Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02278946 1999-07-27
1
Textile fabrics
Specification
The present invention relates to textile fabrics comprising a web
of fibers joined together by means of a polymeric binder, i.e.,
nonwoven fabrics, and a process for their production.
A nonwoven is produced by laying down a web of fibers which is
subsequently consolidated or adhered together. The fibers can
have a preferential direction or be randomly disposed. Various
processes are known for forming the web, for example (1)
mechanical webbing from staple fibers or filaments; (2)
aerodynamic webbing from staple fibers or filaments; (3)
hydrodynamic webbing from staple fibers or filaments; and (4)
electrostatic webbing from very fine fibers or filaments. The
webs obtained in this way are consolidated into nonwovens by
various processes.
Wet processes are the most important. In these processes, the web
is treated with an aqueous binder, for example a polymer latex,
and subsequently, if necessary after removal of excess binder,
dried and optionally cured. This basic principle has ultimately
given rise to a large number of further developed processes.
Nonwovens are used in a large number of applications. For
instance, nonwovens are increasingly used, for example, as
cleaning cloths, wipes, dishcloths and napkins. In these
applications, it is important that, for example, spilt liquids,
such as milk, coffee, etc., be rapidly and completely absorbed
when wiped away with the nonwoven and that moist surfaces be
completely dried. The rate at which and the degree of
completeness to which liquids are absorbed determine the
performance characteristics of a wipe and are the main criteria
for the quality of the wipe article.
The rate at which a wipe will absorb a liquid increases with the
speed at which the liquid is transported on the fiber surface. A
hydrophilic surface is easily and rapidly wetted by water. The
water will then spread very quickly over the entire surface of
the nonwoven and will be "sucked away" from the point of contact.
Hydrophobic surfaces, in contrast, are not wetted. They therefore
do not convey the liquid either and are unsuitable for
application as a cleaning or wiping cloth. The amount of liquid
which can be absorbed is decisively determined, inter alia, by
the swelling behavior of the fiber. A hydrophobic binder forming
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substantially an envelope around the fiber impairs the kinetics
of water absorption.
The water absorption properties of nonwovens are occasionally
improved by using surface-active hydrophilicizing agents, such as
emulsifiers, surfactants or wetting agents, in the course of
their production. This does indeed provide excellent initial
hydrophilicity. However, these nonwovens have the disadvantage
that the hydrophilic agents are gradually washed off by water or
other aqueous media. The product becomes increasingly more
hydrophobic on repeated contact with water. After repeated
rinsing, therefore, the dishcloth, cleaning cloth or wipe loses
its ability to take up aqueous liquids rapidly. The cloth
consequently loses its utility and has to be disposed of, even
though its mechanical strength would be sufficient for further
use cycles. This is undesirable in terms of a responsible
handling of resources.
It is an object of the present invention to provide a hydrophilic
textile fabric whose hydrophilicity survives repeated rinsing.
We have found that this object is achieved, surprisingly, by
using certain oxides and/or hydroxides in a state of colloidally
disperse subdivision in conjunction with certain wetting agents.
The present invention accordingly provides a textile fabric
comprising a web of fibers joined together by means of a
polymeric binder, said fabric comprising an oxide and/or
hydroxide of A1, B, Si, Mg, Ti and/or Zn in a state of
colloidally disperse subdivision and a wetting agent selected
from sulfosuccinates and sulfosuccinamates.
The present invention further provides a process for producing a
textile fabric by impregnating a web of fibers with a dispersion
of a polymeric binder and drying and optionally curing the
impregnated web, which comprises further impregnating said web
with (i) a colloidal suspension of an oxide and/or hydroxide of
Al, B, Si, Mg, Ti and/or Zn or a solution of a precursor of an
oxide and/or hydroxide of Al, B, Si, Mg, Ti and/or Zn and
inducing the formation of the oxide and/or hydroxide in a state
of colloidally disperse subdivision and (ii) a wetting agent
selected from sulfosuccinates and sulfosuccinamates.
Statements herein in relation to the textile fabric of the
invention also apply, where appropriate, to the process of the
invention, and vice versa.
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The textile fabric of the invention preferably comprises 1 - 20g
by weight, based on the dry weight of the polymeric binder,
especially 3 - 15~ by weight, particularly preferably 5 - 15~ by
weight, of oxide and/or hydroxide of A1, B, Si, Mg, Ti and/or Zn.
The textile fabric of the invention preferably comprises 1 - 20%
by weight, based on the dry weight of the polymeric binder,
especially 2 - 10~ by weight, of wetting agent.
For the purposes of the present invention, "oxide and/or
hydroxide of A1, B, Si, Mg, Ti and/or Zn" shall have a very wide
meaning. As well as the simple oxides and hydroxides of the
elements indicated, the expression shall encompass their hydrated
forms of varying water content and the oxo anion salts with, for
example, alkali metal or alkaline earth metal cations, for
example the silicates and aluminates. The expression shall
further encompass oxides and hydroxides in various states of
condensation, for example the nesosilicates, amphiboles and
phyllosilicates, and also mixed oxides and/or hydroxides.
Preferred oxides and/or hydroxides are silica, aluminum oxide,
aluminum hydroxide, aluminosilicates, e.g., bentonites,
montmorillonites.
The textile fabrics of the invention include, in uniformly
dispersed form, a wetting agent selected from sulfosuccinates and
sulfosuccinamates. The wetting agents used have in particular the
following general structural formula
0 0
II ii
X-C -CH2 -CH -C-Y
I
S03M
where M is an alkali metal, especially sodium, or one equivalent
of an alkaline earth metal or ammonium, which may be substituted
by from 1 to 4 C1-C4-alkyl or C1-C4-hydroxyalkyl groups;
X and Y, which may be identical or different, are each
0-(CnH2n0)m-Rr (CnH2n0)m-NHCOR, OM, OH, or NHR, Subject to the
proviso that at least one of X and Y is not OM or OH, and R is
linear or branched CS-C18-alkyl, C5-C18-alkenyl, C5-C18-cycloalkyl,
(C1-C12-alkyl)aryl or phenyl;
n is an integer from 2 to 4; and
m is an integer from 0 to 30.
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It is particularly advantageous to use sulfosuccinic diesters in
which the esterifying alcohols have a chain length of from 4 to 8
carbon atoms, e.g., sodium di(ethylhexyl) sulfosuccinate.
As to the fibers used, the invention is not subject to any
significant restrictions. All fiber varieties are suitable which
are currently used for producing nonwovens, e.g., polypropylene,
polyester, polyamide fibers, cellulose fibers, such as viscose
fibers, bicomponent fibers, e.g., polyester/copolyester,
polypropylene/polyethylene, polyester/polyamide,
polyester/polypropylene and nylon-6/nylon-6,6 fibers. Further
suitable fibers are polyacrylonitrile, polyimide,
polytetrafluoroethylene and polyphenylene sulfide fibers, mineral
fibers or glass fibers and semisynthetic fibers, such as acetate
fibers. Polypropylene fibers, polyester fibers and cellulose
fibers and blends thereof are preferred.
All customary polymeric binders can be used. This includes in
particular the polyacrylate dispersions, for example on the basis
of C1-C4-alkyl (meth)acrylates, (meth)acrylic acid and/or
(meth)acrylamide. Amide polymers or copolymers can be crosslinked
with N-methylol compounds, such as urea-formaldehyde or
melamine-formaldehyde resins. Internal crosslinking takes place
on incorporating N-methylol(meth)acrylamide. It is also possible
to use rubber latices, for example synthetic styrene-butadiene
rubbers (SBR) and acrylonitrile-butadiene rubber (NBR), polyvinyl
ester dispersions, optionally copolymerized with ethylene and/or
vinyl chloride, for example copolymers of vinyl acetate and
ethylene or vinyl acetate, vinyl chloride and ethylene, and also
polyvinyl alcohols. It is further possible to cite polyurethane
dispersions and also aminoplast and phenoplast precondensates.
Preference is given to the use of a binder comprising a polymer
of monomers selected from the group consisting of C1-C4-alkyl
(meth)acrylates, (meth)acrylic acid, (meth)acrylamide,
N-methylol(meth)acrylamide, styrene, butadiene,
(meth)acrylonitrile, vinyl C1-C6-alkanoates, vinyl chloride,
ethylene and vinyl alcohol. The amount of binder used, expressed
as dry binder on the basis of the total weight of the
consolidated nonwoven, is generally within the range from 10 to
40~ by weight, preferably about 20~ by weight.
It is of critical importance for the present invention that the
oxide and/or hydroxide of A1, B, Si, Mg, Ti and/or Zn be present
in the nonwoven of the invention in a state of colloidally
disperse subdivision. Noncolloidal, coarser particles, as
occasionally used as antiblocking additives or other aggregates,
do not provide the desired effect. By colloidally disperse is
CA 02278946 1999-07-27
meant that the majority of the particles, e.g., more than 90~ by
weight, of the oxide and/or hydroxide are < 1 N.m, especially
< 0.1 Eun, in size. The state of colloidally disperse subdivision
can be achieved in the context of the present invention, for
5 example, by starting from a colloidal suspension of the oxide
and/or hydroxide, for example a sol, such as a hydrosol, or a
gel, or else by inducing the formation of the oxide and/or
hydroxide in colloidally disperse form, for example in the form
of a gel, within the web.
The web may be impregnated with the binder dispersion by all
common impregnating methods, for example impregnation using an
impregnator or in a pad-mangle. When the oxide and/or hydroxide
forms a stable colloidal suspension in the presence of the
polymeric binder, it is advantageous to incorporate the oxide
and/or hydroxide into the binder dispersion. In this way, it-is
possible to process, for example, colloidal.silicas. Colloidal
dispersions of certain oxides and/or hydroxides cannot be
prepared in situ in the binder dispersion. For instance, A13+
salts tend to coagulate the dispersion or, to be more precise, a
coagulation occurs when it is attempted to convert the A13+ salts
into A1(OH)3 by addition of a base, for example ammonia. In these
cases, it is advantageous for the web to be impregnated with a
colloidal suspension, preferably with a freshly prepared
colloidal suspension, in the form of a sol or gel and dried and
then impregnated with the polymeric binder. On the other hand, it
is possible to impregnate the web with the solution of a
precursor of the oxide and/or hydroxide and to induce the
formation of the oxide and/or hydroxide in the web. For instance,
the web can be saturated, for example, with a solution of A13+
ions, for example an A12(S04)3 solution or an A1(N03)3 solution,
and preferably dried. It is only then that the web is impregnated
with the binder dispersion. The neutral to slightly alkaline pH
of the dispersion leads to conversion of the A13+ ions into
A1(OH)3. If necessary, the binder dispersion may have a pH
regulator, for example a buffer, added to it so as to establish a
neutral to slightly alkaline pH, for example within the range
from 6 to 9.
The web or nonwoven could further be saturated with a waterglass
solution, i.e., a sodium orthosilicate solution, in which case
colloidal silica can be generated by treatment with a dilute
mineral acid, for example hydrochloric acid. A further example is
the treatment with an aqueous solution of borax (Na2B407 ~ 10 H20)
with subsequent drying.
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The impregnation of the web or nonwoven with the colloidal
suspension of the oxide and/or hydroxide, or the impregnation
with the solution of the precursor and the inducing of the
oxide/hydroxide formation, can take place at any time during the
production of the textile fabric. It is preferred that they take
place before or simultaneously with the impregnation with the
binder.
The impregnation of the web or nonwoven with the wetting agent
can take place at any time during the production of the textile
fabric of the invention. In general, it is advantageous to effect
the impregnation with the wetting agent simultaneously with the
binder impregnation. To this end, the wetting agent is simply
added to the aqueous binder dispersion.
The Examples which follow illustrate the invention.
Examples 1 to 10
70/30 polyester/staple viscose rayon webs (1.7 dtex; fiber length
38 mm; 30 g/m2) from 35 to 50 cm in length and from 25 to 28 cm in
width were carried in longitudinal direction through a 25~
strength binder liquor and over an aspirator on an endless PES
sieve belt forming part of an impregnating and aspirating range.
The binder dispersion used was Acronal DS 2350 X ~ (polyacrylate
dispersion based on butyl acrylate and acrylonitrile). The belt
speed was within the range from 1 to 2 m per min. The degree of
aspiration was varied to set the wet add-on to about 160, which
corresponds to a dry add-on of about 40~. The binder liquor
included the additives reported in the table which follows (in $
of dry weight of binder). The impregnated webs were placed on the
belt of a Mathis TH sieve belt dryer, secured against slippage
and dried at 150~C for 2 min. The upper surface of each web was
labeled, and the add-on level was determined by weighing.
The nonwovens thus obtained were subjected to a wetting test
immediately thereafter and after being rinsed out five times. To
rinse the nonwoven, it was immersed in a 5 1 bucket of tap water,
squeezed (or wrung) out by hand about 15 times, then wrapped in a
towel and wrung dry in the towel. This sequence was repeated
5 times.
Hydrophilicity was quantified by using the colored runoff test.
This test is carried out essentially as follows: The nonwoven is
fixed at an incline and has a defined amount of colored water
applied to it. Depending on the hydrophilicity of the nonwoven,
the water will run off or pass into the nonwoven at a certain
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speed. Characteristic colored spots are obtained, which are, for
example, circular for rapid penetration into the nonwoven or
narrow and elongate for slow penetration and preferential runoff.
The assessments are rated on a scale.
To carry out the test, a specimen 21 x 5 cm in size is clamped
into a frame which is at an angle of 30 degrees to the
horizontal. The side which was the upper surface in the dryer
faces downwards in this test. A pipette is used to apply 0.5 ml
of test liquid from a height of 10 mm and at a distance of 30 mm
from the upper edge of the web. The test liquid was made up of
2 g of Hostapal CV solution and 2.5 g of Lurantin Lightfast
Turquoise Blue GL per 1 1 of completely ion-free water. After the
test specimen had been hung up and has dried, the upper surface
of the web is inspected and rated on a scale from 0 for no
wetting (all the test liquid has run off) to 5 for total wetting.
The results are reported in the table which follows.
Table
Colored
runoff
test
Trial Mineral Emulsifier*5 before after
5
No. additive rinsing rinses
1 - - 0-1 0-1
2 - 3.0~ of sodium di(2-ethylhexyl)4 0-1
sulfosuccinate *1
3 5~ of - 0 0
silica
*4
4 5~ of 3.0~ of sodium di(2-ethylhexyl)5 5
silica sulfosuccinate *1
*4
5 5~ of 3~ of dodecylbenzenesulfonate5 1-2
silica
*4
6 5~ of 5~ of sodium alkylnaphthalene-0-1 0-1
silica sulfonic acid *z
*4
7 5~ of 5$ of sodium alkylnaphthalene-0-1 0-1
silica sulfonic acid *2
*4
8 5~ of 3~ of ammonium polyacrylate 2 0-1
*3
silica
*4
9 10$ of - 0 0
silica
*4
10 10~ of 3.0$ of sodium di(2-ethylhexyl)5 5
silica sulfosuccinate *1
*4
*1 Lumiten IRA
*2 alkyl = diisobutyl (Nekal BX ~)
*3 Pigmentverteiler [pigment dispersant] A
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*4 Levasil 200 ~ (Bayer)
*5 emulsifier was added in liquor
It is clear from the table that only Examples 4 and IO provide a
nonwoven which is still hydrophilic after 5 rinses. These
Examples included a sulfosuccinic ester in conjunction with
colloidal silica. Without silica (Example 2), even the use of the
same emulsifier does not provide durable hydrophilicity. Other
emulsifiers (Examples 5, 6) do not lead to the desired durable
hydrophilicity. Nor do polymeric additives (Example 8) or higher
amounts of silica lead to the desired properties in the absence
of sulfosuccinic esters (Example 9).
Examples 11 to 18
Standard pulp webs (Whatman #4; 100 pulp) from 35 to 50 cm in
length and from 25 to 28 cm in width were pad-mangled with a lOg
strength binder liquor (Acronal DS 2350 X) and then dried in a
Mathis tenter dryer with laydown gauze. The liquor included the
additives reported in the table which follows. In Examples 13 and
14, the webs were initially pad-mangled with a 5~ strength
A12(S04)3 solution and dried and only then saturated with binder
in the pad-mangle and redried.
The nonwovens obtained were subjected to an absorbency test. To
this end, a strip of nonwoven, measuring 70 x 30 mm, which had
been rinsed and dried 5 times was suspended in the
above-described test liquid at a depth of about 5 mm and the
wicking height of the test liquid recorded after 30 s. In
addition, the penetration rate in the nonwoven was measured. To
this end, 0.1 ml of test liquid was placed on the front surface
of nonwoven samples which had been rinsed and dried 5 times and
the time recorded for the drop to penetrate completely into the
nonwoven. The results are reported in the table which follows.
40
CA 02278946 1999-07-27
Table
9
Trial Mineral Emulsifier *5 Wicking Penetration
No. additive height (min)
in mm
11 - - 0 none
12 - 3.0~ of sodium 9 6
di(2-ethylhexyl)
sulfosuccinate *1
13 A1z03 from- 0 none
A12(S04)3
14 A1203 from3.Og of sodium 11,5 1
A12(S04)3 di(2-ethylhexyl)
sulfosuccinate *1
5~ of 3.0~ of sodium 11 immediate
silica di(2-ethylhexyl)
*4
15 sulfosuccinate *1
16 10~ of 3.0~ of sodium 7 29
Sipern.D di(2-ethylhexyl)
10*6 sulfosuccinate *1
17 10~ of 3.0~ of sodium 9 8
china di(2-ethylhexyl}
clay *7 sulfosuccinate *1
18 10~ of 3.Og of sodium 13 5
Gelb-s. di(2-ethylhexyl)
kreide sulfosuccinate *1
*8
*4 Levasil 200 ~ (Bayer)
*5 emulsifier was added in liquor
*6 Sipernat D 10 = silica powder
*~ aluminum silicate powder
*$ CaC03
It is clear from the table that only the combination of mineral
filler (aluminum oxide/hydroxide or silica; trials 14, 15) with
sulfosuccinic ester leads to the desired durable hydrophilicity.
The components alone (trials 12, 13) are not sufficient. The
examples featuring noncolloidal mineral additives (Examples 16,
17 and 18) demonstrate the criticality of the state of
colloidally disperse subdivision.
45
