JPH1147192A - Water absorbing structure and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-function water absorbing material having both a water absorbing property and liquid nonpermeability by providing a liquid- nonpermeable sheet material having many recesses on one surface, and storing and fixing a water absorbing material in the recesses. SOLUTION: A liquid-nonpermeable sheet material 1 is formed with a flexible thermoplastic film, and many recesses 13 each having an opening 12 at the bottom section are formed. High-hygroscopicity resin grains 14 are stored in the recesses 13 and fixed to the inner walls of the recesses 13 by microfibril fine fibers 15. The resin grains 14 are preferably filled so that fine grains are located at the narrow portions of the recesses 13 and large grains are located at the wide portions. A polyethylene film is used for the thermoplastic film, and an acrylate polymer cross-linked object is used for the high-hygroscopicity resin respectively. No leak occurs at the water column of about 800 mm H2 O, and tissue paper is not wetted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-shaped water-absorbing structure having both a leakage-preventing function and a water-absorbing function, and particularly to an absorbent product such as a disposable diaper which is used as a back sheet or an outer sheet. In this case, the present invention relates to a water-absorbing structure which functions alone or as an absorber having sufficient water-absorbing ability.

[0002]

2. Description of the Related Art Most absorbent products such as diapers and napkins are composed of a water-permeable top sheet, a liquid-impermeable sheet back sheet, and an absorbent material interposed therebetween. With the recent trend of development, in conjunction with the spread of ultra-thin products, the direction to combine and integrate the topsheet and the absorber and the direction to integrate the absorber and the liquid-impermeable sheet backsheet have been shifting. Yes, and some proposals have already been made.

[0003]

However, there is naturally a limit to reducing the thickness of the absorber while maintaining the water absorbing ability of the absorber. Also, since the absorber has no function of preventing liquid permeation even if it has absorptivity, it is indispensable to use it in combination with a liquid impermeable sheet material, and therefore no matter how thin the absorber is, ,
It is not possible to eliminate the sense of incongruity due to the difference in behavior between the liquid impermeable sheet and the liquid impermeable sheet, and this is one of the biggest causes of a decrease in the usability of the absorbent product.

[0004] It is an object of the present invention to provide a multifunctional water-absorbing material having two incompatible properties of water absorption and liquid impermeability.

[0005]

According to the present invention, there is provided a liquid-impermeable sheet material having a large number of recesses on one surface;
A water-absorbing material contained and fixed in the recess,
A water-absorbing structure having both a leak-proof function and a water-absorbing function is provided.

The liquid impermeable sheet material is, for example, a thermoplastic film having a thickness of 5 μm to 50 μm or a thickness of 5 μm.
μm to 50 μm is a bonded body of a thermoplastic film and a non-woven fabric, the recesses formed in this sheet material may be the same liquid impermeable as other parts, or at the bottom of the recess or a part thereof Alternatively, there may be an open portion or a porous portion through which liquid flows as it is, and the open portion or the porous portion may be closed with the water-absorbing material.

The water-absorbing structure having such a structure is liquid-impermeable as a whole and exhibits a large liquid-absorbing capacity due to the water-absorbing material accommodated and fixed in the concave portion. It has the two functions of an absorber.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to achieve the above objects of the present invention, it is necessary to clear the following requirements. (1) Use a liquid-impermeable sheet material having a concavo-convex structure, and more preferably, a material having waterproofness and air permeability. (2) Use a water-absorbing material with the largest possible water-absorbing capacity. (3) Fill the recess with a water-absorbing material and fix it in the recess.

First, a liquid-impermeable sheet material having a concave portion, preferably, a material having waterproofness and air permeability will be described.

The material having an uneven structure used in the present invention includes PE, PP, E having a thickness of about 5 μm to 50 μm.
Most commonly, a flexible thermoplastic film such as VA is formed with a large number of holes or recesses in an arbitrary shape by means of mechanical perforation, thermoforming, vacuum forming, etc., but a liquid-impermeable sheet material A hole having a waterproof and leakproof property can be advantageously used by closing the hole with a water-absorbing material described later.

The water-absorbing material filling the recess is required to have a fine size in order to fill the relatively narrow space. On the other hand, a predetermined amount of water absorption, which is an amount to be filled in the narrow space, is required. In order to ensure this, a high water absorption capacity per unit volume is required.

Such requirements cannot be satisfied only with wood pulp or water-absorbing fibers. Therefore, in the present invention, a superabsorbent resin (hereinafter, referred to as “SAP”) in any form such as a particle or a fiber is used. SAP
For example, cross-linked acrylate polymer, starch-acrylic acid graft copolymer, hydrolyzate of starch-acrylonitrile graft copolymer, cross-linked polyoxyethylene, cross-linked carboxymethyl cellulose and the like are generally known. . The process for producing the SAP includes the following steps: In general, a polymer is synthesized by a method such as reverse-phase suspension polymerization, reverse-phase emulsion polymerization, and aqueous solution polymerization; by drying the polymer, or by drying the polymer. Subsequent milling gives the base polymer particles;
Post-treatment is performed to increase the crosslink density of the particle surface, and at the same time, an anti-blocking agent is added to suppress the blocking property of the product powder due to moisture absorption.

[0013] SAP is generally in the form of powder or flake-like particles, but in some cases, fibrous or flake-like particles.
Film-shaped products have also been commercialized, and any form of SAP can be used in the present invention. For the purposes of the present invention, which is achieved by being stably held in a narrow space, particulate, preferably finer, is desirable,
If expressed in terms of particle size, those having a diameter of 0.4 mm or less, more preferably about 0.3 mm to 0.1 mm are suitable. Further, ultrafine particles of about 0.1 mm and coarse particles of 0.4 mm or more may coexist. When SAP is made to coexist with a fiber material such as wood pulp, the larger the SAP content, the better, and it is desirable to contain at least 50% of SAP.

As a method for filling and fixing SAP or a water-absorbing material containing SAP into a concave portion provided in a liquid-impermeable sheet material, in principle, an ordinary absorbent manufacturing process such as diapers and napkins is used. The same method that has been applied can be applied, one preferred method is
For example, the method includes a step of dispersing the SAP and the wood pulp in an air flow, a step of filling the dispersion with the dispersion, and a step of fixing the dispersion with hot melt at the location.

Another preferable method in which problems such as non-uniformity and generation of dust do not occur is a method using SAP in a slurry state. For example, the present inventors have previously proposed SAP in Japanese Patent Application No. 8-333520.
And a mixed slurry of microfibrillar fine fibers. The microfibrillated fine fibers form a high concentration and stable slurry with SAP in a mixed solvent of a hydrophilic organic solvent and water. By removing the solvent from the slurry and drying the slurry, the microfibrillated fine fibers effectively work as a binder for binding the SAP particles to each other and the sheet material. Therefore, the slurry is filled into the recesses of the liquid-impermeable sheet material by means such as coating with a coater or spray, and then the solvent is removed to obtain a water-absorbing structure having both a leak-proof function and a water-absorbing function. Can be

If the concave portion of the liquid-impermeable sheet material has a hole or a liquid-permeable structure in a part thereof, the liquid-impermeable sheet material is placed on a conveyor provided with a vacuum dehydrator. And by continuously supplying the slurry from above the liquid-impermeable sheet material, the solvent in the slurry is separated by permeating the sheet material through the openings or liquid passages, and only the solid content Is left in the recess. Then, by performing further desolvation and drying,
The SAP particles are bonded to each other and between the SAP particles and the sheet material by the microfibrillated fine fibers, and are stably fixed at the position, and at the same time, waterproofness is also provided. Also, by appropriately selecting the ratio between the amount of the SAP and the properties and amount of the microfibrillated fine fibers,
It is also possible to provide desirable properties as a material of the absorbent product, which exhibits a certain degree of air permeability while maintaining the desired leak-proof property.

Next, an example of the structure of the water-absorbing structure of the present invention will be described with reference to the drawings.

FIG. 1 shows a liquid impermeable sheet material 11 made of a flexible thermoplastic film, and an opening 1 at the bottom.
2 shows a sheet material in which a number of recesses 13 having 2 are formed. FIGS. 2 and 3 show a water-absorbing structure in which the concave portion 13 is filled with a water-absorbing material. The water absorbing material is
The SAP particles 14 are fixed to the inner wall of the concave portion 13 of the liquid impermeable sheet material 11 by microfibrillar fine fibers 15.

In general, it is desirable to have a structure in which finer particles fill a narrow part and a larger part fills a relatively wide part.

FIG. 4 shows a process of manufacturing another water absorbing structure of the present invention. In step A of FIG. 4, the liquid impermeable sheet material 21 and the liquid permeable nonwoven fabric 22 having lateral extensibility are overlapped via a hot melt adhesive layer (not shown).
By the processing by the heated grid roll, a multiplicity of grooves 23 extending in parallel with each other are formed, and at the same time, are bonded to the sheet material 21 via the hot melt at the positions of the recesses. In step C, the composite sheet is
The liquid-permeable sheet material 21 is cut off at the position of each groove 23 to form a concave portion 24. The portion 24 is composed of only a liquid-permeable nonwoven fabric.

Next, in step D, the above-mentioned slurry obtained by uniformly dispersing the SAP and the microfibrillar fine fibers in the mixed solvent of the hydrophilic organic solvent and water is placed on the liquid-permeable sheet material 24. The concave portion 24 is filled with a water-absorbing material 25 composed of SAP and microfibril-like fine fibers. Finally, in step E, a topsheet 26 such as a nonwoven fabric is disposed on the liquid-impermeable sheet material 21 and each of the water-absorbing materials 25, and is joined to the topsheet at a portion 21 where no absorber is present.

FIG. 5 shows a liquid-impermeable sheet material in which a large number of concave portions 24 formed in step B are circular, and FIG. 6 shows a sheet material in which concave portions 24 are filled with a water-absorbent material 25 in step D. Is shown.

In the water-absorbent structure shown in FIG. 4, the nonwoven fabric 22 forming the composite sheet together with the liquid impermeable sheet material 21 is a water-resistant synthetic nonwoven fabric such as PE, PP, or PET, or a synthetic fiber made of rayon. lyocell, obtained from a mixed material of cellulosic fibers such as cotton, basis weight 10g / m ² ~50g / m ² non-woven fabric is preferable.

FIGS. 7 and 8 show that the liquid-impermeable sheet material 21 is formed into a corrugated plate, and the water-absorbent material 2 is formed in a narrow band or rod shape at the bottom of a valley-shaped recess 24 extending parallel to each other.
5 is arranged and fixed at that position.

FIG. 9 shows an example in which the water-absorbing material 25 is provided in a dot shape instead of the band-shaped or rod-shaped water-absorbing material 25 used in FIGS.

In the configuration shown in FIGS. 7 to 9, the liquid impermeable sheet material 21 may or may not have an opening at the bottom of the concave portion 24.

In any case, the recess 24 formed in the liquid impermeable sheet material may have an inner wall surface that extends substantially perpendicular to the surface of the sheet material, but preferably is formed of a water absorbing material. It has a funnel-shaped taper that narrows from top to bottom for ease of filling.

The size of the concave portion depends on the size and shape of the water-absorbing material.
If it is rectangular or elongated, such as a groove, its width in the short direction is at least 0.3 mm, preferably 0.5 mm.
mm or more is desirable. This is because if the diameter or width is too small, it becomes difficult to stably hold a sufficient amount of the water-absorbing material in the concave portion.

[0029]

Embodiments will be described below with reference to embodiments.

(Example 1) <Preparation of a liquid-impermeable sheet material having an uneven portion> A polyethylene film of about 30 μm having an opening as shown in FIG. "VISP
ORE X-6170 ”).

<Preparation of slurry of water-absorbing material>
FC gel (manufactured by Daicel Chemical Industries, trade name "Selish KY-
100G ") was dispersed in a mixed solvent of ethanol / water = 70/30 to prepare 1 liter of a 0.5% dispersion of MFC. In this dispersion, particulate SA having an average particle size of 0.3 mm
P (Mitsubishi Chemical, product name "US40") 200g,
A co-dispersed slurry of SAP and MFC was prepared.

<Preparation of Water Absorbent Structure> The above-mentioned perforated polyethylene film is supplied onto a belt conveyor composed of an 80 mesh plastic belt provided with a suction zone and conveyed, with the surface having the larger perforations facing upward. Meanwhile, the SAP / MFC co-dispersion slurry was applied onto the open polyethylene sheet.

In the suction zone, the SAP / MFC co-dispersed slurry on the perforated polyethylene sheet was drained from the co-dispersed slurry through the perforated portion, and the solid portion was filled in the perforated portion. Then, the solid was dried by blowing hot air at 80 ° C.

The opening of the water-absorbing structure obtained had a structure as shown in FIG. 2 when observed with a microscope.

<Evaluation of Air Permeability> The obtained water-absorbent structure was subjected to a gas permeability test based on the Gurley type test of JIS P8117, and the air permeability (sec / 100c)
c) = 100 was obtained.

<Measurement of Water Resistance>
A zero-layer commercially available tissue paper was spread, and a water column made of physiological saline was set up using a 20 mm diameter glass tube so as to cover the opening filled with the superabsorbent material, and the water pressure resistance was measured. In the portion filled with the superabsorbent material, SAP had a swelling due to swelling.
Even if the water column was raised to 00 mmH ² O, the liquid did not leak and the tissue did not get wet.

(Example 2) <Preparation of base material to be liquid impermeable sheet material> LLDP
A hot-melt adhesive was spray-coated on the surface of a matted E-coated polyethylene sheet having a thickness of 25 μm, and a PP fiber staple (1.5 d ×
A nonwoven fabric-film composite having a structure shown in FIG. 4A was prepared by laminating a spunlace nonwoven fabric having a large lateral extensibility of 30 g / m ² and having a structure shown in FIG. 4A.

This complex was processed according to the process shown in FIG. First, the film was passed through a stainless steel grid roll having a surface temperature of 100 ° C. (peak pitch 10 mm, peak width 0.5 mm, depth 2 mm) to form a linear groove in the film (FIG. 4). In step B), the width was expanded 1.5 times in the horizontal direction to obtain a nonwoven fabric / film composite in which the film portion and the nonwoven fabric were exposed in a strip shape (step C in FIG. 4).

<Preparation of Slurry of Water Absorbent Material> Ethanol and water were added to a BC gel (manufactured by Ajinomoto, 5% aqueous dispersion of “Biocellulose”) to obtain ethanol / water = 60.
/ 40 0.4% dispersion was prepared, and a particulate SAP having an average particle diameter of 0.3 mm (Mitsubishi Chemical,
Add 300g of product name “US40”, SAP and BC
Was prepared.

<Preparation of Water Absorbent Structure> The nonwoven fabric portion (about 5 mm) of the nonwoven fabric / film composite was covered with
The above co-dispersed slurry was prepared to a thickness of 200 g / m ² and a width of about 10
mm (Step D in FIG. 4).

<Preparation of uneven water-absorbing structure> The water-absorbing structure was formed into a corrugated sheet using a grooved guide, and a hydrophilically treated PE / PET spun bond 20 g / m ² (manufactured by Unitika Ltd.) The product was then laminated with a brand name “Elves”) to obtain an absorber with a top sheet (step E in FIG. 4).

<Evaluation of Air Permeability> The above water-absorbing structure was subjected to an air permeability test according to the Gurley method of JIS P8117, and the air permeability (sec / 100 cc) was 80.
And showed good air permeability.

<Wearing test as a water-absorbent product> Ten pieces of diapers for infants were trial-produced by attaching gathers and binding tapes to the above-mentioned uneven water-absorbing structure, and a wearing test was carried out. Two leaks occurred, but no leak from the back side occurred.

Example 3 <Preparation of Waterproof Uneven Material> PP Melt Blown (5
g / m ²⁾ and a combination of PP spunbond (13g / m ²⁾ melt blown, it was prepared spunbond (MS) composite nonwoven fabric (18g / m ^2). On the other hand, a PE film having a thickness of 2 mm was formed on a 30 μm thick PE film containing LLDPE as a main component.
A hole-perforated film having a hole was prepared. A small amount of hot melt type adhesive is sprayed on the spun bond surface of the perforated film, and an MS non-woven fabric is stuck on this surface.
Was obtained.

A water column test was performed on the composite sheet under the same conditions as in Example 1 to obtain a value of about 200 mmH ² O.

<Preparation of Slurry of Water Absorber> A slurry of the absorber was prepared under the same conditions as in Example 1.

<Preparation of Water Absorbing Structure> The composite of the MS nonwoven fabric and the apertured film was supplied onto a belt conveyor provided with a suction zone, with the apertured film facing upward, as in Example 1. The top was supplied with the water-absorbent slurry. The solvent was removed in the suction zone, and the exposed surface of the MS nonwoven fabric was bonded and filled with SAP particles as a water absorbing material by MFC to obtain a water absorbing structure as shown in FIG.

<Permeability of Water Absorbent Structure> The obtained water absorbent structure was subjected to a gas permeability test based on the Gurley type test of JIS P8117.
c / 100 cc) = 160.

<Evaluation of waterproofness of water-absorbing structure> Under the water-absorbing structure, 10 layers of commercially available tissue paper were laid, and a glass tube having a diameter of 20 mm was covered so as to cover the opening filled with SAP particles. Was used to set up a column of physiological saline to measure the water resistance. The SAP in contact with the physiological saline swelled and swelled to raise the water column to 800 mmH ² O, but the liquid did not leak and the tissue did not get wet.

[0050]

As described above, the water-absorbing structure of the present invention is liquid-impermeable as a whole and exhibits a large liquid-absorbing capacity due to the water-absorbing material housed and fixed in the recess. It has both functions of a liquid impermeable sheet and an absorber. For this reason, a sense of incongruity due to a shift in the behavior between the absorber and the liquid impermeable sheet is eliminated, and the usability of the absorber product can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a partial perspective view of a perforated liquid impermeable sheet constituting a water absorbing structure of the present invention.

FIG. 2 is a plan view showing a part of the surface of the water-absorbing structure of the present invention.

FIG. 3 is a longitudinal sectional view of the water absorbing structure of FIG.

FIG. 4 is an explanatory view showing a step of manufacturing the water-absorbing structure of the present invention.

FIG. 5 is a plan view of a liquid impermeable sheet material used for the water absorbing structure of the present invention.

FIG. 6 is a plan view showing a state in which a concave portion of the liquid impermeable sheet material of FIG. 5 is filled with a water absorbing material.

FIG. 7 is a partial plan view showing another water absorbing structure of the present invention.

FIG. 8 is a partial longitudinal sectional view of FIG. 7;

FIG. 9 is a partial plan view showing still another water absorbing structure of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Liquid impermeable sheet material 12 Opening 13 Depression 14 SAP particle 15 Microfibril-like fine fiber 21 Liquid impermeable sheet material 22 Liquid permeable nonwoven fabric 23 Groove part 24 Depression 25 Water absorbing material

Claims (11)

[Claims] 1. A liquid-impermeable sheet material having a large number of recesses on one surface, and a water-absorbing material containing a highly water-absorbing resin, which is accommodated and fixed in the recesses, and has a leak-proof function. A water-absorbing structure that also has a water-absorbing function. 2. The liquid-impermeable sheet material having a thickness of 5 μm.
The water-absorbing structure according to claim 1, which is a thermoplastic film having a size of m to 50 m. 3. The liquid-impermeable sheet material having a thickness of 5 μm.
The water-absorbing structure according to claim 1, which is a bonded body of a thermoplastic film having a thickness of 50 m to 50 m and a nonwoven fabric. 4. An opening portion or a porous portion which allows liquid to pass through the bottom portion or a portion of the concave portion of the liquid impermeable sheet material, and the opening portion or the porous portion is The water-absorbing structure according to any one of claims 1 to 3, wherein the water-absorbing structure is closed with the water-absorbing material, thereby providing leakproofness. 5. The liquid-impermeable sheet according to claim 5, wherein
The water-absorbing structure according to any one of claims 1 to 4, wherein the water-absorbing structure has a funnel-shaped taper such that an upper portion is wide and narrows toward a lower portion. 6. The liquid-impermeable sheet material is a film in which the opening portions have openings, and a water-resistant nonwoven fabric in which the porous portions are joined to the film so as to cover the openings. 3. The water-absorbing structure according to item 2. 7. The water-absorbent material contains 50% of a superabsorbent resin.
The water-absorbing structure according to any one of claims 1 to 6, which includes the above. 8. The water-absorbing material has an average particle size of 0.4 mm.
The water-absorbent structure according to any one of claims 1 to 7, comprising the following particulate superabsorbent resin and microfibrillar fine fibers that bind the resin. 9. The water absorbing structure according to claim 4, wherein the portion filled with the water absorbing material has air permeability. 10. An absorbent product comprising the water-absorbing structure according to any one of claims 1 to 9. 11. A slurry containing a particulate water-absorbent resin is continuously supplied from above a liquid-permeable sheet material having a large number of recesses having openings formed in a bottom portion, so that the inside of the recesses is formed. By filling the slurry and separating the solvent in the slurry through the opening through the sheet material, leaving only the solid content in the concave portion, and then removing the solvent and drying. Of producing a water-absorbing structure.