Note: Descriptions are shown in the official language in which they were submitted.
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2126~
The present invention relates to polyolefin fibers
suitable for the production of nonwoven fabrics by spun-bonding
process, having improved strength and softness characteristics.
The present invention also relates to a process for the
production of said fibers, a process to produce nonwoven
fabrics by spun-bonding using said fibers, and the nonwoven
fabrics obtained by said process.
The definition of ~'fibers~ includes also products similar
to fibers, such as fibrils.
Nonwoven fabrics are widely used in various applications.
They are used, for example, in the preparation of articles to
be utilized in the agricultural field, and for domestic and
industrial "throwaway" articles. For some specific uses said
fabrics must possess good softness characteristics (which
depend on the flexibility index of the fiber), strength (which
depends on the thermowelding strength of the fiber) and
resistance to yellowing. These characteristics are
particularly important in the health and medical fields. ;~
Polyolefin fibers which can be used for the preparation
of nonwoven fibers possessing good aging and yellowing
resistance are already known in the art. For example, fibers
with thé above mentioned properties are described in published
European patent application EP-A-391438, in the name of the
Applicant. Said patent application describes some combinations
of stabilizers which can render the fibers particularly
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resistant to yellowing and aging.
United States patent application 07/968.766 in the name
of the Applicant describes nonwoven fabrics whlch have, among
other things, good softness and strenyth properties (in the
examples the maximum thermowelding strength of the fibers
constituting the fabrics is slightly higher than 3 N). `
Now some polyolefin fibers have been found which possess
a high flexibility index and/or thermowelding strength, besides
presenting good yellowing and aging resistance. These - ` `
properties allow one to obtain nonwoven fabrics which offer
good softness and strength.
One embodiment of the present lnvention is a process for
the preparation of nonwoven fabrics which comprise said fibers
and present both softness and strength properties.
~ .
Another embodiment of the present invention is a process
used to prepare said fibers.
Yet another embodiment of the present invention relates
to the nonwoven fabrics obtained with said process.
Accordingly the present invention provides a fiber for
nonwoven fabrics having thermowelding strength equal to or
greater than 5 N and/or flexibility higher than 800, comprising
a polymer material additivated with organic phosphites and/or
phosphonites, HALS and optionally phenolic antioxidants, said
polymer material being selected from:
1) isotactic propylene homopolymers having an isotactic
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index greater than 90;
2) random copolymers of propylene wlth ethylene and/or a C4-
C0 ~-olefin; and
3) blends of homopolymers (1) with copolymers (2), or blends
of at least one of the above mentioned homopolymers and
copolymers with heterophasic propylene polymers, said
heterophasic polymers comprising (by weight):
A) from 10 to 60 parts of a propylene homopolymer, or
a copolymer of propylene with ethylene and/or a C4-C8
~-olefin, containing over 80~ of propylene and
having an isotactic index.greater than 80 (Fraction
A~;
B) from 1 to 25 parts of an essentially linear
semicrystalline copolymer of ethylene with a C3-Ca ~-
olefin, insoluble in xylene at ambient temperature
(Fraction B); and
C) from 15 to 87 parts o~ a copolymer fraction of
: . ethylene with propylene and/or a C4-C8 a-olefin, and
optionally minor quantity of diene, said copolymer
Fraction containing from 10 to 80~ of ethylene and
being soluble in xylene at ambient temperature
(Fraction C).;
.said fiber being obtained by a spinni.ng process operating
with a real or equivalent output hole diameter of less
than 0.5 mm, with a hole flow-rate ranging from 0.1 to
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0.6 g/minute and at a spinning temperature ranging from
260C to 320C, using polymers (1) or (2), or polymer
blends (3), having MFR from 5 to 40 g/10 min, and in the
absence of a drawing step. ~;
The C4-C8 ~-olefins to be used for the preparation of the .
copolymers which can be present in random copolymers (2),
Fraction A and Fraction C are linear or branched alkenes, and ~ ~;
are preferably selected from the following compounds~
butene, l-pentene, l-hexene, l-octene and 4-methyl-1-pentene.
, ~,
The l-butene is the preferred ~-olefin.
The random copolymers (2) contain a quantity of comonomer
ranging from 0.05 to 20% by weight. When the quantity of
comonomer exceeds 5%, said copolymers must be blended with the
propylene homopolymer.
Preferably Fraction A is present in the heterophasic
polymer in quantities ranging from 10 to 50 parts by weight,
~ - ;,:
and is made up of a propylene homopolymer with an isotactlc
index preferably greater than 90, more preferably from 95 to
98, or of the copolymer defined above, preferably containing
over 85%, more preferably from 90 to 99~ of propylene.
Preferably Fraction B is present in the heterophasic
polymer in quantities ranging from 7 to 15 parts by weight and
: - .
has a crystallinity ranging from about 20 to 60%, determined
by way of DSC (Differential Scanning Calorimetry). The
copolymer of said fraction is preferably selected from the
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following types of copolymers: ethylene/propylene, containing
over 55% of ethylene; ethylene/propylene/C4-CB ~-olefin,
containing from 1 to 10% of said ~-olefin and from 55% to 98%,
preferably from 80 to 95%, of ethylene plus said ~-olefin;
ethylene/C4-C8 ~-olefin, containing from 55% to 98%, preferably
from 80 to 95~, of said ~-olefin.
Preferably Fraction C is present in the heterophasic
polymer in quantities ranging from 30 to 75 parts by weight,
and is made up of a copolymer selected from: an
ethylene/propylene copolymer containing from 15% to 70% of
ethylene, preferably from 20 to 60%; an ethylene/propylene/C4- -~
C8 ~-olefin copolymer, containing from 1 to 10% of said ~-
olefin, preferably from 1 to 5%, wherein the total quantity of
ethylene plus ~-olefin ranges from 20 to less than 40~; an ~;
ethylene/~-olefin copolymer, containing from 20 to less than
40%, preferably from 20 to 38%, more preferably from 25 to 38%, ~ ¦
of said ~-olefin. The dienes, optionally present in the
copolymers of said Fraction are present in quantities equal to
or less than 10%, and are preferably aelected from: butadiene,
1,4-hexadiene, 1,5-hexadiene and 2-ethylidene-5-norbornene.
The heterophasic propylene polymers are prepared either
by mechanically blending components (A), (B), ahd (C) in the
molten state, or by using a sequential polymerization process
carried out in one or more steps, and using highly ~ `
stereospecific Ziegler-Natta catalysts.
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Examples of the heterophasic polypropylene compositions ~
: . .
mentioned above, as well as the catalysts and polymerization
processes commonly used for their preparation, are described
in published European patent applications 400333 and 472946.
The blends ~3) are obtained by melting and pelletizing the
polymers, or by blending them without melting. In these
blends, the quantity of heterophasic polymer and/or random
copolymer (2) containing over 5% of comonomer preferably does
not exceed 30% of the total weight of the blend.
..
The stabilizers which are added to the polyolefins
described above are the following:
a) one or more organic phosphite and/or phosphonites,
preferably in quantities ranging from 0.01 to 0.5~ by
weight, more preferably from 0.02 to 0.15%; ~ ~
, .;:
b) one or more HALS (Hindered Amine Light Stabilizers),
preferably in quantities ranging from 0.005 to 0.5% by
weight, more preferably from 0.01 to 0.025;
c) optionalIy one or more phenolic oxidants, preferably in ~-~
concentrations not exceeding 0.02% by weight.
The following compounds are examples of phosphites that
., .
~; can be used as additives for the polyolefins of the fibera of
the present invention:
; tris(2,4-di-tert-butylphenyl)phosphite! marketed by CIBA GEIGY ~-
under the trademark Irgafos 168; distearyl pentaerythritol
diphosphite, marketed by BORG-WARNER CHEMICAL under the
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12601'~
trademark Weston 618; 4,4'-butylidenebis(3-methyl-6-tert-
butylphenyl-di-tridecyl)phosphite, marketed by ADEKA ARGUS
CHEMICAL under the trademark Mark P; tris(monononyl
phenyl)phosphite; bis(2,4-di-tert-butyl)pentaerythritol
diphosphite, marketed by BORG-WARNER CHEMICAL under the
trademark Ultranox 626.
The preferred organic phosphonite that can be used as
additive for the polyolefins of the fibers of the present
invention is tetrakis(2,4-di-tert-butylphenyl)4,4-diphenylene
diphosphonite, marketed by SANDOZ under the trademark Sandostab
P-EPQ.
Examples of HALS that can be added to the polyolefins of
the fibers of the present invention are:
poly{[6-(1,1,3,3,-tetramethylbutyl)-imine]-1,3,5-triazine-2,4-
diol] [2-(tetramethylpiperidyl)amine]hexamethylene-[4-(2,2,6,6- -~
tetramethylpiperidyl)imine~ (Chimassorb 944), Chimassorb 905,
bis(2,2,6,6,-tetramethyl-4-piperidyl)sebacate (Tinuvin 770),
Tinuvin 992, poly(N-~-hydroxymethyl-2,2,6,6,-tetramethyl-4-
hydroxy-piperidyl succinate (Tinuvin 622), Tinuvin 144,
Spinuvex A36, marketed by CIBA-GEIGY; Cyasorb UV 3346 marketed
by AMERICAN CYANAMIDE.
Examples of preferred phenolic antioxidants to be used as
additives in the polyolefins making up the fibers of the M -:
present invention ?~e: tris(4-t-butyl-3-hydroxy-2,6-
dimethylbenzyl)-s-triazine-2-4-6-(lH,3H,5H)-trione, sold by
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AMERICAN CYANAMID under the Cyanox 1790 trademark; calcium
bi[monoethyl(3,s-di-tert-butyl-4-hydroxybenzyl)phosphonate]; ~ ;
1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl)-s-triazine-
2,4,6(1H,3H,5H)trione; 1,3,s-trimethyl-2,4,6-tris (3,5-di-
tert-butyl-4-hydroxybenzyl)benzene; pentaerythrityl-
tetrakis[3-(3,5-di-tert-butyl-4-hydroxy-phenyl)propionate], ;
sold by CIBA-GEIGY under the following trademarks: Irganox
1425, Irganox 3114; Irganox 1330; Irganox 1010; 2,6-dimethyl-
3-hydroxy-4-tert-butyl benzyl abietate.
Besides the above mentioned stabilizers, one can add to
the olefins which are consequently converted into the fibers
of the present invention, the usual additives, such as
pigments, opacifiers, fillers, W stabilizers, and flame
retardants.
The polymers (containing the necessary additives) which
are converted in fibers according to the present invention have ;~
a melt flow rate (MFR) ranging from 5 to 40 g/10 min. In
particular, the polymers of points (1) and (2) have a MFR
preferably ranging from 5 to 25 g/10 min. The MFR is measured
according to ASTM D 1238, condition L. High MFR values are
obtained directly in polymerization, or by controlled radical
visbreaking.
-The process of controlled radical visbreaking is carried
out using, for example, some organic peroxides, such as 2,5~
dimethyl-2,5-di(tert-butylperoxy)hexane, during the pelletizing
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phase or directly in the fiber extrusion step.
The molecular weight distribution of the polymers making
up the fibers of the present invention, expressed as Mw/Mn,
ranges from 3 to 6, preferably from 3.5 to 4.5.
The polymers to be converted into the fibers of the
present invention can be in the form of pellets or nonextruded
particles, such as fla]ces, or spheroidal particles with a
diameter ranging from 0.5 to 4.5 mm. Said particles are
covered or impregnated, at least on the surface, with the
stabilizers (or additives in general) mentioned above, and/or
peroxides, if the latter should be necessary to obtain a
molecular weight distribution within the range mentioned above.
Additives such as opacifiers, fillers and pigments can
also be added while the fiber is being spun.
In order to obtain fibers which present both a high
flexibility index (which is important to ensure nonwoven
fabrics with good softness characteristics) and a high
thermowelding strength (which is important to ensure nonwoven
fabrica with good strength characteristics), the spinning
process must be carried out preferably at a die temperature
,:
ranging from 280C to 320C, and a hole flow-rate from 0.25 to
1 0.4 g/min/hole for polymers (1) and (2) having MFR ranging f-rom
:
5 to 25 g/10 min., or it can be carried out preferably at a die
- - temperature ranging from 260C ~o 320C and a hole flow-r~te . . " .
; from 0.25 to 0.4 g/min/hole for polymer blends (3) having a MFR ~
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26014
ranging from 5 to 40 g/10 min. The fibers thus obtalned have
a flexibility index higher than 800 and a thermowelding
strength not lower than 5 N.
As previously mentioned, the process for the production
of the fibers is also an embodiment of the present invention.
The process for the preparation of fibers according to the
present invention is carried out by using~extruders equipped
with a die and without subjecting the fibers to a subsequent
drawing. The die is characterized by a real or equivalent
output hole diameter is than 0.5 mm.
By "output diameter of the holes~ is meant the diameter of the
holes measured at the external 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 one at the output. Moreover, the "equivalent
output diameter" definition applies to those cases where the
hole shape is not circular. In these cases, for the purposes
of the present invention one considers the diameter of an ideal
circle having one area equal to the area of the output hole,
which corresponds to the above mentioned equivalent diameter.
The temperature of both the extruder and the die during the
processing of the polymers ranges from 260C to 320C; in
particular it is best to operate at temperatures ranging from
280C- to 320C when the fibers are obtained from polymers (1~
and (2), while when using the polymer blends (3) the
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temperatures can range from 260C to 320C.
The dimensions of the fibers of the present invention if
they are to be used for the preparation of nonwoven fabrics,
have a count ranging from 1 to 10 dtex. In order to obtain
said count, the hole flow-rate must range from 0.1 to 0.6
g/min/hole, preferably from 0.25 to 0.45 g/min/hole.
Tests were carried out on the polymer material and the
fibers of the present invention to evaluate their
characteristics and properties; the methods used for said
tests are described below.
Melt Flow Rate (MFR): according to ASTM-D 1238, condition L. ;~
Weight average molecular weight (Mw): GPC (Gel Permeation
Chromatography) in
ortho-dichlorobenzol `~
at 150C.
Number average molecular weight (Mn~: GPC (Gel Permeatlon
Chromatography) in ;
ortho-dichlorobenzol
at 150C.
Thermowelding strength: in order to evaluate the
thermoweldability of staple fibers, one manufactures a nonwoven
fabric with the fiber being tested by way of calendering under
~ r~
set conditions. Then one measures the strength needed to tear
said nonwoven fabric when the stress is applied in directions `~
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which are both parallel and transversal to that of the
calendering.
The thermoweldability index (ITS) is defined as follows~
ITS = (TM-TC) 1/2
where TM and TC represent the tear strengths of the nonwoven
fabric measured according to ASTM 1682, for the parallel and
transversal directions respectively, and expressed in Newton.
The value of the strength determined in this fashion is
considered a measure of the capability of the fibers to be
thermowelded.
, ;-,
The result obtained, however, is influenced substantially
by the characteristics regarding the finishing of the fibers I ;~
(crimping, surface finishing, thermosetting, etc.), and the
conditions under which the card web fed to the calender is
prepared. To avoid these inconveniences and obtain a more
direct evaluation of the thermoweldabillty characteristics of
the fibers, a method has been perfected which will be descrlbed
below in details.
Some specimens were prepared from a 400 tex roving (method
ASTM D 1577-7) 0.4 meter long, made up of continuous fibers.
After the roving was twisted eighty times, the two
.
extremities were united, thus obtaining a product where the two
halves of the roving are entwined as in a ~rope. On said
specimen one produced one or more thermowelded areas by means
~'
of a thermowelding machine commonly used in a laboratory to
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test the thermoweldability of film.
A dynamometer was used to measure the average strength
required to separate the two halves of the roving at each
thermowelded area. The result, expressed in Newton, was
obtained by averaging out at least eight measurements. The
welding machine used was the Brugger HSC-ETK. The clamping
force of the welding plates is 800 N; the clamping time was 1
second, and the temperature of the plates was 150C. ~;;
Flexibility index
The flexibility of the filaments is represented by an
index defined in the following manner~
IF=(1/W)~100
where W is the minimum quantity in grams of a twisted roving
specimen which when tested with the Clarks Softness-Stiffness ;~
Tester changes the direction of the flexion when the plane, on
which the specimen is fixed in a perpendicular position,
rotates alternatively of +/- 45 with respect to the horizontal
plane.
. .
The specimen has the same characteristics as the one used
to measure thermowelding strength and is prepared using the
same process described above.
Resistance to yellowing
:.~
Norm ISO/TC 38/SC1 at 60C was applied to measure the ~ ;
resistance of the ~lbers to fading caused by gases produced
- by hydrocarbon combustion. In particular, the resistance to
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212601~
yellowing value referred to in the examples concerns the ~: -
variation caused by gas fading measured at 60C after 4 cycles.
Filaments' count
Measured according to ASTM D 1577-79.
The following examples are given in order to illustrate
and not limit the present invention.
Example 1
10 Kg of polypropylene pellets having an isotactic index
of 96.5 (calculated as residue insoluble in xylene at 25C),
MFR of 3S g/10 min., Mw/Mn of 4.2, and containing ~000 ppm of
the phosphite Irgafos 168 and 200 ppm of the HALS Chimassorb
944, have been prepared by extrusion at 220C. The peroxide
Lupersol 101 (marketed by Lucidol, Pennwalt Corp., USA) has
been used to visbreak the polypropylene to a Mw/Mn of 4,2. The ;~
polypropylene pellets are spun using a spinning apparatus
having the following characteristics:
- extruder equipped with a screw having a 25 mm diameter,
a length/diameter ratio of 25 and a capacity from 1 to 6
Kg/h;
- die with 40 holes, said holes having a diameter of 0.4 mm
and a length/diameter ratio of 5;
- metering pump;
- air quenching system at temperature from 18 to 20C;
- mechanical winding device with a velocity of up to 600
m/min, or air j et.
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2126014
The spinning conditions and characteristics of the
filaments obtained in this manner are shown on Table 1.
Example 2
Flake polypropylene, having a MFR of 2 g/10 min. and
additivated with the same additives listed in Example 1, is
visbroken with Lupersol until it reaches a MFR of 12 g/10 min,
and a Mw/Mn o'r 4. 10 kg of said polymer are then subjected
to spinning in the spinning apparatus described in Example 1.
The spinning conditions and characteristics of the
filaments obtained in this manner are shown on Table 1.
Example 3
A polymer blend comprising: 90 parts by weight of
polypropylene having a MFR of 5 g/10 min., and 10 parts by
weight of heterophasic polymer having a MFR of 5 g/10 min,
intrinsic viscosity of 2.6 dl/g, and the following composition:
55% by weight of ethylene/propylene random copolymer
(containing 2.5~ of ethylene), and 45% by weight of
ethylene/propylene rubber at a 60/40 ratio is used. ~ ~
The polymer blend, additivated with the same additives of ~ ;
Example 1 and ~isbroken with Lupersol 101 until a MFR of 35 ~ -~
g/10 min. is reached, is subjected to spinning, under the
conditions listed in Table 1, in the spinning apparatus
described in Example 1.
The properties of the fibers obtained are reported in
Table 1.
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Comparative example 1 (lc)
10 kg of polypropylene polymer flakes with an isotactic
lndex of 96.5, MFR of 5 g/10 min., and Mw/Mn of 6, addltivated
wlth the same stabilizers as in Example 1, ln the same
quantltles shown thereln, and vlsbro]cen wlth Lupersol 101, used
in such quantities as to visbreak the polymer to a MFR of 35
g/10 min (Mw/Mn equal to 3.8), are extru~ed at 220C. The
pellets obtained have been spun in a spinnlng apparatus having
the same characteristics described in Example 1.
The spinnlng condltlons and properties of the fiber
obtained are shown on Table 1.
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