Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-06-04
2003-12-23
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C525S477000, C525S478000, C528S031000, C528S086000, C528S212000, C528S214000
Reexamination Certificate
active
06667104
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wet friction material used in oil, particularly in an automatic transmission fluid (ATF), and to a phenol resin composition for the wet friction material used as a binder for the wet friction material.
2. Description of Background Art
Since wet friction materials for automatic transmissions for automatic vehicles are used in oil, the material must be thoroughly impregnated with oil. Such a wet friction material is therefore made from a porous material. A commonly used wet friction material is prepared by impregnating a paper body made of a fibrous material with a phenolic resin diluted in an organic solvent, followed by drying and heat-curing steps. As a phenolic resin, a resol-type phenol resin using an organic solvent such as an alcohol and ketone as a solvent is commonly used due to excellent heat resistance and excellent adhesion with the fibrous material. As a fibrous material, wood pulp, cotton lint, aramid fiber, and the like can be given. For preparing the paper body, fillers such as a friction-adjusting agent, solid lubricant, and the like are added as appropriate.
In recent years, downsizing and lightening of automatic transmissions are progressing aiming at a low fuel consumption in view of energy saving and environment protection. For this reason, miniaturization and a decrease in the number of wet friction materials used for the automatic transmissions are desired. Because the torque capacity is insufficient if conventional wet friction materials are used, an increase in the coefficient of friction is desired. If the coefficient of friction is increased, the materials generate a greater heat of friction. Therefore, improvement in durability of the wet friction materials is desired. The durability of wet friction materials is expressed by a permanent cycle number (life of the wet friction material) until the friction material exfoliates and the total thickness changes for the wet friction material itself. Therefore, three parameters, i.e. an increase in the coefficient of friction, an increase in the number of permanent cycles, and decrease of the total thickness change, are strongly desired for wet friction materials. Similarly, binders contributing to these three parameters are desired.
As a material for satisfying this requirement, Japanese Patent Application Laid-open No. 1996-259782 discloses a composite material consisting of a heat-curable resin and a metal oxide, a method of manufacturing such a composite material, and the like. The manufacturing method comprises hydrolyzing and poly-condensing a metal alkoxide containing a silicon alkoxide or its low condensate in a solution of a heat-curable resin containing a phenol resin, while removing the solvent or curing the resin, whereby a composite material with metal oxide particles having an average particle size of 0.01 to 5 &mgr;m homogeneously dispersed in the heat-curable resin in the amount of 1 to 35 wt % in such a manner that no macro-phase separation may occur can be obtained. Among numerous applications of the composite material, the use as a friction material is mentioned. Japanese Patent Application Laid-open No. 2000-336177 discloses a wet friction material made by impregnating a paper substrate with a heat-curable resin. The patent application describes that this wet friction material exhibits an improved strength without decreasing porosity due to either a three-dimensional network structure of SiO
2
or dispersed SiO
2
particles in the heat-curable resin. A mixture of a hydrolysis solution of tetraalkoxysilane and a phenol resin is used as a binder for the wet friction material in the examples. Materials containing SiO
2
in the amount of 24.5 to 26.7 wt % in the resins and the like are given as examples.
As conventional composite materials of heat-curable resin and metal oxide have improved sliding characteristics such as particularly controlled friction characteristics, a high limit PV value, and low wearing characteristics, but do not necessarily possess a high coefficient of friction as a binder for wet friction materials, further improvement was desired. In addition, the content of SiO
2
in the SiO
2
-containing heat-curable resin is no more than 30 wt %, which is not necessarily sufficient for ensuring a high coefficient of friction, an increased number of permanent cycles, and a decrease in the total thickness change.
Accordingly, an object of the present invention is to provide a phenol resin composition for wet friction material which can satisfy the requirements for a high coefficient of friction, a decrease in the total thickness change, and an increased number of permanent cycles until the friction material is peeled off at the same time, as well as a wet friction material. Another object of the present invention is to improve the storage stability of the phenol resin composition and improve usability of the phenol resin composition as a binder for wet friction material.
SUMMARY OF THE INVENTION
Specifically, the present invention provides a phenol resin composition for wet friction material comprising a curable resin composition obtained by mixing a resol-type phenol resin and a hydrolysis solution of an alkoxysilane or a condensate thereof, wherein the ratio (R/S) by weight of the nonvolatile components of the resol-type phenol resin (R) and the nonvolatile components of the hydrolysis solution of the alkoxysilane or the condensate thereof (S), obtained after heat-treatment at 135° C. for one hour, is in the range of 64/36 to 10/90.
The present invention also provides a wet friction material in which the above phenol resin composition for wet friction material is used as a binder.
The present invention further provides a wet friction material product with the above wet friction material attached to one or both sides of a core material using an adhesive.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention will be described in detail below. The phenol resin composition for wet friction material of the present invention is a liquid resin composition which is a binder precursor for a wet friction material. Although not specifically limited, the resol-type phenol resin used in the present invention can be prepared by mixing a phenol compound (P) and an aldehyde compound (A) at a molar ratio of A/P=0.8 to 1.4, preferably 0.9 to 1.3, reacting the mixture in the presence of an alkali catalyst, removing water by distillation under reduced pressure to a water content of 10 wt % or less, and dissolving the resulting product in alcohol. The product with a molar ratio of more than 1.4 has such a large cross-linking density that when the product is used in a wet friction material, the total thickness change may unacceptably increase. If the molar ratio is less than 0.8, phenol compounds may remain unreacted, resulting in a decreased yield of the resin. The number average molecular weight of the resol-type phenol resin is preferably from 150 to 400, and particularly preferably from 180 to 350. If the number average molecular weight is less than 150, monomers may remain unreacted, resulting in a decreased yield of the resin. If the number average molecular weight is more than 400, the fibrous material is impregnated with the resin only with difficulty and the resin exhibits impaired adhesion with the fibrous material, resulting in a composite material in which the number of permanent cycles under high surface pressure can be improved only with difficulty when used as a wet friction material. Here, the number average molecular weight is a polystyrene-reduced number average molecular weight measured by using HPLC. Because the resol-type phenol resin of the present invention can be obtained by the above method, the resin may be used in the form containing an alcohol and a small amount of water when preparing an impregnation solution by mixing it with the hydrolysis solution of an alkoxysilane or a condensate thereof, described later in this specification.
There are no sp
Aiba Hiroshi
Mori Masahiro
Keehan Christopher M
Sumitomo Bakelite Company Limited
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