Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to crosslinked polymers,
especially blends of polymers, and shaped articles constructed
therefrom. In particular, the present invention relates to
crosslinked polyethylenes.
It is known that the properties of polymers may be considerably
modified by crosslinking of the polymer chains. This is
particularly true of polyethylenes which, in crosslinked Eorm, I;
have found important commercial applications.
The present invention is based on the finding that a certain
class of polyethylenes, when crosslinked, exhibits substantial
advantages.
Accordingly, the present invention provides à substantial~y
cross-linked polymeric material (sometimes referred to herein
as a polymeric composition~ comprising a linear low density
ethylene homo - or copolymer which, prior to crosslinking,
is characterised by a density at 25C of 0.940 gm/cm3 or less
and a linearity expressed in terms of pendant methyl groups
per 10 carbon atoms of the polymer chain of less than 30
with a substantial absence of long chain branches.
,
~3~1~3~ r~9 1
For the avoidance o doub-t, the term "copolymer" as emplo~ed
herein i.s used i.n -l broacl sense to mcan polymers produced
xom at leac;~ two cliffererit monorlleric species ancl to include
terpo:Lynlexs and the li.ke.
The ethylcne homo or copolymer pxeferably has a density at
25C ~rior to crossli.n]~.ing of from 0.916 to 0.940 c~n/cm3,
particularly ~rom 0.919 to 0.940 gm/cm3 especiall.y less t'nan
0.930 gm/cm3 e.g. from 0.919 to 0.930 gm/cm3.
The deyree of bxanciling of the po:L~neric chains pr.io.r to
cross-linking i5 expressed in terms of the average number of
pendarlt methyl groups per 103 carbon atoms of the eth~lene
homo -- or copol~ner chain wh:Lch, as will be appreciated, is
~ mea~sure of all slde gxoups ~lhich contain a meth~l group~
e.g. any alkyl group and may be determined in accordance
with kno~m analytical procedures, for example the infra-red
analytical -technique reported by A.H. Willbourn in J~ Poly.
Sci 1~59 34 559. Preferred polymers are those haviny 10
less pendant meth~71 groups per 103 carbon atoms of the
pol~nex chain and those having 15 to 30 pendant methyl
~xoups per 103 carbon atoms c~ the po].~ner chain. Preferabl-~7
the pol-~mer contains on average less than 20 pendant methi71
groups pex 103 ca.rbon atoms o the pol~7mex chain.
~ 3 ~
;3~
~K~3.
The e~hylerle holno or copolymel-s are characte~isea by a
subs~ant1.al absellce of long chain b.ranches and pxe~erab].y
have no more than 5 long chain branches and more preferably
nc morc than 1 long chaln branch, on average E~er 103
carbon atoms o:E the polymeL- chain. By long chain branches
as employed herein is preferably meant branches yreater in
length than C~ more preferably greater in length than C6.
The degree of long chain branching may, for example, be
established by computing the differences between the number
of shor~ hranches, determined for example, hy 13C nuclear
ma~netic resonance spectroscopy, in accordance witth the
method reported by M.E.A. Cuddy and ~. Bunn in Polymer, 1976
Vol, 17 April page 345, and the total number of branches
determined as pendant methyl groups by infra-red spectroscopy.
! .
Of particular interest are those polymers wherein substanti.ally
all branches are C2 to C6 branches especially C2 branches.
The linear low density ethylene homo or copolymers of the
invention may be distingui.shed from the conventional~ i.e.
hranched, low density polyethylencs by their higher ~T
values where ~T as employed herein is defined as the difference
in C between the temperature at which the po]~er melts and
the temperat.ure at which the onsett of crystallisa~ion occurs.
Typically ~1~ values of greater than 15C, for example 15 to
20C particularly 16 to 20C, are observed in the linear low
density ethylene homo or copolymers employed in the com- '~
positions of the invention.
The linear low density ethylene homo or copolymers employed in
the compositions of the invention may be characterised by their
molecular weight distribution index (Mw rn) as measured by
standard methods (e.g. GPC). Thus the preferred polymers are
characterised by a molecular wei~ht distribution index of
below 8 and preferably in the range 3 to 8 e.g. 3 to 7. A
related parameter is the stress exponent, the preferred poly-
mers being characterised by a stress exponent in the range
1.20 to 1.40 where ~tress exponent is defined as
1 _ melt index usinq 6480q at 190C. I
0.477 log10 melt index using 2160g at 190C
A further characteristic feature of the polymers employed in
the compositions in accordance with the invention is their
~egree of unsaturation particularly in terms of terminal
vinyl groups per 103 carbon atoms of the polymeric chain,
values of at least 0.2, particularly 0~2 to 1.5 for example
0.3 to 1.5 as measured for example by infra-red spectroscopy
being preferred.
~he degree of cross-linking of the compositions may be
expressed in terms of the gel content (A~SI/ASl'M D2765-68).
Preferably the gel content of the cross-linked compositions
,
~ 91
is at leasl~ ~0.., nlo]e prefel-ably abovc 50~, pal^~iculc:rly
abovc fi5~, and up to ~5%, of the polymeric componerlts of the
coml,~os:ition .
The cross-lin}~ed compositions of the invention may be further
characterised by their higll elongation versus modulus
performance. Thus typical elon~ation at brea}c values at
150C exceed 300~, or example 300 to 1000~, for filled and
unfilled cross-linked compositions having a. 100~ secant
modulu.s at 150C in the range ~.5 to 4 K~/cm2 measured in
accordance with As~rM n 1708-66. Preferred composi.tions are
ch~r.lcterised by elongatiorl at break values at 150C o at
least 300%, parti.cularly at least 500%, for exarnpl.e at least
600%, 700%, 800%, and often 900% for cross-linked compositions
havinq at 100% secant modulus at 150C in the range 3.5 to 4
Kg/cm2. I
.. , , ~
Ethylene copolymers which may be employed in the composi-~ions
of the invention are pxeferably low density copolymers o
ethylene wi~nh ol.efinically unsaturated monomers po1.ymeri.~a.~le
therewith. Suitable such monomers are C3 to C20, preferably
C3 to C~, olef.ins, preferabl~ olefins such as n--propyl~
ena, n-but~l~ene,. n-pent-l-ene, n--hex-l enej n-hept-l-ene
and n-oct-l ene, or olefin;.cally unsatura-ted esters such as
C2 C8 alkenyl. C~ - CB c~rboxylic acid esters for example
.:
- 6
-.
~ ,3~3 RIC91
v.inyl aceta~.e anc~ CI~C~ alky]. C3 - C~ al~enoate~; or example
~hyl acJyl.aJ~e~. Copol~yrner; preferably cont.a.irI greater than
~Q weight per cent r more preferahI.y greclter than 60 weicJht
per cent, ~or exarnple ~rea~er than 70 ~eight per cent,
especi.ally ~r~ater ~han 85 ~reig]lt per cent, for e~clmple 95
~o 9$ weicJht per cent, et.hylene, the optimum amount depend;ng
o cour;se on ~he cornonomer employed.
~n~om, block or graft copol~ners may bë employe~, particularly
r~ndom cspol~ners.
O:E speci.al in~erest in the composi.tions of the invention are
b~en~s sE ~he linear ethylene homo or copol~ners with other
homo ~ or c~pclymcrs hlended prior to cross~linking. Examples
o~ ~uitable ~Iomo - or copolymers which may be blended .into
the c~mpositions include therrnoplastic polymers, particularly
other polyethylenes, for example branched low density
pol~ethylcnes especially those having at least 5 more preferably
a~ least 10 lvn~ cha.in branches (e.g. greater than CIO
pre~erably greater than C20) per 103 carbon atoms of the
p~l~ethylen~ chain such as those having on avexage at least
5 more preferably at least 10 especi.all-y at least 15 pendent
methyl gxo~lps per 103 carbon atoms of the polyethylene chai.n
(par-ticularly those polyethy].enes having at least 20 more
preferab].y at leas~ ~.0 branches greater i..n ].ength than C200
per ~erage molecule), and a density at 25C below 0~9~0
.- 7
.
`3 -- -
gm/cm3 for example i.n the :rarl~e 0.910 to ~,940 cJm/cm3, or
linear higll densi~y polye~}ly]elles haviny on avera~e less
than 20 preferabl.y less than 15, :Eor example less than 10,
especiall~r 0.5 to 5, pendent methyl cJroups pe~ 103 carbon
atoms oE -the polyethyleIl2 chain and a density at 25C
greater than 0,940 gm/cm3 for example 0.941 to 0.960 gm/cm3,
otheî pol~olefills for e~ample polypro~ylene, a~d copolymers
for example ethylene/propylene copolymers and EPDM terpolymer.
Further e~:amples of suitable hlend polymers include elastomeric
polymers particularly silicone elastomers as well as copolymers
of ethylene wi.th ethylenically unsaturated a].iphatic esters,
especially such copblymers when substantia:lly ~ree of
halogen-containing subs'cituents. Preferred el.astomerlc
polymers are those e~hibiting a characteristic ru~ber-like
elastic deformabili'ty under the action of comparatively
small stress the m~terial returning substantially to its
undeformed state on the removal of the applied.stressr
particularly those which in the uncross-].inked state havc an
elastic modulus of 30N/mm2 or less, measured at room temperature
in accordance with the method described in AST~ D638 - 72.
The preferred elastomers for use in the present invention
are ethylene/acr~l.ic ester copolymers and ethylene/vinyl
acetate copolymers, especi.all~y those containin~ a~ least 3.6
mo7es of etllylene per 1000 ~rams of polymer. Examp].es o~
suitable e].as',omers include:
;~
~.3~ Rl~]
a) ~n et}lylenc/allcyl acr~late or ethylene/;llJcyl rnc1:.nacry.].clt:e
copolymer, wherein t.h~ al~;~rl cJroup nc~ car:bon
atoms; the proportion of the acrylic ester being about
2.5-8.0 moles o ester groups per kiloyram of ~he
copolymer .
b) ~ terpol~ner o~ ethylene with an alkyl acrylate or
methacrylate wherein the alkyl group has 3.~4 carbon
atoms alld a third copolymeri.zable monomer, which may
~e, for eYam~le one of the ~ollowing:
.
i~ a Cl-C12 a].kyl monoester or diester of a
~utenedioic acid, ~.
ii~ acrylic acid,
iii) methacrylic acid~ ..
: iv) carbon monoxide,
~) acrylonitrile,
vi.) a v nyl ester,
vii) an alkyl acrylate or alkyl me-thacryl.ate, 'che alkyl
group having at least fi.ve carbon atoms; and
viii)maleic anhydride; or
c~ ~thylene/vi.nyl acetate copolymers especially tho~e
containing at least 35~ by weight vinyl acetate.
In the above terpolymer the proportlon of the acry.l.ic ester
ls r~quivalent to about 2.5-8.0 moles of est.er yroups per
kiloyram of the pol~ner, and the proportion of the third
monomer is no hlgher tllan about 10 welght per cent cf tlle
polymer .
RKQl
The e~.ClS~Olne]^ can be a simple copol~ner o~ ethylene with
methyl acryl.~e, eth~l acry]at.e, propy]. acrylate isopropyl
ac:rylat:e, a butyl acry]..lte, methyl mcthacryla~e, ethyl
methacrylate, propyl methacr~:Lclte, isopropy:l methacrylate, a
butyl. metllacry].ate or vinyl acetate. Such copolymers that
are not commereially ava:llab].e can be made by conventional
and well known methods. These copo]ymers preEerably have a
melt index within the ran~e of 0.1-70 at 190C, more preerably
0.5-15 as measured by ASTM method number D-1~38-52T, or the
suhstantially equi.valent method A5TL~ D-1238-73.
The terpolymer o~ el~hylene with an acrylic ester and a third
monomer may contain as the third monomer an ester or half
ester of fumaric aci.d or maleic ac:id J wherein the alcohol
moiety ean be, for e~ample, methyll ethyl, propyl, isopropyl,
various isomers of butyl, pentyl, hexyl, heptyl, octyl,
nonyl, decyl, undecyl, dodecyl and the like~ The third
monomer may also be, among others, a vinyl ester such as,
for exampl.e, vinyl acetate or vinyl butyrate. It can also
be an aerylie ester such asr for example, various isomeric
~orms of pentyl, hexyl~ heptyl, octy]., nonyl, decyl, undesyl,
dodeeyl~ pentadeeyl and oetadecyl aerylate and methaerylates.
It is not practical to use as the third monomer an aery]lc
ester i.n ~mieh the alcohol moiety contains more than 18
earl~on atoms.
-- 10
}~9l
Exoe]l~nL re;~.~.3.l:s !~clve be.~en ol-~t:ained using as l.he e].astome].
componen~ o~ ~hc~ pol.ylner composi-ti.on a terpolymer o~ eth~lerle,
methyl acryla~e and a cure~site monomer comprls.i.ng carbo~yl
gro-~ps availablc .rom Du ~?on-t unc1er the trade name Vamac.
Physical properties and other deJ;ails concerni.ng this material
are to ~e found in a brochure available from Du Pont entitled
"Vamac ethylene/a~rylic Elastomers - A new Class of Heat &
Oi.l Resistant ~ubber" by J.F. ~Iaymon, R.E. Fuller, W.X. Witsiep~
and R.~. Greene under ref-erence ~A-0002, the disclosure of
which i5 incorporated herei.n by reference, correspondirlg
essenticllly to articles appearing in Rubber Age, May 1~76,
~nd De Nederlands Rubberindustrie No. 7177.
Mixtures of any 03-. the above mentioned elastomers with each
~ther or with o-ther.elastomers may be used where appropriate
al~hougll it has been found that the presence 03 hydrocarbon
elastomers has a deleterious effect upon the oil resistance
of the polymer composition and thus these are preferably not
included, or if present, are prefe3:ably incorpordted in an
amount of not more ~han 5% by weight based on the tota].
w~ight of the polymer compositionu
It is be.li.eved to be advantageous for the solubi].i1~ parameter
of the e]astomer to be greater than 9, and, in advanta~20us
cvmposJ.tions according ~o the invention, it i.s further
~referred that the soluhili. ty paramet:ers of tlle polvmeYi.c
componeTlts o the hlend should b~ similar, e.g. Wley w.~11
r,~ PL~
RY~q 1
di.,~er by not more thcln 0~5, preferably by not ~ore tllan
0.25.
For the purposes o~ thi-s 5pec; E.icat-..ion, solu~i.lity parameter
i.s defined a5 that: measl1red by tne method o~ Brandrup ~
I~nergut, Polymer Handbook Chapter 4 page 340 (2nd ~dition)
and is expressed as (cals/cm3)~.
Some types of polymer ma~erials inherently have a soluhility
paramet:er greater than 9 whereas others can have solubil:ity
parameters gr~ater than or less than 9 depend.ing on their
prccis~ che~l].cal composi.cion. Still others, of course, have
solubility parameters which are inherently less than 9.
The cross-linked polymeric compositions of the inventi.on
whicil have be.~n derived from hlends of linear low dens:ity
homo or copolymers with thexmoplastic or elas-tomeric homo -
or copolymers offer ~arious unforeseen advanta~es and are
accordinyly of special interest. Thus reduced hot creep and
hot t-ensic)n se-t ph~nomena are typically exhibited by the
blend compos..tions, paxticularly the blends with other
polyethylenes, considerably facilitating moulding of ~he
compositions. In addition cross-linking may be more readi.l~
achie~red, particu:larly the hlends with other polyet:hylenes
such as branched low den~it~l ~olyetllylenes, fOL e~arnP1e
~ 12 ~
is~
after incorporating from 5 to 50 we:ight per cent of the blend polymer.
l`he blend polymers frequently offer increased thermal ageing and resistance
to hydrocarbon fluids particularly where the solubility paramete~ of the
blend component exceeds 9, for example blends with elastomers such as
ethylene/vinyl acetate.
Preferably the weight ratio of the blended polymeric component
or components to the linear low density ethylene homo - or copolymer in the
composition lies in the range O to 20~ articularly O to l:lS more
preferably O to 0.5 : 1, especially O to 0.2 : 1, for example O to 0.15 : 1
respectively.
The preferred blends have a density at 25C below 0.960 gm/cm3,
especially below 0.940 gmtcm3 with branched low density polyethylenes. In
some cases blends with a density at 25C of below 0.925 gm/cm3 exhibit
particularly interesting properties especially high elongation at break
versus 100% secant modulus at 150C properties.
Particularly interesting linear low density ethylene homo or
copolymers, including blends, are the resins commercially available from
.I. Du Pont de ~emours (Canada), Corruna, Ontario under the trade name
"Sclair" and in particular the resins listed below in Table 1 under type
reference
3~3.~
RK91
Du ~ont~ Scl.~ n~,il y ~,m/cm Ind~lx Exponent
q~y~ r~llc~
8 405 0 ~ 937 2 ~ 26
.].]~-1 0~ 9190~ S0 1~ 40
llW 0. 919O~ J0 lo37
lLS 0. 920 1.40 1.35
. ~
llU 0. 92151~ ~0 1.35
llY 0. 924 5.1 1.26
2107 0. 924 5~ 26
8107 0~ 924 5~ 26
210~Vl V. 92~ 8~ 5 1.26
2109 1 0~ 92410~ 0 ~
2113 ~ 0~ 92429 ~0
211a 0~ 924~ 53~ 0 ~ -
8307 0~ 930 5~0 1~ 2
8305 1 0~ 932 3~0 1.26
44F . 0~ 935 1. 5 1. 67
15B 0~939 0~35 1~69
8506 0~ 9403 ~ 8 1.26
8109 0.92]. 12.0 1.26
~309 0~ 93012 r 0 1.26
2316 Ou930 73~0
8507 0~ 940 5~0 1~ 26
~51~ 0. 940~5 . 0
~91.4 ~ 92~ 50~0
~105 0 ~ 9222 ~ 7
.
~ P P ~
,.. . .
~3~3~ ~Kgl :
E.~amples of linear low density l~olyethylene homo - or ::opolymers
including blends of special interest are further characterised
in Table 2.
TAB I E 2
Du Pont De~ree of Pendant S~.ort No. of double bonds per 103
Sclair CrystallinityMethyl Chain C atoms
~ype % groups branches
~ef per 103 per 103 ---- tennnal pen~ t
C ato~ns C atomsYinylenevinyl methylene
8107UVl 44 7 ~7 ~.23 ~.48 ~.0~
83û7 64 ll ~ll 0.19 0.55 ~.08
83Q5 5~ 9 - 9C2 ~.16 -0.48 Q.07
8105 47 l~ 16C2 0.16 0.46 ~.09
8705 ~g 4 l -2C2 û . 0~ 3 0.~6
~4û5 ~5 7 ~7 --0.1l 0.52 0.07
46 17 17C2 ~.26 o.a.9 o~g
. .,
-~ llW 53 27 ~27 0.23 û.23 ~.12
. . .
- 15 -
~h~'~3
.~'J
~ 3~
For most purposes, it is preferred that the compositions in-
corporate at least 10 weight per cent filler, either reinforc-
ing fillers (e.g. of particle size from 0.01 to 1 micron) or
non~reinforcing fillers (e.g. of particle size from 1 to 120
microns). It is generally found that a higher degree of rein-
forcement is secured by the use of reinforcing fillers such as
high surface area carbon blacks or silicas than would be
obtained with other types of polyethylenes and that usually no
significant detriment to physical properties is observed with
non-reinforcing fillers such as calcium carbonate or thermal
black, as would be observed in other types of polyethylenes.
The compositions of the invention may include other
additives, such as stabilizers, for example W stabilisers
and anti-oxidants, flame retardants, anti-tracking fillers
and pigments, the nature and amounts of additives included
depending naturally on the specific use for which the com
positions are intended.
The compositions of the invention may be produced
in conventional manner e.g. by milling the components in a
Banbury mixer. ~hey may then be processed into shaped articles
e.g. by extrusion or moulding. Shaped articles so produced
also form part of the present invention. When it is proposed
to cross-link the compositions of the invention in the solid
s-tate, e.g. by exposure to ionising radiation, preferably the
compositions are quenched after the hot shaping stage, at least
across the crystalline melting point of the composition. Pre-
ferably quenching rates of at least 5 C/sec, e.g. at least
10/Sec, more preferably at least 20C/sec and, in the case of
- 16 -
thin articles such as films, advantageously at least 100C/sec,
are employed. Quenching may be achieved by contacting the
shaped article with a heat exchange fluid such as water. It
has been found that quenching achieves a decrease in crystal-
linity and thereby an increase in modulus e.g. 2 per cent
secant modulus, in the cross-linked material. Il ~
Cros~-linking preferably takes place at or sub- ~;
sequent to the shaping stage, depending
- 16a ~
~ 3 ~ ~ c~ ~
1~9~-
on l.he manller o~ cros~ ;,.ncJ and the natul-e ~E the shaped
art.icle. It may ~e ef:ectecl by tl~e i.ncorporatj.on of ~rom
0.2 to 5 weiyht per cent of a cross--l.inkiny agent such as a
free radi.cal ini~iator for exarnple an oryani.c perox.ide, such
as dicumyl perox:icle or 2,5-d.i-(~butyl~pero~y) hexane~ alone
or i.n com~ina~ion with a co-eur:ing agent such as a poly
~unctional vinyl or allyl compound, for examp~.e tria].lyl
eyanurate, triallyl isocyanurate or pentaerythritol tetra-
methacrylate. One preferred mocle oE chemically cross-
linklny invol.ved graftin~ a hydrolysable silanP or silane
de~:iva~ives e.cJ. an alkoxysilane such as vinyl trimethoxysilane
to the polyeth,71ene base structure and subsequently hydrolysing
to effect cross-linking by silanol condensation in manner
known per se. Catalysts may be employed to ~acili~ate
silanol condensation e.y. organotin catalysts such as
dibutyltindilaurate.
. .
Alternatl~ely, cross-linking may be effected by exposure to
high encr~y irra~iation such as an electron beam or y-rays.
Dosages i.n the range 2 to 80 Mrads, preferably 5 to 50
~rads r e.g. 8 to 20 Mrads are appropriate r For the purposes
of cross-linkincf by irradiation, preferably Erom 0.2 to 5
~7eiyht per cent or a pro-rad SllCh as a poly-functional vinyl
0~ allyl compo~ d/ for example triallyl cyanurate or triallyl
isocyanura~e are!incorporated i.nto the compositi.on prior to
~lle c.oss-linkln~ ~.reatment.
: ~- .t7
~ $~ 91
The above mentioned -.on-cl^oss l~.nked compositi.ons incorporatj.ny
an ecc~i~e ~llount of a cross-lin~in~J a(~ent or pio~:a~l are
new ard also form parl~ o the present: :inventlon.
The composi.lions oE the present inventi.on are particu.l.clrly
suitable for ~he production of dimensioncllly recovera~hle
articies that is to say articlesJ ~he dimensional coniyurati.o.
v which may be made substantially to chanye wh~n sub~ected
to an ~ppropriate ~.rea~menc. Of particular interest are - -
heat recoverable articles the dlmensi.onal confiyuration of
which may be made substantially to chanc~e when subjected to
hea.t ~crea~nent. ~leat recoverable articles may be produced
by deorm.ing a dimensiollally heat stable conf~guration to a
heat unstable con~iguxation in whi.ch case the articla tends
to assume t.he original heat stable confi~uration on the
application of heat alone. As is made clear in US Patent
No. 2 027 962 however the orlginal dimensionally hed C
stable con~iguration may be a transient form in a continuous
process in which ~or e~ample an extruded tube i.s expanded
whilst hot to a di.mensionally heat-unstahle form~ Alternatively
a preformed dimensionally heat stable ar-cicle may be deforlned
t~ a dimerlsional].y heat-~nstaDle form in a separate staye
In the pxoduction of di.mensior)ally recoverable articles the
compositior; may be c~oss-li.nked at any stage in the production
process t}lat will accomplish the desired climensional recovera}~ility
~ 18
~ 3~ K91.
e.y. prior to l:he shap:in~ oE the dl.mensiollal.l.y ~nstable
confl(~uration. One manner o:E producin~ a heat recovcrable
article comp.rises shaping thc pre-cross-linked composit.ion
into the desired heat stable forln, subsecluently cxoss-
lin~incJ the composition, heating the article to a temperature
above the crystalline melting point of the composit.ion,
deforming the artlcle and cooling the article whilst in the
deformed state so that the deformed shape of the artlcle is
retai.ned. In use, since the deformed state of the article is
hea~ unstable, application of heat will cause the article to
assume its original heat stable shape. Such di.mensionally
recoverable articles may be employed as sleeves for cove~.ng
and sealing splices and terminations in electri.cal conductors,
for environmentally sealing damaged regions or joints in
utili~y supply systems, e.g. gas or water pipes, di.strict
heating systems, ventilation and heatlng ducts and conduits
Oî pipes carrying domestic or industrial ef~luent.
The compositions of the present invention are also particularly
suitable for the produc-t.ion of insulation materiai., particularly
jacketing materiais for wi.res and cables. Such materials
may be ~roduced in conventional manner, for example by
extrusion onto conductors to form wires or onto wires to
form cables with simultaneous or subse~uent cross-linking.
1~ ~
RK9~
I'hey ~re also usefuL as lli~h volta~e insulation i.ncQrporating
an anti-tracki.ll~ fi.~.~er sucll as alumina trih~dr~te especially
to ~Ich:i.eve all ini.ti.al ~rack,ng vo].ta~e zccorcli.llcJ to I~STM
D2303 o ~re.lter tharl ~.5 ]cV ancl/or when includin~ as a
bl.enc1 componcll~, in the l~.ne~.r low density e-thylene homo -
or copolylncr, silicone el.as-~omers or ethylene copol~mers.
Suitable an~i.-tracking ~illers and blendahle silicone elastomers
and ethy~.ene copolymers are described by R.J. Penneck and
.J.T. Cl~bburn in l'Heat Shrin~ab].e Cable Terminati.on System
for High Voltage Cables" Proc. 10th Electrical Insulation
Con~erence, Chicago USA September 20 - 23 1971, page 292 -
297 and in U~ "Patent Nos. 1,303,43~ and 1,137,952 the
contents of which are incorpor~ted herein by reEerence.
Furthermore, by the incorporation o;E app~opriate illers,
e.g. carbon black, the compositions may be rendered se~
. eondueting or corlducting and in such form are particularly
.~ suitable ~s semi conducti~e Oï conductive polymers for use
in electxical heating ma-terials, e.g. in the form of heating
tapes, stri.ps or pane].s, in the elec-trical screening of
electrical power cables or in the electrical stress relief
of splices and termination in high voltage electric cables.
~nother important app~.ication of the cross linked compositions
o~ the invention is in the produc~ion of semi~permeable
mem}.)ralles. Yor such use the composi~.ions of the invention
are produced in ~ilm ~orm preferably with a film thickness
o less 1han l.V~m, mo-e prefera~ly in the ran~e 0.001 to
0.5 mm. The ilm is a~.sc) prefcrably gra~ed with monomers
des;.gne~ ~o moclifv ~:ile selecl.-ivity of thc membr2ne to ~clr~
~0
!
RI~'31
the perme~.~?~li.t~ t~he.r.eo:~` to val:ious iOlliC s~ecies . ~xaml?lc-'s
o:E grai~t:able Inonomers :i.rlclude olef illica.l~ly unsatura-ted acicls
or deriva~-.ives thereof, parti.cularly met.h;-lcryllc and acryli.c
~eids. .Sllch graft;.ncJ may be accompli.shed in known manner by
sub-jectin~ the film to hi~h energy radiatio}l, e.s. to an
elect3^0n heam, U.V. or y-radiation in the presence of the
monomeric species to be cJrafted. The film may be in non-
cross lin};ed form prior to exposure to the xadiation such
that the radiation treatment serves also to cross-link the
eomposition. Preferably, however, the fi.lm is cross-li.nked
prior to c~rafting to achieve bet-ter ion selectivity
~lembranes produceæ in accordance ~7ith the inventi.on are
particu:Larl~ useful as separators in electrochcrnica]. processes,
for example as separators in electrolytic cells and particularly
ba-~teries such as Ag/Znr Hg/æn/ Ni/Cd and Ni/Zn cells. Such
mem~ranes possess several advantac~es such as longer service
li~e in electroli-tic cell environrnents, irnproved wet strength
and lower swelLing tendency than convent.ional. polyethylene
melr,brane s .
The compositi.ons are particularly useful in any of the above
applications in view of their notable ability to accept
loadings of a~ditl~Tes, particularly fillers, e.g. 10 weight
per cent or more, without detriment to the properti.es of the
eomposi.t-.on, theLr notahle mechani.cal properties in cross-
3~ R~
linked form, e.CJ, elonga~i.on at breakr hot modulus, abrasionresis~clnce c~.nd t_nsi.le s~rength, and/or theil chemical
res.istance, e.g. to solvents, particularly orcJanic sol.vents
such a~: o.il and pel:roleum jelly.
The in~rention is i.llustrated by the followillg examples
wherein par~s and percenta~es are by weight and ternperatures
are in C.
EX~MPLE 1 - Chemically cross-linked systems
_ _
Various cross-linked compositions are produced by mi.lling
the ingl-edients of~each Eormulation (see belcw) togetller on
a ~win roll mill to form a hide. The hides are pressed in~o
unifo~n p].aques ~na cured at 200C for 10 minutes. The
ingredi.ents of the various formulations emp'oyed are set out
. below: -
;
- ~2
,~ ' ' .
~3~ 3~ R~
FORM _~'I'ION l
Sclair~aO5 61.75
Wh:it-:in~J G'100 30.00
(yroulld calc:ium carbonate)
~.illC s~eara~e 1.50
Macflite D 1.50
(hi~h surface area magneslum
oxide com!nercia].ly availab]e
~rom Merc]c Chemlcals Inc)
Irganox~Y1010 1.25
pentearithritol tetra~is -
3-(3,5 ai-tert~but.yl-4-nydro~y
phenyl)~?ropionate, antioxidant
commerci.ally availab1e from
~iba Geigy A..G.
Tr.ia:Llyl cyanurate 0.20
Varox~ 0.80
2~5~dimethyl--2,5--di-(ter-t-
~utyl-peroxy)hexane
.
FOPU~U A~ ON 2 %
Sclai~ 8105 55
Elvax ~50 15
~an ethylene/vinyl acetate
copo]ymer containing 25% vinyl
ac~tate commercially available
from Du Pont de Nemours)
Whitincj G400 21.5
Maglite ~ 1.5
Vulcan~9 (a ~q~O~ bl~) 2 . 7
Irgano~ 1010 1.25
~inc stearate 1.75
Tr:ia11.yl cyanurclte ; 0.30
Varo~ 1.00
.
~ I ,..... , ~"
.
- - i
~3~3~ ,
FORMULATION 3 /0
_
Sclair 8305 55
Elvax 360 15
Whiting G400 21.5
Maglite D 1.5
Vulcan 9 2.7
Irganox 1010 1.25
Zinc stearate 1.75
Triallyl cyanurate 0.30
Varox 0.80
The tensile properties of the resultant plaques are set out
below and determined by standard test methods:
Formulation Formulation Formulation
Tensile Property l 2 3
1 0CP/o Secant Modulus 150~
(~g/c~ ) S.6 4.8 ~8
Tensile strength 15~C
(kg/cm ) 7.5 6.0 8.5
Elongation at break 150C
(%) ~450 ~420 ~450
Tensile strength 23 C 2
(kg/cm ) 220 230 214
Elongation at break 23
(%) >500 ~500 ~00 ~.
:
- 24 -
~'
3~
RK9L
~ .[,E 2 ~ ^o~ d ~ mc
The followlrl~ E~rmulations ~ and B were melt exkruded at
19S at ~hicll -Lempel-ature ~ra~tincJ o the silaIIe onto the
polyetl~lene base structure is init:i.ated via the decom~ositior
o~ the peroxide.
FOl~~UI,~TIOM A
part.s Sclair 8105
~ ,~ a r /~
pal-~s ~YI~I-I 3 (trade ~ a branched low density
polyethylene available from Union Carbide)
~ parts Vir-yltrimethoxysilane
0.1 p~rts Vicu.nyl peroxide
FoRMl;lr?~trIo-N B
100 parts VYNH 3
2 parts Vinyltrimetho~ysilane
0.2 parts Dicum~1 peroxide
The re~ultiny material was cooled and pelletised.
The following fo:-mulation C was also melt extruded and
p~lletised:
FORMULAT~:O~J C
100 parts ~YNH-3
1 part Vi.butyltindilaurate
~ arK
paxts Salltanox R (tracle ~ n ant:ioxidant c~vailable
from Monsallto LL-d)
_. ~ r~
3~
95 parts of pelletised formulation A were blended with 5
parts of pelletised formulation C and injection moulded into
short tube sections. The resulting tube sections were
allowed to cool, and then immersed in water at 80 for 24
hours, The procedure was repeated for a blend of formulations
B and C.
m e materials produced form formulation A were found to
possess substantially superior elongation at 150 than those
produced from formulation B.
EXAMPLE 3 - Radlation cross-linked sy~stems
Pla~ues are made up in analogous manner to that described in
Example 1 from commercial grade Sclair linear low density
polyethylenes (11W, 11D, 8105, 8305 and 8405) in the absence
of any additives other than any already present in the
commercial grade product. Instead of the heat cure step of
Example 1, the plaques are exposed to electron beaming at
radiation dosages of 10, 15, 20 and 25 Mrads. Thereafter, the
various plaques are examined to determine their 100% secant
modulus at 150. For comparison purposes, the procedure was
repeated with the following commercially available branched
low density polyethylenes i.e. DY~H-3, PN220 (BXL) and CARLO~A
30-002BA (Shell). The results are set out graphically in
Figures 1 and 2 and define two envelopes, one characteristic
of the linear low density polyethylenes and the other charac-
teristic of the branched low density polyethylenes. These
figures demonstrate the greater ability of the linear low
* trade mark - 26 -
~L~.3~
density polyethylenes -to crosslink at any given radiation
dosage khan the branched low density polyethylenes (E'igure 1)
and th~ superior hot properties of the crosslinked linear low
density polyethylenes than the crosslinked conventional
branched low density polyethylenes (Figure 2~. In Figures
1 and 2 the units for th~ 100% secant modulus are Mæa~
~me~ '
m e procedure of Example 3 is repeated incorporating 0.2% of
triallyl cyanurate as prorad in each product prior to cross-
linking. Re~ults are slightly improved o~er those obtained
in Example 3.
~e~
In order to demonstrate how ethylene homo and copolymers
employed in the compositions of the invention are distinguished
from branched low density polyethylenes, accompanying Figure
3 shows a plot of ~T (Tm ~ Tc) versus density at 25C values
for the linear low density Dupont Sclair resins 11W1, 81052,
81073, 83074, 83055 and 84056 against commercially available
branched low density polymers DY~H-37 (Union Carbide), P~ 2208
(BXL) Carlona 25-002GA9 (Shell), Carlona 30-002BA~O (Shell),
EXXON LT-117 1 ~EXXON) and Gulf 2604M (Gulf Oil), the
materials being represented on the Figure by the superscripts
1 to 12.
Example 3 is repeated at radiation dosages of 10, 15 and 20
trade mark - 27 -
~3~3~
Mrads on plaques made up from blends of commercial grade
Sclair linear low density polyethylenes with varying amoun-ts
of a conventional branched low density polyethylene and the
100% secant modulus at 150C determined for each plaque.
The results are shown graphically in Figure 4 indicating a
synergistic effect in 100% secant modulus properties at 150
for cross-linked mixtures of linear and branched low density .
polyethylenes. In Figure 4 the 10~/o secant modulus at 150C
is given in MPa.
EXAMPLE 7 - Heat Shrinkable Sleeve
A formulation of the following composition: ¦
Sclair 8405 62.55 parts
Whiting G400 30.00 parts
Vulcan 9 3.00 parts
Zinc stearate 1.50 parts
Maglite D 1.50 parts
Irganox 1010 1.25 parts
and Triallyl cyanurate 0.20 parts
is formed into tubing ln a laboratory ex~ruder under the
following operating conditions~
barrel temperature zone 1 120-130
barrel temperature zone 2 130-140
die temperature 140-150
die diameter 25+ lmm
wail thickness 1~ O.Ol mm
haul off speed 0.4 metres/minute
- 28 -
The extruded tubinK is subjected to a dosage of 10 Mrads electron beaming
in an electron accelerator and then cut into 20cm lengths. Each length is
expanded after heating, on a former to give 500% expansion as measured by
change in wall thickness. The resulting heat shrinkable product is suitable
for shrinking onto a substrate of from 26 to 120mm diameter without danger
of splitting.
The example is repeated with the additional stag~ of quenching
the extruded tube by immersion in water as soon as it leaves the extruder
thereby achieving an increase in modulus of the material after cross-linking.
xample 8 - Heat Shrinkable Sleeve
The procedure of Example 7 is repeated employing the following formulation.
Parts
Sclair 8105 39.98
Commercially available ethylene/ 15.99
vinyl acetate copolymer
containing 25% vinyl acetate melt
flow index 2
Commercially available branched 19.49
low density polyethylene ~ density
at 25C 0.918 and melt flow index
0.1
G~00 Whiting 13.00
Maglite D 1.5
Zinc Stearate 1.0
Irganox 1010 1.25
Vulcan 9 6.49
Triallyl cyanurate 0.30
Varox 1.00
100 . 00
- 29 -
- :,
.:
.
~ ~ ~ 3 RK91
l'he slecvc so l?t:oduc~od could he e~:panclec~ t:o yreater than
600~ tllout e~ ltillg split se~llsit:iv:i.ty and in ad~it.ion an
e~cellcnt- balallce o proper-ti.cs is achi.eved. Typi.cal
~:L^o~?~ arc set out helow.
150C Pro~?er~it~s
lOO~o secant modulus 0.35 - 0.40 MPa
Tens.ile strength O.g5 MPa
Elongatlon >~30 %
Room Tel~erat,~lre l'roperties
Tensile strength 24.5 MPa
Elongation 590 %
2~ Secant, modulus 130.0 MPa
-40 ~ ,ertles
Tensile ~t,rength ' 29.0 ~Pa
Elongation 365 %
eat, At~eint
L68 houl^s_ t 150C
- Tensi.le strength 22.4 MPa
Elongation 525
., .
......
Solvent Resistance
168 hours Petroleum Jélly 70C
Tensile streng~h 1CJ~5 MPa
E~ongation 532 %
E_ c~ri al Prop_~ties
~lectrical strenc~th 161 Kv~cm
Permat,lvit~ 3.L4
Volume Resistivity 7.7 x 1013ohm cm
Wate~ ak.e 0.21~
~ecific Gravity 1.057 g/cm3
- 30
f~ K91.
~ MI~ 9 - ';eJni-corlcll:lc~ ive ~leat: _h in]~a~]e S_eeve
The procedure of J',xamp~.e 7 .i.s repeated employing'a formulatlor
of ~the following compos:itioll
Scla:ir 8105 61.55 parts
Thermax (trade ~e a thermal.30.00 part-s
carbon b:Lack availcLble rom
VanderbiJ.t I.td)
Zinc stearc~-te 1.50 parts
Magl.i~e D lo50 parts
Irganox 1010 1~25 parts
q'r.iallyl cyanurate 0.20 parts
The resultillg semi-conductive heat shrinkable tube may be
em.ployed in the stress gracling o the termination in a
screened h.igh voltage cable.
EXAMPLE lo _- Conducti.ve Heat Shrinkable Sleeve
'~ The pxocedure of Example 7 is xepeated employing the following
formulation ,
Sclair 8105 51.70
Comrilet-cially availabl.e eth~lene/ 17.25
vinyl ace-tate copolyrner contai.ni.ng
25% vinyl acetate - melt flow index
w~ r ~t
Ketjen EC (trade ~- a conductive 17.00
carbon black avaiIable from AKZ0 I.td)
The~ma~ 6.65
.
- 31
f '?3 f ~
R1~91
Z inc .stearc;it 2 '. OQ
Ma~li.te D 1~50
Ayeri.te resin D 1.50
T.r~ allyl cyan~lrate 0. '10
ma~,Y
Lupero~ 130 (trade ~ ~ a peroxide 1.00
available from l,u~erco)
head fumarate _.1.00
100 . 00
The conductive sleeve so produced possesses an excellent
balance of properfies, allowing its use as a screen or
elec-tr~cal cables, typical properties being set out below
Tensile strength (MPa~ 19.57
: . Elongation (%) 325
150C ' ,
.. . ~ .
Tensile streng~h ~MPa) 2.3
Elongation (%) 365
100~ secant modulus (MPa~ 0.8
Heat- Shoc~ : 4;hrs @ 200C
EloncJation (%) 275
Heat ac3einc~ 7 days @ 150C
E;.lonc~aticn 1%) 225
Solvent Reslslance : 7 days
___ _ .__ _
Trans~ormer Oil
E].o~ya tiOIl ( % ) ~ 7 0
j ~ 32 ~-
.
RK9.l
~)ecific Grav.i.ty 1.086
Volume 1~esis-tivi-ty ohm cm 6.0
__ _ __ __. __
EXAMI~I,E 1~ _ _ lliqh Voltaqe A_t~- trtl ckin~ Sleeve
The procedure o~ ample 7 is repeated ~mploying -the following
hi~h volta~e anti~tracking insulation ~ormulations:
Formulation 1 Formulation 2
Component Parts Parts
__ . __ __
Sclair 8105 23~10
DPD 6169 (~rade ~ ~ 22.73 22.73
~n et.hyleIIe/e~hyl acrylate
copolymer available from
UYIion ~,arbl.le )
Sllastic~437 (Silicone ~elastomer 22.73 22.73
availab~.e from Dow ~ornin~)
A~nina trihydrate 24.99 24.99
Ferric oxide ' 3.79 3.79
~gerite Resin D ~ 1.52 1.52
Triallyl cyanurate 0.76 0.60
2rS~bis~tert-butyl-peroxy-2,5- 0.76 0.55
dimethyl heY~yne
DYNH~3 22.73 ~-
.'
.... --- - " .
~ ~R~ ~ ~ 3~
,
.
~' .
'
3¢~
The sleeves so produc ~ were found to have the following
properties.
Formulation 1 Formulation 2
Tansile stren~th 23 (MPa~ 9.48 9.7
Elongation a~ break 23 (%~ 425 , 482
10~/o secant modulus 150C ~MPa~ 0.62 0~67
Elongation a~ break 150 (%~ 189 299
Tensile strength 150 (MPa~ 1~16 1.55
Failure time (mins~ according >200 > 200
to ASTM D 2303 involving
progressive increase of stress
starting at 2~5 kV with
increment~ of 0.25 kV~hour and .
determination of the time to
failure
As will be ohserved, the sleeve produced ~rom the linear low
density polyethylene (Formulation 2~ is significantly superior
in all its physical propertie~ particularly elongation at
break at 150, to that produced ~rom the branched low density
polyethylene (Formulation 1~ whilst retaining the high anti-
tracking property according to ASTM D 2303u
EXAMPLE 12 Wire Jacket
A formulation having the composition:
Sclair 8405 74.5 parts
Timinox (antimony trioxide~ 8.0 parts
Chlorowax (Hoechst)16.0 parts
Agerite Resin D (Vanderbilt) 1.5 parts
(a commercially available antioxi-
dant~
* trade mark ~ 34 ~
~3~
RK91
was ex~rucled onto a he~tecl copper conductor (110C) to yield
a -iac~e~ }lavincJ excelle~nt: insulation characteristics and
particulclrly good mecllallical p~opel^t:ies e.y~ hi~h abrclsion
rec,:is-~ance.
EXAMPLE 13 -- 5emi-permeable membrane
Sclair llD was extruded as a film 0.025 mm thick under the
~ollo~A7i.llg extrusion conditions:
one 1 140
Zone 2 165
Zone 3 175C'
Die I ' 175
Blow up ratio 2.5:1
-
~'he resulting film is immersed in a solution comprisiny by
volume 55O benzene, ,5% carbon,tetrachloride and 40% acrylic
acid and irradiated with y~radiation to a dosage Ot- O, 5
Mrads at a dosaye rate of 0.05 Mrads per hour. ~he film is
washed with a 40% aqueous solution of potassium hydroxide.
The resulting film i.5 emmlnently suitable for use as a
bai'ter~ separator ha~iny all areal resistivity in 40,; aqueous
potassium hydro~id~ of 0.1 to 0.2 ohm/cm2 and excellent
mechanical properti~s, for example tensile s~renyth.
- 35
~L~
RK91
EX~ TlrJ ~ t)~ c.~ . E3~ r~
Th~. ~ollow.i.ng cc~mposi~.;.on~ were blet-lde~d employi.ncJ a 1.aboratory
P,allhur~ i.nt.c~J^ncll. mi.xer.
Vamac N3.23 (Trade name ~ an ethyl.erie/ 30
methyl acrylclte elastQmer ava.i.].able from
L~upc,nt and having a soluhi.lity parame-t:er
o~ 9.1)
Carbvn black
Antimony trioY~ide 6
Dec~ahromodiphenylether 12
Cxodami.ne II-~T (Trade ~ a release 0.37
a~en~ avai.lable from (Crode Ltd)
I.rganox 1010 0.375
Triallyl cyanu.rak.e
WI~Lting G400 16
Sclair resi.n 30
.
The Sclair resin, Vàmac N123 and Irganox 1010 were loaded
inko the mixer and ~nixed at room temQerature ~or 1 minuteO
The carbon black, alltimony trioxide, deca~romod.iphe.nylether
~nd c~].cium carbona~e were then added and ~.ixed unt:i.l temperature
of the mix .ro~e to 1~0. Crodamine IHl~ and '~ri.allyl cyailurate
3G
~ 3'~ RK91
___
were the~n intrc)duced and mixed i.n fox ~5 seconds. This mi.x
was thell put on-to a mi.l]. and sheeted off. Compression
mo~l.cl.ecl plaqlles wert? maclc l-rom the sheetecl matc!rial and
irradiated with an elect:ron ~eam to a dosage oE 12 ~rads.
The plaqucs were tested for heat shock resistance (4 hours
at 200C) and for resisttance to l-,STM Oil No. 2 and diesel
oil by immersion i.n the fluids for 24 hours at 90. The
resu:Lts are set out below. As a coMparison the sclair resin
is replaced by DYNH-3.
.
. ' , , ' ' ' ' ,
.. . \ ~
37 -
. ` .
. ~
3~
~a, r-l
t~C) r~ o In ~ ~l
Q) d~ t~ r--lt`~ t~
Q~ ! "
r~ r~
f~ ___..____ _~ __
r~ n
~ :~' O ~- ln ~ t~o ~D
a) ~ ,_
''~ rS
~____ .___ _ ____ _
r~O
1~ m o In O o In O
tn O t~ ~fl r-l ~I r-l n ~s~
a) o ~ ~ t~ r~
.,~ ~I O ~
~ ~J ~ o\o
~td __ __ __~_
5~ ~1 ~--
~, ~ ~ ~
O ~ f~
~ d~ h ~~ r,~ t~ I_
ri tn tO r; O r-lt) O r~
a~ .In ~ r-l r-lr~~ -1
P~ ~1 r~ , ,
rS ~ td,
~ '
. Co___._ ~
t~ o o O O m ~n
U~ ~\ o\, r-l ~D t~ n c~
~r-l r-l~t~ t77 ~ t~)
P-! ~ _ ~
PiO~n ~ .
r-l t~ a tY- o In L~ ~D
~r-l tJ~ 'tl~ 7
tn
,t~ r~ ~r-~ r~ r-l r-l
tn .
~ .
._~ _
l~or~ O t~
. I ~r~ 1.') t~lr~) r~ ~ ~
r lm ~t~ ~ ~ ~i~ .
)~I-) O O O O O ~r)
,r, l ____ ___ _ _
rl X
,1 1) al t- t- ~ ~1
U) o ~ n r.~lr~
- 3~ -~
