Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
E
78866MHR
MET~iUD OF PROD~(TCZNG SI~APED CEL~JLOSTC HO~T~:S
SPECII~xCAT~ON
Kiel ~f the)Enventi_on
Our pxesent invention relates to a method of producing shaped
cellulosic bodies in which a cellulosic amine oxide solution is
extruded from a shaping orifice, e.g. a spinneret nozzle or a
shaping die, and is passed into a coagulating or precipitating bath
from which the Shaped object is withdrawn. Typical Shaped objects
within the purview of the present invention are filaments or fibers
lp and sheets or films.
~_Se.~~.~~L~~ ~! ~h~ nVA X11
=t is known to produce high polymer fibers with good fiber
and film characteristics when, within the elongated body which is
fabricated, a fiber structure is generated (see the Ullmann Encyclo-
lg pedia, 5th Edition, Volume A10, page 456). Zt is desirable and,
indeed, necessary to align micro-oriented regions, such as fibrides,
in the fiber along the fiber axis. The alignment or orientation can
be effBCted by various fabrication techniques and can dapend upon
the physical or physical-chemical processes to which the fiber or
film is subjected. xn many cases, this orientation can be effected
by a stretching.
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The process steps and the conditions in which and under which
this stretching is caxried out has an impact upon the fiber
properties whzch are produced, zn melt spinning, the fiY~ers are
stretched in a hot plastic state while the molecules are mobile.
Soluble polymers can be wet spun or dry spun. zn dry spinning, the
stretching is effected while the solvent is removed or is
evaporated. Extruded Fibers which axe coagulated in a precipitating
or coagulating bath are commonly stretched during the coagulation.
Processes of these types are well known and are widely
described. zn all of these cases, however, it is important that the
transition From the liquid state (independently of whethex this
state is a melt state or a solution state) to the solid state be so
e!leoted that during the filament formation, an orienxation of the
polymer chains or polymer chain packetra, referred to as gibride~s,
librilts or the like, is brought about.
xo inhibit the flash evaporation of a solvent from a filament
during dry spinning, there are numerous possibilities. However, the
problem of extremely rapid coagulation o! polymers during wet spin-
ning, as is the case with the spinning a! csilulosio amin~ oxide
solutions, has been solved heretoEars only by a combination of dry
spinning and wet spinning.
zt is, therefore, known to pass solutions of polymers into
the coagulation medium via an air gap. In EP~A~2~~ 672, in the
production of aramid fibers which are brought into a noncoagulating
medium via an air gap, stretched and then subjected to coagulation,
there is a combination of features of both dry and wet rpinning.
20~904~
In the East German patent 218 ~.~7., the spinning l:rom
cellulose zn amine oxides is effected via an air gap and precautions
must be taken to prevent adhesion of the objects produced. U.S.
patent 4,501,886 describes the spinning of a solution of cellulose
triacetate using an air gap. In U.S. patent 3,414,645, 'the
production of aromatic polyamide objects from solution is effected
in a dry-wet spinning process.
In all of these processes, an orientation is effected in the
air gap if only because the downwardly emerging solution from the
la orifice is at least stretched by the gravitational force on the
solution. The orientation effected by the gravitational action can
be increased when the extruder velocity, they velaaity at which the
solution emerges from the orifice, and the withdrawal speed of the
fiber passing through the coagulating bath are so adjusted that
15 further stretching occurs. A process of this latter typ~ is
described in Austrian patent 387,792 and the equivalent t7.S. patents
4,246,221 and 4,416,698. A solution of cellulose in NMMO ~NNMO r
t~-Methylmorpholine-N-oxide) and water is formed. The stretching ie
effected with a stretching ratio of at least 3:1.
The drawback of this process is the poor flexibility
avai~.able for a7.tering characteristics of the shaped body which is
produced. A minimum spanning-stre~tahing ratio is necessary to
provide aorx~esponding textile characteristics of the spun filament.
rn practice, only a limited range of textile fiber
25 characteristics can be produced and the fiber products by and large
have a rather low average toughness, defined as the product of the
Fiber tenacity arid the fiber elongation at break.
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7856-~MR 2D59fl42
A further drawback is that so-called velocity res~anance,
relating the withdrawal velocity and the orifice emergen~~e velocity,
leads to fluctuation in fiber diameter, the latter growing with
spinning/stretching ratio (see Navard, ~taudin, "Spinning of a
Cellulose N-Methylmorpholine-N~-oxide solution", Polymer Process
engineering, 3(3), 291 (1985)).
Finally, we may mention the disadvantage that the shape is
imparted to the bod~r t~raatically only in the air gap. A change in
the shape subsequently can only be accomplished with difficulty. As
a result, the band width of the products which can be potentially
made by the process is greatly limited. It is also desirable to be
able to influence the product characteristics after aaagulation and,
indeed, to provide a process fox fabricating shaped products from
cellulosia solutions, which will have significant fl~xibility.
l, Obiects of t~~ Invention
It is, therefore, the principal abject of the present
invention to provide a pxoc~ass for producing shaped objects of
cellulosic material by a process involving the forcing of the
solution from a shaping orifice via an air gap into a coagulating
2D bath, whereby these drawbacks can be avoided.
Another object op this invention is to provide an improved
method which will have increased versatility with respect to th~
range of properties of the products which are produced and which
will facilitate the reproducibility of the process.
25 Another object of the invention is simply to avoid the
drawbacks of earlier methods as described.
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~ummarv of thwgntion
These objects and others which will become apparent
hereinafter are attained, in accordance with the invention, which
provides that the ratio of the withdrawal velocity to the orifice
emergence velocity is at most l, and that the shaped body which is
produced is stretched only after the coagulation.
The reference to stretching here is intended to inca.ude deep
drawing, i.e. any process in which the shaped body is extended in
any dimension.
More particularly, the method of the present invention can
comprise the steps of:
(a) extruding a cellulosic solution capable of
coagulation in a coagulation bath through an orifice to shape a
stream of the solution;
(b) passing the stream of tha solution acxoss an air
gap into the coagulation bath, thereby coagulating the solution and
forming a continuous shaped body therefromt
(c) controlling a withdraw2tl velocity at whioh the body
is withdrawn from the coagulation bath and an orifice-emexgenc~
velocity at which the body emerges from the orifice eo that a ratio
of the withdrawal velocity to the orifica-emergence ve~looity is at
most 1: and
(d) thereafter stretching the continuous shaped body,
whereby the continuous shaped body composed of coagulated cellulose
ig stretched only after the body has been withdrawn Pram the bath.
The withdrawal velocity a~ the body according to the inven-
Lion is generally smallex than the orifice emergence velocity of the
mass which i.s spun or is at most equaX to the orifice emergence
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velocity so that there is no stretching in the air gap and,
preferably, na stxetching at any point prior to emergenc~a of the
body from the coagulation bath. The cellulose until and during
coagulation ire the coagulatiar bath, therefore, remains in a
relatively nonoriented stated.
It has been found that it is highly advantageous to minimize
the orientation before or during the coagulation and the greater the
extent to which the orientation prior to or during coagulation is
reduced, the greater is the possibility of influencing the
characteristics o! the product, a.g. during the later orientation
step. with slight orientation, the coagulated or precipitated
cellulose has an elasticity which resembl~s that of rubber. This
cellulo:e can then be stretched or deep drawn to impart to it they
dee~ired characteristics; thereby thm flexibility with r~spect to the
13 property of the product is achieved.
According to a lectors o! this i»vention, they pxoduct is
stretched in air or in water and can be a fiber or ~ilm or sheet.
Best results are obtained when the product is spun from a cellulose
solution in NMMO and water and they coagulating bath contains t~rr~to
a»d water.
A further advantage o~ the method o! thisc invention is that,
since thm stretching does not occur in thd air gap, this air gap can
be made relatively short. Therefore, even in cases when the
spinneret has a high hole density there is little danger that
neighboring ;fibers or filaments will adhere togeth~r. ~ince
large-scale production requires a maximum hole density, the short
air gap which promotes hale density has been found to be highly
desirable in modern pxoductian techniques.
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ar~.ef' ~escril~Qn, a the Ipraw nar
The above and other ob~eats, features and advantages of the
present invention will become more readily apparent from the
following description, reference being made to the accompanying
drawing, the sole FTGtJR~ of which is a flow diagram illustrating the
principles of the present invention.
speciE~ES sGri,ptiorl
=n the drawing, we have shown an apparatus camprising a pump
1 supplying a spinning solution of cellulose, NI~IO and water, to an
lp inlet 11 of a spinneret 10 having a multiplicity of discharge
orifices, one of which is shown to emit a stream x2 of the solution
through an air gap 13. Instead of a spinneret, an extrusion die of
the wide orifice type can be used to extrude the solution in the
chaps o! a sheet, if desired.
Atter passing through the air gap 13, the shaped stream 12 of
the solution enters a bath of a precipitating or coagulating
ac~lution as represented $t 14 in a vassal 26, ~khe coagulating
solutian being, e.g. a solution of NMMO in water.
Depleted precipitating solution can b~ drawn~off from the
v,~ssel 26 by a pump 2? and recycled via a bath regeneration stage.
The bath regeneration stags 22 can also receive an NI~IO and water
solution from a fiber washing stage, not shown, as represent~d at
21. Ths regeneratian can include evaporation of water to
concentrate th~ NI~O which can be fed in part as represontad at 24
to a vessel in which the spinning solution is formed and in part, as
represented at 25, back to the vessel 26.
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CA 02059042 2001-09-14
Water which is recovered can be fed at 23 to a fiber
washing stage which may be coordinated with a stretching
stage when the stretching is to take place under water.
The coagulated body 17 emerges from.t:he bath 14 and, after
such emergence, is subjected to stretching in a stretching
stage represented at 30. The stretching stage may include
godet rolls 18, 19 driven at different speeds to Stretch
the filament 31 between them. The st:retched filament 32 is
supplied to a yarn take-up stage represented at 20.
A controller 33 regulates the pump 1, a motor 34
driving the roller 35 in the bath 14 around which the
filament is guided, and the godet roll 18 so that the
withdrawal speed or velocity of the filament 17 from the
bath 14 is no greater than the speed with which the stream
12 emerges from the spinneret orifice, thereby excluding
stretch in the air gap 13, in the bath 14 between the air
gap and the roller 35 and in the bath between the roller 35
and emergence of the filament 17 from the bath and prior to
its engagement by the godet roll 18. All stretch is
confined between the rolls 18 and 19 and hence takes place
after the filament 17 emerges from the bath.
The following examples will c:Larify the invention
further.
Examples
Example 1:
Production of a fiber with a .ratio of withdrawal
velocity of orifice emergence velocity of less than 1.
(Comparative test.)
A 13% cellu.losic NMMO solution (cellulose of the
ViscokraftTM type marketed by the Firrn ICP, loo by weight
water, 77o by weight NMMO, 0.1% oxalic acid as stabilizer)
is forced through a spinneret having 100 holes each of a
diameter of 130 micrometers.
_ g _
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The volumetric flow through the orifices of the spinneret was
16.5 g/min. The orifice emergence ve7.ocity for the filament stream
was ltt.35 m/min. xhe 100 threads there passed through an 8 mm long
air gap and then guided with a velocity of 6 m/min through a spin-
ning bath of a path length of 15 cm. The temperature of the bath
was 2°G and the bath consisted of aqueaus NMMe3 solut~.on with an NMM~
concentration of 5%.
The ratio of the withdrawal velocity to the orifice emergence
velocity was therefore 0.58.
The resulting fiber had a tenacity of 11.8 cN/tex with an
elongation of 77.5%. xhe value of the elongation was extremely high
indicating that the cellulose strand had a relatively unordered
structure.
Stretching of the fiber after coagulation in air.
In this test, Example 1 was followed but after leaving the
spinning bath, i.e. after coagulation, was wound upon a first godet
roll of a speed of 6 m per minute and the fiber bundle then fed to a
second godet roll operating with a speed of 13 m per minute to
effect a stretching between the rolls of 117%. Stretching in % is
calculated as follows: S ~ ((EL ~- SL)/SL) x 100, where 8 ie the
stretch in %, SL is th~ starting length, i.~. thd length prior to
~ctretchi»g, EL is the end length, i.e. the length subsequent to
stretching. The resulting fibers had a tenacity of 22.4 cN/tex with
an elongation of 15.3%.
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example 3
Stretching of the fiber after coagulation in water.
The fiber was produced as in Example 1 and passed from the
spinning bath at 6 m/mxn (ratio of withdrawal speed to orifice
emergence speed : 0.58) and then passed through an 89 cm long
stretching bath aF water at a temperature pf 77°C. The godet rolls
were immersed in the water of the stretching bath and the second
godet rail wag driven at two different peripheral speeds y. The
resulting fibers had the following characteristics.
v Stretching Titer Tenacity Elongation
m/min S % dtex (Conditioned) (Conditioned)
a~llte~ %
14 133 32.4 19.7 17.5
21 250 10.3 22.3 9.2
E~D~e
Production of a fiber with a ratio of withdrawal velocity to
orifice emergence velocity of greater than 1 (comparativ~ test).
A 13% ceilulosia NI~tO solution of the same typ~ as in Exampie
1 wag forced through a spinneret with 100 holes each having a
24 diameter of 70 micrometers. The volumetric flow was 5.1 g/min
Corresponding to an orifice emergence velocity of 11.1 m/min. The
withdrawal velocity at tha first godet roll was 33.3 m/min, i.e. the
ratio of withdrawal velocity to orifice discharge velocity was
3.0:1. The fibers were passed through the spinning bath at the
veloc~.ty of the first godet roll and the spinning bath had a
temperature of 33°C and an Nt~to concentration of l0%.
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The subsequent stretching bath had a temperature
of 79°C and an NMMO concentration of: 90. The second
godet roll downstream of the stretching bath had a
withdrawal velocity of 46.9 m/min. The stretch amounted
to 410. The textile characteristics of the resulting
fibers were:
Titer: 3.5 dtex
Tenacity (conditioned): 25 cN/tex
Elongation (conditioned): 8.80
With a ratio of the withdrawal velocity to the
orifice emergence velocity in excess; of l, the fibers
remained stretchable not to the degree found with the
systems of Examples 2-4.
Example 5:
Production of a foil.
A 9% cellulosic NMMO solution (cellulose: buckey
V5T"" of Procter & Gamble, 12% water, 79% NMMO, 0.1% oxalic
acid stabilizer) is forced through a. slit-type orifice
(gap width = 50 micrometers, length = 30 mm).
The rate of flow is 21.3 g/m.in corresponding to an
orifice emergence velocity of 11.7 rrl/min. The extruded
stream was passed through a 7 mm lor..g air gap and then in
contact with a spinning bath over a length of 15 cm. The
spinning bath had a temperature of 24°C and an NMMO
concentration of 200.
The film is drawn via a first pair of rollers with
a velocity of 6 m/min. The ratio of withdrawal velocity
to orifice velocity was thus 0.51. In the same step, the
foil is guided through an 80 cm lone stretching bath
(temperature: 90°C; NMMO concentration: 200) and engaged
by a second pair of rollers, operating with a peripheral
speed of 11 m/min.
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The stretching amounted to 83%. The eharacteristiGS of the
washed and dried fol7. were:
thickness: 10 micrometers;
strength: 200 N/mm2;
elongatir~n : 6 . 5% .
Example
production of a shaped body.
A foil is produced as in Example 5 but snot stretched, i.e.
after the first tall, the foil is removed. In ~Ghe unstretched state
it i$ deep drawn with a g~.ass rod through 3 mm, washed arid dried tc~
a stable shaped body.
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