JPWO2008108295A1 - Non-woven - Google Patents

Abstract

While making a mixed web of wet heat adhesive fibers and superabsorbent fibers at a ratio (mass ratio) of wet heat adhesive fibers / superabsorbent fibers = 20/80 to 80/20, while transporting in a specific direction By heat-processing with high temperature steam, the fiber which comprises the said nonwoven fabric is orientated, and the fiber adhesion rate in the cross section of the said nonwoven fabric is substantially uniform along the thickness direction, and the nonwoven fabric which is 5-50% is manufactured. This non-woven fabric has low density and light weight in the dry state, and has an excellent water absorption rate when absorbing water and exhibits excellent expansibility in at least one direction, and at the same time expands in at least one direction. It does not occur.

Description

  The present invention is composed of a web containing wet heat adhesive fibers, water-absorbing fibers, and other fibers as necessary, and these fibers fix the fibers without using a chemical binder or special chemicals. The present invention relates to a non-woven fabric that is low density, lightweight, has a high water absorption rate, and has a low dimensional change rate in the surface direction due to water absorption. Moreover, it is related with the water sandbag and water retention sheet | seat comprised with this nonwoven fabric.

  Many water-absorbing articles suitable for absorbing water and aqueous liquids are known, such as porous bodies such as sponges and water-absorbing gels. Among them, a highly water-absorbing article having a high water-absorbing property is one that takes in water between molecules of a hydrophilic polymer material and expands in volume, and these are used in various applications such as diapers and water-absorbing sandbags. Among these, those having high water absorption and quick drainage due to pressurization are preferably used for repetitive use and water retention medium.

  These highly water-absorbent articles normally expand in volume in all directions due to water absorption, and the volume expansion coefficient changes depending on the difference in distance from the surface that absorbs the liquid and the internal structure. Have difficulty. This not only restricts the arrangement method at the time of use of the article, but also the generation of gaps due to deformation causes water leakage and also causes efficient water absorption.

  Therefore, normally, a method is adopted in which the water-absorbing material is coated and controlled with a material having a small volume expansion due to water absorption, but as a result, the manufacturing becomes complicated, and the water absorption of the coating material is low, and the expansion due to the coating is inhibited. As a result, the water absorption of the water absorbing material is lowered.

  In order to improve this, for example, JP-A-01-304127 (Patent Document 1) has developed a resin that suppresses volume expansion due to water absorption. However, this resin is preferably low in water absorption in principle. Absent. Japanese Patent Application Laid-Open No. 09-183856 (Patent Document 2) has developed a water-absorbing resin that exhibits anisotropic swelling after water absorption by stretching the resin under pressure. This resin develops anisotropy by relaxing to the state before pressure stretching by water absorption, and therefore has the property of expanding in one direction while contracting in the other direction. However, this resin becomes a gel after water absorption, the gel blocking occurs, the gel is difficult to dehydrate, it is difficult to use repeatedly, the mechanical strength is inferior, the anisotropy of the obtained resin is molecular There is a problem that it may be resolved over time due to the movement of the body.

  On the other hand, there are many non-woven fabrics exhibiting high water absorption, and many patent applications have been filed. Many of them are cellulose, such as JP-A-2003-020626 (Patent Document 3). There are cases where high hydrophilicity is ensured by adding a hydrophilic agent such as a surfactant, a highly water-absorbent resin (SAP), or a polymer absorber to a nonwoven fabric mainly composed of water-absorbing fibers, such as a system or polyvinyl alcohol. It is almost.

  However, the details of the dimensional change caused by the water absorption and swelling of the nonwoven fabric are hardly disclosed.

  In particular, as a nonwoven fabric using wet heat adhesive fibers, JP-A 63-235558 (Patent Document 4) discloses a nonwoven fabric containing ethylene-vinyl alcohol fibers having ethylene units at a predetermined molar ratio. . An object of this invention is to swell ethylene-vinyl alcohol fibers with water and further heat the fibers in contact with a heated body to obtain a nonwoven fabric having bulkiness, flexibility and sufficient strength. . However, even in this document, no mention is made of dimensional changes associated with swelling due to water absorption of the nonwoven fabric, and in the method described in this document, only the fibers in contact with the heating body are heat-set, In the central portion of the thickness, the amount of heat transmitted to the heating of the added moisture is used, and it can be easily estimated that fiber adhesion in the central portion in the thickness direction is not promoted and it is very difficult to develop fiber fusion.

  In JP 2002-115161 A (Patent Document 5), fibers are fixed by impregnating water into a fiber web mainly composed of wet heat adhesive fibers made of ethylene-vinyl alcohol and applying heat thereto. A fiber structure is disclosed. However, no information is disclosed regarding water absorption performance and dimensional changes before and after water absorption for this fiber structure.

  Thus, the actual situation is that the fiber structure in which the change in form upon water absorption is clarified and the change in form is controlled has not yet been disclosed.

  In addition, Japanese Utility Model Publication No. 7-51312 (Patent Document 6) discloses a water-absorbing property comprising a highly water-absorbing fiber composed of an acrylate-type residue-containing copolymer having a water swelling degree of 3 times or more as an essential component. An absorbent sheet for laying in which protective sheets are integrated on both sides of a nonwoven sheet has been proposed. This document describes that heat-adhesive fibers such as polypropylene and polyester are mixed with the superabsorbent fibers and thermally bonded with hot air, a heating roll, a heating needle, or the like.

  Furthermore, JP-A-2006-45730 (Patent Document 7) discloses 5 to 60% adhesive fibers having a fineness of 0.5 to 2.7 dtex and 40 to 95 water-absorbing fibers having a water absorption rate of 200 to 30000%. Has been proposed. In this document, an acrylonitrile-based fiber having a carboxylate group is exemplified as the water-absorbing fiber, a polyolefin-based hot-melt adhesive fiber is exemplified as the adhesive fiber, and 10 to 20 ° C. higher than the melting point of the adhesive fiber. It is described that a water-absorbing fiber is bonded by an adhesive fiber by heating with a heat roller at a temperature.

  However, in the nonwoven fabric fixed with these heat-adhesive fibers, a uniform adhesive structure cannot be obtained inside the nonwoven fabric, so that sufficient fiber adhesion cannot be secured to maintain the shape during swelling, and the shape tends to collapse. . In particular, when the nonwoven fabric is bulky, this tendency becomes even stronger.

  By the way, sandbags are used to prevent intrusion when the water level of rivers, drains, reservoirs, etc. rises due to heavy rain or typhoon, and the surrounding area may be flooded or flooded. Recently, there have been an increasing number of cases where water sandbags are used that are light in weight when dry and easy to handle. For example, Japanese Unexamined Patent Application Publication No. 2002-142557 (Patent Document 8) discloses a water sandbag having water absorbability. This sandbag is a water sandbag that is obtained by drying and compressing a biodegradable cellulose sponge to form a light and small-capacity plate-like sponge and attaching a superabsorbent polymer thereto, and then storing it in a sandbag.

  However, the plate-like sponge to which the superabsorbent polymer, which is a sandbag water-absorbing body disclosed herein, is attached is sewn around the sponge once laminated at least two sheets, and is further stored in the sandbag bag. Therefore, this sandbag is not a rectangular parallelepiped, and has a rounded shape on each side. Therefore, when the sandbags are stacked or arranged, a large gap is generated between the sandbags. In addition, polymer powder is attached to a plate-like sponge body in order to improve water absorption, but powder that is not in a sufficiently bonded state will fall off and become unevenly distributed when subjected to vibration, such as during transportation, or plate-like There is a possibility of leakage to the outside through the gap between the sponge and sandbag.

Furthermore, it is also disclosed that this plate-like sponge is used as a breeding bed for seedlings, seedlings and the like. That is, a cylindrical concave portion is formed in the plate-like sponge, and the concave portion is used as a seedbed, and water is retained by watering, so that the trouble of watering seeds and seedlings can be avoided. However, in this case too, dimensional changes and shape changes due to water absorption are not fully taken into account, so it is specified by the shape and arrangement of the seedlings finally grown by storing the required number of seedlings accurately within the limited dimensions. It is difficult to use it for a usage method that reveals the shape and design of the plant and a method for accurately arranging a desired number of seedlings in a narrow place.
Japanese Patent Laid-Open No. 01-304127 JP 09-183856 A JP 2003-020626 A JP-A 63-235558 JP 2002-115161 A No. 7-51312 JP 2006-45730 A JP 2002-142557 A

  An object of the present invention is to provide a nonwoven fabric having a low density, a light weight, excellent water absorption and quick drainage, and having small and regular dimensional change at the time of water absorption and a method for producing the same. There is.

  Another object of the present invention is to provide a nonwoven fabric that swells in the thickness direction and that does not collapse due to swelling even in a bulky shape and a method for producing the same.

  Still another object of the present invention is suitable for repeated use, does not require coating for form control with other media, has a high degree of freedom in arrangement, and can suppress the occurrence of gaps, thereby preventing water leakage from the gaps. An object of the present invention is to provide a nonwoven fabric that can be suppressed and absorb water efficiently and a method for producing the same.

  Another object of the present invention is to provide a water-retaining sheet suitable for applications such as a water sandbag, a breeding floor for seedlings, seedlings and the like.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have achieved low density, light weight, and excellent water absorption and drainage by uniformly bonding oriented fibers with wet heat adhesive fibers. In addition, the present inventors have found that a non-woven fabric can be obtained that has a small dimensional change in a specific direction at the time of water absorption and can be obtained, thereby completing the present invention.

That is, the nonwoven fabric of the present invention is composed of wet heat adhesive fibers and superabsorbent fibers, and the ratio (mass ratio) of the wet heat adhesive fibers and the superabsorbent fibers is wet heat adhesive fibers / high water absorbency. Fiber = 20/80 to 80/20 non-woven fabric, the fibers constituting the non-woven fabric are oriented, and the fiber adhesion rate in the cross section of the non-woven fabric is generally uniform along the thickness direction, 5 to 50 %. When the nonwoven fabric of the present invention absorbs water from a dry state, the dimensional change rate due to water absorption may be 5.0% or less in the length direction of the nonwoven fabric and 50% or more in the thickness direction. Further, the density in the dry state may be about 0.03 to 0.3 g / cm ³ . Further, the water absorption may be 500% by mass or more. Furthermore, in the cross section in the thickness direction, the ratio of the minimum value to the maximum value of the fiber adhesion rate in each region divided in three in the thickness direction may be 50% or more. The superabsorbent fiber is a polymer having at least one hydrophilic group selected from the group consisting of hydroxyl group, carboxyl group or its base, sulfonic acid group or its base, and ether group (for example, poly (meta ) A component containing an acrylic acid polymer or a salt thereof). The wet heat adhesive fiber is composed of an ethylene-vinyl alcohol copolymer having an ethylene unit content of 10 to 60 mol% and a non-wet heat adhesive resin, and the ethylene-vinyl alcohol copolymer The ratio (mass ratio) with the non-wet heat adhesive resin is the former / the latter = 90/10 to 10/90, and the ethylene-vinyl alcohol copolymer is at least one of the wet heat adhesive fiber surfaces. You may occupy the part continuously in the length direction. The wet heat adhesive fiber may be a core-sheath type composite fiber formed of a sheath part made of an ethylene-vinyl alcohol copolymer and a core part made of a polyester resin.

  Further, the present invention includes a water sandbag and a water retaining sheet made of the nonwoven fabric.

  Furthermore, the present invention includes the step of forming a wet web adhesive fiber and a superabsorbent fiber into a mixed web and the step of fusing the fiber by heat treatment with high-temperature steam while conveying the generated mixed web. A method for producing a nonwoven fabric is also included.

  In this invention, since it is the nonwoven fabric which orientated fiber was adhere | attached uniformly with the wet heat adhesive fiber, while having a low density, a lightweight and outstanding water absorption, it has quick drainage property. Further, it is possible to realize that the dimensional change is small in a specific direction and the dimensional change is regular at the time of water absorption. In particular, even if the shape swells in the thickness direction and is bulky, the form does not collapse due to swelling. Further, due to such characteristics, it is suitable for repeated use, does not require coating for form control with other media, has a high degree of freedom in arrangement, and can efficiently absorb water by suppressing the generation of gaps. Furthermore, by using such a non-woven fabric, form control is easy, water absorption is high, drainage is high, installation and removal are easy, and it is suitable for repeated use, and the occurrence of gaps is suppressed, so that water leaks. It is possible to provide a water retaining sheet suitable for uses such as a water sandbag, a seedling seedling, a seedling seedling raising bed, etc., in which the decrease in water absorption efficiency due to water is improved.

1 is an electron micrograph of a cross section in the thickness direction of the nonwoven fabric obtained in Example 1. FIG.

Detailed Description of the Invention

[Nonwoven fabric]
The non-woven fabric of the present invention is composed of superabsorbent fibers and wet heat-adhesive fibers, and high temperature steam is allowed to act to bond the fibers together at the intersections with the wet heat adhesive fibers. Water absorbent fibers are fixed. With such a structure, the nonwoven fabric of the present invention can ensure a desired water absorption amount and water absorption, and a dimensional change due to water absorption is greatly expressed in the thickness direction, and a dimensional change in the nonwoven fabric surface direction is very small. That is, the nonwoven fabric of the present invention is a nonwoven fabric that secures lightness, water absorption and form stability upon water absorption, and quick drainage due to pressurization.

  The nonwoven fabric of the present invention is produced efficiently by making wet web adhesive fibers and superabsorbent fibers into a mixed web, feeding the resulting mixed web by a belt conveyor, etc., and then exposing the mixed web to a high-temperature steam flow can do. In this method, the web is sent onto a belt conveyor that is continuously operated, so that the constituent fibers of the web are oriented in a plane direction parallel to the belt surface of the belt conveyor. That is, in the nonwoven fabric obtained by this method, the constituent fibers are oriented in the plane direction. Further, by adjusting the speed of the belt conveyor and the like, the orientation in the length direction parallel to the flow direction of the belt conveyor can be further increased. Furthermore, by performing heat treatment with high-temperature steam, a uniform fiber adhesion rate can be obtained in the thickness direction perpendicular to the surface direction. That is, the high-temperature steam flow penetrates throughout the thickness direction of the mixed web and uniformly adheres the wet heat-adhesive fibers, so that high fiber adhesion rate uniformity can be obtained compared to other methods such as thermal bonding and chemical bonding. It is done.

  In the present invention, the thickness direction is a direction perpendicular to the surface of the nonwoven fabric, the length direction is a direction parallel to the surface of the nonwoven fabric, and the nonwoven fabric is obtained by a continuous manufacturing method. Means a direction perpendicular to the width direction of the belt conveyor in the case of manufacturing on the belt conveyor.

(Wet heat adhesive fiber)
The wet heat adhesive fiber used for this invention should just be comprised with the wet heat adhesive resin at least. In the present invention, the wet heat adhesive resin means a resin that can absorb water and soften at a temperature and humidity that can be easily realized by high-temperature steam, and develop adhesiveness. Specifically, it can be softened with hot water or high-temperature steam (for example, steam at about 80 to 150 ° C., preferably about 80 to 120 ° C., more preferably about 90 to 110 ° C.) to be self-adhesive or adhere to other fibers. Thermoplastic resins, for example, cellulose resins (C _1-3 alkyl cellulose such as methyl cellulose, hydroxy C _2-3 alkyl cellulose such as hydroxyethyl cellulose, carboxy C _1-3 alkyl cellulose such as carboxymethyl cellulose or salts thereof), poly Alkylene glycol resins (poly C _2-4 alkylene oxides such as polyethylene oxide and polypropylene oxide), polyvinyl resins (polyvinyl pyrrolidone, polyvinyl ether, vinyl alcohol polymers, polyvinyl acetals, etc.), acrylic polymers and salts thereof [Copolymers containing units composed of acrylic monomers such as (meth) acrylic acid and (meth) acrylamide or alkali metal salts thereof], modified vinyl copolymers (isobutylene, styrene, ethylene, vinyl ether) A copolymer of a vinyl monomer such as maleic anhydride and an unsaturated carboxylic acid such as maleic anhydride or an anhydride thereof, or a salt thereof), a polymer having a hydrophilic substituent (such as a sulfonic acid group or a carboxyl group, And polyesters introduced with hydroxyl groups, polyamides, polystyrenes or salts thereof), aliphatic polyester resins (polylactic acid resins, etc.). Also, among polyolefin resins, polyester resins, polyamide resins, polyurethane resins, thermoplastic elastomers or rubbers (such as styrene elastomers), it can be softened at the temperature of hot water (high-temperature steam) to exhibit an adhesive function. Other resins are also included.

These wet heat adhesive resins can be used alone or in combination of two or more. The wet heat adhesive resin is usually composed of a hydrophilic or water-soluble polymer. Among these wet heat adhesive resins, vinyl alcohol polymers such as ethylene-vinyl alcohol copolymers, polylactic acid resins such as polylactic acid, (meth) acrylic copolymers containing (meth) acrylamide units, In particular, vinyl alcohol polymers containing α-C _2-10 olefin units such as ethylene and propylene, particularly ethylene-vinyl alcohol copolymers are preferred.

  In the ethylene-vinyl alcohol copolymer, the ethylene unit content (copolymerization ratio) is, for example, about 10 to 60 mol%, preferably about 20 to 55 mol%, and more preferably about 30 to 50 mol%. Such an ethylene-vinyl alcohol copolymer has a unique property that it has wet heat adhesiveness but is not hot water soluble. In particular, the range of 30 to 50 mol% of ethylene units is preferable for ensuring the processability of the nonwoven fabric.

  If the ethylene unit content is too small, the ethylene-vinyl alcohol copolymer will easily swell and gel with low-temperature steam (water), and once wetted with water, the fibers will melt due to swelling pressure and external force. Since the landing point is easily removed, expansion in at least one direction cannot be suppressed during water absorption, and expansion in all directions may occur. On the other hand, if the proportion of ethylene units is too large, the water absorption is reduced and fiber fusion due to wet heat is difficult to occur. Therefore, it is difficult to secure sufficient fiber fusion, and in particular, the fiber fusion in the central portion of the thickness is difficult. Since it becomes difficult to develop the wearing, it is difficult to obtain the desired nonwoven fabric.

  The saponification degree of the vinyl alcohol unit in the ethylene-vinyl alcohol copolymer is, for example, 95 mol% or more, preferably 95 to 99.99 mol%, more preferably about 96 to 99.98 mol%. When the degree of saponification is too small, the thermal stability is lowered, and the stability is lowered by thermal decomposition or gelation. On the other hand, if the degree of saponification is too large, it is difficult to produce the fiber itself.

  Although the viscosity average degree of polymerization of an ethylene-vinyl alcohol-type copolymer can be selected as needed, it is 200-2500, for example, Preferably it is 300-2000, More preferably, it is about 400-1500. Such an ethylene-vinyl alcohol copolymer has an excellent balance between spinnability and wet heat adhesiveness.

  The cross-sectional shape (cross-sectional shape perpendicular to the fiber length direction) of the wet heat-adhesive fiber is a general solid cross-sectional shape, such as a round cross-section or an irregular cross-section [flat, elliptical, polygonal, 3-14 Leaf shape, T-shape, H-shape, V-shape, dogbone (I-shape, etc.)], and may be a hollow cross-section. The wet heat adhesive fiber may be a composite fiber composed of a plurality of resins including at least a wet heat adhesive resin. The composite fiber only needs to have the wet heat adhesive resin on at least a part of the fiber surface, but from the viewpoint of adhesiveness, the wet heat adhesive resin continuously occupies at least a part of the surface in the length direction. Is preferred.

  Examples of the cross-sectional structure of the composite fiber in which the wet heat adhesive fiber occupies the surface include a core-sheath type, a sea-island type, a side-by-side type, a multilayer bonding type, a radial bonding type, and a random composite type. Furthermore, it may be a fiber in which a wet heat adhesive resin is coated on the surface of a fiber composed of another fiber-forming polymer. Among these cross-sectional structures, the core-sheath structure (that is, the sheath part is wet-heat-adhesive, which is a structure in which the wet-heat adhesive resin occupies the entire surface continuously in the length direction because it is a highly adhesive structure. A core-sheath structure made of resin is preferred.

  In the case of a composite fiber, wet heat adhesive resins may be combined with each other, but may be combined with non-wet heat adhesive resins. The non-wet heat adhesive resin may be a fiber-forming polymer (hereinafter also referred to as a dimensional stability resin) that has little dimensional change even when water is present in the surroundings. The non-wet heat adhesive resin (dimensional stability resin) is not particularly limited as long as it is a fiber capable of forming a composite fiber that can achieve the object of the present invention, but its versatility, productivity, and manufacturing cost are not limited. Examples thereof include polypropylene resins, (meth) acrylic resins, vinyl chloride resins, styrene resins, polyester resins, polyamide resins, polycarbonate resins, polyurethane resins, and thermoplastic elastomers. These non-wet heat adhesive resins can be used alone or in combination of two or more.

  The nonwoven fabric of this invention will have the preferential expansibility to the direction perpendicular | vertical with respect to this orientation direction, when the fiber containing such a dimensionally stable resin orientates in a specific direction. The orientation direction is not particularly limited, but the nonwoven fabric has preferential expansibility in the thickness direction when the fibers containing the dimensionally stable resin are oriented along the surface direction of the nonwoven fabric. That is, in order to prepare a nonwoven fabric having preferential expansibility in the thickness direction, it is important to orient the orientation direction of the fiber containing the dimensionally stable resin so that the plane direction is higher than the thickness direction. . In particular, in the nonwoven fabric having such an orientation, the fibers oriented along the plane direction may be further oriented in one direction parallel to the plane direction (for example, the length direction). The dimensional stability in one direction (for example, the length direction with respect to the thickness direction and the width direction) is further enhanced. On the other hand, when the expandability in the plane direction is suppressed as much as possible and the expandability is desired to be imparted only in the thickness direction, the alignment property on the surface of the fibers aligned along the plane direction may be random. Furthermore, in order to improve the expansibility in the thickness direction of the nonwoven fabric of the present invention, it is preferable to align the superabsorbent fibers described later in the plane direction. Although it is not necessary for the orientation of the fibers containing the dimensionally stable resin and the superabsorbent fibers to be perfectly matched, by making the orientation directions of these fibers substantially the same, the nonwoven fabric can be easily produced and expanded ( In particular, the expansibility in one direction can be improved. Confirmation of the fiber orientation direction can usually be observed using a scanning electron microscope (SEM) photograph of the cross section. Moreover, when observation is difficult for reasons such as when the orientation in a specific direction is weak or when the density of the fiber is high, it can also be estimated by confirming the direction dependency of the expansion coefficient of the nonwoven fabric due to water absorption.

  Among these non-wet heat adhesive resins, from the viewpoint of heat resistance and dimensional stability, resins having a melting point higher than that of wet heat adhesive resins (particularly ethylene-vinyl alcohol copolymers), such as polypropylene resins and polyester resins. Resins and polyamide resins, particularly polyester resins and polyamide resins are preferred from the standpoint of excellent balance between heat resistance and fiber-forming properties.

Polyester resins include aromatic polyester resins such as poly C _2-4 alkylene arylate resins (polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), especially polyethylene such as PET. A terephthalate resin is preferred. In addition to the ethylene terephthalate unit, the polyethylene terephthalate resin is not limited to other dicarboxylic acids (for example, isophthalic acid, naphthalene-2,6-dicarboxylic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, bis (carboxyphenyl) ethane. Aromatic dicarboxylic acids such as 5-sodiumsulfoisophthalic acid, aliphatic dicarboxylic acids such as azelaic acid, adipic acid, and sebacic acid) and diols (eg, diethylene glycol, 1,3-propanediol, 1,4-butanediol) 1,6-hexanediol, neopentyl glycol, cyclohexane-1,4-dimethanol, polyethylene glycol, polytetramethylene glycol, and the like) may be included at a ratio of about 20 mol% or less.

  Examples of the polyamide-based resin are synthesized from aliphatic polyamides such as polyamide 6, polyamide 66, polyamide 610, polyamide 10, polyamide 12, and polyamide 6-12 and copolymers thereof, aromatic dicarboxylic acid and aliphatic diamine. Semi-aromatic polyamides are preferred. These polyamide-based resins may also contain other copolymerizable units.

  In the fibers constituting such a composite fiber, the ratio (mass ratio) between the wet heat adhesive resin and the non-wet heat adhesive resin (dimensional stability resin) can be selected according to the structure (for example, the core-sheath structure). The wet heat adhesive resin is not particularly limited as long as it exists on the surface. For example, wet heat adhesive resin / non-wet heat adhesive resin = 10/90 to 90/10, preferably 20/80 to 80/20, more preferably It is about 30/70 to 70/30. When the mass ratio of the wet heat adhesive resin constituting the fiber is too large, other resins cannot maintain the fiber form, and it is difficult to sufficiently secure the strength of the composite fiber itself. Conversely, if the mass ratio of the wet heat adhesive resin is too small, the amount of the wet heat adhesive resin is so small that the resin layer cannot maintain the fiber form, and there is a continuous wet heat adhesive resin layer in the length direction. In addition to being extremely difficult to achieve, this ratio makes it impossible to ensure sufficient fiber bond strength. The wet heat adhesive fiber is composed of an ethylene-vinyl alcohol copolymer having an ethylene unit content of 10 to 60 mol% and a fiber-forming polymer (non-wet heat adhesive resin) different from this, The mass ratio of each component is 90/10 to 10/90, and the ethylene-vinyl alcohol copolymer occupies a part of the fiber surface continuously in the length direction. This is preferable because the dimensional change rate in the direction can be effectively suppressed.

  In the wet-heat adhesive fiber of the present invention, in the core-sheath type composite fiber, the hydrophilic sheath is exposed on the entire surface, and has a hydrophobic core that contributes to dimensional stability. It is preferable because dimensional stability can be secured without impairing the properties. In particular, the wet heat adhesive fiber is a core-sheath type composite fiber, the sheath component is composed of an ethylene-vinyl alcohol copolymer, the core component is composed of a fiber-forming polymer, and the fiber-forming polymer is A polyester resin is preferred.

  And regarding the dimension stability resin which comprises this fiber, when this composite fiber absorbs water, in order to suppress the dimensional change in a fiber length direction as much as possible, it is important that it is continuous in the fiber length direction. This is because even if this composite fiber is exposed to water and absorbs water, the dimensional stability resin portion continuous in the length direction hardly causes dimensional change. Therefore, the wet heat adhesive resin having water absorption expands due to water absorption, but the expansion in the fiber length direction is limited to the hydrophobic resin (dimensional stability resin) component. The direction of expansion can be controlled in order to expand in the direction). Therefore, for example, if these fibers are arranged in the plane direction, the expansion direction can be easily adjusted mainly in the thickness direction.

  The crimp rate of the wet heat adhesive fiber is, for example, about 1 to 50%, preferably 3 to 40%, more preferably about 5 to 30% (particularly 10 to 20%). The number of crimps is, for example, about 1 to 100 pieces / 25 mm, preferably about 5 to 50 pieces / 25 mm, and more preferably about 10 to 30 pieces / 25 mm.

(Superabsorbent fiber)
In order to ensure the dimensional change at the time of water absorption, which is the purpose of the nonwoven fabric of the present invention, it is necessary to use a wet heat adhesive fiber and a superabsorbent fiber together. The fiber is not particularly limited as long as it is made of a resin having a property of expanding and absorbing water, but a fiber containing a polymer having a hydrophilic group is preferably used.

  Examples of the hydrophilic group include a hydroxyl group, a carboxyl group or a base thereof, a sulfonic acid group or a base thereof, and an ether group. Examples of the base include metal salts (for example, alkali metal salts such as sodium and potassium, alkaline earth metal salts such as calcium), ammonium salts and amine salts. These hydrophilic groups can be used alone or in combination of two or more.

  Such a hydrophilic group may be a group introduced by grafting or the like into a side chain or a terminal of the polymer constituting the superabsorbent fiber. From the viewpoint of ensuring high water absorption, It is preferable that the monomer itself constituting the main chain has a hydrophilic group. Such monomers include, for example, unsaturated carboxylic acids such as (meth) acrylic acid and maleic anhydride or salts thereof, vinyl alcohols derived from vinyl acetate, and ether formation such as ethylene oxide (oxyethylene group). And the like can be exemplified. These monomers can also be used alone or in combination of two or more.

  The highly water-absorbing fiber in the present invention has high water absorption, and the amount of pure water (distilled water) absorbed is, for example, 1.5 to 1000 ml / g, preferably 2 to 500 ml / g, more preferably. It is about 10-300 ml / g (especially 50-200 ml / g). Here, the absorption amount of pure water means the amount of water relative to its own weight after the fibers are immersed in water and then drained on the mesh.

  Unlike the above-mentioned wet heat adhesive fiber, the superabsorbent fiber is a polymer that does not have wet heat properties, that is, a polymer that does not soften to such an extent that it can be bonded with high-temperature steam (or the above-mentioned hot water) ( Usually, it is comprised with a crosslinkable polymer). Furthermore, even if the superabsorbent fiber has or does not have the melting point or the melting point or softening point of the polymer, for example, 110 ° C. or more, preferably 120 to 300 ° C., more preferably Is about 130-250 ° C. When the superabsorbent fiber has such non-moisture heat resistance, the degree of adhesion by high-temperature steam is in an appropriate range, and a moderately hard nonwoven fabric can be maintained.

  Examples of the polymer constituting such a superabsorbent fiber include an unsaturated carboxylic acid polymer [for example, starch- (meth) acrylic acid copolymer or a salt thereof, poly (meth) acrylic acid or a salt thereof. Styrene-maleic anhydride copolymer or salt thereof, vinyl alcohol-maleic anhydride copolymer or salt thereof, poly (meth) acrylic acid-vinyl alcohol copolymer or salt thereof, isobutylene-maleic anhydride copolymer Or a salt thereof, a cross-linked product of these polymers], a superabsorbent polyurethane resin (urethane resin using polyethylene glycol as a diol component), a polyether polymer (for example, high molecular weight polyethylene oxide, etc.) , Vinyl alcohol polymers (for example, crosslinked products of polyvinyl alcohol polymers), cellulose derivatives [For example, hydroxyethyl cellulose, hydroxypropyl alcohol celluloses such as hydroxypropyl cellulose, carboxymethyl cellulose or salts thereof, such as cross-linked product of these cellulose derivatives] and the like can be exemplified. These polymers can be used alone or in combination of two or more.

  Among these polymers, an unsaturated carboxylic acid polymer, particularly a poly (meth) acrylic acid polymer or a salt thereof is preferable from the viewpoint of high water absorption. The poly (meth) acrylic acid polymer is a polymer having (meth) acrylic acid or a salt thereof as a main polymerization component, and may contain another copolymerizable monomer as a polymerization component.

Other copolymerizable monomers include, for example, other unsaturated monocarboxylic acids (such as crotonic acid), unsaturated monocarboxylic acid esters [for example, methyl (meth) acrylate, ethyl (meth) acrylate such as (meth) acrylic acid C _1-4 alkyl esters, unsaturated dicarboxylic acid [(anhydrous) maleic acid, (anhydrous) citraconic acid, or C _4-10 unsaturated dicarboxylic acid such as (anhydrous) itaconic acid thereof Anhydrides, etc.], unsaturated nitriles (eg, (meth) acrylonitrile, etc.), olefinic monomers (eg, C _2-4 alkenes such as ethylene and propylene), aromatic vinyl monomers (eg, styrene or vinyl toluene), alkyl vinyl ether (e.g., C _1-4 alkyl such as methyl vinyl ether or ethyl vinyl ether - vinyl ethers ), And the like. These comonomer can be used individually or in combination of 2 or more types.

  The poly (meth) acrylic acid polymer may be block- or graft-bonded with a polysaccharide such as starch or a hydrophilic polymer unit such as a polyvinyl alcohol unit. Furthermore, poly (meth) acrylic acid polymers include, for example, polyhydric alcohols (for example, (poly) ethylene glycol, (poly) propylene glycol, etc.), polyvalent metal compounds [for example, calcium compounds (calcium hydroxide, etc.). And a crosslinking agent such as an aluminum compound (such as aluminum hydroxide or potassium aluminum sulfate). As the poly (meth) acrylic acid polymer or a salt thereof, a polymer mainly composed of an alkali metal salt of poly (meth) acrylic acid such as sodium poly (meth) acrylate is used from the viewpoint of high water absorption. preferable.

  Specifically, examples of commercially available superabsorbent fibers include “Lanseer (registered trademark)” manufactured by Toyobo Co., Ltd., and “Bel Oasis (registered trademark)” manufactured by Kanebo (Teijin Fibers).

  The ratio (mass ratio) between the wet heat adhesive fiber and the superabsorbent fiber is wet heat adhesive fiber / superabsorbent fiber = 80/20 to 20/80, preferably 75/25 to 30/70, more preferably 70. / 30 to 40/60 (for example, 65/35 to 45/55). Superabsorbent fibers can be mixed substantially up to 80% by mass, and if they are mixed at a ratio exceeding this, it becomes impossible to sufficiently bond and fix the fibers and control the dimensional change during water absorption. Since it becomes difficult, it is not preferable. In particular, it is not preferable in the central portion of the nonwoven fabric because it is more difficult. Moreover, when the superabsorbent fiber is less than 20% by mass, it is difficult to ensure sufficient water absorption, which is not preferable.

(Other fibers)
In the nonwoven fabric of this invention, you may mix other fibers other than the fiber already described when manufacturing a web as needed. Other fibers include non-wet heat adhesive fibers other than the superabsorbent fibers such as polyester fibers (polyethylene terephthalate fibers, polytrimethylene terephthalate fibers, polybutylene terephthalate fibers, polyethylene naphthalate fibers, etc. Etc.), polyamide fibers (polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 612 and other aliphatic polyamide fibers, alicyclic polyamide fibers, semi-aromatic polyamide fibers, polyphenylene isophthalamide, Aromatic polyamide fibers such as polyhexamethylene terephthalamide and poly p-phenylene terephthalamide), polyolefin fibers (poly C _2-4 olefin fibers such as polyethylene and polypropylene) , Acrylic fibers (acrylonitrile fibers having acrylonitrile units such as acrylonitrile-vinyl chloride copolymer), polyvinyl fibers (polyvinyl acetal fibers, etc.), polyvinyl chloride fibers (polyvinyl chloride, vinyl chloride-vinyl acetate) Copolymer, vinyl chloride-acrylonitrile copolymer fiber, etc.), polyvinylidene chloride fiber (fiber such as vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl acetate copolymer), polyparaphenylenebenzobisoxazole Examples thereof include fibers, polyphenylene sulfide fibers, and cellulosic fibers (for example, rayon fibers and acetate fibers). These other fibers can be used alone or in combination of two or more. Among these other fibers, when controlling texture or water absorption or when it is necessary to keep costs low, natural fibers such as cotton and wool, regenerated cellulose fibers such as rayon, polyester fibers, polyamides Synthetic fibers such as fiber, polyacrylonitrile fiber, polypropylene fiber, and polyethylene fiber. However, since these fibers are preconditions for the nonwoven fabric to maintain desired properties, the mixing ratio is about 0 to 30% by mass (for example, 0.1 to 20% by mass) with respect to the entire nonwoven fabric. . If these fibers are mixed in excess of 30% by mass, the target water-absorbing expansibility is remarkably lowered, which is not preferable.

  The non-woven fabric (or fiber) further includes conventional additives such as stabilizers (heat stabilizers such as copper compounds, ultraviolet absorbers, light stabilizers, antioxidants, etc.), dispersants, thickeners, fine particles, Colorant, Antistatic agent, Flame retardant, Plasticizer, Lubricant, Crystallization rate retarding agent, Lubricant, Antibacterial agent, Insect / Acaricide, Antifungal agent, Matting agent, Animal heat agent, Fragrance, Optical brightener And may contain a wetting agent and the like. These additives can be used alone or in combination of two or more. These additives may be carried on the surface of the nonwoven fabric or may be contained in the fiber.

(Nonwoven fabric properties)
The average fineness of the fibers (wet heat-adhesive fibers, superabsorbent fibers, and other fibers) used in the present invention can be selected from a range of about 0.01 to 100 dtex, for example, 0.1 to 50 dtex, preferably It is about 0.3 to 30 dtex, more preferably about 0.5 to 10 dtex (particularly 1 to 10 dtex), and the wet heat adhesive fiber may be, for example, about 1 to 5 dtex, preferably about 1.5 to 3.5 dtex. Good. If the fineness of the fiber is thin, it will be difficult to produce the fiber itself, and it will be difficult to ensure sufficient fiber strength. Therefore, when the nonwoven fabric of the present invention expands due to water absorption, the expansion in the length direction is limited. Things become difficult.

  On the other hand, in the nonwoven fabric internal structure of the present invention, a gap is generated in the vicinity of the intersection of the fibers, but this portion retains moisture that has not been absorbed into the fiber resin while being absorbed by the nonwoven fabric. However, if the nonwoven fabric constituting fiber is too thick, voids generated in the vicinity of the intersections of these fibers become too large, and sufficient moisture cannot be retained in these voids, and as a result, the water absorption tends to decrease.

  Moreover, the average fiber length of these fibers (wet heat adhesive fiber, superabsorbent fiber, other fibers) is, for example, about 10 to 100 mm, preferably about 25 to 75 mm, and more preferably about 40 to 60 mm. When the fiber length is short, the fiber web formation becomes difficult, and the level of entanglement with other fibers in the web becomes low. As a result, sufficient nonwoven fabric strength and dimensional stability in the length direction when expanded It is difficult to secure sex. In addition, when the fiber length is long, not only is it difficult to form a fiber web with a uniform basis weight, but also the entanglement between the fibers becomes complicated at the time of web formation, and the fibers bind to each other, resulting in a thickness. There is a tendency to prevent expansion in the direction.

  Next, in the present invention, a composite fiber composed of such a wet heat adhesive resin and a dimensionally stable resin is formed into a web, and the fiber is fixed to obtain a desired hard nonwoven fabric. Alternatively, a direct method such as a melt blow method may be used, or a web may be formed by using a dry method such as a card method or an air lay method using staple fibers. As the staple fiber web, a random web, a semi-random web, a parallel web, a cross wrap web or the like is preferably used.

  It is important that the constituent fibers of the formed web (wet heat-adhesive fibers, superabsorbent fibers, and other fibers as necessary) are arranged substantially in parallel with the web surface direction. In the present invention, the fibers are arranged in parallel to the web surface and heat-treated with high-temperature steam, so that the wet heat-adhesive fibers are mainly melted and bonded at their contact points or deformed and part of the partner fibers. Each fiber is slightly fixed to each other while preventing superfluous fibers (and other fibers) from being entangled between the wet heat-adhesive fibers. The non-woven fabric fixed in this way has a structure in which fibers are stacked in a direction perpendicular to the surface having a surface arranged substantially in parallel. By directing the fibers in the surface direction in this way, the length direction of the fibers is oriented in the surface direction (longitudinal and lateral directions) on a specific surface when the sheet absorbs water. Therefore, the fiber length depends on the expansion characteristics of each fiber. There is almost no dimensional change in the vertical direction, and there is no change in the dimensionality of the sheet in the plane direction because fibers are not laminated in the plane direction and there are voids. On the other hand, since the fibers are laminated in the thickness direction, the fibers expand in the diameter direction due to water absorption, and the sheet expands in the thickness direction.

  However, in this web, when there are many fibers oriented in the direction crossing the plane where the fibers are oriented, that is, in the thickness direction, the movement of the fibers in the thickness direction during water absorption is suppressed by the fibers, It is not preferable because the nonwoven fabric is prevented from expanding due to water absorption, and at the same time, it is difficult to secure a place where new water is produced. In particular, when the fiber is a wet heat adhesive fiber, it is not particularly preferable because each fiber is bonded and fixed in the thickness direction.

  Further, the fibers extending in the thickness direction cause disturbance of the fiber arrangement in the vicinity thereof, thereby generating unnecessary voids in the nonwoven fabric. It is sufficient if the voids are at a level that can secure in-situ moisture that could not be absorbed due to the swelling of the fibers, but if the size becomes larger than that, voids that are not filled with water after water absorption are formed. As a result, the water absorption rate decreases, which is not preferable. If this gap is larger, the fibers move in the direction of filling the gap due to the expansion of the fibers due to water absorption, and it is possible to change the shape of the nonwoven fabric, which leads to a dimensional change in all directions of the nonwoven fabric. It is not preferable.

  And by such disturbance, possibility that the distribution of the adhesion point of the fiber in the thickness direction of a nonwoven fabric will become non-uniform | heterogenous becomes large. When this happens, when the nonwoven fabric of the present invention is cut into a necessary size or shape with a blade in a portion having a small number of adhesion points, fibers fall off from the cut surface and contaminate the surroundings. When it is made smaller, the shape cannot be maintained and it tends to fall apart.

  Here, “arranged substantially parallel to the sheet surface” means that a large number of fibers are locally arranged in a direction perpendicular to the surface direction in which main fibers are oriented (thickness direction). It shows a state where there is no repetition of the existing part. More specifically, for example, when an arbitrary cross section in the nonwoven fabric is observed with a microscope, the existence ratio (number ratio) of fibers continuously extending in the thickness direction over 30% or more of the thickness of the nonwoven fabric is The state is 10% or less (particularly 5% or less) with respect to the total fibers.

  In the nonwoven fabric of the present invention, the constituent fibers are fused at the intersection with the wet heat adhesive fibers, but in order to increase the swelling property, it is preferable that the number of adhesion points by fusion is smaller. Further, it is preferable that such adhesion points are distributed with higher uniformity from the point of structural stability to the inside of the nonwoven fabric. The nonwoven fabric of the present invention can have more small voids depending on such an adhesive state. If there is a portion having extremely few fiber adhesion points in the nonwoven fabric of the present invention, the water absorption expansion of the portion having a small fiber fusion point is remarkably exhibited, and it becomes difficult to ensure uniform water absorption expansion behavior in the thickness direction. On the other hand, if the fiber bonding points are increased in order to ensure sufficient form stability, water cannot be held between the fibers, and the apparent water absorption amount decreases. In the present invention, a nonwoven fabric structure having substantially uniform fiber fusion in the thickness direction can be obtained by heat treatment using high-temperature steam.

  Furthermore, the substantially uniform fiber fusion in the thickness direction means that in the nonwoven fabric of the present invention, the ratio of the number of fiber adhesion points in the cross section from one surface to the inside (center) and the back surface (opposite surface) is predetermined. It is within the range. However, in the surface portion of the nonwoven fabric, if the fiber shape is unclear in part due to surface processing such as hot embossing or resin coating, the measurement is performed in a region excluding the portion.

  Specifically, in the nonwoven fabric of the present invention, the fibers constituting the non-woven fiber structure have a fiber adhesion rate of 3 to 60%, preferably 5 to 55%, more preferably 10 to 50 by fusing the wet heat adhesive fibers. It is adhered at about%. Although the fiber adhesion rate in this invention can be measured by the method as described in the Example mentioned later, the ratio of the cross section number of the fiber which adhered 2 or more with respect to the cross section number of all the fibers in a non-woven fiber cross section is shown. Therefore, a low fiber adhesion rate means that a ratio of a plurality of fibers fused to each other (a ratio of fibers fused by fusing) is small.

  In particular, when the cross section of the nonwoven fabric of the present invention is divided into three equal parts along the thickness direction, it is important to secure a fiber adhesion rate of 5 to 50% in the central region divided into three. The fiber adhesion rate is more preferably 10 to 40%, and further preferably 15 to 30%. If the adhesion rate is too small, it will be difficult to ensure the form stability in the nonwoven fabric surface direction at the time of water absorption as described above, and the distance between the adhesion points will increase due to swelling, so the apparent fiber fixation Since the density is lowered, the constituent fibers are easily dropped. Furthermore, if this adhesion rate is too large, the fiber adhesion becomes too dense and the expansion in all directions during water absorption is suppressed, so there is no room for water to enter and a space to hold the absorbed water. It is not preferable because it is difficult to ensure.

  Furthermore, in the cross section in the thickness direction of the nonwoven fabric, the difference between the maximum value and the minimum value of the fiber adhesion rate in each region divided in three in the thickness direction is 20% or less (for example, 0.1 to 20%), preferably 15 % Or less (for example, 0.3 to 15%), more preferably 10% or less (for example, 0.5 to 10%). Further, the ratio of the minimum value to the maximum value of the fiber adhesion rate in each region (minimum value / maximum value) (ratio of the minimum region to the region with the maximum fiber adhesion rate) is, for example, 50% or more (for example, 50 to 100%), preferably 55 to 99%, more preferably 60 to 98% (especially 70 to 97%). In the present invention, since the fiber adhesion rate has such uniformity in the thickness direction, shape stability and dimensional stability are high, and water absorption is excellent.

  In the present invention, the “region divided into three in the thickness direction” means each region divided into three equal parts by slicing in a direction orthogonal to the thickness direction of the nonwoven fabric.

  The fiber fusion rate of the nonwoven fabric of the present invention can be adjusted by controlling the ratio of wet heat adhesive fibers in the constituent fibers and wet heat bonding conditions. That is, by changing the ratio of wet heat adhesive fibers present in the web during wet heat treatment, the chances of wet heat adhesive fibers contacting each other are increased or decreased, and the wet heat adhesive fibers present in the web are efficiently It can be adjusted by changing the conditions during the high-temperature steam treatment so as to adhere. For example, when high fiber bonding efficiency is required, increase the ratio of wet heat adhesive fibers, increase the web compression ratio during wet heat treatment, increase the pressure or discharge rate of high-temperature steam, slow the line speed It is possible to improve the fiber adhesion rate by adjusting the conditions such as to be performed while considering the influence on other target quality.

  The nonwoven fabric of the present invention has a structure as described above, and thus has high water absorption after securing the form stability at the time of water absorption. This water absorption can be expressed by a water absorption rate. The water absorption rate is, for example, 500% by mass or more, preferably 1000 to 5000% by mass (for example, 1200 to 4000% by mass), and more preferably 1500 to 3000% by mass. Degree. If this water absorption is too small, there is almost no expansion in the thickness direction even if water is absorbed. In addition, it is better that the water absorption rate is higher, but if it is practically 5000 mass% or more, the moisture in the tissue is excessively increased, so that the fibers are easy to move and it is difficult to keep the shape stable.

  Furthermore, although the nonwoven fabric of the present invention expands when it absorbs water, it is necessary that this expansion expands in the thickness direction and hardly expands in at least one direction other than the thickness direction. This is because if the expansion due to water absorption occurs in all directions, the size in all directions after water absorption will change. This is because problems such as being unable to do so occur. For example, when this water-absorbent sheet is used as a water sandbag, especially when the dimensions in the horizontal direction change, the weight balance changes due to expansion due to water absorption after laying, or it is not originally blocked by expansion due to water absorption. You can expect a phenomenon that will block the place you should not.

  Therefore, in the nonwoven fabric of the present invention, the dimensional change rate (water absorption expansion or contraction rate) due to water absorption in the length direction of the nonwoven fabric is preferably 5% or less, more preferably the dimensional change rate is 3% or less. Preferably it is 1 to -1%. If this value is too large, it is not preferable because it is difficult to design in use in anticipation of a dimensional change after expansion. A dimensional change rate of less than -1% is not preferable because a gap is formed after water absorption. Similarly, it is preferable to show the same rate of dimensional change in an arbitrary direction parallel to the surface of the nonwoven fabric (for example, the width direction). For such a nonwoven fabric, a large number of such nonwoven fabrics are arranged, for example, in a two-dimensional direction. Is suitable. On the other hand, the dimensional change rate in the thickness direction is, for example, about 10% or more, preferably about 20% or more, and more preferably about 30 to 300% (particularly about 50 to 250%). If the dimensional change rate in the thickness direction is too small, it is difficult to secure a high water absorption rate. Moreover, when the dimensional change rate exceeding 300% is secured, it is difficult to stably maintain the form of the nonwoven fabric after expansion. The nonwoven fabric of the present invention can absorb water efficiently when the dimensional change rate due to water absorption is 50% or more in the thickness direction when water is absorbed from the dry state. Moreover, since the volume expands due to a dimensional change, it is preferable, for example, for the use of a water sandbag. Furthermore, since the nonwoven fabric of the present invention has anisotropy in the dimensional change rate, drainage can be easily performed simply by pushing the absorbed water in the thickness direction, and the drainage is also excellent. Moreover, since the morphological change due to swelling is unidirectional, there is little destruction of the fiber structure and it is suitable for repeated use.

  In the present invention, the dimensional change rate is a value indicating how much the dimension after the dimensional change in a predetermined direction is increased by a percentage with respect to the dimension before the dimensional change. Therefore, if the dimension decreases after the change, the value is negative. Specifically, the dimensional change rate in the present invention is expressed as a percentage obtained by dividing the dimension after the dimension change by the dimension before the dimension change and subtracting one. In this invention, the dimension of the nonwoven fabric at the time of drying is used as a dimension before a dimension change, and the dimension in the nonwoven fabric which absorbed water is used as a dimension after a dimension change. Since the nonwoven fabric of the present invention is excellent in uniformity of dimensional change in each direction, the dimensional change rate of an arbitrary external dimension may be used as the dimensional change rate in that direction. Ordinary knowledge such as a method of measuring at a long position, a method using an average value of the dimensional change rate of several representative points in the same direction (for example, several points taken periodically including the vicinity of the center and the vicinity) Can be used.

Since the nonwoven fabric of this invention becomes lightweight when the density of a dry state is 0.03-0.3 g / cm < ³ >, it is preferable from viewpoints, such as installation and removal. Moreover, it becomes a porous material having a suitable space, can absorb water efficiently, and is also preferable in terms of controlling dimensional changes due to water absorption. If the density in the dry state is too small, it is difficult to secure a sufficient number of adhesion points between the fibers, so it is difficult not only to control the dimensional change due to water absorption but also to obtain the mechanical strength of the nonwoven fabric. Become. Moreover, if too much, it is not preferable from the viewpoint of installation, removal, and water absorption efficiency, and the inter-fiber interaction works too much, so that expansion due to water absorption cannot be specified in a predetermined direction. From the above viewpoint, the dry density is preferably about 0.05 to 0.27 g / cm ³ , and more preferably about 0.07 to 0.23 g / cm ³ .

  And the nonwoven fabric of this invention can ensure the lightweight property which was excellent at the time of drying with the space | gap which arises between constituent fibers. In addition, unlike the resin foam such as sponge, each of these voids is continuous without being independent, and thus has air permeability. This air permeability also ensures the performance of the nonwoven fabric of the present invention. Useful above. That is, as a nonwoven fabric, air permeability is not necessarily required, but having air permeability means that there is a path through which the substance can move through the nonwoven fabric even though it is minute. By doing so, it leads to the high water absorption speed | rate and water absorption efficiency of the nonwoven fabric of this invention, or the high discharge property of water. Such a structure is extremely difficult to achieve with conventional general nonwoven fiber bonding techniques in which a nonwoven fabric surface portion is closely bonded by hot press or hot roll to form a film-like structure. It is difficult, and the conventional method usually requires drilling.

Regarding this air permeability, the air permeability according to the Frazier method is, for example, 0.1 cm ³ / (cm ² · sec) or more, preferably 1 to 250 cm ³ / (cm ² · sec), more preferably 5 to 5 cm. It is about 200 cm ³ / (cm ² · sec). If the air permeability is too small, the resistance when sucking water increases, and even if the hole is open, it is difficult to show the effect of sucking and discharging water, which is not preferable. On the other hand, if the air permeability is too large, the fiber voids in the nonwoven fabric become large and water easily passes through the inside, but on the other hand, there are cases where it is difficult to efficiently retain moisture in the structure.

Also, the basis weight of the nonwoven fabric of the present invention, for example, 50~10000g / ^{m 2,} preferably 150~8000g / ^{m 2,} more preferably 300~6000g / ^{m 2} (particularly 400~3000g / ^{m 2)} approximately. If the basis weight is too small, the amount of water absorption is small and overall dimensional change is difficult to occur. In particular, the dimensional change in the direction in which the dimensional change is easy to occur is less likely to occur. If the basis weight is too large, the web is too thick and too heavy, making it difficult to handle. Furthermore, high-temperature steam cannot sufficiently enter the web, and it may be difficult to obtain a uniform structure in the thickness direction.

  On the other hand, the thickness of a nonwoven fabric is 1-100 mm, for example, Preferably it is 3-50 mm, More preferably, it is about 5-30 mm. If the thickness is less than 1 mm, the absolute value of the dimensional change due to water absorption is still too small to obtain the desired dimensional change. On the other hand, when the thickness exceeds 100 mm, this is also unfavorably deteriorated in handleability because it is very thick.

[Method for producing nonwoven fabric]
Next, the manufacturing method of the nonwoven fabric of this invention is demonstrated.

  The web composed of the mixed fiber of wet heat adhesive fiber and superabsorbent fiber obtained by the above-described method is sent to the next process by a belt conveyor and then exposed to a high-temperature steam (high-pressure steam) stream. The nonwoven fabric of the invention is obtained.

  The belt conveyor to be used is not particularly limited as long as it can basically transport the fiber web used for processing without disturbing its form, but an endless conveyor is preferably used. In addition, it may be a general single belt conveyor, or may be transported by combining two belt conveyors as necessary and sandwiching the web between both belts. By doing in this way, when processing a web, it can control that the form of the web conveyed by external forces, such as water used for processing, high temperature steam, or vibration of a conveyor, changes. It is also possible to control the density and thickness of the processed nonwoven fabric by adjusting the distance between the belts.

  The nonwoven fabric of the present invention can be obtained by supplying high-temperature steam to the web thus transported and fusing the wet heat adhesive fibers among the constituent fibers. A conventional water vapor jet apparatus is used. As this steam spraying device, a device capable of spraying steam substantially uniformly over the entire width of the web at a desired pressure and amount is preferable. When two belt conveyors are combined, the steam spraying device is installed in one conveyor and supplies water vapor to the web through a water-permeable conveyor belt or a conveyor net placed on the conveyor. A suction box may be mounted on the conveyor on the opposite side (the other side). In this case, excess water vapor that has passed through the web can be sucked and discharged by the suction box. Further, in order to perform steam treatment on both the front and back sides of the web at a time, the conveyor on the side opposite to the conveyor on which the steam spraying device is mounted is more than the portion on which the steam spraying device is mounted. A steam injection device may be installed in the downstream conveyor. In the case where there is no downstream steam injection device and suction box, if it is desired to steam-treat the front and back of the web, it can be substituted by inverting the front and back of the web once processed and passing through the processing device again.

  In the present invention, when passing through a high-speed high-temperature steam flow ejected from a nozzle, the fibers are three-dimensionally bonded by the sprayed high-temperature steam.

  The endless belt used for the conveyor is not particularly limited as long as it does not hinder the conveyance of the fiber web or the high-temperature steam treatment. However, when high-temperature steam treatment is performed, the surface shape of the belt may be transferred to the surface of the fiber web depending on the conditions. In particular, when it is desired to obtain a nonwoven fabric having a flat surface, a net with fine mesh may be used. The upper limit is about 90 mesh, and a net that is roughly coarser than 90 mesh (for example, a net of about 10 to 50 mesh) is preferable. A finer mesh net than this has low air permeability and makes it difficult for water vapor to pass through. The mesh belt is made of metal, heat-treated polyester resin, polyphenylene sulfide resin, polyarylate resin (fully aromatic polyester resin), aromatic polyamide resin, etc. The heat resistant resin is preferable.

  High-temperature steam (superheated steam) is an air stream, so the fibers in the web that is the object to be treated are different from the hydroentanglement treatment and needle punching treatment, without greatly moving the fibers in the web that is the object to be treated. Moreover, it enters the web without heating concentrating on the surface area of the nonwoven fabric like hot air or hot roll. It is considered that the invasion action and the wet heat action of the steam flow into the web efficiently cover the surface of each fiber existing in the web in a wet heat state, and enables uniform thermal bonding. In addition, since this treatment is performed in a very short time under a high-speed air stream, the heat conduction of the water vapor to the fiber surface is fast, but the treatment is completed before the heat conduction to the inside of the fiber is sufficiently performed. Due to the pressure and heat of the high-temperature steam, the deformation that damages the thickness of the web itself to be processed is unlikely to occur. As a result, wet-heat bonding is performed so that the degree of bonding in the surface and the thickness direction is substantially uniform without causing large deformation of the web. Moreover, since heat can be sufficiently transmitted to the inside of the nonwoven fabric as compared with the dry heat treatment, the degree of fusion in the surface and the thickness direction becomes substantially uniform.

Furthermore, when obtaining a hard nonwoven fabric, when supplying high temperature water vapor | steam to a web and processing it, the web processed is predetermined | prescribed with a predetermined apparent density (for example, 0.03-0) between a conveyor belt or a roller. .. about ³ g / cm ³ ) and may be exposed to high temperature steam. In particular, when trying to obtain a relatively high density nonwoven fabric, it is necessary to compress the web with sufficient pressure when processing with high temperature steam. Furthermore, it is also possible to adjust to a target thickness and density by securing an appropriate clearance between rollers or between conveyors. In the case of a conveyor, since it is difficult to compress the web at once, it is preferable to set the belt tension as high as possible and gradually narrow the clearance from the upstream of the steam treatment point. Furthermore, it is processed into a non-woven fabric having desired lightness and air permeability by adjusting the water vapor pressure and the processing speed.

  At this time, if the back side of the endless belt on the opposite side of the nozzle across the web is made of a stainless steel plate or the like so that water vapor cannot pass through, the water vapor that has passed through the web that is the object to be treated is reflected here. It is more firmly bonded by the heat retaining effect. On the other hand, when light adhesion is necessary, a suction box may be arranged to discharge excess water vapor to the outside.

  The nozzle for injecting the water vapor may be a plate or die in which predetermined orifices are continuously arranged in the width direction, and may be arranged so that the orifices are arranged in the width direction of the web to be supplied. There may be one or more orifice rows, and a plurality of rows may be arranged in parallel. A plurality of nozzle dies having a single orifice array may be installed in parallel.

  In the case of using a nozzle having an orifice in the plate, the thickness of the plate may be about 0.5 to 1.0 mm. The orifice diameter and pitch are not particularly limited as long as the target fiber can be fixed, but the orifice diameter is usually 0.05 to 2.0 mm, preferably 0.1 to 1.0 mm, More preferably, it is about 0.2 to 0.5 mm. On the other hand, the orifice pitch is usually about 0.5 to 3.0 mm, preferably about 1.0 to 2.5 mm, and more preferably about 1.0 to 1.5 mm.

  Also, the high-temperature steam used for fiber bonding is not particularly limited as long as the target fiber fixation can be realized, and may be set depending on the material and form of the fiber to be used. 0 MPa, preferably 0.2 to 1.5 MPa, more preferably about 0.3 to 1.0 MPa. If the water vapor pressure is too high or too strong, the fibers that make up the web may move more than necessary, causing turbulence, or the fibers may melt too much to partially retain the fiber shape. There is. In addition, when the pressure is too weak, there is a problem that the heat necessary for fiber fusion cannot be given to the object to be processed, water vapor cannot penetrate the web, and fiber fusion spots are generated in the thickness direction. It becomes easy to generate | occur | produce troubles, such as generating and it becomes difficult to control the uniform ejection of the water vapor | steam from a nozzle.

  The temperature of the high-temperature steam is, for example, about 70 to 150 ° C, preferably about 80 to 120 ° C, and more preferably about 90 to 110 ° C. The processing speed of the high temperature steam is, for example, 200 m / min or less, preferably 0.1 to 100 m / min, and more preferably about 1 to 50 m / min.

  If necessary, it is also possible to give a concavo-convex groove, a mark, or the like to a nonwoven fabric obtained by applying a predetermined concavo-convex pattern or letters to the conveyor belt and transferring them. Moreover, you may laminate | stack with another material in the range which does not reduce the characteristic as a nonwoven fabric, and may form a laminated body.

  After the fibers of the fiber web are partially wet-heat bonded in this way, moisture may remain on the nonwoven fabric, and the web may be dried as necessary. Regarding drying, it is necessary that the surface of the non-woven fabric in contact with the heating element for drying is maintained in a fiber form without being formed into a film (disappearance of the fiber form by melting) after drying, and this can be achieved. The method is not particularly limited. Therefore, you may use a large drying facility such as a cylinder dryer or tenter that has been used for drying nonwoven fabrics in the past. Since it is often a level that can be dried by means, a non-contact method such as far-infrared irradiation, microwave irradiation, or electron beam irradiation, a method of blowing hot air, or the like is preferable.

  Further, as described above, the nonwoven fabric of the present invention can be obtained by adhering wet heat-adhesive fibers with high-temperature steam, but partially (such as bonding of nonwoven fabrics obtained by wet heat adhesion), other conventional methods. For example, they may be bonded by a processing method such as partial hot-pressure fusion (such as hot embossing) or mechanical compression (such as needle punch).

  The wet heat adhesive fibers can be fused by dipping the fiber web in hot water. However, it is difficult to control the fiber adhesion rate by such a method, and a nonwoven fabric with high uniformity of the fiber adhesion rate is obtained. Is difficult. The reason for this is that the wet heat adhesiveness varies depending on the position due to the air that is inevitably contained in the web, the structure is affected by this air being pushed out of the web, and the wet bonded web is removed from the hot water. It can be presumed that the deformation of the fine structure inside the fiber by the take-off roller at the time of taking out or the difference in the deformation of the fine structure in the vertical direction due to the weight of hot water contained in the picked-up fiber web.

  The nonwoven fabric obtained by such a method is usually in the form of a sheet or plate and can be processed into a desired shape by cutting or the like depending on the application.

  The non-woven fabric of the present invention has a low density comparable to that of a general non-woven fabric, and even though it has air permeability, there is very little falling off of the constituent fibers, and it expands in a specific direction due to water absorption. It has excellent water absorption. Accordingly, such a nonwoven fabric is particularly suitable for applications in which a large amount of water is impregnated and applications in which deformation due to water absorption is utilized. Specific applications include water-absorbing and water-retaining materials in various fields, for example, water retaining materials for construction or civil engineering (for example, water sandbags), water retaining materials for gardening or culture, or water retaining sheets (for example, floors for plant cultivation) ), Water-retaining materials for daily necessities.

  That is, since the nonwoven fabric of the present invention is light and dry in a dry state, the target performance can be exhibited by increasing the weight and increasing the thickness due to water absorption during use. For this reason, storing in a dry state is advantageous for transport during storage and for securing space. Moreover, since the nonwoven fabric of this invention has mutually fixed fibers, the form is stable. For this reason, it is very easy to cut and remove an unnecessary part and adjust the size when it is necessary to use in a narrow space such as a water sandbag.

  Moreover, when using the nonwoven fabric of this invention as a water sandbag, since a highly water-absorbent fiber is being fixed by fiber bonding, it is not necessary to put in a bag like a normal sandbag. For this reason, it can be set as a rectangular parallelepiped sandbag which is straight to an edge part, and since a corner | angular part and a corner | corner can match with chitin, the clearance gap between sandbags can be suppressed very small. In addition, since it has moderate hardness (morphological stability), it is not necessary to use a cover material (bag) that can absorb water at the time of water absorption, and water can be absorbed quickly at the time of water absorption. Be ready to use it quickly when you need it.

  On the other hand, the nonwoven fabric of the present invention is suitable as a nursery bed for plant cultivation. For example, it is suitable for applications where there are many restrictions on the method of use, such as the location and space used, such as when used for rooftop greening. That is, the non-woven fabric of the present invention is very light and compact in a dry state before use before and after water absorption, and is particularly easy to transport and install. In addition, it is possible to cut and use an extra portion according to the shape and size of the place of use.

  Furthermore, the non-woven fabric of the present invention can be used as a substitute for water-absorbing bodies and water-absorbing sponges used for rooftop greening and as a microorganism-immobilizing carrier by taking advantage of such performance. Furthermore, it can be applied to various uses such as a wiping material (dishwashing sponge, pen-type wiper, etc.), a core such as a magic pen and a fluorescent pen, an ink holding material for an ink jet printer cartridge, and a core material for fragrances such as a fragrance.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In addition, each physical-property value in an Example was measured with the following method.

(1) Weight per unit area (g / m ² )
Measured according to JIS L1913 “Testing method for general short fiber nonwoven fabric”.

(2) Thickness (mm), density (g / cm ³ )
The thickness was measured according to JIS L1913 “Test method for general short fiber nonwoven fabric”, and the density was calculated from this value and the basis weight measured by the method (1).

(3) Air permeability (cm ³ / (cm ² · sec))
According to JIS L1096, it measured by the fragile type method.

(4) Water absorption The nonwoven fabric sample was cut into a size of 5 cm × 5 cm, and the weight of the sample left in a standard state (20 ± 2 ° C., 65 ± 4% RH) for 24 hours was measured (W1). did. The sample was immersed in distilled water in an amount capable of completely covering the sample for 5 minutes, and then the sample was pulled up and suspended vertically for 1 minute to drain the sample (W2). From these measurement results, the water absorption was calculated according to the following equation. For each measurement value, an average value of values measured for five samples was used.

Water absorption = [weight of sample after water absorption (W2) −weight of standard state of sample (W1)] / [weight of standard state of sample (W1)] × 100 (%)
(5) Water absorption expandability After cutting the nonwoven fabric sample into the same size as the sample for water absorption measurement and leaving it under the same conditions for 24 hours, the dimension under the standard condition (L1) is set in the length direction, width direction and thickness direction. Each was measured. After immersing this sample in an amount of distilled water that can completely cover it for 5 minutes, pulling it up and suspending it vertically by hanging for 1 minute, the length direction, width direction, and thickness of the sample are the same. The dimension (L2) after water absorption was measured for the direction, and the dimensional change rate was calculated according to the following formula. For each measurement value, an average value of values measured for five samples was used.

Dimensional change rate = [(L2) − (L1)] / (L1) × 100 (%)
(6) Fiber adhesion rate (%)
Using a scanning electron microscope (SEM), a photograph in which the cross section of the nonwoven fabric was magnified 100 times was taken. The cross-sectional photograph of the photographed nonwoven fabric in the thickness direction is divided into three equal parts in the thickness direction, and the fiber cut surface (fiber end face) that can be found in each of the three divided areas (front surface, inside (center), back surface (opposite surface)) The ratio of the number of cut surfaces in contact with another cut surface to the number of was determined. Of the total number of cuts that can be found in each region, the ratio of the number of cross-sections in a state where two or more fibers are bonded is expressed as a percentage based on the following formula. In addition, in the part which fibers contact, there exists a part which is simply contacting, without melt | fusion, and a part which has adhere | attached by melt | fusion. However, by cutting the nonwoven fabric for microscopic photography, the fibers in contact with each other are separated from each other by the stress of each fiber on the cut surface of the nonwoven fabric. Therefore, in the cross-sectional photograph, it can be determined that the contacting fibers are bonded to each other.

Fiber adhesion rate (%) = (number of cross sections of fibers bonded two or more) / (total number of cross sections of fibers) × 100
However, for each photograph, all the fibers with a visible cross section were counted, and when the number of fiber cross sections was 100 or less, a photograph to be observed was added so that the total fiber cross section exceeded 100. In addition, the fiber adhesion rate is obtained for each of the three divided regions, the difference between the maximum value and the minimum value, the ratio of the minimum value to the maximum value (minimum value / maximum value) is also obtained, and the thickness of the fiber adhesion rate is determined. It was used as an index of directional uniformity.

(7) Nonwoven fabric shape retention The nonwoven fabric sample was cut into a 5 mm square cube shape, placed in an Erlenmeyer flask (100 cm ³ ) containing 50 cm ³ of water, and allowed to stand for 1 minute. It was the shape before processing. This flask was mounted on a shaker (manufactured by Yamato Kagaku Co., “MK160 type”), and was shaken at a speed of 60 rpm for 30 minutes by a swirling method with an amplitude of 30 mm. After shaking, the morphological change and the morphological state were visually confirmed, and the following three-level evaluation was performed.

A: The shape before processing is almost maintained. O: A large missing part is not seen, but deformation of the form is seen. X: A missing part is seen.

Example 1
As the wet heat adhesive fiber, a core-sheath type composite staple fiber having a core component of polyethylene terephthalate and a sheath component of an ethylene-vinyl alcohol copolymer (ethylene content 44 mol%, saponification degree 98.4 mol%) ( “Sophistica” manufactured by Kuraray Co., Ltd., 3.3 dtex, 51 mm length, core-sheath mass ratio = 50/50, number of crimps 21/25 mm, crimp ratio 13.5% was prepared. Furthermore, Toyobo Co., Ltd. highly water-absorbing fiber “Lanseal (registered trademark) F” (5.6 dtex, 51 mm length) was prepared as a highly water-absorbing fiber.

The wet heat adhesive fiber and the superabsorbent fiber are mixed in a mass ratio of wet heat adhesive fiber / superabsorbent fiber = 50/50, and a web having a basis weight of about 100 g / m ² is prepared by a card method. Five webs were stacked to form a card web having a total basis weight of 522.2 g / m ² .

  The card web was transferred to a belt conveyor equipped with a 50 mesh, 500 mm wide stainless steel endless wire mesh. In addition, the belt conveyor which has the same metal mesh is equipped in the upper part of the metal mesh of this belt conveyor, and each used the belt conveyor which can adjust the space | interval of these metal meshes arbitrarily, rotating in the same direction at the same speed. .

  Next, the card web is introduced into a water vapor jetting device provided on the belt conveyor, and water vapor treatment is performed by ejecting high-temperature water vapor of 0.4 MPa from the device so as to pass in the thickness direction of the card web (perpendicularly). The nonwoven fabric of the present invention was obtained. In this steam spraying device, a nozzle is installed in one (lower) conveyor so that high-temperature steam is blown toward the web via a conveyor net, and a suction device is installed in the other (upper) conveyor. It was. In addition, another injection device, which is a combination in which the arrangement of the nozzle and the suction device is reversed, is installed on the downstream side in the web traveling direction of this injection device, and steam treatment is performed on both the front and back surfaces of the web. .

  In addition, the hole diameter of the water vapor | steam injection nozzle was 0.3 mm, and the water vapor | steam injection apparatus with which the nozzle was arranged in 1 row at 1 mm pitch along the width direction of the conveyor was used. The processing speed was 3 m / min, and the interval (distance) between the upper and lower conveyor belts on the nozzle side and the suction side was 5 mm. The nozzles were arranged on the back side of the conveyor belt so as to be almost in contact with the belt.

  Table 1 shows the measured physical properties of the obtained samples. The obtained non-woven fabric had excellent water absorption, and although the dimensional change in the length direction and the width direction was small before and after water absorption, expansion in the thickness direction occurred during water absorption. In addition, good shape retention was exhibited.

  The result of having taken the cross section of the thickness direction of the obtained nonwoven fabric with the SEM photograph is shown in FIG. The scale bar in the photograph shows a length of 500 μm. As is clear from FIG. 1, it was confirmed that the obtained nonwoven fabric had the constituent fibers oriented along the surface direction.

Example 2
A nonwoven fabric was obtained in the same manner as in Example 1 except that 40% by mass of the wet heat adhesive fiber and 60% by mass of the superabsorbent fiber used in Example 1 were mixed. The physical property measurement results of the obtained nonwoven fabric are shown in Table 1. The obtained nonwoven fabric was softer than the nonwoven fabric of Example 1 and had a higher water absorption rate. Further, in the form retention test, a slight fiber dropout was observed, but the form was generally retained. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

Example 3
A nonwoven fabric was obtained in the same manner as in Example 1 except that the basis weight of the nonwoven fabric was about 280 g / m ² . The physical property measurement results of the obtained nonwoven fabric are shown in Table 1. The obtained nonwoven fabric was softer than the nonwoven fabric of Example 1 and exhibited a higher water absorption rate. Further, in the form retention test, a slight fiber dropout was observed, but the form was generally retained. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

Example 4
A nonwoven fabric was obtained in the same manner as in Example 1 except that the water vapor injection pressure in the water vapor injection device was 0.8 MPa and the conveyor belt interval was 2 mm. The physical property measurement results of the obtained nonwoven fabric are shown in Table 1. The obtained non-woven fabric showed a water absorption rate lower than that of the non-woven fabric of Example 1, but had a desired water-absorbing performance and an excellent shape retention. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

Example 5
A nonwoven fabric was obtained in the same manner as in Example 1 except that wet heat adhesive fibers having a fiber diameter of 2.2 dtex were used. The physical property measurement results of the obtained nonwoven fabric are shown in Table 1. The obtained non-woven fabric was slightly denser than the non-woven fabric of Example 1, and had a slightly lower water absorption. Further, in the form retention test, a slight fiber dropout was observed, but the form was generally retained. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

Example 6
A nonwoven fabric was obtained in the same manner as in Example 1 except that the mixture was mixed at a ratio of 80% by mass of wet heat adhesive fiber and 20% by mass of superabsorbent fiber. The results are shown in Table 1. The obtained non-woven fabric exhibited a water absorption rate lower than that of the non-woven fabric of Example 4, but had the desired water-absorbing performance and excellent shape retention. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

Example 7
A nonwoven fabric was obtained in the same manner as in Example 1 except that 20% by mass of wet heat adhesive fiber and 80% by mass of superabsorbent fiber were mixed. The results are shown in Table 1. The obtained non-woven fabric has a more board-like form as compared with the non-woven fabric of Example 1, and has a higher dimensional change rate and water absorption rate in water absorption in the thickness direction than the samples of other examples. In this sample, there was no phenomenon of fiber dropout or shape collapse. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

Comparative Example 1
A nonwoven fabric was obtained in the same manner as in Example 1 except that the mixture was mixed at a ratio of 10% by mass of wet heat adhesive fiber and 90% by mass of superabsorbent fiber. The results are shown in Table 1. The obtained non-woven fabric was very soft compared to the non-woven fabric of Example 1, and showed good water absorption, but the fiber adhesion rate at the center of the thickness was low, and when the water was absorbed to saturation, the surface expanded greatly. The constituent fibers of the part dropped out, and part of the form collapsed. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

Comparative Example 2
In Example 1, instead of guiding the web to the steam injection device and securing the form, calendering was performed with a flat calender device set at a roll temperature of 120 ° C. both in the upper and lower directions. Further, a nonwoven fabric was obtained in the same manner as in Example 1 except that the clearance between the rolls was 5 mm and the processing was performed at a speed of 5 m / min. The results are shown in Table 1. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

  The obtained non-woven fabric is closely bonded to the film of the surface portion in contact with the heat calender roll, and has a film-like shape, while the fiber bonding at the central portion in the thickness direction is very little, and the fiber bonding state in the thickness direction is uneven. It became a structure with a gradient. For this reason, when water was absorbed to a saturated state, only the fiber center part expanded greatly and it divided into two from the thickness center part.

Comparative Example 3
A non-woven fabric is obtained in the same manner as in Example 1 except that 90% by mass of the wet heat adhesive fiber and 10% by mass of the superabsorbent fiber are mixed, and the interval between the conveyor belts in the water vapor jet apparatus is 1.5 mm. It was. The results are shown in Table 1. The obtained nonwoven fabric had low water absorption and water absorption expansion. As a result of observing a cross section in the thickness direction of the obtained nonwoven fabric with SEM, it was confirmed that the constituent fibers were oriented along the surface direction.

  As is clear from the results in Table 1, the nonwoven fabric of the present invention is low in density and light in the dry state, and has a very high water absorption rate when absorbed, and expands only in the thickness direction when absorbed. , There was no expansion in the length direction and width direction.

Claims (13)

  It is composed of wet heat adhesive fibers and superabsorbent fibers, and the ratio (mass ratio) between the wet heat adhesive fibers and the superabsorbent fibers is wet heat adhesive fibers / superabsorbent fibers = 20 / 80-80 / The nonwoven fabric which is 20, the fiber which comprises the said nonwoven fabric is orientated, and the fiber adhesion rate in the cross section of the said nonwoven fabric is substantially uniform along the thickness direction, and is 5 to 50%.   The nonwoven fabric according to claim 1, wherein, when water is absorbed from a dry state, the dimensional change rate due to water absorption is 5.0% or less in the length direction of the nonwoven fabric and 50% or more in the thickness direction. The nonwoven fabric according to claim 1 or 2, wherein a density in a dry state is 0.03 to 0.3 g / cm ³ .   The nonwoven fabric according to any one of claims 1 to 3, which has a water absorption of 500% by mass or more.   The nonwoven fabric according to any one of claims 1 to 4, wherein, in the cross section in the thickness direction, the ratio of the minimum value to the maximum value of the fiber adhesion rate in each of the three regions divided in the thickness direction is 50% or more.   The superabsorbent fiber is composed of a polymer having at least one hydrophilic group selected from the group consisting of a hydroxyl group, a carboxyl group or a base thereof, a sulfonic acid group or a base thereof, and an ether group. The nonwoven fabric in any one of -5.   The nonwoven fabric according to any one of claims 1 to 6, wherein the superabsorbent fiber is composed of a component containing a poly (meth) acrylic acid polymer or a salt thereof.   The wet heat adhesive fiber is composed of an ethylene-vinyl alcohol copolymer having an ethylene unit content of 10 to 60 mol% and a non-wet heat adhesive resin, and the ethylene-vinyl alcohol copolymer and the above-mentioned The ratio (mass ratio) with the non-wet heat adhesive resin is the former / the latter = 90/10 to 10/90, and the ethylene-vinyl alcohol copolymer is at least a part of the wet heat adhesive fiber surface. The nonwoven fabric in any one of Claims 1-7 which occupies continuously in a length direction.   The wet-heat adhesive fiber is a core-sheath type composite fiber formed of a sheath part made of an ethylene-vinyl alcohol copolymer and a core part made of a polyester resin. The non-woven fabric according to crab.   The nonwoven fabric according to any one of claims 1 to 9, which is obtained by forming wet web adhesive fibers and superabsorbent fibers into a mixed web and then heat-treating the mixed web with a high-temperature steam flow while conveying the mixed web.   The water sandbag comprised with the nonwoven fabric in any one of Claims 1-10.   The water retention sheet | seat comprised with the nonwoven fabric in any one of Claims 1-10.   The process according to any one of claims 1 to 9, comprising a step of forming a wet web adhesive fiber and a superabsorbent fiber into a mixed web, and a step of heat-treating the produced mixed web with high-temperature steam while fusing the produced mixed web. The manufacturing method of the nonwoven fabric as described in any one of.