Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
1998-10-02
2003-02-25
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S147000, C428S172000, C192S10700R, C188S25100R, C188S257000, C180S337000, C105S001400, C104S002000, C104S018000, C074S340000
Reexamination Certificate
active
06524681
ABSTRACT:
This invention pertains to patterned surface friction materials for use in clutch plate members, brake pads, transmissions and the like, and methods of making and using these constructions.
Friction materials are used in a wide variety of different automotive applications such as for brake linings, brake pads, for torque converter clutches in automatic transmissions, synchronizer rings in manual transmissions, and in so-called “slipping” clutches in newer automobiles (a variation of a torque converter clutch).
In general, friction materials need to meet requirements in a wide variety of properties. Desired attributes of a friction material include toughness, strength, heat resistance, good frictional properties, and long life. Friction materials for transmissions should have a generally level torque curve, display no bond failure under standard usage conditions, and have retention of torque curve levelness and torque capacity. In addition, as smooth operation of the clutch is enhanced by friction modifiers in the transmission fluid, the friction material should hold or retain an appropriate amount of fluid at the engaging surface. Towards these and other objectives, patterned or textured friction surfaces for a friction material have been proposed heretofore.
One method to make such a patterned surface for a friction material is by a batch thermocompression molding process, such as disclosed in U.S. Pat. No. 5,004,089 (Hara et al.), wherein the mold has essentially the inverse shape of the desired dimpled surface. Since the molding processes are generally batch processes that require considerable time and energy, they are disfavored for large scale production facilities. U.S. Pat. No. 3,841,949 (Black) describes a composite friction plate provided with a facing of synthetic rubber presenting small islands in which friction material, such as sintered powdered bronze particles, is embedded to form the actual friction surface. Preferably, such particles or lands are said to be in the shape of circular buttons, which project from a thin base of an outer coating, such as heat resistant synthetic rubber, and are distributed over the base in spaced relation to each other. This arrangement is said to reduce the requirements for the quantity of cooling oil needed for the dissipation of a given amount of heat in the clutch or brake.
Abrasive articles are known having a contoured topography abrasive layer characterized as being a three-dimensionally shaped, radiation-cured dispersion of abrasive particles in an organic binder, such as described in U.S. Pat. No. 5,152,917 (Pieper et al.). This patent in general describes abrasive materials made by coating a slurry of UV curable resin and abrasive particles onto a patterned surface, contacting the slurry-coated patterned surface with a backing, curing the resin, and removing the finished abrasive article from the patterned surface. However, the abrasive materials as described therein are inadequate for use as friction materials, they do not have the combination of ingredients commonly used in friction materials needed to meet the rigorous standard tests for friction materials used in automotive transmissions. Also, as described in U.S. Pat. No. 5,234,740 (Reeves et al.), slip control sheeting is known comprising a backing having first and second major surfaces with an array of protrusions on the first major surface, useful for covering, e.g., gymnastics apparatuses, and tool and racquet handles. The protrusions formed in Reeves et al. do not contain granular carbon friction particles, among other things, needed to provide a friction material suitable for automotive transmission applications, such as a clutch plate member.
U.S. Pat. No. 5,083,650 (Seitz et al.) disclose a friction member having a roughened surface suitable for use as a friction facing member in a transmission. The friction member of Seitz et al. involves a heat-resistant paper supporting granular carbon friction particles resin-bonded via underlying and overlying thermoset polymeric binder containing carbon filler particles. An undulated (roughened) contour is formed on the surface of the friction member of Seitz et al. It would be desirable to form a friction facing layer with increased texture control and without the need for providing sequential coatings as employed in Seitz et al.
SUMMARY OF THE INVENTION
In accordance with the present invention, friction materials and clutch plate members are presented having a patterned friction surface. Methods of making and using the inventive friction materials are also presented. One embodiment of the invention is a friction material for a friction facing member, the friction material comprising: a backing having a front surface and a rear surface, and a plurality of precisely shaped composites forming a patterned friction coating on the front surface of the backing, the precisely shaped composites comprising a plurality of friction particles dispersed in a binder.
The plurality of precisely shaped friction composites define an overall friction surface topography having a three-dimensional pattern, such as an array having a non-random pattern. This patterned friction surface generally comprises a plurality of peaks or asperities associated with the shape of each friction composite, with adjacent friction composite peaks or asperities separated from one another. Since the peaks are separated from one another, cavities are formed therebetween. These cavities provide a means for dynamically retaining a fluid, e.g., transmission fluid. The precisely shaped friction composites each have a precise shape defined by a distinct and discernible boundary. Adjacent shaped composites are preferably the same shapes, although different shapes are also contemplated to be within the scope of the invention. It is preferred that the composites are equally spaced apart, although random spacing is also contemplated within the scope of the invention.
Preferably, each of the plurality of precisely shaped friction composites comprise a three-dimensional shape selected from the group of parallelpiped, cubic, conical, truncated pyramid, cylindrical, pyramid, and mixtures thereof, more preferably, each of the plurality of precisely shaped composites comprise a pyramid having a triangular-shaped base, even more preferably, each of the plurality of precisely shaped friction composites comprise a pyramid having a quadrilateral-shaped base, and most preferably, each of the pyramids include flat upper surfaces. Optionally, the precisely shaped composites may further comprise an additive.
In another embodiment, the friction material is resilient, i.e., the friction material has an elastic modulus of about 10
7
dynes/cm
2
or less, and more preferably about 10
6
dynes/cm
2
to about 10
7
dynes/cm
2
. Elastic modulus typically is determined using a Rheometrics Solids Analyzer Model RSA II, from Rheometrics Scientific, of Piscataway, N.J. In one preferred embodiment, the friction material further comprises a tie layer on the rear surface of the backing, more preferably, the tie layer comprises a fluoroelastomer, preferably the elastic modulus is about 3.5×10
6
dynes/cm
2
. In another preferred embodiment, the elastic modulus is about 4.5×10
6
dynes/cm
2
, wherein the patterned friction coating has a coefficient of friction of about 0.14 or greater at an energy level of about 26.62 kJ.
Preferably, the friction material includes friction particles selected from the group of an organic material, a metallic material, a semimetallic material, an inorganic material, and mixtures thereof, more preferably, the friction particles comprise an organic material, even more preferably, the organic material comprises coke, wherein the coke is selected from the group of metallurgical coke, petroleum coke, coconut shell activated carbon, and mixtures thereof.
The patterned friction coating is formed from a coatable binder precursor slurry comprising a plurality of friction particles and a resin, preferably a thermosetting resin. While in the slurry form, the resin
Edblom Elizabeth C.
McKeague Karl T.
Seitz David S.
3M Innovative Properties Company
Knecht III Harold C.
Loney Donald J.
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