WO1996033303A1

WO1996033303A1 - Rewettable polyolefin fibres

Info

Publication number: WO1996033303A1
Application number: PCT/DK1996/000178
Authority: WO
Inventors: Peter Carstensen; Per Revsbaaek; Katharine Dyrmose-Jensen
Original assignee: Danaklon A/S
Priority date: 1995-04-21
Filing date: 1996-04-19
Publication date: 1996-10-24
Also published as: TW313595B; AU5396796A

Abstract

A method for producing cardable, hydrophilic polyolefin-based staple fibres which maintain their hydrophilic properties after at least one wetting with water or an aqueous liquid, the method comprising applying to spun filaments a first spin finish comprising at least one hydrophilic lubricant, stretching the filaments, applying to the stretched filaments a second spin finish comprising at least one cationic antistatic agent, and crimping, drying and cutting the filaments to obtain hydrophilic staple fibres. The first and second spin finishes, which may each contain a hydrophilic lubricant and a cationic antistatic agent, may also contain a small amount of a polydiorganosiloxane. The fibres may be carded at high speeds and are useful for the preparation of hydrophilic nonwoven materials that can maintain wettability after one or several wettings.

Description

REWETTABLE POLYOLEFIN FIBRES

FIELD OF THE INVENTION

The present invention relates to rewettable thermobondable polyolefin-based synthetic fibres treated with hydrophilic spin finishes, a method for producing the fibres, and nonwoven products prepared from the fibres.

The fibres are suitable for the preparation of hydrophilic nonwoven materials which are required to be able to maintain a substantial degree of wettability after one or, preferably, several wettings, e.g. for use as a topsheet or distribution layer in disposable diapers.

BACKGROUND OF THE INVENTION

Numerous different materials are produced using various types for synthetic fibres that are essentially hydrophobic, for example various polyolefin fibres, but which in the finished product are required to have a greater or lesser degree of hydrophilicity. This is for example the case in certain materials found in hygienic absorbent products such as disposable diapers, in which certain layers or portions of the absorbent products must be able to transport and/or hold aqueous liquids such as urine or blood.

The alteration of the hydrophobic surface of a polyolefin fibre to one that is more or less hydrophilic may be performed in various ways, and is typically performed by means of various "spin finishes" applied to the fibre surface during production of the fibres. A problem common to such surface-treated fibres, however, is that they generally lose their hydrophilic properties relatively easily. For example, such "hydrophilic" fibres of e.g. polypropylene, in which the hydrophilicity is provided by means of a spin finish, will generally lose their hydrophilic properties after a single wetting. This is obviously undesirable when the fibres must be able to maintain a certain hydrophilic nature after several wettings, e.g. in a disposable diaper.

It is known in the art to provide a certain permanence in the hydrophilic nature of such spin finish-treated fibres by employing silicone-containing compounds in the spin finishes. Thus, EP 0 410 485-Al (corresponding to US 5,045,387) describes a method for imparting hydrophilic properties to nonwoven material containing hydrophobic polyolefin- containing fiber or fibrillated film by applying onto the surface of the fiber or fibrillated film a surfactant composition comprising a water-soluble polyalkoxylated polydimethylsiloxane combined with an antistatic compound and/or an alkoxylated ricinolein.

However, the use of silicone compounds such as those described in EP 0 410 485-Al for the treatment of polyolefin fibres is associated with certain disadvantages. These include 1) the fact that the silicone on the surface of the fibres results in a decrease in the strength of the nonwoven materials containing the fibres, 2) production problems during production of the fibres, since silicone compounds have a tendency to result in a very bulky fibre tow, 3) difficulty in crimping and carding the fibres, since silicone compounds often result in a low fibre/metal friction, 4) the fact that silicone compounds are not readily biologically degradable, which gives problems in terms of disposal of waste products, e.g. after cleaning of the equipment used for producing the fibres, and 5) the fact that silicone compounds are relatively expensive. It would therefore be desirable to be able to obtain hydrophilic surface properties in otherwise hydrophobic polyolefin fibres by means of spin finishes which, firstly, contain compounds that are hydrophilic but nevertheless only slightly soluble in water, so that the hydrophilic properties are more permanent, and secondly, which contain no or only a very small amount of silicone, so that the above-mentioned disadvantage of reduced nonwoven strength due to silicone is avoided. Another method by which polyolefin fibres may be provided with permanent hydrophilic properties is by incorporating a surface active agent into the molten polyolefin prior to spinning of the fibres. Such methods are described in US 4,578,414 (incorporation of a wetting agent into the polyolefin of a monocomponent fibre) and EP 0 340 763-Al (incorporation of a surface active agent into the polyolefin forming the sheath component of a sheath-and-core type bicomponent fibre) . However, such methods have the disadvantage, compared to methods in which a surface active agent is applied only as a surface treatment, that a relatively large amount of the surface active agent is required. Since such agents are generally quite expensive compared to the polymer of the fibre (e.g. polyolefins such as polypropylene or polyethylene) , this tends to result in a significant increase in the cost of producing the fibres. As a result, even though the hydrophilic properties of such fibres can be good, their relatively high price puts a practical limitation on their usefulness. A further consideration with such methods is that in systems which are dependent upon a migration of an additive through the polymer to the fibre surface, from which the additive is partially removed upon wetting, the restoration of a sufficient additive concentration on the fibre surface will take some time, typically a few hours. In the meantime, i.e. until an effective surface concentration of the additive has been obtained, the fibre may not have the desired hydrophilic properties.

These disadvantages of the prior art are solved by the present invention, which provides a method for producing rewettable hydrophilic polyolefin fibres using spin finishes substantially free of silicone compounds or containing only a very small amount of a silicone compound. BRIEF DISCLOSURE OF THE INVENTION

In one aspect, the present invention relates to a method for producing cardable, hydrophilic polyolefin-based staple fibres which substantially maintain their hydrophilic properties after at least one wetting with water or an aqueous liquid, the method comprising the following steps: a. applying to spun filaments a first spin finish comprising at least one hydrophilic lubricant, the first spin finish having a polydiorganosiloxane content of at the most 5% by weight, based on the active content of the first spin finish, b. stretching the filaments, c. applying to the stretched filaments a second spin finish comprising at least one cationic antistatic agent, the second spin finish having a polydiorganosiloxane content of at the most 5% by weight, based on the active content of the second spin finish, d. crimping the filaments, e. drying the filaments, and f. cutting the filaments to obtain hydrophilic staple fibres.

The hydrophilic staple fibres may further be characterized as having a liquid absorbency time of at the most 1 min. as determined by the EDANA recommended test for nonwovens absorption (No. 10.1-72) using a fibre sample with a weight of 5 g taken from a carding web with a base weight of 10 g/m² and prepared by carding the fibres at 15 m/min.

Further aspects of the invention relate to fibres produced according to this method, to hydrophilic nonwovens produced from such fibres and to a method for producing such nonwovens. DETAILED DISCLOSURE OF THE INVENTION

The term "polyolefin-based" refers to the fact that at least one component of the fibres of the present invention is produced from a polyolefin or a copolymer thereof, including isotactic polypropylene homopolymers as well as random copolymers thereof with ethylene, 1-butene, 4-methyl-1- pentene, etc., and linear polyethylenes of different densities, such as high density polyethylene, low density polyethylene and linear low density polyethylene. The melts used to produce the polyolefin-based fibres may also contain various conventional fibre additives, such as calcium stea- rate, antioxidants, process stabilizers, and pigments, in¬ cluding whiteners and colourants such as Ti0₂, etc.

The fibres may be either monocomponent or bicomponent fibres, the latter being for example sheath-and-core type bicomponent fibres with the core being located either eccentrically (off- center) or concentrically (substantially in the center) . Bicomponent fibres will typically have a core and sheath which comprise, respectively, polypropylene/polyethylene, high density polyethylene/linear low density polyethylene, polypropylene random copolymer/polyethylene, or polypropylene/polypropylene random copolymer. Bicomponent fibres prepared according to the invention may also be of the sheath-core type with a polyester core and a polyolefin sheath. In this case, the polyolefin component may be any of the polyolefin polymers mentioned above.

Fibres prepared according to the present invention may be white (unpigmented) or coloured (pigmented) .

The spinning of the fibres is preferably accomplished using conventional melt spinning (also known as "long spinning"), in particular medium-speed conventional spinning. Convention¬ al spinning involves a two-step process, the first step being the extrusion of the melts and the actual spinning of the fibres, and the second step being the stretching of the spun fibres, in contrast to so-called "short spinning", which is a one-step process in which the fibres are both spun and stretched in a single operation.

For spinning, the melted fibre components are led from their respective extruders, through a distribution system, and passed through the holes of a spinnerette. The extruded melts are then led through a quenching duct, where they are cooled and solidified by a stream of air, and at the same time drawn into filaments, which are gathered into bundles of typically several hundred filaments. The spinning speed after the quenching duct is typically at least about 200 m/min, more typically about 400-2500 m/min. After having solidified, the filaments are treated with the first spin finish. This is typically performed by means of lick rollers, but alternative systems, such as spraying the bundles of filaments or dipping them in the spin finish, are also suitable.

Stretching in a long spin process is performed using so- called off-line stretching or off-line drawing, which, as mentioned above, takes place separately from the spinning process. The stretching process typically involves a series of hot rollers and a hot air oven, in which a number of bundles of filaments are stretched simultaneously. The bun¬ dles of filaments pass first through one set of rollers, followed by passage through a hot air oven, and then passage through a second set of rollers. Both the hot rollers and the hot air oven typically have a temperature of about 50-140°C, e.g. about 70-130°C, the temperature being chosen according to the type of fibre, e.g. typically 115-135°C for polypropylene fibres, 95-105°C for polyethylene fibres, and 110-120°C for polypropylene/polyethylene bicomponent fibres. The speed of the second set of rollers is faster than the speed of the first set, and the heated bundles of filaments are therefore stretched according to the ratio between the two speeds (called the stretch ratio or draw ratio) . A second oven and a third set of rollers can also be used (two-stage stretching) , with the third set of rollers having a higher speed than the second set. In this case the stretch ratio is the ratio between the speed of the last and the first set of rollers. Similarly, additional sets of rollers and ovens may be used. The fibres of the present invention are typically stretched using a stretch ratio of from about 1.05:1 to about 6:1, e.g. from 1.05:1 to 2:1 for polypropylene fibres, and from 2:1 to 4.5:1 for polyethylene fibres and polypropylene/- polyethylene bicomponent fibres, resulting in an appropriate fineness, i.e. about 1-7 dtex, typically about 1.5-5 dtex, more typically about 1.6-3.4 dtex.

After stretching, the bundles of filaments are treated with the second spin finish, for example using lick rollers or by spraying or dipping. The filaments may optionally be heated prior to crimping, e.g. by means of steam, either superheated or saturated, or infrared heaters, etc. to increase the temperature and melt the spin finish components. Melting of the spin finish components preferably takes place before the crimper, but it can also take place in the crimper itself or during the subsequent drying step. The energy used to heat and melt the lubricant may come from the filament tow itself, which becomes heated during the stretching process, or, alternatively, it can come from e.g. steam or infrared radiation as explained above.

Friction in the crimper (which in turn influences cohesion of the web produced by the fibres) can be regulated to a certain extent by regulation of the process parameters, in particular pressure in the stuffer box chamber used for crimping. However, this is only possible within certain boundaries, the boundaries being defined by the composition of the spin finishes.

The stretched fibres are normally texturized (crimped) in order to make the fibres suitable for carding by giving them a "wavy" form. An effective texturization, i.e. a relatively large number of crimps in the fibres, allows for high pro- cessing speeds in the carding machine, e.g. a continuous carding speed of at least 80 m/min, typically at least about 100 m/min, and in many cases at least 150 m/min or even 200 m/min or more.

Crimping is typically carried out using a so-called stuffer box. The bundles of filaments are led by a pair of pressure rollers into a chamber in the stuffer box, where they become crimped due to the pressure that results from the fact that they are not drawn forward inside the chamber. The degree of crimping can be controlled by the pressure of the rollers prior to the stuffer box, the pressure and temperature in the chamber, and the thickness of the bundle of filaments. As an alternative, the filaments can be air-texturized by passing them through a nozzle by means of a jet air stream. In cer¬ tain cases, i.e. for asymmetric bicomponent fibres, crimping devices may be eliminated, since heat treatment of such fibres, which releases tension in the fibres, leads to con¬ traction and thus three-dimensional self-crimping.

The fibres of the present invention are typically texturized to a level of about 5-15 crimps/cm, typically about 7-12 crimps/cm (the number of crimps being the number of bends in the fibres) .

After the fibres have been crimped, e.g. in a stuffer box, they are typically fixed by heat treatment in order to reduce tensions which may be present after the stretching and crimp- ing processes, thereby making the texturization more perma¬ nent. Fixation and drying of the fibres are important factors for the hydrophilicity of the final product, since the durable hydrophilic effect is in part dependent upon the hydrophilic components being only slowly soluble in water. These components are more readily dissolved when they already are mixed with a certain small amount of water, e.g. residual water from the production process on the surface of the fibres, so that it is important to remove as much of this residual water as possible. In particular, it is important that the drying unit, e.g. drum dryer, oven, drying and heat setting channel, etc., has a uniform distribution of the hot air, since this results in a low and uniform distribution of moisture in the fibres, which in turn effects the permanency of the hydrophilicity of the final product as explained above. The residual moisture content is preferably less than 2.0%, more preferably less than 1.5% by weight based on the weight of the fibre. Fixation and drying of the fibres may take place simultaneously, typically by leading the bundles of filaments from the stuffer box, e.g. via a conveyer belt, through a hot air oven. The temperature of the oven will depend on the composition of the fibres, but must obviously be below the melting point of the fibre polymer or (in the case of bicomponent fibres) the low melting component. During the fixation the fibres are subjected to a crystallization process which "locks" the fibres in their crimped form, thereby making the texturization more permanent. The heat treatment also removes a certain amount of the water from the spin finishes. The filaments are typically dried at a temperature in the range of 90-130°C, e.g. 95-125°C, depending on factors such as the type of fibre.

The fixed and dried bundles of filaments are then led to a cutter, where the fibres are cut to staple fibres of the desired length. Cutting is typically accomplished by passing the fibres over a wheel containing radially placed knives. The fibres are pressed against the knives by pressure from rollers, and are thus cut to the desired length, which is equal to the distance between the knives. The fibres of the present invention are typically cut to staple fibres of a length of about 18-150 mm, more typically about 25-100 mm, in particular about 30-65 mm, depending on the carding equipment and the fineness of the fibres. A length of about 38-40 mm will thus often be suitable for a fibre with a fineness of about 2.2 dtex, while a length of 45-50 mm is often suitable for a 3.3 dtex fibre.

Quite generally, the main requirements for a spin finish for spinning and stretching polymer fibres include the following: 1. It should contain an amount of antistatic agent which ensures that the fibres do not become electrically charged during the spinning and stretching process or during the carding process; anionic, cationic and non- ionic antistatic agents are all employed in spin finishes, as well as amphoteric compounds and salts.

2. If necessary, it should contain an amount of cohesion conferring agent sufficient to ensure that the filaments are held together in bundles, allowing them to be pro- cessed without becoming entangled; neutral vegetable oils, long chained alcohols, ethers and esters, sarco- sines and non-ionic surface active agents are often employed for this purpose.

3. It should contain components which regulate both fibre/fibre and fibre/metal friction during the pro¬ duction process, so that the filaments do not become worn or frayed during processing. In particular, fibre/metal friction during the spinning stage, fibre/metal friction against the stretch rollers, and fibre/fibre and fibre/metal friction in the crimper need to be regulated.

4. Water plus emulsifiers or surface active agents which keep the more or less water-soluble components in the aqueous solution are normally necessary.

Spin finishes also serve to regulate the fibre/fibre and fibre/metal friction during carding, and spin finishes used for spinning and stretching are generally adapted so that the fibres do not require any further processing before carding.

Antistatic agents are a necessary component for all spin finishes used in the production of polyolefin fibres. The following typical values for normal antistatic components serve as a guideline for the relative efficiency of their antistatic properties: inorganic salts 100, cationic 80-100, anionic 75-90, nonionic 50-70, fixing agents 30, mineral oils and silicones 0-10, lubricants 30-50. Cationic antistatic agents are known to be more effective than anionic agents, and suitable cationic antistatic agents can therefore be used in much smaller concentrations.

The present invention is based on spin finishes used in connection with both the spinning and stretching steps which fulfil the requirements listed above with regard to the content of antistatic agent and hydrophilic lubricant(s) , as well as regulation of fibre/fibre and fibre/metal friction. These spin finishes have the further advantage that they function as a processing aid during carding and thus provide the fibre/fibre and fibre/metal friction necessary to obtain sufficient carding of the fibres. As a result, a carding web with a uniform distribution of the fibres is obtained, even when using relatively high carding speeds.

The pH of prior art spin finishes comprising an amide-based cationic antistatic agent or a fatty acid amide condensate is generally somewhat acidic, typically below pH 4. Under these conditions, the amide nitrogen is often protonized and can thus act as a cationic antistatic agent. It is likely that this protonization also contributes to making the dispersions more stable. However, at higher pH values, e.g. 5-6, the amide group is not protonized, and the amide is thus not cationic in nature. For applications in which an absence of skin irritation is not important, e.g. for technical applications such as carpet fibres, these amides are therefore often used at a low pH. This is also related to the fact that a low pH tends to prevent microbial growth and reduces the possibility of gasfading discolouration in textiles.

For purposes of the present invention, however, which is related to fibres for use in hygienic absorbent products such as disposable diapers, it is important to avoid skin irritation caused by excessively low pH values. The pH of the spin finishes used in the production of the fibres of the present invention is therefore relatively high so as to avoid acid-induced skin irritation. In cases in which some acid is necessary to stabilize an emulsion or dispersion, it is preferred to use acetic acid or another volatile acid which will at least partly evaporate during the drying step of the stretching process, so that the pH of the coating on the finished fibres is sufficiently high to avoid acid-induced skin irritation (this volatilization of the acid leading to an increase in pH from e.g. 4 or less in the spin finish dispersion to about 5-6 in the dried coating on the fibre) .

The cationic antistatic agent of the present invention should therefore have a pH (in a 10% aqueous solution) of not less than 4.0. More preferably, the pH is not less than 4.5, e.g. between 4.5 and 6.5, such as 5.0-6.0.

The cationic spin finish components used according to the invention have a particular advantage that is related to the fact that polyolefins, and particularly polypropylene during processing by long spin techniques, become partially oxidized on the surface. Thus, while polyolefins are known to be hydrophobic, they can in certain cases have surface proper¬ ties that are not strictly hydrophobic. As a result of this partial oxidation, some hydroxy and carboxy groups as well as aldehyde and ketone groups are introduced on the surface. These oxidized sites will have an anionic character, which means that they will in principle repel any aqueous solution of anionic component that one attempts to apply to the fibres. This leads to a non-uniform, less efficient coating of the fibre surface, and thus a risk of the fibres having non-durable hydrophilic properties as well as a risk of deposits on the equipment during carding.

The affinity of the cationic spin finish of the present invention (i.e. in the pH ranges listed above) towards the filaments makes a positive contribution to the permanent hydrophilic properties of the system. The bonds created between the filaments (see below regarding degradation of the fibre/filament surface) and the cationic components of the spin finish are not covalent, but are of an ionic nature and are therefore not permanent, especially when the fibres subsequently are in contact with water or an aqueous liquid. However, according to the present invention, when this ionic bonding between the fibre surface and the hydrophilic spin finish is combined with the low solubility/dispersibility of the spin finish components, the effect is nevertheless sufficient to fulfil the demands of "semidurability" of the hydrophilic properties (i.e. rewettability after one or more wettings) .

The hydrophilic lubricant of the spin finish is one which is able to remain on the fibre surface and thus provide the fibres with "semi-durable" hydrophilic properties by virtue of the fact that the lubricant has a low affinity for water and/or is only slightly soluble in water. Of particular interest are hydrophilic components that due to their size and/or structure are only slightly soluble in water.

A "lubricant" may be defined in general terms as an agent that controls friction, i.e. one that can either increase or decrease friction. The friction to be controlled is either fibre/fibre friction (e.g. friction between filaments of the filament tow) or fibre/metal friction (e.g. friction between the filaments and metal parts of the fibre-producing equipment) and can be measured under either static or dynamic conditions. The friction concerned with here acts in the fibre direction, the friction (or force) in the cross-fibre direction being referred to as "cohesion". Of course, both types of friction are influenced by the spin finishes.

When producing fibres for high speed carding operations the following characteristics are desirable:

1. High cohesion is desirable in order to obtain reasonable production properties such as easy handling due to a more compact tow. This also has an influence on the degree of filling in the cans, which in turn allows larger batch sizes and consequently higher productivity. Bulky tows (due to low fibre cohesion) tend to give undesired accumulations of fibres on the rollers and at the "sunflower wheel" in the spinning section.

2. Moderate (controlled) fibre/metal friction is desirable, a high fibre/metal friction being desirable for some purposes and a low fibre/metal friction being desirable for others. The static fibre/metal friction should be high enough to prevent undesired sliding of the filaments during processing. On the other hand, an excessively high fibre/metal friction may result in problems during carding, as the fibres may have difficulties in transferring from one roller to another.

3. High fibre/fibre friction is desirable for high speed carding, as this is necessary in order to be able to pull the unbonded web out of the carding equipment into the bonding oven or calender.

The hydrophilic lubricant may suitably be selected from the group consisting of alkoxylated alcohols, alkoxylated esters and alkoxylated amides, and may contain a minor portion of a hydrophilic-modified (alkoxylated) hydrocarbon wax. The hydrophilic lubricant may in particular be a compound of the general formula I

R¹ X^"

Z¹-(CH₂)_n-[N⁺-(CH₂)J_m-Z²

R²

wherein Z¹ and Z² are Alk-CONH-, (Alk)₂-N-, Alk-COO-, or H, wherein Alk is a linear aliphatic alkyl or alkenyl group containing up to 24 carbon atoms or a mixture of more than one such group, with the proviso that both Z¹ and Z² cannot be H; R¹ is H, CH₃, alkyl with up to 24 carbon atoms, or a dimethylene fatty acid ester; R² is H or CH₃; n is an integer greater than 0; m is an integer greater than 0; and X^" is a counterion. Alk is in particular an alkyl group containing 6-14 carbon atoms, preferably 8-12 carbon atoms; n is 1-4; m is 1-10; and X^" is an acetate, citrate, lactate, metasulfate or chloride ion.

In order to regulate the friction characteristics of the fibres, the second spin finish may further comprise a relatively small amount, i.e. not more than about 10% by weight, typically at the most 5% by weight, based on the active content, of a natural or synthetic hydrocarbon wax with a melting point in the range of 40-120°C, typically 40-90°C, e.g. 50-80°C, or a wax mixture comprising at least one such hydrocarbon wax and having a melting point in the same ranges. The hydrocarbon wax is in particular a paraffin wax or microcrystalline wax, although natural waxes, i.e. an insect or plant wax, may also be employed. The wax may also contain a certain amount, e.g. up to about 40% by weight, of a "hydrocarbon resin", i.e. a partially cross-linked hydrocarbon wax with a relatively high melting point, e.g. up to about 120°C.

The use of waxes in order to regulate the friction characteristics of polyolefin-based staple fibres is discussed in detail in WO 95/19465 (application No. PCT/DK95/00024) , to which reference is made. It should be noted with regard to the use of such waxes that although waxes are by nature hydrophobic, they may nevertheless be incorporated into the spin finishes of the present invention in relatively small amounts, e.g. not more than 5 or 10% as indicated above, without adversely affecting the hydrophilicity of the fibres.

The antistatic agent used in the context of the present invention is chosen so as to obtain a sufficient antistatic effect, while at the same time not substantially interfering with the semi-durable hydrophilic properties provided by the hydrophilic lubricant. Since effective antistatic agents often will be water-soluble, choosing the right antistatic agent will often be a question of compromise between the desired hydrophilic effect of the lubricant on the one hand and the desired antistatic effect on the other hand.

Quaternary ammonium compounds are generally good antistatic agents. Ethoxylation of such products will increase their solubility in water, but the antistatic effect will be less pronounced due to a thinning effect. Water-soluble or hygroscopic compounds will contribute to the antistatic action, but since these kinds of compounds tend to transfer to the liquid phase when the system is wetted, thereby reducing the permanence of the effect, the compounds must be chosen very carefully. One way to deal with this task is to incorporate the ionic or polar groups responsible for the antistatic action in a polymeric material.

The cationic antistatic agent may suitably be selected from the group consisting of amines, amides and alkoxylated compounds, in particular alkoxylated, e.g. ethoxylated, amines and amides. The cationic antistatic agent may in particular be a compound of the general formula II

R¹ X^" I R³-[θ- (CH₂)J_y-0- (CH₂)_n-[N⁺- (CH₂)J_m-0-[(CH₂)_χ-θ]_z-R³ II l ₂ R²

wherein R¹ is H, CH₃, alkyl with up to 24 carbon atoms, or a dimethylene fatty acid ester; R² is H or CH₃; each R³ is independently H, methyl, ethyl or Alk-carbonyl.. where Alk is a linear aliphatic alkyl or alkenyl group containing up to 24 carbon atoms or a mixture of more than one such group; m is an integer greater than 0; n is an integer greater than 0; x is 2 or 3; y and z are independently integers greater than 0, the sum of y and z being at least 5; and X^" is a counterion. Alk is in particular an alkyl group containing 6-14 carbon atoms, preferably 8-12 carbon atoms; n is 1-4; when R³ is alkyl, it is alkyl with 6-14 carbon atoms; m is 1-10; and X^" is an acetate, citrate, lactate, metasulfate or chloride ion. Cationic antistatic agents of this type preferably have a molecular weight of at the most about 1000, e.g. at the most about 600.

A common characteristic of the cationic antistatic agents used according to the present invention is that they are non- irritant compounds. The term "non-irritant" refers to the fact they would be classified as "non-irritant" in a skin irritation test or an eye irritation test. Among the test methods available are those of the OECD Guideline No. 404: "Acute Dermal Irritation/Corrosion", May 1981, and the OECD Guideline No. 405: "Acute Eye Irritation/Corrosion", Feb. 1987, performed on rabbits. Classification can be according to that described in the Official Journal of the European Communities, L 257, 1983.

The viscosity of the spin finish dispersions is influenced by the size of the dispersed particles or droplets. A small particle size thus generally provides a low viscosity, which enables the obtainment of a thin and uniform coating of the spin finish components on the fibre surface. This in turn provides the fibres with uniform fibre/fibre and fibre/metal friction characteristics, which allows a uniform texturiza- tion in the crimper and subsequently the production of a uniform carding web during carding. The end result is a consistent nonwoven material with good hydrophilicity. It is important to note, however, that ultrafine particles, e.g. with a diameter of less than about 0.1 μm, can lead to an increased viscosity. The particle size in the spin finish dispersions is therefore preferably in the range of 0.1-5 μm, more preferably 0.1-2 μm.

In general, the average size of the dispersed particles should be significantly less than the fibre diameter. For typical fine fibres with a diameter of e.g. 15-20 μm, this means that the particle size in the spin finish dispersions is preferably at the most about 5 μm, more preferably at the most about 2 μm, more preferably at the most about 1 μm. As a rule of thumb, the average particle size should normally be at least about one order of magnitude smaller than the diame- ter of the fibres, although this depends to a certain degree on the nature of both materials.

The desired small particle size of the dispersed particles can be accomplished in two ways. The first of these is by use of a relatively large amount of emulsifier. However, it is undesirable to have large amounts of emulsifier on the surface of the finished fibres, since this leads to a loss of the permanence of the hydrophilic properties. The second way that a small particle size may be obtained, and that which is preferred, is by means of mechanical methods during preparation of the dispersions, such as use of special homogenizing devices, high shear dispersion devices or high speed mixers.

While it is desired that the amount of emulsifier is kept to a minimum, emulsifiers aid in the creation and maintainance of a stable dispersion of very small dispersed particles

(typically with an average size of less than 2 μm) or of a stable emulsion with droplets, and are therefore generally necessary as such in limited amounts. The emulsifier is therefore typically present in an amount of less than 10% by weight, more typically less than 8% by weight, such as 4-7% by weight. Ideally, the amount of emulsifier is as small as possible or even completely eliminated.

Suitable emulsifiers for use in the spin finishes of the present invention are e.g. fatty acid ethoxylates and fatty acid ethoxylates, e.g. a compound of the general formula III R^x -X- (CH₂ - CH- 0) _m- H HI

R²

herein R¹ is a linear or branched alkyl or alkenyl group with 8-100 carbon atoms, preferably 10-80 carbon atoms, X is NH, 0, S, COO or CO, R² is H, CH₃ or alkyl with up to 4 carbon atoms, and m is 3-100, preferably 5-60.

As explained above, the viscosity of the spin finishes is preferably as low as possible. In particular, the viscosity of the second spin finish is preferably at the most 7 mPa-s, more preferably at the most 5 mPa's, more preferably at the most 3 mPa's, most preferably at the most 2 mPa^*s, as deter¬ mined e.g. by viscosimetry at 23°C and a shear rate of 2.0 sec^"1 using a viscosimeter of the couvette type.

It is important that after application of the spin finishes, which are in the form of dispersions or emulsions in water, with water as the continuous phase, the active compounds in the spin finishes are able to dissipate into a uniform layer on the fibre surface. This is ensured by subjecting the spin finish coated filaments to a temperature above the melting point of the main active compound in the spin finish dispersion, i.e. as described above either before, during or after crimping.

An antifoaming agent may be added to the antistatic agent, typically in the second spin finish. The antifoaming agent may e.g. be a silicone compound, for example a dimethylsiloxane or a polydimethylsiloxane, e.g. a hydrophilic modified polydimethylsiloxane, and is typically added in an amount of less than 1% by weight, more typically less than 0.5% by weight, such as about 0.25% by weight, based on the active content of the spin finish. Such silicon compounds may, however, in certain cases be added in a somewhat larger amount, i.e. up to about 5% by weight, even though amounts of less than 1% by weight are normally preferred. The first spin finish is preferably free of silicone compounds. Other non-silicone based antifoaming agents may also be used.

In addition to the fact that the first spin finish comprises at least one hydrophilic lubricant, it may also comprise at least one cationic antistatic agent of the type contained in the second spin finish. Similarly, the second spin finish may contain at least one hydrophilic lubricant of the type contained in the first spin finish. If desired, the same spin finish may be used as both the first and second spin finish.

The active content of the first and/or second spin finish preferably comprises at least 50%, typically at least 65%, of one or more lubricants, and at the most 50%, typically at the most 35%, of one or more antistatic agents and/or emulsifiers.

The total concentration of the active components (i.e. anti¬ static agent, lubricant(s) , emulsifier) in the spin finishes is typically about 1-10% by weight, with amounts in the low end of this range often being used in the first spin finish and amounts in the middle to high end of this range often being used in the second spin finish, resulting in fibres with a dried spin finish coating of typically about 0.2-0.5% by weight of the fibres.

Degradation of the fibre surface

According to the present invention it is desirable to achieve a certain degradation of the fibre surface during the production of the fibres. The term "degradation" refers in this context to a controlled degradation of the polymer chains at the surface of the fibres to obtain anionic surface groups that are able to form ionic bonds with the cationic components of the spin finish, thereby helping to maintain the spin finish at the fibre surface. Degradation of the filament surface takes place when the polymer exits the dies and is exposed to air, oxygen in the air reacting to a certain extent with the polymer, which is degraded. The degradation consists in particular of chain scission and at some sites oxidation of carbon. As a result, oxygen- containing chemical groups such as =CO, -CHO and -COOH can be detected on the fibre surface. These groups will be of an anionic nature, whereby they will tend to be attracted to any cationic groups found in the spin finishes used to treat the fibres.

A number of factors are to be taken into consideration in order to achieve the desired degradation of the fibre surface. The first of these is that the spinning process should take place at a temperature that is significantly above the melting point of the polymer(s) . The spinning temperature is therefore preferably at least 90°C above the melting temperature of the polymer, more preferably at least 100°C, typically at least 110°C above the polymer melting temperature. Another factor is the flow of quenching air in the spinning cabinets. Thus, high quenching air speeds cool the fibres quickly and result in a low degree of fibre surface degradation, while a higher degree of degradation is obtained using lower air speeds. A high degree of degradation (obtained e.g. by means of lower quenching air speeds or by delayed quench) and a hydrophilic spin finish with a high affinity towards the partially degraded fiber surface will lead to improved permanent hydrophilic properties of the fibres and similarly of nonwovens produced from the fibres. However, the degree of fibre surface degradation should not be too high, since this tends to result in nonwovens with reduced strength, even though the permanence of the hydrophilic properties for such fibres and nonwovens is good.

In principle, the degree of fibre surface degradation should be determined on the surface layer alone, since this degradation is believed to be a phenomenon affecting only the outer surface of the fibre, whereas the central portion of fibre is believed to be essentially unaffected by the degradation process. However, direct methods suitable for practical use for determining the degree of degradation of the fibre surface alone are not readily available. The fibre surface degradation referred to in the following is therefore actually an approximation based on an analysis of the entire fibre. The degree of fibre surface degradation can thus be quantified as the relationship of the MFI (melt flow index) of the spun fibres compared to the MFI of the polymer raw material, the MFI being determined according to ISO 1133-81 (E). The ratio MFI_fibres/MFI_{raw material} may for polypropylene fibres for example be in the range of about 2.4-3.0.

Bonding of the carding web containing the fibres of the invention to produce a nonwoven may be performed by known means, e.g. by thermobonding using a calender or hot-air oven, ultrasonic bonding or infrared heating.

Methods for quantifying the semi -durable and hydrophilic properties of nonwovens

The tests described below are, unless indicated otherwise, based on the use of nonwoven samples with a base weight of 20 g/m², as determined in accordance with ISO 9073.1:1989 ("Determination of mass per unit area") .

3xstrike-through method

This is a modified EDANA method based on EDANA standard No. ERT 150.2-93. The modification in relation to the standard method is that the strike-through measurement is performed three times on precisely the same spot on the nonwoven. The underlying absorbent pad (filter paper) is replaced after each of the individual strike-through runs. The nonwoven is not dried or wiped off in any way between runs. Three sequences (each with three runs) are conducted, and the mean and standard deviation of the measurements are calculated for each run. In this test, the third strike-through time should be at the most 20 sec, preferably at the most 10 sec, more preferably at the most 5 sec.

3x10 holes method

Two sheets of filter paper are placed one on top of the other with the smooth side up, and a nonwoven sample is placed in the center and on top of the filter paper. A stainless steel 10-hole plate (220 x 50 x 5 mm, hole diameter 15 mm) is then placed on top of the nonwoven. One drop of synthetic urine (0.9% NaCl solution) is placed on the nonwoven in each of the 10 holes, and if the drop is absorbed by the nonwoven within two seconds one point is given. After 60 seconds another 10 drops are place in the same manner as the first round and points are given again for drops absorbed within two seconds. After 60 seconds a third round is conducted in the same manner, so that the total number of points obtainable is 30. The nonwoven is regarded as being "semi-durable" if the sum of the points is greater than 27.

Liquid absorbency test

Another suitable test method for determining the hydrophilic properties of nonwovens is a test for liquid absorbency time according to the EDANA recommended test for nonwovens absorp¬ tion (No. 10.1-72). This test involves determining the time required for the complete wetting of a specimen strip (5 g) loosely rolled into a cylindrical wire basket (3 g) and dropped onto the surface of the liquid (typically water) from a height of 25 mm. Nonwoven samples for use in this test are for the purpose of the present invention conditioned for at least 2 hours at a temperature of 23°C and a relative humidi¬ ty of 50%.

The above liquid absorbency test may also be used, with certain minor amendments, for determining the hydrophilic properties of fibres. For determining the absorbency of fibres, a carding web with a base weight of approximately 10 g/m² is prepared from the fibres to be tested by carding at 15 m/min. , and samples having a weight of 5 g are then taken from the web. The remainder of the test is carried out according to the EDANA test procedure (10.1-72) . When testing either nonwovens or fibres, the absorbency time is defined as the time interval from the moment the wire basket containing the nonwoven or fibre sample hits the liquid to the moment the sample is completely immersed under the surface of the liquid.

In the above test for liquid absorbency in water, the wetting time (i.e. the sinking time) for a sample of a nonwoven or hydrophilic fibres should be at the most l minute and is typically at the most 30 sec, preferably at the most 20 sec, more preferably at the most 10 sec, most preferably at the most 5 sec.

Rewet test

The rewet of the nonwovens is determined in accordance with EDANA standard No. ERT 151.0-93. The results, expressed in g, are the average of three individual measurements. This test measures the ability of a nonwoven to act as a barrier against the transport of liquid from a nearly saturated absorbing material to a dry absorbing material. The absorbing material under under the nonwoven is 85% saturated with a liquid, and after a compression time of 3 min. , a piece of filter paper is placed on top of the nonwoven and a weight is placed on top of the filter paper. After 2 min. the weight is removed and the weight gain of the filter paper is recorded. In this test, the rewet, i.e. weight gain of the filter paper, is preferably at the most 0.3 g, more preferably at the most 0.2 g, most preferably at the most 0.1 g.

Tensile strength

Tensile strength is determined according to EDANA 70.2-89 in the machine direction (MD) and the cross direction (CD) . A 25 bonding index (BI) is calculated at different bonding temperatures, the bonding index being defined as the square root of the product of the machine direction strength and the cross direction strength. In order to arrive at a standard bonding index for a standard nonwoven base weight of 20 g/m² (BI₂₀) , the calculated bonding index for a given sample is multiplied by 20 and divided by the actual base weight in g/m², thereby compensating for the fact that the strength of a nonwoven varies with the base weight. BI_max refers to the maximum bonding index within a range of bonding temperatures.

EXAMPLES

Fibres and nonwovens were prepared as follows:

The polyolefin raw material (isotactic polypropylene) was spun into fibres by conventional spinning (long spinning) technology, using a spinning speed of 2000 m/min, resulting in a bundle of several hundred filaments. After quenching of the filaments by air cooling, the filaments were treated by means of a lick roller with a first spin finish, followed by off-line stretching in a two-stage drawing operation using a combination of hot rollers and a hot air oven, with temperatures in the range of 115-135°C. The stretch ratios were about 1.25:1. The stretched filaments were then treated (by means of a lick roller) with a second spin finish, which for the purpose of these examples was identical to the first spin finish. The filaments were then crimped in a stuffer-box crimper and subsequently annealed in an oven at a temperature of about 125°C to reduce contraction of the fibres during the thermal bonding process and to allow the hydrophilic components of the spin finishes to become uniformly distributed on the surface of the filaments. Staple fibres were then produced by cutting the filaments to the desired length. The fibres of Examples 1-7 had a fineness of 2.2 dtex, a fibre tenacity of 1.8-2.1 cN/dtex, an elongation at break of 350-420%, about 10-13 crimps/cm, and a cut length of 41 or 45 mm. In Examples 8-11, the fibre fineness was 1.7, 2.2, 3.3 and 6.7 dtex, respectively. The fineness of the finished fibres was measured according to DIN 53812/2, the elongation at break and tenacity of the fibres was measured according to DIN 53816, and the crimp frequency was measured according to ASTM D 3937-82.

Nonwovens were prepared from the various fibres by carding at 100 m/min and thermally bonding (calender bonding) the webs at 161°C. For each nonwoven, the tensile strength and elongation was measured in both the machine direction and the cross direction as described above (i.e. using the EDANA recommended test) , and a bondability index was calculated as described above on the basis of the measured tensile strengths. In addition, the strike-through, rewet and repel- lency were also determined, the methods used also being those described above.

The cardability, i.e. the suitability of the fibres for carding, was determined using a simple web cohesion test. This test is carried out by measuring the length a thin carding web of approximately 10 g/m² can support in a substantially horizontal position before it breaks due to its own weight, the length of the carding web being increased at a rate of about 15 m/min. This it performed by taking the carding web off the card in a horizontal direction at a speed of 15 m/min, which is the carding speed used for this test.

A higher cardability as a result of a higher fibre/fibre friction gives a higher web cohesion length. The fibre/fibre friction is dependent upon factors such as the composition of the second spin finish and the degree of texturization, as well as how permanent the texturization is. Fibre/metal friction is also important for the cardability; if it is either too high or too low, the fibres are difficult to transport through the card.

Polyolefin fibres which are well suited for carding will typically be able to support about 1.5 m or more, e.g. 1.5-2.5 m, in the above-described web cohesion length test. Fibres designed for high speed carding should preferably be able to support somewhat more, i.e. at least about 2.0 m.

The table below shows the first, second and third strike- through values (in seconds) , the rewet (in grams) , the amount of spin finish on the fibres (in % by weight of the fibres) , the web cohesion (in meters) , the tensile strength in the machine direction and the cross direction (in N/5 cm) and the maximum bondability index, all of which were determined as explained above. Further comments regarding the individual examples are provided after the table.

Ex. Spin finish type Strike-through Rewet % spin Web cohe- Strength ^BIma No. 1st 2nd 3rd finish sion MD CD

1* Anionic, EO-mod. silicone 1.9 2.6 3.9 0.26 0.45 2.25 36.3 9.7 16.1

2* Anionic, w.out silicone 2.81 3.99 7.88 0.07 0.45 2.00 33.5 11.2 17.8

3.1* as #1, low degradation 2.09 5.67 14.64 0.19 0.30 1.75 35.3 8.6 17.4

3.2* as #1, med. degradation 2.22 4.28 11.18 0.15 0.35 2.25 31.6 9.6 16.5

3.3* as #1, high degradation 1.94 2.40 3.23 0.12 0.45 2.75 35.7 11.5 19.1

4 Cationic 2.6 3.7 5.1 0.3 0.40 2.25 42.0 13.1 23

5 Cationic, high degrad. 2.2 3.3 4.8 0.1 0.45 1.75 17.7 6.1 10

6 Cationic, low degrad. 2.7 4.8 12.3 0.1 0.20 1.75 29.9 6.9 14

7 Cationic, prod, scale 2.8 2.8 4.8 0.12 0.50 1.75 34.4 11.3 19

8 Cationic, prod, scale 2.73 3.12 5.17 1.04 0.65 1.75 35.2 10.8 19.5

9 Cationic, prod, scale 2.72 2.88 4.55 0.10 0.47 1.75 32.4 9.6 17.4

10 Cationic, prod, scale 2.35 2.62 3.53 0.10 0.38 1.75 25.8 6.9 13.3

11 Cationic, prod, scale 2.4 2.6 4.2 0.11 0.30 2.00 13 5.5 8.5 * Comparative example

Coiπments on the examples

Example l (comparative example) used a typical modified (ethoxylated) silicone spin finish, the fibres having a relatively low tenacity and moderate rewet. The permanence of the system was quite good. The spin finish contained approximately 30% of a modified silicone, and the antistatic agents were mostly salts of ethoxylated fatty acids.

Example 2 (comparative example) used the same antistatic components as Example 1, but the silicone was replaced by a surfactant of the ester type. The permanence and the tenacity were not quite as good, but the properties of the fibres were otherwise satisfactory.

Examples 3.1, 3.2 and 3.3 (comparative examples) show degradation of the fibre surface obtained by increasing the temperature of the polymer melt (295°C, 300°C and 305°C, respectively) , while the cooling air and other conditions remained constant. It can be seen that the amount of spin finish applied to the fibres increases with increasing fibre surface degradation. This may be due to the fact that the spin finish is more easily lost from the fibre with a low degree of degradation. The same tendency is also seen with the cationic spin finish of the invention (see Examples 5 and 6) .

In Example 4 the antistatic agent was a fatty acid/polyamine condensation product (compound of formula II in which R¹ is a dimethylene stearic acid ester, with acetate as the counterion) and the hydrophilic lubricant was an ethoxylated fatty alcohol. The fibre showed good properties, even though the rewet was slightly high.

In Examples 5 and 6 the antistatic agent was a fatty acid/polyamine condensation product (as in Example 4) and the hydrophilic lubricant was a fatty acid alkoxylate. The fibre surface degradation in Example 5 was performed by means of a low cooling air velocity, while the velocity was higher in Example 6. These examples show the importance of controlling the degradation, since although the fibres of Example 5 with a high degradation show good strike-through and rewet properties, they show poor strength characteristics.

The fibres of Example 7 were produced on a production scale using the same spin finish components as in Examples 5 and 6. These fibres show good properties both in terms of permanence of the hydrophilicity and in terms of strength.

Examples 8-11, which were produced on a production scale using the same spin finish as in Example 7, show the effect of varying the fibre fineness, the fineness being 1.7, 2.2, 3.3 and 6.7, respectively, in Examples 8, 9, 10 and 11. These examples show a decrease in the multiple strike-through (second and third strike-through) with increasing fibre dtex, and also a higher rewet with the very fine (1.7 dtex) fibres.

Claims

1. A method for producing cardable, hydrophilic polyolefin- based staple fibres which substantially maintain their hydrophilic properties after at least one wetting with water or an aqueous liquid, the method comprising the following steps: a. applying to spun filaments a first spin finish comprising at least one hydrophilic lubricant, the first spin finish having a polydiorganosiloxane content of at the most 5% by weight, based on the active content of the first spin finish, b. stretching the filaments, c applying to the stretched filaments a second spin finish comprising at least one cationic antistatic agent, the second spin finish having a polydiorganosiloxane content of at the most 5% by weight, based on the active content of the second spin finish, d. crimping the filaments, e. drying the filaments, and f. cutting the filaments to obtain hydrophilic staple fibres.

2. A method according to claim 1 wherein the first spin finish further comprises at least one cationic antistatic agent.

3. A method according to claim 1 or 2 wherein the second spin finish further comprises at least one hydrophilic lubricant.

4. A method according to any of the preceding claims wherein the hydrophilic lubricant is selected from the group consisting of alkoxylated alcohols, alkoxylated esters and alkoxylated amides.

5. A method according to any of the preceding claims wherein the hydrophilic lubricant is a compound of the general formula I R¹ X^"

Z¹ - (CH₂ ) _n- [N⁺ - ( CH₂ ) J_m- Z^: R²

wherein Z¹ and Z² are Alk-CONH-, (Alk)₂-N-, Alk-COO-, or H, wherein Alk is a linear aliphatic alkyl or alkenyl group containing up to 24 carbon atoms or a mixture of more than one such group, with the proviso that both Z¹ and Z² cannot be H; R¹ is H, CH₃, alkyl with up to 24 carbon atoms, or a dimethylene fatty acid ester; R² is H or CH₃; n is an integer greater than 0; m is an integer greater than 0; and X^" is a counterion.

6. A method according to claim 5 wherein, in the compound of formula I, Alk is an alkyl group containing 6-14 carbon atoms, preferably 8-12 carbon atoms; n is 1-4; m is 1-10; and X^" is an acetate, citrate, lactate, metasulfate or chloride ion.

7. A method according to any of the preceding claims wherein the cationic antistatic agent is selected from the group consisting of amines, amides and alkoxylated compounds, in particular alkoxylated amines and amides.

8. A method according to any of the preceding claims, wherein the cationic antistatic agent is a compound of the general formula II

R¹ X^" I R³-[θ- (CH₂)J_y-0- (CH₂)_n-[N⁺- (CH₂)_n]_m-0-[(CH₂)_χ-θ]_iS-R³ II l ₂ R²

wherein R¹ is H, CH₃, alkyl with up to 24 carbon atoms, or a dimethylene fatty acid ester; R² is H or CH₃; each R³ is independently H, methyl, ethyl or Alk-carbonyl, where Alk is a linear aliphatic alkyl or alkenyl group containing up to 24 carbon atoms or a mixture of more than one such group; m is an integer greater than 0; n is an integer greater than 0; x is 2 or 3; y and z are independently integers greater than 0, the sum of y and z being at least 5; and X^" is a counterion.

9. A method according to claim 8 wherein, in the compound of formula II, Alk is an alkyl group containing 6-14 carbon atoms, preferably 8-12 carbon atoms; n is 1-4; when R³ is alkyl, it is alkyl with 6-14 carbon atoms; m is 1-10; and X^" is an acetate, citrate, lactate, metasulfate or chloride ion.

10. A method according to claim 8 or 9 wherein the cationic antistatic agent has a molecular weight of at the most about 1000, e.g. at the most about 600.

11. A method according to any of claims 1-10 wherein the first and second spin finish each comprise less than 1% by weight, preferably less than 0.5% by weight, based on the active content of the second spin finish, of a polydiorganosiloxane compound.

12. A method according to any of claims 1-10 wherein the first and second spin finishes are substantially free of polydiorganosiloxane compounds.

13. A method according to any of the preceding claims wherein the same spin finish composition is used both as the first spin finish and the second spin finish.

14. A method according to any of the preceding claims wherein the second spin finish comprises, as a lubricant for the regulation of friction, at the most 10% by weight, typically at the most 5% by weight, based on the active content, of a natural or synthetic hydrocarbon wax with a melting point in the range of 40-120°C, or a wax mixture comprising at least one such hydrocarbon wax and having a melting point in the range of 40-120°C.

15. A method according to claim 14 wherein the hydrocarbon wax or wax mixture has a melting point in the range of 40-90°C.

16. A method according to any of the preceding claims wherein the active content of the first and/or second spin finish comprises at least 50%, typically at least 65%, of one or more lubricants, and at the most 50%, typically at the most 35%, of one or more antistatic agents and/or emulsifiers.

17. A method according to any of the preceding claims wherein the fibres are polypropylene fibres.

18. A method according to claim 17 wherein the ratio ^MFIfibres/^MFIra material ^{is in the} range Of 2.4-3.0.

19. A method according to any of the preceding claims wherein the hydrophilic staple fibres have a liquid absorbency time of at the most 1 min., preferably at the most 30 sec, more preferably at the most 20 sec, more preferably at the most 10 sec, most preferably at the most 5 sec, as determined by the EDANA recommended test for nonwovens absorption (No. 10.1-72) using a fibre sample with a weight of 5 g taken from a carding web with a base weight of 10 g/m² and prepared by carding the fibres at 15 m/min.

20. A texturized, cardable, polyolefin-based staple fibre prepared according to the method of any of the preceding claims.

21. A texturized, cardable, polyolefin-based staple fibre carrying, at its surface, a hydrophilic spin finish coating comprising at least one cationic antistatic agent and at least one hydrophilic lubricant, the spin finish coating containing at the most 5% by weight, preferably at the most 1% by weight, based on the weight of the spin finish coating, of a polydiorganosiloxane compound, the fibre having a degree and uniformity of texturization sufficient for it to be carded continuously at a speed of 100 m/min. , preferably 150 m/min. , more preferably at a speed of 200 m/min, to a nonwoven material showing at least one of the following characteristics for a nonwoven base weight of 20 g/m²: a) a third strike-through time of at the most 20 sec, preferably at the most 10 sec, more preferably at the most 5 sec. as determined by the modified EDANA test method described herein based on EDANA standard No. ERT 150.2-93 and referred to as the "3xstrike-through method"; b) a score of more than 27 in the "3x10 holes method" described herein; c) a rewet of at the most 0.3 g, preferably at the most 0.2 g, more preferably at the most 0.1 g, as determined in accordance with EDANA standard No. ERT 151.0-93; d) a liquid absorbency time of at the most 1 min. , typically at the most 30 sec, preferably at the most 20 sec, more preferably at the most 10 sec, most preferably at the most 5 sec. as determined by the EDANA recommended test for nonwovens absorption (No. 10.1-72) .

22. A fibre according to claim 21 wherein the hydrophilic lubricant is as defined in any of claims 4-6.

23. A fibre according to claim 24 or 24a wherein the cationic antistatic agent is as defined in any of claims 7-10.

24. A hydrophilic nonwoven material comprising the fibres according to any of claims 21-23.

25. A hydrophilic nonwoven material according to claim 24 which after wetting substantially maintains its hydrophilic characteristics as defined by at least one of the following: a) a third strike-through time of at the most 20 sec, preferably at the most 10 sec, more preferably at the most 5 sec. as determined by the modified EDANA test method described herein based on EDANA standard No. ERT 150.2-93 and referred to as the "3xstrike-through method"; b) a score of more than 27 in the "3x10 holes method" described herein; c) a rewet of at the most 0.3 g, preferably at the most

0.2 g, more preferably at the most 0.1 g, as determined in accordance with EDANA standard No. ERT 151.0-93.

26. A hydrophilic nonwoven material comprising fibres prepared according to the method of any of claims 1-18.

27. A method for producing a rewettable hydrophilic nonwoven material, comprising processing fibres according to any of claims 21-24 or fibres prepared according to the method of any of claims 1-18 to obtain a web for bonding, and bonding the resulting web to obtain the nonwoven material.