Absorbant disposable article.

The invention relates to a surface-treated nonwoven fabric made of synthetic fibers with wicking for use in particular as a covering nonwoven fabric for absorbent layers.

Covering nonwovens made of synthetic fibers are known per se. They are often used directly or in combination with other materials for the production of various hygienic and medical articles. For example, disposable diapers are made from an absorbent layer consisting essentially of cellulose^Ge-poses. The absorbent layer is covered with a well-covering and firm nonwoven made of synthetic fibers. Bandages and tanpons for feminine hygiene and surgical tanpons are structured similarly. Furthermore, multilayer fabrics (conposites) are known in which absorbent layers are covered on the outside with a nonwoven fabric, the multilayer structures being used as disposable towels, wipes, etc. can be used in the home, in industry or in clinical areas. Finally, such nonwovens are used directly or as multi-layer fabrics in combination with other sheet materials as materials for the production of disposable clothing for clinical use or else for other purposes.

Nonwovens, which are to be used as cover materials or also directly for the purposes mentioned, must be mechanically sufficiently strong, have sufficient opacity and be capable of assembly. In addition, it is essential that the cover nonwovens allow sufficient transport of aqueous liquids or vapors into the absorbent layers.

Covering nonwovens are known and commercially available which have a wicking effect to ensure the liquid transport. Wicking is understood to mean the ability to be wettable by liquids and at the same time to transfer the liquid as a result of capillary action. If the wicking is not sufficient, the removal of the liquid is not guaranteed and the suction properties of the manufactured product are poor.

In hygienic and medical multilayer structures, a simple wicking is generally not sufficient, because it is necessary that the transport of the liquid now stored in the absorbent layer to the outside is largely prevented, so that a "dry" impression is created. Reverse wicking must therefore be reduced, if not prevented entirely. This means that the two requirements - the primary transport and then the blocking effect - are in stark contradiction to one another.

The object of the invention is to develop a nonwoven fabric with wicking properties that optimally fulfills both requirements. The liquid should very quickly get into the absorbent layer^Ge-lines, whereby a return transport is not or only insignificantly.

The object of the invention is achieved by a surface-treated nonwoven fabric made of synthetic fibers with wicking, characterized in that it contains, as an active substance, a wetting agent that is substantive against cellulose in such a way that it can be chemosorbed on the cellulose or the cellulose-containing substrate. Surprisingly, it was found that the completely contradictory requirements of rapid primary transport to the suction pad and a blocking effect in the opposite direction were optimally met in this way.

For good wicking it is necessary that the surface of the nonwoven or the surface of the fibers forming the nonwoven is first wetted by the liquid. It is known that most synthetic polymers now have a relatively low surface energy, whereas water and most aqueous liquids are characterized by a relatively high interfacial energy (72.7 x 10-³ N / m). The following table shows the interfacial energy of the most important fiber-forming polymers:<tables id="tabl0001" num="0001"><img file="EP0053221A2_D0001.tif" /></tables>

The critical interfacial energy is the value of the interfacial energy that a liquid can at most reach while still wetting the surface. The part of the total interfacial energy that only results from dispersion forces is called the disperse part of the interfacial energy, whereas the part that is based exclusively on the polar interactions is called the polar part. In the case of water, it is assumed that the predominant part - approximately 2/3 - is due to the polar and only approximately 1/3 to the disperse interactions.

The wicking depends on the capillarity of the porous material and on its surface energy in relation to that of the liquid to be transported. A difference in the surface energies has the effect of reducing the porosity. For a given porous material, wicking can thus be improved by increasing the critical interfacial energy value and adapting it to the value of the aqueous liquid to be transported. This can be done, for example by treating the fleece or fiber surface with surfactants. Known nonionic surfactants which are known per se can be considered as effective surfactants which have sufficient adsorptivity on the polymer surfaces.

Ethoxylated alkylaryl compounds are very effective, the effect of which can be adjusted to suit the particular use by appropriate variation of the composition. By using such surfactants, an improvement in the wettability of the nonwoven surface can be achieved and the liquid transport through the nonwoven fabric is accelerated. This is due to the fact that the approximation of the surface_Henergies of the nonwoven and the liquid to be transported acts as an effective increase in porosity. Once the surface has been completely wetted, the liquid can be passed through the capillaries to the absorbent layer. The liquid is then stored in the absorbent layer.

Although the wicking effect of a nonwoven fabric treated in this way is very good, there are serious deficiencies because of the unimpeded transport of the liquid back when pressing on the surface of the absorbent pad covered with such a nonwoven fabric. The cover nonwoven is immediately wetted again with the liquid stored in the suction pad. It appears wet and there is almost unhindered liquid return in the opposite direction. The improved wettability, which helped the original liquid transport in the desired direction towards the suction pad, is now disadvantageous and undesirable. Non-ionic surfactants, as they are usually used industrially as wetting agents, thus enable wicking, but they prove unsuitable for finishing nonwovens because they remain on the nonwoven or The fiber surface adsorbs and thereby accelerates the liquid transport in both directions. The object of the invention is therefore not achieved with conventional nonionic surfactants.

If at all, non-ionic surfactants pass into the liquid phase only to a very small extent. There, too, they ensure the full maintenance of the wetting effect in both directions. If you want to reduce the return transport of the stored liquid, you have to fine-tune the tensi_drenge strive for a state of equilibrium in which both the primary transport to the suction pad and the return transport must be taken into account. At most, it is possible to achieve an almost satisfactory result through a compromise solution.

Since the invention is based on the object of developing a nonwoven fabric which largely prevents the backward transport of the stored liquid with a very good wicking effect towards the absorbent pad, nonwovens equipped with conventional nonionic surfactants cannot solve this object for the reasons set out above. However, if surfactants are used which are based on cellulose or the cellulose-containing material of the absorbent pad can be chemically sorbed and can be transported through the liquid into the absorbent pad, the task is solved in an optimal manner. It was found that the completely contradictory requirements of rapid primary transport to the suction pad and a blocking effect in the opposite direction can be reconciled so well. To a very special extent, cationic surfactants of the general formula have been found as wetting agents for the cover nonwoven<chemistry id="chem0001" num="0001"><img file="EP0053221A2_D0002.tif" /></chemistry>proven, whereby R₁, R₂, R₃ and R₄ Alkyl, aryl, alkylaryl, ethoxyl, alkylethoxyl, arylethoxyl and / or alkylarylethoxyl radicals can be. The radical A denotes a common anion, for example a halide.

It has been found that the cationic surfactants have an excellent wetting action. They improve the wicking significantly because on the one hand they are only weakly adsorbed by the polymer surface, so that a substantial part passes into the liquid phase during wetting and on the other hand they have a substantive behavior towards cellulose, i.e. they are chenosorbed on cellulose-containing substrates and thereby withdrawn from the liquid phase. The liquid phase thus serves as a means of transport of the wetting agent from the water-repellent fiber into the absorbent medium. The covering nonwoven can therefore be wetted well to improve the primary transport because a sufficient amount of the surfactant can be used. Due to the migration of the cationic surfactant and the subsequent binding to the cellulose-containing substrate, it acts as a barrier for the undesired return transport of the liquid. Since the nonwoven fabric, which consists of synthetic fibers, absorbs or binds very little water itself, it appears "dry" even if it is stretched over a damp absorbent pad.

The cationic surfactants proposed according to the invention can be dosed in high doses. It is thus possible to achieve rapid wetting without promoting the return transport. Optimal properties of the covering nonwoven fabric are obtained with regard to the very contradicting requirements of the wicking and blocking effect.

The proposed cationic surfactants also have the advantage that they are bacteriostatic or even bactericidal, which is very desirable for many areas of application, especially in the medical field. Covering nonwovens equipped according to the invention can be safely used in the clinical and medical fields and also in the cosmetic-hygienic field. It is important that the surfactants have no negative side effects on the human organism.

Among the proposed cationic surfactants, the following compounds have proven to be particularly useful:<ul id="ul0001" list-style="none"><li>Stearyldimethylbenzylammonium chloride:<chemistry id="chem0002" num="0002"><img file="EP0053221A2_D0003.tif" /></chemistry></li><li>Methyldodocylbenzyltrimethylammnium chloride:<chemistry id="chem0003" num="0003"><img file="EP0053221A2_D0004.tif" /></chemistry></li><li>Dodecyldimethylbenzylammonium chloride:<chemistry id="chem0004" num="0004"><img file="EP0053221A2_D0005.tif" /></chemistry></li><li>Tetradecyldimthylbenzylanmnium chloride:<chemistry id="chem0005" num="0005"><img file="EP0053221A2_D0006.tif" /></chemistry></li><li>Hexadecyldimethylbenzylanamnimnchlorid:<chemistry id="chem0006" num="0006"><img file="EP0053221A2_D0007.tif" /></chemistry></li><li>Diisobutylcresoxyethoxyethyldimetitylbenzammonium chloride:<chemistry id="chem0007" num="0007"><img file="EP0053221A2_D0008.tif" /></chemistry></li><li>Diiscbutylphenoxyethoxyethyldiwethylbenzylammoniumchlorid:<chemistry id="chem0008" num="0008"><img file="EP0053221A2_D0009.tif" /></chemistry></li><li>Methyldodecylxylylene-bis- (trimethylammonium chloride):<chemistry id="chem0009" num="0009"><img file="EP0053221A2_D0010.tif" /></chemistry></li></ul>

Although arbitrarily high proportions of cationic surfactants can be used, application amounts of 0.05 to 1.0% by weight, based on the weight of the nonwoven fabric, have generally proven useful for the finishing of nonwovens. In many cases, quantities of up to 0.5% by weight are sufficient.

The nonwoven can be finished in a manner known per se by padding, slapping or spraying on the aqueous solutions or dispersions and subsequent drying, if appropriate under pressure. Nonwovens of any composition can be treated in this way. The cationic surfactants can also be added to conventional finishing agents and thus used in a particularly simple manner. A particularly advantageous finishing option is to add the catenary-active surfactants in an appropriate dosage to the polymer melt during the spinning process. The cationic surfactants represent a phase foreign to the polymer melt and immiscible with it, which is transported to the fiber surface due to its low viscosity.

example 1

A spunbonded nonwoven made of polypropylene filaments with a filament titer of 2.2 dtex and a basis weight of 15 g / m2, bound by the point calender technique and having a thickness of 0.16 mm, is treated with an aqueous solution of diiscbutylphenoxyethoxyethyldimethylbenzylamncnium chloride as a cationic surfactant. The application amount is set by the concentration of the solution and the amount of liquid applied, as shown in the table. It is then dried in an air dryer at 100 ° C.

The finished nonwoven is tested for wicking (run-off) and rewetting (rewet) using the procedure described below. The results are shown in the table.

Wicking (run-off) test:<ul id="ul0002" list-style="none"><li>A 300 g / m² heavy cellulose suction pads with a length of at least 250 mm are covered on a smooth, impermeable surface with the cover nonwoven to be tested and arranged at an angle of 45 ° to the vertical. At the upper end of the suction pad thus produced, an outlet nozzle is attached at a distance of 200 mm from the lower end, which is connected with an automatic pipette with a volume of 30 ml. The outlet nozzle is constructed so that it has a flow rate of 0.5 ml / sec in the arrangement described. backs up. Several layers of filter paper are arranged under the lower edge of the suction pad to absorb the excess amount. Then the 30 ml of the test liquid is poured onto the suction pad from the pipette for 60 seconds. The test liquid is distilled water, the interfacial tension of which is 42 x 10 by adding the cationic surfactant^-3N / m at 23 ° C is used. The liquid flow initially flows down the surface of the cover nonwoven until it wets. Then the rest of the test liquid^Gsucked up and stored by the suction pad. The excess of the test liquid, which reaches the lower edge of the suction pad, is sucked up by the filter paper underneath and recorded by difference paths. A good cover fleece should lead to an excess of at most 0.5 g. The wicking effect is better, the smaller the excess caught on the lower edge.</li></ul>

Rewet test:<ul id="ul0003" list-style="none"><li>A cellulose suction pad with a basis weight of 300 g / m is stretched over a smooth, horizontal plate and covered with the nonwoven fabric to be tested. A 20 mm long tube with a diameter of 20 mm, on the underside of which there is a sieve for distributing the liquid, is placed on the suction pad. Then 30 ml of the test liquid specified in the run-off test described above are poured in. After the liquid has been sucked up through the suction pad, the wetted area is covered with a roller-shaped metal body weighing 30 N and a contact area of ​​100 cm² Stressed for 3 minutes. A filter paper folded several times is then placed under the metal body and the wetted area is stressed for a further 2 minutes. The liquid penetrating through the cover nonwoven fabric is sucked up by the filter paper and detected via differential paths. The result is referred to as rewet and should be less than 1.0 g in the case of a nonwoven fabric which can still be described as "dry".</li></ul>

Example 2

Under the conditions of Example 1, a mixture of 80% by weight of methyldadecylbenzyltriammnium chloride and 20% by weight of methyldodecylxylylene-bis - (trimethylammonium chloride) is used as the cationic surfactant. The results are again shown in the table.

Comparative example

Under the conditions of Examples 1 and 2, a commercially available nonionic surfactant is used instead of the cationic surfactant according to the invention. used. The result is also shown in the table.<tables id="tabl0002" num="0002"><img file="EP0053221A2_D0011.tif" /></tables>