Man-made cellulose fiber

Abstract

The present invention relates to a man-made cellulose fiber which comprises, incorporated in the cellulose matrix, a hydrophobic substance selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkylsuccinic anhydrides, alkenylsuccinic anhydrides, alkylglutaric anhydrides, alkenylglutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides and the reaction products thereof with water and / or cellulose and mixtures thereof. The fiber according to the invention is characterized in that the fiber has a multi-limb fiber cross section.

Description

[0001] Man-made cellulose fiber

[0002] Subject of the invention

[0003] The present invention relates to a man-made cellulose fiber, in particular a regenerated cellulose fiber obtained by the viscose process. The fiber according to the invention is particularly suitable as a filling fiber.

[0004] Description

[0005] The traditional filling material for jackets, blankets, cushions, sleeping bags, and other products where thermal insulation and fill power are desired is down, especially goose down. Disadvantages of this natural material include its limited availability, high price, and declining acceptance by many customers due to animal welfare concerns. Furthermore, the natural hydrophobicity of down is lost in the living animal during processing, so down products have a high tendency to absorb moisture, and when wet, their good thermal insulation properties are largely lost.

[0006] Polyester fibers offer a well-known, more affordable alternative to down. However, these fully synthetic fibers exhibit significant disadvantages in terms of thermal insulation and breathability. Furthermore, they are not biodegradable.

[0007] Therefore, several approaches are known in which polyester fibers are mixed with down or with natural fibers.

[0008] DE4445085C2 describes the addition of ramie fibers to polyester fibers. However, these natural fibers have the disadvantage of low elasticity and the associated susceptibility to breakage. Another disadvantage of pure natural fibers is their susceptibility to rot.

[0009] The use of man-made cellulose fibers as filling fibers is also discussed in the prior art. The term "man-made cellulose fibers" refers to cellulose fibers obtained by dissolving cellulose or cellulose derivatives and spinning the solution. Man-made cellulose fibers can be easily distinguished from natural cellulose fibers by various properties, such as crystal structure, uniformity, etc. Cellulosic staple fibers of the Lyocell genus are commercially available as filling material for quilts (in the form of fleeces) and for pillows (in the form of balls).

[0010] Similar to pure natural products, these fibers are also extremely absorbent and therefore susceptible to moisture. When wet, the nonwovens constructed from these fibers collapse and lose (sometimes irreversibly) their fill power and thus their thermal insulation properties. EP 0 941 209 proposes a solution to this problem by blending polyester fibers with lyocell fibers.

[0011] All approaches that attempt to combine the positive properties of natural fibers with those of synthetic fibers through blends are inherently plagued by the problems of segregation and ball formation (EP 1 646 738). Therefore, they are generally limited to staple fibers with narrow limits in fiber length and linear density. Given the susceptibility to breakage (EP 1 067 227) of many fibers, this leads to a decrease in performance over the product's lifetime.

[0012] EP 1 067 227 describes a mixture of polyester fibres with viscose fibres as filling fibre.

[0013] The production of regenerated cellulose fibers produced using the viscose process is well known to those skilled in the art. Depending on the specific process parameters, these fibers are referred to as "standard viscose fibers," "modal fibers," or "polynosic fibers."

[0014] In the following, the term “viscose fibers” is used to represent all regenerated cellulose fibers obtained by the viscose process.

[0015] Cellulose fibers in general (both natural and man-made) are hydrophilic and swellable. This is due to the chemical structure of cellulose, which contains numerous hydroxyl groups that bind water. Therefore, many applications of cellulose fibers are in areas where water absorption is either not harmful or even desirable, for example, in absorbent hygiene articles or medical products.

[0016] For all these reasons, the use of man-made cellulose fibers, especially viscose fibers, as filling fibers has not been of great importance to date. Those skilled in the art are also aware of measures for producing viscose fibers with increased surface area. According to the current state of the art, such cross-sectional modifications serve to increase absorbency.

[0017] Known measures to increase the fiber surface area, compared to fibers with a round cross-section, include the production of hollow fibers (US-A4, 129,679) on the one hand and cross-section-optimized, in particular trilobal fibers on the other.

[0018] The production of multi-leg viscose fibers has been described, for example, in US patents 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 art, through extrusion holes of multi-leg shape, in particular trilobal shape, into a conventional spin bath. The essential feature of this process is that the shape of the multi-leg 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 fiber cross-section, and by appropriate design of the extrusion holes, a specific length-to-width ratio of the fiber cross-section can be obtained.

[0019] The state of the art regarding multi-leg fibers teaches that such multi-leg fibers have an increased adsorption capacity compared to round viscose fibers.

[0020] A special form is represented by the fiber profiles composed of several trilobal fibers disclosed in WO 2013 / 010759 A1, which increase the space requirement of the fibers to a particularly high degree.

[0021] The fact that voids in the cross-section of viscose fibers increase the absorption capacity of these fibers and the products made from them is also known from US-A 4,362,159.

[0022] This literature review shows that developments in the field of cross-sectional modifications are largely focused on absorbent products. However, in other applications, particularly for use as thermal insulation fillers, these hydrophilic properties are not desired, and increased hydrophobicity is sought.

[0023] Several approaches to surface hydrophobization of viscose fibers are known, e.g., a coating with a polymer (e.g., polyurethane (PU) or silicone). This coating prevents the fibers from becoming wet and thus from collapsing under humid / wet conditions. This solution is no longer suitable for sustainability in this day and age.

[0024] A surface coating creates a water-repellent surface, but once it is destroyed, the fiber absorbs water unhindered and irreversibly.

[0025] WO 2014 / 090665A1 describes a regenerative cellulose fiber which contains a hydrophobic substance selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides, alkenyl succinic anhydrides,

[0026] Alkylglutaric anhydrides, alkenylglutaric anhydrides, alkyl isocyanates, alkenyl isocyanates, fatty acid anhydrides and mixtures thereof incorporated into the cellulose matrix.

[0027] This creates a hydrophobic effect across the entire fiber cross-section, which is "permanent," i.e., it is not removed by surface treatment of the fibers, such as washing steps or other treatments.

[0028] It was further described that the incorporation of reactive hydrophobic substances into the cellulose matrix does not affect the basic properties of the viscose fibers, e.g. the ability to absorb water vapor.

[0029] It is known from the specialist literature that cellulosic fibers lose their strength and stiffness when exposed to increased humidity, e.g. in C. Ganser, Cellulose 22, 2777-2786 (2015).

[0030] For this reason, nonwoven structures made of cellulosic fibers tend to collapse upon contact with moisture, thus losing their volume and fill power. It is also known that the flexural rigidity of the fibers contributes significantly to the fill power of the fiber ball (WO 2013 / 010759 A1), since the loose, undirected arrangement of stiffer fibers creates more voids.

[0031] The relationship between stiffness and fill power also means that fibers with too small a linear density are often unsuitable, even for absorbent products, despite having larger surface areas (relative to the same mass). This is because thin cellulose fibers are particularly prone to collapse when wet.

[0032] The object of the present invention is to provide a cellulose fiber which is particularly suitable as a filling fiber.

[0033] This object is achieved with the regenerated cellulose fiber according to claim 1. Preferred embodiments are described in the subclaims.

[0034] SHORT DESCRIPTION OF THE CHARACTERS

[0035] FIGURE 1 shows a photomicrograph of fibers according to the invention with a trilobal fiber cross-section according to Example A.

[0036] FIGURE 2 shows a photomicrograph of fibers according to the invention with a double trilobal fiber cross-section according to Example B.

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038] The fiber according to the invention is a man-made cellulose fiber with a multi-limbed cross-section, which contains a hydrophobic substance selected from the group consisting of alkyl ketene dimers, alkenyl ketene dimers, alkyl succinic anhydrides,

[0039] 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 and mixtures thereof incorporated in the cellulose matrix.

[0040] By "incorporation," the skilled person understands that the hydrophobic substance is not essentially present only on the surface of the fiber, but is distributed throughout the entire fiber cross-section. This is achieved by adding the hydrophobic substance to the spinning solution used to produce the man-made cellulose fiber, or to a precursor thereof. Upon precipitation of the solution filaments containing the substance, the substance is evenly distributed throughout the fiber.

[0041] The chemical nature of the hydrophobic substances used here means that they partly react (hydrolyze) with the water used in the spinning process, for example as a coagulant, and on the other hand they can also react with the cellulose itself.

[0042] In the case of alkyl ketene dimers (AKD), for example, beta-ketocarboxylic acid esters can be formed during the reaction of AKD with cellulose. AKD can also hydrolyze to form beta-keto acids.

[0043] Thus, the finished fiber contains a mixture of unreacted hydrophobic substance, hydrolyzed hydrophobic substance and cellulose-reacted hydrophobic substance.

[0044] The latter two variants are summarized under the term “reaction products with water and / or cellulose”.

[0045] The presence of all alternatives (substance itself or respective reaction products) is analytically measurable and quantifiable.

[0046] The fiber according to the invention is preferably a regenerated cellulose fiber obtained by the viscose process. However, the invention is also applicable to other types of man-made cellulose fibers.

[0047] The fiber according to the invention is a cellulose fiber, in particular a viscose fiber, with a particularly high volumetric requirement and therefore high fill power. This is achieved by a multi-limbed fiber cross-section, which results in a high area moment of inertia.

[0048] In contrast to the state of the art described above, the cross-sectional modification here does not serve to increase absorbency.

[0049] Quite the opposite, the problem now solved was to produce a cellulose fiber that, despite its high volumetric requirements (i.e., large free volume and necessarily increased surface area), was as resistant to moisture as possible. The fiber should not collapse even in humid conditions and retain its thermal insulation properties.

[0050] This is achieved according to the invention in that the fiber contains a hydrophobic substance incorporated in addition to its multi-limbed cross-section.

[0051] From the expert's point of view, hydrophobization on the one hand and multi-limb cross-sectional modification on the other hand initially represent diametrically opposed, mutually counteracting measures. This is because the multi-limb cross-sectional modification results in increased absorbency of the fiber.

[0052] It was therefore all the more surprising to find that hydrophobicized cellulose fibers with multi-limbed fiber cross-sections according to the invention are particularly suitable as filling fibers with the associated special requirements.

[0053] The multi-limbed fiber cross-section is preferably regular, i.e., essentially uniform over the entire length of the fiber. This is achieved by spinning the spinning solution through a spinneret with spinning orifices that have the desired cross-sectional shape.

[0054] "Regular" in the context of a large number of fibers (as occurs in industrial fiber production) also means that the cross-section is essentially the same across the entire range of fibers. "Essentially the same" also includes blends of fibers spun from spinnerets with spinning orifices that have two or more different cross-sections.

[0055] In a preferred embodiment, the fiber cross-section is trilobal or double trilobal. A double trilobal fiber cross-section consists of two Y-shaped profiles connected by one of the legs. The cross-section can also be composed of more than two trilobal shapes. Such fibers and their production are described, among others, in WO 2013 / 010759.

[0056] In a further preferred embodiment, the content of hydrophobic substance in the fiber is 0.05 wt.% to 3 wt.%, preferably 0.1 wt.% to 1 wt.%, based on cellulose. The hydrophobic substance preferably contains or is preferably an alkyl ketene dimer (AKD), a hydrolysis product of AKD, or AKD reacted with cellulose.

[0057] In a particular embodiment, the fibers are characterized in that they have a titre of 2.5 dtex to 30 dtex, in particular 3 dtex to 12 dtex, particularly preferably 3 dtex to 7 dtex.

[0058] It is known from WO 2013 / 010759 A1 that there is a relationship between the linear density and the space requirement (ie the “filling power”) of fibers with a round cross-section in loose, random arrangement.

[0059] This relationship is composed of two opposing effects. On the one hand, fibers with a larger cross-section (i.e., higher denier) have higher area moments of inertia and therefore higher bending stiffnesses. It is clear that an accumulation of stiffer fibers takes up more space than one of more flexible fibers. On the other hand, the mass of the fibers increases with the denier, thus decreasing the space requirement relative to the mass.

[0060] This dilemma is solved in the present invention by modifying the cross-section. These more spatially demanding cross-sections possess significantly higher area moments of inertia compared to round cross-sections of the same linear density.

[0061] The area moment of inertia is important for the flexural rigidity of the fiber, and it is also a suitable measure of the fiber's spatial requirements. It is defined as the integral of the cross-sectional areas multiplied by the square of their distance from the centroid. Thus, the higher the area moment of inertia, the greater the area is located and the further away from the centroid of the cross-section.

[0062] The spatial demands of the cross-sectional shape, expressed by the area moment of inertia, have a direct impact on the space requirements of a fiber cluster, even beyond the effect of flexural rigidity. Even in cases where flexibility plays no role, for example, when largely uniformly oriented fiber bundles form, the cross-sectional modification, especially the trilobal or multiply trilobal cross-sectional shape, leads to an increased number of voids.

[0063] For purely geometric reasons, an increase in the area moment of inertia at the same linear density always results in a simultaneous increase in the surface area. Furthermore, the move away from round cross-sections is accompanied by the formation of acute-angled inner edges, which can increase absorbency due to capillary action.

[0064] The specific shape of the legs of the multi-leg cross-section also contributes in particular to the area moment of inertia of the fiber according to the invention.

[0065] In a preferred embodiment, some of the limbs of the multi-limb fiber cross-section, preferably all limbs, have a length-to-width ratio of 2:1 to 10:1. The limbs should therefore be clearly defined (lower limit 2:1). On the other hand, the stability of the limbs against kinking decreases at higher length-to-width ratios.

[0066] The cellulose fibers according to the invention are ideally suited for use as fillers, for example, as down substitutes for winter clothing, in sleeping bags or pillows, or as insulation in construction. They also offer the advantage of biodegradability.

[0067] In particular, in an advantageous embodiment, the cellulose fibers according to the invention have a filling fiber suitability value of at least 75%.

[0068] The fill fiber suitability value defined here combines the results from the fill power measurement with the hydrophobic properties of the fibers to produce a meaningful value. It is determined as follows:

[0069] A) Hydrophobic properties / hydrophobicity test

[0070] A defined amount of fiber (consistent across all measurements compared) is weighed and slightly compacted. The fibers are placed in a container filled with water at room temperature.

[0071] It is observed whether the fiber sample floats, with the level after 24 hours being decisive.

[0072] If it floats completely on the water surface without penetrating the water, it achieves a grade of 1. If 25% of the sample is below the water surface, it achieves a grade of 2, if 50% is below the water surface, it achieves a grade of 3, and if 75% is below the water surface, it achieves a grade of 4. If the sample is completely submerged in water but in contact with the surface, it is awarded a grade of 5. If the fiber sample does not at least maintain contact with the water surface, it is awarded a grade of 6. The goal is to achieve at least a grade of 3. This ensures sufficient hydrophobicity for many applications.

[0073] A grade of three in the hydrophobicity test described above represents a suitable result. Therefore, all other grades are standardized to this value (100%). This results in upgrading or downgrading factors (grade 1 corresponds to a factor of 1.5; grade 2 to a factor of 1.25; grade 3 corresponds to 1; grade 4 corresponds to 0.75, etc.)

[0074] B) Filling force test:

[0075] The test is carried out in accordance with DIN EN 12130:2018.

[0076] The fibers are carded in preparation to ensure parallelism. Fiber samples weighing 28 g are then weighed and placed in a square glass container measuring 39.2 cm x 24.2 cm.

[0077] The height of the fibers in the glass vessel is initially measured. A 100 g weight is then placed across the entire surface of the fibers in the vessel. The height of the fibers in the vessel is measured again. The vessel with the weighted fibers is then left to stand at room temperature for 24 hours. The height of the fibers is measured again after these 24 hours. The weight is then removed, and the height is immediately measured again. Finally, the fibers are allowed another 10 minutes to relax, and then the height of the fibers in the vessel is measured.

[0078] The ratio of the volume of the fibers at the beginning and end of the test represents the recovery behavior of the fibers in %.

[0079] The fill fiber suitability value is now determined by multiplying the upgrading / downgrading factor obtained from the hydrophobicity test (A) with the result of the fill power test (B) (in %):

[0080] The highest theoretically achievable filling fiber suitability value is therefore (100% filling power (restoring force) * 1.5 (grade 1 hydrophobicity test)) 150%.

[0081] Example: A fiber with a recovery of 80% and a hydrophobicity rating of 3 (upgrade / downgrade factor: 1.0) has a fill fiber suitability value of 80%. The cellulose according to the invention is also suitable for medical applications that require a specific level of absorbency.

[0082] Fibers that are inherently hydrophobic but nevertheless have a certain absorbency for aqueous liquids due to their high internal surface area and free volume have advantages in applications where efficient drying of the fibers (e.g. for reuse) is desired.

[0083] 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.

[0084] Accordingly, the present invention also relates to a use of the fiber according to the invention in hygiene products, for example in the so-called “acquisition distribution layers” of hygiene products.

[0085] For the production of the cellulose fibers according to the invention, a process is suitable comprising the step of adding the hydrophobic substance to a spinning solution (e.g. spinning viscose) or a precursor thereof and spinning the spinning solution (e.g. spinning viscose) through a spinneret whose openings have a cross-section corresponding to the desired multi-limbed fiber cross-section.

[0086] Depending on the chemical nature of the hydrophobic substance, a certain excess of hydrophobic substance is necessary to achieve the desired incorporation level. In the case of AKD added to viscose, the desired AKD content in the fiber is achieved with an addition of, for example, 3% to 15% based on viscose.

[0087] It has been shown that for the production of the fibre according to the invention, no significant changes are necessary to the measures already known from the prior art for the production of cellulose fibres with, in particular, a regular fibre cross-section on the one hand or for the production of fibres containing hydrophobic substances on the other hand.

[0088] From a purely qualitative point of view, a comparatively higher use of hydrophobic substance and somewhat lower degrees of stretching have proven to be advantageous.

[0089] EXAMPLES: Example 1

[0090] In a pilot plant for the production of regenerated cellulose fibers using the viscose process, AKD was blended into a standard viscose.

[0091] Production of fibers with trilobal cross-section:

[0092] The spinning solution was extruded through nozzles with a trilobal cross-section of the spinning orifices, and viscose fibers were obtained from it in the usual way.

[0093] Production of fibers with double-trilobal cross-section:

[0094] The spinning solution was extruded through nozzles whose openings, analogous to WO 2013 / 010759, had a cross-section that was theoretically composed of two trilobal cross-sections.

[0095] The following table shows the respective production parameters and the properties of the fibers obtained.

[0096] The textile data such as elongation and strength were measured in the usual way.

[0097] Table 1 - Fiber properties

[0098] * based on viscose

[0099] FIGURE 1 is a photomicrograph of the trilobal cross-section fibers of Example A. FIGURE 2 is a photomicrograph of the double trilobal cross-section fibers of Example B.

[0100] Comparison example 1

[0101] A viscose fiber with a linear density of 1.3 dtex was spun from a standard viscose (without incorporation of AKD) through a round-orifice die in a conventional manner. The fibers were cut to 40 mm lengths.

[0102] Comparison example 2

[0103] A fiber with a trilobal cross-section, but without incorporation of AKD, with a linear density of 3.3 dtex was produced. The fibers were cut to 40 mm lengths.

[0104] Evaluation

[0105] A hydrophobicity test was conducted on the fibers according to Examples A and B, as well as on the fibers of the comparative examples, as described above. Furthermore, a fill power test was conducted as described above.

[0106] Table 1 Result of the hydrophobicity test:

[0107] Comparative example 1 (standard viscose fiber): Grade 6

[0108] Comparative example 2 (trilobal fiber without AKD): Grade 6

[0109] Example A Note 2

[0110] Example B Grade 1

[0111] Table 2 - Results of the filling force test

[0112] From the values ​​obtained from the hydrophobicity test and the filling power test, the filling fiber suitability value was determined, as also described above.

[0113] Table 3 - Filling fiber suitability value

Claims

Claims 1. Man-made cellulose fiber which has a hydrophobic substance 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 and mixtures thereof incorporated in the cellulose matrix, characterized in that the fiber has a multi-limbed fiber cross-section.

2. Cellulose fiber according to claim 1, characterized in that it is a regenerated cellulose fiber obtained by the viscose process.

3. Cellulose fiber according to claim 1 or 2, characterized in that the multi-limbed fiber cross-section is selected from the group consisting of: trilobal, double-trilobal, and mixtures thereof.

4. Cellulose fiber according to one of the preceding claims, characterized in that the content of hydrophobic substance in the fiber is 0.05 wt.% to 3 wt.%, preferably 0.1 wt.% to 1 wt.%, based on cellulose.

5. Cellulose fiber according to one of the preceding claims, characterized in that the hydrophobic substance contains an alkyl ketene dimer (AKD), a hydrolysis product of AKD or AKD reacted with cellulose, or is an alkyl ketene dimer (AKD), a hydrolysis product of AKD or AKD reacted with cellulose.

6. Cellulose fiber according to one of the preceding claims, characterized in that it has a linear density of 2.5 dtex to 30 dtex, in particular 3 dtex to 12 dtex, particularly preferably 3 dtex to 7 dtex.

7. Cellulose fiber according to one of the preceding claims, characterized in that some of the legs of the multi-leg fiber cross-section, preferably all legs, have a length to width ratio of 2: 1 to 10:

1.

8. Cellulose fiber according to one of the preceding claims, characterized in that it has a fill fiber suitability value, determined as stated in the description, of at least 75%.

9. Use of a cellulose fiber according to one of the preceding claims as a filling fiber, in particular as a down substitute for winter clothing, in sleeping bags or pillows, as an insulating material in construction and in hygiene products, in particular in acquisition distribution layers.

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