U.S. patent application number 10/357232 was filed with the patent office on 2003-06-19 for highly absorbent composite sheets and methods of manufacturing the same.
Invention is credited to Mori, Shingo, Suzuki, Migaku.
Application Number | 20030114059 10/357232 |
Document ID | / |
Family ID | 16504372 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030114059 |
Kind Code |
A1 |
Suzuki, Migaku ; et
al. |
June 19, 2003 |
Highly absorbent composite sheets and methods of manufacturing the
same
Abstract
An absorbent composite sheet mainly consisting of a fibrous
substrate web, a super absorbent polymer, and a bonding component
bonding both of them with each other, wherein (a) the fibrous
substrate web is a non-bonded web with a few of the constituent
fibers bonded with each other, (b) a liquid mixture system is used
of a medium mainly consisting of the super absorbent polymer and
the bonding component. (c) a composite web is formed by adding the
liquid mixture system to the fibrous substrate web, and (d) a
liquid component is separated from the composite web so that fixing
of the super absorbent polymer to the fibrous substrate web and
bonding of the webs of the fibrous substrate web with one another
are carried out at the same time. Methods of manufacturing such
absorbent composite sheets are also provided.
Inventors: |
Suzuki, Migaku; (Kanagawa,
JP) ; Mori, Shingo; (Tokyo, JP) |
Correspondence
Address: |
John F. Gulbin
Pitney, Hardin, Kipp & Szuch LLP
685 Third Avenue
New York
NY
10017
US
|
Family ID: |
16504372 |
Appl. No.: |
10/357232 |
Filed: |
February 3, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10357232 |
Feb 3, 2003 |
|
|
|
09744063 |
Jan 18, 2001 |
|
|
|
6540853 |
|
|
|
|
Current U.S.
Class: |
442/118 |
Current CPC
Class: |
D04H 1/4374 20130101;
D04H 1/559 20130101; D04H 1/541 20130101; Y10T 442/2484 20150401;
D21H 21/22 20130101; D21H 13/24 20130101; D04H 1/732 20130101; D21H
13/14 20130101; A61F 13/15642 20130101 |
Class at
Publication: |
442/118 |
International
Class: |
B32B 027/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 21, 1998 |
JP |
205280/1998 |
Jul 19, 1999 |
WO |
PCT/JP99/03875 |
Claims
1. A method of manufacturing a highly absorbent composite sheet
mainly consisting of a fibrous web substrate, a super absorbent
resin, and a bonding agent to bond said substrate and said super
absorbent resin, wherein (a) said fibrous web substrate is an
unbonded web having substantially no bonding portions among its
constituent fibers, (b) said super absorbent resin and said bonding
agent are dispersed in a liquid mixture containing an aqueous
medium which does not swell said absorbent resin, (c) the resulting
dispersion mixture is added to said unbonded fibrous web substrate
to obtain a composite web, and (d) a liquid component is removed
from said composite web, whereby fixing of said super absorbent
resin onto said fibrous web substrate is effected simultaneously
with bonding of constituent webs of said fibrous web substrate with
one another.
2. The method of manufacturing a highly absorbent composite sheet
of claim 1, wherein said unbonded web is a carded web or a laminate
of the carded web.
3. The method of manufacturing a highly absorbent composite sheet
of claim 1, wherein said unbonded web consists of a carded web and
a carrier for guiding the carded web.
4. The method of manufacturing a highly absorbent composite sheet
of claim 1, wherein said unbonded web is an air laid web obtained
by an air laid process or a laminate of the air laid web.
5. The method of manufacturing a highly absorbent composite sheet
of claim 1, wherein said unbonded web is a spun bonded web or a
laminated of the spun bonded web.
6. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 5, wherein an aqueous medium consisting
of water or a water miscible medium solution is preliminarily
applied to the unbonded web obtained in a dry state.
7. The method of manufacturing a highly absorbent composite sheet
of claim 1, wherein said unbonded web is an aqueous web obtained by
a wet-laid forming method or a laminate of the aqueous web.
8. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 7, wherein said unbonded web is an
aqueous web obtained only by pretreating the unbonded web in a
pressurized water stream or a laminate of the aqueous web.
9. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 8, wherein a fiber component
constituting said unbonded web consists of a combination of
thermally fusible fibers and synthetic fibers.
10. The method of manufacturing a highly absorbent composite sheet
of any of claims 1, 2, 3, 6, 8 and 9, wherein a fiber component
constituting said unbonded web consists of a first fibrous layer
mainly consisting of 2 denier or coarser and 10 denier or finer
hydrophobic fibers and a second fibrous layer mainly consisting of
3 denier or finer hydrophilic fibers.
11. The method of manufacturing a highly absorbent composite sheet
of any of claims 1, 4, 6, 7, 8 and 9, wherein said unbonded web
consists of fibers obtained by opening wood pulp and thermally
fusible fibers which are 20 mm long or shorter.
12. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 11, wherein said liquid mixture is a
slurry made by dispersing super absorbent resin particles in a
solution in which 1% or less of polyethylene oxide of high degree
of polymerization of 100,000 or more in molecular weight is
dispersed.
13. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 11, wherein said liquid mixture is a
slurry made by dispersing super absorbent resin particles in an
aqueous emulsion of ethylene-vinyl acetate copolymer.
14. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 11, wherein said liquid mixture system
is an aqueous slurry of a super absorbent resin containing a
solvent obtained by inverse phase suspension polymerization.
15. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 11, wherein said liquid mixture is made
fluid by diluting an aggregated gel of a super absorbent resin
obtained through all aqueous solution polymerization with
polypropylene glycol.
16. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 11, wherein said liquid mixture is a
slurry made by dispersing super absorbent resin particles in an
aqueous dispersion liquid of microfibrillated fibrils having a
hydrating property.
17. The method of manufacturing a highly absorbent composite sheet
of claim 12, wherein microfibrillated fibrils having a hydrating
property are added to said liquid mixture.
18. The method of manufacturing a highly absorbent composite sheet
of claim 13, wherein microfibrillated fibrils having a hydrating
property are added to said liquid mixture.
19. The method of manufacturing a highly absorbent composite sheet
of claim 14, wherein microfibrillated fibrils having a hydrating
property are added to said liquid mixture system.
20. The method of manufacturing a highly absorbent composite sheet
of claim 15, wherein microfibrillated fibrils having a hydrating
property are added to said liquid mixture system.
21. The method of manufacturing a highly absorbent composite sheet
of claim 6, wherein microfibrillated fibrils having a hydrating
property are added to said pretreatment liquid.
22. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 21, wherein said super absorbent resin
is so surface cross-linked that it has 25 ml/g or higher AUL
(absorbance under load) under 20 g/cm.sup.2 in a saline water
containing 0.9% salt.
23. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 14, wherein said super absorbent resin
is a polymer of an amino acid type having as a platform asparaginic
acid having a biodegrading property as not surface
cross-linked.
24. The method of manufacturing a highly absorbent composite sheet
of any of claims 1 through 21, wherein said super absorbent resin
is a polyacrylic acid type polymer with surface cross-linking
treatment not applied on.
25. The method of manufacturing a highly absorbent composite sheet
of any of claims 16 through 24, wherein said microfibrillated
fibrils having a hydrating property are microfibrillated cellulose
or bacterium cellulose consisting of cellulose.
26. The method of manufacturing a highly absorbent composite sheet
of any of claims 16 through 25, wherein as said microfibrillated
fibrils having a hydrating property microfibrillated cellulose
fibers are used and the microfibrillated cellulose fibers are
uniformly dispersed in a mixed solvent of water and propylene
glycol at a concentration of 1.5% to 0.2% and a slurry made by
dispersing super absorbent resin particles at a concentration of 5%
to 50% in the dispersion liquid is used.
27. The method of manufacturing a highly absorbent composite sheet
of any of claims 16 through 25, wherein as said microfibrillated
fibrils having a hydrating property microfibrillated cellulose
fibers are used and the microfibrillated cellulose fibers are
uniformly dispersed in a mixed solvent of water and ethyl alcohol
at a concentration of 1.5% to 0.2% and a slurry made by dispersing
super absorbent resin particles at a concentration of 5% to 50% in
the dispersion liquid is used.
28. The method of manufacturing highly absorbent composite sheet of
any of claims 16 through 25, wherein as said microfibrillated
fibrils having a hydrating property microfibrillated cellulose
fibers are used and the microfibrillated cellulose fibers are
uniformly dispersed in a three component mixed solvent of water,
ethanol and propylene glycol at a concentration of 1.5% to 0.2% and
a slurry made by dispersing super absorbent resin particles at a
concentration of 5% to 50% in the dispersion liquid is used.
29. A highly absorbent composite sheet composed by (A) said
unbonded web, (B) said super absorbent resin and (C) said bonding
agent, obtained by a method of manufacturing of any of claims 1
through 28, wherein the ratio of (B) said super absorbent resin to
the whole of the highly absorbent composite sheet is 50% or more,
satisfying the following formula:
[B/(A+B+C)].times.100.gtoreq.50
30. A highly absorbent composite sheet composed by (A) said
unbonded web, (B) said super absorbent resin and (C) said bonding
agent, obtained by a method of manufacturing of any of claims 1
through 28, wherein the ratio of (B) said super absorbent resin to
the sum of (B) said super absorbent resin and (C) said bonding
agent which are absorbent components except for (A) said unbonded
web is 70% or more, satisfying the following formula:
[B/(B+C)].times.100.gtoreq.70
Description
FIELD OF ART
[0001] The present invention relates to methods of manufacturing
super absorbent composite sheets wherein the making of a web into a
non-woven fabric, the bonding of the web to a super absorbent
polymer and the bonding of the particles of the super absorbent
polymer with each other are all carried out effectively and little
super absorbent polymer drops out in both wet and dry states. The
present invention also relates to super absorbent composite sheets
manufactured by any of such methods.
PRIOR ART
[0002] As an absorbent member for such absorbent article as a baby
diaper, an adult incontinence diaper, a feminine hygiene product, a
blood absorbent material and a mother's milk pad, the development
of a highly absorbent sheet mainly consisting of a super absorbent
resin polymer (SAP) and a wood pulp fluff the SAP being held in a
thinner and more dimensionally stable non-woven fabric structure
has been made energetically.
[0003] In order for a non-woven fabric to hold SAP, such methods as
ma method where a non-woven fabric having a structure preferable a
substrate is prepared, the non-woven fabric is impregnated with
acrylic acid monomer so that the monomer is polymerized, a method
where acrylic acid monomer is polymerized on a non-woven fabric,
gelated non-cross-linked polymer is used to coat the non-woven
fabric and cross-linking is then performed, a method where slurry
of SAP dispersed in a medium is used to coat a non-woven fabric are
applied.
[0004] First, there may be three fundamental properties required of
a non-woven fabric substrate; (1) properties of a supporting
member, (2) properties of holding and fixing SAP, and (3)
properties to penetrate and disperse. In order for a non-woven
fabric to hold SAP in its structure, the non-woven fabric needs to
have a bulkier structure having spaces among its constituent fibers
and, if stated in extreme terms, the bulkier the non-woven fabric,
the better the results. If such bulky non-woven fabric is supplied
in a bulky wound-up roll from a non-woven fabric manufacturer,
however, the transportation would be much costly and the amount of
non-woven fabric wound up on roll would be greatly limited.
[0005] In such cases, it is conceivable to directly link a step of
manufacturing a non-woven fabric to a step of having the non-woven
fabric hold SAP, and there is an example in commercial practice of
linking a step of manufacturing a thermally bonded non-woven fabric
to a step of having the non-woven fabric hold SAP, which may be,
however, complicated process-wise and costly
initial-investment-wise.
[0006] Then, as an alternative a method of having the manufacture
of a non-woven fabric and the holding of SAP carried out at the
same time in a step of manufacturing a non-woven fabric may be
thought of. As an example of such method, SAP in powder form is
usually made to co-form with pulp or fiber as SAP is carried on an
air stream. But dust may be generated or SAP powder moves inside an
absorbent member, which is not desirable. Also, a so-called wet
method is patented for; SAP is dispersed in a pulp slurry or a
fiber slurry to form a sheet. Such method has a serious inherent
limitation in that the fiber concentration is too low and the
manufacturing cost becomes high.
[0007] In order to solve any such problems, a method should be
adopted in which by having a component as a bonding agent co-exist
with SAP in holding SAP so that the holding of SAP and the function
of the bonding agent making a non-woven fabric are made to work at
the same time. In general, a non-woven fabric is bulkiest when it
is in an unbonded web and loses its bulkiness when it is finally
made into a non-woven fabric.
SUMMARY OF THE INVENTION
[0008] The present invention makes it possible to manufacture a
highly absorbent composite sheet having little SAP dropping out of
it at both dry and wet states by a method in which an unbonded web
in an original raw material condition is prepared, a liquid phase
is formed in which a component is mixed to co-exist in the web to
bond SAPs with each other and to function as a bonding agent to the
web, the mixed liquid system is added to the web to stabilize it as
a composite, and then liquid remaining in the web is removed, heat
treated and then dried whereby the web is made into a non-woven
fabric, the web is bonded with the SAP and the bonding of the SAPs
is completed.
[0009] That is to say, the present invention relates to a method
for manufacturing a highly absorbent composite sheet mainly
consisting of a fibrous substrate web, a super absorbent polymer
resin and a component to bond the resin and the substrate, herein
(a) said fibrous substrate web is a-yet-to-be-bonded web having
little constituent fibers bonded with each other. (b) a liquid
mixture system mainly consisting of a medium containing said highly
absorbent polymer resin and said bonding agent, (c) a composite web
is formed by adding said liquid mixture system to said fibrous
substrate web, and (d) liquid component remaining in the composite
is removed whereby said highly absorbent polymer resin is made to
be fixed to said fibrous substrate web and the webs comprising said
fibrous substrate web are bonded with each other at the same
time.
[0010] In the present invention, a preferable unbonded web may be a
carded web or a laminated carded web and a carrier for guide may be
used together with the carded web.
[0011] An unbonded web as obtained at dry state may be pretreated
by means of a pretreatment liquid consisting of water or a medium
miscible with water.
[0012] Also, an yet-to-be-bonded web may be an aqueous web to be
obtained by a wet formation method or its laminate. Such unbonded
web may be obtained by preliminarily treating a carded web or a wet
formed web under a high pressure water stream.
[0013] The fiber component comprising an unbonded web is preferably
a combination of easy-to-thermally-fuse fibers and synthetic
fibers, and the fiber component is preferably finer than 2 d
composed of a first fiber layer mainly consisting of finer than 10
d hydrophobic synthetic fibers and a second fiber layer mainly
consisting of finer than 3 d hydrophilic fibers.
[0014] A yet-to-be-bonded web may be formed from opened fibers of a
wood pulp and easy-to-be-thermally-fuse fibers of 20 mm or
shorter.
[0015] In the present invention, as examples of a liquid mixture
system, such systems may be applied as a system where in a 1% or
less melted solution of polyethylene oxide having a molecular
weight of 100,000 or more particulate highly absorbent resin is
dispersed to make a slurry, a system where in an aqueous emulsion
of in ethylene-vinyl acetate copolymer a particulate highly
absorbent resin is dispersed to make a slurry, a system where in an
aqueous slurry of a highly absorbent resin containing a solvent
system to be obtained by negative phase suspension polymerization
and an aggregated gel of a highly absorbent resin to be obtained by
aqueous solution polymerization are diluted in polypropylene glycol
to make an easy-to-flow mixture, and a system where in an aqueous
dispersion liquid of microfibrillated fibrils having a hydrating
property a particulate highly absorbent resin is dispersed to make
a slurry.
[0016] To this liquid mixture system, microfibrillated fibrils
having a hydrating property may be added.
[0017] Furthermore, to said pretreatment liquid, microfibrillated
fibrils having a hydrating property may be added.
[0018] In the present invention, a highly absorbent resin is
preferably the one cross-linked on the surface so that it is 0.9%
saline and has an AUL (absorbance under load) of 25 ml/g or higher
under 20 g/cm.sup.2.
[0019] As other specific examples of a highly absorbent resin, an
amino acid type polymer having a main component of aspartic acid
and a polyacrylic acid type polymer with surface cross-linking
omitted are listed.
[0020] Microfibrillated fibrils having a hydrating property are
specifically microfibrillated cellulose or bacteria cellulose
consisting of cellulose.
[0021] The micro fibrillated fibril cellulose fibers may be used as
such systems as a system where the fibril cellulose fibers are
uniformly dispersed at 1.5% to 0.2% concentration in a mixed medium
of water and propylene glycol and particulate highly absorbent
resin is dispersed at 5% to 50% concentration in the dispersion
liquid to make a slurry, a system where the fibril cellulose fibers
are uniformly dispersed at 1.5% to 0.2% concentration in a mixed
medium of water and ethylene alcohol and particulate highly
absorbent resin is dispersed at 5% to 50% concentration in the
dispersion liquid to make a slurry, and a system where the fibril
cellulose fibers are uniformly dispersed at 1.5% to 0.2%
concentration in a three component mixed medium of water, ethanol
and propylene glycol and particulate highly absorbent resin is
dispersed at 0.5% to 50% concentration in the dispersion liquid to
make a slurry.
[0022] A highly absorbent composite sheet according to the present
invention is preferably a highly absorbent composite sheet
consisting of all unbonded web (A), said highly absorbent resin (B)
and said bonding component (C), wherein the percentage of said
highly absorbent resin (B) is 50% or more satisfying the following
formula:
B/(A+B+C).times.100.gtoreq.50
[0023] More preferably, a highly absorbent composite sheet
according to the present invention is a highly absorbent composite
sheet consisting of an unbonded web (A) said highly absorbent resin
(B) and said bonding component (C), wherein the percentage of said
highly absorbent resin (B) in the total of said highly absorbent
resin (B) and said bonding component except for said
yet-to-be-bonded web which are absorbance contributing components
is 70% or more satisfying the following formula:
B/(B+C).times.100.gtoreq.70
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic diagram showing a first manufacturing
process based on a method of manufacturing a highly absorbent
composite according to the present invention;
[0025] FIG. 2 is a schematic diagram showing a second manufacturing
process based on a method of manufacturing a highly absorbent
composite according to the present invention;
[0026] FIG. 3 is a schematic diagram showing a third manufacturing
process based on a method of manufacturing a highly absorbent
composite according to the present invention;
[0027] FIG. 4 is a schematic diagram showing a fourth manufacturing
process based on a method of manufacturing a highly absorbent
composite according to the present invention;
[0028] FIG. 5 is a schematic diagram showing a fifth manufacturing
process based on a method of manufacturing a highly absorbent
composite according to the present invention;
[0029] FIG. 6 is a schematic diagram showing a sixth manufacturing
process based on a method of manufacturing a highly absorbent
composite according to the present invention; and
[0030] FIG. 7 is a schematic diagram showing a seventh
manufacturing process based on a method of manufacturing a highly
absorbent composite according to the present invention.
BEST MODES OF EMBODYING THE INVENTION
[0031] (Manufacturing of Unbonded Web)
[0032] In the present invention, a non-woven fabric is bonded by
means of a bonding agent which co-exists with SAP, so that if a web
is manufactured it is sufficient for the manufacturing of a
non-woven fabric; that is to say, such steps of bonding, drying and
heat treating of a non-woven fabric are not required. The web can
be used whether it is dry or wet if manufactured by a wet
method.
[0033] It is very important how bulky such unbonded web is
prepared, and its strength is sufficient if it does not break when
transported in roll or net. For example, a carded web of synthetic
fiber, an air formation mat of synthetic fiber and a wet formation
mat of short cut synthetic fiber and pulp are good for such
unbonded web. A wet formation method in general cannot impart
bulkiness to a web so that for the present invention, such
specialized methods as the addition of hydrophobic synthetic fiber
and the making of a foamed paper like product are preferable.
[0034] To make a non-woven fabric as bulky as possible, however, it
would not be sufficient only if it is left unbonded, and various
means are adopted for making such unbonded web bulkier. One of such
means is to use a coarse denier hydrophobic fiber having high
resilience or a composite fiber having a crimpability mainly as a
constituent fiber element. For example, polyester fiber of 5 denier
or coarser, a coarse and hollow polyester fiber developed for
wadding of "futon" comforter or a conjugate fiber of polyethylene
and polyester are good candidates.
[0035] These so-called hibulk and highly resilient fibers,
however,:
[0036] (1) do not have a self-holding property of web and are too
weak for handling; and
[0037] (2) are lacking in such capability of absorbing and
dispersing liquid as required of a substrate for holding SAP.
[0038] These drawbacks of such hibulk and highly resilient fibers
pose very important problems. Solutions of such problems are a
method of feeding the bulky web on a carrier sheet, a method of
making and using a carrier sheet of a thin non-woven fabric of more
or less than 10 to 15 g/m.sup.2 made into hydrophilic SM or SMS, a
method of making and using a carrier where cotton or spin rayon
yarns are arranged, and a method of making and using a carrier
where relatively hydrophilic and length-wise strong rayon spun
laces are arranged in tapes. The most practical and secure method
is to preliminarily treat in a low pressure water jet (hereinafter
called "WJ") of 20 to 30 kg/cm.sup.2, for the purpose of
pre-needling, a multilayer web of a bulky synthetic fiber web and a
thin rayon web as folded on each other. By this method the bulky
synthetic fiber web is never entangled in the WJ and keeps its
bulkiness while the rayon web layer only is lightly entangled to
function as a future penetrating and dispersing layer and at the
same time plays the role of a carrier sheet when a bulky web is
manufactured. A web layer treated in the WJ does not dry and is, as
it is wet, guided into a next step of holding SAP.
[0039] As well understood from the foregoing, the term "unbonded
web" used in the present invention means a web with the bonding of
its constituent fibers with each other not yet completed. That is
to say, a web whose strength, thickness and surface condition when
an unbonded web is made into a "bonded web" where its constituent
fibers are bonded with each other through a non-woven fabric making
process have not yet been realized is meant by the term "unbonded
web". If one attempts to define it in numerical values, when the
tensile strength (P1) and the thickness (T1) of an "unbonded web"
are compared with the tensile strength (P2) and the thickness (T2)
of a "bonded web" which has passed through a usual non-woven fabric
making process, P1/P2 is 0.5 or lower and T1/T2 is 1.2 or higher.
For example, in the case of an unbonded web containing
easy-to-thermally-fuse fibers to be bonded by a thermal bond, on
average P1/P2 was 0.2 or lower and T1/T2 was 1.5 or higher. In
addition, in case a water jet entangling of a carded web is
applied, when a web only pretreated in water steam entangling is
compared with a web completely treated in entangling, on average
P1/P2 was 0.4 or lower and T1/T2 was 1.3 or higher.
[0040] If another definition is applied, a liquid mixture system
containing a super absorbent polymer resin and a bonding agent is
added to an "unbonded web" to make a composite and then drying and
heat treatment are applied so that a "highly absorbent composite
sheet" is obtained. If the tensile strength (P1) and the thickness
(T1) of the "unbonded web" are compared with the tensile strength
(P3) and the thickness (T3) of the "highly absorbent composite
sheet", P3/P1 is on average 3.0 or higher and preferably is 5.0 or
higher, while, in the comparison of T1 and T3, since the super
absorbent resin is compressed as surrounded by the spaces made by
the fibers in spite of the weight being more than doubled by being
made into a composite, T1>T3. Preferably, T1>T3.
[0041] The thicknesses are measured in the-present invention as
follows: in case of an unbonded web, since it is susceptible to
loading, 100 cm.sup.2 or larger samples are folded in at least five
layers to make a sample for thickness measuring and pressurizing is
applied on the entire area of the sample and that under 3 g 1
cm.sup.2.
[0042] (Preparation of Liquid Mixture System)
[0043] A super absorbent resin to be added to an unbonded web to
make a composite as described above and a liquid mixture system
containing a bonding agent for bonding the resin and the web are
explained below:
[0044] First of all, a liquid mixture system is a concept including
solution, slurry, sol and fluid gel states. Examples to be used in
the present invention being shown, a first group is a method of
uniformly dispersing a super absorbent resin in an organic solvent
solution of a polymer having a capability of bonding. For example,
if a super absorbent resin is dispersed in a solvent such as an
acetone solution of cellulose acetate or an amine oxide solution of
cellulose as shown in Patent Publication Hei 9-299399, an alcohol
solution of hydroxypropyl cellulose as shown in Patent Publication
Sho 60-217241, or polyethylene oxide solution dissolved in an
organic solvent such as acetonitrile as shown in Patent Publication
Hei 1-182362, the super absorbent resin is dispersed uniformly
without swollen and is formed into a stable slurry without being
coagulated by the high viscosity of the solution. A polymer
solution functions satisfactorily as a binder of a super absorbent
resin or an unbonded web, but, in case a bonding agent component is
used to cover the whole of the super absorbent resin like a film in
an obtained highly absorbent composite sheet, may impede the rate
of penetration of liquid to be absorbed. In such case, such means
needs to be applied as adding inorganic powder to the liquid
mixture system or making it foamed. Among other examples of using
organic solvents is a method of dispersing super absorbent resin
powder into an organic solvent emulsion of a rubber type binder
usually used as a base of coating. Among the first group, a
preferred method is to disperse super absorbent resin in a diluted
solvent of polyethylene oxide (PEO) of a high degree of
polymerization of 100,000 or higher and 5,000,000 or lower because
in that method the penetration is relatively good. The
concentration of PEO in the diluted solution is 1% or lower and
preferably 0.1 to 0.5%.
[0045] Among the second group is a method of dispersing super
absorbent resin in all aqueous solution of a polymer having a
bonding property. For example, there are a method of dispersing
super absorbent resin in a viscous aqueous solution of P.V.C. CMC,
polyvinyl pyrrolidone, acrylamide or polyethylene oxide or a method
of dispersing super absorbent resin in an aqueous emulsion very
often used as an emulsion binder for non-woven fabrics such as an
ethylene-vinyl acetate copolymer or an aqueous dispersion of
polyethylene. In either of these methods, since the super absorbent
resin becomes easier to gelate in water, a swelling inhibitor needs
to be added to co-exist with the liquid mixture system, for
example, a small amount of an inorganic salt being added or a water
soluble organic solvent being added, so that the swelling may be
controlled and the emulsion does not coagulate to break down. Among
the second group, a method of adding super absorbent resin powder
to a system in which propylene glycol is added to an aqueous
emulsion of ethylene-vinyl acetate copolymer containing a
relatively high content of vinyl acetate such as Everflex (Mitsui
Chemical Co., Ltd.) and Sumikaflex (Sumitomo Chemical Co., Ltd.) is
a preferable method.
[0046] As a third group of methods, a method of dispersing super
absorbent resin to make a slurry in an aqueous dispersion liquid of
microfibrillated fibrils having a hydrating property or a mixture
solvent of water and a water soluble organic solvent is a preferred
method.
[0047] In the present invention, a network structure of holding SAP
particles in position is composed of so-called microfibrillated
fibrils. This network functions to prevent SAP particles from
coagulating with each other when a highly absorbent composite sheet
is manufactured, to stabilize and to make uniform the dispersion
condition and at the same time to serve as a binder to bond SAPs
with each other and SAPs with a supporting sheet.
[0048] These microfibrillated fibrils are very fine in general
having an average diameter of 2.0 .mu.m to 0.01 .mu.m with a mean
value of 0.1 .mu.m or finer, and having a sufficient water
resistance to prevent the structure of a highly absorbent composite
sheet from breaking down immediately when SAP absorbs water to
swell, without holding back the water perviousness and the swelling
of SAP. It is to be particularly noted here that the
microfibrillated fibrils have an extremely strong hydrating
property to bond with water as a solvation, and that by virtue of
such strong hydrating property when the fibrils are dispersed in an
aqueous medium, they hydrate with water to give a high viscosity
and keep stably the dispersed condition. The hydrating property is
measured in terms of the amount of water contained when the fibrils
as dispersed in water are centrifuged at 2000 G for 10 min and the
preferable hydrating property is expressed in terms of the amount
of water of 200% or higher as measured by tappi of 20 ml/g or
more.
[0049] In this specification the term "microfibrillated fibrils" is
used to mean collectively fibrous materials exhibiting a strong
hydrating property and in some cases those having an average
diameter of 2.0 .mu.m or coarser and even a mixture of fibrils with
microfibrils.
[0050] Also, the components constituting the fibrils are in general
cellulosic, but may be fibrillated polyethylene, polypropylene,
ethylene-vinyl acetate copolymer and co-fibrils of any such
synthetic polymer with cellulose. These fibrils may be prepared by
any method described in Examined Patent Publication Sho 9-1245.
[0051] Cellulosic microfibrillated fibrils preferable for the
present invention may be obtained by microfibrillating cellulose or
any cellulose derivative. For example, such fibrils may be obtained
by grinding down by friction and finely opening by beating wood
pulp. Such microfibrils are called "MFC (microfibrillated
cellulose)" and, if further microfibrillated, "S-MFC (super
microfibrillated cellulose)".
[0052] Also, such fibrils may be obtained by grinding by friction
and finely opening by beating short cut staples of man-made
cellulose fibers (Polynosic, Bemberg, or solvent spun Lyocel).
[0053] Furthermore, microfibrillated fibrils may also be obtained
through the metabolism of microorganism. In general, a so-called
acetic acid bacterium such as Acetobactor Xylinum is cultured by
agitation in a medium containing an appropriate carbon source to
produce crude microfibrils which microfibrils are then refined.
These microfibrillated fibrils are called "BC (bacteria
cellulose)".
[0054] Also, so-called fibril-like material to be obtained by
coagulating under shearing stress a copper ammonia solution of
spinnable cellulose, an amine oxide solution, a cellulose xanthate
aqueous solution, or an acetone solution of diacetyl cellulose is
further dissociated to obtain a microfibril-like material which
material may be used for the present invention.
[0055] Details of these microfibrillated fibrils are described in
Patent Publication Sho 48-6641 and Patent Publication Sho 50-38720
and such fibrils are available on the market under the trademarks
"Celcream" (manufactured by Asahi Chemical Industry Co., Ltd.) and
"Celish" (manufactured by Daicel Chemical Industries, Ltd.).
[0056] Particularly suitable for the present invention are MFC,
S-MFC and BC. The details of S-MFC are described in Examined Patent
Publication Hei 8-284090 and Unexamined Patent Publication Hei
5-80484.
[0057] The uses of MFC and S-MFC as collectively called "MFC" are
explained in more detail below. Such MFC whose solid content is
concentrated up to as high as 30% is available on the market, and
such MFC needs a step of dilution and dissociation so that it costs
labor on top of the concentration cost required. For the present
invention such MFC as has higher water content and a solid content
of 10% or lower is more preferable. However, if the solid content
is made down to 2% or lower, the water content gets too much and
the range of selecting the content of MFC in a mixture system of an
organic solvent and water becomes-narrow. In case such MFC as is so
low in the solid content is used, it is recommended that
microfibrillation is performed not in a single water system, but in
an organic solvent/water system prepared to contain an organic
solvent in making microfibrillete fibrils of raw material pulp
whereby an MFC dispersion liquid of around 2% dilution as may be
obtained on the market can be used for the present invention.
[0058] The uses of BC are also explained in detail. Since BC is
obtained as a metabolism product of bacterium, the concentration
and the form of BC depend on the manners of culturing and of
harvesting. In order to make it uniform, BC after harvested and
refined as diluted down to 2% or lower needs to be dissociated by
means of a mixer or a defibrator whereby clusters of fibrils in
coagulation are made further finer and more uniform and thus
becomes much high in viscosity providing a better binder for SAP.
Such BC undergoing such dissociation treatment is more suitable for
the present invention.
[0059] To prepare a mixture system of microfibrillated fibrils as
represented by MFC and of a super absorbent resin, first of all, a
mixture liquid of water and an organic solvent is prepared and in
the liquid MFC is dispersed to make a dispersion liquid of 2% to 1%
MFC. Then, a super absorbent resin is dispersed in the MFC
dispersion liquid to make a slurry. This is a generally applied
method of preparing a slurry. An organic solvent to be used for the
method is selected from such solvents as are soluble in water,
function to prevent a super absorbent resin from coagulating and
controls the swelling of the resin. Its representative composition
is glycol/water=70/30 or ethanol/water=60/40. The dispersion
concentration of a super absorbent resin is preferably 10% to
50%.
[0060] As a fourth group, there is a method of having a super
absorbent resin, as in sol or gel to be obtained in making the
resin, play the dual roles of bonding an unbonded web and serving
as an absorbent component utilizing the viscosity which it may have
before it is dehydrated and any remaining solvent is removed. This
method may be further divided into two submethods: one of utilizing
an aqueous gel to be obtained after negative phase suspension
polymerization and the other one of utilizing an aqueous gel after
polymerization of an aqueous solution.
[0061] A: Utilization of Aqueous Gel After Negative Phase
Suspension Polymerization
[0062] For example, acrylic acid is added to a solution in which
sorbitan monostearate is added to and solved in cyclohexane, which
is then neutralized with NaOH. A solvent and a chain transfer agent
are then added and the system is heated to perform radical
polymerization under agitation to obtain an aqueous polymer liquid
containing the solvent in suspension. This suspension liquid
contains an aqueous polymer of more or less 30% concentration and
the water content of the aqueous polymer is approximately 60%. This
suspension liquid is added to an unbonded web, which is then made
to pass through a vacuum zone to remove any remaining solvent and
water to obtain an absorbent composite sheet. The absorbent
composite sheet as thus obtained can be used in some applications,
however, the bonding of SAPs with each other and with the web
turned out to be insufficient. Then, all aqueous dispersion liquid
of 1% MFC as microfibrillated fibrils is added to the suspension
liquid after the polymerization reaction in a way that the added
MFC was 2 to 10% against the polymer, so that the dispersion liquid
well mixes with the aqueous resin slurry stably to form a viscous
slurry. The unbonded web is spray-coated with this slurry
containing MFC, and when dried after suction operation and removal
of solvent by pressing, an absorbent composite sheet in which the
polymers are strongly bonded with each other and with the web is
obtained.
[0063] In adding MFC, it may be added in an aqueous dispersion or
co-existed with polypropylene glycol or ethanol.
[0064] B. Utilization of Aqueous Gel After Aqueous Solution
Polymerization
[0065] For example, to a reaction liquid in which to 30% aqueous
solution of acrylic acid (neutralization rate 75%) polyethylene
glycol diacrylate is added as a cross-linking agent, a redox type
catalyst system of sodium persulfate/L-ascorbic acid is added to
run polymerization so that an aggregated aqueous gel is obtained.
This gel has a water content of 70% or so, and as such is difficult
to handle for it is gelated as a whole, so if propylene glycol of
0.5 to 2.0 times as much as the gel is added to the gel and the gel
is agitated, it is made to change into a fluid viscous gel. This
gel can be extruded into film-like form by means of a pressurized
extruder or the like. The film-like product is then added to the
above-mentioned unbonded web so that an integrated composite
condition is obtained after vacuum removing of any remaining liquid
and compressing operations. Then, the composite in such condition
is made to undergo the steps of dehydrating, removing of remaining
solvent and drying so that an absorbent composite sheet is
obtained. This sheet as it is thus obtained, however, is observed
to have a drawback of insufficient bonding capability; if the
surface strength of such sheet is measured by a scotch tape test,
it is seen that super absorbent resin drops off and the bonding of
SAPs with each other and with the web is insufficient. In addition,
the result of an absorbance test shows that the surface of such
sheet becomes filmy and the rate of absorbance is low.
[0066] With that, to the gel after the above-mentioned
polymerization a dispersion liquid in which 1.5% of MFC is
dispersed in a mixture solvent of propylene glycol 80% and water
20% is added in the ratio of MFC being 2% to 10% against the gel
and the agitation is run in a kneader, so that the gel is made to
change into a fluid viscous gel. This gel is further diluted to
make a slurry-like product, which can easily be transferred by a
slurry pump just like a common slurry.
[0067] Then, such slurry to be obtained by adding a dispersion
liquid containing MFC of two times as much as the aggregated gel is
added to the unbonded web by means of a slurry pump in slit lines.
After the vacuum removing of any remaining liquid and compressing,
an integrated composite is obtained and then after dehydrating by
hot air and removing of any remaining solvent, an absorbent
composite sheet is obtained. When a scotch tape test is applied on
the absorbent composite sheet, it is observed that the SAPs are
bonded with each other and the SAP is bonded with the web strongly
enough so that very little super absorbent resin peels off.
[0068] As such gel after the polymerization, as proposed in
Unexamined Patent Publication Hei 10-120818, a gel containing air
bubbles of water content of 30% to 90% to be obtained by having a
foaming agent in co-existence when the polymerization reaction is
run may be used in order to improve the absorbance and
permeability. In this case, too, the absorbance can be much
improved by having the above-mentioned microfibrillated fibrils in
co-existence in a polyvalent alcohol as a plasticizer.
[0069] (SAP (Super Absorbent Polymer) to be Used and its Form of
Use)
[0070] Super absorbent polymer generally abbreviated as SAP is in
general a carboxymethyl cellulose, polyacrylic acid and its salts,
a cross-linked acrylate polymer, starch-acrylic acid grafted
copolymer, a hydrolysis product of starch-acrylonitrile grafted
copolymer, a cross-linked polyoxyethylene, a cross-linked
carboxymethyl cellulose, polyethylene oxide, a partially
cross-linked water swellable polymer such as polyacrylamide, or a
isobutylene-maleic acid copolymer. By drying any such polymer, base
polymer particles are obtained. Next, in general an after treatment
of the surface of such polymer is run to improve the cross-linking
density and at the same time an anti-blocking agent is added to
control the blocking propensity caused by the absorbing of product
particles.
[0071] Also, a biodegradable amino acid cross-linked polymer or a
super absorbent polymer of bacterium source, a cultured product
from Alcaligenes Latus, may also be used.
[0072] SAPs may be in the various forms of particles, granules,
film, sols, suspension, gels or non-woven fabrics. Any of these
SAPs may be used for the present invention. Those SAPs which are
preferable for the present invention are such SAPs in the forms of
particles, granules, flake, pellets or short needles as are
uniformly dispersable in a dispersing medium. These SAPs are herein
called "particles or particulate".
[0073] In general, the SAP whose surface is cross-linked is high in
AUL value (absorbance under load); specifically, it has an AUL of
at least 20 ml/g under the load of 20 g/cm.sup.2 and in general an
AUL of 25 ml/g or higher under such load. Such SAPs have a wide
selection of dispersion mediums so that they can be uniformly
dispersed in mixture mediums of organic solvents and water among
organic mediums.
[0074] On the other hand, however, such SAPs as are not surface
cross-linked or difficult to surface cross-link have a narrow
selection of dispersion mediums, and they need to be dispersed in a
hydrophobic medium such as cyclohexane using a surfactant or in a
three component system such as propylene glycol/ethanol/water under
selected appropriate conditions.
[0075] In the present invention, to have an effective binding agent
for the purposes of binding SAPs with each other and SAP with a
web, the surface treatment of the SAP needs to be limited to as
much as surface cross-linking. For example, the surface treatment
using an anti-blocking agent or an anti-caking agent should not be
applied for such surface treatment may impede the bonding
effects.
[0076] (Application of Liquid Mixture System to Unbonded Web)
[0077] There are various means of applying a liquid mixture system
to an unbonded web, i.e. adding and making a composite of the web,
which means will be explained later. Here particularly important is
a pretreatment of an unbonded web.
[0078] An unbonded web to be used in the present invention may
obtained by a variety of methods, as describe in the above, and any
such web is very bulky with an apparent specific gravity, as
calculated from the thickness obtained under 3 g/cm.sup.2, of at
least 0.1 g/cm.sup.2 or lower or preferably 0.08 g/cm.sup.2 to
0.005 g/cm.sup.2 and has dents and has a rugged surface very much
susceptible to change if pressing or the like, so that it needs to
be transferred to the process of applying a liquid mixture system
to the web on a carrier sheet or a belt conveyor without being
pressed by a roll. The web being on such carrier sheet or a belt
conveyor tends to be more uneven or non-uniform for air dwells on
the carrier sheet or the belt and that there may be formed spaces
between the web and the sheet or belt, so some or other means needs
to be applied to have the web well fit onto the sheet or belt.
[0079] In addition, as described later, in case a liquid mixture
system is applied to a web by means of a coater, being a contact
type, the coating tends to be non-uniform, so that a pretreatment
to make the surface of the web uniform or a substrate smooth is
needed. Also, since a web being bulky means that it is porous, too,
in case a relatively large slurry is applied by means of a curtain
coat and a vacuum zone is provided under the coat, a liquid mixture
as applied man leak down passing through a porous unbonded web. In
such case, any voids formed need to be filled by means of a
pretreatment before a liquid mixture system is applied. In handling
an unbonded web containing a fibrous material having a hydrophobic
or water repellent property, the liquid mixture tends to poorly fit
onto the web and delamination may take place, and in such case a
pretreatment is preferably needed to make the web hydrophilic.
[0080] For the reasons given above, in practicing the present
invention, it is preferable that, only after an unbonded web is
pretreated, a liquid mixture system is applied. As a typical method
of doing so, there is a method of preliminarily saturating a web in
a component as a medium of a liquid mixture system, i.e. in water
if it is of an aqueous system or in a mixture medium if it is of a
mixture system. In general, water or such mixture medium is added
by means of a flow coater, and after an excessive part of water is
made to drop down to be removed, a web is guided to a process of
applying a liquid mixture system to the web, whereby the surface is
made smooth and thus well slithery, dents on the surface are filled
and air partially dwelling is made to go out. Such process is
herein called a more generic term "precoat treatment". For this
precoat treatment, water or an aqueous medium solution is
preferably used or the above-mentioned microfibrillated fibrils may
be dispersed to co-exist in such water or aqueous medium solution.
Note that this precoat treament can be omitted for a web in a wet
condition obtained through a wet formation method or, a water
entangling treatment.
[0081] To thus precoat treated unbonded web, a liquid mixture
system is added to make a composite of it in a contact or a
non-contact way. The patterns of adding and making a composite may
be in the various forms of dots, lines, whole area, and sea
islands. An application device suitable for each of such forms is
selected. Application systems ma be, typically for example,
impregnation, coating with such device as a roll coater, a knife
coater, a transfer coater, an extrusion coater, a kiss coater or a
curtain coater, nozzle extrusion, an extrusion into film or
spraying.
[0082] A liquid mixture system as is applied to an unbonded web is
made integrated with the unbonded web passing through a vacuum zone
and a pressurizing zone. Excess water and solvent which were
contained in the web are removed in the vacuum zone and the
pressurizing zone as recovered liquids and at the same time a
structure in which a super absorbent resin component together with
a bonding component are contained in the spaces of fibers
comprising the web is formed.
[0083] A composite made integrated by the pressuring is made then
to pass through a drying and a heat treatment step in which any
residual water and solvent are removed and at the same time the
structure is fixed. In the drying and heat treatment steps a
thermal fusion is made to progress and at the same time the web is
made into a non-woven fabric in case the unbonded web contains
thermally fusible fibers, which is an important feature of the
present invention.
[0084] The processes of manufacturing highly absorbent composite
sheets according to the present invention are explained below with
reference to the drawings showing the specific configurations of
the devices therefor.
[0085] (In Line Manufacturing Process of Coating Substrates Based
on Carded Web)
[0086] FIG. 1 shows an example of a process of manufacturing a
non-woven fabric substrate, in which a carded web line is
incorporated, wherein a manufacturing process of a highly absorbent
composite sheet according to the present invention is embodied. In
FIG. 1, fibers sent from an opener are processed into a carded web
on a card and sent to an application unit on a conveyor. An example
of the composition of a carded web consists of:
[0087] Top layer: PET (5 d)/bicomponent fibesr (2 d), 20 g/m.sup.2,
and
[0088] Bottom layer: rayon (1.5 d)/bicomponent fibers (2 d, 20
g/m.sup.2
[0089] The application unit functions in a step of moving a carded
web along a planate treatment region structured on an endless belt
to coat the carded web with water from a precoater and then with a
slurry from a coater.
[0090] The slurry fed from the coater, as used in this example, is
prepared by mixing and agitating polyethylene glycol (PG),
microfibrillated fibrils (MFC), a super absorbent resin polymer
(SAP) and water in a slurry manufacturing unit. This slurry is
formed into a coating of a desired thickness as liquids contained
in the slurry are removed while it is made to move through the
treatment region.
[0091] In the treatment region, to the carded web water is fed from
the precoater and the slurry is fed from the coater, and then in
order to remove any excessive water and solvent from the carded
web, a suction unit is provided on the bottom surface of the
endless belt in the treatment region. Each suction unit serves to
remove by suction any excessive liquids from the carded web on the
endless belt by means of a vacuum pump via a gas-liquid separation
unit. Such liquids removed by suction undergo a gas-liquid
separation in the gas-liquid separation unit, and the liquid
component, which contains much propylene glycol, coming from a
suction unit provided after the coater is recovered at a propylene
glycol recovery unit after only the liquid is separated at the
gas-liquid separation unit, which propylene glycol is reused at the
slurry manufacturing unit.
[0092] The carded web coated at the application unit is heat
treated and dried as it is made to pass through on the surfaces of
heat treatment and drying rolls in succession and finally wound up
on a roll at a winder.
[0093] This manufacturing process performs the making of an
unbonded web into a non-woven fabric and the fixing of super
absorbent resin particles on the non-woven fabric at the same
time.
[0094] (Manufacturing in Line of Coating Substrate in Combination
of Carded Web and SB)
[0095] In the manufacturing process shown in FIG. 2, a spun-bonded
non-woven fabric (SB) is drawn from an SB unwinder, and on the SB a
carded web is laminated as it is led to an application unit via a
conveyor and then the SB as it is laminated is led to the
application unit. The spun-bonded non-woven fabric is a carrier for
the carded web which is laminated on the non-woven fabric, and by
means of the carrier the unbonded web which is not sufficiently
strong can be transferred stably. Any other configuration and
operations are the same as those of the manufacturing process of
FIG. 1, so that detailed explanation is omitted.
[0096] A preferable example of the composition of the carded web is
PET (5 d)/rayon (1.5 d)/bicomponent fibers (2 d), 20 g/m.sup.2.
[0097] (Manufacturing in Line of Coating Substrate in Combination
of Carded Web and Cotton Yarns)
[0098] In the manufacturing process shown in FIG. 3, many cotton
yarns (spun cotton yarns) are as a carrier drawn from a cotton yarn
creel stand in parallel at appropriate intervals of, for example, 5
mm, and on the cotton yarns a carded web from a card is laminated
as the yarns are led to an application unit via a conveyor and then
the cotton yarns as they are laminated are led to the application
unit. Any other configuration and operations are the same as those
of the manufacturing process of FIG. 1.
[0099] A preferable example of the composition of the carded web is
PET (5 d)/rayon 1.5 d)/bicomponent fibers (2 d), 20 g/m.sup.2.
[0100] It is noted that, instead of the cotton yarns as the
carrier, spun-laced non-woven fabric as slitted into tapes of an
appropriate width of, for example, approximately 10 mm may be used
as the carrier as arranged in parallel.
[0101] Also, it is feasible that, after a carded web is laminated,
the carded web can be made wider by expanding the interval widths
of the yarns or the tapes as the carrier.
[0102] The cotton yarns drawn from the cotton creed stand are
introduced beneath the carded web in the above process, but the
cotton yarns drawn from the cotton creed stand are introduced on
the carded web, thereby to form a laminate to be led to the
application unit.
[0103] (Manufacturing in Line of Coating Substrate with WJ Unit
Incorporated)
[0104] In the manufacturing process shown in FIG. 4, two cards are
provided. As a first carded web as manufactured at a first card is
transferred on a conveyor a second carded web as manufactured at a
second card is laminated on the first carded web, and the laminated
two-layer carded web is fed to a water jet (WJ) unit via a
conveyor.
[0105] The WJ unit is so configured that a carded web as
transferred on the peripheral surface of a roll with its peripheral
wall constructed of a perforated plate is coated first with water
to make it wet and a jet stream is applied on the carded web to
entangle the constituent fibers of the carded web with each other.
This water stream entangling is to give a shape retention of an
extent not causing any trouble in the subsequent transferring and
handling operations, so that it may be relatively light. Any excess
liquid coming out of the WJ unit is suctioned at a suction unit
similar to the suction unit at a subsequent application unit and
discharged out of the system by means of a gas-liquid separation
unit.
[0106] Any other configuration and operations are the same as those
of the manufacturing process of FIG. 1, only except a precoat is
omitted for coating water.
[0107] A preferable example of the composition of the first carded
web is PET (5 d)/Melty (2 d), 20 g/m.sup.2, and a preferable
example of the composition of the second carded web is rayon (1 d),
20 g/m.sup.2.
[0108] An advantage of this manufacturing process is that, since
water used after the water entangling treatment at the WJ unit can
be handled as it is in a precoated condition, a precoat is not
required and that naturally a separate step of removing such water
is not required to be provided.
[0109] (Manufacturing in Line of Coating Substrate with Foaming Wet
Laid Process Incorporated)
[0110] The foaming process shown in FIG. 5 is a processes which a
foaming agent and an activator as required are added to a mixed
slurry of short cut fibers (for example, PE/PET (2 d.times.5 mm))
and pulp to foam the slurry and the foamed mixture is formed into a
wet web on a sheet on a plastic conveyor of paper making.
[0111] The wet web as obtained in the foaming wet laid process is
sent to an application unit via a conveyor and given slurry there.
In this case, too, the wet web is a water precoated web as it were
and as such the slurry can be applied with no precoat applied.
[0112] All the subsequent parts of the manufacturing process are
the same as those shown in FIG. 1. In this case, too, a separate
step of removing used water is not required.
[0113] (Manufacturing in Line of Coating Substrate with Air Laid
Former Incorporated)
[0114] An air laid former is a device for making a fiber mat of air
laid short cut fibers such as PE/PET and PP/PE, and in the
manufacturing process shown in FIG. 6 an air laid former is
provided in the upstream side and an application unit is provided
in the downstream side of the belt running direction in a planate
treatment region constructed on an endless belt.
[0115] Slurry is applied on the surface of an unbonded web of air
laid mat form in the application unit, and then the web is led to a
heat treatment and drying roll jus as in the above-described
processes. All the subsequent configurations and operations are the
same as those in FIGS. 1 to 5 above.
[0116] Interlayer separation is likely to take place in an unbonded
web of air laid mat form, so it may be sometimes preferable to have
and use a carrier arranged in parallel such as tapes of spun yarn
or spun laced non-woven fabric just as in FIG. 3 above.
[0117] (Manufacturing in Line of Substrate to be Obtained with a
Bonded Spun Bond and an Unbonded Spun Bond as Combined)
[0118] FIG. 7 shows an example of a process for manufacturing a
non-woven fabric substrate with a bonded spun bond and an unbonded
spun bond as combined, which is an embodiment of the present
invention for manufacturing a highly absorbent composite sheet. The
substrate is made by combining a relatively dense layer consisting
of fine denier fibers (preferably 2 d or finer) which is a first
spun bond layer and a relatively bulky layer consisting of coarse
denier fibers (preferably 3 d or coarser), and it is preferable to
bond the first layer relatively strongly and the second layer
relatively weakly in combining the first and the second layer.
Therefore, in this embodiment of the present invention, an unbonded
second web is folded on a web bonded in which the first layer is
bonded on a heat embossing roll, and the folded webs are precoated
with a water dispersion liquid containing MFC for imparting a
hydrophilic property and led to the application unit.
UTILIZATION OF THE PRESENT INVENTION IN INDUSTRY
[0119] As explained in the foregoing, according to the present
invention in the process of manufacturing non-woven fabrics the
manufacturing of non-woven fabrics and carrying and holding SAP in
the non-woven fabrics can be fulfilled almost concurrently, and
furthermore, neither powder dust is generated nor SAP particles
move in an absorbent member, and with the fundamental properties of
a non-woven fabric as a substrate sufficiently maintained, a highly
absorbent composite sheet is obtained having all three functions of
a supporter, holding and fixing SAP and permeation and
dispersion.
[0120] Such highly absorbent composite sheet can be advantageously
used as an absorbent member of an absorbent article such as a baby
diaper, an adult incontinence diaper, female hygiene product,
sanitary napkin, a blood absorbent and mother's milk pad.
[0121] In addition, no web of a bulky structure, which has spaces
among its constituent fibers, needs to be transported, the
transportation and handling costs are much reduced and thus the
highly absorbent composite sheet according to the present invention
has outstanding benefits in terms of the costs.
* * * * *