JP3981745B2 - Water-absorbing structure and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sheet-like water-absorbing structure having both a leak-proof function and a water-absorbing function, and in particular, an absorbent product such as a disposable diaper. The present invention relates to a water-absorbing structure that also functions as an absorbent having capacity.
[0002]
[Prior art]
Most of the absorbent products such as diapers and napkins are composed of a water-permeable top sheet, a liquid-impermeable sheet back sheet, and an absorbent body interposed therebetween. As a recent development trend, coupled with the spread of ultra-thin products, the trend is toward the direction of combining and integrating the top sheet and the absorber, and the direction of integrating the absorber and the liquid-impermeable sheet back sheet. There are already some proposals.
[0003]
[Problems to be solved by the invention]
However, there is a limit to reducing the thickness of the absorber while maintaining the water absorption capability. Even if the absorber has an absorptivity, it does not have a function of preventing the permeation of liquid, so it is indispensable to use it in combination with a liquid-impermeable sheet material, so no matter how thin the absorber is. However, it is not possible to eliminate the uncomfortable feeling caused by the difference in behavior between the liquid-impermeable sheet, and this is one of the biggest causes of a decrease in the feeling of use of the absorbent product.
[0004]
An object of the present invention is to provide a multifunctional water-absorbing material having two incompatible properties, water absorption and liquid impermeability.
[0005]
[Means for Solving the Problems]
According to the present invention, a liquid-impermeable sheet material having a large number of recesses on one surface and a water-absorbing material housed and fixed in the recesses have both a leak-proof function and a water-absorbing function. A water absorbent structure is provided.
[0006]
The liquid-impermeable sheet material is, for example, a thermoplastic film having a thickness of 5 μm to 50 μm, or a joined body of a thermoplastic film having a thickness of 5 μm to 50 μm and a non-woven fabric. It may be the same liquid impermeability as the part, or there is an open part or a porous part that allows liquid to pass through as it is at the bottom or part of the recess, and the open part or porous part is It may be closed with the water-absorbing material.
[0007]
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 housed and fixed in the recess. Therefore, the liquid-impermeable sheet and the absorbent body It has two functions.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In order to achieve the object of the present invention as described above, 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 that is waterproof and breathable.
(2) Use a water-absorbing material with as much water absorption capacity as possible.
(3) Fill the recess with a water-absorbing material and fix it in the recess.
[0009]
First, a liquid-impermeable sheet material having a recess, preferably a material that is waterproof and breathable will be described.
[0010]
As a material having a concavo-convex structure used in the present invention, a flexible thermoplastic film such as PE, PP, EVA or the like having a thickness of about 5 μm to 50 μm can be arbitrarily formed by means such as mechanical perforation, thermoforming, and vacuum forming. The most common is a shape in which a large number of holes or recesses are formed, but an opening is formed in a part of the liquid-impermeable sheet material, and the opening is closed by a water-absorbing material described later. Those that are waterproof and leakproof can also be used advantageously.
[0011]
In addition, the water-absorbing material filling the recess is required to have a fine size in order to fill the relatively narrow space, while ensuring a predetermined amount of water absorption, which is the amount to fill the narrow space. Is required to have a high water absorption capacity per unit volume.
[0012]
Such a request cannot be satisfied only with wood pulp and water-absorbing fibers. Therefore, in the present invention, any form of superabsorbent resin (hereinafter referred to as “SAP”) such as particulate or fibrous is used. As SAP, for example, acrylate polymer cross-linked product, starch-acrylic acid graft copolymer, hydrolyzate of starch-acrylonitrile graft copolymer, polyoxyethylene cross-linked product, carboxymethyl cellulose cross-linked product are generally known. Yes. The process for producing SAP comprises the following steps: In general, the polymer is synthesized by methods such as reverse phase suspension polymerization, reverse phase emulsion polymerization, aqueous solution polymerization; drying the polymer, or drying Subsequent grinding yields base polymer particles; then a post-treatment is applied to increase the cross-linking density of the particle surface and at the same time an anti-blocking agent is added to suppress blocking due to moisture absorption of the product powder Is done.
[0013]
SAP is generally in the form of powder and flaky particles, but in some cases, fibrous and film-like products are also commercialized, and any form of SAP can be used in the present invention. It is. For the purpose of the present invention to be achieved by being stably held in a narrow space, it is desirable to be particulate, preferably finer, and more desirably 0.4 mm or less when expressed in particle size. Is about 0.3 mm to 0.1 mm. 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 in a fiber material such as wood pulp, the SAP content is preferably as high as possible, and at least 50% or more of SAP is desirably contained.
[0014]
As a method for filling and fixing SAP or a water-absorbing material containing SAP in a recess provided in a liquid-impermeable sheet material, in principle, it is carried out in a manufacturing process of an absorbent body such as a normal diaper or napkin. The same method can be applied, and one preferred method is, for example, the step of dispersing SAP and wood pulp in an air stream, the step of filling this dispersion into the recesses, and then hot-melting in place. And fixing with.
[0015]
Another method that is more preferable in that problems such as non-uniformity and generation of dust do not occur is a method using SAP in the form of a slurry. For example, there is a method using a mixed slurry of SAP and microfibrillar fine fibers previously proposed by the present inventors in Japanese Patent Application No. 8-333520. The microfibrillar fine fiber forms a stable slurry with SAP at a high concentration in a mixed solvent of a hydrophilic organic solvent and water. By removing the solvent from the slurry and drying the slurry, the microfibril-like fine fibers effectively function as a binder for binding the SAP particles to each other and the sheet material. Therefore, the slurry is filled in the recesses of the liquid-impermeable sheet material by means such as a coater or spray coating, and then desolvated to obtain a water-absorbing structure having both a leak-proof function and a water-absorbing function. It is done.
[0016]
If the recess of the liquid-impermeable sheet material has an opening or a liquid-permeable structure in a part thereof, the liquid-impermeable sheet material is supplied onto a conveyor equipped with a vacuum dehydrator. By continuously supplying the slurry from above the liquid-impermeable sheet material, the solvent in the slurry permeates and separates the sheet material through the opening or liquid passing portion, and only the solid content is in the recess. Left behind. Subsequently, by further desolvation and drying, the SAP particles and between the SAP particles and the sheet material are bonded by microfibril-like fine fibers, and are stably fixed at the position, and at the same time, waterproofing is also imparted. It will be. In addition, by appropriately selecting the ratio between the amount of SAP and the properties and amount of microfibrillar fine fibers, the material of the absorbent product can exhibit a certain degree of air permeability while maintaining desirable leakage prevention properties. It is also possible to give favorable characteristics.
[0017]
Next, an example of the structure of the water absorbing structure of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 shows a sheet material in which a large number of recesses 13 having openings 12 at the bottom are formed in a liquid-impermeable sheet material 11 made of a flexible thermoplastic film. 2 and 3 show a water absorbent structure filled with a water absorbent material in the recess 13. The water-absorbing material is obtained by fixing the SAP particles 14 to the inner wall of the concave portion 13 of the liquid-impermeable sheet material 11 with microfibril-like fine fibers 15.
[0019]
In general, a structure in which finer particles are filled in a narrow portion and a larger portion is filled in a relatively wide portion is desirable.
[0020]
FIG. 4 shows a process for producing 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 stretchability are superposed via a hot melt adhesive layer (not shown), and heated in Step B. A plurality of groove portions 23 extending in parallel with each other are formed by the processing by the grid roll, and are simultaneously bonded to the sheet material 21 at the positions of the respective concave portions via the hot melt. In step C, the composite sheet is stretched in a direction perpendicular to the length direction of the groove portions 23, whereby the liquid permeable sheet material 21 is cut off at the positions of the groove portions 23 to form the recesses 24. The portion 24 is composed only of a liquid-permeable nonwoven fabric.
[0021]
Next, in Step D, the slurry described above, in which SAP and microfibril-like fine fibers are uniformly dispersed in the mixed solvent of the hydrophilic organic solvent and water, is applied onto the liquid permeable sheet material 24. Then, by removing the solvent and drying, the recess 24 is filled with the water-absorbing material 25 composed of SAP and microfibrillar fine fibers. Finally, in Step E, a top sheet 26 such as a nonwoven fabric is disposed on the liquid-impermeable sheet material 21 and each water-absorbing material 25, and is joined to the top sheet at 21 portions where there is no absorbent.
[0022]
FIG. 5 shows a liquid-impermeable sheet material in which a large number of recesses 24 formed in step B are circular, and FIG. 6 shows a sheet material in which recesses 24 are filled with water-absorbing material 25 in step D. Yes.
[0023]
In the water-absorbing structure shown in FIG. 4, the nonwoven fabric 22 constituting 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 synthetic fiber with rayon, lyocell, obtained from mixed materials cellulosic fibers such as cotton, non-woven fabric of basis weight 10g / m ² ~50g / m ² is desirable.
[0024]
7 and 8, the liquid-impermeable sheet material 21 is formed into a corrugated plate shape, and a water-absorbing material 25 is disposed in the form of a thin strip or rod at the bottom of a valley-shaped recess 24 extending in parallel with each other. The structure fixed to the position is shown.
[0025]
FIG. 9 shows an example in which the water-absorbing material 25 is provided in the form of dots instead of the water-absorbing material 25 in the band shape or the rod shape used in FIGS. 7 and 8.
[0026]
7 to 9, the liquid-impermeable sheet material 21 may or may not have an opening at the bottom of the recess 24.
[0027]
In any case, the recess 24 formed in the liquid-impermeable sheet material may have an inner wall surface extending substantially perpendicular to the surface of the sheet material, but is preferably filled with a water-absorbing material. For ease, it has a funnel-shaped taper that narrows from the top to the bottom.
[0028]
The size of the recess depends on the size and shape of the water-absorbing material, but if it is circular, its diameter is at least 0, and if it is elongated like an ellipse, rectangle, or groove, its width in the short direction is at least 0. 0.3 mm, preferably 0.5 mm or more. This is because if the diameter or width is too small, it is difficult to stably hold a sufficient amount of the water-absorbing material in the recess.
[0029]
【Example】
Examples will be described below.
[0030]
Example 1
<Preparation of liquid impervious sheet material with irregularities>
An approximately 30 μm polyethylene film (trade name “VISPORE X-6170” manufactured by Toledo Co., Ltd.) having a taper shape on the entire surface and having openings as shown in FIG. 1 was prepared.
[0031]
<Preparation of water-absorbing material slurry>
Separately, MFC gel (manufactured by Daicel Chemical Industries, trade name “Serisch KY-100G”) was dispersed in a mixed solvent of ethanol / water = 70/30 to prepare 1 liter of a 0.5% dispersion of MFC. To this dispersion, 200 g of particulate SAP (Mitsubishi Chemical, trade name “US40”) having an average particle size of 0.3 mm was added to prepare a co-dispersed slurry of SAP and MFC.
[0032]
<Preparation of water-absorbing structure>
While supplying the above-mentioned perforated polyethylene film on a belt conveyor made of an 80 mesh plastic belt equipped with a suction zone with the surface on the large aperture side facing up, on the perforated polyethylene sheet, SAP / A co-dispersed slurry of MFC was applied.
[0033]
In the suction zone, the SAP / MFC co-dispersed slurry on the open polyethylene sheet was drained through the open hole, and the open solid was filled with slurry solids. Subsequently, warm air of 80 ° C. was blown onto the solid material and dried.
[0034]
The pore portion of the obtained water-absorbing structure had a structure as shown in FIG. 2 when observed with a microscope.
[0035]
<Evaluation of air permeability>
About the obtained water absorbing structure, the air permeability test was performed based on the Gurley test of JIS P8117, and the result of air permeability (sec / 100 cc) = 100 was obtained.
[0036]
<Measurement of water resistance>
Under the water-absorbing structure, 10 layers of commercially available tissue paper are laid, and a water column made of physiological saline is formed using a 20 mm diameter glass tube so as to cover the opening filled with the highly water-absorbing material. Then, the water pressure resistance was measured. In the portion filled with the superabsorbent material, the SAP was swollen due to swelling, but even when the water column was increased to 800 mmH ² O, the liquid did not leak and the tissue did not get wet.
[0037]
(Example 2)
<Preparation of base material to be liquid-impermeable sheet material>
A hot melt adhesive was spray-coated on the surface of a 25 μm-thick polyethylene sheet matted from LLDPE, and 30 g / m ² composed of PP fiber staples (1.5 d × 35 mm) was applied to the coated surface. A non-woven fabric and a film composite having the structure shown in FIG. 4A were prepared by stacking the spun lace nonwoven fabrics having a large lateral stretchability and bonding them together by applying pressure under heating.
[0038]
This composite was processed according to the steps shown in FIG. First, a stainless steel grid roll having a surface temperature of 100 ° C. (crest pitch 10 mm, top width 0.5 mm, depth 2 mm) was passed through to form grooves in a line shape on the film (FIG. 4). Step B) was expanded 1.5 times in the transverse 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).
[0039]
<Preparation of water-absorbing material slurry>
Ethanol and water were added to BC gel (Ajinomoto, 5% aqueous dispersion of trade name “Biocellulose”) to prepare 1 liter of 0.4% dispersion of ethanol / water = 60/40. 300 g of particulate SAP having an average particle size of 0.3 mm (product name “US40”, manufactured by Mitsubishi Chemical Corporation) was added to prepare a co-dispersed slurry of SAP and BC.
[0040]
<Preparation of water-absorbing structure>
The co-dispersed slurry was coated at a thickness of 200 g / m ² and a width of about 10 mm so as to cover the nonwoven fabric portion (about 5 mm) of the nonwoven fabric / film composite (Step D in FIG. 4).
[0041]
<Preparation of uneven water-absorbing structure>
The above water-absorbing structure is formed into a corrugated plate shape with a grooved guide, and bonded with hydrophilic treated PE / PET spunbond 20 g / m ² (trade name “Elves” manufactured by Unitika) to absorb with a top sheet. A body was formed (Step E in FIG. 4).
[0042]
<Evaluation of air permeability>
When the air-absorbing structure was subjected to a JIS P8117 Gurley air permeability test, the air permeability (sec / 100 cc) was 80, indicating good air permeability.
[0043]
<Wear test as a water absorbent product>
Ten pieces of diapers for infants were made on the uneven water-absorbent structure with gathers and binding tape, and a wearing test was conducted. As a result, two leaks from the side part occurred. No leaks occurred.
[0044]
(Example 3)
<Preparation of waterproof uneven material>
A meltblown and spunbond (MS) composite nonwoven fabric (18 g / m ² ) comprising a combination of PP meltblown (5 g / m ² ) and PP spunbond (13 g / m ² ) was prepared. On the other hand, a perforated film in which an opening having a diameter of 2 mm was provided on a 30 μm thick PE film mainly composed of LLDPE was prepared. A small amount of hot melt adhesive was sprayed on the spunbonded surface of this perforated film, and MS nonwoven fabric was bonded to this surface to obtain a composite sheet shown in FIG.
[0045]
The water pressure resistance of this composite sheet was tested under the same conditions as in Example 1 to obtain a value of about 200 mmH ² O.
[0046]
<Preparation of water absorbent slurry>
An absorbent slurry was prepared under the same conditions as in Example 1.
[0047]
<Preparation of water absorbing structure>
As in Example 1, the composite of the MS nonwoven fabric and the apertured film was supplied on a belt conveyor equipped with a suction zone with the apertured film facing up, and the water absorbent slurry was supplied thereon. The solvent was removed in the suction zone, and SAP particles as a water-absorbing material were bonded and filled on the exposed surface of the MS nonwoven fabric by MFC to obtain a water-absorbing structure as shown in FIG.
[0048]
<Breathability of water absorbing structure>
When the obtained water absorbing structure was subjected to a breathability test based on the Gurley test of JIS P8117, a value of air permeability (sec / 100 cc) = 160 was obtained.
[0049]
<Waterproof evaluation of water absorbing structure>
Under the water-absorbing structure, 10 layers of commercially available tissue paper are laid, and a glass tube with a diameter of 20 mm is used so as to cover the opening filled with SAP particles, and a column of physiological saline is set up. Water resistance was measured. The SAP in the portion in contact with the physiological saline swelled and swelled and raised the water column to 800 mmH ² O, but the liquid did not leak and the tissue did not get wet.
[0050]
【The invention's effect】
As described above, the water-absorbent 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, and thus the liquid-impermeable sheet. And has two functions of absorber. For this reason, the uncomfortable feeling resulting from the shift | offset | difference of a behavior between an absorber and a liquid impermeable sheet can be eliminated, and the feeling of use of the absorbent 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-absorbent structure of the present invention.
FIG. 3 is a longitudinal sectional view of the water absorbing structure shown in FIG.
FIG. 4 is an explanatory view showing a process for producing the water-absorbing structure of the present invention.
FIG. 5 is a plan view of a liquid-impermeable sheet material used in the water-absorbent structure of the present invention.
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.
8 is a partial longitudinal sectional view of FIG.
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 impervious sheet material 12 Open hole 13 Concave 14 SAP particle 15 Microfibril-like fine fiber 21 Liquid impervious sheet material 22 Liquid permeable nonwoven fabric 23 Groove part 24 Concave part 25 Water absorbing material

Claims (10)

A liquid-impermeable sheet material having a large number of recesses on one surface, and a water-absorbing material containing and fixed in the recesses and containing a highly water-absorbing resin, having both a leak-proof function and a water-absorbing function And
The water-absorbent structure having a funnel-shaped taper in which the concave portion of the liquid-impermeable sheet has a wide upper portion and becomes narrower toward the lower portion .   The water-absorbent structure according to claim 1, wherein the liquid-impermeable sheet material is a thermoplastic film having a thickness of 5 to 50 µm.   The water-absorbent structure according to claim 1, wherein the liquid-impermeable sheet material is a joined body of a thermoplastic film having a thickness of 5 μm to 50 μm and a nonwoven fabric.   There is an open portion or a porous portion that allows liquid to pass through as it is, or the open portion or the porous portion is made of the water-absorbing material. The water-absorbent structure according to any one of claims 1 to 3, wherein the water-absorbent structure is closed and thereby has a leak-proof property.   The water absorbing property according to claim 4, wherein the aperture portion of the liquid-impermeable sheet material is a film having an aperture, and the porous portion is a water-resistant nonwoven fabric bonded to the film so as to block the aperture. Structure. The water absorbent structure according to any one of claims 1 to 5 , wherein the water absorbent material contains 50% or more of a highly water absorbent resin. The water-absorbing material according to any one of claims 1 to 6 , wherein the water-absorbing material is composed of a particulate high water-absorbing resin having an average particle size of 0.4 mm or less and microfibril-like fine fibers that bind the resin. Sex structure. The water-absorbing structure according to any one of claims 4 to 7 , wherein a portion filled with the water-absorbing material has air permeability. The absorbent product comprised with the water absorptive structure of any one of Claims 1-8 .   The slurry is filled into the recess by continuously supplying the slurry containing the particulate superabsorbent resin from the top of the liquid-permeable sheet material having a large number of recesses having openings at the bottom. And the solvent in the slurry permeates and separates the sheet material through the apertures so that only the solid content remains in the recesses, followed by desolvation and drying. Manufacturing method.

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