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United States Patent |
5,045,600
|
Giatras
,   et al.
|
September 3, 1991
|
Abrasion-resistant fluorocarbon polymer composites
Abstract
This invention relates to composites of fluorocarbon polymers, preferably
polytetrafluoroethylene, which contain less than about 23% by weight
polyamide-imide resin. More particularly, this invention relates to
extrudable polytetrafluoroethylene composites which exhibit improved
abrasion and friction resistance and other improved properties over a wide
range of temperature and load conditions, and which are particularly
adaptable for use as liners in wire insulation and in push-pull cable
assemblies.
Inventors:
|
Giatras; James L. (Port Huron, MI);
Kray; Kevin P. (Phoenixville, PA);
Marino; Charles P. (Philadelphia, PA)
|
Assignee:
|
Markel Corporation (Norristown, PA)
|
Appl. No.:
|
263182 |
Filed:
|
October 27, 1988 |
Intern'l Class: |
C08L 079/08; F16C 001/26 |
Field of Search: |
525/180
|
References Cited
U.S. Patent Documents
3356759 | Dec., 1967 | Gerow.
| |
3391221 | Jul., 1968 | Gore et al. | 525/180.
|
3409584 | Nov., 1968 | Buschman et al. | 525/199.
|
3772249 | Nov., 1973 | Morgans.
| |
3819594 | Jun., 1974 | Holmes | 526/255.
|
4026863 | May., 1977 | Iseki et al. | 525/189.
|
4118532 | Oct., 1978 | Homsy.
| |
4139576 | Feb., 1979 | Yoshimura et al. | 525/180.
|
4143204 | Mar., 1979 | Fang | 428/413.
|
4300408 | Nov., 1981 | Yoshifuji.
| |
4362069 | Dec., 1982 | Giatras et al. | 525/189.
|
4417020 | Nov., 2388 | Bailey et al.
| |
4451616 | May., 1984 | Kawachi et al. | 525/180.
|
4780490 | Oct., 1988 | Mizuno et al.
| |
Other References
"Abrasion Resistant Anti-Friction Tubing in Push-Pull Cable Assemblies",
Markel Corporation.
|
Primary Examiner: Bleutge; John C.
Assistant Examiner: Jagannathan; Vasu S.
Attorney, Agent or Firm: Posillico; Joseph F.
Claims
What is claimed is:
1. An abrasion resistant paste extruded tubular product having high
frictional efficiency in the dry state, said tubular product comprising a
major proportion by weight of fluorocarbon polymer resin and from about 5%
by weight to about 15% by weight of polyamide-imide resin, said product
being made according to a process comprising mixing fluorocarbon polymer
resin particles and polyamide-imide resin particles under conditions
sufficient to produce a uniform, homogenous blend of said resin particles;
preforming said blend and paste extruding said preform.
2. The paste extruded tubular product of claim 1 wherein said tubular
product comprises from about 10% by weight to about 15% by weight of
polyamide-imide resin.
3. The paste extruded tubular product of claim 2 wherein said tubular
product comprises about 10% by weight of polyamide-imide resin.
4. The extruded tubular product of claim 3 wherein said fluorocarbon
polymer resin comprises fine powder and said polyamide-imide resin
comprises a powder having a maximum particle size of about 150 micron.
5. The extruded tubular product of claim 1 consisting essentially of
fluorocarbon polymer resin and polyamide-imide resin.
6. The extruded tubular product of claim 3 wherein said tubular product is
a sintered tubular product.
7. The extruded tubular product of claim 3 including up to about 10% by
weight of an inorganic filler.
8. A paste extrudable, abrasion resistant composition comprising:
a major proportion by weight of fluorocarbon polymer resin; and
from about 5% to about 15% by weight of polyamide-imide resin, said
composition being made according to a process comprising mechanically
mixing fluorocarbon polymer resin particles and polyamide-imide resin
particles under conditions sufficient to produce a uniform, homogenous
blend of said resins particles.
9. The composition of claim 8 wherein said fluorocarbon polymer resin
comprises polytetrafluoroethylene resin.
10. The composition of claim 9 comprising from about 10% to about 15% by
weight of polyamide-imide resin.
11. The composition of claim 8 wherein said fluorocarbon resin comprises
polytetrafluoroethylene resin.
12. The composition of claim 10 wherein said polyamide-imide resin
comprises a fine powder.
13. The composition of claim 8 wherein said fluorocarbon polymer resin
comprises from about 85% to about 95% by weight of said composition and
said polyamide-imide resin comprises from about 5% to about 15% by weight
of the composition.
14. The composition of claim 8 comprising from about 10% to about 15% by
weight of polyamide-imide resin.
15. The composition of claim 14 comprising about 10% by weight of
polyamide-imide resin.
16. The composition of claim 8 wherein said paste extrudable,
abrasion-resistant composition consists essentially of from about 78% to
about 98% by weight of fluorocarbon polymer resin, and from about 5% to
about 15% by weight of polyamide-imide resin.
17. The composition of claim 16 wherein said fluorocarbon polymer resin
comprises a polytetrafluoroethylene polymer resin.
18. The composition of claim 17 wherein said polyamide-imide resin is
present in an amount from about 10% to about 15% by weight.
19. The composition of claim 1 comprising from about 5% to 15% by weight of
polyamide-imide resin.
20. The paste extruded tubular product of claim 1 wherein said fluorocarbon
polymer resin comprises resin of polytetrafluoroethylene and wherein said
paste extruded tubular product comprises about 10% by weight of
polyamide-imide resin.
Description
BACKGROUND OF THE INVENTION
The present invention relates to abrasion-resistant fluorocarbon polymer
composites, such as polytetrafluoroethylene ("PTFE") composites, having
high frictional efficiency over a wide range of temperature and load
conditions. More particularly, the present invention relates to
abrasion-resistant, anti-friction tubing.
Fluorocarbon polymers, such as PTFE resins, are well known in the art and
have heretofore been utilized in extruded tubular products. Although PTFE
resins in their pure form exhibit excellent frictional efficiencies, they
generally have unacceptably low abrasion resistance, that is, they wear
too rapidly. Attempts have been made to improve the abrasion resistance of
PTFE resins by the addition of fillers, both inorganic and organic.
The wear resistance of PTFE extruded tubular products has traditionally
been enhanced by the inclusion of inert, inorganic fillers such as glass
fibers, carbon, asbestos fibers, mica, metals and metal oxides. See, for
example, U.S. Pat. No. 3,409,584. While a measure of improvement in wear
resistance has thus been achieved, PTFE composites comprising inorganic
fillers nevertheless have several disadvantages. For example, such
composites generally exhibit rapid deterioration in frictional efficiency
after relatively short periods of use. Moreover, the use of such
composites as liners for externally lubricated push-pull cable assemblies
is not generally recommended because the inorganic fillers have been found
to separate from the composite and form an abrasive slurry with the
lubricant. This abrasive slurry not only decreases frictional efficiency,
but it can also cause catastrophic and rapid failure of the liner. As a
practical result, therefore, it has previously not been possible to
successfully use inorganically filled PTFE composites in lubricated
push-pull cable assemblies.
Fluorocarbon polymers have also been modified to include organic fillers.
See, for example, U.S. Pat. Nos. 3,652,409 and 4,362,069. Generally, such
organically filled fluorocarbon polymers, and particularly those filled
with polyamide resins, do not lend themselves readily to extrusion, being
more adapted to molding techniques. On the other hand, it has been found
that prior art polymeric composites found suitable for producing tubular
products by extrusion generally suffer from early deterioration under
severe temperature and load conditions.
U.S. Pat. No. 4,451,616, issued to Kawachi et al, discloses a process for
the preparation of a composite comprising PTFE and an organic filler is
disclosed. Kwachi et al teach the use of a filler selected from the group
consisting of polyimide resins, polyamide-imide resins, polyamide resins
and carbon fiber powders. The Kawachi process involves coagulation of PTFE
and one of the above mentioned fillers from an aqueous dispersion of these
two components. The weight proportion of PTFE and the filler in their
aqueous dispersion is disclosed as being from 100:5 to 80. Although the
patent discloses that the abrasion resistance of PTFE can be enhanced by
the incorporation of the above mentioned fillers, there is no indication
that any one of those fillers is preferred over another, or that a
particular concentration of filler in the composite is preferred.
U.S. Pat. No. 3,391,221, issued to Gore et al, discloses fluorocarbon
polymer molding compositions containing from about 10 to about 55 volume
percent of what are called "permanent lubricant modifiers" selected from
the class consisting of (a) nonvolatile liquids which remain thermally
stable and liquid at the sintering temperatures of the fluorocarbon
polymer, and have lower vapor pressures at those temperatures and (b)
materials which are liquid during the forming of the fluorocarbon polymer
article and are transformed into a solid in the final shaped article. One
important function of the lubricant modifiers of Gore is to act as a
lubricating agent during shaping of the polymer. A variety of materials
are disclosed as lubricant modifiers, including: aromatic polyamides
formed by the reaction of aromatic dicarboxylic acids such as terephthalic
acid with aromatic amines such as phenyl diamine or biphenyl diamine; the
aromatic polyimides formed by the reaction of such acid dianhydrides as
pyromellitic dianhydride with the stated aromatic diamine; the polyamide,
polyimide copolymers from the above named components; aromatic polyesters
formed from the aromatic dicarboxylic acids and aromatic diols;
polybenzimidiazoles formed from the aromatic tetracarboxylic acids such as
pyromellitic acid and aromatic tetramines; aromatic polyethers; and
Novolac epoxy resins. The only guidance that the patent provides with
respect to the selection of modifiers for the enhancement of frictional
efficiency is that phenyl silicone lubricants are said to provide high
lubricity under high unit loads, and that polymerizable monomers and
prepolymers that are polymerized in situ provide molded articles that have
a low coefficient of friction. The patent provides no indication that any
particular concentration of filler is preferred over another.
U.S. Pat. No. 3,356,759, issued to Gerow, discloses compositions of
aromatic polypyromellitimides and a polyfluorocarbon resin. Although this
patent broadly refers to the presence of from about 10 to about 90% by
weight of fluorocarbon resin in the composite, it expressly teaches that
the composite preferably have no more than 50% by weight of the
fluorocarbon resin. Accordingly, the Gerow reference teaches composites in
which the polyfluorocarbon components preferably constitute a minor
proportion of the composite.
Composites comprising a mixture of PTFE and polyarylene sulfide have
heretofore been used in fabricating flexible liner or tubing for push-pull
cable assemblies. For example, U.S. Pat. No. 4,362,069, issued to Gitras
and assigned to the assignee of the present invention, describes a
fluorocarbon composite fabricated from a mixture of PTFE resin and a
polymer of arylene sulfide. The composite described in this patent has
exceptional anti-friction, anti-abrasion characteristics across a
relatively wide range of load and temperature conditions. However, as
explained in the brochure entitled Abrasion Resistant Anti-friction Tubing
in Push-pull Assemblies by the Markel Corporation, these composites must
be used with an external lubricant in order to realize a performance
advantage over unfilled PTFE products. When used without an external
lubricant, these composites exhibit performance characteristics that are
no better than conventional unfilled PTFE. Such composites not only have
the disadvantage of requiring a lubricant, but also of precluding the use
of significant amounts of inorganic filler in the organically filled
composite. See, for example, col 5, lines 8-33 of the Gitras patent
described above.
The compositions of the present invention are particularly well adapted for
use as liners in push-pull cable assemblies and the like. Push-pull cable
assemblies are typically used for the transmission of force or other
mechanical control commands from one location to another in apparatus such
as automobiles, aircraft, motorcycles, boats and bicycles. Such cable
assemblies typically comprise a wire cable for transmitting the
appropriate force and an abrasion-resistant, anti-friction liner
surrounding the wire cable. Since the anti-friction, abrasion-resistant
liner is the primary bearing surface in push-pull cable assemblies, it is
subjected to unidirectional, reciprocating and/or rotary contact with the
internal wire cable. In order to achieve superior or even acceptable liner
life under these conditions, push-pull cable assemblies have heretofore
typically required the application of lubricant between the liner and the
wire cable.
SUMMARY OF THE INVENTION
The abrasion resistant, high efficiency composites of the present invention
comprise a major proportion by weight of a resin of fluorocarbon polymers,
and from about 2% to less than about 23% by weight of polyamide-imide
resin filler. More particulary, it has been found that a critical range
exists in the amount of polyamide-imide filler used in the abrasion
resistant, high efficiency compositions of the present invention.
Applicants have unexpectedly discovered that the abrasion resistance and
frictional efficiency of the present composites vary with the amount of
the polyamide-imide included in the composite. At the same time, the
desirability of providing composites that are readily paste extrudable
places additional constraints upon the amount of polyamide-imide filler to
be used in conjunction with the fluorocarbon polymers in accordance with
this invention. Accordingly, it has been found that amounts of
polyamide-imide filler of from about 2% to less than about 23% by weight
are required to meet both of these requirements. It is even more preferred
that amounts of polyamide-imide filler of from about 5% to about 20% by
weight be so included.
Applicants have found that composites formulated according to the present
invention have exceptional frictional efficiencies in the dry state, that
is, in the absence of an external lubricant. Moreover, the present
composites have exceptional abrasion-resistance over extended periods of
use. The ability of the present composites to maintain high frictional
efficiencies in the dry state is not only unexpected, it satisfies an
important need in the art. As discussed above, tubular products formulated
from heretofore used fluorocarbon polymer composites are typically only
used in push-pull cable assemblies in conjunction with an external
lubricant. These cable assemblies are frequently responsible for throttle,
choke and transmission control in automobiles, trucks and the like. If the
external lubricant is properly applied to such assemblies, their
performance is generally satisfactory. If, on the other hand, the
lubricant is omitted from or improperly applied to the cable assembly, the
incidence of liner wear-through and resultant control cable failure
increases dramatically. Thus, liners that require lubricants to maintain
high frictional efficiencies and prolong useful life are not only
disadvantageous, they are potential safety hazards.
Accordingly, one aspect of the present invention is a push-pull cable
assembly having an extruded tubular liner PG,9 comprising a composite
comprising a major proportion by weight of resin of fluorocarbon polymers,
and from about 2% to less than about 23% by weight of a polyamide-imide
resin filler. It has been discovered that such push-pull cable assemblies
can be exposed to relatively long periods of constant use without a
substantial decrease in frictional efficiency and without wear-through of
the tubular liner. Moreover, it has been found that push-pull cable
assemblies according to the present invention do not require the presence
of an external lubricant to achieve this result. These characteristics are
not only unexpected, but they also satisfy an important need for increased
safety in the operation of push-pull cable assemblies for use as throttle,
gear box, clutch, brake, choke and transmission cables, and the like.
Accordingly, it is an object of the present invention to provide
fluorocarbon polymer compositions useful to provide composite having high
frictional efficiencies in the dry state.
It is a further object of the present invention to provide a fluorocarbon
polymer composite having a high degree of abrasion resistance in the dry
state.
It is also an object of the present invention to provide a fluorocarbon
polymer composite adapted for fabricating extruded tubular products.
It is a further object to provide high efficiency, anti-friction,
abrasion-resistant, extruded tubing for use as liners in unidirectional,
reciprocating, or rotary cable assemblies.
It is yet another object to provide abrasion-resistant, anti-friction
tubing for push-pull cable assemblies, said tubing operating efficiently
over a wide range of temperatures and load conditions.
It is still a further object to provide fluorocarbon polymer composites
which perform efficiently and effectively at temperatures ranging from
about room temperature to 250.degree. F. and which obviate the effects of
stress relaxation generally occurring over a period of use.
These and other objects and advantages are attained through employment of
one or more embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a fragmentary view of an exemplary extruded tubular product used
in push-pull cable assemblies of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The abrasion-resistant, high efficiency compositions of the present
invention comprise a major proportion by weight of a resin of fluorocarbon
polymer, and less than about 23% by weight of polyamide-imide resin
filler. Such compositions may optionally include inorganic fillers,
lubricants, pigments and other modificants as will be appreciated by those
skilled in the art. According to preferred embodiments, the composites
consist essentially of from about 77% to about 98% of a single
fluorocarbon polymer or a mixture of two or more fluorocarbon polymers,
and from about 2% to less than about 23% polyamide-imide resin.
Fluorocarbon polymers suitable for use according to the present invention
include a wide variety of fluorocarbon polymers but preferably comprise
polytetrafluoroethylene ("PTFE"). PTFE polymers useful in the practice of
the present invention preferably comprise a major proportion of PTFE
homopolymer, although it is contemplated that copolymers of
tetrafluoroethylene with other halocarbon monomers may also be used
according to some embodiments. The PTFE polymers suitable for use in the
composites of the present invention include conventional PTFE polymers
obtained by conventional means, for example, by the polymerization of
tetrafluoroethylene under pressure using free radical catalysts such as
peroxides or persulfates.
According to one preferred aspect of this invention, the PTFE polymer
resins are paste extrudable polymer resins. Such resins are generally in
the form of extrusion grade powders, fine powders, and the like. The
preferable PTFE powders are dispersion grade and not granular. Techniques
for the production of fine PTFE powders are well known, and the use of
polymers produced by any of these techniques is within the scope of this
invention. For example, fine PTFE powder may be produced by coagulating
colloidal PTFE particles as disclosed in U.S. Pat. No. 4,451,616, which is
incorporated herein by reference.
The polyamide-imide resins of the present invention are polymers having
both an amide bond and an imide bond in the molecule. Techniques for
fabricating such polymers are well known and readily available to those
skilled in the art. For example, polyamide-imide resins can be obtained by
reacting an aromatic diamine having an amide group with an aromatic
tetracarboxylic acid, such as pyromellitic acid. Polyamide-imide resins
can also be obtained by reacting a tricarboxylic acid, such as anhydrous
trimellitic acid with a diamine, such as 4,4'-diaminodiphenyl ether.
Polyamide-imide resins are generally represented by the following
structural formula:
##STR1##
Polyamide-imide resins of the type suitable for use in the practice of the
invention are preferably high temperature, thermoplastic polyamide-imide
resins such as those available commercially from Amoco Chemicals
Corporation under the general designation "TORLON". Although most grades
of polyamide-imide resins are generally adaptable for use in the present
compositions, TORLON resins having the grade designation "4000TF" are
preferred. TORLON-400TF is a high molecular weight, high performance,
thermoplastic material with exceptional thermal resistance, creep
resistance and superior mechanical stress properties.
Polyamide-imide resins are available in a wide variety of particle sizes,
and resins having all such particle sizes are believed to be readily
adaptable for use according to the present invention. Applicants have
found, however, that the particle size of the polyamide-imide resins used
in the present composites has an impact on the properties of the shaped
article produced from the composite. For example, when the composites are
processed as hereinafter described to produce extruded tubular products,
polyamide-imide powders having average particle sizes up to about 50
microns are typically preferred. Applicants have found that powders having
average particle sizes in excess of about 50 microns tend to result in
extruded products that have relatively low frictional efficiency and
abrasion resistance. Moreover, the smaller particle sizes tend to
facilitate the paste extrusion process.
In accordance with the present invention, the polyamide-imide resins are
blended with the PTFE resin in amounts sufficient to attain a composite
that is at once readily extrudable by paste extrusion, has a relatively
high frictional efficiency and exhibits excellent abrasion resistance over
extended periods of use. It has been discovered that polyamide-imide
resins are preferably present in amounts from about 2% to less than about
23% by weight of the composite. Composites formulated within this range
contain sufficient polyamide-imide resin to ensure that abrasion
resistance and high frictional efficiency are imparted to the composite
while leaving the composite in a condition such that it is readily
extrudable by the paste extrusion process. It has further been discovered
that it is generally more preferred that the polyamide-imide resins be
incorporated in the composites of the present invention in amounts from
about 5% to about 20% by weight of the composite, with about 10% to about
15% being the most preferred.
The composites of the present invention may optionally include further
additives such as lubricating fluids, inorganic fillers, pigments and
other modificants generally known to those skilled in the art. Useful
inorganic fillers include glass, metal and metal oxide components. These
and other inorganic fillers can generally be employed in the form of
beads, fibers, powders, liquids and the like, as is well understood by
those skilled in the art. Inorganic fillers may be incorporated in amounts
sufficient to impart the desired increase in tensile strength, as is well
understood by those skilled in the art. In typical prior art composites
utilizing polypheylene sulfide as the organic filler, the amount of
inorganic filler was limited to about 4% by weight of the composite. Since
the present compositions do not rely on external lubricants for their
superior performance, it is contemplated that inorganic fillers can
advantageously be added to the present composites in amounts up to about
10%.
Methods for formulating polymer composites are well known to those skilled
in the art and may be used in the formulation of the composites of the
present invention. One preferred method of formulating such composites
comprises mixing a fine PTFE powder resin with a fine polyamide-imide
powder resin. Any well known mixing process that achieves homogeneous and
uniform mixing may be employed, although mixing by tumbling in a suitable
commercial blender such as Patterson-Kelly Twin-Shell at temperatures up
to about 68.degree. F. for a period of about 3 minutes is generally
preferred. In formulating the blend, it has been found that the PTFE and
the polyamide-imide resins are preferably in powder form and have an
average particle size estimated to be from about 2 to about 50 microns.
It is contemplated that the fluorocarbon-based polymeric composites of the
present invention may be processed using various fabricating methods,
including extrusion, to produce abrasion resistant shaped articles having
high frictional efficiencies in the dry state. Although it is contemplated
that the present composites may be processed by any one of various well
known extrusion techniques, the present composites are particularly well
adapted for processing by paste extrusion to fabricate tubes, rods, wire
coatings, liners, and the like. In the paste extrusion process, the
fluorocarbon-based polymeric composite is compressed into a cylindrical
preform by techniques well known in the art. An extrusion aid, typically a
volatile lubricant such as naphtha or other volatile paraffinic
hydrocarbon, is optionally added to the preformed composite in an amount
of from 10% to 25% by weight. The preformed composite is then shaped into
the desired form by cold flow extrusion. After extrusion, the extrusion
aid is substantially removed from the shaped article. According to one
embodiment, removal of the extrusion aid comprises heating the shaped
composite for a time and at a temperature sufficient to effect removal of
the extrusion aid, typically for about 15 seconds at about 350.degree. F.
The shaping process further preferably comprises a sintering step in which
the extruded composite is heated for a time and at a temperature
sufficient to fuse or sinter the compressed powders into a homogeneous
product, typically for about 20 seconds at about a temperature of at least
about 647.degree. F. (342.degree. C.). The shaping process may be, and
preferably is, carried out continuously.
The shaped articles of the present invention may be further treated after
extrusion by post curing at temperatures from about 500.degree. F. to
about 900.degree. F. for time periods from about 5 minutes to about 24
hours, and preferably at from about 500.degree. F. to about 527.degree. F.
for at least about 16 hours, depending on the state of the cure of the
polyamide-imide prior to blending. It also should be understood that the
polyamide-imide can be precured and then ground prior to blending and
fabrication.
The shaped articles prepared according to the present invention are
abrasion-resistant extruded products having superior frictional efficiency
and wear resistance in the dry state, excellent resistance to cold flow,
and extended useful life. Unlike composites which contain inert inorganic
materials as fillers or additives, it has been found that increased wear
resistance is achieved with the composites of the present invention
without attendant decrease in frictional efficiency and/or shortened life
cycles.
Applicants have found that the present composites are particularly well
adapted for use as tubular liners for push-pull cable assemblies. A
exemplary push-pull cable assembly is illustrated in FIG. 1. The assembly
of FIG. 1 is indicated generally by the reference numeral 1 and comprises
a central core 5. As is well understood by those skilled in the art,
central core 5 is typically a standard braided steel rope or any other
means for transmitting a force along the length of the assembly. A tubular
liner 2 comprising the composite of the present invention surrounds the
central core 5. More particularly, tubular liner 2 forms a material
chamber 4 having a mating surface with core 5. The outside surface 3 of
the tubular liner 2 is, in most cases, covered by steel ribbon armor or
wire serve (not shown) which is in turn placed in a metal supporting
conduit or jacket (not shown).
Shaped articles, particularly tubular liners for use in push-pull cable
assemblies, comprising the present composites exhibit excellent and
altogether unexpected results. For example, one important aspect of the
present composites and the shaped articles produced therefrom is the dry
state characteristic of the material. The present shaped articles exhibit
substantially reduced coefficients of friction in the dry state and this
frictional efficiency is generally maintained over a relatively extended
product life. It will be appreciated by those skilled in the art, however
that the addition of external lubricants to push-pull cable assemblies of
the present invention may nevertheless produce even further performance
improvements. Accordingly, push-pull cable assemblies that include
external lubricants are also within the scope of the present invention.
The following examples, set forth by way of illustration but not
limitation, depict the improvements which are achieved utilizing the
fluorocarbon-based polymeric composites of the present invention.
EXAMPLE 1
A series of tests that illustrate the effect of polyamide-imide ("PAI")
concentration on the compositions of the present invention were performed.
Each of the formulas, labeled as A through E in Table I, were prepared
according to the following procedure. A polyamide-imide resin was mixed in
a Patterson Kelly Twin Shell mixer with a PTFE resin according to the
proportions indicated in Table I. The polyamide-imide resin was a product
of the Amoco Chemicals Company sold under the designation "TORLON 4000TF".
The PTFE resin was a product of the E.I. duPont de Nemours Company sold
under the designation "Grade 6C". The resins were mixed for about 3
minutes at a temperature of about 65.degree. F. to produce a uniform and
homogeneous blend. A volatile extrusion lubricant was added to the blend
in amount sufficient to constitute about 18% by weight of the composite.
The composite was removed from the mixer and compressed into a cylindrical
preform. The preformed composite was then paste extruded into a tubular
product. After extrusion, the extrusion lubricant was removed from the
tubular product by heating at a temperature of about 350.degree. F. for
about 15 seconds. The tubular product was then sintered for about 20
seconds at a temperature of above about 650.degree. F. An extruded tubular
product having an inside diameter of about 0.095" (2.4 mm) and a wall
thickness of about 0.013" (3.3 mm) was produced.
Tests were performed by securing the tubular product over an "S" shaped
routed fixture wherein the curvilinear portions of the inner radii of the
"S" fixture extend about 120.degree. and wherein a flexible cable is drawn
through the liner, reciprocating at 60 cycles per minute, each cycle
consisting of a forward travel of 11/2 inches and a like return.
Frictional efficiency and abrasion resistance of the composite are
determined by applying a variable load to the fixture. The variable load
is applied by springs which may be adjusted over a range of 0 to 18
pounds-force. As the term is used herein, "low-load frictional efficiency"
refers to a frictional efficiency determined with the load springs set to
range from about 0 to about 6 pounds-force. As the term is used herein,
"high-load frictional efficiency" refers to a frictional efficiency
determined with the load springs set to range from about 6 to about 18
pounds-force. Frictional efficiency measurements are taken at various
intervals of cycles by employing a load cell (transducer) and recording
the actual load necessary to move the cable over the surface of the liner
at 4 cycles per minute. For the actual measurement, the spring is replaced
by a 5 pound dead-weight. The frictional efficiency is calculated as a
percentage by dividing the measured force into the five pound dead-weight.
In the test results, the letter "F" following a given calculated
efficiency at a given number of cycles indicates a failure of the liner,
i.e., a wearing through of the liner by the cable. Such a failure is
determined by the cable contacting a base metal after wear-through and
closing an electrical circuit which stops the tester. The frictional
efficiencies, as measured according to the technique described above, have
been found to accurately predict the properties of the composites and the
tubular products made therefrom.
Formulas A through E were tested in the dry state at room temperature and
found to have the low-load frictional efficiencies shown in Table II. As
illustrated by the data provided in Table II, applicants have found that
at least about 2% by weight of PAI must be included in the present
composites in order to obtain acceptable abrasion resistance in the dry
state. Unexpectedly, the data also illustrate that there is a decrease in
frictional efficiency when the weight concentration of PAI in the
composite is increased from about 13% to about 20%, although both
formulations satisfy the objects of the invention.
Applicants have attempted to paste extrude a composite comprising about 23%
by weight of PAI according to the procedure described above. It has been
found, however, that paste extrusion of composites comprising about 23%
PAI by weight or more is not generally possible. The composite formulation
labeled as formulation F in Tables I and II was formulated according to
the procedures described above, except that the formula was extruded
according to the well known hot melt extrusion process. The data in Table
II illustrates that the hot melt extruded product has properties generally
inferior to composites made according to the present invention.
EXAMPLE 2
A series of tests that illustrate the effect of PAI resin particle size on
composite performance were performed. In particular, formulations G and H
were prepared according to the same procedure used to prepare formulations
A through E of Example 1, except that formula H was not sifted prior to
blending. Formulations G and H each consisted essentially of about 10% by
weight PAI and about 90% by weight PTFE. Thus, formulations G and H are
essentially identical except that the PAI resin included in formula G had
a maximum particle size of about 150 micron while the maximum particle
size for formula H is estimated to be about 300 micron.
Tests were performed on the above described formulas by securing the
tubular product over an "S" shaped routed fixture as described above,
except that the high-load frictional efficiencies were measured.
Applicants believe that high-load efficiency tests more accurately
simulate the conditions experienced by tubular liners in actual push-pull
cable assembly operation than do low-load tests. The temperature
conditions under which the various formulations were tested, together with
the frictional efficiency of each during testing, are set forth in Table
III.
As illustrated by the data provided in Table III, applicants have found
that the particle size of the PAI resin used in the present compositions
has an affect on the properties of the resulting extruded tubular product.
In particular, applicants have found that when the PAI resin is sifted to
exclude substantially all those particles greater than about 150 micron,
an increase in the initial frictional efficiency of about 17% is realized.
Moreover, an advantage in frictional efficiency is maintained over the
life of the product. A comparison of abrasion resistance based upon life
cycle data cannot be made for formulas G and H because the testing
apparatus malfunctioned at about 330,000 cycles. However, a comparison of
the weight loss data indicates that the abrasion resistance of formula G
is superior to that of formula H.
EXAMPLE 3
A series of tests were performed to illustrate the superior performance of
the present composites in comparison to two of the most commonly used
materials for tubular liners in push-pull cable assemblies. In particular,
PTFE composites sold under the designation "AR-500" and "AR-425" were
tested under load conditions described above with respect to Example 2.
AR-500 is a PTFE composite manufactured by the assignee of the present
invention and consists essentially of about 10% by weight of a resin of
polyphenylene sulphide and about 90% by weight of PTFE resin. AR-425 is a
PTFE composite manufactured by the assignee of the present invention and
consists essentially of about 6% by weight of glass beads and about 94% by
weight of PTFE resin.
The temperature conditions under which the AR-425 and AR-500 products were
tested, together with the frictional efficiencies of each during testing,
are set forth in Table IV. For comparison purposes, the test results from
formula G are repeated in Table IV. As illustrated by the data provided in
Table IV, the present composites possess dry state abrasion resistance
that is dramatically superior to two of the most widely used prior art
products. Importantly and unexpectedly, the present composites also
exhibit truly extraordinary properties at high temperature conditions. For
example, the present composites are capable of withstanding 500,000 cycles
at 250.degree. F. without breakthrough, while the state of the art AR-500
material wore through at about 100,000 cycles. Moreover, the frictional
efficiency of the present composite is substantially higher at 250.degree.
F. than either AR-425 or AR-500. These results are especially important
with respect to the use of the present composites in tubular liners for
push-pull cable assemblies. Push-pull cable assemblies are typically
exposed to engine temperatures that range from below freezing to above
250.degree. F. The present composites provide liners that exhibit long
life and high frictional efficiencies in the dry state over a wide range
of temperature conditions.
TABLE I
______________________________________
Formula PTFE (pbw) PAI (pbw)
______________________________________
A 100 (virgin)
--
B 100 2
C 100 5
D 100 15
E 100 25
F 30 100
______________________________________
TABLE II
__________________________________________________________________________
LIFE CYCLE TEST DATA
Initial Cycles (Thousands) Weight
Formula
Efficiency
25
50
100
150
200
250
300
350
400
450
500
loss, mg
__________________________________________________________________________
A 70 F.
(wear-through at 15,600 cycles)
B 72 70
70
69 66 F.
C 70 70
69
68 68 68 67 67 66 65 64 64 25
D 74 75
76
75 75 76 76 75 76 75 75 76 8
E 64 63
62
63 61 60 60 60 60 60 58 56 6
F 63 62
62
61 59 58 56 54 53 52 50 48 2
__________________________________________________________________________
TABLE III
__________________________________________________________________________
Test Initial
LIFE CYCLE TEST DATA Cycles (Thousands)
Weight
Formula
Temp. .degree.F.
Efficiency
40 95
100 180 265 355
358 loss, mg
__________________________________________________________________________
G Rm. Temp.
84 68 --
66 65 64 * 38
H Rm. Temp.
67 -- 64
-- 62.5
61.5
62 F 45
__________________________________________________________________________
*No failure Testing Apparatus Malfunction at 330,000 cycles
TABLE IV
__________________________________________________________________________
LIFE CYCLE TEST DATA
Test Initial
Cycles (Thousands)
Formula
Temp. .degree.F.
Efficiency
40
80 100
160
180
250
265
330
403
403
500
__________________________________________________________________________
G Rm Temp
84 68
-- 66 -- 65 -- 64 *
G 250 79 --
79 -- 78.5
-- 79 -- 78 76 -- 5
AR 425
Rm Temp
68.5 --
58.5
-- 53.5
-- 56.5
-- 55 -- 54 52
AR 500
Rm Temp
69 F (wear-through at 7740 cycles)
AR 500
250 72 --
75 F (wear-through at 107,900 cycles)
__________________________________________________________________________
*No Failure Testing apparatus Malfunction at 330,000 cycles
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