Note: Descriptions are shown in the official language in which they were submitted.
1 155~
Thls inventlon relates to a thick-walled, seamless,
rlgid condult conslsting essentlally of an oriented crystalllne
thermoplastic polymer havlng lmproved propertles; to a sheet
made thererrom and to an artlcle of manufacture made from
the conduit or sheet.
The condult is fabricated by solld sta~e hydro-
statlc extrusion of the polymer in an apparatus including an
annular orlfice having a diametricallJ diverglng geometry
and converging walls and~orlfice area whereby the polymer-ls
substantially simultaneously elongated clrcumrerentially and
axlally. ~ ~
It ls well known that the physical and mechanlcal
properties of semi-crystalline thermoplastic polymers can be
lmproved by orienting their struckures. Polymer processlng
~lS methods, such as drawing, blow molding, in~ectlon molding
and the ll~e have all been used to rabricate articles of
thermoplastic polymers having oriented structures.
In recent years, extensive study has been dlrected
I
to methods of de~orming the t~ermoplastic polymers in a
~; 20 ~ ` solid s~tate. In khese methods,~the polymer is~mechanically
:
` de~ormed to obtain a deslred uniaxial or biaxlal molecular
~ ~ ~ 3 ~
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11552B~
orlentatlon. The polymer may be drawn, extruded or processed
at temperatures within the range from the glass transltion
temperature to temperatures ~ust below the crys~alline melt
temperatures of the polymers. In the case of stereoregular
polypropylene, the polymer may be processed at temperatures
as low as 0C (32F). Products such as strlp~ tubes, rods and
shapes, usually havln~ predominantly unidirectlonal orienta-
tion, have been fabricated by such processing methods. The
extrusion methods and apparatus used for processing the
poIymers are similar to those used in the metal industry.
Short tubular artlcles with high axial elongation and low
circumferentlal elongation, for example shotgun shells, have
been produced by solid s~tate extrusion.
One method for processlng a polymer ls described
by Robert A. Covlngton, Jr. et al in U. S. Patent No.~
3,205,290 entitled "Method O:r Making Tubing for Cartrldge
easings and the Like." In the method, a molten polymer, ror
example polyethylene or polypropylene, is ~ormed lnto a
thick-walled tubular prerorm or billet. The billet is
processed ln a two-step process into a short~ thlck-waIled
tubular article having one closed end.~ Initially, the
~ billet ls expanded circumferentially by an average of about
;~ 40~ to~50 percent Oy rorcing lt onto a solid mandrel.
Circumferentlal elon~atlon re~ers to the expanslon o~ the
medlan circum~erence of the billet. The expanded blllet on
the solid mandrel ls then forced through a drawing dle to
elongate the expanded billet ln an axlal direction while the
circum~erentlal elon~atlon remains constant The axial
elongatlon can be as much as 350 percent resulting ln a
predominantly axial orlentation.
h~
1 ~52~5
The Covington et al method does not allow a
clrcumrerential expansion Or at least 100 percent. If such
large circumferential expansions were a~tempted, the blllet
would buckle or collapse in an effort to push lt over the
mandrel. If large circumrerential deformations Or 100
percent or more could be made by Covington et al, the
deformations would be tensile ln nature because the billet
would be drawn over the mandrel. Drawing the blllet over
the mandrel would result in non-homogeneous deformation of
the polymer structure.
U. S. Patent No. 3,198,866 to R. A. Covington et
al entitled "Method and Apparatus for producing Plastic
Tubular Members" ls directed to a contlnuous method ror
producl~g tubular members. In the method, thlck-walled,
bored slugs of a thermoplastic polymer, polyethylene having
a crystallinity o~ 60 to 85 percent, are rorced over a
mandrel b~ ram pressure.
The patent contends that the molecular structure
of the polymer is orlented both longitudinally and trans-
versely. However, the apparatus o~ Covington et al lsdesigned to prevent any slgniflcant increase ln the outsids
diameter Or the slug, l.e. the polymer ls not expanded
circumferentially into a conduit having a larger outside
diameter than the outside diameter o~ the slug.~ Slnce, the
!
slug is lncreased ln length and the wall thickness is
decreased but;the outside diameter is not increased~ the
polymer ls highly orlented in the longitudlnal directlon but
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I 15526~ 1
is not hiKhly orlented in the clrcum~erential directlon.
There is little median clrcumferential elongation there~ore
there ls little, lf any, improvement of the average propertles
in the circumferential direction.
Another process used to produce orlented shotshells
is described by Donald Urquhart Flndla~ et al in U,S. Patent
No. 3,929,960 entitled "Method for Producing 0riented
Plastic Shotshells." The method is directed to making an
; orlented polyo~lerinic shotshell with an axial tenslle
strength between about 1400 and 2100 kilograms of ~orce per
square centimeter (20,000 and 30,000 pounds per square inch)
and a circumferential tensile~strength between about 387 and
600 kilograms of ~orce per square centimeter (5,500 and
8,500 pounds~per square inch).~ A polyole~inic blank which
,
~ is 2.54 centlmete~rs (1 inchj in length and having a wall
thlckness or l.06 centimeters (0.42 lnch) is heated to a
temperature between 27C and 115C (80F and 240F) and ls
placed on a solidlmovable mandrel. The blank 1~ moved into
a die cavity. A ram forces the blank over the mandrel in a
back extrusi.on to reduce the blank wall with very llttle, ir i
any, expansion Or the outside diameter o~ the blank.
The method~o~ Findlay et al limits the clrcum-
ferential expansio n Or the polymer, hence limlts the cir-
cumrerential~derormation~ o~ the polymer structure. Since
the axlal elongatlon is hleh, the molecular structure is
hlghly oriented ln the axial dlrection, The structure,
~comprised of spherulltic crystalllne aggregates, is highly
--6
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1 1~52~
elongated axlally but with very llttle elongatlon clrcum-
ferentially. The structure, thererore, is not comprised of
platelet or wafer-like, radially compressed spherulltlc
crystalline aggregates nor are the circumferential properties
improved signi~lcantly.
The indirect extrusion method Or Findlay et al
limits the expansion of the outside dlameter o~ the blank to
below 25 percent which is well below the minimum circum-
~erential expansion achleved in the method Or the invention
hereinafter described.
As noted by Robert Shaw in U.S. Patent No. 3,714,320
entltled "Cold Extrusion Process", polymers, particularly
stereoregular polypropylene, can be fabricated by various
methods such as rolling, ~orging, swaging and peening at
temperatures below the crystalline melt temperature. Shaw
teaches that cold extrusion o~ polymers has limited appllca-
~lon because excessive heat i9 generated during large defor-
matlons thereby increasing the temperature of the polymer to
lts melting temperature. Shaw attempts to overcome the
problem Or extruding polymers by cooling them to temperatures
as low as OC (32F). I~ necessary, the extrusion apparatus
can also be cooIed to low temperatures. Forward extruslon
results ln the conversion of rod-like shapes into rod-like
extrudates of various cross-sectlonal shapes having a
~enerally reduced cross-sectional area. It is apparent that
Shaw does not envision ma}cing circum~erentlally elongated
pipes and conduit by extruslon since he teaches that tubes
--7--
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11552B~ ,
or plpes may be formed by a known manner similar to the so-
called Mannesmann method in which a mandrel is placed lnside
a tube and a rolllng or hammering force is applied to the
outside surface. Back extrusion can be used to produce cup-
like shapes.
Shaw's teaching is dlametrically opposed to an
extrusion process in which a thermoplastic polymer is heated
to a temperature which ls between lts 4.64 kilo~rams force
; per square centimeter (66 pounds per square inch) heat
derlection temperature and lts crystalline melt temperature
for extrusion through a die conflgura~ion whlch will substan-
tially slmultaneously elongate the polymer circumferentially
and axlally.
In the limited appllcation of Shaw's process to
extrusion in which he teaches that the polymer must be
cooled to low temperatures, it would requlre exoessively
high pressures, on the order of lO times as great as those
required to warm extrude the polymer, in order to extrude
the cooled polymer into a tube comprised of highly orlented
polymer. The use of excessively high pressures applied to a
relatively strong msterial would result in stlck-slip, high
strain rate, high energy extrusion and perlodic generation
o~ hlgh temperatures at whlch the polymer would melt. When
a polymer melts, the crystalllnity and orientatlon ln the
polymer are adversely af~ected and the product is damaged
beyond use. There~ore, a polymer processed accordlng to Shaw
could not possibly have a structure comprlsed Or platelst or
:
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wafer-llke, radially compressed spherulitlc crystalline
aggregates oriented both clrcumferentially and axially and
having improved circumferentlal propert~es.
The use of the Mannesmann method wherein a har~er-
ing or rolling pressure is applled locally to the surface of
a tube or a mandrel to produce an elongated tube would not
produce homogeneously deformed spherulitic crystalllne
aggregates, since lar~e localized shear strain gradients
would be induced in the polymer resulting in non-homogeneous
deformation of the spherulites. Non-homogeneous deformation
results in damage to the spherulitic crystalline aggregates
~nd to the ~ormatlon Or~ microvids and the enlargement of
existing microvoids. The density of a polymer so worked is
less than the denslty of the original blllet. Thls non-
homogeneous deformation would also adversely affect the lowtemperature tenslle impact strength and the density related
properties of the polymer.
Long, thick-walled high strength tubular polymer
products, such as high pressure hoses, tubes and pipes have
been produced by plasticatlng extrusion Or riber reinrorced
plastics and medlum pressure tubes by ~lasticati~g extrusion
methods.
One such method for producing medlum pressure
thermoplastic pipe having a diameter as lar~e as 152.4
centimeters (6Q inches) and a wall khickness of over 5 . o8
centimeters (2 inches) is described in UOS. Patent No.
3,907,961 to Guy E. Carrow entitled "Flexlble Cylinder ~or
Cooling an Extruded Pipe." The pipe can be made by either
1 1552~ ~
screw extrusion or impact extrusion. In either case, the
thermoplastlc polymer is heated to a molten state and is
extruded through a conical shape passag~ onto a flexlble
mandrel. A coolln~ medium is provided to cool the surfaces
of the pipe to a solldiried state. The polymer is extruded
in the molten state and the resultant pipe has an unoriented
structure.
A method for producing high pressure plpe is
described in U. S. Patent No. 4,056,591 to Lloyd A. Goet~ler
et al which is directed to a process for controlling~the
orientation of dlscontinuous fiber in a flber reinforced
product produced by melt or plasticatlng extrusion. The
flber-fllled matrix is extruded through a dlverglng die
having a generally constant channel. The walls Or the dle
may taper sllghtly so that the area Or the outlet Or the die
is larger than the area of the inlet of the dle. The amounk
Or orientation of the fibers in the hoop direction ls
directly related to the area expansion of the channel rrom
the inlet to the outlet Or the channel. The product produced
is a reinforced hose contai~ing flbers which are oriented in
the circumferential direction to improve the circumferential
properties. While the fibers may be oriented, the polymer
is unoriented since it is processed in a molten state.
Since the fiber reinforced polymer is processed in
a molten state, the structure is not comprised of platelet
or wafer-like, radially compressed spherulitic crystalllne
aggregates highly oriented both circumferentially and
axially, although the fibers added to the polymer may be
oriented circumferentlally.
--10-- 1.
1 ~S52~5
Blaxially orlented contalners, such as bo~tles
used ln the sort drink lndustry are made by a melt extrusion-
stretching or in~ection molding-blowing expandln~ process.
One such process in which a biaxially oriented
hollow artlcle ha~ing good transparency and strength and
made from polypropylene is processed by the method described
ln U.S. Patent No. 3,923,943 to Fumio Iriko et al entltled
"Method for Molding Synthetic Resin Hollow Artlcles." In
the method, the lnitial step is the production of a parlson
by in~ection molding. The parison is expanded by stretching
in contradistinction to belng expanded by compressive ~orcec
therefore the structure is non-homogeneously deformed and ls
susceptlble to the formation o~ microvoids thereby decreasing
- the density of the polymer typically about 0.5 percent.
A second method employed to produce a biaxially
oriented container is described by Fred E. Wlley et al in
U.S. Pat,ent No. 3,896,200 entitled "Method Or Moldlng
Biaxially Oriented Hollow Articles." A parison is held in
constant ten9ion and ls stretched in the axlal direction
be~ore or as it is expanded radially lnto a cavity. i,
, Stlll another method ror producln~ containers
;
which have clarlty ls descrlbed in U.S. Patent No. 4,002,709
to Larry P. Mozer entitled "Controlled Air in Polyester Tube
Extrusion rOr Clear Sealable Parison." In the process a
polyester, for example polyethylene terephthalate, is melt
extruded into a clear thlck-w~lled tublng which ls then
heated and blown into a container. The polyester is in an
amorphous state as evldenced by the clarit~ o~ the tublng.
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The containers ln the above processes are produced
by stretching the polymer, typically over 250 percent. Such
large stretchlng deformatlons result in non-homogeneous
derormation of the structure thereby damaging the spherulitic ',
crystalline aggregates, causing the formation of microvolds
; and the enlargement of microvoids already present in the
polymer. Th0 density of the polymer is decreased and the
mlcrostructural sensltlve properties, such as stress whitenlng
and low temperature brittleness are not eliminated.
It is desired to provlde a deformation method
which ~s compressive in nature whereby the problems of non-
homogeneous deformation and the associated defects are
suppressed and an oriented spherulitic crystalllne aggregate
structure substantially free rrom such defects ls produced.
The prior art processes described above, by which
tubular products consisting essentially vr thermoplastlc
polymers are produced are lncapable o~ and cannot be adapted
to expand a polymer by at least 100 percent in the cir- j
cumferential direction in a compresslon-type deformatlon.
Prlor art processes ~or producing hoses or elongated tubular
products are directed to melt or plasticating extrusion
processes whlch result ln the production Or non-oriented
products. Prior art processes for produclng large diameter
containers are directed to stretching or tensioning processes
in which a polymer is expanded at least 100 percent ln the
circumrerential direction. Stretching or tensioning causes
non-homogeneous de~ormation o~ the spherulltic crystalline
aggregates in the polymer structure. The spherulites are
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11~5~5
ruptured and kllted. Microvolds, microribrils and eventually
- fibrils are ~ormed. Defects, such as microvoids already
present in the polymer are enlarged. The resultlng products
are hlghly oriente~ in a circumferentlal directlon, but have
defects formed ln the structure. None of the prior art
processes desoribed above produces a conduit conslsting
essentially of a crystalline thermoplastic polymer which ls
expanded at least 100 percent in the clrcumferential
direction and is expanded at least 50 percent ln the axial
direct~on and has a structure consisting essentially of
dlscrete platelet or wafer-like, radially compressed
spherulitic crystalline aggregates which are oriented ln
both the clrcu~erential and axial directions, which is
substantially devold of process induced defects, such as
mlcroVOidS and has a density which is the same as or h~gher
than the same polymer processed into a conduit by prlor art
processes and whlch has improved circumferential tensile
' impact strength and ls less susceptible to ~urther micro-
; skructural damage on subsequent stretching.
Neither do the prlor (~rt rererences produce a
sheet from a conduit~, which~sheet retalns the unique morphology
and propertles of the conduitS nor an artlcle Or manufacture
whlch is made ~rom the conduit or sheet, whlch article will
retain the microstructure and properties of the condult or
sheet in at least a portion thereof
: '
The prior art re~erences also do not produce a
conduit, sheet or article of manufacture from a substan-
tlally non-oriented seml-crystalline thermoplastic polymer
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1 ~52~
which contains a rlller and whlch has a matrix comprlsed of
the unlque oriented microstructure and properties hereinafter
described.
It ls an ob~ect of thls invention to provide a
conduit consisting essentially of a crystalline thermo-
! plastic polymer which ls substantially ~ree from defects
caused by non-homogeneous deformation o~ the polymer, is
orlented in both a circumrerent1al direction and an axial
; dlrection, and has particularly improved circumferential
tensile impact strength over the ambient to low temperature
range, and retains the density of the polymer from which it
ls p.rocessed.
It is a rurther ob~ect of thls invention to provide
a commercially feasible process by which said conduit is
produced from a substantially non-oriented semi-crystalline
thermoplastic polymer.
It ls a ~urther ob~ect of this invention to produce
a ~heet ~rom the condult by solid state heat-~lattenin~
techniques and which is characterized by retaining substan-
tially the same morpholo~y and properties o~ the conduit and
having a substantially uniform thickness and excellent
formability.
It is a ~urther ob~ect o~ this invention to produce
an article Or manufacture ~rom the conduit or sheet by known
solid state processing techniques whereby the article will
retaln the unique morphology and properties of the conduit
or sheet in at least a portion thererore.
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Broadly stated, the invention is a hydrostat1c extrusion
press provided with means for apply;ng extrusion pressure to extrude a
generally cylindrical semi-crystalline thermoplastic polymer preform
having an outer surface and a bore surface whereby the preform is forced
to pass in a solid state through an annular orifice defined by the surface
of a d;e section in spaced relationsh;p w;th the surface of a mandrel-head
supported by a mandrel and means for ri.gi:dly aligning the press during
; extrusion. The press comprises: (a) an outer support means having two
ends, (b) a container means aligned within one end of the outer support
means and including a shell having an outer surface and an inner surface
and two end surfaces, a plug and piston assemblage closing one end of the
shell, (c) the die sect;on being a continuous surface with respect to one
end of the inner surface of the shell of the container means and including
: a converging first section, a first generally cylindrical land surface
axially aligned with respect to the apparatus, a second generally cy-
lindrical land surface larger in diameter than the first generally
cylindrical land surface and parallel thereto and a diverging conical
surface connecting the first and second generally cylindrical parallel
land surfaces and forming an angle ~ of between 15 and 45 with the axis
of the apparatus, (d) an extrudate receiving means aligned wlthin the
other end of the outer support means and including a shell having an
outer surface and an inner surface and two end surfaces, a mandrel having
two ends coaxially aligned within the outer shell and generally in spaced
relationship to the inner surface thereof, (e) a generally conical mandrel-
head suppo.rted on the::other end of the mandrel and in spaced relation
: with the surfaces of the die section, having a recessed base surface, a
generally cylindrical tapering upper portion which forms an angle
of between 20 and 50 with the axis of the apparatus and a generally
cylindrical nose portlon, (f) an annular orifice ~ormed by surfaces of
- 14a -
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1 1~5265
the mandrel-head and the die section comprised o~: (;) a generally
converging conical entrance, (ii) a generally cyllndrical sealing
zone, (iii) a generally con;cally shaped expanding zone h~v~ng a generally
converging cross-sectional area and a d;:ametrically diverging geometry,
(iv) a generally cylindrical s;zi'ng zone parallel to the seali'ng zone
and having a smaller cross-secti'onal area and a median diame-ter which is at
least 100 percent larger than the median diameter of the sealing zone, and
(v) transition zones of desired radi'i and smooth surfaces between any two
of the zones whereby the billet is substantially simultaneously expanded
circumferentially at least 100 percent and axially elongated at least 50
percent, and (g) sealing means formed by the surfaces oF the mandrel-
head in contact with the inner surface of the billet and the die surfaces
in contact with the outer surface of the billet in the container assembly
whereby leakage of fluid ;s prevented during loading and prior to extrusion
and a film of the hydrostatic fluid is formed on the surfaces of the
billet during extrusion, (h) a first pressurizing means disposed adjacent
one of the two ends of the outer support means and contiguous with the
plug and piston assembly and one end surface of the container assembly
of-(d) whereby pressure for extrusion is applied to the preform, and (i) a
second pressurizing means disposed adjacent the opposite end of the outer
support means and contiguous with one end of the extrudate receiving
means and co-acting with the first pressurizi'ng means to rigidly align
the extrusion press.
- 14 b -
1 ~52~
~IGURE 1 is a diagrammatic representation Or the
extrusion Or a thermoplastic polymer preform lnto a conduit
and the formation of a sheet product rrom the condult
and showing a plctorlal representation Or the structure
formed in the prerorm and the conduit.
~IGURE lA is a test coupon cut from the thermo-
- plast~c polymer preform shown in Figure 1.
FIGURE lB is a test coupon cut from the conduit
shown in Figure 1.
FIGURE 2 is an elevation vlew ln cross-section Or
a vertical batch extrusion apparatus, which may be used ln
the method of the lnvention, showing a substantlally non-
orlented seml-crystalllne heated thermoplastic polymer
~ prerorm in posltlon at the start Or the hydrostatlc extrusion
process.
FIGURE 3 shows the apparatus o~' FIGURF, 2 arter the
preform has been ex~ruded.
FIGU~E 4 is a top vlew or a slotted washer used in
the apparatus o~ the inventlon.
FIGURE 5 ls a top view Or a grooved washer used in
the apparatus Or the lnvention.
FIGUR~ 6 is~a schematic vlew in cross-sectlon of a
second embodiment of an apparatus which may be used in a
semi-contlnuous process for~hydrostatlcally ex~ruding a
semi-crystalllne thermoplastic polymer prerorm.
~ICURE 7 shows the apparatus Or FIGURE 6 arter the
thermoplastic polymer pre~orm has been extruded.
,
- 15 -
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~ 1~52~
FIGURE 8 shows a cross-sect~onal v;ew of a portion of a
heating tank which ~s used in the apparatus shown in FIGURE 6.
FI.GURE 9 is an isometric view of a frozen food container
made from the sheet of the invention.
FIGURE 10 is an isometric vi.ew of a re~ri:gerator door liner
which can be made ~rom a sheet of the ;nvention.
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In accordance wlth this lnvention~ there is
provided a thick-walled, seamless, rigid conduit havlng a
wall thickne~s from about 0.5 percent to about 6.25 percent
of the outside diameter, conslsting essentially of an
oriented crystalline thermoplastlc polymer characterlzed by
a density which is at least equal to the denslty Or the
unoriented polymer and by a memory urglng the polymer back
to its unoriented state when sub~ected to heating in an
unconstralned state for a time ~ust below lts crystalline
melt temperature. The polymer has a structure which is
substantially free from process induced defects and is
comprised of discrete, platelet or wafer-like, radlally
compressed spherulltic crystalline aggregates which are
oriented in the plane of the conduit wall. The circumfer-
ential ultimate tensile strength of the conduit is at least
one and three quarters as great as that of the polymer in a
substantially non-orlented state and the circumrerenkial
tensile lmpact strength is at least five times as great as
that o~ the polymer in the substantially non-orierlted state
at 24C (75F). The polymer retains at least 20 percen~ of
such clrcumferentlal tensile impact strength at -45C (-50F).
~: The ratlo of the tensile impact strength (TIS) to the ultimate
tensile strength (UTS) as determined by ASTM D1822 S-type
specimens is at least 50% greater than that ratio determlned
~or the same polymer composition wh~ch is biaxlally oriented
.
,
11~S~65 ,
to the same ultimate tenslle ~trength level by conventional
solld state de~ormatlon processes, ~or example blow moldlng
or thermoforming or tentering. The conduit ls less susceptlble
to mlcrostructural damage on subsequent solid state derormatlon
processing than conduits comprised of non-oriented thermo-
plastic polymers.
In a second embodiment of ~he invention, a conduit
of thls invention in which the clrcumferential and axial
i orientations are substantially equal is slit and heat
flattened under pressure to produce sheet which ls formable
at temperatures below the crystalllne melt temperature,
i.e., in a solid state by methods, such as hot stamping,
thermoforming, pressing and the like, into usable products
such as luggage,` automotive hoods, trunk lids, front panels
15~ and the like. Suoh sheets retain the morphology and properties
of the conduit and are less permeable than oriented sheets
prepared by conventional drawing and stretching process.
In a third embodiment, a conduit Or this lnvention
is prepared ~rom a filled seml-crystalline thermoplastlc
hornopolymer3 for example lsotactic polypropylene. The
conduit is sllt and heat flattened to produce a fllled
polymer sheet having a matrix comprised of an oriented
microstructure.
In a fourth embodiment o~ the invention the ~illed
orlented sheet can be processed by solid state processes
into articles Or manufacture such as refrigerator accessories,
such as door linersg chiller trays, ve~etable and frult
- 17 -
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1 ~5~5
trays, gaskets; automotive parts, such as hoods, and trunk
lids; deep contalners, such as garbage pails, storage drums,
water buckets; luggage, etc.
The conduit of the lnvention ls produced by solid
state hydrostatic extrusion of a substantially non-oriented
semi-crystalline thermoplastlc polymer. The polymer is
preferably heated to a temperature whlch is ln a range
between about its 4.64 kilograms of force per square centi-
meter (66 pounds per square inch) deflection temperature and
8C (14F) below the crystalline melt temperature. Sufficient
pressure is applled through a hydrostatic fluld to extrude
the polymer through an annular orifice having converging
walls, a converging cross-sectional area and a diametrically
diverglng geometry~ The polymer ls elongated substantially
slmultaneously in both the clrcumferential and axlal
¦ directions. The pressure required for extrusion ls maintalned
; ln the rluid by a sealing means which allows a thin film of
the rluid to be extruded wlth the preform and to act as a
lubricant for the polymer during extrusion. The extrudate
i 20 is lubrlcated and cooled by a second fluid as it passes over
a mandrel surface. Cooling ~lxes the polymer and reduces
the lnherent tendency of the polymer to spring back and
recover its shape.
.
The polymer ls extruded in a hydrostatlc extrusion
press. The press is~comprised o~ a hydraulic pressurizlng
means coactlng with a contalner assembly and an extrudate
; . receiving assembly. A die and a ~andrel-head posltioned in
the contalner assembly form an annular oriflce through whlch
- 18 -
li,~ .
5 ~
the polymer 15 extrude~. The mandrel-hea~ 1~ conkiguous and
aligned with a mandrel in the extrudate receivlng assembly.
A pressurized force surflcient to extrude the thermoplastic
polymer is applled to a polymer preform by a pressurlzlng
means. The sealing means in the contalner assembly prevents
leakage of hydrostatlc-fluld thereby maintalnlng extrusion
pressure ln the fluld while allowing a fllm Or the fluid to
be extruded wlth the preform to provlde lubricity durlng
extrusion. The annular orifice has an axially allgned inlet
or sealing zone, an expanding and elongating 20ne having
converging walls, a converging cross-sectlonal area and a
diametrlcally diverging geometry and an outlet or slzing
zone. The sizlng zone ls smaller~in cross-sectional area
~ and has larger outside and lnslde dlameters than the seallng
zone.
~ ~ ~ The polymer is extruded into an extrudate receivlng;~ assembly axla`lly allgned and contl~uous wlth the container
assembly. The mandrel in the extrudate containing assembly
i5 con~lguous and allgned with the ~ase Or the nlan~rel-head.
A clamping force is applied to the mandrel to provide
rlgidlty to the apparatus and to prevent lateral and axial
movement of~the mandrel-head during extrusion. Means for
lntroducing and e~xhausting a lubricating and/or coollng
fluid into the extrudate contalning assembly are also
provided.
~, ` ~ ' `
.
' `:
`'1 9
.. . ....................................... .. , ___. .
1 1~5~
This inventlon ls dlrected to an oriented crystal-
llne thermoplastic polymer product produced by solid state
de~ormatlon processes o~ a substantially non-oriented semi-
crystalllne thermoplastic polymer which may contaln up to 60
weight percent additlve. The final product may be a conduit,
a sheet or an article Or manuracture made by solld state
deformatlon processlng of the condult or sheet. At least a
portlon of the final product ls characterized by having a
microstructure comprised Or spherulltic crystalline a~gregates
whlch are compressed transversely to the plane Or the
product and are biaxlally orlented ln the plane Or the
product. The product is substantially devold of any process
induced microvoids and mlcrofibrils. The product is also
characterlzed by havlng ln at least a portlon thereor an
lmproved comblnation Or tensile impact strength and ultlmate
tensile strength at amblent and low temperatures; the ratlo
Or the tensile impact strength to ultimate tensile strength
) belng at least 50 percent greaSer than that ratlo
determined ~or the same polymer compositlon which is biaxlally
orlented to the same ultlmate tenslle strength level by
.
- 20 -
.
~. , ' .
.
2 6 5
conventional solid state de~ormation processes, for example
blow moldlng. The tensile lmpact strength ln at least a
portion o~ the product is at least 5 times greater and the
ult~mate tensile strength is at least 1-3/4 times greater
than that of the unoriented polymer from which the product
is made. The product retalns at least the same denslty as
the unoriented polymer and ls less permeable than a product
made by conventional solid state tensioning processes, such
as blow moldin~ from the same polymer composition- -
The product or products are made by lnitially
extruding a substantially non-oriented semi-crystalline
thermoplastic polymer prerorm in the solld state with a
hydrostatic fluid through an extrusion zone at a temperature
whlch is between the 4.64 kilograms force per square
centimeter heat deflection temperature, i.e. maxlmum use
temperature,~ and 8C below the crystalline melt temperature
of the thermoplastic polymer while expandin~ the preform
substantially simultaneously clrcumferentially at least 100
percent and axially at least 50 percent~ The resulting
product or intermediate tubular or conduit type product has
a substantially uniform wall~thickness which is about 0.5 to
6.5 percent Or the outside dlameter wlth an actual thickness
of not less than 0.079 centimeter in conduits havin~ an
outside diameter Or between 2.54 centimeters and 152.0
ce~ntimeters~and consists of~at;least one oriented crystalline
thermoplastic po~lymer characterlzed by a density which ls at
.
least equal to the density Or the unoriented polymer and a
mlcrostructure substantially devold Or any microvolds and
~:::: . ~:
~ ,
.
-21-
.
, . . .~ .
~ 1~52~
microl'ibrlls induced durlng processlng and comprlsed o~
radially compressed, dlscrete, platelet-llke spherulitic
crystalllne aggregat/es which are orlented in the pl~ne Or
the condult, the conduit havlng a tensile impact strength
at -45C which ls not less than 20 percent of lts tensile
impact strength at 24C and having a tensile impact strength
at 24C which is at least five times and a circumrerential
ultlmate tensile strength whlch is at least one and three
quarters that of the corresponding conduit of the same
polymer ln the unorlented state.
The oriented semi-crystalline thermoplastlc condult
may contaln up to about 60 weight percent flller material.
It has ln the past been very difrlcult, lf not lmposslble,
~ to orient thermoplastlc material which contains substantial
lS ~ filllng materlal. However, when the thermoplastlc polymer
, contains a filler and is extruded ln accordance with the
present inventlon it is found that the~thermoplastic polymer
can be successfully oriented as descrlbed above and will
have a tructure unllke previous~products substantlally
devoid Or microvoIds and mlcrofibrils and havlng within the
thermoplastio polymer discrete, platelet-like spherulitlc
crystalllne aggregates oriented in the plane of the conduit.
After the tubular or conduit product Or the
invention ls made~the product can be used as a condult or
structural member~or~the llke, but more frequently will be
spllt and heat rlattened in a solld state into a sheet
:
product. The amoun;t Or heat used ln flattenlng ls insufrlcient
to afrect the properties or microstructure Or the oriented
,
-22-
'' :
the~mcplastic ~ol~mer and th~ shcet prod~r~ ~hus ha3 ~he
same superlor properties as the conduit.
The sheet product ln turn can be used as is for
structural or the like purposes, or other uses, but will in
many cases be used as a blank to rorm a final product such
as, for example, a solid state ~ormed product. Many solid
state formed products are so called stretch formed products
where the thermoplastic polymer is formed ln a die under
- sufflcient heat and pressure to deform the thermoplastic
polymer in a solid state. The properties of the flnal solld
state stretch-formed product will depend primarily upon the
extent of derormatlon. However, it has been found that
solid state stretch formed products made from the oriented
sheet blanks Or the inventlon have superior properties
lS compared with the properties Or similar products made with
unoriented thermoplastic polymer. For example, stretch
formed products made rrom the oriented thermoplastic polymer
sheet blanks of the lnvention will have a more uni~orm cross
section. The superior propertles Or the oriented thermo
plastic polymer prevent the thermoplastlc polymer ~rom
"necklng" down appreciably and the resulting product is thus
much more` uniformly stl~ and strong than would otherwise be
the case. The actual properties of the stretch formed
;~ product may vary from place to place ln the product
~25 depending upon the amount of work or deformation applied to
any given portion of the product. Any flanges on the
product, belng substantlally unworked~ will have the same
superlor characteristic propertles as the origlnal orlented
:
~.
,
5~$
blank. In some products this ls very lmportant as the
flanges provide important structural strength and toughness.
The lips or rlanges around the edges Or rerrigerator freezer
door liners, freezer food containers, pans or tote boxes are
representative o~ this type of product. Likewise any
portion of the product which is expanded less than roughly
50% will havè essentially the same property characteristics
as the original oriented blank material. Thus the properties
of shallow drawn or formed articles are very superior.
Beyond about 50% expansion the characteristic properties of
the thermoplastic polymer are progressively changed due to
the progressive destruction of the spherulitic crystalline
aggregates and the increase in planar orientation as
de~ormation continues. Initially, an lncrease in deformation
lncreases the ultimate tensile strength while retaining at
least the same tensile lmpact properties but at high elon~ation
the properties begin to decrease. Thererore, products made
; from the oriented blanks Or the invention will usually have
very signirlcant portions which have very superior properties
compared to products made from an unoriented thermoplastlc
polymer, ~illed or unfilled, of the same composltion.
In a detailed descrip~ion o~ the invention, the
product is a thlck-waIled, seamless, conduit (a conduit is a
cylindrical member indeterminate in length and includes such
forms as a tube, pipe and the like~ consisting essentlally
Or an orlented crystalline thermoplastlc polymer. The
conduit can have an outside dlameter between about 2.54
centlmeters (l lnch) to 152 centimeters (60 lnches), however
-24_
~ 1~5~6~ ;
a prererred range is about 5 centimeters (2 lnches) to 63.5
centimeters (24 inches) and the most preferred range ls
about 20 centimeters (8 inches) to 41 centimeters (16
inches). The thickness of the wall is substantially uniform
radially and circumferentially from end to end and will not
vary by more than plus or minus 10 percent, and prererably
by not more than plus or minus 5 percent and most prererably
not more than plus or minus:2.5 percent. The thlckness of
the wall is about 0.5 percent to about 6.25~percent,
pre~erably about 1.0 to 3.0 percent and most preferably
about 1.0 to ~.0 percent, of the outside diameter. However,
in conduits which have an outside diameter o~ 2.54 to 7.62
centimeters (1 to 3 inches), the wall thickness is at least
~: 0.074 centimeters (1/32 of an inch). The conduit may be
short as about 7.6 centimeters (3 inches) and as long as
commercially practical and dictated by machine limltatlons~ ;
however it is preferred to make a conduit which is between
about 30 centimeters (12 inches) and 244 centimeters (96
lnches). The condult is dimensionally stable and has at
least about one and three quarters the circumferential
ultimate tensile strength and not less than five times the
circumrerentlal tensile lmpact stren~th at 24C (75F) o~ a
similar conduit made from the same substantially non-
orlented semi-crystalline thermoplastic polymer by con-
ventional methods. The condult retalns at least 20 percent
o~ the room ~emperature tenslle impact strength at -45C
(-50F).
11~52~
The structure o~ the condult is comprised Or
spherulltiC crystalline aggregates which are discrete and
platelet or wafer-like and have a generally polygonal shape.
The aggregates are radially compressed and circum~erentially
and axlally elongated and are planar oriented, that is, are
oriented in the plane of the condult wall. The structure is
substantlally free of press induced mlcrovoids and mlcrofibrils
ln the boundaries between the spherulitic crystalline
aggregates and in the spherulitlc crystalllne aggregates.
The startlng thermoplastic polymer which can be
used ln this inventlon is a substantially non-oriented semi-
crystalllne or crystalline homopolymer or copolymer having a
crystallinlty o~ at least 45 percent, a relatlvely sharp
crystalline melklng polnt observed by difrerentlal thermal
1~ analy-sis and having a structure contalning long chaln
molecules which~solldl~y in the ~orm o~ spherulitic crystal-
llne aggregates. The polymer can be sortened and f'ormed by
heat or stress and can be molecularly oriented by drawlng
and stretching at a temperature between the glass transitlon
temperature and the crystalline melting point as shown by
ma~or lmprovements in properties, such as ultimate tensile
strength and tensile impact strength. The polymer can have
a molecular weight between 104 and 106. Such thermoplastlc
polymers include orientable polyole~ins, ~or example
lsotactic polypropylene, high density polyethylene; polyamides,
for example nylon 6,6; polyacetals, for example poly~
oxymethylene; polyesters, ~or example polybutyl~ne
terephthalate; and polycarbonates.
-26-
By way of example only, a typical structure Or a
polymer, whlch in this instance is isotactic polypropylene,
processed by the method o~ the inventlon and the structure
of the startlng polymer preform are shown pictorially in
FIG. l. Test coupons A ln FIGURE lA and A' ln FIGURE lB
were cut from the pre~orm X and conduit Y, respectlvely, as
shown. The outer surfaces B and B', and transverse surfaces
C and C' and D and D' were polished and etched and were
exam~ned at a magnificatlon of lOOx by llght optical micro-
scopy. The surfaces were polished in a two-step sequence
using a first paste containing .6 micron dlamond dust and a
second aqueous paste containlng .3 mlcron alumlnwn oxide
partlcles. The surfaces were carefully cleaned of any paste
resldue and were etched in a solution containing equal parts
of benzene, xylene and chloroform heated to a temperature of
about 80C (175F). It required three to four minutes ~o etch
the surfaces Or coupon A and five to six mlnutes ~o etch the
surfaces of coupon A'. The sur~aces B, C and D Or coupon A
were round to be comprised o~ substantially non-oriented
spherulltlc crystalllne aggregates as shown. It is
generally recognized that the crystallihe aggregates grow
radially from nuclei and are referred to as spherulites.
The spherulitic crystalline aggregates appear as generally
polygonal in shape on polished ~aces. While the structure
of the polymer is predominantly crystalline in nature, small
areas Or non-crystalline or amorphous structures become
entrapped in and between the spherulites during their growth.
1 ~55265
i
The sur~ace B' shows a structure comprised Or
spherulltic crystalline a6gregates whlch are discrete
platelets generally polygonal in shape. The sur~aces C' and
D' show the aggregates to be radlally compressed into
relatively thln lamellae elongated in both the circumrer-
ential and axial dlrections and oriented ln the plane of the
conduit wall, l.e. oriented circumferentially and axially.
No evidence of microvoids or enlargement of existing
microvoids was seen in the conduit.
A coupon of the conduit Y material was notched
with a sharp knlfe blade on two transverse surfaces perpen-
dicularly to the plane o~ the conduit. The material was
then torn circumferentially and axially. Microscoplc
examination o~ the tear surfaces at lO0 magnificatlons
showed what appeared to be radlally compressed platelet or
warer-like spherulitlc crystalline aggregates arranged in an
overlapping pattern.
The sheet product E was formed by slitting the
; condult Y along llne a-a as shown in FIGURE l. The slit
conduit was heat flattened under pressure at about 129C
(265F) ror five minutes. A test coupon F was cut from the
sheet, polished and etched and examined as descrlbed above.
The microstructure appeared to be identicaI to the mlcr~-
structure Or the conduit.
Coupons K and H cut from the heavy wall flange
areas of the.~reezer food container9 FIGURE 9, and
re~rlgerator rreezer door llner, FIGUR~ lO respectively,
have mlcrostructure~ comprlsed of radially compressed
-28-
~ ~ 55~
dlscrete platelet like spherulitic crystalllne aggregates
slmllar to those seen in hydrostatically extruded conduit
and sheet made therefrom as seen in coupon B' Or FIGURE lB.
In c,ontrast to the structure formed by the method
Or the invention, polypropylene of the same resin batch was
compression molded by a conventional process into sheet and
thermoformed at 149C (300F) and 2.8 kilograms force per
square centimeter (40 pounds per square inch) air pressure,
to provlde comparative samples of biaxially streched sheet.
Microscoplc examination by the aforementioned procedure
showed substantial spherulite damage at 70 percent, biaxial
elongation and the original discrete spherulite st'ructure
pattern substantially destroyed by 100 percent biaxial
elongation by conventional compression molding techniques.
A tes~ coupon from the sheet was notched on a transverse
surface and torn. Mlcroscopic examination Or ~he tear
surfaces at 100 magnirications showed the absence of an
overlappin~ spherulikic crystalllne aggregate structure.
A coupon G was cut from the conduit. The coupon
was placed in an oil bath and was heated to a temperature of
165C ~330F) without any restraining pressure being applied
and held at temperature ~or ~ifteen minutes. The section
reverted to about 85 percent of the shape, size and structure
it would have had it been cut from the preform used in the
manuracture of the conduitO The substantially complete
recovery of.the spherulitic crystalline aggregate structure
indlcates that the strain lnduced in the spherulltlc
crystalline aggregate structure by the compressive forces
-2~-
~ 155~65
employed to elongate the polymer was,homogeneously distrlbuted.
As a result, the polymer retained its memory and density.
The formation of microvoids and the e~largement of existing
microvoids was eliminated. It is postulated that the unique
spherulitic crystalline ag~regate structure wherein the
aggregates are radially compressed and clrcumferentially and
axially elongated ls responsible for the lncrease in the
clrcumferentlal tensile lmpact strength9 the unusual low
temperature tensile impact strength; a ratlo to the tensile
impact strength (referred to as TIS) over the ultimate
tensile strength (referred to as UTS) determined by ASTM
; D1822 S-type specimens which is at least 50 percent greater
than that ratio determined for a thermoplastic polymer Or
the same composition whlch has been bia~lally oriented to
the same ultimate strength level by conventional solid state
deformatlons, such as blow molding, tentering and the like,
and the retentlon Or the density and reduced permeability Or
; the polymer in ~he conduit.
The conduit of the invention ls fabri aked by a
solid state hydrostatlc extrusion method in which a polymer
is heated to a tem~erature between its 4.64 kilograms force
per square centlmeter (66 pounds per square inch) heat
derlection temperature as determined by ASTM D-648 and about
8G (14F) below its crystalline melt temperature and is
extruded by hydrostatic fluid pressure through an annular
ori~ice at a.straln rate which does not exceed 20 seconds 1
and pre~erably is less than 10 seconds 1. The polymer is
substantially simultaneously elongated ln the axial dlrection
-30
& ~ ,
and expanded in the circumferential direction by forces
whlch are compressive in nature. The expansion or elon~ation
- in the circumferential direction is at least l00 percent and
is preferably at least 200 percent. The elongation in the
axial direction may be less than l00 percent but it is
preferred that the axial elongation be at least 50 percent
and most preferably equal to the circumferential elongation.
The temperature to which the polymer ls heated for
extrusion must be such that the crystalline melt temperature
will not be exceeded durlng extrusion and excessive extrusion
pressures resulting in stick-slip extrusion and its attendant
overheating problems are not permitted. Broadly, the
polymer may be heated to any temperature within the range o~
lts 4.64 kilograms force per square centimeter l66 pounds
per square inch~ heat deflectlon temperature and about 8C
(14F) below the crystalline melt temperature. However, a
temperature range between about 50C (90F) and 18C (32F)
below the crystalllne melt temperatures is preferred but the
most prererred range is betweerl 30C (54F) and 18C (32F)
below its crystalline melt temperature. The temperature
range is dependent upon the polymer, the e.YtrUSiOn rate and
the reduction ratio. By way of example, the broad temperature
ranges, the preferred temperature ranges and the most
preferred temperature ranges at which some polymers may be
extruded in the method of the invention are shown in Table
I, below. .
-31-
2 ~ 5
a) ~ ~ ~
b~ t~ O
J O O U~
~) N tr7 J J
~; ~
t~ C~ t~ C~
~V 0~ N t-- N
tl) o Ir~ O (r~
h ~ ~ ~ c~
L.
tl~
. ~ ,~
tl) ~ 1~
h O o o o
1~
N ~Jt~ 3
U~ ~ V
0 3 ~~
O N QO ~1
~l N
~ ,_ ~
~ ¢ 4 ~ '
~ O
3 0 0 U-\
Q) N t''l ~ 3
bl
~ C~
~a G~ N ~-- N
~ O - ~ O
U~ ~ ,1
h tl~
S~ ~ ~ ~ _~
h li~
t~ a1 O ~O O O
H 5~ ~
tl) tL) ~ N trl 3
. ~ h .
O ~ ~
Z O r~l N 3 r-l
E-l ~ O L~ N
kl
~:
h Is~ 3 t~
~O N N
X N tfl 3 3
t~ t~ C~
~( a~ N t-- N
C~ N
~:: r-l ~ N N
~ ~4 ~ ~ ~ . ' 1
O O ~ O O
~1
a~ r-l N tr~ 3
r--l N 3 ~1
~ O U~ t~J
- r-l ~i N
.
tl)
S: tL~
tl~
J
~1
~ h ~
tL~ tl~ O ~ ~D
~; O :~ ~ O
O O ~,
m a. ~ ~
,
.
~ 5
The thermoplastlc polymer preform is ~abrlcated on
a hydrostatic extrusion press. The press may be a batch,
semi-continuous or contlnuous press. In any event, the
press is comprlsed of a supporting structure and ~oollng.
The tooling is comprised of a pressure means which provides
the extruslon pressure; clamping means ~or maintaining
alignment of the tooling; a contalner assembly in which a
polymer preform is placed ~or extruslon which assembly
includes a die, a mandrel-head and sealing means to retain
the extrusion pressure; and a receiving assembly ln which
the extrudate is recei~ed, lubricated and cooled a~ter
extrusion, which assembly includes a mandrel and means ror
lubrlcatlng and cooling the extrudate.
The die and mandrel-head are spatially and coaxially
aligned wlthin the container assembly. The sur~ace o~ the
die and the sur~ace of the mandrel-head form the walls Or an
annular ori~ice having a converging conlcal entrance; a
cylindrlcal inlet or 9ealing zone; an expansion zon~ having
converging walls, a conver~lng cross-sectlonal area and a
dlverging geometry and a cylindrical outlet or sizing zone.
The sealing zone has an outside diameter which ls smaller
than the outside diameter Or the preform. As the preform is
extruded, inltially the cross-sectional area o~ lts wall is
reduced by about 5 percent and axial elongation begins. The
preform enters the expansion zone and is circumrerentially
elongated, i.e. the outslde and inside diameters o~ the
preform are increased. At the same time, because of the
converging walls and the converging cross-sectlonal area of
the orifice, t~.e wall o~ the preform continues to be reducéd
-33-
. ' ' ' '
6 5
in cross-sectional area untll lt passes through the exlt Or
the expanslon zone into the sizing zone. The extruded
preform or extrudate in the slzlng zone is cooled to prevent
recovery and shrlnkage of the polymer. The extrudate is
lubricated and cooled as it passes into the receiv1ng
assembly. The lubrication and cooling assures the production
of a condult having wall surfaces which are smooth and
substantially wrlnkle-free. The wall is concentric and of
; substantially uniform thickness.
In the hydrostatic extrusion of the thermoplastic
polymer in the sol~d state whereby an elongated, expanded,
concentric, substantially unlform thick-walied conduit ls
produced, lt is necessary to maintain sufriclent constant
extruslon pressure in the container assembly and to prevent
lateral and axial movement of the tooling. To maintaln the
constant extruslon pressure~ it is necessary to e~ectlvely
seal the hydrostatic rluid in the container assembly while
allowlng a f.tlm o~ the hydrostakic rluid to be extruded
along the preform surfaces to provide the lubrlclty needed
for extruslon. An effective seal is obtained by providing a
preform havlng a cross-sectional area Or the wall which is
about 5 percent greater than the cross-sectional area of the
sealing zone ln the annular orifice and a converging conical
entrance to the sealing zone. When extrusion begins, the
outside sur~ace o~ the preform contacts the surface o~ the
outside wall Or annular orifice as lt enters the conical
entrance and is guided into the sealing zone. The outslde
surface Or the prerorm remalns in contact wlth the surface
-34~
1 ~526S
Or the outslde wall of the annular orifice thereby making an
efrectlve seal which prevents leakage Or hydrostatlc rlu~d
from the container assembly and at the same time allows a
rllm Or the fluid to be extruded on the surfaces Or the
prerorm to provlde lubricity between the surfaces Or the
preform and the walls of the orlrlce.
The extrudate is lubricated and cooled by a second
~luid~ such as air, ln the receiving assembly. The fluid is
applied to the inner surface o~ the extrudate and acts as a
0 CUs~liOn ~et~!eel: the extrudate and the tooling ln the receiving
assem~ly thereby preventing damage to the sur~aces ~r t}le
extrudate due to frictlon. The fluid also prevents wrinkllng
of a thin-walled extrudate and undue thickening or a heavy-
walled extrudate due to the elimination Or frictlonal drag.
l~ Ir deslred, additional fluld may be applied to the outer
surrace Or the extrudate ror cooling.
A hydrostatic fluld blow-out, caused when one slde
Or the prerorm contlnues to rlow while an acl~acent section
Or the pre~orm does not ~low as well causln~ uneven extruslon
and introduclng a derect in the extrudate, can occur near
the end Or the extrusion Or the prerorm. The blow-out can
be prevented by termlnating the extrusion Or the preform
before the rear portlon Or the preform enters the seallng
zone, inserting a second pre~orm lnto the press with its
front end contlguous wlth the rear portion of the orlginal
preform and continuing the extruslon. T~e extrudate can be
removed concurrently wlth the lnsertion Or a n-w billet.
-3s-
1 ~i$526~ .
It is possible to continuously constrain anneal,
1,e. under su~ricient pressure to suppress recovery of the
polymer, and heat stabilize the extrudate ln the press by
; heatin~ the preform to a temperature near the upper llmlt Or
the temperature range and extruding the prerorm at a low
extrusion rate and by usin~ a long sizlng zone.
A high hydrostatlc compressive stress state may be
increased in the deformatlon zone by using a longer sizin~
zone with a higher friction rela~ed pressure drop.
By using the combination o~ the above techniques,
it is possible to extrude a split preform to produce a split
conduit suitable ror heat flattening into a thermop'lastic
polymer sheet. It is also within the scope of this invention
to produce thick thermoplastlc polymer sheet by slitting and
heat ~lattening the extruded conduit. Any means, such as a
heat knlfe or slitter well known in t~e art, can be used to
slit the conduit. The slit conduit can'be heat flattened by
clamping it in a restralning device such as press platens
which are heated to a temperature whlch is between 16C (30F~
~20 and 44C (80F) below lts crystalline melt temperature. A
suitable pressure is applied to the polymer durlng heatlng.
The polymer is held at temperature and pressure for between
one to twenty minutes depending upon the initial temperature
and thickness o~ the polymer, ~or example a 0.16 centimeter
(1~16 inch) thlck polypropylene sheet at a temperature Or
24C (75F) in~erted between the press platens at a temperature
o~ 129C (265F) and held at a pressure Or 14.06 kllograms
rorce per square centlmeter (200 pounds per square inch) ia
-36-
-
2 ~ 5
heated to 143C (290F) and is held ror flve minutes. The
sheet may be cooled in the press or may be removed and
cooled between metal plates.
The sheet produced as described above retains
substantially the same morphology and propertles Or the
condult. The sheet also exhibits excellent drawability.
The polymer sheet may be solld state thermally
formed by known technlques, for example stamping or uslng
pressurized gas with the use o~ a plug asslst being optional
and the like. The temperature to which the polymer is heated
must be between lIC (20F) and 44C (80F) and preferably 16C
(30F) to 22C (40F) below the crystalline meit temperature of
the polymer.
Products produced by solld state thermal treatment
lS are useful articles ln many ~ields, for example rerrigerator
door liners, ~reézer food conkainers, stamped aukomobile
hoods, luggage, and the like. In any article produced by
such processes, the portion Or the article ~hich undergoes a
mlnlmum amounk o~ derormation, i.e. less than 50 percent~
will retaln substantia11y the same morphology and properties
Or the sheet from whlch it iB produced.i Of course, the
`~ ~ portion o~ the~article sub~ected to maximum derormation may
~ not retain the same morphology.
;~ It also has been found that a substantially non~
orlented seml-crystalline~thermoplastic homopolymer whlch
contains particles of a flller can be processed into a
condult and sheet~and subsequently an article of manufacture
by the processus previously described. An article o~
-37-
.
1 1~$2B~ I
man~facture produced as described ~bove is n~vel iJI itselI
slnce it wll~ have a matrix which ls an oriented crystalline
structure. Heretofore, such orlentation Or the structure
: has not been posslble wlth solid state high draw ratio
stretch orlentatlon processes, for example, tentering, blow
molding and other known stretching processes. Such processes,
while orlenting the structure also damage areas Or the thermo-
plastic polymer by producing volds in the matrix ad~acent to
the particles of the filler or enlarglng exlsting microvoids
thereby adversely a~recting the properties of the finished
product.
The biaxially oriented filled crystalline thermo-
plastlc polymer products produced by the prlor art solid
state processes mentioned above do not have a tensile lmpact
strength whlch is 5 times and an ultimate tensile strength
wh~ch is 1-3/4 t~lmes that of an unorlented polymer Or the
:. same composltion. Nor do such products have a ratio Or
; tensile impact strength to ultimate stren~th ~-Tu~s) which
is at least 50 percent greater than that ratio determlned
f'or a semi-orystalllne thermoplastic polymer Or the same
! composltion which has been biaxlally oriented to the same
ultimate tensile strength level by con~entional solid state
,
deformations, for example blow molding,:tentering and the
e~ The voids around the particles of the filler adversely
affect the~appearance, stiffness and density of the product.
A hydrostatic fluid suitable for use in the hydro-
static extruslon of a thermoplastic polyme:r i:s a fluld which
~: has the requlred high temperature properties to resist
`, ' "
-38-
5 2 6 5
,
degradatlon at extruslon temperature and which is insoluble
in and will not react with the thermoplastic polymers, Such
oils can be castor oll, sillcone oils~ synthetlc olls~ and
various mineral and vegetable oils. It is presently preferred
to use silicone oils.
The thermoplastic polymers processed ln the method
of the inventlon may also contaln additlves, such as flame
retardants, liquid or solid colorants and fillers, such as
talc, mica, silica and the like and elastomerlc particles.
By a ~llled thermoplastic polymer we mean a
polymer which contains up to about 60 weight percent of a
material inert to the polymer and which is in the form of
dlscrete partlcles or short flbers wlth length over diameter
ratios not greater than flve and whlch wlll modi~y the
propertles o~ the polymer or reduce the materlal and
processlng costs of the polymer. The inert materlal can be
lnorganlc, for example talc, calclum carbonate, clay, sillca
and the like, and includes such materials as colorants and
flame retarders,
By a substantlally non-oriented semi~crystalllne
thermoplastic polymer preform, we mean a solid or hollow
billet or plug formed from a polymeric melt which is fabri-
.
cated into the deslred shape by a process, such as extrusion,
compression molding or in~ectlon molding. A minor amount of
; 25 orientation may occur ln the polymer preform during processing,
however the amount Or orientation is insurficlent to cause
any substantial lmprovement ln the propertles of the polymer.
As noted previously the polymer can contain a flller.
-39-
5S~85
It ls wlthin the scope Or this lnvention to produce
slngle-layered and multllayered conduits rrom single-layered
and multllayered prerorms produced by conventional plast-
icating methods.
The oriented thermoplastic polymer conduit of the
inventlon may be produced ln a batch extrusion process using
an apparatus as shown, by way Or example only, in FIGURES 2
and 3. FIGURE 2 is a cross-sectional view ln elevatlon of a
,
vertical hydrostatlc extrusion press 10 sho~n at the start
lo of the extrusion process. FIGURE 3 ls a cross-sectional
; view of the extrusion press 10 at the finish of the extrusion
process O
~ The hydrostatlc extrus~ion press 10 comprises a
cyllndrical outer casing 11 havlng threaded open ends 12 and
13, a first hydraulio pressurizlng means 14 and a second
~ : hydraullc pressurizing means 15~ a billet container assembly
.l 16 and an extrudate receiving assembly 17 ali~ned in spaced
relationship coaxially within said outer casing 11.
Since pressurizing means 14 and 15 are identical,
only means 14 wlll be described. The pressurizing means 14
18 a hydraullc apparatus comprlslng a cylinder 18 definlng
an annular chamber~l9 with an axial bore 20. A hollow
cyllndrlcal piston 21 is posltioned in chamber l9 whereby
force is transmitted to a cylindrical plug 30 in the billet
.
contalner assembly 16. Pressure ls applied to the piston 21
from a source (no~ shown) through piping assembly 22.
The assembly 16 lncludes a cylindrlcal shell 23
coaxial withln outer casin~ 11. The shell 23 has cyllndrical
outer surface 24 and a ~enerally cylindrical lnner surface
--40--
1 ~55~5
25. A vent 23a is provided in the shell 23 tu vent pressure
from cavity 26 during extension. The lnner surrace 25
defines an axial cavity or bore 26 whlch ls dlvided lnto a
flrst cylindrical section 27, an intermediate cyllndrical
sectlon 28 and a third section 29. The ~irst sect~on 27 has
a greater cross-sectional areà than the intermediate sectlon
28. A generally cylindriGal plug 30 havlng the shape shown
has generally parallel upper and lower surfaces 31 and 33,
respectlvely, and a pro~ection 3~ extending downwardly from
the lower surface 33. The lower surface 33 rests on and is
contiguous with the piston rod 21. Extension 32 provides
i means to center the plug 30 on the piston rod 21. An 0-ring
30c in groove 30b of wall 30a provides a friction means for
keeping assembly 16 together after it has been assembled and
during subsequent heating and lnsertlon lnto the press 10.
The upper sur~ace 31 is provided with a cylindrlcal proJection
34 generally U-shaped in cross-sectlon as shown. A hollow
cyllndrical piston 36 comprised Or metallic wall 37 having
an outer sur~ace 38 and an inner surface 39 definlng an
axial cavlty 39a, ls supported by plug 30 as shown. A 1'
clrcular elastomer seal washer 40 provides a seat ~or
cylindrical plston head 42 having generally parallel upper
and lower sur~aces 43 and 44, respectively and also seals
hydrostatic ~luLd 51 lnto the cavity 39a. A solld pro-
~ection 45 extendlng downwardly from surrace 43 provides
means for centering plston head 42. A sealing 0-rlng 46 and
a support rlng 47 generally triangular in cross-section on
shoulder 48 or the hollow pi~ton 36 provlde seallng means to
:
~41
.
2 6 ~
preven~ leakage Or rluld 51. The plstorl 36 is supported on
the upper surface 31 of the plug 30. The hydrostatic fluid
51 fllls the cavity 39a of the lntermediate section 28 and
plston 36 and provides means for transmittlng pressure to a
cyllndrical thermoplastlc polymer billet 53 in the assembly
16. Durlng extrusion, a very thin ~ilm o~ the hydrostatic
fluld 51 ls extruded on the surfaces Or the blllet 53 to
thereby provide lubrication ~or extrusion. The third
sectlon 29 is the die of the~apparatus 10 and is comprlsed
Or a converging conical entrance 54a, a generally cylindrical
axial land surface 54, a generally conical di~erging wall
surface 55 and a generally cylindrical axial land surface 56
substantially parallel to the land surface 54. The land
surface 56 may be any length sufficient to ald in setting
the extrudate. The dlameter Or land surface 54 ls smaller
than the diameter of land surface 56. ~ mandrel head 57
j having a recessed base surface 58, a cylindrical lower
portion 59 and a conlcal upper portion 60 tapering into an
elongated cylindrlcal nose portion 61, is positioned axially
wlthln the annulus formed by the die 29. The nose portion
61 is Or a size such that when lnserted lnto the bore 53a ol`
the blllet 53, an lnterference flt is produced whlch is
sufflclently strong to keep the mandrel head 57 in posltion
whlle assembly 16 is being assembled and to maintain the
position of the mandrel head 57 during subsequent heating
and insertion into the press 10. The outside surface 53b Or
the billet 53 contac:ts land surface 54 to thereby form a seal
which prevents leakage Or hydrostatic fluid 51 during subse-
quen~ heating and assembly Or the apparatus 10. The surface
.
-42- ~
5~5
.
Or die 29 and sur~ace Or the mandrel head 57 are spaced a
desired distance apart to ~orm an annular orifice or extruslon
zone 57a which has a generally converging conical entrance 54a
and three zones: a seal$ng zone 57b formed by the annular
cylindrlcal land surrace 54 and the surface Or cylindrical
nose 61 respectlvely, a conlcal expanslon zone 57c ~Figure
3) having a converging cross sectional area rormed by
diverging wall surface 55 and the surrace of conical portlon
60, respectively, and a cylindrical sizing zone 57d formed
by the land surface 56 and the sur~ace of portion 59. The
transition zones t between the surfaces of the sealing zone
57b and the expansion zone 57c and the sizing zone 57d on
the dle a~d mandrel-head respectively are provided with
curved surfaces having predetermined radil to provide smooth
transition areas between any two zones. The angle a that
the diverging wall surface 55 makes wlth the axls o~ the
press 10 may be between 45 and 15 and the angle ~ that the
~urface Or conical portion 60 makes with the axis of press
10 may vary between 50 and 20. The angle ~ and the angle
~ are chosen so that diver~ing wall surface 55 and the
surface Or conical section 60 will meet if extended, i.e.
the annular oriflce formed by these surfaces is generally
converging and has a con1~erging cross-sectional area whlle
being diametrically diverging. By extruding a thermoplastic
polymer blllet through the annular orifice shaped as descrlbed,
the blllet is substantially simultaneously expanded circum- ;
ferentially and elongated axially. It is preferred that the
angle a be about 30~ and the angle ~ be about 40, The
.
, .
.,
~ ~ ~5~ ~
blllet 53 has a diameter which ls sllghtly larger than the
dlameter of surface 54. When extruded, the outer surface Or
the billet 53 contacts surface 54 to rorm a seal whlch holds
the hydrostatic ~luid 51 in the assembly 16 to maintaln
extrusion pressure but at the same time allows a thln ~ilm
of ~luld 51 to be extruded on the surface of the billet 53
to thereby provide lubrlcatlon durlng extrusion. As the
billet 53 enters the zone 57c, lt is substantially slmul-
taneously expanded circumferentlally and elongated axially
and flows to the sizlng zone 57d. It is posslble to vary
the axial elongation Or the thermoplastic polymer while
keeplng the circumferentlal expansion constant by varying
the distance between the conical surface of the mandrel-head
and the wall sur~ace 55.
The extrudate receiving assembly 17 lncludes an
outer shell 63 coaxially within and spaced from casing 11
and a cylindrlcal hollow mandrel 62 coaxially within shell
63. The mandrel 62 has an open lower end and an open upper
end 64 and 65, respectlvely, an inner surface 66 derinlng a
cylindrical bore 67.and an outer surface 68. A shoulder 69
and a plurality of radial orifices 70 extending from inner
surface 66 to outer surface 68 are formed in lower end 64.
; : The upper end 65 has a greater cross-sectional area than the
remalnder o~ the bore 67 and is provlded with threads 71.
~ Outer shell 63 has an open lower end 72 and an open upper
end 73~ an outer surface 76 and a generally cylindrlcal
inner surface 74 defining a generally cylindrical bore 75.
The inner surface 74 has an upper portion 74a and a lower
-44-
I
~ ~ 5.~
portion 74b. A shoulder 78 is formed on end 72. A plurality
Or radial orlfices 79 extend from the lower surface 74b to
the outer surface 76. The upper portion 74a is contlguous
wlth the outer surface 68. The lower portion 74b and outer
surface 68 are spaced apart to provlde a chamber 82 into
which the polymer is extruded.
The mandrel 62 ls separated from the mandrel head
57 by a grooved washer 83, shown in FIGURE 5. A plurality
Or radial grooves 84 communicate with the orifices 70 ~o
provide unlnterrupted passageways between the bore 67 and
the chamber 82.
A clrcular bearlng plate 85~havlng an outer
dlameter equal to the;diameter~or the outer shell~63 and an
axlal opening havlng a diameter equal to the diameter of the
15 ~ upper end 65 or~the mandrel is contlguous with the ends
74a and 73, respectlvely. A slotted washer 86, shown in
FIGU~E 4, ls lnser~ed between bearlng plate 85 and plston
21' in the hydraullc cylinder 15. A hollow plug 87 and pipe
assembly 88 are attached to the mandrel 62 as shown whereby
a lubricating and/or cooling fluld may be introduced into
:~. the assembly 17. :The plug~87 is spaced a distance from
~` plston rod 21' to provlde a passage for the lubricating
and/or cooling ~luid.
:To extrude,:a seml-crystalline thermopla~tic
~25 : polymer blllet 53, for;example lsotactlc polypropylene is
inserted ~nto the shell 23 so that the outer surface 53b of
the billet:53 contacts the~land sur~ace 54b. The nose 61 of
the mandrel-head 57 is inserted into the bore 53a of the
. .
-45-
~ 1552~5
blllet 53 to make a tight fit. Piston 36 and seal parts 46
and 47 are inserted into section 28. A quantlty of a
; hydrostatic flu~d 51, ~or example castor oil, is poured into
the sub~assembly. The sub-assembly is placed in an oven and
is heated to a temperature which ls between the 4.64 kilo-
grams force per square centimeter (66 pounds per square
lnch) heat deflection temperature and 8C (14F~ below the
crystalline melt temperature of the polymer, for example ln
the case of polypropylene, the temperature is 129C (265F).
Plston head 42 and seal washer 40 are preheated to the same
temperature. When at the desired temperature, piston head
42 and washer 40 are inserted lnto the bottom portion of
plston 36. Plug 30 and 0-rlng 30b also heated to the desired
temperature and protrusion 34 is inserted into plston 36
thereby forming assembly 16. The heated assembly 16 i5
lowered lnto the casing 11 and is fltted to be contlguous
with hydraullc cylinder 14. Assembly 17 is also preheated
and ls then lowered into casing 11 and is ali~ned to be
conti~uou5 wlth assembly 16. The mandrel 62 and mandrel
head 57 are allgned as shown. Hydraulic cylinder 15 is
screwed into place in the open upper en~ 13. The pipe
assembly 88 is placed in position and is connected to a
fluid, for example pressurized air which is introduced lnto
the assembly 17. Hydraulic pressure Or about 633 kilograms
~orce per.square centlmeter (9000 pounds per square inch) 1s
applied by pressur~z~ng means 15 which clamps the press
together wlth 26.6 x 104 N (30 tons o~ ~orce`) and prevents
lateral and axial movement Or the mandrel head 57 and other
tooling ln the press during extrusion. Simulkaneously,
-46~ .
S 2 6 ~
hydraulic pre~sure is applled to plston 21 ln cyllnder 14
which in turn transmlts the pressure to plug 30 and hollow
piston 37 and pressurizes the ~luld 51. Initially, the
fluid 51 and the billet 53 are compressed by the force
generated in cylinder 14. When the billet 53 and fluld 51
are ~ully compressed to a pressure of about 520 kilograms
force per square centlmeter (7,400 pounds per square inch
gage) or higher~ extrusion begins. The pressure remains
relatively constant throughout the extrusion time. As noted
above~ during extrusion a portion Or the hydraullc fluid 51
~orms a thin ~ilm between the sur~aces o~ the biliet 53 and
the surfaces Or the mandrel head 57 and the die 29;
respectivjely, to provide lubricatlon ~or the billet as it ls
being extruded. A lubricating and~or cooling rluid9
pre~erably alr at a desired pressure, rOr example 2.81 to
6.33 kilograms ~orcé per square centimeter (4Q to 90 pounds
per square inah ~age), is red into the chamber 82 through
bore 67 and radial orifices 70. The air forms a rlowing
fllm or cushion between the extrudate and the mandrel
sur~ace to lubricate the extrudate. The fluid flows along
the surface 68, around the extrudate and along sur~ace 74 to
radial orifices 79 to cool the extrudate. The fluld then
flows along outer sur~ace 76 through the slots 86a in
washer 86 and along space between plug 87 and the pressurizing
means 15 passes and out Or the apparatus through the top o~
pressurizing means 15. The use Or the lubricatlng and/or
cooling fluid assures a smooth substantial~y wrinkle-~ree
sur~ace and a substantlally uni~ormly thlck wall article.
,
~55~
Arter a tlme, ror example about one minute, the billet 53
has been extruded and the hydraullc pressure in the hydraulic
cyllnders 14 and 15 ls relieved. Hydraulic cylinder 15 is
removed from the press 10. The assembly 17 and the e~trudate
are removed ~rom the press lO. A portion Or the blllet
remalns unextruded and is retalned on the mandrel head 57.
The extrudate is separated from the unextruded portion by
slitting with any conventlonal known cutting tool,~such as a
slitter kni~eO
While we have shown a batch process, it is also
posslble to produce the tubular product of the invention by
a semi-continuous process using an apparatus such as shown
by way Or example in FIGUR~S 6, 7 and B.
FIGURE 6 is an elevatlon view in cross-section of
a press in which a polymer billet is ready to be extruded.
FIGUR~ 7 shows the same apparatus as FIGURE 6 in whlch the
polymer blllet has been extruded and is being eJected from
the apparatu~. FIGU~E 8 ls an elevation view in cross-
section of the fluld tank showlng several billets being
heated prior to being charged lnto khe apparatus.
The extrusion apparatus includes an outer support
structure (not 9hown)~ a generally rectangular, tank 95 with
, an open top an`d bounded by two side walls 96 and 97, two end
; walls 98 and~99 (not shown), and a bottom lO0. A hydrostatic
and 1ubr1cating fluid~51' which is also used to heat blllet
53' fills the tank 95. The fluid 51' ls heated by internal
or external conventional means, such as a hea~inK coll (not
shown~, to a temperature which is between the 4.64 kilograms
-48
~ ~ 5, 5 ~ r~ f
force pe~ square centlmeter (66 pounds per square inch) heat
deflection temperature and 8C (14F) below the crystalllne
melt temperature of the polymer. Piston 102 ls rully
movable throu~h openlng 101 in wall 96. A seal 103 prevents
leakage of hot fluid. One end (not shown) of ptston 102 ls
attached to and activated by hydraulic means. A sprlng- f
loaded cavity 104 ln end 105 guides the billet 53' into the
rear or pressure chamber portion 106 of axial cavlty 107 ln
die assembly 108. The forward portion of die assembly 108
is a dle 29' comprised of a first axial land sectlon 54', a
second axlal land section 56' and a diverging section 55'
connecting the rirst and second land sections 54' and 56'.
Dte assembly 108 is mounted in a~ openlng 109 in wall 97. A
mandrel head 57' supported by mandrel 62' 1s axially
positioned within cavity 107. The mandrel head 57' has a
recessed base surface 58', a generally cylindrical lower
portlon 59', a generally diverglng conical upper portion 60'
and an elongated nose 61'. The lower porti.on 59' and the
diver~ing upper portion 60' and the portion Or the nose 61'
ln cooperation with die 29' derlne an orlfice 57a' which has
converging walls but has a generally di~erging geometry.
The partially extruded blllet 53" holds the mandrel head
57' in place during eJection of the product and whlle heated
blllet 53' is being placed in position to be extruded. A
pro~ectlon on the front face of mandrel 62' ~its into the
recess 58a to ~orm a male-~emale rlt whereby any movement o~
the mandrel head 5~7' ls vlrtually eliminated. The other end
(not shown) Or the mandrel 62' ls attached to a hydraulic
-49-
265
cylinder (not shown). The mandrel 62' is rreely movable
through an openlng 110 ln stripper plate 111. The extrudate
53" ' ls strlpped ~rom the mandrel 62' when the mandrel 62'
is withdrawn through opening 110 and is re~ected ~rom the
apparatus. The billet 53' is shown in the ~ingers 112 of a
manipulator (not shswn). FIGURE 8 is a partial view in
cross-section o~ the tank 95. A sloping ramp 114 as shown
allows billet 53' to be fed into the hot fluld 51'. The arm
and ringers 112 of the manlpulator may be any type well
known in the art.
FIGURE 6 shows a billet 53' ln pressure chamber
106. Pressure is applied to the billet 53' by piston 102
through hydrostatic fluid 51'. At ~irst, the blllet 53' is
compressed until a pressure is reached at which the billet
53' begins to be extruded through orifice 57a' onto the
mandrel 62'. The billets 53' and 53'' are elongated sub-
stantlally simultaneously circumferentially and axially. As
noted previously, the expansion in the circurnferentlal
direction is at least 100% and prererably is at least 200
percent. The axial elongation may be less than the circum-
rerent1al expansion but it is preferred that the axial
elongatlon be at least 50 percent and preferably 100 percent
the circumferential expansion.
, Although a hollow billet and a mandrel head having
~5 an elongated nose have been shown, the use of a solld billet
and a mandrel head with a sharp needle-like nose and mandrel-
heads of various shapes and sizes are well wlthin the scope
of this lnvention. In all cases the billet must be extruded
-50-
~ ~s~s~ ~
ln the solid state and be substantially slmultaneously
elongated in both circumferential and axial directions with
the circumferential expansion bein~ lOo percent and pre~erably
200 percent.
As explained previously, the circumferential and
- axlal elongatlon o~ the thermoplastic polymer billet are
controlled by the converging cross-sectional area and the
diverging geometry o~ the annular orirlce through which the
billet is extruded. In all extrusions, the lncrease Or the
inside and outside diameters of the billet to the conduit
must be sufficient to expand the medium circumference o~ the
polymer by at least lO0 percent and preferably 200 percent.
As noted above, a portion Or the press in which
the billet,~hydrostatio fluid and mandrel-head are assembled,
ls heated to a temperature within the range of about 4.64
kilograms force pe~r square cen~imeter (66 pounds per square
lnch) heat deflection temperature to 8C (14F) below the
crystalline melt temperature o~ the polymer. The crystalllne
melt temperature o~ a polymer is that temperature at which
the polymer melts and ls no longer crystalllne. The crystal-
line melt temperature varles for each polymer, there~ore the
temperature to which each thermoplastic polymer is heated
prior to extruslon also varies. The thermoplastic polymer
is extruded at a pressure and a strain-rate commensurate
wlth good extrusion practices wblch will prevent surface
tearing, loss of dimensional control and melting of the
thermoplastic polymer. In extrusion, the temperature~
pressure, strain-rate and degree~ of elongation are inter-
.
~ . .
dependent, therefore if three o~ the parameters are speciriedthe fourth is ~ixed. The maximum extrusion rate ls a functlon
of the thermoplastlc polymer being extruded, the temperature
at which extrusion occurs and the degree Or elongation Or
the thermoplastic polymer. The extrusion rate may be
expressed as the average strain rate which is de~ined as
the product o~ the circumferentlal and axial elongatlon
dlvided by the time required for the thermoplastic polymer
to pass through the expansion zone~ As an example, the
highest strain rate observed for a successful extrusion of
an isotactic polypropylene hollow billet which i5 2.54
centimeters (1 inch) in outside diameter and 12.7 centimeter~
t5 inches ? long and has a wall thickness Or 0.67 cenSimeter
(0.266 inch), at a temperature of 113C (235F~ into a conduit
whlch is 5.o8 centlmeters (2 inches) outside diameter, 17.78
centimeters (7 inches) long and having a wall thlckness o~
0.14 centlmeter (0.055 inch) with a circumferentlal expansion
coefficient o~ 2.6 and an axlal elongation coefficient of
1.9, was 8 sec 1 On a practioal basls, lt is p~sslble to
extrude an isotactic polypropylene preform or billet into a
conduit havlng a diameter of 40.64 centimeters (16 inchesj
at a strain rate of 6.7 sec to yleld a throughput of about
10,884 kilograms (24,000 pounds) per hour. The thermoplastlc
polymer is extruded over a generally conically-shaped
mandrel head through an annular ori~ice rormed by the outer
surface of the mandrel head and the surface o~ the die.
While the mandrel-head and die have generally diverging
geometries, the annular oFifice formed by thelr diverging
-52-
.
. .
1 ~55~6~
surfaces has a converging cross-sectlonal areaO The polymer
is thus substantially simultaneously expanded clrcum~erentally
and elongated axially resulting in a conduit which has a
larger outside diameter, a greater length and a wall thickness
smaller in cross-sectional area than the starting blllet.
The divergent geometry of the annular ori~ice controls the
circumferential expansion or elongation while the convergence
of the surfaces of the orifice, i.e. the converging cross-
' sectional area, controls the axial deformation or elongation.
Such elongations may be varied independently to obtain
desired circumferential and axial properties. Stating this
relationship in terms o~ the billet and product geometry,
the lncrease in the median clrcumrerence of the billet to
the medlan circumference Or the article defines the cir-
cumferential deformation while the reduction of the cross-
sectlonal area of the billet wall to that of the conduit or
extrudate controls the axial deformation. By median cir-
.
cum~erence we mean the circumrerence whlch divides thecross-sectional area Or either the blllet or conduit ln
half. By median dlameter we mean the diameter o~ the median
circumference. An elongation coefficient is obtalned by
dividing the extruded dlmension by the originaI unextended
dimension.
Whenever tensile impact strengths are shown such
stren~th has been determined by ASTM Dl822 short specimen
and ultimate tenslle stren~th is determined by ASTM D638
unles~ otherwise stated.
-53-
.
~ ~5~2¢S~
: A comparison Or the ultimate tensile strength and
tensile lmpact strength of conduits fabricated by the method
of the invention and consistlng essentially Or polypropylene,
polyethylene or nylon 6,6 and conduits fabrlcated from the
same resin lots by conventional plasticate extruslon method
was made. The results of the tests are shown in Table II
(metric units) and Table IIA (English units), below: .
'
.. ~ .
i
-54-
.
. ... . , . ~ .
1 ~5~5
*
~ ) ~ *
O tl~
r- ~ U~
Z; N N
O ~:)
rl r-l N ~
~1 ~U 0~0 I
:z ~o o
O
C.) O ~Is *
h 3 U~ * *
5 3
~ 1 ~ C
~0 0
h
P~
0
h
X a~ ~ ~,~
C~ . .
O
O C~ O r~ ~a
3 ~J t~
~) S--~
C) t~ X~ 0 3J
U~
C~ O
O ~ :
~ 3 0 C--O
H h C) o '~:3
Z r ~ h e
. ~ o~ ~ .
¢ ~d ,~
E~ ~ ~ .. ..
h rcl ~N r-l ~1 ~--1 C>
O ~;3 C~ 'Cl
~. ~J 3 ~) ~ ~co ~ t--
O o ~1 ~ ~o~
h ~O :~ O . O h
~ ~ ~ 2 ~ s
O td ~ ~ O ~ O ~ U~
o J~ O O ~ ~r) ~ ~ ~ rl
u~ h
h
t~ ~ h O O
~, P~ * * r-l V
E ::-, * ** * ~ .,~
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C~ o
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r~ O
e
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U~
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O (~ t~J N ~ ~I
r-l ~ ~ . . f
U~ N N
:Z O O
O ~ O O
0 ~ N 0 ~ E--
~Z ~D O ~Joo 3
U~
O ~
C~ O
Z r~ J~
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h ~1
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h ~ N
x a)
S::~ O O U~ i
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O C~ O ~ r-~ ~D O
,
J~ s u~ ~ t-- .
C~ ~ X~
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v~ o 0~:; ~ h
h ce O ~1: o o ~ =r
5 ~4 O O
D. ~ h ~1
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o a ~ ,~
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a~~) o ~ (u ,~
c~~1 tn ~ ~
h '~J ~) O O ~ o
~ o o ~o 1~ c) a.l
O O ~i ~ ~ N ~ ~ ~I P;
O ~ O ~1 ~ C~
rl O O h
J~ :Z h C.~ ~ ~ i
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¢ O O N ~1 0 ~ u~
O ~ O O O O N ~i ~ O
h u~ E
d O
h ~1 ~ 1~1~ b~
;
~ O O S
E :~ ~1 C~
O ~ :~C :~C
t~ * * * *
r ~ O
bD h
r-l a) 5:: .0
~ O~1
a) ~~ ~ Ei :~
E S:~ ~ r~
1 ~ r ~i5 ~
~? a) ~ ~ ~ X ~
bO ~ bO~ ~) cl ¢
rl ~ r-l
h ~:: h ~ *
* *
i
.
- . , ' : ~ -
~ ~55~5
Illustrative examples Or polymer compositions
whlch can be processed by the method herein described to
produce conduits having improved propertles are shown below.
All the polymers were compression extruded in the apparatus
shown in FIGURES 2 and 3. The angles a and ~~ were kept
constant at 30 and 40, respectively,
Exam~le I
Isotactic polypropylene rods of Novamont Corpora-
tion Moplen DoO4W homopolymer produced by melt extruslon and
machining and having an outslde diameter Or 2.54 centimeters
(1 lnch) were obtained. The polymer had a density of 0.909,
a crystallinity of 68.3%~ a crystalline melt temperature Or
, 168C (335F), a melt ~low lndex Or 0.4 dg. per minute, an
,~ ultlmate tensile strength of 387 kllograms force per square
centlmeter (5?100 pounds per square lnch), and, a tensile
impact strength o~ 3.55 ~oules per square centlmeter ak 24C
(19 foot pounds per square inch at 75F').
The rods were divided lnto billets having a length
of 12.7 centimeters (5 inches) and were drllled to produce
an axial bore Or 1.2 centimeters (0.4~8 inch). A billet was
placed ln the blllet container assembly and 69 milliliters
~2.33 ~luid ounces) of castor oil were poured into the
assembly. The 9traight 1.27 centimeter (0.5 inch) diameter
tip of a mandrel head wa~ wedged into place in the bore Or
the billet. An orifice having converglng walls and a con-
ver~ing cross-sectional area and a diverging dlameter having
an entrance Or 1.27 centlmeters (O.5 inch) internal diameter
'
-57-
- : .
~ . 1 1$5~65
and 2.51 centimeters (0.99 inch) external diameter and an
exit of 5.o8 centlmeters (2.0 inches) internal diameter and
5O32 centlmeters ~2.096 inches) external diameter was formed
by the surfaces of the mandrel head and the dle, respectively.
The blllet ,container assembly was placed in an
oven and was held ~or about 160 mlnutes to heat all the
parts and materials in the assembly to a temperature of 129C
(265F). The assembly was removed from the oven and placed
in the prevlously described batch extrusion apparatus and
the extrusion apparatus assembled for extrusion. The pressure
applied to the billet through the castor oil was increased
from 0 to 600 kilograms force per square centimeter (0 to
7900 pounds per square inch) at which pressure the billet
was extruded through the orifice into the extrudate receiving
assembly. In this example, the extrudate was not lubricated
or cooled by a fluid introduced into the extruda~e chamber.
The polymer did recover sornewhat, resultlng in thickening Or
the wall and decreasin~ the length of the produc~. However,
no evldence Or wrinkling was seen and the wall had a uniform
thlckness whlch did not vary more than plus or minus 10
percent the length or clrcumference o~ the product. The
condult had a length of 13.9 centlmeters (5.5 inches) and
had an outside dlameter of 4.94 centimeters ~1.945 inches)
and an lnside dlameter of 4.76 centimeters (1.875 inches)
and a wall ~hickness~of 0.089 centimeter (0.075 inch). A
length of polymer about 5 . o8 centimeters (2.0 lnches)
remained in the billet contal'ner assembly. The wall thickness
-58~
,
~ ~55~$
was about 1.8 percent of the outside dlameter. The circum-
~erentlal elongatlon was 2.6 which ls 160 percent and the
axlal elongatlon was 2.6 or 160 percent.
; Circumferential and axial tenslle and tenslle
lmpact test specimens were cut from the conduit. The
results of the tests are shown below:
Ultimate Modulus Tensile Impact
Tensile Or Strength at
Stren~th Elasticlty 24C (75F)
Circumfer-
ential
(psl) 2 10,900 32.9 x 105
(Kgf/cm ) 2 766 0.20 x 10
(Ft.lbs/In.2) , 1~0
(Joules/cm. ) 38
Axial
(psl) 2 13,400 5
(Kfg/cm ) 2 9630.23 ~ 105
(Ft.lbs/In.2) 310
(Joules/cm. ) 65
The oriented circumrerential ultimate strength o~'
766 kllograms rorce per square centimeter ls 1.9 klme.s the
unorlented circum~erentlal ultlmate tensile strength Or 387
kllograms ~orce per square centlmeter. The or~ented circum-
ferential tensile impact strength Or 38 ~oules per square
centimeter at 24C ls 8.2 tlmes greater than the circumferen
tial tensile impact strength o~ 4.6 Joules per square
centimeters at 24C o~ an unoriented cond~it made by a con-
ventional plastlcating method.
Samples o~ the conduit were polished and etched and
examlned by techniques prevlously described in these speciri-
catlons. The microstructure was-comprised Or platele~ or
-59-
wa~er-llke spherulitlc crystalline a~gregates when vlewed
on a sur~ace radial to the plane Or the conduit. When viewed
on transverse surfaces the micro~tructure showed relatively
thln lamellae elongated circum~erentially and axlally and
oriented in the plane o~ the conduit.
Example II
Rods Or Valox 310, a General Electric resln of
polybutylene terephthalate, havlng a length of 12.7 centi-
meters (5 inches) and an outside diameter of 2.54 centime~ers
(l inch) were obtained. The polymer had a published ultimate
tensile strength of 563 kilograms force per square centi-
meter (8,ooo pounds per square inch) at yield, an ;impact
strength of 0.403 ~oules per centimeter at ~4C (0~9 root
pounds at 75F) on a~notched Izod impact speclmen.
The rods were divided into billets having a length
12.7 oentimeters (5 inches) and were drilled to produce
an axial bore of 1-27 centlmeters (0-5 inch). A billet was
placed in the billet container assembly and 69 mllliliters
(2.33 ~luid ounces) of castor oil were poured lnto the
assembly. A =andrel-head was force-~lt into place in the
bore o~ the billet. An annular oririce havlng an entrance
of 1,27 centimeters (0~.5 inch) internal diameter and 2.5
centimeters (0.99 inch) external diameter and an exit o~
5 . o8 centimeters (~2.0 inches) internal diameter and 5.32
centimeters (2.096 inches) external diameter was ~ormed by
the sur~aces ~f the mandrel head and the die, respectively.
The mandrel had a diameter o~ 5.08 centimeters (2 lnches).
The billet container asse=bly was placed ln an
oven and was held ror about 200 minutes to heat all the
.
--60--
1~ ~5~5
parts and materials ln the assembly to a temperature or 192C
(375F). The assembly was removed from the oven and placed
in the prevlously descrlbed batch extrusion apparatus whlch
was then completely assembled for extrusion. Pressure~
applied to the billet through the castor oil, was increased
from 0 to 281 kllograms force per square centimeter (0 to
4000 pounds per square inch) at which pressure the b~llet
began to be extruded through the orifice lnto the extrudate
receivlng chamber. Pressure was kept substantlally constant
at 281 kilograms force per square centimet~r (4000 pounds
per square inch) durlng extruslon. In this example, the
~- extrudate was lubricated and cooled by air introduced in~o
the extrudate recelving chamber at 3.5 kilograms force per
square centimeter (50 pounds per square inch). Visual
examlnatlon of the extrudate did not elicit any evidence Or
wrinkling on the wall surface. The wall thickness was
substantlally unirorm and did not vary more than plus or
minus 3.5 percent the length Or the article. The condult
had a length o~ l3.97 centimeters (5.5 inches) and had an
outslde dlameter Or 5.26 centimeters (2.07 inches) and an
lnside diameter of 4.1 centimeters (1.98 inches) and a wall
thickness o~ 0.12 centimeters (0.046~inch). The circum- :
~erential elongat:lon was 2,55 or 155 percent and the axia
elongation was 2.00 or lO0 percent.
Clrcumrerential and axial tensile and tensile
impact test specimens were cut ~rom the conduit. The results.
of the tests are shown below:
. ' ''' - .
61-
1 ~5~5
Ultlmate Modulus Tenslle Impact
Tenslle Or Strength at ',
Stren~h Elasticit~ 24C (75F)
Clrcumfer-
5' ential
(psi) 215,500 3.4 x'105
(Kgr/cm. ) 2 lOgO0.24 x 105
(Ft.lbs/In.2) 449
(Joules/cm. ) 94
10 Axial
(psi) 2 15,200 3.5 x 105
~ (Kgf/cm. ) 2 10690.25 x 105
(Ft.lbs/In.2) 414
(Joules/cm. ) 87
The oriented, circum~erential ultimate kenslle
skrength o~ 1090 kilograms force per square,centimeter ls
more than 1.9 tlmes the published unoriented ultlmate tenslle
strength Or 56t3 kilograms force per square centlmeter and
the oriented clrcum~erentlal tenslle impact strength of 94
~oules per square centimeter at 2lic is more than ten times
the estimated unoriented tenslle impact strength oI g.0
~oules per square centimeter at 24C.
.
A polyamide, Polypenco Nylon 101 ~Nylon 6,6) in
the rorm Or rods having an oukside dlameter of 2~54 centi-
meters (1 inch) were obtained frc,m Polymer Corporakion. The
polymer had an ultlmate tensile strength Or 633 to ~44
kilograms ~orce per square centimeter at 24C (~,000 to
12~000 pounds per square inch at 75F), a modulus o~ elas~
ticity o~ 2,8000 kilograms rorce per square centimeter
(400,000 pounds per square inch), a tensile impact strength
~r 18.9 to 35.7 ~oules per square,centimeter (90 to 170 root
. 62-
1 ~i55~
pounds per square inch), an Izod impact strength or 0.258 to
.515 ~oules per centimeter at 23C (.5 to 1.0 foot pounds per
lnch at 75F).
; The rods were d~vided into billets havlng a length
Or 12.7 centimeters (5 inches) and were drllled to produce
an axial bore o~ 1.27 centimeters (0.5 lnch). A billet was
placed in the billet holder assembly and 69 milliliters
(2.33 fluid ounces) of castor oll were poured into the
assembly. A mandrel head was wedged lnto place in the bore
of the billet. An annular orifice having an entrance Or
1.27 ~entlmeters (0.5 inch) internal diameter and 2.51
centimeters (0.99 inch) external diameter and an exit of
5. o8 centimeters (2.0 lnches) internal dlameter and 5.32
centimeters (2.096 inches) external diameter was formed by
the surfaces of the mandrel head and the die, respectively.
The mandrel had a dlameter Or 5.08 centimeters (2.0 inches).
The billet container assembly was placed in an
oven and was held rOr about 230 minutes to heat all the
parts and materials in the assembly to a temperature o~ 221C
(430F). The assembly was removed from the oven and placed
in the previously described batch extruslon apparatus and
the extrusion apparatus assembled for extrusion. The
pressure applied to the billet through the castor oil was
slowly increased ~rom 0 to 457 kilograms force per square
centimeter (0 to~6500 pounds per square inch) a~ whlch
pressure the blllet was extruded through the orlflce lnto
the extrudate recei~ing chamber. The extrusion strain rate
was about 2 sec 1, In this examplej the extrudate was not
I
- -63
~, ' . ~ . .
5~65
lubricated or cooled by a fluid lntroduced into the extrudate
chamber.' The polymer did recover somewhat, resulting ln
thickening of the wall and decreaslng the length Or the
product. However, no evidence of wrinkling was seen and the
wall had a unirorm thlckness which did not vary more than
plus or mlnus 10 percent the length,or circum~erence o~ the
product. The conduit had a length of 14 centimeters (5.5
lnches) and had an outside diameter of 5.245 centimeters
(2.065 inches~ and an lnslde diameter Or 5.01 centimeters
(1.972 inches) and a wall thickness of 0.102 centimeters
(0.046 lnch). The wall thlckness was 2.2 percent o~ the
outside diameter. The circumferential elongation was 2.56
or 156 pelcent and the axial elongatlon was 2.15 or 115
percent.
Gircumferential and axial tensile and tensile
impact test speclmens were cut rrom the conduit. The
results Or the tests are shown below:
Ultimate Modulu~ Tensile Impact
Tenslle of Strength
, Stren~th Elasticlt,y 24C(75F) -45C(-50F)
20Circumfer- ~,
ential -'
.
(psi) 2 ~6,300 4.3 x 105
;' (Kgf/cm. ) 2 1850 0.30 x 105
(Ft.lbs/In.2) 426.5 109.5
(Joules/cm. )' 9 23
Axial
(psi) 2 18,800 3.7 x 105
(Kgf/cm. ) 2 1322 0.26 x 105
(Ft.lbs/In.2) 457 155.5
(Joules/cm. ) ,: 96 33
-64-
8 ~ l
.
The oriented circumferential ultlmate ~enslle ji
strength of 1850 kilograms ~orce per square centlmeter i5
2.2 tlmes the unoriented circum~erenkial ultlmate tensile
strength Or 844 kllograms rorce per square centimeter. The
orlented clrcum~erential tenslle impact strength of ga
~oules per square centimeter at 24C is slx tlmes greater the
unorlented circumferential tensile impact strength of 15
~oules per square centimeter at 24C of an unoriented conduit
made by a conventlonal plasticatlng method. The -45C tenslle
impact strength Or 23 ~oules per square centimeter is 25.6
percent of the tenslle impact strength o~ 90 ~aules per
square centimeter at 24C.
,Specimens were removed rrom both the billet and the
conduit and their surfaces prepared for microscopic examination
by the techniques previously described. Microscopic examina-
15 tlon Or the surfaces showed the blllet to be comprised o~underormed unl~ormly distributed spherulitic crystalllne
aggregates and the conduit to be comprlsed Or radlally
compressed platelet or warer-like spherulitic crystalllne
aggregates clrcumrerentlally and axially oriented in the
plane of the conduit.
- Example _ -
!: :
Extruded Samples of Delrin 100, an E.I. DuPont
Gorp. homopolymer polyoxymethylene (polyacetal) which were
2.54 cent~meters (1 lnch~ in outside diameter were purchased.
:
The polymer had a pubIished tenslle strength Or 703 kilo-
grams force per ~square centimeter (10,000 pounds per square
inch), a ten~lle~modulus Or o. 32 x 105 kllograms ~orce per
,
. ,
-65- !
.
. ~ , .
6 ~
square centimeter (4.5 x 105 pounds per square lnch), a
tensile impact strength o~ 8.4 ~oules per square centlmeter
at 24C (40 foot pounds per square inch at 75F).
The rods were cut into lengths of 12.7 centimeters
; 5 (5 inches) and a 1.27 centimeters (0.5 inch) diameter bore
was drilled through the speclmens. A billet was placed ln
the blllet contalner assembly together wlth 69 milliliters
(~.33 ounces) of castor oil. A mandrel head was force-fit
into the bore of the billet. The mandrel head had a bore
diameter o~ 5. o8 centimeters (2 inches). The ~ssembly was
placed ln an oven and to heat the parts and blllet held for
160 minutes to a temperature of 129C (265F). The assembly
was placed into the extrusion press and the press was
completely assembled. The mandrel which had a dlameter Or
5.08 centimeters (2 lnches) was placed contiguous with the
~ase of the mandrel head and a clamping ~orce of 27,200
kilograms (30 tons) was applied to the apparatus to keep the
mandrel rlgld and to prevent vertical or lateral movement Or
the mandrel head during extrusion. Air at a pressure Or 3.5
kilograms ~orce per~square centimeter (50 pounds per square
inch) was introduced into the extrudate chamber. The
extrusion pressure was 499 kilograms ~orce per square
~centimeter (7100 pounds per square inch). The extrudate had
an outside diameter of 5.26 centlmeters (2.07 inches), an
lnslde diameter of 5.03 centlmeters (1.98 lnches) and a
uniform wall thiakness o~ 0.11 centimeter (0.045 inch). The
wall thickness was about 2.0 percent of the outside dlameter,
and wall thlckness varlatlons were wlthln plus or mlnus 2.5
66-
5~6~ ;
percent. The circumrerent~al elongatlon o~ the polymer w~s
2.47 or 147 percent and the axlal elongation was 2.1 or 110
percent.
Tenslle and tenslle lmpact test specimens were
; 5 taken from the sheet. The test results are shown below:
Ultimate Modulus Tensile Impact
Tensile of Strength
Elasti~ 24Ct75F) --~5C(-50F)
Circumfer-
ential
~psi) 2 20,600 4.57 x 105
(Kgf/cm. ) 2 1450 0.32 x 105
(~t.lbs/In.2) 348 75
(Joules/cm. ) 73 16
The oriented~ clrcumferential ultimate tenslle
stren~th of 1450 kllograms force per s~uare centlmeter ls
twice the published unoriented ultlmate tensile strength of
703 kilograms force per square centimeter and the oriented
circum~erential tensile impact strength Or 73 ~oules per
~20 square centlmet~r is 8.7 tlmes the unoriented tensile
impact strength of 8.4 ~ou~es per square centimeter at 24C.
, The -45~ tensile impact strength o~ 16 Joules per square
centimeter is 22 percent of the tensile impact strength of
73 loules per~sq,uare centimeter at 24C~
~, ~ 25 ~ ~ Example V
¦~ A plurality of extruded rods consisting essentially
o~ Marlex 5G03, a Phil~llps Petroleum Corporation hlgh density
po~lyethylene~ were obtained. The rods had an outslde diameter
of 2.54 centimeters (1 lnch). The polymer had a density o~
0.95 grams per cublc centimeter, a melt lndex Or 0.3 grams
per 10 mlnutes, an ultlmate tenslle strength Or 232 klIo-
grams rorce per square centimeter (3,300 pounds per square
- 67 -
.
2 6 ~
inch) and a rlexural modu~us o~ 11,600 kllo~rams rorce per
square centimeter (165,000 pounds per square inch) . The
rods were prepared for extruslon and were extruded by the
method of the lnventlon as descrlbed in Fxample I except
that the rods were heated to a temperature Or 113C
(235F) and were extruded at a pressure Or 113 kilog~ams
force per square centlmeter (1600 pounds per square inch).
The extrudate was cooled by air at a pressure Or 3.5 kllograms
force per square centimeter t50 pounds per square inch).
The extrudate produ.ced was a conduit which had a length of
14 centimeters (5.5 inches), an outside diameter of 5.2
: centimeters (2.06 inches), an inslde diameter of 5.0
centlmeters (1.972 inches) and:a wall thickness of .11
centimeter (.044 inch). The wall thickness was 2.11 times
the outside dlameter. The circumferential elongation was
2.65 or 165 percent and axial:elongation was 2.12 or 112
percent.
The results o~ testing are shown below:
Vltimate Impact Tenslle
Tensile Strength
E~ 24C(75~) -45C(~
Circumfer-
ential
. (psl~ 26,630
. 25 (Kgf/cm- ~ 2466
(Ft.lbs/In-2) 352 167
; (Joules/cm. ) ~ 7.4 35
: Axial
~psi) 26,650
(Kgf/cm. ) 2 468
(Ft.lbs/In.2) : 3g5 201
(Joules/cm. ) 83 42
:
'
- 68 -
1~ 5$~B ~
The circum~erentlal ultimate tenslle strength of
466 kilograms force per square centimeter is about one and
three quarters times the circumferentlal ultimate tensile
strength of 274 kllograms force per square centimeter and
the circum~erential tensile lmpact strength o~ 74 Joules per
square centimeter at 24C ls eleven tlmes greater than the
circumferential tensile impact strength Or 6.7 Joules per
square centlmeter at 24C Or an unoriented conduit made by a
con~entional plastlcating method.
The circum~erential tenslle lmpact strength of 35
~oules per square centimeter at -45C was 47 percent of the
clrcumferential tensile impact strength of 74 '?oules per
~ square ce~timeter at 24C. :
:' ExamPle VI
A useful article Or manu:~acture which can be made
by the process Or the invention ls a relatively deep ~reezer
.
food container as shown at 116 in FIGURE 9. The contalner
,? had a dlameter of l9.~ centimeters ~8 inches) and a depth of
9.6 cen~imeters (4 inches). The container was made from an
isotactlc polypropylene de~scribed ln Example I and which was
initially made into a conduit by the process described in
Example I. The conduit had a length of 61.0 centlmeters ~24
: inches), an outslde~diameter of 20.6 centimeters (8.4
inches), an inside diameter o~ 19.2 centimeters (8 inches)~
: 25 and a wall thickness of 5.1 centimeters ~.20 inch). The
: conduit was slit~by a heat kni~e. The slit conduit was
placed in a heated platen press and was held far 6 minutes
at a temperature~or 129C (265F) and under a pressure Or 24.4
: -69- . I
~ ~ ?
1 ~52~5
kilograms rorce per square centlmeter (347 pounds per square
lnch) to form a heat ~lattened sheet which was cut into a
disc having a dlameter of 24.1 centimeters (9.5 inches) and
a thlckness of 4~83 millimeters (.20 inch). The disc-shaped
sheet and appropriate solid state thermal forming apparatus
were heated to a temperature of 149C (300F) for about 60
minutes in an oven. The apparatus and sheet were removed
from the oven and the outer periphery Or the sheet was
clamped in place in the thermoforming apparatus. Air at a
pressure of 2.8 kilograms of force per square centimeter (40
pounds per square inch) was lntroduced into the apparatus
and forced the sheet to be formed lnto the shape of the
cavlty ln the apparatus. After about 10 mlnutes, the air
pressure in the apparatus was relleved. The container thus
formed was removed from the apparatus. The bottom 118 Or
the container was sub,~ected to a total biaxial draw ratlo of
4:1 when compared to the unoriented polymer. A portlon Or
the flange 117 which measured 1.6 centlmeters (5/~ inch) (not
shown) by which the dlsc was clamped in the apparatus was
trlmmed from tbe product. The flange 117 which remained was
substantially undeformed and hence was subjected to an
average biaxial draw ratio of 2.2 to 1~ The side wall 119
of the container was sub~ected to lntermediate draw ratlos
between 2.2:1 and 4:1. The flange 117 had a thickness Or
4.45 millimeters ~.175 inch). In the area immediately
beneath the ~lange, the wall 119 had a thickness of 3.43
mllllmeters (.l35 inch) about 2.54 centlmeters (1 inch)
below the rlange 117 and 1.9 millimeters (.075 lnch) in
-70-
1 ~5$~6~
the area lmrnediately above the radius 120. The bottom 118
Or the contalner had an average thickness Or 1.6 millimeters
(.063 lnch). These dlmensions lndicate that the polymer
sheet had excellent drawabllity and resisted "necking"
during processing. For comparison, a 5.8 millimeters (.23
lnch) thlck sheet of unfilled substantlally non-orlented
isotactlc polypropylene of the same resln batch was thermo-
formed lnto a dish of identical overall dimensions by the
same thermoforming process as outllned above. The dlsh
bottom was thinned to .53 millimeter (.021 inch) and there-
fore was sub~ected to a blaxial draw ratlo Or 3.3:1.
The tensile impact strengths and ultimate tensile
.
I strengths of the freezer container Or the invention compare~
~avorably! wlth the tenslle ~mpact strengths and tensile
strengths of a condult produced by the method of the invention
as seen in ~xample I.
i
Tenslle and tensile impact test speclmens were cut
from the sheet of the inventlon prior to solid state thermal
treatment and also ~rom the bottom Or the khermorormed
container and from the bottom Or a contalner made rrom
; unoriented semi-crystaIllne thermoplastic polymer sheet
~prepared from the same polymer by the same solld state
thermal treatment process. The results Or the tests are
, shown below:
;
.
:
,
-71-
.
- .
.. .
2 6 5
Average Total Avera~e
Vl~imate AverageTenslle Impact
Tensile BlaxialStrength
Strength Draw Ratio24C(75F)
Sheet Or Invention 2.2
psl 2 11,0o0
(Kgf/cm ) 2 773 __
(Ft.lbs/In2) __ 280
(Joules/cm ) -- 5g
Dish Bottom from
Orlented Sheet 4.1
~psi) 2 18jl00 --
(K~f/cm ) 2 1,305 __
(Ft~lbs/In2) ~~ . 380
tJoules/cm ) -- 80
Dish Bottom from :
, Non-Oriented~Sheet 3.3
(psi) 2 17,400
(Kgf~cm ) 2 1,255
; 20 (Ft.lbs/In2)
(Joules/cm ) .43
I
xample VII -
!Another artlcle:;of the invention ls a rerrigerator
freezer door llner,~shown at 121 ln FIGURE 10. The llner is
~25 mad:e from a fllled substantially non-oriented thermoplastic
homopolymer Profax 68F-5-4 which is a polypropylene homo-
polymer containing 40 weight percent calcium carbonate
filler and made by the ~ercules Corporation, 910 Market
Steet, Wilmington, DE 19899. The properties of the melt
l 30 extruded homopolymer at 23C (74F)~are listed below:
1- : Ultlmate Tensile Strength - 274 kilograms force per
. square centimeter
(3900 pounds per square
inch)
~: 35 :~Flexural Modulus: - 23,700 kllograms force per
square centlmeter
(337,000 pounds per
square lnch)
~longation at Fracture - 41%
.
.
-7 2-
I
6 ~
Tenslle Impact Strength - l.9 Joules per centlmeter
s~uares (9.2 rOOt pounds
per square inch) at
23C (74F)
. l.5 Joules per centlmeter
squares (7.0 ~oot pounds
per square inch) at
-45C (-50F)
Notched Izod Impact - 0.5 Joules per centimeter
(l.0 foot pounds per
lnch) at 23F (74F)
l.2 Joules per centimeter
(0.4 foot pounds per
inch) at -45F (-50F)
The polymer has a melt.index Or 0.3 to 0.6 at 230C
(446F~ and crystalline melting point Or 168C (335F). A
', billet having an outside diameter of lO.16 centimeters (4.0
inches), an inside dlamter of 6.99 centlmeters (2.75 inches)
- and 25.4 centimeters (lO inches) long was hydrostatically
extruded at 143.3C t290F) in a large press Or appropriate
size by the technique described ln Example I. Dow Corning
.
3000 Sllicone rluid manufactured by Dow Corning Corporation,
Mldland, MI 48640 was used as the hydrostatic ~luid.
The conduit which had an outside diameter Or 20.8
: , 25 centlmeters (8.2 inches), an inside d~ameter of l9~2 centi~
meters (8.o lnches) and 61 centlmeters (24 inches~ long was
. alr cooled as lt was extruded into the extrudate zone. The
- : : olrcumferential elongatlon and the axial elongatlon were
essentially the same 2.5 or 250 percent which is greater
than lO0 percent deformatlon. The condult was slit wlth a
heat knife and was heat~flattened as described ln Example VI.
Specimens to determlne the ultimate tenslle strength
: .and tensile impact strength were cut from th~ sheet. Since
: :the draw ratio is the same in the clrcumrerential and axlal
1 ~5526~
directlons, the average propertles are reported and are the
same in either direction. The results of the tests are
shown below:
Average Average Average
Ultimate Biaxial Tensile Impact
Tenslle Draw Strength
Strength Ratio _24C(75F) -45C(-50F)
i (psi) 2 8goo 2 . 5
(Kgf/cm ) 2
(Ft.lbs/In2) 86.4 63.4
(Joules/cm )
The sheet can be thermoformed by the techniques
descrlbed ln Example VI to form the article in FIGURE 10.
A coupon taken from the flange 122 ~ show that
the propertles were essentially the same as those Or the
sheet rrom which ~t was produced.~ The rlange 122 had a
thickness Or 0.254 centlme-ers (0.10 lnohes).
,
' -
.
-74- I
