U.S. patent application number 16/940660 was filed with the patent office on 2021-01-14 for process for fabricating polymeric articles.
This patent application is currently assigned to Propex Operating Company, LLC. The applicant listed for this patent is Propex Operating Company, LLC. Invention is credited to Peter John HINE, Keith Norris, Ian MacMillan WARD.
Application Number | 20210008850 16/940660 |
Document ID | / |
Family ID | 1000005106233 |
Filed Date | 2021-01-14 |
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United States Patent
Application |
20210008850 |
Kind Code |
A1 |
WARD; Ian MacMillan ; et
al. |
January 14, 2021 |
Process for Fabricating Polymeric Articles
Abstract
A process for the production of a polymeric article directed to
(a)forming apply having successive layers, namely, (i) a first
layer made up of strands of an oriented polymer material; (ii)a
second layer of a polymeric material; (iii)a third layer made up of
strands of an oriented polymeric material, wherein the second layer
has a lower peak melting temperature that of the first and third
layers; (b)subjecting the ply to conditions of time, temperature,
and pressure sufficient to melt a proportion of the firsts layer to
melt the second layer entirely, and to melt a proportion of the
third layer, and to compact the ply; and (c)cooling the compacted
ply. The resultant articles have good mechanical properties yet may
be made at a lower compaction temperature than articles not
employing the second layer, leading to a more controllable
manufacturing process.
Inventors: |
WARD; Ian MacMillan;
(Bramhope, GB) ; HINE; Peter John; (Meanwood,
GB) ; Norris; Keith; (Silsden, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Propex Operating Company, LLC |
Chattanooga |
TN |
US |
|
|
Assignee: |
Propex Operating Company,
LLC
Chattanooga
TN
|
Family ID: |
1000005106233 |
Appl. No.: |
16/940660 |
Filed: |
July 28, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15845671 |
Dec 18, 2017 |
10850479 |
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16940660 |
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15195277 |
Jun 28, 2016 |
9873239 |
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15845671 |
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14502377 |
Sep 30, 2014 |
9403341 |
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15195277 |
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13561330 |
Jul 30, 2012 |
8871333 |
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14502377 |
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13276118 |
Oct 18, 2011 |
8268439 |
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13561330 |
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10556402 |
Jan 23, 2006 |
8052913 |
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PCT/GB04/02184 |
May 21, 2004 |
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13276118 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 428/249998
20150401; B32B 5/26 20130101; B32B 2250/40 20130101; B32B 2250/20
20130101; B32B 2250/24 20130101; B32B 5/024 20130101; Y10T
428/31504 20150401; B32B 2250/242 20130101; Y10T 428/24992
20150115; B32B 2262/0284 20130101; B29K 2105/0854 20130101; B29K
2105/06 20130101; Y10T 428/24942 20150115; B32B 2250/03 20130101;
B29C 43/006 20130101; B29K 2105/256 20130101; B29C 43/52 20130101;
B29C 43/203 20130101; B29K 2105/0079 20130101; Y10T 428/2495
20150115; D04H 1/559 20130101; B32B 2307/536 20130101; D04H 13/00
20130101; B32B 2262/0253 20130101; B32B 27/36 20130101; B32B
2323/10 20130101; Y10T 428/24628 20150115; B29L 2009/00 20130101;
B32B 27/08 20130101; B32B 2323/04 20130101; B29C 43/003 20130101;
Y10S 428/91 20130101; B32B 27/32 20130101 |
International
Class: |
B32B 27/08 20060101
B32B027/08; B29C 43/00 20060101 B29C043/00; B29C 43/20 20060101
B29C043/20; D04H 1/559 20060101 D04H001/559; D04H 13/00 20060101
D04H013/00; B32B 5/26 20060101 B32B005/26; B32B 27/32 20060101
B32B027/32; B29C 43/52 20060101 B29C043/52; B32B 5/02 20060101
B32B005/02; B32B 27/36 20060101 B32B027/36 |
Foreign Application Data
Date |
Code |
Application Number |
May 22, 2003 |
GB |
0311819.7 |
May 25, 2003 |
EP |
03253211.1 |
Claims
1. A polymeric article comprising: a ply having a plurality of
layers such that at least one of the plurality of layers is not
oriented; at least one of the plurality of layers has a thickness
of less than or equal to 1 mm; and at least one of the plurality of
layers comprises a polymeric material of polyethylene,
polypropylene, polyoxymethylene, polyester, or a homopolymer,
copolymer or terpolymer thereof.
2. The polymeric article of claim 1, wherein at least one of the
plurality of layers is biaxially oriented.
3. The polymeric article of claim 1, wherein at least one of the
plurality of layers is uniaxially oriented.
4. The polymeric article of claim 1, wherein said ply has from 2 to
40 layers.
5. The polymeric article of claim 1, wherein at least one of the
plurality of layers is a non-woven web.
6. The polymeric article of claim 1, wherein at least one of the
layers is formed into a fabric by knitting or weaving.
7. The polymeric article of claim 1, comprising a plurality of
interleaved polypropylene film layers in combination with woven
polypropylene tapes;
8. The polymeric article of claim 7 wherein the article has a
molecular weight within 5% of 360,000.
9. The polymeric article of claim 7, wherein said article has a
density within 5% of 910 kg/m.sup.3.
10. The polymeric article of claim 7, wherein said article has a
thickness after extrusion within 5% of 15 .mu.m.
11. A polymeric article comprising: an oriented layer laid onto an
initial polymeric material such that the oriented layer is a
polyethylene, polypropylene, polyoxymethylene or polyester,
including as homopolymer, copolymer or terpolymer, and/or blends
mixtures thereof; a thickness of said initial polymeric material
exceeds that of the oriented layer; and the oriented layer has a
oriented layer peak temperature, and the polymeric material has a
polymeric material peak temperature, where the oriented layer peak
temperature is lower than the polymeric material peak
temperature.
12. The polymeric article of claim 8, wherein said oriented layer
peak temperature is at least 5.degree. C. lower than the polymeric
material peak temperature.
13. The polymeric article of claim 8, further comprising an
additional layer of polymeric material.
14. The polymeric article of claim 10, wherein said additional
layer of polymeric material and said initial layer have a thickness
that together is at least five times more than that of said
oriented layer.
15. The polymeric article of claim 8, wherein said thickness of
said initial polymeric layer exceeds 50 .mu.m.
16. The polymeric article of claim 8, wherein said oriented layer
is biaxially oriented.
17. The polymeric article of claim 8, wherein said oriented layer
is comprised of a plurality of film layers.
18. A method of using a pressure process for a polymeric article
comprising: providing at least two layers of a woven material;
applying an initial pressure in a hot press to said layers of said
woven material while said polymeric article is heated to a
compaction temperature of at least 130.degree. C.; applying a
second pressure to said layers of said woven material higher than
said initial pressure; and cooling said layers.
19. The method of claim 16 wherein said initial pressure is within
5% of 0.7 Pa.
20. The method of claim 16, wherein the method further comprises
placing a layer of LDPE film between said at least two layers of
said woven material.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of co-pending application
Ser. No. 14/502,377, filed Sept. 30, 2014, which is a continuation
of Ser. No. 13/561,330, filed Jul. 30, 2012, (now U.S. Pat. No.
8,871,333, issued Oct. 28, 2014) which is a continuation of Ser.
No. 13/276,118, filed Oct. 18, 2011, (now U.S. Pat. No. 8,268,439,
issued Sep. 18, 2012), which is a divisional of application Ser.
No. 10/556,402, filed on Jan. 23, 2006, (now U.S. Pat. No.
8,052,913 B2, issued Nov. 8, 2011), which is the national stage
entry of PCT/GB04/02184, filed May 21, 2004, claiming priority to
GB 0311819.7, filed May 22, 2003 and EP 03253211.1, filed May 25,
2003, whose disclosures are incorporated herein by reference.
[0002] The present invention relates to polymeric articles made
from oriented polymeric strands, and in particular to an improved
process for making such articles.
BACKGROUND OF THE INVENTION
[0003] In recent years, developments have been made in processes
for compacting polymeric strands in order to make sheets of high
stiffness and strength. An example is disclosed in GB 2253420A, in
which an assembly of strands of an oriented polymer is hot
compacted in a two-step process to form a sheet having good
mechanical properties. The process involves an initial step in
which the strands are brought to and held at the compaction
temperature whilst subject to a pressure sufficient to maintain the
strands in contact, and thereafter compacted at a high pressure
(40-50 MPa) for a few seconds (the compaction pressure). In this
process a proportion of the surfaces of the strands melts and
subsequently recrystallises on cooling. This recrystallised phase
binds the strands together, resulting in good mechanical properties
of the final sheet. It is mentioned in GB 2253420A that the process
can be applied to many types of oriented polymer including
polyester and PEEK (polyether ether ketone) but that preferred
polymers are oriented polyolefins.
[0004] One drawback of the process described in GB 2253420A is that
the temperature span across which melting occurs is very narrow.
Accordingly it is difficult to achieve the desired degree of
partial melting of the outer regions of the strands. Inadequate
melting of the strands results in poor mechanical properties.
Excessive melting of the strands results in loss of orientation,
and diminished mechanical properties. Precise process control is
needed if the article is not to be "under-melted" or
"over-melted".
[0005] In WO 98/15397 a related process is disclosed in which an
assembly of melt-formed polyolefin strands is maintained in
intimate contact at elevated temperature sufficient to melt a
proportion of the strands, whilst being subjected to a compaction
pressure of no greater than 10 MPa. If wished the strands may have
been subjected to a prior crosslinking process, preferably an
irradiation crosslinking process comprising irradiating the strands
with an ionising radiation in an inert environment containing
alkyne or diene compounds, and then carrying out an annealing step
comprising annealing the irradiated polymer at an elevated
temperature, in an inert environment containing alkyne or diene
compounds. It is said that the prior crosslinking can make the
compaction temperature less critical, and improve mechanical
properties, in particular the failure strength at elevated
temperature.
[0006] There is published work on the use of articles in which a
polyethylene film is sandwiched between polyethylene fibre layers,
and the ply subjected to hot compaction.
[0007] Marais et al., in Composites Science and Technology, 45,
1992, pp. 247-255, disclose a process in which compaction takes
place at a temperature above the melting point of the film but
below the melting point of the fibre layers. The resulting articles
have modest mechanical properties.
[0008] Ogawa et al., in Journal of Applied Polymer Science, 68,
1998, pp. 1431-1439 describe articles made up of layers of
ultra-high molecular weight polyethylene fibres (mp 145-152.degree.
C.) and low density polyethylene films (mp 118.degree. C.). The
moulding temperature is said to be between the melting points of
the fibre and the interlayer (matrix). The volume fraction of the
fibres is stated to be 0.69 or 0.74. However the articles are said
to have surprisingly poor properties, possibly because of weak
adhesion between fibres and matrix (melted film). Another article
was made with polyethylene fibres alone, and the process conditions
induced partial melting, with poorer properties.
SUMMARY OF THE INVENTION
[0009] There is a need for a simple, practical means which can
reduce the criticality of the compaction temperature, in a hot
compaction process. There is in addition a continuing need for
improvement in mechanical properties in the resulting articles. It
is an object of the present invention to achieve embodiments in
which one or both of these needs are met, at least in part, in a
practicable manner.
[0010] Accordingly in a first aspect of the present invention there
is provided a process for the production of a polymeric article,
the process comprising the steps of:
[0011] (a) forming a ply having successive layers, namely
[0012] (i) a first layer made up of strands of an oriented
polymeric material;
[0013] (ii) a second layer of a polymeric material;
[0014] (iii) a third layer made up of strands of an oriented
polymeric material, wherein the second layer has a lower peak
melting temperature than that of the first and third layers;
[0015] (b) subjecting the ply to conditions of time, temperature
and pressure sufficient to melt a proportion of the first layer, to
melt the second layer entirely, and to melt a proportion of the
third layer; and to compact the ply; and
[0016] (c) cooling the compacted ply.
[0017] "Cooling" in the first and second aspects can include
permitting the compacted ply to cool naturally; forced draught
cooling; plunge cooling; any other type of accelerated cooling; and
retarded cooling.
[0018] The term "strands" is used herein to denote all oriented
elongate elements of polymeric material useful in this invention.
They may be in the form of fibres or filaments. They may be in the
form of bands, ribbons or tapes, formed for example by slitting
melt formed films, or by extrusion. Whatever their form the strands
may be laid in a non-woven web for the process of the invention.
Alternatively they may be formed into yarns comprising multiple
filaments or fibres, or used in the form of a monofilament yarn.
The strands are usually formed into a fabric by weaving or
knitting. Optionally the strands may have been subjected to a
crosslinking process, as described in WO 98/15397. Woven fabrics
are preferably made up of tapes, fibre yarns or filament yarns, or
they may comprise a mixture of fibre or filament yarns and tapes.
Most preferred for use in the said first and third layers are
fabrics which are woven from flat tapes, as this geometry is
believed to give the best translation of the oriented phase
properties into the properties of the final compacted sheet.
[0019] The strands can be made by any suitable process, for example
solution or gel or melt forming, preferably by melt forming.
[0020] Preferably at least 1% of each of the first layer melts,
preferably at least 3%, more preferably at least 5%. Especially
preferred are embodiments in which at least 10% of the first layer
melts (vol/vol of first layer).
[0021] Preferably not more than 30% of the first layer melts, more
preferably not more than 25%. Highly preferred are embodiments in
which not more than 20% of the first layer melts, and especially
not more than 15% (vol/vol of the first layer).
[0022] Preferably at least 1% of each of the third layer melts,
preferably at least 3%, more preferably at least 5%. Especially
preferred are embodiments in which at least 10% of the third layer
melts (vol/vol of third layer).
[0023] Preferably not more than 30% of the third layer melts, more
preferably not more than 25%. Highly preferred are embodiments in
which not more than 20% of the third layer melts, and especially
not more than 15% (vol/vol of the third layer).
[0024] Preferably at least 1% of the ply melts, preferably at least
3%, more preferably at least 5%, and most preferably at least 10%
(vol/vol of total ply).
[0025] Preferably not more than 35% of the ply melts, preferably
not more than 25%, more preferably not more than 20%, and most
preferably not more than 15% (vol/vol of total ply).
[0026] Preferably the ply comprises a plurality of layers of the
type defined above as the second layer, for example from 2 to 40,
preferably from 4 to 30, each such layer being sandwiched between
layers of the type defined above as the first and third layers.
[0027] In certain embodiments of the invention the strands of an
oriented polymeric material of the first and third layers may
comprise--preferably may consist of--polyethylene, polypropylene,
polyoxymethylene or polyester, including as homopolymer, copolymer
or terpolymer. Polymer blends and filled polymers could be employed
in certain embodiments. In especially preferred embodiments the
strands are of a homopolymeric material, most preferably a
polypropylene or polyethylene homopolymer.
[0028] In certain embodiments of the invention the or each second
layer may comprise--preferably may consist of--polyethylene,
polypropylene, polyoxymethylene or polyester, including as
homopolymer, copolymer or terpolymer. Polymer blends and filled
polymers could be employed in certain embodiments. In especially
preferred embodiments the or each second layer is of a
homopolymeric material, most preferably a polypropylene or
polyethylene homopolymer.
[0029] Preferably the first and third layers are of the same type
of polymeric material (e.g., both polypropylene). Preferably the
second layer is of the same type of polymeric material. Most
preferably the second layer is of the same chemical composition and
grade, except for the fact that it is preferably of lower
orientation (and accordingly melts at a lower temperature than the
first and third layers).
[0030] The minimum temperature at which the fibres should be
compacted is preferably that at which the leading edge of the
endotherm, measured by Differential Scanning calorimetry (DSC), of
the constrained polymer fibres extrapolated to zero intersects the
temperature axis. Preferably, the temperature at which the fibres
are compacted is no greater than the constrained peak temperature
of melting at the ambient compaction pressure--i.e. the temperature
at which the endotherm reaches its highest point.
[0031] The second layer could be formed in situ on the first or
third layer, for example by delivering the polymeric material of
the second layer to the respective first or third layer in
particulate form, for example by spraying.
[0032] Alternatively, and preferably, the second layer is
pre-formed, and is laid onto the first or third layer. The second
layer could be pre-formed from strands of the polymeric material.
The strands could be laid into a non-woven web. They could be
formed into yarns comprising multiple filaments or fibres, or used
in the form of a monofilament yarn. Strands--for example filament
yarns, fibre yarns or tapes--could be formed into a fabric by
weaving or knitting. Most preferably, however, the second layer
comprises--preferably consists of--a film. The film may typically
have a uniaxial or biaxial orientation resulting from its
formation, but such that the degree of orientation will typically
be much less than that of the strands which make up the first and
third layers. The or each second layer may be made up of a
plurality of films, for example 2-5, but is preferably constituted
by a single film.
[0033] Preferably the or each second layer (however constituted) is
of thickness not exceeding 100 .mu.m, more preferably not exceeding
40 .mu.m, and most preferably not exceeding 20 .mu.m (with
reference to its thickness when under compression in the ply, at a
temperature below its melting temperature).
[0034] Preferably the or each second layer (however constituted) is
of thickness at least 5 .mu.m, more preferably at least 10 .mu.m
(with reference to its thickness when under compression in the ply,
but below its melting temperature).
[0035] Preferably the thickness of each of the first and third
layers exceeds that of the or each second layer. Preferably the
thickness of each is at least 5 times that of the or each second
layer.
[0036] Preferably the thickness of each of the first and third
layers exceeds 50 .mu.m, and more preferably exceeds 100 .mu.m.
[0037] Preferably the thickness of each of the first and third
layers does not exceed 1 mm, and preferably does not exceed 400
.mu.m.
[0038] Preferably the or each second layer has a peak melting
temperature at least 5.degree. C. lower . than the peak melting
temperature of the first and third layers, more preferably at least
10.degree. C. lower, most preferably at least 20.degree. C.
lower.
[0039] It is preferred that the hot compaction process of the
invention uses a compaction pressure not exceeding 10 MPa. It is
also preferred that a single pressure is used throughout the hot
compaction process. Most preferred pressures are between 1 and 7
MPa, particularly between 2 and 5 MPa. It is preferred that the hot
compaction pressure is maintained during cooling.
[0040] Preferably the polymeric materials have not been subjected
to a crosslinking process prior to compaction, for example of the
type described in WO 98/15397. It is found that the present
invention gives benefits in terms of the "temperature window"
without the need for crosslinking.
[0041] Preferably the polymeric materials have not been subjected
to a prior corona discharge treatment prior to compaction. More
preferably the polymeric materials have not been subjected to
surface treatment prior to compaction.
[0042] Compaction of the polymeric materials may be carried out in
an autoclave, or in a double belt press or other apparatus in which
the assembly is fed through a compaction zone where it is subjected
to the required elevated temperature and pressure. Thus, the
process may be operated as a continuous or semi-continuous process.
Cooling is preferably effected whilst the compacted web is
restrained against dimensional change, for example by being held
under tension, which may be applied uniaxially or biaxially, or by
being still under a compaction pressure. The restraint may assist
the maintenance of good properties in the oriented phase.
[0043] The article may be regarded as a polymer composite made up
of an interlayer or binding phase produced during the process,
derived from full melting of the second layer and partial melting
of the first and third layers, and an oriented phase, being the
unmelted major proportion of the fibres of the first and third
layers.
[0044] By means of the present invention articles can be made with
certain mechanical properties exceeding those which would be
obtained using a conventional process which does not employ a
melted second layer. In particular peel strength and failure
strength may be significantly improved, with tensile modulus being
maintained at a good level.
[0045] In accordance with a second aspect of the present invention
there is provided an article made by a process of the first
aspect.
[0046] Articles made by the process of the present invention are
suitable for forming into shape, by a process carried out
subsequent to compaction (post-forming).
[0047] In accordance with a third aspect of the present invention
there is provided a process for forming a shaped article by the
application of heat and a shaping force to an article of the third
aspect of the present invention. Suitably the article of the third
aspect may be a flat sheet and the shaped article may, for example,
be bent, curved, domed or otherwise non-planar.
[0048] In accordance with a fourth aspect of the present invention
there is provided an article formed into a shape by a process of
the third aspect.
[0049] In accordance with a fifth aspect of the present invention
there is provided a ply as defined by step (a) of the first aspect,
prior to the carrying out of steps (b) and (c) of the first
aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] The invention will now be described in more detail with
reference to the accompanying drawings, in which:
[0051] FIG. 1 is a graph of tensile modulus versus temperature;
[0052] FIG. 2 is a graph of peel strength versus temperature;
[0053] FIG. 3 is a graph of tensile strength versus
temperature;
[0054] FIG. 4 is a graph of performance index versus
temperature;
[0055] FIG. 5 is a graph of peel strength versus temperature;
[0056] FIG. 6 is a graph of tensile modulus versus temperature;
[0057] FIG. 7 is a graph of tensile strength versus
temperature;
[0058] FIG. 8 is a graph of performance index versus
temperature;
[0059] FIG. 9 is a low magnification micrograph (x50) showing the
sample edge and fracture structure;
[0060] FIG. 10 is a micrograph of the sample of FIG. 9 (x30)
showing the peel fracture surface for the sample made at
175.degree. C. without a film.
[0061] FIG. 11 is a low magnification micrograph (x50) of the
sample edge;
[0062] FIG. 12 is a micrograph of the sample of FIG. 11 (x30)
showing surface damage associated with the interface where the film
was located;
[0063] FIG. 13 is a low magnification micrograph (x50) showing the
sample edge and fracture surface.
[0064] FIG. 14 is a micrograph of the sample of FIG. 13 (x30)
showing the peel fracture surface for the sample made at
191.degree. C. without a film.
[0065] FIG. 15 is a low magnification micrograph (x50) of the
sample edge;
[0066] FIG. 16 is a micrograph is the sample of FIG. 15 (x30)
showing that a sample made at 191.degree. C. with a film develops
surface damaging on peeling;
[0067] FIG. 17 is a micrograph (x30) showing a peel fracture
surface from a sample made at 193.degree. C. without a film.
[0068] FIG. 18 is a micrograph of the sample of FIG. 17 (x30)
showing regions where there has been cohesive failure at the
film/tape interface;
[0069] FIG. 19 shows the results for both the flexural modulus and
flexural strength for example set E;
[0070] FIG. 20 and FIG. 21 are views of a corresponding peel tested
product that have two and three layers of the 100GA02 polymer film,
respectively;
[0071] FIGS. 22-25 show low magnification micrographs of typical
fracture surfaces from samples made without a film at 135.degree.,
148.degree., 152.degree., and 154.degree. C., respectively;
[0072] FIGS. 26-29 are four micrographs showing samples made with a
film at 135.degree., 148.degree., 152.degree., and 154.degree. C.,
respectively;
[0073] FIG. 30 is at 135.degree. C. with no film;
[0074] FIG. 31 is at 135.degree. C. with film;
[0075] FIG. 32 is at 148.degree. C. with no film;
[0076] FIG. 33 is at 148.degree. C. with film;
[0077] FIG. 34 is at 152.degree. C. with no film;
[0078] FIG. 35 is at 152.degree. C. with film;
[0079] FIG. 36 is at 154.degree. C. with no film;
[0080] FIG. 37 is at 154.degree. C. with film.
DETAILED DESCRIPTION OF THE INVENTION
[0081] The invention will now be further exemplified, with
reference to the following examples, set out in sets.
[0082] In these examples standard test methods were used.
[0083] Tensile modulus and tensile strength were determined
following the protocols of ASTM D638. Flexural strength was
determined following the protocols of ASTM D790.
[0084] Peel strength was determined by the protocols of the T-Peel
test, ASTM D1876. Samples for testing were 10 mm wide and 100 nun
long and were tested using a crosshead speed of 100 mm/min. The
testing was carried out parallel to the warp direction.
[0085] In all cases three samples were tested and the results
averaged.
[0086] The percentage of material melted was determined by
Differential Scanning calorimetry (DSC) carried out at a heating
rate of 10.degree. C./min.
Example Set A
[0087] Fabric layers were woven, in a plain weave, from CERTRAN, a
250 denier multifilament yarn of melt spun filaments of oriented
homopolymeric polyethylene available from Hoechst Celanese, and
characterised as follows:
TABLE-US-00001 TABLE 1 Molecular weight Breaking Tensile initial
Modulus (Mw) (Mn) strength (GPa) secant (GPa) 2% (GPa) 130,000
12,000 1.3 58 43
[0088] Samples, using two layers of woven cloth, were processed in
a hot press using a two stage pressure process. An initial pressure
of 0.7 MPa (100 psi) was applied while the assembly reached the
compaction temperature. After a 2 minute dwell time at this
temperature, a higher pressure of 2.8 MPa (400 psi) was applied for
1 minute upon which time the assembly was cooled at a rate of
approximately 20.degree. C. per minute to 100.degree. C. Samples
were made under three conditions. Firstly, standard compaction at a
temperature of 138.degree. C. Secondly, a layer of the LDPE film
was laid between the two layers of woven cloth and then processed
at 126.degree. C. (above the melting point of the film but below
the melting point of the oriented fibres). Finally a sample was
made by interleaving one layer of the LDPE film between the two
layers of woven cloth and processing at a temperature of
136.degree. C.
[0089] The results of these tests are shown in the table below.
TABLE-US-00002 TABLE 2 % Compaction fibre Peel Tensile temperature
melted strength modulus Sample (.degree. C.) material (N/10 mm)
(GPa) Standard compaction 138 26 7.2 9.2 technique (comparison)
Woven PE cloth + 126 0 6.8 3.1 interleaved LDPE film (comparison)
Woven PE cloth + 136 14 11.2 8.1 interleaved LDPE film
[0090] For the standard compaction technique without the film, a
compaction temperature of 138.degree. C. was found to be optimum
for giving a good modulus and reasonable level of interlayer
bonding (peel strength). This optimum temperature was very close to
the point where major crystalline inciting occurred, at 139.degree.
C. Using an interleaved film, but processing at 126.degree. C.,
just enough to completely melt the interlayer film, but not the
surfaces of the fibres, good interlayer bonding was developed but
modulus was poor due, presumably, to poor interfibre bonding as it
will be difficult for the molten material to penetrate the fibre
bundles. Finally, the sample made with the interlayer film but
processed at 136.degree. C., where selective inciting of the
oriented fibres occurred, shows the highest peel strength and a
good modulus. In addition, those properties were obtained at a
temperature 2.degree. C. below the temperature required for
compaction without the film, widening the processing window as
there is less risk of over melting at a temperature of 139.degree.
C.
Example Set B
[0091] In these examples partially melted monolithic articles were
prepared, using TENSYLON oriented polyethylene tape produced by
Synthetic Industries, USA, having the following
characteristics:
TABLE-US-00003 TABLE 3 Tensile strength 1.5 GPa Tensile modulus 88
GPa Denier 720
[0092] This was woven into a fabric. For the interlayer a
polyethylene of closely similar type was obtained, FL5580 film
grade from Borealis A/S, Denmark, melting point 130.degree. C. This
was extruded into a film approximately 10-15 .mu.m in thickness,
using a standard film extruder and film die.
[0093] Compaction experiments were carried out at a range of
temperatures between the melting point of the film (approximately
130.degree. C.) up to and including the normal compaction range for
this material (148.degree.-156.degree. C.). The woven cloth was
thin (areal density 83 g/m.sup.2) and to obtain an even pressure
over the assembly during compaction rubber sheets were used inside
the normal metal plates utilised for compaction, with soft aluminum
foils between the rubber sheets and the ply being compacted. Dwell
time was 5 minutes. Cooling was 20.degree. C./min.
[0094] In the first series of tests, samples were compacted over
the temperature range 148 to 156.degree. C., with and without the
interleaved film. FIGS. 1, 2 and 3 show the tensile modulus, peel
strength and tensile strength of these samples.
[0095] It will be seen from FIG. 1 that when an interlayer is used,
the tensile modulus shows a monotonic decrease with temperature, as
opposed to the peak seen with normal compaction. We infer that the
interlayer is producing higher levels of bonding at low compaction
temperatures making the properties less sensitive to the amount of
melted material produced.
[0096] The peel strength of the interleaved film samples (FIG. 2)
is higher throughout the temperature range, compared to normal
compaction.
[0097] The tensile strength (FIG. 3) was similar for the two
samples; concern that this property might be compromised by use of
the interlayer was allayed.
[0098] We have developed a performance index (PI) in an attempt to
discern the optimum combination of the compacted sheet properties.
If we consider the tensile modulus E, the tensile strength c and
the peel strength, Peel, assuming each property is equally
important, this is defined as follows:
PI=100.times.[(E.sub.T/E.sub.max)+(.sigma..sub.T/.sigma..sub.max)+(Peel.-
sub.T/-Peel.sub.max)]/3
where the subscript T refers to a particular compaction temperature
and the subscript max refers to the maximum value measured for all
the samples. Values of the performance index are shown below in
FIG. 4. From this it is seen that the interlayer samples show a
less variable combination of properties, in particular having
better properties at lower compaction temperatures, than
corresponding samples without an interlayer. This confirms the view
that a lower compaction temperature can be used when an interlayer
is employed, giving processing advantages.
Example Set C
[0099] The tests of this example employed the same materials,
equipment and techniques as Example Set B. It provides a comparison
of the properties of compacted sheets made at three temperatures: a
normal compacted sample made at the standard optimum temperature of
154.degree. C., an interlayer sample made at 152.degree. C. and a
comparison interlayer sample made at 135.degree. C., which is
enough to melt the interlayer but not any part of the TENSYLON
tapes. The results are shown below.
TABLE-US-00004 TABLE 4 Assembly Peel Tensile Tensile Sample
temperature strength modulus strength configuration (.degree. C.)
(N/10 mm) (GPa) (MPa) Standard 154 10 +- 2.7 29.6 +- 3.9 535 +- 55
compaction technique (comparison) Woven PE 152 10.6 +-. 1.5 26.8 +-
1.6 483 +- 28 cloth + interlayer Woven PE 135 5.9 +- 0.9 14.5 +-
2.7 283 +- 25 cloth + interlayer (comparison)
[0100] Compacting at a temperature just above the melting
temperature of the interlayer but below the melting range of the
oriented tapes (135.degree. C.) gives modest mechanical properties.
The sample made at 152.degree. C. with the interlayer shows
comparable values of tensile modulus, strength and peel strength,
compared with the normal compacted sample made at 154.degree. C.
Using the film therefore gives the prospect of lowering the
compaction temperature 2.degree. C., increasing the width of the
processing window.
Example Set D
[0101] Tests were carried out to investigate the impact of using
interleaved layers of polypropylene (PP) film in combination with
the normal layers of woven PP tapes. The PP film this time was the
same polymer grade as used for the drawn and woven tapes. The
polymer, grade 100GA02, was obtained from BP Chemicals,
Grangemouth, UK.
[0102] The film had the following properties:
[0103] Mn=78,100
[0104] Mw=360,000
[0105] Density=910 Kg/m.sup.3
[0106] It was extruded using a Brabender single screw extruder and
a standard film die set to a temperature of 260.degree. C.
Extrusion screw and wind up speeds (8 rpm and 4.6 m/min) were
chosen such that a film thickness of approximately 15 .mu.m was
produced.
[0107] The next stage in the study was to manufacture a range of
samples, with the film as an interlayer, and without (comparison),
to assess the impact of an interlayer on compacted sheet
properties. DSC tests, carried out a heating rate of 10.degree.
C./min, showed that the peak melting point of the film was
162.degree. C., while the constrained peak melting point of the
oriented tapes was 194.degree. C. Compacted samples were therefore
made at a temperature of 175.degree. C., high enough to melt the
film completely but not high enough to cause any melting of the
oriented phase.
[0108] The material used was a fabric woven tape, formed from a
slit film, draw ratio nominally 10:1, woven in a 6060 style. A
single pressure process (4.6 MPa) with a dwell time of 5 minutes
was used. Samples were also compacted at 180, 187, 189, 191, 193,
195, 197 and 200.degree. C. Cooling rate was 50.degree. C./min,
achieved by passing cold water through the heating platens.
[0109] In the first set of tests, 4 layer samples were made for
measurement of the interlayer bond strength, using the `T` peel
test. The results are given in FIG. 5.
[0110] It is seen that at all compaction temperatures, the peel
strength is higher when using the interlayer.
[0111] The next stage was to measure the stress-strain behaviour of
various materials to see if these had been reduced in any way.
[0112] The results are shown in FIGS. 6 and 7.
[0113] As shown in FIG. 6, within the experimental scatter no
significant difference was seen between the initial tensile modulus
of the two groups of samples. The modulus is seen to be relatively
constant between 191 and 197.degree. C. for both sets of samples.
Thus in this set of tests the introduction of a thin film of
material between the woven layers has no discernible detrimental
effect on the compacted sample modulus.
[0114] For the tensile strength results shown in FIG. 7 there was a
clearer difference seen between the two sets of samples. Here the
samples made with the film showed a higher tensile strength than
those compacted normally. This difference is largest at the lower
temperatures when there is little surface melting of the oriented
tapes. However, even in the `optimum` compaction range, the film
samples still show a slightly higher tensile strength.
[0115] The table below presents a summary of the results from the
tensile and peel strength tests (ASTM protocols as noted above), in
respect of peel strength, tensile modulus, tensile strength and
failure strain.
[0116] In an attempt to discern the optimum combination of the four
parameters mentioned above, and help assess the impact of the
interleaved film, the following performance index (PI) was derived.
Assuming each property tested is equally important, this is as
follows
PT=100.times.[(E.sub.T/E.sub.max)+(.sigma..sub.T/.sigma..sub.max)+(.epsi-
lon..sub.T/.epsilon..sub.max)+(Peel.sub.T/Peel.sub.max)]/4
where the subscript T refers to a particular compaction temperature
and the subscript max refers to the maximum value measured for all
the samples. Values of the performance index are also shown in the
table below and in FIG. 8. It is seen that the interlayer samples
have a better balance of properties compared to the normal samples
when analysed in this way, but with the peel strength showing the
most marked improvement.
[0117] It will be seen that the PI value of the samples made in
accordance with the invention, employing a film as interlayer,
exceeded the corresponding "no film" value at each given compaction
temperature. The best performance was achieved when some melting of
the woven fabric took place, notably at a compaction temperature of
around 189-197.degree. C. The PI value was higher in the
"interlayer" sample.
TABLE-US-00005 TABLE 5 Compaction Tensile Tensile Failure Peel
Performance temperature modulus strength strain strength Index
(.degree. C.) E (GPa) .sigma. (MPa) .epsilon. (N/10 mm) (PI) No
film.dagger-dbl. 175 2.99 67 5 0.63 38 180 2.31 93 12 1.17 46 187
2.24 123 15 1.89 55 189 2.87 148 18 3.7 69 191 3.41 154 18 4.98 76
193 3.43 155 15 7.53 77 195 3.4 138 21 7.2 80 197 3.39 137 20
>7.2* 79 200 1.4 29 20 >7.2* 49 with film.dagger-dbl. 175
3.09 100 7 5.21 53 180 2.59 155 16 6.23 70 187 2.47 145 17 8.66 72
189 3.1 163 18 11 84 191 3.13 168 18 12.3 87 193 3.18 173 20 13.7
93 195 3.44 150 19 16.6 94 197 3.49 136 20 >16.6* 94 200 1.4 29
20 >16.6* 63 *samples too well bonded to be tested in peel test
.dagger-dbl.comparisons SEM Images of Polypropylene Peel Fracture
Surfaces
[0118] The samples compacted at 175, 191 and 193.degree. C. were
selected for SEM microscopy of their fracture surfaces following
peel testing. The samples were as follows.
TABLE-US-00006 TABLE 6 Compaction Sample temperature (.degree. C.)
Details comparison 175 No film comparison 175 1 layer 100GA02
comparison 191 No film invention 191 1 layer 100GA02 comparison 193
No film Invention 193 1 layer 100GA02
[0119] The measured peel strengths for these samples are as shown
in the Table below.
TABLE-US-00007 TABLE 7 Compaction temperature (.degree. C.) Without
film With film 175 0.63 +- 0.12 5.21 +- 0.98 191 4.98 +- 1.6 12.3
+- 4.1 193 7.53 +- 3.52 13.7 +- 3.5 Peel fracture loads (N/10
mm)
[0120] The associated SEM micrographs are FIGS. 9-18. Comments on
these micrographs are as follows.
[0121] 175.degree. C.--No Film
[0122] FIG. 9: This is a low magnification micrograph (x50) showing
the sample edge and fracture surface. The key point is that at this
compaction temperature of 175.degree. C., the tapes and the layers
are very poorly bonded.
[0123] FIG. 10: This micrograph (x30) shows the peel fracture
surface for the sample made at 175.degree. C. without a film. There
is very little surface damage. As will be seen from the later
micrographs, the amount of surface damage correlates very well with
the peel strength, as being evidence of the amount of energy needed
to separate the surfaces. If the woven layers are poorly bonded,
the failure proceeds between the layers causing little damage and a
low peel load. If the layers are well bonded, the failure path has
to move into the oriented tapes, or the film layer, which increases
the peel load and the samples then show a much rougher surface
appearance. 175.degree. C.--with Film
[0124] FIG. 11: This is a low magnification micrograph (x50) of the
sample edge. It is seen again, that at this temperature the layers
and tapes are in general poorly bonded.
[0125] FIG. 12: This micrograph (x30) shows that there is
considerable surface damage associated with the interface where the
film was located, which correlates with the measured increase in
peel strength. However it is also seen that the tapes themselves
are not well bonded to those underneath, i.e. where there is no
film. To Summarise--175.degree. C. Results
[0126] Using a film, and processing at a temperature above the film
melting point but below the temperature where the oriented tapes
melt, gives a structure which is well bonded where the film is
present, but poorly bonded elsewhere. It is clear that it would be
very difficult for the film to penetrate through the woven tape
layers.
[0127] Processing at a temperature well below the melting
temperature of the oriented tapes, and using no film, gives poor
bonding throughout the structure. 191.degree. C.--no Film
[0128] FIG. 13: This is a low magnification micrograph (x50)
showing the sample edge and fracture surface. The key point is that
at this compaction temperature of 191.degree. C., where the
surfaces of the oriented tapes are now beginning to melt, the
layers are now much better bonded and the compacted sheet is more
homogeneous. The individual tapes in the compacted sheet are less
apparent than at 175.degree. C. (FIG. 10).
[0129] FIG. 14: This micrograph (x30) shows the peel fracture
surface for the sample made at 191.degree. C. without a film. As
would be expected, there is increased surface damage compared to
the sample made at 175.degree. C. As with most traditionally
compacted samples (i.e. without a film) the surface damage is
patchy: there are some regions where the damage is pronounced and
others where it is less so. 191.degree. C.--with Film
[0130] FIG. 15: This is a low magnification micrograph (x50) of the
sample edge. It is seen that at this temperature the layers are
well bonded; the structure is now homogeneous.
[0131] FIG. 16: This micrograph (x30) shows that a sample made at
191.degree. C. with a film develops a large amount of surface
damage on peeling, reflecting the higher peel force measured for
this sample. The damage is now seen to be more even across the
sample surface. Perhaps the introduction of the film at the
interlayer is able to even out any local differences in the way the
two woven layers fit together. To Summarise--191.degree. C.
Results
[0132] Using a film, and processing at a temperature where the
oriented tapes begin to melt, produces the combination of an
overall homogeneous structure and interlayer regions (the weak
point in the structure) which are very well bonded.
[0133] The level of damage (i.e. bonding) is more even over the
surface when using an interleaved film
[0134] The level of damage for the sample made at 175.degree. C.
with a film is similar to that seen for the sample made at
191.degree. C. without a film, reflecting the similarity in the
peel load values. 193.degree. C.--without Film
[0135] FIG. 17: This shows (x30) a peel fracture surface from a
sample made at 193.degree. C. without a film. The fracture surface
shows a similar amount of damage to that on the sample made at
191.degree. C. without the film (FIG. 14) but not as much as that
on the sample made at 191.degree. C. with the film. The amount of
surface damage correlates well with the measured peel loads. As
with the sample made at 191.degree. C. without the film, the damage
seen over the area is patchy. 193.degree. C.--with Film
[0136] FIG. 18: This micrograph (x30) which shows regions where
there has been cohesive failure within the film and regions of
adhesive failure at the film/tape interface. This suggests that the
failure could be a combination of these two modes. To
Summarise--193.degree. C. Results
[0137] Using a film, and processing at a temperature where the
oriented tapes begin to melt, produces the combination of an
overall homogeneous structure and interlayer regions which are well
bonded.
[0138] The level of damage (i.e. bonding) is more even over the
surface when using an interleaved film. It is proposed that the
interleaved film is able to more easily fill any gaps which might
be present when the woven layers are pressed together.
[0139] The level of damage seen on the 193.degree. C. compacted
sample fracture surfaces is higher than that on the corresponding
191.degree. C. surfaces (FIGS. 15, 16) reflecting the associated
increase in peel strengths.
Example Set E
[0140] In this example set the flexural properties of samples
compacted at different temperatures, with and without an
interlayer, were tested.
[0141] The sample preparation was as described previously. The ASTM
testing regimes noted above were used.
[0142] FIG. 19 shows the results for both the flexural modulus and
flexural strength. Below the onset of selective surface melting of
the oriented tapes (about 187.degree. C.), the flexural properties
of the interleaved film samples are better than the conventionally
compacted samples. Above this temperature, the flexural properties
of the two sets of samples are very similar. Flexural properties
peak at a compaction temperature of 195.degree. C. for both sets of
samples.
Example Set F
[0143] In this set of tests effect of interlayer thickness was
studied, using the same method and polypropylene material as was
used in Example Set D. As with the examples above a film of
thickness 10-15 pm was used as an interlayer, with 0-3 such films
being used, multiple films being placed together in a stack.
[0144] Average values for stress-strain behaviour and peel strength
are shown below in the following table.
TABLE-US-00008 TABLE 8 Compaction Tensile Tensile Peel Temperature
modulus strength strength (.degree. C.) Interlayer (GPa) .sigma.
(MPa) (N/10 mm) 191.degree. C. No film 3.41 +- 0.25 154 +- 8 4.98
+- 1.6 1 layer 3.13 +- 0.05 168 +- 8 12.3 +- 4.1 2 layers 3.17 +-
0.15 135 +- 9 8.8 +- 1.3 3 layers 3.00 +- 0.36 137 +- 3 12.5 +- 4.7
193.degree. C. No film 3.43 +- 0.29 155 +- 7 7.53 +- 3.52 1 layer
3.18 +- 0.09 173 +- 4 13.7 +- 3.5 2 layers 3.22 +- 0.18 144 +- 5
9.6 +- 2.3 3 layers 3.01 +- 0.37 160 +- 9 11.7 +- 4.3
[0145] The results indicate that the tensile modulus falls for both
temperatures as the film thickness is increased; that the tensile
strength peaks for the single layer film thickness and then falls
again as the thickness is increased; and that the peel strengths
are similar for all layers of film thickness, and all significantly
higher than the comparative samples without an interlayer.
[0146] The results, taken together, suggest that the single layer
is the optimum, giving the maximum increase in peel strength for
the minimum loss of tensile modulus, and with retention or slight
improvement in tensile strength.
Example Set G
[0147] In this example set SEM microscopy was used to study peel
fracture surfaces using the same materials and processing as
described in Example Set B but having multiple interlayers. The
processing temperature was 193.degree. C., so the figures of
Example Set D which provide comparisons are FIG. 17 (no film) and
FIG. 18 (one layer of film). FIGS. 20 and 21 are views of a
corresponding peel tested product, but having two and three layers
of the 100GA02 polymer film, respectively. By way of comparison, in
the single layer sample of FIG. 18 of Example Set D, one can see
the film layers F lying on top of the oriented tapes underneath. In
FIG. 20 a sample made with two layers of film the edge of the
sample clearly shows the film layer F located within the sample,
and the film layer on the peel surface itself. It appears that
failure has proceeded at this point predominantly through the film
layer. From this micrograph we can see that the damage zone is
located within the film layer. FIG. 21 shows a region of the
surface showing the thick film layer, now composed of three film
layers F. The damage zone is now seen to be much thinner than the
overall film thickness.
Example Set H
[0148] This example set examined the importance of the type of film
used. In some of the tests the interlayer was made from the same
polymer as was used to make the oriented tapes (PP 100GA 02
material as described above). In other tests two further interlayer
films were investigated, namely.
[0149] 1) A (30 .mu.m thick) polypropylene film of m.p. 163.degree.
C., obtained from ICI.
[0150] 2) A PE film made in-house: this employed the Brabender
single screw extruder and the same film die used to make the PP
film described above. This used a BOREALIS PE (Film grade FL5580)
and the final extruded film was between 10 and 15 .mu.m thick.
[0151] Compaction experiments were carried out using the same woven
PP cloth as described above (10:1 drawn tape, 6060 style, 100GA 02
polymer). Experiments were conducted at two compaction
temperatures: 175.degree. C., for comparison, enough to melt each
film but not enough to melt the surfaces of the oriented materials
and 193.degree. C. which is in the optimum value for normal hot
compaction
[0152] The results are shown in the table below.
TABLE-US-00009 TABLE 9 Peel Sample Film E .sigma. strength
thickness thickness (Gpa) (MPa) .epsilon. (N/10 mm) (mm) .mu.m
175.degree. C. 2.99 67 5 0.6 0.64 10-12 no film.dagger-dbl.
matching 3.09 100 7 5.2 0.64 30 PP film.dagger-dbl. ICI PP 2.45 86
1.3 0.72 30 film.dagger-dbl. PE film.dagger-dbl. 2.51 92 0.7 0.68
10-15 193.degree. C. 3.43 155 15 7.5 0.47 no film.dagger-dbl.
matching 3.18 173 20 13.7 0.51 10-12 PP film ICI PP 3.08 103 23 8.7
0.58 30 film PE film 2.70 113 28 2.3 0.53 10-15
.dagger-dbl.comparisons
[0153] The results indicate that the best samples are those made
with the matching PP film.
Example Set I
[0154] In this example as assessment was made of the application of
the invention to polyester (PET) materials.
[0155] Woven PET fabric, and polymer of an identical chemical
composition, were supplied by KOSA, GmbH and Co. KG.
[0156] The polymer and fabric details were as follows
TABLE-US-00010 TABLE 10 Polymer Type T51-IV ~0.85, Mn ~22,500
Fabric weight 200 g/m.sup.2 Oriented shape multifilament bundles
1100 decitex Weave style Plain weave 9/9 threads/cm Peak m.p.
250.degree. C.
[0157] PET film (.about.15 .mu.m thick) was cast from the polymer
using a standard extruder and a film die. A second PET film, of a
different chemical composition to the woven cloth, was also used in
these tests: this film was slightly biaxially oriented.
[0158] The work reported looked at the application of the invention
to the woven PET material, both with and without an interleaved
film. Samples were made using both films.
[0159] The table below shows a comparison between the stress-strain
and peel strength behaviour of samples made with and without the
film of the same composition at 257, 258 and 259/260.degree. C. As
is seen all the samples made with the film showed increased tensile
modulus, tensile strength and peel strength over the samples made
without the film, at a given temperature.
TABLE-US-00011 TABLE 11 Compaction Tensile Tensile Peel temperature
modulus strength strength (.degree. C.) Sample (GPa) (MPa) (N/10
mm) 257 No film.dagger-dbl. 4.51 +- 0.18 88 +- 18 1.2 +- 0.2 Same
film 5.69 +- 0.52 178 +- 16 5.1 +- 0.6 258 No film.dagger-dbl. 4.96
+- 0.4 120 +- 5 2.0 +- 0.4 Same film 6.65 +- 0.69 175 +- 5 5 9 +-
1.4 260/259 No film.dagger-dbl. 6.41 +- 0.77 138 +- 16 7.2 +- 1.2
Same film 7.27 +- 0.64 188 +- 8 6.9 +- 0.9
.dagger-dbl.comparisons
[0160] As a further experiment samples were also made, using a
compaction temperature of 257.degree. C., using no film, and both
PET films, and tested in the manner described previously. The
results are as follows.
TABLE-US-00012 TABLE 12 Tensile Tensile Peel modulus strength
strength Samples (GPa) (MPa) (N/10 mm) No film 4.51 +- 0.18 88 +-
18 1.2 +- 0.17 Different film 6.85 +- 0.32 158 +- 13 3.9 +- 0.6
Same film 5.69 +- 0.52 178 +- 16 5.1 +- 0.6
[0161] It can be seen that in this experiment the mechanical
properties were significantly boosted by the presence of either
film; and that the films gave rise to enhancement of different
mechanical properties. Namely the tensile modulus of the sample
with the different film is higher than with the identical film,
although the tensile strength and peel strength are higher with the
identical film.
[0162] A significant finding is that these mechanical properties
were achieved using a compaction temperature of 257.degree. C. The
optimum temperature for compacting PET by the prior method (no
film) is regarded as 260.degree. C. With PET the processing window
is narrow, which could inhibit the commercialisation of hot
compaction processes as applied to PET. A lowering of the
compaction temperature to 257.degree. C., yet with achievement of
good mechanical properties, suggests a significant practical
benefit.
Example Set J
[0163] SEM Images of Polyethylene Peel Fracture Surfaces
[0164] Peel samples were manufactured as described in Example Set B
using woven TENSYLON 10:1 PE tapes (6060 style). Samples were made
with and without an interleaved film. In these tests a film of the
same grade as the oriented tapes was not available and so the.
Borealis FL5580 material, a similar grade, was sourced.
[0165] 8 samples were studied, having been compacted at 135.degree.
C., 148.degree. C., 152.degree. C. and 154.degree. C., with and
without an interlayer film, and subjected to the peel test.
TABLE-US-00013 TABLE 13 Compaction temperature (.degree. C.)
Without Film With film 135 0.72 +- 0.31 5.94 +- 0.92 148 4.23 +-
0.78 9.02 +- 1.18 152 5.56 +- 1.05 10.6 +- 1.5 154 10 +- 2.73 13.4
+- 3.3 Peel fracture loads (N/10 mm)
[0166] The associated SEM micrographs are FIGS. 22-37 herein.
Comments on these micrographs are as follows.
[0167] FIGS. 22-25: These figures show low magnification
micrographs of typical fracture surfaces from samples made without
a film at 135, 148, 152 and 154.degree. C. respectively. As the
compaction temperature is increased the level of surface damage
increases. At the lowest temperature, where there is no surface
melting of the PE tapes, there is no bonding of the tapes.
[0168] At 148.degree. C., where the surfaces of the tapes are just
beginning to melt, the tapes appear better bonded although the peel
surfaces are clear of damage.
[0169] At 152.degree. C. surface damage has increased, reflecting
the increase in the measured peel load. As with the PP studies, the
areas of surface damage are variable when a film is not used.
[0170] At 154.degree. C. the damage is further increased.
[0171] FIGS. 26-29:
[0172] These four micrographs show samples made with a film at 135,
148, 152 and 148.degree. C. respectively. All show increased
surface damage compared to the equivalent samples made at the same
temperature. Unlike the PP studies, the film is still visible on
some of the fracture surfaces, particularly at 135.degree. C. As
the compaction temperature is increased the amount of damage
increases. Only at 154.degree. C. is substantial damage seen within
the oriented tapes (i.e. at the temperature where there is
substantial surface melting of the tapes).
[0173] For the other temperatures the failure mode seems to have
occurred at the film/woven cloth surface, i.e. at least partial
adhesive failure. The best performance is therefore confirmed as a
combination of film melting and melting of the tape outer
surfaces.
[0174] FIG. 30: 135.degree. C.
[0175] no film: shows one tape going underneath another at
90.degree. to it, and confirms no bonding between the tapes at this
temperature.
[0176] FIG. 31:
[0177] 135.degree. C. with film: this high magnification micrograph
shows surface damage and tearing of the interleaved film, but that
failure has occurred between the film and the woven layer in some
instances.
[0178] FIG. 32:
[0179] 148.degree. C. no film: this micrograph shows a junction
between tapes and indicates much better bonding between the tapes.
However there is minimal surface damage suggesting the surfaces
were fairly easily separated (i.e. low peel strength).
[0180] FIG. 33: 148.degree. C. with film: shows increased surface
damage but still adhesive failure.
[0181] FIG. 34: 152.degree. C. no film: increased surface damage on
this sample compared to the lower temperatures made without a
film.
[0182] FIG. 35: 152.degree. C. with film: shows adhesive
failure.
[0183] FIG. 36: 154.degree. C. no film: optimum temperature without
a film: substantial damage of the oriented tapes produced during
peeling.
[0184] FIG. 37: 154.degree. C. with film: this sample gave the
roughest peeled surface seen, which correlates with the highest
peel load measured. At this compaction temperature the failure
appears to be cohesive. The piece of film on the left shows
evidence of material peeled off the adjoining tape on the other
surface.
* * * * *