JP7102812B2 - Water-absorbent sheet - Google Patents

Description

The present invention relates to a water-absorbent sheet.

Conventionally, sheets containing super absorbent polymers (SAP) and superabsorbent fibers (SAF) have been known, and their uses are diverse. For example, sheets containing superabsorbent polymers include sanitary materials such as disposable diapers and sanitary products, dew condensation prevention sheets, pet sheets, hardened curing sheets, simple toilets, sandbag sheets, and drip absorbing 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 the body fluid is diffused in the horizontal direction by providing such a diffusion layer. Further, Patent Document 2 describes a desorbing / releasing sheet composed of a front surface layer, an inner layer, and a back surface layer. Also in Patent Document 2, pulp fiber is used for the inner layer.

Further, Patent Document 3 discloses an absorber composed of a highly water-absorbent fiber and a hot-melt adhesive fiber. In the example of Patent Document 3, a columnar molded absorber is obtained by mixing a highly water-absorbent fiber having a fiber length of 51 mm and a hot-melt adhesive fiber to form a sliver, and then thermoforming the fiber. Further, in the examples of Patent Document 3, a mixture of rayon fibers having a length of 51 mm is also exemplified.

Japanese Unexamined Patent Publication No. 2005-95481 Japanese Unexamined Patent Publication No. 2008-155566 Japanese Unexamined Patent Publication No. 11-20209

A water-absorbent sheet containing a super absorbent polymer (SAP) or a superabsorbent fiber (SAF) 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.
Further, in the water-absorbent sheet, there may be a problem that fibers derived from the raw material are shed or dust is generated during use or production (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 is water-absorbent in which fibers are suppressed from falling off and dust is generated during use and manufacturing (processing). The purpose is to provide a sheet.

As a result of diligent studies to solve the above problems, the present inventors have formed a water-absorbing layer of a highly water-absorbent fiber having a predetermined fiber length and a water-absorbing layer having a predetermined fiber length and having a melting point of 140 ° C. or higher. By composing a resin fiber containing a first resin having a high temperature and a second resin having a melting point of 140 ° C. or lower, excellent absorption performance can be exhibited, and the fiber falls off during use and manufacturing (processing). It has been found that a water-absorbent sheet in which the generation of dust and dirt is suppressed can be obtained.
Specifically, the present invention provides the following [1] to [7].

[1] A water-absorbent sheet including a water-absorbent layer.
The water-absorbent layer contains high water-absorbent fibers, 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.
The length of the highly water-absorbent fiber, the weighted average fiber length, and the length of the resin fiber, the weighted average fiber length is 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-absorbent layer.
[2] The water-absorbent sheet according to [1], wherein the first resin and the second resin are polyolefin-based resins.
[3] The water-absorbent sheet according to [1] or [2], wherein the first resin is polypropylene and the second resin is polyethylene.
[4] The content of the highly water-absorbent fiber 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 with respect to the total mass of the water-absorbing layer. 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 non-woven fabric layer on one surface side of the water absorption 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 air-laid web.

According to the present invention, it is possible to obtain a water-absorbent sheet capable of exhibiting excellent absorption performance, in which fibers are suppressed from falling off and dust is not generated during use and production (processing).

FIG. 1 is a cross-sectional view illustrating a configuration of a water-absorbent sheet according to an embodiment.

Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be based on typical embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, the numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

(Water absorption sheet)
The present invention relates to a water-absorbent sheet including a water-absorbent layer. The water-absorbent layer contains high-water-absorbent fibers, 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, and the length-weighted average fiber length of the high water-absorbent fiber and Length of resin fiber The weighted average fiber length is 10 mm or less. Further, the pulp content with respect to the total mass of the water absorption layer is 1% by mass or less.

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

In the water-absorbent sheet of the present invention, the water-absorbent layer has a high water-absorbent fiber having a length-weighted average fiber length of 10 mm or less and a length-weighted average fiber length of 10 mm or less, and has a melting point of more than 140 ° C. It has resin fibers containing a high first resin. The length-weighted average fiber length of the highly water-absorbent fiber may be 10 mm or less, preferably 8 mm or less, more preferably 7 mm or less, and further preferably 6 mm or less. The length-weighted average fiber length of the highly water-absorbent fiber is preferably 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. .. The length-weighted average fiber length of the resin fiber containing the first resin is preferably 3 mm or more. As described above, when the water absorption layer has fibers having a short fiber length, the mobility of the fibers constituting the water absorption layer can be enhanced. When the fibers have high mobility, when the highly water-absorbent fibers absorb the liquid and swell, each fiber can flow so as to follow the swelling movement of the highly water-absorbent fibers, so that the swelling of the highly water-absorbent fibers is hindered. It is thought that it will not be done. As a result, the absorption performance of the entire water absorption layer can be improved. Here, the length-weighted average fiber lengths of the highly water-absorbent fibers and the resin fibers are the fiber lengths calculated by the following formula from the fiber lengths of a plurality of fibers observed by visual observation or microscopic observation and the number of observed fibers. Is.
Length-weighted average fiber length = (Σni ・ Li ² ) / (Σni ・ Li)
ni: Number of fibers having a fiber length of Li Li: Length of fiber

Further, when the water-absorbent sheet of the present invention is used and when it is manufactured (processed), the fibers are suppressed from falling off from the water-absorbent sheet and the generation of dust is suppressed. This is achieved by setting the pulp content to 1% by mass or less based on the total mass of the water absorption 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 even more preferable. That is, it is preferable that the water absorption layer does not substantially contain pulp fibers. By setting the pulp content with respect to the total mass of the water-absorbent layer within the above range, it is possible to prevent the pulp fibers from falling off from the water-absorbent sheet and the generation of dust (paper dust) derived from the pulp fibers. As a result, when the water-absorbent sheet is used, it is possible to prevent the pulp fibers from falling off and the generation of dust (paper dust) derived from the pulp fibers. In addition, in a processing process such as a manufacturing process, pulp fibers may fall off or dust (paper dust) derived from pulp fibers may adhere to the manufacturing equipment, or dust (paper dust) derived from pulp fibers may fly to the surrounding environment. It can be suppressed.

In the present invention, by setting the pulp content in the water-absorbent layer to a predetermined value or less, it is possible to prevent fibers from falling off from the water-absorbent sheet and dust generation during use and production (processing). Will be done. Conventionally, it has been considered that the pulp component contained in the water absorption layer works 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 enhanced by using the highly water-absorbent fiber and the resin fiber having the fiber length in the predetermined range. I succeeded in doing so. That is, the present invention has been able to achieve both suppression of fiber shedding and generation of dust and improvement of absorption performance, which were difficult to achieve in 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 air gaps between the fibers can be controlled to the desired size. Further, in the air-laid web, since the fibers are randomly oriented in three dimensions, the liquid contained in the sheet can be diffused in any of the vertical direction, the horizontal direction, and the thickness direction. In addition, since the fibers are randomly oriented three-dimensionally, the expansion of the highly water-absorbent fiber is less likely to be hindered, which makes it possible to improve the absorption performance of the water-absorbent layer. Furthermore, by randomly orienting the fibers three-dimensionally in the water-absorbent sheet, the gaps between the fibers can be increased to increase the flexibility of the water-absorbent layer, and the softness and softness of the entire water-absorbent sheet can be improved. Can be done.

(Water absorption layer)
The water-absorbent sheet of the present invention includes a water-absorbent layer. The water-absorbent sheet of the present invention may be composed of a water-absorbent layer, or may include another layer in addition to the water-absorbent layer. When the water-absorbent sheet contains another layer 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-absorbent layer includes high water-absorbent fibers, 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. Further, it is preferable that the pulp content with respect to the total mass of the water absorbing layer is 1% by mass or less, and the water absorbing layer does not substantially contain pulp.

The content of the highly water-absorbent fiber 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 with respect to the total mass of the water-absorbing layer. It is preferably%. The content of the highly water-absorbent fiber with respect to the total mass of the water-absorbent 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 setting the content of each component in the water absorption layer within the above range, it is possible to achieve a high level of balance between the absorption amount in the water absorption layer and the shape retention of the water absorption layer. Specifically, it is possible to maintain a high absorption amount and suppress the leakage of the liquid, while suppressing the deformation of the water-absorbing layer after absorbing the liquid and the protrusion of the highly water-absorbent fiber from the end face of the water-absorbing layer. can. Further, by setting the content of each component in the water absorption layer within the above range, the strength of the water absorption layer after absorbing the liquid can be increased.

The density of the water absorbing layer is preferably 0.05 g / cm ³ or more, more preferably 0.10 g / cm ³ or more, and further preferably 0.11 g / cm ³ or more. The density of the water absorbing 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, it is possible to provide appropriate voids between the fibers contained in the water-absorbing layer, and it is possible to enhance the mobility of the fibers. As a result, the absorption performance of the water absorption layer can be enhanced more effectively.

The thickness of the water absorption layer is preferably 0.5 mm or more, more preferably 1.0 mm or more, and further preferably 1.5 mm or more. The thickness of the water absorption 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 the present invention, excellent absorption performance can be exhibited by setting the thickness of the water absorption layer within the above range. Further, by setting the thickness of the water absorption layer within the above range, the mobility of the fibers contained in the water absorption layer can be more effectively increased, and thereby the absorption amount can 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. The basis weight of the water absorption layer is preferably 500 g / m ² or less. By setting the basis weight of the water absorption layer within the above range, it is possible to provide appropriate voids between the fibers contained in the water absorption layer, and it is possible to enhance the mobility of the fibers. As a result, the absorption amount of the water absorption layer can be increased more effectively.

<High water absorption fiber>
The super absorbent polymer (SAF) is a fiberized superabsorbent polymer (SAP) that absorbs moisture and swells. Here, "high water absorption" means that it can absorb 20 times or more of its own weight. Highly water-absorbent fibers (SAF) gel when in contact with a liquid and play a role of retaining water.

Examples of the super absorbent polymer include synthetic polymers such as polyacrylic acid (salt) type, polysulfonic acid (salt) type, maleic anhydride (salt) type, polyacrylamide type, polyvinyl alcohol type, and polyethylene oxide type, and polyaspartic acid (polyaspartic acid (salt) type. Polymers derived from natural products such as salt) type, polyglutamic acid (salt) type, polyargic acid (salt) type, starch type, cellulosic type, crosslinked products thereof, and composites (copolymers, etc.) of these. Can be mentioned. Above all, 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 highly water-absorbent fiber may be 10 mm or less, preferably 8 mm or less, more preferably 7 mm or less, and further preferably 6 mm or less. The length-weighted average fiber length of the highly water-absorbent fiber is preferably 3 mm or more. Here, the length-weighted average fiber length of the highly water-absorbent fiber is a fiber length calculated by the above-mentioned formula from the fiber lengths of a plurality of fibers observed by visual observation or microscopic observation and the number of observed fibers. ..

The thickness of the highly water-absorbent fiber is preferably 1 dtex or more, and more preferably 5 dtex or more. The thickness of the highly water-absorbent fiber is preferably 20 dtex or less, and more preferably 15 dtex or less.

As the highly water-absorbent fiber, a composite fiber containing two or more kinds of superabsorbent polymers in the above-mentioned one fiber may be used, and two or more kinds of fibers made of one kind of superabsorbent polymer may be used. May be good.

<First resin>
The water absorption layer contains 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 even more preferably 160 ° C. or higher. The melting point of the first resin is preferably 300 ° C. or lower. Examples of the first resin having a melting point higher than 140 ° C. include polyolefin-based resins, polyester-based resins, nylon, polylactic acid, and the like. Among them, the first resin is preferably a polyolefin-based resin, and more preferably polypropylene. By using a polyolefin-based resin as the first resin, the flexibility of the water-absorbent layer can be enhanced, and the softness and softness of the entire water-absorbent sheet can be enhanced.

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. The length-weighted average fiber length of the resin fiber containing the first resin is preferably 3 mm or more. Here, the length-weighted average fiber length of the resin fiber containing the first resin is calculated by the above-mentioned formula from the fiber lengths of a plurality of fibers observed by visual observation or microscopic observation and the number of observed fibers. 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. 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 contains a second resin having a melting point of 140 ° C. or lower. The second resin also plays a role of improving the adhesiveness between the highly water-absorbent fiber and the fiber of the resin fiber containing the first resin and imparting the shape-retaining property of the water-absorbent layer. Since the second resin has a lower melting point than the first resin, it can also be called a binder component.

The melting point of the second resin may be 140 ° C. or lower, preferably 135 ° C. or lower, and more preferably 130 ° C. or lower. 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), ethylene-vinyl acetate copolymer (EVA) and the like. Among them, the second resin is preferably a polyolefin-based resin, and more preferably polyethylene. By using a polyolefin-based resin as the second resin, the flexibility of the water-absorbent layer can be enhanced, and the softness and softness of the entire water-absorbent sheet can be enhanced.

The second resin is a component derived from a resin fiber containing the second resin. Therefore, the second resin contained in the water absorption layer may be a resin that exists in a state where at least a part thereof is spread in a matrix shape, or a resin that exists partly while maintaining the fiber shape. good. Further, the entire second resin may be present in a state of being spread 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. Especially preferable.

In the present invention, a core-sheath type composite fiber can also be used as the resin fiber. In this case, it is preferable to use a core-sheath type composite fiber in which the core is made of the first resin and the shell is made of the second resin. When a core-sheath type composite fiber is used, in the water absorption layer, the second resin constituting the shell (sheath) may be melted into a matrix, and the second resin forming the core (core) may be formed. The resin of 1 may be present in a fibrous state.

<Arbitrary ingredient>
The water-absorbent layer may be composed of only high water-absorbent fibers, 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, but it is necessary. Other components may be contained depending on the circumstances. Other ingredients include, for example, moisturizers, deodorants, refreshers, air fresheners, anti-inflammatory agents, preservatives, antibacterial agents, bactericides, oily bases, surfactants, alcohols, polymers / thickening / gels. Examples thereof include agents, antioxidants, chelating agents, pH adjusters / acids / alkalis, ultraviolet absorbers, flame retardants and the like.

(Laminated body)
The water-absorbent sheet of the present invention may include another layer in addition to the water-absorbent layer. Examples of the other layer include a non-woven fabric layer and a film layer. Among them, as shown in FIG. 1, the water-absorbent sheet 100 of the present invention further includes a polyester non-woven 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 10. It is preferably a sheet to have. By having the water-absorbent sheet having the above structure, it is possible to prevent liquid leakage, and it is possible to prevent the water-absorbent layer from drying in applications where water retention is required. Further, by adopting the above-mentioned structure of the water-absorbent sheet, it is possible to suppress a decrease in interlayer strength due to sheet swelling during liquid absorption, and even when other layers are provided in addition to the above, the adhesiveness between layers can be improved. It will be easier to maintain.

When the water-absorbent sheet has a polyester non-woven fabric layer, a water-absorbent layer, and a resin film layer in this order, a heat-sealing resin is supplied between the layers to enhance the adhesiveness (heat-sealing property) between the layers. You may. Examples of the heat-sealing resin include hot-melt adhesives and heat-sealing resins such as polyethylene.

<Polyester non-woven fabric layer>
The polyester non-woven fabric layer plays a role of absorbing the liquid and allowing the liquid to permeate through the water absorbing layer, and also plays a role of retaining the gelled liquid absorbed by the water absorbing layer and preventing the liquid from retreating. Therefore, the polyester non-woven fabric layer is preferably located on the skin contact surface side with respect to the water absorption layer.

As the polyester non-woven fabric layer, a non-woven fabric produced 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 polyester include polyethylene terephthalate, polyethylene naphthalate, polymethylene terephthalate, and polybutylene terephthalate.

Above all, it is preferable to use a polyethylene terephthalate non-woven fabric sheet obtained by the spunbond method as the non-woven fabric layer. The polyethylene terephthalate non-woven fabric sheet obtained by the spunbond method is preferably used from the viewpoints of liquid permeability, liquid absorption, anti-return property, shape retention and strength.

The basis weight of the polyester non-woven 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 gelled liquid in the water-absorbing layer, plays a role of preventing the liquid from leaking from the water-absorbing layer, and also plays a role of imparting shape retention. Such a film layer can also be called 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. Further, a film or sheet containing a polyimide resin, a fluororesin or the like may be used. Among them, the resin film layer is preferably a polyolefin-based resin film layer, and preferably 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 have an additional layer in addition to the above-mentioned layer. Examples of other layers include an adhesive layer, a resin layer, a non-woven fabric layer, a reinforcing layer, a peeling layer, and the like.

(Manufacturing method of water-absorbent sheet)
The water-absorbent sheet of the present invention is preferably formed by an air-laid method. Here, the airlaid method is one of the methods for forming a dry non-woven fabric. Specifically, the fibers constituting the water absorption layer are defibrated in a dry manner, and the defibrated fibers are mixed and deposited on a traveling wire mesh using air as a medium to form a web (water absorption layer). be. It is preferable that a part of the fibers constituting the web (water absorption layer) thus formed is joined by a second heat-melted resin (binder component).

The manufacturing process of the water-absorbent sheet preferably includes a step of forming a water-absorbent layer on the polyester spunbonded non-woven fabric layer by an air-laid method and a step of laminating a resin film layer on the water-absorbent layer. In the present invention, by using the highly water-absorbent fiber and the resin fiber having a fiber length of 10 mm or less, the water-absorbent layer can be formed by the air-laid method, and a sheet having desired physical properties can be formed. ..

The step of forming the water-absorbent layer is a step of mixing high water-absorbent fibers, a resin fiber containing a first resin having a melting point higher than 140 ° C., and a resin fiber containing 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 spunbonded non-woven layer (depositing step). Here, the length-weighted average fiber length of the highly water-absorbent 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 lower 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 the respective resin fibers, but the core is the first resin and the shell is A core-sheath type composite fiber composed of a second resin may be used. In this case, the step of forming the water-absorbent layer is a step of mixing the highly water-absorbent fiber with 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 lower ( The mixing step) and the step of depositing the mixed fibers on the polyester spunbonded non-woven layer (depositing step) are included.

In the mixing step, the highly water-absorbent fiber and the resin fiber are uniformly mixed in the air. When mixing the fibers, a stirrer may be used, but it is preferable to use an air stream for mixing. Further, in the mixing step, it is preferable to defibrate the fibers. By defibrating the fibers, the density of the sheet can be controlled.

In the deposition step, the fiber mixture obtained in the mixing step is deposited on the running polyester spunbonded non-woven fabric layer. In the deposition process, the fiber mixture is three-dimensionally and randomly deposited using an air flow. Such a water absorption layer forming step is called an air-laid method, and a sheet formed by the air-laid method is called an air-laid web. Typical processes of the airlaid method include, for example, the J & J method, the KCC method, or the Scott method as the picker rotor method, and the Oji method (also called the Honshu method), the Croyer method, or the Danweb method as the screen method. Are known.

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

The water-absorbing layer formed in the step of forming the water-absorbing layer contains resin fibers containing a second resin. Since the second resin is a binder component, it is preferable to provide a step of heat-treating the water absorbing layer to melt the second resin (binding step). By performing such a heat treatment, at least a part of the resin fiber containing the second resin is melted, and the highly water-absorbent fiber and the resin fiber containing 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. The method of binding the fibers by melting at least a part of the heat-sealing resin in this way is sometimes called 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 brought into contact with a through-air dryer provided with a rotating drum having air permeability on the peripheral surface for heat treatment. Further, a method of heat-treating the air-laid web by passing it through a box-type dryer and passing hot air through the air-laid web (hot air circulation conveyor oven method) is also exemplified.

After the step of forming the water absorbing layer, it is preferable to provide a step of laminating a resin film layer on the water absorbing layer. In the step of laminating the resin film layer, the heat-sealing resin is applied to the water-absorbing layer, and then the resin film layer is laminated on the coated surface of the heat-sealing resin. Here, it is preferable to apply a hot melt adhesive containing a heat-sealing resin to the water-absorbing layer, then laminate the resin film layer and bring them into close contact with each other using a pressure roll or the like.

After the binding step, a step of compressing using a heating roll or the like may be provided for the purpose of adjusting the thickness and density of the sheet. Further, the formed sheet may be rolled up and stored.

(Use)
The water-absorbent sheet of the present invention can be used, for example, for an absorbent article, a curing sheet, a drug-containing sheet, a beauty sheet, a dew condensation prevention sheet, a sanitary material, a sandbag sheet, and a medical sheet. In this case, in addition to the above-mentioned sheet, other sheet materials such as an adhesive sheet and a surface protection sheet can be laminated and used for various purposes.

The features of the present invention will be described in more detail with reference to Examples and Comparative Examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed in a limited manner by the specific examples shown below.

(Example 1)
A polyester spunbonded non-woven fabric having a basis weight of 15 g / m ² is unwound on a mesh conveyor having a suction box, and a powder feeder is used on the polyester spunbonded non-woven fabric so that the heat-sealing resin (polyethylene powder) becomes 9 g / m ² . Was sprayed. Then, using a mat former, 36 parts by mass of a polyacrylate-based highly water-absorbent fiber (fiber length 6 mm, fineness 10 dtex), 32 parts by mass of polypropylene fiber (fiber length 5 mm, fineness 6.6 dtex), and polypropylene / 32 parts by mass of polyethylene (1: 1) core-sheath type heat-sealing fiber (fiber length 5 mm, fineness 3.3 dtex) was mixed, and a water absorbing layer (intermediate layer) was formed from the fiber mixture obtained by defibration. After the web thus obtained was heated to 140 ° C. in a heating furnace, hot melt (ethylene-vinyl acetate copolymer) was applied so as to be 8 g / m ² , and 26 g / m ² was applied on the coated surface. A polyethylene film was laminated. The web thus obtained was treated with a heat-pressurized 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 absorption layer (intermediate layer) was 242 g / m ² .

(Comparative Example 1)
20 parts by mass of sodium polyacrylate-based highly water-absorbent 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 and carded to be intermediate from the fiber mixture. A layer was formed. Then, a polypropylene spunbonded non-woven fabric having a basis weight of 26 g / m ² was placed on both sides of the intermediate layer, 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 of polyester / polyethylene heat-sealed fibers having a basis weight of 22 g / m ² is fed onto a mesh conveyor having a suction box, and a powder feeder is used on the air-through non-woven fabric so as to have a basis weight of 9 g / m ² . A heat-sealing resin (polyethylene powder) was sprayed. Next, using a mat former, 50% by mass of polysodium polyacrylate-based highly water-absorbent fiber (fiber length 6 mm, fineness 10 dtex), pulp fiber (fiber length 0.05 to 5 mm, coniferous chemical pulp) 20% by mass, And 30% by mass of polypropylene fiber (fiber diameter 6.6dtex) was mixed and defibrated to form an intermediate layer from the fiber mixture. Subsequent operations were carried out 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 amount>
Approximately 5 g of water-absorbent sheet was placed in a test basket with 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 manufactured using a copper wire with a wire diameter of 0.4 mm, and the water temperature was 24. A car containing a water-absorbent sheet was immersed in water at ~ 26 ° C. At this time, the basket was dropped from a height of 12 mm from the water surface in a horizontal state, and immersed in water having a depth of 200 mm. Then, after the uppermost end of the basket had sunk below the surface of the water, the basket was left to stand for 3 minutes, and then the basket was taken out of the water with the basket lying down, and the water was dropped on the wire mesh of the No. 10 sieve for 1 minute. Next, the mass of the water-absorbent sheet was measured, and the amount of water absorbed per unit area was determined by the following formula.
Absorption amount (g / m ² ) = (mass of water-absorbent sheet after immersion in water-mass of water-absorbent sheet before immersion in water) / area of water-absorbent sheet (area when dried)

<Fiber dropout>
On the black mount, I held the upper side of the water-absorbent sheet cut to a size of 100 mm x 100 mm, and flicked the central part of the lower side with my finger three times. The degree of fiber shedding at this time was observed and evaluated according to the following evaluation criteria.
◯: Almost no fibers are shed (the number of fibers shed is 5 or less)
X: Many fibers fall off (the number of fibers that fall off is more than 5)

In Example 1, the amount of water absorbed was large, and the fibers were suppressed from falling off from the edge of the sheet. 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 amount of absorption does not increase because the voids in the sheet become smaller. Moreover, in Comparative Example 2, a large number of fibers were found to fall off.

10 Water-absorbent layer 20 Polyester non-woven fabric layer 30 Resin film layer 100 Water-absorbent sheet

Claims (7)

A water-absorbent sheet containing a water-absorbent layer
The water-absorbent layer includes a high water-absorbent fiber, a resin fiber containing a first resin having a melting point higher than 140 ° C., a core 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. Contains core-sheath composite fibers composed of a resin-containing shell
The length-weighted average fiber length of the highly water-absorbent fiber, the length-weighted average fiber length of the resin fiber, and the length-weighted average fiber length of the composite 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-absorbent layer. The water-absorbent sheet according to claim 1, wherein the first resin and the second resin are polyolefin-based 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 highly water-absorbent fiber 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 20 to 50% by mass with respect to the total mass of the water-absorbing layer. 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-absorbent layer is 0.05 to 0.30 g / cm ³ . A polyester non-woven fabric layer on one surface side of the water absorption 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, wherein the water-absorbent layer is an air-laid web.

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