U.S. patent application number 12/620173 was filed with the patent office on 2010-03-11 for highly absorbent composite and method of making the same.
Invention is credited to Ryoichi Matsumoto, Shingo Mori, Migaku SUZUKI.
Application Number | 20100063470 12/620173 |
Document ID | / |
Family ID | 27552659 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100063470 |
Kind Code |
A1 |
SUZUKI; Migaku ; et
al. |
March 11, 2010 |
HIGHLY ABSORBENT COMPOSITE AND METHOD OF MAKING THE SAME
Abstract
A composite structure mainly composed of hydratable fine fibers
in the form of microfibril and a water swellable solid body, the
fibers being obtained from cellulose or derivatives thereof, and at
least part of the surface of the solid body is covered with the
fine fibers. The absorbent composite can be formed in various form
of, for example, particle, pellet, sheet and the like, especially
of a sheet type with a supporting sheet of a non-woven fabric. The
present invention further provides a method of making the composite
structure.
Inventors: |
SUZUKI; Migaku; (Kamakura,
JP) ; Matsumoto; Ryoichi; (Kunitachi, JP) ;
Mori; Shingo; (Ota, JP) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE- 10TH FL.
NEW YORK
NY
10151
US
|
Family ID: |
27552659 |
Appl. No.: |
12/620173 |
Filed: |
November 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09242482 |
Oct 22, 1999 |
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PCT/JP97/04606 |
Dec 15, 1997 |
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12620173 |
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Current U.S.
Class: |
604/367 ;
428/36.1; 428/36.91 |
Current CPC
Class: |
A61F 2013/530145
20130101; Y10T 428/23993 20150401; A61F 13/53 20130101; Y10T
428/1386 20150115; D06M 23/16 20130101; Y10T 428/23921 20150401;
Y10T 428/13 20150115; Y10T 428/1314 20150115; Y10T 428/1348
20150115; Y10T 428/23929 20150401; D06M 23/08 20130101; D21H 21/22
20130101; A61F 13/5323 20130101; Y10T 428/1393 20150115; A61L 15/60
20130101; C08K 7/02 20130101; D06M 23/10 20130101; Y10T 428/296
20150115; A61L 15/28 20130101; D06M 15/07 20130101; Y10T 428/1359
20150115; Y10T 428/23979 20150401; Y10T 428/1303 20150115; Y10T
428/139 20150115; D06M 15/05 20130101; Y10T 428/1352 20150115; Y10T
428/1362 20150115; Y10T 428/23936 20150401 |
Class at
Publication: |
604/367 ;
428/36.91; 428/36.1 |
International
Class: |
A61F 13/53 20060101
A61F013/53; B32B 1/08 20060101 B32B001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 1996 |
JP |
333520/1996 |
May 15, 1997 |
JP |
124623/1997 |
Jul 17, 1997 |
JP |
192159/1997 |
Aug 7, 1997 |
JP |
213222/1997 |
Nov 14, 1997 |
JP |
313368/1997 |
Dec 1, 1997 |
JP |
329830/1997 |
Claims
1. An absorbent tube composed of a supporting sheet consisting of a
fiber web and absorbent polymer component supported by and bonded
to the surface of said supporting sheet, said supporting sheet
being formed into a tube with the surface supporting said absorbent
polymer component being positioned inside.
2. The absorbent tube of claim 1, wherein the cross section of said
supporting sheet is of a closed ring.
3. The absorbent tube of claim 1, wherein the cross section of said
supporting sheet is of an open ring, the two free margins of said
open ring facing each other forming a closed ring by being mutually
bonded at the margins.
4. The absorbent tube of claim 1, wherein the cross section of said
supporting sheet is of an open ring, the two free margins of said
open ring facing each other being mutually connected by a sheet to
form a closed ring.
5. The absorbent tube of claim 1, wherein said supporting sheet on
which said absorbent polymer component is supported has one or more
gussets as formed by folding part of the circumference edges.
6. The absorbent tube of claim 1, wherein said supporting sheet is
a non-woven fabric sheet, and wherein said absorbent polymer
component comprises an absorbent polymer particles which are bonded
to said non-woven fabric sheet by hydratable fine fibers in the
form of microfibril.
7. The absorbent tube of claim 1, wherein said supporting sheet is
an easily extendable non-woven fabric which improves the ability of
said absorbent polymer component to follow possible increase in
volume when swollen.
8. The absorbent tube of claim 7, wherein said easily extendable
non-woven fabric is obtained by stretching and heat setting a spun
bond of bi-component fibers.
9. The absorbent tube of claim 7, wherein said easily extendable
non-woven fabric is obtained by bonding said fiber web partially on
both sides of an elastic net by spun lace method.
10. An absorbent product comprising a liquid pervious inner sheet,
a liquid impervious outer sheet and an absorbent core disposed
between said inner and outer sheets, said absorbent core comprising
a supporting sheet consisting of a fiber web and absorbent polymer
component bonded to one surface of said supporting sheet, and said
supporting sheet being formed in the shape of a tube with the side
on which said absorbent polymer being disposed inside.
11. The absorbent product of claim 10, wherein the cross section of
said supporting sheet is of a closed ring.
12. The absorbent product of claim 10, wherein the cross section of
said supporting sheet is of an open ring, the two free margins of
the open ring facing each other forming a closed ring by being
mutually bonded at the margins.
13. The absorbent product of claim 10, wherein the cross section of
said supporting sheet is of an open ring, the two free margins of
the open ring facing each other being mutually connected by a sheet
to form a closed ring.
14. The absorbent product of claim 10, wherein said absorbent core
is composed of a combination of said absorbent tube and a further
absorbent material.
15. The absorbent product of claim 10, wherein said absorbent core
comprises a plurality of said absorbent tubes.
16. The absorbent product of claim 15, wherein said absorbent tube
are different in shapes or cross sectional area among one disposed
in the center and the ones on the sides of the center one.
17. The absorbent product of claim 16, wherein said absorbent tube
disposed in the center is partially laid in the top and bottom
direction over said absorbent tubes disposed on both sides of the
center absorbent tube.
18. The absorbent product of claim 10, wherein part or parts of
said absorbent tubes are connected to said outer sheet.
19. The absorbent product of claim 10, wherein said absorbent tubes
are connected at part thereof to said inner sheet.
20. The absorbent product of claim 10, wherein said supporting
sheet is a non-woven sheet containing a cellulose component having
water dispersing capability, and wherein said absorbent polymer is
bonded to said non-woven fabric sheet by hydratable fine fibers in
the form of microfibril.
21. The absorbent product comprising the absorbent tube of claim 1.
Description
[0001] This application is a division of U.S. patent application
Ser. No. 09/242,482 filed Oct. 22, 1999 entitled "Highly Absorbent
Composite Compositions, Absorbent Sheets Provided with the
Compositions, and Process for Producing the Same" which is a 371
application of PCT/JP97/04606 filed Dec. 15, 1997 which claims
priority of Japanese Patent Application Number 333520/1996 filed
Dec. 13, 1996 and Japanese Patent Application Number 124623/1997
filed May 15, 1997 and Japanese Patent Application Number
192159/1997 filed Jul. 17, 1997 and Japanese Patent Application
Number 213222/1997 filed Aug. 7, 1997 and Japanese Patent
Application Number 313368/1997 filed Nov. 14, 1997 and Japanese
Patent Application Number 329830/1997 filed Dec. 1, 1997, all the
disclosures of which are herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a new type absorbent
composite wherein a water swellable solid body, particularly
consisting of particles of various sin and shapes from powder to
pellets is improved in functioning and handling characteristics.
More particularly, the present invention relates to a highly
absorbent composite composed of containing an absorbent polymer as
a water swellable solid body and having a shape entirely different
from conventional absorbent materials and a capability of stably
absorbing a liquid of much higher quantity than its own volume and
to a highly absorbent composite mainly composed of the
composite.
[0004] The highly absorbent composite of the present invention can
widely be used in diapers for babies and adults, feminine hygiene
products, products for handling liquid and solid wastes of animals,
and medical blood absorbent products just like conventional highly
absorbent products and thus is particularly useful as a super thin
pulpless absorbent making the best use of the capabilities of a
so-called absorbent polymer. In addition, the absorbent composite
can be used for a cold insulator, water holding material, an
anti-dewing material, covering material of submarine cables,
material for preventing water related accidents.
[0005] In addition, the present invention relates to methods and
apparatuses for making the absorbent composite and the composite
mainly composed of the absorbent composite.
[0006] Moreover, the present invention relates to an absorbent
sheet which provides also the leakage resistance of a conventional
backsheet when the absorbent composite is used in absorbent
products in combination with various sheet substrates, to an
absorbent sheet which provides also the acquisition capability of a
conventional topsheet when the absorbent composite is used in
absorbent products in combination with various sheet substrates,
and to an absorbent sheet which can be used alone providing also
the capabilities of conventional backsheet and topsheet.
[0007] 2. Prior Art
[0008] A main absorbent component used in a absorbent product,
which absorbs water and liquid exudates, is composed of a
combination of fluff type wood pulp and so-called super absorbent
polymer (hereinafter referred to as the "SAP"). However, in recent
years, in order to improve the distribution efficiency of absorbent
products, to reduce the inventory and display space thereof, and to
save natural resources, social needs for reducing the dimensions of
otherwise relatively bulky absorbent products are becoming
strong.
[0009] A means for making an absorbent product more compact and
thinner, in a combination of SAP and pulp, would be to increase the
content of SAP that has a higher absorbency than that of pulp by 2
to 10 times and accordingly decrease the content of pulp.
Eventually, if the content of the SAP is made 100 percent, the
thinnest and most compact absorbent product would be able to be
obtained.
[0010] However, as the content of the SAP increases, when it
absorbs water, so-called "gel blocking phenomenon" due to the
characteristic of SAP occurs. Thus, the absorbent product does not
work as designed. At the present time, it is said that the ratio of
the contents of the SAP and pulp is at most 1 to 1. A structure in
which the ratio of the contents of the SAP to pulp is 2 or higher
to 1, or so-called pulpless in which the content of the SAP is
nearly 100 percent is very difficult to achieve at the present
time. According to the conventional concepts generally applied in
the field of absorbent products, the term "pulpless" means that the
ratio of the contents of pulp to the SAP is approximately 1 or
lower.
[0011] So far, various attempts for the pulpless structure have
been made. A fiber type or web type SAP is made by directly
spinning into acrylic acid type fiber or partially hydrolyzing
acrylic acid type fiber. Another method is to make a web type
absorbent polymer by impregnating a web with a monomer such as
acrylic monomer and then polymerizing the monomer applying
ultraviolet ray or electron beam. Still other method is to make an
absorbent polymer sheet by carboxymethylating a non-woven fabric of
cellulose or the like and then partially cross-linking the
carboxymethyl cellulose.
[0012] However, so far, no successfully commercialized examples
have been reported because of high costs of raw materials and high
capital investments involved.
[0013] Liquid exudates discharged from living bodies are very
different from each other depending upon their environmental and
living conditions, and the frequency of discharging is not constant
among them. Therefore, absorbent sheets used in many kinds of
absorbent products need, responding to varied environs, to exhibit
stably the capability of absorbing quickly and frequently.
[0014] As described above, a conventional two component (pulp and
the SAP) absorbent is capable of meeting the need of frequently
absorbing to some extent by taking advantage of the temporary
retaining by pulp of liquids and the stably retaining by the SAP of
liquids. However, an absorbent product in which the content of the
SAP is made high or the SAP alone is used in order to secure high
absorbency has a serious drawback; upon a liquid being discharged
at first the SAP starts to absorb it all at once and thus an
initial absorbing is very speedy but as the discharging is
repeated, the absorbing speed drastically decreases.
SUMMARY OF THE INVENTION
[0015] A first embodiment of the present invention provides a
highly absorbent composite comprising hydratable fine fibers in the
form of microfibril obtained from cellulose or an derivative
thereof, and water swellable solid particles, at least part of the
surfaces of said water swellable solid particles being covered with
said fine fibers in the form of microfibril.
[0016] Said hydratable fine fibers in the form of microfibril
obtained from cellulose or an derivative thereof useful in the
present invention will be hereinafter referred to as the
"HFFM".
[0017] The absorbent composite can be formed in a three dimensional
structure such as powder type, particle type, pellet type, sheet
type, and any other type, and also in a sheet type with a
supporting sheet of a non-woven fabric or the like as the base.
[0018] The present invention further provides a method of making
the absorbent composite. The method comprises the steps of
dispersing a water swellable solid body and the HFFM, in a
dispersion medium comprising a mixture of an organic solvent and
water, the organic solvent being capable of controlling the
swelling of the water swellable solid body and dispersing the HFFM
and thus being miscible with water, of separating the water
swellable solid body and the HFFM from the resultant dispersion
liquid from the dispersion medium, and of removing the liquid
component and of drying them.
[0019] The absorbent composite of the present invention is
basically a composite of a water swellable solid body and the HFFM
covering the solid body. Examples of a water swellable solid body
are various kinds of polysaccharides, flocculents, super water
swellable absorbent polymer (the SAP) particles and the like. Among
them, a drawback of the SAP, which is that the SAP is not easy to
handle and store because of its high water absorbency, can be
solved by covering it with the HFFM according to the present
invention. In addition, in a structure in which the SAP particles
are bonded together with the HFFM, the SAP particles are each held
in position by the HFFM and an appropriate space surrounding each
particle is secured. Thus, an extremely thin absorbent sheet is
obtained.
[0020] A second embodiment of the present invention provides an
absorbent sheet, wherein a supporting sheet and an absorbent layer
provided on at least either surface of the supporting sheet are
provided and wherein the absorbent layer has the HFFM, the SAP
particles, and a short-cut staple fiber component having longer
fiber length than the average particle diameter of the SAP
particles and has an improved dimensional stability when wet
swollen.
[0021] In the present invention, the short-cut staple fiber
component having longer fiber length than the average diameter of
the SAP particles connects the SAP particles with each other and at
the same time provides a network structure which covers in network
the top surface of a layer formed by the SAP particles and thus
serves to prevent the SAP particles as wet swollen from going
away.
[0022] The present invention further provides a method of making
the absorbent sheet. The method comprises the steps of preparing a
three-component dispersion slurry by adding and dispersing a
short-cut staple fiber component and the SAP particles in a
dispersion liquid wherein the HFFM is dispersed in a dispersion
medium, of forming a layer of the slurry by spreading the
three-component dispersion slurry onto a supporting sheet, of
removing the dispersion medium from the slurry layer, and then of
drying.
[0023] The absorbent sheet of this embodiment of the present
invention consists of four components the SAP particles, the HFFM,
a short-cut staple fiber component, and a substrate fabric
supporting them. The SAP particles are a basic component giving a
water absorbing capability. The SAP is available in various forms
such as film and non-woven fabric besides the above described
particles.
[0024] The HFFM prevents the SAP from settling as the dispersion
stabilizer and also the SAP particles from coagulating with each
other in making the absorbent sheet of the present invention and,
after the absorbent sheet is made, play the role of a binder to
bond the SAP particles together and the SAP with the substrate
fabric. The short-cut staple fiber component takes the SAP
particles into a network structure in cooperation with a supporting
sheet by dividing the SAP particles covered with the HFFM and then
covering the SAP particles in a network form.
[0025] A third embodiment of the present invention provides a
composite absorbent sheet, wherein, in an absorbent sheet provided
with a liquid pervious supporting sheet and an absorbent layer
containing the SAP particles as bonded onto either surface of the
liquid pervious supporting sheet, the absorbent layer forms a
plurality of high absorbing regions having higher absorbing
capability than otherwise as distributed onto the surface of the
liquid pervious supporting sheet in a desired pattern.
[0026] In the composite absorbent sheet of the present invention, a
liquid such as discharged liquid exudates, when it comes into
contact with surface of the liquid pervious supporting sheet of an
absorbent sheet, i.e., the surface where no absorbent layer exists,
is first absorbed by the liquid pervious supporting sheet,
penetrates inside the sheet by virtue of the liquid permeability,
then diffuses, and contacts and is absorbed by an absorbent layer
provided in contact with the opposite side of the surface where the
liquid was discharged. The speed of absorption of the absorbent
sheet as a whole is determined by the speed of absorption and
diffusion into the liquid pervious supporting sheet and by the
speed of the swelling and the absorption which occur in succession
from the surface of the absorbent layer into its inside.
[0027] Therefore, if there is any difference in the thickness or
density of the absorbent layer, as a liquid is discharged, the
swelling and absorption progress first from thinner regions or
regions of lower density. Also, if there is any difference in
particle diameter of the SAP particles contained in the absorbent
layer, the swelling and absorption progress first from regions of
smaller diameters of particles. A basic concept of the present
invention is that differences in absorbing capability caused by
distributing regions of higher absorbency onto the surface of an
absorbent sheet in a desired pattern are made to be reflected in
differences in swelling and absorbing speeds.
[0028] In addition, by giving irregularly shaped circumference to
the absorbent layer, the length of the circumference is made much
longer than a straight or simply curved line of the circumference
which would be if the irregular shape were not given, and
therefore, a liquid once absorbed by the supporting sheet is
absorbed rapidly by the absorbent layer having the long contact
line so that the absorbing speed is thus further improved.
[0029] In order to distribute and form in a desired pattern the
component forming the absorbent layer onto the supporting sheet, a
method of making the component a slurry and applying and fixing the
slurry onto the supporting sheet in a desired pattern meeting
objectives is effective. The method needs to consist of a
dispersing step where a slurry dispersion liquid containing the SAP
particles is prepared, of a coating step where the dispersion
liquid prepared in the dispersing step is applied onto the surface
of the liquid pervious supporting sheet to form a plurality of
regions of higher absorption distributed in a desired pattern and
having higher absorbing capability than otherwise, and of a drying
step where the absorbent layer formed in the coating step is
dried.
[0030] In addition, the present invention provides an apparatus for
working the methods. The apparatus comprises a plurality of nozzles
for applying a dispersion slurry liquid containing the SAP
particles in bands onto either surface of a liquid pervious
supporting sheet running continuously and a supplying means for
supplying the dispersion slurry liquid to the nozzles, and is
characterized in that the supplying means has a mechanism of
pulsating the flow of the dispersion liquid.
[0031] The present invention further provides an apparatus for
making an absorbent sheet wherein a plurality of nozzles for
applying a dispersion slurry liquid containing the SAP particles in
bands onto either surface of a liquid pervious supporting sheet
running continuously and a supplying means for supplying the
dispersion slurry liquid to the nozzles are provided, and wherein
the nozzles each have a plurality of discharging outlets.
[0032] The apparatus can be provided with a hot pressing means for
pressing the liquid pervious supporting sheet as heated after a
dispersion slurry liquid is applied.
[0033] A fourth embodiment of the present invention provides an
absorbent tube, wherein the absorbent tube is composed of a
supporting sheet consisting of a fiber web and the SAP particles or
fibers supported by either surface of the supporting sheet, and
wherein the supporting sheet is formed in a tube shape with the
surface supporting the SAP facing inside.
[0034] The absorbent tube of the present invention has a novel
three-dimensional structure, wherein a space for the SAP to swell
is provided as the inherent structure of the absorbent by forming a
tube of an absorbent sheet supporting the SAP.
[0035] In the absorbent tube of the present invention by virtue of
the above described structure, an absolute quantity of the SAP
existent in a unit area is approximately two times as much as that
of an absorbent of a plane structure, and the absorbing capability
of a unit area is also approximately two times as high as that of
an absorbent of a plane structure. In addition, in the absorbent
tube of the present invention, because the SAP is supported as
attached onto the inner wall of a tube shaped supporting sheet, an
adequate space for swelling is secured, and even if the SAP has
swollen to its maximum absorbing capability absorbing a liquid, the
absorbent as a whole still maintains its flexibility.
[0036] Various types of absorbent sheets have been spreaded so far.
In order to make the function of an absorbent as used in an
absorbent product exhibit to its maximum, the absorbent before it
absorbs a liquid needs to be very thin like an underwear so that a
sufficient space for swelling needs to be provided not to prevent
the swelling of the absorbent. The present invention satisfies the
need adequately, and provides an absorbent exhibiting an
outstanding absorbing capability as assisted by the capability of a
supporting sheet to diffuse a liquid.
[0037] The present invention further provides an absorbent product,
wherein a absorbent tube consisting of a highly absorbent composite
having a three-dimensional structure as described in the above is
disposed in regions of desired absorptions as an absorbent core.
The absorbent tube of the present invention is flat as not yet
swollen and extremely thin like a crushed flat hollow tube, and
when swollen absorbing water rises up as it as a whole swells with
the cross-section area showing a nearby circular shape for the
inside vacancy is filled with the SAP which increases in volume as
swollen. In the absorbent product of the present invention, a
single absorbent tube may be disposed in the absorbing region, but
more preferably, a plurality of absorbent tubes are disposed in
parallel. In the latter case, the structure is more stable and more
flexible, and may more smoothly follow the body movement of the
wearer of the absorbent product.
[0038] A fifth embodiment of the present invention provides an
absorbent sheet, wherein a liquid impervious sheet material one of
whose surfaces has many dents and absorbent material received and
fixed in the dents are provided and thus leakage resistance and
absorbing capability are imparted at the same time. In this
embodiment of the present invention, the absorbent composite forms
a structure where in the many dents provided on one of the surfaces
of a liquid impervious sheet material, absorbent material
containing absorbent polymer particles is filled. The composite
absorbent has leakage resistance and absorbing capability at the
same time satisfying the following requirements:
(1) A liquid impervious sheet material having dents on its surface,
and, preferably, air permeability as well as water proofing is
used. (2) Absorbent material having such absorbing capability that
is as high as possible is used. (3) Absorbent material is filled
and fixed in the dents.
[0039] The commonest form of material having a structure of dents
as used in the present invention is flexible thermoplastic film
such as polyethylene, polypropylene, and EVA of approximately 5 to
50 micron thickness on which many holes or recesses of given shapes
are formed by mechanical punching, thermal forming, vacuum forming,
or the like. Liquid impervious sheet material can also be used
effectively and efficiently part of which has openings formed which
are filled with absorbent material, to be described later, so that
water proofing and leakage resistance are imparted.
[0040] Absorbent material to fill the dents needs to be of fine
sizes to fill a relatively small space, and at the same time to
have a high absorbing capability per a unit volume to secure a
required absorbency with the quantity of the material to fill the
small space.
[0041] The liquid impervious sheet material is, for example,
thermoplastic film of 5 to 50 micron thickness, or a conjugate of 5
to 50 thick thermoplastic film and non-woven fabric. The dents
formed on the sheet material may have the same liquid
imperviousness as otherwise, or, an alternative configuration is
that, in the bottoms of all or part of the dents, opening or porous
portions which, as they are, liquid may pass through may exist and
are stopped up with the absorbent material. The absorbent sheet of
this configuration is liquid impervious as a whole, and at the same
time, with the absorbent material received ad fixed in the
recesses, exhibits a high liquid absorbing capability so that it
combines the two functions of a liquid impervious sheet and an
absorbent.
[0042] As a method of filling and fixing the dents provided on a
liquid impervious sheet material with the SAP or absorbent material
containing the SAP, a method generally applied in making absorbents
for use in diapers and sanitary napkins can be applied as it is.
One preferable method comprises the steps of dispersing, for
example, the SAP and the HFFM in air current, of filling the
dispersed materials into the dents, and of fixing the filled dents
by means of hot melt.
[0043] If each and every dent on a liquid impervious sheet material
is provided with an opening or liquid pervious structure, by
supplying the liquid impervious sheet material onto a conveyor with
a vacuum provided and supplying the slurry from above the liquid
impervious sheet material continuously, the liquid contained in the
slurry passes the sheet material through the opening or liquid
pervious structure to be separated, leaving only the solid
component in the slurry in the dents. Further, by removing the
liquid component and drying, the SAP particles or the SAP particles
and the sheet material are bonded by the HFFM with each other, and
fixed in the positions that they are situated, so that water
proofing is imparted, too. By selecting an appropriate ratio
between the quantity of the SAP and the quantity of the HFFM as
well as the properties of the HFFM, preferable properties can be
imparted as material for an absorbent: while desired leakage
resistance and some air permeability are obtained at the same
time.
[0044] The SAP which is used for these purposes should be
particles, preferably, fine particles, so that it may be held
stably in a small space, and specifically, the diameter of the
particles should be 0.4 mm or less, or, more preferably, 0.3 mm to
0.1 mm. Very fine particles, such as those of 0.1 mm diameter, can
be coexistent with coarser particles, such as those of 0.4 mm or
coarser. In case fiber material such as wood pulp is made to
coexist with the SAP, the more the content of the SAP, the better
the result: the content of the SAP is preferably 50 percent or
higher.
[0045] As discussed in the above, in making the composite absorbent
of the present invention, the HFFM, the SAP and, as required, a
short-cut staple fiber component are dispersed in a dispersion
medium. A particularly effective dispersion medium is a polyvalent
alcohol, which has the tendency to be highly viscous at a low
temperature and logarithmically to reduce in viscosity as heated.
Specifically, by utilizing the behavior in the relation between
temperature and viscosity of a mixed system of a polyvalent alcohol
and water, the transferring and forming are carried out while the
system is stably maintained which is made at a low temperature and
highly viscous at the time of dispersion and storing, and the
forming and removal of the liquid component are made easier while
the system is heated and hydrated at the time of removing the
liquid component so that the viscosity is decreased and the
liquidity is increased.
DETAILED DESCRIPTION OF THE INVENTION
[0046] Hereunder, the elements constituting each structure of the
highly absorbent composite and the absorbent sheet provided with
the absorbent composite of the present invention will be
described.
[0047] In a first aspect of the present invention, the absorbent
composite is composed of the SAP and the HFFM.
[0048] In a second aspect of the present invention, the absorbent
composite is composed of the SAP, the HFFM, and a short-cut staple
fiber component, which is larger than the SAP.
[0049] In a third aspect of the present invention, either of the
absorbent composites of the first and the second aspects forms an
absorbent sheet combined with a supporting sheet.
[0050] If components are extracted from these absorbent composites
and these absorbent sheets to be made by combining the absorbent
composites, the following four components will come out.
[0051] First of all, each component will be described:
(1) SAP Particles
[0052] Absorbent polymer particles, herein called the "SAP", are
generally carboxy methyl cellulose, polyacrylic acid and
polyacrylates, cross-linked acrylate polymers, starch-acrylic acid
grafted copolymers, hydrolysates of starch-acrylonitrile grafted
copolymers, cross-linked polyoxyethylene, cross-linked
carboxymethyl cellulose, partially cross-linked water swellable
polymers such as polyethylene oxide and polyacrylamide,
isobutylenemaleic acid copolymer, etc. Base polymer particles are
obtained by drying any of these polymers. Then, after treatment is
applied to increase the cross-linking density of the surface of the
particles, and at the same time, a blocking inhibitor is added to
control the blocking of product particles due to absorbing
moisture.
[0053] Also, an amino acid cross-linked polyaspartic acid which is
biodegradable or a microorganism based highly absorbent polymer
which is a cultured product of Alcaligenes Latus is added, too.
[0054] SAP products are available on the market in such forms as
particles, granules, films, and non-woven fabrics. The SAP product
in any of such forms can be used in the present invention. A
preferable SAP product for the present invention is in such forms
as particles, granules, pellets, flakes, short needless and the
like which can be uniformly dispersed in a dispersion medium. In
this specification of the present invention, the term "particle(s)"
is used to generally mean any of these forms.
(2) HFFM
[0055] In the present invention, a micro-network structure holding
the SAP particles in position is fixed with the HFFM. The structure
prevents the SAP particles from coagulating with each other, and
stabilizes and makes uniform dispersion condition in making the
composite absorbent of the present invention, and serves as a
binder for binding the SAP particles with each other and the SAP
with a supporting sheet after drying is carried out.
[0056] The HFFM is, in general, extremely fine fibrous material of
2.0 to 0.01 microns in average diameter, and of 0.1 microns or
finer on average, and sufficiently water resistant to prevent the
structure from collapsing immediately after or when the SAP absorbs
water and so swells, and besides, has such properties as do not
hinder the permeability of water and the swelling of the SAP. What
is specially noteworthy here is that the HFFM has an extremely
strong hydratable property of binding with water. By virtue of the
strong hydratable property, the HFFM hydrates when dispersed in a
medium containing water to show a high viscosity which serves to
maintain a stable dispersion condition.
[0057] A characteristic of the hydrating property of microfibril is
a high amount of retained water. For example, the desired hydrating
property of microfibril after their dispersion is centrifuged at
2,000 G for 10 minutes as calculated by the following formula
should be 10 ml/g or higher, and preferrably 20 ml/g or higher:
Amount of water retained (ml/g)=Precipitated volume
(ml)/Microfibrils (g)
[0058] In this specification of the present invention, the term
"HFFM" is used to mean generally strongly hydratable fibrous
materials in the form of microfibril. In some cases, the HFFM of
2.0 microns or larger in average diameter can be used, and may be a
mixture of so-called fibrils and the HFFM.
[0059] The HFFM can be obtained by microfibrillating cellulose or a
cellulose derivative. For example, the HFFM is obtained by grinding
and sufficiently beating wood pulp. The HFFM is called
"microfibrillated cellulose (MFC)", and if further fibrillated, is
called "super microfibrillated cellulose (S-MFC)".
[0060] Also, the HFFM can be obtained by grinding and sufficiently
beating finely cut fiber of man-made cellulosic fiber such as
Polynosic modified rayon staple fiber, Bemberg cuprammonium rayon
yarn, and solvent spun Lyocell rayon fiber.
[0061] Alternatively, the HFFM can also be obtained by metabolizing
microorganism. In general, acetic acid bacteria such as Acetobactor
Xylinum is cultivated, while stirred, in a nutrient containing an
appropriate carbon source so as to generate crude HFFM, which is in
turn refined to obtain the HFFM. Such HFFM is called "bacteria
cellulose(BC)".
[0062] Also, so-called fibril type material which is obtained by
coagulating under a shear force a copper ammonium solution of
cellulose, an amine oxide solution of cellulose, an aqueous
solution of cellulose xanthate, or an acetone solution of
cellulose, all of which can be spun into fibers, is refined to
obtain microfibril-type material, which material can also be used
for the present invention. The details of the HFFM are described in
Japanese Patent Examined Publication Nos. SHO 48-6641 and SHO
50-38720.
[0063] Such HFFM is commercially available under trademarks
"CELLCREAM" (made by Asahi Chemical Industry Co. Ltd.), "CELLISH"
(made by Daicel Chemical Industries, Ltd.), and so forth.
[0064] MFC, S-MFC, and BC are particularly preferable for the
present invention. The technical details of the S-MFC are described
in Japanese Patent Publication No. HEI 8-284090, and of the BC in
Japanese Patent Examined Publication No. HEI 5-80484.
[0065] How to use the MFC and the S-MFC, (both being hereinafter
referred to as the "MFC") is explained in detail below. The MFC
which is concentrated to approximately 30 percent of solid content
is available on the market. To use such concentrated MFC, an
additional procedure of diluting and refining such MFC is required,
which requires an additional time, and the concentrating needs an
additional cost. For the present invention, the MFC whose
concentrated solid content is 10 percent or lower is preferable.
However, if the MFC is diluted to 2 percent or lower, the water
content will become too high, and the selection of the contents of
the MFC in an organic solvent/water mixture system will be too
narrow. In case the MFC in a diluted system like this is used, it
is recommended that a organic solvent/water system in which an
organic solvent to be used in a dispersion medium is used rather
than a simple water system in microfibrillating raw material pulp.
Hence, a dispersion liquid of the MFC which is diluted to around 2
percent can also be used for the present invention.
[0066] How to use the BC is also described in detail below. The BC
is obtained as a metabolized product of microorganism. Depending on
the methods of cultivating and harvesting, the concentrations and
the forms of the BC will be different. In order to obtain as
uniform concentrations and forms as possible, a refining treatment
is recommended. Macerating harvested and refined BC which is
diluted to 2 percent or lower by means of a mixer or a defibrator
will make finer and more uniform HFFM in coagulated condition, and
its viscosity will be much increased and its capacity of binding
the SAP will also be improved. For the present invention,
therefore, the use of the BC which is refined is recommended.
(3) Short-Cut Staple Fiber Component
[0067] The preferable denier of short-cut staple fibers
constituting a short-cut staple fiber component is 10 or more times
as coarse as that of the MFC. The average denier is preferably
approximately 0.01 denier or corner and approximately 3.0 denier or
finer.
[0068] In the present invention, the length of short-cut staple
fibers constituting a short-cut staple fiber component is an
important element. The short-cut staple fibers which are to divide
in sections the SAP particles covered by the MFC and to cover the
particles in a network structure need to have longer fiber length
than the average diameter of the SAP particles. In general, the
average particle diameter of the SAP available on the market is
approximately 0.1 mm to 0.6 mm.
[0069] The SAP which is made by dispersion polymerization has
relatively small particle diameter. If such SAP is used, short-cut
staple fibers which are relatively short can adequately be used. On
the hand, if the SAP in pelletized or flake form is used, short-cut
staple fibers which are relatively long should preferably be
used.
[0070] These short-cut staple fibers play the role of covering
swollen SAP. If the short-cut staple fibers swell or dissolve in
the same way as the SAP, they will not be effective. The short-cut
staple fibers, therefore, need to have a property that they will
not swell or dissolve in water.
[0071] The short-cut staple fibers which can be effectively used
for the present invention are grouped into the following two
kinds:
(i) Pulp State Fibers
[0072] Typical pulp fibers are wood pulp obtained by digester
reclaiming needle- or broad-leaved trees, linter pulp obtained with
cotton linter as raw material, or the like. Other pulp state fibers
are obtained by shear coagulation, flush spinning, or spray
spinning of polymer solutions to make solidified fibers: acetate
(ACe) fibril, polyacrylonitrile (PAN) fibril, polyethylene (PE)
based synthetic fiber pulp, polypropylene (PP) based synthetic
fiber pulp or the like are available. In addition, in case fine SAP
is used, pulp state fiber obtained from strained lees of beet or
coffee beans can also be used as the short-cut fibers.
[0073] PP and PE based synthetic fiber pulps are easy to thermally
melt, and as such preferably used to make more stable structure by
thermal treatment.
(ii) Short Cut Synthetic Fibers
[0074] Of cellulosic fibers such as rayon, Polynosic modified
rayon, and Lyocell, short-cut staple fibers and their fibrillated
materials of 10 mm or shorter in fiber length made for making
paper. [0075] Short-cut staple fibers such as PET, PP, PVA, and
PAN, and short-cut staple fibers of bicomponent fibers such as low
melting point polyester/PET, PP/PE, and PE/PET. [0076] Short-cut
fibers of very fine fibers obtained by blending of different
polymers, or by spinning is land-like fibers.
[0077] Particularly, bicomponent fibers such as PE/PET, PE/PP, and
low melting point polyester/PET are preferable to aim at
stabilizing the SAP by heat treatment through utilizing the effects
of the component in the composite fibers that is easy to thermally
dissolve. Also, those of such fibers on which an antibacterial
agent or a deodorant is applied are preferable.
(4) Supporting Sheet
[0078] A supporting sheet functions as follows: through binding the
SAP particles covered and bonded by the MFC to a supporting sheet,
the strength and dimensional stability are improved, and the liquid
to be absorbed through the supporting sheet is diffused and
distributed, and the SAP particles are stopped up in the dents,
raised fibers, entangled fibers, or vacancies which are likely to
exist on the supporting sheet so that the stability is
achieved.
[0079] The supporting sheets which can be used for the present
invention are described in detail here: In the present invention
porous sheets such as dry laid fluff pulp mat and its bonded sheet,
wet formed pulp mat, carded dry laid non-woven fabric, spun lace,
spunbond, melt-blown non-woven fabric, and non-woven fabric made of
opened tow of acetate or polyester fibers can be used. A supporting
sheet is preferably of a bulky structure to hold and stabilize the
SAP particles in its spaces. As for the bulkiness of the supporting
sheet, an apparent density as calculated from a thickness measured
using a thickness gauge (as described later) and a weight should be
0.2 g/cm.sup.3 or less, and preferably 0.1 g/cm.sup.3 or less.
[0080] To obtain such bulky non-woven fabric, the following means
are taken:
<Web Comprising a Combination of Finer Denier Fibers and Coarser
Denier Fibers>
[0081] While coarser denier fibers are high in resilience and
compression resistance, but a web of such coarser fibers is not
high in bonding strength, finer fibers give the opposite tendency.
Therefore, it is preferable to combine both types of fibers. Such
combination is obtained by blending coarser denier fibers and finer
denier fibers or laying a layer of coarser denier fibers on top of
a layer of finer denier fibers. To achieve an object of the present
invention, a two-layer structure, particularly, a non-woven fabric
comprising a combination of a layer of hydrophilic fibers which are
relatively high in density and of finer denier and a layer of
hydrophobic fibers which are relatively low in density and of
coarser denier, is preferable.
<Non-Woven Fabric Given Bulkiness>
[0082] In addition to combining fibers of different deniers,
shrinkable fibers can be combined. By shrinking such shrinkable
fibers, an uneven surface having dents or a corrugated surface
having furrows is made, which is a method of making a bulky
supporting sheet as is suitable for the present invention.
<Bulky Supporting Sheet Whose Surface is Treated>
[0083] By flocking a non-woven fabric of a smooth surface or
raising a relatively thick non-woven fabric mechanically, a bulky
supporting sheet suitable for the present invention can be
made.
[0084] The composite absorbent sheet of the present invention
comprising the above-described four components is required to have
the following structure in order to fully exhibit the functions as
are expected of an absorbent sheet: the sheet needs to have a
stable structure so that when it is dry it can be folded, sated and
stretched to extend, and formed to be corrugated, and when it is
worn to absorb body exudates, it needs to have outstanding
absorbing and diffusing capabilities, and after it is used, no SAP
particles should exfoliate or come off.
[0085] Even if the absorbing rate is high, the sheet should not
have such structure which may collapse. On the other hand, even if
the SAP particles are stably fixed, if the sheet takes a long time
to absorb and swell, it will not be suitable for the present
invention. Hence, an important requirement of the present invention
is how best the above-described four components are combined in a
rational way.
(5) Combinations of the Four Components
[0086] Next, various combinations of the four components and their
advantages are described in detail below:
(a) Combination of Supporting Sheet and Short-Cut Staple Fibers
[0087] Whether a supporting sheet is hydrophilic or hydrophobic
determines desirable properties of short-cut staple fibers to be
used in combination with the supporting sheet. That is to say, in
case the supporting sheet is of hydrophobic fibers such as PP and
PET, short-cut staple fibers to be combined with the supporting
sheet are preferably cellulosic fibers such as wood pulp and
fibrillated Lyocell. By using such fibers, the absorbency and
diffusion will be much improved. On the other hand, in case
hydrophilic fibers such as rayon are used, they should be combined
with PE synthetic pulp, or short cut PE/PET bicomponent fibers,
which will maintain a preferable balance between the absorbency and
diffusion and the retention of form.
(b) Combination of Supporting Sheet and Heat Meltable Short-Cut
Staple Fibers
[0088] To obtain a good wet stability of a absorbent sheet, heat
setting a combination of a supporting sheet of a specified
structure with short-cut staple fibers is preferable, which makes
it possible to obtain a strong structure.
[0089] For example, if a carded web of 15 g/m.sup.2 consisting of
1.5 denier rayon fiber and a carded web of 15 g/m.sup.2 consisting
of 6 denier PET fiber are water-jet entangled, then a web of a two
layer structure having a strongly hydrophilic bottom layer and a
bulky top layer is obtained. On the other hand, by dispersing a
short-cut staple fiber (a bicomponent fiber of PET/low melting
point polyester which is easy to heat melt, of 1.2 denier and 2 mm
fiber length) in the MFC/SAP slurry, a co-dispersed slurry is
obtained, and by spreading this co-dispersed slurry onto the PET
layer of the two layer web, a solid layer is obtained. Next, by
drying and then heat setting this solid layer, a network structure
where PET of the supporting sheet and easy to heat melt polyester,
of the short-cut staple fiber component are thermally fused is
formed, in which network structure the SAP particles are contained
in closed spaces.
[0090] In a structure like this, when liquid is absorbed, the
liquid is rapidly supplied from the hydrophilic supporting sheet
layer to the SAP particles to start swelling, and even after
sufficiently swollen, the SAP will hardly come off the supporting
sheet. The kinds of fibers forming the bulky layer of the non-woven
fabric of a two layer structure and the combinations with the
short-cut staple fibers suitable to such bulky layer fibers are
shown below:
TABLE-US-00001 Bulky fiber component of a supporting sheet of a
Short-cut staple fiber component to be two layer structure added as
slurry Coarser denier PE/PET PE synthetic pulp, finer denier PE/PET
Coarser denier PE/PET PE synthetic pulp, finer denier PE/PET
Coarser denier PET Finer denier PET/easy-to-melt polyester Coarser
denier Rayon Easily-soluble-in-hot-water PVA fibers
(c) Blending Ratio of MFC and Short-Cut Staple Fibers
[0091] In general, short-cut staple fibers are added to a slurry of
the MFC to provide a two-component dispersion liquid, and, the SAP
particles are added further to provide a three-component slurry.
The three component slurry is spreaded onto a supporting sheet. In
the three-component slurry, if the ratio of short-cut staple fibers
to the MFC in quantity is too high, the MFC will be used only to
cover and bond the short-cut staple fibers and decease the bonding
efficiency of the SAP, and the stability of the slurry becomes
lower. On the other hand, if the quantity of short-cut staple
fibers is too small, the desired network function will not be
obtained. The ratio of the MFC (P) and short-cut staple fibers (Q)
ranges between P/Q=1/5-5/1, and preferably P/Q=1/3-3/1.
[0092] In the present invention, as described in the above, the
three components, the SAP, the HFFM, and a short-cut staple fiber
component as required, are dispersed in a dispersion medium. The
dispersion medium is described below:
[0093] To handle the SAP particles and the HFFM, and as required, a
short-cut staple fiber component as a stable slurry-like dispersion
liquid, it is important to select an appropriate dispersion medium.
If the SAP is slurry-like already from the beginning of its making
process, for instance, in a system such as a dispersion
polymerization of acrylic acid where polymerization reaction is run
in a cyclohexane/water system, by cross-linking in dispersion (if
necessary) after polymerization reaction is finished and then
adding to the slurry a water dispersion liquid of the HFFM or a
solvent/water dispersion liquid while the liquid is stirred, a
stable slurry containing partially swollen SAP and the HFFM can be
obtained.
[0094] To obtain a stable dispersed slurry using dry SAP available
on the market and the HFFM, and as required, the short-cut staple
fiber component, it is preferable to disperse them in a mixture
medium of water and a organic solvent.
[0095] If the SAP particles, the HFFM, and as required, the
short-cut staple fiber component are dispersed in a dispersion
medium like this consisting of an organic solvent and water, a
dispersion liquid where the HFFM and the SAP particles are
uniformly and stably dispersed is obtained owing to the viscosity
generated by the combination of the HFFM and the dispersion
medium.
[0096] As organic solvents used for the present invention, alcohols
such as methanol, ethanol, and isopropyl alcohol, polyvalent
alcohols such as ethylene glycol, diethylene glycol, propylene
glycol, low molecular weight polyethylene glycol, and glycerin, and
representative water soluble organic solvents such as acetone,
methyl ethyl ketone, dioxane, and dimethyl sulfoxide are available.
In using low boiling point alcohols, an apparatus may need to be of
an explosion proof construction because of their high volatility
and flammability. On the other hand, ethanol and propylene glycol
are preferable because of their safety to the environment and to
the skin of a wearer and low possibility of remaining in a product.
To any of these solvents, a water insoluble solvent such as
cyclohexane may be added in a quantity that does not interfere with
dispersion.
[0097] As a dispersion medium used to maintain a condition where
the HFFM, the SAP particles, and as required, the short-cut staple
fiber component are uniformly dispersed, without being coagulated
and settling, for a relatively long period of time, solvents of a
group of polyvalent alcohols are particularly preferable. Solvents
of a group of polyvalent alcohols are water soluble, and do not ice
even below 0.degree. C. or lower as are mixed with water showing a
highly viscous condition, and thus can be stably stored for some
time. As the temperature goes up, the viscosity will decrease,
which makes easier the transfer by means of a pump and forming of
the composite sheet.
[0098] Examples of polyvalent alcohol solvents are ethylene glycol,
propylene glycol, diethylene glycol, triethylene glycol, low
molecular weight polyethylene glycol, and glycerin. The viscosity
of the polyvalent alcohol solvents will vary with the temperature
very much. For example, as shown in Table 1 below, the viscosity
greatly changes for the difference of 30.degree. C. between
20.degree. C. to 50.degree. C.
TABLE-US-00002 TABLE 1 Viscosity (cp) Solvents 20.degree. C.
50.degree. C. Ethylene glycol 22.0 7.3 Propylene glycol 56.0 8.6
Diethylene glycol 30.0 11.5 Triethylene glycol 49.0 14.0 Glycerine
1412.0 142.0
[0099] A manufacturing process can be efficiently designed through
incorporating this change in viscosity successfully in the process.
However, a drawback of polyvalent alcohol solvents is that, because
they show a high viscosity even when they contain water, they may
cause uneven coating in coating a substrate sheet material because
they do not fit well with the substrate material due to their
hardly penetrating the material. In such case, adding of methanol
or ethanol to combine with this polyvalent alcohol solvent, for
example, applying of a three-component system, PG/ethanol/water,
may be effective.
[0100] The slurry obtained in the way described in the above which
consists of the SAP particles, the HFFM, and as required, a
short-cut staple fiber component forms an absorbent layer as
applied on the surface of a liquid pervious supporting sheet. In
general, the slurry is applied onto the whole surface of the
absorbent sheet uniformly and evenly, but depending upon the uses,
can be applied in an appropriate pattern.
[0101] In the event that the absorbent layer is formed in a
pattern, a liquid pervious supporting sheet is a substrate
supporting the absorbent layer and concurrently, plays the role of
solid-liquid separating from the slurry in the manufacturing
process. It is, therefore, preferable that the components of a
supporting sheet have affinity to an absorbent layer and that at
the same time the supporting sheet is of a structure having fine
openings through which solid does not permeate, but liquid does
permeate. For this purpose, a non-woven fabric made of natural
fiber, chemical fiber and synthetic fiber provides a preferable
supporting sheet. Especially, in case the HFFM of cellulose fiber
is used as a bonding agent, cellulose fiber which has a bonding to
hydrogen is preferably combined to make a supporting sheet.
[0102] In the present invention, an absorbent layer is formed by
applying the above-described slurry onto the surface of a liquid
pervious supporting sheet, and it is required that as a result of
such application of the slurry a plurality of highly absorbing
regions having higher absorbing capability distributed in a desired
pattern need to be formed.
[0103] A representative means of forming an absorbent layer as
non-uniformly distributed is to form a distribution in a pattern by
pulsating in some appropriate way the discharging quantity or width
of a slurry dispersion liquid or to form the absorbent layer yet to
be solidified after the slurry is applied.
[0104] Means for pulsating the dispersion liquid as discharged is
to use a plunger pump or a tube pump which discharges the liquid
with pulsation. When a pump which does not pulsate the quantity of
discharge is used, a device of giving pulsation needs to be
installed at the side of discharging.
BRIEF DESCRIPTION OF THE DRAWINGS
[0105] FIG. 1 is a graph showing the relationship between the
concentration and the viscosity of the HFFM in a solvent,
[0106] FIG. 2 is an explanatory diagram showing a process of
obtaining the HFFM from cellulose;
[0107] FIG. 3 is a graph showing the concentration of an organic
solvent and the swelling rate of the SAP in a dispersion
medium;
[0108] FIG. 4 is a graph showing the relationship between the
viscosity of ethylene glycol and of propylene glycol and the
temperature from minus 10.degree. C. to 100-140.degree. C.;
[0109] FIG. 5 is a graph showing the relationship between the
viscosity of propylene glycol and the temperature in an aqueous
solution for the cases of mixing ratios of 4/6, 6/4 and 8/2;
[0110] FIG. 6 is an explanatory diagram showing a concept of
forming various absorbent composites from slurry dispersion
liquids;
[0111] FIG. 7 is a sectional view of an absorbent composite
embodying the present invention; FIG. 7(a) shows an absorbent
composite in particles, and FIG. 7(b) shows an absorbent composite
in flake;
[0112] FIG. 8 shows a sheet material consisting of an absorbent
composite embodying the present invention; FIG. 8(a) is a schematic
sectional view and FIG. 8(b) is a sketch of a microphotograph
thereof;
[0113] FIG. 9 shows another sheet material consisting of an
absorbent composite embodying the present invention; FIG. 9(a) is a
schematic longitudinal section and FIG. 9(b) is a sketch of a
microphotograph thereof;
[0114] FIG. 10 is a schematic longitudinal sectional view of a
composite sheet material embodying the present invention;
[0115] FIG. 11 is a longitudinal sectional view of a composite
sheet material embodying the present invention;
[0116] FIG. 12 is a longitudinal sectional view of a composite
sheet material embodying the present invention;
[0117] FIG. 13 is a longitudinal sectional view of a composite
sheet material embodying the present invention;
[0118] FIG. 14 is a partial perspective view of a composite sheet
material embodying the present invention;
[0119] FIG. 15 is a longitudinal sectional view of a composite
sheet material embodying the present invention;
[0120] FIG. 16 is an explanatory drawing typically showing an
example of an absorbent sheet having a distribution of
patterns;
[0121] FIG. 17 is an explanatory drawing typically showing another
example of an absorbent sheet having a distribution of
patterns;
[0122] FIG. 18 is an explanatory drawing typically showing still
other example of an absorbent sheet having a distribution of
patterns;
[0123] FIGS. 19(A), (B) and (C) are longitudinal sectional views of
different forms of an absorbent tube embodying the present
invention;
[0124] FIG. 20(A) is a sectional view of an absorbent sheet which
can be used for the present invention, and FIG. 20(B) is a cross
sectional view of an absorbent tube consisting of the absorbent
sheet of FIG. 20(A);
[0125] FIG. 21(A) is a sectional view of an absorbent sheet which
can be used for the present invention, and FIG. 21(B) is a cross
sectional view of an absorbent tube consisting of the absorbent
sheet of FIG. 21(B);
[0126] FIG. 22 is a cross sectional view of another example of an
absorbent tube of the present invention;
[0127] FIG. 23 is a plan view of an example of an absorbent product
of the present invention;
[0128] FIG. 24 is a fragmentary sectional view taken along section
line A-A of FIG. 23;
[0129] FIG. 25 is a sectional view of another absorbent product of
the present invention as shown in the same way as in FIG. 23;
[0130] FIG. 26 is a sectional view of other absorbent product of
the present invention as shown in the same way as in FIG. 23;
[0131] FIG. 27 is a sectional view of still other absorbent product
of the present invention as shown in the same way as in FIG.
23;
[0132] FIG. 28 is a sectional view of an absorbent tube, as
swollen, used in the absorbent product of the present invention as
shown in FIG. 24;
[0133] FIG. 29 is a sectional view of still other absorbent of the
present invention as shown in the same way as in FIG. 23;
[0134] FIG. 30 is a sectional view of still other absorbent of the
present invention as shown in the same way as in FIG. 23;
[0135] FIG. 31 is a cross sectional view of other example of the
absorbent tube of the present invention;
[0136] FIG. 32 is a cross sectional view of other example of the
absorbent tube of the present invention;
[0137] FIG. 33 is a cross sectional view of other example of the
absorbent tube of the present invention;
[0138] FIG. 34 is a cross sectional view of other example of the
absorbent tube of the present invention;
[0139] FIG. 35 is a cross sectional view of other example of the
absorbent tube of the present invention;
[0140] FIG. 36 is a sectional view of a supporting sheet which can
be used to constitute the absorbent tube of the present
invention;
[0141] FIG. 37 is a sectional view show the condition where the SAP
particles are carried and held by the supporting sheet of FIG.
37;
[0142] FIG. 38 is a fragmentary sectional view of an absorbent
product constituted by using an absorbent tube having the structure
of FIG. 37;
[0143] FIG. 39 is a partial perspective view of a porous liquid
impervious sheet constituting the absorbent of the present
invention;
[0144] FIG. 40 is a plan view showing a part of the surface of the
absorbent sheet of the present
[0145] FIG. 41 is a longitudinal sectional view of the absorbent
sheet of FIG. 40;
[0146] FIG. 42 is a schematic diagram showing a process of making
the absorbent sheet of the present invention;
[0147] FIG. 43 is a plan view of a liquid impervious sheet material
used for the absorbent sheet of the present invention;
[0148] FIG. 44 is a plan view showing the condition where in the
recesses of the liquid impervious sheet of FIG. 43 absorbent
material is filled;
[0149] FIG. 45 is a fragmentary plan view showing other absorbent
sheet of the present invention;
[0150] FIG. 46 is a fragmentary longitudinal sectional view of FIG.
45;
[0151] FIG. 47 is a fragmentary plan view showing still other
absorbent sheet of the present invention;
[0152] FIG. 48 is a block diagram showing an example of a process
of adding a short-cut staple fiber component to the HFFM in the
present invention;
[0153] FIG. 49 is a block diagram showing an example of a process
of adding a short-cut staple fiber component to the HFFM in the
present invention;
[0154] FIG. 50 is a block diagram showing an example of a process
of adding a short-cut staple fiber component to the HFFM in the
present invention;
[0155] FIG. 51 is a block diagram showing an example of a process
of adding a short-cut staple fiber component to the HFFM in the
present invention;
[0156] FIG. 52 is a fragmentary longitudinal sectional view showing
an absorbent sheet of the present invention while it is in dry
condition;
[0157] FIG. 53 is a fragmentary longitudinal sectional view showing
the absorbent sheet shown in FIG. 52 while it is in wet
condition;
[0158] FIG. 54 is a fragmentary longitudinal sectional view showing
other absorbent sheet of the present invention while it is in dry
condition;
[0159] FIG. 55 is a plan view showing an example of an absorbent
sheet of the present invention;
[0160] FIG. 56 is a fragmentary enlarged sectional view of the
absorbent sheet of FIG. 55;
[0161] FIG. 57 is a flow chart showing an example of a process of
making a supporting sheet to be used in the present invention;
[0162] FIG. 58 is an explanatory drawing showing the sectional view
of the supporting sheet made by the process of FIG. 57;
[0163] FIG. 59 is a fragmentary hatched plan view showing an
example of a supporting sheet suitable
[0164] FIG. 60 is a fragmentary enlarged sectional view of FIG.
59;
[0165] FIG. 61 is a schematic longitudinal sectional view of an
apparatus for making a composite sheet material according to the
present invention;
[0166] FIG. 62 is a schematic longitudinal sectional view showing a
modified example of the apparatus of FIG. 61;
[0167] FIG. 63 is a schematic longitudinal sectional view showing
another coating apparatus to be used in the apparatus shown in FIG.
61;
[0168] FIG. 64 is a plan view of a grooved roll used in the
apparatus of FIG. 63;
[0169] FIG. 65 is a cross sectional view of a supporting sheet
which is coated with a dispersion liquid by the apparatus shown in
FIG. 63 and FIG. 64;
[0170] FIG. 66 is a perspective view schematically showing an
example of an apparatus for making an absorbent sheet of the
present invention;
[0171] FIG. 67 shows an example of a nozzle for discharging a
slurry dispersion liquid to be applied in the apparatus of FIG. 66:
(A) is a side view thereof and (B) is a bottom view thereof;
[0172] FIG. 68 shows another example of a nozzle for discharging a
slurry dispersion liquid to be applied in the apparatus of FIG. 66:
(A) is a side view thereof and (B) is a bottom view thereof;
[0173] FIG. 69 is a perspective view showing an example of a nozzle
for discharging a slurry dispersion liquid to be used for making an
absorbent sheet of the present invention;
[0174] FIG. 70 is a perspective view showing an example of a nozzle
for discharging a slurry dispersion liquid to be used for making an
absorbent sheet of the present invention;
[0175] FIG. 71 is a perspective view showing an example of a nozzle
for discharging a slurry dispersion liquid to be used for making an
absorbent sheet of the present invention;
[0176] FIG. 72 is an explanatory drawing showing an example of the
condition where a nozzle contacts a liquid pervious supporting
sheet;
[0177] FIG. 73 is an explanatory drawing showing another example of
the condition where a nozzle contacts a liquid pervious supporting
sheet;
[0178] FIG. 74 is a schematic flow diagram showing an apparatus for
making an absorbent sheet of the present invention;
[0179] FIG. 75 is a schematic flow diagram showing another
apparatus for making an absorbent sheet of the present
invention;
[0180] FIG. 76 is a schematic flow diagram showing other apparatus
for making an absorbent sheet of the present invention;
[0181] FIG. 77 is an explanatory drawing showing a method of
measuring a stiffness and flexibility (mm);
[0182] FIG. 78 is a fragmentary sectional view taken along section
line A-A of FIG. 77;
[0183] FIG. 79 is a chart drawing showing a criterion of the
bonding stability of the SAP;
[0184] FIG. 80 is a plan view showing a composite absorbent sheet
prepared for incorporating into a sample piece in an example of the
present invention;
[0185] FIG. 81 shows other example of a composite absorbent of the
present invention: (a) is a plan view thereof and (b) is a
sectional view thereof;
[0186] FIG. 82 is an explanatory drawing showing a process of
making still other form of a composite absorbent of the present
invention;
[0187] FIG. 83 shows an incontinent pad for a woman in which a
composite absorbent of the present invention is applied: (a) is a
plan view thereof, (b) is a sectional view of the composite
absorbent, (c) is a perspective view showing the condition where
the composite absorbent of (a) is folded, (d) is a side view of a
finished incontinent pad for a woman;
[0188] FIG. 84 is a perspective view showing material of an
absorbent tube used in an example of the present invention;
[0189] FIG. 85 is a cross sectional view of an absorbent tube
constituted by the material of FIG. 84;
[0190] FIG. 86 is a cross sectional view of an absorbent tube used
in an example of the present invention;
[0191] FIG. 87 shows an example of setting a viscosity and a
temperature in each area of a process with propylene glycol as an
example: (A) is a process flow thereof, (B) is a chart showing a
fluctuation of temperature in each area of the process, and (C) is
a chart showing a fluctuation of viscosity in each area of the
process;
[0192] FIGS. 88 (A) through (E) each are an explanatory drawing
showing an embodiment of how the preparation of a dispersion slurry
is carried out in each step leading to a coating header;
[0193] FIG. 89 is an explanatory drawing showing, with steam as a
source of heating and hydrating, the order of a process consisting
of removal of the liquid component by decompression in a liquid
phase of a formed SAP sheet containing propylene glycol and
removing the liquid component in a gaseous phase by hot air drying
and fluctuations of propylene glycol/water composition and of
residual quantity of propylene glycol;
[0194] FIG. 90 is an explanatory drawing showing a process of
applying a slurry onto a supporting sheet in many bands extending
in parallel at intervals; and
[0195] FIG. 91 is an explanatory drawing showing a process of
applying a slurry onto a supporting sheet in many bands extending
in parallel in contact with each other.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0196] The present invention will be described in detail with
reference to the accompanying drawings.
[0197] FIG. 1 is an example showing the concentration and viscosity
of super microfibrillated cellulose in the form of microfibril
(hereinafter sometimes referred to as the "S-MFC") in a dispersion
liquid. It will be understood from FIG. 1 that even at low
concentration a high viscosity is still maintained. The dispersion
liquid of the HFFM exhibits a structural viscosity, and a fluidized
orientation is exhibited and the viscosity is reduced when a shear
force is applied. However, as the shear force is reduced, the
viscosity is restored. Thus, if the SAP particles are added and
dispersed in the dispersion medium of the HFFM, in a low sheared
dispersion state, the SAP particles are stably taken in a network
structure of the HFFM, and consequently, the SAP of a high
concentration can stably be dispersed. The dispersion is
transferred with ease by means of a pump or the like, because then
the viscosity is deceased.
[0198] Therefore, when the SAP is dispersed in a dispersion medium
of the HFFM, the SAP of a high concentration can be stably
dispersed. In the process where the dispersion medium is removed,
the HFFM are in a plaster state to form a network structure as they
are firmly self-bonded and contain and mechanically enclose the SAP
particles, and as the HFFM is bonded with each other in the effect
of hydrogen bons, hold securely the SAP particles.
[0199] Fine fibers in the form of microfibril (the "HFFM") can be
obtained by microfibrillating cellulose or its derivative. For
example, by grinding and sufficiently beating wood pulp, the HFFM
is obtained in a process as shown in FIG. 2. The HFFM is sometimes
referred to as the "MFC"
(microfibrillated cellulose) and if further fibrillated, as the
"S-MFC" (super microfibrillated cellulose).
[0200] Next, a method of making a highly absorbent composite
composed of the above-described HFFM and the SAP is described
below:
[0201] According to the present invention, in making the
above-described highly absorbent composite, the dispersion behavior
of the SAP in a dispersion medium of the HFFM and the behavior of
the HFFM after removing the liquid component are ingeniously
utilized. In other words, the highly absorbent composite of the
present invention can be obtained by dispersing the SAP particles
and the HFFM in a dispersion medium that is a mixture of an organic
solvent miscible with water and water where the HFFM is stably
hydrated and dispersed, by separating the SAP particles and the
HFFM from the resultant dispersion liquid, and by removing the
liquid component, followed by drying. As a result of this
procedure, a typical pulpless highly absorbent composite where the
content of the SAP is 90 percent or higher can be obtained.
[0202] To prepare a dispersion liquid of the HFFM, a dispersion
liquid where the HFFM is dispersed in water is first prepared as a
stock liquid. As the concentration of the stock liquid becomes
higher, an apparatus preparing the HFFM dispersion becomes more
compact. On the other hand, however, the viscosity of the stock
liquid increases at higher concentrations, which makes the handling
of the stock liquid more difficult. Therefore, a water dispersion
liquid with a concentration of 10 percent or lower, preferably 5 to
1 percent, is used. The stock liquid is added to a dispersion
medium consisting of an organic solvent and water to obtain a
dispersion liquid of the HFFM having a prescribed concentration of
the HFFM and a viscosity accompanied by the concentration. As a
means of adding and mixing the SAP to the dispersion liquid, a
means of dispersing the SAP particles into the above-described
dispersion liquid is generally applied.
[0203] By dispersing the HFFM and the SAP in this dispersion liquid
of an organic solvent and water, a network structure of the HFFM is
formed and the SAP particles are incorporated in the network
structure so that a stable dispersion state is secured. When the
dispersion medium is removed later, the physical entwined structure
of the HFFM and the stable hydrogen bonding of the HFFM with each
other are formed, and as a result, it is assumed that a three
dimensional structure is formed.
[0204] The mixture ratio of an organic solvent and water is
established in a range enabling the formation of a network
structure of the HFFM and suppressing as much as possible the
absorption of water by the SAP.
[0205] Of the above-described organic solvents, representative
solvents are described here. In the graph of FIG. 3 is shown the
relationship between the concentration of an organic solvent and
the water absorbing ratio of the SAP in the case that as such
organic solvent methyl alcohol, ethyl alcohol, and acetone are
used. It is shown in FIG. 3 that in case ethyl alcohol or acetone
is used, when the concentration of the solvent is 50 percent or
lower, the water absorbing ratio of the SAP sharply increases, and
that, in case methyl alcohol is used, when the concentration is 60
percent or lower, the water absorbing ratio of the SAP sharply
increases. It is, therefore, preferable to have a higher
concentration of an organic solvent.
[0206] Of the above-described solvents, solvents of polyvalent
alcohols are more viscous, and among them ethylene glycol and
propylene glycol are relatively easy to handle and easily available
on the market. FIG. 4 shows the relationship between the viscosity
and the temperature from minus 10.degree. C. to 12.degree. C. for
both of them. With safety to the environment and to the persons who
wear sanitary material taken into consideration, the most
preferable organic solvent is propylene glycol (hereinafter
abbreviated as the "PG").
[0207] The above-described solvents are used mainly in mixture with
water in the present invention. An appropriate mixture ratio
between water and a solvent needs to be selected in order to
prevent coagulation and swelling of the SAP particles and to
disperse stably the SAP particles with the MFC and the short-cut
staple fiber component. The mixture ratio of solvent water is
approximately 9/1 to 5/5. If water is more than 5/5, the swelling
of the SAP is rapidly increased, and if a solvent is more than 9/1,
the MFC starts to settle. The transition region and nature are
somewhat different depending on the kinds of the solvents used. If
the PG is taken as an example, a particularly preferable mixture
ratio is 6/4 to 8/2. FIG. 5 shows the relationship between the
viscosity and the temperature of the PG in an aqueous solution for
the mixture ratios of 4/6, 6/4 and 8/2. It is shown that, as the
content of water increases, the viscosity relatively decreases, and
that a difference in viscosity caused by difference in temperature
is large even when the solvent is in an aqueous solution.
[0208] On the other hand, in order to hydrate and disperse the HFFM
stably, it is more advantageous to have higher content of water in
a dispersion medium. Therefore, an appropriate range of the ratio
of an organic solvent/water is 90/10 to 40/60. Note that the ratio
varies to some extent depending upon the organic solvents used and
the properties of the SAP used.
[0209] The dispersion concentration each of the SAP and the HFFM in
coexistence in this dispersion medium and the ratio in
concentration between the SAP and the HFFM are described in more
detail below. The concentration of the SAP is selected from a range
of 60 percent or lower, preferably 50 percent to 5 percent from the
standpoint of ease to handle, although it may be somewhat different
depending upon the methods of slurry transportation. A preferable
concentration of the HFFM is selected to obtain the bonding
strength and the dispersion stability of the SAP. To maintain a
good dispersion stability, the concentration of the HFFM needs to
be 0.2 percent or higher, preferably 0.3 percent to 1.0
percent.
[0210] At this concentration of the HFFM, a dispersion medium
containing the HFFM exhibits a good dispersion stability. Even
after the medium is allowed to stand for a long period of time, no
settling occurs.
[0211] Experimental results show that, as the concentration of the
HFFM increases, the dispersion stability improves. When the
concentration of the HFFM was 0.3 percent, no settling occurred for
one hour. At the concentration of 0.5 percent, no settling occurred
for 65 hours. It proves that, with this good dispersion stability,
not only the coating procedure becomes easier, but also, the HFFM
enclose the SAP particles completely so that a stable dispersion is
realized.
[0212] As the ratio of the HFFM to the SAP (MFC/SAP.times.100(%))
increases, the strength of the absorbent composite becomes higher,
but at the same time, the absorbent composite hardens to a
paper-like hand. Therefore, the ratio of the HFFM to the SAP is
preferably 20% or lower. On the other hand, at the ratio of 0.3% or
lower, a sufficient bonding strength cannot be obtained. The
bonding strength is evaluated by applying a cellophane adhesive
tape method for measuring a surface strength. The results of
applying the method to the evaluation of the bonding strength show
that more preferable range of the ratio is 5% to 0.5%.
[0213] Next, a method of forming a composite from a dispersion
liquid which is made by dispersing the HFFM and the SAP in a
dispersion medium is described with reference to the accompanying
drawings below. As a method of forming an absorbent composite from
the above-described dispersion liquid slurry, for example, as shown
in a conceptual drawing of FIG. 6, (1) by drying a block-like
substance obtained by separating the solvent from the slurry and
crushing the substance into particles, composite particles with the
surface of the SAP covered by the HFFM, cubic-shaped as shown in
FIG. 7(a) or flake-shaped as shown in FIG. 7(b), are obtained, (2)
if the slurry is poured into a mold made of, for example, a net and
solid and liquid components are separated and dried, a pellet-,
rod-, cylinder-, or corrugated-plate-shaped three dimensional
formed composite is obtained depending upon the mold used, and (3)
if thin film is formed continuously and dried, a composite sheet is
obtained.
[0214] An absorbent composite obtained in each of the
above-described manners has flexibility depending upon the water
content. Therefore, a composite sheet is formed in a mat shape
together with fibers, for example, by an air-laid method and the
mat is moistened, pressed, and dried so that it can be reformed
into a sheet shaped composite.
[0215] Next, a method of directly forming a sheet from a dispersion
liquid, which can be widely used, is described in detail. As
described in the above, a network structure of the HFFM, while
maintaining a condition where the SAP is stably and firmly held
inside, enables the formation of a very thin layer. In other words,
a dispersion liquid where the HFFM and the SAP are dispersed in a
dispersion medium is applied onto a suitable flat surface, and a
sheet-shaped highly absorbent composite can be formed which is
composed of only the HFFM and the SAP.
[0216] A highly absorbent composite of a shape described in the
above is shown in FIG. 8(a). In FIG. 8(a), reference numerals 11
and 12 represent the HFFM and the SAP particles, respectively. In
fact, as shown in FIG. 8(b) which is a sketch of a microphotograph
magnified by 70 times, each SAP particle is completely covered by
the HFFM and at the same time, the SAP particles are taken in a
network structure of the HFFM as the adjoining particles are
entwined with each other by the HFFM.
[0217] Alternatively, when a dispersion liquid is applied onto a
suitable supporting sheet, a highly absorbent composite sheet
material composed of the supporting sheet and an absorbent
composite layer is obtained after the dispersion liquid is dried.
When a porous non-woven fabric is used as the supporting sheet,
part of the dispersion liquid enters spaces made by the fibers of
the non-woven fabric depending upon the density of the non-woven
fabric, and a composite sheet where non-woven fabric 13 and the
absorbent composite layer 10 are entwined as they are in contact
with each other is formed as shown in FIG. 9(a) and FIG. 9(b) which
is a sketch of a microphotograph, after the liquid is dried. A
preferable density of the non-woven fabric is 0.2 g/cm.sup.3 or
lower in terms of the apparent specific density, and, more
preferably, 0.01 to 0.1 g/cm.sup.3.
[0218] Preferable fibers constituting the non-woven fabric are,
from a viewpoint of the permeability of a liquid, a hydrophilic
material such as cotton, rayon and wood pulp or synthetic fibers
treated to be hydrophilic such as polyethylene, polypropylene and
polyester. In particular, the HFFM which is of the S-MFC or the BC
has a very strong hydrogen bonding strength in addition to being
easily entangled physically. Therefore, when a cellulosic
supporting sheet is used, such HFFM is more strongly and stably
bonded with each other and with the supporting sheet in a dry
state, and exhibits an outstanding permeability in a wet state.
[0219] In addition, in a structure as shown in FIG. 9, other sheet
material 14 can be bonded in contact with the highly absorbent
composite layer 10 as against the non-woven fabric 13, as shown in
FIG. 10. If, as this other material 14, a liquid impervious sheet
material is used, the composite sheet of FIG. 10 alone may have the
function of an absorbent product composed of a topsheet, an
absorbent, and a backsheet.
[0220] Furthermore, in the structure of FIG. 9, a highly absorbent
composite layer can be provided not only on the whole front surface
of a supporting sheet, but also partially in a desired pattern. For
example, as shown in FIG. 11, a plurality of the absorbent
composite layers 10 are provided in bands of a desired width at
prescribed intervals only on either surface of the supporting sheet
13, with the composite supporting sheet folded in between the
adjoining absorbent composite layers in a zigzag pattern. Since a
composite sheet of this structure has a larger volume of the
absorbent composite layer 10 per unit area than a flat composite
sheet, and accordingly a higher absorbing capability than the
latter. Alternatively, as shown in FIG. 12, when the top portions
of the zigzag pattern are largely brought down in one direction,
the volume of the absorbent composite layer 10 per unit area can be
further increased. In addition, as shown in FIG. 13, the top
portions of the zigzag pattern can be brought down outwardly in
mutually opposing directions to either side with a flat area
provided in the center.
[0221] Such a zigzag structure provides a free and sufficient space
that enables the SAP as used in an absorbent product to easily
swell by absorbing a liquid.
[0222] FIG. 14 shows an example of a highly absorbent composite
sheet material as composed according to the present invention. This
highly absorbent composite sheet material has a structure where a
highly absorbent composite layer 10 is disposed in bands extending
in parallel to each other at prescribed intervals on either surface
of the supporting sheet 13 made of a elastic substance, over the
highly absorbent composite layer a corrugated (zigzag) liquid
pervious non-woven fabric 14 is disposed, and in the bottom
portions of the zigzag of the non-woven fabric 14 the non-woven
fabric 14 and the supporting sheet 13 are bonded in the bonding
areas 15. Thus, each highly absorbent composite layer 10 is
contained in the channel 16 which is formed between the supporting
sheet 13 and the non-woven fabric 14. A highly absorbent composite
sheet material of a structure described in the above can be
preferably used, for example, in absorbent products such as
feminine hygiene products and diapers, as highly elastic and
absorbent sheet material: the highly absorbent composite sheet
material has a high elasticity in the direction perpendicular to
the longitudinal direction of the highly absorbent composite layer
10. In this case, the non-woven fabric 14 is used in contact with
the body of a wearer, and body exudates of the wearer are first
absorbed by and distributed in the non-woven fabric 14 and then
absorbed by the highly absorbent composite layer 10. As the
absorbed amount of body exudates increases, the volume of the
highly absorbent composite layer 10 increases. However, since each
band of the highly absorbent composite layer 10 is contained in the
channel 16 formed between the supporting sheet 13 and the non-woven
fabric 14, the layer is allowed to swell freely.
[0223] FIG. 15 shows a highly absorbent composite sheet material
embodying the present invention. A liquid impervious sheet
designated by reference numeral 21 in FIG. 15 is liquid impervious
and reasonably elastic. A highly absorbent composite sheet material
22 is laid on top of the liquid impervious sheet 21. Both of them
are bonded with each other at many bonding areas 23 extending in
lines or bands parallel with each other disposed at prescribed
intervals. The bonding areas 23 are formed by thermally fusing, by
a conventional method such as heat sealing and high frequency
bonding, the liquid impervious sheet 21 and the highly absorbent
composite sheet material 22 with a predetermined width. In between
the adjoining bonding areas 23 and 23, the length of the highly
absorbent composite sheet material 22 is longer than the length of
the liquid impervious sheet 21, and, therefore, in between the
bonding areas 23 and 23, a channel 24 is formed between the highly
absorbent composite sheet material 22 and the liquid impervious
sheet 21 by the sagging of the former. The highly absorbent
composite sheet material 22 has a structure, as shown in FIG. 15,
where, on either surface of a supporting sheet 13 of spun-bond or
dry-laid non-woven fabric made of polyolefin such as PP and PE, an
absorbent composite layer 10 is supported which layer 10 is
disposed on the side facing the liquid impervious sheet 21. A sheet
product of this structure is outstanding in retaining stably its
own sheet shape even when the sheet product absorbs a large amount
of liquid.
[0224] FIGS. 16 to 18 show typically examples of an absorbent sheet
having a distribution of patterns as obtained by the
above-described means. FIG. 16 shows a pattern made by utilizing
pulsation, FIG. 17 shows a pattern made by utilizing a branched
nozzle, and FIG. 18 shows a pattern made in combination of the two.
Examples of a distribution of higher absorbing regions are
classified into the following three types: (1) on top of a thin
absorbent layer distributed on the whole area a partially thick
layer exists; (2) parts of a supporting sheet exposed without any
absorbent layer, and parts thereof with such absorbent layer exist
separately; and (3) in the higher absorbing regions thin and thick
layers coexist. The distribution pattern of high absorbing regions
is, for example, a pattern of islands in the sea as shown in FIG.
16, a continuous band-type pattern with a thin margin as shown in
FIG. 17, and a combination of island and band patterns as shown in
FIG. 18. An absorbent sheet which is coated with a slurry in a
distribution of patterns is bonded with a supporting sheet stably
by press, and the structure is fixed by removing the liquid
component and drying. In doing so, a absorbent sheet yet to be
dried which has a distribution of patterns, is high in difference
in thickness, and contains a lot of solvent is likely to adhere on
a press roll and to partially peel off. To prevent this, a means of
pressing an absorbent sheet covered with tissue or non-woven fabric
is available, but an effective means is as follows: an absorbent
sheet is first heat pressed to fit well a supporting sheet and the
absorbent layer on the roll is subjected to removal of the liquid
component to fix the structure so that the surface is stabilized.
Then, if peeling is done only after the surface is thus stabilized,
no absorbent sheet is wound on the roll without any covering.
[0225] FIGS. 19(A), (B), (C) and D) show typically the simplest
shape of a absorbent tube of the present invention. In FIG. 19,
reference numeral 401 represents a supporting sheet in tube, and
402 represents the SAP carried by the supporting sheet 401 only on
the inner wall. In the absorbent tube as shown in FIG. 19(A) the
supporting sheet 401 is formed having a cross-section of a closed
ring, and made into tube with the adjoining of both ends bonded
with an adhesive agent 403 such as hot melt type adhesive agent,
and carries the SAP 402 nearly uniformly on the whole surface of
the inner wall. In FIG. 19(B), a reinforcing sheet 404 is disposed
at the adjoining point of both ends of the supporting sheet 401,
and both ends of the supporting sheet 401 together with the
reinforcing sheet 404 are bonded with the adhesive agent 403. In
the absorbent tube of FIG. 19(C), a flat supporting sheet 401
carrying the SAP 402 on one surface is formed into tube only with
one end of the supporting sheet 401 with the surface carrying the
SAP 402 inside, and the side ends of both of them facing each other
in opposition are adjoined as laid on top of each other with a
appropriate width of margin provided and the portion where they are
adjoined is bonded with the adhesive agent 403. Thus, on one end of
the flat absorbent is a tube formed. In the absorbent tube of FIG.
19 (D), on the side end disposed outside no SAP 402 exists, and,
therefore, the adhesive agent 403 is directly applied on the
surface of the supporting sheet 401.
[0226] As a supporting sheet which can be used in the present
invention, substantially all kinds of sheet material composed of
fiber web, if they are liquid pervious and do not have openings
large enough for the SAP particles to pass through, can be used.
Examples thereof are melt blown non-woven fabric, foamed net,
extruded fibrillated net, spun-bond non-woven fabric, carded web
non-woven fabric, spun-laced non-woven fabric, and any combinations
of the foregoing materials.
[0227] The basic roles of this supporting sheet are to carry the
SAP stably and, at the same time, to prevent the SAP swollen by
absorbing a liquid from leaking and going out of an absorbent tube.
If required, the supporting sheet can be given other roles by
selecting the kinds and shapes of the constituting materials of the
supporting sheet. For example, by selecting a cellulosic fiber or a
blending with a cellulosic fiber as the fiber constituting the
supporting sheet, the diffusion of liquid into carried SAP can be
increased. Also, another example of giving a different role is
that, by using non-woven fabric which is of high elongation, can be
elongated with a small force, for the supporting sheet, the sheet
itself can be elongated by the absorption and swelling of the SAP.
By utilizing these effects, the liquid absorbing capability of the
SAP can be made to exhibit to the maximum extent, and the diameter
of the absorbent tube while no liquid is absorbed can be made small
which in turn makes small absorbent products using such small
absorbent tube. In this specification, the term "high elongation"
of a substance means the property that the substance can be
elongated or extended easily by a small force applied at least in
one direction.
[0228] A composite sheet obtained by this method has a structure,
for example, as typically shown in FIG. 20(A). In FIG. 20(A),
reference numeral 411 represents a supporting sheet, 412 represents
the SAP, and 413 represents the HFFM which bonds the particles of
the SAP 412 are bonded with each other and on the supporting sheet
411. Because this composite sheet can be formed as an extremely
thin sheet as thin as 1 mm, it can be formed in tube as shown in
FIG. 20(B), and is suitable as an absorbent tube of the present
invention.
[0229] FIG. 21(A) shows a composite sheet of a structure where,
unlike an absorbent tube shown in FIG. 21(B) in which particles of
the SAP 412 are distributed in nearly uniform density, blocks in
which a plurality of the SAP 412 particles are gathered are formed
which blocks are disposed in a suitable distribution. An absorbent
tube as shown in FIG. 21(B) can be formed by Folding the composite
sheet of FIG. 21(A) in the shape of a tube with the surface thereof
carrying the SAP 412 particles facing inside. In the structures of
FIG. 19 tubes in an O-letter shape are formed by directly bonding
the side ends of the supporting sheet with each other, but in the
structures of FIGS. 20(B), 21(B) and 22, tubes in a C-letter shape
are formed where the side ends of a supporting sheet as it is made
in such tube area bit away from each other. The absorbent of a tube
in such C-letter may dispose a slit between the side ends of a
supporting sheet facing either upward or downward. Also, another
sheet material 414 may be bonded by means of adhesive 403 to the
slit as shown in FIG. 22.
[0230] It should be noted that in the above description and in the
sketches that are shown in the description to follow a absorbent
tube is shown in a circle or ellipse or a shape that is somewhat
swollen in order to help better understand it, but in fact, the
absorbent tube before it absorbs liquid to swell takes a shape that
is flat or collapsed.
[0231] One or a group of absorbent tubes having a structure
described in the above can be incorporated into a conventional
absorbent product as an absorbent core, but in practice, are
advantageously used as linked to a sheet comprising an absorbent
product. For example, one absorbent tube or a plurality of
absorbent tubes disposed in parallel to each other comprises or
comprise an absorbent core as linked in an absorbing region of an
absorbent product to a liquid pervious inner sheet disposed on the
side of the absorbent product in contact with the skin of a wearer
or a leakage resistant outer sheet.
[0232] FIG. 23 shows a disposable diaper as an absorbent product of
the present invention having a structure described in the above. In
FIG. 23, reference numeral 500 represents the body of an absorbent
product. This body 500 is, as shown in FIG. 24, composed of a
liquid pervious inner sheet 520 and of a liquid impervious outer
sheet 530, and in its absorbing region three absorbent tubes 501,
502 and 503 disposed in parallel to each other are contained. The
absorbent tubes 501, 502 and 503 are, in this embodiment of the
present invention, linked to a liquid impervious outer sheet 530 by
means of an adhesive 504 such as hot melt adhesive.
[0233] FIG. 25 shows a sectional view of the structure of another
absorbent product of the present invention like FIG. 22. In this
example, the inner sheet 520 is linked to the outer sheet 530 on
both sides of the absorbent tube by adhesive 504.
[0234] In the example of FIG. 26, the absorbent tube 502 disposed
in the center is wider than the absorbent tubes 501 and 503
disposed on the respective sides of the absorbent tube 502 so that
both side ends of the absorbent tube 502 are laid on the side ends
of the absorbent tubes 501 and 503.
[0235] In the example of FIG. 27, the relation in widths among the
absorbent tubes 501, 502 and 503 is the same as in the example of
FIG. 26, but the absorbent tubes 501 and 503 on the sides are
disposed at positions higher than the absorbent tube 502 disposed
in the center and the inside ends of the absorbent tubes 501 and
503 are laid on the side ends of the absorbent tube 502.
[0236] The absorbent products of the present invention provided
with an absorbent core of a configuration shown each in FIGS. 24 to
27 exhibit a high absorbing property with the absorbing capability
of the above-described absorbent tubes. Particularly, in a
configuration as shown in FIGS. 26 and 27 where each absorbent tube
is partially laid on an adjoining absorbent tube, because the
amount of the SAP per unit area can be made larger, further higher
absorbing property can be expected. For example, a condition where
the absorbent tubes 501, 502 and 503 have absorbed to swell in a
configuration of FIG. 26 is shown in FIG. 28. Also, in examples of
FIGS. 24 to 27, each absorbent tube may be linked to the inner
sheet 520, too, so that the absorbent tube may be secured in
position.
[0237] In the absorbent products of the present invention, an
absorbent core to be disposed in an absorbing region may be
comprised only by a plurality of absorbent materials, as described
in the above, but one of the absorbent tubes may be replaced by
another absorbent 506, as shown in FIG. 29.
[0238] Alternatively, as shown in FIG. 30, a configuration can be
made where absorbent tubes of long length and narrow width 507 are
disposed in parallel to each other and tapes 508 made of a soft
hand sheet such as non-woven fabric extending along the outer sides
of each absorbent tube are disposed. This tape 508 allows a liquid
coming to the absorbing region to reach the absorbent tube 507 and
at the same time improves the touch existing between the absorbent
tube and the skin of a wearer.
[0239] The number and the size of the absorbent tubes disposed in
the absorbing region of an absorbent product can be selected
depending upon the shape, use and desired absorbing property of the
absorbent product, and the selection can easily be made by those
skilled in the art.
[0240] In the descriptions and drawings made and shown in the
above, the above-mentioned absorbent tubes are shown to have a
virtually ellipsoidal cross-section, but the absorbent tube is
normally thin having a flat shape before it absorbs a liquid to
swell, as shown in FIG. 31. If the absorbent tube is of a single
layer, the circumference length of the cross-section is constant
regardless of the shape of the cross-section. The longer the
circumference length is, the larger the area becomes to be provided
to carry the SAP 402, and when the SAP 402 swells and increases in
volume, the thickness or the height of the absorbent tube becomes
larger. FIGS. 32 to 35 show examples where the supporting sheet 401
is provided with a gusset for such purpose. In the example of FIG.
32, a gusset 510 is disposed on the top surface of the absorbent
tube, and in the examples of FIGS. 33 to 35, a gusset 510 is
disposed on each side end of the absorbent tube. Note that in FIG.
34 the side ends on which gussets 510 are provided are linked at
portions facing each other by heat sealing 511, forming a cell 512
as distinguished from the rest.
[0241] In the absorbent tube of the present invention, a supporting
sheet can be composed of any sheet material which is liquid
pervious and has some degree of softness and tear strength. A
preferable material is a non-woven fabric 601 as described in the
above, and a non-woven fabric of an absorbent composite as shown in
FIG. 36 can also be advantageously used. This composite non-woven
fabric 601 may be made by composing one or two kinds of staple
fiber 602 such as PET and rayon with spunbond non-woven fabric 601
made of synthetic fiber such as polypropylene by means of water jet
entanglement. A composite non-woven fabric like this has a feature
where the spun bond non-woven fabric 601 functions as the inner
sheet and, as shown in FIG. 37, on the surface of the staple fiber
the SAP 402 particles are securely held so that there is no need to
cover the absorbent core with the inner sheet.
[0242] FIG. 38 shows an absorbent product of a structure where the
absorbent sheet 600 of FIG. 37 is formed into a tube and linked to
the outer sheet 411 of an absorbent product by means of adhesive
504, and on both sides leg gathers 603 are provided composed of a
liquid impervious sheet. Either side of each leg gather 603 is
linked to the outer sheet 411, and the other side is made to face
the end of the other leg gather 603 at some interval in which
interval the center portion of the absorbent tube 600 is
located.
[0243] Other examples of an absorbent sheet of the present
invention are described with reference to the accompanying
drawings:
[0244] FIG. 39 shows a sheet material where on a liquid impervious
sheet material 711 made of flexible thermoplastic film many dents
713 are formed having openings 712 in the bottom. An absorbent
sheet where the dents 713 are filled with absorbent material is
shown in FIGS. 40 and 41. The absorbent material is made by fixing
the SAP particles 714 on the inner wall of the dent 713 of the
liquid impervious sheet material 711 with the HFFM 715.
[0245] In general, such a structure is preferable as smaller dents
are filled with finer particles and larger dents are filled with
coarser particles.
[0246] Also, FIG. 42 shows the steps of making other absorbent
sheet of the present invention. In the step of FIG. 42(A) a liquid
impervious sheet material 721 and a liquid pervious non-woven
fabric 722 having a lateral extensibility are laid one each other
with a hot melt adhesive layer (not shown) in between, and in the
step of FIG. 42(B) many grooved portions 723 extending in parallel
to each other are formed by means of hated grid roll, and at the
same time, the liquid impervious sheet material 721 is bonded with
the liquid pervious non-woven fabric 722 at the positions of the
grooves with hot melt in between. This composite sheet is, in the
step of FIG. 42(c), extended in a direction perpendicular to the
longitudinal direction of the grooved portion 723, whereby the
liquid impervious sheet material 721 is cut off at the positions of
the grooves 723 to form dents 724. The dent portion is made up of
only the liquid pervious non-woven fabric. Next, in the step of
FIG. 42(D), slurry where the SAP and the HFFM are uniformly
dispersed in a dispersion medium of a water miscible organic
solvent and water is applied onto the liquid pervious sheet
material 724 and then after removing the liquid component and
drying, the dents 724 are filled with absorbent material 725
composed of the SAP and the HFFM. Lastly, in the step of FIG.
42(E), the topsheet 726 such as non-woven fabric is disposed on the
liquid impervious sheet material 721 and the absorbent material 725
and the liquid impervious sheet material 721 and the absorbent
material 725 are bonded to the topsheet 726 at the position 721
where no absorbent exists.
[0247] FIG. 43 shows a liquid impervious sheet material where the
many dents formed in the step C of FIG. 42 are circular. FIG. 44
shows a sheet material where the dents 724 in the step D of FIG. 42
are filled with the absorbent material 725.
[0248] In the absorbent sheet as shown in FIG. 42, the non-woven
fabric 722 constituting the composite sheet together with the
liquid impervious sheet material 721 is preferably a non-woven
fabric of 10 g/m.sup.2 to 50 g/m.sup.2 weight such as a non-woven
fabric of a hydrophobic synthetic fiber such as PE, PP and PET and
a non-woven fabric of a mixture of a synthetic fiber and a
cellulosic fiber such as rayon, Lyocell and cotton.
[0249] FIGS. 45 and 46 show configuration where a liquid impervious
sheet material 721 is formed in a corrugated sheet and absorbent
material 725 is disposed and fixed in narrow bands or in bars in
the bottoms of dents 724 of V-letter shape extending in parallel to
each other.
[0250] Also, FIG. 47 shows an example where the absorbent material
725 is disposed in dots, not in bands or bars as shown in FIGS. 45
and 46.
[0251] In the structures shown in FIGS. 45 to 47, the liquid
impervious sheet material 721 may have or have not openings in the
bottoms of the dents 724.
[0252] In any case, the dents 724 formed on the liquid impervious
sheet material may have an inner wall extending perpendicularly to
the surface of the sheet material, but preferably, should have a
funnel-like taper with the size becoming smaller from top to bottom
which allows absorbent material to fill in more easily. The size of
dents depends upon the size or shape of the absorbent material, but
should be at least 0.3 mm, preferably 0.5 mm in the diameter if the
dents are circular or, in the width of the shorter direction if the
dents are long and narrow in the shape of ellipse, rectangle or
groove. It is because if the diameter or width is too small, it is
difficult to hold a sufficient amount of absorbent material stably
in the dents.
[0253] Next, briefly, processes preferably applied in making the
absorbent sheet of the present invention are described using the
HFFM, the SAP and a short-cut staple fiber component. A process of
adding the short-cut staple fiber component is selected, which is
optimum depending upon the characteristic or property of the
short-cut staple fiber component, namely in dry state or wet state,
the necessity of fibrillation. FIGS. 48 to 51 show several examples
of representative processes of making the absorbent sheet. From
these flow charts the configuration of each process can easily be
understood.
[0254] First of all, typical model examples of the composite
absorbent of the present invention composed of four components of
the SAP, the MFC, short-cut staple fibers and a supporting sheet
are shown in FIGS. 52 and 53. FIG. 52 shows the composite absorbent
in a dry state, and FIG. 53 shows the composite absorbent of FIG.
52 which has absorbed a liquid and swollen. In FIGS. 52 and 53,
reference numeral 111 represents a substrate, on the surface of
which the SAP particles 112, a short-cut staple fiber component
113, and the HFFM 114 are held. As shown in FIG. 52, the SAP
particles exist dispersed or with plural particles securely bonded
by the MFC when they are in dry state, while groups of the SAP
particles are contains with leeway as covered by the short-cut
staple fiber component just like an umbrella.
[0255] When body exudates are discharged into the composite
absorbent, the SAP absorbs them to swell. At that time the hydrogen
bonds of the MFC are cutoff, and the SAP swells more freely but
within the network where the SAP is contains so that the SAP is
prevents from going out of the network.
[0256] FIG. 54 is a structure where, by using a bulky substrate,
the effects of the network are improved in concert with the effects
of the short-cut staple fiber component. In FIG. 54, reference
numeral 111a represents a high density layer of the substrate, 111b
represents a low density layer of the substrate, 112 represents the
SAP particles, 113 represents short-cut staple fibers, and 114
represents the HFFM. It is shown that the SAP particles are
captured with relative leeway among the fibers of the low density
layer of the substrate 111b. In the present invention, absorbent
layer may be provided all over completely on either surface of the
supporting sheet, but may also be provided in rows or any desired
pattern. Also, by providing absorbent layer only on either surface
of the supporting sheet, a composite absorbent having a sufficient
absorbing capacity can be constituted, but in case the supporting
sheet is used in such uses as a liquid contacts both sides of the
supporting sheet, absorbent layer may be provided on both sides of
the supporting sheet.
[0257] Methods of evaluating the properties applied in the present
invention are described below:
1) Standing Sustainability of the Swollen Sap in a Composite
Absorbent when Wetted Cut a Rectangle of 2 cm.times.10 cm from the
Composite Absorbent to Make a Sample. {circle around (1)} Standing
Sustainability of the SAP
[0258] Place two rectangular sample pieces with the SAP side upward
at approximately 2 cm interval on a Petri dish of 12 cm diameter,
add 50 ml of 0.9% NaCl (a physiological saline solution) gently and
allow to stand for 10 minutes for the SAP to swell. Visually
observe the condition where the SAP as swollen come off from the
samples into the liquid.
(Judgement Criteria)
[0259] .circleincircle. The SAP swells but little SAP is observed
to come off. .largecircle. As the SAP swells, a little SAP is
observed to come off. .DELTA. As the SAP swells, the SAP is
observed to come off appreciably. x As the SAP swells, the SAP is
observed to come off very much to pile up in the liquid. {circle
around (2)} Standing Coming Off of the SAP
[0260] The procedure is the same including the judgment criteria as
in the standing sustainability test, except that two sample pieces
are placed with the SAP side downward.
{circle around (2)} Vertically Suspending Sustainability of the
SAP
[0261] Take out the samples from the liquid with a pair of tweezers
immediately after the evaluation in the above-described standing
sustainability test, hold one end of the longitudinal direction
with a clip to vertically suspend, and virtually judge the
condition of the swollen SAP coming off from the supporting
sheet.
(Judgement Criteria)
[0262] .circleincircle. Little swollen SAP is observed to come off.
.largecircle. A little SAP as swollen on the surface is observed to
come off. .DELTA. Of swollen SAP, a part of the SAP on the surface
is observed to come off, but the SAP in direct contact with the
supporting sheet is not observed to come off. x A majority of
swollen SAP is observed to come off.
2) Dispersion of an Absorbed Liquid by a Composite Absorbent
[0263] Cut a circle of 5 cm diameter from the composite absorbent
to make a sample.
{circle around (1)} Absorbing Time of Dropped liquid (Seconds)
[0264] Place the sample on a Petri dish of 12 cm diameter with the
SAP side upward, drop 1 ml of 0.9% NaCl (a physiological saline
solution) with a burette in the center of the sample taking
approximately one second, and measure the time (seconds) until the
dropped liquid is absorbed.
{circle around (2)} Dispersing Time (Seconds)
[0265] Put 100 ml of 0.9% NaCl (a physiological saline solution) in
a Petri dish of 12 cm diameter, float the sample with the SAP side
upward with the side of the supporting sheet in contact with the
liquid, and measure the time until the liquid disperses on the
whole surface of the sample and the applied SAP finishes swelling
on the whole surface.
3) Thickness of Supporting Sheet (mm)
[0266] Cut a circle of 5 cm diameter from the supporting sheet to
make a sample. Measure using a thickness gauge of Daiei Chemical
Precision Instruments Mgt. Co., Ltd. with the area of the probe of
15 cm.sup.2 (43.7 mm diameter) and the measuring pressure of 3
g/cm.sup.2.
4) Apparent Density of Supporting Sheet (g/cm.sup.3)
[0267] Calculate from the weight (g/cm.sup.2) and the thickness of
the supporting sheet by the following formula:
Apparent
density(g/cm.sup.3)=[weight(g/m.sup.2)/10.sup.4].times.[10/thic-
kness(mm)]
[0268] Other composite absorbent sheet embodying the present
invention are described where an absorbent sheet is provided with a
liquid pervious supporting sheet and an absorbent layer containing
the SAP particles bonded to either surface of the liquid pervious
supporting sheet with the absorbent layer forming a plurality of
high absorbing regions having higher absorbing capability than the
other regions as distributed in a desired pattern on the surface of
the liquid pervious supporting sheet.
[0269] FIG. 55 typically shows a plurality of high absorbing
regions having higher absorbing capability of the absorbent layer
and low absorbing regions having lower absorbing capability on the
supporting sheet embodying the present invention; on the drawing
the white colored pans show high absorbing regions 210 and the
black colored pans show low absorbing regions 220.
[0270] FIG. 56 is a longitudinal cross-sectional view of a part of
the absorbent sheet shown in FIG. 55. Reference numeral 203
represents a supporting sheet made of material such as non-woven
fabric having an appropriate liquid perviousness, and on either
surface of this supporting sheet 203 absorbent layers 200 are
provided forming regions of higher absorbing capability 210 and
regions of lower absorbing capability 220.
[0271] The absorbent layers 200 are composed of the SAP particles
201 and the HFFM 202 existing around each particle 201, and the
HFFM 202 bonds the SAP particles 201 together and is bonded to the
surface of the supporting sheet 203 to function as a means of
transferring a liquid to be absorbed to each particle.
[0272] In the examples shown in FIGS. 55 and 56, the difference in
absorbing capability between the high absorbing region 210 and the
low absorbing region 220 of the absorbent layer is realized by the
difference in the thickness of the absorbent layer. This thickness
is represented apparently by the configuration of the layer of the
absorbent polymer, and as shown in FIG. 56, the thinner layer is in
one layer, and the thicker layer is in two or more layers.
[0273] An example of non-woven fabric having preferable properties
as material of the absorbent sheet of the present invention is, as
previously proposed in Japanese Patent Examined Publication No. HEI
9-59862 of the present applicant, non-woven fabric where spunbond
having a bi-component structure is used, stretched and heat set by
a method shown in FIG. 57 to provide a cross-sectional structure as
shown in FIG. 58. This non-woven fabric has a property of being
more likely to elongate much only in one direction. In FIG. 58, the
preferable range of H is 0.2 mm to 2 mm, and the preferable range
of L is 1 mm to 5 mm.
[0274] Another example of non-woven fabric is, as previously
proposed by the present applicant in his Japanese Patent
Application No HEI 8-345410, non-woven fabric where a highly
elastic net and a fiber web are partially laminated. This laminated
non-woven fabric has a structure, as shown in FIGS. 59 and 60,
where on both surfaces of a net 407 where longitudinal elastic
string 405 and lateral elastic string 406 are intersected with each
other and bonded at points of intersection, identical or different
webs 408 and 409 are laminated, and the net and the web are bonded
along bonding lines 410 arranged in parallel to each other so that
the laminated non-woven fabric has a property of being likely to
elongate much only in one direction perpendicular to the bonding
lines 410.
[0275] The SAP can be beforehand carried by a supporting member
previously formed in the shape of a sheet, but can also be
introduced into a supporting sheet when the supporting sheet is
manufactured by practising the present invention. An absorbent
composite can be obtained, for example, by making a carded web of
easy-to-melt synthetic staple fiber and fibrous SAP, by, after
laminating a pulp, the SAP and easy-smelt staple fibers by an
air-laid method, heat treating to fix the laminated composite, or
by, after impregnating a non-woven web with acrylic acid monomer,
polymerizing and cross-linking such impregnated non-woven web. The
surface of the carried SAP may be exposed or may be covered by
tissue or the like.
[0276] Next, with reference to the accompanying drawings, an
apparatus suitable for making the absorbent composite of the
present invention is described below:
[0277] In FIG. 61, reference numeral 31 represents a tank for
storing ion-exchanged water, 32 represents a tank for storing the
HFFM stock solution, 33 represents a tank for storing acetone, and
34 represents a tank for storing the SAP. The HFFM water dispersed
stock solution taken from the tank 32 is introduced into a mixing
unit 35 provided with a stirrer, diluted in the mixing unit 35 with
water taken from the tank 31, and, then, pumped into a second
mixing unit provided with a stirrer. Into the mixing unit 36,
acetone taken from the tank 33 is introduced, and this mixture is
pumped into a third mixing unit 37 provided with a stirrer. Into
the mixing unit 37 the SAP particles are introduced from the tank
34, and in this mixing unit the HFFM, the organic solvent, water
and the SAP are mixed to form their mixture.
[0278] On the other hand, an appropriate supporting sheet 13 of
such material as non-woven fabric is unrolled from a roll 38 and
then introduced to a forming area 40. The forming area is provided
with a belt conveyor 41 and a nozzle 42 located disposed over the
belt of the belt conveyor. The mixed dispersion liquid from the
mixing unit 37 is pumped to this nozzle 42. While the supporting
sheet 13 is being conveyed by the belt conveyor 41 at a prescribed
speed, the mixture dispersion liquid is sprayed from the nozzle 42
onto the supporting sheet 13. The nozzle 42 may be of various
configurations depending upon the pattern of absorbent composite
layers formed on the supporting sheet 13.
[0279] The forming area 40 is further provided with a roll press 43
composed of a pair of rollers. The supporting sheet coated with the
mixture dispersion liquid is pressed by the roll press 43 so that
the solvent contained in the dispersion medium is squeezed and the
solvent as separated is pumped to the second mixing unit 36.
[0280] The supporting sheet 13 after coming out of the forming area
is sent to a drying area 50. To the drying area 50 hot air is
supplied in which area a pair of porous rolls 51 and 52 are
provided. The supporting sheet 13 and the mixture dispersion liquid
sprayed on the sheet are dried while they are being conveyed along
the peripheries of the porous rolls 51 and 52.
[0281] The supporting sheet after coming out of the drying area is
compressed in a compressing area 60 consisting of a pair of press
rolls 61 and 62, and thus, a product where absorbent composite
layers are formed on the supporting sheet 13 is obtained.
[0282] FIG. 62 shows a system wherein an apparatus for making the
HFFM from acetyl cellulose is combined with the apparatus shown in
FIG. 61. In this system acetate dope is stored in a tank 31a, a
coagulation liquid is stored in a tank 32a, and acetone is stored
in a tank 33a. The acetate dope and the coagulation liquid from the
tanks 31a and 32a are sent to an aspirator type fibrillating unit,
where fibrillation is carried out. The fibrils are refined in a
mixing unit 35a to obtain finer fibrils, namely the HFFM in slurry.
The HFFM are then mixed in a second mixing unit 36a with acetone
from the tank 33a, and again mixed with the SAP in another mixing
unit (not shown). The subsequent steps are the same as those of the
process of FIG. 61.
[0283] FIG. 63 shows an example of another apparatus for applying a
mixture dispersion liquid onto the supporting sheet 13 in the
forming area 40 of FIG. 61. In FIG. 63, reference numeral 44
represents a top-opened tank for storing a mixture dispersion
liquid, and in the tank 44 a dipping roll 45 is disposed which is
rotatable with a horizontal shaft in the center with a part of the
periphery being dipped in the mixture dispersion liquid. Also, a
pair of rolls 46 and 47 are provided which are rotatable with a
shaft in the center in parallel, respectively, to the dipping rolls
45. The roll 46 is contacted with the periphery of the dipping roll
45 with pressure, and, as, for example, shown in FIG. 64, has many
ring shaped grooves on the periphery. Through the nip between the
roll 46 and the other roll 47 which has a flat surface, the
supporting sheet which is to be coated with the mixture dispersion
liquid is made to pass. The mixture dispersion liquid stored in the
tank 44 deposits by its own viscosity on the periphery of the
dipping roll 45 rotating in the tank, and is transferred onto the
supporting sheet via the groove roll 46. Thus, as shown in FIG. 65,
mixture dispersion liquid layers 48 in many bands arranged in
parallel to each other are formed on the surface of the supporting
sheet. The grooved pattern formed on the roll 46 can be freely
designed, and the mixture dispersion liquid can be applied onto the
supporting sheet in a pattern corresponding to the pattern on the
roll 46.
[0284] The features and properties of an absorbent product in which
the highly absorbent composite is incorporated are described
briefly below:
[0285] When the highly absorbent composite is used in an absorbent
product, firstly, the product is extremely thin and compact before
worn and while worn before it absorbs a liquid, so that the SAP
particles are held securely and stably and therefore, if it is
folded or bent, the SAP particles do not move or come off. The
structure of the product does not break down.
[0286] Secondly, when a liquid is absorbed by the absorbent
product, although it is of a structure of pulpless with 90% or more
of the SAP, the product absorbs the liquid very quickly without
blocking thanks to the hydrophilicity and physical forms of the
HFFM.
[0287] Thirdly, after a liquid is absorbed, swollen polymer
particles are held still securely by the network of the HFFM and
are thus prevented from coming off.
[0288] The fourth feature of the absorbent product relates to a
characteristic when it is disposed of. The absorbent of the present
invention when it is in contact with excessive water remains stable
as it is, but, if shearing force is applied, it immediately is
dissociated. The absorbent is suitable for making a flushable. In
addition, since the cellulosic HFFM is extremely high in cellulase
enzyme activity, the structure of such HFFM if buried in the land
is dissociated in a short period of time. Further, if any
biodegradable aminoacetic type absorbent polymer or the like is
combined to make the SAP, an ideal nature-friendly absorbent can be
designed.
[0289] The configuration of an example of an apparatus for making
the absorbent sheet as shown in FIGS. 55 and 56 is described with
reference to FIG. 66 below. In FIG. 66, reference numeral 311
represents a slurry supplying pipe by means of which a slurry
dispersion liquid containing the HFFM and the SAP is supplied, and
to the slurry supplying pipe 311a plurality of pipes 313 each on
the top end of which a nozzle 312 is provided is connected. Each
pipe 313 is provided with a pump 314 as a transferring means of
sucking the slurry dispersion liquid from the slurry supplying pipe
311 and discharging the liquid from the nozzle 312. The pump is
driven by a motor 315 which is used in common.
[0290] On the other hand, it is so designed that the liquid
pervious supporting sheet 203 which is to be coated with the slurry
dispersion liquid discharged from the nozzle 312 is conveyed at a
constant speed in a direction indicated by an arrow in the drawing.
Each pump 314 is capable of supplying the slurry dispersion liquid
at a periodically varying pressure to the nozzle 312, and as a
result, on the liquid pervious supporting sheet 203, bands 316 of
slurry dispersion liquid of a number corresponding to the number of
the nozzles 312 are formed and each band 316 can be made different
in the thickness of the absorbent layer and has a indefinite
margin.
[0291] A means of forming a distribution of patterns is that, at
the step of coating the surface of the liquid pervious supporting
sheet with the dispersion liquid supplied in a constant flow, a
nozzle is used having a structure or function of imparting an
appropriate pattern to the thickness and/or width of the coated
layers.
[0292] A nozzle of this function may be ones shown in FIGS. 67 and
68. The nozzle 312 shown in FIG. 67 has a structure that two slits
having a prescribed length each are formed from the tip portion of
the tube shaped body 320 and the tip portion is divided into two
tips 321 and 322, and, as a result, a discharging outlet is formed
on each of the tips 321 and 322.
[0293] In addition, the nozzle 312 shown in FIG. 68 has a structure
that four slits having a prescribed length each are formed from the
tip portion of the tube shaped body 320 and the tip portion is thus
divided into four portions 323 to 326. In this case, on each tip of
the four portions 323 to 326 a discharging outlet is formed.
[0294] Examples of other structures of the nozzle are shown in
FIGS. 69 to 71. The nozzle 312 of FIG. 69 has a structure in which
on the tip of the tube 331 having rigidity or some flexibility a
tongue portion 332 is formed in an integrated way. Also, the nozzle
312 of FIG. 70 has a structure in which on the tip of the tube 331a
separately prepared tongue portion having rigidity or some
flexibility is mounted. Further, the nozzle 312 of FIG. 71 has a
structure in which on the tip of the tube 331a separately prepared
flexible tongue portion 334 and a reinforcing member 335 on the
outside of the tongue portion are mounted.
[0295] In the cases of the nozzles shown in FIGS. 69 to 71, a
discharging outlet on the opening on the tip of the body 331 and a
discharging outlet on the tip of each tongue portion 332 to 334 are
formed so that each nozzle is provided with a plurality of
discharging outlets.
[0296] These nozzles 312 are disposed at right angles to the liquid
pervious supporting sheet 203 to be coated with the slurry
dispersion liquid as shown in FIG. 72 or inclined by some degrees q
to the liquid pervious supporting sheet to be coated with the
slurry dispersion liquid as shown in FIG. 73. When the slurry
dispersion liquid is discharged from the nozzle of this
disposition, the dispersion liquid is discharged in a direction of
lower resistance depending upon the discharging pressure so that
coating is conducted in a pattern having indefinite margins.
[0297] The reason why the above-described operation is conducted
with relative ease is because the slurry containing the SAP and the
HFFM has a structural viscosity (thixotropic flow). The property of
the slurry may be contributing to the easy operation of the coating
that the slurry is discharged from the nozzle keeping a high
liquidity while it has a discharging flow velocity, but after
discharged it loses the liquidity and solidifies.
[0298] As a result of this, a plurality of high absorbing regions
in bands varied in thickness and having indefinite margins are
formed on the surface of the liquid pervious supporting sheet.
[0299] Another means of forming a distributed pattern of absorbent
layers on the supporting sheet is to give pulsation effects by
incorporating a pulsation generating area in either of or both of
the nozzle portion including a header and the feeding mechanism of
the supporting sheet. By this means absorbent layers which are
periodically varied in thickness and width can be formed. In the
above, the methods of utilizing the pulsation of a pump, utilizing
a special type of a nozzle, and vibrating an apparatus to give
pulsating effects to the dispersion slurry as the means of forming
a distribution of patterns are described. To be combined with
either of the methods there is a means of making such SAP as is
different in particle size or shape or gives a large difference in
absorbing speed co-exist in the dispersion slurry. In this case,
with the uniform dispersion and the stable discharging from the
nozzle taken into consideration, it is preferable to disperse such
SAP as is of larger particle size or of different shape in a
dispersion system of such SAP as is of relatively fine particle
size.
[0300] Now, the purpose of forming a distribution of patterns like
this is that while, having different distributions of
concentrations (higher and lower concentrations), of densities
(higher and lower densities), and of thickness (thicker and
thinner) and at the same time increasing the surface area of lower
concentration portions, rapid absorbing and diffusion are obtained
by utilizing lower concentration portions or non-absorbing portions
and time requiring but stable absorbing is realized by utilizing
thicker concentration portions so that an absorbent suitable for
absorbing as many times as possible utilizing a structure of as
many phases as possible can be designed. On the other hand, by
imparting this structure sufficient flexibility can be imparted to
the whole of an absorbent sheet to fit well the body of a wearer.
In other words the portion which is coated thick with absorbent
layer has rigidity and is hard to be bent while the portion which
is little or not coated with absorbent layer is very easy to be
bent with the property of the supporting sheet itself
maintained.
[0301] This method is extremely effective from the commercial
viewpoint. FIGS. 74 and 75 show examples a process of making an
absorbent sheet having a plurality of high absorbing regions having
high absorbing capability distributed in a pattern according to the
present invention.
[0302] A coating apparatus shown in FIG. 74 is composed as follows:
a suction roll 341 and a heat press roll 342 supported with a shaft
and arranged in parallel to each other are provided and a liquid
pervious supporting sheet 203 is guided via guide roll 343 to the
suction roll 341 and at the position where the liquid pervious
supporting sheet 203 is rotated approximately one fourth of the
periphery of the suction roll 341, the liquid pervious supporting
sheet 203 comes in contact with the heat press roll 342, and then
while in contact with the heat-press roll 342 the liquid pervious
supporting sheet 203 is rotated approximately one half of the
periphery of the heat press roll 342, and finally is guided via a
guide roll 344 to a dryer (not shown).
[0303] A suction area 345 is provided in the suction roll 341,
which area forms a region for sucking the liquid pervious
supporting sheet 203 conveyed in contact with the periphery of the
suction roll 341. A nozzle 312 is disposed at a position where the
nozzle 312 can discharge a slurry dispersion liquid onto the
surface of the liquid pervious supporting sheet 203 in this suction
area, and forms layers in a desired pattern on the liquid pervious
supporting sheet 203. Reduced pressure generated in the suction
area makes the slurry dispersion liquid adhere to the surface of
the liquid pervious supporting sheet 203 and at the same time sucks
an excess of the solvent contained in the slurry dispersion liquid
together with surrounding air. The sucked liquid is guided via a
pipe 346 to a strainer 347 where the liquid is separated into
solvent and gas. The solvent thus separated is taken out via a pipe
349 for recycle to form a slurry dispersion liquid, and the gas is
discharged outside from a pipe 348 via a vacuum pump (not
shown).
[0304] The liquid pervious supporting sheet 203 is then conveyed
while in contact with the heat press roll 342, in the process of
which slurry dispersion liquid as heated is adhered to the liquid
pervious supporting sheet 203, and the obtained absorbent sheet is
then guided via the guide roll 344 to the dryer where the absorbent
sheet is dried finally.
[0305] A coating apparatus shown in FIG. 75 is only different from
the coating apparatus of FIG. 74 in that in addition to the suction
area 345 disposed facing the nozzle 312, a second suction area 350
is provided as disposed in the nip with a heat press roll 342. In
the second suction area 350, the solvent is further strongly sucked
and separated from the slurry dispersion liquid while the slurry
dispersion liquid is pressed between a suction roll 341 and a heat
press roll 342.
[0306] A coating apparatus shown in FIG. 76 is different only in
that a nozzle 312 is designed to apply a slurry dispersion liquid
not over a suction roll 341 but on the periphery of a supporting
roll 351 provided before the suction roll 341.
[0307] Slurry to be obtained by dispersing the SAP and the MFC in a
dispersion medium of water/organic solvent, when the slurry is
discharged from a nozzle and applied to a supporting sheet to form
a absorbent sheet, is likely to be separated into two phases
depending upon the conditions of the dispersion medium, solids may
settle. Therefore, the solids in the slurry may settle in the
transportation in a configuration of the apparatus where, as shown
in FIG. 61, the slurry is guided to a nozzle via a dispersion tank,
a slurry pump, a pipe, and a header (supplying tank). In such case,
it is preferable to directly connect a discharging nozzle to each
slurry pump and to apply the slurry from this discharging nozzle.
FIG. 90 shows an example of this structure: slurry is applied in
may bands extending in parallel at intervals.
[0308] In the configuration illustrated in FIG. 90, slurry is
applied in many bands extending in parallel at intervals on a
supporting sheet as shown in FIG. 91. In applying the slurry on the
whole surface of the supporting sheet, two pairs of a plurality of
slurry pumps provided with a plurality of discharging outlets may
be arranged in front and in rear in the direction of running of the
supporting sheet so that the discharging nozzle in rear are
disposed in between the discharging nozzles in front.
EXAMPLES
[0309] The examples of practicing the present invention are
described hereunder:
Example 1
Preparing the HFFM Dispersion Liquids
[0310] Ethyl alcohol and ion-exchanged water were added to a
dispersion liquid of the S-MFC (made by Tokushu Paper Mfg. Co.,
Ltd.) in gel state of 3.0% water dispersion as a stock liquid, to
make three kinds of microfibril dispersion liquid where the ratio
of ethyl alcohol/water was 70/30 and the concentrations of the
S-MFC were 0.25%, 0.5% and 1%, respectively.
Preparing the HFFM/SAP Coexistent Dispersion Liquids
[0311] 10 grams of the SAP (made by Sanyo Chemical Industries, Ltd.
under the trademark "IM-6700") passed by 60 to 100 mesh was added
to 50 cc of each of the above-mentioned three kinds of the HFFM
dispersion liquid to prepare the HFFM/SAP dispersion slurry.
[0312] The prepared dispersion slurry is described as follows:
TABLE-US-00003 TABLE 2 Experiment Ethyl Concentration S-MFC/SAP
.times. No. alcohol/water of S-MFC(%) 100(%) No. 1 70/30 0.2 0.1
No. 2 70/30 0.5 2.5 No. 3 70/30 1.0 5.0
Forming the HFFM/SAP Composite Sheet Material
[0313] Each of the dispersion liquids while stirred was subjected
to removing the liquid component under a pressure reduced by an
aspirator, and then dried at 5.degree. C. under reduced pressure
while spread on a PP non-woven fabric.
[0314] The composite after dried was formed in soybean shaped
lumps. The composite in lumps as wrapped in a fine mesh shirting
was crushed with a wood hammer, and passed by a 40 to 60 mesh to
run absorbing tests.
TABLE-US-00004 TABLE 3 Experiment No. Crushed state No. 1
Relatively easily crushed No. 2 Hardened and hard to be crushed No.
3 Hardened in pebble-like lumps and stickly, and extremely ahrd to
be crushed
[0315] The highly absorbent composite crushed into powder had,
observed by a microscope, its surface covered with the HFFM as
shown in FIGS. 7(a) and 7(b).
Evaluating Absorbency
[0316] The water absorbing speed, gel block state, absorbed amount
of water, and retained amount of water of the above-described SAP
(both passing by 60 to 100 mesh and 40 to 60 mesh) were measured.
For the absorbing speed, an initial absorbing time (sec.) required
for absorbing 20 cc of water was measured. For the absorbed amount
of water and the retained amount of water, the SAP, after dipped in
an excessive amount of physiological saline solution, was measured
in accordance with JIS K-7223. The measured results are as shown in
Table 4:
TABLE-US-00005 TABLE 4 Blnak No. 1 No. 2 No. 3 Absorbed amount of
45 47 44 46 physiological saline solution (g/g) Retailed amount of
35 34 34 36 physiological saline solution (g/g) Absorbing speed of
15 5 10 30 physiological saline (Unswollen (Unswollen solution
(sec.) lump lump partly generated) generated)
[0317] As clearly shown in the above-tabulated results of
measurements, the absorbency and the water retention were little
affected by adding the S-MFC. On the other hand, as the
concentration of the S-MFC was increased from No. 1 to No. 3, the
bonding strength of the SAP was increased, but the SAP became
harder to handle because it was hardened. Moreover, since the
concentration increased, the absorbing speed was lowered.
Therefore, in such applications as such properties (absorbing speed
and the like) are important, the percentage of the HFFM to be added
to the SAP should be preferably 5% or lower.
Example 2
Concentration of the HFFM and the Properties of a Composite Sheet
Material
Preparing the HFFM Dispersion Liquid
[0318] Preparing a Bacteria Cellulose (BC) Stock Solution
[0319] BC (made by B.P.R.) where the concentration of solids was
30% was stirred and dissolved in ion-exchanged water by a mixer for
approximately 2 hours to prepare a stock solution where the
concentration of solids was 1.2%.
Preparing Ethyl Alcohol/Water Dispersion Liquids of BC
[0320] Ethyl alcohol and water were added to a prescribed amount of
the stock solution to prepare BC dispersion liquids of 0.02% to
0.80% BC.
Preparing the HFFM/SAP Coexistent Dispersion Liquid
[0321] 5 grams of the SAP (made by Sanyo Chemical Industries, Ltd.)
was added to 50 cc of each of the dispersion liquids of 0.02% to
0.8% BC to prepare BC/SAP dispersion liquids. In case the
concentration of the BC was lower in the dispersion liquid, the SAP
settled, but as the concentration of the BC became higher, it
became stabilized. By stirring with a stirrer, the systems were
kept stabilized to match the conditions of the systems as
desired.
[0322] The descriptions of thus obtained BC/SAP coexistent
dispersion liquids are as follows:
TABLE-US-00006 TABLE 5 Experiment Ethyl alcohol/ Concentration
EC/SAP .times. 100 No. water of BC (%) (%) No. 11 70/30 0.02 0.2
No. 12 70/30 0.05 0.5 No. 13 70/30 0.10 1.0 No. 14 70/30 0.20 2.0
No. 15 70/30 0.40 4.0 No. 16 70/30 0.80 8.0 Blank 70/30 0 0
Forming the HFFM/SAP Composite Sheet Material
[0323] A filter paper and a substrate non-woven fabric (made by
Futamura Chemical Co., Ltd. under the trademark "TCF 403", of an
apparent specific density of 0.07 gram/cm.sup.3) were laid on a
Buchner funnel of a 11 cm inner diameter as connected to a pressure
reducing apparatus, and 20 cc of the sticky dispersion liquid was
poured quickly onto the substrate non-woven fabric. The non-woven
fabric was subjected to removal of the liquid component under
reduced pressure and dried in hot air to form a composite
sheet.
Comparison of the Properties of Composite Sheet Materials
[0324] The properties of the composite sheet materials where the
concentrations of the BC were different were evaluated and
compared, which results are shown in Table 6. The experimental
results show that, as the added amount of the BC was increased, the
surface strength of the composite sheet materials was increased
very much while the rigidity of the sheets was increased on the
other hand. Therefore, it is necessary to properly select the added
amount of the BC according to the applications.
TABLE-US-00007 TABLE 6 Experiment No. No. 11 No. 12 No. 13 No. 14
No. 15 No. 16 Blank BC/SAP ratio (%) 0.2 0.5 1.0 2.0 4.0 8.0 0
Thickness (mm) 0.60 0.60 0.55 0.56 0.58 0.57 0.55 Weight
(g/cm.sup.2) 126 131 128 126 135 130 135 Deposited SAP + 88 93 90
88 97 92 97 BC (g/cm.sup.2) Apparent specific 0.22 0.24 0.24 0.24
0.25 0.24 0.28 gravity(g/cm.sup.3) Rigidity (mm) 85 78 68 40 25 15
85 180 degree Grade 2 Grade 3 Grade 3 Grade 4 Grade 5 Grade 5 Grade
1 peeling test using cellophane adhesive tape
[0325] The evaluation methods for evaluation items are described
below:
[0326] Thickness (mm): Measured by a thickness gauge (JIS) in the
same way as described in the above.
[0327] Weight (g): Measured together with the substrate of 110 mm
diameter by an electronic Roberval balance.
[0328] Deposited SAP and BC (g/m.sup.2): Calculated by deducting
the substrate non-woven fabric from the above weight and expressed
in grams per square meter.
[0329] Apparent specific density (g/cm.sup.3): Calculated from the
thickness and the weight of the substrate non-woven fabric and the
weight of the deposited SAP and BC.
[0330] Rigidity (mm): A sample of 110 mm.times.20 mm was measured
by a method as shown in FIGS. 77 and 78. One end of the sample S
was placed at the edge of a stainless steel measure M at right
angle, and the scale of the measure was read at the position where
the sample sagged (a mm).
Evaluating the Bonding Stability of the Sap (180 Degree Peeling
Test Using Cellophane Adhesive Tape)
[0331] A cellophane adhesive tape (made by Nichiban Co., Ltd. under
trademark "CELLOTAPE") of 15 mm width was adhered on the sample in
an adhered area of 15 mm.times.10 mm, and the adhered area was
pressed lightly with a flannel cloth, and a load of 1 kg/cm.sup.2
was applied for 10 minutes. After the load was removed, the
cellophane adhesive tape was peeled off by hand from the sample in
a 180 degree peeling condition. By measuring the adhered area (%)
of the SAP adhered on the cellophane tape, the bonding strength of
the HFFM was judged by such adhered area of the SAP. The judgement
criteria are shown in FIG. 79.
Evaluating Absorbed Amounts of Water and Retained Amounts of Water
by Composite Samples
[0332] The composite samples were dipped in a sufficient amount of
physiological saline solution for 30 minutes and then the absorbed
amounts of water and the retained amounts of water were measured by
MS K-7223. The measurements were converted into the SAP contents.
The results are shown in Table 7 below:
TABLE-US-00008 TABLE 7 Absorbed amount Retained amount Experiment
No. of water (times) of water (times) Used SAP samples 45 37
(Blank) No. 12 44 36 No. 13 46 38 No. 14 48 36
Example 3
Continuous Coating Experiments
[0333] A highly absorbent composite was made by using an apparatus
as shown in FIG. 61 provided with a coating unit as shown in FIG.
63, using the following materials:
(1) Microfibril: S-MFC (made by Tokushu Paper Mfg. Co., Ltd.) (2)
SAP: 1M-4000 (made by Hoechst-Celanese Co.) (3) Suspension medium:
Acetone/water system (4) Coating composition:
TABLE-US-00009 Component % by weight S-MFC 0.4 SAP 30.0 Acetone
48.8 Water 20.8
(5) Supporting sheet: A two-layered through-air thermal bond web
non-woven fabric (40 g/cm.sup.2, apparent specific density of 0.06)
having the following composition was used:
[0334] Upper layer: Mixed web of rayon (4 denier.times.45 mm length
(70%)) and PE/PET (2 denier.times.45 mm length (30%)),
approximately 25 g/cm.sup.2
[0335] Lower layer: Single web of PE/PET bicomponent fiber (2
denier.times.45 mm length), approximately 15 g/cm.sup.2.
[0336] A mixture dispersion liquid of the composition in (4) above
was continuously applied in approximately 10 mm width at an
interval of 5 mm width onto the surface of the supporting sheet 13
while the sheet was conveyed at a speed of 10 m/min. Afterwards,
the solvent was removed from the supporting sheet as compressed by
a roll, and then dried in hot air.
[0337] The obtained highly absorbent composite sheet had the
following characteristics:
TABLE-US-00010 Weight 195 g/cm.sup.2 Amount of SAP 150 g/m.sup.2
Rigidity Longitudinal: 20 mm Lateral 75 mm Surface strength class 5
(180 degree peeling test)
[0338] The retained amount of water in the absorbent was measured
by JIS K-7223. As a result, the SAP retained water at the rate of
40.2 grams of water per 1 gram of the SAP, which was nearly
equivalent to the level of the "blank".
Example 4
[0339] A commercially available ultra thin disposable diaper was
used as the "blank". A sample was prepared by removing absorbent
components including tissue from one of such disposable diapers and
by, for such absorbent components, incorporating an absorbent
composed of a highly absorbent composite of the present
invention.
[0340] The absorbent incorporated in the sample was prepared in the
following procedure: first, a composite sheet as obtained in
Example 3 above was cut in a shape and dimensions as shown in FIG.
80. On the other hand, a pulp mat provided with tissue of
approximately 90 g/cm.sup.2 was prepared. Water drops were sprayed
onto the composite sheet by a hand spray for a domestic use iron to
make the weight of the sheet 2 to 3 g/cm.sup.2. The cut absorbent
was laid on the sheet, and pressed under pressure by a iron at a
temperature of 140 to 150.degree. C.
[0341] Five pieces of the sample were prepared. For each sample
piece, the absorbed amount of water, retained amount of water and
rewet were measured. The absorbed amount of water and the retained
amount of water were measured by JIS K-7223. The rewet was measured
as follows: 120 cc of physiological saline solution was poured onto
a sample three times at 5 minute interval, and the rewet was
measured for each of the three times under the pressure of 12.5 kg
per absorbent area.
[0342] The above-mentioned test results are tabulated in the
following table. The measurements are shown in the average of the
five sample pieces.
TABLE-US-00011 TABLE 8 Sample of the Blank present invention
Configuration of absorbent Measurement item Thickness (mm) 3.2 1.5
Weight of whole absorbent (g/p) 26.0 17.5 Fluff pulp (g/p) 11.8 6.1
Tissue(g/p) 4.0 0.5 SAP(g/p) 10.2 10.9 Property of absorbent
Measurement item Absorbed amount of water (g/p) 665 557 Retained
amount of water (g/p) 420 42.5 Re-wet (g) First re-wet (120 cc) 0.6
0.4 Second re-wet (240 cc) 0.8 0.9 Third re-wet (360 cc) 3.9
2.2
[0343] From Table 8 it is shown that a sample where an absorbent
composed of a highly absorbent composite of the present invention,
which is approximately 70% in weight and one half in thickness of a
commercially available disposable diaper, has equivalent or
superior absorbing properties compared with the latter.
Example 5
1) Preparing a SAP Slurry
[0344] To a dispersion liquid of 2.15% water of the S-MFC (made by
Tokushu Paper Mfg. Co., Ltd. under trademark "Super Microfibril
Cellulose"), required amounts of water and ethanol were added to
prepare a ethanol/water dispersion liquid (ethanol/water ratio
being 60/40) where the concentration of MFC was 0.86% by
weight.
[0345] To this dispersion liquid a short-cut staple fiber component
composed of low melting point polyester/PET bicomponent fiber of
1.5 denier and 2 mm fiber length was added in an amount equivalent
to the amount of the S-MFC, and dispersed with a mixer. Then, as it
was stirred in a stirrer with a propeller, a required amount of the
SAP (made by Mitsubishi Chemical Co., Ltd. under the trademark
"Aquapearl US-40") was added to make a three component slurry
composed of 30% by weight SAP, 0.6% by weight MFC and 0.6% by
weight short-cut staple fiber component.
2) Preparing a Supporting Sheet
[0346] A two-layered spun-lace non-woven fabric where a first layer
was composed of fine denier rayon fiber of 1.25 denier and 51 mm
length and a second layer was composed of coarse denier PET fiber
of 6 denier and 51 mm length was prepared. The weight of this
non-woven fabric was 30 g/m.sup.2, with an apparent specific
density of 0.025 g/cm.sup.3, with the first later of higher density
and the second layer of lower density.
3) Preparing Composite Absorbent
[0347] The three-component slurry was applied onto the second layer
of the supporting sheet with a coater in an amount to make the
deposited amount of the SAP 150 g/m.sup.2. Then, immediately after
it was sucked and the liquid component was removed, it was hot
pressed for a few minutes at 180.degree. C. The supporting sheet
was then dried in hot air to make a composite absorbent (I).
[0348] Also, the composite absorbent (I) was then dried in hot air
again at 150.degree. C. to make a composite absorbent (II).
[0349] The structure of the absorbent composites (I) and (II) was
observed by a microscope. As shown in a sketch of FIG. 54, it was
confirmed that on a second layer 111b of a supporting sheet
composed of a first layer 111a and the bulky second layer 111b and
in the space, the SAP particles 112 were piled and the short-cut
staple fiber component existed as entangled with the SAP particles
and covering the SAP particles like an umbrella, and, on the
surfaces of the SAP particles and of the short-cut staple fiber
component, the MFC 114 was deposited.
Comparative Example 1
[0350] In Example 1, a procedure applied in making the composite
absorbent (II) was applied to make a composite absorbent (ii)
except that no short-cut staple fiber component was added.
<Evaluating the Composite Absorbents>
[0351] With the three kinds of absorbent composites obtained in
Example 1 and Comparative Example 1 used, the sustainability of the
swollen SAP and the diffusion of absorbed liquid by the swollen SAP
when wet were tested by the above-described testing methods. The
test results are summarized in Table 9 below:
1) 2)
TABLE-US-00012 TABLE 9 Sustainability of swollen SAP Dispersion of
absorbed liquid Composite Standing Standing Vertically Absorbing
Time till dispersion absorbent Sustainability falling-off suspended
time (sec.) finished (sec.) (I) .circleincircle.
.circleincircle.~.largecircle. .circleincircle.~.largecircle. 3~4
40~50 (II) .circleincircle. .circleincircle. .circleincircle. 3~5
50~60 (ii) .DELTA. .DELTA. .DELTA. 3~4 40~50
[0352] From the test results tabulated in the above, the following
judgements can be made:
{circle around (1)} Sustainability of the Swollen SAP
[0353] The composite absorbent (I) showed a good retention of the
swollen SAP, which was made with a bicomponent short-cut staple
fiber containing an easy-to-melt component incorporated.
[0354] The composite absorbent (II) which was heat treated
adequately showed an outstanding sustainability in a particularly
rigorous test of a vertically suspended sustainability.
[0355] However, the composite absorbent (ii) in Comparative Example
1 where no short-cut staple fiber component was incorporated showed
substantially lower sustainability of the swollen SAP than the
absorbent composites (I) and (II) in Example 1.
[0356] This was probably because, by incorporating short-cut staple
fibers containing easy-to-melt fibers and by heat treating, the
short-cut staple fibers were fused with each other and the
short-cut staple fibers and the stereo-specific fibers of the
supporting sheet were fused in their contact points, so that
stereo-specific networks were generated, which networks held the
swollen SAP.
{circle around (2)} Dispersion of Absorbed Liquid
[0357] Although it was feared that the combination of the
easy-to-melt short-cut staple fibers and the thermal fusion of
fibers by heat treatment would affect unfavorably the absorption
and the diffusion speed of a liquid, there was none or little
influence on the absorbing time and only a little influence on the
time until diffusion was finished, which was a level never giving
rise to any problems in practical use at all.
Example 6
1) Preparing the SAP Slurries
[0358] To a 0.5% water dispersion liquid of the BC (made by
Ajinomoto Co., Ltd. under the trade-mark "Bacteria Cellulose") as
the HFFM, required amounts of water and ethanol were added to
prepare an ethanol/water dispersion liquid (the ratio of ethanol to
water being 60 to 40) where the concentration of the BC is 0.21% by
weight.
[0359] To this dispersion liquid, PE pulp (made by Mitsui Chemical
Co., Ltd. under the trademark "SWP-E400") of 0.1 to 3 denier and
0.3 to 5 mm fiber length as the short-cut staple fiber component
was added in amounts to make seven ratios of the short-cut staple
fiber component to BC (P/Q ratio), and the mixture was dispersed
uniformly by a mixer to prepare seven kinds of dispersion liquid of
different mixing ratios.
[0360] In addition, to each of the seven kinds (different in mixing
ratios of the BC and the SWP) of BC/SWP dispersion liquid while it
was stirred by a propeller mixer, a required amount of the SAP
(made by Mitsubishi Chemical Co., Ltd. under trademark "Aquapearl")
was added to prepare seven kinds of three component slurry. In all
the three-component slurries the concentration of the SAP was 15%
and the ratio of the BC to the SAP was 1%. The concentrations of
the components and the dispersion of the SAP in all the three
component slurries are shown in Table 10 below:
TABLE-US-00013 TABLE 10 Concentration 0.15 0.15 0.15 0.15 0.15 0.15
0.15 of BC (P) (%) Concentration 0.015 0.03 0.05 0.15 0.45 0.75
1.50 of SWP (Q) (%) P/Q ratio 10/1 5/1 3/1 1/1 1/3 1/5 1/10
Suspension of SWP SWP SWP SWP SWP not SWP SWP SWP stably stably
stably stably coagurated, coagurated, coagurated, though but can be
like soybean concentration used as cake, and can gets high. slurry.
not be used as slurry.
[0361] In the P/Q ratios of 10/1 to 1/3 (concentration of the SWP
being 0.45%), there was no coagulation of the SWP and the SWP was
stably dispersed, but when the ratio exceeded 1/5 (concentration of
the SWP being 0.75%), the slurry became cloudy with a little
coagulation seen but still could be practically used. However, in
case the P/Q ratio was around 1/10, the SWP coagulated too much to
make a slurry. Therefore, from the viewpoint of stable dispersion,
the upper limit was judged to be 1/5 for practical purposes.
2) Preparing Supporting Sheets
[0362] A two-layered through-air thermal bond non-woven fabric was
prepared, with a first layer composed of a mixed carded web of 50%
rayon of 1.5 denier and 40 mm length and 50% PE/PET bicomponent
fiber of 2 denier and 51 mm length and a second layer composed of
only PE/PET bicomponent fiber of 3 denier and 51 mm length laid on
each other and bonded in hot air. The weight of the non-woven
fabric was 30 g/m.sup.2, and the apparent specific density was 0.02
g/cm.sup.2.
3) Preparing Composite Absorbent
[0363] Onto the second layer of this supporting sheet each of the
six kinds of three-component slurry (excepting the one which could
not be prepared into a dispersion slurry because of the P/Q ratio
1/10 from the seven kinds of the three-component slurry) was
applied by a coater in an amount to make the deposited amount of
the SAP 150 g/m.sup.2. After sucking and removing the liquid
component were done, supporting sheets were heat pressed for
several minutes by means of a heated roller at 180.degree. C. and
then dried in hot air to prepare six kinds of composite absorbent
(III) to (VIII).
<Evaluating Composite Absorbents>
[0364] For the six kinds of composite absorbent the sustainability
of the swollen SAP and the diffusion of absorbed liquid by the
swollen SAP when wet were tested by the above-described testing
methods. The test results are summarized in the following
table:
TABLE-US-00014 TABLE 11 Dispersion of absorbed liquid
Sustainability of swollen SAP Time till Composite P/Q Standing
Standing Vertically Absorbing dispersion absorbent ratio
Sustainability sustainability suspended time (sec.) finished (sec.)
(III) 10/1 .largecircle. .largecircle. .largecircle. 3~5 50~60 (IV)
5/1 .circleincircle. .largecircle. .largecircle. 5~7 50~60 (V) 3/1
.circleincircle. .largecircle. .largecircle. 6~8 60~80 (VI) 1/1
.circleincircle. .circleincircle. .circleincircle. 8~10 80~100
(VII) 1/3 .circleincircle. .circleincircle. .circleincircle. 20~30
150~200 (VIII) 1/5 .circleincircle. .circleincircle.
.circleincircle. 30~50 240~300
[0365] From the above-tabulated test results the following
judgements can be made:
{circle around (1)} Sustainability of the Swollen SAP
[0366] In the composite absorbent where the content of the SWP was
low (P/Q=10/1), no remarkable improvement in sustainability of the
swollen SAP was seen, but as the content of the SWP increased, the
sustainability of the swollen SAP improved: at around 3/1 of the
P/Q ratio, the retention reached a nearly constant level, and at
the P/Q ratio of 1/1 or higher, the sustainability of the swollen
SAP in wet state was excellent. The lowest limit for realizing the
effects of the SWP seemed to be around the P/Q ratio of 5/1 for
practical purposes.
{circle around (2)} Dispersion of Absorbed Liquid
[0367] The speed of a composite absorbent absorbing a liquid and
the speed of the absorbed liquid being dispersed in the composite
absorbent were affected by the concentration of a short-cut staple
fiber component combined and the P/Q ratio. For example, in the
absorbent composites (III) to (VI) of the P/Q ratio ranging from
10/1 to 1/1, there was no appreciable difference among them and
they were all good. However, in the absorbent composites (VII) and
(VIII) of the P/Q ratio of 1/3 and 1/5, while the sustainability of
the swollen SAP improved, the absorption of a liquid and the
diffusion of a liquid tended to be lowered.
Example 7
1) Preparing a SAP Slurry
[0368] To a 2.15% water dispersion liquid of the S-MFC (made by
Tokushu Paper Mfg. Co., Ltd. under the trademark "Super Micro
Fibril Cellulose"), required amounts of water and propylene glycol
were added to prepare a water/propylene glycol (PG) dispersion
liquid (PG/water=70/30) where the concentration of the MFC was
0.86. % by weight. To this dispersion liquid, a required amount of
the SAP (made by Mitsubishi Chemical Co., Ltd. under the trademark
"Aquapearl US-40") was added to prepare a two-component slurry of
30% by weight SAP and 0.6% by weight MFC.
2) Preparing a Supporting Sheet
[0369] A two-layered through-air thermal bond non-woven fabric was
prepared, with a first layer composed of carded web of PE/PET
bicomponent fibers of 1.5 denier and 51 mm length and a second
layer composed of PE/PET bicomponent fibers of 3 denier and 51 mm
length laid on each other and bonded in hot air. The weight of this
non-woven fabric was 30 g/m.sup.2, and the apparent specific
density was 0.03 g/cm.sup.3.
3) Preparing a Composite Absorbent
[0370] The supporting sheet was placed on a plastic net with the
second layer facing upward, and the above-described two-component
slurry was applied by a roll coater onto the whole surface of the
supporting sheet, as it was continuously conveyed, in an amount to
make the deposited amount of the SAP 200 g/m.sup.2. Immediately
thereafter, sucking and removal of the liquid component were
carried out. Then, a 0.5% wood pulp dispersion liquid was poured
onto the slurry layer as a thin layer stream from a flow coater in
an amount to make the wood pulp 2% (4 g/m.sup.2) to the SAP.
Immediately thereafter, sucking and removal of the liquid component
were run so that no SAP swelled, the supporting sheet was then hot
pressed for several minutes by means of a heated roller whose
surface temperature was 150.degree. C. Further, the supporting
sheet was again dried in hot air at 140.degree. C. to make a
composite absorbent.
<Evaluating the Composite Absorbent>
[0371] The composite absorbent showed an outstanding sustainability
of the swollen SAP: No swollen SAP came off or peeled off from the
substrate. Also, since the surface of the supporting sheet was
coated with hydrophilic wood pulp, the absorbency of a liquid was
excellent and the diffusion of an absorbed liquid was also at a
level not giving rise to any practical problems. It was confirmed
that, when this composite absorbent was used as the absorbent of a
baby diaper, no additional non-woven fabric layer for acquisition
was required because, as the first layer and the topsheet were used
as bonded together, the first layer functioned as the acquisition
layer.
Example 8
[0372] The surface of a wet process non-woven fabric of 40
g/m.sup.2 weight (made by Futamura Chemical Industries Co., Ltd.
under the trademark "TCF 404") was raised by a brush to make the
apparent specific density 0.04 g/cm.sup.3.
[0373] On the raised surface of this supporting sheet, the SAP
particles (made by Mitsubishi Chemical Co., Ltd. under the
trademark "US-40") was scattered using a sieve as it was vibrated
in an amount to make the scattered amount of 120 g/m.sup.2.
[0374] Separately, a mixture dispersion liquid where the S-MFC and
easy-to dissolve-in-hot-water PVA staple fiber (of 1.5 denier and 2
mm length) were dispersed in water in a way that the concentration
of each of the MFC and the PVA fiber was 0.5% was prepared. The
raised surface of the supporting sheet was coated with the mixture
dispersion liquid by a flow coater in an amount to make the
percentage each of the S-MFC and the PVA fiber to the SAP 1% (1.5
g/m.sup.2), and immediately thereafter, sucking and liquid removing
of the liquid component were run. Then, the supporting sheet was
hot pressed by a roller heated at 200.degree. C., and dried in hot
air at 100.degree. C. to make a composite absorbent.
[0375] Only a little SAP came off or peeled off from the obtained
composite absorbent, and thus had a level of sustainability of the
swollen SAP not giving rise to any practical problems. The
absorbing and diffusion of a liquid were extremely good. This was
probably because both the supporting sheet and the short-cut staple
fiber component were hydrophilic.
Example 9
1) Preparing a Three-Component Dispersion Liquid
[0376] 1.4 denier and 3 mm length Lyocell (trademark, made by
Coutaulds) was added to and dispersed in a dispersion medium of
ethanol/water=60/40 to prepare a 0.5% dispersion liquid. This
dispersion liquid was stirred by a mixer to fibrillate Lyocell.
Then, the MFC was added to and dispersed in the dispersion liquid
in an amount to make the concentration of the MFC in the dispersion
liquid 0.5%, and the dispersion liquid was treated for 5 minutes by
a mixer to prepare a two-component dispersion liquid.
[0377] SAP flake (made by Hoechst-Celanese under the trademark
"IM-4000") of 50 mesh was added to the two-component dispersion
liquid while the dispersion liquid was slowly stirred in an amount
to make the concentration of the SAP 25%, to make a three-component
dispersion liquid of the SAP, the MFC and Lyocell.
2) Preparing a Supporting Sheet
[0378] A mixed carded web was prepared composed of 50% rayon staple
fiber (of 1.5 denier.times.35 mm length) and 50% PE/PET bicomponent
fiber (of 3 denier.times.41 mm length) with the weight of 15
g/m.sup.2, and the carded web laid on PP spun-bond non-woven fabric
of 15 g/m.sup.2 weight was entangled by water jet to make a plural
layered non-woven fabric, which was made a supporting sheet.
3) Making a Composite Absorbent
[0379] As shown in FIG. 81, the three-component slurry 822 was
discharged from a plurality of discharging tubes directly connected
to a slurry pump onto the rayon staple fiber/bicomponent fiber
surface of a supporting sheet 821 in the pattern as shown in FIG.
81. After removal of the liquid component under reduced pressure,
the supporting sheet was fixed by a heat press and dried to make a
composite absorbent.
[0380] The obtained composite absorbent was approximately 130
g/m.sup.2 in terms of the total SAP applied, and the portions (SAP)
formed in lines on the obtained composite absorbent was
approximately 200 to 250 g/m.sup.2.
4) Applying to the Absorbent for Use in Baby Diaper
[0381] As shown in FIG. 82(a), a dry laid carded web non-woven
fabric 831 as the topsheet in contact with the skin of a wearer, as
mainly composed of 18 g/m.sup.2 PE/PET bicomponent fiber of 1.5
denier.times.41 mm length was prepared. Onto this non-woven fabric
831, polyurethane filament yarns 832 (made by Toray Co., Ltd. under
the trademark "Lycra") was bonded by hot melt method in rows at
such intervals as shown in FIG. 82(a) to form a topsheet. The
topsheet provided with an elastic member and a composite absorbent
833 as shown in FIG. 82(b) obtained in this Example 9 of the
present invention were bonded by thermal fusion at the portions
where no absorbent existed thereby a bonded member of the topsheet
and the composite absorbent having a structure shown in FIG. 82(c)
was obtained.
[0382] The bonded member was covered at the side of the composite
absorbent by a leakage resistant member 834 made by bonding PE film
and non-woven fabric as shown in FIG. 82(d) to obtain an absorbent
for use in a baby diaper, of 200 mm width and 400 mm length. This
absorbent was dipped in a physiological saline solution and then
taken out and placed on a net so that a free liquid is removed from
the absorbent. The total amount of the solution absorbed, as
measured, was 600 cc. The initial penetration speed was 20 seconds
with 100 cc, and the rewet was 0.5 gram. Thus, the composite
absorbent of the present invention was proved to have excellent
properties as the absorbent.
5) Applying for Use in Incontinent Pad for Women
[0383] As shown in FIG. 83, a slurry of the above-described
composition 842 was applied onto a circular supporting sheet 841 as
shown in FIG. 83(a) in a doughnut shape of 120 mm a circular
supporting sheet 841 as shown in FIG. 83(a) in a doughnut shape of
120 mm diameter with a center hole of 50 mm diameter, and, after
drying, the surface was covered with a hydrophobic spun-bond 843 to
make a composite absorbent. This composite absorbent was folded in
a folding fan-like shape as shown in FIG. 83(c), and the tip of the
composite absorbent was covered with an apertured PE non-woven
fabric 844 to make an incontinent pad of a structure as shown in
FIG. 83(d). No absorbent existed at the portion where the apertured
PE non-woven fabric 844 was provided and the portion which was in
thin sheet was for partial insertion in a vagina for securing the
pad to the body of a wearer. The amount of liquid retained by this
incontinent pad was 50 cc, and the incontinent pad was used as a
sample in a wearing test by a patient having a light incontinence
with the result that the patient's underwear was not stained and
that it can be used stably.
Example 10
Preparing a Slurry
[0384] A water dispersion stock solution of 3% by weight S-MFC was
added to make a dispersion medium composed of 60 parts ethanol and
40 parts water, to prepare a dispersion liquid of 0.6% by weight
S-MFC. Into this dispersion liquid, the SAP equivalent to 30% by
weight (made by Mitsubishi Chemical Co., Ltd. Under the trademark
"US-40" with the average particle diameter of 200 microns) was
added while the SAP was stirred by a propeller mixer to prepare a
slurry.
<Forming with the Slurry Pattern on a Supporting Sheet>
[0385] Using a slurry coating apparatus as shown in FIG. 76 (a
slurry discharging part thereof being shown, as enlarged, in FIG.
66), the slurry was applied onto the top surface of 40 g/m.sup.2
TCF (cellulosic non-woven fabric) used as a supporting sheet to
form a pattern of slurry by means of tube pumps arranged in many
rows in an amount to make the average deposited amount of the SAP
125 g/m.sup.2. By the pulsation generated by the stroke of the tube
pump, a sheet having the ellipsoidal pattern which has
intermittently thicker slurry in the center regions was formed.
<Bonding the Slurry Formed in a Pattern to the Supporting
Sheet>
[0386] A supporting sheet on which the slurry was formed in a
pattern was hot pressed by means of a hot press roll of 160.degree.
C. and a suction roll, as shown in FIG. 76, and at the same time an
excess of the dispersion medium was sucked and removed. Thereafter,
the sheet was made to contact with a hot roll for approximately 5
seconds to remove the liquid component from the sheet and the
applied slurry was bonded to the supporting sheet securely.
Afterwards, the supporting sheet was peeled off from the hot roll
and air dried to make an absorbent sheet. At that time, there was
no deposit of the slurry on the hot roll because partially peeled
off from the supporting sheet. For comparison, the sheet was passed
at room temperature, with the hot roll not heated, in which case a
majority of the slurry formed in a pattern on the supporting sheet
was peeled off and deposited on the surface of the roll. From this
fact the effects of bonding the SAP to the supporting sheet by hot
roll were be confirmed.
[0387] After hot pressing, the dried sheet showed a distribution of
patterns as shown in FIG. 55. The bonding to the supporting sheet
was as shown in a fragmentary sectional view of FIG. 56, and the
applied SAP was in one layer at the thin regions, in nearly three
layers at the thick regions and in nearly two layers at the medium
regions. This difference in thickness, or in the number of layers,
gave a desired distribution of the concentrations which were not
uniform, but continuous.
<Properties of Pattern-Formed Sheets>
[0388] A sample piece taken from each of the regions having the
thick SAP pattern, the thin SAP pattern and the medium SAP pattern
was observed in cross-section by a magnifying glass, to confirm the
number of the SAP layers whereby the amount of absorbed liquid and
the absorbing speed were evaluated as the liquid absorbing
properties of the SAP.
{circle around (1)} Amount of absorbed liquid: Using a 0.9% NaCl
aqueous solution (physiological saline solution), a method
corresponding to a method of testing an amount of absorbed water of
JIS K-7223 was applied. {circle around (2)} Absorbing speed: A
plurality of sample pieces of approximately 5 mm.times.10 mm were
dipped in a large amount of a 0.9% NaCl aqueous solution and the
time until the SAP in a sample became nearly completely swollen in
seconds was measured.
[0389] For the amount of liquid absorbed, sample pieces of 10
cm.times.10 cm were taken from the supporting sheet including from
thickly to thinly coated portions and as the average value of the
whole sheet, the total amount of liquid absorbed was 6.0
kg/m.sup.2. As the process of absorbing a liquid was observed, it
was confirmed that the thinly coated region, first, absorbed, and
the absorbing progressed gradually to the medium coated and then to
the thickly coated region. The differences in liquid absorbing
speed among the regions are shown in Table 12:
TABLE-US-00015 TABLE 12 Thinly coated Medium coated Thickly coated
Region region (one region (two region (three of sample layer of
SAP) layer of SAP) layer of SAP) Absorbing 10-15 30-60 90-180 speed
(sec.)
[0390] From the above-tabulated results, it was confirmed that the
obtained absorbent sheet was flexible and had a characteristic
property of providing a distribution of highly absorbing regions
different in absorbing speeds.
Example 11
Preparing a Slurry from the Sap Having Different Particle
Diameters
[0391] The SAP whose average particle diameters were 200 microns
and 800 microns were prepared. As the 200 micron sample Mitsubishi
Chemical's US-40 as used in Example 10 was used as the blank, while
as the 800 micron sample a pelletized SAP with higher surface
cross-linking was used.
[0392] The following table shows the measurements of the time of
absorbing 20 cc of physiological saline solution by 1 g of the SAP:
As for the time of absorbing a liquid by the SAP (Refer to Example
10 above), as the particle diameter became larger, liquid took more
time to penetrate into inside and the swelling became lower.
TABLE-US-00016 TABLE 13 Average particle diameter of SAP (micron)
200 800 Speed of absorbing liquid 10-15 60-150
[0393] Two kinds of slurry of 30% by weight SAP having the
above-described properties were prepared in the same way as in
Example 10 above.
<Coating of a Supporting Sheet with the Slurry>
[0394] Two headers were provided on a slurry coating apparatus as
shown in FIG. 66 in order to feed two kinds of slurry containing
the SAP whose particle diameters were different, and the apparatus
was modified to feed different kinds of slurry alternately to the
respective pumps.
[0395] Using this apparatus, two kinds of slurry were deposited in
a pattern on the TCF side of a supporting sheet in an amount to
make the average deposited amount of SAP 125 g/m.sup.2,
respectively, in a procedure similar to the one applied in Example
10 above. Thus, absorbent sheets with the slurry deposited in a
pattern were obtained. In the distribution of the pattern in this
case, as mentioned in the above, the rows of the pattern were
coated with the SAP of different particle diameters alternately.
Although the SAP of the same concentration was applied, because of
the difference in particle diameter, the pattern where larger
particle diameter SAP was applied was relatively thick.
[0396] The obtained sheet on which the SAP of different particle
diameters was applied was cut into a size of 10 cm.times.10 cm, and
placed in a Petri dish. 60 cc of physiological saline solution was
added at three times of 200 cc each at 5 minute interval, and the
state of absorption was observed. The observation results are shown
in Table 14.
[0397] It was confirmed that finer particle SAP first swelled and
the absorption progressed to coarser particle diameters.
TABLE-US-00017 TABLE 14 Patterns in absorbent layer Patterns in
absorbent layer composed of SAP of small composed of SAP of large
Liquid supplied particle diameter particle diameter First 200 cc
Swelling rapidly started Surface a little seemed to be absorbing,
but nearly dry condition continued Second 200 cc Swelling reach
saturation Overall swelling started, but there remained ample room
left for absorbing Third 200 cc Excess of water travelling Swollen
overall reaching in supporting sheet and saturation transferred to
patterns of larger particle diameter SAP
Example 12
Preparing a First Dispersion Liquid
[0398] To wood pulp (made by Weyerhaeuser, NBKP, needle leaf wood
bleached kraft pulp) and the SAP (made by Hoechst-Celanese under
the trademark "IM-4500"), a small amount of thickener (P.E.O.) for
paper-making was added to prepare a dispersion liquid of
EtOH/water=50/50 containing pulp/SAP=4 parts/6 parts. The
concentration of thus prepared slurry was approximately 2%.
<Forming an Absorbent Sheet from the First Dispersion
Liquid>
[0399] The above-described slurry dispersion liquid was poured onto
a PE/PET non-woven fabric (made by Unitika Co., Ltd. under the
trade name "Elves") of 20 g/m.sup.2 treated to be hydrophilic
disposed on a plastic mesh of 60 mesh to prepare a wet formed
absorbent mat. By pressing and drying this absorbent mat, an
absorbent sheet having 100 g/m.sup.2 absorbent layers composed of
pulp/SAP=4/6 was obtained.
<Preparing a Second Dispersion Liquid>
[0400] A slurry was prepared by including 30% SAP and 0.6% MFC in a
dispersion liquid of EtOH/water=6/4 prepared in a procedure
identical with the one applied in Example 10 above.
<Forming an Absorbent Sheet from the Second Dispersion
Liquid>
[0401] Onto an absorbent sheet made from the above-described first
dispersion liquid having uniform layers of pulp/SAP, slurry was fed
in a sea island-like pattern at 5 mm intervals, using an
experimental use tube pump (marketed under the trademark "MASTER
FLEX") with the second dispersion liquid contained in a silicone
rubber tube of 3 mm inside diameter. Then, the absorbent sheet was
hot pressed, using a Teflon-coated domestic use iron heated at
130.degree. C. and then dried. The layers formed from the second
dispersion liquid had the SAP of approximately 120 g/m.sup.2 on
average, although thicker at some places and thinner at others.
<Absorbent Sheet Having Highly Absorbing Regions in a Sea Island
Pattern and its Properties>
[0402] Thus obtained absorbent sheet had a distribution of nearly
uniform absorbent layers (containing the SAP of approximately 60
g/m.sup.2) derived from the first dispersion liquid and of
absorbent layers (containing SAP of approximately 120 g/m.sup.2)
derived from the second dispersion liquid which latter absorbent
layers were distributed in a pattern given tails partly to the
pattern shown in FIG. 16. Thus, an absorbent sheet having a thick
and thin two layered structure was obtained.
[0403] The absorbent sheet was cut in 10 cm.times.10 cm to make a
sample. The sample was placed in a Petri dish, and 0.9%
physiological saline solution was poured to run multi times of
absorbing test. The absorbing test was run four times at 5 minute
intervals with 15 cc each. The test results are shown in Table
15.
TABLE-US-00018 TABLE 15 Amount of water State of Results of added
absorption observation First 150 cc added Only thin layers
Dispersed all over first layer, absorbed second layer remained dry
Second 150 cc added Absorption partly Whole first layer became wet,
moved from first but second layer only partly layer to second
wetted layer Third 150 cc added Whole second Boundary between first
and layers started second layers still distinct to swell Fourth 150
cc added Whoel first and Second layer much swollen to second layers
have ridges swollen
Example 13
Preparing a SAP Slurry
[0404] A slurry composed of the SAP and the MFC was prepared in a
procedure identical with the one applied in Example 10 above.
<Preparing a Liquid Pervious Supporting Sheet>
[0405] An air laid pulp sheet containing the SAP (made by Honshu
Kinocloth under the trademark "B-SAP") whose weight was 85
g/m.sup.2 was prepared. In this pulp sheet, the SAP of 20 g/m.sup.2
was blended.
<Discharging the Slurry to Form a Pattern>
[0406] The above-described slurry from a slurry pump was discharged
in a pattern arranged in many rows of bands having indefinite
circumference each onto the above-described supporting sheet, as
moving, from a nozzle having a cleavage-like discharging outlet as
shown in FIG. 68. Then, the supporting sheet was pressed under
pressure by a hot roll whose surface temperature was 140.degree. C.
and air dried to make an absorbent sheet. In the distribution of
the patterns on this absorbent sheet, absorbent layers were
distributed in a pattern similar to the one in the sketch of FIG.
17.
Example 14
[0407] The HFFM (made by Daicel Co., Ltd. under the trademark
"Cellish KY100G") in gel state was dispersed in a dispersed medium
of MeOH/water=70/30 to make a dispersion liquid of 0.6%
concentration. In 1 liter of this dispersion liquid, 400 g of the
SAP (made by Mitsubishi Chemical Co., Ltd. under the trademark
"US40") was added and stirred to prepare a dispersion slurry of the
HFFM and the SAP.
[0408] This co-dispersion slurry was applied on either surface of a
cellulose non-woven fabric of 30 g/m.sup.2 (made by Futamura
Chemical Co., Ltd. under the trademark "TCF#403"), and the
non-woven fabric was subjected to removal of the liquid component
and dried to obtain an absorbent sheet. The thickness of this
absorbent sheet was approximately 0.6 mm and the content of the SAP
was 150 g/m.sup.2.
[0409] The absorbent sheet was cut in 350 cm.times.250 cm. As shown
in FIG. 84, the sheet was folded inside at the position 75 mm each
from both sides with the surface coated with the SAP facing inside
to make an absorbent. Then, as shown in FIG. 85, the sheet was
bonded to a liquid impervious sheet 902 at the folded sides via
adhesive 901 to make an absorbent tube 900. The thickness of thus
obtained absorbent tube 900 was 1.3 mm including the liquid
impervious sheet 902.
[0410] Swelling test was run by pouring physiological saline
solution of 200 cc each time twice, 400 cc in total, onto the
absorbent side of the absorbent tube. The result was that 2 minutes
after the first 200 cc was poured the absorbent side swelled in a
tube having an ellipsoidal cross-section of approximately 6 mm
thickness, and 2 minutes after the second 200 cc was poured, the
thickness increased to approximately 12 mm.
Example 15
[0411] A non-woven fabric (made by Oji Paper Co., Ltd. under the
trademark "Teccel") obtained by entangling PP/PE bicomponent
spun-bond non-woven fabric and pulp together in high pressure jet
stream was prepared.
[0412] On the other hand, commercially available bio-cellulose gel
was dispersed in a dispersion medium of EtOH/water=60/40 to prepare
a dispersion liquid of 0.3% concentration. In 1 liter of this
dispersion liquid, 400 g of the SAP (made by Mitsubishi Chemical
Co., Ltd. under the trade-mark "US 40") was added and stirred to
prepare a co-dispersion slurry of the HFFM and the SAP.
[0413] Either surface of the above-described non-woven fabric was
line-coated with this co-dispersion slurry in a plurality of bands
of 7 mm width at 5 mm intervals, and the non-woven fabric was
subjected to removal of the liquid component and dried to obtain an
absorbent sheet.
[0414] The absorbent sheet was cut in 350 mm.times.250 mm, and
then, the cut sheet was folded with the SAP applied surface facing
inside in a flat cylindrical shape as shown in FIG. 86, and the
folded portions of both sides were bonded together via adhesive 903
to make an absorbent tube 900. The thickness of thus obtained
absorbent tube was approximately 2 mm.
[0415] Swelling test was run by pouring physiological saline
solution of 200 cc each twice, 400 cc in total, onto the absorbent
tube. The result was that 2 minutes after the first 200 cc was
poured, the absorbent tube swelled in a tube shape having a
ellipsoidal cross-section of approximately 10 mm, and 2 minutes
after the second 200 cc was poured, the thickness increased to
approximately 20 mm.
Example 16
[0416] A PP spun-bond of 18 g/m.sup.2 and a mixed carded fiber web
of 30 g/gm.sup.2 composed of 60% PET staple fiber (3
denier.times.51 mm length) and 40% rayon staple fiber (1.5
denier.times.35 mm length) were prepared. Such mixed carded web
laid on such spun-bond non-woven fabric was entangled in high
pressure water jet stream to prepare a composite non-woven fabric
of a structure as shown in FIG. 37.
[0417] The composite non-woven fabric was coated with a
co-dispersion slurry of the HFFM and the SAP used in Example 14
above, and subjected to removal of the liquid components and dried
to obtain an absorbent sheet of approximately 2 mm thickness
composed of three layers of the spun-bond non-woven fabric, the
carded web, and the SAP layer fixed by the HFFM, only on either
surface of which absorbent sheet the SAP particles were carried at
the density of 150 g/cm.sup.2.
[0418] This absorbent sheet was cut in bands of 350 mm width, and
the cut sheet was formed in tube with both longitudinal sides made
to face each other at approximately 30 mm interval.
[0419] Separately, from a disposable diaper (manufactured by Kao
Corporation under the trade name "Super Merries (L size)"), the
inner sheet and the absorbent core were taken out, and, instead in
the region where such sheet and core existed as shown in FIG. 38,
the above-described absorbent tube in contact with the exposed
outer sheet of the diaper was linked to the liquid impervious sheet
at both side ends via adhesive.
[0420] On thus obtained diaper, absorbing tests were conducted in a
procedure generally practiced in this field. As the result of the
tests, the following results were obtained:
{circle around (1)} Amount of Rewet (3 Minute Interval) [0421]
First rewet (100 cc): 0.5 g [0422] Second rewet (100 cc): 0.8 g
[0423] Third rewet (100 cc): 2.0 g {circle around (2)} Total
Absorbed Amount (Physiological Saline Solution): 680 cc Retained
amount: 480 cc
Example 17
[0424] A PE/PET bicomponent non-woven fabric of 20 g/m.sup.2 weight
(made by Unitika Co., Ltd. under the trademark "Elves") was
stretched and heat set as shown in FIG. 57 to prepare a
easy-to-elongate non-woven fabric. This non-woven fabric had the
following properties:
TABLE-US-00019 Weight 31.2 g/m.sup.2 Thickness 0.24 mm Density
0.132 g/cm.sup.3 Breaking elongation 35% (MD)/370% (CD) 100%
elongation modulus in CR 83 g/5 cm.
[0425] The above-described easy-to-elongate non-woven fabric was
coated with a co-dispersion slurry of the HFFM and the SAP in a
procedure identical with the one applied in Example 14 above, and
heated and pressed and subjected to removal of the liquid component
and dried to obtain an absorbent sheet with the SAP particles
carried in a density of 180 g/m.sup.2 only on either surface. The
absorbent sheet was folded in tube with the surface carrying the
SAP facing inside. Both side ends of the sheet were made to face
and bonded at the meeting portion of both side ends with a thermal
adhesive tape disposed on the outside to prepare an absorbent tube
of approximately 30 mm outer diameter having nearly circular
cross-section.
[0426] Thus obtained absorbent tube was placed in a plastic vat,
and ion exchanged water was poured on the absorbent tube until the
tube did not absorb water any more, and allowed to stand for 10
minutes. As a result, the diameter of the absorbent tube increased
to 66 mm, but no SAP was observed to leak from the outside of the
non-woven fabric.
Example 18
[0427] An elastic net of 60 g/m.sup.2 weight commercially available
on the market was prepared as an absorbent sheet, where
polyethylene monofilaments as longitudinal filament members and
SEBS monofilaments as lateral filament members were crossed at
right angle with each other and bonded at the points of
intersection.
[0428] Separately, a carded parallel web of 25 g/m.sup.2 composed
of the following fibers A and B was prepared:
[0429] A: bicomponent fiber of 2 denier.times.51 mm length,
composed of a random polymer of poly-propylene as the core and
ethylene/propylene as the sheath.
[0430] B: Lyocell made by Coutaulds of 1.5 denier.times.35 mm
length.
[0431] A carded parallel web A was laminated on one surface of the
above-described elastic net and another carded parallel web B was
laminated on the other surface of the net, and the net with the
carded parallel webs were entangled by water jet stream one time
each on the top and the bottom side of the laminated members under
the pressure of 50 kg/cm.sup.2 from a nozzle having orifices of
0.13 mm diameter provided at 0.6 mm interval. Further, water stream
was jetted from the top under the pressure of 80 kg/cm.sup.2 from a
nozzle having orifices of 0.13 mm diameter provided in one row at 5
mm interval. Then, the laminated members were dehydrated and dried
to make an easy-to-stretch non-woven fabric with bonded portions in
parallel lines formed longitudinally, of a structure as shown in
FIGS. 59 and 60.
[0432] The properties of the non-woven fabric were as follows:
TABLE-US-00020 Weight 110.00 g/m.sup.2 Thickness 1.22 mm Tensile
strength in CD 1.50 kg/5 cm Elongation in CR 270.00% Elongation
modulus in CD 50% 150 g/5 cm 100% 200 g/5 cm 150% 320 g/5 cm
(Notes) The above-described properties were measured under the
following conditions:
[0433] Tensile strength: A sample piece of 5 cm width and 15 cm
length (the cross direction of the non-woven fabric being the
longitudinal direction of the sample) was held at the holding
distance of 10 cm, and elongated at the rate of 30 cm per minute by
means of a constant rate stretching type tensile tester. The load
value at breaking was taken as the tensile strength.
[0434] Elongation modulus: A sample piece of 5 cm width and 15 cm
length (the direction of the non-woven fabric being the
longitudinal direction of the sample) was held at the holding
distance of 10 cm, and elongated 150% at the rate of 30 cm per
minute by means of a constant rate stretching type tensile tester.
From the stress-strain curve obtained at that time, the stress each
at 50%, 100% and 150% elongation was read out. The readings were
taken as the elongation modulus.
[0435] Thickness: The thickness was measured by a thickness gauge
(made by Daiei Kagaku Seiki Co., Ltd. under the trademark
"THICKNESS GAUGE") under a load of 3 g per 1 cm.sup.2.
[0436] The Lyocell side of the above-described easy-to-stretch
non-woven fabric was coated with a co-dispersion slurry of the HFFM
and the SAP in a procedure identical with the one applied in
Example 14 above. The non-woven fabric was subjected to removal of
the liquid component and dried to obtain an absorbent sheet with
the SAP particles carried in a density of 125 g/m.sup.2 only on one
surface. Further, a crushed wood pulp layer of 150 g/m.sup.2 was
laid on the side of the absorbent sheet that carried the SAP
particles, with such side facing inside the absorbent sheet was
folded in a tube with the side ends facing each other at 30 mm
interval and bonded to a separately prepared polyethylene outer
sheet by means of hot melt type adhesive to obtain a absorbent tube
bonded in an integrated way to the outer sheet. The thickness of
this absorbent tube was approximately 4 mm.
[0437] The thus obtained absorbent tube was placed in a plastic
vat, and from the top of the absorbent tube ion-exchanged water was
poured until the absorbent tube did not absorb water any more, and
allowed to stand for 10 minutes. As a result, the thickness of the
absorbent tube increased to 30 mm, but no SAP was observed to leak
to the outside of the non-woven fabric.
Example 19
Preparing a Liquid Impervious Sheet Having Dents on the Surface
[0438] Polyethylene film of 30 microns having taper-like openings,
as shown in FIG. 39, all over the surface (made by Tredgar under
the trademark "VISPORE X-6170") was prepared.
<Preparing a Slurry of Absorbent Materials>
[0439] Separately, MFC gel (made by Daicel Co., Ltd. under the
trademark "Celish KY-100G") was dispersed in a dispersion medium of
ethanol/water=70/30 to prepare 1 liter of dispersion liquid of 0.5
MFC. To this dispersion liquid, 200 g of the SAP particles (made by
Mitsubishi Chemical Co., Ltd. under the trademark "US40") was added
to prepare a co-dispersion slurry of the SAP and the MFC.
<Preparing an Absorbent Sheet>
[0440] The above-described polyethylene film having openings was,
with the surface having larger openings facing upward, was coated
with the co-dispersion slurry of the SAP and the MFC as the
polyethylene film was fed and conveyed on a belt conveyor of
plastic belt of 80 mesh provided with a suction zone.
[0441] In the suction zone the co-dispersion slurry of the SAP and
the MFC on the polyethylene film having openings was subjected to
removal of the liquid component through the openings to fill inside
the openings with the solid substance in the slurry. Then, the
solid substance was dried by blowing hot air of 80.degree. C. onto
the solid substance.
[0442] The openings of the absorbent sheet had, as observed by a
microscope, a structure as shown in FIG. 40.
<Evaluating the Permeability>
[0443] Permeability tests were conducted on the absorbent sheet by
a Garret type test method provided in JIS P117. The result was that
the air permeability of the absorbent sheet was 100 sec/100 cc.
<Measuring the Water Resistance>
[0444] 10 sheets of commercially available tissue were placed under
the absorbent sheet, and a water column of physiological saline
solution made by utilizing a glass tube of 20 mm diameter was built
covering the openings filled with highly absorbent material to
measure the water resistance pressure. At the portion which was
filled with the highly absorbent material, the SAP was observed to
mount due to its swelling, and although the water column was raised
up to 800 mm H.sub.2O, the liquid did not leak out to wet the
tissue.
Example 20
Preparing a Substrate for Liquid Impervious Sheet Material
[0445] Hot melt type adhesive was sprayed on the surface of a
matte-finished polyethylene sheet of 25 microns composed of LLDPE,
and a spun-lace non-woven fabric having a high elasticity in the
cross direction composed of PP staple fiber (1.5 denier.times.35 mm
length) was laid on the sprayed surface of the polyethylene sheet
and pressed together as heated to be bonded to prepare a composite
of the non-woven fabric and the film having a structure as shown in
FIG. 42A.
[0446] This composite was treated in a process shown in FIG. 42.
First, the composite was made to pass on a grid roll (crest pitch
10 mm, width of top 0.5 mm, and depth 2 mm) of stainless steel
whose surface temperature was 100.degree. C. to make linear grooves
formed on the film (step B of FIG. 42), ad then laterally extended
1.5 times to obtain a composite of the non-woven fiber and the film
with the film portion and the non-woven exposed in bands (step C of
FIG. 42).
<Preparing a Slurry of Absorbent Material>
[0447] Ethanol and water were added to a water dispersion liquid of
5% BC gel (made by Ajinomoto Corporation under the trademark
"Biocellulose") to prepare one liter of 0.4% dispersion liquid of
ethanol/water=60/40. To this dispersion liquid the SAP particles
(made by Mitsubishi Chemical Co., Ltd. under the trademark "US 40")
of 0.3 mm average particle diameter were added to prepare a
co-dispersion slurry of the SAP and the BC.
<Preparing an Absorbent Sheet>
[0448] The non-woven fabric and film composite was coated with the
above-describe co-dispersion slurry in 200 g/m.sup.2 weight and
approximately 10 mm width in a way that the non-woven fabric
portion was covered (step D of FIG. 42).
<Preparing an Absorbent Composite Having Dents>
[0449] The above-described absorbent sheet was formed in a
corrugated shape by means of a grooved guide, and was laid on a
PE/PET spun-bond of 20 g/m.sup.2 (made by Unitika Co., Ltd. under
the trademark "Elves") treated to be hydrophilic to make an
absorbent with a topsheet (step E of FIG. 42).
<Evaluating the Air Permeability>
[0450] Air permeability tests (of a Garret type provided for in JIS
P8117) were conducted on the above-described absorbent sheet with
the result that the air permeability was good, 80 sec/100 cc.
<Wearing Tests of Absorbent Products>
[0451] 10 pieces of baby diaper were made by attaching a gather and
a fastening tape to the above-described absorbent sheet having
dents, and wearing tests were conducted. With two pieces of baby
diaper leakage occurred from the side portion, but no leakage
occurred at all for the back side with any of the diapers.
Example 21
Preparing a Water Resistant Material Having Dents and
Projections
[0452] An MS (melt-blown and spun-bond composite) non-woven fabric
(18 g/m.sup.2) mainly composed of PP melt-blown (5 g/m.sup.2) and
PP spun-bond (13 g/m.sup.2) was prepared. On the other hand, an
apertured film made by providing openings of 2 mm diameter on PE
film of 30 micron thickness mainly composed of LLDPE was prepared.
A small amount of hot melt type adhesive was sprayed onto the
apertured film, and a MS non-woven fabric was attached onto the
sprayed side to obtain a composite sheet as shown in FIG. 43.
[0453] On this composite sheet a water column test was conducted in
a procedure identical with the one applied in Example 19 above with
the result that the value was approximately 200 mm H.sub.2O.
<Preparing an Absorbent Slurry>
[0454] An absorbent slurry was prepared under the same conditions
as in Example 19 above. The above-described composite of the MS
non-woven fabric and the apertured film was, in a procedure
identical with the one applied in Example 19 above, supplied with
the apertured film side facing upward on a conveyor belt provided
with a suction zone and the absorbent slurry was fed onto the
composite. The composite was subjected to removal of the liquid
component in the suction zone and the SAP particles as absorbent
material were bonded to and filled in the exposed surface of the MS
non-woven fabric by means of the MFC to obtain a absorbent sheet as
shown in FIG. 44.
<Air Permeability of the Absorbent Sheet>
[0455] Air permeability test (based on the Garret test provided for
in ES P8117) was conducted on the obtained absorbent sheet with the
result that the air permeability was 160 sec/100 cc.
<Evaluating the Water Resistance of the Absorbent Sheet>
[0456] 10 sheets of tissue paper commercially available on the
market were placed under the above-described absorbent sheet, a
column of physiological saline solution was built by using a glass
tube of 20 mm diameter covering the openings which were filled with
the SAP particles to measure the water resistance. The SAP in
contact with physiological saline solution swelled to mount raising
the water column up to 800 mm H.sub.2O, but no liquid leaked nor
the tissue wetted.
Example 22
Varying Viscosity and Temperature of a Dispersion Slurry in a
Process of Making a Composite
[0457] FIG. 86 shows an example of a process of making a composite
with the PG taken as an example showing the varying viscosity and
temperature of a slurry in each step of the process. In this
example a dispersion slurry was used where 30% SAP particles (made
by Mitsubishi Chemical Co., Ltd. under the trademark "US 40") and
0.5% MFC (made by Tokushu Paper Mfg. Co., Ltd. under the trademark
"S-MFC") were dispersed in a dispersion medium of
PG/water=70/30.
[0458] In preparing the dispersion slurry, stirring was required
for mixing and dispersing the SAP and the MFC, and in order to save
energy for stirring the stirring was conducted at 30.degree. C. and
400 rpm. The obtained dispersion slurry was guided to a storage
tank provided with a cooling jacket, where the slurry was stored at
10.degree. C. while it was stirred slowly at approximately 400 rpm,
and from the storage tank was transferred to a coating header
through a heating jacketed pipe by means of a Moino pump (made by
Hyojin Pump Mfg. Co., Ltd.).
[0459] The coating header had a dwelling capacity of approximately
20 minutes and provided inside with a heating unit by a steam pipe.
At this coating header, the temperature of the slurry was
controlled at approximately 50.degree. C. The heated slurry was
supplied to a coating roll provided with a grid, and applied in 10
mm width at 1 mm interval onto a non-woven fabric. The non-woven
fabric was Teccel of 50 g/m.sup.2 (made by Oji Paper Co., Ltd.).
The amount of coating was approximately 150 g/m.sup.2. The
non-woven fabric with the coated surface facing upward was guided
to steaming zones provided with a steam generator where adding of
water and heating were performed, and then, was made to pass a
reduced pressure suction zone where the PG and water were removed.
Remaining PG and water were further removed as the coated non-woven
fabric was dried in hot air of 130.degree. C. to make an absorbent
sheet.
Embodiments of the Present Invention in Dispersing Process
[0460] The SAP particles/MFC were dispersed in a water/PG
dispersion medium to make a dispersion slurry. In a process of
making a composite absorbent by forming the dispersion slurry, the
SAP particles were bonded with each other and the SAP and the
substrate were bonded by the strong hydrogen bonds of the MFC
covering the surface of the SAP particles. Hydrogen bonds were only
completed with the PG removed first and then moisture removed, in a
mixed dispersion medium system having higher content of the PG.
Also, since the boiling point of an aqueous solution of the PG
becomes lower, as the content of water becomes higher, it is
advantageous process-wise to have as much water as possible in the
process for removing the PG
TABLE-US-00021 TABLE 16 PG/water 90/10 80/20 70/30 60/40 50/50
Boiling 135 116 110 106 104 point (.degree. C.)
[0461] On the other hand, however, as, in a dispersion medium of
PG/water, the content of water was raised in the ratio of PG/water,
the dispersion slurry containing the SAP became less stable as it
changed against time, as shown in the following Table:
TABLE-US-00022 TABLE 17 Duration of stability of PG/water slurry
containing SAP confirmed Changing condition 80/20 Longer than 24
hours Not changed 70/30 Around 4 hours Viscosity of system
increased 60/40 Around 30 minutes Viscosity of system rapidly
increased 50/50 Around 5 minutes Whole solidified
[0462] It is, therefore, important from the technical viewpoint how
to replace the PG with water in the process. A first point of
technical importance is how a system where the content of water is
high can be adopted, and a second point of technical importance is
how to replace the PG with water, after the slurry system is formed
into a sheet. FIG. 88 shows an embodiment of the present invention
showing in which steps the preparation of the dispersion slurry
should be conducted leading to the slurry supplying zone of the
forming process, i.e. the coating header.
[0463] Both of processes A and B are for preparing a dispersion
slurry from a dispersion medium of PG/water-70/30. In process A, a
water dispersion liquid of the MFC is added to a SAP dispersion
liquid of 100% PG eventually to make the ratio of 70/30. Suspending
is a simple process, but stirring is important because in adding a
water dispersion liquid if the water ratio is higher locally, the
SAP swells and the dispersion system becomes non-uniform.
[0464] In process B, after a PG/water dispersion liquid of the MFC
is prepared at the mixed ratio of 70/30, the SAP particles are
dispersed. Thus, a dispersion slurry can be prepared with relative
ease.
[0465] In process C, when a slurry of mixed ratio of 70/30 obtained
in the same way as applied in process B is heated at a coating
header, heating and uniformly adding of water are carried out at
the same time in a short period of time by adding steam directly,
whereby the content of water is increased in a short period of
time, that is to say, only during the dwelling time at the header,
and the viscosity is much lowered and the liquidity is increased by
the heating and adding of water for forming the coating.
[0466] In processes D and E embodying the present invention, an
amount of water is made relatively larger in a short period of the
dwelling time of the slurry by making the addition of the SAP
particles immediately before the header. In process D, a case is
conceived that the amount of water is made larger, i.e. the mixing
ratio being 60/40, by adding the SAP particles immediately before
the header. Process E attempts to prepare a dispersion slurry of
higher water content, i.e. the mixing ratio being 55/45, by
preparing higher water content dispersion liquid of the MFC and
adding to the dispersion liquid and mixing a 100% PG dispersion
liquid of the SAP so that a uniform mixing is realized in a short
period of time immediately before the header.
Embodiment of a Process of Removing the Liquid Component from
PG/Water Dispersion Liquid System
[0467] Embodiments of the present invention of preparing a
dispersion slurry of PG/water of higher water content were
described in the above. In order to efficiently remove the liquid
component from a formed SAP sheet containing the PG and to have a
higher content of water, such means are available as spraying water
in droplets and making water stream flowing down the sheet in thin
layer by means of a flow coater so that the PG is replaced with
water. However, if such means is carelessly applied, the surface of
the sheet may be non-uniform.
[0468] FIG. 89 shows an example where steam is used in place of
water stream as the source for adding water and heating. This is an
embodiment of the present invention showing a means for removing
the liquid component in the liquid phase by removing the liquid
component under reduced pressure the formed SAP sheet containing
the PG and for afterwards removing the liquid component in the gas
phase by hot press and hot air. A SAP composite sheet formed on a
substrate from the PG/water medium in slurry of mixed ratio of
70/30 is guided together with the substrate to a first steam
treatment zone where heating and removing of the liquid component
under reduced pressure are performed with the water content raised
to approximately 50/50 and the residual amount of the PG lowered,
and then guided to a second steam treatment zone. In the second
steam treatment zone, further heating and removing of the liquid
component under reduced pressure with the water content raised to
approximately 30/70 are performed and part of the surface of the
sheet is dried by hot press with the content of the PG lowered so
that the surface of the sheet is stabilized, and with the surface
thus stabilized and with the content of the PG further lowered, the
sheet is guided into a hot air dryer to remove water together with
the PG so that eventually the liquid removed and dried highly
absorbent sheet of the present invention may be obtained. It should
be noted that in FIG. 89 the residual amount of the PG is indicated
as a relative value when the residual amount of the PG in a sheet
immediately after it is formed is 100.
[0469] The above-described examples are designed to provide a
system of making a highly absorbent sheet by utilizing a dispersion
medium of a polyvalent alcohol and water as a dispersion medium of
the SAP and by dexterously combining the viscosity and temperature
characteristic of the dispersion medium in the configuration of the
processes.
[0470] As described above, the absorbent composite of the present
invention is such that the water swollen solid member contained in
the structure can be formed in any shape such as powder, particle,
pellet, sheet and any given three-dimensional structure and
accordingly, the handling of the absorbent composite is made easier
and the range of its applications is widened. When the SAP is
utilized as such member and held stably in the network structure of
the HFFM, not only the SAP can be used as it is in particles, but
also an absorbent of any shape can be easily formed. Especially,
formed in the shape of a sheet, the SAP can be made thin while
having an extremely high capacity of absorbing water, and the
thickness of absorbent products such as baby and adult diapers and
feminine hygiene products can be minimized to the limits.
[0471] In the present invention in case an absorbent layer of a
composite absorbent provided at least on either surface of a
supporting sheet is composed of three components consisting of the
SAP particles, the HFFM and short-cut staple fibers, the SAP
particles among themselves and the top surface of layers formed by
the SAP particles are covered in network structure by the short-cut
staple fibers whose fiber length is longer than the diameter length
of the SAP particles so that the SAP is taken in the network
structure whereby, even when swollen with liquid, the swollen SAP
particles can be prevented from coming off.
[0472] Further, the absorbent sheet of the present invention,
unlike conventional absorbent sheets, can exhibit the capacity of
absorbing quickly and stably many times body exudates discharged in
varied ways and irregularly in terms of frequency depending upon
environments and living conditions, in addition to being of
excellent flexibility. Besides, the absorbent sheet of the present
invention very quickly absorbs a discharged liquid first time, but
also similarly very quickly absorbs second and third times of
repeated discharging.
[0473] In addition, in case a dispersion medium system composed of
a polyvalent alcohol system or a polyvalent alcohol/water system,
polyvalent alcohol being highly viscous at low temperatures and
logarithmically reduced in viscosity as heated, is used, forming
and removing of the liquid component can easily be performed so
that the efficiency of making highly absorbent sheets can be
improved and the cost of making such sheets can be reduced.
* * * * *