U.S. patent application number 12/142632 was filed with the patent office on 2009-01-08 for friction material.
This patent application is currently assigned to Nisshinbo Industries, Inc.. Invention is credited to Norio Chinda, Tatsuji Kuroda, Yuji Shishido.
Application Number | 20090011962 12/142632 |
Document ID | / |
Family ID | 40221924 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090011962 |
Kind Code |
A1 |
Chinda; Norio ; et
al. |
January 8, 2009 |
FRICTION MATERIAL
Abstract
To provide a friction material with an excellent balance for
both service brake and parking brake usage that satisfies the
required performance for the service brake and improves the static
coefficient of friction for the parking brake. The friction
material comprising a fibrous base material, a friction modifier,
and a binder, wherein said friction modifier comprises 2-20 volume
% of cashew dust, 10-25 volume % of a rubber composition, and 2-5
volume % of a solid lubricant, a total volume of the cashew dust
and the rubber composition is 30 volume % or less, and said
friction modifier does not use graphite because it can cause the
reduction of the coefficient of friction during the parking brake
operation.
Inventors: |
Chinda; Norio; (Gunma-ken,
JP) ; Shishido; Yuji; (Gunma-ken, JP) ;
Kuroda; Tatsuji; (Gunma-ken, JP) |
Correspondence
Address: |
APEX JURIS, PLLC
12360 LAKE CITY WAY NORTHEAST, SUITE 410
SEATTLE
WA
98125
US
|
Assignee: |
Nisshinbo Industries, Inc.
Tokyo
JP
|
Family ID: |
40221924 |
Appl. No.: |
12/142632 |
Filed: |
June 19, 2008 |
Current U.S.
Class: |
508/167 ;
508/216 |
Current CPC
Class: |
F16D 69/026
20130101 |
Class at
Publication: |
508/167 ;
508/216 |
International
Class: |
C10M 125/22 20060101
C10M125/22; C10M 159/02 20060101 C10M159/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 4, 2007 |
JP |
2007-176029 |
Claims
1. A friction material comprising: a fibrous base material, a
friction modifier, and a binder, wherein said friction modifier
includes 5-20 volume % of cashew dust, 10-25 volume % of a rubber
composition, and 2-5 volume % of a solid lubricant, a total volume
of said cashew dust and said rubber composition is less than 30
volume %, and said friction modifier is without graphite.
2. The friction material according to claim 1, wherein said cashew
dust is manufactured using furfural as a curing agent.
3. The friction material according to claim 1, wherein a part of
said rubber composition is a vulcanized acrylic rubber powder, and
said friction material includes at least 5 volume % or more of a
vulcanized acrylic rubber powder as said rubber composition.
4. The friction material according to claim 2, wherein a part of
said rubber composition is a vulcanized acrylic rubber powder, and
said friction material includes at least 5 volume % or more of a
vulcanized acrylic rubber powder as said rubber composition.
5. The friction material according to claim 1, wherein said solid
lubricant is molybdenum disulfide.
6. The friction material according to claim 2, wherein said solid
lubricant is molybdenum disulfide.
7. The friction material according to claim 3, wherein said solid
lubricant is molybdenum disulfide.
8. The friction material according to claim 4, wherein said solid
lubricant is molybdenum disulfide.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY
[0001] The present application claims the benefit under 35 U.S.C.
section 119(a) of Japanese Patent Application filed in the Japan
Patent Office on Jul. 4, 2007 and assigned serial number
2007-176029, the disclosure of which is incorporated herein by
reference.
FIELD OF INVENTION
[0002] This invention relates to a friction material for use as a
disc brake pad and a brake lining for automobiles.
BACKGROUND OF THE INVENTION
[0003] A friction material mounted on a rear brake of an automobile
is often used for both service brakes and parking brakes. The
required performance for the friction material to be used in the
service brake is different from the required performance for the
friction material to be used in the parking brake. The service
brake needs such as excellent and stable brake effectiveness, good
fading resistance and good wearing resistance, high mechanical
strength, and low incidence of noise. The parking brake needs high
static coefficient of friction and a small amount of thermal
expansion and contraction so as to securely hold an automobile on a
slope.
[0004] For the friction material with high static coefficient of
friction when using the parking brake, the patent document 1
(Japanese Unexamined Patent Publication No. 9-67449) discloses a
friction material for a parking brake made by entirely or partially
coating a rubber or solution of rubber compounds on a friction
surface of the friction material and by heating and vulcanizing the
same, and the patent document 2 (Japanese Unexamined Patent
Publication No. 9-67450) discloses a hybrid friction material for a
parking brake made by forming as placing a high dumping raw
material plate made of rubber or rubber compounds, when pre-forming
the friction material, on agitation compounds for the friction
material manufacturing to be embedded therein to coexist surfaces
with different characteristics on the friction surface. Also, the
patent document 3 (Japanese Unexamined Patent Publication No.
2005-233283) discloses a friction material for a parking brake
which uses 25-40 volume % of a hard inorganic particle with an
average particle diameter of between 200 and 400 .mu.m and Mohs
hardness of 7-9 as the abrasive.
[0005] However, these friction materials are used solely for
parking brakes, and they cannot satisfy the required performance
when used for service brakes. Even if a material with a high
dumping capacity is applied on the friction surface of the friction
material, just like the patent documents 1 and 2, effective
performance does not last because the high dumping material becomes
worn out after continuous use of the same for the service brake,
and the friction material includes abrasive largely just like the
patent document 3 and thus causes a problem of increasing the
abrasiveness against a mating member (such as a disc brake rotor
and a brake drum) when the service brake is applied.
[0006] On the other hand, study regarding the friction material
used to secure both service brake and parking brake performances
has been done, and the patent document 4 (Japanese Unexamined
Patent Publication No. 2002-275452) discloses a friction material
that offers superior brake effectiveness for the service brake and
at the parking brake operation restricts the noise generation due
to oscillation of a vehicle body when the driver gets off the
vehicle after applying the parking brake. This friction material
includes 1-15 volume % of an inorganic fiber with Mohs hardness of
lower than 4.5 and 1-15 volume % of cashew dust. However, no study
has ever been conducted as to the improvement of the static
coefficient of friction during the parking brake and restriction of
the thermal expansion and contraction of the friction material.
[0007] Patent Documents [0008] [Patent Document 1] Japanese
Unexamined Patent Publication No. 9-67449. [0009] [Patent Document
2] Japanese Unexamined Patent Publication No. 9-67450. [0010]
[Patent Document 3] Japanese Unexamined Patent Publication No.
2005-233283. [0011] [Patent Document 4] Japanese Unexamined Patent
Publication No. 2002-275452.
SUMMARY OF THE INVENTION
[0012] This invention was made in consideration of the
above-situations and provides a friction material with an excellent
balance for both service brake and parking brake usages which
satisfies the required performance for the service brake and
maintains the high static coefficient of friction during parking
brake operation; and restricts the thermal expansion or contraction
of the friction material to restrain reduction of the pressing
force against the mating member.
[0013] The inventors of the present application conducted a
thorough study to achieve the above-described objects and then
found that eliminating a factor of reducing the brake force is more
effective than positively increasing the static coefficient of
friction during the parking brake operation for the friction
material generally used for both service brake and parking brake
and that (1) the pressing force against the mating member (e.g.,
disc brake rotor or brake drum) is reduced by contracting the
friction material by naturally cooling the same when the friction
material, which is expanded due to the frictional heating during
the service brake operation, is used for the parking brake, and (2)
graphite generally applied as the solid lubricant for the friction
material reduces the static friction coefficient when a high
humidity atmosphere exists, such as during the night time when the
parking brake is frequently used.
[0014] <1> This invention discloses a friction material
comprising a fibrous base material, a friction modifier, and a
binder, wherein said friction modifier includes 5-20 volume % of
cashew dust, 10-25 volume % of a rubber composition, and 2-5 volume
% of a solid lubricant, a total volume of said cashew dust and said
rubber composition is less than 30 volume %, and said friction
modifier is without graphite.
[0015] <2> This invention also discloses the friction
material according to <1>, wherein the cashew dust is
manufactured using furfural as a curing agent
[0016] <3> This invention also discloses the friction
material according to <1> and <2> wherein a part of the
rubber composition is a vulcanized acrylic rubber powder, and the
friction material includes at least 5 volume % or more of a
vulcanized acrylic rubber powder as the rubber composition
[0017] <4> This invention also discloses the friction
material according to <1>-<4>, wherein the solid
lubricant is molybdenum disulfide.
[0018] This invention can provide a friction material that: [0019]
(1) gives a superior braking effect, good fading and wearing
resistance, high mechanical strength, and low incidence of noise
when used as a service brake; [0020] (2) can maintain a high static
friction coefficient and at the same time minimizes and reduces the
pressing force required to brake by restricting the thermal
expansion and contraction of the friction material against the
surface of the mating member and also securely keeps the vehicle on
the slope when used as a parking brake, and [0021] (3) can be used
as both service brake and parking brake.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and other objects of the present invention will
become readily apparent by reference to the following detailed
description when considered in conjunction with the accompanying
drawings wherein:
[0023] FIG. 1 is a table showing evaluation results of embodiments
1-8 and comparative examples 1-4;
[0024] FIG. 2 shows the evaluation method and standards; and
[0025] FIG. 3 shows the evaluation method for the static
coefficient of friction during parking brake operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] The friction material of the present invention is prepared
by forming a friction material granulation which is comprised of a
fibrous base material, a friction modifier, and a binder and then
curing the same thereafter. Here, in the friction material of the
present invention, the friction modifier is characterized to
include cashew dust and rubber composition but does not include
graphite.
[0027] An inorganic fiber and organic fiber without asbestos, which
is generally used for the friction material, may be used as the
above-addressed fibrous base material. Examples of the inorganic
fibers are a steel fiber, stainless fiber, copper fiber, brass
fiber, bronze fiber, aluminum fiber, potassium titanate fiber,
glass fiber, rockwool, wollastonite, and more, and examples of the
organic fibers are aramid fiber, carbon fiber, polyimide fiber,
cellulose fiber, acrylic fiber, and more. Among these fibrous base
materials they can be used alone or as a combination of two or more
types. An amount of overall fibrous base materials included in the
friction material may be adjusted within a range that does not lose
the advantages of the present invention.
[0028] The friction modifier is added to adjust the coefficient of
friction, suppress the noise, and to prevent rust and has such as
an inorganic filler, an organic filler, and a solid lubricant as
appropriate, where the organic filler may be such as cashew dust
and rubber composition. The cashew dust is added to stabilize the
coefficient of friction during the service brake operation. If the
friction material frictionally engages the surface of the mating
member during the service brake operation, the cashew dust in the
friction material melts due to the frictional heating, and a thin
organic film uniformly covers the surface of the mating member.
Covering the surface with the film stabilizes the coefficient of
the friction material. However, the cashew dust expands and
contracts in great extent due to the heat, which causes the
friction material to thermally expand and contract. Here, adding
the rubber composition helps to restrict the thermal expansion of
the friction material. The rubber composition, functioning as an
elastic member, contracts the same, or in equal proportion to,
(equally) the amount of expansion of the cashew dust due to the
frictional heating so that the thermal expansion of the friction
material itself is restricted.
[0029] Also, the addition of the rubber composition increases the
elasticity of the friction material, and therefore the amount of
contraction of the friction material increases when pressing the
friction material against the mating member. If the amount of
contraction of the rubber composition is equal to or more than the
amount of expansion of the friction material, then when the
friction material is contracted by cooling, no radical reduction of
the pressing force can be seen, thereby restraining a decrease of
the pressing force against the mating member.
[0030] Also, the solid lubricant is used to secure the wearing
resistance during the service brake operation. Adding a solid
lubricant that is something other than graphite to the friction
material can effectively restrict the reduction of the static
coefficient of friction during parking brake operation. This is
true because graphite is characterized by the fact that the
coefficient of friction thereof becomes lower in humid air than in
dry air.
[0031] The amount of cashew dust is preferably 5-20 volume %. If
the amount of cashew dust is less than 5 volume %, it is difficult
for the cashew dust film to form on the mating member. If the
cashew dust film is not formed on the mating member, iron
composition of the mating member is transferred to stick on the
friction material, which causes an iron to iron grinding type
friction to increase the abrasiveness against the mating member and
to damage the wearing resistance. Also, if the amount of cashew
dust is more than 20 volume %, the cashew dust film formed on the
mating member becomes too thick, which tends to reduce the
coefficient of friction during the service brake operation.
[0032] The cashew dust is made by curing cashew nut shell liquid,
or polymer of the same, by curing agents such as furfural,
formaldehyde (as one type of an aldehyde), or
hexamethylenetetramine, then cooling and crushing. In this
invention, the cashew dust, which is obtained by using such as
formaldehyde and hexamine as a curing agent, and the cashew dust,
which is obtained as using furfural as a curing agent, can be used
independently or in combination; however, the cashew dust, which is
obtained as using the furfural as the curing agent is preferable.
Comparing the cashew dust which is obtained using the furfural as
the curing agent, and the cashew dust which is obtained using such
as the formaldehyde and hexamine as the curing agent, the former
cashew dust, shows high heat resistance and can restrict the
thermal expansion.
[0033] The amount of rubber composition is preferably 10-25 volume
%. If the amount of the rubber composition is less than 10 volume
%, the thermal expansion of the friction material itself becomes
larger and the elasticity of the friction material itself becomes
smaller, and therefore the static coefficient of friction, during
the parking brake operation, tends to decrease. Also, the vibration
damping effect becomes less effective, and a squealing noise tends
to be caused during the service brake operation. If the amount of
the rubber composition is more than 25 volume %, the wearing
resistance is decreased.
[0034] The rubber composition may be any one of or any combination
of natural rubber, polyisoprene rubber (IR), acrylonitrile
butadiene rubber (NBR), styrene butadiene rubber (SBR), butadiene
rubber (BR), chloroprene rubber (CR), butyl rubber (IIR), ethylene
propylene rubber (EPM or EPDM), urethane rubber, silicone rubber,
fluoro rubber, powder of vulcanized rubber or unvulcanized rubber
of acrylic rubber, and crushed powder of tire tread rubber or wiper
rubber or window strip rubber. Also, as a part of the rubber
composition, vulcanized acrylic rubber powder with high heat
resistance is preferably included at 5 volume % or more relative to
the total amount of friction material.
[0035] The amount of the cashew dust and the rubber composition
combined is preferably 30 volume % in total or less. If the total
amount of the cashew dust and the rubber composition is more than
30 volume %, the amount of organic substance involved in the
friction material becomes too much, which worsens the fading
resistance (tends to fading).
[0036] Next, the solid lubricant can be one of or a combination of
metallic sulfide, without graphite, such as molybdenum disulfide,
stannic sulfide, and tungsten sulfide; however, the molybdenum
disulfide, which is especially not likely to be affected by
humidity, is preferably used independently. The amount of the solid
lubricant relative to the entire amount of the friction material is
preferably 2-5 volume %. If the amount of the solid lubricant is
less than 2 volume %, lubrication of the friction material agency
is insufficient, which damages the wearing resistance during the
service brake operation. Also, if the amount of solid lubricant is
more than 5 volume %, the lubrication agency becomes too much,
which reduces the coefficient of friction during the service brake
operation, and therefore sufficient brake effectiveness cannot be
obtained.
[0037] An inorganic filler may be zirconium silicate, zirconium
oxide, magnesium oxide, silicon carbide, silicon dioxide, aluminum
oxide, barium sulfate, calcium carbonate, calcium hydroxide, mica,
vermiculite, triiron tetroxide, a metal powder such as steel,
stainless, copper, brass, bronze, aluminum, tin, and zinc. The
above-listed examples of metal powders can be used alone or in
combination of two or more types.
[0038] A binder that can generally be provided for the friction
material can be used. For example, one of or a combination of two
or more of such as phenol resin, acrylic rubber denatured phenol
resin, NBR denatured phenol resin, phenol alkyl resin, melamine
resin, epoxy resin, and benzoxazine resin may be used. The amount
of binder relative to the entire amount of the friction material is
preferably 10-30 volume %.
[0039] The manufacturing method of the friction material of the
present invention is to mix the above-identified compositions
evenly using mixers such as a Henschel mixer, a Loedige mixer, an
Eirich mixer, to pre-mold in a mold, and to form the molded product
by forming the pre-molded product at 140-180.degree. C., 20-50 MPa
for 5-15 minutes. Next, the obtained molded product is heat-treated
(postcured) at 140-250.degree. C. for 2-48 hours and then is
spray-painted, baked, and grinded on the surface as necessary to
achieve a final product. When manufacturing a disc brake pad, the
disc brake pad is manufactured by placing the pre-molded product on
a steel or aluminum plate which is cleaned, surface-treated, and
adhesive-coated in advance, and in this situation, molding by the
mold for molding, heat-treating, painting, baking, and
grinding.
Embodiments
[0040] Embodiments and comparative examples are shown in the
following sections to explain the present invention concretely, but
the present invention is not limited to the following
embodiments.
[0041] The composition of the friction material as shown in FIG. 1
is mixed with the Loedige mixer for 5 minutes and is pressed in the
metal mold for molding at 10 MPa for 1 minute so as to pre-form.
The pre-molded product is mounted on the iron plate which is
cleaned, surface-treated, and adhesive-coated in advance, and in
this situation, molding by the mold for molding at the molding
temperature of 150.degree. C., the molding pressure of 40 MPa for
10 minutes, heat-treated (postcured) at 200.degree. C. for 5 hours,
and grinded to manufacture the friction material (disc brake pad
for passenger cars) (as appears in the embodiments 1-8 and the
comparative examples 1-4). The friction material is evaluated with
respect to the dynamic coefficient of friction during the service
brake operation, the static coefficient of friction during the
parking brake operation, the wearing resistance, and the fading
resistance. FIG. 1 shows the evaluation results; FIG. 2 shows the
evaluation method and standards; and FIG. 3 shows the evaluation
method for the static coefficient of friction during parking brake
operation.
[0042] While the embodiments of the present invention disclosed
herein are presently considered to be preferred embodiments,
various changes and modifications can be made without departing
from the spirit and scope of the present invention. The scope of
the invention is indicated in the appended claims, and all changes
that come within the meaning and range of equivalents are intended
to be embraced therein.
* * * * *