LIGNIN-BASED FRICTION MATERIAL

MATERIAU DE FROTTEMENT A BASE DE LIGNINE

English Abstract

This invention provides for a friction material composition suitable for
friction element formulation. The composition comprises an essentially sulfur-
free lignin with low water solubility. The lignin replaces from about 1 to
about 30 % on a weight basis with the phenolic resin in the friction material
composition. A method of reducing noise within the range of human hearing
resulting from friction element performance is also provided.

French Abstract

La présente invention concerne une composition de matériau de frottement convenant à la formulation d'éléments de frottement. La composition comprend une lignine sensiblement exempte de soufre et à faible solubilité dans l'eau. La lignine remplace environ 1 % à environ 30 % en poids de la résine phénolique entrant dans la composition du matériau de frottement. Grâce au rendement de l'élément de frottement, l'invention concerne également un procédé d'atténuation du bruit dans la plage audible par l'homme.

Claims

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We claim:
1. A friction material composition comprising an
essentially sulfur-free lignin with low water solubility,
said lignin replacing from about 1 to about 30% on a
weight basis with the phenolic resin in said friction
material composition.
2. The composition of claim 1 wherein said
lignin is an organosolv lignin.
3. A friction material composition comprising on
a weight basis from about 20% to about 35% iron powder,
from about 0.1% to about 1.5% hexamethylene tetramine,
from about 10% to about 15% steel fiber or asbestos, from
about 8% to about 14% phenolic resin, from about 7% to
about 11% graphite and of from about 0.08% to about 4.2%
of an essentially sulfur-free lignin with low water
solubility on a weight basis with said composition.
4. The composition of claim 3 wherein said
lignin is an organosolv lignin.
5. A method for reducing noise within the range
of human hearing, said noise resulting from friction
element performance, said method comprising the step of
incorporating in a friction element formulation a friction
material composition comprising an essentially sulfur-free
lignin with low water solubility, said lignin replacing
from about 1 to about 30% on a weight basis with the
phenolic resin in said friction material composition.
6. The method of claim 5 wherein said lignin is
an organosolv lignin.
7. A method for reducing noise within the range
of human hearing, said noise resulting from friction
element performance, said method comprising the step of

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incorporating in a friction element formulation a friction
material composition comprising on a weight basis from
about 20% to about 35% iron powder, from about 0.1% to
about 1.5% hexamethylene tetramine, from about 10% to
about 15% steel fiber or asbestos, from about 8% to about
14% phenolic resin, from about 7% to about 11% graphite
and of from about 0.08% to about 4.2% of an essentially
sulfur-free lignin with low water solubility on a weight
basis with said composition.
8. The method of claim 7 wherein said lignin is
an organosolv lignin.

Description

CA 02242~4 1998-04-17
WO 97/14747 PCT/US95/13286
LIGNIN-BASED FRICTION MATERIAL
BACKGROIJND OF 1~ lNvl~;NlIoN
When the brakes of a vehicle are applied, the
brake lining on each wheel frictionally engages another
member to reduce the rotary motion o~ the wheel. During
the ~rictional engagement, thermal energy is created as
the drum or disc slide on the brake lining. Conventional
organic brake linings are made up o~ a mixture of asbestos
or steel ~ibers and modi~iers held together in a ~ixed
matrix created by a phenolic resin The asbestos or steel
fibers remain stable when subjected to thermal changes up
to 800~ F. However, asbestos deteriorates at higher
temperatures due to loss of water. When asbestos
dehydrates, it is trans~ormed into ~orsterites or olivine
while the phenolic resin is reduced to a carbonaceous
resin as the matrix engages the drum or disc. However,
when a phenolic resin is utilized, a melting of the
phenolic resin at the surfaces o~ all particles occurs to
wet the same and reduce the wear of the ~riction producing
elements. Upon curing the phenolic resin reestablishes
the matrix bond which holds the ~riction modifiers and
asbestos in a ~ixed relationship.
Phenolic resins are produced through the
conA~n~ation of a phenol with ~ormaldehyde in the presence
o~ a catalyst. Phenol is derived ~rom benzene and the
supply o~ benzene has been reduced because of industry
changes. Because o~ the reduction in the supply o~ phenol
and the elevated price o~ phenol, it has been a necessity
to find an extender or substitute ~or phenolic resin.
In view of the ~oregoing, it was suggested that
lignin or a lignin derivative be combined with a phenolic
resin to produce a ~ixed matrix In U.S Patent No.
4,239,666 it is disclosed a composition ~or a ~riction
material ~or use in Friction elements such as brake pads,

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brake linings and clutch facings. In the friction
material, lignosulfonate or kraft lignin are substituted
for a portion of the phenolic resin binder However, such
a combination presented severe limitations since the
resulting friction elements emitted sulfur-based odors
upon normal use and erratic brake performance.
The choice of lignin or lignin derivative that
can be combined in friction material is greatly affected
by the environmental considerations which affect the
development of pulping technologies Due to increasing
environmental demands during the last three decades,
traditional sulfite pulping has almost completely been
replaced by the kraft pulping process. Both sulfite and
kraft pulping processes are noted for their contribution
to air and water pollution, which requires costly
pollution control equipment to bring kraft and sulfite
pulping operations into environmental compliance. These
pulping technologies can now be economically replaced by
more environmentally friendly processes. One of these
20 prOCesseS i8 the organosolv pulping process which has
~;n;m~l impact on the environment. Unlike the traditional
sulfite process, the organosolv process allows for the
recovery of a highly pure, essentially sulfur-free and
hydrophobic form of lignin with low water solubility.
This lignin can be suitable for the preparation of a
lignin-based friction material for use in friction
elements.
By the method o~ the present invention is
provided an environmentally friendly lignin-based friction
material composition. The composition when formulated in
friction elements can greatly reduce the noise, wear and
sulfur-based emissions which are generally encountered
with prior art friction elements.

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SUMMARY OF THE INVENTION
The invention provides for a friction material
composition for use in friction element~ wherein an
essentially sulfur-free lignin low water solubility
replaces from about 1~ to about 30~ of the phenolic resin
in the composition. The friction material composition when
formulated into friction elements such as brake pads
results in a significant reduction in wear, noise level,
and sulfur-based emissions resulting ~rom the performance
of the friction element.
Novel features and aspects of the invention, as
well as other benefits will be readily ascertained from
the more detailed description and claims which follow.
DESCRIPTION OF THE FIGURES
Figures 1 and 2 show the effect of 20~ lignin
replacement on the uniformity of the coefficient of
friction of the resulting brake pad as a function of
temperature.
Figures 3 and 4 show the effect of 20~ lignin
replacement on the noise performance of the resulting
brake pad at different frequencies.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention provides ~or a friction material
composition having stability in the thermal operating
range of most vehicle ~riction elements. The friction
material composition when used in ~riction elements such

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brake pads reduces noise levels and improves the wear of
the friction element. The friction material composition
comprises a highly pure, essentially sulfur-free and
hydrophobic form of lignin with low water solubility at
neutral or acidic pH.
A lignin which can be combined into the friction
material can be selected from steam explosion,
autohydrolysis extraction or soda lignins A preferred
lignin to accomplish the objectives of this invention is
lO the lignin described in U.S Patent No. 4,764,596. Such a
lignin is a high purity organosolv lignin and is separated
as a coproduct of the pulping and chemical delignification
o~ plant biomass with organic solvents, for example
ethanol. This lignin is an essentially sulfur-i~ree powder.
15 It has low water solubility at neutral or acidic pH and is
soluble in aqueous alkali and selected organic solvents.
It is generally characterized by its hydrophobicity, high
purity, melt flow and a low level of carbohydrates and
inorganic cont~m;n~nts.
In a preferred embodiment, organosolv lignin can
be used as a partial replacement ~or the phenol-
formaldehyde resin binder used in friction material
formulations wherein powder phenol-formaldehyde resin is
used. Lignin can be formulated to replace on a weight
25 basis from about l to about 30~ of the phenolic resin. An
example of such a friction material formulation comprises
from about 20~ to about 35~ iron powder, from about O.l~
to about l.5~ hexamethylene tetramine, from about lO~ to
about 15~ steel fiber or asbestos, from about 8~ to about
30 14~ phenolic resin, from about 7~ to about ll~ graphite
and the balance is a modifier which comprises friction
coe~ficient modifiers such as barium sul~ate, aluminum
oxide and in certain ~ormulations, brown or black organic
particles. Such a :Eormulation can comprise lignin o~ ~rom
35 about 0 08~ to about 4.2~ on a weight basis with the
resulting ~riction material composition.

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An important property of the lignin-based
friction material composition of this invention is its
water solubility. It has been observed that the water
solubility of a friction material composition comprising a
lignosulfonate shows a tenfold increase in water
solubility as compared to a friction material composition
comprising the same level of substitution with organosolv
lignin. This observation can be explained by the fact that
the lignosulfonate-based friction material composition has
not been incorporated into the phenolic matrix to the same
extent as the lignin of this invention.
Brake pads are manufactured by blending the
friction material composition and then pressing the blend
at from about 375~F to about 500~F for from about 10
minutes to about 45 minutes and at a pressure of from
about 350 psig to about 750 psig. Manufacturing techniques
are well known in the art.
In order to evaluate the friction material
composition, a series of tests were performed on friction
elements such as brake pads comprising the lignin of the
invention. The pads were all formed by techniques well
known in the art.
Figures 1 and 2 show that replacing 20~ of the
phenolic resin with organosolv lignin did not affect the
stability of the coefficient of friction as the
temperature was changed. A stable coefficient of friction
is a requirement of friction element products since
drivers require the same braking power or feel regardless
of the temperature of the friction elements.
The friction material composition of this
invention when formulated in brake pads result in an
improvement in wear characteristics (Table 1)

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Table 1
Inner Outer Average
(mm/qm of brake ~ad)
Control 0.102 0.142 0.122
10~ Lignin 0.071 0.122 0.096
20~ Lignin 0.090 0.139 0.114
A reduction of oryanic deposits on the rotor can
also be observed resulting in an improvement in vibration
characteristics as confirmed by noise data as shown in
Figure 4 (20~ lignin) as compared to Figure 3 (control).
The use of the lignin in brake pad formulations
were tested at about 300 rpm, 50 psig and 300~F according
to a modified Ford Test. Figure 4 demonstrates a shift of
the peak of the frequency to the (hllm~n) non-audible part
of the spectrum (approximately above 16 KHz).
The invention and many of its attendant
advantages will be understood from the foregoing
description, and it will be apparent that various
modifications and changes can be made without departing
from the spirit and scope of the invention or sacrificing
all of its material advantages, the compositions and
processes hereinbe~ore described being merely preferred
embodiments.