EP4660360A1

EP4660360A1 - Nonwoven fiber material

Info

Publication number: EP4660360A1
Application number: EP24179711.7A
Authority: EP
Inventors: Gisela Goldhalm; Michael BERGFELD
Original assignee: Lenzing AG; Chemiefaser Lenzing AG
Current assignee: Lenzing AG
Priority date: 2024-06-03
Filing date: 2024-06-03
Publication date: 2025-12-10
Also published as: WO2025252690A1

Abstract

Production of a nonwoven fiber material comprising at least one step of carding fibers to form the fiber material and at least one subsequent step of bonding the fiber material, preferably by hydroentanglement. The fiber material comprises lyocell fibers with a flat cross section and a cross-sectional aspect ratio of at least 1.8. The surface of the flat lyocell fibers is free of fibrillation grooves.

Description

Field of the invention

The present disclosure relates to innovations concerning the production of nonwoven fiber materials and their composition.

Description of the Related Art

Carded spunlacing is a well-known method for producing nonwoven fiber materials. The method compises at least one step of carding fibers to form the fiber material and at least one subsequent step of binding the fiber material, e.g. by hydroentanglement. Although the process is well understood and has been in industrial use for many years, some material properties were found to be difficult or even impossible to achieve.
WO2012054663A1 discloses nonwoven articles comprising ribbon-shaped fibers. The ribbon-shaped fibers can be produced from a sulfopolyester polymer. The nonwoven article can be produced with a carded-spunlacing technology and can comprise additional fibers, e.g. lyocell fibers.

Summary

The present disclosure describes methods and materials that overcome the drawback of known techniques and products.
According to one aspect, the present application discloses a nonwoven fiber material produced by a method comprising at least one step of carding fibers to form the fiber material and at least one subsequent step of bonding the fiber material, preferably by hydroentanglement, wherein the fiber material comprises lyocell fibers with a flat cross section and a cross-sectional aspect ratio of at least 1.8, preferably of at least 4 or even more preferred of at least 6, and wherein the surface of the flat lyocell fibers is free of fibrillation grooves.
The term "nonwoven fiber material", as it is used herein, denotes a layer material comprising or consisting of a plurality of fibers arranged in a random structure.
If any intentional fibrillation step has been carried out on fibers, this can easily be observed by microscopic imaging of the fibers. Fibers that have been subjected to any intentional fibrillation step show a strong fibrillation and a characteristic pattern of surface irregularities appearing as ripples or grooves. This pattern is herein referred to as "fibrillation grooves". Conversely, if the fiber surface is free of fibrillation grooves, it is obvious that the fibers have not been subjected to any intentional fibrillation step. Fibers that are free of fibrillations grooves have a smooth surface and can also be denoted as essentially unfibrillated fibers (although a small amount of fibrillation can also be observed with essentially unfibrillated fibers).
Generally speaking, the term "fibrillation grooves", as used herein, denotes surface irregularities that originate from a fibrillation treatment. Fibrillations grooves appear on fibers that have undergone a fibrillation treatment.
The term "fibrillation treatment", as it is used herein, denotes the application of a shearing force with a so-called refiner. Depending on the desired extend of fibrillation, the fibrillation treatment can be performed from few minutes up to several hours. Different types of refiners are known in the art and can be used to perform a fibrillation treatment. Most common examples for refiners comprise (but are not limited to) disc refiners applying a rotor/stator principle, cone refiners and cylinder refiners. The fibrillation treatment step is generally applied to staple fibers before they are being used to produce the nonwoven material.
The term "essentially unfibrillated", as it is used herein, denotes fibers that have not been subjected to any intentional fibrillation step before being used to produce the nonwoven material. Essentially unfibrillated fibers can have some fibrils, but do not have the characteristic fibrillation grooves.
The use of flat lyocell fibers free of fibrillation grooves, i.e. essentially unfibrillated lyocell fibers, allows for the production of carded nonwovens with surprisingly different properties compared to nonwovens comprising similar, but round-shaped fibers. For example, such carded nonwovens can be provided with a higher bulk at similar tensile strength. These improved properties can be achieved with lower energy settings for the hydroentanglement step. On the other hand, higher energy settings can be used to produce an even stronger material. It is surprising that such improved properties can be achieved by using essentially unfibrillated flat lyocell fibers in a carded-spunlacing technology.
Further, it was found that the nonwovens according to the present disclosure have exceptional and surprising liquid distribution properties.
The term "flat" or "ribbon-like", as it is used herein, generally refers to a fiber having a cross-sectional aspect ratio significantly bigger than 1. The cross-sectional aspect ratio of the fiber is defined as the width to height ratio of a minimum bounding rectangle around the cross section of the fiber. The minimum bounding rectangle is the smallest rectangle circumscribing the perimeter of the fiber cross section. The width of the bounding rectangle thereby is measured along the longer direction of the fiber cross section. By all means, a fiber can be considered flat if its cross section has a cross-sectional aspect ratio of at least 1.8. In preferred embodiments the cross-sectional aspect ratio can be at least 4 or even more preferred at least 6. It has to be noted that an increase of the cross-sectional aspect ratio also increases the costs of the fibers. Therefore the fibers will be chosen not broader than necessary to achieve the desired results so that the costs will be minimized. The optimal value of the cross-sectional aspect ratio is therefore based on an optimization process taking into account the costs and the achieved results.
In a preferred embodiment, the nonwoven fiber material comprises at least 2 % per weight, preferably at least 5% per weight and even more preferred at least 10 % per weight of the flat lyocell fibers.
By an adjustment of the proportion of flat, essentially unfibrillated lyocell fibers the specific properties of the nonwoven fiber material can be adjusted in a broad range according to the specific needs. While even a low percentage of flat lyocell fibers can already significantly improve at least some of the properties of the nonwoven fiber material, using an even higher proportion can release the full potential.
In another embodiment, the nonwoven fiber material comprises 100 % per weight flat lyocell fibers or less, preferably 70 % per weight or less and even more preferred 55 % per weight or less of the flat lyocell fibers.
As the flat, essentially unfibrillated lyocell fibers are generally more expensive than many other staple fibers, the raw material costs can be reduced by using blends of different fiber types.
According to a further embodiment, a rate of spread in 24 h of the nonwoven fiber material is 2500 mm² or more, preferably 3000 mm² or more, and/or a rate of spread in 5 min of the nonwoven fiber material is 1900 mm² or more, preferably 2200 mm² or more.
It has been found that the rate of spread of nonwoven fiber materials according to the present disclosure is significantly and surprisingly elevated compared to carded nonwoven fiber materials made with standard fibers having an essentially circular diameter. This effect can, for example, be used for many applications where a high liquid distribution is desired.
According to another embodiment, a wicking height in CD after 300 s of the nonwoven fiber material is 110 mm or more, preferably 120 mm or more.
A high wicking height indicates a strong liquid distribution and absorption capacity. This can, for example, be advantageously used for absorbent hygiene products, specifically for an acquisition-distribution layer.
Preferably, the flat lyocell fibers can have an average cut-length in the range of 20 mm to 150 mm, preferably of 20 mm to 120 mm.
By adjusting the cut-length of the flat lyocell fibers, the tensile strength of the nonwoven fiber material can be adjusted. Also the processability of the fibers on the carding machine can be optimized by adjusting the cut length. The optimal cut length can also depend on other fiber components that are being used.
In one embodiment, the nonwoven fiber material can have, in a dry state, a specific tensile strength (Fmax) of between 0.5 Nm²/g and 1.5 Nm²/g.
According to another embodiment, the nonwoven fiber material can comprise at least one layer comprising or consisting of natural plant-based fibers.
The term "natural plant-based fibers" refers to fibers that are produced by separating fibrous material from plant material. Examples for natural plant-based fibers include, but are not limited to, cotton, cotton linters, hemp, abaca, sisal, kenaf, esparto, hardwood pulp, softwood pulp and the like. For example, a layer of pulp can be applied on top of the nonwoven material that comprises the flat, essentially unfibrillated lyocell fibers and attached to the nonwoven material in a subsequent bonding step. The bonding step can be a hydroentanglement step.
For example, the combination of the nonwoven material with an additional layer of natural plant-based fibers allows for the production of nonwoven materials having special properties at reasonable costs.
The nonwoven fiber material, according to a preferred embodiment, can comprise natural plant-based fibers and/or man-made cellulosic fibers.
The term "man-made cellulosic fibers" refers to fibers produced from regenerated cellulose. Examples for man-made cellulosic fibers include, but are not limited to fibers produced according to a viscose process, a lyocell process, a cupra process, a cold-alkali process or a similar process.
The term "natural plant-based fibers and/or man-made cellulosic fibers ", as it is used herein, denotes fibers that are produced directly or indirectly from plants as a raw material or any mixture of such fibers.
According to another aspect, the present disclosure pertains to a product comprising a nonwoven fiber material as disclosed herein, wherein the product is selected from the list comprising wipes, absorbent hygiene products, sheet masks, medical would dressings, filter materials, fillings, acoustic insulation.
According to a further aspect, the present disclosure concerns a use of a nonwoven fiber material as disclosed herein for the production of a product, wherein the product is selected from the list comprising wipes, absorbent hygiene products, sheet masks , medical would dressings, filter materials, fillings, acoustic insulation.
According to another aspect, the present application discloses a method for the production of a nonwoven fiber material comprising at least one step of carding fibers to form the fiber material and at least one subsequent step of bonding the fiber material, preferably by hydroentanglement, wherein the fiber material comprises lyocell fibers with a flat cross section and a cross-sectional aspect ratio of at least 1.8, preferably of at least 4 or even more preferred of at least 6, and wherein the surface of the flat lyocell fibers is free of fibrillation grooves.
The method allows for the production of nonwoven materials having exceptional and unique properties.

Brief Description of the Drawings

Hereinafter, exemplary embodiments of the invention are described with reference to the drawings, wherein

Fig. 1: is a microscopic image of flat lyocell fibers free of fibrillation grooves,
Fig. 2: is another microscopic image of flat, essentially unfibrillated lyocell fibers in a sectional view showing the cross-sections of the fibers,
Fig. 3: is a microscopic image of flat lyocell fibers that have been subjected to a fibrillation step and
Fig. 4: is a higher resolution microscopic image of flat lyocell fibers that have been subjected to a fibrillation step.

Detailed Description of the Drawings

The microscopic images shown in Fig. 1 and 2 were taken with an electron microscope of the type Phenom Pro X with the software Phenom Pro Suite at a magnification of 500x (Fig. 1) and 650x (Fig. 2).
The microscopic images shown in Fig. 3 and 4 were taken with an electron microscope of the type FEI Quanta 450 with the software FEI Quanta Microscope Control, v6.2.10, at a magnification of 500x (Fig. 3) and 1000x (Fig. 4).
Fig. 1 shows a cluster of flat, essentially unfibrillated lyocell fibers. The fibers have a smooth surface free of any fibrillation grooves which clearly shows that they have not undergone any fibrillation step. Nontheless, some minor fibrills can be seen as they normally occur on any lyocell fibers. The fibers shown are quite uniform having a width of about 20 - 30 µm and a thickness of about 5-10 µm. In this case, the average cross-sectional aspect ratio of the fibers, which is defined as the width to height ratio of a minimum bounding rectangle around the cross section of the fiber, is in the range of about 3-4. An exact determination cannot be made from the view shown in Fig. 1, but it is known in the art how to assess and measure an average value of the cross-sectional aspect ratio with an adequate accuracy.
Fig. 2 shows another view of a cluster of flat, essentially unfibrillated lyocell fibers, but this time in a cross-sectional view focused on the fiber-cross-sections. The flat cross-section can be clearly observed in this view. The cross-section differs from one fiber to another, which is also partly due to the cutting angle.
As a comparison, Fig. 3 shows a cluster of fibrillated flat lyocell fibers. It can be observed that the fibrillation not only produced a high number of fibrills, but also affected the surface of the fibers, which are no longer smooth and even, but show a distinctive pattern of fibrillation grooves.
In Fig. 4, which shows fibrillated fibers in a higher resolution, the fibrillation grooves can be seen as a pattern of lines running mainly parallelly to the main axis of the fibers.

Examples

Six different samples of nonwoven materials and one comparison sample were produced according to the same production method and the same machinery but each with a different material composition.
The raw material fibers were provided in bales to a bale opener. In case two different fiber types were used, two parallel bale openers were used and the opened fibers were mixed and fed to a double card (Trützschler model NC) to produce a carded fleece. The carded fleece was then fed to a spunlacing unit (Trützschler model Aquajet) and submitted to a bonding step by hydroentanglement. The hydroentanglement energy was chosen according to manufacturer parameters in a medium range at a linespeed of 50 m/min. To ensure comparability, all samples were produced using the same parameter settings.
The so produced nonwoven material was then dried and rolled according to well known standard procedures.

The fibers used as raw material for the different samples is shown in Table 1 below. The percentages are given in Percent per weight.

Table 1 - Samples and raw material fibers

	Percentage	Fiber type	Fiber cross section	Titer	Cut length
	[% w/w]	Fiber type	Fiber cross section	[dtex]	[mm]
Sample 1	100%	Lyocell	flat	2.0	38
Sample 2	50%	Lyocell	flat	2.0	38
Sample 2	50%	Lyocell	round	1.7	38
Sample 3	20%	Lyocell	flat	2.0	38
Sample 3	80%	Lyocell	round	1.7	38
Sample 4	100%	Lyocell	flat	1.7	38
Sample 5	100%	Lyocell	flat	2.4	38
Sample 6	100%	Lyocell	flat	3.0	38
Comp. Sample	100%	Lyocell	round	1.7	38

All fibers were produced by Lenzing AG according to a standard lyocell procedure. For the round cross section fibers Lenzing standard fibers were used. Flat fibers were produced internally on pilot line level. The single fiber had comparable mechanical properties like Lyocell fiber with wound cross section at same titer. The aspect ratio of the used fiber was between 3.5 and 4.

Parameter measurements

Before taking measurements, all samples were conditioned according to NWSP 003.0.R0 (15). The samples were conditioned at 23°C and 50% rel. humidity for 24 hours.
On all conditioned samples parameters were measured according to the following protocols:

Thickness (THK cond.) - [mm]: Edana Nonwovens Standard Procedure (NWSP) 120.6.R0 (15) [EN]
Thickness wet (THK wet) - [mm]: Edana Nonwovens Standard Procedure (NWSP) 120.6.R0 (15) [EN]

For the measurement of the wet thickness (THK wet) the samples (size 10 cm x 10 cm) were put on a overhead foil and wetted with deionized water without any wetting agent to the 2.5-fold to 3-fold weight. A second overhead foil was put on top and the water was evenly distributed by hand with a ruler. The wetted samples were put into a reclosable zipper-bag and left for at least 1 hour. The thickness measurement was then carried out with a pressure of 0.5 kPa as described in NWSP120.6.R0.

Basis Weight (BW) - [g/m²]: NSWP 130.1.R0(15) [EN]
Bulkiness (Bulk) - [kg/m³] - was calculated according to the formula: $bulk [kg / m^{3}] = basis weight [gsm] / thickness [mm]$
Dry specific tensile strength in cross direction (Fspec CD Dry) - [Nm²/g]: NWSP 110.4.R0 (15) [EN]
Wet specific tensile strength in cross direction (Fspec CD wet) - [Nm²/g]: NWSP 110.4.R0 (15) [EN]

For the measurement of the wet specific tensile strength (Fspec CD wet) the samples (size 25 cm x 5 cm) were were put on a overhead foil and wetted with deionized water without any wetting agent to the 2.5-fold to 3-fold weight. A second overhead foil was put on top and the water was evenly distributed by hand with a ruler. The wetted samples were put into a reclosable zipper-bag and left for at least 1 hour. The strength measurements was then performed as described in NWSP110.4.R0

Rate of spread 5min (ROS 5 min) - [mm²]: For the measurement of the rate of spread 5 min, a sample with a size of 20x20 cm was prepared and conditioned. The sample was placed on a balance and tared. An Eppendorf pipette was used to drop 0.5 ml deionized water with marking dye to the sample from a height of 1 cm. The spread (area) was determined digitally after 5 minutes with the use of the image processing software imaged.
Rate of spread 24h (ROS 24h) - [mm²]: the same protocol as described above for the ROS 5 min was used, but the spread area was determined after 24 hours.
Wicking CD after 300 s (Wicking CD 300s) - NWSP 010.1.R0 (15) [EN]
Handel-o-meter (HOM total) - [mN*m2/g]: NWSP 090.3.R0 (15) [EN]

Results and discussion

The dimensional and mechanical properties of the nonwoven samples were measured according to the protocols described herein. The results of the measurements are shown in table 2 below.

Table 2 - Dimensional and mechanical parameters of the nonwoven samples

Code	Fiber blend	BW	Bulk	THK cond.	THK wet	Fspec CD dry	Fspec CD wet
Code	Fiber blend	[g/m²]	[kg/m³]	[mm]	[mm]	[Nm²/g]	[Nm²/g]
Sample 1	100% flat 2.0/38	46	86.8	0.53	0.58	0.52	0.63
Sample 2	50% flat 2.0/38	49	96.2	0.51	0.58	0.5	0.59
Sample 2	50% round 1.7/38
Sample 3	20% flat 2.0/38	53	108	0.49	0.57	0.48	0.53
Sample 3	80% round 1.7/38
Sample 4	100% flat 1.7/38	51	89	0.57	0.61	0.63	0.73
Sample 5	100% flat 2.4/38	50	87	0.57	0.63	0.52	0.58
Sample 6	100% flat 3.0/38	50	84	0.6	0.64	0.36	0.4
Comp. Sample	100% round 1.7/38	47	95	0.5	0.54	0.46	0.54

It can be seen that the presence of the flat, essentially unfibrillated lyocell fibers in the nonwoven fleece seems to not significantly change the mechanical properties of the nonwoven material in an unexpected way. This suggests that flat, essentially unfibrillated lyocell fibers are suitable for use in the production of nonwoven materials according to the carded-spunlacing process. During the tests the different fiber blends and fiber raw materials were well processed by the card and did not lead to any technical problems.

In Table 3 below further parameters are shown concerning the liquid transport properties and the softness of the nonwoven material.

Table 3 - Liquid transport properties and Handel-o-Meter

Code	Fiber blend	ROS 5min	ROS 24h	Wicking CD 300s	HOM total
		[mm2]	[mm2]	[mm]	[mN*m2/g]
Sample 1	100% flat 2.0/38	3838	5373	124	6.2
Sample 2	50% flat 2.0/38	2378	3034	116	7.7
Sample 2	50% round 1.7/38
Sample 3	20% flat 2.0/38	2060	2581	103	9.1
Sample 3	80% round 1.7/38
Sample 4	100% flat 1.7/38	4047	5026	146	8.4
Sample 5	100% flat 2.4/38	2947	4248	128	6.7
Sample 6	100% flat 3.0/38	1972	3550	94	6.6
Comp. Sample	100% round 1.7/38	1780	2473	106	8.6

The results show that the rate of spread (ROS) are significantly elevated with the nonwoven materials comprising flat, essentially unfibrillated lyocell fibers. For example, a direct comparison between Sample 4 (100 % flat lyocell fibers with a titer of 1.7 dtex and a cut-length of 38mm) with the Comparison Sample (100 % round lyocell fibers with a titer of 1.7 dtex and a cut-length of 38mm) shows that the use of the flat fibers more than doubled the rate of spread not only on the short term (i.e. ROS 5min) but also on the long term (ROS 24h). Also the wicking height (Wicking CD 300s) is significantly raised for Sample 4.
A comparison with Samples 1, 5 and 6 (similar to Sample 4, but having flat, essentially unfibrillated lyocell fibers of a thicker titer of 2.0, 2.4 or 3.0 dtex, respectively) shows, that the same effect can also be reproduced with thicker fibers, but is slightly reduced.
Samples 2 and 3 were produced with a mixture of flat and round fibers. Here it can be seen, that already a small amount of flat, essentially unfibrillated lyocell fibers in a mixture with round standard lyocell fibers increases the rate of spread. Also the wicking height is increased with Sample 2 (50% w/w of flat fibers), but not with sample 4. This can be explained by the fact that in Samples 2 and 3 the flat fibers had a higher titer than the round fibers of the Comparison Sample (2.0 instead of 1.7). Therefore the samples are not fully comparable.
Also shown in Table 3 is the so-called "Handle-o-Meter" value (HOM). This parameter is well known in the field of nonwoven materials and measures the combined effects of flexibility and surface friction of the material. The (objective) handle-o-meter value gives a good representation of the subjective feel of the nonwoven material when touched by hand. It can be seen that a small amount of flat, essentially unfibrillated lyocell fibers (20% in Sample 3) surprisingly can increase the HOM. On the other hand, using 100 % flat fibers instead of round fibers (Sample 4) seems to have no significant effect on the HOM value. The lower HOM values for Samples 1, 5 and 6 seem to be due to the higher titer of the fibers used for these samples.
The test results clearly indicate that with the use of flat, essentially unfibrillated lyocell fibers for the production of a carded-spunlaced nonwoven material the liquid transport properties of the nonwoven material can be significantly improved. Depending on the specific needs, also a small amount of flat, essentially unfibrillated lyocell fibers can already significantly change the properties of the nonwoven material. It is believed that these effects can also be achieved with different fiber mixtures than disclosed in the examples and the scope of the disclosure is not restricted to these examples.

Claims

Nonwoven fiber material produced by a method comprising at least one step of carding fibers to form the fiber material and at least one subsequent step of bonding the fiber material, preferably by hydroentanglement, wherein the fiber material comprises lyocell fibers with a flat cross section and a cross-sectional aspect ratio of at least 1.8, preferably of at least 4 or even more preferred of at least 6, and wherein the surface of the flat lyocell fibers is free of fibrillation grooves.
Nonwoven fiber material according to Claim 1, wherein the nonwoven fiber material comprises at least 2 % per weight, preferably at least 5% per weight and even more preferred at least 10 % per weight of the flat lyocell fibers.
Nonwoven fiber material according to Claim 1 or 2, wherein the nonwoven fiber material comprises 100 % per weight flat lyocell fibers or less, preferably 70 % per weight or less and even more preferred 55 % per weight or less of the flat lyocell fibers.
Nonwoven fiber material according to any of the Claims 1 to 3, wherein a rate of spread in 24 h of the nonwoven fiber material is 2500 mm² or more, preferably 3000 mm² or more, and/or a rate of spread in 5 min of the nonwoven fiber material is 1900 mm² or more, preferably 2200 mm² or more.
Nonwoven fiber material according to any of the Claims 1 to 4, wherein a wicking height in CD after 300 s of the nonwoven fiber material is 110 mm or more, preferably 120 mm or more.
Nonwoven fiber material according to any of the Claims 1 to 5, wherein the flat lyocell fibers have an average cut-length in the range of 20 mm to 150 mm, preferably of 20 mm to 120 mm.
Nonwoven fiber material according to any of the Claims 1 to 6, wherein the nonwoven fiber material has, in a dry state, a specific tensile strength (Fmax) of between 0.5 Nm²/g and 1.5 Nm²/g.
Nonwoven fiber material according to any of the Claims 1 to 7, wherein the nonwoven fiber material comprises at least one layer comprising or consisting of natural plant-based fibers.
Nonwoven fiber material according to any of the Claims 1 to 8, wherein the nonwoven fiber material comprises natural plant-based fibers and/or man-made cellulosic fibers.
Product comprising a nonwoven fiber material according to any of the Claims 1 to 9, wherein the product is selected from the list comprising wipes, absorbent hygiene products, sheet masks, medical would dressings, filter materials, fillings, acoustic insulation.
Use of a nonwoven fiber material according any of the Claims 1 to 9 for the production of a product, wherein the product is selected from the list comprising wipes, absorbent hygiene products, sheet masks, medical would dressings, filter materials, fillings, acoustic insulation.
Method for the production of a nonwoven fiber material comprising at least one step of carding fibers to form the fiber material and at least one subsequent step of bonding the fiber material, preferably by hydroentanglement, wherein the fiber material comprises lyocell fibers with a flat cross section and a cross-sectional aspect ratio of at least 1.8, preferably of at least 4 or even more preferred of at least 6, and wherein the surface of the flat lyocell fibers is free of fibrillation grooves.