U.S. patent application number 12/740475 was filed with the patent office on 2011-07-21 for material sheet and process for its preparation.
Invention is credited to Marcel M. Jongedijk, Reinard Jozef Maria Steeman, Johann J. Van Elburg.
Application Number | 20110174147 12/740475 |
Document ID | / |
Family ID | 40351342 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110174147 |
Kind Code |
A1 |
Steeman; Reinard Jozef Maria ;
et al. |
July 21, 2011 |
MATERIAL SHEET AND PROCESS FOR ITS PREPARATION
Abstract
The invention relates to a material sheet comprising a woven
fabric of polymer tapes, wherein the width of a tape varies less
than 2% on average in the longitudinal direction of the tape. The
invention also relates to a process for the preparation of the
material sheet, and to a ballistic resistant article comprising the
material sheet. A ballistic resistant article comprising the
material sheet exhibits excellent antiballistic properties.
Inventors: |
Steeman; Reinard Jozef Maria;
(Elsloo, NL) ; Jongedijk; Marcel M.; (Sittard,
NL) ; Van Elburg; Johann J.; (Landgraaf, NL) |
Family ID: |
40351342 |
Appl. No.: |
12/740475 |
Filed: |
October 29, 2008 |
PCT Filed: |
October 29, 2008 |
PCT NO: |
PCT/EP2008/009122 |
371 Date: |
April 29, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61001096 |
Oct 31, 2007 |
|
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|
Current U.S.
Class: |
89/36.02 ;
156/148; 156/308.2; 264/109; 442/186; 526/352; 89/903; 89/904;
89/917 |
Current CPC
Class: |
B32B 2262/0246 20130101;
B29L 2031/3076 20130101; B32B 2262/0223 20130101; D02G 3/06
20130101; B32B 15/08 20130101; B32B 2307/54 20130101; B32B 2607/00
20130101; B29L 2023/005 20130101; B32B 2605/18 20130101; D10B
2321/02 20130101; B32B 2307/50 20130101; B32B 2435/00 20130101;
B32B 5/024 20130101; B32B 2262/0276 20130101; B32B 2262/101
20130101; B29C 43/02 20130101; B32B 5/26 20130101; Y10T 442/3041
20150401; B32B 5/022 20130101; B32B 15/14 20130101; B32B 27/32
20130101; D10B 2505/00 20130101; B32B 9/047 20130101; B32B 2260/00
20130101; D03D 15/00 20130101; B29K 2023/0683 20130101; D10B
2331/02 20130101; F41H 5/0471 20130101; B29K 2995/0089 20130101;
B32B 9/005 20130101; B32B 2262/106 20130101; B32B 9/041 20130101;
D10B 2321/10 20130101; B32B 5/028 20130101; B32B 7/12 20130101;
B32B 9/007 20130101; B32B 2307/72 20130101; D03D 1/0052 20130101;
B29K 2105/251 20130101; B32B 15/20 20130101; D10B 2331/04 20130101;
B29C 43/003 20130101; B32B 2439/00 20130101; B32B 2262/0253
20130101; D10B 2321/06 20130101; D10B 2401/062 20130101; F41H
5/0464 20130101; B32B 15/18 20130101; D10B 2401/063 20130101; B29C
55/04 20130101; F41H 5/0435 20130101; B29L 2007/007 20130101; D03D
15/46 20210101; B32B 2262/0261 20130101 |
Class at
Publication: |
89/36.02 ;
156/148; 156/308.2; 264/109; 442/186; 526/352; 89/903; 89/904;
89/917 |
International
Class: |
F41H 5/04 20060101
F41H005/04; B32B 37/02 20060101 B32B037/02; B32B 38/00 20060101
B32B038/00; B29C 67/02 20060101 B29C067/02; B29C 71/00 20060101
B29C071/00; D03D 15/00 20060101 D03D015/00; F41H 5/02 20060101
F41H005/02; C08F 110/02 20060101 C08F110/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2007 |
EP |
07021267.5 |
Jan 31, 2008 |
EP |
08001815.3 |
Claims
1. Material sheet comprising a woven fabric of unidirectional tapes
of drawn polymer, wherein the width of a tape varies less than 2%
on average in the longitudinal direction of the tape.
2. Material sheet according to claim 1, wherein the woven fabric
comprises a plurality of unidirectional tapes of the drawn polymer
in the warp and weft direction, and wherein the gap between
adjacent tapes in the weft and/or warp direction is smaller than
10% of the width of the adjacent unidirectional tapes.
3. Material sheet according to claim 1, wherein the longitudinal
edges of adjacent tapes in the weft and/or warp direction at least
partially fixedly abut each other.
4. Material sheet according to claim 1, wherein the unidirectional
tapes in the weft and/or warp direction are mutually bonded, at
least over an area adjacent to the longitudinal edges of the woven
fabric.
5. Material sheet according to claim 4, wherein the bonded area
comprises a binder.
6. Material sheet according to claim 1, wherein the woven fabric
has a plain weave structure.
7. Material sheet according to claim 1, wherein the strength of at
least one unidirectional tape is at least 0.9 GPa.
8. Material sheet according to claim 1, wherein the polymer is
selected from the group consisting of polyolefins, polyesters,
polyvinyl alcohols, polyacrylonitriles, polyamides, especially
poly(p-phenylene teraphthalamide), liquid crystalline polymers and
ladder-like polymers, such as polybenzimidazole or polybenzoxazole,
especially poly(1,4-phenylene-2,6-benzobisoxazole), or
poly(2,6-diimidazo[4,5-b-4',5'-e]pyridinylene-1,4-(2,5-dihydroxy)phenylen-
e).
9. Process for the preparation of a material sheet according to
claim 1, comprising: (a) providing a plurality of drawn polymer
tapes having a width that varies less than 2% on average in the
longitudinal direction of the tape; (b) weaving said plurality of
drawn polymer tapes to form a woven fabric; (c) compressing the
thus formed woven fabric at least over an area adjacent to the
longitudinal edges of the woven fabric to consolidate the area.
10. Process for the manufacture of a ballistic resistant article
comprising: (a) stacking at least one material sheet according to
claim 1 and a sheet of material selected from the group consisting
of ceramic, steel, aluminum, titanium, glass and graphite, or
combinations thereof; and (b) consolidating the stacked sheets
under temperature and pressure.
11. A ballistic resistant article comprising a material sheet
according to claim 1.
12. Ballistic resistant article according to claim 11, whereby a
bonding layer is present between the further sheet of inorganic
material and the material sheet, the bonding layer comprising a
woven or non woven layer of inorganic fiber.
13. Use of the material sheet according to claim 1 in hard
ballistic applications.
14. A polymeric tape having a width that varies less than 2% on
average in the longitudinal direction of the tape.
15. A process for the preparation of the tape according to claim
14, the process comprising forming a polymeric powder bed,
compression-moulding the polymeric powder bed at a temperature
below the melting point of the polymeric powder, and preferably
drawing the compression-moulded polymer, and wherein the powder bed
is moulded by compression together with at least one compressible
bordering means positioned onto the powder bed.
Description
[0001] The invention relates to polymeric tapes and a process for
the preparation thereof and further to a material sheet comprising
the polymeric tapes, and to its process of preparation. The
invention also relates to articles comprising the material sheet,
in particular to a ballistic resistant article. The invention also
relates to different uses of the polymeric tapes.
[0002] A material sheet comprising a consolidated stack of
monolayers of a unidirectionally drawn polymer is known from EP
1627719 A1. This publication discloses a multilayered material
sheet comprising a plurality of unidirectional monolayers
consisting of ultra high molecular weight polyethylene and
essentially devoid of bonding matrices, whereby the draw direction
of two subsequent monolayers in the stack differs. The monolayers
of the multilayered material disclosed in EP 1627719 A1 are
produced by positioning a plurality of tapes of ultra high
molecular weight polyethylene adjacent to each other whereby
adjacently positioned tapes overlap at least partly along their
side edges. Without the overlap the known multilayered material
cannot be produced.
[0003] Although the multilayered material sheet according to EP
1627719 A1 shows a satisfactory ballistic performance, this
performance can be improved further.
[0004] The object of the present invention is to provide a material
sheet that can be easily produced and having at least similar
properties, in particular similar antiballistic properties, as the
material known from EP 1627719 A1 or other commercially available
materials based on unidirectional PE fibers.
[0005] This object is achieved according to the invention by
providing a material sheet comprising a woven fabric of polymeric
tapes, wherein the width of a tape varies less than 2% on average
in the longitudinal direction of the tape.
[0006] Preferably the polymeric tapes, or simply referred to as
tapes, are tapes of a drawn polymer; more preferably, the tapes are
unidirectional tapes of a drawn polymer. With unidirectional tapes
is meant in the context of the invention tapes which show a
preferred orientation of the polymer chains in one direction, i.e.
in the direction of drawing. Such tapes of a drawn polymer may be
produced by drawing said tapes, preferably by uniaxial drawing if
unidirectional tapes are to be produced and which will exhibit
anisotropic mechanical properties.
[0007] Weaving of tapes and in particular of unidirectional tapes
of drawn polymer is known per se, for instance from WO2006/075961,
the content of which is incorporated herein by reference.
WO2006/075961 describes a method for producing a woven material
from tape-like warps and wefts comprising the steps of feeding
tape-like warps to aid shed formation and fabric take-up; inserting
tape-like weft in the shed formed by said warps; depositing the
inserted tape-like weft at the fabric-fell; and taking-up the
produced woven material; wherein said step of inserting the
tape-like weft involves gripping a weft tape in an essentially flat
condition by means of clamping, and pulling it through the shed.
The inserted weft tape is preferably cut off from its supply source
at a predetermined position before being deposited at the
fabric-fell position. While weft tensioning is a necessary
condition for processing yarns, it is not desirable when processing
tapes. The weaving method and apparatus, as disclosed in
WO2006/075961 therefore allows to feed and process tape-like warps
in a state of low tension. This is achieved by carrying out weaving
in a vertical format because this way the sagging of warps and
wefts due to gravity is significantly reduced.
[0008] Weaving is conventionally carried out on yarns, having a
circle-like cross-section. The conventional weaving elements which
directly interact with the yarns, such as heald-wires, reed and
weft transporting means often cannot be employed when weaving
tapes, since such conventional elements are designed to handle
yarns. Their use in handling tapes will lead to deformation and
weakening of the tapes. When weaving tapes and in particular
unidirectional tapes therefore, specially designed weaving elements
are used. Particularly suitable weaving elements are described in
U.S. Pat. No. 6,450,208, the content of which is also incorporated
in the present application by reference.
[0009] The invention further relates to a polymeric tape having a
width that varies less than 2% on average in the longitudinal
direction of the tape. Preferably, said tape is a tape of a drawn
polymer, more preferably, said tape is a unidirectional tape of a
drawn polymer.
[0010] It was observed that by carefully controlling the width
variation of the polymeric tapes of the invention, a material sheet
is obtained with at least similar properties, in particular
antiballistic properties, as the known material, or other
commercially available materials based on unidirectionally aligned
PE fibers.
[0011] In addition, the material sheet according to the invention
is readily produced. The conventional material sheet, as described
in EP 1627719 A1 for instance, is produced by first making a
monolayer of a plurality of tapes positioned adjacent to each
other, and then applying another similar monolayer at an angle on
top of the first monolayer. To give the material handling
characteristics, adjacently positioned tapes overlap at least
partly along their side edges. This process is time consuming and
involves more steps than the process to make the material structure
of the present invention. With the tapes of the invention, an
overlapping of the tapes is not necessary for obtaining a material
sheet with at least similar properties or handling characteristic,
reducing therefore the number of processing steps. In particular
the tape-overlapping step can be dispensed with.
[0012] The material sheet of the invention is preferably produced
by weaving a plurality of the unidirectional tapes of the invention
with their longitudinal edges as close as possible to each other,
and preferably in touching proximity. This is made possible by
using unidirectional tapes having a width that varies less than 2%
on average in the longitudinal direction of the tape, as is
required by the invention. However, in order to be able to produce
the material sheet of the invention on an industrial scale at
economical speeds, it would be desirable to allow a gap between
adjacent tapes (i.e the adjacent tapes in the material sheets are
not in contact along their longitudinal edges--i.e. a gap of
greater than 0%). Preferably, the material sheet according to the
invention is characterized in that the woven sheet comprises a
plurality of unidirectional tapes of the drawn polymer in the warp
and weft direction, and in that the gap between adjacent tapes in
the weft and/or warp direction is smaller than 10% A of the width
of the adjacent unidirectional tapes, more preferably smaller than
5% of the width of the adjacent unidirectional tapes, even more
preferably smaller than 3% of the width of the adjacent
unidirectional tapes. Most preferably said gap is smaller than 1%
provided that the inventive tapes have a width variation also
smaller than 1% on average in the longitudinal direction of the
tape.
[0013] In a preferred embodiment the tapes of the invention have a
width varying less than 1% on average in the longitudinal direction
of the tape. In an even further preferred embodiment the tapes have
a width of at least 10 mm, more preferably at least 20 mm, most
preferably at least 40 mm and further having a variation in width
which is less than 1% on average in the longitudinal direction of
the tape. It was observed that a material sheet based on the tapes
of this embodiment yields an even better antiballistic
performance.
[0014] A particularly preferred embodiment of the tape according to
the invention is characterized in that the polymer from which it is
made is selected from the group consisting of polyolefins,
polyesters, polyvinyl alcohols, polyacrylonitriles, polyamides,
especially poly(p-phenylene teraphthalamide), liquid crystalline
polymers and ladder-like polymers, such as polybenzimidazole or
polybenzoxazole, especially
poly(1,4-phenylene-2,6-benzobisoxazole), or
poly(2,6-diimidazo[4,5-b-4',5'-e]pyridinylene-1,4-(2,5-dihydroxy)phenylen-
e). Unidirectional tapes from these polymers are preferably highly
oriented, i.e. having a crystallinity as measured by DSC of above
90%, by drawing the formed material, for instance films, at a
suitable temperature.
[0015] An even more preferred embodiment of the tape according to
the invention is characterized in that the polymer from which it is
made is selected from the group consisting of polyolefins,
polyesters, polyvinyl alcohols, polyacrylonitriles, and polyamides.
The material sheets comprising these tapes can be very well
consolidated.
[0016] The material sheet of the invention allows the use of tapes
of drawn polymers, or simply drawn tapes, with relatively low
strength, and therefore does not expressly need high strength drawn
tapes made of e.g. ultra high molecular weight polyethylene to
obtain good antiballistic performance. However, in a preferred
embodiment thereof the tapes of the invention comprise ultra high
molecular weight polyethylene. The ultra high molecular weight
polyethylene may be linear or branched, although preferably linear
polyethylene is used. Linear polyethylene is herein understood to
mean polyethylene with less than 1 side chain per 100 carbon atoms,
and preferably with less than 1 side chain per 300 carbon atoms; a
side chain or branch generally containing at least 10 carbon atoms.
Side chains may suitably be measured by FTIR on a 2 mm thick
compression moulded film, as mentioned in e.g. EP 0269151. The
linear polyethylene may further contain up to 5 mol % of one or
more other alkenes that are copolymerisable therewith, such as
propene, butene, pentene, 4-methylpentene, octene. Preferably, the
linear polyethylene is of high molar mass with an intrinsic
viscosity (IV, as determined on solutions in decalin at 135.degree.
C.) of at least 4 dl/g; more preferably of at least 8 dl/g, most
preferably of at least 10 dl/g. Such polyethylene is also referred
to as ultra high molecular weight polyethylene. Intrinsic viscosity
is a measure for molecular weight that can more easily be
determined than actual molar mass parameters like Mn and Mw. A
polyethylene film of this type yields particularly good
antiballistic properties.
[0017] The tapes according to the invention may be prepared in the
form of films which is subsequently slit into tapes.
[0018] A preferred first process for the preparation of the tape of
the invention comprises forming a polymeric powder bed,
compression-moulding the polymeric powder bed at a temperature
below the melting point of the polymeric powder, and preferably
drawing the compression-moulded polymer, and wherein the powder bed
is moulded by compression together with at least one compressible
bordering means positioned onto the powder bed. The invention also
relates to such a process.
[0019] Preferably, the powder bed is compression-moulded together
with at least two parallel compressible bordering means, said means
defining in the powder bed an in-boundary part and an
out-of-boundary part or parts. The melting point of the polymeric
powder, also called melting temperature is determined by DSC as
detailed below.
[0020] By compressible bordering means it is understood means made
of a compressible material, said means partitioning the powder bed
into at least two parts. By compressible is meant that the means do
not substantially interfere with the compression moulding of the
polymeric powder bed. In a preferred embodiment, the compressible
bordering means are compressible strips. In particular, the
undeformed strips typically only take a negligible part of the
compressive pressure produced by the compression means of the
compression-moulding device, preferably less than 5%, more
preferably less than 2%, most preferably less than 1%. The strips
act as a firm boundary for the polymeric powder and it has turned
out that the use of said strips provides for a polymeric powder bed
that is well controlled and of substantially uniform distribution,
at least between the boundaries formed by the at least two
strips.
[0021] The compressible bordering means and in particular the
strips, may be manufactured from any material that is flexible
enough to provide for the desired compressibility. Preferred
materials include thermoplastic polymers, of which polyolefins,
such as polypropylene are particularly preferred. Another
particularly preferred material comprises a rubber polymer, and
more preferably a high temperature resistant rubber polymer, such
as a silicon rubber. The means, e.g. strips, are preferably made of
a material having a melting temperature as determined by DSC of at
least 10.degree. C., more preferably at least 20.degree. C., and
most preferably at least 30.degree. C. higher than the melting
temperature of the polymeric powder.
[0022] Said means, and in particular the strips, may have any
shape. It is possible for the means, e.g. strips, to for instance
have a rectangular, triangular, circular, or polygonal
cross-section, whereby the means or strips can be solid or hollow.
Preferably, strips are used that are hollow since such strips are
easily compressible. In a particularly preferred process according
to the invention, the strips comprise a hose, or a tube. The
undeformed height of the means, e.g. strips, can be varied within
large boundaries. The undeformed height of the means, e.g. strips,
is preferably equal or higher than the undeformed average thickness
of the polymeric powder bed. In the event of a hollow strip such as
e.g. hose or a tube, the ratio of outer diameter:inner diameter
preferably is 3:2, more preferably 3:1.5 and even more preferably
3:1.
[0023] It is also possible, according to the invention to provide
strips within the polymeric powder bed having a lower undeformed
height than the undeformed average thickness of the polymeric
powder bed. Such strips result in embossed tapes having locally
decreased thickness.
[0024] In a preferred embodiment of the process of making the tapes
of the invention, the compression-moulding process is carried out
according to the process of U.S. Pat. No. 5,091,133, the disclosure
thereof being included herein by reference. Therefore, the
invention relates to a process for the preparation of a polymeric
tape, the process comprising feeding a polymeric powder between a
combination of endless belts thus forming a polymeric powder bed,
compression-moulding the polymeric powder bed at a temperature
below the melting point of the polymeric powder, conveying the
resultant compression-moulded polymer between the endless belts and
preferably drawing the compression-moulded polymer, wherein at
least two strips of compressible material are fed and conveyed
between the endless belts together with the polymeric powder.
According to this preferred embodiment, it is essential that the
strips are compressible, at least in their undeformed state, by
which is meant that the strips do not substantially interfere with
the compression moulding of the polymeric powder bed.
[0025] Preferably, the strips are arranged substantially parallel
to each other and in the conveying direction, whereby the strips
are arranged in such a way that the width of the resulting tape
varies less than 2% on average in the longitudinal direction of the
tape. This may suitably be done by e.g. a creating a fixed distance
between the strips by feeding the strips through a rack with a
predefined width for the strips. Preferably two of such racks are
present for best alignment of the strips, e.g. such racks are
present before and after a conveying section. More preferably the
strips are fed through the said rack while under tension for
alignment. The required tension can be easily be determined by
routine experimentation, whereby too high a tension could lead to
excessive deformation of the strips and too low a tension will not
result in a tape with less than 2% variation of width. An
alternative method could be electronically controlled width-gauges
between and guiding the strips. According to this embodiment, the
polymeric powder is fed or scattered onto the belt over some width,
whereby the width is generally larger than the distance between the
strips. The powder bed therefore overlaps with the strips. In other
words, the strips are arranged such that they extend within the
polymeric powder bed along the outer edges thereof, and at some
distance from the outer edges. The polymeric powder bed is in this
way divided in a part that is in-boundary and extends between the
strips, and in a part that is out-of-boundary, the latter part
extending from the strips to the outer edges of the powder bed.
Preferably, the compression-moulded out-of-boundary part(s) of the
powder bed may be removed and recycled. Such process therefore
offers the possibility to produce a polymeric tape substantially
without waste.
[0026] A further particularly preferred embodiment of the process
of making the tapes of the invention is characterized in that the
number of strips is 2, and are used to create an in-boundary part
between these 2 strips and an out-of boundary part or parts,
whereby the strips are arranged such that they longitudinally
extend within the polymeric powder bed along the outer edges of
said bed such that the width of the out-of boundary part(s) of the
powder bed does not exceed 30% of the total width of the powder
bed. When scattering polymeric powder onto e.g. a belt, the side
regions thereof will generally show a variation in thickness, the
thickness decreasing towards the sides of the powder bed. It has
turned out that by positioning the strips according to this
embodiment, i.e. such that the width of the out-of boundary part(s)
of the powder bed does not exceed 30% of the total width of the
powder bed, the in-boundary part of the powder bed will have a
substantially uniform thickness. With the "width of the
out-of-boundary parts" is meant the total width of the
out-of-boundary part or parts. It is believed that the more uniform
thickness of the in-boundary part of the powder bed is responsible
for the observed improved properties of the final polymeric
tape.
[0027] In an even more preferred embodiment of the process of
making the tapes of the invention, the strips are positioned at a
distance from the outer edges of the polymeric powder bed of at
most 20% of the total width of the polymeric powder bed, and most
preferred at a distance from the outer edges of the polymeric
powder bed of at most 10% of the total width of the polymeric
powder bed.
[0028] If desired, prior to feeding and compression-moulding the
polymer powder, the polymer powder may be mixed with a suitable
liquid organic compound having a boiling point higher than the
melting point of said polymer. Compression moulding is preferably
carried out by temporarily retaining the polymer powder between the
endless belts while conveying. This may for instance be done by
providing pressing platens and/or rollers in connection with the
endless belts. The UHMWPE polymer used in this process is
preferably drawable in the solid state.
[0029] Drawing, preferably uniaxial drawing, of the compression
moulded polymer may be carried out by means known in the art. Such
means comprise extrusion stretching and tensile stretching on
suitable drawing units. To attain increased mechanical strength and
stiffness, drawing may be carried out in multiple steps. In case of
the preferred ultra high molecular weight polyethylene films,
drawing is typically carried out uniaxially in a number of drawing
steps. The first drawing step may for instance comprise drawing to
a stretch factor of 3. Multiple drawing may typically result in a
stretch factor of 9 for drawing temperatures up to 120.degree. C.,
a stretch factor of 25 for drawing temperatures up to 140.degree.
C., and a stretch factor of 50 for drawing temperatures up to and
above 150.degree. C. By multiple drawing at increasing
temperatures, stretch factors of about 50 and more may be
reached.
[0030] Since the polymeric tape of the invention is produced by
providing clear boundaries for the polymeric powder bed, e.g. in
the form of the easily compressible strips, the tape is more
uniform than known hitherto, in particular in the transverse
direction of the tape as produced. Polymeric tape of the invention
may be obtained having further an areal weight varying less than
10% on average in the transverse direction of the tape, and
preferably less than 5% on average in the transverse direction of
the tape. Such more uniform tapes provide better, or at least more
consistent mechanical properties than the known tapes.
[0031] A preferred second process for the formation of films or
tapes comprises feeding a polymer to an extruder, extruding a film
or a tape at a temperature above the melting point thereof and
drawing the extruded film or tape. If desired, prior to feeding the
polymer to the extruder, the polymer may be mixed with a suitable
liquid organic compound, for instance to form a gel, such as is
preferably the case when using ultra high molecular weight
polyethylene. Preferably the polyethylene films are prepared by
such a gel process. A suitable gel spinning process is described in
for example GB-A-2042414, GB-A-2051667, EP 0205960 A and WO
01/73173 A1, and in "Advanced Fibre Spinning Technology", Ed. T.
Nakajima, Woodhead Publ. Ltd (1994), ISBN 185573 182 7. In short,
the gel spinning process comprises preparing a solution of a
polyolefin of high intrinsic viscosity, extruding the solution into
a film at a temperature above the dissolving temperature, cooling
down the film below the gelling temperature, thereby at least
partly gelling the film, and drawing the film before, during and/or
after at least partial removal of the solvent.
[0032] Drawing, preferably uniaxial drawing, of the produced films
or tapes may be carried out by means known in the art. Such means
comprise extrusion stretching and tensile stretching on suitable
drawing units. To attain increased mechanical strength and
stiffness, drawing may be carried out in multiple steps. In case of
the preferred ultra high molecular weight polyethylene films,
drawing is typically carried out uniaxially in a number of drawing
steps. The first drawing step may for instance comprise drawing to
a stretch factor of 3. Multiple drawing may typically result in a
stretch factor of 9 for drawing temperatures up to 120.degree. C.,
a stretch factor of 25 for drawing temperatures up to 140.degree.
C., and a stretch factor of 50 for drawing temperatures up to and
above 150.degree. C. By multiple drawing at increasing
temperatures, stretch factors of about 50 and more may be reached.
This results in high strength tapes, whereby for tapes of ultra
high molecular weight polyethylene, strengths of 1.5 GPa to 1.8 GPa
and more may be obtained.
[0033] According to the invention, the resulting tapes, preferably
the resulting drawn tapes, may be used as such to produce the
material sheet by weaving, if their variation in width is less than
2% on average in the longitudinal direction of the tape, and
preferably less than 1% on average in the longitudinal direction of
the tape. Alternatively, the tapes and in particular the drawn
tapes as produced may be cut to their desired width, or split along
the direction of drawing, to obtain the limited width variation as
required by the invention. Preferably the material sheet is woven
from tape that is not slitted e.g. to form fiber like structures as
disclosed in U.S. Pat. No. 5,091,133.
[0034] The width of the tapes of the invention and in particular
the width of the unidirectional tapes, is only limited by the width
of the film from which they are produced. The width of the tapes
preferably is more than 2 mm, preferably more than 5 mm, more
preferably more than 10 mm, even more preferably more than 20 mm.
Most preferably the width of the tapes is more than 40 mm. It was
observed that wider tapes perform better when woven into material
sheets and furthermore, material sheets comprising wider tapes have
further improved properties, in particular antiballistic
properties, especially when the width of the tapes is more than 40
mm. In principle there is no restriction to the maximum width of
the tape. For practical reasons the preferred maximum width is at
most 400 mm, more preferably at most 300 mm, most preferably at
most 200 mm.
[0035] The areal density of the tapes of the invention can be
varied over a large range, for instance between 5 and 200
g/m.sup.2. Preferred areal density is between 8 and 120 g/m.sup.2,
more preferred between 10 and 80 g/m.sup.2 and most preferred
between 12 and 60 g/m.sup.2, most preferred between 12 and 30
g/m.sup.2. The areal density of a tape can be determined by
weighing a conveniently cut surface from the tape. It was observed
that material sheets made of such tapes have improved antiballistic
performance.
[0036] The thickness of the tapes of the invention, in particular
the unidirectional tapes, can in principle be selected within wide
ranges. Preferably however, the thickness of the tapes used in
weaving the material sheet of the invention does not exceed 120
.mu.m, more preferably does not exceed 50 .mu.m, and most
preferably is comprised between 5 and 29 .mu.m. A further preferred
material sheet according to the invention is characterized in that
the thickness of the tapes used to manufacture thereof is greater
than 10 .mu.m and does not exceed 50 .mu.m, preferably does not
exceed 100 .mu.m and more preferably does not exceed 120 .mu.m. By
limiting the thickness of the tapes in a material sheet to the
claimed thicknesses, sufficient antiballistic properties are
surprisingly achieved even with tapes having rather limited
strengths. The skilled person knows how to determine the thickness
of the tape, e.g. with a micrometer.
[0037] The strength of the tapes of the invention, in particular
the tapes in the material sheet, largely depends on the polymer
from which they are produced, and on their (uniaxial) drawing or
draw ratio. The strength of the tapes is at least 0.75 GPa,
preferably at least 0.9 GPa, more preferably at least 1.2 GPa, even
more preferably at least 1.5 GPa, even more preferably at least 1.8
GPa, and even more preferably at least 2.1 GPa, and most preferably
at least 3 GPa. The unidirectional tapes are preferably
sufficiently interconnected to each other, meaning that the
material sheets according to the invention hardly delaminate under
normal use conditions such as e.g. at room temperature.
[0038] The material sheet according to the invention may comprise
tapes woven into e.g. fabrics of any structure. Suitable woven
fabric structures may include plain weave, twill weave, basket
weave, satin weave, crowfoot weave, and others. Particularly
preferred is a material sheet, wherein the woven fabric has a plain
weave structure. Such a structure offers a stable material sheet,
which is easily processed further. Also, this embodiment shows
excellent antiballistic performance, especially in a stand alone
configuration. Another preferred embodiment of the material sheet
comprises a woven fabric having a twill weave structure. Such an
embodiment is preferred in ballistic resistant articles, comprising
material sheets of the invention and a further sheet of inorganic
material selected from the group consisting of ceramic, steel,
aluminum, magnesium titanium, nickel, chromium and iron or their
alloys, glass and graphite, or combinations thereof. The present
embodiment preferably comprises a twill weave structure with an
interlacing frequency ranging from 3-30:1, and more preferably
ranging from 7-21:1. An interlacing frequency of x:1 means that a
warp (or weft yarn) crosses over x weft (or warp) yarns.
[0039] The material sheet of the invention may also include a
binder which is locally applied to bond and stabilise the plurality
of the tapes, in particular unidirectional tapes used in
manufacturing thereof, such that the structure of the material
sheet is retained during handling and producing of structures, e.g.
antiballistic structures. Suitable binders are described in e.g. EP
0191306 B1, EP 1170925 A1, EP 0683374 B1 and EP 1144740 A1. The
binder may be applied in various forms and ways; for example as a
transverse bonding strip (transverse with respect to the e.g.
unidirectional tapes). The application of the binder during the
formation of the material sheet advantageously stabilises the
tapes, thus enabling faster production cycles to be achieved.
[0040] In one embodiment, a binder is applied to fixedly abut
adjacent unidirectional tapes along their longitudinal edges. As
the role of the binder is to temporarily retain and stabilise the
plurality of unidirectional tapes during handling and making of
material sheets, e.g. antiballistic material sheets, localised
application of the binder is preferred. Local application of the
binder is application that is restricted to the immediate vicinity
of the longitudinal edges and may include intermittent localised
application (spot application along the longitudinal edges).
[0041] In still another preferred embodiment of the material sheet
according to the invention, the unidirectional tapes in the weft
and/or warp direction are mutually bonded, at least over an area
adjacent to the longitudinal edges of the woven fabric. In a
particularly preferred embodiment, the unidirectional tapes of the
drawn polymer in the warp and weft direction of the woven fabric
are at least partly adhered to each other, at least over an area
adjacent to the longitudinal edges of the woven fabric by fusion
bonding. In this embodiment, welding may be used for instance to
intermittently fuse sections of the longitudinal edges of the
material sheet together.
[0042] In embodiments with intermittent localised fusion of the
unidirectional tapes in the weft and/or warp direction, the
proportion of the longitudinal edges of the material sheet
comprising intermittent localised fusion is preferably less than
50%, 30%, 20% 10%, 5% or 2%. When using a binder, the proportion of
the longitudinal edges (or areas adjacent to the longitudinal
edges) of the material sheet which is raised due to the application
of the binder is preferably less than 50%, 30%, 20% 10%, 5% or 2%.
Preferably, the binder comprises less than 20%, 10%, 5%, 2% 1%,
0.5%, or 0.2% of the weight of the material sheet.
[0043] The material sheet according to the invention can be used in
the form of one woven structure, e.g. fabric, as produced. However,
it is also possible to provide a multilayered material sheet by
stacking a plurality of material sheets according to the invention
(e.g. woven fabrics). Such a multilayered material sheet preferably
comprises at least 2 woven fabrics, preferably at least 4 woven
fabrics, more preferably at least 6 woven fabrics, even more
preferably at least 8 woven fabrics, and most preferably at least
10 woven fabrics. Increasing the number of woven fabrics in the
multilayer material sheet of the invention simplifies the
manufacture of articles from these material sheets, for instance
antiballistic plates.
[0044] In one embodiment of the present invention, there is
provided a process for the preparation of a material sheet
comprising:
(a) providing a plurality of drawn polymer tapes, preferably
unidirectional tapes, having a width that varies less than 2% on
average in the longitudinal direction of the tape; (b) weaving said
plurality of drawn polymer tapes to form a woven fabric; (c)
compressing the thus formed woven fabric at least over an area
adjacent to the longitudinal edges of the woven fabric to
consolidate the area.
[0045] In another embodiment, the process is characterised in that,
prior to step (c) the unidirectional tapes of the drawn polymer in
the warp and weft direction of the woven fabric are at least partly
adhered to each other, at least over an area adjacent to the
longitudinal edges of the woven fabric, an example of which is
depicted in FIG. 2. In still another preferred process according to
the invention, adhering the unidirectional tapes is performed by
fusion bonding, and even more preferably by ultrasonic welding.
[0046] The material sheet according to the invention is
particularly useful in manufacturing ballistic resistant articles,
such as vests or armoured plates. Particularly good results are
obtained when drawn tapes, preferably unidirectional tapes
according to the invention are used in manufacturing the material
sheet. Ballistic applications comprise applications with ballistic
threat against projectiles of several kinds including against armor
piercing, so-called AP bullets and hard particles such as e.g.
fragments and shrapnel. The material sheet according to the
invention is most suitable for use in hard ballistics, such as e.g.
panels, for use in vehicles for land/air or sea, or panels for
inserts in bullet resistant vests. The invention therefore also
relates to the enumerated ballistic resistant articles comprising
the material sheet of the invention.
[0047] The ballistic resistant article according to the invention
comprises at least 1 woven fabric layer, preferably at least 5
woven fabric layers, more preferably at least 10 woven fabric
layers, even more preferably at least 15 woven fabric layers and
most preferably at least 20 woven fabric layers.
[0048] Preferably the ballistic resistant article according to the
invention comprises a further sheet of inorganic material selected
from the group consisting of ceramic; metal; glass; graphite, or
combinations thereof. Particularly preferred is metal and in
particular a metal having a melting point of at least 350.degree.
C., more preferably at least 500.degree. C., most preferably at
least 600.degree. C. Suitable metals include aluminum, magnesium,
titanium, copper, nickel, chromium, beryllium, iron and copper
including their alloys as e.g. steel and stainless steel and alloys
of aluminum with magnesium (so-called aluminum 5000 series), and
alloys of aluminum with zinc and magnesium or with zinc, magnesium
and copper (so-called aluminum 7000 series). In said alloys the
amount of e.g. aluminum, magnesium, titanium and iron preferably is
at least 50 wt %. Preferred metal sheets comprising aluminum,
magnesium, titanium, nickel, chromium, beryllium, iron including
their alloys. More preferably the metal sheet is based on aluminum,
magnesium, titanium, nickel, chromium, iron and their alloys. This
results in a light antiballistic article with a good durability.
Even more preferably the iron and its alloys in the metal sheet
have a Brinell hardness of at least 500. Most preferably the metal
sheet is based on aluminum, magnesium, titanium, and their alloys.
This results in the lightest antiballistic article with the highest
durability. Durability in this application means the lifetime of a
composite under conditions of exposure to heat, moisture, light and
UV radiation. Although the further sheet of material may be
positioned anywhere in the stack of woven fabric layers, the
preferred ballistic resistant article is characterized in that the
further sheet of material is positioned at the outside of the stack
of woven fabric layers, most preferably at least at the strike face
thereof.
[0049] The ballistic resistant article according to the invention
preferably comprises a further sheet of the above described
inorganic material having a thickness of at most 100 mm. Preferably
the maximum thickness of the further sheet of inorganic material is
75 mm, more preferably 50 mm, and most preferably 25 mm. This
results in the best balance between weight and antiballistic
properties. Preferably, in the event that the further sheet of
inorganic material is a metal sheet, the thickness of the metal
sheet, is at least 0.25 mm, more preferably at least 0.5 mm, and
most preferably at least 0.75 mm. This results in even better
antiballistic performance.
[0050] The further sheet of inorganic material may optionally be
pre-treated in order to improve adhesion with the multilayer
material sheet. Suitable pre-treatment of the further sheet
includes mechanical treatment e.g. roughening or cleaning the
surface thereof by sanding or grinding, chemical etching with e.g.
nitric acid and laminating with polyethylene film.
[0051] In another embodiment of the ballistic resistant article a
bonding layer, e.g. an adhesive, may be applied between the further
sheet and the multilayer material sheet. Such adhesive may comprise
an epoxy resin, a polyester resin, a polyurethane resin or a
vinylester resin. In another preferred embodiment, the bonding
layer may further comprise a woven or non woven layer of inorganic
fiber, for instance glass fiber or carbon fiber. It is also
possible to attach the further sheet to the multilayer material
sheet by mechanical means, such as e.g. screws, bolts and snap
fits. In the event that the ballistic resistant article according
to the invention is used in ballistic applications where a threat
against AP bullets, fragments or improvised explosive devices may
be encountered the further sheet is preferably comprises a metal
sheet covered with a ceramic layer. In this way an antiballistic
article is obtained with a layered structure as follows: ceramic
layer/metal sheet/at least two unidirectional sheets with the
direction of the fibers in the unidirectional sheet at an angle
.alpha. to the direction of the fibers in an adjacent
unidirectional sheet. Suitable ceramic materials include e.g.
alumina oxide, titanium oxide, silicium oxide, silicium carbide and
boron carbide. The thickness of the ceramic layer depends on the
level of ballistic threat but generally varies between 2 mm and 30
mm. This ballistic resistant article is preferably positioned such
that the ceramic layer faces the ballistic threat.
[0052] In one embodiment of the present invention, there is
provided a process for the manufacture of a ballistic resistant
article comprising: [0053] (a) stacking at least 1 woven fabric
layer of unidirectional tapes of drawn polymer, wherein the width
of a tape varies less than 2% on average in the longitudinal
direction of the tape; and a sheet of material selected from the
group consisting of ceramic, steel, aluminum, titanium, glass and
graphite, or combinations thereof; and [0054] (b) consolidating the
stacked sheets under temperature and pressure.
[0055] In an alternative process a stack of at least 2 woven fabric
layers of unidirectional tapes of drawn polymer, wherein the width
of a tape varies less than 2% on average in the longitudinal
direction of the tape is manufactured in a separate process, such
as has been described above. This pre-manufactured stack is then
combined with the further sheet of material selected from the group
consisting of ceramic, steel, aluminum, titanium, glass and
graphite, or combinations thereof, in step (a) of the process.
[0056] Consolidation for all processes described above may suitably
be done in a hydraulic press. Consolidation is intended to mean
that the monolayers are relatively firmly attached to one another
to form one unit. The temperature during consolidating generally is
controlled through the temperature of the press. A minimum
temperature generally is chosen such that a reasonable speed of
consolidation is obtained. In this respect 80.degree. C. is a
suitable lower temperature limit, preferably this lower limit is at
least 100.degree. C., more preferably at least 120.degree. C., most
preferably at least 140.degree. C. A maximum temperature is chosen
below the temperature at which the drawn polymer woven layers lose
their high mechanical properties due to e.g. melting. Preferably
the temperature is at least 10.degree. C., preferably at least
15.degree. C. and even more at least 20.degree. C. below the
melting temperature of the drawn polymer woven layer. In case the
drawn polymer woven layer does not exhibit a clear melting
temperature, the temperature at which the drawn polymer woven layer
starts to lose its mechanical properties should be read instead of
melting temperature. In the case of the preferred ultra high
molecular weight polyethylene, a temperature below 145.degree. C.
generally will be chosen. The pressure during consolidating
preferably is at least 7 MPa, more preferably at least 15 MPa, even
more preferably at least 20 MPa and most preferably at least 35
MPa. In this way a stiff antiballistic article is obtained. The
optimum time for consolidation generally ranges from 5 to 120
minutes, depending on conditions such as temperature, pressure and
part thickness and can be verified through routine experimentation.
In the event that curved antiballistic articles are to be produced
it may be advantageous to first pre-shape the further sheet of
material into the desired shape, followed by consolidating with the
monolayers and/or multilayer material sheet.
[0057] Preferably, in order to attain a high ballistic resistance,
cooling after compression moulding at high temperature is carried
out under pressure as well. Pressure is preferably maintained at
least until the temperature is sufficiently low to prevent
relaxation. This temperature can be established by one skilled in
the art. When a ballistic resistant article comprising monolayers
of ultra high molecular weight polyethylene is manufactured,
typical compression temperatures range from 90 to 150.degree. C.,
preferably from 115 to 130.degree. C. Typical compression pressures
range between 100 to 300 bar, preferably 100 to 180 bar, more
preferably 120 to 160 bar, whereas compression times are typically
between 40 to 180 minutes.
[0058] The multilayered material sheet and antiballistic article of
the present invention are particularly advantageous over previously
known antiballistic materials as they provide at least the same
level of protection as the known articles at a significantly lower
weight, or an improved ballistic performance at equal weight
compared with the known article. Starting materials are inexpensive
and the manufacturing process is relatively short and thus cost
effective. Since different polymers may be used to produce the
multilayered material sheet of the invention properties may be
optimized according to the particular application. Besides
ballistic resistance, properties include for instance heat
stability, shelf-life, deformation resistance, bonding capacity to
other material sheets, formability, and so on.
[0059] It was also observed that the material sheet of the
invention and the particular constructions comprising said sheet as
described above in the embodiments of the multilayered material
sheet and of the ballistic resistant articles, are products
particularly useful also in manufacturing cargo panels, i.e. panels
used in the construction of cargo containers. Said products proved
also particularly advantageous in manufacturing construction walls;
liners for e.g. cargo holds such as aircraft cargo holds; cargo
pallet sheets and radomes. Furthermore, said products and in
particular the constructions of multilayered material sheets and
ballistic resistant articles proved extremely useful when used to
manufacture impact sensitive aircraft parts, e.g. wing edges, flaps
or other prominent parts which are prone to suffer impacts from
e.g. ice or birds. The invention therefore relates to the use of
the material sheet of the invention in the above enumerated
products and furthermore to the above enumerated products
comprising the material sheet of the invention.
[0060] The invention moreover relates to the use of the tapes of
the invention in woven material sheets and also in a weaving
process for manufacturing material sheets.
[0061] The invention will now be further explained by the following
FIGS. 1-4, without however being limited thereto.
[0062] FIG. 1 schematically represents an embodiment of a material
sheet according to the invention.
[0063] FIG. 2 schematically represents another embodiment of a
material sheet according to the invention.
[0064] FIG. 3 schematically represents still another embodiment of
a material sheet according to the invention.
[0065] FIG. 4 schematically represents a multilayer material sheet
according to the invention.
[0066] Referring to FIG. 1, a woven fabric of unidirectional tapes
of drawn polymer is shown. In the woven fabric, the width of the
tapes of at least 10 mm varies less than 2% on average in the
longitudinal direction of the tapes. The woven fabric has been
obtained by a weaving process as described in WO2006/075961. After
weaving the tapes according to a plain weave pattern (as shown in
FIG. 1), the woven fabric is fed into a belt press or calander
press, known per se, for final consolidation of the material sheet.
In the belt press or calander, the unidirectional tapes running in
the warp and weft direction are bonded at a temperature close to
the melting point of the tapes. It should be noted that tapes of at
least 10 mm can be produced having a width varying less than 2% on
average in the longitudinal direction of the tapes by drawing
polymer films. In instances where this is not possible, a tape as
produced is subsequently slitted along its longitudinal edges to
obtain the limited variation in width, as required by the
invention. Suitable slitting equipment is for instance a Bielloni
Sage machine, model Taglierina, type RP/B1 505, equipped with
chromium steel knives.
[0067] Referring to FIG. 2, another embodiment of a woven fabric of
unidirectional tapes of drawn polymer is shown. As in FIG. 1, the
width of the tapes of at least 10 mm varies less than 2% on average
in the longitudinal direction of the tapes. The woven fabric has
been obtained by a weaving process as described in WO2006/075961.
After weaving the tapes according to a plain weave pattern, the
woven fabric has been partly consolidated over an area adjacent to
the longitudinal edges of the woven fabric only. The dots shown in
FIG. 2 actually represent locations in which the unidirectional
tapes have been fusion bonded, for instance by welding.
[0068] Referring to FIG. 3, still another embodiment of a woven
fabric of unidirectional tapes of drawn polymer is shown. As in the
previous figures, the width of the tapes varies less than 2% on
average in the longitudinal direction of the tapes. The woven
fabric has been obtained by a weaving process as described in
WO2006/075961, and consolidated in a belt press. The woven
structure of this embodiment corresponds to a twill weave with an
interlacing frequency of 3, i.e. a weft (warp) tape crosses over 3
warp (weft) tapes.
[0069] Referring to FIG. 4, a graphical presentation of a
multilayer material sheet according to the invention is shown. The
multilayer material sheet comprises a woven fabric layer of FIG. 1
denoted as number 1 (in full lines), with below it a second woven
fabric layer denoted as number 2 (in dotted lines). The second
woven fabric layer is positioned such that the seam lines of the
respective woven fabric layers are aligned in a staggered
fashion.
[0070] Test methods as referred to in the present application, are
as follows [0071] Intrinsic Viscosity (IV) is determined according
to method PTC-179 (Hercules Inc. Rev. Apr. 29, 1982) at 135.degree.
C. in decalin, the dissolution time being 16 hours, with DBPC as
anti-oxidant in an amount of 2 g/l solution, by extrapolating the
viscosity as measured at different concentrations to zero
concentration; [0072] Tensile properties of yarn (measured at
25.degree. C.): tensile strength (or strength), tensile modulus (or
modulus) and elongation at break (or eab) are defined and
determined on multifilament yarns as specified in ASTM D885M, using
a nominal gauge length of the fiber of 500 mm, a crosshead speed of
50%/min. Tensile properties of tape (measured at 25.degree. C.):
tensile strength (or strength), tensile modulus (or modulus) and
elongation at break (or eab) are defined and determined on tapes of
a width of 20 mm as specified in ASTM D882, using a nominal gauge
length of the tape of 440 mm, a crosshead speed of 50 mm/min.
[0073] Width variation of the tape, is determined by measuring the
largest width L and the smallest width S of a tape of a length of
20 m (or alternatively 20 tapes of a length of 1 m). The variation
is L-S devided by S, expressed as percentage. [0074] The melting
point of a polymer is determined by DSC on a power-compensation
PerkinElmer DSC-7 instrument which is calibrated with indium and
tin with a heating rate of 10.degree. C./min. For calibration (two
point temperature calibration) of the DSC-7 instrument about 5 mg
of indium and about 5 mg of tin are used, both weighed in at least
two decimal places. Indium is used for both temperature and heat
flow calibration; tin is used for temperature calibration only.
[0075] The furnace block of the DSC-7 is cooled with water, with a
temperature of 4.degree. C. in order to provide a constant block
temperature, for a stable baselines and good sample temperature
stability. The temperature of the furnace block should be stable
for at least one hour before the start of the first analysis. For
tape measurements, the tape is cut into small square pieces of 5 mm
maximum and a sample size of at least about 1 mg (+/-0.1 mg) is
taken. Typically, for a tape with a thickness of 40 micron, one
square piece of 5 mm is about 1 mg. For smaller thicknesses more
pieces are stacked. For thicker tapes the size may be reduced, such
that 1 mg sample mass is obtained at minimum. [0076] The
representative sample is put into an aluminum DSC sample pan (50
.mu.l), which is covered with an aluminum lid (round side up) and
then sealed. In the sample pan (or in the lid) a small hole must be
perforated to avoid pressure build-up (leading to pan deformation
and therefore a worsening of the thermal contact). For powder
samples, a minimum of 1 mg (+/-0.1 mg) of powder is taken and
charged into the sample pan. [0077] The sample pan is placed in a
calibrated DSC-7 instrument. In the reference furnace an empty
sample pan (also covered with a pierced lid and sealed) is placed.
[0078] The following temperature program is run: [0079] 1. sample
is kept for 5 min at 40.degree. C. (stabilization period) [0080] 2.
increase temperature from 40 up to 200.degree. C. with 10.degree.
C./min. (first heating curve) [0081] 3. sample is kept for 5 min at
200.degree. C. [0082] 4. temperature is decreased from 200 down to
40.degree. C. (cooling curve) [0083] 5. sample is kept for 5 min at
40.degree. C. [0084] 6. optionally increase temperature from 40 up
to 200.degree. C. with 10.degree. C./min to obtain a second heating
curve. [0085] The same temperature program is run with an empty pan
in the sample side of the DSC furnace (empty pan measurement).
[0086] Analysis of the first heating curve is used as known in the
art to determine the melting temperature of the analyzed sample.
The empty pan measurement is subtracted from the sample curve to
correct for baseline curvature. Correction of the slope of the
sample curve is performed by aligning the baseline at the flat part
before and after the peaks (at 60 and 190.degree. C. for UHMWPE).
The peak height is the distance from the baseline to the top of the
peak. The invention is now further explained by means of the
following example, without being limited hereto.
EXAMPLE I
Ia--Production of Tape
[0087] A ultrahigh molecular weight polyethylene powder as
described in WO 93/15118 having a bulk density of 275 kg/m.sup.3
and an active catalyst residue of 47 ppm was fed into a powder bed
of a width of 30 cm. This bed was heated to a temperature of
135.degree. C. and pressed at a pressure of 35 bar during 1 minute.
The obtained tape precursor was calandered at a temperature of
140.degree. C., i.e. below the melting point of the powder, and
subsequently drawn to a total draw ratio of 150, to form a
tape.
[0088] The tape as produced had a tenacity of 1.7 GPa, measured on
a small (20 mm) slit tape. The tape had a width of about 60 mm, and
was slit to a width of 50.5.+-.0.5 mm, using a Bielloni Sage
machine, model Taglierina, type RP/B1 505, equipped with chromium
steel knives. Thickness of the tape was 37 .mu.m.
Ib--Production of Woven Fabric Material
[0089] The tapes were converted into a woven fabric with a plain
weave structure, as shown in FIG. 1. The tape woven structure had a
width of 130 cm and was stabilized by fusion at the edges of the
product, as shown in FIG. 2. Without stabilizing the "fabric" it
tends to fall apart when cutting it into ballistic panel sized
sheets. The woven fabric thus produced was then fed to a lamination
line (manufactured by Meyer.RTM.), which is a belt press having
different temperature and pressure zones. The heating zone was set
to a temperature of 146.degree. C., followed by coaling. Pressure:
18 N/cm2. Total residence time was 2 minutes.
Ic--Production of Armor Panels from the Tape
[0090] Panels were made of size 50.times.50 cm. A first layer of
woven fabric was placed on a surface. A second layer of woven
fabric was placed on top of the first layer, and in such fashion
that the seam lines of the two layers were positioned in a
staggered manner. The procedure was repeated until an areal density
(AD) of 8 kg/m.sup.2 was reached. The stack was then supplemented
with commercially available 8 mm AL2O3 tiles (50 mm.times.50 mm
tiles) having a purity of at least 98%. The stack was then moved
into a press and pressed at a temperature of 145.degree. C. and a
pressure of 165 bar for 40 minutes. Cooling was performed under
pressure until a temperature of 80.degree. C. was reached. Total
cycle time was about 70 minutes.
Id--Performance Testing of Armored Panels
[0091] The armoured plates were subjected to shooting tests
performed with 7.62.times.51 mm AP-M2 (St. Louis Ordnance Plant,
Mo., USA) bullets. The tests were performed with the aim of
determining the V50 value. V50 is the speed at which 50% of the
projectiles will penetrate the armoured plate. The testing
procedure was as follows. The first projectile was fired at the
anticipated V50 speed. The actual speed was measured shortly before
impact. If the projectile was stopped, a next projectile was fired
at an intended speed of about 20 m/s higher. If it perforated, the
next projectile was fires at an intended speed of about 20 m/s
lower. The actual speed of impact was always measured. V50 was the
average of the two highest stops and the two lowest
perforations.
COMPARATIVE EXPERIMENT A
[0092] Production of Armor Panels [0093] The same procedure was
used for the manufacture of the panels of example I whereby instead
of the woven fabric Dyneema.RTM. HB26 (DSM Dyneema, Netherlands)
was used. This is a commercially available material based on
crossplied unidirectional polyethylene fibers
[0094] Performance Testing of Amored Panels [0095] Was done in the
same way as for Example I.
Results:
TABLE-US-00001 [0096] V50 Ex. Strike face Backing m/s I 8 mm AL2O3
8 kg/m2 888 plain woven fabric A 8 mm AL2O3 8 kg/m2 862 Dyneema
.RTM. HB26
[0097] The results confirm that a ballistic article comprising a
material sheet according to the invention comprising a woven fabric
of drawn polyethylene produces unexpectedly improved anti-ballistic
performance. This is the more surprising since it is common
knowledge that hitherto known woven fabrics show lower ballistic
protection that the commercially available products based on
crossplied unidirectionally aligned polyethylene fibers.
In particular, the ballistic article of the present invention
produced a significantly higher V50 value than is known from the
prior art.
* * * * *