Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02296132 2000-03-O1
1
EXPANDED EXTRUDED POLYMERIC TEXTILE
FIELD OF THE INVENTION
This invention relates to the field of textiles. In particular, it relates to
textiles
wherein a polymeric "plastic" layer is bonded to a fabric substrate, and the
plastic layer is in the
form of a foamed matrix.
BACKGROUND TO THE INVENTION
In the production of plastic coated teactiles, the product has customarily
been made
by one of the following alternate procedures:
1) casting a molten plastic layer onto a fabric carrier;
2) bonding a pre-formed plastic layer onto a fabric carrier by calendering
and/or use
of adhesives; and
3) extruding a molten plastic layer onto a fabric carrier.
When it has been intended to provide a plastic layer that is "foamed" and
resilient
due to included gas-filled cells or voids, it has been customary to create the
expanded plastic
matrix in two stages. First a plastic layer containing a blowing agent in a
quiescent state is cast
on a fabric carrier. Then the formed composite textile is exposed to heat
which causes gas to
evolve within the plastic layer - the process of "blowing".
A disadvantage of this latter process is that the level of heat that is
required to
activate the blowing agent will cause carrier components in many types of
fabric carriers to fuse,
e.g. polyethylene will fuse at 175°F, whereas various types of chemical
blowing agents require a
temperature in excess of 300°F to create foaming conditions.
Attempts have been made to incorporate a blowing agent into an extruded
plastic
to form a foamed plastic layer. However, the use of conventional chemical
blowing agents, this
process produces often a textile wherein the foamed polymeric layer lacks
resistance to crushing
and results in a flattened polymeric layer that has almost no or little foam
voids left in the
CA 02296132 2000-03-O1
2
structure after crushing. In a standard extrusion procedure, a chilled
calendaring roll presses the
extruded sheet of melt into a fabric carrier and sets, and bonds, the plastic
layer with the textile.
Extruded textiles prepared with typical classic blowing agents have typically
lacked the resilience
to recover sufficiently from this compression step to provide a satisfactorily
foamed textile.
A need exists for a foamed plastic composite textile that is formed on a
permeable
carrier, e.g. a woven, knitted or non-woven fabric, with a low fusing
temperature, while
exhibiting good recovery or resilience in response to applied pressure. This
invention addresses
this need as well as providing other advantages.
The invention in its general form will first be described, and then its
implementation
in terms of specific embodiments will be detailed with reference to the
drawings following
hereafter. These embodiments are intends to demonstrate the principle of the
invention, and the
manner of its implementation. The invention in its broadest and more specific
forms will then be
further described, and defined, in each of the individual claims which
conclude this Specification.
SLTMMARY OF THE INVENTION
According to one aspect of the invention, a method of producing a foamed sheet
textile is provided:
1) extruding a polymeric melt from a linear extrusion die in the form of a
sheet with
two faces, the melt containing two or more classes of expanding agents:
(1) a first thermally activated gas generant dispersed within said melt; and
(2) thermally expandable micro-spheres contained with encapsulating shells
each containing compressed gas and being dispersed within said melt
2) allowing the expanding agents to expand, with the gas generant generating
gases
to form a cornpres~ble foamed matrix in the melt and allowing the micro-
capsules
to expand into resilient micro-spheres suspended within said foamed matrix;
3 ) depositing the melt on a permeable carrier that is in sheet form and into
the surface
of which the foamed melt partially penetrates; and
CA 02296132 2000-03-O1
3
4) allowing the foamed polymeric composition so formed to set to provide a
resilient
compression-resistant, foamed plastic layer that is bonded to the carrier to
form
the resulting tactile.
Preferably, the extrusion melt, upon being laid-down on the permeable carrier,
is
carried on the carrier through a rotating gate defined by a gap between two
rollers, one of the
rollers being cooled to set the melt. This establishes a constant height for
the foamed layer on the
textile. The roller delivering the carrier may be powered, and the second
cooled roller may be
traction-driven off of the powered raller by end-rims extending from the
second roller.
The resulting product of the invention is a textile having a permeable carrier
into
the surface of which the foamed plastic layer has expands while still molten
and while the gas
generants, and particularly the encapsulated expanding agent, is still
expanding. Thus, the
boundary surface of the carrier is at least partially embedded within the
foamed plastic layer.
Expansion of the foamed layer both above and within the carrier may continue
after the formed
textile exits the rotating gate.
By inclusion ofthermally expandable micro-spheres in the melt the foamed
plastic
layer contains inclusions of thermally expanded hollow micro-spheres having
encapsulating shells
that are resiliently compressible. This enhances the crushability of the
textile.
An advantage of this process is that polymers like PVC, polypropylene,
polyethylene and other conventional polymers may be used to provide the foamed
plastic layer.
Further, a textile may be produced with an integrally-formed skin region
present
at it's polymer surface, the skin region containing less voids than the
intermediate region of the
foamed layer lying between the skin region and the cawier. This is
accomplished by cooling the
extrusion die through which the melt is extruded.
CA 02296132 2000-03-O1
4
An advantage of this process is that a textile can be produced at lower
temperatures wherein the carrier would otherwise plastically deform at
temperatures above, for
example, 300 degrees Fahrenheit, or even 200 degrees Fahrenheit.
To produce the textile, the extruder is feed with a composition suitable for
generating a foamed polymer comprising:
1) at least one expandable thermoplastic polymer capable of being extruded;
2) a first thermally activated gas generarn dispersed within said polymer, and
3 ) thermally expandable resiliently compressible micro-spheres, disbursed
within said
~10 polymer,
said generant and micro-spheres being capable on heating of expanding said
polymer.
The foregoing summarizes the principal features of the invention and some of
its
optional aspects. The invention may be further understood by the description
of the preferred
embodiments, in conjunction with the drawings, which now follow.
SUMMARY OF THE FIGURES
Figure 1 is a schematic side view of an extrusion coating line.
Figure 2 is a cross-sectional side view of an extrusion screw.
Figure 3 is a schematic side view of the extrusion screw of Figure 2
delivering a
melt of expanding polymer to the nip of a pair of rollers where the melt
becomes bonded to a
fabric carrier.
Figure 4 is a diag~ranunatic cross-sectional side view ofthe foamed polymeric
layer
bonded to a fabric carrier.
Figure 5 is a cross-sectional view through the pair of rollers receiving and
combining the melt with the fabric.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In Figures l and 2 a powdered plastic composition 2 in powder/pellet form is
fed
into the feed-hopper 3 of a spiral extruder screw 4. The gap around the
spiraled flights 5 of the
CA 02296132 2000-03-O1
screw 4 decreases in width proceeding towards the extruder outlet 6 thus
creating an increasing
pressure on the melt 8 contained therein. Heat is applied externally from a
heat source 7 such as
hot oils, gas flames or electric radiam heating coils to convert the powdered
composition 2 to a
melt 8.
5
Molten plastic composition or "melt" 8 passes from the extruder outlet 6 to
the
extrusion die 9 where the pressure that previously arrested the release of gas
by the gas generants
(not shown in Figure 2) is relaxed, allowing the gas generants to "blow" and
produce a foamed
melt 10. This foamed melt 10 is fed into the nip 15 between two counter
rotating rollers 11, 12.
One of the rollers 11, preferably a powered roller 11, carries a sheet of a
permeable, preferable fabric on fibrous matrix of porous, carrier material 13
from a carrier-source
roller 14 to the nip 15. The other roller 12, preferably driven in a counter
rotating direction by
friction off of the powered roller 11, provides a gap 16 having a pre-
determined diameter at the
nip 15 which serves as a gate for metering the thickness of foamed melt 10
that is laid down on
the carrier sheet 13. Desirably, the roller 12 has a protruding
circumferential end rim 25
positioned to bear against an interface 26 between the first and second
rollers 11, 12 whereby a
traction drive effect occurs. Preferably, this "gating" roller 12 is
temperature controlled, e.g.
chilled as by circulating chilling fluid coolant, (not shown) or other
suitable method of cooling in
the normal manner known for extrusion processes.
Preferably, the die 9 is also cooled, as by cooling air, to form a skin 20
surface on
the foamed melt 10 as it leaves the die 9. This skin 20 has less voids than
the core of the foamed
layer, e.g. 50% or less.
In the gap 16 the foamed melt 10 continues its expansion, having infiltrated
or
mixed with the boundary surface of the carrier 13 and set therein. The
composite textile 17 exits
the two rollers 11, 12 and is carried by a series of conveying andJor cooling
rollers 18 to a textile
take-up roll 19. Some partial expansion of the foamed layer 10 may occur while
the textile 19 is
on the conveying rollers 18. As well, expansion within the carrier 13 may also
continue.
CA 02296132 2000-03-O1
6
' In the above process, the powdered plastic composition 2 may be a polymeric
vinyl
compound, a polypropylene compound, a polyethylene compound, or other known
and
conventional polymeric material, or combinations thereof:, for producing
foamed plastic sheet
textiles. In particular, the plastic composition 2 may include dual expansion
agents, comprising:
1) a dispblowing agent or gas generant such as azodicarbonamide or other
chemical blowing agents;
2) a micro-encapsulated expansion agent such as EXPANDCEL - TM (by Casco
Nobel AB of Sweden cf U.S. patent 5,585,119) or such other encapsulated
expansion agents which upon foaming provides compression-resistant micro-
spheres within the plastic layer of the final textile 17; and
3) the compound may or may-not contain an additional, direct gas-injected
blowing
agent.
A typical composition of this invention which is eactrudable may contain one
or
more conventional additives such as fillers, plasticisers, stabilizers, anti-
oxidants, lubricants and
processing aids. Such additives can be used in conventional quantities for
formulating an
extrudable composition. As additives, this composition 2 may include
comrentional binders, such
as an acrylic and\or a nitrile rubber, ar the like, that serve to constrain
and delay the expansion of
the foamed melt 10.
By way of exemplification, the following table shows a typical composition
which
can be used in accordance with this invention. It is highly desirable that all
additives and
components of the composition be chlorine-free.
CA 02296132 2000-03-O1
7
TABLE
COMPOUND WEIGHT IN r~XTURE
Polymer: - PVC 136 pounds
Filler: 40.7 pounds
(Omyacarb)
Micro-encapsulating blowing agent:1.0 pounds
(Expancel 092)
Dispersed blowing agent: 4.1 pounds
(Celogen 754A)
Plasticizer/Co-stabilizer: 102 pounds
(Soy Bean Oil)
Stabilizer: 3.7 pounds
(Nuostabe)
Anti-oxident: .3 pounds
(Irganox)
Lubricants: 3.3 pounds
(InternaUexternal-stearic acid,
"Loxiol" and
Hostalub)
Process Aid: 6.8 pounds
(K120I~
The resulting textile 17 is thereby rendered resilient and crush resistant.
This textile may be
further processed by pressure and/or vacuum-forming or injection molding
without the foam layer
being crushed or destroyed.
A sample textile 17 is depicted in Figure 4 wherein the foamed layer 10 is
bonded
to the carrier 13. Within the foamed layer 10 are two types of voids: voids 21
in the foamed
matrix produced by the dispersed gas generant; and voids 22 present within
expanded micro-
CA 02296132 2000-03-O1
8
spheres 23. Each micro-sphere 23 has an encapsulating shell of resilient,
compression resistant
material. The presence of two types of voids 2l, 22 improves the character and
"feel" of the final
textile product 17.
CONCLUSION
The foregoing has constituted a description of specific embodiments showing
how
the invention may be applied and put into use. These embodiments are only
exemplary. The
invemion in its broadest, and more specific aspects, is fiuther described and
defined in the claims
which now follow.
These claims, and the language used therein, are to be understood in terms of
the
variants of the invention which have been described. They are not to be
restricted to such
variants, but are to be read as covering the full scope of the invention as is
implicit within the
invention and the disclosure that has been provided herein.
