WO2019176980A1

WO2019176980A1 - Water-absorbent sheet

Info

Publication number: WO2019176980A1
Application number: PCT/JP2019/010153
Authority: WO
Inventors: 中野　繁一; 晋平黒川
Original assignee: 王子ホールディングス株式会社
Priority date: 2018-03-16
Filing date: 2019-03-13
Publication date: 2019-09-19
Also published as: JP7102812B2; JP2019157316A

Abstract

The present invention addresses the problem of providing a water-absorbent sheet capable of exhibiting excellent absorption performance, wherein fiber shedding and dust generation during use and production (processing) are suppressed. The present invention pertains to a water-absorbent sheet comprising a water-absorbent layer, the water-absorbent layer containing: a super water-absorbent fiber; a resin fiber containing a first resin having a melting point higher than 140°C; and a second resin having a melting point of 140°C or lower, wherein the length-weighted average fiber length of the super water-absorbent fiber and the length-weighted average fiber length of the resin fiber are 10 mm or less, and the pulp content is 1 mass% or less with respect to the total mass of the water-absorbent layer.

Description

Water absorbent sheet

The present invention relates to a water absorbent sheet.

Conventionally, a sheet containing a superabsorbent polymer (SAP) or a superabsorbent fiber (SAF) is known, and its uses are various. For example, sheets containing highly water-absorbing polymers include sanitary materials such as disposable diapers and sanitary products, anti-condensation sheets, pet sheets, cured curing sheets, simple toilets, sandbag sheets, and drip absorption sheets (tray mats) overseas. It is used as such.

For example, Patent Document 1 describes a thin absorber composed of a diffusion layer, an absorption layer, and a base material layer. Here, pulp fibers are used for the diffusion layer and the absorption layer, and body fluid is diffused in the horizontal direction by providing such a diffusion layer. Patent Document 2 describes a desorption / release sheet comprising a surface layer, an inner layer and a back layer. Also in Patent Document 2, pulp fibers are used for the inner layer.

Patent Document 3 discloses an absorbent body composed of a highly water-absorbent fiber and a hot-melt adhesive fiber. In the Example of patent document 3, after forming the sliver by mixing the highly water-absorbing fiber having a fiber length of 51 mm and the hot melt adhesive fiber, the cylindrical shaped absorbent body is obtained by thermoforming. Moreover, in the Example of patent document 3, what mixed the rayon fiber of length 51mm is illustrated.

JP-A-2005-95481 JP 2008-155666 A JP-A-11-200909

In a water-absorbent sheet containing a superabsorbent polymer (SAP) or a superabsorbent fiber (SAF), it may be required to be thin depending on the application. However, even in such a case, the water absorbent sheet is required to exhibit sufficient absorption performance.
Moreover, in the water-absorbent sheet, there may be a problem that the fiber derived from the raw material is dropped or dust is generated during use or manufacturing (processing).

Therefore, the present invention is a water-absorbent sheet capable of exhibiting excellent absorption performance in order to solve the above-mentioned problems, and water-absorbing sheet in which fiber dropping and dust generation during use and production (processing) are suppressed. The purpose is to provide a sheet.

As a result of earnest studies to solve the above problems, the present inventors have determined that the water absorption layer includes a superabsorbent fiber having a predetermined fiber length, a predetermined fiber length, and a melting point of 140 ° C. It is possible to demonstrate excellent absorption performance by comprising a resin fiber containing a higher first resin and a second resin having a melting point of 140 ° C. or less, and the fiber is dropped during use and during manufacturing (processing) It was found that a water-absorbent sheet in which generation of dust and dust was suppressed was obtained.
Specifically, the present invention provides the following [1] to [7].

[1] A water absorbent sheet including a water absorbent layer,
The water absorption layer includes a highly water-absorbing fiber, a resin fiber containing a first resin having a melting point higher than 140 ° C., and a second resin having a melting point of 140 ° C. or less.
The length weighted average fiber length of the superabsorbent fiber and the length weighted average fiber length of the resin fiber are 10 mm or less,
A water absorbent sheet having a pulp content of 1% by mass or less based on the total mass of the water absorbing layer.
[2] The water absorbent sheet according to [1], wherein the first resin and the second resin are polyolefin resins.
[3] The water absorbent sheet according to [1] or [2], in which the first resin is polypropylene and the second resin is polyethylene.
[4] The content of the superabsorbent fiber with respect to the total mass of the water absorbing layer is 20 to 50% by mass, the content of the first resin is 30 to 70% by mass, and the content of the second resin is 10%. The water-absorbent sheet according to any one of [1] to [3], which is 30% by mass.
[5] The water absorbent sheet according to any one of [1] to [4], wherein the density of the water absorbent layer is 0.05 to 0.30 g / cm ³ .
[6] A polyester nonwoven fabric layer on one surface side of the water absorbing layer,
The water absorbent sheet according to any one of [1] to [5], further comprising a resin film layer on the other surface side of the water absorbent layer.
[7] The water absorbent sheet according to any one of [1] to [6], which is an airlaid web.

According to the present invention, it is possible to obtain a water-absorbent sheet that can exhibit excellent absorption performance and that suppresses fiber dropout and dust generation during use and production (processing).

FIG. 1 is a cross-sectional view illustrating a configuration in one embodiment of a water absorbent sheet.

Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

(Water absorbent sheet)
The present invention relates to a water absorbent sheet including a water absorbing layer. The water-absorbing layer includes a superabsorbent fiber, a resin fiber containing a first resin having a melting point higher than 140 ° C., and a second resin having a melting point of 140 ° C. or less. The length weighted average fiber length of the resin fiber is 10 mm or less. Moreover, pulp content with respect to the total mass of a water absorption layer is 1 mass% or less.

The water absorbent sheet of the present invention exhibits excellent absorption performance by having the above configuration. Specifically, the water absorbent sheet of the present invention has a large amount of absorption per unit area and high absorption efficiency. Absorption of water per unit area in the absorbent sheet is preferably 4000 g / m ² or more, more preferably 4500 g / m ² or more, more preferably 5000 g / m ² or more, 5500 g / M ² or more is more preferable, and 6000 g / m ² or more is particularly preferable. The water absorption amount per unit area in the water absorbent sheet is calculated after the water absorbent sheet is immersed in water for 3 minutes and then dropped on a No. 10 sieve wire mesh for 1 minute. It is a value calculated from the amount of water by the following formula.
Absorption amount (g / m ² ) = (mass of water-absorbing sheet after dipping in water−mass of water-absorbing sheet before dipping in water) / area of water-absorbing sheet (area when dried)

In the water absorbent sheet of the present invention, the water absorbent layer has a highly water absorbent fiber having a length weighted average fiber length of 10 mm or less, a length weighted average fiber length of 10 mm or less, and a melting point of more than 140 ° C. It has a resin fiber containing a high first resin. The length-weighted average fiber length of the superabsorbent fiber may be 10 mm or less, preferably 8 mm or less, more preferably 7 mm or less, and even more preferably 6 mm or less. In addition, it is preferable that the length weighted average fiber length of the superabsorbent fiber is 3 mm or more. The length weighted average fiber length of the resin fiber containing the first resin may be 10 mm or less, preferably 8 mm or less, more preferably 7 mm or less, and further preferably 6 mm or less. . In addition, it is preferable that the length weighted average fiber length of the resin fiber containing 1st resin is 3 mm or more. Thus, the mobility of the fiber which comprises a water absorption layer can be improved because a water absorption layer has a fiber with short fiber length. If the fiber has high mobility, when the superabsorbent fiber swells by absorbing liquid, it can flow so that each fiber follows the swelling movement of the superabsorbent fiber. It is thought that it will not be done. Thereby, the absorption performance of the whole water absorption layer can be improved. Here, the length weighted average fiber length of the superabsorbent fiber and the resin fiber is a fiber length calculated by the following formula from the fiber length of the plurality of fibers observed by visual observation or microscopic observation and the number of fibers observed. It is.
Length weighted average fiber length = (Σni · Li ² ) / (Σni · Li)
ni: number of fibers having a fiber length of Li Li: fiber length

Also, when using the water-absorbent sheet of the present invention and when manufacturing (processing), the fibers are prevented from falling off and the generation of dust from the water-absorbent sheet. This is achieved by setting the pulp content to 1% by mass or less with respect to the total mass of the water absorbing layer. The pulp content with respect to the total mass of the water absorbing layer may be 1% by mass or less, preferably 0.1% by mass or less, more preferably 0.01% by mass or less, and 0% by mass. Is more preferable. That is, it is preferable that the water absorption layer is substantially free of pulp fibers. Thus, by making the pulp content with respect to the total mass of the water-absorbing layer within the above range, it is possible to suppress the pulp fibers from falling off the water-absorbent sheet and the generation of dust (paper dust) derived from the pulp fibers. Thereby, when using a water absorptive sheet, drop-off of a pulp fiber and generation | occurrence | production of the dust (paper powder) originating in a pulp fiber can be suppressed. In addition, in processing processes such as manufacturing processes, pulp fibers fall off or dust (paper powder) derived from pulp fibers adheres to the surrounding environment, or dust (paper powder) derived from pulp fibers dances in the surrounding environment. Can be suppressed.

In the present invention, the pulp content in the water-absorbing layer is set to a predetermined value or less, so that fibers are not dropped from the water-absorbent sheet or dust is generated during use and production (processing). Is done. Conventionally, it has been considered that the pulp component contained in the water absorption layer functions to increase the absorption efficiency in the water absorption layer by diffusing the liquid. However, in the present invention, even when the pulp content in the water absorption layer is set to a predetermined value or less, the absorption efficiency is increased by using highly water-absorbing fibers and resin fibers having a fiber length within a predetermined range. Succeeded. In other words, the present invention can achieve both suppression of fiber dropout and generation of dust and improvement of absorption performance, which are difficult to achieve with the prior art.

The water absorbent sheet of the present invention is preferably an air laid web. The air-laid web is bulky, and the voids between the fibers can be controlled to a desired size. Further, in the airlaid web, the fibers are randomly oriented in three dimensions, so that the liquid contained in the sheet can be diffused in any of the longitudinal direction, the lateral direction, and the thickness direction. In addition, since the fibers are randomly oriented in three dimensions, the expansion of the highly water-absorbent fibers is not easily inhibited, thereby improving the absorption performance of the water absorption layer. Furthermore, the fibers in the water-absorbing sheet are randomly oriented in three dimensions, so that the gap between the fibers can be increased to increase the flexibility of the water-absorbing layer, and the softness of the water-absorbing sheet as a whole and the goodness of the touch can be improved. Can do.

(Water absorption layer)
The water absorbing sheet of the present invention includes a water absorbing layer. The water-absorbent sheet of the present invention may be composed of a water-absorbing layer or may contain other layers in addition to the water-absorbing layer. When the water-absorbent sheet includes other layers in addition to the water-absorbent layer, it is preferable to include a non-woven fabric layer or a film layer as described later.

The water-absorbing layer contains a highly water-absorbing fiber, a resin fiber containing a first resin having a melting point higher than 140 ° C., and a second resin having a melting point of 140 ° C. or lower. Moreover, it is preferable that pulp content with respect to the total mass of a water absorption layer is 1 mass% or less, and a water absorption layer is a thing which does not contain a pulp substantially.

The content of the superabsorbent fiber with respect to the total mass of the water absorbing layer is 20 to 50% by mass, the content of the first resin is 30 to 70% by mass, and the content of the second resin is 10 to 30% by mass. % Is preferred. The content of the superabsorbent fiber with respect to the total mass of the water absorbing layer is more preferably 25 to 40% by mass, further preferably 30 to 40% by mass, and particularly preferably 32 to 40% by mass. The content of the first resin with respect to the total mass of the water absorption layer is more preferably 38 to 60% by mass, further preferably 38 to 53% by mass, and particularly preferably 45 to 53% by mass. The content of the second resin with respect to the total mass of the water absorbing layer is more preferably 13 to 25% by mass, further preferably 13 to 20% by mass, and particularly preferably 15 to 18% by mass. preferable. By making content of each component in a water absorption layer into the said range, the balance of the amount of absorption in a water absorption layer and the shape retention of a water absorption layer can be made compatible at a high level. Specifically, while keeping the absorption amount high and suppressing the leakage of the liquid, it is possible to suppress the deformation of the water absorption layer after absorbing the liquid and the protrusion of the superabsorbent fiber from the end surface of the water absorption layer. it can. Furthermore, the intensity | strength of the water absorption layer after absorbing a liquid can also be made high by making content of each component in a water absorption layer into the said range.

Density of the water-absorbing layer is preferably 0.05 g / cm ³ or more, more preferably 0.10 g / cm ³ or more, more preferably 0.11 g / cm ³ or more. Further, the density of the water absorption layer is preferably 0.30 g / cm ³ or less, more preferably 0.20 g / cm ³ or less, and further preferably 0.17 g / cm ³ or less. By setting the density of the water absorbing layer within the above range, an appropriate gap can be provided between the fibers contained in the water absorbing layer, and the mobility of the fibers can be enhanced. As a result, the absorption performance of the water absorption layer can be improved more effectively.

The thickness of the water absorbing layer is preferably 0.5 mm or more, more preferably 1.0 mm or more, and further preferably 1.5 mm or more. Further, the thickness of the water absorbing layer is preferably 10.0 mm or less, more preferably 8.0 mm or less, further preferably 6.0 mm or less, and particularly preferably 4.0 mm or less. . In this invention, the outstanding absorption performance can be exhibited by making the thickness of a water absorption layer into the said range. Moreover, the mobility of the fiber contained in a water absorption layer can be improved more effectively by making the thickness of a water absorption layer into the said range, and, thereby, the amount of absorption can also be increased.

The basis weight of the water absorption layer is preferably 180 g / m ² or more, more preferably 200 g / m ² or more, and further preferably 250 g / m ² or more. Moreover, it is preferable that the basic weight of a water absorption layer is 500 g / m < ² > or less. By setting the basis weight of the water-absorbing layer within the above range, an appropriate gap can be provided between fibers contained in the water-absorbing layer, and the mobility of the fibers can be enhanced. As a result, the absorption amount of the water absorption layer can be increased more effectively.

<Superabsorbent fiber>
Superabsorbent fiber (SAF) is a fiber formed from superabsorbent polymer (SAP) that swells by absorbing moisture. Here, “high water absorption” means that it can absorb water 20 times or more of its own weight. The superabsorbent fiber (SAF) gels when it comes into contact with the liquid and plays a role of retaining moisture.

Examples of the superabsorbent polymer include polyacrylic acid (salt) -based, polysulfonic acid (salt) -based, maleic anhydride (salt) -based, polyacrylamide-based, polyvinyl alcohol-based, polyethylene oxide-based synthetic polymers, polyaspartic acid ( Salt) -based, polyglutamic acid (salt) -based, polyalginic acid (salt) -based, starch-based, cellulose-based polymers, cross-linked products thereof, and composites (copolymers, etc.) Can be mentioned. Among them, it is preferable to use a sodium polyacrylate polymer from the viewpoint of excellent liquid absorption performance.

The length-weighted average fiber length of the superabsorbent fiber may be 10 mm or less, preferably 8 mm or less, more preferably 7 mm or less, and even more preferably 6 mm or less. In addition, it is preferable that the length weighted average fiber length of the superabsorbent fiber is 3 mm or more. Here, the length weighted average fiber length of the superabsorbent fiber is a fiber length calculated by the above-described formula from the fiber length of the plurality of fibers observed by visual observation or microscopic observation and the number of fibers observed. .

The thickness of the superabsorbent fiber is preferably 1 dtex or more, and more preferably 5 dtex or more. Further, the thickness of the superabsorbent fiber is preferably 20 dtex or less, and more preferably 15 dtex or less.

As the superabsorbent fiber, a composite fiber containing two or more superabsorbent polymers in one fiber described above may be used, or two or more fibers composed of one superabsorbent polymer may be used. Also good.

<First resin>
The water absorption layer includes resin fibers containing a first resin having a melting point higher than 140 ° C., and the length weighted average fiber length of the resin fibers is 10 mm or less. The resin fiber containing the first resin plays a role of imparting shape retention of the water absorption layer.

The melting point of the first resin may be higher than 140 ° C., preferably 150 ° C. or higher, and more preferably 160 ° C. or higher. Moreover, it is preferable that melting | fusing point of 1st resin is 300 degrees C or less. Examples of the first resin having a melting point higher than 140 ° C. include polyolefin resins, polyester resins, nylon, polylactic acid, and the like. Among these, the first resin is preferably a polyolefin resin, and more preferably polypropylene. By using a polyolefin-based resin as the first resin, the flexibility of the water absorbing layer can be increased, and the softness of the entire water absorbent sheet and the good touch can be improved.

The length-weighted average fiber length of the resin fiber containing the first resin may be 10 mm or less, preferably 8 mm or less, more preferably 7 mm or less, and further preferably 6 mm or less. In addition, it is preferable that the length weighted average fiber length of the resin fiber containing 1st resin is 3 mm or more. Here, the length weighted average fiber length of the resin fiber containing the first resin is calculated by the above-described formula from the fiber length of a plurality of fibers observed by visual observation or microscopic observation and the number of fibers observed. The fiber length.

The thickness of the resin fiber containing the first resin is preferably 1 dtex or more, and more preferably 3 dtex or more. Further, the thickness of the resin fiber containing the first resin is preferably 20 dtex or less, and more preferably 10 dtex or less.

<Second resin>
The water absorption layer includes a second resin having a melting point of 140 ° C. or lower. The second resin also improves the adhesion between the highly absorbent fibers and the resin fibers including the first resin, and also plays a role of imparting the shape retention of the water absorbing layer. Note that since the second resin is a resin having a lower melting point than the first resin, it can also be referred to as a binder component.

The melting point of the second resin may be 140 ° C. or less, preferably 135 ° C. or less, and more preferably 130 ° C. or less. The melting point of the second resin is preferably 80 ° C. or higher. Examples of the second resin include polyethylene (including copolymerized polyethylene), polypropylene (including modified polypropylene and copolymerized polypropylene), low melting point polyester (for example, low melting point polyethylene terephthalate), low melting point polyamide, and low melting point. Examples thereof include polylactic acid, polybutylene succinate, acrylic resin, urethane resin, styrene butadiene copolymer, polyvinyl alcohol (PVA), and ethylene-vinyl acetate copolymer (EVA). Among these, the second resin is preferably a polyolefin resin, and more preferably polyethylene. By using a polyolefin-based resin as the second resin, the flexibility of the water-absorbing layer can be increased, and the softness and touch of the entire water-absorbent sheet can be improved.

The second resin is a component derived from a resin fiber containing the second resin. For this reason, the second resin contained in the water absorption layer may be a resin that exists in a state in which at least a part is spread in a matrix shape, or may be a resin that partly exists while maintaining the fiber shape. Good. Further, all of the second resin may exist in a state of spreading in a matrix. The length-weighted average fiber length of the resin fiber containing the second resin is preferably 10 mm or less, more preferably 8 mm or less, further preferably 7 mm or less, and preferably 6 mm or less. Particularly preferred.

In the present invention, a core-sheath type composite fiber may be used as the resin fiber. In this case, it is preferable to use a core-sheath type composite fiber in which the core (core) is the first resin and the shell (sheath) is composed of the second resin. When the core-sheath type composite fiber is used, in the water absorption layer, the second resin constituting the shell (sheath) may be melted to form a matrix, and the second resin constituting the core (core). One resin may exist in a fiber state.

<Optional component>
The water absorption layer may be composed only of superabsorbent fibers, resin fibers containing a first resin having a melting point higher than 140 ° C., and a second resin having a melting point of 140 ° C. or lower. Depending on the case, other components may be contained. Other ingredients include, for example, moisturizers, deodorants, fresheners, fragrances, flame retardants, antiseptics, antibacterial agents, bactericides, oily bases, surfactants, alcohols, polymers, thickeners and gels. Agents, antioxidants, chelating agents, pH adjusters / acids / alkalis, ultraviolet absorbers, flame retardants and the like.

(Laminate)
The water absorbent sheet of the present invention may include other layers in addition to the water absorbent layer. As another layer, a nonwoven fabric layer and a film layer can be mentioned, for example. Among them, as shown in FIG. 1, the water absorbent sheet 100 of the present invention further includes a polyester nonwoven fabric layer 20 on one surface side of the water absorbent layer 10 and a resin film layer 30 on the other surface side of the water absorbent layer. It is preferable that it is a sheet | seat which has. By making the water-absorbent sheet have the above-described configuration, liquid leakage can be prevented, and the water-absorbing layer can be prevented from drying in applications where water retention is required. In addition, by configuring the water-absorbent sheet as described above, it is possible to suppress a decrease in interlayer strength due to sheet swelling at the time of liquid absorption. Easy to maintain.

When the water-absorbent sheet has a polyester nonwoven fabric layer, a water-absorbing layer, and a resin film layer in this order, a heat-fusible resin is supplied between the layers to enhance the adhesion (heat-fusibility) between the layers. May be. Examples of the heat-fusible resin include hot-melt adhesives and heat-fusible resins such as polyethylene.

<Polyester non-woven fabric layer>
The polyester nonwoven fabric layer plays a role of absorbing liquid and allowing the water absorption layer to permeate the liquid, holding the liquid absorbed by the water absorption layer and gelling, and preventing the liquid from returning. For this reason, it is preferable that a polyester nonwoven fabric layer is located in the skin contact surface side rather than a water absorption layer.

For the polyester nonwoven fabric layer, nonwoven fabrics manufactured by various processing methods such as a spunlace method, a spunbond method, a thermal bond method, a chemical bond method, an airlaid method, a melt blown method, a needle punch method, and a stitch bond method can be used. . Examples of the polyester include polyethylene terephthalate, polyethylene naphthalate, polymethylene terephthalate, and polybutylene terephthalate.

Among them, it is preferable to use a polyethylene terephthalate nonwoven fabric sheet by a spunbond method as the nonwoven fabric layer. The polyethylene terephthalate nonwoven fabric sheet by the spunbond method is preferably used from the viewpoints of liquid permeability, liquid absorbability, anti-reverse property, shape retention and strength.

The basis weight of the polyester nonwoven fabric layer is preferably 10 to 30 g / m ² , and the thickness is preferably 0.05 to 0.3 mm.

<Resin film layer>
The resin film layer holds the liquid gelled in the water absorption layer, plays a role of preventing leakage of the liquid from the water absorption layer and imparting shape retention. Such a film layer can also be referred to as a backing layer.

Examples of the resin film layer include films and sheets containing polyester resins, vinyl chloride resins, polystyrene resins, acrylic resins, and polyolefin resins such as polyethylene and polypropylene. Alternatively, a film or sheet containing polyimide resin, fluorine resin, or the like may be used. Especially, it is preferable that a resin film layer is a polyolefin-type resin film layer, and it is preferable that it is a polyethylene film layer.

The basis weight of the polyethylene film layer is preferably 10 to 50 g / m ² and the thickness is preferably 0.1 to 0.5 mm.

<Other layers>
The water absorbent sheet may further have other layers in addition to the above-described layers. Examples of other layers include a pressure-sensitive adhesive layer, a resin layer, a nonwoven fabric layer, a reinforcing layer, and a release layer.

(Method for producing water-absorbent sheet)
The water-absorbent sheet of the present invention is preferably formed by an airlaid method. Here, the airlaid method is one of the methods for forming a dry nonwoven fabric. Specifically, a method of forming a web (water-absorbing layer) by defibrating fibers constituting the water-absorbing layer in a dry manner and mixing the defibrated fibers with air as a medium and depositing on a traveling wire mesh. is there. It is preferable that a part of the fibers constituting the web (water-absorbing layer) formed in this manner is joined by the second resin (binder component) that has been heat-melted.

The manufacturing process of the water absorbent sheet preferably includes a step of forming a water absorbing layer on the polyester spunbond nonwoven fabric layer by an airlaid method and a step of laminating a resin film layer on the water absorbing layer. In the present invention, by using highly water-absorbing fibers and resin fibers having a fiber length of 10 mm or less, it becomes possible to form a water-absorbing layer using an airlaid method, and a sheet having desired physical properties can be formed. .

The step of forming the water-absorbing layer is a step of mixing highly water-absorbing fibers, resin fibers containing a first resin having a melting point higher than 140 ° C., and resin fibers containing a second resin having a melting point of 140 ° C. or less (mixing step). And a step of depositing the mixed fibers on the polyester spunbond nonwoven fabric layer (deposition step). Here, the length-weighted average fiber length of the superabsorbent fiber, the resin fiber containing the first resin having a melting point higher than 140 ° C., and the resin fiber containing the second resin having a melting point of 140 ° C. or less is 10 mm or less. . Further, the resin fiber containing the first resin and the resin fiber containing the second resin may be mixed as each resin fiber, but the core is the first resin and the shell (sheath) is A core-sheath type composite fiber made of the second resin may be used. In this case, the step of forming the water-absorbing layer is a step of mixing the highly water-absorbing fiber with a resin fiber containing a first resin having a melting point higher than 140 ° C. and a second resin having a melting point of 140 ° C. or lower ( Mixing step) and a step of depositing the mixed fibers on the polyester spunbond nonwoven fabric layer (deposition step).

In the mixing process, the superabsorbent fibers and the resin fibers are uniformly mixed in the air. When mixing the fibers, a stirrer may be used, but it is preferable to mix using an air stream. In the mixing step, it is preferable to defibrate the fibers. The density of the sheet can be controlled by defibrating the fibers.

In the deposition step, the fiber mixture obtained in the mixing step is deposited on the running polyester spunbond nonwoven fabric layer. In the deposition process, the fiber mixture is randomly deposited three-dimensionally using an air flow. Such a water absorption layer forming process is called an airlaid method, and a sheet formed by the airlaid method is called an airlaid web. As a typical process of the airlaid method, for example, the J & J method, the KC method, or the Scott method as the picker rotor method, the method such as the Oji method (also called Honshu law), the Croyer method, or the Dunweb method as the screen method Are known.

When forming the water absorbing layer, a step of applying a heat-fusible resin such as polyethylene powder on a breathable nonwoven fabric and / or tissue, preferably a polyester spunbond nonwoven fabric, may be provided. In this way, by applying the heat-fusible resin and depositing the fiber mixture constituting the water absorption layer on this application surface, the layers to be laminated with the water absorption layer can be firmly bonded.

The water absorption layer formed in the step of forming the water absorption layer includes resin fibers including the second resin. Since the second resin is a binder component, it is preferable to provide a step of performing heat treatment on the water absorption layer to melt the second resin (binding step). By performing such heat treatment, at least a part of the resin fibers containing the second resin is melted, and the resin fibers containing the superabsorbent fibers and the first resin are bound. The heating temperature in the binding step is preferably a temperature at which at least a part of the second resin melts. In this way, a method in which at least a part of the heat-fusible resin is melted to bond the fibers together is sometimes referred to as a thermal bond method.

Examples of the heat treatment method in the binding step include hot air treatment and infrared irradiation treatment. As a hot-air treatment method, there is a method (hot-air circulation rotary drum method) in which the air-laid web is heat-treated by bringing it into contact with a through air dryer provided with a rotating drum having air permeability on the peripheral surface. Moreover, the method (hot air circulation conveyor oven system) etc. which heat-process by letting an air laid web pass through a box type dryer and let hot air pass through an air laid web are illustrated.

It is preferable to provide a step of laminating a resin film layer on the water absorption layer after the step of forming the water absorption layer. In the step of laminating the resin film layer, after applying the heat-fusible resin to the water absorbing layer, the resin film layer is laminated on the application surface of the heat-fusible resin. Here, it is preferable that a hot melt adhesive containing a heat-fusible resin is applied to the water absorption layer, and then a resin film layer is laminated and adhered using a pressure roll or the like.

In addition, you may provide the process of compressing using a heating roll etc. for the purpose of adjusting the thickness and density of a sheet | seat after a binding process. Moreover, the formed sheet | seat is good also as winding up and storing it in roll shape.

(Use)
The water-absorbent sheet of the present invention can be used, for example, for absorbent articles, curing sheets, drug-containing sheets, beauty sheets, anti-condensation sheets, sanitary materials, sandbag sheets, and medical sheets. In this case, in addition to the above-described sheet, other sheet materials such as an adhesive sheet and a surface protective sheet can be laminated and used for various applications.

Hereinafter, the features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

Example 1
A polyester spunbonded nonwoven fabric with a basis weight of 15 g / m ² is fed onto a mesh conveyor having a suction box, and a heat-fusing resin (polyethylene powder) is used on it by using a powder feeder to achieve 9 g / m ^2. Sprayed. Next, using a mat former, sodium polyacrylate superabsorbent fiber (fiber length 6 mm, fineness 10 dtex) 36 parts by mass, polypropylene fiber (fiber length 5 mm, fineness 6.6 dtex) 32 parts by mass, and polypropylene / A water-absorbing layer (intermediate layer) was formed from a fiber mixture obtained by mixing 32 parts by mass of polyethylene (1: 1) core-sheath type heat-fusible fiber (fiber length 5 mm, fineness 3.3 dtex). The web thus obtained was heated to 140 ° C. in a heating furnace, and hot melt (ethylene-vinyl acetate copolymer) was applied so as to be 8 g / m ^2, and 26 g / m ² on the coated surface. A polyethylene film was laminated. The web thus obtained was treated with a hot-pressing roll to obtain a water-absorbent sheet having a basis weight of 300 g / m ² and a thickness of 2.4 mm. The basis weight of the water absorbing layer (intermediate layer) was 242 g / m ² .

(Comparative Example 1)
20 parts by mass of a sodium polyacrylate-based superabsorbent fiber (fiber length 51 mm, fineness 6 dtex) and 80 parts by mass of polypropylene fiber (fiber length 51 mm, fineness 6.6 dtex) are mixed, subjected to carding treatment, and intermediate from the fiber mixture A layer was formed. Thereafter, a polypropylene spunbonded nonwoven fabric having a basis weight of 26 g / m ² was placed on both sides of the intermediate layer and laminated and integrated by needle punching to obtain a water absorbent sheet having a basis weight of 170 g / m ² and a thickness of 2.5 mm.

(Comparative Example 2)
An air-through non-woven fabric formed from a polyester / polyethylene heat-bonded fiber having a basis weight of 22 g / m ² is fed out on a mesh conveyor having a suction box, and a powder feeder is used on the nonwoven fabric so as to be 9 g / m ^2. A heat-fusible resin (polyethylene powder) was sprayed. Next, using a mat former, sodium polyacrylate-based superabsorbent fiber (fiber length 6 mm, fineness 10 dtex) 50 mass%, pulp fiber (fiber length 0.05-5 mm, softwood chemical pulp) 20 mass%, An intermediate layer was formed from a fiber mixture obtained by mixing and defibrating 30% by mass of polypropylene fiber (fiber diameter 6.6 dtex). Subsequent operations were performed in the same manner as in Example 1 to obtain a water absorbent sheet having a basis weight of 275 g / m ² and a thickness of 2.4 mm.

(Evaluation)
<Absorption>
About 5 g of the water-absorbent sheet is put in a test cage having a diameter of 50.0 mm, a depth of 80.0 mm, a distance between copper wires of 20 mm, and a weight of 3.0 g, which is manufactured using a copper wire having a wire diameter of 0.4 mm. A cage containing a water absorbent sheet was immersed in water at ˜26 ° C. At this time, the cage was dropped from a height of 12 mm from the water surface and immersed in water having a depth of 200 mm. Then, after the uppermost end of the car sank below the surface of the water, the car was left for 3 minutes, and then the car was taken out from the water in a horizontal state, and water was dropped on a No. 10 sieve wire net for 1 minute. Next, the mass of the water-absorbent sheet was measured, and the amount of absorption per unit area was determined by the following formula.
Absorption amount (g / m ² ) = (mass of water-absorbing sheet after dipping in water−mass of water-absorbing sheet before dipping in water) / area of water-absorbing sheet (area when dried)

<Fiber dropout>
On the black mount, the upper side of the water-absorbent sheet cut to a size of 100 mm × 100 mm was held, and the center of the lower side was flipped with a finger three times. At this time, the degree of fiber dropping was observed and evaluated according to the following evaluation criteria.
◯: Almost no fiber dropout is observed (the number of fibers dropped is 5 or less)
X: There are many dropouts of fibers (the number of fibers dropped is more than 5)

In Example 1, the amount of water absorbed was large, and the fiber falling off from the sheet edge was suppressed. On the other hand, in Comparative Example 1, the amount of water absorbed was small. Even if the basis weight of Comparative Example 1 is increased and the sheet density is increased, the voids in the sheet are reduced, so that the amount of absorption does not increase. Moreover, in the comparative example 2, many dropouts of the fiber were seen.

DESCRIPTION OF SYMBOLS 10 Water absorption layer 20 Polyester nonwoven fabric layer 30 Resin film layer 100 Water absorbing sheet

Claims

A water absorbent sheet including a water absorbing layer,
The water-absorbing layer includes a superabsorbent fiber, a resin fiber containing a first resin having a melting point higher than 140 ° C., and a second resin having a melting point of 140 ° C. or less.
The length-weighted average fiber length of the superabsorbent fiber and the length-weighted average fiber length of the resin fiber are 10 mm or less,
A water absorbent sheet having a pulp content of 1% by mass or less based on the total mass of the water absorbing layer.
The water absorbent sheet according to claim 1, wherein the first resin and the second resin are polyolefin resins.
The water absorbent sheet according to claim 1 or 2, wherein the first resin is polypropylene and the second resin is polyethylene.
The content of the superabsorbent fiber with respect to the total mass of the water absorbing layer is 20 to 50% by mass, the content of the first resin is 30 to 70% by mass, and the content of the second resin is The water-absorbent sheet according to any one of claims 1 to 3, which is 10 to 30% by mass.
The water-absorbent sheet according to any one of claims 1 to 4, wherein the density of the water-absorbing layer is 0.05 to 0.30 g / cm 3 .
A polyester nonwoven fabric layer on one surface side of the water absorbing layer,
The water absorbent sheet according to any one of claims 1 to 5, further comprising a resin film layer on the other surface side of the water absorbent layer.
The water absorbent sheet according to any one of claims 1 to 6, which is an airlaid web.