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Патент USA US2406191

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Patented Aug. 20, 1946
' UNITED
2,406,191
STATES .PATENT OFFICE
2,406,191
‘MANUFACTURE OF ELASTIC COMPOSITION
SUITABLE FOR ELECTRICAL CABLE IN
SULATION
Hugh J. Cameron, Gary, Ind., assignor to Edgar F.
Seifert, Chesterton, Ind.
-
No Drawing. Application January 11, 1943.
>
‘Serial No. 472,071
6 Claims.
(Cl. 260—42)
1
2
The present invention relates to the produc
the mixture made into a ?lm or foil with two
tion of compounds or compositions having some
of the desirable physical characteristics of rub
ber, and in particular to‘ such which are useful
like rubber for extrusion over a centered strand,
rolls running at the same speed, but not with
rolls‘ running at different speeds, otherwise
such as an electric wire conductor, to effect an
bined with a solvent such as carbon tetrachloride.
electrical insulating covering.
In such extrusion the temperature of the ma
The present invention is particularly directed
trouble
is
experienced.
The product of g the
kneader so made, may be extruded when com
chine should be below 80.” C., while the nozzle
to a composition which is a mixture, and which
should be above 100° C. The solvent is used to
derives its properties from its two essential com 10 render the material plastic for the'purpose of
ponents. One of these is polystyrene. The other _ is polyisobutylene.
It is a general object of the invention to com
pound polystyrene and polyisobutylene to form
a rubber substitute.
It is a particular object of the invention to
compound polystyrene and polylsobutylene in
such a way that the resulting composition acts‘
extrusion.
'
'
Others have attempted to secure mixtures op
erative for hot extruding processes, and contain
ing- polystyrene and polyisobutylene, but resort
15 ing to a different method to achieve a product
capable of extrusion. Instead of combining the
said two ingredients, 3, mixture is ?rst made of
styrene monomer and polyisobutylene, and this
as a homogeneous mixture capable of being ex
mixture is treated'to effect polymerization of ‘the
truded while hot and under high pressure to pro 20 styrene to polystyrene. The results so obtained
vide a rigid non-tacky body, such as a sheath on
are not comparable to those attained by the pres
a wire, which sheath presents resistance to sof
- ent invention, and the differences are attributed
tening and ?ow at temperatures “likely to be en
in part to the fact that the polymerization of
styrene in the presence of polyisobutylene as a
countered in use, and presents valuable elec
trical properties for use with high tension and 25 diluent therefor, gives a different type‘iof molec
high frequency currents in an‘ electrical conduc
ular structure to the polystyrene which results.
tor insulated therewith.
The catalyst for the polymerization is not readily
Various other and ancillary objects and ad
eliminated.
'
vantages of the invention will appear from the
The present invention provides a product
following description and explanation of the in 30 which is a physical mixture of one polymer con
vention. _
sisting of polymerized styrene or polystyrene,
with another polymer consisting of polymerized
In one instance British Patent No; 534,464,
accepted June 6, 1939, states that it is impossible
isobutylene or polyisobutylene. It is a type of
to mix the two ingredients on mixing ‘rolls. This
mixture which the art has not heretofore at.- .
is true for some conditions, but not for all con
tained, and, contrary to the teachings of the art,
ditions, as will be explained hereinafter.
it may be subjected .to the action of two mixing
The initial objective giving rise to the present
rolls of differential speed, under certain condi
invention was the provision of a rubber substitute
tions. In fact the mixture may be ' initially
for insulating electric conductors by the extru
effected by use of such rolls, contrary to the
sion procedure. In attaining this objective it has,
been discovered how polystyrene and polyiso
butylene may be successfully combined to give
40 tachings of the art.
'
The conventional practice in use of differential
rolls, as used in the rubber industry, and as used
elastic compositions, some ‘of which are suitable
in the art of rubber substitutes, is to use cored
for the more exacting requirements of electrical
rolls, or hollow rolls, having cooling water run
insulation, and others of which‘ have uses other 45 ning through them to carry away the heat of fric
tion. Such use of cooled rolls applied to the mix
wise.
Attempts heretofore have been made to com
ture produced by the present invention, ruins-the
product, causing it to crumble.
bine polystyrene and polyisobutylene, but failures
In experiments leading to the present inven
and difficulties have been encountered, and prod
50 tion it was discovered that <dispensing with the
ucts of only limited value have been attained.
Also, British Patent No. 506,855, accepted June
cooling water did not overcome the dif?culty, or
permit mixing the two ingredients to e?ect a
6, 1939, teaches that polystyrene and polyisobutyl
ene may be combined in a kneader in proportions
from 1 to 9 parts of any one with the other at
uniform mixture. It was also discovered that the
‘introduction of steam into the rolls did not ef
temperatures from 100° C. to 200°C" and then 55 fect any new result, until the roll temperature
2,400,191
3
'4
-
.
' I with heating. ‘It is commercially defined by mo
attained at least 300° F. Below this point a non
lecular weight, as calculated from viscosity by
uniform mixture merely passes through the rolls
and discharges as a non-uniform mixture. But
the Staudinger vequation.
,
It is believed that the following is the equation
‘at and above this temperature for the differen
tial mixing rolls, the non-uniform mixture be- 5 soemployed:
‘ gins to smooth out, to lose its shortness, and mu-
Ur- l=KMC
=
‘tually to combine the ingredients to produce a
wherein
V
smooth plastic elastic composition having many '
_ viscosity of solution of polymer
physical properties of rubber, including .that of 0 Ur_
viscosity of solvent
‘extrudability while hot.
j
K =constant
The softness of the‘ resulting uniform mixture
when normally cold, and its degree of tackiness,
"
.
C -'—_gram unit groups per liter in solution
M =molecular weight of polymer
or the lack of it, depend upon both the propor-'
tions of the two polymers used, and upon the
In carrying out the present invention it is nec
degree of Polymerization of each of the poly" 15 essary, in producing the desired mixture of any
polystyrene and any solid polyisobutylene, to use
For the purpose‘ of providing a suitable elec-' /'mechanical means to effect both a mixing and
1trical insulation, which is su?iciently non-tacky,
masticating action, and in so doing to have a
and suiliciently resistant to softening and ?ow
contact mechanical means at a temperature of
at temperatures encountered practically in use of 20 at least 300» R The term “masticating” as used
mers.
,
.
‘electrical conductors insulated with it, de?nite
‘herein, is de?ned as a frictional or shearing ac tion on a mass containing the unmixed materials,
wherebythere is a stretching of the mass, as will
occur when a relatively thin mass is pinched be
lower limits of degrees of polymerization have
been determined for each polymer, and‘limitjng
‘proportions of such polymers have also been de
jtermined. However, for other uses, and for less 25 tween two. parts moving relatively to each other
whereby to effect a tearing and shearing of one"
[drastic conditions of exposure of insulated con
ductors, polymers and proportions outside of ‘such
layer of the material from an adjacent layer
speci?cations, may be employed.
Polystyrene
while said material is in contact at-the point of
such mastication with physical means having a
‘30 temperature of at least 300° F, These moving
Polystyrene, as the product referred toin the
present invention, is a product of polymerizing
styrene in the absence of diluents. As ‘the degree of polymerization increases the molecular
‘weight increases. Polystyrene is at normal tem
‘perature a transparent brittle solid, capable of
‘becoming plastic at an elevated softening tem
perature, and of ?owing as a plastic mass, es
pecially under high pressure. The higher the
' parts may be the nip of heated rolls running at'
different speeds in opposite directions, as in con
'
ventional rubber-mixing differential rolls: Being' highly viscous and plastic, the masticating
action pulls one layer from an , adjacent layer
and stretches the mass locally, effecting an ac
tion which produces the desired uniform mutual
incorporation of the two polymers. The temper;
ature of the mass under such action may actually
:degree of polymerization, the less is the plasticity 40 be higher than the contact temperature of. the
mechanical means, due to friction within them '
or ?ow for a given temperature and applied pres
sure. In fact, polystyrene is commercially speci
fied by this property, in terms of time of ?ow at
locally being masticated.
.
.
-
It has been determined that a mass having the
polymers unmixed, must be raised in temperature
a given temperature under'a given pressure in a
‘speci?ed type of plastometer. such an instm- 45 by contact at the point of mastication with means
having a temperature of at least 300° F., in order
‘ment is the Rossi-Peekes plastometer (U; S. Pat
to impart to it the property of responding to the
,ent No. 2,066,016), and it is commonly used at
mastication for mixing to uniformity. In fact,
it has been shown by experience that a product
Testing Machine Company, Philadelphia, Penm 50 already mixed to uniformity in accordancerwith
the present invention, and in process of mastica
sylvania. The method is referred to by the Amer;v
130° C. under 1000 lbs. pressure per sq. in. Such
a plastometer is manufactured by 'I‘inius Olsen
ican Society of Testing Materials publication ‘
tion between di?’erential rolls at 300° F. or above,
will become short and crumble if the temperature
of the rolls drops below 300° F. The mixture is
value for speci?cations, because polystyrene-is a 55.110‘? thereby destroyed, for each crumb remains
as a particle of the mixture. However, the im
‘mixture of higher and lower polymers, and a mo
portant point is that conditions which. crumble
lecular weight identi?cation is merely an average.
‘the mixture are insu?icient to produce the mix
The distribution of all the polymers,-rather than.
ture from a non-uniform mixture of the constitu
the average molecular weight of the composition
‘predetermines the plasticity or ?ow-time, which 60 ems“
D569-41T.
g
.
The molecular weight of polystyrene is, a poor
In producing the composition the preferred
‘are the important properties pertinent to the
presentinvention for vdefining polystyrene to be
used within the prescribed compositions for high
‘frequency electrical insulation.
First, polystyrene is fed to the rolls in quantity "
Polyisobutylene
a portion of the nip with‘ a mobile mass thereof.
method is to use differential rolls heated to at
least 300° F., preferably by steam ‘within the rolls.
. c5 peripherally to cover the slower roll and to ?ll
To this, preferably at the hip, is added a smaller
amount of solid polyisobutylene. The latter is,
‘the present invention, is provided by polymerizing
preferably in particle form, the smaller the par
‘isobutylene at a temperature below —50° C. and
through the use of an amphoteric halide catalyst. 70- ticles, the more speedy the incorporation. 'Con
tinuation of the masticating action carries the
A low degree of polymerization provides a polymer
which is liquid at normal temperature of 70° F. _ added material as a plastic unincorporated sub- stance continually around one roll and through
,As the degree of polymerization increases, a poly- _
Polyisobutylene, as the product referred to in
the nip, gradually e?ecting its distribution uni
‘70° F. is attained, which polymer becomes plastic 75 formly into the polystyrene base‘ or the mixture
' mer which-is solid .at a normal temperature of
5
.which results. More polyisobutylene is added uh-r . ' ous products may be made without departing
til any desired proportion has been assimilated.
from the spirit and scope o1’v the invention as ex
vAll th desired polyisobutylene may be added at
pressed in the appended claims.
,
=
_
once, i the ?rst instance, or it may be added in
I claim:
,
stages, or it may be added gradually at a uniform
1. The method which comprises subjecting
rate. The quickest results are obtained by add
polystyrene consisting of a polymerized mass o'rig- '
ing it throughout a period of time as it is seen
inally consisting substantially entirely of styrene
that the mass is becoming smooth and uniform
and characterized by a ?ow-time of at least 120
from the assimilation of that previously added.
seconds for a flow of 1.5 inches as tested in a.
In the end, a mastic, elastic, rubber-likev sheet
Rossi-Peekes plastometer at 130° C. with 1,000 _
may be removed from the slower roll around
lbs. pressure per sq. in., to the masticating mix
which it forms, as in conventional rubber prac
ing action of two adjacent parallel mixing rolls
tice, the di?erence being that the material is at
having a plastieizing temperature for the poly- '
Y a higher temperature than in the case of using
styrene of at least 300° F. and rotating in oppo
such mixing rolls with other materials.
site directions at different speeds, whereby the
For the purpose of. desirable extrudable elec
polystyrene is rendered plastic and capable of as
trical insulation, which is suitably resistant to
softening and ?ow with heat, and substantially
similating polyisobutylene, continuing the vmasti
cating action and gradually adding to\ the mass
being masticated a polymer consisting of poly
non-tacky, a polystyrene is used having a ?ow
time of at least 120 seconds for a ?ow‘of 1.5 20 isobutylene characterized by a normally solid
inches in a Rossi-Peekes plastometer at ‘130° C.
state at 70° F. and by a molecular weight of at
and at 1000 lbs. pressure per sq, inch. A poly
least 60,000, as determined by viscosity using
isobutylene is used having a molecular weight of
the Staudinger equation, until a quantity of from
at least 60,000 as determined by viscosity by the
1 to 9,)parts of polyisobutylene has been added to ‘
Staudinger equation.
>
Having selected such polymers the proportions
25 1 part of polystyrene, whereby the added poly
isobutylene is gradually incorporated into a re
used are from 1 to 9 parts by weight of polyisoé
sulting uniform ‘mixture of said polystyrene and
butylene to 1 part by weight of polystyrene. This
said polyisobutylene, and after the addition of
gives limiting compositions of one mixture hav
the last of the polyisobutylene continuing the
ing equal parts of each polymer, and another 30 mastication until the last added material is uni
‘mixture having 10% by weight of polystyrene.
formly incorporated into the mixture.
Mixtures within this range are substantially non
2. The method which comprises subjecting
tacky, are extrudable by heat, suitably resistant
polystyrene consisting of a polymerized mass orig
to softening and flow under heat below 300° F.,
inally consisting substantially entirely of styrene
and of varying degrees of softness when cold, the 85 and characterized by a ?ow-time of at least 120
equal-part mixture being the least soft.
seconds for a flow of 1.5 inches as tested in a
Such a mixture may be placed in a rubber
.Rossi-Peekes plastometer at 130° C. with 1,000
extruding machine having a moving conductor
lbs. pressure per sq. in., to the masticating mix
centered in the ori?ce or nozzle, and having high
ing action of two, adjacent parallel mixing rolls
mechanical pressure active on the mixture. The 40 having a plasticizing temperature for the poly
mixture must have a temperature of at least 300°
styrene of at least 300° F. and rotating in oppo
F, in the body behind the ori?ce, but where a
site directions at different speeds, whereby the
nozzle of uniform cross-section may lead from
the initial ori?ce, the nozzle may be colder than
300° F., and preferably is colder, whereby the dis 4
charged extruded mass is chilled to a rubber-like
solid sheath over the conductor.
.
'
Such a sheathed conductor may be bent to
polystyrene is rendered plastic and capable vof
assimilating polyisobutylene, continuing the mas
ticating action and gradually adding to the mass
being masticated a polymer consisting of poly
isobutylene characterized by a normally solid state
at 70° F., until a quantity of from 1 to 9 parts of
polyisobutylenehas been added to 1 part of poly
small angles without breaking, due 'to the clas
ticity of the ‘mass, and in mechanical respects 50 styrene, whereby the added polyisobutylene is
acts like a vulcanized rubber covering.
gradually. incorporated into a resulting uniform
Where a product of the invention is mixed
mixture of said polystyrene and 'said ‘polyiso
as described‘above, it may be sheeted in calender
butylene, and after the addition of the last of
rolls running at the same'speed, provided they
are heated to 300° For higher. Any pressure
molding operation effecting a material tempera_
ture of 300° F. or higher may be employed. Tacki
the polyisobutylene continuing the mastication
until the last added material is uniformly incor
porated into the mixture.
3. The method which comprises subjecting poly
ness of a composition, as for example result
styrene consisting of a polymerized mass origi
ing from use of a solid polyisobutylene having a
nally consisting substantially entirely of styrene
molecular weight value lower than the speci?ed 60 and characterized by a ?ow-time of at least 120
‘ 60,000 is permissible, depending upon the use to
which the product is put. Even tackiness of a
seconds for a ?ow of 1.5 inches as tested in a
Rossi-Peekes plastometer at 130° C. with 1,000 lbs.
sheath on a conductor is permissible, where other
pressure per sq. in., tov the masticating mixing ac
covering, such as fabric or metal is placed over
tion of two adjacent parallel mixing rolls having
a sheath consisting of a mixture of independently 65 a plasticizing temperature for the polystyrene
polymerized styrene and independently polymer- ‘ of at least 300° F.‘ and rotating in opposite di
ized isobutylene, characterizing the present inven
rections at different speeds, whereby the poly
tion.
styrene is rendered plastic and capable of as
'
Tackiness of a layer calendered at 300° F. or
over, as onto a fabric, is advantageous, as for ex
ample in making an adhesive or friction tape. For
such a purpose, ‘paper, cloth, Cellophane and the
like may be adopted as the base.
'similating polyisobutylene, continuing the mas
70 ticating action and gradually adding to the mass
being masticated a polymer consisting of poly
isobutylene characterized by a normally solid state ,
at 70° F. and by a molecular weight‘ of at least
From the foregoing it will be appreciated that
60,000 as determined by viscosity using the ‘Staud
numerous variations of the process, and numer 75 lnger equation, until a quantity of from 1. to 9
' 2,406,191
7
A '
_ parts of polyisobutylene has been added to 1v part
of polystyrene. whereby the added polyisobutylene
' opposite directions at different speeds. whereby
the polystyrene is rendered plastic and capable
of assimilating polyisbbutylene, continuing the
masticating action and gradually adding to the
l is gradually incorporated into a resulting uni
" form mixture of said polystyrene and said poly
‘ isobutylene, and after the addition of the last of
mass being masticated a polymer consisting of
polyisobutylene characterized by a normally solid
the polyisobutylene continuins the mastication
state ‘at 70° F. and by a molecular weight of at
3 until the last added material is uniformly incorii
porated' into the mixture, and sheeting the re:
least 80,000 as determined byviscosity ‘using the
-j suiting uniform mixture between rolls operating . Btaudinger equation, until a ._uantity of from 1
‘ at the same speed and having a'plasticizing tem 10 to"9 parts of polyisobutylene has been added to 1.
part of polystyrene, whereby the added polyiso
‘ perature for the mixture of at least 300° F.
butylene is gradually incorporated into a result
4. The method which comprises subjecting
ing uniform mixture of said polystyrene and said
3 polystyrene consisting of a polymerized mass orig
, inally consisting substantially entirely of styrene ' polyisobutylene, and after the addition of the last
and characterized by a flow-time of at least 120 15 of the polyisobutylene continuing the masticaq
tion until the last added material is uniformly
seconds for a ?ow of 1.5 inches ‘as tested in a
‘ nossil-Peelies plastometer at 130° C.'wi_th 1,000 . . incorporated into the mixture, and extruding the
resulting mixture by. applied mechanical pressure
lbs. pressure per sq. in., to the-masticating mix
while saidimaterial is softened and extrudable at
1 ing action of two adjacent parallel mixing rolls
having a plasticizing temperature for the poly-' 20 a temperature of at least 300° F. .
6. The method which comprises subjecting
styrene or at least 300° F. and-rotating in oppo
~ site directions at different speeds, whereby the
polystyrene consisting of a polymerized mass orig
1 polystyrene is rendered plastic and capable of
assimilating polyisobutylene, continuing the mas
and characterized by a ?ow-time of at least 120
inally consisting substantially entirely of styrene
‘ ticating action and gradually adding to the mass
being masticated a polymer consisting of poly
isobutylene' characterized by a ‘normally solid‘
1 state at 70° F. until a quantity of from 1 to 9
‘ parts of polyisobutylene ‘has been added to 1 part
of polystyrene, whereby the added polyisobutylene
3 is gradually incorporated into a resulting uniform
I mixture of said polystyrene and said polyisobu- 1,
seconds for. a‘?ow of 1.5 inches as tested in a
Rossi-Peekes plastometer at 130° C. with 1,000
lbs. pressure per sq. in., to the masticating mixing
action of two adjacent parallel mixing rolls hav
ing a plasticizing temperature for the polystyrene
of at least 300° F. and rotating in opposite direc
tions at di?érent speeds, whereby the polystyrene
is rendered plastic and‘ capable of assimilating
polyisobutylene, continuing the masticating action
‘ tylene, and after the addition of the last of the
and gradually adding to the mass being masti
. the last added material is uniformly incorporated as cated ‘a polymer consisting of polyisobutylene
characterized by a. normally solid state at 70°F.
1 into the mixture} and sheeting the resulting uni
until _a quantity of from 1 to 9 parts of‘polyiso
form mixture between rolls operating at the same ‘
butylene has been added to 1 part of polystyrene,
‘ speed and having a plasticizing temperature for
polyisobutylene continuing the mastication until
whereby the added polyisobutylene is gradually
' the mixture'of at least 300° F.
5. The method which comprises subjecting
polystyrene consisting ‘of a polymerized inass
5 originally consisting substantially entirely of
40 incorporated into a resulting uniform mixture of
styrene and characterized by a ?ow-time of at
said polystyrene and said polyisobutylene, and
after the addition‘ of the last of the polyisobu
tylene continuing the mastication until the last
; least 120 seconds for a ?ow of 1.5 inches as tested ' , added material is uniformly incorporated into the
f in. a Rossi-Reekes plastometer at 130° C. with
1,000 lbs. pressure per sq. in., to the'masticatins
mixing actiongof two adjacent'parallel mixing
. rolls having a plasticizing temperature for the ~
‘ polystyrene of at least 300° F. and rotating in
> mixture, and extruding the resulting mixture by
applied mechanical pressure while said material
is softened and extrudable at a temperature of
atleast 300° F.
.
'
Y
,
v
p
. HUGH J. CAMERON.
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