Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to shrinkable hollow
articles. Our French Patent Application No. 7,618,236
describes shrinkable hollow articles comprising an inner
member, preferably of an elastomeric material, which is held
in a radially extended condition by an outer restraining
means, the inner member and the restraining means being
secured together by means of a bond which can be broken to
allow the inner member to shrink radially. Preferably the
restraining means is capable of being peeled away from the
inner member; the peeling process can be assisted by applying
a solvent to the bond line. The restraining means may be
composed of a frangible material which can be broken by means
of a sharp blow, for example a rigid thermoplastic such as
polyvinyl chloride. Alternatively the restraining means can
have weakened portions such as score lines which enable it to
be peeled away from the inner member, as for example a
metallic tube which is spirally scored or serrated. These
articles are useful for covering substrates, especially
splices and terminations in electrical cables, e.g. mine
cables.
In the course of further development work, we
observed that the value of such an article would be greatly
enhanced if it could be modified so that it was sufficiently
flexible to permit its cross section to be deformed without
causing recovery of the inner member, while retaining the
ability to bring about recovery when desired. Thus the
expansion ratio required for the inner member, when the
article was used to cover a substrate having a cross~section
different from the cross-section of the article, would be
reduced, thus reducing the force required to maintain the
inner member in a deformed condition and the danger that the
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83
inner member would suffer from "tension set" (i.e. non-
recoverable radial deformation) on storage. The present invention
provides such a modified article.
In one aspect, the present invention provides a
flexible, shrinkable, hollow article which comprises
(1) a hollow inner member which is composed of an
elastomeric material and which is in a
radially extended condition; and
(2) a hollow outer restraining means
(a) whose inner surface is secured to the
outer surface of said inner member and
which maintains said inner member in said
radially extended condition, said inner
and outer surfaces being secured to each
other by a bond whose peel strength is
less than 50, preferably 4 to 30, lb. per
linear inch width (pli) at 21C (8.9,
preferably 0.7 to 5.4 kg per linear cm);
(b) whose outer surface forms the outer
surface of said article; and
(c) is composed of a material which
(i) has a 2% secant modulus at 21C of
4,000 to 120,000 psi (280 to 8,400
kg/cm );
(ii) has an ultimate elongation at 21C
of at least 20% at a separation
speed of 200% per minute and of at
most 150~ at a separation speed of
2000% per minute; and
--3--
33
(iii) has a notch sensitivity such that,
if the restraining means has, in the
outer surface thereof, a score line
whose depth is 5 to 90% of the
S thickness of the restraining means,
then by distorting the article so as
to exert a bending moment about the
axis of such a score line, the depth
of the score line can be
substantially increased.
In the articles of the invention, the outer surface
of the restraining means will generally be provided with at
least one score line whose depth is at least 5% of the
thickness of the restraining means. The term "score line" is
used herein to denote any indentation in the form of a line
(including a series of short indentations, eg. hales, which
together form a line). As explained in more detail below,
the depth of the score line or lines will generally be 5 to
90% of the depth of the restraining means, but the invention
includes articles in which at least part of the score line or
lines passes completely through the thickness of the
restraining means. The function of the score line or lines
is to provide (generally after distortion of the article to
increase the depth of the line) at least one section of the
restraining means which can be peeled away from the inner
member by manual ~or equivalent) force, if desired with the
aid of a solvent applied to the bond line. The term
"solvent" is used herein to denote any fluid which will
substantially weaken the forces securing the inner member to
the restraining means. Since the score line or lines need
not be made until removal of the restraining means is
desired, the invention includes articles which have no score
lines thereon but which can be provided with score lines which
will permit removal of the restraining means.
The invention also provides a method of covering a
substrate which comprises
(1) distorting an article as defined above whose
outer surface is provided with at least one
score line whose depth is 5 to 90~ of the
thickness of the restraining means, and thus
causing the depth of at least one such score
line to increase substantially;
(2) placing the article around a substrate to be
covered; and
(3) peeling at least part of the restraining means
15 away from the inner member to cause recovery
- of the inner member around the substrate, said
peeling being initiated by pulling away from
said inner member a section of said
restraining means adjacent a said score line
: 20 whose depth has been increased in step (1).
Step (1) of this process is generally, but not necessarily,
carried out before step (2). The initiation of peeling by
pulling away a section of the restraining means is usually
- carried out after step (2), immediately before the inner
member is caused to recover. However, it can be carried out
before step (2) provided that premature recovery of the inner
member is not thereby caused to occur.
The invention also provides a method of making an
article as defined above which comprises
(1) radially extending a hollow member composed of
an elastomeric material;
(2) bonding the outer surface of said radially
extended member to the inner surface of a
restraining means to provide a bond between
said inner and outer surfaces whose peel
strength is less than 50 pli (8.9 kg per
linear cm at 21C; and
(3) scoring the outer surface of said restraining
means to provide thereon at least one score
line whose depth is at least 5% of the
thickness of the restraining means;
said restraining means being composed of a material which
(i) has a 2% secant modulus, ultimate elongation
and notch sensitivity as defined above.
In describing the invention, reference is made to a
number of physical properties. These properties are measured
as set out below.
,
Ultimate Elongation
is measured, at the indicated temperature, by the
method of ASTM D412-75 using dumb bell specimens (Die D) and
1 inch (2.54 cm) bench marks, the separation speed being 2
inch (5.1 cm) per minute for measurement at a separation
speed of 200~ per minute and 20 inch (51 cm) per minute for
measurement at a separation speed of 2,000~ per minute.
2% Secant Modulus
is measured, at the indicated temperature, by the
method of ASTM D638-72 using a 0.5 inch (1.25 cm) wide
straight specimen, a cross-head speed of 0.5 inch (1.25 cm)
-6-
per minute, a jaw separation of 5 inch (12.7 cm) and a chart
speed of 20 inch (51 cm) per minute.
% Torn Depth
is measured at 21~C by the notch sensitivity test
5 5 described below. A rectangular strip of the material,
preferably 1 inch (2.54 cm) wide and 0.075 (+0.005) inch
[0.19 cm (+ 0.013 cm)] thick, is used as a test specimen. A
cut whose depth is 0.1 to 0.2 times the thickness of the
specimen te.g. 0.008 inch (0.02 cm) for the preferred
specimen) is made with a razor blade across the strip at ! '
right angles to ~he axis of the strip. As illustrated in
Figure 6, the strip is then placed on a block having a right-
. .
angled edge, with the cut on the upper surface directly above
the edge of the block, and bent through an angle of 90 over
the edge of the block. The cut is propagated, to a greater
or lesser extent, by cracking of the material along the
bending line. The strip is then divided into two parts by
severing with a razor blade any remaining material along the
bending line. Under suitable magnification, the areas of the
~ exposed edge which have been cut by the razor blade can be
clearly distinguished from the area which has been torn by
bending, and the average depth of the torn area can be
~ measured. The ~ Torn Depth is equal to
:
100 x Average depth of torn area
- Thickness o~ speclmen - depth o~ original cut
In order to make the measurements described above, it will
usually be preferable to prepare test specimens from the
material in bulk or in some convenient shaped form. If it is
desired to make the measurements on material which is already
in the form of a restraining means, it may be possible, for
at least some of the measurements, to use test specimens cut
from the article, after removal of the inner member and
adhesive from the specimen. In other cases, the material
should be identified and specimens prepared from the material
in bulk or in some convenient shaped form.
Peel Strength
of the bond between the inner member and the
restraining means is measured at the indicated ~emperature by
the following procedure.
A rectangular specimen free from score lines is cut from the
article. With the aid of solvent applied to one end of the
specimen, the inner member is separated from the restraining
` 15 means over a limited distance. After evaporation of the
solvent, the separated end of the inner member is placed in
one jaw of an Instron Tester and the separated end of the
restraining means is placed in the other jaw. The peel
strength is determined at a jaw separation speed of 2 inches
(5.1 cm) per minute, taking the average of the highest and
lowest values. For peel strengths at 49C., the specimen is
; stored at 49C and then placed in the 49 hot box of an
Instron, and the whole apparatus is allowed to come to
equilibrium for three minutes before the peel strength is
determined.
--8--
83
Ideally the specimens used should be 1 inch (2.54
cm) wide. If suitable specimens cannot be cut from the
article, or for the purpose of determining whether
satisfactory articles can be prepared from a particular
combination of inner member, adhesive and restraining means,
it is often possible to obtain substantially equivalent peel
strengths from a specimen prepared by bonding together under
heat and pressure a sandwich of
(a) an unstretched sheet of the elastomeric
material of the inner member;
(b) a layer of the hot melt adhesive; and
(c) a sheet of the material of the restraining
means.
The articles of the present invention are generally
of tubular configuration. However, the invention includes
end caps and other more complex hollow configurations having
one or more open ends through which a substrate can be
inserted. It is also to be understood that the invention
includes articles which include one or more portions which do
not comprise a said inner member and restraining means, for
example an article having a rigid tubular or T-shaped or Y-
shaped central portion and two or more end portions, each of
which comprises a said inner member and restraining means.
The articles of the invention are preferably of
circular cross-section, these being in general the easiest to
manufacture~ However, where the substrate to be covered is
3;~t~33
one having a non-round cross-section, eg. an oval mine cable,
then the use of a shrinkable article having a corresponding
cross-section has the advantage that the re~uired expansion
of the inner member is reduced. Shrinkable articles of non-
round cross-section can be made by preparing the inner member
and the restraining means in the desired cross-section, and
expanding the inner member uniformly against the restraining
means with the cross-sections aligned.
The end result achieved by the present invention is
a substrate covered by the inner member, after it has
elastically recovered towards the substrate following removal
of at least part of the restraining means. The elastomeric
material of the inner member should therefore be selected
with the end use in mind, for example as electrical
insulating. In articles for insulating splices in mine
cables, we have obtained excellent results using formulations
based on commercially available polychloroprenes
("Neoprene"). Other suitable elastomeric materials are
disclosed in U.S. Patent No. 4,070,746. Materials having low
tension set are preferred. Part or all of the inner surface
of the inner member may be coated with a material which will
improve the sealing and/or adhesion of the member to the
substrate, for example a mastic or a pressure-sensitive
adhesive. The thickness of the inner member, when fully
recovered, is usually in the range 0.02 to 0.25 inch (0.51 to
0.6 cm), preferably 0.05 to 0.15 inch (0.13 to 0.4 cm), but
greater thicknesses, e.g. up to 0.5 inch (1.3 cm), may be
useful in certain circumstances. For covering electrical
cables, the internal diameter of the inner member will
--10--
~LP~i~83
usually be from 0.1 to 3 inch (0.25 to 7.6 cm), preferably
0.4 to 2 inch (1 to 5.1 cm), when fully recovered, and from
0.125 to 4 inch (0.3 to 10 cm), preferably 0.75 to 3 inch
(1.9 to 7.6 cm), in the extended state. For covering other
substrates, such as pipes and ducts these or larger diameters
may be used. The extension ratio of the inner member (i.e.
the ratio of the extended diameter to the fully recovered
diameter) will usually be 1.3:1 to 3:1, preferably 1.7:1 to
2.3:1. An increase in the thickness or extension of the
inner member or the modulus of the elastomeric material will
increase the retractive force of the inner member.
The inner member will normally be bonded to the
restraining means through a layer of adhesive, preferably a
hot-melt adhesive. Suitable adhesives are disclosed in U.S.
Patent No. 4,070,746. The peel strength of the bond at 21C
should be less than 50 pli (8.9 kg per cm). Since on the one
hand the inner member should not separate from the
restraining means under normal storage conditions and on the
other hand it must be possible to initiate peeling by pulling
a section of the restraining means away from the inner member
by manual or equivalent force, it is preferred that the peel
strength of the bond at 21C should be 4 to 30 pli (0.7 to
5.4 kg per cm), particularly 5 to 25 pli (0.9 to 2.7 kg per
cm), especially 7 to 15 pli (1.25 to 2.7 kg per cm). In
order to avoid the need for storage under controlled
temperature conditions, it is preferred that the peel
strength at 49C should be at least 2 pli (0.36 kg per cm),
especially at least 4 pli (0.7 kg per cm).
The restraining means must be sufficiently stiff
that it will not undergo buckling which will interfere with
use of the article, and it is this which gives rise to the
requirement that the material of the restraining means has a
2~ secant modulus at 21C of at least 4,000 psi (280 kg/cm ),
preferably at least 13,000 psi (910 kg/cm ). On the other
hand, the article must be sufficiently flexible that its
cross-section can be deformed without undue force tand
preferably by hand) and it must be possible for peeling to be
initiated by pulling a section of the restraining means from
the inner member. These constraints give rise to the
requirement that the material have a 2% secant modulus at
21C of a~ most 120,000 psi (8,400 kg/cm ). Preferably the
material has a 2% secant modulus at 21C of 15,000 to 100,000
psi (1,050 to 7,000 kg/cm2), especially 15,000 to 40,000 psi
(1,050 to 2,800 kg/cm ). In order to avoid the need for
storage under controlled conditions, it is preferred that the
material have a 2% secant modulus at 49C of at least 4,000
psi ~280 kg/cm ). The thicker the restraining means and the
lower the retractive force of the inner member, the lower the
secant modulus of the material which will give satisfactory
results.
The requirements for ultimate elongation at 21C
are also related to the peelability of the restraining means,
since it is necessary that the section which is pulled away
to initiate peeling should bend without cracking through a
sufficiently large angle (generally 90 to 180) to apply the
-12-
pulling force, but should not be stretched excessively by the
pulling force. The ultimate elongation of the material at
21C and at a separation speed of 200~ per minute is
preferably at least 25%, particularly at least 35~,
especially at least 50%, and preferably does not exceed 120%,
especially 100%.
The last requirement for the material of the
restraining means is that it should be sufficiently notch
sensitive that, by distorting the article so as to exert a
bending moment about the axis of a score line having a depth
of 5 to 90% of the thickness of the restraining means, the
depth of the score line can be substantially increased,
preferably so that the depth of the score line becomes at
least 50%, preferably at least 80%, especially at least 90~,
of the thickness of the restraining means. When the
restraining means has a lip which extends beyond the inner
member, as discussed in more detail below, the score line can
extend right through the restraining means in the lip area.
However, when (as is usually the case) at least part of the
score line passes through an overlapping area of the
restraining means, ie. an area which overlies the inner
member, it is greatly preferred that the depth of the score
line, at least in the overlapping area, should not exceed 90
of the thickness of the restraining means, in view of the
danger of damaging the inner member when making the score
line and from the point of view of storage stability.
Both manufacturing tolerances and storage requirements make
it desirable that the score line should have a depth which
is less than 75%, preferably less than 50%, especially less
-13-
than 25~, of the thickness of the restraining means, and that
the thickness of the restraining means remaining underneath
the score line should be at least 0.010 inch (0.025 cm), particularly
at least 0.020 inch (0.05 cm), especially at least 0.040 inch
(0.1 cm)~ The "% Torn Depth" referred to above is a measure
of the notch sensitivity of the material, and is preferably
at least 40~, especially at least 50%.
We have found that when the 2~ secant modulus at
21C is less than 40,000 psi (2,800 kg/cm2), eg. 15,000 to
40,000 psi (1,050 to 2,800 kg/cm2), the values of the 2% secant
modulus at 21C (S), the ultimate elongation at 21C (E), the
~ torn depth (T) and the peel strength at 21C (P) are such
that the term
T - 0.002S + 0.054E + 0.54P
5 (where S is in pci and P is in pli) [or the term
T - 0.00014S + 0.054E + 0.096P (where S is in
kg/cm2 and P is in kg per cm)]
is preferably 10 to 60, especially 15 to 35.
The material for the restraining means should be
0 selected with a view to the above requirements and
preferences, including of course the requirement that the
material must bond adequately to the adhesive. Preferably
the material comprises an organic polymer. Synthetic organic
polymers are preferred, but materials based on natural or
modified natural polymers, e.g. cellulosic polymers and
polymeric mixtures derived from unsaturated oils, can also be
used. Suitable materials may comprise a mixture of two or
more polymers, which differ substantially in modulus,
elongation or bondability to the adhesive, or two or all of
these. For example the material may comprise a mixture of
-14-
33
two polymers, one polymer having relatively high modulus
[e.g. greater than 5,000 psi (350 kg/cm2), preferably greater
than 7,000 psi ~490 kg/cm2)~ and/or a relatively low ¦
elongation (e.g. less than 100%, preferably less than 50%),
and the other polymer having a relatively low modulus, e.g.
less than 5,000 psi (350 kg/cm2), and/or a relatively high
elongation ~e.g. greater than 100%, preferably greater than
150%), the ratio by weight of the first polymer to the second
polymer generally being from 1.5:1 to 4:1, preferably 2:1 to
3:1. When the adhesive is a polar material, as it usually
will be when a polar rubber such as polychloroprene is used
for the inner member, one or both of the polymers will
usually be a polar polymer. When the adhesive is non-polar,
- the material of the restraining means will normally be non-
polar also or at least comprise a major proportion (by weight
based on the polymeric materials) of a non-polar polymer.
Suitable mixtures of polymers include mixtures of block
copolymers containing polyester blocks and polyether blocks,
for example a polytetramethylene ether/polytetramethylene
terephthalate block copolymer (e.g. the "Hytrel" and "Dyvax"
polymers sold by du Pont), and a low modulus copolymer of at
least one olefin, especially ethylene, and at least one polar
comonomer, especially a vinyl ester of an alkyl carboxylic
acid, e~g. vinyl acetate, or an alkyl ester of acrylic or
methacrylic acid, e.g. ethyl acrylate. Another suitable
mixture of polymers is a blend of polyvinylchloride and a
rubbery chlorinated polyethylene. The material may also
comprise at least one component which will increase the notch
sensitivity of the material. For example the composition may
comprise, an appropriate proportion, e.g. 25 to 75%,
preferably 50 to 65~, by weight of a particulate filler,
~'
-15-
usually of the non-reinforcing type, e.g. an inorganic filler
such as calcium carbonate, amorphous silica or a silicate
such as clay. Generally the greater the amount of such
fillers, the lower the strength of bonds formed between the
material and hot melt adhesives. Alternatively or
additionally the composition may comprise a low molecular
component of low compatibility, such as a wax or a
plasticiser, which reduces the peel strength of bonds formed
between the material and hot melt adhesives. The material
can, and often will, contain other ingredients such as
antioxidants, flame retardants, pigments and extrusion aids.
Preferably the material of the restraining means is
thermoplastic, so that it can be melt-shaped to a desired
configuration, especially melt-extruded as a tube which is
later cut to the desired length. The material can be cross-
linked in order to give it a desired combination of
properties.
Although reference is made herein to the fact that
the inner member is radially extended, it should be noted
that the method of manufacture will generally cause the inner
member to have axial as well as radial retraction forces.
This fact is of practical importance since it means that the
recovery forces of the inner member tend to peel it away from
the restraining member at the ends. This increases the bond
strength which is needed to ensure that the article does not
recover prematurely, and frequently makes it desirable to
insert end plugs into the article for storage purposes, in
order to take the end sections of the inner member out of
peel, especially when the peel strength is less than 4
pli (0.7 kg/cm).
-16-
The configuration of the score lines on the article
can vary widely. In many cases it will be desirable for the
score line or lines to extend to at least one end of the
article, so that peeling can commence at the end of the
article. Especially in this case, the restraining means is
preferably longer than the inner member and is bonded to the
inner member so that it has an overlapping lip at one end,
and preferably at both ends, of the article. The presence of
such a lip is desirable because it provides an area of the
restraining means which can readily be grasped by the
operator, either with his hand or with a suitable tool, to
commence peeling of the restraining means from the inner
member. The lip is preferably at least 0.25 inch (0.6 cm)
long, e.g. 0.5 to 1.0 inch (1.3 to 2.5 cm) long. It is not,
however, necessary for the score line(s) to extend to an end
of the restraining means, provided that, after they have been
cracked open, they provide an area which can be pulled away
from the restraining means. Especially in this case, the
area at which peeling is commenced preferably comprises a
protruberance which can be grasped by the operator to
initiate peeling.
In one embodiment, a plurality of straight,
parallel score lines run from end to end of the article, the
distance between the score lines being for example 0.2 to 1
25 inch (0.5 to 2.5 cm), preferably 0.4 to 0.75 inch (1 to 1.9
cm). Using such score lines, peeling of the restraining
means may be possible by pulling off the restraining means in
strips without the use of any solvent at all, or only
sufficient solvent to loosen the bond in the region where
peeling begins. In a functionally similar embodiment, one or
more score lines run spirally around the article. In a
further embodiment the score line or lines are confined to a
limited area, which may be at one or both ends of the article
or at an intermediate point thereof, and the function of the
score lines is then not to permit the whole of the
restraining means to be pulled away from the inner member,
but rather to allow part of the restraining means to be
pulled away and thus provide an area to which solvent can be
applied and from which the solvent can propagate along the
bond line, so that peeling is mainly effected by elastic
recovery forces pulling the inner member away from the
weakened bond line~ We have found that recovery of the inner
member can be effected surprisingly rapidly in this way,
especially when the article is placed so that the solvent can
run downwards through the bond line and the article is
kneaded during this process to promote spreading out of the
solvent. When the inner member has recovered, it is
generally desirable to remove the restraining means, taking
care not to damage the inner member. Good use can be made of
the notch-sensitive character of the restraining means, since
it is necessary only to score roughly along the outer surface
of the restraining means, which can then be cracked open and
removed.
The score lines can be made by cutting into the
surface of the restraining means with a sharp blade, before
or after the inner member is bonded to the restraining means,
or they can be formed at the time the restraining means is
manufactured, e.g. by extrusion or molding.
-18-
~S~ 3
The score lines can be cracked open by any
distortion of the article which will exer~ a bending moment
about the axis of the score line, for example by crushing the
article. Although it is preferred that all the score ]ines
should be cracked open, this is not essential providing that
the extent of the cracking is sufficient to allow
satisfactory peeling.
The articles of the invention and their use are
illustrated in Figures 1 to 5, and 7 to 9 of the accompanying
drawings.
Figure 1 illustrates an article of the invention
which comprises inner member 1 which is secured to
restraining means 2 by an adhesive layer 3 and is coated
internally with mastic layer 4. Score lines 21 run from end
lS to end of restraining means 2 and have a depth about 20~ of
the thickness of restraining means 2. The restraining means
2 is longer than the inner member 1, providing a lip 22 at
the left hand end. Preferably there is a similar lip at the
other end, but the inner member 1 can be flush with the
restraining means 2 at the other end.
Figure 2 illustrates an end plug 7 having a
truncated cone portion 8 whose diameter and angle of taper
are such that for storage purposes a plug as illustrated can
be placed in each end of the recoverable article to take the
inner member out of peel.
Figure 3 illustrates the article of Figure 1 which
has been distorted so that score lines 21 have propagated
through the restraining means 2, becoming cracks 21A, and
--19--
which has then been placed about a substrate 5 of oval cross-
section. Solvent 61 is sprayed from squeeze bottle 6 onto
the adhesive layer 3 in the region of lip 22. Recovery of
the inner member 1 is then effected by manually peeling off
successive strips of the restraining means 2 between cracks
21A, if desired or necessary with further application of
solvent to the adhesive in the region of peeling. Figures 4A
to 4E are cross-sections through an intermediate point of the
assembly as the strips are removed. For ease of
illustration, adhesive layer 3 and mastic layer 4 are not
shown in Figures 4A to 4E.
Figure 5 illustrates another article of the
invention which is similar to that shown in Figure 1 but
which comprises a single score line which runs spirally
around the restraining means.
Figure 7 illustrates another article of the
invention which is similar to that shown in Figure 1 but
which comprises a pair of short score lines which define a
pull tab which is used to create an area which acts as a
reservoir for solvent which is applied to the bond line
between the inner member and the restraining means, as shown
in Figure 8, and which percolates between the inner member
and the restraining means.
Figure 9 illustrates another article of the
invention which comprises a pair of circumferential score
lines 21 at the mid point of the article and a V-shaped
-20-
score line 21 between the score lines 21. Pull tab 23 is moulded or bonded
to restraining means 2 at the open end of V-shaped score line 21' between
the score lines 21. After the score lines 21 and 21' have been cracked
open, the pull tab 23 is pulled outwards and around the article, thus
peeling off the strip of the restraining means defined by lines 21J if
desired with the aid of a solvent. Solvent is then applied to the exposed
bond line at the edges of the exposed portion of the inner member, and
percolates between the inner member and the restraining means.
The present invention further provides an improved method of
making a flexible, shrinkable hollow article according to the invention
comprising (1) a hollow inner member which is composed of an elastomeric
material and which is elastically radially extended from its natural
dimensions and (2) a hollow outer restraining means whose inner surface is
secured to the outer surface of said inner member through a layer of a hot-
melt adhesive and which thus maintains said member in said radially extended
condition, which method comprises
(1) preparing an assembly comprising a hollow restraining means
and, within said restraining means but not contacting said restraining means,
a heated, hollow inner member composed of an elastomeric material and having
a coating of a hot~melt adhesive on the outer surface thereof, said hot-melt
adhesive being at a temperature above its bonding temperature;
(2) subjecting said hollow member to radial expansion
forces so that said hot-melt adhesive contacts the
inner surface of said restraining means and under
conditions such that the pressure between the
hollow member and the restraining means is from P
to P2, where Pl is the pressure which can be
generated by increasing the radius of the
restraining means by 5% by an expansion of the
hollow member and P2 is the maximum pressure which
can be generated by increasing the radius of the
restraining means by an expansion of the hollow
member within the elastic limit of the exterior of
the restraining means;
(3) cooling said assembly to reduce said hot-melt
adhesive below its bonding temperature; and
(4) removing said expansion forces.
In a preferred embodiment of this process, the
restraining means is freely expanded (ie. without any
external confinement, eg. in air) by an amount between 5
and an amount such that the exterior of the restraining
means is not stretched beyond its elastic limit.
However, an equivalent pressure can be exerted on the
bond line between the restraining means and the inner
member by any means. For example the restraining means
can be surrounded by a shell against which it is pressed
by the expansion forces.
~ he restraining means is preferably composed of
an organic polymeric material such that the restraining
means is capable of a limited degree of elastic radial
-22
expansion, for example at least 5% at 21 ~. On the other
hand, if it is too elastic, it will not serve its function
of maintaining the inner sleeve in a radially extended
condition. Preferably the material has an elastic limit at
21C between 5 and 60~, particularly between 15 and 50~,
especially between 15 and 40%. It is important that the
elastic limit of the exterior of the restraining means
should not be exceeded in the process. Therefore, when the
restraining means is expanded in the process, as is
preferred, the expansion thereof is preferably not more than
80% of the expansion at the elastic limit at 21C, and it is
preferably 10 to 75% of the expansion at the elastic limit
at 21 C. For preferred restraints the expansion ratio will
be 1.05 to 1.4, particularly 1.05 to 1.20.
It will be noted that reference is made above to
the elastic limit of the exterior of the restraining means.
Especially when the restraining means is composed of a
thermoplastic material, as is preferred, the elastic limit
of the material decreases rapidly with increasing
temperature. It is, of course, inevitable that the interior
of the restraining means will be heated by heat transfer
from the inner member and the adhesive, and as a result the
interior of the restraining means may well undergo plastic
deformation. In order to prevent plastic deformation of the
exterior of the restraining means, it is possible to ta~e
positive steps to cool the outside of the restraining means
throughout the expansion step, but satisfactory temperature
control can usually be achieved by expanding the assembly in
air and quenching the assembly, eg. by putting it into a
bath of water or other liquid, as soon as expansion is
complete.
-23-
It is desirable that the inner s~rface of the
restraining member should also carry a layer of the hot melt
adhesive, since this improves bonding between the inner
member and the restraining means.
The expansion forces which are used to expand the
inner member can be generated in any convenient way, for example
by means of an expansible mandrel or hydraulically.
The invention is further illustrated by the
following Examples, in which parts, ratios and percentages
are by weight.
Example 1
Part A
The ingredients shown in Table A were blended
together in a Banbury mixer.
TAB~e A
Ingredient Parts
Polychloroprene (Neoprene TRT) 100
Antioxidant (Agerite Stalite S) 2
Magnesium oxide (Maglite D) 2
20 Carbon black (Vulcan 3) 5
Alumina trihydrate (Hydral 705) 10
Silica (HiSil 233) 15
Antimony trioxide 15
Stearic Acid 0.5
25 Plasticiser (Flexol TOF)
ZnO (Kadox 15) 5
Curing Agent (Thiate E) 0.75
Curing Agent (Epon 828)
-24-
The blend was molded at about 175C for about 10 minutes into
an elastomeric tube having a thickness of about 0.125 inch,
an internal diameter of about 0.75 inch (1.9 cm~ and a length
of about 17 inch (43 cm) (Tube A).
Part B
The ingredients shown in Table B were blended
together in a Banbury mixer
TABLE B
Ingredient Parts
10 Block copolymer of polytetramethylene
ether and polytetramethylene
terephthalate (Hytrel 4056) 70
Ethylene/vinyl acetate (18%) copolymer 30
(Alathon 3170)
lS Antioxidant (Irganox 1010) 0.1
Chalk filler (Vicron 15-15) 125
Pigment (Wilson 50-OR-18) 2.5
The blend was extruded into a tube having a thickness of
about 0.085 inch + 0.005 inch (0.22 + 0.01 cm), an internal
20 diameter of about 1.5 inch + .020 inch (3.8 + 0.05 cm), and
cut into lengths of about 18 inch (45.7 cm) (Tube B)
Part C:
The outer surface of Tube A was coated with a 1%
: solution of a 60/40 mixture of Hytrel 4056 and Dyvax 772 in
methylene chloride. The inner surface of Tube B was abraded
by passing the tube over a rotary abrasion wheel and then
coated with a 10~ solution of a 60/40 mixture of Hytrel 4056
and Dyvax 772 in methylene chloride. (Dyvax 772 is a block
copolymer which is substantially the same as Hytrel 4056 but
-25-
y~
of lower melting point). After evaporation of all the
methylene chloride, Tube A was heated to about 165C and
immediately placed over an expansible mandrel. Without
delay, Tube B, which was not preheated, was placed
symmetrically over Tube A. The mandrel was then expanded
until Tube A had first contacted Tube B and then expanded
Tube B by 5-10%. The whole assembly was then rapidly placed
into water at about 20C, where it was left for about 4
minutes. After the assembly had been removed from the water,
the mandrel was contracted and withdrawn. Tube A and Tube B
contracted until Tube B had returned to about its original
configuration.
Part D
Longitudinal parallel score lines about 0.00~ inch
deep and about 1/2 inch apart were then made with a razor
blade on the outer surface of Tube B, the score lines running
from end to end, as shown in Figure 1.
Part E
The article thus made was stored until it was
required, end plugs being inserted to ensure that Tube A did
not recover prematurely. When the time came to use the
article, the end plugs were removed, and the article crushed,
e.g. between the operator's hands or between his foot and the
floor, to open up the score lines. The article was then
placed over one of two mine cables which were to be spliced.
The cables were spliced and the article positioned around the
splice. A suitable solvent, i~e. a fluid which will
substantially weaken the adhesive bond and which may be, but
is not necessarily, a solvent for the adhesive, e.g.
l,l,l-trichloroethane, was applied to the bond line at one
end of the article. Tube B was grasped by the operator in
the region to which solvent had been applied and was pulled
away from the splice. Tube B tore along the adjacent score
lines, so that a longitudinal strip of Tube B could be peeled
away; further solvent was applied to help in the peeling
process. Successive strips of Tube B were removed in the
S same way until Tube A had completely recovered and Tube B had
been completely removed.
Example 2
Parts A, B and C
.
The procedure of Parts A, B and C of Example 1 was
followed to prepare an article comprising expanded Tube A
secured to Tube B.
Part D
Two parallel, longitudinal score lines, about 0.5
inch apart and each about l inch long, were made with a razor
blade at one end of the article, as shown in Figure 7. The
score lines were about 0.050 inch deep.
Part E
The article thus made was stored until it was
required, end plugs being inserted to ensure that Tube A did
not recover. ~hen the time came to use the article, the end
plugs were removed, and the end of the article bearing the
score lines was crushed to open up the score lines. The
article was then placed over one of two mine cables which
were to be spliced. The cables were spliced and the article
positioned around the splice. The spliced cables and the
article were then placed so that the article was at an angle
of 15-30 to the horizontal, with the score lines at the top.
A solvent was applied to the bond line in the area of the
score lines and the region of Tube B defined by the score
lines was grasped by the operator and pulled away from the
splice, thus creating a pocket into which further solvent was
5 placed. The solvent penetrated between Tube A and Tube B,
and this process was accelerated by the operator kneading the
article between his hands. After about 1.5 to 2.5 minutes,
the penetration of the solvent had weakened the bond between
Tubes A and B sufficiently to cause separation of Tube A from
10 Tube B so that it recovered around the splice. Tube B was
then scored from end to end with a razor blade or knife; the
score line was opened up by crushing the tube along the score
line; and the tube ripped open with a knife or by hand.
The articles prepared in Steps A to D of Examples 1
15 and 2 had the following properties.
Tensile stress at 100% 2
elongation of Tube A 175-250 psi (12.2-17.5 kg/cm )
Peel Strength of Bond between
Tubes A and B 7-12 pli (1.25-2.14 kg/cm)
20 2% Secant Modulus of Tube B
at 21C 20,000 psi (1,400 kg/cm2)
Ultimate Elongation of Tube B
at 21C 79-85%
% Torn Depth of Tube B 50-60%
Example 3
:
The procedure of Example 1 was followed except that
Tube A was made from the ingredients set out in Table C
below.
-28-
15 3
TABLE D
Ingredient Parts
Polychloroprene (Neoprene GW) 100
Magnesium Oxide (Maglite D) 1.5
Silica (Hi Sil 233~ 35
Silane A189 0-5
`Stearic acid 0.6
Antioxidant (Octamine) 1.3
Antioxidant (Agerite DPPD) 0.7
10 Carbon Black (Thermax) 5
Polyethylene oxide glycol (Carbowax 4000) 3
Tricresyl phosphate (plasticiser) 12.5
ZnO (Kadox 15) 5
-29~
