KR20130139859A - Method for strengthening a nonwoven fabric - Google Patents

Abstract

The present invention relates to a method of reinforcing a nonwoven with water jet treatment means.
The process according to the invention is characterized in that the nonwoven comprises flat fibers in the form of collapsed hollow viscose fibers having a ratio of width B to thickness D B: D > 10: 1.

Description

Method for strengthening a nonwoven fabric

The present invention relates to a method of strengthening a nonwoven with water jet treatment means.

Reinforcing nonwovens with water jet means is also referred to as "hydroentanglement" or "spunlacing" and is well known to those skilled in the art.

In nonwoven fabric production according to the water jet process, the reinforcement of the present carded fleece is obtained by laceration and swirling of the fibers. The fibers are surrounded by water jets and are moved and entangled in three dimensions by swirling motion.

Cotton is generally treated with fibrous materials that are particularly suitable for hydroentanglements, for example Alfred Watzl, Messrs. See Fleissner's paper, “Aquajet Spunlace Verfahren-Technik fur Baumwollfasern.” The fact that the low wetting rate of the cotton fibers as well as the circular smooth fiber cross section is not seen is therefore advantageous.

Fibers having a high modulus of elasticity (hereinafter referred to as "e-coefficient") are suitable for obtaining high web strength. These are essentially non-cellulose fibers.

In order to achieve sufficient network strength, high pressures are required in the hydroentanglement process, which results in a method that is energy intensive.

It is an object of the present invention to provide a method of hydroentanglement of a nonwoven fabric, which is feasible with low energy consumption.

This object is achieved by a method of reinforcing a nonwoven with water jet treatment means, said nonwoven comprising flat fibers in the form of collapsed hollow viscose fibers having a ratio of width B to thickness D B: D > 10: 1. do.

Moreover, the present invention relates to a hydroentangled nonwoven fabric comprising flat fibers in the form of collapsed hollow viscose fibers having a ratio of width B to thickness D B: D > 10: 1.

Preferred embodiments are described in the dependent claims.

Surprisingly, the use of collapsed hollow viscose fibers in a non-woven reinforced by water jet is similar to not including any flat fibers during hydroentanglements with the same energy use (ie, application of the same high processing pressure). Compared with the use of the nonwoven material, it has the effect of showing higher net strength results. Likewise, the desired net strength can be achieved with less energy use than in nonwoven materials that do not contain any cellulose flat fibers.

In this way, energy can be saved and thus the process cost can be reduced. In addition, the expense associated with the device can be kept low due to the lower pressure. In addition, more flexible strengthening, ie, strengthening at low pressure, can be performed. This is particularly advantageous, for example in the case of mixtures with cellulose, as high pressures can cause the cellulose to wash off, or even in the case of mixtures with delicate fibers. In addition, the use of synthetic fibers (especially for obtaining high strength) is avoided or at least reduced.

In the process according to the invention, the flat fibers comprised in the nonwovens preferably have a ratio of B: D of 10: 1 to 30: 1, particularly preferably 20: 1.

Preferably, the flat fiber may have a titer of 0.9 to 5 dtex, particularly preferably a titer of 1.3 to 1.9 dtex.

Flat fibers and their preparation are known. In contrast to commonly inherently round fiber cross sections, flat fibers are either essentially flat, or each has a rectangular cross section.

Meanwhile, the cellulose flat fiber may be manufactured by spinning a spinning spinning dope including cellulose or a cellulose derivative through a slot-shaped spinneret. In the case of viscose fibers, the flat fibers can be made in the form of hollow fibers which are optionally collapsed. In doing so, a gas, such as nitrogen, or a blowing agent, such as sodium carbonate, is mixed in the spinning viscose. As is the prior art, during fiber spinning through dies, hollow fibers are formed, but appropriate process conditions are chosen so that their walls are thinned and the fibers will collapse and then be provided in the form of flat fibers.

The production of cellulose flat fibers is known, for example, from GB 945,306 A, US 3,156,605 A, US 3,318,990, GB 1,063,217 A. Such fibers have been particularly recommended for use in paper making, as described in some of the documents mentioned above.

CR Woodings, AJ Bartholomew's paper " The manufacture properties and uses of inflated viscose rayon fibers ”; TAPPI Nonwovens Symposium; 1985; pp. 155-165. Source: http://www.nonwoven.co.uk/publications_cat4.php describes various types of hollow fibers and their use.

WO 2006/134132 describes the use of viscose flat fibers in a fiber composite for the purpose of improving the dissolubility of the fiber composite in water. According to WO 2006/134132, the flat fibers used have a crenelated [pinnacle type] surface and are thus produced by spinning through a slot die, in contrast to the collapsed hollow fibers. The ribbed surface of such flat fibers reduces fiber-fiber adhesion and the resulting strength. On the one hand, with conventional flat fibers, the thickness obtained is limited by the die geometry. Final spinning with a die having an opening of 25 μm in height results in a fiber thickness of about 4-6 μm. In order to continuously produce a fiber thickness of about 2-3 μm, such as with collapsed hollow fibers, a die opening of about 12.5 μm in height is required, which is economically feasible either in die making or viscose fiber making using conventional methods. Not easy

In contrast, the viscose flat fibers used according to the invention are disintegrated hollow fibers and can be prepared by introducing a gas or blowing agent (especially sodium carbonate) into the spinning viscose, as described above. The fibers may collapse completely or slightly open. However, the water retention of the fibers is preferably 200% or less (measured according to DIN 53814). The fiber cross section of the fibers should be mostly flat and preferably not branched.

The content of flat fibers in the nonwoven is preferably 5% to 100%, in particular at least 20%, more preferably at least 50%. The nonwoven material may therefore be made entirely of flat fibers and may also comprise a mixture of flat fibers and other fibers. All cellulose and non-cellulose fiber materials suitable for hydroentanglement are possible mixing partners. It is apparent to one of ordinary skill in the art that the effects according to the invention (ie, increased strength and energy savings of the nonwoven material respectively) appear more as the content of flat fibers in the nonwoven material increases.

The present invention also relates to a hydroentangled nonwoven comprising flat fibers in the form of collapsed hollow viscose fibers having a ratio of width B to thickness D B: D > 10: 1. For details regarding flat fibers as well as their ratios in nonwovens, see the dependent claims and the above description, respectively.

Example :

For the production of hydroentangled nonwovens, the following fibers were used, each with a titer of 1.7 dtex:

a) reference viscose fiber (Type Danufil ®)

b) viscose flat fibers derived from hollow fiber processes; Fiber thickness is about 2-3 ?; Width: thickness ratio = about 20: 1

The fibers were submitted as carded nonwovens and reinforced on both sides in two ways.

A nonwoven fabric with two weights per unit area and, in each case, two reinforcement steps (minimum-maximum reinforcement) was calculated from each fiber.

Weight per unit area: 50g / m ² and 80g / m ^2, respectively

Strength level: (intensification pressure in each case represented as the sum of all pressures of all the die bars in two paths)

Weight per unit area 50 g / m ² -Minimum reinforcement: 65 bar

Weight per unit area 50 g / m ² -Maximum reinforcement: 95 bar

Weight per unit area 80 g / m ² -Minimum reinforcement: 95 bar

Weight per unit area 80 g / m ² -Maximum reinforcement: 145 bar

The maximum strengthening pressure is therefore, in each case, at least about 50% of the highest strengthening pressure.

inspection:

With a standard test specimen of 5x25 cm, the following parameters were found for all nonwovens:

Maximum tensile strength [N / 5cm] in the direction of manufacture (MD) and transverse (CD) for the wet and dry in each case;

The maximum tensile strength elongation and the MD + CD as well as the MD / CD ratio derived therefrom are derived from

The results are summarized in the following table:

Non-woven from Viscose Flat Fiber (according to the invention) Weight per unit area Step deflation Tensile strength [N / 5cm] Elongation [%] MD / CD MD CD MD CD 50 g / m ² at least 40.1 34.0 17.0 31.4 1.18 50 g / m ² maximum 38.9 33.3 16.2 29.1 1.17 80 g / m ² at least 62.0 60.9 18.3 34.5 1.02 80 g / m ² maximum 59.8 59.8 14.7 30.6 1.00

Viscose flat fiber derived nonwoven fabric (according to the present invention) Weight per unit area Step Wet Tensile strength [N / 5cm] Elongation [%] MD / CD MD CD MD CD 50 g / m ² at least 27.4 22.6 27.8 34.1 1.21 50 g / m ² maximum 29.9 24.6 27.9 31.0 1.22 80 g / m ² at least 44.3 40.3 28.6 35.8 1.10 80 g / m ² maximum 45.0 37.8 28.5 31.7 1.19

Viscose-derived nonwoven fabric (comparative example) Weight per unit area Step deflation Tensile strength [N / 5cm] Elongation [%] MD / CD MD CD MD CD 50 g / m ² at least 21.0 33.5 26.1 41.6 0.62 50 g / m ² maximum 38.8 42.5 30.6 37.8 0.91 80 g / m ² at least 10.8 51.3 13.6 42.4 0.21 80 g / m ² maximum 29.7 69.2 19.5 36.1 0.43

Viscose fiber-derived nonwoven fabric (comparative example) Weight per area Step Wet Tensile strength [N / 5cm] Elongation [%] MD / CD MD CD MD CD 50 g / m ² at least 18.0 19.8 16.8 29.9 0.91 50 g / m ² maximum 21.3 24.7 25.1 30.5 0.86 80 g / m ² at least 5.9 21.5 16.8 29.9 0.27 80 g / m ² maximum 18.5 41.2 25.1 30.5 0.45

From the data presented above, the following conclusions can be drawn:

Elongation rate :

In dry nonwovens, the maximum tensile strength elongation (same weight per unit area and the same reinforcement conditions) is clearly low in flat fiber derived nonwovens, in contrast to the reference viscose fiber derived nonwovens. Perhaps this is due to the higher content of fiber-fiber bonds.

MD Of CD  ratio:

Under the same experimental settings, nonwovens comprising flat fibers exhibit a substantially higher MD / CD ratio than nonwovens made from reference viscose fibers.

Starting with a low MD / CD ratio, which is the minimum reinforcement, the MD / CD ratio increases as a result of the relocation of the fibers in the reinforcement process. The MD / CD ratio of the nonwoven is made of flat fibers, which ratio is substantially higher than the nonwoven made of reference viscose fibers under the same pressure, which represents a significantly higher flexibility of the flat fibers, which makes the reinforcing process very easy do.

burglar:

Viscose flat fiber derived nonwoven fabric (according to the present invention) Weight per unit area Step deflation Wet Max Tensile Strength [N / 5cm] Max Tensile Strength [N / 5cm] MD + CD MD + CD 50 g / m ² at least 74.1 50.1 50 g / m ² Best 72.3 54.5 80 g / m ² at least 122.9 84.7 80 g / m ² Best 119.6 82.8

Non-woven fabric (comparative example) derived from standard viscose fiber Weight per unit area Step deflation Wet Max Tensile Strength [N / 5cm] Max Tensile Strength [N / 5cm] MD + CD MD + CD 50 g / m ² at least 54.5 37.8 50 g / m ² maximum 81.3 46.0 80 g / m ² at least 62.1 27.4 80 g / m ² maximum 98.8 59.8

To facilitate inspection, the sum of the breaking forces MD + CD in each case is used for strength evaluation:

Referring to the nonwoven fabric according to the invention made of flat fibers, it is clear that higher strength is not obtained by increasing the reinforcement pressure from "minimum" to "highest". This obviously means that the nonwoven material is already already reinforced to the maximum extent at low reinforcement stages.

Equally strengthened, nonwoven strength is usually associated with weight per unit area.

In this case, the ratio of weight per unit area is 80 g / m ² to 50 g / m ² = 1.6.

For example, approximately 72 N / based on the measured intensity of 5cm of highly reinforced non-woven fabric having a weight per unit area of ^{50g / m 2, 72 * 1.6} = as for the non-woven fabric having a weight per unit area 80g / m ² An intensity of 115 N / 5 cm can be predicted, which fits well with the substantially measured value of about 120.

This means that in all four configurations, the nonwoven material has already been fully reinforced.

Another picture appears with a nonwoven fabric made of reference viscose fibers: In the haptic evaluation, the two nonwoven materials of the minimum reinforcement step were just insufficiently reinforced.

When increasing the strengthening pressure from "minimum" to "highest" (always increase by about 50%), in each case, the network strength can obviously be increased. Therefore, additional pressure obviously leads to further strengthening in this case, which will require a higher pressure for maximum strengthening.

In the higher reinforcing step of the 50 g / m ² nonwovens, the strength of the dry nonwovens is slightly higher than that of nonwovens made of flat fibers. This may be caused by the higher single-fiber strength of the fibers used in the experiment (reference viscose fiber: 22 cN / tex; viscose flat fiber: 16 cN / tex). However, it may be assumed that the nonwoven material is therefore very hardened.

Therefore, according to the above calculations, a strength of at least 81.3 x 1.6 = 130 N / 5 cm is expected for a fully reinforced nonwoven material having a weight per unit area of 80 g / m ² . But only about 99N / 5cm was measured. Therefore, even with higher reinforcement pressures, 80 g / m ² nonwovens are still far from being fully reinforced.

In the strengthening step, the nonwoven material achieved only about 75% of the strengthening potential.

Comparative Example :

Examples of 80 g / m ² nonwovens clearly show the advantages of the use of the flat fibers according to the invention in hydroentanglements.

Strength of Viscose Flat Fiber-Based Nonwovens-95bar:

Intensity dry (MD + CD) = 120N / 5cm;

Strength Wet (MD + CD) = 83 N / 5 cm

Reinforcement pressure of non-woven-145 bar derived from reference viscose fiber:

Intensity dry (MD + CD) = 99N / 5cm;

Intensity Wet (MD + CD) = 60N / 5cm

Therefore, by using viscose flat fibers in a nonwoven material, 20% (dry) and 40% (wet) higher strengths, respectively, can be obtained at 50% lower pressures than using reference viscose fibers.

Claims (8)

It is a method of reinforcing the nonwoven with water jet treatment means,
Wherein said nonwoven comprises flat fibers in the form of collapsed hollow viscose fibers having a ratio of width (B) to thickness (D) of B: D > 10: 1. The method of claim 1,
Wherein said flat fibers have a B: D ratio of 10: 1 to 30: 1, preferably 20: 1. 3. The method according to claim 1 or 2,
And wherein said flat fibers have a titer of 0.9 to 5 dtex, preferably 1.3 to 1.9 dtex. 4. The method according to any one of claims 1 to 3,
Method for reinforcing a nonwoven fabric, characterized in that the fiber content of the nonwoven material is from 5% to 100%, preferably at least 20%, particularly preferably at least 50%. A hydroentangled nonwoven fabric comprising flat fibers in the form of collapsed hollow viscose fibers having a ratio of width B to thickness D B: D > 10: 1. The method of claim 5,
Nonwoven fabric, characterized in that the flat fibers have a ratio of B: D of 10: 1 to 30: 1, preferably 20: 1. The method according to claim 5 or 6,
Wherein said flat fiber has a titer of 0.9 to 5 dtex, preferably 1.3 to 1.9 dtex. 8. The method according to any one of claims 5 to 7,
Nonwoven fabric, characterized in that the content of the flat fiber in the nonwoven fabric is 5% to 100%, preferably 20% or more, more preferably 50% or more.