Note: Descriptions are shown in the official language in which they were submitted.
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Hydrophilic polyester-polyurethane foams, a process for their production, and
their use as moisture-absorbing materials
BACKGROUND OF THE INVENTION
The present invention relates to hydrophilic polyester foams, a process for
their
production, and to their use as moisture-absorbing materials in, for example,
the
domestic, hygiene and/or automobile sectors.
In the production of polyether-polyurethane (PUR) or polyester-PUR flexible
foams
according to the one-stage ("one shot") process, which is the most widely
employed
commercial process for slabstock foam production, foams are formed that
exhibit only
insufficient hydrophilic properties, even when these foams are characterized
by a
significant amount of open-cells.
In this connection, there has been no shortage of attempts to alter the rather
hydrophobic character of conventional slabstock foams so as to make them more
hydrophilic. Such attempts include, for example, by post-treatment of the foam
matrix
or by joint foaming of wetting agents or ionic surfactants as is described in,
for
example, DE-A 2,207,356.
Instead of carrying out expensive and complicated post-treatment of foams to
improve their hydrophilic character, attempts have similarly been made to
improve the
hydrophilic properties, principally by joint foaming of hydrophilic additives
per se, in a
"one shot" process. Such additives include, for example, cellulose derivatives
such as,
for example, cellulose esters, methyl cellulose, carboxymethyl- and
hydroxyethyl-
cellulose, etc, as well as amino acid derivatives and sulfonic acid
derivatives, betaines,
lactones and ethoxylation products of glycols or related starting materials.
These are
described in, for example, DE-A-2,207,361, and U.S. Patents 3,413,245 and
3,806,474.
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Propoxylation and ethoxylation products of polyhydric alcohols are suitable
starting
materials for the production of polyether-PUR flexible foams. These polyether-
PURs
can be produced by reacting these raw materials, generally termed polyether
polyols
(normally trifunctional compounds for flexible foam applications), with
diisocyanates
in the presence of water (for the blowing reaction), specific polyether
polysiloxanes
and further auxiliary substances. Conventional polyether polyols in the above
context
(standard polyols) basically contain the propoxylation product of
trifunctional starters
together with a small amount (0-20%) of ethoxylation product in the polyol.
Polyether polyols having a higher degree of ethoxylation (i.e., above about
30%) are
special polyols that are often no longer miscible with the standard polyols.
These
special polyether polyols generally cause foaming difficulties, particularly
with
increasing degrees of ethoxylation, and not the least on account of their
noticeably
increased reactivity.
Polyether polyols with a high degree of ethoxylation of about 50-98% by weight
such
as, for example, the polyol VP PU 41 WBO l(Bayer AG), can only be reacted in
strictly limited quantitative ratios with standard polyether polyols to form
polyether
foams. These result in a softening of the matrix, and form so-called hypersoft
foams.
The addition of pure ethylene oxide polymers is also possible (e.g., PEG 200
to
PEG 600 of Hoechst AG), though with a substantially reduced proportion of
about 2-
15% of the standard polyether polyol. Likewise, these result in a marked
softening of
the resultant polyether foam matrix.
Similarly, the joint foaming of polyether diols mixed with standard polyether
polyol is
also described in, for example, BE-A 707,412. According to this disclosure,
predetermined polyoxyethylene glycols of various molecular weights in the
range of
the products PEG 600 to PEG 2000 (Hoechst AG) are propoxylated in a separate
stage in order to bring the reactivity of the resulting polyether diols into a
range that is
compatible for foaming with standard polyether polyols. As used herein,
standard
polyether polyols are those polyether polyols which contain secondary OH
terminal
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groups due to propoxylation, instead of primary OH terminal groups due to
ethoxylation.
The direct foaming of pure polyoxyethylene glycols or at least of polyols with
a high
degree of ethoxylation and a high proportion of primary OH terminal groups
such as,
for example VP PU 41 WBO 1, VP PU 3170 (both from Bayer AG) or VoranoI*1421
(DOW Chemical) in the "one shot" process according to ether formulations
without
mixing with standard polyether polyols has not hitherto been possible. One of
the
reasons for this is that the reactivity of such highly ethoxylated polyols is
no longer
controllable.
The foaming of pure polyoxyethylene glycols in conventional plants has
hitherto been
possible only via the intermediate step of prepolymeriza-tion. Moreover, a
specific
product family of prepolymers (e.g., Hyporpolymers produced by W.R. Grace
Ltd.)
exists as a special range of products for various applications with the
corresponding
process technology disadvantages.
The production of hydrophilically adjusted polyester-PUR foams of relatively
high
density (> 50 kg/m3) is described in, for example, U.S. Patent 3,806,474.
These
polyester-PUR foams comprise prepolymerized polyoxyethylene diols in a
molecular
weight range from 500 to 2000, in a conventional ester formulation, with
special
surfactants for emulsification and stabilization purposes.
Polyester-PUR foams are preferably used as domestic sponges since their sponge
structure and handling characteristics are significantly better and can more
readily
simulate the properties of natural sponges than is the case with the
homologous
polyether-PUR foams. In addition, polyester-PUR foams have, in comparison to
polyether-PUR foams of the same density, superior properties with regard to
tensile
strength and elongation at break. Properties such as these are important for
their use
as domestic sponges and related applications.
* trademark
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Thus, the object of the present invention is to provide a process according to
which
hydrophilic polyester-PUR foams can be produced, preferably via a "one shot"
process, without the use of propoxylated or prepolymerized polyoxyethylene
diol
components, and without the addition of special emulsifying agents.
Surprisingly, this object was achieved by a process in which hydrophilic PUR
foams
having the properties of polyester-PUR foams are produced by mixing
commercially
available, highly ethoxylated polyether polyols which have a degree of
ethoxylation of
more than 30% by weight, with conventional polyester polyols according to
typical
ester formulations.
SUMMARY OF THE INVENTION
The present invention thus provides a process for the production of
hydrophilic
polyester-PUR foams, comprising reacting
a) one or more polyisocyanates, with
b) one or more polyester polyols containing at least two hydroxyl groups and
having a mean molecular weight in the range from 400 to 10, 000,
and
c) one or more ethoxylated polyether polyols containing at least two hydroxyl
groups, preferably having a functionality in the range of from 2 to 6, and
having a degree of ethoxylation of more than 30% by weight,
and, optionally,
d) one or more components, for example chain extenders and/or crosslinking
agents, containing at least two active hydrogen atoms and having a mean
molecular weight in the range from 32 to less than 400,
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in the presence of
e) catalysts, water and/or blowing agents,
and, optionally,
f) auxiliary substances and/or additives.
The degree of ethoxylation of the polyether polyols which are suitable for the
present
invention is typically above 30% by weight, preferably between 50 and 95% by
weight
(based on 100% by weight of alkoxylation of the polyether polyol). Generally
speaking, polyether polyols started on trimethylol propane and/or glycerol are
used as
the highly ethoxylated polyether polyols of the present invention. It is
preferred that
glycerol-started highly ethoxylated polyether polyols are used.
The quantity of highly ethoxylated polyether polyols required in the present
process is
generally between 2 to 80% by weight, based on the total weight of components
b), c)
and d).
For the foaming reaction, about 2% to 80% of the previously described highly
ethoxylated polyether polyols such as, for example, VP PU 41 WBO 1(a
trifunctional
polyether polyol from Bayer AG), appropriately mixed with conventional
polyester
polyols, are used.
Suitable polyester polyols can be produced from organic dicarboxylic acids
with 2 to
12 carbon atoms and polyhydric alcohols by condensation.
Some examples of suitable dicarboxylic acids for the production of polyester
polyols
include compounds such as succinic acid, glutaric acid, adipic acid, etc. and
mixtures
thereof. The corresponding dicarboxylic acid mixtures are preferably used.
Araliphatic
dicarboxylic acids such as orthophthalic or terephthalic acid and/or
unsaturated
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carboxylic acids such as maleic acid and fumaric acid can also be used to form
the
polyester polyols of the present invention.
Suitable polyhydric alcohols which act as condensation partners for the
dicarboxylic
acids to produce polyester polyols include polyhydric compounds which, in
general,
contain from 2 to 12 carbon atoms. Particularly preferred in this connection
are
dihydric alcohols (i.e., glycols) from the range comprising ethylene glycol up
to 1,6-
hexanediol, as well as diethylene glycol and dipropylene glycol. Small amounts
of
glycerol, trimethylol propane or higher functional homologues are often used
in
conjunction with the polyhydric compounds described above, as higher
functional
alcohol components having a branching action.
Polyester polyols such as Desmophe&2200, Desmophen*2300 or VP PU 60WB01 (all
available from Bayer AG) are preferably used. These polyols are condensation
products of adipic acid, diethylene glycol and some trimethylolpropane as
branching
component. VP PU 60WB01 additionally is treated to "defog" it (see US Patent
5286761).
Suitable ethoxylated polyether polyols for the present invention include those
compounds in which the degree of ethoxylation is above 30% by weight, and
preferably between 50% and 95% by weight (based on 100% by weight of
alkoxylation). These ethoxylated polyether polyols contain at least two
hydroxyl
groups, and preferably have a functionality of from 2 to 6. Suitable compounds
include, for example, highly ethoxylated polyether diols (difunctional
compounds),
highly ethoxylated polyether triols such as, for example, VP PU 41 WB01 (a
trifunctional compound with mean molecular weight of 4500 and degree of
ethoxylation of _70%) and similar products, as well as higher functional
highly
ethoxylated polyether polyols such as VP PU 3170 (a hexafunctional compound,
with
mean molecular weight of 3400 and degree of ethoxylation - 80%). Both polyols
are
available from Bayer AG.
* trademark
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Suitable polyisocyanates for the present invention include, for example,
aliphatic,
cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates such as
are
described in, for example, Justus Liebigs Annalen der Chemie, 562, pp. 75 to
136, by
W. Siefken. Suitable polyisocyanates include, for example, those which
correspond to
the formula:
Q(NCO)n
in which:
n represents a number from 2 to 4, preferably 2 or 3,
and
Q represents an aliphatic hydrocarbon radical having 2 to 8 carbon atoms,
preferably 6 to 10 carbon atoms; a cycloaliphatic hydrocarbon radical
having 4 to 15 carbon atoms, preferably 5 to 10 carbon atoms; an
aromatic hydrocarbon radical having 6 to 15 carbon atoms, preferably
6 to 13 carbon atoms; or an araliphatic hydrocarbon radical having 8 to
15 carbon atoms, preferably 8 to 13 carbon atoms.
Examples of suitable polyisocyanates include those as are described in, for
example,
DE-OS 2,832,253, pp. 10 to 11.
It is preferred that the polyisocyanates are those which are readily available
by
commercial processes. Some examples of such easily obtainable polyisocyanates
include compounds such as, for example, 2,4- and 2,6-toluylene diisocyanate as
well
as arbitrary mixtures of these isomers ("TDI"), polyphenylpolymethylene poly-
isocyanates, such as are prepared by aniline-formaldehyde condensation
followed by
phosgenation ("crude MDI"), and polyisocyanates containing carbodiimide
groups,
urethane groups, allophanate groups, isocyanurate groups, urea groups or
biuret
groups (i.e., the so-called "modified polyisocyanates"), and, in particular,
those
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modified polyisocyanates that are derived from 2,4- and/or 2,6-toluylene
diisocyanate
and/or from 4,4- and/or 2,4-diphenylmethane diisocyanate.
Particularly preferred are the normally used TDI isomer mixtures T 80, T 65
and
mixtures thereof.
Foams having densities in the range from about 20 to 80 kg/m3, which are
normal for
polyester-PUR foams, can be obtained in accordance with the present invention.
The
density range and potential applications of the polyester-PUR foams of this
invention
can be appropriately broadened by the co-use of additional blowing agents such
as,
for example, by means of liquid carbon dioxide according to the Nova Flex
technique
(Hennecke/-Bayer AG) and related processes, by the reduced pressure technique
according to the VPF method (Prefoam AG), or other similar techniques. It is,
however, particularly preferred that these polyester-PUR foams have a density
in the
range of from about 25 to 60 kg/m3. This density range is preferred due to the
fact
that, on the one hand, the water absorption capacity rises with increasing
density, and,
on the other hand, the wetability (i.e., accessible internal surface of the
foam) depends
on the extent of the final open-cell character of the foam. The wetability
normally
falls with increasing density.
The polyester-PUR foams produced according to the present invention exhibit
hydrophilic properties. These foams are able to absorb about 10 times the
amount of
water, with respect to the total weight of the dry foam, within 20-25 seconds.
When
dry foams produced from a polyol mixture containing at least about 10% by
weight,
based on the combined weight of components b), c) and d), of the highly
ethoxylated
polyether polyols described above are placed on an aqueous surface, the foam
sample
sinks within a few seconds. This phenomenon, which is extremely desirable for
some
applications, occurs without swelling of the foam matrix, until the polyol
mixture used
to prepare the polyester-PUR foams contains up to about 30% by weight, based
on
the combined weight of components b), c) and d), of the highly ethoxylated
polyether
polyols described above. When higher proportions of highly ethoxylated
polyether
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polyol are present in the polyol mixture used to produce polyester-PUR foams,
the
result is then, in addition, a recognizable swelling of the foam matrix.
Suitable amines that can be employed to catalyze the foaming reaction include
those
conventional amines which are known in the field of polyurethane chemistry
such as,
for example N-methylmorpholine, N-ethylmorpholine, trimethylamine,
triethylamine
and homologous trialkylamines, dimethylpiperazine, dimethylbenzylamine, N-
cocomorpholine, and other known amine activators, as well as various mixtures
of
such amines or urea/amine combinations.
In accordance with the present invention, it is particularly preferred that
the amine
catalysts used are those that, due to their nature and quantity required,
contribute as
little as possible to the smell and/or to the fogging of the foams produced
therefrom.
Other auxiliary substances and/or additives may optionally be added to the
foam
formulation. Suitable auxiliary substances and/or additives include, for
example, flame
retardants, stabilizers, and/or dispersing agents, etc.
In addition to silicone stabilizers such as, for example, SE 232 (available
from OSI),
VP Al 3613 and VP AI 3614 (available from Bayer AG) and/or B 8300 and B 8301
(available from Goldschmidt AG), it is possible that silicone-free surfactants
or
surfactant mixtures such as, for example, the combinations EM/TX or EM/PU 3240
(available from Rhein Chemie and Bayer AG), or Arcopal* N 90/Genapot PF 20
(available from Hoechst AG) can be used as stabilizers.
It is particularly preferred, however, that stabilizers are modem silicone
stabilizers
such as VP Al 3613, VP Al 3614 (available from Bayer AG) or B 8300 and B 8301
(available from Goldschmidt AG). Silicone stabilizers such as these result in
a fine and
more open-cell foam structure. In principle, these are "tailor-made"
organically
modified polyether-polysiloxanes based on polydimethylsiloxane. The latter can
simply be characterized as follows:
* trademark
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(H3C)3SI-O SI(CH3)z O- etc.
A further object of the invention is a moisture-absorbing material comprising
the
hydrophilic polyester-PUR foams produced in accordance with the invention as
described above. Moisture-absorbing materials based on these hydrophilic foams
have
end-use applications in areas such as, for example, the domestic and hygiene
sectors.
Some examples of suitable end-use applications include sponges, cleaning
and/or
wiping cloths, or as moisture-absorbing substrates or underlays in the
hospital
maintenance and domestic maintenance sector, as linings in disposable diapers,
or as
stripware for flame lamination or adhesive lamination with textiles or films
in order to
improve the moisture absorption capacity of the resultant composite materials.
In the above applications mentioned by way of example, requirements for
additional
properties quite often also have to be met. A particularly open-cell foam
structure
can be obtained by, for example, reticulation (post-treatment step to achieve
maximum cell opening) of the foams.
Furthermore, the foams according to the invention may be used in a preferred
variant
in automobile interior finishes such as, for example, textile-covered seat and
back
supports.
In automobile interior applications, an essential additional aspect of these
hydrophilic
foams is the compliance with fogging requirements. These fogging requirements
can
be met by using low-fogging polyester polyols such as, for example, VP PU
60WB01
(available from Bayer AG).
In other areas of end-use applications, such as, for example, sponges and
wiping
cloths, the achievement of high values with respect to breaking elongation,
tensile
strength and tear propagation resistance are also important factors. The
desired values
for these properties can be achieved by, for example, the use of Desmophen
2300
(available from Bayer AG) as the polyester-polyol component.
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Since a significant increase in water absorption capacity can be readily
achieved by the
presence of about 5% by weight of polyether polyol having a high degree of
ethoxylation, hydrophilically adjusted foams can be produced that, for the
most part,
also exhibit the high values of "textile ester foams" based on the special
polyol
Desmophen 2300.
Accordingly, the desired foam properties can be adjusted within a wide range
by the
admixture, within widely varying limits, of the highly ethoxylated polyether
polyols
and by the possibility of using various polyester polyols for the foaming
reaction.
The following examples further illustrate details for the process of this
invention. The
invention, which is set forth in the foregoing disclosure, is not to be
limited either in
spirit or scope by these examples. Those skilled in the art will readily
understand that
known variations of the conditions of the following procedures can be used.
Unless
otherwise noted, all temperatures are degrees Celsius and the numerical data
are parts
by weight, with respect to 100 parts of polyol.
Examples
Production of the foams:
The following reaction components were reacted according to known and
conventional processes and mechanical equipment normally used for this
purpose.
Details of the processing equipment that is used in accordance with the
invention are
set forth in, for example, Polyurethane Handbook, Carl Hanser-Verlag,
Munich/Vienna, New York, 2nd Edition, 1993, edited by Gunter Oertel, pp. 177-
202.
The reaction components were intensively mixed according to the specified
formulations and were then reacted.
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Example 1:
90 parts by wt. VP PU 60WB01 (a low-fogging polyester polyol having an OH
number of 60; available from Bayer AG)
parts by wt. VP PU 41 WBO 1(a trifunctional polyether polyol having a
degree of ethoxylation of > 70% and an OH number of 37;
available from Bayer AG)
4.0 parts by wt. water
10 0.25 part by wt. Niax*A 30 (an amine catalyst; available from OSI)
0.25 part by wt. RC-Al 17 (an amine catalyst; available from Rhein-Chemie,
Mannheim)
2.0 parts by wt. VP A13613 (a stabilizer, available from Bayer AG)
23.8 parts by wt. toluylene diisocyanate T 80 (a mixture of 80% by weight of
2,4-TDI and 20% by weight of 2,6-TDI)
23.8 parts by wt. toluylene diisocyanate T 65 (a mixture of 65% by weight of
2,4-TDI and 35% by weight of 2,6-TDI)
Example 2-
90 parts by wt. DE 2300, (a polyester polyol having an OH number of 50;
commercially available from Bayer AG)
10 parts by wt. VP PU 3170 (a hexafunctional polyether polyol having a degree
of ethoxylation > 80% and an OH number of 100; available
from Bayer AG)
3.0 parts by wt. water
0.2 part by wt. Niax A 30 (an amine catalyst, available from OSI)
0.2 part by wt. RC-A117 (an amine catalyst, available from Rhein-Chemie,
Mannheim)
1.8 parts by wt. VP Al 3613 (a stabilizer, available from Bayer AG)
18.8 parts by wt. toluylene diisocyanate T80
18.8 parts by wt. toluylene diisocyanate T65
* trademark
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Example 3:
80 parts by wt. DE 2200 (a standard polyester polyol having an OH number of
60; available from Bayer AG)
20 parts by wt. VP PU 41WB01 (a polyether polyol having an OH number of
37; available from Bayer AG)
5.0 parts by wt. water
1.2 parts by wt. KST 100 (an amine catalyst, available from Goldschmidt AG)
2.0 parts by wt. VP AI 3613 (a stabilizer, available from Bayer AG)
28.5 parts by wt. toluylene diisocyanate T 80
28.5 parts by wt. toluylene diisocyanate T 65
Example 4:
50 parts by wt. DE 2300 (a polyester polyol having an OH number of 50;
available from Bayer AG)
50 parts by wt. VP PU 41WB01 (a polyether polyol having an OH number of
37; available from Bayer AG)
3.0 parts by wt. water
0.2 part by wt. Niax A 30 (an amine catalyst, available from OSI)
0.2 part by wt. RC-A117 (an amine catalyst, available from Rhein-Chemie,
Mannheim)
1.5 parts by wt. SE 232 (a silicone stabilizer, available from OSI)
18 parts by wt. toluylene diisocyanate T 80
18 parts by wt. toluylene diisocyanate T 65
Example 5:
20 parts by wt. DE 2200 (a polyester polyol having an OH number of 60;
available from Bayer AG)
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80 parts by wt. VP PU 41WB01 (a polyether polyol having an OH number of
37; available from Bayer AG)
2.0 parts by wt. water
0.2 part by wt Niax A 30 (an amine catalyst; available from OSI)
0.2 part by wt. RC-Al 17 (an amine catalyst; available from Rhein-Chemie,
Mannheim)
1.5 parts by wt. B 8300 (a silicone stabilizer; available from Goldschmidt AG)
25.6 parts by wt. toluylene diisocyanate T 65
Example 6:
80 parts by wt. DE 2300 (a polyester polyol having an OH number of 50;
available from Bayer AG)
parts by wt. VP PU 41 WBO 1(a polyether polyol having an OH number of
15 37; available from Bayer AG)
3.0 parts by wt. water
1.0 part by wt. KST 100 (an amine catalyst; available from Goldschmidt AG)
2.0 parts by wt. VP AI 3614 (a stabilizer; available from Bayer AG)
3.0 parts by wt. sponge paste, consisting of 90% VP PU 41WB01 (a polyether
20 polyol having an OH number of 37; available from Bayer AG)
and 10% Loxiol G 20 (stearic acid; available from Dehydag,
Diisseldorf)
19.3 parts by wt. toluylene diisocyanate T 80
19.3 parts by wt. toluylene diisocyanate T 65
Example 7:
90 parts by wt. DE 2300 (a polyester polyol having an OH number of 50;
available from Bayer AG)
10 parts by wt. VP PU 41WB01 (a polyether polyol having an OH number of
37; available from Bayer AG)
3.0 parts by wt. water
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0.2 part by wt. Niax A 30 (an amine catalyst; available from OSI)
0.2 part by wt. RC-Al 17 (an amine catalyst; available from Rhein-Chemie,
Mannheim)
2.0 parts by wt. dispersing agent EM (available from Rhein-Chemie, Mannheim)
1.0 part by wt. additive VP PU 3240 (available from Bayer AG)
4.0 parts by wt. sponge paste, consisting of 90% VP PU 41WB01 (a polyether
polyol having an OH number of 37; available from Bayer AG)
and 10% Loxiol G 20 (stearic acid; available from Dehydag,
Diisseldorf)
38.0 parts by wt. toluylene diisocyanate T 80
Determination of the hydrophilic character of the resultant foams:
In order to assess the hydrophilic character, the foams specified in the
Examples were
tested in application-specific simulation tests against a standard ester foam.
The
formulation of the standard ester foam was as follows:
100 parts by wt. Desmophen 2300
3.0 parts by wt. water
1.0 part by wt. Al 3613
0.2 part by wt. Niax A 30
0.2 part by wt. RC A117
36.8 parts by wt. toluylene diisocyanate T 80
The tests were carried out as follows:
1. The dry foams were placed on an aqueous surface, and the hydrophilic foams
produced according to Examples 1 to 7 sank completely in the water within
25 sec. By comparison, the standard foam floated for more than 1 hour on the
surface of the water. When moist foams (produced in accordance with
Examples 1-7 above) from which the water had been largely removed were
placed on the surface of the water, the hydrophilic foams sank within 2 secs.
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The standard foam when moist, however, floated for more than 1 hour on the
surface of the water.
2. Water droplets were applied using a wash bottle to a dry foam surface; the
hydrophilically adjusted foams produced according to the present invention
directly absorbed the water droplets. In the case of the standard polyester
foam, however, the water droplets retained their spherical shape.
3. Wiping tests:
Water droplets were applied to a tabletop, and were directly absorbed when
the tabletop was wiped with the hydrophilic foams produced according to the
present invention. However, when the standard polyester foam was used to
wipe the tabletop, it was necessary to wipe the tabletop several times before
the droplets were absorbed by this foam.
Although the invention has been described in detail in the foregoing for the
purpose of
illustration, it is to be understood that such detail is solely for that
purpose and that
variations can be made therein by those skilled in the art without departing
from the
spirit and scope of the invention except as it may be limited by the claims.
