Note: Descriptions are shown in the official language in which they were submitted.
METHODS OF PRODUCING THERMOPLASTIC COMPOSITES USING FABRIC-BASED
THERMOPLASTIC PREPREGS
BACKGROUND
[0001] The use of fiber-reinforced composites is growing in popularity with
applications in
transportation, consumer goods, wind energy, and infrastructure. Some of the
nnany reasons
for choosing composites over traditional materials such as metals, wood, or
non-reinforced
plastics include reduced weight, corrosion resistance, and improved mechanical
strength.
Thermoset materials are used in many of the fiber-reinforced composites. The
reinforcing fibers
are commonly infused with the thermoset materials during production of the
fiber-reinforced
composites. The thermoset materials may then be cured or polymerized. A common
method of
producing such fiber-reinforced composites is filament winding where a
thermoset resin infused
fiber roving is wound about a mandrel.
BRIEF SUMMARY
[0002] The embodiments described herein provide reinforced thermoplastic
products having
improved properties over conventional products. The manufacture of the
reinforced
thermoplastic products is also greatly simplified. According to one aspect, a
reinforced
thermoplastic product has a tube shaped main body having a hollow interior.
The tube shaped
main body includes a fabric-based reinforcing sheet and a thermoplastic
polymer material. The
fabric-based reinforcing sheet is wound about an axis of the tube shaped main
body to form a
plurality of circumferentially positioned layers. The fabric-based reinforcing
sheet includes a
plurality of fiber bundles that are oriented along a first direction and a
second direction, with the
second direction having an angled orientation relative to the first direction.
[0003] The thermoplastic polymer material is saturated within each of the
circumferentially
positioned layers of the fabric-based reinforcing sheet and fully impregnates
each fiber bundle
of the plurality of fiber bundles of each layer. The layers of the fabric-
based reinforcing sheet
and the thermoplastic polymer material form a unitary thermoplastic product.
[0004] According to another aspect, a thermoplastic product has a main body
that includes a
fabric-based reinforcing sheet and a polymerized thermoplastic material. The
fabric-based
reinforcing sheet is wound about a mandrel to form a plurality of layers
having a cross-sectional
shape that corresponds to the mandrel. The fabric-based reinforcing sheet also
includes a
plurality of fiber bundles. The polymerized thermoplastic material is disposed
within each layer
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of the fabric-based reinforcing sheet. The polymerized thermoplastic material
bonds each layer
of the fabric-based reinforcing sheet to an adjacent layer of the fabric-based
reinforcing sheet.
The plurality of layers of the fabric-based reinforcing sheet and the
polymerized thermoplastic
material form a unitary thermoplastic product.
[0005] According to another aspect, a method of forming a reinforced
thermoplastic product
includes winding a fabric-based thermoplastic prepreg about a mandrel to form
a plurality of
layers of the thermoplastic prepreg around the mandrel. The thermoplastic
prepreg includes a
plurality of fiber bundles and a polymerized thermoplastic material that is
disposed within each
layer of the plurality of layers of the thermoplastic prepreg. The method also
includes applying
heat to the thermoplastic prepreg as it is wound about the mandrel to at least
partially melt or
soften the polymerized thermoplastic material along the nip line and applying
pressure to the at
least partially melted or softened polymerized thermoplastic material of the
prepreg sheet, so as
to weld an inner surface of an outer layer of the thermoplastic prepreg to an
outer surface of an
inner layer of the thermoplastic prepreg. Said method does not involve curing
or polymerization.
In some embodiments, the method may also include cooling the at least
partially melted or
softened polymerized thermoplastic material of the prepreg sheet.
[0006] According to another aspect, a thermoplastic product includes a main
body and a
polymerized thermoplastic material. The main body includes a plurality of
layers of a woven
fabric reinforcing sheet with a shape that corresponds to a mandrel. Each
layer of the woven
fabric reinforcing sheet includes a plurality of fiber bundles that are
oriented according to a first
direction and a second direction with the second direction having an angled
orientation relative
to the first direction. The polymerized thermoplastic material is saturated
within each layer of
the woven fabric reinforcing sheet and fully impregnates each fiber bundle of
the plurality of fiber
bundles. The woven fabric reinforcing sheet and the polymerized thermoplastic
material form a
unitary thermoplastic product.
[0007] According to another aspect, a method of forming a reinforced
thermoplastic product
includes positioning a thermoplastic prepreg atop previously consolidated
thermoplastic
prepregs so that the thermoplastic prepreg forms an outer layer of the
reinforced thermoplastic
product. The thermoplastic prepreg includes a plurality of fiber bundles that
are oriented
according to a first direction and a second direction, with the second
direction having an angled
orientation relative to the first direction, and a polymerized thermoplastic
material that fully
impregnates each fiber bundle of the plurality of fiber bundles. The method
also includes
moving a pressure application component along a top surface of the
thermoplastic prepreg and
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applying heat and pressure to the thermoplastic prepreg as the pressure
application component
is moved along the top surface thereof to at least partially melt or soften
the polymerized
thermoplastic material. The method further includes welding the thermoplastic
prepreg to the
previously consolidated thermoplastic prepregs. Said method does flot involve
curing or
polymerization. In some embodiments, the method also includes cooling the at
least partially
melted or softened polynnerized thermoplastic material of the prepreg sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present technology is described in conjunction with the appended
figures:
[0009] Fig. 1 illustrates a roll of a fabric-based thermoplastic prepreg.
[0010] Fig. 2 illustrates a winding process that employs a fabric-based
thermoplastic prepreg.
[0011] Fig. 3 illustrates a prepreg laying process that employs a fabric-based
thermoplastic
prepreg.
[0012] Fig. 4 illustrates a wind turbine blade that includes one or more
components made of
or from a fabric-based thermoplastic prepreg.
[0013] Fig. 5 illustrates an embodiment of a reinforced thermoplastic product
that includes a
tube shaped main body having a circular cross-section.
[0014] Figs. 6A-B illustrate other embodiments of reinforced thermoplastic
products having
non-circular cross-sections.
[0015] Fig. 7 illustrates a method of forming a reinforced thermoplastic
product.
[0016] Fig. 8 illustrates another method of forming a reinforced thermoplastic
product.
[0017] In the appended figures, similar components and/or features may have
the same
numerical reference label. Further, various components of the same type may be
distinguished
by following the reference label by a letter that distinguishes among the
similar components
and/or features. If only the first numerical reference label is used in the
specification, the
description is applicable to any one of the similar components and/or features
having the same
first numerical reference label irrespective of the letter suffix.
DETAILED DESCRIPTION
[0018] The embodiments described herein relate to products that employ fabric-
based
thermoplastic prepreg products and to methods of using fabric-based
thermoplastic prepreg
products in the manufacturing various products. The prepreg products are
preferably fully
impregnated with thermoplastic materials and may be reheated and consolidated
into a given
shape. In some embodiments, the prepreg products may be made using reactive
thermoplastic
resins. Reactive thermoplastic resins include monomers or oligomers that may
in situ
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polymerize to form thermoplastic polymers. Exemplary reactive thermoplastic
resins include, but
not linnited to, lactams such as caprolactam and laurolactam, acrylates,
methacrylates such as
methyl methacrylate, cyclic olefins such as norbornene and cyclopentene,
macrocyclic polyester
oligonners such as cyclic butylene terephthalate (CBT), macrocyclic Bisphenol-
A oligomers, and
thermoplastic polyurethanes. ln an exemplary embodiment, the reactive
thermoplastic resin
comprises caprolactam.
[0019] In other embodiments, the prepreg products may be made using a
dispersion of a
polymeric powder material or a polymeric film that is softened and/or melted
to form the
prepreg. The products made by the processes described herein exhibit increased
isotropic
properties or characteristics than those achieved or exhibited in conventional
thermoplastic
wound products due to the use of the fabric-based thermoplastic prepregs and
the fiber
orientations within the products that may be achieved due to the use of these
materials.
[0020] The prepreg products may be used in various processes including winding
processes
and laying processes. Filament winding is a type of winding process. Filament
winding has
been widely used to produce axisynnmetrical thermoset composites with
continuous fiber
reinforcement. Filament winding may be used for applications such as producing
cylinders and
pressure vessels. The process involves winding thermoset resin impregnated
filaments over a
rotating mandrel.
[0021] Filament strands, such as glass or carbon fibers, are typically
impregnated in a bath of
thermoset resin as they arc wound onto the mandrel. Once the mandrel is
covered to a desired
thickness, the resin is cured in an aven or under radiant heaters.
Conventional filament winding
is linnited to the use of thermoset resins due to their relatively low
viscosity, which is suitable for
in line impregnation of the fiber strands. The use of thermoset resins,
however, has a number
of drawbacks. For example, the slipping of the fiber strands (e.g., rovings
and tows) on or about
the mandrel linnits the fiber orientations that may be achieved in the final
part.
[0022] In addition, in the manufacturing of large and thick composite parts,
the exothermic
curing reaction of the thermoset resins may create problems. As large and
thick composite
parts contain considerable amounts of thermoset resins, the large amount heat
generation from
the exothermal curing reaction may destroy the composite part during curing.
Often times a low
curing temperature or a slow curing thermoset resin is used, which greatly
increases the
manufacturing time. Moreover, the resulting composite parts contain cross-
linked thermoset
resin matrix and, therefore, they cannot be recycled.
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[0023] In contrast to thermoset resins, thermoplastic resins offer several
advantages
including: unlimited shelf life, high fracture toughness, recyclability, and
continuous processing
without the need for curing. Thermoplastic polymer resins, however, typically
have melt
viscosities that are significantly greater than thermoset resins and,
therefore, they are not
suitable for conventional filament winding where inline impregnation of fiber
strands is required.
[0024] In the embodiments herein, fabric-based thermoplastic prepregs are used
in the
winding or laying process. In an exemplary embodiment, the fabric-based
thermoplastic
prepregs (hereinafter thermoplastic prepregs) are fully impregnated with the
thermoplastic
material, although partially impregnated prepregs may also be used. In some
embodiments,
these thermoplastic prepregs can be produced through impregnation of the
fabric materials with
low viscosity monomers or oligomers, followed by in-situ polymerization to
form a thermoplastic
matrix. Exennplary methods of producing fully impregnated thermoplastic
prepregs are further
described in U.S. Patent Application No. 14/088,034, filed November 22, 2013,
entitled "Fiber-
Containing Prepregs and Methods and Systems of Making''; U.S. Patent
Application No.
14/794,634, filed July 8, 2015, entitled "System for Producing a Fully
lmpregnated
Thermoplastic Prepreg"; U.S. Patent Application No. 14/845,007, filed
September 3, 2015,
entitled "System for Producing a Fully lmpregnated Thermoplastic Prepreg";
U.S. Patent
Application No. 14/880,307, filed October 12, 2015, entitled "System for
Producing a Fully
lmpregnated Thermoplastic Prepreg"; and U.S. Patent No. 9,186,852, entitled
"Fiber-Containing
Prepregs and Methods and Systems of Making". Each of the above U.S. Patents
and U.S.
Patent Applications are incorporated by reference herein.
[0025] In other embodiments, the thermoplastic prepregs can be produced
through the use of
a thermoplastic polymer powder material that is positioned and impregnated
within the fabric, or
through the use of a thermoplastic polymer film that is positioned atop the
fabric material and
impregnated within the fabric under heat and pressure. Exemplary methods of
producing such
thermoplastic prepregs are further described in U.S. Patent Application No.
13/915,023, filed
June 11, 2013, entitled "Sized Glass Fibers for Fiber-Containing Composite
Articles and
Methods of Making Them", the entire disclosure of which is incorporated by
reference herein.
[0026] Fabric-Based Thermoplastic Prepregs
[0027] Referring now to Fig. 1, illustrated is an example of a fabric-based
thermoplastic
prepreg 100 that may be used in the various processes described herein. In an
exennplary
embodiment, the thermoplastic prepreg 100 may be fully impregnated with the
thermoplastic
material. For example, a Nylon-6 prepreg may be produced through the
impregnation of a
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reinforcement fabric with molten caprolactam followed by in-situ anionic
polymerization of the
caprolactam.
[0028] The fabric-based thermoplastic prepreg 100 (also referred to as a
fabric-based
reinforcing sheet) may include a plurality of fibers, rovings, or fiber
bundles (hereinafter fiber
bundles or rovings). The rovings may contain continuous glass fibers or other
fibers. In some
embodiments, the rovings may be woven together. In other embodiments, the
rovings may be
held together via stitching, or the fibers may be entangled and intermeshed in
a randomly
oriented configuration. In embodiments that ennploy stitching, the stitching
threads that are
used may be polymeric fibers, glass fibers, or other fibers. The ternn roving
or fiber bundle as
used herein refers to a bundle of fibers that are positioned adjacent one
another to form a rope,
thread, or cord like component. A common type of fiber that is used in the
rovings is glass
fibers, although various other fibers could be used such as carbon fibers,
basait fibers, metal
fibers, ceramic fiber, natural fibers, synthetic organic fibers such as aramid
fibers, and other
inorganic fibers. Exemplary glass fibers may include "E-glass", "A-glass", "C-
glass", "S-glass",
"ECR-glass" (corrosion resistant glass), "T-glass", and fluorine and/or boron-
free derivatives
thereof.
[0029] In some embodiments, the rovings may be oriented along a first
direction and along a
second direction that is angled relative to the first direction. For example,
the second direction
may be angled relative to the first direction by 45 degrees, 90 degrees, and
the like. The woven
materials are nnaterials that are produced by weaving multiple roving strands
together. The
roving strands are commonly woven so that a first plurality of strands extend
in a first direction
(e.g., weft direction) and a second plurality of strands extend in a second
direction that is
typically orthogonal to the first direction (e.g., warp direction). The first
plurality of strands are
roughly parallel with one another as are the second plurality of strands.
Various weaves may be
used to form the fabric-based thermoplastic prepreg 100 described herein,
including: plain
weaves, twill weaves, satin weaves, multi-axial weaves, or stitching. The
fabric-based
thermoplastic prepreg 100 that is employed may contain any kind of woven
fabric, stitched
fabric, or multi-axial fabric material. The fabric-based thermoplastic prepreg
100 may also
contain chopped fibers in addition to the continuous fibers. The fabric-based
thermoplastic
prepreg 100 may be a hybrid from different type of fibers. For example, the
fabric-based
thermoplastic prepreg may contain both glass and carbon fibers. For ease in
describing the
embodiments herein, the embodiments will generally refer to the use of glass
fibers, although if
should be realized that various other fiber types may be used.
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[0030] The embodiments wherein the rovings are oriented along at least two
directions or
orientations, or where the rovings are held together via stitching, are
different than conventional
thermoplastic tapes that include pre-impregnated unidirectionally oriented
rovings where the
rovings are oriented along a single direction (e.g., the longitudinal
direction of the tape). These
unidirectional thermoplastic tapes highly limit the fiber orientations that
are achieved in the
resulting composite parts from a winding process. For example, the tapes
cannot be oriented
so that the rovings are aligned longitudinally with the resulting composite
parts. Relatively low
longitudinal strengths can be achieved in the composite parts employing
unidirectional
thermoplastic tapes, due to the limitation in how these tapes may be wound
around a mandrel.
As a result, the thermoplastic composites that are made with unidirectional
thermoplastic tapes
are limited to applications where significant longitudinal strengths are flot
needed.
[0031] The fabric-based thermoplastic prepreg 100 includes a thermoplastic
polymer material
that is at least partially saturated or impregnated within the fabric material
so that at least some
of the fiber bundles are impregnated with the thermoplastic material. In some
embodiments, the
fabric-based thermoplastic prepreg 100 may be fully impregnated with the
thermoplastic
polymer material. For example, thermoplastic prepregs that are manufactured
according to the
disclosures of the '034, '634, '007, and/or '307 application incorporated by
reference herein
and/or the '852 patent incorporated by reference herein may be used, which
prepregs are fully
impregnated with a thermoplastic polymer material. In such embodiments, the
thermoplastic
polymer material fully impregnates each fiber bundle of the fabric-based
thermoplastic prepreg
100.
[0032] Fig. 1 illustrates a roll of the fabric-based thermoplastic prepreg
100. The fabric-based
thermoplastic prepreg 100 is a flexible material with a high content of
reinforcing fibers. As
described herein, the fabric-based thermoplastic prepreg 100 may include a
plurality of rovings
that are woven together with the rovings oriented along multiple directions.
As described
herein, when the fabric-based thermoplastic prepreg 100 is subjected to a
subsequent heating
and/or pressure process, the thermoplastic polymer melts or softens to allow
the thermoplastic
prepreg to be welded or consolidated into a composite part.
[0033] Since the fabric-based thermoplastic prepreg 100 is based on fabrics
(often woven
fabrics), the fiber distribution and orientation needed for a given
application can be pre-built into
the fabric design. This provides significant advantages over conventional
filament winding
processes and processes that include unidirectional thermoplastic tapes since
the process is
much quicker and since the complex distribution and orientation of the fibers
cannot be
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achieved via filament winding and/or unidirectional thermoplastic tapes.
Accordingly, the fabric-
based thermoplastic prepregs 100 provide significantly higher design freedom
and can be used
to produce reinforced thermoplastic composite parts which are not attainable
through filament
winding and/or winding of unidirectional thermoplastic tapes. A specific
example of this
advantage is provided in applications where longitudinal strength is needed.
In such
applications, the fabric-based thermoplastic prepreg 100 can be formed from
fabrics with a
required amount of fibers oriented along a longitudinal direction of the
desired end product.
[0034] In addition, the fabric-based thermoplastic prepreg 100 allows the
winding process to
be significantly simplified since the non-circumferential strength (e.g., the
axial or longitudinal
strength) of the resulting composite relies on the fabric design employed in
the fabric-based
thermoplastic prepreg 100 rather than on the winding pattern employed in
filament or
unidirectional tape winding. Typically, a circunnferential winding is ail that
is needed for the
fabric-based thermoplastic prepregs 100, which simplifies the process and
increases
productivity. Stated differently, since the fiber orientation and distribution
is pre-built into the
fabric, the fabric-based thermoplastic prepreg 100 does not need to be angled
relative to, or
applied diagonally about the mandrel during the winding process, which is
required with filament
winding and/or unidirectional tapes in order to achieve a non-circumferential
orientation of the
fibers.
[0035] An additional benefit may be realized in embodiments that employ fabric-
based
thermoplastic prepregs 100 produced through in-situ polymerization of reactive
monomers or
oligomers. ln such embodiments, the fiber sizings can be developed to impart
strong chemical
bonding between the reinforcing fibers and the thermoplastic resin matrix. As
such, a significant
improvement in the composite property can be achieved, especially in
connparison with
unidirectional thermoplastic tapes produced from thermoplastic polymer resins.
For example,
reinforcing fibers in the fabric-based thermoplastic prepregs may be sized
with a sizing
composition that contains a polymerization agent for monomers or oligomers.
Exemplary
polymerization agents for the in-situ anionic polymerization of caprolactam
may include coupling
activator compound described in U.S. Patent Application No. 12/008,041, filed
January 8, 2008,
entitled "Surfaces Containing Coupling Activator Compounds and Reinforced
Composites
Produced Therefrom"; and U.S. Patent Application No. 12/724,024, filed May 15,
2010, entitled
"Polymerization lnitiators for Fiber-Reinforced Polymer Composites and
Materials Made from
the Composites", which are incorporated herein by reference for ail purposes.
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[0036] Systems for Manufacturing Fabric-Based Thermoplastic Prepreg Products
[0037] Referring now to Fig. 2, illustrated is a winding process 200 that
employs a fabric-
based thermoplastic prepreg 202. The fabric-based thermoplastic prepreg 202 is
wound about
a mandrel 206 one or more times to create one or more layers of the fabric-
based thermoplastic
prepreg 202 atop the mandrel 206. The one or more layers of the fabric-based
thermoplastic
prepreg 202 are in-situ welded or coupled together as they are wound about the
mandrel 206 to
create a product having a cross sectional shape that corresponds to the shape
of the mandrel
206.
[0038] The prepreg winding process may involve a compaction force F that is
applied via a
pressure application device 204, such as a compression roller, nip, or bar,
that is moved or
pressed radially toward the mandrel 206 with the fabric-based thermoplastic
prepreg 202
positioned there between. The compaction force F may be applied by the
compression roller
204 to create an intimate contact between the joining or mating surfaces of an
underlying fabric-
based thermoplastic prepreg 202 and a fabric-based thermoplastic prepreg 202
positioned atop
the underlying fabric-based thermoplastic prepreg 202. The compaction force F
may aid in
welding or coupling the two layers of the fabric-based thermoplastic prepreg
202.
[0039] Local heating is applied via a heating source 208, typically along the
nip line between
the two layers of the fabric-based thermoplastic prepregs 202 during the
winding process. The
local heating is applied to melt the thermoplastic resin of the fabric-based
thermoplastic prepreg
202 along the nip line. The local heating may be applied to melt the resin of
both the underlying
fabric-based thermoplastic prepreg 202 and the fabric-based thermoplastic
prepreg 202 being
applied atop the underlying prepreg. In this manner, the two fabric-based
thermoplastic prepreg
202 layers that are being welded or coupled together may both be in a weldable
or couplable
state. In some embodiments, the heating source 208 may be moveable relative to
the mandrel
206 and/or roller 204 to vary the location of the applied local heat.
[0040] The local heating may be applied to the prepreg surfaces to effect
diffusion of the
polymer chains through the contact areas of the layers of the fabric-based
thermoplastic
prepreg 202. Local heating of the fabric-based thermoplastic prepregs 202
along the nip line
during the winding process can be achieved by a variety of methods, including
but flot limited to,
laser radiation, infrared heating, hot gas, direct flame, and the like.
[0041] The winding process of Fig. 2 can be used to produce various products
including, but
flot limited to, pipes, cylinders, tanks, components for wind turbine blades,
and the like. An
exennplary application of the prepreg winding is to produce roots for wind
turbine blades as
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illustrated in Fig. 4. VVinding of fully impregnated thermoplastic prepregs,
such as Nylon-6
prepregs produced through the impregnation of reinforcing fabrics with
caprolactam, can be
used to produce thermoplastic composite products with superior properties,
such as high
fracture toughness, high impact resistance, and recyclability. Additionally,
the prepreg winding
process may be conducted under tension, which ensures or maintains the fiber
orientation and
prevents fabric wrinkling.
[0042] Referring now to Fig. 3, illustrated is a prepreg laying process 300
that employs a
fabric-based thermoplastic prepreg 302. High performance thermoplastic
composite laminates
can be produced through the process of laying and in-situ welding of the
fabric-based
thermoplastic prepregs 302. In the process 300, a fabric-based thermoplastic
prepreg 302 is
laid atop one or more underlying fabric-based thermoplastic prepregs 310,
which may be
previously consolidated or welded prepregs that form multiple layers. The one
or more
underlying fabric-based thermoplastic prepregs 310 may be positioned atop a
substrate, a nnold,
and the like, and may have a shape or configuration that correspond to the
substrate or mold.
[0043] As the fabric-based thermoplastic prepreg 302 is laid, a pressure
application
component 304, such as a compression roller, bar, or nip, is passed over the
fabric-based
thermoplastic prepreg 302 and applies a downward force F to the fabric-based
thermoplastic
prepreg 302 and previously consolidated prepreg layers 310. Heat may be
applied from a heat
source 306 to the prepregs along the nip line to melt or soften the
thermoplastic material of the
fabric-based thermoplastic prepreg 302 and one or more of the previously
consolidated prepreg
layers 310. The compression roller 304 may be moved across the prepreg layers
at a given
velocity depending on various factors, including the thickness of the
material. The application of
a downward force F and applied heat 306 may form a heat applied zone 308 in
which the
thermoplastic material is sufficiently nnelted or softened for welding of the
prepreg layers.
[0044] Conventional tape laying processes employ unidirectional tapes.
Different fiber
orientations are achieved through sequential laying of individual layers of
the unidirectional
tapes along different directions. The tape laying process is time consuming
and generates a
significant annount of waste through cutting of the unidirectional tapes to
the dimension needed
for tape laying. In contrast, the laying of the fabric-based thermoplastic
prepreg 302 is
significantly faster and effective, as the desired fiber orientation and
distribution is achieved
through the fabric design, rather than through the application of the
unidirectional tapes along
different directions.
CA 2969929 2017-06-07
[0045] Fabric-Based Thermoplastic Prepreg Products
[0046] An exemplary application of the fabric-based thermoplastic prepreg 302
laying process
is the production of spar caps 404 for wind turbine blades 400, which is
illustrated in Fig. 4.
VVind turbine blades 400 are commonly extremely large components (e.g., 50
meters or
greater). The large sizes of these components make employing reactive
thermoplastic resins,
via processes such as vacuum infusion, extremely difficult. For example, the
sensitivity of
reactive thermoplastic resins to various conditions, such as the moisture
sensitivity of the in-situ
anionic polymerization of caprolactam, renders the use of such materials
extremely difficult for
large composite components. As such, various components of wind turbine
blades, such as
spar caps and root sections, are conventionally produced through vacuum
infusion of thermoset
resins, such as epoxy.
[0047] In contrast to the conventional processes, laying and in-situ welding
of fabric-based
thermoplastic prepregs 302 can be used to produce thermoplastic composite spar
caps 404 with
superior mechanical properties. Fig. 4 also shows a thick circular root
section 402 consisting of
fiber reinforced composites. The root section 402 is nornnally positioned on
the root of the wind
turbine blade 400 and is the component that is attached to the rotor. The root
section 402
extends into the wind turbine blade 400 and is bolted to the rotor. As
described above, winding
of fabric-based thermoplastic prepregs 202, such as Nylon-6 prepregs, can be
used to produce
thermoplastic composite root sections 402 with superior properties, such as
high fracture
toughness, high impact resistance, and recyclability. The prepreg winding
process may also be
conducted under tension to ensure the fiber orientation and prevent fabric
wrinkling. As such,
the prepreg winding process 200 can produce thermoplastic composite root
sections 402 with
superior mechanical properties. Other components of the wind turbine 400 may
likewise be
made of or from one or more fabric-based thermoplastic prepregs.
[0048] Referring now to Fig. 5, illustrated is an embodiment of a reinforced
thermoplastic
product that includes a tube shaped main body 502 having a hollow interior 508
and a
longitudinal length extending between a first end 504 and a second end 506.
The tube shaped
main body 502 includes a fabric-based reinforcing sheet or prepreg. The fabric-
based
reinforcing sheet includes a plurality of fiber bundles or rovings. In one
embodiment, the rovings
may be woven together so that the rovings are oriented along a first direction
and along a
second direction having an angled orientation relative to the first direction.
In other
embodinnents, the rovings may be held together via stitching or threads. In
yet another
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embodiment, the fabric-based reinforcing sheet may be a nonwoven material
having randomly
oriented entangled fibers.
[0049] The fabric-based reinforcing sheet includes a polymerized thermoplastic
material that
may be disposed partially or fully within the fabric-based reinforcing sheet
as described herein.
In an exemplary embodiment, the fabric-based reinforcing sheet is fully
saturated or
impregnated with the polymerized thermoplastic material so that each of the
rovings, and the
individuel fibers contained therein, are impregnated, saturated, or otherwise
in contact with the
polymerized thermoplastic material.
[0050] The tube shaped main body 502 is formed by winding the fabric-based
reinforcing
sheet about an axis 510 of the tube shaped main body, such as a tubular shaped
mandrel. The
fabric-based reinforcing sheet may be wound about the mandrel to form a
plurality of
circumferentially positioned layers of the fabric-based reinforcing sheet. The
various layers of
the fabric-based reinforcing sheets are welded or coupled together by melting
the thermoplastic
material along the nip line and allowing the thermoplastic material to re-
harden. In some
embodiments, the thermoplastic material is saturated within each of the
circumferentially
positioned layers of the fabric-based reinforcing sheet in which the
thermoplastic polynner
material fully impregnates each roving or fiber bundle of each layer. The
welded fabric
reinforcing sheet layers form a unitary thermoplastic product.
[0051] In some embodiments, the first direction of the rovings is aligned with
the axis 510 or
longitudinal direction of the tube shaped main body 502. Because some of the
rovings are
aligned with the axis 510 of the tube shaped main body 502, the rovings
greatly reinforce the
product in the longitudinal direction. As described above, it is flot possible
to orient fibers in this
direction with conventional thermoplastic unidirectional tape materials and
thus, the fabric-based
thermoplastic prepregs described herein provide significant advantages over
conventional
materials.
[0052] The second direction of the rovings may be angled at 45 degrees or 90
degrees
relative to the first direction. In a specific embodiment, the second
direction of the rovings may
be aligned with the circumferential direction so that some of the rovings
extend circumferentially
around the tube shaped main body 502. The fabric-based reinforcing sheets
significantly
reinforce the tube shaped main body 502. As such, a thickness of the tube
shaped main body's
wall may be substantially reduced while maintaining a similar, or even
greater, pressure rating.
Stated differently, the cylindrical wall of the tube shaped main body 502 may
be significantly
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thinner than conventional polynner based tube products without compromising
the products
ability to withstand a given pressure.
[0053] In some instances, the tube shaped main body may have a cylindrical
configuration as
shown in Fig. 5. In other instances, the tube shaped main body may have a non-
circular
shaped cross section or configuration. For example, Fig. 6A illustrates a tube
shaped main
body 602 having an elliptical or oval cross section or configuration. Fig. 6B
illustrates a tube
shaped main body 620 having a conical shaped configuration where the outer
diameter tapers
between a first end 622 and a second end 624. It should be realized that
various other
configurations are possible, such as rectangular shapes, square shapes, or any
other shape
that may be produced by winding the fabric material about a mandrel. The
fabric-based
reinforcing sheet may be wound about a correspondingly shaped mandrel to form
such shapes.
Also, while some embodinnents are described as having a hollow interior, it
should be
recognized that in other instances the tube shaped main body may not have a
hollow interior.
For example, the mandrel may be left within the tube shaped main body as a
solid or non-hollow
core or interior. The solid or non-hollow core or interior may be fornned for
weathering
purposes, reinforcement purposes, or other purposes.
[0054] As described above, the formation of the reinforced thermoplastic
products, such as
the tube shaped bodies of Figs. 5-6B, does not involve a polymerization
process. Rather, the
polymerization may be previously performed in manufacturing the fabric-based
thermoplastic
prepregs. As such, the formation of the reinforced thermoplastic products
merely involves
heating the prepregs to melt the thermoplastic material and to consolidate the
prepregs into the
thermoplastic composite material.
[0055] Another advantage of using some of the thermoplastic prepregs described
herein is
the ability to wet out essentially ail of the bundles of fibers or rovings in
the fabric material. For
example, in a typical fabric material each roving contains numerous individual
fibers (e.g.,
around 2,400 fibers). The thermoplastic prepregs may be saturated or fully
wetted with low
viscosity reactive thermoplastic resin material and in-situ polymerized. As
such, the resulting
product is likewise fully wetted or impregnated with the thermoplastic
material. The fully wetted
fiber strands of the prepregs can be expected to perform equivalent to, or
better than, those
used in conventional products.
[0056] An additional advantage of the present disclosure is that the final
thermoplastic
product may include two or more fiber orientations, typically within the same
layer, which is not
achievable with conventional wound thermoplastic products. As described
herein, the use of
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unidirectional tapes often does flot enable fibers to be placed or extend in a
longitudinal or axial
direction of the wound product since the tapes cannot be wound about the
product in an axial or
longitudinal direction.
[0057] Moreover, the thickness of the unidirectional tape is often
significantly lower than that
of the fabric-based prepregs described herein. For example, in unidirectional
tapes, the roving
is often spread laterally before the molten thermoplastic resin is applied.
The result is that the
unidirectional tape typically is very thin (e.g., 0.2 mm) and includes far
fewer individual fibers
than the instant prepreg materials. Given the higher density of the fibers
employed in the
instant prepregs, the thickness of the prepregs may be greater than those of
unidirectional
tapes. As such, winding of fabric-based prepregs may achieve the desired
thickness and
strength of the composite materials in a much higher throughput than thin
unidirectional tapes.
[0058] Further, when unidirectional tapes are employed, the tape is typically
wound at an
angle relative to the mandrel. This may result in the winding process being
interrupted several
times to properly orient the tape before winding the tape a subsequent time.
In contrast, the
instant prepregs that have multiple fiber orientations may allow the winding
process to be
performed continually without reorienting the prepreg. Stated differently, the
prepreg may be
continually wound about the mandrel to achieve a desired fiber orientation.
The prepreg may
also remain oriented circumferentially about the mandrel. For example, one or
more edges of
the prepreg may be parallel with the circumferential direction of the mandrel.
[0059] Methods
[0060] Conventional filament winding processes involve a curing or
polymerization process.
For example, conventional filament winding involves infusing a thermoset
material into a bundle
of dry filaments that is wound about a mandrel. The infusion of the thermoset
material may be
achieved by passing the bundle of dry filaments through a bath of the
thermoset resin material.
[0061] In contrast, the process herein involves a negligible amount of curing
or polymerization
since the fabric-based prepregs contain a polymerized thermoplastic resin. It
should be realized
that some minimal amount of curing or polymerization may occur since the
polymer resin
employed in the prepreg may not be entirely polymerized. However, any
polymerization that
does occur is insubstantial and is significantly less than that experienced in
conventional
systems employing thermoset materials that are uncured or unpolymerized. The
process
employed herein involves a mere heating/melting of the thermoplastic polymer
material and a
subsequent welding of the material. In some instances, the process may also
involve a cooling
and solidification of the thermoplastic polymer material.
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[0062] Referring now ta Fig. 7, illustrated is a method 700 of forming a
reinforced
thermoplastic product. At block 710, a fabric-based thermoplastic prepreg is
wound about a
mandrel. The thermoplastic prepreg may be wound around the mandrel one or more
times ta
form a plurality of layers of the thermoplastic prepreg around the mandrel.
The thermoplastic
prepreg includes a plurality of fiber bundles or rovings and a polymerized
thermoplastic material.
In some embodinnents, the rovings may be oriented accord ing ta a first
direction and a second
direction wherein the second direction is angled relative ta the first
direction. In some
embodiments, the polymerized thermoplastic material may fully impregnate each
fiber bundle of
the fa bric.
[0063] At block 720, heat is applied ta the thermoplastic prepreg along the
nip line as it is
wound about the mandrel ta at least partially melt or soften the polymerized
thermoplastic
material. At block 730, pressure is applied ta the at least partially melted
or softened
polymerized thermoplastic material of the prepreg sheet. At block 740, an
inner surface of an
outer thermoplastic prepreg layer is welded onto an outer surface of an inner
thermoplastic
prepreg layer. The method 700 does not involve curing or polymerization.
Rather, the method
700 involves heating of the thermoplastic material in order ta melt and weld
the thermoplastic
material. In some instances, the at least partially melted or softened
polymerized thermoplastic
material may be cooled following the welding of the prepreg layers.
[0064] In some instances, winding of the thermoplastic prepreg about the
mandrel is
perfornned without moving the thermoplastic prepreg axially or longitudinally
along the mandrel.
In such instances, the entire winding process, or a portion thereof, may be
performed in a single
continuous process ta the spec. ln some instances, the method may further
include aligning at
least some of the rovings with an axis or longitudinal direction of the
mandrel sa that said
rovings are aligned with the axis or longitudinal direction in the final
product. In some
instances, the mandrel may be maintained within an interior of the reinforced
thermoplastic
product after the completion of the winding process sa that the mandrel forms
part of, or is a
component of, the reinforced thermoplastic product.
[0065] Referring now ta Fig. 8, illustrated is another method 800 of forming a
reinforced
thermoplastic product. At block 810, a thermoplastic prepreg is positioned
atop previously
consolidated thermoplastic prepregs sa that the thermoplastic prepreg forms an
outer layer of
the reinforced thermoplastic product. The thermoplastic prepreg may include a
plurality of fiber
bundles that are oriented according ta a first direction and a second
direction with the second
direction having an angled orientation relative ta the first direction. The
thermoplastic prepreg
CA 2969929 2017-06-07
may have any configuration similar to the prepregs described herein. The
thermoplastic
prepreg may also have a polymerized thermoplastic material that partially or
fully impregnates
each fiber bundle of the plurality of fiber bundles as described herein.
[0066] At block 820, a pressure application component is moved along a top
surface of the
thermoplastic prepreg. At block 830, heat and pressure are applied to the
thermoplastic
prepreg as the pressure application component is moved along the top surface
thereof to at
least partially melt or soften the polymerized thermoplastic material. At
block 840, the at least
partially melted or softened polymerized thermoplastic material of the prepreg
sheet is welded
onto previously consolidated thermoplastic prepregs. The method 800 does not
involve curing
or polymerization. In some instances, the at least partially melted or
softened polymerized
thermoplastic may be cooled following the welding of the prepreg sheet onto
the previously
consolidated thermoplastic prepregs.
[0067] Having described several embodiments, if will be recognized by those of
skill in the art
that various modifications, alternative constructions, and equivalents may be
used without
departing from the spirit of the invention. Additionally, a number of well-
known processes and
elements have flot been described in order to avoid unnecessarily obscuring
the present
invention. Accordingly, the above description should flot be taken as limiting
the scope of the
invention.
[0068] VVhere a range of values is provided, it is understood that each
intervening value, to
the tenth of the unit of the lower limit unless the context clearly dictates
otherwise, between the
upper and lower limits of that range is also specifically disclosed. Each
smaller range between
any stated value or intervening value in a stated range and any other stated
or intervening value
in that stated range is encompassed. The upper and lower limits of these
smaller ranges may
independently be included or excluded in the range, and each range where
either, neither, or
bath limits are included in the smaller ranges is also encompassed within the
invention, subject
to any specifically excluded linnit in the stated range. VVhere the stated
range includes one or
bath of the limits, ranges excluding either or bath of those included limits
are also included.
[0069] As used herein and in the appended claims, the singular forms "a",
"an", and "the"
include plural referents unless the context clearly dictates otherwise. Thus,
for example,
reference to "a method" includes a plurality of such methods and reference to
"the glass fiber"
includes reference to one or more glass fibers and equivalents thereof known
to those skilled in
the art, and sa forth. The invention has now been described in detail for the
purposes of clarity
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and understanding. However, it will be appreciated that certain changes and
modifications may
be practice within the scope of the appended daims.
[0070] Also, the words "comprise," "comprising," "include," "including," and
"includes" when
used in this specification and in the following claims are intended ta specify
the presence of
stated features, integers, components, or steps, but they do flot preclude the
presence or
addition of one or more other features, integers, components, steps, acts, or
groups.
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