Note: Descriptions are shown in the official language in which they were submitted.
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Process for Preparin~ Friction Clutch Facings
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Background of the_Invention
This invention relates to facings for friction
clutches and to a method for making friction clutch
facings. The clutch facings comprise continuous
strands or filaments which are extrusion-coated with a
curable friction resin composition, wound into a
preform and thermally cured under pressure. Clutch
facings prepared by this process are asbestos-free and
exhibit excellent burst streng~h.
Because of its great thermal resistance, asbestos
has long been used as the mainstay of friction elements,
particularly in the automotive industry. When used
with suitable friction resin compositions, highly
satisfactory riction elements result. Recently,
however, health hazards associated with the manufacture
and use of asbestos-containing compositions and articles
have become apparent. As a result there has been an
increasing effort to develop asbestos-free compositions
for use in the manufacture of friction elements. The
use of glass fiber in such replacement compositions has
been disclosed in the art, as for example, in U.S.
Patents 3,743,069, 4,130,537 and 4,137,214. In these
prior art compositions, glass fiber is included either
in chopped fiber form or as continuous strand. Where
glass fi~er in the form of continuous strand is employed,
the glass fiber is normally sized and then impregnated
with a friction resin composition. The strand is
usually impregnated by dip-coating, that is, by first
passing the strand through a dip tank containing a
dilute solution or dispersion of the friction resin
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composi~ion (cement). The wet, impregnated strand is
then passed through a drying tower or other equipment
to evaporate the solven~ and produce a dried cement-
impregnated strand in an uncured state. The strand is
used to wind a preform which then is thermally cured
under pressure by well-known techniques to produce a
cured friction element.
The dip coating process for impregnating the
continuous strand generally requires the use of cement
lQ containing substantial quantities of solvent, often
greater than 50 ~t~ of the total composition, to ensur~
adequate penetration of the strand as well as to
provide cements having a viscosity suitable for u~e in
coating equipment. Where the cement is a dispersion or
contains dispersed solids, settling or separation of
the solid components in the dip tank may become a
problem. Further, the cement-impregnated strand must
be dry to be suitable for use in winding, which
requires the use of a drying tower or other drying
equipment. To meet ever more restrictive environmental
regulations, the solvents removed in the drying step
will nor.nally be recovered by means of elaborate and
expensive solvent recovery equipment and then recycled.
These drying and solvent recovery steps add materially to
th~ overall production costs. A substantial reduction
or elimination of solvent use in the production of clutch
facings would thus be of substantial benefit.
Summary of _he Invention
This invention is a friction clutch facing comprising
a continuous strand extrusion-coated with a friction
resin composition, and a process for making a friction
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clutch facing wherein a continuous strand is ex~rusion-
coated with a thermosetting friction resin composition,
wound into a preform, and then thermally cured under
pressure. The clutch facings exhibit excellent burst
strength, and the process of their manufacture avoids
the need for elaborate drying and solvent recovery
steps in the coating process by eliminating or substan-
tially reducing the use of solvents.
Detailed Description of the Invention
Clutch facings made in accordance with the teachings
of this invention comprise continuous strand or filament
extrusion coated with a friction resin composition.
The continuous strand or filament useful in the
practice of this invention may be formed of any of
the known reinforcement fibers such as glass, cotton,
graphite, aramide and the like as well as combinations
of two or more of these fibers. Preferably the continuous
strand will be formed o~ glass fiber and will be treated
with coupling agents to enhance resin adhesion according
to practices well known in the art. The strand will
preferably be sized by being impregnated with a sizing
such as an RFL coating latex, employing methods and
compositions known in the art and shown, for example, in
V.S. Patents 3,973,071 and 3,925,286.
The friction resin composition may be any of the
thermosetting, rubber~modified resin compositions
commonly employed in the production of friction elements.
The standard compositions commonly include a curable
phenolic resin~ i.e., a thermosetting resin derived
from a phenol and an aldehyde, together with a rubbery
modi~ier such as a natural rubber or a rubbery polymer
z' chloroprene, butadiene, isoprene or the like,
or a copolymer ~hereof with one or more copolymerizable
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monomers such as an acrylate, methacrylate or other
alkylacrylate, acrylonitrile, styrene, alpha methylstyrene,
ethylene, propylene, vinyl pyridine and the like.
The composition may further include other additives
including vulcanizing agents, accellerators, cross-linking
aids, friction modifiers and the like according to
well-known practice. Fillers such as carbon black,
graphite, clay and the like may also be included, as
well as chopped inorganic or orqanic fiber such as for
example wollastonite, aramide fiber, glass fiber
and th~ like. Friction resin compositions as such are
generally well known in the art.
The continuous strand is extrusion coated with the
friction resin composition. Any of the methods known
in the art for the extrusion coating of wire may be
employed for the purposes of this invention. One
example of a machine for extrusion coating wire with
viscous pasty material is disclosed and described in
V. S. Patent 2,315,645 and employs a wire coating die.
Alternatively, the continuous filament or strand may be
passed through a wire coating die fed by a conventional
extruder. Further variations including continuous
calendaring which have been widely employed for wire
coating may also be used to coat the continuous
strand or filament. The friction resin composition
wiii be applied at room temperature or at an elevated
temperature below the cure temperature of the particular
resin employed. Where the viscosity of the friction
resin composition, even at elevated temperatures, is
too high for statisfactory coating, it may be desirable
to dilute the resin composition with a minor amount of
solv~nt to lower the viscosity and improve the coating
rate. The strand exiting the extrusion die will thus
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be coated wlth substantially dry friction resin composition
in an uncured condition.
The extrusion coating process may also be employed
to coat a plurality of strands simultaneously to
form a ribbon or tape having strands spaced apart
in a side by side rela~ionship.
The coated strand or tape is then fed to a winding
machine and wound into a preformO A preform is a
loosely structured article composed of woven or wound
reinforcing constituents impregnated with a curable
resin composition in a n uncured or partially~cured
stateO In one method for forming a preform9 one or
more extrusion-coated tapes are spirally-wound in a
face to face relationship to form a wound annular disc
preform of the desired size and weight. A second
technique for preparing a preform is to cam-wind a
coated strand or a tape in an undulating pattern such
as is shown for example in U.S. Patent 3,600,258 to
form an annular disc preform of the desired size and
weight.
The preform is then subjected to heat and pressure
to produce~a cured friction element according to
methods well known in the art.
The friction clutch facings of this invention and
the method for their preparation will be better understood
by consideration of the following examples ~hich are
provided by way of illustration.
.
Example 1
A friction resin composition comprising 16 wt~
elastomer and 26.6 wt~ phenolic resin together with
min~ral fillers, curing aids, tackifier and graphite,
was extrusion coated onto a sized glass fiber strand.
The extrusion coating was accomplished by passing the
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fiber strand through a wire coating extr~sion die fed
by ~ ~rabender extruder, using a barrel temperature of
~5 r' to extrude the resin composition. The coated
strand consisted 35 wt% glass fiber (average), and
65 wt~ resin composition in a partially-cured stateO
The coated strand was cam-wound to form a clutch
facing pre-rorm. The preform was placed in a mola
under 2000 psi pressure and heated at 350F for 5
min, then post-cured at 400F for 5 hrs. The cured
clutch ~acings had burst strengths of 13,100 RPM ave.
Example 2
A friction resin composition was prepared containing
20.7 wt% elastomer, and 10~ wt% phenolic resin together
with mineral fillers, curatives, friction modifiers and
chopped ~1/4") fluffed aramid fibers (obtained as ~evlar*
fiher from DuPont Co.). The composition was mixed with
methyl ethyl ketone to reduce the viscosity and extruded
at 90~ onto a fiber glass strand using a wire
~ extrusion coating die fitted to a Brabender extruder.
The coated strand was cam-wound into a clutch facing
preform. The preform was air dried to remove solvent,
then placed in a mold under 2,000 psi pressure and
heated at 350F for 5 min to cure the preform. The
racing was then post cured at 400F for 5 hours under
500 psi pressure. The cured clutch facings had average
burst strengths of 11,300 RPM.
~ le 3
The friction resin composition of Example 1 was
employed to extrusion coat four parallel fiber glass
strands simultaneously by passing the strands through a
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wire die having a flat ribbon die at the exit port and
fed by a Brabender extruder~ The resulting flat tape
was used in preparing a cam-wound preform which then
wa cured under 2000 psi pressure at 350 F as before
to give a friction clutch facing.
Example 4
A friction resin composition comprising 15.5 wt%
elastomer, 8.0 wt% phenolic resin, 19.3 wt% chopped
glass fiber and 5.5 wt~ ~ramid fiber (obtained as dry
Kevlar aramid pulp from E. I. DuPont Co.), together
with mineral fillers, curatives and friction modifiers,
was prepared by dry powder blending. The pow~er blend
was fed directly to a Brabender* extruder and extruded
at 210F through a ribbon die, to demonstrate the
ready extrudability of the composition.
It will be apparent from the Examples that continuous
strand or filament may be extrusion coated with a friction
resin composition and employed in the filament winding
of preforms to provide friction clutch facings having
excellent burst strength characteristics. The friction
resin composition may be used directly in the extrusion
process (Example 1) or mixed with a solvent to modify
the resin viscosity as in Example 2. The resulting
extrusion-coated strand requires no further drying
25 ~ prior to use in winding the preform. Where solve~ts
are employed to modify the extrusion viscosity of the
resin, the resulting coated strand may be wound without
-drying into a pre-form. The preform may then be dried
in less complex equipment wherein solvent recovery is
33 facilitated, thus reducing solvent loss and improving
the cost factors associated therewith.
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The including of short fibers such as chopped
aramid fiber (Example 2) or aramid pulp (Example 4~
markedly improves the wear character of the resulting
friction elements. The use of chopped fiber (Example
2) required the further including of a solvent to
reduce the viscosity of the friction resin composition
to ~ level suitable for extrusion coating. Where the
aramid fiber was employed in the form of a pulp comprised
of highly fibrillated fibers, the friction resin
composition could be readily extruded without the need
for the including of a solvent. Friction clutch facings
can readily be prepared by this process employing aramid
fiber pulp in the friction resin composition.
The instant invention will thus be seen to be a
method for making friction clutch facings comprising
extrusion-coating continuous fiber strand with a
curable friction resin composition, winding the strand
into preform, and thermally-curing the preform under
pressure.
It will be understood by those skilled in the art
that various modific3tions of the instant process are
possible and may be undertaken without departing from
the spirit and scope of the invention which is defined
solely by the appended claims.
