HK1237006B - Water absorbent laminate and method for producing same - Google Patents

Description

Water-absorbent laminate and method for producing the same

Technical Field

The present invention relates to a water-absorbing laminate that can be suitably used as a water-absorbing material such as a wiping material for wiping water, and a method for producing the same.

Background Art

Water-absorbing materials, which are placed at a given location and remove water present or generated there, absorb and remove it by wiping, or retain absorbed water, are widely used not only for general consumers and households but also in industry. Among various water-absorbing materials, nonwoven fabrics composed of hydrophilic fibers are often used due to their absorbency.

For example, Japanese Patent Application Laid-Open No. 11-291377 (Patent Document 1) describes the use of a composite nonwoven fabric in absorbent articles such as disposable diapers. The composite nonwoven fabric is formed by laminating a heat-fusible fiber nonwoven fabric onto a papermaking nonwoven fabric comprising a blend of heat-fusible staple fibers and hydrophilic staple fibers using heat-pressing bonding using embossing. Japanese Patent Application Laid-Open No. 2004-313425 (Patent Document 2) describes the use of a nonwoven fabric interwoven with ultrafine fibers and water-absorbent fibers in wipes for wiping water.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent Application Laid-Open No. 11-291377

Patent Document 2: Japanese Patent Application Laid-Open No. 2004-313425

Summary of the Invention

Problems to be solved by the invention

An object of the present invention is to provide a novel high-strength water-absorbing material having high strength and excellent water absorption and water retention.

Technical solutions to problems

The present invention provides the following water-absorbing laminate and a method for producing the same.

[1] A water-absorbent laminate comprising:

a first fiber layer composed of a first fiber aggregate containing first hydrophilic fibers, and

The second fiber layer is composed of a second fiber aggregate containing 80% by mass or more of heat-adhesive fibers under moisture, wherein:

The surface of the first fiber layer on the side opposite to the second fiber layer has a water absorption rate of 10 seconds or less as measured by a dropping method specified in JIS L 1907.

[2] The water-absorbent laminate according to [1], wherein the first fiber aggregate is a nonwoven fiber aggregate of the first hydrophilic fibers having an average fiber diameter of 10 μm or less.

[3] The water-absorbent laminate according to [1] or [2], wherein the average pore diameter of the first fiber layer is 0.5 to 50 μm.

[4] The water-absorbent laminate according to any one of [1] to [3], wherein the first fiber aggregate is a meltblown nonwoven fiber aggregate.

[5] The water-absorbent laminate according to any one of [1] to [4], wherein the first hydrophilic fibers are fibers formed of a polyamide-based resin.

[6] The water-absorbent laminate as described in any one of [1] to [5], which further includes a third fiber layer composed of a third fiber aggregate containing second hydrophilic fibers, and the third fiber layer is a fiber layer sandwiched between the first fiber layer and the second fiber layer.

[7] The water-absorbent laminate according to any one of [1] to [6], wherein the longitudinal tensile strength when wet as measured in accordance with JIS L 1913 is 160 N/5 cm or more.

[8] The water-absorbent laminate according to any one of [1] to [7], which is used for wiping abrasive grains and water from the surface of an object.

[9] A method for producing the water-absorbent laminate according to [6], comprising:

The first step is to join the first fiber layer and the third fiber layer by interweaving or melting the fibers constituting the first fiber aggregate and the fibers constituting the third fiber aggregate, or to join the second fiber layer and the third fiber layer by interweaving or melting the fibers constituting the second fiber aggregate and the fibers constituting the third fiber aggregate;

The second step is to join the first fiber layer and the third fiber layer by interweaving or melting the fibers constituting the second fiber aggregate and the fibers constituting the third fiber aggregate in the case where the first fiber layer and the third fiber layer are joined in the first step, and to join the first fiber layer and the third fiber layer by interweaving or melting the fibers constituting the first fiber aggregate and the fibers constituting the third fiber aggregate in the case where the second fiber layer and the third fiber layer are joined in the first step, wherein

The interlacing or melt-bonding in the first and second steps is performed by water spunlace, steam jet or needle punching.

Effects of the Invention

The present invention can provide a water-absorbing laminate having excellent water absorption and water retention. The water-absorbing laminate of the present invention can be suitably used as a water-absorbing material, typified by a wiping material for wiping water or water-containing deposits from the surfaces of various objects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a cross-sectional view schematically showing an example of the water-absorbent laminate of the present invention.

FIG2 is a cross-sectional view schematically showing another example of the water-absorbent laminate of the present invention.

FIG3 is a cross-sectional view schematically showing another example of the water-absorbent laminate of the present invention.

Reference numerals

10: first fiber layer, 21, 22: second fiber layer, 30: third fiber layer, 100, 200, 300: water-absorbent laminate.

DETAILED DESCRIPTION

The present invention relates to a water-absorbent laminate comprising at least a first fiber layer comprising a first fiber aggregate containing first hydrophilic fibers, and a second fiber layer comprising a second fiber aggregate containing 80% by mass or more of heat-adhesive fibers under moisture. The present invention will be described in detail below using embodiments thereof.

<Implementation Method 1>

FIG1 is a cross-sectional view schematically showing an example of a water-absorbent laminate according to the present embodiment. The water-absorbent laminate 100 shown in FIG1 includes a first fiber layer 10 and a second fiber layer 21 laminated adjacent to one side of the first fiber layer 10 in the thickness direction (i.e., the second fiber layer 21 is laminated on the first fiber layer 10 so as to contact one side of the first fiber layer 10).

(1) 1st fiber layer

The first fiber layer 10 is a layer that at least plays a water-absorbing role in the water-absorbent laminate 100. The surface of the first fiber layer 10 on the opposite side to the second fiber layer 21 (i.e., the surface on the other side of the thickness direction of the first fiber layer 10) can be a water-absorbing surface that absorbs water from this surface. For example, when the water-absorbent laminate 100 is a wiping material used to wipe water from the surface of various objects, or to wipe attachments containing other components together with water, it can be the wiping surface that contacts the surface of the object.

The first fiber layer 10 is a layer composed of a first fiber aggregate. The first fiber aggregate has water absorption and preferably allows water to pass through the second fiber layer 21. From the perspective of water absorption and water permeability, the first fiber aggregate constituting the first fiber layer 10 is composed of hydrophilic fibers (first hydrophilic fibers). The hydrophilic fibers may be synthetic fibers, natural fibers, regenerated fibers, etc. One type of hydrophilic fiber may be used alone, or two or more types may be used in combination.

Examples of hydrophilic synthetic fibers include synthetic fibers composed of thermoplastic resins having hydrophilic groups such as hydroxyl groups, carboxyl groups, and sulfonic acid groups and/or hydrophilic bonds such as amide bonds. Specific examples of such thermoplastic resins include: polyvinyl alcohol resins (ethylene-vinyl alcohol copolymers, etc.), polyamide resins [aliphatic polyamides such as polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 612, polyamide 92, and polyamide 9C (polyamides formed from nonanediamine and cyclohexanedicarboxylic acid), and copolymers thereof, semi-aromatic polyamides synthesized from aromatic dicarboxylic acids and aliphatic diamines such as polyamide 9T (polyamides formed from nonanediamine and terephthalic acid), and copolymers thereof, etc.], polyester resins (polylactic acid resins such as polylactic acid), and (meth) acrylic resins [resins containing (meth) acrylamide units, etc.]. Among these, polyvinyl alcohol resins and polyamide resins are preferably used. Hydrophilic synthetic fibers may be used alone or in combination of two or more. On the other hand, when the first fiber structure is composed of fibers of a non-hydrophilic resin (hydrophobic resin) such as a polyolefin resin or a polyester resin, a laminate having good water absorbency cannot be obtained.

In an ethylene-vinyl alcohol copolymer, which is a preferred example of a polyvinyl alcohol resin, the ethylene unit content (copolymerization ratio) is, for example, 10 to 60 mol%, preferably 20 to 55 mol%, and more preferably 30 to 50 mol%. The saponification degree of the vinyl alcohol unit is, for example, 90 to 99.99 mol%, preferably 95 to 99.98 mol%, and more preferably 96 to 99.97 mol%. The viscosity-average degree of polymerization of the ethylene-vinyl alcohol copolymer is, for example, 200 to 2500, preferably 300 to 2000, and more preferably 400 to 1500.

Examples of hydrophilic natural fibers include cotton, satin, linen, silk, and wool. Examples of hydrophilic regenerated fibers include cellulose fibers such as rayon, lyocell, cupra, and polynosic. These natural fibers and regenerated fibers may be used alone or in combination of two or more.

The hydrophilic fiber may be composed of a hydrophilic resin at least on its surface. For example, it may be a fiber in which the surface of a hydrophobic resin is hydrophilized, or a core-sheath type composite fiber in which a hydrophilic resin continuously covers the entire surface of the core in the longitudinal direction. The core of the core-sheath type composite fiber may be composed of a thermoplastic resin such as a polyolefin resin such as polyethylene or polypropylene, a polyester resin, a polyamide resin, or a polyurethane resin. For examples of hydrophilic resins constituting the sheath, the description of hydrophilic synthetic fibers is cited. The ratio of the core to the sheath in the core-sheath type composite fiber is, for example, sheath/core = 90/10 to 10/90, preferably 80/20 to 15/85, and more preferably 60/40 to 20/80 in terms of mass ratio.

The first fiber aggregate constituting the first fiber layer 10 may contain fibers other than hydrophilic fibers (e.g., hydrophobic fibers). From the perspective of water absorption, a high content of hydrophilic fibers is preferred. Specifically, the content of hydrophilic fibers in the first fiber aggregate is preferably 70% by mass or greater, more preferably 80% by mass or greater, and even more preferably 90% by mass or greater (e.g., 100% by mass). Fibers other than hydrophilic fibers include fibers made of polyolefin resins such as polyethylene and polypropylene, polyester resins, and polyurethane resins.

The water-absorbent laminate 100 has excellent water absorption. The surface of the first fiber layer 10 (the surface on the other side in the thickness direction of the first fiber layer 10), which serves as the water-absorbing surface, opposite to the second fiber layer 21, has a water absorption rate of 10 seconds or less, preferably 5 seconds or less, as measured by the dropping method specified in 7.1.1 of JIS L 1907, "Test Methods for Water Absorption of Textile Products." The water absorption rate is typically 0.01 seconds or more. The water absorption rate referred to herein refers to the water absorption rate of the outer surface of the water-absorbent laminate 100 when it is formed.

To improve the surface smoothness of the outer surface of the first fiber layer 10, which serves as the water-absorbing surface, the hydrophilic fibers comprising the first fiber aggregate (and fibers other than hydrophilic fibers, if included) preferably have an extremely fine fiber diameter, finer than that of the fibers comprising the other layers of the water-absorbent laminate 100. Specifically, the average fiber diameter (number average fiber diameter) is preferably 10 μm or less, more preferably 0.1 to 9 μm, even more preferably 0.5 to 8 μm, even more preferably 1 to 7 μm, and particularly preferably 2 to 6 μm. When the average fiber diameter falls within this range, the outer surface of the first fiber layer 10 exhibits excellent surface smoothness, effectively preventing damage to the surface of an object being wiped when the water-absorbent laminate 100 is used, for example, as a wiping material. High surface smoothness also contributes to improved water absorption and uniformity in wiping operations, particularly in terms of the contact surface with the surface of an object to be absorbed and removed. Excessively small average fiber diameters may reduce the permeability of absorbed water into the second fiber layer 21. It should be noted that the cross-sectional shape of the fibers constituting the first fiber aggregate can generally be a perfect circular cross-section, an elliptical cross-section, etc. In addition, when the first fiber aggregate contains fibers other than the hydrophilic fibers, the average fiber diameter of the other fibers is also preferably within the above range.

The fibers comprising the first fiber aggregate may contain one or more additives as needed. Specific examples of additives include colorants, heat stabilizers, UV absorbers, light stabilizers, antioxidants, microparticles, crystallization rate retarders, antistatic agents, flame retardants, plasticizers, and lubricants. The additives may be carried on the surface of the fibers or contained within the fibers.

The first fiber aggregate constituting the first fiber layer 10 is preferably a nonwoven fiber aggregate, more preferably a meltblown nonwoven fiber aggregate. The meltblowing method can easily form the first fiber layer 10 composed of ultrafine fibers. Furthermore, while improving the water absorption performance of the water-absorbent laminate 100, it is easy to form the first fiber layer 10 having favorable structure and properties.

The average pore diameter of the first fiber layer 10 in the water-absorbent laminate 100 is preferably 0.5 to 50 μm, more preferably 5 to 40 μm. By making the average pore diameter within this range, good water absorbency can be imparted to the first fiber layer 10. In addition, the average pore diameter within the above range is also advantageous in terms of improving particle capture. That is, as described below, for the water-absorbent laminate 100, it can be suitably used even as a wiping material (cleaning tape) for wiping abrasive slurry (water with abrasive particles dispersed therein) attached to the surface of a substrate such as a hard disk substrate after a grinding process, and as a result, when the average pore diameter is within the above range, the abrasive particles can be effectively captured and retained. The average pore diameter of the first fiber layer 10 is preferably adjusted to a value larger than the abrasive particle diameter. The water-absorbent laminate 100 can capture not only abrasive particles but also other particles (solid substances). In this case, the average pore diameter of the first fiber layer 10 can be adjusted according to the particle size of the particles (solid substances) to be captured and removed within a range that provides good water absorption.

From the perspective of water absorption rate and permeability of absorbed water to the second fiber layer 21, the porosity of the first fiber layer 10 in the water-absorbent laminate 100 is preferably 70% or greater, more preferably 75% or greater, and even more preferably 80% or greater. The porosity of the first fiber layer 10 is generally 99% or less, more typically 95% or less.

The first fiber layer 10 is preferably a dense layer composed of the ultrafine first fiber aggregate described above, and has a basis weight of, for example, 3 to 100 g/m ² , preferably 5 to 90 g/m ² , and more preferably 10 to 80 g/m ² (e.g., 30 to 70 g/m ² ). If the basis weight of the first fiber layer 10 is too low, the fibers constituting the second fiber layer 21 in the water-absorbent laminate 100 are likely to be exposed on the outer surface of the first fiber layer 10, potentially impairing the surface smoothness of the outer surface. On the other hand, if the basis weight of the first fiber layer 10 is too high, the permeability of absorbed water to the second fiber layer 21 is likely to be reduced.

The apparent density of the first fiber layer 10 in the water-absorbent laminate 100 is preferably 0.35 g/ ^cm³ or less, more preferably 0.3 g/ ^cm³ or less, and even more preferably 0.25 g/cm³ or ^less (e.g., 0.2 g/ ^cm³ or less). If the apparent density of the first fiber layer 10 is too high, the permeability of absorbed water to the second fiber layer 21 is likely to decrease. The apparent density of the first fiber layer 10 is generally 0.01 g/ ^cm³ or greater, more typically 0.1 g/ ^cm³ or greater.

The thickness of the first fiber layer 10 in the water-absorbent laminate 100 is, for example, 10 to 600 μm. From the perspective of water absorption, it is preferably 50 μm or greater, and more preferably 100 μm or greater. If the thickness of the first fiber layer 10 is too small, good water absorption is difficult to achieve. Furthermore, from the perspective of permeability of absorbed water to the second fiber layer 21, the thickness of the first fiber layer 10 is preferably 550 μm or less, and more preferably 500 μm or less.

The manufacturing method of the first fiber layer 10 (first fiber aggregate) is not particularly limited as long as it can form the first fiber aggregate given above. The first fiber layer 10 composed of ultrafine fibers can be easily formed. In addition, the first fiber layer 10 with favorable structure and characteristics can be easily formed on the basis of improving the water absorption performance of the water-absorbent laminate 100. Therefore, it is preferred to use the meltblowing method as mentioned above.

In the meltblowing method, for example, a heated and molten thermoplastic resin is extruded (spun) from the spinning holes of a nozzle having nozzles (spinning holes) arranged in a row, and high-temperature air heated to the same temperature as the nozzle is blown out from a slit provided near the spinning holes. The high-temperature air is brought into contact with the molten resin spun from the spinning holes to refine the molten resin. The refined fibers are collected on the collecting surface of a conveyor arranged below the nozzle, thereby obtaining a nonwoven fabric.

The spacing of the spinning holes in the meltblowing method is, for example, 100 to 4000 holes/m, preferably 500 to 3000 holes/m, and more preferably 1000 to 2500 holes/m. The discharge rate per hole is, for example, 0.01 to 1 g/hole/minute, preferably 0.05 to 0.5 g/hole/minute, and more preferably 0.1 to 0.3 g/hole/minute. The spinning temperature can be selected according to the type of thermoplastic resin and is, for example, 150 to 300°C, preferably 200 to 280°C, and more preferably 220 to 270°C.

The air pressure of the high-temperature air is, for example, 0.01 to 1 MPa, preferably 0.05 to 0.8 MPa, more preferably 0.1 to 0.6 MPa, and even more preferably 0.2 to 0.5 MPa. The air temperature is, for example, near the spinning temperature, preferably 0 to 50°C higher than the spinning temperature, more preferably 3 to 30°C higher than the spinning temperature, and even more preferably 5 to 20°C higher than the spinning temperature.

The conveyor speed is, for example, 1 to 200 m/min, preferably 5 to 100 m/min, and more preferably 10 to 80 m/min. By adjusting the air pressure, conveyor speed, the distance (collection distance) between the spinning hole and the conveyor (such as a mesh belt conveyor), etc., the average pore diameter, porosity, basis weight, apparent density, thickness, etc. of the obtained first fiber layer 10 can be controlled.

(2) Second fiber layer

The second fiber layer 21 is a fiber layer composed of a second fiber aggregate containing 80% or more by mass of heat-and-wet adhesive fibers. The second fiber aggregate is preferably a nonwoven fiber aggregate. This nonwoven fiber aggregate (second fiber layer 21) can be obtained by subjecting a web containing heat-and-wet adhesive fibers to high-temperature (superheated or heated) steam, causing the fibers to partially bond, secure, and bundle together by exhibiting a bonding effect at a temperature below the melting point of the heat-and-wet adhesive fibers.

By laminating the second fiber layer 21 on one side of the first fiber layer 10 in the thickness direction, the water-absorbent laminate 100 can be endowed with excellent water retention and strength, and can also contribute to improving the water absorption of the water-absorbent laminate 100. Furthermore, when the water-absorbent laminate 100 is used as a wiping material, it is required that the water-absorbent laminate 100 does not neck during wiping, and the surface of the object being wiped is uniformly wiped. As a result, the lamination of the second fiber layer 21 can also improve the necking resistance of the water-absorbent laminate 100. Furthermore, when the water-absorbent laminate 100 is used as a wiping material, it is required to prevent the surface of the object being wiped from being damaged. As a result, the lamination of the second fiber layer 21 can improve the cushioning properties (compression elastic modulus) of the water-absorbent laminate 100, effectively preventing surface damage.

In this embodiment, the heat-and-wet adhesive fibers constituting the second fiber aggregate are composed of at least a heat-and-wet adhesive resin. The heat-and-wet adhesive resin is a resin that can flow or deform easily at a temperature easily achieved by high-temperature steam, thereby exhibiting an adhesive function. More specifically, it can be a thermoplastic resin that softens in hot water (e.g., 80-120°C, particularly 95-100°C) and can bond to itself or to other fibers. Specific examples of such moist heat adhesive resins include: cellulose resins ( _C1-3 alkyl cellulose ethers such as methyl cellulose, hydroxy _C1-3 alkyl cellulose ethers such as hydroxymethyl cellulose, carboxy _C1-3 alkyl cellulose ethers such as carboxymethyl cellulose, or their salts); polyalkylene glycol resins (poly _C2-4 epoxides such as polyethylene oxide and polypropylene oxide); polyvinyl resins (polyvinyl pyrrolidone, polyvinyl ether, vinyl alcohol polymers, polyvinyl acetal, etc.); (meth)acrylic resins and alkali metal salts thereof [copolymers containing units composed of acrylic monomers such as (meth)acrylic acid and (meth)acrylamide, or their salts); modified vinyl copolymers (copolymers of vinyl monomers such as isobutylene, styrene, ethylene, and vinyl ether and unsaturated carboxylic acids or their anhydrides such as maleic anhydride, or their salts); polymers into which hydrophilic substituents have been introduced (polyesters, polyamides, polystyrenes, or their salts into which sulfonic acid groups, carboxyl groups, hydroxyl groups, etc. have been introduced); and aliphatic polyester resins (polylactic acid resins, etc.). In addition, polyolefin resins, polyester resins, polyamide resins, polyurethane resins, thermoplastic elastomers, and rubbers (such as styrene elastomers) also include resins that soften at hot water (high-temperature steam) temperatures and exhibit adhesive properties. The heat-under-wet adhesive resin may be used alone or in combination of two or more.

The heat-under-wet adhesive resin is preferably a vinyl alcohol polymer, a polylactic acid resin such as polylactic acid, or a (meth)acrylic resin containing a (meth)acrylamide unit, more preferably a vinyl alcohol polymer containing an α-C _2-10 olefin unit such as ethylene or propylene, and even more preferably an ethylene-vinyl alcohol copolymer.

In ethylene-vinyl alcohol copolymers, the content of ethylene units (copolymerization ratio) is, for example, 10 to 60 mol%, preferably 20 to 55 mol%, more preferably 30 to 50 mol%. By making the ethylene units within this range, it is possible to obtain a special property of wet heat adhesion but not hot water solubility. When the ratio of ethylene units is too little, ethylene-vinyl alcohol copolymers are prone to swelling or gelation in low-temperature steam (water), and their form is easily changed by only wetting once in water. On the other hand, when the ratio of ethylene units is too much, hygroscopicity is reduced and it is difficult to show the fiber fusion caused by wet heat. Therefore, for the nonwoven fiber aggregate obtained, it is difficult to ensure the strength with practicality. In particular, when the ratio of ethylene units is within the range of 30 to 50 mol%, the processability of the nonwoven fiber aggregate is particularly excellent.

The degree of saponification of the vinyl alcohol units in the ethylene-vinyl alcohol copolymer is, for example, 90 to 99.99 mol%, preferably 95 to 99.98 mol%, and more preferably 96 to 99.97 mol%. If the saponification degree is too low, thermal stability decreases, and thermal decomposition and gelation tend to occur. On the other hand, if the saponification degree is too high, production of the fiber itself becomes difficult.

The viscosity average degree of polymerization of the ethylene-vinyl alcohol copolymer is, for example, 200 to 2500, preferably 300 to 2000, and more preferably 400 to 1500. When the degree of polymerization is within this range, the balance between spinnability and heat-under-wet adhesiveness is excellent.

The cross-sectional shape of the wet heat bonding fiber (the cross-sectional shape perpendicular to the longitudinal direction of the fiber) is not limited to a generally solid circular cross-sectional shape, an irregular cross-sectional shape [flat, elliptical, polygonal, 3 to 14 petal, T-shaped, H-shaped, V-shaped, dog bone (I-shaped), etc.], and can be, for example, a hollow cross-sectional shape.

The heat-adhesive fiber under moisture may be a composite fiber composed of multiple resins including at least a heat-adhesive resin under moisture. The composite fiber only needs to have the heat-adhesive resin under moisture on at least a portion of the fiber surface. However, from the perspective of interfiber adhesion, it is preferred that the heat-adhesive resin under moisture continuously occupies at least a portion of the surface in the longitudinal direction.

The cross-sectional structure of the composite fiber in which the heat-under-moisture adhesive fiber occupies the surface may be a core-sheath type, an island-in-the-sea type, a side-by-side type or a multi-layer laminated type, a radial laminated type, a random composite type, etc. Among them, a core-sheath type structure in which the heat-under-moisture adhesive resin continuously occupies the entire surface of the core in the longitudinal direction (i.e., a core-sheath type structure in which the sheath is composed of the heat-under-moisture adhesive resin) is preferred because it has a high adhesiveness between the fibers.

In the composite fiber, heat-adhesive resins under moisture can be combined with each other, or non-heat-adhesive resins under moisture can be combined with heat-adhesive resins under moisture. A preferred example of the latter is a core-sheath type composite fiber comprising a core portion consisting of a non-heat-adhesive resin under moisture and a sheath portion consisting of a heat-adhesive resin under moisture. Examples of the non-heat-adhesive resin under moisture include polyolefin resins, (meth) acrylic resins, vinyl chloride resins, styrene resins, polyester resins, polyamide resins, polycarbonate resins, polyurethane resins, and thermoplastic elastomers. The non-heat-adhesive resin under moisture can be used alone or in combination of two or more.

Among them, as a non-wet heat adhesive resin, from the perspective of heat resistance and dimensional stability of the composite fiber, it is preferred to use a resin with a melting point higher than that of the wet heat adhesive resin (especially ethylene-vinyl alcohol copolymer), such as polypropylene resin, polyester resin, and polyamide resin. From the perspective of excellent balance between heat resistance, fiber forming properties, etc., it is more preferred to use polyester resin and polyamide resin.

Examples of polyester resins include aromatic polyester resins such as polyethylene terephthalate resins, polytrimethylene terephthalate resins, polybutylene terephthalate resins, and polyethylene naphthalate resins, with polyethylene terephthalate resins being preferred. Polyethylene terephthalate resins may contain, in addition to ethylene terephthalate units, units derived from other dicarboxylic acids (e.g., isophthalic acid, naphthalene-2,6-dicarboxylic acid, phthalic acid, 4,4'-diphenylcarboxylic acid, bis(carboxyphenyl)ethane, sodium 5-sulfoisophthalate, etc.) and diols (e.g., diethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexane-1,4-dimethanol, polyethylene glycol, and polytetramethylene glycol) at a ratio of approximately 20 mol% or less.

Examples of polyamide resins include aliphatic polyamides such as polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 612, polyamide 92, and polyamide 9C (a polyamide formed from nonanediamine and cyclohexanedicarboxylic acid), and copolymers thereof; and semi-aromatic polyamides synthesized from aromatic dicarboxylic acids and aliphatic diamines such as polyamide 9T (a polyamide formed from nonanediamine and terephthalic acid), and copolymers thereof. Polyamide resins may also contain units derived from other copolymerizable monomers.

In composite fibers composed of a heat-adhesive resin under moisture and a non-heat-adhesive resin under moisture (fiber-forming polymer), the ratio (mass ratio) of the two can be selected based on the structure (e.g., a core-sheath structure), with the ratio of heat-adhesive resin under moisture to non-heat-adhesive resin under moisture being, for example, 90/10 to 10/90, preferably 80/20 to 15/85, and more preferably 60/40 to 20/80. If the ratio of the heat-adhesive resin under moisture is too high, it is difficult to ensure fiber strength. If the ratio of the heat-adhesive resin under moisture is too low, it is difficult to ensure that the heat-adhesive resin under moisture is continuously present along the longitudinal direction of the fiber surface, resulting in reduced heat-adhesive properties under moisture. This tendency also applies when the heat-adhesive resin under moisture is applied to the surface of non-heat-adhesive fibers.

The average fineness of the heat-under-wet adhesive fiber can be selected from the range of 0.01 to 100 dtex, preferably 0.1 to 50 dtex, more preferably 0.5 to 30 dtex (particularly 1 to 10 dtex). When the average fineness is within this range, the balance between fiber strength and heat-under-wet adhesiveness is excellent.

The average fiber length of the wet heat adhesive fibers can be selected from a range of, for example, 10 to 100 mm, preferably 20 to 80 mm, and more preferably 25 to 75 mm (particularly 35 to 55 mm). When the average fiber length is within this range, the fibers are fully entangled, thereby improving the mechanical strength of the second fiber aggregate (second fiber layer 21).

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

The second fiber aggregate constituting the second fiber layer 21 may contain non-thermal adhesive fibers in addition to the thermal adhesive fibers. Specific examples of the non-thermal adhesive fibers include polyester fibers (aromatic polyester fibers such as polyethylene terephthalate fibers, polytrimethylene terephthalate fibers, polybutylene terephthalate fibers, and polyethylene naphthalate fibers), polyamide fibers (aliphatic polyamide fibers such as polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, and polyamide 612, semi-aromatic polyamide fibers, aromatic polyamide fibers such as polyphenylene isophthalamide, polyhexamethylene terephthalamide, and polyparaphenylene terephthalamide), polyolefin fibers (polyolefin fibers such as polyethylene and polypropylene), and polyolefin fibers. _2-4 olefin fibers, etc.), acrylic fibers (acrylonitrile fibers having acrylonitrile units such as acrylonitrile-vinyl chloride copolymers, etc.), polyvinyl fibers (polyvinyl acetal fibers, etc.), polyvinyl chloride fibers (fibers of polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-acrylonitrile copolymers, etc.), polyvinylidene chloride fibers (fibers of vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-vinyl acetate copolymers, etc.), polyparaphenylene benzobisazole fibers, polyphenylene sulfide fibers, and cellulose fibers. The non-heat-under-wet adhesive resins may be used alone or in combination. The average fineness and average fiber length of the non-heat-under-wet adhesive fibers may be the same as those of the heat-under-wet adhesive fibers.

For example, when hydrophilic cellulose fibers such as rayon are combined with heat-bonding fibers containing ethylene-vinyl alcohol copolymer, their mutual affinity is high. Therefore, as shrinkage progresses, the bonding property also increases, and a second fiber layer 21 with high mechanical strength and necking resistance can be obtained at a relatively high density. On the other hand, when low-hygroscopic polyester fibers (e.g., polyethylene terephthalate fibers) are combined with heat-bonding fibers containing ethylene-vinyl alcohol copolymer, a highly lightweight second fiber layer 21 can be obtained. Using hydrophilic fibers as non-heat-bonding fibers tends to improve the water retention of the water-absorbent laminate 100.

The ratio (mass ratio) of the thermal adhesive fibers under moisture to the non-thermal adhesive fibers under moisture in the second fiber aggregate constituting the second fiber layer 21 is thermal adhesive fibers under moisture/non-thermal adhesive fibers under moisture = 80/20 to 100/0, preferably 90/10 to 100/0, and more preferably 95/5 to 100/0. When the ratio of the thermal adhesive fibers under moisture is within this range, the water-absorbent laminate 100 can be provided with excellent water retention, mechanical strength, and necking resistance.

The fibers constituting the second fiber aggregate may contain one or more additives as needed. Specific examples of additives include colorants, heat stabilizers, UV absorbers, light stabilizers, antioxidants, microparticles, crystallization rate retarders, antistatic agents, flame retardants, plasticizers, and lubricants. The additives may be carried on the surface of the fibers or contained within the fibers.

The second fiber layer 21 can be a non-woven fiber aggregate obtained from a web composed of the above-mentioned fibers. The web of the non-woven fiber aggregate is preferably formed by appropriately adjusting the arrangement and bonding state of the fibers constituting it. That is, the fibers constituting the fiber web are preferably arranged so that they are arranged roughly parallel to the surface of the fiber web (non-woven fiber aggregate) and intersect with each other. In addition, each fiber is preferably melt-bonded at the intersection. In particular, when high hardness and mechanical strength are required, in the portion where the fibers other than the intersection are arranged roughly parallel, a bundle of several to dozens of fibers can be formed that are melt-bonded into a bundle. By partially forming a structure in which these fibers are melt-bonded at the intersections of single fibers, the intersections of bundled fibers, or the intersections of single fibers and bundled fibers, the second fiber layer 21 can be formed. The second fiber layer 21 has a structure in which the fibers are bonded at the intersections and entangled like a mesh, or a structure in which the fibers are bonded at the intersections and mutually restrict adjacent fibers, and a passage formed by small gaps is appropriately formed. The water-absorbent laminate 100 having such a second fiber layer 21 has excellent water absorption, water retention, necking resistance, cushioning properties, and permeability of absorbed water to the second fiber layer 21.

"Arranged substantially parallel to the fiber web surface" means that there are no repeated portions of fibers partially aligned in the thickness direction. More specifically, it means that, when microscopically observing any cross-section of the fiber web of a nonwoven fiber aggregate, the proportion (number ratio) of fibers extending continuously in the thickness direction within a range of 30% or more of the fiber web's thickness is 10% or less (particularly 5% or less) relative to the total number of fibers in the cross-section.

The reason for arranging the fibers parallel to the fiber web surface is that if a large number of fibers are oriented in the thickness direction (perpendicular to the web surface), there is a tendency for the fibers to be arranged in a disordered manner at the periphery, resulting in unnecessarily large voids within the nonwoven fiber, which can reduce necking resistance, etc. Therefore, it is preferable to minimize such large voids, and therefore, it is preferable to arrange the fibers as parallel to the fiber web surface as possible.

The second fiber aggregate constituting the second fiber layer 21 is preferably a nonwoven fiber aggregate in which the fibers constituting the second fiber aggregate are partially bonded and fixed by melt-bonding of wet heat adhesive fibers. The fibers are preferably bonded by melt-bonding of wet heat adhesive fibers at a fiber bonding ratio of 85% or less (e.g., 1 to 85%). The fiber bonding ratio is more preferably 3 to 70%, and even more preferably 5 to 60% (particularly 10 to 35%).

The fiber bonding ratio represents the ratio of the cross-sectional number of two or more bonded fibers to the cross-sectional number of all fibers in the nonwoven fiber aggregate (the second fiber aggregate). A low fiber bonding ratio means that the ratio of multiple fibers fused to each other (the ratio of fibers fused together) is low.

The fiber bonding rate, which indicates the degree of melt bonding, can be measured simply by taking an enlarged photograph of a cross section of a nonwoven fiber aggregate (the second fiber aggregate) using a scanning electron microscope (SEM), based on the number of fiber cross sections formed by bonding within a given area. However, when the fibers are melt-bonded into bundles, it is sometimes difficult to observe them as a single fiber. In this case, for example, when a nonwoven fiber aggregate is bonded with a core-sheath type composite fiber composed of a sheath portion composed of a wet-heat adhesive fiber and a core portion composed of a fiber-forming polymer, the melt bonding of the bonding portion is eliminated by melting, washing, or other methods, and the fiber bonding rate can be measured by comparing the cross section with the cross section before elimination.

The bonding points of the fibers constituting the nonwoven fiber aggregate are preferably evenly distributed along the thickness direction from the surface of the nonwoven fiber aggregate to the interior (center) and then to the back. When the bonding points are locally present on the surface or the interior, sufficient necking resistance cannot be obtained. In addition, the morphological stability of the portion with fewer bonding points is reduced. In addition, when the bonding points of the fibers are locally present on the surface or the interior, there is a tendency that appropriate gaps cannot be formed, water retention, cushioning properties, and the permeability of absorbed water to the second fiber layer 21 are reduced. Therefore, it is preferred that on the cross-section in the thickness direction of the nonwoven fiber aggregate, the fiber bonding rates in each region divided into three equal parts in the thickness direction are all within the above range.

In addition, the difference between the maximum and minimum fiber bonding rates in each region is 20% or less (e.g., 0.1-20%), preferably 15% or less (e.g., 0.5-15%), and more preferably 10% or less (e.g., 1-10%), or the ratio of the minimum fiber bonding rate to the maximum fiber bonding rate in each region (minimum value/maximum value) (the ratio of the region with the minimum fiber bonding rate to the region with the maximum fiber bonding rate) is, for example, 50% or more (e.g., 50-100%), preferably 55-99%, and more preferably 60-98% (particularly 70-97%). When the fiber bonding rate has such uniformity in the thickness direction, it is excellent in hardness, bending strength, folding resistance, toughness, and necking resistance. "Regions divided into three equal parts in the thickness direction" refers to each region divided into three equal parts by slicing in a direction perpendicular to the thickness direction of the nonwoven fiber aggregate (second fiber layer 21) (the same will be applied hereinafter).

From the perspective of the water retention and cushioning properties of the water-absorbent laminate 100, the porosity of the second fiber layer 21 in the water-absorbent laminate 100 is preferably 70% or greater, more preferably 75% or greater, and even more preferably 80% or greater. The porosity of the second fiber layer 21 is generally 99% or less, more typically 95% or less.

The basis weight of the second fiber layer 21 can be, for example, 20 to 1000 g/ ^m² , preferably 30 to 600 g/ ^m² , and more preferably 50 to 400 g/ ^m² . If the basis weight is too low, at least one of water retention, necking resistance, and cushioning properties tends to be insufficient. On the other hand, if the basis weight is too high, the web becomes too thick, and high-temperature steam cannot fully penetrate the web during the wet heat (steam jet) process, making it difficult to produce a nonwoven fiber aggregate that is uniform in the thickness direction.

The apparent density of the second fiber layer 21 in the water-absorbent laminate 100 is preferably 0.5 g/ ^cm³ or less, more preferably 0.4 g/ ^cm³ or less, and even more preferably 0.3 g/ ^cm³ or less (e.g., 0.2 g/ ^cm³ or less, and further preferably 0.15 g/ ^cm³ or less). If the apparent density of the second fiber layer 21 is too high, the water-retention and cushioning properties of the water-absorbent laminate 100 may be insufficient. The apparent density of the second fiber layer 21 is typically 0.01 g/ ^cm³ or greater, more typically 0.05 g/ ^cm³ or greater. By reducing the apparent density, the water-retention properties of the water-absorbent laminate 100 can be improved.

The thickness of the second fiber layer 21 in the water-absorbent laminate 100 is, for example, 20 μm or greater. From the perspectives of water retention, necking resistance, and cushioning properties, it is preferably 100 μm or greater, and more preferably 200 μm or greater. Furthermore, from the perspective of avoiding an excessive increase in the mass of the water-absorbent laminate 100, the thickness of the second fiber layer 21 is typically 2000 μm or less, preferably 1000 μm or less, and more preferably 800 μm or less.

Next, the manufacturing method of the second fiber aggregate which is the non-woven fiber aggregate constituting the second fiber layer 21 is described. The second fiber aggregate can be well manufactured by a steam jet method in which a fiber web is exposed to high-temperature and high-pressure steam and subjected to non-woven fabric formation. In this manufacturing method, first, a fiber containing the above-mentioned wet heat adhesive fiber is formed into a web. As a method for forming the web, conventional methods can be used, such as direct methods such as spunbonding and meltblowing; dry methods such as carding methods using meltblown fibers, staple fibers, etc., and air-laid methods. Among these methods, carding methods using meltblown fibers and staple fibers are widely used, and carding methods using staple fibers are particularly used. As webs obtained using staple fibers, for example, random webs, semi-random webs, parallel-laid webs, cross-laid webs, etc. can be cited. When the proportion of bundled melt-bonded fibers is increased, semi-random webs and parallel-laid webs are preferred.

The resulting fiber web is then conveyed to the next step via a conveyor belt, where it is exposed to a stream of superheated or high-temperature steam (high-pressure steam) to produce a second fiber aggregate, a nonwoven fiber aggregate. Specifically, as the fiber web, transported by the conveyor belt, passes through a stream of high-speed, high-temperature steam ejected from the nozzles of a steam jet device, the high-temperature steam causes the fibers to three-dimensionally bond to one another. This treatment with high-temperature steam achieves uniform melt bonding from the surface to the interior of the nonwoven fiber aggregate.

The conveyor belt used is not particularly limited as long as it can essentially compress the fiber web to the target density and perform the high-temperature steam treatment. An endless conveyor is preferably used. Alternatively, two conveyor belts can be combined as needed, with the fiber web sandwiched between them for transport. This conveying method can suppress deformation of the fiber web due to external forces such as the water used for treatment, high-temperature steam, and vibration of the conveyor belt during treatment. Furthermore, the apparent density and thickness of the resulting nonwoven fiber aggregate can be controlled by adjusting the spacing between the conveyor belts.

To supply water vapor to the fiber web, a conventional water vapor injection device can be used. Preferably, the water vapor injection device is capable of spraying water vapor at the desired pressure and volume approximately uniformly across the entire width of the web. In the case of a two-belt conveyor system, water vapor can be supplied to the fiber web via a breathable conveyor belt or a conveyor net mounted on one conveyor. A suction box can be installed on the other conveyor. The suction box allows excess water vapor that passes through the fiber web to be extracted and discharged. Furthermore, to steam both the front and back sides of the fiber web, an additional water vapor injection device can be installed on the conveyor opposite the conveyor equipped with the water vapor injection device, downstream of the location of the water vapor injection device. In the absence of a downstream steam injection device and suction box, to steam both the front and back sides of the fiber web, the fiber web can be turned over after the first treatment and then passed through the treatment device again.

The endless belt that can be used in the conveyor is not particularly limited as long as it does not hinder the transportation and high-temperature steam treatment of the fiber web. However, when performing high-temperature steam treatment, the surface shape of the belt is sometimes transferred to the surface of the fiber web depending on the conditions. Therefore, it is preferably selected appropriately according to the purpose. In particular, when it is desired to obtain a non-woven fiber aggregate with a flat surface, it is preferred to use a net with a fine mesh. It should be noted that about 90 mesh is the upper limit, and a net that is roughly coarser than 90 mesh (for example, a net of about 10 to 50 mesh) is preferred. Nets with fine meshes above this have low air permeability and are difficult for water vapor to pass through. From the viewpoint of heat resistance to water vapor treatment, the material of the mesh belt is preferably a heat-resistant resin such as metal, polyester resin that has been heat-resistant treated, polyphenylene sulfide resin, polyarylate resin (wholly aromatic polyester resin), or aromatic polyamide resin.

Because the high-temperature steam ejected from the steam jet device is an air stream, unlike water-jet entangling and needling treatments, it does not significantly displace the fibers within the treated web and allow them to penetrate the web. It is believed that the steam's penetration and moist heat effect on the web effectively covers the surface of each fiber within the web with moist heat, resulting in uniform thermal bonding. Furthermore, because the treatment is performed in a very short time under high-speed airflow, the steam conducts sufficient heat to the fiber surfaces, but the treatment ends before sufficient heat conduction into the fibers is complete. Therefore, the pressure and heat of the high-temperature steam are less likely to cause the treated web to break apart or deform, potentially damaging its thickness. As a result, significant deformation of the web is avoided, achieving a substantially uniform bond across the surface and thickness. Furthermore, compared to dry heat treatment, sufficient heat transfer is achieved within the nonwoven fiber aggregate, resulting in a substantially uniform melt bond across the surface and thickness.

To improve water retention and necking resistance, high-temperature steam can be applied to the fiber web during treatment. The web can be exposed to the steam between conveyor belts or rollers, compressed to the target apparent density. By ensuring appropriate gaps between the rollers or conveyors, the target thickness and apparent density can be adjusted. In the case of conveyors, since it is difficult to compress the fiber web all at once, it is best to set the belt tension as high as possible, gradually narrowing the gap from upstream of the steam treatment point. By adjusting the steam pressure and treatment speed, various physical properties of the resulting nonwoven fiber aggregate, such as porosity and apparent density, as well as water retention, necking resistance, and cushioning properties, can be adjusted.

The nozzles for ejecting high-temperature steam can be a plate or die head with predetermined nozzles arranged continuously across the width of the web. The plate or die head is configured so that the nozzles are aligned across the width of the web being fed. The nozzle array can be more than one, or multiple rows can be arranged in parallel. Furthermore, multiple nozzle dies each having a single nozzle array can be arranged side by side.

When using a nozzle with a nozzle opening on a plate, the thickness of the plate can be about 0.5 to 1 mm. There are no particular restrictions on the diameter and spacing of the nozzles as long as they are conditions that can fix the target fiber. The diameter of the nozzles is usually 0.05 to 2 mm, preferably 0.1 to 1 mm, and more preferably 0.2 to 0.5 mm. The spacing of the nozzles is usually 0.5 to 3 mm, preferably 1 to 2.5 mm, and more preferably 1 to 1.5 mm. If the diameter of the nozzle is too small, the processing accuracy of the nozzle is reduced, which can easily cause equipment problems such as processing becoming difficult and operational problems such as clogging. Conversely, when the nozzle is too large, the water vapor injection force is reduced. On the other hand, if the spacing is too small, the nozzle holes are too dense, so the strength of the nozzle itself is reduced. On the other hand, if the spacing is too large, sometimes the high-temperature water vapor does not fully contact the fiber web, so sometimes the web strength is reduced.

There are no particular restrictions on the high-temperature steam, as long as it can achieve the desired fiber fixation. The pressure can be set according to the material and form of the fibers used. For example, the pressure is 0.1 to 2 MPa, preferably 0.2 to 1.5 MPa, and more preferably 0.3 to 1 MPa. If the steam pressure is too high, the fibers forming the fiber web may move more than necessary, resulting in a disordered texture, or the fibers may melt excessively, partially losing their shape. If the pressure is too low, the fiber web may not be heated enough to achieve fiber melt-bonding, the steam may not penetrate the web, resulting in fiber melt-bonding spots in the thickness direction, and uniform steam discharge from the nozzle may be difficult to control.

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

The obtained nonwoven fiber aggregate can be dried as needed. During drying, the fiber morphology of the surface of the nonwoven fiber aggregate that needs to be in contact with the heating element for drying does not need to disappear due to melting of the fibers, etc., as long as the fiber morphology can be maintained, conventional methods can be used. For example, large drying equipment such as a rotary dryer or a tenter frame used in drying nonwoven fabrics can be used, but since the residual moisture is only a trace amount and is mostly at a level that can be dried by a relatively mild drying method, non-contact methods such as far-infrared irradiation, microwave irradiation, and electron beam irradiation, and methods using hot air, etc. are preferred.

It should be noted that, as described above, the nonwoven fiber aggregate constituting the second fiber layer 21 is obtained by bonding the heat-wet adhesive fibers using high-temperature steam, but the fibers may also be partially bonded by other treatments such as heat embossing or needle punching.

(3) Composition, characteristics and uses of water-absorbent laminates

The water-absorbent laminate 100 of this embodiment is formed by directly joining (integrating) the second fiber layer 21 onto the first fiber layer 10. This joining is preferably achieved by interweaving or fusion bonding of the fibers, preferably avoiding bonding using adhesives, for example. This joining by interweaving or fusion bonding of the fibers maintains high connectivity between the voids in the first fiber layer 10 and the voids in the second fiber layer, thereby achieving high water retention and water absorption, as well as high permeability of absorbed water into the second fiber layer 21.

The water-absorbent laminate 100 has a basis weight of, for example, 20 to 1100 g/m ² , preferably 30 to 700 g/m ² , and more preferably 60 to 500 g/m ² (e.g., 100 to 300 g/m ² ). A basis weight of the water-absorbent laminate 100 within this range is advantageous in terms of water retention, permeability of absorbed water to the second fiber layer 21 , necking resistance, and cushioning properties.

The water-absorbent laminate 100 has high water retention. The water retention rate specified in 6.9.2 of JIS L 1913 "Test Methods for General Nonwoven Fabrics" can be, for example, 200% or greater, further 300% or greater, and even further 400% or greater. Water retention can be improved by, for example, increasing the thickness of the second fiber layer 21, increasing the porosity, decreasing the apparent density, and reducing the fiber bonding ratio.

The water-absorbent laminate 100 can have excellent necking resistance, allowing for uniform wiping of the surface of an object when used as a wiping material. The wet stretchability of the water-absorbent laminate 100, which serves as an indicator of necking resistance, can be, for example, 160 N/5 cm or greater, or even 180 N/5 cm or greater (e.g., 200 N/5 cm or greater), as measured by the longitudinal tensile strength when wet as specified in 6.3.2 of JIS L1913, "Test Methods for General Nonwoven Fabrics." If the longitudinal tensile strength when wet is less than this range, necking may occur during wiping, resulting in unstable wiping and difficulty in achieving uniform wiping.

The water-absorbent laminate 100 can have excellent cushioning properties (compression elastic modulus), thereby effectively preventing scratches on the surface of the object being wiped. To improve cushioning properties, for example, the apparent density of the water-absorbent laminate 100 can be reduced or the thickness can be increased.

The water-absorbent laminate 100 can be suitably used as a variety of water-absorbing materials for general consumer, household, and industrial applications. A water-absorbing material refers to a material or product used to absorb water or a substance containing water for any purpose, including substances that retain absorbed water. The water-absorbent laminate 100 exhibits excellent water absorption and water retention, making it particularly effective for applications requiring water retention.

If we enumerate examples of applicable water-absorbing materials, there are wiping materials (wipers, waste, etc.) used to wipe water from the surface of various objects, or to wipe off attachments containing other components simultaneously with water; skin care sheets such as facial masks; body fluid absorption sheets such as paper diapers; anti-condensation materials; packaging materials with the function of preventing water leakage, etc. Among them, the water-absorbing laminate 100 can be suitable for use as a wiping material, which is used to capture and remove particles (solid substances) attached to the surface of an object by utilizing the micropores of the first fiber layer 10 while absorbing water. An example of such a use is a wiping material (cleaning tape) used to wipe abrasive slurry (water with abrasives dispersed therein) attached to the surface of a substrate such as a hard disk substrate after the grinding process of the substrate. For example, in the manufacture of hard disks, free abrasives (abrasives) are attached to the surface of a grinding cloth (non-woven fabric, fabric, etc.), and the substrate surface is textured and ground. The water-absorbing laminate 100 can be used as such a grinding cloth.

(4) Production of water-absorbent laminate

As described above, in the manufacture of the absorbent laminate 100, the first fiber layer 10 (first fiber aggregate) and the second fiber layer 21 (second fiber aggregate) are preferably joined (integrated) by interweaving the fibers, fusing the fibers together, or the like. Examples of interweaving methods include hydroentangling and needle punching, and examples of fusing methods include steam jetting. Steam jetting is a method that can be used when at least one of the fiber layers being joined contains fibers that are heat-adhesive under moisture. Since the second fiber layer 21 forming the absorbent laminate 100 contains fibers that are heat-adhesive under moisture, steam jetting can be applied to the manufacture of the absorbent laminate 100. By using this joining method of interweaving or fusing the fibers together, high connectivity between the voids in the first fiber layer 10 and the voids in the second fiber layer 21 can be maintained, thereby achieving high water retention and absorbency.

Among these, hydroentanglement is preferred because it is relatively easy to achieve the aforementioned high connectivity. In the case of steam jetting, excessive fusion bonding of fibers can lead to pore occlusion and reduced connectivity. In the case of needle punching, it is sometimes difficult to ensure high connectivity and good bonding, particularly when joining fiber aggregates with low basis weights.

<Implementation Method 2>

FIG2 is a cross-sectional view schematically illustrating an example of a water-absorbent laminate according to this embodiment. The water-absorbent laminate 200 shown in FIG2 has the same structure as that of the first embodiment, except that a second fiber layer 22 is laminated on one side of the first fiber layer 10 in the thickness direction, instead of the second fiber layer 21. The second fiber layer 22 is composed of a nonwoven fiber aggregate containing wet-heat-bonding fibers and latently crimped conjugate fibers having a phase-separated structure formed by multiple resins having different thermal shrinkage rates (or thermal expansion rates).

In the nonwoven fiber aggregate (second fiber aggregate) constituting the second fiber layer 22, the moisture-heat adhesive fibers are substantially uniformly fused, and the latently crimped conjugate fibers are substantially uniformly crimped with an average curvature radius of 20 to 200 μm, with the fibers being fully intertwined. This nonwoven fiber aggregate (second fiber layer 22) can be obtained by allowing high-temperature (superheated or heated) water vapor to act on a web containing moisture-heat adhesive fibers and latently crimped conjugate fibers. This causes the adhesive to partially bond and secure the fibers to each other at a temperature below the melting point of the moisture-heat adhesive fibers. Simultaneously, the latently crimped conjugate fibers are crimped, mechanically entwining the fibers. By laminating the second fiber layer 22 on one side in the thickness direction of the first fiber layer 10, the same effects as those of the first embodiment can be achieved. Furthermore, according to this embodiment, the intertwining of the latently crimped conjugate fibers, utilizing the crimping, can further enhance the cushioning properties of the water-absorbent laminate 200.

In this embodiment, the second fiber assembly contains heat-bonding fibers under moisture and latent crimping conjugate fibers. The heat-bonding fibers under moisture can be the same as those used in the second fiber layer 21 in the first embodiment. For details, refer to the above description.

Latently crimped composite fibers are fibers (latently crimped fibers) that curl upon heating due to the different thermal shrinkage (or thermal expansion) rates of multiple resins. These fibers typically have different softening or melting points. The various resins can be selected from, for example, polyolefin resins (poly _C2-4 olefin resins such as low-density, medium-density or high-density polyethylene and polypropylene), acrylic resins (acrylonitrile resins having acrylonitrile units such as acrylonitrile-vinyl chloride copolymers), polyvinyl acetal resins (polyvinyl acetal resins), polyvinyl chloride resins (polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, vinyl chloride-acrylonitrile copolymers), polyvinylidene chloride resins (vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-vinyl acetate copolymers), styrene resins (heat-resistant polystyrene), polyester resins (polyethylene terephthalate resins, polytrimethylene terephthalate resins, polybutylene terephthalate resins, polyethylene naphthalate resins), and polyvinyl chloride resins. Thermoplastic resins include polyamide resins (polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, polyamide 612, polyamide 92, and polyamide 9C (a polyamide formed from nonanediamine and cyclohexanedicarboxylic acid), and copolymers thereof; _semi -aromatic polyamide resins (polyamide 9T (a polyamide formed from nonanediamine and terephthalic acid), and copolymers thereof; aromatic polyamide resins (polyphenylene isophthalamide, polyhexamethylene terephthalamide, and polyparaphenylene terephthalamide), and copolymers thereof); polycarbonate resins (such as bisphenol A polycarbonate); polyparaphenylene benzobisazole resins; polyphenylene sulfide resins; polyurethane resins; and cellulose resins (such as cellulose esters). These thermoplastic resins may contain units derived from other copolymerizable monomers.

Among the above-mentioned thermoplastic resins, non-heat-under-wet adhesive resins (or heat-resistant hydrophobic resins or non-aqueous resins) with a softening or melting point of 100°C or higher are preferred, as they prevent the fibers from fusing even when heated and humidified in high-temperature steam to melt or soften the fibers. Examples of these resins include polypropylene resins, polyester resins, and polyamide resins. Aromatic polyester resins and polyamide resins are particularly preferred, as they offer an excellent balance between heat resistance and fiber-forming properties. The resin exposed on the surface of the latently crimped conjugate fibers is preferably a non-heat-under-wet adhesive fiber, so that the latently crimped conjugate fibers do not fuse even when treated in high-temperature steam.

The thermal shrinkage rates (or thermal expansion rates) of the plurality of resins constituting the latently crimped conjugate fiber may be different, and the combination may be of the same type or a combination of different types of resins.

From the viewpoint of adhesion, the multiple resins constituting the latent crimped composite fiber are preferably a combination of resins of the same type. In this case, a combination of component (A) forming a homopolymer (essential component) and component (B) forming a modified polymer (copolymer) can generally be used. That is, relative to the homopolymer as an essential component, for example, by copolymerizing and modifying a copolymerizable monomer that reduces the degree of crystallinity, melting point or softening point, the degree of crystallinity is lower than that of the homopolymer, or by making the melting point or softening point lower than that of the homopolymer as amorphous. This produces a difference in thermal shrinkage. The difference in melting point or softening point is, for example, 5 to 150°C, preferably 50 to 130°C, and more preferably 70 to 120°C. The proportion of the copolymerizable monomer used for modification is, for example, 1 to 50 mol% relative to all monomers, preferably 2 to 40 mol%, and more preferably 3 to 30 mol% (particularly 5 to 20 mol%). The composite ratio (mass ratio) of the components forming the homopolymer and the components forming the modified polymer can be selected according to the structure of the fiber, for example, homopolymer component (A)/modified polymer component (B) = 90/10 to 10/90, preferably 70/30 to 30/70, and more preferably 60/40 to 40/60.

Because latently crimped conjugate fibers are easy to produce, the multiple resins comprising them are preferably a combination of aromatic polyester resins, more preferably a combination of a polyalkylene arylate resin (a) and a modified polyalkylene arylate resin (b). Particularly preferred are those that exhibit crimping after web formation, and this combination is also preferred from this perspective. By exhibiting crimping after web formation, the fibers can be efficiently interwoven, maintaining the web shape with a reduced number of fusion points, thereby achieving excellent water retention, cushioning properties, and necking resistance.

The polyalkylene arylate resin (a) may be a homopolymer of an aromatic dicarboxylic acid (e.g., a symmetrical aromatic dicarboxylic acid such as terephthalic acid and naphthalene-2,6-dicarboxylic acid) and an alkanediol component (e.g., a C _3-6 alkanediol such as ethylene glycol and butanediol). Specifically, poly (C _2-4 alkylene terephthalate) resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) can be used. Generally, PET used for general PET fibers having an intrinsic viscosity of approximately 0.6 to 0.7 can be used.

In the modified polyalkylene arylate resin (b), as copolymer components for lowering the melting point, softening point, and crystallinity of the essential component polyalkylene arylate resin (a), for example, dicarboxylic acid components such as asymmetric aromatic dicarboxylic acids, alicyclic dicarboxylic acids, and aliphatic dicarboxylic acids, alkanediol components having a longer chain length than the alkanediol component constituting the polyalkylene arylate resin (a), and/or diol components containing ether bonds can be used. The copolymer components may be used alone or in combination of two or more.

Preferred examples of the dicarboxylic acid component include asymmetric aromatic carboxylic acids (such as isophthalic acid, phthalic acid, and sodium 5-sulfoisophthalate), and aliphatic dicarboxylic acids (C _6-12 aliphatic dicarboxylic acids such as adipic acid). Preferred examples of the diol component include alkanediols (such as 1,3-propylene glycol, 1,4-butanediol, _1,6 -hexanediol, and neopentyl glycol), and (poly)oxyalkylene glycols (such as diethylene glycol, triethylene glycol, polyethylene glycol, and polytetramethylene glycol). Among these, asymmetric aromatic dicarboxylic acids such as isophthalic acid and polyoxy _{C 2-4 alkylene} glycols such as diethylene glycol are more preferred. Alternatively, the modified polyalkylene arylate resin (b) may be an elastomer having a C _2-4 alkylene arylate (such as ethylene terephthalate and butylene terephthalate) as a hard segment and a (poly)oxyalkylene glycol as a soft segment.

In the modified polyalkylene arylate resin (b), the proportion of the dicarboxylic acid component (such as isophthalic acid) used to lower the melting point or softening point is, for example, 1 to 50 mol%, preferably 5 to 50 mol%, and more preferably 15 to 40 mol%, relative to the total amount of the dicarboxylic acid component. The proportion of the glycol component (such as diethylene glycol) used to lower the melting point or softening point is, for example, 30 mol% or less, preferably 10 mol% or less (e.g., 0.1 to 10 mol%) relative to the total amount of the glycol component. If the proportion of the copolymer component is too low, sufficient crimping is not achieved, and the morphological stability of the crimped nonwoven fiber aggregate is reduced. Furthermore, the effect of using the latent crimping conjugate fiber in improving water retention, cushioning properties, and/or necking resistance tends to be reduced, or any of these properties tend to be reduced compared to when no latent crimping conjugate fiber is used. On the other hand, if the proportion of the copolymer component is too high, crimping performance is improved, but stable spinning becomes difficult.

The modified polyalkylene arylate resin (b) may contain units derived from a polycarboxylic acid component such as trimellitic acid and pyromellitic acid, a polyol component such as glycerol, trimethylolpropane, trimethylolethane, and pentaerythritol, and the like, as needed.

The cross-sectional shape of the latently crimped conjugate fiber (the cross-sectional shape perpendicular to the longitudinal direction of the fiber) is not limited to a true circular cross-section or a special cross-section [flat, elliptical, polygonal, 3-14 petal, T-shaped, H-shaped, V-shaped, dog-bone (I-shaped), etc.], which are generally solid cross-sectional shapes. For example, it may have a hollow cross-sectional shape, but is usually a true circular cross-sectional shape.

The cross-sectional structure of the latently crimpable composite fiber can be a phase-separated structure formed from multiple resins, such as a core-sheath type, island-in-the-sea type, a hybrid type, a parallel type (side-by-side or multi-layer laminated type), a radial type (radially laminated type), a hollow radial type, a block type, a random composite type, etc. Of these, structures in which the phases are partially adjacent (so-called bimetallic structures) are preferred because they facilitate spontaneous crimping upon heating. Asymmetric phase-separated structures, such as an eccentric core-sheath type or a parallel type, are also preferred.

It should be noted that when the potentially curling composite fiber has a core-sheath structure such as an eccentric core-sheath type, it has a thermal shrinkage difference relative to the non-wet heat adhesive resin of the sheath located on the surface. As long as it can curl, the core can be composed of a wet heat adhesive resin (ethylene-vinyl alcohol copolymer, vinyl alcohol polymers such as polyvinyl alcohol, etc.) or a thermoplastic resin with a low melting point or softening point (polystyrene, low-density polyethylene, etc.).

The average fineness of the latently crimpable conjugate fiber can be selected, for example, from a range of 0.1 to 50 dtex, preferably 0.5 to 10 dtex, and more preferably 1 to 5 dtex (particularly 1.5 to 3 dtex). If the average fineness is too small, the fiber itself is difficult to manufacture and it is difficult to ensure fiber strength. In addition, it is difficult to develop good coiled crimps during the crimping process. On the other hand, if the average fineness is too large, the fiber becomes rigid and it is difficult to develop sufficient crimps.

The average fiber length of the latent crimping composite fiber can be selected from the range of 10 to 100 mm, preferably 20 to 80 mm, and more preferably 25 to 75 mm (particularly 40 to 60 mm). When the average fiber length is too short, it is difficult to form a fiber web, and in the process of making the crimp appear, it becomes a major factor that the interweaving of the fibers becomes insufficient, and the strength, cushioning and/or necking resistance become insufficient. In addition, when the average fiber length is too long, it is difficult to form a fiber web with a uniform unit area weight, and the fibers are more interwoven at the time of forming the web, and interfere with each other when showing the crimp, which also becomes a major factor that the strength, cushioning and/or necking resistance become insufficient.

The latently crimped conjugate fiber develops crimps (becomes visible) by heat treatment, and becomes a fiber having three-dimensional crimps that are substantially coil-shaped (helical or coil spring-shaped).

The number of crimps before heating (mechanical crimps) is, for example, 0 to 30/25 mm, preferably 1 to 25/25 mm, and more preferably 5 to 20/25 mm. The number of crimps after heating is, for example, 30 or more/25 mm (e.g., 30 to 200/25 mm), preferably 35 to 150/25 mm, more preferably 40 to 120/25 mm, and can be 45 to 120/25 mm (particularly 50 to 100/25 mm).

The latently crimped composite fibers contained in the nonwoven fiber aggregate (the second fiber aggregate constituting the second fiber layer 22) are crimped in high-temperature steam. The crimping of the latently crimped composite fibers is preferably substantially uniformly expressed within the nonwoven fiber aggregate. Specifically, in a cross-section in the thickness direction, in each region divided into three equal parts in the thickness direction, the number of fibers that form coiled curls of more than one turn in the central portion (inner layer) is, for example, 5 to 50 fibers/5 mm (length in the plane) × 0.2 mm (thickness), preferably 5 to 40 fibers/5 mm (length in the plane) × 0.2 mm (thickness), and more preferably 10 to 40 fibers/5 mm (length in the plane) × 0.2 mm (thickness).

The uniformity of the curl inside the nonwoven fiber aggregate can also be evaluated, for example, based on the uniformity of the fiber curvature in the thickness direction. The fiber curvature refers to the ratio (L2/L1) of the fiber length (L2) to the distance (L1) between the two ends of the fiber (fiber in a curled state). The fiber curvature (especially the fiber curvature in the central area in the thickness direction) is, for example, 1.3 or more (for example, 1.35 to 5), preferably 1.4 to 4 (for example, 1.5 to 3.5), and more preferably 1.6 to 3 (especially 1.8 to 2.5). The fiber curvature can be measured based on an electron microscope photograph of a cross-section of the nonwoven fiber aggregate. Therefore, the fiber length (L2) is not the fiber length (actual length) obtained by straightening the three-dimensionally curled fiber into a straight line, but refers to the fiber length (fiber length on the photograph) obtained by straightening the two-dimensionally curled fiber taken in the electron microscope photograph into a straight line.

When the internal crimp of a nonwoven fiber aggregate is substantially uniform, the fiber curvature is also uniform. The uniformity of the fiber curvature can be evaluated, for example, by comparing the fiber curvature in each region divided into three equal parts in the thickness direction of a cross-section of the nonwoven fiber aggregate. That is, in the cross-section in the thickness direction, the fiber curvature in each region divided into three equal parts in the thickness direction is within the above-mentioned range, and the ratio of the minimum fiber curvature to the maximum fiber curvature in each region (the ratio of the region with the minimum fiber curvature to the region with the maximum fiber curvature) is, for example, 75% or more (e.g., 75-100%), preferably 80-99%, and more preferably 82-98% (particularly 85-97%).

As a specific method for measuring fiber curvature and its uniformity, a method for measuring fiber curvature by taking a cross-section of a nonwoven fiber aggregate with an electron microscope photograph and selecting a region selected from each region divided into three equal parts in the thickness direction can be used. For the measured region, for each layer of the surface layer (surface domain), inner layer (central domain), and back layer (back domain) divided into three equal parts, the region above 2 mm in the length direction is measured. In addition, for the thickness direction of each measured region, each measured region is set to have the same thickness and width near the center of each layer. In addition, each measured region is set to be parallel in the thickness direction and to contain more than 100 fiber sheets (preferably more than 300, more preferably about 500 to 1000) that can measure fiber curvature within each measured region. After setting these measured regions, the fiber curvature of all fibers in the measured region is measured, and the average value is calculated according to each measured region. The uniformity of the fiber curvature is then calculated by comparing the region showing the maximum average value and the region showing the minimum average value.

The crimped fibers that comprise the nonwoven fiber aggregate exhibit essentially coil-like curls after curling. The average radius of curvature of the circle formed by the coils of the crimped fibers can be selected from a range of, for example, 10 to 250 μm, for example, 20 to 200 μm (e.g., 50 to 200 μm), preferably 50 to 160 μm (e.g., 60 to 150 μm), more preferably 70 to 130 μm, and typically around 20 to 150 μm (e.g., 30 to 100 μm). The average radius of curvature is an indicator of the average size of the circle formed by the coils of the crimped fibers. A large value indicates that the coils formed have a loose shape, i.e., a shape with a small number of coils. Furthermore, a small number of coils reduces interweaving of the fibers, which is disadvantageous in terms of strength, cushioning properties, and necking resistance. Conversely, when the coils exhibit a coil-like curl with an average radius of curvature that is too small, the fibers are not interwoven sufficiently, making it difficult to ensure the strength of the web.

In the latently crimpable conjugate fiber crimped into a coil shape, the average pitch of the coils is, for example, 0.03 to 0.5 mm, preferably 0.03 to 0.3 mm, and more preferably 0.05 to 0.2 mm.

The ratio (mass ratio) of the thermal adhesive fibers under moisture to the latently crimping conjugate fibers in the second fiber aggregate constituting the second fiber layer 22 is 99/1 to 80/20, preferably 95/5 to 80/20, and more preferably 90/10 to 80/20. When the ratio of the thermal adhesive fibers under moisture is within this range, the water-absorbent laminate 200 can be provided with excellent water retention, mechanical strength, necking resistance, and cushioning properties.

The second fiber aggregate constituting the second fiber layer 22 may contain fibers other than the wet heat adhesive fibers and the latent crimping composite fibers. Examples of the other fibers include regenerated fibers such as rayon, semisynthetic fibers such as acetate, polyolefin fibers such as polypropylene and polyethylene, polyester fibers, and polyamide fibers. Considering aspects such as blendability, the other fibers are preferably fibers of the same type as the latent crimping composite fibers. For example, when the latent crimping composite fibers are polyester fibers, the other fibers may also be polyester fibers.

The fibers constituting the second fiber aggregate may contain one or more additives as needed. Specific examples of additives include colorants, heat stabilizers, UV absorbers, light stabilizers, antioxidants, microparticles, crystallization rate retarders, antistatic agents, flame retardants, plasticizers, and lubricants. The additives may be carried on the surface of the fibers or contained within the fibers.

The second fiber layer 22 can be a non-woven fiber aggregate obtained from a net composed of the above-mentioned fibers. The net of the non-woven fiber aggregate is preferably configured to appropriately adjust the arrangement and bonding state of the fibers constituting it. That is, the non-woven fiber aggregate containing the latent curling composite fiber is preferably melt-bonded at the intersections where the wet heat adhesive fiber intersects with the curled latent curling composite fiber or other wet heat adhesive fibers (that is, the intersections between the wet heat adhesive fibers, and the intersections between the wet heat adhesive fibers and the curled latent curling composite fibers). Thus, the second fiber layer 22 having passages provided by small gaps is appropriately formed. Moreover, in order to maintain the form of the non-woven fiber aggregate with as few contact points as possible, it is preferred that the bonding points are roughly evenly distributed from the surface of the non-woven fiber aggregate to the inside. More specifically, it is preferred that the bonding points are evenly distributed from the surface of the non-woven fiber aggregate to the inside (center) and to the back side along the surface direction and the thickness direction (especially the thickness direction which is difficult to uniformize). When the bonding points are locally present on the surface or inside, the cushioning properties and the necking resistance are reduced. In addition, the morphological stability of the portion with fewer bonding points is reduced.

Specifically, the second fiber aggregate constituting the second fiber layer 22 is preferably a nonwoven fiber aggregate in which the fibers constituting the second fiber aggregate are partially bonded and fixed by melt-bonding of wet-heat adhesive fibers. These fibers are preferably bonded by melt-bonding of wet-heat adhesive fibers at a fiber bonding ratio of 45% or less (e.g., 1-45% or 1-30%). The definition of fiber bonding ratio is as described above. The low fiber bonding ratio, combined with the coiled crimping of the latently crimped composite fibers, provides excellent cushioning properties.

Regarding the uniformity of melt bonding, it is preferred that the fiber bonding ratio in each region of the nonwoven fiber aggregate, divided into three equal parts in the thickness direction, be within the above-mentioned range. Furthermore, the ratio of the minimum fiber bonding ratio to the maximum fiber bonding ratio in each region (minimum/maximum) is, for example, 50% or more (e.g., 50-100%), preferably 55-99%, and more preferably 60-98% (particularly 70-97%). Such uniformity of fiber bonding ratio in the thickness direction allows the shape to be maintained with fewer melt points, and can improve cushioning properties, etc.

In order to produce a nonwoven fiber aggregate with a well-balanced water retention and cushioning properties, it is preferred to appropriately adjust the fiber bonding state by melt-bonding the wet heat adhesive fibers, while simultaneously interweaving adjacent or intersecting fibers at the crimped loop portion by crimping the latently crimped conjugate fibers. The nonwoven fiber aggregate containing the latently crimped fibers exhibits the crimping of the latently crimped conjugate fibers and is deformed into a coil shape. As a result, the crimped loop portion provides a structure in which adjacent or intersecting fibers (crimped fibers with each other, or crimped fibers with the wet heat adhesive fibers) are entangled and restrained or locked.

The fibers constituting the nonwoven fiber aggregate (in the case of coiled crimped fibers, in the axial direction of the coil) can be arranged substantially parallel to and intersecting each other relative to the surface of the nonwoven fiber aggregate. "Arranged parallel to the surface of the nonwoven fiber aggregate" means that there are no repeated portions of fibers partially arranged in the thickness direction. When there are a large number of fibers oriented in the thickness direction, the fibers also form coiled curls, and therefore the fibers are extremely complexly entangled with each other, resulting in a tendency for the cushioning properties to decrease.

From the perspective of the water retention and cushioning properties of the water-absorbent laminate 200, the porosity of the second fiber layer 22 in the water-absorbent laminate 200 is preferably 70% or greater, more preferably 75% or greater, and even more preferably 80% or greater. The porosity of the second fiber layer 22 is generally 99% or less, more typically 95% or less.

The basis weight, apparent density, and thickness of the second fiber layer 22 may be the same as those of the second fiber layer 21 in the first embodiment. For details, the above description is cited.

The second fiber aggregate, which constitutes the nonwoven fiber aggregate of the second fiber layer 22, can be readily produced by exposing a fiber web to high-temperature, high-pressure steam and performing a steam jet method to form a nonwoven fabric, similar to the second fiber layer 21 in the first embodiment. In this case, the fibers are three-dimensionally bonded to each other by the fusion bonding of the wet-heat adhesive fibers, while the fibers are interwoven with each other by the crimping of the latently crimped composite fibers. Furthermore, uniform fusion bonding can be achieved within the nonwoven fiber aggregate, and uniform crimping can be achieved from the surface to the interior of the nonwoven fiber aggregate.

The structure, characteristics, uses, and production of the water-absorbent laminate 200 may be the same as those of the water-absorbent laminate 100 in the first embodiment, and the above description is incorporated herein by reference for details.

<Implementation Method 3>

FIG3 is a cross-sectional view schematically showing an example of a water-absorbent laminate according to the present embodiment. The water-absorbent laminate 300 shown in FIG3 has the same structure as the first embodiment described above, except that the second fiber layer 21 is laminated on one side of the first fiber layer 10 in the thickness direction via the third fiber layer 30. Thus, if the water-absorbent laminate of the present invention includes a first fiber layer and a second fiber layer, the third fiber layer can be sandwiched between the first and second fiber layers. The third fiber layer 30 is a layer composed of a third fiber aggregate containing hydrophilic fibers (second hydrophilic fibers). By sandwiching the third fiber layer 30, the water-absorbent laminate can further improve its water retention, tensile strength, cushioning properties, and the like. It should be noted that in the water-absorbent laminate 300, the second fiber layer 22 used in the second embodiment described above can also be used instead of the second fiber layer 21.

The hydrophilic fiber constituting the third fiber aggregate can be a synthetic fiber, a natural fiber, a regenerated fiber, etc. The hydrophilic fiber can be used alone or in combination of two or more. As the hydrophilic fiber (the second hydrophilic fiber) constituting the third fiber aggregate, the same fiber as the hydrophilic fiber (the first hydrophilic fiber) constituting the first fiber aggregate of the first fiber layer 10 can be used. For details, the above description of the hydrophilic fiber (the first hydrophilic fiber) is cited. The second hydrophilic fiber and the first hydrophilic fiber can be fibers of the same species or fibers of different species.

However, unlike the first hydrophilic fiber, the average fiber diameter of the second hydrophilic fiber is not necessarily preferably 10 μm or less, and may be, for example, 0.1 to 20 μm. From the perspective of further improving water retention, tensile strength, cushioning properties, etc., the average fiber diameter is preferably 0.5 to 15 μm.

The third fiber aggregate constituting the third fiber layer 30 may contain fibers other than hydrophilic fibers (e.g., hydrophobic fibers). However, from the perspective of water absorption, a higher content of hydrophilic fibers is preferred. Specifically, the content of hydrophilic fibers in the third fiber aggregate is preferably 70% by mass or greater, more preferably 80% by mass or greater, and even more preferably 90% by mass or greater (e.g., 100% by mass). Examples of fibers other than hydrophilic fibers include fibers made of polyolefin resins such as polyethylene and polypropylene, polyester resins, and polyurethane resins.

The fibers comprising the third fiber aggregate may contain one or more additives as needed. Specific examples of additives include colorants, heat stabilizers, UV absorbers, light stabilizers, antioxidants, microparticles, crystallization rate retarders, antistatic agents, flame retardants, plasticizers, and lubricants. The additives may be carried on the surface of the fibers or contained within the fibers.

The third fiber aggregate constituting the third fiber layer 30 is preferably a nonwoven fiber aggregate, more preferably a spunlace nonwoven fiber aggregate. The spunlace method can easily form a soft third fiber layer 30 that can impart excellent cushioning properties, water retention, and tensile strength to the water-absorbent laminate 300.

From the perspectives of cushioning properties and water retention, the porosity of the third fiber layer 30 in the water-absorbent laminate 300 is preferably 80% or greater, more preferably 85% or greater, and even more preferably 90% or greater. The porosity of the third fiber layer 30 is generally 99% or less, more typically 97% or less.

The basis weight of the third fiber layer 30 is, for example, 10 to 200 g/m ² , preferably 20 to 150 g/m ² , and more preferably 30 to 100 g/m ² . A basis weight of the third fiber layer 30 within this range is advantageous in terms of water retention and permeability of absorbed water to the second fiber layer 21 .

The apparent density of the third fiber layer 30 in the water-absorbent laminate 300 is preferably set so that the apparent density of the water-absorbent laminate as a whole is 0.3 g/cm³ or ^less , more preferably 0.25 g/ ^cm³ or less, and even more preferably 0.2 g/ ^cm³ or less (e.g., 0.15 g/ ^cm³ or less). If the apparent density of the third fiber layer 30 is too high, the permeability of absorbed water into the second fiber layer 21 is likely to decrease, and the effect of improving cushioning properties is less likely to be achieved. The apparent density of the third fiber layer 30 is typically 0.01 g/ ^cm³ or greater, more typically 0.1 g/ ^cm³ or greater.

The thickness of the third fiber layer 30 in the water-absorbent laminate 300 is, for example, 50 to 2000 μm, preferably 100 μm or greater, and more preferably 200 μm or greater. If the thickness of the third fiber layer 30 is too small, the effects of improving water retention, cushioning properties, and tensile strength are less pronounced. Furthermore, from the perspective of permeability of absorbed water to the second fiber layer 21, the thickness of the third fiber layer 30 is preferably 1500 μm or less, and more preferably 1000 μm or less.

The third fiber layer 30 (third fiber aggregate) can preferably be manufactured by forming the fibers forming the third fiber aggregate into a web and entangled with each other by water flow. As a method for forming the web, conventional methods can be used, such as direct methods such as spunbonding and meltblowing; dry methods such as carding using meltblown fibers, staple fibers, etc., and air-laid methods. Among these methods, carding using meltblown fibers and staple fibers is widely used, and carding using staple fibers is particularly popular. Examples of webs obtained using staple fibers include random webs, semi-random webs, parallel-laid webs, and cross-laid webs.

Next, the resulting fiber web can be subjected to a water jet entanglement treatment to intertwine the constituent fibers, thereby obtaining a third fiber aggregate. In the water jet entanglement treatment, for example, a high-pressure columnar stream of water jetted from a nozzle plate having jet holes arranged in one or two rows with a diameter of approximately 0.05 to 0.20 mm and a spacing of approximately 0.30 to 1.50 mm is caused to collide with the fiber web placed on a porous support member, thereby intertwining the fibers constituting the fiber web in three dimensions. In this case, it is preferred to place the fiber web on a moving porous support member and perform the treatment once or multiple times with a water jet at a water pressure of approximately 1 to 15 MPa, preferably 2 to 12 MPa, and more preferably 3 to 10 MPa. The jet holes are preferably arranged in rows perpendicular to the direction of travel of the fiber web, and the nozzle plate having the jet holes is vibrated perpendicular to the direction of travel of the fiber web at intervals equal to the jet spacing. The fiber web is placed on the porous support member, thereby causing the water jet to collide uniformly with the fiber web. The porous support member on which the fiber web is placed is not particularly limited, as long as it can be a mesh screen such as a wire mesh or a perforated plate that allows water to flow through the fiber web. The distance between the spray holes and the fiber web can be selected according to the water pressure, for example, about 1 to 10 cm.

The water-absorbent laminate 300 of this embodiment has the same water absorption rate (water absorption rate of the outer surface of the first fiber layer 10) as the water-absorbent laminate 100 of the first embodiment described above. Furthermore, the apparent density, water retention rate, and wet longitudinal tensile strength of the water-absorbent laminate 300 may be within the same ranges as those described for the water-absorbent laminate 100. However, the basis weight and thickness of the water-absorbent laminate 300, including the third fiber layer 30, may be greater than those of the water-absorbent laminate 100.

The water-absorbent laminate 300 has a basis weight of, for example, 30 to 1500 g/ ^m² , preferably 50 to 1000 g/ ^m² , and more preferably 100 to 600 g/ ^m² (e.g., 200 to 304 g/ ^m² ). A basis weight of the water-absorbent laminate 300 within this range is advantageous in terms of water retention, permeability of absorbed water to the second fiber layer 21, necking resistance, and cushioning properties. The thickness of the water-absorbent laminate 300 is typically 100 to 4000 μm, preferably 500 to 2500 μm.

The water-absorbent laminate 300 can be used for the same purpose as the water-absorbent laminate 100 of the first embodiment.

The apparent density of the water-absorbent laminate as a whole is preferably set to 0.6 g/ ^cm³ or less, more preferably 0.5 g/ ^cm³ or less, even more preferably 0.4 g/ ^cm³ or less, and particularly preferably 0.35 g/cm³ or ^less (e.g., 0.3 g/ ^cm³ or less). If the apparent density of the water-absorbent laminate as a whole is too high, the water retention rate and water retention capacity will decrease. The apparent density of the water-absorbent laminate as a whole is generally 0.01 g/ ^cm³ or more, more typically 0.1 g/ ^cm³ or more.

Next, the method for manufacturing the water-absorbent laminate 300 will be described. It is preferred that the first fiber layer 10 (first fiber aggregate), the third fiber layer 30 (third fiber aggregate), and the second fiber layer 21 (second fiber aggregate) be joined (integrated) by interweaving fibers, fusion bonding, or the like, similar to the water-absorbent laminate 100 of the first embodiment described above. Examples of interweaving methods include hydroentangling and needle punching, while examples of fusion bonding methods include steam jetting. Steam jetting is a method that can be used when at least one of the fiber layers being joined contains moisture-heat adhesive fibers. Since the second fiber layer 21 contains moisture-heat adhesive fibers, steam jetting can be applied to at least the joining of the second fiber layer 21 and the third fiber layer 30. In addition, when the hydrophilic fiber constituting at least one of the first fiber aggregate and the third fiber aggregate is a wet heat adhesive fiber such as an ethylene-vinyl alcohol copolymer, a steam spray method can be applied to the joining of the first fiber layer 10 and the third fiber layer 30.

According to the above-mentioned joining method of interweaving or fusing the fibers, high connectivity among the voids in the first fiber layer 10, the voids in the second fiber layer 21, and the voids in the third fiber layer 30 can be maintained, thereby achieving high water retention and water absorption.

Specifically, the water-absorbent laminate 300 can be produced by a method including the following steps in sequence:

(1) A first step of joining the first fiber layer 10 and the third fiber layer 30 by interweaving or fusing the fibers constituting the first fiber aggregate and the fibers constituting the third fiber aggregate; and

(2) In the second step, the second fiber layer 21 and the third fiber layer 30 are joined by intertwining or fusing the fibers constituting the second fiber aggregate and the fibers constituting the third fiber aggregate.

Alternatively, the water-absorbent laminate 300 may be produced by a method comprising the following steps in sequence:

(A) a first step of joining the second fiber layer 21 and the third fiber layer 30 by interweaving or fusing the fibers constituting the second fiber aggregate with the fibers constituting the third fiber aggregate; and

(B) In the second step, the first fiber layer 10 and the third fiber layer 30 are joined by intertwining or fusing the fibers constituting the first fiber aggregate and the fibers constituting the third fiber aggregate.

<Other embodiments>

The water-absorbent laminates of the first to third embodiments can be subjected to various deformations within a range that does not hinder the effects of the present invention. For example, the third fiber layer used in the third embodiment can be laminated on one side of the second fiber layer in the thickness direction of the first or second embodiment (the opposite side of the second fiber layer to the first fiber layer). In this case, a layer structure of the first fiber layer/the second fiber layer/the third fiber layer is formed. In the embodiment described above, the first fiber layer 10 (first fiber aggregate), the second fiber layer 21 (second fiber aggregate) and the third fiber layer 30 (third fiber aggregate) are preferably joined (integrated) by interweaving of fibers, melting of fibers, etc. Compared with the water-absorbent laminate in the first or second embodiment, by further laminating the third fiber layer, the water retention, cushioning properties and necking resistance can be further improved.

Example

The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples. It should be noted that the physical property values in the following Examples and Comparative Examples were measured or evaluated by the following methods.

[1] Measurement of water absorption rate of the surface of the first fiber layer opposite to the second fiber layer

The water absorption rate of the surface of the first fiber layer opposite to the second fiber layer (the surface on the other side in the thickness direction of the first fiber layer) was measured using the dropping method specified in 7.1.1 of JIS L 1907, "Test Methods for Water Absorption of Textile Products." Specifically, a single drop of water at 0.05 g/drop was added to the first fiber layer of the resulting water-absorbent laminate using a burette from a height of 10 mm, and the time (in seconds) until the specular reflection disappeared due to absorption of the water drop was measured.

[2] Measurement of the average fiber diameter of the fibers constituting the first fiber layer

A test piece (5 cm x 5 cm x 5 cm) was collected from the resulting water-absorbent laminate. A photograph of the central portion of the surface of the test piece (centered at the intersection of the diagonals) was taken at 1000x magnification using a scanning electron microscope (SEM). A circle with a radius of 30 cm was drawn on the photograph, centered at the center (intersection of the diagonals). 100 fibers were randomly selected from this circle. The fiber diameters at or near the center in the longitudinal direction were measured using a vernier caliper, and the average value was used as the average fiber diameter (number-average fiber diameter, μm). It should be noted that when selecting fibers, the fibers within the circle in the photograph were selected regardless of whether they were located on the outermost surface of the test piece or located on the inner side.

[3] Determination of the average pore diameter of the first fiber layer

The measurement was performed by mercury intrusion porosimetry using a micropore size distribution apparatus ("AutoPore III 9420" manufactured by Shimadzu Corporation).

[4] Weight per unit area, thickness, and apparent density of the fiber layer or absorbent laminate

Basis weight and thickness were measured according to 6.1 and 6.2 of JIS L 1913, "Test Methods for General Nonwoven Fabrics." The apparent density was calculated by dividing the basis weight by the thickness. The basis weight, thickness, and apparent density of each fiber layer (first to third fiber layers) constituting the water-absorbent laminate shown in the table below are values obtained before joining to form the water-absorbent laminate.

[5] Water retention rate and water retention capacity of water-absorbent laminates

The water retention rate was measured in accordance with 6.9.2 of JIS L 1913 "General non-woven fabric test methods". Specifically, three test pieces of 100 mm x 100 mm square were collected and their mass (mass before immersion) was measured. Next, the test piece was immersed in water for 15 minutes, then picked up and hung in the air with one corner facing upward for 1 minute to remove the surface water, and then the mass was measured (mass after immersion). The water retention rate of the three test pieces was calculated based on the following formula, and their average value was calculated as the water retention rate of the water-absorbent laminate. In addition, the mass after immersion minus the mass before immersion was taken as the water retention amount (g).

Water retention (mass %) = 100 × (mass after immersion - mass before immersion) / mass before immersion

[6] Necking resistance of water-absorbent laminates (longitudinal tensile strength when wet)

The tensile strength (N/5 cm) in the machine direction (MD) when wet was measured using a constant-rate extension tensile tester ("AG-IS" manufactured by Shimadzu Corporation) according to 6.3.2 of JIS L 1913 "General Nonwoven Fabric Test Methods." The temperature of the water in which the test piece was immersed was set to 20°C.

<Example 1>

(1) Preparation of the first fiber aggregate forming the first fiber layer

A meltblown nonwoven fabric sheet (first fiber aggregate, average fiber diameter: 3.67 μm, average pore diameter: 19.9 μm, basis weight: 50.2 g/m ² , thickness: 0.38 mm, apparent density: 0.13 g/cm ³ ) composed of polyamide resin (nylon 6) fibers was produced using a meltblown production apparatus. Specifically, meltblown spinning was performed using a nozzle having a diameter of 0.3 mm and 1,300 holes per meter length at a pitch of 0.8 mm. The spinning temperature was 280°C, the air temperature was 290°C, the air pressure was 0.4 MPa, and the single hole discharge rate was 0.3 g/hole/minute. The meltblown nonwoven fabric sheet was collected using a rotating mesh conveyor as a support to obtain the meltblown nonwoven fabric sheet.

(2) Preparation of the third fiber aggregate forming the third fiber layer

A semi-random web having a basis weight of approximately 50 g/ ^m² was prepared using "SOPHISTA" manufactured by Kuraray Co., Ltd. (SOPHISTA 1, for details, see the following abbreviations and symbols [c]). This carded web was placed on a press roll support having an opening ratio of 25% and a pore size of 0.3 mm and continuously conveyed in the longitudinal direction at a speed of 5 m/min while being sprayed with high-pressure water from above to perform an interlacing treatment, thereby producing an interlaced nonwoven fiber aggregate (third fiber aggregate, basis weight: 52.3 g/ ^m² , thickness: 0.61 mm, apparent density: 0.09 g/ ^cm³ ). In this interweaving process, three nozzles with nozzles of 10 mm in diameter are arranged at intervals of 0.6 mm along the width direction of the mesh (the interval between adjacent nozzles is 20 cm), the water pressure of the high-pressure water flow ejected from the first row of nozzles is set to 3.0 MPa, the water pressure of the high-pressure water flow ejected from the second row of nozzles is set to 5.0 MPa, and the water pressure of the high-pressure water flow ejected from the third row of nozzles is set to 10.0 MPa.

(3) Joining the first fiber aggregate and the third fiber aggregate

The meltblown nonwoven fabric sheet (first fiber aggregate) produced in (1) is rolled up and overlapped with the third fiber aggregate produced in (2) above. The sheet is then placed on a flat support having a fine mesh as a whole and continuously transferred while being sprayed with high-pressure water to perform an interweaving process. By this interweaving process, the fibers constituting the two nonwoven fiber aggregates are interwoven and composited to form a composite nonwoven fabric. In this interweaving process, three nozzles with nozzles having an aperture of 0.10 mm are provided at intervals of 0.6 mm along the width direction of the web (the interval between adjacent nozzles is 20 cm), the water pressure of the high-pressure water jetted from the first row of nozzles is set to 3.0 MPa, the water pressure of the high-pressure water jetted from the second row of nozzles is set to 5.0 MPa, and the water pressure of the high-pressure water jetted from the third row of nozzles is set to 10.0 MPa.

(4) Preparation of the Second Fiber Aggregate Forming the Second Fiber Layer and Preparation of the Water-Absorbent Laminated Body

The composite nonwoven fabric prepared in (3) above was placed on a semi-random mesh having a unit area weight of approximately 100 g/m ² made of "SOPHISTA" (SOPHISTA 2, for details, refer to the details of the abbreviations [d] below) manufactured by Kuraray Co., Ltd. to form a laminated sheet, which was then transferred between an upper conveyor and a lower conveyor equipped with a 50-mesh, 500 mm wide stainless steel endless mesh, which rotated at the same speed and in the same direction. The laminated sheet was introduced into a steam jet device provided on the upper conveyor and subjected to a steam treatment by jetting high-temperature water vapor at 0.2 MPa by the device, thereby obtaining a water-absorbent laminate. The jetting direction of the high-temperature water vapor was parallel to the thickness direction of the laminated sheet. The steam jet device used had a steam jet nozzle with an aperture of 0.3 mm and nozzles arranged in a row at a pitch of 1 mm along the width direction of the conveyor. The interval between the upper conveyor and the lower conveyor was set to 1.5 mm. In addition, the nozzle is arranged so as to be almost in contact with the conveyor belt on the back side of the conveyor belt.

<Examples 2 to 10, 12>

A three-layered water-absorbent laminate was produced in the same manner as in Example 1, except that the materials and other structures of the first to third fiber layers were set as described in Tables 1 and 2. Note that in Examples 6 to 10, the third fiber layer was composed of a third fiber aggregate using two types of fibers, with the mass ratio of the two types of fibers being 50/50.

<Example 11>

(1) Preparation of the first fiber aggregate forming the first fiber layer

A melt-blown nonwoven fabric sheet (first fiber aggregate) composed of polyamide resin (nylon 6) fibers was produced in the same manner as in Example 1 (1).

(2) Preparation of the second fiber aggregate forming the second fiber layer

A semi-random web with a unit area weight of about 100 g/m ² made of "SOPHISTA" (SOPHISTA 2) manufactured by Kuraray Co., Ltd. was prepared. The carded web was transferred between an upper conveyor and a lower conveyor equipped with a stainless steel endless net having a mesh size of 50 and a width of 500 mm, which rotated at the same speed and in the same direction. The web was introduced into a steam injection device provided on the upper conveyor, and subjected to a steam treatment in which high-temperature water vapor of 0.2 MPa was injected from the device to obtain a second fiber aggregate. The injection direction of the high-temperature water vapor was made parallel to the thickness direction of the second fiber aggregate. For the steam injection device, a steam injection device was used in which the aperture of the steam injection nozzle was 0.3 mm and the nozzles were arranged in a row at a pitch of 1 mm along the width direction of the conveyor. The interval between the upper conveyor and the lower conveyor was set to 1.5 mm. In addition, the nozzle was set so that it was almost in contact with the conveyor on the back side of the conveyor.

(3) Preparation of water-absorbent laminate

The meltblown nonwoven fabric sheet (first fiber aggregate) produced in (1) above is rolled up and superimposed on the second fiber aggregate produced in (2) above. The sheet is then placed on a flat support having a fine mesh and continuously transferred while being sprayed with high-pressure water to perform an interlacing treatment. Through this interlacing treatment, the fibers constituting the two nonwoven fiber aggregates are interlaced and integrated to obtain a water-absorbent laminate. In this interlacing treatment, three nozzles with nozzles having an aperture of 0.10 mm are arranged at intervals of 0.6 mm along the width of the web (the interval between adjacent nozzles is 20 cm). The water pressure of the high-pressure water jet from the first row of nozzles is set to 3.0 MPa, the water pressure of the high-pressure water jet from the second row of nozzles is set to 5.0 MPa, and the water pressure of the high-pressure water jet from the third row of nozzles is set to 10.0 MPa.

<Example 13>

(1) Preparation of the first fiber aggregate forming the first fiber layer

A semi-random web with a basis weight of approximately 50 g/ ^m² was prepared using "SOPHISTA" (SOPHISTA 1) manufactured by Kuraray Co., Ltd. This carded web was placed on a press roll support having an opening ratio of 25% and a pore diameter of 0.3 mm and continuously conveyed in the longitudinal direction at a speed of 5 m/min while being sprayed with high-pressure water from above to perform an interlacing treatment. This produced an interlaced nonwoven fiber aggregate (fiber aggregate No. 1, average fiber diameter: 11.00 μm, average pore diameter: 59.0 μm, basis weight: 52.3 g/ ^m² , thickness: 0.61 mm, apparent density: 0.09 g/ ^cm³ ). In this interweaving process, three nozzles with nozzles of 10 mm in diameter are arranged at intervals of 0.6 mm along the width direction of the mesh (the interval between adjacent nozzles is 20 cm), the water pressure of the high-pressure water flow ejected from the first row of nozzles is set to 3.0 MPa, the water pressure of the high-pressure water flow ejected from the second row of nozzles is set to 5.0 MPa, and the water pressure of the high-pressure water flow ejected from the third row of nozzles is set to 10.0 MPa.

(2) Preparation of the second fiber aggregate forming the second fiber layer

A semi-random web with a unit area weight of about 100 g/m ² made of "SOPHISTA" (SOPHISTA 2) manufactured by Kuraray Co., Ltd. was prepared. The carded web was transferred between an upper conveyor and a lower conveyor equipped with a stainless steel endless net having a mesh size of 50 and a width of 500 mm, which rotated at the same speed and in the same direction. The web was introduced into a steam injection device provided on the upper conveyor, and subjected to a steam treatment in which high-temperature water vapor of 0.2 MPa was injected from the device to obtain a second fiber aggregate. The injection direction of the high-temperature water vapor was made parallel to the thickness direction of the second fiber aggregate. For the steam injection device, a steam injection device having a steam injection nozzle having an aperture of 0.3 mm and nozzles arranged in a row at a pitch of 1 mm along the width direction of the conveyor was used. The interval between the upper conveyor and the lower conveyor was set to 1.5 mm. In addition, the nozzle was set so that it was almost in contact with the conveyor on the back side of the conveyor.

(3) Preparation of water-absorbent laminate

The first fiber aggregate prepared in (1) is rolled up and superimposed on the second fiber aggregate prepared in (2), and then placed on a flat support having a fine mesh as a whole and continuously transferred, while being sprayed with high-pressure water to perform an interlacing treatment. Through this interlacing treatment, the fibers constituting the two non-woven fiber aggregates are interwoven and composited to form a water-absorbent laminate. In this interlacing treatment, three nozzles with nozzles having an aperture of 0.10 mm are arranged at intervals of 0.6 mm along the width direction of the web (the interval between adjacent nozzles is 20 cm), the water pressure of the high-pressure water jetted from the first row of nozzles is set to 3.0 MPa, the water pressure of the high-pressure water jetted from the second row of nozzles is set to 5.0 MPa, and the water pressure of the high-pressure water jetted from the third row of nozzles is set to 10.0 MPa.

<Example 14>

(1) Preparation of the first fiber aggregate forming the first fiber layer

A meltblown nonwoven fabric sheet (first fiber aggregate) composed of polyamide resin (nylon 6) fibers was prepared in the same manner as in Example 1 (1).

(2) Preparation of the third fiber aggregate forming the third fiber layer

A third fiber aggregate consisting of a hydroentangled nonwoven fiber aggregate composed of SOPHISTA 1 was prepared in the same manner as in Example 1 (2).

(3) Joining the first fiber aggregate and the third fiber aggregate

A composite nonwoven fabric in which the first fiber aggregate and the third fiber aggregate were composited and integrated was obtained by the same method as in Example 1 (3).

(4) Preparation of the Second Fiber Aggregate Forming the Second Fiber Layer and Preparation of the Water-Absorbent Laminated Body

A water-absorbent laminate was produced by joining the second fiber aggregate to the composite nonwoven fabric in the same manner as in Example (4) except that the interval between the upper conveyor and the lower conveyor was set to 1.0 mm.

<Example 15>

A water-absorbent laminate was produced in the same manner as in Example (4) except that the interval between the upper conveyor and the lower conveyor was set to 2.5 mm.

Comparative Examples 1 to 3

A water-absorbent laminate having a three-layer structure was produced in the same manner as in Example 1, except that the materials and other structures of the first to third fiber layers were provided as shown in Table 3.

Comparative Examples 4 to 7

The nonwoven fabric of Comparative Example 4 is the meltblown nonwoven fabric sheet used to constitute the first fiber layer of the water-absorbent laminate described in Example 1. The nonwoven fabric of Comparative Example 5 is the spunlace nonwoven fabric used to constitute the third fiber layer of the water-absorbent laminate described in Example 1. The nonwoven fabric of Comparative Example 6 is the steam-blown nonwoven fabric used to constitute the second fiber layer of the water-absorbent laminate described in Example 1. Furthermore, the nonwoven fabric of Comparative Example 7 is a spunlace nonwoven fabric formed from layered laminated cross-section split fibers (for details, see the following abbreviation [k]) composed of nylon 6 and polyethylene terephthalate.

Table 1

Table 2

Table 3

The details of the abbreviations shown in Tables 1 to 3 are as follows.

[a] Ny: Nylon 6, a polyamide resin

[b] EVOH: ethylene-vinyl alcohol copolymer [ethylene content: 44 mol%, saponification degree: 98.4%]

[c] SOPHISTA 1: A high-melting-point core-sheath type composite staple fiber with a core of polyethylene terephthalate and a sheath of ethylene-vinyl alcohol copolymer (ethylene content: 44 mol%, saponification degree: 98.4%) [Kuraray Co., Ltd., "SOPHISTA," average fineness: 1.7 dtex, average fiber diameter: 11 μm, average fiber length: 51 mm, core-sheath mass ratio: 50/50, circular cross section, core diameter: 8.9 μm]

[d] SOPHISTA 2: A low-melting-point core-sheath type composite staple fiber with a core of polyethylene terephthalate and a sheath of ethylene-vinyl alcohol copolymer (ethylene content: 44 mol%, saponification degree: 98.4%) [Kuraray Co., Ltd., "SOPHISTA," average fineness: 1.7 dtex, average fiber diameter: 11 μm, average fiber length: 51 mm, core-sheath mass ratio: 50/50, circular cross section, core diameter: 8.9 μm]

[e] SOPHISTA 3: A low-melting-point core-sheath composite staple fiber with a core of polyethylene terephthalate and a sheath of ethylene-vinyl alcohol copolymer (ethylene content: 44 mol%, saponification degree: 98.4%) [Kuraray Co., Ltd., "SOPHISTA," average fineness: 3.3 dtex, average fiber length: 51 mm, core-sheath mass ratio: 50/50, circular cross-section, core diameter: 12.5 μm]

[f] SOPHISTA 4: A low-melting-point core-sheath composite staple fiber with a polypropylene core and an ethylene-vinyl alcohol copolymer sheath (ethylene content: 44 mol%, saponification degree: 98.4%) [Kuraray Co., Ltd., "SOPHISTA," average fineness: 1.7 dtex, average fiber length: 51 mm, core-sheath mass ratio: 50/50, circular cross-section, core diameter: 8.9 μm]

[g] Rayon: Rayon fiber ["HOPE" manufactured by Omikenshi Co., Ltd., average fiber diameter: 12 μm, average fiber length: 40 mm]

[h]PET: Polyethylene terephthalate fiber [manufactured by Toray Industries, Inc., average fiber diameter: 12 μm, average fiber length: 51 mm]

[i] PP: polypropylene resin [MFR (230°C, 2.16 kg) = 1100 g/10 min]

[j] PBT: polybutylene terephthalate resin [MFR (235°C, 2.16 kg) = 90 g/10 min]

[k] Split fiber: Layered laminated cross-section split fiber composed of nylon 6 and polyethylene terephthalate [Kuraray Co., Ltd. "WRAMP", 3.8 dtex, average fiber diameter 23.0 μm, average fiber length 51 mm, mass ratio of nylon 6 to polyethylene terephthalate: 33/67]

[l]MB: meltblown

[m]SL: Hydroentanglement

[n]SJ: Steam jet method

Claims (8)

1. A water-absorbing laminate comprising: The first fiber layer, consisting of a first fiber aggregate containing a first hydrophilic fiber, and A second fiber layer is composed of a second fiber aggregate containing more than 80% by mass of moist heat-adhesive fibers, wherein, The water absorption rate of the surface of the first fiber layer opposite to the second fiber layer, as determined by the dropwise addition method specified in JIS L 1907, is less than 10 seconds. The first fiber aggregate is a nonwoven fiber aggregate of the first hydrophilic fiber with an average fiber diameter of less than 10 μm. The unit area weight of the second fiber layer is 50–400 g/ ^m² . The layers are joined together by the interweaving and fusion of fibers. 2. The absorbent laminate as described in claim 1, wherein the average micropore diameter of the first fiber layer is 0.5 to 50 μm. 3. The absorbent laminate as described in claim 1, wherein the first fiber aggregate is a meltblown nonwoven fiber aggregate. 4. The absorbent laminate as claimed in claim 1, wherein the first hydrophilic fiber is a fiber formed from a polyamide resin. 5. The absorbent laminate as claimed in claim 1, further comprising a third fiber layer composed of a third fiber aggregate containing a second hydrophilic fiber, the third fiber layer being a fiber layer sandwiched between the first fiber layer and the second fiber layer. 6. The absorbent laminate as claimed in claim 1, wherein the longitudinal tensile strength when wet, as determined according to JIS L 1913, is 160 N/5 cm or more. 7. The absorbent laminate as described in any one of claims 1 to 6, used for wiping abrasive particles and water from the surface of an object. 8. A manufacturing method, which is a method for manufacturing the water-absorbing laminate of claim 5, the method comprising: In the first step, the first fiber layer and the third fiber layer are joined by interlacing or fusion bonding of the fibers constituting the first fiber aggregate and the fibers constituting the third fiber aggregate, or by interlacing or fusion bonding of the fibers constituting the second fiber aggregate and the fibers constituting the third fiber aggregate; and In the second step, if the first fiber layer and the third fiber layer were joined in the first step, the second fiber layer and the third fiber layer are joined by interlacing or fusion bonding of the fibers constituting the second fiber aggregate and the fibers constituting the third fiber aggregate. In the first step, if the second fiber layer and the third fiber layer were joined, the first fiber layer and the third fiber layer are joined by interlacing or fusion bonding of the fibers constituting the first fiber aggregate and the fibers constituting the third fiber aggregate. The interlacing or bonding in the first and second processes are carried out by hydroentangling, steam jetting or needle punching.