Note: Descriptions are shown in the official language in which they were submitted.
WO 93/04101 2 1 1 4 4 1 ~ PCI`/GB92/01527
POLYURETHANE FOAMS
The present invention relates to hydrophilic
polyurethane foams, blends used to prepare these foams,
absorptive devices co~prising the foams and methods for
their preparation.
There have been several proposals to the use of
hydrophilic polyur~thane foams, fcr example as an
absorbent material, in hygienic and medical absorptive
devices such as sanitary towels, tampons, diapers,
incqntinence pads and wound dressings. Hydrophilic
polyurethane foams, however, are usually more expensive
than the conventional cellulosie absor~ent materials
used in such devices and have there~ore not been
ex~ensively used in commercial absorptive devices.
British Patent No. 1429711 (see also United States
Patent Nos. 3Bl~618, 3812619 t 3874694, 388g417,
3928138, 3929574 and 4137200~ discloses a hydrophilic
polyurethane foam formed by reacting with water an
isocyanate capped polyoxyethylene glycol prepolymer.
It was found, however, that a large molar excess
of wa~er was r quired to obtain satisfactory foams.
Removal of this excess water, for example, by drying,
rendered these foams relatively expensive to
manu~acture.
WO 93/W101 - 2 - PCr/GB92/01527
2114~11
British Patent No. 2188055 discloses hydrophilic
polyurethane foams formed by reacting with water the
reaction product of polyisocyanate which has a
functionality of greater than 2 and polyalkylene glycol
mono alkyl or alkaryl ether. These prepolymers require
t~ be mixed with only relatively low a~ounts of water,
~hus obviating the need for an elaborate drying stage~
~he foams are therefore more econo~ical to manufacture
than previously known hy~ropilic foa~s.
The reaction rates of aliphatic isocyanate based
polyurethane foam systems tend to be ~ndesirably slow
for commerical use unless high levels of ethylene oxide
containing residues are incorporated into ~he reactive
system.
The presence of high levels of such residues
increases the linear swell value of the foa~ when
hydra~ed. Whil~ this effect may not be del~terious
for foa~ ptoducts such as ta~pons or sanitary towels,
high linear swell will adver ely affect thin foam
p~oducts such as wound dressings and in particular
dressings such as first aid dressings,
Such dressings need to be able ~o absorb aqueous
materials such as wound exudate and to be produced
;
WO 93/04101 - 3 - 2 1 1 ~ I 1 1 PCr/GB92/01527
quickly and economically to compare f-~ourably with
conventional fa~ric and pad dressings.
The present invention seeks to ~-rovide a -~
polyurethane foam which is hydrophili- ~nd has good
di~ensional sta~ility whe~ produced i~ thin flat sheets
and which can be produ~ed rapidly and economically.
Accordingly the present inventi~n provides a
polyurethane hydrophilic foam, suitab'e ~or u~,e as
first aid dressing which and comprise residues of a
aromatic isocyanate, of an aliphatic :socyanate, of a
polyoxyalkylene monoether and of a pc:yoxyalkylene
polyol such as a polyether polyol.
In another aspect the present i~.vention further
provides an absorptive device which c~prises a
hydrophilic polyurethane foam of the ~nvention. The
absorptive device of the invention is preferably a
medical or hygienic device such as a Yound dressing eg.
a first aid dre~sing~ sanitary towel, diaper,
incontinence pad ta~pon, or th~ e.
In a further aspect the invention provides a
process for preparing a hydrophilic ~lyurethane foam
of the invention whi~h comprises bler.~ing at least
one aromatic based prepolymer with at least one
WO93~04101 ~ ~ 4 ~ PCT/GB92/01527
21 l 1~11
aliphatic based prepolymer. An aqueous phase is then
added to effect the foaming reaction and the foam
formed is allowed to set.
According to an embodiment of the present
invention there is provided a hydrophilic polyurethane
foam comprising resid~es of a first isocyanate
prepolymer derived from a polyoxyalkylene mono ether
and an aro~atic isocyanate containing at least two
isocy~nate groups and residues of a second isocyanate
prepolymer derived from a polyoxyalkylene mono ether
and an aliphatic isocyanate containing at least two
isocyanate g~oups and in which at least one of said
isocyanate prepolymers contains residues fro~ a
polyether polyol.
The present invention also p~ovides a hydrophilic
polyurethane foam for~ed by blend~ng at least one of
said aromatic isocyanate based prepoly~ers and at least
one aliphatic isocya~ate based prepoly~ers and
subsequently adding an aqeous phase to ea~alyse the
foaming reaction wherein at least one of the
prepolymers is additionally derived from a polyether
polyol.
According to the process of the present
invention, control over a wider ran~e of processing
W093~04101 211 4 4 1 1 PCT/GB92/01527
variables and foam properties can be ~-hieved than was
hitherto possib.~
Processing variables which may ~e controlled more
readily than was previously possible :~clude efficiency
of mixing and ease of dispensing, cre~ ti~e, rise
time, gel time and cure time.
Foa~ properties which may be cc-trolled more ~;
.. readily according to the pro~ess of t~e invention
include softness and resiliency, dens:ty, cell size and .
structure, water content and capacit~. linear swell on :~:
hydrat`ion and rate of wicking. :~
~ hese properties may be ~chieve~ by blending the
prepolymers over a wide range of rati-s of the aromatic
b~sed prepolymer to ~he aliphata~ bac~ prepolymer
properties. Thus foams displaying e~^ellent water
uptake, water ~apacity ~nd strength ~ve been found.
The foa~s also possess a low~r level ^f ex~ractables.
Furthermore they can be form~d in~o ~~in sheets which
show excellen~ confsrMabil~ty.
S~itably the prepolymer blend s~ould contain at
least lOw/w% of the solids weight of ~liphatic based
prepolymer. Similarly it has been fc_nd that the blend
should contain at least lOw/w% of th~ solids weight of
WO93/~101 ` 211 4 41 1 - 6 - PCT/GB92/01527
aromatic based prepolymer. Aptly the ratio of aromatic
isocyanate to aliphatic isocyanate prepolymers will be
from 25-75 to 75:25 weight percent. ~ore aptly the
ratio of prepolymers will be about 50:50 weight
percent.
The hydrophilic polyurethane foa~s of the
invention can be formed by mixing the blend with a
stoichiometri~ amoun~ of water~ It is preferr~d,
however, to mix the blend with a low ~olar exce~s af
wa~er for example 10% by weight of water. It has been
found that this low molar ex~ess of water can be easily
absorb~d by the hydrophilic foa~.
Suitable polyoxyalkylene ~ono ethers for
preparin~ the prepolymer co~ponents of the blend of the
presen~ invention, may be polyoxyalkylene monoalkyl or
monoalkaryl ethers. Prefera~ly the ~ono ethers are
polyalkylene glycol monoethers.
The al~ylene ~oiety of the ~ono ethers ~ay
contain l to 4 carbons~
Preferred polyalkylene glycol ~ono alkaryl ethers
are those in w~ich the alkylene group is ethylene.
Suitable polyalkylene glycol mono alkaryl ethers
WO93/~101 ~ 211 ~1;41 1 PCT/GB92/01527 ~
include those in which the a~yl moeity is phenyl.
Preferred ethers are those in which the alkyl moeity
contains from 1 to 20 carbon atoms eg. octyl or nonyl.
Suitable polyalkylene qlycol mono alkyl ethers
for forming the reaction product are those in which the
alkyl group contains 1 to 20 carbon atoms. Aikylene
favoured ethers are thos~ in which the alkyl group is a
methyl group. Another class of preferred poly~lkylene
glycol mono alkyl ethers are those in which the alkyl
group contains 10 to 18 carbon atoms, eg. lauryl or
cetyl~
Preferred polyalkylene glycol ~ono alkyl ethers
are those in which the alkyle~ie grs~up is ethylene.
The polyalkylene glycol alkyl or alkaryl ether
can suitably have an average ~olecular weight of 180 to
6000.
Apt e~her~ are polyethylene glycol ~ono lauryl
ether~ haviny an average molecular weight of
approxi~ately 1090 and 360 known 25 Brij 35 and ~rij 30
respectively, available from Hone~well Atlas and
polyethylene glycol mono methyl ethers having an
average molecular weight of approximately 500 and 5000
known as PEG monomethylethe~ ~olecular weight 550 and
WO93/04101 , 211 9 ~ 1 1 PCT/GB92/01527
5000 respectively, available from Aldrich Chemicals.
Suitable polyethylene glycol ~ono nonyl phenyl
ethers are commercially available under the Trade names
Antarox C0-320 / Antarox Co-990, available f rom GAF
( Great ~ri tain ) Co . Ltd . Apt polyethylene glycol mono
nonyl phenyl ethers t are Dowafax 9N6 and 9N20 having an
average molecular wieght in the range of 400-500 and
1100-1200 respectively and av~ilable from K~l~ Greeft
Ltd. Typically tbe ethylene oxide molecular weight can
vary in the range 220 to 2200.
The polyethylene glycol ~ono al~yl or alkaryl
ether used in the invention will nor~a}ly contain
water. It is preferr~d, however, that the ether
contains less than 1% by weight water, to li~it the
number of urea groups formed in the reaction with the
polyisocyanate during the prepolymer formul3tion.
The polye~her polyol residues present in at least
one of the blend prepolymers, ~ay be derived from
polyhydric alcohol~, alkylene polya~ines, ~lkylene
amines, cyclic amines, amides and polycarboxylic acids.
In addition suitable polyols ~ay be derived from
hydrophilic reactants. A particularly suitable
hydrophilic reactant is ethylene oxide.
WO93/04101 ` 21 i 4 4 1 1PcT/GB92/ols27
Preferred polyether polyols are ~erived from
ethylene oxide and aliphatic polyhydr_- alcohols.
Suitable alcohols may have from 2 to ~ carbon atoms eg.
ethylene glycol, pentaerythritol, prorvlene glycol,
2,3-butylene glycol, glycerol, 1,5-pe-:anediol and the
like.
The polyether polyols may be derived from the
polymerisation of ethylene oxide in t~e presence of the
above mentioned di- or polyfunctional reactants.
Particularly suitable polyether ?olyols for the
preparàtion of foams of the present i-~ention are
polyether t~iols. Preferred polyethe: triols are
polyoxypropylene lPPG) ether triols, ~d-capped with
p~lyethylene oxide (PEG). Suitably t~- PEG may
comprise 2 to 30w/w~ of the polyether ~riol. Typi~ally
the PEG comprises 5 to 15w/w% of the -Q~yether.
Apt polyoxypropylene ether tric:s, end-capped
with PEG have an aYerage ~olecular we~ght of 700 to
7000. Typically the PPG ether triols, end c~pped with
PEG will have an average molecular we:ght in the range
of 3000-3500 eg. Arcol 132 available -rom Arco Chemical
Products Europe~
At least one of the blend prepc:ymers may further
WO93/04101 211 4 4 1 1 1 o PCT/GB92/01527
be derived from a copolymer polyether triol d~rived
from the polyether polyols described -erein. A
particularly preferred copolymer poly~ther is based on
PPG and PEG blocks. Suitably the PEG may be present in
the range of 40 to 75w/w of the copol~mer. More
suitably the PEG may comprise 45-55w~%. Preferably
the PEG comprises 45w/w% of the copol~mer. A preferred
copolymer polyether is Voranol CP1421 which has an
average molecular weight in the range of 3000-3500 and
is supplied by Dow Chemicals Europe.
The ratio of triol equivalents :o mono ether
equivalents may be varied to alter t~.~ processing
variables and the foam properties. ~ has been found
that suitably the ratio of triol equ~Jalents to mono
ether equivalents is in the range of ~,3 1 to 10:1,
more suitab}y from 1:1 to 5:1 and pre~erably about 3:1.
The isocyanates used for for~i~ the blend
prepolymers will have a functionalit~ of at least 2.
Suitably both the aliphatic aro~atic isocyanates will
have a functionality of le~s than ab~u~ 2.5.
Suitable aliphatic polyisocyana~es for use in the
invention include 4,4'-dicyclohexyl nethane
di-isocyanate (Desmodur W) which has a functionali~y of
2.0 and is available from Bayer A.G. ~nd hexamethylene
W093/0410l 2 1 1 ~-4 1 1
di-isocyanate.
Suitable aromatic isocyanates f_- forming the
blend prepolymers are polymeric methy:Gne
di-isocyanates. Polymeric methylene ~-isocyanates
comprise a mixture of 4,4'-diphenyl ~hane
diisocyanates and one or more of poly~eric homologues.
Apt polymeric methylene di-isocyanates are known as
suprasec VM 10, VM 20 and VM 50 available from ICI and
have a functionality of 2.07, 2.13 an~ 2.49
respectively. Further aromatic isocyanates which may
be used include toluene di-isocyanate,
methylene-bis-(4-phenyl isocyanate),
3,3'-bitolylene-4,4'-di-is~cyanate, 1.4-phenylene
di-isocyana~e, naphthalene-l,S-di-iso~yanate and the
lilc~ .
A favoured blend for for~ing fo~s of the present
inven~ion comprises an aliphatic base_ prepoly~Qer
de r ived f rom polyoxyethylene glycol ~no-nonyl phenyl
ether, a polyoxypropylene ether trioli end-capped with
PEG; a copolymer poplyether triol and 4~4' dicyclohexyl
meth~ne di-isocyana~e (~esmodur W~ ~he blend further
comprises an aromatic based prepolymer derived f r~m
polyoxyethylene gylcol mono-nonyl phe~yl ether, a
polyoxypropylene ether triol, end-ca~_ed with PEG and
a polymeric methylene di-isocyanate c-~prising a
WO93/~101 21~14~ 12 - PCT/GB92/01~27
mixture of 4,4'-diphenyl methane di-isocyanate and one
or more polymeric homologues.
In forming the prepolymers, the isocyanate and
reactive hydrogen containing compound are present in an
amount to ensure that the prepolymers contain an excess
of isoycanate groups. Aptly the isocyanate ~o hydroxyl
ratio ~NCO:OH) is at least 2:1. Suitably the ~CO:OH
ratio should be less than 6:l. Typifally the NCO:OH
ratio is in the range of 2.7:l and 4:l.
. The prepolymers employed in the invention contain
an excess of isocyanate groups. Suit~bly they contain
an excess of at least 2 w/w% NCO groups, more suitably
upto l2~w/w excess NCO groups; Typicall~ the
prepolymers contain an excess of 5 tc 7w/w% NCO groups.
Normally the mono ethers and pclyols will be
pre-dried to a wa~er content of less than 1%.
The blend can be reacted with an aqueous phase to
form a hydrophili~ polyurethane foa~ of the inventio~.
The hydrophilic polyurethane so formed will normally be
a cross-linked hydrophilic polyureth~ne foam. The
hydrophilicity of the foam is believed to be dependent
on the oxyethylene groups. Varying the wei~ht % of
oxyethylene groups in the constituents of the blend,
WO 93/04101 2i~
can provide the hydrophilic polyurethane foams of the
invention with a wide range of water absorption
properties. Suitably the hydrophilic foam will absorb
at lea~t 5% by weight of its weight of water. The
water absorption of the hydrophilic polyurethane foams
aptly ranqe from 25% to 95% by weight of polym~r.
Preferred hydrophilic polyurethane foams of the
invention, however, have a water absorption of 50% to
92% by weight of polymer.
The water absorption of the foa~ is determined by
wei~hing a lcm cube of the foam, then immersing the
foam in water (at 20C) for ~4 hours, removing excess
water by lightly blotting the foam with absorbent paper
and then re-weighing the foam cube. The water
absorption of the foam (% by weight) can then be
calculated as
weiqht of wet foaml q) - wei~ht of_dry_foam (~_x 100
weight of wet foa~
The hydrophilic polyureth~ne foa~ of the
invention will normally be an open cell foam. The open
cell foam can suitably have a density of 20 to 350
Rg/m3 and can preferably have a density of 4 to
150Rg/m3.
WO93tO4101 21 l 4 ~ 14 - PCT/GR92/01527
The hydrophilic polyurethane f~æn can be in a
sheet, moulded or particulate form.
The hydrophilic polyurethane foa~s of the
invention can be used in absorptive devices for example
as an absorbent component thereof.
If desired, the prepolymer forming reaction may
be catalysed. Suitable catalysts inc~ude Dioctyl tin
dilaurate (Metatin 812 ES ); dioctyl t rl mercapt.ide
ester (Metatin 813 and Metatin 713); cibutyl tin
dilaurate (T-12); stannous octate (T -~ and Bismuth
neodecanoate (Coscat 83). Suitably t~.~ catalysts may
be added in the range o f O . 5 to O . OOl~w %.
Suitably the a~ueous phase may :~nt~in a catalyst
to increase the rate of reaction.
It has been found that a suitab'e amount of water
required to be added to the prepoly~e~ blend can be the
s~oichiometric amount of water needed to react with the
NC~ groups in the prepolymers. ~ is pre~erred,
however, in order to o~tain a homogen~us mixture of
water and prepolymers to use up ~o 12~ eg. 4 to 10% by
weight of water and preferably 5% by ~eight water in
the process.
WO 93/04101 21 1 4 4 1 1
A suitable catalyst for the reaction is an alkali
metal carbonate such as potassium carbonate which can
be present in amounts of 0~5 to 1.5~ by weight of the
blend.
In the process of the in~ention water or an
aqueous solution will normally be provided in liquid
form which is mixed and reacted with the prepolymer
blend. The water in the process, however, can also be
provided by a material such as a metal salt hy~drate
which releases water in liquid or vapour ~orm when
heated. Suitable metal hydrates for use in the
invention include Na2B40~.10H20, ~a2 SO4 . 1OH2 0,
Na~SiO3.9H20 and M~SO4.7H20 which is preferred. In the
process the metal salt hydrate which is preferably in
particulate form is mixed into the prepolymer blend.
The mixture can then be heated to a suitable
temperature to release the water for reaction with the
prepolymer blend.
The foam can be formed into a sheet or a desired
shape by casting the foaming mixture into a release
carrier or into a shaped mould and allowing the mixture
to rise and set 4
The foams produced by the process of the
invention can then be incorporated into absorptive
WO93/~101 211 ~ 41 1 - 16 - PCT/GB92/01527
devices using conventional methods. -n particular the
hydrophilic foams of the present inver.~ion may be used
in the preparation of first aid dressings sinee they
can be used to form thin flexible and onformable
sheets which are ideally suited for ~a~ing such
dressings.
Aptly the polyurethane foam co~position of the
invention may cast into first aid dressings, for ~:
example as disclosed in WO91/01706 and WO91/01707. ~
Suitably su~h dressin~s may be cast to thi~knesses of ~:
O.5.to 20mm, more aptly fro~ 0.75 to 4~m.
The invention will now be illustrated by
referen~e to the following example:
W0 93/04101 _ 17 ~ L PCI /GB92/01527
ALIPHATIC PREPOLYMEX FORMULATION
Polyoxypropylene (PP~) ether triol, 2 equiv.
polyethylene oxide (PEG) end-capped lArcol 1132)
Polyoxyethylene mono-nonyl phenyl 1 equiv.
ether (Dowfax 9N20)
Copolymer polyether triol (Voranol CP 1421) 1 equiv.
4,4'-dicyclohexylmethane di-isocyanate
(Desmodur W~ to give an NCO:OH ratio of 3.0:1.
Tin catalyst
lMetatin 812ES, ~cima Chemicals L~d) 0.05 w~w%
.
AROMATIC PR POLYM R_FORMU~ATION
Arcol 1132 2 equiv
Polyoxyethylene ~ono-n~nyl phenyl ether l equiv~
lDowfax 9N6~
Methylene diphenyl di-isocyanate
(VM10) to sive an NCO:O~ ratio of 3.5:1
Tin catalyst (Metatin 812ES) 0.01 w/w~
.:, . .
, . . .
WO93/~101 - 18 - PCT/GB92/01527
2111~11
The aliphatie prepolymer is syn~esised ~y first
heating the triols and mono ethe~ in an oven at 60~C to
melt them. The melted triols and monc ether are then
added to a 700ml flange flask followe~ by the
d,-isocyanate. The flask is fitted ~ith an ai r-driven
anchor stirrer, a lid, a dry nitrogen blanket and
placed in a water bath at 60~C. The co~ponents are
stirred vigourously until homogenous. The tin catlayst
is added via a diposable syringe, whi'e the contents o
the flask are being stirred continuously. The water
bath is adjusted to 90C and the reac~ion is allowed to
continue for 60 minutes until complet ~n, as indicated
by the subsiding exotherm. After ~o~letion, the
prepolymer is poured while still war~ into an air-tight
jar.
.. .
The aromatic prepolymer is for~d by followin~
the sa~e steps as indicated above for preparation of
the aliphatic prepoly~er, except that after sdjusting
the water bath t~ gOC, the reaction is all~wed to
proceed for 30 rathe~ than 60 ~inute~.
The aliphatic and aromatic prepoly~ers are then
blended~ When a homogenous prepolyme~ blend is
obtained the aqueous phase is added t~ effect foaming.
.. ... . , ~ .........
2114 ~ ~ PCT/GB92/01527
WO93/~101
The foam formed possesses all the properties
discussed a~ove which render it ideally suited for use
in absorptive devices, particularly first-aid
dressings.
