Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-08-18
2001-05-15
Howard, Jacqueline V. (Department: 1764)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C523S156000, C523S157000, C508S154000, C508S161000
Reexamination Certificate
active
06231977
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wet friction material employed in friction engagement devices such as clutches and brakes used in oil in automatic transmissions of automobiles.
2. Related Background Art
An automatic transmission of an automobile, which is incorporated with a multiple-disc clutch comprising a plurality of friction plates formed by adhering a wet friction material on the surface a base plate (core plate) generally made of metals and separator plates as a friction counterpart made of a single sheet such as a metal sheet in an alternative manner, transmits or breaks a driving force by contacting these plates mutually under pressure or releasing the contact in an automatic transmission fluid (ATF) employed as a lubricant oil.
Paper wet friction materials called “paper friction materials” are generally employed as wet friction materials for friction engagement devices used in these oils. The wet friction materials are generally obtained by subjecting a fiber base material such as natural pulp fibers, organic synthetic fibers and inorganic fibers together with a filler such as diatomaceous earth as cashew resin and a friction controller to wet paper machining followed by impregnation of a resin binder comprising a thermosetting resin and heat hardening.
In the paper wet friction materials, thermosetting resins impregnated in machined paper material as resin binders not only bind a fiber base material and a filler, etc. and retain binding but also greatly affect friction properties and friction resistance of the wet friction materials. As resin binders, phenolic resins with excellent heat-resistance, high mechanical strength, and relatively good friction resistance are generally employed. The phenolic resins are produced by addition polymerization of phenols, such as phenol and cresol, and aldehydes, such as formaldehyde and paraformaldehyde, in the presence of an acid catalyst or alkaline catalyst. In the case of wet friction materials, resol-type phenolic resins obtained by addition polymerization in the presence of an alkaline catalyst are generally employed. As phenolic resins, unmodified phenolic resins have been employed practically in the past. They have such problems, however, that initial variations in friction coefficient are large in such a manner that a friction coefficient is low in an early phase due to local contact of a friction surface because they have a high cross-linking density and are thus hard, and a friction coefficient becomes higher with use due to increased conformability; and that burned spots called heat spots are generated due to a high temperature on a friction surface on a friction counterpart (separator plate) under high temperature and high load conditions, resulting of lack in long-term stability of friction properties.
In recent years, in order to improve these problems, modified phenolic resins have been extensively investigated and oil-modified phenolic resins and epoxy-modified phenolic resins, etc. with excellent flexibility have been studied and some of them have already been employed practically. These modified phenolic resins, however, are still inferior to unmodified phenolic resins in terms of heat resistance and friction resistance. Thus, satisfactory ones have not yet been attained.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a wet friction material that exhibits small initial variations in friction coefficient, suppresses generation of heat spots, and is excellent in heat resistance and friction resistance.
In order to attain the above object, a wet friction material of the present invention is characterized in that a resin binder is a phenolic resin modified with p-nonyl phenol in a wet friction material comprising a fiber base material, a filler, a friction controller, and a resin binder.
The present inventors focused on to modification of phenolic resins as resin binders, and investigated materials used for the modification. As a result, we found that a wet friction material comprising, as a resin binder, p-nonyl phenol-modified phenolic resin obtained using a bifunctional p-nonyl phenol having a nonyl group at a para-position against OH-group of phenol, one of phenols as a material for modification of phenols, is excellent in flexibility and also has heat resistance and friction resistance comparable or superior to those of unmodified phenolic resins.
Although the reason for this improved performance is not completely understood, it is hypothesized that when a p-nonyl phenol-modified phenolic resin, in which hydrophilic phenol or methylol phenol, etc. and p-nonyl phenol having a hydrophilic hydroxy group and lyophilic nonyl group (—C
9
H
19
) or its methylol compound, etc. are present together, is employed as a resin binder for a paper friction material, hydrophilic compounds with a low molecular weight such as phenol or methylol phenol penetrate well in capillary spaces of a fiber base material, while p-nonyl phenol, with a relatively high molecular weight or its methylol compounds, etc., covers the surface of the fiber base material to enable it to retain porosity of the fiber base material of the wet friction material, to be excellent in flexibility, and also to secure mechanical strength.
The p-nonyl phenol-modified phenolic resins employed as resin binders according to the present invention are obtained by either of known methods comprising charging phenol, p-nonyl phenol, aldehydes, and a catalyst in a reaction tank, then heating for copolymerization, subjecting to dehydration treatment, and adding a solvent to adjust involatile components; and comprising charging phenol, aldehydes, and a catalyst in a reaction tank, then charging p-nonyl phenol, aldehydes, and a catalyst in another reaction tank, and then separately heating for addition polymerization, subjecting to dehydration treatment, adding a solvent to adjust involatile component, and after that, combining unmodified phenolic resin and p-nonyl phenolic resin thus obtained to form one liquid. A molar ratio of aldehydes to phenols is 1:1 to 2.5:1.
As aldehydes, formaldehyde, paraformaldehyde, benzaldehyde, etc. are employed.
As a catalyst employed for synthesis, alkalis such as sodium hydroxide, potassium hydroxide, barium hydroxide, and calcium hydroxide and ammonia and amines such as triethylamine are employed alone or as a combination of two or more.
As a solvent, alcohols such as methanol and ethanol, glycols such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol, as well as ethers, esters, ether esters, ketones or the like are employed alone or as a combination of two or more.
An amount of p-nonyl phenol employed to modify phenols is preferably 5 to 60 mol %, more preferably 10 to 50 mol % of the phenols. An amount of p-nonyl phenol for modification less than 5 mol % cannot provide sufficient flexibility to resins after setting, so that difficulties due to a local contact between a wet friction material and a friction counterpart material cannot be fully improved. On the other hand, when an amount of p-nonyl phenol for modification exceeds 60 mol %, heat resistance of resins after setting is reduced due to a decrease in cross-linking density of the resins. It is thus not preferable due to decreases in heat resistance and friction resistance.
Machined paper materials employed according to the present invention are manufactured by ordinary methods from slurry solutions in which a fiber base material such as natural pulp fibers such as wood pulp, organic synthetic fibers such as aramid, and inorganic fibers such as glass, a filler, and a friction controller such as cashew resin are suspended in water in a predetermined ratio and they are not limited specifically.
To the machined paper material, 20 to 80 parts by weight of the above-mentioned p-nonyl phenol-modified phenolic resin is impregnated to 100 parts by weight of the base material, dried, and heated at about 150 to 250° C. for 15 to 30 minutes to be set. Then the resin is
Mori Masahiro
Suzuki Makoto
Howard Jacqueline V.
NSK-Warner K. K.
Vorys Sater Seymour and Pease LLP
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