Note: Descriptions are shown in the official language in which they were submitted.
CA 02239383 1998-06-03
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WO 97/24916
Thermoplastic Three-Dimensional Fiber Network
Field of the Invention
This invention relates to three-dimensional networks of thermoplastic
fibers.
Back4round of the Invention
Three-dimensional fiber networks are known. These are generally
1o derived from textile fabrics that have been impregnated with a thermoset
polymer or a low melting thermoplastic and then molded into the desired shape.
For example, U.S. Patent No. 4,631,221 describes a laminate containing a rigid
three-dimensional fiber network having regularly arranged projections. The
three-dimensional network is placed between two sheets of rigid material. The
1s three-dimensional network used in the laminate is made by the deep-drawing
of
a sheet-Like textile fabric to make projections. The textile fabric was
previously
impregnated with a thermoset resin and dried to yield a pre-preg, and is cured
after deep-drawing. The textile fabric is made from a multifilament yam so
that a
larger amount of resin can be absorbed in the intertilament regions. U.S.
Patent
20 5,364,686 describes a three-dimensional shaped material which is made from
a
fabric comprising a yam that has thermoplastic fibers mixed with higher
melting
reinforcing fibers; the fabric is shaped by deep drawing at a temperature high
enough to melt the lower melting thermoplastic material but not the
reinforcing
fiber to yield a three-dimensional structure which becomes rigid after it is
cooled,
25 possibly due to the fixing of fiber crossover points. Finally, U.S. Patent
4,890,877 describes an energy absorbing structure for use in automobile doors,
wherein the energy absorbing structure is a highly stretchable lightweight
material that has been coated with a resin (e.g. a thermoset) and then molded
so that it has a series of projections, which are preferably truncated cones.
The
3o structure after molding does not appear to have an open fiber network
appearance.
The fiber network structures described above and elsewhere generally
are rigid and are intended for use mainly as lightweight structural materials.
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2
Summary of the Invention
Three dimensional fiber network structures can be made that are semi-
rigid and dimensionally stable, but have sufficient flexibility to be useful
as
cushioning materials. These fiber network structures are compressible, and
when the compressive force is removed, the materials return to their original
shape (i.e. they are resilient). These fiber network structures comprise
filaments
that are made of a single thermoplastic polymer and do not include a thermoset
polymer. The networks are made up of a multiplicity of projections rising from
1o the plane of the textile fabric from which the fiber network is made.
Projections
are portions of the textile fabric that rise above the base plane, generally
in an
abrupt way. Depressions, which are projections on the opposite side and in the
opposite direction from the base plane, may optionally also be present. The
projections and optional depressions have retained an open fabric-like
appearance, consisting of discrete filaments which are generally not bonded at
the intersections where the individual filaments cross over one another. There
may be bonds at the intersections if the attachments are easily broken (i.e.
they
are not "tightly bonded") when the network is initially compressed, after
which
the network becomes resilient. The network is "resilient" if the projections
and
optional depressions substantially recover their shape after being compressed
to
50% of their height. However, there may be minor changes in the shapes of the
projections and optional depressions, as for example a change in the curvature
of the edges at the top of the projection. As the density of tight bonds at
the
points at which the fibers cross over one another increases, the fiber network
structure and the projections become more rigid, and the projections lose
their
resilience.
Because of the open structure of the textile fabric and the large void
volume within the projections and/or depressions, the network has a low
density
compared with the polymer (generally less than about 10%, preferably less than
3o about 5%) based on the amount of space occupied by the network. Air and
other fluids can flow through the fiber network structure with little
resistance.
The filaments can be in the form of a monofilament having a diameter of at
least
about 0.1 mm, corresponding to about 100 dpf in the case of polyethylene
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3
terephthalate). The filaments used in the fiber networks can also be derived
from multifilament yarns having approximately the same total diameter,
provided
that the individual filaments of the yams have coalesced to larger filaments
under heat and pressure during the shaping process, and further provided that
the multifilament yams have not become so firmly bonded at the points where
they cross over one another that these bonds can't be broken when the fiber
networks are compressed.
The fibers are made of a single thermoplastic polymer or copolymer (or
optionally a blend or polymer alloy) that generally melts at a temperature in
the
1o range of about 80°C to about 375°C. The fiber is not derived
from hybrid yarn
or bicomponent fiber. The polymer is preferably made into fiber by a melt
spinning process. Preferred classes of polymers include polyesters,
polyamides,
thermoplastic copolyetherester elastomers, poly(arylene sulfides),
polyolefins,
aliphatic-aromatic polyamides, polyacrylates, and thermotropic liquid
crystalline
is polymers.
The three-dimensional fiber network structure is generally made by
deforming a textile fabric into the desired shape at a temperature high enough
that the fibers can be permanently deformed, as would occur, for example, in a
fiber drawing process. The temperature will generally be above the glass
2o transition temperature (Tg), and, preferably will also remain below the
melting
temperature. The deformation is brought about using a thermomechanical
process, which means the application of a mechanical force at an elevated
temperature. The mechanical force can be applied using numerous methods,
such as solid phase pressure fom~ing, vacuum bladder match plate molding,
2s interdigitation, deep drawing, use of a heated mold, and the like. Heat and
pressure are applied for a sufficient time that the textile fabric is
permanently
deformed, but not for such a long time or at such a high temperature (e.g.
well
above the melting temperature) that the filaments coalesce, causing the shaped
fiber network to lose its open net-like structure and resilience. The
individual
3o filaments in the three-dimensional fiber network structure still have
retained
much of their individual fiber-like appearance and properties.
The starting two-dimensional textile fabric that is utilized in making the
three-dimensional fiber network structure is selected from any of the standard
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4
classes of fabrics, such as knit, woven, or non-woven
textile fabrics. The type of fabric depends on the kind of
resulting network structure that is desired. Knit fabrics
have the advantage that their structure is readily deformed
without excessive elongation of individual fibers, which
leads to breakage of the fibers. They are also drapable.
Woven fabrics have the advantage that they are more readily
produced from larger diameter fibers, such as monofils.
In accordance with an aspect of the present
invention, there is provided a three-dimensional fiber
network comprising a textile fabric selected from one of a
woven fabric and a knit fabric, the textile fabric having a
multiplicity of compressible projections which return
substantially to their original shape after being compressed
by 50%, said textile fabric comprising thermoplastic
filaments which consist essentially of a thermoplastic
polymer, said filaments having a diameter of at least
about 0.1 mm, wherein said filaments in said fabric cross
over one another at intersections, said filaments at said
intersections being unbonded.
In accordance with another aspect of the present
invention, there is provided a method of making a material
suitable for cushioning, comprising the steps of (a) making
a monofilament having a diameter of at least about 0.1 mm
from a thermoplastic polymer; (b) making said monofilament
into one of a knit and woven textile fabric; and (c) making
a series of projections and depressions in said textile
fabric by a thermo-mechanical process, wherein said
filaments in said fabric cross over one another at
intersections, wherein said filaments at said intersections
being unbonded.
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4a
Brief Description of the Drawinas
Fig. 1 shows schematically a section of a three-
dimensional fiber network structure 1 having a multiplicity
of "hat-shaped" projections 3 on base area 2. The open mesh
structure of the fiber network is illustrated. These
illustrative hat-shaped projections have a square base and
square top, with the top having smaller dimensions than the
base.
Fig. 2 schematically depicts an enlargement of one
of the hat shaped projections 3 of Fig. 1, showing the
widening of the mesh structure of the textile material which
occurs in the area that is deformed.
Fig. 3 schematically depicts an enlargement of
four projections that are in the shape of truncated cones.
Detailed Description of the Invention
The three-dimensional fiber networks that have
particular utility as cushioning materials are made up of a
multiplicity of projections on the plane of the textile
fabric from which the network is made. Depressions may
optionally also be present on the opposite side of the
fabric from the projections. Examples of three-dimensional
fiber networks and methods of making them are summarized in
U.S. Patent Nos. 5,364,686 and 9,631,221. The projections
and optional depressions can be in the shape of cones or
truncated cones, pyramids or truncated pyramids having
polygonal bases, cylinders, prisms, spherical elements, and
the like. Generally, the apex points or surfaces of the
projections define a plane parallel to the base plane.
Similarly if there are also depressions, their apex points
or surfaces define a second surface, such as a plane
parallel to the base plane. As a result, the preferred
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4b
three-dimensional networks define two surfaces or planes,
one being
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defined by the tops of the projections and the other being defined by either
the
base plane or the plane or surface defined by the depressions. Furthermore,
the projections and optional depressions are generally arranged in a uniform
or
repetitive pattern with a uniform spacing. However, the shapes, heights, sizes
5 and spacings of the projections and optional depressions can be modified to
suit
a specific application. For example, they may vary to conform to a specific
shape, such as the shape of the human foot for use in shoes, and they may vary
in rigidity to increase or decrease their weight-bearing capacity. The
projections
and/or depressions can also be elongated along one direction of the plane, and
1o in the extreme case, can run the entire length or width of the textile, in
which
case the projections are really corrugations, like those typically seem in
cardboard. Non-corrugated structures are preferred for most applications.
The sizes, heights, shapes and spacings of the pattern of projections
and depressions affect the cushioning properties and "feel" of the three-
dimensional networks. The rigidity of the individual fibers in the network
structure also is a major factor in determining the cushioning properties of
the
three-dimensional networks, and the rigidity of the fibers in tum depends on
the
diameter of the filaments and the kind of materials (e.g. polymers) from which
the filaments are made. For most applications, filament diameters are in the
2o range of about 0.15 mm to about 0.7 mm. An example of a preferred structure
of regularly spaced projections having a square base and a square top that has
shorter sides than the base is shown in Figure 1. Another preferred structure
consists of a regular array of projections which are truncated cones of
similar
size and shape, as shown in Figure 3, for example.
The polymers used as filaments in the three-dimensional fiber networks
consist essentially of a single thermoplastic polymer rather than composites
of a
reinforcing fiber and a matrix polymer, such as a thermoset, which have been
utilized previously for making rigid networks. The polymers may include minor
amounts of additives, such as flame retardants, spinning lubricants, and the
like.
3o The thermoplastic polymers generally have a melting temperature in the
range
of about 80 ° C to about 375 °C, preferably about 150 ° C
to about 350 ° C.
Thermoplastic polymers that are preferred include: (1) polyesters of alkylene
glycols having 2-10 carbon atoms and aromatic diacids. Poly(alkylene
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6
terephthalates), especially poly{ethylene terephthalate) and poly(butylene
terephthalate), are particularly preferred. Afso preferred are poly(alkylene
naphthalates), which are polyesters of 2,6-naphthalenedicarboxylic acid and
alkylene glycols, as for example polyethylene naphthalate); (2) thermoplastic
s copolyetherester elastomers, described in more detail below; (3) polyamides,
especially nylon 6 and nylon 66, which are commonly used in making fibers; (4)
poly{arylene sulfides), especially poly(phenylene sulfide); (5) poiyolefins,
particularly polyethylene and polypropylene; (6) aliphatic aromatic
pofyamides,
such as polyamides derived from terephthalic acid and 2-methyl-1,5-
1o pentanediamine; (7) polyesters derived from 1,4-cyclohexanedimethanol and
terephthafic acid; and {8) thermotropic liquid crystalline polymers, such as
for
example polyesters derived from 6-hydroxy-2-naphthoic acid and 4-
hydroxybenzoic acid.
Specific preferred polymers include polyethylene terephtha(ate) (PET),
15 thermoplastic copolyetherester elastomers, nylon 6 and 66, and
polypropylene.
PET is widely available from many manufacturers, including Hoechst Celanese
Corporation, Somenrille, NJ. The PET should be of high enough molecular
weight to be suitable for spinning into fibers; generally a molecular weight
corresponding to an intrinsic viscosity (LV.) of at least about 0.6 di/gm is
2o suitable, where the LV. is determined by measuring the relative viscosity
of a 4%
solution (weight/volume) in o-chlorophenol at 25°C. The relative
viscosity is then
converted to intrinsic viscosity. Polypropylene and nylons are also widely
available from many manufacturers.
Thermoplastic copolyetherester elastomers, also referred to as
25 thermoplastic elastomers, consist essentially of a multiplicity of
recurring long
chain ether ester units and short chain ester units joined head-to-fail
through
ester linkages. The long chain ether ester units are made up of poly(alkylene
oxide) glycol units attached by way of ester linkages to terephthalic and/or
isophthalic acid. The short chain ester un~s are the product of the reaction
of a
3o short chain glycol with isophthalic and/or terephthalic acid. The short
chain ester
units make up about 15% to about 95% by weight of the thermoplastic
elastomer. Thermoplastic elastomers used in making the three-dimensional
fiber networks are well known and are described in numerous references,
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7
including U.S. Patent No. 3,023,192, 3,651,014, 3,763,109, 3,766,146,
3,784,520, 4,355,155, 4,405,749 and 4,520,150. Poly(tetramethylene oxide)
glycol, also known as poly-THF, is the preferred poly(alkyiene oxide) glycol
for
the long chain ether ester units. The preferred glycol in the short chain
ester
s units is a mixture of 1,4-butanediol with up to about 40% by weight of 1,4-
butenediol. Most preferably, the short chain glycol is only 1,4-butanediol.
The
preferred aromatic diacid used in making the short and long chain ester units
is
terephthalic acid containing up to about 20% isophthalic acid. Most
preferably,
terephthalic acid is the only diacid that is present. Thermoplastic
to copolyetherester elastomers that are composed of long chain ether ester
units
of poly-THF and terephthalic acid and short chain ester units of 1,4-
butanediol
and terephthalic acid are commercially available from Hoechst Celanese
Corporation under the RITEFLEX~ trademark.
Many of the polymers listed above, such as PET and nylon are
15 flammable. Since many of the uses of these materials are in vehicles,
homes,
furniture, and apparel, the polymers will often need to have a flame retardant
additive included. Most flame retardants come from one of six chemical
classes:
aluminum trihydrate; organochlorine compounds; organobromine compounds;
organophosphorous (including halogenated phosphorus) compounds; antimony
20 oxides; and boron compounds. Flame retardants can also be divided into
additives which are blended with the substrate, and reactives, which are
chemically bound to the substrate during polymerization in a separate step.
Polymers that contain reactives as comonomers may contain up to about 10
mole % of the flame retardant monomers in the polymer composition. Other
25 kinds of flame retardants that are sometimes used include intumescent
coatings,
sulfur or sulfur compounds (e.g. ammonium sulfamate and thiourea compounds)
and oxides and carbonates of bismuth, tin, iron, and molybdenum. Ali of the
above classes and kinds of flame retardants are reviewed in an article
entitled
"Flammability," by R.G. Gann, et al., in Encyclonedia of Polymer Science and
3o Engineerina, Second Edition, Volume 7, John Wiley and Sons, New York, 1987,
pages 184-195. For PET, the preferred flame retardant is a reactive
phosphorous compound that is incorporated into the polymer structure during
polymerization and is available from Hoechst AG under the name Oxa-
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phosphoiane {a solid) or Oxa-phosphoiane Glycol Ester {a solution). The Oxa-
phospholane products contain 2-carboxyethytmethytphosphinic acid as the free
acid or as one or more ethylene glycol esters and diesters of the phosphintc
.acid. The 2-carboxyethytmethytphosphinic acid is incorporated into the
polyester backbone at a level of up to about 5°~6 of the polyester
monomer units
and ads as a flame retardant. The reactive phosphinic. acid and its use as a
flame retardant monomer are in U.S. Patent Nos. 4,033,936 and 3,941,752 .
The spacing, size, height, and shape of the projections and optional
1o depressions, the diameter of the filaments, and fabric construction are
chosen~to
give the desired cushioning properties for the specific application. The
shapes
of the deformations also depend on the process used to make them. For
example, in a deformation process in which the textile fabric is held against
a
ptate with round holes and a cylindrical rod' is pushed through the hole on
the
same side as the textile fabric, so that the textile fabric is pushed through
the
hole, the projections that are made in the textile.~~abric will be in the
shape of
truncated cones {i.e:;'fhe base and top of the projections wi8 both be round),
with the diameter of the top of the cone bet' the diameter . of the rod that
pushes the textile through the hole. Similarly, if'a plate with square holes
and a
2o rod with a square cross section is used, the projections will be "hat-
~,haped".
The fiber networks described herein are lightweight, durable and
breathable. They are springy and resilient which means that they can be
compressed (preferably repeatedly) without a signficant loss in properties.
Depending on the stiffness of the fibers and the sizes of the projections,
they
may be used as cushioning materials, as. impact absorbing materials, or as
semi-rigid suppod materials. Because they are generally made of only one
po~mer, such as PET, they cap be easily recycled after use with other
recyclable plastics, (e.g. bottles in the case of PI=~ j. The fiber network
materials
can be used as single layers, they can be nested face to face, with the
projections interlocking, or they can be- stacked with the projections of one
Layer
against the base plane of the next layer or with the base planes ~of the two
Layers against each ot>1er to provide thicker spacers and cushions. The
materials having more than. one layer can be bonded together .by 'such methods
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9
as adhesive bonding or ultrasonic welding. The fiber network structures can be
used as components or sub-components in numerous applications, including
mattresses, mattress topper pads, infant mattresses and mattress covers to
prevent suffocation, footwear, (sock liners, collar linings, and midsoles for
s shoes), pads for protective head gear, seat cushions such as for example
automobile seats, wrappings for medical casts, protective braces, protective
helmet liners, spacelsound barriers for wall part~ions and panels, protective
packaging for electronics, automotive headliners which provide head cushioning
and channels for wiring, liners for athletic and outdoor clothing, carpet
pads,
Zo liners for women's brassieres and men's athletic supporters, and cushions
for
outdoor furniture, which dry easily and don't retain moisture. The invention
is
further described in the following non-limiting examples.
Examples
15 Example 1
RlTEFLEX~640 copolyetherester elastomer having a melting
temperature of about 180°C, obtained from Hoechst Celanese Corporation,
was
melt spun to yield a 0.20 mm (435 denier) monofil having the following
properties. The fiber tenacity was measured by ASTM Test Method D-3822 as
20 2.8 gpd, with 98% elongation at break. The elastic recovery of the fiber
was
measured by the same test method as 100% after 100 cycles at either 20% or
50% elongation. The monofil was knitted into a textile fabric having a wale of
8
walesrnch and a weft of 42 courselinch.
The knit fabric was shaped into a three-dimensional structure by using a
25 heated press plate. The press plate was a metallic plate having 3/8 inch
diameter holes, and was heated to about 160° - 230°C. The fabric
was pressed
against the heated plate for 9 seconds, and pins that were 1/4 inch in
diameter
were then pushed through the holes. This yielded truncated cone shaped
projections on the fabric which were about 3/8 inch in diameter at the base
and
30 1/4 inch in diameter at the top. The projections were about 3/16 inches in
height
and were spaced in a square grid array with the nearest distance between the
projections (center to center) being about 3/4 inch.
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This shaped fiber network had a soft springy feel and could be
repeatedly compressed without a loss of springiness.
Example 2
5 RITEFLEXa672 thermoplastic copolyetherester elastomer, which melts at
about 205°C, was obtained from Hoechst Celanese Corporation, and was
melt
spun into 823 denier monofil (about 0.28 mm in diameter). The tenacity at
break
of the fiber was 2.4 gpd, and it had an elongation at break of 87%, as
measured
by ASTM Test Method D-3822. The elastic recovery of the fiber, measured by
io the same method, was 100% after 100 cycles at either 20% or 50% elongation.
The fiber was knitted into a fabric having the same wale and weft as that
in Example 1. The fabric was deformed into a three-dimensional network using
the press plate apparatus of Example 1 under the same conditions as in
Example 1. This shaped fiber network also had a soft springy feel and could be
is repeatedly compressed without a loss of springiness.
Examale 3
Commercial PET that was made for use in textile fabrics was melt spun
into a 0.182 mm monofil (about 321 denier). The monofil was then made into a
2o plain knit fabric with 16 wates and 24 courses per inch.
The fabric samples were deformed into a three-dimensional network
using a similar kind of apparatus as described in Example 1, but having 1/4
inch
holes in the press plate and 1/8 inch diameter cylindrical pins to yield
conical
projections with flat tops. The base and tops of the projections were the same
25 as the diameter of the holes in the base plate and the diameter of the
pins. The
projections were arranged in a square grid array and were separated by 1I2
inch
(center to center). The height of the projections was about 1/4 inch. The
projections were made by heating the base plate and the pins to 240°C
and
pressing the fabric through the holes for about 30 seconds. The deformed
3o fabric was resilient and had a comfortable, springy feel when pressed down
by
hand, and retained its feel even after multiple compressions.
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11
Exam le 4
A series of polyethylene terephthalate) (PET) fabric samples (both knit
and woven) were made into three dimensional fiber network materials by the
method of pressing the fabric against a heated base plate having a square grid
array of evenly spaced holes at about 200°C for two minutes and then
pushing
the fabric through holes in the base plates using cylindrical pins that were
heated to about 180°C. The pins were kept in place (projected through
the
holes at temperature) for 15 seconds before being withdrawn, except in Sample
No. 4 (below), where the pins were kept in place for 600 seconds. This
resulted
1o in three-dimensional networks of cone-shaped projections with fiat tops
which
were evenly spaced and in which the bases of the projections had the diameter
of the holes and the tops of the projections had the diameter of the pins. The
heights of the projections (the thickness of the samples) was somewhat less
than the depth of the penetrations through the holes by the pins due to
shrinkage after the mechanical force was removed. Both knit and woven fabrics
were tested.
These samples were subjected to compression tests using a modification
of methods that are used for polyurethane foams and latex foams. Samples of
the materials were placed between the plates of an Instron tensile tester and
2o then pre-loaded to a load of 0.02 psi. The distance between the plates at
0.02
psi of compression was defined as the thickness of the sample. The samples
were then compressed to 60% compression for two cycles at test speeds of 0.2
in/min for samples 0.10 - 0.29 inches in thickness, 0.5 in/min for samples
0.30 -
0.69 inches in thickness, and 1.0 in/min for samples 0.70 - 1.39 inches in
thickness. The two pre-cycles above made a significant change in two of the
samples (Nos. 4 and 6 in Table 1 ); the precycling measurements are also
reported for these two samples. Six minutes after the pre-cycling above, a
compression test was run to 60% compression at the same speed as in the pre-
cycfing. Stress and percent compression were measured, and the stress at 25%
3o and 50% compression was measured. These values are recorded in Table 1,
along with the averages for runs where there were duplicate measurements.
These measurements show an increase in stress with increasing compression,
which is a characteristic that is desirable for cushioning applications.
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12
PCT/US96/19686
The apparent volume was computed based on the thickness as
measured at 0.02 psi above and the measured dimensions of the sample. This
was used to compute the apparent density, which ranged from 0.016 to 0.067
gms/cc. By comparison solid PET has a density of about 1.4 gms/cc. Thus the
apparent density of the three dimensional fiber network is less than about 5%
of
the density of solid PET (1.1% - 4.8% in these examples). The apparent
densities of the samples in gms/cc are also fisted in Table 1; these can be
converted to pounds/cu. ft. by multiplying by 62.4.
It is to be understood that the above embodiments of the invention are
io illustrative only and that modification throughout may occur to one skilled
in the
art. Accordingly, this invention is not to be regarded as limited to the
embodiments disclosed herein.
CA 02239383 1998-07-06
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