Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
18;~2
This invention relates to recoverable articles. This
application is a divisional application of copending applicant
No. 444,695 filed February 5, 1984.
A recoverable article is an article the dimensional
configuration of which may be made subc;tantially to change when
subjected to a particular treatment for example heat treatment.
Usually these articles recover, on heating, towards an original
shape from which they have previously been deformed, but the term
"heat-recoverable'~, as used herein, also includes an article
which, on heating, adopts a new configuration, even if it has not
been previously deformed.
In their most common form, such articles comprise a
heat-shrinkable sleeve made from a polymeric material exhibiting
the property of elastlc or plastic memory as described, for
example, in U.S. Patents 2,027,962; 3,085,242 and 3,597,372. As
is made clear in, for example, U.S. Patent 2,027,962, the
original dimensionally heat-stable form may be a transient form
in a continuous process in which, for example, an extruded tube
is expanded, whilst hot, to a dimensionally heat-unstable form
but, in other applications, a preformed dimensionally heat stable
article is deformed to a dimensionally heat unstable form in a
separate stage.
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In the production of heat recoverable articles
the polymeric material may be cross-linked at any stage
in the production of the article that will enhance the
desired dimensional recoverability. One method of
producing a heat-recoverable article comprises shaping
the polymeric material into the desired heat-stable
form, subsequently cross-linking the polymeric mat-
erial, heating the article to a temperature above the
crystalline melting point or, for amorphous materials
the softening point, as the case may be, of the poly-
mer, deforming the article and cooling the article
whilst in the deformed state so that the deformed
state of the article is retained. In use, since the
deformed state of the article is heat-unstable, appli-
cation of heat will cause the article to assume itsoriginal heat-stable shape. A further method comprises
deforming a substantially non-crosslinked polymeric
material at a temperature below the crystalline melting
point or softening point of the material, tusing
together parts of the material or a part or parts of
the material and at least one other polymeric component
to produce the configuration of at least one hollow
heat-recoverable article and subsequently cross-linking
the substantially non-cross-linked material.
In other articles, an elastomeric member is held
in a stretched state by a second member, which, upon
heating weakens and thus allows the elastomeric member
to recover. Heat-recoverable articles of this type are
described, or example, in British Patent 1,440,524 in
which an outer tubular elastomeric member is held in a
stretched state by an inner tubular member.
iL~3~ ;2
_ - MP0790
Heat-recoverable articles have found particular
use in the environmental protection of elongate sub-
strates such as for example spllces in telecommunica-
tion cables.
In addition to making the environmental seal the sleeve
may be required to withstand an internal pressure,
either because the complete splice enclosure is pres-
sure tested for leaks, as for example in the Bell cycle
and British Telecom specifications, or because tempera-
tures reached in service create a significant internalpressure. Whereas the known heat-recoverable sleeves
are quite suitable for the conditions encountered with
distribution splice enclosures, many larger telecom-
munication cables are internally pressurised to
exclude moisture and the thicker-walled sleeves which
would be required to withstand such pressures long term
are more difficult and expensive to manufacture and
require greater skill to install in the field.
It has been proposed, in U.S. Patent 3 669 157 to
Carolina Narrow Fabric Company and in Japanese Patent
53-13805 to Matsushita, to provide heat-shrinkable
tubular fabric articles which may be impregnated with
certain thermosetting resins. However, we have found
that the articles disclosed therein are very difficult
to install because they are subject to displacement of
the resin on recovery, resulting in burst-through of
fabric by the resin, or delamination of the resin from
the fabric. Thus these prior art articles are of
limited utility and are too craft-sensitive for use in
most telecommunications applications.
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The present invention provides an article which
has an improved resistance to the forces of recover.y
and can retain its integrity so as to produce in the
appropriate circumstances as described herein an
effective environmental and if desired a pressure-retaining
seal.
In one aspect the invention provides a dimension
ally heat-recoverable article comprising a composite
structure of a heat-recoverable fabric and a polymer
matrix material wherein:
(a) the heat-recoverable fabric comprises fibres that t
will recover when heatedr the fibres having a recovery
stress Y of at least 5 X 10 2 MPa at a temperature
above their recovery temperature; and
(b) the polymer matrix material has an elongation/
temperature profile such that there exists a tempera
ture (T) which is at or above the recovery tempera-
ture of the fibres at which temperature the polymer
matrix material has an elongation to break of greater
than 20~ and a 20~ secant modulus X of at least 10 2
MPa (measured at a strain rate of 300~ per minute), and
at which temperature the inequality (1) is satisfied:
X (1 - R) is less than one (1)
Y R
wherein R is the mean effective volume fraction of
heat-recoverable fibres in the composite structure
along a given direction based on the total volume of
the composite structure, or relevant portion thereof.
The invention also provides a method of producing
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a dimensionally heat recoverable article, comprising a
composite structure which is recoverable by virtue
of a recoverable fibre component thereof, which method
comprises combining a heat-recoverable fabric as
defined above with a polymeric material as defined
above for the matrix.
The term "fibre" as used herein includes filaments
e.g. monofilaments or multifilaments, and also staple
fibres, wires and tapes. The fabrics used in the
articles according to the invention preferably employ
the heat shrinkable fibres in the form of filaments,
especially monofilaments.
The heat-recoverable fibres used in the article of
the invention preferably have a minimum recovery stress
of 10 lMPa, more preferably 5 X 10 1 and usually at
least 1 MPa at a temperature above the transition
temperature of the fibres. There is in theory no upper
limit of recovery stress, but in practice 200 MPa and
more usually lOOMPa is the highest figure normally
achievable with polymeric fibres.
The fibres are preferably formed prom a polymeric
heat-recoverable material. By "the recovery tempera-
ture" of polymeric heat-recoverable materials is meant
that temperature at which the recovery of the polymeric
material will go substantially to completion. In
general, the recovery temperature will be the crystal-
line melting transition temperature if the polymer is
crystalline or the glass transition temperature if the
polymer is amorphous.
In most forms of article according to the inven-
tion the polymer matrix will become soft at tempera-
tures below the recovery temperature of the heat-
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recoverable fibres so that the temperature (T) at
which the matrix material has the required elongation
and secant modulus and at which the inequality (1) is
satisfied will be the same as the recovery temperature
of the fibres. The invention includes, however, those
cases in which a rigid matrix material holds out the
fibres against recovery over a temperature range above
the recovery temperature of the fibres and then softens
so that the fibres can recover.
The heat-recoverable fibres are preferably formed
from a polymeric material that imparts good physical
properties and, in particular, good creep resistance to
the fibres. Olefin polymers such as polyethylene and
ethylene copolymers, polyamides, polyesters, acrylic
polymers and other polymers may be employed and prefer-
ably those that are capable of being cross-linked. A
particularly preferred polymeric material for the
fibres is based on polyethylene having a density of
from 0.94 to 0~97/gms/cc, a weight average molecular
weight Mw of from 80 X 103 to 200 X 103 and a number
average molecular weight Mn of from 15 X 103 to
30 X 103.
Preferably the recovery temperature of the
fibres is 60C or more, most preferably from 80C to
250C, such as, for example, 120 - 150C.
When the fibre is cross-linked by irradiation it
is convenient to incorporate the cross-linking step
into manufacture of the fibre. The fibre can be
extruded, stretched at a temperature below its melting
temperature, preferably by an amount of from 800 to
2000 I, then subjected to irradiation to effect cross-
linking. A less preferred way of making the fibre is
to extrude the fibre, irradiate to cross-link, then
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heat the fibre, preferably to above its melting tem-
perature, stretching the fibre, and then cooling the
stretched fibre. High density polyethylene fibres are
preferably irradiated with a dose of from about 5 to
about 35 megarads, preferably from about 5 to about 25
megarads and in particular from about 7 to about 18
megarads, especially from 10 to about 18 megaradsO
Usually the gel content of the cross-linked fibre is
yreater than 20~, preferably greater than 30%, most
preferably greater than 40~. In practice, gel contents
greater than 90% are not easily achievable. Fibres
produced in this way can have a high strength after
recovery. A further advantage of fibre irradiation
will be mentioned below in connection with lamination.
The heat-recoverable fabric can, if desired, be
made solely of heat-recoverable fibres as described
above or can contain other fibres in addition to the
heat-recoverable fibres. Where the fabric contains
such other fibres, R in equation (1) relates only to
the heat-recoverable fibre component. The fabric can
be knitted, woven, non-woven, braided, or the like. The
recoverable fibres can form part of the fabric itself
as it is made or may be additional and inserted after
production of the basic fabric. In a preferred embodiment
the fabric is a woven fabric. The woven fabric can
contain only heat-recoverable fibres or it can contain
heat-recoverable fibres together with non-heat-recoverable
fibres or filaments. The fabric can be woven in a
pattern, for example, twill, broken twill, satin,
sateen, Leno, plain, hop sack, sack and various weave
combinations, in single or multiple ply weaves for
example two or three ply weaves. Preferably the fabric
is a woven fabric that has heat-recoverable fibres in
one direction and dimensionally heat stable fibres in
the other direction so that the fabric as a whole is
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~9~ MP790
recoverable in a single direction only, and the description
below will, in general, be made in terms of such a
fabric. however, the features described rnay be applied
to other fabrics.
The fabric may alternatively be knitted if desired,
either warp knitted or weft knitted. If the fabric is
made solely from heat-recoverable fibres it will be
recoverable in two dimensions, but if, as is preferred
for the knitted fabrics, it is knitted from a heat
stable fibre and a heat-recoverable fibre i5 either
warp or weft inserted, it will be recoverable in only
one direction.
The mean effective volume fraction of heat-
recoverable fibres in the composite structure along any
given direction will depend inter alia on the size of
the fibre, the type of weave or knit used and the
direction considered. The mean effective volume
fraction R used in inequality (1) above is defined
herein as the mean value along the direction considered
of the summation of the product of the cross-sectional
area of each heat-recoverable fibre multiplied by the vector
component of the fibre in the given direction divided
by the total cross-sectional area of the composite
structure taken in the plane normal to the direction
considered. Thus if the heat-recoverable fibres lie at
an angle alpha to the considered direction, the product
of the cross-sectional area of the fibre and its
component in the considered direction is given by
(fibre area multiplied by cos alpha1. The sum of this value
3~ for all the fibres cut by the plane normal to the
considered direction divided by the total area of the
composite structure gives the value R at a specific
point along the direction considered, and the mean
value of R over the whole length of the relevant fabric
3~L8Z:2
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portion in the direction considered is used in inequality
(1) above and in Claim 1 below.
In the case of a weave where all the heat-
recoverable fibres are parallel to each other (either
the warp or weft in the case of a weave) and the
direction considered is parallel to the recoverable
fibres (i.e. the direction of recovery), then the mean
value of R is given by the total cross-sectional area
of all the recoverable fibres divided by the total
cross-sectional area of the composite structure.
The heat-recoverable fabric is preferably bonded
to, and preferably embedded in, the polymer matrix
material. The previously mentioned advantage of irradiation
is relevant here; if the fibres, before or after
formation of the fabric are irradiated (particularly in
the presence of oxygen), a chemical change to their
surface occurs which significantly improves bonding of
the matrix material. At or above the recovery temperature
of the fibres the polymer matrix material should be
capable of limited flow under pressure so that it
retains the integrity of the composite structure
without substantially impeding recovery of the fibres.
It preferably has, at the aforesaid temperature, an
elongation to break of greater than 50~, most preferably
25 greater than 100% particularly 400-700~, ar.d a 20~
secant modulus of preferably at least 5 X 10 2 MPa,
most preferably at least 10 1 MPa, measured at a
strain rate of 300~ per minute.
The specified properties of the polymer matrix
material need not necessarily apply after recovery
although it may be desirable that the product be
flexible at room temperature. Thus, for example, the
polymer matrix material may eventually cure to a
~L~3~
Il- MP790
thermoset on heating, provided that the cure rate is
sufficiently slow under the recovery conditions not to
affect adversely the above mentioned physical properties
of the polymer matrix material during the recovery of
the fibres. Thus, for example, the polymer forming the
matrix material may contain grafted hydrolysahle silane
groups which are capable of crosslinking the material
subsequently in the presence of moisture. Alternatively
the matrix material may include a polymer, preferably a
rubber and especially an acrylic rubber, which contains
epoxy groups and a room temperature insoluble curing
agent e.g. dicyandiamide.
The polymer matrix material can be either a
thermoplastic or an elastomer. In general, we prefer
that the polymeric matrix material and the material of
the recoverable fibres be chemically or physically
compatible, and preferably both chemically and physically
compatible. By this we mean that they be of similar or
identical chemical types and that their relevant
physical properties during lamination, installation and
use be similar or idential in particular we prefer that
the matrix and fibres be low density polyethylene and
high density polypropylene respectively. The skilled man
will be able to choose other pairs of compatible
polymers. Example of thermoplastic materials suitabe
as the matrix material include ethylene/vinyl acetate
copolymers, ethylene/ethyl acrylate copolymers,
polyethylenes including the linear low, low density and
high density grades, polypropylene, polybutylene,
polyesters, polyamides, polyetheramides, perfluoroethylene
/ethylene copolymer and polyvinylidene fluoride. Considering
the second class of materials this can include
acrylonitrile butadiene styrene block co-polymer,
acrylic elastomers including the acrylates and
methacrylates and their copolymers, e.g~ polybutyl
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acrylate, and poly 2-ethylhexyl acrylate, the high
vinyl acetate copolymers with ethylene (~AE's), posy-
norbornene, polyurethanes and silicone elastomers and
the like. The polymeric material forming the matrix
S may be transparent (at least to visible radiation) or
completely opague or it may have any opacity between
these two extremes. If the opacity is increased for
example by blending a small quantity eg up to about 5%
by weight of carbon black into the matrix, the time
taken for recovery appears to be reduced. Also, the
resistance of the material to heat damage, especially
by flame, and to UV damage is reduced. The matrix
material ( or part of it) can be cross-linked, for
example, a cross-linked ethylene/vinyl acetate copolymer,
linear low density or high density grade polyethylene
or an acrylic elastomer. The material can be cross-
linked by irradiation or by other means such as chemical
cross~linking using, for example, a peroxide cross-linking
agent, provided that the physical properties of the
matrix at the recovery temperature are as specified
after the cross-linking step. Where irradiation is
used a dose of 10 megarads or less, in particular from
3-7 megarads, is preferred. The resulting extent of
cross-linking ailows the matrix to recover with the
fabric and also prevents the matrix running or dripping
during heat recovery, especially during heat recovery
by means of a torch. The recovery ratio of the composite
after irradation is preferably at least 50% especially
at least 70% of that before irradiation. These dose
values may regarded as typical for olefinic polymers
such as polyethylene of low irradiation, and the
skilled man will be able to select suitable dose
values depending on the presence of various concentrations
of prorads if any. The composite structure may be
produced using a single irradiation step if the beam
~L23~8~;2
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response of the matrix and fibre be made compatible;
the beam response of the oriented fibres may be increased
by the addition of prorads and that of the less oriented
matrix be reduced by the addition of there of antirads.
Otherwise separate cross-linking steps will be preferred.
further feature of post lamination cross-linking
(particularly by irradiation) is that a cross-link bond
may be formed between the recoverable fibres and/or any
other fibres which can help to maintain the structure
as a true composite, particularly under severe recovery
conditions. This may allow a much less severe laminating
process, since it can obviate the need for physical
interlocking.
The heat-recoverable fabric is preferably bonded
to the polymer matrix material, and this bonding may be
adhesive, that is to say by chemical or physical
surface interaction, or alternatively mechanical
interlocking may be provided.
Most preferably, the heat-recoverable fabric is
embedded in the polymer matrix material thereby forming
a composite structure. By embedded" is meant that the
polymer matrix material surrounds at least a major
portion of the fibre surface area of the fibres making
up the fabric.
The fibres are preferably totally surrounded by
polymer matrix material; however it is possible and at
times desirable, that substantially less than the total
fibre surface area be surrounded by polymer matrix
material. An instance where this is possible is where
a fibre matrix bond is formed. Sufficient fibre area
should be bonded to the polymer matrix material or
interlocked therewith to result in a composite structure
which retains its integral structure during recovery of
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the article. For the avoidance of doubt it is here
stated that the term matrix is used to include materials
which surround (partially or tot:ally) the fibres and
also those materials which are merely afEixed to a
S surface of the fabric but do not penetrate the interstices
of the fabric.
Preferably the polymer matrix material at least on
the surface of the composite structure facing the
source of heat is substantially unstressed and has a
thickness of at least 0.03mm especially at least 0~01
mm, more especially at least 0.2, particularly from 0.2
to 2mm as described in OK patent application No.8300217,
as this improves the ability of the composite structure I
to be heat recovered using a conventional propane
torch.
In the composite structure, the ratio of the
volume occupied by the heat-recoverable fibres of the
fabric to the total volume of the composite is at least
about 0.01:1, preferably from about 0.1:1 to about
0.8:1 and most preferably from about 0~2:1 to about
0.4:1.
In the composite structure the heat-recoverable
fibre volume in any given unit volume of composite is
dependent on the fibre strength, polymer matrix
strength and the integrity of the fibre/polymer matrix
structure under recovery conditions. We have found
that an acceptable recoverable product results if the in-
equality (1) is satisfied:
X (1-R) < 1 (1)
Y R
wherein X is the 20% secant modulus of the polymer
~--~3~8~
-15- MP790
matrix material and Y is the recovery stress of the
fibres, both at a temperature T above the recovery
temperature of the fibres, and R is the mean effective
volume fraction of heat-recoverable fibres in the
composite structure.
Preferably _ ( _ J < 0.5 most preferably < 0.05.
The composite structure can be formed for example
by laminating one or more layers of polymer matrix
material to the heat-recoverable fabricO Sufficient
heat and pressure is preferably applied so that at
least a major part of the fabric is bonded to the
polymer matrix material, or so that a significant
amount of mechanical interlocking occurs. The result is
a composite structure which on application of heat
recovers as a unit.
other methods of bonding the fabric to the
matrix can be used, for example, impregnation, solution
coating, slurry coating, powder coating, reactive
pre-polymers, e.g. acrylic prepolymers activated by UV
or peroxide, and the like. In any bonding method
employed sufficient heat to cause the fabric to recover
to any significant extent should be avoided, unless the
fabric is suitably restrained from recovery.
The heat-recoverable article can be used in
numerous applications. It is particularly suitable
for enclosing elongate substrates such as pipes,
conduits, cables and the like. The heat-recoverable
~LZ3~
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article can be coated on a surface thereof with a layer
of a sealant or adhesive composition. The sealant can
be a mastic and the adhesive can be a heat activatable
adhesive such as a hot-melt adhesive. Hot-melt
adhesives which can be used include polyamide and
ethylene vinyl acetate copolymer based adhesives.
Such adhesives are well known, for example see ~.S.
Patents Nos. 4,018,733, 4,181,775. If desired a heat-
curable adhesive may be used for example as described
in U.K. patent publication No. 21048000
y appropriate selection of the polymer matrix
material, the polymer matrix material can function as
an adhesive to secure and seal the recovered composite
structure to the substrate. The fabric can be embedded
in more than one polymer matrix material to provide
desired properties. For use in enclosing elongate
substrates, the fabric can be laminated with a layer of
matrix material on each of its surfaces, the surface
which will be the inner surface when in use can
be laminated to a polymer matrix material which has
adhesive properties while the outer surface can be
laminated to a material which is not. As will be
readily apparent the matrix material can be selected
for various other desirable properties inherent in the
polymer material itself or provided with various
additives such as antioxidants, ultra violet stabili-
zers, pigments, anti-tracking agents and the like.
The heat-recoverable article of this invention
is typically a sheet but can be of any configuration
such as tubular, including multiple tubular portions
interconnected, for example, a brea~-out structure for
cable splices where one cable is spliced to two or more
other cables, or where two or more pipes are joined
together.
~2~8~
-17-
A heat-recoverable sheet in accordance with
this invention can be used to form a cable splice
case, a pipe segment, or pressure vessel as described
in UK patent application No 8300221. Heat recoverable
articles according to the present invention have been
found to be particularly suitable for use in enclosing
a splice between pressurized telecommunication cables.
The recovered article is exceptionally resistant to the
effects of pressure and preferred embodiments are
impervious and have sufficient hoop strength to resist
rupturing under about 70 KPa pressure (the pressure
typically used in pressurized telecommunication systems)
at the operating temperatures of such systems.
I
Where a cable splice case is to be formed, the
sheet of the invention will be used in conjunction with
some kind of internal support, such as a generally
cylindrical liner having tapered ends. The liner is
preferably shaped in this way such that its larger
central section fits around the bulky cable splice, and
its tapered ends accomodate the transition in size down
to the cables. The liner may be of the wrap-around
type, in which case it preferably comprises half-shells
having crowned or other end supports, or it comprises a
sheet of stiff material which may be rolled around the
cable splice and again crowned ends may provide the end
supports which can be taped down onto the cables. In this
way, a pressure vessel may be built around an object
(such as a cable splice); the sheet material providing
an impermeable, creep resistant and split resistant
surround, and the liner providing impact resistance,
axial strength and other mechanical requirements.
If the splice case or pressure vessel is intended
to retain pressure during use, rather than merely be
pressure tested for integrity before use, certain other
z'~
-18-
features may be provided. A valve on otner pressure
access point will be usefully provided in the recoverable
sheet, and may also be affixed to the internal liner.
A sheet based on fabric is well suited to the provision
of a valve or other device which must pass though the
sheet, since splitting is less lively to occur. Even
if some fibres are broken when the valve is inserted,
the damage should not spread, and if care is taken a
hole for the valve may be produced simply by moving
adjacent fibres apart.
A second feature desirable in a pressurized
splice case is some means for preventing any bond
between outer sleeve and cable being put into peel
by the internal pressure. We have obtained satisfactory
lS results using a strip of material having one surface
which abuts (and preferably bonds to) the cable and
another surface which abuts (and preferably bond to)
the sleeve, such that the two surfaces can open out.
The strip of material preferably has a U-or V-shaped
cross-section and is installed with the re-entrant side
facing into the splice case.
Other uses for the composite structure include
environmental protection or repair or insulation of a
wide range of substrates in the telecommunicatlons,
high voltage, electronic, oil and gas, and process
industries. For example in addition to the production
of cable splice cases, cables jackets may be repaired
by the installation of the new composite, with particular
benefit due to its high strength! flexibility and
3G abrasion resistance. Also, pipes may be protected from
corrosion or other damage, in which case a sealant,
particularly a mastic, coating on the composite is
desirable. Pipe insulation can also be built up by
means of the composite, optionally with some other
~23~3t~2
,g
insulation material such as a foaming material. Thermal
and/or electrical insulation may be provided.
A further use for the composite is in the production
of hollow articles for housing and protection of a wide
variety of components.
Yet another use of the composite is for securing
together two or more articles, for example a pipe or a
cable onto an elongate substrate. Where pipes or
cables have to be held secure under adverse conditions
some tight and environmentally resistant fixing is
needed. One particularly important example of such a
use is for the protection of electrical wiring extending
along the external surface of a helicoptor rotor blade
spar. In certain instances it may be necessary for
electrical wiring to extend along the external surface
of the rotor blade spar before it passes into the
blade. Such wiring may, for example, be used to
transmit electrical power for heating elements located
along the leading edge of the blade in order to prevent
the blade icing. In this instance the wiring is
retained along the spar surface by recovering thereon a
heat recoverable article according to the invention.
It has been found that the fabric recoverable articles
are particularly suited to this application in view of
their relatively high abrasion reslstance which prevents
or reduces any damage thereto that may be caused by
exposure to the elements. In addition, the relatively
high forces exerted on the substrate by the installed
heat recoverable article prevent or reduce any movement
of the electrical wiring caused by the centrifugal
force or other fcrces when the blade is in operation.
Furthermore, the fact that the fabric articles have
relatively high split resistances enable them to be
recovered over protuberances on the spar such as nuts
and bolts.
12~ Z
-20-
Helicopter rotor blades are supported by spars
one end of which is attached to the rotor blade gearbox.
A number of heating pads may be arranged along the
length of the leading edge of the rotor blade to
prevent icing of the blade, and the electrical power is
transmitted to the heating pads along a wire harness.
in order to retain the harness securely on the spar, a
heat-shrinkable wraparound composite structure is
recovered onto that portion of the spar along which the
harness extends. The composite structure is preferably
formed from a laminated heat-shrinkable fabric in which
the laminated polymeric layers are unirradiated and the
recovery ratio of the composite structure is approximately
2:1. It is, of course possible for the laminated
layers to be irradiated or for the recovery ratio to be
varied. The cover is preferably formed as a wraparound
article and is provided with a rail and channel type
closure arrangement. The under surface of the cover
may be provided with a layer of a hot-melt adhesive
e.g. an ethylene/vinyl acetate copolymer based or
polyamide based adhesive in order to secure the cover
to the spar and to prevent ingress of water along the
harness Depending on the use of the cover, it may be
desirable to coat the entire surface thereof with the
adhesive or only to coat marginal portions extending
along the edges thereof.
For many uses, the recoverable composite structure
of the invention is preferably produced open as opposed
to tubular. The sheet is easier to manufacture
that way, and also easier to install since a free end
of the substrate to be covered need not be accessible.
The problem that results, however, is how to secure the
sheet in the wrapped configuration around the substrate;
what is required is some means whereby the recoverable
fibres at opposing edges of the sleeve be trapped
8%~
-21-
together. The solutions can be regarded as of four
broad types. Firstly a lap or other bond may be made
between opposing edges of the sheetloptionally wit a
patch to prevent peel-back of the overlapping edge on
recovery. Here the bond will generally be between the
matrices of the opposing edge portions, and one must
therefore ensure that the fibre recovery force is
proper]y transmitted from the fabric to the matrix at
those edges. Secondly some means which penetrates the
sheet may be used, and here the fabric will be directly
involved. In general, this technique was not possible
with continuous sheet materials due to the problem ox
splitting. With a fabric based material, however, split
resistance may be extremely high. Examples of this
type of closure include stitching, stapling, riveting,
the use of pre-inserted catches such as press-studs or
the use of means which may be positioned adjacent a lap
joint in the sheet and which has a plurality of projections
which penetrate both thicknesses of sheet. This second
2~ type is mentioned in more general terms below. The
third broad type of closure involves forming or
building up opposing edge portions of the sheet in
order that they may be held together by some form of
clamping means such as a channel of C-shaped
cross-section or by a re-usable tool. This may
be achieved by bonding material to the edge portions or
by folding the edge portions back on themselves (optionally
around a rod running lengthwise of the sheet). The
resulting edge portions of the sleeve may then have a
shape similar to the rails of the classic rail-and-channel
closure disclosed in UK patent 1155470.
The fourth technique to be mentioned comprises
forming the fabric in such a way that the recoverable
fibres do not terminate at the opposing edges to be
jointed, but instead double back. An example is to use
recoverable weft on a shuttle loom and insert
-22-
a closure member into the weave at each edge,
or to employ special selvedges. further possibility is
to weave closed pockets at each edge, or to weave a,
tubular structure and flatten the tube, the flattened
tube then being used as a sheet which can accommodate
closure rods or other members within it. These ideas,
although mentioned in terms of weaves, apply mutatis
mutandis to other fabrics such as braids and knits.
Several of the above closure techniques are
10 described in OK patent application 8300223.
Where the recoverable sheet of the invention
is used in the wrap-around form, it may be desirable to
employ a slap under the opposing edges which are
brought together. Such a flap, which may be integral
with the sheet, will improve environmental sealing and
if need be, pressure retention.
The second technique for maintaining the
sheet in a wrap-around configuration may now be returned
to in more general terms. The ability of the recoverable
composite to be penetrated allows portions of it to be
joined together to form not ony a tubular structure,
but also form various shaped hollow articles such as
bends and tees and also to form diverging branch-offs
in simple cylindrical articles. In general terms
therefore two or more portions of the composite structure
may be joined together by means of a mechanical
joining arrangement that penetrates the fabric. The
joining arrangement is preferably one or more lines of
stitches or one or more staples. The portions joined
together may be discrete or may merely be separate
portions of a single piece of composite material. Where
stitching is used each line of stitches preferably has
from 200~800 stitches per metre, and the line of
-23-
stitches closes to an edge of the fabric is preferably
separated from that edge by at least four rows of
fibres, and in the case of high float fabrics such as
sateens where the high float is perpendicular to the
join line a spacing of at least 6 rows may be preferred.
This will correspond to an edge overlap of at least
8-10 mm, preferably at least 16 or ~0 mm for the fabric
types preferred. A hem may, of course, be provided but
this will increase the thickness of the fabric which in
general is not desirable. In order to reduce the
possibility of breakage of the heat-recoverable fibres
by the stitching or sewing (or stapling) operation, the
needles ( or staples) should be very sharp at their
tips and have a maximum used diameter of the same order
of magnitude as the distance between the heat-shrinkable
fibres of the fabric.
An advantage of stitching or stapling arises as
follows. When the fibres recover by shrinking axially,
their diameter or titre increases. As a result the
perforations in the fabric through which the stitches
or staples pass close up and the fabric grips the
stitches or staples, thereby increasing the strength of
the join. The reduction in size of the perforations
also helps any adhesive layer or matrix material to
fill the perforations completely and so reduce the
possibility of leakage of fluids though the recovered
article, this being particularly useful in articles used
for environmental sealing, for example cable splice
cases or corrosion protection for pipes or pipe insulation.
Usually, it will be necessary only for the compo-
site structure to contain a single fabric embedded in
or bonded to the matrix polymer. However it is quite
possible, and in some instances it may be desirable,
for the composite structure to comprise a plurality of
~2~ 2
-2~-
fabrics, e.g. two fabrics having a layer of the matrix
polymer therebetween, and optionally on one or more of the
outwardly facing surfaces Articles that employ more
than one fabric are especially useful for enclosing
substrates that have high internal pressures or for
use in cases in which the article may be subject to
particularly severe mechanical abuse.
The invention is further illustrated by the
accompanying drawings in which:
Figure 1 is a perspective view of a wrap-around
article according to the invention with the thickness
of the composite structure exaggerated for the sake of
clarity;
Figure 2 is a section through part of the article
of figure 1;
Figure 3 is an exploded sectional view showing
the edge regions of the article shown in figure 1 after
it has been wrapped around a substrate; and
Figures 4 and 5 are exploded sectional views
showing edge regions of modifications of the article
shown in figures 1 to 3 after whey have been wrapped
around a substrate.
Figure 1 shows in perspective an article according
to the invention which is in the form of a wraparound
device suitable for enclosing an elongate substrate
such as a splice in a telecommunication cable. The
article is formed from a composite sheet 1 comprising a
fabric having heat-shrinkable filaments 3 in the warp
direction and multifilament glass yarn 4 in the weft
direction.
8~:
- 25 - MP0790
The fabric is entirely embedded in a matrix polymer
material 5 as shown more clearly in figure 2. The
matrix material 5 comprises two laminae 6 and 7
formed from a thermoplastic polymer, the laminae having
been laminated onto opposite sides of the fabric e.g.
by a melt lamination process and subsequently cross
linked so that each lamina 6 and 7 adheres both to the
fabric and to the other lamina, and so that they
exhibit the desired flow characteristics under the
chosen recovery conditions. After the composite sheet
has been formed, a rail is formed along each of
the edges that extend along the weft direction in order
to provide means for retaining those edges together
after the article has been wrapped around a substrate.
Before or after the rails have been formed in the
article, the composite sheet 1 is provided with a
layer 10 of a sealant or adhesive, e.g. a mastic or a
hot melt adhesive. The article has been found to have
significant advantages over prior art articles. Its
ability to withstand hoop stress, resulting for example
from internal pressure is higher; it can be heat-shrunk
using a torch with reduced liklihood of damage, it is
abrasion resistant; and it is highly split resistant.
Figure 3 is an enlarged exploded sectional view
showing the closure rails of the article in their
disposition after the article has been wrapped around a
substrate Each rail is formed by wrapping a marginal
portion of the composite sheet around a rod 12 formed
from a high melting point material e.g. nylon, press-
ing faces 13, 14 or the marginal portion together toform a wall between the rod 12 and the rest of the
sheet, and heating the marginal portions to set them in
8;;~:~
- 26 - MP0790
the configuration shown and to allow partial recovery
of the fibres in the wall. As shown in one of the edge
portions the composite sheet is bent back on itself
while in the other edge portion the sheet extends
beyond the rail to form an underlying sealing flap.
After the device has been wrapped around the substrate
the two edge portions are brought together until they
abut and a metal channel, for example as shown in
patent specification No. 1,155,470, is slid over
the rails to retain the edge portions together and the
article is then recovered.
Figure 4 shows a modification of the article
shown in figures 1 to 3 in which the composite sheet is
bent back along each edge portion and a separate
polymeric sealing member 15 having a sealant layer 16
is provided. The sealant member may be formed from
rubber or other elastomer, polyethylene or the like.
Figure 5 shows a further modification of the article in
which the sealing member 15 is bonded to one of the
edge portions during manufacture
Example 1
Heat-recoverable fabrics suitable for use in the
heat-recoverable article of this invention were pre-
pared by weaving high density polyethylene monofila-
ments into fabrics of various weave patterns andsubjecting the fabric to irradiation. The fabrics were
irradiated using 6 MeV electrons in air at a dose rate
of 0.24 Mrads/minute. Properties of the fibres and
fabrics are listed in Tables I and II.
~2318~Z
- 27 - MP0790
TABLE I
Fiber Properties
Radiation Dosage fads
Fibre Property 8 16 32
1 100% Modulus (MPa) at 150C 0~13 0.3 0.42
Tensile Strength (MPa) at 150C 0.93 1.4 1.46
Elongation to Break (%) at 150C 1480 924 754
Gel Content (%)* 27.0 58~0 67.0
Recovery Force (MPa) (peak value) 1.17 1.2 1.3
Recovery (%) 89 88.5 85.5
2 100% Modulus (MPa) at 150C 0.27 0.21 0.34
Tensile Strength (MPa) at 150C 1.361.93 2.98
Elongation to Break (%) at 150C 752 487 777
Gel Content (%)* 10.0 40.0 61.0
Recovery Force (MPa) (Peak Value) 0.57 0.6 0.65
Recovery (%) 89 87 85
* Obtained by refluxing in xylene
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- 29 - MP0790
Example 2
Heat-recoverable composite sheets were prepar,ed
by laminating a 60/10 (23.6/3.9 in cms) twill fabric
woven from polyethylene monofilament identified as
fiber 1 in the above example, with polymer matrix
material in the form of extruded sheet 0.5 mm thickness
having little, if any, irradiation. The lamination was
conducted in a press between silicone rubber sheets
under conditions appropriate for the particular polymer
matrix material used. The laminating conditions are
shown in table III.
TABLE III
-
Laminating Conditions
Composite
No. Polymer Temperature (C) Pressure (kg/cm2) Time (mins.)
1 460 105 45 5
2 EVA 250 100 ~5 3
3 Low density 150 22.5 5
polyethy-
lene
~Z3~L8~:
- 30 - MP0790
The resulting composite structures were subjected
to irradiation with 6 MeV electrons in air at room'
temperature at a dose rate of 0.24 Mrads/minute for
times sufficient to produce a radiation dose of 2,4 or
6 Mrads in respective samples. The properties of the
polymer matrix materials are shown in Table IV and
recovery of composite structures are shown in Table V.
In Table V, the composite structures were prepared from
Fabric No. 11 preparation in Example 1, laminated with
the polymer matrix identified in Table IV and the
composite irradiated with an absorbed dose of 4
Mrads. The recovery ratio of the composite structure
is preferably at least 40%, more preferably at least
65~ especially at least 70% of that of the free fabric.
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- 33 - MP0790
TABLE V
Composite No. Polymer Matrix Recovery
1 EVA 460 70
2 EVA 250 69
3 Linear low 68
density poly-
ethylene
4 DYNH-3 60
~Z3~8~
- 34 - MP0790
EXAMPLE 3
A fabric was formed using an eight shaft satin
employing 0~29mm diameter high density polyethylene
filaments in the warp and 75 E.C.G. glass fibre yarn in
the weft. The fabric density (warp density/weft
5 density, measured in fibres,/inch, fibres/cm was 90/16,
35.4/6.3 The fabric was irradiated with 1.5 MeV
electrons to a dose of 15 Mrads to give the warp fibres
a gel content of 37.3% (refluxing in xylene) and a 100%
secant modulus of 0.60 at 150C.
The fabric was then extrusion laminated Wittl low
density polyethylene at a melt temeperature of 260C
between a cooled metal roller and a rubber faced
roller. The polyethylene had a thickness of 0.6mm on
one side of the fabric and a thickness of 0.3mm on
15 the other side and, after lamination, the composite was
irradiated with high energy electrons to a further dose
of 4 Mrads. The low density polyethylene used had a
melt flow index of 3.0, a number average molecular
weight Mu of 14,800 and a weight average molecular
20 weight Mw of 114,800. After the second electron
irradiation step the low density polyethylene laminae
which constituted the matrix material, had the follow-
ing properties:
100% secant modulus at 60C 4.8 MPa
25 100% secant modulus at 150C 0.03 MPa
Tensile strength at 150C0O13 MPa
Elongation to break at 150C 67096
Gel content (reflux in xylene) 39.2%
Complex viscosity at 150C
30 and at 1.0 rad 5 2.79x105 poise
~2~ Z2,
- 35 - MP0790
The high density polyethylene fibres, which had
been irradiated to a dose of 20 ~lrads, had the
following properties:
100% secant modulus at 150C 0.29 MPa
tensile strength at 150C2.18 MPa
elongation to break at 1~0C 780
gel content (reflux in xylene) 42.25~
recovery force 0.62 Mpa
recovery 87%
A sample of the sheet so formed was cut with
dimensions of 15 inches (6 cmJ in the warp direction
and 30 inches (12 cm) in the weft direction, and was
provided with a closure arrangement as shown in figure
5 by wrapping opposite edges parallel to the weft
direction around 3.5mm diameter nylon rods, pressing
the closure region into the desired shape and heating
to allow partial recovery of the fabric. Before the
closure arrangement was formed, a 0.4mm thick layer of
polyamide adhesive as described in U.S. patent Nos
4018733 or 4181775 was applied to the surface of the
0.6mm polyethylene lamina by a hot melt coating technique.
The wraparound article so produced had a 4.1
recovery ratio (i.e. 75%) in the wrap direction.
The article was tested by forming a branch-off in
which a 43mm polyethylene jacketed telecommunication
cable was divided into two lgmm diameter polyethylene
jacketed cables. A Raychem "XAGA" (registered trade
mark) aluminium liner having collapsible end crowns was
positioned over the branch off so that the central,
~2~3Z~
- 36 - MP0790
cylindrical portion had a diameter of 92mm. The
article was ttlen wrapped around the cables and liner
and recovered thereon by being heated with a propane
torchO The article had been sealed against leakage of
pressurising gas between the article and the cable
jacket in known manner and a clip as described in U.S.
patent No. ~298415 to Nolf was used to seal the crotch
region of the branch-off. The cables were pressurised
to an internal gauge pressure of 15 p.s.i. (1.05 kg
cm 2) and the branch off was subjected to a temperature
cycle test in which in each cycle, the temperature was
raised from ambient (23C) to ~50C over a period of
one hour, maintained at +60C for four hours, lowered
from 60 to -30C over two hours, maintained at -30C
for four hours and then raised to ambient (23C) over
one hour. No leakage was recorded after ten cycles.
EXAMPLE 4
Example 3 was repeated with the exception that the
fabric had a weft density of 18 fibres per inch ~7.1
fibres per cm) giving a recovery ratio of the composite
fabric of 3.7:1 (i.e. 73%).
EXAMPLE 5
Example 3 was repeated with the exception that the
weft yarn was changed from E.C.G. 75 glass fibre
to E.C.G. 150 glas fibre yarn, and the fabric density
was 90/18 (30.5/6.3 in cms) giving a 4:1 recovery ratio
ir. the warp direction.
~3~L8~:
37 - MP0790
EXAMPLE 6
Example 3 was repeated with the exception that.the
glass fibre was replaced by a multifilament yarn formed
from aromatic polyamide filaments sold by Du Pont under
the tradename "Kevlar". This product had substantially
the same properties as that of Example 3 but had a
substantially higher trouser tear value (measured
according to the British standard) of 150N.
COMPARATIVE EXAMPLE 1
A heat-shrinkable woven fabric using a standard
b-staged epoxy resin matrix polymer was produced as a
comparison. An epoxy resin was formed having the
formulation:
COMPONEN_ Parts by weight
Epoxy resin (Epoxy No. 475) sold 70
15 by Shell Chemicals under trade-
name EPON 1001
Epoxy grafted acrylic rubber 30
modifier (note 1)
Anchor 1699 (tradename)-Azelaic 9.8
20 dihydrazide
Imidazole (accelerator)
Note (1): produced by compounding an acrylic
elastomer (acid value 3000) sold by Du Pont under the
tradename "Vamac" with a bisphenol A epoxy resin sold
under the tradename "Epikote 100 l ll to give eleven epoxy
groups per acid group.
3~LBX2
- 38 - MP0790
The components were dissolved in methyl ethyl-
ketone to yield a solution of 2~% solids content.
The solution was applied several times to a 60/12
(23.6~4.7 in cms) twill 2up 2 down fabirc having 0O35
mm diameter unirradiated high density polyethylene warp
fibres and E.C.G. 150 glass yarn in the weft, so that
the thickness of the resulting composite fabric was
approximately 0.75 mm. The composite fabric was
then heated for one hour at 60C to b-stage the
epoxy resin.
When the article so formed is heated by means oE a
torch to recover it, the viscosity of the matrix poly-
mer drops almost immediately to a value of about 50
poise and then, within a very short time the viscosity
of the surface layer of the matrix increased to greater
than lo8 poise forming a skin on the matrix material
which blistered and prevented recovery of the fibres to
some extent. In addition, a significant number of the
polyethylene fibres snapped on recovery.
COMPARATIVE EXAMPLE 2
A fabric as described in comparative Example 1 was
irradiated with high energy electrons to a dose of
10 Mrads. When heated by means of a torch the matrix
material blistered and cracked and a large number of
bubbles were produced in the matrix material The
maximum recovery ratio recorded was about 2:1 in view of
the effect of the cured or partially cured matrix
material holding out the fibres against their recovery
forces.
