Patent Application
20170121855
Field of the Invention
The present invention relates to a Lyocell staple fiber.
A Lyocell fiber is a celluosic fiber which is spun from a solution from cellulose in an organic solvent, especially in an aqueous tertiary amine-oxide. Today, N-methyl-morpholine-N-oxide (NMMO) is commercially used a solvent to produced Lyocell fibers.
Description of the Prior Art
The process for producing standard Lyocell fibers is well known from, inter alia, U.S. Pat. No. 4,246,221 or WO 93/19230. This process is called “amine-oxide process” or also “Lyocell process”.
Lyocell staple fiber is a product resulting from cutting a plurality of (endless) filaments which are obtained by spinning the cellulose solution through a spinneret and precipitating the spun filaments.
Typically, the cross-sectional shape of Lyocell fibers is essentially round. This is in contrast to standard viscose fibers, which exhibit a rather serrated cross-sectional shape.
Various processes to produce cellulosic fibers with defined non-circular cross-sectional shapes have been proposed. For example, EP 0 301 874 A discloses a process for the manufacture of so-called multi-lobal cellulosic staple fibers. A further process for the manufacture of cellulosic staple fibers by spinning of a spinning solution through a spinneret with multi-lobal spinneret holes is disclosed in WO 04/85720. Cellulosic fibers of a “Y”-shaped cross-section are also mentioned in GB-A-2 085 304.
JP-A 61-113812 and the publication “Verzug, Verstreckung and Querschnittsmodifizierung beim Viskosespinnen”, Treiber E., Chemiefasern 5 (1967) 344 348 disclose the manufacture of (endless) cellulosic filaments by extruding a spinning solution through a spinneret with multi-lobal spinneret holes.
All the above references are limited to the production of cellulosic fibers via the viscose process. Viscose fibers are quite distinct from Lyocell fibers in terms of their physical and textile properties.
The manufacture of a “Y”-shaped Lyocell fiber is mentioned in EP 0 574 870 A.
JP 10-140429 A discloses regenerated cellulose fibers which are produced by spinning a viscose solution through a spinneret exhibiting arrangements of fiber-forming holes which are located adjacent. Upon spinning the solution through the spinneret, the filaments extruded through these fiber-forming holes are fused to form one fiber exhibiting an anomal cross-sectional shape.
It is an object of the present invention to provide a Lyocell staple fiber having a defined non-circular cross-sectional shape.
This object is solved by a Lyocell staple fiber consisting of a plurality of cut filaments, which is characterized in that at least part of said cut filaments exhibit an overall cross-sectional shape which is a bi- or multi-filar cross-sectional shape resulting from notionally partially overlapping two or more fiber cross-sectional shapes.
The term “bi- or multi-filar” cross-sectional shape, for the purposes of the present invention, means a cross-sectional shape which results from notionally partially overlapping two or more fiber cross-sectional shapes.
I.e. a bi-filar cross-sectional shape is a shape resulting from partially overlapping two fiber cross-sectional shapes. A tri-filar cross-sectional shape is a shape resulting from partially overlapping three fiber cross-sectional shapes, and so on. This resulting cross-sectional shape will in the following also be referred to as the “overall cross-sectional shape”, in contrast to the single cross-sectional shapes which are partially overlapped.
If in the following terms such as “cross-sectional shape of the staple fiber” are used, this is to be understood as referring to the overall cross-sectional shape of the filaments which are constituting the staple fiber according to the invention.
In a preferred embodiment, at least part of, and preferably all of said partially overlapped cross-sectional shapes are essentially circular shapes.
A bi- or multi-filar cross-sectional shape according to this preferred embodiment, therefore, exhibits several sections in the form of segments of circles, i.e. those segments of the circular shapes which are not overlapped. Furthermore, the bi- or multifilar cross-sectional shape exhibits notches or indentations in those sections where the circular shapes are notionally overlapped.
Said two or more partially overlapped circular shapes may have essentially the same diameter. Alternatively, one or more of said partially overlapped circular shapes may have a higher diameter than the rest of said overlapped circular shapes. This means that the overall resulting cross-sectional shape consists of a mixture of smaller and larger circular shapes which are partially overlapped.
As will be described in more detail below, the Lyocell staple fiber according to the present invention may be produced by spinning a cellulose solution through a spinneret wherein at least part of said spinneret orifices consists of an assembly of two or more holes being located adjacent such that when the solution is extruded through said holes, the filaments extruded from said holes are partially fused to form one fused filament.
This means that in order to produce a Lyocell staple fiber the bi- or multi-filar cross-sectional shape of which is a mixture of smaller and larger circular shapes which are partially overlapped, as mentioned above, a cellulose solution may be extruded through a certain geometrical arrangement of adjacent circular holes with different diameter.
This not only results in a specific overall cross-sectional shape as already defined, but furthermore, inventive staple fiber of this kind exhibits surprisingly high crimp values.
Without wishing to be bound to any theory, it is believed that the high crimp of this embodiment of inventive staple fiber results from the fact that, given a certain overall extrusion velocity and a certain overall draw ratio in the air gap, if filaments are extruded from spinning holes with different diameters, the resulting single filaments which are fused together to form a fused filament have different tensile properties, resulting in a certain amount of natural tension and, hence, natural crimp, in the fused filament.
In a preferred embodiment, the overall cross-sectional shape of the fiber according to the invention is a bi-filar cross-sectional shape resulting from notionally overlapping two essentially circular shapes.
In another preferred embodiment, said overall cross-sectional shape is a tri-filar cross-sectional shape resulting from notionally overlapping three essentially circular shapes.
Said three overlapped circular shapes may be arranged in a row or in the form of a triangle. Said triangle preferably may be an essentially isosceles triangle.
In another preferred embodiment, said overall cross-sectional shape is a quadri-filar cross-sectional shape resulting from notionally overlapping four essentially circular shapes.
Said four overlapped circular shapes may alternatively be arranged in a row, in the form of a square, a parallelogram or a rhombus, or in the form of a triangle, with one of said circular shapes forming the centre of said triangle.
Lyocell staple fiber comprising filaments with a bi-, tri- or quadri-filar cross-sectional shape as described above may exhibit a decitex of from 0.5 to 8 dtex. Staple fiber of this decitex is especially useful for textile applications. In the field of absorbent products, or in the field of fiber fillings or carpets, staple fiber according to the present invention may be used in a decitex up to 40 dtex or more.
The overall cross-sectional shape of the staple fiber according to the present invention may also be a multi-filar cross-sectional shape resulting from notionally overlapping five or more, preferably five or seven essentially circular shapes. In this embodiment, the fibers typically exhibit a decitex of higher than 6 dtex.
At least one of the partially overlapped cross-sectional shapes of the staple fiber according to the present invention may be a non-circular cross-sectional shape.
I.e. the overall cross-sectional shape of a filament component of the staple fiber according to the invention may be a mixture of partially overlapped circular and non-circular cross-sectional shapes or it may even consist exclusively of partially overlapped non-circular cross-sectional shapes.
Said non-circular cross-sectional shape may be a multilobal, preferably trilobal, or triangular shape.
An especially preferred embodiment of the staple fiber according to the present invention is characterized in that essentially all of the cut filaments exhibit essentially the same overall cross-sectional shape.
Staple fiber according to this preferred embodiment has quite uniform properties in terms of its cross-sectional shape and the various physical and textile properties achieved thereby.
In yet a further embodiment, the filament constituting the Lyocell staple fiber according to the invention may at least partly exhibit a bi- or multi-filar cross-sectional shape which is hollow. A hollow structure may be obtained by choosing the spinning parameters in terms of size and distance of the spinning holes such that the extruded single filaments are not completely fused, but rather a gap is left in the centre of the formed fused filament.
It has surprisingly been found that the Lyocell staple fiber according to the invention has a significantly higher tenacity than comparable standard Lyocell staple fiber of the same decitex. Especially, Lyocell staple fiber according to the present invention exhibits a fiber tenacity in conditioned state which is higher by at least 15%, preferably at least 20%, than the fiber tenacity of a comparison Lyocell staple fiber of the same decitex, wherein all cut filaments of said comparison Lyocell staple fiber exhibit an essentially round cross-section.
Furthermore, Lyocell staple fiber according to the present invention has a surprisingly high flexural rigidity.
Especially, Lyocell staple fiber according to the present invention exhibits a decitex-related flexural rigidity of at least 0.5 mN.mm2/tex2, preferably more than 0.6 mN.mm2/tex2.
The flexural rigidity is measured by a method developed by the applicant. The measured value is displayed as the relation of the gradient of the force to path over a linear measuring range, based on the decitex.
In order to carry out the measurement, a conditioned fiber is clamped into a clamping bar and cut with a cutting device to a length of exactly 5 mm. The clamping bar is moved upwardly at constant speed by an electric gear. Thereby, the fiber is pressed onto a small sensor plate which is adapted to a force sensor. The stiffer the fiber, the higher is the measured force.
Due to the lack of possibilities to calibrate, no effective force is given for the calculation of the flexural stiffness. However, it is possible to make a relative comparison of fibers in a specified measuring range. Thereby, the gradient is measured in a linear measuring range of the measured force over the path and related to the decitex of the fiber.
A process for the manufacture of a Lyocell staple fiber according to the present invention comprises the steps of
It has surprisingly been found that if a cellulose solution in NMMO is extruded through a spinneret as specified above, fused filaments result which exhibit a very uniform and reproducible bi- or multi-filar cross-sectional shape.
In the process according to the present invention, preferably at least part of, and more preferably all of said spinneret holes have a circular shape. All of said holes may have the same diameter.
Alternatively, one or more of said holes may have a higher diameter than the rest of said holes. In this case, a cross-sectional shape results which is a mixture of partially overlapped smaller and larger circular shapes, as mentioned above. The ratio of the cross-sectional area of the hole(s) with the higher diameter to the hole cross-sectional area of the hole(s) with a smaller diameter is preferably from more than 1:1 to 16:1, preferably 1.6 to 1 to 2.7 to 1.
In a further preferred embodiment, said spinneret orifice consists of two holes, each having a circular shape.
Said spinneret orifice may also consist of three holes, each having a circular shape. The three holes may be arranged in a row, resulting in an overall flat, oblong cross-sectional shape of the fused filament.
Furthermore, said three holes may be arranged in the form of a triangle, preferably an isosceles triangle. If the diameter of all the spinning holes is the same, or especially if the diameter of the hole in the intersection point of the two equal sides of the isosceles triangle is bigger than the diameter of the other two holes, the resulting overall cross-sectional shape of the fused filament will be of a “teddy-bear”-like nature, two of the partially overlapped circular shapes forming the “ears” of the bear, and the circular shape of the filament spun from the hole at the intersection point of the two equal sides of the isosceles triangle forming the “face”.
Said spinneret orifice may also consist of four holes, each having a circular shape.
The four holes may be arranged in a row, again resulting in an flat and oblong overall cross-sectional shape of the fused filament.
Alternatively, said four holes may be arranged in the form of a square, a parallelogram, or a rhombus. If the diameter of all the spinning holes is the same, the resulting overall cross- sectional shape of the fused filament will then resemble a square, a parallelogram or a rhombus, respectively.
Said four holes may also be arranged in the form of a triangle, with one of said holes forming the centre of said triangle. Again, depending on the diameter of the spinning holes employed, a triangular or “teddy-bear”-like shape may result.
Said spinneret orifice may also consist of five or more holes, preferably five or seven holes, each having a circular shape. Of course, many different geometrical arrangements of the holes are possible, resulting in a variety of different cross-sectional shapes of the fused filaments, which will be shown in more detail below with reference to the drawings.
As will already be apparent from the above, the overall cross-sectional shape of the fused filaments does not only depend on the number and geometrical arrangement of the spinneret holes employed in said spinneret orifice, but there is also a strong correlation to the size of the hole diameters. I.e. by varying the hole diameters or by providing a geometrical arrangement of holes with different diameters, the resulting cross-sectional shape of the fused filament will be strongly influenced.
In a further embodiment of the present invention, at least one of said holes has a non-circular shape. Said non-circular shape may be a multilobal, preferably trilobal, or triangular shape.
Preferably, all of said spinneret orifices consist of an identical assembly of holes in terms of the geometrical arrangement, the shape and the size of said holes. I.e. in this embodiment all assemblies of holes have the same geometrical arrangement, and the respective sizes and shapes of the holes within said arrangement are the same for all the assemblies. By this embodiment, it has been found that it is possible to obtain a plurality of fused filaments which exhibit essentially the same bi- or multifilar cross-sectional shape. It is quite surprising that such a uniform and reproducible filament (and staple fiber) cross-section can be obtained in the amine-oxide or Lyocell process.
In case of spinning through uniform spinneret orifices, these may preferably be positioned in a plurality of parallel rows. Within each of said rows, all assemblies of holes may be oriented essentially parallel to each other.
Furthermore, it has been found that the geometrical arrangement of the spinneret holes, and their respective size and shape can be optimally reproduced in the fused filaments if the air which is blown on said filaments in the air gap is directed onto said filaments in a specific direction:
Examples for the main orientation axis of several geometrical arrangements are given below with regard to the drawings.
The diameter of said holes in said hole assembly may be from 35 to 200 μm. In case of non-circular holes, the term “diameter” means the diameter of the circle which can be circumscribed around the non-circular shape. As already mentioned, holes of different diameter may be employed in one hole assembly.
The distance from the centre of one hole to the centre of the next adjacent hole in said hole assembly may preferably be from 100 to 500 μ, preferably from 150 to 250 μm. The distance may be adjusted by the skilled artisan in dependency of the desired overall cross-sectional shape of the fused filament. By appropriately adjusting the respective distance between the holes and the respective hole diameters, a staple fiber with a hollow cross-sectional shape may be produced.
The Lyocell staple fiber according to the present invention may be used in a variety of end-uses, such as medical-, hygiene-, household textiles-, technical- and apparel applications, especially wound dressings, laparotomy pads, bed pads, tampons, sanitary towels, wipes, incontinence products, pillows, duvets, towels, carpets, pile fabrics, damask, satin, insulation materials, reinforcement fiber for polymers, paper or concrete, textile articles, such as knitted or woven textile articles, shirtings, velour, chinos, cotton-like hand fabrics and garments made thereof.
Especially, the Lyocell staple fiber according to the invention is useful in any application where a stiffer, crisper, more “cotton-like” hand, or altered thermal and moisture management properties or different optics are desirable.
Preferred embodiments of the present invention will now be described by way of the drawings and examples.
According to
The shaded structures shown on the right side of
The arrow in
Therefore, in the following only a few comments are to be made with regard to
With regard to
In
The preferred blowing direction with regard to both
The same applies to
In each case, a spinneret with various spinneret orifices each consisting of three holes, arranged in the form of a triangle, were used. In each orifice, two of the holes had a diameter of 80 μm, and one of the holes had a diameter of 120 μm. The distance from the center of the bigger hole to the center of the adjacent holes was 250 μm each.
All other spinning parameters being constant, the only variation resided in the direction of the blowing air (indicated by the arrows in
As apparent from
A standard spinning solution of 13% cellulose in NMMO was spun at 110° C. through the spinneret configuration as described, and was led through an air gap with a length of around 20 mm.
Blowing air was directed onto the extruded filaments. The blowing direction was essentially parallel to the base line of the triangle defined by the two smaller spinneret holes (cf.
Both
For the production of the staple fiber depicted in
As apparent from
Applying a constant set of spinning parameters, standard Lyocell staple fiber with an essentially round cross-section and Lyocell staple fiber with a tri-filar cross-sectional shape (spun from a spinneret with orifices as described with regard to example 1 and
It can easily be seen that the Lyocell staple fiber according to the invention has a significantly higher fiber tenacity than a standard Lyocell staple with the same decitex.
Lyocell staple fiber according to the present invention produced with a spinneret configuration as described with regard to example 1 and
The Modal fiber in the above example was produced according to the teaching of PCT/AT/000493 (not pre-published).
From table 2, it is apparent that the Lyocell staple fiber with a tri-filar “teddy-bear”-like cross-sectional shape has a significantly higher decitex-related flexural rigidity than the other cellulosic fibers observed. Especially the decitex-related flexural rigidity of the staple fiber according to the invention was higher than 0.5 mN mm2/tex2 in all of the examples.
| Number | Date | Country | Kind |
|---|---|---|---|
| A 1015/2006 | Jun 2006 | AT | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12304622 | Jul 2009 | US |
| Child | 14871155 | US |
