U.S. patent application number 13/750155 was filed with the patent office on 2013-06-06 for method of making a composite sheet.
This patent application is currently assigned to GENTEX CORPORATION. The applicant listed for this patent is GENTEX CORPORATION. Invention is credited to Amit Chatterjee, Leonard Peter Frieder, Ramesh Kaushal, John LaJesse.
Application Number | 20130139958 13/750155 |
Document ID | / |
Family ID | 43464446 |
Filed Date | 2013-06-06 |
United States Patent
Application |
20130139958 |
Kind Code |
A1 |
Kaushal; Ramesh ; et
al. |
June 6, 2013 |
Method of Making a Composite Sheet
Abstract
The invention relates to a method of making a composite sheet. A
plurality of layers is first assembled, each layer being comprised
of an untreated, unidirectional array of strands. The assembled
layers are then placed adjacent one another to form an assembled
sheet, with adjacent layers being in a non-parallel orientation,
and without any of the layers having been treated with a matrix or
binding component. The assembled sheet is then impregnated with a
matrix component, which comprises a binding component and may also
comprise a radiation-absorbing component.
Inventors: |
Kaushal; Ramesh; (South
Riding, VA) ; Frieder; Leonard Peter; (Dalton,
PA) ; LaJesse; John; (Waymart, PA) ;
Chatterjee; Amit; (Howrah, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENTEX CORPORATION; |
Carbondale |
PA |
US |
|
|
Assignee: |
GENTEX CORPORATION
Carbondale
PA
|
Family ID: |
43464446 |
Appl. No.: |
13/750155 |
Filed: |
January 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12835406 |
Jul 13, 2010 |
8388787 |
|
|
13750155 |
|
|
|
|
61226457 |
Jul 17, 2009 |
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Current U.S.
Class: |
156/174 ;
156/181 |
Current CPC
Class: |
D04H 3/12 20130101; D04H
3/04 20130101 |
Class at
Publication: |
156/174 ;
156/181 |
International
Class: |
D04H 3/12 20060101
D04H003/12 |
Claims
1. A method of making a composite sheet, comprising: assembling a
first layer and a second layer positioned adjacent to the first
layer to form an assembled sheet, the first and second layers each
comprising an unbound, unidirectional array of strands, the strands
of the first layer being non-parallel to the strands of the second
layer; and adding a matrix material to the assembled sheet after
the assembling step.
2. The method of claim 1, wherein the first and second layers are
assembled by wrapping the strands around a winding frame.
3. The method of claim 2, wherein the first and second layers are
assembled by rotating the winding frame.
4. The method of claim 3, wherein rotation of the winding frame is
affected by joining the winding frame with a support means.
5. The method of claim 1, wherein the strands of the first layer
are orthogonal to the strands of the second layer.
6. The method of claim 1, wherein the first and second layers are
assembled from a continuous strand.
7. The method of claim 1, wherein forming the assembled sheet
further comprises positioning the first and second layers adjacent
to another by pressing a nesting frame against one of the first and
second layers, the nesting frame being adapted to fit within an
inner perimeter of a winding frame, the winding frame also having
an outer perimeter around which the first and second layers are
formed.
8. The method of claim 7, wherein the nesting frame has an inner
perimeter and an outer perimeter, the inner perimeter having an
inner edge and an outer edge, the nesting frame having at least one
tab located along its inner perimeter.
9. The method of claim 8, further comprising placing a screen
adjacent to the at least one tab, the at least one tab being
adapted to prevent the screen from extending beyond the inner
edge.
10. The method of claim 1, further comprising adding the matrix
material to the assembled sheet by positioning a screen adjacent to
the assembled sheet, the screen having a plurality of holes formed
therein, and causing the matrix material to flow through the
plurality of holes and onto the assembled sheet.
11. The method of claim 1, further comprising adding the matrix
material to the assembled sheet by the use of a B-staging
process.
12. The method of claim 1, wherein the matrix material comprises a
binding component and a radiation-absorbing component.
13. A method of making a composite material, comprising:
positioning a screen adjacent to a substrate, the screen having a
plurality of holes formed therein, the substrate comprising a
plurality of unidirectional, unbound strands; and causing a matrix
material to flow through the plurality of holes and onto the
substrate.
14. The method of claim 13, wherein the plurality of holes is
comprised of holes of uniform size.
15. The method of claim 13, wherein the plurality of holes is
comprised of a first set of holes located in a central portion of
the screen and a second set of holes located in a peripheral
portion of the screen, the holes that comprise the first set of
holes having a smaller area than the holes that comprise the second
set of holes.
16. The method of claim 13, wherein the matrix material comprises a
binding component and a radiation-absorbing component.
17. A method, comprising: impregnating a substrate with a matrix
material, the substrate comprising a plurality of strands, the
matrix material comprising a binding component and a
radiation-absorbing component.
18. The method of claim 17, wherein the binding component comprises
a polymer.
19. The method of claim 17, wherein when the radiation-absorbing
component is activated, it generates an amount of thermal energy
sufficient to melt the binding component.
20. The method of claim 17, wherein the plurality of strands
comprises a first material, the first material having a lower
minimum melting temperature than the binding component.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/226,457, filed Jul. 17, 2009.
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to a method of making a
composite material.
[0003] A composite material is constructed by assembling an
arrangement of reinforcing fibers, then encapsulating or embedding
the fiber arrangement in a binder or "matrix" material. Such
composite materials have application as ballistic articles such as
bulletproof vests, helmets, and structural members of military and
law enforcement vehicles, as well as briefcases, raincoats,
parachutes, umbrellas, and other items. Fibers conventionally used
include aramid fibers, graphite fibers, nylon fibers, ceramic
fibers, glass fibers, and the like.
[0004] It is known in the art to construct the building blocks for
impact resistant composites--known as prepreg layers--by bonding or
laminating together individual layers of unidirectional coplanar
fibers that have been impregnated with a matrix material.
Generally, the individual fibers are impregnated with the matrix
material by immersing them in a bath or film of the matrix material
before forming each prepreg layer so that the individual strands
within each layer have sufficient structural integrity to remain
coplanar. It is also known in the art to orient adjacent
unidirectional fiber layers non-parallel to one another to increase
the structural integrity of the prepreg layers.
[0005] A problem with these known techniques is that a large amount
of matrix material must be used to create the composite material,
which increases both the assembled weight and the cost of creating
the composite material. Prior art methods for constructing a
composite material have taught away from assembling multiple
adjacent layers of unidirectional fibers without first treating the
individual fibers and/or fiber layers with a matrix component.
These prior art references have reasoned that the distribution of
the fiber layers will be disordered by the impregnation process if
matrix material is not already present on the individual fibers or
fiber layers, hence causing technical issues such as the occurrence
of sink marks due to differences in fiber volume fractions, and
thereby damaging the structural integrity of the composite
material. Furthermore, as noted above, the prior art has reasoned
that impregnating the individual strands before forming them into
prepreg layers is necessary to give the individual strands
sufficient structural integrity to remain coplanar within each
layer.
[0006] Hence, an improved method is needed for constructing a
composite material that minimizes the amount of matrix component
that is required to impregnate the fiber arrangement, while not
diminishing the performance characteristics of the constructed
composite sheet.
[0007] Relevant prior art patents include U.S. Pat. No. 5,112,667,
U.S. Pat. No. 5,480,706, and U.S. Pat. No. 5,874,152.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention will hereinafter be described in
conjunction with the appended drawing figures wherein like numerals
denote like elements.
[0009] FIG. 1 is a perspective view showing a winding station in
which a first strand pass is being wound around a strand frame;
[0010] FIG. 2 is a perspective view showing the winding station of
FIG. 1, with the first strand pass fully wound and a second strand
pass being wound around the strand frame;
[0011] FIG. 3 is a flow chart showing an exemplary process for
constructing a fully wound strand frame;
[0012] FIG. 4 is a perspective view showing two nesting frames that
are to be inserted into the fully wound strand frame;
[0013] FIG. 5 is a sectional view taken along 5-5 of FIG. 4,
showing the nesting frames pressed together to create an assembled
sheet;
[0014] FIG. 6 is a perspective view showing two impregnation
screens that are to be inserted into the nesting frames in a
position adjacent to the assembled sheet;
[0015] FIG. 7 is a perspective view showing one of the impregnation
screens inserted into one of the nesting frames;
[0016] FIG. 8 is a front view showing an alternative embodiment of
the impregnation screen shown in FIG. 7; and
[0017] FIG. 9 is a flow chart showing the steps of an exemplary
process in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The ensuing detailed description provides preferred
exemplary embodiments only, and is not intended to limit the scope,
applicability, or configuration of the invention. Rather, the
ensuing detailed description of the preferred exemplary embodiments
will provide those skilled in the art with an enabling description
for implementing the preferred exemplary embodiments of the
invention. It being understood that various changes may be made in
the function and arrangement of elements without departing from the
spirit and scope of the invention, as set forth in the appended
claims.
[0019] To aid in describing the invention, directional terms are
used in the specification and claims to describe portions of the
present invention (e.g., upper, lower, left, right, etc.). These
directional definitions are merely intended to assist in describing
and claiming the invention and are not intended to limit the
invention in any way. In addition, reference numerals that are
introduced in the specification in association with a drawing
figure may be repeated in one or more subsequent figures without
additional description in the specification in order to provide
context for other features.
[0020] As used herein, the term "strand" means a long fiber
reinforcing component of a composite material, including, but not
limited to, a string, fiber, yarn, thread, fibril, or filament,
whether a monofilament or an aggregate of filaments, whether
chemically treated or untreated.
[0021] FIGS. 1 and 2 show an exemplary embodiment of a winding
station 10. In this embodiment, a guide 33 guides a strand 30 as it
is unraveled from a spool 32. In this embodiment, the strand 30 is
being fed around a strand frame 12 to create a first strand pass
34, which is partially completed in FIG. 1. In this embodiment,
creation of the first strand pass 34 is accomplished by engaging
the strand frame 12 with a frame support apparatus 14. The frame
support apparatus 14 has support arms 18a, 18b which engage,
respectively, with support points 22, 23 located at corners of the
strand frame 12. While the frame support apparatus 14 is engaged
with the strand frame 12, the frame support apparatus 14 is rotated
in a first winding direction A. As the frame support apparatus 14
is being rotated in the first winding direction A, it also moves
intermittently in a direction D. Rotation of the frame support
apparatus 14 in the first winding direction A and movement of the
strand frame 12 in the direction D allows the strand 30 to feed
from the spool 32, through the guide 33, and around the strand
frame 12 to create the first strand pass 34. The first strand pass
34 is comprised of a pair of strand layers 36a, 36b, each located
on an opposing side of the strand frame 12. While the first strand
pass 34 is being created, the frame support apparatus 16 is
disengaged from the strand frame 12. In this embodiment, the first
strand pass 34 is comprised of unidirectional strands.
[0022] The speed of rotation of the frame support apparatus 14 in
the first winding direction A is variable, and dependent on such
factors as, for example, the desired distance between the
individual strands that comprise the first strand pass 34 and the
diameter of the strand 30. Movement of the strand frame 12 in the
direction D is variable and dependent on the proximity of the
strand 30 to the top or bottom of the strand frame 12. That is, in
order to achieve a strand pass 34 having unidirectional strands 30
that are precisely perpendicular to left and right sides of the
strand frame 12, movement of the strand frame 12 in the direction D
occurs only while the strand 30 is being wound around the upper or
lower edge of the strand frame 12, i.e. once per revolution. As a
result, the strand 30 is at a slight angle as it is being wrapped
around, for example, the top edge of the strand frame 12. A series
of shallow channels or raised dimples (not shown) could be arranged
on the outer edges of the strand frame 12 to help guide the strand
30 as it is wrapped around the strand frame. The size and spacing
of the channels or dimples would depend on factors such as, for
example, the thickness of the strand 30 and the desired strand pass
spacing.
[0023] In FIG. 2, the first strand pass 34 is fully completed. The
strand 30 is then fed around the strand frame 12 to create a second
strand pass 35, which is shown partially completed in FIG. 2. Like
the first strand pass 34, the second strand pass 35 is comprised of
unidirectional strands. Creation of the second strand pass 35 is
accomplished by engaging the strand frame 12 with the frame support
apparatus 16. Frame support apparatus 16 has support arms 19a, 19b
which engage, respectively, with support points 21, 22 located at
corners of the strand frame 12. While the frame support apparatus
16 is engaged with the strand frame 12, the frame support apparatus
16 is rotated in the second winding direction B. As the frame
support apparatus 16 is being rotated in the second winding
direction B, it also moves intermittently in a direction E. It
should be understood that in this embodiment the second strand pass
35 is constructed in the same manner as the first strand pass 34,
described above. The second strand pass 35 is comprised of a pair
of strand layers 37a, 37b, each located on an opposing side of the
strand frame 12. While the second strand pass 35 is being created,
the frame support apparatus 14 is disengaged from the strand frame
12.
[0024] In this embodiment, the first and second strand passes 34,
35 are oriented such that their respective strands are arranged
orthogonally to one another on either side of the strand frame 12;
that is, strand layer 36a is oriented orthogonal to strand layer
37a, and strand layer 36b is oriented orthogonal to strand layer
37b. If a third strand pass were constructed on top of the second
strand pass 35, its respective strand layers would preferably be
oriented orthogonal to the strand layers 37a, 37b of the second
strand pass 35. Though it is preferable to have orthogonal
arrangement of adjacent strand passes, it should be understood that
any non-parallel relative orientation of the adjacent strand passes
could be used. This non-parallel strand pass orientation will be
paramount to the structural integrity of the fully constructed
composite material, as will be discussed in greater detail
below.
[0025] Several embodiments of the winding station 10 could be used
to achieve the precise orthogonal orientation of adjacent strand
passes. In a preferred embodiment, at the end of formation of the
first strand pass 34, the strand 30 may be situated in a groove 38b
at the upper right corner of the strand frame 12. The groove 38b is
oriented so that the strand 30 is guided from one edge of the
strand frame 12 (e.g., the top edge in FIG. 1) to an adjacent edge
(e.g., the right edge in FIG. 1). In a preferred embodiment, the
strand 30 is guided through the groove 38b by the combined
engagement and movement of the frame support apparatuses 14, 16.
Once the strand 30 is in position on the right edge of the strand
frame 12, frame support apparatus 14 disengages from the strand
frame 12, and winding of the second strand pass 35 begins. Grooves
38a, 38c, and 38d, located at the other corners of the strand frame
12, allow for transitioning between adjacent strand passes where a
strand pass terminates at one of these other corners of the strand
frame 12. It should be understood that identical grooves 39a-39d
(not shown) may also be placed on the reverse side of the strand
frame 12.
[0026] The above winding method is provided by way of example only.
It should be understood that many other methods of winding the
strand passes could be employed, such as for example, where the
strand frame 12 is maintained in a stationary position and the
spool 32 and/or guide 33 is rotated around the strand frame, or
multiple spools, strands, or guides are used to create the
unidirectional strand passes. It should be further understood that
many other techniques and apparatuses could be used to affect the
orthogonal orientation of adjacent strand passes within the scope
of this invention. For example, one or more mechanical guide arms
(not shown) could be used to carefully support and direct the
strand 30 in order to affect the orthogonal orientation of the
adjacent strand passes.
[0027] In the present embodiment, a total of two strand passes 34,
35 are assembled (see FIG. 4). It should be understood, however,
that any number of desired strand passes could be created in
accordance with, for example, the particular design specifications,
cost sensitivities, and time constraints which may dictate the
creation of the composite material. For example, a third strand
pass could be assembled on top of the second strand pass 35. A
fourth strand pass could then be assembled on top of the third
strand pass. This process could continue until the desired number
of strand passes is reached. In the present embodiment, the first
and second strand passes 34, 35 are constructed from a continuous
length of strand 30. In the alternative, each strand pass could be
constructed from a separate length of strand 30.
[0028] FIG. 3 is a flow chart showing the functional steps involved
in an exemplary winding method of the strand frame 12. The process
begins at step 301. At step 302, the frame support apparatus 14
engages the strand frame 12. The first strand pass 34 is wound at
step 303, followed by the frame support apparatus 14 disengaging
from the strand frame 12 at step 304. At step 305, a determination
is made whether the desired number of strand passes has been
reached. If it is determined that the desired number of strand
passes has not been reached, the frame support apparatus 16 engages
the strand frame 12 at step 306. The second strand pass 35 is wound
at step 307, followed by the frame support apparatus 16 disengaging
from the strand frame 12 at step 308. At step 309, a second
determination is made whether the desired number of strand passes
has been reached. If it is determined at step 309 that the desired
number of strand passes has not been reached, the method returns to
step 302. If it is determined at either of steps 305 or 309 that
the desired number of strand passes has been reached, the process
ends at step 310.
[0029] Referring now to FIGS. 4-5, strand layers 36a, 37a comprise
a first layer set 40, which is located on the side of the strand
frame 12 closer to the first nesting frame 44. Strand layers 36b,
37b comprise a second layer set 41, which is located on the side of
the strand frame 12 closer to the second nesting frame 45. In FIG.
4, the first and second nesting frames 44, 45, which are adapted to
be inserted within the strand frame 12, are shown with arrows
indicating their respective insertion direction.
[0030] An exemplary method for pressing the first and second layer
sets 40, 41 together will herein be described. The first and second
nesting frames 44, 45 are placed against the first and second layer
sets 40, 41, respectively, and then pressed together inside of the
strand frame 12. As the first and second nesting frames 44, 45 are
pressed together, as seen in the sectional view of FIG. 5, the
first and second layer sets 40, 41 are brought adjacent to one
another to form the assembled sheet 50. The first and second
nesting frames 44, 45 could be brought together in a variety of
ways, for example, by being pressed together manually or by being
guided into their respective positions by the use of one or more
support means. Further, the first and second nesting frames 44, 45
could have means for being releasably adjoined to each other, such
that any means that may be used to press the first and second
nesting frames 44, 45 into the strand frame 12 would not need to
apply continuous pressure to keep the first and second nesting
frames 44, 45 adjacent another. The first and second nesting frames
44, 45 act to maintain the strand layers 36a, 36b, 37a, 37b firmly
and fixedly in a uniform orientation. As will be discussed below,
impregnation of the assembled sheet 50 with a matrix component will
subsequently occur. The present method overcomes technical
difficulties related to disorientation of the strand layers as the
matrix component is introduced to the assembled sheet 50.
[0031] In this embodiment, the first nesting frame 44 has tabs
48a-48d (48b not shown) located at the corners of its inner
perimeter on the side of the first nesting frame 44 that is first
inserted into the strand frame 12. The second nesting frame 45 is
identical to the first nesting frame 44 in structure, and has tabs
49a-49d, respectively. Referring now to FIG. 6, the tabs 48, 49 are
designed to support the insertion of the first and second
impregnation screens 54, 55 within the inner perimeter of the first
and second nesting frames 44, 45, respectively. The tabs 48, 49
serve to maintain the first and second impregnation screens 54, 55
in a stable position adjacent to respective sides of the assembled
sheet 50, while preventing the first and second impregnation
screens 54, 55 from being moved beyond the edges of the first and
second nesting frames 44, 45, respectively, which are in contact
with the assembled sheet 50. This is desirable in order to prevent
the first and second impregnation screens 54, 55 from being pressed
beyond the inner perimeter of the first and second nesting frames
44, 45, where they might alter the arrangement of the strands by
coming in contact with the assembled sheet 50. It should be
understood that any number, size, and location of the tabs 48, 49,
respectively, around the inner perimeter of the first and second
nesting frames 44, 45 could be used, for example, where more or
less than four tabs are used in each nesting frame, and where the
tabs 48, 49 are located at positions other than the corners of the
first and second nesting frames 44, 45, respectively. For example,
a single tab that extends around the entire inner perimeter of the
first and second nesting frames 44, 45 could be used.
[0032] In FIG. 6, the first and second impregnation screens 54, 55,
which are adapted to be inserted within the first and second
nesting frames 44, 45, respectively, are shown with arrows
indicating their respective insertion direction. The first
impregnation screen 54 is inserted within first nesting frame 44
until it is in contact with tabs 48a-48d. Likewise, the second
impregnation screen 55 is inserted within the second nesting frame
45 until it is in contact with tabs 49a-49d (see FIG. 4). In this
embodiment, the first and second impregnation screens 54, 55, are
separate units from the first and second nesting frames 44, 45,
respectively. It should be understood that in the alternative, the
first and second impregnation screens 54, 55 could be built into
the first and second nesting frames 44, 45, respectively, such that
for example the first nesting frame 44 and the first impregnation
screen 54 would comprise a single unit.
[0033] As stated above, tabs 48, 49 prevent the first and second
impregnation screens 54, 55 from making contact with the assembled
sheet 50, in order to prevent the first and second impregnation
screens 54, 55 from altering the arrangement of the strands which
comprise the assembled sheet 50. The unidirectional arrangement of
strands within a strand layer, coupled with the non-parallel
orientation of adjacent strand layers, are important features
affecting the structural integrity of the fully constructed
composite material. For example, when orthogonally oriented strand
layers are placed on top of another, a tightly arranged
"checkerboard" pattern of strand layers is constructed. Not only
does this strand arrangement maximize the structural integrity of
the unimpregnated layer sets, but it also creates a highly uniform
arrangement of spaces between the strands that will subsequently be
filled with matrix component. The uniform and efficient placement
of the matrix component within the assembled sheet 50 further acts
to maximize the structural integrity of the composite sheet.
[0034] FIG. 7 is a perspective view of a first embodiment of the
first impregnation screen 54 installed within the first nesting
frame 44. The first impregnation screen 54 has screen holes 56,
which will be used to allow for the distribution of a matrix
component to the assembled sheet 50. In this embodiment, screen
holes 56 are circular in shape and of a constant diameter across
the surface of the first impregnation screen 54.
[0035] FIG. 8 shows a front view of an alternative embodiment of
the first impregnation screen 154 installed within the first
nesting frame 44. The first impregnation screen 154 has screen
holes 156a located around the periphery of its surface, i.e. near
the first nesting frame 44. Towards the center of its surface, the
first impregnation screen 154 has screen holes 156b, which have a
smaller diameter than the screen holes 156a. When the matrix
component is introduced to the assembled sheet 50 through the
screen holes 156a, 156b, this variation in screen hole sizing
allows for less matrix component to be used, and results in more
uniform distribution of the matrix component throughout the
assembled sheet 50.
[0036] In the embodiments shown in FIGS. 7 and 8, screen holes 56,
156a, 156b are circular in shape. It should be understood that any
number of screen hole shapes could be used, for example, square,
oval, triangular, elongated slits, etc. It should be further
understood that any number and relative placement of screen holes
could be used in an impregnation screen to help achieve maximum
distribution of the matrix component when it is introduced to the
assembled sheet 50 through the screen holes. It will be obvious to
one having ordinary skill in the art to vary the number, shape,
size, and location of the screen holes to achieve the most
efficient result based on, for example, the viscosity of the matrix
component used.
[0037] It is preferable that separate impregnation screens, such as
first and second impregnation screens 54 and 55, be brought into
contact with either side of the assembled sheet 50. The use of an
impregnation screen on both sides of the assembled sheet 50 allows
for the matrix component to be applied, alternately or
simultaneously, to both sides of the assembled sheet 50, which will
lead to a more even and efficient distribution of the matrix
component throughout the assembled sheet 50 and will tend to reduce
the amount of matrix component that will need to be used. However,
it should be understood that, in the alternative, an impregnation
screen could be introduced to just one side of the assembled sheet
50.
[0038] Introduction of the matrix component to the assembled sheet
50 could be accomplished in a variety of ways. Preferably, the
matrix component is allowed to flow by the force of gravity through
the screen holes 56 located in the first and second impregnation
screens 54, 55. In the alternative, the matrix component could be
generally introduced onto the surface of the first and second
impregnation screens 54, 55, or directed specifically into the
screen holes 56 by the means of a spray device. B-staging--a
process that uses heat or UV-light to remove the majority of a
solvent from an adhesive--can also be used effectively to introduce
the matrix component to the assembled sheet 50. B-staging works
very well with volatile organic compound (VOC)-blended resins as
the matrix component; after the B-staging process, very low resin
content remains in the matrix component. It should be understood
that other means of introducing the matrix component to the
assembled sheet 50 are possible within the scope of this
invention.
[0039] FIG. 9 is a flow chart showing the steps of an exemplary
process for making a composite sheet, in accordance with the
present invention. The process begins at step 901. At step 902, a
fully wound strand frame 46 is constructed, having the desired
number of strand passes arranged around the strand frame 12. The
first and second nesting frames 44, 45 are inserted within the
strand frame 12 to create the assembled sheet 50 at step 903. At
step 904, a cutting mechanism is used to cut the strand frame 12
away from the assembled sheet 50. The first and second impregnation
screens 54, 55 are inserted within the first and second nesting
frames 44, 45, respectively, at step 905. At step 906, a matrix
component is introduced to the assembled sheet 50. The process ends
at step 907.
[0040] It should be understood that the steps described above could
be performed in a variety of alternative orders. For example, the
strand frame 12 could be cut away from the first and second nesting
frames 44, 45 after the first and second impregnation screens 54,
55 have been inserted within the first and second nesting frames
44, 45, respectively, or after the assembled sheet 50 has been
impregnated with the matrix component. Further, as stated above,
the first and second impregnation screens 54, 55 could be part of
the first and second nesting frames 44, 45, respectively, and
therefore could be introduced at the time that the first and second
nesting frames 44, 45 are inserted within the strand frame 12.
Other modifications to the order of the above steps, as well as the
omission or addition of one or more steps, are also possible within
the scope of this invention.
[0041] As mentioned above, adjacent strand passes are most
preferably arranged such that their respective unidirectional
strands are arranged orthogonal to one another on either side of
the strand frame 12. It should be understood that any non-parallel
orientation of adjacent strand passes could be used. All of the
strands passes are arranged around the strand frame 12 without any
matrix component being added to the individual strand layers. It
should be understood, however, that the strand 30, as carefully
defined above, may be pre-treated with a chemical, which may
comprise a binding or hardening component. In the present
invention, the individual strand layers are not treated with a
matrix component until after the assembled sheet 50 has been
created.
[0042] The orthogonal arrangement of adjacent strand passes
substitutes for the structural integrity that is conventionally
provided by separately impregnating individual strand layers (i.e.
prepreg layers) before assembling the individual strand layers into
a composite sheet. In the present invention, only after the
assembled sheet 50 has been constructed and the first and second
impregnation screens 54, 55 brought into adjacent positions thereto
is the matrix component applied to the assembled sheet 50. In this
fashion, a number of benefits can be achieved, including: (i) a
reduction in the amount of matrix component used to fully
impregnate the assembled sheet 50; and (ii) an increase in the
contact time between the matrix component and the strands prior to
evaporation of the volatiles contained in the matrix component. The
significance of benefit (i) is that, in the composite material, the
ratio of the volume of the strands to the volume of the matrix
component is maximized; accordingly, the strength of the composite
material is increased, while its weight is minimized. This benefit
has particular importance with respect to ballistic applications,
where the strength-to-weight ratio of for example, body armor and
helmets, is of high value. In addition, the matrix component can be
costly, and the efficiency of the above method results in cost
savings as less matrix component needs be used to fully impregnate
the assembled sheet 50. The significance of benefit (ii) is that it
allows for the use of a matrix component having a higher volatile
organic compound (VOC) content than would otherwise be permitted
without sacrificing contact time.
[0043] The matrix component that is applied to the assembled sheet
50 through the first and second impregnation screens 54, 55 fills
the gaps between and binds together the strand layers 36a, 36b,
37a, 37b. In addition to a standard binding component, the matrix
component could include a radiation-absorbing component, such as
Clearweld.RTM., manufactured by Gentex Corporation of Carbondale,
Pa. Clearweld is a compound that generates heat when it absorbs
near infra-red (near-IR) light, such as that emitted by a laser,
for example a Nd:YAG or diode laser.
[0044] In the present invention, Clearweld could be incorporated
into the matrix component that is used to impregnate the assembled
sheet 50. Thereafter, localized and precise activation of the
Clearweld could be performed to generate a sufficient amount of
heat to melt the matrix component, thus causing it to flow into the
voids between the strand layers and binding them together. In
addition, activation of the Clearweld allows for highly localized
heating of the matrix component containing the Clearweld, without
causing equivalent heating of any adjacent strand layers to occur,
due to the fact that heat dissipation will not permit complete
thermal transfer. Consequently, a matrix component could be used
that has a higher minimum melting temperature than what would
otherwise be allowable without thermally degrading the material
that comprises the strand layers. For example, a polymer such as
polyetherimide (PEI), having a melting point of approximately 350
degrees Centigrade (.degree. C.), could comprise the matrix
component. In this example, a polymer such as polyetheretherketone
(PEEK), having a melting point of approximately 343.degree. C.,
could thus comprise the strand layers. Because heat dissipation
prevents equivalent heating of the strand layers, the melted PEI
will not cause the PEEK strand layers to melt. It should be
understood that many other polymers could be used for the matrix
component and strand layers within the scope of this invention. The
advantage of being able to use a polymer having a high minimum
melting temperature in the matrix component is that the composite
sheet formed therefrom will have improved performance
characteristics, for example a higher density, thereby improving
the ballistic quality of the composite sheet without adding
significantly to its weight.
[0045] While the principles of the invention have been described
above in connection with preferred embodiments, it is to be clearly
understood that this description is made only by way of example and
not as a limitation of the scope of the invention.
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