EP4163430A1

EP4163430A1 - Nonwoven layer comprising a network of substantially endless regenerated cellulosic fibers

Info

Publication number: EP4163430A1
Application number: EP21201629.9A
Authority: EP
Inventors: Katharina Gregorich; Gisela Goldhalm
Original assignee: Lenzing AG; Chemiefaser Lenzing AG
Current assignee: Lenzing AG
Priority date: 2021-10-08
Filing date: 2021-10-08
Publication date: 2023-04-12

Abstract

The invention relates to a nonwoven layer comprising a network of substantially continuous regenerated cellulosic fibers. The nonwoven layer has a dimensional stability (DS) of 1.5 mN·M²/g·% or more, preferably even 3.5 mN·m²/g·% or more, measured in at least one direction, preferably measured in machine direction (DS MD) or measured as an average value (DS total). The dimensional stability (DS) of the nonwoven layer is defined according to the formula

DS = \frac{sHOM}{ELO}

with
DS ... dimensional stability [mN.m²/g·%]
sHOM ... specific HOM-value [mN·m²/g],
ELO ... dry elongation [%].

Description

The current disclosure relates to improvements concerning the production and use of nonwoven layers comprising a network (also called "web") of substantially continuous regenerated cellulosic fibers. More specifically, the current disclosure relates to nonwoven layers having improved properties.
Cellulosic fibres can be produced by various processes. In one embodiment a lyocell fibre is spun from cellulose dissolved in N-methyl morpholine N-oxide (NMMO) by a meltblown process, in principle known from e.g. EP 1093536 B1 , EP 2013390 B1 and EP 2212456 B1 . Where the term meltblown is used, it will be understood that it refers to a process that is similar or analogous to the process used for the production of synthetic thermoplastic fibres (filaments are extruded under pressure through nozzles and stretched to required degree by high velocity/high temperature extension air flowing substantially parallel to the filament direction), even though the cellulose is dissolved in solution (i.e. not a molten thermoplastic) and the spinning & air temperatures are only moderately elevated. Therefore the term "solution blown" may be even more appropriate here instead of the term "meltblown" which has already become somewhat common for these kinds of technologies. For the purposes of the present invention both terms can be used synonymously.
According to another approach, the web of the nonwoven layer can be formed by a spun bonding process, where filaments are stretched via lower temperature air. In general, spunbonded synthetic fibers are longer than meltblown synthetic fibers which usually come in discrete shorter lengths.
Fibers formed by the solution blown lyocell process can be continuous or discontinuous depending on process conditions such as extension air velocity, air pressure, air temperature, viscosity of the solution, cellulose molecular weight and distribution and combinations thereof.
In one embodiment for making a nonwoven web the fibres are contacted with a nonsolvent such as water (or water/NMMO mixture) by spraying, after extrusion but before web formation. The fibres are subsequently taken up on a moving foraminous support to form a nonwoven web, washed and dried.
Freshly-extruded lyocell solution ('solvent spun', which will contain only, for example, 5-15% cellulose) behaves in a similar way to 'sticky' and deformable thermoplastic filaments. Causing the freshly-spun filaments to contact each other while still swollen with solvent and with a 'sticky' surface under even low pressure will cause merged filament bonding, where molecules from one filament mix irreversibly with molecules from a different filament. Once the solvent is removed and coagulation of filaments completed, this type of bonding is impossible.
EP3730111 discloses a liquid permeable topsheet for use in an absorbent hygiene article, comprising at least one nonwoven layer directly manufactured from lyocell spinning solution, forming a network of substantially endless regenerated cellulosic fibers. The top sheet has a dry elongation of preferably less than or equal to 10 percent in MD.
EP3604652 discloses a nonwoven including a network of molded bodies. In order to create a nonwoven of low basis weight, the molded bodies are regenerated cellulosic molded bodies and are materially interconnected via node points to form the network.
WO18184038A1 discloses a nonwoven material consisting of one or more layers of nonwoven webs of essentially continuous cellulosic filaments. Within each layer each of the three bonding mechanisms: a) hydrogen bonding, b) filament intermingling and c) merged filament bonding, occur for bonding the essentially continuous cellulosic filaments.

Summary

The current application discloses innovations relating to nonwoven layers containing regenerated nonwoven fibers and methods for their production.
According to a first aspect, the current disclosure relates to a nonwoven layer comprising a network of substantially continuous regenerated cellulosic fibers. The nonwoven layer has a dimensional stability (DS) of 1.5 mN·m²/g·% or more, preferably even 3.5 mN·m²/g·% or more, measured in at least one direction, preferably measured in machine direction (DS MD) or measured as an average value (DS total), wherein the dimensional stability (DS) of the nonwoven layer is defined according to the formula $DS = \frac{sHOM}{ELO}$
with

DS ... dimensional stability [mN·m²/g·%]
sHOM ... specific HOM-value [mN·m²/g],
ELO ... dry elongation [%].

It has surprisingly been found that a cellulosic nonwoven layer having these properties can advantageously be used as a scrim material for textile production. This fulfills a long-felt need for providing an alternative to the use of synthetic fabrics, such as nonwovens or mesh fabrics, which are currently used for scrim materials. This substitution is ecologically desired and facilitates textile recycling.
The term "dimensional stability" (DS), as it is used herein, is defined as the specific HOM-value divided by the dry elongation. To be used as a scrim material for textiles, a high specific HOM-value and a low dry elongation are preferred. Nonetheless, it is difficult to improve both parameters at the same time. Most nonwoven materials available on the market only have a rather low dimensional stability, mostly ranging from about 0.1 to about 0.9 mN·M²/g·%. Such materials can only be used as a scrim layer material as a rather thick layer with a high basis weight. One reason for the rather low dimensional stability of common fibers lies in the production processes. For example, to increase the dimensional stability in commonly produced cellulosic staple fiber nonwovens, thicker fibers would have to be used. Nonetheless, it is technically complicated or even impossible to produce such staple fibers, due to the technical restrictions of the known production processes for cellulosic staple fibers. According to the present disclosure, even very thin materials having a low basis weight can be used as a scrim material due to their high dimensional stability.
According to one embodiment, the nonwoven layer has a dry elongation (ELO) in at least one direction, preferably in machine direction, of equal to or less than 8 % and/or a specific HOM-value (sHOM) in at least one direction, preferably in machine direction, of 3 mN·m²/g or more, preferably 9 mN·m²/g or more and even more preferred of 12 mN·m²/g or more. This provides a good dimensional stability of the material.
According to another embodiment, the nonwoven layer has a basis weight between 10 and 200 g/m², preferably between 15 and 90 g/m². The nonwoven layer provides a high dimensional stability and stiffness even at a low basis weight, e.g. at a basis weight of only about 10 to 20 g/m². Nonetheless, for specific needs also heavier (and thicker) materials can be preferred. Nonwoven layers with a basis weight of more than 50 g/m² can, for example, be used as scrim layer materials for bags, handbags and pouches.
According to still another embodiment, the nonwoven layer has a specific maximum tensile force in at least one direction, preferably in machine direction, of 0.3 N·m²/g or more, preferably of 0.5 N·m²/g or more and even more preferred of 0.7 N·m²/g or more. A high specific strength improves the handling and processability of the material.
According to one embodiment, the nonwoven layer has a moisture uptake of at least 15% after 24 h at 98% relative humidity and/or at least 7% after 24 h at 76% relative humidity and/or at least 4% after 24 h at 50% relative humidity. A high moisture uptake improves the moisture balance of textiles comprising the nonwoven layer and provides for a comfortable wearing sensation.
In another embodiment, at least a part of the nonwoven layer is directly manufactured from lyocell spinning solution. Preferably the complete carrier layer is directly manufactured from Lyocell spinning solution, in particular by a so-called "meltblowing" process. A process to obtain such a carrier material is disclosed in WO 2018/184938 A1 . In jurisdictions where this is legally possible, the disclosure of WO2018/184938 A1 in its entirety is included herein by reference.
According to one embodiment, the cellulosic fibers in the nonwoven layer are multibonded by merging, hydrogen bonding and/or physically intermingling. This allows for an increased stiffness and dimensional stability in combination with a low basis weight.
In another embodiment, the fibers of the carrier layer have diameters ranging from 1 µm to 5000 µm, preferably from 8 µm to 500 µm. This broad scope includes cellulosic materials that are made according to a meltblown process. In this case the larger diameters in particular belong to merging points. Most of the suitable meltblown materials according to the present disclosure may show fiber diameters of up to 500 µm only, however materials with the larger diameters may be suitable, as well. If the nonwoven cellulosic material is not manufactured by a meltblown process, the diameter range is much narrower, more comparable to that of a nonwovens consisting of staple fibers. In such case the fiber diameter may range from 1 µm to 100 µm, preferably from 7 µm to 50 µm.
The nonwoven layer according to another embodiment can further comprise fibers that are selected from a list comprising natural plant or animal fibers, man-made cellulosic fibers, such as viscose or lyocell fibers, synthetic polymer fibers, such as polypropylene fibers, polyester fibers, polylactic acid fibers, polyhydroxyalkanoate (PHA) fibers, or the like, wherein the ratio of these fibers is independently selected in an amount of between 0 percent per weight and 95 percent per weight. The addition of other fibers can improve the look and feel of the material, on the other hand it can reduce the costs of the material.
According to one embodiment, the physical properties of the nonwoven material are modified by at least one process selected from a list comprising bonding, hydroentanglement, hydroembossing, perforation, needlepunch, calendering and/or chemical bonding. By using such process steps the dimensional stability of the nonwoven layer can be further regulated, i.e. increased or decreased, as the case may be.
In another preferred embodiment, the nonwoven layer is essentially free of copper and/or nickel. This can be realized by the use of operating fluids (in particular lyocell spinning solution, coagulation fluid, washing liquor, gas flow, etc.) during the manufacturing process that are substantially free of heavy metal sources such as copper salt. As a result of this design of the manufacturing process, the cellulosic fibers according to the present disclosure may be of high quality and may substantially consist of pure microfibrillar cellulose. The absence of any mentionable heavy metal impurities in the manufacturing process prevents highly undesired decomposition of involved media (in particular of the lyocell spinning solution) and therefore allows to obtain highly reproducible and highly pure cellulose fibers that are biodegradable and skin-friendly.
The term "essentially free of copper and/or nickel", as it is used herein, denotes that these substances are maximally present in practically negligible amounts. For example, a copper contents of less than 5 ppm and/or a nickel contents of less than 3 ppm is practically negligible in most cases and therefore can be considered as essentially free of copper and/or nickel, respectively.
According to a second aspect, the present document discloses a Scrim layer material comprising at least one nonwoven layer according to the embodiments disclosed herein. Scrim layer materials according to the present disclosure are advantageous in terms of a low weight, a high dimensional stability and a good washability. The scrim layer material can be used in many textile applications, such as (but not restricted to) quilts, blankets, quilted jackets, jackets, sack coats, upholstery, pillows, bags, pockets, cases, luggages or the like. The scrim layer material can also comprise two or more nonwoven layers which can be of the same or different material. The several layers of such a scrim material can be interconnected by any known technique, such as needlepunching, hydroentanglement, sewing together, calandering, use of meltable poylmers and/or chemical binders.
In a third aspect, the current disclosure relates to a Textile product having at least one layer comprising a nonwoven layer according to the embodiments disclosed herein and/or a scrim layer material as it is disclosed herein.
According to a forth aspect, the present document discloses a method for producing a nonwoven layer comprising essentially continuous cellulosic filaments, wherein the filaments are spun in a meltblown-process, wherein the dimensional stability (DS) of the nonwoven layer is adjusted to a value of 1.5 mN·M²/g·% or more, preferably even 3.5 mN·m²/g·% or more, measured in at least one direction, preferably measured in machine direction (DS MD) or measured as an average value (DS total), wherein the dimensional stability (DS) of the nonwoven layer is defined according to the formula $DS = \frac{sHOM}{ELO}$
with

By adjusting the production parameters according to this method, a very thin nonwoven material with a very good dimensional stability can be produced. To adjust the dimensional stability numerous parameters can be adjusted, as it is detailedly described within this disclosure. For example, the dimensional stability can be adjusted by multibonding the fibers in the nonwoven layer, e.g. by merging, hydrogen bonding, physically intermingling and/or the use of chemical binders, by increasing the fiber diameter of the essentially continuous fibers, by fast drying the nonwoven material at elevated temperature, by fixed drying (i.e. fixed in machine direction) of the nonwoven material or the like.
According to one embodiment, the nonwoven layer is fixed at a constant elongation in at least the machine direction during at least one drying step. It has been surprisingly found, that the dimensional stability can be increased by fixing the nonwoven layer so that a shrinking of the nonwoven layer is avoided during drying at least in machine direction. Without being bound to this theory, it is believed that during drying the cellulosic fibers within the (fixed) nonwoven layer shrink in length which induces local areas of tension in the nonwoven layer. This leads to a stiffer material while reducing the elongation. The effect can be increased by the micro-fiber distribution within the nonwoven layer and the correspondingly high amount of hydrogen bonds.

Description of the Drawings

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

Fig. 1: shows a schematic block diagram showing the steps of a method for producing a nonwoven material according to the present disclosure,
Fig. 2: shows a schematic diagram of a production line adapted for producing a nonwoven layer according to the present disclosure,
Fig. 3: shows a photograph of a nonwoven layer produced in a production line according to Fig. 2, taken from a stereomicroscope. Diameters of the fibers were determined by image analysis software. The free areas between the cellulosic fibers and their distances can be measured from this photograph, as well.
Fig. 4: shows a diagram of the moisture uptake of nonwoven layers at 50% humidity,
Fig. 5: shows a diagram of the moisture uptake of nonwoven layers at 76% humidity and
Fig. 6: shows a diagram of the moisture uptake of nonwoven layers at 98% humidity.

Detailed Description

According to the present disclosure, a process for the manufacture of a nonwoven material consisting of essentially continuous cellulosic fibers can comprise the following steps, which are schematically shown in Fig. 1:

I. Preparation of a cellulose-containing spinning solution
II. Extrusion of the spinning solution through at least one spinneret containing closely-spaced meltblown jet nozzles
III. Attenuation of the extruded spinning solution using high velocity air streams,
IV. Forming of the web onto a moving surface (e.g. a perforated belt or drum),
V. Washing of the formed web
VI. Drying of the washed web under controlled tension.

In step III. and/or step IV. a coagulation liquor, i.e. a liquid which is able to cause coagulation of the dissolved cellulose can be applied to the fibers. In a lyocell process preferably water or a diluted solution of NMMO in water is applied as a coagulation liquor to control the merged filament bonding. The amount of merged filament bonding is directly dependent on the stage of coagulation of the filaments when the filaments come into contact. The earlier in the coagulation process that the filaments come into contact, the greater the degree of filament merging that is possible. Both, placement of the coagulation liquor application and the speed at which the coagulation liquor is applied, can either increase or decrease the rate of coagulation. Therefore, the degree (or amount) of merged filament bonding that occurs in the material can be controlled and adjusted.
According to the current disclosure a nonwoven layer is produced, which is characterized by a very high dry stiffness and a low dry elongation, so that the nonwoven layer can be used as a scrim layer material for textile production. The scrim layer material can be used in various applications, including clothes, furniture, blankets, pillows, bags, pockets, cases, luggage and the like. Apart form the dry stiffness and the dry elongation, a low basis weight, a high water and water vapour uptake capability, a good dimensional stability, and a proper washability are desirable properties of a scrim material that can be advantageously used in the textile industry.
Fig. 2 shows a schematic depiction of a production facility adapted for the production of a nonwoven layer according to the present disclosure.
A lyocell spin dope 1 is extruded via a spinneret 2 comprising a plurality of closely-spaced nozzels. The freshly extruded fibers are attenuated by a high velocity stream of air 3, as it is, e.g., known from WO 9701660 A1 .
In Fig. 2 two independent spinnerets 2 are shown, each extruding a plurality of fibers that are first at least partly coagulated by the application of a coagulation spray 4 and then collected on a moving belt 5, where they form a nonwoven layer 11 comprising a network of substantially continuous regenerated cellulosic fibers. The amount of coagulation spray 4 can be independently set for both spinnerets 2. A high amount of coagulation liquid leads to a quick coagulation of the fibers and reduces the amount of bonding sites by merging. On the contrary, a low amount of coagulation liquid produces a multibonded nonwoven layer.
The nonwoven layer 11 is then transported on the moving belt to a washing facility 6 and an optional hydroentanglement station 7. Then the nonwoven layer 11 is dried in a dryer 8 and wound up in a coil-formation device 9 onto a coil 10.
The dryer 8 is only schematically shown in Fig. 2. Preferably, according to the present disclosure, the nonwoven layer 11 can be transported within the dryer 8 with a fixed elongation in machine direction, so that a shrinking of the nonwoven layer 11 during drying is prevented ("fixed drying"). With the water evaporation in the dryer and the material having no possibility to shrink a self stretching effect is generated delivering surprisingly low dry Elongation values. In other embodiments, loose drying of the nonwoven layer 11 can be allowed, so that the nonwoven layer 11 is allowed to shrink during the drying step. It was observed that the dry elongation in machine direction (ELO MD) was decreased by at least 50 % with the fixed drying (versus lose drying). Additionally it was observed that the specific HOM value MD was increased by 60 % (versus loose drying).

Measurement protocols

As it is described herein, the measurements on nonwoven samples were either taken in a conditioned or in a wet state. If not specifically stated otherwise, the all values refer to the conditioned state.
The term "conditioned" or "dry", as it is used herein, denotes a sample that was subjected to the following protocol:
If not specifically stated otherwise, for the measurements in a dry or conditioned state all samples were conditioned at 23°C (±2°C) and 50% (±5%) relative humidity for 24 hours. The term "wet", as it is used herein, denotes samples that were wetted out 3 fold with demineralized water and were sealed within a plastic bag for 60 min to equilibrate moisture.
The "perceived stiffness" of a fabric (i.e. how the stiffness is rated by a user on a look-and-feel basis) can be measured with a so-called "Handel-O-Meter" as a HOM-value. Materials that are estimated by users as being stiffer, are generally characterized by a higher HOM-value.
The term "HOM-value", as it is used herein, denotes the measurement result of a so-called Handle-o-meter (HOM) test, which measures the combined effects of flexibility and surface friction of sheeted materials including nonwovens, tissue, toweling, film and textiles. Specifically, the HOM-value is measured using a Handle-o-meter (available from Thwing-Albert Instrument Company), Model 211-300, according to standard method NWSP 090.3.R0 (15) [EN], with ¼ inch slot width, stainless steel surface, 1000 g beam, 20x20cm sample size. The HOM-value can either be measured in a specific direction, for example in machine direction (i.e. the blade of the Handle-o-meter is arranged at 90 degree to the machine direction) or cross direction (i.e. the blade of the Handle-o-meter is arranged parallel to the machine direction). Further, a "total HOM-value" can be determined, which is an average value calculated according to NWSP 090.3.R0 (15) [EN]. The dimension of the HOM-value, as it is used herein, is millinewton [mN].
Based on the HOM-values, a specific HOM-value (sHOM) can be determined by dividing the HOM-value by the basis weight of the nonwoven layer. The dimension of the specific HOM-value, as it is used herein, is [mN·m²/g]. Corresponding to the HOM-value, also the specific HOM-value can be determined in a specific direction (e.g. MD or CD) or as a total specific HOM-value.
The HOM-value can, for example, be adjusted by the fiber diameter. Generally the use of thicker fibers leads to a higher HOM-value. Also multibonding the fibers in the nonwoven layer, e.g. by merging, hydrogen bonding and/or physically intermingling, can increase the HOM-value of the layer. In case the nonwoven layer is treated by hydroentanglement (also referred to as "spunlacing"), a decrease of the spunlace pressure can increase the HOM-value, especially in connection with highly multibonded nonwoven layers. Also the use of chemical binders can increase the HOM-value. Preferably biodegradable binders can be used. Generally, a higher basis weight also increases the HOM-value.
The term "basis weight", as it is used herein, denotes the mass per unit area as it is determined according to NWSP 130.1.R0 (15). The basis weight can, for example, be adjusted by the cellulose throughput at the spinneret(s) and/or the speed of the moving belt.
The term "dry elongation" (ELO) as it is used herein, denotes the elongation of the nonwoven layer at maximum tensile force. The dry elongation can usually be measured in machine direction (MD) or cross direction (CD), but can also be defined in any other direction. Also, a value for a total dry elongation can be derived as the mean value of the MD- and CD-values. If not specifically stated otherwise, the elongation is measured in a dry, conditioned state.
The maximum tensile force and the elongation at maximum tensile force was measured according to the following protocol:
Prior to all measurements, the samples were conditioned as described above. For all measurements, the samples had a size of 5 cm x 10 cm (width x length).
Maximum tensile force (Fmax) and the elongation (ELO) at maximum tensile force of the conditioned samples were measured according to DIN EN 29 073 part 3 / ISO 9073 3 (in the version of year 1992) in MD and/or CD. The clamping length was 8 cm and the speed for testing 10 cm/min.
To calculate the specific maximum tensile force (sFmax) the maximum tensile force was divided by the basis weight of each sample.
To adjust the dry elongation, the merging of the fibers, e.g. by multibonding or by the use of a chemical binder, can be increased or decreased. An increased merging decreases the dry elongation. Also, decreasing the spunlace pressure in a hydroentanglement step decreases the elongation.
The term "dimensional stability" (DS), as it is used herein, is defined as the specific HOM-value divided by the dry elongation. Also the dimensional stability can be determined in machine direction (MD), cross direction (CD) or as a total value, depending on the input values it is based on.

Examples

Example 1 - Fixed Drying

Three samples have been produced by the cellulose-meltblown process described above in connection with Fig. 2. Reference numbers that are used in the following description relate to Fig. 2.
A cellulose nonwoven web was produced by the following steps:
A lyocell spinning solution 1 containing 9% cellulose was prepared using a similar method as it is disclosed in WO 2018/184938 A1 . The spinning solution was extruded through a closely-spaced jet nozzles 2 and attenuated using high velocity air streams 3.
The web was formed onto a moving belt 5, washed 6 and dried 8, giving a web weight of 20 gsm and average diameter of unmerged filaments of around 5 microns. The final fabric was then wound 9 to create the final roll good 10. The hydroentanglement step 7 shown in Fig. 2 was omitted for the production of the samples.
Four different sample webs were produced: Samples A and C using a low amount of coagulation spray 4 (producing a highly multibonded nonwoven material) and Samples B and D using the double amount of coagulation spray than with Samples A and C (leading to a nonwoven material having less bonding sites).
Samples C and D were dried under full MD stretch, which means that the material was fixed in machine direction and not allowed to shrink during drying. All other production parameters were kept unchanged, compared to Samples A and B, respectively. All samples A, B, C and D were produced with a basis weight of 20 g/m². Samples A and B were dried using a lose drying approach, meaning that the material stayed relaxed in machine direction during drying and was allowed to shrink. The fixed drying (Samples C and D) led to a significantly reduced dry elongation (ELO MD) in the final dry fabric compared to the loose drying (Samples A and B).
It can be seen from a comparison of Sample A with Sample C or Sample B with Sample D, respectively, that the elongation was decreased by at least 50 %, as it is shown in Table 1. Additionally it was observed that the specific HOM value MD of the fixedly dried Samples C and D was increased by about 60 % versus the corresponding loose drying Samples A and B, respectively.
The results are shown in the Table 1 below. Samples A and B are the reference webs that were dried without fixation in MD but produced with two different coagulation spray levels.
Samples C and D are the materials dried with fixation in MD, i.e. with the material being fixed in at least MD during drying over the drum dryer.

Further, it can be seen that a low amount of coagulation spray leads to a higher sHOM-value due to the higher amount of bonding sites in the web.

Table 1

Sample code	Coagulation spray amount	Drying condition	Average filament diameter [µm]	Specific HOM MD [mN·m²/g]	Dry Elongation MD [%]
A	1x	lose drying	20	9.2	5
B	2x of A	lose drying	10	3.6	8
C	Same as for A	MD fixed drying	20	23	2.5
D	Same as for B	MD fixed drying	10	9	3.7

Example 2 - Hydroentanglement

In a second example samples of the web were produced according to the same protocol as described in Example 1, but this time comprising a hydroentanglement step 7 with a hydroentangling pressure of 45 bar. All other settings were kept constant.
It was observed that when applying the hydroentangling pressure the given MD dry Elongation was increased by at least 30 % and the specific MD HOM value was decreased by at least 40 %. It is therefore concluded that omitting the hydroentanglement step, or at least reducing the hydroentangling pressure, decreases the dry elongation and increases the HOM-value.

Example 3 - Binder

In a third example the material described above was coated offline with a biodegradable binder (10 % application level). The binder was found to increase specific total HOM value by at least a factor of 2 versus no binder applied. The MD dry elongation was not influenced by the binder in this experiment.

Example 4 - Moisture Uptake

Two Samples and one comparison Sample were tested for their moisture uptake (MU) from different air climates with varying relative humidity:

Sample 1 (S1): fabric according to the present disclosure - 15 gsm
Sample 2 (S2): fabric according to the present disclosure - 68 gsm
Comparison Sample (CS): kitchen paper "Zewa" - 43 gsm

The Samples S1 and S2 were produced according to the methods disclosed herein, wherein the production parameters were adjusted to minimize the dry elongation in machine direction (ELO MD) and to maximize the sHOM MD value, mainly by variation of the amount of coagulation fluid (to reach a high amount of multibonding), the speed of the moving belt, the cellulose throughput at the spinneret and the drying conditions.
As a comparison sample a commonly available household kitchen roll paper was used. When it comes to mechanical properties, kitchen paper is not comparable to scrim material nonwovens. Nonetheless, kitchen paper comprises highly absorptive cellulose paper that has a good moisture uptake and therefore was used as a reference for moisture uptake.
The moisture uptake was measured according to the following protocol:
The test climates in use were:

TC50:: 23°C(±2°C), 50% (±5%) relative humidity: test climate of climate room
TC76:: 23 °C(±2°C), 76 % relative humidity with supersaturated NaCl solution in exsiccator
TC98:: 23 °C(±2°C), 98 % relative humidity with supersaturated CuSO4 * 5 H₂O solution in exsiccator

For the supersaturated salt solutions used in a closed exsiccator 24 h were used for specific climate setting. All the test climates were checked with a moisture measurement equipment (Testo 625) before starting the testing.
For each test sample three test specimens with 5 cm diameter were prepared for each test climate evaluation. The specimens were dried in a vacuum drying chamber (Thermo Electron CORPORATION Heraeus vacutherm) at 60 °C for 14 h at 200 mbar and for 1 h at 350 mbar. After drying the specimens were cooled down to 23°C (±2°C) ambient temperature in an exsiccator with a drying agent (Orange - Gel in a glass bowl) for 15 min.
Afterwards the specimens were weighted on an analytical balance to generate the starting weight.
Then the specimens were placed into the test climate systems and taken out to be weighted on an analytical balance after 1, 2, 4, 6 and 24 h.
The moisture uptake % for each specimen was calculated as follows: $Moisture uptake % = ((\begin{array}{l} weight of specimen after time interval t [g] / starting weight of \\ specimen [g] \end{array}) * 100) - 100$
t = 1h or 2h or 4h or 6h or 24 h
For each sample type and test climate type the average moisture uptake value in % for the 3 specimen after the time interval t were calculated.
Fig. 4, 5 and 6 show diagrams of the moisture uptake (MU [%]) over Time (t [h]) of the two samples (S1 and S2) and the comparison sample (CS). Fig. 4 shows the results for 50% test climate (TC50%), Fig. 5 shows the results for 76% test climate (TC76%) and Fig. 6 shows the results for 98% test climate (TC98%)
These results show that the nonwoven layers according to the present disclosure equilibrate well with the humidity of the environment which provides for a high wear comfort of textiles using this nonwoven layers as a scrim material.

Example 5 - Dimensional Stability

Several Samples were produced according to the methods described herein, wherein the production parameters were adjusted to minimize the dry elongation in machine direction (ELO MD) and to maximize the sHOM MD value, manly by variation of the amount of coagulation fluid (to reach a high amount of multibonding), the speed of the moving belt, the cellulose throughput at the spinneret and the drying conditions. From the so produced nonwoven layers Samples E to L were chosen (to represent different basic weights and parameters) and analyzed for their properties.

The measurement results of the Samples are shown in Table 2 below.

Table 2

Sample code	BW	ELO MD	ELO CD	sFmax MD	sHOM Total	sHOM MD	sHOM CD	DS MD	DS CD	DS Total
	[g/ m²]	[%]	[%]	[N·m² /g]	[mN·m² /g]	[mN·m² /g]	[mN·m² /g]	[mN·m² /g·%]	[mN·m² /g·%]	[mN·m² /g·%]
E	20	3.2	16.1	0.5	6.60	9.05	3.75	2.83	0.23	1.53
F	24	3.5	12.9	0.5	10.12	13.33	5.43	3.81	0.42	2.12
G	20	2.5	10.3	0.8	14.16	18.68	9.65	7.47	0.94	4.21
H	21	2.6	11.9	0.7	13.68	17.67	9.69	6.79	0.81	3.80
I	28	3.4	34.9	0.5	10.98	17.51	4.44	5.15	0.13	2.64
J	60	3.3	9.7	0.8	37.74	53.17	22.30	16.11	2.30	9.21
K	54	4.4	11.3	0.7	13.11	17.57	8.64	3.99	0.76	2.38
L	19	3.7	13.8	0.4	16.24	22.99	9.48	6.21	0.69	3.45

The measurement results of the samples given in Table 2 show a very high dimensional stability of the nonwoven layers according to the present disclosure. The dimensional stability is especially high in machine direction, but also in cross direction the values are significantly higher than common nonwovens (see comparison examples).
Fig. 3 shows a microscopic photograph of the nonwoven of Sample L. The microscopic pictures were taken with a Stereomicroscope Zeiss V12 and a camera DP 71, Software: Olympus Stream Motion. Magnification 20 fold.

Comparative examples

To provide a comparison, 11 nonwovens that are commercially available were tested according to the same protocol as described above. The following products have been used as comparative examples (Comparative codes M to W):

M: Polypropylene spunbond
N: Polypropylene spunbond/meltblown/spunbond (SMS)
O: Polypropylene spunbond/meltblown/spunbond (SMS)
P: Polypropylene spunbond/meltblown/spunbond (SMS)
Q: Polypropylene spunbond/meltblown/spunbond (SMS)
R: 100 % cellulosic Bemliese fabric
S: carded-hydroentangled staple fiber Lyocell
T: carded-hydroentangled staple fiber Lyocell
U: carded-hydroentangled staple fiber Lyocell
V: carded-hydroentangled staple fiber Lyocell
W: carded-hydroentangled staple fiber Lyocell

The results of the measurements are shown in Table 3 below.

Table 3

Comp. code	BW	ELO MD	ELO CD	sFmax MD	sHOM Total	sHOM MD	sHOM CD	DS MD	DS CD	DS Total
	[g/m²]	[%]	[%]	[N·m² /g]	[mN·m² /g]	[mN·m² /g]	[mN·m² /g]	[mN·m² /g·%]	[mN·m² /g·%]	[mN·m² /g·%]
M	31	74.4	141.2	1.3	14.99	18.42	11.57	0.25	0.08	0.17
N	8	47.4	72.3	2.2	8.38	8.28	8.48	0.17	0.12	0.15
O	11	43.1	62.5	2.0	5.24	5.35	5.13	0.12	0.08	0.10
P	12	47.7	57.7	2.1	5.99	6.79	5.19	0.14	0.09	0.12
Q	15	42.7	50.1	1.9	5.53	7.30	3.76	0.17	0.08	0.13
R	37	17.7	52	0.9	13.47	21.47	5.48	1.21	0.11	0.66
S	32	10.0	54.1	2.2	5.59	8.25	2.94	0.82	0.05	0.44
T	44	15.0	48.1	2.1	7.71	12.89	2.53	0.86	0.05	0.46
U	34	29.4	71.2	1.4	6.54	10.40	2.68	0.35	0.04	0.20
V	51	23.0	49.4	1.9	10.69	15.88	5.50	0.69	0.11	0.40
w	28	10.8	72	1.9	8.05	13.15	2.95	1.22	0.04	0.63

The results show that common nonwoven materials that are available in commerce exhibit a very low dimensional stability. Most nonwoven materials have a maximum dimensional stability ranging from about 0.1 to about 0.9 mN·M²/g·%. Only two materials (comparative examples R and W) showed an elevated dimensional stability of 1.21 or 1.22 mN·M²/g·%, respectively.

Claims

Nonwoven layer comprising a network of substantially continuous regenerated cellulosic fibers, characterized in that the nonwoven layer has a dimensional stability (DS) of 1.5 mN·m²/g·% or more, preferably even 3.5 mN·m²/g·% or more, measured in at least one direction, preferably measured in machine direction (DS MD) or measured as an average value (DS total), wherein the dimensional stability (DS) of the nonwoven layer is defined according to the formula $DS = \frac{sHOM}{ELO}$
with
DS ... dimensional stability [mN·m²/g·%]

sHOM ... specific HOM-value [mN·m²/g],

ELO ... dry elongation [%].
Nonwoven layer according to Claim 1, wherein the nonwoven layer has a dry elongation (ELO) in at least one direction, preferably in machine direction, of equal to or less than 8 % and/or a specific HOM-value (sHOM) in at least one direction, preferably in machine direction, of 3 mN·m²/g or more, preferably 9 mN·m²/g or more and even more preferred of 12 mN·m²/g or more.
Nonwoven layer according to Claim 1 or 2, wherein the nonwoven layer has a basis weight between 10 and 200 g/m², preferably between 15 and 90 g/m².
Nonwoven layer according to any of the Claims 1 to 3, wherein the nonwoven layer has a specific maximum tensile force in at least one direction, preferably in machine direction, of 0.3 N·m²/g or more, preferably of 0.5 N·m²/g or more and even more preferred of 0.7 N·m²/g or more.
Nonwoven layer according to any of the Claims 1 to 4, wherein the nonwoven layer has a moisture uptake of at least 15% after 24 h at 98% relative humidity and/or at least 7% after 24 h at 76% relative humidity and/or at least 4% after 24 h at 50% relative humidity.
Nonwoven layer according to any of the Claims 1 to 5, wherein at least a part of the nonwoven layer is directly manufactured from lyocell spinning solution.
Nonwoven layer according to any of the claims 1 to 6, wherein the cellulosic fibers in the nonwoven layer are multibonded by merging, hydrogen bonding and/or physically intermingling.
Nonwoven layer according to any of the claims 1 to 7, wherein the fibers of the carrier layer have diameters ranging from 1 µm to 5000 µm, preferably from 8 µm to 500 µm.
Nonwoven layer according to any of the Claims 1 to 8, wherein the nonwoven layer further comprises fibers that are selected from a list comprising natural plant or animal fibers, man-made cellulosic fibers, such as viscose or lyocell fibers, synthetic polymer fibers, such as polypropylene fibers, polyester fibers, polylactic acid fibers, polyhydroxyalkanoate (PHA) fibers or the like, wherein the ratio of these fibers is independently selected in an amount of between 0 percent per weight and 95 percent per weight.
Nonwoven layer according to any of the Claims 1 to 9, wherein the physical properties of the nonwoven material are modified by at least one process selected from a list comprising bonding, hydroentanglement, hydroembossing, perforation, needlepunch, calendering and/or chemical bonding.
Nonwoven layer according to any of the Claims 1 to 10, wherein the nonwoven layer is essentially free of copper and/or nickel.
Scrim layer material comprising at least one nonwoven layer according to any of the Claims 1 to 11.
Textile product having at least one layer comprising the nonwoven layer according to any of the claims 1 to 11 and/or the scrim layer material according to Claim 12.
Method for producing a nonwoven layer comprising essentially continuous cellulosic filaments, wherein the filaments are spun in a meltblown-process, wherein the dimensional stability (DS) of the nonwoven layer is adjusted to a value of 1.5 mN·m²/g·% or more, preferably even 3.5 mN·m²/g·% or more, measured in at least one direction, preferably measured in machine direction (DS MD) or measured as an average value (DS total), wherein the dimensional stability (DS) of the nonwoven layer is defined according to the formula $DS = \frac{sHOM}{ELO}$
with
DS ... dimensional stability [mN·m²/g·%]

sHOM ... specific HOM-value [mN·m²/g],

ELO ... dry elongation [%].
Method according to according to Claim 14, wherein the nonwoven layer is fixed at a constant elongation in at least the machine direction during at least one drying step.