Process for producing two-ply friction material

Details Process for producing two-ply friction material Process for producing two-ply friction material

1999-03-22

2001-02-27

Cole, Elizabeth M. (Department: 1771)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S300700, C428S301400, C523S149000, C523S152000

Reexamination Certificate

active

06194059

ABSTRACT:

TECHNICAL FIELD
This invention relates to a two-ply fibrous base material. The fibrous base has a primary layer and a secondary layer which are joined together during a wet paper making process. The two-ply fibrous base material is useful in friction material applications.
The two-ply friction material of the present invention has increased dynamic friction and wear resistant characteristics. The two-ply friction material of the present invention has higher durability and is less costly to produce than conventional one-ply friction materials.
BACKGROUND ART
New and advanced transmission systems and braking systems are being developed by the automotive industry. These new systems often involve high energy requirements. Therefore, the friction materials technology must be also developed to meet the increasing energy requirements of these advanced systems.
In particular, a new high energy type friction material is needed. The new high energy friction material must be able to withstand high speeds wherein surface speeds are up to about 65 m/second. Also, the friction material must be able to withstand high facing lining pressures up to about 1500 psi. It is also important that the friction material be useful under limited lubrication conditions.
The friction material must be durable and have high heat resistance in order to be useful in the advanced transmission and braking systems. Not only must the friction material remain stable at high temperatures, it must also be able to rapidly dissipate the high heat that is being generated during operating conditions.
The high speeds generated during engagement and disengagement of the new transmission and braking systems mean that a friction material must be able to maintain a relatively constant friction throughout the engagement. It is important that the frictional engagement be relatively constant over a wide range of speeds and temperatures in order to minimize “shuddering” of materials during braking or the transmission system during power shift from one gear to another.
Previously, asbestos fibers were included in the friction material for temperature stability. For example, the Arledter et al. U.S. Pat. No. 3,270,846 patent describes phenolic and phenolic-modified resins used with asbestos. Now, however, due to health and environmental problems, asbestos is no longer being used. More recent friction materials have attempted to overcome the absence of the asbestos in the friction material by modifying the impregnating paper or fiber materials with phenolic or phenolic-modified resins. These friction materials, however, do not rapidly dissipate the high heat generated, and do not have the necessary heat resistance and satisfactory high coefficient of friction performance now needed for use in the high speed systems currently being developed.
Friction materials are often used in “wet” applications where the friction material is “wetted” or impregnated with a liquid such as brake fluid or automatic transmission fluid during use. During use of the “wet” friction material, the fluid is ultimately squeezed from or is impregnating the friction material. Wet friction materials differ greatly, both in their compositions and physical characteristics from “dry” friction materials.
In order for friction materials to be useful in “wet” applications, the friction material must have a wide variety of acceptable characteristics. The friction material must be resilient or elastic yet resistant to compression set, abrasion and stress; have high heat resistance and be able to dissipate heat quickly; and, have long lasting, stable and consistent frictional performance. If any of these characteristics are not met, optimum performance of the friction material is not met.
Thus, it is also important that a suitable friction lining or fibrous base material be used to form a high energy application friction material. The friction material must have good shear strength both when saturated with the wet resin during impregnation and when saturated with brake fluid or transmission oil during use.
It is also important, under certain applications, that the friction material have high porosity such that there is a high fluid permeation capacity during use. Thus, it is important that the friction material not only be porous, it must also be compressible. The fluids permeated into the friction material must be capable of being squeezed or released from the friction material quickly under the pressures applied during operation of the brake or transmission, yet the lining material must not collapse. It is also important that the friction material have high thermal conductivity to also help rapidly dissipate the heat generated during operation of the brake or transmission.
Friction materials which met these demanding characteristics often include a fibrous base material having aramid-type fibers. However, these fibers and other ingredients used in the fibrous base material are expensive which increases the cost of the friction material.
As far as is known, there is no disclosure of a friction material for use in transmission systems which includes two-plies or layers of fibrous base materials which have sufficient strength to be useful in high energy applications.
Accordingly, it is an object of the present invention to provide an improved friction material with reliable and improved properties compared to those of the prior art.
A further object of this invention is to provide friction materials with high thermal conductivity, porosity and strength.
As a result of extensive research in view of the need for a better friction material, a friction material with improved characteristics has now been developed.
DISCLOSURE OF THE INVENTION
In order to achieve the requirements discussed above, many materials were evaluated for friction and heat resistant characteristics under conditions similar to those encountered during operation. Both commercially available brake linings and transmission materials were investigated and proved not to be suitable for use in high energy applications. The present invention is especially useful in brakes and in clutch applications. In one aspect, the present invention provides a fibrous base material comprising two-plies or layers of material.
The two-ply fibrous base material comprises a first or bottom layer and a second or top layer adjacent the first layer. The second layer comprises high temperature resistant and high strength fibers and friction paper-forming materials such as, for example, fillers and/or friction modifying particles. In certain preferred embodiments, the first layer is more elastic and more oil absorbent that the second layer.
Another aspect of the present invention relates to the two-ply fibrous base material impregnated with at least one suitable resin for forming a friction material. The two-ply friction material is especially useful for friction materials for clutch friction plates, bands, synchronizer rings and related transmission friction products.
The fibrous base material can be impregnated using different resin systems. In certain embodiments, it is useful to impregnate the fibrous based material with a phenolic resin or a modified phenolic-based resin. It has now been discovered that, in certain embodiments, when a silicone resin is blended or mixed with a phenolic resin in compatible solvents and that silicone-phenolic resin blend is used to impregnate a fibrous base material of the present invention, a high energy friction material is formed. Such high energy friction material has high friction stability and high heat resistance.
The friction material of the present invention prevents uneven lining wear and therefore the formation of separator plate “hot spots” from developing during the useful life of the friction material. When there is little uneven wear on the friction material, there is more likelihood to maintain “steady state” of the clutch or brake components and therefore, more consistent performance of the clutch and brake. Further, the friction material of the present invention shows good shear

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