U.S. patent application number 11/519134 was filed with the patent office on 2008-05-29 for moldable fabric with unidirectional tape yarns.
Invention is credited to Howell B. Eleazer, Heather J. Hayes.
Application Number | 20080124513 11/519134 |
Document ID | / |
Family ID | 39464043 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080124513 |
Kind Code |
A1 |
Eleazer; Howell B. ; et
al. |
May 29, 2008 |
Moldable fabric with unidirectional tape yarns
Abstract
The invention relates to an impact resistant component
comprising at least two composite sheets fused together, each
composite sheet comprising an adhesive layer fused between two
unidirectional sheets, wherein each unidirectional sheet comprises
a plurality of monoaxially drawn fibers arranged substantially
parallel to one another along a common fiber direction, the fibers
comprising a base layer of a strain oriented polymer disposed
between surface layer(s) of a heat fusible polymer, wherein the
surface layer(s) are characterized by a melting temperature below
that of the base layer to permit fusion bonding upon application of
heat, and wherein the adhesive layer has a melting temperature
below that of the base layer of the unidirectional sheet.
Inventors: |
Eleazer; Howell B.; (Moore,
SC) ; Hayes; Heather J.; (Chesnee, SC) |
Correspondence
Address: |
Legal Department (M-495)
P.O. Box 1926
Spartanburg
SC
29304
US
|
Family ID: |
39464043 |
Appl. No.: |
11/519134 |
Filed: |
September 11, 2006 |
Current U.S.
Class: |
428/113 ;
428/114; 428/297.4 |
Current CPC
Class: |
B32B 7/12 20130101; Y10T
428/24124 20150115; Y10T 428/24994 20150401; F41H 5/0478 20130101;
Y10T 428/24132 20150115; B32B 5/26 20130101 |
Class at
Publication: |
428/113 ;
428/114; 428/297.4 |
International
Class: |
B32B 5/12 20060101
B32B005/12; B32B 27/12 20060101 B32B027/12 |
Claims
1. An impact resistant component comprising: at least two composite
sheets fused together, each composite sheet comprising two
unidirectional sheets and an adhesive layer, wherein the adhesive
layer fuses the unidirectional sheets to one another; wherein each
unidirectional sheet comprises a plurality of monoaxially drawn
fiber elements arranged substantially parallel to one another along
a common fiber direction, the fiber elements comprising a core of a
strain oriented polymer and one surface layer of a heat fusible
polymer that covers at least a portion of one side of the core,
wherein the surface layer is characterized by a softening
temperature below that of the core to permit fusion bonding upon
application of heat and wherein the adhesive layer has a softening
point lower than the surface layer of the fiber elements, wherein
the unidirectional sheets are oriented such that the adhesive layer
adheres to the core layers of the fiber elements and the surface
layers form the outer surface of the composite sheets, wherein the
unidirectional sheets of each composite sheet have the same common
fiber direction, and: wherein the surface layers of the composite
sheets fuse together to form the fused impact resistant
component.
2. (canceled)
3. The impact resistant component of claim 1, wherein the at least
one surface layer of the fiber elements comprises an olefin
polymer.
4. The impact resistant component of claim 1, wherein the core of
the fiber elements comprises an olefin polymer.
5-6. (canceled)
7. The impact resistant component of claim 1, wherein the core is
comprised of one or more fibers having a cross-sectional shape
selected from the group consisting of circular, oblong, and
elliptical and the at least one surface layer covers the entire
surface area of the core.
8. The impact resistant component of claim 1, wherein the adhesive
layer is in an amount of between about 0.2 to 10% of the weight of
the impact resistant component.
9. The impact resistant component of claim 1, wherein the at least
two composite sheets are fused together without additional
adhesives.
10. The impact resistant component of claim 1, wherein the
unidirectional sheets of each composite sheet have the same common
fiber direction.
11. The impact resistant component of claim 10, wherein the common
fiber direction of the unidirectional sheets of one composite sheet
are perpendicular to the common fiber direction of the
unidirectional sheets of the adjacent composite sheets.
12. The impact resistant component claim 1, wherein the core,
surface layer, and the adhesive layer comprise a polymer selected
from the group consisting of polypropylene and polyethylene.
13. An impact resistant component comprising: at least 10 composite
sheets fused together, each composite sheet comprising two
unidirectional sheets and an adhesive layer, wherein the adhesive
layer fuses the unidirectional sheets to one another, wherein each
unidirectional sheet comprises a plurality of monoaxially drawn
fiber elements arranged substantially parallel to one another along
a common fiber direction, the fiber elements comprising a core of a
strain oriented polymer and one surface layer of a heat fusible
polymer that covers at least a portion of one side of the core,
wherein the surface layer is characterized by a softening
temperature below that of the core to permit fusion bonding upon
application of heat and wherein the adhesive layer fuses the
unidirectional sheets together, where in the adhesive layer has a
softening point lower than the surface layer of the fiber elements,
wherein the unidirectional sheets are oriented such that the
adhesive layer adheres to the core layers of the fiber elements and
the surface layers form the outer surface of the composite sheets,
and; wherein the surface layers of the composite sheets fuse
together to form the fused impact resistant component.
14. (canceled)
15. The impact resistant component of claim 13, wherein the at
least one surface layer and the core of the fiber elements
comprises an olefin polymer.
16-27. (canceled)
28. An impact resistant component comprising: at least two
composite sheets fused together, each composite sheet comprising
two unidirectional sheets and an adhesive layer, wherein each
unidirectional sheet comprises a plurality of monoaxially drawn
fiber elements arranged substantially parallel to one another along
a common fiber direction, the fiber elements comprising a core of a
strain oriented polymer and surface layers of a heat fusible
polymer that covers at least a portion of each side of the core,
wherein the surface layers are characterized by a softening
temperature below that of the core to permit fusion bonding upon
application of heat; and, wherein the unidirectional sheets within
each composite sheet have the same common fiber direction, wherein
the adhesive layer fuses the unidirectional sheets together,
wherein the adhesive layer has a softening point lower than the
surface layer of the fiber elements, and wherein the surface layers
of the composite sheets fuse together to form the fused impact
resistant component.
29. The impact resistant component of claim 29, wherein the
unidirectional sheets of each composite sheet have the same common
fiber direction.
30. The impact resistant component of claim 29, wherein the at
least two composite sheets are fused together without additional
adhesives.
31. The impact resistant component of claim 29, wherein the common
fiber direction of the unidirectional sheets of one composite sheet
are perpendicular to the common fiber direction of the
unidirectional sheets of the adjacent composite sheets.
32. An impact resistant component comprising: at least ten
composite sheets fused together, each composite sheet comprising
two unidirectional sheets and an adhesive layer, wherein each
unidirectional sheet comprises a plurality of monoaxially drawn
fiber elements arranged substantially parallel to one another along
a common fiber direction, the fiber elements comprising a core of a
strain oriented polymer and surface layers of a heat fusible
polymer that covers at least a portion of each side of the core,
wherein the surface layers are characterized by a softening
temperature below that of the core to permit fusion bonding upon
application of heat; and, wherein the unidirectional sheets within
each composite sheet have the same common fiber direction, wherein
the adhesive layer fuses the unidirectional sheets together,
wherein the adhesive layer has a softening point lower than the
surface layer of the fiber elements, and wherein the surface layers
of the composite sheets fuse together to form the fused impact
resistant component.
33. The impact resistant component of claim 32, wherein the at
least two composite sheets are fused together without additional
adhesives.
34. The impact resistant component of claim 32, wherein the common
fiber direction of the unidirectional sheets of one composite sheet
are perpendicular to the common fiber direction of the
unidirectional sheets of the adjacent composite sheets.
Description
TECHNICAL FIELD
[0001] The present invention generally relates to impact resistant
components, anti-ballistics panels and methods for making the
components and panels. In particular, the invention relates to
impact resistant components incorporating at least two composite
sheets fused together, each composite sheet comprising an adhesive
layer between two unidirectional sheets of aligned fiber elements
or tape elements.
BACKGROUND
[0002] It has been proposed to form tape structures from
polypropylene film that is coated with a layer of propylene
copolymer including ethylene units such that the coating has a
lower softening point than the core. Such tape structures are
disclosed, for example, in U.S. Pat. No. 5,578,370 the teachings of
which are hereby incorporated by reference in their entirety. U.S.
Patent Application 2004/0242103A1 (incorporated by reference) has
also proposed to form monoaxially drawn tape structures
characterized by substantial draw ratios and incorporating a
central layer of a polyolefin with one or two surface layers of a
polyolefin from the same class as the central layer. The DSC
melting point of the outer layers is lower than that of the central
layer to facilitate heat bonding. Such drawn tape elements may be
interwoven so as to form a mat structure which is then subjected to
heat thereby fusing the tape elements in place. Multiple layers of
such interwoven mat structures may be combined to form moldable
structures of substantial thickness that may be shaped to
three-dimensional configurations.
[0003] In addition to tape elements, there commonly exists fiber
elements that are also characterized by having a lower melting
surface than the main fiber component. A core/shell fiber generally
consists of a core of one type of polymer, with a surface layer
(also called a shell or cladding) of a different polymer. The
fiber's mechanical properties are mainly a result of the core
material, whereas the surface layer determines the external
properties (e.g., adhesion, friction, softness). One advantage of a
core/shell fiber is the ability to achieve a combination of such
properties that would be impossible in a simple, homogeneous fiber.
One type of core/shell fiber has a polyester core and a polyolefin
shell (e.g., polypropylene). A typical application for this fiber
is in nonwoven fabrics where the lower melting point of the
polypropylene surface layer allows these strong polyester core
fibers to be bonded together without losing their strength.
[0004] Anti-ballistics fibers and yarns tend to be expensive,
leading to expensive anti-ballistics panels and impact resistant
components made from the anti-ballistics yarns. The anti-ballistics
panels made from unidirectional Kevlar and aramid fibers are
typically embedded in a matrix. There is a need to produce a
unidirectional anti-ballistics component or panel of fiber or tape
elements using a lower amount of matrix material.
BRIEF DESCIPTION OF THE DRAWINGS
[0005] The accompanying drawings which are incorporated in and
which constitute a part of this specification illustrate several
exemplary constructions and procedures in accordance with the
present invention and, together with the general description of the
invention given above and the detailed description set forth below,
serve to explain the principles of the invention wherein:
[0006] FIG. 1 illustrates schematically a cross-section of one
embodiment of the monoaxially drawn tape element;
[0007] FIG. 2 illustrates schematically a cross-section of one
embodiment of the monoaxially drawn tape element;
[0008] FIGS. 3A-C illustrate schematically cross-sections of
embodiments of core/shell fibers elements.
[0009] FIGS. 3D-E illustrate schematically additional
cross-sections of fiber elements.
[0010] FIG. 4A illustrates schematically a unidirectional sheet
made up of monoaxially drawn tape elements.
[0011] FIG. 4B illustrates schematically a unidirectional sheet
made up of core/shell fiber elements.
[0012] FIG. 5A illustrates schematically a cross-section of one
embodiment of the composite sheet;
[0013] FIG. 5B illustrates schematically a cross-section of one
embodiment of the composite sheet;
[0014] FIG. 6 illustrates schematically a cross-section of one
embodiment of the composite sheet;
[0015] FIGS. 7A and B illustrate schematically a cross-section of
one embodiment of the impact resistant component;
[0016] FIGS. 8A and B illustrate schematically a cross-section of
one embodiment of the impact resistant component;
[0017] FIGS. 9A and B illustrate schematically a cross-section of
one embodiment of the impact resistant component;
[0018] FIGS. 10A-B illustrate schematically an anti-ballistics
panel;
[0019] FIG. 11 illustrates schematically a molded article.
DETAILED DESCRIPTION
[0020] Embodiments of the present invention will now be described
by reference to the accompanying drawings, in which, to the extent
possible, like reference numerals are used to designate like
components in the various views.
[0021] Referring to FIG. 1, there is shown one embodiment of a
fiber element having a core of a strain oriented polymer and at
least one surface layer of a heat fusible polymer covering at least
a portion of the core, wherein the at least one surface layer is
characterized by a softening temperature below that of the core to
permit fusion bonding upon application of heat. Preferably, the
core and/or the surface layer are an olefin polymer. In one
embodiment, the fiber element is a monoaxially drawn tape element
10 made up of a surface layer 14 disposed on a core 12. The core is
a tape shaped core layer having an upper and lower surface and the
surface layer 14 covers one side (upper or lower surface) of the
core layer 12. The tape element 10 may be formed by any
conventional means of extruding multilayer polymeric films and then
slitting the films into tape elements 10. Referring to FIG. 2,
there is shown another embodiment of the tape elements 10 made up
of a core layer 12 disposed between two surface layers 14 and 14'
(the surface layers being disposed on the upper and lower surface
of the core layer 12).
[0022] By way of example, and not limitation, the film may be
formed by blown film or cast film extrusion. The film is then cut
into a multiplicity of longitudinal strips of a desired width by
slitting the film in a direction transverse to the layered
orientation of core layer 12 and surface layer 14 to form tape
elements 10 with cross-sections as shown in FIG. 1. The tape
elements 10 are then drawn in order to increase the orientation of
the core layer 10 so as to provide increased strength and stiffness
of the material. In another embodiment, the surface layer(s) may be
added after the drawing step. After the drawing process is
complete, the resulting tape elements are in the range of about 1.0
to about 5 millimeters wide. In one embodiment, the tape elements
10 have a width to thickness ratio of between about 10 and 1000. In
another embodiment, the tape elements have a modulus of between 5
and 200.
[0023] Referring to Figures now to 3A-C, there is shown some
embodiments of a fiber element being a core/shell type fiber
element 15 made up of a surface layer 17 disposed on a core 16
covering at least a portion of the core. Preferably, the surface
layer 17 covers the core 16 surface area completely. The core 16 is
typically a fiber with a circular, oblong, elliptical, elongated or
other cross-section. In one embodiment, the cross-section of the
core has a major to minor axis aspect ratio of between 1 and 30.
The core 16 and surface layer 17 may be co-extruded together, or
the surface layer 17 may be applied to the core 16 after the core
16 has been formed. The fiber element 15 is oriented before or
after the surface layer 17 is formed in order to increase the
orientation of the core 16 so as to provide increased strength and
stiffness.
[0024] Referring to FIG. 3D, there is shown an additional
embodiment of a number of fiber elements being of a core/shell type
fiber elements together (each made up of a surface layer 17
disposed on a core 16 covering at least a portion of the core).
While it is shown that the shape grouping or cluster of fibers
elements is a circular, the group shape may also be elongated or
other shapes. Additionally, each fiber element 15 may have the same
or different cross-sectional shapes. Once in the composite, the
shape of the grouping may also change. FIG. 3E shows a number of
fiber elements with cores 16 surrounded by a surface layer 17. In
this embodiment, the surface layer 17 surrounds all of the cores
16. In one embodiment, the core 16 has a major axis diameter of
between 1 and 1000 micrometers (preferably between 50 and 500
micrometers) and the surface layer has a thickness of between about
5 and 30% of the total.
[0025] The core 12, 16 of the tape and fiber elements 10,15 are
preferably made up of a molecularly-oriented thermoplastic polymer,
the core 12, 16 being fusible to each of surface layers 14, 14',17
at their respective intersections. The core 12,16 is compatibly
bonded to each of surface layers 14, 14', 17 between their
contiguous surfaces. It is further contemplated that the surface
layers 14, 14', 17 have a softening temperature, or melting
temperature, lower than that of the core 12, 16. By way of example
only, it is contemplated that the core 12,16 is a polyolefin
polymer such as polypropylene, polyethylene, polyester such as
polyethylene terephthalate, or polyamide such as Nylon 6 or Nylon
6,6 (polyester and polyurethane are common core materials with
low-melt polyester, polypropylene or polyethylene shells).
Core-wrap yarns are also common materials and include elastomeric
yarns wrapped with fibers of other materials to impart different
aesthetics, hand, color, UV resistance, etc. The preferred
core/shell materials for this invention are polyolefin in nature
where a highly drawn and therefore highly oriented polypropylene or
polyethylene has a lower softening point polyolefin surface layer
commonly comprised of homopolymers or copolymers of ethylene,
propylene, butene, 4-methyl-1-pentene, and/or like monomers.
According to one potentially preferred practice, the core 12, 16
may be polypropylene or polyethylene. The core 12, 16 may account
for about 50-99 wt. % of the tape or fiber element, while the
surface layers 14, 14', 17 account for about 1-50 wt. % of the tape
or fiber element. The core 12, 16 and surface layers 14, 14', 17
being made up of the same class of materials to provide an
advantage with regard to recycling, as the core 12, 16 may include
production scrap.
[0026] In an embodiment where the core 12 or 17 is polypropylene,
the material of surface layers 14, 14', 17 is preferably a
copolymer of propylene and ethylene or an .alpha.-olefin. In one
embodiment, the surface layers 14, 14', 17 comprise a random
copolymer of propylene-ethylene with an ethylene content of about
1-25 mol. %, and a propylene content of about 75-99 mol. %. It may
be further preferred to use said copolymer with a ratio of about 95
mol. % propylene to about 5 mol. % ethylene. Instead of said
copolymer or in combination therewith, a polyolefin, preferably a
polypropylene homopolymer or polypropylene copolymer, prepared with
a metallocene catalyst, may be used for the surface layers 14, 14',
17. It is also contemplated that materials such as
poly(4-methyl-1-pentene) (PMP) and polyethylene may be useful as a
blend with such copolymers in the surface layers 14, 14', 17. The
surface layer material should be selected such that the softening
point of the surface layer 14, 14', 17 is at least about 10.degree.
C. lower than that of the core layer 12, and preferably between
about 15-40.degree. C. lower. The upper limit of this difference is
not thought to be critical, and the difference in softening points
is typically less than 70.degree. C. Softening point, for this
application, is defined as the Vicat softening temperature (ASTM
D1525). It is desirable to minimize the amount of adhesive used to
maximize the amount of fiber elements in a composite.
[0027] By way of example only, and not limitation, one tape element
10 that may be particularly useful is believed to be marketed under
the trade designation PURE by Lankhorst/Indutech having a place of
business in Sneek, The Netherlands.
[0028] FIG. 4A illustrates a unidirectional sheet 50 formed from a
multiplicity of fiber elements being tape elements 10. The tape
elements are aligned parallel along a common fiber direction of the
unidirectional sheet 50. In one embodiment, the tape elements 10 in
the unidirectional sheet 50 do not overlap one another, and may
have gaps between the tape elements 10. In another embodiment, the
tape elements overlap one another up to 90% in the unidirectional
sheet 50. The unidirectional sheet 50 is preferably able to be bent
to a radius of about 1 cm without affecting its physical
performance. One approach for aligning the tape elements is to
align the tape elements into a sheet by pulling yarn from a creel.
Using a roll-off creel is helpful to reduce twist in the yarn.
[0029] FIG. 4B illustrates a unidirectional sheet 52 formed from a
multiplicity of core/shell type fiber elements 15. The fiber
elements 15 are aligned parallel along a common fiber direction of
the unidirectional sheet 52. In one embodiment the fiber elements
15 in the unidirectional sheet 52 do not overlap one another, and
may have gaps between the fiber elements 15. In another embodiment,
the fiber elements may overlap one another up to 90% in the
unidirectional sheet 52. The unidirectional sheet 52 may
additionally have a polymer matrix. The unidirectional sheet 52 is
preferably able to be bent to a radius of about 1 cm without
affecting its physical performance. One approach for aligning the
fiber elements is to align the tape elements into a sheet by
pulling yarn from a creel. Using a roll-off creel is helpful to
reduce twist in the yarn.
[0030] FIGS. 5 and 5B illustrate composite sheets, each made up of
two unidirectional sheets 50 and one adhesive layer 60. The
composite sheets are easier to handle than the unidirectional
sheets, as the unidirectional sheets are composed of the tape
elements 10 not bound in any way to one another. In the embodiment
where the unidirectional sheets are made up of tape elements 10
with a core layer 12 and one surface layer 14 (as shown in FIG. 5A)
the adhesive layer 60 is adjacent and sandwiched between the core
layers 12 of the tape elements 10 in the unidirectional sheet 50.
In the embodiment where the unidirectional sheets are made up of
tape elements 10 with a core layer 12 and two surface layers 14 and
14' (shown in FIG. 5B), the adhesive layer 60 is adjacent to and
sandwiched between the surface layers 14' of the tape elements 10.
Within each composite sheet 100, the common fiber direction of the
unidirectional sheets 50 may be aligned, or rotated relative to
each other, for example 90 degrees. Preferably, the common fiber
direction of the unidirectional sheets 50 in the composite sheet
100 are the same.
[0031] FIG. 6 illustrates composite sheets, each made up of two
unidirectional sheets 52 formed from fiber elements 15 and one
adhesive layer 60. The composite sheets are easier to handle than
the unidirectional sheets, as the unidirectional sheets are
composed of the fiber elements 15 not bound in any way to one
another. The adhesive layer 60 is adjacent and sandwiched between
the surface layers 17 of the fiber elements 15. Within each
composite sheet 102, the common fiber direction of the
unidirectional sheets 52 may be aligned, or rotated relative to
each other, for example 90 degrees. Preferably, the common fiber
direction of the unidirectional sheets 52 in the composite sheet
102 are the same.
[0032] The adhesive layer 60 preferably comprises a material which
is compatible with the unidirectional material and fuses the
unidirectional material into a unidirectional sheet 52. The
adhesive layer may be activated to fuse the unidirectional material
by pressure, heat, UV, other activation methods, or any combination
thereof. In one embodiment, the adhesive is a pressure sensitive
adhesive. In another embodiment, the adhesive has a softening point
less than that of the surface layer of the fiber elements.
Preferably, the softening point of the adhesive is at least
10.degree. C. less than that of the surface layer of the fiber
elements. In one embodiment, a melting point of less than
130.degree. C. is preferred. For unidirectional sheets made up of
tape or fiber elements with an olefin core and surface layers, the
adhesive layer 60 may be, but is not limited to EVA, LLDPE, LDPE,
HDPE, copolymers of polypropylene, and the like. The adhesive layer
60 preferably has a lower softening temperature than the layer of
the tape or fiber element 10, 15 adjacent to the adhesive layer 60.
This corresponds to the core layer 12 for the tape element 10
having a core layer 12 and one surface layer 14 (as shown in FIG.
5A), the surface layer 14' for the tape element 10 having a core
layer 12 and surface layers 14 and 14' (as shown in FIG. 5B), and
the surface layer 17 for a fiber element 15 (as shown in FIG. 6).
The adhesive layer 60 preferably has a thickness of between about
10 .mu.m and 100 .mu.m. For pressure sensitive adhesives, the
amount of tack is preferably high enough to stabilize the
unidirectional sheets for handling.
[0033] The adhesive layer may be applied to the unidirectional
sheets 50, 52 by any method known in the art. Preferred methods
include any well known coating method such as air knife coating,
gravure coating, hopper coating, roller coating, spray coating, and
the like. The coating composition can be based on water or organic
solvent(s) or a mixture of water and organic solvent(s).
Alternatively, the adhesive layer 60 can be formed by thermal
processing such as extrusion and co-extrusion with and without
stretching, blow molding, injection molding, lamination, etc. The
adhesive layer 60 may also be an adhesive scrim, powder coating, or
the like.
[0034] Referring now to FIGS. 7A-B and 8A-B, there is shown
different embodiments of the impact resistant component 200. While
the impact resistant components 200 shown in FIG. 7A-B and 8A-B are
formed from 2 composite sheets 100, additional composites sheets
100 may be added to the top or bottom of the impact resistant
component 200 shown. Preferably, the adhesive layers 60 are in an
amount of about 0.2 to 20%, more preferably about 2-10% of the
weight of the impact resistant component. In one embodiment, the
tape elements and the adhesive layer comprise polypropylene. This
creates an impact resistant component that is essentially
polypropylene increasing the recycleability of the component.
[0035] Referring now to FIGS. 9A-B, there is shown another
embodiment of the impact resistant component 202 formed from
shell/core type fiber elements 15. While the impact resistant
components 202 shown in FIG. 9A-B are formed from 2 composite
sheets 102, additional composites sheets 102 may be added to the
top or bottom of the impact resistant component 202 shown.
Preferably, the adhesive layers 60 are in an amount of about 0.2 to
20%, more preferably about 2-10% of the weight of the impact
resistant component. In one embodiment, the fiber elements and the
adhesive layer comprise polypropylene. This creates an impact
resistant component that is completely or essentially polypropylene
increasing the recycleability of the component.
[0036] Referring back to FIGS. 7A and B, there is shown impact
resistant components formed from tape elements 10 with a core layer
12 and one surface layer 14. The impact resistant component 200 is
formed when the surface layers 14 from the composite sheets 100 are
fused using heat and optionally pressure. There are no additional
layers, adhesives, or treatments added to the surface layers 14 of
the tape elements 10. In FIG. 7A, the common fiber direction of the
unidirectional sheets 50 in one composite sheet 100 is the same
(parallel to) as the common fiber direction of the unidirectional
sheets 50 of the adjacent composite sheet 100. In FIG. 7B, the
common fiber direction of the unidirectional sheets 50 in one
composite sheet 100 is the perpendicular (rotated 90 degrees) to
the common fiber direction of the unidirectional sheets 50 of the
adjacent composite sheet 100. While in FIGS. 7A and B, 0 and 90
degree rotations have been shown; any rotation angle is feasible
and contemplated. The structure of the impact resistant component
of FIGS. 7A and B in written form is as follows: [0037] . . .
AB-Adh-BA-AB-Adh-AB . . .
[0038] (B being the core layer, A being a surface layer, and Adh
being the adhesive layer)
[0039] The impact resistant components shown in FIGS. 8A and B are
formed from tape elements 10 with a core layer 12 and two surface
layers 14 and 14'. The impact resistant component 200 is formed
when the surface layers 14 from the composite sheets 100 are fused
using heat and optionally pressure. There are no additional layers,
adhesives, or treatments added to the surface layers 14 of the tape
elements 10. In FIG. 8A, the common fiber direction of the
unidirectional sheets 50 in one composite sheet 100 is the same
(parallel to) as the common fiber direction of the unidirectional
sheets 50 of the adjacent composite sheet 100. In FIG. 8B, the
common fiber direction of the unidirectional sheets 50 in one
composite sheet 100 is the perpendicular (rotated 90 degrees) to
the common fiber direction of the unidirectional sheets 50 of the
adjacent composite sheet 100. While in FIGS. 8A and B, 0 and 90
degree rotations have been shown, any rotation angle is
contemplated. The structure of the impact resistant component of
FIGS. 8A and B in written form is as follows: [0040] . . .
ABA'-Adh-A'BA-ABA'-Adh-A'BA . . .
[0041] (B being the core layer, A and A' being surface layers, and
Adh being the adhesive layer).
[0042] The impact resistant components 202 shown in FIGS. 9A and B
are formed from fiber elements 15 with a core 16 and a surface
layer 17. The impact resistant component 202 is formed when the
surface layers 17 from the composite sheets 102 are fused using
heat and optionally pressure. There are no additional layers,
adhesives, or treatments added to the surface layers 17 of the
fiber elements 15. In FIG. 9A, the common fiber direction of the
unidirectional sheets 52 in one composite sheet 102 is the same
(parallel to) as the common fiber direction of the unidirectional
sheets 52 of the adjacent composite sheet 102. In FIG. 9B, the
common fiber direction of the unidirectional sheets 52 in one
composite sheet 102 is the perpendicular (rotated 90 degrees) to
the common fiber direction of the unidirectional sheets 52 of the
adjacent composite sheet 102. While in FIGS. 9A and B, 0 and 90
degree rotations have been shown, any rotation angle is
contemplated.
[0043] FIG. 10A illustrates an anti-ballistics panel 300, according
to one embodiment of the invention. The anti-ballistics panel 300
is made up of at least 10 composite sheets 100 formed from tape
elements 10 fused together, more preferably 20 to 100. The
core/shell nature of the fiber elements 15 has not been shown to
reduce the complexity of the illustration. It has been shown that
10 composite sheets 100 fused together resist penetration by
objects. While the anti-ballistics panel 300 is shown with the
common fiber direction of each unidirectional sheet 50 parallel to
the adjacent sheets, each unidirectional sheet 50 may be rotated
any amount with respect to the adjacent unidirectional sheets
50.
[0044] FIG. 10B illustrates an anti-ballistics panel 302, according
to one embodiment of the invention. The anti-ballistics panel 302
is made up of at least 10 composite sheets formed from fiber
elements 15 fused together, more preferably 20 to 100. It has been
shown that 10 composite sheets 102 fused together resist
penetration by objects. While the anti-ballistics panel 302 is
shown with the common fiber direction of each unidirectional sheet
52 rotated 90 degrees with respect to the adjacent layers, each
unidirectional sheet 52 may be rotated any amount with respect to
the adjacent unidirectional sheets 52.
[0045] The impact resistant component 200, 202 and the
anti-ballistics panel 300, 302 are adapted for three dimensional
thermo-molding. One example is shown in FIG. 11 of a molded helmet
400. Other articles of the impact resistant component 200, 202 and
the anti-ballistics panel 300, 302 may be molded into include chest
plates, extremity protection, vehicle panels, or other applications
where anti-ballistic properties are required with a light weight
panel.
[0046] The process for forming an impact resistant component
comprises:
[0047] 1) forming unidirectional sheets comprising arranging a
plurality of monoaxially drawn fibers substantially parallel to one
another along a common fiber direction, the fiber elements (10 or
15) comprising a core (12 or 16) of a strain oriented polymer and
at least one surface layer (14 or 17) of a heat fusible polymer
surface at least a portion of the core (12 or 16), wherein the at
least one surface layer (14 or 17) is characterized by a softening
temperature below that of the core (12 or 16) to permit fusion
bonding upon application of heat.
[0048] 2) sandwiching an adhesive layer 60 between two
unidirectional sheets (50 or 52).
[0049] 3) activating (preferably by heat) the sandwiched adhesive
layer 60 and unidirectional sheets (50 or 52) to a approximately
the melting temperature of the adhesive layer 60 to form a
composite sheet (100 or 102) with optional pressure.
[0050] 4) stacking at least 2 composite sheets (100 or 102).
[0051] 5) applying heat (and optionally pressure of between about
0.5 and 150 bars) to the stacked composite sheets (100 or 102) to
bond the surface layers (14 or 17) of the composite sheets (100 or
102) together.
[0052] Forming an anti-ballistics panel (300 and 302) follows the
same steps as above, except that at least 10 composite sheets (100,
102) are stacked together. The method discloses the tape elements
10 comprising a core layer 12 and surface layers 14 and 14', the
method also applies for impact resistant components 200 and
anti-ballistics panels 300 made from tape elements 10 having a core
layer 12 and one surface layer 14. The surface layers 14 between
the composite sheets fuse to form the component 200 or panel
300.
[0053] According to one contemplated practice, the layers of
composite sheets 100 or 102 may be formed from a single composite
sheet 100 or 102 that is repeatedly folded over itself, or from
several discrete overlaid composite sheets 100 or 102.
Alternatively, the impact resistant component 200 or 202 may be
formed by reheating several previously fused composite sheets 100
or 102. The anti-ballistics panel 300 or 302 may be formed by
reheating several previously fused composite sheets 100 or 102 or
impact resistant components 200 or 202. When such previously fused
material is subjected to a temperature above the softening point of
the surface layers 14, 14' or 17 and below that of the core 12, 17,
the matrix will again melt while the core layers remain
substantially solid. Upon cooling, the surface layers 14, 14', 17
will again fuse and re-form the matrix. Any of these methods may be
employed to form a component 200 or 202 or panel 300 or 303 with
any desired thickness or number of sheets. Additionally, it is
contemplated that a component or panel may be made with a mixture
of unidirectional sheets 50 with tape and elements and
unidirectional sheets 52 with core/shell fiber elements.
[0054] Consolidation of composite sheets 100, 102 are preferably
carried out at suitable temperature and pressure conditions to
facilitate both interface bonding fusion and partial migration of
the melted surface layer material between the layers. Heated batch
or platen presses may be used for multi-layer consolidation.
However, it is contemplated that any other suitable press may
likewise be used to provide appropriate combinations of temperature
and pressure. According to a potentially preferred practice,
heating is carried out at a temperature of about 130-160.degree. C.
and a pressure of about 0.5-70 bar. When exposed to such an
elevated temperature and pressure, the surface layers 14, 14', 17
will soften or even melt while the core layer 12, 16 will remain
substantially solid. Upon cooling, the surface layers 14, 14', 17
will fuse thereby forming a matrix through which the stiff core
layers 12, 16 are distributed. According to a potentially preferred
practice, cooling is carried out under pressure to a temperature
less than about 115.degree. C. It is contemplated that maintaining
pressure during the cooling step tends to inhibit shrinkage.
Without wishing to be limited to a specific theory, it is believed
that higher pressures may facilitate polymer flow at lower
temperatures. Thus, at the higher end of the pressure range,
(greater than about 20 bar) the processing temperature may be about
90-135.degree. C. Moreover, the need for cooling under pressure may
be reduced or eliminated when these lower temperatures are
utilized. The temperature operating window to fuse the sheets is
wide allowing for various levels of consolidation to occur thus
achieving either a more structural panel or one that would
delaminate more with impact. This delamination helps in the energy
absorption of an impact such as a bullet.
EXAMPLES
[0055] The tape elements used in each of the examples were fusible
mono-axially drawn tape elements having dimensions of 2.2 mm
wide.times.65 microns thick sold under the trade designation PURE
by Lankhorst/Indutech having a place of business in Sneek, The
Netherlands. The tape elements had a polypropylene core layer
surrounded by two polypropylene copolymer surface layers. The
surface layers comprised about 15% by thickness of the total tape
element.
[0056] The adhesive layer was a 0.00035 in (approximately 8 .mu.m)
polyethylene film having a melting point of about 115.degree.
C.
[0057] The composite sheets were formed by loading a roll of creel
with 224 packages of yarn and creating two unidirectional sheets
with 11.2 yarns per inch. The low melt polyethylene film was
sandwiched between the sheets, heating the composite up to the melt
pointing of the film, pressing the composite together, and cooling
to lock the yarns together into a unidirectional sheet. The
composite was heated to a temperature of about 220.degree. F. and
run through a nip with about 90 pli (pounds per linear inch). The
common fiber directions of the two unidirectional sheets were
aligned. The yarn spacing was 11.2 ends/inch. Each composite sheet
was then cut into 10.times.12 inch pieces and stacked so that the
common fiber direction in the unidirectional sheets alternated from
0 degrees to 90 degrees from composite sheet to adjacent composite
sheet. This alternating cross plying process continued until the
weight equaled 1.5 pounds per square foot (psf and 2.3 psf to form
the impact resistant unidirectional component examples. The weight
of the adhesive layer was 8% of the total weight of the example.
This stack of cross plied unidirectional sheet was then placed in
to a cold platen press. Pressure was applied to achieve 300 psi and
the platens were then heated to 300.degree. F. After the
temperature reached 290.degree. F. in the center of the stack
(measured by a thermocouple), cooling was initiated. This process
was completed on several panels so that ballistic testing could be
completed.
[0058] The standard twill fabric samples (comparison examples) were
formed from the tape elements as described woven into a twill weave
mat fabric with 11 picks and ends per inch. The layers were stacked
until the weight equaled 1.5 pounds per square foot (psf) and 2.3
psf for the testing examples. The stacked layers were placed in a
platen press at 300.degree. F. where 300 psi pressure was applied
until the core reached 290.degree. F. The examples were then cooled
to 150.degree. F., had the pressure released and were removed from
the press.
[0059] Examples were then subjected to ballistic testing under the
Department of Defense MIL-STD-662 V50 Ballistic Test for Armor. The
resulting V.sub.50 measurements for each threat and conditions are
below. The V.sub.50 is the calculated speed in feet per second that
the projectile travels during testing. This speed represents the
speed in which the bullet would pass through the panel 50% of the
time and be stopped by the panel 50% of the time.
TABLE-US-00001 Panal % Fabric Arial Normalized reduction const.
Density Areal Density Bullet V.sub.50 in V.sub.50 Unidirectional
1.5 psf 1.38 psf 17 grain 1483 26% FSP Twill 1.5 psf 1.5 psf 17
grain 1522 Fabric FSP Unidirectional 2.3 psf 2.12 psf 44 1377 2.6%
magnum Twill 2.3 psf 2.3 psf 44 1414 Fabric magnum
[0060] The unidirectional panels had approximately 8% by weight of
the adhesive layer. The normalized areal density is the density of
the tape elements in the panel (therefore, for the unidirectional
panels, the normalized areal density is 8% less than the actual
density). For equivalent normalized areal densities, the V50 of
these unidirectional panels is expected to be 5% better than the
panel made from twill fabric. The reduction in V.sub.50 as the
unidirectional panel is compared to the panel made from twill
fabric in both cases was approximately 2.6%. The unidirectional
panel had 8% less by weight of the tape elements (the reinforcing
elements), but the resultant panel had a reduction in V.sub.50
performance of only 2.6%.
[0061] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *