Man-made cellulose fiber

Abstract

The present invention relates to a man-made cellulose fibre which has a hydrophobic substance incorporated in the cellulose matrix, said substance being selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides, alkyl glutaric anhydrides, alkenyl glutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides and their reaction products with water and / or cellulose, as well as mixtures thereof. The fibre according to the invention is characterized in that the fibre has a multi-limbed fibre cross-section.

Description

SUBJECT MATTER OF THE INVENTION

[0001] The present invention relates to a man-made cellulose fibre, in particular a regenerated cellulose fibre obtained by the viscose process. The fibre according to the invention is particularly suitable as a filling fibre.SPECIFICATION

[0002] The traditional filling material for jackets, blankets, upholstery, sleeping bags and other products for which thermal insulation and fill power are desired is down, in particular goose down. Disadvantages associated with this natural material are, on the one hand, limited availability, a high price and the declining acceptance by many customers due to animal welfare concerns. On the other hand, the natural hydrophobicity of down in the living animal is lost in the course of processing so that down products exhibit a high tendency to absorb moisture, with the good thermal insulation properties being mostly lost in the wet state.

[0003] Polyester fibres provide a well-known, less expensive alternative to down. However, such fully synthetic fibres exhibit significant disadvantages in terms of thermal insulation and breathability. Furthermore, they are not biodegradable.

[0004] Therefore, several approaches are known in which polyester fibres are mixed with down or with natural fibres.

[0005] DE4445085C2 describes the admixture of ramie fibres to polyester fibres. However, these natural fibres exhibit the disadvantage of low elasticity and of susceptibility to breakage associated therewith. Another disadvantage of pure natural fibres is their susceptibility to rot.

[0006] The use of man-made cellulose fibres as filling fibres is also discussed in the prior art. The term “man-made cellulose fibres” is understood by a person skilled in the art as referring to cellulose fibres obtained by dissolving cellulose or cellulose derivatives and spinning the solution. Man-made cellulose fibres can easily be distinguished from natural cellulose fibres based on various properties, such as crystal structure, uniformity, etc.

[0007] Cellulosic staple fibres of the Lyocell type are commercially available as a filling material for quilts (in the form of fleeces) and for pillows (in the form of balls).

[0008] Similarly to purely natural products, these fibres are also extremely absorbent and therefore susceptible to moisture. In the wet state, the nonwovens constructed from the fibres collapse and lose (sometimes irreversibly) their fill power and thus their thermal insulation properties. EP 0 941 209 shows an attempt to solve this problem by admixing polyester fibres to Lyocell fibres.

[0009] All approaches that attempt to combine the positive properties of natural fibres with those of synthetic fibres by using blends are inherently affected by the problems of segregation and ball formation (EP 1 646 738). Therefore, they are generally limited to staple fibres with narrow limits in terms of fibre length and titre. With regard to the susceptibility to breakage (EP 1 067 227) of many fibres, this leads to a decrease in performance over the product's service life.

[0010] EP 1 067 227 describes a mixture of polyester fibres with viscose fibres as filling fibres. The production of regenerated cellulose fibres produced by the viscose process is well known to those skilled in the art. Depending on the specific process parameters, these fibres are referred to as “standard viscose fibres,”“modal fibres” or even “polynosic fibres”.

[0011] In the following, the term “viscose fibres” is used to represent all regenerated cellulose fibres obtained by the viscose process.

[0012] Cellulose fibres in general (both natural cellulose fibres and man-made cellulose fibres) are hydrophilic and swellable. First of all, this is due to the chemical structure of cellulose, which contains a large number of hydroxyl groups suitable for binding water. Therefore, many applications of cellulose fibres are in areas in which water absorption is either not harmful or even desirable, for example, in absorbent sanitary articles or medical products.

[0013] For all those reasons, the use of man-made cellulose fibres, especially viscose fibres, as filling fibres has so far not been of great importance.

[0014] Furthermore, a person skilled in the art is aware of measures of producing viscose fibres with an increased surface area. According to the previous state of the art, such cross-sectional modifications serve to increase absorbency.

[0015] Known measures for increasing the fibre surface area, compared to fibres with round cross-sections, include the production of hollow fibres (U.S. Pat. No. 4,129,679), on the one hand, and of cross-sectionally optimized, particularly trilobal, fibres, on the other hand.

[0016] The production of multi-limbed viscose fibres has been described, for example, in the U.S. Pat. Nos. 5,634,914 and 5,458,835 and in EP-A1 0 301 874. The process disclosed therein describes the spinning of a commonly used viscose, which may contain a certain amount of a modifier known in the prior art, through extrusion holes of a multi-limbed shape, particularly a trilobal shape, into a conventional spinning bath. The key feature of this process is that the shape of the multi-limbed extrusion holes in the spinneret is similar to the desired shape of the cross-section of the filaments. According to the teachings of these documents, the geometry of the spinneret hole determines the shape of the fibre cross-section, and a specific length-to-width ratio of the fibre cross-section can be obtained by appropriately designing the extrusion holes.

[0017] The prior art regarding multi-limbed fibres teaches that such multi-limbed fibres have an adsorption capacity that is increased in comparison to round viscose fibres.

[0018] A special form is represented by the fibre profiles disclosed in WO 2013 / 010759 A1, which are composed of several trilobal fibres and significantly increase the space requirements of the fibres.

[0019] The fact that voids in the cross-sections of viscose fibres increase the absorption capacity of these fibres and of the products produced therefrom is furthermore known from U.S. Pat. No. 4,362,159.

[0020] From this compilation of literature, it is possible to gather that developments in the area of cross-sectional modifications are largely focused on the field of absorbent products.

[0021] However, in other use cases, especially for an application as a heat-insulating filling material, these hydrophilic properties are undesirable, and increased hydrophobicity is strived for.

[0022] Several approaches for a surface hydrophobization of viscose fibres are known, e.g., a coating using a polymer (e.g., polyurethane (PU) or silicone). This coating prevents the fibres from being wetted with water and thus from collapsing under humid / wet conditions. In today's world, this solution is no longer suitable within the framework of sustainability.

[0023] A water-repellent surface is indeed created by a surface coating, but after its destruction, the fibre continues to absorb water unhindered and irreversibly.

[0024] WO 2014 / 090665A1 describes a regenerative cellulose fibre which has a hydrophobic substance incorporated in the cellulose matrix, said substance being selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides, alkyl glutaric anhydrides, alkenyl glutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides, and mixtures thereof.

[0025] As a result, a hydrophobic effect distributed across the entire fibre cross-section is achieved, which is “permanent,” i.e., which is not removed by surface treatment of the fibres, such as, e.g., washing steps or other treatments.

[0026] It has furthermore been described that the basic properties of viscose fibres, e.g., the ability to absorb water vapour, has not been impaired by the incorporation of reactive hydrophobic substances into the cellulose matrix.

[0027] From specialist literature it is known that cellulosic fibres lose their strength and stiffness when humidity is increased, e.g., in C. Ganser, Cellulose 22, 2777-2786 (2015).

[0028] For this reason, nonwoven structures made of cellulosic fibres tend to collapse upon contact with moisture, thus losing their volume and their fill power.

[0029] It is also known that the flexural rigidity of the fibres contributes significantly to the fill power of the fibre ball (WO 2013 / 010759 A1), since the loose, non-directional attachment of stiffer fibres creates more voids.

[0030] The relationship between stiffness and fill power also results in the fact that fibres whose titres are too small are often unsuitable, even for absorbent products, even though they have larger surface areas (relative to the same mass). This is because thin cellulose fibres are particularly prone to collapsing when wet.

[0031] It is the object of the present invention to provide a cellulose fibre that is perfectly suitable especially as a filling fibre.

[0032] This object is achieved with the regenerated cellulose fibre according to claim 1. Preferred embodiments are described in the subclaims.BRIEF DESCRIPTION OF THE FIGURES

[0033] FIG. 1 shows a photomicrograph of fibres according to the invention with trilobal fibre cross-sections according to Example A.

[0034] FIG. 2 shows a photomicrograph of fibres according to the invention with double trilobal fibre cross-sections according to Example B.DETAILED DESCRIPTION OF THE INVENTION

[0035] The fibre according to the invention is a man-made cellulose fibre with a multi-limbed cross-section which has a hydrophobic substance incorporated in the cellulose matrix, said substance being selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides, alkyl glutaric anhydrides, alkenyl glutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides and their reaction products with water and / or cellulose, as well as mixtures thereof.

[0036] A person skilled in the art understands “incorporation” as referring to the fact that the hydrophobic substance is not present essentially only on the surface of the fibre, but is distributed across the entire fibre cross-section.

[0037] This is achieved in that the hydrophobic substance is added to the spinning solution used for producing the man-made cellulose fibre, or to a precursor thereof. Upon precipitation of the solution filaments containing the substance, the substance is evenly distributed within the fibre.

[0038] The chemical nature of the hydrophobic substances used in this case entails that said substances can react (hydrolyze) sometimes with the water used in the spinning process, e.g., as a coagulant, and, conversely, they can react also with the cellulose itself.

[0039] In cases where, for example, alkyl ketene dimer (AKD) is used, beta-keto carboxylic acid esters can form when AKD reacts with cellulose. Furthermore, AKD can hydrolyze to form beta-keto acids.

[0040] Thus, the finished fibre contains a mixture of unreacted hydrophobic substance, hydrolyzed hydrophobic substance, and hydrophobic substance reacted with cellulose.

[0041] The latter two variants are summarized under the term “reaction products with water and / or cellulose.”

[0042] The presence of all alternatives (substance as such or, respectively, the respective reaction products) is analytically measurable and quantifiable.

[0043] The fibre according to the invention is preferably a regenerated cellulose fibre obtained by the viscose process. However, the invention is also applicable to other types of man-made cellulose fibres.

[0044] The fibre according to the invention is a cellulose fibre, in particular a viscose fibre, having particularly high space requirements and therefore a high fill power. This is achieved by a multi-limbed fibre cross-section, which results in a high area moment of inertia.

[0045] In contrast to the prior art described above, the cross-sectional modification hence does not serve to increase absorbency in this case.

[0046] Quite to the contrary, the problem now solved was to produce a cellulose fibre which, despite its high space requirements (i.e., a large free volume and inevitably an increased surface area), is as moisture-resistant as possible.

[0047] The fibre should not collapse even under humid conditions and should retain its heat-insulating properties.

[0048] According to the invention, this is achieved in that the fibre contains a hydrophobic substance which is incorporated into it, in addition to its multi-limbed cross-section.

[0049] From the perspective of a person skilled in the art, hydrophobization, on the one hand, and a multi-limbed cross-sectional modification, on the other hand, first of all represent diametrically opposed measures that thwart each other. This is because the multi-limbed cross-sectional modification actually results in increased absorbency of the fibre.

[0050] It was therefore all the more surprising to find that cellulose fibres with multi-limbed fibre cross-sections, which have been hydrophobized according to the invention, are perfectly suitable especially as filling fibres, with the special requirements associated therewith.

[0051] The multi-limbed fibre cross-section is preferably regular, i.e., it is essentially the same across the entire length of the fibre. This is achieved by spinning the spinning solution through a spinneret with spinning orifices that exhibit the cross-sectional shape that is desired in each case.

[0052] In the context of a multitude of fibres (as it occurs during industrial fibre production), “regular” also means that the cross-section is essentially the same across the multitude of fibres. “Essentially the same” also includes mixtures of fibres spun from spinnerets with spinning orifices having two or more different cross-sections.

[0053] In a preferred embodiment variant, the fibre cross-section is trilobal or double trilobal. A double trilobal fibre cross-section consists of two Y-shaped profiles interconnected by one of the limbs. The cross-section can also be composed of more than two trilobal shapes. Such fibres and their production are described, among others, in WO 2013 / 010759.

[0054] In a further preferred embodiment, the content of hydrophobic substance in the fibre ranges from 0.05% by weight to 3% by weight, preferably from 0.1% by weight to 1% by weight, based on cellulose.

[0055] The hydrophobic substance preferably contains or is preferably an alkyl ketene dimer (AKD), a hydrolysis product of AKD, or AKD reacted with cellulose.

[0056] In a particular embodiment variant, the fibres are characterized in that they have a titre of 2.5 dtex to 30 dtex, in particular of 3 dtex to 12 dtex, particularly preferably of 3 dtex to 7 dtex.

[0057] It is known from WO 2013 / 010759 A1 that there is a relationship between the titre and the space requirements (i.e., the “fill power”) of fibres with round cross-sections in a loose, non-directional mutual attachment.

[0058] This relationship is composed of two opposing effects. On the one hand, fibres with larger cross-sections (i.e., with higher titres) have higher area moments of inertia and therefore higher flexural rigidities. It goes without saying that a cluster of stiffer fibres takes up more space than one of more flexible fibres. On the other hand, the mass of the fibres increases with the titre, whereby the space requirements relative to the mass decrease.

[0059] This dilemma is solved in the present invention by the cross-sectional modification. Cross-sections that are more demanding in terms of space have significantly increased area moments of inertia in comparison to round cross-sections with the titre being the same.

[0060] On the one hand, the area moment of inertia is important for the flexural rigidity of the fibre, and, on the other hand, it is suitable as a measure of the spatial requirements of the fibre itself. It is defined by the integral of the cross-sectional partial areas multiplied by the square of their distance from the centroid. Therefore, the higher the area moment of inertia, the more area there is and the further away from the centroid of the cross-section it is located.

[0061] The spatial requirement of the cross-sectional shape, which is expressed by the area moment of inertia, has a direct impact on the space required by a fibre cluster, even beyond the effect of flexural rigidity. Even in cases where flexibility plays no role, for example, when largely equally oriented fibre bundles form, voids are increasingly created by the cross-sectional modification, particularly by the trilobal or multi-trilobal cross-sectional shape.

[0062] For purely geometric reasons, an increase in the area moment of inertia, with the titre remaining the same, always results in a simultaneous increase in the surface area. In addition, the renunciation of round cross-sections is associated with the formation of acute-angled inner edges, which may increase absorbency due to capillary action.

[0063] The specific shape of the limbs of the multi-limbed cross-section also contributes in particular to the area moment of inertia of the fibre according to the invention.

[0064] In a preferred embodiment, some of the limbs of the multi-limbed fibre cross-section, preferably all limbs, have a length-to-width ratio of 2:1 to 10:1. The limbs should thus be clearly defined (lower limit 2:1). On the other hand, the limbs' stability against buckling decreases if length-to-width ratios are higher.

[0065] The cellulose fibres according to the invention are perfectly suited for use as filling materials, for example, as down substitutes for winter clothing, in sleeping bags or pillows, or as an insulating material in construction. Furthermore, they offer the advantage of biodegradability.

[0066] In particular in one advantageous embodiment, the cellulose fibres according to the invention have a suitability value of the filling fibre of at least 75%.

[0067] The suitability value of the filling fibre defined in this case combines the results of the measurement of the fill power with the hydrophobic properties of the fibres to produce a conclusive value. It is determined as follows:A) Hydrophobic Properties / Hydrophobicity Test

[0068] A defined amount of fibres (consistent for all compared measurements) is weighed and slightly compacted. The fibres are placed in a container filled with water. The water is at room temperature.

[0069] The fibre sample is observed to see whether it floats, with the level after 24 hours being crucial.

[0070] If it floats completely on the water surface without penetrating into it, it achieves a grade of 1, if 25% of the sample is below the water surface, the grade is 2, in case of 50%, it is 3, and, in case of 75%, it is 4. If the sample is completely under water while keeping contact with the surface, a grade of 5 is awarded. If the fibre sample does not at least maintain contact with the water surface, the grade is 6.

[0071] The goal is to achieve at least a grade of 3. Thus, the result is a hydrophobicity sufficient for many applications.

[0072] A grade of 3 in the hydrophobicity test described above constitutes a suitable result. Therefore, all other grades are standardized to this value (100%). Upgrading and downgrading factors, respectively, are obtained in this way (grade 1 corresponds to a factor of 1.5; grade 2 corresponds to a factor of 1.25; grade 3 corresponds to 1; grade 4 corresponds to 0.75, etc.).B) Fill Power Test:

[0073] The test is conducted in accordance with DIN EN 12130:2018.

[0074] The fibres are carded in preparation and thereby parallelized. Subsequently, fibre samples weighing 28 g are weighed and placed in a square glass container measuring 39.2 cm×24.2 cm.

[0075] The height of the fibres in the glass container is measured at the beginning. Thereupon, the fibres in the container are loaded planarly with a weight of 100 g. The height of the fibres in the container is measured again. The container with the loaded fibres is then left to stand at room temperature for 24 hours. The height of the fibres is measured again after these 24 hours. Subsequently, the weight is removed, and immediately the height is measured again. At the end, the fibres are allowed to relax for 10 more minutes, and the height of the fibres in the container is finally measured.

[0076] The ratio of the volume of the fibres at the beginning of the experiment and at the end determines the elastic recovery of the fibres in %.

[0077] The suitability value of the filling fibre is then determined by multiplying the upgrading / downgrading factor obtained from the hydrophobicity test (A) by the result of the fill power test (B) (in %):

[0078] The highest theoretically achievable suitability value of the filling fibre is therefore (100% fill power (restoring force)*1.5 (grade 1 hydrophobicity test)) 150%.

[0079] Example: A fibre with an elastic recovery of 80% and a hydrophobicity grade of 3 (upgrading / downgrading factor: 1.0) has a suitability value of the filling fibre of 80%.

[0080] The cellulose according to the invention is also suitable for applications in the field of medicine requiring a specific level of absorbency.

[0081] Fibres that are inherently hydrophobic but nevertheless possess a certain amount of absorbency for aqueous liquids due to their high internal surface area and free volume offer advantages in applications where efficient drying of the fibres (e.g., for reuse) is desired.

[0082] This is because the desorption of purely physically bound water is far more efficient than the desorption of chemically bound water, where hydrogen bonds with the hydroxyl groups of the cellulose must be broken.

[0083] Accordingly, the present invention also relates to the use of the fibre according to the invention in sanitary products, for example, in the so-called “acquisition distribution layers” of sanitary products.

[0084] A process suitable for producing the cellulose fibres according to the invention comprises the step of adding the hydrophobic substance to a spinning solution (e.g., spinning viscose) or to a precursor thereof and spinning the spinning solution (e.g., spinning viscose) through a spinneret whose orifices have a cross-section corresponding to the desired multi-limbed fibre cross-section.

[0085] Depending on the chemical nature of the hydrophobic substance, a certain excess of hydrophobic substance is necessary to achieve the desired incorporation content. In cases where AKD is added to viscose, the desired content of AKD in the fibre is achieved with an addition of, for example, 3% to 15%, based on viscose.

[0086] It has been shown that no significant changes to the measures already known from the prior art for producing cellulose fibres with, in particular, regular fibre cross-sections, on the one hand, or for producing fibres containing hydrophobic substances, on the other hand, are necessary for the production of the fibre according to the invention.

[0087] From a purely qualitative perspective, a comparatively slightly higher use of hydrophobic substance and slightly lower degrees of stretching have proved to be beneficial.EXAMPLESExample 1

[0088] In a pilot plant for the production of regenerated cellulose fibres according to the viscose process, AKD was admixed to a standard viscose.Production of Fibres with Trilobal Cross-Sections:

[0089] The spinning solution was extruded through nozzles with a trilobal cross-section of the spinning orifices, and viscose fibres were obtained therefrom in the usual way.Production of Fibres with Double-Trilobal Cross-Sections:

[0090] The spinning solution was extruded through nozzles the orifices of which, in line with WO 2013 / 010759, had a cross-section that was theoretically composed of two trilobal cross-sections.

[0091] The respective parameters of the production and the properties of the obtained fibres are illustrated in the following table.

[0092] The measurement of textile data such as elongation and strength was performed in the usual way.TABLE 1Fibre propertiesCross-sectional shapeTrilobalDouble trilobalExample No.ABTarget titre [dtex]3.36.4Cut length [mm]4040Additive addition [%]*4.58Stretching12%20%*based on viscose

[0093] FIG. 1 is a photomicrograph of the fibres with trilobal fibre cross-sections according to Example A.

[0094] FIG. 2 is a photomicrograph of the fibres with double trilobal fibre cross-sections according to Example B.Comparative Example 1

[0095] A viscose fibre with a titre of 1.3 dtex was spun in a conventional manner from a standard viscose (without incorporation of AKD) through a nozzle with round orifices. The fibres were cut to a length of 40 mm.Comparative Example 2

[0096] A fibre with a trilobal cross-section, but without incorporation of AKD, and with a titre of 3.3 dtex was produced. The fibres were cut to a length of 40 mm.Evaluation

[0097] A hydrophobicity test as indicated above was performed on the fibres according to Examples A and B, as well as on the fibres of the comparative examples. Furthermore, a fill power test as indicated above was performed.TABLE 1Result of the hydrophobicity test:Comparative example 1 (standard viscose fibre):Grade 6Comparative example 2 (trilobal fibre without AKD):Grade 6Example A:Grade 2Example B:Grade 1TABLE 2Result of the fill power testExample)Comparative example 1Comparative example 2Example AExample BAmount of28282828282828fibres in gHeight of fibres15013012013010593110in the glasscontainer after0 h withoutweight in mmHeight of fibres1109591103777268in the glasscontainer after0 h with weightin mmHeight of fibres82868998746963in the glasscontainer after24 h withweight in mmHeight of fibres889298109897880in the glasscontainer after24 hourswithout weightand 0 minutesof waiting timein mmHeight of fibres8995100110948080in the glasscontainer after24 hourswithout weightand 10 minutesof waiting timein mmVolume at the868753695753608538637beginning ofthe experiment[cuin]Volume at the515550579637544463463end of theexperiment[cuin]Difference353203116116647517459%73%83%85%90%86%73%Mean value66%84%88%73%The suitability value of the filling fibre was determined from the values obtained from the hydrophobicity test and the fill power test, also as described above.TABLE 3Suitability value of the filling fibreGradeRatingElastichydro-hydro-recoverySuitabilityphobicityphobicity(Fill Powervalue of theFibre typetesttestTest)filling fibreComparative6* 0.2566%16.5%example 1Comparative6* 0.2584%21.0%example 2Example A2* 1.2588% 110%Example B1* 1.5 73%109.5%

Examples

example 1

[0088]In a pilot plant for the production of regenerated cellulose fibres according to the viscose process, AKD was admixed to a standard viscose.

Production of Fibres with Trilobal Cross-Sections:

[0089]The spinning solution was extruded through nozzles with a trilobal cross-section of the spinning orifices, and viscose fibres were obtained therefrom in the usual way.

Production of Fibres with Double-Trilobal Cross-Sections:

[0090]The spinning solution was extruded through nozzles the orifices of which, in line with WO 2013 / 010759, had a cross-section that was theoretically composed of two trilobal cross-sections.

[0091]The respective parameters of the production and the properties of the obtained fibres are illustrated in the following table.

[0092]The measurement of textile data such as elongation and strength was performed in the usual way.

TABLE 1Fibre propertiesCross-sectional shapeTrilobalDouble trilobalExample No.ABTarget titre [dtex]3.36.4Cut length [mm]4040Additive addition [%]*4...

SUBJECT MATTER OF THE INVENTION

[0001] The present invention relates to a man-made cellulose fibre, in particular a regenerated cellulose fibre obtained by the viscose process. The fibre according to the invention is particularly suitable as a filling fibre.SPECIFICATION

[0002] The traditional filling material for jackets, blankets, upholstery, sleeping bags and other products for which thermal insulation and fill power are desired is down, in particular goose down. Disadvantages associated with this natural material are, on the one hand, limited availability, a high price and the declining acceptance by many customers due to animal welfare concerns. On the other hand, the natural hydrophobicity of down in the living animal is lost in the course of processing so that down products exhibit a high tendency to absorb moisture, with the good thermal insulation properties being mostly lost in the wet state.

[0003] Polyester fibres provide a well-known, less expensive alternative to down. However, such fully synthetic fibres exhibit significant disadvantages in terms of thermal insulation and breathability. Furthermore, they are not biodegradable.

[0004] Therefore, several approaches are known in which polyester fibres are mixed with down or with natural fibres.

[0005] DE4445085C2 describes the admixture of ramie fibres to polyester fibres. However, these natural fibres exhibit the disadvantage of low elasticity and of susceptibility to breakage associated therewith. Another disadvantage of pure natural fibres is their susceptibility to rot.

[0006] The use of man-made cellulose fibres as filling fibres is also discussed in the prior art. The term “man-made cellulose fibres” is understood by a person skilled in the art as referring to cellulose fibres obtained by dissolving cellulose or cellulose derivatives and spinning the solution. Man-made cellulose fibres can easily be distinguished from natural cellulose fibres based on various properties, such as crystal structure, uniformity, etc.

[0007] Cellulosic staple fibres of the Lyocell type are commercially available as a filling material for quilts (in the form of fleeces) and for pillows (in the form of balls).

[0008] Similarly to purely natural products, these fibres are also extremely absorbent and therefore susceptible to moisture. In the wet state, the nonwovens constructed from the fibres collapse and lose (sometimes irreversibly) their fill power and thus their thermal insulation properties. EP 0 941 209 shows an attempt to solve this problem by admixing polyester fibres to Lyocell fibres.

[0009] All approaches that attempt to combine the positive properties of natural fibres with those of synthetic fibres by using blends are inherently affected by the problems of segregation and ball formation (EP 1 646 738). Therefore, they are generally limited to staple fibres with narrow limits in terms of fibre length and titre. With regard to the susceptibility to breakage (EP 1 067 227) of many fibres, this leads to a decrease in performance over the product's service life.

[0010] EP 1 067 227 describes a mixture of polyester fibres with viscose fibres as filling fibres. The production of regenerated cellulose fibres produced by the viscose process is well known to those skilled in the art. Depending on the specific process parameters, these fibres are referred to as “standard viscose fibres,”“modal fibres” or even “polynosic fibres”.

[0011] In the following, the term “viscose fibres” is used to represent all regenerated cellulose fibres obtained by the viscose process.

[0012] Cellulose fibres in general (both natural cellulose fibres and man-made cellulose fibres) are hydrophilic and swellable. First of all, this is due to the chemical structure of cellulose, which contains a large number of hydroxyl groups suitable for binding water. Therefore, many applications of cellulose fibres are in areas in which water absorption is either not harmful or even desirable, for example, in absorbent sanitary articles or medical products.

[0013] For all those reasons, the use of man-made cellulose fibres, especially viscose fibres, as filling fibres has so far not been of great importance.

[0014] Furthermore, a person skilled in the art is aware of measures of producing viscose fibres with an increased surface area. According to the previous state of the art, such cross-sectional modifications serve to increase absorbency.

[0015] Known measures for increasing the fibre surface area, compared to fibres with round cross-sections, include the production of hollow fibres (U.S. Pat. No. 4,129,679), on the one hand, and of cross-sectionally optimized, particularly trilobal, fibres, on the other hand.

[0016] The production of multi-limbed viscose fibres has been described, for example, in the U.S. Pat. Nos. 5,634,914 and 5,458,835 and in EP-A1 0 301 874. The process disclosed therein describes the spinning of a commonly used viscose, which may contain a certain amount of a modifier known in the prior art, through extrusion holes of a multi-limbed shape, particularly a trilobal shape, into a conventional spinning bath. The key feature of this process is that the shape of the multi-limbed extrusion holes in the spinneret is similar to the desired shape of the cross-section of the filaments. According to the teachings of these documents, the geometry of the spinneret hole determines the shape of the fibre cross-section, and a specific length-to-width ratio of the fibre cross-section can be obtained by appropriately designing the extrusion holes.

[0017] The prior art regarding multi-limbed fibres teaches that such multi-limbed fibres have an adsorption capacity that is increased in comparison to round viscose fibres.

[0018] A special form is represented by the fibre profiles disclosed in WO 2013 / 010759 A1, which are composed of several trilobal fibres and significantly increase the space requirements of the fibres.

[0019] The fact that voids in the cross-sections of viscose fibres increase the absorption capacity of these fibres and of the products produced therefrom is furthermore known from U.S. Pat. No. 4,362,159.

[0020] From this compilation of literature, it is possible to gather that developments in the area of cross-sectional modifications are largely focused on the field of absorbent products.

[0021] However, in other use cases, especially for an application as a heat-insulating filling material, these hydrophilic properties are undesirable, and increased hydrophobicity is strived for.

[0022] Several approaches for a surface hydrophobization of viscose fibres are known, e.g., a coating using a polymer (e.g., polyurethane (PU) or silicone). This coating prevents the fibres from being wetted with water and thus from collapsing under humid / wet conditions. In today's world, this solution is no longer suitable within the framework of sustainability.

[0023] A water-repellent surface is indeed created by a surface coating, but after its destruction, the fibre continues to absorb water unhindered and irreversibly.

[0024] WO 2014 / 090665A1 describes a regenerative cellulose fibre which has a hydrophobic substance incorporated in the cellulose matrix, said substance being selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides, alkyl glutaric anhydrides, alkenyl glutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides, and mixtures thereof.

[0025] As a result, a hydrophobic effect distributed across the entire fibre cross-section is achieved, which is “permanent,” i.e., which is not removed by surface treatment of the fibres, such as, e.g., washing steps or other treatments.

[0026] It has furthermore been described that the basic properties of viscose fibres, e.g., the ability to absorb water vapour, has not been impaired by the incorporation of reactive hydrophobic substances into the cellulose matrix.

[0027] From specialist literature it is known that cellulosic fibres lose their strength and stiffness when humidity is increased, e.g., in C. Ganser, Cellulose 22, 2777-2786 (2015).

[0028] For this reason, nonwoven structures made of cellulosic fibres tend to collapse upon contact with moisture, thus losing their volume and their fill power.

[0029] It is also known that the flexural rigidity of the fibres contributes significantly to the fill power of the fibre ball (WO 2013 / 010759 A1), since the loose, non-directional attachment of stiffer fibres creates more voids.

[0030] The relationship between stiffness and fill power also results in the fact that fibres whose titres are too small are often unsuitable, even for absorbent products, even though they have larger surface areas (relative to the same mass). This is because thin cellulose fibres are particularly prone to collapsing when wet.

[0031] It is the object of the present invention to provide a cellulose fibre that is perfectly suitable especially as a filling fibre.

[0032] This object is achieved with the regenerated cellulose fibre according to claim 1. Preferred embodiments are described in the subclaims.BRIEF DESCRIPTION OF THE FIGURES

[0033] FIG. 1 shows a photomicrograph of fibres according to the invention with trilobal fibre cross-sections according to Example A.

[0034] FIG. 2 shows a photomicrograph of fibres according to the invention with double trilobal fibre cross-sections according to Example B.DETAILED DESCRIPTION OF THE INVENTION

[0035] The fibre according to the invention is a man-made cellulose fibre with a multi-limbed cross-section which has a hydrophobic substance incorporated in the cellulose matrix, said substance being selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides, alkyl glutaric anhydrides, alkenyl glutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides and their reaction products with water and / or cellulose, as well as mixtures thereof.

[0036] A person skilled in the art understands “incorporation” as referring to the fact that the hydrophobic substance is not present essentially only on the surface of the fibre, but is distributed across the entire fibre cross-section.

[0037] This is achieved in that the hydrophobic substance is added to the spinning solution used for producing the man-made cellulose fibre, or to a precursor thereof. Upon precipitation of the solution filaments containing the substance, the substance is evenly distributed within the fibre.

[0038] The chemical nature of the hydrophobic substances used in this case entails that said substances can react (hydrolyze) sometimes with the water used in the spinning process, e.g., as a coagulant, and, conversely, they can react also with the cellulose itself.

[0039] In cases where, for example, alkyl ketene dimer (AKD) is used, beta-keto carboxylic acid esters can form when AKD reacts with cellulose. Furthermore, AKD can hydrolyze to form beta-keto acids.

[0040] Thus, the finished fibre contains a mixture of unreacted hydrophobic substance, hydrolyzed hydrophobic substance, and hydrophobic substance reacted with cellulose.

[0041] The latter two variants are summarized under the term “reaction products with water and / or cellulose.”

[0042] The presence of all alternatives (substance as such or, respectively, the respective reaction products) is analytically measurable and quantifiable.

[0043] The fibre according to the invention is preferably a regenerated cellulose fibre obtained by the viscose process. However, the invention is also applicable to other types of man-made cellulose fibres.

[0044] The fibre according to the invention is a cellulose fibre, in particular a viscose fibre, having particularly high space requirements and therefore a high fill power. This is achieved by a multi-limbed fibre cross-section, which results in a high area moment of inertia.

[0045] In contrast to the prior art described above, the cross-sectional modification hence does not serve to increase absorbency in this case.

[0046] Quite to the contrary, the problem now solved was to produce a cellulose fibre which, despite its high space requirements (i.e., a large free volume and inevitably an increased surface area), is as moisture-resistant as possible.

[0047] The fibre should not collapse even under humid conditions and should retain its heat-insulating properties.

[0048] According to the invention, this is achieved in that the fibre contains a hydrophobic substance which is incorporated into it, in addition to its multi-limbed cross-section.

[0049] From the perspective of a person skilled in the art, hydrophobization, on the one hand, and a multi-limbed cross-sectional modification, on the other hand, first of all represent diametrically opposed measures that thwart each other. This is because the multi-limbed cross-sectional modification actually results in increased absorbency of the fibre.

[0050] It was therefore all the more surprising to find that cellulose fibres with multi-limbed fibre cross-sections, which have been hydrophobized according to the invention, are perfectly suitable especially as filling fibres, with the special requirements associated therewith.

[0051] The multi-limbed fibre cross-section is preferably regular, i.e., it is essentially the same across the entire length of the fibre. This is achieved by spinning the spinning solution through a spinneret with spinning orifices that exhibit the cross-sectional shape that is desired in each case.

[0052] In the context of a multitude of fibres (as it occurs during industrial fibre production), “regular” also means that the cross-section is essentially the same across the multitude of fibres. “Essentially the same” also includes mixtures of fibres spun from spinnerets with spinning orifices having two or more different cross-sections.

[0053] In a preferred embodiment variant, the fibre cross-section is trilobal or double trilobal. A double trilobal fibre cross-section consists of two Y-shaped profiles interconnected by one of the limbs. The cross-section can also be composed of more than two trilobal shapes. Such fibres and their production are described, among others, in WO 2013 / 010759.

[0054] In a further preferred embodiment, the content of hydrophobic substance in the fibre ranges from 0.05% by weight to 3% by weight, preferably from 0.1% by weight to 1% by weight, based on cellulose.

[0055] The hydrophobic substance preferably contains or is preferably an alkyl ketene dimer (AKD), a hydrolysis product of AKD, or AKD reacted with cellulose.

[0056] In a particular embodiment variant, the fibres are characterized in that they have a titre of 2.5 dtex to 30 dtex, in particular of 3 dtex to 12 dtex, particularly preferably of 3 dtex to 7 dtex.

[0057] It is known from WO 2013 / 010759 A1 that there is a relationship between the titre and the space requirements (i.e., the “fill power”) of fibres with round cross-sections in a loose, non-directional mutual attachment.

[0058] This relationship is composed of two opposing effects. On the one hand, fibres with larger cross-sections (i.e., with higher titres) have higher area moments of inertia and therefore higher flexural rigidities. It goes without saying that a cluster of stiffer fibres takes up more space than one of more flexible fibres. On the other hand, the mass of the fibres increases with the titre, whereby the space requirements relative to the mass decrease.

[0059] This dilemma is solved in the present invention by the cross-sectional modification. Cross-sections that are more demanding in terms of space have significantly increased area moments of inertia in comparison to round cross-sections with the titre being the same.

[0060] On the one hand, the area moment of inertia is important for the flexural rigidity of the fibre, and, on the other hand, it is suitable as a measure of the spatial requirements of the fibre itself. It is defined by the integral of the cross-sectional partial areas multiplied by the square of their distance from the centroid. Therefore, the higher the area moment of inertia, the more area there is and the further away from the centroid of the cross-section it is located.

[0061] The spatial requirement of the cross-sectional shape, which is expressed by the area moment of inertia, has a direct impact on the space required by a fibre cluster, even beyond the effect of flexural rigidity. Even in cases where flexibility plays no role, for example, when largely equally oriented fibre bundles form, voids are increasingly created by the cross-sectional modification, particularly by the trilobal or multi-trilobal cross-sectional shape.

[0062] For purely geometric reasons, an increase in the area moment of inertia, with the titre remaining the same, always results in a simultaneous increase in the surface area. In addition, the renunciation of round cross-sections is associated with the formation of acute-angled inner edges, which may increase absorbency due to capillary action.

[0063] The specific shape of the limbs of the multi-limbed cross-section also contributes in particular to the area moment of inertia of the fibre according to the invention.

[0064] In a preferred embodiment, some of the limbs of the multi-limbed fibre cross-section, preferably all limbs, have a length-to-width ratio of 2:1 to 10:1. The limbs should thus be clearly defined (lower limit 2:1). On the other hand, the limbs' stability against buckling decreases if length-to-width ratios are higher.

[0065] The cellulose fibres according to the invention are perfectly suited for use as filling materials, for example, as down substitutes for winter clothing, in sleeping bags or pillows, or as an insulating material in construction. Furthermore, they offer the advantage of biodegradability.

[0066] In particular in one advantageous embodiment, the cellulose fibres according to the invention have a suitability value of the filling fibre of at least 75%.

[0067] The suitability value of the filling fibre defined in this case combines the results of the measurement of the fill power with the hydrophobic properties of the fibres to produce a conclusive value. It is determined as follows:A) Hydrophobic Properties / Hydrophobicity Test

[0068] A defined amount of fibres (consistent for all compared measurements) is weighed and slightly compacted. The fibres are placed in a container filled with water. The water is at room temperature.

[0069] The fibre sample is observed to see whether it floats, with the level after 24 hours being crucial.

[0070] If it floats completely on the water surface without penetrating into it, it achieves a grade of 1, if 25% of the sample is below the water surface, the grade is 2, in case of 50%, it is 3, and, in case of 75%, it is 4. If the sample is completely under water while keeping contact with the surface, a grade of 5 is awarded. If the fibre sample does not at least maintain contact with the water surface, the grade is 6.

[0071] The goal is to achieve at least a grade of 3. Thus, the result is a hydrophobicity sufficient for many applications.

[0072] A grade of 3 in the hydrophobicity test described above constitutes a suitable result. Therefore, all other grades are standardized to this value (100%). Upgrading and downgrading factors, respectively, are obtained in this way (grade 1 corresponds to a factor of 1.5; grade 2 corresponds to a factor of 1.25; grade 3 corresponds to 1; grade 4 corresponds to 0.75, etc.).B) Fill Power Test:

[0073] The test is conducted in accordance with DIN EN 12130:2018.

[0074] The fibres are carded in preparation and thereby parallelized. Subsequently, fibre samples weighing 28 g are weighed and placed in a square glass container measuring 39.2 cm×24.2 cm.

[0075] The height of the fibres in the glass container is measured at the beginning. Thereupon, the fibres in the container are loaded planarly with a weight of 100 g. The height of the fibres in the container is measured again. The container with the loaded fibres is then left to stand at room temperature for 24 hours. The height of the fibres is measured again after these 24 hours. Subsequently, the weight is removed, and immediately the height is measured again. At the end, the fibres are allowed to relax for 10 more minutes, and the height of the fibres in the container is finally measured.

[0076] The ratio of the volume of the fibres at the beginning of the experiment and at the end determines the elastic recovery of the fibres in %.

[0077] The suitability value of the filling fibre is then determined by multiplying the upgrading / downgrading factor obtained from the hydrophobicity test (A) by the result of the fill power test (B) (in %):

[0078] The highest theoretically achievable suitability value of the filling fibre is therefore (100% fill power (restoring force)*1.5 (grade 1 hydrophobicity test)) 150%.

[0079] Example: A fibre with an elastic recovery of 80% and a hydrophobicity grade of 3 (upgrading / downgrading factor: 1.0) has a suitability value of the filling fibre of 80%.

[0080] The cellulose according to the invention is also suitable for applications in the field of medicine requiring a specific level of absorbency.

[0081] Fibres that are inherently hydrophobic but nevertheless possess a certain amount of absorbency for aqueous liquids due to their high internal surface area and free volume offer advantages in applications where efficient drying of the fibres (e.g., for reuse) is desired.

[0082] This is because the desorption of purely physically bound water is far more efficient than the desorption of chemically bound water, where hydrogen bonds with the hydroxyl groups of the cellulose must be broken.

[0083] Accordingly, the present invention also relates to the use of the fibre according to the invention in sanitary products, for example, in the so-called “acquisition distribution layers” of sanitary products.

[0084] A process suitable for producing the cellulose fibres according to the invention comprises the step of adding the hydrophobic substance to a spinning solution (e.g., spinning viscose) or to a precursor thereof and spinning the spinning solution (e.g., spinning viscose) through a spinneret whose orifices have a cross-section corresponding to the desired multi-limbed fibre cross-section.

[0085] Depending on the chemical nature of the hydrophobic substance, a certain excess of hydrophobic substance is necessary to achieve the desired incorporation content. In cases where AKD is added to viscose, the desired content of AKD in the fibre is achieved with an addition of, for example, 3% to 15%, based on viscose.

[0086] It has been shown that no significant changes to the measures already known from the prior art for producing cellulose fibres with, in particular, regular fibre cross-sections, on the one hand, or for producing fibres containing hydrophobic substances, on the other hand, are necessary for the production of the fibre according to the invention.

[0087] From a purely qualitative perspective, a comparatively slightly higher use of hydrophobic substance and slightly lower degrees of stretching have proved to be beneficial.EXAMPLESExample 1

[0088] In a pilot plant for the production of regenerated cellulose fibres according to the viscose process, AKD was admixed to a standard viscose.Production of Fibres with Trilobal Cross-Sections:

[0089] The spinning solution was extruded through nozzles with a trilobal cross-section of the spinning orifices, and viscose fibres were obtained therefrom in the usual way.Production of Fibres with Double-Trilobal Cross-Sections:

[0090] The spinning solution was extruded through nozzles the orifices of which, in line with WO 2013 / 010759, had a cross-section that was theoretically composed of two trilobal cross-sections.

[0091] The respective parameters of the production and the properties of the obtained fibres are illustrated in the following table.

[0092] The measurement of textile data such as elongation and strength was performed in the usual way.TABLE 1Fibre propertiesCross-sectional shapeTrilobalDouble trilobalExample No.ABTarget titre [dtex]3.36.4Cut length [mm]4040Additive addition [%]*4.58Stretching12%20%*based on viscose

[0093] FIG. 1 is a photomicrograph of the fibres with trilobal fibre cross-sections according to Example A.

[0094] FIG. 2 is a photomicrograph of the fibres with double trilobal fibre cross-sections according to Example B.Comparative Example 1

[0095] A viscose fibre with a titre of 1.3 dtex was spun in a conventional manner from a standard viscose (without incorporation of AKD) through a nozzle with round orifices. The fibres were cut to a length of 40 mm.Comparative Example 2

[0096] A fibre with a trilobal cross-section, but without incorporation of AKD, and with a titre of 3.3 dtex was produced. The fibres were cut to a length of 40 mm.Evaluation

[0097] A hydrophobicity test as indicated above was performed on the fibres according to Examples A and B, as well as on the fibres of the comparative examples. Furthermore, a fill power test as indicated above was performed.TABLE 1Result of the hydrophobicity test:Comparative example 1 (standard viscose fibre):Grade 6Comparative example 2 (trilobal fibre without AKD):Grade 6Example A:Grade 2Example B:Grade 1TABLE 2Result of the fill power testExample)Comparative example 1Comparative example 2Example AExample BAmount of28282828282828fibres in gHeight of fibres15013012013010593110in the glasscontainer after0 h withoutweight in mmHeight of fibres1109591103777268in the glasscontainer after0 h with weightin mmHeight of fibres82868998746963in the glasscontainer after24 h withweight in mmHeight of fibres889298109897880in the glasscontainer after24 hourswithout weightand 0 minutesof waiting timein mmHeight of fibres8995100110948080in the glasscontainer after24 hourswithout weightand 10 minutesof waiting timein mmVolume at the868753695753608538637beginning ofthe experiment[cuin]Volume at the515550579637544463463end of theexperiment[cuin]Difference353203116116647517459%73%83%85%90%86%73%Mean value66%84%88%73%The suitability value of the filling fibre was determined from the values obtained from the hydrophobicity test and the fill power test, also as described above.TABLE 3Suitability value of the filling fibreGradeRatingElastichydro-hydro-recoverySuitabilityphobicityphobicity(Fill Powervalue of theFibre typetesttestTest)filling fibreComparative6* 0.2566%16.5%example 1Comparative6* 0.2584%21.0%example 2Example A2* 1.2588% 110%Example B1* 1.5 73%109.5%

Examples

example 1

[0088]In a pilot plant for the production of regenerated cellulose fibres according to the viscose process, AKD was admixed to a standard viscose.

Production of Fibres with Trilobal Cross-Sections:

[0089]The spinning solution was extruded through nozzles with a trilobal cross-section of the spinning orifices, and viscose fibres were obtained therefrom in the usual way.

Production of Fibres with Double-Trilobal Cross-Sections:

[0090]The spinning solution was extruded through nozzles the orifices of which, in line with WO 2013 / 010759, had a cross-section that was theoretically composed of two trilobal cross-sections.

[0091]The respective parameters of the production and the properties of the obtained fibres are illustrated in the following table.

[0092]The measurement of textile data such as elongation and strength was performed in the usual way.

TABLE 1Fibre propertiesCross-sectional shapeTrilobalDouble trilobalExample No.ABTarget titre [dtex]3.36.4Cut length [mm]4040Additive addition [%]*4...

Claims

1. A man-made cellulose fibre which has a hydrophobic substance incorporated in the cellulose matrix, said substance being selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides, alkyl glutaric anhydrides, alkenyl glutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides and their reaction products with water and / or cellulose, as well as mixtures thereof,wherein the fibre has a multi-limbed fibre cross-section.

2. A cellulose fibre according to claim 1, wherein the cellulose fibre is a regenerated cellulose fibre obtained by the viscose process.

3. A cellulose fibre according to claim 1, wherein the multi-limbed fibre cross-section is selected from the group consisting of: trilobal, double trilobal, and mixtures thereof.

4. A cellulose fibre according to claim 1, wherein the content of hydrophobic substance in the fibre ranges from 0.05% by weight to 3% by weight based on cellulose.

5. A cellulose fibre according to claim 1, wherein the hydrophobic substance contains an alkyl ketene dimer (AKD), a hydrolysis product of AKD, or AKD reacted with cellulose.

6. A cellulose fibre according to claim 1, wherein the cellulose fibre has a titre of 2.5 dtex to 30 dtex.

7. A cellulose fibre according to claim 1, wherein the limbs of the multi-limbed fibre cross-section, preferably all limbs, have a length-to-width ratio of 2:1 to 10:1.

8. A cellulose fibre according to claim 1, wherein the cellulose fibre has a suitability value of the filling fibre, which is determined as indicated in the specification, of at least 75%.

9. The use of a cellulose fibre according to claim 1 as a filling fibre, in particular as a down substitute for winter clothing, in sleeping bags or pillows, as an insulating material in construction and in sanitary products, in particular in acquisition distribution layers.

10. A cellulose fibre according to claim 3, wherein the multi-limbed fibre cross-section is trilobal.

11. A cellulose fibre according to claim 3, wherein the multi-limbed fibre cross-section is double trilobal.

12. A cellulose fibre according to claim 3, wherein the multi-limbed fibre cross-section is both trilobal and double trilobal.

13. A cellulose fibre according to claim 4, wherein the content of hydrophobic substance in the fibre ranges from 0.1% by weight to 1% by weight based on cellulose.

14. A cellulose fibre according to claim 5, wherein the hydrophobic substance is an alkyl ketene dimer (AKD), a hydrolysis product of AKD, or AKD reacted with cellulose.

15. A cellulose fibre according to claim 6, wherein the cellulose fibre has a titre of 3 dtex to 12 dtex.

16. A cellulose fibre according to claim 6, wherein the cellulose fibre has a titre of 3 dtex to 7 dtex.

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