Process for the manufacture of cellulose fibres

The invention is concerned with a process for the production of cellulose fibers wherein a solution of cellulose in a tertiary amine-oxide is extruded through spinning holes of a spinneret, whereby filaments are extruded, the extruded filaments are conducted across an air gap, a precipitation bath and a drawing device whereby the filaments are drawn, the drawn filaments are further processed into cellulose fibers, the drawn filaments being exposed during further processing to a tensile stress in longitudinal direction not exceeding 5.5 cN/tex.

INTRODUCTION 
The present invention is concerned with a process for the production of 
cellulose fibres. In this process, a solution of cellulose in a tertiary 
amine-oxide is extruded through spinning holes of a spinneret, whereby 
filaments are extruded, the extruded filaments are conducted across an air 
gap, a precipitation bath and a drawing device whereby the filaments are 
drawn, and the drawn filaments are further processed into cellulose 
fibres. 
BACKGROUND OF THE INVENTION 
As an alternative to the viscose process, in recent years there has been 
described a number of processes wherein cellulose, without forming a 
derivative, is dissolved in an organic solvent, a combination of an 
organic solvent and an inorganic salt, or in aqueous saline solutions. 
Cellulose fibres made from such solutions have received by BISFA (The 
International Bureau for the Standardisation of man made Fibres) the 
generic name Lyocell. As Lyocell, BISFA defines a cellulose fibre obtained 
by a spinning process from an organic solvent. By "organic solvent", BISFA 
understands a mixture of an organic chemical and water. "solvent-spinning" 
means dissolving and spinning without derivatisation. 
So far, however, only one process for the production of a cellulose fibre 
of the Lyocell type has achieved industrial-scale realization. In this 
process N-methylmorpholine-N-oxide (NMMO) is used as a solvent. Such a 
process is described e.g. in U.S. Pat. No. 4,246,221 and provides fibres 
having a high tensile strength, a high wet-modulus and a high loop 
strength. 
However, the usefulness of plane fibre assemblies such as fabrics produced 
from the above fibres is significantly restricted by the pronounced 
tendency of the fibres to fibrillate when wet. Fibrillation means breaking 
off of the wet fibre in longitudinal direction at mechanical stress, so 
that the fibre gets hairy, furry. A fabric made from these fibres and dyed 
significantly loses colour intensity as it is washed several times. 
Additionally, light stripes are formed at abrasion and crease edges. The 
reason for fibrillation may be that the fibres consist of fibrils arranged 
in fibre direction, and that there is only little crosslinking between 
these. 
WO 92/14871 describes a process for the production of a fibre having a 
reduced tendency to fibrillation. This is achieved by providing all the 
baths with which the fibre is contacted before the first drying with a 
maximum pH value of 8.5. 
WO 92/07124 also describes a process for the production of a fibre having a 
reduced tendency to fibrillation, according to which the never dried fibre 
is treated with a cationic polymer. As such a polymer, a polymer having 
imidazole and azetidine groups is indicated. Additionally, a treatment 
with an emulsifiable polymer, such as polyethylene or polyvinylacetate, or 
a crosslinking with glyoxal may be carried out. 
In the lecture "Spinning of fibres through the N-methylmorpholine-N-oxide 
process", held by S. A. Mortimer and A. Peguy at the CELLUCON conference 
1993 in Lund, Sweden, published in "Cellulose and cellulose derivatives: 
Physico-chemical aspects and industrial applications" edited by J. F. 
Kennedy, G. O. Phillips and P-O. Williams, Woodhead Publishing Ltd., 
Cambridge, England, pp. 561-567, it was mentioned that the tendency to 
fibrillation rises as drawing is increased. 
From the lecture "Besonderheiten des im TITK entwickelten 
Aminoxidprozesses" held by Ch. Michels, R. Maron and E. Taeger at the 
symposium "Alternative Cellulose--Herstellen, Verformen, Eigenschaften" at 
Rudolstadt, Germany, in September 1994, published in Lenzinger Berichte 
September, 1994, pp. 57-60, it is known that there is a relation between 
the filament tension in the air gap and the mechanical properties of the 
fibrous materials. At the same symposium, P. Weigel, J. Gensrich and H.-P. 
Fink mentioned in their lecture "Strukturbildung von Cellulosefasern aus 
Aminoxidlosungen", published in Lenzinger Berichte September, 1984, pp. 
31-36, that the fibre properties may be improved when the filaments are 
dried without simultaneously exposing them to a tensile stress. 
In DE-A-42 19 658 and EP-A-0 574 870 it is described that post-drawing of 
the precipitated filaments has a negative effect on the textile properties 
of the fibres, particularly on their elongation. 
From WO 96/18760 cellulose filaments are known which exhibit a strength of 
50 to 80 cN/tex, a breaking elongation of 6 to 25% and a specific tear 
time of at least 300 s/tex. During production these filaments are exposed 
to a tension in the range of 5 to 93 cN/tex. It is disclosed that these 
fibres exhibit a low tendency to fibrillation. 
SUMMARY OF THE INVENTION 
It has been shown that the known cellulose fibres of the Lyocell type are 
insufficient regarding their fibre properties and their tendency to 
fibrillation, and thus it particularly is the object of the present 
invention to provide a process whereby fibres having improved properties 
may be produced, wherein the so-called working capacity, i.e. the 
mathematical product from fibre strength (conditioned) and elongation 
(conditioned) is improved. 
In a process for the production of cellulose fibres, this objective is 
attained by combining the steps of 
extruding a solution of cellulose in a tertiary amine-oxide through 
spinning holes of a spinneret, whereby filaments are extruded, 
conducting the extruded filaments across an air gap, a precipitation bath 
and a drawing device whereby the filaments are drawn, 
further processing the drawn filaments into cellulose fibres, and 
exposing the drawn filaments while being further processed to a tensile 
stress in longitudinal direction not exceeding 5.5 cN/tex.

DETAILED DESCRIPTION OF THE INVENTION 
It has been shown that good fibre properties may be achieved in an easy way 
by carrying out further processing of the drawn filaments such as washing 
out the tertiary amine-oxide from the filament and post-treatment 
(finishing), as well as particularly the transportation of the filaments 
while they are further processed, applying as little tension as possible, 
i.e. a tensile stress which should not exceed 5.5 cN/tex, to the 
filaments. 
For the purposes of the present invention, the term "further processing" 
comprises all the steps carried out on the filaments, including 
transportation of the filaments, after they have passed the first take up 
point of the drawing device. 
Conveniently, the drawn filaments are cut while being further processed and 
subsequently washed. 
Moreover, it has been shown that the length of the distance whereover the 
filaments are conducted from the spinneret to the drawing device has an 
effect on the fibre properties insofar as the fibre properties are the 
better the shorter this distance is. A preferred embodiment of the process 
according to the invention consists in that the length of this distance 
does not exceed 12 m and in particular does not exceed 1 m. 
The invention is further concerned with a process for the production of 
cellulose fibres characterized by the combination of steps of 
extruding a solution of cellulose in a tertiary amine-oxide through 
spinning holes of a spinneret, whereby filaments are extruded, 
conducting the extruded filaments across an air gap, a precipitation bath 
and a drawing device whereby the filaments are drawn, 
further processing the drawn filaments into dried cellulose fibres, 
the length of the distance whereover the filaments are conducted from the 
spinneret to the drawing device not exceeding 12 m and in particular not 
exceeding 1 m. 
Moreover, it has proven convenient to conduct the drawn filaments while 
being further processed and before an optionally provided cutting step 
across several godets provided subsequently to each other, the rate of 
each godet being lower than that of the godet provided immediately before 
it. 
All known cellulose dopes may be processed according to the process 
according to the invention. Thus, these dopes may contain of from 5 to 25% 
of cellulose. Cellulose contents of from 10 to 18%, however, are 
preferred. As raw material for the production of pulp, hard or soft wood 
may be employed, and the polymerisation degree of the pulp(s) may be 
within the range of the usual commercially available technical products. 
It has been shown however that when the molecular weight of the pulp is 
higher, the spinning behaviour will be better. The spinning temperature 
may range of from 75.degree. to 140.degree. C., depending on the 
polymerisation degree of the pulp and the solution concentration 
respectively, and may be optimized for each pulp or for each concentration 
in a simple way. 
In the following, the test procedures and preferred embodiments of the 
invention will be described in more detail. 
Fibrillation Evaluation 
The friction of the wet fibres during washing or finishing processes was 
simulated by the following test: 8 fibres were put in a 20 ml sample 
bottle with 4 ml of water and were shaken for 9 hours in a laboratory 
shaker of the RO-10 type made by the company Gerhardt, Bonn (Germany), at 
stage 12. 
Afterwards, the fibrillation behaviour of the fibres was evaluated under 
the microscope by counting the number of fibrils per 0.276 mm of fibre 
length. 
Textile Data 
Strength and elongation conditioned were analyzed according to the BISFA 
rule "Internationally agreed methods for testing viscose, modal, cupro, 
lyocell, acetat and triacetate staple fibres and tows", edition 1993. 
Loop Strength and Elongation (Conditioned) Test 
The loop strength was tested by forming a loop with two fibres and 
subjecting this loop to a tensile strength test. To determine the average, 
only those fibres which broke at the loop were considered. 
To measure the loop strength and elongation, a vibroscope, i.e. a titre 
measuring apparatus of the Lenzing AG type for the non-destructive titre 
determination according to the vibration method and a vibrodyn, i.e. an 
apparatus for tensile strength tests at single fibres at a constant 
deformation rate were employed. 
As the standard reference atmosphere, air of 20.degree. C. and a relative 
humidity of 65% was employed. 
EXAMPLE 1 
A 15% spinning solution of sulphite and sulphate pulp (9% of water, 76% of 
NMMO) having a temperature of 125.degree. C. was spun using a spinneret 
comprising 100 spinning holes with a diameter of 100 .mu.m each. The 
output of dope was 0.017 g/hole per minute. The titre of each of the 
filaments was 1.9 dtex. 
The filaments were conducted across an air gap into the precipitation bath 
and over a godet whereby a tension was exerted on the filaments, which 
thus were drawn in the air gap. After passing the godet, the filaments 
were immediately cut and only afterwards further processed by washing out 
the amine-oxide, avivage and drying. Thus, the further processing of the 
filaments was without tension. The textile data of the fibres obtained are 
shown in Table 1. 
EXAMPLE 2 
(Comparative Example) 
The procedure was analogous to that of Example 1, except that the filaments 
were not cut immediately after passing the godet, i.e. the first take up 
point, but conducted towards a further godet located at a distance of 2.2 
meters from the first godet. The rate of the second godet was adjusted 
such that the filament cable between the first and the second godet was 
exposed to a tension of 11.6 cN/tex. 
After passing the second godet, the filaments were immediately cut and only 
afterwards further processed by washing out the amine-oxide, avivage and 
drying. Thus the further processing of the filaments after the first take 
up point was not without tension. The textile data of the fibres obtained 
are shown in Table 1. 
TABLE 1 
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Example 1 
Example 2 
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Tension on the cable (cN/tex) 
0 11.6 
Strength cond. (cN/tex) 
37.5 34.3 
Elongation cond. (%) 
15.0 10.8 
Loop strength (cN/tex) 
20.9 18.8 
Loop elongation (%) 
5.8 4.1 
Fibrils 14 29 
working capacity 562 370 
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In the row "fibrils", the average number of fibrils on a fibre length of 
276 .mu.m is indicated. The working capacity is the mathematical product 
from strength (cond.) and elongation (cond.). 
From Table 1 it can be seen that further processing of the fibres without 
tension results in a product having improved properties. Among these 
properties, above all the lower number of fibrils and the higher working 
capacity should be pointed out. 
EXAMPLE 3 
A dope having the composition of Example 1 was extruded at 120.degree. 
through a spinneret having 1 spinning hole with a diameter of 100 .mu.m, 
producing filaments having a single fibre titre of 1.8 dtex. On the 
filaments produced, the effect of a drawing stress on the tendency to 
fibrillation was analyzed by exposing the filaments to different weights, 
varying also the exposure duration. The results are shown in Table 2. 
TABLE 2 
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Test no. 
Stress (cN/tex) 
Time (s) Number of fibrils 
______________________________________ 
A 2.2 10 1 
B 2.2 600 4 
C 5.6 10 3 
D 5.6 600 8.9 
E 10.9 10 7 
F 10.9 600 12 
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The Tests no. E and F are Comparative Tests. From Table 2 it can be seen 
that the tendency to fibrillation is the more pronounced the higher the 
stress is and the longer it acts upon the filament. 
EXAMPLE 4 
The procedure employed was analogous to that of Example 1, except that the 
distance from the spinneret to the godet was varied. The results are shown 
in Table 3. 
TABLE 3 
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Test 1 Test 2 Test 3 
______________________________________ 
Distance spinneret/godet (m) 
12 25 48 
Titre (dtex) 1.30 1.39 1.29 
Strength cond. (cN/tex) 
34.8 32.7 34.5 
Elongation cond. (%) 
11.8 11.6 11.1 
Fibrils 38 38 41 
working capacity 403 379 383 
______________________________________ 
From the results of Table 3 it can be seen that the length of the distance 
whereover the filaments are conducted to the drawing devise (godet) has an 
influence on the working capacity of the fibre insofar as the working 
capacity significantly declines when the distance exceeds 12 m.