Note: Descriptions are shown in the official language in which they were submitted.
~ ~ ~ 7 ~ ~ ~ 9~57
BACKGROUND OF THE INVENTION
The invention relate~s to the prevention of
scorching, prior to uulcaniza~ion, of peroxide curable
ethylene polymer based c~mposit:ions.
Descri~tion of the Prior Art
Insulation compositions which are employed on
: electrical wire and cable are, in many cases, prepared
from composltions which are based on vulcanizable, or
cross-linkable, ethylene polymers. These ethylene poly~
. . .
mer based compositions may be vulcanized, or cured, or ~ .
crosslinked, with various organic peroxide compoundsJ as
disclosed for example in United States Patents, 2.826,570;
2,888,4~4; 2,916,481, 3,079,370 ~nd 3,296,189..
In the orgnnic peroxide compounds which have
; been used to date for commercial purposesin these vul-
. .
canizable ethylene polymer based compositions, each
oxygen atam in the peroxlde group, i.e.~ -0'0-, of such
compounds is directly attached to a carbon at~m;of an
20 organic radical. The commerclally useful compositions
,
dc not employ hydroperoxide campounds therein as curing
.` - agents because they have relatively high dec~mposition
,
tempera~ures, and the free radicals provided by the de- :
.
compQsed hydroperoxides are not effective for cross-
linklng ethylene polymer~.
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~57
In order to process the ~rganic peroxide con-
talning c~mpositions so a~ to adapt them to be placed,
a~ insulation, on the electrical ~onductor components
of the wire and cable it is usually necessary ~o adm~x
the componen~s of the compositions at hlgh temperatures,
and to extrude them, again at high temp~ratures, onto . .
the electrical conductor. Thes~e processing ac~ivities
~; occur prior to the intended vulcanlzatlon of the per-
oxide containlng compositions~ which is usually accomp-
lished after such compositions are extruded onto the
electrical conductor.
It has been found, however, that when certain
of the organic peroxide compounds, such a~ dicumyl ~-
perox~de, are used in combination with certain types of
ethylene polymers or in certain types of ethylene poly
mer based compos~tions, that the entire curable compo- -
sition is susceptible to scorching during the high temp-
erature processing thereof prior to the vulcanization
of the composit~on on the electrical conductor.
Scorching is, in effect, the prenature vulcanization of
the insulation compo~ition. This premature vulcani-
zation usually occurs, when it occurs, i~ the barrel
~'
or die~head of the extruder in which ~he insulation
composition is being processedJ at elevated tempera- -
~ures~ prior ~o its being extruded~onto ~n electrical ~ -
conductor, and prior to its intended vulcanization.
. ~
~'.57
~76~Ei
When an insulation compositisn is scorched in the extrud-
er, the extruded composition will have imperfections in
the form of discontinuity an~ roughness in the surface
oE the e~rudate; and l~mps or Isurace ripple caused
by gel particles in the body of the extrudate. In
addition, excessive scorching ~y cause enough of a
.~...................................................................... . :pressure build-up in the extrusion device to require a
cessation of the extrusion operation entirely.
The tendency of a camposition to e~perience
~' ...
~- 10 scorch ls a relative matter, since any vuLc~nizable
, :,
ethylene polymer based compostion can be made to scorch `~
if processed under conditions designed to produce such
result. Under a given set of conditions some compo-
... , . ~
sitions are more prone to~scorching than are others.
- Compositions which have been found to be more
succeptible to scorching under a given ~et of conditions
are ~hose in which the ethylene polymer has a relatively
: .................................................................. ..
. .
low melt index and/or a relati~ely narrow molecular
weight distribution.
The tendency of a composition to scorch under
- commercial~operating conditions may be measured by
means of the M~nsanto Rheometer Test Procedure. The
. ;.
Monssnto Rheometer Test ProcPdure is de~cribed in
ASTM-D-2084-71T.
4.
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.
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~ . :, .. ~ :, ~, . , . ., . ,. ; . .. . . . . ... . .
9457
Prior to the work of the present inventor as
disclosed in this patent application, scorch prevention
has been accomplished by the use oE additives such as
nitrites as disclosed in U.S. 3,202,648; the specific
antioxidants and vulcanization accelerators disclosed in
U.S. 3,335~124; and the chain trans~Eer agents disclosed
in U.S. 3,578,647. A mixture of two specific peroxides
has also been used to provide a rate of cure that is
intermediate the rate of cure of either of such peroxides,
as disclosed in U.S. 3,661,877. ~ -
SummarY of the Invention
It has now been found that vulcanizable
ethylene polymer based compositions which employ dicumyl
peroxide therein as a vulcanizing agent, and which
compositions are susceptible to scorching under a given
;~ set of conditions, can be protected against scorching
under such conditions by incorporating in such compositions
cumene hydroperoxide and/or tertiary butyl hydroperoxide.
An object of the present invention is to pro-
; 20 vide scorch resistant, vulcanizable, ethylene polymer
based compositions.
, j~ .
Another object of the present invention is to
"..~
provide a process for protectlng against scorching
vulcanizable ethylene polymer based compositions which
~, . . : :;
employ dicumyl peroxide as a vulcanizing agent and which -~
; are susceptible to scorching.
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.:
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~ 4~ 945/
. A further object of the presen.t invention is to
provide scorch resistant insulation for electrical wire
and cable.
- A further object of the present invention is to
provide a process whereby vulcanizable ethylene polymer
. based compositions which employ dicumyl peroxide as a ~.
vulcani~ing agent and which compositions are susceptible .:
to scorching, may be processed in mixing and extruding
devices, prior to the vulcanization thereoE, at fast
: 10 throughput rates and at relatively high processing temper~
atures without experiencing scorching. .~
: These and other objects of the present invention :
are achieved by employing cumene hydroperoxide and/or
~ tertiary butyl hydroperoxide as scorch preventing agents
in the compositions of the present inventions.
THE DRAWINGS
Figures 1 and 2 of the drawings show, graphically,
Monsanto Rheometer Test curves which were used to illustrate
the derivation of an efficiency factor as described below.
. 20 Figure 3 shows, graphically, Monsanto Rheo~eter
. .; .
Test curves ~or the compositions of Examples 7 and 8
.. ` Figure 4 shows, graphically, plots of the
: ~,
- : ex~truder head pressure vs extruder rpm which were
,:
encountered in the extrusion of the compositions of
:~ Examples 10 and 11~
Figure 5 shows, graphically, Monsanto Rheometer~:
Test curves for the compositions of Examples 12 and 13.
i, .
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:
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C~45'
DESGRIPTION OF THE PREFERRED EMBODIMENTThe Scorch Resistant Composition
The scorch resistant compositions of the present
in~ention comprise, in weight ratio,
100 parts by weight of ethylene polymer,
about 0.1 to 5.0, and preferably 0.2 to 2.0,
parts by weight of dicumyl peroxiide, and
about 0.05 to 2.0, and preferably about 0.1 to
-~ 1.0, parts by weight of at least one hydroperoxide which
is cumene hydroperoxide and/or tertiary butyl hydroperoxide.
The dicumyl peroxide and the hydroperoxides are
used in a weight ratio, to each other, of about 4:1 to 40:1
and preferably of about 8:1 to 15:1.
Eth lene Polymer
The ethylene polymers which are used in the ;
compositions of the present invention are solid (at
25C.) materials which may~be homopolymers, or copoly-
mers of ethylene. The ethylene copolymers contain at
least 30 weight percent of ethylene and up to about 70
weight percent of propylene, and/or up to about 50 weight
perc~ent~ of one or more other organic compounds which are
interpolymerizable with ethylene. These other compounds
which are interpolymerizable with ethylene are preferab]y
~ ;, :.. .
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7.
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,
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... .
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945'
those which contain polymerizable unsaturation, such as
is present in compounds containing a;l ethylene linkage,
- > C = C < . These other interpoiymerizable compounds may
be hydrocarbon compounds such as, bu~ene-l, pentene-l,
isoprene, butadiene, bicycloheptene, bicycloheptadiene,
and styrene, as well as vinyl compounds such as vinyl
acetate and ethyl acrylate.
'~
These copolymers could thus include those con-
~; taining ~0 to 70 weight percent of propylene and 30 to
< I00 weight percent of ethylene; and ~ 0 to ~ 50 weight
percent of butene-l or ethylene vinyl acetate and 50 to
~ 100 weight percent of ethylene; and ~ 0 to ~30 weight
percent of propylene, ~ 0 to 20 weight percent of butene-l
and 50 to ~100 weight percent of ethylene.
The ethylene polymers may be used individually,
. . ~ ,
or in combinations thereof. The ethylene polymers have a
~; density (ASTM 1505 test procedure with conditioning as in
.. ~, . ...
ASTM D-1248-72) of about 0.86 to 0.96 and a melt index
~ASTM D-1238 at 44 psi test pressure) of about 0.1 to 20
decigrams per minute.
Adjuvants ~-
. ,
In addition to the ethylene polymer, and the ~ ~
, ", . .
peroxide compounds, the compositions of the present inven-
tion also advantageously include about 0.01 to 3.0 and,
preferably 0.05 to 1.0, parts by weight of one or more
~ ~ suitable high temperature~antioxidants for the ethylene
polymer, per 100 parts by weig~t of ethylene polymer in
:
`;; ~ such compositions.
, :
8.
, :
. .
': ,
~ '~4~7
These antloxldants are preferably sterically
hindered phenols. Such compounds would include 1,3,5-
trimethyl-2,4,6-~rls(3,5-ditertiary butyl-4-hydroxy
benzyl)benzene; 1,3,5-tris(3,5-ditertiaxy butyl -4-
hydroxy benzyl)~5-triazine-2,4,6-(lH,3H,5H)trione;
tetrakis- Cmethylene-3-~3',5-di-t-blutyl-4'-hydroxy
phenyl)-propionat~ methane; and di(2-methyl-4-hydroxy-
5-t-butyl phenyl)sulfide. Polymerized 2,2,4-trlmethyl
dihydroquinoline may also be used.
Other adjuvants whioh may be employed iLn the
compositions of the present lnvention would include
adjuvants commonly employed in vulcanizable ethylene
polymer based compositlons including fillers, such as
carbon black, clay, ~alc and calcium carbonate; blowing
agents; nucleating agents for ~lown systems;
lubricants; UV stabilizers; dyes and colorants; volta~e
stabilizers; metal deact~vators and eoupling agents.
, . . .
These adjuv~ntæ would be used in a~ounts de~
~igned to provide the intended effect in the resulting
composition.
. The compositions of the presen~ invention
may also be extended, or f~ lled, with polymers other
than the ethylene polymer which are compatible, i.e.,
,~
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9~
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9~57
can be physically bIended or alloyed, with the ethy~ene
polymer. ~he resulting c'omposi~ions should contain
at ~eas~ about 30 we~ght` percent of inkerpolymerized
et~ylene in all the polymers that may be present in the
compos~tlon~ ~ased on the'total weight of the resultlng
;~; composit~ofn. T~e other polymers which may be used would
include poly~in~l chloride'and polypropylene.
The total amoun~ o~ adjuvants used will range
from 0 to a~out 60 weight percent ~fased on the total
we~ght of the composition.
` Pro'ce's's'ing'o'f' th'e''Compo's'i't'ions '
; ~11 of the components of the compositions o~ ;~
the present invention are'usually blended or compounded
together prior to their introduction into the extrusion
~, . ,
device from w~ich the~ are to Be extruded onto an electri-
'~ cal conductor. The eth~lene`polymer and the other '
desired constituents may be blended together by any of '~
..,
' the techn~ques used in the art to blend and compound
~; thermoplastics to homogeneous masses. For instance,
the components may be 1uxed on a variety of apparatus
including multi-roll mills, screw mills, continuous
mixers, compounding extruders and Banbury* mixers, or
..~-
. -
dissolved in mutual or compatibffle solvents.
' ;''
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-'' *Trade Mark or Trade Name
;,,~1 ~ , . . ..
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476~
When all the solid components of the composi-
tion are available in the form of a powder, or as small
particles, the compositions are most convenien~ly pre-
` pared by first making a blend of the components, say
in a Banbury mixer or a continuous extruder, and then
masticating this blend on a heated mill, for instance
~- a two-roll millg and the milling continued until an
intimate mixture of the components is obtained.
Alternatively, a master batch containing the ethylene ~
polymer(s) and the antioxidants(s) and, if desired, some ~-
or all of the other components, may be added to the ;
mass of polymer. Where the ethylene polymer is not
available in powder form, the compositions may be made
by introducing the polymer to the mill, masticating it ~
until it forms a band around one roll, after which a ~ -
1~ blend of the remaining components is added and the
m~ ng continued untiL an intimate~mixtur~e is obtained.
The rolls are preferably maintained at a temperature
;which iS within the ran~e 80~C to 150C. and which iY
; 20 below the decomposition temperatures of the first per-
oxide compound(s)O The composition, in th~ form of a
sheet, is removed from the~mill and;then brought into
a~orm,~typica~lly dice-like piYceyJ suitable for~sub-
:~f~ :f~ sequent~processin~g.
,~ :: : -
945;
G96
After thc various components of the compositions
of the present invention are unifor~iy admixed and blended
together, they are further processed, in accordance wi.~h
the process of the present invention, in conventional
extrusion ~pparatus a~ about 120 to 160C.
~,
After being extruded onto a wire or cable, or
other substrate, the compositions of the present invention
are vulcanized at elevated temperatures of about ~ 180C.
and preferably at > 215-230C. usi~g conventiollal
: lO vulcanizing procedures.
Derivation of Curin~ System Efficiency Factor
In the Monsanto Rheometer Test Procedure a
sample of the vulcanizable composition is measured in
~ .:
a rheometer be~ore the composition is subject to high
-~; temperature mixing or extrusion conditions. The test
., ~ .
results are plotted as functions of inch-pounds o
~- torque versus time. The compositions which are
less susceptible to scorching are those that experience,
after the minimum torque value is achieved, a de:lay ln
the rise of the torque values followed by a fast rise
in the torque values to the level required for the in-
tended end use of the composition being evaluated~
The Monsanto Rheometer Test Procedure is, in
:.
effect, a means for comparitively evaluating, graphically~
~-~ the susceptibility o different vulcanizable compositions
, ~
to scorch. In thls `way the use of different curing agents,
or curing agent composltions, in such vulcanizable com-
positions, can also be graphically compared
. 12.
: ~ .
~ 9457
For the purposes of the present invention, a
procedure has now been devised w~ereby, using the
graphical results of Monsanto Rheometer Test procedures,
the efficiency of different curable compositions, relative
to the susceptibility of s~lch compositions to scorching,
can also be numerically compared. By using this new
evaluation procedure, a separate and distinct numerical-
efficiency factor ~E) can be assigned to each curable
.
composition. To make these efficiency factors more
` 10 meaningful, for comparison purposes, they should be based
on rheometer curves which are all obtained when the `~
curable compositions being compared are evaluated under
the same test conditions. In all the experiments reported
herein the test samples were evaluated in a Monsanto
Rheometer at a cure temperature of 360F., using a rheometer
oscillation o~ 110 CP~ and an arc of + 5.
There is also provided here below, the derivation `
; of a numerical efficiency factor ~E) for vulcanizable `
compositions. The derivation employs typical rheometer `
curves that were ar~itrarily drawn, and which are not
based on actual experiments. Such curves are shown in
Fig~res 1 and 2 of the drawings.
,`~, ......
A typlcal Monsanto Rheometer curve, as shown
` graphically in Figure 1, contains several parameters which
are used in the derivation of the efficiency factor (E~.
The optimum cure level (highest cross-link densit~ is
designated as H. H is measured in terms o~ inch-pounds
of torque on the rheometer test equipment. A higher value
for H corresponds to a higher cross-link density.
13.
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The time, in minutes, require~ to reach 90/O of the
maximum cure (H) is designated as CT. Thus, in E'igure 1,
H is 50 inch-pounds and CT is 5~5 minutes, which is the
time required to reach a level of 45 (or 90% o~ 50) inch-
pounds of torque during the test procedure.
The scorch time, ST, is defined as the point in
time, in minutes, at which the curve reaches a rheometer
level of lO inch-pounds of torque on the upswing o the
curve. In Figure 1, ST is about 2.1 minutes.
In general, one is interested in getting to the
maximum cure (H) as soon as possible. In other words,
a short CT is desirable. At the same time, one would
like ST to be as long as possible since a longer ST means
the vulcanizable composition being evaluated can be
processed at a higher speed or at a higher temperature.
.~, .
That is, it would be less scorchy. Thu5 it is important
to discuss the time intervals between ~T and ST, or
. .
CT ~ ST since CT is, arbitrarily, always longer than ST
Then, too, lt is of interest to compare ST with
; 20 CT - ST since the best vulcanizable system would be one
whose ST is relatively long, and whose difference between
j
CT and ST 7 (CT - ST), yould be relatively short. Thus,
the rati~o STiCT - S~ is of importance. The larger is this
~~ ratio, the less susceptible is ~he vulcanizable composition
to scoxching.
1; , . .
Finally, the times (CT and ST) are related to
~ the maximum cure point, H. Thus, i one can malntain
:,~
14.
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. .
. . . . . . . . . . ... . . . . .. . .. . .
6~ 9457
:
the same ST, and yet reach a higher H, one can thereby
: provide a vulcanizable composition that is less
. susceptible to scorch. When vuicanizable composltions
are cured by peroxide curing agent systems, particularly
those using individual peroxides such as dicumyl
- peroxide, as you increase the value of H, by simply
adding more of the peroxide curing agent,you decrease ST.
The ef-ficiency of a particular curing agent
system, therefore, when used with a given vulcanizable
~ 10 composition, and cured at a given temperature, can be
determined by multiplying H by ST / CT - ST or, as
shown in Equation I;
. E = H x ST (I)
T ~ ST
The numerical efficiency (~) of the arbitrary
curing agent system shown graphically in Figure 1 therefore,
: ',~' .
` would, be
E = H x ST = (50) (2.1) = 30.9
CT ~ ST 5.5 - 2.1
, .
: 20 To further illustrate the utility of this method,
for the purposes of comparitively evaluating different
vulcanizable compositions, reference is made to Figure 2
~: of the drawings in which there is graphically presented
~ typical Monsanto Rheometer curves 1 and 2 that were also
: ~ arbitrarily drawn, and wh:ich are not based on actual
,. ,
. experiments.
~ :It should be noted from a review of Figure 2 .;
.` that the cure times CT 1 for composition l and CT 2 for
` composition 2, are the same for both compositions and .-
: 15. . :
. ' ' . .
~ 94~7
each curve reaches a relatively high torr~ue level with
the value of Hl (for composition 1) ~hich is 70, being
relatively close to ~he value f ~2 (for composition 2)
which is 62~ ST_2 (f~r composition 2~,however, is more
than a minute longer than ST_l (for composltion 1),
3.2 vs 2.0 minutes. Thus, it is quite obvious ~rom a
review of these two curves that curve 2 represents the
better cure system. If one maintains the same CT~ and
reaches almost the same maximum cross -link density ~H),
then increasing ST must lead to a better curing system,
ln accordance with the above definition of E.
A calculation of the relative numerical effi-
ciencies of the curable compositions shown graphically
. ".,.
in Figure 2 is shown below:
Efficiency ~El) of composition 1, based on curve 1:
. . .
El - Hl x STl - (70) (2) ~ 140 - 35.0
CTl STl ~6 - 2~ 4
Efficieny (E2) of composition 2, based on curve 2
E2 - H2 x ST2 - (62) (3-2~ _ 198.4 : 70.8
C~2 ~ ST2 (6 - 3.2) 2.8
.~ Thus, this efficiency factor, E, is a useful
parameter and it can be shown that in fact a higher value
for E represents a better system, as defined above, and
represents improved utility for such better system~ The
. ~ , - .
use of this efficiency factor, ~, can also apply to -
comparisons of Rheometer test curves where the maximum
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9~57
cure (H) shown in each curve is vastly di~erent, since the
calculation of E is, in e~fect, a normalization procedure.
The compositions of the present invention have
an efficiency factor (E) 9 as determined above, which is
.
at least about 3, and is preferably more than 10 to 15,
units of such ef~iciency factor above the efficiency
factor of such compositions in the absence o~ the cumene
hydroperoxide and/or tertiary butyl hydroperoxide. .
The following examples are merely illustrative
of the present invention and are not intended as a limit-
ation upon the scope thereof.
General Admixin.g Procedure
The vulcanizable compositions used in Examples
1-15 below were all prepared by the following procedure: ~
100 parts by weight of the ethylene polymer were .
fluxed in a Banbury mixer at approximately 120C. The
. additives, i.e., anti-oxidant, and the peroxides and,
. where used, other adjuvants, were then added to the
fluxed mixture. The resulting composition was then
. 20 blended for 2-3 minutes and then trans-ferred to a
.. 2-roll mill for sheeting. The hot rolled sheet was then
.;
, chopped on a hot granulator to yield a chipped product.
. The chips were then compression molded into .:
~- plaques -for use in Monsanto Rheometer test procedures. .. :
. ~ All of the rheometer data which was then obtained on the `~
: samples, ~mless otherwise stipulated, was obtained at :
.. , :
360Fo (182.2C.). . .
: 17 :.:
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EXAMPLES 1-3
The following three vulcanizable compositions
were prepared as in The General Admixing Procedure
utilizing dicumyl peroxide (DC~) with a low density
ethylene homopolymer I ~having a density oE 0.919, a
melt index of 1.6 to 2.2 (IP, 190C.)3 and the hydro-
peroxides as shown in Table I. All of the samples
contained 0.2 parts by weight di(2-methyl-4-hydroxy-5-t-
, . . -.~
butyl phenyl)sulfide as antioxidant.
` TABLE I -~
-
:~ Compositions of Examples 1-3 in
j parts by weight
: Components 1 2 3
ethylene homopolymer I 100.0 100.0 100.0
dicumyl peroxide 2.0 2.0 2.0
. Cumene hydroperoxide - 0.2
:
t-butyl hydroperoxide . - ~ - 0.2
":
Efficiency Factor - E ~ 20.5 24.1 23.5
~:~ The efficiency Factors for each of the com- :
,~ .,; .
. 20 positions of Examples 1-3 were obtained on the basis of
Monsanto Rheometer Test Curves (not shown) which dis- :-
closed the follow mg test data for each of the test :~
compositions: :
, . . ~
~- TABLE ~
:~.( Test data - for compositions of Examples 1 2 3 : -
.! -
; ST, minute~s 1.75 2.8 2.5 ::
`CT, minutes . 5.S 5.6 5.6 :~:
..
: H, inch-pounds 44.0 24.0 29.0 ..
~ 18.
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~ 94L17
The Efficiency Factors for these compositions
indicates that the addition of either hydroperoxide to
the homopolymer based system im~proved the scorch
resistance of the system which also contained dicumyl
peroxide.
:~ EXAMPLES 4-6 . -
The following three mixtures were prepared as in
The General Admixing Procedure utilizing dicumyl peroxide
: in a low density ethylene-vinyl acetate copolymer I
(containing 10% of vinyl acetate by weight, and having a
density of about 0.92 and a melt index of about 3) and
the peroxides as shown in Table III. All the compositions
contained the same amount of the same antioxidant as was
utilized in Examples 1-3.
TABLE III
Compositions of Examples 4-6
in parts by weight
.
.; Component 4 5 ` . 6 :
Ethylene copolymer I 100.0 100.0 100.0
; Dicumyl peroxide 2.0 2.0 2.0
Cumene Hydroperoxide - 0.5 -
~:` t-butyl Hydroperoxide - - 0.5 :
'~,!' ' Efficiency Factor - E 15.4 31.4 34.6
.. ,..:
... . .
The Efficiency Factors ~or each of the com~
'. positions of Examples 4-6 were obtained on the basis of
;` Monsanto:Rheometer Test Curves ~not shown) which disclosed
, the following test data for each of the test compositions:
, .:
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TABLE IV
Test Data - for the compositions of Examples 4 5 6
ST~ minutes 0.9 2.15 2.3
CT, minutes 4.9 5.5 5.5
H, inch-pounds 68.5 ~9.0 48.0
The Efficiency Factors for these compositions
indicates that the addition oE either of the hydroperoxides
also improves the scorch resistance of ethylene vinyl
acetate copolymer based composition containing dicumyl
peroxide.
EXAMPLES 7 to 9
Three vulcanizable mixtures were prepared using
the ethylene polymer (Copolymer I) employed in Examples
4-6 with the addition of 35 parts by weight of a furnace
grade carbon black and polymerized 2,2,4 trimethyl .-~
dihydroquinoline as the antioxidant. The results are
shown in Table V. .
TABLE V
Compositions o-E Examples 7-9
in parts by weight
Component 7 8 9
Copolymer I 100.0 100.0 100.0 ::
Carbon Black 35.0 35.0 35.0 :
Antioxidant 0.5 0.5 0.5
Dicumyl peroxide 1.6 2.0 2.0
Cumene Hydroperoxide -- 0.5 -- ..
t-butyl Hydroperoxide - -- 0.2
EEfici.ency Factor 20.6 33.7 33.3 :
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The Efficiency Factors for eac'n of the composi-
tions of Examples 7-9 was obtained on the basis of Monsanto
Rheometer Test Curves. The test curve for the composition
of Example 9 ls not shown. The test curves for the
compositions of Examples 7 and 8 are shown in Figure 3
of the drawings. The test curves ~Eor these three composi-
tions disclosed the following test data for each of the
test compositions:
TABLE VI
Test Data - for the compositions of Examples 7 8 9
.. . .
ST, minutes 1.1 1.8 1.1
CT, minutes 5.0 5.5 4.6
;, H, inch-pounds 73.0 69.0 106.0
The Efficiency Factors for these compositions
` indicates that the addition of either hydroperoxide to -~;
the filled composition greatly improves the scorch
~` resistance of the formulation.
EXAMPLES 10
- . . .
..
, As a further illustration of the increase in
scorch resistance, and of the increased extrusion rate,
that can be realized from the principles of this inven-
tion, the compositions of Examples 7 and 8 were extruded
on wire and the effect of the resulting changes in
extruder rpm on "scorch" was observed during such
.~ , .
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Scorch can easily be detected in such an
operation. The first thing that is noticeable is the
sudden increase in the head pressure in the extruder,
and with that, the appearance c E gels in the extruded
coating on -the coated cable, indicating that scorch has
occurred in the coating.
In this set of experiments, the extruder heater
profile was kept the same (240F. for all S zones), the
screw water temperature was maintained at 150F., and the
10 temperature of the composition in the head of the extruder
was measured by the use of a thermocouple. This extrusion
work was performed on a 2 1/2 inch, 16 :1 (length/diameter
ratio) Roy:l.e extruder using 0.032" of insulation coating
. ~
on ~14 Cu conductor substrate.
AEter the extruder was first purged with some
of the test composition and the wire- line adjusted
properly, the rpm of the extruder was slowly increased
until the scorch point, ~as defined abo~e, was observed.
The relevant data on head pressures 3 composition
20 temperatures~ extruder rpm, and output of extruded
composition are shown below in Tables VII and VIII.
TABLE VII
~ Example 10 (1)
''. : : :
Composition Head Output
RPM Temp. ~C.) Pressure (psi) (~rams/min.)
118 2200 --
138 2400 -- ~-`
,
~` 60 145 ~ 2450 --
150 2550 --
157(3) 2900(2) 708
22.
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~7Ç;~6
1. contains only dicumyl peroxide (composition
of Example 7).
2. Scorch point - gels appeared on cable.
Pressure measured at the extruder head,
3. Compound temperature inside the extruder
head.
An examination o-f the data reported ln Table
VII indicates that the basic peroxide system (dicumyl
peroxide with ethylene polymer) begins to scorch at 80 RPM
~- 10 when the composition temperature reaches 157C. at an
extruder output o~ 708 grams/minute. The resulting profile
oE head pressure vs rpm which was achieved in the extrusion
process of Example 10 is shown in Figure 4 of the clrawings.
TABLE VIII
Exa~ple ll(4) ~ ~
Composition Head Output ~-
-~ ~ RPM Temp. (C.) Pressure (pSi~ t~rams/min.) ;
118 2050
~` 50 135 ~ 2150
2060 142 2200 -
150 2200
~, :: :
~ ; 80 L56 2200
:, .~, ~
163 ~ ~ 230~ -
100 ~ ~ 170(63 3(5) 840 gms/min
~1; 4. contains dicumyl peroxide and cumene
hydroperoxide (composition of Example 8)
~ 23.
: : ;. . .
~ 9457
,~, 5~ scorc~ pointi p~essure measured at ;
extruder head
: 6, compo~md ~'emper.ature'~nslde the'ex~ruder .-
~ead.
An examinat~on of the data reported in Table VIII
~ ~ndi,cates that in fact thb'mi~ed per'oxide system of '''
:~ ~xample 11 does ~ndeed run ~ 2Q% faster ~100 rpm vs 80
: rpm~ before scorch sets in~ ~lso, this is reflected in
the increase of the'temperature o~ the composition which~ :
can ~e achieved ~17C5C. vs 157C.~ in the extruder before::'
scorch appears. ~ .
The resulting proflle of head pressure vs rpm:.,'.
,~ w~ich was ac~ieved in the e~truslon process of Example 11
is also shown in Figure 4 of the drawings in comparison~, ,
..
", to the profile obtained in ~xample 10. .
.
An examination of all the data obtained in '.
Examples lO and 11 illuskrates the u~ility of the present .~',
' i,nvention in providing for increased extrusion rates and
'~l greater scorch resistance with et~ylene polymer based
;,, 20 compositions which are cured with peroxide curing agents. ~.
:: EXAMPLES 1'2-13 ''
.~ The following two mixtures were prepared as in
Examples 1-3 utilizing dicumyl peroxide with an ethylene- ,~
,, propylene-diene terpolymer (Nordell* 1500 resin sold by ;;
::l duPont*) that contained a~out 16 mole per cent (22.4
` , weight %~ o~ .propy~ene, ~nd 83 mole per cent C77.5 weight: .
-, %~ o~ eth~lene and:a small am~unt Cabou~ 1 mole~/O~ of an
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unidentified (diene) monomer. Cumene hydro~"eroxide was
used as the hydroperoxide and di(2-meth~,ri-4-hydroxy-5-t-
butylphenyl)sulfide was used as the antioxidant as shown
in Table IX.
TABLE IX
Compositions of Examples 12-13
Com~onent in parts by weight
~- 12 13 --
Terpolymer 100.0 100.0 ;-
Antioxidant 0.2 0.2
Dicumyl peroxide1.5 2.0
; Cumene hydroperoxide 0.0 0.5
Efficiency Factor22.5 34.3
The Efficiency Factors for each of the composi-
tions of Examples 12-13 were obtained on the basis o-f
Monsanto Rheometer Test Curves. The test curves for
..
the compositions of Examples 12 and 13 are shown in
Figure 5 of the drawings. The test curves for these
two compositions disclosed the following test data for
..
each of the test compositions:
TABLE X
Test Data - for the compositions o-f Examples 12 13
ST, minutes 0.8 1.2
;~ ~ CT, minutes 2.9 3.6
H, inch-pounds 59.0~ 68.5
, `me Efficiency Factors for these compositions
`indicates ~that the addition of the hydroperoxide to the
~-; 25
.
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~ 5
terpolymer based system substanti.ally improved the scorcll
resistance of the system which contained dicumyl peroxicle.
EXAMPLES 14-lS
The following four mixtures were prepared as in
Examples 1-3 with an ethylene-ethyl acryla-te copolymer
(Copolymer III) which contained 15% by weight of ethyl
acrylate and which had a density of about 0.92 and a
~ melt index of 1.6 - 2.2, and the peroxides as shown in
.~ Table XI. Di(2-methyl-4-hydroxy-5-t-butylphenyl)sulfide .:
was used as the antioxidant.
TABLE XI
Component Compositions of Examples 14-15 in
parts by weight
. Copolymer III 100.0 100.0
Antioxidant 0.2 0.2
dicumyl peroxide 2.0 2.0
. , .
. cumene hydroperoxide 0 0.3
~: Eff-lciency Factor 14.7 25,g
The Efficiency Factors for each of the composi~
tions of ~.xamples 14-15 were obtained on the basis of .~.
Monsanto Rheometer Test Curves (not shown). The test ~
~; curves for these two compositions disclosed the following ~
test data for each of the test compositions: ~.
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TABLE XII
Test Data - for the compositions of Examples
1~ 15 :
~ ST, minutes 0.9 1.8
:. CT, minutes 5.0 5,7
H, inch-pounds 67.0 56.0 :
The Efficiency Factors -for these compositions
indicates that the addition of the hydroperoxide -to
. the Copolymer III based system can provide excellent
. '.~ , .
~; 10 . improvement in scorch resistance.
In all cases the TBH was used in the form of
a mixture of 90% tertiary butyl hydroperoxide and 10%
tertiary butyl alcohol.
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