web may be subjected to entanglement treatment such as needle punch treatment or hydroentanglement treatment before and / or after heat treatment, if necessary.

  In order to obtain a heat-bonding nonwoven fabric, the fiber web is subjected to heat treatment by a known heat treatment means. As the heat treatment means, a heat treatment machine that does not apply much pressure such as wind pressure to the fiber web, such as a hot air penetration type heat treatment machine, a hot air blowing type heat treatment machine, and an infrared heat treatment machine, is preferably used. The heat treatment conditions such as the heat treatment temperature are selected and carried out, for example, such that the sheath component is sufficiently melted and / or softened so that the fibers are joined at the contact or intersection and the crimp is not crushed. For example, the heat treatment temperature is the melting point of the high-density polyethylene contained in the sheath component before spinning (if a plurality of high-density polyethylenes are contained in the sheath component, the melting point of the high-density polyethylene having the highest melting point) is Tm. In this case, it is preferable that the temperature be in the range of Tm or more and (Tm + 40 ° C.) or less.

  The heat-bonding nonwoven fabric for absorbent articles is a nonwoven fabric having a good surface feel. The surface tactile sensation of the heat-bonded nonwoven fabric can be sensory evaluated. The surface tactile sensation of the heat-bonded nonwoven fabric can be measured and evaluated based on the KES (Kawabata Evaluation System) method, which is one of methods for objectively evaluating the texture of the fabric. Specifically, as a characteristic value of the surface friction, an average friction coefficient (hereinafter also referred to as MIU) and a variation of the average friction coefficient (sometimes referred to as an average deviation of the friction coefficient μ, hereinafter also referred to as MMD). Measured. MIU represents the difficulty (or ease of slipping) of slipping on the surface, and the larger the value, the more difficult it is to slip. MMD shows the dispersion | variation in friction, and it shows that the surface is so rough that this is large. The surface of the heat-bonded nonwoven fabric of the present invention tends to have a relatively small MIU, and MMD tends to be particularly small compared to conventional nonwoven fabrics. Such a non-woven fabric not only has a small feeling of friction when touching the hand or skin, but also has a small coefficient of friction variation, that is, any part of the non-woven fabric surface has a low coefficient of friction, and feels like it gets caught on fingers or skin. Because it does not give, it gives a light touch that is slippery even when it comes into contact with the skin. The equipment for measuring the characteristic value of the surface friction is not particularly limited as long as the equipment can measure the surface friction based on the KES method. For the characteristic value of surface friction, for example, a friction tester (“KES-SE”, manufactured by Kato Tech Co., Ltd.), an automated surface tester (“KES-FB4-AUTO-A”, manufactured by Kato Tech Co., Ltd.), etc. are used. Can be measured.

  The surface characteristics of the heat-bonded nonwoven fabric, that is, the surface friction of the heat-bonded nonwoven fabric, is determined by applying heat treatment with hot air to the surface opposite to the surface on which the hot air is blown when manufacturing the heat-bonded nonwoven fabric. When making the nonwoven fabric, the fiber web was placed and was in contact with the conveyance support used to convey the inside of the heat treatment machine (for example, a conveyor net that introduces and conveys the fiber web into the hot air through heat treatment machine). Measure on the surface. The surface that was in contact with the transport support is more likely to be smoother than the surface to which hot air is blown, and a smooth tactile sensation is likely to be obtained.Therefore, in the surface sheet of the absorbent article, this surface is directly applied to the wearer's skin. This is because, when used on a contact surface (skin contact surface), the tactile sensation becomes smoother than when a surface blown by hot air is applied to the skin, and the usability of the absorbent article is improved. When measuring the surface friction of the heat-bonded nonwoven fabric, if it is not clear which surface is the surface to which hot air was blown during heat treatment or the surface that was placed on the transport support during heat treatment, the surface friction The surface where the MMD is a smaller value is taken as the measurement surface.

  The heat-bonding nonwoven fabric for absorbent articles of the present invention is smooth and soft to the touch. Among the characteristic values of surface friction based on the KES method described above, MMD affects the smoothness when the nonwoven fabric is touched. Since the nonwoven fabric containing the composite short fiber for absorbent articles of the present invention not only has a small MMD, but also has a relatively small average coefficient of friction (MIU), the surface of the nonwoven fabric is in contact with the skin as described above. Gives a slippery and light touch.

  Some composite short fibers have a large MIU and a small MMD when the surface of the nonwoven fabric containing the composite short fibers is evaluated based on the KES method. Since such a non-woven fabric is transmitted to the fingers and skin without a relatively large friction, it gives a “moist touch” and “smoothness” to feel the friction in a smooth touch. Since such a non-woven fabric is also preferable as a non-woven fabric used in the absorbent article, it is considered that the non-woven fabric used in the absorbent article is required to have as small an average friction coefficient variation (MMD) as possible.

  The heat-bonding nonwoven fabric using the composite short fiber for absorbent articles of the present invention preferably has an average coefficient of friction fluctuation (MMD) of less than 0.01, more preferably 0.0095 or less. Preferably, it is 0.009 or less. The lower limit of the average friction coefficient variation (MMD) is not particularly limited and is preferably closer to 0, but may be 0.0005 or more, or 0.001 or more.

  The heat-bonding nonwoven fabric for absorbent articles of the present invention is soft as a whole and gives a smooth feel when touched on the surface of the nonwoven fabric. The above heat-bonding nonwoven fabric for absorbent articles is preferably used as a surface sheet for various absorbent articles such as sanitary napkins, infant paper diapers, adult paper diapers, animal diapers such as mammals, panty liners, and incontinence liners. It can be used for applications such as infant paper diapers and adult paper diaper backsheets that can be touched from the outside. When used as a surface sheet of an absorbent article, it is preferable that the composite short fiber for absorbent articles of the present invention is contained in an amount of 20% by mass or more on the skin contact surface. In addition, in order to take advantage of the flexibility of the entire nonwoven fabric and the concealing property of the nonwoven fabric, the absorbent article also absorbs the above-mentioned absorption on the absorber side, for example, a so-called second sheet located directly below the surface sheet. A heat-bonding nonwoven fabric for adhesive articles can be preferably used.

The basis weight of the heat-bonding nonwoven fabric for absorbent articles of the present invention is not particularly limited, but is preferably 5 g / m ² or more and 70 g / m ² or less, more preferably 8 g / m ² or more and 60 g / m ² or less. It is more preferably 10 g / m ² or more and 55 g / m ² or less, and particularly preferably 15 g / m ² or more and 50 g / m ² or less. The basis weight of the heat-bonding nonwoven fabric for absorbent articles of the present invention may be outside these ranges depending on the type of absorbent article. In addition, the heat-bonding nonwoven fabric for absorbent articles is used in various applications, such as various paper diapers and sanitary napkin surface sheets, various paper diaper back sheets, and second sheets disposed directly under the absorbent article surface sheet. When used, the basis weight is appropriately selected according to the application.

  When the heat-bonding nonwoven fabric for absorbent articles is used as a surface sheet of the absorbent article, the heat-bonding nonwoven fabric for absorbent articles contains 20% by mass or more of the composite short fiber for absorbent articles. Preferably, the heat-bonding nonwoven fabric for absorbent articles contains 25% by mass or more of the composite short fibers for absorbent articles, and more preferably contains 30% by mass or more. In the heat-bonding nonwoven fabric for absorbent articles, when the ratio of the composite staple fibers for absorbent articles is within the above range, a nonwoven fabric that has excellent surface tactile sensation and that feels smooth when touched can be easily obtained. is there. In the heat-bonding nonwoven fabric for absorbent articles, the content of the composite short fibers for absorbent articles may be 100% by mass, 90% by mass or less, or 80% by mass or less. .

  When the heat-adhesive nonwoven fabric for absorbent articles is used as a surface sheet of the absorbent article, the composite staple fibers for absorbent articles may be dispersed throughout the nonwoven fabric, and the nonwoven fabric is composed only of the composite staple fibers for absorbent articles. However, the composite short fibers for absorbent articles are unevenly distributed on one surface of the nonwoven fabric, that is, one surface is a fiber layer containing 25% by mass or more of the composite short fibers for absorbent articles of the present invention. One surface is preferably a fiber layer containing the composite short fiber for absorbent articles of the present invention in a proportion of less than 25% by mass. And it is preferable to use the fiber layer containing 25% by mass or more of the composite short fiber for absorbent articles as a skin contact surface that is directly touched by the skin of the wearer of the absorbent article. By using the nonwoven fabric having such a laminated structure as a surface sheet, the surface of the nonwoven fabric containing 25% by mass or more of the composite short fiber for absorbent articles hits the skin, so that the user of the absorbent article can use comfortably. In addition to giving a feeling, by making the fiber layer containing the composite short fibers for absorbent articles in a proportion of less than 25% by mass into a more bulky fiber layer, the surface sheet becomes a surface sheet excellent in cushioning properties.

  When the heat-adhesive nonwoven fabric for absorbent articles is used as a surface sheet of the absorbent article, one surface is an upper fiber layer containing 50% by mass or more of the composite short fiber for absorbent articles, and the other surface is the absorbent. It is preferable to set it as the 2 layer nonwoven fabric which is a lower fiber layer containing 20 mass% or less of composite short fibers for adhesive articles. The content of the composite short fiber for absorbent articles of the present invention in the upper fiber layer is preferably 75% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. A fiber layer substantially consisting of 100% by mass of the composite short fiber for absorbent articles is particularly preferable. The content of the composite short fiber for absorbent articles of the present invention in the lower fiber layer is preferably 15% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less. .

  The above-mentioned heat-bonding nonwoven fabric for absorbent articles has the strength required when used as a nonwoven fabric (for example, a surface sheet or a back sheet) constituting the absorbent article, prevents fuzz on the surface due to friction during use, and when touched From the viewpoint of soft tactile feel, the longitudinal breaking strength measured according to JIS L 1096 8.14.1 A method (strip method) is preferably 15 N / 5 cm or more, more preferably 20 N / 5 cm or more. More preferably, it is more preferably 25 N / 5 cm or more.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to these Examples.

  The measurement method and evaluation method used in this example are as follows.

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

  The Q value of PP before spinning was measured using the used PP resin pellets as it was, and the Q value of PP after spinning was measured using the obtained composite short fiber. The PP Q value after spinning is determined by melting and extruding the PP resin from the extruder with the spinning nozzle set at 290 ° C. and without attaching the spinning nozzle when performing melt spinning. A rod-shaped resin strand having a diameter of 5 to 8 mm may be produced, and the rod-shaped resin strand cut into a length of about 3 mm may be used as a sample for measurement.

(Spinnability during melt spinning)
The spinnability of the composite short fiber for absorbent articles was evaluated based on the following criteria based on the occurrence state and frequency of yarn breakage when melt spinning for 30 minutes continuously.
A: The number of yarn breaks is 0 to 2 in 30 minutes of continuous melt spinning, and the spinnability is good.
B: Although the number of yarn breaks is 3 to 5 in 30 minutes of continuous melt spinning, there is no problem in the process.
C: The number of yarn breakage is 6 times or more in 30 minutes of continuous melt spinning, or yarn breakage occurs frequently and spinning is impossible.

(Extensible)
The drawability of the composite short fibers for absorbent articles was evaluated based on the following criteria based on the occurrence of yarn breakage during the drawing process and the passability of the stuffing box type crimper used for crimping.
A: Yarn breakage hardly occurs in the drawing process, and the stuffing box type crimper passes easily, so there is no problem in production.
B: In the drawing process, thread breakage or clogging in the stuffing box type crimper occurs, but there is no problem in production.
C: Productivity is very poor because yarn breakage frequently occurs and winding around the drawing tank and drawing roll occurs, or clogging frequently occurs in the stuffing box type crimper or in the discharge port.

(Card passability)
Evaluation of the card passability of composite short fibers for absorbent articles based on the following conditions, based on the occurrence of neps and flies when a fiber web is produced using a card machine, and the texture of the obtained fiber web did.
A: Since the fiber easily passes through the card machine, and almost no nep or fly occurs, a fiber web having a good texture can be obtained.
B: Nep is slightly generated but does not significantly affect the formation of the fiber web.
C: The fiber web cannot be obtained because the card passing property is poor or a large amount of neps are generated.

(Number of crimps and crimp rate)
It measured according to JIS L 1015 (2010).

(Single fiber strength, elongation at break and apparent Young's modulus)
The single fiber strength and elongation at break of the fiber were measured according to JIS L 1015 (2010). The apparent Young's modulus was obtained from the single fiber strength.

(Breaking strength of nonwoven fabric)
In accordance with JIS L 1096 8.14.1 A method (strip method), using a constant-speed tension type tensile tester, tension was performed under the conditions of a sample piece width of 5 cm, a grip interval of 10 cm, and a tensile speed of 30 ± 2 cm / min. It applied to the test and the load value (tensile strength) at the time of cutting was measured, and it was set as the breaking strength. The tensile test was carried out with the longitudinal direction (MD direction) of the nonwoven fabric as the tensile direction. All the evaluation results are shown as an average of values measured for three samples.

(Surface feel)
The surface of the nonwoven fabric was touched and evaluated according to the following evaluation criteria.
A: Very smooth.
B: I feel a little rough.
C: It is rough.

(Bulky)
The bulkiness of the nonwoven fabric was evaluated by measuring the thickness at a load of 3 g / cm ² . The thickness was measured according to JIS-L-1096 using a thickness measuring device (trade name “THICKNESS GAUGE”, model “CR-60A”, manufactured by Daiei Kagaku Seiki Seisakusho Co., Ltd.).

Polypropylene (PP), high density polyethylene (HDPE), and titanium oxide-containing polypropylene (titanium oxide-containing PP) used in Examples and Comparative Examples are as follows.
(1) PP-A (melting point: 160 ° C., MFR230: 30 g / 10 min, Q value (before spinning): 4.6)
(2) PP-B (melting point: 160 ° C., MFR230: 20 g / 10 min, Q value (before spinning): 5.6)
(3) PP-C (melting point: 161 ° C., MFR230: 13.5 g / 10 min, Q value (before spinning): 2.8)
(4) HDPE-A (melting point: 130 ° C., MFR190: 12 g / 10 min)
(5) HDPE-B (melting point: 130 ° C., MFR190: 22 g / 10 min)
(6) Titanium oxide-containing PP (hereinafter also referred to as master batch, MB): 60 parts by mass of titanium oxide powder and 40 parts by mass of PP are kneaded by a twin screw extruder, and the obtained kneaded product is about 5 mm square. To obtain PP containing 60% by mass of titanium oxide.

(Examples 1-10, Comparative Examples 1-4)
The above-described high-density polyethylene was used as the sheath component, and the above-described polypropylene was used as the core component. Further, in the core component polypropylene, a master batch was mixed so that the content of titanium oxide in the entire composite short fiber was in the proportions shown in Tables 1 and 2. Each of the prepared sheath component and core component was adjusted so that the composite ratio (volume ratio) between the sheath component and the core component became the composite ratios shown in Tables 1 and 2 using a concentric core-sheath composite nozzle (600 holes). Melt spinning was performed by adjusting the discharge amount of the components. The spinning temperature of the sheath component was 270 ° C., the spinning temperature of the core component was 290 ° C., and the extruded molten filament was taken out at the take-up speed shown in Tables 1 and 2, and the spinning filaments having the finenesses shown in Tables 1 and 2 were used. Got.

  The obtained spinning filament was wet-drawn in hot water at 90 ° C. at the draw ratios shown in Tables 1 and 2, and further drawn to a draw ratio of 1.1 times in hot water at 95 ° C. Of drawn filaments (finenesses listed in Tables 1 and 2). Next, 0.3% by mass of an oil agent obtained by blending 35 parts by mass of C8 alkyl phosphate potassium salt and 65 parts by mass of C12 alkyl phosphate potassium salt was added as a fiber treatment agent, and then the stuffing box type was applied to the drawn filament. Mechanical crimp was applied with a crimper. And the annealing process and the drying process were simultaneously performed in the relaxed state for 15 minutes with the hot air spraying apparatus set to 110 degreeC. Thereafter, the filament was cut into the predetermined lengths shown in Tables 1 and 2 to obtain composite short fibers for absorbent articles.

  In any of the examples and comparative examples, the spinnability and stretchability were good.

(Measurement of thermal bonding nonwoven fabric manufacturing method and number of neps)
Using the fibers obtained in Examples and Comparative Examples, a fiber web having a basis weight of about 25 g / m ² was produced by a roller type card machine. Under the present circumstances, the card | curd permeability of the composite short fiber was evaluated with the said evaluation criteria. The obtained fiber web was subjected to heat treatment for 10 seconds using a hot air spraying device set at 135 ° C., and the sheath component was melted to obtain a heat-bonded nonwoven fabric. The obtained heat-bonded nonwoven fabric was cut into a size of 60 cm × 25 cm, and the number of neps generated in the nonwoven fabric was visually confirmed and measured. And the mass of the nonwoven fabric cut | judged to the said predetermined | prescribed magnitude | size was measured, and the number of neps (pieces / g) per nonwoven fabric mass was computed from the measured number of neps and the mass of a nonwoven fabric. These results are shown in Tables 1 and 2 below.

  The performances of the fibers and nonwoven fabrics obtained in each Example and each Comparative Example are shown in Table 1 and Table 2 below. In Table 1, the Q value is the Q value of PP after spinning.

  As can be seen from the data in Table 1 and Table 2, the core-sheath type composite short fibers of Examples 1 to 10 had 20 or less neps per 1 g of fiber, and the card passing property was good. From the result of Examples 8-10, it turned out that generation | occurrence | production of a nep reduces, so that there is much content of the titanium oxide in the composite staple fiber for absorbent articles. Moreover, the heat-bonding nonwoven fabric containing the composite short fibers for absorbent articles of Examples 1 to 10 was bulky, had a smooth feel, and was excellent in texture. Moreover, the heat bonding nonwoven fabric containing the composite short fiber for absorbent articles of Examples 1 to 10 was also excellent in breaking strength.

  On the other hand, the heat-bonding nonwoven fabric containing the eccentric core-sheath composite short fiber of Comparative Example 1 in which the center of gravity of the core component deviates from the position of the center of gravity of the fiber had a low breaking strength. Due to the low breaking strength, when the heat-bonded nonwoven fabric is used as a surface sheet for absorbent articles, the surface of the nonwoven fabric becomes fuzzy due to friction during use, and it tends to have a rough feel. The heat-bonded nonwoven fabric containing the core-sheath composite short fiber of Comparative Example 2 having a core-sheath ratio of 50/50 and a large amount of sheath components had poor touch feeling. The core-sheath type composite short fiber of Comparative Example 4 having a fineness of less than 1.1 dtex had more than 20 neps per 1 g of fiber, and the card passing property was poor. The core-sheath type composite short fiber of Comparative Example 3 in which the Q value after spinning of the polypropylene constituting the core component is less than 3.0 has more than 20 neps per 1 g of fiber, and the card passing property is poor. It was.

(Examples 11-12, Comparative Examples 5-6)
A heat-bonding nonwoven fabric was produced using the core-sheath composite short fibers obtained in Examples 6 and 7 and the fibers 1 to 3 shown below. First, as the first fiber layer, predetermined fibers were put into a roller card machine so as to have a basis weight described in Table 3, and a fiber web (first fiber layer) was produced. Next, as the second fiber layer, predetermined fibers were put into a roller-type card machine so as to have a basis weight described in Table 3, and a fiber web (second fiber layer) was produced. A fiber web to be the second fiber layer was placed on the fiber web to be the first fiber layer to obtain a laminated fiber web. The laminated fiber web was subjected to hot air treatment for 15 seconds using a hot air spraying device set at 135 ° C., and the sheath component was melted to bond the core-sheath composite short fibers to obtain a heat-bonded nonwoven fabric. At this time, the hot air was blown against the fiber web from the second fiber layer side, and the first fiber layer side was in contact with the conveyor net of the hot air blowing device.

(1) Fiber 1: Core component is PET (melting point 256 ° C.), sheath component is HPDE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and volume ratio of core component / sheath component (core-sheath ratio) ) Was 64/36, and an eccentric core-sheath type composite short fiber (fineness: 2.6 dtex, fiber length: 51 mm) having an eccentricity of 25% was used.
(2) Fiber 2: The core component is PET (melting point 256 ° C.), the sheath component is HPDE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and the volume ratio of the core component / sheath component (core-sheath ratio) ) Was 64/36, and a core-sheath type composite short fiber (fineness: 2.2 dtex, fiber length: 51 mm) having a concentric structure in which a core component and a sheath component were arranged concentrically was used.
(3) Fiber 3: The core component is PET (melting point 256 ° C.), the sheath component is HPDE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and the volume ratio of the core component / sheath component (core-sheath ratio) ) Was 64/36, and an eccentric core-sheath composite short fiber (fineness: 3.3 dtex, fiber length: 51 mm) having an eccentricity of 25% was used.

  About each obtained heat bonding nonwoven fabric, the surface characteristic was measured and evaluated based on KES (Kawabata Evaluation System) method.

  Specifically, in order to evaluate the surface characteristics, a surface friction test of the heat-bonded nonwoven fabric was performed, and the average friction coefficient (MIU) and the variation of the average friction coefficient (MMD) were measured as the surface characteristic values. A “KES-SE” friction tester manufactured by Kato Tech Co., Ltd. was used for the test and measurement of the surface friction on the heat-bonded nonwoven fabric. At the time of measurement, the measurement surface is the opposite side of the surface to which the hot-bonded nonwoven fabric was blown with hot air during manufacture (that is, the surface placed on the conveyor net surface of the hot air blowing device), and the static load on the friction element is 25 gf ( 245N), the friction element was moved in a direction parallel to the vertical direction of the nonwoven fabric at a moving speed of 1 mm / sec, and the average friction coefficient (MIU) and the variation of the average friction coefficient (MMD) of the heat-bonded nonwoven fabric were measured. The measurement results are shown in Table 3.

  As can be seen from the data in Table 3, the nonwoven fabrics of Examples 11 and 12 using the polyolefin-based composite short fibers of the present invention have particularly a change in average friction coefficient (MMD) that affects smoothness when touching the skin. It was small. This is because the fineness is reduced, the core component and the sheath component constituting the composite short fiber are mainly composed of polyolefin resin, and the number of fibers contained in the nonwoven fabric with the same basis weight because the fineness of the fiber itself is small. This is thought to be due to the fine texture on the nonwoven fabric surface. Further, when the nonwoven fabric of Example 11 and the nonwoven fabric of Example 12 are compared, since the value of MMD is smaller in Example 11 in which the composite short fibers having a finer fineness are used, the smaller the fineness, the present invention. It is considered that the texture of the heat-bonded nonwoven fabric is improved.

  On the other hand, the nonwoven fabrics of Comparative Examples 5 to 6 each using a polyester composite short fiber having a fineness of 2.2 dtex and a polyester composite short fiber having a fineness of 2.6 dtex have an average friction coefficient (MIU) of the nonwoven fabric surface of Example 11, Although it is about the same as 12 nonwoven fabrics, the average coefficient of variation (MMD) value is not as small as the nonwoven fabrics of the examples. From these results, the composite staple fiber for absorbent articles of the present invention is a composite staple fiber having a fineness mainly composed of polyolefin resin, and compared with conventional composite staple fibers, particularly polyester composite staple fibers. And it can be said that it becomes a heat-bonding nonwoven fabric with a smoother tactile sensation when touching the skin.

  The composite staple fiber for absorbent articles of the present invention can be contained in a heat-bonded nonwoven fabric, and the heat-bonded nonwoven fabric is a paper diaper for animals including sanitary napkins, infant paper diapers, adult paper diapers, and mammals. In addition, it can be preferably used for the surface sheet of various absorbent articles such as panty liners, incontinence liners, etc. In applications such as infant paper diapers and adult paper diaper back sheets, in absorbent articles, the absorbent side, for example, the surface It can also be preferably used for a second sheet located directly under the sheet.

DESCRIPTION OF SYMBOLS 1 Sheath component 2 Core component 3 Center of gravity position in fiber cross section of core component 4 Center of gravity position in fiber cross section of composite short fiber 5 Radius in fiber cross section of composite short fiber 10 Composite short fiber

Claims (9)

A composite short fiber for absorbent articles comprising a core component and a sheath component,
In the composite short fiber, the core component and the sheath component are arranged substantially concentrically, and the composite ratio of the core component and the sheath component is 52/48 to 73/27 in the volume ratio of the core component / sheath component. Is a core-sheath type composite short fiber,
The core component includes 50% by mass or more of polypropylene having a ratio Mw / Mn of 3.0 or more and 8.0 or less of the weight average molecular weight Mw and the number average molecular weight Mn after spinning,
The sheath component contains 60% by mass or more of high-density polyethylene having a melting point lower than that of the polypropylene by 5 ° C. or more,
The composite short fiber contains 0.5% by mass to 10% by mass of an inorganic filler with respect to 100% by mass of the composite short fiber,
A composite short fiber for absorbent articles, wherein the fineness of the composite short fiber is 1.1 dtex or more and 2.0 dtex or less.   The melt flow rate measured under the conditions of a measurement temperature of 190 ° C and a load of 21.18 N according to JIS-K-7210 of the high-density polyethylene is 5 g / 10 min or more and 30 g / 10 min or less. Composite short fiber for absorbent articles.   The composite short fiber for absorbent articles according to claim 1 or 2, wherein the fiber length is 25 mm or more and less than 65 mm.   The inorganic filler is at least one inorganic filler selected from the group consisting of titanium dioxide, zinc oxide, calcium carbonate, and talc, and contains the inorganic filler in the core component. The composite short fiber for absorbent articles as described in the item. The single fiber strength is 2.4 cN / dtex or more and 6.0 cN / dtex or less, the elongation at break is 20% or more and 120% or less, and the apparent Young's modulus is 1200 N / mm ² or more. The composite short fiber for absorbent articles according to claim 1.   The composite staple fiber for absorbent articles according to any one of claims 1 to 5, wherein the number of crimps is 5/25 mm or more and 25/25 mm or less, and the crimp rate is 5% or more and 20% or less. It is a manufacturing method of the composite staple fiber for absorptive articles given in any 1 paragraph of Claims 1-6,
A core component containing 50% by mass or more of a polypropylene having a ratio Mw / Mn of 3.0 or more and 10.0 or less and a mass average molecular weight Mw to a number average molecular weight Mn of 60, and a high-density polyethylene having a melting point of 5 ° C. or more lower than the polypropylene. The sheath component containing mass% or more is arranged in a fiber cross section so that the sheath component covers the surface of the composite short fiber, and the center of gravity of the core component coincides with the center of gravity of the composite short fiber. A composite short fiber for absorbent articles comprising a step of supplying to a composite nozzle and melt-spinning the core component at a spinning temperature of 250 ° C to 350 ° C and the sheath component at a spinning temperature of 230 ° C to 330 ° C. Production method.   The composite short fiber for absorbent articles according to any one of claims 1 to 6 is contained in an amount of 20% by mass or more, and at least a part of the composite short fibers for absorbent article is bonded by a sheath component. A heat-bonding nonwoven fabric for absorbent articles.   An absorbent article comprising the heat-bonding nonwoven fabric for absorbent articles according to claim 8, wherein the heat-bonding nonwoven fabric for absorbent articles is arranged as a topsheet and / or a backsheet. Goods.

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