Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-11-30
2003-05-06
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S395000, C428S399000
Reexamination Certificate
active
06558793
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a substrate fiber for a dry friction material, to a method of manufacturing the substrate fiber, and to a dry friction material. More particularly, the present invention relates to a substrate fiber that can stabilize the coefficient of friction (&mgr;) of dry friction material containing the substrate fiber, to a method of manufacturing the substrate fiber, and to a dry friction material containing the substrate fiber.
2. Discussion of the Background
A conventional dry friction material used in, e.g., a vehicular clutch or brake pad is manufactured by forming and heating a compounded mixture of substrate fiber, a variety of composition materials and thermosetting resins. In the past asbestos has been used as the substrate fiber. Recently, environmental and sanitation concerns have led to aramid fiber as an alternative substrate fiber material.
The engaging and disengaging point of a clutch and the deceleration caused by a brake pad are dependent on the performance of the dry friction material in the clutch and brake pad. Consistent clutching and braking requires that the dry friction material have a stable coefficient of friction (&mgr;). This requires that the substrate fiber and the variety of composition materials in the dry friction material be uniformly distributed throughout the dry friction material. This also requires that the uniform distribution of substrate fiber and composition materials be stable regardless of the frequency of engagement of the dry friction material in the clutch or brake.
FIG. 3
shows a dry friction material in which the substrate fiber consists of straight aramid fiber chops
20
. However, the ability of straight cylindrical fiber chops
20
to hold composition materials
13
and
14
in the dry friction material is poor. As a result, the adhesion between the substrate fiber and the composition materials (e.g. metallic fiber and son) in the dry friction material is poor. In addition, because the chops
20
do not include divergent portions (e.g., fine fibers) extending from the fiber cylinders, the chops
20
are apt to cohere, so the dispersibility of the substrate fiber chops
20
is poor. As a result, when cylindrical fiber chops
20
are used to form dry friction material, great care must be taken in mixing the chops
20
with other composition materials if satisfactory dry friction material performance is to be achieved. For example, the type of mixer used, the nature of the mixed components, the order of mixing, and the frequency of mixing must all be considered. This makes the manufacture of dry friction material containing cylindrical substrate fiber chops
20
extremely difficult.
FIGS. 2 and 8
show one approach to avoiding the difficulties presented by cylindrical substrate fiber in forming dry friction material. In
FIG. 2
a fiber pulp
10
comprises aramid fibers each having a trunk portion
11
with a diameter of about 0.1 to several &mgr;m and a length on the order of 2 mm. In this pulp
10
numerous divergent portions
12
with diameters on the order of nm to several &mgr;m diverge from the trunk portion
11
. The divergent portions
12
enhance the dispersibility of the fiber pulp
10
, so the fiber pulp
10
can be distributed uniformly. This makes it relatively easy to mix the fiber pulp
10
in a dry friction material.
However, the fiber pulp
10
can make it difficult to mix various other composition materials in a dry friction material. Composition material
13
, which is smaller than several &mgr;m, can be distributed fairly uniformly in the small spaces left by the divergent portions
12
of the fiber pulp
10
. However, composition material
14
, which is larger than several tens of &mgr;m, cannot be distributed uniformly in the fiber pulp
10
and tends to cohere. As a result, dry friction materials containing fiber pulp
10
do not contain a uniform distribution of composition materials.
When dry friction material having a non-uniform distribution of substrate fibers and composition materials is used repeatedly, a large number of divergent portions which are diverged from the substrate fibers subsist and tend to appear at the periphery of the frictional surface of the dry friction material. As a result, the condition of the frictional surface changes in response to the frictional history and the coefficient of friction (&mgr;) of the surface becomes unstable.
SUMMARY OF THE INVENTION
The present invention provides an improved substrate fiber for a dry friction material that allows the substrate fiber and other composition materials in the dry friction material to be dispersed equally or uniformly in the dry friction material. Each substrate fiber includes a trunk portion extending in the axial direction of the fiber. The trunk portion fits within a maximum diameter of from about 10 to 20 &mgr;m. The length of the trunk portion is from about 0.5 to 5 mm. Slightly diverging from a part of the trunk portion is at least one divergent portion having a small diameter less than the maximum diameter. The divergent portions in the substrate fibers prevent the fibers from cohering, while allowing the substrate fiber and the composition materials to be uniformly dispersed in the dry friction material.
REFERENCES:
patent: 4811908 (1989-03-01), Galati
patent: 5324811 (1994-06-01), You et al.
patent: 5707905 (1998-01-01), Lam et al.
patent: 5753356 (1998-05-01), Lam et al.
patent: 5856244 (1999-01-01), Lam et al.
patent: 5858883 (1999-01-01), Lam et al.
patent: 5998307 (1999-12-01), Lam et al.
patent: 6001750 (1999-12-01), Lam
patent: 6130176 (2000-10-01), Lam
Kakihara Kenji
Kawade Tunehisa
Kobayashi Masa-aki
Odani Naoki
Aisin Seiki Kabushiki Kaisha
Edwards N.
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