Note: Descriptions are shown in the official language in which they were submitted.
2~3
METHOD OF PRODITCING A COMPOSITE WEB
FIELD OF THE INVENTION
Our present invention relates to a method of producing
a composite web from a nonwoven fleece of synthetic resin
(thermoplastic) filaments and/or synthetic-resin (thermoplastic)
fibers, and a synthetic resin foil on one side of said fleece and
also composed of a thermoplastic synthetic resin. The nonwoven
fleece itself can be composed of one or more layers but
preferably is a single layer or a layer composed of synthetic
resin filaments and a further layer of synthetic resin fibers.
In other words, the fleece can be of one or more layers and each
of the layers can be either composed of spun-bond or melt-blown
material.
BACKGROUND OF THE INVENTION
A composite web of a fleece and a foil has been made in
the past by applying the nonwoven fleece to the synthetic resin
foil or vice versa and pressing them together by mechanical
pressing forces, with heating, to bond the two materials together
or by bonding the two materials through the intermediary of an
adhesive. Generally an appropriate calender is provided for
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pressing the two materials together and the calender can thus be
considered a pressing unit.
The calenders required for this purpose are relatively
expensive and the product which is fabricated by the use of such
calenders, as well as the produciton rate, can be improved.
It is the principal object ofthe present disclosure,
therefore, to provide an improved method of or process for
producing a composite web of a nonwoven fleece and a synthetic
resin foil which will provide an improved product at lower cost
than earlier systems and is also free from drawbacks of earlier
systems.
Another object is to provide a method for the
continuous production of a composite web in which the nonwoven
fleece is composed of spun-bond or synthetic resin filaments
and/or of melt-blown or synthetic resin fibers which does not
require the use of expensive calenders.
Still another object is to provide a method of forming
a composite web in which the bond between the synthetic resin
foil and the melt-blown fibers and/or spun-bond filaments of the
fleece is enhanced_
More particularly, this disclosure provides a
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continuous process for producing a composite web of a nonwoven
fleece of synthetic resin filaments and/or synthetic resin fibers
of a thermoplastic synthetic resin and a synthetic resin foil
bonded on one side of the fleece and composed of a thermoplastic
synthetic resin, which is characterized by the following
features:
the nonwoven fleece is fed at a,temperature which is
significantly lower than the melting temperature of the
thermoplastified synthetic resin thereof to the station at which
it is to be bonded to the foil:
the nonwoven fleece at this temperature is fed onto a
roller or drum on which the bonding to the foil is to be effected
while the roller is rotated at a peripheral speed corresponding
to the feed speed of the fleece, the roller extending at least
over the full width of the nonwoven fleece;
the synthetic resin foil is produced by a wide-slit
nozzle from a melt of thermoplastic synthetic resin of the foil
with the mouth of the nozzle being located in the region at which
the nonwoven fleece is fed onto the roller or drum and the
synthetic resin foil in a virgin plastic state is directed
substantially tangentially into contact with the fleece on the
drum so that contact is made between the synthetic resin of the
foil and the fleece at approximately the melting or
thermoplastified temperature of the foil material and before full
solidification thereof; and
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in the region in which the foil, still in its plastic
state, comes into contact with the fleece on the roller or the
drum, the foil is electrostatically charged with the aid of at
least one electron-generating corona electrode which extends
transversely to the direction of travel of the fleece and the
foil.
As a consequence, there is an electrostatic bonding of
the foil to the fleece before the foil is fully cooled, whereupon
cooling can be carried out on the drum or roller or thereafter to
yield the resulting composite web.
while we have mentioned a synthetic resin foil and
indeed the continuous layer bonded to the fleece can be properly
described as such following the cooling stage, it will be
understood that at the time this "foil" contacts the nonwoven
fleece.and until cooling is complete, the continuous strand of
the synthetic resin material emerging from the wide slit nozzle
and contacting the fleece may not have sufficient coherency to
consider it a web, i.e. this strand has not cooled or solidified
sufficiently to be fully coherent. It emerges from the wide slit
nozzle over the width of the fleece and with the thickness of the
foil rather as a molten strand of the thermoplastic material and
is deposited as such after being electrostatically charged, on
the fleece_
With the new system, mechanical pressure as has been
applied in the past in a calender is no longer required to
consolidate the nonwoven fleece and the synthetic
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resin foil. Surprisingly, the electrostatic charging of the foil
provides sufficient force to enable the foil to bond to the
filaments or fibers and indeed to mold around the filaments and
fibers so as to hug them with a substantial contact area between
the filaments or fibers and the foil to. provide an improved bond
without the mechanical consolidation hitherto deemed to be
necessary. The electrostatic charging can be effected with at
least one electron=discharging corona electrode which can extend
transversely to the feed direction and, if desired, two or more
such electrodes can be provided. The electrostatic forces which
result have been found to be very high.
The new process can be carried out with
the nonwoven fleece at a range of temperatures, depending upon
the material used, including ambient or room temperature. When
high outputs are desired, it has been found to be advantageous to
preheat the fleece before it is fed to the bonding station.
Indeed, optimum temperatures for any particular material can be
readily determined empirically by trial techniques with which the
effective fleece and foil temperatures, the feed rate, the degree
of heating of the roller or drum, the extrusion rate of the
synthetic resin foil and the electrostatic charge to be applied
can be readily determined.
It has been found to be advantageous to adjust these
parameters so that the foil material slumps around the filaments
or fibers so that it will lie in contact with the filaments or
fibers over an arc length of 900 or more. As a result, the
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material of thefoil is so intimately intercalated in the fleece.
that an improved bond is obtained over any which can be provided
merely by mechanical pressing between two rollers. Indeed, the
molten strand emerging from the wide-slit nozzle is sufficiently
plastic and its surface tension remains sufficiently effective to
promote the flow of the foil material around the individual
filaments or fibers of the fleece.
Electron-emitting corona electrodes are widely used for
a variety of purposes and any of the material variants thereof
can be utilized for the purposes described herein. They are
utilized, for example, in electrostatic filters where, in
principle, they also promote adhesion, albeit of dust particles
to a surface. As far as we are aware, it has not been recognized
heretofore that electrostatic forces can promote bonding of a
molten strand of synthetic resin from a wide-slit nozzle to a
thermoplastic fleece of spun bond and/or melt blown.
It has been found to be advantageous to subject the
nonwoven fleece prior to bonding to the foil to a biaxial
stretching with a preferred stretching ratio in each of two
mutually perpendicular directions of say 1.4. The fleece can be
composed of spun bond or melt-blown filaments or fibers which, in
the filament-producing or fiber-producing processes can be
subjected to stretching at ratios of 1:20 to 1:30.
The speed of the nonwoven fleece at the bonding station
and the speed with which the molten strand of thermoplastic is
extruded from the wide-slit nozzle can be more or less the same;
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although it is also possible to subject the foil to some
elongation upon contact with the web or to cause the foil
material to bunch up at contact with the fleece.
According to one feature of this disclosure the
nonwoven fleece is heated to a laminating temperature lower than
the melting temperature of thermoplastified synthetic resin of
the fleece but higher than ambient temperature. -
Preferably the temperature of the nonwoven fleece on
the roller, the speed with which the thermoplastic foil is
extruded from the wide-slit nozzle and the electrostatic charge
applied to the thermoplastic foil are so selected that the
thermoplastic foil has a contact angle with thermoplastic
synthetic resin fibers or filaments of the nonwoven fleece of 900
to in excess of 1800.
Of course, the parameters with which the new process
operates will depend upon the materials used. It has been found
to be most advantageous, however, to operate with a nonwoven
flesce with a basis weight of 15 to 25 g/m', preferably 17 g/m',
and a synthetic.resin foil with a melting point temperature of
80oC to 160°G and with foil thicknesses of 12 to 18 ~Cm,
preferably about 14 um, with the nonwoven fleece being preheated
to a bonding temperature of about 60°C and the drum or roller
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held at a temperature of about 50°C so that at least partial
cooling is effected on the drum or roller.
The nonwoven fleece can be composed of polypropylene
fibers and/or.filaments while the synthetic resin foil can be an
ethylene-acrylic acid ester thermoplastic-to which the
aforementioned parameters are especially applicable. The foil
can also be composed of PP (polypropylene), LPDE (low-density
polyethylene), LLDPE and HDPE (high-density polyethylene) or
mixtures thereof.
The electrostatic charging must, of course, be
sufficient to effect the bonding previously described and, of
course, the maximum possible electrostatic charge should thus be
applied for that purpose. This can be achieved by providing the
bonding roller or drum with a metallic surface or making the drum
or roller of metal and connecting the drum surface with respect
to the corona electrode as an anode. It is, however, also
possible to provide at least the surface of the drum or roller of
a dielectric material.
Between the corona electrode and the synthetic resin
strand forming the foil, a further nonwoven fleece can be fed so
that it is additionally bonded electrostatically to the foil_
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This additional nonwoven fleece can be composed of cellulosic
filaments and/or fibers.
More particularly, in accordance with the invention,
there is provided a process forthe continuous production of a
composite web comprising the steps of.
(a) continuously supplying a nonwoven fleece of
thermoplastic synthetic resin fibers or filaments to a laminating
station at a temperature substantially below a melting
temperature of thermoplastified synthetic resin of the fleece;
(b) passing the nonwoven fleece of thermoplastic
synthetic resin fibers or filament at the temperature
substantially below the melting temperature of the
thermoplastified synthetic resin of the fleece over a laminating
roller rotating at aperipheral speed at the station
IS corresponding to a speed with which the nonwoven fleece is fed to
the station and of a length at least equal to a width of the
nonwoven fleece;
(c) extruding a thermoplastic foil directly onto one
side of the nonwoven fleece on the roller from a wide-slit nozzle
supplied with a thermoplastic melt at a region at which the
nonwoven fleece runs onto the roller and in a direction which is
generally tangential to the nonwovenfleece on the roller upon
contact of the thermoplastic foil with the nonwoven fleece,
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20123
whereby the foil contacts the nonwoven fleece in a virgin plastic
state of the thermoplastic foil;
(d) electrostatically charging the thermoplastic foil
while the thermoplastic foil is in the plastic state in a region
in which the thermoplastic foil initially contacts the nonwoven
fleece with a corona electrode extending transversely of a
direction of advance of the nonwoven fleece and the foil whereby
the foil bonds intimately to the nonwoven fleece to form a
laminate web on the roller; and
{e) cooling the laminate web.
The advantages of the process include the elimination
of any need for-mechanical pressing and hence of the calenders
hitherto utilized for the purpose while nevertheless obtaining an
improved bond. The new process-therefore also facilitates mass
production.
Embodiments of the invention will now be described,
reference being made to the accompanying drawings in which:
FIG_ 1 is a diagram of an apparatus for carrying out a
process embodying theinvention;
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20123
FIG. 2 is a diagram of another embodiment of the
apparatus;
FIG. 3 is a diagram of a third embodiment for
practicing the method of the-invention; and
FIG. 4 is a diagram illustrating the bond formed
between the foil and the filaments or fibers of the web.
SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIGS. 1-3 of- the drawing, corresponding elements
have been identified with the same reference numerals. In all of
these embodiments, a nonwoven fleece 2, is withdrawn from a
supply unit 1 which can be a supply coil, a fabricating machine
for the nonwoven fleece, a system for biaxial stretching thereof,
an arrangement for combining a spun bond (filaments) fleece with
a melt-blown (fiber) fleece or the like. A synthetic resin
molten strand 3 which can be cooled to form a foil, is extruded
from a wide-slit nozzle 4 extending over the entire width of the
fleece 2 in the same direction as that in which the fleece is
fed. In-all cases, moreover, just upstream of the location at
which the strand of molten thermoplastic synthetic resin of the
foil meets the fleece, there is an electron-emitting corona
electrode 5 extending transversely to the direction of feed of
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the fleece and the foil and perpendicular to the plane of the
paper in FIGS. 1-3 to electrostatically charge the foil 3.
The fleece 2 can be heated to a bonding temperature
which is substantially less than the melting temperature of the
fibers or filaments of the fleece which can be about 250°C. The
preheated fleece 2 is fed to the receiving region 6 of a bonding
roller or drum 7 which is rotated, e.g. in the clockwise sense in
FIGS. 1-3 at a peripheral speed that can correspond to the speed
with which the nonwoven fleece 2 is fed to the roller which
extends over the full width of the fleece. The rotation of the
roller or drum 7 has been indicated by a curved arrow.
In the embodiment of FIG. l, the supply 1 can be a coil
of the nonwoven fleece 2 which is drawn from this coil and passed
over a heating roller 8 on which the nonwoven fleece is preheated
to the bonding temperature of 60°C. The roller or drum 7 itself
is heated to the temperature of 50°C and the mouth or slit 9 of
the nozzle 4 is located in the receiving region 6 of the roller
or drum 7 and the virgin plastic material from the wide nozzle
contacts the fleece 2 in the still at least partially molten form
of the plastic material which has been previously charged. The
electrostatic forces which result from charging of the foil draw
the fbil around the filaments or fibers so that contact between
the foil material and the fibers or filaments can extend over
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20123
arcs in excess of 90°. On the roller 7 or downstream of the
roller 7, the composite web 2, 3 is cooled.
From FIGS. 2 and 3, it will be apparent that an
additional nonwoven fleece 10 can be passed between the corona
electrode 5 and the contact point of the foil with the fleece 2
so that the electrostatic forces also draw the additional fleece
against the foil and produce a sandwich composite in which the
foil is sandwiched between the thermoplastic fiber and/or
filament fleece 2 and the fleece 10 which can be composed of a
10 cellulose, fluff, fiber or filament product.
From FIG. 4, it can be seen that the contact with the
fibers or filaments 1l of the foil material 3 can be in the form
of loops or undulations around the fibers or filaments with arc
lengths up to 180° and more, the preferred arc length of contact
being 90° to 180°.
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