Note: Descriptions are shown in the official language in which they were submitted.
21~4934
Case 11007 + 11007-2
This invention relates to a process of preparing fibers,
in particular, an improved process of preparing thermal
bondable fibers of fiber grade material.
Fibers of certain thermoplastic materials are used widely
in the manufacturing of thermally bonded products, such as
nonwoven textiles, by various processes. Said processes, such
as calendering and spun bonding, require that the fibers have
the capability of thermally bonding at temperatures lower than
the melting point of the particular polymer(s) from which they
are made, and that the fibers and articles manufactured
therefrom be resistant to aging, yellowing and color
variations caused by gas fading and oxidation.
There have been various attempts made to improve the
thermal bondability of fibers, such as incorporating additives
into the fiber grade polymer, elevating of spinning
temperatures, forming fibers having two components and
modifying the fiber surface. For example, U.S 4,473,677 to
Pellegrini et al discloses adding a dianhydride of a 3,3',4,4'
benzophenone tetracarboxylic acid or an alkyl derivative
thereof to polyolefins to improve the thermal bonding of the
fibers prepared therefrom. However, substantial problems are
encountered during spinning at elevated temperatures and
relatively slow spinning speeds are required.
Another approach is to add to the fiber grade polymer a
low melting material, such as oligomers and waxes. The
disadvantage of this approach is that the process must be
modified to ensure adequate mixing of the materials so that
gels are not formed in the fiber.
In the approach where fibers are formed from two
21~g3~
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different polymers, one component of the fiber has a lower
melting point than the other, and covers the surface of the
other component which has a higher melting point. These
fibers are generally referred to as a "sheath-core" or "side-
by-side" bicomponent fibers. The lower melting component
enables thermal bonding at a temperature below the melting
point of the fiber core.
Another approach is to modify the surface of the fiber
once the fiber has been formed. Typically, these fibers
contain only one fiber grade polymer, such as "skin fiber".
Modification of the fiber surface can be obtained using
various methods, such as irradiation, plasma treatment, ozone
treatment, corona discharge treatment or chemical treatment.
In the typical process of melt spinning, the polymer is
heated in an extruder to the melting point and the molten
polymer is pumped at a constant rate under pressure through a
spinneret containing one or more orifices of desired diameter,
thereby producing filaments of the molten polymer. The molten
polymer filaments are fed downward from the face of the
spinneret into a cooling stream of gas, generally air. The
filaments of molten polymer are solidified as a result of
cooling to form fibers. Depending upon the spinning method
used, the fibers are spread to form a fiber web and bonded
directly, like in the spun bond method. Alternatively, in
long spin methods, the fibers are gathered together and, if
desired, drawn to orient the macromolecular structure of the
fibers, and are then wound on bobbins. Bonding or calendering
is then performed in a separate step. Generally, if there is
any type of modification to be done to the filaments or
fibers, such as surface modification carried out by chemical
treatment or radiation treatment, the modification of the
filaments or fibers takes place after the molten polymer
filaments have solidified as a result of cooling to form the
fiber, or on the preformed fiber itself.
214l93~
It has now been found that the thermal bondability of
fibers can be enhanced by treating the fiber grade polymer
during the formation of the filaments, instead of treating the
filaments or fibers after they are formed. The process of the
5present invention is not limited to any specific fiber
preparation technique where a resin is melted and formed into
a fiber, such as long spin, short spin, spun bond and melt
blown fiber production methods. Nor is the spinning process
limited to being carried out in any particular spinning
10environment, e.g. the presence or absence of oxygen or
nitrogen.
Applicant has found that fibers having improved thermal
bondability can be produced at lower spinning temperatures and
increased spinning speeds by irradiating the molten fiber
15grade polymer filaments as soon as the filaments exit the
orifices of the spinneret with electromagnetic radiation.
Accordingly, the present invention provides an improved
process for the production of thermal bondable fibers
comprising exposing the molten polymer filaments to from 1 x
20104 to 100 W/cm2 of electromagnetic energy at the spinneret
face.
Figure 1 is a schematic representation of a melt spinning
arrangement used in the process of the present invention.
As used herein "spinneret face" is intended to include
25the upper portion of the spin line and the exit point of the
molten material from one or more orifices, having any desired
diameter, of the spinneret.
The phrase "fiber grade polymer" as used herein means any
polymer that is capable of being spun into filaments to
30produce a fiber.
Referring to Figure 1, showing a typical melt-spinning
apparatus, for use in preparing fibers according the
invention, the fiber grade polymer is charged into a hopper 1,
21~493~
and fed into an extruder 2 of known or conventional type,
containing single or multiple screws and equipped with
controls for regulating the temperature of the barrel in
various zones along the length of the barrel, where the
polymer is heated to its melting point. The molten polymer is
then fed to a metering pump 3, which delivers the molten
polymer at a constant rate to a heated spinneret 4 containing
one or more orifices. The fluid molten polymer filaments
emerging in a downward direction from the face of the
spinneret are exposed to electromagnetic radiation from a
radiation source 5. The radiation source is positioned
whereby the source encompasses the spinneret face. The molten
polymer filaments are then solidified by cooling to form
fibers 6.
The filaments produced by the process of this invention
are typically combined into one or more fibers of varying
thickness. Fibers made up of one filament are generally
referred to as monofilament fibers and fibers made up of more
than one filament are generally referred to as multifilament
fibers. The spun denier of the fibers produced according to
the method of this invention range from less than 1 to at
least SO dpf, denier per filament. Denier is the weight in
grams of 9000 meters of fiber.
The fiber forming polymers useful in the present
invention can be any polymer typically used to prepare fibers.
Preferably, the fiber grade polymer is polyethylene,
polypropylene, random copolymer of propylene and ethylene,
polyisobutylene, polyamide, polyester, polystyrene, polyvinyl
chloride, polyacrylate and mixtures thereof. Most preferred
3 0 is polypropylene and random copolymers of propylene and
ethylene.
In the process of the present invention the
electromagnetic radiation can be ultraviolet, visible or
infrared radiation. The total amount of electromagnetic
214q934
energy that reaches the filament(s), referred to as
irradiance, can be adjusted by changing the distance between
the source of the radiation and the filament(s), changing the
wavelength emitted by the source, and by changing the power,
intensity, of the source. In the present invention, the total
amount of electromagnetic energy that reaches the filamentts)
is from 1 x 104 to 100 W/cm2, preferably from 1 x 10-2 to 50
W/cm2 and, most preferably, from 1 x 10-l to 10 W/cm2.
Conventional additives may be blended with the fiber
forming polymer used to produce the thermal bondable fibers of
the present invention. Such additives include, stabilizers,
antioxidants, antislip agents, antistatic agents, flame
retardants, nucleating agents, pigments, antisoiling agents,
photosensitizers and the like.
The present invention will be illustrated in greater
detail with reference to the examples of the invention set
forth below.
ExamPle
Fibers of Profax P-165 propylene homopolymer, stabilized
with 100 ppm wt. Irganox 1010 tetrakis[methylene(3,5-di-tert-
butyl-4-hydroxyhydrocinnamate)] methane stabilizer, 1000 ppm
wt. Irgafos 168 tris-(2,4-di-tert-butylphenyl)phosphite
stabilizer and 1000 ppm wt. calcium stearate is prepared by
charging the polymer composition into hopper, under a nitrogen
blanket and fed into a single screw extruder, where the
polymer composition is heated to its melting point. The
molten polymer is fed to the meter pump, and pumped at a
constant rate under pressure to a spinneret, containing one
orifice with a diameter of 0.020 inches. The molten polymer
filament emerging downward from the orifice of the spinneret
is exposed to 0.88 W/cm2 ultraviolet radiation. The filament
of molten polymer is solidified as a result of cooling to form
211~9~g
a monofilament fiber, and is collected on the godet. The
processing conditions are as follows:
Extruder Feed Zone Temp. 220C
Metering Pump Temp. 300C
Spinneret Temp. 300C
Fiber Spun Denier 2 g/9oO0 m
Godet Take-up Speed 1000 m/min
The monofilament fibers prepared above were then tested
for bond strength according to the following procedure. The
fibers were cut into 400 mm lengths. The samples weighed
between 0.160 and 0.170 grams. The fibers were then
mechanically twisted eighty times and folded in half. The
bundle was hand twisted six times and allowed to wrap around
itself. The sample was bonded in a Sentinel Model 1212 heat
sealer at 40 psi for 1.50 seconds at the desired temperature.
The force required to separate the bonded segments (in grams)
was recorded on an Instron Model 114 universal testing
machine.
The results are set forth below in Table 1.
Comparative Example 1
Fibers were prepared according to the procedure of
Example 1 using the same ingredients and processing
conditions, except that the molten polymer filament emerging
downward from the face of the spinneret was not exposed to the
ultraviolet radiation.
The samples used to determine the bond strength were
prepared and tested according to the method set for in Example
1.
The results of the thermal bonding are set forth below in
Table 1.
- 21~93g
Table 1
Bonding Temperatures
135C 140C 145C 150C
Ex. 1 528 g 553 g 896 g 1650 g
Comp. Ex. 1 328 g 402 g 556 g 985 g
It can be seen that the bonding strength of the fibers of
the present invention, even at the lower bonding temperature,
is substantially higher than the bonding strength of the
fibers of the Comparative Example 1 at the same bonding
temperature.
Example 2
Fibers of propylene homopolymer having a MFR of 2.9 g/10
min., stabilized with Irganox 1076 octadecyl-3-(3',5'-di-tert-
butyl-4'-hydroxyphenyl) propanoate, 100 ppm wt. Irganox 1010
tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]
methane stabilizer, 1000 ppm wt. Irgafos 168 tris(2,4-di-tert-
butylphenyl)phosphite stabilizer and 1000 ppm wt. calcium
stearate are prepared by according to the process of Example
1, except the processing conditions were as follows:
Extruder Feed Zone Temp. 220C
Metering Pump Temp. 275C
Spinneret Temp. 275C
Fiber Spun Denier g g/gOoo m
Godet Take-up Speed 1000 m/min
Ultraviolet radiation 2.8 W/cm2
The samples used to determine the bond strength were
prepared and tested according to the method set for in Example
1.
Comparative Example 2
30Fibers were prepared according to the procedure of
21l4934
Example 2 using the same ingredients and processing
conditions, except that the molten polymer filament emerging
downward from the face of the spinneret was not exposed to the
ultraviolet radiation.
The samples used to determine the bond strength were
prepared and tested according to the method set for in Example
1.
The results of the thermal bonding are set forth below in
Table 2.
Table 2
Bonding Temperatures
130C 140C 145C 150C
Ex. 2 269 g 534 g 1033 g 1958 g
Comp. Ex. 2 160 g 236 g 271 g 492 g
The fibers of the present invention demonstrate better
bonding strength as compared to the fibers of Comparative
Example 2.
Exam~le 3
Fibers of Profax P-165 propylene homopolymer stabilized
with Irganox 1076 octadecyl-3-(3',5'-di-tert-butyl-4'-
hydroxyphenyl) propanoate, 100 ppm wt. Irganox 1010
tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]
methane stabilizer, 1000 ppm wt. Irgafos 168 tris-(2,4-di-
tert-butylphenyl)phosphite stabilizer and 1000 ppm wt. calcium
stearate were prepared by according to the process of Example
1, except the processing conditions were as follows:
Extruder Feed Zone Temp. 220C
Metering Pump Temp. 300C
Spinneret Temp. 300C
Fiber Spun Denier 2 g/9000 m
21g~93g
Godet Take-up Speed 4000 m/min
Ultraviolet radiation 0.88 W/cm2
The samples used to determine the thermal bonding
strength were prepared and tested according to the method set
forth above in Example 1.
The results are set forth below in Table 3.
ComParative Example 3
Fibers were prepared according to the procedure of
Example 4 using the same ingredients and processing
conditions, except that the molten polymer filament emerging
downward from the face of the spinneret was not exposed to the
ultraviolet radiation.
The samples used to determine the bond strength were
prepared and tested according to the method set for in Example
1.
The results of the thermal bonding are set forth below in
Table 3.
Table 3
Bondinq Temperatures
135C 140C 145C 150C
Ex. 3 528 g 553 g 896 g 1650 g
Comp. Ex. 3 328 g 403 g 556 g 985 g
The fibers of the present invention demonstrate better
bonding strength as compared to the fibers of Comparative
Example 3.
ExamPle 4
Fibers of Profax P-165 propylene homopolymer, stabilized
with loo ppm wt. Irganox 1010 tetrakis[methylene(3,5-di-tert-
butyl-4-hydroxyhydrocinnamate)] methane stabilizer, 1000 ppm
21~4934
wt. Irgafos 168 tris-(2,4-di-tert-butylphenyl)phosphite
stabilizer and 1000 ppm wt. calcium stearate were prepared by
according to the process of Example 1, except the processing
conditions were as follows:
Extruder Feed Zone Temp. 220C
Metering Pump Temp. 250C
Spinneret Temp. 250C
Fiber Spun Denier 2 g/9000 m
Godet Take-up Speed 2250 m/min
Ultraviolet radiation 0.88 W/cm2
The samples used to determine the thermal bonding
strength were prepared and tested according to the method set
forth above in Example 1.
The results are set forth below in Table 4.
Comparative ExamPle 4
Fibers were prepared according to the procedure of
Example 4 using the same ingredients and processing
conditions, except that the molten polymer filament emerging
downward from the face of the spinneret was not exposed to the
ultraviolet radiation.
The samples used to determine the bond strength were
prepared and tested according to the method set for in Example
1.
The results are set forth below in Table 4.
Table 4
Bondinq Temperatures
130C 140C 145C
Ex. 4 196 g 341 g 533 g
Comp. Ex. 4 132 g 291 g 350 g
--10--
- 21~1934
.
The fibers of the present invention demonstrate better
bonding strength as compared to the fibers of Comparative
Example 4.
The thermal bondable fibers prepared according to the
process of the present invention can be used in the
manufacturing of nonwovens, by spun bonded and melt blown
processes. Nonwovens are useful in the production of personal
hygiene products, for example, infant care and adult
incontinence products, protective covering, for example
surgical gowns and shoe covers and other disposable medical
and clothing products.
Other features, advantages and embodiments of the
invention disclosed herein will be readily apparent to those
exercising ordinary skill after reading the foregoing
disclosures. In this regard, while specific embodiments of
the invention have been described in considerable detail,
variations and modifications of these embodiments can be
effected without departing from the spirit and scope of the
invention as described and claimed.
