Note: Descriptions are shown in the official language in which they were submitted.
~-z~
~ . BACKGROUND OF T~E INVENTION
The present invention is directed to an improved method
for the~production of composite articles by pultrusion.
It has long been known to produce composite reinforced
articles such as prepreg tapes and rovings by various pultrusion
- methods. See, for example, U.S. Patent Nos. 3,042,570;
3,608,033; 3,684,622; 3,742,107; 3,793,108; 3,960,629; 3,993,726;
4,132,756; and 4,312,917. While such methods are generally
capable of producing acceptable products, it is desir.able in
certain instances to employ a matrix material which enhances the
ability of the product to be employed in certain environments
where thermal and chemical stability are important. High~ degrees
of orientation of the polymer matrix are also sometimes desirable
to optimize the mechanical properties.of the product.
~ It is further necessary that articles produced by
pultrusion satisfy the following basic requirements during pro-
cessing: ~1) that the reinforcing fibers be uniformly
distributed throughout the polymer matrix material; (2) that the
bundles of the reinforcing fibers which are employed should be
well impregnated with the matrix polymer; and (3) that the fibers
should be sufficiently bonded to the matrix polymer.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to
provide a method for the continuous production of a composite
article by pultrusion whereby a thermotropic liquid crystalline
matrix polymer is uniformly distributed among the reinforcing
fibers.
Q~
.
It is also an object of the present invention to
provide a method for the production o~ a composite article by
pultrusion whereby a thermotropic liquid crystalline matrix
-polymer is sufficiently bonded to the reinforcing fibers.
It is also an object of the present invention to pro-
vide a composite article produced by pultrusion which comprises a
thermotropic liquid crystalline matrix polymer and exhibits
desirable mechanical properties, and chemical and thermal
stability.
In accordance with the present invention, there is thus
provided a method for the production of a composite reinforced
article by pultrusion whereby said article is formed by causing
at least one continuous length bundle of reinforcing fibers to
adv~nce into a crosshead extruder diel forcing a molten thermo-
plastic matrix polymer into said die under pressure to impregnate
said at least one fiber bundle, and continuously extruding and
pulling said at least one impregnated bundle through at least one
exit orifice of said die to shape said at least one impregnated
fiber bundle into said composite reinforced article, the improve-
ment wherein said polymer comprises a thermotropic liquid
crystalline polymer which possesses rheological properties such
that a dynamic viscosity-frequency cur~e based on such character-
istics has a negative slope of less than about 0.35 when measured
at a frequency of 1 sec~l.
In accordance with the present invention there is also
provided a composite article produced by the above method.
--3--
BRIEF DESCRIPTION OF THE DRAWINGS
~~ Fig. 1 is a graphical depiction of the dynamic v}s-
cosity-frequency curves for various thermotropic liquia
-crystalline polymers.
Fig. 2 is a graphical depiction o~ the correlation
between the slope of the dynarllic viscosity-frequency curv~ for
various polymers and the acceptability rating accorded t~e
product comprised of such polymers.
DETAILED DESCRIPTION OF THE INVENTION
It has been surprisingly and unexpectedly discovered
that thermotropic liquid crystalline polymers (as defined) are
particularly suitable for use in the production of a composite
article by pultrusion wherein the article comprises a fiber-
reinforced matrix of the polymer.
Thermotropic liquid crystal polymers are polymers which
are liquid crystalline (i.e., anisotropic) in the melt p~ase.
These polymers have been described by various terms, including
"liquid crystalline,n "liquid crystaln, "mesophase" and
"anisotropic". Briefly, the polymers of this class are thought
to involve a parallel ordering of the molecular chains. The
state wherein the molecules are so ordered is often referred to
either as the liquid crystal state or the nematic phase of the
liquid crystalline material. These polymers are prepared from
monomers which are generally long, flat and fairly rigid along
the long axis of the molecule and commonly have chain-extendin~
linkages that are either coaxial or parallel.
Such polymers readily form liquîd cry~tals (i.e., exhi-
bit anisotropic properties) in the melt phase. ~uch properties
~ ^~
may be confirmed by conventional polarized light techniques
whereby crossed polari~ers are utilized. More specifically, the
anisotropic melt phase may be confirmed by the use of a Leitz
polarizing microscope at a magnification of 40X with the sample
on a Leitz hot stage and under nitrogen atmosphere. The polymer
is optically anisotropic; i.e., it transmits light when examined
between crossed polarizers. Polarized light is transmitted when
the sample is optically anisotropic even in the static state.
Thermotropic liquid crystal polymers include but are
not limited to wholly and non-wholly aromatic polyesters,
aromatic-aliphatic polyesters, aromatic polyazomethines, aromatic
polyester-carbonates and aromatic and non-wholly aromatic poly-
ester-amides.
The aromatic polyesters and polyester-amides are
considered to be "wholly" aromatic in the sense that each moiety
present in the polyester contributes at least one aromatic ring
to the polymer backbone and which enable the polymer to exhibit
anisotropic properties in the melt phase. Such moieties may be
derived from aromatic diols, aromatic amines, aromatic diacids
and aromatic hydroxy acids. Moieties which may be present in the
thermotropic liquid crystal polymers employed in the present
invention (wholly or non-wholly aromatic) include but are not
limited to the following:
~ ~
~a~, ~c-,
Q~.
~~ ra~ o~
~ æ ~ ~
-c~s~c-- , ~C-- ,
_ NH ~ O ~ r ~ and - N~ ~ NH - -
Preferably, the thermotropic liquid crystal polymers
which are empl~yed comprise not less than about 10 mole percent
of recurring units which include a naphthalene moiety. Preferred
naphthalene moieties include 6-oxy-2-naphthoyl, 2,6-dioxynaphtha-
lene and 2,6-dicarboxynaphthalene.
Specific examples of aromatic-aliphatic polyesters are
copolymers of polyethylene terephthalate and hydroxybenzoic acid
as disclosed in Polyester X7G-A Self Reinforced Thermoplastic, by
W. J. Jackson, Jr. ~. F. Kuhfuss, and T. F. Gray, Jr., 30th
Anniversary Technical Conference~ 1975 Reinforced Plastics~Compo-
sites Institute, The Society of the Plastics Industry, Inc~,
Section 17-D, Pages 1-40 A further disclosure of such copolymers
can be found in "Liquid Crystal Polymers: I. Preparation and
Properties of p-~ydroxybenzoic Acid Copolymers, n Journal of
Polymer Science, Polymer ChemistrY Edition, Vol. 14, pp. 2043-58
(1976), by W. J. Jackson. Jr., and H. F. Ruhfuss. The above-
cited references are herein incorporated by reference in their
entirety.
Aromatic polyazomethines and processes of preparing the
same are disclosed in U. S. Patent Nos. 3,493,522; 3,493,524;
3,503,739; 3,516,970; 3,516~971; 3,526,611; 4,048,148; and
4,122.070. Each of these patents is herein incorpora-ted by
reference in its entirety. Specific examples of such polymers
include poly(nitrilo-2-methyl-1,4-phenylenenitriloethylidyne-1,4-
phenyleneethylidyne); poly(nitrolo-2-methyl-1,4-phenylenenitrolo-
methylidyne-1,4-phenylene-methylidyne); and poly(nitrolo-2-chloro-
1,4-phenylenenitrilomethyldyne-1,4-phenylene-methylidyne).
Aromatic polyester-carbor.ates are disclosed in U.S.
Patent Nos. 4,107,143, 4,284,757, and 4,371,660. Examples of
such polymers include those consisting essentially of p-oxybenzoyl
units, p-dio~yphenyl units, dioxycarbonyl units, and terephthoyl
units.
Aromatic polyester-amides and processes of preparing
the same are disclosed in U.S. Patent No. 4,182,842. Further
disclosure of such copolymers can be found in "Liquid Crystal
Polymers: III Preparation of Properties of Poly(Ester Amides)
fEom p-Aminobenzoic Acid and Poly(Ethylene Terephthalate),"
Journal of Applied Polymer Science, Vol. 25, pp. 1685-1694 (1980),
by W. J. Jackson, Jx., and H. F. Kuhfuss. The above-cited
references are herein incorporated by reference in their entirety.
The liquid crystal polymers which are preferred for
use in the present invention are the thermotropic wholly aromatic
polyesters. Recent pub]ications disclosin~ such polyesters
include (a) Belgian Pat. Nos. 828,935 and 828,936, (b) Dutch Pat.
No. 7505551, (c) West German Pat. Nos. 2,520,819, 2~520,820 and
2,722,120, (d) Japanese Pat. Nos. 43-223, 2132-116, 3017-692, and
3021-293, (e) U.S. Pat. Nos. 3,991,013; 3,99],014; 4,057,597;
t.~3~'
4,066,620; 4,075,262; 4,118,372; 4,146,702; 4,153,779; 4,156,070
4,159,365; 4,169,933; 4,181,7g2; 4,188,476; 4,201,856; 4,226,970;
4,232,143; 4,232,144; 4,238,600; and 4,245,082: and (f) U. K.
Application No. 2,002,404, published February 21, 1979.
Wholly aromatic-polyesters and polyester-amides are
also disclosed in commonly-assigned U.S. Patent Nos. 4,067,852;
4,083,829; 4,130,545; 4,16].,47Q; 4,184,996; 4,219,461; 4,230,817;
4,238,598; 4,238,599; 4,244,433; 4,256,624; 4,279,803; 4,299,756;
4,330,457; 4,337,191; 4,339,375; 4,341,688; 4,351,917; 4,351,918;
and 4,355,132. The wholly aromatic polyesters and polyester-
amides disclosed therein typically are capable of forming an
anisotropic melt phase at a temperature below approximately 400C.,
and preferably below approximately 350C.
The thermotropic liquid crystal polymers i~cluding
wholly aromatic polyesters and polyester-amides which are suitable
for use in the present inventioh may be formed by a variety of
ester-forming techniques whereby organic monomer compounds
possessing functional groups which, upon condensation, form the
requlsite recurring moieties are reacted. For instance, the
functional groups of the organic monomer compounds may be carboxy-
lic acid groups, hydroxyl groups, ester groups, acyloxy groups,
acid halides, amine groups, etc. The organic monomer compounds
may be reacted in the absence of a heat exchange fluid via a melt
acidolysis procedure. They, accordingly, may be heated initially
to form a melt solution of the reactants with the reaction con-
tinuing as said polymer particles are suspended therein. A
vacuum may be applied to facilitate removal of vola-
~2~
tiles formed during the final stage of the condensation (e.g.,acetic acid or water).
Commonly-assigned U. S. Patent No. 4,083,829, entitled
"Melt Processable Thermotropic Wholly Aromatic Polyester,~
describes a slurry polymerization process which may be employed
to form the wholly aromatic polyesters which are preferred for
use in the present invention. According to such a process, the
solid product is suspended in a heat exchange medium. The dis-
closure of this patent has previously been incorporated herein by
reference in its entirety. Although that patent is directed to
the preparation of wholly aromatic polyesters, the process may
also be employed to form polyester-amides.
When employing either the melt acidolysis procedure or
the slurry procedure of U. S. Patent No. 4,083,829, the organic
monomer reactants from which the wholly aromatic polyesters are
derived may be initially provided in a modified form whereby the
us~al hydroxy groups of such monomers are esterified (i.e., they
are provided as lower acyl esters). The lower acyl groups
preferably have from about two to about four carbon atoms. Pre-
ferably, the acetate esters of organic monomer reactants are
provided. When polyester-amides are to be formed, an amine group
may be provided as lower acyl amide.
Representative catalysts which optionally may be
employed in either the melt acidolysis procedure or in the slurry
procedure of U.S. Patent No. 4,083,829 include dialkyl tin oxide
(e.g., dibutyl tin oxide), diaryl tin oxide, titanium dioxide,
antimony trioxide, alkoxy titanium silicates, titanium alkoxides,
alkali and alkaline earth metal salts of carboxylic acids (e.g~,
zinc acetate), the gaseous acid catalysts such as ~ewis acids
if~
(e.g., BF31, hydrogen halides (e.g., ~Cl), etc. The quantity of
catalyst utilized typically is about 0.001 to 1 percent by weight
based upon the total monomer weight, and most commonly about 0~01
to 0.2 percent by weight.
The wholly aromatic polyesters and polyester-amides
suitable for use in the present invention tend to be substan-
tially insoluble in common polyester solvents and accordingly are
not susceptible to solution processing. As discussed previously,
they can be readily processed by common melt processing tech-
niques. Most suitable wholly aromatic polymers are soluble in
pentafluorophenol to a limited extent.
The wholly aromatic polyesters which are preferred for
use in the presen~ invention commonly exhibit a weight average
molecular weight of about 2,000 to 200,000, and preerably about
10,000 to 50,000, and most preferably about 20,000 to 25,000.
The wholly aromatic polyester-amides which are preferred for use
in the present invention commonly exhibit a molecular weight of
about 5,000 to 50,000, and preferably about 10,000 to 30,000
e.g., 15,000 to 17,000. Such molecular weight may be determ;ned
by gel permeation chromatography and other standard techniques
not involving the solutioning of the polymer; e.g., by end group
determination via infrared spectroscopy on compression molded
films. Alternatively, light scattering techniques in penta-
fluorophenol solution may be employed to determine the molecular
weight.
The wholly aromatic polyesters and polyester-amides
additionally commonly exhibit an inherent viscosity ~i.e., I.V.)
of at least approximately 2.0 dl./g., e.g., approximately 2.0 to
10.0 dl./g., when dissolved in a concentration of 0.1 percent by
weight in pentafluorophenol at 60C.
--10--
--
n ~
.
For the purposes of the present invention, the aromatic
rings which are included in the polymer backbones of the polymer
components may include substitution of at least some of the
-hydrogen atoms present upon an aromatic ring. Such substituents
include alkyl groups of up to four carbon atoms; alkoxy groups
having up to four carbon atoms; halogens; and additional aromatic
rings, such as phenyl and substi~uted phenyl. Preferred halogens
include fluorine, chlorine and bromine. Although bromine atoms
tend to be released from organic compounds at high temperatures,
bromine is more stable on aromatic rings than on aliphatic
chains, and therefore is suitable for inclusion as a possible
substituent on the aromatic rings.
The thermotropic liquid crystalline polymers which are
sui~able for use in the present invention possess rheological
characteristics such that the negative slope of a dynamic viscos-
ity-frequency curve based on such characteristics for the
specific polymer is less than about 0.35 and preferably less than
about 0.15 at a frequency of 1 sec 1. It should be noted that
the actual values of the slopes of the viscosity~frequency curves
depicted in Figure 1 are less than zero due to the orientation of
the curves. In order to obtain a positive value, the slope is
denoted as a negative slope.
The dynamic viscosity-frequency curve is determined by
use of a mechanical oscillatory spectrometer by standard proce-
dures. Once the data points for the viscosity-frequency
relationship have been determined, the curve may be plotted. The
slope may then be determined by drawing a tangent to the curve at
a frequency of one reciprocal second (1 sec 1) and measuring the
slope of the tangent. The theory, design and use of such an
--11--
--
~2P.~
instrument is fully described in the literature and will not be
discussed in detail herein. See, for example, ~ Dealy,
~Rheometrics for Molten Plastics", van Nostrand Reinhold, New
York, 1982; R.W. Whorlow, "Rheological Techniques", Wiley, New
York, 19~0; and ~. Walters, "Rheometry", Wiley, New York, 1975.
The use of a polymer having such characteristics
enables a composite article to be produced wherein the polymer is
uniformly dispersed among the reinforcing fibers. By way of
contrast, the polymer will otherwise tend to disperse in a non-
uniform manner such that the reinforcing fibers are no longer
evenly disposed and substantially parallel. Such non-uniformity
has an adverse effect upon the ultimate physical characteristics
of the composite article.
A specific advantage of the method of the present
,~
invention resides in the fact that a composite article can be
produced by pultrusion which exhibits satisfactory properties
even with a polymer which possesses a high viscosity. A surpris-
ing and unexpected advantage of the invention is the fact that a
satisfactory composite article can be produced irrespective of
the viscosity of the polymer if the polymer otherwise satisfies
the dynamic viscosity-frequency requirements. It is, however,
preferable for the viscosity of the polymer to be as low as
possible since, given the same viscosity-frequency charac-
teristics, a polymer having the lower viscosity will generally
produce a composite article having a higher rating (i.e., the
polymer is more uniformly distributed) than a polymer of higher
viscosity. The polymer viscosit~ (I.V.) is preferably in the
range of about 2.5 to 4.5 dl./g.
n ~
.
-
In support of the above, Figure l depicts the vis-
cosity-frequency curves for the five thermotropic liquid
crystalline polymers identified in Table l below with the
-viscosity of each being measured by small amplitude oscillatory
rheometry on the Rheometrics Mechanical Spectrometer at a
temperature approximately 20C. above the melting temperature of
the polymers. Specifically, the viscosity of polymers A and C
was measured at 300~C., the viscosity of polymer B was measured
at 230C. and the viscosity of polymers D and E was measured at
310C.
TABLE 1
Rheological Characteristics of
Exemplary Li~uid Crystalline Polvmers
Viscosity at 1 sec l Negative
Polvmer (~oise) Slope at l sec~
A 3700 0.10
B 230 0.13
C 600 0.32
D 1700 0.34
E 3000 0.55
Polymer A is identified in Example l.
Polymer B is identified in Example 2.
Polymer C is identified in Example 3.
Polymer D is identified in Example 4.
Polymer E is identified in the Comparative Example.
Composite articles produced by pultrusion and comprised
of the above matrix polymers were also examined to determine
their acceptability ratings indicative of the uniformity of fiber
impregnation and fiber dispersal. Such ratings (from l to lO
-13-
--
with a 1 rating being the most desirable) were correlated versus
the slope of the viscosity-frequency curve of the polymer
employed and are depicted in Figure 2. Figure 2 confirms that
the acceptability of the ultimate product is ~enerally independ-
ent of the viscosity of the polymer. The exception to such a
condition is that, given the same slope for the viscosity-
frequency curve, the polymer having the lower viscosity will
generally provide the more acceptable product. Such advantages
are further verified in Examples 1 to 4.
Especially preferred wholly aromatic polyesters and
polyester-amides which possess the necessary rheological charac-
teristics are those which are disclosed in above-noted U.S.
Patent Nos. 4,219,461, 4,256,624 and 4,330,457.
The polyester disclosed in U.S. Patent No. 4,219,461 is
a melt processable wholly aromatic polyester which is capable of
forming an anisotropic melt phase at a temperature below approx-
imately 320Co The polyester consists essentially of the
recurring moieties I, II, III and IV wherein:
I is ~ c-
II is
_~,~c--
III is a dioxy aryl moiety of the formula ~O-Ar-O~
wherein Ar is a divalent radical comprising at
least one aromatic ring, and
-14-
IV is a dicarboxy aryl moiety of the formula
~C-Ar'-~ where Ar' is a divalent radical compris-
ing at least one aromatic ring, and
wherein the polyester comprises approximately 20 to 40 mole per-
cent of moiety I, in excess of 10 up to about 50 mole percent of
moiety II, in excess of 5 up to about 30 mole percent of moiety
III, and in excess of 5 up to about 30 mole percent of moiety
IV. The polyester preferably comprises approximately 20 to 30
(e.g., approximately 25) mole percent of moiety I, approximately
25 to 40 (e.g., approximately 35) mole percent of moiety II,
approximately 15 to 25 (eOg., approximately 20) mole percent of
moiety III and approximately 15 to 25 (e.g., approximately 20)
mole percent of moiety IV In addition, at least some of the
hydrogen atoms present upon the rings optionally may be replaced
by substitution selected from the group consisting of an alkyl
group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon
atoms, halogen, phenyl, substituted phenyl, and mixtures thereof.
Moieties III and IV are preferably symmetrical in the
sense that the divalent bonds which join these moieties to other
moieties in the main polymer chain are symmetrically disposed on
one or more aromatic rings (e.g., are para to each other or
diagonally disposed when present on a naphthalene ring). How-
ever, non-symmetrical moieties, such as those derived from
resorcinol and isophthalic acid, may also be used.
Preferred moieties III and IV are set forth in above-
noted U.5. Patent No. 4,219,461. The preferred dioxy aryl moiety
III is:
and the preferred dicarboxy aryl moiety IV is:
n ~ 1l
_c~ .
The polyester disclosed in U.S. Patent No. 4,256,624 is
a melt processable wholly aromatic polyester which is capable of
forming an anisotropic melt phase at a tempera~ure below approx-
imately 400C. The polyester consists essentially of the
recurring moieties I, II, and III wherein:
I is
.
II is a dioxy aryl moiety of the formula ~O-Ar-O~
there Ar is a divalent radical comprising at least
one aromatic ring, and
III is a dicarboxy aryl moiety of the formula
~C-Ar'-~ where Ar' is a divalent radical compris-
ing at ieast one aromatic ring, and
wherein the polyester comprises approximately 10 to 90 mole
percent of moiety I, approximately 5 to 45 mole percent of moiety
II, and approximately 5 to 45 mole percent of moiety III~ The
polyester preferably comprises approximately 20 to 80 mole per-
cent of moiety I, approximately lO to 40 mole percent of moiety
--1~--
-
II, and approximately 10 to 40 mole percent of moiety III. The
polyester more preferably comprises approximately 60 to 80 mole
percent of moiety I, approximately 10 to 20 mole percent of
molety II, and approximately 10 to 20 mole percent of moiety
III. In addition, at least some of the hydrogen atoms present
upon the rings optionally may be replaced by substitution
selected from the group consisting of an alkyl group of 1 to 4
carbon atoms, an alkoxy group of 1 to 4 carbon atoms, halogen,
phenyl, substituted phenyl, and mixtures thereof.
Moieties II and III of the polyester described immedi-
ately above are preferably symmetrical in the sense that the
divalent bonds which join these moieties to other moieties in the
main polymer chain are symmetrically disposed on one or more
aromatic rings (e.~., are para to each other or diagonally
disposed when present on a naphthalene ring). However, non-
symmetrical moieties, such as those derived from resorcinol and
isophthalic acid, may also be used.
Preferred moieties II and III are set forth in above-
noted U.S. Patent No. 4,256,624. The preferred dioxy aryl moiety
II is:
--o~o---
and the preferred dicarboxy aryl moi2ty IIT is:
1l
--c~c-- .
U.S. Patent No. 4,330,457 discloses a melt processable
polyester-amide which is capable of forming an aniso~ropic melt
-17-
~2~
phase at a temperature below approximately 400C. The polyester-
amide consists essentially of the recurring moieties I, II, III
and optionally IV wherein:
I is ~ ~~ ;
II is ~C-A-C~ where A i5 a divalent radical compris-
ing at least one aromatic ring or a divalent
trans-cyclohexane radical;
III is ~Y-Ar-Z~ where Ar is a d;valent radical compri-
sing at least one aromatic ring, Y is O, NH, or
NR, and Z is N~ or NR, where R is an alkyl group
of l to 5 carbon atoms or an aryl group; and
IV is ~O-Ar'-O~ where Ar' is a divalent radical com-
prising at least one aromatic ring;
and wherein said polyester-amide comprises approximately lO to 90
mole percent of moiety I, approximately 5 to 45 mole percent of
moiety II, approximately 5 to 45 mole percent of moiety III and
approximately 0 to 40 mole percent of moiety IV. In addition, at
least some of the hydrogen atoms present upon the rings option-
ally may be replaced by substitution selected from the group
consisting of an alkyl group of l to 4 carbon atoms, an alkoxy
group of 1 to 4 carbon atoms, halogen, phenyl, substituted
phenyl, and mixtures thereof.
Preferred moieties, II, III and IV are set forth in
above-noted U.S. Patent No. 4,330,457. The preferred dicarboxy
aryl ~oiety II is:
-18-
:12~
o ,~ o
Il \ 11
--C- ~
the preferred moiety III is:
- NH ~ NH - or NH ~ O -
and the preferred dioxy aryl moiety IV is:
The articles of the present invention may be produced
by convention pultrusion processes. The pultrusion molding
apparatus used in conjunction with the method of the present
invention is not critical to practice of the invention and may be
any conventional pultrusion apparatus. Pultrusion processes are
well-known in the art as evidenced by U.S. Patent Nos. 3,793,108;
3,960,629; and 3,993,726,
with the articles being produced basically by extrusion of the
matrix polymer as the reinforcing fiber passes through the die.
More specifically, the composite article is formed by causing at
least one continuous length bundle or yarn of reinforcing fibers
to advance into a crosshead extruder die, forcing a molten
thermoplastic matrix polymer into the die under pressure to
impregnate the at least one fiber bundle or yarn and continuously
extruding and pulling the at least one impregnated bundle or yarn
through at least one exit orifice of the die to shape the at
least one impregnated fiber bundle or yarn into the desired
composite reinforced article.
--19--
, . .~
Articles produced by the method of the present inven-
tion include approximately 1 to 65 and preferably approximately
50 to 60 percent by volume of a reinforcing agent. Representa-
tive fibers which may serve as reinforcing agents include but are
not limited to glass fibers, graphitic carbon fibers, amorphous
carbon fibers, synthetic polymeric fibers, aluminum fibers,
titanium fibers, steel fibers, tungsten fibers, ceramic fibers,
etc. Such reinforcing fibers are generally present in the form
of long, substantially straight, parallel strands and normally
present as fiber bundles for enhanced reinforcing ability.
Carbon fibers are the preferred reinforcing fiber for use in the
present invention. In the resulting article, the fiber bundles
are desirab]y spread into a single continuous bundle for optimum
reinforcement.
Representative filler materials may also be employed in
amounts ranging from about 1 to 50 percent by weight. Exemplary
filler materials include calcium ~ilicate, silica, clays, talc,
mica, polytetrafl~oroethylene, graphite, alumina trihydrate,
sodium aluminum carbonate, barium ferrite, etc.
In order to form the article of the present invention
by pultrusion, the polymer or molding compound is brought to the
melt temperature of the polymer, e.g., approximately 270 to
300C., and is then extruded into a die cavity. The die cavity
is commonly maintained at a temperature of approximately 310C.
The polymer in its melt phase is injected into the die cavity at
a pressure of approximately 5 to 50 psi while the reinforcing
fiber is caused to pass through the extrusion zone at a speçd
ranging from about several inches/minute to about 20 feet/minute.
-20-
-
The composite articles produced according to the method
of the present invention may take many forms depending upon the
type of extrusion die employed and the manner by which the rein-
-forcing fibers are passed through the zone. Typically, the~
composite article will be in the form of a tape which is substan-
tially planar in dimension. The tape subsequent to formation can
be employed in the production of other articles whereby the tape
is laminated upon other tapes similarly produced by means of
temperature and pressure. A reinforced laminate can thus be
obtained which exhibits desirable mechanical properties.
The invention is additionally illustrated in connection
with the following Examples which are to be considered as illus-
trative of the present invention. It should be understood,
however, that the invention is not limited to the specific
details of the Examples.
EXAMPLE 1
A reinforced tape was produced by pultrusion with a
crosshead extrusion die with the matrix polymer comprising a
thermotropic liquid crystalline polymer prepared from 40 mole
percent of 6-acetoxy-2-naphthoic acid, 40 mole percent of
p-acetoxybenzoic acid, 10 mole percent of hydroquinone diacetate,
and 10 mole percent of terephthalic acid (I.V. of 4.3) and rein-
forcing carbon fibers marketed by Celanese Corporation under the
designation Celion 6000. The value of the negative slope of the
dynamic viscosity-frequency curve for the matrix resin was
determined to be 0.10 at 1 sec~l (see Figure 1, Polymer A).
The crosshead die employed was approximately 6 inches
wide and 9 inches long, having entrance and exit slits approx-
-
- / /
imately 3 inches wide. ~he maximum thickness of the interior of
the die was approximately 0.5 inch.
The carbon fiber was in the form of a yarn of car-
bonaceous filamentary material derived from an acrylonitrile
copolymer consisting of approximately 98 mole percent of acrylo-
nitrile units and 2 mole percent of methylacrylate units. The
carbonaceous material consisted of about 6000 substantially
pa~allel filaments, containing about 93 percent carbon by
weight. Approximately 30 carbdn fiber yarns were caused to pass
through the die along a horizontal plane. RepresentatiVe average
filament properties for the carbon fiber include a denier of 0.6,
a tensile strength of approximately 470,000 psi, a Young's
modulus of approximately 34 million psi, and an elongation of
approximately 1.4 percent. A die temperature of 250C. and
extrusion pressure of 5 psi together with a fiber speed of 5
feet/minute were employed. The tape thus produced had a width of
approximately 3 inches and was approximately 0.012 inch in thick-
ness.
The tape was examined under a microscope and determined
to consist of reinforcing fibers uniformly dispersed within the
matrix resin and well impregnated with the resin. The resin
desirably dispersed the individual fibers within the yarns across
the width of the tape such that uniform fibrous reinforcement was
obtained. The tape was accorded a rating of 2 as being indica-
tive of being nearly totally acceptable.
COMPARATIVE EXAMPLE A
The procedure of Example l was repeated under similar
conditions with the die temperature and pressure being adjusted
--
to the melting temperature of the polymer employed with the
thermotropic liquid crystalline matrix polymer being comprised of
73 mole percent of p-oxybenzoyl moieties and ~7 mole percent of
-6-oxy-2-naphthoyl moieties (I.V. of 5.2). The value of the nega-
tive slope of the dynamic viscosity-frequency curve for the
matrix resin was determine~ to be 0.55 at l sec~l (see Figure l,
Polymer E). The tape produced by the pultrusion process was
examined and determined to be unsatisfactory in that the fibers
were not sufficiently uniformly dispersed within the matrix resin
and the matrix resin did not uniformly impregnate the fibers,
resulting in the formation of non uniform alternating bands of
resin and carbon fibers. The tape was thus accorded a rating of
10 as being indicative of total unsuitability.
EXAMPLE 2
The procedure of Example 1 was repeated under similar
conditions with the die temperature and pressure being adjusted
to the melting temperature of the polymer employed with the
thermotropic liquid crystalline matrix polymer being prepared
from 60 mole percent of 6-hydroxy-2-naphthoic acid, 20 mole
percent of terephthalic acid and 20 mole percent of hydroquinone
diacetate (I.V. of 4.2). The value of the negative slope of the
dynamic viscosity-frequency curve for the matrix resin was
determined to be 0.13 at l sec l (see Figure 1, Polymer B). As
was the case with Example 1, the tape produced was determined to
be totally acceptable and accorded a rating of l~
-23-
--
EXAMPLE 3
The procedure of Example 2 was repeated under similar
conditions with a matrix polymer of identical composition with
-the exception that the polymer exhibited an I.V. of 4.8 and the
value of the negative slope of the dynamic viscosity-frequency
curve for the matrix resin was determined to be 0.3~ at 1 sec 1
(see Figure 1, Polymer C). The tape produced was accorded a
rating of 4.
EXAMPLE 4
The procedure of Example 1 was repeated under similar
conditions with the die temperature and pressure being adjusted
to the melting temperature of the polymer employed with the
thermotropic liquid crystalline matrix polymer being prepared
from ~0 mole percent of 6-hydroxy-~-naphthoic acid, 20 mole
percent of terephthalic acid and 20 mole percent of p-acet-
oxyacetanilide (I.V. of 3.9). The value of the negative slope of
the dynamic viscosity-frequency curve for the matrix resin was
determined to be 0.34 at 1 sec 1 tsee Figure 1, Polymer D). The
tape produced was determined to be acceptable although less so
than the tapes of Examples 1 and 2 and accorded a rating of 7.
The principles, preferred embodiments and ~odes of
operation of the present invention have been described in the
foregoing specification. The invention which is intended to be
protected herein, however, is not to be construed as limited to
the particular forms disclosed, since these are to be regarded as
illustrative rather than restrictive. Variations and changes may
be made by those skilled in the art without departing from the
spirit of the invention.
-24-
_
