CN112204185A

CN112204185A - Fibrous nonwoven web

Info

Publication number: CN112204185A
Application number: CN201980037331.3A
Authority: CN
Inventors: T·迈尔; R·伊尔克
Original assignee: Lenzing AG
Current assignee: Lenzing AG
Priority date: 2018-04-06
Filing date: 2019-04-08
Publication date: 2021-01-08
Also published as: US20210222335A1; WO2019193201A1; EP3550062A1; EP3775345A1

Abstract

The present invention relates to fibrous nonwoven webs, methods of making the same, and uses of the novel fibrous nonwoven webs.

Description

Fibrous nonwoven web

Prior Art

Fibrous nonwoven webs are used in a wide variety of technical fields, from flushable toilet tissue and baby wipes to industrial wipes. These nonwoven fabrics typically employ pulp and viscose. If higher mechanical strength is required, thermoplastic binders (which may be in powder or fiber form) and reinforcing fibers are employed, since it is not believed possible to ensure the required strength without the use of these components.

US 4,755,421 discloses a nonwoven web which is generally described in (5 to 30): (95 to 70) comprises cellulose fibers and pulp fibers. The web is designed for use as a flushable toilet paper, i.e., the web is intended to disintegrate in water under mild agitation conditions. The cellulose fiber is a rayon fiber having a denier of 3.3 to 6.7. The pulp is not described in any further detail.

US 6,287,419 discloses a water-disintegratable nonwoven fabric comprising first and second regenerated cellulose fibers and natural fibers. These different fibers are characterized by their fiber length and the natural fibers are preferably pulp fibers. US 6,287,419 emphasizes the importance of using binder resins if improved mechanical properties are desired.

EP 2441869 discloses a water-disintegratable fibrous sheet comprising two different types of pulp, fibrillated cellulose and regenerated cellulose fibres. These sheets are intended to be used as simple wipes for single use and are designed to disintegrate under mild agitation conditions (e.g. flushing of a toilet) so that they can be easily disposed of after use.

US 2004/0013859 discloses a fibrous nonwoven web material comprising man-made cellulose fibers, natural cellulose fibers and synthetic binder fibers. Also, the web is intended to disintegrate by mild agitation conditions (e.g., flushing of a toilet) so that wipes made from the web can be easily disposed of after use.

These prior art methods, while providing useful wipes, generally suffer from the following disadvantages: at least three different fibrous materials are used or a synthetic binder material (e.g., synthetic fibers) is required to provide sufficient mechanical strength. The use of such synthetic fibers has a detrimental effect on the sustainability of the product, since, for example, petroleum-based materials are used as binder materials. Furthermore, the use of synthetic binder materials has a negative impact on biodegradability, since for example not all components of the web can be decomposed within a suitable time frame and additional filtration and/or purification steps are required in wastewater treatment plants (for example for flushable toilet tissue or baby wipes comprising such materials).

WO 2011/046478 a1 discloses a flushable wet wipe or sanitary napkin. The tissue is a nonwoven material comprising pulp fibers and man-made and/or natural fibers. WO 2014/092806 a1 discloses a hydroentangled air-laid production process and products obtained therefrom. The product comprises natural cellulose fibres as well as staple fibres (stable fibres). WO 2013/015735 a1 discloses a flushable wet wipe or tissue and a method of making the same. The paper towel comprises pulp fibers and polylactic acid fibers. US 2008/0268205 a1 discloses a disposable nonwoven web having at least 3 layers. WO 2013/067557 a1 discloses disposable nonwoven fabrics comprising pulp and lyocell fibers.

Several types of wipes based on cellulose fibers are already commercially available. Possible uses extend from baby wipes and wet toilet tissue (i.e., low mechanical strength webs typically comprising pulp and viscose fibers) to industrial wipes (i.e., high mechanical strength webs comprising binder fibers and/or reinforcing fibers, typically synthetic fibers such as olefin-based fibers or PET fibers). Commercially available industrial wipes do exhibit basis weights in the range of 20 to 100 g/m²In the range, the tensile strength properties (machine direction, MD) are in the range of 10 to 100N/5 cm (dry and wet, with slightly lower wet tensile strength). For wipes with less mechanical requirements, the respective measured value is 50 to 120 g/m²And in the range of 10 to 80N/5 cm. With such a web, Water Retention Values (WRV) and Liquid Absorption Capacity (LAC) of 10 to 50% and 350 to 1000%, respectively, can be achieved. It is interesting to note, however, that even low strength webs for baby wipes do employ synthetic fibers, such as polyester fibers, polyolefin fibers, and the like, so that even those requiring relatively low or moderate levels of mechanical strength propertiesIs not 100% based on materials produced from renewable resources and synthetic non-biodegradable materials are introduced into waste treatment systems. It therefore appears that up to now webs based only on cellulosic materials do not solve the market demands related to mechanical properties.

However, as with the wipes disclosed in the prior art documents discussed above, commercially available wipes do also suffer from drawbacks such as the need for petroleum based fibres such as polyolefin fibres or polyester fibres, which are necessary to achieve high mechanical strength levels, or the use of cellulose fibres which require specific fibrillation treatments or are based on the need for regenerated cellulose fibres using chemicals which cannot be reused.

Objects of the invention

Thus, it would be preferred that fibrous nonwoven web materials would be available that ensure a high level of mechanical strength without the use of synthetic bonding or reinforcing fibers. At the same time, it would be advantageous to be able to provide such web materials that require only a minimal amount of fibrous material while still enabling the preparation of nonwoven webs or fabrics suitable as wipes in a wide variety of applications. It would also be advantageous if such a web would only require the presence of decomposable fibers (preferably fibers that do not require any post-fiber production treatment, such as a chemical fibrillation treatment), and if the fibers to be employed were natural or regenerated fibers (which may be produced in an efficient and environmentally friendly manner, such as in a manner that enables a large degree of reuse of any chemicals required for the regeneration process).

Brief description of the invention

The invention achieves this object with a fibrous nonwoven web as defined in claims 1 to 9 and a method as defined in claims 10 to 15. Other embodiments and illustrations of the invention are summarized below.

Detailed Description

As outlined in claim 1, an essential component of the web of the invention is pulp. Such pulp may be of any origin as long as the requirements as outlined in claim 1 are met, in particular a fiber length of 1.5 to 5 mm, preferably 2 to 5 mm, and in particular 2.2 to 2.8 mm, for example 2.4 to 2.6 mm. The pulp may be bleached or unbleached pulp and preferably the pulp has a fines content (LWL (%)) of from 1 to 5, preferably from 2 to 4, more preferably from 2.5 to 3.5. In embodiments, the pulp may have a thickness (mg/100m) of 5 to 25, preferably 8 to 20, more preferably 10 to 15, for example 12 to 14. Particularly preferred pulp materials have a fiber length (LWL, mm) of 2.2 to 2.8 mm, a fiber thickness of 10 to 15 and a fines content of 2.5 to 3.5. Such pulps are commercially available at low cost and contribute to the overall commercial viability of the webs of the present invention.

As also outlined in claim 1, the second essential component of the web of the present invention is lyocell (lyocell) fibres having a length of 5 to 25 mm. Preferably the length is from 7 to 20 mm, and especially from 8 to 15 mm, for example from 10 to 12 mm. The lyocell fibers may be standard fibers, fibers containing matting agents, fibrillated fibers, and the like. The type of lyocell fiber has no relevant effect on the requisite product properties as discussed further below, as long as the fiber has a length as indicated above. Preferably, the lyocell fibre has a titre in the range 0.9 to 3.3 dtex, more preferably 1.15 to 2.5 dtex, most preferably 1.3 to 2 dtex, for example 1.4 or 1.7 dtex. Particularly suitable lyocell fibres have a fibre length of from 8 to 15 mm and a titre of from 1.3 to 2 dtex. Such fibers are commercially available, for example under the trade name LENZING^TMLyocell Shortcut is commercially available from Lenzing AG.

In a preferred embodiment, these two fiber types (i.e. pulp and lyocell) are the only fiber components present in the web according to the invention. Preferably, the two fiber components equal 90 wt.% or more, more preferably 95 wt.% or more, even more preferably 98 wt.% or more (based on the dry weight of the web) of the web. In an embodiment of the invention, the fibrous nonwoven web according to the invention contains only pulp and lyocell fibers, and any unavoidable processing additives. In embodiments, however, the web may also contain additional components, typically in amounts not exceeding 10 wt.% in total, such as other types of cellulose-based fibers, including viscose fibers, fibers made from cellulose derivatives (e.g., carboxymethyl cellulose, etc.), other fibers based on natural and/or renewable resources such as hemp fibers, etc., and in embodiments, also synthetic fibers. Preferably, however, the web comprises only fibers based on natural and/or renewable resources, in particular only cellulose-based fibers.

It is particularly preferred that the product according to the invention does not comprise (complex) polylactic acid fibres. It is also preferred that the product according to the invention is a single layer product, since it is possible to obtain the desired mechanical properties even with a high proportion of pulp fibres having a small fibre length without requiring the presence of an additional layer, which in the prior art is sometimes used to reinforce tissue or wipe products.

The weight of pulp and lyocell fibres is as defined in claim 1, wherein the pulp fibres amount to at least 35%, preferably at least 40% and in particular 50% or more, based on the weight of the pulp and lyocell fibres. Preferably, the weight ratio is from 90:10 to 50:50, more preferably from 85:15 to 55: 45. Particularly suitable weight ratios are in the range of 80:20 to 60:40, in embodiments 70: 30. However, in particular, when the weight of the pulp is equal to at least 50%, the mixture of pulp and lyocell enables the production of a web having the desired balance of properties, while maintaining cost-effectiveness.

As will be explained in more detail later in the context of the method of making the web of the present invention, the pulp and lyocell fibers are thoroughly mixed prior to making the web to ensure a uniform mixture and uniform web properties. Such mixing typically comprises mixing in an aqueous medium, preferably in water. Suitable mixing equipment and mixing parameters (agitation, shear rate, amount of fiber in aqueous medium) are known to the skilled person.

The fibrous nonwoven web according to the invention typically has a basis weight in the range of from 25 to 200 gsm, for example from 50 to 175 gsm, preferably from 60 to 150 gsm. Such basis weights are common in the field of webs for wipes, but webs according to the present invention do provide a unique combination of mechanical properties at these basis weights without requiring the presence of synthetic reinforcing fibers or synthetic binders for high mechanical strength levels, or requiring the use of a mixture of three or even more types of fibers for lower mechanical strength levels.

As will be further explained in relation to the process of the present invention, by means of the energy consumption during hydroentangling (i.e. the energy impact on the web material during hydroentangling of the fibers), it is possible to adjust the final mechanical properties of the resulting web simply by adjusting the weight ratio between pulp and lyocell fibers, and to a lesser extent also by optionally adjusting the fiber length, to produce webs with lower mechanical strength levels (lower energy consumption) or webs with higher strength levels (higher energy consumption) which in the prior art has generally only been possible by means of the use of synthetic reinforcing fibers or binders (in fibrous powder). Higher strength levels according to the present invention are strength levels represented by tensile strengths (MD, dry, N/5cm) greater than 50 and in embodiments up to 150 or more. The strength levels achieved by the present invention must be considered extremely surprising in comparison to commercial high strength wipes which do exhibit tensile strengths from about 30 up to 100(MD, dry, N/5cm), since all high strength level materials known in the art require the use of reinforcing and/or binding fibers, such as polyolefin or polyester fibers, for similar but still lower strength levels. It is in no way foreseeable that a rather simple mixture of fibers according to the invention, which does not even require the presence of reinforcing or binding fibers, as explained and exemplified above, makes it possible to provide nonwoven materials having at least equal, but in embodiments even higher, strength levels.

Thus, the present invention provides fibrous nonwoven webs based on fibrous materials that are biodegradable and further based on natural (i.e., renewable/sustainable) raw materials. According to the present invention, there is no need to use a petrochemical-based material, and the lyocell fiber employed in the present invention is produced by the following method: the process largely reuses all the chemicals employed, particularly the solvents required for dissolution and spinning, and thus the present invention provides an overall green and sustainable product. Since the starting materials pulp and lyocell fibers to be used in the present invention are standard materials, the total cost of the novel product can be kept at a very competitive level. Due to the possibility of adjusting the properties of the product by means of raw material composition and energy consumption during hydroentanglement, it is possible to produce products specifically adapted to the intended end use, so that the present invention can be seen as providing a module-based system which enables the production of a wide variety of products using only a small number of variables (see above) without the need to use additional components, such as reinforcing fibers, agents improving biodegradability, etc. These advantages associated with the present invention must be seen as a vast and unexpected improvement over the prior art.

As already outlined in the claims, it is possible to provide the fibrous nonwoven web according to the invention with a two-dimensional or three-dimensional structure using methods known to the person skilled in the art of fibrous nonwoven webs, for example by embossing, by providing perforations or the like. The net according to the invention allows to provide such a structure without adversely affecting the mechanical properties (strength) of the net. As exemplified in the examples, it has been found that providing such a structure improves other properties, such as oil absorption, so that the high strength web according to the invention does show promise in the field of industrial wipes where only reinforced wipes so far have shown sufficient mechanical strength to allow practical use.

The web according to the invention does in any case show a very good balance of properties, in particular of mechanical properties (tensile strength) and properties relevant to the application (for example WRV and LAC). The webs according to the invention do show satisfactory LAC values of significantly above 400, in embodiments exceeding 600, typically in combination with WRV values above 50. This is roughly equivalent to the balance of performance properties of commercial wipes. However, the tensile strength values of these webs according to the invention are generally higher than those of commercial wipes, since these typically show tensile strength values of up to 25N/5 cm (dry, MD) for low strength products (for baby wipes and wet toilet tissue) and up to 80N/5 cm (dry, MD) for medium strength products. For low strength products, the webs of the invention have values of up to 60N/5 cm (dry, MD) and for medium strength products, values of up to 150N/5 cm (dry, MD). The invention thus makes it possible to provide a fibrous nonwoven web with an overall improved balance of performance properties (WRV, LAC) and mechanical properties (tensile strength), simply by using two standard products (pulp and lyocell) in a defined weight ratio. This becomes even more pronounced when considering the high strength web according to the invention. These do again show similar use properties as the commercial products, such as WRV and LAC, while achieving the desired mechanical properties, in particular tensile strength values, without the need to add bonding and/or reinforcing fibers. Commercial industrial wipes, which are a prominent example of high strength webs in the art, have tensile strength values ranging from 30 up to about 100N/5 cm (dry, MD), while values up to 250N/5 cm (dry, MD) are achieved without the use of reinforcing or bonding fibers in the present invention. This is a completely unexpected and significant achievement over the prior art.

As indicated above, the present invention enables the performance to be adjusted simply by adjusting the weight ratio of pulp to lyocell fibers and by adjusting the energy consumption during hydroentanglement. Generally, higher lyocell fiber content improves mechanical properties. At the same time, even for webs comprising a lower proportion of lyocell fibres, the same effect is achieved in increasing the energy consumption during hydroentanglement. Thus, high strength webs according to the present invention are typically webs having a higher basis weight (typically 150 or more), 80:20 to 40:60 pulp to lyocell fiber weight ratio. Webs having a lower basis weight and a pulp to lyocell weight ratio of 70:30 to 90:10 are typically medium or low strength webs.

As indicated above, the particular use of lyocell fibers ensures that combination with pulp provides a very cost effective web that can be considered sustainable. However, the use of lyocell fibres is also unexpectedly used to improve the mechanical properties, in particular the tensile strength properties, of the web according to the invention. Surprisingly, the inventors have found that the use of lyocell fibres alone ensures good mechanical properties, as compared for example to other regenerated cellulose fibres (e.g. viscose fibres). Webs produced with viscose instead of lyocell fibres (of the same length and titre) do not produce webs with the strength levels achieved with corresponding webs of lyocell fibres (under the same production conditions and using an otherwise identical mixture with pulp). It is therefore evident that the invention is based on the specific selection of raw materials, which makes the indicated achievement possible.

The present invention will now be described with respect to a method of making a fibrous nonwoven web according to the present invention. It is to be understood that all embodiments described above in relation to the web of the invention as preferred are equally applicable to the process disclosed herein.

Hydroentangling processes can be used to produce fibrous nonwoven webs according to the present invention. Such processes are known to the skilled person and conventional equipment for such processes can be used to prepare the webs of the present invention.

Typically, the process first comprises intimate mixing of pulp and lyocell fibers, which may be carried out in a pulper. Water is typically added to the mixture to ensure proper dispersion. In order to adjust the water content of the initial mixture, it may be passed through a station suitable for adjusting the concentration, for example a mixing tank. This ensures that the mixture can be pumped to the next stage of the process and in particular that the mixture can be evenly distributed onto the web required for feeding the web that has not yet been entangled to the hydroentangling station. After mixing, the prepared mixture (slurry) is provided to a distribution station that distributes the mixture onto a moving belt in a desired amount and width. The amount provided to the belt is adjusted, in particular with respect to a target basis weight of the fibrous nonwoven web to be produced. The belt is generally adapted to perform a special dewatering step so that the distributed slurry results in a so-called wet-laid material. Additional stations for further water removal may be provided, such as vacuum stations, which generally also ensure improved uniformity of the wet laid material. Subsequently, in a typical process, an additional drying step is carried out, for example by using a steam-heated tank dryer or other conventional drying means. After these treatments, the dried wet-laid web may be wound onto a roll to be sent to a hydroentangling step, however, it is also possible to send the wet-laid web directly to a hydroentangling process according to steps known in the art, and of course, when the wet-laid web is sent directly to hydroentangling, it is also possible to omit some or all of the drying steps. Typical continuous processes do not include a drying step prior to the hydroentangling step. However, a dewatering step (typically including a vacuum dewatering step) is typically used in such continuous processes.

The hydroentanglement can be carried out using water jets or water jets, which are arranged on one side of the web to be entangled or on both sides of the web to be entangled. The number of water jets is not critical, but two or more jets are conventional. A process employing a total of four water jets (preferably two on each side of the web) has been shown to be well suited for producing the fibrous nonwoven web of the present invention. The process conditions during entangling may be selected from conventional conditions known to the skilled person, such as water pressure etc. It has been found that in order to reproducibly produce the fibrous nonwoven web of the present invention, the so-called energy expenditure (sometimes referred to as hydroentanglement energy expenditure) is a good measure to ensure that the desired target values in the fibrous nonwoven web are achieved. The energy consumption (related to water jet) is the theoretical value given in kWh/kg (dry fibrous nonwoven web) calculated based on water pressure, production rate and basis weight. Calculations can be performed based on the principles disclosed in Vliesstoffe, w.albrecht, h.fuchs, w.kittelmann (eds.), Wiley-VCH 2000, page 329, equation (23).

Energy consumption values generally in the range of 0.05 to 1 kWh/kg are suitable for the present invention. However, it is to be understood that higher and/or lower values are not to be excluded, but that the values given above are typical values, which are given here as an illustration, also taking into account the specific conditions employed in the examples described below. A suitable range of energy consumption is in particular a value of 0.1 to 0.9 kWh/kg. As already indicated above, the adjustment of the energy consumption with due consideration of the basis weight and the weight ratio of pulp to lyocell fibres can adjust the mechanical properties of the produced web. Tensile strength values (dry, MD) above 250N/5 cm can be obtained using an energy expenditure of 0.3659 kWh/kg with a basis weight of, for example, (also as exemplified in the examples) 170 gsm and a pulp to lyocell fiber ratio of 40: 60. Lower tensile strength values are obtained with lower energy expenditure, for example below 250N/5 cm at 0.1464 kWh/kg. Tensile strength values (dry, MD) of about 170 and about 150N/5 cm, respectively, were obtained using a basis weight of 170 gsm but a 80:20 pulp to lyocell fiber ratio at the same energy expenditure value. These experimental results indeed demonstrate the general feasibility of the concept and modular system provided by the present invention.

In general, as is known to the skilled person, the energy consumption can easily be adjusted by varying the production speed (the speed at which the moving belt moves the wet-laid web through the hydroentangling station) and/or by varying the water pressure during the hydroentangling. In the present invention, when considering these two options, it is preferable to increase the energy consumption by increasing the water pressure, as compared to increasing the energy consumption by decreasing the production speed.

The web may, after having been entangled, be subjected to any desired post-treatment steps, such as a dewatering and drying process, using, for example, a vacuum dewatering unit and/or a through air drying unit, etc., in accordance with common knowledge. The web can then be wound on a roll to be transported to further processing steps, such as cutting to a desired size, applying additives, such as lotions for cosmetic wipes, and the like. As indicated above, the web according to the invention may be provided with a two-dimensional or three-dimensional structure by embossing or the like. Such methods are known to the skilled person and the method steps may be provided at any suitable stage of the above-described method.

The invention will now be further described by means of exemplary embodiments.

Examples

Measuring method

Determination of the WRV value in accordance with DIN 53814

Determination of the LAC value according to DIN 53923

Basis weight determination according to DIN EN 29073 part 1

Determination of tensile Strength according to DIN EN 29073 part 3

The materials used

Mixing a pulp having a fiber length of 2.4 to 2.6 mm, a thickness of 12 to 14 mg/100m and a fines content of 3 wt.% (Canfor ECF 90 bleached pulp) with LENZING^TMLyocell short fibers 1.7dtex/10mm (bright) and 1.4dtex/10mm (bright) were mixed in the ratios further exemplified below. If the examples do not explicitly indicate the lyocell fibres used, those of titer 1.4dtex which are indicated above are usedAnd (3) a plurality of.

Method for making a web

The substrate was laid down, dewatered, dried and wound onto rolls using a wet-laid line from PILL Nassvliestechnik GmbH (1-schichtie Pilo-Schr ä gsiebanlage NVLA-58). The roll is then unwound to convey the not yet entangled web material to a hydroentangling (hydro-entangling) line comprising a pre-wetting unit, two water jets on the top side of the web followed by two water jets on the bottom side of the web, a vacuum box for dewatering and a through-air dryer for drying the hydroentangled material.

Example 1

The following fibrous nonwoven webs were made:

a.) basis weight 170 gsm, pulp to lyocell fiber weight ratio 40/60

b.) basis weight 170 gsm, pulp to lyocell fiber weight ratio 80/20

c.) basis weight 100 gsm, pulp to lyocell fiber weight ratio 80/20

The webs were hydroentangled with different energy consumptions of 0.1464 kWh/kg (a.)), 0.1746 kWh/kg (b.), 0.2614 kWh/kg (c.)), 0.3118 kWh/kg (d.)), 0.3659 kWh/kg (e.)) and 0.4366 kWh/kg (f.)), respectively.

The resulting web showed the following properties:

these results do show that: with high pulp content and lower basis weight, very high WRV values and especially LAC values can be obtained while the mechanical properties are still satisfactory. Increasing the basis weight from 100 gsm to 170 gsm resulted in a slight decrease in LAC, but increased mechanical properties by a factor of 2 or more. Increasing the lyocell content to 2-fold (a pulp to lyocell weight ratio of 60/40) yields a still high LAC value, but increases the mechanical properties to a level that is not reached even by commercial webs containing reinforcing/binding fibers.

Example 2

To demonstrate that the present invention also provides a lower basis weight of valuable products, additional webs were prepared according to the following:

d.1) to d.3.) basis weight 60 gsm, pulp to lyocell fiber weight ratios 60/40, 70/30 and 80/20

e.1) to e.3.) basis weight 80 gsm, pulp to lyocell fiber weight ratios 60/40, 70/30, and 80/20

f.1) to f.3.) basis weight 100 gsm, pulp to lyocell fiber weight ratios 60/40, 70/30 and 80/20

The web was hydroentangled with an energy expenditure of 0.4136 kWh/kg (g.)). The webs do show a favourable combination of high LAC values and very satisfactory mechanical properties.

These results do show that: with low basis weight and high energy consumption, very high LAC values can be obtained while the mechanical properties are still satisfactory. Increasing basis weight resulted in a reduction in LAC, but significantly improved mechanical properties, and thus, very high mechanical property levels were obtained even for very high pulp webs (pulp to lyocell weight ratios of 70/30 and 80/20), even for wet webs. From these results it can be concluded that: even with high pulp content, increased energy consumption enables the production of low basis weight webs that do exhibit surprisingly high strength levels despite the absence of reinforcing fibers or binders. At the same time, these nets only contain biodegradable materials from renewable resources, so that these nets can obviously be considered as sustainable products.

Example 3

To demonstrate the superiority of the fibrous nonwoven webs of the present invention compared to webs comprising other types of cellulosic fibers and/or to demonstrate the correlation of fiber denier, additional tests were run using webs subjected to hydroentanglement with an energy expenditure of 0.481 kWh/kg.

g.) basis weight 80 gsm, pulp to lyocell fiber weight ratio 60/40, lyocell fiber type: LENZING^TM10mm Lyocell short cut with a fineness of 1.4dtex (g.1)) and 1.7dtex (g.2)),viscose fiber: daiwabo 10mm, titer 1.7dtex (g.3)) and Viloft 10mm, titer 2.7 dtex (g.4)).

h.) basis weight 80 gsm, pulp to lyocell fiber weight ratio 80/20, lyocell fiber type: LENZING^TMLyocell short 10mm, fineness 1.4dtex (h.1)) and 1.7dtex (h.2)), viscose: daiwabo 10mm, titer 1.7dtex (h.3)) and Viloft 10mm, titer 2.7 dtex (h.4)).

In each case, the webs using lyocell fibres do show the best mechanical properties. The best results were achieved with lyocell fibres having a titre of 1.4dtex, whereas viscose fibres result in a loss of mechanical strength values (dry and wet, MD) to almost 1/2. The same trend is observed when considering the mechanical strength values in the Cross Direction (CD). These webs again further showed that increasing the amount of lyocell fibers in the web resulted in improved mechanical properties. Collectively, these test runs demonstrate that: as already outlined above, the present invention is based on the specific and not implied selection of raw materials for the fibrous nonwoven web, i.e. the pulp component and the fiber component (which is specifically the lyocell fiber component).

Example 4

Additional test runs were performed to demonstrate the effect of the weight ratio of pulp to lyocell fibers at constant basis weight and constant energy consumption and the effect of energy consumption at constant basis weight and constant weight ratio of pulp to lyocell fibers. The fibrous nonwoven webs having basis weights of 60 gsm and 80 gsm were hydroentangled with energy consumptions of 0.5445 kWh/kg and 0.4084 kWh/kg, respectively, while changing the weight ratio of pulp to lyocell fibers from 90/10 to 50/50 with intermediate ratios of 80/20, 70/30 and 60/40. Other samples were prepared with blends of 70/30, again at 60 gsm and 80 gsm, respectively, while varying the energy consumption from 0.1343 kWh/kg to 0.8084 kWh/kg for webs having a basis weight of 60 gsm, with intermediate values of 0.2598 kWh/kg, 0.381 kWh/kg and 0.5445 kWh/kg, and from 0.1007 kWh/kg to 0.6063 kWh/kg for webs having a basis weight of 80 gsm, with intermediate values of 0.1949 kWh/kg, 0.2858 kWh/kg and 0.4084 kWh/kg.

The results show that: the amount of lyocell fibers in the web increases and the energy consumption increases and the tensile strength values (dry and wet (MD and CD)) increase. Comparison of blends with increasing lyocell fibre content shows: an optimum balance of properties can be achieved at a pulp to lyocell weight ratio of 70/30 to 60/40, while also taking into account the cost of the raw material mixture. Although the 50/50 weight ratio sample showed a slight improvement in mechanical properties, the additional cost associated with the higher lyocell fiber content resulted in a detrimental balance of cost improvement and mechanical property increase.

Test runs with increasing energy consumption showed similar trends: the energy consumption is improved, and the mechanical property is improved. Within the energy consumption range evaluated, the respective increase in energy consumption did lead to a significant increase in mechanical properties, so that no flattening of the increase in strength was observed. At the same time, it was observed that: at the energy consumption level (0.1343 kWh/kg) typically used to produce dispersible wipes, which are typically used as flushable wet toilet tissue, strength values can be obtained that yield higher value products.

These tests also again demonstrate that: the invention makes it possible to obtain a fibrous nonwoven web having very satisfactory properties despite the use of a simple raw material mixture based on materials from renewable resources, i.e. pulp and lyocell fibres.

Example 5

To demonstrate the efficiency of the present invention in providing fibrous nonwoven webs that can be used as sustainable alternatives to dry industrial wipes that do contain polyester or polyolefin fibers, additional fibrous nonwoven webs according to the present invention were prepared. These fibrous nonwoven webs were compared to high quality industrial wipes having a basis weight of about 95 gsm and tensile strength values of about 96N/5 cm (dry as well as wet, the difference between the dry and wet states being expected to be negligible due to the high content of PET fibers in the thin industrial wipe). The wipe did exhibit an oil absorption value of about 800%.

Accordingly, samples with basis weights of 80 gsm, 100 gsm and 120 gsm were prepared with a pulp to lyocell fiber blend ratio of 70/30 and 50/50, respectively. These samples were hydroentangled and embossed to have a three-dimensional structure with energy expenditure of 0.3109 kWh/kg, 0.2719 kWh/kg and 0.2847 kWh/kg or provided with a three-dimensional structure by providing perforations. The results show that: basis weight is increased and mechanical properties are increased (dry tensile strength, MD and CD) to levels similar to those shown for the commercial control product. Neither embossing nor perforation results in a significant reduction in mechanical values and the reduction in strength values when measured in the wet state is only about 30%. In general, these fibrous nonwoven webs according to the present invention do exhibit a balance of properties that makes them useful as sustainable alternatives to commercial industrial wipes.

To further demonstrate the suitability of the fibrous nonwoven webs of the present invention, webs having a basis weight of 100 gsm were evaluated for their oil absorption capacity. The fibrous nonwoven web of the present invention did exhibit an oil absorption of over 800%, with the embossed web having an oil absorption value of about 900% and the perforated web having an oil absorption value of about 1100%. These values are even higher than those measured for high quality commercial industrial wipes, again demonstrating the unexpected superiority of the present invention.

Claims

1. A fibrous nonwoven web comprising pulp and lyocell fibers, wherein the weight of pulp is at least 35 wt.% and preferably equal to or greater than the weight of the lyocell fibers, and wherein the lyocell fibers have a length of 5 to 25 mm and the pulp fibers have a length of 1.5 to 5 mm.

2. The fibrous nonwoven web of claim 1 wherein the weight ratio of lyocell fibers to pulp is from 50:50 to 10:90, preferably from 15:85 to 45: 55.

3. The fibrous nonwoven web of claim 1 or 2, wherein the pulp has a fiber thickness of from 8 to 20, preferably from 10 to 15, more preferably from 12 to 14.

4. The fibrous nonwoven web according to any one of the preceding claims, wherein the lyocell fibers have a titer of 0.9 to 3.3 dtex, preferably 1.15 to 2 dtex.

5. The fibrous nonwoven web according to any of the preceding claims, wherein said web has a basis weight of from 25 to 200 gsm, preferably from 50 to 150 gsm.

6. The fibrous nonwoven web according to any one of the preceding claims, wherein the web is constructed by providing embossing, perforations, and/or a three-dimensional structure.

7. The fibrous nonwoven web of any one of the preceding claims, wherein said web has a Machine Direction (MD) dry tensile strength of greater than 50N/5 cm and a cross-direction (CD) dry tensile strength of greater than 10N/5 cm.

8. The web according to any of the preceding claims, wherein said web has a Machine Direction (MD) wet tensile greater than 15N/5 cm and a Cross Direction (CD) wet tensile greater than 5N/5 cm.

9. The fibrous nonwoven web of any one of the preceding claims, wherein the web is free of synthetic thermoplastic binder components and/or synthetic fibers.

10. A method of making the fibrous nonwoven web of any of claims 1 to 9, comprising the steps of: providing a mixture of pulp and lyocell fibers in an aqueous medium, wherein the weight of pulp is equal to or greater than the weight of the lyocell fibers, and wherein the lyocell fibers have a length of 5 to 25 mm and the pulp fibers have a length of 1.5 to 5 mm, distributing the mixture on a belt, dewatering the distributed mixture and hydroentangling the dewatered mixture to obtain a fibrous nonwoven web.

11. The method according to claim 10, wherein the hydroentangling is performed using at least two water jets, preferably at least 4 water jets.

12. The method according to claim 10 or 11, wherein a drying step is provided after dewatering and before hydroentangling.

13. The process according to any one of claims 10 to 12, wherein the energy consumption during hydroentangling is adjusted to a value of 0.05 to 1 kWh/kg, preferably 0.1 to 0.75 kWh/kg.

14. The method according to any one of claims 10 to 13, wherein all water beams are provided on the same side of the material to be hydroentangled or wherein the water beams are provided on different sides of the material to be hydroentangled.

15. The process according to any one of claims, wherein after hydroentangling, dewatering and drying of the hydroentangled web are performed, preferably by means of a vacuum system and a through-air dryer, respectively.