Note: Descriptions are shown in the official language in which they were submitted.
- 1327688
BIAXIALLY ORIENTED ORDERED POLYMER FII,M8
*
~ STATENENT OF GOVERMNENT INTEREST
:E ; ' `
Funding for the present invention was obtained from
the Government of the United States by virtue of Contract
Nos. F33615-83-C-sl20 and N00164-87-C-0050, from the
Departments of the Air Force and the Navy, respectively. `
Thus, the Government of the United States has certain
rights in and to the invention claimed herein. -
.
CROSS-REFERENCE TO ANOTHER APPLICATION
Reference is made to Canadian patent application no.
602,577 filed on June 13, 1989.
' '
FIELD OF THE INVENTION
~ This invention relates in general to the formation
'I .
~ ~'.
:~ 1327688
:`
--2--
of multiaxially (e.q., biaxially) oriented films from
; high molecular weight lyotropic or thermotropic
polymers (homopolymers, copolymers, and the like),
wherein due to the processing conditions employed, the
films have a controlled molecular orientation
The films of the present invention are preferably
prepared from rod-like extended-chain, aromatic-
heterocyclic polymers. These polymers generally fall
into two classes, those that are modified in solution
form, i.e., lyotropic liquid crystalline polymers, and
those that are modified by temperature changes, i . 8 .,
thermotropic liquid crystalline polymers. For a
shorthand expression covering both types of polymers,
the present disclosure will use the term "ordered
lS polymers. n
BACKGROUND OF THE INVENTION
As used herein, "ordèred polymers" "extended-chain
aromat ic-heterocyclic ordered polymers,"
"tbQrmotropic,~ and "lyotropic" liquid crystalline
polymers, all refer to one or more of the known classes
of polymers having a fixed molecular orientation in
space i.e., linear, circular, star shaped, or the like.
This molecular orientation is believed to be
imposed on the polymer structure by the nature of the
monomer units making up the polymer. Many ordered
polymers possess a linear "order" due to the linear
nature of the monomeric repeating units comprising the
polymeric chain. Linear ordered polymers are also
known as "rod-like" polymers. `
I For example, U.S. Patent No. 4,423,202 to Choe,
~ discloses a process for the production of para-
~ .
132768g
ordered, aromatic heterocyclic polymers having an average
~olecular weight in the range of from about 10,000 to
30,000.
U.S. Patent No~ ~,377,546 to Helminiak, discloses a
5process for the preparation of composite films prepared
from para-ordered, rod-like, aromatic, heterocyclic
polymers embedded in an amorphous heterocyclic system.
U.S. Patent No~ 4,323,493 and 4,321,357 to Keske et
al. , disclose melt prepared, ordered, linear, crystalline
10injection moldable polymers containing aliphatic,
cycloaliphatic and araliphatic moieties.
U.S. Patent No. 4,229,566 to Everts et al~, describes
~ E~E~-ordered aromatic heterocyclic polymers characterized
`; by the presence of diphenoxybenzene "swivel" sections in
15the polymer chain.
U.S. Patent No. 4,207,407 to Helminiak et al.,
discloses composite films prepared from a ~3~-ordered,
rod-like aromatic heterocyclic polymer admixed with a
flexible, coil-like amorphous heterocyclic polymer.
20U.S. Patent No. 4,108,835 to Arnold et al., describes
-ordered aromatic heterocyclic polymers containing
pendant phenyl groups along the polymer chain backbone.
U.S. patent No. 4,051,108 to Helminiak et al.,
¦ discloses a process for the preparation of films and
~ 25coatings fro~ ~a-ordered aromatic heterocyclic polymers.
i Ordered polymer solutions in polyphosphoric acids
(including PBzT compositions) useful as a dope in the
production of polymeric fibers and films are described in
I U.S. Patent Nos. 4,!;33,692, 4,533,693 and 4,533,724 (to
¦ ~0 Wolfe ~ al.).
" . ...
'
.' ''' `.
1327~88
Film processing methods and apparatus have been
available for a number of years. However, it is not
believed that the methods previously utilized for
standard polymeric films, can readily be employed in
the formation of lyotropic or thermotropic polymer
films, especially films having the unique
characteristics of those prepared herein.
For example, U.S. Patent ~o. 4,370,293 to
Petersen-Ho; describes a method and apparatus for the
manufacture of biaxially oriented plastic films,
particularly polyester films. The process described
~or polyester comprises extruding polyester through an
annular die to form a seamless tube and inflating the
tube by means of a pressurized gas. The expanded tube
thus formed is drawn out in a longitudinal direction,
cooled and flattened. The flattened tube is heated to
the oriantation temperature of the film, expanded
again, and stretched in its longitudinal direction~
These stretching techniques are said to impart a
biaxial orientation to the polymeric backbone of the
film.
Similarly, U.S. Patent No. 4,011,128 to Suzuki
describes a method and apparatus for forming a
cross-oriented film, wherein a non-oriented film to be
treated is first formed by conventional methods, then
cross-oriented by stretching and twisting. In addition
the cross-orientecl film is flattened so as to
continuously form a laminated cross-oriented film.
U.S. Patent No. 4,358,330 to Aronovici describes a
method and apparatus for manufacturing films having
pairs of adjacent layers whose molecular orientation is
in differ~nt directions. The method employed is a
modification of the conventional "blown film" technique
such that the molecular chains forming the layers of
1327688
- 5
film are oriented substantially immediately prior to their
solidifying.
U.S. Patent No . 4 , 496 , 413 to Sharps, Jr~, describes a
process and apparatus for the preparation of a blocked
cross-plied polymer film which involves the extrusion of a
polymer melt through a tubular rotary die. The rotation of
a single member of the die is said to impart a molecular
orientation to the polymer in a transverse direction during
the extrusion~ The film is bIocked by expanding the film
and then pressing opposing walls together to produce a
composite film having at least two layers, each having a
transverse molecular orientation opposing the other. The
composite film is said to have a balanced cross-ply.
SUMMARY OF THE INVENTION
,.
. The present invention is directed to the production of
¦ films having heretofore unavailable strength
characteristics in more than one direction, i e., films
ha~ing a multiaxial orientation, and preferably a high
1 20 degree of biaxial orientation.
I In some preferred embodiments of the present
invention, thick films, i.e., films having a thickness
greater tha~n or equal to about 0.10 mm, preferably greater
than or equal to about 0.20 mm, are formed and used. In
other preferred embodiments, thin films, i.e., films having
a thickne~s of less than or equal to about 0.10 mm,
preferably less than or equal to about 0.05 mm, are formed.
The starting mat;erials useful herein include those ;~
:.--. '
:; .
.. .. . . .
13276~8
- ~6--
lyotropic or thermotropic polymeric materials in which
strain produces a material orientation in the
microscale structure and which are relatively weak if
this orientation is in only one direction, i.e.,
uniaxial.
The method of the present invention comprises
producing an initial microscale structural orientation
within a polymer by a sequence of straining methods,
followed by solidifying t~is orientation by a sequence
of thermal and~or chemical conditioning operations.
The films of the present invention have a
controllable coefficient of thermal expansion (CTE),
low dielectric constant, low moisture pickup
- characteristics, low outgassing, high tensile strength,
high modulus, and superior environmental resistance
characteristics in comparison to uniaxial films of
similar composition. The films of the present
invention also exhibit excellent thermal stability,
- chlemical resistance and toughness, even at low
te~peratures.
The present invention is also directed to methods
and apparatus suitable for producing multiaxially
oriented films, coatings, and like materials from
thermotropic and lyotropic liquid crystalline polymers.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
.
The present invention is especially directed to
multiaxially, preferably, biaxially, oriented films,
coatings, and like materials, formed from linear - -
thermotropic and lyotropic liquid crystalline polymers.
Preferred lyotropic polymers for use in the present ~ `
invention are poly~ - phenylenebenzobisthiazole), ~ ~
1327688
: - 7 -
(PBzT); poly-(~ara-phenylenebenzobisoxazole), ~PBxO); and
poly-(~ara-phenylenebenzobisimidazole), (PBzI).
These compounds have the generic structure:
~,< X ~ X~
wherein each X is independently selected from the group
consisting o~ sulfur and oxygen; and each Y is nitrogen. -:
~ An especially preferred PBzX compound is cis-PBzO,.'~ 15 which has the following structure:
.
~ N
n
Two especially preferred thermotropic liquid
crystalline polymers from which multiaxially oriented films
can be pre~ared are Datrco Manufacturing Company~s Xydar* .::
and Celanese~s Vectra* polymers.
` The structures of these two polymers are:
to~ ~- ~ ~c ~ C ~
Xydar
* Trade-marks
I
1327688
` -8-
.
r~~ ~ ~ ~ c 1
Vectra
`
s When ordered polymers such as PBzT, PBzI, PBzO,
Xydar and~or Vectra are subjected to a shear force they
10 become highly aligned in the direction of the applied
force. By imparting to such polymers more than one
such force, each in a praferred orientation, one
obtains material with an overall high tensile value.
The present invention is thus directed to the
- 15 production of polymer films that have highly controlled
o.~ientation resulting in films that have property
balances that are much more useful from a practical
standpoint than ordinary uniaxially oriented films.
Films producad according to the present invention
20 h~vQ high tensile values (e.~., greater t~an about
4~,000) in the machine direction and substantial
strength in the transverse direction (ç~g~, greater
than about 10,000). These films maintain their film
int~grity in two diractioni3, and as a result are useful
25 in many applications reguiring good film properties.
For example, the process of the present invention
affords films that have strangth characteristics making
them suitable for the production of laminate film
composites and like structures.
The essential strength characteristics of the films
of the present invention are the result of a two stage
orientation process followed by post treatment to
optimize tbe film property balance.
In preferred embodiments, the biaxial molecular
1327688
.
g
- orientation is achieved by utilizing a homogenized dope
~ consisting of cis-PBzo in polyphosphoric acid.
3 The term "polyphosphoric acid" as used herein,
means any of the members of the continuous series of
~` 5 amorphous condensed phosphoric acid/water mixtures,
generally given by the formula:
~ .,.
-3 H P 0
.~ .
i lo wherein the value of n depends upon the molar ratio of
:~ water to phosphorous pentoxide present. Such
compositions are described in U.S. Patent Nos.
,533,6g2, 4,s33,724, and 4,533,693 (to Wolfe et al.).
The first ~tep in processing lyotropic liquid
crystalline polymers such as cis-PBzo~ comprises a
conditioning of the polymer which preferably is about a
10 to 30 weight percent tpreferably about 15-20 wt.
p~rcent) solution in poly(phosphoric acid), or PPA. `-
j PPA is the preferred solvent, alt~ough methanesulfonic
acid (MSA) or chlorosulfonic acid (CSA~ may also be
u~ed.
A degassing step may be employed to prevent
interference of entrapped qas within the polymer
solution with the molecular orientation of the film.
The second step is the orientation step. This may
be accomplished by the use of any of the extrusion
means which induce shear flow, stretching, and the
like. Preferred extrusion means of the present
invention include counter rotating tube dies, plates,
or roller dies. It has been discovered that such
extrusion means, preferably combined with subsequent
stretching of the extrudate, may be employed to impart
varying degrees of molecular orientation (i.e.,
multiaxial orientation) to these polymers.
. , .
-` 1327~88
,, --10--
A third step comprises coagulation of the polymeric
solution.
~- The fourth step is a densification step wherein the
PPA is removed.
~ 5 The penultimate step is generally a drying and heat
;~ treatment step.
Finally at the ultimate step, the product film is
packaged.
. ~
The cis-PBzO films of the present invention exhibit
controlled coefficient of thermal expansion (or CTE)
behavior. ~his control has been demonstrated over a
range of cis-PBzO films of different multiaxial
orientation characteristics.
The c s-PBzO films of the present invention have
comparable thermal stability with the previously
prepared P~zT films.
The present inventors have also demonstrated the
production of thin films from cis-PB~0 with controlled
biaxial orientation.
Thin-walled PBzO film-based composites have
significant advantages over fiber-reinforced
composites. In addition to all o~ the properties of
fiber-based composites including predictable high
strength ànd stiffness, low coefficient of thermal
expansion (CTE) and light weight, film-based structures
will have advantages of more rapid fabrication, higher
volume fractions of reinforcement and internal
reinforcement at a very fine scale, without interfaces
0 between fiber and matrix. The lyotropic liquid-
crystalline rod-like polymer PBzO is especially
attractive because of its high thermal and chemical
stability, and its extremely high tensile mechanical
properties.
1327688
. .
--11--
..
Table I compares machine-direction and transverse-
direction thermal expansion properties of PBzO and PBzT
films, in three different orientations. Negative CTE
~` is a consequence of rigid-rod molecular alignment in
S the test direction, while CTE is positive transverse to
the direction of orientation.
It is clear from Table I that like PBzT, PBzO can
exhibit a variation in molecular alignment sufficient
to alter CTE characteristics. Controlled CTE and
dimensional stability are critical to optical
structures and electronic circuit boards, two areas
where PBzT has been applied and which will be of equal
importance to P8zO.
. 15
..
'.'
21~
.~
~; '"
~ ' , ~ ' ' ; ' , ; ` I '
1327~88
- TABLE I
` PBzT v. PBzO FILM CHARACTERISTICS
CTE, In.
In.-c
POLYMER I.V. FI~M NACHINE TRANSVERSE
DIRECTION DIRECTION
cis-PBzo 11 BAL~NCED BIAXIALl -11 +2
11 HIGHLY DRAWN2 -12 +13
11 HIGHLY DRAWN3 -11 +21
PB2T 40 BALa;tlCED BI~XIAL4 -7 +5
HIGHLY DRANN2 -14 +4
HIGHLY DRAWN3 -15 +30
~`
1 Balanced Biaxial: Maximum strength and stiffness
at approximately + 22.5 Deg. to Film machine direction,
but with least angular dependence of these properties.
2 Predominantly Uniaxial: Naximum strength and
stif~ness in the machine direction, but also with high
properties within +20 degrees of machine direction
3 Nearly Uniaxial: Maximum strength and stiffness in
the machine direction, with high properties only within
+5 degrees of machine direction
4 Balanced Biaxial: Maximum strength and stiffness
at approximately +45 degrees to film machine
direction, but with least angular dependence of these
properties
` 1327688
-13-
Blown dope compositions that have not been
subjected to controlled shear fields prior to expansion
do not have physical property balances anywhere
approaching those of the films of the present
invention~ Furthiermore, films extruded by the counter
~irotated die but not with the blowing process do not
have good property balances. It is the combination of
~shear field extrusion followed by internal expansion
àiiand extension that yields films with a useful property
lo balance.
The extruded, sheared and blown film is quenched,
both on the internal and external surfaces, by an
agueous coagulation bath or other controlled aqueous
coagulant composition. This quenching operation serves
to "gel" the polymer dope composition, producing a
strong, tough, solution-~illed film.
By controlling the composition of the coagulation
bath many other materials can be incorporated into the
film microstructure.
20In addition to causing the film microstructure to
gel and become strong, the aqueous solution serves to
~ydroliz~ the polyphosphoric acid to phosphoric acid,
facilitating its removal from the film. The
solution-filled film is then washed free of phosphoric
acid before it is subjected to controlled drying
conditions.
¦ The film is preferably dried under controlled
internal pressure, also known as a restrained drying
! process. This is accomplished by drying the film under
0 a regulated air or nitrogen pressure of from about 5 to
1 10 psi as illustrated. The pressurized film tube in
the example may have about 1.5 to 3 inches diameter and
a length of from about 5 to 12 inches. Drying under
such conditions results in a highly oriented film of
1327688
-14-
: high strength characteristics.
When tube-blowing is employed, if the tube is not
-- slit after coagulation but is merely collapsed flat for
water-solution and drying treatments, it can then be
re-blown and stretched biaxially in a tower- or
~ tunnel-oven~ The tube is slit into tape and
roll-packaged just downstream of a central plug mandrel
and guide rolls. Tube-blowing gas is advantageously
introduced through the mandrel.
~ 10 Transverse shear, longitudinal flow shear, axial
~ stretch, and radial expansion forces all interact in
Ji the dies to impart a partial biaxial orientation to the
ordered polymer fed therethrough. Variation of the
speed of the movement of the shaft and cylinder of the
illustrated die, as well as flow rate, temperature,
etc. effect the degree of orientation imparted to the
ordered polymer feedstock. Additional orientation is
imparted to the extruded film by virtue of the blowing
processes, both following the extrusion and as a part
of the heat treatment.
In the preparation of twisted nematic orientation
with cis-PBZo by solution processing, molecules in
ad~acent planes with twisted orientation are not be
able to pack closely on solvent removal. Thus, each
"layer" will have to densify by diffusion transverse to
~. the rod axis, an unlikely process on the microscopic
2 scale of the sheet. Consequently, if twisted nematic
orientation is smooth and gradual through the film
thickness, the densification can occur with the least
30 amount of strain or disruption between adjacent layers. -
Biaxial shearing as well as biaxial direct stresses
and strains can be imposed and controlled in this
system. A useful combination of strain patterns is -
achieved by an apparatus where first a twisted nematic
1327688
(cholesteric) orientation is promoted in the dies and
then a uniform biaxial strain is promoted in the
blow/stretch. The former provides enough
~- bi-directional strength for the latter, as well as
near-order of layers, conducive to densification in the
normal (thickness) direction. The biaxial strain can
be symmetric or asymmetric. If this system is operated
with low strain in the dies, then biaxial blow/stretch
will promote biaxial nematic orientation rather than
twisted nematic.
Of course, the system of the present invention
could be used to produce uniaxial nematic tube or film
as well.
A common characteristic of laminates of the
preferred biaxial film materials is that they can be
weak in the transverse direction (i.e., perpendicular
to the plane of the laminated film). It is therefore
desirable to increase the so called trans-laminar
strength of biaxial films by using additional
processing steps in the ~anufacture of the films.
These additional steps can be during the
pr~paration of the dope or in the washing or solution
processing of the coagulated film. Trans-laminar
strength of the film can be increased either by
. 25 increasing the cohesivity betwe~n the ordered,
rigid-rod polymer structure, and/or by enclosing the
ordered structure in a binding, surrounding network of
the added material. This added material typical does
not interfere with the rest of the processing steps,
because the added material is not rendered strong and
cohesive except by a subsequent processing step, e.g.,
heat treating or chemical conversion.
An important aspect of the methods envisioned for
increasing trans-laminar film strength is that the
1327~88
-16-
added material is not necessarily intended to be a
major fraction of the final structural material or
film; the added material can be a very minor
constituent of the final structure and still provide
substantial trans-laminar cohesivity or strength. In
fact, since the rigid-rod ordered polymeric structure
is relatively very competent, the added material most
preferably is a very minor componentt such that the
final overall material has the highest specific
strength and stiffness properties, i.e., highest
strength and stiffness per weight and volume.
One method of increasing the trans-laminar strength
of biaxial cis-PBzO film is to blend a finely divided
powder of compatible material with the PBzO dope during
the dope-preparation step of the total process. A
preferred material is polyphenylene sulfide (PPS), at
about 10 percent by volume (or more) of the final
dcpe. PPS is a strong, highly resistant, thermotropic
polymer. This powder remains in the dope and the
prepared *ilm through all of the processing steps up to
tha final drying stage. During drying and heat
treating, the film is heated to a temperature that
melts the PPS, causing it to flow around and between
the PBsO rod-like microscale structure. Subsequant
pressing or rolling and cooling produces a structure
that is strong in all directions of stress.
Another method of increasing trans-laminar strength
is to diffuse a precursor of a strong binder material
into the PBzO film during the washing stage of the
process. This precursor can be an organometallic
precursor of an inorganic glass, such as
tetramethoxysilane; or an organically-modified glass
precursor that has reactive organic groups incorporated
therein, such as expoxides; or a precursor of a
', .'~
~ - 17 - 1327688
t.
:"
`". thermotropic plastic, such as caprolactam as a precursor
`~ for nylon, or polyamic acid as a precursor for polyimide.
;~ After the precursor has diffused into the washed but
still swollen PBzO film, e.g., via various sequential
`~ 5 solvent exchanges, the film is dried and heat treated,
causing a transformation of the added material to its final
form as a strong trans-laminar binder material. As a final
binder material, glasses and polyimides are preferred over
nylons, because the former materials more nearly complement
the high te~perature and strength properties of the PBzT
film structure.
The processing equipment of the present invention is
straight forward in design and fabrication, with the
exception of the counter-rotating die assembly. The
storage tank must be heated, is preferably made of
stainless steel (e.g., type 316L suitable for PPA
processes), and is pressurized with dry/inert gas (e.a., N2)
i~ order to prevent both coagulation of the dope and/or
starvatio~n of the pump~ The pump is typically a precision-
g~ar type (such as is marketed by Zenith). Other types of
pump, Quch as piston-ram, extruder, or traveling-cavity
(Moyno*), are possible.
While other counter-rotating tube-dies exist, the
design of the die of the present invention is specialized
in that a wide range of parameters can be explored by using
different speeds and die-inserts. Sealing between the hot
block and die cylinders is affected by spring loaded face-
bushing (Teflon~ or graphite), and alignment is maintained
by remote collar bearings. Because the extrudate undergoes
~ 30 so much densificatioin to final thickness, the die annulus
¦ is usually large, moderating die pressure required. The
* trade-mark
,':
~i~
~.~. .
~- 1327688
.
--18--
-- central gas for film blowing (N2) is provided through
a remote, cooler, standard rotating coupling.
Function and operation of the extrusion-blowing
system are thus straightfor~rard:
Counter-rotation of the dies generates
transverse shear without any net twist or torque on the
s extruded tube.
The pump generates the axial flow and, in
combination with the annular gap, determines the axial
`~ 10 shear ~flow profile).
Draw-down of tbe tube at a 1 inear rate greater
than die-discharge causes an axial strain in the hot,
uncoagulated extrudate.
Blowing of the film tube causes
15 circumferential stress and strain in the extrudate.
` Immersion in a water bath after blow/stretch
causes coagulation and, below the central water level,
a balance of pressure and nulling of pressure
differential, unless th~ tube is pinched closed at the
20 bottom.
The applications thus far identi~ied for lyotropic
liquid crystalline polymer films are numerous,
including structural, aerospace, electronic, optical,
ballistic-protection and coDunications aE~plications.
25 The speed ~ and ease of development in many of these
areas will be enhanced when large quantities of low
cost films, having properties and behavior quite like
those of PBzT, became readily available.
In addition to processing PBzX type polymers (e.g~,
30 PBzT, PBzO, etc. ) the processing conditions of the
present invention have beerl extended to thermotropic
liquid crystalline polymers, especially Xydar and
Vectra.
Xydar is the tradename of Dartco ' s high temperature
. . .
1327688
thermotropic resin. Vectra is Celanese's trademark for
their range of plastic resins exhibiting performance
~^ characteristics similar to those of Xydar.
Xydar has the highest temperature resistance of all
commercially available liquid crystalline polymers.
Because Xydar is a thermotropic polymer, the film can
be molded at high temperature. This allows Xydar to be
employed in a vast array of applications not available
to the lyotropic polymers, e.g., in the automotive
industry for sheet molded parts.
Xydar resin melts at about 800F, and is the
highest strength unfilled thermotropic liquid
crystalline polymer (LCP) commercially available. The
m~lt characteristics of this resin are generally
- 15 tailored for injection molding, i,e , low pressure and
easy flow when pu~ped through narrow cavities (high
shear conditions). There was some speculation that
this material could not be extruded at all.
For use with Xydar, the present inventors modified
the pump block, extrusion die, and the exit end of the
extruder. These changes included modifying the pump
block and extruder end reflect the need to sustain high
shear, minimize pressure drops, and avoid dead spots in
the melt flow path. This was achieved through use of a
conventional injection-molding type screw end and
coupling on the extruder, and through incorporation of
a split pump block which facilitated machining of the
curved flow passages.
A summary of t:he die construction changes is
pro~lded in Table II.
.' ', .
! . ; ; ; ~ ~ ' ` ~
1327688
..
-20-
TABLE II
DIE CONSTRUCTION MODIFICATIONS
-.
.,
Fe~turePBz.T~PBzO Die Xy~ar ~ie
Operating temperature 250F 800F
Feed ~oles 12 x 1/4 in. 48 x 1/16 in. :
Extruded tube diameter1-1/2 in. 1-1/4 in.
Temperature control zones 1 3 .~
:15 hear zone gap 2 in. 4 in in- ~-
Exit gap 0.080 in. 0.030 in. -
Full flow pressure drop1,000 psi 4,000 psi -
' `
.``' .
'...,',':
` ~`
~;.;.
:
~ `.:
":
1327688
.
-21-
In order to obtain better control of the tubular
extrusion process of Xydar and Vectra, an air ring
system, converging rack, and nip roll unit were
assembled downstream of the extrusion die.
This equipment allows more precise draw and
orientation control for the blown film. The air ring
permits controlled rapid cooling of the hot film, while
the nip unit allows controlled extensional draw and
po~itive bubble closure, and the converging rack
minimizes potential wrinkling of the flattened bubble
during nipping.
The redesigned die also incorporated three separate
temperature control zones. The center zone, where the
polymer melt is introduced, was designed to operate at
high temperatures t750 to 850F). The exit zone
hax the capability of control at lower temperatures, so
as to effect greater orientation through rotational and
longitudinal shear. Finally, the uppar end of the die,
which contains the ali~nment bearings, operates below
250F, so as to maintain proper functioning of the
be~rings. Other features of ~he die, and comparison
with the PBzT counter-rotational die, are reviewed in
Table III.
~ .
. .
` 30
. .
1327688
~ - 22 - .
~.
TABLE III
PBzT/PBzO ~. XYDAR DIE CONSTUCTION
~`
Feature PBzT Die Zydar Die
Bore diameter 3~4 in. 1 in.
Able to handle standard
1/8 in. pellet feed No Yes
.".,
L/D 20 24 -
`: '
BarrelXaloy* plated Xaloy plated .
steel steel .`
''.: '
Screw Hastelloy C* Chrome plated .
steel
Maximum barrel ~;.-
Pressure 10,000 psi 10,000 psi
M~ximum resin
t~oughput 30 cc/min 60 cc/min ` .
Maximum operating
temperatur~e 600F 2800F `:
Metering pump :.
maximum operating `
temperature 950F 950F
Material M2 tool steelD2 tool steel
cc/rev , 0~3 0.6
.:
' ''
* trade-mark~
:
1327688
-23-
Equipment was fabricated to supply the starved-feed
condition recommended by Dartco for the SRT-300 resin. A
` simple auger feed apparatus was assembled.
Resin was fed into the preheated empty extruder and
die, and film was extruded. Operating conditions are
summarized in Table IV.
The resin was fed manually into the entry port
simulating starved feed conditions. Preliminary
calculations predicted that high melt pressures would be
experienced in the die. To minimize these pressures the
die temperature controller was set initially to 800F,
with the intention of reducing this temperature after
extrusion reached steady state. This scheme would reduce
- the possibilities of pressure surges and equipment
damage~
. .-
'~
.`
~'
': ~
~`
,:
-. '.
.
~ :.
" 1327688
--2 4--
TABLE IV
OPERATING CONDITIONS OF XYDAR EXTRUSION
~J S
~ Temperature
~ . .
~ Barrel - 800F
.
Melt - 742F
Die Zone 1 - ~ 160F
2 - 800F
3 - 800F :
Resin throughput 7.7 cc/min
Drnw (estimated) 5 max
blowout 2 max
Counter-rotational mandrel rpm 2.4
25 Counter-rotàtional shear 4.72 sec~l :
. ,~'`'.
Film ~Lade
¦ 30 ~ree fall from die: 1-1/8 in. diameter
15 mil thick
Maximum blow and draw: 2-1/4 in. diameter
5-1/2 mil thick ~ ~
,.,~.
1327~88
The extruded Xydar film was golden in color
(similar to that of the resin pellets), quite heavily
textured on its outside surface, and much less so on
the inside. The heavy texture appeared to relate to
voids, especially notable in the thinnest, most highly
hlown areas of the tubes. While Xydar resin neither
~` absorbs moisture readily, nor retains much moisture at
equilibrium, the possibility exists that the film
texture relates to moisture loss. Pre-drying of resin
in a heated vacuum oven should help resolve the
proble~.
The voids in the film give it a nonAomogeneous
appearance and result in rough surface texture. When
held up to the light, the Xydar film looks liXe a
lS connected network with the characteristic "fibrils" at
roughly balanced angles to the machine direction.
The "mottled" nature of the Xydar film could be due
to evolution of gas bubbles from moisture entrained in
th~ Xydar. Even a small percentage of moisture can
cause foaming, as in nylon extrusion. Pre-drying of
the Xydar resin should check this moisture effect.
It is also likely that the Xydar melt did not flow
evenly during extrusion, rasulting in regions of high
and low consolidation. This problem could be solved by
using the "èxtrusion grade" material which should have
better draw characteristics. Also, changes in
temperature, pressure and throughput will improve
properties and surface finish.
t
Fifteen pounds of Vectra B900 resin was procured
from Celanese, dried per manufacturer's
recommendations, and successfully extruded into a film
with a variety of biaxial orientations. Table V
r~views the conditions and results from extrusion.
1327688
-26-
; .
The Vectra films exhibited much less porosity than
the Xydar films, showed biaxial fibrillation and
strength at the time of extrusion, and possessed an
extremely smooth surface. Film thicknesses from 2 to
10 mils were readily obtained with some tubes as thick
as 17 mils.
As was done with Xydar film, thermally bonded
laminates were obtained, both with the uniaxial
~ Celanese Vectra film and with the freshly prepared
-~ 10 biaxial Vectra films. Because of the differences
between the two grades of resin ~the Celanese film uses
A900 Vectra, while the films of the present invention
~ used B900), temperatures and pressures were optimized
-~ for each laminate type. Copper cladding was
successfully accomplished with the the biaxial film as
WQll. ,.'.
.,
,~ .....
.': '
. '
' ':'
.-.
: ,, .
` 1327~88
--27--
. .
"` TABLE V
VECTRA EXTRUSION CONDITIONS and
RESULTING FILM
A. Ext~sion Conditions
Melt temperature - 600 to 650F
Melt pressure - 2,000 to 2,S00 psi
x Die shear - 3 to 9 sec~l
.,
Draw - 1 to 3
Die annulus - 1.25 in. diameter x 0.0125 in.
thicknesses
Blowou~ - 1 to 2
B. Resul~in~ Film
2~ ~-
Type of Film Ft of
orientation Thickness Film
+20 to ~25 2 to 7 mils 10
Predominantly Uniaxial
+25 to ~35 2 to 3 mils 20
Nearly Balanced E~iaxial
'.
: 30 + 10 2 to 3 mils 10
. Nearly Uniaxial
. '' ',
1327688
~ -28-
,
--~ Table VI represents preliminary data for the above
~ identified vectra film samples:
~ .
~ TABLE VI
'. PRELIMINARY CHARA~ ISTICS OF VEC:TRA FILNS
`
Sample No. of TensileTensile
10 Orientation Samples Strength,Mod., CTE
to MD Tested ksi___msi ppm~Qc
. OO 5 103 2.66 - .` .
o 2 - - -14.4
90o 2 ~10 - ~31.9 .
. . ,:
The high tensile properties indicate that Vectra
indeed offers desirable properties i~or PWB
applications. However, the highly anisotropic CTE
propertiss of the unidirectional film must be modified
if isotropic x and y CTE in the 3.7 ppm/C range is
to be achieved. ~his desired CTE characteristic can be
tailored into the film by inducing biaxial orientation
of the molecules in the film as is done with PBzT.
The present invention has been described in detail,
including the preferred embodiments thereof. However,
it will be appreciated that those skilled in the art~
upon consideration oi' the present disclosure, may make
modifications and/or improvements on this invention and
still be within the scope and spirit of this invention
as set forth in the following claims.
.
