Note: Descriptions are shown in the official language in which they were submitted.
~OS'~5~5
~ his invention xelates to a method o~ joining
articles and to articles so joined.
Sleeves, which may be thin-walled, of polymeric
materials, particularly polymeric material~ crosslinked by
high energy ionizing radiation to impart form stability at
melt temperatures, are frequently used to protect articles,
particularly those having a tubular or otherwise regular
elongate configuration. Another use ~or such sleeves is for
sealing joints between lengths o~ pipes or other conduits.
Of particular utility ~or these purposes are heat-recoverable
sleeves, especially heat-shrinkable sleeves that is, sleeves
that possess the property of being able to shrink to a smaller
diameter when heated. A heat-shrinkable sleeve is constructed
with a diameter large enough so that it can be conveniently
placed about the substrate whereupon it is heated causing it to
shrink into close contact with the substrate. Heat-recoverable
sleeve~ have been found highly ef~ective, inter ~1~3~ for
producing corrosion-resistant coverings *or pipe joints as
disclosed in, Ior egample, U.S. Patents Noæ. 3,297,819,
3,379,218, 3,415,287, 3,455,336, 3,530,598 and 3,770,556.
Materials suitable for making heat-recoverable
sleeves are well knownO ~hus, ~or example, in U.S. Patent
~o. 3,086,242 there is described a variety OI suitable
materials obtained by crosslinking, particularly by radiation,
organopolymeric precursors.
~ leeves o~ relatively small diameter can conveniently
be e~truded directly as tubes. ~his however is not the case
with sleeves having a diameter large enough to enable them to
be used to cover sections o~ pip~- of a size that might be
employed in pi~elines for the transmission of oil or gas over
lon~ distances. ~ecause o~ this di~icul-ty~ it has been the
_ 2 - ~
~oS~5~5
practice in the past to employ ~o-called "~rap-around"
sleeves ~or large diameter pipes. Sléeves o~ this type may
be made, for e~ample, by wrapping a length oP heat-recoverable
material about the substrate, for example, at a joint between
two lengths of pipe, and joining its ends by mechanical means
that prevent the ends from separating when the sleeve is sub-
jected to heat to cause it to recover. Examples o~ such
sleeves are described in certain of the patents mentioned above.
It is still preferred to use a wrap-around sleeve in
situations where it would be inconvenient to position a pre-
formed sleeve about the substrate, for example, ~hen the end
of the substrate is remote from the point where $he sleeve is
desired, as might be the case when the sleeve is to be used in
the repair o~ a pipeline. Nevertheless, there are many
situation~ in which it would be advantageous to have available
a supply of prefabricated sleeves o~ large diameter.
In order to obtain large diameter preformed sleeves
it has hitherto been proposed to overlap the opposite edges
of a polymeric sheet, disposing between the overlapping
segments a pero~ide crosslinking agent which is then activated.
This technique has gen~rally proved unsuccessful because,
apparently because of uneven crosslink formation, the edges of
the overlapped sur~aces pucker severely upon expansion,
presenting an unsightly weld which is also potentially subject
to ~ailure because of a low peel strength. Joints have been
alternatively proposed to be formed by disposing thermoplastic
materials between crosslinked polymeric articles to be joined,
and subsequently heating the thermoplastic substance to its
melt temperature~ ~hat approach is unsuited to the production
~0 of heat-reco~erable sleeves because the process by which heat-
recoverability is imparted involves e~pansion of the sleeve at
lOSZS~S
high temperatures which will cause the failure of a thermo-
plastic joint.
Another method by ~hich pre~ormed large diameter
sleeves maU be made is described in Canadian Patent Application
~erial No. 218,597, filed 24th January, 1975 in the name of
Robert James Naidoff; this method is generally carried out
using non-heat-recoverable polymeric sheet material, and a
sleeve obtained from this process may subsequently be processed
to make it heat-recoverable. A further method is described in
U.S. Patent No. 3,991,243 granted 9th Se~tember, 1976 to
William G. Biddell. ~y using the latter method, heat-recover-
able sleeves may be made directly from heat-recoverable sheet
material.
The aforementioned Naidoff and Biddell specifieations
describe, inter alia, inserting the end~ of polymeric sheet
material into the channels of a generally "I"-shaped member
referred to as an "insert" fabricated from a thermoplastic
material containing a heat-activatable crosælinking agent
followed by heating the assembly under pressure to form a weld.
~he insert, in e~fect, functions as a thermosetting member and
bonds itæelf covalently to the polymeric sheet. In these
methods, the length of the insert is typically substantially
the same as the width of the sheet ends to be joined.
The welds formed using the inserts disclosed in the
above-numbered Naidoff and Biddell specificationæ, however, are
frequently marred by the presence of blisters or voids. ~hese
appear to be caused either by gaseous products formed in the
welding process, for example, by decomposition of the heat-
activatable crosslinking agent as the assembly is heated, or
by air entrapped in the welding procesæO Whatever their source,
these defects can æignificantly reduce the strength of the weld.
-- 4 --
105'h5~5
In order to avoid the occurrence of these defect~
it has previously been -proposed to use two or more inserts
separated by a space or spaces which is or are thought to
provide a pathway by which the gases can escape as they are
formed. If properly spaced, the section~ of insert will flow
together before thermosetting is complete, thereby filling the
gap and ensuring that a substantially uniform bond is obtained.
~his process i~ described in Canadian Application Serial I\To.
228,638 filed 5th June, 1975 by ~iilliam Harry Humphries.
Although the use of a plurality of spaced inserts
constitutes a valuable improvement in the process of insert
welding polymeric sheet material, the use of a plurality of
separate inserts may be somewhat inconvenient in some circum-
stances. Thus, the multiple inserts must be properly aligned
relative to each other and to the polymeric material to be
joined if a uniform bond is to be obtained. '~his requirement
necessarily increases the time required to assemble the
components of the weld thereby making the use o~ a plurality
of inserts less attractive for the manufacture of large
numbers of sleeves.
Furthermore, the alignment of the sleeves may in some
circumstances be lost in the steps of the welding process when
a plurality of inserts are usedO For example, as the heated
platens used to provide the pressure and heat that cause the
insert to soften and flow as well as initiate the thermosetting
reaction are closed, they may tend to displace the insert.
Also, inasmuch as the clearance between the platens when the
opening is not large, the proper positioning of a plurality of
inserts and sheet ends constitutes an additional hazard to the
operator.
The present invention provides a method of joining
lOSZ5~5
abutting surfaces of polymeric material which comprises
disposing between the æur~aceC an insert formed of thermo-
plastic material having dispersed therein a heat-activatable
crosslinking agent~ the insert having one or more perforations
therein whereby escape of gaseous products from the weld area
is facilitated, and heating the surfaces and insert under
compression, to cause the insert to flow and the cross-linking
agent to be activated, whereby the surfaces are joined by cross-
linked weld material.
In a preferred embodiment of the invention, butt
welded articles may be made by disposing a thermoplastic "I"
beam shaped insert between the ends of thin-walled crosslinked
thermoplastic polymeric sheet material to be joined, insertin~
the ends into the channels defined by the "I"-shaped insert,
and heatin~ the assembly under pressure to form a weld. ~he
material of the "I"-shaped member, in addition to its thermo-
plastic component, further comprises a heat-activatable cross-
linking agent that during weld formation initiates crosslinking
within the insert and the formation of covalent bonds between
the insert and polymeric sheet material.
The invention also provides an article having a weld
made by the method of the invention. The article may be in
the form of a sleeve, the weld line being parallel to the a~is
o~ the sleeve, and the weld is preferably continuous from one
end o~ the sleeve to the other and is of essentially the same
thickness as the walls of the sleeve. In a sleeve made in
accordance with the invention, one of the surfaces of poly-
meric material may be part of a dimensionally heat-stable thin-
walled segment, while another of the surfaces of polymerio
~0 material is part of a heat-recoverable thin-walled segment.
In a preferred embodiment of the invention, the sleeve is
lOSZ5~5
heat-recoverable, and large diameter heat-recoverable sleeve~
in accordance with the invention may be used in an~ of the ways
indicated above J for example for protecting pipe joints from
corrosion.
~he method of the invention makes it possible to
obtain butt-welded articles wherein the weld area is substan-
tially free from voids caused by air and gaseous by-products of
the weldin~ process.
The polymeric material joined by the method of the
invention is preferably cro~slinked, and the modl~us of the
weld material is advantageously at least equal to that of the
polymeric material joined thereby. Welding is effected at
temperatures sufficient to cause the thermoplastic insert
material to flow and wet the surfaces to be joined, and also
sufficient to actlvate the crosslinking ~ystem.
~he iasert used in accordance with the inv~ntion is
preferably I-shaped in cross-section. Such an insert not only
makes it possible substantially to avoid the problems of void
formation attributable to entrapped air or gas, but i9 also
convenient to use.
~he perforations in the preferred insert of the in-
vention can be located through the ~lange~ of an "I"-shaped
insert, but preferably extend ~rom top to bottom through the
centre upright joining the flanges. The inserts can be extruded
or otherwise moulded from suitable thermoplastic compositions
and can then be provided with perforations by any suitable
meansO ~he per~orations can be of any convenient, usually
regular, configuration and are preferably either square, rec-
tangular or circular in shapeO
~he number and size of the perforations giving optimum
results can vary and depends upon a number of parameters
105'~S15
including tne flow characteristics of the polymeric con-
stituents of the material to be joined and the inser~, on the
location of the perforations in the insert and on the width
and thickne~s o the material to be joined. Fixed requirements
applicable in every situation thus cannot be laid down.
Nevertheless, the optimum number and arrangement o-~ perforations
can readily be determined empirically by routine experiment by
one skilled in the art. To achieve greater insert flow,
however, it is pre~erable to use I-shaped inserts the per-
forations o~ which are made through the centre upright portion
- of the insert, the diameter of the perforations being at least
as great as the width of the upright.
~ he insert can be as long as the polymeric sheet
material to be joined is wide. Pre~erably, however, the
length of the insert is slightly less than this width and in
the welding process it is centred between the ends o~ the ~heet
ends to leave gaps at each end that provide an additional area
through which gaseous material can escape. ~he width of the
gaps is pre~erably gauged to be such that in the welding
proces~ they are filled as the insert flows under ~eat and
pressure.
In a preferred embodiment of the invention, heat-
recoverable sleeves are made ~rom heat-recoverable polymeric
material or from material capable of being rendered heat-
recoverable after sleeve formation. A heat-recoverable
article is a dimensionally heat-unstable article having an
elastic or plastic memory. Such an article can be obtained,
~or example J by heating a sheet of a suitable thermoplastic
crosslinked crystalline polymer above its crystalline melting
point and elongating or expanding it in one or more directionsO
The sheet is allowed to cool below the crystalline melting
~S~'~5~ 5
temperature while maintaining the deforming force. If heated
without restraint above its crystalline melting point, such
a sheet will exhibit its `'elastic memory`' by returning to its
pre-e~panded dimenæions. For use as an element o~ a heat-
recoverable sleeve, it is preferred to employ heat-recoverable
material expanded in a single directionO
Polymeric materials that have been crosslinked by
chemical means or by irradiation, for e~ample, with high
energy electrons or nuclear radiation, are preferred for use in
making heat-recoverable articles in accordance with this in-
vention, although other polymers capable of having the property
of heat-recoverability imparted to them can also be used. The
polymeric material to be joined in accordance ~ith the in-
vention must be capable of undergoing further crosslinking in
the presence o~ heat-activatable crosslinking agents since,
in the formation of the weld, the insert and the polymeric
sheet are believed to become covalently bonded to each other,
this bond formation being induced by the crosslinking agent.
Examples of polymeric materials which may be
joined by the method of the invention include polyolefins;
saturated and unsaturated polyesters; polyvinyl halides; and
elastomers, for example natural rubber, butadiene-styrene
copolymers, butadiene-acrylonitrile copolymers, isoprene-
isobutylene copolymers, polyisoprene, polybutadiene, poly-
sulphides (Thiokol)*, polychloroprene (neoprene), polysiloxanes(silicone)~ fluorocarbons (for example Viton)*, chlorosul-
phonated polyethylene (for example Hypalon)*, plasticized
polyvinyl chloride, and polybutene. ~Iost preferred are the
polyolefins, for e~ample, polyethyle~e; poly (butene-l);
various copolymers of ethylene, propylene and butene; ethylene/
ethyl acrylate, ethylene/vinyl acetate, or ethylene/methyl
* "Thiokol", "Viton" and ~l-nypalonl~ are -trade marksO
iO5'~5~5
acrylate copolymers in which re~eat u~its derived from ethylene
predominate (~or example, about 80 to 90~o), and blends of such
copolymers with major proportions of polyethylene itself.
method for rendering polymeric materials heat-recoverable is
described in U.S. Patent ~o. 3,086,242.
As previously noted, the polymeric artioles to be
joined are preferably crosslinked ~rom the outset, and pre-
ferably exhibit a modulus in the range ~rom about 20 to about
60 psi (1.4 to 4.2 KgJcm2). ~s used herein, the term
"modulus" is the modulus determined at 150C and 100~o elonga-
tion. The determination i6 carried out at a jaw separa,tion
rate o~ 2 inches (about 501 cm) per minute~ Articles to be
joîned are ~referably crosslinked by high energy ionizing
radiation a,t dosage levels ranging from, for example, about
5 to about 20 megarads, pre~erably from about 12 to 15 megaracls.
~he invention is es~ecially useful ~or joining
thin-walled articles ~or example, sheet ranging in thickness
from about 60 to about 120 mils (0.15 to 0.30 cm). An article
is "thin-walled" for present pur~oses when its thickness is
substantially less than its length or width.
- 10 -
-
~05i~515
A "primary face" of an article is that surface which is
the product of length and width as so defined. The invention
has proved well suited to joining polymeric sheet, which may
be heat-recoverable, to form sleeves whose recovered diameter
is equal to or greater than 12 inches (30 cm) and commonly
equal to or greater than about 18 inches (45 cm).
The thermoplastic polymeric constituent of the
insert can be chosen within wide bounds, including a great
variety of melt processable materials capable of being cross-
linked by heat-activated systems. Since the crosslinking
agent is most desirably blended with the polymeric constitu0nt
of the insert in the melt phase, an important consideration
in choice of insert thermoplastic is melt processability at
temperature less than the heat activation temperature of
the crosslinking agent. The insert thermoplastic should al-
so be compatible with t'ne polymeric material being joined in
the sense that they are capable of adhering and bonding to-
gether under heat and pressure. The criteria by which the
insert thermoplastic is to be chosen are well known to those
skilled in the art. With the polyethylenic materials most
preferably employed in the articles to be joined, preferred
insert polymeric constituents include ethylene/vinyl acetate,
ethylene/methyl acrylate and ethylene/ethyl acrylate
copolymers and blends of such copolymers with low density
polyethylene or minor proportions of polyethylene. Such
copolymers commonly contain from about 60 to about 90 to
96 % by weight of structural units derived from ethylene,
lO~'~SlS
and preferably contain -~rom about 75 or 80 to about 96f~ b~
weight of such units.
~ s examples of crosslinking agents, there may be
mentioned a wide variet~ of free radical generators, for
example bisazodicarboxylates, for example, ~thyl and ethyl
bisazodiformates, sulphonazides, ~or example 1,10-decane bis
(sulphonazide), a~odicarbonamine, 3,3'-dimethoxy-4,4'-dia-
zodiphenyl and 2,2'-azobisisobutyronitrile. Mo~t preferred
are peroxide crosslinking agents, for example, t-butyl per-
benzoate, 2,5-dimethyl-2,5-di(t-butyl peroxy3 hexyne-3, dicumyl
peroxide, benzoyl peroxide, methylethylketone peroxide, cumene
hydropero~ide, t-butyl hydropero~ide and di-t-butyl peroxide.
Such agents are empolyed in e~fective crosslinking proportions,
as in conventional practice. Most commonly, the agents are
coated on a calcium carbonate or other particulate substrate,
and are employed in proportions ranging from about ~/~ to
about 2~ by weight active agent, most preferably from about ~
to about 1a~o by weight active agent, based on the weight o~ the
composition used for the insert body. ~ preferred agent,
which is known to experts in the art as "Varox"*, is a
mixture o~ 50~ calcium carbonate and 50~o 2,5-dimethyl-2,5-di
(t-butyl peroxy) hexane.
Expecially where the amount of crosslinking agent
employed is at the lower end of the ranges mentioned above,
andmost especially where non-peroxide crosslinking agents are
used, it is preferred additionally to use in the insert
material a so called "co-agent" to maximize the number of
crosslinks formed through the agency of a given number of
free radicals generated by the agent itself. The use of such
co-agents is conventional and is discussed in, for example,
~. P. ~enaf, I & E Chem. Prod. Research & Development, 2,
1~
* "Varox" is a trade mark
lOS;Z51S
~o. ~, 202 (196~). Among conventionally employed co-agents,
otherwi~e known as ~olyfunctional monomers, may be mentioned
m-phenylene dimaleimide, trimethylol propane trimethacrylate,
pentaerythritol tetra-acrylate, triallyl cyanurate, triallyl
i~ocyanurate, allyl methacrylate, diallyl phthalate, triallyl
citrate, tetra-allyl pyromellitate and triallyl mellitate.
~uch co-agents are employed in minor proportions, ~r example,
0.5 to 2~, most preferably ~rom about ~ to about 1~o by weight
o~ the composition.
The quantities of crosslinking agents and co-agent
are chosen bearing in mind the ~ollowing two points. Cross-
linking is preferably sufficient to ensure that the modulus of
the ultimate weld is at least equal to, and preferably greater
than, that of the thin-walled articles Joined. Othex~lise, the
weld may be subject to failure during the high temperature
treatment associated with imparting the ~roperty of heat-
recoverability or effecting heat~recovery. On the other hand,
care must be taken to ensure that the ~eld is not crosslinked
to too great an extent, with concomitant embrittlement.
Preferably, the modulus of the weld is not greater th~n about
three times that o~ the article joined. It will be appreciated
by those skilled in the art that for a given combination of
material to be joined, the material of the body forming the
insert, and the identity o~ the crosslinking agent and co-agent,
the optimum ~roportions of the two last-mentioned are a matter
of routine e~eriment only. Weld modulus can in ~articular
cases range from about 20 to about 250 psi (1.4 to 17.5 Eg/cm2).
However, a substantial failure rate may be experienced at
moduli greater than about 150 psi (10.5 ~g/cm2), and most
pre~erably the weld modulus is in the range ~rom about 50 to
about 100 psi t3.5 to 7.0 KgJcm2).
105'~5~5
Of course, in addition to crosslinking agent,
polymeric constituent and, where used, co-agent, the insert
may contain additional conventional addends, ~or example,
fillers, ultra-violet stabilizers, antio~idants, and acid
acceptors. ~illers, for example carbon black, calcium
carbonate and the like, are employed in substantial (albeit
minor~ proportions in order, inter alia, to assist in con-
du¢ting heat from the surface to the interior of the insert.
Preferably, on the order of about ~ociO such filler is employed.
Specific examples of various co~positions useful as inserts
for bonding crosslinked articles are disclosed in Canadian
~pplication No. 218~597 referred to previously.
A preferred insert formulation for use with sheet
material containing a substantial proportion of polyethylene
or polyethylene copolymer comprises:
Wt~ (~o)
low density polyethylene 48
copolymer of ethylene and
methyl acrylate (1 6~o) 20
20terpolymer of ethylene, vinyl
acetate and methacrylic acid 5
carbon black 22.5
stabilizers 2.5
Varo~* 200
~he method of this invention has generally been
described above with reference to joining Polymeric sheet
material, for examPlef in the making o-~ sleeves from a sheet
of such material by joining two opposing edges~ It is un-
necessary to enumerate all the diverse ap lications to which
~0 this invention can be ~ut, but it will be apparent to those
skilled in the art that it can be employed in numerous other
- 14 -
* "Varox" is a trade mark
lOS;~515
instances when it is desired to join polymeric materlal,
particularly material that is heat-recoverable or capable of
being so rendered at the edges to be joinedO ~or example,
the method of this invention can be adapted to join two or
more discrete lengths of heat-recoverable sheet materi~l to
make a longer length. Such a length cot~d be employed to
make wrap-around sleeves in the many ways known to the prior
art or its opposing end edges could be joined by the method
of this invention to form a ~leeve. In another application,
material that is not heat-recoverable except along the edges
which are to be joined can be satisfactorily welded by the
method of this invention.
If the welding ~rocess of the invention is used to
form large diameter sleeves which are not heat-recoverable
but to which the property of heat-recoverability can be im-
parted, the welded sleeves may be heated to above the
crystalline melting temperature o~ the material ~rom which the
sleeve is formed and expanded in diameter.
r~he method o~ making sleeves described in detail
in this specification results in a sleeve o~ relatively uni-
form cross-section~ However, the method of this invention can
also be applied to making sleeve~ of irregular shape. ~or
example, sleeves that taper from a relatively large diameter
at one end to a smaller diameter at the other can be made by
the method of this invention. Similarly, generally "Y"-shaped
sleeves can also be fabricated from heat-recoverable or non-
heat-recoverable material using the method disclosed herein.
r~he invention will now be described, by ~ray o~
E2ample only, with re~erence to the accompanying drawings,
~0 in which:
Figure 1 is a cross-section through a thermoplastic
- 15 -
~05~515
in~ert, prior to com~ression bonding,
taken along the length o~ two sheets to
be joined;
~?i~ure 2 is a cross-section through the assembly
o~ l?igure 1 during bonding;
~igure 3 is a cross-section through the assembly
of ~igure 1 after bonding;
igure 4 is a perspective view of an insert which
may be used in accordance with the present
invention;
Figure 5 is a perspective view of a further insert;
~i~ure 6 is a top view of an assembly having a
perforated insert according to the present
invention;
Figure 7 is a cross-section through an assembly ~or
joining the ends of polymeric sheet material,
the assembly having a foraminous rein~orc-
ing member; and
Figure 8 is a cross-section through an insert which
may be used in accordance with the in-
vention.
Referring now the drawings, Figures 1 to 3 depict
a welding operation taken in cross-section along -the length
of the sheets to be joined. An insert 1, which is generally
"I"-shaped in cro~s-section is disposed between the abutting
edges oi~ polyneric sheet segrnents 2 and 3, the edges of the
segments being inserted in the channels bottoming on the up-
standing portion o~ the "I". To make a sleeve, the edges
would be the opposite ends of a single length of m~terial.
The resulting assembly is compressed, as by heated platens 4
and 5 (~?igure 2), thus causing the polyrnerlc constitutent o~
- 16 -
~OS~5~5
the in~ert to ~low and wet adjoining sur~aces of the segments
to be joined as well as activating the crosslinking agent.
Preferably, dams (not shown) approximating in thickness to
the compres~ed thickness of the polymeric sheet are dispos~d
at each end of the area to be welded and inhibit flow of the
melted insert material begond the weld ends.
Once crosslinking bet~een the melted insert and the
polymeric sheet has been ef~ected, the platen may be cooled
to reduce the tem~erature, whereafter the upper ~laten 4 is
withdrawn, freeing the formed joint (~igure 3~. ~he platens
may be conventionally heated, either electrically or with
steam. Preferably, heating and cooling are e*fected by
sequentially forcing steam and cooling water through passage-
ways formed in the platen itself,
With reference to ~igure 3, it will be noted that
the resulting butt-weld 6 is contiguous both with the aligned
edges 7 and 8 of sheets ~ and 3 and with regions of their
primary sur~aces immediately adjacent to those edgeæ. In
this fashion, the weld is made continuous past the aligned
edges of the polymeric sheet and the cloth in the foraminous
member tif used - see below), so that failure along the
interfaces between the weld and edges 7 and 8 is less likely.
To this end, the insert is so configured and positioned as to
ensure that those regions of the primary sheet surfaces are
wetted during melting of the insert material. ~he generally
"I"-shaped insert depicted in ~igures 1 to 3 is desi~ned with
this in mind.
Perforated inserts having generally "I" beam sha~ed
profiles which may be used in accordance with the present in-
vention are illustrated in ~igures 4 and 5. In ~igure 4,insert member 13 is shown having perforations 14 through the
- 17 -
:105iZS~5
flanges 15 and 16 forming the channels of the "I"-shaped
memberO As shown in ~ ure 4, the perforations are paired,
althou~h it will be appreciated that other relationships, for
example, a staggered arrangement, will be satisfactory.
Figure 5 shows a pre~erred perforated insert, wherein a
generally "I"-shaped member 17 is provided with perforations
18 through the upright portion 19 connecting flanges 20 and 21.
Unexpectedly, it has been found that by u~ing a
perforated insert as illustrated, for example, in ~igure 4 or
~igure 5 in a butt welding assembly, a top view of which is
shown in ~igure 6, substantial advantages may be obtained,
even though the use of a perforated insert 22 does not provide
any unimpeded channels by which the gaseous matter leading to
voids or blisters can escape as the weld is formed. Althougrh
the applicants do not wish to be bound by any hypothesis, it
is thought that the gaseous products or entrapped air gather
within the perforations as the platens are closed and heating
beginsO As the insert flows to fill the perforations, the air
is displaced from between the insert and platens. ~ccordingly,
when the perforations pass through the centre upright of the
insert, the diameter of the perforations should in general be
at least as great as the width of the upright in order to
provide a means by which air trapped ~ithin the channels ca~
migrate into the perforations. Preferably, as shown in
Fi~ure 6, they are wider.
When the sheet material to be joined by the process
Or the invention is heat-recoverable, a foraminous rein-
forcing member, or example~ member 23 shown in ~`igure 7 is
preferably used in conjunction with the insert. Member 22 may
comprise, for e~ample, a length of fibre glass cloth. ~he
manner in which reinforcing members may be employed and the
- 18 -
iOS;~515
adva~tages attainable by their use are fully set out in U.~.
Patent l~o. 3,991,24~ need not be repeated hereO
With reference no~1 to Figure 8, there is shown, in
cross section, a pre~erred insert 24 for use in accordance
with this inventionO An end of the heat-recoverable sheet i~
~irst inserted in the channel formed by converging flanges 25
of the generally "I'l-shaped member. ~he insert may have a
reinforcement attached to it, ~or example, by using double-
faced tape or adhesive to fa,cilitate alignment of the com-
ponents of the assembly between the platens. ~he resultingsubassembly is inserted between the platens and the free end
of the sheet inserted into the other channel of the "I"-shaped
member. ~he diverging flanges 26 o~ this i~ert form an
opening which is pre~erably wider th~n the thickness of the
sheet and thereby facilitate the insertion.
~he ~ollowing Example illustrates the invention:
A perforated insert was used to butt weld sheet
material having the ~ollowing composition:
Wt. (%~
Hytrel* 5555 2500
Vistalon* 702 24.0
Alathon* 3170 30.0
aarbon black 15.0
Finely divided carbon black 2.0
I~,N-m-phenylenedimaleimide 0.5
Polycarbodiimide 1.5
Acid accepter 1.5
Irganox* 1010 0.5
Eytrel* 5555 is a segmented polyether ester having
a shore D hardness o~ 55, available from the Dupont ~oO
_ 19 _
* "Hytrel", "Vistalon", "Alathon" and "Irganox" are trade marks
~ o~Sl5
Vistalon* 702, available from th~ Exxon Co., is an ethylene-
propylene rubber comprising about 70~0 ethylene. Alathon*
3170 is an ethylene/vinyl acetate (18%) copolymer o~ melt
index 2.5 at 190C and 2160 gm. Polycarbodiimide is a
stabilizer again~t hydrolysi~. ~he acid accepter employed
tLectro* 78) was a tetraba~ic lead ~umarate. Irgano~* 1010
is an antio~idant of the ~ormula tetrakis [methylene-3-(3',5'-
di-t-butyl-4'-hydro~yphenyl)propionate] methane.
3heet material o~ this composition 24 inche~ wide
and 60 milæ thick was joined using ~n insert hav~gthe compo~ition
previously described as pre~erred ~or the insert. ~he insert
had a cross-section as sho~n in ~igure 8 and was provided with
perforations through each flange, the perforations being 3/16
inch in diameter and separated by ~ inch (measured centre to
ce~tre). ~he insert wa~ 2~ inches long to provide 1/4 inch
gap~ between the insert and a dam at either end. A~ter welding,
no void~ were visible. Small pits resulting ~rom lncomplete
filling of the perforations ~ere, however, visible.
A similar insert having 1/4 inch perforatio~s
separated by ~ inch (measured centre to centre) through the
centre of the insert was used to weld the same sheet material
resulting in a weld with no visible pits or void~. The~e
E~amples demonstrate that void-free sleeves can be obtained by
the method o~ this inventionO
- 2~ -
"Vistalon", "Alathon", "Lectro" and "Irgano~" are trade mark~.
