Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PIPE EXTRUSIO~ POLYMERIC BLEND
This invention relates to the extrusion of plastic pipe. In one of
its aspects this invention relates to polymers suitable for use in pipe extru-
sion. In another of its aspects this invention relates to polymeric blends
useful in pipe extrusion.
Polymers and polymeric blends used for pipe extrusion should,
ideally, combine good flow capabilities and good performance capabilities in
producing smooth extrudate. It has now been found that certain ethylene-
hexene copolymers can be blended wi.h other ethylene copolymers and process
aids to produce polymeric blends having desirable characteristics for pipe
extrusion using either conventional extrusion or dynamic extrusion apparatus.
It is an object of this invention to provide polymeric blends useful
in the extrusion of plastic pipe.
Other aspects, objects and the various advantages of this invention
will become apparent upon reading this specification and the appended claims.
A polymeric blend composition suitable for use in dynamic and
conventional extrusion apparatus is provided. The composition comprises from
about 80 to about 15 weight percent of copolymer A, an ethylene-hexene copoly-
mer of about 0.936 to about 0.940 density and a melt index of about 0.30 to
about 0.45 (ASTM D 1238-65T, condition E); and about 10 to about 75 weight
percent of copolymer B, a copolymer chosen from either ethylene butene copoly-
mer of about 0.940 to about 0.942 density and high load melt index (HLMI) of
about O to about 2 (ASTM D 1238-65T, condition F) or ethylene-hexene copolymer
of about 0.942 to about 0.945 density and an HLMI of about 3 to about 5
(ASTM D 1238-65T, condition F); and about 5 to about 15 weight percent of a
concentrate of copolymer A containing sufficient carbon black to produce a
constant concentrate density in the range of about 1.0 to about 1.1.
In a preferred embodiment of the inYention the polymeric blend will
contain, in addition to the components listed above~ an antioxidant in an
amount equal to up to about 0.5 percent by weight of the polymer and a slip
agent in an amount up to about 1.0 percent weight of the polymers.
Conventional extrusion of melted polymer through a screw extruder is
well-known in the art. In conventional extrusion of plastic pipe, the extrudate
may be forced through a die with no cooling or through a die having some cool-
ing, but the cooling is only of such sufficiency that the extrudate must be
sized and further cooled outside the die. In such extrusion, the extruded
pipe requires support as it emerges from the die in a softened condition. In
a dynamic extruder the extrusion apparatus is equipped with a die which has
cooling channels so that the pipe emerges from the die in a froæen or hardened
condition. The die completes the sizing of the pipe so that no external sizing
operation is necessary. The polymer compositions of the present invention are
useful in both types of extrusion.
The copolymers used both as copolymer A, the ethylene-hexene copoly-
mer having melt index in the range measured by (ASTM D 1238-65T, condition E),
and the copolymer chosen from ethylene butene copolymer and ethylene-hexene
copolymer having high load melt index measured by tASTM D 1238-65T, condition
F) are standard olefin copolymers which are well-known in the art. These
copolymers can be prepared by methods such as those set out in U.S. 2,825,721.
The concentrate of copolymer A containing sufficient carbon black
to produce a concentrate having a density in the range of about 1.0 to about
1.1 can also be prepared by well-known methods. The concentrate is made by
blending the appropriate copolymer with a sufficient amount of carbon black
to produce the desired density range with plasticizing, extrusion, and pellet-
ing of a concentrate of the desired density.
To produce the blends useful in the process of this invention,
appropriate amounts of the various components are dry blended and fed into
extruder equipment either for dynamic extrusion or conventional screw extru-
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sion. The blend is plasticized and extruded by conventional means as taught
by U.S. 3,239,881 and U.S. 3,309,436 for dynamic extrusion and by conventional
extrusion as well-known in the art. Antioxidant and processing aids such as
slip agents, can be added to the blend before extrusion as desired.
In the process of this invention and the compositions useful in the
process, any of the well-known antioxidants useful with olefin polymers can be
used. It has been found that 4,4-thiobis-(6-t-butyl-n-cresol) is particularly
useful with the combination of components herein described.
Similarly, whereas slip agents normally found useful in the process-
ing of extruded pipe are useful in the compositions herein described, a process-ing aid comprising two parts of Carbowax and one part glycerine has been found
particularly suitable. Carbowax is polyethylene glycol sold by Union Carbide
Company. The following examples are offered to describe the processing of the
compositions described above into finished pipe using either dynamic extrusion
or conventional screw extrusion.
Example I
A blend useful for pipe extrusion in a screw extruder was made
containing 15 weight percent of an ethylene butene copolymer, density of
O.940 to 0.942 and an ULMI of 1 to 2; 74.6 weight percent of an ethylene-
hexene copolymer, density 0.936 to 0.940, and an MI of 0.30 to 0.45; 10 weight
percent of a concentrate of the ethylene-hexene copolymer containing 25 weight
percent carbon black; 0.1 weight percent of an antioxidant 4,4-thiobis-(6-t-
butyl-n-cresol); and 0.3 weight percent of liquid ingredient containing five
parts Carbowax sold by Union Carbide Company and two parts glycerine. The
blend was fed to a 2 1~2 inch NRM extruder with a 4 inch pipe die attached.
The die had channels in both the mandrel and the die ring for circulation of
cooling water for partially cooling the extrudate. Sufficient cooling was
supplied to cause the extrudate to emerge f~om the die in a softened condition.
The softened extrudate was drawn down into a 3 inch sizing sleeve positioned
at the entry to a cooling water tank to produce 3 inch pipe.
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Example II
A blend was made containing 20 weight percent of an ethylene-
hexene copolymer, density 0.942 to 0.`945 and an HLMI of 3 to 5; 69.8 weight
percent of an ethylene-hexene copolymer, density 0.936 to 0.940, an MI of 0.30
to 0.45; and 10 weight percent of a concentrate of 0.936 to 0.940 hexene co-
polymer containing 25 weight percent carbon black; 0.1 weight percent of the
antioxidant 4,4-thiobis-(6-t-butyl-n-cresol); and 0.1 weight percent of liquid
ingredient containing five parts Carbowax and two parts glycerine. The blend
was fed to a 2 1/2 inch NRM extruder with a 1 1/4 inch pipe die attached.
The die had cooling channels in both the mandrel and die ring for partially
cooling the extrudate. Sufficient cooling was supplied to cause the extrudate
to emerge in a softened condition. The softened extrudate was drawn down into
a 1 inch sizing sleeve attached in the entry of a cooling water tank to pro-
duce 1 inch pipe.
Example III
Using the same blend, extruder, and pipe die as described in
Example I, the die was operated as a dynamic extrusion die cooling the extru-
date to the point that it emerged from the die in a frozen or hardened condi-
tion and required no external sizing to produce 4 inch pipe.
