Process for providing fibers or nonwovens with a hydrophilic coating

A process for making synthetic fibers or nonwoven substrates hydrophilic made from the synthetic fibers comprising applying an effective amount of a finish composition onto the fibers or nonwoven substrates, the finish composition containing: (a) from 50 to 95% by weight of a hydrophobicizing agent selected from the group consisting of at least one quaternary ester amine salt corresponding to formula I: ##STR1## wherein R.sup.1 is an aliphatic alkyl group containing from 12 to 22 carbon atoms, R.sup.2 is either (CH.sub.2).sub.n --O--COR.sup.1 or an alkyl group containing from 12 to 22 carbon atoms, R.sup.3 and R.sup.4, independently of one another, represent (CH.sub.2).sub.n --R.sup.5, where R.sup.5 is H or OH and n is a number from 1 to 3, and X is either a halide, methosulfate, methophosphate or phosphate ion, a quaternary ester amine salt corresponding to formula II: ##STR2## wherein COR.sup.6 is an aliphatic acyl group containing from 12 to 22 carbon atoms and 0, 1, 2 or 3 double bonds, R.sup.7 is H or OH, n has a value of 1, 2 or 3 and X is either a halide, methosulfate, methophosphate or phosphate ion, and mixtures thereof; and (b) from 5 to 50% by weight of at least one alkyl glycoside corresponding to formula III: EQU RO(G).sub.x (III) wherein R is a primary linear or methyl-branched aliphatic radical containing from 8 to 22 carbon atoms, G is a glycoside unit containing 5 or 6 carbon atoms and x is a number from 1 to 10, all weights being based on the total weight of the composition.

BACKGROUND OF THE INVENTION
 This invention relates to a process for the hydrophilic finishing of
 fibers, which exclusively or predominantly contain polyolefins or
 polyesters, or of nonwovens containing polyolefin or polyester fibers and
 to fibers or nonwovens which are given a hydrophilic finish by this
 process.
 In the manufacture of sanitary articles, such as diapers or sanitary
 napkins, absorbent materials are used to absorb aqueous liquids. In order
 to prevent direct contact with the absorbent material during wear and to
 increase comfort, the absorbent material is wrapped in a thin
 water-permeable nonwoven. The nonwovens used for this purpose are normally
 made of synthetic fibers, such as polyolefin or polyester fibers, because
 fibers such as these are inexpensive to produce, exhibit good mechanical
 properties and, in the case of polyolefin, can be heat-bonded. However,
 untreated polyolefin or polyester fibers are not suitable for this
 particular application because, in view of their hydrophobic surface, they
 are not sufficiently permeable to aqueous liquids. Accordingly, the fiber
 surface has to be made hydrophilic by a corresponding finish. It is also
 desirable that the hydrophilic finish of the fibers should remain intact
 for as long as possible without any reduction in the permeability to water
 of the nonwoven. If nonwovens of the type in question are made up, for
 example, into diapers, the diapers thus produced can be subjected to
 repeated stressing without becoming leaky. In this way, the wearing time
 of the diapers is increased and the waste caused by used diapers can be
 reduced accordingly.
 U.S. Pat. No. 5,045,387 describes, for example, a formulation for the
 hydrophilic finishing of polyolefin fibers which contains a mixture of an
 alkoxylated ricinoleic acid derivative, a hydrogenated ricinoleic acid
 derivative, a C.sub.18 fatty acid and a polyalkoxylated polymethyl
 siloxane. EP 372 890 B1 discloses fibers which contain polyolefins or
 polyesters and which have been treated with a finish containing a fatty
 acid diethanolamide, a polyether-modified silicone, a sorbitan fatty acid
 ester and a metal salt of an alkyl sulfonate. The disadvantage of finishes
 such as these lies above all in their high price. In addition,
 correspondingly finished fibers show poorer behavior in the nonwoven
 production process, particularly during thermobonding, which results in
 reduced strength of the nonwoven. According to DE 42 43 547 C2, certain
 quaternized fatty acid triethanolamine ester salts are suitable for the
 production of spin finishes for synthetic fibers. These compounds are
 physiologically safe and show good biodegradability. However, there is
 nothing in the cited document to suggest that the compounds in question
 are also suitable for the hydrophilic finishing of synthetic fibers.
 French patent application 96/2024 discloses water-based preparations with
 solids contents of 1 to 50% by weight which contain linear saturated fatty
 alcohols, wax esters, nonionic and/or amphoteric or zwitterionic
 emulsifiers and cationic surfactants and their use for the production of
 utility papers with improved softness and as softeners for cellulose and
 textile fibers.
 The problem addressed by the present invention was to provide an improved
 process for hydrophilically finishing polyolefin- or polyester-containing
 fibers or nonwovens containing polyolefin or polyester fibers, the
 hydrophilic finish applied remaining intact, even after repeated wetting.
 BRIEF SUMMARY OF THE INVENTION
 It has now been found that these requirements are satisfied by a process in
 which the fibers or nonwovens are treated with a finish which contains
 quaternary ester amine salts and alkyl glycosides.
 Accordingly, the present invention relates to a process for the hydrophilic
 finishing of fibers, which exclusively or predominantly contain
 polyolefins or polyesters, or of nonwovens which predominantly contain
 fibers such as these, characterized in that the nonwovens are treated with
 an aqueous dispersion of a finish which contains 50 to 95% by weight,
 based on the total weight of the finish, of at least one quaternary ester
 amine salt corresponding to formula (I):
 ##STR3##
 in which R.sup.1 is an aliphatic alkyl group containing 12 to 22 carbon
 atoms, R.sup.2 is either a group (CH.sub.2).sub.n --O--COR.sup.1 or an
 alkyl group containing 12 to 22 carbon atoms, R.sup.3 and R.sup.4
 independently of one another represent a group (CH.sub.2).sub.n --R.sup.5,
 where R.sup.5 is H or OH and n is a number of 1 to 3, and X is either a
 halide, methosulfate, methophosphate or phosphate ion, 5 to 50% by weight
 of at least one alkyl glycoside corresponding to the general formula
 RO(G).sub.x, in which R is a primary linear or methyl-branched aliphatic
 radical containing 8 to 22 carbon atoms, G is a glycoside unit containing
 5 or 6 carbon atoms and x is a number of 1 to 10, and 0 to 30% by weight
 of glycerol.
 DETAILED DESCRIPTION OF THE INVENTION
 The process according to the invention is suitable for fibers which
 exclusively or predominantly, i.e. more than 50% by weight of which,
 contain polyolefins or polyesters, and for nonwovens which predominantly
 contain fibers such as these, fibers exclusively containing polyolefins or
 polyesters being preferred. Nonwovens containing 100% by weight of
 polyolefin or polyester fibers are particularly suitable. Polyolefin
 fibers are among the most commonly used fibers for the production of
 nonwovens. Examples of suitable polyolefins are polypropylene,
 polyethylene or copolymers of ethylene or propylene with butadiene.
 Polyester fibers, mainly polyethylene terephthalate fibers, are also used.
 Besides the fibers mentioned, other synthetic fibers suitable for the
 production of nonwovens may also be used, including for example fibers of
 Nylon.RTM.. Fibers consisting of two or more components, for example
 polyester/copolyester fibers or polypropylene/polyethylene fibers, are
 also particularly suitable.
 The nonwovens used in the process according to the invention may be
 produced by any of the known processes for producing nonwovens which are
 described, for example, in Ullmann's Encyclopedia of Industrial Chemistry,
 Vol. A 17, VCH Weinheim 1994 pages 572-581. Nonwovens produced either by
 the dry laid process or by the spunbonded process are preferred. The dry
 laid process starts out from staple fibers which are normally separated by
 carding into individual fibers and are then laid together by an
 aerodynamic or hydrodynamic process to form the unbonded nonwoven. The
 semi-finished nonwoven thus produced is then made up into the final
 nonwoven by a heat treatment known as thermobonding. To this end, the
 synthetic fibers are either heated to such an extent that their surface
 melts and the individual fibers are joined together at their points of
 contact or the fibers are coated with an additive which melts during the
 heat treatment, thus joining the individual fibers to one another. The
 bonds between the individual fibers are fixed by cooling. Besides this
 process, any of the other processes known for bonding nonwovens may of
 course also be used.
 By contrast, the spunbonded process starts out from individual filaments
 which are formed by melt spinning from extruded polymers which are forced
 under high pressure through spinning jets. The filaments emerging from the
 spinning jets are bundled, stretched and laid to form a nonwoven which,
 normally, is then thermobonded.
 The process according to the invention is particularly suitable for
 nonwovens produced by the spunbonded process or by the dry laid process.
 In the process according to the invention, the fibers or nonwovens are
 treated with the finish of quaternary ester amine salt, alkyl glycoside
 and optionally glycerol by applying the finish to the fibers or to the
 nonwoven in the form of an aqueous dispersion preferably containing from 5
 to 30% by weight of the finish, based on the total weight of the
 dispersion. Any of the methods and machines typically used in the textiles
 industry, for example a padding machine, may be used for this purpose. The
 nonwoven is first contacted with the aqueous dispersion in a bath and the
 nonwoven thus treated is passed between two rollers, the water being
 squeezed out by the pressure of the rollers. The process according to the
 invention is preferably designed in such a way that the fibers or
 nonwovens receive an add-on of finish in a quantity of 0.3 to 1.5% by
 weight and, more particularly, in a quantity of 0.5 to 1.0% by weight,
 based on the weight of the fibers or nonwovens.
 The finish used in the process according to the invention contains between
 50 and 95% by weight, based on the total weight of the finish, of at least
 one quaternary ester amine salt corresponding to formula (I). However,
 finishes containing quaternary ester amine salts corresponding to general
 formula (II):
 ##STR4##
 in which COR.sup.6 is an aliphatic acyl group containing 12 to 22 carbon
 atoms and 0, 1, 2 or 3 double bonds, R.sup.7 is H or OH, n has a value of
 1, 2 or 3 and X is either a halide, methosulfate, methophosphate or
 phosphate ion, are particularly preferred. The compounds corresponding to
 formula (II) may be obtained, for example, by reaction of diethanol alkyl
 amines with technical fatty acids and subsequent quaternization. Examples
 of such compounds are
 methyl-N-(2-hydroxyethyl)-N,N-di(tallowacyloxyethyl)-ammonium methosulfate
 and bis-(acyloxyethyl)hydroxyethyl methylammonium methosulfate. Compounds
 containing alkyl chains with 16 to 18 carbon atoms and 1 to 3 double bonds
 are particularly preferred. Mixtures of different ester amine salts
 corresponding to formulae (I) and/or (II) may also be used.
 The finish used in the process according to the invention contains alkyl
 glycosides corresponding to the general formula RO(G).sub.x, where R is a
 primary linear or methyl-branched, more particularly 2-methyl-branched,
 aliphatic radical containing 8 to 22 and preferably 12 to 18 carbon atoms
 and G is a glycoside unit containing 5 or 6 carbon atoms, preferably
 glucose, as an additional component in quantities of 5 to 50% by weight.
 The degree of oligomerization x, which represents the distribution of
 monoglycosides and oligoglycosides, is a number of 1 to 10 and preferably
 a number of 1.2 to 1.4. Finishes containing alkyl glycosides in quantities
 of 5 to 30% by weight are particularly preferred.
 It has been found that the addition of glycerol in quantities of up to 30%
 by weight, based on the total weight of the finish used in the process
 according to the invention, provides the fibers and nonwovens with
 improved hydrophilic properties and dermatological compatibility. The
 process according to the invention is preferably carried out by treating
 the fibers or nonwovens with a glycerol-containing finish which contains
 glycerol in quantities of 1.0 to 15% by weight, based on the total weight
 of the finish.
 In addition to the compounds described above, other substances known in the
 textiles field, for example antistatic agents or lubricants, may also be
 used in the finish. They are normally used in quantities of up to 20% by
 weight, based on the total weight of the finish.
 It can also be of advantage to carry out the process according to the
 invention by treating the fibers or the nonwovens with a finish which, in
 addition to the components already described, also contains monoesters of
 glycerol and a C.sub.6-14 fatty acid in quantities of 5 to 35% by weight,
 based on the total quantity of the mixture. A particularly preferred
 monoester is glycerol monolaurate.
 In another embodiment, the invention relates to hydrophilic fibers
 exclusively or predominantly containing polyolefins or polyesters or to
 nonwovens predominantly containing such fibers which have been produced by
 the process according to the invention. The fibers or nonwovens show
 hydrophilic properties which preferably remain intact, even after repeated
 wetting. In particular, the nonwovens produced in accordance with the
 invention have liquid strike-through times of less than 10 seconds and,
 more particularly, less than 5 seconds. In the context of the present
 invention, liquid strike-through times are understood to be the times
 which a certain quantity of water or synthetic urine takes to pass through
 the nonwoven to an absorbent underlayer. This time is determined by EDANA
 Method No. 150.0-84 (EDANA=European Association of Nonwoven
 Manufacturers). For use in diapers or similar sanitary articles, the
 liquid strike-through time should be as short as possible in order to
 guarantee rapid transport of the liquid through the nonwoven to the
 absorbent material. In this way, the surface of the nonwoven remains dry
 and thus leads to increased wearing comfort. The nonwovens produced in
 accordance with the invention retain this favorable property, even after
 repeated use, and are further distinguished by the fact that, when the
 liquid strike-through time is determined by EDANA Method No. 150.0-8
 preferably three times and more preferably five times in succession, they
 always have a liquid strike-through time of less than 10 seconds and, more
 particularly, less than 5 seconds.

EXAMPLES
 To determine the hydrophilicity of the variously produced nonwovens, the
 strike-through times of the test nonwovens were measured by EDANA Method
 No. 150.0-84.
 The measurements were carried out using a test instrument with a timer
 (Lister Tester from Lenzing AG). The test nonwovens (polypropylene
 spunbonded nonwoven weighing 20 g/m.sup.2 -Lutrasil.RTM. 4420 from
 Freudenberg) were sprayed with an aqueous dispersion of the finish. The
 test nonwovens were then dried for one hour at 70.degree. C.
 For the actual measurements, 6 layers of a filter paper (Evans-Adlard FF3
 WIS 150) were placed beneath one layer of the finished test nonwoven and
 then contacted with 5 ml of synthetic urine (1000 ml of dist. H.sub.2 O, 9
 g NaCl) from the Lister Tester. The measurements were carried out at
 20.degree. C./65% relative air humidity. The time which the liquid takes
 to penetrate through the nonwoven was read off in seconds from the timer.
 In order to measure the hydrophilic properties of the nonwovens after
 repeated stressing, the test nonwoven was placed on a new layer of filter
 paper after the first measurement without being dried and the measurement
 was repeated. Times of at most 5 seconds after 5 repetitions were regarded
 as good. Times of more than 10 seconds were not reproduced.
 The results are set out in Table 1 which shows the strike-through times in
 seconds for nonwovens treated with various finishes (average values of 5
 measurements). The nonwovens were coated with 0.5 and 1.0% by weight,
 based on their weight, of the corresponding finish.
 Nonwovens treated with the following finishes were tested. The figures in %
 by weight are based on the total weight of the finish. The respective
 finishes were used in the form of an aqueous dispersion containing 20% by
 weight of active substance, based on the aqueous dispersion.
 Finish 1
 70% by weight bis-(acyloxyethyl)-hydroxyethyl methylammonium methosulfate
 20% by weight C.sub.8-14 alkyl polyglucoside
 10% by weight glycerol
 Finish 2
 60% by weight bis-(acyloxyethyl)-hydroxyethyl methylammonium methosulfate
 10% by weight C.sub.8-14 alkyl polyglucoside
 30% by weight glycerol
 Finish 3
 60% by weight bis-(acyloxyethyl)-hydroxyethyl methylammonium methosulfate
 40% by weight C.sub.8-14 alkyl polyglucoside
 The following finishes were used for comparison:
 Finish C1
 100% by weight methyl-N-2-hydroxyethyl)-N,N-di(tallowacyloxyethyl)-ammonium
 methosulfate
 Finish C2
 50% by weight C.sub.8-14 alkyl polyglucoside
 50% by weight glycerol
 TABLE 1
 Number of measurements
 Finish 1 2 3 4 5 6
 1 3.36 3.39 3.84 4.32 5.07 --
 (Add-on 0.5%)
 1 3.66 4.12 3.67 3.81 4.90 5.92
 (Add-on 1.0%)
 2 4.0 3.89 4.57 5.74 -- --
 (Add-on 0.5%)
 2 3.72 3.58 3.78 4.04 5.50 --
 (Add-on 1.0%)
 3 3.66 3.63 4.44 6.10 -- --
 (Add-on 0.5%)
 3 3.29 3.45 4.02 4.11 5.18 --
 (Add-on 1.0%)
 C1 3.26 5.66 7.57 -- -- --
 (Add-on 0.5%)
 C1 3.53 4.66 7.41 9.93 -- --
 (Add-on 1.0%)
 C2 3.34 9.52 -- -- -- --
 (Add-on 0.5%)
 C2 3.50 -- -- -- -- --
 (Add-on 1.0%)
 It can be seen that a nonwoven produced in accordance with the invention
 treated with finish 1 still produces liquid strike-through times of less
 than 5 seconds at the fourth measurement both with an add-on of 1.0% and
 with an add-on of 0.5%. This effect is obtained merely with the
 combination of a quaternized ester amine salt and an alkyl polyglucoside,
 as the nonwoven treated with finish 3 shows. A nonwoven treated with a
 commercially available ester ammonium salt, such as finish C1, also shows
 favorable hydrophilic properties. However, it does not retain these
 properties as well in the event of repeated stressing, so that the liquid
 strike-through times become much longer in the following measurements. The
 nonwoven treated with finish C2 proves that the use of alkyl polyglucoside
 and glycerol alone does not lead to the required hydrophilic nonwovens.
 This shows that the required hydrophilic finish is only achieved by the
 suitable combination of quaternary ester amine salt and alkyl glycosides.