Spunbond Fleece of Polymer Fibers and Its Use

Abstract

The invention relates to a spun-bonded non-woven made of polymer fibers. These polymer fibers have a non-circular cross-section and a low fiber count. The polymer fibers have predominant directions in the spun-bonded non-woven. The spun-bonded non-woven has a high optical and/or physical opacity while having a low mass per unit area.

Description

FIG. 1 is a schematic representation of fibers whose fiber cross section has a round, flat, and trilobal form, as well as of their overlap.

FIG. 2 is a schematic representation of the adhesive passage for fleeces with round fibers and fleeces with trilobal fibers.

In FIG. 3 the reduction of the light permeability [sic] as a function of the weight per unit area of the fleece and of the form of the fiber cross section is shown.

In FIG. 4 the air permeability [sic] as a function of the weight per unit area of the fleece and of the form of their fiber cross section is represented.

In FIG. 5 the relationship between the sieve residue [sic] and the weight per unit area of the fleece is represented for different fiber cross sections.

FIG. 6 gives an overview of the development of the tensile strength of the fleece in the machine direction and transverse to the machine direction as a function of the weight per unit area of the fleece and of the form of the fiber cross section.

FIG. 7 shows the fleece extension in the machine direction and transverse to the machine direction for fleeces with trilobal and round fleeces.

FIG. 1 illustrates the cross sections of the fibers considered in more detail in the scope of the invention. The representation 1.1 shows a circular cross section F which has the same surface area as the surface F′ which belongs to a trilobal fiber, where it can be seen that the projected edge length 1 of the fibers with a trilobal form for the cross section is ca. 30% larger than the diameter d of the fiber with a round cross section, which corresponds to a ratio 1=1.3 d. If according to the invention these trilobal fibers are laid in the preferred direction perpendicular to the Z-direction, i.e., in the machine direction and/or transverse to the machine direction, to form a fleece, a fiber overlap can consequently be achieved which is 30% higher than the maximum possible overlap which would be achievable using round fibers. Flat fibers with an edge ratio b=2a according to FIG. 1.2 have in comparison to round fibers a ca. 25% greater projected edge length and fibers with an edge ratio of b=3a according to FIG. 1.3 a ca. 53% greater edge length. The FIGS. 1.4 to 1.7 illustrate the facts of fiber overlap.

FIG. 2 shows by way of example how, according to the laid fleece's gap volume present in the case of the fiber geometry in question, an adhesive can penetrate through the fleece, or in the more favorable case only penetrate into the fleece and harden the fleece without going through it. With this, it becomes clear that through the use of trilobal fibers a higher packing density within the fleece is achieved and the narrower flow paths associated therewith reduce the penetration of the adhesive drastically.

The invention will be explained in more detail with the aid of examples in order to present a comparison between fleece with round fibers and fleeces with trilobal fibers with regard to their permeability to light, air, and powdery particles.

EXAMPLE 1

As raw material, a polypropylene produced according to the Ziegler-Natta process was used for the production of the samples, where 0.25% by weight titanium oxide relative to the polymer melt was used.

In so doing, the round or trilobal fibers were produced according to the known spunbond process.

The throughput of the spinning plate was held constant at 162 kg/h, where the spinning plate had in total 5000 holes with a diameter of 0.6 mm. The fibers were easily stretched and had fiber extensions of 279%. This value was determined on a tensile testing machine from the Zwick company with a pretensioning force of 0.1 N, a traction speed of 100 mm/min, and a restraint length of 20 mm.

For the fibers thus obtained and having a round cross section, the fiber diameters were measured in a microscope and relative to the weight of the fiber per unit length, where it was possible to determine a fiber titer of 2.8 dtex. In the case of the trilobal fibers the so-called apparent titer was determined, i.e., the fiber cross section was also measured in a microscope and computed based on the weight per unit length of the round fiber with the same diameter, where for these fibers a titer of 3.7 dtex was determined.

The fibers were preferably laid to form a fleece in the machine direction and transverse to the machine direction. Weights per unit area of 17 g/m², 20 g/m², 34 g/m², 40 g/m², and 51 g/m² were measured according to DIN EN 29073-1 for the laid fleece, both with round and trilobal fiber cross sections, as a function of the fleece density and of the fiber cross section. In this measurement, the fleece densities were between 250 μm and 600 μm. After thermal hardening these fleeces have densities between 0.045 and 0.065 g/cm³ and specific volumes between 15.5 and 20.8 cm³/g.

In these fleeces the air permeability and the screen residue were measured to characterize the physical opacity. According to FIG. 3, for fleeces with a round fiber form, air permeability values which lie between ca. 9000 to 11000 /m² sec were measured. Fleeces with a trilobal cross-sectional form have, due to the higher overlap of the fibers, somewhat lower air permeability values, which are below 8000 /m² sec.

According to FIG. 4, the screen residue for these fleeces was determined, where SAP 35, a superabsorber polymer of the Atofina company, was used as screen feed. Here, the values determined for the screen residue are higher for fleeces with trilobal fibers than the values for fleeces with round fibers with the same weight per unit area. While fleeces with round fibers only have a screen residue>90% at a weight per unit area of 20 g/m², for fleeces with a trilobal cross section these values had already been measured at a weight per unit area of 17 g/m². For fleeces of 15 g/m² and 20 g/m², for the determination of optical opacity, according to FIG. 5 values for reducing the light permeability were measured, which for round fibers lies in the range from ca. 1.5 to 2.5% and for trilobal fibers lies in the range from ca. 6.3 to 8.8%.

Furthermore, for the fleeces according to FIG. 6, the tensile strengths were measured as F_max according to DIN EN 20973-3 in the CD and MD directions, where for fleeces with trilobal fibers and weights per unit area of 17 g/m² to 51 g/m² the tensile strengths lie in the range of 38 N to 85 N in the machine direction and in the range of 25 N and 55 N perpendicular to the machine direction. In a range of weights per unit area of the fleece, specifically the range preferred according to the invention, i.e., from 10 to 20 g/m², fleeces with trilobal fibers have higher strengths than fleeces with round fibers with the same weight per unit area and at the same titer. Thus, for example, for fleeces with trilobal fibers in this range, strengths in the range of 38 N to 50 N in the machine direction and strengths in the range of 25 N and 30 N transverse to the machine direction were measured.

Values for the extension at F_max were determined for these fleeces according to FIG. 7 and according to DIN EN 20973-3. In that determination, in the machine direction the values lie, as a function of the weight per unit area, between 35% and 65% and transverse to the machine direction between 38% and 68%.

EXAMPLE 2

In all the samples, Ziegler-Natta-catalyzed polypropylene was used as the polymer with the addition of titanium oxide according to example 1, where the spinning process was carried out using the spinning plate according to example 1 with a throughput of 185 kg/h and per meter of spinning plate. Therein round fibers with a fiber titer relative to the weight per unit area of 2.4 dtex and trilobal fibers with a fiber titer of 2.8 dtex were produced, where the determination of the fiber titer was carried out analogously to example 1. In the laid fleeces air permeabilities were measured, which for fleeces with round fibers lie, as a function of the weight per unit area, between 8000 and 10000 /m²sec and for fleeces with trilobal fibers lie between 6500 and 8500 /m²sec. For the determination of the sieve residue the SAP 35 according to example 1 was used. The measured values for fleeces of trilobal fibers are, as a function of the weight per unit area, on the order of magnitude of 88-99% and for fleeces of round fibers between 76 and 95%.

The fleeces according to the invention are suitable for numerous fields of application, in particular in the field of hygiene but also in the field of filter technology or in the field of household cloths.

In the field of hygiene they are used, for example, as a topsheet or backsheet. In this application, the topsheet or backsheet comprise polymer fibers with a non-circular cross section and very low titers and have preferred directions in the spunbond fleece. By using the spunbond fleece hygiene articles made therefrom have a high optical and physical opacity. The high physical opacity has an impact in particular due to the reduced adhesive penetration of the fleece since processing can be done with very small portions of adhesive and low viscosities in the production of the hygiene products.

In the field of filter technology these fleeces of polymer fibers with a non-circular cross section exhibit, due to their fiber geometry, the preferred directions of the fibers in the fleece, and the high packing density associated therewith, a very good retention behavior for dust without in so doing drastically increasing the resistance to air flowing through.

Likewise, the fleeces with a non-circular cross section are suitable in the household field, e.g., as wiping cloths. Since the fiber dimensions correspond to the size of the impurities they are in the position to be able to pick up fine particles and microscopically small dust particles very well.

Claims

1. Spunbond fleece of polymer fibers, characterized by the fact that the polymer fibers have a non-circular cross section,the polymer fibers have a low fiber titer,the polymer fibers have preferred directions in the spunbond fleece, andthe spunbond fleece has a high optical and physical opacity with a low weight per unit area.

2. Spunbond fleece according to claim 1, characterized by the fact that the polymer fibers have a flat, trilobal, multi-lobal, or similar structure.

3. Spunbond fleece according to claim 1, characterized by the fact that the polymer fibers have fiber titers in the range of 0.5 dtex to 5 dtex, preferably between 1.4 dtex and 3.5 dtex.

4. Spunbond fleece according to claim 1, characterized by the fact that the polymer fibers are in a preferred direction along and transverse to the machine direction.

5. Spunbond fleece according to claim 1, characterized by the fact that the optical opacity, measured as the reduction of the light permeability, lies in the range of 5 to 20%, preferably 6-9%, relative to the weight per unit area.

6. Spunbond fleece according to claim 1, characterized by the fact that it has weights per unit area between 7 g/m2 and 50 g/m2, preferably 10 g/m2 to 20 g/m2.

7. Spunbond fleece according to claim 1, characterized by the fact that the physical opacity relative to the weight per unit area, measured as sieve residue, lies in the range of 75% to 99%, preferably between 90% and 95%.

8. Spunbond fleece according to claim 1, characterized by the fact that the physical opacity relative to the weight per unit area, measured as air permeability, lies in the range of 6·103 l/m2 sec to 9·103 /m2 sec, preferably between 7·103 l/m2 sec and 8·103/m2 sec.

9. Spunbond fleece according to claim 1, characterized by the fact that the polymer fibers consist of polyolefins, PA, or polyester, preferably polypropylene.

10. Spunbond fleece according to claim 1, characterized by the fact that the fleece is coated with an adhesive.

11. Spunbond fleece according to claim 1, characterized by the fact that the fleece has a low penetration of adhesive.

12. Spunbond fleece according to claim 10, characterized by the fact that in the temperature range between 140° C.-160° C. the adhesive has dynamic viscosities in the range of 3000 mPas to 33000 mPas, preferably 4000 mPas to 6000 mpas.

13. Spunbond fleece according to claim 10, characterized by the fact that the portion of adhesive per m2 of spunbond fleece lies between 0.5 g and 10 g, preferably between 3 g and 6 g.

14. Spunbond fleece according to claim 1, characterized by the fact that additives, preferably inorganic salts, are used.

15. Spunbond fleece according to claim 13, characterized by the fact that titanium oxides and/or calcium carbonates between 0.1 and 5% by weight, preferably between 0.2 and 0.7% by weight, are used as additives.

16. Use of the spunbond fleece in a hygiene product.

17. Use of the spunbond fleece in a filter material.

18. Use of the spunbond fleece in a household cloth.