Method for producing a fibrous web containing polylactide fibres

Abstract

A method for producing a fibrous web includes: (a) a fibrous ply containing polylactide fibers and, as necessary, other fibers are laid on a substrate in a random fiber arrangement, (b) initially a loose, pre-compressed nonwoven is created by applying a first pressure to the fibrous ply, the tear resistance of which nonwoven permits free bridging of a span between 0.1 m and 1 m before the nonwoven tears, (c) the pre-compressed nonwoven is then passed through the calender gap, wherein a pattern consisting of point or linear pressure zones is formed in the gap, with the fibers in the pressure zones being exposed to a second pressure, which is higher than the first pressure, and to a temperature such that the fibers fuse.

Claims

1.-18. (canceled)

19. A method of producing a fibrous web comprising polylactide fibers, comprising: (a) placing a fiber ply comprising polylactide fibers and optionally further fibers in a random fiber arrangement onto a substrate; (b) exerting a first pressure on the fiber ply, thereby producing a loose precompacted mat, a tear strength of which permits unsupported bridging a span before the mat tears; and (c) subsequently running the precompacted mat through a nip of a calender, wherein a pattern of dotted or linear compression regions is produced in the nip, and wherein the fibers in the compression regions are subjected to a second pressure higher than the first pressure, in conjunction with such a temperature that fusion of the polylactide fibers occurs.

20. The method as claimed in claim 19, wherein the fiber ply contains a mixture of the polylactide fibers and cellulose fibers.

21. The method as claimed in claim 19, wherein the polylactide fibers have a fiber length of 3 to 10 mm.

22. The method as claimed in claim 19, wherein the polylactide fibers have a fineness between 0.7 and 3.0 dtex.

23. The method as claimed in claim 19, wherein the polylactide fibers have a fineness between 1.0 to 1.5 dtex.

24. The method as claimed in claim 19, wherein, in method step c), the second pressure and the temperature are adjusted such that a melting range of the polylactide fibers is attained.

25. The method as claimed in claim 19, further comprising subjecting the fibrous web to electromagnetic waves with a wavelength of 300 mm to 1 mm.

26. The method as claimed in claim 19, further comprising subjecting the fibrous web to a hot gas stream.

27. The method as claimed in claim 19, further comprising subjecting the fibrous web to a hot calendering method.

28. A fibrous web, comprising: 5% by weight to 30% by weight of polylactide fibers; and 70% by weight to 95% by weight of cellulose fibers, wherein the polylactide fibers and the cellulose fibers are fused in an embossed pattern of dotted or linear embossment regions.

29. A hygiene product, a food packaging, or a filter materials for filtering of liquids and gases, comprising the fibrous web as claimed in claim 28 as an absorption material.

30. The fibrous web as claimed in claim 28, further comprising, on at least one of its surfaces, a web of textile, fleece-like or film-like material to which the fibrous web is adhesive bonded and/or welded and/or mechanically bonded.

31. A hygiene product, a food packaging, or a filter materials for filtering of liquids and gases, comprising the fibrous web as claimed in claim 30 as a carrier material for auxiliaries.

32. A fibrous web, comprising: 17% by weight to 40% by weight of polylactide fibers; and 60% by weight to 83% by weight of cellulose fibers, wherein the polylactide fibers and cellulose fibers are fused in an embossed pattern of dotted or linear embossment regions.

33. A hygiene product, a food packaging, or a filter materials for filtering of liquids and gases, comprising the fibrous web as claimed in claim 32 as an absorption material.

34. The fibrous web as claimed in claim 32, further comprising, on at least one of its surfaces, a web of textile, fleece-like or film-like material to which the fibrous web is adhesive bonded and/or welded and/or mechanically bonded.

35. A hygiene product, a food packaging, or a filter materials for filtering of liquids and gases, comprising the fibrous web as claimed in claim 34 as a carrier material for auxiliaries.

36. The fibrous web produced by the method as claimed in claim 19, wherein the fibrous web contains 10% by weight to 100% by weight of polylactide fibers and 0% by weight to 90% by weight of cellulose fibers, and wherein the polylactide fibers and cellulose fibers are fused in an embossed pattern of dotted or linear embossment regions.

37. The fibrous web as claimed in claim 35, wherein the fibrous web is dimensionally stable and can be converted to a three- dimensional form by a shaping method.

38. The fibrous web as claimed in claim 37, wherein the shaping method is a thermoforming method.

39. The fibrous web as claimed in claim 37, wherein the shaping method is a pipe production method.

40. A three-dimensional shaped bodies comprising the fibrous web as claimed in claim 35.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The invention is illustrated and explained in detail with reference to the following figures.

[0051] FIG. 1 shows an enlarged diagram of a fiber web in cross section through the compression region of two calender rolls with pyramid-shaped pimples;

[0052] FIG. 2 shows a section through the fiber material in the crimped state;

[0053] FIG. 3 shows a perspective view of a body in tubular configuration, produced from the fiber material according to FIG. 1, with partial omission of a sheath layer;

[0054] FIG. 4 shows a cross section in the A/A plane in FIG. 3;

[0055] FIG. 5 shows a schematic overview diagram of the method.

DETAILED DESCRIPTION

[0056] FIG. 1 shows a cross section of a step in the formation of a fiber web 1 containing polylactide fibers 3 and cellulose fibers 4. FIG. 1 shows, on the right-hand side, a loose, only precompacted mat 2 containing both fibers 3 of polylactide (polylactide fibers) and cellulose fibers 4. The fibers 3 and 4 shown are shown merely by way of example and do not reflect the amount, thickness and length of the fibers actually present.

[0057] On the top side and/or on the bottom side of the fiber web 1, it is additionally possible to apply a thin web material 5.1, 5.2, for example webs of textile, fleece-like or film-like material.

[0058] The precompacted mat is run through the nip of a calender roll pair 6.1, 6.2 which is shown in each case only in segments in FIG. 1. The surfaces of the calender rolls have projections 7.1 and 7.2, such that, in the regions in which these projections 7.1 and 7.2 meet, discrete, e.g. dotted, pressure regions are formed, in which a considerable pressure is applied to the mat. In these regions, the fibers are compressed, forming discrete embossment regions 8. The pressure in these embossment regions should be at least 100 MPa; in the present embodiment, the pressure is about 520 MPa. The rolls or projections on the rolls may be configured correspondingly for generation of such a pressure. For example, it is possible to use rolls with pimples, mutually interlaced line patterns or other protruding dotted or linear compression surfaces 7.1, 7.2. The pattern density of these dotted compression regions is preferably between 1 and 16 pattern dots per cm.sup.2.

[0059] The rolls of the calender roll pair 6.1, 6.2 are heated, for example by means of electrical heating elements, such that the temperature at least in the compression regions 7.1, 7.2, in addition to the pressure, is such that the polylactide fibers are partly or fully melted, so as to result in a cohesive bond between the individual polylactide fibers and optionally also with inclusion of the cellulose fibers.

[0060] The (partial) melting of the polylactide fibers allow the cellulose fibers also to be completely enclosed by polylactide melt. In these regions, also called embossment regions, fusion of the fibers occurs, such that these fibers cannot be separated from one another without difficulty, especially not without destroying the embossment region 8.

[0061] After exiting from the calender 6.1, 6.2, a fibrous web 1 is obtained, in which the fibers in the regions 9 form a loose composite. The elevated stability and strength of the fiber web 1 is attributable to the cohesive bonding of the polylactide fibers in the embossment regions 8.

[0062] In a further step, the fibrous web 1, for example, is processed further to give a filter material for cleaning of air and gases. For this purpose, the fibrous web is preferably first crimped, as shown in FIG. 2. The individual layers are not shown here. In the configuration shown here, the fiber web material is laid in irregular folds. A filter material is obtained, which, in addition to the existing embossment regions 8, has a crimped surface structure with alternating elevations 11 and depressions 12. This achieves an increase in surface area which is advantageous for the filter process.

[0063] FIG. 3 shows a rod-shaped filter 17, formed from the fiber web material 1 in the form of a sheet-like structure as shown in FIG. 1 and from a surrounding sheath layer 18 that has been partly omitted in FIG. 3. The web material 1 in the embodiment shown here is alternately laid or folded, forming channels 19 that extend in longitudinal direction of the filter. The alternate laying may be uniform or nonuniform. The gas to be cleaned can pass through the channels 19 and through the fiber layer 1 of the filter material. The gas to be cleaned thus preferably flows along the folded layers, i.e. along the surfaces of the fibrous material, and not transverse thereto, and if it does so, only to a small extent through the layers 1. The pressure drops are therefore only low.

[0064] The strength of the embossment regions 8 and the stability thereof to moisture has the effect that the channels 19 do not collapse but retain their shape even under relatively high air humidity and at a relatively high moisture content of the gases to be filtered or cleaned.

[0065] In the embodiment shown here, the filter is surrounded by a sheath layer 18. In the case of use of the filter 17 as cigarette filter, the sheath layer 18 may be a simple wrapping paper that may surround both the tobacco rod of the cigarette (not shown here) and the cigarette filter in one-piece form. It is also possible that the sheath layer 18 surrounds the filter 17 only.

[0066] The surface of the fiber web 1 forms the inner surface of the channels 19. The embossment regions 8 and the crimping of the material result in formation of an uneven surface structure of the channel walls, which has a positive effect on the filtering action of the filter.

[0067] FIG. 4 shows a section through the filter along the line A-A in FIG. 3. The filter material 1, as shown here, is laid alternately, such that the channels 19 form in longitudinal direction of the rod-shaped filter. The alternately laid filter material may be in a symmetric or unsymmetric arrangement within the filter 17. In the embodiment shown here, the alternately laid filter materials form individual circle segments. The arrangement of the plies of filter material may also be irregular.

[0068] The filter material can also be used in systems for cleaning of air and gases. The web material 1, as shown in FIGS. 3 and 4, may be laid in the form of a cylinder; the shape of the filter used in the systems may otherwise be as desired, for example box- shaped or in any other conceivable shapes.

[0069] In a further method step, the strength of the fibrous web 1 may be increased by subjecting the fibrous web 1 to a thermal treatment. The inventors assume that even the polylactide fibers present in the uncompressed regions 9 (FIG. 1) are (partly) melted and become bonded to one another or enter into a bond with any other fibers present, such as cellulose fibers. The thermal treatment can be effected by methods known to the person skilled in the art, such as by means of hot gas or microwaves, or else by running the fibrous web through hot calender rolls.

[0070] In a further processing step, it is possible to produce a three-dimensional shaped body from the material of the above-described fibrous web 1. For this purpose, the fibrous web 1, after passing through method step c), i.e. when it leaves the nip of the calender roll pair 6.1, 6.2, is subjected to a shaping method, for example a thermoforming method. For this purpose, the fibrous web or a blank obtained therefrom is converted to the desired shape by means of reduced pressure or other methods and then subjected to a thermal aftertreatment as already described above. During the thermal aftertreatment, the polylactide fibers are (partly) melted to such an extent that the fibrous web 1 adapts to the shape. After cooling, the shape thus formed remains dimensionally stable, and a permanent three-dimensional body is obtained. The individual shapes thus produced are separated from one another even during the shaping process or during or after the thermal aftertreatment and sent to further use.

[0071] FIG. 5 shows the method scheme for production of the fibrous web 1 and further processing thereof.

[0072] Fibers of polylactide 3 via a feed 23, and further fibers, for example cellulose fibers 4, via a separate feed 24 enter a mixing space 20 in which the different fibers are mixed, before they arrive at a substrate, here a revolving conveyor belt 21, as a mixture in an air stream, and form a fiber layer on the conveyor belt 21. The conveyor belt 21 may, for example, be an air-permeable screen belt. The fiber layer thus positioned is then guided together with the revolving belt 21 through a lightly compressing calender 22 or compaction gap. This exerts a first pressure on the fiber ply, so as to form a compacted mat 2.

[0073] The mat 2 thus precompacted is then run through the nip of the calender roll pair 6.1, 6.2 according to FIG. 1. This calender roll pair 6.1, 6.2 has the pattern of projections 7.1, 7.2. These projections constitute the compression regions, which generate a higher pressure than in the calender, and result in a pattern of dotted or linear compression regions. The second, higher pressure in combination with the application of heat to the mat has the effect that fusion of the fibers occurs.

[0074] After exiting from the calender roll pair 6.1, 6.2, the fibrous web 1 thus obtained is sent to further processing. In the embodiment shown here, the fibrous 1 is first sent to a further, independent thermal treatment 25, for which purpose it is subjected, for example, to electromagnetic rays, for example a treatment with microwaves.

[0075] The intermediate product that has thus undergone thermal aftertreatment can be processed further to corresponding blanks and/or processed in a subsequent shaping process 30 to give a three-dimensional product. For example, the blanks may be processed further in the shaping process 30 by thermoforming to give a three-dimensionally configured end product, for example to give a dish or a rod-shaped body. The shaping process 30 may be followed by a further thermal treatment 32 by which sustained consolidation of the product is achieved.

LIST OF REFERENCE NUMERALS

[0076] 1 fibrous web

[0077] 2 mat from method step b)

[0078] 3 fibers of polylactide

[0079] 4 cellulose fibers

[0080] 5.1, 5.2 web material

[0081] 6.1, 6.2 calender roll pair

[0082] 7.1, 7.2 projections

[0083] 8 embossment regions

[0084] 9 uncompressed regions

[0085] 10 shape

[0086] 11 elevations

[0087] 12 depressions

[0088] 17 filter

[0089] 18 sheath layer

[0090] 19 channels

[0091] 20 mixing space

[0092] 21 conveyor belt

[0093] 22 calender

[0094] 23 feed

[0095] 24 feed

[0096] 25 thermal treatment

[0097] 30 shaping process

[0098] 32 thermal treatment