Note: Descriptions are shown in the official language in which they were submitted.
~C-0215
POLYOLEFIN CONCENTRATE
The present invention relates to polyolefin
blends and in particular to a concentrate of a modifying
agent in a polyolefin matrix.
Polyolefins, for example homopolymers of ethy-
lene and copolymers of ethylene and higher alpha-olefins,
are used in large quantities for a variety of end-uses.
In general, polyolefins are manufactured in particulate
form, and are sold for further processing into shaped
articles, e.g. film, pipe, rods, sheet, moulded articles.
It is common for polyolefins to be blended with compounds
which modify the chemical and/or physical properties of
the polyolefin r For example, polyalkylene glycols may be
added to polyolefins to reduce the formation of gel
streaks in film manufacture or to reduce the incidence of
film breakdown, as disclosed, for example, in Canadian
Patent 961 998 to Hancock et al, which issued 1975 January
28 and U.S. Patent 4 013 622 to De Juneas et aI, which
issued 1977 March 22. Also, for example, polybutenes or
polyisobutylenes may be added to polyethylenes for the
manufacture of self-sealing or cling-stretch films, as
disclosed, for example, in U.S. Patent 3 821 332 to E.
Solop, which issued 1974 June 28, U.S. Patent 4 588 650 to
Mientus et al, which issued 1986 May 13 and U.S. Patent
4 425 2S8 to B.A. Cooper, which issued 1984 January 10.
The shaped polyolefin articles which contain
modifying agents such as those described above, genPrally
contain minor amounts of the modifying agents. Usually
the concentration of modifying agent in the shaped article
is less that 10 wt. % and most often is less than about 5
wt. ~. The modifying agent may be added directly, in the
shaped-article manufacturing process, or may be added in
the form of a concentrate ~sometimes known as a master-
batch) which may contain as high as 40-60 wt. ~ of the
~:89~
modifying agent in a polyolefin carrier. Addition in the
form of a concentrate is particularly desirable for some
shaped-article manufacturers in that it is not necessary
to purchase special equipment to handle the modifying
agent per se.
The present invention is particularly directed
to the manufacture of polyolefin concentrates containing
up to about 60 wt. % of a modifying agent. The maximum
concentration of the modifying agent depends in a large
part upon the properties of the modifying agent but may be
determined through easy experimentation.
According to the disclosures in U.S. Patent
4 607 979 which issued 1~86 August 26 to Enikolopow et al.
it is known to pulverize polymers in an extruder, using a
technique whereby the polymer is first melted~ then cooled
below its melting temperature. The cooled polymer is
crushed and pulverized and then discharged from the
extruder, thus forming a powdered polymer.
A method has now been found which is suitable
for the manufacture of strands or pellets of polyolefin
concentrate.
Accordingly the present invention provides a
process for making particulate polyolefin compositions
comprising:
a) thoroughly mixing a molten blend of a polyolefin
and at least one modifying agent;
b) cooling said blend to a temperature below the
melting temperature of the polyolefin, while
masticating the blend;
c) continuing to masticate the blend; and
d) subsequently extruding said blend below its
melting temperature to produce strands or
pellets.
The extrusion step may be omitted if the method
i5 a batch process, for example if carried out using a
~897~L~
Banbury (trade mark) mixer. The masticated blend would
then be in an uncompacted irregularly shaped particulate
form e.g. fluff, fibrous form.
The term "crumble" as used herein indicates that
the particulate is in a form which is friable or may be
subdivided relatively easily. It may be possible for
example, in some instances, to subdivide the crumble
merely by using a thumbnail to split the crumble, or to
crush the crumble with the flat end of a pencil. The
crumble is never as hard to subdivide as polyolefin
pellets which have been formed from conventional melt
extrusion processes. After the crumble has been sub-
divided, the particles are soft.
The term "polyolefin" as used herein encompasses
normally solid polymers of at least one hydrocarbon
alpha-olefin having 2-10 carbon atoms. Such polymers may
be homopolymers or copolymers. Examples of such
polyolefins include homopolymers of ethylene/ propylene
and 4-methyl pentene-l, copolymers of ethylene and/or
propylene with at least one of butene-l, hexene-l 4-methyl
pentene-l and octene-l, and copolymers of ethylene and
vinyl acetate.
In a preferred embodiment the polyolefin is a
homopolymer of ethylene, a copolymer of ethylene and at
least one C4 to C10 alpha-olefin or a copolymer of
ethylene and vinyl acetate.
In yet another embodiment a process, for the
manufacture of particulate polyolefin concentrate ln an
extruder which is adapted for the manufacture of strands
of polyolefin, said extruder having at least two segments,
the segment at or adjacent to the place or places of
introduction of the polyolefin and a modifying agent
(Segment A) being adapted to heat a blend of a polyolefin
and a modifying agent to a temperature above their melting
temperatures and to mix said polyolefin and modifying
7~L1
agent thoroughly to form a blend, and the remaining
segments being adapted to cool said blend and to maint~in
the temperature of said blend at temperatures belo~ the
melting temperature of the polyolefin and to masticate the
blend, said extruder also having an extrusion head which
is adapted to permit extrusion of strands of said blend
through holes in a die in said head, said process
comprising:
a) feeding said polyolefin and said modifying agent
to Segment A;
b) in Segment A, heating said polyolefin and said
modifying agent to a temperature above the melt-
ing temperatures of the polyolefin and modifying
agent, and mixing the polyolefin and modifying
agent to form a substantially homogeneous
blend;
c) in the remaining segments of the extruder,
masticating the blend and cooling the blend to a
temperature below the melting temperature of the
polyolefin; and
d) extruding the cooled blend through the extrusion
head or die at a temperature, said temperature
being above the temperature at which the poly-
olefin will plug said holes and below the
temperature at which the polyolefin will melt.
In a preferred embodiment the remaining segments
are cooled in order to cool the blend. In another
embodiment, a cooling fluid is added to the blend in order
to cool the blend. A preferred cooling fluid is water.
Modifying agents suitable in the present inven-
tion for blending with the polyolefin may be compatible or
incompatible with the polyolefin but must be capable of
being in liquid or molten form when the polyolefin is
molten. The modifying agents may be solid or liquid under
conditions of Standard Temperature and Pressure, viz. 20C
~ ~2B~37~
, . . .
and 101.325 kilopascals, but should be mobile at the high-
est processing temperature of the process of the present
invention and should not degrade or "flash off"
(evaporate) at processing temperatures and pressures.
Examples of such modifying agents include polyisobuty-
lenes, silicones, polyalkylene glycols, ethoxylated
tertiary salts of carboxylic acids. For example,
polyethylene glycols having molecular weights of 900 to
6000, polyisobutylenes having molecular weights between
300 and 15000, and lithium stearate are suitable for use
as modifying agents in the present invention.
The various aspects of the invention are now
described, with particular emphasis on concentrates of
polyisobutylene in a polyolefin base. Some aspects may be
described, with reference to the drawing which shows,
schematically, an extruder and an artist's conception of
the physical forms of the polyolefin blend.
The preferred process of the present invention
involves the blending of the polyolefin and modifying
agent in an extruder. Such process is preferred because
it is continuous and relatively inexpensive. The
concentrate of the present invention may be made with
other apparatus, e.g. a Banbury (trade mark) mixer, a
Brabender (trade mark) mixer.
Although single screw extruders may be used in
the present invention, twin screw extruders are preferred
commercially because the intensity of mixing is greater~
which means that the extruder barrel may be shorter. This
is important not only from a capital cost standpoint but
also the factory space required for siting the extruderO
The screw configuration is important, too, in being able
to keep the barrel length as short as possible. For
example, mixing and dispersion of the modifying agent in
the polyole~in may be aided by the use of mixing elements,
e.g. kneading blocks or the like, on the screw in the
~2~9~1
segment of the extruder wherein the polyolef;n i5 melted.
As is known in the art, mixing elements which shear and
mix the polyolefin intensely, e.g. kneading blocks,
generate much heat in the mixing process. In the segments
of the extruder where cooling takes place the use of such
intense mixing elements is usually not desirable but may
be used if sufficient cooling of the polyolefin can be
accomplished in order to keep the polyole~in below its
melting temperature.
With reference to the drawing, the twin screw
extruder 10 comprises a feeder hopper ll which is con-
nected to barrel segment 12, barrel segments 13 to 18, a
so-called "8-0" adapter 19, and an extrusion die 20.
Barrel segment 13 has an injection port 21 therein.
Although not shown in the drawing, barrels 13 and 14 have
twin screws with kneading blocks thereon. Barrels 15 to
18 have twin-scréws with conveying elements and mixing
rings thereon. The exterior of barrel segments 15 to 18
are water-cooled.
The polyolefin, P, is introduced into the
extruder through hopper 11 by known means, e.g. using a
so-called loss-in-weight feeder. The polyolefin may be in
pellet or powder form. If the modifying agent is a solid
at room temperature it may be added, as part of a "salt
and pepper" blend with the polyolefin or through a
separate feeder hopper (not shown). The modifying agent,
A, may be injected in liquid form through injection port
21, which may be upstream of one or more kneading blocks
or between kneading blocks. The polyolefin and modifying
agent are melted and mixed intensively in barrel segments
13 and 14 so that the modifying agent is thoroughly dis-
persed into the molten polyolefin. The temperatures of
barrel segments 13 and 14 may be, for example, lO-100C
higher than the melting temperature of the polyolefin, and
are typically about 2-80C higher than the melting
~2~3~7~
temperature of the polyolefin, while the temperatures of
barrel segments 15 to 18 are substantially below the
melting temperature of the polyolefin. Typical
temperatures of the barrels are 20-80C. As the blend
polyolefin and modifying agent is cooled below the melting
temperature of the polyolefin the solidifying polyolefin
is cut up, as indicated by ~1 in the drawing. Further
mastication caused by the twin screws, and optionally
mixing rings, causes the solidified blend to be further
subdivided to a mass with high surface area as indicated
by F2 in the drawing. Conveying elements then compress
the mass through the 8-0 adapter 19 and the die 20. The
compacted mass, now in crumble or wax form, is extruded
into strands through holes in the die. The strands may
then be divided into pellets or the like, as indicated by
F3 in the drawing, for ease of handling. For ease of
extrusion it is desirable to maintain the temperature of
the die somewhat closer to the melting temperature of the
polyolefin than that o the last barrel segment, e.g.
about 10-30C below the melting temperature of the
polyolefin. It is essential, however that the die
temperature be below the melting temperature of the
polyolefin, and higher than the temperature at which the
polyolefin will plug the holes in the extrusion die. Even
partial pluggage may cause the pressure to build up behind
the die, thus leading to heating and melting of the
polyolefin.
When a linear ethylene C4 to Clo alpha-
olefin copolymer is used as the polyolefin, typical
apparatus temperatures are 125-225C for barrel segments
13 and 14, 20-60C for the remaining barrels and 90-110C
for the die.
The process is now described in more detail with
reference to polyisobutylene as the modifying agent.
Polyisobutylene is used as a tackifying agent. At room
~.~8~7~
temperature many useful polyisobutylenes are oily in
nature. A problem experienced heretofore with
melt-blending 70 wt. ~ polyethylene and 30 wt. %
polyisobutylene in a conventional melt extrusion process
is that newly extruded pellets have the polyisobutylene
well-captured within the polyethylene matrix. However,
within 24 h at about 20C, the polyisobutylene migrates to
the surface of the pellet, causing the pellets to adhere
to one another. The pellets have the appearance of having
corn syrup poured over them. In order to overcome this
problem, such pellets have to be blended with pellets or
powder of a polyolefin which does not contain
polyisobutylene. The present method appears to overcome,
to a large extent, the problem of migration of the
polyisobutylene. In the present method the problem of
migration is principally lessened by a) producing a blend
as homogeneous as possible, which may be accomplished by
kneading blocks in the intensive mixing section and the
like and increasing the length of the intensive mixing
section, b) ensuring that the blend is rapidly cooled
between the intensive mixing section and the masticating
section, and c) ensuring that the blend is thoroughly
cooled before extruding through the die. If, for any
reason the resulting crumble or waxy solid is tacky then
provided that the polyisobutylene content is not too high
e.g. greater than about 60%, the tackiness may be removed
by re-extruding the crumble, keeping the polyolefin below
its melting temperature, or by dusting the crumble or waxy
solid with powdered polyethylene. The dusting technique
is not as effective as the "double extrusion" technique
but tends to be less expensive.
In the embodiment where a cooling fluid is
added, such cooling fluid is added downstream of the
intensive mixing segment, e.g. in barrel segment 15. The
7~1
cooling fluid is advantageously water but may be other
fluids e.g. liquid nitrogen, alcohols, fluorocarbons.
The cooling action of the cooling 1uid may be
accomplished by "flooding" the blend with sufficient
cooling fluid to lower the temperature of the polyolefin
to below its melting temperature. This may not be
entirely satisfactory in some situations ~ecause some of
the cooling fluid may remain entrapped in the crumble or
waxy solid. In order to overcome this difficulty, the
cooling fluid may then be vented from vent ports in the
barrels of the extruder e.g. in barrel segments 16 and 17,
in order to attain some evaporative cooling. The cooling
fluid may be the sole means of cooling the blend but it is
preferable that the barrel segments of the extruder also
be cooled externally. Additional cooling by internal
screw cooling may also be used.
The form of the extrudate depends in a large
part upon the characteristics of the modifying agent and
the concentration of the modifying agent in the
concentrate. For example, at concentrations of less than
about 30 wt. % polyisobutylene in polyethylene, the
extruded mass is in crumble form, whereas at
concentrations of more than about 30-35% polyisobutylene
in polyethylene, the extruded mass is in waxy form.
The present invention also provides for strands
or pellets made by the present process.
The present invention is exemplified further by
the following:
Example 1
100 parts by weight Sclair 1311E (trade mark)
linear low density polyethylene and 4~ parts by weight of
a polyisobutylene blend were melted and mixed intensively
in a Brabender Plasticorder (trade mark) twin rotor
; compounder. The polyisobutylene blend consisted of 14.7
parts by weight of Indopol H-300 (trade mark) and 29.3
.. . .
~23~397~
parts by weight of Indopol H-l900 polyisobutylenes. After
such mixing about 14 parts by weight water was added to
the compounder, thus bringing the temperature of the blend
to 100-105C. Most of the water flashed off as steam.
Further mixing and kneading of the blend, which was in
soft plastic form, permitted folding of the resin onto
itself to form a crumbled mass. The crumble so formed
remained free of tackiness even after 24 h.
This experiment showed that the twin rotor
action of sigma-blade mixer of the Brabender Plasticorder
compounder provided sufficiently intense mixing of the
polyethylene and polyisobutylene and sufficient mastica-
tion of the cooled blend.
Example 2
The polyethylene ar.d polyisobutylene of Example
1 were mixed and melted in a Gelimat (trade mark) high
speed 1 litre mixer. 250 ml water was added to the molten
blend. This type of mixer gave insufficient mastication
to the cooled blend and a solid blob of polymer was
formed. It was very sticky after 24 h due to the migra-
tion of the polyisobutylene to the surface of the polymer
mass. This does not fall within the scope of the present
invention.
Example 3
In this experiment a 90 mm Berstorff twin screw,
six-segment extruder, equipped with a 100-hole die, was
used. The die holes were 2.2 mm in diameter. In the
first two barrel segments of the extruder, adjacent the
polyolefin feed hopper, two kneading blocks were used to
ensure melting of the polyethylene feed. Polyisobutylene
was fed into the first barrel segment and water into the
third barrel segment. Mo venting of water was done. The
first two barrel segments were heated to 200C and the
last four barrel segments cooled to 65C. Sclair 2114
~2~
linear low density polyethylene, ground to 30 mesh, was
fed to the extruder at 80 kg~h; the polyisobutylene (the
blend of Example 1 was used) was fed to the extruder at
90C at a rate of 49 kg/h; and water was fed to the
extruder at a rate of 6 kg/h. The die temperature was set
at about 80C. The resulting extruded pellets had smooth
but lumpy surfaces. The pellets were hard and wax-like,
and soft enough to break with fingernails. The pellets
were analysed to contain about 40 wt. ~ polyisobutylene
and 5 wt. % water. This indicated that venting of the
water would have been desirable. The pellets also had
some surface tackiness and the pellets became sticky after
24 h.
The pellets were re-extruded, without melting,
in a 63.5 mm single screw extruder at 80C. The pellets
so formed were free of surface tackiness and were free
flowing. These pellets also were soft enough to be
pierced wi h a fingernail, and had a rough sur~ace
texture.
Example 4
In this experiment, a 90 mm Berstorf~ twin screw
six-segment extruder, equipped with a 100 hole die was
used. The die holes were 3.18 mm in diameter. The barrel
segment temperatures were 220, 150, 43, 60, 55, 46C
for barrel segments 1 through 6. Barrel segment 6 was
closest to the extrusion die. The die temperature was
kept at 90C. Sclair 1311E linear low density poly-
ethylene ground to 30 mesh, was fed to the extruder at
70 kg/h. Indopol H-1500 polyisobutylene was fed into the
first barrel segment at 100C at a rate of 42.5 kg/h. The
resulting extruded pellets were hard, waxy, and had a
lumpy surface, but they were still soft enough to be
divisible by piercing the pellet with fingernails. The
pellets were slightly tacky, and the ~ackiness was reduced
11
~LZ897~1
12
by mixing polyethylene powder to the pellets.
Example 5
In this experiment, a 90 mm Berstorff twin screw
six-segment extruder was used with no die or adapter
attached to the last barrel. The extruder temperatures
were 160, 113, 42, 30, 29, and 39C for barrel segments 1
through 6.
Sclair 1311E polyethylene powder (30 mesh) was
fed into the extruder at 101 kg/h. Indopol H-1500
polyisobutene was fed into the first barrel segment at a
rate of 60 kg/h. The discharged material was irregular in
size and shape and had a "crumble"-like texture.
This crumble was later pelletized in a 30.5 cm
California (trademark) Pellet Mill using a 4.76 mm x
25.4 mm with R die. The material was pelletized at a
rate of 1160 kg/h. The material was tack free even after
six months storage at 20C.
12
