Use of cellulosic fibers for the manufacture of a nonwoven fabric

Abstract

This invention relates to the use of Lyocell fibers with a tendency to fibrillate for the manufacture of a nonwoven fibrous web material, in particular for the use in a wipe, by using a foam technique.

Claims

1. A method for the manufacture of a fibrous web of paper, comprising the steps of: a. providing a foam of water and a surfactant, b. incorporating Lyocell fibers and a pulp into the foam, wherein the Lyocell fibers have a titer of between 0.5 and 30 dtex, and a fibrillation coefficient Q of between 10 and 65, and wherein fibers in the pulp have a greater fiber length than the Lyocell fibers, c. supplying the foam onto a forming fabric, d. dewatering the foam on the forming fabric by suction to form a web, and e. subjecting the web to final drying.

2. The method of claim 1, wherein the the fibrillation coefficient Q of the Lyocell fibers is between 10 and 50.

3. The method of claim 1, wherein the Lyocell fibers are Lyocell fibers with an increased tendency to fibrillate.

4. The method of claim 1, wherein a continuous fibrous web is formed on a running forming fabric of a paper machine, dewatered by suction through the web and the forming fabric, and finally dried in a drying section of the paper machine.

5. The method of claim 1, wherein the web is dewatered by suction of air through the web and the forming fabric at a pressure of at most 0.6 bar, followed by predrying by suction of air at a pressure of at most about 0.3 bar.

6. The method of claim 1, wherein about 5 to 40 wt-%, of the Lyocell fibers and about 60 to 95 wt-%, of the pulp are incorporated into the foam.

7. The method of claim 1, wherein the foam is brought to an air content of 60 to 70 vol-% before being supplied onto the forming fabric.

8. The method of claim 1, wherein the titer of the Lyocell fibers is between 0.9 and 15 dtex.

9. The method of claim 6, wherein about 10 to 40 wt-% of the Lyocell fibers are incorporated into the foam.

10. The method of claim 9, wherein about 10 to 25 wt-% of the Lyocell fibers are incorporated into the foam.

11. The method of claim 6, wherein about 60 to 90 wt-% of the pulp is incorporated into the foam.

12. The method of claim 11, wherein about 75 to 90 wt-% of the pulp is incorporated into the foam.

13. A fibrous web obtainable by the method of claim 1, wherein the web has a bulk of at least 2.5 cm.sup.3/g.

14. The fibrous web of claim 13, wherein the the fibrillation coefficient Q of the Lyocell fibers is between 10 and 50.

15. The fibrous web of claim 13, wherein the Lyocell fibers are Lyocell fibers with an increased tendency to fibrillate.

16. The fibrous web of claim 13, wherein the web has the bulk of between 2.5 cm.sup.3/g and 15.0 cm.sup.3/g.

17. The fibrous web of claim 13, wherein the web comprises about 5 to 40 wt-%, of the Lyocell fibers and about 60 to 95 wt-%, of the pulp.

18. The fibrous web of claim 13, wherein the web has the bulk of between 8.0 cm.sup.3/g and 11 cm.sup.3/g.

19. The fibrous web of claim 13, wherein the titer of the Lyocell fibers is between 0.9 and 15 dtex.

20. The fibrous web of claim 17, wherein the web comprises about 10 to 40 wt-% of the Lyocell fibers.

21. The fibrous web of claim 20, wherein the web comprises about 10 to 25 wt-% of the Lyocell fibers.

22. The fibrous web of claim 17, wherein the web comprises about 60 to 90 wt-% of the pulp.

23. The fibrous web of claim 22, wherein the web comprises about 75 to 90 wt-% of the pulp.

24. A wipe comprising the fibrous web of claim 13, wherein the fibrous web is used as at least one layer of the wipe.

25. The wipe according to claim 24, wherein the fibrous web comprises a middle layer of the wipe and the wipe further comprises outer layers having a bulk lower than in the middle layer.

26. The wipe of the fibrous web of claim 24, wherein the wipe is selected from the manufacture of dispersible wet wipes, flushable wipes, dry wipes, paper towels, face masks, flushable face masks, napkins, disposable tablecloths, absorbent core products, sealing materials, wet wipes, baby wipes, cosmetic wipes, other body care wipes, wipes for technical and cleaning uses and toilet tissues.

Description

EXAMPLES

Example 1: Manufacture of CLY-HF

(1) Fast fibrillating Lyocell fibers according to the invention are manufactured as follows: a Lyocell fiber tow having an individual fiber titer of 1.7 dtex is impregnated with diluted sulfuric acid at room temperature and a liquor ratio of 1:10 and pressed to approximately 200% moisture. The impregnated fiber tow is subjected to steam under pressure for approximately 10 min in a laboratory steamer, then washed free of acid with water, and dried. The dry fiber tow is cut to a staple length of 6 mm.

Example 2: Forming of Nonwoven Web

(2) The webs were manufactured according to the following general procedure:

(3) Raw Materials Used:

(4) Pulp: A commercially available longfiber spruce Kraft pulp with a weight weighted average fiber length of 2.6 mm.

(5) Man-made fibers (the content of these fibers hereinafter is named Fiber content while the remaining quantity is pulp)see Table 1:

(6) a. Lyocell shortcut fiber made by Lenzing Aktiengesellschaft, Austria according to a conventional Lyocell process and cut to 6 mm staple length; titer 1.7 dtex; commercially available as Tencel Shortcut

(7) b. Viscose fiber with rectangular cross-section; 10 mm staple length, titer 2.4 dtex; commercially available (Viscose)

(8) c. The fiber made according to Example 1; 6 mm staple length, titer 1.7 dtex (CLY-HF)

(9) TABLE-US-00001 TABLE 1 Pulp Fiber Example Fiber type [wt. %] [wt. %] 2A None 100 0 2B Tencel Shortcut 90 10 2C Tencel Shortcut 80 20 2D Tencel Shortcut 70 30 2E Viscose 85 15 2F Viscose 80 20 2G CLY-HF 90 10 2H CLY-HF 80 20

(10) The trial set-up at the pilot-scale paper machine SUORA included using foam generation in a pulper and a hybrid former (containing the head box and the dewatering and defoaming section). A pulp suspension was prepared by filling the required amount of water into the pulper and then adding the pulp while stirring. Thereafter sodium dodecyl sulfate (SDS, a tenside) was dosed into the pulper at a feed rate adjusted to control the foam density (target foam density 500 kg/m.sup.3). Then the production phase was started. When all steps of the process were stabilized the man-made fiber was added into the pulper to obtain the ratio pulp:man-made fiber according to Table 1. At the hybrid former the basis weight per unit area target for the nonwoven samples was set to 70 gsm in all trials. The machine speed was 500 m/min in all trials and the wet pressing load at the final dewatering pressing unit was 600 kN/m. After this squeezing the nonwoven material thus formed was collected on a winding unit. At this wet pressing load the solids content of the nonwoven material at the winding unit ranged from 38.9%-46.3%. The samples were dried in a discontinuous laboratory drum drier and reconditioned before testing.

(11) The tensile strength values which are listed below were measured according to DIN 29073 Teil 3 (identical to ISO 9073-3) in machine direction (MD) and cross direction (CD). The values which are measured here are the maximum force at break in the unit Newton as well as the elongation in %.

(12) The results of Example 2 show that the papers made according to the invention showed even in the original dried state an equal or even higher tenacity (i.e. strength) in both directions as papers consisting of pure pulp, while the blends with other man-made cellulosic fibers always show decreased tenacity compared to pure pulp paper made according to the same procedure.

(13) Another possible method to produce foam-formed products in lab scale is the forming of handsheets according to the following procedure, which gives comparable results: Foam laid handsheets of the size of a A4 piece of paper were made by the following procedure: Foam was produced by mixing water and sodium dodecyl sulphate (SDS) as a surface active agent in ratio 0.15-0.2 g/l with a stirrer (3500 rpm) as far as the air content of foam is 60-70%. The target air content of foam was determined by the foaming set-up; when the foam reaches the target air content the level of the foam surface does not rise anymore and the mixing starts to decrease the bubble size of the foam. When the foam was ready a fiber suspension comprising CLY-HF (produced according to Example 1) and the pulp in the ratios according to Table 1 was mixed with the prefabricated foam. Mixing was continued until the target air content was reached again. In stable condition the distances between fibrous particles in the foam remained constant and no flocculation happened. After that the foam was decanted into a handsheet mold and filtrated through a wire using an exhauster and a vacuum chamber. The wire was of the type conventionally used for water based forming. Then the wire and the handsheet formed thereon were removed from the mold and pre-dried on a suction table by use of an exhauster. The suction table has a suction slit, width 5 mm that suck air through the sheet with 0.2 bar vacuum. The webs were dried according to the following method: The wet sample sheets in the size of A4 were dried on a special drum dryer: This dryer rotates (1 cycle within 3 minutes) to dry the sample to a bone dry state. To transport the sheet over the rotating drum, a woven fabric presses the sample onto the heated drum. As a certain area at the bottom end of the dryer is open, the sheet falls down into a gathering section when passing through the whole process. After drying the bone dry sheets are reconditioned in a reconditioning room overnight.

Example 3: Rewetting of Dried Nonwoven Webs

(14) The tensile strength values which are shown in FIG. 3 and FIG. 4 were measured according to DIN 29073 Teil 3 (identical to ISO 9073-3) in machine direction (MD) and cross direction (CD). In this example the samples were rewetted with 150 w.-% of water to 2.5 times its dry weight.

(15) The rewetted state is the state commercially relevant as wet wipes are usually produced by the converter (the roll good producer produced the fabric, the converter converts the fabric by adding lotion and slitting the wipe to its needed size).

(16) According to Example 3 in the rewetted state the papers made according to the invention show a gain in wet strength compared to the 100% pulp product. Also when comparing the papers made according to the invention to the other fibers, the CLY-HF again shows a benefit. This effect is seen clearly in MD as well as in CD.

(17) Resume:

(18) Over all samples, compared to the rewetted state, the strength of the sheets made according to the invention are higher. When increasing the fiber content into the sheets, the tensile strength goes down. Lyocell fiber herewith does not show this effect. In MD the tensile strength is comparable, in CD there is a gain in tensile strength.