U.S. patent application number 14/642987 was filed with the patent office on 2016-09-15 for structured flock fiber reinforced layer.
The applicant listed for this patent is University of Massachusetts Dartmouth. Invention is credited to Yong K. Kim, Armand F. Lewis, John M. Rice.
Application Number | 20160265157 14/642987 |
Document ID | / |
Family ID | 56878970 |
Filed Date | 2016-09-15 |
United States Patent
Application |
20160265157 |
Kind Code |
A1 |
Rice; John M. ; et
al. |
September 15, 2016 |
STRUCTURED FLOCK FIBER REINFORCED LAYER
Abstract
Various embodiments of structured flock fiber reinforced layers
include fibrous organic polymer composite reinforcing materials
that have been "pre-flocked" with Z-Axis reinforcing fibers. These
"pre-flocked" fibrous materials (woven, knitted, mat, nonwoven or
pre-pregs) are then supplied as "off-the-shelf," "ready-to-use,"
already flock reinforced, dry to the touch, pre-manufactured,
storable, inventoried organic polymer composite structured flock
fiber reinforced layers that are ready as needed to be laid-up and
impregnated with matrix resin and cured to form fiber based
z-directional reinforced composites having enhanced inter-laminar
strength, impact toughness, transmission properties (electrical and
thermal conduction) and coefficient of thermal expansion are
provided. Methods for forming such reinforced layers are also
provided.
Inventors: |
Rice; John M.; (Portsmouth,
RI) ; Lewis; Armand F.; (Mattapoisett, MA) ;
Kim; Yong K.; (N. Dartmouth, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Massachusetts Dartmouth |
Boston |
MA |
US |
|
|
Family ID: |
56878970 |
Appl. No.: |
14/642987 |
Filed: |
March 10, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B32B 2262/106 20130101;
B32B 2262/0269 20130101; B32B 2605/16 20130101; B32B 2307/542
20130101; B32B 2260/023 20130101; B32B 2262/103 20130101; B32B
2260/046 20130101; B32B 2307/558 20130101; B32B 5/026 20130101;
B32B 2597/00 20130101; B32B 5/024 20130101; B32B 5/26 20130101;
B32B 2262/02 20130101; B32B 2405/00 20130101; B32B 2255/02
20130101; B32B 2605/18 20130101; B32B 2255/26 20130101; B32B
2250/20 20130101; C08J 5/24 20130101; B32B 2262/101 20130101; B32B
2262/0276 20130101; B32B 2307/58 20130101; B32B 2262/0261 20130101;
C08J 2363/00 20130101; B32B 2307/546 20130101; B32B 5/00 20130101;
B32B 5/10 20130101; D06N 7/0097 20130101; B32B 5/022 20130101; B32B
2307/718 20130101; B32B 2307/732 20130101; B32B 2571/02 20130101;
B32B 2307/724 20130101; B32B 27/12 20130101; B32B 2262/0253
20130101 |
International
Class: |
D06N 7/00 20060101
D06N007/00; D06N 3/14 20060101 D06N003/14; D06N 3/04 20060101
D06N003/04 |
Claims
1. A structured flock fiber reinforced layer comprising: a fibrous
laminar base-ply substrate comprising a plurality of fabric yarns
forming a plurality of interstices; a thin adhesive sizing layer
disposed on the fibrous laminar base-ply substrate; a plurality of
reinforcing flock fibers, a majority of which are oriented
substantially perpendicular to a first surface of the fibrous
laminar base-ply substrate, the substantially perpendicularly
oriented reinforcing flock fibers being partially embedded in the
plurality of interstices, wherein the plurality of reinforcing
flock fibers are bonded to surfaces of the plurality of fabric
yarns by the thin adhesive sizing layer for subsequent composite
ply material assembly; and wherein the sized and flocked fibrous
laminar base-ply substrate remains flexible to conform to contour
layups.
2. The structured flock fiber reinforced layer of claim 1, wherein
the thin adhesive sizing layer is a resin and comprises one of: a
sprayable polyurethane lacquer coating; a sprayable epoxy-based
lacquer coating; a sprayable water based acrylic adhesive; a dilute
water dip-able, water based acrylic adhesive; and a dilute solvent
based dip-able resin/lacquer coating system.
3. The structured flock fiber reinforced layer of claim 1, wherein
the plurality of a reinforcing flock fibers has a flock density of
about 70 fibers/mm.sup.2 to about 200 fibers/mm.sup.2.
4. The structured flock fiber reinforced layer of claim 1, wherein
the plurality of reinforcing flock fibers has an average fiber
length of about 0.5mm to about 2.0 mm.
5. The structured flock fiber reinforced layer of claim 1, wherein
the plurality of reinforcing flock fibers has an average fiber
fineness of about 1.0 denier to about 20 denier.
6. The structured flock fiber reinforced layer of claim 1, wherein
the plurality of reinforcing flock fibers are selected from a group
consisting of synthetic fibers, glass fibers, carbon fibers,
natural fibers, and metal fibers.
7. The structured flock fiber reinforced layer of claim 1 further
comprising a release sheet disposed adjacent to free ends of the
plurality of reinforcing flock fibers.
8. The structured flock fiber reinforced layer of claim 7 wherein
the release sheet comprises one of a thin, light-weight fabric
lightly flocked with a plurality of high denier packaging flock
fibers; and a thin, light-weight fabric lightly flocked with a
plurality of high denier packaging flock fibers; and wherein the
plurality of high denier packaging flock fibers are longer and
stiffer than the plurality of reinforcing flock fibers positioned
on the surface of the fibrous laminar base-ply substrate.
9. The structured flock fiber reinforced layer of claim 1 wherein
the majority of perpendicularly oriented reinforcing flock fibers
being are embedded in the fibrous laminar base-ply substrate to a
depth of approximately about 0.05 to about 0.1 mm.
10. A method for fabricating a flock fiber composite reinforcement
layer comprising: applying a thin coating of resinous flock
adhesive sizing to a dry substrate, the dry substrate comprising a
plurality of fabric yarns forming a plurality of interstices; and
flocking a plurality of reinforcing flock fibers onto a first
surface of the sized dry substrate comprising: embedding the
plurality of reinforcing flock fibers into the plurality of
interstices while the resinous flock adhesive sizing is still
fluidic and uncured; and attaching the plurality of reinforcing
flock fibers to surfaces of the plurality of fabric yarns by curing
the adhesive sizing.
11. The method of claim 10, wherein flocking a plurality of
reinforcing flock fibers further comprises one of: vacuum assisted
flocking (VAF); shaking and vibration assisted flocking (SAF); and
a combination of VAF and SAF.
12. The method of claim 10, wherein the resinous flock adhesive
sizing comprises one of: a water based acrylic adhesive; a
sprayable polyurethane lacquer coating; a sprayable epoxy-based
lacquer coating; a sprayable water based acrylic adhesive; a dilute
water dip-able, water based acrylic adhesive; and a dilute solvent
based dip-able resin/lacquer coating system.
13. The method of claim 10, wherein applying a thin coating of
resinous flock adhesive sizing to the dry substrate comprises
applying uncured resinous flock adhesive sizing at a thickness of
about 0.01 mm to about 0.05 mm.
14. The method of claim 10, further comprising applying a release
sheet adjacent to free ends of the plurality of the flocked
reinforcing flock fibers.
15. A structured flock fiber reinforced layer comprising: a
pre-preg composite reinforcement ply layer structure, including a
B-staged epoxy matrix outer surface; a plurality of reinforcing
flock fibers, a majority of which are oriented substantially
perpendicular to a first surface of the pre-preg composite
reinforcement ply structure, the majority of substantially
perpendicularly oriented reinforcing flock fibers being partially
embedded in the B-staged epoxy matrix outer surface of the B-staged
epoxy resin pre-preg composite reinforcement ply structure, wherein
the plurality of reinforcing flock fibers are secured in place
within the B-staged epoxy matrix outer surface for subsequent
composite ply material assembly; and wherein the pre-preg composite
reinforcement ply structure remains flexible to conform contour
layups.
16. A method for fabricating a flock fiber composite reinforcement
layer comprising: providing a pre-preg composite reinforcement ply
structure, including B-stage epoxy matrix; softening the B-stage
epoxy matrix of the pre-preg composite reinforcement ply structure
to lower a B-stage epoxy matrix viscosity forming a tacky surface;
and flocking a plurality of reinforcing flock fibers onto a first
surface of the pre-preg composite reinforcement ply structure such
that the plurality of reinforcing flock fibers penetrate an outer
surface of the B-staged epoxy matrix.
17. The method of claim 16, wherein softening the B-stage epoxy
matrix comprises heating the B-stage epoxy matrix after the
pre-preg composite reinforcement ply structure is initially
manufactured; and further comprising cooling down the epoxy matrix
of the pre-preg composite reinforcement ply structure.
18. The method of claim 17, wherein heating the epoxy matrix of the
pre-preg composite reinforcement ply structure comprises heating
the B-staged epoxy matrix such that the B-staged epoxy matrix
becomes tacky enough to accept impinging flock fibers while the
pre-preg composite reinforcement ply structure remains partially
uncured.
19. The method of claim 18, wherein heating the epoxy matrix of the
pre-preg composite reinforcement ply structure comprises heating
the epoxy matrix to a maximum temperatures of about 65.degree.
C.
20. The method of claim 16, wherein flocking a plurality of
reinforcing flock fibers comprises up-flocking; and wherein the
method further comprises: orienting the flocked pre-preg composite
reinforcement ply structure, flock side down; and shaking the
composite reinforcement layer vigorously to remove unsecured flock
fibers; and refreezing the composite reinforcement layer to inhibit
further curing of the B-staged epoxy matrix of the pre-preg
composite reinforcement ply structure.
21. The method of claim 16, wherein softening the B-stage epoxy
matrix comprises: spraying the pre-preg surface with a solvent for
the B-staged epoxy matrix; and applying a thin coating of B-staged
epoxy resin to the surface of the pre-preg composite reinforcement
ply structure.
Description
RELATED APPLICATION(S)
[0001] This application is related to U.S. Provisional Patent
Application Ser. No. 60/863,680, filed on Oct. 31, 2006, entitled
"Fabric Based Laminar Composite and Method for Manufacture
Thereof," and U.S. patent application Ser. No. 11/931,416, filed on
Oct. 31, 2007, entitled "Materials Methodology To Improve The
Delamination Strength Of Laminar Composites," issued as U.S. Pat.
No. 7,981,495 on Jul. 19, 2011. The entire teachings and contents
of these Patent Applications are hereby incorporated by reference
herein in their entirety.
FIELD OF USE
[0002] The present disclosure relates to structured flock fiber
reinforced layers used to manufacture fabric based laminar
composites showing high inter-laminar strength, in particular to
z-axis oriented, structured flock fiber reinforced layers.
BACKGROUND
[0003] Delamination of layered fabric-reinforced composites
represents one of the most prevalent structural, life-limiting
failure modes of such materials. As an example, Organic Polymer
Laminar Composite (OPLC) materials based on layered fabrics have
many advantageous property and processing features. However, one
structural drawback is their generally poor interlaminar shear
strength. Layered OPLCs have little or no fiber reinforcement in
the thickness direction. Therefore, their inter-ply strength is
less than their longitudinal strength which can result in poor
impact and/or inter-laminar flexural fatigue strength.
[0004] Various techniques have been introduced to enhance the
inter-laminar strength of layered composite materials. A common
technique is to use a rubber-toughened matrix material resin.
However, these resins are generally not thermally durable. An
alternative approach is to manufacture special pre-forms using
advanced textile technologies such as 3-D knitting/weaving/braiding
or through-the-fabric stitching/pinning processes. However, these
methods are slow, inefficient, and expensive. While fabricated
pre-forms may include yarns in a z-directional orientation, these
reinforcements are generally not conducive to an optimized stress
distribution in the mechanically functioning structure component.
Such 3-D structures are prone to stress concentrations under
mechanical service leading to poor fatigue resistance. These
approaches appear to work in their primary goal, but they degrade
the composite's in-plane properties.
[0005] Furthermore, Kim et al., "Fracture Toughness of Flock
Reinforced Layered Composites", Proceedings of 1.sup.st Industrial
Simulation Conference 2003, Jun. 9-11, UPV, Valencia, Spain, p.
477-482 (2003) and Kim et al., "Through-Thickness Reinforcement of
Laminar Composites", Journal of Advanced Materials", Vol. 36, no.
3, July 2004, pp 25-31, the entirety of these references hereby
incorporated herein by reference, disclose that composites
reinforced with z-directional fibers appear to have the potential
to exhibit improved inter-laminar strength. However, z-directional
reinforcement remains highly unpredictable due to the large number
of variables (e.g., fiber type, flock fiber density (the number of
perpendicularly-oriented flock fibers per unit area of interface
between the substrates), fiber denier (mass in grams per 9000 m),
fiber length, binder resin type, bonding strength between fiber and
binder resin, etc.) present in such a composite. As a result, many
such composites do not show improved inter-laminar shear properties
and/or suffer a decrease in toughness.
[0006] Conventional fiber reinforcement for organic polymer
composites include the flocking of short Z-Axis reinforcing fibers
onto individual (uncured) resin impregnated fibrous layers, for
example, woven fabric, nonwoven random mat, and pre-impregnated
fabrics (pre-preg). When these flock fiber z-axis containing
fibrous layers are consolidated into a so-called "wet lay-up"
laminar assembly, this Z-Axis reinforced organic polymer organic
structure is subsequently cured in a heated laminating press (or
autoclave under "vacuum bagging") type process. The resulting
Z-Axis reinforced by flock fibers composite material was found to
have dramatically improved inter-laminar shear strength and impact
resistance.
[0007] Reinforcing fibers are re-arranged or placed so that they
can bridge across the laminar plies. This could lead to a more
structurally isotropic laminate. In pursuing this approach, special
pre-form fabrics were fabricated using advanced textile
technologies such as multi-directional knitting, 3-D weaving or
through-the-fabric stitching and pinning processes. While these
methods are found to be slow, they resulted in the desired 3-D
orientation of yarn fibers in the reinforcing fabric's structure.
Unfortunately, these methods are very expensive as well as design
restrictive; they also have scalability difficulties. Furthermore,
these 3-D fiber orientations are usually not conducive to optimized
strength utilization of the parent yarn due to the obliqueness at
the yarn structure's interlacing points. Therefore, some of these
3-D structures are prone to stress concentrations under mechanical
service leading to poor fatigue resistance. All these approaches
work in their special application area but in many cases they often
degrade the composite's in-plane properties. This is especially
true for the through-thickness textile stitching methods.
Therefore, there is a need in the art for a composite showing
improved characteristics such as inter-laminar shear strength
and/or fracture toughness and corresponding sub structures which
facilitate the manufacture of these composites.
SUMMARY
[0008] Various embodiments of structured flock fiber reinforced
layers include fibrous organic polymer composite reinforcing
materials that have been "pre-flocked" with Z-Axis reinforcing
fibers. These "pre-flocked" fibrous materials (woven, knitted, mat,
nonwoven or pre-pregs) are then supplied as "off-the-shelf,"
"ready-to-use," already flock reinforced, dry to the touch,
pre-manufactured, storable, inventoried organic polymer composite
structured flock fiber reinforced layers that are ready as needed
to be laid-up and impregnated with matrix resin and cured.
[0009] In one embodiment, a structured flock fiber reinforced layer
(referred to as TYPE 1) includes a fibrous laminar base-ply
substrate comprising a plurality of fabric yarns forming a
plurality of interstices, a thin adhesive sizing layer disposed on
the fibrous laminar base-ply substrate, a plurality of reinforcing
flock fibers, a majority of which are oriented substantially
perpendicular to a first surface of the fibrous laminar base-ply
substrate, the substantially perpendicularly oriented reinforcing
flock fibers being partially embedded in the plurality of
interstices, wherein the plurality of reinforcing flock fibers are
bonded to surfaces of the plurality of fabric yarns by the thin
adhesive sizing layer for subsequent composite ply material
assembly and the sized and flocked fibrous laminar base-ply
substrate remains flexible to conform to contour layups. Such
reinforced layers can be combined to produce z-directional fiber
reinforced composites exhibiting enhanced properties (e.g.,
inter-laminar strength, toughness).
[0010] In another embodiment, a structured flock fiber reinforced
layer (referred to as TYPE 2) includes a pre-preg composite
reinforcement ply layer structure, including a B-staged epoxy
matrix outer surface; a plurality of reinforcing flock fibers, a
majority of which are oriented substantially perpendicular to a
first surface of the pre-preg composite reinforcement ply
structure, the substantially perpendicularly oriented reinforcing
flock fibers being partially embedded in the B-staged epoxy matrix
outer surface of the B-staged epoxy resin pre-preg composite
reinforcement ply structure, wherein the plurality of reinforcing
flock fibers are secured in place within the B-staged epoxy matrix
outer surface for subsequent composite ply material assembly and
the pre-preg composite reinforcement ply structure remains flexible
to conform contour layups.
[0011] In another embodiment, a technique for fabricating a flock
fiber composite reinforcement layer includes applying a thin
coating of resinous flock adhesive sizing to a dry substrate, the
dry substrate comprising a plurality of fabric yarns forming a
plurality of interstices and flocking a plurality of reinforcing
flock fibers onto a first surface of the sized dry substrate.
Flocking includes embedding the plurality of reinforcing flock
fibers into the plurality of interstices while the resinous flock
adhesive sizing is still fluidic and uncured and attaching the
plurality of reinforcing flock fibers to surfaces of the plurality
of fabric yarns by curing the adhesive sizing.
[0012] In yet another embodiment, a technique for fabricating a
flock fiber composite reinforcement layer includes providing a
pre-preg composite reinforcement ply structure, including B-stage
epoxy matrix, softening the B-stage epoxy matrix of the pre-preg
composite reinforcement ply structure to lower a B-stage epoxy
matrix viscosity forming a tacky surface; and flocking a plurality
of reinforcing flock fibers onto a first surface of the pre-preg
composite reinforcement ply structure such that the plurality of
reinforcing flock fibers penetrate an outer surface of the B-staged
epoxy matrix.
[0013] Both TYPE 1 and TYPE 2 pre-flocked fibrous reinforcing
layers provide the material for fabricating high laminar shear
strength organic polymer composites which have many applications.
Potential applications include: aerospace, aircraft, marine
structures, ship hulls, military ballistic plate/panel manufacture
and many other applications. Embodiments of Z-Axis pre-flocked
fibrous reinforcing layers allow manufacturers to avoid getting
involved with the intricacies of the flocking processes within
their manufacturing plant or operation. Compared to conventional
non-Z-axis reinforced composites, composites fabricated with
pre-flocked fibrous reinforcing layers have an increase in
inter-laminar shear strength. When manufacture design and fabricate
laminar composites using pre-flocked fibrous reinforcing layers
lay-up, the inter-laminar plies of the finished composite lay-up
will be rendered Z-axis reinforced. A manufacturer does not have to
do their own flocking capability or be concerned with flocking
quality when using TYPE 1 and TYPE 2 pre-flocked fibrous
reinforced/ reinforcing layers disclosed herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of embodiments of the invention, as illustrated in the
accompanying drawings and figures in which like reference
characters refer to the same parts throughout the different views.
The drawings are not necessarily to scale, with emphasis instead
being placed upon illustrating the embodiments, principles and
concepts of the invention. These and other features of the
invention will be understood from the description and claims
herein, taken together with the drawings of illustrative
embodiments, wherein:
[0015] FIG. 1A schematically illustrates an exemplary embodiment of
multiple structured flock fiber reinforced layers before being
combined to form a z-directional fiber based reinforced
composite;
[0016] FIG. 1B schematically illustrates the multiple structured
flock fiber reinforced layers of FIG. 1 after being combined to
form a z-directional fiber based reinforced composite;
[0017] FIG. 1C schematically illustrates an exemplary embodiment of
a double sided structured flock fiber reinforced layer;
[0018] FIG. 1D schematically illustrates an exemplary embodiment of
the double sided structured flock fiber reinforced layer of FIG.
1D, inter-layered or inter-leaved with non-structured flock
reinforced fibrous layers;
[0019] FIG. 2 is a side view of an exemplary embodiment of a dry
substrate structured flock fiber reinforced layer;
[0020] FIG. 3 is a cross sectional view (along section 3-3) of the
dry substrate structured flock fiber reinforced layer of FIG. 2
showing a thin adhesive sizing layer disposed on the dry fibrous
laminar base-ply substrate;
[0021] FIG. 4 is a side view of an exemplary embodiment of a
pre-preg substrate structured flock fiber reinforced layer;
[0022] FIG. 5 is a cross sectional view (along section 5-5) of the
pre-preg substrate structured flock fiber reinforced layer of FIG.
4 showing the flock fibers embedded in the B-staged epoxy matrix of
the pre-preg fibrous laminar base-ply substrate; and
[0023] FIG. 6 is a top view of an exemplary embodiment of a woven
dry substrate structured flock fiber reinforced layer showing a
thin adhesive sizing layer disposed on the dry fibrous laminar
base-ply woven substrate.
DETAILED DESCRIPTION
[0024] Certain exemplary embodiments will now be described to
provide an overall understanding of the principles of the
structure, function, manufacture, and use of the reinforced layers
and methods of fabrication disclosed herein. One or more examples
of these embodiments are illustrated in the accompanying drawings.
Those skilled in the art will understand that the reinforced layers
and methods specifically described herein and illustrated in the
accompanying drawings are non-limiting embodiments and that the
scope of the present disclosure is defined solely by the claims.
The features illustrated or described in connection with one
embodiment may be combined with the features of other embodiments.
Such modifications and variations are intended to be included
within the scope of the present disclosure.
[0025] In general, the present disclosure provides fiber based
z-directional reinforced layers specifically configured and
optimized to allow manufacturers to employ flocked Z-Axis
reinforced layer materials without getting involved with any in the
intricacies of flocking processes within their manufacturing plant
or operation. Off-the-shelf availability of Z-Axis fiber modified
organic polymer fibrous reinforcing materials is facilitated by
embodiments disclosed herein.
[0026] The inventors have discovered that fracture toughness
(inter-laminar shear strength) of organic polymer laminar
composites (OPLC) can be improved by applying Z-Axis oriented flock
fibers to the interfacial zones of the composites and have
demonstrated several Z-Axis reinforcement application processes
functionally applicable to their use in OPLC fabrication. In one
embodiment, a "pre-flocking" process is an efficient technique for
introducing Z-Axis flock fibers into a fabricated OPLC.
[0027] Now referring to FIG. 1A, multiple structured flock fiber
reinforced layer 100a-100n (commonly referred to as reinforced
layers 100) before being laid up to form composite 10. Here the
layers 100 are shown with release sheets 104 disposed adjacent to
the free ends of a plurality of reinforcing flock fibers 110. In
one embodiment the release sheets include but are not limited to a
thin, light-weight fabric lightly flocked with high denier
packaging flock fibers and a thin, light-weight fabric lightly
flocked with high denier packaging flock fibers. The high denier
packaging flock fibers are longer and stiffer than the reinforcing
flock fibers 110 positioned on the surface of the pre-flocked
substrate layer.
[0028] The structured flock fiber reinforced layers for organic
polymer laminar composites can be groups into two basic fibrous
material types. TYPE-1: "Bare", as-received from the textile mill,
woven and knitted yarn fabrics, nonwoven fabrics and fibrous (open)
mat products, and TYPE 2: so-called pre-preg composite reinforcing
layers. The primary types of fibers that can be used to prepare
TYPE 1 and TYPE 2 base "pre-flocked" reinforcing layers, include
but are not limited to glass, carbon, polyaramid (Kevlar.RTM.)
based textile fibers and generally yarns. In the TYPE 2 pre-flocks,
the main resin composition here would be "B" staged epoxy
resin--also the pre-preg's fiber yarn that is imbedded in the "B"
staged epoxy resin is unidirectional yarn, woven fabric and chopped
fiber mat type fiber reinforcement geometry. The methodology for
fabricating TYPE 1 and TYPE 2 pre-flocked composite reinforcement
entities is described below in more detail. "Pre-Flocking" of OPLC
structured flock fiber reinforced layers before they are assembled
into a laminar composite is an effective way of introducing flocked
Z-Axis fibers into an OPLC structure.
[0029] FIG. 1B shows a finished OPLC after the release sheets have
been removed, the layers 100 have been combined with a non-flocked
substrate 106 and the combined laminar configuration 20 is then, in
one embodiment, impregnated (throughout) with the liquid matrix
resin 140 and this stack of Z-axis fiber reinforced fibrous plies
are then consolidated by a vacuum bag or flat-press curing
process.
[0030] FIG. 1C shows double-sided structured flock fiber reinforced
layer 102 (also referred to as a double sided pre-Flocked
reinforcement fabric ply DSP). In one embodiment, a double-sided
flock fiber structured reinforced layer is fabricated by applying
an un-cured layer of adhesive sizing resin to both opposed surfaces
of the substrate, and then flocking reinforcing fibers onto both
opposed coated surfaces of a fibrous laminar base-ply substrate
130.
[0031] FIG. 1D shows the double-sided structured flock fiber
reinforced layer 102 inter-layered (inter-leaved) with
non-structured flock reinforced fibrous layers (SNF) 106 in an
SNF/DSP/SNF/DSP/SNF lay-up configuration before a matrix resin is
applied. It is understood that in various embodiments DSPs can be
combined with SNF layers of different compositions and in different
lay-up configurations.
[0032] Now referring to FIG. 2, a structured flock fiber reinforced
layer 100 includes a fibrous laminar base-ply substrate 130, a thin
adhesive sizing layer 120 disposed on the fibrous laminar base-ply
substrate 130, a plurality of reinforcing flock fibers 110a-110n
(commonly referred to as reinforcing flock fibers 110), a majority
of which are oriented substantially perpendicular to a first
surface 128 of the fibrous laminar base-ply substrate 130. In one
embodiment, the fibrous laminar base-ply substrate 130 is a fibrous
mat and in another embodiment it is similar to the non-flocked
substrate 106. During the manufacturing process the fibrous laminar
base-ply substrate 130 is coated with a thin adhesive sizing layer
120 which in one embodiment is fluid before the flock fibers are
attached and subsequently cured to attach the flock fibers in
place. In one embodiment, the thin adhesive sizing layer is a
resin, including but not limited to a sprayable polyurethane
lacquer coating, a sprayable epoxy-based lacquer coating, a
sprayable water based acrylic adhesive, a dilute water dip-able,
water based acrylic adhesive and a dilute solvent based dip-able
resin/lacquer coating system.
[0033] In one embodiment, the flock density of the reinforcing
flock fibers is about 70 fibers/mm.sup.2 to about 200
fibers/mm.sup.2. In another embodiment, the reinforcing flock
fibers have an average fiber length of about 0.5 mm to about 2.0
mm. In yet another embodiment, the reinforcing flock fibers have an
average fiber fineness of about 1.0 denier to about 20 denier. The
flock fibers include, but are not limited to synthetic fibers,
glass fibers, carbon fibers, natural fibers, and metal fibers.
[0034] An exemplary manufacturing process generally includes
applying a thin coating of resinous flock adhesive sizing to a dry
fibrous substrate and flocking a plurality of reinforcing flock
fibers onto a first surface of the sized dry substrate. The dry
substrate includes a plurality of fabric yarns forming a plurality
of interstices. The flocking step includes embedding the
reinforcing flock fibers into the interstices and attaching the
plurality of reinforcing flock fibers to surfaces of the plurality
of fabric yarns while the resinous flock adhesive sizing is still
fluidic and uncured. Flocking the reinforcing flock fibers can be
accomplished by various techniques including, but not limited to,
vacuum assisted flocking (VAF), shaking and vibration assisted
flocking (SAF) and a combination of VAF and SAF. The resinous flock
adhesive sizing includes, but is not limited to: [0035] a water
based acrylic adhesive; [0036] a sprayable polyurethane lacquer
coating; [0037] a sprayable epoxy-based lacquer coating; [0038] a
sprayable water based acrylic adhesive; [0039] a dilute water
dip-able, water based acrylic adhesive; and [0040] a dilute solvent
based dip-able resin/lacquer coating system. In one embodiment,
applying a thin coating of resinous flock adhesive sizing to the
dry substrate includes applying uncured resinous flock adhesive
sizing at a thickness of about 0.01 mm to about 0.05 mm.
[0041] FIG. 3 shows a cross sectional view (along section 3-3) of
the dry substrate structured flock fiber reinforced layer 100 of
FIG. 2 showing a thin adhesive sizing layer 120 disposed on the dry
fibrous laminar base-ply substrate 130. In this embodiment the dry
fibrous laminar base-ply substrate 130 includes multiple fabric
yarns 134 which can have multiple filaments 136 and can also have
individual filaments 132 forming multiple interstices 210. The
substantially perpendicularly oriented reinforcing flock fibers 110
are partially embedded in the plurality of interstices 210. Some
reinforcing flock fibers (e.g., reinforcing flock fiber 110h) are
attached to a top surface of the filaments 132 or yarns 134 of the
dry fibrous laminar base-ply substrate 130. The reinforcing flock
fibers 110 are attached to surfaces of the plurality of fabric
yarns 134, and filaments 132 by the thin adhesive sizing layer 120
for subsequent composite ply material assembly. The amount of
adhesive sizing and processing of the flock fiber reinforced layer
100 allows the flock fiber reinforced layer 100 (i.e., the sized
and flocked fibrous laminar base-ply substrate) to remain flexible,
open and porous to conform to contour-shaped layups.
[0042] Now referring to FIG. 4, a structured flock fiber reinforced
layer 400 similar to the structured flock fiber reinforced layer
100 of FIG. 2 includes a pre-preg fibrous laminar base-ply
substrate 430, a B-staged epoxy matrix outer surface 420 of the
pre-preg fibrous laminar base-ply substrate 430, reinforcing flock
fibers 110, a majority of which are oriented substantially
perpendicular to a first surface 428 of the pre-preg fibrous
laminar base-ply substrate 430.
[0043] During the manufacturing process the pre-preg fibrous
laminar base-ply substrate 430 is processed such that the
reinforcing flock fibers 110 are partially embedded in the B-staged
epoxy matrix outer surface 420. In one embodiment, the matrix outer
surface 420 (top layer) of the pre-preg fibrous laminar base-ply
substrate 430 includes a portion of a B-staged epoxy matrix of the
pre-preg fibrous laminar base-ply substrate 430 which has been
processed (e.g., by careful heating) so that the reinforcing flock
fibers 110 can be embedded (by flocking) into the pre-preg fibrous
laminar base-ply substrate 430.
[0044] FIG. 5 shows a cross sectional view (along section 5-5) of
the structured flock fiber reinforced layer 400 of FIG. 4 showing
the B-staged epoxy matrix outer surface 420 on the dry fibrous
laminar base-ply substrate 130. In this embodiment the pre-preg
fibrous laminar base-ply substrate 430 includes multiple fabric
yarns 134 which can have multiple filaments 136 and can also have
individual filaments 132 embedded in B-staged epoxy matrix 432. The
substantially perpendicularly oriented reinforcing flock fibers 110
are partially embedded in the B-staged epoxy matrix outer surface
420 for subsequent composite ply material assembly. The structured
flock fiber reinforced layer 400 is processed to remain flexible in
order to conform to contour layups.
[0045] Now referring to FIG. 6, a structured flock fiber reinforced
layer 600 similar to the structured flock fiber reinforced layer
100 of FIG. 2 includes a woven fibrous laminar base-ply substrate
630 including horizontal fibers 634a-634l and vertical fibers
632a-632k forming interstices 610, a thin adhesive sizing layer 120
disposed on the woven fibrous laminar base-ply substrate 630, a
plurality of reinforcing flock fibers 110a - 110n (commonly
referred to as reinforcing flock fibers 110), a majority of which
are oriented substantially perpendicular to the woven fibrous
laminar base-ply substrate 630. During the manufacturing process
the fibrous laminar base-ply substrate 130 is coated with a thin
adhesive sizing layer 120.
Dry Substrate and Pre-Preg Embodiments
[0046] Z-Axis "pre-flocked" structured flock fiber reinforced
layers can be grouped into two base/substrate fibrous material
types. The structural and composition details and the fabrication
methodology for these two exemplary types of pre-flocked structured
flock fiber reinforced layers are described in more detail
below.
Pre-Flocked Type 1
[0047] The primary types of fibers that can be used to prepare TYPE
1 base "pre-flocked" reinforcing/flock support layers are glass,
carbon, polyaramid (Kevlar.RTM.) based textile fibers and yarns.
Reinforcing fibrous "geometries" that can be pre-flocked include:
fibrous mats (long fiber and short fiber), woven and knitted
fabrics, and loosely consolidated nonwoven fabrics. Reinforcing
flock fibers that can be pre-flocked include, but are not limited
to: nylon, polyester, carbon, graphite, and polyolefin.
Pre-Flocked Preparation Methodology
[0048] Exemplary TYPE 1 fibrous base reinforcement materials
include reasonably-loose, consolidated, breathable, semi-open fiber
structures. In one embodiment the fibrous substrate includes
interstices (e.g., an open mesh texture) so that the reinforcing
flock fibers 110 can penetrate into the fibrous structure. The
deeper the reinforcing flock fibers 110 are embedded into the
fibrous base material structure the stronger the reinforcing effect
is achieved by these Z-Axis reinforcing flock fibers 110 when
subsequently used in fabricating composite materials.
[0049] The following are exemplary steps for preparing pre-flocked
TYPE 1 structured flock fiber reinforced layers: [0050] (a) Apply
thin adhesive sizing layer onto the fibrous laminar base-ply
substrate 130. This step sizes (e.g., lightly coats) the fibrous
laminar base-ply substrate with a thin resinous (e.g., sticky)
coating. One principle of fabricating pre-flocked Type 1 structured
flock fiber reinforced layers is to flock these "bare" structured
flock fiber reinforced layer using a thin adhesive sizing layer.
The thin adhesive sizing layer attaches these Z-Axis reinforcing
flock fibers 110 in an upright position. These reinforcing flock
fibers 110 are attached to the substrate surface (e.g., sides and
top surfaces to the filaments and yarns) such that the reinforcing
flock fibers 110 will not shake or drop off the surface during
normal packaging, storing, shipping, typical handling and
fabrication lay-up manipulations. These reinforcing flock fibers
110 need not be attached to their substrate surface in a permanent
manner. The adhesive sizing is also referred to as resinous coating
materials or pre-flock fiber securing adhesives.
[0051] This use of the thin adhesive sizing coatings in the context
of pre-flocked fibrous reinforcement layer are chosen to assure
that the presence of the resinous coating does not adversely affect
the mechanical properties of the final organic polymer engineering
composite material. Therefore, the polymer chemical nature of the
pre-flock fiber adhesive sizing is selected to be compatible with
the chemistry of the resinous matrix material. In various
embodiments, polyurethane (spray-able) lacquer coatings have been
successfully used. In other embodiments, an epoxy coating system,
EV-400 Epoxy Varnish from Polyfiber Aircraft Coatings is used.
Additionally water based acrylic adhesives are also used as a
pre-flock fiber securing adhesive.
[0052] In one embodiment, the average thicknesses of the thin
adhesive sizing layer disposed on the fibrous laminar base-ply
substrate fabric ranges from about 0.017 mm to about 0.038 mm with
an intermediate thickness of about 0.026 mm. This corresponds to an
areal mass density of about 0.00002 gm/mm.sup.2 to about an areal
mass density of about 0.00004 gm/mm.sup.2 with an intermediate
areal mass density of about 0.000029 gm/mm.sup.2; where the mass
density of the epoxy varnish is about 0.00114 gm/mm.sup.3. [0053]
(b) Applying reinforcing flock fibers 110 onto the resin coated
surfaces of the fibrous laminar base-ply substrate 130: The elapsed
time between adhesive size coating the fibrous laminar base-ply
substrate 130 and flocking (applying) reinforcing flock fibers 110,
in one embodiment, is kept to a minimum so that the reinforcing
flock fibers 110 contact the resin coated surfaces of the fibrous
laminar base-ply substrate 130 before the thin adhesive sizing
layer dries or cures depending on the type of adhesive sizing. This
is especially true if the size-coating resin system is contains
solvent or is solvent based. This applied resinous coating must be
in a fluid "sticky" state when the flocking process commences.
There is also the need for the reinforcing flock fibers 110 to
penetrate as deeply as possible into the fibrous laminar base-ply
substrate's structure. It is also desirable for the for reinforcing
flock fibers to be applied at a low to moderate flock density,
about 70 to about 200 fibers/mm.sup.2. In addition to embedding the
reinforcing flock fibers 110 it is understood that some of the
reinforcing flock fibers 110 will be applied to top surfaces of the
plurality of fabric yarns in the fibrous laminar base-ply substrate
130.
[0054] Several flock processing methods are used to assure the
maximum penetration of the flock fibers into the fibrous laminar
base-ply substrate's interstices. Exemplary processes are (1)
Vacuum Assisted Flocking (VAF); (2) Shaking (or vibration) Assisted
Flocking (SAF), and (3) a combination of VAF and SAF. These
flocking processes take advantage of the open porosity and
breathability of these thinly resin coated and sized fibrous
structures. These processes provide a suction or vacuum force that
(during the flocking process) which sucks the impinging flock
fibers deeper into the fibrous laminar base-ply substrate's
interstices and spaces; shaking or vibrating the fibrous mass also
causes the interstices to oscillate/move back-and-fourth and
therefore allows the impinging reinforcing flock fibers 110 to be
embedded more deeply into the fibrous laminar base-ply substrate's
interstices. [0055] (c) Attaching the reinforcing flock fibers:
After the flocking procedure, the flocked fibrous layer is cured
(i.e., curing the adhesive sizing) undisturbed on a flat surface.
In one embodiment, this is done at room temperature. After a
quiescent "setting" period, that could last, for example, up to 16
hours, the flocked on reinforcing flock fibers 110 should be
attached to the fibrous laminar base-ply substrate 130. The flocked
surface is then vacuumed to remove any loose, unattached
reinforcing flock fibers. Finally, in one embodiment, these
vacuumed "pre-flocked" surfaces are then transferred to an oven
cure for a final cure (or solvent evaporation). This oven cure
evaporates off solvent to reinforce the attachment of the Z-Axis
reinforcing flock fibers 110 to the fibrous laminar base-ply
substrate's structure. The pre-flocked composite flock fiber
composite reinforcement layer 100 is then ready for packing and
storage. [0056] (d) Packing and Storing "Pre-Flocked Fibrous
Reinforcement Layers: In one embodiment, after the final curing
step the material is ready to be cut into inventory-able sheets or
carefully rolled up into a loose coil. In some embodiment, the
pre-flocked surfaces are kept separated from each other using a
release sheet 104. The release sheet 104, similar to release paper
or polymer film is used to separate the "dry" stacked up
pre-flocked layers. Care is taken not to stack the pre-flocked
layers too high so as to "Crush" the Z-Axis oriented reinforcing
flock fibers 110. These pre-flocked fibrous reinforcement sheets
are treated with care and not submitted to abrasion or rough
touching. The attached reinforcing flock fibers 110 are attached to
the fibrous laminar base-ply substrate 130 with a minimum of
adhesive sizing as to not adversely affect the chemical make-up,
fibrous porosity, mesh or mat openness and mechanical integrity of
the final composite's matrix resin. The thin pre-flock adhesive
sizing coatings also help in assuring that the lay-up flexibility
of the fibrous composite reinforcement layer material will not be
adversely affected. It is desirable that the lay-up flexibility of
these Pre-Flocked reinforcement layers be similar to
non-pre-flocked reinforcement layer material. [0057] (e) Pre-Flock
Storing and Shipping Separator/Release Sheet Material:
[0058] Pre-Flocked materials are stored and shipped in either flat
sheet or roll form. The release sheet 104 is placed between the
stacked or rolled up Pre-Flocked sheets. In one embodiment, thin,
light-weight fabric or film material that is lightly flocked with
longer, stiff flock fibers is used as the release sheet during the
storage and shipping of the pre-flocked structured flock fiber
reinforced layer. The release sheet materials include, but are not
limit to, a light weight polyester or nylon nonwoven fabric base
and a base nonwoven fabric will be flocked with 40 to 60 Denier
Polyester or nylon flock fibers. The length of these flocked fibers
on the release sheet are, in one embodiment, at least 25 percent
longer than the length of the reinforcing flock fibers. The flock
density of the flocked release sheet is in the range of 2 to 50
fibers per square millimeter. The flock adhesive for the release
sheet can be flexible water based acrylic or polyurethane based. In
another embodiment, the release sheet is coated or finished with a
chemical release coat (e.g., silicone, fluorocarbon) as a final
treatment. This assures that there is an easy release from the
structured flock fiber reinforced layers. The release sheets
described above are generally re-useable and low cost. Generally
the release sheets protect the pre-flocked structured flock fiber
reinforced layer from being crushed or damaged during warehouse
storage and material shipping. The long-stiff and sparsely
positioned release sheet flock fibers penetrate the pre-flocked
structured flock fiber reinforced layers and serve as a stand-off
to protect against any damaging abrasions and compressions that
might occur during the handling, storage and shipping of
pre-flocked structured flock fiber reinforced layers.
Pre-Flocked Type 2
[0059] These TYPE 2 structured flock fiber reinforced layers are
fabricated using epoxy pre-preg composite reinforcement ply layer
structures. The primary types of reinforcing fibers that in
pre-preg composite reinforcement ply layer structures include, but
are not limited to, glass, carbon and polyaramid (Kevlar.RTM.)
based textile fibers and yarns impregnated with "B" staged epoxy
resin. These pre-preg reinforcing fibers or yarns imbedded in the
"B" staged epoxy resin can be positioned in the resin as
unidirectional yarn, woven fabric or chopped fiber mat type fiber
reinforcement geometry. Reinforcing flock fibers that can be used
for z-axis flocking include, but are not limited to, nylon,
polyester, carbon, graphite, polyolefin and metal.
Type 2 Pre-Flocked Preparation Methodology
[0060] Steps in Preparing Pre-Flocked Type 2 Composite
Reinforcement Layers: [0061] (a) Heating the pre-preg composite
reinforcement ply layer structure (also referred to as just
pre-preg) to lower the epoxy viscosity: In one embodiment, the
pre-preg is heated to temperatures limited to 55.degree. C. and is
later cooled down to its storage temperature where it retains its
partially cured properties and can still be formed into a composite
laminate. When uniformly heated between 45.degree. C-55.degree. C.
the pre-preg become tacky and is an ideal substrate for flocking.
In one embodiment, a layer of the pre-preg in a desiccated plastic
bag was removed from a -20.degree. C. freezer and allowed to reach
room temperature. The pre-preg layer is fixed in a griddle type
apparatus and heated to 50.degree. C. to ease flock penetration
into the carbon fiber/ pre-preg substrate. [0062] (b) Applying
flock fibers to the tacky substrate: in one embodiment, after the
carbon fiber/ pre-preg layer is heated it is almost immediately
attached to the ceiling of an up-flocking apparatus (i.e., applying
fibers from below) and the flock is applied at two density levels,
20 fibers/mm.sup.2 and 50 fibers/mm.sup.2. Any loose fibers are
removed by orienting the layer, flock side down, and shaking it
vigorously. The flocked layer is then fixed in a cardboard frame to
isolate it from damage and almost immediately placed back in the
freezer. The procedures can be repeated for additional layers.
[0063] In one embodiment, a unidirectional carbon prepreg IM7/977-3
that is infused with a B-stage epoxy resin system CYCOM 977-3 is
flocked with a 3 denier, 1.22 mm long nylon fiber. The pre-preg
remains "tacky" up to 270.degree. F. (132.degree. C.) and can be
cured at 350.degree. F. (177.degree. C.) for six hours. The
viscosity of the epoxy system is a function of temperature. [0064]
(c) Packing and Storing "Pre-Flocked Fibrous Reinforcement Layers:
the procedures for packing and storing are similar to the
procedures described above in conjunction with the TYPE 1
structured flock fiber reinforced layers. After flocking is
performed, the pre-preg material is covered with a release sheet
and almost immediately cooled and frozen so as to stop any further
thermal cure of the "B" staged epoxy matrix resin. These Type 2
pre-flocked materials are kept frozen (e.g., below 15.degree. C.)
after flocking and during subsequent storage and shipping. Keeping
these pre-preg materials in a frozen state prevents the latent
curing epoxy matrix resin of the composite from curing
pre-maturely. The thermal aging history of pre-pregs is a very
important issue because the more "heat history" the (latent cure)
epoxy resin matrix resin is subjected to, the shorter the
pre-preg's workable shelf life will be.
[0065] In one exemplary manufacturing technique, a manufacturer of
Pre-Preg materials applies Z-Axis flock fibers to the surface of a
pre-preg at the end of a manufacturing run. This technique
introduces reinforcing flock fibers to pre-preg composite
reinforcement materials. Applying reinforcing flock fibers to the
surface of pre-preg at the time of initial manufacture is an
effective and practical way of preparing "Pre-Flocked" pre-preg
without subjection the latent curing epoxy matrix resin to the
additional pre-preg heating stage to apply the flock.
[0066] One skilled in the art will appreciate further features and
advantages of the present disclosure based on the above-described
embodiments. Accordingly, the present disclosure is not to be
limited by what has been particularly shown and described, except
as indicated by the appended claims. All publications and
references cited herein are expressly incorporated herein by
reference in their entirety.
* * * * *