METHOD FOR PRODUCING A NONWOVEN ITEM, NONWOVEN ITEM AND HYGIENE ARTICLE

Abstract

A method for producing a nonwoven element particularly for hygiene products, has at least the following steps: forming a fibrous web sheet with a width direction extending transverse to the production direction and a thickness direction perpendicular thereto by supplying staple fibers from at least a first group which are formed from a thermoplastic material, consolidating the fibrous web sheet to form a nonwoven web by heating exclusively a first side of the fibrous web sheet through contact with a heated surface such that the staple fibers of the first group are partially melted, and cooling the nonwoven web.

Claims

1. A method for producing a nonwoven element for hygiene products, comprising at least the following steps: forming a fibrous web sheet with a width direction extending transverse to a production direction and a thickness direction perpendicular to the width direction by supplying staple fibers from at least a first group which are formed from a thermoplastic material, consolidating the fibrous web sheet to form a nonwoven web by heating exclusively a first side of the fibrous web sheet through contact with a heated surface such that the staple fibers of the first group are partially melted, and cooling the nonwoven web.

2. The method according to claim 1, wherein the heated surface is part of a heating roll over which the fibrous web sheet is guided.

3. The method according to claim 2, wherein a contact time between a portion of the fibrous web sheet and the heated surface amounts to between 0.05 s and 0.4 s.

4. The method according to claim 1, wherein the heated surface has a heating temperature of between 120 and 250° C.

5. The method according to claim 1, wherein the staple fibers of the first group are formed at least partially from polyolefin.

6. The method according to claim 1, wherein the staple fibers of the first group are formed at least partially from biodegradable thermoplastic polymers.

7. The method according to claim 1, wherein a second side of the fibrous web sheet is partially cooled.

8. The method according to claim 1, wherein at least staple fibers from a second group formed from a non-fusible material are supplied to form the fibrous web sheet.

9. The method according to claim 8, wherein the staple fibers of the second group are natural fibers selected from the group consisting of cotton, wool, silk, linen, hemp and fibers of regenerated cellulose.

10. The method according to claim 1, wherein the staple fibers are carded to form the fibrous web sheet.

11. The method according to claim 1, wherein through-air bonding or a thermal calendering is used to consolidate the fibrous web sheet.

12. The method according to claim 11, wherein the heating roll is formed as a calender roll of a calendering device.

13. The method according to claim 1, wherein at least a further layer is supplied, the further layer being selected from the group consisting of staple fibers, carded web and film.

14. The method according to claim 1, further comprising the step of severing individual nonwoven elements from the nonwoven web, after said step of cooling.

15. A nonwoven element for hygiene products, obtained according to the method of claim 1, wherein the element comprises a layer of staple fibers which extends in a longitudinal direction, a width direction running transverse to the longitudinal direction and a thickness direction running perpendicular to the width direction, and wherein the staple fibers are partially fused together proceeding from a first side.

16. The nonwoven element according to claim 15, wherein a density decreases along the thickness proceeding from the first side.

17. The nonwoven element according to claim 15, wherein the element has a mass per unit area between 10 and 60 g/m.sup.2.

18. A hygiene element which is at least partially formed from a nonwoven element according to claim 15.

19. The hygiene element according to claim 18, which is selected from the group consisting of diapers, hygiene wet wipes and incontinence articles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The invention will be described in more detail in the following referring to an embodiment example. In the drawings:

[0047] FIGS. 1, 1A show a schematic diagram of the method according to the invention;

[0048] FIGS. 2, 2A show a variant of the method according to FIG. 1;

[0049] FIGS. 3, 3A show a further variant of the method according to FIG. 1;

[0050] FIG. 4 show an alternative adjustment possibility for the consolidation;

[0051] FIG. 5 show a nonwoven element according to the invention; and

[0052] FIG. 6 show an alternative embodiment of the nonwoven element according to FIG. 5.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0053] FIG. 1 schematically shows the method according to the invention. In a first work step, staple fibers of at least a first group 1 and of a second group 2 are fed to a carding machine 3 in which the staple fibers 1, 2 are aligned via a plurality of carding rolls and formed as a fibrous web sheet 4.

[0054] The fibrous web sheet 4 is guided in production direction P and extends in a width direction, not shown in more detail in FIG. 1, and in a thickness direction D perpendicular thereto. Accordingly, the fibrous web sheet 4 is formed exclusively from staple fibers 1, 2 and therefore requires subsequent consolidation to form a nonwoven web 5.

[0055] To this end, two separate consolidation steps are provided. A preconsolidation is carried out in the form of a thermal calendering. For this purpose, the fibrous web sheet 4 is guided between a calendering roll 16 and a heating roll 6. The fibrous web sheet 4 is compacted through the gap formed between the calendering roll 16 and the heating roll 6. Further, the calendering roll 16 has a surface structure such that the fibrous web sheet 4 is correspondingly compacted only in discrete locations. At the same time, heat is transferred to the fibrous web sheet 4 via the calendering roll 16 so that the fibrous web sheet 4 correspondingly melts in the compacted locations and accordingly connects the individual staple fibers 1, 2 to one another. The calendering roll 16 can also be dispensed with in principle. In that case, the fibrous web sheet 4 must be stabilized before being fed to the heating roll 6, for example, via a one-sided thermal preconsolidation so that the fibrous web sheet 4 does not disintegrate over the course of the thermal smoothing. Referring to FIG. 1A, this takes place by means of a roll arrangement 17 which acts on the horizontally running fibrous web sheet 4.

[0056] With this in mind, the staple fibers of the first group 1 are formed from a fusible material. The staple fibers of the second group 2, on the other hand, are formed from a non-fusible material, preferably natural fibers, e.g., cotton, wool, silk, linen, hemp or fibers of regenerated cellulose.

[0057] Consequently, the heating roll 6 forms a kind of counter-pressure element for the calendering roll 16. Moreover, a further consolidation step is carried out downstream of the first consolidation step via the heating roll 6. The heating roll 6 is a steel roll which is heated in the manner described above. The guide roll 6 has a heated surface 7 along which the fibrous web sheet 4 is guided. The fibrous web sheet 4 wraps around the heating roll 6 with a wrap angle α, the contact surface area between the fibrous web sheet 4 and the guide roll 6 increasing as angle α increases. Thus it will be seen that the fibrous web sheet 4 is guided past the heating roll 6 exclusively via a first side 8 and is heated through contact with the heated surface 7 such that the staple fibers of the first group 1 are partially fused. Since the second side 9 of the fibrous web sheet 4 is heated and, beyond this, the fibrous web sheet 4 is pressed against the heating roll 6 via the first side 8, a varying material density results along the thickness direction D in the nonwoven web 5 formed therefrom.

[0058] The extent to which the fibrous web sheet 4 is consolidated through contact with the heated surface 7 of the heating roll 6 depends substantially on the web velocity in production direction P, the contact surface area between the heated surface 7 and the fibrous web sheet 4, and on the web tension. The contact surface area is in turn decisively determined by the wrap angle α. Further, this wrap angle α is also decisive for the pressure between the heated surface 7 and the fibrous web sheet 4. In order to adjust this, a further guide roll 10 is provided and is formed in the depicted example to be displaceable in direction V to the heating roll 6. Alternatively, it is also possible, of course, to provide a horizontal displacement. In both cases, the wrap angle α is influenced. In the depicted example, the wrap angle α increases with decreasing distance so that the contact surface area between the fibrous web sheet 4 and the heated surface 7 is increased. Consequently, when the distance between the heating roll 6 and the guide roll 10 increases, the wrap angle α decreases and the contact surface area becomes smaller. On the whole, it is provided that the time during which a portion of the fibrous web sheet 4 is in contact with the heated surface 7 is between 0.05 s and 0.4 s based on the web velocity and the wrap angle α. The temperature of the heated surface 7 which is also decisive for the stiffening of the fibrous web sheet 4 is between 120 and 200° C.

[0059] Further, in the depicted example, bicomponent fibers comprising a core of polyethylene terephthalate and a cladding of polyethylene are used as staple fibers of the first group 1. The staple fibers of the second group 2 are cotton fibers. The exact composition of the utilized staple fibers will be apparent from Table 1.

[0060] The method shown in FIG. 2 is largely identical to the method according to FIG. 1 except that two separate calendering rolls 16, 16′ are now provided for preconsolidation and the heating roll 6 provided for the actual consolidation is not a component part of the calendering device. As will be apparent from Table 1, the staple fibers of the first group 1 are staple fibers of polypropylene. The staple fibers of the second group 2 are again staple fibers of cotton.

TABLE-US-00001 TABLE 1 Staple fibers Staple fibers Basis Example Group 1 Group 2 Mixture weight FIG. 1 polypropylene (PP) cotton length: 85% PP + 30 g/m.sup.2 length: 35-45 mm 24-28 mm; 15% cotton linear density: micronaire 2.2 dtex value: 4 melting point: 158-161° C. FIG. 2 bicomponent fiber cotton length: 85% BiCo + 35 g/m.sup.2 (BiCo): 24-28 mm; 15% cotton PET/PE (core/ micronaire cladding) length: value: 4 35-45 mm linear density: 1.7 dtex (PET) 2.2 dtex (PE) melting point cladding: 130-133° C.

[0061] With the method according to FIGS. 1 and 2, tests were carried out with the process parameters listed in Table 2. Examples Ia to Ic refer to a process flow according to FIG. 1. Examples IIa to IIc refer to a process flow according to FIG. 2.

TABLE-US-00002 TABLE 2 Example T.sub.cal A.sub.emb P.sub.cal T.sub.heat t.sub.heat l.sub.heat v.sub.web Ia 165/157° C. 20% 110-125 — 0 s 0 mm 10 m/min N/mm Ib 165/157° C. 20% 110-125 150° C. 1.26 s 209 mm 10 m/min N/mm Ic 165/157° C. 20% 110-125 160° C. 1.26 s 209 mm 10 m/min N/mm IIa 171° C. 10% 110-125 161° C. 0.01 s 3 mm 140 m/min N/mm IIb 145° C. 10% 110-125 157° C. 0.10 s 24 mm 140 m/min N/mm IIc 145° C. 10% 110-125 157° C. 0.24 s 24 mm 60 m/min N/mm T.sub.cal: temperature of the calender roll 16 A.sub.emb: proportion of regions compacted over the course of calendering P.sub.cal: calendering pressure T.sub.heat: temperature of the heating roll 6 t.sub.heat: contact time with the heating roll 6 l.sub.heat: contact length of the heating roll 6 v.sub.web: velocity of the nonwoven web 5

[0062] Based on these process parameters, various nonwoven elements 14 were formed and underwent various quality tests. The results of these tests are shown in Table 3.

TABLE-US-00003 TABLE 3 MDT MDE CDT CDT20 CDE MAR MDBL Example [N/5 cm] [%] [N/5 cm] [N/5 cm] [%] [degree] [mN*cm] Ia 35.6 35.5 5.9 2.55 74 2 0.8 Ib 40.6 26.7 6.2 4.35 68 1 1.34 Ic 46.8 26.2 7.7 8.00 43 1 2.31 IIa 18.9 15.4 1.6 1.07 59 5 0.61 IIb 22.3 11.7 2.2 1.73 37 3.5 0.86 IIc 40.4 16.8 4.1 3.23 47 2 2.18 where, MDT = tensile strength in machine direction MDE = elongation at break in machine direction CDT = tensile strength in transverse direction CDT20 = tensile strength in transverse direction at 20% elongation CDE = elongation at break in transverse direction MAR = Martindale test MDBL = bending length in machine direction

[0063] The values for tensile strength and elongation at break were determined in accordance with EN ISO 13934-1:1999, and the bending length was determined in accordance with EN ISO 9073-7:1998. The MAR value is a measurement of abrasion resistance and pilling tendency. The determination is made by measurement using the Martindale method in accordance with ASTM D4966-98 and WSP 20.5(05). Wear of material is measured by subjecting the respective product to rubbing motion in the form of a geometric figure. The abrasion resistance is evaluated with a grade by then comparing the material to the known visual standard under the stated criteria. The lower the grade, the better the abrasion behavior of the nonwoven. Within the framework of the invention, a grade of at least 2 is aimed for. The criteria for grading are listed in the following Table 4:

TABLE-US-00004 TABLE 4 Grade Acceptable Criteria 5 − pilling or cords form network of a plurality of individual fibers and a loft >10 mm hole formation >10 mm large portion of the sample is worn away 4 pilling or cords form network of a plurality of individual fibers and a loft >5 mm 3 formation of a kind of yarn from long twisted fibers >2 mm height of yarn <5 mm no network formation 2 + pill formation diameter <2 mm thread formation with a width <2 mm no network formation 1 short fibers are raised slight pilling with diameter <2 mm

[0064] Further, it is decisive for the quality of the nonwoven element 14 that the CDT20 value is especially high. A certain compromise must always be made between wear resistance and the softness of the material. Trials have shown that the quality increases with an increasing contact time and also at higher temperatures of the heating roll 6.

[0065] The method according to FIG. 2A substantially conforms to the method according to FIG. 2, but now a cooled steel roll 11 is provided which cools the second surface 9 of the fibrous web sheet 4 at the start of consolidation, while the first side 8 of the fibrous web sheet 4 is heated via the heated surface 7 of the heating roll 6. In this way, it is ensured that the staple fibers on the second side 9 of the fibrous web sheet 4 remain substantially unaffected by the introduction of heat through the heating roll 6. Further, instead of a cooled roll 11, another kind of cooling mechanism can be provided. For example, the second surface 9 may be acted upon by cooled air.

[0066] In the method according to FIG. 3, an oven 12 is provided instead of calendering rolls 16, 16′, the fibrous web sheet 4 running through this oven 12. The fibrous web sheet 4 is acted upon by hot air in the oven 12 so that the staple fibers of the first group 1 are partially fused and bond with one another and with the staple fibers of the second group 2 homogeneously over the thickness D. Only then is the fibrous web sheet 4 which is consolidated in this way fed to the heating roll 6 having the heated surface 7 and additionally consolidated on one side. According to FIG. 3A, the oven can also first be arranged after the heating roll 6.

[0067] FIG. 4 shows an alternative possibility for adjusting the heating roll 6 and the guide roll 10 relative to one another. This adjusting possibility is crucial for the wrap angle α. As angle α increases, the contact surface between the fibrous web sheet 4 and the heated surface 7 is also increased. According to the adjusting possibility in FIGS. 1 to 3, the guide roll 10 is moved linearly in direction of the heating roll 6 for this purpose. However, in the embodiment according to FIG. 4 the guide roll 10 is rotatable along a circular path 13, and the wrap angle α increases in rotational direction D. The guide roll 10 is shown in a total of two different positions in FIG. 4. The wrap angle α according to the first position is smaller than wrap angle α.sub.1 according to the second position of the guide roll 10. In the second position, the wrap angle α.sub.1 amounts to approximately 180° so that the heated surface 7 rotates halfway corresponding to the fibrous web sheet 4 and a contact time between the fibrous web sheet 4 and the heated surface 7 is much longer than in the first position of the wrap angle α with the web velocity remaining the same.

[0068] FIG. 5 shows a nonwoven element 14 which is formed from the nonwoven web 5 and severed therefrom. The nonwoven element 14 extends over a length running in production direction P, a width which is not shown in more detail and a thickness extending perpendicular thereto. It can be clearly seen that there are different densities on the two sides 8, 9 of the nonwoven element 14 as a result of treating with the hot surface 7. While the side 8 directly contacting the heated surface 7 was very highly compacted, the second side 9 is hardly influenced, if at all, by the consolidation step. Accordingly, the density decreases in direction of the second surface 9 proceeding from the first surface 8. This drop in density is not necessarily continuous but rather approximately stepwise.

[0069] FIG. 6 shows a nonwoven element 14 according to FIG. 5 in which regions 15 are additionally provided by thermal calendering at discrete points at which the nonwoven element 14 has been completely compacted and consolidated and correspondingly has a much smaller thickness than in regions which have not been thermally calendered. Such an embodiment may be useful in order to additionally consolidate the nonwoven element 14. By combining the two consolidation methods, the quantity of thermally calendered regions 15 can be significantly reduced compared to consolidation exclusively by thermal calendering. It should be noted here that these points are always weakened points in the material which should be kept as small as possible depending on the embodiment of the nonwoven element 14.