Note: Descriptions are shown in the official language in which they were submitted.
2 1 ~ 3 ~ 9 ~
67487-458
ISGLATION COMPOSITIONS IN HUMIDITY RETICULATED POLYETHYLENE (XLPE)
WITH COMTRACTION REDUCED ~T 130C,
FOR USE IN LOW TENSION POWER CABLES
The current inventlon refers to an electrlc cable,
lsolated wlth composltlons o~ low denslty polyethylene, whlch are
humldlty retlculate. More preclsely, lt refers to the appllcatlon
of composltlons wlth a low denslty polyethylene base, and whlch
are humldlty retlculate for lsolatlng and coverlng cables. The
process ls known as "SIOPLAS". The commercial processes for
obtalnlng the retlculate polyethylene ln the lndustry of cables
are baslcally the followlng. The oldest one consists ln applylng
addltlves to the polyethylene wlth organlc peroxldes, wlth an
actlvatlng temperature above the temperature for softenlng the
polyethylene used. These composltes are applled ln the case of
cables manufactured through an extruslon process followed by a
thermo-chemlcal retlculatlon process slmultaneously wlth the
instant heatlng of the lsolated cable above the peroxlde actlva-
tlng temperature, for lnstance, through saturated vapor heatlng or
through radlant heat produced by electrlc reslstances, followed by
~0 a process correspondlng to water coollng. In both cases, the
process ls done under pressure, slnce the decomposltlon gases
generated by the chemlcal reactlons cause the exlstence of bubbles
ln the extruded lsolatlon. Thls process ls stlll wldely used for
the productlon of medlum/hlgh tenslon cables, because lt ls the
only way to obtaln large extruded and retlculated lsolatlon
sectlons wlthout empty spots. Thls process requlres hlgh cost
lndustrlal lnstallatlons.
., , . . . , . , . . . ., . , . ~ ~, . .......... . . . . .. .
. ~ . . .. - .. ..
2103896
67487-458
Another process for obtalnlng retlculate polyethylene
isolatlon ls the radlatlon by means of electron beams or sources
o gamma radlatlon. Through thls process, the cable ls lsolated
by means of a normal extruslon process that may be applled to
thermoplastlc polyethylene, followed by a retlculatlon process,
and ln a subsequent phase, by means of hlgh energy electron beam
radlatlon or gamma radlatlon sources. In thls case the process ls
malnly used for cables wlth a small extruded section, since the
penetratlon capaclty of the electrons ls llmlted. Both processes,
the electronlc radlatlon and gamma sources, require hlgh cost
lnstallatlons, malnly because of special protectlon needed for the
operator and for the envlronment. The productlon speed of cables
ls llmlted by the amount of energy that these sources can llberate
and by the amount of material (lsolatlon) to be retlculated.
These processes are ùsually lndlcated and applled to speclal
cables.
Another process ls the chemlcal retlculatlon done by
means of humldlty. In thls process, an organo-sllane that can be
hydrolysed ls lntroduced to the polyethylene molecule whlch stlll
malntalns lts thermoplastlc characterlstlcs, belng applled on the
cable by means of a usual extruslon that can be applled to the
thermoplastlc polyethylene, where the extruslon speed ls only
llmlted by the extruslon and the materlal characterlstlcs. The
polyethylene retlculatlon ln the cable occurs ln the reel, depend-
lng on the materlal ln the envlronmental temperature and humldlty
condltlons or by exposlng the reel to a "sauna" type envlronment.
~;3~9g
67487-4S8
Thls ls a low cost process for the productlon of low
tenslon cables, slnce lt only requlres usual process equlpment for
thez-moplastlc materlals. And, above all, lt ls advantageous for
the lsolatlon of conductors whlch have a non-round sectlon, as,
for lnstance, sector conductors (shape of a shell), whlch are pre-
vio~lsly twlsted. Thls process ls not advantageous for the produc-
tlon of medlum/hlgh tenslon cables, slnce the dlffuslon of humldl-
ty through large extruded sectlons ls slow and the humldlty ls one
of the factors for the formatlon of arborescence ln polyethylene
that are under electrlc "stress" of hlgh gradlent.
Thls last process for obtalnlng retlculated polyethylene
as described above ls, nowadays, wldely used by the manufacturers
of cables, malnly as lsolatlon of power cables for low tenslon.
The process i8 widely mastered by the manufacturers of cables,
with at least t~o ways of obtalning the composlte for extruslon.
a) Composltes wlth organo-sllane that ls prevlousl~
lnserted lnto the polyethylene are commercially avallable or can
be prepared locally by the manufacturer of cables. Here, two
families of composites are identified~
a.l) Polyethylene wlth lnserted organo-silane
applled to commerclal polyethylene (thls process may be
done by any thermoplastlc processor that has adequate
equlpment);
a.2) Polyethylene wlth organo-sllane that is co-
polymerized during the ethylene polymerlzation process
(obvlously, this process is only known to the
:. . . . :
, . : :-
210`~896
67487-458
petrochemlcal lndustry whlch ls lnvolved ln the
productlon of polyethylene).
b) Composltes wlth the organo-silane lnserted durlng
the cable extruslon process. Usually, thls process ls known by
the cable manufacturers. The varlatlons for this process are
b.l) Humectatlon of the granules wlth organo-sllane
and peroxlde lmmedlately before the extruslon;
b.2) Dosage and dlrect in~ection of the organo-
sllane and peroxlde in the extrudlng material (Monosil
Process);
b.3) Dosage and direct in~ectlon of the organo-
silane and peroxide through "CTN" (Cavity Transfer
Mlxer), connected to the head of the extruding material,
known as Sllanox Process
The reticulation process of the polyethylene through
humldlty, as descrlbed above, has been widely accepted for the
manufacture of power cables for low tension in relatlon to the
other processes, due, malnly, to the cost savlng aspect of the
process, that ls, the larger productlvlty, less consumptlon of
energy, less lnvestment. On the other hand, the humidlty reticu-
lation process presents technical advantages for the applicatlon
process. The most lmportant ones are the posslbllity of extrusion
for any conductor proflle and the possibillty of embossing during
the extruslon.
The extruslon processes commonly used for isolating
conductors differ according to the type of tools used for the
formatlon of isolatlon ln the conductor. The keywords used to
.... ,, . . ~ . . ~ . -- - - , - - - - -
.. : . . . ~ . . .. . .
2 ~ 9 ~
67487-458
dlffer the processes are "Extruslon under Pressure", "Extruslon
under Seml-tubes" and "Extruslon under tubes". For the "Extrusion
under Pressure", the tools used have, approxlmatelyl the flnal
isolatlon dlmenslons ~the polyethylene ls placed over the conduc-
tor wlthout stretching); for the "Extruslon under Seml-tubes", the
tools are sllghtly blgger than the dlmenslons of lsolatlon and
they are generally used when the composlte tends to flow backwards
by the male; and for the "Extruslon under tubes", the male and
female are, generally, much blgger than the isolatlon dlmenslon of
~he conductor, and they are used when the proflle of the conductor
ls not round, which makes lt lmposslble to use tlght tools or ln
the case of composites applled on very thln materlals (typlcal
example, FEP "Teflon"). In thls case, the flnal shape of the
lsolation ls obtalned by stretchlng the tube up to the flnal dl-
mension.
A problem that ls always present in the extruslon of
thermoplastlc materlals are the resldual tenslons left by the
conformatlon process, slnce the thermoplastlc materlals are poly-
merlc ~macro-molecules) whlch, ln the extrusion process, are
Z0 squeezed and stretched. Usually, the polymerlc materlals requlre
a relatlvely long tlme for relaxlng the tenslons stored durlng the
passage through the tools. SInce the lsolatlon ls rapldly cooled,
to obtaln productlvlty and to avold deformltles ln the reel, a
large part of the tenslons ls stored.
The power cables for low tenslon are covered by lnter-
national speclflcatlons, such as IEC 502183), NBR ABNT Pro~ect
3.20.3-026~90). Under the servlce condltlons, these cables are
: ., :, :, . ~ .. . .. .
2~5896
67487-458
classlfied for contlnuous servlce at a 90C temperature (ln the
conductor), and at an overload process, durlng a short perlod of
tlme, up to 130C, and under a short-clrcuit condltion up to
250C.
The retlculated polyethylene obtalned by the "Sloplas"
process, when heated above lts softenlng temperature (95 to
115C), tends to relax the tenslons left by the extruslon process,
creatlng a contractlon, especlally ln the ends of the cable expos-
lng the conductor. --
To prevent accldents created by the contractlon agalnst
the installatlons, the rules descrlbed above lnclude a quallflca-
tlon test. Such a test conslsts in cuttlrlg 200mm from the central
part of a sample that has at least 1200mm of the lsolated cable,
then exposlng thls sample to heat ~or 1 hour at 130C ln an alr
stove, and measuring the lsolation contractlon at both ends The
value found mu~t not exceed 4~.
In practice, what was notlced was that for the poly-
ethylene that were retlculated through the "Tu~e Extruded
Sloplas", the contractlon can reach 20% causlng serlous lncon-
veniences for the use of the cable.
~; The current lnventlon has the purpose of solvlng the
current technlcal problems, through the modlflcatlon of the
polyethylene that are usually employed ln the "Sloplas" process,
wlth the addltlon of polypropylene (PP). The polypropylene has a
softenlng temperature between 155 up to 165C, whlch guarantees,
up to 130C, the dlmenslonal stablllty of the extruded materlal.
::
2~ ~S~96
~7487-458
The mlxture of the PP with the low density polyethylene
(LDI?E) or linear low denslty polyethylene (LLDPE) or co-polymeric
pol~yethylene of vlnyl ethylene acetate (EVA) ln an adequate con-
centratlon ls the solutlon for the contractlon problem.
The low denslty polyethylene (LDPE) ls a homopolymerlc
or co-polymerlc vlnyl acetate (VA) or methylacrylate (MA) up to
10%. The llnear low denslty polyethylene (LLDPE) ls a butene or
hexene co-polymerlc. The polypropylene ls a propylene-ethylene
co-polymerlc wlth a co-monomerous level (ethylene) over 6%, belng
used ln a preferred proportlon between 15 and 25%.
Below ls the descrlptlon of experlmental results obtaln- -
ed wlth composltlons of the known technlque and of the current
inventlon.
Exàmples 1, 2, 3 (wlth contractlon):
Usual compo~ltlon~ wlth polyethylene ba~e whlch can be retlculated
through the "Sloplas" proces~.
Ingredient Example 1 Example 2 Example 3
LDPE (MFI 1,3) 100
LDPE (Co-polymerlc 9% Vlnyl
Acetate) MFI 4 - - 100
LLDPE (MFI 4) - 100
Antl-oxldatlng 0.2 0.2 0.2
VIMO 1.5 1.5 1.5
Cumlla
Peroxlde (96-100%~ 0.12 0.12 0.12
DBTL 0.05 0.05 0.05
NOTESs VIMO (Vlnyl Trlmethoxy Sllane), Organo Sllane wlth three
methoxy radlcal~ to one vlnyl radlcal - DBTL (Dl-Butyl Tln
.-. . . :.. :- : .:
~, . . . .
21 05~ 9 ~
67487-458
Laurate) Organlc salt of tin used as a catalyzer for hydrolysis.
- These compositions can be easily reproduced in a laboratory
uslng the technlque of humectation for the granulated polyethylene
wlth the silane, peroxlde and DBTL. The above compositions were
extruded with tube extrusion tools over a flat proflle conductor
with a rate of section reduction of 2 (DDR - draw down ratio).
To enable the reaction of the lnsertlon of the silane to
occur, a fuslon temperature (Melt) of 220C was used. After
treatlng them ln waterbath at 70C for 16 hours, ln a contractlon
controlled way, they became faded and a fracture in the flection
occurred.
Pesults obtained
Property Example 1: Example 2: Example 3
Contraction 13% 5.5% 19%
Fading none none none
Fracture none none none
Examples 4 and 5 (with fracture): Polyethylene
compositions modlfied with homo-polymeric polypropylene.
Ingredient Example 4, Example 5:
LDPE (MFI 1,33 80
LLDPE (MFI 1,0) - 80
Homopolymeric PP tMFI 4,0 -
KMT 6100 from Polibrasil) 20 20
Antloxldatlng 0.2 0.2
VTMO 1.5 1.5
Cumlla Peroxlde (96-100%) 0.12 0.12
DBTL 0 05 0 05
:: .
. , ~ . .; . ., . ..... - , .. .. . .. .
.. ~ . ~ ~ ..... . . ..... ... . .
2~03~9~
~7487-458
Examples 4 and 5 were processed the same way as examples
1, 2, and 3.
Results obtained:
Property Example 4: Example 5
Contraction 1.5% 1.0%
Fadlng occurred occurred ~-
Fracture occurred occurred
Examples 6 and 7 (wlthout contractlon or fracture): :
Composltlons of polyethylene modlfled wlth co-polymerlc
polypropylene.
Ingredlent Example 6: Example 7-
LDPE (MFI 1,3) 80 - ~
LLDPE (MFI 1,0) - 80 ~-.
Copolymerlc PP (8% ethylene) MFI 4;
EPT30RSF Spheripol from
HIMONT 20 20
Antloxldant 0.2 0.2
VTMO 1.5 1.5
Cumlla Peroxide Ig6-100~) 0.12 0.12
DBTL 0.05 0.05
Examples 6 and 7 were processed the same way as examples
1, 2, 3, 4, and 5.
Re ults obtalned:
Property Example 6, Example 7:
Contractlon 3.0% 3.0%
~:: Fadlng none none
: : Fracture none none
.~ ,
; ~, 9
- 2~ 0~9~ -
67487-458
Examples 8, 9, and 10 aimed at estlmatlng the best
PP/LDPE relatlon; the smaller PP level, the greater cost
reductlon.
In~r.edlent Example 8: Example 9 Example 10
LDPE (MFI 1,3) 85.0 82.5 80.0
Copolymerlc PP ~8% ethylene) MFI 4;
EPT30RSF from HIMONT 15.0 17.5 20.0
Antloxldatlng 0.2 0.2 0.2
VTMO 1.5 1.5 1.5
Cumlla Peroxlde (96-100%) 0.12 0.12 0.12
DBTL 0.05 0.05 0.05
Examples 8, 9, and 10 were processed the same way as
examples 1, 2, 3, 4, 5, 6, and 7.
Results obtalned:
Property Example 8- Example 9 Example 10:
Contraction 7.0% 4.5% 4.0~
Fadlng none none none
Fracture none none none
COMPARATIVE TABLE BETWEEN EXAMPLES 7 AND 9 AND SPECIFICATIONS IEC
502/83 ~3rd ISSUE 1991) AND ABNT 3.20.3-026/90 (REVISION NBR-
6251/86): ~oth speclflcatlons have the same requlrements.
Propertles Unlt Requlrement Example 7 Example 9
I) Inltlal
Tenslon and
rupture MPa 12.5 21.9 16.6
Stretchlng and
rupture ~ 200 480 480
2~ Oa89~
67487-458
II) After aglng ln alr stove
at 135C for 168 hours
Varlatlon o~ tenslon and
rupture % MAX 25 +4 +5
Varlatlon of stretchlng at
rupture % MAX 25 -2 -3
Stretchlng at heat (200C) wlth
load of 0.2MPa % MAX 175 60 60
Permanent deformlty after
stretchlng test at
heat % MAX 15 15 15
.- ~ . . : .
., ~ .... , . . ~ . .
- . . - . . . . . ..
