Note: Descriptions are shown in the official language in which they were submitted.
W 0 91/18042 PCT/GB91/00780
.~ 1 . ,.
2 ~3~5~3
WATER-ABSORBENT RESIN PARTICLES FOR ABSORBENT STRUCTURES
:~ This invention relates to novel water-absorbent
resin particles, a process or the preparation of such ~ :
water-absorbe~t resin particles and to absorbent ::
. . .
; 5 structures contai~ing the water-absorbe~t resin
' particles. The invention further relates to water-
;~ absorbent resin compositions with improved aqueous fluid
absorption properties, and ~ater-absorbent structures
co~taining these water-absorbent resin compositions.
. , , ., . .;
It is kno~n to form woven and non-woven
structures `of celluloisic f;bers5 ~iatural cotton fibers,
sy~thetic fibers or mixt~res thereof for use in .
~absorbing aqueous fluids.-I~ one example, the fibers are
formed into op~n-structured absorbe~ webs~ and i~ .
~ Y~ r ~ J ~ ; L; , " ~
another, the ~ibers are thermally bonded to.form co~pLex
s~ructures. The flbers used 1~ such structures ca~ ,
quickly absorb aqueous 1uids and distribute them over
the whole absorbent structure by capillary forces~ The .
structures, i~ the absence o~:water.-absorbe~t~resln~ ~ r
particles7 have limited absorptIon capaclty,.a~d are
very ~ulky due to the large amou~t .of materlal neeted.to
provide acceptable absorptio~ capacltyO Further, the
.
WO91/18~2 PCT~GB91/00780
2 ~ ~i~ 5 ~ 3 2
ahsorbent structures do not retain fluid under pressure.
. A means for improving the absorbency characteristics is
to incorporate in the absorbent structures water
absorbent resin particles which imbibe fluid to form a
swollen hydrogel material, as described for example in
US Pate~t 4,610,678. This hydrogel serves to retain the
absorbed fluid even under pressure and gives the ''
absorbent structure a "dry feel" even when wetted. I~i . .
order to reduce the bulk of absorbent structures ':
containing ~ater absorbent resin particles, large
volumes of the absorbent structure material can be
replaced with s~all volumes of absorbent resin
particles. The absorbent resin particles must ~uickly
absorb fluids and 'retain such fluids to pre~ent leakage. ' '
Water absorbent resin particles (als~ referred to as
superabsorbent polymers) are primarily used in personal
care products to absorb body fluids, ~or example baby
diapers, adult incontinence products, feminine hygiene
products, a~d the like. '
' ' ' ' ' '''
.
Water-absorbing resins well known in the art
include, for exa'mple',' the hydrolyzate of'a s`tarch~
acrylonitrile' graft'poly~èr as^discloséd in US Patent
25 3,661,815;' the'nèùtralization product of à starch- - `'
a'crylonitrile acid `graft polymer 'as discloséd in US ' .
Patent'`4,0i6,663; thë'saponificat-on produc~ o~ `a vi~yl
acetate-acrylic ester copolymer as disclosed ln Japa~ese
Laid-Op"én Pat'ènt`'PubIi'cation No"." 14689/1977; thé' '
hytroly~a~e of an acrylonitrile copolymer and t~e ' `~
hy'droly'za~te' of an acrylamide copolymer as disclosed ln
~: Japan'ese Patei~'-Publii`ation ~5959/1978, the crosslinke~
' ~ ' products 'of'thes~ hydrolyzates and a self-curable
poly(sodium acrylate) obtalned by inverse phase ~ -
J j r r, ~ , 7,, ,~r . ~ "t ~
, ' '.
.
',: ' ' . ,,, ' , ,. ' . . -. ~ ' .. ' , ' ' :
WO91/18~2 PCT/GB91/00780
. . ~ .
Z~ 23
- .
suspension polymerization as disclosed in US Pa~ent
4,093,776; and the crosslinked product of partially
neutralized polyacrylic acid as disclosed in Japanese
Laid-Open Patent Publication 84304/1980.
: 5
The absorbent structures demonstrate limited
ability to retain the water-absorbent resin particles . ,- -
which are randomly dispersed throughout the structure in
the desired locations. This can cause loss of the water-
absorbent resin particles during the manufacturing
process of such s~ructures~ irritation of the subject
durin~ the end use, such as, baby's skin when the
structure is used as a disposable diaper. It is - ,
difficult.to distribute the water-absorbent resin
particles evenly~within the absorbent.structure.
Further, the water-absorbent resin particles can ~igrate
within the structure9 causing a loss in absorbent
p'roperties of the.entire struc~ure. Such water-absorbent
resin particles can.a~glomerate.or be too close.to one
:' another.c:.Water-absorbent. resiniparticles;in the prese~ce
. of -aqueous~.fluids form gels.,If,the gel~parti`cl LS of. ;
.: resi'~s:.,particles are too' close:'toione.another gel~
blockage can occur`-and:the-ability.-of.-the:closely~
,, 25 associated.water-absorbent.:resin particle's~to.~ully :--' , .'. ,
' : . absorb iqueous~fluids:is.~s-ignificantly,~reduced~;In,:order ,,
, ' to maintain'~.a~minimum'.~absorpt;on~capaci'tyj!more w'ater.
.; absorbent~.. rasin~:parti'cles'~may~`be'rused'.. ;t'han.would:.be'
30 . ~ecessary;in'the:absence'o~^the.rrisk~o~;improper~
dist`ribution':andl:'gel~bl'o'ckàge.J.,Further.,:in~:the~
i pr'epara~ion~oflwater'-abscrbent`'~:s'`t'ru'ctures,'.~handling and
~ cutti~g~'ca~rcause~los~s~ o~ 'ater-ab~orbe~t~:resin~
'' .: par~i'c`l~s ~romJthe~st:ructu'r~e';~re'suIti~glin-~aste,L~a~d~
coùld ~`'presentL~industrial~chygiëne.~.problems.~ . C.3~L~r;.
, .
, .
' ~
.,,, :,, , , ,, , ... . ,.. .. . . .. . . .. '... ".
WO9~/18~ PCT/GB91/OQ780
i' ``.- 4 ....
Water-absorbent structures function to re~ove
aqueous fluids from a source and retain such aqueous
fluids. The structures contain hydrophilic fibers which
are designed to absorb and ~ransport the aqueous fluid
quickly to the interior structure by capillary and
wicking means. Such fibers transport the fluid to the
water absorbent resin particles wh ch absorb and reeain
the aqueous fluids. One problem associated with such -:
water-absorbent structures is the speed of absorption of
fluids from ~he exterior of the structure by the fibers. '
EP 90,311,527.7 and GB-A-2237205 disclose a
~ethod of increasing the rate of aqueous fluid flow into
the absorbent s~ructures, such'as a baby diaper or
fe~inine hygiene napkin, by the.addition of a surface
active agent to the body side of the membrane of the
absorbent structure. The surface active agent has the
ef~ect,of reducing thei-surface tension of,the body fluid
or aqueous fluid to enhance the speed at which said
-aqueous fluid passes through.the~body.side Pf.the ~ .~-:.,.;, ,
membrane of the absorbent-structure and into ~he fiber,
structure. This method ,o~ reducing the sur~ace:tension ''
of aqueous.:body,fluids is,extremely effecti,vP in . ~
achiev'ing rapid.flow and distribution~:of-the body fluid
throughout.the~absorbent',structure~.~owever,~this
reduction.~ofisurface~tensi`on:has~the disadvantage,,of
i~pairing'the;ability;.~of~.:the~absorbentJfiber,.structure
'to'hold-and.retain`the~aqueous body fluid., Water~
absorbent!resins,are~ cluded;withi~ the,:structure :to;:-,
aid.in.;retaining~,such~;fluids,.~,Afproblem 1l associated.with ''
the use of.~water~absorbent;:.r.esin particles.,~is~,,tha,t.,~the~
speed.~,o~-~.absorption,~of..,.the~hydrophilic~fibe,rs in~the~s~ .
structure is fasteri~.than..the.speed~,o~abso~ption.of.~he
water-absorbent resin particles. Therefore, there is a . '
':
-- : . , ... ~
: : . . ~ . . . . .. .
WO91/18042 pcT/Gs9l/oo78o
1~ 5 Z~
~ime differential between absorption of the aqueaus
fluid by the hydrophilic fibers and absorption of the
fluid by the water-absorbent resin particles. During
this time differential, there is a risk that the
absorbent structure could lose such aqueous fluid before
being absorbed and bound by the water-absorbent resin
s truo tures .
What is needed is a water-absorbent reisin
particle which can bie effectively distributed within a
absorbent structure and a means of effectively retaining
the water-absorbent resins at the desired points in the
absorbent structure~
In one embodiment the inven~ion provides water-
absorbent res~n particles comprising a carboxyl
containing water-absorbent resin, wherein the water-
absorbent resin particles also co~prise a thermoplasticpolymer with hydrophilic character. Optionally, the
particles also comprise a flow control additive. In
a~other embodiment the invention comprises a water-
absorbent-structure1whichjcomprise a ~oven or non-woven
~5 mass of fibers having bound thereto particles as
described above.
In aanother embodiment, the invention provides
a process for preparlng water-absorbent resin particles l,~
havi~g adhesive properties which comprises blending
~ater-absorbent resin particles containing carboxyl
~ ,3 ~ r~ ; r'3~ J~ 3 2.,i3'~S.~;'S;~ ?~ r~ / 3
~oieties ~ith a ~her~oplastlc resl~ having hydrophilic
character until the mixture ~o longer flows freely and,~ -
~ ,r ~ h,~ r~7 ~ t ! .~ s~ 7 ,; ~
optio~al ~ ? atding ~to the wat~er,-~a~b!sor~bent resln ~ ~ ~ *
. :
' ~
-
.
- , , , , : ,...... . .
WO91/l8042 PCT/GB91/00780
~ ~ ~ ?~ 6
!~` ~
particles and thermoplastic polymer mixture a flow
control additive and blending until the mixt~re flows
freely.
The flow control additive can comprise an
inorganic material which functions to give ehe
compos;tion flowability ~ithout tackiness.
Alternatively, the flow control additive can comprise a
water-soluble pol~mer which functions to increaise the
viscosity of aqueous -fluids and ~hich further ~unctions
to restore the flowability of the mixture of water-
absorbent resin and thermoplastic polymer. In the
embodiment where the flow control additive is the water-
soluble hydrophilic polymer, the absorbent resincomposition improves the function of the water-absorbent
structures into which they are incorporated as the flow
control additive increases the viscosity of aqueous
fluids ab'sorbed by the structure'such that the absorbent
fluid'cannot easily be release'd by the structure before
being bound by'the ~ater-absorb'ent resin particles.
~., , .... .., - . - . . :. . - .. ,
The adhesivized'wa~er-absorbent resin'particles
of the invention can be more effec~ively distributed ' '
within absorbent structures, and facilitate the"
maintenance of such effective distribution. As a sesult
the invention allows the preparation of absorbent
; s~ructures wherë gel blockagë is' mini~ized.''Further, the
uYe o~ such adheslv~xed ~ater-absorbent resins r~sult in
less 10BS o res~ln during manufa'cturing"and handling of
the wàter-absorbent' structures and prevent the problems
~ r L~tt ,~ ?.-~ ; 2 ~ r ~ } ; 3 i;-
assoc~ated` wlth such loss. The adhesivized~water-
~, ~, . .`.'jdX,.~" ~ .t ~ L ~ r1i ~ J~ u ^
; absorbe~t resln par~lcles of the lnventlo~ allow more
~ficient use of such particles in water-absorbent
1 ,
-.. : ........... ... . : . :,
.: '` ': .: ~'' ' : ,, ' .' ;: .
.
WO91/l8042 PCT/GB91/00780
t ~
7 ~8~
structures, and allow the fabricator to use the optimum
amount without significant waste. In those embodiments
where the flow control additive is a water-soluble
hydrophilic polymer, the retention of fluids by the
absorbent structure is significantly enhanced.
Adhesivized as used herein refers to resin
particles that are modified such that at a later time
they can be adhered to a portion of an absorbent
stru~~ture~ e.g. to the fibers of an absorbent s~ructure.
The water-absc,rb~nt resins useful in this
invention are well-known to those skilled in the art. In
particular, water-absorbent polymers useful in this
invention are water-absorbent polymers which contain
carboxyl moieties. Among preferred carboxyl containing
water absorbent polymers are hydrolyzates of starch-
acrylo~itrile graft copolymers? partially neutralizedproducts,o~ a starch-acrylic acid graft,copo,ly~ers,
saponificatio~ products of vinyl acetate acrylic ester-
copolymers, hydrolyzates of acrylo~itrile copolymers,
crosslinked products of hydrolyzates of acrylonitrile
copolymers, hydrolyza~es ofJacsylamide copolymers,
crosslinked,products"ofihydrolyzates of~acrylamide~: :
copolymers,~-~partially~Reutralized;produc~s of
polyacrylic ~ acidq ~ and l crosslinked; products of partially~
neutralizedjlpolyacrylic~;acids. ~ - s~
,r~Eispecialily,preferred aire ~alkal i metal ,~c~
~ype polymers obtained~by copolymierizing 100 parts of a~
acrylic^ai~id-tjpe~o;nol~er~com~ sedj,o~f~ o~ 50,mo~1~e ~
percent of acrylic, ac-ld~and 50 to;!99 mole percent of5i~a
. : ' ' '''
~ ~.
WO91/l8042 pcT/Gs9l/oo78o
(, .~ .
~ 8 ::-
2 ~
alkali metal acrylate and 0 to S parts by weight of a
crosslinkable monomer in aqueous solution in a monomer
concentration of at least 20 percent by weight. In
another preferred embodi~ent the alkali metal acrylate-
type polymers are obtained by polymerizing acrylic acid
and post neutral.izing the polymer ~i~h an alkali ~etal
base.
There is no limitation to the amount of the
carboxyl groups of the wa~er-absorbi~g resin.
Preferably, at least 0.01 equivalent of carboxyl groups
are present per 100 g of the water-absorbing resin~ In
the case of the partially neutralized polyacrylic acid,
the proportion of the unneutralized portion is
preferably 1 to 50 mole percent. In one preferred
embodiment the water-absorbent resins are crosslinked at
or ~ear the particle surface by a polyhydroxy compound
capable of reacting with the carboxyL moieties of the
water-absorbent resin and ~ay optionally have coated on
.
or bound to ~he surface a non-ionic surfactant with an
~LB from 3 to 10.
.
, . . .. . . . ... , .
.The:polyhydroxy compound which is used asja
surface~crosslinki~g agent~is a;compollnd which contains-
at least ~wo~hydroxyl groups.~hich.arercapable or .. ...~-
readily,reacting with the:carboxyl groups.of.:the water-
absorbent ~esin, a~d which is~.capable o~.,being dispersed~
over the surface of a water-absorbe~t resin p~rticle.
Preferably, the polyhydroxy compound used in this
invé ~ on comp`~ises~~ethyle~e.iglyc`ol,-'diethylene glycol,
ylene giycol~ polyethy~lrè-neV~`gly`co`
polyglycrlrol~ propyléne gI~yco'iJ dipropyle~e giycol~
tripropylë~è giy`col~ po ~propyie~e glycoi!s , ' ` ` ` ';
' .:
'
- - . . - - . , . - , , , , . -
... . ` ,, ... :.: , ~ ` . : .
W091/18042 PCT/GB91/00780
g ~ ; ,s~ Ç~%~
.; ~ ; .
diethanolamine, triethanolamine~ propane diol, butanediol, hydroxy terminated oxyethylene-oxypropylene block
copolymers, sorbitan fatty acid esters, polyoxyethylene
sorbitan fatty acid esters, trimethylolpropane,
pentaerythritol, sorbitol, mannitol, sugars, sugar
derivatives or the like. More preferred polyhydroxy
compounds include diethylene glycol, triethylene glycol,
glycerol, propylene glycol, trimethylol propane, ~.
pentaerythritol or sorbitol. Even more preferred are
~0 sorbitol or glycerol.
:.
The surfactants which may be coated on the
surface of, or bound to the surface of the water-
lS absorbent resin particles are nonionic:surfactantshaving an HLB in the range of 3 to lO and which are
: dispersible in water. Preferable sur~actants co~prise .
sorbitan fatty acid esters, polyoxyethylene sorbitan
:fatty acid esters? glycerol or polyglycerol fatty acid
20 esters, polyoxy ethylene alkyl ethers~ polyoxyethylene .
alkylphenol ethers, polyoxyethylene acyl esters, sucrose
fatty acid esters or modified surace a`ctive polyesters.
.~More preferred sur~actants are polyethoxylated sorbitol
1~lanolin deriva~ives, for example a surfactant available
from ICI under the Tradename Gl425. A sufficient amount
:: of surfactant is.. used toi~facili~ate a homogeneous
distribution.~of thelsurface.crosslinking.~.agent-.on the~
: surface.. lof:~the.gel.iparticlei,~to improve.the
processability..of the.~gel.~by reducing .its.stickinessj to .
reduce the tendency.o~.the dried powder to agglomerate:.. ri
~: when exposed to hu~id.air./or water,~and to bind-fine.~
dust of the water-absorbent.. resin. r~ ;s./~ ;
,
, .
`
' 1.:'.
'' I '
~ . . . -- - - , .
'` , ' ' ' ' ' , , ~ ', . ' , .` '
WO9~/l8042 pcT/Gs91/oo78o
'
%~5~3
The water-absorben~ resins are adhesivized by
contacting and blending with a thermoplastic polymer
with hydrophilic character. Thermoplastic as used herein
refers to a polymer which softens, flows and becomes
tacky at elevated temperatures. For the purposes of this
invention, the polymer must soften? begin eo flow and
become tacky at a temperature wh;ch does not harm the
wa~er-absorbent resins or materials from which .the
~ater-absorbent structures are prepared and which does
not cause the proper~ies of the final water-absorbent
resin structure to be significantly degraded.
PrPferably~ the polymer begins to soften at a
temperature at or above 35C and more preferably at or
above 70C. As the absorbent:resin struc~ures could be
and often are exposed to temperatures approaching 35C,
it is preferable ~hat the thermoplastic polymer be `
relatively stable at temperatures approaching 35C.
Preferably the thermoplastic polymer begins to 1OW and
become tacky at temperatures of 170C or less, more
preférably 130C or less, and most preferably 80C or
léss.` The''material'used`in the absorbent resin structure
.. . , . ~ . .. ..
may be deleteriously effected by exposure to
', tempèratures'abové 170C. ' ;
~ydrophilic character:means. herein.that the ;,
thermoplastic~polymer.~has a:portion which demonstrates.'. ' , '`
affinity for water.Such afinity for,water can`~be ,~. ..
indicated by:its:ability,to dissolve or disperseiin .
wBter.~ Thermoplastic.~polymers::,which have: both a~ .~ ,:,,.~. '!
' hydrophobic~portion~.and.a hydrophilic~portion may-~be ,.j.
used in this inven~ion~providedi.they have~the w~ o
` ' eppropriate ther~oplastic charact`eristics. Thus ertain . .
8urfactants which have ther~oplastic character may be
.. .. .
,! :
WO9l/l8~2 PCT/GB91l00780
. .
, "i ,
11 2 ~ ~ ~ 6
used in the invention. Among preferred classes of
thermoplastic polymers are the polyvinyl pyrrolidone
polymers, copolymers of polyvinyl pyrrolidone and vinyl
.acetate, polyethylene oxides, and polyethoxylated
surfactants having a hydrocarbon cap. Hydrocarbon cap
means herein a hydrophobic hydrocarbon moiety at one end
of the polyethylene oxide chain. Such hydrocarbon caps
can be aromatic, aliphaticj or have both aromatic and
elevatic components. In one preferred embodiment, the
hydrocarbon cap is a nonyl-phenoxy moiety. Examples 0?-
surfactants which are useful as ~he thermoplas~ic
polymer with hydrophilic character include Synperonic NP
35 available from ICI, straight chain fatty alcohol
inititated ethrylates.such as Lutensol AO 30 available
. 15 from BASF, and ocyl phenoxy ethrylates Triton X-100
available from Rohm & Haas.
Among more preferred thermaplastic polymers
useul in the invention are the polyvinylpyrrol;dones, - polyvinylpyrrolidone vinyl acetate copolymers?.and.the
polyethylene oxide based materials. Most preferred
. ehermoplastic polymers are the polyvinyl pyrrolidones.
Polymers of a wide.`range.of molecular weights-mày be
used in the.invention,.provided the-above-mentioned
characteristicsmare exhibited by;the polymers.~
. . The optional flow ,control additive.functio~s.. to;
JU maintain the flowabiLity of.the.co~position.o~ thei.,~ l~
inventiotn,-~ T~h,ere;~;ar~e~L~two j~clas;ses `,Ei fflow,,c,ontrol" ~ ti;
additives which can be used. One class comprises..an~
inorganic ma~erial ~hich functions to improve and
maintain the flowability of the adhesivized water- ~.
absorbe~t resins particles of the i~vention. Such
,, - .
, .
:: :
~' . .
, , - .
WO91/18~2 PCT/GB91/00780
f~
2 ~i~ 6 ~ ~ 12
materials are well-known to those skilled in the art.
Examples of materials ~hich may be used include zinc
oxide, talc, silica powders and the like. The most
preferred of this class of flow control additives is
zinc oxide. In a second embodiment the flow control
additive can be a polymer which dissolves in or is
dispersible in aqueous based fluids and increases the
viscosity of aqueous fluids in which it is dissolved or
dispersed. Such polymers are well-known to those skilled
in the art. Among preferred classes of such polymers are
polymers derived from carbohydrates, and modified
poly~ers derived from carbohydrates. Included are the
polysaccharides, modified polysaccharides, xanthum gums,
and ~uar gums. Preferred polysaccharides are the
oellulosic materials such as alkyl substituted
cellulosics, hydroxyalkyl substituted cellul-osics and
the like~ examples of such are cellulose,
methylcellulose, ethylcellulose, hydroxyethyl cellulose .~.
and hydroxypropyl cellulose. In another preferred
embodiment a mixture of guar and Xanthum may be used as
tne nyarOpnlLlC polymer. -~'
. .:
, . . . , ~ . ... ... . . . . .. . . . . . . . .
~- .. The.inclusion of.the water-.soluble polymers as :
flow control.additives resultsiin absorbent.'resi'n ~
composition.whi~h:.causes aqueous 'fluids;.in:contact-with
such eomposition to ha~e an increased viscosity. By
increasing the viscosi~y of such aqueous fluids such
aqueous~luids are retained for~a significant'period i~ i!'.
the abs~o"rbentlstruc'~'u're wh'ile the water-absorbe~ti!resins
ab~orb thë''aqueoùs-fluid;and;b'ind'''them'within'the''''`' ''
strUCtUre'.'; ' ~c ~if~ ? ~ C -. D~ J ~ rl~3 ~ `?~
.' . , ' .
.
WO91/18042 pcT/Gsfgl/foo78fd
f~' 13
2 ~ ~ ~f5~f~'
The water-absorbent resin is contacted with a
sufficient amount of thermoplastic polymer to adhesivize
substantially all of the resin particles. If too much
thermoplastic polymer is used, the ability of the water- '
absorbent ~esin to absorb aqueous fluids will be
deleteriously effected. Conversely, if an insufficient
amount of thermoplastîc pol~mer is-used,'~all of the
water-absorbent resin particles will not be adhesivized.
Preferably, at least one part of thermoplastic polymer
per hundred parts of water-absorbent resin is used, more
preferably at l.east 3 parts by weight of thermoplastic
polymer per hundred parts by.weight of water-absorbent
resin~ Pre~erably, 20 parts by wfeight or less of
thermoplastic polymer per hundred parts of water-
15 absor~ent resin is used, more preferably lO parts by .
weight or less and ~ost preferably 8 parts by weight or '
less are used. It is believed that by choice of a
polymer which has hydrophilic character, such polymer
. when contacted with the water-absorbent resins at
ambifent;temperature forms.'a physical bond on the surface
of the water-absorbent-:resin particle. As the'`~` ''
thermoplastic;polymer~bound.to.-the surface of 'the water-
absorbent resin particle blocks-access of aqueous-fluids
to the water~.absorbent.resin particle, if too ~uch
thermoplastic~polymer.-:is usedj:the ability of':water to ..
come in contact:~ithr~the.water-absorbfent:resin'particle
i8 significantly reduced.~ mm~
.
The amount of~flow.control~.additive'which is
'used .,is.dependent.~upo~.the class-.:o'flow-'control~f ~{`I~f'~
addi~t~ive chosen.~In;~hat-~embodiment wh'ere 'th'e''~flowr-'~
contJr;o~additi.ve ~i,s ;an~inorga~ic'..~ ert material';,':~San'~ Si
amount.lwhich.results i~ free..flow..'o'f;~thetcompo'si~'io'n'''o'f
:,
' '' '
... . . .. . .. . . . . . . ..... . . . . .... . .
WO9l/18~2 PCT/GB91/00780
(
Z~i~5~3 1 4
the invention is used. The effective lower limit is ~hat
minimum amount which results in free flow of the
adhesivized water-absorbent resin composition of the
invention. The upper limit is based on econ~mics. In a
preferred embodi~ent, at least 0.25 parts by weight per
hundred parts of water absorbent resin is used~ In a
more preferred embodiment at least O.S parts by weight
of flow control additive per hundred parts of water-
absorbent resiin is used. Preferably, one part by weight
10 or Iess of flow control additive is used per hundred ''
parts of water-absorbent resin. In that embodiment where
the flow control additive is a water-soluble polymer
which increases the viscosity of aqueous fluids into
which it is dissolved, a sufficient a~ount is added to
allow the adhesivized water-absorbent resins to freely
flow. If too little of such flow control additive is '
used, the adhesivized water-absorbent resins will not
flow freely. If too much is used, the functioning of the
water-absorbent resin structure ~ay be deleteriously
effected. In this embodiment, preferably, one or more
parts by weight of such'flow control additive per'
hundred parts,of resin is used, more preferably 5 parts
by wei'gh~ and most preferably..at least:10 parts by
weight. Preferably 20 parts by ~eight per hundred parts
of water-absorbent:resin.-are u~ed, more:preferably'l5
' parts by weight,or-less;are;used, and'most'preferably 12
parts by weight or less are used. .
. The,iadhesivized water-absorbent'resin ':;
compositions .of,,~this`~invention may be .prèparè'd`'by'the ''!'
~ollowi~g.process,.,..The:.~ate'r-absorbe~'t 're i~n'~`par'~iclés L ~ `
ar'e co~tacted wi,t,h,:a~suffic'ie~tA~amount o~-:thèrm`oplasitic`-'
poly~er ~wlth a ,hydrophilic charac`ter tn`d~blended under ~
, ~ .
WO91/18042 PCT/GB9t/00780
~..~ .
'' '
2 ~ ~ 5
condi~ions such that the resin particles become
adhesivized. More particularly, the thermoplastic ;,
polymer and water-absorbent resin particles are blended
by standard means at ambient temperature until the
composition is ~ell mixed. Evidence that the composition
is well-mixed is indicated by the material beco~ing
fluffy and demonstrating poor flow characteristics. ~ ,
Temperatures other than ambient may be used as long as
it does it deletereously effect the properties of the
adhesivized resins. The time period for such blending
depends on the scale at which the blending occurs the
type of mixer used and whether a batch or continuous
process is used', and can be empirically deter~ined as
described before. In a continous process at least 2 to
3 seconds contact time is preferred. In a batch process
as little as five seconds contact time may be used and
as much as 3 to 4 hours may be used. Once the flow
characteristics of the adhesivized resin deteriorate,
the flow control additive can optionally be added and
blending may continuè. This blending can continue for a
suf~icient time~'such`'that thë adhesivized resins fiows
freely.-This can take place`,at any temperature which
does not deleteriously affect the properties of the
adhesivized ~ater-absorbènt rësin, and most conveniently `
takes plàce at`ambiënt temper tures. This blending ,,,
continues for a time such that the ~aterial flows
i~reely..'The time period for'snch blending depends on
the scale at which.the~blending occurs the,type of mixer
30 used and,whether.a batch;or~co,ntinuou,s,process:is used,i '-'
and can be empirically~determined as ~described before. .
Itn?Ja ~ continous~;proces~s~ !at ~lea,st~2,jt,o,53-,iseconds,~,contact;
time is~pre~erred. ~,In~aybatch processias~little as~five
seconds contact time,may,be^~use,d,~,and~asjimuch,,as~,3ito 4^:~
hours may,be,used. Blending~ca~occur by ~any means ;~hich
:
WOgltl8042 PCT/~B91/00780
z~ ?~5~ 16
effectively results in contact of all of the components.
Such mea~s well-known to those skilled in the art, and
the choice of such is not critical to the invention.
The adhesivized water-absorbent resins of the
inve~tion are primarily used by incorporating them into
absorbent structures. Such structures are primarily
composed of natural and/or synthetic fibers, the fibers
can be formed into woven and non-woven structures. Such
structures are well-known'to those skilled in the art.
The water-absorbent resins of this invention can be
~ contacted with finished structures or mixed 1n with the
; component parts prior to ~ormation of the structure~ In
general, the adhesivized abs~rbent resins of the
invention are incorporatèd into the absorbent structure
and 'the absorbent structure is exposed to temperatures
at which the thermoplastic polym,er softens and becomes
tacky.'Under such conditions, the adhesivized water-
absorbent resin particles are then bound to fibers ofthe ~absorbent'stru'ctu'rë. The thermal bonding technique
resùlts in'fixating the'water-absorbent resin particlés
in the`'absorbent st'ructure. This prevents loss of
., " , . , ,, , .~ .. .... . . . . .. .. .
absorbent resin particl~es during hand1ing and prevents
migration and agglomeration of water-absorbent resin
partlcles .
'In one~embodiment absorben't' resin'structûres ' ~
a~e~preparediby'~what`i~;'kD,own"'in"'t~è'art:às~a'l'lofting' i
process~ In~such''proces'5'"a'mixtùre'0~'fibers'~is;là;d 1`'
', ~ dowrl,~san,d!the~fibèrsiare'~hëàtèd to"èpàrîd't~e;;strùcturè.
In'such procéss``the''f;bers':~càn'either bè'~prët~eated w'ith
the adhesivizedf'water~àbSorbent re'sini~or f~ithe
temperature of~the lofti~g';process`~is high~e~ough~ thë^-
',
WO 91tl8042 P~/GB91/00780
: `
17
adhesive structures can be bound to ehe fibers during
the lofting step, provided the lofting temperature is
sufficient to cause the thermoplastic polymer to soften
and become tacky. In a~other embodiment~ absorbent
structures are prepared via a thermal bonding process.
In such process, a mixture of hydrophilie fibers and
hydrophobic thermoplastic fibers are mixed and water-
absorbent resin par~icles are contacted ~ith such
mixture. Thereafter the mixture of fibers and water-
absorbent resin particle is exposed to temperatures atwhioh the thermoplastic polymer with hydrophilic
character a~d the thermoplastic fibers of the struc~ure
begin to flow and beeome tacky such that the mass of
fibers and resin become bound together upon cooling.
Synthetic fibers such as polyes~er, and polyolefin and
natural or regenerated cellulosic fibers are preferably
used. Preferably, the structure comprises a mixture o
hydrophilic fibers, such as cellulosic and regenerated
cellulose based fibers, with hydrophobic polyolefin and
polyester fibers. Preferably such mixture contains 20
percent or greater cellulosic fibers.
'
The particle size of the water-absorbent resin
is not critical with respect to this invention. Particle
sizes useful are those commonly known as useful in
absorbent structures. In a preferred embodiment the
particle size is less than about 2 millimeters, more
pre~erably 0.8 millimeters or less. Preferably the
particles have a size of 0.2 millimeters or greater, and
more preferably 0.5 millimeters or greater.
In one embodiment of the inve~tion~ water-
absorbent resin particles of the invention csn be
.
'' ~
..
WO91/18~2 PCT/GB91/00780
18
blended with the flow control additive which is a
hydrophilic polymer soluble in water in the absence of
the thermoplastic polymer. Such a composition can be
used in those uses in which the adhesive is not required
in the final structure. These CompOsitiQns provide a
means for improving the retention of aqueous fluids in
an absorbent structure by holding the fluids in t~e
structure while the absorbent resins are absorbing the
liquid.
. , . ... . , , ~ . . .. ..
: ~ ' ' ' ' , :'
, '',
:
''.
", ., ' ' ' ~'. ' . ': ' ' '
:
WOgl/18~2 pcT/Gs91/oo78o
7................................................ ' ,, ~ , :~ '
1 9 z~ s~3
.
EXAMPLES 1-6
Several ther~soplastic poly~sers are contacted
with water-absorbent resin particles and subjected to
: the following tests. ....
.
Coatin~ Affinity Test
Into a 500 ml glass jar are weighed 100 g of a water-.
- absorbent resin particle. To this is added a portion of
thermoplastic polymer. A top is placed on the jar and it
is shaken or ~bout 10 seconds. The physical condition
: of the mixture is noted aftër shaking. This is repeated
for each thermoplastic polymer at levels of 5, 10, 15
- and 20 g.
-.
Polymer Bondin~
Mixtures of water-absorbent resin and
: 20 thermoplastic polymer (5, 10, 15 and 20 parts of :
thermoplastic polymer per 100 parts of resin)?are ..-..
prepared by blending. The mixtures are separately
sandwiched betwee~ two pieces ~of filter paper and hea~ed
: ~o~ a ceramic hot platé. Evidënce of thërmal âdhesion is
noted`at ~arlous temperatures.
i; ..The water-absorben~resin particlesiàrè basèd `
on~polyacrylic;a~id cros'sii~ed'with~rtrimlethylol propane
30 sandspartially.~neu~ràlized wiæh~isodium'jhydroxidë'to!à
level.~ofi~68 pèrcent~neutralization'. The~ ther~soplastic 3i
polymers are polyvinylide~e~pyrroiidd~ë~of~thrëë
molecular weights (8000~ 38~000 and 630~000); ~wo
polyethylene oxite based polymers (MW lOO,OOO and : -- : .
600~0003 and a low molecular weight polyvinyl alcohol, :. .
,0 - . . . . .
.
'1
, ~ : .
~: ,
... . . , . . .. . . . . ~ ... - .
WO91/18~2 PCT/GB91~00780
~ ~. 20
".~
available fro~ Air Products under the trade name Airvol
205.
Results Coatin~ Affinity Test
Good coating affinil:y is demonstrated by the
polymer adhering to the water absorbent resin
thermoplastic particles. Poor coating afflnity is
demonstrated by the presence of the thermoplastic
polymer as a slowly settling dust once shaking is
discontinued. The polyvinyl pyrrolidone demonstrated
excellent coating affinity at all molecular weights. The
polyethylene oxide polymers demonstrate limited affi~ity
for the water absorbent resin by the presence of dust at
10, 15 and 20 parts of thermoplastic polymer per hundred
parts of resin. The polyvinyl alcohol exhibits excellent
powder coating affinicy, as only a slight amount of free
dust is detected at 20 parts of polyvinyl alcohol.
Results Bondin:~ Testi;
, .. ... . . . . ............... .
The watèr absorbént resin blendéd with
polyethyie~e oxide at 5 parts demonstrate good adhesio~.
Water absorbeit resin particles coated wlth polyvinyl
pyrrolido~es of all ~hree molecular ~eights demonstrate
good bonding characteristics at 75~C~ The polyvinyl
alcohoa coated water-absorbent~resins-demonstrate a
~sl,i~ht adhesive character~at 100,C.~ The;results:of~both
tests are.~jom~iled.r~in,Table~ L refers:.to low~molecular ~.
~eight,4Mire~ers t~o medlum molecular,weight, and ~ ~ :
refers to~highùmolecularlweight. ..;~ Lt~
,,
~: ' : . ' ', . : :: ' . . , : :,. : ' ' ' ,, - ~,
Wo 91/~8042 pcr/GBs1/oo78o
2 1
Tabl e
E~am Polymer ~ ~rer Bond ng Coating Affinity
~ . . _ ._
. 1 Polyvinyl Good (75C) ExcellenVall levels
pyrrolidone L
. ., _ _
2 Polyvinyl Good (75C~ Excellent/all levels
pyrroltdone M
. ~
3 Polyvinyl Good (75C) ExcellenVall levels
p~l~one H _
4 Polyethylene oxide Good Good/ 5 parts; dust
L present at 10, 15
and 20 parts
5 Polyetbyl-e ~-iCe G ~d bo~d ~ 5 p-~-
H . dust present atlO,
15 and 2Q parts
6 Polyvinyl alcohol Slight (100C) Excellent/ Slight
. dust at 20 parts
_~ . ...
EXAMPLES 7-19 .'
- 20 The properties of several adhesivized absorbent
resin samples ~are:determi~ed.'':The :foll'owing'''standard ' '
test methods are'used.~
Absorption Under Load. , ;~.~. , ,,,. . ,. ~'
A:nylQ~ screen (37:;~diàmeter; 100 m`esh) is pu't
on top of perforated metal plate (holes with'~5 ..)~
followed by a filter paper and finally by a stai~less -
steel cylinder, whose both ends are open, of 26 mm inner, :'`
' diameter~ 37 mm outer diameter and a hel'ght`'of 50'mm.''''
160,.,~mg:,of:water-absorbent~resin:"partic'l'e's'`;a'r'e';pL`aced ',
into ~he cyli~der;la~d~evenly~distributed,~-cove'~edlby 'a~
non-,woven~.sheet.~o~ a,diameter~of~'26-tmm-r'ànd'J`fin~ally'~'Ri3-'~ ;i
presscd~down.~with a teflon pisto~'of 26'?=''~diàmèter~
.. . .
WO9lt18M2 PCT/GB91/007B0
z ~ ' 22 -'' i.
which carries the weight. The total weight of piston and
cylinder is 104.4 g. The metal plate with the product in
the cylinder on top is immersed into the 0.9 percent
saline solu~ion such, that the nylon screen and the
water surface have the same level so that the filter
paper and the water-absorbent resin particles are able
to absorb water without any static pressure.
A soak time of one hour is applied. The plate
10 is removed from the water reservoir and the excess water .:
in the holes of the plate and in the nylon screen is
soaked up by paper tissues. Then the weight is removed
from ~he swollen gel and the gel is weighed. The weight
ratio of saline solution absorbed under load to wa~er~
absorben~ resin particles is ~he absorption under load
(AUL).
' Centrifu~e Capacity
~ . 200 mg ,of~water-absorbent resin particles are
place within a sealable tea bag (63,5 x 76.2 mm),
i~mersed for 30 minutes into a 0.9 percent saline
sol~ion and then centrifuged for three minutes at 1600
rpm. The weigh~ ratio of saline'solution absorbed'~o'-- '' ''
. water-absorbent..resin particles,:is the:absorbency
capacity!.~cc)- ~. ,,.; .i,: .;."~.~ .,'. m i.~ ,`; i r \ `~
3 0 1 ~ I r ~ t~ u .
Sp'ee~d''~,o,f Absorption'
~ ,,A.6.cm~di met,er~,non~ ,o,ve~,:sheet,:available from`
- Suominen~Novelling 3 T,.391~is;,plac'ed -.! on~the~.test-.~plate of~i
a Demand Absorbency,.~,~ester~ availablei~rom Co~5MS,rJ0.50;~
g o~ water-absorbent resin~isrplaced in the.cen~ër~5 cm^-;
`' '
. .
. ~
. .
WO9l/l8042 PCT/GB91/00780
3 ;2~523`~
of the non-woven sheet. A 0.9 percent NaCl in water
solution is contacted with the resin. The time over
which 10.1 ml of solution is absorbed by the resin is
noted. This is the speed of absorption. The solution is
added for 30 minutes. The absorbed volume i~ recorded.
20 filter papers (11.5 x ll.S cm) are weighed. An 11.3
c~ diameter non-woven sheet is placed over the swollen
absorbent resin and 20 square filter papers 11.5 x 11.5
cm are placed over the non-woven sheet. Thereafter a
load of 1917.7 g (11.5 x ll.S cm) is placed over the
filter papers to give a load of 1973 g (3.~5 kPa on 8 cm
diameter area). After 5 minutes the load is released and
the wetted filter papers are weighed. The maximum free
absorp~ion capacity (MFAC 91 g) is calculated as
follows:
; MFAC = (Vl-Vlb) d
0.5
Vl is the absorbed volume of the absorbent resin
Vlb is the absorbed volume of the filter papers znd non-
woven sheets of a blank, run without~absorbent resin;
d is the density of the saline solution (1.01)
The retention under pressure (PT, g/~) is
25 calculated as follows: `
R = Vl x d - (P2-Pl)
0.5
Pl is the weight of the dry filter papers ;i~
P~ is the weight of the wetted filter papers.
.
: .,
-
, .
.; .
.
'" ' ,~
: ~ ' ' ',
WO91/18~2 PCT/GB91/00780
2 ~ 24
Bulk Density
Bulk density is calculated acc~rding to ASTM D-
l895-69.
FLow Rate
.
Flow rate is determinated according eO ASTM
Dl895-69, and represents the time it takes lO0 grams of
material to flow out of a funnel ha~ing a 9.5 mm
opening.
` ,
The water absorbent resin is a polyacrylic acid
crosslinked with trimethylol propane and partially
:15 ~eutralized with sodium hydroxide, 68 percent. The water
absorbent resin particles demonstrate two particle size
distributions, Standard, 97 percent between O.l and 0.8
mm; and fine 99 percent less than 0.31 mm. The
:. thermoplastic polymer used is polyvinyl pyrrolidone
:~20 (PVP) of;three different molecular weights; (L) 8000,
tM) 38,000, and (H)-:630,000. The results are compiled in
. . .
TabIe II. ~ . -. ~ . . .. : . .
,~ . . .
, .
,. . : . ., , i ,, -
c
,~ ~
; : . . i ' - ` ' ' ! ' "
'
' ' ' . ' ' ' ' ' ~:
..-
~:
- ~ . . .. . . . .. ~ . . ,,. , ,: . . .. . . . . . . . .
WO 91/~8042 PCI`/GB91/00780
! `` 2 5 ~ ~ ,
Z~
.
~'o~ o c~l o Oo o r~ I~ r~ O O L~. ~ ~ ..
_ ~ O~ _ O~ _ CJ~ . ~ _ _ _
,~_ ... ___ _ _ _ _ _ _ _
~ c ~ . . r ~ r~ o ~ ~ o~ ~ ~ ~ r~l
~ ~ .r~l O ~ O~ ~ a~ ~, ~D O U~ O
m C~ ~ ~D D D r~ ~D D 9 ~ ID ~D D ~ ~
o o o o o o o o C~ o o o o
___ _ _ _ _ _ _ _ _ _ '.
~:n . . .'
~r, o~, .- oo, ~ ~ oo , ~- C:~ ~
~: u~ r~J , ~ O ~ _ O O ,~ ~ ~ ~D .
___ _ _ _ _ _ __ _
~ o C ~ .
E ~ a~ E ~ ~ ^~ ~ ~D o c~. ~r
~ ~ ~ ~ ~i cn O ~1 _ a~ o ~ o I~ o r~ ~
/~ es ~r i. e~ ~ ~ ~ ~ ~ ~ ~ ~ :
U
~C~_
,o c~_ ~ co ~ ~ r~l ~ ~2 c ~ ~ ~D es Lr~ ,.
n~ _ o ~s, . _ . . ~ ~ o L~l ~ ,
~ ~ _ ~ . r~l _ ~l ~ ~ _ ~ ~ ~ ~
_ __ _ _ . _ _ __ __ _
cn ., ..
cn o~ L~ o L~l Ln ~ c~ u: 9
_ ~ .- ~ O L~l D L~ ~ ~ ~9 O
_ o~ ~ ~ Lr~ I~ o~ I~ co r~ oo r~ D
~ ~ r~l ~ ~ ~ ~l ~ ~ ~ ~l ~ ~
.._. _ , _ _ .~ _ _ _ _ . _-- ' .
n ~ " ~ '~r~'' ' ~ ' ,~- --~
. cn ~ ~i r~ ~_ I~' ~ .. I~ I~ .. Lri
. U-
.,,.- ,, - - - - . - ~ - - , - - ,........
~ ~ ' ~ ~ ~ ~ . ..0~:, '~ ~8'. ....~.,. ~. . . '' ` `' ' ~
:` 3 O O O O . O C~ .
~ U~ L~ _ Lrs Lrs _ ~ Lrl Ln
.. _ _ ~ _ _ _ _ _ _ _ _ _
. .''.. " _` ,,,,~ ,`,,S'
;~ ~,'.t .. :~' ~ L~. ;~ _~ _ C ), LL . C ~ L~ ,., C ~ .C; ~; ~.. ..
._ -, .... __ ._. _ : ; _ _ _ _ _ _
,!,, ., .,,~,,. ~1 ':,` ,,.. /.: ., .~ ".~ ~ . ,~,, . j~ - , ,.
s C. ~ 4;1 ~ _ ' .! 1 `;~:-i .i ;1, .~ - ,,; n ' ! ,j ~ ~ ~,S ~:~ ,''J
,, Q ~ - ~ . o ~;. ' ,.~ ~;~ :~ ~ ~ ~ :~ ~ I I ~ o ~ 3 ~
., , _ _ __ _ _ _ _ _ ; __ _ _ ~
r, ; f 1~ ~ . ~ . ~ ,. ~O _r .i '; _ ~ ~ ; ~ ~ ~
: :.
,: : : : .
.: : ~ ' ;. ' . ` ` ' '
WO91/18~12 pcT/Gs9l/oo78o
2 3 26 -`
Examples 20-2~
83 parts by weight of the water absorbent resin
described in the previous examples, 5 parts by weight of
polyvinylpyrrolidone (8,000 mw) and 12 parts by weight
of a hydrophilic polymer are put into a 200 ml plastic
bottle. Two different hydrophilic polymers are
separately usedj methyl cellulose and a mix~ure of 12
percent xanthum and 88'percent guar. The bo~tle is
closed and shaken for 2 hours.' The compositions are then
tested for centrifuge capacity, retention under pressure
(PF), speed of absorption and Demand Absorption (DAT). A
Control is prepared without the hydrophilic polymer
using 9S par~s absorbent resin and 5 parts ,
polyvinylpyrrolidone. The results are compiled in Table
III.
- - ~ ,
- Table III
.~_ _ . _ _ _ _
Exa Hydrophilic Centrifug under Absorben Absorptio
10 mp Polymer e apaclty P~euure cy~DA~ nSpeec
. ;31.1 31 :` 40 ~ 1~3?
21GuarXanthum 306 ~83 ~ ` 40 '~ 7~ '
22Methylceilulose 273 246 39 51
15, ~ ; , ' ' ' , ' '
Examples;23-~4i
,A mixture of ,130 gràms'of 56 percent by'weight
cellulosic fiber,~l4 percént~by"weight':'sy`nthetic fiber
(polyethylene coated polypropyle~e fiber? and 30 percent
,by weight of a~wa'ter, absorbent res'in~comprising.95
percen~.. of- a plrtially ~eutralized polya~rylic acid ,',~
crossllnked Iw1th, !trimethylol~ propan. ~t68 percent `~ h
NaOH) and 0.5 percent by weight~polyvinylpyrrolidone are
. . .
.,
,; ': ' ,
. . . ..... . .. . . .. ..
WO91/18~2 PCT/GB91/00~80
f- 27 2~8~-3 `
contacted and thermally bonded at elevated temperacures
such that a coherent matrix is formed.
A second sample comprises two substantially
equal layers o~ non-wove~`celIulosic fibérs with a layer
of the water abso~bent resin, without a thermoplastic
polymer, disposed between ~he layers of cellulosic
fibers. The sample comprises 90 percent by weight of the
cellulosic fiber, and 10 percent by weight of water
absorbent resin, and has a unit weight of 470 g/m2.
The two samples are tes~ed as described
hereinaf~er.
.
; A Fritsch "Analysette 3" apparatus is arranged
such tha~ five sieves are arra~ged from top to bottom,
800 um~ 400 um, 315 um~ 200 um, and lO0 um~ with a pan
~ below the screens~ A sample of 5 to lO grams is weighed.
; The sample is placed on the top sieve, and a cover is
placed over the sieve. The sieve assembly is securely
fastened in the Fritsch apparatus.
": ~ .
The apparatus is shaken for 15 minutes. The top
screen with ~he sample is placed on a balance and the ~
bala~ce is set ~o 0Ø The sample is removed from the
~, . . . . . . . .
top scree~ and th~ screen is brushed. The empty screen
is placed on the balance. The negative weight is the
final weight o~ the sample on the screen. The weight ~t~
loss of each sample due to shaking is calculated. The
results are compiled in Table-IV.
: . . -
?~
.~ . .
: ,
WO91/18~2 PCT/GB91/00780
3 28
Table IV
,__ ._~ ~ ~
Example Beglnnlng End weight g 1~ We gh~
23~ 9.5 g.1 4
, ~
24 6.7 6.7 0 .
~-~r-t an exa ~ lnvention ~
The loss in Examp~e 23 show loss of both water
absorbent polymer and cellulosic fibers 7 it is difficult
to determine the exact composieion of the material
removed rom the absorbent structure.
; 5
, . '' ' ' "
'~ , ,. ',' ,.' ~' ``~ ` ' ;``' ' ' ,
' ' ` . ' '`~' ~
~71~s
1 5 .P ~ `` ~ ~ t
,
.
~ 25 ~ :
, ~
~,: ' ;''.
' ` `'
. ~ - .
.. . . . . .
.
