WO2012132460A1

Movatterモバイル変換

Info

Publication number: WO2012132460A1
Application number: PCT/JP2012/002204
Authority: WO
Inventors: Kenichi Sasayama; Makoto Ichikawa; Kunihiko Katsuragawa; Kazuaki Onishi; Masashi Nakashita
Original assignee: Unicharm Corporation
Priority date: 2011-03-31
Filing date: 2012-03-29
Publication date: 2012-10-04
Also published as: EP2525757A4; AR085729A1; JP5818483B2; TWI603720B; EP2525757A1; TW201302171A; JP2012213516A

Abstract

Water-absorbent articles improved to alleviate an uncomfortable feeling due to water-soluble matter contained in superabsorbent polymer particles are provided. In an absorbent article (1) adapted to be used, for example, as an absorbent structure in a disposable diaper, superabsorbent polymer particles (4) are interposed between opposed surfaces (2a, 3a) of a pair of sheet materials (2, 3) overlapping each other. The superabsorbent polymer particles (4) used in this invention has a water-soluble matter content percentage corresponding to 15% or less of a mass of the superabsorbent polymer particles (4) as measured by immersing them in 0.9% physiological saline.

Description

WATER-ABSORBENT ARTICLE

This disclosure relates to water-absorbent articles containing therein superabsorbent polymer particles and more particularly to water-absorbent articles suitable to be used as an absorbent structure in various types of bodily fluid absorbent wearing articles such as disposable diapers and the other water-absorbent articles such as disposable wipes.

Background

Pad-shaped water-absorbent articles are known to include a pair of sheet materials, at least one of which are water-permeable, and superabsorbent polymer particles interposed between these two sheet materials.

For example, an absorbent sheet disclosed in JP H5-38350 A (PTL 1) is formed by coating a sheet-like absorbent material with pressure-sensitive adhesives, spraying superabsorbent polymer particles thereon, laying another sheet-like absorbent material thereon and compressively integrating these components.

In the absorbent sheet disclosed in JP 2009-131510 A (PTL 2), superabsorbent polymer particles are interposed between an upper sheet and a lower sheet, wherein pockets are defined between the upper sheet and the lower sheet in respective non-bond regions surrounded by a bond region in which the upper sheet and the lower sheet are bonded to each other and these pockets contain therein the superabsorbent polymer particles. The superabsorbent polymer particles are movable within the respective pockets.

JP H5-38350 AJP 2009-131510 A

Summary

The superabsorbent polymer particles of the types used in the prior art as has mentioned above may contain a matter or ingredient which is soluble in water such as urine. The inventors have recognized that, when superabsorbent polymer particles containing a matter or ingredient which is soluble in water such as urine are used in an absorbent article, such as a disposable diaper, such matter or ingredient dissolved in urine after urination may exude on the surface of the absorbent article. In consequence, the surface of the absorbent article may become sticky and slimy and may create a feeling of discomfort when the wearer's skin comes in contact with such sticky and slimy surface.

According to some embodiments of this invention, there is provided a water-absorbent article including a pair of sheet materials at least one of which is water-permeable and superabsorbent polymer particles lying between opposed surfaces of these two sheet materials.

A water-soluble matter content percentage of the superabsorbent polymer particles measured by immersing the superabsorbent polymer particles in 0.9% physiological saline is 15% or less of a mass of the superabsorbent polymer particles.

Fig. 1 is a partially cutaway plan view of a water-absorbent article.Fig. 2 is a sectional view taken along line II-II in Fig. 1.Fig. 3 is a diagram exemplarily illustrating a process of manufacturing a water-absorbent article.Fig. 4 is a partially scale-enlarged diagram illustrating a part of Fig. 3.Fig. 5 is a view similar to Fig. 1, showing one embodiment.Fig. 6 is a view similar to Fig. 5, showing another embodiment.Fig. 7 is a sectional view taken along line VII-VII in Fig. 6.Fig. 8 is a graphic diagram plotting a water-soluble matter content percentage versus the quantity of exudation.

Details of a pad-shaped water-absorbent article 1 according to some embodiments of this invention will be described hereinafter with reference to the accompanying drawings.

Referring to Fig. 1, the absorbingregions 6 are surrounded by thesealing regions 7 and respectively contain thesuperabsorbent polymer particles 4 therein to define liquid absorbing regions. In other words, theabsorbing regions 6 may be referred to as the presence regions of thesuperabsorbent polymer particles 4 in which thesuperabsorbent polymer particles 4 are present at the rate of a predetermined mass per unit area of theinner surface 3a of thelower layer sheet 3. In theabsorbing regions 6, thesuperabsorbent polymer particles 4 are bonded to thelower layer sheet 3 at the rate in a range of 30 to 300 g/m², more preferably at the rate in a range of 40 to 280 g/m² withhot melt adhesive 11 uniformly applied to thelower layer sheet 3 for fixation of thesuperabsorbent polymer particles 4 thereto. The absorbingregions 6 may contain therein a moiety of thesuperabsorbent polymer particles 4 not bonded to thelower layer sheet 3 and an upper limit for a total quantity of thesuperabsorbent polymer particles 4 containable between thelower layer sheet 3 and theupper layer sheet 2 is 400 g/m². While it is preferred that theinner surface 3a of thelower layer sheet 3 and theinner surface 2a of theupper layer sheet 2 facing each other in the respectiveabsorbing regions 6 should not be bonded to each other, theupper layer sheet 2 may be unintentionally bonded to thelower layer sheet 3 over an insignificant area in the course of manufacturing process (See Figs. 3 and 4).

sheets

2, 3. In any way, theupper layer sheet 2 and thelower layer sheet 3 are not to be peeled off from each other even during use of thearticle 1. It should be appreciated here that, in thearticle 1 exemplarily illustrated in Fig. 2, the polymer particle fixing hot melt adhesive 11 and anotherhot melt adhesive 102 to be described later in detail (See Figs. 3 and 4) are applied to overlap each other to compose thehot melt adhesive 12 with which theupper layer sheet 2 and thelower layer sheet 3 are sealed to each other. Such types of hot melt adhesive used in thearticle 1 may be selected from those commonly used in the relevant technical field or to be developed in the future.

Thearticle 1 exemplarily illustrated is configured to be relatively long in the longitudinal direction A. In the longitudinal direction A thereof, eight compartments designated byreference signs 6a through 6h each defined by each of theabsorbing regions 6, i.e., the water-absorbing regions each are arranged. The absorbingregions 6a through 6h respectively haveperipheries 61 contouring respective planar shapes thereof. Theperipheries 61 of the absorbing regions which are adjacent in the longitudinal direction A respectively includeperipheral segments 62 facing each other in the longitudinal direction A and extending in the transverse direction B. For example, theperipheries 61 of the adjacent absorbing

zones

6a, 6b in Fig. 1 include suchperipheral segments 62 facing each other in the longitudinal direction A and extending in the transverse direction B and theseperipheral segments 62 are denoted by

reference signs

62a and 62b.

In thisarticle 1, thesealing regions 7 have oppositelateral segments 7a defined on both sides of thearticle 1 and extending in the longitudinal direction A,end segments 7b defined on opposite ends of thearticle 1 andintermediate segments 7c defined between each pair of theabsorbing regions 6 adjacent in the longitudinal direction A and extending in the transverse direction B as well as connected to thelateral segments 7a. As will be apparent from Fig. 2, theintermediate segments 7c may be referred to as grooves defined between the adjacentabsorbing regions 6 and a dimension W between each pair of the adjacentintermediate segments 7c corresponds to a width dimension of each groove.

Whensuch article 1 is used, for example, as an absorbent structure in a disposable diaper or as a urine absorbent pad in pants for incontinent patient, the longitudinal direction A of thearticle 1 is aligned with the longitudinal direction of the diaper so that a midsection of thearticle 1 in the longitudinal direction A may lie in a crotch region of the diaper. Theupper layer sheet 2 is made of a water-permeable sheet material and adapted to face the wearer's skin, i.e., on a skin-contactable side of thearticle 1.

The use of thearticle 1 for this diaper is capable of achieving various functional effects. For example, urine excreted from the wearer permeating theupper layer sheet 2 in the absorbingregions 6 is absorbed and contained by thesuperabsorbent polymer particles 4 so that the urine does not leak outside. Also in this diaper, by fixing thesuperabsorbent polymer particles 4 to thelower layer sheet 3 formed of the low water-permeable or the water-impervious sheet material, an even distribution of thesuperabsorbent polymer particles 4 in the wearer's crotch region is ensured even if the wearer changes postures in various ways, thesuperabsorbent polymer particles 4 are prevented from concentrating at one side within theabsorbing regions 6. As an advantageous consequence, urine excreted from the wearer onto thearticle 1 may permeate theupper layer sheet 2 over a wide range and may be absorbed and contained by the absorbingregions 6 over a wide range. In addition, issues associated with an uneven distribution of thesuperabsorbent polymer particles 4 in the respective absorbing regions 6 (i.e., the thickness of thearticle 1 may become uneven due to the uneven distribution of thesuperabsorbent polymer particles 4, eventually causing thearticle 1 to compress locally the wearer's skin) may be avoided. In theabsorbing regions 6, thelower layer sheet 3 is coated with thehot melt adhesive 11 but theupper layer sheet 2 is not coated with this and, therefore, thehot melt adhesive 11 is unlikely to interfere with the desired water-permeability of theupper layer sheet 2. Thesuperabsorbent polymer particles 4 fixed to thelower layer sheet 3 serve to prevent theupper layer sheet 2 from moving closer to and being bonded to thelower layer sheet 3 coated with thehot melt adhesive 11 and thereby to prevent a desired flexibility of thearticle 1 from being deteriorated. When thearticle 1 is placed in the diaper's crotch region, a plurality of theintermediate segments 7c extending in parallel to one another as exemplarily illustrated function to facilitate thearticle 1 to curve in the longitudinal direction A of thearticle 1. Each of theintermediate segments 7c functioning in this way has a width dimension W as measured in the longitudinal direction A preferably in a range of 2 to 15 mm.

In one example of thearticle 1 used for the diaper, a water-permeable nonwoven fabric sheet formed of thermoplastic synthetic fibers and hydrophilized such as, for example, an SMS nonwoven fabric (spunbonded/meltblown/spunbonded) nonwoven fabric made of polypropylene fibers and hydrophilized may be used as theupper layer sheet 2. An example of such SMS nonwoven fabric includes two layers of a spunbonded nonwoven fabric made of polypropylene fibers each having a basis mass in a range of 4 to 5 g/m² and a meltblown nonwoven fabric having a basis mass in a range of 0.5 to 2 g/m² interposed therebetween so as to have a basis mass in a range of 10 to 12 g/m² as a whole. It is also possible to use a laminate of two-layered structure (See Fig. 5) such as a laminate including a hydrophilized spunbonded nonwoven fabric and a hydrophilized spunbonded SMS nonwoven fabric as theupper layer sheet 2. Furthermore, it is possible to use a water-permeable perforated plastic film instead of the water-permeable nonwoven fabric as theupper layer sheet 2.

It is possible to use a low water-permeable or a water-impervious nonwoven fabric sheet formed of hydrophobic thermoplastic synthetic fibers as thelower layer sheet 3. For example, the low water-permeable SMS nonwoven fabric sheet including two layers of a spunbonded nonwoven fabric made of polypropylene fibers each having a basis mass in a range of 4 to 6 g/m² and a meltblown nonwoven fabric having a basis mass in a range of 0.5 to 2 g/m² interposed therebetween so as to have a basis mass in a range of 10 to 13 g/m² as a whole may be used as thelower layer sheet 3. It is also possible to use a water-impervious sheet made of a plastic film such as a polyethylene film having a thickness in a range of 0.01 to 0.03 mm or a water-impervious sheet in the form of a laminate including a water-impervious plastic film and a water-permeable or low water-permeable nonwoven fabric as thelower layer sheet 3. Preferably such laminate is formed with the nonwoven fabric lying on the inner side of thearticle 1 and the water-impervious plastic film lying on the outer side of thearticle 1 and thesuperabsorbent polymer particles 4 are bonded to the nonwoven fabric to ensure that the plastic film prevents bodily fluids from leaking through fiber interstices in the nonwoven fabric (See Fig. 5).

As thesuperabsorbent polymer particles 4, those are used having a soluble matter content percentage of 15% or less, more preferably 13% or less as measured on a method for measurement of soluble matter content percentage to be described later in detail. Upon contact with moisture such as urine, water-soluble matter contained in thesuperabsorbent polymer particles 4 may exude together with the moisture on the surface of theupper layer sheet 2 in thearticle 1 and may make the surface sticky and slimy. Thearticle 1 may create a feeling of discomfort when the wearer's skin comes in contact with such sticky and slimy surface. To avoid such problem, in thearticle 1 according to some embodiments of this invention, the soluble matter content percentage in thesuperabsorbent polymer particles 4 is controlled to restrict an amount of water-soluble matter exuding together with urine excreted from the wearer to prevent the surface of theupper layer sheet 2 from becoming uncomfortably sticky and slimy.

Thesuperabsorbent polymer particles 4 preferably exhibit a water-retention ratio in a range of 10 to 50 g/g as measured by a method to be described later in detail. When the superabsorbent polymer particles exhibiting a water-retention ratio less than 10 g/g are used, to ensure a water absorption capacity necessary for thearticle 1, a quantity of the superabsorbent polymer particles per unit area will be necessarily increased and, in consequence, a quantity of the particles which are not fixed in the absorbingregions 6 will unacceptably increase. For thearticle 1 containing such excessive quantity of the particles, it may be difficult to provide the functions as well as the effects expected for thearticle 1 and the article may create a feeling of discomfort against the wearer. If the water-retention ratio exceeds 50 g/g, a large quantity of absorbed moisture may deteriorate the gel strength and the moisture (urine) having been once absorbed may be readily discharged under external pressure.

However, it is desired for thearticle 1 containing thesuperabsorbent polymer particles 4 that a quantity of moisture such as urine as large as possible may be absorbed by thearticle 1 even under external pressure. For this requirement to be satisfied, thesuperabsorbent polymer particles 4 preferably exhibit a pressurized water absorption ratio at least of 15 g/g as measured by a method to be described later in detail.

Furthermore, thesuperabsorbent polymer particles 4 preferably exhibit a water-absorption rate in a range of 1 to 50 seconds as measured by VORTEX method prescribed by JIS K 7224. If thesuperabsorbent polymer particles 4 exhibiting a water-absorption rate exceeding 50 seconds are used in thearticle 1, there is a possibility that the quantity of moisture (urine) has permeated theupper layer sheet 2 but still not absorbed by thesuperabsorbent polymer particles 4 might flow back onto the skin-contactable side of theupper layer sheet 2.

In a specific example of thearticle 1, thesuperabsorbent polymer particles 4 exhibiting a water-absorption rate of about 30 seconds may be used at a rate of a basis mass of 400 g/m² or less. It should be noted here that a quantity of thesuperabsorbent polymer particles 4 to be used is preferably adjusted in consideration of factors such as an area of the absorbingregions 6 and a usage pattern of thearticle 1.

While the hot melt adhesive 11 is fundamentally adapted to be applied to thelower layer sheet 3 in the respective absorbingregions 6 in order to fix thesuperabsorbent polymer particles 4 to thelower layer sheet 3, the hot melt adhesive 11 may be applied to thelower layer sheet 3 also in thesealing regions 7. For example, Fig. 2 illustrates a case in which theinner surface 3a of thelower layer sheet 3 is coated over its entire area with the hot melt adhesive 11 fundamentally adapted to be used for fixation of the particles at a rate of the basis mass in a range of 1 to 12 g/m² so as to be uniformly distributed. An application quantity of the hot melt adhesive 11 in the absorbingregions 3 per unit area is preferably reduced as much as possible in order to prevent the entire surfaces of the respectivesuperabsorbent polymer particles 4 fixed to thelower layer sheet 3 from being covered with the hot melt adhesive 11. The hot melt adhesive 11 may be intermittently applied to thelower layer sheet 3, for example, in a dotted pattern or a beaded pattern or applied so as to cover the whole areas of the respective absorbingregions 6 in a continuous manner. Preferably, in any case, the partial surfaces of the respectivesuperabsorbent polymer particles 4 facing the inner surfaces of the respective absorbing regions are covered with the hot melt adhesive 11 and bonded to theinner surface 3a of thelower layer sheet 3 but the partial surfaces of therespective particles 4 facing theinner surface 2a of the upper layer sheet 2 (See Fig. 2) are not covered with the hot melt adhesive 11 and are ready for rapid absorption of urine.

While thelower layer sheet 3 may be formed of a plastic film instead of a nonwoven fabric, the use of a plastic film may sometimes lead to an increased application quantity of the hot melt adhesive 11 in order to bond thesuperabsorbent polymer particles 4 to this plastic film in a reliable manner. In such a case, thehot adhesive 11 is apt to cover the surfaces of the individualsuperabsorbent polymer particles 4 over unacceptably large areas.

In thearticle 1 used as the component member of the diaper, dimensions of the respective absorbingregions 6 in the longitudinal direction A and the transverse direction B, i.e., the dimensions defining each of the absorbingregions 6 in Fig. 1 in the longitudinal direction A and the transverse direction B may be set to appropriate values depending on a particular size of the diaper. By way of example, it is possible to set these dimensions to a range of 25 to 100 mm and a range of 150 to 250 mm, respectively, and, for the diaper having such dimensions, the number of the absorbingregions 6 is preferably in a range of 5 to 15. Each of thelateral segments 7a and each of theend segments 7b preferably have a width (in the longitudinal direction A) in a range of 5 to 30 mm, respectively.

Fig. 3 is a schematic diagram illustrating a process of continuously manufacturing thearticle 1 and Fig. 4 is a partially scale-enlarged diagram illustrating asuction drum 130 in Fig. 3. Referring to Fig. 3, afirst web 131 corresponding to a contiguous sheet of theupper layer sheets 2 is fed from the right side as viewed in the diagram to aperipheral surface 135 of thesuction drum 130. Thefirst web 131 put in close contact with theperipheral surface 135 under a pressurizing effect by aguide roll 141 and a suction effect directed to the inside of thesuction drum 130 is fed with thesuperabsorbent polymer particles 4 from a polymerparticle feed unit 136 set above thesuction drum 130.

From the left side as viewed in Fig. 4, asecond web 132 corresponding to a contiguous sheet of thelower layer sheets 3 is continuously fed via aguide roll 142 to theperipheral surface 135 of thesuction drum 130. Thesecond web 132 is coated on one surface thereof by afirst coater 121 located on upstream side of thesuction drum 130 with hot melt adhesive 101 and then coated by asecond coater 122 located on downstream side of thefirst coater 121 with hot melt adhesive 102 so that the hot melt adhesive 102 may partially overlap the hot melt adhesive 101.

Thefirst web 131 having been fed with thesuperabsorbent polymer particles 4 and thesecond web 132 having been coated with the hot melt

adhesive layers

101, 102 flow into each other on theperipheral surface 135 of thesuction drum 130 and are bonded to each other with the hot melt adhesive 101 and the hot melt adhesive 102 to form acomposite web 137. Thecomposite web 137 is intermittently cut by acutter 138 into theindividual articles 1. The hot melt adhesive 101 corresponds to the hot melt adhesive 11 and a portion of the hot melt adhesive 101 overlapping the hot melt adhesive 102 is integrated with this hot melt adhesive 102 to form the hot melt adhesive 12 in thearticle 1. Details of the process of forming thecomposite web 137 will be described below with reference to Fig. 4.

Fig. 4 illustrates a step in which thefirst web 131 and thesecond web 132 flow into each other to form thecomposite web 137 on theperipheral surface 135 of thesuction drum 130 shown in a sectional view. Thesuction drum 130 is formed on theperipheral surface 135 thereof with a plurality ofdepressions 141 arranged in the circumferential direction. Each of thesedepressions 141 has a planar shape corresponding to the planar shape of each of the absorbingregions 6 arranged in the longitudinal direction A in Fig. 1. Therespective depressions 141 have a depth dimensioned so as to contain a batch of thesuperabsorbent polymer particles 4 intermittently fed from thepolymer feed unit 136. Thesedepressions 141 are under the suction effect directed to the inner side of thesuction drum 130 so that thefirst web 131 placed on theperipheral surface 135 is deformed along the contours of therespective depressions 141. In the segments of thefirst web 131 deformed in this manner, thesuperabsorbent polymer particles 4 fed from thepolymer feed unit 136 to therespective depressions 141 are deposited. Inperipheral segments 135a each defined between a pair of theadjacent depressions 141 in the form of a raised portion, thefirst web 131 and thesecond web 132 join together and are squeezed between theperipheral segment 135a and afirst pressure roll 143 so as to be bonded to each other as these two

webs

131, 132 pass thepressure roll 143. In this way, thecomposite web 137 is formed. Thecomposite web 137 is transported in a machine direction MD apart from thesuction drum 130 to a pair of second pressure rolls 144 wherein thecomposite web 137 is nipped between these pressure rolls 144 so that thesuperabsorbent polymer particles 4 may be reliably put in contact with the hot melt adhesive 101 and thesuperabsorbent polymer particles 4 may be reliably fixed to thesecond web 132 with the hot melt adhesive 101. While thecomposite web 137 passes through paired second pressure rolls 144 at a slant with respect to the machine direction MD indicated by a horizontal arrow mark in Fig. 3, thecomposite web 137 having left thesuction drum 130 preferably passes through the nip of the paired second pressure rolls 144 in a substantially horizontal posture so that thesuperabsorbent polymer particles 4 may be substantially dispersed substantially in a horizontal direction between thefirst web 131 and thesecond web 132.

While it is preferable for thearticle 1 that a total quantity of thesuperabsorbent polymer particles 4 in the respective absorbingregions 6 are bonded and fixed to theinner surface 3a of thelower layer sheet 3, in some embodiments of this invention, a certain quantity of thesuperabsorbent polymer particles 4 which is free from thelower layer sheet 3 and movable between thelower layer sheet 3 and theupper layer sheet 2 is present in the absorbingregions 6. In order that suchsuperabsorbent polymer particles 4 may be contained within the absorbingregions 6 without problems when theupper layer sheet 2 and thelower layer sheet 3 are formed of a nonwoven fabric, both theupper layer sheet 2 and thelower layer sheet 3 are preferably formed of the nonwoven fabric having sufficiently fine fiber interstices to prevent the movablesuperabsorbent polymer particles 4 from readily breaking thereinto or passing therethrough. To select such an appropriate nonwoven fabric, a nonwoven fabric sprayed on its surface with thesuperabsorbent polymer particles 4 may be oscillated and it may be visually confirmed that none of thepolymer particles 4 breaks into the fiber interstices of this nonwoven fabric. Alternatively, the nonwoven fabric exhibiting an airflow resistance value in a range of 0.40 to 0.04 KPa*s/m, more preferably in a range of 0.30 to 0.05 KPa*s/m may be used. In KPa*s/m, "s" is second and "m" is meter. The higher the airflow resistance, the smaller the interstices of the fibers forming this nonwoven fabric. The airflow resistance as an index for selection of the nonwoven fabric was measured using Air Permeability Tester KES-FB manufactured by KATO TECH CO., LTD.

For thearticle 1, shapes of thearticle 1 itself and the absorbingregions 6 as well as the number of these absorbingregions 6 are not specified and the shapes as well as the number in the illustrated embodiment may be appropriately modified. For example, it is possible to modify the shape of the sealingregions 7 in thearticle 1 of Fig. 1 so that the absorbingregions 6 may be bisected or divided into three parts in the transverse direction B.

Fig. 5 is a view similar to Fig. 1, illustrating one embodiment of this invention. In thearticle 1 of Fig. 5, theupper layer sheet 2 includes a firstupper layer sheet 21 and a secondupper layer sheet 22 overlapping each other and thelower layer sheet 3 includes a firstlower layer sheet 31 and a secondlower layer sheet 32 overlapping each other. The firstupper layer sheet 21 is used to cooperate with the firstlower layer sheet 31 in thearticle 1 to cover and thereby to retain thesuperabsorbent polymer particles 4. As a specific example, theupper layer sheet 21 is a water-permeable nonwoven fabric formed of hydrophilized thermoplastic synthetic fiber and having a basis mass in a range of 10 to 12 g/m², as theupper layer sheet 2 in Fig. 1. The firstupper layer sheet 21 is formed with the absorbingregions 6 and thesealing regions 7 as theupper layer sheet 2 in Fig. 1. The secondupper layer sheet 22 serves to cover and thereby to protect the firstupper layer sheet 21 when thearticle 1 is used for disposable diapers or the like and formed, for example, of a hydrophilized water-permeable spunbonded nonwoven fabric having a basis mass in a range of 10 to 25 g/m². The firstupper layer sheet 21 and the secondupper layer sheet 22 are bonded to each other with hot melt adhesive 36 intermittently applied to the firstupper layer sheet 21 or the secondupper layer sheet 22. It should be noted here that the firstupper layer sheet 21 and the secondupper layer sheet 22 may sometimes be spaced apart from each other (i.e., free of direct attachment to each other) in aperipheral region 38 surrounding the absorbingregions 6. The groove-likeintermediate segments 7c in Fig. 2 are included in thisperipheral region 38.

Thesuperabsorbent polymer particles 4 are bonded to the firstlower layer sheet 31 composing thelower layer sheet 3 with the hot melt adhesive 11 (See Figs. 1 and 2) applied to this firstlower layer sheet 31. The firstlower layer sheet 31 is also bonded to the firstupper layer sheet 21 with the hot melt adhesive 12. While the firstlower layer sheet 31 may be formed of a nonwoven fabric or a plastic film, the exemplarily illustrated firstlower layer sheet 31 is formed of a liquid-pervious SMS nonwoven fabric made of hydrophilized polypropylene fibers having a basis mass of 10 g/m². The secondlower layer sheet 32 composing thelower layer sheet 3 is used to make the outer side of thearticle 1 water-resistant and the exemplarily illustrated secondlower layer sheet 32 is formed of a polyethylene film having a thickness of 15 um. The firstlower layer sheet 31 and the secondlower layer sheet 32 are bonded to each other with hot melt adhesive 37 applied to the secondlower layer sheet 32.

The secondupper layer sheet 22 and the secondlower layer sheet 32 are formed to be the same in shape as well as in size and extend outward beyond peripheral edges of the firstupper layer sheet 21 and the firstlower layer sheet 31 bonded to each other and, along these respective extensions, the secondupper layer sheet 22 and the secondlower layer sheet 32 are put flat and bonded together with the hot melt adhesive 36 and/or 37.

In the diaper using thearticle 1 having such laminated structure, even if a water-soluble matter contained in thesuperabsorbent polymer particles 4 exudates together with a certain quantity of urine to the surface of the firstupper layer sheet 21, for example, as a quantity of urine is absorbed by thearticle 1, the present of the secondupper layer sheet 22 prevents such water-soluble matter from coming in direct contact with the wearer's skin and, in addition, such water-soluble matter is kept apart from the wearer's skin as the water-soluble matter flows toward theperipheral region 38 surrounding the absorbingregions 6. In this way, contact of the water-soluble matter with the wearer's skin may be effectively restricted. In consequence, the problem such that the surface of the secondupper layer sheets 22 might become sticky and slimy and create the wearer to experience a feeling of discomfort against the wearer may be alleviated or eliminated.

Fig. 6 is a view similar to Fig. 5, illustrating another embodiment of thearticle 1 and Fig. 7 is a sectional view taken along line VII-VII in Fig. 6.

Thearticle 1 in Fig. 6 has substantially the same laminated structure as that of thearticle 1 in Fig. 5 wherein theupper layer sheet 2 includes the firstupper layer sheet 21 and the secondupper layer sheet 22 and thelower layer sheet 3 includes the firstlower layer sheet 31 and the secondlower layer sheet 32. Between the firstupper layer sheet 21 and the firstlower layer sheet 31, the absorbingregions 6 in which thesuperabsorbent polymer particles 4 are bonded to the firstlower layer sheet 31 with the hot melt adhesive 11 and thesealing regions 7 in which the firstupper layer sheet 21 and the firstlower layer sheet 31 are bonded to each other with the hot melt adhesive 21 are defined. It should be noted here that thearticle 1 illustrated in Fig. 6 includes only one rectangularabsorbing region 6 having a dimension M in the longitudinal direction and a dimension N in the transverse direction.

In some embodiments of this invention, an exudation quantity of the water-soluble matter contained in thesuperabsorbent polymer particles 4 to the surface of the upper layer sheet was measured using thearticle 1 of which both the dimensions M and N indicated in Figs. 6 and 7 are 10 cm as a sample for measurement. In thisarticle 1 used as the sample for measurement, a spunbonded/meltblown/spunbonded nonwoven fabric (SMS nonwoven fabric) formed of hydrophilized polypropylene fibers and having a basis mass of 10 g/m² was used for the firstupper layer sheet 21 and the firstlower layer sheet 31. As the spunbonded nonwoven fabric composing the SMS nonwoven fabric, a spunbonded nonwoven fabric having a basis mass in a range of 4 to 4.5 g/m² was used. As the meltblown nonwoven fabric composing the SMS nonwoven fabric, the meltblown nonwoven fabric having a basis mass in a range of 1 to 2 g/m² was used. As the polypropylene fibers in the spunbonded nonwoven fabric, polypropylene fibers having a fineness of 1.4 dtex was used and as the polypropylene fibers in the meltblown nonwoven fabric, polypropylene fibers having a fineness in a range of 0.03 to 0.09 dtex was used. As the secondupper layer sheet 22 in thearticle 1, hydrophilized spunbonded nonwoven fabric formed of polypropylene fibers and having a basis mass of 18 g/m² was used.

Respective airflow resistance values of the firstupper layer sheet 21 and the firstlower layer sheet 31 formed in this manner were measured on five sample sheets, respectively, and measured five values are averaged. The averaged value was 0.0595 KPa*s/m on both the firstupper layer sheet 21 and the firstlower layer sheet 31. The average value of the airflow resistance values measured on the secondupper layer sheet 22 was 0.0176 KPa*s/m.

The

hot melt adhesives

11, 36, 37 used in thearticle 1 for measurement was respectively applied using a spiral sprayer. Application quantities were 10 g/m² for the first hot melt adhesive 11, 5 g/m² for the hot melt adhesive 36 and 10 g/m² for the hot melt adhesive 37. Concerning the hot melt adhesive 36, an operation condition of the spiral sprayer was regulated so that a coated area percentage in the absorbingregions 6 may be limited to a range of 15 to 25% of an entire area of the secondupper layer sheet 22, in other words, a coated area percentage on the secondupper layer sheet 22 may be limited to a range of 15 to 25% so that the hot melt adhesive 36 may not interfere with permeation of urine through theupper layer sheet 2.

A coated area percentage of the hot melt adhesive 36 on the secondupper layer sheet 22 was measured using Formation Tester FMT-MIII manufactured by NOMURA SHOJI CO., LTD. For measurement of the coated area percentage, black powder toner was sprayed to the hot melt adhesive 36 applied to the secondupper layer sheet 22 used for the measurement and thereby the hot melt adhesive 36 was colored. The toner having been attached to the nonwoven fabric defining the secondupper layer sheet 22 outside the hot melt adhesive 36 in the course of spraying the toner was blasted off by pressurized air. As use conditions for Tester, a correction sensibility of the camera was set to 100%, a migration factor was set to 1 and an effective size was set to 10 x 10 cm. The absorbingregions 6 of the secondupper layer sheet 22 for measurement was irradiated from its skin-contactable side with luminous ray and a quantity of light transmitted through the absorbingregions 6 as a whole was measured by Tester from the surface opposite to the skin-contactable side coated with the hot melt adhesive 36. A ratio of the quantity of transmitted light to the quantity of irradiated light was calculated to obtain an average light transmittance (%). Tester was used also as image analyzing means to determine a total area colored in black and exhibiting a light transmittance lower than the average light transmittance by 10% or more and this total area per 100 cm² of the area of the absorbingregion 6 was obtained as a coated area percentage of the hot melt adhesive 36.

In Fig. 7, a pressurizingunit 80 including synthetic leather 81 (Part-number PBZ13001 manufactured by Idemitsu Technofine Co., Ltd.) of 10 x 10 cm placed on the secondupper layer sheet 22, anacrylic resin plate 82 of 10 x 10 cm bonded to the synthetic leather and aweight 83 placed on theacrylic resin plate 82 is indicated by imaginary lines. The pressurizingunit 80 is adjusted so as to have a mass per 100 cm² of 3.5 kg.

To measure a quantity of the water-soluble matter exuded from thesuperabsorbent polymer particles 4 on thearticle 1 illustrated in Figs. 6 and 7 as a measuring object, the water-retention ratio and the water-soluble matter content percentage may be previously measured. For thearticle 1 illustrated in Fig. 6, a mass of thesuperabsorbent polymer particles 4 as the measuring object is predetermined so that a water-absorption capacity of 4000 g/m² comparable to a water-retention ratio of thesuperabsorbent polymer particles 4 in the absorbingregion 6 may be ensured. For example, when it is desired to measure a quantity of exudation with respect to thesuperabsorbent polymer particles 4 exhibiting a water-retention ratio of 40 g/g, thearticle 1 using thesuperabsorbent polymer particles 4 in the absorbingregion 7 in a rate represented by the following formula may be used.
(4000 g/m²)/(40 g/g) = 100 g/m²

The quantity of the water-soluble matter's exudation in thisarticle 1 may be measured by following procedures as described below:
(1) At least ninearticles 1 are placed on a horizontal plate in a room at a temperature of 20^oC and a relative humidity of 75%;
(2) Artificial urine of a mass corresponding to a water-retention ratio of thesuperabsorbent polymer particles 4 is evenly and slowly poured to the absorbingregion 6 of thearticle 1 so as to be absorbed by thesuperabsorbent polymer particles 4. The artificial urine having a composition as follows are used. Specifically, aqueous solution containing urea of 2% by mass, sodium chloride of 0.8% by mass, magnesium nitrate hydrate of 0.08% by mass and calcium chloride hydrate of 0.03% by mass is used.
(3) Then, thearticles 1 are respectively transferred into envelopes made of polyethylene and the envelopes are sealed. These envelopes containing therein therespective articles 1 are left at rest in a room at a temperature of 35^oC.Acrylic resin plates 82 each including a piece of artificial leather 81 bonded thereto are respectively weighed to determine a mass X of the respectiveacrylic resin plates 82.
(4) Thearticles 1 having been sealed and left rest are taken out from the respective envelopes three by three after 1 hour, 3 hours and 6 hours and, on thesearticles 1, the quantity of exudation is measured by following the steps (5) to (8) described below.
(5) Thearticles 1 are placed on a horizontal plate in a room at a temperature of 20^oC and a relative humidity of 75%.
(6) A pressurizing unit 80 (See Fig. 7) is placed on each of thearticles 1 and left at rest for 1 minute.
(7) Then, theacrylic resin plate 82 including the artificial leather 81 bonded thereto is weighed to determine a mass Y thereof.
(8) Quantity Z of the water-soluble matter having exuded from thearticle 1 to the surface of theartificial leather 82 and attached thereto is calculated according to a formula as follows:
Z = Y - X

The water-retention ratio of thesuperabsorbent polymer particles 4 used in such measurement is measured by following the procedures as described below:
(1) The superabsorbent polymer particles having a mass W₀ (g) is poured into mesh-envelope made of nylon and immersed into 1 liter of 0.9% physiological saline for 1 hour.
(2) Then, the envelope is suspended for 15 minutes to drain off the physiological saline and thereafter treated by a centrifuge at 850 rpm for 90 seconds.
(3) A mass W₁ (g) of the superabsorbent polymer particles after such treatment is determined and the water-retention ratio H is calculated according to a following formula:
H = (W₁ - W₀)/W₀

TABLES 1 and 2 indicate measurement result of water-retention ratio, water-soluble matter content percentage, pressurized water-absorption ratio, water-absorption rate and, quantity of water-soluble matter's exudation carried out on the commercially available superabsorbent polymer particles (SAP-A, B, C, D, E) respectively exhibiting different water-retention ratios, and evaluation result of feeling of the artificial leather including water-soluble matter exuding thereon.

The values of the water-soluble matter content percentage, the pressurized water-absorption ratio and the airflow resistance listed in TABLES 1 and 2 are measured by the previously described method.

Method of measuring a water-soluble matter content percentage
As a specific example, details of the method using 2.0 g of the superabsorbent polymer particles and 500 g of 0.9% physiological saline will be described below.
(1) Measurement environment
Room temperature: 23 +/- 2^oC
Relative humidity: 75 +/- 3%
(2) Measurement utensils
100ml glass beakers 2
glass beaker No. 1: mass of a₁ g
glass beaker No. 2: mass of a₂ g
500ml glass beaker 1
0.9% physiological saline
magnetic stirrer
(3) Measuring steps
a. 500 g of 0.9% physiological saline is poured into the 500 ml beaker.
b. The magnetic stirrer is rotated at 600 rpm to stir 0.9% physiological saline.
c. 2.0 g of the superabsorbent polymer particles is picked up, added this to 0.9% physiological saline in the step b and stirred for 3 hours.
d. Mixture of the superabsorbent polymer particles and 0.9% physiological saline is filtered by a screen having 75um openings and filtrate is recovered.
e. ADVANTEC No. 6 filter paper is used to suction-filter the filtrate and to collect about 100 ml of filtrate.
f. About 80 ml of the collected filtrate is transferred to the glass beaker No. 1 and weighed to determine an accurate mass (bg) of the filtrate.
g. About 80 g of 0.9% physiological saline is poured into the glass beaker No. 2 and an accurate mass (cg) of 0.9% physiological saline is determined.
h. The glass beakers Nos. 1 and 2 are put into a hot air drying machine and heated at a temperature of 140^oC for 15 hours to convert the content to dry solid matter and a total mass d₁ of the glass beaker No. 1 and a total mass d₂ of the glass beaker No. 2 are determined.
i. A water-soluble matter content percentage (%) of the superabsorbent polymer particles are calculated according to the following formulae.

Dry mass of mixture of superabsorbent polymer particles and 0.9% physiological saline:
P (g) = (d₁) - (a₁)

Dry mass of 0.9% physiological saline:
R (g) = (d₂) - (a₂)

Water-soluble matter content percentage:
Q (%) = {(P/b) x 500 - (R/c) x 500} x 100/2.0

Method of measuring a pressurized water-absorption ratio
A testing circular cylinder is prepared in the form of an acrylic resin circular cylinder having an inner diameter of 30 mm and a height of 60 mm and a bottom formed of 250 mesh nylon net and a mass of this testing circular cylinder is previously determined. 0.1 g of superabsorbent polymer particles is poured into the testing circular cylinder and weighed together with the testing circular cylinder and then the superabsorbent polymer particles are evenly distributed on the bottom of the testing circular cylinder. The testing circular cylinder is set up in a laboratory dish having a diameter of 200 mm and a mass having an outer diameter in a range of 29 to 29.5 mm and shaped to be introduced into the testing circular cylinder is placed on the superabsorbent polymer particles so that a mass par unit area of 20 g/cm² may be ensured. Then, 20 ml of the 0.9% physiological saline is poured into the dish and the testing circular cylinder is kept in this posture for 60 minutes, allowing the superabsorbent polymer particles to absorb the 0.9% physiological saline. After elapse of 60 minutes, the testing circular cylinder containing therein the superabsorbent polymer particles is weighed to determine a mass increment. This increment is decupled to determine a water-absorption capacity of the superabsorbent polymer particles per 1 g and this water-absorption capacity is obtained as the pressurized water-absorption ratio.

TABLE 1 indicates values such as the water-soluble matter content percentage and the water-retention ratio measured on the superabsorbent polymer particles SAP-A through SAP-E used in thearticle 1 based on Figs. 6 and 7 for the purpose of measurement.

TABLE 2 indicates quantities of the superabsorbent polymer particles SAP-A through SAP-E used in therespective articles 1 prepared for the purpose of measurement, quantity of retained water corresponding to a product of the used quantity of respective polymer particles and water-retention ratio thereof, quantity of exudate and evaluation result whether feeling of the artificial leather 82 (See Fig. 7) wetted with exuding water-soluble matter is good or not when testers' fingers come in contact with the surface of theartificial leather 82. Referring to TABLE 2, the used quantity of the superabsorbent polymer particles is previously adjusted so that the water-retention capacity may be ensured in a range of 4000 to 4200 g. Evaluation result whether the feeling is good or not is based on the evaluation by five 40 to 60-year-old testers composed of two males and three females. In TABLE 2, "excellent" means that the quantity of water-soluble matter's exudation was extremely small and correspondingly the surface of theartificial leather 82 scarcely became sticky at any point of the elapsed time in the range of 1 to 6 hours and none of five testers experienced uncomfortable slimy feeling. The evaluation result "good" means that five testers sensed at any point of the elapsed time in a range of 1 to 6 hours the surface of theartificial leather 82 as being slimy but such feeling of sliminess was within an acceptable range for five testers. The evaluation result "poor" means that the surface of theartificial leather 82 caused five testers to have an uncomfortable feeling at any point of the elapsed time in a range of 1 to 6 hours. As will be apparent from TABLE 2, the evaluation result "excellent" or "good" was obtained when the quantity of exudation was 80 mg or less. For the quantity of exudation in a range of 80 mg to 100 mg, the evaluation results having been released by five testers were uneven, i.e., the evaluation result was divided into "good" and "poor". For the quantity of exudation exceeding 100 mg, five testers equally made the evaluation "poor".

Fig. 8 plots a relationship of the water-soluble matter content percentage in TABLE 1 versus the quantity of exudation in TABLE 2. As will be apparent from the graphic diagram of Fig. 8, the relationship of the water-soluble matter content percentage versus the quantity of exudation linearly progresses. Comparison of the evaluation result of feeling in TABLE 2 with Fig. 8 suggests that the evaluation result of feeling is "good" or "excellent" (i.e., the quantity of exudation is 80 mg or less) when the water-soluble matter content percentage of the superabsorbent polymer particles is 15% or less and, more preferably, when the water-soluble matter content percentage is 13% or less.

Thearticle 1 according to embodiments of this invention is applicable not only to the disposable diaper but also to the other various finished products such as a urine-absorbent pad to be used in combination with a diaper or diaper chassis and a urine-absorbent pad to be used in combination with pants for incontinent patients. Thearticle 1 may be used also as the water-absorbent article for absorptive treatment of water such as wipes. When thearticle 1 is used as wipes, a water-permeable or low water-permeable or water impermeable sheet material may be used as thelower layer sheet 3.

The aspect(s) of the present invention described above may be arranged in at least the following features:
(i) A water-absorbent article including a pair of sheet materials at least one of which is water-permeable and superabsorbent polymer particles lying between opposed surfaces of these two sheet materials, wherein:
a water-soluble matter content percentage of the superabsorbent polymer particles measured by immersing the superabsorbent polymer particles in 0.9% physiological saline is 15% or less of a mass of the superabsorbent polymer particles.

The aspects described in the above item (i) may include at least the following embodiments, which may be taken in isolation or in combination with one another:
(ii) An exuding quantity of the water-soluble matter when the superabsorbent polymer particles have absorbed a quantity of 0.9 % physiological saline corresponding to a water-retention ratio of the superabsorbent polymer particles is 80 mg or less.
(iii) The superabsorbent polymer particles are at least partially bonded to one of the opposed surfaces of the two sheet materials with hot melt adhesive.
(iv) The article includes
absorbing regions in which a predetermined quantity of the superabsorbent polymer particles are interposed between the opposed surfaces, and
sealing regions in which the two sheet materials are bonded to each other so as to surround the respective absorbing regions and to prevent the predetermined quantity of the superabsorbent polymer particles interposed between the two sheet materials from escaping the respective absorbing regions.
(v) The water-retention ratio of the superabsorbent polymer particles in the course of absorbing 0.9% physiological saline is in a range of 10 to 50 g/g.
(vi) A pressurized water-absorption ratio of the superabsorbent polymer particles in the course of absorbing 0.9% physiological saline is at least 15 g/g.
(vii) A water-absorption rate of the superabsorbent polymer particles in the course of absorbing 0.9% physiological saline is in a range of 1 to 50 seconds.
(viii) At least one of the two sheet materials is formed of one of a nonwoven fabric of thermoplastic synthetic fibers and a perforated film of thermoplastic synthetic resin and the sheet materials exhibits an airflow resistance value in a range of 0.40 to 0.04 KPa*s/m.
(ix) In one or more embodiments of this invention, the superabsorbent polymer particles are bonded at a rate of 30 to 300 g/m² between the opposed surfaces of the two sheet materials.
(x) The water-permeable sheet material is adapted to face a wearer's skin in use, and
the superabsorbent polymer particles are bonded to the other sheet material.
(xi) The superabsorbent polymer particles have an absorption speed of AS₁ and second superabsorbent polymer particles with a lower absorption speed of AS₂than AS₁ are interposed between the two sheet materials in the absorbing regions.
(xii) The second superabsorbent polymer particles are present in a vicinity of the water-permeable sheet material, whereas the superabsorbent polymer particles are bonded to the other sheet material.
(xiii) The second superabsorbent polymer particles are not bonded to either of the opposed surfaces of the two sheet materials.
(xiv) The water-permeable sheet material is a first upper layer sheet adapted to face a wearer's skin in use, the article further includes a second upper layer sheet that serves to cover and thereby to protect the first upper layer sheet;
the first upper layer sheet and the second upper layer sheet are bonded to each other with hot melt adhesive intermittently applied to the first upper layer sheet or the second upper layer sheet.
(xv) The first upper layer sheet and the second upper layer sheet are spaced apart from each other in a peripheral region surrounding the absorbing regions.

The described aspects and/or embodiments provide one or more of the following effects:
In the water-absorbent articles according to this invention, the water-soluble matter content percentage of the superabsorbent polymer particles interposed between a pair of the sheet materials overlapping each other may be restricted to 15% or less of a mass of the superabsorbent polymer particles to reduce a quantity of the water-soluble matter exuding on the surface of the water-absorbent article when this water-absorbent article absorbs water. In this way, it is possible to overcome the problems that the surface of the water-absorbent article would become sticky and slimy and the article would create a feeling of discomfort against the wearer experience come in contact with such surface of the article.

This application claims the benefit of Japanese Application No. 2011-080894 the entire disclosure of which is incorporated by reference herein.

Claims

A water-absorbent article comprising a pair of sheet materials at least one of which is water-permeable and superabsorbent polymer particles lying between opposed surfaces of these two sheet materials, wherein:
a water-soluble matter content percentage of the superabsorbent polymer particles measured by immersing the superabsorbent polymer particles in 0.9% physiological saline is 15% or less of a mass of the superabsorbent polymer particles.
The article defined by claim 1, wherein an exuding quantity of the water-soluble matter when the superabsorbent polymer particles have absorbed a quantity of 0.9% physiological saline corresponding to a water-retention ratio of the superabsorbent polymer particles is 80 mg or less.
The article defined by claim 1 or 2, wherein the superabsorbent polymer particles are at least partially bonded to one of the opposed surfaces of the two sheet materials with hot melt adhesive.
The article defined by any one of claims 1 through 3, wherein the article comprises
absorbing regions in which a predetermined quantity of the superabsorbent polymer particles are interposed between the opposed surfaces, and
sealing regions in which the two sheet materials are bonded to each other so as to surround the respective absorbing regions and to prevent the predetermined quantity of the superabsorbent polymer particles interposed between the two sheet materials from escaping the respective absorbing regions.
The article defined by any one of claims 1 through 4, wherein the water-retention ratio of the superabsorbent polymer particles in the course of absorbing 0.9% physiological saline is in a range of 10 to 50 g/g.
The article defined by any one of claims 1 through 5, wherein a pressurized water-absorption ratio of the superabsorbent polymer particles in the course of absorbing 0.9% physiological saline is at least 15 g/g.
The article defined by any one of claims 1 through 6, wherein a water-absorption rate of the superabsorbent polymer particles in the course of absorbing 0.9% physiological saline is in a range of 1 to 50 seconds.
The article defined by any one of claims 1 through 7, wherein at least one of the two sheet materials is formed of one of a nonwoven fabric of thermoplastic synthetic fibers and a perforated film of thermoplastic synthetic resin and this sheet material exhibits an airflow resistance value in a range of 0.40 to 0.04 KPa*s/m.
The article defined by any one of claims 3 through 8, wherein the superabsorbent polymer particles are bonded at a rate of 30 to 300 g/m² to one of the opposed surfaces of the two sheet materials.
The article defined by claim 1, wherein
the water-permeable sheet material is adapted to face a wearer's skin in use, and
the superabsorbent polymer particles are bonded to the other sheet material.
The article defined by claim 1, wherein the superabsorbent polymer particles have an absorption speed of AS₁ and second superabsorbent polymer particles with a lower absorption speed of AS₂than AS₁ are interposed between the two sheet materials in the absorbing regions.
The article defined by claim 11, wherein the second superabsorbent polymer particles are present in a vicinity of the water-permeable sheet material, whereas the superabsorbent polymer particles are bonded to the other sheet material.
The article defined by claim 11 or 12, wherein the second superabsorbent polymer particles are not bonded to either of the opposed surfaces of the two sheet materials.
The article defined by claim 1, wherein
the water-permeable sheet material is a first upper layer sheet adapted to face a wearer's skin in use, the article further comprises a second upper layer sheet that serves to cover and thereby to protect the first upper layer sheet;
the first upper layer sheet and the second upper layer sheet are bonded to each other with hot melt adhesive intermittently applied to the first upper layer sheet or the second upper layer sheet.
The article defined by claim 14, wherein
the first upper layer sheet and the second upper layer sheet are spaced apart from each other in a peripheral region surrounding the absorbing regions.