Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-07-28
2002-09-17
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S156000, C260S998130
Reexamination Certificate
active
06451872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to non-asbestos friction materials of excellent performance which can be used for braking in automobiles, large trucks, railroad cars and various types of industrial equipment.
2. Prior Art
Friction materials used for braking in automobiles, large trucks, railroad cars and various industrial equipment are desired to have a number of performance features. These features include excellent wear resistance, a friction coefficient that is both high and stable, outstanding resistance to brake fade, no generation of undesirable noises such as squeal during brake operation, and minimal attack of the rotor serving as the counter surface.
The friction material in such cases is generally fabricated by mixing together primarily a fibrous base, a binder and a filler, subjecting the mixed composition to preforming, thermoforming (pressing) and, if necessary, postcuring by heat treatment, then painting, baking and polishing to give a finished article. Mixture of the starting materials may be carried out by dry mixing or by wet mixing using a solvent or water.
However, during mixture of the starting materials, the fibrous substance tends to form clumps (masses of starting material), which discourages uniform dispersion. Also, because hard particles and hard fibrous substances are highly abrasive, inadequate mixture resulting in non-uniform distribution, or segregation, within the friction material leads to a poor friction performance (e.g., noise performance, fading resistance, wear resistance, resistance to counter surface attack, vibration during high-speed braking).
SUMMARY OF THE INVENTION
Therefore, one object of the invention is to provide a non-asbestos friction material of outstanding friction performance within which a fibrous substance and hard particles can be uniformly mixed and dispersed so as to enable the capabilities of these friction material constituents to be used to their fullest advantage.
The inventor has learned that by incorporating within a friction material composition particles of a rubber composite composed primarily of either rubber and a fibrous substance or of rubber, a fibrous substance and hard particles, the fibrous substance or the fibrous substance and the hard particles can be blended in a uniformly dispersed state within the friction material, enabling the friction material to exhibit an excellent friction performance.
That is, the inventor has found that the incorporation of rubber composite particles composed primarily of at least one fibrous substance and rubber, or the incorporation of rubber composite particles composed primarily of at least one fibrous substance, at least one type of hard particle and rubber, within a non-asbestos friction material comprised of a molded and cured composition that includes a fibrous base, a binder and a filler allows the uniform mixture and dispersion within the friction material of the fibrous substance or the fibrous substance and the hard particles so that these interlock well with the other constituents to form a non-asbestos friction material in which the capabilities of each constituent are used to fullest advantage. As a result, there can be obtained high-quality non-asbestos friction materials in which counter surface (rotor) attack and the amount of wear due to segregation of the hard particles and hard fibrous substance within the friction material are reduced, noise performance is improved, a decline in the friction coefficient at high temperatures is reliably prevented, and tearing and loss of rubber during brake operation are minimized.
In the non-asbestos friction materials to which the present invention is directed, incorporating particles of a rubber composite composed primarily of soft rubber, a fibrous substance and, according to one embodiment, hard particles within a non-asbestos friction material composition substantially eliminates the drawbacks described above because the fibrous substance, which tends to clump and disperses with difficulty, can be uniformly mixed and dispersed, and because segregation of the hard particles and the hard fibrous substance within the friction material, which causes high abrasiveness and ultimately leads to poor friction performance, such as noise and vibrations, can be prevented.
Also, the rubber within the friction material forms a transfer film on the counter surface (rotor), and so the friction performance is adversely affected by too much transfer or too much abrasion. Therefore, by including in the friction material of the invention particles of a rubber composite composed primarily of either rubber and a fibrous substance or of rubber, a fibrous substance and hard particles, a balance between rubber abrasion and film transfer is achieved. This balance discourages the loss of rubber composite particles from the friction material, leaves the rubber less susceptible to tearing even when subjected to shear forces during friction, and greatly reduces the amount of wear by the friction material. Moreover, loss of these rubber composite particles is less likely to occur even at high brake temperatures, making it possible to assure good performance by the friction material even when it is subjected to friction under high-temperature, high-load, high-speed conditions.
Thus, according to a first aspect of the invention, there is provided a non-asbestos friction material comprising a molded and cured composition that includes (A) a fibrous base, (B) a binder, (C) a filler, and (D) particles of a rubber composite composed primarily of at least one fibrous substance and rubber.
According to a second aspect of the invention, there is provided a non-asbestos friction material comprising a molded and cured composition that includes (A) a fibrous base, (B) a binder, (C) a filler, and (D) particles of a rubber composite composed primarily of at least one fibrous substance, at least one type of hard particle and rubber.
DETAILED DESCRIPTION OF THE INVENTION
The non-asbestos friction material of the invention is made by incorporating, in a composition of primarily a fibrous base, a binder and a filler, particles of a rubber composite composed primarily of at least one fibrous substance and rubber, or of at least one fibrous substance, at least one type of hard particle and rubber.
The rubber used in the rubber composite particles is not subject to any particular limitation. Exemplary rubbers include acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), chlorobutyl rubber (CBR), silicone rubber, chloroprene rubber (CR), fluororubber (FR), isoprene rubber (IR), natural rubber (NR), butadiene rubber (BR), butyl rubber (IIR), acrylic rubber (AR), urethane rubber (UR), polysulfide rubber (such as that bearing the trade name designation Polysulfide TR), ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM) and chlorosulfonated polyethylene (CSM, such as that bearing the trade name designation Hypalon). Any one or combinations of two or more thereof may be used. Of these, acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), chlorobutyl rubber (CBR), silicone rubber, chloroprene rubber (CR) and fluororubber (FR) are preferred.
Use of the rubber in an uncrosslinked (unvulcanized) or semi-crosslinked (semi-vulcanized) state (including partially crosslinked or vulcanized rubber) is advantageous because rubber in this state mixes well with the other constituents such as the fibrous substance and the hard particles, and because crosslinkage (vulcanization) during molding and curing helps to enhance adhesion with the other constituents. In some cases, crosslinked (vulcanized) rubber can be used.
The fibrous substances referred to above include both fibers and fiber components. In the practice of the invention, such substances are divided into hard fibrous substances and soft fibrous substances. Generally, fibrous substances which have the ability to abrade the counter surface (rotor) are called “hard,” while those which lack this ability and are instead the
Cain Edward J.
Lee Katarzyna W.
Nisshinbo Industries Inc.
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