EP3212846B1 - Fast-fibrillating lyocell fibers, and use thereof - Google Patents

Description

The present invention relates to fibrillated lyocell fibers having a fibrillation quotient Q of 20 or greater and having a content of microfibers with a fineness of less than 14 mesh and a diameter of less than 2 microns at least 50%, and their use for producing a wipe, the pulp and 5 to 20% by weight of fibrillated lyocell fibers.

State of the art

The US 6042769 discloses a method of increasing the fibrillation tendency of lyocell fibers by a treatment which reduces the degree of polymerization of the cellulose by at least 200 units. The fiber thus obtained should be used mainly in nonwovens and paper. The treatment is preferably carried out with a bleaching agent, in particular with sodium hypochlorite. Alternatively, the treatment with an acid, preferably a mineral acid such as hydrochloric acid, sulfuric acid or nitric acid is possible. However, this process has not been implemented commercially until today.

The use of regenerated cellulose fibers such as viscose and lyocell in nonwovens is well known. In particular, by grinding or in so-called refiners, which are known from papermaking, lyocell fibers are fibrillated and used as cellulose microfibers in admixture with paper pulp in so-called wet-laying processes (also referred to in the art as "wet-laid processes") A wide variety of products are produced, such as wipes or wipes, and paper structures for, for example, tissues US 8187422 in that the incorporation of fibrillated lyocell microfibers into paper pulp enables the properties of disposable cellulosic wipes to be optimized accordingly. In contrast to pure cellulose wipes, the cleaning behavior should be correspondingly improved by this admixture. The optimized property profile should be improved by an increased opacity (light scattering) and porosity, distinguished by the improvement of the soft grip. The higher porosity is said to result in a higher absorbency of water and oil, resulting in improved cleaning performance.

The US 8187422 does not describe exactly how the lyocell microfibers used are made. It merely indicates that conventional lyocell staple fibers, as used, for example, for the production of textiles, can be fibrillated in a disk refiner or similar aggregate in an aqueous medium at low solids content. The according to the US 8187422 used lyocell microfibers were purchased in an already fibrillated state from a supplier. They have a fibrillation degree of CSF <175ml and a diameter of <2μm. 40% of the fibers should have a fineness of finer than 14mesh. The in the US 8187422 Disposable wipes disclosed contain between 25 and 75% of the Lyocell microfibers so prepared.

The according to the US 8187422 Although used lyocell fibers fibrillieren under mechanical milling stress in an aqueous medium. However, the effort is in accordance with the US 8187422 achieve a certain degree of fibrillation, in terms of time and energy use with the current Refiner technologies significantly larger than for example for pulp.

task

The object of this prior art was to provide fibers for use in wipes, which can be fibrillated for a cost-effective and on the other hand in a lower proportion in wipes nor the same mechanical properties of the wipes, such as high strength allow.

Description of the invention

The above-described object has been achieved by fibrillated lyocell fibers, which are characterized in that they have a Fibrillation quotient Q of 20 or greater and their content of microfibers with a fineness of less than 14 mesh and a diameter of less than 2 microns is at least 50%. To avoid misunderstandings, it should be clarified that the term "fibrillated lyocell fibers" in the context of the present invention does not mean a total amount of completely identical fibers, but a mixture of fibers of basically the same nature, wherein in the mixture fibers of different fineness (measured in mesh ) and different diameters.

The fibrillation quotient Q is defined as $$\mathrm{Q}=200/{\mathrm{<figure-callout\; id="200"\; label="t\; CSF"\; filenames="imgf0001.png"\; state="\{\{state\}\}">t\; </figure-callout>}}_{\mathrm{CSF}}$$

Where t _{CSF200 is} the time (in minutes) required in the CSF check to achieve a CSF value of 200. The larger Q is, the less time is needed at constant fibrillation conditions to achieve the same degree of fibrillation. Depending on the nature of the starting fibers and the acid treatment according to the invention, a Q value of up to 400 can be achieved.

Another object of the present invention is a wipe containing pulp and 5 to 20% by weight of fibrillated lyocell fibers and wherein the fibrillated lyocell fibers have a fibrillation quotient Q of 20 or greater. In a preferred embodiment, the pulp is a paper pulp.

Surprisingly, the fast-fibrillating lyocell fibers could be prepared by acid treatment of conventional lyocell fibers. This acid treatment can be carried out according to the invention by using a fiber cable extruded from spinnerets in a known manner with a single fiber titer of for example between 1.0 and 6.0 dtex with dilute mineral acid, for example hydrochloric, sulfuric or nitric acid, with a concentration for example, between 0.5 and 5% at room temperature in a container at a liquor ratio of for example, impregnated 1:10 and then pressed to a certain residual moisture of, for example, 200%. The impregnated fiber cable is then exposed to water vapor at overpressure in a suitable device, then washed free of acid and dried.

To determine the fibrillation tendency, the fiber cable is cut to a staple length of 5 mm and subjected to the CSF test (Canadian Standard Freeness according to TAPPI Standard T227 om-94).

The fiber cable is cut to produce the wipes according to the invention in staple fibers suitable cut length, for example 4 to 6 mm. The fibrillation can then take place in a comminution unit customary in the paper industry, for example a grinding unit, a refiner, a disintegrator or a hydrapulper. It is carried out there until the desired degree of fibrillation is reached.

The effect of acid treatment and consequent reduction of CSF can be influenced by varying the treatment parameters. For longer treatment duration in the overpressure steam, the same effect can be achieved with lower acid concentrations and vice versa. Similarly, with lower or higher steaming temperatures, the CSF value can be affected.

It seems that the fiber structure is deliberately weakened, thus increasing the fibrillation tendency.

In a subsequent CSF test, the grinding time required to achieve a CSF of 200 ml for untreated lyocell fibers, depending on pulp type and production parameters, is in the range of 12-16 minutes (see Fig. 1 ). This procedure is with the in US 8187422 comparable. The acid-treated lyocell fibers require only about 3-4 minutes for the same Mahlungsart until reaching a CSF of 200ml ( Fig. 1 ). In addition, it was found that the proportion of microfibers with <14 mesh and <2 μm diameter formed during milling increased significantly to over 50% as a result of the acid pretreatment.

This makes it possible to reduce the proportion of lyocell fibers in a cleaning cloth to significantly <25 wt .-%, according to the invention even below 20 wt.% And still the required, for example in the US 8187422 to obtain described property profiles.

The fast-fibrillating lyocell fibers according to the invention can be used according to the invention for the production of a wide variety of products, such as wipes, in particular disposable wipes, papers, in particular filter papers and papers for technical applications, such as batteries. These and other products as well as the suitable manufacturing processes are among others in the WO 95/35399 described, which is hereby incorporated by reference.

In particular, wipes according to the invention can be prepared by basically known processes from the fibers and pulp according to the invention. In a preferred embodiment, the solidification takes place by water needling.

The present invention also relates to the use of the inventive fibers described above for producing a wipe, wherein the wipe comprises pulp and 5 to 20 wt .-% fibrillated lyocell fibers. The pulp is preferably a paper pulp.

In the following the invention will be described by way of examples. However, the invention is expressly not limited to these examples, but includes all other embodiments based on the same inventive concept.

Examples Example 1: Acid treatment

Fast fibrillating lyocell fibers according to the invention are produced as follows: A lyocell fiber strand having a single fiber titer of 1.7 dtex is impregnated with dilute sulfuric acid at room temperature and a liquor ratio of 1:10 and pressed to about 200% humidity. The impregnated fiber strand is subjected to steam in a laboratory damper for about 10 minutes under pressure, then washed free of acid with water and dried. The dry fiber strand is cut to 5mm staple length and subjected to the CSF test.

Example 2: Comparison of fibrillation dynamics

1. A. handelsübliche unbehandelte 1,7 dtex/6mm Lyocell-Fasern, kommerziell erhältlich als Tencel® von der Lenzing AG ("Tencel®- Standard")
2. B. Gemäß Beispiel 1 säurebehandelte Fasern ("Tencel® schnell fibrillierend")

The fibrillation tendency is measured by means of a CSF (Canadian Standard of Freeness) test according to TAPPI Standard T227 om-94 and the fibrillation quotient Q is determined. Compared:

1. A. Commercially available untreated 1.7 dtex / 6 mm lyocell fibers, commercially available as Tencel® from Lenzing AG ("Tencel® Standard")
2. B. Acid-treated fibers according to Example 1 ("Tencel® fast fibrillating")

Fig. 1 shows the decrease of the CSF value with increasing comminution time in the measuring device. It can be clearly seen that the acid-treated fibers fibrillate much faster than the untreated. For the commercial production of fibrillated lyocell fibers, this means a considerably lower expenditure of time and energy than when using untreated lyocell fibers.

Table 1 shows the t _CSF200 values determined for the various samples and the Q values calculated from them. Tab. 1: sample t _CSF200 [min] Q [min ^-1 ] A 15.5 12.9 B 3.5 57.1

Example 3: Comparison of Suitability for Wetlaying Methods

The same fiber samples were compared as in Example 1:
Each 1% aqueous fiber suspensions of both fiber samples A and B were ground in a laboratory refiner of the type Andritz R1L at a power of 500W, both the energy consumption in kWh / to and the duration to reach a degree of milling of CSF 200 (Canadian Standard of Freeness Test in accordance with TAPPI Standard T227 om-94). The fibrillating lyocell fiber could be processed in less than 80% of the energy consumption compared to the standard lyocell fiber in only 50% of the milling time (see Table 2). Tab. 2: sample Grinding time [min] Energy consumption [kWh / to] A 5 400 B 2.5 65

From 2000 ml of these, experimental sheets were produced in a Rapith Köthen sheet former and SEM photographs of these test sheets were taken. Fig. 2 shows an SEM image of the leaf from the suspension of sample B.

Claims (7)

1. A wipe containing cellulosic fibers and 5 to 20 wt.% of fibrillated lyocell fibers, characterized in that the fibrillated lyocell fibers have a fibrillation ratio Q of 20 or more.
2. The wipe according to claim 1, wherein the cellulosic fibers are paper cellulosic fibers.
3. Fibrillated lyocell fibers, characterized in that they have a fibrillation ratio Q of 20 or more and their content of microfibers with a fineness of less than 14 mesh and a diameter of less than 2 µm is at least 50%.
4. Use of the fibers according to claim 3 for producing a wipe, characterized in that the wipe contains cellulosic fibers and 5 to 20 wt.% of fibrillated lyocell fibers.
5. The use according to claim 4, wherein the cellulosic fibers are paper cellulosic fibers.
6. The use of said fibrillated lyocell fibers according to claim 5 in wet-laying processes.
7. The use according to claim 6 in a mixture of the fibrillated lyocell fibers with paper cellulosic fibers with a lyocell fiber content of between 5 and 20 wt.%.

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