JP2015204983A - Surface sheet for absorbent article, and absorbent article including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface sheet for an absorbent article, having excellent liquid-absorbing property.SOLUTION: There are included a first fiber layer 11 contacting the skin, and a second fiber layer 12 adjacent to the first fiber layer 11. The first fiber layer 11 includes 50 mass% or more of a first core-sheath type composite short fiber whose core component includes polypropylene, and whose sheath component includes thermoplastic resin having a melting point lower by 5°C or more than that of polypropylene. The second fiber layer 12 includes 50 mass% or more of a second core-sheath type composite short fiber whose core component includes polyester resin, and whose sheath component includes thermoplastic resin having a melting point lower by 50°C or more than that of polyester resin, and where a centroid position of the core component is out of the centroid position of the fiber. The first core-sheath type composite short fiber has a fineness of 0.5dtex-2.1dtex, and the second core-sheath type composite short fiber has a fineness of 2.2dtex-5.2dtex. At least part each of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber is thermally adhered by the sheath components of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber.

Description

  TECHNICAL FIELD The present invention relates to an absorbent article surface sheet used for absorbent articles such as sanitary napkins and paper diapers (including baby diapers and adult paper diapers), and an absorbent article including the same. In detail, it is related with the surface sheet for absorbent articles which has a multilayered structure, and the absorbent article containing this.

  Absorbent articles such as sanitary napkins and paper diapers are mainly composed of a surface sheet that contacts the skin of the wearer, an absorbent that absorbs liquid, and a leak-proof sheet that does not allow liquid to leak out. And the surface sheet used for the absorbent article has a soft and smooth tactile sensation for comfort when worn, blood excreted from the body such as menstrual blood, excretion of urine, fluid feces, etc. What is called for is a concealing property, etc. that is excellent in liquid-absorbing properties for absorbing substances, and that prevents absorbed menstrual blood, excrement and the like from being visible from the surface.

  As a surface sheet used for an absorbent article, Patent Document 1 is formed of a non-woven fabric having an upper layer facing the skin and a lower layer located below the upper layer, and at least the fibers constituting the upper layer contain titanium oxide. A surface material has been proposed in which the elongation rate of the fibers constituting the lower layer is lower than that of the fibers constituting the upper layer and the tensile strength is increased. Patent Document 2 includes a first layer having a fiber diameter of 11 to 18 μm and a second layer having a fiber diameter of 19 to 31 μm arranged adjacent to the first layer. A top sheet used for an absorbent article made of a nonwoven fabric has been proposed.

JP 2001-61891 A JP 2004-166831 A

  The surface sheets described in Patent Document 1 and Patent Document 2 have high concealability, have a smooth texture, and are difficult to cause rewet, but liquid absorption characteristics such as run-off and liquid absorption speed have not been studied.

  The present invention has been made in view of such circumstances, and has a surface sheet for an absorbent article having a smooth tactile sensation and good liquid absorption characteristics such as run-off and liquid absorption speed, and an absorbent article including the same. provide.

  The present invention is an absorbent article surface sheet including a first fiber layer in contact with the skin and a second fiber layer adjacent to the first fiber layer, wherein the first fiber layer includes a core component. Is a fiber layer containing 50% by mass or more of a first core-sheath-type composite short fiber containing a thermoplastic resin having a melting point of 5 ° C. or more lower than the melting point of the polypropylene. The core component includes a polyester resin, the sheath component includes a thermoplastic resin having a melting point lower by 50 ° C. or more than the melting point of the polyester resin, and the center of gravity of the core component is shifted from the center of gravity of the fiber. A fiber layer containing 50% by mass or more of core-sheath type composite short fiber, wherein the first core-sheath type composite short fiber has a fineness of 0.5 dtex to 2.1 dtex, and the second core-sheath type composite short fiber Has a fineness of 2.2 dtex or more .2 dtex or less, and at least part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber are the first core-sheath type composite short fiber and the second core-sheath type composite short fiber. It is related with the surface sheet for absorbent articles characterized by being heat-bonded by the sheath component.

  The first core-sheath type composite short fiber is a core-sheath type composite short fiber having a concentric structure in which the core component and the sheath component are arranged substantially concentrically, and a composite ratio of the core component and the sheath component. Is preferably 52/48 to 73/27 in the volume ratio of the core component / sheath component. The content of polypropylene in the core component of the first core-sheath-type composite short fiber is 50% by mass or more, and the ratio Mw / Mn of the weight average molecular weight Mw and the number average molecular weight Mn after spinning of the polypropylene is 3.0 or more. It is preferable that it is 8.0 or less. In the sheath component of the first core-sheath-type composite short fiber, the thermoplastic resin having a melting point lower by 5 ° C. or more than the melting point of polypropylene contained in the core component of the first core-sheath-type composite short fiber is high-density polyethylene. The content of the high-density polyethylene in the sheath component of the first core-sheath composite short fiber is 50% by mass or more, the measurement temperature is 190 ° C., the load is 21. 21 according to JIS-K-7210 of the high-density polyethylene. The melt flow rate measured under the condition of 18N is preferably 5 g / 10 min or more and 30 g / 10 min or less. The fiber length of the first core-sheath type composite short fiber is preferably 25 mm or more and less than 65 mm.

The basis weight of the first fiber layer is 4 g / m ² or more and 18 g / m ² or less, the basis weight of the second fiber layer is 10 g / m ² or more and 30 g / m ² or less, and the basis weight of the second fiber layer is The basis weight of the first fiber layer is preferably larger.

  In the top sheet for absorbent articles, it is preferable that a variation (MMD) of an average friction coefficient measured based on the KES method using the surface of the first fiber layer as a measurement surface is 0.0092 or less.

  The present invention also relates to an absorbent article comprising the above-described top sheet for absorbent articles.

  The present invention provides a surface sheet for absorbent articles that has a smooth tactile sensation and has good liquid absorption characteristics such as run-off and liquid absorption speed, and an absorbent article including the same.

FIG. 1 is a schematic cross-sectional view of a top sheet for absorbent articles according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a fiber cross section of a core-sheath composite short fiber having a concentric structure used in the present invention. FIG. 3 is a schematic cross-sectional view showing a fiber cross section of an eccentric core-sheath type composite short fiber used in the present invention. 4A to 4D are schematic views showing crimped forms of core-sheath type composite short fibers used in the present invention.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have obtained a surface for an absorbent article that includes a first fiber layer in contact with the skin and a second fiber layer adjacent to the first fiber layer. In the sheet, the first fiber layer includes 50% by mass of a first core-sheath type composite short fiber containing a thermoplastic resin having a core component containing polypropylene and a sheath component having a melting point lower by 5 ° C. or more than the melting point of the polypropylene. The fiber layer includes the second fiber layer, the core component includes a polyester resin, the sheath component includes a thermoplastic resin having a melting point lower by 50 ° C. than the melting point of the polyester resin, and the center of gravity of the core component. Is a fiber layer containing 50% by mass or more of second core-sheath type composite short fibers shifted from the center of gravity of the fiber, and the fineness of the first core-sheath type composite short fibers is 0.5 dtex or more and 2.1 dtex or less, Second core sheath type The fineness of the combined short fiber is 2.2 dtex or more and 5.2 dtex or less, and at least a part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber is used as the first core-sheath type composite short fiber. And heat-bonding with the sheath component of the second core-sheath type composite short fiber, the surface sheet for absorbent articles has a smooth tactile sensation, and liquid absorption characteristics such as run-off and liquid absorption speed are improved. The headline, the present invention has been reached. That is, in the absorbent article topsheet including the first fiber layer that contacts the skin and the second fiber layer adjacent to the first fiber layer, the first fiber layer that forms the first fiber layer that contacts the skin. The fineness of the core-sheath type composite short fiber and the fineness of the second core-sheath type composite short fiber constituting the second fiber layer adjacent to the first fiber layer are set within a specific range, and The fineness is smaller than that of the second core-sheath composite short fiber. In addition, polypropylene is included in the core component of the first core-sheath type composite short fiber, polyester resin is included in the core component of the second core-sheath type composite short fiber, and the cross section of the second core-sheath type composite short fiber is shown. It has an eccentric cross section. As a result, it was found that the surface sheet for absorbent articles has a smooth tactile sensation and good liquid absorption characteristics such as run-off and liquid absorption speed.

  The top sheet for absorbent articles of the present invention includes a first fiber layer that contacts the skin and a second fiber layer adjacent to the first fiber layer. FIG. 1 is a schematic cross-sectional view of a top sheet for absorbent articles according to an embodiment of the present invention. As shown in FIG. 1, the top sheet 1 for absorbent articles includes a first fiber layer 11 and a second fiber layer 12 adjacent to the first fiber layer 11.

(First fiber layer)
The first fiber layer contains 50% by mass or more of a first core-sheath type composite short fiber including a thermoplastic resin having a core component containing polypropylene and a sheath component having a melting point lower than the melting point of the polypropylene by 5 ° C. or more. It is. The first fiber layer preferably contains 60% by mass or more of the first core-sheath type composite short fiber, more preferably 70% by mass of the first core-sheath type composite short fiber, from the viewpoint of excellent tactile sensation and liquid absorption characteristics. More preferably, the first core-sheath type composite short fiber is contained in an amount of 80% by mass or more, and particularly preferably the first core-sheath type composite short fiber is contained in an amount of 90% by mass or more. When the first fiber layer includes other fibers in addition to the first core-sheath composite short fibers, for example, natural fibers, regenerated 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 synthetic fiber include acrylic fiber, polyester fiber, polyamide fiber, polyolefin fiber, and polyurethane fiber. As the other fibers, one or more kinds of fibers can be appropriately selected from the above-described fibers depending on the application.

<Core component>
The content of polypropylene in the core component of the first core-sheath composite short fiber is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 80% by mass or more, and particularly preferably. It is 90 mass% or more, Most preferably, it is the structure in which all the resin components except the inorganic filler mentioned later are polypropylene in a core component. The polypropylene (hereinafter also referred to as PP) 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, 1-octadecene and the like. The propylene content in the copolymer is preferably 50% by mass or more. Among these, from the viewpoint of improving the bulk recoverability of the surface sheet for absorbent articles, it is a kind selected from the group consisting of a propylene homopolymer, an ethylene-propylene copolymer, and an ethylene-butene-1-propylene terpolymer. It is preferable that the polypropylene in the core component is a propylene homopolymer in consideration of the productivity, card passing property and economy (manufacturing cost) of the first core-sheath composite short fiber.

  In the core component of the first core-sheath type composite short fiber, the ratio Mw / Mn (hereinafter also referred to as “Q value”) of the weight average molecular weight Mw and the number average molecular weight Mn after spinning of the polypropylene is 3.0 or more. It is preferably 8.0 or less, more preferably 3.0 or more and 6.5 or less, further preferably 3.2 or more and 6.0 or less, and 3.4 or more and 5.5 or less. It is particularly preferred. The first core-sheath-type composite short fiber has excellent card-passability, and the first core-sheath-type composite short fiber is produced by having the Q value after spinning of the polypropylene of 3.0 or more and 8.0 or less. Productivity is also improved.

  The 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 is 120,000 or more, the polypropylene has a high molecular weight polypropylene molecule in the polypropylene, and the Q value after spinning of the polypropylene easily satisfies the above-mentioned range. Many high molecular weight polypropylene molecules remain in the single-core-sheath type composite short fiber. The upper limit of the weight average molecular weight Mw after spinning of the polypropylene is not particularly limited, but may be 300,000 or less, 240000 or less, or 220,000 or less. When the weight average molecular weight Mw after spinning of polypropylene exceeds 300,000, the spinnability and stretchability are lowered, and it is difficult to obtain the first core-sheath-type composite short fibers with high productivity.

  The Q value and mass average molecular weight Mw of the 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 Q value and the value of Mw are values after spinning unless otherwise stated as values before spinning.

  In the first core-sheath composite short fiber, the core component may contain other resin in addition to the polypropylene. Although it does not specifically limit as said other resin, For example, polyolefin resin other than the said polypropylene, a polyester resin, a polyamide resin, a polycarbonate, a 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 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, 1,6 hexanediol and other glycol components, polytetramethylene glycol, polyoxymethylene glycol and other copolymers, 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, 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, various known various core components of the first core-sheath composite short fiber Additives may be added. Additives that can be added to the core component of the first core-sheath composite short fiber include known crystal nucleating agents, antistatic agents, pigments, matting agents, heat stabilizers, light stabilizers, flame retardants, antibacterial agents, and lubricants. , Plasticizers, softeners, antioxidants, ultraviolet absorbers and the like.

  In the core component of the first core-sheath composite short fiber, the melt flow rate of the 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). (21.18N), 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 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 first core The card | curd permeability of a sheath type composite short fiber becomes favorable.

  In the core component of the first core-sheath-type composite short fiber, the melting point of the polypropylene is not particularly limited, but considering the card passing property and the strength and heat resistance of the surface sheet for absorbent articles (heat-bonded nonwoven fabric) using the same. The melting point of the polypropylene is preferably 150 ° C. or higher, more preferably 152 ° C. or higher, and particularly preferably 155 ° C. or higher. When the polypropylene has a melting point of 150 ° C. or higher, a fiber web is produced using the first core-sheath type composite short fiber, and when the fiber web is subjected to heat treatment such as hot air processing, the volume of the nonwoven fiber web is increased. Is less likely to be reduced, and it is easy to obtain a heat-bonded nonwoven fabric that is bulky and soft to the touch. Although the upper limit of the melting point of the polypropylene is not particularly limited, it 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 first core-sheath-type composite short fiber, the polypropylene preferably has a tensile modulus measured according to JIS-K-7161 of 1600 MPa or more, more preferably 1650 MPa or more, and 1680 MPa. The above is particularly preferable. When the tensile modulus of the polypropylene contained in the core component is 1600 MPa or more, the core component has sufficient elasticity to pass through the card machine, and the card-passability of the first core-sheath composite short fiber is improved. Become good. In addition, since the core component of the composite short fiber has sufficient elasticity, when a mechanical crimp is applied using a crimper or the like, the shape of the given mechanical crimp is easily maintained, and the crimp expression is also good. It will be a thing.

<Sheath component>
In the first core-sheath-type composite short fiber, the sheath component includes a thermoplastic resin having a melting point lower than that of polypropylene in the core component by 5 ° C. or more. In the sheath component of the first core-sheath type composite short fiber, the thermoplastic resin having a melting point of 5 ° C. or more lower than that of the polypropylene in the core component is not particularly limited, but high-density polyethylene (hereinafter also referred to as HDPE) is used. It is preferable. When the sheath component of the first core-sheath-type composite short fiber contains high-density polyethylene, the first core-sheath-type composite short fiber is likely to be highly rigid and combined with polypropylene that satisfies the above-mentioned specific Q value range. By configuring the composite short fiber, the elasticity of the entire fiber becomes high, and the card passing property and crimp expression of the first core-sheath type composite short fiber are likely to be good. Moreover, the 1st fiber layer containing a 1st core-sheath-type composite short fiber and the surface sheet for absorbent articles containing a 1st fiber layer are easy to become bulky. The content of the high-density polyethylene contained in the sheath component of the first core-sheath composite short fiber is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. Particularly preferably, in the sheath component, all the resin components excluding the inorganic filler described later are high-density polyethylene.

  In the first core-sheath type composite short fiber, 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 card passing property of the first core-sheath type composite short fiber is improved.

  In the sheath component of the first core-sheath composite short fiber, the melting point of the high-density polyethylene is not particularly limited as long as it is lower by 5 ° C. or more than the melting point of polypropylene contained in the core component. Considering the fiber card passability and the productivity, strength and heat resistance of the absorbent article surface sheet, the high-density polyethylene preferably has a melting point of 125 ° C. or higher and 140 ° C. or lower, and 128 ° C. or higher and 138 ° C. The following is more preferable.

  In the first core-sheath composite short fiber, the sheath component may contain other resin in addition to the high-density polyethylene. Although it does not specifically limit as said other resin, For example, what was enumerated as other resin added to the core component of a 1st core-sheath-type composite short fiber can be used. Further, the sheath component of the first core-sheath type composite short fiber is also known as long as the effect of the present invention is not hindered and does not affect fiber productivity, nonwoven fabric productivity, thermal adhesiveness, and touch. Various additives can be added.

The first core-sheath type composite short fiber preferably contains an inorganic filler in an amount of 0.5% by mass to 10% by mass with respect to 100% by mass of the composite short fiber. By including the inorganic filler in the above-described range, the apparent whiteness, that is, the whiteness of the surface sheet for absorbent articles is increased. In addition, since the fineness of the first core-sheath-type composite short fiber is 2.1 dtex or less, the surface of the first fiber layer containing the first core-sheath-type composite short fiber only easily diffuses visible light. If the nonwoven fabric has the same basis weight, the number of fibers constituting the nonwoven fabric increases, and the whiteness of the surface sheet for absorbent articles is likely to be further increased. When the absorbent article absorbs excrement such as menstrual blood and urine due to the high whiteness of the surface sheet for absorbent articles, the menstrual blood, urine, etc. absorbed by the absorber located under the surface sheet The color of the excrement becomes difficult to see from the surface, so that the so-called concealing property 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 (TiO ₂ , hereinafter also simply referred to as titanium oxide), zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, silica (silicon dioxide), mica, zeolite, talc, etc. The first core-sheath composite short fiber is contained 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 first core-sheath type composite short fiber, the content of the inorganic filler is preferably 0.8% by mass or more and 8% by mass or less, more preferably 1.0% by mass or more with respect to 100% by mass of the composite short fiber. It is 6.0 mass% or less, More preferably, it is 1.2 mass% or more and 5.0 mass% or less, Most preferably, it is 1.3 mass% or more and 3.5 mass% or less. When the first core-sheath-type composite short fiber contains an inorganic filler, as described above, when the surface sheet for absorbent articles containing the composite short fiber is used for an absorbent article, it exhibits excellent concealability. In addition, the tactile sensation of the composite short fiber itself and the surface sheet for absorbent articles containing this tends to be soft by including the inorganic filler. The inorganic filler may be contained in one or both of the sheath component and the core component constituting the first core-sheath type composite short fiber. From the viewpoint of concealing the surface sheet for absorbent articles, it is preferable to contain an inorganic filler in at least the core component of the first core-sheath composite short fiber. Further, when the content of the inorganic filler with respect to 100% by mass of the first core-sheath-type composite short fiber exceeds 4% by mass or 5% by mass, when the inorganic filler is contained only in one resin component of the sheath component or the core component, Since the spinnability of the resin component including the inorganic filler is extremely lowered, it is preferable to include the inorganic filler in both the sheath component and the core component.

  The first core-sheath type composite short fiber is preferably a core-sheath type composite short fiber having a concentric structure in which the core component and the sheath component are arranged substantially concentrically. FIG. 2 is a schematic cross-sectional view showing a fiber cross section of a core-sheath type composite short fiber having a concentric circular structure. As shown in FIG. 2, in the core-sheath type composite short fiber 2 having a concentric circular structure, the sheath component 21 and the core component 22 are arranged substantially concentrically. That is, in the fiber cross section, the center of gravity position 23 of the core component 22 is not substantially deviated from the center of gravity position 24 of the core-sheath type composite short fiber 2. When the first core-sheath type composite short fiber is a core-sheath type composite short fiber having a concentric circular structure, the sheath component 21 is arranged around the core component 22, and the sheath component 21 surrounds the periphery of the core component 22. Thus, in the core-sheath type composite short fiber 2 having a concentric circular structure, the fiber surface other than the cut surface is covered with the sheath component 21. Thus, when the fiber web composed of the first core-sheath type composite short fibers having the concentric circular structure is thermally bonded, the sheath component constituting the surface of the first core-sheath type composite short fibers is melted, and the fibers are thermally bonded. To do. In the first core-sheath type composite short fiber, the core component is not decentered, that is, has a concentric circular structure. Therefore, the thickness of the sheath component in the fiber cross section is almost constant in any part of the fiber cross section. ing. As a result, when heat-treating the fiber web composed of the first core-sheath type composite short fibers, any portion other than the first core-sheath type composite short fibers in which the sheath component on the fiber surface is softened and melted Even if the fibers are contacted with each other, a uniform strength thermal bonding point is formed. Therefore, the first fiber layer using the first core-sheath-type composite short fiber has high adhesive strength, is resistant to friction and is difficult to fluff. Become. 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 core-sheath composite short fiber is magnified with a scanning electron microscope or the like, the center of gravity 23 of the core component 22 is C1, the center of gravity 24 of the core-sheath composite short fiber 2 is Cf, and the core-sheath composite When the radius 25 of the short fiber is rf, it is calculated by the following mathematical formula 1.

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

  In the first core-sheath composite short fiber, the composite ratio of the core component to the sheath component is preferably 52/48 to 73/27, more preferably 55/45 to 70/27, as the volume ratio of the core component / sheath component. 30, more preferably 60/40 to 70/30, and particularly preferably 62/38 to 68/32. When the composite ratio of the core component to the sheath component in the first core-sheath-type composite short fiber is in the above-described range, the card-passability of the first core-sheath-type composite short fiber and the first core-sheath-type composite short fiber are included. The tactile sensation of the surface sheet for absorbent articles is improved.

  In the first core-sheath type composite short fiber, 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 first core-sheath type composite short fiber has a fineness of 0.5 dtex or more and 2.1 dtex or less. When the fineness of the first core-sheath-type composite short fiber is 2.1 dtex or less, the tactile sensation of the surface sheet for absorbent articles tends to be smooth and the concealability tends to be high. From the viewpoint of improving the tactile sensation and concealing property of the surface sheet for absorbent articles, the fineness of the first core-sheath type composite short fiber is preferably 1.8 dtex or less, and more preferably 1.7 dtex or less. When the fineness is 0.5 dtex or more, the liquid absorption characteristics such as the run-off of the top sheet for absorbent articles is shortened and the liquid absorption speed is increased. From the viewpoint of shortening the run-off of the top sheet for absorbent articles and improving the liquid absorption characteristics, the fineness of the first core-sheath composite short fiber is preferably 0.8 dtex or more, and 1.0 dtex or more. Is more preferable and 1.1 dtex or more is particularly preferable.

  The first core-sheath type composite short fiber 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. 4A and a corrugated crimp shown in FIG. 4B. The number of crimps is preferably 5/25 mm or more and 25/25 mm or less. A surface sheet for absorbent articles that is soft and has a smooth texture can be obtained without reducing the card-passing property. A more preferable number of crimps is 8 pieces / 25 mm or more and 20 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 first core-sheath type composite short fiber has a crimp rate of 5% or more and 20% from the viewpoint of the card passing property of the composite short fiber and the touch and bulk recovery of the nonwoven fabric containing the first core-sheath type composite short fiber. % 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 first core-sheath-type composite short fiber is not particularly limited, but considering the card passing property, the fiber length is preferably 25 mm or more and less than 65 mm. When the fiber length satisfies this range, even if the first core-sheath-type composite short fiber has a fineness, it is possible to produce a card web that has excellent card passage and good formation. In the case of fine fibers, 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. In the case of fine fibers, if the fiber length is 65 mm or more, so-called nep, in which the composite short fibers are excessively applied to the wire of the card machine or the composite short fibers are easily entangled with each other, the fibers gather in a hairball shape. There is a risk that card webs cannot be manufactured frequently. The fiber length of the first core-sheath type composite short fiber is more preferably 28 mm or more and 55 mm or less, further preferably 30 mm or more and 48 mm or less, and particularly preferably 34 mm or more and 45 mm or less.

(Second fiber layer)
In the second fiber layer, the core component includes a polyester resin, the sheath component includes a thermoplastic resin having a melting point that is lower by 50 ° C. than the melting point of the polyester resin, and the center of gravity of the core component deviates from the center of gravity of the fiber. It is a fiber layer containing 50 mass% or more of the second core-sheath type composite short fiber. The second fiber layer preferably includes 60% by mass or more of the second core-sheath type composite short fiber, more preferably 70% by mass or more, and further preferably 80% by mass or more from the viewpoint of excellent liquid absorption characteristics. Especially preferably, it contains 90 mass% or more. When the second fiber layer includes other fibers in addition to the second core-sheath composite short fibers, for example, natural fibers, regenerated 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 recycled fiber include rayon and cupra. Examples of the synthetic fiber include acrylic fiber, polyester fiber, polyamide fiber, polyolefin fiber, and polyurethane fiber. As the other fibers, one or more kinds of fibers can be appropriately selected from the above-described fibers depending on the application.

  The second core-sheath type composite short fiber is an eccentric core-sheath type composite short fiber in which the center of gravity of the core component is shifted from the center of gravity of the fiber. FIG. 3 is a schematic cross-sectional view showing a fiber cross section of an eccentric core-sheath type composite short fiber. As shown in FIG. 3, the center of gravity position 33 of the core component 32 is shifted from the center of gravity position 34 of the core-sheath-type composite short fiber 3. The crimped shape of the eccentric core-sheath type composite short fiber is generally a corrugated crimp shown in FIG. 4B or a helical crimp shown in FIG. 4C (also called a coiled crimp) rather than the sawtooth crimp shown in FIG. 4A. ). Further, the crimped shape of the eccentric core-sheath type composite short fiber may be a crimped shape in which a wave-shaped crimp and / or a spiral crimp are mixed in a sawtooth-shaped crimp. FIG. 4D is a schematic view of a crimped shape in which serrated crimps and corrugated crimps are mixed. And compared with the composite short fiber which has a serrated crimp, the composite short fiber in which a wave shape crimp, a spiral crimp, a serrated crimp, a wave shape crimp, and / or a spiral crimp are mixed. The heat-bonded nonwoven fabric using is likely to be a bulky, non-woven fabric having a sparse internal structure in which many voids are present inside the nonwoven fabric. Therefore, by including the second core-sheath type composite short fiber, which is an eccentric core-sheath type composite short fiber, in the second fiber layer, the second fiber layer becomes a fiber layer having a sparse structure with many voids. The liquid absorbed by one fiber layer (for example, blood such as menstrual blood or excrement such as urine) can be easily drawn into the second fiber layer, and the core-sheath type composite short has a concentric structure as a fiber constituting the second fiber layer. As compared with the case where fibers are used, the liquid absorption characteristics such as the run-off becomes shorter and the liquid absorption speed becomes faster. The second core-sheath type composite short fiber preferably has an eccentricity of more than 10% and 50% or less, more preferably 15% or more and 30% or less. The eccentricity of the second core-sheath composite short fiber is obtained by magnifying a cross section of the core-sheath composite short fiber with a scanning electron microscope or the like, the center of gravity position 33 of the core component 32 is C1, and the core-sheath composite short fiber. 3 is Cf, and the composite short fiber radius 35 is rf.

  The second core-sheath type composite short fiber has a fineness of 2.2 dtex or more and 5.2 dtex or less. By making the fineness of the second core-sheath type composite short fiber constituting the second fiber layer larger than the fineness of the first core-sheath type composite short fiber constituting the first fiber layer, the surface sheet for absorbent articles is appropriate. It has excellent cushioning properties, and the tactile sensation is smooth, and the liquid absorption property is also good. If the fineness of the second core-sheath type composite short fiber is less than 2.2 dtex, even if the second core-sheath type composite short fiber is an eccentric core-sheath type composite short fiber, the second fiber layer has a small fineness. As a result, the second fiber layer has a dense structure and does not absorb excreta such as menstrual blood or urine. Further, when the fineness of the second core-sheath type composite short fiber exceeds 5.2 dtex, the number of constituents of the second fiber layer is relatively reduced due to the high fineness of the second core-sheath type composite short fiber. The second fiber layer becomes too sparse, so that capillary action is less likely to occur, and excretion such as menstrual blood and urine is not absorbed. The fineness of the second core-sheath type composite short fiber is more preferably 2.6 dtex or more and 4.8 dtex or less, and further preferably 2.8 dtex or more and 4.6 dtex or less.

  In the second core-sheath type composite short fiber, the core component preferably contains 50% by mass or more of the polyester resin, more preferably 60% by mass or more, further preferably 70% by mass or more, and particularly preferably 80% by mass or more. Including. When the core component contains 50% by mass or more of the polyester resin, the card passing property of the second core-sheath composite short fiber becomes good. 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, 1,6 hexanediol and other glycol components, polytetramethylene glycol, polyoxymethylene glycol and other copolymers, and elastomers thereof. The polyester resin is preferably polyethylene terephthalate (hereinafter also referred to as PET) from the viewpoints of bulkiness, cushioning properties, and liquid absorption speed of the surface sheet for absorbent articles.

  In the second core-sheath composite short fiber, the thermoplastic resin having a melting point lower by 50 ° C. or more than the polyester resin contained in the core component is not particularly limited, but high-density polyethylene is preferably used. When the sheath component of the second core-sheath-type composite short fiber contains high-density polyethylene, the second core-sheath-type composite short fiber tends to have high rigidity, and the card-passing property of the second core-sheath-type composite short fiber can be improved. Shrinkage tends to be good. The content of the high-density polyethylene contained in the sheath component of the second core-sheath type composite short fiber is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. Especially preferably, it is 100 mass%. As said high density polyethylene, the high density polyethylene which can be used for the sheath component of the 1st core sheath type | mold composite short fiber mentioned above can be used. It is preferable that the high-density polyethylene contained in the sheath component of the first core-sheath composite short fiber and the high-density polyethylene contained in the sheath component of the second core-sheath composite short fiber have substantially the same melting point. It becomes easy to thermally bond the first core-sheath type composite short fiber and the second core-sheath type composite short fiber by the sheath component of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber.

  In the second core-sheath type composite short fiber, 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 fiber length of the second core-sheath type composite short fiber is not particularly limited, and may be, for example, 76 mm or less. From the viewpoint of processability when producing the surface sheet for absorbent articles, the fiber length is preferably 35 mm or more and 65 mm or less, more preferably 40 mm or more and 60 mm or less, and further preferably 44 mm or more and 55 mm or less.

  In the top sheet for absorbent articles of the present invention, at least a part of the first core-sheath composite short fiber and the second core-sheath composite short fiber is composed of the first core-sheath composite short fiber and the second core-sheath composite short fiber. It is thermally bonded by the sheath component of the fiber. A first fiber web containing 50 mass% or more of the first core-sheath type composite short fiber and a second fiber web containing 50 mass% or more of the second core-sheath type composite short fiber are laminated, and a fiber web having a laminated structure is obtained. Heat treatment is performed to thermally bond at least a part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber with the sheath component.

  Examples of the fiber web include card webs such as parallel webs, semi-random webs, random webs, cross webs, and Chris cross webs, airlaid webs, and the like. Since the surface sheet for absorbent articles is required to be bulky, flexible, and to have an appropriate porosity with some gaps between the fibers, the fiber web is preferably a card web. The first fiber layer and the second fiber layer may be different types of fiber webs.

  The fiber web having the laminated structure is subjected to heat treatment, and the first core-sheath composite short fiber and the second core-sheath composite short fiber are formed by the sheath component of the first core-sheath composite short fiber and the second core-sheath composite short fiber. The surface sheet for absorbent articles of the present invention can be obtained in the form of a heat-bonded nonwoven fabric including a first fiber layer (first fiber web) and a second fiber layer (second fiber web). it can. This is because, in the form of a heat-bonded nonwoven fabric, effects such as flexibility in the thickness direction, bulk recoverability, and a smooth texture on the nonwoven fabric surface are remarkably exhibited. 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. The first fiber web and the second fiber web may be entangled with each other near the boundary.

  The heat treatment can be performed by a known heat treatment machine. For example, a heat treatment machine in which pressure such as wind pressure is not so much applied to the fiber web, such as a hot air through heat treatment machine, a hot air blowing type heat treatment machine, and an infrared heat treatment machine, is preferably used for the heat treatment. The heat treatment conditions such as the heat treatment temperature are selected and implemented, 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. A more preferable heat treatment temperature range is (Tm + 5 ° C.) or more and (Tm + 30 ° C.) or less.

  The surface sheet for absorbent articles has good tactile sensation. The tactile sensation of the surface sheet for absorbent articles 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, in the above surface sheet for absorbent articles, the surface of the first fiber layer is the measurement surface, and the variation of the average friction coefficient based on the KES method (sometimes referred to as the average deviation of the friction coefficient μ, It is also referred to as MMD.) And the tactile sensation is evaluated. MMD shows the dispersion | variation in friction, and it shows that the surface is so rough that this is large. The instrument for measuring the variation of the average friction coefficient is not particularly limited as long as it is an instrument capable of measuring surface friction based on the KES method. For example, a friction tester (“KES-SE”, manufactured by Kato Tech), an automated surface tester (“KES-FB4-AUTO-A”, manufactured by Kato Tech), or the like can be used.

  From the viewpoint that the surface sheet for absorbent articles has a smooth tactile sensation and is excellent in texture, the surface of the first fiber layer is the measurement surface, and the variation in the average friction coefficient measured based on the KES method is 0.0092. Or less, more preferably 0.009 or less, and even more preferably 0.0088 or less.

  From the viewpoint that the top sheet for absorbent articles has no liquid leakage of excrement such as menstrual blood or urine and is excellent in liquid absorption characteristics, the run-off measured as described later is preferably 45 mm or less, and 40 mm or less. More preferably, it is 35 mm or less. In addition, from the viewpoint that the absorbent sheet top sheet is excellent in repeated liquid absorption characteristics, the third liquid absorption rate measured as described later is preferably 40 seconds or less, more preferably 35 seconds or less. Yes, more preferably 30 seconds or less.

In the said surface sheet for absorbent articles, it is preferable that the fabric weight of a 1st fiber layer is lower than the fabric weight of a 2nd fiber layer from a viewpoint of a liquid absorption characteristic. From the viewpoint of low liquid return and excellent wetback resistance, the basis weight of the first fiber layer is preferably 4 g / m ² or more and 18 g / m ² or less, and preferably 5 g / m ² or more and 18 g / m ² or less. Is more preferably 6 g / m ² or more and 15 g / m ² or less, and particularly preferably 7 g / m ² or more and 14 g / m ² or less. Further, from the viewpoint of low liquid return and excellent wet-back resistance, the basis weight of the second fiber layer is preferably 10 g / m ² or more and 30 g / m ² or less, and 12 g / m ² or more and 28 g / m ² or less. It is more preferable that it is 12 g / m ² or more and 25 g / m ² or less.

  In the top sheet for absorbent articles, the first fiber layer contacts the skin of the wearer wearing the absorbent article. When the first fiber layer including the first core-sheath type composite short fiber hits the skin, a comfortable feeling of use can be given to the user of the absorbent article. The above surface sheet for absorbent articles includes various absorbent articles such as sanitary napkins, infant paper diapers, adult paper diapers, paper diapers for animals including mammals, panty liners (origami sheets), and incontinence liners. It can be preferably used as a surface sheet.

  The absorbent article of the present invention is not particularly limited as long as it includes the above surface sheet for absorbent articles. For example, sanitary napkins, infant paper diapers, adult paper diapers, paper diapers for animals including mammals, panty liners (orimono sheets), incontinence liners, and the like.

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

  In the examples and comparative examples, the following fibers were used.

(1) Fiber 1: Core component is PP (melting point: 160 ° C., MFR230: 12 g / 10 min, Q value (before spinning): 4.6), and sheath component is HDPE (melting point: 130 ° C., MFR190: 12 g) Core-sheath-type composite short fiber (fineness) having a core-sheath ratio (core component / sheath component volume ratio) of 65/35 and a core-sheath component and a core component arranged concentrically. : 1.4 dtex, fiber length: 38 mm).
(2) Fiber 2: The core component is PP (melting point: 160 ° C., MFR230: 12 g / 10 min, Q value (before spinning): 4.6), and the sheath component is HDPE (melting point: 130 ° C., MFR190: 12 g Core-sheath composite short fiber having a concentric structure in which the core component and the sheath component are arranged concentrically (fineness: 1.6 dtex, fiber length: 38 mm).
(3) Fiber 3: The core component is PP (melting point: 160 ° C., MFR230: 22 g / 10 min, Q value (before spinning): 5.2), and the sheath component is HDPE (melting point: 130 ° C., MFR190: 22 g) Core-sheath-type composite short fiber (fineness) having a core-sheath ratio (core component / sheath component volume ratio) of 65/35 and a core-sheath component and a core component arranged concentrically. : 1.1 dtex, fiber length: 38 mm).
(4) Fiber 4: The core component is PET (melting point: 256 ° C.), the sheath component is HDPE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and the core-sheath ratio (core component / sheath component volume) Ratio) was 45/55, and an eccentric core-sheath type composite short fiber (fineness: 2.6 dtex, fiber length: 51 mm) having an eccentricity of 25% was used.
(5) Fiber 5: The core component is PET (melting point: 256 ° C.), the sheath component is HDPE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and the core-sheath ratio (core component / sheath component volume) The ratio was 45/55, and an eccentric core-sheath composite short fiber (fineness: 3.3 dtex, fiber length: 51 mm) having an eccentricity of 25% was used.
(6) Fiber 6: Core component is PET (melting point: 256 ° C.), sheath component is HDPE (melting point: 130 ° C., MFR 190: 12 g / 10 min), core-sheath ratio (volume ratio): core component / An eccentric core-sheath type composite short fiber (fineness: 4.4 dtex, fiber length: 51 mm) having a sheath component of 45/55 and an eccentricity of 25% was used.
(7) Fiber 7: The core component is PET (melting point: 256 ° C.), the sheath component is HDPE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and the core-sheath ratio (core component / sheath component volume) Ratio) was 45/55, and an eccentric core-sheath type composite short fiber (fineness: 5.6 dtex, fiber length: 51 mm) having an eccentricity of 25% was used.
(8) Fiber 8: The core component is PET (melting point: 256 ° C.), the sheath component is HDPE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and the core-sheath ratio (core component / sheath component volume) Ratio) was 37/63, 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.
(9) Fiber 9: Core component is PET (melting point: 256 ° C.), sheath component is HDPE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and core-sheath ratio (core component / sheath component volume) The ratio was 40/60, and a core-sheath type composite short fiber (fineness: 3.3 dtex, fiber length: 51 mm) having a concentric structure in which a core component and a sheath component were arranged concentrically was used.
(10) Fiber 10: Core component is PET (melting point: 256 ° C.), sheath component is HDPE (melting point: 130 ° C., MFR 190: 12 g / 10 min), and core-sheath ratio (core component / sheath component volume) The ratio was 40/60, and a core-sheath type composite short fiber (fineness: 4.4 dtex, fiber length: 51 mm) having a concentric structure in which a core component and a sheath component were arranged concentrically was used.
In addition, in the composite short fiber of the fibers 1-7, titanium dioxide was added with respect to the core component. In the fibers 1 to 3, the content of titanium dioxide was 1.95% by mass with respect to 100% by mass of the fiber. Moreover, in the fibers 4 to 7, the content of titanium dioxide was 1.67% by mass with respect to 100% by mass of the fiber.

  In the above fiber, the Q value of the polymer is a value measured 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 average molecular weight Mw, z average molecular weight Mz, and mass average molecular weight / number average molecular weight (Mn / Mw: Q value) was measured.

  The Q value of PP before spinning was measured using the used PP resin pellets as they were. The Q value of PP after spinning can be measured using the obtained composite short fiber. Alternatively, the Q value of PP after spinning is set such that the temperature of the extruder is 290 ° C. when melt spinning is performed, the PP resin is melted and extruded from the extruder without attaching the spinning nozzle, and air-cooled in the air. Thus, 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.

Example 1
First, the 1st fiber web of 10 g / m < ² > of fabric weight was produced using the fiber 1 with the roller-type card machine. Next, a second fiber web having a basis weight of 15 g / m ² was produced using the fiber 4 with a roller type card machine. Next, after laminating the second fiber web on the first fiber web, the obtained laminated fiber web was heat-treated for 15 seconds using a hot air through heat treatment machine set at 135 ° C. The sheath component was melted and the fibers 1 and 4 were thermally bonded to obtain a heat-bonded nonwoven fabric (weight per unit: 26.0 g / m ² ) including the first fiber layer and the second fiber layer. At this time, the laminated fiber web is heat-treated in a state in which the first fiber web to be the first fiber layer is in contact with the conveyor net surface of the hot air penetration type heat treatment machine, and the hot air is applied to the laminated fiber web from the second fiber layer side. I sprayed.

(Example 2)
A heat-bonded nonwoven fabric (weight per unit area 24.0 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 1 except that the fiber 5 was used instead of the fiber 4.

(Example 3)
A heat-bonded nonwoven fabric including a first fiber layer and a second fiber layer in the same manner as in Example 1 except that the fiber 2 is used instead of the fiber 1 and the fiber 6 is used instead of the fiber 4 (25.7 g per unit area) / M ² ).

Example 4
Implemented except that fiber 2 was used instead of fiber 1, fiber 5 was used instead of fiber 4, the basis weight of the first fiber web was 7 g / m ² and the basis weight of the second fiber web was 18 g / m ^2. In the same manner as in Example 1, a heat-bonded nonwoven fabric (weight per unit area: 24.7 g / m ² ) including the first fiber layer and the second fiber layer was obtained.

(Example 5)
A heat-bonded non-woven fabric including a first fiber layer and a second fiber layer (weight per unit: 25.0 g) is the same as in Example 1 except that fiber 3 is used instead of fiber 1 and fiber 5 is used instead of fiber 4. / M ² ).

(Example 6)
First, the 1st fiber web was produced using the fiber 2 so that a fabric weight might be set to about 7 g / m < ² > with a parallel card machine. Subsequently, the 2nd fiber web was produced using the fiber 5 so that a fabric weight might be 18 g / m < ² > with a parallel card machine. After laminating the second fiber web on the first fiber web, the laminated fiber web obtained was heat treated using a hot air through heat treatment machine set at 135 ° C. to melt the sheath component in the fibers 2 and 5. Then, the fiber 2 and the fiber 5 were thermally bonded to obtain a heat-bonded nonwoven fabric (weight per unit area 25.0 g / m ² ) including the first fiber layer and the second fiber layer. At this time, it heat-processed in the state which the 1st fiber web used as a 1st fiber layer contacted the conveyor net | network surface of a hot air penetration type heat processing machine, and the hot air was sprayed with respect to the laminated fiber web from the 2nd fiber layer side.

(Example 7)
Implemented except that fiber 2 was used instead of fiber 1, fiber 5 was used instead of fiber 4, the basis weight of the first fiber web was 20 g / m ² , and the basis weight of the second fiber web was 18 g / m ^2. In the same manner as in Example 1, a heat-bonding nonwoven fabric (weight per unit area: 38.0 g / m ² ) including the first fiber layer and the second fiber layer was obtained.

(Example 8)
Implemented except that fiber 2 was used instead of fiber 1, fiber 5 was used instead of fiber 4, the basis weight of the first fiber web was 7 g / m ² , and the basis weight of the second fiber web was 35 g / m ^2. In the same manner as in Example 1, a heat-bonding nonwoven fabric (weight per unit area: 45.0 g / m ² ) including the first fiber layer and the second fiber layer was obtained.

(Comparative Example 1)
A heat-bonded nonwoven fabric (weight per unit area 26.3 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 2 except that the fiber 9 was used instead of the fiber 5.

(Comparative Example 2)
A heat-bonding nonwoven fabric (weight per unit area 24.7 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 3 except that the fiber 10 was used instead of the fiber 6.

(Comparative Example 3)
A heat-bonded nonwoven fabric (weight per unit area 26.7 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 3 except that the fiber 7 was used instead of the fiber 6.

(Comparative Example 4)
A heat-bonded nonwoven fabric (weight per unit area 26.0 g / m ² ) including the first fiber layer and the second fiber layer was obtained in the same manner as in Example 4 except that the fiber 8 was used instead of the fiber ² .

  The thickness, run-off, liquid absorption speed, and liquid return amount of the heat-bonded nonwoven fabrics (surface sheets for absorbent articles) of Examples 1 to 8 and Comparative Examples 1 to 4 were evaluated as follows. Moreover, the fluctuation | variation (MMD) of the average friction coefficient of the thermobonding nonwoven fabric (surface sheet for absorbent articles) of Examples 1-8 and Comparative Examples 1-4 was evaluated as follows. The results are shown in Table 1 below.

(thickness)
The thickness of the nonwoven fabric is 3 g per 1 cm ^{2 of} the sample 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.). It measured in the state which added the load.

(Runoff)
(1) On a support base having a substantially vertical isosceles triangle cross section having a slope that forms an angle of 45 degrees with the horizontal plane, a sheet of “Kim towel (registered trademark)” made by Nippon Paper Crecia Co., Ltd. A nonwoven fabric (longitudinal direction (machine direction) 18 cm, lateral direction 7 cm) was placed thereon and fixed so that the longitudinal direction of the nonwoven fabric forms an angle of 45 degrees with the horizontal plane.
(2) A total of 6 g of physiological saline is dropped from the position of the upper end of the nonwoven fabric surface at a rate of 1 g / 10 sec with a microtube pump, and all of the poured physiological saline is absorbed by the nonwoven fabric, and the saline water drops Was measured from the surface of the nonwoven fabric, and the distance between the position and the position at which the physiological saline was dropped on the nonwoven fabric surface where the saline water droplets flowed on the nonwoven fabric surface was determined. In the above, physiological saline may be dropped using a burette instead of the microtube pump.

(Liquid absorption speed, liquid return amount)
(1) In order to measure the liquid absorption speed and the liquid return amount, the following articles were prepared.
Absorber: MEZGER inc. A laminate of three manufactured Lister Papers (Grade 989, 10 cm × 10 cm) was used as an absorber.
Saline filter paper: ADVANTEC (registered trademark) No. 2, 10cm x 10cm
Weight: 4kg
Plate: Made of acrylic resin, 125mm x 125mm, thickness 5mm
Measuring instrument: “Lister” manufactured by Lenzing Instruments (hereinafter also simply referred to as “Lister tester”)
(2) Method The liquid absorption speed and the liquid return amount were measured according to the following procedures.
(I) A nonwoven fabric ((longitudinal direction (machine direction) 10 cm, lateral direction 10 cm)) is placed on the absorbent body (three layers of Lister Paper (Grade 989, 10 cm × 10 cm) manufactured by MEZGER Inc.), and this state To set the measuring instrument.
(Ii) 5 ml of physiological saline was dropped onto the set nonwoven fabric using a Lister tester. At this time, the physiological saline is not visible from the nonwoven fabric surface (the physiological saline is transferred from the nonwoven fabric to the absorbent body located under the nonwoven fabric, and no physiological saline is confirmed as a liquid on the nonwoven fabric surface). Liquid time) was measured and used as the first liquid absorption rate.
(Iii) The physiological saline is left for 30 seconds after it disappears from the nonwoven fabric surface, and after 30 seconds, the same part as the part where the physiological saline was dropped in the first liquid absorption test is the same as the procedure (ii). 5 ml of physiological saline was dropped again by the method, and the time until the physiological saline disappeared from the nonwoven fabric surface (liquid absorption time) was measured to obtain the second liquid absorption speed.
(Iv) After measuring the second liquid absorption rate, the procedure (iii) was repeated, and the time until the physiological saline disappeared from the nonwoven fabric surface (liquid absorption time) was measured to obtain the third liquid absorption rate. .
(V) After the measurement of the third absorption rate was completed, the strike through plate of the Lister tester was removed, an acrylic resin plate was placed on the surface of the nonwoven fabric, and a 4 kg weight was placed thereon for 3 minutes.
(Vi) After 3 minutes, the weight and the acrylic resin plate are removed, and a filter paper (ADVANTEC (registered trademark) No. 2 manufactured by Toyo Roshi Kaisha, Ltd.) whose mass has been measured in advance is placed on the nonwoven fabric. A 4 kg weight was placed on the top for 2 minutes. Two minutes later, the filter paper was taken out, the mass of the filter paper that absorbed physiological saline was measured, the mass of the filter paper before being placed on the nonwoven fabric was subtracted, and the liquid return amount was calculated.

(Change in average friction coefficient)
The variation of the average friction coefficient was measured based on the KES (Kawabata Evaluation System) method. Specifically, “KES-SE” friction tester manufactured by Kato Tech Co., Ltd. was used. The measurement surface is the surface of the first fiber layer, a static load of 25 gf (245 N) is applied to the friction element, and the friction element is moved in the direction parallel to the longitudinal direction of the nonwoven fabric at a moving speed of 1 mm / sec. Friction coefficient variation (MMD) was measured.

As can be seen from the data in Table 1, the top sheets for absorbent articles of Examples 1 to 8 have a short run-off of 45 mm or less, the third liquid absorption speed is a fast speed of 40 seconds or less, and is excellent. It had a liquid-absorbing property. Moreover, the surface sheets for absorbent articles of Examples 2, 4, and 6 had a small variation of the average friction coefficient of 0.0092 or less, a smooth feel, and an excellent texture. From the comparison of Examples 1 to 6 and Examples 7 to 8, the basis weight of the first fiber layer is 18 g / m ² or less, the basis weight of the second fiber layer is 30 g / m ² or less, It can be seen that when the basis weight of the second fiber layer is larger than the basis weight, the liquid return is less and the liquid absorption property is more excellent.

  On the other hand, the surface sheet for absorbent articles of Comparative Example 1 had a run-off exceeding 45 mm and had poor liquid absorption characteristics. The top sheet for absorbent articles of Comparative Example 2 had a third liquid absorption speed exceeding 40 seconds, and the liquid absorption characteristics were poor. In the top sheet for absorbent articles of Comparative Example 1 and Comparative Example 2, the second fiber layer is composed of concentric core-sheath composite short fibers and has a dense structure, so that the liquid is the second fiber layer. It was difficult to move to. The surface sheet for absorbent articles of Comparative Example 3 had a run-off exceeding 45 mm and had poor liquid absorption characteristics. In the surface sheet for absorbent articles of Comparative Example 3, the second fiber layer is composed of an eccentric core-sheath type composite short fiber having a fineness exceeding 5.2 dtex, and the second fiber layer is too sparse to cause a capillary phenomenon. It was difficult to do. In the surface sheet for absorbent articles of Comparative Example 4, the average coefficient of friction exceeded 0.0092, and the texture was poor. This is because, in the top sheet for absorbent articles of Comparative Example 4, the fineness of the first core-sheath type composite short fiber constituting the first fiber layer exceeded 2.1 dtex, and therefore the surface was not rough. Conceivable. Moreover, the surface sheet for absorbent articles of Comparative Example 4 had a third liquid absorption speed exceeding 40 seconds, and the liquid absorption characteristics were poor. This is because the fineness of the core-sheath type composite short fiber constituting the first fiber layer exceeds 2.1 dtex in the top sheet for absorbent articles of Comparative Example 4, and the first fiber layer is too sparse and liquid. It is thought that this is because it was difficult to transfer to the second fiber layer.

  The surface sheet for absorbent articles according to the present invention has various absorbent properties such as sanitary napkins, infant paper diapers, adult paper diapers, paper diapers for animals including mammals, panty liners (orimono sheets), incontinence liners, and the like. It can be preferably used as a surface sheet of an article.

DESCRIPTION OF SYMBOLS 1 Top sheet | seat for absorbent articles 2, 3 Core sheath type composite short fiber 11 1st fiber layer 12 2nd fiber layer 21, 31 Sheath component 22, 32 Core component 23, 33 The gravity center position in the fiber cross section of the core component 24, 34 Center of gravity position in fiber cross section of core-sheath type composite short fiber 25, 35 Radius in fiber cross section of core-sheath type composite short fiber

Claims (8)

A top sheet for absorbent articles comprising a first fiber layer in contact with the skin and a second fiber layer adjacent to the first fiber layer,
The first fiber layer includes a fiber in which the core component includes polypropylene and the sheath component includes 50% by mass or more of a first core-sheath type composite short fiber including a thermoplastic resin having a melting point that is lower by 5 ° C. than the melting point of the polypropylene. Layer,
In the second fiber layer, the core component includes a polyester resin, the sheath component includes a thermoplastic resin having a melting point that is lower by 50 ° C. than the melting point of the polyester resin, and the center of gravity of the core component is from the center of gravity of the fiber. It is a fiber layer containing 50 mass% or more of the second core-sheath type composite short fiber that is displaced,
The first core-sheath type composite short fiber has a fineness of 0.5 dtex or more and 2.1 dtex or less,
The second core-sheath type composite short fiber has a fineness of 2.2 dtex or more and 5.2 dtex or less,
At least a part of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber are thermally bonded by a sheath component of the first core-sheath type composite short fiber and the second core-sheath type composite short fiber. A top sheet for absorbent articles, characterized by comprising:   The first core-sheath type composite short fiber is a core-sheath type composite short fiber having a concentric structure in which the core component and the sheath component are arranged substantially concentrically, and a composite ratio of the core component and the sheath component The surface sheet for absorbent articles according to claim 1, wherein the core component / sheath component volume ratio is 52/48 to 73/27.   The content of the polypropylene in the core component of the first core-sheath-type composite short fiber is 50% by mass or more, and the ratio Mw / Mn of the weight average molecular weight Mw / number average molecular weight Mn after spinning of the polypropylene is 3.0. The top sheet for absorbent articles according to claim 1 or 2, wherein the surface sheet is 8.0 or less.   In the sheath component of the first core-sheath type composite short fiber, the thermoplastic resin having a melting point lower by 5 ° C. or more than the melting point of polypropylene contained in the core component of the first core-sheath type composite short fiber is high-density polyethylene. The content of the high-density polyethylene in the sheath component of the first core-sheath composite short fiber is 50% by mass or more, the measurement temperature is 190 ° C., the load is 21. 21 according to JIS-K-7210 of the high-density polyethylene. The surface sheet for absorbent articles according to any one of claims 1 to 3, wherein the melt flow rate measured under a condition of 18N is 5 g / 10 min or more and 30 g / 10 min or less.   The top sheet for absorbent articles according to any one of claims 1 to 4, wherein a fiber length of the first core-sheath composite short fiber is 25 mm or more and less than 65 mm. The basis weight of the first fiber layer is 4 g / m ² or more and 18 g / m ² or less, the basis weight of the second fiber layer is 10 g / m ² or more and 30 g / m ² or less, and the basis weight of the second fiber layer is The top sheet for absorbent articles according to any one of claims 1 to 5, wherein the surface sheet is larger than the basis weight of the first fiber layer.   In the said surface sheet for absorbent articles, the fluctuation | variation (MMD) of the average friction coefficient measured based on KES method by making the surface of the said 1st fiber layer into a measurement surface is 0.0092 or less, Either of Claims 1-6 The top sheet for absorbent articles according to item 1.   An absorbent article comprising the top sheet for absorbent articles according to any one of claims 1 to 7.

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