Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
21 26p 13
Spinning Process For The Preparation Of High
Thermoweldability Polyolefin Fibers
The present invention relates to a spinning process
for the preparation of thermowelda.ble polyolefin fibers, in
particular polypropylene based fibers, suitable for the
preparation of nonwoven fabrics.
Said nonwoven fabrics are particularly suitable for
uses requiring considerable softness and tear resistance,
1o as is the case with coverstock for diapers and sanitary
wear, which are made from low count fibers generally
ranging from 0.2 to 5 dtex, or with other membranes made
from fibers having a count between 3 and 10 dtex. The
fundamental requirement of polyolefin fibers for nonwoven
fabrics is that they must bond to each other by means of
the joint action of temperature arid pressure on which the
hot calendering processes are basE:d. This characteristic,
called "thermoweldability", is not: always present in
1
iB
21 260 13
polyolefin fibers, or at least not in the same degree. In
fact thermoweldability basically depends on the type of
polyolefin being span, the additives it contains, the type
of process, and the spinning conditions used.
Published European Patent Application 391438 describes
polyolefin compositions suitable for spinning and
characterized by the presence of stabilizers selected from
organic phosphites and/or phosphonites, HALS (Hindered
Amine Light Stabilizers) and optionally phenolic
to antioxidants.
The same patent application describes thermoweldable
fibers obtained from the above mentioned stabilized
polyolefin compositions by conventional spinning processes,
in particular processes for the production of staple
fibers. In this case the good levels of thermoweldability
shown in the examples are due to the selection of the
stabilizers. In the above mentioned examples fibers having
a count ranging from 1.9 to 2.2 dtex are prepared by using
n
s
2126p13
a typical "long-spinning" apparatus (characterized, among
other things, by high fiber-winding speed) equipped with a
die having holes with 0.4 mm diameter.
Using a die whose holes have a small diameter (less
than or equal to 0.4 mm) to produce low count fibers is
typical of both the above mentioned long-spinning
apparatus, as well as the "short-spinning" apparatus both
used for producing staple fibers, and of the spun-bonding
machines, because it enables high production levels to be
to obtained.
In fact, the smaller the diameter of the holes, the
higher the numbers of holes in the die, which means more
fibers per unit of time. This is the reason why in the art
the use of dies with diameters of the holes greater than
0.4 mm is limited to the productic>n of high-count fibers
(higher than 5 dtex).
Now it has surprisingly been found that, both in the
production of staple fibers and in the spun-bonding
(B '
21 260 1 3
process, the use of dies with holes having diameters
greater than or equal to 0.5 mm results in a marked
increase of the thermoweldability of the fibers, provided
that, for fibers having a count greater than 4 dtex, the
ratio of hole diameter to the count is high enough.
Accordingly, the present invention provides a process
for the preparation of thermoweldable fibers having a count
ranging preferably from 0.2 to 10 dtex, more preferably
from 0.5 to 3 dtex. The process comprises spinning an
olefin polymer using a short-spinning or a spun-bonding
apparatus including dies with holes. The holes of the dies
have a real or equivalent output diameter of greater than
or equal to 0.5 mm, particularly ranging from 0.5 to 2 mm.
Preferably, for fibers having a count greater than or equal
to 4 dtex, the ratio of the said output hole diameter to
the count is greater than or equal to 0.06 mm/dtex, more
preferably greater than or equal t:o 0.08 mm/dtex, even more
preferably greater than or equal i=o 0.1 mm/dtex.
4
21 260 13
As used herein, "output diameter of the holes" is the
diameter of the holes at the outside surface of the die,
i.e., on the front face of the die from which the fibers
exit. Inside the thickness of the die, the diameter of the
holes can be different from the diameter of the holes at
the output. The "equivalent output diameter of the holes"
refers to instances where the hole is not round, in which
case, for the purpose of the presE:nt invention, one
considers the diameter of the ideal circle having an area
1o equal to the area of the output he>le, which corresponds to
the above mentioned equivalent diameter.
The process of the present invention can be carried
out by using both short-spinning apparatuses for the
production of staple fibers, and :>pun-bonding apparatuses.
It has been found that thermoweldability of staple
fibers improves as the fibers gathering speed decreases.
In particular, in the case of staple fibers, short-
_ 21 260 13
spinning apparatuses are used; the apparatuses being
characterized, among other things, by low fiber-gathering
speeds (less than 500 m/min).
The above mentioned short-spinning apparatuses allow
for a continuous operation, since the spinning speed is
compatible with the drawing, crimping and cutting speeds,
and due to their simplicity and reduced overall volume,
these apparatuses are more economical than the long-
spinning ones and suited for small scale productions.
1o However, up until now short-spinning apparatuses did not
allow one to obtain staple fibers having good
thermoweldability values (higher than 2.5 N, for example,
according to the measuring method described in the
examples). The process of the present invention,
therefore, assumes particular importance when short-
spinning apparatuses are used, because it solves the
problem of producing thermoweldable staple fibers even when
operating with said apparatuses.
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21 260 13
The process conditions which are best suited to be
used according to the present invention using short-
spinning apparatuses are the following.
The hole flow rate ranges from 0.005 to 0.18 g/min,
preferably from 0.008 to 0.070 g/min, more preferably from
0.010 to 0.030 g/min. The fiber gathering speed ranges
from 30 to 500 m/min, preferably :From 40 to 250 m/min, more
preferably from 50 to 100 m/min. The draw ratios range
from 1.10 to 3.50, preferably from 1.20 to 2.50. Moreover,
1o the fiber cooling and solidification space at the output of
the die (cooling space) is preferably greater than 2 mm,
more preferably greater than 10 mm, in particular from 10
to 350 mm.
The cooling is generally induced by an air jet or
flow. Therefore, the cooling space is the distance between
the die and the above mentioned air jet or flow.
Finally, according to the present invention it is
preferable that the draw temperature be lower than 100°C,
(B '
.. 21 260 13
in particular it should range from 15°C to 50°C. For
further details on the short-spinning apparatuses reference
is made to M. Ahmed, "Polypropylene fibers science and
technology", Elsevier Scientific Publishing Company (1982)
pages 344-346.
The spinning temperature for the above short-spinning
apparatus generally ranges from 29:0°C to 310°C, preferably
from 270°C to 300°C.
The equipment used in the process of spun-bonding
1o normally includes an extruder with a die on its spinning
head, a cooling tower, and an air suction gathering device
that uses Venturi tubes.
Underneath this device, that uses air speed to control
the fiber gathering speed, the filaments are usually
gathered over a conveyor belt, where they are distributed
forming a web for heat welding in a calender.
According to this invention, when using typical spun-
bonding machinery, it is convenient to apply the process
conditions that follows.
fB a
~i2~oi3
The hole flow rate ranges from 0.1 to 2.0 g/min;
preferably from 0.2 to 1.0 g/min.
The space where fibers cool and solidify after leaving the
die (the cooling space) is preferably greater than 2 mm, more
preferably greater than 10 mm and in particular in the range
between 10 and 350 mm.
The fibers are generally cooled by means of an air jet or
flow. The cooling space is the distance between the die and
this air jet or flow.
The spinning temperature is generally between 230°C adn
300°C, preferably between 240°C and 280°C.
Generally, the olefin polymers that can be used in the
process of the present invention for the production of
thermoweldable fibers are polymers or copolymers, and their
mixtures, of R-CH=CHZ olefins where R is a hydrogen atom or a
C1-C6 alkyl radical. Particularly preferred are the following
polymers:
1) isotactic or mainly isotactic propylene homopolymers;
2) crystalline copolymers of propylene with ethylene and/or
C4-CB alpha-olefins, such as for example 1-butene, 1-
hexene, 1-octene, 4-methyl-1-pentene, wherein the total
comonomer content ranges from 0.050 to 20o by weight, or
mixtures of said copolymers with isotactic or mainly
isotactic propylene homopolym~=rs ;
3) heterophasic copolymers comprising (A) a propylene
(HM 5198 + HM 5238 EST) - 9 -
212fi013
homopolymer and/or one of the copolymers of item 2), and
an elastomeric fraction (B) comprising copolymers of
ethylene with propylene and/or a C4-Cg alpha-olefin,
optionally containing minor cluantities of a dime, such
as butadiene, 1,4-hexadiene, 1,5-hexadiene, ethylidene-1-
norbornene.
Preferably the amount of dime in (B) is from 1% to 10%
by weight.
The heterophasic copolymers (a) are prepared according to
known methods by mixing the components in the molten state, or
by sequential copolymerization, and generally contain the
copolymer fraction (B) in quantities ranging from 5% to 80% by
weight.
Specific examples of olefin polymers particularly suitable
for the preparation of thermoweldable fibers are the following
propylene random copolymers:
a) crystalline propylene random copolymers containing from
1 . 5 % to 20 % by weight of ethy:Lene or C4-Ca alpha-olefins;
b) crystalline propylene random copolymers containing from
85 % to 96 % by weight of propylene, from 1 . 5 % to 5% by
weight of ethylene, and from 2.5% to 10% by weight of a
C4-C8 alpha- olefin;
c) crystalline propylene random copolymers compositions
comprising (percentages by weight):
(1) from 30% to 65% of a copolymer of propylene with a
(HM 5198 + HM 5238 EST) - 10 -
~_ zzzsa~3
C4-C8 alpha-olefin, containing from 80% to 98% of
propylene; and
(2) from 35% to 70% of a propylene copolymer with
ethylene, and optionally with a C4-Cg alpha-olefin in
quantity ranging from 2% to 10%; said copolymer
containing from 2 % to 10%' of ethylene when the above
mentioned C4-CB alpha-olei_in is not present, and from
0 . 5 % to 5 % of ethylene when the C4-Cg alpha-olef in is
present;
d) compositions of crystalline propylene random copolymers
and crystalline ethylene copolymers comprising
(percentages by weight)
(1) from 40% to 70% of one or more crystalline propylene
copolymers with one or more comonomers selected from
ethylene and/or C4-CA alpha-olefin, wherein the
comonomer or comonomers content is from 5% to 20%;
(2) from 30% to 60% of LLDPE having a MFR E (according
to ASTM D 1238) from 0.1 to 15.
The above mentioned copolymers can also be used mixed with
each other and/or with isotactic or mainly isotactic propylene
homopolymers.
Other specific examples of olefin polymers particularly
suitable for the preparation of thermoweldable fibers are
heterophasic copolymers comprising from 5% to 95 % by weight of
an isotactic or mainly isotactic propylene homopolymer, and/or
(HM 5198 + HM 5238 EST) - 11 -
- 2126013
a random propylene copolymer of the above mentioned types from
a) to d), and from 95% to 5% by weight of a composition
selected from:
(I) a composition comprising:
(i) 10-60 parts by weight of propylene homopolymer with
an isotactic index higher than 90, or of a
crystalline copolymer of propylene with ethylene
and/or another C4-C8 alpha-olefin, containing over
85% by weight of propylene, and having an isotactic
index higher than 85;
(ii) 10-40 parts by weight of a crystalline polymer
fraction containing ethylene, insoluble in xylene at
ambient temperature;
(iii) 30-60 parts by weight of an amorphous ethylene-
propylene copolymer fraction optionally containing
minor portions of a diene, soluble in xylene at
ambient temperature and containing from 40 to 70% by
weight of ethylene;
(II) a composition comprising:
(i) 10-50 parts by weight of propylene homopolymer with
an isotactic index higher than 80, or a copolymer of
propylene with ethylene and/or a C4-CB alpha-olefin
containing over 85% by weight of propylene;
(ii) 5-20 parts by weight of a copolymer fraction
containing ethylene, insoluble in xylene at ambient
(HM 5198 + HM 5238 EST) - 12 -
212601.3
temperature;
(iii) 40-80 parts by weight ~of a copolymer fraction of
ethylene with propylene and/or a C4-CB alpha-olefin,
and optionally with minor portions of dime,
containing less than 40s by weight of ethylene, said
fraction being soluble in xylene at ambient
temperature, and havin~3 an intrinsic viscosity
ranging from 1.5 to 4 dl/g.
Specific examples of C4-CB alpha olefins and dienes have
been given above.
Generally, when used in the production of staple fibers
the above mentioned olefin polymers have a Melt Flow Rate
(MFR), determined according to ASTNID 1238-L, ranging from 0.5
to 100 g/10 min., preferably from 1.5 to 35 g/10 min..
When used in the spun-bonding apparatuses with the process
of the present invention, the above. mentioned olefin polymers
have preferably a MFR value between 5 and 25 g/10 min., in
particular from 8 to 15 g/10 min.. These values of MFR
constitute an additional distinctive feature of the process of
the invention, because in conventional spun-bonding processes
polyolefins have a MFR greater than 25 g/10 min.
The above said values of MFR. are obtained directly in
polymerization, or by controlled degradation. In order to
obtain said controlled degradation c:~e adds, for example,
organic peroxides in the spinning line or in the preceding
(HM 5198 + HM 5238 EST) - 13 -
. _. _ __.__ ...~_5.*~:,.__ __....,".....~.. _ __
. _. . _ , _ ...:
212603
steps of pelletization of the olefin polymers. Olefin polymers
are generally used in the form of pellets or nonextruded
particles, such as flakes or spheres, for example.
Preferably the olefin polymers which are subjected to
spinning with either process of the present invention are
stabilized with the types and ~xuantities of stabilizers
described in published European patent application 391438.
According to said patent application the polyolefins to be used
for spinning contain one or more of the following stabilizers
a) from 0.01 to 0.5o by weight: of one or more organic
phosphites and/or phosphonites;
b) from 0.005 to 0.5% by weight of one or more HALS
(Hindered Amine Light Stabilizer);
and optionally one or more phenolic antioxidants in
concentration which does not exceed 0.02% by weight.
The above stabilizers car. be added to the polyolefins by
means of pelletization or surface coating, or they can be
mechanically mixed with the polyole~fins.
Specific examples of phosphite~s are:
tris(2,4-di-tert-butylphenyl)phosph.ite marketed by CIBA GEIGY
under the trademark Irgafos 168; distearyl pentaerythritol
diphosphite marketed by BORG-WA~tNER CHEMICAL under the
trademark Weston 618; 4,4'-buty:Lidenebis(3-methyl-6-tert-
butylphenyl-di-tridecyl)phosphite 'marketed by ADEKA ARGUS
CHEMICAL under the trademark Mark P; tris(monononyl
(HM 5198 + HM 5238 EST) - 14 -
2126013
phenyl)phosphite; bis(2,4-di-tert-butyl)-pentaerythritol
diphosphite, marketed by BORG-WARNER CHEMICAL under the
trademark Ultranox 626.
A preferred example of phosphonites is the tetrakis(2,4-
di-tert-butylphenyl)4,4'-diphenylilenediphosphonite, on which
Sandostab P-EPQ, marketed by Sandoz, is based.
The HALS ara monomeric or oligomeric compounds containing
in the molecule one or more substituted amine, preferably
piperidine, groups.
Specific examples of HALS containing substituted
piperidine groups are the compounds sold by CIBA-GEIGY under
the following trademarks:
Chimassorb 944
Chimassorb 905
Tinuvin 770
Tinuvin 292
Tinuvin 622
Tinuvin 144
Spinuvex A36
and the product sold by American CYANAMID under the mark
Cyasorb UV 3346.
Examples of phenolic antioxidants are: tris-(4-tert-
butyl-3-hydroxy-2,6-dimethylbenzyl)-s-triazine-2-4-6-
(1H,3H,5H)-trione, marketed by American CYANAMID under the
trademark Cyanox 1790; calcium bi[monoethyl(3,5-di-tert-butyl-
(HM 5198 + HM 5238 EST) - 15 -
_ -- 212fi413
4-hydroxy-benzyl)phosphonate];1,3,5-tris(3,5-di-tert-butyl-4-
hydroxybenzyl)-s-triazine-2,4,6(1H,3H,5H)trione; 1,3,5-
trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene;
pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-
hydroxyphenyl)propionate]; octadecyl 3-(3,5-di-tert-butyl-4-
hydroxyphenyl)-propionate, marketed by CIBA GEIGY under the
trademarks Irganox 1425; Irganox 3114; Irganox 1330, Irganox
1010, Irganox 1076 respectively; 2,6-dimethyl-3-hydroxy-4-
tert-butyl benzyl abietate.
The following examples are given in order to illustrate
and not limit the present invention.
EVALUATION OF THE THERMOWELDABILIT'Y OF THE FIBERS
Generally, in order to evaluate the thermoweldability of
fibers, a nonwoven fabric is prepared from the fiber being
tested by calendering under certain given conditions.
Subsequently, the tension needed to tear said nonwoven fabric
both in the direction parallel and transversal to the
calendering is measured.
The tension value determined in this fashion is considered
a measure of the fiber thermowelding capability.
The result, however, is influenced substantially by the
finishing characteristics of the fibers (crimping, surface
finishing, thermosetting, etc.), <~nd by the homogeneity of
distribution of the fibers entering the calender. To avoid
these inconveniences and obtain a more direct evaluation of the
(HM 5198 + HM 5238 EST) - 16 -
21 260 13
fiber thermoweldability characteristics a method has been
perfected that will be described below.
Specimens are prepared from a 400 tex roving (method ASTM
D 1577-7) 0.4 meter long, made up of continuous fibers.
After the roving has been twisted eighty times, the two
extremities are united, thus obtaining a product where the two
halves of the roving are entwined as in a rope.
The thermowelding is carried out on said specimen using
a Bruggel HSC-ETK#thermowelding machine, operating at a plate
temperature of 150°C, using a clamping pressure of 800 N and 1
second welding times.
A dynamometer is used to measure the average strength
required to separate the two halves of the roving which
constitute each specimen at the thermowelding point. The
result, expressed in Newton, is obtained by averaging out at
least eight measurements, and represents the thermowelding
strength of the fibers.
POLYMERS SUBJECTED TO SPINNING
The polymers used in the exannples to produce the fibers
are the following:
Polypropylene I
Mechanical mixture of propylE~ne homopolymer having MFRh
of 13 g/10 min and a fraction soluble in xylene at 25°C equal
to 3 . 5 0 by weight, in the form o:E flakes with a controlled
particle size distribution (average diameter of the particles
* Trademark - 17 -
fB
_.. ~ 2126p'3
450~.m) , containing:
additive concentration (by weight)
Irganox 1076* 0.01%
Irganox 3114* 0.01%
Irgafos 168* 0 . 07
Calcium stearate 0.05%
Said mechanical mixture has been obtained by introducing
the components into a CACCIA speed mixer model LABO 30, and
mixing for 4 minutes at 1400 rpm.
Polypropylene II
Same composition as for Polypropylene I, but in the form
of pellets, as the above said mechanical mixture has been
granulated by extrusion.
Polypropylene III
Propylene homopolymer in spheroidal particle form with a
diameter ranging from 2 to 3 mm, having a MFR of 12.2 g/10 min.
and a fraction soluble in xylene at 25°C equal to 4.2% by
weight, surface additivated with:
additive concentration (by weight)
Irganox 1076 0.01%
Chimassorb 944 0.02%
Sandostab P-EPQ 0.05%
Calcium stearate 0.05%
* Trademark
- 18 -
(B
212gp ~3
The Chimassorb 944 is a HALS having the formula
N w_t~Nz-~-N
G
N N 1_
N.
l I
NH ~ N
n
wherein n generally ranges from 2 to 20.
Comparative Example 1
Using the above defined polypropylene I, staple fibers are
prepared on a LEONARD 25* long spinning apparatus, built and
marketed by Costruzioni Meccaniche Leonard - Sumirago (VA) -
Italy. The set-up of the apparatus is as follows:
- extruder with a screw having a 25 mm diameter and a
length/diameter ratio of 25, a:nd a flow-rate ranging from
1 to 6 Kg/h;
- 2.5 cm'/rev. metering pump;
- die having 61 round holes with an output diameter of 0.8
mm;
- cooling system for the extruded filaments by means of
transversal air jet at 18-20°C;
- gathering apparatus with a spE~ed ranging from 1000-6000
m/min.;
- drawing apparatus in steam oven.
The following process conditions are used for the spinning
t~3
operation:
* Trademark
- 19 -
2126013
- die temperature 280°C
- hole flow rate 0.3 g/min.
- gathering speed 1400 m/min.
- draw ratio 1.3
- draw temperature 100°C
The characteristics of the fibE~rs obtained in this manner
are:
- single fiber count 1.7 dtex
(according to ASTM D 1577-79)
- weldability 4.1 N
Example 1
Using the above defined polypropylene I, staple fibers .
with a short-spinning pilot apparatus set up as follows are
prepared:
- single-screw extruder with a 120mm diameter and a length
equal to 30 diameters;
- 150 cm'/rev. metering pump;
- 20 -
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21 260 13
- die with 3.5x104 round holes a:nd a 0.6 mm output diameter;
said holes being situated in the form of a crown;
- cooling device, coaxial to thf~ crown of holes of the die,
emitting 20°C air on a plane perpendicular to the exiting
fibers.
The spinning conditions are as follows:
- temperature 300°C
- hole flow rate 0.018 g/min.
- distance between the die and
cooling airflow 5 mm
- gathering speed 70 m/min.
- draw temperature 80°C
- draw ratio 1.4
The characteristics of the fibers obtained in this manner
are:
- single fiber count 2.3 dtex
- weldability 6.85 N
Example 2
The same apparatus and conditions of Example 1 are used
to produce staple fibers, except that one uses the
polypropylene III.
The characteristics of the fibers obtained in this manner
are:
- single fiber count 2.3 dtex
- weldability 6.5 N
- 21 -
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2~26p ~~
Example 3
Staple fibers are produced using the same polymer,
apparatus and conditions of Example 1, except that the distance
between the die and the cooling airflow is 15 mm.
The characteristics of the fibers obtained in this manner
are:
- single fiber count 2.3 dtex
- weldability 7.6 N
Example 4
Staple fibers are produced using the same polymer,
apparatus and conditions of Examples 1, except that the drawing
occurs at ambient temperature.
The characteristics of the fibers obtained in this manner
are:
- single fiber count 2.3 dtex
- weldability 10 N
Comparative Example 2
Staple fibers are produced using the same polymer of
Example 1, an industrial apparatus made up of 8 spinning units
identical to the one described in Example 1, but whose dies
have 5.18x104 round holes having a output diameter of 0.4 mm.
The spinning conditions are:
- temperature 285°C
- hole flow rate 0.018 g/min.
- distance between the die and
- 22 -
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21 260 13
cooling airflow 5 mm
- gathering speed 64 m/min.
- draw temperature g0°C
- draw ratio 1.5
The characteristics of the fibers obtained in this manner
are:
- single fiber count 2.3 dtex
- weldability 2.35 N
Comparative Example 3
The same apparatus and conditions of Comparative example
2 are used to produce staple fibers, except that polypropylene
III is used.
The spinning conditions are:
- temperature 295°C
- hole draw ratio 0.024 g/min.
- distance between the die and
cooling airflow 5 mm
- gathering speed 70 m/min.
- draw temperature 80°C
- draw ratio 1.35
The characteristics of the fibers obtained in this manner
are:
- single fiber count 2.3 dtex
- weldability 2.2 N
Example 5
- 23 -
CB
~- 2~zsa13
Using polypropylene I, fibers are prepared using a BARMAG
25 mod. 2E1/24D apparatus for spun-bonding, manufactured and
sold by BARMER MASHINENFABRIK A.G. Manufacture. The lay out of
the apparatus is as follows:
- an extruder with a screw 25 mm in diameter and a ratio
lenght/diameter of 24; the extruder has a flow rate
between 0.3 and 1.2 kg/hr;
- a metering pump of 0.6 cm3/rev.
- a die with 37 holes of circular section having a output
hole diameter of 0.8 mm;
- a cooling system for the extruded fibers by transverse
air jet at 18-20°C;
- an air suction gathering device using a Venturi tube,
with a gathering speed ranging between 500-4000 m/min.
The process conditions for spinning are as follows:
- die temperature 280°C
- hole flow rate 0.6 g/min.
- gathering speed 2700 m/min.
- distance between the die and
and the cooling air jet. 20 mm
The characteristics of the obtained fibers are:
- single fiber count 2.2 dtex
- weldability 5.4 N
Comparison example 4
The same polymer is used, with the same apparatus and
(HM 5198 + HM 5238 EST) - 24 -
21 260 13
working under the same conditions as in Example 5, except that
the die has 37 circular section holes with a output hole
diameter of 0.4 mm.
The characteristics of the obtained fibers are:
single fiber count 2.2 dtex
- weldability 2.04 N
Example 6
Using polypropylene II, fibers and nonwoven fabrics are
prepared with a pilot appartus for spun-bonding made by the
German company LURGI. The layout: of the apparatus is as
follows
rectangular dies containing 931 holes of circular section
and with a output hole diameter of 0.9 mm.
- an air cooling device at 20°C, acting on a plane
perpendicular to the emergent fibers.
The spinning conditions are as fol:Lows:
- temperature 280°C
- hole flow rate 0.52 g/min.
- distance between the die
and the cooling air flow 30 mm
- gathering speed 2300 m/min.
The fibers obtained under these conditions have the following
characteristics:
- single fiber count 2.3 dtex
- weldability 6.4 N
- 25 -
21 26013
Example 7
Fibers are produced with the same apparatus and working
under the same conditions as in Example 5, but using
polypropylene III.
The obtained fibers have the following characteristics:
- single fiber count 2.2 dtex
- weldability 5.8 N
Comparison Example 5
Fibers are produced with the ~~ame polymer used in Example
7~ and the same apparatus used :in Example 5, but the die
contains 37 holes of circular section and the output hole
diameter is equal to 0.4 mm.
The obtained fibers have the following characteristics:
- single fiber count 2.2 dtex
- weldability 2.1 N
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