Adhesive composition

An adhesive composition particularly useful for bonding a heat-recoverable polymeric sleeve around a cable splice to form a cable splice case comprises a polyamide and a copolymer of ethylene and an ester of an ethylenically unsaturated carboxylic acid, said copolymer having a melt flow index of at least 40 as measured according to ASTM D12380-70; the amount of copolymer being at least 38% based on the weight of the polyamide.

The present invention relates to an adhesive composition, particularly to a 
hot-melt adhesive composition containing polyamide and being suitable for 
use in the cable accessories or pipe line industry, particularly for 
adhesion to non-flame-brushed polyethylene and/or lead. 
Environmental protection frequently has to be provided around substrates 
such as cables to protect them from contaminants such as moisture. An 
excellent way of providing such protection is to surround the substrate 
with an adhesive composition, conveniently applied as a coating on a 
dimensionally-recoverable, preferably heat-shrinkable sleeve. Such a 
sleeve may be positioned around the substrate and heated causing the 
adhesive composition to become molten or softened and causing the sleeve 
to shrink, driving the adhesive into bonding engagement with the 
substrate. The sleeve itself may of course provide environmental 
protection, and the quantity of adhesive required may be reduced by 
coating the sleeve at only its edges to provide a bond to the substrate. 
A specific instance where environmental protection is required is around a 
cable splice, particularly in a multicore telecommunications cable, where 
missing cable sheath (removed in order to form the splice) has to be made 
good. This may be done by installing a liner around the splice, the liner 
preferably being shaped to provide a smooth transition between the bulky 
splice and the smaller diameter cable or cables that enter and leave it. 
The liner is then surrounded by a heat-recoverable sleeve that extends 
past each end of the liner down onto contact intact cable jacket. The 
sleeve is internally coated with a hot-melt adhesive composition and, when 
heated, it shrinks down and becomes bonded to each cable jacket and to the 
liner between them. In this way leak paths from the outside environment 
into the now-formed splice case are avoided, and the conductors of the 
cable protected from moisture etc. 
Such splice cases may be expected to provide an environmental barrier for 
the life-time of the cable, say at least twenty-five years. The cable, and 
splice case, may be subjected to temperature variations ranging from say 
-40.degree. C. in winter to say '70.degree. C. in the case of a cable 
exposed to direct sunlight, and the cable may be internally pressurized. 
As will be appreciated, these requirements of life-time, temperature and 
pressure put severe demands on the performance of the adhesive. The 
problem is made more difficult because, for practical purposes, a given 
product may have to be suitable for many different environments, for 
example around buried cables in cold countries, and aerial cables in 
hot-countries. 
These performances requirements are themselves difficult to achieve at an 
acceptable price, but the difficulty can be seen to be particularly acute 
when one considers installation conditions. Installation is at present 
carried out by heating the sleeve and consequently the adhesive with an 
open-flame torch, although electrical heating may be used. It is clearly 
desirable that the amount of heat required to soften the adhesive be kept 
to a minimum. The weather may be cold, there may be little room in a man 
hole for vigorous heating, an electrical heater may have limited power, 
and the cable or the sleeve may be damaged by high temperatures etc. Thus, 
there is a maximum acceptable installation temperature. Also, as noted 
above there is a wide temperature range over which the adhesive must 
retain its adhesive power. Unfortunately, the maximum allowable 
installation temperature is not very much higher than the minimum 
acceptable upper limit to the range of service temperatures. We have found 
therefore that our adhesive should have a sharp melt transition. 
In addition to a sharp melt transition, the adhesive should have a high 
peel strength to polyethylene, preferably both flame-brushed and 
non-flame-brushed, and to lead, it should have good low temperature impact 
strength, and low temperature flexibility, and it should have low 
viscosity at the installation temperature say at 160.degree. C. 
Attempts have been made to formulate adhesive compositions that combine, 
for example, high impact strength and high peel strength over a wide 
temperature range. The following adhesive compositions based on polyamides 
may be noted. 
U.S. Pat. No. 4,018,733 (Lopez, Glover and Lyons) discloses a hot-melt 
adhesive composition comprising a compatible mixture of: (a) an acidic 
polymer of ethylene having an acid number ranging from about 3 to about 80 
selected from the group consisting of a terpolymer of ethylene, and 
ethylenically unsaturated mono- or di-carboxylic acid and a vinyl ester of 
C.sub.1 to C.sub.6 aliphatic carboxylic acid and a copolymer of ethylene 
and a C.sub.2 to C.sub.20 aliphatic ester of a monoethylenically mono- or 
di-carboxylic acid wherein a portion of the carboxlic acid moieties of the 
said mono- or di-carboxylic acid component are not esterified, and (b) a 
polyamide having an amine number ranging from about 70 to about 400 with a 
tackifying agent wherein said tackifying agent is present in an amount 
ranging from about 3 to about 20 parts by weight per 100 parts of (a) and 
(b) together, components (a) and (b) being present in a relative 
proportion by weight ranging from about 40:60 to 60:40. 
EP 0040926 (Raychem) discloses a hot-melt adhesive composition comprising a 
polyamide based in one or more dimeric fatty acids and an ethylene/acrylic 
acid/butyl acrylate terpolymer containing free carboxylic acid groups. The 
acid terpolymer is preferably present at an amount of less than 20% by 
weight based on the weight of the polyamide. 
GB 1563030 (Allied Chemical Corporation) discloses a hot-melt adhesive 
composition comprising a compatible admixture of: 
(a) 15 to 99 weight percent of a polyamide adhesive based component; and 
correspondingly 
(b) 85 to 1 weight percent of a normally solid, homogeneous component of 
ethylene and an unsaturated carboxylic acid having an acid number of at 
least 70 and a number average molecular weight between 500 and 5000, said 
copolymer containing at least a major proportion of ethylene by weight, 
said percentages being by weight of (a) plus (b). 
We have now formulated an adhesive composition that can provide excellent 
peel strength to polyethylene, can have excellent low temperature impact 
strength and flexibility, and can be produced at reasonable cost. The new 
adhesive also can allow good installability due to low viscosity at 
installation temperatures. We have found that an ethylene copolymer of 
high melt flow index can be blended with suitable quantities of one or 
more polyamides to produce the desired properties. 
Thus, the present invention provides an adhesive composition comprising a 
blend of 
(a) (at least one) polyamide; and 
(b) copolymer of ethylene and an ester of an ethylenically unsaturated 
carboxylic acid, said copolymer having a melt-flow index of at least 40, 
preferably at least 70, especially from 100-300, as measured according to 
ASTM D1238-70; the amount of the copolymer being at least 38%, preferably 
from 38-126% based on the weight of the polyamide. 
The composition may additionally comprise other components for example for 
controlling viscosity or flow temperatures or adhesive strength. A 
preferred further component comprises a ethylene acrylic acid copolymer, 
(which can help control viscosity or flow temperature), which is 
preferably present up to 57% based on the weight of the polyamide, and is 
preferably less than 20% based on the weight of the composition, more 
preferably less than 15%, especially less than 10%, say 3-7% particularly 
when low acidity is desired. Other components may comprise Versamid 100 
(trade mark for polyamide of Schering), tackifiers, such as a terpene 
phenol, for example that known by the trade mark SP553 (Schenetady Corp.) 
or, polyisobutylene and antioxidants such as that known by the trade mark 
Irganox 1010 (Ciba Geigy). We prefer that the composition has 
substantially no vinyl acetate nor vinyl acetate copolymer content. 
A preferred composition comprises: 
(a) from 35-65, preferably 50-60, especially 53-56 parts by weight of one 
or more polyamides; 
(b) from 25-44, preferably 25-35, especially 27-31 parts by weight of one 
or more copolymers of ethylene and an ester, particularly poly(ethylene 
ethylacrylate) and/or poly(ethylene butylacrylate); 
(c) from 5-20, preferably 10-15, especially 12-15 parts by weight of 
ethylene acrylic acid copolymer; and 
(d) from 0-4, preferably 1-4, especially 1-3 parts by weight of a vinyl 
terminated rubber, particularly vinyl terminated butadiene nitrile rubber. 
The or each polyamide preferably has a ring and ball softening point 
according to ASTM E28 of from 80.degree.-120.degree. C., more preferably 
from 90.degree.-110.degree. C., a molecular weight of from 2000-10000, and 
a viscosity at 210.degree. C. according to ASTM D3236 of 2-8, preferably 
3-5 Pa.s. and an amine number from 50-400. Suitable polyamides include 
those known by the trade marks Macromelt 6735 (Henkel), Macromelt 6766 
(Henkel) and Macromelt 6301 (Henkel). In general, a polyamide (or blend of 
polyamides) may be chosen that has the desired physical and chemical 
properties (for example melt flow index, softening point, viscosity, and 
adhesive strength) substantially similar to those of the quoted examples. 
Two (or more) polyamides may be chosen particularly where low temperature 
flexibility is required, especially in combination with low cost. 
The copolymer of ethylene and an ester preferably contains only two 
comonomers, and we preferably substantially exclude terpolymers from the 
composition, although if the terpolymer is carefully selected it may be 
acceptable. The terpolymer content is preferably less than 10% by weight 
based on the weight of the polyamide. Preferred copolymers have a ring and 
ball softening point according to ASTM E28 of 80.degree.-125.degree. C., 
especially 95.degree.-120.degree. C. Examples of preferred copolymers and 
acceptable terpolymers include: poly(ethylene ethylacrylate), such as 
those known by the trade marks Lotader 8200 (Companie de France), Lotader 
7500 (Companie de France), EA 89821 (USI) and Alathon 704 (DuPont); and 
poly(ethylene butylacrylate), such as that known by the trade mark Lotader 
HX 8280 (Companie de France). (Lotader 7500 and 8200 are terpolymers that 
additionally contain maleic anhydride.) As with the polyamide, other 
copolymers can be used having similar physical and chemical properties to 
those quoted. 
Where a ethylene acrylic acid copolymer is used, we prefer that known by 
the trade mark Alathon 5120 (DuPont) or AC5120 (Allied Chemical 
Corporation) or equivalents. 
We have identified a problem that may occur when using some prior art 
adhesives, and that may be solved with the present invention. 
Adhesion may be poor to certain materials, particularly metals, such as 
that used for lead cables in Belgium. We have noticed that the lead used 
for Belgian cables is substantially pure and therefore soft. As a result 
of this softness, and as a result of a disparity between the thermal 
coefficient of expansion of adhesives and of lead, thermal cycling may 
cause cohesive failure of the lead: a very thin surface layer of the lead 
may peel away from the bulk. The problem is less likely to occur with 
harder lead compositions, for example those containing impurities or 
additives such as antimony, copper, silver or tin. The skilled man will be 
able to determine where there is a risk that this problem will occur, but 
typically at risk are lead compositions having a melting point as 
determined by differential scanning calorimetery at 8 degrees centigrade 
per minute of at least 322 degrees centigrade. An alternative indication 
(which applies to lead and to other metals and other materials) is 
hardness: a Vickers hardness of less than 5.5, preferably less than 5.0 
microns may lead to poor bonding, the measurement being made on Leitz 
Miniload equipment using a 100 gm core. 
Recognition of this possible failure mode has led us to reduce the acidity 
of our adhesive composition and thereby reduce stress on cycling at the 
adhesive/lead interface. This may be done by, for example, reducing the 
acidity of say AC 5120 (ethylene acrylic acid copolymer) itself. In one 
embodiment AC 5120 (ethylene acrylic acid copolymer) may be at least 
partially replaced by SP 553 (a trade mark of Schenectady, France, for a 
tackifier), and/or by AC 540 (a trade mark for a polyethylene acrylic acid 
copolymer of Allied Chemical Corporation). AC 540 (ethylene acrylic acid 
copolymer) has a lower concentration of acid functionality than AC 5120 
(ethylene acrylic acid copolymer). Often components which may be added 
include Oppanol B-12 (a trade mark for polyisobutylene of BASF). Peel 
strengths at room temperature of at least 100N/25 mm, generally at least 
150N/25 mm especially at least 170N/25 mm to Belgian lead can be achieved 
after 10 temperature cycles from -40 degrees centigrade to +60 degrees 
centigrade. 
The primary components selected, and their relative amounts, and any 
further components such as viscosity or flow modifiers are preferably such 
as to achieve a peel strength to non-flame brushed polyethylene, 
preferably also to lead, of at least 100N/25 mm at room temperature (test 
QAPK027), a ring and ball softening temperature of 90.degree.-110.degree. 
C. (test ASTM E28), a viscosity at 160.degree. C. of 40-110 Pa.S (test 
ASTM D3236), a low temperature mandrel flexibility of -30.degree. C. or 
lower, and an impact brittleness of -30.degree. of lower (test ISO 974). 
The adhesive composition may be provided with, preferably as a coating on, 
a dimensionally-recoverable, preferably heat-shrinkable article. The 
article may comprise a sleeve, which may be tubular or of the wrap-around 
type, such as that disclosed in UK Patent 1155470 (Raychem). We 
particularly prefer that the sleeve or other recoverable article comprises 
a recoverable composite material recoverable by virtue of a recoverable 
fabric component thereof. The recoverable fibre may be part of a 
recoverable fabric, such as one that comprises a weave of recoverable 
fibres in one direction and dimensionally stable fibres in another 
direction. We prefer that the recoverable fibres comprise polyethylene and 
that the stable fibres comprise glass. The composite material may comprise 
recoverable fibres and a matrix material, such as polyethylene, by means 
of which the composite is rendered substantially impermeable. The matrix 
material is preferably such that the adhesive composition is able to bond 
thereto. 
Where a branched cable splice is to be environmentally sealed by means of a 
sleeve, a branch-off clip may be applied to an end of the sleeve to hold 
together circumferentially-spaced portions of the sleeve between the 
branching cables. The use of such a clip to bring together such portions 
of a recoverable sleeve is disclosed in GB 1604981. Such a clip may have 
three legs, the outer two lying outside the sleeve, and an inner lying 
within the sleeve, generally between the branching cables. The branch-off 
seal formed using such a clip may be enhanced if an inner leg of the clip 
comprises an adhesive, and the adhesive of the invention may be used for 
such purpose. The adhesive may provide substantially the whole of the 
inner leg, or may provide a coating over a heat-conducting or other 
support. 
The adhesive of the invention may be supplied separately from any sleeve 
instead of or in addition to the sleeve coating as mentioned above. For 
example, such adhesive may be supplied in strip form for wrapping around a 
cable prior to installation of a recoverable sleeve or other cable 
enclosure.

The invention is further illustrated by the following examples. 
EXAMPLE 1 
An adhesive composition was made by mixing in a blend mixer the following 
materials: 
______________________________________ 
Macromelt 6301 (polyamide) 
93 parts by weight 
VTBNX (vinyl-terminated 
5 parts by weight 
butadiene nitrile rubber) 
Antioxidant 2 parts by weight 
______________________________________ 
Sixty parts by weight of the resulting first blend were mixed with 35 parts 
by weight of ethylene ethylacrylate (Alathon 704) and 5 parts by weight of 
polyethylene acrylic acid (AC5120). 
The resulting adhesive composition was then laminated onto a 
heat-recoverable composite comprising a weave of recoverable high density 
polyethylene in the weft and glass fibres in the warp having a matrix 
material of low density polyethylene. The lamination was carried out to a 
thickness of 0.4 mm using a belt laminator. 
A wrap-around sleeve was formed from the resulting coated composite by 
forming at edge regions thereof closure members that could be held 
together by a C-shaped channel, as disclosed in EP 0116392 (Raychem). The 
sleeve was then heat-shrunk around a polyethylene cable splice of 1 in 3 
out configuration, using a branch-off clip between the branching cables. 
The size of the sleeve was that known by Raychem's trade mark VASM 4/6. 
The sleeve was tested for leaks on a pressure/temperature cycle at 40 KPa 
from -40.degree. C. to +60.degree. C. at 3 cycles per day. Excellent 
performance was noted. 
The adhesive composition of this example had a viscosity at 160.degree. C. 
of 80.7 Pa.S, and a ring and ball softening point of 102.degree. C. 
Viscosity was determined according to ASTM D-3236-1978, using a Brookfield 
Model HBT, Spindle SC-27 at 160.degree. C. at a shear rate of 5 rpm. The 
softening point was determined by the ring and ball method according to 
ASTM E28-1977. The sample preparation being by the pour method, at a 
heat-up speed of 5.degree. C./minute. 
EXAMPLE 2 
Example 1 was repeated, but using the following components: 
______________________________________ 
First blend 42.5 parts by weight 
Alathon 704 (poly(ethylene ethylacrylate) 
40 parts by weight 
AC 5120 (ethylene acrylic acid copolymer) 
17.5 parts by weight 
______________________________________ 
Viscosity at 160.degree. C. was 44 Pa.S, and the softening point was 
98.degree. C. 
EXAMPLE 3 
Example 1 was repeated, but using the following components; 
______________________________________ 
First blend 50 parts by weight 
Alathon 704 poly(ethylene ethylacrylate) 
38 parts by weight 
AC 5120 (ethylene acrylic acid copolymer) 
12 parts by weight 
______________________________________ 
Viscosity at 160.degree. C. was 67 Pa.S, and softening point was 
105.degree. C. Peel strength at room temperature to non-flame-brushed 
polyethylene averaged 167N/25 mm determined according to QAPK 027. 
EXAMPLE 4 
Example 1 was repeated, but using the following components: 
______________________________________ 
Macromelt 6301 (polyamide) 
46.5 parts by weight 
VTBNX (vinyl-terminated 
2.5 parts by weight 
butadiene nitrile rubber) 
Antioxidant 1 part by weight 
Alathon 704 (poly(ethylene ethylacrylate) 
38 parts by weight 
AC 5120 (ethylene acrylic acid copolymer) 
12 parts by weight. 
______________________________________ 
Viscosity at 160.degree. C. was 56.5 Pa.s, and the softening point was 
104.degree. C. Peel strength at room temperature to non-flame-brushed 
polyethylene averaged 120N/25 mm. 
EXAMPLE 5 
Example 1 was repeated, but using the following components: 
______________________________________ 
Macromelt 6301 (polyamide) 
46.5 parts by weight 
Antioxidant 1 part by weight.sup. 
Lotader HX 8280 38 parts by weight 
AC 5120 12 parts by weight 
VTBNX (vinyl-terminated 
2.5 part by weight 
butadiene nitrile rubber) 
______________________________________ 
Viscosity at 160.degree. C. was 63.1 Pa.s, and the softening point was 
99.degree. C. Peel strength at room temperature to non-flame-brushed 
polyethylene was 301N/25 mm. 
EXAMPLE 6 
Example 1 was repeated but using the following components 
______________________________________ 
Macromelt 6301 (polyamide) 
54.4 parts by weight 
VTBNX (vinyl-terminated 
2 parts by weight 
butadiene nitrile rubber) 
Antioxidant 1 part by weight 
Lotader HX 8280 (poly(ethylene 
29 parts by weight 
butylacrylate) 
AC 5120 (ethylene acrylic acid copolymer) 
13.6 parts by weight 
______________________________________ 
Viscosity at 160.degree. C. was 58 Pa.s, and softening point was 99.degree. 
C. Peel strength at room temperature to non-flame-brushed polyethylene was 
386N/25 mm. 
EXAMPLE 7 
Example 1 was repeated but using the following components. 
______________________________________ 
Macromelt 6301 (polyamide) 
50 parts by weight 
VTBNX (vinyl-terminated 
2 parts by weight 
butadiene nitrile rubber) 
Antioxidant 1 part by weight.sup. 
Lotader HX 8280 (polyethylene 
37 parts by weight 
butylacrylate) 
AC 5120 (ethylene acrylic acid copolymer) 
10 parts by weight 
______________________________________ 
Viscosity at 160.degree. C. was 89 Pa.S, and the softening point was 
96.degree. C. Peel strength at room temperature to non-flame-brushed 
polyethylene was 277N/25 mm. 
EXAMPLE 8 
Example 1 was repeated but using the following components. 
______________________________________ 
Macromelt 6301 (polyamide) 
60 parts by weight 
Antioxidant 1 part by weight.sup. 
Lotader 8600 B (polyethylene 
19 parts by weight 
butylacrylate copolymer) 
Oppanol B-12 (polyisobutylene) 
10 parts by weight 
SP 553 (a tackifier) 5 parts by weight 
AC 540 (ethylene acrylic acid copolymer) 
5 parts by weight 
______________________________________ 
(Lotader 8600 B (polyethylene butyl acrylate copolymer) is a trade mark of 
Companie de France for polyethylene butyl acrylate copolymer.) 
The resulting composition, which can be seen to contain no AC 5120 
(polyethylene acrylic acid copolymer), had a viscosity at 160.degree. C. 
of 77.5 Pa.S, and at 200.degree. C. of 28.1 Pa.S. Its ring and ball 
softening point was 101.4.degree. C. Peel strength to flame-brushed 
polyethylene at PG,15 room temperature was 438.2N/25 mm. Peel strenth to 
Belgian lead cable at room temperature after temperature cycling of 10 
cycles from -40.degree. C. to +60.degree. C. was 183N/25 mm, and before 
cycling it was 192N/25 mm. Such values are surprisingly different from 
those for compositions containing large quantities of AC 5120, where the 
peel strength to Belgian lead drops substantially to zero. 
The quantity of these components may, of course, be varied. The Oppanol 
B-12 is preferably present from 5-10 parts, the SP 553 from 0-7 parts, and 
the Lotader from 15-25 parts. Preferably the relative amounts are as 
follows: Lotader/Oppanol/SP 553 3.8-4.2: 1.8-2.2: 0.8-1.2. 
EXAMPLE 9 
Example 1 was repeated but using the following components. 
______________________________________ 
Macromelt 6301 (polamide) 
60 parts by weight 
Antioxidant 1 part by weight.sup. 
Lotader 8600 B (polyethylene 
19 parts by weight 
butylacrylate copolymer) 
Oppanol B-12 (polyisobutylene) 
10 parts by weight 
SP 553 (a tackifie) 5 parts by weight 
AC 5120 (ethylene acrylic acid copolymer) 
5 parts by weight 
______________________________________ 
The resulting composition, which can be seen to contain less AC 5120 
(polyethylene acrylic acid copolymer) than the early examples, had a 
viscosity at 160.degree. C. of 64 Pa.S and at 200.degree. C. of 19.2 Pa.S. 
Its ring and ball softening point was 99.8.degree. C. Peel strength to 
flame brushed polyethylene at room temperature was 400.degree. C. Peel 
strength to Belgian lead cable at room temperature after temperature 
cycling of 10 cycles from -40.degree. C. to +60.degree. C. was 175N/25 mm, 
and before cycling it was 201N/25 mm. 
The retention of some AC 5120 may be desirable in order to achieve a low 
viscosity and high peel strength to lead. 
For the avoidance of doubt, it is here stated that the invention provides 
an adhesive composition, and an article particularly a recoverable article 
having such a composition, that exhibits the properties mentioned herein 
as desirable. Any of the components mentioned herein may be selected to 
achieve these properties, particularly the selection of an acid copolymer 
with a high melt flow index, together with a polyamide, the high melt flow 
index of the copolymer allowing it to be used at high relative amounts 
based on the amount of the polyamide, and inclusion of other components 
such as viscosity or melt flow temperature modifiers, rubbers and 
antioxidants, etc.