WO2007137609A1

WO2007137609A1 - Asymmetric multilayered non woven fabric

Info

Publication number: WO2007137609A1
Application number: PCT/EP2006/005201
Authority: WO
Inventors: Xavier Conillera Trias; Robert Garcia Pano; Rosa Maria Guasch Riera; Josep Maria Pamies Baldris
Original assignee: Tesalca-99, S.A.
Priority date: 2006-05-25
Filing date: 2006-05-31
Publication date: 2007-12-06
Also published as: ES2304848A1; ES2304848B1

Abstract

Asymmetric multilayered non woven fabric which also provides fluid absorption properties. By being multilayered, the features of isolating against moisture in one direction and the permeability of fluids in the opposite direction are increased. The non woven fabric comprises: one or more layers of hydrophobic filaments which comprise a polyolefin; one or more layers of hydrophilic elements which comprise a mixture of a polyolefin and an additive or combination of additives; where the layer at one of the ends of the non woven fabric is hydrophobic and the layer at the other end of the non woven fabric is hydrophilic, and where the aforementioned additive or combination of additives provides the polyolefin with hydrophilic properties as well as fluid absorption properties.

Description

ASYMMETRIC MULTILAYERED NON WOVEN FABRIC

DESCRIPTION

FIELD OF THE INVENTION

The present invention pertains to the field of non woven fabrics for the manufacture of the upper layer of sanitary or hygiene products, for the manufacture of the upper layer of cleaning cloths, for the manufacture of thermal blankets in agriculture or for the manufacture of membranes for packaging. More specifically, the present invention refers to an asymmetric non woven fabric made up of several layers, at least one of which is hydrophilic and at least another which is hydrophobic.

BACKGROXJND OF THE INVENTION

Absorbent sanitary or hygiene products, such as nappies (diapers) , sanitary towels or the like, are manufactured by the superimposition of several layers, firstly, an upper layer or "upper covering" being permeable to fluid, destined to be in contact with the skin, next an absorbent layer and, lastly, a layer impermeable to fluid. The objective of the upper covering is to enable fluids to pass through so that these do not remain in contact with the skin.

A known way of manufacturing these products is based on non woven fabrics, which are defined below.

A non woven fabric is an assembly of textile fibres or filaments which are bound to each other forming a mesh or sheet by fusion (in the case of thermoplastic filaments) , using means such as glue, casein, rubber, latex, or the like, or by mechanical methods, such as water jets or puncture. Unlike traditional fabrics, where threads are interwoven between each other, the filaments of non woven material are deposited at random and tangled and are bound to each other by using one of the methods mentioned (thermally, mechanically or chemically) . Among other applications, non woven fabrics are used to manufacture the upper layer or upper covering of sanitary or hygiene products, such as nappies (diapers) , sanitary towels and others.

If the non woven fabric is made up of filaments which have been extruded, placed on a conveyer belt and finally bound using different methods, such as using a calender at a high temperature and subjected to a high pressure, the non woven fabric is called spunbond.

The Japanese patent JP5176954 describes an upper covering made up of two elements: a spunbond non woven fabric made up of continuous hydrophobic filaments and a paper sheet made up of a paste of hydrophilic fibres, in which one of the elements is placed over the other, and in which the continuous hydrophobic filaments and paste fibres are entangled by the action of a flow of water. Thus, fluids are easily absorbed by the hydrophilic fibre paste which makes up the paper sheet. The function of the hydrophobic fibres is to provide mechanical resistance to the assembly, particularly when the sample is wet.

However, the presence of a paper paste decreases the smoothness of the upper covering. Also, this upper covering requires a flow of water for its manufacture, which makes the manufacturing process more expensive.

On the other hand, the Japanese patent JP9510374 describes an upper layer made up a first sheet and a second sheet placed, separated from each other by a third separating sheet which makes the passage of fluids easier.

However, this upper layer has a very complicated structure, which requires placing two sheets spaced by another separating sheet, making its manufacture difficult.

Another type of nappy (diaper) configuration, destined to improving the dryness performance of the layer of the nappy (diaper) which comes into contact with the skin of the wearer of the same, is described in the patent application GB2023067 A, which demonstrates an upper layer or top sheet manufactured with a hydrophobic material which is bound at several points or lines of its surface to the lower layer, that is, the absorbent or hydrophilic layer. The binding is obtained in different ways, such as using adhesive, heat sealing or others. The binding points or lines allow the fluid to come into contact with the absorbent layer and be absorbed into it immediately.

The problem derived from this upper layer or top sheet is that it requires the binding points or lines with the absorbent layer to prevent fluids remaining in the upper layer or top sheet, and thus in contact with the skin.

OBJECT OF THE INVENTION

In one aspect of the present invention, an asymmetric multilayer non woven fabric is provided which overcomes the disadvantages of the non woven fabrics mentioned previously. Thus, in one aspect of the present invention, the multilayered non woven fabric is asymmetric, allowing the passing of fluid in one direction, but preventing it in the opposite direction. The non woven fabric also provides fluid absorption properties. By being multilayered, it increases the performance of insulation against wetness in one direction and the permeability of fluids in the opposite direction. The multilayered asymmetric non woven fabric includes, one or more layers of hydrophobic filaments which include a polyolefin; one or more hydrophilic layers of filaments which include a mixture of a polyolefin and an additive or combination of additives; where the layer of one of the ends of the non woven fabric is hydrophobic and the layer at the other end is hydrophilic, and where the aforementioned additive or combination of additives provides the hydrophilic as well as the fluid absorption properties to the polyolefin. Preferably, the aforementioned polyolefin is a polypropylene .

Also, another object of the invention is the top sheet which includes the non woven fabric of the present invention.

Another object of the present invention are the absorbent articles or products which incorporate a top sheet which comprises the aforementioned non woven fabric, such as nappies (diapers) , sanitary towels, surgical materials, cleaning cloths, etc.

Another object of the invention is thermal blankets for agriculture which include the aforementioned non woven fabric.

A membrane for packaging which includes the aforementioned non woven fabric is also an object of the present invention. Another aspect of the present invention includes the method for obtaining asymmetric multilayered non woven fabrics .

Finally, another aspect of the present invention provides an installation or system to carry out the previous method.

BRIEF DESCRIPTION OF THE FIGURES

To complement the description which is being made and with the objective of a better understanding of the characteristics of the invention, in accordance with a preferred example of a practical embodiment of the same, a group of diagrams which are illustrative in character and not limiting is attached as an integral part of the aforementioned description, in which the following has been represented:

Figure 1 shows a cross-section of a multilayered non woven fabric according to an embodiment of the present invention.

Figure 2 shows a cross-section of a multilayered non woven fabric according to another embodiment of the present invention.

Figure 3 shows a cross-section of a multilayered non woven fabric according to another embodiment of the present invention.

Figure 4 shows a cross-section of a multilayered non woven fabric according to another embodiment of the present invention. Figure 5 shows a schematic representation of the installation for the manufacture of a non woven fabric according to a possible embodiment of the procedure described in the present invention.

Figure 6 shows the detail of the calender which can be used in the procedure schematised in Figure 5.

Figure 7 shows another schematic representation of the installation for the manufacture of a non woven fabric according to another possible embodiment of the procedure described in the present invention.

Figure 8 shows another schematic representation of the installation for the manufacture of a non woven fabric according to another possible embodiment of the procedure described in the present invention.

Figure 9 shows a cross section of a hydrophilic filament extruded by a head according to a possible embodiment of the procedure described in the present invention.

Figure 10 illustrates the cross section of a hydrophilic filament extruded by a head according to another possible embodiment of the procedure described in the present invention.

Figure 11 shows a schematic representation of the behaviour and hydrophilic/hydrophobic properties of the non woven fabric obtained by means of any of the embodiments of the procedure described in the present invention.

DETAILED DESCRIPTION OF THE INVENTION Below, and with reference to the Figures, the different ways of embodiment of the non woven fabric of asymmetric continuous filaments and of the procedure for obtaining the aforementioned non woven fabric of the present invention.

In the context of the present invention, "asymmetric" is understood as the property which allows the passage of fluid in one direction, but prevents it in the opposite direction. That is to say, the non woven fabric of the present invention is asymmetric by having hydrophilic properties in one direction and hydrophobic properties in the opposite direction.

Also, when the density values of the non woven fabric or the weight of the filaments per unit of length are described, the term "approximately" has to be understood as indicating values very near to those which accompany the aforementioned term. The expert in the technique will understand that a small deviation from the values indicated is inevitable due to measurement inaccuracies, etc.

Figure 1 shows a non woven fabric of asymmetric continuous filaments according to an embodiment of the procedure of the present invention, which comprises three layers obtained from filaments. These filaments are obtained from a molten mass of a polyolefin normally used in the manufacture of hydrophobic non woven fabrics. Preferably, the aforementioned polyolefin is a polypropylene. The non woven fabric is a porous structure due to spaces being created between the fibres that form it. With reference to Figure 1, the layer (2) represents a hydrophobic layer formed from the filaments of the aforementioned polyolefin. These filaments are obtained from a molten mass of a composition which comprises a polyolefin, preferably polypropylene, as is indicated later in this description. This layer (2), by being hydrophobic, offers a resistance to the passage and/or return of fluids: When the fluid, for example, urine, is deposited on this hydrophobic layer, the hydrophobic fibres tend to repel the aforementioned fluid, and therefore, not allowing it to pass through. However, due to the porous structure of the non woven fabric, and also due to the layers (3, 3') situated underneath being hydrophilic, the fluid retained by the hydrophobic layer comes into contact with some hydrophilic fibres of the lower layers (3, 3'), which allow and favour the transfer of the fluid. When the fluid tries to displace itself in the opposite direction, the hydrophobic layer acts as a barrier, due to the fact that, on the other side of the aforementioned hydrophobic layer, there is not another hydrophilic layer that attracts fluid.

The other layers (3, 3' ) of Figure 1 represent tracks of hydrophilic layer paths formed from the filaments which enable the passage of the fluids. The hydrophilic layers are formed from filaments of a mixture which comprises a polyolefin and an additive or a combination of additives which provide the polyolefin with hydrophilic properties. This mixture is obtained hot, in the form of a molten mass. The use of additives to convert a hydrophobic material into a hydrophilic one is known by the expert on the subject. A known way of obtaining textiles that have hydrophilic properties instead of hydrophobic ones is by treatments with surfactants. Suitable conventional additives include, but are not limited to ionic surfactants such as ethoxylated aliphatic alcohols, ethoxylated phenol alkyls, fatty acid esters, derived from amines, derived from amides, copolymers of ethylene oxide and propylene oxide, anionic surfactants such as alkyl sulphates, such as alcohol sulphate esters, alkyl sulphate esters, such as alcohol ether sulphates, sulphated alkanolamides, diglyceride sulphates, alpha-olefin sulphates, sulphocarboxylic compounds, cationic surfactants such as linear alkylamines, linear alkyl ammoniums, amphoteric surfactants such as the propionic amino acids, betaines, taurine sulphobetaines, silicone surfactants and their mixtures. Some of these additives or mixtures of the same are commercially available, for example: Cirrasol PP682, which consists of a mixture of ethoxylated hydrogenated castor oil and sorbitan mono-oleate; Stantex S 6327, which is polyethylene glycol fatty acid ester; Silastol PST, which consists of a mixture of sodium dioctyl sulphosuccinate and ethoxylated alkylamine; Silwet L- 7608, marketed by GE Silicones, which consists of a copolymer of modified polyalkylenoxide and heptamethyltrisiloxane and Standapol 1345, marketed by Cognis .

However, the majority of additives which provide the polyolefin with hydrophilic properties have certain limitations, among which are highlighted the low durability and the relatively rapid elimination of the hydrophilic properties after exposure to an aqueous medium (which is known in chemistry as an "insult") .

To avoid these problems derived from the majority of conventional hydrophilic additives, in the present invention preferably an ethoxylated aliphatic alcohol of the formula: CH₃CH₂ (CH₂CH₂) 3CH₂CH₂ (OCH₂CH₂) _b0H, is used, where "a" is an integer number between 9 and 25 and "b" is am integer number between 1 and 10. This additive is marketed by Ciba under the name of Irgasurf® HL 560.

The advantage which this additive has is not only that it provides hydrophilic properties to the polypropylene, but it also provides the capacity of fluid absorption. Specifically, it has been proven that a non woven fabric which comprises a polypropylene to which is added 2.5% IRGASURF® HL 560 is capable of the repeated and continuous absorption of eight times its weight in water, which represents a huge step in the use of polypropylene fibres in nappies (diapers) , surgical products, thermal blankets, membranes for packaging and other products manufactured from non woven fabrics. Lastly, the additives used to increase the hydrophilic properties of polypropylene in the non woven fabric of the present invention improve the anti-static properties and decrease the friction coefficient of the polypropylene textiles.

Also, the mixture of the hydrophilic layer or layers

(3, 3' ) can also comprise any other additive from those known by the expert in the technique. Examples of other suitable additives which can be used are absorbents of ultraviolet radiation, stabilised against light, antioxidants, flame retardants, processing aids, colour pigments and others similar.

A normal way of characterising linear materials is by using a measurement unit called "denier", referring to the weight per unit of length. Thus, a "denier" is defined as the weight in grams of a circular section of filament which has a length of 9000 metres, or which is the same as: denier = volume of a filament of 9000 metre * density of the material. As the volume of a filament of length L is: πR²L , knowing the density of the material and the radius R of the filament, its "denier" value can be obtained. For example, if polypropylene is chosen as a material, with a density at ambient (room) temperature is 0.91* 10⁶ g/m³ and filaments with a radius of 5 μm are manufactured:

Volume =

0.706 * 10^"6 m³

denier = V * D = 0.706 * 10^"6 * 0.91* 10⁶ = 0.6432 g

Therefore, the denier is an indirect way of measuring the radius or diameter of the filament.

The filaments of the composition which comprises a polyolefin from which the hydrophobic layer (2) of Figure 1 is formed are extruded in such a way that they have a denier of between approximately 1.0 and 4.0. That is to say, the filaments of the aforementioned polyolefin of 9000 m weigh between 1.0 and 4.0 grams. Equally, the diameters of the aforementioned filaments vary between 1.0 and 4.0 denier. The diameter of the fibres of the non woven fabric is a property which influences different properties of the non woven fabric, beyond the mechanical resistance properties and it has a great importance in the functioning of the non woven fabrics. Among others, some of the aforementioned properties are the softness (at less denier, the fibres are finer, and the textile is softer to the touch) , the permeability (the finer the fibres, the higher the cover the textile has, therefore the permeability is lower) , the visual appearance of the textile (by the same concept of cover, the finer the fibres, the better the aspect the textile acquires), the dryness of the textiles (fluids have a tendency to be retained in the intersections of the fibres due to the surface tension effect (the finer the fibres are, the greater the number of intersections there are in the fibres) , and the resistance to a column of water (to significantly improve this property of non woven fabrics such as meltblown with fibre diameters of less than 5 microns are normally used, and therefore with a higher cover) . The most suitable combination of diameters is selected depending on each application. Due to the influence that the diameters of the fibres have on the properties of non woven fabrics, in the case of multilayered fabrics layers with different deniers in each layer can be combined to selectively improve any of the aforementioned properties.

In a particular embodiment, in which the non woven fabric is used to manufacture the top sheet of absorbent hygiene products, such as nappies (diapers) , sanitary towels, cleaning cloths, etc., the filaments are chosen in such a way that they will have between approximately 1 and 2.5 denier. To manufacture these products, the properties of appearance and softness need to be enhanced.

In another particular embodiment, in which the non woven fabric is used to manufacture the top sheet of absorbent sanitary products, such as surgical sheets, the filaments are chosen in such a way that they will have between approximately 1.0 and 2.5 denier.

In another particular embodiment, in which the non woven fabric is used to manufacture thermal blankets for agriculture, the filaments are chosen in such a way that they will have between approximately 2.0 and 4.0 denier. A higher denier than hygiene and sanitary products in this case because it is required to increase the property of permeability to the air and the appearance and softness properties are less important.

In another particular embodiment, in which the non woven fabric is used to manufacture membranes for packaging, the filaments are chosen in such a way that they will have between approximately 1.5 and 4.0 denier.

This composition which includes a polyolefin also preferably comprises an additive or a combination of additives which increase the hydrophobic properties of the polyolefin. Suitable additives that can be used include, fluoropolymers, siloxanes, such as polymethylsiloxanes or guerbet esters and their mixtures. An example of a useful commercial fluoropolymer in the present invention is @2spin PP-352, marketed by DEVAN CHEMICALS. In general the guerbet esters are substituted alcohols with an alkyl group in position 2. Examples of guerbet esters include, for illustration only, 2- butyloctanol, 2-pentyinonenol, pentyinonenol, 2- hexyldecanol, 2-nonyltridecanol, 2-decyltetradecanol, and similar.

An example of a commercial product of siloxane is NUDRY® 470 from the company, GE Bayer Silicones.

The quantity of hydrophobic agent which can be incorporated into the polyolefin to form a non woven fabric according to the present invention can vary depending on the particular application and the desired result. For the majority of applications, the hydrophobic agent is present in the polymer in a proportion which varies between approximately 0.1% and 10% by weight. In a particular embodiment, the hydrophobic agent is in the polymer in a proportion which varies between approximately 0.1% and 5% by weight, and in another particular embodiment, the hydrophobic agent is approximately between 0.5% and approximately 3% by weight. In general, the hydrophobic agent can be combined with any polyolefin. In a preferred embodiment, the aforementioned polyolefin is polypropylene.

This proportion of additives causes a negligible variation in the density of the composition as regards the density of the polyolefin, preferably polypropylene. It can be stated, therefore, without any mistake, that the density of the composition is practically the same as that of the polyolefin, preferably polypropylene.

The fact of adding an additive or combination of additives that increase the hydrophobic properties of the polypropylene gives the resulting composition certain advantages over polypropylene without an additive. For example, it has been observed that non woven fabrics which comprise at least one hydrophobic layer in which additive has been added which provides hydrophobic properties to the polyolefin, exhibit an outstanding water repellent property. For example, it has been observed that when a fluid is deposited over a hydrophobic layer, the hydrophobic fibres tend to repel it. However, due to the hydrophilic filaments of the layer or layers situated below, the fluid retained by the hydrophobic layer comes into contact with some of these hydrophilic fibres, favouring the transfer of the fluid. When the fluid tries to move in the opposite direction, the hydrophobic filaments prevent it, due to not having hydrophilic fibres on the other side to attract the fluid.

This additive which confers hydrophobic properties to the polyolefin is preferably applied to the polyolefin in a molten mass, but its application can also be carried out topically.

As has already been mentioned, the layers (3, 3' ) of Figure 1 are formed from filaments of a mixture of a polyolefin and an additive or combination of additives (described previously) that give the polyolefin hydrophilic properties. This mixture is obtained hot, in the form of a molten mass, and comprises a proportion of polyolefin which varies between approximately 90% and 99.9% by weight and a proportion of an additive or combination of additives which vary between approximately 0.1% and 10%. This proportion of additives causes a negligible variation in the density of the mixture as regards the density of the polyolefin, preferably polypropylene. It can be stated, therefore, without any mistake, that the density of the mixture is practically the same as that of the polyolefin. Thus the filaments of the mixture from which the hydrophilic layers are formed

(3, 3' ) of Figure 1 are extruded in such a way that they have a denier of between approximately 1.0 and 4.0. Similarly in the case of the hydrophobic filaments, one denier range or another is chosen depending on the application for which the non woven fabric is used.

Both the hydrophilic and hydrophobic filaments of the present invention are extruded in such a way that they have a section preferably circular, but the aforementioned circular section not being limiting, but can be an oval section or any other form, obtained by the appropriate design of the geometry of the capillaries of the threads used on coming out of the extrusion heads.

On the other hand, Figure 9 illustrates a cross section of a hydrophilic filament extruded by a head, according to a possible embodiment of the present invention. This hydrophilic filament is made up of a single part (8) which comprises the mixture of the polyolefin and the additive or combination of hydrophilic producing additives.

Figure 10 illustrates the cross section of a hydrophilic filament extruded by a head, according to another possible embodiment of the present invention. In this embodiment, the filaments which form the hydrophilic layer or layers of the non woven fabric comprise two different parts (8' , 9) , therefore the filament has been called a "bicomponent". The internal part (9) of the aforementioned filaments is limited by a circular section, with a diameter less than the total diameter of the section of the filament. This internal part is formed by the polyolefin, preferably, polypropylene, without mixing with any hydrophilic producing additive. The other part of the filament which can be called the external part (8'), comprises a section in a ring, which surrounds the already described internal part (9). Said external part (8') comprises the mixture of said polyolefin and said additive or combination of hydrophilic producing additives. Both parts (8', 9) form a single filament, which is extruded in one of the extrusion heads which are described later. The extrusion heads are chosen that enable filaments to be obtained with an internal part (9) formed by a polyolefin and an external part (8' ) formed by the aforementioned mixture, since so that the filaments may acquire hydrophilic properties it is sufficient that the hydrophilic property giving additive or combination of additives impregnate the external part of the filament. These hydrophilic property giving additives or combination of additives increase the price of the non woven fabric, as well as the procedure for obtaining it. Therefore, the fact of limiting the hydrophilic part to the external part (8' ) of the filament gives an additional advantage as regards the hydrophilic filament formed by a single part (8) which comprises the aforementioned mixture. Although Figure 10 has given an example of a "bicomponent" filament, the present embodiment of the invention is not limited to the aforementioned "bicomponent" filaments, but which also comprises a more general case in which the filaments are "multicomponents" .

The non woven fabric (1) of the present invention allows for different configurations of the different layers of which they comprise, with the characteristic that, in all the possible embodiments of the present invention, the layer situated at one end of the non woven fabric (1) is a hydrophobic layer (2) and the layer situated at the other end of the non woven fabric (1) is a hydrophilic layer (3).

This configuration has been chosen because it has been observed that the fact of placing a hydrophobic layer in contact with the skin of the user instead of a hydrophilic layer, enormously improves the performance of the final product (nappy (diaper) , sanitary towel or other hygiene or sanitary product) . This fact is particularly relevant in the applications of non woven fabrics of the present invention associated with health and hygiene products, and in that case which requires contact between the aforementioned non woven fabric and the skin or body of the user.

This can also be seen in Figures 2, 3 and 4, which represent other possible embodiments of the non woven fabric (1) of the present invention. Thus, Figure 2 shows a non woven fabric of asymmetric continuous filaments (1) in which the layers (2, 2' ) are hydrophobic, formed from the filaments of a polyolefin. These filaments are obtained by extrusion of a molten mass of a composition which comprises a polyolefin, or preferably a polypropylene, as is indicated later in this description.

This composition can also include an additive or a combination of additives which increases the hydrophobic properties of the polypropylene. For its part, the layer (3) of Figure 2 represents a hydrophilic layer, that is, it allows the passage of the fluids. Like the hydrophilic layers (3, 3') of Figure 1, the layer (3) of Figure 2 is formed by the filaments of a mixture of a polyolefin, which preferably is a polypropylene, and an additive or a combination of additives which increases the hydrophilic properties of the polypropylene. As can be seen in Figure 2, at one of the ends of the non woven fabric (1) a hydrophobic layer (2) is situated and at the other end of the non woven fabric (1) a hydrophilic layer is situated (3).

Figure 3 represents a minimal configuration of the asymmetric continuous filaments of the non woven fabric

(1) of the present invention, in which a single hydrophobic layer (2) and a single hydrophilic layer (3) are included.

Finally, Figure 4 represents another possible embodiment of the present invention, in which asymmetric continuous filaments of the non woven fabric (1) of the present invention comprises two hydrophobic layers (2, 2') and two hydrophilic layers (3, 3')- As can be seen in Figure 4, at one of the ends of the non woven fabric (1) a hydrophobic layer (2) is situated and at the other end of the non woven fabric (1) a hydrophilic layer is situated (3) .

As in the case of Figure 1, the filaments of a composition of which comprises a polyolefin, preferably of a polypropylene, and which preferably also comprises an additive or a combination of additives which improves its hydrophobic properties, as well as those of a mixture of the polyolefin, preferably polypropylene, with an additive or a combination of additives, from which the different hydrophobic (2, 2') and hydrophilic (3, 3') layers, respectively of Figures 2, 3 and 4, are extruded in such a way that they have a denier of between 1.0 and

4.0. That is to say, a filament of 9000 m weighing between 1.0 and 4.0 grams.

Also, in any of the four cases given as examples, the density of the non woven fabric (1) varies between 8 and 90 gr/m². One range or other of denier is chosen depending on the application in which the non woven fabric is used.

In one particular embodiment, in which the non woven fabric is used to manufacture the upper layer or top sheet of absorbent hygiene products, such as nappies

(diapers) , sanitary towels, etc or cleaning products such as cloths, the non woven fabric is manufactured with a density of approximately between 8 and 30 gr/m², preferably between 12 and 18 gr/m². In another particular embodiment, in which the non woven fabric is used to manufacture the upper layer or top sheet of absorbent sanitary products, such as surgical sheets, the non woven fabric is manufactured with a density of approximately between 15 and 40 gr/m².

In another particular embodiment, in which the non woven fabric is used to manufacture thermal blankets for agriculture, the non woven fabric is manufactured with a density of approximately between 12 and 30 gr/m².

In another particular embodiment, in which the non woven fabric is used to manufacture membranes for packaging, the non woven fabric is manufactured with a density of approximately between 15 and 90 gr/m².

The machines that extrude the filaments of the polyolefin can have one or more heads. Depending on the number of heads and the density which is desired to be obtained in the resulting non woven fabric, the quantity of polyolefin used is distributed in one form or another. That is to say, if only one head is available, all the polyolefin is deposited in that head. If two heads are available, normally 50% of the polyolefin is deposited in each head, although it can also be worked on with decompensated heads (for example: 60% in one head and 40% in the other) depending on the final product which it is desired to be obtained. This directly affects the speed of the conveyor belt: the higher the number of heads, the higher is the speed at which the extruded filaments can be deposited of the aforementioned conveyor belt.

The expert on the subject will appreciate that these four possible embodiments are not unique, but their objective is to give examples of the construction of an asymmetric continuous filament non woven fabric (1) with several hydrophilic layers and several hydrophobic layers, in which at one of its ends is situated a hydrophobic layer (2) and at the other end is situated a hydrophilic layer (3) .

The described non woven fabric (1) can be a spunbond non woven fabric or a non woven fabric formed by a combination of several spunbond non woven fabrics. It will be one type or another of non woven fabric depending on the procedure to be used for its manufacture.

An upper layer or top sheet is also the object of the present invention which comprises the non woven fabric (1) of the present invention, as well as absorbent hygiene and sanitary products, such as nappies (diapers) for babies, pads for adult incontinence, sanitary towels for female hygiene, or surgical towels which comprise said upper layer or top sheet. It is known that the upper layer or top sheet of absorbent products, such as nappies (diapers) or sanitary towels, is designed in such a way that the part left in contact with the skin of the user remains dry, but allows the passage of the fluids to other parts of the absorbent product of which it is a part. The multilayered non woven fabric of the present invention achieves this objective due to its asymmetric property, allowing the passage of fluids in one direction but preventing their passage in the opposite direction. More specifically, the layer of the non woven fabric that forms the top sheet of the absorbent hygiene or sanitary products of the present invention that are destined to come into contact with the skin during the use of the product is hydrophobic. Also, this non woven fabric is capable of absorbing repeated and continually several times its weight in water, apart from having good antistatic properties.

Another object of the present invention is a cloth or similar cleaning product which comprises a top sheet manufactured from the non woven fabric of the present invention. This top sheet is what comes into contact with the surface it is desired to dry. Thus, the hydrophilic

(passage of fluid) and absorption and fluid retention properties, and the hydrophobia of the top sheet to dry the surface are taken advantage of.

Another object of the present invention is a thermal blanket, specifically destined for the agriculture sector, which protects the cultivations from the cold to advance the planting dates and shorten the development cycles of the cultivations. The non woven fabric which forms a part of this thermal blanket enables the water to be absorbed and retained by the water absorption layer, thus allowing a higher humidity to be maintained below the thermal blanket.

Another object of the present invention is a membrane for packaging in applications where it important that the external surface remains dry, for example in certain products which are stored at low temperatures and on which water tends to condense. The non woven fabric which forms part of this membrane enables the water to be absorbed and retained by the water absorption layer.

Below, and with reference to Figures 5 and 8, the different ways of carrying out the procedure to obtain the asymmetric continuous filaments of the non woven fabric of the present invention are described. A possible method of manufacture is the following:

The first step consists of the extrusion of the product of the invention in molten mass form. As has already been indicated, the product of the invention is a composition which comprises a polyolefin. Preferably, the polyolefin is a polypropylene. The aforementioned composition can also include an additive or combination of additives, from those indicated previously throughout this description, which increases the hydrophobic properties of the polyolefin.

As Figure 5 indicates, the molten mass of the aforementioned composition which comprises at least a polyolefin is extruded in one or several heads (10, 10' ) . The outlet of the head or heads (10, 10'), therefore, provides one or more groups of hot hydrophobic filaments

(4, 4') of the composition which comprises an extruded polyolefin. Preferably, this composition also contains an additive or combination of additives of those which have been indicated previously throughout this description, which increase the hydrophobic properties of the polyolefin. The hot hydrophobic filaments (4, 4') extruded by each head (10, 10') are stretched and cooled by passing through stretching zones with air.

On the other hand, in another group of heads (11,

11' ) a mixture is extruded in a form of a molten mass formed by an polyolefin and an additive or combination of additives of those indicated previously, which provide the polyolefin with hydrophilic properties.

When a polyolefin and an additive or a combination of additives is mixed in a molten mass, for the mixture to be subsequently extruded, the extruded filaments of the aforementioned mixture do not normally acquire the hydrophilic behaviour until after a few hours, since the incorporated additive has to act on the surface of the aforementioned filaments, as it requires time to migrate to the aforementioned surface.

Therefore, in the context of the present invention, it is understood by "hydrophilic filaments" those formed from a mixture comprising of at least an additive destined to confer hydrophilic properties to the aforementioned filaments, although at the time that the aforementioned filaments are extruded, stretched and cooled, they can still not be hydrophilic.

As has already been described the aforementioned mixture is obtained in heat. The outlet of -the aforementioned head or heads 11, 11' ) provide, therefore, one or more groups of hot hydrophilic filaments (5, 5' ) extruded from the mixture in molten mass form. The hydrophilic filaments (5, 5' ) of the mixture extruded by each head (11, 11') are stretched and cooled by passing through stretching zones with air.

The heads (10, 10', 11, 11') are situated along the length of a conveyor belt (12). The order of the heads (10, 10', 11, 11') makes no difference. This means that the head situated at the beginning of the conveyor belt

(12) can be that which provides a group of hydrophobic filaments (head (10, 10') or it can be that which provides a group of hydrophilic filaments (head (11, 11').

Next, a first group of stretched and cooled filaments (6) of any of the different groups of filaments 4, 4', 5, 5') is deposited on the conveyor belt (12), that is to say, a group of hydrophobic filaments (4, 4') or a group of hydrophilic filaments (5, 5') is deposited. One group or another of filaments will be deposited depending on which head (10, 10', 11, 11') is situated at the beginning of the conveyor belt (12). Next a second group

(4') of stretched and cooled filaments (5, 5') are deposited over that first group of hydrophobic or hydrophilic filaments (6) already deposited on the conveyor belt (12) . The rest of the groups of filaments (5, 5') extruded by the rest of the heads (11, 11') also continue being deposited over the groups of already deposited filaments.

The deposit order of the different groups of filaments makes no difference, except in one aspect: if a group of hydrophobic filaments has been deposited first, a group of hydrophilic filaments is deposited last. In the same way, if a group of hydrophilic filaments has been deposited first, a group of hydrophobic filaments is deposited last. Obviously, the groups of filaments continue being deposited on the conveyor belt (12) in an orderly manner, following the order which the heads (10, 10' , 11, 11' ) occupy over the aforementioned conveyor belt (12).

The different groups of filaments produced by the heads (10, 10' , 11, 11' ) and deposited over the conveyor belt (12) are capable of becoming, once a binding a consolidation process (13) which we describe below is carried out, an asymmetric multilayered spunbond non woven fabric (18) .

The expert on the subject will understand that it is possible to incorporate a greater number of heads (10, 10', 11, 11') which would provide more hydrophobic and hydrophilic filament groups.

The binding and consolidation stage (13) of the different groups of deposited (6, 6', 7, 7') one next to another can be carried out by several techniques. One of them is using calendering (13) of the assembly formed by all the filament groups (6, 6', 7, 7'), at a high temperatures and pressures. As an alternative, the water jet technique can be used. A combination of both techniques can also be used. By whatever means, an asymmetric multilayered spunbond non woven fabric (18) is obtained formed by all the layers deposited. After the caledaring, the resulting multilayered spunbond non woven fabric is spun. Figure 5 illustrates the case in which the aforementioned binding and consolidation is carried out using calendering (13) .

Preferably, binding by calendering is chosen, which is carried out on a machine similar to that illustrated in Figure 6. As can be seen the calender machine (13) comprises an etched roller (35) and another smooth one (36). The etched roller(35) is very thin. The different groups of filaments deposited on the conveyor belt (12) pass between the two rollers (35, 36) and are subjected to a high temperature and pressure in such a way that the product on exiting the process is a non woven fabric

(18). The temperature and pressure values are the conventional ones for these types of calendering processes. In this process, of the two layers at the two ends, the hydrophilic filaments layer is that which preferably, on passing through the machinery, comes into contact with the etched roller (35), while the hydrophobic filaments layer comes into contact with the smooth roller (36). In this solution preferably, the etch of the etched roller (35) only affects the hydrophilic layer.

The non woven fabric (18) obtained from any of the embodiments of this procedure includes, at one of its ends, a layer of hydrophobic filaments, and at its opposite end, a layer of hydrophilic filaments. To achieve this characteristic, the heads (10, 10', 11, 11') are designed in such a way that the head at one of the ends deposits hydrophilic filaments and the head at the other end deposits hydrophobic filaments. It makes no difference if it is the first or the last that deposits the hydrophilic or hydrophobic filaments.

Likewise, the procedure of the present invention allows asymmetric multilayered spunbond non woven fabrics to be produced with different possibilities for the distribution of the intermediate layers. Thus, the intermediate layers can be all hydrophilic, all hydrophobic, or a combination of hydrophilic layers and hydrophobic layers. In this latter case, all the hydrophilic filament groups can be deposited in succession and all the hydrophobic groups can be deposited in succession, or they can be alternated.

Also, the hydrophilic filaments can be or are formed of a single part which comprises said polyolefin mixture and additive (as illustrated in Figure 9) , can be or are formed of two parts, one internal (9) formed by the polyolefin, and an external (8') formed by said mixture (as illustrated in Figure 10) .

An alternative method of manufacturing a non woven fabric from asymmetric continuous filaments according to the present invention is illustrated in Figures 7 and and is the following:

The first step consists of the extrusion of a molten mass of a composition which comprises a polyolefin, preferably a polypropylene into filaments, in several heads (20, 20' ) . The aforementioned composition can also include an additive or combination of additives, from those indicated previously throughout this description, which increases the hydrophobic properties of the polyolefin. Each one of the heads (20, 20' ) provides a group of hot hydrophobic filaments (14, 14') of the extruded polyolefin, which is stretched and cooled on passing through stretching zones with air.

As in the previous case, preferably, this composition also includes an additive or combination of additives, which increases the hydrophobic properties of the polyolefin.

Next, the filaments extruded in the different heads

(20, 20'), are deposited on a conveyor belt (22), in such a way that the conveyor belt (22) accumulates one or more groups of hydrophobic filaments (16, 16' ) , deposited upon one another.

Next, once all the layers of hydrophobic filaments (16, 16') are deposited on the conveyor belt (22) they are calendered (23) at a high temperature and pressure, in such a way that a hydrophobic spunbond non woven fabric (24) formed by all the deposited layers is obtained. On the other hand, on proceeding to manufacture a hydrophilic non woven fabric (34), there are two possibilities:

The first possibility, illustrated in Figure 7, consists of obtaining hydrophilic filaments using the mixture in a molten mass of a polyolefin, preferably polypropylene, and an additive or combination of additives that confer hydrophilic properties to the polyolefin. This possibility is carried out in a similar way to that described in the previous case: A mixture in a molten mass form of the polyolefin, preferably polypropylene and an additive or combination of additives is extruded into filaments. As explained earlier, the additive confers hydrophilic properties to the polyolefin, preferably polypropylene. This extrusion process of the aforementioned mixture is carried out in several heads (21, 21'). Each one of these heads (21, 21') provides a group of hot hydrophilic filaments (15, 15' ) of the extruded mixture, which are stretched and cooled by passing through stretching zones with air.

As has been indicated previously, the hydrophilic elements can be or are formed by a single part which comprises said mixture of polyolefin and additive (as illustrated in Figure 9) , or can be or are formed by two parts, an internal part (9) formed by the polyolefin, and external part (8' ) formed by said mixture (as illustrated in Figure 10) .

Next, the filaments extruded in the different heads (21, 21') are deposited on a conveyor belt (32), in such a way that the conveyor belt (32) accumulates one or more groups of hydrophilic filaments (17, 17'). Next, once all the filament groups (17, 17') are deposited on the conveyor belt (32) they proceed to be calendered (33) at a high temperature and pressure, in such a way that a hydrophilic spunbond non woven fabric (34) formed by all the deposited layers is obtained.

The second possibility, illustrated in Figure 8, consists of providing the hydrophilic properties by traditional topical or surface methods instead of using the additive in the mixture in molten mass.

As indicated in Figure 8, the molten mass of a polyolefin, preferably a polypropylene, is extruded in one or several heads (29, 29'). The outlet of the head or heads, therefore, provides one or more hot hydrophobic filament groups (18, 18') of the extruded polyolefin. The hot hydrophobic filaments (18, 18') extruded from each head (29, 29' ) are stretched and cooled by passing through stretching zones with air.

Next, the filaments extruded in the different heads

(29, 29') are deposited on a conveyor belt (29, 29'), in such a way that the conveyor belt (42) accumulates one or more groups of hydrophobic filaments (19, 19'), deposited one upon another.

Next, once all the filament groups (19, 19') are deposited on the conveyor belt (42) they proceed to be calendered (33) at a high temperature and pressure, in such a way that a hydrophobic spunbond non woven fabric

(37) formed by all the deposited layers is obtained.

Next, the additive that confers hydrophilic properties to this hydrophobic non woven fabric is applied. This application is carried out, preferably, but not limiting, using a kiss roll rotary roller (38) which is partially submerged in an aqueous solution that contains the additive or combination of surfactants or agents from those indicated previously in this description that confer hydrophilic properties, and is also in contact with the non woven fabric (37) , to which the aforementioned additive is transferred. After the water is eliminated and the "adhered" additive remains on the surface of the fibres which from the non woven fabric (34), changing its surface tension. As an alternative to the rotary kiss roller, the application using a spray or surface activator can be used using plasma technology.

In the embodiment of Figure 7, as well as that in Figure 8, once the two non woven fabrics, one hydrophobic (24) and another hydrophilic (34), manufactured separately are obtained, they are spun. This spinning stage is illustrated in Figures 7 and 8. After the spinning of the aforementioned non woven fabrics (24, 34), the two textiles from the bobbins are bound and consolidated (25) both forming an asymmetric multilayered non woven fabric (28) . This non woven fabric is the combination of the two non woven fabrics (24, 34) . The binding and consolidation stage (25) of both non woven fabrics (24, 34) can be carried out using several techniques: by means of calendering at high temperatures and pressures, using the water jet technique, using sheetting by ultrasound or by any other conventional type of sheetting, using low fusion point fibres, or using a combination of more than one of these techniques. For example, binding and consolidation by water jet is based on the interweaving of the filaments by using a multitude of very fine jets of water. To create this effect, the water is uniformly distributed at a high pressure along the width of the layer of filaments that requires binding, in a so-called jet head, where it is forced through the holes towards the filaments. The jets of water thus created make contact with the filaments at high speed, and in the process condense and interweave the filaments. Anyway, an asymmetric continuous non woven fabric of multilayered filaments is obtained. After binding, the resulting non woven fabric (28) is spun. Figures 7 and 8 illustrate the case in which the aforementioned binding and consolidation is carried using calendering (25) .

The non woven fabric (28) obtained from this embodiment comprises, at one of its ends, a layer of hydrophobic filaments, and at its opposite end, a layer of hydrophilic filaments. Also, unlike the previous procedure, in this case all the layers of hydrophilic filaments are consecutive, and all the layers of hydrophobic filaments are also consecutive.

The density of the multilayered non woven fabric obtained using this second procedure is similar to the multilayered non woven fabric obtained using the previous procedure, although, given the need to manipulate the textiles, it will be between approximately 15 and 90 g/m², depending on the application for which it is destined.

The non woven fabric (18, 28) obtained by any of the described procedures is asymmetric, that is to say, it favours the passage of fluids and liquids in one direction, but not in the opposite direction. On a fluid being deposited over the hydrophobic layer, the hydrophobic fibres which form it tend to repel the fluid and therefore it cannot pass through. However, as one or more hydrophilic layers are next, the fluid retained by the hydrophobic layer comes into contact with some hydrophilic filaments of the lower layers, which allows the aforementioned to be transferred. When the fluid tries to move in the opposite direction, as there is no hydrophilic layer on the other side of the hydrophobic layer, the hydrophobic layer creates a barrier and does not allow the passage of the fluid. This is illustrated in Figure 11. The non woven fabric also has the capacity to absorb several times its weight in water. Also, the appearance of the non woven fabric is that of a single material .

In any of the embodiments of the procedure used to obtain a non woven fabric, the polyolefin used is preferably a polypropylene. Also, the additive or combination of additives used to give the polyolefin, preferably polypropylene, hydrophilic properties, is chosen among selected surfactants of the group formed by ethoxylated aliphatic alcohols, ethoxylated phenol esters, fatty acid esters, non-ionic surfactants derived from amines, non-ionic surfactants derived from amides, copolymers of ethylene oxide and propylene oxide, alkyl sulphates, alkyl ester sulphates, sulphated alkane- amides, diglyceride sulphates, sulphonated alpha-olefins, sulphocarboxylic anionic surfactants, cationic linear alkylamines, propionic amino acids, propionic imido acids, betaines, taurine sulphobetaines, silicone surfactants and their mixtures. In a particular embodiment an aforementioned additive is an ethoxylated aliphatic alcohol of formula:

CH₃CH₂ (CH₂CHz)₃CH₂CH₂ (OCH₂CH₂) _bOH, where "a" is an integer number between 9 and 25 and "b" is an integer number between 1 and 10. Alternatively, the additive, Silwet® L-7608 of the GE Bayer Silicones company applied at 1.0% is chosen.

Finally, the installation or system to carry out the procedures described here is also an objective of the present invention.

Claims

1.- Non woven fabric of asymmetric continuous filaments (1) that comprises: - one or more hydrophobic layers (2, 2' ) of filaments that comprise a polyolefin;

- one or more hydrophilic layers (3, 3') of filaments that comprise a mixture of a polyolefin and an additive or combination of additives; characterised in that the layer of one of the ends of the non woven fabric (1) is hydrophobic (2) and the layer at the other end of the non woven fabric (1) is hydrophilic (3) , and characterised in that said additive or combination of additives provides the polyolefin with both hydrophilic and fluid absorption properties.

2.- Non woven fabric (1) according to claim 1, characterised by having a density between 8 and 90 gr/m².

3.- Non woven fabric (1) according to any of the preceding claims, characterised in that the layers of hydrophobic filaments (2, 2' ) also comprise an additive or combination of additives which increase the hydrophobic properties of the polyolefin.

4.- Non woven fabric (1) according to claim 3, characterised in that the layers of hydrophobic filaments (2, 2') comprise said additive or combination of additives in a proportion which varies between approximately 0.1% and 10% by weight, preferably between 0.5% and 3% by weight.

5.- Non woven fabric (1) according to either of claims 3 or 4, characterised in that said additive or combination of additives that increases the hydrophobic properties of the polyolefin are chosen from fluoropolymers, siloxanes, guerbet esters and their mixtures.

6.- Non woven fabric (1) according to claim 5, where the siloxane is chosen from among polymethylsiloxanes .

7.- Non woven fabric (1) according to any of the preceding claims, characterised in that hydrophobic layers (2, 2') as well as the hydrophilic layers (3, 3') comprise filaments with a diameter that varies between approximately 1.0 and 4.0 denier.

8.- Non woven fabric (1) according to claim 7, where the diameter of said filaments vary between approximately 1.0 and 2.5 denier.

9.- Non woven fabric (1) according to any of the preceding claims, characterised in that the polyolefin used is a polypropylene.

10.- Non woven fabric (1) according to any of the preceding claims, characterised in that the filaments of the hydrophilic layer or layers (3, 3' ) comprise a mixture which includes a polyolefin proportion which varies between approximately 90% and 99% by weight and an additive or combination of additives proportion which varies between approximately 0.1% and 10% by weight.

11.- Non woven fabric (1) according to any of the preceding claims, characterised in that an additive or combination of additives of the hydrophilic layers (3, 3' ) are chosen from among surfactants of the group formed by, ethoxylated aliphatic alcohols, ethoxylated phenol esters, fatty acid esters, non-ionic surfactants derived from amines, non-ionic surfactants derived from amides, copolymers of ethylene oxide and propylene oxide, alkyl sulphates, alkyl ester sulphates, sulphated alkane- amides, diglyceride sulphates, sulphonated alpha-olefins, sulphocarboxylic anionic surfactants, cationic linear alkylamines, propionic amino acids, propionic imido acids, betaines, taurine sulphobetaines, silicone surfactants and their mixtures.

12.- Non woven fabric (1) according to claim 11, characterised in that the additive or combination of additives of the hydrophilic layers (3, 3') comprises a compound of formula:

CH₃CH₂ (CH₂CH₂) _aCH₂CH₂ (OCH₂CH₂) _bOH, where "a" is an integer number between 9 and 25 and "b" is an integer number between 1 and 10.

13.- Non woven fabric (1) according to any of the preceding claims, characterised by being capable of absorbing a quantity of fluid up to eight times its weight .

14.- Non woven fabric (1) according to any of the preceding claims, characterised in that the filaments which form the hydrophilic layer or layers (3, 3' ) comprise at least two different parts: a circular section internal nucleus formed by the polyolefin and an external shell in a ring section which comprises the mixture of said polyolefin and said hydrophilic property giving additive or combination of additives.

15.- Non woven fabric (1) according to any of the preceding claims, characterised by being a spunbond non woven fabric.

16.- Non woven fabric (1) according to any of the claims 1 to 14, characterised by being the combination of several spunbond non woven fabrics.

17.- A top sheet for an absorbent product which comprises a non woven fabric (1) according to any of the claims 1 to 16.

18.- Absorbent hygiene product which is chosen among nappies (diapers) for babies, incontinence pads for adults and sanitary towels for feminine hygiene characterised by comprising a top sheet according to claim 17.

19,- Absorbent sanitary or cleaning product which is chosen from between surgical towels and cleaning cloths characterised by comprising a top sheet according to claim 17.

20.- Thermal blanket to protect agricultural cultivations which comprises a non woven fabric (1) according to any of the claims 1 to 16.

21.- Membrane for packaging which comprises a non woven fabric (1) according to any of the claims 1 to 16.

22.- Absorbent hygiene or sanitary product which comprises a top sheet formed by an asymmetric non woven fabric with one or more hydrophobic layers (2, 2' ) of filaments which comprise a polyolefin and one or more hydrophilic layers (3, 3' ) of filaments which comprise a mixture of a polyolefin an additive or combination of additives, characterised in that the layer of said non woven fabric destined to come into contact with the skin during the use of the product is hydrophobic.

23.- Absorbent hygiene or sanitary product according to claim 22, characterised in that said additive or combination of additives provide the polyolefin with hydrophilic properties as well as fluid absorption properties.

24.- Absorbent hygiene or sanitary product according to claim 22 or 23, characterised by the fact the non woven fabric has a density of between 8 and 40 gr/m².

25.- Absorbent hygiene or sanitary product according to claims 22 to 24, characterised in that the hydrophobic layers (2, 2') of the top sheet of the non woven fabric also comprise an additive or combination of additives which increases the hydrophobic properties of the polyolefin.

26.- Absorbent hygiene or sanitary product according to claim 25, characterised by the fact that said hydrophobic layers (2, 2') comprise an additive or combination of additives in a proportion which varies between approximately 0.1% and 10% by weight, preferably between 0.5% and 3% by weight.

27.- Absorbent hygiene or sanitary product according to either of the claims 25 or 26, characterised in that top sheet additive or combination of additives that increase the hydrophobic properties of the polyolefin are chosen from among fluoropolymers, siloxanes, guerbet esters and their mixtures.

28.- Absorbent hygiene or sanitary product according to claim 27, where siloxane is chosen between polymethylsiloxanes .

29.- Absorbent hygiene or sanitary product according to any of the claims 22 to 28, characterised in that the hydrophobic layers (2, 2' ) as well as the hydrophilic layers (3, 3') comprise filaments of which the diameter varies between approximately 1.0 and 2.5 denier.

30.- Absorbent hygiene or sanitary product according to any of the claims 22 to 29, characterised in that the polyolefin used is a polypropylene.

31.- Absorbent hygiene or sanitary product according to any of the claims 22 to 30, characterised in that the filaments of the hydrophilic layer or layers (3, 3' ) comprise a mixture that comprises a polyolefin proportion that varies between approximately 90% and 99% by weight and an additive or combination of additives proportion that varies between approximately 0.1% and 10% by weight.

32.- Absorbent hygiene or sanitary product according to any of the claims 22 to 31, characterised in that the additive or combination of additives of the hydrophilic layers (3, 3' ) are chosen between surfactants selected from the group formed by ethoxylated aliphatic alcohols, ethoxylated phenol esters, fatty acid esters, non-ionic surfactants derived from amines, non-ionic surfactants derived from amides, copolymers of ethylene oxide and propylene oxide, alkyl sulphates, alkyl ester sulphates, sulphated alkane-amides, diglyceride sulphates, sulphonated alpha-olefins, sulphocarboxylic anionic surfactants, cationic linear alkylamines, propionic amino acids, propionic imido acids, betaines, taurine sulphobetaines, silicone surfactants and their mixtures.

33.- Absorbent hygiene or sanitary product according to claim 32, characterised in that the additive or combination of additives of the hydrophilic layers of the top sheet of the non woven fabric comprises a compound of formula:

CH₃CH₂ (CH₂CH₂)_SCH₂CH₂ (OCH₂CH₂) _bOH, where "a" is an integer number between 9 and 25 and "b" is an integer number between 1 and 10.

34.- Absorbent hygiene or sanitary product according to any of the claims 22 to 33, characterised in that the asymmetric non woven fabric included in the top sheet is capable of absorbing a quantity of fluid up to eight times its weight.

35.- Absorbent hygiene or sanitary product according to any of the claims 22 to 34, characterised in that the filaments which form the hydrophilic layer or layers (3, 3' ) of the non woven fabric comprise at least two different parts: a circular section internal nucleus formed by the polyolefin and an external shell in a ring section which comprise the mixture of said polyolefin and said hydrophilic property giving additive or combination of additives.

36.- Absorbent hygiene or sanitary product according to any of the claims 22 to 35, characterised in that the non woven fabric is a spunbond non woven fabric.

37.- Absorbent hygiene or sanitary product according to any of the claims 22 to 35, characterised in that the non woven fabric is a combination of several spunbond the non woven fabrics.

38.- A method for obtaining an asymmetric non woven fabric which comprises the following stages: - obtaining one or more groups of hydrophobic filaments (4, 4') by the extrusion of a composition which comprises a polyolefin in one or more heads (10, 10'); stretching and cooling said groups of hydrophobic filaments (4, 4' ) ; characterised by the stages of:

- mixing a polyolefin in a mass with an additive or combination of additives that provide the polyolefin with hydrophilic properties;

- obtaining one or more groups of hydrophilic filaments (5, 5' ) by the extrusion of said mixture in one or more heads (11, 11'); stretching and cooling said group of hydrophilic filaments (5, 5' ) ;

- depositing, (6, 6', 7, 7') on a conveyor belt (12), in an ordered manner according to the order the heads (10,

10' 11, 11') occupy as regards said conveyor belt (12), the different groups of hydrophobic (4, 4') and hydrophilic (5, 5' ) filaments, where if the first of the heads produces hydrophobic filaments, the last of the heads produces hydrophilic filaments and vice versa;

- binding and consolidating (13) the assembly formed by the different groups of filaments (6, 6', 7, 7') deposited on the conveyor belt (12), in such a way that an asymmetric non woven fabric is obtained (18).

39.- A method for obtaining an asymmetric non woven fabric characterised by the following stages:

- obtaining one or more groups of hydrophobic filaments (14, 14') by the extrusion of a composition which comprises a polyolefin in one or more heads (20, 20' ) ; stretching and cooling said groups of hydrophobic filaments (14, 14');

- depositing, (16, 16') on a conveyor belt (22), the different groups of hydrophobic filaments (14, 14') stretched and cooled in the previous stage;

- calendering (23) the assembly formed by the different groups of hydrophobic filaments (16, 16') to a temperature and pressure increased in such a way that a hydrophobic spunbond non woven fabric is obtained (24);

- obtaining a hydrophilic spunbond non woven fabric (34) formed by at least one layer of hydrophilic filaments;

- binding and consolidating (25) a hydrophobic spunbond non woven fabric (24) with a hydrophilic spunbond non woven fabric (34) in such a way that an asymmetric non woven fabric (28) is obtained.

40.- A method according to claim 39, where the stage of obtaining a hydrophilic spunbond non woven fabric (34) formed by at least one layer of hydrophilic filaments comprising of the following steps:

- mixing a polyolefin in a mass with an additive or combination of additives that provide the polyolefin with hydrophilic properties; - obtaining one or more groups of hydrophilic filaments (15, 15') by the extrusion of said mixture in one or more heads (21, 21'). stretching and cooling said groups of hydrophilic filaments (15, 15' ) ; - depositing, (17, 176') on a conveyor belt (32), the different groups of hydrophilic filaments (15, 15') stretched and cooled in the previous stage;

- calendering (33) the assembly formed by the different groups of hydrophilic filaments (17, 17') to a temperature and pressure increased in such a way that a hydrophilic spunbond non woven fabric is obtained (34) .

41.- A method according to claim 39, where the stage of obtaining a hydrophilic spunbond non woven fabric (34) formed by at least one layer of hydrophilic filaments includes the following steps:

- obtaining one or more groups of hydrophobic filaments (18, 18') by the extrusion of a composition which comprises a polyolefin in one or more heads (29, 29' ) ; - stretching and cooling said groups of hydrophobic filaments (18, 18');

- depositing, (19, 19') on a conveyor belt (42), the different groups of hydrophobic filaments (18, 18') stretched and cooled in the previous stage; - calendering (33) the assembly formed by the different groups of hydrophobic filaments (19, 19') to a temperature and pressure increased in such a way that a hydrophobic spunbond non woven fabric is obtained (37); - applying (38) to the hydrophobic spunbond non woven fabric (37) an additive or combination of additives that provide hydrophilic properties to said hydrophobic spunbond non woven fabric (37), in such a way that a hydrophilic spunbond non woven fabric (34).

42.- A method according to claim 41, where the stage of applying an additive or combination of additives which provide hydrophilic properties to said hydrophobic spunbond non woven fabric (37) is carried out using a kiss roll rotary roller (38) which is partially submerged in an aqueous solution which contains said additive or combination of additives.

43.- A method according to any of the claims 38 to 42, characterised in that said composition which comprises a polyolefin also comprises an additive or combination of additives which increases the hydrophobic properties of the polyolefin.

44.- A method according to claim 43, characterised in that said additive or combination of additives which increases the hydrophobic properties of the polyolefin are chosen between fluoropolymers, siloxanes, guerbet esters and their mixtures.

45.- A method according to any of the claims 38 to 44, characterised in that the polyolefin is a polypropylene.

46.- A method according to any of the claims 38 to 45, characterised in that the additive or combination of additives of the layers of hydrophilic filaments are chosen between surfactants of the group formed by, ethoxylated aliphatic alcohols, ethoxylated phenol esters, fatty acid esters, non-ionic surfactants derived from amines, non-ionic surfactants derived from amides, copolymers of ethylene oxide and propylene oxide, alkyl sulphates, alkyl ester sulphates, sulphated alkane- amides, diglyceride sulphates, sulphonated alpha-olefins, sulphocarboxylic anionic surfactants, cationic linear alkylamines, propionic amino acids, propionic imido acids, betaines, taurine sulphobetaines, silicone surfactants and their mixtures.

47.- A method according to claim 46, characterised in that the additive or combination of additives of the layer of hydrophilic filaments comprises a compound of the formula:

CH₃CH₂ (CH₂CH₂JaCH₂CH₂ (OCH₂CH₂)_b0H, where "a" is an integer number between 9 and 25 and "b" is an integer number between 1 and 10.

48.- A method according to any of the claims 38 to 44 characterised in that the additive or combination of additives of the layer of hydrophilic filaments comprises Silwet® L-7608.

49.- A method according to any of the claims 38 to 47, characterised in that the binding and consolidation stage

(13, 25) is carried out using the following techniques: by means of calendering at increased temperatures and pressures, water jets , sheetting by ultrasounds or by any other type of sheetting, adhesives, using low fusion point fibre and/or a combination of several of these technologies.

50.- An installation to carry out the method described in any of the claims 38 to 49.